395 research outputs found
Sulphur in the protein molecule
METABOLISM EXPERIMENTS WITH METHIONINE:
(a) Feeding experiments with methionine and
a description of a characteristic
syndrone of cystine deficiency in the
albino rat.
(b) An apparatus and method for the
determination of the respiratory
quotient of small animals.
(c) The respiratory quotients of albino
rats on normal and cystine deficient
diets
Charge qubits and limitations of electrostatic quantum gates
We investigate the characteristics of purely electrostatic interactions with
external gates in constructing full single qubit manipulations. The quantum bit
is naturally encoded in the spatial wave function of the electron system.
Single-electron{transistor arrays based on quantum dots or insulating
interfaces typically allow for electrostatic controls where the inter-island
tunneling is considered constant, e.g. determined by the thickness of an
insulating layer. A representative array of 3x3 quantum dots with two mobile
electrons is analyzed using a Hubbard Hamiltonian and a capacitance matrix
formalism. Our study shows that it is easy to realize the first quantum gate
for single qubit operations, but that a second quantum gate only comes at the
cost of compromising the low-energy two-level system needed to encode the
qubit. We use perturbative arguments and the Feshbach formalism to show that
the compromising of the two-level system is a rather general feature for
electrostatically interacting qubits and is not just related to the specific
details of the system chosen. We show further that full implementation requires
tunable tunneling or external magnetic fields.Comment: 7 pages, 5 figures, submitted to PR
Spatially resolved manipulation of single electrons in quantum dots using a scanned probe
The scanning metallic tip of a scanning force microscope was coupled
capacitively to electrons confined in a lithographically defined gate-tunable
quantum dot at a temperature of 300 mK. Single electrons were made to hop on or
off the dot by moving the tip or by changing the tip bias voltage owing to the
Coulomb-blockade effect. Spatial images of conductance resonances map the
interaction potential between the tip and individual electronic quantum dot
states. Under certain conditions this interaction is found to contain a
tip-voltage induced and a tip-voltage independent contribution.Comment: 4 pages, 4 figure
Shared developmental gait disruptions across two mouse models of neurodevelopmental disorders
BACKGROUND: Motor deficits such as abnormal gait are an underappreciated yet characteristic phenotype of many neurodevelopmental disorders (NDDs), including Williams Syndrome (WS) and Neurofibromatosis Type 1 (NF1). Compared to cognitive phenotypes, gait phenotypes are readily and comparably assessed in both humans and model organisms and are controlled by well-defined CNS circuits. Discovery of a common gait phenotype between NDDs might suggest shared cellular and molecular deficits and highlight simple outcome variables to potentially quantify longitudinal treatment efficacy in NDDs.
METHODS: We characterized gait using the DigiGait assay in two different murine NDD models: the complete deletion (CD) mouse, which models hemizygous loss of the complete WS locus, and the Nf1
RESULTS: Compared to wildtype littermate controls, both models displayed markedly similar spatial, temporal, and postural gait abnormalities during development. Developing CD mice also displayed significant decreases in variability metrics. Multiple gait abnormalities observed across development in the Nf1
CONCLUSIONS: These findings suggest that the subcomponents of gait affected in NDDs show overlap between disorders as well as some disorder-specific features, which may change over the course of development. Our incorporation of spatial, temporal, and postural gait measures also provides a template for gait characterization in other NDD models and a platform to examining circuits or longitudinal therapeutics
Interaction quench dynamics in the Kondo model in presence of a local magnetic field
In this work we investigate the quench dynamics in the Kondo model on the
Toulouse line in presence of a local magnetic field. It is shown that this
setup can be realized by either applying the local magnetic field directly or
by preparing the system in a macroscopically spin-polarized initial state. In
the latter case, the magnetic field results from a subtlety in applying the
bosonization technique where terms that are usually referred to as finite-size
corrections become important in the present non-equilibrium setting. The
transient dynamics is studied by analyzing exact analytical results for the
local spin dynamics. The time scale for the relaxation of the local dynamical
quantities turns out to be exclusively determined by the Kondo scale. In the
transient regime, one observes damped oscillations in the local correlation
functions with a frequency set by the magnetic field.Comment: 8 pages, 2 figures; minor changes, version as publishe
DNA repair biomarkers XPF and phospho-MAPKAP kinase 2 correlate with clinical outcome in advanced head and neck cancer.
BackgroundInduction chemotherapy is a common therapeutic option for patients with locoregionally-advanced head and neck cancer (HNC), but it remains unclear which patients will benefit. In this study, we searched for biomarkers predicting the response of patients with locoregionally-advanced HNC to induction chemotherapy by evaluating the expression pattern of DNA repair proteins.MethodsExpression of a panel of DNA-repair proteins in formalin-fixed paraffin embedded specimens from a cohort of 37 HNC patients undergoing platinum-based induction chemotherapy prior to definitive chemoradiation were analyzed using quantitative immunohistochemistry.ResultsWe found that XPF (an ERCC1 binding partner) and phospho-MAPKAP Kinase 2 (pMK2) are novel biomarkers for HNSCC patients undergoing platinum-based induction chemotherapy. Low XPF expression in HNSCC patients is associated with better response to induction chemoradiotherapy, while high XPF expression correlates with a worse response (p = 0.02). Furthermore, low pMK2 expression was found to correlate significantly with overall survival after induction plus chemoradiation therapy (p = 0.01), suggesting that pMK2 may relate to chemoradiation therapy.ConclusionsWe identified XPF and pMK2 as novel DNA-repair biomarkers for locoregionally-advanced HNC patients undergoing platinum-based induction chemotherapy prior to definitive chemoradiation. Our study provides insights for the use of DNA repair biomarkers in personalized diagnostics strategies. Further validation in a larger cohort is indicated
Meta-orbital Transition in Heavy-fermion Systems: Analysis by Dynamical Mean Field Theory and Self-consistent Renormalization Theory of Orbital Fluctuations
We investigate a two-orbital Anderson lattice model with Ising orbital
intersite exchange interactions by means of dynamical mean field theory
combined with the static mean field approximation of the intersite orbital
interactions. Focusing on Ce-based heavy-fermion compounds, we examine the
orbital crossover between the two orbital states, when the total f-electron
number per site n_f is n_f ~ 1. We show that a "meta-orbital" transition, at
which the occupancy of the two orbitals changes steeply, occurs when the
hybridization between the ground-state f-electron orbital and conduction
electrons are smaller than that between the excited f-electron orbital and
conduction electrons. Near the meta-orbital critical end point, the orbital
fluctuations are enhanced, and couple with the charge fluctuations. A critical
theory of the meta-orbital fluctuations is also developed by applying the
self-consistent renormalization theory of itinerant electron magnetism to the
orbital fluctuations. The critical end point, first-order transition and
crossover are described within Gaussian approximations of orbital fluctuations.
We discuss the relevance of our results to CeAl2, CeCu2Si2, CeCu2Ge2 and the
related compounds, which all have low-lying crystalline-electric-field excited
states.Comment: 11 pages, 6 figures, J. Phys. Soc. Jpn. 79, (2010) 11471
Transport Properties of Multiple Quantum Dots Arranged in Parallel: Results from the Bethe Ansatz
In this paper we analyze transport through a double dot system connected to
two external leads. Imagining each dot possessing a single active level, we
model the system through a generalization of the Anderson model. We argue that
this model is exactly solvable when certain constraints are placed upon the dot
Coulomb charging energy, the dot-lead hybridization, and the value of the
applied gate voltage. Using this exact solvability, we access the zero
temperature linear response conductance both in and out of the presence of a
Zeeman field. We are also able to study the finite temperature linear response
conductance. We focus on universal behaviour and identify three primary
features in the transport of the dots: i) a so-called RKKY Kondo effect; ii) a
standard Kondo effect; and iii) interference phenomena leading to sharp
variations in the conductance including conductance zeros. We are able to use
the exact solvability of the dot model to characterize these phenomena
quantitatively. While here we primarily consider a double dot system, the
approach adopted applies equally well to N-dot systems.Comment: 28 pages, 10 figures; references added in v
Radioresistance of Stat1 over-expressing tumour cells is associated with suppressed apoptotic response to cytotoxic agents and increased IL6-IL8 signalling
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