1,651 research outputs found
Stable unidimensional arrays of coherent strained islands
We investigate the equilibrium properties of arrays of coherent strained
islands in heteroepitaxial thin films of bidimensional materials. The model we
use takes into account only three essential ingredients : surface energies,
elastic energies of the film and of the substrate and interaction energies
between islands via the substrate. Using numerical simulations for a simple
Lennard-Jones solid, we can assess the validity of the analytical expressions
used to describe each of these contributions. A simple analytical expression is
obtained for the total energy of the system. Minimizing this energy, we show
that arrays of coherent islands can exist as stable configurations. Even in
this simple approach, the quantitative results turn out to be very sensitive to
some details of the surface energy.Comment: 24 pages, 7 figures. to be published in Surface Scienc
Halo-model Analysis of the Clustering of Photometrically Selected Galaxies from SDSS
We measure the angular 2-point correlation functions of galaxies in a volume
limited, photometrically selected galaxy sample from the fifth data release of
the Sloan Digital Sky Survey. We split the sample both by luminosity and galaxy
type and use a halo-model analysis to find halo-occupation distributions that
can simultaneously model the clustering of all, early-, and late-type galaxies
in a given sample. Our results for the full galaxy sample are generally
consistent with previous results using the SDSS spectroscopic sample, taking
the differences between the median redshifts of the photometric and
spectroscopic samples into account. We find that our early- and late- type
measurements cannot be fit by a model that allows early- and late-type galaxies
to be well-mixed within halos. Instead, we introduce a new model that
segregates early- and late-type galaxies into separate halos to the maximum
allowed extent. We determine that, in all cases, it provides a good fit to our
data and thus provides a new statistical description of the manner in which
early- and late-type galaxies occupy halos.Comment: Accepted to MNRAS 11 pages, 6 figure
Correlation function of quasars in real and redshift space from the Sloan Digital Sky Survey Data Release 7
We analyze the quasar two-point correlation function (2pCF) within the
redshift interval using a sample of 52303 quasars selected from the
recent 7th Data Release of the Sloan Digital Sky Survey. Our approach to 2pCF
uses a concept of locally Lorentz (Fermi) frame for determination of the
distance between objects and permutation method of the random catalogue
generation. Assuming the spatially flat cosmological model with given
, we found that the real-space 2pCF is fitted well with
the power-low model within the distance range Mpc with
the correlation length Mpc and the slope
. The redshift-space 2pCF is approximated with
Mpc and for
Mpc, and Mpc and for
Mpc the parameter
describing the large-scale infall to density inhomogeneities is
with the linear bias that marginally
(within 2) agrees with the linear theory of cosmological perturbations.
We discuss possibilities to obtain a statistical estimate of the random
component of quasars velocities (different from the large-scale infall). We
note rather slight dependence of quasars velocity dispersion upon the 2pCF
parameters in the region Mpc.Comment: 15 pages, 17 figures, online published in MNRAS; final version to
match the published versio
Models for the Clustering of Far-Infrared and Sub-millimetre selected Galaxies
We discuss and compare two alternative models for the two-point angular
correlation function of galaxies detected through the sub-millimetre emission
using the Herschel Space Observatory. The first, now-standard Halo Model, which
represents the angular correlations as arising from one-halo and two-halo
contributions, is flexible but complex and rather unwieldy. The second model is
based on a much simpler approach: we incorporate a fitting function method to
estimate the matter correlation function with approximate model of the bias
inferred from the estimated redshift distribution to find the galaxy angular
correlation function. We find that both models give a good account of the shape
of the correlation functions obtained from published preliminary studies of the
HerMES and H-ATLAS surveys performed using Herschel, and yield consistent
estimates of the minimum halo mass within which the sub-millimetre galaxies
must reside. We note also that both models predict an inflection in the
correlation function at intermediate angular scales, so the presence of the
feature in the measured correlation function does not unambiguously indicate
the presence of intra-halo correlations. The primary barrier to more detailed
interpretation of these clustering measurements lies in the substantial
uncertainty surrounding the redshift distribution of the sources.Comment: 5 pages, 6 figures, 1 table, accepted for publication in MNRA
Applicability and safety of dual-frequency ultrasonic treatment for the transdermal delivery of drugs
Low-frequency ultrasound presents an attractive method for transdermal drug delivery. The controlled, yet non-specific nature of enhancement broadens the range of therapeutics that can be delivered, while minimizing necessary reformulation efforts for differing compounds. Long and inconsistent treatment times, however, have partially limited the attractiveness of this method. Building on recent advances made in this area, the simultaneous use of low- and high-frequency ultrasound is explored in a physiologically relevant experimental setup to enable the translation of this treatment to testing in vivo. Dual-frequency ultrasound, utilizing 20 kHz and 1 MHz wavelengths simultaneously, was found to significantly enhance the size of localized transport regions (LTRs) in both in vitro and in vivo models while decreasing the necessary treatment time compared to 20 kHz alone. Additionally, LTRs generated by treatment with 20 kHz + 1 MHz were found to be more permeable than those generated with 20 kHz alone. This was further corroborated with pore-size estimates utilizing hindered-transport theory, in which the pores in skin treated with 20 kHz + 1 MHz were calculated to be significantly larger than the pores in skin treated with 20 kHz alone. This demonstrates for the first time that LTRs generated with 20 kHz + 1 MHz are also more permeable than those generated with 20 kHz alone, which could broaden the range of therapeutics and doses administered transdermally. With regard to safety, treatment with 20 kHz + 1 MHz both in vitro and in vivo appeared to result in no greater skin disruption than that observed in skin treated with 20 kHz alone, an FDA-approved modality. This study demonstrates that dual-frequency ultrasound is more efficient and effective than single-frequency ultrasound and is well-tolerated in vivo.National Institutes of Health (U.S.) (Grant EB-00351)National Institutes of Health (U.S.) (Grant CA014051
A Consistent Comparison of Bias Models using Observational Data
We investigate five different models for the dark matter halo bias, ie., the
ratio of the fluctuations of mass tracers to those of the underlying mass, by
comparing their cosmological evolution using optical QSO and galaxy bias data
at different redshifts, consistently scaled to the WMAP7 cosmology. Under the
assumption that each halo hosts one extragalactic mass tracer, we use a
minimization procedure to determine the free parameters of the bias
models as well as to statistically quantify their ability to represent the
observational data. Using the Akaike information criterion we find that the
model that represents best the observational data is the Basilakos & Plionis
(2001; 2003) model with the tracer merger extension of Basilakos, Plionis &
Ragone-Figueroa (2008) model. The only other statistically equivalent model, as
indicated by the same criterion, is the Tinker et al. (2010) model. Finally, we
find an average, over the different models, dark matter halo mass that hosts
optical QSOs of: ,
while the corresponding value for optical galaxies is: .Comment: MNRAS in press, 12 pages, 6 color figures, 4 table
Fibroblast growth factor receptor 3 activation plays a causative role in urothelial cancer pathogenesis in cooperation with Pten loss in mice
Although somatic mutations and overexpression of the tyrosine kinase fibroblast growth factor receptor 3 (FGFR3) are strongly associated with bladder cancer, evidence for their functional involvement in the pathogenesis remains elusive. Previously we showed that activation of Fgfr3 alone is not sufficient to initiate urothelial tumourigenesis in mice. Here we hypothesize that cooperating mutations are required for Fgfr3-dependent tumourigenesis in the urothelium and analyse a mouse model in which an inhibitor of Pi3k–Akt signalling, Pten, is deleted in concert with Fgfr3 activation (UroIICreFgfr3+/K644EPtenflox/flox). Two main phenotypical characteristics were observed in the urothelium: increased urothelial thickness and abnormal cellular histopathology, including vacuolization, condensed cellular appearance, enlargement of cells and nuclei, and loss of polarity. These changes were not observed when either mutation was present individually. Expression patterns of known urothelial proteins indicated the abnormal cellular differentiation. Furthermore, quantitative analysis showed that Fgfr3 and Pten mutations cooperatively caused cellular enlargement, while Pten contributed to increased cell proliferation. Finally, FGFR3 overexpression was analysed along the level of phosphorylated mTOR in 66 T1 urothelial tumours in tissue microarray, which supported the occurrence of functional association of these two signalling pathways in urothelial pathogenesis. Taken together, this study provides evidence supporting a functional role of FGFR3 in the process of pathogenesis in urothelial neoplasms. Given the wide availability of inhibitors specific to FGF signalling pathways, our model may open the avenue for FGFR3-targeted translation in urothelial disease. Copyright © 2014 Pathological Society of Great Britain and Ireland
A Cross-Correlation Analysis of Mg II Absorption Line Systems and Luminous Red Galaxies from the SDSS DR5
We analyze the cross-correlation of 2,705 unambiguously intervening Mg II
(2796,2803A) quasar absorption line systems with 1,495,604 luminous red
galaxies (LRGs) from the Fifth Data Release of the Sloan Digital Sky Survey
within the redshift range 0.36<=z<=0.8. We confirm with high precision a
previously reported weak anti-correlation of equivalent width and dark matter
halo mass, measuring the average masses to be log M_h(M_[solar]h^-1)=11.29
[+0.36,-0.62] and log M_h(M_[solar]h^-1)=12.70 [+0.53,-1.16] for systems with
W[2796A]>=1.4A and 0.8A<=W[2796A]<1.4A, respectively. Additionally, we
investigate the significance of a number of potential sources of bias inherent
in absorber-LRG cross-correlation measurements, including absorber velocity
distributions and the weak lensing of background quasars, which we determine is
capable of producing a 20-30% bias in angular cross-correlation measurements on
scales less than 2'. We measure the Mg II - LRG cross-correlation for 719
absorption systems with v<60,000 km s^-1 in the quasar rest frame and find that
these associated absorbers typically reside in dark matter haloes that are
~10-100 times more massive than those hosting unambiguously intervening Mg II
absorbers. Furthermore, we find evidence for evolution of the redshift number
density, dN/dz, with 2-sigma significance for the strongest (W>2.0A) absorbers
in the DR5 sample. This width-dependent dN/dz evolution does not significantly
affect the recovered equivalent width-halo mass anti-correlation and adds to
existing evidence that the strongest Mg II absorption systems are correlated
with an evolving population of field galaxies at z<0.8, while the non-evolving
dN/dz of the weakest absorbers more closely resembles that of the LRG
population.Comment: 21 pages, 19 figures; Published in Astrophysical Journa
Galaxy clustering and projected density profiles as traced by satellites in photometric surveys: Methodology and luminosity dependence
We develop a new method which measures the projected density distribution
w_p(r_p)n of photometric galaxies surrounding a set of
spectroscopically-identified galaxies, and simultaneously the projected
correlation function w_p(r_p) between the two populations. In this method we
are able to divide the photometric galaxies into subsamples in luminosity
intervals when redshift information is unavailable, enabling us to measure
w_p(r_p)n and w_p(r_p) as a function of not only the luminosity of the
spectroscopic galaxy, but also that of the photometric galaxy. Extensive tests
show that our method can measure w_p(r_p) in a statistically unbiased way. The
accuracy of the measurement depends on the validity of the assumption in the
method that the foreground/background galaxies are randomly distributed and
thus uncorrelated with those galaxies of interest. Therefore, our method can be
applied to the cases where foreground/background galaxies are distributed in
large volumes, which is usually valid in real observations. We applied our
method to data from SDSS including a sample of 10^5 LRGs at z~0.4 and a sample
of about half a million galaxies at z~0.1, both of which are cross-correlated
with a deep photometric sample drawn from the SDSS. On large scales, the
relative bias factor of galaxies measured from w_p(r_p) at z~0.4 depends on
luminosity in a manner similar to what is found at z~0.1, which are usually
probed by autocorrelations of spectroscopic samples. On scales smaller than a
few Mpc and at both z~0.4 and z~0.1, the photometric galaxies of different
luminosities exhibit similar density profiles around spectroscopic galaxies at
fixed luminosity and redshift. This provides clear support for the assumption
commonly-adopted in HOD models that satellite galaxies of different
luminosities are distributed in a similar way, following the dark matter
distribution within their host halos.Comment: 38 pages, 12 figures, published in Ap
Modeling the cosmological co-evolution of supermassive black holes and galaxies: II. The clustering of quasars and their dark environment
We use semi-analytic modeling on top of the Millennium simulation to study
the joint formation of galaxies and their embedded supermassive black holes.
Our goal is to test scenarios in which black hole accretion and quasar
activity are triggered by galaxy mergers, and to constrain different models for
the lightcurves associated with individual quasar events. In the present work
we focus on studying the spatial distribution of simulated quasars. At all
luminosities, we find that the simulated quasar two-point correlation function
is fit well by a single power-law in the range 0.5 < r < 20 h^{-1} Mpc, but its
normalization is a strong function of redshift. When we select only quasars
with luminosities within the range typically accessible by today's quasar
surveys, their clustering strength depends only weakly on luminosity, in
agreement with observations. This holds independently of the assumed lightcurve
model, since bright quasars are black holes accreting close to the Eddington
limit, and are hosted by dark matter haloes with a narrow mass range of a few
10^12 h^{-1} M_sun. Therefore the clustering of bright quasars cannot be used
to disentangle lightcurve models, but such a discrimination would become
possible if the observational samples can be pushed to significantly fainter
limits.
Overall, our clustering results for the simulated quasar population agree
rather well with observations, lending support to the conjecture that galaxy
mergers could be the main physical process responsible for triggering black
hole accretion and quasar activity.Comment: 17 pages, 16 figures, to be published on MNRA
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