395 research outputs found
Inducing Transport in a Dissipation-Free Lattice with Super Bloch Oscillations
Particles in a perfect lattice potential perform Bloch oscillations when
subject to a constant force, leading to localization and preventing
conductivity. For a weakly-interacting Bose-Einstein condensate (BEC) of Cs
atoms, we observe giant center-of-mass oscillations in position space with a
displacement across hundreds of lattice sites when we add a periodic modulation
to the force near the Bloch frequency. We study the dependence of these "super"
Bloch oscillations on lattice depth, modulation amplitude, and modulation
frequency and show that they provide a means to induce linear transport in a
dissipation-free lattice. Surprisingly, we find that, for an interacting
quantum system, super Bloch oscillations strongly suppress the appearance of
dynamical instabilities and, for our parameters, increase the phase-coherence
time by more than a factor of hundred.Comment: 4 pages, 5 figure
Optical echo in photonic crystals
The dynamics of photonic wavepacket in the effective oscillator potential is
studied. The oscillator potential is constructed on a base of one dimensional
photonic crystal with a period of unit cell adiabatically varied in space. The
structure has a locally equidistant discrete spectrum. This leads to an echo
effect, i.e. the periodical reconstruction of the packet shape. The effect can
be observed in a nonlinear response of the system. Numerical estimations for
porous-silicon based structures are presented for femtosecond Ti:Sapphire laser
pump.Comment: 4 page
Direct observation of free excitons in luminescence spectra of xenon clusters
Luminescence of surface and free bulk excitons is detected in xenon for the
first time for substrate-free rare-gas clusters. Xenon clusters were produced
by the method of gas condensation in a supersonic jet emitted into vacuum.
Optical study was accompanied by electron diffraction measurements to determine
the structure of clusters.Comment: The more complete version of the paper is to be published in 'Low
Temperature Physics' (2007
Optical properties of structurally-relaxed Si/SiO superlattices: the role of bonding at interfaces
We have constructed microscopic, structurally-relaxed atomistic models of
Si/SiO superlattices. The structural distortion and oxidation-state
characteristics of the interface Si atoms are examined in detail. The role
played by the interface Si suboxides in raising the band gap and producing
dispersionless energy bands is established. The suboxide atoms are shown to
generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and
optical-absorption calculations at the Fermi Golden rule level are used to
demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue
shift in the spectrum, and (c) an enhancement of the absorption intensity in
the threshold-energy region. Some aspects of this behaviour appear not only in
the symmetry direction associated with the superlattice axis, but also in the
orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO
superlattices show clear optical enhancement and a shift of the optical
spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B
Role of chymase in cigarette smoke-induced pulmonary artery remodeling and pulmonary hypertension in hamsters
<p>Abstract</p> <p>Background</p> <p>Cigarette smoking is an important risk factor for pulmonary arterial hypertension (PAH) in chronic obstructive pulmonary disease (COPD). Chymase has been shown to function in the enzymatic production of angiotensin II (AngII) and the activation of transforming growth factor (TGF)-ÎČ1 in the cardiovascular system. The aim of this study was to determine the potential role of chymase in cigarette smoke-induced pulmonary artery remodeling and PAH.</p> <p>Methods</p> <p>Hamsters were exposed to cigarette smoke; after 4 months, lung morphology and tissue biochemical changes were examined using immunohistochemistry, Western blotting, radioimmunoassay and reverse-transcription polymerase chain reaction.</p> <p>Results</p> <p>Our results show that chronic cigarette smoke exposure significantly induced elevation of right ventricular systolic pressures (RVSP) and medial hypertrophy of pulmonary arterioles in hamsters, concurrent with an increase of chymase activity and synthesis in the lung. Elevated Ang II levels and enhanced TGF-ÎČ1/Smad signaling activation were also observed in smoke-exposed lungs. Chymase inhibition with chymostatin reduced the cigarette smoke-induced increase in chymase activity and Ang II concentration in the lung, and attenuated the RVSP elevation and the remodeling of pulmonary arterioles. Chymostatin did not affect angiotensin converting enzyme (ACE) activity in hamster lungs.</p> <p>Conclusions</p> <p>These results suggest that chronic cigarette smoke exposure can increase chymase activity and expression in hamster lungs. The capability of activated chymase to induce Ang II formation and TGF-ÎČ1 signaling may be part of the mechanism for smoking-induced pulmonary vascular remodeling. Thus, our study implies that blockade of chymase might provide benefits to PAH smokers.</p
Elevated creatine kinase activity in primary hepatocellular carcinoma
BACKGROUND: Inconsistent findings have been reported on the occurrence and relevance of creatine kinase (CK) isoenzymes in mammalian liver cells. Part of this confusion might be due to induction of CK expression during metabolic and energetic stress. METHODS: The specific activities and isoenzyme patterns of CK and adenylate kinase (AdK) were analysed in pathological liver tissue of patients undergoing orthotopic liver transplantation. RESULTS: The brain-type, cytosolic BB-CK isoenzyme was detected in all liver specimens analysed. Conversely, CK activity was strongly increased and a mitochondrial CK (Mi-CK) isoenzyme was detected only in tissue samples of two primary hepatocellular carcinomas (HCCs). CONCLUSION: The findings do not support significant expression of CK in normal liver and most liver pathologies. Instead, many of the previous misconceptions in this field can be explained by interference from AdK isoenzymes. Moreover, the data suggest a possible interplay between p53 mutations, HCC, CK expression, and the growth-inhibitory effects of cyclocreatine in HCC. These results, if confirmed, could provide important hints at improved therapies and cures for HCC
Effect of thermal treatment on the growth, structure and luminescence of nitride-passivated silicon nanoclusters
Silicon nanoclusters (Si-ncs) embedded in silicon nitride films have been studied to determine the effects that deposition and processing parameters have on their growth, luminescent properties, and electronic structure. Luminescence was observed from Si-ncs formed in silicon-rich silicon nitride films with a broad range of compositions and grown using three different types of chemical vapour deposition systems. Photoluminescence (PL) experiments revealed broad, tunable emissions with peaks ranging from the near-infrared across the full visible spectrum. The emission energy was highly dependent on the film composition and changed only slightly with annealing temperature and time, which primarily affected the emission intensity. The PL spectra from films annealed for duration of times ranging from 2 s to 2 h at 600 and 800°C indicated a fast initial formation and growth of nanoclusters in the first few seconds of annealing followed by a slow, but steady growth as annealing time was further increased. X-ray absorption near edge structure at the Si K- and L3,2-edges exhibited composition-dependent phase separation and structural re-ordering of the Si-ncs and silicon nitride host matrix under different post-deposition annealing conditions and generally supported the trends observed in the PL spectra
Atomic characterization of Si nanoclusters embedded in SiO2 by atom probe tomography
Silicon nanoclusters are of prime interest for new generation of optoelectronic and microelectronics components. Physical properties (light emission, carrier storage...) of systems using such nanoclusters are strongly dependent on nanostructural characteristics. These characteristics (size, composition, distribution, and interface nature) are until now obtained using conventional high-resolution analytic methods, such as high-resolution transmission electron microscopy, EFTEM, or EELS. In this article, a complementary technique, the atom probe tomography, was used for studying a multilayer (ML) system containing silicon clusters. Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques. A description of the different steps for such analysis: sample preparation, atom probe analysis, and data treatment are detailed. An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described. This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C
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