9,160 research outputs found
Environmental manipulations generate bidirectional shifts in both behavior and gene regulation in a crossbred mouse model of extremes in trait anxiety
Although gene-environment interactions are known to significantly influence psychopathology related disease states, only few animal models cover both the genetic background and environmental manipulations. Therefore, we have taken advantage of the bidirectionally inbred high (HAB) and low (LAB) anxiety-related behavior mouse lines to generate HAB x LAB F1 hybrids that intrinsically carry both lines' genetic characteristics, and subsequently raised them in three different environments standard, enriched (EE) and chronic mild stress (CMS). Assessing genetic correlates of trait anxiety, we focused on two genes already known to play a role in HAB vs. LAB mice, corticotropin releasing hormone receptor type 1 (Crhr1) and high mobility group nucleosomal binding domain 3 (Hmgn3). While EE F1 mice showed decreased anxiety related and increased explorative behaviors compared to controls, CMS sparked effects in the opposite direction. However, environmental treatments affected the expression of the two genes in distinct ways. Thus, while expression ratios of Hmgn3 between the HAB- and LAB-specific alleles remained equal, total expression resembled the one observed in HAB vs. LAB mice, i.e., decreased after EE and increased after CMS treatment. On the other hand, while total expression of Crhr1 remained unchanged between the groups, the relative expression of HAB- and LAB-specific alleles showed a clear effect following the environmental modifications. Thus, the environmentally driven bidirectional shift of trait anxiety in this F1 model strongly correlated with Hmgn3 expression, irrespective of allele-specific expression patterns that retained the proportions of basic differential HAB vs. LAB expression, making this gene a match for environment-induced modifications. An involvement of Crhr1 in the bidirectional behavioral shift could, however, rather be due to different effects of the HAB- and LAB specific alleles described here. Both candidate genes therefore deserve attention in the complex regulation of anxiety-related phenotypes including environment-mediated effects
X-ray properties of the microquasar GRS 1915+105 during a variability class transition
We present a detailed X-ray study of the microquasar GRS 1915+105 during a
variability class transition observed in 2000 June with the PPCs of the Indian
X-ray Astronomy Experiment. We supplement this observation with data from the
RXTE archives. The source made a transition from a steady low-hard state to a
regular oscillatory behaviour in the light curve known as bursts or class `rho'
(Belloni et al. 2000) between 2000 May 11 and 17 and reverted back to the
low-hard state on 2000 June 27. A gradual change in the burst recurrence time
from about 75 s to about 40 s was observed which then increased to about 120 s
during the ~ 40 days of class `rho'. The regular bursts disappeared from the
X-ray light curves and the class transition was observed to occur within 1.5
hours on 2000 June 27 with the PPCs. A correlation is found between the
observed QPO frequency at 5-8 Hz in the quiescent phase and the average X-ray
intensity of the source during the class `rho'. We notice a strong similarity
between the properties of the source during the class `rho' and those during
the oscillatory phase of the observations of class `alpha'. From the timing and
spectral analysis, it is found that the observed properties of the source over
tens of days during the class `rho' are identical to those over a time scale of
a few hundreds of seconds in the class `alpha'. Examining the light curves from
the beginning of the RXTE/PCA and RXTE/ASM observations, it is found that the
change of state from radio-quiet low-hard state to high state occurs through
the X-ray classes `rho' and `alpha' which appear together during the state
transition. It is further inferred that the source switches from low-hard state
to the class `rho' through the intermediate class `alpha'.Comment: 10 pages with 9 figures, LaTex. To be appeared in MNRA
Total cross sections for neutron-nucleus scattering
Systematics of neutron scattering cross sections on various materials for
neutron energies up to several hundred MeV are important for ADSS applications.
Ramsauer model is well known and widely applied to understand systematics of
neutron nucleus total cross sections. In this work, we examined the role of
nuclear effective radius parameter (r) on Ramsauer model fits of neutron
total cross sections. We performed Ramsauer model global analysis of the
experimental neutron total cross sections reported by W. P. Abfalterer, F. B.
Bateman, {\it et. al.,}, from 20MeV to 550MeV for nuclei ranging from Be to U .
The global fit functions which can fit total cross section data over periodic
table are provided along with the required global set of parameters. The global
fits predict within deviation to data, showing the scope for
improvement. It has been observed that a finer adjustment of r parameter
alone can give very good Ramsauer model description of neutron total scattering
data within deviation. The required r values for Ramsauer model
fits are shown as a function of nuclear mass number and an empirical formula is
suggested for r values as a function of mass number. In optical model
approach for neutron scattering, we have modified the real part of
Koning-Deleroche potentails to fit the neutron total cross sections using SCAT2
code. The modified potentails have a different energy dependence beyond 200MeV
of neutron energy and fit the total cross sections from Al to Pb.Comment: 9 pages, 20figures, Poster number ND-1457, ND2010 Conference in Kore
Fatigue damage growth mechanisms in continuous fiber reinforced titanium matrix composites
The role of fiber/matrix interface strength, residual thermal stresses, and fiber and matrix properties on fatigue damage accumulation in continuous fiber metal matrix composites (MMC) is discussed. Results from titanium matrix silicon carbide fiber composites is the primary topic of discussion. Results were obtained from both notched and unnotched specimens at room and elevated temperatures. The stress in the 0 deg fibers was identified as the controlling factor in fatigue life. Fatigue of the notched specimens indicated that cracks can grow in the matrix materials without breaking fibers
On the origin of the various types of radio emission in GRS 1915+105
We investigate the association between the radio ``plateau'' states and the
large superluminal flares in GRS 1915+105 and propose a qualitative scenario to
explain this association. We identify several candidate superluminal flare
events from available monitoring data on this source and analyze the
contemporaneous RXTE pointed observations. We detect a strong correlation
between the average X-ray flux during the ``plateau'' state and the total
energy emitted in radio during the subsequent radio flare. We find that the
sequence of events is similar for all large radio flares with a fast rise and
exponential decay morphology. Based on these results, we propose a qualitative
scenario in which the separating ejecta during the superluminal flares are
observed due to the interaction of the matter blob ejected during the X-ray
soft dips, with the steady jet already established during the ``plateau''
state. This picture can explain all types of radio emission observed from this
source in terms of its X-ray emission characteristics.Comment: Corrected typo in the author names, contents unchanged, accepted in
Ap
Fast Transition between High-soft and Low-soft States in GRS 1915+105: Evidence for a Critically Viscous Accretion Flow
We present the results of a detailed analysis of RXTE observations of class
which show an unusual state transition between high-soft and low-soft
states in the microquasar GRS 1915+105. Out of about 600 pointed RXTE
observations, the source was found to exhibit such state transition only on 16
occasions. An examination of the RXTE/ASM data in conjunction with the pointed
observations reveals that these events appeared as a series of quasi-regular
dips in two stretches of long duration (about 20 days during each occasions)
when hard X-ray and radio flux were very low. The X-ray light curve and
color-color diagram of the source during these observations are found to be
different from any reported so far. The duration of these dips is found to be
of the order of a few tens of seconds with a repetition time of a few hundred
seconds. The transition between these dips and non-dips which differ in
intensity by a factor of ~ 3.5, is observed to be very fast (~ a few seconds).
It is observed that the low-frequency narrow QPOs are absent in the power
density spectrum (PDS) of the dip and non-dip regions of class and the
PDS is a power law in 0.1 - 10 Hz frequency range. There is a remarkable
similarity in the spectral and timing properties of the source during the dip
and non-dip regions in these set of observations. These properties of the
source are distinctly different from those seen in the observations of other
classes. This indicates that the basic accretion disk structure during both dip
and non-dip regions of class is similar, but differ only in intensity.
To explain these observations, we invoke a model in which the viscosity is very
close to critical viscosity and the shock wave is weak or absent.Comment: Replaced with correct figures, Jour. of Astrophysics and Astronomy
(accepted
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