1,792 research outputs found
High-Temperature Transport Properties of Yb4−xSmxSb3
Polycrystalline L4Sb3 (L = La, Ce, Sm, and Yb) and Yb4−x Sm x Sb3, which crystallizes in the anti-Th3P4 structure type (I-43d no. 220), were synthesized via high-temperature reaction. Structural and chemical characterization were performed by x-ray diffraction and electronic microscopy with energy-dispersive x-ray analysis. Pucks were densified by spark plasma sintering. Transport property measurements showed that these compounds are n-type with low Seebeck coefficients, except for Yb4Sb3, which shows semimetallic behavior with hole conduction above 523 K. By partially substituting Yb by a trivalent rare earth we successfully improved the thermoelectric figure of merit of Yb4Sb3 up to 0.7 at 1273 K
Photonic analog of graphene model and its extension -- Dirac cone, symmetry, and edge states --
This paper presents a theoretical analysis on bulk and edge states in
honeycomb lattice photonic crystals with and without time-reversal and/or
space-inversion symmetries. Multiple Dirac cones are found in the photonic band
structure and the mass gaps are controllable via symmetry breaking. The zigzag
and armchair edges of the photonic crystals can support novel edge states that
reflect the symmetries of the photonic crystals. The dispersion relation and
the field configuration of the edge states are analyzed in detail in comparison
to electronic edge states. Leakage of the edge states to free space is inherent
in photonic systems and is fully taken into account in the analysis. A
topological relation between bulk and edge, which is analogous to that found in
quantum Hall systems, is also verified.Comment: 9 pages, 7 figure
Symmetry characterization of eigenstates in opal-based photonic crystals
The complete symmetry characterization of eigenstates in bare opal systems is
obtained by means of group theory. This symmetry assignment has allowed us to
identify several bands that cannot couple with an incident external plane wave.
Our prediction is supported by layer-KKR calculations, which are also
performed: the coupling coefficients between bulk modes and externally excited
field tend to zero when symmetry properties mismatch.Comment: 7 pages, 5 figures, submitted to Physical Review
Reentrant charge order transition in the extended Hubbard model
We study the extended Hubbard model with both on-site and nearest neighbor
Coulomb repulsion ( and , respectively) in the Dynamical Mean Field
theory. At quarter filling, the model shows a transition to a charge ordered
phase with different sublattice occupancies n_A \nen_B. The effective mass
increases drastically at the critical and a pseudo-gap opens in the
single-particle spectral function for higher values of . The -curve
has a negative slope for small temperatures, i.e. the charge ordering
transition can be driven by increasing the temperature. This is due to the
higher spin-entropy of the charge ordered phase.Comment: 4 pages, 4 EPS figures included, REVTe
Reentrant charge ordering caused by polaron formation
Based on a two-dimensional extended Hubbard model with electron-phonon
interaction, we have studied the effect of polaron formation on the charge
ordering (CO) transition. It is found that for fully ferromagnetically ordered
spins the CO state may go through a process of appearance, collapse and
reappearance with decreasing temperature. This is entirely due to a
emperature-dependent polaron bandwidth. On the other hand, when a paramagnetic
spin state is considered, only a simple reentrant behavior of the CO transition
is found, which is only partly due to polaron effect. This model is proposed as
an explanation of the observed reentrant behavior of the CO transition in the
layered manganite LaSrMnO.Comment: 4 pages, 2 eps figures, revised version accepted by Phys. Rev. Let
Short-term hemodynamic effects of nebivolol in acute decompensated heart failure: a randomized clinical trial
Modular symbols in Iwasawa theory
This survey paper is focused on a connection between the geometry of
and the arithmetic of over global fields,
for integers . For over , there is an explicit
conjecture of the third author relating the geometry of modular curves and the
arithmetic of cyclotomic fields, and it is proven in many instances by the work
of the first two authors. The paper is divided into three parts: in the first,
we explain the conjecture of the third author and the main result of the first
two authors on it. In the second, we explain an analogous conjecture and result
for over . In the third, we pose questions for general
over the rationals, imaginary quadratic fields, and global function fields.Comment: 43 page
Delirium in Hospitalized Elderly Patients and Post-Discharge Mortality
OBJECTIVE: To determine the impact of delirium on post-discharge mortality in hospitalized older patients. INTRODUCTION: Delirium is frequent in hospitalized older patients and correlates with high hospital mortality. There are only a few studies about its impact on post-discharge mortality. METHODS: This is a prospective study of patients over 60 years old who were hospitalized in the Geriatric Unit at Hospital das ClÃnicas of São Paulo between May 2006 and March 2007. Upon admission, demographics, comorbidities, number of drugs taken, and serum albumin concentration were evaluated for each patient. Delirium was diagnosed according to the DSM-IV criteria. Patients were divided into group A (with delirium) and group B (without delirium). One year after discharge, the patients or their caregivers were contacted to assess days of survival. RESULTS: The sample included 199 patients, 66 (33%) of whom developed delirium (Group A). After one year, 33 (50%) group A patients had died, and 45 (33.8%) group B patients had died (p = 0.03). There was a significant statistical difference in average age (p = 0.001) and immobility (p <0.001) between groups A and B. There were no statistically significant differences between groups A and B in number of drugs taken greater than four (p = 0.62), sex (p = 0.54) and number of diagnoses greater than four (p = 0.21). According to a multivariate analysis, delirium was not an independent predictor of post-discharge mortality. The predictors of post-discharge mortality were age > 80 years (p = 0.029), albumin concentration < 3.5 g/dl (p = 0.001) and immobility (p = 0.007). CONCLUSION: Delirium is associated with higher post-discharge mortality as a dependent predictor
Semiclassical instability of the brane-world: Randall-Sundrum bubbles
We discuss the semiclassical instability of the Randall-Sundrum brane-world
model against a creation of a kind of Kaluza-Klein bubble. An example
describing such a bubble space-time is constructed from the five-dimensional
AdS-Schwarzschild metric. The induced geometry of the brane looks like the
Einstein-Rosen bridge, which connects the positive and the negative tension
branes. The bubble rapidly expands and there also form a trapped region around
it.Comment: 4 pages, 3 figures, two references adde
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