15,700 research outputs found
On the Penrose Inequality for general horizons
For asymptotically flat initial data of Einstein's equations satisfying an
energy condition, we show that the Penrose inequality holds between the ADM
mass and the area of an outermost apparent horizon, if the data are restricted
suitably. We prove this by generalizing Geroch's proof of monotonicity of the
Hawking mass under a smooth inverse mean curvature flow, for data with
non-negative Ricci scalar. Unlike Geroch we need not confine ourselves to
minimal surfaces as horizons. Modulo smoothness issues we also show that our
restrictions on the data can locally be fulfilled by a suitable choice of the
initial surface in a given spacetime.Comment: 4 pages, revtex, no figures. Some comments added. No essential
changes. To be published in Phys. Rev. Let
Versatile spectral imaging with an algorithm-based spectrometer using highly tuneable quantum dot infrared photodetectors
We report on the implementation of an algorithm-based spectrometer capable of reconstructing the spectral shape of materials in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) wavelengths using only experimental photocurrent measurements from quantum dot infrared photodetectors (QDIPs). The theory and implementation of the algorithm will be described, followed by an investigation into this algorithmic spectrometer's performance. Compared to the QDIPs utilized in an earlier implementation, the ones used here have highly varying spectral shapes and four spectral peaks across the MWIR and LWIR wavelengths. It has been found that the spectrometer is capable of reconstructing broad spectral features of a range of bandpass infrared filters between wavelengths of 4 and 12 mu m as well as identifying absorption features as narrow as 0.3 mu m in the IR spectrum of a polyethylene sheet
Superconducting energy gap in MgCNi3 single crystals: Point-contact spectroscopy and specific-heat measurements
Specific heat has been measured down to 600 mK and up to 8 Tesla by the
highly sensitive AC microcalorimetry on the MgCNi3 single crystals with Tc ~ 7
K. Exponential decay of the electronic specific heat at low temperatures proved
that a superconducting energy gap is fully open on the whole Fermi surface, in
agreement with our previous magnetic penetration depth measurements on the same
crystals. The specific-heat data analysis shows consistently the strong
coupling strength 2D/kTc ~ 4. This scenario is supported by the direct gap
measurements via the point-contact spectroscopy. Moreover, the spectroscopy
measurements show a decrease in the critical temperature at the sample surface
accounting for the observed differences of the superfluid density deduced from
the measurements by different techniques
How many photons are needed to distinguish two transparencies?
We give a bound on the minimum number of photons that must be absorbed by any
quantum protocol to distinguish between two transparencies. We show how a
quantum Zeno method in which the angle of rotation is varied at each iteration
can attain this bound in certain situations.Comment: 5 pages, 4 figure
One-Dimensional Dispersive Magnon Excitation in the Frustrated Spin-2 Chain System Ca3Co2O6
Using inelastic neutron scattering, we have observed a quasi-one-dimensional
dispersive magnetic excitation in the frustrated triangular-lattice spin-2
chain oxide Ca3Co2O6. At the lowest temperature (T = 1.5 K), this magnon is
characterized by a large zone-center spin gap of ~27 meV, which we attribute to
the large single-ion anisotropy, and disperses along the chain direction with a
bandwidth of ~3.5 meV. In the directions orthogonal to the chains, no
measurable dispersion was found. With increasing temperature, the magnon
dispersion shifts towards lower energies, yet persists up to at least 150 K,
indicating that the ferromagnetic intrachain correlations survive up to 6 times
higher temperatures than the long-range interchain antiferromagnetic order. The
magnon dispersion can be well described within the predictions of linear
spin-wave theory for a system of weakly coupled ferromagnetic chains with large
single-ion anisotropy, enabling the direct quantitative determination of the
magnetic exchange and anisotropy parameters.Comment: 7 pages, 6 figures including one animatio
The Balance of Apoptotic and Necrotic Cell Death in Mycobacterium tuberculosis Infected Macrophages Is Not Dependent on Bacterial Virulence
An important mechanism of Mycobacterium tuberculosis pathogenesis is the ability to control cell death pathways in infected macrophages: apoptotic cell death is bactericidal, whereas necrotic cell death may facilitate bacterial dissemination and transmission
Magnetic charge, angular momentum and negative cosmological constant
We argue that there are no axially symmetric rotating monopole solutions for
a Yang-Mills-Higgs theory in flat spacetime background. We construct axially
symmetric Yang-Mills-Higgs solutions in the presence of a negative cosmological
constant, carrying magnetic charge and a nonvanishing electric charge.
However, these solution are also nonrotating.Comment: 17 pages, LaTeX, 7 figure
Abstract Feature Space Representation for Volumetric Transfer Function Exploration
The application of n-dimensional transfer functions for feature segmentation has become increasingly popular in volume rendering. Recent work has focused on the utilization of higher order dimensional transfer functions incorporating spatial dimensions (x,y, and z) along with traditional feature space dimensions (value and value gradient). However, as the dimensionality increases, it becomes exceedingly difficult to abstract the transfer function into an intuitive and interactive workspace. In this work we focus on populating the traditional two-dimensional histogram with a set of derived metrics from the spatial (x, y and z) and feature space (value, value gradient, etc.) domain to create a set of abstract feature space transfer function domains. Current two-dimensional transfer function widgets typically consist of a two-dimensional histogram where each entry in the histogram represents the number of voxels that maps to that entry. In the case of an abstract transfer function design, the amount of spatial variance at that histogram
coordinate is mapped instead, thereby relating additional information about the data abstraction in the projected space. Finally, a non-parametric kernel density estimation approach for feature space clustering is applied in the abstracted space, and the resultant transfer functions are discussed with respect to the space abstraction
Production and optical properties of liquid scintillator for the JSNS experiment
The JSNS (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron
Source) experiment will search for neutrino oscillations over a 24 m short
baseline at J-PARC. The JSNS inner detector will be filled with 17 tons
of gadolinium-loaded liquid scintillator (LS) with an additional 31 tons of
unloaded LS in the intermediate -catcher and outer veto volumes.
JSNS has chosen Linear Alkyl Benzene (LAB) as an organic solvent because
of its chemical properties. The unloaded LS was produced at a refurbished
facility, originally used for scintillator production by the RENO experiment.
JSNS plans to use ISO tanks for the storage and transportation of the LS.
In this paper, we describe the LS production, and present measurements of its
optical properties and long term stability. Our measurements show that storing
the LS in ISO tanks does not result in degradation of its optical properties.Comment: 7 pages, 4 figures
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