1,354 research outputs found
Dusty star forming galaxies at high redshift
The global star formation rate in high redshift galaxies, based on optical
surveys, shows a strong peak at a redshift of z=1.5, which implies that we have
already seen most of the formation. High redshift galaxies may, however, emit
most of their energy at submillimeter wavelengths if they contain substantial
amounts of dust. The dust would absorb the starlight and reradiate it as
far-infrared light, which would be redshifted to the submillimeter range. Here
we report a deep survey of two blank regions of sky performed at submillimeter
wavelengths (450 and 850-micron). If the sources we detect in the 850-micron
band are powered by star formation, then each must be converting more than 100
solar masses of gas per year into stars, which is larger than the maximum star
formation rates inferred for most optically-selected galaxies. The total amount
of high redshift star formation is essentially fixed by the level of background
light, but where the peak occurs in redshift for the submillimeter is not yet
established. However, the background light contribution from only the sources
detected at 850-micron is already comparable to that from the
optically-selected sources. Establishing the main epoch of star formation will
therefore require a combination of optical and submillimeter studies.Comment: 10 pages + 2 Postscript figures, under embargo at Natur
Dynamics of orientational ordering in fluid membranes
We study the dynamics of orientational phase ordering in fluid membranes.
Through numerical simulation we find an unusually slow coarsening of
topological texture, which is limited by subdiffusive propagation of membrane
curvature. The growth of the orientational correlation length obeys a
power law with in the late stage. We also discuss
defect profiles and correlation patterns in terms of long-range interaction
mediated by curvature elasticity.Comment: 5 pages, 3 figures (1 in color); Eq.(9) correcte
Different regulation of limb development by p63 transcript variants
The apical ectodermal ridge (AER), located at the distal end of each limb bud, is a key signaling center which controls outgrowth and patterning of the proximal-distal axis of the limb through secretion of various molecules. Fibroblast growth factors (FGFs), particularly Fgf8 and Fgf4, are representative molecules produced by AER cells, and essential to maintain the AER and cell proliferation in the underlying mesenchyme, meanwhile Jag2-Notch pathway negatively regulates the AER and limb development. p63, a transcription factor of the p53 family, is expressed in the AER and indispensable for limb formation. However, the underlying mechanisms and specific roles of p63 variants are unknown. Here, we quantified the expression of p63 variants in mouse limbs from embryonic day (E) 10.5 to E12.5, and found that DeltaNp63gamma was strongly expressed in limbs at all stages, while TAp63gamma expression was rapidly increased in the later stages. Fluorescence-activated cell sorting analysis of limb bud cells from reporter mouse embryos at E11.5 revealed that all variants were abundantly expressed in AER cells, and their expression was very low in mesenchymal cells. We then generated AER-specific p63 knockout mice by mating mice with a null and a flox allele of p63, and Msx2-Cre mice (Msx2-Cre;p63Delta/fl). Msx2-Cre;p63Delta/fl neonates showed limb malformation that was more obvious in distal elements. Expression of various AER-related genes was decreased in Msx2-Cre;p63Delta/fl limb buds and embryoid bodies formed by p63-knockdown induced pluripotent stem cells. Promoter analyses and chromatin immunoprecipitation assays demonstrated Fgf8 and Fgf4 as transcriptional targets of DeltaNp63gamma, and Jag2 as that of TAp63gamma. Furthermore, TAp63gamma overexpression exacerbated the phenotype of Msx2-Cre;p63Delta/fl mice. These data indicate that DeltaNp63 and TAp63 control limb development through transcriptional regulation of different target molecules with different roles in the AER. Our findings contribute to further understanding of the molecular network of limb development
LRG J0239-0134: A Ring Galaxy or a Pair of Superbubbles at z=1 ?
The unusual morphology of LRG J02390134 at =1.062 has been interpreted
as a ring galaxy. Here we propose an alternative idea that the ring-like
morphology is attributed to a pair of superbubbles driven by the intense
starburst in the central region of this galaxy. Supporting evidence for a
superbubble model is; 1) the poststarburst nature in the central body suggests
that a burst of supernova explosions could occur at least yr ago,
2) the dark lane seen in the central body suggests that we observe this object
from a nearly edge-on view, and, 3) the ring-like morphology is not
inconsistent with an idea that it is a pair of superbubbles. All these pieces
of evidence for the superbubble model seem circumstantial. However, if this is
the case, this galaxy provides an important example of the superwind activity
at high redshift.Comment: 5 pages (3 ps files are included) [emulateapj]. The Astrophysical
Journal (Letters), in pres
Magnetotunneling spectroscopy of mesoscopic correlations in two-dimensional electron systems
An approach to experimentally exploring electronic correlation functions in
mesoscopic regimes is proposed. The idea is to monitor the mesoscopic
fluctuations of a tunneling current flowing between the two layers of a
semiconductor double-quantum-well structure. From the dependence of these
fluctuations on external parameters, such as in-plane or perpendicular magnetic
fields, external bias voltages, etc., the temporal and spatial dependence of
various prominent correlation functions of mesoscopic physics can be
determined. Due to the absence of spatially localized external probes, the
method provides a way to explore the interplay of interaction and localization
effects in two-dimensional systems within a relatively unperturbed environment.
We describe the theoretical background of the approach and quantitatively
discuss the behavior of the current fluctuations in diffusive and ergodic
regimes. The influence of both various interaction mechanisms and localization
effects on the current is discussed. Finally a proposal is made on how, at
least in principle, the method may be used to experimentally determine the
relevant critical exponents of localization-delocalization transitions.Comment: 15 pages, 3 figures include
Chiral Symmetry Restoration at Finite Temperature and Chemical Potential in the Improved Ladder Approximation
The chiral symmetry of QCD is studied at finite temperature and chemical
potential using the Schwinger-Dyson equation in the improved ladder
approximation. We calculate three order parameters; the vacuum expectation
value of the quark bilinear operator, the pion decay constant and the quark
mass gap. We have a second order phase transition at the temperature
MeV along the zero chemical potential line, and a first order phase transition
at the chemical potential MeV along the zero temperature line. We
also calculate the critical exponents of the three order parameters.Comment: 16 pages + 10 uuencoded eps figures, LaTe
Symmetrized mean-field description of magnetic instabilities in k-(BEDT-TTF)_2Cu[N(CN)]_2 Y salts
We present a novel and convenient mean-field method, and apply it to study
the metallic/antiferromagnetic interface of k-(BEDT-TTF)_2Cu[N(CN)]_2 Y organic
superconductors (BEDT_TTF is bis-ethylen-dithio-tetrathiafulvalene, Y=Cl, Br).
The method, which fully exploits the crystal symmetry, allows one to obtain the
mean-field solution of the 2D Hubbard model for very large lattices, up to
6x10^5 sites, yielding a reliable description of the phase boundary in a wide
region of the parameter space. The metal/antiferromagnet transtion appears to
be second order, except for a narrow region of the parameter space, where the
transition is very sharp and possibly first order. The cohexistence of metallic
and antiferromagnetic properties is only observed for the transient state in
the case of smooth second order transitions. The relevance of the present
resaults to the complex experimental behavior of centrosymmetric k-phase
BEDT-TTF salts is discussed.Comment: 9 pages in PS format, 7 figures (included in PS), 1 tabl
Parametric Conductance Correlation for Irregularly Shaped Quantum Dots
We propose the autocorrelator of conductance peak heights as a signature of
the underlying chaotic dynamics in quantum dots in the Coulomb blockade regime.
This correlation function is directly accessible to experiments and its decay
width contains interesting information about the underlying electron dynamics.
Analytical results are derived in the framework of random matrix theory in the
regime of broken time-reversal symmetry. The final expression, upon rescaling,
becomes independent of the details of the system. For the situation when the
external parameter is a variable magnetic field, the system-dependent,
nonuniversal field scaling factor is obtained by a semiclassical approach. The
validity of our findings is confirmed by a comparison with results of an exact
numerical diagonalization of the conformal billiard threaded by a magnetic flux
line.Comment: Minor corrections added to the text and references (36 pages RevTeX
3, epsf, 10 figure
Friedel phases and phases of transmission amplitudes in quantum scattering systems
We illustrate the relation between the scattering phase appearing in the
Friedel sum rule and the phase of the transmission amplitude for quantum
scatterers connected to two one-dimensional leads. Transmission zero points
cause abrupt phase changes of the phase of the transmission amplitude.
In contrast the Friedel phase is a continuous function of energy. We
investigate these scattering phases for simple scattering problems and
illustrate the behavior of these models by following the path of the
transmission amplitude in the complex plane as a function of energy. We verify
the Friedel sum rule for these models by direct calculation of the scattering
phases and by direct calculation of the density of states.Comment: 12 pages, 12 figure
Mesoscopic Fano Effect in a Quantum Dot Embedded in an Aharonov-Bohm Ring
The Fano effect, which occurs through the quantum-mechanical cooperation
between resonance and interference, can be observed in electron transport
through a hybrid system of a quantum dot and an Aharonov-Bohm ring. While a
clear correlation appears between the height of the Coulomb peak and the real
asymmetric parameter for the corresponding Fano lineshape, we need to
introduce a complex to describe the variation of the lineshape by the
magnetic and electrostatic fields. The present analysis demonstrates that the
Fano effect with complex asymmetric parameters provides a good probe to detect
a quantum-mechanical phase of traversing electrons.Comment: REVTEX, 9 pages including 8 figure
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