248 research outputs found
78 Pseudomonas aeruginosa cupA encoded fimbria expression is regulated by a GGDEF and EAL domain dependent modulation of the intracellular level of cyclic diguanylate
Thermopower and magnetotransport properties of Bi100âxSbx topological insulator thin films prepared by flash evaporation
We have measured the temperature dependence of resistance R(T), thermopower S(T), magnetoresistance (MR) and the Hall effect (HE) of Bi80Sb20, Bi85Sb15 and Bi90Sb10 topological insulator thin films. Samples were prepared by sequential flash-evaporation at room temperature and annealing at T = 350 K. The R(T) of the three investigated samples show metallic-like behavior at temperatures less than T = 75 K, while at higher temperatures, R(T) curves show a semiconducting-like behavior. The thermopower S(T) of the three investigated samples is negative in the entire temperature range measured in this work, with a linear behavior from 5 K up to â100 K. The magnetoresistance of all samples is positive with a small temperature dependence. The highest MR(B = 7 T) was observed in Bi85Sb15 with a â600% and â125% change at 5 K and 300 K, respectively. Clear evidence of weak antilocalization contribution to the MR was observed only in sample Bi85Sb15 at temperatures T < 75 K. Quantum oscillations in the MR originating from the Fermi surface, which has a clear two-dimensional character, were observed in sample Bi85Sb15 up to â21 K. Carrier mobility information of sample Bi85Sb15 was extracted from low field HE data, showing a remarkably high value of ÎŒ â 2.8 Ă 104 cm2/Vs at 5 K, with a small decrease for increasing temperature.Fil: Osmic, E.. Universitat Leipzig. Felix Bloch Institut Fur Festkorperphysik.; AlemaniaFil: Barzola Quiquia, Jose Luis. Universitat Leipzig. Felix Bloch Institut Fur Festkorperphysik.; AlemaniaFil: Böhlmann, W.. Universitat Leipzig. Felix Bloch Institut Fur Festkorperphysik.; AlemaniaFil: Bercoff, Paula Gabriela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de FĂsica Enrique Gaviola. Universidad Nacional de CĂłrdoba. Instituto de FĂsica Enrique Gaviola; ArgentinaFil: Venosta, Lisandro Francisco. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Instituto de FĂsica Enrique Gaviola. Universidad Nacional de CĂłrdoba. Instituto de FĂsica Enrique Gaviola; ArgentinaFil: HĂ€ussler, P.. Chemnitz University Of Technology; Alemani
Tracking the effects of rigidity percolation down to the liquid state: relaxational dynamics of binary chalcogen melts
4 pags. ; 4 figs.The stochastic dynamics of binary liquids with formula AxB1-x, x=0â0.4 is investigated by neutron spin-echo spectroscopy. These compositions comprise samples of varying chemical connectivity, ranging from twofold-coordinated liquid Se to higher average coordinated As2S3. The parameters giving the temperature dependence of the relaxation patterns show a quasilinear dependence on the average coordination number. The results thus extend the validity of the rigidity concept into the normal liquid state and emphasize the role played by the fine details of atomic bonding on the dynamics at 10 psâ1 ns scales.Work supported in part by Grant No. MAT2007-65711-C-4-01, MEC, Spain.Peer reviewe
Classification of one-dimensional quasilattices into mutual local-derivability classes
One-dimensional quasilattices are classified into mutual local-derivability
(MLD) classes on the basis of geometrical and number-theoretical
considerations. Most quasilattices are ternary, and there exist an infinite
number of MLD classes. Every MLD class has a finite number of quasilattices
with inflation symmetries. We can choose one of them as the representative of
the MLD class, and other members are given as decorations of the
representative. Several MLD classes of particular importance are listed. The
symmetry-preserving decorations rules are investigated extensively.Comment: 42 pages, latex, 5 eps figures, Published in JPS
Antiferromagnetic interlayer exchange coupling across an amorphous metallic spacer layer
By means of magneto-optical Kerr effect we observe for the first time
antiferromagnetic coupling between ferromagnetic layers across an amorphous
metallic spacer layer. Biquadratic coupling occurs at the transition from a
ferromagnetically to an antiferromagnetically coupled region. Scanning
tunneling microscopy images of all involved layers are used to extract
thickness fluctuations and to verify the amorphous state of the spacer. The
observed antiferromagnetic coupling behavior is explained by RKKY interaction
taking into account the amorphous structure of the spacer material.Comment: Typset using RevTex, 4 pages with 4 figures (.eps
Non-equilibrium electronic transport and interaction in short metallic nanobridges
We have observed interaction effects in the differential conductance of
short, disordered metal bridges in a well-controlled non-equilibrium situation,
where the distribution function has a double Fermi step. A logarithmic scaling
law is found both for the temperature and for the voltage dependence of in
all samples. The absence of magnetic field dependence and the low
dimensionality of our samples allow us to distinguish between several possible
interaction effects, proposed recently in nanoscopic samples. The universal
scaling curve is explained quantitatively by the theory of electron-electron
interaction in diffusive metals, adapted to the present case, where the sample
size is smaller than the thermal diffusion length.Comment: Published version, 6 Pages, 6 postscript figures, 1 tabl
The evolutionary sequence of sub-mm galaxies: from diffuse discs to massive compact ellipticals?
The population of compact massive galaxies observed at z > 1 are
hypothesised, both observationally and in simulations, to be merger remnants of
gas-rich disc galaxies. To probe such a scenario we analyse a sample of 12
gas-rich and active star forming sub-mm galaxies (SMGs) at 1.8 < z < 3. We
present a structural and size measurement analysis for all of these objects
using very deep ACS and NICMOS imaging in the GOODS-North field. Our analysis
reveals a heterogeneous mix of morphologies and sizes. We find that four
galaxies (33% \pm 17%) show clear signs of mergers or interactions, which we
classify as early-stage mergers. The remaining galaxies are divided into two
categories: five of them (42% \pm 18%) are diffuse and regular disc-like
objects, while three (25% \pm 14%) are very compact, spheroidal systems. We
argue that these three categories can be accommodated into an evolutionary
sequence, showing the transformation from isolated, gas-rich discs with typical
sizes of 2-3 kpc, into compact (< 1 kpc) galaxies through violent major merger
events, compatible with the scenario depicted by theoretical models. Our
findings that some SMGs are already dense and compact provides strong support
to the idea that SMGs are the precursors of the compact, massive galaxies found
at slightly lower redshift.Comment: Accepted for publication in MNRAS. 8 pages, 4 figures and 1 tabl
The Multiwavelength Survey by Yale-Chile (MUSYC): Deep Medium-Band optical imaging and high quality 32-band photometric redshifts in the ECDF-S
We present deep optical 18-medium-band photometry from the Subaru telescope
over the ~30' x 30' Extended Chandra Deep Field-South (ECDF-S), as part of the
Multiwavelength Survey by Yale-Chile (MUSYC). This field has a wealth of
ground- and space-based ancillary data, and contains the GOODS-South field and
the Hubble Ultra Deep Field. We combine the Subaru imaging with existing
UBVRIzJHK and Spitzer IRAC images to create a uniform catalog. Detecting
sources in the MUSYC BVR image we find ~40,000 galaxies with R_AB<25.3, the
median 5 sigma limit of the 18 medium bands. Photometric redshifts are
determined using the EAZY code and compared to ~2000 spectroscopic redshifts in
this field. The medium band filters provide very accurate redshifts for the
(bright) subset of galaxies with spectroscopic redshifts, particularly at 0.1 <
z 3.5. For 0.1 < z < 1.2, we find a 1 sigma scatter in \Delta
z/(1+z) of 0.007, similar to results obtained with a similar filter set in the
COSMOS field. As a demonstration of the data quality, we show that the red
sequence and blue cloud can be cleanly identified in rest-frame color-magnitude
diagrams at 0.1 < z < 1.2. We find that ~20% of the red-sequence-galaxies show
evidence of dust-emission at longer rest-frame wavelengths. The reduced images,
photometric catalog, and photometric redshifts are provided through the public
MUSYC website.Comment: 19 pages, 14 image
CANDELS Observations of the Structural Properties and Evolution of Galaxies in a Cluster at z=1.62
We discuss the structural and morphological properties of galaxies in a
z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope
Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic
Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology
relation: galaxies with colors of quiescent stellar populations generally have
morphologies consistent with spheroids, and galaxies with colors consistent
with ongoing star formation have disk-like and irregular morphologies. The size
distribution of the quiescent cluster galaxies shows a deficit of compact (<
1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a
result the cluster quiescent galaxies have larger average effective sizes
compared to field galaxies at fixed mass at greater than 90% significance.
Combined with data from the literature, the size evolution of quiescent cluster
galaxies is relatively slow from z~1.6 to the present, growing as
(1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that
physical processes associated with the denser cluster region seems to have
caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower
subsequent growth at z<1.6 compared to galaxies in the lower density field. The
quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower
redshift samples at fixed mass, and their surface-brightness profiles suggest
that they contain extended stellar disks. We argue the cluster galaxies require
dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk
material and to match the relations for ellipticity, stellar mass, size, and
color of early-type galaxies in z<1 clusters.Comment: Accepted for publication in ApJ. 14 pages in emulateapj format.
Replacement includes improvements from referee report, and updates and
additions to reference
The Effects of an AGN on Host Galaxy Colour and Morphology Measurements
We assess the effects of simulated active galactic nuclei (AGNs) on the
colour and morphology measurements of their host galaxies. To test the
morphology measurements, we select a sample of galaxies not known to host AGNs
and add a series of point sources scaled to represent specified fractions of
the observed V band light detected from the resulting systems; we then compare
morphology measurements of the simulated systems to measurements of the
original galaxies. AGN contributions >20 per cent bias most of the morphology
measurements tested, though the extent of the apparent bias depends on the
morphological characteristics of the original galaxies. We test colour
measurements by adding to non-AGN galaxy spectra a quasar spectrum scaled to
contribute specified fractions of the rest-frame B band light detected from the
resulting systems. A quasar fraction of 5 per cent can move the NUV-r colour of
an elliptical galaxy from the UV-optical red sequence to the green valley, and
20 per cent can move it into the blue cloud. Combining the colour and
morphology results, we find that a galaxy/AGN system with an AGN contribution
>20 per cent may appear bluer and more bulge-dominated than the underlying
galaxy. We conclude that (1) bulge-dominated, E/S0/Sa, and early-type
morphology classifications are accurate for red AGN host galaxies and may be
accurate for blue host galaxies, unless the AGN manifests itself as a
well-defined point source; and (2) although highly unobscured AGNs, such as the
quasar used for our experiments, can significantly bias the measured colours of
AGN host galaxies, it is possible to identify such systems by examining optical
images of the hosts for the presence of a point source and/or measuring the
level of nuclear obscuration.Comment: 18 pages, 19 figures, 1 table. Accepted for publication in MNRA
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