6,652 research outputs found
Renormalization Group Flow Equations and the Phase Transition in O(N)-models
We derive and solve flow equations for a general O(N)-symmetric effective
potential including wavefunction renormalization corrections combined with a
heat-kernel regularization. We investigate the model at finite temperature and
study the nature of the phase transition in detail. Beta functions, fixed
points and critical exponents \beta, \nu, \delta and \eta for various N are
independently calculated which allow for a verification of universal scaling
relations.Comment: 34 pages, 3 tables, 11 postscript figures, LaTe
Soil Nitrification Inhibition with Plantain (\u3ci\u3ePlantago lanceolata\u3c/i\u3e)
One strategy to reduce nitrogen losses from intensively grazed forage systems is to slow the first stage of soil nitrification, specifically inhibiting the microbial oxidation of ammonium to nitrite. Plantain (Plantago lanceolata) leaves and roots are known to contain several bioactive compounds (e.g., aucubin, catalpol and verbascoside) that may contribute to this inhibition. Recent laboratory studies indicate that this inhibition occurs via consumption by grazing animals of precursor bioactive compounds in aboveground biomass and their subsequent excretion as secondary metabolites in urine and/or via active exudation from the roots. Different cultivars of plantain have been shown to impart differing nitrification inhibition activity via both mechanisms. The urinary effect was assessed by determination of net soil nitrification in soil microcosms treated with urine from sheep fed a diet containing either perennial ryegrass or plantain. Analyses showed significant treatment effects on the rate of net nitrification and microbial community structure over time. A preliminary evaluation of the root exudate effect involved the collection of root exudates from six plantain cultivars grown in a hydroponic system. The assay of the root exudates against a pure culture of an ammonium-oxidising bacterium indicated differences in the amount of inhibition imparted by the exudates of each cultivar. The exact means of soil nitrification inhibition by either mechanism is as yet unconfirmed. However, it is likely that these compounds (or derivatives thereof) inhibit the first enzymatic step of nitrification directly, without harm to the soil microbiome as a whole
Effect of floor type on the performance, physiological and behavioural responses of finishing beef steers
peer-reviewedBackground:The study objective was to investigate the effect of bare concrete slats (Control), two types of mats [(Easyfix mats (mat 1) and Irish Custom Extruder mats (mat 2)] fitted on top of concrete slats, and wood-chip to simulate deep bedding (wood-chip placed on top of a plastic membrane overlying the concrete slats) on performance, physiological and behavioral responses of finishing beef steers. One-hundred and forty-four finishing steers (503 kg; standard deviation 51.8 kg) were randomly assigned according to their breed (124 Continental cross and 20 Holstein–Friesian) and body weight to one of four treatments for 148 days. All steers were subjected to the same weighing, blood sampling (jugular venipuncture), dirt and hoof scoring pre study (day 0) and on days 23, 45, 65, 86, 107, 128 and 148 of the study. Cameras were fitted over each pen for 72 h recording over five periods and subsequent 10 min sampling scans were analysed.
Results: Live weight gain and carcass characteristics were similar among treatments. The number of lesions on the hooves of the animals was greater (P < 0.05) on mats 1 and 2 and wood-chip treatments compared with the animals on the slats. Dirt scores were similar for the mat and slat treatments while the wood-chip treatment had greater dirt scores. Animals housed on either slats or wood-chip had similar lying times. The percent of animals lying was greater for animals housed on mat 1 and mat 2 compared with those housed on concrete slats and wood chips. Physiological variables showed no significant difference among treatments.
Conclusions:
In this exploratory study, the performance or welfare of steers was not adversely affected by slats, differing mat types or wood-chip as underfoot material
Fluctuations of the Condensate in Ideal and Interacting Bose Gases
We investigate the fluctuations of the condensate in the ideal and weakly
interacting Bose gases confined in a box of volume V within canonical ensemble.
Canonical ensemble is developed to describe the behavior of the fluctuations
when different methods of approximation to the weakly interacting Bose gases
are used. Research shows that the fluctuations of the condensate exhibit
anomalous behavior for the interacting Bose gas confined in a box.Comment: RevTex, 4 Figs,E-mail:[email protected], corrected typo
On the Derivative Expansion at Finite Temperature
In this short note, we indicate the origin of nonanalyticity in the method of
derivative expansion at finite temperature and discuss some of its
consequences.Comment: 7 pages, UR-1363, ER40685-81
Solid-phase crystallization of Si films in contact with Al layers
Low-temperature (400–540 °C) crystallization of amorphous and polycrystalline Si films deposited on SiO2 and covered with an evaporated Al layer has been studied using SEM, TEM, electron diffraction, electron channeling, and MeV 4He + backscattering. Silicon deposited by evaporation and chemical vapor deposition (CVD) at 640 °C (both amorphous) was found to crystallize into islands of polycrystalline aggregates. Silicon deposited by CVD at 900 °C (polycrystalline with ~2000-Å grains) produced relatively large (~10 µm) single-crystal islands. In both cases island size increased with annealing time, and the rate of crystallization increased with temperature. Crystallization rates were observed to be the same for both sources of amorphous Si, while 900 °C CVD Si was noticeably slower, consistent with the postulate that the driving force for the reaction is the free-energy difference between initial and final states. The crystallization rate for 900 °C CVD Si decreased when the Al layer thickness was reduced to a value less than the initial Si grain size. The inclusion of a native oxide layer between the deposited Si and Al layers greatly retarded the crystallization process
Lyapunov spectral analysis of a nonequilibrium Ising-like transition
By simulating a nonequilibrium coupled map lattice that undergoes an
Ising-like phase transition, we show that the Lyapunov spectrum and related
dynamical quantities such as the dimension correlation length~ are
insensitive to the onset of long-range ferromagnetic order. As a function of
lattice coupling constant~ and for certain lattice maps, the Lyapunov
dimension density and other dynamical order parameters go through a minimum.
The occurrence of this minimum as a function of~ depends on the number of
nearest neighbors of a lattice point but not on the lattice symmetry, on the
lattice dimensionality or on the position of the Ising-like transition. In
one-space dimension, the spatial correlation length associated with magnitude
fluctuations and the length~ are approximately equal, with both
varying linearly with the radius of the lattice coupling.Comment: 29 pages of text plus 15 figures, uses REVTeX macros. Submitted to
Phys. Rev. E
Testing the neutrality of matter by acoustic means in a spherical resonator
New measurements to test the neutrality of matter by acoustic means are
reported. The apparatus is based on a spherical capacitor filled with gaseous
SF excited by an oscillating electric field. The apparatus has been
calibrated measuring the electric polarizability. Assuming charge conservation
in the decay of the neutron, the experiment gives a limit of
for the electron-proton charge
difference, the same limit holding for the charge of the neutron. Previous
measurements are critically reviewed and found incorrect: the present result is
the best limit obtained with this technique
Water Chemisorption and Reconstruction of the MgO Surface
The observed reactivity of MgO with water is in apparent conflict with
theoretical calculations which show that molecular dissociation does not occur
on a perfect (001) surface. We have performed ab-initio total energy
calculations which show that a chemisorption reaction involving a
reconstruction to form a (111) hydroxyl surface is strongly preferred with
Delta E = -90.2kJ/mol. We conclude that protonation stabilizes the otherwise
unstable (111) surface and that this, not the bare (001), is the most stable
surface of MgO under ambient conditions.Comment: RevTeX, 4 pages, 1 Encapsulated Postscript Figur
The TAOS Project: Upper Bounds on the Population of Small KBOs and Tests of Models of Formation and Evolution of the Outer Solar System
We have analyzed the first 3.75 years of data from TAOS, the Taiwanese
American Occultation Survey. TAOS monitors bright stars to search for
occultations by Kuiper Belt Objects (KBOs). This dataset comprises 5e5
star-hours of multi-telescope photometric data taken at 4 or 5 Hz. No events
consistent with KBO occultations were found in this dataset. We compute the
number of events expected for the Kuiper Belt formation and evolution models of
Pan & Sari (2005), Kenyon & Bromley (2004), Benavidez & Campo Bagatin (2009),
and Fraser (2009). A comparison with the upper limits we derive from our data
constrains the parameter space of these models. This is the first detailed
comparison of models of the KBO size distribution with data from an occultation
survey. Our results suggest that the KBO population is comprised of objects
with low internal strength and that planetary migration played a role in the
shaping of the size distribution.Comment: 18 pages, 16 figures, Aj submitte
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