21,876 research outputs found
Performance criteria guideline for three explosion protection methods of electrical equipment rated up to 15,000 volts AC
The Bureau of Mines, U.S. Department of the Interior, is reviewing explosion protection methods for use in gassy coal mines. This performance criteria guideline is an evaluation of three explosion protection methods of machines electrically powered with voltages up to 15,000 volts ac. A sufficient amount of basic research has been accomplished to verify that the explosion proof and pressurized enclosure methods can provide adequate explosion protection with the present state of the art up to 15,000 volts ac. This routine application of the potted enclosure as a stand alone protection method requires further investigation or development in order to clarify performance criteria and verification certification requirements. An extensive literature search, a series of high voltage tests, and a design evaluation of the three explosion protection methods indicate that the explosion proof, pressurized, and potted enclosures can all be used to enclose up to 15,000 volts ac
Mineralogy and Surface Composition of Asteroids
Methods to constrain the surface mineralogy of asteroids have seen
considerable development during the last decade with advancement in laboratory
spectral calibrations and validation of our interpretive methodologies by
spacecraft rendezvous missions. This has enabled the accurate identification of
several meteorite parent bodies in the main asteroid belt and helped constrain
the mineral chemistries and abundances in ordinary chondrites and basaltic
achondrites. With better quantification of spectral effects due to temperature,
phase angle, and grain size, systematic discrepancies due to non-compositional
factors can now be virtually eliminated for mafic silicate-bearing asteroids.
Interpretation of spectrally featureless asteroids remains a challenge. This
paper presents a review of all mineralogical interpretive tools currently in
use and outlines procedures for their application.Comment: Chapter to appear in the Space Science Series Book: Asteroids IV, 51
pages, 7 figures, 2 table
Spin Torque Dynamics with Noise in Magnetic Nano-System
We investigate the role of equilibrium and nonequilibrium noise in the
magnetization dynamics on mono-domain ferromagnets. Starting from a microscopic
model we present a detailed derivation of the spin shot noise correlator. We
investigate the ramifications of the nonequilibrium noise on the spin torque
dynamics, both in the steady state precessional regime and the spin switching
regime. In the latter case we apply a generalized Fokker-Planck approach to
spin switching, which models the switching by an Arrhenius law with an
effective elevated temperature. We calculate the renormalization of the
effective temperature due to spin shot noise and show that the nonequilibrium
noise leads to the creation of cold and hot spot with respect to the noise
intensity.Comment: 10 pages, 7 figure
Sonic levitation apparatus
A sonic levitation apparatus is disclosed which includes a sonic transducer which generates acoustical energy responsive to the level of an electrical amplifier. A duct communicates with an acoustical chamber to deliver an oscillatory motion of air to a plenum section which contains a collimated hole structure having a plurality of parallel orifices. The collimated hole structure converts the motion of the air to a pulsed. Unidirectional stream providing enough force to levitate a material specimen. Particular application to the production of microballoons in low gravity environment is discussed
Photon signature analysis using template matching
We describe an approach to detect improvised explosive devices (IEDs) by using a template matching procedure. This approach relies on the signature due to backstreaming ? photons from various targets. In this work we have simulated cylindrical targets of aluminum, iron, copper, water and ammonium nitrate (nitrogen-rich fertilizer). We simulate 3.5 MeV source photons distributed on a plane inside a shielded area using Monte Carlo N-Particle (MCNP TM) code version 5 (V5). The 3.5 MeV source gamma rays yield 511 keV peaks due to pair production and scattered gamma rays. In this work, we simulate capture of those photons that backstream, after impinging on the target element, toward a NaI detector. The captured backstreamed photons are expected to produce a unique spectrum that will become part of a simple signal processing recognition system based on the template matching method. Different elements were simulated using different sets of random numbers in the Monte Carlo simulation. To date, the sum of absolute differences (SAD) method has been used to match the template. In the examples investigated, template matching was found to detect all elements correctly
The temporal dynamic of response inhibition in early childhood: An ERP study of partial and successful inhibition
Event-related potentials were recorded while five-year-old children completed a Go/No-Go task that distinguished between partial inhibition (i.e., response is initiated but cancelled before completion) and successful inhibition (i.e., response is inhibited before it is initiated). Partial inhibition trials were characterized by faster response initiation and later latency of the lateral frontal negativity (LFN) than successful Go and successful inhibition trials. The speed of response initiation was influenced by the response speed on previous trials and influenced the response speed on subsequent trials. Response initiation and action decision dynamically influenced each other, and their temporal interplay determined response inhibition success
Vibronic interactions in the visible and near-infrared spectra of C60− anions
Electron-phonon coupling is an important factor in understanding many properties of the C60 fullerides. However, there has been little success in quantifying the strength of the vibronic coupling in C60 ions, with considerable disagreement between experimental and theoretical results. We will show that neglect of quadratic coupling in previous models for C60- ions results in a significant overestimate of the linear coupling constants. Including quadratic coupling allows a coherent interpretation to be made of earlier experimental and theoretical results which at first sight are incompatible
- …