From ab initio quantum chemistry to molecular dynamics: The delicate case of hydrogen bonding in ammonia

The ammonia dimer (NH3)2 has been investigated using high--level ab initio quantum chemistry methods and density functional theory (DFT). The structure and energetics of important isomers is obtained to unprecedented accuracy without resorting to experiment. The global minimum of eclipsed C_s symmetry is characterized by a significantly bent hydrogen bond which deviates from linearity by about 20 degrees. In addition, the so-called cyclic C_{2h} structure is extremely close in energy on an overall flat potential energy surface. It is demonstrated that none of the currently available (GGA, meta--GGA, and hybrid) density functionals satisfactorily describe the structure and relative energies of this nonlinear hydrogen bond. We present a novel density functional, HCTH/407+, designed to describe this sort of hydrogen bond quantitatively on the level of the dimer, contrary to e.g. the widely used BLYP functional. This improved functional is employed in Car-Parrinello ab initio molecular dynamics simulations of liquid ammonia to judge its performance in describing the associated liquid. Both the HCTH/407+ and BLYP functionals describe the properties of the liquid well as judged by analysis of radial distribution functions, hydrogen bonding structure and dynamics, translational diffusion, and orientational relaxation processes. It is demonstrated that the solvation shell of the ammonia molecule in the liquid phase is dominated by steric packing effects and not so much by directional hydrogen bonding interactions. In addition, the propensity of ammonia molecules to form bifurcated and multifurcated hydrogen bonds in the liquid phase is found to be negligibly small.Comment: Journal of Chemical Physics, in press (305335JCP

Strategi Kampanye “Breast Cancer Awareness Month”

Salah satu komunitas di Indonesia yang berpusat di Surabaya adalah Reach To Recovery Surabaya (RRS). Pada bulan Oktober 2012 RRS mengadakan kampanye “Breast Cancer Awareness Month”. Tujuan dari kampanye tersebut diadakan adalah untuk meningkatkan awareness masyarakat Surabaya terutama remaja putri untuk melakukan deteksi dini atau yang biasa disebut sebagai SADARI (Periksa Payudara Sendiri). Penelitian ini dilakukan dengan pendekatan kualitatif bertujuan untuk mengetahui bagaimana strategi yang dilakukan oleh “Reach To Recovery Surabaya” (RRS) dengan menggunakan studi kasus kampanye “Breast Cancer Awareness Month”. Melalui penelitian ini dapat diketahui bagaimana kampanye digunakan oleh sebuah komunitas untuk mencapai tujuan organisasinya. Metode penelitian yang digunakan dalam penelitian ini adalah studi kasus dan observasi

A test of the bosonic spinon theory for the triangular antiferromagnet spectrum

We compute the dynamical structure factor of the spin-1/2 triangular Heisenberg model using the mean field Schwinger boson theory. We find that a reconstructed dispersion, resulting from a non trivial redistribution of the spectral weight, agrees quite well with the spin excitation spectrum recently found with series expansions. In particular, we recover the strong renormalization with respect to linear spin wave theory along with the appearance of roton-like minima. Furthermore, near the roton-like minima the contribution of the two spinon continuum to the static structure factor is about 40 % of the total weight. By computing the density-density dynamical structure factor, we identify an unphysical weak signal of the spin excitation spectrum with the relaxation of the local constraint of the Schwinger bosons at the mean field level. Based on the accurate description obtained for the static and dynamic ground state properties, we argue that the bosonic spinon theory should be considered seriously as a valid alternative to interpret the physics of the triangular Heisenberg model.Comment: 6 pages, 5 figures, extended version including: a table with ground state energy and magnetization; and the density-density dynamical structure factor. Accepted for publication in Europhysics Letter

Enumeration of States in a Periodic Glass

We present an analytic enumeration of the metastable states, $N_s$, in a periodic long-range Josephson array frustrated by a transverse field. We find that the configurational entropy, $S_{conf} \equiv \ln N_s$, is extensive and scales with frustration, confirming that the non-random system is glassy. We also find that $S_{conf}$ is different from that of its disordered analogue, despite that fact that the two models share the same dynamical equations

The Cost of Monitoring Alone

We compare the succinctness of two monitoring systems for properties of infinite traces, namely parallel and regular monitors. Although a parallel monitor can be turned into an equivalent regular monitor, the cost of this transformation is a double-exponential blowup in the syntactic size of the monitors, and a triple-exponential blowup when the goal is a deterministic monitor. We show that these bounds are tight and that they also hold for translations between corresponding fragments of Hennessy-Milner logic with recursion over infinite traces.Comment: 22 page

Top-Gated Chemical Vapor Deposited Mos2 Field-Effect Transistors On Si3N4 Substrates

We report the electrical characteristics of chemical vapor deposited (CVD) monolayer molybdenum disulfide (MoS2) top-gated field-effect transistors (FETs) on silicon nitride (Si3N4) substrates. We show that Si3N4 substrates offer comparable electrical performance to thermally grown SiO2 substrates for MoS2 FETs, offering an attractive passivating substrate for transition-metal dichalcogenides (TMD) with a smooth surface morphology. Single-crystal MoS2 grains are grown via vapor transport process using solid precursors directly on low pressure CVD Si3N4, eliminating the need for transfer processes which degrade electrical performance. Monolayer top-gated MoS2 FETs with Al2O3 gate dielectric on Si3N4 achieve a room temperature mobility of 24 cm(2)/V s with I-on/I-off current ratios exceeding 10(7). Using HfO2 as a gate dielectric, monolayer top-gated CVD MoS2 FETs on Si3N4 achieve current densities of 55 mu A/mu m and a transconductance of 6.12 mu S/mu m at V-tg of -5V and V-ds of 2V. We observe an increase in mobility at lower temperatures, indicating phonon scattering may dominate over charged impurity scattering in our devices. Our results show that Si3N4 is an attractive alternative to thermally grown SiO2 substrate for TMD FETs. (C) 2015 AIP Publishing LLC.STTR programNSF NASCENT ERCArmy Research Office under STTR W911NF-14-P-0030Microelectronics Research Cente

Fear of Negative Evaluation, Social Anxiety and Response to Positive and Negative Online Social Cues

High social anxiety is associated with negative interpretations of social feedback, maladaptive attributions for success and failure, and excessive attention to internal and external threat cues. In the present study, 40 undergraduate participants with either high or low levels of social anxiety engaged in a series of social interactions with varying types of social feedback: negative, mixed-negative, mixed-positive, and positive. Given the increasing engagement in computer-mediated communication among individuals with high levels of social anxiety, these interactions took place via instant messaging software. Compared to participants with low social anxiety, participants with high social anxiety experienced more self-focused thoughts, negative thoughts, and state anxiety in response to increases in negative feedback. Participants with low social anxiety experienced fewer self-focused thoughts in response to increased negative feedback, resulting in a significant crossover interaction. Qualitative and quantitative differences regarding cognitive processes and computer-mediated communication among individuals with high and low social anxiety are discussed

Extending Training in Multicultural Competencies to Include Individuals Identifying as Lesbian, Gay, and Bisexual: Key Choice Points for Clinical Psychology Training Programs

Traditional models of multicultural training for professional psychology have focused primarily on racial and ethnic minorities and have not included competencies focused on individuals identifying as lesbian, gay, and bisexual (LGB), despite documented evidence of health disparities for sexual minorities. Ways to adapt models based on Sue’s (1992) 3 × 3 competencies (attitudes and beliefs, knowledge, and skills across the dimensions of awareness of one’s own cultural influences and biases, understanding the client perspective, and appropriate interventions for an individual client) for LGB health are described. This includes the addition of an action/advocacy dimension. Six key choice points for clinical psychology training programs adding LGB competency to a multicultural competency training component are outlined. Potential challenges and solutions for expanding multicultural training are discussed