Thermoelectric effects in Kondo correlated quantum dots

In this Letter we study thermoelectric effects in ultra small quantum dots. We study the behaviour of the thermopower, Peltier coefficient and thermal conductance both in the sequencial tunneling regime and in the regime where Kondo correlations develope. Both cases of linear response and non-equilibrium induced by strong temperature gradients are considered. The thermopower is a very sensitive tool to detect Kondo correlations. It changes sign both as a function of temperature and temperature gradient. We also discuss violations of the Wiedemann-Franz law.Comment: 7 pages; 5 figure

Extremal transmission at the Dirac point of a photonic band structure

We calculate the effect of a Dirac point (a conical singularity in the band structure) on the transmission of monochromatic radiation through a photonic crystal. The transmission as a function of frequency has an extremum at the Dirac point, depending on the transparencies of the interfaces with free space. The extremal transmission $T_{0}=\Gamma_{0} W/L$ is inversely proportional to the longitudinal dimension $L$ of the crystal (for $L$ larger than the lattice constant and smaller than the transverse dimension $W$). The interface transparencies affect the proportionality constant $\Gamma_{0}$, and they determine whether the extremum is a minimum or a maximum, but they do not affect the ``pseudo-diffusive'' 1/L dependence of $T_{0}$.Comment: 6 pages, 4 figures. Fig. 1 revised, Fig. 4 adde

Communication: key factor in multidisciplinary system design

System design research often looks at ways to model the system that is developing. Many modelling techniques and model representations exist. Another aspect these models can be used for is to enable, facilitate and improve communication among the developers during the process. The young System Design Group at the faculty of Engineering Technology of the University of Twente, the Netherlands, aims at focusing on this communication aspect in system design.\ud In the paper, a few finished and running projects undertaken in close cooperation with industry are described concisely. From these projects three research themes are derived. These are: creation of high-level models, combining model representations and condense information. The paper ends with plans for future research

Experiments feeding butter-milk

The objects of the following feeding trials were to determine the relative values of wash water from the creamery churn, of buttermilk fed alone, and in conjunction with soaked corn, and to determine the effect of corn following a long period of feeding with a very narrow ratio. Each lot was given all the diluted milk that it would drink. The total solids of this milk amounted to 4.5 per cent, being about one-half the total solids in ordinary buttermilk, showing that the milk was reduced about one-half its value. Lot two was fed ,two pounds of shelled corn, soaked, per day and head. Lot three was fed four pounds of shelled corn, soaked, per day and head. Lot four was fed all the corn they would eat which was from six to seven pounds per day and head. The result for lot one shows that the so-called wash water is not a sustaining ration. The pigs losing a little rising one-half pound of live weight per day and head. A part of this loss can be accounted for in stomach contents

A general introduction to the biochemistry of mitochondrial fatty acid β-oxidation

Over the years, the mitochondrial fatty acid β-oxidation (FAO) pathway has been characterised at the biochemical level as well as the molecular biological level. FAO plays a pivotal role in energy homoeostasis, but it competes with glucose as the primary oxidative substrate. The mechanisms behind this so-called glucose–fatty acid cycle operate at the hormonal, transcriptional and biochemical levels. Inherited defects for most of the FAO enzymes have been identified and characterised and are currently included in neonatal screening programmes. Symptoms range from hypoketotic hypoglycaemia to skeletal and cardiac myopathies. The pathophysiology of these diseases is still not completely understood, hampering optimal treatment. Studies of patients and mouse models will contribute to our understanding of the pathogenesis and will ultimately lead to better treatment

Inelastic cotunneling in quantum dots and molecules with weakly broken degeneracies

We calculate the nonlinear cotunneling conductance through interacting quantum dot systems in the deep Coulomb blockade regime using a rate equation approach based on the T-matrix formalism, which shows in the concerned regions very good agreement with a generalized master equation approach. Our focus is on inelastic cotunneling in systems with weakly broken degeneracies, such as complex quantum dots or molecules. We find for these systems a characteristic gate dependence of the non-equilibrium cotunneling conductance. While on one side of a Coulomb diamond the conductance decreases after the inelastic cotunneling threshold towards its saturation value, on the other side it increases monotonously even after the threshold. We show that this behavior originates from an asymmetric gate voltage dependence of the effective cotunneling amplitudes.Comment: 12 pages, 12 figures; revised published versio

Integer quantum Hall effect on a six valley hydrogen-passivated silicon (111) surface

We report magneto-transport studies of a two-dimensional electron system formed in an inversion layer at the interface between a hydrogen-passivated Si(111) surface and vacuum. Measurements in the integer quantum Hall regime demonstrate the expected sixfold valley degeneracy for these surfaces is broken, resulting in an unequal occupation of the six valleys and anisotropy in the resistance. We hypothesize the misorientation of Si surface breaks the valley states into three unequally spaced pairs, but the observation of odd filling factors, is difficult to reconcile with non-interacting electron theory.Comment: 4 pages, 4 figures, to appear in Physical Review Letter

Magnetic Kronig-Penney model for Dirac electrons in single-layer graphene

The properties of Dirac electrons in a magnetic superlattice (SL) on graphene consisting of very high and thin (delta-function) barriers are investigated. We obtain the energy spectrum analytically and study the transmission through a finite number of barriers. The results are contrasted with those for electrons described by the Schrodinger equation. In addition, a collimation of an incident beam of electrons is obtained along the direction perpendicular to that of the SL. We also highlight the analogy with optical media in which the refractive index varies in space.Comment: 21 pages, 13 figures, to appear in New Journal of Physic