| 1. |
- Forslind, Bo, et al.
(författare)
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Aspects on the physiology of human skin : studies using particle probe analysis
- 1997
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Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 38:4, s. 373-386
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Tidskriftsartikel (refereegranskat)abstract
- The cellular part of the skin, the epidermis, is a very thin structure, approximately 120 microns thick, a fact which has hindered the exploration of the physiology of the epidermis in normal and pathological conditions. An additional complication is the fact that the epidermis contains layers of cells at different stages of differentiation. Therefore, conventional physiological capillary probes cannot, with any satisfactory precision, be located within a specified cell of a specified layer of the skin in vivo. Hence, alternative ways for the exploration of skin physiology have been sought for. In the past, analysis of the elemental content of skin was done was done as bulk measurements, and surprisingly wide ranges of elemental content were recorded. The width of these ranges was most certainly due to the sampling methods used rather than the sensitivity of the chosen method of analysis. Also, these older measurements did not discriminate between the different strata, and therefore the information provided little if any substance for a functional analysis of processes involved in normal and pathological differentiation of the epidermis. Particle probes, however, have been able to overcome such methodological problems. Over a period of 15 years we have studied normal human skin, normal-looking, paralesional skin from psoriatics, and skin from persons suffering from atopic dermatitis using PIXE analysis. In recent years, trace elements have been shown to work as secondary messengers or regulatory substances. As an example, calcium (Ca2+) has proven to be a very important signalling substance in a great variety of cellular systems. Studies with the transmission electron microscope (TEM) as well as histochemical methods have allowed an understanding of the role of Ca2+ in the differentiation process of the epidermis. Ca2+ has also been shown to play an important role in apoptosis (programmed cell death), which is currently a hot subject for the obvious reason that the final differentiation step between the stratum granulosum level and the stratum corneum represents a particular aspect of programmed cell death. The importance of the balance between calcium and zinc in apoptosis has been clearly demonstrated in a number of cellular systems, but we have still to clarify the validity of topical treatment with Zn ointments in different skin conditions. Substantial iron (Fe) losses via psoriatic lesions were demonstrated more than two decades ago, and these data were given new meaning when we found that a more discrete loss occurs in clinically normal-looking psoriatic skin. Obviously, such findings stress the importance of understanding the relation between the elemental content and normal and abnormal physiology. The ultimate goal of particle probe studies is to provide an understanding of the formation of a mature stratum corneum with a functional barrier reflected in physiological/biochemical mechanisms behind the properties of changed skin in patients afflicted with skin disorders of genetic or constitutional origin. This paper aims to give an overview of the state of the art in skin physiology made possible through the use of particle probes.
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| 2. |
- Wei, Liu-Ying, et al.
(författare)
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Ultramicrotomy of powder material for TEM/STEM study
- 1997
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Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 36:5, s. 380-381
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Tidskriftsartikel (refereegranskat)abstract
- This paper summarizes methods conventionally used to prepare thin foil samples of powder materials for transmission electron microscopy (TEM) and introduces another variant, ultramicrotomy, for the preparation of TEM samples of industrial dust powder. The choice of ultramicrotoming in the present work was based on two features of this technique: (1) it can produce thin-sectioned specimens with a uniform thickness; (2) it can retain the original elemental distribution in phases of the sample during sectioning. Dust powder preparation and the sectioning procedure are described in this paper. The results of the method are illustrated by examples of TEM/STEM micrographs of industrial dust.
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| 3. |
- Westman, Anna-Karin, et al.
(författare)
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Preparation for TEM of layered samples with fragile microstructure and weak layer interface
- 1999
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Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 45:3, s. 198-202
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work was to prepare for transmission electron microscopy (TEM) a layered structure of materials with fragile microstructure. The samples consisted of two layers of different materials, silicon nitride and borosilicate glass, loosely bonded together. The low strength of the sample resulted in fragmentation during more conventional preparation. However, it was possible to prepare the fragments by mounting them in a titanium specimen carrier with aluminium strips as support. After grinding and polishing, a technique of low-angle ion milling was used to obtain electron beam transparent areas at the nitride/glass interface.
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| 4. |
- Aldskogius, Håkan
(författare)
-
Microglia in neuroregeneration
- 2001
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 54:1, s. 40-46
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Tidskriftsartikel (refereegranskat)abstract
- Microglia has the potential to produce and release a range of factors that directly and/or indirectly promote regeneration in the injured nervous system. The overwhelming evidence indicates, however, that this potential is generally not expressed in vivo. Activated microglia may enhance neuronal degeneration following axotomy, thereby counteracting functional recovery. Microglia does not seem to contribute significantly to axonal outgrowth after peripheral nerve injury, since this process proceeds uneventful even if perineuronal microglia is eliminated. The phagocytic phenotype of microglia is highly suppressed during Wallerian degeneration in the central nervous system. Therefore, microglia is incapable of rapid and efficient removal of myelin debris and its putative growth inhibitory components. In this way, microglia may contribute to regeneration failure in the central nervous system. Structural and temporal correlations are compatible with participation by perineuronal microglia in axotomy-induced shedding of presynaptic terminals, but direct evidence for such participation is lacking. Currently, the most promising case for a promoting effect on neural repair by activated microglia appears to be as a mediator of collateral sprouting, at least in certain brain areas. However, final proof for a critical role of microglia in these instances is still lacking. Results from in vitro studies demonstrate that microglia can develop a regeneration supportive phenotype. Altering the microglial involvement following neural injury from a typically passive or even counterproductive state and into a condition where these cells are actively supporting regeneration and plasticity is, therefore, an exciting challenge and probably a realistic goal.
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| 5. |
- Andersson, C, et al.
(författare)
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Determination of chloride efflux by X-ray microanalysis versus MQAE-fluorescence
- 2002
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 59:6, s. 531-355
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Tidskriftsartikel (refereegranskat)abstract
- The importance of chloride channels for the cell is demonstrated by a number of serious human diseases that are due to mutations in chloride channels. The most well-known of these diseases is cystic fibrosis. Investigations into the mechanisms of the disease and possible treatments require the study of chloride fluxes at the level of individual cells. The present study compares two methods for studies of chloride transport: X-ray microanalysis and MQAE fluorescence with image analysis. As an experimental system, the cAMP-activated chloride channel in cultured respiratory epithelial cells was chosen. Both methods showed that stimulation with the cAMP-elevating agents forskolin and IBMX decreased the chloride content of the cells by about 20-27%. Inducing a driving force for chloride by replacing extracellular chloride by nitrate resulted in a chloride efflux that was significantly increased in the presence of forskolin and IBMX. This study shows that X-ray microanalysis and MQAE fluorescence are adequate and comparable methods for measuring cAMP-dependent chloride transport in individual cells.
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| 6. |
- Anton, Sylvia, et al.
(författare)
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Developmental changes in the structure and function of the central olfactory system in gregarious and solitary desert locusts
- 2002
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Ingår i: Microscopy Research and Technique. - : Wiley. - 1059-910X .- 1097-0029. ; 56:4, s. 281-291
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Desert locusts are guided by olfactory cues in different behavioural contexts. In order to understand the basis for the variable olfactory guided behaviour displayed by different developmental stages and by solitary and gregarious locusts, we investigated their central olfactory system with neuroanatomical and neurophysiological methods. The primary olfactory centre of the brain, the antennal lobe (AL), increases in size during development due to an increased number and size of glomeruli. These glomeruli are innervated by a constant number of projection neurons that display increased dendritic arborizations during the development of the locust. The anatomical parameters do not differ between gregarious and solitary locusts, In parallel with the observed neuroanatomical changes, neurophysiological changes in response spectra and response specificity of AL neurons were found. During development, the percentage of neurons responding specifically to aggregation pheromone components decreases, whereas an increase in both pheromone-generalists and plant-pheromone generalist neurons is observed. The percentage of neurons responding to green leaf volatiles, however, remains constant. A decrease in the number of nymph blend-specific neurons was also observed. Our data show that anatomical and physiological properties of the AL and its neurons to a large extent reflect the changes in olfactory guided behaviour during development and between phases. The majority of our results are also in accordance with findings that the number of olfactory receptor neurons increases during development, resulting in increasing convergence on AL neurons.
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| 7. |
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| 8. |
- Blom, Hans, et al.
(författare)
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Nearest neighbor analysis of dopamine D1 receptors and Na plus -K plus -ATPases in dendritic spines dissected by STED microscopy
- 2012
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 75:2, s. 220-228
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Tidskriftsartikel (refereegranskat)abstract
- Protein localization in dendritic spines is the focus of intense investigations within neuroscience. Applications of super-resolution microscopy to dissect nanoscale protein distributions, as shown in this work with dual-color STED, generate spatial correlation coefficients having quite small values. This means that colocalization analysis to some extent looses part of its correlative impact. In this study we thus introduced nearest neighbor analysis to quantify the spatial relations between two important proteins in neurons, the dopamine D1 receptor and Na+,K+-ATPase. The analysis gave new information on how dense the D1 receptor and Na+,K+-ATPase constituting nanoclusters are located both with respect to the homogenous (self to same) and the heterogeneous (same to other) topology. The STED dissected nanoscale topologies provide evidence for both a joint as well as a separated confinement of the D1 receptor and the Na+,K+-ATPase in the postsynaptic areas of dendritic spines. This confined topology may have implications for generation of local sodium gradients and for structural and functional interactions modulating slow synaptic transmission processes. Microsc. Res. Tech., 2011.
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| 9. |
- Danielson, Patrik, et al.
(författare)
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Immunohistochemical and histochemical findings favoring the occurrence of autocrine/paracrine as well as nerve-related cholinergic effects in chronic painful patellar tendon tendinosis.
- 2006
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 69:10, s. 808-819
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Tidskriftsartikel (refereegranskat)abstract
- The pathogenesis of the pain in patellar tendon tendinosis ("jumper's knee") is unclear. We have recently presented new information about the sensory nervous system in the human patellar tendon, but there is very little information regarding the possible occurrence of a cholinergic system in this tendon. In the present study, specimens of pain-free normal tendons and chronically painful tendinosis tendons were examined by different immunohistochemical and histochemical methods. Antibodies against the M(2) receptor, choline acetyltransferase (ChAT), and vesicular acetylcholine transporter (VAChT) were applied, and staining for demonstration of activity of acetylcholinesterase (AChE) was also utilized. It was found that immunoreactions for the M(2) receptor could be detected intracellularly in both blood vessel cells and tenocytes, especially in tendinosis specimens. Furthermore, in the tendinosis specimens, some tenocytes were seen to exhibit immunoreaction for ChAT and VAChT. AChE reactions were seen in fine nerve fibers associated with small blood vessels in both the normal control tendons and the tendinosis tendons. The observations suggest that there is both a nerve related and a local cholinergic system in the human patellar tendon. As ChAT and VAChT immunoreactions were detected in tenocytes of tendinosis tendons, these cells might be a source of local acetylcholine (Ach) production. As both tenocytes and blood vessel cells were found to exhibit immunoreactions for the M(2) receptor, it is likely that both of these tissue cells may be influenced by ACh. Thus, in conclusion, there appears to be an upregulation of the cholinergic system, and an occurrence of autocrine/paracrine effects in this system, in the tendinosis patellar tendon.
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| 10. |
- Danielson, Patrik, et al.
(författare)
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In situ hybridization studies confirming recent findings of the existence of a local nonneuronal catecholamine production in human patellar tendinosis.
- 2007
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 70:10, s. 908-911
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have in recent studies presented unexpected immunohistochemical evidence favoring the existence of a local production of catecholamines, and an occurrence of adrenergic receptors on the tendon cells (tenocytes), in the human patellar tendon. This was particularly noticed for tendons from patients suffering from tendinosis (chronic tendon pain), which has led us to propose an involvement of this autocrine/paracrine system in the development of tendinosis, especially since catecholamines have been reported to be modulators of tissue remodeling and pain processes. However, the findings concerning catecholamine production have so far only been noted at the level of protein detection, and for this reason, the aim of the present study was to confirm the previous immunohistochemical results by using in situ hybridization (ISH) technique. A ssDNA probe detecting human mRNA for the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) was applied. The ISH results revealed that there were clear reactions indicating the existence of mRNA for TH in tenocytes of tendinosis specimens. It was generally noted that disfigured tenocytes were the ones with the most distinct reactions, while normally looking tenocytes hardly displayed any reactions at all. In conclusion, this study presents the first evidence at the mRNA level of the existence of a local nonneuronal production of catecholamines in human patellar tendon tissue. The findings add to recent observations of the occurrence of a local production in tendons of signal substances traditionally related to neurons. (c) 2007 Wiley-Liss, Inc.
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| 11. |
- Danielson, Patrik, et al.
(författare)
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Studies on the importance of sympathetic innervation, adrenergic receptors, and a possible local catecholamine production in the development of patellar tendinopathy (tendinosis) in man.
- 2007
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 70:4, s. 310-324
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the patterns of production and in the effects of signal substances may be involved in the development of tendinosis, a chronic condition of pain in human tendons. There is no previous information concerning the patterns of sympathetic innervation in the human patellar tendon. In this study, biopsies of normal and tendinosis patellar tendons were investigated with immunohistochemical methods, including the use of antibodies against tyrosine hydroxylase (TH) and neuropeptide Y, and against alpha(1)-, alpha(2A)-, and beta(1)-adrenoreceptors. It was noticed that most of the sympathetic innervation was detected in the walls of the blood vessels entering the tendon through the paratendinous tissue, and that the tendon tissue proper of the normal and tendinosis tendons was very scarcely innervated. Immunoreactions for adrenergic receptors were noticed in nerve fascicles containing both sensory and sympathetic nerve fibers. High levels of these receptors were also detected in the blood vessel walls; alpha(1)-adrenoreceptor immunoreactions being clearly more pronounced in the tendinosis tendons than in the tendons of controls. Interestingly, immunoreactions for adrenergic receptors and TH were noted for the tendon cells (tenocytes), especially in tendinosis tendons. The findings give a morphological correlate for the occurrence of sympathetically mediated effects in the patellar tendon and autocrine/paracrine catecholamine mechanisms for the tenocytes, particularly, in tendinosis. The observation of adrenergic receptors on tenocytes is interesting, as stimulation of these receptors can lead to cell proliferation, degeneration, and apoptosis, events which are all known to occur in tendinosis. Furthermore, the results imply that a possible source of catecholamine production might be the tenocytes themselves. Microsc. Res. Tech., 2007. (c) 2007 Wiley-Liss, Inc.
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| 12. |
- Ferraz, Natalia, 1976-, et al.
(författare)
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Time sequence of blood activation by nanoporous alumina : Studies on platelets and complement system
- 2010
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Ingår i: Microscopy research and technique (Print). - : Wiley-Liss Inc.. - 1059-910X .- 1097-0029. ; 73:12, s. 1101-1109
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Tidskriftsartikel (refereegranskat)abstract
- In the present work the time sequence of blood activation by alumina membranes with different porosities (20 and 200 nm in diameter) was studied. The membranes were incubated with whole blood from 2 min to 4 h. Platelet adhesion and activation in addition to complement activation were monitored at different time points. Evaluation of platelet adhesion and activation was done by determining the change in platelet number and the levels of thrombospondin-1 in the fluid phase. Scanning electron microscopy studies were done to further evaluate platelet adhesion and morphology. Immunocytochemical staining was used to evaluate the presence of CD41 and CD62P antigens on the material surface. Complement activation was monitored by measuring C3a and sC5b-9 in plasma samples by means of enzyme immunoassays. Both alumina membranes displayed similar complement activation time profiles, with levels of C3a and sC5b-9 increasing with incubation time. A statistically significant difference between the membranes was found after 60 min of incubation. Platelet activation characteristics and time profile were different between the two membranes. Platelet adhesion increased over time for the 20 nm surface, while the clusters of microparticles on the 200 nm surface did not appreciably change during the course of the experiment. The release of thrombospondin-1 increased with time for both membranes, however much later for the 200 nm alumina (240 min) as compared to the 20 nm membrane (60 min). The surface topography of the alumina most probably influence protein transition rate, which in turn affects material-platelet activation kinetics.
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| 13. |
- Govindaraju, Indira, et al.
(författare)
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Microscopic and spectroscopic characterization of rice and corn starch
- 2020
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Ingår i: Microscopy research and technique (Print). - : John Wiley & Sons. - 1059-910X .- 1097-0029. ; 83:5, s. 490-498
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Tidskriftsartikel (refereegranskat)abstract
- Starch granules from rice and corn were isolated, and their molecular mechanism on interaction with alpha-amylase was characterized through biochemical test, microscopic imaging, and spectroscopic measurements. The micro-scale structure of starch granules were observed under an optical microscope and their average size was in the range 1-100 mu m. The surface topological structures of starch with micro-holes due to the effect of alpha- amylase were also visualized under scanning electron microscope. The crystallinity was confirmed by X-ray diffraction patterns as well as second-harmonic generation microscopy. The change in chemical bonds before and after hydrolysis of the starch granules by alpha- amylase was determined by Fourier transform infrared spectroscopy. Combination of microscopy and spectroscopy techniques relates structural and chemical features that explain starch enzymatic hydrolysis which will provide a valid basis for future studies in food science and insights into the energy transformation dynamics.
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| 14. |
- Habibi, Maryam, et al.
(författare)
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Corrosion resistance and surface microstructure of Mg 3 N 2 / SS thin films by plasma focus instrument
- 2022
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 85:8, s. 2880-2893
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing a plasma focus (PF) instrument, magnesium nitride (Mg3 N2 ) thin films were synthesized on stainless steel substrates. Twenty five optimum focus shots at 8 cm distance from the anode tip were used to deposit the films at different angular positions regarded to the anode axis. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analyses were performed to assess the surface morphology and structural characteristics of Mg3 N2 films. Based on AFM images, these films were studied to understand the effect of angular position variation on their surfaces through morphological and fractal parameters. By increasing the angle, we verify that the grain size decreased from 130(0) nm to 75(5) nm and also the mean quadratic surface roughness of the films reduced in its average values from (28.97 ± 3.24) nm to (23.10 ± 1.34) nm. Power spectrum density analysis indicated that films become more self-affine at larger angles. Furthermore, the corrosion behavior of the films was investigated through a potentiodynamic polarization test in H2 SO4 solution. It was found that the ion energy and flux, varying with the angular positions from the anode tip, directly affected the nanostructured roughness and surface morphology of the samples. The electrochemical studies of films show that the uncoated sample presented the lowest corrosion resistance. The highest corrosion resistance was obtained for the sample deposited with 25 optimum shots and at 0° angular position reaching a reduction in the corrosion current density of almost 800 times compared to the pure stainless steel-304 substrate.
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| 15. |
- Hansson, Magnus, et al.
(författare)
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Expression of brain natriuretic peptide in the rat heart studies during heart growth and in relation to sympathectomy
- 2004
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 64:1, s. 30-42
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Tidskriftsartikel (refereegranskat)abstract
- Brain natriuretic peptide (BNP) might be of importance during heart development and is described to be increasingly expressed in congestive heart failure and to affect the progress of this condition. However, details in the normal expression of BNP are still unclear in various parts of the adult and growing heart, including the conduction system. In this study, we investigated the expression of BNP in relation to that of atrial natriuretic peptide (ANP) in the growing as well as in the adult rat heart. The effects of chemical sympathectomy in adult rats were also examined. Contrary to previous BNP immunohistochemical studies, the BNP antiserum was preabsorbed with an excess of ANP before staining to abolish the crossreactivity with ANP. There was a pronounced BNP immunoreaction in the auricles, the trabeculated ventricular walls, and the peripheral parts of the conduction system at 0-1 days postnatally. The degree of immunoreaction gradually decreased with increasing age. A similar developmental pattern was seen concerning ANP expression, but the magnitude of the latter clearly exceeded that for BNP. Immunoreaction for BNP was never detected in the atrioventricular (AV) node and AV bundle at any stage. In contrast to the situation for ANP previously observed, no obvious changes in BNP immunoreaction patterns were observed in response to sympathectomy. This is the first study to thoroughly demonstrate the expression of BNP in the various regions of the rat heart during growth and in the normal and sympathectomized adult stage. The observations are related to possible functions of natriuretic peptides in the growing and adult heart.
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| 16. |
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| 17. |
- Johansson, K U I, et al.
(författare)
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The aesthetasc concept: structural variations of putative olfactory cell complexes in Crustacea
- 1992
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Ingår i: Microscopy Research and Technique. - : Wiley. - 1059-910X .- 1097-0029. ; 22, s. 325-335
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the aesthetascs has been investigated in the prawn Macrobrachium rosenbergii (larvae and juveniles), the opossum shrimp Neomysis integer, the euphausid Meganyctiphanes, and in the water-fleas Daphnia magna and D. longispina. The aesthetascs, that are thought to represent olfactory receptors, exhibit a considerable structural variation, ranging from the well known aesthetascs of higher crustaceans (lobster, crab, crayfish) to the corresponding sensilla found in the water-fleas and the males of opossum shrimps. The two following morphological characteristics of the aesthetascs are thought to indicate an olfactory function: the shape of the cuticular hair that is long and essentially hose-shaped, and the thin, loosely arranged cuticle of at least the outer part of the cuticular hair. The presence of other structural elements such as sensory cells, cilia, and enveloping cells are vital for the olfactory function, but the development is variable, which makes their use in the morphological definition of aesthetascs problematic.
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| 18. |
- Lundberg, Simon, et al.
(författare)
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Natriuretic peptide expression in the heart of the TTR-ANP transgenic mouse-Comparison to the normal heart.
- 2005
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Ingår i: Microscopy Research & Technique. - : Wiley. - 1059-910X .- 1097-0029. ; 68:2, s. 97-106
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Tidskriftsartikel (refereegranskat)abstract
- The transgenic mice, TTR-ANP, carrying a fusion gene comprising the transthyretin promoter and the atrial natriuretic peptide (ANP) structural sequence, are known to have elevated ANP plasma levels as well as lowered blood pressure levels. On the other hand, it is not known whether these transgenic mice show changed natriuretic peptide (NP) expression patterns in the heart. Therefore, we examined the distribution of NPs in the myocardium and the conduction system of transgenic mice overexpressing ANP, as well as in wild-type littermates. The hearts were serially sectioned and processed for immunohistochemistry, with antisera against ANP and brain natriuretic peptide (BNP). Florescence microscopy was performed for qualitative analysis. Immunoreactivity for ANP and BNP was detected to a similar degree in the conduction system of both transgenic and wild-type mice. The nodal tissues never exhibited immunoreactions for ANP or BNP, whereas Purkinje fibers of the atrioventricular junctional tissue, bundle branches, and the peripheral Purkinje fiber network exhibited specific immunoreactivity. Atrial and ventricular myocytes of both transgenic and wild-type mice exhibited ANP and BNP to a similar extent. This is the first study examining the expression pattern of NPs in the cardiac conduction system of the mouse as well as the pattern of ANP and BNP expression in the conduction system of TTR-ANP transgenic mice and its wild-type siblings. The findings in this study suggest that ectopic ANP expression and release do not repress cardiac production of ANP.
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| 19. |
- Malmberg, Per, 1974, et al.
(författare)
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Imaging of lipids in human adipose tissue by cluster ion TOF-SIMS
- 2007
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Ingår i: Microsc Res Tech. - : Wiley. - 1059-910X .- 1097-0029. ; 70:9, s. 828-35
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Tidskriftsartikel (refereegranskat)abstract
- Biopsies of human subcutaneous adipose tissue were taken from healthy donors. Samples were high-pressure frozen, freeze-fractured, and freeze dried. Imaging mass spectrometry of samples was performed in a TOF-SIMS mass spectrometer equipped with a bismuth cluster ion source. Blood vessels, the connective tissue, and adipocytes can be seen in TOF-SIMS images. Blood vessels were found labeled by a high content of sodium ions and potassium ions in their lumen and phosphocholine signal in smooth muscle cells of the vessel wall. The connective tissue showed high signal levels of CN(-) fragments, derived from proteins and nucleic acids. Adipocytes showed high signal levels of phosphocholine and cholesterol ubiquitously in their membranes and diacylglycerols in some membrane sites. The central part of adipocytes showed high levels of triacylglycerols and fatty acids. These results are in accordance to those of biochemical studies; however, a precise spatial localization of lipids in adipocytes is demonstrated with MS imaging.
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| 20. |
- Nešić, Nebojša, et al.
(författare)
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Automated segmentation of cell organelles in volume electron microscopy using deep learning
- 2024
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Ingår i: Microscopy Research and Technique. - 1059-910X .- 1097-0029.
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in computing power triggered the use of artificial intelligence in image analysis in life sciences. To train these algorithms, a large enough set of certified labeled data is required. The trained neural network is then capable of producing accurate instance segmentation results that will then need to be re-assembled into the original dataset: the entire process requires substantial expertise and time to achieve quantifiable results. To speed-up the process, from cell organelle detection to quantification across electron microscopy modalities, we propose a deep-learning based approach for fast automatic outline segmentation (FAMOUS), that involves organelle detection combined with image morphology, and 3D meshing to automatically segment, visualize and quantify cell organelles within volume electron microscopy datasets. From start to finish, FAMOUS provides full segmentation results within a week on previously unseen datasets. FAMOUS was showcased on a HeLa cell dataset acquired using a focused ion beam scanning electron microscope, and on yeast cells acquired by transmission electron tomography. Research Highlights: Introducing a rapid, multimodal machine-learning workflow for the automatic segmentation of 3D cell organelles. Successfully applied to a variety of volume electron microscopy datasets and cell lines. Outperforming manual segmentation methods in time and accuracy. Enabling high-throughput quantitative cell biology.
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| 21. |
- Nilsson, Harriet, et al.
(författare)
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A modified technique for the impregnation of lanthanum tracer to study the integrity of tight junctions on cells grown on a permeable substrate
- 2006
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 69:10, s. 776-783
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Tidskriftsartikel (refereegranskat)abstract
- Ionic lanthanum is commonly used to trace permeability pathways across epithelia and endothelia in biological electron microscopy. A method for obtaining a uniformly dense precipitate of lanthanum is described. The method, which is a modification of the technique described by Shaklai and Tavassoli (1977) was suitable for fixation of cell cultures grown on permeable filter inserts and was successfully applied to study opening of tight junctions by hypertonic solutions in the airway epithelial cell line 16HBE14o(-). The preparation method formed the basis for a semi-quantitative morphological determination in which the tight junctions were subdivided as "intact," "weakened," and "open." By using this modified technique, it could be demonstrated that opening of tight junctions in airway epithelial cells increased, with increasing osmolarity with electrolytes having a stronger effect than nonelectrolytes. A significant linear relationship was found between the osmolarity of the medium and the open state of the tight junctions (as determined by the semi-quantitative morphological technique) or the transepithelial electrical resistance.
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| 22. |
- Nygren, Håkan, 1952, et al.
(författare)
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Bioimaging TOF-SIMS: High resolution 3D imaging of single cells.
- 2007
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Ingår i: Microscopy research and technique. - : Wiley. - 1059-910X .- 1097-0029. ; 70:11, s. 969-74
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of phosphocholine ions (m/z 184, m/z 86), sodium ions, and potassium ions in thyroid tumor cells was analyzed by imaging TOF-SIMS. Repeated sputtering with a C(60) (+) source and subsequent analysis with a Bi(3) (+) gun produced a series of 138 images that were stacked to make a 3D display of the chemistry of cells. Phosphocholine was seen in the plasma membrane (m/z 184) and intracellular membranes (m/z 86). The different fragmentation of the phospholipid probably reflects the chemical composition of membranes at these sites. High intensity of secondary ion signals of potassium was seen in membrane-encompassed cellular compartments. The data indicate that potassium ions are compartmentalized in thyroid tumor cells.
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| 23. |
- Nygren, Håkan, 1952, et al.
(författare)
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Bioimaging TOF-SIMS of tissues by gold ion bombardment of a silver-coated thin section.
- 2004
-
Ingår i: Microscopy research and technique. - : Wiley. - 1059-910X .- 1097-0029. ; 65:6, s. 282-6
-
Tidskriftsartikel (refereegranskat)abstract
- The imaging time-of-flight secondary-ion-mass-spectrometry (TOF-SIMS) method was utilized to address the problem of cholesterol localization in rat tissues. Rat kidneys were fixed, cryoprotected by sucrose, frozen, sectioned by cryoultramicrotomy, and dried at room temperature. The samples were either covered with a thin silver layer or analyzed uncovered in an imaging TOF-SIMS instrument equipped with an Au1-3(+)-source. The yield of desorbed secondary ions for some species was up to 600-fold higher after silver coating of the samples. Reference samples of cholesterol were silver-coated and analyzed by TOF-SIMS to define significant peaks, specific for cholesterol. Such peaks were found at m/z = 386 (C27H46O+), m/z = 493 (C27H46O107Ag+), m/z = 495 (C27H46O109Ag+), m/z = 879 (C54H92O2 107Ag+), and m/z = 881 (C54H92O2 109Ag+). The silver-cationized cholesterol (493 < or = m/z < or = 495) signal was localized by imaging TOF-SIMS in the kidney sections and showed a high cholesterol content in the kidney glomeruli. A more diffuse distribution of cholesterol was also found over areas representing the cytoplasm or plasma membrane of the epithelial cells in the proximal tubules of rat kidney.
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| 24. |
- Nygren, Håkan, 1952, et al.
(författare)
-
Imaging TOF-SIMS of rat kidney prepared by high-pressure freezing.
- 2005
-
Ingår i: Microscopy research and technique. - : Wiley. - 1059-910X .- 1097-0029. ; 68:6, s. 329-34
-
Tidskriftsartikel (refereegranskat)abstract
- Phosphocholine, potassium ions, and sodium ions were localized in rat kidney with imaging TOF-SIMS. Tissue preparation was performed with high-pressure freezing, freeze-fracturing and freeze-drying. The distribution of sodium ions was visualized by imaging the signal at m/z 23 of positively charged secondary ions, and the distribution of potassium ions was visualized by imaging the signal at m/z 39. Potassium was found localized within cells of the proximal tubulus epithelium and within cells of the glomeruli. High signals of sodium ions were seen in the interstitial tissue and also in epithelial cells of the collecting ducts and in glomeruli. The overlay image showed that the distribution of sodium ions and potassium ions were largely complementary with color mixing in glomeruli and in the interstitium surrounding proximal tubules. The ion distribution was further analyzed by correlation analysis. Phosphocholine-containing phospholipids were visualized by imaging the phosphocholine head group at m/z 184 of positively charged ions. The m/z 184 signal shows a ubiquitous distribution with a high intensity of phosphocholine in epithelial cells. Overlay image of m/z 184, m/z 39, and m/z 23 and multivariate analysis showed that the localization of high levels of phosphocholine colocalizes with high levels of potassium ions, as expected for an ion with intracellular localization.
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| 25. |
- Palisaitis, Justinas
(författare)
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Use of cleaved wedge geometry for plan-view transmission electron microscopy sample preparation
- 2021
-
Ingår i: Microscopy research and technique (Print). - : Wiley-Blackwell. - 1059-910X .- 1097-0029. ; 84:12, s. 3182-3190
-
Tidskriftsartikel (refereegranskat)abstract
- A fast, convenient, and easy to perform method for preparing plan-view transmission electron microscopy (TEM) specimens of brittle materials is proposed. The method is ideal for thin films/coatings and based on obtaining wedge-shape geometries of the samples via conventional cutting and cleaving followed by gentle focused ion beam (FIB) milling to electron transparency. It enables multiple parallel windows for depth sectioning of the samples and facilitates FIB lift-out procedure. The method has been successfully applied for preparing high-quality plan-view TEM samples for a range of films deposited on Si, SiC, and Al2O3 which significantly enhances throughput and reduces time at the FIB. The method further offers high success rate even for the novice, stable handling and reproducibility, which greatly widens the application of advanced plan-view TEM studies in material science.
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| 26. |
- Richter, Katrin, 1979, et al.
(författare)
-
Localization of fatty acids with selective chain length by imaging time-of-flight secondary ion mass spectrometry.
- 2007
-
Ingår i: Microscopy research and technique. - : Wiley. - 1059-910X .- 1097-0029. ; 70:7, s. 640-7
-
Tidskriftsartikel (refereegranskat)abstract
- Localization of fatty acids in biological tissues was made by using TOF-SIMS (time-of-flight secondary ion mass spectrometry). Two cell-types with a specific fatty acid distribution are shown. In rat cerebellum, different distribution patterns of stearic acid (C18:0), palmitic acid (C16:0), and oleic acid (C18:1) were found. Stearic acid signals were observed accumulated in Purkinje cells with high intensities inside the cell, but not in the nucleus region. The signals colocalized with high intensity signals of the phosphocholine head group, indicating origin from phosphatidylcholine or sphingomyelin. In mouse intestine, high palmitic acid signals were found in the secretory crypt cells together with high levels of phosphorylinositol colocalized in the crypt region. Palmitic acid was also seen in the intestinal lumen that contains high amounts of mucine, which is known to be produced in the crypt cells. Linoleic acid signals (C18:2) were low in the crypt region and high in the villus region. Oleic acid signals were seen in the villi and stearic acid signals were ubiquitous with no specific localization in the intestine. We conclude that the results obtained by using imaging TOF-SIMS are consistent with known brain and intestine biochemistry and that the localization of fatty acids is specific in differentiated cells.
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| 27. |
- Rieppo, Lassi, et al.
(författare)
-
Quantitative analysis of spatial proteoglycan content in articular cartilage with Fourier transform infrared imaging spectroscopy : Critical evaluation of analysis methods and specificity of the parameters.
- 2010
-
Ingår i: Microscopy research and technique (Print). - : John Wiley & Sons. - 1059-910X .- 1097-0029. ; 73:5, s. 503-512
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To evaluate the specificity of the current Fourier transform infrared imaging spectroscopy (FT-IRIS) methods for the determination of depthwise proteoglycan (PG) content in articular cartilage (AC). In addition, curve fitting was applied to study whether the specificity of FT-IRIS parameters for PG determination could be improved.METHODS: Two sample groups from the steer AC were prepared for the study (n = 8 samples/group). In the first group, chondroitinase ABC enzyme was used to degrade the PGs from the superficial cartilage, while the samples in the second group served as the controls. Samples were examined with FT-IRIS and analyzed using previously reported direct absorption spectrum techniques and multivariate methods and, in comparison, by curve fitting. Safranin O-stained sections were measured with digital densitometry to obtain a reference for depthwise PG distribution.RESULTS: Carbohydrate region-based absorption spectrum methods showed a statistically weaker correlation with the PG reference distributions than the results of the curve fitting (subpeak located approximately at 1,060 cm(-1)). Furthermore, the shape of the depthwise profiles obtained using the curve fitting was more similar to the reference profiles than with the direct absorption spectrum analysis.CONCLUSIONS: Results suggest that the current FT-IRIS methods for PG analysis lack the specificity for quantitative measurement of PGs in AC. The curve fitting approach demonstrated that it is possible to improve the specificity of the PG analysis. However, the findings of the present study suggest that further development of the FT-IRIS analysis techniques is still needed.
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| 28. |
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| 29. |
- Salford, Leif G., et al.
(författare)
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Permeability of the blood‐brain barrier induced by 915 MHz electromagnetic radiation, continuous wave and modulated at 8, 16, 50, and 200 Hz
- 1994
-
Ingår i: Microscopy Research and Technique. - : Wiley. - 1059-910X .- 1097-0029. ; 27:6, s. 535-542
-
Tidskriftsartikel (refereegranskat)abstract
- Biological effects of electromagnetic fields (EMF) on the blood‐brain barrier (BBB) can be studied in sensitive and specific models. In a previous investigation of the permeability of the blood‐brain barrier after exposure to the various EMF‐components of proton magnetic resonance imaging (MRI), we found that the exposure to MRI induced leakage of Evans Blue labeled proteins normally not passing the BBB of rats [Salford et al. (1992), in: Resonance Phenomena in Biology, Oxford University Press, pp. 87–91]. In the present investigation we exposed male and female Fischer 344 rats in a transverse electromagnetic transmission line chamber to microwaves of 915 MHz as continuous wave (CW) and pulse‐modulated with repetition rates of 8, 16, 50, and 200 s−1. The specific energy absorption rate (SAR) varied between 0.016 and 5 W/kg. The rats were not anesthetized during the 2‐hour exposure. All animals were sacrificed by perfusion‐fixation of the brains under chloral hydrate anesthesia about 1 hour after the exposure. The brains were perfused with saline for 3–4 minutes, and thereafter fixed in 4% formaldehyde for 5–6 minutes. Central coronal sections of the brains were dehydrated and embedded in paraffin and sectioned at 5 μm. Albumin and fibrinogen were demonstrated immunohistochemically. The results show albumin leakage in 5 of 62 of the controls and in 56 of 184 of the animals exposed to 915 MHz microwaves. Continuous wave resulted in 14 positive findings of 35, which differ significantly from the controls (P = 0.002). With pulsed 915 MHz microwaves with repetition rates of 200, 50, 16, and 8 s−1, 42 of 149 were positive, which is highly significant at the P = 0.001 level. This reveals that both CW and pulsed 915 MHz microwaves have the potential to open up the BBB for albumin passage. However, there is no significant difference between continuous and pulsed 915 MHz microwaves in this respect. The frequency of occurrence of extravasates (26%) was found to be independent of SAR for SAR < 2.5 W/kg, but rose significantly for the higher SAR values (to 43%). The question of whether the opening of the blood‐brain barrier constitutes a health hazard demands further investigation. © 1994 Wiley‐Liss, Inc.
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| 30. |
- Sandberg, Tomas, et al.
(författare)
-
Mucin coatings suppress neutrophil adhesion to a polymeric model biomaterial
- 2007
-
Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 70:10, s. 864-868
-
Tidskriftsartikel (refereegranskat)abstract
- Following our recent study on the fractionation, characterization, and model adsorption of mucins derived from bovine salivary glands (BSM), porcine stomach scrapings (PGM), and human whole saliva (MG1), we here present a microscopic evaluation of the interactions between mucin-coated substrates and human neutrophils. Our results show that surface-coating with BSM, PGM, and MG1 can be effectively used to suppress the adhesion of neutrophils to a polymeric model biomaterial (Thermanox). Neutrophil morphologies found on Thermanox substrates coated with mucins resemble those observed for nonactivated neutrophils found in circulation. Notably, low neutrophil adhesion can be obtained at a significantly lower coating concentration (0.125 mg/mL) for the compositionally complex MG1 mucin than for the relatively pure BSM and PGM mucins (1 mg/mL). Furthermore, since coating at a low BSM and PGM concentration (0.25 mg/mL) results in higher cell counts and more spread cells than in the high-concentration case, we suggest that dense mucin surface packing is critical for good coating performance. In conclusion, the present study demonstrates how mucins from three different sources, of different compositional and structural status, efficiently can be used to suppress neutrophil adhesion and activation. This finding makes them potent candidates for use as biomaterial coatings.
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| 31. |
- Siegel, G, et al.
(författare)
-
Tumor cell locomotion and metastatic spread
- 1998
-
Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 43, s. 276-282
-
Tidskriftsartikel (refereegranskat)abstract
- The cytoskeletal filament proteins cu-actinin, filamin, desmin, and filamin-desmin aggregates were adsorbed to a hydrophobic silica surface. The adsorbed amount as measured by ellipsometric methods after rinsing and equilibration was 2.7 mg/m(2) for alpha-actinin and 0.4 mg/m(2) for filamin plus desmin, respectively. Adsorbed layer thicknesses in physiological salt solution were about 107 nm, 89 nm, 108 nm and 93 nm for alpha-actinin, filamin, desmin, and cross-linked filamin-desmin, respectively. Ca2+ ions in a concentration of 10(-4), 10(-3), and 2.52 mmol/l had no effect on the adsorbed amount, refractive index, and adsorbed layer thickness of the individual intermediate filament proteins. Cross-linked filamin-desmin, however, reacted markedly upon the addition of these Ca2+ concentrations with a change in refractive index and adsorbed layer thickness. The layer formed by the filamin- desmin complex contracted by 2-3, 6-7, and 6-7 nm, respectively. The maximum shortening occurred at 1 mu mol/l Ca2+. The Ca2+-dependent adsorbed layer changes of cross-linked filamin-desmin supports the contractile mechanisms in muscular tissues and forms the basis for migration and motility in nonmuscular cells. These motional events are crucially involved in peripheral organ perfusion, inflammation, and tumor invasion and metastasis.
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| 32. |
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| 33. |
- Sun, Y, et al.
(författare)
-
Volumetric flow mapping for microvascular networks by bimodality imaging with light microscope and laser Doppler imager
- 2004
-
Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 65:3, s. 130-138
-
Tidskriftsartikel (refereegranskat)abstract
- A method was developed to produce a composite image of microvascular networks with grayscales proportional to volumetric flows. Velocities in arterioles and venules were assessed with a high-resolution laser Doppler imager (LDI). The vascular structures were quantified from the micrograph with a computerized vessel detection algorithm. After registering the detected vascular network with the LDI scan, volumetric flows were calculated along the centerlines of the vessels. In vivo data were obtained from the hamster cheek pouch in 6 studies. Flow continuity of the flow map was evaluated by comparing the main flow (Q) with the sum of branch flows (Qs), averaging over the respective vessel segments incident to each bifurcation. The method was reproducible across the 6 studies with the correlation coefficient (r) between Qs and Q ranging from 0.913 to 0.986. In all, over 20,000 flow estimates from 360 vessel segments (24-160 μm in diameter) at 166 bifurcations were analyzed. With flow normalized between 0 and 1, the linear regression yielded: Qs = 1.03 Q + 0.006, r = 0.952, n = 166, P < 0.0005. The bimodality imaging method exploits a large amount of velocity and diameter data, and therefore should be useful for studying heterogeneous flows in the microvasculature. © 2004 Wiley-Liss, Inc.
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| 34. |
- Tanner, Hugh, et al.
(författare)
-
Labelling strategies for correlative light electron microscopy
- 2023
-
Ingår i: Microscopy research and technique (Print). - : John Wiley & Sons. - 1059-910X .- 1097-0029. ; 86:8, s. 901-910
-
Forskningsöversikt (refereegranskat)abstract
- Imaging is one of the key technologies underpinning discoveries in biomedical research. Each imaging technique however usually only provides a specific type of information. For instance, live-cell imaging using fluorescent tags can show us the dynamics of a system. On the other hand, electron microscopy (EM) gives us better resolution combined with the structural reference space. By applying a combination of light and electron microscopy modalities to a single sample one can exploit the advantages of both techniques in correlative light electron microscopy (CLEM). Although CLEM approaches can generate additional insights into the sample that cannot be gained by either technique in isolation, the visualization of the object of interest via markers or probes is still one of the bottlenecks in a Correlative Microscopy workflow. Whereas fluorescence is not directly visible in a standard electron microscope, gold particles, as the most common choice of probe for EM can also only be visualized using specialized light microscopes. In this review we will discuss some of the latest developments of probes for CLEM and some strategies how to choose a probe, discussing pros and cons of specific probes, and ensuring that they function as a dual modality marker.
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| 35. |
- Verissimo, Ana, et al.
(författare)
-
Nuclear microscopy: A tool for and percutaneous absorption imaging elemental distribution in vivo
- 2007
-
Ingår i: Microscopy Research and Technique. - : Wiley. - 1059-910X .- 1097-0029. ; 70:4, s. 302-309
-
Tidskriftsartikel (refereegranskat)abstract
- Nuclear microscopy is a technique based on a focused beam of accelerated particles that has the ability of imaging the morphology of the tissue in vivo and of producing the correspondent elemental maps, whether in major, minor, or trace concentrations. These characteristics constitute a strong advantage in studying the morphology of human skin, its elemental distributions and the permeation mechanisms of chemical compounds. In this study, nuclear microscopy techniques such as scanning transmission ion microscopy and particle induced X-ray emission were applied simultaneously, to cryopreserved human skin samples with the purpose of obtaining high-resolution images of cells and tissue morphology. In addition, quantitative elemental profiling and mapping of phosphorus, calcium, chlorine, and potassium in skin cross-sections were obtained. This procedure accurately distinguishes the epidermal strata and dermis by overlapping in real time the elemental information with density images obtained from the transmitted beam. A validation procedure for elemental distributions in human skin based on differential density of epidermal strata and dermis was established. As demonstrated, this procedure can be used in future studies as a tool for the in vivo examination of trans-epidermal and -dermal delivery of products. .
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| 36. |
- Von Tiedemann, M., et al.
(författare)
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Image adaptive point-spread function estimation and deconvolution for in vivo confocal microscopy
- 2006
-
Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 69:1, s. 10-20
-
Tidskriftsartikel (refereegranskat)abstract
- Visualizing deep inside the tissue of a thick biological sample often poses severe constraints on image conditions. Standard restoration techniques (denoising and deconvolution) can then be very useful, allowing one to increase the signal-to-noise ratio and the resolution of the images. In this paper, we consider the problem of obtaining a good determination of the point-spread function (PSF) of a confocal microscope, a prerequisite for applying deconvolution to three-dimensional image stacks acquired with this system. Because of scattering and optical distortion induced by the sample, the PSF has to be acquired anew for each experiment. To tackle this problem, we used a screening approach to estimate the PSF adaptively and automatically from the images. Small PSF-like structures were detected in the images, and a theoretical PSF model reshaped to match the geometric characteristics of these structures. We used numerical experiments to quantify the sensitivity of our detection method, and we demonstrated its usefulness by deconvolving images of the hearing organ acquired in vitro and in vivo.
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| 37. |
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| 38. |
- Thore, Carl-Johan, 1981-, et al.
(författare)
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Game formulations for structural optimization under uncertainty
- 2020
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Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 121:1, s. 165-185
-
Tidskriftsartikel (refereegranskat)abstract
- We consider structural optimization (SO) under uncertainty formulated as a mathematical game between two players -- a "designer" and "nature". The first player wants to design a structure that performs optimally, whereas the second player tries to find the worst possible conditions to impose on the structure. Several solution concepts exist for such games, including Stackelberg and Nash equilibria and Pareto optima. Pareto optimality is shown not to be a useful solution concept. Stackelberg and Nash games are, however, both of potential interest, but these concepts are hardly ever discussed in the literature on SO under uncertainty. Based on concrete examples of topology optimization of trusses and finite element-discretized continua under worst-case load uncertainty, we therefore analyze and compare the two solution concepts. In all examples, Stackelberg equilibria exist and can be found numerically, but for some cases we demonstrate nonexistence of Nash equilibria. This motivates a view of the Stackelberg solution concept as the correct one. However, we also demonstrate that existing Nash equilibria can be found using a simple so-called decomposition algorithm, which could be of interest for other instances of SO under uncertainty, where it is difficult to find a numerically efficient Stackelberg formulation.
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| 39. |
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| 40. |
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| 41. |
- Alastrue, V., et al.
(författare)
-
On the use of non-linear transformations for the evaluation of anisotropic rotationally symmetric directional integrals. Application to the stress analysis in fibred soft tissues
- 2009
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 1097-0207 .- 0029-5981. ; 79:4, s. 474-504
-
Tidskriftsartikel (refereegranskat)abstract
- Microsphere-based constitutive models are a helpful tool in the modelling of materials with a microstructure composed of contributing elements directionally arranged. This is the case, for instance, for fibred soft tissues. In these models, the macroscopic mechanical behaviour is obtained from the integration of the micro-structural contribution of each component (e.g. each fibre) over the surface of an underlying microsphere, which allows incorporating the mechanical features of the micro-constituents to the macroscopic response. The combination of this sort of models and the associated numerical techniques constitutes a powerful modelling tool for which an efficient integration scheme is required. In this regard, the unit sphere discretizations proposed by Bazant and Oh (ZAMM-J Appl Math Mech Z Angew Math Mech 1986; 66(1):37-49) have been used for the integration of the microscopic contributions in isotropic materials. Nevertheless, the inclusion of anisotropy has important implications with regard to the integration scheme, since very fine discretizations are needed to perform the integration accurately, causing the integration process to be very costly. In addition, the storage of internal variables at each integration direction of every integration point is required for constitutive models based on the use of internal variables at the micro-structural level, which renders this approach rather complex and memory demanding. In order to reduce the number of necessary integration directions, several non-linear transformations for the integration of rotationally symmetric functions over the Surface of the unit sphere are here presented. Their accuracy in the integration of the von Mises orientation distribution function is evaluated. Furthermore, a hyperelastic microsphere-based constitutive law for the modelling of soft biological tissues is used in order to check the accuracy and computational efficiency of the proposed transformations within a Finite Element context in inhomogeneous deformation problems. Simulation results show the suitability of the proposed methodology in order to accurately approximate the Value of the integrals within reasonable computational costs. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 42. |
- Appelo, D., et al.
(författare)
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An energy-based discontinuous Galerkin method for coupled elasto-acoustic wave equations in second-order form
- 2019
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 119:7, s. 618-638
-
Tidskriftsartikel (refereegranskat)abstract
- We consider wave propagation in a coupled fluid-solid region separated by a static but possibly curved interface. The wave propagation is modeled by the acoustic wave equation in terms of a velocity potential in the fluid, and the elastic wave equation for the displacement in the solid. At the fluid solid interface, we impose suitable interface conditions to couple the two equations. We use a recently developed energy-based discontinuous Galerkin method to discretize the governing equations in space. Both energy conserving and upwind numerical fluxes are derived to impose the interface conditions. The highlights of the developed scheme include provable energy stability and high order accuracy. We present numerical experiments to illustrate the accuracy property and robustness of the developed scheme.
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| 43. |
- Araujo-Cabarcas, Juan Carlos, 1981-, et al.
(författare)
-
Shape optimization for the strong directional scattering of dielectric nanorods
- 2021
-
Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 122:8, s. 3683-3704
-
Tidskriftsartikel (refereegranskat)abstract
- In this project, we consider the shape optimization of a dielectric scatterer aiming at efficient directional routing of light. In the studied setting, light interacts with a penetrable scatterer with dimension comparable to the wavelength of an incoming planar wave. The design objective is to maximize the scattering efficiency inside a target angle window. For this, a Helmholtz problem with a piecewise constant refractive index medium models the wave propagation, and an accurate Dirichlet-to-Neumann map models an exterior domain. The strategy consists of using a high-order finite element (FE) discretization combined with gradient-based numerical optimization. The latter consists of a quasi-Newton (BFGS) with backtracking line search. A discrete adjoint method is used to compute the sensitivities with respect to the design variables. Particularly, for the FE representation of the curved shape, we use a bilinear transfinite interpolation formula, which admits explicit differentiation with respect to the design variables. We exploit this fact and show in detail how sensitivities are obtained in the discrete setting. We test our strategy for a variety of target angles, different wave frequencies, and refractive indexes. In all cases, we efficiently reach designs featuring high scattering efficiencies that satisfy the required criteria.
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| 44. |
- Ask, Anna, et al.
(författare)
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Inverse-motion-based form finding for quasi-incompressible finite electroelasticity
- 2013
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 1097-0207 .- 0029-5981. ; 94:6, s. 554-572
-
Tidskriftsartikel (refereegranskat)abstract
- This work deals with inverse-motion-based form finding for electroelasticity. The inverse motion problem is formulated for the electroelastic case, and the resulting equations are implemented within a finite element framework. A four-field variational approach is adopted, taking into consideration the typically incompressible behavior of the elastomer materials commonly used in electromechanical applications. By means of numerical simulations, the inverse-motion-based form finding makes it possible to design the referential configuration so that a given set of loads and boundary conditions results in a prespecified deformed configuration. The computational finite element framework established in this work allows for such numerical simulations and testing and thereby the possibility to improve the design and accuracy in electroelastic applications such as grippers, sensors, and seals.
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| 45. |
- Auth, Kim Louisa, 1995, et al.
(författare)
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Modeling of environmentally assisted intergranular crack propagation in polycrystals
- 2023
-
Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 124:23, s. 5183-5199
-
Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline nickel-based superalloys experience accelerated intergranular crack growth when exposed to dwell times in oxygen-rich environments and a combination of high temperature and tensile mechanical loading. Increasing crack growth rates are observed for increasing amounts of environmental oxygen in a certain oxygen concentration range, while below and above that range crack growth rates remain approximately constant. A fully coupled chemo-mechanical modeling framework accounting for the degradation of grain boundaries by oxygen has been presented by the authors. In this work, we expand the framework by a moving boundary condition to capture a realistic oxygen flux in grain boundary cracks for both edge cracks connected to the environment and interior cracks. In numerical simulation results, the behavior of the moving boundary condition is shown for intergranular crack propagation through a polycrystal subjected to cyclic loading. Finally, the capabilities of the modeling framework to qualitatively predict the dependence of the average crack growth rate on the environmental oxygen content, load level, and dwell time are evaluated and it is shown that predictions qualitatively agree with experimental observations for intergranular fracture.
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| 46. |
- Battini, Jean-Marc
(författare)
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A rotation-free corotational plane beam element for non-linear analyses
- 2008
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 75:6, s. 672-689
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a plane beam element without rotational degrees of freedom that can be used for the analysis of non-linear problems. The element is based on two main ideas. First, a corotational approach is adopted, which means that the kinematics of the element is decomposed into a rigid body motion part and a deformational part. Next, in the deformational part. the local nodal rotations are extrapolated as a function of the local displacements of the two nodes of the element and the first nodes to the left and right of the element. Six numerical applications are presented in order to assess the performance of the formulation.
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| 47. |
- Becker, R., et al.
(författare)
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A hierarchical NXFEM for fictitious domain simulations
- 2011
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 86:4-5, s. 549-559
-
Tidskriftsartikel (refereegranskat)abstract
- We suggest a fictitious domain method, based on the Nitsche XFEM method of (Comput. Meth. Appl. Mech. Engrg 2002; 191: 5537-5552), that employs a band of elements adjacent to the boundary. In contrast, the classical fictitious domain method uses Lagrange multipliers on a line (surface) where the boundary condition is to be enforced. The idea can be seen as an extension of the Chimera method of (ESAIM: Math. Model Numer. Anal. 2003; 37: 495-514), but with a hierarchical representation of the discontinuous solution field. The hierarchical formulation is better suited for moving fictitious boundaries since the stiffness matrix of the underlying structured mesh can be retained during the computations. Our technique allows for optimal convergence properties irrespective of the order of the underlying finite element method.
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| 48. |
- Bengzon, Fredrik, 1978-, et al.
(författare)
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Adaptive finite element approximation of multiphysics problems : a fluid structure interaction model problem
- 2010
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 84:12, s. 1451-1465
-
Tidskriftsartikel (refereegranskat)abstract
- We consider computation of the displacement of an elastic object immersed into a viscous incompressible flow. For simplicity, we assume that the mechanics of the solid is governed by linear elasticity and the motion of the fluid by the Stokes equation. We derive an a posteriori error estimate for this one way coupled problem using duality techniques. Based on these estimates we develop an adaptive algorithm that automatically constructs a suitable adapted mesh for the fluid and solid domains given goal quantities specified on the solid problem.
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| 49. |
- Bergman, Greger, et al.
(författare)
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A finite element model for thermomechanical analysis of sheet metal forming
- 2004
-
Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 59:9, s. 1167-1186
-
Tidskriftsartikel (refereegranskat)abstract
- A thermal model based on explicit time integration is developed and implemented into the explicit finite element code DYNA3D to model simultaneous forming and quenching of thin-walled structures. A staggered approach is used for coupling the thermal and mechanical analysis, wherein each analysis is performed with different time step sizes. The implementation includes a thermal shell element with linear temperature approximation in the plane and quadratic in the thickness direction, and contact heat transfer. The material behaviour is described by a temperature-dependent elastic-plastic model with a non-linear isotropic hardening law. Transformation plasticity is included in the model. Examples are presented to validate and evaluate the proposed model. The model is evaluated by comparison with a one-sided forming and quenching experiment
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| 50. |
- Bernland, Anders, et al.
(författare)
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Acoustic shape optimization using cut finite elements
- 2018
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Ingår i: International Journal for Numerical Methods in Engineering. - Hoboken : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 113:3, s. 432-449
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Tidskriftsartikel (refereegranskat)abstract
- Fictitious domain methods are attractive for shape optimization applications, since they do not require deformed or regenerated meshes. A recently developed such method is the CutFEM approach, which allows crisp boundary representations and for which uniformly well-conditioned system matrices can be guaranteed. Here, we investigate the use of the CutFEM approach for acoustic shape optimization, using as test problem the design of an acoustic horn for favorable impedance-matching properties. The CutFEM approach is used to solve the Helmholtz equation, and the geometry of the horn is implicitly described by a level-set function. To promote smooth algorithmic updates of the geometry, we propose to use the nodal values of the Laplacian of the level-set function as design variables. This strategy also improves the algorithm's convergence rate, counteracts mesh dependence, and, in combination with Tikhonov regularization, controls small details in the optimized designs. An advantage with the proposed method is that the exact derivatives of the discrete objective function can be expressed as boundary integrals, as opposed to when using a traditional method that uses mesh deformations. The resulting horns possess excellent impedance-matching properties and exhibit surprising subwavelength structures, not previously seen, which are possible to capture due to the fixed mesh approach.
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