5,380 research outputs found
On vanishing theorems for Higgs bundles
We introduce the notion of Hermitian Higgs bundle as a natural generalization
of the notion of Hermitian vector bundle and we study some vanishing theorems
concerning Hermitian Higgs bundles when the base manifold is a compact complex
manifold. We show that a first vanishing result, proved for these objects when
the base manifold was K\"ahler, also holds when the manifold is compact
complex. From this fact and some basic properties of Hermitian Higgs bundles,
we conclude several results. In particular we show that, in analogy to the
classical case, there are vanishing theorems for invariant sections of tensor
products of Higgs bundles. Then, we prove that a Higgs bundle admits no nonzero
invariant sections if there is a condition of negativity on the greatest
eigenvalue of the Hitchin-Simpson mean curvature. Finally, we prove that
invariant sections of certain tensor products of a weak Hermitian-Yang-Mills
Higgs bundle are all parallel in the classical sense.Comment: 10 Pages, some typos corrected and minor change
Age problem in holographic dark energy
We study the age problem of the universe with the holographic DE model
introduced in [21], and test the model with some known old high redshift
objects (OHRO). The parameters of the model have been constrained using the
SNIa, CMB and BAO data set. We found that the age of the old quasar APM 08
279+5255 at z = 3.91 can be described by the model.Comment: 13 page
Predictive validity of the CriSTAL tool for short-term mortality in older people presenting at Emergency Departments: a prospective study
© 2018, The Author(s). Abstract: To determine the validity of the Australian clinical prediction tool Criteria for Screening and Triaging to Appropriate aLternative care (CRISTAL) based on objective clinical criteria to accurately identify risk of death within 3 months of admission among older patients. Methods: Prospective study of ≥ 65 year-olds presenting at emergency departments in five Australian (Aus) and four Danish (DK) hospitals. Logistic regression analysis was used to model factors for death prediction; Sensitivity, specificity, area under the ROC curve and calibration with bootstrapping techniques were used to describe predictive accuracy. Results: 2493 patients, with median age 78–80 years (DK–Aus). The deceased had significantly higher mean CriSTAL with Australian mean of 8.1 (95% CI 7.7–8.6 vs. 5.8 95% CI 5.6–5.9) and Danish mean 7.1 (95% CI 6.6–7.5 vs. 5.5 95% CI 5.4–5.6). The model with Fried Frailty score was optimal for the Australian cohort but prediction with the Clinical Frailty Scale (CFS) was also good (AUROC 0.825 and 0.81, respectively). Values for the Danish cohort were AUROC 0.764 with Fried and 0.794 using CFS. The most significant independent predictors of short-term death in both cohorts were advanced malignancy, frailty, male gender and advanced age. CriSTAL’s accuracy was only modest for in-hospital death prediction in either setting. Conclusions: The modified CriSTAL tool (with CFS instead of Fried’s frailty instrument) has good discriminant power to improve prognostic certainty of short-term mortality for ED physicians in both health systems. This shows promise in enhancing clinician’s confidence in initiating earlier end-of-life discussions
Bivariate Nakagami-m distribution with arbitrary fading parameters
[EN] The bivariate Nakagami-m distribution with arbitrary fading
parameters is derived, obtaining the probability density function (PDF), the
cumulative density function (CDF) and the central moments. Additionally,
limitations of that distribution are discussed.Reig, J.; Rubio Arjona, L.; Cardona Marcet, N. (2002). Bivariate Nakagami-m distribution with arbitrary fading parameters. Electronics Letters. 38(25):1715-1717. doi:10.1049/el:20021124S171517173825Nakagami, M.: ‘Them-distribution—a general formula of intensity distribution of rapid fading’, Hoffman, W.G., Statistical methods in radio wave propagation, (Pergamon 1960)Abramowitz, M., and Stegun, I.A.: ‘Handbook of mathematical functions’, (Dover, New York 1972)Tan, C. C., & Beaulieu, N. C. (1997). Infinite series representations of the bivariate Rayleigh and Nakagami-m distributions. IEEE Transactions on Communications, 45(10), 1159-1161. doi:10.1109/26.63467
Dielectric screening in extended systems using the self-consistent Sternheimer equation and localized basis sets
We develop a first-principles computational method for investigating the
dielectric screening in extended systems using the self-consistent Sternheimer
equation and localized non-orthogonal basis sets. Our approach does not require
the explicit calculation of unoccupied electronic states, only uses two-center
integrals, and has a theoretical scaling of order O(N^3). We demonstrate this
method by comparing our calculations for silicon, germanium, diamond, and LiCl
with reference planewaves calculations. We show that accuracy comparable to
planewaves calculations can be achieved via a systematic optimization of the
basis set.Comment: 6 pages, 3 figure
Strain-Induced Conduction Band Spin Splitting in GaAs from First Principles Calculations
We use a recently developed self-consistent GW approximation to present first
principles calculations of the conduction band spin splitting in GaAs under
[110] strain. The spin orbit interaction is taken into account as a
perturbation to the scalar relativistic hamiltonian. These are the first
calculations of conduction band spin splitting under deformation based on a
quasiparticle approach; and because the self-consistent GW scheme accurately
reproduces the relevant band parameters, it is expected to be a reliable
predictor of spin splittings. We also discuss the spin relaxation time under
[110] strain and show that it exhibits an in-plane anisotropy, which can be
exploited to obtain the magnitude and sign of the conduction band spin
splitting experimentally.Comment: 8 pages, 4 figures, 1 tabl
Layer dependent band dispersion and correlations using tunable Soft X-ray ARPES
Soft X-ray Angle-Resolved Photoemission Spectroscopy is applied to study
in-plane band dispersions of Nickel as a function of probing depth. Photon
energies between 190 and 780 eV were used to effectively probe up to 3-7
layers. The results show layer dependent band dispersion of the Delta_2
minority-spin band which crosses the Fermi level in 3 or more layers, in
contrast to known top 1-2 layers dispersion obtained using ultra-violet rays.
The layer dependence corresponds to an increased value of exchange splitting
and suggests reduced correlation effects in the bulk compared to the surface.Comment: 7 pages, 3 figures Revised text and figur
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