9,980 research outputs found
Probing the evolving massive star population in Orion with kinematic and radioactive tracers
We assemble a census of the most massive stars in Orion, then use stellar
isochrones to estimate their masses and ages, and use these results to
establish the stellar content of Orion's individual OB associations. From this,
our new population synthesis code is utilized to derive the history of the
emission of UV radiation and kinetic energy of the material ejected by the
massive stars, and also follow the ejection of the long-lived radioactive
isotopes 26Al and 60Fe. In order to estimate the precision of our method, we
compare and contrast three distinct representations of the massive stars. We
compare the expected outputs with observations of 26Al gamma-ray signal and the
extent of the Eridanus cavity. We find an integrated kinetic energy emitted by
the massive stars of 1.8(+1.5-0.4)times 10^52 erg. This number is consistent
with the energy thought to be required to create the Eridanus superbubble. We
also find good agreement between our model and the observed 26Al signal,
estimating a mass of 5.8(+2.7-2.5) times 10^-4 Msol of 26Al in the Orion
region. Our population synthesis approach is demonstrated for the Orion region
to reproduce three different kinds of observable outputs from massive stars in
a consistent manner: Kinetic energy as manifested in ISM excavation, ionization
as manifested in free-free emission, and nucleosynthesis ejecta as manifested
in radioactivity gamma-rays. The good match between our model and the
observables does not argue for considerable modifications of mass loss. If
clumping effects turn out to be strong, other processes would need to be
identified to compensate for their impact on massive-star outputs. Our
population synthesis analysis jointly treats kinematic output and the return of
radioactive isotopes, which proves a powerful extension of the methodology that
constrains feedback from massive stars.Comment: Accepted for publication in A&A, 10 page
Ion and electron temperatures in the SUMMA mirror device by emission spectroscopy
Ion and electron temperatures, and ion drift were measured in a superconducting magnetic mirror apparatus by observing the Doppler-broadened charge-exchange component of the 667.8 and 587.6 nanometer He lines in He plasma, and the H sub alpha and H sub beta lines in H2 plasma. The second moment of the line profiles was used as the parameter for determining ion temperature. Corrections for magnetic splitting, fine structure, monochromator slit function, and variation in charge-exchange cross section with energy are included. Electron temperatures were measured by the line ratio method for the corona model, and correlations of ion and electron temperatures with plasma parameters are presented
Optical-fiber source of polarization-entangled photon pairs in the 1550nm telecom band
We present a fiber based source of polarization-entangled photon pairs that
is well suited for quantum communication applications in the 1550nm band of
standard fiber-optic telecommunications. Polarization entanglement is created
by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed
orthogonally-polarized pump pulses and subsequently removing the time
distinguishability by passing the parametrically scattered signal-idler photon
pairs through a piece of birefringent fiber. Coincidence detection of the
signal-idler photons yields biphoton interference with visibility greater than
90%, while no interference is observed in direct detection of either the signal
or the idler photons. All four Bell states can be prepared with our setup and
we demonstrate violations of CHSH form of Bell's inequalities by up to 10
standard deviations of measurement uncertainty.Comment: 12 pages, 4 figures, to be submitted to Phys. Rev. Lett. See also
paper QTuB4 in QELS'03 Technical Digest (OSA, Washington, D.C., 2003). This
is a more complete versio
A feasibility study: California Department of Forestry and Fire Protection utilization of infrared technologies for wildland fire suppression and management
NASA's JPL has completed a feasibility study using infrared technologies for wildland fire suppression and management. The study surveyed user needs, examined available technologies, matched the user needs with technologies, and defined an integrated infrared wildland fire mapping concept system configuration. System component trade-offs were presented for evaluation in the concept system configuration. The economic benefits of using infrared technologies in fire suppression and management were examined. Follow-on concept system configuration development and implementation were proposed
Universal Behavior of the Resistance Noise across the Metal-Insulator Transition in Silicon Inversion Layers
Studies of low-frequency resistance noise show that the glassy freezing of
the two-dimensional (2D) electron system in the vicinity of the metal-insulator
transition occurs in all Si inversion layers. The size of the metallic glass
phase, which separates the 2D metal and the (glassy) insulator, depends
strongly on disorder, becoming extremely small in high-mobility samples. The
behavior of the second spectrum, an important fourth-order noise statistic,
indicates the presence of long-range correlations between fluctuators in the
glassy phase, consistent with the hierarchical picture of glassy dynamics.Comment: revtex4; 4+ pages, 5 figure
Measuring the electrical impedance of mouse brain tissue
We report on an experimental method to measure conductivity of cortical tissue. We use a pair of 5mm diameter Ag/AgCl electrodes in a Perspex sandwich device that can be brought to a distance of 400 microns apart. The apparatus is brought to uniform temperature before use. Electrical impedance of a sample is measured across the frequency range 20 Hz-2.0 MHz with an Agilent 4980A four-point impedance monitor in a shielded room. The equipment has been used to measure the conductivity of mature mouse brain cortex in vitro. Slices 400 microns in thickness are prepared on a vibratome. Slices are bathed in artificial cerebrospinal fluid (ACSF) to keep them alive. Slices are removed from the ACSF and sections of cortical tissue approximately 2 mm times 2 mm are cut with a razor blade. The sections are photographed through a calibrated microscope to allow identification of their cross-sectional areas. Excess ACSF is removed from the sample and the sections places between the electrodes. The impedance is measured across the frequency range and electrical conductivity calculated. Results show two regions of dispersion. A low frequency region is evident below approximately 10 kHz, and a high frequency dispersion above this. Results at the higher frequencies show a good fit to the Cole-Cole model of impedance of biological tissue; this model consists of resistive and non-linear capacitive elements. Physically, these elements are likely to arise due to membrane polarization and migration of ions both intra- and extra-cellularly.http://www.iupab2014.org/assets/IUPAB/NewFolder/iupab-abstracts.pd
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