1,711 research outputs found
Synthesis and characterization of atomically-thin graphite films on a silicon carbide substrate
This paper reports the synthesis and detailed characterization of graphite
thin films produced by thermal decomposition of the (0001) face of a 6H-SiC
wafer, demonstrating the successful growth of single crystalline films down to
approximately one graphene layer. The growth and characterization were carried
out in ultrahigh vacuum (UHV) conditions. The growth process and sample quality
were monitored by low-energy electron diffraction, and the thickness of the
sample was determined by core level x-ray photoelectron spectroscopy.
High-resolution angle-resolved photoemission spectroscopy shows constant energy
map patterns, which are very sharp and fully momentum-resolved, but nonetheless
not resolution limited. We discuss the implications of this observation in
connection with scanning electron microscopy data, as well as with previous
studies
An InGaAlAs-InGaAs two-color photodetector for ratio thermometry
We report the evaluation of a molecular-beam epitaxy grown two-color photodetector for radiation thermometry. This two-color photodetector consists of two p+in+ diodes, an In0.53Ga0.25Al0.22As (hereafter InGaAlAs) p+in+ diode, which has a cutoff wavelength of 1180 nm, and an In0.53Ga0.47As (hereafter InGaAs) p+in+ diode with a cutoff wavelength of 1700 nm. Our simple monolithic integrated two-color photodetector achieved comparable output signal and signal-to-noise (SNR) ratio to that of a commercial two-color Si-InGaAs photodetector. The InGaAlAs and InGaAs diodes detect blackbody temperature as low as 275°C and 125°C, respectively, with an SNR above 10. The temperature errors extracted from our data are 4°C at 275°C for the InGaAlAs diode and 2.3°C at 125°C for the InGaAs diode. As a ratio thermometer, our two-color photodetector achieves a temperature error of 12.8°C at 275°C, but this improves with temperature to 0.1°C at 450°C. These results demonstrated the potential of InGaAlAs-InGaAs two-color photodetector for the development of high performance two-color array detectors for radiation thermometry and thermal imaging of hot objects
Ca2+ Sparks and Embers of Mammalian Muscle. Properties of the Sources
Ca2+ sparks of membrane-permeabilized rat muscle cells were analyzed to derive properties of their sources. Most events identified in longitudinal confocal line scans looked like sparks, but 23% (1,000 out of 4,300) were followed by long-lasting embers. Some were preceded by embers, and 48 were “lone embers.” Average spatial width was ∼2 μm in the rat and 1.5 μm in frog events in analogous solutions. Amplitudes were 33% smaller and rise times 50% greater in the rat. Differences were highly significant. The greater spatial width was not a consequence of greater open time of the rat source, and was greatest at the shortest rise times, suggesting a wider Ca2+ source. In the rat, but not the frog, spark width was greater in scans transversal to the fiber axis. These features suggested that rat spark sources were elongated transversally. Ca2+ release was calculated in averages of sparks with long embers. Release current during the averaged ember started at 3 or 7 pA (depending on assumptions), whereas in lone embers it was 0.7 or 1.3 pA, which suggests that embers that trail sparks start with five open channels. Analysis of a spark with leading ember yielded a current ratio ranging from 37 to 160 in spark and ember, as if 37–160 channels opened in the spark. In simulations, 25–60 pA of Ca2+ current exiting a point source was required to reproduce frog sparks. 130 pA, exiting a cylindric source of 3 μm, qualitatively reproduced rat sparks. In conclusion, sparks of rat muscle require a greater current than frog sparks, exiting a source elongated transversally to the fiber axis, constituted by 35–260 channels. Not infrequently, a few of those remain open and produce the trailing ember
Multi-resolution texture classification based on local image orientation
The aim of this paper is to evaluate quantitatively the discriminative power of the image orientation in the texture classification process. In this regard, we have evaluated the performance of two texture classification schemes where the image orientation is extracted using the partial derivatives of the Gaussian function. Since the texture descriptors are dependent on the observation scale, in this study the main emphasis is placed on the implementation of multi-resolution texture analysis schemes. The experimental results were obtained when the analysed texture descriptors were applied to standard texture databases
High-Gain InAs Planar Avalanche Photodiodes
We report the fabrication of InAs planar avalanche photodiodes (APDs) using Be ion implantation. The planar APDs have a low background doping of and large depletion widths approaching 8 μm. The thick depletion width enabled a gain of 330 to be achieved at −26 V at 200 K without inducing a significant tunneling current. No edge breakdown was observed within the APDs. The surface leakage current was found to be low with a gain normalized dark current density of 400 μAcm−2 at −20 V at 200 K
Proton strangeness form factors in (4,1) clustering configurations
We reexamine a recent result within a nonrelativistic constituent quark model
(NRCQM) which maintains that the uuds\bar s component in the proton has its
uuds subsystem in P state, with its \bar s in S state (configuration I). When
the result are corrected, contrary to the previous result, we find that all the
empirical signs of the form factors data can be described by the lowest-lying
uuds\bar s configuration with \bar s in P state that has its uuds subsystem in
state (configuration II). Further, it is also found that the removal of the
center-of-mass (CM) motion of the clusters will enhance the contributions of
the transition current considerably. We also show that a reasonable description
of the existing form factors data can be obtained with a very small probability
P_{s\bar s}=0.025% for the uuds\bar s component. We further see that the
agreement of our prediction with the data for G_A^s at low-q^2 region can be
markedly improved by a small admixture of configuration I. It is also found
that by not removing CM motion, P_{s\bar s} would be overestimated by about a
factor of four in the case when transition dominates over direct currents.
Then, we also study the consequence of a recent estimate reached from analyzing
the existing data on quark distributions that P_{s\bar s} lies between 2.4-2.9%
which would lead to a large size for the five-quark (5q) system, as well as a
small bump in both G^s_E+\eta G^s_M and G^s_E in the region of q^2 =< 0.1
GeV^2.Comment: Prepared for The Fifth Asia-Pacific Conference on Few-Body Problems
in Physics 2011 in Seoul, South Korea, 22-26 August 201
Mechanisms for Decays
Exclusive decays of into are investigated in
the framework of perturbative quantum chromodynamics(pQCD) and \tpz quark
pair creation model. The results show that these two mechanisms exhibit a quite
different behavior in evaluating the decay width for the and
. In pQCD method with nonrelativistic(NR) approximation, while the
calculated \cxpp{2} decay width is comparable with measured one, the result
for the \cxpp{0} decay width is suppressed and much smaller than experimental
value. However, in \tpz quark pair creation model, the situation is reversed:
the decay width of \cxpp{0} is greatly enhanced and can reproduce the large
measured value, while the contribution to the \cxpp{2} decay width is small.
The results suggest that while the pQCD mechanism is the dominant mechanism for
\cxpp{2} decay, the \tpz quark pair creation mechanism is the dominant one
for \cxpp{0} decay.Comment: 10 pages, 2 figure
Mass measurements of neutron-deficient Y, Zr, and Nb isotopes and their impact on rp and νp nucleosynthesis processes
© 2018 The Authors. Published by Elsevier B.V. This manuscript is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence (CC BY-NC-ND 4.0). For further details please see: https://creativecommons.org/licenses/by-nc-nd/4.0/Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of 82Zr and 84Nb were measured for the first time with an uncertainty of ∼10 keV, and the masses of 79Y, 81Zr, and 83Nb were re-determined with a higher precision. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low α separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr–Nb cycle in the rp-process unlikely. The new proton separation energy of 83Nb was determined to be 490(400) keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the p-nucleus 84Sr relative to the neutron-deficient molybdenum isotopes in the previous νp-process simulations.Peer reviewe
Transport properties of strongly correlated metals:a dynamical mean-field approach
The temperature dependence of the transport properties of the metallic phase
of a frustrated Hubbard model on the hypercubic lattice at half-filling are
calculated. Dynamical mean-field theory, which maps the Hubbard model onto a
single impurity Anderson model that is solved self-consistently, and becomes
exact in the limit of large dimensionality, is used. As the temperature
increases there is a smooth crossover from coherent Fermi liquid excitations at
low temperatures to incoherent excitations at high temperatures. This crossover
leads to a non-monotonic temperature dependence for the resistance,
thermopower, and Hall coefficient, unlike in conventional metals. The
resistance smoothly increases from a quadratic temperature dependence at low
temperatures to large values which can exceed the Mott-Ioffe-Regel value, hbar
a/e^2 (where "a" is a lattice constant) associated with mean-free paths less
than a lattice constant. Further signatures of the thermal destruction of
quasiparticle excitations are a peak in the thermopower and the absence of a
Drude peak in the optical conductivity. The results presented here are relevant
to a wide range of strongly correlated metals, including transition metal
oxides, strontium ruthenates, and organic metals.Comment: 19 pages, 9 eps figure
BESII Detector Simulation
A Monte Carlo program based on Geant3 has been developed for BESII detector
simulation. The organization of the program is outlined, and the digitization
procedure for simulating the response of various sub-detectors is described.
Comparisons with data show that the performance of the program is generally
satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM
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