Interface induced uniaxial magnetic anisotropy in amorphous CoFeB films on AlGaAs(001).

We demonstrate an isolated magnetic interface anisotropy in amorphous CoFeB films on (Al)GaAs(001), similar to that in epitaxial films but without a magnetocrystalline anisotropy term. The direction of the easy axis corresponds to that due to the interfacial interaction proposed for epitaxial films. We show that the anisotropy is determined by the relative orbital component of the atomic magnetic moments. Charge transfer is ruled out as the origin of the interface anisotropy, and it is postulated that the spin-orbit interaction in the semiconductor is crucial in determining the magnetic anisotropy.

A new design of specimen stage for in situ magnetising experiments in the transmission electron microscope.

A new stage for carrying out in situ magnetising experiments in the transmission electron microscope has been designed, constructed and tested. The principal advantages of the stage are that it delivers horizontal fields with negligible perturbation to the illumination and is suitable for operation in pulsed or continuous field mode. Details of its performance, including field calibration, are given. The paper concludes with a description of where the stage is likely to be of most use.

Effects of blood pressure lowering with amlodipine or lisinopril on vascular structure of the common carotid artery.

Increased intima-media thickness of the common carotid artery predicts increased risk of myocardial infarction and stroke. Preliminary evidence suggests that a decrease in blood pressure (BP) is associated with diminished wall thickness. It is not known if all classes of anti-hypertensive agents have similar protective effects. In this double-blind parallel-group clinical trial, 69 previously untreated patients with hypertension were allocated randomly to 1 year of treatment with either amlodipine (5-10 mg daily) or lisinopril (5-20 mg daily). Doxazosin and bendrofluazide were added if required to achieve BP control. After 12 months of treatment, clinic BP, ambulatory BP and cardiac mass were reduced similarly by the two treatment regimens. Common carotid artery intima-media thickness decreased by 0.048 mm (95% confidence intervals -0.066, -0.031 mm) in the amlodipine-treated group, but decreased by only 0.027 mm (-0.046, -0.007 mm) in the lisinopril-treated group (P<0.05 for difference between treatments). Common carotid artery lumen diameter declined significantly only in patients treated with lisinopril [amlodipine, -0.02 mm (-0.14, 0.10 mm); lisinopril, -0.21 mm (-0.32, -0.11 mm); P<0.02], while intima-media area declined similarly in the two treatment groups [amlodipine -1.32 mm(2) (-1.91, -0.74 mm(2)), lisinopril -1.26 mm(2) (-1.80, -0.72 mm(2)); not significant]. The results confirm that a decrease in BP causes regression of structural changes in the carotid artery in hypertensive patients. The nature of the structural regression differed markedly between the two treatment regimens, in spite of similar decreases in BP. The calcium channel blocker induced greater regression of common carotid artery intima-media thickness than the angiotensin-converting enzyme inhibitor. However, carotid artery wall mass, as indicated by intima-media area, was reduced to a similar extent by the two treatments. It remains to be established whether such differences confer a prognostic advantage.

Ethnic differences in the identification of left ventricular hypertrophy in the hypertensive patient.

Left ventricular hypertrophy (LVH) is more prevalent in black than white hypertensives, but this difference is greater when identified by electrocardiography (ECG) than by echocardiography. We evaluated the proposal that current ECG criteria for LVH are less specific, and therefore, less useful, in blacks than whites. In a retrospective cross-sectional study, 408 subjects (271 white, 137 black) referred to a hypertension clinic for assessment of hypertension underwent measurement of blood pressure, ECG voltages (Sokolow-Lyon and Cornell sex-specific), and echocardiographic left ventricular mass index (LVMI). Black subjects had greater ECG voltages than whites, even when closely matched for LVMI. In black subjects, current ECG criteria were twice as sensitive as in whites (Sokolow-Lyon: 44.9% v 22.5%, P = .003. Cornell: 30.4% v 15.7%, P = .03). They were less specific in blacks using the Sokolow-Lyon criteria (73.5% v 86.8%, P = .02) but this failed to reach significance using the Cornell criteria (83.8% v 91.8%, P = .07). When voltage criteria were adjusted to give matched sensitivities and specificities, respectively, differences in specificity and sensitivity were no longer apparent. Receiver operating characteristic curve analyses confirmed no significant differences in overall performance of either ECG criteria between blacks and whites. In conclusion, ECG detection of LVH is insensitive in both ethnic groups. Sensitivity is higher in blacks due to higher LVMI in those with LVH. Apparent differences in specificity are due to ethnic differences in ECG voltages that are unrelated to differences in LVMI. When these differences are taken into account, there are no overall differences in test accuracy. However, given the prognostic importance of the detection of LVH, currently accepted ECG voltage criteria for the detection of LVH remain of equal or greater value in black hypertensives compared with whites.

Intraventricular dispersion of E wave velocity: an alternative measure of left ventricular diastolic function in hypertensive patients?

The E/A ratio (of peak mitral blood flow velocity during early diastole to that during atrial contraction) has limitations in the assessment of diastolic function. Previous studies have suggested that peak blood flow velocity is normally maintained or increased towards the cardiac apex but that it decreases in diastolic dysfunction. We evaluated the proposal that intraventricular dispersion of E wave velocity is an effective means of assessing diastolic function in hypertensives. Fifty-five untreated hypertensive patients underwent echocardiographic examination. Pulsed-wave Doppler recordings were made from the apical four-chamber view. Peak flow velocities were measured during early diastole at the level of the mitral valve (E0), and 3 cm distally (E3), and during atrial contraction at the level of the mitral valve (A). Mean peak flow velocities were 64.4 +/- 16.1 m/s for E0, 50.6 +/- 17.9 m/s for E3 and 61.1 +/- 12.1 m/s for A. Peak flow velocity during early diastole slowed towards the cardiac apex in most patients (E3/E0 range: 0.42-1.86, mean 0.81 +/- 0.29). There was no significant difference in E3/E0 between those with and without left ventricular hypertrophy (LVH) (0.76 +/- 0.25 vs 0.82 +/- 0.29, P = 0. 39). E3/E0 did not correlate with age (r = -0.02, P = 0.89), systolic blood pressure (BP) (r = 0.17, P = 0.20), diastolic BP (r = 0.21, P = 0.12) or LVMI (r = -0.11, P = 0.40). In contrast the E/A ratio correlated strongly with age (r = -0.66, P < 0.0001) and negatively, though not significantly, with systolic BP (r = -0.24, P = 0.07), diastolic BP (r = -0.23, P = 0.09) and LVMI (r = -0.23, P = 0.08). Although there is some intraventricular dispersion of E wave velocity in this group of hypertensive patients, the ratio of E3/E0 correlates poorly with parameters which are known to influence diastolic function. In spite of its limitations, the E/A ratio appears to be a more reliable measure of diastolic function in hypertensive heart disease than intraventricular dispersion of early diastolic filling.

Instrumentation, techniques, and applications of electron microscopy in the solid state physics group at Glasgow University.

This review discusses some of the work performed by the Solid State Physics Group at Glasgow University. A major aim of the group is to obtain quantitative information with high spatial resolution and to do this reliably requires a thorough understanding of both the instrumentation and the interactions between the electron beam and the specimen. Thus the first part of the review discusses those aspects of instrumentation and techniques that the group has considered in detail while the final part deals with applications which involve the study of a wide range of materials covering metallurgical, semiconductor, organic, and magnetic systems. In all these applications, the results from a range of techniques have been required to provide as complete a picture of the material as possible.

Optimum conditions for cryoquenching of small tissue blocks in liquid coolants.

Three approaches were taken with the aim of defining the optimum conditions of rapid cryopreservation in liquid quenchants. In a theoretical approach, two mathematical models were used. The first is of value in defining the absolute maximum rates of cooling which could be achieved at various depths in the tissues. The second highlights the poor thermal properties of liquid coolants and therefore emphasizes the essential requirement for vigorous quenchant mixing and rapid specimen entry. Experimental work with thermocouples showed that fastest cooling rates occur at the leading edge of the object entering coolant. Of five quenchants investigated, cooling rates were in the order, propane greater than Freon 22 greater than Freon 12 greater than liquid nitrogen slush greater than liquid nitrogen. Other considerations, however, may affect the choice of quenchant. For a given quenchant, cooling rate is maximal near the equilibrium freezing point. The consequences of quenching in the presence of thermal gradients either within the coolant or in the gas layer above it are shown. Cooling rate was found to be approximately proportional to entry velocity at least up to approximately 2 m s-1 in our system. Stereological analysis of rapidly quenched, freeze-substituted tissue samples, of geometry which imposed an approximately unidirectional heat flow, revealed four zones: (i) a narrow surface layer (approximately 10 micrometers) of low image contrast and apparent of ice crystals; (ii) a zone of enhanced contrast with ice crystals whose size increased rapidly with depth from the surface (the 'slope'); (iii) a sharply defined zone (the 'ridge') of maximum ice crystal size beyond which there is (iv) an extensive 'plateau' with smaller ice crystals and no marked increase in size with depth. The 'ridge' of maximal ice-crystal damage was consistently found but varied considerably in depth from the surface (approximately 25-120 micrometers) between samples. The existence of the deeper plateau region of relatively uniform ice-crystal-size may be of significance in X-ray microanalytical studies of physiological processes at some depth from the sample surface. In terms of our present understanding of the quenching process, the conditions for optimal cryofixation of small tissue samples are listed.

The direct determination of magnetic domain wall profiles by differential phase contrast electron microscopy.

A new technique for the quantitative investigation of magnetic structures in ferromagnetic thin films is proposed. Unlike previous techniques the detected signal is simply related to the magnetic induction in the film, and as such the direct determination of domain wall profiles is possible. The technique utilizes a differential phase contrast mode of scanning transmission electron microscopy in which the normal bright field detector is replaced by a split-detector lying symmetrically about the optic axis of the system. The difference signal from the two halves of the detector provides the required magnetic information. Analysis of the image formation mechanism shows that, using a commercially available scanning transmission electron microscope equipped with a field emission gun, wall profiles should be obtainable directly from most structures of interest in Lorentz microscopy. Furthermore, signal-to-noise considerations indicate that these results can be obtained in acceptably short recording times. Finally, experimental results using both polycrystalline and single crystal specimens are presented, which confirm the theoretical predictions.