3,747 research outputs found
Algebraic treatment of the confluent Natanzon potentials
Using the so(2,1) Lie algebra and the Baker, Campbell and Hausdorff formulas,
the Green's function for the class of the confluent Natanzon potentials is
constructed straightforwardly. The bound-state energy spectrum is then
determined. Eventually, the three-dimensional harmonic potential, the
three-dimensional Coulomb potential and the Morse potential may all be
considered as particular cases.Comment: 9 page
A Brief Review Of Actions To Strengthen Gender Equality At The University Of Costa Rica
This article discusses efforts at the University of Costa Rica since the 1980s to incorporate a gender perspective and stimulate feminist studies at this institution of higher education. The dynamic of the national context together with the efforts of the feminist movement and of Costa Rican institutions have created an environment propitious to the establishment of various laws and the ratification of international agreements that defend the rights of Costa Rican citizens and particularly to fight discrimination against women. The article reflects on the advances achieved in the university and reports on other studies about the presence of men and women in the fields of science and technology. It concludes that, despite a stronger female presence among undergraduate and graduate students, there are still inequalities in participation and the access to careers. Some fields in the basic sciences and technology, such as the engineering fields, have a lower presence of women. The university situation certainly provides material for reflection and analysis about how to create incentives and transform female and male participation in a more equitable manner. © 2016, All rights reserved.20174
Evaluating Modeled Intra- to Multidecadal Climate Variability Using Running Mann–Whitney \u3cem\u3eZ\u3c/em\u3e Statistics
An analysis method previously used to detect observed intra- to multidecadal (IMD) climate regimes was adapted to compare observed and modeled IMD climate variations. Pending the availability of the more appropriate phase 5 Coupled Model Intercomparison Project (CMIP-5) simulations, the method is demonstrated using CMIP-3 model simulations. Although the CMIP-3 experimental design will almost certainly prevent these model runs from reproducing features of historical IMD climate variability, these simulations allow for the demonstration of the method and illustrate how the models and observations disagree. This method samples a time series’s data rankings over moving time windows, converts those ranking sets to a Mann–Whitney U statistic, and then normalizes the U statistic into a Z statistic. By detecting optimally significant IMD ranking regimes of arbitrary onset and varying duration, this process generates time series of Z values that are an adaptively low-passed and normalized transformation of the original time series. Principal component (PC) analysis of the Z series derived from observed annual temperatures at 92 U.S. grid locations during 1919–2008 shows two dominant modes: a PC1 mode with cool temperatures before the late 1960s and warm temperatures after the mid-1980s, and a PC2 mode indicating a multidecadal temperature cycle over the Southeast. Using a graphic analysis of a Z error metric that compares modeled and observed Z series, the three CMIP-3 model simulations tested here are shown to reproduce the PC1 mode but not the PC2 mode. By providing a way to compare grid-level IMD climate response patterns in observed and modeled data, this method can play a useful diagnostic role in future model development and decadal climate forecasting
The Effect of Zonally Asymmetric Ozone Heating on the Northern Hemisphere Winter Polar Stratosphere
[1] Previous modeling studies have found significant differences in winter extratropical stratospheric temperatures depending on the presence or absence of zonally asymmetric ozone heating (ZAOH), yet the physical mechanism causing these differences has not been fully explained. The present study describes the effect of ZAOH on the dynamics of the Northern Hemisphere extratropical stratosphere using an ensemble of free-running atmospheric general circulation model simulations over the 1 December - 31 March period. We find that the simulations including ZAOH produce a significantly warmer and weaker stratospheric polar vortex in mid-February due to more frequent major stratospheric sudden warmings compared to the simulations using only zonal mean ozone heating. This is due to regions of enhanced Eliassen-Palm flux convergence found in the region between 40°N–70°N latitude and 10–0.05 hPa. These results are consistent with changes in the propagation of planetary waves in the presence of ZAOH predicted by an ozone-modified refractive index
Effect of doping and oxygen vacancies on the octahedral tilt transitions in the BaCeO3 perovskite
We present a systematic study of the effect of Y doping and hydration level
on the structural transformations of BaCeO3 based on anelastic spectroscopy
experiments. The temperature of the intermediate transformation between
rhombohedral and orthorhombic Imma phases rises with increasing the molar
fraction x of Y roughly as (500 K)x in the hydrated state, and is depressed of
more than twice that amount after complete dehydration. This is explained in
terms of the effect of doping on the average (Ce/Y)-O and Ba-O bond lengths,
and of lattice relaxation from O vacancies. The different behavior of the
transition to the lower temperature Pnma orthorhombic phase is tentatively
explained in terms of progressive flattening of the effective shape of the OH
ion and ordering of the O vacancies during cooling.Comment: 8 pages, 5 figure
Comparing the Model-simulated Global Warming Signal to Observations Using Empirical Estimates of Unforced Noise
The comparison of observed global mean surface air temperature (GMT) change to the mean change simulated by climate models has received much public and scientific attention. For a given global warming signal produced by a climate model ensemble, there exists an envelope of GMT values representing the range of possible unforced states of the climate system (the Envelope of Unforced Noise; EUN). Typically, the EUN is derived from climate models themselves, but climate models might not accurately simulate the correct characteristics of unforced GMT variability. Here, we simulate a new, empirical, EUN that is based on instrumental and reconstructed surface temperature records. We compare the forced GMT signal produced by climate models to observations while noting the range of GMT values provided by the empirical EUN. We find that the empirical EUN is wide enough so that the interdecadal variability in the rate of global warming over the 20th century does not necessarily require corresponding variability in the rate-of-increase of the forced signal. The empirical EUN also indicates that the reduced GMT warming over the past decade or so is still consistent with a middle emission scenario’s forced signal, but is likely inconsistent with the steepest emission scenario’s forced signal
Intrinsic Spectral Geometry of the Kerr-Newman Event Horizon
We uniquely and explicitly reconstruct the instantaneous intrinsic metric of
the Kerr-Newman Event Horizon from the spectrum of its Laplacian. In the
process we find that the angular momentum parameter, radius, area; and in the
uncharged case, mass, can be written in terms of these eigenvalues. In the
uncharged case this immediately leads to the unique and explicit determination
of the Kerr metric in terms of the spectrum of the event horizon. Robinson's
``no hair" theorem now yields the corollary: One can ``hear the shape" of
noncharged stationary axially symmetric black hole space-times by listening to
the vibrational frequencies of its event horizon only.Comment: Final version with improved abstract, updated references, corrected
typos, and additional discussio
Probing ferroelectricity in highly conducting materials through their elastic response: persistence of ferroelectricity in metallic BaTiO3-d
The question whether ferroelectricity (FE) may coexist with a metallic or
highly conducting state, or rather it must be suppressed by the screening from
the free charges, is the focus of a rapidly increasing number of theoretical
studies and is finally receiving positive experimental responses. The issue is
closely related to the thermoelectric and multiferroic (also magnetic)
applications of FE materials, where the electrical conductivity is required or
spurious. In these circumstances, the traditional methods for probing
ferroelectricity are hampered or made totally ineffective by the free charges,
which screen the polar response to an external electric field. This fact may
explain why more than 40 years passed between the first proposals of FE metals
and the present experimental and theoretical activity. The measurement of the
elastic moduli, Young's modulus in the present case, versus temperature is an
effective method for studying the influence of doping on a FE transition
because the elastic properties are unaffected by electrical conductivity. In
this manner, it is shown that the FE transitions of BaTiO3-d are not suppressed
by electron doping through O vacancies; only the onset temperatures are
depressed, but the magnitudes of the softenings, and hence of the piezoelectric
activity, are initially even increased
Strichartz Estimates for the Vibrating Plate Equation
We study the dispersive properties of the linear vibrating plate (LVP)
equation. Splitting it into two Schr\"odinger-type equations we show its close
relation with the Schr\"odinger equation. Then, the homogeneous Sobolev spaces
appear to be the natural setting to show Strichartz-type estimates for the LVP
equation. By showing a Kato-Ponce inequality for homogeneous Sobolev spaces we
prove the well-posedness of the Cauchy problem for the LVP equation with
time-dependent potentials. Finally, we exhibit the sharpness of our results.
This is achieved by finding a suitable solution for the stationary homogeneous
vibrating plate equation.Comment: 18 pages, 4 figures, some misprints correcte
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