2,114 research outputs found
Regularized diffusion adaptation via conjugate smoothing
The purpose of this work is to develop and study a decentralized strategy for Pareto optimization of an aggregate cost consisting of regularized risks. Each risk is modeled as the expectation of some loss function with unknown probability distribution while the regularizers are assumed deterministic, but are not required to be differentiable or even continuous. The individual, regularized, cost functions are distributed across a strongly-connected network of agents and the Pareto optimal solution is sought by appealing to a multi-agent diffusion strategy. To this end, the regularizers are smoothed by means of infimal convolution and it is shown that the Pareto solution of the approximate, smooth problem can be made arbitrarily close to the solution of the original, non-smooth problem. Performance bounds are established under conditions that are weaker than assumed before in the literature, and hence applicable to a broader class of adaptation and learning problems
Local Hidden Variable Theories for Quantum States
While all bipartite pure entangled states violate some Bell inequality, the
relationship between entanglement and non-locality for mixed quantum states is
not well understood. We introduce a simple and efficient algorithmic approach
for the problem of constructing local hidden variable theories for quantum
states. The method is based on constructing a so-called symmetric
quasi-extension of the quantum state that gives rise to a local hidden variable
model with a certain number of settings for the observers Alice and Bob.Comment: 8 pages Revtex; v2 contains substantial changes, a strengthened main
theorem and more reference
Improved quantum algorithms for the ordered search problem via semidefinite programming
One of the most basic computational problems is the task of finding a desired
item in an ordered list of N items. While the best classical algorithm for this
problem uses log_2 N queries to the list, a quantum computer can solve the
problem using a constant factor fewer queries. However, the precise value of
this constant is unknown. By characterizing a class of quantum query algorithms
for ordered search in terms of a semidefinite program, we find new quantum
algorithms for small instances of the ordered search problem. Extending these
algorithms to arbitrarily large instances using recursion, we show that there
is an exact quantum ordered search algorithm using 4 log_{605} N \approx 0.433
log_2 N queries, which improves upon the previously best known exact algorithm.Comment: 8 pages, 4 figure
Generalized phonon-assisted Zener tunneling in indirect semiconductors with non-uniform electric fields : a rigorous approach
A general framework to calculate the Zener current in an indirect
semiconductor with an externally applied potential is provided. Assuming a
parabolic valence and conduction band dispersion, the semiconductor is in
equilibrium in the presence of the external field as long as the electronphonon
interaction is absent. The linear response to the electron-phonon interaction
results in a non-equilibrium system. The Zener tunneling current is calculated
from the number of electrons making the transition from valence to conduction
band per unit time. A convenient expression based on the single particle
spectral functions is provided, enabling the numerical calculation of the Zener
current under any three-dimensional potential profile. For a one dimensional
potential profile an analytical expression is obtained for the current in a
bulk semiconductor, a semiconductor under uniform field and a semiconductor
under a non-uniform field using the WKB (Wentzel-Kramers-Brillouin)
approximation. The obtained results agree with the Kane result in the low field
limit. A numerical example for abrupt p - n diodes with different doping
concentrations is given, from which it can be seen that the uniform field model
is a better approximation than the WKB model but a direct numerical treatment
is required for low bias conditions.Comment: 29 pages, 7 figure
Budget Feasible Mechanisms for Experimental Design
In the classical experimental design setting, an experimenter E has access to
a population of potential experiment subjects , each
associated with a vector of features . Conducting an experiment
with subject reveals an unknown value to E. E typically assumes
some hypothetical relationship between 's and 's, e.g., , and estimates from experiments, e.g., through linear
regression. As a proxy for various practical constraints, E may select only a
subset of subjects on which to conduct the experiment.
We initiate the study of budgeted mechanisms for experimental design. In this
setting, E has a budget . Each subject declares an associated cost to be part of the experiment, and must be paid at least her cost. In
particular, the Experimental Design Problem (EDP) is to find a set of
subjects for the experiment that maximizes V(S) = \log\det(I_d+\sum_{i\in
S}x_i\T{x_i}) under the constraint ; our objective
function corresponds to the information gain in parameter that is
learned through linear regression methods, and is related to the so-called
-optimality criterion. Further, the subjects are strategic and may lie about
their costs.
We present a deterministic, polynomial time, budget feasible mechanism
scheme, that is approximately truthful and yields a constant factor
approximation to EDP. In particular, for any small and , we can construct a (12.98, )-approximate mechanism that is
-truthful and runs in polynomial time in both and
. We also establish that no truthful,
budget-feasible algorithms is possible within a factor 2 approximation, and
show how to generalize our approach to a wide class of learning problems,
beyond linear regression
Stable oxygen isotope record of the Eocene-Oligocene transition in the southern North Sea Basin: positioning the Oi-1 event
Preliminary stable oxygen isotope data are presented from the southern North Sea Basin successions, ranging from the Lutetian to Rupelian. Analyses were performed on fish otoliths, nuculid bivalves and benthic foraminifera and are presented as bulk delta(18)O values relative to a well established regional sequence stratigraphic framework. The most significant positive shift in delta(18)O values clearly falls at the top of the regionally recognised Bassevelde 3 sequence, which base corresponds to the Eocene-Oligocene GSSP boundary. The here documented delta(18)O shift is closely associated with the base of the traditional Rupelian unit-stratotype and is tentatively correlated to the globally recognised Oi-1 event
Genetics of Chronic Lymphocytic Leukemia: Practical Aspects and Prognostic Significance
status: publishe
Theoretical study of scattering in graphene ribbons in the presence of structural and atomistic edge roughness
We investigate the diffusive electron-transport properties of charge-doped
graphene ribbons and nanoribbons with imperfect edges. We consider different
regimes of edge scattering, ranging from wide graphene ribbons with (partially)
diffusive edge scattering to ribbons with large width variations and
nanoribbons with atomistic edge roughness. For the latter, we introduce an
approach based on pseudopotentials, allowing for an atomistic treatment of the
band structure and the scattering potential, on the self-consistent solution of
the Boltzmann transport equation within the relaxation-time approximation and
taking into account the edge-roughness properties and statistics. The resulting
resistivity depends strongly on the ribbon orientation, with zigzag (armchair)
ribbons showing the smallest (largest) resistivity and intermediate ribbon
orientations exhibiting intermediate resistivity values. The results also show
clear resistivity peaks, corresponding to peaks in the density of states due to
the confinement-induced subband quantization, except for armchair-edge ribbons
that show a very strong width dependence because of their claromatic behavior.
Furthermore, we identify a strong interplay between the relative position of
the two valleys of graphene along the transport direction, the correlation
profile of the atomistic edge roughness, and the chiral valley modes, leading
to a peculiar strongly suppressed resistivity regime, most pronounced for the
zigzag orientation.Comment: 13 pages, 7 figure
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