| 81471. |
- Kovacs, Mihaly, 1977, et al.
(författare)
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Weak convergence of finite element approximations of linear stochastic evolution equations with additive noise II. Fully discrete schemes
- 2012
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Ingår i: arXiv:1203.2029v1 [math.NA]. ; , s. 1-24
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present an abstract framework for analyzing the weak error of fully discrete approximation schemes for linear evolution equations driven by additive Gaussian noise. First, an abstract representation formula is derived for sufficiently smooth test functions. The formula is then applied to the wave equation, where the spatial approximation is done via the standard continu- ous finite element method and the time discretization via an I-stable rational approximation to the exponential function. It is found that the rate of weak convergence is twice that of strong convergence. Furthermore, in contrast to the parabolic case, higher order schemes in time, such as the Crank-Nicolson scheme, are worthwhile to use if the solution is not very regular. Finally we ap- ply the theory to parabolic equations and detail a weak error estimate for the linearized Cahn-Hilliard-Cook equation as well as comment on the stochastic heat equation.
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| 81472. |
- Kovacs, Mihaly, 1977, et al.
(författare)
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Weak convergence of finite element approximations of linear stochastic evolution equations with additive noise II. Fully discrete schemes
- 2013
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Ingår i: BIT Numerical Mathematics. - : Springer Science and Business Media LLC. - 1572-9125 .- 0006-3835. ; 53:2, s. 497-525
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Tidskriftsartikel (refereegranskat)abstract
- We present an abstract framework for analyzing the weak error of fully discrete approximation schemes for linear evolution equations driven by additive Gaussian noise. First, an abstract representation formula is derived for sufficiently smooth test functions. The formula is then applied to the wave equation, where the spatial approximation is done via the standard continuous finite element method and the time discretization via an I-stable rational approximation to the exponential function. It is found that the rate of weak convergence is twice that of strong convergence. Furthermore, in contrast to the parabolic case, higher order schemes in time, such as the Crank-Nicolson scheme, are worthwhile to use if the solution is not very regular. Finally we apply the theory to parabolic equations and detail a weak error estimate for the linearized Cahn-Hilliard-Cook equation as well as comment on the stochastic heat equation.
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| 81473. |
- Kovacs, Mihaly, 1977, et al.
(författare)
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Weak convergence of fully discrete finite element approximations of semilinear hyperbolic SPDE with additive noise
- 2020
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Ingår i: Esaim-Mathematical Modelling and Numerical Analysis-Modelisation Mathematique Et Analyse Numerique. - : EDP Sciences. - 0764-583X .- 2822-7840 .- 1290-3841. ; 54:6, s. 2199-2227
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Tidskriftsartikel (refereegranskat)abstract
- The numerical approximation of the mild solution to a semilinear stochastic wave equation driven by additive noise is considered. A standard finite element method is employed for the spatial approximation and a a rational approximation of the exponential function for the temporal approximation. First, strong convergence of this approximation in both positive and negative order norms is proven. With the help of Malliavin calculus techniques this result is then used to deduce weak convergence rates for the class of twice continuously differentiable test functions with polynomially bounded derivatives. Under appropriate assumptions on the parameters of the equation, the weak rate is found to be essentially twice the strong rate. This extends earlier work by one of the authors to the semilinear setting. Numerical simulations illustrate the theoretical results.
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| 81474. |
- Kovacs, Roxanne, 1991, et al.
(författare)
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Can patients improve the quality of care they receive? Experimental evidence from Senegal
- 2022
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Ingår i: World Development. - : Elsevier BV. - 0305-750X. ; 150
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Tidskriftsartikel (refereegranskat)abstract
- Providers in many low and middle-income countries (LMICs) often fail to correctly diagnose and treat their patients, even though they have the clinical knowledge to do so. Against the backdrop of many failed attempts to increase provider effort, this study examines whether quality of care can be improved by encouraging patients to be more active during consultations. We design a simple experiment with undercover standardised patients who randomly vary how much information they disclose about their symptoms. We find that providers are 27% more likely to correctly manage a patient who volunteers several key symptoms of their condition at the start of the consultation, compared to a typical patient who shares less information. Lower performance in the control group is not due to providers' lack of knowledge, an incapacity to ask the right questions, or a response to time or resource constraints. Instead, providers' low motivation seems to limit their ability to adapt their effort to patients' inputs in the consultation. Our findings provide proof-of-concept evidence that interventions making patients more active in their consultations could significantly improve the quality of care in LMICs. (C) 2021 The Authors. Published by Elsevier Ltd.
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| 81475. |
- Kovacs, Roxanne, 1991, et al.
(författare)
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Does high workload reduce the quality of healthcare? Evidence from rural Senegal
- 2022
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Ingår i: Journal of Health Economics. - : Elsevier BV. - 0167-6296. ; 82
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Tidskriftsartikel (refereegranskat)abstract
- There is a widely held perception that staff shortages in low and middle-income countries (LMICs) lead to excessive workloads, which in turn worsen the quality of healthcare. Yet there is little evidence supporting these claims. We use data from standardised patient visits in Senegal and determine the effect of workload on the quality of primary care by exploiting quasi-random variation in workload. We find that despite a lack of staff, average levels of workload are low. Even at times when workload is high, there is no evidence that provider effort or quality of care are significantly reduced. Our data indicate that providers operate below their production possibility frontier and have sufficient capacity to attend more patients without compromising quality. This contradicts the prevailing discourse that staff shortages are a key reason for poor quality primary care in LMICs and suggests that the origins likely lie elsewhere.
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| 81476. |
- Kovacs, Roxanne, 1991, et al.
(författare)
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The effect of compulsory face mask policies on community mobility in Germany
- 2023
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Ingår i: Scandinavian Journal of Economics. - 0347-0520 .- 1467-9442. ; 125:4, s. 1027-1055
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Tidskriftsartikel (refereegranskat)abstract
- There is an ongoing debate about face masks being made compulsory in public spaces to contain COVID-19. A key concern is that such policies could undermine efforts to maintain social distancing and reduce mobility. We provide first evidence on the impact of compulsory face mask policies on community mobility. We exploit the staggered implementation of policies by German states during the first wave of the pandemic and measure mobility using geo-located smartphone data. We find that compulsory face mask policies led to a short-term reduction in community mobility, with no significant medium-term effects. We can rule out even small increases in mobility.
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| 81477. |
- Kovácsová, Gabriela, et al.
(författare)
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Cell-free expression of a functional pore-only sodium channel.
- 2015
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Ingår i: Protein expression and purification. - : Elsevier BV. - 1096-0279 .- 1046-5928. ; 111, s. 42-7
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Tidskriftsartikel (refereegranskat)abstract
- Voltage-gated sodium channels participate in the propagation of action potentials in excitable cells. Eukaryotic Navs are pseudo homotetrameric polypeptides, comprising four repeats of six transmembrane segments (S1-S6). The first four segments form the voltage-sensing domain and S5 and S6 create the pore domain with the selectivity filter. Prokaryotic Navs resemble these characteristics, but are truly tetrameric. They can typically be efficiently synthesized in bacteria, but production in vitro with cell-free synthesis has not been demonstrated. Here we report the cell-free expression and purification of a prokaryotic tetrameric pore-only sodium channel. We produced milligram quantities of the functional channel protein as characterized by size-exclusion chromatography, infrared spectroscopy and electrophysiological recordings. Cell-free expression enables advanced site-directed labelling, post-translational modifications, and special solubilization schemes. This enables next-generation biophysical experiments to study the principle of sodium ion selectivity and transport in sodium channels.
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| 81478. |
- Kovalchuk, Yury, et al.
(författare)
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Postsynaptic Induction of BDNF-Mediated Long-Term Potentiation.
- 2002
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Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 295:5560, s. 1729-34
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Tidskriftsartikel (refereegranskat)abstract
- Brain-derived neurotrophic factor (BDNF) and other neurotrophins are critically involved in long-term potentiation (LTP). Previous reports point to a presynaptic site of neurotrophin action. By imaging dentate granule cells in mouse hippocampal slices, we identified BDNF-evoked Ca2+ transients in dendrites and spines, but not at presynaptic sites. Pairing a weak burst of synaptic stimulation with a brief dendritic BDNF application caused an immediate and robust induction of LTP. LTP induction required activation of postsynaptic Ca2+ channels and N-methyl-d-aspartate receptors and was prevented by the blockage of postsynaptic Ca2+ transients. Thus, our results suggest that BDNF-mediated LTP is induced postsynaptically. Our finding that dendritic spines are the exclusive synaptic sites for rapid BDNF-evoked Ca2+ signaling supports this conclusion.
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| 81479. |
- Kovalenko, A. A., et al.
(författare)
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Risk Factors for hypospadias in Northwest Russia: A Murmansk County Birth Registry Study
- 2019
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 14:4
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Tidskriftsartikel (refereegranskat)abstract
- Background Hypospadias is the most common congenital anomaly of the penis, but its causes are mainly unknown. Of the risk factors identified, the most plausible are hormonal and genetic. The aim of this study was to identify risk factors for hypospadias in Northwest Russia based on registry data. The study population included male infants registered in the Murmansk County Birth Registry between 1 January 2006 and 31 December 2011 (n = 25 475). These infants were followed-up for 2 years using the Murmansk Regional Congenital Defects Registry to identify cases of hypospadias not diagnosed at birth. We used logistic regression analysis to examine the contributions of hypospadias risk factors. Out of 25 475 male infants born during the study period, 148 had isolated hypospadias. The overall prevalence rate was 54.2 (95% CI 53.6-54.8) per 10 000 male infants. Those born to mothers with preeclampsia (OR = 1.65; 95% CI 1.03-2.66) or infant birthweight < 2500 g (OR = 2.06; 95% CI 1.18-3.60) exhibited increased risk for hypospadias. Maternal age, smoking during pregnancy, folic acid intake during pregnancy or hepatitis B surface antigen positivity did not associate with increased risk of hypospadias. Combining data from a birth registry with those from a congenital defects registry provided optimal information about the prevalence of hypospadias and its association with low infant birthweight and preeclampsia. These factors have in common changes in hormone levels during pregnancy, which in turn may have contributed to hypospadias development.
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| 81480. |
- Kovalenko, A. A., et al.
(författare)
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Risk Factors for Ventricular Septal Defects in Murmansk County, Russia: A Registry-Based Study
- 2018
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Ingår i: International Journal of Environmental Research and Public Health. - : MDPI AG. - 1660-4601 .- 1661-7827. ; 15:7
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Tidskriftsartikel (refereegranskat)abstract
- Cardiovascular malformations are one of the most common birth defects among newborns and constitute a leading cause of perinatal and infant mortality. Although some risk factors are recognized, the causes of cardiovascular malformations (CVMs) remain largely unknown. In this study, we aim to identify risk factors for ventricular septal defects (VSDs) in Northwest Russia. The study population included singleton births registered in the Murmansk County Birth Registry (MCBR) between 1 January 2006 and 31 December 2011. Infants with a diagnosis of VSD in the MCBR and/or in the Murmansk Regional Congenital Defects Registry (up to two years post-delivery) constituted the study sample. Among the 52,253 infants born during the study period there were 744 cases of septal heart defects (SHDs), which corresponds to a prevalence of 14.2 [95% confidence interval (CI) of 13.2-15.3] per 1000 infants. Logistic regression analyses were carried out to identify VSD risk factors. Increased risk of VSDs was observed among infants born to mothers who abused alcohol [OR = 4.83; 95% CI 1.88-12.41], or smoked during pregnancy [OR = 1.35; 95% CI 1.02-1.80]. Maternal diabetes mellitus was also a significant risk factor [OR = 8.72; 95% CI 3.16-24.07], while maternal age, body mass index, folic acid and multivitamin intake were not associated with increased risk. Overall risks of VSDs for male babies were lower [OR = 0.67; 95% CI 0.52-0.88].
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