3,442 research outputs found
Vaporization thermodynamics of K2S and K2SO3
The vaporization reactions, vapor pressures, and thermodynamics of potassium sulfide and potassium sulfite were studied for purposes of providing fundamental data for the seed cycle in magnetohydrodynamic electric power generation. Rate of effusion studies, supported by tube furnace experiments, X-ray powder diffraction, mass spectrometry and appropriate chemical analyses and tests, revealed that potassium sulfite disproportionates at high temperatures to form potassium sulfide and potassium sulfate. Potassium sulfide was observed to vaporize incongruently, the initial vapors beng predominantly potassium atoms, with minor species being S2 and various K-S molecules. The ratio of K/S2 in the vapor is very large initially and decreases steadily with prolonged heating. Several materials were evaluated for purposes of containing K2S/K2SO3 at temperatures or = 800 C: Pt, Mo, W, quartz, machinable glass, BN, high density graphite, pyrolytic coated graphite, and alumina. Of these, only alumina was observed to be chemically inert to both K2S but reacted with K2SO3. The other materials were not suitable for either substance. Thermodynamic calculations based on measured vapor pressures and approximate free energy functions are described. Results from isothermal total mass loss experiments and from thermogravimetric experiments are also included
Dynamics of Global Entanglement under Decoherence
We investigate the dynamics of global entanglement, the Meyer-Wallach
measure, under decoherence, analytically. We study two important class of
multi-partite entangled states, the Greenberger-Horne-Zeilinger and the W
state. We obtain exact results for various models of system-environment
interactions (decoherence). Our results shows distinctly different scaling
behavior for these initially entangled states indicating a relative robustness
of the W state, consistent with previous studies.Comment: 5 pages and 5 figure
Gravitational Radiation Damping and the Three-Body Problem
A model of three-body motion is developed which includes the effects of
gravitational radiation reaction. The radiation reaction due to the emission of
gravitational waves is the only post-Newtonian effect that is included here.
For simplicity, all of the motion is taken to be planar. Two of the masses are
viewed as a binary system and the third mass, whose motion will be a fixed
orbit around the center-of-mass of the binary system, is viewed as a
perturbation. This model aims to describe the motion of a relativistic binary
pulsar that is perturbed by a third mass. Numerical integration of this
simplified model reveals that given the right initial conditions and parameters
one can see resonances. These (m,n) resonances are defined by the resonance
condition, , where and are relatively prime integers
and and are the angular frequencies of the binary orbit and
third mass orbit, respectively. The resonance condition consequently fixes a
value for the semimajor axis of the binary orbit for the duration of the
resonance; therefore, the binary energy remains constant on the average while
its angular momentum changes during the resonance.Comment: 16 pages, 3 Postscript figures, to appear in MNRA
It\u27s Your Land, and My Land
https://digitalcommons.library.umaine.edu/mmb-me/1108/thumbnail.jp
Signal Decomposition Using Masked Proximal Operators
We consider the well-studied problem of decomposing a vector time series
signal into components with different characteristics, such as smooth,
periodic, nonnegative, or sparse. We describe a simple and general framework in
which the components are defined by loss functions (which include constraints),
and the signal decomposition is carried out by minimizing the sum of losses of
the components (subject to the constraints). When each loss function is the
negative log-likelihood of a density for the signal component, this framework
coincides with maximum a posteriori probability (MAP) estimation; but it also
includes many other interesting cases. Summarizing and clarifying prior
results, we give two distributed optimization methods for computing the
decomposition, which find the optimal decomposition when the component class
loss functions are convex, and are good heuristics when they are not. Both
methods require only the masked proximal operator of each of the component loss
functions, a generalization of the well-known proximal operator that handles
missing entries in its argument. Both methods are distributed, i.e., handle
each component separately. We derive tractable methods for evaluating the
masked proximal operators of some loss functions that, to our knowledge, have
not appeared in the literature.Comment: The manuscript has 61 pages, 22 figures and 2 tables. Also hosted at
https://web.stanford.edu/~boyd/papers/sig_decomp_mprox.html. For code, see
https://github.com/cvxgrp/signal-decompositio
Mechanisms of Spontaneous Current Generation in an Inhomogeneous d-Wave Superconductor
A boundary between two d-wave superconductors or an s-wave and a d-wave
superconductor generally breaks time-reversal symmetry and can generate
spontaneous currents due to proximity effect. On the other hand, surfaces and
interfaces in d-wave superconductors can produce localized current-carrying
states by supporting the T-breaking combination of dominant and subdominant
order parameters. We investigate spontaneous currents in the presence of both
mechanisms and show that at low temperature, counter-intuitively, the
subdominant coupling decreases the amplitude of the spontaneous current due to
proximity effect. Superscreening of spontaneous currents is demonstrated to be
present in any d-d (but not s-d) junction and surface with d+id' order
parameter symmetry. We show that this supercreening is the result of
contributions from the local magnetic moment of the condensate to the
spontaneous current.Comment: 4 pages, 5 figures, RevTe
A deterministic cavity-QED source of polarization entangled photon pairs
We present two cavity quantum electrodynamics proposals that, sharing the
same basic elements, allow for the deterministic generation of entangled
photons pairs by means of a three-level atom successively coupled to two single
longitudinal mode high-Q optical resonators presenting polarization degeneracy.
In the faster proposal, the three-level atom yields a polarization entangled
photon pair via two truncated Rabi oscillations, whereas in the adiabatic
proposal a counterintuitive Stimulated Raman Adiabatic Passage process is
considered. Although slower than the former process, this second method is very
efficient and robust under fluctuations of the experimental parameters and,
particularly interesting, almost completely insensitive to atomic decay.Comment: 5 pages, 5 figure
Quantum error-correcting codes associated with graphs
We present a construction scheme for quantum error correcting codes. The
basic ingredients are a graph and a finite abelian group, from which the code
can explicitly be obtained. We prove necessary and sufficient conditions for
the graph such that the resulting code corrects a certain number of errors.
This allows a simple verification of the 1-error correcting property of
fivefold codes in any dimension. As new examples we construct a large class of
codes saturating the singleton bound, as well as a tenfold code detecting 3
errors.Comment: 8 pages revtex, 5 figure
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