14,434 research outputs found
Neural network modeling of memory deterioration in Alzheimer's disease
The clinical course of Alzheimer's disease (AD) is generally characterized by progressive gradual deterioration, although large clinical variability exists. Motivated by the recent quantitative reports of synaptic changes in AD, we use a neural network model to investigate how the interplay between synaptic deletion and compensation determines the pattern of memory deterioration, a clinical hallmark of AD. Within the model we show that the deterioration of memory retrieval due to synaptic deletion can be much delayed by multiplying all the remaining synaptic weights by a common factor, which keeps the average input to each neuron at the same level. This parallels the experimental observation that the total synaptic area per unit volume (TSA) is initially preserved when synaptic deletion occurs. By using different dependencies of the compensatory factor on the amount of synaptic deletion one can define various compensation strategies, which can account for the observed variation in the severity and progression rate of AD
Laid Off: American Workers and Employers Assess a Volatile Labor Market
This Work Trends survey shows that despite economic growth, worker concern for the economy, their job security, and the threat of terrorism is increasing; workers and employers express fear about outsourcing jobs abroad
Entanglement-Saving Channels
The set of Entanglement Saving (ES) quantum channels is introduced and
characterized. These are completely positive, trace preserving transformations
which when acting locally on a bipartite quantum system initially prepared into
a maximally entangled configuration, preserve its entanglement even when
applied an arbitrary number of times. In other words, a quantum channel
is said to be ES if its powers are not entanglement-breaking for all
integers . We also characterize the properties of the Asymptotic
Entanglement Saving (AES) maps. These form a proper subset of the ES channels
that is constituted by those maps which, not only preserve entanglement for all
finite , but which also sustain an explicitly not null level of entanglement
in the asymptotic limit~. Structure theorems are provided
for ES and for AES maps which yield an almost complete characterization of the
former and a full characterization of the latter.Comment: 26 page
Singular value decomposition and matrix reorderings in quantum information theory
We review Schmidt and Kraus decompositions in the form of singular value
decomposition using operations of reshaping, vectorization and reshuffling. We
use the introduced notation to analyse the correspondence between quantum
states and operations with the help of Jamiolkowski isomorphism. The presented
matrix reorderings allow us to obtain simple formulae for the composition of
quantum channels and partial operations used in quantum information theory. To
provide examples of the discussed operations we utilize a package for the
Mathematica computing system implementing basic functions used in the
calculations related to quantum information theory.Comment: 11 pages, no figures, see
http://zksi.iitis.pl/wiki/projects:mathematica-qi for related softwar
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
Structural and electronic properties of the graphene/Al/Ni(111) intercalation-like system
Decoupling of the graphene layer from the ferromagnetic substrate via
intercalation of sp metal has recently been proposed as an effective way to
realize single-layer graphene-based spin-filter. Here, the structural and
electronic properties of the prototype system, graphene/Al/Ni(111), are
investigated via combination of electron diffraction and spectroscopic methods.
These studies are accompanied by state-of-the-art electronic structure
calculations. The properties of this prospective Al-intercalation-like system
and its possible implementations in future graphene-based devices are
discussed.Comment: 20 pages, 8 figures, and supplementary materia
Graphene on ferromagnetic surfaces and its functionalization with water and ammonia
Here we present an angle-resolved photoelectron spectroscopy (ARPES), x-ray
absorption spec-troscopy (XAS), and density-functional theory (DFT)
investigations of water and ammonia ad-sorption on graphene/Ni(111). Our
results on graphene/Ni(111) reveal the existence of interface states,
originating from the strong hybridization of the graphene {\pi} and
spin-polarized Ni 3d valence band states. ARPES and XAS data of the H2O
(NH3)/graphene/Ni(111) system give an information about the kind of interaction
between adsorbed molecules and graphene on Ni(111). The presented experimental
data are compared with the results obtained in the framework of the DFT
approach.Comment: accepted in Nanoscale Research Letters; 16 pages, 4 figures, 2 table
Observation of Three-dimensional Long-range Order in Smaller Ion Coulomb Crystals in an rf Trap
Three-dimensional long-range ordered structures in smaller and
near-spherically symmetric Coulomb crystals of ^{40}Ca^+ ions confined in a
linear rf Paul trap have been observed when the number of ions exceeds ~1000
ions. This result is unexpected from ground state molecular dynamics (MD)
simulations, but found to be in agreement with MD simulations of metastable ion
configurations. Previously, three-dimensional long-range ordered structures
have only been reported in Penning traps in systems of ~50,000 ions or more.Comment: 5 pages; 4 figures; to appear in Phys. Rev. Lett.; changed content
General criterion for the entanglement of two indistinguishable particles
We relate the notion of entanglement for quantum systems composed of two
identical constituents to the impossibility of attributing a complete set of
properties to both particles. This implies definite constraints on the
mathematical form of the state vector associated with the whole system. We then
analyze separately the cases of fermion and boson systems, and we show how the
consideration of both the Slater-Schmidt number of the fermionic and bosonic
analog of the Schmidt decomposition of the global state vector and the von
Neumann entropy of the one-particle reduced density operators can supply us
with a consistent criterion for detecting entanglement. In particular, the
consideration of the von Neumann entropy is particularly useful in deciding
whether the correlations of the considered states are simply due to the
indistinguishability of the particles involved or are a genuine manifestation
of the entanglement. The treatment leads to a full clarification of the subtle
aspects of entanglement of two identical constituents which have been a source
of embarrassment and of serious misunderstandings in the recent literature.Comment: 18 pages, Latex; revised version: Section 3.2 rewritten, new Theorems
added, reference [1] corrected. To appear on Phys.Rev.A 70, (2004
The - divergence and Mixing times of quantum Markov processes
We introduce quantum versions of the -divergence, provide a detailed
analysis of their properties, and apply them in the investigation of mixing
times of quantum Markov processes. An approach similar to the one presented in
[1-3] for classical Markov chains is taken to bound the trace-distance from the
steady state of a quantum processes. A strict spectral bound to the convergence
rate can be given for time-discrete as well as for time-continuous quantum
Markov processes. Furthermore the contractive behavior of the
-divergence under the action of a completely positive map is
investigated and contrasted to the contraction of the trace norm. In this
context we analyse different versions of quantum detailed balance and, finally,
give a geometric conductance bound to the convergence rate for unital quantum
Markov processes
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