3,387 research outputs found
Nonspherical and Spherical Characterization of Ice in Hurricane Erin for Wideband Passive Microwave Comparisons
In order to better understand the characteristics of frozen cloud particles in hurricane systems, computed brightness temperatures were compared with radiometric observations of Hurricane Erin (2001) from the NASA ER-2 aircraft. The focus was oil the frozen particle microphysics and the high frequencies (2 85 GHz) that are particularly sensitive to frozen particles. Frozen particles in hurricanes are an indicator of increasing hurricane intensity. In fact "hot towers" associated with increasing hurricane intensity are composed of frozen ice cloud particles. (They are called hot towers because their column of air is warmer than the surrounding air temperature, but above about 5-7 km to the tops of the towers at 15-19 km, the cloud particles are frozen.) This work showed that indeed, one can model information about cloud ice particle characteristics and indicated that nonspherical ice shapes, instead of spherical particles, provided the best match to the observations. Overall, this work shows that while non-spherical particles show promise, selecting and modeling a proper ice particle parameterization can be difficult and additional in situ measurements are needed to define and validate appropriate parameterizations. This work is important for developing Global Precipitation Measurement (GPM) mission satellite algorithms for the retrieval of ice characteristics both above the melting layer, as in Hurricane Erin, and for ice particles that reach the surface as falling snow
Total Angular Momentum Waves for Scalar, Vector, and Tensor Fields
Most calculations in cosmological perturbation theorydecompose those
perturbations into plane waves (Fourier modes). However, for some calculations,
particularly those involving observations performed on a spherical sky, a
decomposition into waves of fixed total angular momentum (TAM) may be more
appropriate. Here we introduce TAM waves, solutions of fixed total angular
momentum to the Helmholtz equation, for three-dimensional scalar, vector, and
tensor fields. The vector TAM waves of given total angular momentum can be
decomposed further into a set of three basis functions of fixed orbital angular
momentum (OAM), a set of fixed helicity, or a basis consisting of a
longitudinal (L) and two transverse (E and B) TAM waves. The symmetric
traceless rank-2 tensor TAM waves can be similarly decomposed into a basis of
fixed OAM or fixed helicity, or a basis that consists of a longitudinal (L),
two vector (VE and VB, of opposite parity), and two tensor (TE and TB, of
opposite parity) waves. We show how all of the vector and tensor TAM waves can
be obtained by applying derivative operators to scalar TAM waves. This operator
approach then allows one to decompose a vector field into three covariant
scalar fields for the L, E, and B components and symmetric-traceless-tensor
fields into five covariant scalar fields for the L, VE, VB, TE, and TB
components. We provide projections of the vector and tensor TAM waves onto
vector and tensor spherical harmonics. We provide calculational detail to
facilitate the assimilation of this formalism into cosmological calculations.
As an example, we calculate the power spectra of the deflection angle for
gravitational lensing by density perturbations and by gravitational waves. We
comment on an alternative approach to CMB fluctuations based on TAM waves. Our
work may have applications elsewhere in field theory and in general relativity.Comment: 32 pages, Published version in PR
Excitation of stellar oscillations by gravitational waves: hydrodynamic model and numerical results for the Sun
Starting from a general relativistic framework a hydrodynamic formalism is
derived that yields the mean-square amplitudes and rms surface velocities of
normal modes of non-relativistic stars excited by arbitrary gravitational wave
(GW) radiation. In particular, stationary GW fields are considered and the
resulting formulae are evaluated for two general types of GW radiation:
radiation from a particular astrophysical source (e.g., a binary system) and a
stochastic background of gravitational waves (SBGW). Expected sources and
signal strengths for both types of GW radiation are reviewed and discussed.
Numerical results for the Sun show that low-order quadrupolar g modes are
excited more strongly than p modes by orders of magnitude. Maximal rms surface
velocities in the case of excitation by astrophysical sources are found to be v
{\le} 10^(-8) mm/s, assuming GW strain amplitudes of h {\le} 10^(-20). It is
shown that current models for an SBGW produced by cosmic strings, with Omega_GW
~ 10^(-8)-10^(-5) in the frequency range of solar g modes, are able to produce
maximal solar g-mode rms surface velocities of 10^(-5)-10^(-3) mm/s. This
result lies close to or within the amplitude range of 10^(-3)-1 mm/s expected
from excitation by turbulent convection, which is currently considered to be
responsible for stellar g-mode excitation. It is concluded that studying g-mode
observations of stars other than the Sun, in which excitation by GWs could be
even more effective due to different stellar structures, might provide a new
method to either detect GWs or to deduce a significant direct upper limit on an
SBGW at intermediate frequencies between the pulsar bound and the bounds from
interferometric detectors on Earth.Comment: 20 pages, 5 figure
Quantitation of selective autophagic protein aggregate degradation in vitro and in vivo using luciferase reporters
The analysis of autophagy in cells and tissue has principally been performed via qualitative measures. These assays identify autophagosomes or measure the conversion of LC3I to LC3II. However, qualitative assays fail to quantitate the degradation of an autophagic substrate and therefore only indirectly measure an intact autophagic system. “Autophagic flux” can be measured using long-lived proteins that are degraded via autophagy. We developed a quantifiable luciferase reporter assay that measures the degradation of a long-lived polyglutamine protein aggregate, polyQ80-luciferase. Using this reporter, the induction of autophagy via starvation or rapamycin in cells preferentially decreases polyQ80-luciferase when compared with a non-aggregating polyQ19-luciferase after four hours of treatment. This response was both time- and concentration-dependent, prevented by autophagy inhibitors and absent in ATG5 knockout cells. We adapted this assay to living animals by electroporating polyQ19-luciferase and polyQ80-luciferase expression constructs into the right and left tibialis anterior (TA) muscles of mice, respectively. The change in the ratio of polyQ80-luciferase to polyQ19-luciferase signal before and after autophagic stimulation or inhibition was quantified via in vivo bioluminescent imaging. Following two days of starvation or treatment with intraperitoneal rapamycin, there was a ~35% reduction in the ratio of polyQ80:polyQ19-luciferase activity, consistent with the selective autophagic degradation of polyQ80 protein. This autophagic response in skeletal muscle in vivo was abrogated by co-treatment with chloroquine and in ATG16L1 hypomorphic mice. Our study demonstrates a method to quantify the autophagic flux of an expanded polyglutamine via luciferase reporters in vitro and in vivo
Instability and network effects in innovative markets
We consider a network of interacting agents and we model the process of
choice on the adoption of a given innovative product by means of
statistical-mechanics tools. The modelization allows us to focus on the effects
of direct interactions among agents in establishing the success or failure of
the product itself. Mimicking real systems, the whole population is divided
into two sub-communities called, respectively, Innovators and Followers, where
the former are assumed to display more influence power. We study in detail and
via numerical simulations on a random graph two different scenarios:
no-feedback interaction, where innovators are cohesive and not sensitively
affected by the remaining population, and feedback interaction, where the
influence of followers on innovators is non negligible. The outcomes are
markedly different: in the former case, which corresponds to the creation of a
niche in the market, Innovators are able to drive and polarize the whole
market. In the latter case the behavior of the market cannot be definitely
predicted and become unstable. In both cases we highlight the emergence of
collective phenomena and we show how the final outcome, in terms of the number
of buyers, is affected by the concentration of innovators and by the
interaction strengths among agents.Comment: 20 pages, 6 figures. 7th workshop on "Dynamic Models in Economics and
Finance" - MDEF2012 (COST Action IS1104), Urbino (2012
Molecular environment and thermal X-ray spectroscopy of the semicircular young composite supernova remnant 3C 396
We have investigated the molecular environment of the semicircular composite
supernova remnant (SNR) 3C396 and performed a Chandra spatially resolved
thermal X-ray spectroscopic study of this young SNR. With our CO millimeter
observations, we find that the molecular clouds (MCs) at V(LSR)~84km/s can
better explain the multiwavelength properties of the remnant than the
V(LSR)=67-72km/s MCs that are suggested by Lee et al. (2009). At around 84km/s,
the western boundary of the SNR is perfectly confined by the western molecular
wall. The CO emission fades out from west to east, indicating that the eastern
region is of low gas density. In particular, an intruding finger/pillar-like
MC, which may be shocked at the tip, can well explain the X-ray and radio
enhancement in the southwest and some infrared filaments there. The SNR-MC
interaction is also favored by the relatively elevated 12CO J=2-1/J=1-0 line
ratios in the southwestern "pillar tip" and the molecular patch on the
northwestern boundary. The redshifted 12CO (J=1-0 and J=2-1) wings (86-90km/s)
of an eastern 81km/s molecular patch may be the kinematic evidence for shock-MC
interaction. We suggest that the 69km/s MCs are in the foreground based on HI
self-absorption while the 84km/s MCs at a distance of 6.2 kpc (the tangent
point) are in physical contact with SNR 3C396. The X-ray spectral analysis
suggests an SNR age of ~3kyr. The metal enrichment of the X-ray emitting gas in
the north and south implies a 13-15Msun B1-B2 progenitor star.Comment: 17 amulateapj pages, including 11 figures and 3 tables. Accepted to
ApJ. Version 2: minor correction
The evolution of circular loops of a cosmic string with periodic tension
In this paper the equation of circular loops of cosmic string with periodic
tension is investigated in the Minkowski spacetime and Robertson-Walker
universe respectively. We find that the cosmic string loops possessing this
kind of time-varying tension will evolve to oscillate instead of collapsing to
form a black hole if their initial radii are not small enough.Comment: 9 pages, 3 figure
Fully nonlinear and exact perturbations of the Friedmann world model
In 1988 Bardeen has suggested a pragmatic formulation of cosmological
perturbation theory which is powerful in practice to employ various fundamental
gauge conditions easily depending on the character of the problem. The
perturbation equations are presented without fixing the temporal gauge
condition and are arranged so that one can easily impose fundamental gauge
conditions by simply setting one of the perturbation variables in the equations
equal to zero. In this way one can use the gauge degrees of freedom as an
advantage in handling problems. Except for the synchronous gauge condition, all
the other fundamental gauge conditions completely fix the gauge mode, and
consequently, each variable in such a gauge has a unique gauge invariant
counterpart, so that we can identify the variable as the gauge-invariant one.
Here, we extend Bardeen's linear formulation to fully nonlinear order in
perturbations, with the gauge advantage kept intact. Derived equations are
exact, and from these we can easily expand to higher order perturbations in a
gauge-ready form. We consider scalar- and vector-type perturbations of an ideal
fluid in a flat background; we also present the multiple components of ideal
fluid case. As applications we present fully nonlinear density and velocity
perturbation equations in Einstein's gravity in the zero-pressure medium,
vorticity generation from pure scalar-type perturbation, and fluid formulation
of a minimally coupled scalar field, all in the comoving gauge. We also present
the equation of gravitational waves generated from pure scalar- and vector-type
perturbations.Comment: 23 pages, to appear in MNRA
Analysis of tissue transglutaminase function in the migration of swiss 3T3 fibroblasts - the active-state conformation of the enzyme does not affect cell motility but is important for its secretion
Increasing evidence suggests that tissue transglutaminase (tTGase; type II) is externalized from cells, where it may play a key role in cell attachment and spreading and in the stabilization of the extracellular matrix (ECM) through protein cross-linking. However, the relationship between these different functions and the enzyme’s mechanism of secretion is not fully understood. We have investigated the role of tTGase in cell migration using two stably transfected fibroblast cell lines in which expression of tTGase in its active and inactive (C277S mutant) states is inducible through the tetracycline-regulated system. Cells overexpressing both forms of tTGase showed increased cell attachment and decreased cell migration on fibronectin. Both forms of the enzyme could be detected on the cell surface, but only the clone overexpressing catalytically active tTGase deposited the enzyme into the ECM and cell growth medium. Cells overexpressing the inactive form of tTGase did not deposit the enzyme into the ECM or secrete it into the cell culture medium. Similar results were obtained when cells were transfected with tTGase mutated at Tyr274 (Y274A), the proposed site for the cis- ,trans peptide bond, suggesting that tTGase activity and/or its tertiary conformation dependent on this bond may be essential for its externalization mechanism. These results indicate that tTGase regulates cell motility as a novel cell-surface adhesion protein rather than as a matrix-cross-linking enzyme. They also provide further important insights into the mechanism of externalization of the enzyme into the extracellular matrix
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