2,234 research outputs found
Temperature control of a cryogenic bath
Foreign gas introduced into vapor phase above liquid region cools cryogenic baths. Equipment consists of gas tank and cover of styrofoam. Helium is considered the best choice to produce cooling, though any gas with boiling point lower than that of bath liquid may be used
Helicity Conservation via the Noether Theorem
The conservation of helicity in ideal barotropic fluids is discussed from a
group theoretical point of view. A new symmetry group is introduced i.e. the
alpha group of translations. It is proven via the Noether theorem that this
group generates helicity conservation.Comment: 7 pages of te
Communications Biophysics
Contains reports on two research projects.National Institutes of Health (Grant 5 P01 GM14940-05
Relativistic Doppler effect in quantum communication
When an electromagnetic signal propagates in vacuo, a polarization detector
cannot be rigorously perpendicular to the wave vector because of diffraction
effects. The vacuum behaves as a noisy channel, even if the detectors are
perfect. The ``noise'' can however be reduced and nearly cancelled by a
relative motion of the observer toward the source. The standard definition of a
reduced density matrix fails for photon polarization, because the
transversality condition behaves like a superselection rule. We can however
define an effective reduced density matrix which corresponds to a restricted
class of positive operator-valued measures. There are no pure photon qubits,
and no exactly orthogonal qubit states.Comment: 10 pages LaTe
Non-Hermitian Anharmonicity Induces Single-Photon Emission
Single-photon sources are in high demand for quantum information
applications. A paradigmatic way to achieve single-photon emission is through
anharmonicity in the energy levels, such that the absorption of a single photon
from a coherent drive shifts the system out of resonance and prevents
absorption of a second one. In this Letter, we identify a novel mechanism for
single-photon emission through non-Hermitian anharmonicity, i.e., anharmonicity
in the losses instead of in the energy levels. We demonstrate the mechanism in
two types of systems and show that it induces high-purity single-photon
emission at high repetition rates. Furthermore, we show that it can be observed
in the weak-coupling regime of a cavity quantum electrodynamical setup
The Photoeccentric Effect and Proto-hot Jupiters. III. A Paucity of Proto-hot Jupiters on Super-eccentric Orbits
Gas giant planets orbiting within 0.1 AU of their host stars are unlikely to have formed in situ and are evidence for planetary migration. It is debated whether the typical hot Jupiter smoothly migrated inward from its formation location through the proto-planetary disk, or was perturbed by another body onto a highly eccentric orbit, which tidal dissipation subsequently shrank and circularized during close stellar passages. Socrates and collaborators predicted that the latter model should produce a population of super-eccentric proto-hot Jupiters readily observable by Kepler. We find a paucity of such planets in the Kepler sample, which is inconsistent with the theoretical prediction with 96.9% confidence. Observational effects are unlikely to explain this discrepancy. We find that the fraction of hot Jupiters with an orbital period P > 3 days produced by the star-planet Kozai mechanism does not exceed (at two-sigma) 44%. Our results may indicate that disk migration is the dominant channel for producing hot Jupiters with P > 3 days. Alternatively, the typical hot Jupiter may have been perturbed to a high eccentricity by interactions with a planetary rather than stellar companion, and began tidal circularization much interior to 1 AU after multiple scatterings. A final alternative is that early in the tidal circularization process at high eccentricities tidal circularization occurs much more rapidly than later in the process at low eccentricities, although this is contrary to current tidal theories
Predication and cognitive context: Between minimalism and contextualism
In this paper, we suggest a strategy for modelling cognitive context within a truth\u2010conditional semantics, using Asher's model of predication. This allows us to introduce the notion of type presupposition intended as a lexical constraint to the composition of the truth\u2010conditional content. More specifi\u2010cally, we suggest that this model of predication produces a notion of truth\u2010conditional meaning where the cognitive context fixes a set of lexical restrictions and forced modifi\u2010cations. We conclude that this model might offer an inter\u2010mediate position between Minimalism and Contextualism: an account that provides intuitive truth conditions within a formal semantic theory
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