1,368 research outputs found
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
The enzymology of mitochondrial fatty acid beta-oxidation and its application to follow-up analysis of positive neonatal screening results
The enzymology of mitochondrial fatty acid beta-oxidation and its application to follow-up analysis of positive neonatal screening results
Quantum point contact due to Fermi-level pinning and doping profiles in semiconductor nanocolumns
We show that nanoscale doping profiles inside a nanocolumn in combination
with Fermi-level pinning at the surface give rise to the formation of a
saddle-point in the potential profile. Consequently, the lateral confinement
inside the channel varies along the transport direction, yielding an embedded
quantum point contact. An analytical estimation of the quantization energies
will be given
Efficient processing of TFO-directed psoralen DNA interstrand crosslinks by the UvrABC nuclease
Photoreactive psoralens can form interstrand crosslinks (ICLs) in double-stranded DNA. In eubacteria, the endonuclease UvrABC plays a key role in processing psoralen ICLs. Psoralen-modified triplex-forming oligonucleotides (TFOs) can be used to direct ICLs to specific genomic sites. Previous studies of pyrimidine-rich methoxypsoralenāmodified TFOs indicated that the TFO inhibits cleavage by UvrABC. Because different chemistries may alter the processing of TFO-directed ICLs, we investigated the effect of another type of triplex formed by purine-rich TFOs on the processing of 4ā²-(hydroxymethyl)-4,5ā²,8-trimethylpsoralen (HMT) ICLs by the UvrABC nuclease. Using an HMT-modified TFO to direct ICLs to a specific site, we found that UvrABC made incisions on the purine-rich strand of the duplex ā¼3 bases from the 3ā²-side and ā¼9 bases from the 5ā²-side of the ICL, within the TFO-binding region. In contrast to previous reports, the UvrABC nuclease cleaved the TFO-directed psoralen ICL with a greater efficiency than that of the psoralen ICL alone. Furthermore, the TFO was dissociated from its duplex binding site by UvrA and UvrB. As mutagenesis by TFO-directed ICLs requires nucleotide excision repair, the efficient processing of these lesions supports the use of triplex technology to direct DNA damage for genome modification
Statistics of conductance oscillations of a quantum dot in the Coulomb-blockade regime
The fluctuations and the distribution of the conductance peak spacings of a
quantum dot in the Coulomb-blockade regime are studied and compared with the
predictions of random matrix theory (RMT). The experimental data were obtained
in transport measurements performed on a semiconductor quantum dot fabricated
in a GaAs-AlGaAs heterostructure. It is found that the fluctuations in the peak
spacings are considerably larger than the mean level spacing in the quantum
dot. The distribution of the spacings appears Gaussian both for zero and for
non-zero magnetic field and deviates strongly from the RMT-predictions.Comment: 7 pages, 4 figure
Thermo-Electric Properties of Quantum Point Contacts
I. Introduction
II. Theoretical background (Landauer-Buttiker formalism of
thermo-electricity, Quantum point contacts as ideal electron waveguides,
Saddle-shaped potential)
III. Experiments (Thermopower, Thermal conductance, Peltier effect)
IV. ConclusionsComment: #4 of a series of 4 legacy reviews on QPC'
When the path is never shortest: a reality check on shortest path biocomputation
Shortest path problems are a touchstone for evaluating the computing
performance and functional range of novel computing substrates. Much has been
published in recent years regarding the use of biocomputers to solve minimal
path problems such as route optimisation and labyrinth navigation, but their
outputs are typically difficult to reproduce and somewhat abstract in nature,
suggesting that both experimental design and analysis in the field require
standardising. This chapter details laboratory experimental data which probe
the path finding process in two single-celled protistic model organisms,
Physarum polycephalum and Paramecium caudatum, comprising a shortest path
problem and labyrinth navigation, respectively. The results presented
illustrate several of the key difficulties that are encountered in categorising
biological behaviours in the language of computing, including biological
variability, non-halting operations and adverse reactions to experimental
stimuli. It is concluded that neither organism examined are able to efficiently
or reproducibly solve shortest path problems in the specific experimental
conditions that were tested. Data presented are contextualised with biological
theory and design principles for maximising the usefulness of experimental
biocomputer prototypes.Comment: To appear in: Adamatzky, A (Ed.) Shortest path solvers. From software
to wetware. Springer, 201
Non-equilibrium transport through a vertical quantum dot in the absence of spin-flip energy relaxation
We investigate non-equilibrium transport in the absence of spin-flip energy
relaxation in a few-electron quantum dot artificial atom. Novel non-equilibrium
tunneling processes involving high-spin states which cannot be excited from the
ground state because of spin-blockade, and other processes involving more than
two charge states are observed. These processes cannot be explained by orthodox
Coulomb blockade theory. The absence of effective spin relaxation induces
considerable fluctuation of the spin, charge, and total energy of the quantum
dot. Although these features are revealed clearly by pulse excitation
measurements, they are also observed in conventional dc current characteristics
of quantum dots.Comment: accepted for publication in Phys. Rev.Let
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