164 research outputs found
Ab initio study of bilateral doping within the MoS2-NbS2 system
We present a systematic study on the stability and the structural and
electronic properties of mixed molybdenum-niobium disulphides. Using density
functional theory we investigate bilateral doping with up to 25 % of MoS2
(NbS2) by Nb (Mo) atoms, focusing on the precise arrangement of dopants within
the host lattices. We find that over the whole range of considered
concentrations, Nb doping of MoS2 occurs through a substitutional mechanism.
For Mo in NbS2 both interstitial and substitutional doping can co-exist,
depending upon the particular synthesis conditions. The analysis of the
structural and electronic modifications of the perfect bulk systems due to the
doping is presented. We show that substitutional Nb atoms introduce electron
holes to the MoS2, leading to a semiconductor-metal transition. On the other
hand, the Mo doping of Nb2, does not alter the metallic behavior of the initial
system. The results of the present study are compared with available
experimental data on mixed MoS2-NbS2 (bulk and nanoparticles).Comment: 7 pages, 6 figure
The universal Glivenko-Cantelli property
Let F be a separable uniformly bounded family of measurable functions on a
standard measurable space, and let N_{[]}(F,\epsilon,\mu) be the smallest
number of \epsilon-brackets in L^1(\mu) needed to cover F. The following are
equivalent:
1. F is a universal Glivenko-Cantelli class.
2. N_{[]}(F,\epsilon,\mu)0 and every probability
measure \mu.
3. F is totally bounded in L^1(\mu) for every probability measure \mu.
4. F does not contain a Boolean \sigma-independent sequence.
It follows that universal Glivenko-Cantelli classes are uniformity classes
for general sequences of almost surely convergent random measures.Comment: 26 page
Data Set Models and Exponential Families in Statistical Physics and Beyond
The exponential family of models is defined in a general setting, not relying
on probability theory. Some results of information geometry are shown to remain
valid. Exponential families both of classical and of quantum mechanical
statistical physics fit into the new formalism. Other less obvious applications
are predicted. For instance, quantum states can be modeled as points in a
classical phase space and the resulting model belongs to the exponential
family
Continuity of the Maximum-Entropy Inference
We study the inverse problem of inferring the state of a finite-level quantum
system from expected values of a fixed set of observables, by maximizing a
continuous ranking function. We have proved earlier that the maximum-entropy
inference can be a discontinuous map from the convex set of expected values to
the convex set of states because the image contains states of reduced support,
while this map restricts to a smooth parametrization of a Gibbsian family of
fully supported states. Here we prove for arbitrary ranking functions that the
inference is continuous up to boundary points. This follows from a continuity
condition in terms of the openness of the restricted linear map from states to
their expected values. The openness condition shows also that ranking functions
with a discontinuous inference are typical. Moreover it shows that the
inference is continuous in the restriction to any polytope which implies that a
discontinuity belongs to the quantum domain of non-commutative observables and
that a geodesic closure of a Gibbsian family equals the set of maximum-entropy
states. We discuss eight descriptions of the set of maximum-entropy states with
proofs of accuracy and an analysis of deviations.Comment: 34 pages, 1 figur
Oscillatory Behavior during the Catalytic Partial Oxidation of Methane: Following Dynamic Structural Changes of Palladium Using the QEXAFS Technique
Promotion of sulfidized W/Al2O3 systems by the decomposition of chemisorbed nickel carbonyl
- …