65 research outputs found
Invariance of density correlations with charge density in polyelectrolyte solutions
We present a theory for the equilibrium structure of polyelectrolyte
solutions. The main element is a simple, new optimization scheme that allows
theories such as the random phase approximation (RPA) to handle the harsh
repulsive forces present in such systems. Comparison is made with data from
recent neutron scattering experiments of randomly charged, hydrophilic polymers
in salt-free, semi-dilute solution at various charge densities. Models with
varying degrees of realism are examined. The usual explanation of the
invariance observed at high charge density has been counterion condensation.
However, when polymer-polymer correlations are treated properly, we find that
modeling polymer-counterion correlations at the level of Debye-Huckel theory is
sufficient.Comment: 4 pages, 2 figure
A Model for the Two-Phase Behavior of Fluids in Dilute Porous Media
Experiments show that the coexistence region of a vapor-liquid system or binary liquid mixture is dramatically narrowed when the fluid is confined in a dilute porous medium such as a silica aerogel. We propose a simple model of the gel as a periodic array of cylindrical strands, and study the phase behavior of an Ising system confined in this geometry. Our results suggest that the coexistence region should widen out at lower temperatures, and that the narrowness observed near the critical point may be a fluctuation-induced effect
CANDELS Multi-wavelength Catalogs: Source Detection and Photometry in the GOODS-South Field
We present a UV-to-mid infrared multi-wavelength catalog in the
CANDELS/GOODS-S field, combining the newly obtained CANDELS HST/WFC3 F105W,
F125W, and F160W data with existing public data. The catalog is based on source
detection in the WFC3 F160W band. The F160W mosaic includes the data from
CANDELS deep and wide observations as well as previous ERS and HUDF09 programs.
The mosaic reaches a 5 limiting depth (within an aperture of radius
0.17 arcsec) of 27.4, 28.2, and 29.7 AB for CANDELS wide, deep, and HUDF
regions, respectively. The catalog contains 34930 sources with the
representative 50% completeness reaching 25.9, 26.6, and 28.1 AB in the F160W
band for the three regions. In addition to WFC3 bands, the catalog also
includes data from UV (U-band from both CTIO/MOSAIC and VLT/VIMOS), optical
(HST/ACS F435W, F606W, F775W, F814W, and F850LP), and infrared (HST/WFC3 F098M,
VLT/ISAAC Ks, VLT/HAWK-I Ks, and Spitzer/IRAC 3.6, 4.5, 5.8, 8.0 m)
observations. The catalog is validated via stellar colors, comparison with
other published catalogs, zeropoint offsets determined from the best-fit
templates of the spectral energy distribution of spectroscopically observed
objects, and the accuracy of photometric redshifts. The catalog is able to
detect unreddened star-forming (passive) galaxies with stellar mass of
10^{10}M_\odot at a 50% completeness level to z3.4 (2.8), 4.6 (3.2), and
7.0 (4.2) in the three regions. As an example of application, the catalog is
used to select both star-forming and passive galaxies at z2--4 via the
Balmer break. It is also used to study the color--magnitude diagram of galaxies
at 0<z<4.Comment: The full resolution article is now published in ApJS (2013, 207, 24).
22 pages, 21 figures, and 5 tables. The catalogue is available on the CANDELS
website: http://candels.ucolick.org/data_access/GOODS-S.html MAST:
http://archive.stsci.edu/prepds/candels and Rainbow Database:
https://arcoiris.ucolick.org/Rainbow_navigator_public and
https://rainbowx.fis.ucm.es/Rainbow_navigator_publi
Model study on the photoassociation of a pair of trapped atoms into an ultralong-range molecule
Using the method of quantum-defect theory, we calculate the ultralong-range
molecular vibrational states near the dissociation threshold of a diatomic
molecular potential which asymptotically varies as . The properties of
these states are of considerable interest as they can be formed by
photoassociation (PA) of two ground state atoms. The Franck-Condon overlap
integrals between the harmonically trapped atom-pair states and the
ultralong-range molecular vibrational states are estimated and compared with
their values for a pair of untrapped free atoms in the low-energy scattering
state. We find that the binding between a pair of ground-state atoms by a
harmonic trap has significant effect on the Franck-Condon integrals and thus
can be used to influence PA. Trap-induced binding between two ground-state
atoms may facilitate coherent PA dynamics between the two atoms and the
photoassociated diatomic molecule.Comment: 11 pages, 4 figures, to appear in Phys. Rev. A (September, 2003
A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z~2: A Mix of Nuclear Activity and Low-Metallicity Star Formation
We present Hubble Space Telescope Wide Field Camera 3 slitless grism
spectroscopy of 28 emission-line galaxies at z~2, in the GOODS-S region of the
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The
high sensitivity of these grism observations, with 1-sigma detections of
emission lines to f > 2.5x10^{-18} erg/s/cm^2, means that the galaxies in the
sample are typically ~7 times less massive (median M_* = 10^{9.5} M_sun) than
previously studied z~2 emission-line galaxies. Despite their lower mass, the
galaxies have OIII/Hb ratios which are very similar to previously studied z~2
galaxies and much higher than the typical emission-line ratios of local
galaxies. The WFC3 grism allows for unique studies of spatial gradients in
emission lines, and we stack the two-dimensional spectra of the galaxies for
this purpose. In the stacked data the OIII emission line is more spatially
concentrated than the Hb emission line with 98.1 confidence. We additionally
stack the X-ray data (all sources are individually undetected), and find that
the average L(OIII)/L(0.5-10 keV) ratio is intermediate between typical z~0
obscured active galaxies and star-forming galaxies. Together the compactness of
the stacked OIII spatial profile and the stacked X-ray data suggest that at
least some of these low-mass, low-metallicity galaxies harbor weak active
galactic nuclei.Comment: ApJ accepted. 8 pages, 6 figure
Comment Re: Non-Compete Clause Rulemaking, Matter No. P201200
Within signed law professors and law students submitted this letter to the Federal Trade Commission, writing in their individual capacities, not as agents of their affiliated institutions, in support of the Federal Trade Commission’s proposed rule to ban most non-compete clauses (the “Proposal”) as an unfair method of competition.
This letter offers comments in response to areas where the FTC has requested public comment. To make our views clear, this letter contains the following sections:
I. Summary of the Proposal;
II. The Commission Should Consider Expanding Its Definition of Non-Compete Clauses to Prevent Employers from Requiring Workers to Quit Before Seeking Alternative Employment;
III. Non-Compete Clauses Are Unfair Methods of Competition;
IV. Non-Compete Clauses Negatively Impact Workers and Their Families;
V. The Proposed Rule Protects Small Businesses and Entrepreneurs; and
VI. The Commission Should Consider a Factor Test for Its Unfairness Analysis for Senior Executive
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