Intentional ρ-type doping by carbon in metalorganic MBE of GaAs

We report on the intentional ρ-type doping of GaAs layers grown in an UHV system from molecular beams of arsine (AsH₃) and mixtures of frimethyl gallium (TMG) and friethyl gallium (TEG). The entire doping range between 10¹⁴ cm^-3 (growth from pure TEG) and 10²⁰ cm^-3 (growth from pure TMG) can be covered by using mixtures of TMG and TEG. As revealed by SIMS and photoluminescence (PL) carbon is the dominant acceptor in the layers. Comparison of the Hall mobility and of the PL spectra shows that the quality of our films equals that of the best LPE and MBE grown ρ-type GaAs layers.     

Effects of age, gender and ear side on SOAE parameters in infancy and childhood

We investigated 267 infants and children aged 9 days to 16.8 years to study the spontaneous otoacoustic emission (SOAE) data prevalence, number per ear, level and frequency as a function of growth. Dependence on age, gender and ear side was statistically analyzed using the method of generalized estimation equations. Except in the 1st year of life, SOAE prevalence per ear and SOAE number per ear decreased significantly with increasing age. Both SOAE parameters were significantly higher in female than in male subjects, with gender difference of SOAE prevalence per ear being more distinct in the 1st year of life. Although a clear ear side effect on SOAE prevalence per ear could already be seen in ears of female children in this age group, only SOAE number per ear was significantly higher in right ears than in left ears from the 1st year of life on. Except in the first 12 months, SOAE level and SOAE frequency decreased significantly with increasing age. Neither a significant gender difference nor a significant ear side difference could be determined. Our results found in infancy and childhood are discussed within the framework of the current literature.     

Potential benefit from implantable cardioverter-defibrillator therapy in patients with and without heart failure

BACKGROUND: Whether patients with heart failure derive a benefit from therapy with implantable cardioverter-defibrillators (ICDs) has been questioned. The purpose of this study was to investigate whether New York Heart Association (NYHA) functional class had an impact on the potential benefit from ICD therapy as assessed from data stored in the memory of ICDs. METHODS AND RESULTS: Between 1989 and 1996, 603 patients (77% men; 59% with coronary artery disease and 16% with dilated cardiomyopathy; age, 57+/-13 years; ejection fraction, 44+/-18%) were treated with an ICD with extended memory function (storage of electrograms and/or RR intervals from treated episodes) in combination with endocardial lead systems. The stages of heart failure (NYHA functional class I through III) at implantation were correlated with overall mortality and the recurrence of fast ventricular tachyarrhythmias (>240 bpm) during follow-up. The potential benefit of the device was estimated as the difference between overall mortality and the hypothetical death rate had the device not been implanted. The latter was based on the recurrence of fast and, without termination by the devices, presumably fatal ventricular tachyarrhythmias. In the overall group, a significant difference between hypothetical death rate and overall mortality was observed (13.9%, 23.5%, and 26.6% at 1, 3, and 5 years, respectively) that suggested a benefit from ICD implantation. In patients in NYHA class I, the estimated benefit, which increased over time, was 15.2%, 29.2%, and 35.6% after 1, 3, and 5 years, respectively. In patients in NYHA class II or III, the estimated benefit increased until the third year (21.8% and 21.9%, respectively) and then remained constant until the fifth year (22.9% and 23.8%, respectively). Even those patients in NYHA class III with a history of decompensated heart failure benefited from ICD implantation. CONCLUSIONS: Analysis of stored ECG data suggests that in patients with a history of ventricular tachycardia or ventricular fibrillation, ICD therapy may lead to a prolongation of life in NYHA classes I through III. The initial benefit is greatest in patients in NYHA class II and class III, but the estimated benefit might persist longest for patients in NYHA class I.     

High speed waveguide-integrated photodiodes grown by metal organic molecular beam epitaxy

Using InP/InGaAs layers grown by metal organic molecular beam epitaxy (MOMBE) on semi-insulating (SI) InP substrate the authors have fabricated waveguide-integrated pin-photodiodes working on the principle of evanescent field coupling. A 3 dB cutoff frequency of 9.6 GHz has been found in a 50 Omega system. The 100 mu m long diodes exhibit a capacitance of <0.1 pF at -5 V bias. In addition design criteria are given to improve the speed of the devices.<>     

A statistical approach to the ecology of Actinobacillus actinomycetemcomitans in subgingival plaque

Experimental renal disease models establish glomerular hypertension as a crucial determinant in glomerulosclerosis progression and demonstrate that glomerular capillary pressure reduction delays sclerosis development. An oscillating pressure (OP) chamber was constructed as an in vitro model to study human mesangial cells. Cell cultures were grown under atmospheric pressure (AP) and a controlled OP corresponding to intraglomerular capillary pressure. We show that OP significantly decreases mesangial cell proliferation within 24 hours and attenuates DNA synthesis throughout a 7-day period. To explore the effects of OP on cell metabolism, cell-associated and medium-secreted extracellular (CA and EC, respectively) collagen synthesis were measured by [3H]proline incorporation. In subconfluent cultures, total CA and EC collagen synthesis was unaffected by OP, while in confluent cultures total EC collagen [3H]proline incorporation was increased. To determine whether OP influenced mesangial cell growth induction, the effects of increasing glucose in the cell culture media were investigated. Our data show that the high glucose growth stimulatory effect on cell number and DNA synthesis was suppressed by OP. Under high glucose conditions, total CA collagen synthesis was increased in confluent cultures, whereas the EC collagen fraction remained unchanged. In these cultures, OP caused an additional increase in CA collagen synthesis. This study shows that mesangial cell growth and collagen synthesis are influenced by hyperbaric OP, supporting the hypothesis that glomerular capillary pressure plays a role in progressive glomerulosclerosis development.     

Kinetics of GaAs growth by low pressure MO-CVD

We have studied the growth of GaAs films from Ga(CH₃)₃ and AsH₃ in a H₂ carrier in the pressure range from 10⁴ to 10⁵ Pa. Over this entire range one finds a temperature region where growth is mainly limited by the supply of reactants. It is bounded at the high temperature side by a region of reduced growth caused by depletion of the gas phase due to precipitaton at the walls. At the low temperature side the rate drops off again, here due to surface kinetic limitations. The uniformity of film thickness improves upon reduction of the pressure. However, the increasing importance of surface reactions in the overall growth process has a negative effect on the morphology of the layers and limits the usable range of deposition parameters.     

Facet formation and characterization of III–V structures grown on patterned surfaces

In selective area growth there is a lateral transition from growth to non-growth areas. At this point the growth is determined by the lowest growing crystal planes. This review summarizes the mechanisms during the facet formation in the InP/GaInAsP material system with respect to the growth conditions in metalorganic molecular beam epitaxy. The effect of interfacet diffusion and the anisotropic surface diffusion process as well as the molecular beam flux density at the facets is discussed. Planar selective area epitaxy (SAE), where the facets can evolve freely, is selected as the starting point. Low lateral growth rates at side wall (01 ) planes of the structure are achieved under perpendicular molecular beam geometry. The results are transferred to embedded SAE for the lateral coupling of heterostructures having constant material compositions up to the lateral contact. Applications for SAE-grown waveguides and laser-waveguide integration are presented.     

Nitrogen fluxes on catchment scale: the influence of hydrological aspects.

In two catchment areas with altogether eight subcatchments characterising different site-specific situations the interaction between anthropogenic activities (e.g. agriculture, nutrition and waste water management), nitrogen emissions and in stream loads as well as concentrations were studied in detail. Groundwater is the most important pathway for nitrogen inputs into surface waters. Denitrification in the soil/subsurface/groundwater system controls the amount of this input to a high extent. Key factors influencing this process are organic carbon availability, geology, precipitation and groundwater recharge rates as well as residence time in groundwater. The MONERIS emission model is a useful tool to quantify these relationships on (sub-)catchment scale. Areas where concentrations in groundwater (e.g. nitrate) tend to be higher due to little dilution with water and might be problematic in respect to limit values for drinking water, are much less relevant in respect to the loads transported to river systems and receiving seas, than regions with high precipitation. In cases with high water availability mainly high loads transported downstream and finally to the receiving sea are a considerable problem. Within a region mainly areas close to river systems contribute to nitrogen discharges to the river system because of the short residence times of the groundwater from these areas and--related to this--a lower influence of denitrification in the groundwater.     

3-Chlorotyrosine, a specific marker of myeloperoxidase-catalyzed oxidation, is markedly elevated in low density lipoprotein isolated from human atherosclerotic intima

Oxidation of LDL may be of pivotal importance in atherogenesis, but the mechanisms that promote oxidation in vivo remain poorly understood. We have explored the possibility that one pathway involves myeloperoxidase, a heme protein secreted by phagocytes. Myeloperoxidase is the only human enzyme known to generate hypochlorous acid (HOCl), a potent oxidizing agent, at physiological halide concentrations. LDL exposed to the complete myeloperoxidase-H2O2-Cl- system underwent chlorination of its protein tyrosyl residues. Treatment of LDL with reagent HOCl resulted in 3-chlorotyrosine formation, implicating HOCl as an intermediate in the enzymatic reaction pathway. In contrast, 3-chlorotyrosine was undetectable in LDL oxidized by hydroxyl radical, copper, iron, hemin, glucose, peroxynitrite, horseradish peroxidase, lactoperoxidase, or lipoxygenase. These results indicate that 3-chlorotyrosine is a specific marker for LDL oxidation by myeloperoxidase. To address the role of myeloperoxidase in promoting LDL oxidation in vivo, we used stable isotope dilution gas chromatography-mass spectrometry to quantify 3-chlorotyrosine in human aortic tissue and in LDL isolated from atherosclerotic lesions. The level of 3-chlorotyrosine in atherosclerotic tissue obtained during vascular surgery was sixfold higher than that of normal aortic intima. Moreover, the level of 3-chlorotyrosine was 30-fold higher in LDL isolated from atherosclerotic intima compared with circulating LDL. The detection of 3-chlorotyrosine in human atherosclerotic lesions indicates that halogenation reactions catalyzed by the myeloperoxidase system of phagocytes constitute one pathway for protein oxidation in vivo. These findings raise the possibility that the myeloperoxidase-H2O2-Cl- system plays a critical role in converting LDL into an atherogenic form.     

Fermi surface studies of the borocarbide superconductor YNi2B2C

The Fermi surface of the nonmagnetic borocarbide superconductor YN_i2B₂C was studied by the de Haas-van Alphen (dHvA) effect. Five branches of dH-vA frequencies are observed in the normal state for B c and the angular dependence was investigated with magnetic fields in the (110) plane. Together with the effective cyclotron masses, m_c, the result is discussed in the context of electronic band-structure calculations.This work has been supported by the Human Capital and Mobility Programme of the European Community through Grant No. ERBCH-BICT941212.