359,415 research outputs found
Bit-Vector Model Counting using Statistical Estimation
Approximate model counting for bit-vector SMT formulas (generalizing \#SAT)
has many applications such as probabilistic inference and quantitative
information-flow security, but it is computationally difficult. Adding random
parity constraints (XOR streamlining) and then checking satisfiability is an
effective approximation technique, but it requires a prior hypothesis about the
model count to produce useful results. We propose an approach inspired by
statistical estimation to continually refine a probabilistic estimate of the
model count for a formula, so that each XOR-streamlined query yields as much
information as possible. We implement this approach, with an approximate
probability model, as a wrapper around an off-the-shelf SMT solver or SAT
solver. Experimental results show that the implementation is faster than the
most similar previous approaches which used simpler refinement strategies. The
technique also lets us model count formulas over floating-point constraints,
which we demonstrate with an application to a vulnerability in differential
privacy mechanisms
Computationally efficient algorithms for the two-dimensional Kolmogorov-Smirnov test
Goodness-of-fit statistics measure the compatibility of random samples against some theoretical or reference probability distribution function. The classical one-dimensional Kolmogorov-Smirnov test is a non-parametric statistic for comparing two empirical distributions which defines the largest absolute difference between the two cumulative distribution functions as a measure of disagreement. Adapting this test to more than one dimension is a challenge because there are 2^d-1 independent ways of ordering a cumulative distribution function in d dimensions. We discuss Peacock's version of the Kolmogorov-Smirnov test for two-dimensional data sets which computes the differences between cumulative distribution functions in 4n^2 quadrants. We also examine Fasano and Franceschini's variation of Peacock's test, Cooke's algorithm for Peacock's test, and ROOT's version of the two-dimensional Kolmogorov-Smirnov test. We establish a lower-bound limit on the work for computing Peacock's test of
Omega(n^2.lg(n)), introducing optimal algorithms for both this and Fasano and Franceschini's test, and show that Cooke's algorithm is not a faithful implementation of Peacock's test. We also discuss and evaluate parallel algorithms for Peacock's test
Recommended from our members
Modeling of on-chip (bio)-particle separation and counting using 3D electrode structures
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In lab-on-a-chip applications, manipulation and quantification of (bio)particles is required in a
variety of biomedical applications such as drug screening, disease detection and treatment. For manipulation
of particles, electrical techniques such as dielectrophoresis (DEP) is very suitable. For the quantification or
counting of the bioparticles, flow cytometer, fluorescence-activated cell sorting (FACS) and magneticactivated
cell sorting (MACS) are common techniques. In this study, modeling of microfluidic (bio)-particle
separation based on dielectrophoresis and counting based on capacitance measurement using COMSOL
Multiphysics have been presented. The device performance with planar and 3D electrode structures have
been compared. Microfluidic devices with an asymmetric pair (for separation) and a symmetric pair (for
counting) of electrodes are considered. The effects of the geometrical parameters, material properties, flow
rate, particle size and applied voltage on the device performance have been discussed. The fabrication
procedure of 3D electrode structures is also addressed
Dynamical Screening Effects in Correlated Electron Materials -- A Progress Report on Combined Many-Body Perturbation and Dynamical Mean Field Theory: "GW+DMFT"
We give a summary of recent progress in the field of electronic structure
calculations for materials with strong electronic Coulomb correlations. The
discussion focuses on developments beyond the by now well established
combination of density functional and dynamical mean field theory dubbed
"LDA+DMFT". It is organized around the description of dynamical screening
effects in the solid. Indeed, screening in the solid gives rise to dynamical
local Coulomb interactions U(w) (Aryasetiawan et al 2004 Phys. Rev. B 70
195104), and this frequency-dependence leads to effects that cannot be
neglected in a truly first principles description. We review the recently
introduced extension of LDA+DMFT to dynamical local Coulomb interactions
"LDA+U(w)+DMFT" (Casula et al. Phys. Rev. B 85 035115 (2012), Werner et al.
Nature Phys. 8 331 (2012)). A reliable description of dynamical screening
effects is also a central ingredient of the "GW+DMFT" scheme (Biermann et al.
Phys. Rev. Lett. 90 086402 (2003)), a combination of many-body perturbation
theory in Hedin's GW approximation and dynamical mean field theory. Recently,
the first GW+DMFT calculations including dynamical screening effects for real
materials have been achieved, with applications to SrVO3 (Tomczak et al.
Europhys. Lett. 100 67001 (2012); Phys. Rev. B 90 165138 (2014)) and adatom
systems on surfaces (Hansmann et al. Phys. Rev. Lett. 110 166401 (2013)). We
review these and comment on further perspectives in the field. This review is
an attempt to put elements of the original works (Refs. 1-11) into the broad
perspective of the development of truly first principles techniques for
correlated electron materials.Comment: 40 pages, 12 figures. First published as "Highlight of the Month"
(June 2013), of the Psi-k Network on "Ab initio calculation of complex
processes in materials", see
http://www.psi-k.org/newsletters/News_117/Highlight_117.pd
Detecting short periods of elevated workload. A compariÂson of nine workload assessment techniques
The present experiment tested the merits of 9 common workload assessment techniques with relatively short periods of workload in a car-driving task. Twelve participants drove an instrumented car and performed a visually loading task and a mentally loading task for 10, 30, and 60 s. The results show that 10-s periods of visual and mental workload can be measured successfully with subjective ratings and secondary task performance. With respect to longer loading periods (30 and 60 s), steering frequency was found to be sensitive to visual workload, and skin conductance response (SCR) was sensitive to mental workload. The results lead to preliminary guidelines that will help applied researchers to determine which techniques are best suited for assessing visual and mental workload
Comparing Simulations and Observations of the Lyman-Alpha Forest I. Methodology
We describe techniques for comparing spectra extracted from cosmological
simulations and observational data, using the same methodology to link
Lyman-alpha properties derived from the simulations with properties derived
from observational data. The eventual goal is to measure the coherence or
clustering properties of Lyman-alpha absorbers using observations of quasar
pairs and groups. We quantify the systematic underestimate in opacity that is
inherent in the continuum fitting process of observed spectra over a range of
resolution and signal-to-noise ratio. We present an automated process for
detecting and selecting absorption features over the range of resolution and
signal-to-noise of typical observational data on the Lyman-alpha "forest".
Using these techniques, we detect coherence over transverse scales out to 500
h^{-1}_{50} kpc in spectra extracted from a cosmological simulation at z = 2.Comment: 52 pages, includes 14 figures, to appear in ApJ v566 Feb 200
- …