141 research outputs found
Helium mixtures in nanotube bundles
An analogue to Raoult's law is determined for the case of a 3He-4He mixture
adsorbed in the interstitial channels of a bundle of carbon nanotubes. Unlike
the case of He mixtures in other environments, the ratio of the partial
pressures of the coexisting vapor is found to be a simple function of the ratio
of concentrations within the nanotube bundle.Comment: 3 pages, no figures, submitted to Phys. Rev. Let
Quantum states and specific heat of low-density He gas adsorbed within the carbon nanotube interstitial channels: Band structure effects and potential dependence
We calculate the energy-band structure of a He atom trapped within the
interstitial channel between close-packed nanotubes within a bundle and its
influence on the specific heat of the adsorbed gas. A robust prediction of our
calculations is that the contribution of the low-density adsorbed gas to the
specific heat of the nanotube material shows pronounced nonmonotonic variations
with temperature. These variations are shown to be closely related to the band
gaps in the adsorbate density of states
A Mach-Zehnder Interferometer for a Two-Photon Wave Packet
We propose an experiment that permits observation of the de Broglie
two-photon wave packet behavior for a pair of photons, using a Mach-Zehnder
interferometer. It is based on the use of pulsed lasers to generate pairs of
photons via spontaneous parametric down-conversion and the post-selection of
events. It differs from previous realizations by the use of a third
time-correlated photon to engineer the state of the photons. The same technique
can give us which-path information via an ``interaction-free'' experiment and
can be used in other experiments on the foundations of quantum mechanics
related to wave-particle duality and to nonlocality.Comment: Submmited for publication in Physical Review
Behavior of the giant-dipole resonance in Sn and Pb at high excitation energ
The properties of the giant-dipole resonance (GDR) are calculated as a
function of excitation energy, angular momentum, and the compound nucleus
particle decay width in the nuclei Sn and Pb, and are compared
with recent experimental data. Differences observed in the behavior of the
full-width-at-half-maximum of the GDR for Sn and Pb are
attributed to the fact that shell corrections in Pb are stronger than
in Sn, and favor the spherical shape at low temperatures. The effects
shell corrections have on both the free energy and the moments of inertia are
discussed in detail. At high temperature, the FWHM in Sn exhibits
effects due to the evaporation width of the compound nucleus, while these
effects are predicted for Pb.Comment: 28 pages in RevTeX plus eight postscript figures. Submitted to Nucl.
Phys.
Uptake of gases in bundles of carbon nanotubes
Model calculations are presented which predict whether or not an arbitrary
gas experiences significant absorption within carbon nanotubes and/or bundles
of nanotubes. The potentials used in these calculations assume a conventional
form, based on a sum of two-body interactions with individual carbon atoms; the
latter employ energy and distance parameters which are derived from empirical
combining rules. The results confirm intuitive expectation that small atoms and
molecules are absorbed within both the interstitial channels and the tubes,
while large atoms and molecules are absorbed almost exclusively within the
tubes.Comment: 9 pages, 12 figures, submitted to PRB Newer version (8MAR2K). There
was an error in the old one (23JAN2K). Please download thi
On the Behavior of the Effective QCD Coupling alpha_tau(s) at Low Scales
The hadronic decays of the tau lepton can be used to determine the effective
charge alpha_tau(m^2_tau') for a hypothetical tau-lepton with mass in the range
0 < m_tau' < m_tau. This definition provides a fundamental definition of the
QCD coupling at low mass scales. We study the behavior of alpha_tau at low mass
scales directly from first principles and without any renormalization-scheme
dependence by looking at the experimental data from the OPAL Collaboration. The
results are consistent with the freezing of the physical coupling at mass
scales s = m^2_tau' of order 1 GeV^2 with a magnitude alpha_tau ~ 0.9 +/- 0.1.Comment: 15 pages, 4 figures, submitted to Physical Review D, added
references, some text added, no results nor figures change
Choice of tracers for the evaluation of spray deposits
Tracer substances, used to evaluate spraying effectiveness, ordinarily modify the surface tension of aqueous solutions. This study aimed to establish a method of using tracers to evaluate distribution and amount of spray deposits, adjusted to the surface tension of the spraying solution. The following products were tested: 0.15% Brilliant Blue, 0.15% Saturn Yellow in 0.015% Vixilperse lignosulfonate, and 0.005% sodium fluorescein, and mixtures of Brilliant Blue plus Saturn Yellow and Brilliant Blue plus sodium fluorescein at the same concentrations. Solutions were deposited on citrus leaves and stability was determined by measuring fluorescence and optical density of solutions without drying, dried in the dark and exposed to sunlight for 2, 4 and 8 h. These values were compared to those obtained directly in water. The static surface tension of the tracer solution was determined by weighing droplets formed during a period of 20 to 40 seconds. The Brilliant Blue and Saturn Yellow mixture at 0.15% was stable under all conditions tested. It was not absorbed by the leaves and maintained the same surface tension as that of water, thus permitting concentration adjustment to the same levels used for agrochemical products, and allowing the development of a qualitative method based on visual evaluation of the distribution of the pigment under ultraviolet light and of a quantitative method based on the determination of the amount of the dye deposited in the same solution. Spray deposition could be evaluated at different surface tensions of the spraying solution, simulating the effect of agrochemical formulations
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
Produção e valor nutritivo da forragem de capim-elefante em dois sistemas de produção.
Esta pesquisa foi realizada com o objetivo de avaliar a produção e o valor nutritivo da forragem de capimelefante cultivado em sistemas convencional e agroecológico. No sistema convencional, o capim-elefante foi estabelecido em cultivo exclusivo, em linhas com espaçamento de 1,4 m e, no sistema agroecológico, em linhas afastadas 3 m. Nas entrelinhas, estabeleceu-se azevém no período hibernal para desenvolvimento de espécies de crescimento espontâneo no período estival. Avaliaram-se a massa, a produção e a composição botânica e estrutural da forragem e a carga animal. Amostras de simulação de pastejo foram coletadas para determinação dos teores de proteína bruta e fibra em detergente neutro e da digestibilidade in vitro da matéria seca e matéria orgânica. O delineamento experimental foi o inteiramente casualizado com dois tratamentos (sistemas convencional e agroecológico) e duas repetições (piquetes). Valores mais elevados para massa de forragem, produção de forragem, taxa de acúmulo diário e carga animal foram observados no sistema convencional. A relação folha:colmo foi similar entre os sistemas. Valor mais elevado de proteína bruta foi observado no sistema agroecológico. O capim-elefante sob manejo convencional apresenta maior produção de forragem, com menores teores de proteína bruta. O sistema agroecológico apresenta melhor distribuição da produção de forragem no decorrer do ano
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