15,519 research outputs found
Mass transfer enhancement produced by laser induced cavitation
A microelectrode is used to measure the mass transfer perturbation and characteristics during the growth and subsequent collapse of a single bubble (which, following its initial expansion, achieved a maximum radius, Rm, of not, vert, similar500–1000 ?m). This mass transfer enhancement was associated with the forced convection, driven by bubble motion, as the result of a single cavitation event generated by a laser pulse beneath a 25 ?m diameter Au microelectrode. Evidence for bubble growth and rebound is gained from the electrochemical and acoustic measurements. This is supported with high-speed video footage of the events generated. A threshold for the formation of large cavitation bubbles in electrolyte solutions is suggested
Fundamental and harmonic emission in interplanetary type 2 radio bursts
Three interplanetary type II radio bursts which show two prominent and long duration bands in their dynamic spectra were analyzed in detail and compared to similar bands in meter wavelength type II events. These bands, which differ by a factor of about two in frequency, were interpreted in terms of fundamental and harmonic emission. The fundamental component has a greater average intensity than the harmonic, due largely to short intense brightenings. The fundamental spectral profile is more narrow than that of the harmonic, with harmonic band typically exhibiting a larger bandwidth to frequency ratio than the fundamental by a factor of two. The fundamental has a larger source size than the harmonic, 160 degrees versus 110 degrees, on average, as viewed from the Sun. Two of the events have source positions which correlate well with the associated flare positions
Ultrafast control of inelastic tunneling in a double semiconductor quantum
In a semiconductor-based double quantum well (QW) coupled to a degree of
freedom with an internal dynamics, we demonstrate that the electronic motion is
controllable within femtoseconds by applying appropriately shaped
electromagnetic pulses. In particular, we consider a pulse-driven AlxGa1-xAs
based symmetric double QW coupled to uniformly distributed or localized
vibrational modes and present analytical results for the lowest two levels.
These predictions are assessed and generalized by full-fledged numerical
simulations showing that localization and time-stabilization of the driven
electron dynamics is indeed possible under the conditions identified here, even
with a simultaneous excitations of vibrational modes.Comment: to be published in Appl.Phys.Let
Elasticity of Stiff Polymer Networks
We study the elasticity of a two-dimensional random network of rigid rods
(``Mikado model''). The essential features incorporated into the model are the
anisotropic elasticity of the rods and the random geometry of the network. We
show that there are three distinct scaling regimes, characterized by two
distinct length scales on the elastic backbone. In addition to a critical
rigidiy percolation region and a homogeneously elastic regime we find a novel
intermediate scaling regime, where elasticity is dominated by bending
deformations.Comment: 4 pages, 4 figure
Predictions of the causal entropic principle for environmental conditions of the universe
The causal entropic principle has been proposed as a superior alternative to
the anthropic principle for understanding the magnitude of the cosmological
constant. In this approach, the probability to create observers is assumed to
be proportional to the entropy production \Delta S in a maximal causally
connected region -- the causal diamond. We improve on the original treatment by
better quantifying the entropy production due to stars, using an analytic model
for the star formation history which accurately accounts for changes in
cosmological parameters. We calculate the dependence of \Delta S on the density
contrast Q=\delta\rho/\rho, and find that our universe is much closer to the
most probable value of Q than in the usual anthropic approach and that
probabilities are relatively weakly dependent on this amplitude. In addition,
we make first estimates of the dependence of \Delta S on the baryon fraction
and overall matter abundance. Finally, we also explore the possibility that
decays of dark matter, suggested by various observed gamma ray excesses, might
produce a comparable amount of entropy to stars.Comment: RevTeX4, 13pp, 10 figures; v2. clarified introduction, added ref
Nonlinear ptychographic coherent diffractive imaging
Ptychographic Coherent diffractive imaging (PCDI) is a significant advance in imaging allowing the measurement of the full electric field at a sample without use of any imaging optics. So far it has been confined solely to imaging of linear optical responses. In this paper we show that because of the coherence-preserving nature of nonlinear optical interactions, PCDI can be generalised to nonlinear optical imaging. We demonstrate second harmonic generation PCDI, directly revealing phase information about the nonlinear coefficients, and showing the general applicability of PCDI to nonlinear interactions
The use of happiness research for public policy
Research on happiness tends to follow a "benevolent dictator" approach where politicians pursue people's happiness. This paper takes an antithetic approach based on the insights of public choice theory. First, we inquire how the results of happiness research may be used to improve the choice of institutions. Second, we show that the policy approach matters for the choice of research questions and the kind of knowledge happiness research aims to provide. Third, we emphasize that there is no shortcut to an optimal policy maximizing some happiness indicator or social welfare function since governments have an incentive to manipulate this indicator
Development of Readout Interconnections for the Si-W Calorimeter of SiD
The SiD collaboration is developing a Si-W sampling electromagnetic
calorimeter, with anticipated application for the International Linear
Collider. Assembling the modules for such a detector will involve special
bonding technologies for the interconnections, especially for attaching a
silicon detector wafer to a flex cable readout bus. We review the interconnect
technologies involved, including oxidation removal processes, pad surface
preparation, solder ball selection and placement, and bond quality assurance.
Our results show that solder ball bonding is a promising technique for the Si-W
ECAL, and unresolved issues are being addressed.Comment: 8 pages + title, 6 figure
The Universal Kaehler Modulus in Warped Compactifications
We construct the effective theory of the universal Kaehler modulus in warped
compactifications using the Hamiltonian formulation of general relativity. The
spacetime dependent 10d solution is constructed at the linear level for both
the volume modulus and its axionic partner, and nontrivial cancellations of
warping effects are found in the dimensional reduction. Our main result is that
the Kaehler potential is not corrected by warping, up to an overall shift in
the background value of the volume modulus. We extend the analysis beyond the
linearized approximation by computing the fully backreacted 10d metric
corresponding to a finite volume modulus fluctuation. Also, we discuss the
behavior of the modulus in strongly warped regions and show that there are no
mixings with light Kaluza-Klein modes. These results are important for the
phenomenology and cosmology of flux compactifications.Comment: 28 pages, 1 figure; v2. corrected typos, added refs & minor
clarification
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