| 1721. |
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| 1722. |
- Larsson, Mårten, 1972-
(författare)
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Megalin, an Endocytotic Receptor with Signalling Potential
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Megalin is an endocytotic receptor belonging to the low-density lipoprotein family. It has often been viewed only as merely a scavenger receptor of absorptive and secretory epithelia. Recent work has revealed that the megalin intracellular domain contains several motifs potentially binding proteins involved in signal transduction.To find potential intracellular proteins binding to megalin, a yeast two-hybrid screening was initiated with the intracellular tail of megalin as the bait. A partial clone encoding the scaffolding protein postsynaptic protein 95 (PSD-95) was found to bind to megalin with its second PDZ-domain. Co-localization experiments in HEK-293 cells and kidney, placenta and parathyroid tissue confirmed this interaction. The PSD-95 related proteins PSD-93 and SAP102 were also confirmed to bind megalin with their PDZ2-domains, but the corresponding domain from SAP97 did not bind. Mutation analysis revealed that an amino acid residue change Ala to Thr was the cause of this.Megalin has within the central nervous system (CNS) been shown to be expressed only in the ependymal cells and choroid plexus. Nothing has been known about megalin expression in the spinal cord. To study spatio-temporal expression of megalin in the spinal cord, extensive staining of prenatal and postnatal mouse spinal cord was undertaken. Megalin expression was found in the dorsal part of the embryonic spinal cord. Most of these cells also expressed vimentin, suggesting that megalin has a role in the normal development of astrocytes. In the postnatal mouse, megalin seems to be expressed in oligodendrocytes only in the spinal cord white matter, and co-incident with myelination. This suggests that megalin is involved in the formation and maintenance of myelin along long spinal pathways. Megalin staining was clearly seen in the nucleus of these cells, indicating that megalin works in a notch-like signalling pathway.Uptake of retinol to the retina pigment epithelium (RPE) has long been thought to be a diffusion process. Staining for megalin in RPE revealed strong expression, and uptake experiments with 3H-retinol bound to retinol-binding protein and blocking with the LDL-receptor family specific antagonist receptor-associated protein (RAP) showed that megalin is a receptor for uptake of retinol to the RPE.
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| 1723. |
- Larsson, Martin, et al.
(författare)
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Microphone Windscreens for Turbulent Noise Suppression when Applying Active Noise Control to Ducts
- 2005
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Konferensbidrag (refereegranskat)abstract
- Low noise level is an essential feature when installing ventilation systems nowadays. The traditional noise control approaches use passive silencers to attenuate the undesired ventilation noise. These silencers have a high attenuation over a broad frequency range. However, traditional passive silencers are ineffective at low frequencies and tend to be relatively large and bulky when they are used for low frequencies. An approach to improve the low frequency noise attenuation and to reduce the size of a low frequency silencer is active noise control (ANC). A problem when applying ANC to attenuate noise in ducts is that both the reference microphone and the error microphone are placed in an air flow. Accordingly, the microphones sense the sound propagating through the duct as well as the turbulent fluctuations generated by the wind passing over the microphones. The turbulent flow noise reduces the coherence between the reference microphone and the error microphone, resulting in reduced performance of a feedforward ANC system. For improving the performance it is important with as little corruption from turbulent flow noise as possible. The coherence can be improved by reducing the flow velocity around the microphones by using some kind of windscreen. This paper presents comparison results for microphone installations based on different windscreens for suppression of the turbulent wind noise. The presented measurements are carried out in the frequency range 0-400 Hz - the plane wave propagation region for the ducts in use - and for flow speeds up to 5,9 m/s. The results show that with appropriate screens and placement the attenuation and frequency range of attenuation can be significantly improved.
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| 1724. |
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| 1725. |
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| 1726. |
- Larsson, Maria, et al.
(författare)
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Olfactory memory in the old and very old : relations to episodic and semantic memory and APOE genotype
- 2016
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Ingår i: Neurobiology of Aging. - : Elsevier BV. - 0197-4580 .- 1558-1497. ; 38, s. 118-126
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Tidskriftsartikel (refereegranskat)abstract
- The neuroanatomical organization that underlies olfactory memory is different from that of other memory types. The present work examines olfactory memory in an elderly population-based sample (Swedish National Study on Aging and Care in Kungsholmen) aged 60-100 years (n = 2280). We used structural equation modeling to investigate whether olfactory memory in old age is best conceptualized as a distinct category, differentiated from episodic and semantic memory. Further, potential olfactory dedifferentiation and genetic associations (APOE) to olfactory function in late senescence were investigated. Results are in support of a 3-factor solution where olfactory memory, as indexed by episodic odor recognition and odor identification, is modeled separately from episodic and semantic memory for visual and verbal information. Increasing age was associated with poorer olfactory memory performance, and observed age-related deficits were further exacerbated for carriers of the APOE epsilon 4 allele; these effects tended to be larger for olfactory memory compared to episodic and semantic memory pertaining to other sensory systems (vision, auditory). Finally, stronger correlations between olfactory and episodic memory, indicating dedifferentiation, were observed in the older age groups.
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| 1727. |
- Larsson, Martin, et al.
(författare)
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Performance Evaluation of a Module Configured Active Silencer for Robust Active Noise Control of Low Frequency Noise in Ducts
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Low noise level is an essential feature when installing ventilation systems today. Since the passive silencers traditionally used to attenuate ventilation noise tend to become bulky, impractical, and expensive when designed for low frequency attenuation, other solutions for the reduction of the low frequency duct noise often present in ducts are of interest. Active noise control (ANC) is a well known method for attenuating low frequency noise and much research has been performed to successfully apply ANC to duct noise. To insure reliable operation and desirable levels of attenuation when applying ANC to duct noise, it is of highest importance to be able to suppress the contamination of the microphone signals due to the turbulent pressure fluctuations arising as the microphones are exposed to the airflow in the duct. The work presented in this report is concerned with analysis of the influence of the turbulence induced noise on the adaptive algorithm in the ANC system, and design of microphone installations which produce sufficient turbulence suppression while also meeting industrial requirements. These requirements are, for example, that the installations should be based on standard ventilation parts, and that they should be easily installed and maintained. Furthermore, results concerning the performance of an ANC system with different microphone installations are presented. Some of the results were obtained at an acoustic laboratory according to an ISO standard. The attenuation of duct noise achieved with ANC was approximately 15-25 dB between 50-315 Hz, even for airflow speeds up to 20 m/s.
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| 1728. |
- Larsson, Magnus, et al.
(författare)
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Probing of individual semiconductor nanowhiskers by TEM-STM
- 2004
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Ingår i: Microscopy and Microanalysis. - 1435-8115. ; 10:1, s. 41-46
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Tidskriftsartikel (refereegranskat)abstract
- Along with rapidly developing nanotechnology, new types of analytical instruments and techniques are needed. Here we report an alternative procedure for electrical measurements on semiconductor nanowhiskers, allowing precise selection and visual control at close to atomic resolution. We use a combination of two powerful microscope techniques, scanning tunneling microscopy (STM) and simultaneous viewing in a transmission electron microscope (TEM). The STM is mounted in the sample holder for the TEM. We describe here a method for creating an ohmic contact between the STM tip and the nanowhisker. We examine three different types of STM tips and present a technique for cleaning the STM tip in situ. Measurements on 1-mum-tall and 40-nm-thick epitaxially grown InAs nanowhiskers show an ohmic contact and a resistance of down to 7 kOmega.
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| 1729. |
- Larsson, Matilda, 1981-
(författare)
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Quantification and Visualization of Cardiovascular Function using Ultrasound
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a large need for accurate methods detecting cardiovascular diseases, since they are one of the leading causes of mortality in the world, accounting for 29.3% of all deaths. Due to the complexity of the cardiovascular system, it is very challenging to develop methods for quantification of its function in order to diagnose, prevent and treat cardiovascular diseases. Ultrasound is a technique allowing for inexpensive, noninvasive imaging, but requires an experienced echocardiographer. Nowadays, methods like Tissue Doppler imaging (TDI) and Speckle tracking imaging (STI), measuring motion and deformation in the myocardium and the vessel walls, are getting more common in routine clinical practice, but without a proper visualization of the data provided by these methods, they are time-consuming and difficult to interpret. Thus, the general aim of this thesis was to develop novel ultrasound-based methods for accurate quantification and easily interpretable visualization of cardiovascular function. Five methods based on TDI and STI were developed in the present studies. The first study comprised development of a method for generation of bull’s-eye plots providing a color-coded two-dimensional visualization of myocardial longitudinal velocities. The second study proposed the state diagram of the heart as a new circular visualization tool for cardiac mechanics, including segmental color-coding of cardiac time intervals. The third study included development of a method describing the rotation pattern of the left ventricle by calculating rotation axes at different levels of the left ventricle throughout the cardiac cycle. In the fourth study, deformation data from the artery wall were tested as input to wave intensity analysis providing information of the ventricular – arterial interaction. The fifth study included an in-silico feasibility study to test the assessment of both radial and longitudinal strain in a kinematic model of the carotid artery. The studies showed promising results indicating that the methods have potential for the detection of different cardiovascular diseases and are feasible for use in the clinical setting. However, further development of the methods and both quantitative comparison of user dependency, accuracy and ease of use with other established methods evaluating cardiovascular function, as well as additional testing of the clinical potential in larger study populations, are needed.
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| 1730. |
- Larsson, Magnus R., et al.
(författare)
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The stability of alexithymia during work in a high-stress environment : A prospective study of Swedish peacekeepers serving in Kosovo
- 2010
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Ingår i: Scandinavian Journal of Psychology. - : Wiley. - 0036-5564 .- 1467-9450. ; 51:4, s. 350-355
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Tidskriftsartikel (refereegranskat)abstract
- We applied a prospective design to reinvestigate the issue whether the sub-domains of alexithymia could be considered stable traits or distress-related states. Assessments of alexithymia and subjective distress were conducted before deployment to Kosovo in a sample of male peacekeepers. A second assessment was conducted approximately six months later during the final phase of service. The results showed evidence of moderate to high relative stability in all alexithymic sub-domains. It was also found that a relative change in subjective distress predicted a relative change in difficulty identifying feelings and difficulty describing feelings but not in externally oriented thinking. We suggest therefore that the alexithymic sub-domains could be considered relatively stable traits but that the level of difficulty identifying and describing feeling varies with the level of subjective distress.
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