1,557 research outputs found
Quasi-conservation laws for compressible 3D Navier-Stokes flow
We formulate the quasi-Lagrangian fluid transport dynamics of mass density
and the projection q=\bom\cdot\nabla\rho of the vorticity \bom onto
the density gradient, as determined by the 3D compressible Navier-Stokes
equations for an ideal gas, although the results apply for an arbitrary
equation of state. It turns out that the quasi-Lagrangian transport of
cannot cross a level set of . That is, in this formulation, level sets of
(isopychnals) are impermeable to the transport of the projection .Comment: 2 page note, to appear in Phys Rev
Relativistic Doppler effect: universal spectra and zeptosecond pulses
We report on a numerical observation of the train of zeptosecond pulses
produced by reflection of a relativistically intense femtosecond laser pulse
from the oscillating boundary of an overdense plasma because of the Doppler
effect. These pulses promise to become a unique experimental and technological
tool since their length is of the order of the Bohr radius and the intensity is
extremely high W/cm. We present the physical mechanism,
analytical theory, and direct particle-in-cell simulations. We show that the
harmonic spectrum is universal: the intensity of th harmonic scales as
for , where is the largest --factor
of the electron fluid boundary, and for the broadband and
quasimonochromatic laser pulses respectively.Comment: 4 figure
The effect of lower limb strengthening exercise on orthostatic blood pressure and the skeletal muscle pump in older people with orthostatic hypotension
\ua9 2023 The Authors. Clinical Physiology and Functional Imaging published by John Wiley & Sons Ltd on behalf of Scandinavian Society of Clinical Physiology and Nuclear Medicine.Introduction: Activation of muscles during standing is recommended to activate the skeletal muscle pump, increasing venous return and increasing blood pressure (BP) in people with orthostatic hypotension (OH). Aim: The aim of this study is to determine if increasing the strength of the lower limb muscles can improve the effectiveness of the venous pump and postural BP in older people with OH. Methods: Ten older people with OH underwent an 8-week lower limb strengthening intervention. Repeated measurements of orthostatic BP, calf venous ejection fraction (EF) and muscle strength took place before, during and after intervention. Results: The intervention increased calf muscle strength by 21% (interquartile range: 18–28), p = 0.018, from a median baseline of 38 (34–45) kg. Participants had normal levels of venous EF 64% (51–75) at baseline, with little to no venous reflux. The median ejection volume at baseline was 44 (36–58) mL per calf. Despite increasing muscle strength, venous EF did not increase (percentage change −10% (−16 to 24), p = 0.8) and systolic BP drop did not improve (percentage change 0% (−17 to 16), p = 1.0). Similarly, visual analysis of individual case-series trends revealed increasing muscle strength with no clinically meaningful change in EF or orthostatic BP. Conclusions: Muscle strengthening exercise does not increase the effectiveness of the skeletal muscle pump and is not an efficacious intervention for OH. As there is little to no venous pooling in the calf during standing in older people with OH, below knee compression is unlikely to be clinically effective
A review of experimental design in forensic taphonomy: moving towards forensic realism
Forensic taphonomy as a discipline requires standardization to satisfy Daubert criteria for scientific data to be admissible in court. In response, there has been a shift towards quantification of methodology and estimating the post-mortem interval. Despite these advances, there are still biases and limitations within the discipline not explicitly addressed in the early stages of experimental design nor in final published works. In this article, unresolved debates with respect to the conductance and reporting of forensic taphonomic research are reviewed, beginning with the nature of experimental cadavers, human or animal analogues and their body size, and second, the forensic realism of experimental setups, specifically with respect to caging, clothing and number of carcases. Pigs, albeit imperfect, are a good model to gain a general idea of the trends that may be seen in humans in subsequent validation studies in facilities where human donors are available. To date, there is no consensus among taphonomists on the extent of the effect that body mass has on decomposition progression. More research is required with both human cadavers and non-human analogues that builds on our current knowledge of forensic taphonomy to answer these nagging questions. This will enable the discipline to make the reliable assumption that pigs and donor decomposition data can be applied to homicide cases. A suite of experimental design aspects is suggested to ensure systematic and standardized data collection across different biogeoclimatic circumstances to identify and quantify the effects of potential confounding variables. Such studies in multiple, varied biogeographic circumstances with standardized protocols, equipment and carrion will facilitate independent global validation of patterns. These factors are reviewed to show the need for adjustments in experimental design to ensure relevance and applicability of data within locally realistic forensic situations. The initiation of a global decomposition data network for forensic taphonomists is recommended
Estimates for the two-dimensional Navier-Stokes equations in terms of the Reynolds number
The tradition in Navier-Stokes analysis of finding estimates in terms of the
Grashof number \bG, whose character depends on the ratio of the forcing to
the viscosity , means that it is difficult to make comparisons with other
results expressed in terms of Reynolds number \Rey, whose character depends
on the fluid response to the forcing. The first task of this paper is to apply
the approach of Doering and Foias \cite{DF} to the two-dimensional
Navier-Stokes equations on a periodic domain by estimating
quantities of physical relevance, particularly long-time averages
\left, in terms of the Reynolds number \Rey = U\ell/\nu, where
U^{2}= L^{-2}\left and is the forcing scale. In
particular, the Constantin-Foias-Temam upper bound \cite{CFT} on the attractor
dimension converts to a_{\ell}^{2}\Rey(1 + \ln\Rey)^{1/3}, while the estimate
for the inverse Kraichnan length is (a_{\ell}^{2}\Rey)^{1/2}, where
is the aspect ratio of the forcing. Other inverse length scales,
based on time averages, and associated with higher derivatives, are estimated
in a similar manner. The second task is to address the issue of intermittency :
it is shown how the time axis is broken up into very short intervals on which
various quantities have lower bounds, larger than long time-averages, which are
themselves interspersed by longer, more quiescent, intervals of time.Comment: 21 pages, 1 figure, accepted for publication from J. Math. Phys. for
the special issue on mathematical fluid mechanic
Self-Efficacy of Registered Nurse Faculty to Facilitate a Flipped Classroom Pedagogy
Nurse educators struggle with developing innovative teaching strategies that improve learnersâ critical thinking, sound clinical judgment, and ability to provide safe patient care. In the local setting, nurse educators relied on passive teaching strategies. The purpose of this study was to explore the perceptions of nursing faculty members concerning their self-efficacy with implementation of a flipped classroom. The conceptual framework was transformative learning theory. The research question explored how nurse educators described their self-efficacy with implementing student-centered, active teaching methods. Participants included 9 experienced nursing faculty members at the local setting from the Associate Science of Nursing program. Data were collected through semi-structured interviews and analyzed by applying value coding to categorize the data and identify themes. The 4 themes include (a) assessment of student learning, (b) barriers for nurse educators, (c) perceptions, and (d) professional development. As a result of the findings from this study a 3-day professional development seminar was created to address the deficiencies in skills and knowledge regarding the implementation of the flipped classroom pedagogy. Implications for positive social change include (a) assisting nurse educators in making informed curriculum changes as they transition to an active pedagogy; (b) identifying teaching strategies that could help better prepare future nurses for clinical practice; and (c) assisting nurse educators to better understand the value of active, learner-centered pedagogical practices
A macroscopic multifractal analysis of parabolic stochastic PDEs
It is generally argued that the solution to a stochastic PDE with
multiplicative noise---such as , where denotes
space-time white noise---routinely produces exceptionally-large peaks that are
"macroscopically multifractal." See, for example, Gibbon and Doering (2005),
Gibbon and Titi (2005), and Zimmermann et al (2000). A few years ago, we proved
that the spatial peaks of the solution to the mentioned stochastic PDE indeed
form a random multifractal in the macroscopic sense of Barlow and Taylor (1989;
1992). The main result of the present paper is a proof of a rigorous
formulation of the assertion that the spatio-temporal peaks of the solution
form infinitely-many different multifractals on infinitely-many different
scales, which we sometimes refer to as "stretch factors." A simpler, though
still complex, such structure is shown to also exist for the
constant-coefficient version of the said stochastic PDE.Comment: 41 page
Identity, community and care in online accounts of hereditary colorectal cancer syndrome
Sociological literature has explored how shifts in the point at which individuals may be designated as diseased impact upon experiences of ill health. Research has shown that experiences of being genetically “at risk” are shaped by and shape familial relations, coping strategies, and new forms of biosociality. Less is known about how living with genetic risk is negotiated in the everyday and over time, and the wider forms of identity, communities and care this involves. This article explores these arrangements drawing on online bloggers’ accounts of Familial Adenomatous Polyposis (FAP). We show how accounts of genetic risk co-exist with more palpable experiences of FAP in everyday life, notably the consequences of prophylactic surgeries. We consider how the act of blogging represents but also constitutes everyday experiences of hereditary cancer syndrome as simultaneously ordinary and exceptional, and reflect on the implications of our analysis for understanding experiences of genetic cancer risk
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