207 research outputs found
Madelung potentials and covalency effect in strained LaSrMnO thin films studied by core-level photoemission spectroscopy
We have investigated the shifts of the core-level photoemission spectra of
LaSrMnO thin films grown on three kinds of substrates,
SrTiO, (LaAlO)-(SrAlTaO), and
LaAlO. The experimental shifts of the La 4d and Sr 3d core levels are
almost the same as the calculation, which we attribute to the absence of
covalency effects on the Madelung potentials at these atomic sites due to the
nearly ionic character of these atoms. On the other hand, the experimental
shifts of the O and Mn core levels are negligibly small, in
disagreement with the calculation. We consider that this is due to the strong
covalent character of the Mn-O bonds.Comment: 4 pages, 5 figure
In-situ photoemission study of Pr_{1-x}Ca_xMnO_3 epitaxial thin films with suppressed charge fluctuations
We have performed an {\it in-situ} photoemission study of Pr_{1-x}Ca_xMnO_3
(PCMO) thin films grown on LaAlO_3 (001) substrates and observed the effect of
epitaxial strain on the electronic structure. We found that the chemical
potential shifted monotonically with doping, unlike bulk PCMO, implying the
disappearance of incommensurate charge fluctuations of bulk PCMO. In the
valence-band spectra, we found a doping-induced energy shift toward the Fermi
level (E_F) but there was no spectral weight transfer, which was observed in
bulk PCMO. The gap at E_F was clearly seen in the experimental band dispersions
determined by angle-resolved photoemission spectroscopy and could not be
explained by the metallic band structure of the C-type antiferromagnetic state,
probably due to localization of electrons along the ferromagnetic chain
direction or due to another type of spin-orbital ordering.Comment: 5 pages, 4 figure
Detection by NMR of a "local spin-gap" in quenched CsC60
We present a 13C and 133Cs NMR investigation of the CsC60 cubic quenched
phase. Previous ESR measurements suggest that this phase is metallic, but NMR
reveals contrasting electronic behavior on the local scale. The 13C
spin-lattice relaxation time (T1) exhibits a typical metallic behavior down to
50 K, but indicates that a partial spin-gap opens for T<50 K. Unexpectedly,
133Cs NMR shows that there are two inequivalent Cs sites. For one of these
sites, the NMR shift and (T1T)^{-1} follow an activated law, confirming the
existence of a spin-gap. We ascribe this spin-gap to the occurrence of
localized spin-singlets on a small fraction of the C60 molecules.Comment: 4 figure
Nonadiabatic Pauli susceptibility in fullerene compounds
Pauli paramagnetic susceptibility is unaffected by the electron-phonon
interaction in the Migdal-Eliashberg context. Fullerene compounds however do
not fulfill the adiabatic assumption of Migdal's theorem and nonadiabatic
effects are expected to be relevant in these materials. In this paper we
investigate the Pauli spin susceptibility in nonadiabatic regime by following a
conserving approach based on Ward's identity. We find that a sizable
renormalization of due to electron-phonon coupling appears when
nonadiabatic effects are taken into account. The intrinsic dependence of
on the electron-phonon interaction gives rise to a finite and negative isotope
effect which could be experimentally detected in fullerides. In addition, we
find an enhancement of the spin susceptibility with temperature increasing, in
agreement with the temperature dependence of observed in fullerene
compounds. The role of electronic correlation is also discussed.Comment: Revtex, 10 pages, 8 figures include
Effect of Secondary Echo Signals in Spin-Systems with a Large Inhomogeneous Broadening of NMR Line
The possibility of comparatively simple and fast determination of
characteristic relaxation parameters T1, T2 and T3 for nuclear spin-systems
with strong Larmor and Rabi inhomogeneous broadenings of NMR lines using the
secondary echo signal effect was experimentally shown. Resides, this method
gives opportunity to obtain a valuable infomation on the inhomogeneous NMR
broadening which reflects the character of magnetic field microscopic
destribution in such systems, as example, multidomain magnetics and
superconductors.Comment: 12 pages, 5 figure
Clinical significance of VEGF-A, -C and -D expression in esophageal malignancies
Vascular endothelial growth factors ( VEGF)- A, - C and - D are members of the proangiogenic VEGF family of glycoproteins. VEGF-A is known to be the most important angiogenic factor under physiological and pathological conditions, while VEGF-C and VEGF-D are implicated in the development and sprouting of lymphatic vessels, so called lymphangiogenesis. Local tumor progression, lymph node metastases and hematogenous tumor spread are important prognostic factors for esophageal carcinoma ( EC), one of the most lethal malignancies throughout the world. We found solid evidence in the literature that VEGF expression contributes to tumor angiogenesis, tumor progression and lymph node metastasis in esophageal squamous cell carcinoma ( SCC), and many authors could show a prognostic value for VEGF-assessment. In adenocarcinoma (AC) of the esophagus angiogenic properties are acquired in early stages, particularly in precancerous lesions like Barrett's dysplasia. However, VEGF expression fails to give prognostic information in AC of the esophagus. VEGF-C and VEGF-D were detected in SCC and dysplastic lesions, but not in normal mucosa of the esophagus. VEGF-C expression might be associated with lymphatic tumor invasion, lymph node metastases and advanced disease in esophageal SCC and AC. Therapeutic interference with VEGF signaling may prove to be a promising way of anti-angiogenic co-treatment in esophageal carcinoma. However, concrete clinical data are still pending
Perception of clear fricatives by normal-hearing and simulated hearing-impaired listeners
This is the publisher's version, also available electronically from http://scitation.aip.org/content/asa/journal/jasa/123/2/10.1121/1.2821966.Speakers may adapt the phonetic details of their productions when they anticipate perceptual difficulty or comprehension failure on the part of a listener. Previous research suggests that a speaking style known as clear speech is more intelligible overall than casual, conversational speech for a variety of listener populations. However, it is unknown whether clear speech improves the intelligibility of fricative consonants specifically, or how its effects on fricative perception might differ depending on listener population. The primary goal of this study was to determine whether clear speech enhances fricative intelligibility for normal-hearing listeners and listeners with simulated impairment. Two experiments measured babble signal-to-noise ratio thresholds for fricative minimal pair distinctions for 14 normal-hearing listeners and 14 listeners with simulated sloping, recruiting impairment. Results indicated that clear speech helped both groups overall. However, for impaired listeners, reliable clear speech intelligibility advantages were not found for non-sibilant pairs. Correlation analyses comparing acoustic and perceptual data indicated that a shift of energy concentration toward higher frequency regions and greater source strength contributed to the clear speecheffect for normal-hearing listeners. Correlations between acoustic and perceptual data were less consistent for listeners with simulated impairment, and suggested that lower-frequency information may play a role
Stearoyl-CoA Desaturase-1 (SCD1) Augments Saturated Fatty Acid-Induced Lipid Accumulation and Inhibits Apoptosis in Cardiac Myocytes
Mismatch between the uptake and utilization of long-chain fatty acids in the myocardium leads to abnormally high intracellular fatty acid concentration, which ultimately induces myocardial dysfunction. Stearoyl-Coenzyme A desaturase-1 (SCD1) is a rate-limiting enzyme that converts saturated fatty acids (SFAs) to monounsaturated fatty acids. Previous studies have shown that SCD1-deficinent mice are protected from insulin resistance and diet-induced obesity; however, the role of SCD1 in the heart remains to be determined. We examined the expression of SCD1 in obese rat hearts induced by a sucrose-rich diet for 3 months. We also examined the effect of SCD1 on myocardial energy metabolism and apoptotic cell death in neonatal rat cardiac myocytes in the presence of SFAs. Here we showed that the expression of SCD1 increases 3.6-fold without measurable change in the expression of lipogenic genes in the heart of rats fed a high-sucrose diet. Forced SCD1 expression augmented palmitic acid-induced lipid accumulation, but attenuated excess fatty acid oxidation and restored reduced glucose oxidation. Of importance, SCD1 substantially inhibited SFA-induced caspase 3 activation, ceramide synthesis, diacylglycerol synthesis, apoptotic cell death, and mitochondrial reactive oxygen species (ROS) generation. Experiments using SCD1 siRNA confirmed these observations. Furthermore, we showed that exposure of cardiac myocytes to glucose and insulin induced SCD1 expression. Our results indicate that SCD1 is highly regulated by a metabolic syndrome component in the heart, and such induction of SCD1 serves to alleviate SFA-induced adverse fatty acid catabolism, and eventually to prevent SFAs-induced apoptosis
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