An Extended Huckel Theory based Atomistic Model for Graphene Nanoelectronics

An atomistic model based on the spin-restricted extended Huckel theory (EHT) is presented for simulating electronic structure and I-V characteristics of graphene devices. The model is applied to zigzag and armchair graphene nano-ribbons (GNR) with and without hydrogen passivation, as well as for bilayer graphene. Further calculations are presented for electric fields in the nano-ribbon width direction and in the bilayer direction to show electronic structure modification. Finally, the EHT Hamiltonian and NEGF (Nonequilibrium Green's function) formalism are used for a paramagnetic zigzag GNR to show 2e2/h quantum conductance.Comment: 5 pages, 8 figure

Ultrafast Electronic Energy Transfer in an orthogonal molecular dyad

The St Andrews group acknowledges support from the European Research Council (grant number 321305) and the Engineering and Physical Sciences Research Council (grant EP/L017008/1). I.D.W.S. also acknowledges support from a Royal Society Wolfson Research Merit Award.Understanding electronic energy transfer (EET) is an important ingredient in the development of artificial photosynthetic systems and photovoltaic technologies. Although EET is at the heart of these applications and crucially influences their light-harvesting efficiency, the nature of EET over short distances for covalently bound donor and acceptor units is often not well understood. Here we investigate EET in an orthogonal molecular dyad (BODT4) in which simple models fail to explain the very origin of EET. Based on nonadiabatic ab initio molecular dynamics calculations and fluorescence depolarization experiments we gain detailed microscopic insights into the ultrafast electro-vibrational dynamics following photoexcitation. Our analysis offers molecular-level insights into these processes and reveals that it takes place on timescales ≲ 100 fs and occurs through an intermediate charge-transfer state.PostprintPeer reviewe

An atomistic quantum transport solver with dephasing for field-effect transistors

Extended Huckel theory (EHT) along with NEGF (Non-equilibrium Green's function formalism) has been used for modeling coherent transport through molecules. Incorporating dephasing has been proposed to theoretically reproduce experimental characteristics for such devices. These elastic and inelastic dephasing effects are expected to be important in quantum devices with the feature size around 10nm, and hence an efficient and versatile solver is needed. This model should have flexibility to be applied to a wide range of nano-scale devices, along with 3D electrostatics, for arbitrary shaped contacts and surface roughness. We report one such EHT-NEGF solver with dephasing by self-consistent Born approximation (SCBA). 3D electrostatics is included using a finite-element scheme. The model is applied to a single wall carbon nanotube (CNT) cross-bar structure with a C60 molecule as the active channel. Without dephasing, a negative differential resistance (NDR) peak appears when the C60 lowest unoccupied molecular orbital level crosses a van Hove singularity in the 1D density of states of the metallic CNTs acting as contacts. This NDR diminishes with increasing dephasing in the channel as expected.Comment: to appear in Journal of Computational Electronic

Knot-isomers of Moebius Cyclacene: How Does the Number of Knots Influence the Structure and First Hyperpolarizability?

Four large ring molecules composed by 15 nitrogen-substituted benzene rings, named as "knot-isomers of Moebius cyclacene", i.e. non-Moebius cyclacenes without a knot (0), Moebius cyclacenes with a knot (1), non-Moebius cyclacenes with two knots (2), and Moebius cyclacenes with three knots (3), are systematically studied for their structures and nonlinear optical properties. The first hyperpolarizability (beta_0) values of these four knot-isomers structures are 4693 (0) < 10484 (2) < 25419 (3) < 60846 au (1). The beta_0 values (60846 for 1, 10484 for 2 and 25419 au for 3) of the knot-isomers with knot(s) are larger than that (4693 au for 0) of the knot-isomer without a knot. It shows that the beta_0 value can be dramatically increases (13 times) by introducing the knot(s) to the cyclacenes structures. It is found that introducing knots to cyclacenes is a new means to enhance the first hyperpolarizability.Comment: 12 pages, 4 figure

Cyclodextrin Complexes of Reduced Bromonoscapine in Guar Gum Microspheres Enhance Colonic Drug Delivery

Here, we report improved solubility and enhanced colonic delivery of reduced bromonoscapine (Red-Br-Nos), a cyclic ether brominated analogue of noscapine, upon encapsulation of its cyclodextrin (CD) complexes in bioresponsive guar gum microspheres (GGM). Phase−solubility analysis suggested that Red-Br-Nos complexed with β-CD and methyl-β-CD in a 1:1 stoichiometry, with a stability constant (Kc) of 2.29 × 103 M−1 and 4.27 × 103 M−1. Fourier transforms infrared spectroscopy indicated entrance of an O−CH2 or OCH3−C6H4−OCH3 moiety of Red-Br-Nos in the β-CD or methyl-β- CD cavity. Furthermore, the cage complex of Red-Br-Nos with β-CD and methyl-β-CD was validated by several spectral techniques. Rotating frame Overhauser enhancement spectroscopy revealed that the Ha proton of the OCH3−C6H4−OCH3 moiety was closer to the H5 proton of β-CD and the H3 proton of the methyl-β-CD cavity. The solubility of Red-Br-Nos in phosphate buffer saline (PBS, pH ∼ 7.4) was improved by ∼10.7-fold and ∼21.2-fold when mixed with β-CD and methyl-β-CD, respectively. This increase in solubility led to a favorable decline in the IC50 by ∼2-fold and ∼3-fold for Red-Br-Nos−β-CD-GGM and Red-Br-Nos−methyl-β-CD-GGM formulations respectively, compared to free Red-Br-Nos−β-CD and Red-Br-Nos−methyl-β-CD in human colon HT-29 cells. GGM-bearing drug complex formulations were found to be highly cytotoxic to the HT-29 cell line and further effective with simultaneous continuous release of Red-Br-Nos from microspheres. This is the first study to showing the preparation of drug-complex loaded GGMS for colon delivery of Red-Br-Nos that warrants preclinical assessment for the effective management of colon cancer

Psychological and social effects of orthodontic treatment

Adolescents with commonly occurring forms of malocclusion often are presumed to be at risk for negative self-esteem and social maladjustment. A randomized control group design was used to assess the psychosocial effects of orthodontic treatment for esthetic impairment. Ninety-three participants, 11 to 14 years old, with mild to moderate malocclusions, were randomly assigned to receive orthodontic treatment immediately or after serving as delayed controls. A battery of psychological and social measures was administered before treatment, during treatment, and three times after completion of treatment, the last occurring one year after termination. Repeated measures analyses of variance assessed group differences at the five time points. Parent-, peer-, and self-evaluations of dental-facial attractiveness significantly improved after treatment, but treatment did not affect parent- and self-reported social competency or social goals, nor subjects' self-esteem. In summary, dental-specific evaluations appear to be influenced by treatment, while more general psychosocial responses are not.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44814/1/10865_2005_Article_BF01856884.pd

A randomised controlled trial of a brief intervention for illicit drug use linked to ASSIST screening in a primary healthcare setting: results from the Australian component of the World Health Organization Phase III ASSIST studies

This report presents the findings from the Australian component of the Phase III World Health Organization (WHO) Alcohol, Smoking and Substance Involvement Screening Test (ASSIST) randomised controlled trial investigating the effectiveness of a 5-10-min brief intervention (BI) for illicit drug use delivered in primary healthcare (PHC) settings. Participants (n=171) recruited from a South Australian PHC setting (sexual health clinic) who scored in the 'moderate risk' range on the ASSIST were randomly allocated to an intervention group or wait-list control group at baseline and were followed up 3 months later. The ASSIST was administered to both groups at baseline and follow up as a measure of relative risk. Those in the intervention group received a prescribed 10-step BI at baseline. The majority (n=63) of participants received the BI for amphetamine-type stimulants (ATS) or cannabis (n=17). There was a significant reduction in total illicit substance (P<0.001) and ATS Involvement (P<0.01) for those receiving the ASSIST-linked BI, compared with control participants. There was no significant effect on cannabis involvement. The results of this study demonstrate that the ASSIST-linked BI may be a reasonably easy and effective way of reducing illicit substance use by Australian PHC clients.Rachel Humeniuk, David A. L. Newcombe, Victoria Dennington and Robert Al