Conductance through an array of quantum dots

We propose a simple approach to study the conductance through an array of $N$ interacting quantum dots, weakly coupled to metallic leads. Using a mapping to an effective site which describes the low-lying excitations and a slave-boson representation in the saddle-point approximation, we calculated the conductance through the system. Explicit results are presented for N=1 and N=3: a linear array and an isosceles triangle. For N=1 in the Kondo limit, the results are in very good agreement with previous results obtained with numerical renormalization group (NRG). In the case of the linear trimer for odd $N$, when the parameters are such that electron-hole symmetry is induced, we obtain perfect conductance $G_0=2e^2/h$. The validity of the approach is discussed in detail.Comment: to appear in Phys. Rev.

Eelgrass Health Survey and Results

Researchers at the University of New Hampshire designed, tested, and conducted an eelgrass health survey. The primary goal of the survey was to collect health ratings from respondents who had viewed pre-selected images of eelgrass representing a wide range of health conditions. Survey results were used as a calibration and validation to a novel eelgrass health index developed using video-monitoring. Two secondary goals of this this survey were the identification of plant-specific and environmental characteristics important to respondents and the introduction of the new eelgrass health index. This published dataset includes de-identified survey respondent background and demographic data, the survey images and questions, and respondents’ eelgrass health ratings and selection rationale

Engineering Fano resonances in discrete networks

We study transmission properties of discrete networks composed of linear arrays coupled to systems of N side defects, and demonstrate the basic principles of the resonant scattering management through engineering Fano resonances. We find exact solutions for the wave transmission coefficient and reveal the conditions for the perfect reflections and transmissions due to either destructive or constructive interferences. We associate these reflections and transmissions with Fano resonances, and demonstrate how they can be tuned by introducing nonlinear defects into the network.Comment: 6 pages, 5 figures, accepted for publication in Phys. Rev.

Nonlinear Fano resonance and bistable wave transmission

We consider a discrete model that describes a linear chain of particles coupled to a single-site defect with instantaneous Kerr nonlinearity. We show that this model can be regarded as a nonlinear generalization of the familiar Fano-Anderson model, and it can generate the amplitude depended bistable resonant transmission or reflection. We identify these effects as the nonlinear Fano resonance, and study its properties for continuous waves and pulses.Comment: 9 pages, 14 figure, submitted to Phys. Rev.

Effect of Cromoglycate on Gas Changes, During Bronchial Challenge by UNCDW in Children with Asthma

Eighteen asthmatic children were challenged with ultrasonically nebulized cold distilled water (UNCDW). Blood gas composition was monitored transcutaneously (tcpO2 and tcpCO2) during and after the challenge. Assuming as basal the response to this UNCDW test, nine children (Group A) were then chosen at random to inhale cromoglycate by aerosol delivery for 8 days. Nine children (Group B), acting as a control, inhaled saline for 8 days. At the end of this therapy, each child repeated the UNCDW test. Statistical analysis with t-test for paired data was used to compare the results of each child to both tests. Mean basal tcpO2 and tcpCO2 were all within the expected normal range. In all children, both mean tcpO2 and tcpCO2 were reduced during and after UNCDW inhalation. Mean tcpCO2 values during the challenge were significantly (p < 0.001) lower than the corresponding steady state 2 rain after the UNCDW challenge, with a mean drop of −7% (2.1 S.D.). Mean tcpO2 values remained significantly decreased (p < 0.001) from the fifth mitt of the UNCDW challenge to the end of the observation period, with a mean drop of −20% (15.5 S.D.). After treatment with cromoglycate (Group A), the mean tcpCO2 values during UNCDW did not change significantly from those ofsteady state conditions: −0.8% (0.5 S.D.); whereas mean tcpO2 values decreased by −4% (4.9 S.D.). The control children treated with saline (Group B) showed mean tcpCO2 and tcpO2 values which were significantly different (p < 0.001) from those of the steady state conditions: mean drop of tcpCO2, −6% (4.2 S.D.); mean drop of tcpO2, −20% (4.7 S.D.). In conclusion, it emerges that: UNCDW induces nonspecific broncho-constriction in asthmatic children with a typical drop of tcpCO2 and tcpO2; the treatment with cromoglycate normalizes the time course of tcpCO2 (hyper-reactivity) and reduces dramatically the drop of tcpO2 time course (hyper-responsivity) during and after the UNCDW test

Angiogenesis in tissue engineering : Breathing life into constructed tissue substitutes

Long-term function of three-dimensional (3D) tissue constructs depends on adequate vascularization after implantation. Accordingly, research in tissue engineering has focused on the analysis of angiogenesis. For this purpose, 2 sophisticated in vivo models (the chorioallantoic membrane and the dorsal skinfold chamber) have recently been introduced in tissue engineering research, allowing a more detailed analysis of angiogenic dysfunction and engraftment failure. To achieve vascularization of tissue constructs, several approaches are currently under investigation. These include the modification of biomaterial properties of scaffolds and the stimulation of blood vessel development and maturation by different growth factors using slow-release devices through pre-encapsulated microspheres. Moreover, new microvascular networks in tissue substitutes can be engineered by using endothelial cells and stem cells or by creating arteriovenous shunt loops. Nonetheless, the currently used techniques are not sufficient to induce the rapid vascularization necessary for an adequate cellular oxygen supply. Thus, future directions of research should focus on the creation of microvascular networks within 3D tissue constructs in vitro before implantation or by co-stimulation of angiogenesis and parenchymal cell proliferation to engineer the vascularized tissue substitute in situ

Site Selective Detection of Methane Dissociation on Stepped Pt Surfaces

We report a combined experimental and theoretical study comparing methane dissociation on three di erent platinum surfaces Pt(111), Pt(211), and Pt(110)-(1 × 2). Re ection absorption infrared spectroscopy (RAIRS) was used to detect chemisorbed methyl species formed by dissociative chemisorption of CH4 on speci c surface sites and to measure surface- site-speci c sticking coe cients of CH4 on the terrace, step, and ridge sites as function of incident translational energy. Methane dissociation is observed to be direct on all sites and di usion of the chemisorbed methyl species is absent for surface temperature below 150 K. The experimental data are compared with the results of density functional (DFT) calculations that give minimum energy barriers for CH4 chemisorption that properly account for the experimental relative site-speci c reactivities. Also in agreement with experiments, DFT results predict a negligible e ect of co-adsorbed H and CH3 species on the vibrational frequency of a methyl group chemisorbed on terrace and step sites of Pt(211). However, the origin of the red-shift of the RAIRS peak of CH3 chemisorbed on terrace sites compared with that on step sites of Pt(211) remains elusive and still demands further investigation

Interaction between Kondo impurities in a quantum corral

We calculate the spectral densities for two impurities inside an elliptical quantum corral using exact diagonalization in the relevant Hilbert subspace and embedding into the rest of the system. For one impurity, the space and energy dependence of the change in differential conductance $\Delta = dI/dV$ observed in the quantum mirage experiment is reproduced. In presence of another impurity, $\Delta = dI/dV$ is very sensitive to the hybridization between impurity and bulk. The impurities are correlated ferromagnetically between them. A hopping $\gtrsim 0.15$ eV between impurities destroy the Kondo resonance.Comment: 4 pages, 4 figure

Kondo resonances and Fano antiresonances in transport through quantum dots

The transmission of electrons through a non-interacting tight-binding chain with an interacting side quantum dot (QD) is analized. When the Kondo effect develops at the dot the conductance presents a wide minimum, reaching zero at the unitary limit. This result is compared to the opposite behaviour found in an embedded QD. Application of a magnetic field destroys the Kondo effect and the conductance shows pairs of dips separated by the charging energy U. The results are discussed in terms of Fano antiresonances and explain qualitatively recent experimental results.Comment: 4 pages including 4 figure