Previous experiments on the neutron structure factor S ( q ) for heavy water near 11.2°C have been extended so that the next term in the Taylor expansion may be examined. An improved result for the isochoric temp...
Previous experiments on the neutron structure factor S ( q ) for heavy water near 11.2°C have been extended so that the next term in the Taylor expansion may be examined. An improved result for the isochoric temperature derivative of S ( q ) at 11.2°C is obtained. These data and those for the (Δ T ) 2 coefficient in the Taylor expansion may be explained on a simple basis: namely that OH and HH distances between neighbouring molecules vary as ( T t 0 ) −n where ( T T 0 ) ≈ 1200 n for T ≈ 300 K.
The Green function with an insertion of the gauge-invariant twist-four operator O(x) = − 1 4 (F μν u ) 2 is calculated to one-loop order in the light-cone gauge. We show that the renormalization requires gauge-nonin...
The Green function with an insertion of the gauge-invariant twist-four operator O(x) = − 1 4 (F μν u ) 2 is calculated to one-loop order in the light-cone gauge. We show that the renormalization requires gauge-noninvariant counterterms satisfying the Slavnov-Taylor identity.
In recent work on the structure of water I have exploited both time-of-flight neutron diffraction (TOF) and conventional reactor neutron diffraction to extract the hydrogen-hydrogen correlation function in liquid wate...
In recent work on the structure of water I have exploited both time-of-flight neutron diffraction (TOF) and conventional reactor neutron diffraction to extract the hydrogen-hydrogen correlation function in liquid water using the technique of hydrogen/deuterium substitution. Because the dynamic effects on the TOF data have a very different dependence on momentum transfer ( Q ) from those for the reactor data, the two sets of data offer a unique opportunity to establish an estimate of the magnitude of the dynamic correction. Apart from a discrepancy at small Q which is not fully understood at present, the different diffraction techniques show good agreement over most of the Q range. The comparison is used to discuss the applicability of the H/D subtraction (which involves no arbitrary fitting parameters) to molecular liquids in general: the main features in the structure factors can be determined readily. On the other hand, it is likely that finer details such as quantum effects will be obscured by experimental imitations.
Gamma rays from a radioisotope source, 241 Am, are scattered from samples of light water (H 2 O) and heavy water (D 2 O) at temperature 297 K and density 0.0334 molecules/Å 3 to determine what differences occur i...
Gamma rays from a radioisotope source, 241 Am, are scattered from samples of light water (H 2 O) and heavy water (D 2 O) at temperature 297 K and density 0.0334 molecules/Å 3 to determine what differences occur in their structure factors. The apparatus, method of data collection and data analysis are described in detail. The results are compared to the predictions of a computer simulation, in which ground state librational motion of rigid molecules causes significant quantum effects in the site-site correlation functions of the two liquids. Differences between our data and the simulation suggest that coupling occurs between intramolecular and intermolecular modes, and influences the structure of water. It is noted that the structural changes due to quantum effects are similar to those that occur in water upon formation of a 0.55 M solution of LiOH.
Some ideas as to what the important factors are that will produce a reliable indium O‐ring seal are discussed. Four novel indium seal designs which are based on these ideas are presented. Three of these seals have be...
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Some ideas as to what the important factors are that will produce a reliable indium O‐ring seal are discussed. Four novel indium seal designs which are based on these ideas are presented. Three of these seals have been incorporated in a Brillouin cell. They include a simple sapphire window seal, a filling line union, and a flange seal. All of them have withstood low temperatures down to 77 K and moderate pressures up to 177 bar. The fourth seal described is a Pyrex tube seal for a Raman cell.
Series of submerged arc welds of HSLA steel made with three different fluxes and metallic additions of Ti, Mo, and Cr have been examined to study the inclusions and their role in the nucleation of acicular ferrite. In...
High‐density polyethylene has good spectral transmission characteristics in the range from 20–500 cm? 1. This, coupled with its ease of fabrication and low cost, make it an excellent choice for far‐infrared absorpt...
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High‐density polyethylene has good spectral transmission characteristics in the range from 20–500 cm?1. This, coupled with its ease of fabrication and low cost, make it an excellent choice for far‐infrared absorption cell windows which operate at room temperature. However, because of its relatively large thermal coefficient of expansion and its brittleness (at low temperatures), the usual type of polyethylene absorption cell windows are difficult to make leaktight at low temperatures, especially if there is a moderately high pressure inside the absorption cell. In this article the problems associated with the use of such windows at low temperatures and moderately high pressures are discussed and a successful window design which overcomes these problems is described. These windows have been incorporated in a cell which has been used to measure the collision‐induced absorption of various nonpolar gases at low temperatures. In these experiments the cell was cycled hundreds of times at pressures up to 96.5 bar and at temperatures down to 126 K.
The problem of chemisorbing a hydrogen atom on a Cu-Ni or Au-Pt disordered binary alloy (DBA) is addressed. The DBA is modeled by a semi-infinite linear array of atomic sites each of which is randomly occupied by an a...
The problem of chemisorbing a hydrogen atom on a Cu-Ni or Au-Pt disordered binary alloy (DBA) is addressed. The DBA is modeled by a semi-infinite linear array of atomic sites each of which is randomly occupied by an atom of either component. The electronic properties of such a DBA are obtained via a Green’s-function technique based on the coherent-potential (CP) approximation. The chemisorption process is described by the Anderson-Newns approach, which takes account of the intra-atomic electron interaction on the adatom. The chemisorption energy and the adatom charge transfer are then computed as a function of the alloy concentration. The calculations at the surface involve the solution of two coupled self-consistent equations, one being concerned with the CP on the surface atom and the other with the adatom occupancy. In the case of the Cu-Ni system, the effect of surface segregation is also investigated.
Spatially resolved carrier lifetimes have been measured at the same grain boundary using a series of adjacent samples doped to different levels by neutron transmutation. The samples had dopant concentration levels bet...
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Spatially resolved carrier lifetimes have been measured at the same grain boundary using a series of adjacent samples doped to different levels by neutron transmutation. The samples had dopant concentration levels between 1013 and 1017 atoms/cm3. The carrier lifetime was measured using a contactless microwave absorption technique to monitor the decay of photoconductivity which allowed us to perform either isothermal or isochronal annealing to remove the damage caused by irradiation. An optimum anneal of 30 min at 700?°C resulted in almost full recovery to the lifetime before irradiation. A short laser pulse of wavelength 900 nm was focused to a 0.3‐mm‐diam spot on the samples. Lifetimes of two different sets of carriers were measured, the bulk carrier lifetime at the center of a grain and the carrier lifetime at a grain boundary. This latter carrier lifetime involves both fast and slow recombination mechanisms. The slow decay mechanism is due to interface states at the grain boundary. The fast recombination lifetime was found to be of the same order as the bulk recombination lifetime (of the order of 1 μs) and the slow one was of the order of 1 ms. Doping levels up to 1016 atoms/cm3 show no significant effect on the measured bulk carrier lifetime.
I discuss current issues in hadron spectroscopy and their connection to Quantum Chromodynamics and to more general issues of hadron physics. The discussion is in elementary terms and is directed to non‐experts.
I discuss current issues in hadron spectroscopy and their connection to Quantum Chromodynamics and to more general issues of hadron physics. The discussion is in elementary terms and is directed to non‐experts.
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