1,700 research outputs found
Xenon forms stable compound with fluorine
Experiments show that xenon and fluorine combine readily at 400 deg C to form xenon tetrafluoride, which is colorless, crystalline, chemically stable and solid at room temperature. This process can be used for the separation of xenon from mixtures with other noble gases
Toward RADSCAT measurements over the sea and their interpretation
Investigations into several areas which are essential to the execution and interpretation of suborbital observations by composite radiometer - scatterometer sensor (RADSCAT) are reported. Experiments and theory were developed to demonstrate the remote anemometric capability of the sensor over the sea through various weather conditions. It is shown that weather situations found in extra tropical cyclones are useful for demonstrating the all weather capability of the composite sensor. The large scale fluctuations of the wind over the sea dictate the observational coverage required to correlate measurements with the mean surface wind speed. Various theoretical investigations were performed to establish a premise for the joint interpretation of the experiment data. The effects of clouds and rains on downward radiometric observations over the sea were computed. A method of predicting atmospheric attenuation from joint observations is developed. In other theoretical efforts, the emission and scattering characteristics of the sea were derived. Composite surface theories with coherent and noncoherent assumptions were employed
Entanglement and Topology in Su-Schrieffer-Heeger Cavity Quantum Electrodynamics
Cavity materials are a frontier to investigate the role of light-matter
interactions on the properties of electronic phases of matter. In this work, we
raise a fundamental question: can non-local interactions mediated by cavity
photons destabilize a topological electronic phase? We investigate this
question by characterizing entanglement, energy spectrum and correlation
functions of the topological Su-Schrieffer-Heeger (SSH) chain interacting with
an optical cavity mode. Employing density-matrix renormalization group (DMRG)
and exact diagonalization (ED), we demonstrate the stability of the edge state
and establish an area law scaling for the ground state entanglement entropy,
despite long-range correlations induced by light-matter interactions. These
features are linked to gauge invariance and the scaling of virtual photon
excitations entangled with matter, effectively computed in a low-dimensional
Krylov subspace of the full Hilbert space. This work provides a framework for
characterizing novel equilibrium phenomena in topological cavity materials.Comment: 4.5 pages and 3 figure
ac Losses in a Finite Z Stack Using an Anisotropic Homogeneous-Medium Approximation
A finite stack of thin superconducting tapes, all carrying a fixed current I,
can be approximated by an anisotropic superconducting bar with critical current
density Jc=Ic/2aD, where Ic is the critical current of each tape, 2a is the
tape width, and D is the tape-to-tape periodicity. The current density J must
obey the constraint \int J dx = I/D, where the tapes lie parallel to the x axis
and are stacked along the z axis. We suppose that Jc is independent of field
(Bean approximation) and look for a solution to the critical state for
arbitrary height 2b of the stack. For c<|x|<a we have J=Jc, and for |x|<c the
critical state requires that Bz=0. We show that this implies \partial
J/\partial x=0 in the central region. Setting c as a constant (independent of
z) results in field profiles remarkably close to the desired one (Bz=0 for
|x|<c) as long as the aspect ratio b/a is not too small. We evaluate various
criteria for choosing c, and we show that the calculated hysteretic losses
depend only weakly on how c is chosen. We argue that for small D/a the
anisotropic homogeneous-medium approximation gives a reasonably accurate
estimate of the ac losses in a finite Z stack. The results for a Z stack can be
used to calculate the transport losses in a pancake coil wound with
superconducting tape.Comment: 21 pages, 17 figures, accepted by Supercond. Sci. Techno
Causal Shapley Values: Exploiting Causal Knowledge to Explain Individual Predictions of Complex Models
Shapley values underlie one of the most popular model-agnostic methods within
explainable artificial intelligence. These values are designed to attribute the
difference between a model's prediction and an average baseline to the
different features used as input to the model. Being based on solid
game-theoretic principles, Shapley values uniquely satisfy several desirable
properties, which is why they are increasingly used to explain the predictions
of possibly complex and highly non-linear machine learning models. Shapley
values are well calibrated to a user's intuition when features are independent,
but may lead to undesirable, counterintuitive explanations when the
independence assumption is violated.
In this paper, we propose a novel framework for computing Shapley values that
generalizes recent work that aims to circumvent the independence assumption. By
employing Pearl's do-calculus, we show how these 'causal' Shapley values can be
derived for general causal graphs without sacrificing any of their desirable
properties. Moreover, causal Shapley values enable us to separate the
contribution of direct and indirect effects. We provide a practical
implementation for computing causal Shapley values based on causal chain graphs
when only partial information is available and illustrate their utility on a
real-world example.Comment: Accepted at 34th Conference on Neural Information Processing Systems
(NeurIPS 2020
Higher harmonics of ac voltage response in narrow strips of YBa2Cu3O7 thin films: Evidence for strong thermal fluctuations
We report on measurements of higher harmonics of the ac voltage response in
strips of YBa2Cu3O7 thin films as a function of temperature, frequency and ac
current amplitude. The third (fifth) harmonic of the local voltage is found to
exhibit a negative (positive) peak at the superconducting transition
temperature and their amplitudes are closely related to the slope (derivative)
of the first (Ohmic) harmonic. The peaks practically do not depend on frequency
and no even (second or fourth) harmonics are detected. The observed data can be
interpreted in terms of ac current induced thermal modulation of the sample
temperature added to strong thermally activated fluctuations in the transition
region.Comment: 9 pages, 4 figures (PDF file
Media Distribution in a Pervasive Computing Environment
Distribution of media in the fast growing world of digital stored content and multimedia supporting devices with connectivity, calls for a new media distribution architecture. The user should be provided with the experience of having an overview of his full media collection, regardless of the time, the place, and the connectivity. Transparent distributed data management is crucial to Ambient Intelligent applications. The proposed media distribution architecture offers a possible solution. It provides the user with the experience of having all his media collections available at any time, in any place, and managing them regardless of connection availability in the heterogeneous environment. This experience is enabled in our system by the separation of metadata and content handling. Other features are efficient handling of snapshots, usage of various database technologies, and leveraging device and service discovery mechanisms
Early postural blood pressure response and cause-specific mortality among middle-aged adults: what is the role of diastolic blood pressure?
Rabies virus cross-reactive murine T cell clones: analysis of helper and delayed-type hypersensitivity function.
Three T cell clones derived from rabies virus-immunized BALB/c mice were analysed for specificity and function. The clones proved to be broadly cross-reactive by responding to different rabies virus isolates (PM, ERA, CVS, HEP) and other representatives of the genus Lyssavirus, like the Duvenhage-6 (DUV6) and Mokola (MOK) viruses. The clones detected three different epitopes: an epitope expressed on the matrix protein (M) shared by PM, HEP, MOK and DUV6 viruses (clone AA8), an epitope expressed on the M-protein shared by PM, ERA, CVS, HEP and MOK viruses (clone 35A) and finally an epitope expressed on the glycoprotein (G-protein) shared by PM, ERA, CVS, HEP and MOK viruses (clone BG2). Antigen recognition of all clones proved to be MHC-restricted and they all displayed the CD4+ CD8- phenotype. Intravenous inoculation of the T cells in syngeneic mice, which had been injected intracutaneously in the ear with HEP virus, resulted in a localized DTH reaction characteristic for TH1 cells. In vitro, the clones were able to provide help to rabies virus-primed B cells, resulting in the production of virus-specific antibodies directed against all the four structural proteins of rabies virus. Further analysis of this antibody response revealed that part of it was directed against antigenic determinants of the G-protein which induce virus neutralizing antibody
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