15 research outputs found
Efficient algorithm for current spectral density calculation in single-electron tunneling and hopping
This write-up describes an efficient numerical method for the Monte Carlo
calculation of the spectral density of current in the multi-junction
single-electron devices and hopping structures. In future we plan to expand
this write-up into a full-size paper.Comment: 4 page
A Numerical Study of Transport and Shot Noise at 2D Hopping
We have used modern supercomputer facilities to carry out extensive Monte
Carlo simulations of 2D hopping (at negligible Coulomb interaction) in
conductors with the completely random distribution of localized sites in both
space and energy, within a broad range of the applied electric field and
temperature , both within and beyond the variable-range hopping region. The
calculated properties include not only dc current and statistics of localized
site occupation and hop lengths, but also the current fluctuation spectrum.
Within the calculation accuracy, the model does not exhibit noise, so
that the low-frequency noise at low temperatures may be characterized by the
Fano factor . For sufficiently large samples, scales with conductor
length as , where , and
parameter is interpreted as the average percolation cluster length. At
relatively low , the electric field dependence of parameter is
compatible with the law which follows from directed
percolation theory arguments.Comment: 17 pages, 8 figures; Fixed minor typos and updated reference
A Numerical Study of Coulomb Interaction Effects on 2D Hopping Transport
We have extended our supercomputer-enabled Monte Carlo simulations of hopping
transport in completely disordered 2D conductors to the case of substantial
electron-electron Coulomb interaction. Such interaction may not only suppress
the average value of hopping current, but also affect its fluctuations rather
substantially. In particular, the spectral density of current
fluctuations exhibits, at sufficiently low frequencies, a -like increase
which approximately follows the Hooge scaling, even at vanishing temperature.
At higher , there is a crossover to a broad range of frequencies in which
is nearly constant, hence allowing characterization of the current
noise by the effective Fano factor F\equiv S_I(f)/2e \left. For
sufficiently large conductor samples and low temperatures, the Fano factor is
suppressed below the Schottky value (F=1), scaling with the length of the
conductor as . The exponent is significantly
affected by the Coulomb interaction effects, changing from when such effects are negligible to virtually unity when they are
substantial. The scaling parameter , interpreted as the average
percolation cluster length along the electric field direction, scales as when Coulomb interaction effects are negligible
and when such effects are substantial, in
good agreement with estimates based on the theory of directed percolation.Comment: 19 pages, 7 figures. Fixed minor typos and updated reference
Variability and Reliability of Graphene Field-Effect Transistors with CaF2 Insulators
Graphene is a promising material for applications as a channel in graphene
field-effect transistors (GFETs) which may be used as a building block for
optoelectronics, high-frequency devices and sensors. However, these devices
require gate insulators which ideally should form atomically flat interfaces
with graphene and at the same time contain small densities of traps to maintain
high device stability. Previously used amorphous oxides, such as SiO2 and
Al2O3, however, typically suffer from oxide dangling bonds at the interface,
high surface roughness and numerous border oxide traps. In order to address
these challenges, here we use for the first time 2nm thick epitaxial CaF2 as a
gate insulator in GFETs. By analyzing device-to-device variability for over 200
devices fabricated in two batches, we find that tens of them show similar gate
transfer characteristics. Our statistical analysis of the hysteresis up to 175C
has revealed that while an ambient-sensitive counterclockwise hysteresis can be
present in some devices, the dominant mechanism is thermally activated charge
trapping by border defects in CaF2 which results in the conventional clockwise
hysteresis. We demonstrate that both the hysteresis and bias-temperature
instabilities in our GFETs with CaF2 are comparable to similar devices with
SiO2 and Al2O3. In particular, we achieve a small hysteresis below 0.01 V for
equivalent oxide thickness (EOT) of about 1 nm at the electric fields up to 15
MV/cm and sweep times in the kilosecond range. Thus, our results demonstrate
that crystalline CaF2 is a promising insulator for highly-stable GFETs
Omecamtiv mecarbil in chronic heart failure with reduced ejection fraction, GALACTICâHF: baseline characteristics and comparison with contemporary clinical trials
Aims:
The safety and efficacy of the novel selective cardiac myosin activator, omecamtiv mecarbil, in patients with heart failure with reduced ejection fraction (HFrEF) is tested in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure (GALACTICâHF) trial. Here we describe the baseline characteristics of participants in GALACTICâHF and how these compare with other contemporary trials.
Methods and Results:
Adults with established HFrEF, New York Heart Association functional class (NYHA)ââ„âII, EF â€35%, elevated natriuretic peptides and either current hospitalization for HF or history of hospitalization/ emergency department visit for HF within a year were randomized to either placebo or omecamtiv mecarbil (pharmacokineticâguided dosing: 25, 37.5 or 50âmg bid). 8256 patients [male (79%), nonâwhite (22%), mean age 65âyears] were enrolled with a mean EF 27%, ischemic etiology in 54%, NYHA II 53% and III/IV 47%, and median NTâproBNP 1971âpg/mL. HF therapies at baseline were among the most effectively employed in contemporary HF trials. GALACTICâHF randomized patients representative of recent HF registries and trials with substantial numbers of patients also having characteristics understudied in previous trials including more from North America (n = 1386), enrolled as inpatients (n = 2084), systolic blood pressureâ<â100âmmHg (n = 1127), estimated glomerular filtration rate <â30âmL/min/1.73 m2 (n = 528), and treated with sacubitrilâvalsartan at baseline (n = 1594).
Conclusions:
GALACTICâHF enrolled a wellâtreated, highârisk population from both inpatient and outpatient settings, which will provide a definitive evaluation of the efficacy and safety of this novel therapy, as well as informing its potential future implementation
A numerical study of Coulomb interaction effects on 2D hopping transport
Abstract We have extended our supercomputer-enabled Monte Carlo simulations of hopping transport in completely disordered 2D conductors to the case of substantial electron-electron Coulomb interaction. Such interaction may not only suppress the average value of hopping current, but also affect its fluctuations rather substantially. In particular, the spectral density S I ( f ) of current fluctuations exhibits, at sufficiently low frequencies, a 1/ f -like increase which approximately follows the Hooge scaling, even at vanishing temperature. At higher f , there is a crossover to a broad range of frequencies in which S I ( f ) is nearly constant, hence allowing characterization of the current noise by the effective Fano factor F ⥠S I ( f )/2e I . For sufficiently large conductor samples and low temperatures, the Fano factor is suppressed below the Schottky value (F = 1), scaling with the length L of the conductor as F = (L c /L) α . The exponent α is significantly affected by the Coulomb interaction effects, changing from α = 0.76 ± 0.08 when such effects are negligible to virtually unity when they are substantial. The scaling parameter L c , interpreted as the average percolation cluster length along the electric field direction, scales as L c â E â(0.98±0.08) when Coulomb interaction effects are negligible and L c â E â(1.26±0.15) when such effects are substantial, in good agreement with estimates based on the theory of directed percolation
Recommended from our members
Efficient algorithm for current spectral density calculation in single-electron tunneling and hopping
This write-up describes an efficient numerical method for the Monte Carlo
calculation of the spectral density of current in the multi-junction
single-electron devices and hopping structures. In future we plan to expand
this write-up into a full-size paper