1,159 research outputs found
Energy loss mechanism for suspended micro- and nanoresonators due to the Casimir force
A so far not considered energy loss mechanism in suspended micro- and
nanoresonators due to noncontact acoustical energy loss is investigated
theoretically. The mechanism consists on the conversion of the mechanical
energy from the vibratory motion of the resonator into acoustic waves on large
nearby structures, such as the substrate, due to the coupling between the
resonator and those structures resulting from the Casimir force acting over the
separation gaps. Analytical expressions for the resulting quality factor Q for
cantilever and bridge micro- and nanoresonators in close proximity to an
underlying substrate are derived and the relevance of the mechanism is
investigated, demonstrating its importance when nanometric gaps are involved
Simulations of Time-Resolved X-Ray Diffraction in Laue Geometry
A method of computer simulation of Time-Resolved X-ray Diffraction (TRXD) in
asymmetric Laue (transmission) geometry with an arbitrary propagating strain
perpendicular to the crystal surface is presented. We present two case studies
for possible strain generation by short-pulse laser irradiation: (i) a
thermoelastic-like analytic model; (ii) a numerical model including effects of
electron-hole diffusion, Auger recombination, deformation potential and thermal
diffusion. A comparison with recent experimental results is also presented.Comment: 9 pages, 11 figure
An Assessment of the Commission’s Proposal on Privacy and Electronic Communications:Study for the LIBE Committee
Correlation effects in a quantum dot at high magnetic fields
We investigate the effects of electron correlations on the ground state
energy and the chemical potential of a droplet confined by a parabolic
potential at high magnetic fields. We demonstrate the importance of
correlations in estimating the transition field at which the first edge
reconstruction of the maximum density droplet occurs in the spin polarized
regime.Comment: 11 pages (revtex) 3 postscript figures are included at the end of the
tex file. To appear in Phys. Rev.
Impulsive light-scattering by coherent phonons in LaAlO3: Disorder and boundary effects
Pump-probe measurements of coherent-phonon-induced changes of refractive index in LaAlO3 are dominated by normally weak boundary effects. Atomic displacements in the range 50–500 μÅ were generated and probed by femtosecond laser pulses through impulsive Raman scattering. The absence of a bulk contribution is ascribed to phase mismatch due to domain disorder. Selection rules are consistent with a Raman model considering reflection and transmission at interfaces. Intensities and phonon parameters as a function of temperature agree well with incoherent Raman data
Modal Rayleigh-like streaming in layered acoustofluidic devices
Classical Rayleigh streaming is well known and can be modelled using Nyborg’s limiting velocity method as driven by fluid velocities adjacent to the walls parallel to the axis of the main acoustic resonance. We have demonstrated previously the existence and the mechanism of four-quadrant transducer plane streaming patterns in thin-layered acoustofluidic devices which are driven by the limiting velocities on the walls perpendicular to the axis of the main acoustic propagation. We have recently found experimentally that there is a third case which resembles Rayleigh streaming but is a more complex pattern related to three-dimensional cavity modes of an enclosure. This streaming has vortex sizes related to the effective wavelength in each cavity axis of the modes which can be much larger than those found in the one-dimensional case with Rayleigh streaming. We will call this here modal Rayleigh-like streaming and show that it can be important in layered acoustofluidic manipulation devices. This paper seeks to establish the conditions under which each of these is dominant and shows how the limiting velocity field for each relates to different parts of the complex acoustic intensity patterns at the driving boundaries
Sound power emitted by a pure-tone source in a reverberation room
Energy considerations are of enormous practical importance in acoustics. In "energy acoustics," sources of noise are described in terms of the sound power they emit, the underlying assumption being that this property is independent of the particular environment where the sources are placed. However, it is well known that the sound power output of a source emitting a pure tone or a narrow band of noise actually varies significantly with its position in a reverberation room at low frequencies, and even larger variations occur between different rooms. The resulting substantial uncertainty in measurements of sound power as well as in predictions based on knowledge of sound power is one of the fundamental limitations of energy acoustics. The existing theory for this phenomenon is fairly complicated and has only been validated rather indirectly. This paper describes a far simpler theory and demonstrates that it gives predictions in excellent agreement with the established theory. The results are confirmed by experimental results as well as finite element calculations
Loss of starch synthase IIIa changes starch molecular structure and granule morphology in grains of hexaploid bread wheat.
Starch synthase III plays a key role in starch biosynthesis and is highly expressed in developing wheat grains. To understand the contribution of SSIII to starch and grain properties, we developed wheat ssIIIa mutants in the elite cultivar Cadenza using in silico TILLING in a mutagenized population. SSIIIa protein was undetectable by immunoblot analysis in triple ssIIIa mutants carrying mutations in each homoeologous copy of ssIIIa (A, B and D). Loss of SSIIIa in triple mutants led to significant changes in starch phenotype including smaller A-type granules and altered granule morphology. Starch chain-length distributions of double and triple mutants indicated greater levels of amylose than sibling controls (33.8% of starch in triple mutants, and 29.3% in double mutants vs. 25.5% in sibling controls) and fewer long amylopectin chains. Wholemeal flour of triple mutants had more resistant starch (6.0% vs. 2.9% in sibling controls) and greater levels of non-starch polysaccharides; the grains appeared shrunken and weighed ~ 11% less than the sibling control which was partially explained by loss in starch content. Interestingly, our study revealed gene dosage effects which could be useful for fine-tuning starch properties in wheat breeding applications while minimizing impact on grain weight and quality
Correlation effects in MgO and CaO: Cohesive energies and lattice constants
A recently proposed computational scheme based on local increments has been
applied to the calculation of correlation contributions to the cohesive energy
of the CaO crystal. Using ab-initio quantum chemical methods for evaluating
individual increments, we obtain 80% of the difference between the experimental
and Hartree-Fock cohesive energies. Lattice constants corrected for correlation
effects deviate by less than 1% from experimental values, in the case of MgO
and CaO.Comment: LaTeX, 4 figure
Roundoff-induced Coalescence of Chaotic Trajectories
Numerical experiments recently discussed in the literature show that
identical nonlinear chaotic systems linked by a common noise term (or signal)
may synchronize after a finite time. We study the process of synchronization as
function of precision of calculations. Two generic behaviors of the average
coalescence time are identified: exponential or linear. In both cases no
synchronization occurs if iterations are done with {\em infinite} precision.Comment: 6 pages, 3 postscript figures, to be published in Phys. Rev.
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