The objective of this study was to examine if hyperhomocysteinemia is associated with occlusive vascular disease in hemodialysis patients. The study design included risk factor analysis and ...determination of serum homocysteine in hemodialysis patients. Fifty chronic uremic patients on regular hemodialysis treatment were studied. Twenty-four patients had coronary, cerebral, or peripheral signs of occlusive vascular disease. Cerebral vascular disease was diagnosed by computed tomography, arterial angiography, or Doppler sonography of the carotid and vertebral arteries. Coronary vascular disease was diagnosed by documented history of myocardial infarction or by coronary angiography. The diagnosis of peripheral vascular disease was established by angiography of the lower limb arteries. In all control patients, Doppler sonography of the carotid, vertebral, and lower limb arteries and thallium-201 exercise imaging were without pathologic results. Measurements included blood pressure, body mass index, smoking behavior, serum homocysteine (measured by gas chromatography/mass spectrometry), serum total, low-density lipoprotein, and high-density lipoprotein cholesterol, lipoprotein (a), triglycerides, and plasma fibrinogen. In a stepwise multiple logistic regression analysis, high serum homocysteine was significantly associated with occlusive arterial disease (R = 0.23; P = 0.031). Furthermore, hypertension (R = 0.18; P = 0.058), but not serum total, low-density lipoprotein, and high-density lipoprotein cholesterol, lipoprotein (a), triglycerides, diabetes mellitus, body mass index, plasma fibrinogen, and smoking behavior, was significantly associated with atherosclerosis. Our results support the hypothesis that hyperhomocysteinemia is an independent risk factor for vascular disease in hemodialysis patients.
Diurnal blood pressure variation was studied by ambulatory 24-hour monitoring in patients with advanced chronic renal failure (n = 20), on chronic hemodialysis (n = 20), after renal transplantation ...(n = 21) and in matched control groups without renal disease. Nocturnal blood pressure reductions were significantly blunted in all patient groups as compared with the respective control groups. In almost none of the 61 controls did the mean values during nighttime (8 p.m.-8 a.m.) exceed the mean day time values (8 a.m.-8 p.m.). In 10 of the 61 renal patients blood pressure was higher during the night. In patients with chronic renal disease nocturnal blood pressure elevation may be diagnosed by ambulatory 24-hour monitoring. This may require adaptation of antihypertensive treatment.
A continuous spectrum of misorientations of all azimuthal angles and inclinations varying from 0° to 8° occurring on spherically shaped substrates was used to study the development of terrace-step ...structures of homoepitaxially grown GaAs (001) by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The singular GaAs (001) surface shows growth instabilities with respect to the step-edge profile and the terrace width distribution ranging from 0.1 to 1 μm. The vicinal surface is composed of straight Ga-terminated and ragged As-terminated steps reflecting the interplay of the different nature of both kinds of steps. Obviously, self-similar terrace and step structures are reproduced on different length scales as revealed by a comparison of the atomic force microscopy images with images known from scanning tunnelling microscopy. This scaling leads to terrace and step dimensions which are comparable to the length scale of electronic excitations, thus, influencing the electronic properties of the material. All surfaces under investigation showed a common lateral roughness on the 0.5 to 4 μm scale caused by fluctuations of the terrace width distribution (two-dimensional step bunching). This lateral modulation length increases with increasing misorientation and is always larger, parallel to the 11̄0 direction than perpendicular to this direction. The vertical roughness increases with the amount of misorientation and is stronger for misorientations towards (11̄1)As.
Relaxation of strained layer systems is still not well understood. It is time dependent and changes considerably for samples with different growth history. This has to be discussed in terms of ...nucleation, glide velocity and blocking of misfit dislocations. We have investigated these phenomena at samples with SiGe layer thicknesses ranging from 60 nm up to 120 nm grown by molecular beam epitaxy (MBE) or chemical vapor deposition (CVD) by means of X‐ray topography. The samples were annealed at temperatures between 500° and 600° C. Nucleation of misfit dislocations is heterogeneous and the rate is obviously dependent on layer strain and thickness. A quantified nucleation rate was not yet accessible, mainly due to the preferential formation of dislocation bundles. The propagation velocities of misfit dislocation segments were measured during annealing by means of synchrotron radiation plane wave topography (reflection geometry). The values agree well with theory and there is no evidence that they depend on growth regime. It is shown that the interaction of propagating misfit dislocations with crossing ones may lead to blocking or cross slip in different glide systems. These results are corroborated by investigations with atomic force and transmission electron microscopy.
We have grown defect-free semiconductor-on-insulator (SOI) layers by liquid phase epitaxy. Defect-free Si layers grow laterally over SiO2 by starting from seeding windows or ridge seeds on ...selectively oxide-masked (111) Si substrates. Growth is terminated when {111} facets at the sidewalls develop. The thin SOI layers are slightly bent in relation to the substrate and adhere firmly to the oxide film. The surface of defect-free SOI layers is formed by a perfect (111) facet, whereas monoatomic steps are found at the interfacial bottom of the layers. Although the Si layers are slightly bent, layers grown from different seeds may coalesce defect-free with seams of up to 150 μm in length. In SiGe layers on patterned Si substrates misfit and threading dislocations promote vertical growth of relaxed layers; SiGe layers grown laterally over oxide-covered Si substrates contain only few dislocations.
PDF
