10,293 research outputs found
Structure and correlation effects in semiconducting SrTiO₃
We have investigated the effects of structure change and electron correlation on SrTiO₃ single crystals using angle-resolved photoemission spectroscopy. We show that the cubic to tetragonal phase transition at 105 K is manifested by a charge transfer from in-plane (dyz and dzx) bands to out-of-plane (dxy) band, which is opposite to the theoretical predictions. Along this second-order phase transition, we find a smooth evolution of the quasiparticle strength and effective masses. The in-plane band exhibits a peak-dip-hump lineshape, indicating a high degree of correlation on a relatively large (170 meV) energy scale, which is attributed to the polaron formation
Theory of impedance networks: The two-point impedance and LC resonances
We present a formulation of the determination of the impedance between any
two nodes in an impedance network. An impedance network is described by its
Laplacian matrix L which has generally complex matrix elements. We show that by
solving the equation L u_a = lambda_a u_a^* with orthonormal vectors u_a, the
effective impedance between nodes p and q of the network is Z = Sum_a [u_{a,p}
- u_{a,q}]^2/lambda_a where the summation is over all lambda_a not identically
equal to zero and u_{a,p} is the p-th component of u_a. For networks consisting
of inductances (L) and capacitances (C), the formulation leads to the
occurrence of resonances at frequencies associated with the vanishing of
lambda_a. This curious result suggests the possibility of practical
applications to resonant circuits. Our formulation is illustrated by explicit
examples.Comment: 21 pages, 3 figures; v4: typesetting corrected; v5: Eq. (63)
correcte
Rate-dependent morphology of Li2O2 growth in Li-O2 batteries
Compact solid discharge products enable energy storage devices with high
gravimetric and volumetric energy densities, but solid deposits on active
surfaces can disturb charge transport and induce mechanical stress. In this
Letter we develop a nanoscale continuum model for the growth of Li2O2 crystals
in lithium-oxygen batteries with organic electrolytes, based on a theory of
electrochemical non-equilibrium thermodynamics originally applied to Li-ion
batteries. As in the case of lithium insertion in phase-separating LiFePO4
nanoparticles, the theory predicts a transition from complex to uniform
morphologies of Li2O2 with increasing current. Discrete particle growth at low
discharge rates becomes suppressed at high rates, resulting in a film of
electronically insulating Li2O2 that limits cell performance. We predict that
the transition between these surface growth modes occurs at current densities
close to the exchange current density of the cathode reaction, consistent with
experimental observations.Comment: 8 pages, 6 fig
Induced magnetism of carbon atoms at the graphene/Ni(111) interface
We report an element-specific investigation of electronic and magnetic
properties of the graphene/Ni(111) system. Using magnetic circular dichroism,
the occurrence of an induced magnetic moment of the carbon atoms in the
graphene layer aligned parallel to the Ni 3d magnetization is observed. We
attribute this magnetic moment to the strong hybridization between C and
Ni 3d valence band states. The net magnetic moment of carbon in the graphene
layer is estimated to be in the range of per atom.Comment: 10 pages, 3 figure
Using a neural network approach for muon reconstruction and triggering
The extremely high rate of events that will be produced in the future Large
Hadron Collider requires the triggering mechanism to take precise decisions in
a few nano-seconds. We present a study which used an artificial neural network
triggering algorithm and compared it to the performance of a dedicated
electronic muon triggering system. Relatively simple architecture was used to
solve a complicated inverse problem. A comparison with a realistic example of
the ATLAS first level trigger simulation was in favour of the neural network. A
similar architecture trained after the simulation of the electronics first
trigger stage showed a further background rejection.Comment: A talk given at ACAT03, KEK, Japan, November 2003. Submitted to
Nuclear Instruments and Methods in Physics Research, Section
Enhanced electron correlations, local moments, and Curie temperature in strained MnAs nanocrystals embedded in GaAs
We have studied the electronic structure of hexagonal MnAs, as epitaxial
continuous film on GaAs(001) and as nanocrystals embedded in GaAs, by Mn 2p
core-level photoemission spectroscopy. Configuration-interaction analyses based
on a cluster model show that the ground state of the embedded MnAs nanocrystals
is dominated by a d5 configuration that maximizes the local Mn moment.
Nanoscaling and strain significantly alter the properties of MnAs. Internal
strain in the nanocrystals results in reduced p-d hybridization and enhanced
ionic character of the Mn-As bonding interactions. The spatial confinement and
reduced p-d hybridization in the nanocrystals lead to enhanced d-electron
localization, triggering d-d electron correlations and enhancing local Mn
moments. These changes in the electronic structure of MnAs have an advantageous
effect on the Curie temperature of the nanocrystals, which is measured to be
remarkably higher than that of bulk MnAs.Comment: 4 figures, 2 table
Compatibility Relations between the Reduced and Global Density Matrixes
It is a hard and important problem to find the criterion of the set of
positive-definite matrixes which can be written as reduced density operators of
a multi-partite quantum state. This problem is closely related to the study of
many-body quantum entanglement which is one of the focuses of current quantum
information theory. We give several results on the necessary compatibility
relations between a set of reduced density matrixes, including: (i)
compatibility conditions for the one-party reduced density matrixes of any
dimensional bi-partite mixed quantum state, (ii) compatibility
conditions for the one-party and two-party reduced density matrixes of any
dimensional tri-partite mixed quantum state, and
(iii) compatibility conditions for the one-party reduced matrixes of any
-partite pure quantum state with the dimension .Comment: 14 page
Prediction and classification for GPCR sequences based on ligand specific features
Functional identification of G-Protein Coupled Receptors (GPCRs) is one of the current focus areas of pharmaceutical research. Although thousands of GPCR sequences are known, many of them are orphan sequences (the activating ligand is unknown). Therefore, classification methods for automated characterization of orphan GPCRs are imperative. In this study, for predicting Level 1 subfamilies of GPCRs, a novel method for obtaining class specific features, based on the existence of activating ligand specific patterns, has been developed and utilized for a majority voting classification. Exploiting the fact that there is a non-promiscuous relationship between the specific binding of GPCRs into their ligands and their functional classification, our method classifies Level 1 subfamilies of GPCRs with a high predictive accuracy between 99% and 87% in a three-fold cross validation test. The method also tells us which motifs are significant for class determination which has important design implications. The presented machine learning approach, bridges the gulf between the excess amount of GPCR sequence data and their poor functional characterization
On the Triality Theory for a Quartic Polynomial Optimization Problem
This paper presents a detailed proof of the triality theorem for a class of
fourth-order polynomial optimization problems. The method is based on linear
algebra but it solves an open problem on the double-min duality left in 2003.
Results show that the triality theory holds strongly in a tri-duality form if
the primal problem and its canonical dual have the same dimension; otherwise,
both the canonical min-max duality and the double-max duality still hold
strongly, but the double-min duality holds weakly in a symmetrical form. Four
numerical examples are presented to illustrate that this theory can be used to
identify not only the global minimum, but also the largest local minimum and
local maximum.Comment: 16 pages, 1 figure; J. Industrial and Management Optimization, 2011.
arXiv admin note: substantial text overlap with arXiv:1104.297
- …