Single-stage electrohydraulic servosystem for actuating on airflow valve with frequencies to 500 hertz

An airflow valve and its electrohydraulic actuation servosystem are described. The servosystem uses a high-power, single-stage servovalve to obtain a dynamic response beyond that of systems designed with conventional two-stage servovalves. The electrohydraulic servosystem is analyzed and the limitations imposed on system performance by such nonlinearities as signal saturations and power limitations are discussed. Descriptions of the mechanical design concepts and developmental considerations are included. Dynamic data, in the form of sweep-frequency test results, are presented and comparison with analytical results obtained with an analog computer model is made

STEREO Space Weather and the Space Weather Beacon

The Solar Terrestrial Relations Observatory (STEREO) is first and foremost a solar and interplanetary research mission, with one of the natural applications being in the area of space weather. The obvious potential for space weather applications is so great that NOAA has worked to incorporate the real-time data into their forecast center as much as possible. A subset of the STEREO data will be continuously downlinked in a real-time broadcast mode, called the Space Weather Beacon. Within the research community there has been considerable interest in conducting space weather related research with STEREO. Some of this research is geared towards making an immediate impact while other work is still very much in the research domain. There are many areas where STEREO might contribute and we cannot predict where all the successes will come. Here we discuss how STEREO will contribute to space weather and many of the specific research projects proposed to address STEREO space weather issues. We also discuss some specific uses of the STEREO data in the NOAA Space Environment Center

Dynamics of a structured slug population model in the absence of seasonal variation

We develop a novel, nonlinear structured population model for the slug Deroceras reticulatum, a highly significant agricultural pest of great economic impact, in both organic and non-organic settings. In the absence of seasonal variations, we numerically explore the effect of life history traits that are dependent on an individual's size and measures of population biomass. We conduct a systematic exploration of parameter space and highlight the main mechanisms and implications of model design. A major conclusion of this work is that strong size dependent predation significantly adjusts the competitive balance, leading to non-monotonic steady state solutions and slowly decaying transients consisting of distinct generational cycles. Furthermore, we demonstrate how a simple ratio of adult to juvenile biomass can act as a useful diagnostic to distinguish between predated and non-predated environments, and may be useful in agricultural settings

Identification of a nearby stellar association in the Hipparcos catalog: implications for recent, local star formation

The TW Hydrae Association (~55 pc from Earth) is the nearest known region of recent star formation. Based primarily on the Hipparcos catalog, we have now identified a group of 9 or 10 co-moving star systems at a common distance (~45 pc) from Earth that appear to comprise another, somewhat older, association (``the Tucanae Association''). Together with ages and motions recently determined for some nearby field stars, the existence of the Tucanae and TW Hydrae Associations suggests that the Sun is now close to a region that was the site of substantial star formation only 10-40 million years ago. The TW Hydrae Association represents a final chapter in the local star formation history.Comment: 5 pages incl figs and table

L-arginase induces vascular dysfunction in old spontaneously hypertensive rats

Background: Aging is a major non-modifiable risk factor for hypertension. Changes in aging are similar to those seen in hypertension in the vasculature. Also, aging increases the vascular dysfunction that occurs in hypertension. L-arginase action reduces substrate (L-arginine) availability for the formation of nitric oxide (NO). This reduces the level of NO and leads to reduced vasodilation and ultimately, vascular dysfunction. This study examines the hypothesis that age-dependent vascular dysfunction in SHRs is mediated by arginase.Methods: Young (12-14 weeks) and old (11-12 months) male Wistar and spontaneously hypertensive rats (SHR) were used. Mean arterial pressure (MAP) was measured in the rats. They were then euthanized and mesenteric resistance arteries (MRAs) and thoracic aortae were excised and placed in ice-cold physiological salt solution (PSS). Arterial segments were either snap-frozen in liquid nitrogen and stored for immunoblotting studies or cut into 2mm rings for reactivity studies. Cumulative concentration-response curves to acetylcholine (Ach; 10-9 – 3x10-5M) and sodium nitroprusside (SNP; 10-12 – 3x10-5 M) were performed in the absence or presence (30-minute exposure) of L-arginase, 0.05U/ML (MRA) or 0.5U/ML (aorta). Vessels were pre-contracted with phenylephrine (PE; 3x10-6M)Results: MAP increased during aging in the SHRs p<0.05 but not in the Wistar rats. Arginase impaired the endothelium-dependent relaxation responses of thoracic aortic and MRA arterial rings to Ach in the old Wistars and SHRs (Emax aorta: 29.42±2.19% vs 7.94±1.86%). Arginase also impaired endothelium-independent relaxation response to SNP in the old SHRs only (Emax aorta: 88.62±4.10% vs 31.45±10.61%). We also observed no differences in the serum arginase activity in the four groups of rats. On the contrary, arginase activity in the aortae of young Wistar rats was reduced compared to other groups.Conclusions: Arginase impairs both endothelium-dependent and –independent vasorelaxation responses, through the NO signaling pathway.Keywords: Hypertension, Arginase, aging, vascular dysfunction, endothelium, Nitric oxid

XMM-Newton spectral and timing analysis of the faint millisecond pulsars PSR J0751+1807 and PSR J1012+5307

We present XMM-Newton MOS imaging and PN timing data of the faint millisecond pulsars PSR J0751+1807 and PSR J1012+5307. We find 46 sources in the MOS field of view of PSR J0751+1807 searching down to an unabsorbed flux limit of 3 x 10^-15 ergs cm^-2 s^-1 (0.2-10.0 keV). We present, for the first time, the X-ray spectra of these two faint millisecond pulsars. We find that a power law model best fits the spectrum of PSR J0751+1807, Gamma=1.59+/-0.20, with an unabsorbed flux of 4.4 x 10^-14 ergs cm^-2 s^-1 (0.2-10.0 keV). A power law is also a good description of the spectrum of PSR J1012+5307, Gamma=1.78+/-0.36, with an unabsorbed flux of 1.2 x 10^-13 ergs cm^-2 s^-1 (0.2-10.0 keV). However, a blackbody model can not be excluded as the best fit to this data. We present some evidence to suggest that both of these millisecond pulsars show pulsations in this X-ray band. We find some evidence for a single broad X-ray pulse for PSR J0751+1807 and we discuss the possibility that there are two pulses per spin period for PSR J1012+5307.Comment: 8 pages, 9 figures, accepted for publication in Astronomy & Astrophysic

Evidence of a Curved Synchrotron Spectrum in the Supernova Remnant SN 1006

A joint spectral analysis of some Chandra ACIS X-ray data and Molonglo Observatory Synthesis Telescope radio data was performed for 13 small regions along the bright northeastern rim of the supernova remnant SN 1006. These data were fitted with a synchrotron radiation model. The nonthermal electron spectrum used to compute the photon emission spectra is the traditional exponentially cut off power law, with one notable difference: The power-law index is not a constant. It is a linear function of the logarithm of the momentum. This functional form enables us to show, for the first time, that the synchrotron spectrum of SN 1006 seems to flatten with increasing energy. The effective power-law index of the electron spectrum is 2.2 at 1 GeV (i.e., radio synchrotron-emitting momenta) and 2.0 at about 10 TeV (i.e., X-ray synchrotron-emitting momenta). This amount of change in the index is qualitatively consistent with theoretical models of the amount of curvature in the proton spectrum of the remnant. The evidence of spectral curvature implies that cosmic rays are dynamically important instead of being "test" particles. The spectral analysis also provides a means of determining the critical frequency of the synchrotron spectrum associated with the highest-energy electrons. The critical frequency seems to vary along the northeastern rim, with a maximum value of 1.1e17 (0.6e17 - 2.1e17) Hz. This value implies that the electron diffusion coefficient can be no larger than a factor of ~4.5-21 times the Bohm diffusion coefficient if the velocity of the forward shock is in the range 2300-5000 km/s. Since the coefficient is close to the Bohm limit, electrons are accelerated nearly as fast as possible in the regions where the critical frequency is about 1.0e17 Hz.Comment: 41 pages, 8 figures, accepted by Ap

Reduction Operators of Linear Second-Order Parabolic Equations

The reduction operators, i.e., the operators of nonclassical (conditional) symmetry, of (1+1)-dimensional second order linear parabolic partial differential equations and all the possible reductions of these equations to ordinary differential ones are exhaustively described. This problem proves to be equivalent, in some sense, to solving the initial equations. The ``no-go'' result is extended to the investigation of point transformations (admissible transformations, equivalence transformations, Lie symmetries) and Lie reductions of the determining equations for the nonclassical symmetries. Transformations linearizing the determining equations are obtained in the general case and under different additional constraints. A nontrivial example illustrating applications of reduction operators to finding exact solutions of equations from the class under consideration is presented. An observed connection between reduction operators and Darboux transformations is discussed.Comment: 31 pages, minor misprints are correcte