729 research outputs found
Focusing Vacuum Fluctuations II
The quantization of the scalar and electromagnetic fields in the presence of
a parabolic mirror is further developed in the context of a geometric optics
approximation. We extend results in a previous paper to more general
geometries, and also correct an error in one section of that paper. We
calculate the mean squared scalar and electric fields near the focal line of a
parabolic cylindrical mirror. These quantities are found to grow as inverse
powers of the distance from the focus. We give a combination of analytic and
numerical results for the mean squared fields. In particular, we find that the
mean squared electric field can be either negative or positive, depending upon
the choice of parameters. The case of a negative mean squared electric field
corresponds to a repulsive Van der Waals force on an atom near the focus, and
to a region of negative energy density. Similarly, a positive value corresponds
to an attractive force and a possibility of atom trapping in the vicinity of
the focus.Comment: 26 pages, 15 figures; additional discussion added in Sects. IV and I
Focusing Vacuum Fluctuations
The focusing of the vacuum modes of a quantized field by a parabolic mirror
is investigated. We use a geometric optics approximation to calculate the
energy density and mean squared field averages for scalar and electromagnetic
fields near the focus. We find that these quantities grow as an inverse power
of the distance to the focus. There is an attractive Casimir-Polder force on an
atom which will draw it into the focus. Some estimates of the magnitude of the
effects of this focusing indicate that it may be observable.Comment: 20 pages, 4 figures; typos corrected, two refs and some comments
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Effect of feeding three lysine to energy diets on growth, body composition and age at puberty in replacement gilts
This study evaluated the effect of diets differing in standard ileal digestible (SID) lysine on lysine intake, growth rate, body composition and age at puberty on maternal line gilts. Crossbred Large White×Landrace gilts (n =641) were fed corn-soybean diets differing in SID lysine concentration (%, g SID lysine:Mcal ME); diets were not isocaloric. Gilts received three grower, finisher diet combinations: low (0.68% lysine grower, 0.52% lysine finisher), medium (0.79% lysine grower, 0.60% lysine finisher) or high (0.90% lysine grower, 0.68% lysine finisher). Grower diets were fed from 100 until 142 days of age, and finisher diets were fed until they reached 220 days of age. Body weight (BW), backfat thickness (BF), and loin depth (LD) were recorded every 28 days. From 160–220 days of age, gilts were exposed daily to vasectomized boars and observed for behavioral estrus. Gilts fed the low lysine diet had lower average daily gain and BW (P \u3c 0.05), but not fat depth:LD ratio. The percentage of gilts that displayed natural estrus by 220 days of age was low but not different among dietary treatments (low 27.7%, medium 31.0% and high 37.7%, respectively; P=0.1201). Gilts fed the high and medium diets reached puberty 10 and 6 days earlier, however, than gilts fed the low lysine diet (P \u3c 0.05). The rate of puberty attainment may have been less because all gilts contracted porcine epidemic diarrhea (PEDv) just as boar exposure was to begin for the first group of gilts. Results from the present study indicate that growth rate and age at puberty can be altered by ad libitum fed diets that differ in SID lysine concentration
RF and Structural Characterization of SRF Thin Films
In the past years, energetic vacuum deposition methods have been developed in different laboratories to improve Nb/Cu technology for superconducting cavities. JLab is pursuing energetic condensation deposition via Electron Cyclotron Resonance. As part of this study, the influence of the deposition energy on the material and RF properties of the Nb thin film is investigated. The film surface and structure analyses are conducted with various techniques like X-ray diffraction, Transmission Electron Microscopy, Auger Electron Spectroscopy and RHEED. The microwave properties of the films are characterized on 50 mm disk samples with a 7.5 GHz surface impedance characterization system. This paper presents early results on surface impedance measurements in correlation with surface and material characterization for Nb films produced on sapphire and copper substrates
Breaking CPT by mixed non-commutativity
The mixed component of the non-commutative parameter \theta_{\mu M}, where
\mu = 0,1,2,3 and M is an extra dimensional index may violate four-dimensional
CPT invariance. We calculate one and two-loop induced couplings of \theta_{\mu
5} with the four-dimensional axial vector current and with the CPT odd dim=6
operators starting from five-dimensional Yukawa and U(1) theories. The
resulting bounds from clock comparison experiments place a stringent constraint
on \theta_{\mu 5}, |\theta_{\mu 5}|^{-1/2} > 5\times 10^{11} GeV. The orbifold
projection and/or localization of fermions on a 3-brane lead to CPT-conserving
physics, in which case the constraints on \theta{\mu 5} are softened.Comment: 4 pages, latex, 1 figur
Unbalanced synaptic inhibition can create intensity-tuned auditory cortex neurons
Intensity-tuned auditory cortex neurons may be formed by intensity-tuned
synaptic excitation. Synaptic inhibition has also been shown to enhance, and
possibly even create intensity-tuned neurons. Here we show, using in vivo whole
cell recordings in pentobarbital-anesthetized rats, that some intensity-tuned
neurons are indeed created solely through disproportionally large inhibition at
high intensities, without any intensity-tuned excitation. Since inhibition is
essentially cortical in origin, these neurons provide examples of auditory
feature-selectivity arising de novo at the cortex.Comment: 22 pages, 5 figure
Threshold criterion for wetting at the triple point
Grand canonical simulations are used to calculate adsorption isotherms of
various classical gases on alkali metal and Mg surfaces. Ab initio adsorption
potentials and Lennard-Jones gas-gas interactions are used. Depending on the
system, the resulting behavior can be nonwetting for all temperatures studied,
complete wetting, or (in the intermediate case) exhibit a wetting transition.
An unusual variety of wetting transitions at the triple point is found in the
case of a specific adsorption potential of intermediate strength. The general
threshold for wetting near the triple point is found to be close to that
predicted with a heuristic model of Cheng et al. This same conclusion was drawn
in a recent experimental and simulation study of Ar on CO_2 by Mistura et al.
These results imply that a dimensionless wetting parameter w is useful for
predicting whether wetting behavior is present at and above the triple
temperature. The nonwetting/wetting crossover value found here is w circa 3.3.Comment: 15 pages, 8 figure
Tomato: a crop species amenable to improvement by cellular and molecular methods
Tomato is a crop plant with a relatively small DNA content per haploid genome and a well developed genetics. Plant regeneration from explants and protoplasts is feasable which led to the development of efficient transformation procedures.
In view of the current data, the isolation of useful mutants at the cellular level probably will be of limited value in the genetic improvement of tomato. Protoplast fusion may lead to novel combinations of organelle and nuclear DNA (cybrids), whereas this technique also provides a means of introducing genetic information from alien species into tomato. Important developments have come from molecular approaches. Following the construction of an RFLP map, these RFLP markers can be used in tomato to tag quantitative traits bred in from related species. Both RFLP's and transposons are in the process of being used to clone desired genes for which no gene products are known. Cloned genes can be introduced and potentially improve specific properties of tomato especially those controlled by single genes. Recent results suggest that, in principle, phenotypic mutants can be created for cloned and characterized genes and will prove their value in further improving the cultivated tomato.
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