956 research outputs found
A coherent synchrotron X-ray microradiology investigation of bubble and droplet coalescence
Microradiology with coherent X-rays is shown to be very effective in revealing interfaces in multiphase systems and in particular gas bubbles. Its use has been tested in the study of bubble colescence validating the results with a simple theoretical analysis based on mass conservation
Synchrotron radiography and x-ray topography studies of hexagonal habitus SiC bulk crystals
Phase-sensitive synchrotron radiation (SR) radiography was combined with x-ray diffraction topography to study structural defects of SiC crystals. The particular bulk SiC crystals examined had a low micropipe density and a hexagonal habitus composed of prismatic, pyramidal, and basal faces well developed. X-ray diffraction topography images of the sliced (0001) wafers, which were formed due to the complex lattice distortions associated with defective boundaries, demonstrated the existence of two-dimensional defective boundaries in the radial direction, normal to the (0001) planes. In particular, those parallel to the 〈1120〉 directions extended rather far from the seed. On the other hand, by phase-sensitive SR radiography the effect of micropipe collection was detected. Micropipes grouped mostly in the vicinities of the defective boundaries but rarely appeared between groups. Some general remarks about possible reasons for the development of such peculiar defect structures were mad
Boundary Effects on Spectral Properties of Interacting Electrons in One Dimension
The single electron Green's function of the one-dimensional
Tomonaga-Luttinger model in the presence of open boundaries is calculated with
bosonization methods. We show that the critical exponents of the local spectral
density and of the momentum distribution change in the presence of a boundary.
The well understood universal bulk behavior always crosses over to a boundary
dominated regime for small energies or small momenta. We show this crossover
explicitly for the large-U Hubbard model in the low-temperature limit.
Consequences for photoemission experiments are discussed.Comment: revised and reformatted paper to appear in Phys. Rev. Lett. (Feb.
1996). 5 pages (revtex) and 3 embedded figures (macro included). A complete
postscript file is available from http://FY.CHALMERS.SE/~eggert/luttinger.ps
or by request from [email protected]
S and D Wave Mixing in High Superconductors
For a tight binding model with nearest neighbour attraction and a small
orthorhombic distortion, we find a phase diagram for the gap at zero
temperature which includes three distinct regions as a function of filling. In
the first, the gap is a mixture of mainly -wave with a smaller extended
-wave part. This is followed by a region in which there is a rapid increase
in the -wave part accompanied by a rapid increase in relative phase between
and from 0 to . Finally, there is a region of dominant with a
mixture of and zero phase. In the mixed region with a finite phase, the
-wave part of the gap can show a sudden increase with decreasing temperature
accompanied with a rapid increase in phase which shows many of the
characteristics measured in the angular resolved photoemission experiments of
Ma {\em et al.} in Comment: 12 pages, RevTeX 3.0, 3 PostScript figures uuencoded and compresse
Interpretation of Photoemission Spectra of (TaSe4)2I as Evidence of Charge Density Wave Fluctuations
The competition between different and unusual effects in
quasi-one-dimensional conductors makes the direct interpretation of
experimental measurements of these materials both difficult and interesting. We
consider evidence for the existence of large charge-density-wave fluctuations
in the conducting phase of the Peierls insulator (TaSe4)2I, by comparing the
predictions of a simple Lee, Rice and Anderson theory for such a system with
recent angle-resolved photoemission spectra. The agreement obtained suggests
that many of the unusual features of these spectra may be explained in this
way. This view of the system is contrasted with the behaviour expected of a
Luttinger liquid.Comment: Archive copy of published paper. 19 pages, 12 figures, uses IOP
macro
T145 Comprehensive flow cytometry tracking of regulatory T cells and other lymphocyte subsets during HD IL-2 therapy for melanoma
High dose IL-2 (HD IL-2) has been extensively used as an immunotherapy against metastatic melanoma However, why HD IL-2 is effective only in a subset of patients and whether predictive biomarkers, before or early during the course of therapy, can be used to improve response rates remain unresolved. In addition, it has been found that IL-2 therapy potently expands CD4+CD25+Foxp3+ T-regulatory cells (Tregs) but how Treg cell levels, phenotype, and function change and whether specific subsets of Tregs are activated and expanded during HD IL-2 therapy is remain unclear. In this study, we performed comprehensive multi-parameter FACS analysis of patient blood before and two days after the last bolus of IL-2 infusion during cycle 1 of HD IL-2 therapy. Two lymphocyte subsets were found to expand the most during the first cycle of IL-2 therapy: CD4+CD25+Foxp3+ Tregs expressing an activation marker, inducible costimulator (ICOS), and CD3-CD56hiCD16loPerforin+ NK cells. ICOS+ Tregs expressed significantly higher levels of CD25, Foxp3 and had a more activated phenotype than ICOS− Tregs as indicated by lower levels of CD45RA and CD127 expression. Further phenotypic characterization revealed a more suppressive phenotype on ICOS+ Treg with higher expression levels of CD39, CD73, and TGF-β/LAP than ICOS− Treg. ICOS+ Tregs were also the predominant Treg cells that secreted IL-10 and have potent T-cell suppressor function. Majority of ICOS+ Tregs from HD IL-2-treated patients were Ki67+ and exhibited an enhanced proliferative response to IL-2 ex vivo relative to ICOS− Tregs. Functional analysis revealed that ICOS+ Tregs secreted little IFN- and IL-2 in comparison to CD4+Foxp3 – cells. Furthermore, analysis on 38 IL-2-treated patients at MD Anderson, we found that non-responders had a significantly higher degree of ICOS+ Treg expansion than responders during the first cycle of IL-2 therapy, while no significant changes in the ICOS− or bulk Treg population. In conclusion, our data suggests that tracking changes in ICOS+ Tregs early during the course of HD IL-2 therapy may be a new predictive biomarker of clinical outcome
A GMSK VHF-uplink/UHF-downlink transceiver for the CubeSat missions: Thermo-functional performance
© 2018, CEAS. Functional and thermal performance characteristics of a very high frequency/ultra high frequency (VHF/UHF) transceiver based on Gaussian minimum shift keying (GMSK) modulation are presented. The transceiver has been designed for CubeSats telemetry and commanding needs or low rate data download. The design is validated at 27 dBm, 30 dBm and 33 dBm transmitting powers over −20 ∘C to +51 ∘C. Under these thermal conditions, the transmitter spurious dynamic response shows little if any change and the average sensitivity of receiver at the 12 dB signal noise and distortion (SINAD) is −116.7 dBm at 140 MHz and −116.78 dBm at 149.98 MHz. The transmitter and receiver frequencies are stable and the current consumption as well the output RF levels are steady. The design has been verified against a simulation model which allows system tradeoff analysis. The measurements demonstrate the transceiver made with commercial grade parts has dependable performance at the low earth altitudes and orbital heating conditions
Critical Properties of Spectral Functions for the 1D Anisotropic t-J Models with an Energy Gap
We exactly calculate the momentum-dependent critical exponents for spectral
functions in the one-dimensional anisotropic t-J models with a gap either in
the spin or charge excitation spectrum. Our approach is based on the Bethe
ansatz technique combined with finite-size scaling techniques in conformal
field theory. It is found that the spectral functions show a power-law
singularity, which occurs at frequencies determined by the dispersion of a
massive spin (or charge) excitation.We discuss how the nontrivial contribution
of a massive excitation controls the singular behavior in optical response
functions.Comment: 4 pages, REVTeX, 2 figures(available upon request), accepted for
publication in JPSJ 66 (1997) No.
No Far-Infrared-Spectroscopic Gap in Clean and Dirty High-T Superconductors
We report far infrared transmission measurements on single crystal samples
derived from BiSrCaCuO. The impurity scattering rate of
the samples was varied by electron-beam irradiation, 50MeV O ion
irradiation, heat treatment in vacuum, and Y doping. Although substantial
changes in the infrared spectra were produced, in no case was a feature
observed that could be associated with the superconducting energy gap. These
results all but rule out ``clean limit'' explanations for the absence of the
spectroscopic gap in this material, and provide evidence that the
superconductivity in BiSrCaCuO is gapless.Comment: 4 pages and 3 postscript figures attached. REVTEX v3.0. Accepted for
publication in Phys. Rev. Lett. IRDIRT
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