| 1. |
- Alrifaiy, Ahmed
(författare)
-
A gastight microfluidic system combined with optical tweezers and optical spectroscopy for electrophysiological investigations of single biological cells
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stroke affects around 20 million people around the world every year. Clinically, stroke is a result of brain damage due to the shortage of oxygen delivered to the nerve cells. To minimize suffering and costs related to the disease, extensive research is performed on different levels. The focus of our research is to achieve fundamental understanding on how the lack of oxygen in brain tissue activates intrinsic biomolecular defense mechanisms that may reduce brain damage. More knowledge may hopefully lead to new therapeutic and preventive strategies on the molecular level for individuals in the risk zone for stroke or those who have just suffered a stroke. The area of study is based on the discovery of a hemoprotein called neuroglobin (Ngb), which is found in various regions in the brain, in the islets of Langerhans, and in the retina. Several studies have shown that Ngb seems to have a protective function against hypoxia-related damage. However, until now, it has not been understood how Ngb affects the nerve system and protects neurons from damage. The well-established patch-clamp technique is routinely used to measure and analyze the electrophysiological activity of individual biological cells. To perform accurate patchclamp experiments, it is important to create well-controlled physiological conditions, i.e. different oxygen levels and fast changes of nutrients and other biochemical substances. A promising approach is to apply lab-on-a-chip technologies combined with optical manipulation techniques. These give optimal control over fast changing environmental conditions and enable multiple readouts. The conventional open patch-clamp configuration cannot provide adequate control of the oxygen content. Therefore, it was substituted by a gas-tight multifunctional microfluidic system, a lab-on-a-chip, with an integrated patch-clamp micropipette. The system was combined with optical tweezers and optical spectroscopy. Laser tweezers were used to optically guide and steer single cells towards the fixed micropipette. Optical spectroscopy was used to investigate the biochemical composition of the sample. The designed, closed lab-on-a-chip acted as a multifunctional system for simultaneous electrophysiological and spectroscopic experiments with good control over the oxygen content in the liquid perifusing the cells. The system was tested in a series of experiments: optically trapped human red blood cells were steered to the fixed patch-clamp pipette within the microfluidic system. The oxygen content within the microfluidic channels was measured to 1 % compared to the usual 4-7 %. The trapping dynamics were monitored in real-time while the spectroscopic measurements were performed simultaneously to acquire absorption spectra of the trapped cell under varying environments. To measure the effect of the optical tweezers on the sample, neurons from rats in a Petri dish were optically trapped and steered towards the patch-clamp micropipette where electrophysiological investigations were performed. The optical tweezers had no effect on the electrophysiological measurements. Similar investigations within a closed microfluidic system were initiated and showed promising results for further developments of a complete lab-on-a-chip multifunctional system for reliable patch-clamp measurements. The future aim is to perform complete protocols of patch-clamp electrophysiological investigations while simultaneously monitoring the biochemical composition of the sample by optical spectroscopy. The straightforwardness and stability of the microfluidic chip have shown excellent potential to enable high volume production of scalable microchips for various biomedical applications. The subsequent ambition is to use this system as a mini laboratory that has benefits in cell sorting, patch-clamp, and fertilization experiments where the gaseous and the biochemical content is of importance. The long-term goal is to study the response of individual neurons and defense mechanisms under hypoxic conditions that may establish new ways to understand cell behavior related to Ngb for various diseases such as stroke, Alzheimer’s and Parkinson’s.
|
|
| 2. |
- Aspholm, Marina, et al.
(författare)
-
Helicobacter pylori adhesion to carbohydrates
- 2006
-
Ingår i: Methods in Enzymology. - 0076-6879 .- 1557-7988. ; 417, s. 293-339
-
Tidskriftsartikel (refereegranskat)abstract
- Adherence of bacterial pathogens to host tissues contributes to colonization and virulence and typically involves specific interactions between bacterial proteins called adhesins and cognate oligosaccharide (glycan) or protein motifs in the host that are used as receptors. A given pathogen may have multiple adhesins, each specific for a different set of receptors and, potentially, with different roles in infection and disease. This chapter provides strategies for identifying and analyzing host glycan receptors and the bacterial adhesins that exploit them as receptors, with particular reference to adherence of the gastric pathogen Helicobacter pylori.
|
|
| 3. |
- Axner, Ove, 1957-, et al.
(författare)
-
Assessing bacterial adhesion on an individual adhesin and single pili level using optical tweezers
- 2011
-
Ingår i: Bacterial adhesion. - Berlin : Springer Berlin/Heidelberg. ; , s. 301-313
-
Bokkapitel (refereegranskat)abstract
- Optical tweezers (OT) are a technique that, by focused laser light, can both manipulate micrometer sized objects and measure minute forces (in the pN range) in biological systems. The technique is therefore suitable for assessment of bacterial adhesion on an individual adhesin-receptor and single attachment organelle (pili) level. This chapter summarizes the use of OT for assessment of adhesion mechanisms of both non-piliated and piliated bacteria. The latter include the important helix-like pili expressed by uropathogenic Escherichia coli (UPEC), which have shown to have unique and intricate biomechanical properties. It is conjectured that the large flexibility of this type of pili allows for a redistribution of an external shear force among several pili, thereby extending the adhesion lifetime of bacteria. Systems with helix-like adhesion organelles may therefore act as dynamic biomechanical machineries, enhancing the ability of bacteria to withstand high shear forces originating from rinsing flows such as in the urinary tract. This implies that pili constitute an important virulence factor and a possible target for future anti-microbial drugs.
|
|
| 4. |
- Axner, Ove, et al.
(författare)
-
Unraveling the secrets of bacterial adhesion organelles using single-molecule force spectroscopy
- 2010
-
Ingår i: Single molecule spectroscopy in chemistry, physics and biology. - Berlin, Heidelberg : Springer. - 9783642025969 ; , s. 337-362
-
Konferensbidrag (refereegranskat)abstract
- Many types of bacterium express micrometer-long attachment organelles (so-called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Force-measuring optical tweezers (FMOT) have since then been used to unravel the biomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated at the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g., urine flow. It has been found that many types of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.
|
|
| 5. |
- Axner, Ove, et al.
(författare)
-
Unraveling the secrets of bacterial adhesion organelles using single molecule force spectroscopy
- 2010. - 96
-
Ingår i: Springer series in chemical physics. - : Springer Verlag. - 9783642025969 ; , s. 337-362
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Many types of bacterium express micrometer-long attachment organelles (so called pili) whose role is to mediate adhesion to host tissue. Until recently, little was known about their function in the adhesion process. Forcemeasuring ptical tweezers (FMOT) have since then been used to unravel the iomechanical properties of various types of pili, primarily those from uropathogenic E. coli, in particular their force-vs.-elongation response, but lately also some properties of the adhesin situated and the distal end of the pilus. This knowledge provides an understanding of how piliated bacteria can sustain external shear forces caused by rinsing processes, e.g. urine flow. It has been found that anytypes of pilus exhibit unique and complex force-vs.-elongation responses. It has been conjectured that their dissimilar properties impose significant differences in their ability to sustain external forces and that different types of pilus therefore have dissimilar predisposition to withstand different types of rinsing conditions. An understanding of these properties is of high importance since it can serve as a basis for finding new means to combat bacterial adhesion, including that caused by antibiotic-resistance bacteria. This work presents a review of the current status of the assessment of biophysical properties of individual pili on single bacteria exposed to strain/stress, primarily by the FMOT technique. It also addresses, for the first time, how the elongation and retraction properties of the rod couple to the adhesive properties of the tip adhesin.
|
|
| 6. |
- Björnham, Oscar, 1976-
(författare)
-
A study of bacterial adhesion on a single-cell level by means of force measuring optical tweezers and simulations
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The intriguing world of microbiology is nowadays accessible for detailed exploration at a single–molecular level. Optical tweezers are a novel instrument that allows for non–invasive manipulation of single cells by the sole use of laser light and operates on the nano– and micrometer scale which corresponds to the same length scale as living cells. Moreover, forces within the field of microbiology are typically in the picoNewton range which is in accordance with the capability of force measuring optical tweezers systems. Both these conformabilities imply that force measuring optical tweezers is suitable for studies of single living cells. This thesis focuses on the mechanisms of bacterial attachments to host cells which constitute the first step in bacterial infection processes. Bacteria bind specifically to host receptors by means of adhesins that are expressed either directly on the bacterial membrane or on micrometer–long adhesion organelles that are called pili. The properties of single adhesin–receptor bonds that mediate adherence of the bacterium Helicobacter pylori are first examined at various acidities. Further on, biomechanical properties of P pili expressed by Escherichia coli are presented to which computer simulations, that capture the complex kinetics of the pili structure and precisely replicate measured data, are applied. Simulations are found to be a powerful tool for investigations of adhesive attributes of binding systems and are utilized in the analyses of the specific binding properties of P pili on a single–pilus level. However, bacterial binding systems generally involve a multitude of adhesin–receptor bonds. To explore bacterial attachments, the knowledge from single–pilus studies is brought into a full multipili attachment scenario which is analyzed by means of theoretical treatments and simulations. The results are remarkable in several aspects. Not only is it found that the intrinsic properties of P pili are composed in an optimal combination to promote strong multipili bindings. The properties of the pili structure itself are also found to be optimized with respect to its in vivo environment. Indeed, the true meaning of the attributes derived at a single–pilus level cannot be unraveled until a multipili–binding system is considered. Whereas detailed studies are presented for the helix–like P pili expressed by Gram–negative Escherichia coli, conceptual studies are presented for the open coil–like T4 pili expressed by Gram–positive Streptococcus pneumoniae. The structural and adhesive properties of these two types of pili differ considerably. These dissimilarities have far–reaching consequences on the adhesion possibilities at both single–pilus and multipili levels which are discussed qualitatively. Moreover, error analyses of conventional data processing methods in dynamic force spectroscopy as well as development of novel analysis methods are presented. These findings provide better understanding of how to perform refined force measurements on single adhesion organelles as well as how to improve the analyses of measurement data to obtain accurate parameter values of biomechanical entities. In conclusion, this thesis comprises a study of bacterial adhesion organelles and the way they cooperate to establish efficient attachment systems that can successfully withstand strong external forces that acts upon bacteria. Such systems can resist, for instance, rinsing effects and thereby allow bacteria to colonize their host. By understanding the complexity, and thereby possible weaknesses, of bacterial attachments, new targets for combating bacterial infections can be identified.
|
|
| 7. |
- Björnham, Oscar, 1976-, et al.
(författare)
-
Dynamic force spectroscopy of the Helicobacter pylori BabA-Lewis b binding
- 2009
-
Ingår i: Biophysical Chemistry. - Amsterdam : Elsevier. - 0301-4622 .- 1873-4200. ; 143:1-2, s. 102-105
-
Tidskriftsartikel (refereegranskat)abstract
- The binding strength of the Helicobacter pylori adhesin–receptor complex BabA-ABO/Lewis b has been analyzed by means of dynamic force pectroscopy. High-resolution measurements of rupture forces were performed in situ on single bacterial cells, expressing the high-affinity binding BabA adhesin, by the use of force measuring optical tweezers. The resulting force spectra revealed the mechanical properties of a single BabA–Leb bond. It was found that the bond is dominated by one single energy barrier and that it is a slipbond. The bond length and thermal off-rate were assessed to be 0.86±0.07 nm and 0.015±0.006 s−1, respectively.
|
|
| 8. |
- Björnham, Oscar, 1976-, et al.
(författare)
-
Measurements of the binding force between the Helicobacter pylori adhesin BabA and the Lewis b blood group antigen using optical tweezers
- 2005
-
Ingår i: Journal of Biomedical Optics. - Bellingham, WA : SPIE-Intl Soc Optical Eng. - 1083-3668 .- 1560-2281. ; 10:4, s. 044024-044032
-
Tidskriftsartikel (refereegranskat)abstract
- Helicobacter pylori is a world-wide spread bacterium that causes persistent infections and chronic inflammations that can develop into gastritis and peptic ulcer disease. It expresses several adhesin proteins on its surface that bind to specific receptors in the gastric epithelium. The most well-known adhesin is BabA, which has previously been shown to bind specifically to the fucosylated blood group antigen Lewis b (Leb). The adhesion forces between BabA and the Leb antigen are investigated in this work and assessed by means of optical tweezers. A model system for in situ measurements of the interaction forces between individual bacteria and beads coated with Leb is developed. It is found that the de-adhesion force in this model system, measured with a loading rate of ~100 pN/s, ranges from 20 to 200 pN. The de-adhesion force appears predominantly as multiples of an elementary force, which is determined to 25±1.5 pN and identified as the unbinding force of an individual BabA-Leb binding. It is concluded that adhesion in general is mediated by a small number of bindings (most often 1 to 4) despite that the contact surface between the bacterium and the bead encompassed significantly more binding sites.
|
|
| 9. |
- Björnham, Oscar, 1976-, et al.
(författare)
-
Methods and error estimations of uncertainties in single-molecule dynamic force spectroscopy
- 2009
-
Ingår i: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 38:7, s. 911-922
-
Tidskriftsartikel (refereegranskat)abstract
- In dynamic force spectroscopy, access to the characteristic parameters of single molecular bonds requires non-trivial measurements and data processing as the rupture forces are found not only to be distributed over a wide range, but are also dependent on the loading rate. The choice of measurement procedure and data processing methods has a considerable impact on the accuracy and precision of the final results. We analyse, by means of numerical simulations, methods to minimize and assess the magnitude of the expected errors for different combinations of experimental and evaluation methods. It was found that the choice of fitting function is crucial to extract correct parameter values. Applying a Gaussian function, which is a common practice, is equivalent to introducing a systematic error, and leads to a consequent overestimation of the thermal off-rate by more than 30%. We found that the precision of the bond length and the thermal off-rate, in presence of unbiased noise, were improved by reducing the number of loading rates for a given number of measurements. Finally, the results suggest that the minimum number of measurements needed to obtain the bond strength, with acceptable precision, exceeds the common number of ~100 reported in literature.
|
|
| 10. |
- Björnham, Oscar, 1976-, et al.
(författare)
-
Physical properties of the specific PapG–galabiose binding in E. coli P pili-mediated adhesion
- 2009
-
Ingår i: European Biophysics Journal. - New York : Springer. - 0175-7571 .- 1432-1017. ; 38:2, s. 245-254
-
Tidskriftsartikel (refereegranskat)abstract
- Detailed analyses of the mechanisms thatmediate binding of the uropathogenic Escherichia coli tohost cells are essential, as attachment is a prerequisite forthe subsequent infection process. We explore, by means offorce measuring optical tweezers, the interaction betweenthe galabiose receptor and the adhesin PapG expressed byP pili on single bacterial cells. Two variants of dynamicforce spectroscopy were applied based on constant andnon-linear loading force. The specific PapG–galabiosebinding showed typical slip-bond behaviour in the forceinterval (30–100 pN) set by the pilus intrinsic biomechanicalproperties. Moreover, it was found that the bondhas a thermodynamic off-rate and a bond length of2.6×10-3 s-1 and 5.0 Å , respectively. Consequently, thePapG–galabiose complex is significantly stronger thanthe internal bonds in the P pilus structure that stabilizes thehelical chain-like macromolecule. This finding suggeststhat the specific binding is strong enough to enable the Ppili rod to unfold when subjected to strong shear forces inthe urinary tract. The unfolding process of the P pili rodpromotes the formation of strong multipili interaction,which is important for the bacterium to maintain attachmentto the host cells.
|
|
| 11. |
- Brink, Suzanne, et al.
(författare)
-
Curriculum agility at faculty, department, program and course level
- 2022
-
Ingår i: 50th annual conference of the European society for engineering education. - 9788412322262 ; , s. 1872-1877
-
Konferensbidrag (refereegranskat)abstract
- This short paper describes the first prototyping of a self-evaluation process of Curriculum Agility at a Faculty of Technology in Sweden. The process comprises guided, semi-structured, individual interviews at different organisational levels within the faculty, a joint narrative based on those interviews, prioritizing development strategies per level, and jointly mapping them on importance and implementation time. The self-evaluation is part of and based on the research on the principles of Curriculum Agility. The results show the interplay in timely curriculum change for futureproof engineering education between the teaching staff, the systems and the people who control the systems. The self-evaluation brings together the different perspectives and perceptions within the faculty and gives insight in how those affect the willingness towards and occurrence of curriculum development. This work in progress indicates how doing such a qualitative self-evaluation paves the road for transparent strategic dialogues on a holistic level about what to give attention and organize differently.
|
|
| 12. |
|
|
| 13. |
- Bugaytsova, Jeanna, et al.
(författare)
-
pH regulated H. pylori adherence : implications for persistent infection and disease
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Helicobacter pylori’s BabA adhesin binds strongly to gastric mucosal ABH/Leb glycans on the stomach epithelium and overlying mucus, materials continuously shed into the acidic gastric lumen. Here we report that this binding is acid labile, acid inactivation is fully reversible; and acid lability profiles vary with BabA sequence and correlate with disease patterns. Isogenic H. pylori strains from the gastric antrum and more acidic corpus were identified that differed in acid lability of receptor binding and in sequence near BabA’s carbohydrate binding domain. We propose that reversible acid inactivation of receptor binding helps H. pylori avoid clearance by mucosal shedding, and that strain differences in acid lability affect tissue tropism and the spectrum of associated gastric diseases.
|
|
| 14. |
- Castelain, Mickaël, et al.
(författare)
-
Characterization of the Biomechanical Properties of T4 Pili Expressed by Streptococcus pneumoniae – A Comparison between Helix-like and Open Coil-like Pili
- 2009
-
Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 10:9-10, s. 1533-1540
-
Tidskriftsartikel (refereegranskat)abstract
- Bacterial adhesion organelles, known as fimbria or pili, are expressed by Gram–positive as well as Gram–negative bacteria families. These appendages play a key role in the first steps of the invasion and infection processes, and they therefore provide bacteria with pathogenic abilities. To improve the knowledge of pili-mediated bacterial adhesion to host cells and how these pili behave under the presence of an external force, we first characterize, using force measuring optical tweezers, open coil-like T4 pili expressed by Gram–positive Streptococcus pneumoniae with respect to their biomechanicalproperties. It is shown that their elongation behavior can be well described by the worm-like chain model and that they possess a large degree of flexibility. Their properties are then compared with those of helix-like pili expressed by Gram–negative uropathogenic Escherichia coli (UPEC), which have different pili architecture. The differences suggest that these two types of pili have distinctly dissimilar mechanisms to adhere and sustain external forces. Helix-like pili expressed by UPEC bacteria adhere to host cells by single adhesins located at the distal end of the pili while their helix-like structures act as shock absorbers to dampen the irregularly shear forces induced by urine flow and to increase the cooperativity of the pili ensemble. Open coil-like pili expressed by S. pneumoniae adhere to cells by a multitude of adhesins distributed along the pili. It is hypothesized that these two types of pili represent different strategies of adhering to host cells in the presence of external forces. When exposed to significant forces, bacteria expressing helix-like pili remain attached bydistributing the external force among a multitude of pili, whereas bacteria expressing open coil-like pili sustain large forces primarily by their multitude of binding adhesins.
|
|
| 15. |
- Chaigne, Antoine, et al.
(författare)
-
Measurements and modeling of the transient acoustic field at impacted plates
- 1998
-
Ingår i: Journal of the Acoustical Society of America. - : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; :5, s. 2814-1815
-
Tidskriftsartikel (refereegranskat)abstract
- A comparison between measured and simulated transient acoustic fields generated by thin impacted plates is reported. The plate is modeled by using finite difference methods and the radiated pressure is obtained by solving the Rayleigh integral [Ch. Lambourg and A. Chaigne, J. Acoust. Soc. Am. 101(A) (1997)]. The results are evaluated in the form of the spatial pressure distribution at instants short after the excitation. Experimentally, a lead bullet (0.5 g, 100 m/s) is fired towards a cantilever steel plate (300×30×1 mm). The duration of the impact is estimated by using a high-speed camera that can register several million frames per second. An interferometric comparison of the change in optical path length of two holographic recordings, captured before and shortly after the impact, gives a 2-D projection of the acoustic field. A double-pulsed ruby laser, emitting light pulses of short duration (30 ns), is used as light source [S. Schedin, A. O. Waahlin, and P. Gren, J. Acoust. Soc. Am 99, 700-705 (1996)]. A high degree of similarity is observed between measured and simulated sound field, except in the close vicinity of the impact point. It is presumed that the discrepancies are due to nonlinear effects which are not included in the model
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Fällman, Erik, et al.
(författare)
-
Optical tweezers based force measurement system for quantitating binding interactions : system design and application for the study of bacterial adhesion
- 2004
-
Ingår i: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 19:11, s. 1429-1437
-
Tidskriftsartikel (refereegranskat)abstract
- An optical force measurement system for quantitating forces in the pN range between micrometer-sized objects has been developed. The system was based upon optical tweezers in combination with a sensitive position detection system and constructed around an inverted microscope. A trapped particle in the focus of the high numerical aperture microscope-objective behaves like an omnidirectional mechanical spring in response to an external force. The particle’s displacement from the equilibrium position is therefore a direct measure of the exerted force. A weak probe laser beam, focused directly below the trapping focus, was used for position detection of the trapped particle (a polystyrene bead). The bead and the condenser focus the light to a distinct spot in the far field, monitored by a position sensitive detector. Various calibration procedures were implemented in order to provide absolute force measurements. The system has been used to measure the binding forces between Escherichia coli bacterial adhesins and galabiose-functionalized beads
|
|
| 19. |
- Fällman, Erik, et al.
(författare)
-
Optical tweezers for the measurements of binding forces : system description and application for the study of E. coli adhesion
- 2003
-
Ingår i: Manipulation and analysis of biomolecules, cells and tissues. - Bellingham, WA : SPIE-INT SOC OPTICAL ENGINEERING. ; , s. 206-215
-
Konferensbidrag (refereegranskat)abstract
- Optical tweezers together with a position sensitive detection system allows measurements of forces in the pN range between micro-sized biological objects. A prototype force measurement system has been constructed around An inverted microscope with an argon-ion pumped Ti:sapphire laser as light source for optical trapping. A trapped particle in the focus of the high numerical aperture microscope-objective behaves like an omni-directional mechanical spring if an external force displaces it. The displacement from the equilibrium position is a measure of the exerted force. For position detection of the trapped particle (polystyrene beads), a He-Ne laser beam is focused a small distance below the trapping focus. An image of the bead appears as a distinct spot in the far field, monitored by a photosensitive detector. The position data is converted to a force measurement by a calibration procedure. The system has been used for measuring the binding forces between E-coli bacterial adhesin and their receptor sugars.
|
|
| 20. |
- Fällman, Erik, et al.
(författare)
-
The unfolding of the P pili quaternary structure by stretching is reversible, not plastic
- 2005
-
Ingår i: EMBO Reports. - : Wiley-Blackwell. - 1469-221X .- 1469-3178. ; 6:1, s. 52-56
-
Tidskriftsartikel (refereegranskat)abstract
- P pili are protein filaments expressed by uropathogenic Escherichia coli that mediate binding to glycolipids on epithelial cell surfaces, which is a prerequisite for bacterial infection. When a bacterium, attached to a cell surface, is exposed to external forces, the pili, which are composed of ∼103PapA protein subunits arranged in a helical conformation, can elongate by unfolding to a linear conformation. This property is considered important for the ability of a bacterium to withstand shear forces caused by urine flow. It has hitherto been assumed that this elongation is plastic, thus constituting a permanent conformational deformation. We demonstrate, using optical tweezers, that this is not the case; the unfolding of the helical structure to a linear conformation is fully reversible. It is surmised that this reversibility helps the bacteria regain close contact to the host cells after exposure to significant shear forces, which is believed to facilitate their colonization.
|
|
| 21. |
- Fällström, Karl-Evert, et al.
(författare)
-
Dynamic material parameters in an anisotropic plate estimated by phase-stepped holographic interferometry
- 1996
-
Ingår i: Optics and lasers in engineering. - 0143-8166 .- 1873-0302. ; 24:5-6, s. 429-454
-
Tidskriftsartikel (refereegranskat)abstract
- Material parameters in an anisotropic plate are determined using two non-destructive measuring techniques: real-time phase-stepped electronic speckle pattern interferometry and dual-reference-beam pulsed holographic interferometry. The first technique is used to measure the lower modes of vibration of the plate with free-free boundary conditions. Finite element analysis is then used to determine two effective Young's moduli and the in-plane shear modulus. The second technique is used to detect transient bending waves propagating in the plate and acoustic waves propagating in the surrounding air. A double-pulsed laser is used both to generate the waves and to make holographic recordings of the wave fields. The stiffness of the plate is estimated using the measured deformation field and an analytical solution to the plate impact problem.
|
|
| 22. |
- Fällström, Karl-Evert, et al.
(författare)
-
Mechanical and thermal effects in a steel plate impacted by a focused laser pulse
- 1997
-
Ingår i: Nondestructive Testing and Evaluation. - : Informa UK Limited. - 1058-9759 .- 1477-2671. ; 13:5, s. 293-307
-
Tidskriftsartikel (refereegranskat)abstract
- A short laser pulse from a 1 J ruby laser is focused at a steel plate. The effect will be that the material surface at the impact point becomes very rapidly heated. Metal vapour leaves the surface at a very high velocity. That is, both a mechanical impulse and local thermal energy are transferred to the plate. The mechanical impulse creates propagating bending waves in the plate, which in turn creates transient sound waves in the surrounding air. The heated spot at the plate surface creates thermal stresses in the plate which give rise to an out-of-plane deformation of the plate. This deformation is added up to the propagating bending waves. These effects are studied in experiments using pulsed holographic interferometry.
|
|
| 23. |
- Ghorbani, Ramin, 1981-
(författare)
-
Real-time breath gas analysis of carbon monoxide : laser-based detection and pulmonary gas exchange modeling
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Breath gas analysis is a promising approach for non-invasive medical diagnostics and physiological monitoring. Real-time, breath-cycle resolved biomarker detection facilitates data interpretation and has the potential to improve the diagnostic value of breath tests as exhalation profiles carry spatiotemporal information about biomarker origin and gas exchange in the respiratory tract. This thesis presents and scrutinizes a novel methodology for the analysis of real-time breath data, where single-exhalation profiles are simulated using a pulmonary gas exchange model and least-squares fitted to measured expirograms to extract airway and alveolar contributions and diffusing capacities. The methodology is demonstrated on exhaled breath carbon monoxide (eCO), a candidate biomarker for oxidative stress and respiratory diseases. The thesis mainly covers (1) the construction of a compact optical sensor based on tunable diode laser absorption spectroscopy (TDLAS) in the mid-infrared region (4.7 μm) for selective and precise real-time detection of CO in breath and ambient air (detection limit 9 ± 5 ppb at 0.1 s), (2) the design of an advanced online breath sampling system, (3) the implementation of a trumpet model with axial diffusion (TMAD) to simulate the CO gas exchange, and (4) the application of extended eCO analysis in clinical studies to establish the healthy non-smoker baseline of the eCO parameters and to study the response to CO and wood smoke exposure. It is shown that the TMAD adequately describes the gas exchange during systemic CO elimination for different breathing patterns, and that there is no difference between eCO parameters from mouth- and nose exhalations. Expirogram shape and eCO parameters exhibit a dependence on the exhalation flow rate, but for a given breathing maneuverer, the parameters lie in a narrow range. Airway CO is close to and correlates with ambient air CO, indicating negligible airway production in the healthy population. The alveolar diffusing capacity is independent of endogenous CO, even after exposure to elevated exogenous CO, and could be used to assess lung diffusion abnormalities. Compared to CO exposure, no clear additional effect of exposure to wood smoke particles on eCO is observed. The discrimination between endogenous and exogenous CO sources remains a challenge.
|
|
| 24. |
- Gren, Per, et al.
(författare)
-
Tomographic reconstruction of transient acoustic fields recorded by pulsed TV holography
- 1998
-
Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 37:5, s. 834-840
-
Tidskriftsartikel (refereegranskat)abstract
- Pulsed TV holography together with CT reconstruction were used to measure the three-dimensional distribution of transient acoustic fields in air. Holograms from several directions were directly recorded onto a CCD detector. From the recorded holograms, phase maps were quantitatively evaluated
|
|
| 25. |
|
|
