1,179 research outputs found
The Role Of A Catalyst In The Isotopically Excited Laser Photochemistry
Laser photochemistry of BCl3/H2 using catalysis was carried out experimentally. The 10.55 μm radiation from a high power (GW/cm2) TEA CO2 pulse laser was used to selectively excite the 11BCl3 molecules. Using Ti catalyst the reaction products analyzed were 10B11BH2Cl 4, 11B11BH2Cl4, and HCl, whereas those were 10B11BCl4, 11B11BCl4, and HCl when Pb metal powder was employed, i.e., 10B10BH2Cl4 and 10B10BCl4 molecules were not generated in our experiment. Moreover, it was found that the 10BCl3 concentration in the unreacted BCl3 gas increased from 20% to 37% after 360 laser pulses, but the isotopic enrichment was not obtained for the reaction products. The mechanisms for the observed catalytic laser photochemistry are proposed. © 1978 American Institute of Physics.6894233423
Finite-Volume Two-Pion Amplitudes in the I=0 Channel
We perform a calculation in one-loop chiral perturbation theory of the
two-pion matrix elements and correlation functions of an I=0 scalar operator,
in finite and infinite volumes for both full and quenched QCD. We show that
major difficulties arise in the quenched theory due to the lack of unitarity.
Similar problems are expected for quenched lattice calculations of amplitudes with . Our results raise the important question
of whether it is consistent to study amplitudes beyond leading
order in chiral perturbation theory in quenched or partially quenched QCD.Comment: Version to appear on Phys. Lett. B, with only very minor and
stylistic change
Modeling asphalt pavement overlay transverse cracks using the genetic operation tree and Levenberg-Marquardt Method
[[abstract]]The Artificial Neural Network (ANN) and the nonlinear regression method are commonly used to build models from experimental data. However, the ANN has been criticized for incapable of providing clear relationships and physical meanings, and is usually regarded as a black box. The nonlinear regression method needs predefined and correct formula structures to process parameter search in terms of the minimal sum of square errors. Unfortunately, the formula structures of these models are often unclear and cannot be defined in advance. To overcome these challenges, this study proposes a novel approach, called ââLMGOT,ââ that integrates two optimization techniques: the LevenbergâMarquardt (LM) Method and the genetic operation tree (GOT). The GOT borrows the concept from the genetic algorithm, a famous algorithm for solving discrete optimization problems, to generate operation trees (OTs), which represent the structures of the formulas. Meanwhile, the LM takes advantage of its merit for solving nonlinear continuous optimization problems, and determines the coefficients in the GOTs that best fit the experimental data. This paper uses the LMGOT to investigate the data sets of pavement cracks from a 15-year experiment conducted by the Texas Departments of Transportation. Results show a concise formula for predicting the length of pavement transverse cracking, and indicate that the LMGOT is an efficient approach to building an accurate crack model.[[incitationindex]]SCI[[booktype]]紙
Inhomogeneous non-Gaussianity
We propose a method to probe higher-order correlators of the primordial
density field through the inhomogeneity of local non-Gaussian parameters, such
as f_NL, measured within smaller patches of the sky. Correlators between
n-point functions measured in one patch of the sky and k-point functions
measured in another patch depend upon the (n+k)-point functions over the entire
sky. The inhomogeneity of non-Gaussian parameters may be a feasible way to
detect or constrain higher-order correlators in local models of
non-Gaussianity, as well as to distinguish between single and multiple-source
scenarios for generating the primordial density perturbation, and more
generally to probe the details of inflationary physics.Comment: 16 pages, 2 figures; v2: Minor changes and references added. Matches
the published versio
Recreational anglers' valuation of near-shore marine fisheries in Florida
This report describes and summarizes the results from a state-wide survey of Florida
resident saltwater anglers. The survey was designed to provide estimates of the economic value
anglers place on marginal changes in management of selected near-shore marine species.
The Contingent valuation method was used to elicit angler willingness to pay for changes
in management for redfish, seatrout , mullet, sheepshead, pompano. and king mackerel.
Contingent valuation is a process in which respondents are presented with a detailed scenario that
describes an opportunity to express their willingness to pay for a proposed change in current
conditions. The process consists of three parts. First. the change in current conditions, or the
"good" to be valued is described. Second, the payment method is described. The payment
method is usually closely related to typical methods of buying goods similar to the one to be
valued. Finally. the respondent is asked how much they would pay for the good described in
the scenario. A special saltwater fishing license stamp that would allow the holder to take
advantage of the described management change was used as a payment mechanism. (PDF contains 147 pages.
Study of intercalation and deintercalation of Na_xCoO_2 yH_2O single crystals
Single crystals of NaxCoO2 with beta-phase (x=0.55, 0.60 and 0.65),
alpha'-phase (x=0.75) and alpha-phase (x=0.9, 1.0) have been grown by the
floating zone technique. The Na-extraction and hydration were carried out for
the alpha'-sample to get superconducting phase of NaxCoO2.yH2O (x~0.3, y~1.3).
Hydrated single crystals exhibit cracked layers perpendicular to the c-axis due
to a large expansion when the water is inserted into the structure. A study of
intercalation/deintercalation was performed to determine the stability of the
hydrated phase and effects of hydration on the structure of the compound. X-ray
diffraction and Thermogravimetric experiments are used to monitor the process
of water molecules accommodated in and removed from the crystal lattice. The
initial intercalation process takes place with two-water molecules
corresponding to y=0.6) inserted in a formula unit, followed by a group of four
(y=1.3) to form a cluster of Na(H2O)4. Thermogravimetric analysis suggests that
the deintercalation occurs with the removal of the water molecules one by one
from the hydrated cluster at elevated temperatures of approximately 50, 100,
200 and 300 C, respectively. Our investigations reveal that the hydration
process is dynamic and that water molecule inter- and deintercalation follow
different reaction paths in an irreversible way.Comment: 15 pages, 6 figures, figures with higher resolution by email request
from the corresponding autho
Origin of the shadow Fermi surface in Bi-based cuprates
We used angle-resolved photoemission spectroscopy to study the shadow Fermi
surface in one layer Bi2Sr1.6La0.4CuO6+delta and two layer
(Bi,Pb)2Sr2CaCu2O8+delta. We find the shadow band to have the same peakwidth
and dispersion as the main band. In addition, the shadow band/main band
intensity ratio is found to be binding energy independent. Consequently, it is
concluded that the shadow bands in Bi-based HTSC do not originate from
antiferromagnetic interactions but have a structural origin.Comment: 10 pages, 2 figure
Suppression of the structural phase transition and lattice softening in slightly underdoped Ba(1-x)K(x)Fe2As2 with electronic phase separation
We present x-ray powder diffraction (XRPD) and neutron diffraction
measurements on the slightly underdoped iron pnictide superconductor
Ba(1-x)K(x)Fe2As2, Tc = 32K. Below the magnetic transition temperature Tm =
70K, both techniques show an additional broadening of the nuclear Bragg peaks,
suggesting a weak structural phase transition. However, macroscopically the
system does not break its tetragonal symmetry down to 15 K. Instead, XRPD
patterns at low temperature reveal an increase of the anisotropic microstrain
proportionally in all directions. We associate this effect with the electronic
phase separation, previously observed in the same material, and with the effect
of lattice softening below the magnetic phase transition. We employ density
functional theory to evaluate the distribution of atomic positions in the
presence of dopant atoms both in the normal and magnetic states, and to
quantify the lattice softening, showing that it can account for a major part of
the observed increase of the microstrain.Comment: 7 pages, 4 figure
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