19,947 research outputs found
Effect of Vibrational Excitation on the Theoretical Performance of the Stoichiometric Carbon-Oxygen Propellant System
Accurate calculations to evaluate the performance of the stoichiometric carbon-oxygen propellant system have been carried out for nozzle flow with and without chemical reactions and with and without vibrational adjustment. The calculations show that, for frozen chemical flow, a lag of vibrational energy states at chamber conditions nearly doubles the reduction in I_(sp), as compared with flow in which complete vibrational equilibrium is maintained. On the other hand, lags in vibrational adjustment have practically no effect on the theoretical performance of hot propellant systems if chemical equilibrium is maintained during nozzle flow. The preceding conclusions are in agreement with the results on other propellant systems obtained previously by use of an approximate evaluation procedure
Regional gray matter correlates of vocational interests.
BackgroundPrevious studies have identified brain areas related to cognitive abilities and personality, respectively. In this exploratory study, we extend the application of modern neuroimaging techniques to another area of individual differences, vocational interests, and relate the results to an earlier study of cognitive abilities salient for vocations.FindingsFirst, we examined the psychometric relationships between vocational interests and abilities in a large sample. The primary relationships between those domains were between Investigative (scientific) interests and general intelligence and between Realistic ("blue-collar") interests and spatial ability. Then, using MRI and voxel-based morphometry, we investigated the relationships between regional gray matter volume and vocational interests. Specific clusters of gray matter were found to be correlated with Investigative and Realistic interests. Overlap analyses indicated some common brain areas between the correlates of Investigative interests and general intelligence and between the correlates of Realistic interests and spatial ability.ConclusionsTwo of six vocational-interest scales show substantial relationships with regional gray matter volume. The overlap between the brain correlates of these scales and cognitive-ability factors suggest there are relationships between individual differences in brain structure and vocations
Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom in the English Channel
This study used analytical flow cytometry (AFC) to monitor the abundance of phytoplankton, coccoliths, bacteria and viruses in a transect that crossed a high reflectance area in the western English Channel. The high reflectance area, observed by satellite, was caused by the demise of an Emiliania huxleyi bloom. Water samples were collected from depth profiles at four stations, one station outside and three stations inside the high reflectance area. Plots of transect data revealed very obvious differences between Station 1, outside, and Stations 2–4, inside the high reflectance area. Inside, concentrations of viruses were higher; E. huxleyi cells were lower; coccoliths were higher; bacteria were higher and virus:bacteria ratio was lower than at Station 1, outside the high reflectance area. This data can simply be interpreted as virus-induced lysis of E. huxleyi cells in the bloom causing large concentrations of coccoliths to detach, resulting in the high reflectance observed by satellite imagery. This interpretation was supported by the isolation of two viruses, EhV84 and EhV86, from the high reflectance area that lysed cultures of E. huxleyi host strain CCMP1516. Basic characterization revealed that they were lytic viruses approximately 170 nm–190 nm in diameter with an icosahedral symmetry. Taken together, transect and isolation data suggest that viruses were the major contributor to the demise of the E. huxleyi population in the high reflectance area. Close coupling between microalgae, bacteria and viruses contributed to a large organic carbon input. Consequent cycling influenced the succession of an E. huxleyi-dominated population to a more characteristic mixed summer phytoplankton community
Brief Studies
Critique of the Revised Standard Version of the Epistle of St. James
Renaissance or Reformatio
Evidence for multiple structural genes for the γ chain of human fetal hemoglobin
A sequence with a specific residue at each position was proposed for the γ chain of human fetal hemoglobin by Schroeder et al. (1) after a study in which hemoglobin from a number of individual infants was used. We have now examined in part the fetal hemoglobin components of 17 additional infants and have observed that position 136 of the γ chain may be occupied not only by a glycyl residue, as previously reported, but also by an alanyl residue
Feedback in a cavity QED system for control of quantum beats
Conditional measurements on the undriven mode of a two-mode cavity QED system
prepare a coherent superposition of ground states which generate quantum beats.
The continuous system drive induces decoherence through the phase interruptions
from Rayleigh scattering, which manifests as a decrease of the beat amplitude
and an increase of the frequency of oscillation. We report recent experiments
that implement a simple feedback mechanism to protect the quantum beat. We
continuously drive the system until a photon is detected, heralding the
presence of a coherent superposition. We then turn off the drive and let the
superposition evolve in the dark, protecting it against decoherence. At a later
time we reinstate the drive to measure the amplitude, phase, and frequency of
the beats. The amplitude can increase by more than fifty percent, while the
frequency is unchanged by the feedback.Comment: 13 pages, 5 figures, ICAP 2012 23rd International Conference on
Atomic Physic
Air hydrodynamics of the ultrafast laser-triggered spark gap
We present space and time resolved measurements of the air hydrodynamics
induced by ultrafast laser pulse excitation of the air gap between two
electrodes at high potential difference. We explore both plasma-based and
plasma-free gap excitation. The former uses the plasma left in the wake of
femtosecond filamentation, while the latter exploits air heating by
multiple-pulse resonant excitation of quantum molecular wavepackets. We find
that the cumulative electrode-driven air density depression channel initiated
by the laser plays the dominant role in the gap evolution leading to breakdown
Universal macroscopic background formation in surface super-roughening
We study a class of super-rough growth models whose structure factor
satisfies the Family-Vicsek scaling. We demonstrate that a macroscopic
background spontaneously develops in the local surface profile, which dominates
the scaling of the local surface width and the height-difference. The shape of
the macroscopic background takes a form of a finite-order polynomial whose
order is decided from the value of the global roughness exponent. Once the
macroscopic background is subtracted, the width of the resulting local surface
profile satisfies the Family-Vicsek scaling. We show that this feature is
universal to all super-rough growth models, and we also discuss the difference
between the macroscopic background formation and the pattern formation in other
models.Comment: 5 pages, LaTex, 1 figure, minor correction
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