1,973 research outputs found
Random Block Operators
We study fundamental spectral properties of random block operators that are
common in the physical modelling of mesoscopic disordered systems such as dirty
superconductors. Our results include ergodic properties, the location of the
spectrum, existence and regularity of the integrated density of states, as well
as Lifshits tails. Special attention is paid to the peculiarities arising from
the block structure such as the occurrence of a robust gap in the middle of the
spectrum. Without randomness in the off-diagonal blocks the density of states
typically exhibits an inverse square-root singularity at the edges of the gap.
In the presence of randomness we establish a Wegner estimate that is valid at
all energies. It implies that the singularities are smeared out by randomness,
and the density of states is bounded. We also show Lifshits tails at these band
edges. Technically, one has to cope with a non-monotone dependence on the
random couplings.Comment: 22 pages, 3 figure
A fiscal outlook for Poland using generational accounts
During the next few decades the populations of most developed countries will grow older and older as a result of the low fertility rates since the 1970s and/or the continuously increasing life expectancy. Poland, one of the biggest countries in Central Europe, will be confronted rather seriously by this development. Generational Accounting which was introduced in the early nineties, can illustrate the effects of this ageing process on a country's fiscal situation. We show that the demographic development produces a major problem for the long term stability of Polish public finances. In particular the healthcare system deserves special attention for policy makers in the medium and long run, whilst the general pension system shall stabilise in the long term. --Generational Accounting,Fiscal sustainability,Fiscal policy,Poland,Pension reform
Variable Metric Random Pursuit
We consider unconstrained randomized optimization of smooth convex objective
functions in the gradient-free setting. We analyze Random Pursuit (RP)
algorithms with fixed (F-RP) and variable metric (V-RP). The algorithms only
use zeroth-order information about the objective function and compute an
approximate solution by repeated optimization over randomly chosen
one-dimensional subspaces. The distribution of search directions is dictated by
the chosen metric.
Variable Metric RP uses novel variants of a randomized zeroth-order Hessian
approximation scheme recently introduced by Leventhal and Lewis (D. Leventhal
and A. S. Lewis., Optimization 60(3), 329--245, 2011). We here present (i) a
refined analysis of the expected single step progress of RP algorithms and
their global convergence on (strictly) convex functions and (ii) novel
convergence bounds for V-RP on strongly convex functions. We also quantify how
well the employed metric needs to match the local geometry of the function in
order for the RP algorithms to converge with the best possible rate.
Our theoretical results are accompanied by numerical experiments, comparing
V-RP with the derivative-free schemes CMA-ES, Implicit Filtering, Nelder-Mead,
NEWUOA, Pattern-Search and Nesterov's gradient-free algorithms.Comment: 42 pages, 6 figures, 15 tables, submitted to journal, Version 3:
majorly revised second part, i.e. Section 5 and Appendi
The open drug scene in Frankfurt am Main 2002 : MoSyD report as a scene study
Der vorliegende Bericht zur âSzenestudie 2002â vermittelt eine aktuelle Situationsbeschreibung der offenen Drogenszene in Frankfurt am Main. Diese Studie zum Drogengebrauchsverhalten und Alltagsgeschehen auf der offenen Drogenszene versteht sich als eine Teilstudie im Rahmen eines komplexen Monitoringsystems (MoSyD _âMonitoring-System Drogentrendsâ), welches in 2002 in der Stadt Frankfurt eingerichtet wurde, um zeitnah und umfassend neue Entwicklungen im Bereich des Konsums legaler wie illegaler Drogen verfolgen zu können (ausfĂŒhrlich: Kemmesies und Hess 2001). Die folgende Zusammenfassung gibt die zentralen Beobachtungen und Ergebnisse der Erhebung wieder. Diese Teilstudie vom MoSyD fokussiert auf den so genannten problematischen Kern des DrogenphĂ€nomens: Mit der Erscheinung offener Drogenszenen gehen vielfĂ€ltige drogenpolitischen Herausforderungen einher. Diese beziehen sich sowohl auf sozial-medizinische wie strafrechtliche Aspekte, wie sie in den Stichworten Infektionskrankheiten, BeschaffungskriminalitĂ€t, Deprivation, Verelendung et cetera geradezu greifbare RealitĂ€t gewinnen. Aufgrund der enormen sozial-, gesundheits- wie ordnungspolitischen Herausforderungen und einer mitunter rasanten VerĂ€nderungsdynamik im mittelbaren und unmittelbaren Umfeld der offenen Drogenszene dokumentieren wir bereits hiermit - auĂerhalb des projektierten jĂ€hrlichen Berichtsturnus vom MoSyD und zeitnah zur Interviewerhebung - unsere Beobachtungen. Im Vorgriff auf die konkreten Ergebnisse sei bereits angemerkt, dass sich die Situation offenbar innerhalb der letzten Jahre stark verĂ€ndert hat: Wenn bisher eine offene Drogenszene in Deutschland in erster Linie mit dem klassischen Vorstellungsbild von einem intravenös Heroin konsumierenden âJunkieâ assoziiert war, so scheint diese Assoziation â zumindest mit Blick auf Frankfurt â die RealitĂ€t nur noch Ă€uĂerst gebrochen widerzuspiegeln. Denn Heroin hat seine dominierende Position auf dem Drogenschwarzmarkt verloren und an Kokain beziehungsweise dessen Derivat Crack abgegeben. DarĂŒber hinaus hat sich der intravenöse Drogenkonsum insgesamt deutlich â um etwa die HĂ€lfte â reduziert. Da systematisch vergleichbare Daten weit zurĂŒckreichen und erst aus dem Jahre 1995 vorliegen (Kemmesies 1995b), lĂ€sst sich nicht nĂ€her ergrĂŒnden, wie es um die Dynamik der prozessualen VerĂ€nderungen bestellt ist: Befinden wir uns am Ende einer Entwicklung oder aber stecken wir mitten in einem grundsĂ€tzlichen VerĂ€nderungsprozess, innerhalb dessen sich das Bild der offenen Drogenszene grundlegend wandeln wird. Um einen besseren Einblick in die VerĂ€nderungsdynamik gewinnen zu können, schlagen wir vor, von dem ursprĂŒnglich im Rahmen vom MoSyD vorgesehenen zweijĂ€hrigen Erhebungsturnus abzurĂŒcken und die Szenestudie bereits 2003 erneut durchzufĂŒhren. Ausgehend von zentralen Ergebnissen wĂ€re nĂ€her zu ergrĂŒnden, inwieweit der offensichtliche Trend einer Altersanhebung im Umfeld der offenen Drogenszene anhĂ€lt, ob es zu einer fortschreitenden Ausweitung von kokain-/crackorientierten Drogengebrauchsmustern kommt, und inwieweit diese Entwicklungen sich im allgemeinen Gesundheitszustand der Drogenkonsumenten abbilden. Weiterhin wĂ€re zu prĂŒfen, ob die geplante Ausweitung der Substitutionsbehandlung in Gestalt des Heroinerprobungsprogramms sich auch auf das âtypischeâ Drogengebrauchsverhalten auf der offenen Drogenszene auswirkt
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Compact diode laser based light source with alternating dual-wavelength emission at 532 nm
Compact nonlinear frequency conversion of a Y-branch distributed Bragg reflector (DBR) diode laser for alternating dual-wavelength laser emission at 532 nm is presented for the very first time. The developed light source, realized on a 5âĂâ25 mm2 micro-optical bench, is based on single-pass second harmonic generation of a 1064 nm Y-branch DBR diode laser in a periodically poled lithium niobate waveguide crystal with superimposed poling periods. Phase-matching is obtained by intrinsic wavelength stabilization of the laser and wavelength tuning by implemented heater elements above the DBR gratings. Obtained optical output powers of 5.6 mW at 532.45 nm and 6.7 mW at 531.85 nm are limited by central lobe power contents of 52% available for waveguide coupling. With a spectral performance showing narrowband emission with spectral widths of 0.01 nm (0.4 cmâ1) limited by the spectral resolution of the spectrum analyzer and a spectral spacing of 0.6 nm (20 cmâ1), the developed light source is suitable for applications such as Raman spectroscopy and shifted excitation Raman difference spectroscopy (SERDS). Separate electrical contacts of the Y-branch diode laser enable alternating operation at both wavelengths
Effects of requested, forced and denied shift schedule change on work ability and health of nurses in Europe: results from the European NEXT-Study
Background: Previous cross-sectional findings from the European Nurses Early Exit Study (NEXT) show that nurses who were dissatisfied with their work schedule tended to consider leaving the nursing profession. Mediating factors in this decision process may be caused by self-perceived poor work ability and/or health. The aim of this paper is to investigate changes in work ability and general health among nurses in relation to requested, forced and denied change of shift schedule.
Methods: Longitudinal data from the NEXT Study was used. In total 11,102 nurses from Belgium, Germany, Finland, the Netherlands, Poland, Slovakia, France and Italy completed both the âbasic questionnaireâ (t1) and the â12 month follow-up questionnaireâ (t2). To examine the time-effect (repeated measures) and the group-effect of five defined groups of nurses on the Work Ability Index (WAI) and general health (SF36), an adjusted 2-way analysis of covariance (ANCOVA) was performed.
Results: The nurses who wanted to, but could not change their shifts during the 12 month follow-up had the lowest initial and follow-up scores for WAI (t1: 37.6, t2: 36.6, p <0.001), lowest general health (t1: 63.9, t2: 59.2, p <0.001) and showed the highest decrease in both outcomes. Shift pattern change in line with the nursesâ wishes was associated with improved work ability and to a lesser comparatively low extent with increased decline in health scores. A forced change of shift against the nursesâ will was significantly associated with a deteriorating work ability and health.
Conclusions: The findings would suggest that nursesâ desire to change their shift patterns may be an indicator for perceived low work ability and/or low health. The results also indicate that fulfilling nursesâ wishes with respect to their shift work pattern may improve their personal resources such as work ability and â to somewhat lesser extent â health. Disregarding nursesâ preferences, however, bears the risk for further resource deterioration. The findings imply that shift schedule organization may constitute a valuable preventive tool to promote nursesâ work ability and â to lesser extent â their perceived health, not least in aging nursing work forces
Learning Multiple Defaults for Machine Learning Algorithms
The performance of modern machine learning methods highly depends on their
hyperparameter configurations. One simple way of selecting a configuration is
to use default settings, often proposed along with the publication and
implementation of a new algorithm. Those default values are usually chosen in
an ad-hoc manner to work good enough on a wide variety of datasets. To address
this problem, different automatic hyperparameter configuration algorithms have
been proposed, which select an optimal configuration per dataset. This
principled approach usually improves performance, but adds additional
algorithmic complexity and computational costs to the training procedure. As an
alternative to this, we propose learning a set of complementary default values
from a large database of prior empirical results. Selecting an appropriate
configuration on a new dataset then requires only a simple, efficient and
embarrassingly parallel search over this set. We demonstrate the effectiveness
and efficiency of the approach we propose in comparison to random search and
Bayesian Optimization
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