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Search Results: 1 - 10 of 461992 matches for " A. Knecht "
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Electromagnetic Corrections to Charged Pion Scattering at Low Energies
M. Knecht,A. Nehme
Physics , 2002, DOI: 10.1016/S0370-2693(02)01499-5
Abstract: The electromagnetic corrections to the low energy scattering amplitude involving charged pions only are investigated at leading and next-to-leading orders in the two-flavour chiral expansion. As an application, the corresponding variation in the strong $2S-2P$ level shift is evaluated. The relative variation is of the order of 5%.
Actin binding domains direct actin-binding proteins to different cytoskeletal locations
Raymond W Washington, David A Knecht
BMC Cell Biology , 2008, DOI: 10.1186/1471-2121-9-10
Abstract: We have constructed fusion proteins consisting of green fluorescent protein (GFP) with either the entire cross-linking protein or its actin-binding domain (ABD) and examined the localization of these fluorescent proteins in living cells under a variety of conditions. The full-length fusion proteins, but not the ABD's complemented the defects of cells lacking both endogenous proteins indicating that they are functional. The localization patterns of filamin (GFP-FLN) and α-actinin (GFP-αA) were overlapping but distinct. GFP-FLN localized to the peripheral cell cortex as well as to new pseudopods of unpolarized cells, but was observed to localize to the rear of polarized cells during cAMP and folate chemotaxis. GFP-αA was enriched in new pseudopods and at the front of polarized cells, but in all cases was absent from the peripheral cortex. Although both proteins appear to be involved in macropinocytosis, the association time of the GFP-probes with the internalized macropinosome differed. Surprisingly, the localization of the GFP-actin-binding domain fusion proteins precisely reflected that of their respective full length constructs, indicating that the localization of the protein was determined by the actin-binding domain alone. When expressed in a cell line lacking both filamin and α-actinin, the probes maintain their distinct localization patterns suggesting that they are not functionally redundant.These observations strongly suggest that the regulation of the binding of these proteins to actin filaments is built into the actin-binding domains. We suggest that different actin binding domains have different affinities for F-actin filaments in functionally distinct regions of the cytoskeleton.Amoeboid motility plays an important role in the processes of tissue repair, the immune response, morphogenesis and metastatic disease. The polymerization of new actin filaments provides the mechanical force for membrane protrusion and a number of proteins and protein complexes th
Intree-redes en het beeld van het medisch onderwijs in de heel- en verloskunde in Nederland (1865-1900
A. de Knecht-van Eekelen
Tijdschrift voor de Geschiedenis der Geneeskunde, Natuurwetenschappen, Wiskunde en Techniek , 1991,
Abstract: Medical education in The Netherlands as seen from the inaugural addresses in surgery and obstetrics (1865-1900) Medical education in The Netherlands showed major changes during the second half of the nineteenth century. The laws of 1865 and 1876 regulated the medical examinations and the teaching of medicine in the universities. Before 1876 medicine was taught at the universities of Leiden, Utrecht and Groningen, and at the Athenaeum Illustre in Amsterdam. After 1876 the Athenaeum was promoted to university. In 1865 there was a total of 16 ordinary professors in medicine. Their number grew considerably during the next decades. The newly appointed professors usually delivered an inaugural address. From these addresses one gets an interesting view of their aims for medical education. In this article the addresses from 1865 to 1900 of the professors in obstetrics and gynaecology, surgery, ophthalmology and otology are discussed. One of the main aims of the inaugural addresses appears to have been the explanation of the scientific basis of the profession involved. Only at the end of the century this basis was established; the addresses then began to focus on subjects like the need for specialisation and the expansion of clinical teaching. A list of names of professors and lecturers in the four Dutch universities is included as well as a list of the titles of their addresses.
Bakerboekjes in de 19e eeuw: een aanvulling
A. de Knecht-van Eekelen
Tijdschrift voor de Geschiedenis der Geneeskunde, Natuurwetenschappen, Wiskunde en Techniek , 1981,
Abstract:
H.G. Heijmans, Wetenschap tussen universiteit en industrie. De experimentele natuurkunde in Utrecht onder W. H. Julius en L. S. Ornstein 1896-1940
A. de Knecht-van Eekelen
BMGN : Low Countries Historical Review , 1996,
Abstract:
H. van Zon, Tachtig jaar RIVM
A. de Knecht-van Eekelen
BMGN : Low Countries Historical Review , 1993,
Abstract:
L.F. Bakker, Nederlandse orthopaedische vereniging 1898-1998. De geschiedenis van de orthopaedie in Nederland
A. de Knecht-van Eekelen
BMGN : Low Countries Historical Review , 2000,
Abstract:
Metallothionein mediates leukocyte chemotaxis
Xiuyun Yin, David A Knecht, Michael A Lynes
BMC Immunology , 2005, DOI: 10.1186/1471-2172-6-21
Abstract: In the experiments reported here, we show that immune cells migrate chemotactically in the presence of a gradient of MT. This response can be specifically blocked by two different monoclonal anti-MT antibodies. Exposure of cells to MT also leads to a rapid increase in F-actin content. Incubation of Jurkat T cells with cholera toxin or pertussis toxin completely abrogates the chemotactic response to MT. Thus MT may act via G-protein coupled receptors and through the cyclic AMP signaling pathway to initiate chemotaxis.These results suggest that, under inflammatory conditions, metallothionein in the extracellular environment may support the beneficial movement of leukocytes to the site of inflammation. MT may therefore represent a "danger signal"; modifying the character of the immune response when cells sense cellular stress. Elevated metallothionein produced in the context of exposure to environmental toxicants, or as a result of chronic inflammatory disease, may alter the normal chemotactic responses that regulate leukocyte trafficking. Thus, MT synthesis may represent an important factor in immunomodulation that is associated with autoimmune disease and toxicant exposure.Initiation of an immune response is accompanied by physiological changes that can produce a stressful environment for both the cells involved in the immune response, and for bystander cells that are part of adjacent but uninvolved tissues. These stresses can be further increased by the presence of infectious microorganisms. The changes to the environment include increases in reactive oxygen and reactive nitrogen species, products of cellular metabolism, and agents that initiate apoptotic or necrotic cell death.Cells react to stressful environments with a broad range of different homeostatic responses. These responses can include the synthesis of a host of stress response proteins, including the heat shock proteins, acute phase cytokines, and metallothionein. Metallothionein is a novel member of thi
High Efficiency Detection of Argon Scintillation Light of 128nm Using LAAPDs
R. Chandrasekharan,A. Knecht,M. Messina,C. Regenfus,A. Rubbia
Physics , 2005,
Abstract: The possibility of efficient collection and detection of vacuum ultraviolet light as emitted by argon, krypton, and xenon gas is studied. Absolute quantum efficiencies of large area avalanche photodiodes (LAAPDs) are derived at these wavelengths. VUV light of wavelengths down to the 128nm of Ar emission is shown to be detectable with silicon avalanche photodiodes at quantum efficiencies above 42%. Flexible Mylar foil overcoated with Al+MgF$_2$ is measured to have a specular reflectivity of $\sim$91% at argon emission wavelength. Low-pressure argon gas is shown to emit significant amounts of non-UV radiation. The average energy expenditure for the creation of non-UV photons in argon gas at this pressure is measured to be below 378 eV.
Contribution of Filopodia to Cell Migration: A Mechanical Link between Protrusion and Contraction
Fei Xue,Deanna M. Janzen,David A. Knecht
International Journal of Cell Biology , 2010, DOI: 10.1155/2010/507821
Abstract: Numerous F-actin containing structures are involved in regulating protrusion of membrane at the leading edge of motile cells. We have investigated the structure and dynamics of filopodia as they relate to events at the leading edge and the function of the trailing actin networks. We have found that although filopodia contain parallel bundles of actin, they contain a surprisingly nonuniform spatial and temporal distribution of actin binding proteins. Along the length of the actin filaments in a single filopodium, the most distal portion contains primarily T-plastin, while the proximal portion is primarily bound by -actinin and coronin. Some filopodia are stationary, but lateral filopodia move with respect to the leading edge. They appear to form a mechanical link between the actin polymerization network at the front of the cell and the myosin motor activity in the cell body. The direction of lateral filopodial movement is associated with the direction of cell migration. When lateral filopodia initiate from and move toward only one side of a cell, the cell will turn opposite to the direction of filopodial flow. Therefore, this filopodia-myosin II system allows actin polymerization driven protrusion forces and myosin II mediated contractile force to be mechanically coordinated. 1. Introduction Cell migration is a fundamental cellular process essential for embryonic development, wound healing, immune responses, and development of tissues. Almost universally, crawling motility involves a cycle of four steps that spatially and temporally coordinate forces in the actomyosin cytoskeleton with extracellular adhesion: plasma membrane protrusion at the leading edge, formation of new adhesion sites under the protrusion, disruption of older adhesion sites at the cell rear, and contraction resulting in cell body movement [1]. Although many aspects of these processes are understood individually, how they are spatially and temporally coordinated is largely unknown. Crawling cells generate two major types of actin-based protrusive organelles, lamellipodia, and filopodia, which have strikingly different actin polymerization machinery and are regulated by different signaling pathways [2–4]. The lamellipodium is characterized by a dense network of short, branched actin filaments, driven by activation of the Arp2/3 complex, followed by filament elongation and barbed-end capping. Addition of actin between the membrane and the ends of the filaments is hypothesized to produce the physical force for protrusion of the membrane at the leading edge [5–7]. In contrast, filopodia
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