Highly Homogeneous Current Transport in Ultra-Thin Aluminum Nitride (AlN) Epitaxial Films on Gallium Nitride (GaN) Deposited by Plasma Enhanced Atomic Layer Deposition.

This paper reports an investigation of the structural, chemical and electrical properties of ultra-thin (5 nm) aluminum nitride (AlN) films grown by plasma enhanced atomic layer deposition (PE-ALD) on gallium nitride (GaN). A uniform and conformal coverage of the GaN substrate was demonstrated by morphological analyses of as-deposited AlN films. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) analyses showed a sharp epitaxial interface with GaN for the first AlN atomic layers, while a deviation from the perfect wurtzite stacking and oxygen contamination were detected in the upper part of the film. This epitaxial interface resulted in the formation of a two-dimensional electron gas (2DEG) with a sheet charge density ns ≈ 1.45 × 1012 cm-2, revealed by Hg-probe capacitance-voltage (C-V) analyses. Nanoscale resolution current mapping and current-voltage (I-V) measurements by conductive atomic force microscopy (C-AFM) showed a highly homogeneous current transport through the 5 nm AlN barrier, while a uniform flat-band voltage (VFB ≈ 0.3 V) for the AlN/GaN heterostructure was demonstrated by scanning capacitance microscopy (SCM). Electron transport through the AlN film was shown to follow the Fowler-Nordheim (FN) tunneling mechanism with an average barrier height of <ΦB> = 2.08 eV, in good agreement with the expected AlN/GaN conduction band offset.

Statin Use and Cognitive Impairment in Patients With Type 1 Diabetes: An Observational Study.

OBJECTIVE: We aimed to assess a wide range of cognitive functions in patients with type 1 diabetes (DM1) compared with healthy control subjects and to evaluate the effects of statins on cognitive functions in DM1 patients. MATERIALS AND METHODS: The sample studied consisted of 55 DM1 patients (80.0% with hyperlipidemia, 20% with statin treatment) and 36 age-matched control subjects (77.8% with hyperlipidemia) without diabetes or statin use. Their cognitive functions (attention, memory, and executive functions) were evaluated with the trail making test, controlled oral word association test (COWAT), Rey-Osterrieth complex figure test, brain damage test (diagnosticum für cerebralschädigung, DCS), Wisconsin card sorting test (WCST), and digit span and block design tests from the revised Wechsler adult intelligence scale. RESULTS: Cognitive performance was impaired in DM1 patients when compared with the control group with regard to semantic verbal fluency (COWAT_animals), visual learning (DCS), conceptual-level responses, executive functions (WCST random errors), and WCST trials to complete the first category. Subgroups of DM1 patients distinguished on the basis of statin therapy did not differ with regard to verbal fluency (COWAT_animals), visual learning (DCS), conceptual-level responses, executive functions (WCST random errors), and WCST trials to complete the first category. Multivariate analysis also does not show the impact of statin therapy on cognitive functioning regardless of the duration of education, microangiopathic evidence, the presence of hyperlipidemia, or antihypertensive therapy. CONCLUSIONS: We find impairment of cognitive functions in DM1 patients when compared with control subjects without diabetes. However, we show neither the effect of statins nor the significant influence of metabolic control, microangiopathic complications, or the presence of hyperlipidemia on cognitive functions in DM1 patients.

An independent relationship between muscle sympathetic nerve activity and pulse wave velocity in normal humans.

OBJECTIVE: Carotid-femoral pulse wave velocity (PWV) has been shown to be a powerful predictor of cardiovascular morbidity and mortality. Sympathetic neural mechanisms may have a stiffening influence on arterial mechanical properties. The relationship between direct measures of sympathetic traffic and PWV in healthy humans has not been previously studied. We, therefore, tested the hypothesis that PWV is independently linked to muscle sympathetic nerve activity (MSNA) in normal individuals. METHODS: We measured MSNA (microneurography), PWV (Complior device), heart rate and blood pressure in 25 healthy male participants (mean age 43 +/- 10 years). RESULTS: PWV correlated significantly with age (r = 0.63, P < 0.001), SBP (r = 0.43, P < 0.05) and MSNA (r = 0.43, P < 0.05) but not with BMI, waist circumference, waist-to-hip ratio, heart rate, pulse pressure or DBP. Robust multiple linear regression analysis revealed that only age and MSNA were linked independently to PWV (r2 = 0.62, P < 0.001), explaining 39 and 25% of its variance, respectively. After adjustment of PWV for age and SBP, we further divided individuals into 'excessive' PWV (i.e. higher than expected from age and SBP) and 'optimal' PWV (i.e. lower than expected). BMI and blood pressure were similar in both subgroups. Individuals with excessive PWV had significantly greater MSNA than individuals with optimal PWV (30 +/- 10 vs. 18 +/- 11 bursts/min, P = 0.01). CONCLUSION: This study provides the first evidence that PWV is linked to MSNA in normal humans. The relationship between MSNA and PWV is independent of age, BMI, waist circumference, waist-to-hip ratio, heart rate, pulse pressure or blood pressure.

Supine body position is an important factor influencing postprandial ambulatory blood pressure.

BACKGROUND: Although body position is known to be an important factor influencing the results of ambulatory blood pressure monitoring (ABPM), even very recent studies assessing postprandial blood pressure (BP) have not taken into account the possibility that the examined subjects were lying down after a meal. We addressed this issue by analysing diurnal BP profiles together with subject's reports on supine rest periods and meal consumption during ABPM. MATERIAL/METHODS: The ABPM results of 109 non-medicated subjects were analysed (age 40+/-12 years, daytime BP 132/84+/-15/11 mmHg). BP and heart rate (HR) changes were assessed on the basis of 2-hour means. RESULTS: Subjects who lay down within 2 hours after a meal showed significantly greater decreases in systolic and diastolic BP and HR than individuals who did not: -10+/-10 vs. 1+/-10 mmHg, -11+/-10 vs. -3+/-7 mmHg, and -7+/-9 vs. 0+/-11 beats/min, respectively. The BP decrease was greater when the duration of supine rest was longer. There were no significant differences between BP/HR changes during those periods when the subjects lay down within 2 hours after the meal and BP/HR changes during those periods when supine rest was not preceded by a meal. The mean changes for the latter group were -9+/-10 mmHg, -11+/-8 mmHg, and -9+/-9 beats/min. for SBP, DBP, and HR, respectively. CONCLUSIONS: Our results indicate that supine body position is an important factor, which may influence postprandial BP investigated by ABPM. Body position should always be taken into consideration when ABPM results are analysed.