259 research outputs found
Complex eigenvalues for the stability of Couette flow
The eigenvalue problem for the linear stability of Couette flow between rotating concentric cylinders to axisymmetric disturbances is considered. It is shown by numerical calculations and by formal perturbation methods that when the outer cylinder is at rest there exist complex eigenvalues corresponding to oscillatory damped disturbances. The structure of the first few eigenvalues in the spectrum is discussed. The results do not contradict the principle of exchange of stabilities, namely, for a fixed axial wavenumber the first mode to become unstable as the speed of the inner cylinder is increased is nonoscillatory as the stability boundary is crossed
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Manufacturing program for predicting equipment requirements (MAPPER)
A computerized Manufacturing Program for Predicting Equipment Requirements (MAPPER) has been developed. MAPPER can be used to interpret component production requirements from shipping schedules, calculate equipment loading versus equipment capacity, display six months prior equipment utilization and display process yield data. MAPPER is written in BASIC computer language and can be executed using GE Mark II time-sharing equipment. A typical example of the use of MAPPER is presented
Long-Term Functional Effects of Medulloblastoma Treatments
All studies relate directly to components of the evidence-based practice question and were used to understand the possible long-term effects of treatment for clients diagnosed with medulloblastoma cancer. This Critically Appraised Topic (CAT) contains 6 research articles from both national and international journals. Study designs include two cohort studies with a control group, 1 cross sectional study with a control group, 1 retrospective cohort study without a control group, 1 descriptive report on a Randomized Control Trial (RCT), and 1 descriptive study. Through these studies, we found that radiation treatment is associated with impaired IQ and academic achievement and that generalized or separation anxiety is common among medulloblastoma patients after treatment. We also found that better outcomes in functioning were associated with age, dosage, time of diagnosis, and medulloblastoma type. Our recommendations for OT practice include assessing processing speed, working memory, verbal skills, executive function, and attention and monitoring cognitive effects of occupational therapy interventions using a Goal Attainment Scale (GAS)
Halcyon -- A Pathology Imaging and Feature analysis and Management System
Halcyon is a new pathology imaging analysis and feature management system
based on W3C linked-data open standards and is designed to scale to support the
needs for the voluminous production of features from deep-learning feature
pipelines. Halcyon can support multiple users with a web-based UX with access
to all user data over a standards-based web API allowing for integration with
other processes and software systems. Identity management and data security is
also provided.Comment: 15 pages, 11 figures. arXiv admin note: text overlap with
arXiv:2005.0646
Spiral vortices traveling between two rotating defects in the Taylor-Couette system
Numerical calculations of vortex flows in Taylor-Couette systems with counter
rotating cylinders are presented. The full, time dependent Navier-Stokes
equations are solved with a combination of a finite difference and a Galerkin
method. Annular gaps of radius ratio and of several heights are
simulated. They are closed by nonrotating lids that produce localized Ekman
vortices in their vicinity and that prevent axial phase propagation of spiral
vortices. Existence and spatio temporal properties of rotating defects, of
modulated Ekman vortices, and of the spiral vortex structures in the bulk are
elucidated in quantitative detail.Comment: 9 pages, 9 figure
Nonaxisymmetric patterns in the linear theory of MHD Taylor-Couette instability
The linear stability of MHD Taylor-Couette flow of infinite vertical
extension is considered for various magnetic Prandtl numbers Pm. The
calculations are performed for a wide gap container with \hat\eta=0.5 with an
axial uniform magnetic field excluding counterrotating cylinders. For both
hydrodynamically stable and unstable flows the magnetorotational instability
produces characteristic minima of the Reynolds number for certain (low)
magnetic field amplitudes and Pm> 0.01. For Pm <~ 1 there is a characteristic
magnetic field amplitude beyond which the instability sets in in form of
nonaxisymmetric spirals with the azimuthal number m=1. Obviously, the magnetic
field is able to excite nonaxisymmetric configurations despite of the tendency
of differential rotation to favor axisymmetric magnetic fields which is known
from the dynamo theory. If Pm is too big or too small, however, the
axisymmetric mode with m=0 appears to be the most unstable one possessing the
lowest Reynolds numbers -- as it is also true for hydrodynamic Taylor-Couette
flow or for very weak fields. That the most unstable mode for modest Pm proves
to be nonaxisymmetric must be considered as a strong indication for the
possibility of dynamo processes in connection with the magnetorotational
instability.Comment: 5 pages, 5 figures, Astronomy and Astrophysics, accepte
Applying Laser Doppler Anemometry inside a Taylor-Couette geometry - Using a ray-tracer to correct for curvature effects
In the present work it will be shown how the curvature of the outer cylinder
affects Laser Doppler anemometry measurements inside a Taylor-Couette
apparatus. The measurement position and the measured velocity are altered by
curved surfaces. Conventional methods for curvature correction are not
applicable to our setup, and it will be shown how a ray-tracer can be used to
solve this complication.
By using a ray-tracer the focal position can be calculated, and the velocity
can be corrected. The results of the ray-tracer are verified by measuring an a
priori known velocity field, and after applying refractive corrections good
agreement with theoretical predictions are found. The methods described in this
paper are applied to measure the azimuthal velocity profiles in high Reynolds
number Taylor-Couette flow for the case of outer cylinder rotation
Influence of boundaries on pattern selection in through-flow
The problem of pattern selection in absolutely unstable open flow systems is
investigated by considering the example of Rayleigh-B\'{e}nard convection. The
spatiotemporal structure of convection rolls propagating downstream in an
externally imposed flow is determined for six different inlet/outlet boundary
conditions. Results are obtained by numerical simulations of the Navier-Stokes
equations and by comparison with the corresponding Ginzburg-Landau amplitude
equation. A unique selection process is observed being a function of the
control parameters and the boundary conditions but independent of the history
and the system length. The problem can be formulated in terms of a nonlinear
eigen/boundary value problem where the frequency of the propagating pattern is
the eigenvalue. PACS: 47.54.+r, 47.20.Bp, 47.27.Te, 47.20.KyComment: 8 pages, 5 Postscript figures, Physica D 97, 253-263 (1996
Staphylococcus aureus and Coagulase-Negative Staphylococci from Bloodstream Infections: Frequency of Occurrence and Antimicrobial Resistance, 2018–2021
Background: The abuse of antibiotics during the SARS-CoV-2 pandemic might have disrupted efforts to curb the further development and spread of the antimicrobial resistance of Staphylococcus aureus infection and Staphylococcus spp. coagulase-negative (CoNS) agents of nosocomial bloodstream infections (NBSIs). The purpose of our work was to study the resistance patterns of Staphylococcus aureus and CoNS through the analysis of blood cultures in hospitalized SARS-CoV-2-positive and SARS-CoV-2-negative patients (pts.). Materials and methods: During the period January 2018–June 2021, a retrospective case–control study was performed on blood cultures positive for Staphylococcus spp. detected in 177 adult pts. (≥18 years old) hospitalized for >48 hours at Sant’Elia Hospital, Caltanissetta. Results: Staphylococcus aureus was isolated in 33.9% of blood culture samples, and among CoNS, the most frequent strains were Staphylococcus capitis (18.6%) and Staphylococcus hominis (18.1%). Patients aged ≥ 65 years, with a greater number of males, comprised the SARS-CoV-2-negative pts. (71.8% vs. 52.2%, p = 0.0154). Among the SARS-CoV-2-positive patients, the significant resistance of Staphylococcus aureus was only observed for erythromycin (57.1%). The oxacillin resistance of Staphylococcus capitis was higher in SARS-CoV-2-positive than in negative pts. (90% and 78.3%, respectively). Comparing the two groups, we found an increase in resistance in SARS-CoV-2-negative patients for the following antibiotics: gentamicin for Staphylococcus aureus (p = 0.007), clindamycin and erythromycin (p = 0.012) for Staphylococcus hominis and oxacillin and rifampicin for Staphylococcus haemoliticus (p = 0.012). Conclusions: Our study confirms the relevance of oxacillin-resistant Staphylococcus aureus in being responsible for bloodstream infection and draws attention to highly oxacillin-resistant CoNS such as Staphylococcus capitis. The presence of resistant strains of CoNS in hospitals can be worrying, as it limits treatment options and worsens outcomes. The Infection Control Committee (ICC) recommends new treatment strategies to decrease colonization and infections. As part of the implementation of a bloodstream infection prevention program, the authors encourage the introduction of a report on the antimicrobial resistance of hospital bacteremia due to CoNS
Pattern selection in the absolutely unstable regime as a nonlinear eigenvalue problem: Taylor vortices in axial flow
A unique pattern selection in the absolutely unstable regime of a driven,
nonlinear, open-flow system is analyzed: The spatiotemporal structures of
rotationally symmetric vortices that propagate downstream in the annulus of the
rotating Taylor-Couette system due to an externally imposed axial through-flow
are investigated for two different axial boundary conditions at the in- and
outlet. Unlike the stationary patterns in systems without through-flow the
spatiotemporal structures of propagating vortices are independent of parameter
history, initial conditions, and system's length. They do, however, depend on
the axial boundary conditions, the driving rate of the inner cylinder and the
through-flow rate. Our analysis of the amplitude equation shows that the
pattern selection can be described by a nonlinear eigenvalue problem with the
frequency being the eigenvalue. Approaching the border between absolute and
convective instability the eigenvalue problem becomes effectively linear and
the selection mechanism approaches that one of linear front propagation.
PACS:47.54.+r,47.20.Ky,47.32.-y,47.20.FtComment: 15 pages (LateX-file), 8 figures (Postscript
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