58,298 research outputs found
Epitaxial growth of Cu (001) on Si (001): Mechanisms of orientation development and defect morphology
We describe the evolution of microstructure during ultrahigh vacuum ion beam sputter deposition of Cu (001) at room temperature on hydrogen-terminated Si (001). In situ reflection high energy electron diffraction indicates growth of an epitaxial Cu (001) film on Si (001) with the intensity of the Bragg rods sharpening during 5–20 nm of Cu film growth. Post-growth x-ray diffraction indicates the Cu film has a mosaic spread of (001) textures of about ±2° and that a small fraction (0.001–0.01) is of (111) textures. High-resolution transmission electron microscopy shows an abrupt Cu/Si interface with no interfacial silicide, and reveals an evolution in texture with Cu thickness so as to reduce the mosaic spread about (001). Moiré contrast suggests a nearly periodic elastic strain field extending into the Cu and Si at the interface. Other aspects of film growth which are critical to epitaxy are also discussed
Planetary companions orbiting M giants HD 208527 and HD 220074
Aims. The purpose of the present study is to research the origin of planetary
companions by using a precise radial velocity (RV) survey.
Methods. The high-resolution spectroscopy of the fiber-fed Bohyunsan
Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy
Observatory (BOAO) is used from September 2008 to June 2012.
Results. We report the detection of two exoplanets in orbit around HD 208527
and HD 220074 exhibiting periodic variations in RV of 875.5 +/- 5.8 and 672.1
+/- 3.7 days. The RV variations are not apparently related to the surface
inhomogeneities and a Keplerian motion of the planetary companion is the most
likely explanation. Assuming possible stellar masses of 1.6 +/- 0.4 and 1.2 +/-
0.3 M_Sun, we obtain the minimum masses for the exoplanets of 9.9 +/- 1.7 and
11.1 +/- 1.8 M_Jup around HD 208527 and HD 220074 with an orbital semi-major
axis of 2.1 +/- 0.2 and 1.6 +/- 0.1 AU and an eccentricity of 0.08 and 0.14,
respectively. We also find that the previously known spectral classification of
HD 208527 and HD 220074 was in error: Our new estimation of stellar parameters
suggest that both HD 208527 and HD 220074 are M giants. Therefore, HD 208527
and HD 220074 are so far the first candidate M giants to harbor a planetary
companion.Comment: 7 pages, 9 figures, 4 tables, accepted for publisation in Astronomy &
Astrophysic
Non-renormalization of two and three Point Correlators of N=4 SYM in N=1 Superspace
Certain two and three point functions of gauge invariant primary operators of
SYM are computed in superspace keeping all the
-components. This allows one to read off many component descendent
correlators. Our results show the only possible corrections to the
free field correlators are contact terms. Therefore they vanish for operators
at separate points, verifying the known non-renormalization theorems. This also
implies the results are consistent with supersymmetry even though
the Lagrangian we use has only manifest supersymmetry. We repeat
some of the calculations using supersymmetric Landau gauge and obtain, as
expected, the same results as those of supersymmetric Feynman gauge.Comment: 10 pages, 20 eps figures, references adde
Electroexcitation of the Roper resonance in the relativistic quark models
The amplitudes of the transition gamma* N -> P11(1440) are calculated within
light-front relativistic quark model assuming that the P11(1440) is the first
radial excitation of the 3q ground state. The results are presented along with
the predictions obtained in other relativistic quark models. In comparison with
the previous calculations, we have extended the range of Q^2 up to 4.5 GeV^2 to
cover the kinematic interval of the forthcoming experimental data. Using
approach based on PCAC, we have checked the relative sign between quark model
predictions for the N and P11(1440) contributions to the pion electroproduction
found in previous investigations.Comment: 5 pages, 1 figure, accepted by PR
Construction of equilibrium networks with an energy function
We construct equilibrium networks by introducing an energy function depending
on the degree of each node as well as the product of neighboring degrees. With
this topological energy function, networks constitute a canonical ensemble,
which follows the Boltzmann distribution for given temperature. It is observed
that the system undergoes a topological phase transition from a random network
to a star or a fully-connected network as the temperature is lowered. Both
mean-field analysis and numerical simulations reveal strong first-order phase
transitions at temperatures which decrease logarithmically with the system
size. Quantitative discrepancies of the simulation results from the mean-field
prediction are discussed in view of the strong first-order nature.Comment: To appear in J. Phys.
Local spectroscopy of a proximity superconductor at very low temperature
We performed the local spectroscopy of a Normal-metal--Superconductor (N-S)
junction with the help of a very low temperature (60 mK) Scanning Tunneling
Microscope (STM). The spatial dependence of the local density of states was
probed locally in the vicinity of the N-S interface. We observed spectra with a
fully-developed gap in the regions where a thin normal metal layer caps the
superconductor dot. Close to the S metal edge, a clear pseudo-gap shows up,
which is characteristic of the superconducting proximity effect in the case of
a long normal metal. The experimental results are compared to the predictions
of the quasiclassical theory.Comment: 7 pages, 3 figure
Quantum information processing based on P-31 nuclear spin qubits in a quasi-one-dimensional Si-28 nanowire
We suggest a new method of quantum information processing based on the
precise placing of P-31 isotope atoms in a quasi-one-dimensional Si-28 nanowire
using isotope engineering and neutron-transmutation doping of the grown
structures. In our structure, interqubit entanglement is based on the indirect
interaction of P-31 nuclear spins with electrons localized in a nanowire. This
allows one to control the coupling between distant qubits and between qubits
separated by non-qubit neighboring nodes. The suggested method enables one to
fabricate structures using present-day nanolithography. Numerical estimates
show the feasibility of the proposed device and method of operation.Comment: 7 pages, 4 figure
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