1,835 research outputs found
Experiments on the injection and containment of electron clouds in a toroidal apparatus
Injection and containment of electron clouds in azimuthally symmetric, toroidal apparatu
Automated measurement of the bit-error rate as a function of signal-to-noise ratio for microwave communications systems
The performance of microwave systems and components for digital data transmission can be characterized by a plot of the bit-error rate as a function of the signal to noise ratio (or E sub b/E sub o). Methods for the efficient automated measurement of bit-error rates and signal-to-noise ratios, developed at NASA Lewis Research Center, are described. Noise measurement considerations and time requirements for measurement accuracy, as well as computer control and data processing methods, are discussed
Developing reverse logistics programs: A resource based view
Previous research proposes a six-process model for reverse logistics (RL) program design and execution. This manuscript advances RL related knowledge by incorporating the previous model into a broader theoretical framework, namely, the Resource Based View (RBV) of the firm. The current research employs exploratory techniques to investigate the applicability of RBV and its main tenants within the RL context. Based on in-depth interviews with 16 executives from seven different companies, the relationships among resources. RL capabilities, and RL competencies are explored
Mathematical models of bipolar disorder
We use limit cycle oscillators to model bipolar II disorder, which is characterized by alternating hypomanic and depressive episodes and afflicts about 1% of the United States adult population. We consider two non-linear oscillator models of a single bipolar patient. In both frameworks, we begin with an untreated individual and examine the mathematical effects and resulting biological consequences of treatment. We also briefly consider the dynamics of interacting bipolar II individuals using weakly-coupled, weakly-damped harmonic oscillators. We discuss how the proposed models can be used as a framework for refined models that incorporate additional biological data. We conclude with a discussion of possible generalizations of our work, as there are several biologically-motivated extensions that can be readily incorporated into the series of models presented here
Very-high-energy gamma radiation associated with the unshocked wind of the Crab pulsar
We show that the relativistic wind in the Crab pulsar, which is commonly
thought to be invisible in the region upstream of the termination shock at R <
0.1 pc, in fact could be directly observed through its inverse Compton gamm-ray
emission. The search for such specific component of radiation in the gamma-ray
spectrum of the Crab can provide unique information about the unshocked pulsar
wind that is not accessible at other wavelengths.Comment: 11 pages, 11 figures, to appear in one of the April issues of MNRA
Electron-Positron Jets from a Critically Magnetized Black Hole
The curved spacetime surrounding a rotating black hole dramatically alters
the structure of nearby electromagnetic fields. The Wald field which is an
asymptotically uniform magnetic field aligned with the angular momentum of the
hole provides a convenient starting point to analyze the effects of radiative
corrections on electrodynamics in curved spacetime. Since the curvature of the
spacetime is small on the scale of the electron's Compton wavelength, the tools
of quantum field theory in flat spacetime are reliable and show that a rotating
black hole immersed in a magnetic field approaching the quantum critical value
of ~G cm is unstable. Specifically, a maximally rotating
three-solar-mass black hole immersed in a magnetic field of ~G would be a copious producer of electron-positron pairs with a
luminosity of erg s.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
X-ray Phase-Resolved Spectroscopy of PSRs B0531+21, B1509-58, and B0540-69 with RXTE
The Rossi X-ray Timing Explorer ({\sl RXTE}) has made hundreds of
observations on three famous young pulsars (PSRs) B0531+21 (Crab), B1509-58,
and B0540-69. Using the archive {\sl RXTE} data, we have studied the
phase-resolved spectral properties of these pulsars in details. The variation
of the X-ray spectrum with phase of PSR B0531+21 is confirmed here much more
precisely and more details are revealed than the previous studies: the spectrum
softens from the beginning of the first pulse, turns to harden right at the
pulse peak and becomes the hardest at the bottom of the bridge, softens
gradually until the second peak, and then softens rapidly. Different from the
previous studies, we found that the spectrum of PSR B1509-58 is significantly
harder in the center of the pulse, which is also in contrast to that of PSR
B0531+21. The variation of the X-ray spectrum of PSR B0540-69 seems similar to
that of PSR B1509-58, but with a lower significance. Using the about 10 years
of data span, we also studied the real time evolution of the spectra of these
pulsars, and no significant evolution has been detected. We have discussed
about the constraints of these results on theoretical models of pulsar X-ray
emission.Comment: 42 pages, 24 figure
Three-dimensional Two-Layer Outer Gap Model: Fermi Energy Dependent Light Curves of the Vela Pulsar
We extend the two-dimensional two-layer outer gap model to a
three-dimensional geometry and use it to study the high-energy emission of the
Vela pulsar. In this model, the outer gap is divided into two parts, i.e. the
main acceleration region on the top of last-open field lines and the screening
region around the upper boundary of the gap. In the main acceleration region,
the charge density is much lower than the Goldreich-Julian charge density and
the charged particles are accelerated by the electric field along the magnetic
field to emit multi-GeV photons. In the screening region, the charge density is
larger than the Goldreich-Julian value to close the gap and particles in this
region are responsible for multi-100MeV photon emission. We apply this three
dimensional two-layer model to the Vela pulsar and compare the model light
curves, the phase-averaged spectrum and the phase-resolved spectra with the
recent Fermi observations, which also reveals the existence of the third peak
between two main peaks. The phase position of the third peak moves with the
photon energy, which cannot be explained by the geometry of magnetic field
structure and the caustic effects of the photon propagation. We suggest that
the existence of the third peak and its energy dependent movement results from
the azimuthal structure of the outer gap.Comment: 11 pages, 15 figures, accepted for publication in MNRA
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