7,995 research outputs found
An Obstruction to Quantization of the Sphere
In the standard example of strict deformation quantization of the symplectic
sphere , the set of allowed values of the quantization parameter
is not connected; indeed, it is almost discrete. Li recently constructed a
class of examples (including ) in which can take any value in an
interval, but these examples are badly behaved. Here, I identify a natural
additional axiom for strict deformation quantization and prove that it implies
that the parameter set for quantizing is never connected.Comment: 23 page. v2: changed sign conventio
Stress, Motivation and Professional Satisfaction among Health Care Workers in HIV/AIDS Care and Treatment Centers in Urban Tanzania: A Cross-Sectional Study.
Shortages of health care workers (HCWs) represents a serious challenge to ensuring effective HIV care in resource-limited settings (RLS). Stress, motivation, and job satisfaction have been linked with HCW retention and are important in addressing HCW shortages. In this cross-sectional study HCW stress, motivation and perceived ability to meet patient needs were assessed in PEPFAR-supported urban HIV care and treatment clinics (CTCs) in Tanzania. A self-administered questionnaire measuring motivation, stress, and perceived ability to and meet patient needs was given to HCWs at 16 CTCs. Scales measuring HCW satisfaction, motivation, and stress were developed using principle components analysis. Hierarchical linear models were used to explore the association of HCW and site characteristics with reported satisfaction, stress, motivation, and ability to meet patients' needs.\ud
Seventy-three percent (279) of HCWs completed the questionnaire. Most (73%) HCWs reported minimal/no work-related stress, with 48% reporting good/excellent motivation, but 41% also reporting feeling emotionally drained. Almost all (98%) reported feeling able to help their patients, with 68% reporting work as rewarding. Most reported receipt of training and supervision, with good availability of resources. In the multivariate model, direct clinical providers reported lower motivation than management (p < 0.05) and HCWs at medium-sized sites reported higher motivation than HCWs at larger sites (p < 0.05). HCWs at small and medium sites were more likely to feel able to help patients than those from larger sites (p < 0.05 and p < 0.001 respectively). Despite significant patient loads, HCWs in these PEPFAR-supported CTCs reported high levels of motivation, job satisfaction, ability to meet patients' needs, low levels of stress but significant emotional toll. Understanding the relationship between support systems such as strong supervision and training and these outcomes is critical in designing interventions to improve motivation, reduce stress and increase retention of HCWs
Assessing Cognitive Processing and Human Factors Challenges in NextGen Air Traffic Control Tower Team Operations
Previous research of Terminal Radar Control Facilities and Standard Terminal Automation Replacement Systems interactions by the authors examined how combined NextGen digitized technology affects air traffic controller functions. Applying their updated SHELL model, human factors implications on the Tower Team before and after implementing NextGen technology were examined, focusing on cognitive loading and automated functions affecting each team member. A survey examined where cognitive difficulties occur when controllers are responsible for multiple screen views, remote airfields or helipads, and digitized cameras and blind spots. Scanning challenges were identified where local traffic, ground operations, and data converge onto one screen, and when attention is diverted to distant screens. Also studied were automatic aircraft handoffs and potential for missed handoffs, and, assessing changes from voice communication to text messaging for human error. Findings indicated a necessity for controllers to manage balanced tasking, vigilance pacing, and resource management
Accelerating and enabling convergence of nonlinear solvers for Navier-Stokes equations by continuous data assimilation
This paper considers improving the Picard and Newton iterative solvers for
the Navier-Stokes equations in the setting where data measurements or solution
observations are available. We construct adapted iterations that use continuous
data assimilation (CDA) style nudging to incorporate the known solution data
into the solvers. For CDA-Picard, we prove the method has an improved
convergence rate compared to usual Picard, and the rate improves as more
measurement data is incorporated. We also prove that CDA-Picard is contractive
for larger Reynolds numbers than usual Picard, and the more measurement data
that is incorporated the larger the Reynolds number can be with CDA-Picard
still being contractive. For CDA-Newton, we prove that the domain of
convergence, with respect to both the initial guess and the Reynolds number,
increases as as the amount of measurement data is increased. Additionally, for
both methods we show that CDA can be implemented as direct enforcement of
measurement data into the solution. Numerical results for common benchmark
Navier-Stokes tests illustrate the theory
Realising MÄori Potential within the Youth Guarantee â An Evaluation of the Youth Guarantee Programme with a Focus on MÄori Learners
MÄori studentsâ educational success is critical to Aotearoa New Zealandâs success. The New Zealand Government is committed to supporting MÄori learners explore and achieve full potential as MÄori. To fulfil this commitment, the Ministry of Education released Ka Hikitia â Managing for Success: The MÄori Education Strategy 2008â2012 in April 2008, which sets the direction for improving education outcomes for and with MÄori learners. The Youth Guarantee (YG) programme is one of the initiatives which aim to increase the educational achievement of 16 and 17 year olds by making the education system more responsive to their needs. The Ministry of Education is currently undertaking a research project to evaluate the YG with a focus on improving these programmes to better meet the needs of MÄori learners. This report offers a snapshot of the achievements of the YG MÄori learners at Wintec and the challenges they face
Electrochemical probing of selective haemoglobin binding in hydrogel-based molecularly imprinted polymers
An electrochemical method has been developed for the probing of hydrogel-based molecularly imprinted polymers (HydroMIPs) on the surface of a glassy carbon electrode. HydroMIPs designed for bovine haemoglobin selectivity were electrochemically characterised and their rebinding properties were monitored using cyclic voltammetry. The electrochemical reduction of bovine oxyhaemoglobin (BHb) in solution was observed to occur at ?0.460 V vs (Ag/AgCl) in 150 mM phosphate buffer solution (PBS). When the protein was selectively bound to the MIP, the electrochemical reduction of oxyhaemoglobin could be observed at a similar peak potential of ?0.480 V vs (Ag/AgCl). When analysing the non-imprinted control polymer (NIP) interfaced at the electrode, which contained no protein, the peak reduction potential corresponded to that observed for dissolved oxygen in solution (?0.65 V vs (Ag/AgCl)). MIP and NIP (in the absence of protein) were interfaced at the electrode and protein allowed to diffuse through the polymers from the bulk solution end to the electrode. It was observed that whereas NIP exhibited a protein response within 10 min of protein exposure, up to 45 min of exposure time was required in the case of the MIP before a protein response could be obtained. Our results suggest that due to the selective nature of the MIP, BHb arrival at the electrode via diffusion is delayed by the MIP due to attractive selective interactions with exposed cavities, but not the NIP which is devoid of selective cavities
A Fast Algorithm for Robust Regression with Penalised Trimmed Squares
The presence of groups containing high leverage outliers makes linear
regression a difficult problem due to the masking effect. The available high
breakdown estimators based on Least Trimmed Squares often do not succeed in
detecting masked high leverage outliers in finite samples.
An alternative to the LTS estimator, called Penalised Trimmed Squares (PTS)
estimator, was introduced by the authors in \cite{ZiouAv:05,ZiAvPi:07} and it
appears to be less sensitive to the masking problem. This estimator is defined
by a Quadratic Mixed Integer Programming (QMIP) problem, where in the objective
function a penalty cost for each observation is included which serves as an
upper bound on the residual error for any feasible regression line. Since the
PTS does not require presetting the number of outliers to delete from the data
set, it has better efficiency with respect to other estimators. However, due to
the high computational complexity of the resulting QMIP problem, exact
solutions for moderately large regression problems is infeasible.
In this paper we further establish the theoretical properties of the PTS
estimator, such as high breakdown and efficiency, and propose an approximate
algorithm called Fast-PTS to compute the PTS estimator for large data sets
efficiently. Extensive computational experiments on sets of benchmark instances
with varying degrees of outlier contamination, indicate that the proposed
algorithm performs well in identifying groups of high leverage outliers in
reasonable computational time.Comment: 27 page
Improving Inference of Gaussian Mixtures Using Auxiliary Variables
Expanding a lower-dimensional problem to a higher-dimensional space and then
projecting back is often beneficial. This article rigorously investigates this
perspective in the context of finite mixture models, namely how to improve
inference for mixture models by using auxiliary variables. Despite the large
literature in mixture models and several empirical examples, there is no
previous work that gives general theoretical justification for including
auxiliary variables in mixture models, even for special cases. We provide a
theoretical basis for comparing inference for mixture multivariate models with
the corresponding inference for marginal univariate mixture models. Analytical
results for several special cases are established. We show that the probability
of correctly allocating mixture memberships and the information number for the
means of the primary outcome in a bivariate model with two Gaussian mixtures
are generally larger than those in each univariate model. Simulations under a
range of scenarios, including misspecified models, are conducted to examine the
improvement. The method is illustrated by two real applications in ecology and
causal inference
The distribution of stellar mass in the low-redshift Universe
We use a complete and uniform sample of almost half a million galaxies from
the Sloan Digital Sky Survey to characterise the distribution of stellar mass
in the low-redshift Universe. Galaxy abundances are well determined over almost
four orders of magnitude in stellar mass, and are reasonably but not perfectly
fit by a Schechter function with characteristic stellar mass m* = 6.7 x 10^10
M_sun and with faint-end slope \alpha = -1.155. For a standard cosmology and a
standard stellar Initial Mass Function, only 3.5% of the baryons in the
low-redshift Universe are locked up in stars. The projected autocorrelation
function of stellar mass is robustly and precisely determined for r_p < 30
Mpc/h. Over the range 10 kpc/kpc < r_p < 10 Mpc/h it is extremely well
represented by a power law. The corresponding three-dimensional autocorrelation
function is \xi*(r) = (r/6.1 Mpc/h)^{-1.84}. Relative to the dark matter, the
bias of the stellar mass distribution is approximately constant on large
scales, but varies by a factor of five for r_p < 1 Mpc/h. This behaviour is
approximately but not perfectly reproduced by current models for galaxy
formation in the concordance LCDM cosmology. Detailed comparison suggests that
a fluctuation amplitude \sigma_8 ~ 0.8 is preferred to the somewhat larger
value adopted in the Millennium Simulation models with which we compare our
data. This comparison also suggests that observations of stellar mass
autocorrelations as a function of redshift might provide a powerful test for
the nature of Dark Energy.Comment: 12 pages, 11 figures, accepted for publication in Monthly Notices,
two appendices added to explore possible systematic biases due to the stellar
mass definition and surface density limit
Widespread recombination, reassortment, and transmission of unbalanced compound viral genotypes in natural arenavirus infections.
Arenaviruses are one of the largest families of human hemorrhagic fever viruses and are known to infect both mammals and snakes. Arenaviruses package a large (L) and small (S) genome segment in their virions. For segmented RNA viruses like these, novel genotypes can be generated through mutation, recombination, and reassortment. Although it is believed that an ancient recombination event led to the emergence of a new lineage of mammalian arenaviruses, neither recombination nor reassortment has been definitively documented in natural arenavirus infections. Here, we used metagenomic sequencing to survey the viral diversity present in captive arenavirus-infected snakes. From 48 infected animals, we determined the complete or near complete sequence of 210 genome segments that grouped into 23 L and 11 S genotypes. The majority of snakes were multiply infected, with up to 4 distinct S and 11 distinct L segment genotypes in individual animals. This S/L imbalance was typical: in all cases intrahost L segment genotypes outnumbered S genotypes, and a particular S segment genotype dominated in individual animals and at a population level. We corroborated sequencing results by qRT-PCR and virus isolation, and isolates replicated as ensembles in culture. Numerous instances of recombination and reassortment were detected, including recombinant segments with unusual organizations featuring 2 intergenic regions and superfluous content, which were capable of stable replication and transmission despite their atypical structures. Overall, this represents intrahost diversity of an extent and form that goes well beyond what has been observed for arenaviruses or for viruses in general. This diversity can be plausibly attributed to the captive intermingling of sub-clinically infected wild-caught snakes. Thus, beyond providing a unique opportunity to study arenavirus evolution and adaptation, these findings allow the investigation of unintended anthropogenic impacts on viral ecology, diversity, and disease potential
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