34,782 research outputs found
Measure Factors, Tension, and Correlations of Fluid Membranes
We study two geometrical factors needed for the correct construction of
statistical ensembles of surfaces. Such ensembles appear in the study of fluid
bilayer membranes, though our results are more generally applicable. The naive
functional measure over height fluctuations must be corrected by these factors
in order to give correct, self-consistent formulas for the free energy and
correlation functions of the height. While one of these corrections -- the
Faddeev-Popov determinant -- has been studied extensively, our derivation
proceeds from very simple geometrical ideas, which we hope removes some of its
mystery. The other factor is similar to the Liouville correction in string
theory. Since our formulas differ from those of previous authors, we include
some explicit calculations of the effective frame tension and two-point
function to show that our version indeed secures coordinate-invariance and
consistency to lowest nontrivial order in a temperature expansion.Comment: 24 pp; plain Te
Global testing against sparse alternatives in time-frequency analysis
In this paper, an over-sampled periodogram higher criticism (OPHC) test is
proposed for the global detection of sparse periodic effects in a
complex-valued time series. An explicit minimax detection boundary is
established between the rareness and weakness of the complex sinusoids hidden
in the series. The OPHC test is shown to be asymptotically powerful in the
detectable region. Numerical simulations illustrate and verify the
effectiveness of the proposed test. Furthermore, the periodogram over-sampled
by is proven universally optimal in global testing for
periodicities under a mild minimum separation condition.Comment: Published at http://dx.doi.org/10.1214/15-AOS1412 in the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Numerical Investigation on Flow Separation Control of Low Reynolds Number Sinusoidal Aerofoils
The paper presents a computational analysis of the characteristics of a NACA 634-
021 aerofoil incorporated with sinusoidal leading-edge protuberances at Re = 14,000.
The protuberances are characterized by an amplitude and wavelength of 12% and 50%
of the aerofoil chord length respectively. An unsteady Reynolds Average Navier Stokes
(RANS) analysis of the full-span aerofoils was carried out using Transition SST (Shear
Stress Transport) turbulence model across five different angles-of-attack (AOA).
Comparisons with previous experimental results reported good qualitative agreements
in terms of flow separation when the aerofoils are pitched at higher AOAs. Results
presented here comprised of near-wall flow visualizations of the flow separation bubble
at the peaks and troughs of the protuberances. Additionally, results indicate that the
aerofoil with leading-edge protuberances displayed distinctive wall shear streamline and
iso-contour characteristics at different span-wise positions. This implies that even at a
low Reynolds number, implementations of these leading-edge protuberances could have
positive or adverse effects on flow separation
Cyclic cosmology from Lagrange-multiplier modified gravity
We investigate cyclic and singularity-free evolutions in a universe governed
by Lagrange-multiplier modified gravity, either in scalar-field cosmology, as
well as in one. In the scalar case, cyclicity can be induced by a
suitably reconstructed simple potential, and the matter content of the universe
can be successfully incorporated. In the case of -gravity, cyclicity can
be induced by a suitable reconstructed second function of a very
simple form, however the matter evolution cannot be analytically handled.
Furthermore, we study the evolution of cosmological perturbations for the two
scenarios. For the scalar case the system possesses no wavelike modes due to a
dust-like sound speed, while for the case there exist an oscillation
mode of perturbations which indicates a dynamical degree of freedom. Both
scenarios allow for stable parameter spaces of cosmological perturbations
through the bouncing point.Comment: 8 pages, 3 figures, references added, accepted for publicatio
Optimization of Dimples in Microchannel Heat Sink with Impinging Jets—Part B: the Influences of Dimple Height and Arrangement
The combination of a microchannel heat sink with impinging jets and dimples (MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxes. Based on the previous work by analysing the effect of dimple radius on the overall performance of MHSIJD, the effects of dimple height and arrangement were numerically analysed. The velocity distribution, pressure drop, and thermal performance of MHSIJD under various dimple heights and arrangements were presented. The results showed that: MHSIJD with higher dimples had better overall performance with dimple radius being fixed; creating a mismatch between the impinging hole and dimple can solve the issue caused by the drift phenomenon; the mismatch between the impinging hole and dimple did not exhibit better overall performance than a well-matched design
Delay-Coordinates Embeddings as a Data Mining Tool for Denoising Speech Signals
In this paper we utilize techniques from the theory of non-linear dynamical
systems to define a notion of embedding threshold estimators. More specifically
we use delay-coordinates embeddings of sets of coefficients of the measured
signal (in some chosen frame) as a data mining tool to separate structures that
are likely to be generated by signals belonging to some predetermined data set.
We describe a particular variation of the embedding threshold estimator
implemented in a windowed Fourier frame, and we apply it to speech signals
heavily corrupted with the addition of several types of white noise. Our
experimental work seems to suggest that, after training on the data sets of
interest,these estimators perform well for a variety of white noise processes
and noise intensity levels. The method is compared, for the case of Gaussian
white noise, to a block thresholding estimator
Gap opening in the zeroth Landau level in gapped graphene: Pseudo-Zeeman splitting in an angular magnetic field
We present a theoretical study of gap opening in the zeroth Landau level in
gapped graphene as a result of pseudo-Zeeman interaction. The applied magnetic
field couples with the valley pseudospin degree of freedom of the charge
carriers leading to the pseudo-Zeeman interaction. To investigate its role in
transport at the Charge Neutrality Point (CNP), we study the integer quantum
Hall effect (QHE) in gapped graphene in an angular magnetic field in the
presence of pseudo-Zeeman interaction. Analytical expressions are derived for
the Hall conductivity using Kubo-Greenwood formula. We also determine the
longitudinal conductivity for elastic impurity scattering in the first Born
approximation. We show that pseudo-Zeeman splitting leads to a minimum in the
collisional conductivity at high magnetic fields and a zero plateau in the Hall
conductivity. Evidence for activated transport at CNP is found from the
temperature dependence of the collisional conductivity.Comment: 20 pages, 4 figures, Accepted in J. Phys. Condensed matte
A 2D systems approach to iterative learning control for discrete linear processes with zero Markov parameters
In this paper a new approach to iterative learning control for the practically relevant case of deterministic discrete linear plants with uniform rank greater than unity is developed. The analysis is undertaken in a 2D systems setting that, by using a strong form of stability for linear repetitive processes, allows simultaneous con-sideration of both trial-to-trial error convergence and along the trial performance, resulting in design algorithms that can be computed using Linear Matrix Inequalities (LMIs). Finally, the control laws are experimentally verified on a gantry robot that replicates a pick and place operation commonly found in a number of applications to which iterative learning control is applicable
Bounce and cyclic cosmology in extended nonlinear massive gravity
We investigate non-singular bounce and cyclic cosmological evolutions in a
universe governed by the extended nonlinear massive gravity, in which the
graviton mass is promoted to a scalar-field potential. The extra freedom of the
theory can lead to certain energy conditions violations and drive cyclicity
with two different mechanisms: either with a suitably chosen scalar-field
potential under a given Stuckelberg-scalar function, or with a suitably chosen
Stuckelberg-scalar function under a given scalar-field potential. Our analysis
shows that extended nonlinear massive gravity can alter significantly the
evolution of the universe at both early and late times.Comment: 20 pages, 5 figures, version published at JCA
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