11,185 research outputs found
Applicability of 100kWe-class of space reactor power systems to NASA manned space station missions
An assessment is made of a manned space station operating with sufficiently high power demands to require a multihundred kilowatt range electrical power system. The nuclear reactor is a competitor for supplying this power level. Load levels were selected at 150kWe and 300kWe. Interactions among the reactor electrical power system, the manned space station, the space transportation system, and the mission were evaluated. The reactor shield and the conversion equipment were assumed to be in different positions with respect to the station; on board, tethered, and on a free flyer platform. Mission analyses showed that the free flyer concept resulted in unacceptable costs and technical problems. The tethered reactor providing power to an electrolyzer for regenerative fuel cells on the space station, results in a minimum weight shield and can be designed to release the reactor power section so that it moves to a high altitude orbit where the decay period is at least 300 years. Placing the reactor on the station, on a structural boom is an attractive design, but heavier than the long tethered reactor design because of the shield weight for manned activity near the reactor
Ionization Mechanisms in Jet-Dominated Seyferts: A Detailed Case Study
For the past 10 years there has been an active debate over whether fast
shocks play an important role in ionizing emission line regions in Seyfert
galaxies. To investigate this claim, we have studied the Seyfert 2 galaxy Mkn
78, using HST UV/optical images and spectroscopy. Since Mkn 78 provides the
archetypal jet-driven bipolar velocity field, if shocks are important anywhere
they should be important in this object. Having mapped the emission line fluxes
and velocity field, we first compare the ionization conditions to standard
photoionization and shock models. We find coherent variations of ionization
consistent with photoionization model sequences which combine optically thick
and thin gas, but are inconsistent with either autoionizing shock models or
photoionization models of just optically thick gas. Furthermore, we find
absolutely no link between the ionization of the gas and its kinematic state,
while we do find a simple decline of ionization degree with radius. We feel
this object provides the strongest case to date against the importance of shock
related ionization in Seyferts.Comment: 4 pages, 1 figure, to appear in the proceedings of IAU Symposium 222
"The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", T.
Storchi Bergmann, L.C. Ho & H.R. Schmitt, ed
Echocardiographic techniques for assessing normal and abnormal fetal cardiac anatomy
Diagnostic quality images of the fetal heart in utero can be obtained as early as 18 to 20 weeks of gestation. The cardiac structures can be imaged primarily by cross-sectional echocardiography and augmented by a combination of simultaneous M-mode echocardiography and range-gated pulsed Doppler ultrasonography. Cross-sectional images from planes through the fetal heart equivalent to planes that can be obtained after birth can be generated in utero. In a study of 168 pregnancies, 10 structural cardiac abnormalities have been defined. These abnormalities and others that have been reported indicate the potential for in utero cardiac diagnosis. The recognition of structural congenital heart disease in utero has been helpful in genetic counseling, planning the method of labor and delivery and making decisions regarding termination of pregnancy and planning postnatal care. Fetal echocardiography offers the potential to change the pattern of health care delivery to those with suspected congenital heart disease
The Full Range of Predictions for B Physics From Iso-singlet Down Quark Mixing
We extend the range of predictions of the isosinglet (or vector) down quark
model to the fully allowed physical ranges, and also update this with the
effect of new physics constraints. We constrain the present allowed ranges of
sin(2*beta) and sin(2*alpha), gamma, x_s, and A_{B_s}. In models allowing
mixing to a new isosinglet down quark (as in E_6) flavor changing neutral
currents are induced that allow a Z^0 mediated contribution to B-Bbar mixing
and which bring in new phases. In (rho, eta), (x_s, sin(gamma)), and (x_s,
A_{B_s}) plots for the extra isosinglet down quark model which are herein
extended to the full physical range, we find new allowed regions that will
require experiments on sin(gamma) and/or x_s to verify or to rule out an extra
down quark contribution.Comment: 13 pages in RevTeX, 7 postscript figure
High-speed, high-frequency ultrasound, \u3ci\u3ein utero\u3c/i\u3e vector-flow imaging of mouse embryos
Real-time imaging of the embryonic murine cardiovascular system is challenging due to the small size of the mouse embryo and rapid heart rate. High-frequency, linear-array ultrasound systems designed for small-animal imaging provide high-frame-rate and Doppler modes but are limited in regards to the field of view that can be imaged at fine-temporal and -spatial resolution. Here, a plane-wave imaging method was used to obtain high-speed image data from in utero mouse embryos and multi-angle, vector-flow algorithms were applied to the data to provide information on blood flow patterns in major organs. An 18-MHz linear array was used to acquire plane-wave data at absolute frame rates ≥10 kHz using a set of fixed transmission angles. After beamforming, vector-flow processing and image compounding, effective frame rates were on the order of 2 kHz. Data were acquired from the embryonic liver, heart and umbilical cord. Vector-flow results clearly revealed the complex nature of blood-flow patterns in the embryo with fine-temporal and -spatial resolution
A Systematic Review of Music Therapy Practice and Outcomes with Acute Adult Psychiatric In-Patients
PMCID: PMC3732280This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Amicable pairs and aliquot cycles for elliptic curves
An amicable pair for an elliptic curve E/Q is a pair of primes (p,q) of good
reduction for E satisfying #E(F_p) = q and #E(F_q) = p. In this paper we study
elliptic amicable pairs and analogously defined longer elliptic aliquot cycles.
We show that there exist elliptic curves with arbitrarily long aliqout cycles,
but that CM elliptic curves (with j not 0) have no aliqout cycles of length
greater than two. We give conjectural formulas for the frequency of amicable
pairs. For CM curves, the derivation of precise conjectural formulas involves a
detailed analysis of the values of the Grossencharacter evaluated at a prime
ideal P in End(E) having the property that #E(F_P) is prime. This is especially
intricate for the family of curves with j = 0.Comment: 53 page
Irreversible growth of binary mixtures on small-world networks
Binary mixtures growing on small-world networks under far-from-equilibrium
conditions are studied by means of extensive Monte Carlo simulations. For any
positive value of the shortcut fraction of the network (), the system
undergoes a continuous order-disorder phase transition, while it is noncritical
in the regular lattice limit (). Using finite-size scaling relations, the
phase diagram is obtained in the thermodynamic limit and the critical exponents
are evaluated. The small-world networks are thus shown to trigger criticality,
a remarkable phenomenon which is analogous to similar observations reported
recently in the investigation of equilibrium systems.Comment: 7 pages, 7 figures; added/removed references and modified
presentation. To appear in PR
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