1,925 research outputs found
Dynamic Labyrinthine Pattern in an Active Liquid Film
We report the generation of a dynamic labyrinthine pattern in an active
alcohol film. A dynamic labyrinthine pattern is formed along the contact line
of air/pentanol/aqueous three phases. The contact line shows a clear
time-dependent change with regard to both perimeter and area of a domain. An
autocorrelation analysis of time-development of the dynamics of the perimeter
and area revealed a strong geometric correlation between neighboring patterns.
The pattern showed autoregressive behavior. The behavior of the dynamic pattern
is strikingly different from those of stationary labyrinthine patterns. The
essential aspects of the observed dynamic pattern are reproduced by a
diffusion-controlled geometric model
Cosmic Mach Number as a Function of Overdensity and Galaxy Age
We carry out an extensive study of the cosmic Mach number (\mach) on scales
of R=5, 10 and 20h^-1Mpc using an LCDM hydrodynamical simulation. We
particularly put emphasis on the environmental dependence of \mach on
overdensity, galaxy mass, and galaxy age. We start by discussing the difference
in the resulting \mach according to different definitions of \mach and
different methods of calculation. The simulated Mach numbers are slightly lower
than the linear theory predictions even when a non-linear power spectrum was
used in the calculation, reflecting the non-linear evolution in the simulation.
We find that the observed \mach is higher than the simulated mean by more than
2-standard deviations, which suggests either that the Local Group is in a
relatively low-density region or that the true value of \Omega_m is ~ 0.2,
significantly lower than the simulated value of 0.37. We show from our
simulation that the Mach number is a weakly decreasing function of overdensity.
We also investigate the correlations between galaxy age, overdensity and \mach
for two different samples of galaxies --- DWARFs and GIANTs. Older systems
cluster in higher density regions with lower \mach, while younger ones tend to
reside in lower density regions with larger \mach, as expected from the
hierarchical structure formation scenario. However, for DWARFs, the correlation
is weakened by the fact that some of the oldest DWARFs are left over in
low-density regions during the structure formation history. For giant systems,
one expects blue-selected samples to have higher \mach than red-selected ones.
We briefly comment on the effect of the warm dark matter on the expected Mach
number.Comment: 43 pages, including 15 figures. Accepted version in ApJ. Included
correlation function of different samples of galaxies, and the cumulative
number fraction distribution as a fcn. of overdensity. Reorganized figures
and added some reference
Hyperfine Populations Prior to Muon Capture
It is shown that the 1S level hyperfine populations prior to muon capture
will be statistical when either target or beam are unpolarised independent of
the atomic level at which the hyperfine interaction becomes appreciable. This
assertion holds in the absence of magnetic transitions during the cascade and
is true because of minimal polarisation after atomic capture and selective
feeding during the cascade.Comment: (revtex, 6 preprint pages, no figures
Luminosity Distribution of Gamma-Ray Burst Host Galaxies at redshift z=1 in Cosmological Smoothed Particle Hydrodynamic Simulations: Implications for the Metallicity Dependence of GRBs
We study the relationship between the metallicity of gamma-ray burst (GRB)
progenitors and the probability distribution function (PDF) of GRB host
galaxies as a function of luminosity using cosmological hydrodynamic
simulations of galaxy formation. We impose a maximum limit to the gas
metallicity in which GRBs can occur, and examine how the predicted luminosity
PDF of GRB host galaxies changes in the simulation. We perform the
Kolmogorov-Smirnov test, and show that the result from our simulation agrees
with the observed luminosity PDF of core-collapse supernovae (SNe) host
galaxies when we assume that the core-collapse SNe trace star formation. When
we assume that GRBs occur only in a low-metallicity environment with Z\lesssim
0.1 \Zsun, GRBs occur in lower luminosity galaxies, and the simulated
luminosity PDF becomes quantitatively consistent with the observed luminosity
PDF. The observational bias against the host galaxies of optically dark GRBs
owing to dust extinction may be another reason for the lower luminosities of
GRB host galaxies, but the observed luminosity PDF of GRB host galaxies cannot
be reproduced solely by the dust bias in our simulation.Comment: 11 pages, 14 figures, minor revisions, one added figure, accepted for
publication in Ap
Role of the amino terminal RHAU-specific motif in the recognition and resolution of guanine quadruplex-RNA by the DEAH-box RNA helicase RHAU
Under physiological conditions, guanine-rich sequences of DNA and RNA can adopt stable and atypical four-stranded helical structures called G-quadruplexes (G4). Such G4 structures have been shown to occur in vivo and to play a role in various processes such as transcription, translation and telomere maintenance. Owing to their high-thermodynamic stability, resolution of G4 structures in vivo requires specialized enzymes. RHAU is a human RNA helicase of the DEAH-box family that exhibits a unique ATP-dependent G4-resolvase activity with a high affinity and specificity for its substrate in vitro. How RHAU recognizes G4-RNAs has not yet been established. Here, we show that the amino-terminal region of RHAU is essential for RHAU to bind G4 structures and further identify within this region the evolutionary conserved RSM (RHAU-specific motif) domain as a major affinity and specificity determinant. G4-resolvase activity and strict RSM dependency are also observed with CG9323, the Drosophila orthologue of RHAU, in the amino terminal region of which the RSM is the only conserved motif. Thus, these results reveal a novel motif in RHAU protein that plays an important role in recognizing and resolving G4-RNA structures, properties unique to RHAU among many known RNA helicase
The DEAH-box RNA helicase RHAU binds an intramolecular RNA G‐quadruplex in TERC and associates with telomerase holoenzyme
Guanine-quadruplexes (G4) consist of non-canonical four-stranded helical arrangements of guanine-rich nucleic acid sequences. The bulky and thermodynamically stable features of G4 structures have been shown in many respects to affect normal nucleic acid metabolism. In vivo conversion of G4 structures to single-stranded nucleic acid requires specialized proteins with G4 destabilizing/unwinding activity. RHAU is a human DEAH-box RNA helicase that exhibits G4-RNA binding and resolving activity. In this study, we employed RIP-chip analysis to identify en masse RNAs associated with RHAU in vivo. Approximately 100 RNAs were found to be associated with RHAU and bioinformatics analysis revealed that the majority contained potential G4-forming sequences. Among the most abundant RNAs selectively enriched with RHAU, we identified the human telomerase RNA template TERC as a true target of RHAU. Remarkably, binding of RHAU to TERC depended on the presence of a stable G4 structure in the 5′-region of TERC, both in vivo and in vitro. RHAU was further found to associate with the telomerase holoenzyme via the 5′-region of TERC. Collectively, these results provide the first evidence that intramolecular G4-RNAs serve as physiologically relevant targets for RHAU. Furthermore, our results suggest the existence of alternatively folded forms of TERC in the fully assembled telomerase holoenyzm
Massive galaxies at redshift 2 in cosmological hydrodynamic simulations
We study the properties of galaxies at z=2 in a Lambda cold dark matter
universe, using two different types of hydrodynamic simulation methods --
Eulerian TVD and smoothed particle hydrodynamics (SPH) -- and a
spectrophotometric analysis in the U_n, G, R filter set. The simulated galaxies
at z=2 satisfy the color-selection criteria proposed by Adelberger et al.
(2004) and Steidel et al. (2004) when we assume Calzetti extinction with
E(B-V)=0.15. We find that the number density of simulated galaxies brighter
than R<25.5 at z=2 is about 1e-2 h^3 Mpc^-3 for E(B-V)=0.15, which is roughly
twice that of the number density found by Erb et al. (2004) for the UV bright
sample. This suggests that roughly half of the massive galaxies with M*>10^{10}
Msun/h at z=2 are UV bright population, and the other half is bright in the
infra-red wavelengths. The most massive galaxies at z=2 have stellar masses >=
10^{11-12} Msun. They typically have been continuously forming stars with a
rate exceeding 30 Msun/yr over a few Gyrs from z=10 to z=2, together with
significant contribution by starbursts reaching up to 1000 Msun/yr which lie on
top of the continuous component. TVD simulations indicate a more sporadic star
formation history than the SPH simulations. Our results do not imply that
hierarchical galaxy formation fails to account for the observed massive
galaxies at z>=1. The global star formation rate density in our simulations
peaks at z>=5, a much higher redshift than predicted by the semianalytic
models. This star formation history suggests early build-up of the stellar mass
density, and predicts that 70 (50, 30)% of the total stellar mass at z=0 had
already been formed by z=1 (2, 3). Upcoming observations by Spitzer and Swift
might help to better constrain the star formation history at high redshift.Comment: 4 pages, Kluwer style files included. To appear in "Starbursts - from
30 Doradus to Lyman break galaxies" (IoA, Cambridge UK, Sep 2004; talk
summary), Astrophysics & Space Science Library, eds. de Grijs R., Gonzalez
Delgado R.M. (Kluwer: Dordrecht
Imaging the cool gas, dust, star formation, and AGN in the first galaxies
When, and how, did the first galaxies and supermassive black holes (SMBH)
form, and how did they reionization the Universe? First galaxy formation and
cosmic reionization are among the last frontiers in studies of cosmic structure
formation. We delineate the detailed astrophysical probes of early galaxy and
SMBH formation afforded by observations at centimeter through submillimeter
wavelengths. These observations include studies of the molecular gas (= the
fuel for star formation in galaxies), atomic fine structure lines (= the
dominant ISM gas coolant), thermal dust continuum emission (= an ideal star
formation rate estimator), and radio continuum emission from star formation and
relativistic jets. High resolution spectroscopic imaging can be used to study
galaxy dynamics and star formation on sub-kpc scales. These cm and mm
observations are the necessary compliment to near-IR observations, which probe
the stars and ionized gas, and X-ray observations, which reveal the AGN.
Together, a suite of revolutionary observatories planned for the next decade
from centimeter to X-ray wavelengths will provide the requisite panchromatic
view of the complex processes involved in the formation of the first generation
of galaxies and SMBHs, and cosmic reionization.Comment: 8 pages total. White paper submitted to the Astro 2010 Decadal Surve
The use of cosmic muons in detecting heterogeneities in large volumes
The muon intensity attenuation method to detect heterogeneities in large
matter volumes is analyzed. Approximate analytical expressions to estimate the
collection time and the signal to noise ratio, are proposed and validated by
Monte Carlo simulations. Important parameters, including point spread function
and coordinate reconstruction uncertainty are also estimated using Monte Carlo
simulations.Comment: 8 pages, 11 figures, submetted to NIM
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