148 research outputs found
Light Element Evolution and Cosmic Ray Energetics
Using cosmic-ray energetics as a discriminator, we investigate evolutionary
models of LiBeB. We employ a Monte Carlo code which incorporates the delayed
mixing into the ISM both of the synthesized Fe, due to its incorporation into
high velocity dust grains, and of the cosmic-ray produced LiBeB, due to the
transport of the cosmic rays. We normalize the LiBeB production to the integral
energy imparted to cosmic rays per supernova. Models in which the cosmic rays
are accelerated mainly out of the average ISM significantly under predict the
measured Be abundance of the early Galaxy, the increase in [O/Fe] with
decreasing [Fe/H] notwithstanding. We suggest that this increase could be due
to the delayed mixing of the Fe. But, if the cosmic-ray metals are accelerated
out of supernova ejecta enriched superbubbles, the measured Be abundances are
consistent with a cosmic-ray acceleration efficiency that is in very good
agreement with the current epoch data. We also find that neither the above
cosmic-ray origin models nor a model employing low energy cosmic rays
originating from the supernovae of only very massive progenitors can account
for the Li data at values of [Fe/H] below 2.Comment: latex 19 pages, 2 tables, 10 eps figures, uses aastex.cls natbib.sty
Submitted to the Astrophysical Journa
Do Airports green cities? : Von der Airport City zur nachhaltigen Region ; Flughafenstrategien und Regionalentwicklung
Multivariate pattern recognition approaches have become a prominent tool in neuroimaging data analysis. These methods enable the classification of groups of participants (e.g. controls and patients) on the basis of subtly different patterns across the whole brain. This study demonstrates that these methods can be used, in combination with automated morphometric analysis of structural MRI, to determine with great accuracy whether a single subject has been engaged in regular mental training or not. The proposed approach allowed us to identify with 94.87% accuracy (p<0.001) if a given participant is a regular meditator (from a sample of 19 regular meditators and 20 non-meditators). Neuroimaging has been a relevant tool for diagnosing neurological and psychiatric impairments. This study may suggest a novel step forward: the emergence of a new field in brain imaging applications, in which participants could be identified based on their mental experience
Extraordinary Late-Time Infrared Emission of Type IIn Supernovae
Near-Infrared (NIR) observations are presented for five Type IIn supernovae
(SN 1995N, SN 1997ab, SN 1998S, SN 1999Z, and SN 1999el) that exhibit strong
infrared excesses at late times (t >= 100 d). H- and K-band emission from these
objects is dominated by a continuum that rises toward longer wavelengths. The
data are interpreted as thermal emission from dust, probably situated in a
pre-existing circumstellar nebula. The IR luminosities implied by single
temperature blackbody fits are quite large,> 10^(41 - 42) erg s^-1, and the
emission evolves slowly, lasting for years after maximum light. For SN 1995N,
the integrated energy release via IR dust emission was 0.5 -- 1 * 10^50 erg. A
number of dust heating scenarios are considered, the most likely being an
infrared echo poweredby X-ray and UV emissions from the shock interaction with
a dense circumstellar medium.Comment: 14 Pages, 3 Figures, Accecpted for publication in The Astrophysical
Journa
The origin of dust in galaxies revisited: the mechanism determining dust content
The origin of cosmic dust is a fundamental issue in planetary science. This
paper revisits the origin of dust in galaxies, in particular, in the Milky Way,
by using a chemical evolution model of a galaxy composed of stars, interstellar
medium, metals (elements heavier than helium), and dust. We start from a review
of time-evolutionary equations of the four components, and then, we present
simple recipes for the stellar remnant mass and yields of metal and dust based
on models of stellar nucleosynthesis and dust formation. After calibrating some
model parameters with the data from the solar neighborhood, we have confirmed a
shortage of the stellar dust production rate relative to the dust destruction
rate by supernovae if the destruction efficiency suggested by theoretical works
is correct. If the dust mass growth by material accretion in molecular clouds
is active, the observed dust amount in the solar neighborhood is reproduced. We
present a clear analytic explanation of the mechanism for determining dust
content in galaxies after the activation of accretion growth: a balance between
accretion growth and supernova destruction. Thus, the dust content is
independent of the uncertainty of the stellar dust yield after the growth
activation. The timing of the activation is determined by a critical metal mass
fraction which depends on the growth and destruction efficiencies. The solar
system formation seems to have occurred well after the activation and plenty of
dust would have existed in the proto-solar nebula.Comment: 12 pages, 11 figure
A Yoga and Compassion Meditation Program Reduces Stress in Familial Caregivers of Alzheimer's Disease Patients
Familial caregivers of patients with Alzheimer's disease exhibit reduced quality of life and increased stress levels. the aim of this study was to investigate the effects of an 8-week yoga and compassion meditation program on the perceived stress, anxiety, depression, and salivary cortisol levels in familial caregivers. A total of 46 volunteers were randomly assigned to participate in a stress-reduction program for a 2-month period (yoga and compassion meditation program-YCMP group) (n = 25) or an untreated group for the same period of time (control group) (n = 21). the levels of stress, anxiety, depression, and morning salivary cortisol of the participants were measured before and after intervention. the groups were initially homogeneous; however, after intervention, the groups diverged significantly. the YCMP group exhibited a reduction of the stress (P < 0.05), anxiety (P < 0.000001), and depression (P < 0.00001) levels, as well as a reduction in the concentration of salivary cortisol (P < 0.05). Our study suggests that an 8-week yoga and compassion meditation program may offer an effective intervention for reducing perceived stress, anxiety, depression, and salivary cortisol in familial caregivers.Associacao Fundo de Incentivo a Pesquisa-AFIPUniversidade Federal de São Paulo UNIFESP, Dept Psychobiol, BR-04024002 São Paulo, BrazilInst Appana Mind Desenvolvimento Humano, Departiment Res, BR-05436020 São Paulo, BrazilHosp Israelita Albert Einstein, Inst Cerebro, BR-05601901 São Paulo, BrazilUniversidade Federal de São Paulo UNIFESP, Div Endocrinol, Dept Med, BR-04023062 São Paulo, BrazilUniversidade Federal de São Paulo UNIFESP, Dept Psychobiol, BR-04024002 São Paulo, BrazilUniversidade Federal de São Paulo UNIFESP, Div Endocrinol, Dept Med, BR-04023062 São Paulo, BrazilWeb of Scienc
AKARI and BLAST Observations of the Cassiopeia A Supernova Remnant and Surrounding Interstellar Medium
We use new large area far infrared maps ranging from 65 - 500 microns
obtained with the AKARI and the Balloon-borne Large Aperture Submillimeter
Telescope (BLAST) missions to characterize the dust emission toward the
Cassiopeia A supernova remnant (SNR). Using the AKARI high resolution data we
find a new "tepid" dust grain population at a temperature of ~35K and with an
estimated mass of 0.06 solar masses. This component is confined to the central
area of the SNR and may represent newly-formed dust in the unshocked supernova
ejecta. While the mass of tepid dust that we measure is insufficient by itself
to account for the dust observed at high redshift, it does constitute an
additional dust population to contribute to those previously reported. We fit
our maps at 65, 90, 140, 250, 350, and 500 microns to obtain maps of the column
density and temperature of "cold" dust (near 16 K) distributed throughout the
region. The large column density of cold dust associated with clouds seen in
molecular emission extends continuously from the surrounding interstellar
medium to project on the SNR, where the foreground component of the clouds is
also detectable through optical, X-ray, and molecular extinction. At the
resolution available here, there is no morphological signature to isolate any
cold dust associated only with the SNR from this confusing interstellar
emission. Our fit also recovers the previously detected "hot" dust in the
remnant, with characteristic temperature 100 K.Comment: Accepted for publication in the Astrophysical Journal. Maps and
related data are available at http://blastexperiment.info
Late Spectral Evolution of SN 1987A: I. Temperature and Ionization
The temperature and ionization of SN 1987A is modeled between 200 and 2000
days in its nebular phase, using a time-dependent model. We include all
important elements, as well as the primary composition zones in the supernova.
The energy input is provided by radioactive decay of Co-56, Co-57, and Ti-44.
The thermalization of the resulting gamma-rays and positrons is calculated by
solving the Spencer-Fano equation. Both the ionization and the individual level
populations are calculated time-dependently. Adiabatic cooling is included in
the energy equation. Charge transfer is important for determining the
ionization and is included with available and estimated rates. Full, multilevel
atoms are used for the observationally important ions. As input models to the
calculations we use explosion models for SN 1987A calculated by Woosley et al
and Nomoto et al. The most important result in this paper refers to the
evolution of the temperature and ionization of the various abundance zones. The
metal-rich core undergoes a thermal instability, often referred to as the
IR-catastrophe, at 600 - 1000 days. The hydrogen-rich zones evolve
adiabatically after 500 - 800 days, while in the helium region both adiabatic
cooling and line cooling are of equal importance after ~1000 days. Freeze-out
of the recombination is important in the hydrogen and helium zones. Concomitant
with the IR-catastrophe, the bulk of the emission shifts from optical and
near-IR lines to the mid- and far-IR. After the IR-catastrophe, the cooling is
mainly due to far-IR lines and adiabatic expansion. Dust cooling is likely to
be important in the zones where dust forms. We find that the dust condensation
temperatures occur later than ~500 days in the oxygen-rich zones, and the most
favorable zone for dust condensation is the iron core.Comment: 53 pages, including 10 figures; ApJ (Main Journal); scheduled for
April 1, 1998, Vol. 49
Optical properties of dust
http://arxiv.org/abs/0808.4123Except in a few cases cosmic dust can be studied in situ or in terrestrial laboratories, essentially all of our information concerning the nature of cosmic dust depends upon its interaction with electromagnetic radiation. This chapter presents the theoretical basis for describing the optical properties of dust -- how it absorbs and scatters starlight and reradiates the absorbed energy at longer wavelengths.Partial support by a Chandra Theory program
and HST Theory Programs is gratefully acknowledged
Evolution of a Signaling Nexus Constrained by Protein Interfaces and Conformational States
Heterotrimeric G proteins act as the physical nexus between numerous receptors that respond to extracellular signals and proteins that drive the cytoplasmic response. The Gα subunit of the G protein, in particular, is highly constrained due to its many interactions with proteins that control or react to its conformational state. Various organisms contain differing sets of Gα-interacting proteins, clearly indicating that shifts in sequence and associated Gα functionality were acquired over time. These numerous interactions constrained much of Gα evolution; yet Gα has diversified, through poorly understood processes, into several functionally specialized classes, each with a unique set of interacting proteins. Applying a synthetic sequence-based approach to mammalian Gα subunits, we established a set of seventy-five evolutionarily important class-distinctive residues, sites where a single Gα class is differentiated from the three other classes. We tested the hypothesis that shifts at these sites are important for class-specific functionality. Importantly, we mapped known and well-studied class-specific functionalities from all four mammalian classes to sixteen of our class-distinctive sites, validating the hypothesis. Our results show how unique functionality can evolve through the recruitment of residues that were ancestrally functional. We also studied acquisition of functionalities by following these evolutionarily important sites in non-mammalian organisms. Our results suggest that many class-distinctive sites were established early on in eukaryotic diversification and were critical for the establishment of new Gα classes, whereas others arose in punctuated bursts throughout metazoan evolution. These Gα class-distinctive residues are rational targets for future structural and functional studies
- …