291 research outputs found
Scalar cosmological perturbations in the Gauss-Bonnet braneworld
We study scalar cosmological perturbations in a braneworld model with a bulk
Gauss-Bonnet term. For an anti-de Sitter bulk, the five-dimensional
perturbation equations share the same form as in the Randall-Sundrum model,
which allows us to obtain metric perturbations in terms of a master variable.
We derive the boundary conditions for the master variable from the generalized
junction conditions on the brane. We then investigate several limiting cases in
which the junction equations are reduced to a feasible level. In the low energy
limit, we confirm that the standard result of four-dimensional Einstein gravity
is reproduced on large scales, whereas on small scales we find that the
perturbation dynamics is described by the four-dimensional Brans-Dicke theory.
In the high energy limit, all the non-local contributions drop off from the
junction equations, leaving a closed system of equations on the brane. We show
that, for inflation models driven by a scalar field on the brane, the
Sasaki-Mukhanov equation holds on the high energy brane in its original
four-dimensional form.Comment: 18 pages, v2: minor changes, reference added, v3: comments and
references added, accepted for publication in JCA
Self-accelerating solutions in the cascading DGP braneworld
The self-accelerating branch of the Dvali-Gabadadze-Porrati (DGP)
five-dimensional braneworld has provided a compelling model for the current
cosmic acceleration. Recent observations, however, have not favored it so much.
We discuss the solutions which contain a de Sitter 3-brane in the cascading DGP
braneworld model, which is a kind of higher-dimensional generalizations of the
DGP model,where a -dimensional brane is placed on a -dimensional one
and the -brane action contains the -dimensional induced scalar
curvature term. In the simplest six-dimensional model, we derive the solutions.
Our solutions can be classified into two branches, which reduce to the
self-accelerating and normal solutions in the limit of the original
five-dimensional DGP model. In the presence of the six-dimensional bulk
gravity, the `normal' branch provides a new self-accelerating solution. The
expansion rate of this new branch is generically lower than that of the
original one, which may alleviate the fine-tuning problem.Comment: 4 pages, critical change
Correlation between national surveillance and search engine query data on respiratory syncytial virus infections in Japan
Background The respiratory syncytial virus (RSV) disease burden is significant, especially in infants and children with an underlying disease. Prophylaxis with palivizumab is recommended for these high-risk groups. Early recognition of a RSV epidemic is important for timely administration of palivizumab. We herein aimed to assess the correlation between national surveillance and Google Trends data pertaining to RSV infections in Japan. Methods The present, retrospective survey was performed between January 1, 2018 and November 14, 2021 and evaluated the correlation between national surveillance data and Google Trends data. Joinpoint regression was used to identify the points at which changes in trends occurred. Results A strong correlation was observed every study year (2018 [r = 0.87, p < 0.01], 2019 [r = 0.83, p < 0.01], 2020 [r = 0.83, p < 0.01], and 2021 [r = 0.96, p < 0.01]). The change-points in the Google Trends data indicating the start of the RSV epidemic were observed earlier than by sentinel surveillance in 2018 and 2021 and simultaneously with sentinel surveillance in 2019. No epidemic surge was observed in either the Google Trends or the surveillance data from 2020. Conclusions Our data suggested that Google Trends has the potential to enable the early identification of RSV epidemics. In countries without a national surveillance system, Google Trends may serve as an alternative early warning system
Hierarchy of the Selberg zeta functions
We introduce a Selberg type zeta function of two variables which interpolates
several higher Selberg zeta functions. The analytic continuation, the
functional equation and the determinant expression of this function via the
Laplacian on a Riemann surface are obtained.Comment: 14 page
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
Diffusion-Based Speech Enhancement with Joint Generative and Predictive Decoders
Diffusion-based generative speech enhancement (SE) has recently received
attention, but reverse diffusion remains time-consuming. One solution is to
initialize the reverse diffusion process with enhanced features estimated by a
predictive SE system. However, the pipeline structure currently does not
consider for a combined use of generative and predictive decoders. The
predictive decoder allows us to use the further complementarity between
predictive and diffusion-based generative SE. In this paper, we propose a
unified system that use jointly generative and predictive decoders across two
levels. The encoder encodes both generative and predictive information at the
shared encoding level. At the decoded feature level, we fuse the two decoded
features by generative and predictive decoders. Specifically, the two SE
modules are fused in the initial and final diffusion steps: the initial fusion
initializes the diffusion process with the predictive SE to improve
convergence, and the final fusion combines the two complementary SE outputs to
enhance SE performance. Experiments conducted on the Voice-Bank dataset
demonstrate that incorporating predictive information leads to faster decoding
and higher PESQ scores compared with other score-based diffusion SE (StoRM and
SGMSE+)
Quantum fluctuations on a thick de Sitter brane
We investigate quantum fluctuations on a de Sitter (dS) brane, which has its
own thickness, in order to examine whether or not the finite thickness of the
brane can act as a natural cut-off for the Kaluza-Klein (KK) spectrum. We
calculate the amplitude of the KK modes and the bound state by using the zeta
function method after a dimensional reduction.We show that the KK amplitude is
finite for a given brane thickness and in the thin wall limit the standard
surface divergent behavior is recovered. The strength of the divergence in the
thin wall limit depends on the number of dimensions, e.g., logarithmic on a two
dimensional brane and quadratic on a four dimensional brane. We also find that
the amplitude of the bound state mode and KK modes depends on the choice of
renormalization scale; and for fixed renormalization scales the bound state
mode is insensitive to the brane thickness both for two and four-dimensional dS
branes.Comment: 23 pages, typos correcte
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