25,947 research outputs found
Electron beam fluorescence measurements in the Boeing hypersonic shock tunnel
The Calspan electron beam fluorescence (EBF) measurement system is described along with the results of measurements made in hypersonic flow. Numerous self-emitting metallic species were identified, many of which may be associated with an aging/erosion process within the B30HST. Because there were only 16 tunnel runs, it was only possible to obtain spectral measurements over a limited range of wavelengths and time sampling periods. Many spectral features of the flow remain uninvestigated. Because flow self-emission is important to all optical diagnostic techniques, it is recommended that additional spectral studies by performed. The three electron beam-excited species that were identified are nitrogen, helium, and nitric oxide. The high metallic radiation background interfered with attempts to obtain the time-wise variation of N2 density and He radiation with the optical fiber/PMT channels. In the case of the N2 density measurements the result of interference was increased uncertainty. Unfortunately, the interference caused the time-wise He measurements to fail completely. It is recommended that the electron beam be modulated to provide discrimination against the background radiation in future N2 density measurements. Careful data reduction produced useful measurements of N2 vibrational temperature, even though the high background from metallic species significantly increased measurement uncertainty. Perhaps the recommended additional spectral studies would reveal N2(+) First Negative System band-pair regions having less background. Detection of the He arrival was easily accomplished with the spectrometer/array detector system. Because of this, it is recommended that this means of detecting He arrival be used in the future. With proper calibrations of the system an He number density could be obtained. Although the flow conditions were out of limits for the run in which the NO spectrum was recorded, the usefulness of the NO spectrum for determination of free-stream rotational temperature was demonstrated and should be exploited in future experiments. Indeed, based on the strong NO signals, it is recommended that lower resolution NO spectra be obtained to provide a measure of NO vibrational temperature in the same manner that the N2 temperature was obtained
Impact of low gravity on water electrolysis operation
Advanced space missions will require oxygen and hydrogen utilities for several important operations including the following: (1) propulsion; (2) electrical power generation and storage; (3) environmental control and life support; (4) extravehicular activity; (5) in-space manufacturing and (6) in-space science activities. An experiment suited to a Space Shuttle standard middeck payload has been designed for the Static Feed Water Electrolysis technology which has been viewed as being capable of efficient, reliable oxygen and hydrogen generation with few subsystem components. The program included: end use design requirements, phenomena to be studied, Space Shuttle Orbiter experiment constraints, experiment design and data requirements, and test hardware requirements. The objectives are to obtain scientific and engineering data for future research and development and to focus on demonstrating and monitoring for safety of a standard middeck payload
Implementing Quantum Gates by Optimal Control with Doubly Exponential Convergence
We introduce a novel algorithm for the task of coherently controlling a
quantum mechanical system to implement any chosen unitary dynamics. It performs
faster than existing state of the art methods by one to three orders of
magnitude (depending on which one we compare to), particularly for quantum
information processing purposes. This substantially enhances the ability to
both study the control capabilities of physical systems within their coherence
times, and constrain solutions for control tasks to lie within experimentally
feasible regions. Natural extensions of the algorithm are also discussed.Comment: 4+2 figures; to appear in PR
First-principle density-functional calculation of the Raman spectra of BEDT-TTF
We present a first-principles density-functional calculation for the Raman
spectra of a neutral BEDT-TTF molecule. Our results are in excellent agreement
with experimental results. We show that a planar structure is not a stable
state of a neutral BEDT-TTF molecule. We consider three possible conformations
and discuss their relation to disorder in these systems.Comment: 3 pages, 2 figures, submitted to the proceedings of ISCOM 200
Diet Effects on Dairy Manure Nitrogen Excretion and Cycling
The amount and forms of (nitrogen) N excreted by ruminant livestock and post excretion manure N cycling are highly influenced by what is fed. For example, the relative amount of urinary N, faecal endogenous N of microbial and gut origin, and faecal undigested feed N is affected by how much dietary fibre and secondary compounds (e.g., tannins, polyphneolics) are consumed. Each manure N component has a different propensity for loss; for example via ammonia (NH3) volatilisation (Misselbrook et al., 2004), leaching, and cycles differently in the soil-plant continuum (Powell, 2003). We evaluated dairy diet effects on amount and forms of manure N excreted and post excretion cycling of manure N from different diets after application to soil
Electronic and magnetic properties of the ionic Hubbard model on the striped triangular lattice at 3/4 filling
We report a detailed study of a model Hamiltonian which exhibits a rich
interplay of geometrical spin frustration, strong electronic correlations, and
charge ordering. The character of the insulating phase depends on the magnitude
of Delta/|t| and on the sign of t. We find a Mott insulator for Delta >> U >>
|t|; a charge transfer insulator for U >> \Delta >> |t|; and a correlated
covalent insulator for U >> \Delta ~ |t|. The charge transfer insulating state
is investigated using a strong coupling expansion. The frustration of the
triangular lattice can lead to antiferromagnetism or ferromagnetism depending
on the sign of the hopping matrix element, t. We identify the "ring" exchange
process around a triangular plaquette which determines the sign of the magnetic
interactions. Exact diagonalization calculations are performed on the model for
a wide range of parameters and compared to the strong coupling expansion. The
regime U >> \Delta ~ |t| and t<0 is relevant to Na05CoO2. The calculated
optical conductivity and the spectral density are discussed in the light of
recent experiments on Na05CoO2.Comment: 15 pages, 15 figure
Calcium Oxalate Crystal Production in Two Members of the Mucorales
Calcium oxalate crystals are found in association with the sporangia of Mucor hiemalis and Rhizopus oryzae. Crystals observed in each species vary in morphology from simple crystals consisting of single spines in M. hiemalis to complex crystals with twin spines, sometimes three-parted, on a common base in R. oryzae. The early development of the crystals is similar in both species with a layer of the cell wall covering in the initial crystals. The spines of M. hiemalis rapidly emerge while the crystals of R. oryzae appear to remain covered with a layer of outer wall material. The crystals of both species become fully developed just prior to spore release. Details of crystal development are compared and possible mechanisms for crystal development are explored
Antiferromagnetic Spin Fluctuations in the Metallic Phase of Quasi-Two-Dimensional Organic Superconductors
We give a quantitative analysis of the previously published nuclear magnetic
resonance (NMR) experiments in the k-(ET)2X family of organic charge transfer
salts by using the phenomenological spin fluctuation model of Moriya, and
Millis, Monien and Pines (M-MMP). For temperatures above T_nmr ~ 50 K, the
model gives a good quantitative description of the data in the metallic phases
of several k-(ET)2X materials. These materials display antiferromagnetic
correlation lengths which increase with decreasing temperature and grow to
several lattice constants by T_nmr. It is shown that the fact that the
dimensionless Korringa ratio is much larger than unity is inconsistent with a
broad class of theoretical models (such as dynamical mean-field theory) which
neglects spatial correlations and/or vertex corrections. For materials close to
the Mott insulating phase the nuclear spin relaxation rate, the Knight shift
and the Korringa ratio all decrease significantly with decreasing temperature
below T_nmr. This cannot be described by the M-MMP model and the most natural
explanation is that a pseudogap, similar to that observed in the underdoped
cuprate superconductors, opens up in the density of states below T_nmr. Such a
pseudogap has recently been predicted to occur in the dimerised organic charge
transfer salts materials by the resonating valence bond (RVB) theory. We
propose specific new experiments on organic superconductors to elucidate these
issues. For example, measurements to see if high magnetic fields or high
pressures can be used to close the pseudogap would be extremely valuable.Comment: 11 pages, 2 figures. Accepted for publication in Phys. Rev.
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