3,249 research outputs found
Environmental and genetic influences on neurocognitive development: the importance of multiple methodologies and time-dependent intervention
Genetic mutations and environmental factors dynamically influence gene expression and developmental trajectories at the neural, cognitive, and behavioral levels. The examples in this article cover different periods of neurocognitive developmentâearly childhood, adolescence, and adulthoodâand focus on studies in which researchers have used a variety of methodologies to illustrate the early effects of socioeconomic status and stress on brain function, as well as how allelic differences explain why some individuals respond to intervention and others do not. These studies highlight how similar behaviors can be driven by different underlying neural processes and show how a neurocomputational model of early development can account for neurodevelopmental syndromes, such as autism spectrum disorders, with novel implications for intervention. Finally, these studies illustrate the importance of the timing of environmental and genetic factors on development, consistent with our view that phenotypes are emergent, not predetermined
A rare case of bilateral high origin of the testicular artery with variations in the course and branches.
In general, testicular artery (TA) usually arises from the antero-lateral part of the abdominal aorta below the origin of the renal arteries at second lumbar vertebrae level. Very rarely variations in the origin of the testicular arteries are observed. We here report a rare case of bilateral unusual origin and course of the testicular artery. On the right side, testicular artery aroused from the aorta about 0.5cm above the origin of the renal artery and gave off inferior suprarenal artery. In contrast, left testicular artery springs from the pre-hilar branch of the left renal artery, 2cm before reaching the hilum of kidney. On both sides, testicular arteries descended in front of the hilar structures of the kidney. Since, the origin and course of the testicular artery is important to consider during surgical and diagnostic interventions, knowledge of such variation may be helpful in avoiding diagnostic and surgical errors and adverse consequences especially during laparoscopic approaches
The Stability of Double White Dwarf Binaries Undergoing Direct Impact Accretion
We present numerical simulations of dynamically unstable mass transfer in a
double white dwarf binary with initial mass ratio, q = 0.4. The binary
components are approximated as polytropes of index n = 3/2 and the initially
synchronously rotating, semi-detached equilibrium binary is evolved
hydrodynamically with the gravitational potential being computed through the
solution of Poisson's equation. Upon initiating deep contact in our baseline
simulation, the mass transfer rate grows by more than an order of magnitude
over approximately ten orbits, as would be expected for dynamically unstable
mass transfer. However, the mass transfer rate then reaches a peak value, the
binary expands and the mass transfer event subsides. The binary must therefore
have crossed the critical mass ratio for stability against dynamical mass
transfer. Despite the initial loss of orbital angular momentum into the spin of
the accreting star, we find that the accretor's spin saturates and angular
momentum is returned to the orbit more efficiently than has been previously
suspected for binaries in the direct impact accretion mode. To explore this
surprising result, we directly measure the critical mass ratio for stability by
imposing artificial angular momentum loss at various rates to drive the binary
to an equilibrium mass transfer rate. For one of these driven evolutions, we
attain equilibrium mass transfer and deduce that effectively q_crit has evolved
to approximately 2/3. Despite the absence of a fully developed disk, tidal
interactions appear effective in returning excess spin angular momentum to the
orbit.Comment: 27 pages, 6 figures. Please see
http://www.phys.lsu.edu/faculty/tohline/astroph/mftd07/ for animations and
full resolution figures. Accepted for publication in the Astrophysical
Journa
Use of Linear Free Energy Relationships (LFERs) to Elucidate the Mechanisms of Reaction of a Îł-Methyl-ÎČ-alkynyl and an ortho-Substituted Aryl Chloroformate Ester
The specific rates of solvolysis of 2-butyn-1-yl-chloroformate (1) and 2-methoxyphenyl chloroformate (2) are studied at 25.0 °C in a series of binary aqueousorganic mixtures. The rates of reaction obtained are then analyzed using the extended Grunwald-Winstein (G-W) equation and the results are compared to previously published G-W analyses for phenyl chloroformate (3), propargyl chloroformate (4), p-methoxyphenyl choroformate (5), and p-nitrophenyl chloroformate (6). For 1, the results indicate that dual side-by-side addition-elimination and ionization pathways are occurring in some highly ionizing solvents due to the presence of the electron-donating γ-methyl group. For 2, the analyses indicate that the dominant mechanism is a bimolecular one where the formation of a tetrahedral intermediate is rate-determining
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