Bubble oscillations and motion under vibration. (arXiv:1110.2777v1 [physics.flu-dyn])

Bubbles under vibration can behave in unusual ways, e.g., moving downward
against the force of buoyancy. While the bubble downward motion due to the
Bjerknes force is well known at acoustic frequencies close to the bubble
resonant frequency, these experiments demonstrate that these effects can be
observed at relatively low frequencies as well. Experiments were performed in a
thin, quasi-two-dimensional rectangular acrylic box partially filled with
20-cSt PDMS silicone oil with overlying ambient air. The apparatus was
subjected to sinusoidal axial vibration that produced breakup of the gas-liquid
free surface, producing liquid jets into the air, droplets pinching off from
these jets, gas cavities in the liquid from impacts of these droplets, and
bubble transport below the interface. Vibration conditions for the attached
videos are 280 Hz frequency, 15 g acceleration, and 94 micron peak-to-peak
displacement. Behaviors shown in the videos include the following. 1. Free
surface breakup into jets and droplets, and formation of bubbles under the free
surface. 2. Bubbles thus generated moving downward in the cell. 3. Bubbles
attracted to the first bubble deep in the cell and eventually merging to form a
large bubble at the base of the cell. 4. Bubble cluster at the base of the cell
merging to form a larger bubble, which stabilizes at a levitated location below
the free surface and acts to damp out the surface breakup. 5. The levitated
bubble interface and its breakup are similar to the free surface breakup into
jets and droplets, but the jets in the bubble are facing downward. Sandia
National Laboratories is a multi-program laboratory managed and operated by
Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation,
for the U.S. Department of Energy’s National Nuclear Security Administration
under contract DE-AC04-94AL85000.

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Resonant multi-photon IR dissociation spectroscopy of a trapped and sympathetically cooled biomolecular ion species. (arXiv:1110.2774v1 [physics.chem-ph])

In this work we demonstrate vibrational spectroscopy of polyatomic ions that
are trapped and sympathetically cooled by laser-cooled atomic ions. We use the
protonated dipeptide tryptophane-alanine (HTyrAla+) as a model system, cooled
by Barium ions to less than 800mK secular temperature. The spectroscopy is
performed on the fundamental vibrational transition of a local vibrational mode
at 2.74 {\mu}m using a continuous-wave optical parametric oscillator (OPO).
Resonant multi-photon IR dissociation spectroscopy (without the use of a UV
laser) generates charged molecular fragments, which are sympathetically cooled
and trapped, and subsequently released from the trap and counted. We measured
the cross section for R-IRMPD under conditions of low intensity, and found it
to be approximately two orders smaller than the vibrational excitation cross
section. The observed rotational bandwidth of the vibrational transition is
larger than the one expected from the combined effects of 300 K black-body
temperature, conformer-dependent line shifts, and intermolecular vibrational
relaxation broadening (J. Stearns et al., J. Chem. Phys., 127, 154322-7
(2007)). This indicates that as the internal energy of the molecule grows, an
increase of the rotational temperature of the molecular ions well above room
temperature (up to on the order of 1000K), and/or an appreciable shift of the
vibrational transition frequency (approx. 6-8 cm$ ^{-1}$ ) occurs.

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An effect of abrupt current disruption. (arXiv:1110.0483v1 [physics.plasm-ph])

Every engine, let it internal combustion engine in car or turbine of
airplane, needs a high quality fuel igniter. During last decades there have
been some minor changes made in ignition systems, like invention of Capacitive
Discharge Ignition, Multiple Discharge Ignition, Ignition with Direct Current
Discharge, but all based on the same priciple of High Voltage spark path
creation. This work contains description, schematics and photographs of a new
spark creation approach, providing high robustness through high power, big
volume, long duration plasma. The system uses less or the same amount of energy
as would CDI ignition, jet providing many times more efficient energy output.
The solution is a highly applicable innovation, being able to significantly
improve spark robustnes in all current HV spark ignition systems. Despite a
simplicity of setup, it is still unclear why the effect persists, thus calling
for additional research input.

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Thin films flowing down inverted substrates: Three dimensional flow. (arXiv:1109.6353v1 [physics.flu-dyn])

We study contact line induced instabilities for a thin film of fluid under
destabilizing gravitational force in three dimensional setting. In the previous
work (Phys. Fluids, {\bf 22}, 052105 (2010)), we considered two dimensional
flow, finding formation of surface waves whose properties within the
implemented long wave model depend on a single parameter,
$ D=(3Ca)^{1/3}\cot\alpha$ , where $ Ca$ is the capillary number and $ \alpha$ is
the inclination angle. In the present work we consider fully 3D setting and
discuss the influence of the additional dimension on stability properties of
the flow. In particular, we concentrate on the coupling between the surface
instability and the transverse (fingering) instabilities of the film front. We
furthermore consider these instabilities in the setting where fluid viscosity
varies in the transverse direction. It is found that the flow pattern strongly
depends on the inclination angle and the viscosity gradient.

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Incremental Versus Optimized Network Design. (arXiv:1109.6347v1 [cs.NI])

Even though the problem of network topology design is often studied as a
“clean-slate” optimization, in practice most service-provider and enterprise
networks are designed incrementally over time. This evolutionary process is
driven by changes in the underlying parameters and constraints (the
“environment”) and it aims to minimize the modification cost after each change
in the environment. In this paper, we first formulate the incremental design
approach (in three variations), and compare that with the more traditional
optimized design approach in which the objective is to minimize the total
network cost. We evaluate the cost overhead and evolvability of incremental
design under two network expansion models (random and gradual), comparing
incremental and optimized networks in terms of cost, topological similarity,
delay and robustness. We find that even though incremental design has some cost
overhead, that overhead does not increase as the network grows. Also, it is
less costly to evolve an existing network than to design it “from scratch” as
long as the network expansion factor is less than a critical value.

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Masses of Fundamental Particles. (arXiv:1109.3705v1 [physics.gen-ph])

Not only the masses of fundamental particles including the weak bosons, Higgs
scalar, quarks, and leptons, but also the mixing angles of quarks and those of
neutrinos are all explained and/or predicted in the unified composite model of
quarks and leptons successfully. In addition, both of the two anomalies
recently found by the CDF Collaboration are suggested to be taken as evidences
for the substructure of the fundamental particles.

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Improving Correlation Function Fitting with Ridge Regression: Application to Cross-Correlation Reconstruction. (arXiv:1109.2121v1 [astro-ph.IM])

Cross-correlation techniques provide a promising avenue for calibrating
photometric redshifts and determining redshift distributions using spectroscopy
which is systematically incomplete (e.g., current deep spectroscopic surveys
fail to obtain secure redshifts for 30-50% or more of the galaxies targeted).
In this paper we improve on the redshift distribution reconstruction methods
presented in Matthews & Newman (2010) by incorporating full covariance
information into our correlation function fits. Correlation function
measurements are strongly covariant between angular or spatial bins, and
accounting for this in fitting can yield substantial reduction in errors.
However, frequently the covariance matrices used in these calculations are
determined from a relatively small set (dozens rather than hundreds) of
subsamples or mock catalogs, resulting in noisy covariance matrices whose
inversion is ill-conditioned and numerically unstable. We present here a method
of conditioning the covariance matrix known as ridge regression which results
in a more well behaved inversion than other techniques common in large-scale
structure studies. We demonstrate that ridge regression significantly improves
the determination of correlation function parameters. We then apply these
improved techniques to the problem of reconstructing redshift distributions. By
incorporating full covariance information, applying ridge regression, and
changing the weighting of fields in obtaining average correlation functions, we
obtain reductions in the mean redshift distribution reconstruction error of as
much as ~40% compared to previous methods. In an appendix, we provide a
description of POWERFIT, an IDL code for performing power-law fits to
correlation functions with ridge regression conditioning that we are making
publicly available.

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Rotational predissociation of extremely weakly bound atom-molecule complexes produced by Feshbach resonance association. (arXiv:1109.1008v1 [physics.chem-ph])

We study the rotational predissociation of atom – molecule complexes with
very small binding energy. Such complexes can be produced by Feshbach resonance
association of ultracold molecules with ultracold atoms. Numerical calculations
of the predissociation lifetimes based on the computation of the energy
dependence of the scattering matrix elements become inaccurate when the binding
energy is smaller than the energy width of the predissociating state. We derive
expressions that represent accurately the predissociation lifetimes in terms of
the real and imaginary parts of the scattering length and effective range for
molecules in an excited rotational state. Our results show that the
predissociation lifetimes are the longest when the binding energy is positive,
i.e. when the predissociating state is just above the excited state threshold.

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Effects of long-range links on metastable states in a dynamic interaction network. (arXiv:1109.0556v1 [cond-mat.stat-mech])

We introduce a model for random-walking nodes on a periodic lattice, where
the dynamic interaction network is defined from local interactions and E
randomly-added long-range links. With periodic states for nodes and an
interaction rule of repeated averaging, we numerically find two types of
metastable states at low- and high-E limits, respectively, along with consensus
states. If we apply this model to opinion dynamics, metastable states can be
interpreted as sustainable diversities in our societies, and our result then
implies that, while diversities decrease and eventually disappear with more
long-range connections, another type of states of diversities can appear when
networks are almost fully-connected.

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Structural preferential attachment: Stochastic process for the growth of scale-free, modular and self-similar systems. (arXiv:1109.0034v1 [physics.soc-ph])

Many complex systems have been shown to share universal properties of
organization, such as scale independence, modularity and self-similarity. We
borrow tools from statistical physics in order to study structural preferential
attachment (SPA), a recently proposed growth principle for the emergence of the
aforementioned properties. We study the corresponding stochastic process in
terms of its time evolution, its asymptotic behaviour and the scaling
properties of its statistical steady state. Moreover, approximations are
introduced to facilitate the reproduction of real systems, mainly complex
networks, using SPA. Finally, we investigate a particular behaviour observed in
the stochastic process, the peloton dynamics, and show how it predicts some
features of real growing systems using prose samples as an example.

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