Direct subsurface absorption of hydrogen on Pd(111)

We summarize and discuss some of the available experimental and theoretical data important for understanding the role played by subsurface sites in dissociative chemisorption calculations for the H$_2$/Pd(111) system. Then we use a semi-empirical potential energy surface (PES) to model the interaction of a H$_2$ molecule impinging on a Pd(111) surface. The London-Eyring-Polanyi-Sato (LEPS) construction has been extended to make direct subsurface absorption possible. A 2-dimensional wave packet calculation is used to find qualitative trends in the direct subsurface absorption and to reveal the time scales involved. We suggest that a partial in-plane relaxation occurs for the slowest incoming particles, thus resulting in a higher direct subsurface absorption probability for low energies.Comment: Journal of Chemical Physics (in press), 19 pages, REVTeX, 4 Postscript figure

Coverage Centrality Maximization in Undirected Networks

Centrality metrics are among the main tools in social network analysis. Being central for a user of a network leads to several benefits to the user: central users are highly influential and play key roles within the network. Therefore, the optimization problem of increasing the centrality of a network user recently received considerable attention. Given a network and a target user $v$, the centrality maximization problem consists in creating $k$ new links incident to $v$ in such a way that the centrality of $v$ is maximized, according to some centrality metric. Most of the algorithms proposed in the literature are based on showing that a given centrality metric is monotone and submodular with respect to link addition. However, this property does not hold for several shortest-path based centrality metrics if the links are undirected. In this paper we study the centrality maximization problem in undirected networks for one of the most important shortest-path based centrality measures, the coverage centrality. We provide several hardness and approximation results. We first show that the problem cannot be approximated within a factor greater than $1-1/e$, unless $P=NP$, and, under the stronger gap-ETH hypothesis, the problem cannot be approximated within a factor better than $1/n^{o(1)}$, where $n$ is the number of users. We then propose two greedy approximation algorithms, and show that, by suitably combining them, we can guarantee an approximation factor of $\Omega(1/\sqrt{n})$. We experimentally compare the solutions provided by our approximation algorithm with optimal solutions computed by means of an exact IP formulation. We show that our algorithm produces solutions that are very close to the optimum.Comment: Accepted to AAAI 201

Impact of nuclear mass uncertainties on the rr-process

Nuclear masses play a fundamental role in understanding how the heaviest elements in the Universe are created in the $r$-process. We predict $r$-process nucleosynthesis yields using neutron capture and photodissociation rates that are based on nuclear density functional theory. Using six Skyrme energy density functionals based on different optimization protocols, we determine for the first time systematic uncertainty bands -- related to mass modeling -- for $r$-process abundances in realistic astrophysical scenarios. We find that features of the underlying microphysics make an imprint on abundances especially in the vicinity of neutron shell closures: abundance peaks and troughs are reflected in trends of neutron separation energy. Further advances in nuclear theory and experiments, when linked to observations, will help in the understanding of astrophysical conditions in extreme $r$-process sites.Comment: 7 pages, 3 figure

Book Review: Archives for the Lay Person: A Guide to Managing Cultural Collections

Review of the book Archives for the Lay Person: A Guide to Managing Cultural Collections, by Lois Hamill. New York: Altamira Press, Rowman & Littlefield Publishers, 2013

Homotaurine, a safe blood-brain barrier permeable GABAA-R-specific agonist, ameliorates disease in mouse models of multiple sclerosis.

There is a need for treatments that can safely promote regulatory lymphocyte responses. T cells express GABA receptors (GABAA-Rs) and GABA administration can inhibit Th1-mediated processes such as type 1 diabetes and rheumatoid arthritis in mouse models. Whether GABAA-R agonists can also inhibit Th17-driven processes such as experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS), is an open question. GABA does not pass through the blood-brain barrier (BBB) making it ill-suited to inhibit the spreading of autoreactivity within the CNS. Homotaurine is a BBB-permeable amino acid that antagonizes amyloid fibril formation and was found to be safe but ineffective in long-term Alzheimer's disease clinical trials. Homotaurine also acts as GABAA-R agonist with better pharmacokinetics than that of GABA. Working with both monophasic and relapsing-remitting mouse models of EAE, we show that oral administration of homotaurine can (1) enhance CD8+CD122+PD-1+ and CD4+Foxp3+ Treg, but not Breg, responses, (2) inhibit autoreactive Th17 and Th1 responses, and (3) effectively ameliorate ongoing disease. These observations demonstrate the potential of BBB-permeable GABAA-R agonists as a new class of treatment to enhance CD8+ and CD4+ Treg responses and limit Th17 and Th1-medaited inflammation in the CNS

Nonharmonic oscillations of nanosized cantilevers due to quantum-size effects

Using a one-dimensional jellium model and standard beam theory we calculate the spring constant of a vibrating nanowire cantilever. By using the asymptotic energy eigenvalues of the standing electron waves over the nanometer-sized cross-section area, the change in the grand canonical potential is calculated and hence the force and the spring constant. As the wire is bent more electron states fits in its cross section. This has an impact on the spring"constant" which oscillates slightly with the bending of the wire. In this way we obtain an amplitude-dependent resonance frequency of the oscillations that should be detectable.Comment: 6 pages, 5 figure

Follow-Up: Provision of Buprenorphine to Pregnant Women by For-Profit Clinics in an Appalachian City

Objective: This study was completed as a follow up to research regarding buprenorphine Medication Assisted Therapy (MAT) in Johnson City Tennessee for-profit clinics. We wished to determine the practice patterns over the last three years. Methods: Johnson City for-profit Medical Assisted Therapy clinics were called with a telephone survey. When the clinic representative answered the phone, they were asked questions regarding patient costs for therapy, insurance coverage, counseling offered on site, and opportunities for tapering while 20 weeks pregnant. Results: At all the MAT clinics contacted, the representative informed us that tapering in pregnancy could be considered contrary to current national guidelines. 43% of the clinics are now accepting insurance as compared to 0% in the 2016 study. The average weekly cost per visit remained consistent. Conclusion: The concept of tapering buprenorphine during pregnancy appears to have become a standard of care for this community and it is offered at all of the clinics that were contacted, some even require it, even though national organizations such as American College of Obstetricians and Gynecologists and American Society of Addiction Medicine; do not recommend this approach. Patients who have insurance including government funded insurance, are now able to obtain buprenorphine with no out of pocket expense at numerous clinics. The high cost for the uninsured patient continues to create an environment conducive to buprenorphine diversion

Business Cycles and Mortality Rates - Aggregate Data for the EU-15 Countries 1990-2012

The relationship between business cycles and mortality has been a highly debated subject in the field of economics. The majority of previous studies, using the unemployment rate as the main proxy for macroeconomic conditions, have found ambiguous effects largely depending on how the effect is estimated. This thesis follows the methodology used by Ruhm (2000), but instead applies aggregate data for a sample of European countries; namely the EU-15 countries. Our sample period stretches from 1990 to 2012, extending upon previous research by looking at the associated relationship in more recent times. Using fixed-effects estimations with the unemployment rate as the main proxy for macroeconomic conditions, we investigate the effect of joblessness on total mortality rates, age-specific mortality, sex-specific death rates as well as cause-specific mortality rates. Our findings demonstrate evidence of a significant procyclical relationship between unemployment and mortality, implying that aggregate average health improves as the economy deteriorates. The procyclical association is found to be significant for age groups 15-44 and 60-74, and the male sub-sample seemed to benefit more from increased unemployment than female counterparts. The thesis also contributed to the existing literature by showing that alternative business cycles, such as GDP growth, follow a similar pattern as unemployment rates