3,698 research outputs found
Fast Monotone Summation over Disjoint Sets
We study the problem of computing an ensemble of multiple sums where the
summands in each sum are indexed by subsets of size of an -element
ground set. More precisely, the task is to compute, for each subset of size
of the ground set, the sum over the values of all subsets of size that are
disjoint from the subset of size . We present an arithmetic circuit that,
without subtraction, solves the problem using arithmetic
gates, all monotone; for constant , this is within the factor
of the optimal. The circuit design is based on viewing the summation as a "set
nucleation" task and using a tree-projection approach to implement the
nucleation. Applications include improved algorithms for counting heaviest
-paths in a weighted graph, computing permanents of rectangular matrices,
and dynamic feature selection in machine learning
Information Security
The online threat landscape does not stand still. One of the best ways to understand the threats is to understand the attackers and their motives. Who are the attackers? What makes them tic? Where are they going? And what\u27s going to happen next
37 GHz observations of a large sample of BL Lacertae objects
We present 37 GHz data obtained at Metsahovi Radio Observatory in 2001
December - 2005 April for a large sample of BL Lacertae objects. We also report
the mean variability indices and radio spectral indices in frequency intervals
5 - 37 GHz and 37 - 90 GHz. Approximately 34 % of the sample was detected at 37
GHz, 136 BL Lacertae objects in all. A large majority of the detected sources
were low-energy BL Lacs (LBLs). The variability index values of the sample were
diverse, the mean fractional variability of the sample being \Delta S_2 = 0.31.
The spectral indices also varied widely, but the average radio spectrum of the
sample sources is flat. Our observations show that many of the high-energy BL
Lacs (HBL), which are usually considered radio-quiet, can at times be detected
at 37 GHz.Comment: 12 pages, 5 figures + 5 tables. Published in Astronomical Journa
Computationally efficient implementation of hybrid functionals in SIESTA
In this work we have implemented hybrid functionals into the SIESTA code, with the main goal to implement a fast general solver within the SIESTA framework that performs efficiently and scales linearly with increasing system size. We describe the implementation of the solver and apply it to study the properties of five insulating materials; NaCl, CaF2, CeO2, TiO2 and HfO2. We show that a systematic improvement in the basic description of the properties of these materials over standard Density Functional approaches can be obtained at a reasonable additional computational cost
Direct enhancement of nuclear singlet order by dynamic nuclear polarization
Hyperpolarized singlet order is available immediately after dissolution DNP, avoiding need for additional preparation steps. We demonstrate this procedure on a sample of [1,2–13C2]pyruvic aci
Deterministic Walks in Quenched Random Environments of Chaotic Maps
This paper concerns the propagation of particles through a quenched random
medium. In the one- and two-dimensional models considered, the local dynamics
is given by expanding circle maps and hyperbolic toral automorphisms,
respectively. The particle motion in both models is chaotic and found to
fluctuate about a linear drift. In the proper scaling limit, the cumulative
distribution function of the fluctuations converges to a Gaussian one with
system dependent variance while the density function shows no convergence to
any function. We have verified our analytical results using extreme precision
numerical computations.Comment: 18 pages, 9 figure
Measurement scheme of the Berry phase in superconducting circuits
We present a measurement scheme for observing the Berry phase in a flux
assisted Cooper pair pump - the Cooper pair sluice. In contrast to the recent
experiments, in which the sluice was employed to generate accurate current
through a resistance, we consider a device in a superconducting loop. This
arrangement introduces a connection between the pumped current and the Berry
phase accumulated during the adiabatic pumping cycles. From the adiabaticity
criterion, we derive equations for the maximum pumped current and optimize the
sluice accordingly. These results apply also to the high accuracy pumping which
results in a potential candidate for a metrological current standard. For
measuring the pumped current, an additional Josephson junction is installed
into the superconducting loop. We show in detail that the switching of this
system from superconducting state into normal state as a consequence of an
external current pulse through it may be employed to probe the pumped current.
The experimental realization of our scheme would be the first observation of
the Berry phase in superconducting circuits.Comment: 19 pages, 5 figure
Fluctuations and scaling in creep deformation
The spatial fluctuations of deformation are studied in creep in the Andrade's
power-law and the logarithmic phases, using paper samples. Measurements by the
Digital Image Correlation technique show that the relative strength of the
strain rate fluctuations increases with time, in both creep regimes. In the
Andrade creep phase characterized by a power law decay of the strain rate
, with , the fluctuations obey
, with . The local
deformation follows a data collapse appropriate for an absorbing
state/depinning transition. Similar behavior is found in a crystal plasticity
model, with a jamming or yielding phase transition
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