Spin-dependent shot noise enhancement in a quantum dot

The spin-dependent dynamical blockade was investigated in a lateral quantum dot in a magnetic field. Spin-polarized edge channels in the two-dimensional leads and the spatial distribution of Landau orbitals in the dot modulate the tunnel coupling of the quantum dot level spectrum. In a measurement of the electron shot noise we observe a pattern of super-Poissonian noise which is correlated to the spin-dependent competition between different transport channels

The Effect of Teacher-Child Interactions on Child Outcomes

There is a strong body of research that suggests teacher-child interactions have a positive impact on child outcomes. Quality preschool programs include a focus on intentional positive interaction between teachers and children. To support positive developmental gains in young children, early childhood settings must include responsive and cognitively stimulating daily interactions between adults and children (Hamre, 2014). Children with more responsive teachers show improved outcomes across social, behavioral and cognitive domains (Hamre, Hatfield, Pianta, & Jamil, 2014). The purpose of this correlation study was to determine the effect of teacher-child interactions on child outcomes. This focus of the study was to measure child outcomes with an authentic measure, Teaching Strategies GOLD Assessment System. Teacher-child interactions were measured with the Classroom Assessment Scoring System (CLASS). This quantitative study also compared teachers’ years of experience and teacher certification to child outcomes. Spearman rank order coefficient analysis indicated there was not a significant relationship between teacher-child interactions and child outcomes nor teacher-child interactions and teacher experience. Furthermore there was not a statistically significant difference in teacher-child interactions between teachers based on the type of teacher certification. Implications from the research worth further examination: teachers need ongoing support and coaching to ensure they are implementing the assessment tool with fidelity, and studies that includes both an authentic assessment and an authentic measure paired with standardized measures to assess child outcomes

Surface melting of the vortex lattice

We discuss the effect of an (ab)-surface on the melting transition of the pancake-vortex lattice in a layered superconductor within a density functional theory approach. Both discontinuous and continuous surface melting are predicted for this system, although the latter scenario occupies the major part of the low-field phase diagram. The formation of a quasi-liquid layer below the bulk melting temperature inhibits the appearance of a superheated solid phase, yielding an asymmetric hysteretic behavior which has been seen in experiments.Comment: 4 pages, 3 figure

Free energies, vacancy concentrations and density distribution anisotropies in hard--sphere crystals: A combined density functional and simulation study

We perform a comparative study of the free energies and the density distributions in hard sphere crystals using Monte Carlo simulations and density functional theory (employing Fundamental Measure functionals). Using a recently introduced technique (Schilling and Schmid, J. Chem. Phys 131, 231102 (2009)) we obtain crystal free energies to a high precision. The free energies from Fundamental Measure theory are in good agreement with the simulation results and demonstrate the applicability of these functionals to the treatment of other problems involving crystallization. The agreement between FMT and simulations on the level of the free energies is also reflected in the density distributions around single lattice sites. Overall, the peak widths and anisotropy signs for different lattice directions agree, however, it is found that Fundamental Measure theory gives slightly narrower peaks with more anisotropy than seen in the simulations. Among the three types of Fundamental Measure functionals studied, only the White Bear II functional (Hansen-Goos and Roth, J. Phys.: Condens. Matter 18, 8413 (2006)) exhibits sensible results for the equilibrium vacancy concentration and a physical behavior of the chemical potential in crystals constrained by a fixed vacancy concentration.Comment: 17 pages, submitted to Phys. Rev.

Quick Design Analysis for Improving Building Energy Performance

AbstractA building's overall energy performance may be understood as the variation of its energy balance and the extent to which additional heating or cooling energy is needed to maintain comfort. Different characteristics of a building impact the energy performance in ways that vary over time. Transmitted solar gain, for instance, might be an asset at one moment and a liability at another. Architects, designers, and builders often want to know how well a building can be expected to perform in this regard, and they are interested to know what improvements might be the most effective to reduce overall energy use. Many projects lack the budget required for an extensive energy analysis, which is a common approach for answering such questions, while often energy-efficiency guidelines do not address project specific performance issues related to the interactions of site, program and design.Quick analysis tools currently available tend to be inflexible and generic, and thus of limited use in giving design teams feedback about a specific design proposal. This paper presents a cost-effective analysis technique that assesses envelope and internal load characteristics (eg, transmitted solar gain, heat gain/loss of thermal mass, heat gain from equipment, etc) of a building design in terms of their relative benefit or liability to overall conditioning loads. Using data from the energy simulation of one design alternative, the tool presents overall performance of each building characteristic as well as a detailed visualization of performance over all 8760hours of a typical year. The cumulative ranking provides a prioritized list for overall building performance improvements, and the detailed data visualization suggests specific time periods on which the design team should focus

Dynamik des Transports in Quantenpunktsystemen

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A quantized current source with mesoscopic feedback

We study a mesoscopic circuit of two quantized current sources, realized by non-adiabatic single- electron pumps connected in series with a small micron-sized island in between. We find that quantum transport through the second pump can be locked onto the quantized current of the first one by a feedback due to charging of the mesoscopic island. This is confirmed by a measurement of the charge variation on the island using a nearby charge detector. Finally, the charge feedback signal clearly evidences loading into excited states of the dynamic quantum dot during single-electron pump operation

Electron spin orientation under in-plane optical excitation in GaAs quantum wells

We study the optical orientation of electron spins in GaAs/AlGaAs quantum wells for excitation in the growth direction and for in-plane excitation. Time- and polarization-resolved photoluminescence excitation measurements show, for resonant excitation of the heavy-hole conduction band transition, a negligible degree of electron spin polarization for in-plane excitation and nearly 100% for excitation in the growth direction. For resonant excitation of the light-hole conduction band transition, the excited electron spin polarization has the same (opposite) direction for in-plane excitation (in the growth direction) as for excitation into the continuum. The experimental results are well explained by an accurate multiband theory of excitonic absorption taking fully into account electron-hole Coulomb correlations and heavy-hole light-hole coupling.Comment: 10 pages, 4 figures, final versio

Surface Melting of the Vortex Lattice in Layered Superconductors: Density Functional Theory

We study the effects of an $ab$-surface on the vortex-solid to vortex-liquid transition in layered superconductors in the limit of vanishing inter-layer Josephson coupling. We derive the interaction between pancake vortices in a semi-infinite sample and adapt the density functional theory of freezing to this system. We obtain an effective one-component order-parameter theory which can be used to describe the effects of the surface on vortex-lattice melting. Due to the absence of protecting layers in the neighbourhood of the surface, the vortex lattice formed near the surface is more susceptible to thermal fluctuations. Depending on the value of the magnetic field, we predict either a continuous or a discontinuous surface melting transition. For intermediate values of the magnetic field, the surface melts continuously, assisting the formation of the liquid phase and suppressing hysteresis above the melting transition, a prediction consistent with experimental results. For very low and very high magnetic fields, the surface melts discontinuously. The two different surface melting scenarios are separated by two surface multicritical points, which we locate on the melting line.Comment: 16 pages, 12 figure