8,706 research outputs found
Experiments in free shear flows: Status and needs for the future
Experiments in free turbulent flows are recommended with the primary concern placed on classical flows in order to augment understanding and for model building. Five classes of experiments dealing with classical free turbulent flows are outlined and proposed as being of particular significance for the near future. These classes include the following: (1) Experiments clarifying the effect of density variation owing to use of different gases, with and without the additional effect of density variation due to high Mach number or other effects; (2) experiments clarifying the role and importance of various parameters which determine the behavior of the near field as well as the condictions under which any of these parameters can be neglected; (3) experiments determining the cumulative effect of initial conditions in terms of distance to fully established flow; (4) experiments for cases where two layers of distinctly different initial turbulence structure flow side by side at the same mean speed; and (5) experiment using contemporary experimental techniques to study structure in free turbulent shear flows in order to compliment and support contemporary work on boundary layers
Gravitational Repulsion within a Black-Hole using the Stueckelberg Quantum Formalism
We wish to study an application of Stueckelberg's relativistic quantum theory
in the framework of general relativity. We study the form of the wave equation
of a massive body in the presence of a Schwarzschild gravitational field. We
treat the mathematical behavior of the wavefunction also around and beyond the
horizon (r=2M). Classically, within the horizon, the time component of the
metric becomes spacelike and distance from the origin singularity becomes
timelike, suggesting an inevitable propagation of all matter within the horizon
to a total collapse at r=0. However, the quantum description of the wave
function provides a different understanding of the behavior of matter within
the horizon. We find that a test particle can almost never be found at the
origin and is more probable to be found at the horizon. Matter outside the
horizon has a very small wave length and therefore interference effects can be
found only on a very small atomic scale. However, within the horizon, matter
becomes totally "tachionic" and is potentially "spread" over all space. Small
location uncertainties on the atomic scale become large around the horizon, and
different mass components of the wave function can therefore interfere on a
stellar scale. This interference phenomenon, where the probability of finding
matter decreases as a function of the distance from the horizon, appears as an
effective gravitational repulsion.Comment: 20 pages, 6 figure
Effect of well-width on the electro-optical properties of a quantum well
We record photoreflectance from Ge/GeSi modulation doped quantum wells
possessing V/cm perpendicular electric fields. Qualitatively very
different spectra are obtained from samples of well-width 100 \AA and 250 \AA.
Comparing the wavefunctions calculated from an \textbf{k.p}
theory, we find that while they remain confined in the narrower 100 \AA QW, the
electric field causes them to tunnel into the forbidden gap in the 250 \AA\
well. This implies that the samples should show a transition from the quantum
confined Franz-Keldysh effect to the bulk-like Franz-Keldysh effect. Close to
the band-edge where Franz-Keldysh effects are important, simulated
photoreflectance spectra reproduce the essential features of the experiment,
without any adjustable parameters.Comment: 8 pages, 8 figures. Submitted to Phys. Rev.
Outpatient treatment of low-risk venous thromboembolism with monotherapy oral anticoagulation: patient quality of life outcomes and clinician acceptance
BACKGROUND:
Oral monotherapy anticoagulation has facilitated home treatment of venous thromboembolism (VTE) in outpatients.
OBJECTIVES:
The aim of this study was to measure efficacy, safety, as well as patient and physician perceptions produced by a protocol that selected VTE patients as low-risk patients by the Hestia criteria, and initiated home anticoagulation with an oral factor Xa antagonist.
METHODS:
Patients were administered the Venous Insufficiency Epidemiological and Economic Study Quality of life/Symptoms questionnaire [VEINEs QoL/Sym] and the physical component summary [PCS] from the Rand 36-Item Short Form Health Survey [SF36]). The primary outcomes were VTE recurrence and hemorrhage at 30 days. Secondary outcomes compared psychometric test scores between patients with deep vein thrombosis (DVT) to those with pulmonary embolism (PE). Patient perceptions were abstracted from written comments and physician perceptions specific to PE outpatient treatment obtained from structured survey.
RESULTS:
From April 2013 to September 2015, 253 patients were treated, including 67 with PE. Within 30 days, 2/253 patients had recurrent DVT and 2/253 had major hemorrhage; all four had DVT at enrollment. The initial PCS scores did not differ between DVT and PE patients (37.2±13.9 and 38.0±12.1, respectively) and both DVT and PE patients had similar improvement over the treatment period (42.2±12.9 and 43.4±12.7, respectively), consistent with prior literature. The most common adverse event was menorrhagia, present in 15% of women. Themes from patient-written responses reflected satisfaction with increased autonomy. Physicians' (N=116) before-to-after protocol comfort level with home treatment of PE increased 48% on visual analog scale.
CONCLUSION:
Hestia-negative VTE patients treated with oral monotherapy at home had low rates of VTE recurrence and bleeding, as well as quality of life measurements similar to prior reports
Noradrenergic Pharmacotherapy, Intracerebral Infusion and Adrenal Transplantation Promote Functional Recovery After Cortical Damage
The research described in this review briefly
summarizes evidence that short term
pharmacological enhancement of noradrenergic
(NA) synaptic activity, combined with symptom
relevant experience (SRE), promotes functional
recovery of some symptoms of cortical damage
in rat, cat and human beings even when
treatment is initiated from days to weeks after
injury. A summary is provided of the numerous
drugs tested in rodent cortical injury models
which have been proven useful for predicting
beneficial or harmful effects on behavioral
outcome in human stroke. The pattern of drug
effects indicates a central role for NA in
functional recovery. Additionally, studies of the
effects of direct intraventricular infusion of
monoamine neurotransmitters are reviewed and
further support the hypothesized role of NA in
recovery from some symptoms of cortical injury.
The site of NA/SRE interaction to promote
recovery from hemiplegia apparently involves
the cerebellar hemisphere contralateral to the
cortical injury. Microinfusions of NA into the
contra- but not ipsilaterai cerebellar hemisphere
dramatically enhance recovery. Furthermore,
like its systemic action, microinfusion of the α1-
NA receptor antagonist, phenoxybenzamine,
reinstates hemiplegia. A “permanent” symptom
of motor cortex injury in the cat is the complete
loss of tactile placing contralateral to the injury
which does not spontaneously recover for as
long as seven years after ablation. This posturai
reflex is temporarily restored for 8-12 hours
following amphetamine administration.
However, this permanently lost reflex can be
enduringly restored by transplanting catecholamine secreting adrenal tissue into the
wound cavity. The experiment is reviewed in
detail and involves chromaffin cell autografts
into the frontal cortex ablation wound cavity
producing a restoration of tactile placing for the
7-10 month duration of the study. This enduring
restoration of tactile placing is considered a
result of the release of catecholamines into the
CNS from the grafted chromaffin cells found, by
histochemical methods, surviving 7-10 months
after transplant. Lastly, we attribute these
delayed treatment effects to an attenuation of a
diaschisis, or remote functional depression, in
morphologically intact areas anatomically
connected to the area of injury. The widespread
reduction of glycolytic and oxidative
metabolism, produced by focal cortical injury, is
normalized by the same treatment which
alleviates symptoms and is worsened by drugs
which exacerbate deficits. These data support
the hypothesis that providing SRE during a
period of enhanced NA synaptic activity
produces an enduring functional recovery after
cortical injury by attenuating remote functional
depression. This treatment for enhancing
recovery is especially attractive since it is
effective even when begun weeks after cortical
damage
Multivariate Granger Causality and Generalized Variance
Granger causality analysis is a popular method for inference on directed
interactions in complex systems of many variables. A shortcoming of the
standard framework for Granger causality is that it only allows for examination
of interactions between single (univariate) variables within a system, perhaps
conditioned on other variables. However, interactions do not necessarily take
place between single variables, but may occur among groups, or "ensembles", of
variables. In this study we establish a principled framework for Granger
causality in the context of causal interactions among two or more multivariate
sets of variables. Building on Geweke's seminal 1982 work, we offer new
justifications for one particular form of multivariate Granger causality based
on the generalized variances of residual errors. Taken together, our results
support a comprehensive and theoretically consistent extension of Granger
causality to the multivariate case. Treated individually, they highlight
several specific advantages of the generalized variance measure, which we
illustrate using applications in neuroscience as an example. We further show
how the measure can be used to define "partial" Granger causality in the
multivariate context and we also motivate reformulations of "causal density"
and "Granger autonomy". Our results are directly applicable to experimental
data and promise to reveal new types of functional relations in complex
systems, neural and otherwise.Comment: added 1 reference, minor change to discussion, typos corrected; 28
pages, 3 figures, 1 table, LaTe
Development and Validation of the Career Competencies Indicators (CCI)
This paper describes the development and validation of the Career Competencies Indicator (CCI); a 43-item measure to assess career competencies. Following an extensive literature review, a comprehensive item generation process involving consultation with subject matter experts, a pilot study and a factor analytic study on a large sample yielded a seven factor structure; goal setting and career planning, self-knowledge, job-performance, career-related skills, knowledge of (office) politics, career guidance and networking, and feedback seeking and self-presentation. Coefficient alpha reliabilities of the seven dimensions ranged from .93 to .81. Convergent validity was established by showing below chance similarity between CCI sub-scales, and discrminant validity between the CCI sub-scales and the big five personality scales. The results also suggested criterion-related validity of the CCI, since career competencies were found to jointly predict objective and subjective career success
Low-dimensional dynamics embedded in a plane Poiseuille flow turbulence : Traveling-wave solution is a saddle point ?
The instability of a streak and its nonlinear evolution are investigated by
direct numerical simulation (DNS) for plane Poiseuille flow at Re=3000. It is
suggested that there exists a traveling-wave solution (TWS). The TWS is
localized around one of the two walls and notably resemble to the coherent
structures observed in experiments and DNS so far. The phase space structure
around this TWS is similar to a saddle point. Since the stable manifold of this
TWS is extended close to the quasi two dimensional (Q2D) energy axis, the
approaching process toward the TWS along the stable manifold is approximately
described as the instability of the streak (Q2D flow) and the succeeding
nonlinear evolution. Bursting corresponds to the escape from the TWS along the
unstable manifold. These manifolds constitute part of basin boundary of the
turbulent state.Comment: 5 pages, 6 figure
Development and evaluation of a health-related quality-of-life tool for dogs with Cushing's syndrome
Autism and the U.K. secondary school experience
This research investigated the self-reported mainstream school experiences of those diagnosed on the autistic spectrum compared with the typically developing school population. Existing literature identifies four key areas that affect the quality of the school experience for students with autism: social skills, perceived relationships with teaching staff, general school functioning, and interpersonal strengths of the young person. These areas were explored in a mainstream U.K. secondary school with 14 students with autism and 14 age and gender matched students without autism, using self-report questionnaires and semi-structured interviews. Quantitative analyses showed consistent school experiences for both groups, although content analysis of interview data highlighted some differences in the ways in which the groups perceive group work, peers, and teaching staff within school. Implications for school inclusion are discussed, drawing attention to how staff awareness of autism could improve school experience and success for students with autism attending mainstream schools
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