22,020 research outputs found
Planet formation around stars of various masses: The snow line and the frequency of giant planets
We use a semi-analytic circumstellar disk model that considers movement of
the snow line through evolution of accretion and the central star to
investigate how gas giant frequency changes with stellar mass. The snow line
distance changes weakly with stellar mass; thus giant planets form over a wide
range of spectral types. The probability that a given star has at least one gas
giant increases linearly with stellar mass from 0.4 M_sun to 3 M_sun. Stars
more massive than 3 M_sun evolve quickly to the main-sequence, which pushes the
snow line to 10-15 AU before protoplanets form and limits the range of disk
masses that form giant planet cores. If the frequency of gas giants around
solar-mass stars is 6%, we predict occurrence rates of 1% for 0.4 M_sun stars
and 10% for 1.5 M_sun stars. This result is largely insensitive to our assumed
model parameters. Finally, the movement of the snow line as stars >2.5 M_sun
move to the main-sequence may allow the ocean planets suggested by Leger et.
al. to form without migration.Comment: Accepted to ApJ. 12 pages of emulateap
Drude Weight of the Two-Dimensional Hubbard Model -- Reexamination of Finite-Size Effect in Exact Diagonalization Study --
The Drude weight of the Hubbard model on the two-dimensional square lattice
is studied by the exact diagonalizations applied to clusters up to 20 sites. We
carefully examine finite-size effects by consideration of the appropriate
shapes of clusters and the appropriate boundary condition beyond the imitation
of employing only the simple periodic boundary condition. We successfully
capture the behavior of the Drude weight that is proportional to the squared
hole doping concentration. Our present result gives a consistent understanding
of the transition between the Mott insulator and doped metals. We also find, in
the frequency dependence of the optical conductivity, that the mid-gap
incoherent part emerges more quickly than the coherent part and rather
insensitive to the doping concentration in accordance with the scaling of the
Drude weight.Comment: 9 pages with 10 figures and 1 table. accepted in J. Phys. Soc. Jp
Decay of a coherent scalar disturbance in a turbulent flow
The time evolution of an initially coherent, sinusoidal passive-scalar disturbance is considered when the wavelength q is less than the length scale of the surrounding isotropic turbulent flow. In 64 sup 3 direct numerical simulations a Gaussian prescription for the average scalar amplitude breaks down after a timescale associated with the wavenumber of the disturbance and there is a transition to a new characteristic decay. The Gaussian prescription is given by exp(-(1/2) q-squared w(t)), where a form for w(t), the Lagrangian mean square displacement of a single fluid particle, is proposed. After the transition the decay is given by exp(-t/tau), where tau is the new characteristic timescale. If q k(sub K), then 1/tau = 1/tau(sub D) + 1/tau(sub K), where k(sub K) is the Kolmogorov wavenumber, tau(sub D) is the diffusive timescale and tau(sub K) is the Kolmogorov timescale. An experiment originally proposed by de Gennesis considered in which the evolution of a coherent laser-induced pattern is read by a diffracting laser. The theory of this experiment involves the dispersion of particle pairs, but it is shown that in a certain limit it reduces to the single Fourier-mode problem and can be described in terms of single particle diffusion. The decay of a single mode after the transition in the simulation best describes the experiment
Comments on differential cross section of phi-meson photoproduction at threshold
We show that the differential cross section d_sigma/d_t of gamma p --> \phi p
reaction at the threshold is finite and its value is crucial to the mechanism
of the phi meson photoproduction and for the models of phi-N interaction.Comment: 8 pages, 2 figure
Long-range and selective coupler for superconducting flux qubits
We propose a qubit-qubit coupling scheme for superconducting flux quantum
bits (qubits), where a quantized Josephson junction resonator and microwave
irradiation are utilized. The junction is used as a tunable inductance
controlled by changing the bias current flowing through the junction, and thus
the circuit works as a tunable resonator. This enables us to make any qubits
interact with the resonator. Entanglement between two of many qubits whose
level splittings satisfy some conditions, is formed by microwave irradiation
causing a two-photon Rabi oscillation. Since the size of the resonator can be
as large as sub-millimeters and qubits interact with it via mutual inductance,
our scheme makes it possible to construct a quantum gate involving remote
qubitsComment: 8 pages, 4 figure
Nontriviality of Gauge-Higgs-Yukawa System and Renormalizability of Gauged NJL Model
In the leading order of a modified 1/Nc expansion, we show that a class of
gauge-Higgs-Yukawa systems in four dimensions give non-trivial and well-defined
theories in the continuum limit. The renormalized Yukawa coupling y and the
quartic scalar coupling \lambda have to lie on a certain line in the
(y,\lambda) plane and the line terminates at an upper bound. The gauged
Nambu--Jona-Lasinio (NJL) model in the limit of its ultraviolet cutoff going to
infinity, is shown to become equivalent to the gauge-Higgs-Yukawa system with
the coupling constants just on that terminating point. This proves the
renormalizability of the gauged NJL model in four dimensions. The effective
potential for the gauged NJL model is calculated by using renormalization group
technique and confirmed to be consistent with the previous result by Kondo,
Tanabashi and Yamawaki obtained by the ladder Schwinger-Dyson equation.Comment: 32 pages, LaTeX, 3 Postscript Figures are included as uuencoded files
(need `epsf.tex'), KUNS-1278, HE(TH) 94/10 / NIIG-DP-94-2. (Several
corrections in the introduction and references.
Robust Object-Based Watermarking Using SURF Feature Matching and DFT Domain
In this paper we propose a robust object-based watermarking method, in which the watermark is embedded into the middle frequencies band of the Discrete Fourier Transform (DFT) magnitude of the selected object region, altogether with the Speeded Up Robust Feature (SURF) algorithm to allow the correct watermark detection, even if the watermarked image has been distorted. To recognize the selected object region after geometric distortions, during the embedding process the SURF features are estimated and stored in advance to be used during the detection process. In the detection stage, the SURF features of the distorted image are estimated and match them with the stored ones. From the matching result, SURF features are used to compute the Affine-transformation parameters and the object region is recovered. The quality of the watermarked image is measured using the Peak Signal to Noise Ratio (PSNR), Structural Similarity Index (SSIM) and the Visual Information Fidelity (VIF). The experimental results show the proposed method provides robustness against several geometric distortions, signal processing operations and combined distortions. The receiver operating characteristics (ROC) curves also show the desirable detection performance of the proposed method. The comparison with a previously reported methods based on different techniques is also provided
Critical magnetic field in AdS/CFT superconductor
We have studied a holographically dual description of superconductor in
(2+1)-dimensions in the presence of applied magnetic field, and observed that
there exists a critical value of magnetic field, below which a charged
condensate can form via a second order phase transition.Comment: 8 pages, 3 figures, REVTeX v4. Typos corrected and Fig.3 replace
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