3,432 research outputs found
Application of special-purpose digital computers to rotorcraft real-time simulation
The use of an array processor as a computational element in rotorcraft real-time simulation is studied. A multilooping scheme was considered in which the rotor would loop over its calculations a number of time while the remainder of the model cycled once on a host computer. To prove that such a method would realistically simulate rotorcraft, a FORTRAN program was constructed to emulate a typical host-array processor computing configuration. The multilooping of an expanded rotor model, which included appropriate kinematic equations, resulted in an accurate and stable simulation
X ray timing observations and gravitational physics
Photon-rich x ray observations on bright compact galactic sources will make it possible to detect many fast processes that may occur in these systems on millisecond and submillisecond timescales. Many of these processes are of direct relevance to gravitational physics because they arise in regions of strong gravity near neutron stars and black holes where the dynamical timescales for compact objects of stellar mass are milliseconds. To date, such observations have been limited by the detector area and telemetry rates available. However, instruments such as the proposed X ray Large Array (XLA) would achieve collecting areas of about 100 sq m. This instrument has been described elsewhere (Wood and Michelson 1988) and was the subject of a recent prephase A feasibility study at Marshall Space Flight Center. Observations with an XLA class instrument will directly impact five primary areas of astrophysics research: the attempt to detect gravitational radiation, the study of black holes, the physics of mass accretion onto compact objects, the structure of neutron stars and nuclear matter, and the characterization of dark matter in the universe. Those observations are discussed that are most directly relevant to gravitational physics: the search for millisecond x ray pulsars that are potential sources of continuous gravitational radiation; and the use of x ray timing observations to probe the physical conditions in extreme relativistic regions of space near black holes, both stellar-sized and supermassive
Microwave sterilization of breast milk infected with the AIDS virus
Includes bibliographical references.The AIDS virus has been identified in breast milk which is donated by expectant and recently delivered mothers in maternity hospitals). In maternity hospitals, where the facilities exist for the treatment of pre-term infants, breast milk is collected from mothers premature even those who have not delivered premature babies) and it is used in its raw state to feed the children. The possibility of some of these mothers being infected with the AIDS virus is high in Third World countries. The premature infants have to be fed with breast milk as they are at risk of being infected if fed with commercial milk formulas. Commercially available milk sterilizers are available in Europe but they are very costly
Impaired endothelial function of the retinal vasculature in hypertensive patients
<p><b>Background and Purpose:</b> Arterial hypertension constitutes a central factor in the pathogenesis of stroke. We examined endothelial function of the retinal vasculature as a model of the cerebral circulation.</p>
<p><b>Methods:</b> Thirty-eight young subjects (19 hypertensive and 19 normotensive) were treated with the AT1-receptor blocker candesartan cilexetil and placebo, each over 7 days. Retinal capillary flow and blood flow velocity in the central retinal artery were assessed with scanning laser Doppler flowmetry and pulsed Doppler ultrasound, respectively. NG-monomethyl-L-arginine (L-NMMA) was infused to inhibit nitric oxide (NO) synthesis. Diffuse luminance flicker was applied to stimulate NO release.</p>
<p><b>Results:</b> In normotensive subjects, L-NMMA decreased retinal capillary flow by 8.2%±13% (P<0.05) and flickering light increased mean blood flow velocity in the central retinal artery by 19%±29% (P<0.01). In contrast, no significant change to these provocative tests was seen in hypertensive subjects. Treatment with candesartan cilexetil restored a normal pattern of reactivity in retinal capillaries (L-NMMA: decrease in perfusion by 10%±17%, P<0.05) and the central retinal artery (flicker: increase in mean blood flow velocity by 42%±31%, P<0.001) in hypertensive patients.</p>
<p><b>Conclusions:</b> Endothelial function of the retinal vasculature is impaired in early essential hypertension but can be improved by AT1-receptor blockade.</p>
AdS_2/CFT_1, Canonical Transformations and Superconformal Mechanics
We propose a simple conformal mechanics model which is classically equivalent
to a charged massive particle propagating near the AdS_2\times S^2 horizon of
an extreme Reissner-Nordstr\"om black hole. The equivalence holds for any
finite value of the black hole mass and with both the radial and angular
degrees of freedom of the particle taken into account. It is ensured by the
existence of a canonical transformation in the Hamiltonian formalism. Using
this transformation, we construct the Hamiltonian of a N=4 superparticle on
AdS_2\times S^2 background.Comment: 10 pages, LaTe
Potential one-forms for hyperk\"ahler structures with torsion
It is shown that an HKT-space with closed parallel potential 1-form has
-symmetry. Every locally conformally hyperk\"ahler manifold
generates this type of geometry. The HKT-spaces with closed parallel potential
1-form arising in this way are characterized by their symmetries and an
inhomogeneous cubic condition on their torsion.Comment: 16 pages, Latex, no figure
Optical Spectroscopy of Bright Fermi LAT Blazars
We report on HET and Palomar 5 m spectroscopy of recently identified
-ray blazars in the {\it Fermi} LAT Bright Source List. These data
provide identifications for 10 newly discovered -ray flat spectrum
radio quasars (FSRQ) and six new BL Lacs plus improved spectroscopy for six
additional BL Lacs. We substantially improve the identification completeness of
the bright LAT blazars and give new redshifts and constraints, new
estimates of the black hole masses and new measurements of the optical SED.Comment: 8 pages, 5 figures, 2 tables. Accepted for publication in Ap
Blazar Counterparts for 3EG Sources at -40 < decl. < 0: Pushing South Through the Bulge
Supplementing existing survey data with VLA observations, we have extended
ray counterpart identifications down to decl. = -40 using our
Figure of Merit approach. We find blazar counterparts for 70% of EGRET
sources above decl. = -40 away from the Galaxy. Spectroscopic
confirmation is in progress, and spectra for two dozen sources are
presented here. We find evidence that increased exposure in the bulge region
allowed EGRET to detect relatively faint blazars; a clear excess of non-blazar
objects in this region however argues for an additional (new) source class.Comment: ApJ accepte
Arago (1810): the first experimental result against the ether
95 years before Special Relativity was born, Arago attempted to detect the
absolute motion of the Earth by measuring the deflection of starlight passing
through a prism fixed to the Earth. The null result of this experiment gave
rise to the Fresnel's hypothesis of an ether partly dragged by a moving
substance. In the context of Einstein's Relativity, the sole frame which is
privileged in Arago's experiment is the proper frame of the prism, and the null
result only says that Snell's law is valid in that frame. We revisit the
history of this premature first evidence against the ether theory and calculate
the Fresnel's dragging coefficient by applying the Huygens' construction in the
frame of the prism. We expose the dissimilar treatment received by the ray and
the wave front as an unavoidable consequence of the classical notions of space
and time.Comment: 16 pages. To appear in European Journal of Physic
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