7,202 research outputs found
Parametric test of a zirconium (4) oxide-polyacrylic acid dual layer hyperfiltration membrane with spacecraft washwater
Performance data consisting of solute rejections and product flux were measured, as dependent on the operation parameters. These parameters and ranges were pressure (500,000 n/m2 to 700,000 n/m2), temperature (74 C to 95 C), velocity (1.6 M/sec to 10 M/sec), and concentration (up to 14x). Tests were carried out on analog washwater. Data presented include rejections of organic materials, ammonia, urea, and an assortment of ions. The membrane used was deposited in situ on a porcelain ceramic substrate
Virial Masses of Black Holes from Single Epoch Spectra of AGN
We describe the general problem of estimating black hole masses of AGN by
calculating the conditional probability distribution of M_BH given some set of
observables. Special attention is given to the case where one uses the AGN
continuum luminosity and emission line widths to estimate M_BH, and we outline
how to set up the conditional probability distribution of M_BH given the
observed luminosity, line width, and redshift. We show how to combine the broad
line estimates of M_BH with information from an intrinsic correlation between
M_BH and L, and from the intrinsic distribution of M_BH, in a manner that
improves the estimates of M_BH. Simulation was used to assess how the
distribution of M_BH inferred from the broad line mass estimates differs from
the intrinsic distribution, and we find that this can lead to an inferred
distribution that is too broad. We use these results and a sample of 25 sources
that have recent reverberation mapping estimates of AGN black hole masses to
investigate the effectiveness of using the C IV emission line to estimate M_BH
and to indirectly probe the C IV region size--luminosity (R--L) relationship.
We estimated M_BH from both C IV and H-Beta for a sample of 100 sources,
including new spectra of 29 quasars. We find that the two emission lines give
consistent estimates if one assumes R \propto L^{1/2}_{UV} for both lines.Comment: 38 pages, 6 figures, accepted by Ap
Discovery of an M9.5 Candidate Brown Dwarf in the TW Hydrae Association - DENIS J124514.1-442907
We report the discovery of a fifth candidate substellar system in the ~5-10
Myr TW Hydrae Association - DENIS J124514.1-442907. This object has a NIR
spectrum remarkably similar to that of 2MASS J1139511-315921, a known TW Hydrae
brown dwarf, with low surface gravity features such as a triangular-shaped
H-band, deep H2O absorption, weak alkali lines, and weak hydride bands. We find
an optical spectral type of M9.5 and estimate a mass of <24 M_Jup, assuming an
age of ~5-10 Myr. While the measured proper motion for DENIS J124514.1-442907
is inconclusive as a test for membership, its position in the sky is coincident
with the TW Hydrae Association. A more accurate proper motion measurement,
higher resolution spectroscopy for radial velocity, and a parallax measurement
are needed to derive the true space motion and to confirm its membership.Comment: 8 pages - emulateapj style, 2 figures, 3 tables. Accepted to ApJL.
Fixed typos, added reference, added footnot
Higher-Form Subsystem Symmetry Breaking: Subdimensional Criticality and Fracton Phase Transitions
Subsystem symmetry has emerged as a powerful organizing principle for
unconventional quantum phases of matter, most prominently fracton topological
orders. Here, we focus on a special subclass of such symmetries, known as
higher-form subsystem symmetries, which allow us to adapt tools from the study
of conventional topological phases to the fracton setting. We demonstrate that
certain transitions out of familiar fracton phases, including the X-cube model,
can be understood in terms of the spontaneous breaking of higher-form subsystem
symmetries. We find simple pictures for these seemingly complicated fracton
topological phase transitions by relating them in an exact manner, via gauging,
to spontaneous higher-form subsystem symmetry breaking phase transitions of
decoupled stacks of lower-dimensional models. We harness this perspective to
construct a sequence of unconventional subdimensional critical points in two
and three spatial dimensions based on the stacking and gauging of canonical
models with higher-form symmetry. Through numerous examples, we illustrate the
ubiquity of coupled layer constructions in theories with higher-form subsystem
symmetries.Comment: 128 pages, 8 tables, 13 figures, minor typos corrected in v2, to
appear in SciPost Physic
Three-Dimensional Spin-Orbit Coupling in a Trap
We investigate the properties of an atom under the influence of a synthetic
three-dimensional spin-orbit coupling (Weyl coupling) in the presence of a
harmonic trap. The conservation of total angular momentum provides a
numerically efficient scheme for finding the spectrum and eigenfunctions of the
system. We show that at large spin-orbit coupling the system undergoes
dimensional reduction from three to one dimension at low energies, and the
spectrum is approximately Landau level-like. At high energies, the spectrum is
approximately given by the three-dimensional isotropic harmonic oscillator. We
explore the properties of the ground state in both position and momentum space.
We find the ground state has spin textures with oscillations set by the
spin-orbit length scale
Computational approach to the Schottky problem
We present a computational approach to the classical Schottky problem based
on Fay's trisecant identity for genus . For a given Riemann matrix
, the Fay identity establishes linear dependence
of secants in the Kummer variety if and only if the Riemann matrix corresponds
to a Jacobian variety as shown by Krichever. The theta functions in terms of
which these secants are expressed depend on the Abel maps of four arbitrary
points on a Riemann surface. However, there is no concept of an Abel map for
general . To establish linear dependence of the
secants, four components of the vectors entering the theta functions can be
chosen freely. The remaining components are determined by a Newton iteration to
minimize the residual of the Fay identity. Krichever's theorem assures that if
this residual vanishes within the finite numerical precision for a generic
choice of input data, then the Riemann matrix is with this numerical precision
the period matrix of a Riemann surface. The algorithm is compared in genus 4
for some examples to the Schottky-Igusa modular form, known to give the Jacobi
locus in this case. It is shown that the same residuals are achieved by the
Schottky-Igusa form and the approach based on the Fay identity in this case. In
genera 5, 6 and 7, we discuss known examples of Riemann matrices and
perturbations thereof for which the Fay identity is not satisfied
Morphological Classification of Galaxies by Shapelet Decomposition in the Sloan Digital Sky Survey II: Multiwavelength Classification
We describe the application of the `shapelet' linear decomposition of galaxy
images to multi-wavelength morphological classification using the
and -band images of 1519 galaxies from the Sloan Digital Sky Survey. We
utilize elliptical shapelets to remove to first-order the effect of inclination
on morphology. After decomposing the galaxies we perform a principal component
analysis on the shapelet coefficients to reduce the dimensionality of the
spectral morphological parameter space. We give a description of each of the
first ten principal component's contribution to a galaxy's spectral morphology.
We find that galaxies of different broad Hubble type separate cleanly in the
principal component space. We apply a mixture of Gaussians model to the
2-dimensional space spanned by the first two principal components and use the
results as a basis for classification. Using the mixture model, we separate
galaxies into three classes and give a description of each class's physical and
morphological properties. We find that the two dominant mixture model classes
correspond to early and late type galaxies, respectively. The third class has,
on average, a blue, extended core surrounded by a faint red halo, and typically
exhibits some asymmetry. We compare our method to a simple cut on color
and find the shapelet method to be superior in separating galaxies.
Furthermore, we find evidence that the decision boundary may not be
optimal for separation between early and late type galaxies, and suggest that
the optimal cut may be .Comment: 42 pages, 18 figs, revised version in press at AJ. Some modification
to the technique, more discussion, addition/deletion/modification of several
figures, color figures have been added. A high resolution version may be
obtained at
http://bllac.as.arizona.edu/~bkelly/shapelets/shapelets_ugriz.ps.g
Low-Temperature Supercapacitors
An effort to extend the low-temperature operational limit of supercapacitors is currently underway. At present, commercially available non-aqueous supercapacitors are rated for a minimum operating temperature of -40 C. A capability to operate at lower temperatures would be desirable for delivering power to systems that must operate in outer space or in the Polar Regions on Earth. Supercapacitors (also known as double-layer or electrochemical capacitors) offer a high power density (>1,000 W/kg) and moderate energy density (about 5 to 10 Wh/kg) technology for storing energy and delivering power. This combination of properties enables delivery of large currents for pulsed applications, or alternatively, smaller currents for low duty cycle applications. The mechanism of storage of electric charge in a supercapacitor -- at the electrical double-layer formed at a solid-electrode/liquid-electrolyte interface -- differs from that of a primary or secondary electrochemical cell (i.e., a battery) in such a manner as to impart a long cycle life (typically >10(exp 6) charge/discharge cycles)
- …