Quantum interference in artificial band structures.

Magnetotransport experiments on two-dimensional electron systems with an atomically precise, one-dimensional potential modulation reveal striking quantum interference oscillations. Within a semiclassical framework, they are recognized either as self-interference along closed orbits, many of them rendered possible by magnetic breakdown between Fermi contour segments of the artificial band structure, or as interference-enhanced backscattering. The known commensurability oscillations appear as a special case of the latter mechanism.

Ising ferromagnetism and domain morphology in the fractional quantum Hall regime.

The density driven quantum phase transition between the unpolarized and fully spin polarized nu = 2/3 fractional quantum Hall state is accompanied by hysteresis in accord with 2D Ising ferromagnetism and domain formation. The temporal behavior is reminiscent of the Barkhausen and time-logarithmic magnetic after-effects ubiquitous in familiar ferromagnets. It too suggests domain morphology and, in conjunction with NMR, intricate domain dynamics, which is partly mediated by the contact hyperfine interaction with nuclear spins of the host semiconductor.

Evidence of Hofstadter's Fractal Energy Spectrum in the Quantized Hall Conductance.

The energy spectrum of a two-dimensional electron system in a perpendicular homogeneous magnetic field and a weak lateral superlattice potential with square symmetry is composed of Landau bands with recursive internal subband structure. The Hall conductance in the minigaps is anticipated to be quantized in integer multiples of e(2)/h that vary erratically from minigap to minigap in accordance with a Diophantine equation. Hall measurements on samples with the requisite properties uncover this long searched for evidence of Hofstadter's butterflylike energy spectrum.

Optical investigation of spin-wave excitations in fractional quantum hall states and of interaction between composite fermions.

We demonstrate that the temperature dependence of the electron spin polarization for the fractional states nu = 1/3 and nu = 2/3 displays activated behavior. This study enables the first measurement of the fractional quantum Hall spin-flip gaps. They are found to be systematically larger in comparison with the gaps simultaneously measured in transport.

[Extensive intramural hematoma of the thoracic aorta].

A[TRACE;del] 53-year-old hypertensive patient presenting with acute chest pain was found to have an intramural haematoma (IMH) of both ascending and descending aorta associated with a 6 cm ascending fusiform aortic aneurysm. Six weeks of antihypertensive treatment allowed complete resolution of the intramural haematoma of the descending aorta. Limited surgical repair of the ascending aorta by Gore-Tex graft prosthesis interposition was then performed.

Unilateral pallidotomy in PD: a controlled study of cognitive and behavioral effects. The Netherlands Pallidotomy Study (NEPAS) group.

Objective: To investigate whether unilateral pallidotomy affects cognitive and behavioral functioning.

Methods: At baseline and after 6 months we assessed neuropsychological functioning in 35 patients with advanced PD. After baseline examination, patients were randomized to pallidotomy within 1 month (6 left-sided, 13 right-sided) or to pallidotomy after follow-up assessment 6 months later (n = 16; control group).

[Role of transesophageal echocardiography in the diagnosis of pulmonary embolism].

The authors report a 72 year-old woman presenting with severe shock after ilio-femoral artery bypass surgery. The transesophageal echocardiography allowed the diagnosis of an unsuspected massive right pulmonary artery embolism. This case emphasizes the role of this procedure for the early bedside diagnosis of massive pulmonary embolism, especially in critically ill patients who require urgent therapeutic interventions.

Candida albicans septic thrombosis of the right atrium is associated with a central venous catheter.

Right atrial thrombus formation is a rare complication of central venous catheterization in adults. Infection of this thrombus is exceptional. A case of a right atrial thrombus associated with Candida albicans infection is described.

Results of mitral valve reconstruction. Experience of Hôpital Erasme, ULB, Brussels.

Background: Reconstructive surgery of the mitral valve has been an alternative to mitral valve replacement in patients with mitral regurgitation. In order to evaluate the early results of mitral valve reconstruction, 38 consecutive cases were analyzed.

Methods: Between January 1985 and May 1993, 38 patients with mitral valve incompetence were treated with a system of reconstructive techniques.

Nature of pulmonary hypertension in congestive heart failure. Effects of cardiac transplantation.

Pulmonary hypertension associated with congestive heart failure carries a risk of right ventricular failure after cardiac transplantation. Few data, however, are available on the hemodynamic behavior of the pulmonary circulation in these patients. We therefore studied mean pulmonary artery pressure minus left atrial pressure (estimated by pulmonary artery occluded pressure) versus cardiac output relationships in 20 patients with congestive heart failure evaluated for orthotopic cardiac transplantation, and we repeated this study either within the first 3 days postoperatively (n = 10) or 1 month postoperatively (n = 11).

Prevotella bivia as an unusual cause of endocarditis.

A case of monomicrobial endocarditis due to Prevotella bivia in a 60-year-old man without previous cardiac lesions is reported. The extremely indolent course with multiple systemic emboli as the only clinical manifestation occurring at least seven months before diagnosis and the persistently negative blood cultures were remarkable features of this case. The incidence, clinical characteristics, treatment and outcome of published cases of infective endocarditis due to anaerobic bacteria are briefly reviewed.

Disturbed frontal regulation of attention in Parkinson's disease.

Parkinson's disease is characterized not only by tremor, akinesia and rigidity, but also by frontal cognitive dysfunction, that can be understood as a disturbance in the 'Supervisory Attentional System' (SAS). This concept refers to a system, located in the frontal cortex, that regulates attentional processes under novel, non-routine conditions. The hypothesis that cognitive dysfunction in Parkinson's disease results from a disturbance in the SAS was investigated by recording 'processing negativity' in 33 parkinsonian patients and 17 controls.

Administration of nebivolol after coronary artery bypass in patients with altered left ventricular function.

This prospective, double-blind study used invasive monitoring and echo-Doppler techniques to compare the hemodynamic effects of nebivolol, a new beta 1-selective beta-blocking agent with those of atenolol in patients recovering from coronary artery bypass grafting surgery. Five milligrams nebivolol and 50 mg atenolol equally decreased heart rate (HR) and blood pressure (BP) but, nebivolol, in contrast to atenolol, caused no decrease in stroke index (SI), cardiac index (CI), and right ventricular ejection fraction (RVEF). These differences appeared to be related in part to different peripheral effects of the two agents because nebivolol administration was associated with a reduction in systemic vascular resistance (SVR).

Influence of the endothelium on the responses to endogenous agonists in human internal mammary and gastroepiploic arteries.

The higher patency rate of internal mammary artery grafts compared to venous grafts has been ascribed to its endothelial function, namely a greater capacity to release endothelium-derived relaxing factor and to inhibit serotonin-induced contractions. Gastroepiploic and mammary arteries were obtained intraoperatively from 27 patients and suspended in organ chambers to record isometric tension. The relaxations to acetylcholine were similar in both vessels.

PEEP inhibits hypoxic pulmonary vasoconstriction in dogs.

The effects of an increase in alveolar pressure on hypoxic pulmonary vasoconstriction (HPV) have been reported variably. We therefore studied the effects of positive end-expiratory pressure (PEEP) on pulmonary hemodynamics in 13 pentobarbital-anesthetized dogs ventilated alternately in hyperoxia [inspired O2 fraction (FIO2) 0.4] and in hypoxia (FIO2 0.

Estimating left ventricular filling pressure during positive end-expiratory pressure in humans.

In the critically ill, accurate measurements of left ventricular (LV) filling pressure using pulmonary artery occlusion pressure (Ppao) are important for diagnostic and therapeutic purposes. In patients receiving positive end-expiratory pressure (PEEP), Ppao may not reflect LV filling pressure because of elevated pericardial pressure (Ppc). It has been proposed that in humans, Ppc and right atrial pressure (PRA) are equal, so that referencing Ppao to PRA may improve the assessment of LV filling pressure when Ppc is elevated.

A survey of nine years heart transplantation at Erasme Hospital, University of Brussels.

Between March 1982 and March 1991, 225 heart transplantations (HTx) have been performed in 220 patients suffering end stage cardiac disease. Thirteen percent were females and 87% were males. Age range was from 5 to 68 years.

Inhibition of hypoxic pulmonary vasoconstriction by increased left atrial pressure in dogs.

To further explore the mechanism of hypoxic pulmonary vasoconstriction, we studied the mean pulmonary arterial pressure (Ppa)/left atrial pressure (Pla) relationship at fixed cardiac index (Q) and the Ppa/Q relationship at several levels of fixed Pla in pentobarbital sodium-anesthetized dogs ventilated alternately in hyperoxia [fraction of inspired O2 (FIO2) 0.4 or 1.0] and in hypoxia (FIO2 0.

[Traumatic rupture of the isthmus of the thoracic aorta (midterm results in a series of 15 cases)].

The authors present a series of 15 cases of traumatic disruption of the aortic isthmus. There were 9 cases of acute rupture and 6 of chronic rupture. All the patients have been operated on.

Mothers' definition of diarrhoea in a suburban community in Tanzania.

A study was conducted in Temeke District, a suburban area of Dar-es-Salaam, Tanzania, to assess the usefulness of a definition coined by mothers in the identification and subsequent management of diarrhoeal diseases. The mothers were asked about stool frequency and consistency of diarrhoeal episodes of their children aged under 5 and at what stage they would initiate remedial action. From their responses, seven categories of stool frequency per 12-hour period were established.

Absence of cardio-depressant effects of CGP 17582 B, a new beta-blocking agent, in patients after coronary surgery.

The hemodynamic effects of CGP 17582 B, a new cardio-selective beta-blocking agent with moderate intrinsic sympathomimetic activity and minimal effects on myocardial contractility, were studied in patients after cardiac surgery for coronary artery bypass graft. Each patient had been treated preoperatively with beta-blocking agents and had a cineangiographic left ventricular ejection fraction between 40 and 60%. Fourteen patients were randomized to receive either 10 mg of propranolol or 50 mg of CGP 17582 B orally.

[Functional non-invasive cardio-respiratory evaluation a month and a year after orthotopic heart transplantation].

Cardio-respiratory stress tests of 14 patients, performed one month and one year after orthotopic heart transplant, are compared in order to demonstrate the functional and metabolic improvements of their adaptation to stress. At maximal stress, we note a 33 p. cent increase of the oxygen consumption (p 0.