14,389 research outputs found
Seismic analysis of 70 Ophiuchi A: A new quantity proposed
The basic intent of this paper is to model 70 Ophiuchi A using the latest
asteroseismic observations as complementary constraints and to determine the
fundamental parameters of the star. Additionally, we propose a new quantity to
lift the degeneracy between the initial chemical composition and stellar age.
Using the Yale stellar evolution code (YREC7), we construct a series of stellar
evolutionary tracks for the mass range = 0.85 -- 0.93 with
different composition (0.26 -- 0.30) and (0.017 -- 0.023).
Along these tracks, we select a grid of stellar model candidates that fall
within the error box in the HR diagram to calculate the theoretical
frequencies, the large- and small- frequency separations using the Guenther's
stellar pulsation code. Following the asymptotic formula of stellar -modes,
we define a quantity which is correlated with stellar age. Also, we
test it by theoretical adiabatic frequencies of many models. Many detailed
models of 70 Ophiuchi A have been listed in Table 3. By combining all
non-asteroseismic observations available for 70 Ophiuchi A with these
seismological data, we think that Model 60, Model 125 and Model 126, listed in
Table 3, are the optimum models presently. Meanwhile, we predict that the
radius of this star is about 0.860 -- 0.865 and the age is about
6.8 -- 7.0 Gyr with mass 0.89 -- 0.90 . Additionally, we prove that
the new quantity can be a useful indicator of stellar age.Comment: 23 pages, 5 figures, accepted by New Astronom
Asteroseismic study of solar-like stars: A method of estimating stellar age
Asteroseismology, as a tool to use the indirect information contained in
stellar oscillations to probe the stellar interiors, is an active field of
research presently. Stellar age, as a fundamental property of star apart from
its mass, is most difficult to estimate. In addition, the estimating of stellar
age can provide the chance to study the time evolution of astronomical
phenomena. In our poster, we summarize our previous work and further present a
method to determine age of low-mass main-sequence star.Comment: 2 pages, 1 figures, submitted to IAUS25
Where thereâs âwillingnessâ thereâs a way: barriers and facilitators to maternal, newborn and child health data sharing by the private health sector in Uttar Pradesh, India
In India and Uttar Pradesh (UP), the private health sector plays an important role in health care services, including institutional deliveries, but there is limited information on the availability of maternal, newborn and child health (MNCH) data that private facilities maintain and share with the public health information system. Sharing data could help the public sector plan their resources more efficiently.
Aim of the study: To explore current practices of MNCH data availability and sharing/reporting by private health facilities and the barriers and facilitators to data sharing
The Complete One-Loop Dilation Operator of N=2 SuperConformal QCD
We evaluate the full planar one-loop dilation operator of N=2 SuperConformal
QCD, the SU(N_c) super Yang-Mills theory with N_f = 2 N_c fundamental
hypermultiplets, in the flavor-singlet sector. Remarkably, the spin-chain
Hamiltonian turns out to be completely fixed by superconformal symmetry, as in
N=4 SYM. We present a more general calculation, for the superconformal quiver
theory with SU(N_c)X SU(N_c) gauge group, which interpolates between N=2 SCQCD
and the Z_2 orbifold of N=4 SYM; here symmetry fixes the Hamiltonian up to a
single parameter, corresponding to the ratio of the two marginal gauge
couplings.Comment: v2: typo corrected, cosmetic changes. JHEP versio
Is the cosmic UV background fluctuating at redshift z ~ 6 ?
We study the Gunn-Peterson effect of the photo-ionized intergalactic
medium(IGM) in the redshift range 5< z <6.4 using semi-analytic simulations
based on the lognormal model. Assuming a rapidly evolved and spatially uniform
ionizing background, the simulation can produce all the observed abnormal
statistical features near redshift z ~ 6. They include: 1) rapidly increase of
absorption depths; 2) large scatter in the optical depths; 3) long-tailed
distributions of transmitted flux and 4) long dark gaps in spectra. These
abnormal features are mainly due to rare events, which correspond to the
long-tailed probability distribution of the IGM density field, and therefore,
they may not imply significantly spatial fluctuations in the UV ionizing
background at z ~ 6.Comment: 12 pages, 4 figs, accepted by ApJ
Structural network heterogeneities and network dynamics: a possible dynamical mechanism for hippocampal memory reactivation
The hippocampus has the capacity for reactivating recently acquired memories
[1-3] and it is hypothesized that one of the functions of sleep reactivation is
the facilitation of consolidation of novel memory traces [4-11]. The dynamic
and network processes underlying such a reactivation remain, however, unknown.
We show that such a reactivation characterized by local, self-sustained
activity of a network region may be an inherent property of the recurrent
excitatory-inhibitory network with a heterogeneous structure. The entry into
the reactivation phase is mediated through a physiologically feasible
regulation of global excitability and external input sources, while the
reactivated component of the network is formed through induced network
heterogeneities during learning. We show that structural changes needed for
robust reactivation of a given network region are well within known
physiological parameters [12,13].Comment: 16 pages, 5 figure
The impact of drought on wheat leaf cuticle properties
BACKGROUND: The plant cuticle is the outermost layer covering aerial tissues and is composed of cutin and waxes. The cuticle plays an important role in protection from environmental stresses and glaucousness, the bluish-white colouration of plant surfaces associated with cuticular waxes, has been suggested as a contributing factor in crop drought tolerance. However, the cuticle structure and composition is complex and it is not clear which aspects are important in determining a role in drought tolerance. Therefore, we analysed residual transpiration rates, cuticle structure and epicuticular wax composition under well-watered conditions and drought in five Australian bread wheat genotypes, Kukri, Excalibur, Drysdale, RAC875 and Gladius, with contrasting glaucousness and drought tolerance. RESULTS: Significant differences were detected in residual transpiration rates between non-glaucous and drought-sensitive Kukri and four glaucous and drought-tolerant lines. No simple correlation was found between residual transpiration rates and the level of glaucousness among glaucous lines. Modest differences in the thickness of cuticle existed between the examined genotypes, while drought significantly increased thickness in Drysdale and RAC875. Wax composition analyses showed various amounts of C31 Ă-diketone among genotypes and increases in the content of alkanes under drought in all examined wheat lines. CONCLUSIONS: The results provide new insights into the relationship between drought stress and the properties and structure of the wheat leaf cuticle. In particular, the data highlight the importance of the cuticleâs biochemical makeup, rather than a simple correlation with glaucousness or stomatal density, for water loss under limited water conditions.Huihui Bi, Nataliya Kovalchuk, Peter Langridge, Penny J. Tricker, Sergiy Lopato, and Nikolai Borisju
Electrically induced tunable cohesion in granular systems
Experimental observations of confined granular materials in the presence of
an electric field that induces cohesive forces are reported. The angle of
repose is found to increase with the cohesive force. A theoretical model for
the stability of a granular heap, including both the effect of the sidewalls
and cohesion is proposed. A good agreement between this model and the
experimental results is found. The steady-state flow angle is practically
unaffected by the electric field except for high field strengths and low flow
rates.Comment: accepted for publication in "Journal of Statistical Mechanics: Theory
and Experiment
A truthful online mechanism for resource allocation in fog computing
Fog computing is a promising Internet of Things (IoT) paradigm in which data is processed near its source. Here, efficient resource allocation mechanisms are needed to assign limited fog resources to competing IoT tasks. To this end, we consider two challenges: (1) near-optimal resource allocation in a fog computing system; (2) incentivising self-interested fog users to report their tasks truthfully. To address these challenges, we develop a truthful online resource allocation mechanism called flexible online greedy. The key idea is that the mechanism only commits a certain amount of computational resources to a task when it arrives. However, when and where to allocate resources stays flexible until the completion of the task. We compare our mechanism to four benchmarks and show that it outperforms all of them in terms of social welfare by up to 10% and achieves a social welfare of about 90% of the offline optimal upper bound
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