3,781 research outputs found
The influence of oscillations on energy estimates for damped wave models with time-dependent propagation speed and dissipation
The aim of this paper is to derive higher order energy estimates for
solutions to the Cauchy problem for damped wave models with time-dependent
propagation speed and dissipation. The model of interest is \begin{equation*}
u_{tt}-\lambda^2(t)\omega^2(t)\Delta u +\rho(t)\omega(t)u_t=0, \quad
u(0,x)=u_0(x), \,\, u_t(0,x)=u_1(x). \end{equation*} The coefficients
and are shape functions and
is an oscillating function. If and
is an "effective" dissipation term, then energy
estimates are proved in [2]. In contrast, the main goal of the present paper is
to generalize the previous results to coefficients including an oscillating
function in the time-dependent coefficients. We will explain how the interplay
between the shape functions and oscillating behavior of the coefficient will
influence energy estimates.Comment: 37 pages, 2 figure
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A shared cis-regulatory module activates transcription in the suspensor of plant embryos.
The mechanisms controlling the transcription of gene sets in specific regions of a plant embryo shortly after fertilization remain unknown. Previously, we showed that G564 mRNA, encoding a protein of unknown function, accumulates to high levels in the giant suspensor of both Scarlet Runner Bean (SRB) and Common Bean embryos, and a cis-regulatory module containing three unique DNA sequences, designated as the 10-bp, Region 2, and Fifth motifs, is required for G564 suspensor-specific transcription [Henry KF, et al. (2015) Plant Mol Biol 88:207-217; Kawashima T, et al. (2009) Proc Natl Acad Sci USA 106:3627-3632]. We tested the hypothesis that these motifs are also required for transcription of the SRB GA 20-oxidase gene, which encodes a gibberellic acid hormone biosynthesis enzyme and is coexpressed with G564 at a high level in giant bean suspensors. We used deletion and gain-of-function experiments in transgenic tobacco embryos to show that two GA 20-oxidase DNA regions are required for suspensor-specific transcription, one in the 5' UTR (+119 to +205) and another in the 5' upstream region (-341 to -316). Mutagenesis of sequences in these two regions determined that the cis-regulatory motifs required for G564 suspensor transcription are also required for GA 20-oxidase transcription within the suspensor, although the motif arrangement differs. Our results demonstrate the flexibility of motif positioning within a cis-regulatory module that activates gene transcription within giant bean suspensors and suggest that G564 and GA 20-oxidase comprise part of a suspensor gene regulatory network
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Learning stationary time series using Gaussian processes with nonparametric kernels
Direct measurements of DOCO isomers in the kinetics of OD+CO
Quantitative and mechanistically-detailed kinetics of the reaction of
hydroxyl radical (OH) with carbon monoxide (CO) have been a longstanding goal
of contemporary chemical kinetics. This fundamental prototype reaction plays an
important role in atmospheric and combustion chemistry, motivating studies for
accurate determination of the reaction rate coefficient and its pressure and
temperature dependence at thermal reaction conditions. This intricate
dependence can be traced directly to details of the underlying dynamics
(formation, isomerization, and dissociation) involving the reactive
intermediates cis- and trans-HOCO, which can only be observed transiently.
Using time-resolved frequency comb spectroscopy, comprehensive mechanistic
elucidation of the kinetics of the isotopic analogue deuteroxyl radical (OD)
with CO has been realized. By monitoring the concentrations of reactants,
intermediates, and products in real-time, the branching and isomerization
kinetics and absolute yields of all species in the OD+CO reaction are
quantified as a function of pressure and collision partner.Comment: 19 pages, 4 figure
Sound emission on bubble coalescence: imaging, acoustic and numerical experim
Laboratory and numerical experiments are presented on the emission of sound on bubble coalescence. The aim was to better understand the fluid-dynamical mechanisms leading to sound emission. Bubbles were formed from a needle. Coordinated high-speed video and acoustic measurements demonstrated that the emission of high-amplitude sound coincided with the coalescence of a primary bubble with a smaller secondary. A numerical simulation was performed using a compressible level-set front-capturing code, in which a compressible gas and nearly compressible liquid are modelled by a single set of the Navier-Stokes equations with a generic equation of state for both phases. In the simulations, the spherical primary and secondary bubbles initially at acoustic equilibrium were brought into contact. The numerical calculations predicted the frequency of emitted sound and the bubble coalescence dynamics very well. The results suggest that the equalization of Laplace pressures could be the mechanism leading to sound emission
Microstructure and mechanical behavior of ultrafine-grained Ni processed by different powder metallurgy methods
Ultrafine-grained samples were produced from a Ni nanopowder by hot isostatic pressing
(HIP) and spark plasma sintering (SPS). The microstructure and mechanical behavior of
the two specimens were compared. The grain coarsening observed during the SPS
procedure was moderated due to a reduced temperature and time of consolidation
compared with HIP processing. The smaller grain-size and higher nickel-oxide content in
the SPS-processed sample resulted in a higher yield strength. Compression experiments
showed that the specimen produced by SPS reached a maximal flow stress at a small
strain, which was followed by a long steady-state softening while the HIP-processed
sample hardened until failure. It was revealed that the softening of the SPS-processed
sample resulted from microcracking along the grain boundaries
A robust algorithm for detection and classification of traffic signs in video data
—The accurate identification and recognition of the traffic signs is a challenging problem as the developed systems have to address a large number of imaging problems such as motion artifacts, various weather conditions, shadows and partial occlusion, issues that are often encountered in video traffic sequences that are captured from a moving vehicle. These factors substantially degrade the performance of the existing traffic sign recognition (TSR) systems and in this paper we detail the implementation of a new strategy that entails three distinct computational stages. The first component addresses the robust identification of the candidate traffic signs in each frame of the video sequence. The second component discards the traffic sign candidates that do not comply with stringent shape constraints, and the last component implements the classification of the traffic signs using Support Vector Machines (SVMs). The main novel elements of our TSR algorithm are given by the approach that has been developed for traffic sign classification and by the experimental evaluation that was employed to identify the optimal image attributes that are able to maximize the traffic sign classification performance. The TSR algorithm has been validated using video sequences that include the most important categories of signs that are used to regulate the traffic on the Irish and UK roads, and it achieved 87.6% sign detection, 99.2% traffic sign classification accuracy and 86.7% overall traffic sign recognition
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