Current and noise expressions for radio-frequency single-electron transistors

We derive self-consistent expressions of current and noise for single-electron transistors driven by time-dependent perturbations. We take into account effects of the electrical environment, higher-order co-tunneling, and time-dependent perturbations under the two-charged state approximation using the Schwinger-Kedysh approach combined with the generating functional technique. For a given generating functional, we derive exact expressions for tunneling currents and noises and present the forms in terms of transport coefficients. It is also shown that in the adiabatic limit our results encompass previous formulas. In order to reveal effects missing in static cases, we apply the derived results to simulate realized radio-frequency single-electron transistor. It is found that photon-assisted tunneling affects largely the performance of the single-electron transistor by enhancing both responses to gate charges and current noises. On various tunneling resistances and frequencies of microwaves, the dependence of the charge sensitivity is also discussed.Comment: 18 pages, 9 figure

Europees Loopkevercongres jubileert in Nederland

De 1e Europese loopkeverovereenkomst werd in 1969 in Wijster georganiseerd. 40 jaar erna wordt in 2009 het jubileumcongres weer in Nederland georganiseerd. Deze bijdrage belicht de bijzondere relatie tussen Nederland en de European Carabidologist Meeting (ECM

Could humans recognize odor by phonon assisted tunneling?

Our sense of smell relies on sensitive, selective atomic-scale processes that are initiated when a scent molecule meets specific receptors in the nose. However, the physical mechanisms of detection are not clear. While odorant shape and size are important, experiment indicates these are insufficient. One novel proposal suggests inelastic electron tunneling from a donor to an acceptor mediated by the odorant actuates a receptor, and provides critical discrimination. We test the physical viability of this mechanism using a simple but general model. Using values of key parameters in line with those for other biomolecular systems, we find the proposed mechanism is consistent both with the underlying physics and with observed features of smell, provided the receptor has certain general properties. This mechanism suggests a distinct paradigm for selective molecular interactions at receptors (the swipe card model): recognition and actuation involve size and shape, but also exploit other processes.Comment: 10 pages, 1 figur

The VITAH Trial Vitamin D supplementation and cardiac autonomic tone in hemodialysis: a blinded, randomized controlled trial

BACKGROUND: Patients with end-stage kidney disease (ESKD) have a high rate of mortality and specifically an increased risk of sudden cardiac death (SCD). Impaired cardiac autonomic tone is associated with elevated risk of SCD. Moreover, patients with ESKD are often vitamin D deficient, which we have shown may be linked to autonomic dysfunction in humans. To date, it is not known whether vitamin D supplementation normalizes cardiac autonomic function in the high-risk ESKD population. The VITamin D supplementation and cardiac Autonomic tone in Hemodialysis (VITAH) randomized trial will determine whether intensive vitamin D supplementation therapies improve cardiac autonomic tone to a greater extent than conventional vitamin D supplementation regimens in ESKD patients requiring chronic hemodialysis. METHODS/DESIGN: A total of 60 subjects with ESKD requiring thrice weekly chronic hemodialysis will be enrolled in this 2x2 crossover, blinded, randomized controlled trial. Following a 4-week washout period from any prior vitamin D therapy, subjects are randomized 1:1 to intensive versus standard vitamin D therapy for 6 weeks, followed by a 12-week washout period, and finally the remaining treatment arm for 6 weeks. Intensive vitamin D treatment includes alfacalcidiol (activated vitamin D) 0.25mcg orally with each dialysis session combined with ergocalciferol (nutritional vitamin D) 50 000 IU orally once per week and placebo the remaining two dialysis days for 6 weeks. The standard vitamin D treatment includes alfacalcidiol 0.25mcg orally combined with placebo each dialysis session per week for 6 weeks. Cardiac autonomic tone is measured via 24 h Holter monitor assessments on the first dialysis day of the week every 6 weeks throughout the study period. The primary outcome is change in the low frequency: high frequency heart rate variability (HRV) ratio during the first 12 h of the Holter recording at 6 weeks versus baseline. Secondary outcomes include additional measures of HRV. The safety of intensive versus conventional vitamin D supplementation is also assessed. DISCUSSION: VITAH will determine whether an intensive vitamin D supplementation regimen will improve cardiac autonomic tone compared to conventional vitamin D supplementation and will assess the safety of these two supplementation regimens in ESKD patients receiving chronic hemodialysis. TRIAL REGISTRATION: ClinicalTrials.gov, NCT0177481

Kidney Function, Albuminuria and Life Expectancy

Background: Lower estimated glomerular filtration rate is associated with reduced life expectancy. Whether this association is modified by the presence or absence of albuminuria, another cardinal finding of chronic kidney disease, is unknown. Objective: Our objective was to estimate the life expectancy of middle-aged men and women with varying levels of eGFR and concomitant albuminuria. Design: A retrospective cohort study. Setting: A large population-based cohort identified from the provincial laboratory registry in Alberta, Canada. Participants: Adults aged ≥30 years who had outpatient measures of serum creatinine and albuminuria between May 1, 2002 and March 31, 2008. Measurements: Predictor : Baseline levels of kidney function identified from serum creatinine and albuminuria measurements. Outcomes : all cause mortality during the follow-up. Methods: Patients were categorized based on their estimated glomerular filtration rate (eGFR) (≥60, 45–59, 30–44, and 15–29 mL/min/1 · 73 m 2 ) as well as albuminuria (normal, mild, and heavy) measured by albumin-to-creatinine ratio or urine dipstick. The abridged life table method was applied to calculate the life expectancies of men and women from age 40 to 80 years across combined eGFR and albuminuria categories. We also categorized participants by severity of kidney disease (low risk, moderately increased risk. high risk, and very high risk) using the combination of eGFR and albuminuria levels. Results: Among men aged 50 years and with eGFR ≥60 mL/min/1.73 m 2 , estimated life expectancy was 24.8 (95% CI: 24.6–25.0), 17.5 (95% CI: 17.1–17.9), and 13.5 (95% CI: 12.6–14.3) years for participants with normal, mild and heavy albuminuria respectively. Life expectancy for men with mild and heavy albuminuria was 7.3 (95% CI: 6.9–7.8) and 11.3 (95% CI: 10.5–12.2) years shorter than men with normal proteinuria, respectively. A reduction in life expectancy was associated with an increasing severity of kidney disease; 24.8 years for low risk (95% CI: 24.6–25.0), 19.1 years for moderately increased risk (95% CI: 18.7–19.5), 14.2 years for high risk (95% CI: 13.5–15.0), and 9.6 years for very high risk (95% CI: 8.4–10.8). Among women of similar age and kidney function, estimated life expectancy was 28.9 (95% CI: 28.7–29.1), 19.8 (95% CI: 19.2–20.3), and 14.8 (95% CI: 13.5–16.0) years for participants with normal, mild and heavy albuminuria respectively. Life expectancy for women with mild and heavy albuminuria was 9.1 (95% CI: 8.5–9.7) and 14.2 (95% CI: 12.9–15.4) years shorter than the women with normal proteinuria, respectively. For women also a graded reduction in life expectancy was observed across the increasing severity of kidney disease; 28.9 years for low risk (95% CI: 28.7–29.1), 22.5 years for moderately increased risk (95% CI: 22.0–22.9), 16.5 years for high risk (95% CI: 15.4–17.5), and 9.2 years for very high risk (95% CI: 7.8–10.7). Limitations: Possible misclassification of long-term kidney function categories cannot be eliminated. Possibility of confounding due to concomitant comorbidities cannot be ruled out. Conclusion: The presence and degree of albuminuria was associated with lower estimated life expectancy for both gender and was especially notable in those with eGFR ≥30 mL/min/1.73 m 2 . Life expectancy associated with a given level of eGFR differs substantially based on the presence and severity of albuminuria