2,124 research outputs found
Lefschetz thimble structure in one-dimensional lattice Thirring model at finite density
We investigate Lefschetz thimble structure of the complexified
path-integration in the one-dimensional lattice massive Thirring model with
finite chemical potential. The lattice model is formulated with staggered
fermions and a compact auxiliary vector boson (a link field), and the whole set
of the critical points (the complex saddle points) are sorted out, where each
critical point turns out to be in a one-to-one correspondence with a singular
point of the effective action (or a zero point of the fermion determinant). For
a subset of critical point solutions in the uniform-field subspace, we examine
the upward and downward cycles and the Stokes phenomenon with varying the
chemical potential, and we identify the intersection numbers to determine the
thimbles contributing to the path-integration of the partition function. We
show that the original integration path becomes equivalent to a single
Lefschetz thimble at small and large chemical potentials, while in the
crossover region multi thimbles must contribute to the path integration.
Finally, reducing the model to a uniform field space, we study the relative
importance of multiple thimble contributions and their behavior toward
continuum and low-temperature limits quantitatively, and see how the rapid
crossover behavior is recovered by adding the multi thimble contributions at
low temperatures. Those findings will be useful for performing Monte-Carlo
simulations on the Lefschetz thimbles.Comment: 32 pages, 14 figures (typo etc. corrected
Diffusion and activation of n-type dopants in germanium
The diffusion and activation of -type impurities (P and As) implanted into
-type Ge(100) substrates were examined under various dose and annealing
conditions. The secondary ion mass spectrometry profiles of chemical
concentrations indicated the existence of a sufficiently high number of
impurities with increasing implanted doses. However, spreading resistance probe
profiles of electrical concentrations showed electrical concentration
saturation in spite of increasing doses and indicated poor activation of As
relative to P in Ge. The relationships between the chemical and electrical
concentrations of P in Ge and Si were calculated, taking into account the
effect of incomplete ionization. The results indicated that the activation of P
was almost the same in Ge and Si. The activation ratios obtained experimentally
were similar to the calculated values, implying insufficient degeneration of
Ge. The profiles of P in Ge substrates with and without damage generated by Ge
ion implantation were compared, and it was clarified that the damage that may
compensate the activated -type dopants has no relationship with the
activation of P in Ge.Comment: 6 pages, 4 figure
Constant-time Bilateral Filter using Spectral Decomposition
This paper presents an efficient constant-time bilateral filter where constant-time means that computational complexity is independent of filter window size. Many state-of-the-art constant-time methods approximate the original bilateral filter by an appropriate combination of a series of convolutions. It is important for this framework to optimize the performance tradeoff between approximate accuracy and the number of convolutions. The proposed method achieves the optimal performance tradeoff in a least-squares manner by using spectral decomposition under the assumption that images consist of discrete intensities such as 8-bit images. This approach is essentially applicable to arbitrary range kernel. Experiments show that the proposed method outperforms state-of-the-art methods in terms of both computational complexity and approximate accuracy
Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar
We present the first spectrum of a highly veiled, strongly accreting
protostar which shows photospheric absorption features and demonstrates the
stellar nature of its central core. We find the spectrum of the luminous (L_bol
= 10 L_sun) protostellar source, YLW 15, to be stellar-like with numerous
atomic and molecular absorption features, indicative of a K5 IV/V spectral type
and a continuum veiling r_k = 3.0. Its derived stellar luminosity (3 L_sun) and
stellar radius (3.1 R_sun) are consistent with those of a 0.5 M_sun
pre-main-sequence star. However, 70% of its bolometric luminosity is due to
mass accretion, whose rate we estimate to be 1.6 E-6 M_sun / yr onto the
protostellar core. We determine that excess infrared emission produced by the
circumstellar accretion disk, the inner infalling envelope, and accretion
shocks at the surface of the stellar core of YLW 15 all contribute signifi-
cantly to its near-IR continuum veiling. Its projected rotation velocity v sin
i = 50 km / s is comparable to those of flat-spectrum protostars but
considerably higher than those of classical T Tauri stars in the rho Oph cloud.
The protostar may be magnetically coupled to its circumstellar disk at a radius
of 2 R_*. It is also plausible that this protostar can shed over half its
angular momentum and evolve into a more slowly rotating classical T Tauri star
by remaining coupled to its circumstellar disk (at increasing radius) as its
accretion rate drops by an order of magnitude during the rapid transition
between the Class I and Class II phases of evolution. The spectrum of WL 6 does
not show any photospheric absorption features, and we estimate that its
continuum veiling is r_k >= 4.6. Together with its low bolometric luminosity (2
L_sun), this dictates that its central core is very low mass, ~0.1 M_sun.Comment: 14 pages including 9 figures (3 figures of 3 panels each, all as
separate files). AASTeX LaTex macros version 5.0. To be published in The
Astronomical Journal (tentatively Oct 2002
General analysis of self-dual solutions for the Einstein-Maxwell-Chern-Simons theory in (1+2) dimensions
The solutions of the Einstein-Maxwell-Chern-Simons theory are studied in
(1+2) dimensions with the self-duality condition imposed on the Maxwell field.
We give a closed form of the general solution which is determined by a single
function having the physical meaning of the quasilocal angular momentum of the
solution. This function completely determines the geometry of spacetime, also
providing the direct computation of the conserved total mass and angular
momentum of the configurations.Comment: 3 pages, REVTEX file, no figure
Reassessing the Role of APOBEC3G in Human Immunodeficiency Virus Type 1 Infection of Quiescent CD4+ T-Cells
HIV-1 is restricted for infection of primary quiescent T-cells. After viral entry, reverse transcription is initiated but is not completed. Various hypotheses have been proposed for this cellular restriction including insufficient nucleotide pools and cellular factors, but none have been confirmed as the primary mechanism for restriction. A recent study by Chiu et al. implicates APOBEC3G, an anti-retroviral cytidine deaminase, as the cellular restriction factor. Here, we attempted to confirm these findings using the same strategy as reported by Chiu et al. of siRNA targeting knock-down of APOBEC3G expression. In contrast to the published study, our results do not support a role for APOBEC3G in restriction of HIV-1 in quiescent CD4+ T-cells. In our study, we tested the same siRNA as reported by Chiu et al. as well as two additional siRNAs targeting APOBEC3G, one of which showed 2-fold greater knock-down of APOBEC3G mRNA. However, none of the three siRNAs tested had a discernable effect on enhancing infection by HIV-1 in quiescent CD4+ T-cells. Therefore, we conclude that the primary mechanism of HIV-1 restriction in quiescent CD4+ T-cells remains to be elucidated
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