3,526 research outputs found
A Transfer Matrix Method for Resonances in Randall-Sundrum Models
In this paper we discuss in detail a numerical method to study resonances in
membranes generated by domain walls in Randall-Sundrum-like scenarios. It is
based on similar works to understand the quantum mechanics of electrons subject
to the potential barriers that exist in heterostructures in semiconductors.
This method was used recently to study resonances of a three form field and
lately generalized to arbitrary forms. We apply it to a lot of important
models, namely those that contain the Gauge, Gravity and Spinor fields. In many
cases we find a rich structure of resonances which depends on the parameters
involved.Comment: 25 pages, 17 figure
Investigation of the cerebral hemodynamic response function in single blood vessels by functional photoacoustic microscopy
The specificity of the hemodynamic response function (HRF) is determined spatially by the vascular architecture and temporally by the evolution of hemodynamic changes. Here, we used functional photoacoustic microscopy (fPAM) to investigate single cerebral blood vessels of rats after left forepaw stimulation. In this system, we analyzed the spatiotemporal evolution of the HRFs of the total hemoglobin concentration (HbT), cerebral blood volume (CBV), and hemoglobin oxygen saturation (SO2). Changes in specific cerebral vessels corresponding to various electrical stimulation intensities and durations were bilaterally imaged with 36 Ă 65-ÎŒm2 spatial resolution. Stimulation intensities of 1, 2, 6, and 10 mA were applied for periods of 5 or 15 s. Our results show that the relative functional changes in HbT, CBV, and SO2 are highly dependent not only on the intensity of the stimulation, but also on its duration. Additionally, the duration of the stimulation has a strong influence on the spatiotemporal characteristics of the HRF as shorter stimuli elicit responses only in the local vasculature (smaller arterioles), whereas longer stimuli lead to greater vascular supply and drainage. This study suggests that the current fPAM system is reliable for studying relative cerebral hemodynamic changes, as well as for offering new insights into the dynamics of functional cerebral hemodynamic changes in small animals. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE)
Effect of coronavirus disease 2019 (COVIDâ19) on maternal, perinatal and neonatal outcome: systematic review.
Objective To evaluate the effect of coronavirus disease
2019 (COVID-19) on maternal, perinatal and neonatal
outcome by performing a systematic review of available
published literature on pregnancies affected by
COVID-19.
Methods We performed a systematic review to evaluate
the effect of COVID-19 on pregnancy, perinatal
and neonatal outcome. We conducted a comprehensive
literature search using PubMed, EMBASE, the
Cochrane Library, China National Knowledge Infrastructure
Database and Wan Fang Data up to and
including 20 April 2020 (studies were identified through
PubMed alert after that date). For the search strategy,
combinations of the following keywords and medical
subject heading (MeSH) terms were used: âSARS-CoV-2â,
âCOVID-19â, âcoronavirus disease 2019â, âpregnancyâ,
âgestationâ, âmaternalâ, âmotherâ, âvertical transmissionâ,
âmaternalâfetal transmissionâ, âintrauterine transmissionâ,
âneonateâ, âinfantâ and âdeliveryâ. Eligibility criteria
included laboratory-confirmed and/or clinically diagnosed
COVID-19, patient being pregnant on admission and
availability of clinical characteristics, including at least
one maternal, perinatal or neonatal outcome. Exclusion
criteria were non-peer-reviewed or unpublished reports,
unspecified date and location of the study, suspicion of duplicate reporting and unreported maternal or perinatal
outcomes. No language restrictions were applied.
Results We identified a high number of relevant case
reports and case series, but only 24 studies, including
a total of 324 pregnant women with COVID-19,
met the eligibility criteria and were included in the
systematic review. These comprised nine case series
(eight consecutive) and 15 case reports. A total of 20
pregnant patients with laboratory-confirmed COVID-19
were included in the case reports. In the combined data
from the eight consecutive case series, including 211
(71.5%) cases of laboratory-confirmed and 84 (28.5%)
of clinically diagnosed COVID-19, the maternal age
ranged from 20 to 44 years and the gestational age
on admission ranged from 5 to 41weeks. The most
common symptoms at presentation were fever, cough,
dyspnea/shortness of breath, fatigue and myalgia. The
rate of severe pneumonia reported amongst the case series
ranged from 0% to 14%, with the majority of the cases
requiring admission to the intensive care unit. Almost
all cases from the case series had positive computed
tomography chest findings. All six and 22 cases that
had nucleic-acid testing in vaginal mucus and breast
milk samples, respectively, were negative for severe acute
respiratory syndrome coronavirus 2 (SARS-CoV-2). Only
four cases of spontaneous miscarriage or termination were
reported. In the consecutive case series, 219/295 women
had delivered at the time of reporting and 78% of them
had Cesarean section. The gestational age at delivery
ranged from 28 to 41 weeks. Apgar scores at both 1 and
5 min ranged from 7 to 10. Only eight neonates had
birth weight <2500 g and nearly one-third of neonates
were transferred to the neonatal intensive care unit. There
was one case of neonatal asphyxia and death. In 155
neonates that had nucleic-acid testing in throat swab, all,
except three cases, were negative for SARS-CoV-2. There
were no cases of maternal death in the eight consecutive
case series. Seven maternal deaths, four intrauterine fetal
deaths (one with twin pregnancy) and two neonatal deaths
(twin pregnancy) were reported in a non-consecutive case
series of nine cases with severe COVID-19. In the case
reports, two maternal deaths, one neonatal death and two
cases of neonatal SARS-CoV-2 infection were reported.
Conclusions Despite the increasing number of published
studies on COVID-19 in pregnancy, there are insufficient
good-quality data to draw unbiased conclusions with
regard to the severity of the disease or specific
complications of COVID-19 in pregnant women, as
well as vertical transmission, perinatal and neonatal
complications. In order to answer specific questions in
relation to the impact of COVID-19 on pregnant women
and their fetuses, through meaningful good-quality
research, we urge researchers and investigators to
present complete outcome data and reference previously
published cases in their publications, and to record such
reporting when the data of a case are entered into one
or several registries.post-print1026 K
Topological structure evolvement of flow and temperature fields in deformable drop Marangoni migration in microgravity
Using the level-set method and the continuum interface model, the axisymmetric thermocapillary migration of a deformable liquid drop immerged in an immiscible bulk liquid with a temperature gradient is simulated numerically with constant material properties of the two phases. Steady terminal state of the motion can always be reached. The dimensionless terminal migration velocity decreases monotonously with the increase of the Marangoni number. Good agreements with space experimental data and most of previous numerical studies in the literature are evident. The terminal topological structure of flow field, in which a recirculation identical to Hill's vortex exists inside the drop, does not change with the Marangoni number. Only slight movement of the location of vortex center can be observed. On the contrary, bifurcations of the terminal topological structure of temperature field occur twice with increasing Marangoni number. At first, the uniform and straight layer-type structure of temperature field at infinitesimal Reynolds and Marangoni numbers wraps inside of the drop due to convective transport of heat as the Marangoni number increases, resulting in the emergence of an onion-type local cooler zone around the center of the drop beyond a lower critical Marangoni number. Expanding of this zone, particularly in the transverse direction, with the increasing of the Marangoni number leads to a cap- or even shell-type structure. The coldest point within the liquid drop locates on the axis. There is a middle critical Marangoni number, beyond which the coldest point will jump from the rear stagnation into the drop, though the topological structure of the temperature field does not change. The second bifurcation occurs at an upper critical Marangoni number, where the shell-type cooler zone inside drops ruptures from the central point and then a torus-type one emerges. The coldest point departs from the axis, and the so-called "cold-eye" appears in the meridian. It is also found that the inner and outer thermal boundary layers along the interface may exist both inside and outside the drop if Ma > 70. But the thickness decreases with the increasing Marangoni number more slowly than the prediction of potential flow at large Marangoni and Reynolds numbers. A velocity shear layer outside the drop is also introduced formally, of which modality may be affected by the convective transports of heat and/or momentum. (C) 2011 Elsevier Ltd. All rights reserved
The Snippets Taxonomy in Web Search Engines
In this paper authors analyzed 50 000 keywords results collected from
localized Polish Google search engine. We proposed a taxonomy for snippets
displayed in search results as regular, rich, news, featured and entity types
snippets. We observed some correlations between overlapping snippets in the
same keywords. Results show that commercial keywords do not cause results
having rich or entity types snippets, whereas keywords resulting with snippets
are not commercial nature. We found that significant number of snippets are
scholarly articles and rich cards carousel. We conclude our findings with
conclusion and research limitations.Comment: 12 pages, 3 table
Effect of Aspect Ratio on Field Emission Properties of ZnO Nanorod Arrays
ZnO nanorod arrays are prepared on a silicon wafer through a multi-step hydrothermal process. The aspect ratios and densities of the ZnO nanorod arrays are controlled by adjusting the reaction times and concentrations of solution. The investigation of field emission properties of ZnO nanorod arrays revealed a strong dependency on the aspect ratio and their density. The aspect ratio and spacing of ZnO nanorod arrays are 39 and 167 nm (sample C), respectively, to exhibit the best field emission properties. The turn-on field and threshold field of the nanorod arrays are 3.83 V/ÎŒm and 5.65 V/ÎŒm, respectively. Importantly, the sample C shows a highest enhancement of factorÎČ, which is 2612. The result shows that an optimum density and aspect ratio of ZnO nanorod arrays have high efficiency of field emission
Statistical Power of Model Selection Strategies for Genome-Wide Association Studies
Genome-wide association studies (GWAS) aim to identify genetic variants related to diseases by examining the associations between phenotypes and hundreds of thousands of genotyped markers. Because many genes are potentially involved in common diseases and a large number of markers are analyzed, it is crucial to devise an effective strategy to identify truly associated variants that have individual and/or interactive effects, while controlling false positives at the desired level. Although a number of model selection methods have been proposed in the literature, including marginal search, exhaustive search, and forward search, their relative performance has only been evaluated through limited simulations due to the lack of an analytical approach to calculating the power of these methods. This article develops a novel statistical approach for power calculation, derives accurate formulas for the power of different model selection strategies, and then uses the formulas to evaluate and compare these strategies in genetic model spaces. In contrast to previous studies, our theoretical framework allows for random genotypes, correlations among test statistics, and a false-positive control based on GWAS practice. After the accuracy of our analytical results is validated through simulations, they are utilized to systematically evaluate and compare the performance of these strategies in a wide class of genetic models. For a specific genetic model, our results clearly reveal how different factors, such as effect size, allele frequency, and interaction, jointly affect the statistical power of each strategy. An example is provided for the application of our approach to empirical research. The statistical approach used in our derivations is general and can be employed to address the model selection problems in other random predictor settings. We have developed an R package markerSearchPower to implement our formulas, which can be downloaded from the Comprehensive R Archive Network (CRAN) or http://bioinformatics.med.yale.edu/group/
Random-phase approximation and its applications in computational chemistry and materials science
The random-phase approximation (RPA) as an approach for computing the
electronic correlation energy is reviewed. After a brief account of its basic
concept and historical development, the paper is devoted to the theoretical
formulations of RPA, and its applications to realistic systems. With several
illustrating applications, we discuss the implications of RPA for computational
chemistry and materials science. The computational cost of RPA is also
addressed which is critical for its widespread use in future applications. In
addition, current correction schemes going beyond RPA and directions of further
development will be discussed.Comment: 25 pages, 11 figures, published online in J. Mater. Sci. (2012
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