23,619 research outputs found
Electrophoresis device
A device for separating cellular particles of a sample substance into fractionated streams of different cellular species includes a casing having a distribution chamber, a separation chamber, and a collection chamber. The electrode chambers are separated from the separation chamber interior by means of passages such that flow variations and membrane variations around the slotted portion of the electrode chamber do not enduce flow perturbations into the laminar buffer curtain flowing in the separation chamber. The cellular particles of the sample are separated under the influence of the electrical field and the separation chamber into streams of different cellular species. The streams of separated cells enter a partition array in the collection chamber where they are fractionated and collected
Flow and thermal effects in continuous flow electrophoresis
In continuous flow electrophoresis the axial flow structure changes from a fully developed rectilinear form to one characterized by meandering as power levels are increased. The origin of this meandering is postulated to lie in a hydrodynamic instability driven by axial (and possibly lateral) temperature gradients. Experiments done at MSFC show agreement with the theory
A Scalable Asynchronous Distributed Algorithm for Topic Modeling
Learning meaningful topic models with massive document collections which
contain millions of documents and billions of tokens is challenging because of
two reasons: First, one needs to deal with a large number of topics (typically
in the order of thousands). Second, one needs a scalable and efficient way of
distributing the computation across multiple machines. In this paper we present
a novel algorithm F+Nomad LDA which simultaneously tackles both these problems.
In order to handle large number of topics we use an appropriately modified
Fenwick tree. This data structure allows us to sample from a multinomial
distribution over items in time. Moreover, when topic counts
change the data structure can be updated in time. In order to
distribute the computation across multiple processor we present a novel
asynchronous framework inspired by the Nomad algorithm of
\cite{YunYuHsietal13}. We show that F+Nomad LDA significantly outperform
state-of-the-art on massive problems which involve millions of documents,
billions of words, and thousands of topics
Wave localization in binary isotopically disordered one-dimensional harmonic chains with impurities having arbitrary cross section and concentration
The localization length for isotopically disordered harmonic one-dimensional
chains is calculated for arbitrary impurity concentration and scattering cross
section. The localization length depends on the scattering cross section of a
single scatterer, which is calculated for a discrete chain having a wavelength
dependent pulse propagation speed. For binary isotopically disordered systems
composed of many scatterers, the localization length decreases with increasing
impurity concentration, reaching a mimimum before diverging toward infinity as
the impurity concentration approaches a value of one. The concentration
dependence of the localization length over the entire impurity concentration
range is approximated accurately by the sum of the behavior at each limiting
concentration. Simultaneous measurements of Lyapunov exponent statistics
indicate practical limits for the minimum system length and the number of
scatterers to achieve representative ensemble averages. Results are discussed
in the context of future investigations of the time-dependent behavior of
disordered anharmonic chains.Comment: 8 pages, 10 figures, submitted to PR
Line element in quantum gravity: the examples of DSR and noncommutative geometry
We question the notion of line element in some quantum spaces that are
expected to play a role in quantum gravity, namely non-commutative deformations
of Minkowski spaces. We recall how the implementation of the Leibniz rule
forbids to see some of the infinitesimal deformed Poincare transformations as
good candidates for Noether symmetries. Then we recall the more fundamental
view on the line element proposed in noncommutative geometry, and re-interprete
at this light some previous results on Connes' distance formula.Comment: some references added. Proceedings of the Second Workshop on Quantum
Gravity and Noncommutative Geometry, Universidade Lusofona, Lisbon 22-24
September 200
Sub-shot-noise photon-number correlation in mesoscopic twin-beam of light
We demonstrate sub-shot-noise photon-number correlations in a (temporal)
multimode mesoscopic ( detected photons) twin-beam produced by
ps-pulsed spontaneous non-degenerate parametric downconversion. We have
separately detected the signal and idler distributions of photons collected in
twin coherence areas and found that the variance of the photon-count difference
goes below the shot-noise limit by 3.25 dB. The number of temporal modes
contained in the twin-beam, as well as the size of the twin coherence areas,
depends on the pump intensity. Our scheme is based on spontaneous
downconversion and thus does not suffer from limitations due to the finite gain
of the parametric process. Twin-beams are also used to demonstrate the
conditional preparation of a nonclassical (sub-Poissonian) state.Comment: 5 pages, 5 (low-res) figures, to appear on PR
Noncommutative D-Brane in Non-Constant NS-NS B Field Background
We show that when the field strength H of the NS-NS B field does not vanish,
the coordinates X and momenta P of an open string endpoints satisfy a set of
mixed commutation relations among themselves. Identifying X and P with the
coordinates and derivatives of the D-brane world volume, we find a new type of
noncommutative spaces which is very different from those associated with a
constant B field background.Comment: 11 pages, Latex, minor modification
Dissipation-driven quantum phase transitions in collective spin systems
We consider two different collective spin systems subjected to strong
dissipation -- on the same scale as interaction strengths and external fields
-- and show that either continuous or discontinuous dissipative quantum phase
transitions can occur as the dissipation strength is varied. First, we consider
a well known model of cooperative resonance fluorescence that can exhibit a
second-order quantum phase transition, and analyze the entanglement properties
near the critical point. Next, we examine a dissipative version of the
Lipkin-Meshkov-Glick interacting collective spin model, where we find that
either first- or second-order quantum phase transitions can occur, depending
only on the ratio of the interaction and external field parameters. We give
detailed results and interpretation for the steady state entanglement in the
vicinity of the critical point, where it reaches a maximum. For the first-order
transition we find that the semiclassical steady states exhibit a region of
bistability.Comment: 12 pages, 16 figures, removed section on homodyne spectr
Ellipsometric study of InGaAs MODFET material
In(x)Ga(1-x)As based MODFET (modulation doped field effect transistor) material was grown by molecular beam epitaxy on semi-insulating InP substrates. Several structures were made, including lattice matched and strained layer InGaAs. All structures also included several layers of In(0.52)Al(0.48)As. Variable angle spectroscopic ellipsometry was used to characterize the structures. The experimental data, together with the calibration function for the constituent materials, were analyzed to yield the thickness of all the layers of the MODFET structure. Results of the ellipsometrically determined thicknesses compare very well with the reflection high energy electron diffraction in situ thickness measurements
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