Strong Spin-Filtering and Spin-Valve Effects in a Molecular V-C60-V Contact

Motivated by the recent achievements in manipulation of C60 molecules in STM experiments, we study theoretically the structure and electronic properties of a C60 molecule in an STM-tunneljunction with a magnetic tip and magnetic adatom on a Cu(111) surface from first-principle calculations. For the case of V tip/adatom, we demonstrate how spin-coupling between the magnetic V atoms mediated by the C60 can be observed in the electronic transport, which display a strong spin-filtering effect, allowing mainly majority-spin electrons to pass(>95%). Moreover, we find a significant change in the conductance between parallel and anti-parallel spin polarizations in the junction (86%) which suggests that STM experiments should be able to characterize the magnetism and spin-coupling for these systems

Extension of the B3LYP - Dispersion-Correcting Potential Approach to the Accurate Treatment of both Inter- and Intramolecular Interactions

We recently showed that dispersion-correcting potentials (DCPs), atom-centered Gaussian-type functions developed for use with B3LYP (J. Phys. Chem. Lett. 2012, 3, 1738-1744) greatly improved the ability of the underlying functional to predict non-covalent interactions. However, the application of B3LYP-DCP for the {\beta}-scission of the cumyloxyl radical led a calculated barrier height that was over-estimated by ca. 8 kcal/mol. We show in the present work that the source of this error arises from the previously developed carbon atom DCPs, which erroneously alters the electron density in the C-C covalent-bonding region. In this work, we present a new C-DCP with a form that was expected to influence the electron density farther from the nucleus. Tests of the new C-DCP, with previously published H-, N- and O-DCPs, with B3LYP-DCP/6-31+G(2d,2p) on the S66, S22B, HSG-A, and HC12 databases of non-covalently interacting dimers showed that it is one of the most accurate methods available for treating intermolecular interactions, giving mean absolute errors (MAEs) of 0.19, 0.27, 0.16, and 0.18 kcal/mol, respectively. Additional testing on the S12L database of complexation systems gave an MAE of 2.6 kcal/mol, showing that the B3LYP-DCP/6-31+G(2d,2p) approach is one of the best-performing and feasible methods for treating large systems dominated by non-covalent interactions. Finally, we showed that C-C making/breaking chemistry is well-predicted using the newly developed DCPs. In addition to predicting a barrier height for the {\beta}-scission of the cumyloxyl radical that is within 1.7 kcal/mol of the high-level value, application of B3LYP-DCP/6-31+G(2d,2p) to 10 databases that include reaction barrier heights and energies, isomerization energies and relative conformation energies gives performance that is amongst the best of all available dispersion-corrected density-functional theory approaches

Gas Doping on the Topological Insulator Bi2Se3 Surface

Gas molecule doping on the topological insulator Bi2 Se3 surface with existing Se vacancies is investigated using first-principles calculations. Consistent with experiments, NO2 and O2 are found to occupy the Se vacancy sites, remove vacancy-doped electrons and restore the band structure of a perfect surface. In contrast, NO and H2 do not favour passivation of such vacancies. Interestingly we have revealed a NO2 dissociation process that can well explain the speculative introduced "photon-doping" effect reported by recent experiments. Experimental strategies to validate this mechanism are presented. The choice and the effect of different passivators are discussed. This step paves the way for the usage of such materials in device applications utilizing robust topological surface states

A comprehensive review of eating disorders and their implications on oral health

In today’s world, eating disorders are plaguing adolescent women at alarming rates. Anorexia nervosa and bulimia nervosa are the two most common disorders and differ in their symptoms and prognoses. While the symptoms of these diseases are not readily visible in systemic health, deteriorating oral health can be a positive indication of abnormal eating habits. Anorexia nervosa and bulimia nervosa result in declining systemic health due to resulting nutritional imbalances and physical harm that patients exert upon themselves. Malnutrition results in altered endocrine function and consequent loss of menstruation, abnormal hair growth, and decreased peak bone mass. Although risk factors for anorexia nervosa and bulimia nervosa vary, the resulting nutritional impoverishment produces the similar systemic effects. In addition to systemic health degradation, symptoms of anorexia and bulimia commonly manifest in the oral cavity. Chemically, salivary composition may be altered resulting in lower pH values. Patients may also exhibit temporary bilateral parotid gland swelling as a result of repeated purge episodes. The most critical oral effect of repeated purge episodes is loss of permanent enamel and is defined as perimolysis. Presently, research does not agree on whether or not eating disorders elevate the risk of dental carries. Although current literature unanimously agrees on the importance of early oral health detection and diagnosis of eating disorders, most dentist are not trained to properly identify and diagnose the manifestations of AN and BN within the oral cavity. Dental school and dental hygiene curriculums lack emphasis on the severity of eating disorders in general and do not allot adequate teaching hours for this matter. Sadly, even when dentists suspect the presence of eating disorders, they are not likely to intervene. Fortunately, full recovery is possible in eating disorder patients if proper therapy and medical attention is provided in a timely manner. Damaged dentition may also be fully restored with the use of crowns, composite fillings, and porcelain veneers. However, if disordered eating habits persist after dental restoration, the dentition will once again erode and deteriorate accordingly. Anorexia nervosa and bulimia nervosa are serious diseases that need proper attention and medical intervention. Their severity should not be minimized as they may ultimately result in grave side effects and eventual death. Dental health practitioners have the ability of observe the presence of these diseases before others as obvious symptoms may present in the oral cavity. Dentists and dental hygienists need to be educated on the oral manifestations of eating disorders and proper protocol regarding timely intervention. With proper education and knowledge, dental health practitioners can reduce the severity of disease, resulting in better prognoses for patients

Verification of temporal-epistemic properties of access control systems

Verification of access control systems against vulnerabilities has always been a challenging problem in the world of computer security. The complication of security policies in large- scale multi-agent systems increases the possible existence of vulnerabilities as a result of mistakes in policy definition. This thesis explores automated methods in order to verify temporal and epistemic properties of access control systems. While temporal property verification can reveal a considerable number of security holes, verification of epistemic properties in multi-agent systems enable us to infer about agents' knowledge in the system and hence, to detect unauthorized information flow. This thesis first presents a framework for knowledge-based verification of dynamic access control policies. This framework models a coalition-based system, which evaluates if a property or a goal can be achieved by a coalition of agents restricted by a set of permissions defined in the policy. Knowledge is restricted to the information that agents can acquire by reading system information in order to increase time and memory efficiency. The framework has its own model-checking method and is implemented in Java and released as an open source tool named \char{cmmi10}{0x50}\char{cmmi10}{0x6f}\char{cmmi10}{0x6c}\char{cmmi10}{0x69}\char{cmmi10}{0x56}\char{cmmi10}{0x65}\char{cmmi10}{0x72}. In order to detect information leakage as a result of reasoning, the second part of this thesis presents a complimentary technique that evaluates access control policies over temporal-epistemic properties where the knowledge is gained by reasoning. We will demonstrate several case studies for a subset of properties that deal with reasoning about knowledge. To increase the efficiency, we develop an automated abstraction refinement technique for evaluating temporal-epistemic properties. For the last part of the thesis, we develop a sound and complete algorithm in order to identify information leakage in Datalog-based trust management systems

On the complementary nature of ANOVA simultaneous component analysis (ASCA+) and Tucker3 tensor decompositions on designed multi-way datasets

The complementary nature of analysis of variance (ANOVA) Simultaneous Component Analysis (ASCA+) and Tucker3 tensor decompositions is demonstrated on designed datasets. We show how ASCA+ can be used to (a) identify statistically sufficient Tucker3 models; (b) identify statistically important triads making their interpretation easier; and (c) eliminate non-significant triads making visualization and interpretation simpler. For multivariate datasets with an experimental design of at least two factors, the data matrix can be folded into a multi-way tensor. ASCA+ can be used on the unfolded matrix, and Tucker3 modeling can be used on the folded matrix (tensor). Two novel strategies are reported to determine the statistical significance of Tucker3 models using a previously published dataset. A statistically sufficient model was created by adding factors to the Tucker3 model in a stepwise manner until no ASCA+ detectable structure was observed in the residuals. Bootstrap analysis of the Tucker3 model residuals was used to determine confidence intervals for the loadings and the individual elements of the core matrix and showed that 21 out of 63 core values of the 3 7 3 model were not significant at the 95% confidence level. Exploiting the mutual orthogonality of the 63 triads of the Tucker3 model, these 21 factors (triads) were removed from the model. An ASCA+ backward elimination strategy is reported to further simplify the Tucker3 3 7 3 model to 36 core values and associated triads. ASCA+ was also used to identify individual factors (triads) with selective responses on experimental factors A, B, or interactions, A B, for improved model visualization and interpretation

Atomic White-Out: Enabling Atomic Circuitry Through Mechanically Induced Bonding of Single Hydrogen Atoms to a Silicon Surface

We report the mechanically induced formation of a silicon-hydrogen covalent bond and its application in engineering nanoelectronic devices. We show that using the tip of a non-contact atomic force microscope (NC-AFM), a single hydrogen atom could be vertically manipulated. When applying a localized electronic excitation, a single hydrogen atom is desorbed from the hydrogen passivated surface and can be transferred to the tip apex as evidenced from a unique signature in frequency shift curves. In the absence of tunnel electrons and electric field in the scanning probe microscope junction at 0 V, the hydrogen atom at the tip apex is brought very close to a silicon dangling bond, inducing the mechanical formation of a silicon-hydrogen covalent bond and the passivation of the dangling bond. The functionalized tip was used to characterize silicon dangling bonds on the hydrogen-silicon surface, was shown to enhance the scanning tunneling microscope (STM) contrast, and allowed NC-AFM imaging with atomic and chemical bond contrasts. Through examples, we show the importance of this atomic scale mechanical manipulation technique in the engineering of the emerging technology of on-surface dangling bond based nanoelectronic devices.Comment: 9 pages (including references and Supplementary Section), 8 figures (5 in the main text, 3 in Supplementary