6,287 research outputs found
Integrable mixing of A_{n-1} type vertex models
Given a family of monodromy matrices {T_u; u=0,1,...,K-1} corresponding to
integrable anisotropic vertex models of A_{(n_u)-1}-type, we build up a related
mixed vertex model by means of glueing the lattices on which they are defined,
in such a way that integrability property is preserved. Algebraically, the
glueing process is implemented through one dimensional representations of
rectangular matrix algebras A(R_p,R_q), namely, the `glueing matrices' zeta_u.
Here R_n indicates the Yang-Baxter operator associated to the standard Hopf
algebra deformation of the simple Lie algebra A_{n-1}. We show there exists a
pseudovacuum subspace with respect to which algebraic Bethe ansatz can be
applied. For each pseudovacuum vector we have a set of nested Bethe ansatz
equations identical to the ones corresponding to an A_{m-1} quasi-periodic
model, with m equal to the minimal range of involved glueing matrices.Comment: REVTeX 28 pages. Here we complete the proof of integrability for
mixed vertex models as defined in the first versio
Detecting and mapping the ‘ephemeral’: magnetometric survey of a Pastoral Neolithic settlement at Luxmanda, Tanzania
Common assumptions about the ephemeral archaeological signature of pastoralist settlements have limited the application of geophysical techniques in the investigation of past herding societies. Here, the authors present a geophysical survey of Luxmanda, Tanzania, the largest-known settlement documented for the Pastoral Neolithic era in eastern Africa (c. 5000–1200 BP). The results demonstrate the value and potential of fluxgate gradiometry for the identification of magnetic anomalies relating to archaeological features, at a category of site where evidence for habitation was long thought to be undetectable. The study provides comparative data to enable archaeologists to identify loci for future investigations of mobile populations in eastern Africa and elsewhere
Joint Elastic Side-Scattering Lidar and Raman Lidar Measurements of Aerosol Optical Properties in South East Colorado
We describe an experiment, located in south-east Colorado, USA, that measured
aerosol optical depth profiles using two Lidar techniques. Two independent
detectors measured scattered light from a vertical UV laser beam. One detector,
located at the laser site, measured light via the inelastic Raman
backscattering process. This is a common method used in atmospheric science for
measuring aerosol optical depth profiles. The other detector, located
approximately 40km distant, viewed the laser beam from the side. This detector
featured a 3.5m2 mirror and measured elastically scattered light in a bistatic
Lidar configuration following the method used at the Pierre Auger cosmic ray
observatory. The goal of this experiment was to assess and improve methods to
measure atmospheric clarity, specifically aerosol optical depth profiles, for
cosmic ray UV fluorescence detectors that use the atmosphere as a giant
calorimeter. The experiment collected data from September 2010 to July 2011
under varying conditions of aerosol loading. We describe the instruments and
techniques and compare the aerosol optical depth profiles measured by the Raman
and bistatic Lidar detectors.Comment: 34 pages, 16 figure
CLASH: New Multiple-Images Constraining the Inner Mass Profile of MACS J1206.2-0847
We present a strong-lensing analysis of the galaxy cluster MACS J1206.2-0847
(=0.44) using UV, Optical, and IR, HST/ACS/WFC3 data taken as part of the
CLASH multi-cycle treasury program, with VLT/VIMOS spectroscopy for some of the
multiply-lensed arcs. The CLASH observations, combined with our mass-model,
allow us to identify 47 new multiply-lensed images of 12 distant sources. These
images, along with the previously known arc, span the redshift range 1\la
z\la5.5, and thus enable us to derive a detailed mass distribution and to
accurately constrain, for the first time, the inner mass-profile of this
cluster. We find an inner profile slope of (in the range [1\arcsec, 53\arcsec], or 5\la r \la300 kpc), as
commonly found for relaxed and well-concentrated clusters. Using the many
systems uncovered here we derive credible critical curves and Einstein radii
for different source redshifts. For a source at , the critical
curve encloses a large area with an effective Einstein radius of
\theta_{E}=28\pm3\arcsec, and a projected mass of . From the current understanding of structure formation in
concordance cosmology, these values are relatively high for clusters at
, so that detailed studies of the inner mass distribution of clusters
such as MACS J1206.2-0847 can provide stringent tests of the CDM
paradigm.Comment: 7 pages, 1 table, 4 figures; submitted to ApJ Letters; V3: minor
correction
Boundary lubrication properties of materials with expansive freezing
We have performed molecular dynamics simulations of solid-solid contacts
lubricated by a model fluid displaying many of the properties of water,
particularly its expansive freezing. Near the region where expansive freezing
occurs, the lubricating film remains fluid, and the friction force decreases
linearly as the shear velocity is reduced. No sign of stick-slip motion is
observed even at the lowest velocities. We give a simple interpretation of
these results, and suggest that in general good boundary lubrication properties
will be found in the family of materials with expansive freezing.Comment: Version to appear in Phys. Rev. Let
CLASH: A Census of Magnified Star-Forming Galaxies at z ~ 6-8
We utilize 16 band Hubble Space Telescope (HST) observations of 18 lensing
clusters obtained as part of the Cluster Lensing And Supernova survey with
Hubble (CLASH) Multi-Cycle Treasury program to search for galaxies.
We report the discovery of 204, 45, and 13 Lyman-break galaxy candidates at
, , and , respectively, identified from purely
photometric redshift selections. This large sample, representing nearly an
order of magnitude increase in the number of magnified star-forming galaxies at
presented to date, is unique in that we have observations in four
WFC3/UVIS UV, seven ACS/WFC optical, and all five WFC3/IR broadband filters,
which enable very accurate photometric redshift selections. We construct
detailed lensing models for 17 of the 18 clusters to estimate object
magnifications and to identify two new multiply lensed
candidates. The median magnifications over the 17 clusters are 4, 4, and 5 for
the , , and samples, respectively, over an average
area of 4.5 arcmin per cluster. We compare our observed number counts with
expectations based on convolving "blank" field UV luminosity functions through
our cluster lens models and find rough agreement down to mag, where we
begin to suffer significant incompleteness. In all three redshift bins, we find
a higher number density at brighter observed magnitudes than the field
predictions, empirically demonstrating for the first time the enhanced
efficiency of lensing clusters over field surveys. Our number counts also are
in general agreement with the lensed expectations from the cluster models,
especially at , where we have the best statistics.Comment: Accepted for publication in the Astrophysical Journal, 25 pages, 13
figures, 7 table
CLASH: Photometric redshifts with 16 HST bands in galaxy cluster fields
The Cluster Lensing And Supernovae survey with Hubble (CLASH) is an Hubble
Space Telescope (HST) Multi-Cycle Treasury program observing 25 massive galaxy
clusters. CLASH observations are carried out in 16 bands from UV to NIR to
derive accurate and reliable estimates of photometric redshifts. We present the
CLASH photometric redshifts and study the photometric redshift accuracy of the
arcs in more detail for the case of MACS1206.2-0847. We use the publicly
available Le Phare and BPZ photometric redshift codes on 17 CLASH galaxy
clusters. Using Le Phare code for objects with StoN>=10, we reach a precision
of 3%(1+z) for the strong lensing arcs, which is reduced to 2.4%(1+z) after
removing outliers. For galaxies in the cluster field the corresponding values
are 4%(1+z) and 3%(1+z). Using mock galaxy catalogues, we show that 3%(1+z)
precision is what one would expect from the CLASH photometry when taking into
account extinction from dust, emission lines and the finite range of SEDs
included in the photo-z template library. We study photo-z results for
different aperture photometry and find that the SExtractor isophotal photometry
works best. Le Phare and BPZ give similar photo-z results for the strong
lensing arcs as well as galaxies of the cluster field. Results are improved
when optimizing the photometric aperture shape showing an optimal aperture size
around 1" radius giving results which are equivalent to isophotal photometry.
Tailored photometry of the arcs improve the photo-z results.Comment: Accepted in A&A on nov 201
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