Many-body theory of electronic transport in single-molecule heterojunctions

A many-body theory of molecular junction transport based on nonequilibrium Green's functions is developed, which treats coherent quantum effects and Coulomb interactions on an equal footing. The central quantity of the many-body theory is the Coulomb self-energy matrix $\Sigma_{\rm C}$ of the junction. $\Sigma_{\rm C}$ is evaluated exactly in the sequential tunneling limit, and the correction due to finite tunneling width is evaluated self-consistently using a conserving approximation based on diagrammatic perturbation theory on the Keldysh contour. Our approach reproduces the key features of both the Coulomb blockade and coherent transport regimes simultaneously in a single unified transport theory. As a first application of our theory, we have calculated the thermoelectric power and differential conductance spectrum of a benzenedithiol-gold junction using a semi-empirical $\pi$-electron Hamiltonian that accurately describes the full spectrum of electronic excitations of the molecule up to 8--10eV.Comment: 13 pages, 7 figure

Application of Single-Station Sigma and Site-Response Characterization in a Probabilistic Seismic-Hazard Analysis for a New Nuclear Site

Aleatory variability in ground-motion prediction, represented by the standard deviation (sigma) of a ground-motion prediction equation, exerts a very strong influence on the results of probabilistic seismic-hazard analysis (PSHA). This is especially so at the low annual exceedance frequencies considered for nuclear facilities; in these cases, even small reductions in sigma can have a marked effect on the hazard estimates. Proper separation and quantification of aleatory variability and epistemic uncertainty can lead to defensible reductions in sigma. One such approach is the single-station sigma concept, which removes that part of sigma corresponding to repeatable site-specific effects. However, the site-to-site component must then be constrained by site-specific measurements or else modeled as epistemic uncertainty and incorporated into the modeling of site effects. The practical application of the single-station sigma concept, including the characterization of the dynamic properties of the site and the incorporation of site-response effects into the hazard calculations, is illustrated for a PSHA conducted at a rock site under consideration for the potential construction of a nuclear power plant.Civil, Architectural, and Environmental Engineerin

Coherent Destruction of Coulomb Blockade Peaks in Molecular Junctions

Coherent electronic transport in single-molecule junctions is investigated in the Coulomb blockade regime. Both the transmission phase and probability are calculated for junctions with various contact symmetries. A dramatic suppression of the Coulomb blockade peaks is predicted for junctions where multiple atomic orbitals of the molecule couple to a single electrode although the charging steps are unaffected.Comment: 6 pages, 4 figure

Jahn-Teller Distortions and the Supershell Effect in Metal Nanowires

A stability analysis of metal nanowires shows that a Jahn-Teller deformation breaking cylindrical symmetry can be energetically favorable, leading to stable nanowires with elliptic cross sections. The sequence of stable cylindrical and elliptical nanowires allows for a consistent interpretation of experimental conductance histograms for alkali metals, including both the shell and supershell structures. It is predicted that for gold, elliptical nanowires are even more likely to form since their eccentricity is smaller than for alkali metals. The existence of certain metastable ``superdeformed'' nanowires is also predicted

Constraining the extra heating of the Diffuse Ionized Gas in the Milky Way

The detailed observations of the diffuse ionized gas through the emission lines H$\alpha$, [NII], and [SII] in the Perseus Arm of our Galaxy by the Wisconsin H$\alpha$ Mapper (WHAM)--survey challenge photoionization models. They have to explain the observed rise in the line ratios [NII]/H$\alpha$ and [SII]/H$\alpha$. The models described here consider for the first time the detailed observational geometry toward the Perseus Arm. The models address the vertical variation of the line ratios up to height of 2 kpc above the midplane. The rising trends of the line ratios are matched. The increase in the line ratios is reflected in a rise of the temperature of the gas layer. This is due to the progressive hardening of the radiation going through the gas. However an extra heating above photoionization is needed to explain the absolute values. Two different extra heating rates are investigated which are proportional to $n^0$ and $n^1$. The models show that a combination of both are best to explain the data, where the extra heating independent of density is dominant for z $>$ 0.8 kpc.Comment: accepted for publication in Ap

Oral Examination

The oral cavity is the first component of the digestive tract, which is delimited by the lips anteriorly and the oropharynx posteriorly. The oral cavity functions as a protective barrier and is an essential component for speech and swallowing, mastication, digestion, and taste sensation. The oral examination comprises a uniform and consistent inspection of the head and neck and an intraoral evaluation of the hard and soft tissues (see the images below) in conjunction with a thorough medical and dental history. The entire mouth should be inspected regardless of the patient’s chief complaint and reasons for the visit. [1, 2] Good patient’s history and careful examination are important to establish the correct diagnosis and provide appropriate treatment. The physical examination begins with an extraoral examination to identify possible lesions (such as rash, erythema, and pigmentation), swelling or facial asymmetry. The head and neck should be palpated to identify any tenderness, masses and lymphadenopathy. All muscles of mastication and temporomandibular joint should be palpated for tenderness; patients should be asked to open and close the mouth multiple times to evaluate any limited opening, deviations or asymmetries. The cranial nerve examination should be performed to assess possible neurosensory and neuromuscular deficits. A good light source is fundamental for a good intraoral examination. Any intraoral lesion should be described with respect to size, extent, thickness, color, texture, consistency, and tenderness

Effect of vasopressin 1b receptor blockade on the hypothalamic-pituitary-adrenal response of chronically stressed rats to a heterotypic stressor

Exposure to chronic restraint (CR) modifies the hypothalamic–pituitary–adrenal (HPA) axis response to subsequent acute stressors with adaptation of the response to a homotypic and sensitization of the response to a heterotypic stressor. Since vasopressin (AVP) activity has been reported to change during chronic stress, we investigated whether this was an important factor in HPA facilitation. We therefore tested whether vasopressin 1b receptor (AVPR1B) blockade altered the ACTH and corticosterone response to heterotypic stressors following CR stress. Adult male rats were exposed to CR, single restraint, or were left undisturbed in the home cage. Twenty-four hours after the last restraint, rats were injected with either a AVPR1B antagonist (Org, 30 mg/kg, s.c.) or vehicle (5% mulgofen in saline, 0.2/kg, s.c.) and then exposed to either restraint, lipopolysaccharide (LPS) or white noise. CR resulted in the adaptation of the ACTH and corticosterone response to restraint and this effect was not prevented by pretreatment with Org. Although we found no effect of CR on LPS-induced ACTH and corticosterone secretion, both repeated and single episodes of restraint induced the sensitization of the ACTH, but not corticosterone response to acute noise. Pretreatment with Org reduced the exaggerated ACTH response to noise after both single and repeated exposure to restraint

Many-body theory of electronic transport in single-molecule heterojunctions

A many-body theory of molecular junction transport based on nonequilibrium Green's functions is developed, which treats coherent quantum effects and Coulomb interactions on an equal footing. The central quantity of the many-body theory is the Coulomb self-energy matrix $\Sigma_{\rm C}$ of the junction. $\Sigma_{\rm C}$ is evaluated exactly in the sequential tunneling limit, and the correction due to finite tunneling width is evaluated self-consistently using a conserving approximation based on diagrammatic perturbation theory on the Keldysh contour. Our approach reproduces the key features of both the Coulomb blockade and coherent transport regimes simultaneously in a single unified transport theory. As a first application of our theory, we have calculated the thermoelectric power and differential conductance spectrum of a benzenedithiol-gold junction using a semi-empirical $\pi$-electron Hamiltonian that accurately describes the full spectrum of electronic excitations of the molecule up to 8--10eV.Comment: 13 pages, 7 figure