Anisotropy of extinction: extrapolation to the kinematical limit by γ-ray diffraction.

A direct experimental approach to the problem of anisotropic extinction is presented. Structure-factor measurements from a vanadium and a niobium crystal, performed with four γ-ray wavelengths in the range 0.02-0.06 Å, substantiate the adequacy of Zachariasen's theory [Acta Cryst. (1967), 23, 558-564] in high-energy diffraction, which provides a theoretical basis for the extrapolation to zero extinction values. Fitting of the theoretical curve to the observed points, placed on a common scale, allows determination of the kinematical structure-factor value without the need for a particular model of anisotropy in the mosaic structure.

Electron-density distribution in cubic SrTiO3: a comparative gamma-ray diffraction study.

The electron density and atomic displacements in the perovskite SrTiO(3) have been studied using extensive and accurate gamma-ray diffraction data (lambda = 0.0392 A) at room temperature. The six strongest low-order structure factors have been determined under extinction-free conditions. Gram-Charlier series expansion of the thermal parameters have revealed no evidence for anharmonicity. The population of the 3d subshell on Ti is found to be close to zero, in agreement with the observed magnetic behaviour. The electronic properties at the bond critical points indicate ionic Ti-O and Sr-O interactions of different strengths, which is corroborated by the net charges of the atomic basins [q(Sr) = 1.18 |e|, q(Ti) = 3.10 |e|, q(O) = -1.42 |e|]. A critical comparison is made with earlier experimental results from laboratory X-ray, synchrotron X-ray, electron and neutron diffraction studies. Agreement and discrepancies are identified and resolved.

Electron densities in relation to magnetism: gamma-ray diffraction from transition-metal monoxides and difluorides.

In this article, results are described from an area of solid-state physics that heretofore has remained unexplored by Bragg charge-scattering experiments. It is shown that gamma-ray electron densities can provide detailed information on magnetic ground-state properties at a subatomic resolution. The use of 316 keV gamma radiation has allowed low-order structure factors at better than 0.1% accuracy to be determined and, at the same time, extended data sets to be collected up to high momentum transfer. Prototypic antiferromagnets such as the late 3d transition-metal monoxides and difluorides have been systematically investigated, in most cases both in the paramagnetic and in the fully ordered phase. At transitions with a lowering of symmetry, multidomain formation was suppressed by application of external mechanical stress or magnetic fields. The results are considered in the context of information provided by recent magnetic neutron and X-ray studies.

Gamma-ray and neutron diffraction studies of CoF2: magnetostriction, electron density and magnetic moments.

Accurate structure factors up to sin theta/lambda = 1.6 A(-1) have been measured with 316.5 keV gamma-rays from CoF(2), both at room temperature and in the antiferromagnetic state at 10 K. The same crystal was used to collect extended time-of-flight neutron diffraction data in the two magnetic states, which allowed an accurate determination of the fluorine positional parameter. For room temperature, the standard structural parameters are reported. At 10 K, a complete charge-density study has been carried out. The total number of 3d electrons on Co is found to be 6.95 (3). The experimental populations of the d orbitals agree with expectation from crystal field theory. The fluorine valence region exhibits a strong dipolar deformation. Electronic properties at the bond critical points and integrated atomic properties are derived from the static model electron density, revealing the Co-F interactions as purely ionic. On magnetic ordering, a shift of the fluorine ions of 1.5 (4) x 10(-3) A is found which confirms a prediction from theory of optical birefringence. The effect of magnetostriction on the distortion of the ligand coordination octahedra is compared for the late members of the 3d transition-metal difluorides. From neutron powder diffraction, an ordered magnetic moment of 2.60 (4) mu(B) per cobalt ion is found. Despite the strong deviation from the ideal spin value of 3 mu(B), there is still an appreciable orbital contribution to the local magnetic moment.

Reconsideration of the wavelength dependence of extinction: a gamma-ray case.

The wavelength dependence of extinction has been re-examined by means of new gamma-ray diffraction data collected from NiF(2) at 0.0205, 0.0265 and 0.0392 A. The standard model of extinction has been confirmed and substantiated by experimentally accessible parameters such as the intrinsic mosaic width. The predicted kinematic limit values are in accordance with the results from charge-density analyses. The model proposed by Mathieson & Stevenson [Acta Cryst. (2002), A58, 185-189] leads to a purely phenomenological polynomial fit function. The extrapolated values are shown to be inconsistent with structure analyses based on extended gamma-ray data sets and cannot be recommended for use.

Absolute spin magnetic moment of FeF2 from high energy photon diffraction.

The magnetic spin structure factor of FeF2 has been directly determined from high energy magnetic x-ray diffraction at 115 keV photon energy. A pure spin moment of mu = 4.01(5)mu(B) was observed, which agrees very well with the spin moment of the free Fe2+ ion and differs significantly from values of the total magnetic moment obtained by other methods. The magnetic phase transition of FeF2 has been carefully investigated and values for the critical exponent of the order parameter obtained by other techniques have been confirmed.

Expected hemoglobin decrease following percutaneous transluminal coronary angioplasty.

To establish expected changes in hemoglobin during and after percutaneous transluminal coronary angioplasty (PTCA), we measured hemoglobin before, at the end of, and on the 2 mornings after PTCA in 177 consecutive patients without obvious out-of-laboratory blood loss. From these data, we calculated confidence intervals that can be used to compare group data, possibly to identify excessive blood loss with new devices or antithrombotic agents, and prediction intervals to identify unexpected blood loss in an individual patient.

Lateral and anterior reciprocal electrocardiographic changes: relationship to ST segment elevation and underlying coronary artery disease in inferior myocardial infarction.

The electrocardiogram in patients with acute inferior myocardial infarction frequently displays ST depression in non-infarct leads. The significance of this finding is uncertain. The relationship between ST depression, ST elevation and arteriographic severity of coronary artery disease was explored. 22 patients with acute inferior myocardial infarction, receiving thrombolysis and undergoing acute (within seven hours of the onset of chest pain) coronary angiography were studied prospectively. The electrocardiographic ST segment elevation in the inferior leads and ST segment depression in the lateral and in the anterior precordial leads were measured. In each group of leads, the maximum value of ST deviation in any lead as well as the sum of the values for ST deviation in the individual leads was determined. Gensini scores of total coronary artery disease and component scores for the major coronary arteries were determined from the coronary arteriogram. There was a strong correlation of maximum inferior ST elevation with both maximum lateral ST depression (r = 0.96, p < 0.001) and with maximum anterior precordial ST depression (r = 0.78, p < 0.001). The corresponding correlations for sum of ST deviations were r = 0.91, p < 0.001 and r = 0.79, p < 0.001 respectively. There was no relationship between Gensini scores of coronary artery disease and measures of electrocardiographic ST segment depression or elevation. Electrocardiographic ST depression in non-infarct leads in patients with inferior myocardial infarction, does not provide information regarding the degree of coronary artery disease. The ST depression in both lateral and anterior precordial leads correlates with and is a reflection of inferior ST elevation.

Effects of contraction-excitation feedback on electrophysiology and arrhythmogenesis in rabbits with experimental left ventricular hypertrophy.

OBJECTIVE: The aim was to investigate the influence of contraction-excitation feedback on myocardial electrophysiology and arrhythmia susceptibility in the setting of experimental left ventricular hypertrophy. METHODS: New Zealand White rabbits with perinephritis hypertension were used. With the hearts perfused in vitro, left ventricular monophasic action potential duration and local effective refractory periods were determined at three sites, namely the anterior, apical, and posterior wall, together with ventricular tachycardia inducibility and ventricular fibrillation threshold under different loading conditions. RESULTS: The left ventricular dry weight to body weight ratio was increased by 31% in the hypertrophied group (3.863 x 10(-4), v 2.955 x 10(-4) in the controls). Left ventricular hypertrophy was associated with prolongation of action potential duration when the left ventricle was not loaded and under normal loading conditions. Changing from unloaded Langendorff to baseline working heart perfusion resulted in a consistent decrease in action potential duration and effective refractory period at all left ventricular sites in both hypertrophied and control hearts. Subsequent manipulations of myocardial loading resulted in decreases in action potential duration and effective refractory period in both groups of hearts. Ventricular tachycardia could not be induced in any heart in Langendorff mode. Under different increased loading conditions, a total of four hypertrophied hearts (44%) became inducible, while control hearts remained non-inducible. The ventricular fibrillation threshold under conditions of increased load tended to be lower in the hypertrophied hearts than the control hearts; in the setting of increased preload the hypertrophied group showed significantly increased vulnerability to ventricular fibrillation (median threshold currents 35 mA v > 100 mA, p < 0.05). CONCLUSIONS: Left ventricular hypertrophy is associated with a prolongation of action potential duration and effective refractory period and an increased arrhythmia susceptibility in the setting of increased myocardial loading. There were no marked differences between the groups in the magnitude of the changes in action potential duration, effective refractory period, or dispersion of repolarisation and refractoriness resulting from manipulations of myocardial loading that could have been implicated in the increased arrhythmia susceptibility of the hypertrophied hearts during changes in load.

Lipoprotein(a) in restenosis after percutaneous transluminal coronary angioplasty and coronary artery disease.

BACKGROUND: The purpose of the study was to investigate the relation of lipoprotein(a) and serum lipid parameters to restenosis after percutaneous transluminal coronary angioplasty (PTCA) and to assess the association of these same biochemical markers to coronary artery disease (CAD) in individuals with angiographically defined normal and diseased coronary arteries. METHODS AND RESULTS: Sixty-two patients with successful PTCA had follow-up angiography at 35 +/- 10 weeks. Restenosis occurred in 21 male patients (46%) and 6 female patients (38%). Elevated apolipoprotein B (P < .01) and decreased high-density lipoprotein-2 cholesterol (P < .02) were found to be independently associated with restenosis after angioplasty, whereas lipoprotein(a) was not. Eighty-five patients undergoing PTCA were compared with 46 subjects who had no evidence of CAD on angiography. Elevated lipoprotein(a) (P < .001) and reduced apolipoprotein A1 to B ratio (P < .001) were found to be strong independent risk factors for the presence of CAD when adjustment was made for age (P < .005), male sex (P < .01), smoking (P < .005), and hypertension (P = .06). CONCLUSIONS: Serum lipoprotein(a) levels are not associated with restenosis after PTCA, but elevated levels are strongly associated with CAD. Low-serum, high-density lipoprotein-2 cholesterol concentration and elevated apolipoprotein B concentration were found to be associated with restenosis after PTCA.

Staphylococcal nasal carriage in medical students with varying clinical exposure.

Nasal carriage and antibiotic sensitivities of coagulase-positive and coagulase-negative staphylococci were assessed among medical students of three different years. Although carriage rates did not change, there was a trend towards multiple resistance with increasing hospital exposure. Gentamicin resistance in Staphylococcus albus showed a similar trend. The relevance of these findings to current views on the origin of gentamicin resistance is discussed.