608 research outputs found
Nitric Oxide Production as an Indication of \u3ci\u3eMycobacterium Bovis \u3c/i\u3eInfection in White-Tailed Deer (\u3ci\u3eOdocoileus virginianus\u3c/i\u3e)
White-tailed deer ( Odocoileus virginianus ) are reservoirs for Mycobacterium bovis in northeast Michigan, USA. Production of nitric oxide (NO) by activated macrophages is a potent mechanism of mycobacterial killing. The capacity of macrophages to produce NO, however, varies among mammalian species. The objective of this study was to determine if mononuclear cells from white-tailed deer produce nitrite as an indication of NO production and, if so, is NO produced in response to stimulation with M. bovis antigens. Supernatants were harvested from adherent peripheral blood mononuclear cell (PBMC) cultures that had been stimulated with either Mannheimia haemolytica lipopolysaccharide (LPS) or media alone (i.e., no stimulation). Nitrite levels within M. haemolytica LPS-stimulated culture supernatants exceeded (P \u3c 0.05) those detected within supernatants from non-stimulated cultures as well as those detected within supernatants from cultures receiving an inhibitor of NO synthase in addition to M. haemolytica LPS. In response to stimulation with M. bovis antigens, nitrite production by PBMC from M. bovis -infected deer exceeded (P \u3c 0.05) the production by PBMC from non-infected deer. The response of PBMC from infected deer to M. bovis antigens exceeded (P \u3c 0.05) the response of parallel cultures from the same deer receiving no stimulation. The response of PBMC from M. bovis -infected deer to M. avium antigens did not differ from that of PBMC from M. bovis infected deer to no stimulation or from that of PBMC from non-infected deer to M. avium antigens. These findings indicate that adherent PBMC from white-tailed deer are capable of NO production and that mononuclear cells isolated from M. bovis -infected white-tailed deer produce NO in an antigen-specific recall response
Nitric Oxide Production as an Indication of \u3ci\u3eMycobacterium Bovis \u3c/i\u3eInfection in White-Tailed Deer (\u3ci\u3eOdocoileus virginianus\u3c/i\u3e)
White-tailed deer ( Odocoileus virginianus ) are reservoirs for Mycobacterium bovis in northeast Michigan, USA. Production of nitric oxide (NO) by activated macrophages is a potent mechanism of mycobacterial killing. The capacity of macrophages to produce NO, however, varies among mammalian species. The objective of this study was to determine if mononuclear cells from white-tailed deer produce nitrite as an indication of NO production and, if so, is NO produced in response to stimulation with M. bovis antigens. Supernatants were harvested from adherent peripheral blood mononuclear cell (PBMC) cultures that had been stimulated with either Mannheimia haemolytica lipopolysaccharide (LPS) or media alone (i.e., no stimulation). Nitrite levels within M. haemolytica LPS-stimulated culture supernatants exceeded (P \u3c 0.05) those detected within supernatants from non-stimulated cultures as well as those detected within supernatants from cultures receiving an inhibitor of NO synthase in addition to M. haemolytica LPS. In response to stimulation with M. bovis antigens, nitrite production by PBMC from M. bovis -infected deer exceeded (P \u3c 0.05) the production by PBMC from non-infected deer. The response of PBMC from infected deer to M. bovis antigens exceeded (P \u3c 0.05) the response of parallel cultures from the same deer receiving no stimulation. The response of PBMC from M. bovis -infected deer to M. avium antigens did not differ from that of PBMC from M. bovis infected deer to no stimulation or from that of PBMC from non-infected deer to M. avium antigens. These findings indicate that adherent PBMC from white-tailed deer are capable of NO production and that mononuclear cells isolated from M. bovis -infected white-tailed deer produce NO in an antigen-specific recall response
Diagnostic Implications of Antigen-Induced Gamma Interferon, Nitric Oxide, and Tumor Necrosis Factor Alpha Production by Peripheral Blood Mononuclear Cells from \u3ci\u3eMycobacterium bovis\u3c/i\u3e-Infected Cattle
Bovine tuberculosis in the United States has proven costly to cattle producers as well as to government regulatory agencies. While in vivo responsiveness to mycobacterial antigens is the current standard for the diagnosis of tuberculosis, in vitro assays are gaining acceptance, especially as ancillary or complementary tests. To evaluate in vitro indices of cellular sensitization, antigen-induced gamma interferon (IFN-γ), nitric oxide (NO), and tumor necrosis factor alpha (TNF-α) responses by blood mononuclear cells from Mycobacterium bovis-infected cattle were quantified and compared. Using an aerosol model of infection, two doses of each of two strains of M. bovis (95-1315 and HC-2045T) were used to induce a range of IFN-γ, NO, and TNF-α responses. Infection-specific increases in NO, but not in IFN-γ or TNF-α, were detected in nonstimulated cultures at 48 h, a finding that is indicative of nonspecific activation and spontaneous release of NO. The infective dose of M. bovis organisms also influenced responses. At 34 days postinfection, IFN-γ, NO, and TNF-α responses in antigen-stimulated cells from cattle receiving 105 CFU of M. bovis organisms were greater than responses of cells from cattle infected with 103 CFU of M. bovis organisms. The NO response, but not the IFN-γ and TNF-α responses, was influenced by infective strains of M. bovis. The TNF-α, NO, and IFN-γ responses followed similar kinetics, with strong positive associations among the three readouts. Overall, these findings indicate that NO and TNF-α, like IFN-γ, may prove useful as indices for the diagnosis of bovine tuberculosis
Gravitational bending of light by planetary multipoles and its measurement with microarcsecond astronomical interferometers
General relativistic deflection of light by mass, dipole, and quadrupole
moments of gravitational field of a moving massive planet in the Solar system
is derived. All terms of order 1 microarcsecond are taken into account,
parametrized, and classified in accordance with their physical origin. We
calculate the instantaneous patterns of the light-ray deflections caused by the
monopole, the dipole and the quadrupole moments, and derive equations
describing apparent motion of the deflected position of the star in the sky
plane as the impact parameter of the light ray with respect to the planet
changes due to its orbital motion. The present paper gives the physical
interpretation of the observed light-ray deflections and discusses the
observational capabilities of the near-future optical (SIM) and radio (SKA)
interferometers for detecting the Doppler modulation of the radial deflection,
and the dipolar and quadrupolar light-ray bendings by the Jupiter and the
Saturn.Comment: 33 pages, 10 figures, accepted to Phys. Rev.
A novel approach to fireball modeling: The observable and the calculated
Estimating the mass of a meteoroid passing through the Earth's atmosphere is essential to determining potential meteorite fall positions. High-resolution fireball images from dedicated camera networks provide the position and timing for fireball bright flight trajectories. There are two established mass determination methods: the photometric and the dynamic. A new approach is proposed, based on the dynamic method. A dynamic optimization initially constrains unknown meteoroid characteristics which are then used in a parametric model for an extended Kalman filter. The extended Kalman filter estimates the position, velocity, and mass of the meteoroid body throughout its flight, and quantitatively models uncertainties. Uncertainties have not previously been modeled so explicitly and are essential for determining fall distributions for potential meteorites. This two-step method aims to automate the process of mass determination for application to any trajectory data set and has been applied to observations of the Bunburra Rockhole fireball. The new method naturally handles noisy raw data. Initial and terminal bright flight mass results are consistent with other works based on the established photometric method and cosmic ray analysis. A full analysis of fragmentation and the variability in the heat-transfer coefficient will be explored in future versions of the model
Search for TeV Gamma-Rays from Shell-Type Supernova Remnants
If cosmic rays with energies <100 TeV originate in the galaxy and are
accelerated in shock waves in shell-type supernova remnants (SNRs), gamma-rays
will be produced as the result of proton and electron interactions with the
local interstellar medium, and by inverse Compton emission from electrons
scattering soft photon fields. We report on observations of two supernova
remnants with the Whipple Observatory's 10 m gamma-ray telescope. No
significant detections have been made and upper limits on the >500 GeV flux are
reported. Non-thermal X-ray emission detected from one of these remnants
(Cassiopeia A) has been interpreted as synchrotron emission from electrons in
the ambient magnetic fields. Gamma-ray emission detected from the
Monoceros/Rosette Nebula region has been interpreted as evidence of cosmic-ray
acceleration. We interpret our results in the context of these observations.Comment: 4 pages, 2 figures, to appear in the proceedings of 26th
International Cosmic Ray Conference (Salt Lake City, 1999
Recommended from our members
The Distance To The Hyades Cluster Based On Hubble Space Telescope Fine Guidance Sensor Parallaxes
Trigonometric parallax observations made with the Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) 3 of seven Hyades members in six fields of view have been analyzed along with their proper motions to determine the distance to the cluster. Knowledge of the convergent point and mean proper motion of the Hyades is critical to the derivation of the distance to the center of the cluster. Depending on the choice of the proper-motion system, the derived cluster center distance varies by 9%. Adopting a reference distance of 46.1 pc or m - M = 3.32, which is derived from the ground-based parallaxes in the General Catalogue of Trigonometric Stellar Parallaxes (1995 edition), the FK5/PPM proper-motion system yields a distance 4% larger, while the Hanson system yields a distance 2% smaller. The HST FGS parallaxes reported here yield either a 14% or 5% larger distance, depending on the choice of the proper-motion system. Orbital parallaxes (Torres et al.) yield an average distance 4% larger than the reference distance. The variation in the distance derived from the HST data illustrates the importance of the proper-motion system and the individual proper motions to the derivation of the distance to the Hyades center; therefore, a full utilization of the HST FGS parallaxes awaits the establishment of an accurate and consistent proper-motion system.NASA HST GTO, HF-1042.01-93A, HF-1046.01-93A, NAS526555Astronom
Global Models of Runaway Accretion in White Dwarf Debris Disks
A growing sample of white dwarfs (WDs) with metal-enriched atmospheres are
accompanied by excess infrared emission, indicating that they are encircled by
a compact dusty disk of solid debris. Such `WD debris disks' are thought to
originate from the tidal disruption of asteroids or other minor bodies, but the
precise mechanism(s) responsible for transporting matter to the WD surface
remains unclear, especially in those systems with the highest inferred metal
accretion rates dM_Z/dt ~ 1e8-1e10 g/s. Here we present global time-dependent
calculations of the coupled evolution of the gaseous and solid components of WD
debris disks. Solids transported inwards (initially due to PR drag) sublimate
at tens of WD radii, producing a source of gas that accretes onto the WD
surface and viscously spreads outwards in radius, where it overlaps with the
solid disk. If the aerodynamic coupling between the solids and gaseous disks is
sufficiently strong (and/or the gas viscosity sufficiently weak), then gas
builds up near the sublimation radius faster than it can viscously spread away.
Since the rate of drag-induced solid accretion increases with gas density, this
results in a runaway accretion process, during which the WD accretion rate
reaches values orders of magnitude higher than can be achieved by PR drag
alone. We explore the evolution of WD debris disks across a wide range of
physical conditions and calculate the predicted distribution of observed
accretion rates dM_Z/dt, finding reasonable agreement with the current sample.
Although the conditions necessary for runaway accretion are at best marginally
satisfied given the minimal level of aerodynamic drag between circular gaseous
and solid disks, the presence of other stronger forms of solid-gas
coupling---such as would result if the gaseous disk is only mildly
eccentric---substantially increase the likelihood of runaway accretion.Comment: 23 pages, 20 figures, submitted to MNRA
Precise Masses for Wolf 1062 AB from Hubble Space Telescope Interferometric Astrometry and McDonald Observatory Radial Velocities
We present an analysis of astrometric data from FGS 3, a white-light
interferometer on {\it HST}, and of radial velocity data from two ground-based
campaigns. We model the astrometric and radial velocity measurements
simultaneously to obtain parallax, proper motion and component masses for Wolf
1062 = Gl 748 AB (M3.5V). To derive the mass fraction, we relate FGS 3 fringe
scanning observations of the science target to a reference frame provided by
fringe tracking observations of a surrounding star field. We obtain an absolute
parallax milliseconds of arc, yielding {\cal M}_A =
0.379 \pm 0.005{\cal M}_{\sun} and {\cal M}_B= 0.192 \pm 0.003 {\cal
M}_{\sun}, high quality component masses with errors of only 1.5%.Comment: 13 pages, 7 figures. To appear in AJ March 200
- …