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Search Results: 1 - 10 of 200580 matches for " Jan W. T. Heemskerk "
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A Current Induced Transition in atomic-sized contacts of metallic Alloys
Jan W. T. Heemskerk,Yves Noat,David J. Bakker,Jan M. van Ruitenbeek,Barend J. Thijsse,Peter Klaver
Physics , 2002, DOI: 10.1103/PhysRevB.67.115416
Abstract: We have measured conductance histograms of atomic point contacts made from the noble-transition metal alloys CuNi, AgPd, and AuPt for a concentration ratio of 1:1. For all alloys these histograms at low bias voltage (below 300 mV) resemble those of the noble metals whereas at high bias (above 300 mV) they resemble those of the transition metals. We interpret this effect as a change in the composition of the point contact with bias voltage. We discuss possible explanations in terms of electromigration and differential diffusion induced by current heating.
Genetic Analysis of the Role of Protein Kinase Cθ in Platelet Function and Thrombus Formation
Kellie J. Hall, Matthew T. Harper, Karen Gilio, Judith M. Cosemans, Johan W. M. Heemskerk, Alastair W. Poole
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003277
Abstract: Background PKCθ is a novel protein kinase C isozyme, predominately expressed in T cells and platelets. PKCθ?/? T cells exhibit reduced activation and PKCθ?/? mice are resistant to autoimmune disease, making PKCθ an attractive therapeutic target for immune modulation. Collagen is a major agonist for platelets, operating through an immunoreceptor-like signalling pathway from its receptor GPVI. Although it has recently been shown that PKCθ positively regulates outside-in signalling through integrin αIIbβ3 in platelets, the role of PKCθ in GPVI-dependent signalling and functional activation of platelets has not been assessed. Methodology/Principal Findings In the present study we assessed static adhesion, cell spreading, granule secretion, integrin αIIbβ3 activation and platelet aggregation in washed mouse platelets lacking PKCθ. Thrombus formation on a collagen-coated surface was assessed in vitro under flow. PKCθ?/? platelets exhibited reduced static adhesion and filopodia generation on fibrinogen, suggesting that PKCθ positively regulates outside-in signalling, in agreement with a previous report. In contrast, PKCθ?/? platelets also exhibited markedly enhanced GPVI-dependent α-granule secretion, although dense granule secretion was unaffected, suggesting that PKCθ differentially regulates these two granules. Inside-out regulation of αIIbβ3 activation was also enhanced downstream of GPVI stimulation. Although this did not result in increased aggregation, importantly thrombus formation on collagen under high shear (1000 s?1) was enhanced. Conclusions/Significance These data suggest that PKCθ is an important negative regulator of thrombus formation on collagen, potentially mediated by α-granule secretion and αIIbβ3 activation. PKCθ therefore may act to restrict thrombus growth, a finding that has important implications for the development and safe clinical use of PKCθ inhibitors.
Uncommon complications of biliary stones  [PDF]
S. Janssen, I. van Mierlo, L. P. L. Gilissen, S. W. Nienhuijs, J. Heemskerk
Open Journal of Internal Medicine (OJIM) , 2012, DOI: 10.4236/ojim.2012.21005
Abstract: Gallstone disease has a high incidence, and most common presentations are well known and recognized. Particulalry in the elderly population though, uncommon presentations of gallstone disease are more frequent, and can easily be missed or misinterpreted. In this article we present 5 such patients with an atypical presentation of gallstone disease. We will then discuss atypical gallstone disease in more detail.
Abnormal coronary artery angiography is not associated with adverse pregnancies outcomes  [PDF]
Margriet A. M. Heemskerk, Hemanth Ramanna, Kitty W. M. Bloemenkamp, Christianne J. M. de Groot
Open Journal of Obstetrics and Gynecology (OJOG) , 2012, DOI: 10.4236/ojog.2012.21012
Abstract: Background: Recently, epidemiologic studies have suggested an association between pregnancy complications and the development of coronary artery disease later in life. The current study investigate the relation between obstructive coronary versus normal coronary angiographies and the prevalence of complications during pregnancy including preeclampsia, pregnancy induced-hypertension, low birth weight, and preterm birth. Methods: All consecutive women aged <55 year, who had coronary angiography were included. Based on angiography outcome, patients were classified as normal (controls: no stenosis, wall irregularity without stenosis, or minimal calcification present) or abnormal (subjects). A standard questionnaire was sent to all participating women. The questionnaires inquired into risk factors for coronary vascular disease, in particular history of hypertensive diseases, and specific obstetric history. The results were analyzed using the unpaired t-test, the Chi-squared test, and Pearson’s correlation coefficients as appropriate. A significance level of P < 0.05 was used. Results: Of the 211 consecutive women aged <55 year, 62% (n = 131) had normal coronary angiography and 38% (n = 80) abnormal coronary angiography. We found no differences of reported pregnancy complications including preeclampsia, hypertension, low birth weight, and preterm birth (combined RR = 0.70, 95% C.I. = 0.38 - 1.3) in case of abnormal coronary angiography compared to women with normal coronary angiography. The traditional risk factors hypercholesterolemia, tobacco use, and diabetes were identified as the major risk factors for developing cardiovascular disease, with a relative risk ranging from 4.2 - 1.8. Conclusion: These data suggest that pregnancy complications are not an important denominator for cardiovascular disease.
Spatial Distribution of Factor Xa, Thrombin, and Fibrin(ogen) on Thrombi at Venous Shear
Michelle A. Berny,Imke C. A. Munnix,Jocelyn M. Auger,Saskia E. M. Schols,Judith M. E. M. Cosemans,Peter Panizzi,Paul E. Bock,Steve P. Watson,Owen J. T. McCarty,Johan W. M. Heemskerk
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0010415
Abstract: The generation of thrombin is a critical process in the formation of venous thrombi. In isolated plasma under static conditions, phosphatidylserine (PS)-exposing platelets support coagulation factor activation and thrombin generation; however, their role in supporting coagulation factor binding under shear conditions remains unclear. We sought to determine where activated factor X (FXa), (pro)thrombin, and fibrin(ogen) are localized in thrombi formed under venous shear.
Niacin Reduces Atherosclerosis Development in APOE*3Leiden.CETP Mice Mainly by Reducing NonHDL-Cholesterol
Susan Kühnast, Mieke C. Louwe, Mattijs M. Heemskerk, Elsbet J. Pieterman, Jan B. van Klinken, Sjoerd A. A. van den Berg, Johannes W. A. Smit, Louis M. Havekes, Patrick C. N. Rensen, José W. A. van der Hoorn, Hans M. G. Princen, J. Wouter Jukema
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0066467
Abstract: Objective Niacin potently lowers triglycerides, mildly decreases LDL-cholesterol, and largely increases HDL-cholesterol. Despite evidence for an atheroprotective effect of niacin from previous small clinical studies, the large outcome trials, AIM-HIGH and HPS2-THRIVE did not reveal additional beneficial effects of niacin (alone or in combination with laropiprant) on top of statin treatment. We aimed to address this apparent discrepancy by investigating the effects of niacin without and with simvastatin on atherosclerosis development and determine the underlying mechanisms, in APOE*3Leiden.CETP mice, a model for familial dysbetalipoproteinemia (FD). Approach and Results Mice were fed a western-type diet containing cholesterol without or with niacin (120 mg/kg/day), simvastatin (36 mg/kg/day) or their combination for 18 weeks. Similarly as in FD patients, niacin reduced total cholesterol by -39% and triglycerides by ?50%, (both P<0.001). Simvastatin and the combination reduced total cholesterol (?30%; ?55%, P<0.001) where the combination revealed a greater reduction compared to simvastatin (?36%, P<0.001). Niacin decreased total cholesterol and triglycerides primarily by increasing VLDL clearance. Niacin increased HDL-cholesterol (+28%, P<0.01) and mildly increased reverse cholesterol transport. All treatments reduced monocyte adhesion to the endothelium (?46%; ?47%, P<0.01; ?53%, P<0.001), atherosclerotic lesion area (?78%; ?49%, P<0.01; ?87%, P<0.001) and severity. Compared to simvastatin, the combination increased plaque stability index [(SMC+collagen)/macrophages] (3-fold, P<0.01). Niacin and the combination reduced T cells in the aortic root (?71%, P<0.01; ?81%, P<0.001). Lesion area was strongly predicted by nonHDL-cholesterol (R2 = 0.69, P<0.001) and to a much lesser extent by HDL-cholesterol (R2 = 0.20, P<0.001). Conclusion Niacin decreases atherosclerosis development mainly by reducing nonHDL-cholesterol with modest HDL-cholesterol-raising and additional anti-inflammatory effects. The additive effect of niacin on top of simvastatin is mostly dependent on its nonHDL-cholesterol-lowering capacities. These data suggest that clinical beneficial effects of niacin are largely dependent on its ability to lower LDL-cholesterol on top of concomitant lipid-lowering therapy.
The Role of Surface Entropy in Statistical Emission of Massive Fragments from Equilibrated Nuclear Systems
Jan T?ke,Jun Lu,W. Udo Schr?der
Physics , 2002, DOI: 10.1103/PhysRevC.67.034609
Abstract: Statistical fragment emission from excited nuclear systems is studied within the framework of a schematic Fermi-gas model combined with Weisskopf's detailed balance approach. The formalism considers thermal expansion of finite nuclear systems and pays special attention to the role of the diffuse surface region in the decay of hot equilibrated systems. It is found that with increasing excitation energy, effects of surface entropy lead to a systematic and significant reduction of effective emission barriers for fragments and, eventually, to the vanishing of these barriers. The formalism provides a natural explanation for the occurrence of negative nuclear heat capacities reported in the literature. It also accounts for the observed linearity of pseudo-Arrhenius plots of the logarithm of the fragment emission probability {\it versus} the inverse square-root of the excitation energy, but does not predict true Arrhenius behavior of these emission probabilities.
Liquid-Gas Coexistence and Critical Behavior in Boxed Pseudo-Fermi Matter
Jan T?ke,Jun Lu,W. Udo Schr?der
Physics , 2002, DOI: 10.1103/PhysRevC.67.044307
Abstract: A schematic model is presented that allows one to study the behavior of interacting pseudo-Fermi matter locked in a thermostatic box. As a function of the box volume and temperature, the matter is seen to show all of the familiar charactersitics of a Van der Waals gas, which include the coexistence of two phases under certain circumstances and the presence of a critical point.
The quiescence optical light curve of Nova Scorpii 1994 (=GRO J1655-40)
Frank van der Hooft,Martin Heemskerk,Frank Alberts,Jan van Paradijs
Physics , 1997,
Abstract: We report on extensive V, R, and i band photometry of the black-hole candidate Nova Sco 1994 (GRO J1655-40) obtained during March 1996, when the source was close to its quiescent pre-outburst optical brightness (V=17.3). From our observations and data taken from the literature we derive a refined ephemeris for inferior conjunction of the secondary star: HJD 2449838.4198(52) + 2.62168(14) x N. We have modeled the V, R, and i band light curves in terms of a Roche lobe filling secondary and an accretion disk around the compact star, the latter described as a flat cylinder with a radial temperature distribution. From the shape of the light curve we constrain the binary inclination and mass of the secondary star to lie in the ranges 63.7-70.7 degrees and 1.60-3.10 Solar masses, respectively. This limits the mass of the black-hole to the range 6.29-7.60 Solar Masses. The mass range we obtained for the secondary star is supported by the results of stellar evolution calculations.
A. Wood, P. Stedman-Edwards, and J. Mang, editors. 2000. The Root Causes of Biodiversity Loss. World Wildlife Fund and Earthscan Publications Ltd., London, UK.
Marieke Heemskerk
Ecology and Society , 2001,
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