963 research outputs found
Translational perspectives on perfusion-diffusion mismatch in ischemic stroke
Magnetic resonance imaging has tremendous potential to illuminate ischemic stroke pathophysiology and guide rational treatment decisions. Clinical applications to date have been largely limited to trials. However, recent analyses of the major clinical studies have led to refinements in selection criteria and improved understanding of the potential implications for the risk vs. benefit of thrombolytic therapy. In parallel, preclinical studies have provided complementary information on the evolution of stroke that is difficult to obtain in humans due to the requirement for continuous or repeated imaging and pathological verification. We review the clinical and preclinical advances that have led to perfusionâdiffusion mismatch being applied in phase 3 randomized trials and, potentially, future routine clinical practice
Regularizing Portfolio Optimization
The optimization of large portfolios displays an inherent instability to
estimation error. This poses a fundamental problem, because solutions that are
not stable under sample fluctuations may look optimal for a given sample, but
are, in effect, very far from optimal with respect to the average risk. In this
paper, we approach the problem from the point of view of statistical learning
theory. The occurrence of the instability is intimately related to over-fitting
which can be avoided using known regularization methods. We show how
regularized portfolio optimization with the expected shortfall as a risk
measure is related to support vector regression. The budget constraint dictates
a modification. We present the resulting optimization problem and discuss the
solution. The L2 norm of the weight vector is used as a regularizer, which
corresponds to a diversification "pressure". This means that diversification,
besides counteracting downward fluctuations in some assets by upward
fluctuations in others, is also crucial because it improves the stability of
the solution. The approach we provide here allows for the simultaneous
treatment of optimization and diversification in one framework that enables the
investor to trade-off between the two, depending on the size of the available
data set
N-[3-(2,6-Dimethylanilino)-1-methylbut-2-enylidene]-2,6-dimethylanilinium chloride1
The title salt, C21H27N2
+·Clâ resulted from the condensation between 2,6-dimethylÂaniline and acetylÂacetone in acidified ethanol. The bulky cation is stabilized in a ÎČ-iminoÂenamine tautomeric form, and presents a W-shaped conformation. The benzene rings are arranged almost parallel, with a dihedral angle of 6.58â
(4)° between the mean planes. Both NâH groups in the cation form strong hydrogen bonds with two symmetry-related chloride anions. The resulting supraÂmolecular structure is a one dimensional polymer running along [001], alternating cations and anions. The ÏâÏ interÂaction observed in the molÂecule, characterized by a centroidâcentroid separation of 4.298â
(4)â
Ă
, is thus extended to the chains, with separations of 5.222â
(4)â
Ă
between benzene rings of neighbouring cations in the crystal
Determination of the scalar polarizabilities of the proton using beam asymmetry in Compton scattering
The scalar dipole polarizabilities, and , are
fundamental properties related to the internal dynamics of the nucleon. The
currently accepted values of the proton polarizabilities were determined by
fitting to unpolarized proton Compton scattering cross section data. The
measurement of the beam asymmetry in a certain kinematical range
provides an alternative approach to the extraction of the scalar
polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured
for Compton scattering below pion photoproduction threshold for the first time.
The results are compared with model calculations and the influence of the
experimental data on the extraction of the scalar polarizabilities is
determined.Comment: 6 pages, 5 figure
From wormhole to time machine: Comments on Hawking's Chronology Protection Conjecture
The recent interest in ``time machines'' has been largely fueled by the
apparent ease with which such systems may be formed in general relativity,
given relatively benign initial conditions such as the existence of traversable
wormholes or of infinite cosmic strings. This rather disturbing state of
affairs has led Hawking to formulate his Chronology Protection Conjecture,
whereby the formation of ``time machines'' is forbidden. This paper will use
several simple examples to argue that the universe appears to exhibit a
``defense in depth'' strategy in this regard. For appropriate parameter regimes
Casimir effects, wormhole disruption effects, and gravitational back reaction
effects all contribute to the fight against time travel. Particular attention
is paid to the role of the quantum gravity cutoff. For the class of model
problems considered it is shown that the gravitational back reaction becomes
large before the Planck scale quantum gravity cutoff is reached, thus
supporting Hawking's conjecture.Comment: 43 pages,ReV_TeX,major revision
Weak signals in healthcare: The case study of the Mid-Staffordshire NHS Foundation Trust
Most organisational disasters have warning signals prior to the event occurring, which are increasingly appearing in accident reports. In the case of the Mid-Staffordshire Disaster, the disaster was not as a result of component failure or human error but rather an organisation that drifted into failure with precursory warning signals being ignored. It has been estimated that between 400 and 1200 patients died as a result of poor care between 2004 and 2009. The aim of this study was to identify the precursory signals and their rationalizations that occurred during this event. Qualitative document analysis was used to analyse the independent and public inquiry reports. Signals were present on numerous system levels. At a person level, there were cases of staff trying to make management aware of the problems, as well as the campaign âCure the NHSâ started by bereaved relatives. At an organisational level, examples of missed signals included the decrease in the trustâs star rating due to failure to meet targets, the NHS care regulator voicing concern regarding the unusually high death rates and auditorsâ reports highlighting concerns regarding risk management. At an external level, examples included negative peer reviews from various external organizations
Diffusion of e-health innovations in 'post-conflict' settings: a qualitative study on the personal experiences of health workers.
BACKGROUND: Technological innovations have the potential to strengthen human resources for health and improve access and quality of care in challenging 'post-conflict' contexts. However, analyses on the adoption of technology for health (that is, 'e-health') and whether and how e-health can strengthen a health workforce in these settings have been limited so far. This study explores the personal experiences of health workers using e-health innovations in selected post-conflict situations. METHODS: This study had a cross-sectional qualitative design. Telephone interviews were conducted with 12 health workers, from a variety of cadres and stages in their careers, from four post-conflict settings (Liberia, West Bank and Gaza, Sierra Leone and Somaliland) in 2012. Everett Roger's diffusion of innovation-decision model (that is, knowledge, persuasion, decision, implementation, contemplation) guided the thematic analysis. RESULTS: All health workers interviewed held positive perceptions of e-health, related to their beliefs that e-health can help them to access information and communicate with other health workers. However, understanding of the scope of e-health was generally limited, and often based on innovations that health workers have been introduced through by their international partners. Health workers reported a range of engagement with e-health innovations, mostly for communication (for example, email) and educational purposes (for example, online learning platforms). Poor, unreliable and unaffordable Internet was a commonly mentioned barrier to e-health use. Scaling-up existing e-health partnerships and innovations were suggested starting points to increase e-health innovation dissemination. CONCLUSIONS: Results from this study showed ICT based e-health innovations can relieve information and communication needs of health workers in post-conflict settings. However, more efforts and investments, preferably driven by healthcare workers within the post-conflict context, are needed to make e-health more widespread and sustainable. Increased awareness is necessary among health professionals, even among current e-health users, and physical and financial access barriers need to be addressed. Future e-health initiatives are likely to increase their impact if based on perceived health information needs of intended users
Impact of age norms and stereotypes on managers' hiring decisions of retirees
Purpose -Our study investigates the role of managers in the re-employment of early retirees and asks what the effect is of managersâ age norms and stereotypes on managersâ employment decisions.
Design/methodology/approach- A combination of a factorial study and a survey was conducted. First, information on the age norms and stereotypes was collected. Secondly, profiles of hypothetical retired job applicants were presented to the employers, who were asked to make a specific hiring decision. The information collected during both studies was combined in the analysis and multilevel models were estimated.
Findings -The results indicate that higher age norms result in a higher propensity to hire an early retiree. Stereotypes, by contrast, do not influence managersâ decisions. Early retireesâ chances for re-employment are also related to their own circumstances (physical appearance and relevant experience) and organisational forces, as they are hired when organisations face labour force shortages.
Research limitation / implications â with the use of vignettes study we deal with hypothetical hiring situation.
Originality value- Although the effect of age norms and age stereotypes has been often suggested, not much empirical evidence was presented to support this notion. Our study estimates the effect of age norms and stereotypes on hiring decision.
key words: bridge employment; early retirees; age norms; age stereotypes; multilevel models.
Diabetes causes marked inhibition of mitochondrial metabolism in pancreatic ÎČ-cells
Diabetes is a global health problem caused primarily by the inability of pancreatic ÎČ-cells to secrete adequate levels of insulin. The molecular mechanisms underlying the progressive failure of ÎČ-cells to respond to glucose in type-2 diabetes remain unresolved. Using a combination of transcriptomics and proteomics, we find significant dysregulation of major metabolic pathways in islets of diabetic ÎČV59M mice, a non-obese, eulipidaemic diabetes model. Multiple genes/proteins involved in glycolysis/gluconeogenesis are upregulated, whereas those involved in oxidative phosphorylation are downregulated. In isolated islets, glucose-induced increases in NADH and ATP are impaired and both oxidative and glycolytic glucose metabolism are reduced. INS-1 ÎČ-cells cultured chronically at high glucose show similar changes in protein expression and reduced glucose-stimulated oxygen consumption: targeted metabolomics reveals impaired metabolism. These data indicate hyperglycaemia induces metabolic changes in ÎČ-cells that markedly reduce mitochondrial metabolism and ATP synthesis. We propose this underlies the progressive failure of ÎČ-cells in diabetes.Peer reviewe
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