Small Mercury Relativity Orbiter

The accuracy of solar system tests of gravitational theory could be very much improved by range and Doppler measurements to a Small Mercury Relativity Orbiter. A nearly circular orbit at roughly 2400 km altitude is assumed in order to minimize problems with orbit determination and thermal radiation from the surface. The spacecraft is spin-stabilized and has a 30 cm diameter de-spun antenna. With K-band and X-band ranging systems using a 50 MHz offset sidetone at K-band, a range accuracy of 3 cm appears to be realistically achievable. The estimated spacecraft mass is 50 kg. A consider-covariance analysis was performed to determine how well the Earth-Mercury distance as a function of time could be determined with such a Relativity Orbiter. The minimum data set is assumed to be 40 independent 8-hour arcs of tracking data at selected times during a two year period. The gravity field of Mercury up through degree and order 10 is solved for, along with the initial conditions for each arc and the Earth-Mercury distance at the center of each arc. The considered parameters include the gravity field parameters of degree 11 and 12 plus the tracking station coordinates, the tropospheric delay, and two parameters in a crude radiation pressure model. The conclusion is that the Earth-Mercury distance can be determined to 6 cm accuracy or better. From a modified worst-case analysis, this would lead to roughly 2 orders of magnitude improvement in the knowledge of the precession of perihelion, the relativistic time delay, and the possible change in the gravitational constant with time

How to Enter, Fly In, and Exit the A-Train Constellation

The collaborative science obtained from the satellites in the A-Train is an unparalleled success. The constellation framework that has evolved is well-formulated and documented by its international members. Communication between teams is enhanced by a web-based Constellation Coordination System. Safety and correlated observations are ensured by defining independent control boxes with buffers in between. Each mission stays within its control box by regular drag makeup maneuvers. Annual inclination adjustments are coordinated by all missions to maintain their absolute and relative Mean Local Time of Ascending Node (MLTAN). Since the satellites are in different orbit planes their separation involves a three-dimensional triad made up of the along track separations, reference groundtracks and MLTAN's. For further safety, a Constellation Envelope has been defined to determine safe entry and exit orbits

Particulate Matter Exposure Impairs Systemic Microvascular Endothelium-Dependent Dilation

Acute exposure to airborne pollutants, such as solid particulate matter (PM), increases the risk of cardiovascular dysfunction, but the mechanisms by which PM evokes systemic effects remain to be identified. The purpose of this study was to determine if pulmonary exposure to a PM surrogate, such as residual oil fly ash (ROFA), affects endothelium-dependent dilation in the systemic microcirculation. Rats were intratracheally instilled with ROFA at 0.1, 0.25, 1 or 2 mg/rat 24 hr before experimental measurements. Rats intratracheally instilled with saline or titanium dioxide (0.25 mg/rat) served as vehicle or particle control groups, respectively. In vivo microscopy of the spinotrapezius muscle was used to study systemic arteriolar dilator responses to the Ca(2+) ionophore A23187, administered by ejection via pressurized micropipette into the arteriolar lumen. We used analysis of bronchoalveolar lavage (BAL) samples to monitor identified pulmonary inflammation and damage. To determine if ROFA exposure affected arteriolar nitric oxide sensitivity, sodium nitroprusside was iontophoretically applied to arterioles of rats exposed to ROFA. In saline-treated rats, A23187 dilated arterioles up to 72 ± 7% of maximum. In ROFA- and TiO(2)-exposed rats, A23187-induced dilation was significantly attenuated. BAL fluid analysis revealed measurable pulmonary inflammation and damage after exposure to 1 and 2 mg ROFA (but not TiO(2) or < 1 mg ROFA), as evidenced by significantly higher polymorphonuclear leukocyte cell counts, enhanced BAL albumin levels, and increased lactate dehydrogenase activity in BAL fluid. The sensitivity of arteriolar smooth muscle to NO was similar in saline-treated and ROFA-exposed rats, suggesting that pulmonary exposure to ROFA affected endothelial rather than smooth muscle function. A significant increase in venular leukocyte adhesion and rolling was observed in ROFA-exposed rats, suggesting local inflammation at the systemic microvascular level. These results indicate that pulmonary PM exposure impairs systemic endothelium-dependent arteriolar dilation. Moreover, because rats exposed to < 1 mg ROFA or TiO(2) did not exhibit BAL signs of pulmonary damage or inflammation, it appears that PM exposure can impair systemic microvascular function independently of detectable pulmonary inflammation

Structure and electronic properties of the quasi-one-dimensional Ba₂Co₁₋ₓZnₓS₃ series

This work focuses on the structure and physical properties of the solid solution Ba₂Co₁₋ₓZnₓS₃ (0 ≤ x ≤ 1), a family of quasi-one-dimensional sulfides with end members Ba₂CoS₃ and Ba₂ZnS₃. The structure of selected compounds with increasing Zn²⁺ content has been analysed using, neutron diffraction, TEM and EXAFS and the physical properties via magnetic susceptibility and resistivity measurements. The progressive substitution of the non-magnetic Zn²⁺ cation for Co²⁺ rapidly destroys the antiferromagnetic transition present at 46 K in the quasi one-dimensional Ba₂CoS₃, leading to paramagnetic behaviour down to the lowest investigated temperature (5K) for compounds with x > 0.25. For compounds with x ≥ 0.4, a pure CW regime is recovered around 300 K, yielding effective moments consistent with the g factor of the tetrahedrally coordinated Co²⁺ previously determined for Ba₂CoS₃. The Zn²⁺/Co²⁺ substitution also removes the metallic-like behaviour of Ba₂CoS₃ causing an increase in the value of the resistivity with all the Ba₂Co₁₋ₓZnₓS₃ compounds showing semiconducting behaviour. The negative magnetoresistance of Ba₂CoS₃ is improved by the Zn²⁺/Co²⁺ substitution, with values of – 6% for Ba₂Co₀.₇₅Zn₀.₂₅S₃, – 9% for Ba₂Co₀.₅Zn₀.₅S₃ and – 8% for Ba₂Co₀.₂₅Zn₀.₇₅S₃. However, there does not seem to be a correlation between the values of the resistivity and the magnetoresistance and the content of Zn²⁺, leading to the hypothesis that transport properties may be linked more closely to extrinsic properties

Unequal mass binary neutron star simulations with neutrino transport: Ejecta and neutrino emission

We present 12 new simulations of unequal mass neutron star mergers. The simulations are performed with the SpEC code, and utilize nuclear-theory-based equations of state and a two-moment gray neutrino transport scheme with an improved energy estimate based on evolving the number density. We model the neutron stars with the SFHo, LS220, and DD2 equations of state (EOS) and we study the neutrino and matter emission of all 12 models to search for robust trends between binary parameters and emission characteristics. We find that the total mass of the dynamical ejecta exceeds 0.01  M⊙ only for SFHo with weak dependence on the mass ratio across all models. We find that the ejecta have a broad electron fraction (Y_e) distribution (≈0.06–0.48), with mean 0.2. Y_e increases with neutrino irradiation over time, but decreases with increasing binary asymmetry. We also find that the models have ejecta with a broad asymptotic velocity distribution (≈0.05–0.7c). The average velocity lies in the range 0.2c−0.3c and decreases with binary asymmetry. Furthermore, we find that disk mass increases with binary asymmetry and stiffness of the EOS. The Y_e of the disk increases with softness of the EOS. The strongest neutrino emission occurs for the models with soft EOS. For (anti) electron neutrinos we find no significant dependence of the magnitude or angular distribution or neutrino luminosity with mass ratio. The heavier neutrino species have a luminosity dependence on mass ratio but an angular distribution which does not change with mass ratio

The development of a position-sensitive CZT detector with orthogonal co-planar anode strips

We report on the simulation, construction, and performance of prototype CdZnTe imaging detectors with orthogonal coplanar anode strips. These detectors employ a novel electrode geometry with non-collecting anode strips in one dimension and collecting anode pixels, interconnected in rows, in the orthogonal direction. These detectors retain the spectroscopic and detection efficiency advantages of single carrier (electron) sensing devices as well as the principal advantage of conventional strip detectors with orthogonal anode and cathode strips, i.e. an N×N array of imaging pixels are with only 2N electronic channels. Charge signals induced on the various electrodes of a prototype detector with 8×8 unit cells (1×1×5 mm3)are compared to the simulations. Results of position and energy resolution measurements are presented and discussed

Optical interferometer in space

The present design concepts for a Laser Gravitational Wave Observatory in Space are described. Laser heterodyne distance measurements are made between test masses located in three spacecraft separated by roughly 10(exp 6) km. The major technology issues are: the reduction of spurious acceleration noise for the test masses to below 2 x 10(exp -15) cm/sq sec/Hz(0.5) from 10(exp -5) to 10(exp -3) Hz; and the measurement of changes in the difference of the antenna arm lengths to 5 x 10(exp -11) cm/Hz(0.5) from 10(exp -3) to 1 Hz with high reliability. The science objectives are: to measure discrete sinusoidal gravitational wave signals from individual sources with periods of 1 second to 1 day; to measure the stochastic background due to unresolved binaries; and to search for gravitational wave pulses with periods longer than 1 sec from possible exotic sources such as gravitational collapse of very massive objects

The site and stoichiometry of the N-phenylmaleimide reaction with myosin when weakly-binding crossbridges are formed in skinned rabbit psoas fibers

AbstractTreatment of relaxed skinned rabbit psoas muscle fibers with 0.1 mM N-phenylmaleimide (NPM) for 1 h locks all of the crossbridges in a weakly-binding state resembling that of the myosin ATP crossbridge. Under these conditions, NPM reacts mainly with myosin heavy chain (Barnett et al. (1992) Biophys. J. 61, 358–367). Here the specific sites for that reaction are explored. Small bundles of rabbit psoas muscle fibers were treated with Triton X-100 to make the fiber sarcolemmas permeable. The bundles were treated with 0.1 mM [14C]NPM for 1 h, and homogenized for SDS-PAGE. 43 ± 2.2% of the muscle fiber protein ran in the myosin heavy chain band, the same as for untreated fibers. An alkylating stoichiometry of 2.2 ± 0.33 moles NPM per mole myosin heavy chain was determined. Exhaustive trypsin digestion followed by two-dimensional thin-layer chromatography and reverse-phase HPLC revealed two major sites on myosin heavy chain for NPM binding. The sites contained about the same amount of linked NPM, suggesting that the reaction stoichiometry of each site under the conditions studied is approx. 1 mol NPM/mol myosin heavy chain. Comparison of the labeled tryptic peptides with NPM-reacted synthetic SH1 and SH2 tryptic peptides and analysis of the treated fiber bundles' ATPase activity suggested that the sites for NPM reaction on myosin heavy chain when it locks crossbridges in a weakly-binding state are Cys-697 (SH2) and Cys-707 (SH1)

The power spectra of CMB and density fluctuations seeded by local cosmic strings

We compute the power spectra in the cosmic microwave background and cold dark matter (CDM) fluctuations seeded by strings, using the largest string simulations performed so far to evaluate the two-point functions of their stress energy tensor. We find that local strings differ from global defects in that the scalar components of the stress-energy tensor dominate over vector and tensor components. This result has far reaching consequences. We find that cosmic strings exhibit a single Doppler peak of acceptable height at high $\ell$. They also seem to have a less severe bias problem than global defects, although the CDM power spectrum in the ``standard'' cosmology (flat geometry, zero cosmological constant, 5% baryonic component) is the wrong shape to fit large scale structure data