Biomedical subjects

T R Welberry

Publications and source records attributed to T R Welberry.

6 recordsLinked to original sources

PubMed2006

Simultaneous fitting of X-ray and neutron diffuse scattering data.

Conventional crystallographic refinement uses the Bragg-peak intensities and gives the single-site average crystal structure. Information about short-range order and local order is contained in the diffuse scattering that is distributed throughout reciprocal space. Models of the short-range order in materials can now be automatically refined. The complementarity of X-ray and neutron diffraction data, and the value of simultaneously refining a structural model against both types of data, has long been known. This paper presents the first refinement of a short-range-order model against comprehensive X-ray and neutron diffuse scattering data simultaneously. The sample is the organic molecular crystal benzil, C(14)H(10)O(2) (for neutron work H is replaced by D). The technique gives new insights into local order in crystalline materials, including the dynamic correlation structure indicative of the dynamics of molecules in the crystalline state, and successfully overcomes limitations of using only the X-ray data set.

Crystallography, X-Ray↗

PubMed2003

Diffuse X-ray scattering from 4,4'-dimethoxybenzil, C16H14O4: analysis via automatic refinement of a Monte Carlo model.

A recently developed method for fitting a Monte Carlo computer-simulation model to observed single-crystal diffuse X-ray scattering has been used to study the diffuse scattering in 4,4'-dimethoxybenzil, C16H14O4. A model involving only nine parameters, consisting of seven intermolecular force constants and two intramolecular torsional force constants, was refined to give an agreement factor, omegaR = [sigma omega(deltaI)2/sigma omegaI2(obs)](1/2), of 18.1% for 118 918 data points in two sections of data. The model was purely thermal in nature. The analysis has shown that the most prominent features of the diffraction patterns, viz. diffuse streaks that occur normal to the [101] direction, are due to longitudinal displacement correlations along chains of molecules extending in this direction. These displacements are transmitted from molecule to molecule via contacts involving pairs of hydrogen bonds between adjacent methoxy groups. In contrast to an earlier study of benzil itself, it was not found to be possible to determine, with any degree of certainty, the torsional force constants for rotations about the single bonds in the molecule. It is supposed that this result may be due to the limited data available in the present study.

Journal Article↗

PubMed2003

High-energy diffuse scattering on the 1-ID beamline at the advanced photon source.

This paper reports on experiments in which high-energy (65.35 keV) X-rays were used to record the detailed diffuse diffraction patterns of a number of ceramic materials. The methodology has enabled a greater q-range to be explored (up to sintheta/lambda approximately 0.97) than is possible with laboratory-based experiments, with better q-space resolution and increased sensitivity, thus allowing previously unseen detail in diffraction patterns to be recorded. In all, 11 sections of data have been collected for Ca-CSZ, eight for Y-CSZ and six for wüstite.

Journal Article↗

PubMed2001

Diffuse X-ray scattering and strain effects in disordered crystals.

It is shown in this paper that a feature that has been observed in the diffuse scattering patterns of a wide variety of different materials - a diffuse 'ring' or 'doughnut'-shaped region of scattering - can be understood in terms of a simple model that has been borrowed from the field of sol-gel science. In this, it is supposed that there is a balance between the local attractive forces that are trying to make a particular structure and a rather longer range repulsive force. In the present context, it is believed that this latter force has its origin in the strain that builds as the preferred local structure tries to fit into the average crystal lattice. Simple Monte Carlo (MC) computer simulations are described that demonstrate this principle for three example materials: cubic stabilized zirconia, the p-didecylbenzene/urea inclusion compound and the pure molecular compound 1,3-dibromo-2,5-diethyl-4,6-dimethylbenzene, C12H16Br2 (BEMB2).

Journal Article↗

PubMed2001

Diffuse X-ray scattering from benzil, C(14)H(10)O(2): analysis via automatic refinement of a Monte Carlo model.

A recently developed method for fitting a Monte Carlo computer-simulation model to observed single-crystal diffuse X-ray scattering has been used to study the diffuse scattering in benzil, diphenylethanedione, C(6)H(5)-CO-CO-C(6)H(5). A model involving 13 parameters consisting of 11 intermolecular force constants, a single intramolecular torsional force constant and a local Debye-Waller factor was refined to give an agreement factor, R = [summation operator omega(Delta I)(2)/summation operator omega I(obs)(2)](1/2), of 14.5% for 101,324 data points. The model was purely thermal in nature. The analysis has shown that the diffuse lines, which feature so prominently in the observed diffraction patterns, are due to strong longitudinal displacement correlations. These are transmitted from molecule to molecule via a network of contacts involving hydrogen bonding of an O atom on one molecule and the para H atom of the phenyl ring of a neighbouring molecule. The analysis also allowed the determination of a torsional force constant for rotations about the single bonds in the molecule. This is the first diffuse scattering study in which measurement of such internal molecular torsion forces has been attempted.

Journal Article↗

PubMed1976

Printed circuit microelectrodes and their application to honeybee brain.

The application of printed circuit technology to the production of a new type of multi-channel microelectrode is described. 2. Recordings have been obtained from the the protocerebrum of the honeybee Apis mellifera L. using printed circuit microelectrodes in both restrained and free-moving preparations. 3. These recordings are compared with those previously obtained from conventional probe microelectrodes and are found to have similar characteristics of transient voltage changes superimposed on an undifferentiated high frequency background. 4. A wide range of development possibilities for the printed circuit microelectrode are discussed.

Action Potentials↗