1,545 research outputs found
Spin-orbit splitting of image states
We quantify the effect of the spin-orbit interaction on the Rydberg-like
series of image state electrons at the (111) and (001) surface of Ir, Pt and
Au. Using relativistic multiple-scattering methods we find Rashba-like
dispersions with Delta E(K)=gamma K with values of gamma for n=1 states in the
range 38-88 meV Angstrom. Extending the phase-accumulation model to include
spin-orbit scattering we find that the splittings vary like 1/(n+a)^3 where a
is the quantum defect and that they are related to the probability of spin-flip
scattering at the surface. The splittings should be observable experimentally
being larger in magnitude than some exchange-splittings that have been resolved
by inverse photoemission, and are comparable to linewidths from inelastic
lifetimes.Comment: 10 pages, 4 figure
Ecological drivers of global gradients in avian dispersal inferred from wing morphology
An organism’s ability to disperse influences many fundamental processes, from speciation and geographical range expansion to community assembly. However, the patterns and underlying drivers of variation in dispersal across species remain unclear, partly because standardised estimates of dispersal ability are rarely available. Here we present a global dataset of avian hand-wing index (HWI), an estimate of wing shape widely adopted as a proxy for dispersal ability in birds. We show that HWI is correlated with geography and ecology across 10,338 (>99%) species, increasing at higher latitudes and with migration, and decreasing with territoriality. After controlling for these effects, the strongest predictor of HWI is temperature variability (seasonality), with secondary effects of diet and habitat type. Finally, we also show that HWI is a strong predictor of geographical range size. Our analyses reveal a prominent latitudinal gradient in HWI shaped by a combination of environmental and behavioural factors, and also provide a global index of avian dispersal ability for use in community ecology, macroecology, and macroevolution
Asymptotic Pade Approximant Predictions: up to Five Loops in QCD and SQCD
We use Asymptotic Pade Approximants (APAP's) to predict the four- and
five-loop \beta-functions in QCD and N=1 supersymmetric QCD (SQCD), as well as
the quark mass anomalous dimensions in Abelian and non-Abelian gauge theories.
We show how the accuracy of our previous \beta-function predictions at the
four-loop level may be further improved by using estimators weighted over
negative numbers of flavours (WAPAP's). The accuracy of the improved four-loop
results encourages confidence in the new five-loop \beta-function predictions
that we present. However, the WAPAP approach does not provide improved results
for the anomalous mass dimension, or for Abelian theories.Comment: Title page revised with deep regret following the untimely death of
our friend and collaborator Mark Samuel; 25 pages, harvmac (b), including 3
figures; requires epsf.tex and tables.te
Geometric phases of mesoscopic spin in Bose-Einstein condensates
We propose a possible scheme for generating spin-J geometric phases using a
coupled two-mode Bose-Einstein condensate (BEC). First we show how to observe
the standard Berry phase using Raman coupling between two hyperfine states of
the BEC. We find that the presence of intrinsic interatomic collisions creates
degeneracy in energy that allows implementation of the non-Abelian geometric
phases as well. The evolutions produced can be used to produce interference
between different atomic species with high numbers of atoms or to fine control
the difference in atoms between the two species. Finally, we show that errors
in the standard Berry phase due to elastic collisions may be corrected by
controlling inelastic collisions between atoms.Comment: 6 pages, 2 figure
Culture change in elite sport performance teams: Examining and advancing effectiveness in the new era
Reflecting the importance of optimizing culture for elite teams, Fletcher and Arnold (2011) recently suggested the need for expertise in culture change. Acknowledging the dearth of literature on the specific process, however, the potential effectiveness of practitioners in this area is unknown. The present paper examines the activity's precise demands and the validity of understanding in sport psychology and organizational research to support its delivery. Recognizing that sport psychologists are being increasingly utilized by elite team management, initial evidence-based guidelines are presented. Finally, to stimulate the development of ecologically valid, practically meaningful knowledge, the paper identifies a number of future research directions
Noncyclic geometric phase for neutrino oscillation
We provide explicit formulae for the noncyclic geometric phases or
Pancharatnam phases of neutrino oscillations. Since Pancharatnam phase is a
generalization of the Berry phase, our results generalize the previous findings
for Berry phase in a recent paper [Phys. Lett. B, 466 (1999) 262]. Unlike the
Berry phase, the noncyclic geometric phase offers distinctive advantage in
terms of measurement and prediction. In particular, for three-flavor mixing,
our explicit formula offers an alternative means of determining the
CP-violating phase. Our results can also be extended easily to explore
geometric phase associated with neutron-antineutron oscillations
Coffee and tea consumption in the early adult lifespan and left ventricular function in middle age: the CARDIA study
AIMS: The long-term impact of coffee or tea consumption on subclinical left ventricular (LV) systolic or diastolic function has not been previously studied. We examined the association between coffee or tea consumption beginning in early adulthood and cardiac function in midlife.
METHODS AND RESULTS: We investigated 2735 Coronary Artery Risk Development in Young Adults (CARDIA) study participants with long-term total caffeine intake, coffee, and tea consumption data from three visits over a 20 year interval and available echocardiography indices at the CARDIA Year-25 exam (2010-2011). Linear regression models were used to assess the association between caffeine intake, tea, and coffee consumption (independent variables) and echocardiography outcomes [LV mass, left atrial volume, and global longitudinal strain (GLS), LV ejection fraction (LVEF), and transmitral Doppler early filling velocity to tissue Doppler early diastolic mitral annular velocity (E/e )]. Models were adjusted for standard cardiovascular risk factors, socioeconomic status, physical activity, alcohol use, and dietary factors (calorie intake, whole and refined grain intake, and fruit and vegetable consumption). Mean (standard deviation) age was 25.2 (3.5) years at the CARDIA Year-0 exam (1985-1986), 57.4% were women, and 41.9% were African-American. In adjusted multivariable linear regression models assessing the relationship between coffee consumption and GLS, beta coefficients when comparing coffee drinkers of \u3c 1, 1-2, 3-4, and \u3e 4 cups/day with non-coffee drinkers were beta = -0.30%, P \u3c 0.05; beta = -0.35%, P \u3c 0.05; beta = -0.32%, P \u3c 0.05; beta = -0.40%, P \u3e 0.05; respectively (more negative values implies better systolic function). In adjusted multivariable linear regression models assessing the relationship between coffee consumption and E/e , beta coefficients when comparing coffee drinkers of \u3c 1, 1-2, 3-4, and \u3e 4 cups/day with non-coffee drinkers were beta = -0.29, P \u3c 0.05; beta = -0.38, P \u3c 0.01; beta = -0.20, P \u3e .05; and beta = -0.37, P \u3e 0.05, respectively (more negative values implies better diastolic function). High daily coffee consumption ( \u3e 4 cups/day) was associated with worse LVEF (beta = -1.69, P \u3c 0.05). There were no associations between either tea drinking or total caffeine intake and cardiac function (P \u3e 0.05 for all).
CONCLUSIONS: Low-to-moderate daily coffee consumption from early adulthood to middle age was associated with better LV systolic and diastolic function in midlife. High daily coffee consumption ( \u3e 4cups/day) was associated with worse LV function. There was no association between caffeine or tea intake and cardiac function
Variational Quark Mass Expansion and the Order Parameters of Chiral Symmetry Breaking
We investigate in some detail a "variational mass" expansion approach,
generalized from a similar construction developed in the Gross-Neveu model, to
evaluate the basic order parameters of the dynamical breaking of the and chiral symmetries in QCD. The
method starts with a reorganization of the ordinary perturbation theory with
the addition of an arbitrary quark mass . The new perturbative series can be
summed to all orders thanks to renormalization group properties, with specific
boundary conditions, and advocated analytic continuation in properties. In
the approximation where the explicit breakdown of the chiral symmetries due to
small current quark masses is neglected, we derive ansatzes for the dynamical
contribution to the "constituent" masses of the quarks; the pion
decay constant ; and the quark condensate in terms of
the basic QCD scale . Those ansatzes are then optimized,
in a sense to be specified, and also explicit symmetry breaking mass terms can
be consistently introduced in the framework. The obtained values of and
are roughly in agreement with what is expected from other
non-perturbative methods. In contrast we obtain quite a small value of within our approach. The possible interpretation of the latter results
is briefly discussed.Comment: 40 pages, LaTex, 2 PS figures. Additions in section 2.2 to better
explain the relation between the current mass and the dynamical mass ansatz.
Minor misprints corrected. Version to appear in Phys. Rev.
First radial velocity results from the MINiature Exoplanet Radial Velocity Array (MINERVA)
The MINiature Exoplanet Radial Velocity Array (MINERVA) is a dedicated
observatory of four 0.7m robotic telescopes fiber-fed to a KiwiSpec
spectrograph. The MINERVA mission is to discover super-Earths in the habitable
zones of nearby stars. This can be accomplished with MINERVA's unique
combination of high precision and high cadence over long time periods. In this
work, we detail changes to the MINERVA facility that have occurred since our
previous paper. We then describe MINERVA's robotic control software, the
process by which we perform 1D spectral extraction, and our forward modeling
Doppler pipeline. In the process of improving our forward modeling procedure,
we found that our spectrograph's intrinsic instrumental profile is stable for
at least nine months. Because of that, we characterized our instrumental
profile with a time-independent, cubic spline function based on the profile in
the cross dispersion direction, with which we achieved a radial velocity
precision similar to using a conventional "sum-of-Gaussians" instrumental
profile: 1.8 m s over 1.5 months on the RV standard star HD 122064.
Therefore, we conclude that the instrumental profile need not be perfectly
accurate as long as it is stable. In addition, we observed 51 Peg and our
results are consistent with the literature, confirming our spectrograph and
Doppler pipeline are producing accurate and precise radial velocities.Comment: 22 pages, 9 figures, submitted to PASP, Peer-Reviewed and Accepte
Gluino mass from dynamical supersymmetry breaking
We present a new mechanism for gluino mass generation in models of dynamical
supersymmetry breaking. The mechanism requires two colored chiral superfields
which feel a nonabelian gauge interaction such that a fermion condensate is
formed at a scale of order 1 TeV. Renormalizable hidden sector models, which
typically yield unacceptably light gauginos, become viable if a gauge singlet
is coupled to these chiral superfields. Moreover, the interactions of the gauge
singlet with the Higgs superfields substitute the -term. Visible sector
models can also incorporate this mechanism; however, the models of dynamical
supersymmetry breaking previously analyzed cannot be fitted in a simple visible
sector model because they lead to vacuum expectation values for charged
scalars.Comment: 17 pages, latex. A statement regarding the discrete symmetry is
revised. Version accepted for publication in Phys.Rev.
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