18,966 research outputs found
Scaling analysis of the screening length in concentrated electrolytes
The interaction between charged objects in an electrolyte solution is a
fundamental question in soft matter physics. It is well-known that the
electrostatic contribution to the interaction energy decays exponentially with
object separation. Recent measurements reveal that, contrary to the
conventional wisdom given by classic Poisson-Boltzmann theory, the decay length
increases with ion concentration for concentrated electrolytes and can be an
order of magnitude larger than the ion diameter in ionic liquids. We derive a
simple scaling theory that explains this anomalous dependence of the decay
length on ion concentration. Our theory successfully collapses the decay
lengths of a wide class of salts onto a single curve. A novel prediction of our
theory is that the decay length increases linearly with the Bjerrum length,
which we experimentally verify by surface force measurements. Moreover, we
quantitatively relate the measured decay length to classic measurements of the
activity coefficient in concentrated electrolytes, thus showing that the
measured decay length is indeed a bulk property of the concentrated electrolyte
as well as contributing a mechanistic insight into empirical activity
coefficients.Comment: To appear in Physical Review Letter
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Sceloporus megalepidurus
Number of Pages: 5Integrative BiologyGeological Science
Keck spectroscopy of z=1-3 ULIRGs from the Spitzer SWIRE survey
(Abridged) High-redshift ultra luminous infrared galaxies contribute the bulk
of the cosmic IR background and are the best candidates for very massive
galaxies in formation at z>1.5. We present Keck/LRIS optical spectroscopy of 35
z>1.4 luminous IR galaxies in the Spitzer Wide-area Infra-Red Extragalactic
survey (SWIRE) northern fields (Lockman Hole, ELAIS-N1, ELAIS-N2). The primary
targets belong to the ``IR-peak'' class of galaxies, having the 1.6 micron
(restframe) stellar feature detected in the IRAC Spitzer channels.The spectral
energy distributions of the main targets are thoroughly analyzed, by means of
spectro-photometric synthesis and multi-component fits (stars + starburst dust
+ AGN torus). The IR-peak selection technique is confirmed to successfully
select objects above z=1.4, though some of the observed sources lie at lower
redshift than expected. Among the 16 galaxies with spectroscopic redshift, 62%
host an AGN component, two thirds being type-1 and one third type-2 objects.
The selection, limited to r'<24.5, is likely biased to optically-bright AGNs.
The SEDs of non-AGN IR-peakers resemble those of starbursts (SFR=20-500
Msun/yr) hosted in massive (M>1e11 Msun) galaxies. The presence of an AGN
component provides a plausible explanation for the spectroscopic/photometric
redshift discrepancies, as the torus produces an apparent shift of the peak to
longer wavelengths. These sources are analyzed in IRAC and optical-IR color
spaces. In addition to the IR-peak galaxies, we present redshifts and spectral
properties for 150 objects, out of a total of 301 sources on slits.Comment: Accepted for publications on Astronomy and Astrophysics (acceprance
date March 8th, 2007). 33 pages. The quality of some figures have been
degrade
Infrared Constraints on AGN Tori Models
This work focuses on the properties of dusty tori in active galactic nuclei
(AGN) derived from the comparison of SDSS type 1 quasars with mid-Infrared
(MIR) counterparts and a new, detailed torus model. The infrared data were
taken by the Spitzer Wide-area InfraRed Extragalactic (SWIRE) Survey. Basic
model parameters are constraint, such as the density law of the graphite and
silicate grains, the torus size and its opening angle. A whole variety of
optical depths is supported. The favoured models are those with decreasing
density with distance from the centre, while there is no clear tendency as to
the covering factor, ie small, medium and large covering factors are almost
equally distributed. Based on the models that better describe the observed
SEDs, properties such as the accretion luminosity, the mass of dust, the inner
to outer radius ratio and the hydrogen column density are computed.Comment: 4 pages, 4 figures, to appear in "Infrared Diagnostics of Galaxy
Evolution", ASP Conference Series, Pasadena, 14-16 November 200
Development and Validation of Makeup and Sexualized Clothing Questionnaires
Background: Body acceptance programs on college campuses indicated that collegiate women often report feeling pressure to dress in a sexualized manner, and use makeup to enhance beauty. Currently, no quantitative measures exist to assess attitudes and daily behaviors that may arise in response to perceived pressure to wear makeup or dress in a provocative manner. The goal of the current studies was to develop brief self-report questionnaires aimed at assessing makeup and sexualized clothing use and attitudes in young women.
Methods: An exploratory factor analysis in a sample of 403 undergraduate women was used in Study 1 to create items to measure the pressure women feel to wear makeup and sexualized clothing. A confirmatory factor analysis (N = 153) was used in Study 2 to confirm the factor structure found in Study 1. An incremental validity analysis was also conducted in Study 2. Across both studies, participants completed online questionnaires.
Results: In Study 1, items were developed for two questionnaires to assess perceived pressure to wear makeup and discomfort when not wearing makeup, and perceived pressure to wear sexualized clothing, and body image concerns with regards to sexualized clothing. The exploratory factor analyses revealed Unconfident and Unease scales for the Makeup Questionnaire (MUQ) and Body Dissatisfaction and Pressure scales for the Sexualized Clothing Questionnaire (SCQ). In Study 2, the confirmatory factor analyses confirmed the factor structure for the MUQ and SCQ. The incremental validity analysis revealed that these measures can be used to predict self-objectification and shape and weight concern in women.
Conclusion: These studies provide preliminary support for the factor structure of two novel questionnaires aimed at assessing perceived pressure to wear makeup and sexualized clothing
Herschel Multitiered Extragalactic Survey: clusters of dusty galaxies uncovered by Herschel and Planck
The potential for Planck to detect clusters of dusty, star-forming galaxies at z > 1 is tested by examining the Herschel-SPIRE images of Planck Early Release Compact Source Catalog sources lying in fields observed by the Herschel Multitiered Extragalactic Survey. Of the 16 Planck sources that lie in the ∼90 sq. deg. examined, we find that 12 are associated with single bright Herschel sources. The remaining four are associated with overdensities of Herschel sources, making them candidate clusters of dusty, star-forming galaxies. We use complementary optical/near-IR data for these ‘clumps’ to test this idea, and find evidence for the presence of galaxy clusters in all four cases. We use photometric redshifts and red sequence galaxies to estimate the redshifts of these clusters, finding that they range from 0.8 to 2.3. These redshifts imply that the Herschel sources in these clusters, which contribute to the detected Planck flux, are forming stars very rapidly, with typical total cluster star formation rates >1000M ? yr −1 . The high-redshift clusters discovered in these observations are used to constrain the epoch of cluster galaxy formation, finding that the galaxies in our clusters are 1–1.5 Gyr old at z ∼ 1–2. Prospects for the discovery of further clusters of dusty galaxies are discussed, using not only all sky Planck surveys, but also deeper, smaller area, Herschel surveys
Large ferroelectric polarization in the new double perovskite NaLaMnWO induced by non-polar instabilities
Based on density functional theory calculations and group theoretical
analysis, we have studied NaLaMnWO compound which has been recently
synthesized [Phys. Rev. B 79, 224428 (2009)] and belongs to the family of double perovskites. At low temperature, the structure has
monoclinic symmetry, with layered ordering of the Na and La ions and
rocksalt ordering of Mn and W ions. The Mn atoms show an antiferromagnetic
(AFM) collinear spin ordering, and the compound has been reported as a
potential multiferroic. By comparing the low symmetry structure with a parent
phase of symmetry, two distortion modes are found dominant. They
correspond to MnO and WO octahedron \textit{tilt} modes, often
found in many simple perovskites. While in the latter these common tilting
instabilities yield non-polar phases, in NaLaMnWO the additional presence
of the - cation ordering is sufficient to make these rigid unit modes
as a source of the ferroelectricity. Through a trilinear coupling with the two
unstable tilting modes, a significant polar distortion is induced, although the
system has no intrinsic polar instability. The calculated electric polarization
resulting from this polar distortion is as large as 16 . Despite its secondary character, this polarization is coupled with
the dominant tilting modes and its switching is bound to produce the switching
of one of two tilts, enhancing in this way a possible interaction with the
magnetic ordering. The transformation of common non-polar purely steric
instabilities into sources of ferroelectricity through a controlled
modification of the parent structure, as done here by the cation ordering, is a
phenomenon to be further explored.Comment: Physical Chemistry Chemical physics (in press
Calibration of Smearing and Cooling Algorithms in SU(3)-Color Gauge Theory
The action and topological charge are used to determine the relative rates of
standard cooling and smearing algorithms in pure SU(3)-color gauge theory. We
consider representative gauge field configurations on lattices
at and lattices at . We find the
relative rate of variation in the action and topological charge under various
algorithms may be succinctly described in terms of simple formulae. The results
are in accord with recent suggestions from fat-link perturbation theory.Comment: RevTeX, 25 pages, 22 figures, full resolution jpeg version of Fig. 22
can be obtained from
http://www.physics.adelaide.edu.au/cssm/papers_etc/SmearingComp.jp
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