8,616 research outputs found
Markets for Reputation: Evidence on Quality and Quantity in Academe
We develop a theory of the market for individual reputation, an indicator of regard by one’s peers and others. The central questions are: 1) Does the quantity of exposures raise reputation independent of their quality? and 2) Assuming that overall quality matters for reputation, does the quality of an individual’s most important exposure have an extra effect on reputation? Using evidence for academic economists, we find that, conditional on its impact, the quantity of output has no or even a negative effect on each of a number of proxies for reputation, and very little evidence that a scholar's most influential work provides any extra enhancement of reputation. Quality ranking matters more than absolute quality. Data on mobility and salaries show, on the contrary, substantial positive effects of quantity, independent of quality. We test various explanations for the differences between the determinants of reputation and salary.mobility, quality/quantity trade-off, salary determination
Two-Sided Learning, Labor Turnover and Displacement
We construct a general dynamic structural model of two-sided learning between a firm and its workers. We estimate an empirical version of the model using personnel data from Fokker Aircraft that cover the path of layoffs and quits through its bankruptcy. We find that the firm learns about its workers' loyalty (demonstrating the role of information in repeated cooperative principal-agent relationships). There is no evidence that workers learn (consistent with earlier empirical results on American workers). The type of data that we use also generates information on the value of learning and on whether and how the characteristics of workers who remain until the firm's death differ from those of all affected workers. It thus allows us to measure the increases in the firm's value from learning about its workers' behavior and to infer the extent of biases in estimated losses from displacement from samples restricted to displaced workers.
Geometric phases in astigmatic optical modes of arbitrary order
The transverse spatial structure of a paraxial beam of light is fully
characterized by a set of parameters that vary only slowly under free
propagation. They specify bosonic ladder operators that connect modes of
different order, in analogy to the ladder operators connecting
harmonic-oscillator wave functions. The parameter spaces underlying sets of
higher-order modes are isomorphic to the parameter space of the ladder
operators. We study the geometry of this space and the geometric phase that
arises from it. This phase constitutes the ultimate generalization of the Gouy
phase in paraxial wave optics. It reduces to the ordinary Gouy phase and the
geometric phase of non-astigmatic optical modes with orbital angular momentum
states in limiting cases. We briefly discuss the well-known analogy between
geometric phases and the Aharonov-Bohm effect, which provides some
complementary insights in the geometric nature and origin of the generalized
Gouy phase shift. Our method also applies to the quantum-mechanical description
of wave packets. It allows for obtaining complete sets of normalized solutions
of the Schr\"odinger equation. Cyclic transformations of such wave packets give
rise to a phase shift, which has a geometric interpretation in terms of the
other degrees of freedom involved.Comment: final versio
Dansgaard-Oeschger events: tipping points in the climate system
Dansgaard-Oeschger events are a prominent mode of variability in the records
of the last glacial cycle. Various prototype models have been proposed to
explain these rapid climate fluctuations, and no agreement has emerged on which
may be the more correct for describing the paleoclimatic signal. In this work,
we assess the bimodality of the system reconstructing the topology of the
multi--dimensional attractor over which the climate system evolves. We use
high-resolution ice core isotope data to investigate the statistical properties
of the climate fluctuations in the period before the onset of the abrupt
change. We show that Dansgaard-Oeschger events have weak early warning signals
if the ensemble of events is considered. We find that the statistics are
consistent with the switches between two different climate equilibrium states
in response to a changing external forcing (e.g. solar, ice sheets...), either
forcing directly the transition or pacing it through stochastic resonance.
These findings are most consistent with a model that associates
Dansgaard-Oeschger with changing boundary conditions, and with the presence of
a bifurcation point.Comment: Final typeset version freely available at: Clim. Past, 9, 323-333,
2013 www.clim-past.net/9/323/2013/ doi:10.5194/cp-9-323-201
Two proposals for testing quantum contextuality of continuous-variable states
We investigate the violation of non-contextuality by a class of continuous
variable states, including variations of entangled coherent states (ECS's) and
a two-mode continuous superposition of coherent states. We generalise the
Kochen-Specker (KS) inequality discussed in A. Cabello, Phys. Rev. Lett. {\bf
101}, 210401 (2008) by using effective bidimensional observables implemented
through physical operations acting on continuous variable states, in a way
similar to an approach to the falsification of Bell-CHSH inequalities put
forward recently. We test for state-independent violation of KS inequalities
under variable degrees of state entanglement and mixedness. We then demonstrate
theoretically the violation of a KS inequality for any two-mode state by using
pseudo-spin observables and a generalized quasi-probability function.Comment: 7 pages, 2 figures, RevTeX
Prompt Beta Spectroscopy as a Diagnostic for Mix in Ignited NIF Capsules
The National Ignition Facility (NIF) technology is designed to drive
deuterium-tritium (DT) internal confinement fusion (ICF) targets to ignition
using indirect radiation from laser beam energy captured in a hohlraum.
Hydrodynamical instabilities at interfaces in the ICF capsule leading to mix
between the DT fue l and the ablator shell material are of fundamental physical
interest and can affect the performance characteristics of the capsule. In this
Letter we describe new radiochemical diagnostics for mix processes in ICF
capsules with plastic or Be (0.9%Cu) ablator shells. Reactions of high-energy
tritons with shell material produce high-energy -emitters.
We show that mix between the DT fuel and the shell material enhances
high-energy prompt beta emission from these reactions by more than an order of
magnitude over that expected in the absence of mix
Minimal Flavor Constraints for Technicolor
We analyze the constraints on the the vacuum polarization of the standard
model gauge bosons from a minimal set of flavor observables valid for a general
class of models of dynamical electroweak symmetry breaking. We will show that
the constraints have a strong impact on the self-coupling and masses of the
lightest spin-one resonances. Our analysis is applicable to any four and higher
dimensional extension of the standard model reducing to models of dynamical
electroweak symmetry breaking.Comment: 26 pages, we have added appendix C and some references and corrected
some typo
Integrated out-of-hours care arrangements in England: observational study of progress towards single call access via NHS Direct and impact on the wider health system
Objectives: To assess the extent of service integration achieved within general practice cooperatives and NHS Direct sites participating in the Department of Health’s national “Exemplar Programme” for single call access to out-of-hours care via NHS Direct. To assess the impact of integrated out-of-hours care arrangements upon general practice cooperatives and the wider health system (use of emergency departments, 999 ambulance services, and minor injuries units).
Design: Observational before and after study of demand, activity, and trends in the use of other health services.
Setting: Thirty four English general practice cooperatives with NHS Direct partners (“exemplars”) of which four acted as “case exemplars”. Also 10 control cooperatives for comparison.
Main Outcome Measures: Extent of integration achieved (defined as the proportion of hours and the proportion of general practice patients covered by integrated arrangements), patterns of general practice cooperative demand and activity and trends in use of the wider health system in the first year.
Results: Of 31 distinct exemplars 21 (68%) integrated all out-of-hours call management by March 2004. Nine (29%) established single call access for all patients. In the only case exemplar where direct comparison was possible, cooperative nurse telephone triage before integration completed a higher proportion of calls with telephone advice than did NHS Direct afterwards (39% v 30%; p<0.0001). The proportion of calls completed by NHS Direct telephone advice at other sites was lower. There is evidence for transfer of demand from case exemplars to 999 ambulance services. A downturn in overall demand for care seen in two case exemplars was also seen in control sites.
Conclusion: The new model of out-of-hours care was implemented in a variety of settings across England by new partnerships between general practice cooperatives and NHS Direct. Single call access was not widely implemented and most patients needed to make at least two telephone calls to contact the service. In the first year, integration may have produced some reduction in total demand, but this may have been accompanied by shifts from one part of the local health system to another. NHS Direct demonstrated capability in handling calls but may not currently have sufficient capacity to support national implementation
Ultrasonic inspection and self-healing of Ge and 3C-SiC semiconductor membranes
Knowledge of the mechanical properties and stability of thin film structures is important for device operation. Potential failures related to crack initiation and growth must be identified early, to enable healing through e.g. annealing. Here, three square suspended membranes, formed from a thin layer of cubic silicon carbide (3C-SiC) or germanium (Ge) on a silicon substrate, were characterised by their response to ultrasonic excitation. The resonant frequencies and mode shapes were measured during thermal cycling over a temperature range of 20--100~C. The influence of temperature on the stress was explored by comparison with predictions from a model of thermal expansion of the combined membrane and substrate. For an ideal, non-cracked sample the stress and Q-factor behaved as predicted. In contrast, for a 3C-SiC and a Ge membrane that had undergone vibration and thermal cycling to simulate extended use, measurements of the stress and Q-factor showed the presence of damage, with the 3C-SiC membrane subsequently breaking. However, the damaged Ge sample showed an improvement to the resonant behaviour on subsequent heating. Scanning electron microscopy showed that this was due to a self-healing of sub-micrometer cracks, caused by expansion of the germanium layer to form bridges over the cracked regions, with the effect also observable in the ultrasonic inspection
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