9,556 research outputs found
A Method Based on Total Variation for Network Modularity Optimization using the MBO Scheme
The study of network structure is pervasive in sociology, biology, computer
science, and many other disciplines. One of the most important areas of network
science is the algorithmic detection of cohesive groups of nodes called
"communities". One popular approach to find communities is to maximize a
quality function known as {\em modularity} to achieve some sort of optimal
clustering of nodes. In this paper, we interpret the modularity function from a
novel perspective: we reformulate modularity optimization as a minimization
problem of an energy functional that consists of a total variation term and an
balance term. By employing numerical techniques from image processing
and compressive sensing -- such as convex splitting and the
Merriman-Bence-Osher (MBO) scheme -- we develop a variational algorithm for the
minimization problem. We present our computational results using both synthetic
benchmark networks and real data.Comment: 23 page
Transonic Navier-Stokes solutions of three-dimensional afterbody flows
The performance of a three-dimensional Navier-Stokes solution technique in predicting the transonic flow past a nonaxisymmetric nozzle was investigated. The investigation was conducted at free-stream Mach numbers ranging from 0.60 to 0.94 and an angle of attack of 0 degrees. The numerical solution procedure employs the three-dimensional, unsteady, Reynolds-averaged Navier-Stokes equations written in strong conservation form, a thin layer assumption, and the Baldwin-Lomax turbulence model. The equations are solved by using the finite-volume principle in conjunction with an approximately factored upwind-biased numerical algorithm. In the numerical procedure, the jet exhaust is represented by a solid sting. Wind-tunnel data with the jet exhaust simulated by high pressure air were also obtained to compare with the numerical calculations
On Estimating the High-Energy Cutoff in the X-ray Spectra of Black Holes via Reflection Spectroscopy
The fundamental parameters describing the coronal spectrum of an accreting
black hole are the slope of the power-law continuum and the energy
at which it rolls over. Remarkably, this parameter can be accurately
measured for values as high as 1 MeV by modeling the spectrum of X-rays
reflected from a black hole accretion disk at energies below 100 keV. This is
possible because the details in the reflection spectrum, rich in fluorescent
lines and other atomic features, are very sensitive to the spectral shape of
the hardest coronal radiation illuminating the disk. We show that fitting
simultaneous NuSTAR (3-79 keV) and low-energy (e.g., Suzaku) data with the most
recent version of our reflection model RELXILL, one can obtain reasonable
constraints on at energies from tens of keV up to 1 MeV, for a source
as faint as 1 mCrab in a 100 ks observation.Comment: Accepted for publication in ApJL, 6 pages, 5 figure
Sub-systems in nearby solar-type wide binaries
We conducted a deep survey of resolved sub-systems among wide binaries with
solar-type components within 67 pc from the Sun. Images of 61 stars in the K
and H bands were obtained with the NICI adaptive-optics instrument on the 8-m
Gemini-South telescope. Our maximum detectable magnitude difference is about
5mag and 7.8mag at 0.15" and 0.9" separations, respectively. This enables a
complete census of sub-systems with stellar companions in the projected
separation range from 5 to 100 AU. Out of 7 such companions found in our
sample, only one was known previously. We determine that the fraction of
sub-systems with projected separations above 5 AU is 0.12 +- 0.04 and that the
distribution of their mass ratio is flat, with a power-law index 0.2 +- 0.5.
Comparing this with the properties of closer spectroscopic sub-systems
(separations below 1 AU), it appears that the mass-ratio distribution does not
depend on the separation. The frequency of sub-systems in the separation ranges
below 1 AU and between 5 and 100 AU is similar, about 0.15. Unbiased statistics
of multiplicity higher than two, advanced by this work, provide constraints on
star-formation theory.Comment: Accepted by Astronomical Journal. 13 pages, 5 figure
Introduction: Celebrating the Mound City Bar Association Centennial: Looking Back, Leading Forward
In 2022, the Mound City Bar Association in St. Louis, one of the first Black bar associations in the country, celebrates its 100th anniversary. In this volume of the Washington University Journal of Law & Policy, distinguished authors look back at a century of contributions of Mound City Bar Association lawyers, judges, and allies, documenting their efforts to eliminate racial discrimination and break down barriers to equal justice. The volume is a testament to the work of countless individuals in the fight for civil rights since the beginning of the association in 1922. The authors also anticipate and examine the challenges ahead and the work yet to be done to achieve equal justice for all in our city, the region, and the country in the years to come
Toward Monodisperse Poly(γ-benzyl α,L-glutamate): Uniform, Polar, Molecular Rods
Poly(γ-benzyl α,L-glutamate) (PBLG) has been widely used in studies of the physics of rod-like polymer chains. The helical structure of PBLG gives rise to considerable chain stiffness, such that the persistence length of the chain is on the order of 70 nm in helicogenic solvents. This feature, coupled with the ease of synthesis and good solubility of the polymer has made PBLG the system of choice for the study of both isotropic and liquid crystalline solutions of rod-like macromolecules
Engineered Proteins in Materials Research
Peptides and proteins have attracted scientific and technological interest largely because
of their intriguing properties as catalysts, receptors, signalling molecules, and
therapeutic agents. In attempts to understand and exploit these properties, protein engineering
has been used primarily to obtain precious proteins in increased quantities,
or to explore systematic alterations in protein sequence through site-directed mutagenesis.
Design of protein structures de novo ("from scratch") has attracted less attention,
and has been directed in the main toward studies of protein folding (Kamtekar et
al., 1993). Such studies represent a key element in the current vigorous investigation
of the connections between amino acid sequence and the three-dimensional structures
of isolated protein chains in aqueous solution. This chapter describes protein engineering
of quite another sort, in which the proteinacious nature of the product is less
important than its macromolecular character
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