5,524 research outputs found
Multiplate focusing collimator
An appartus is described for scanning relatively small near sources of penetrating radiation to obtain the energy distribution thereof, wherein a collimator assembly is interposed between a radiation source and a radiation detector. The collimator assembly has a plurality of plates aligned in parallel planes with respect to a common axis normal to their centers. All the plates have similar random distribution of apertures. All apertures on each plate are the same size. The size of respective plates, the size of the apertures of said respective plates, and the spacing between said respective plates vary precisely according to a predetermined ratio to produce radiation channels which converge to a focal point. The radiation incident to the radiation detector is maximized when the focal point and the radiation source are co-incident
Remarks on NonHamiltonian Statistical Mechanics: Lyapunov Exponents and Phase-Space Dimensionality Loss
The dissipation associated with nonequilibrium flow processes is reflected by
the formation of strange attractor distributions in phase space. The
information dimension of these attractors is less than that of the equilibrium
phase space, corresponding to the extreme rarity of nonequilibrium states. Here
we take advantage of a simple model for heat conduction to demonstrate that the
nonequilibrium dimensionality loss can definitely exceed the number of
phase-space dimensions required to thermostat an otherwise Hamiltonian system.Comment: 5 pages, 2 figures, minor typos correcte
History of nutrient inputs to the northeastern United States, 1930–2000
Humans have dramatically altered nutrient cycles at local to global scales. We examined changes in anthropogenic nutrient inputs to the northeastern United States (NE) from 1930 to 2000. We created a comprehensive time series of anthropogenic N and P inputs to 437 counties in the NE at 5 year intervals. Inputs included atmospheric N deposition, biological N2 fixation, fertilizer, detergent P, livestock feed, and human food. Exports included exports of feed and food and volatilization of ammonia. N inputs to the NE increased throughout the study period, primarily due to increases in atmospheric deposition and fertilizer. P inputs increased until 1970 and then declined due to decreased fertilizer and detergent inputs. Livestock consistently consumed the majority of nutrient inputs over time and space. The area of crop agriculture declined during the study period but consumed more nutrients as fertilizer. We found that stoichiometry (N:P) of inputs and absolute amounts of N matched nutritional needs (livestock, humans, crops) when atmospheric components (N deposition, N2 fixation) were not included. Differences between N and P led to major changes in N:P stoichiometry over time, consistent with global trends. N:P decreased from 1930 to 1970 due to increased inputs of P, and increased from 1970 to 2000 due to increased N deposition and fertilizer and decreases in P fertilizer and detergent use. We found that nutrient use is a dynamic product of social, economic, political, and environmental interactions. Therefore, future nutrient management must take into account these factors to design successful and effective nutrient reduction measures
Time-reversed symmetry and covariant Lyapunov vectors for simple particle models in and out of thermal equilibrium
Recently, a new algorithm for the computation of covariant Lyapunov vectors
and of corresponding local Lyapunov exponents has become available. Here we
study the properties of these still unfamiliar quantities for a number of
simple models, including an harmonic oscillator coupled to a thermal gradient
with a two-stage thermostat, which leaves the system ergodic and fully time
reversible. We explicitly demonstrate how time-reversal invariance affects the
perturbation vectors in tangent space and the associated local Lyapunov
exponents. We also find that the local covariant exponents vary discontinuously
along directions transverse to the phase flow.Comment: 13 pages, 11 figures submitted to Physical Review E, 201
INCORPORATION OF QUANTUM STATISTICAL FEATURES IN MOLECULAR DYNAMICS
We formulate a method for incorporating quantum fluctuations into molecular-
dynamics simulations of many-body systems, such as those employed for energetic
nuclear collision processes. Based on Fermi's Golden Rule, we allow spontaneous
transitions to occur between the wave packets which are not energy eigenstates.
The ensuing diffusive evolution in the space of the wave packet parameters
exhibits appealing physical properties, including relaxation towards quantum-
statistical equilibrium.Comment: 8 latex pages + 1 uuencoded ps figur
NaOH wheat silage and alfalfa haylage for growing steers and heifers
Wheat silage, with and without sodium hydroxide (NaOH), was fed, with
or without alfalfa haylage, in an 80-day growing trial. Calves fed NaOH-silage
consumed 18% more feed and gained 16% faster than those fed control silage,
but feed efficiencies were similar. When 50% of the wheat silage was replaced
with alfalfa haylage (DM basis), gains decreased 3.1 and 3.7%, feed intake
increased 12.3 and 9.7%, and feed efficiency decreased 23.7 and 14.4% for
calves fed control and NaOH silages, respectively. NaOH increased ensiling
temperatures by 9 to 12° C during the first 6 weeks. Dry matter recovery
from the concrete stave silos was similar for both silages (82.1% for control
and 83.9% for NaOH); recoveries from buried bags were 92.3 and 89.5%. NaOH
wheat silage was more stable in air than was either control wheat silage or
alfalfa haylage
Lyapunov instability for a periodic Lorentz gas thermostated by deterministic scattering
In recent work a deterministic and time-reversible boundary thermostat called
thermostating by deterministic scattering has been introduced for the periodic
Lorentz gas [Phys. Rev. Lett. {\bf 84}, 4268 (2000)]. Here we assess the
nonlinear properties of this new dynamical system by numerically calculating
its Lyapunov exponents. Based on a revised method for computing Lyapunov
exponents, which employs periodic orthonormalization with a constraint, we
present results for the Lyapunov exponents and related quantities in
equilibrium and nonequilibrium. Finally, we check whether we obtain the same
relations between quantities characterizing the microscopic chaotic dynamics
and quantities characterizing macroscopic transport as obtained for
conventional deterministic and time-reversible bulk thermostats.Comment: 18 pages (revtex), 7 figures (postscript
Whole-plant forage and grain sorghum silages for growing cattle
Four trials were conducted to determine the feeding value of whole-plant forage and grain sorghum silages. In general, growing cattle fed grain sorghum hybrids (NK2778, Funk\u27s 550, DeKalb 42Y, DeKalb E67) out performed those fed forage sorghum silages. Only moderate to high grain-content, forage sorghums (Buffalo Canex, Pioneer 947, Acco 351) gave performances that approached the grain sorghums. Low grain-content and nonheading forage sorghums (DeKalb 25E, Funk\u27s G-1990) resulted in the poorest cattle performance. These studies indicate that grain content of a sorghum silage is the major determinant of cattle performance and that whole-plant grain sorghums should produce the fastest and most efficient gains in growing programs
Scaling Solutions to 6D Gauged Chiral Supergravity
We construct explicitly time-dependent exact solutions to the field equations
of 6D gauged chiral supergravity, compactified to 4D in the presence of up to
two 3-branes situated within the extra dimensions. The solutions we find are
scaling solutions, and are plausibly attractors which represent the late-time
evolution of a broad class of initial conditions. By matching their near-brane
boundary conditions to physical brane properties we argue that these solutions
(together with the known maximally-symmetric solutions and a new class of
non-Lorentz-invariant static solutions, which we also present here) describe
the bulk geometry between a pair of 3-branes with non-trivial on-brane
equations of state.Comment: Contribution to the New Journal of Physics focus issue on Dark
Energy; 28 page
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