Time-Dependent Transport Through Molecular Junctions

We investigate transport properties of molecular junctions under two types of bias--a short time pulse or an AC bias--by combining a solution for the Green functions in the time domain with electronic structure information coming from ab initio density functional calculations. We find that the short time response depends on lead structure, bias voltage, and barrier heights both at the molecule-lead contacts and within molecules. Under a low frequency AC bias, the electron flow either tracks or leads the bias signal (capacitive or resistive response) depending on whether the junction is perfectly conducting or not. For high frequency, the current lags the bias signal due to the kinetic inductance. The transition frequency is an intrinsic property of the junctions.Comment: 5 pages, 9 figure

The Role of the Exchange-Correlation Potential in ab initio Electron Transport Calculations

The effect of the exchange-correlation potential in ab initio electron transport calculations is investigated by constructing optimized effective potentials (OEP) using different energy functionals or the electron density from second-order perturbation theory. We calculate electron transmission through two atomic chain systems, one with charge transfer and one without. Dramatic effects are caused by two factors: changes in the energy gap and the self-interaction error. The error in conductance caused by the former is about one order of magnitude while that caused by the latter ranges from several times to two orders of magnitude, depending on the coupling strength and charge transfer. The implications for accurate quantum transport calculations are discussed.Comment: 4 pages, published version, substantially revised discussion and revisions for clarit

Intermolecular Effect in Molecular Electronics

We investigate the effects of lateral interactions on the conductance of two molecules connected in parallel to semi-infinite leads. The method we use combines a Green function approach to quantum transport with density functional theory for the electronic properties. The system, modeled after a self-assembled monolayer, consists of benzylmercaptane molecules sandwiched between gold electrodes. We find that the conductance increases when intermolecular interaction comes into play. The source of this increase is the indirect interaction through the gold substrate rather than direct molecule-molecule interaction. A striking resonance is produced only 0.3 eV above the Fermi energy.Comment: 4 pages, 5 figure

Nanotube-Metal Junctions: 2- and 3- Terminal Electrical Transport

We address the quality of electrical contact between carbon nanotubes and metallic electrodes by performing first-principles calculations for the electron transmission through ideal 2- and 3-terminal junctions, thus revealing the physical limit of tube-metal conduction. The structural model constructed involves surrounding the tube by the metal atoms of the electrode as in most experiments; we consider metallic (5,5) and n-doped semiconducting (10,0) tubes surrounded by Au or Pd. In the case of metallic tubes, the contact conductance is shown to approach the ideal 4e^2/h in the limit of large contact area. For three-terminals, the division of flux among the different transmission channels depends strongly on the metal material. A Pd electrode has nearly perfect tube-electrode transmission and therefore turns off the straight transport along the tube. Our results are in good agreement with some recent experimental reports and clarify a fundamental discrepancy between theory and experiment.Comment: 5 pages, 5 figures, published version: some modified figures and clarifications in the tex

PREVALENCE AND FACTORS ASSOCIATED WITH OBESITY AMONG ADULT AT THE KAMPUNG KOLAM, EAST COAST MALAYSIAN PENINSULA-A CROSS SECTIONAL STUDY

Objective: This study assesses the prevalence of obesity and its associated factors among adults aged 18 y and above at the Kampaung kolam, Kuala Terengganu, Malaysia.Methods: This cross-sectional survey comprised of a semi-structured face to face interview questionnaire and collected anthropometric measurements and sex specific waist circumference in cm. The study population was 70 in total with 21 (30%) males and 49 (70%) females aged 18 y and above were selected by universal sampling. Body mass index (BMI) was used for weight status and sex specific waist circumference (WC) in cm was used for assessment of abdominal or central obesity at risk of metabolic complications associated with obesity.Results: Among men, the prevalence of underweight was 9.5%, normal weight 57.1%, overweight 14.3% and obesity 19.1%, while among women, the prevalence of underweight was 12.2%, normal weight 53.1%, overweight 14.3% and obesity 20.4%. Overall, 18 (25.7%) was obese and 52 (74.3%) was non-obese while sex specific WC in cm 19 (27.1%) was abdominal obese who were at risk of metabolic complication associated with obesity and 51 (72.9%) was not at risk. In chi-square association tests revealed that among respondents, currently married, unemployed and having family history with obesity were associated with generalized obesity while respondents who were currently married and having fast food frequently were associated with abdominal obesity and respondents who being currently married, unemployed and having fast food frequently were more likely to obese in generalized as well as abdominally.Conclusion: There was no association between generalized, abdominal and generalized and abdominal obesity with age, gender, education, flat floor structure, dietary patterns and habits, physical activities, sleep pattern and knowledge and attitude level towards obesity but those factors can be utilized in effective health promotion programmers of weight management strategies by targeting those factors in design for prevention of hypertension, diabetes and related cardio vascular diseases CVD

A Multi-Code Analysis Toolkit for Astrophysical Simulation Data

The analysis of complex multiphysics astrophysical simulations presents a unique and rapidly growing set of challenges: reproducibility, parallelization, and vast increases in data size and complexity chief among them. In order to meet these challenges, and in order to open up new avenues for collaboration between users of multiple simulation platforms, we present yt (available at http://yt.enzotools.org/), an open source, community-developed astrophysical analysis and visualization toolkit. Analysis and visualization with yt are oriented around physically relevant quantities rather than quantities native to astrophysical simulation codes. While originally designed for handling Enzo's structure adaptive mesh refinement (AMR) data, yt has been extended to work with several different simulation methods and simulation codes including Orion, RAMSES, and FLASH. We report on its methods for reading, handling, and visualizing data, including projections, multivariate volume rendering, multi-dimensional histograms, halo finding, light cone generation and topologically-connected isocontour identification. Furthermore, we discuss the underlying algorithms yt uses for processing and visualizing data, and its mechanisms for parallelization of analysis tasks.Comment: 18 pages, 6 figures, emulateapj format. Resubmitted to Astrophysical Journal Supplement Series with revisions from referee. yt can be found at http://yt.enzotools.org

Geometric phases in semiconductor spin qubits: Manipulations and decoherence

We describe the effect of geometric phases induced by either classical or quantum electric fields acting on single electron spins in quantum dots in the presence of spin-orbit coupling. On one hand, applied electric fields can be used to control the geometric phases, which allows performing quantum coherent spin manipulations without using high-frequency magnetic fields. On the other hand, fluctuating fields induce random geometric phases that lead to spin relaxation and dephasing, thus limiting the use of such spins as qubits. We estimate the decay rates due to piezoelectric phonons and conduction electrons in the circuit, both representing dominant electric noise sources with characteristically differing power spectra.Comment: 17 pages, 8 figures, published versio