40 research outputs found
The Friedel oscillations in the presence of transport currents
We investigate the Friedel oscillations in a nanowire coupled to two
macroscopic electrodes of different potentials. We show that the wave-length of
the density oscillations monotonically increases with the bias voltage, whereas
the amplitude and the spatial decay exponent of the oscillations remain intact.
Using the nonequilibrium Keldysh Green functions, we derive an explicit formula
that describes voltage dependence of the wave-length of the Friedel
oscillations.Comment: 5 pages, 3 figures, RevTe
Hofstadter butterfly for a finite correlated system
We investigate a finite two-dimensional system in the presence of external
magnetic field. We discuss how the energy spectrum depends on the system size,
boundary conditions and Coulomb repulsion. On one hand, using these results we
present the field dependence of the transport properties of a nanosystem. In
particular, we demonstrate that these properties depend on whether the system
consists of even or odd number of sites. On the other hand, on the basis of
exact results obtained for a finite system we investigate whether the
Hofstadter butterfly is robust against strong electronic correlations. We show
that for sufficiently strong Coulomb repulsion the Hubbard gap decreases when
the magnetic field increases.Comment: 7 pages, 5 figures, revte
Application of the dot-ring nanostructure to control electrical transport in the Coulomb blockade regime
Transport properties of a two-dimensional nanostructure composed of a quantum dot surrounded by a quantum
ring (dot-ring nanostructure), are discussed. This complex system is a highly controllable object. Conduction
through dot-ring nanostructure depends crucially on the coupling strength of its states to the electrodes, which
is related to the spatial distribution of the electron's wave functions in dot-ring nanostructure. This distribution
can be strongly modi ed, e.g., by the electrical gating so that the ground and excited states move between the
inner dot and the outer ring. In this paper we show that this property can be used to control single-electron DC
current through dot-ring nanostructure in the Coulomb blockade regime so that it can be used as a single electron transistor
Dot-ring nanostructure: rigorous analysis of many-electron effects
We discuss the quantum dot-ring nanostructure (DRN) as canonical example of a nanosystem, for which the interelectronic interactions can be evaluated exactly. The system has been selected due to its tunability, i.e., its electron wave functions can be modified much easier than in, e.g., quantum dots. We determine many-particle states for Ne = 2 and 3 electrons and calculate the 3- and 4-state interaction parameters, and discuss their importance. For that purpose, we combine the first- and second-quantization schemes and hence are able to single out the component single-particle contributions to the resultant many-particle state. The method provides both the ground- and the first-excited-state energies, as the exact diagonalization of the many-particle Hamiltonian is carried out. DRN provides one of the few examples for which one can determine theoretically all interaction microscopic parameters to a high accuracy. Thus the evolution of the single-particle vs. many-particle contributions to each state and its energy can be determined and tested with the increasing system size. In this manner, we contribute to the wave-function engineering with the interactions included for those few-electron systems
Feasibility and Comparative Effectiveness for the Delivery of the National Diabetes Prevention Program through Cooperative Extension in Rural Communities
The U.S. Cooperative Extension Service (CE) has potential to deliver the National Diabetes Prevention Program (NDPP) to rural residents with prediabetes. However, the CE remains underutilized for the delivery of NDPP. We compared the feasibility/effectiveness of the NDPP (0–6 mos.) delivered by CE personnel to rural residents with prediabetes using Zoom® (CE-Zoom®) or by our research staff using Facebook® (FB). Adults (n = 31, age ~55 years) were enrolled (CE-Zoom® n = 16, FB n = 15). Attendance did not differ significantly between groups (CE Zoom® = 69%, FB = 83%, p = 0.15). Participant retention was similar in the CE Zoom® (88%) and FB groups (87%). CE-Zoom® and FB® groups provided weekly, self-monitoring data for 83% and 84% of the 24 potential weeks, respectively. Six-month weight loss was not different between groups (CE-Zoom® = −5.99 ± 8.0 kg, −5.4%, FB = −1.68 ± 3.3 kg, −1.6% p = 0.13). Participants achieving ≥5% weight loss was greater in the CE-Zoom® (44%) compared with the FB group (7%, p = 0.04). Participants achieving the NDPP program goal for physical activity (≥150 min/week) did not differ (CE-Zoom® = 75%, FB = 67%, p = 0.91). This pilot trial demonstrated the potential feasibility and effectiveness of the NDPP delivered by CE personnel in a group remote format (Zoom®) to adults with prediabetes living in rural areas
Change in Physical Activity and Sitting Time After Myocardial Infarction and Mortality Among Postmenopausal Women in the Women\u27s Health Initiative-Observational Study
BACKGROUND: How physical activity (PA) and sitting time may change after first myocardial infarction (MI) and the association with mortality in postmenopausal women is unknown.
METHODS AND RESULTS: Participants included postmenopausal women in the Women\u27s Health Initiative-Observational Study, aged 50 to 79 years who experienced a clinical MI during the study. This analysis included 856 women who had adequate data on PA exposure and 533 women for sitting time exposures. Sitting time was self-reported at baseline, year 3, and year 6. Self-reported PA was reported at baseline through year 8. Change in PA and sitting time were calculated as the difference between the cumulative average immediately following MI and the cumulative average immediately preceding MI. The 4 categories of change were: maintained low, decreased, increased, and maintained high. The cut points were \u3e /=7.5 metabolic equivalent of task hours/week versus /=8 h/day versus /day for sitting time. Cox proportional hazard models estimated hazard ratios and 95% CIs for all-cause, coronary heart disease, and cardiovascular disease mortality. Compared with women who maintained low PA (referent), the risk of all-cause mortality was: 0.54 (0.34-0.86) for increased PA and 0.52 (0.36-0.73) for maintained high PA. Women who had pre-MI levels of sitting time /day, every 1 h/day increase in sitting time was associated with a 9% increased risk (hazard ratio=1.09, 95% CI: 1.01, 1.19) of all-cause mortality.
CONCLUSIONS: Meeting the recommended PA guidelines pre- and post-MI may have a protective role against mortality in postmenopausal women