78,424 research outputs found
Topological asymmetry in the damping-pairing contribution of electron-boson scattering
We make a harmonic analysis of the pairing and damping contribution of a
finite range isotropic electron-phonon (or other boson) scattering in an
anisotropic two-dimensional electronic system. We show that the pairing
contribution of the anisotropic part of the electronic system can be much
larger than its damping contribution enhancing significantly T_c. The higher is
the order of the harmonic of the electronic anisotropy, smaller is its damping
contribution and higher can be the asymmetry in its damping-pairing
contribution. This could explain the puzzle of a much broader quasiparticle
peak in the n-doped than in the p-doped cuprates, their smaller T_c's being
also attributed to larger damping effects.Comment: LATEX file and 3 Postscript figure
Compatible Weighted Proper Scoring Rules
Many proper scoring rules such as the Brier and log scoring rules implicitly
reward a probability forecaster relative to a uniform baseline distribution.
Recent work has motivated weighted proper scoring rules, which have an
additional baseline parameter. To date two families of weighted proper scoring
rules have been introduced, the weighted power and pseudospherical scoring
families. These families are compatible with the log scoring rule: when the
baseline maximizes the log scoring rule over some set of distributions, the
baseline also maximizes the weighted power and pseudospherical scoring rules
over the same set. We characterize all weighted proper scoring families and
prove a general property: every proper scoring rule is compatible with some
weighted scoring family, and every weighted scoring family is compatible with
some proper scoring rule
Strategic capital budgeting: asset replacement under market uncertainty
In this paper the impact of product market uncertainty on the optimal replacement timing of a production facility is studied. The existing production facility can be replaced by a technologically more advanced and thus more cost-effective one. We take into account strategic interactions among the firms competing in the product market by analyzing the problem in a duopolistic setting. We calculate the value of each firm and show that i) a preemptive (simultaneous) replacement occurs when the associated sunk cost is low (high), ii) despite the preemption effect uncertainty always raises the expected time to replace, and iii) the relationship between the probability of optimal replacement within a given time interval and uncertainty is decreasing for long time intervals and humped for short time intervals. Furthermore it is shown that result ii) carries over to the case where firms have to decide about starting production rather than about replacing existing facilities
Faculty Productivity in Supervising Doctoral Students’ Dissertations at Cornell University
Excerpt] Economists and academic administrators have long been concerned with issues of faculty productivity. For example, sets of studies have addressed whether faculty research productivity is related to faculty salaries, whether gender differences in faculty salaries remain after one controls for research productivity, and whether a negative association between faculty salary and seniority at an institution is due to universities having monopsony power or due to declining faculty research productivity with seniority.
To take another example, concern that the ending of mandatory retirement, which became effective for tenured faculty in January 1994, would lead to an aging nonproductive faculty has led other researchers to examine how faculty research and teaching productivity, the latter measured by undergraduate student evaluations, have varied over the life cycle. More recently, researchers studied whether declining research productivity is related to the acceptance of an offer for an early retirement incentive. Finally, other researchers have looked at how faculty research productivity varies across cohorts, finding that when a scientist enters the labor market has a substantial effect on his or her productivity over the life cycle and that more recently educated cohorts are not necessarily more productive than earlier cohorts. While some studies have looked at the implicit role that PhD student production has on the quality rankings of PhD programs, to our knowledge no studies have focused on how the distribution of PhD student supervisory responsibilities varies across faculty members at a university. Our study uses data on all PhDs produced during a 7-year period at Cornell University to illustrate how researchers can study whether the degree of inequality in PhD student supervision across faculty members within a broad field of study, varies across fields, as well as what the determinants are of differences in PhD student supervision responsibilities across individual faculty members within each broad field. Of particular concern to us, given the elimination of mandatory retirement, is how faculty members’ productivity in the supervision of PhD students varies over their life cycles
Linear Estimating Equations for Exponential Families with Application to Gaussian Linear Concentration Models
In many families of distributions, maximum likelihood estimation is
intractable because the normalization constant for the density which enters
into the likelihood function is not easily available. The score matching
estimator of Hyv\"arinen (2005) provides an alternative where this
normalization constant is not required. The corresponding estimating equations
become linear for an exponential family. The score matching estimator is shown
to be consistent and asymptotically normally distributed for such models,
although not necessarily efficient. Gaussian linear concentration models are
examples of such families. For linear concentration models that are also linear
in the covariance we show that the score matching estimator is identical to the
maximum likelihood estimator, hence in such cases it is also efficient.
Gaussian graphical models and graphical models with symmetries form
particularly interesting subclasses of linear concentration models and we
investigate the potential use of the score matching estimator for this case
A Fast Algorithm for Sampling from the Posterior of a von Mises distribution
Motivated by molecular biology, there has been an upsurge of research
activities in directional statistics in general and its Bayesian aspect in
particular. The central distribution for the circular case is von Mises
distribution which has two parameters (mean and concentration) akin to the
univariate normal distribution. However, there has been a challenge to sample
efficiently from the posterior distribution of the concentration parameter. We
describe a novel, highly efficient algorithm to sample from the posterior
distribution and fill this long-standing gap
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