Publications

Network topology generators

Following the long-held belief that the Internet is hierarchical, the network topology generators most widely used by the Internet research community, Transit-Stub and Tiers, create networks with a deliberately hierarchical structure. However, in 1999 a seminal paper by Faloutsos et al. revealed that the Internet's degree distribution is a power-law. Because the degree distributions produced by the Transit-Stub and Tiers generators are not power-laws, the research community has largely dismissed them as inadequate and proposed new network generators that attempt to generate graphs with power-law degree distributions.Contrary to much of the current literature on network topology generators, this paper starts with the assumption that it is more important for network generators to accurately model the large-scale structure of the Internet (such as its hierarchical structure) than to faithfully imitate its local properties (such as the degree distribution). The purpose of this paper is to determine, using various topology metrics, which network generators better represent this large-scale structure. We find, much to our surprise, that network generators based on the degree distribution more accurately capture the large-scale structure of measured topologies. We then seek an explanation for this result by examining the nature of hierarchy in the Internet more closely; we find that degree-based generators produce a form of hierarchy that closely resembles the loosely hierarchical nature of the Internet.

French Working-Class <i>Banlieues</i> and Black American Ghetto: From Conflation to Comparison

Research Article| December 01 2007 French Working-Class Banlieues and Black American Ghetto: From Conflation to Comparison Loïc Wacquant Loïc Wacquant Search for other works by this author on: This Site Google Qui Parle (2007) 16 (2): 5–38. https://doi.org/10.1215/quiparle.16.2.5 Cite Icon Cite Share Icon Share Twitter Permissions Search Site Citation Loïc Wacquant; French Working-Class Banlieues and Black American Ghetto: From Conflation to Comparison. Qui Parle 1 December 2007; 16 (2): 5–38. doi: https://doi.org/10.1215/quiparle.16.2.5 Download citation file: Zotero Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search Books & JournalsAll JournalsQui Parle Search Advanced Search The text of this article is only available as a PDF. Copyright © 2007 Qui Parle2007 Article PDF first page preview Close Modal Issue Section: Dossier on Urban Interventions: Politics and Violence of the City You do not currently have access to this content.

Editing the stereochemical elements in an iridium catalyst for enantioselective allylic amination

Individual diastereomeric phosphoramidites and mixtures of diastereomeric phosphoramidites were evaluated in the iridium-catalyzed amination of allylic carbonates. The original process was conducted with a phosphoramidite ligand containing a resolved 2,2-dihydroxy-1,1-binaphthyl (BINOL) group and a diastereomerically and enantiomerically pure bis(phenethyl)amino group. Evaluation of the structure of the active catalyst and relative rates for reactions in the presence of catalysts containing diastereomeric ligands led to the identification of a phosphoramidite that provided the amination product with enantiomeric excess similar to the original, more structurally and stereochemically complex ligand and that contains a racemic BINOLate and an N -benzylphenethylamino group on phosphorus.

An Algorithm for the Newton Resultant

Given a system of $n+1$ generic Laurent polynomials, for $i \\,=\\, 1, \\ldots, n+1$, $$\\eqlabel(\\InputSystem) f_i(\\x) \\quad = \\quad \\sum_{q\\in \\A_i} c_{iq} \\,x^q; \\qquad q \\,=\\, (q_1,\\ldots,q_n); \\qquad \\x^q \\,=\\, x_1^{q_1}x_2^{q_2}\\cdots x_n^{q_n}; \\eqno(\\InputSystem) $$ with (finite) support sets $\\A_i \\subset L$, where $L$ is some affine lattice isomorphic to $\\Z^n$; we consider algorithms for the {\\it Newton resultant} $R(f_1,f_2, \\ldots, f_{n+1})$. This is the unique (up to sign) irreducible polynomial with coefficients in $\\Z$ and monomials in the $c_{iq}$ which determines whether or not system~(\\InputSystem) has common roots in the {\\it algebraic torus} $(\\C-\\{0\\})^n$. The resultant depends only on the {\\it Newton polytopes} $N_i \\,:=\\, conv(\\A_i) \\subset \\R^n$ of the sets $\\A_i$. Our terminology emphasizes the dependence on the combinatorics of the Newton polytopes. The algebraic torus is the natural setting for us because we are interested in the properties of systems of polynomials which are invariant under symmetries of the affine lattice $L$, and translation by $q\\in L$ corresponds to multiplication by $x^q$ at the level of polynomials. Since $x^q$ may have negative exponents, we restrict to points none of whose coordinates are zero.

Discovery of Three New Supernova by the Palomar Transient Factory

Spatial and seasonal variability of photosynthetic parameters and their relationship to leaf nitrogen in a deciduous forest

We used gas exchange techniques to estimate maximum rate of carboxylation (V(cmax)), a measure of photosynthetic capacity, in the understory and upper crown of a closed deciduous forest over two seasons. There was extensive variability in photosynthetic capacity as a result of vertical canopy position, species type, leaf age and drought. Photosynthetic capacity was greater in oaks than in maples and greater in the overstory than in the understory. Parameter V(cmax) was maximal early in the season but declined slowly throughout most of the summer, and then more rapidly during senescence. There was also an apparent decline during drought in some trees. Variability in V(cmax) as a result of species or vertical canopy gradients was described well by changes in leaf nitrogen per unit area (N(a)). However, temporal changes in V(cmax) were often poorly correlated with leaf nitrogen, especially in spring and summer and during drought. This poor correlation may be the result of a seasonally dependent fractional allocation of leaf nitrogen to Rubisco; however, we could not discount Rubisco inactivation, patchy stomatal closure or changes in mesophyll resistance. Consequently, when a single annual regression equation of V(cmax) versus N(a) was used for this site, there were substantial errors in the temporal patterns in V(cmax) that will inevitably result in modeling errors.

Classifications of the Host Galaxies of Supernovae, Set II

A homogeneous sample comprising host galaxies of 604 recent supernovae, including 212 objects discovered primarily in 2003 and 2004, has been classified on the David Dunlap Observatory system. Most SN 1991bg-like SNe Ia occur in E and E/Sa galaxies, whereas the majority of SN 1991T-like SNe Ia occur in intermediate-type galaxies. This difference is significant at the 99.9% level. As expected, all types of SNe II are rare in early-type galaxies, whereas normal SNe Ia occur in all Hubble types. This difference is significant at the 99.99% level. A small number of SNe II in E galaxies might be due to galaxy classification errors, or to a small young-population component in these mainly old objects. No significant difference is found between the distributions over Hubble type of SNe Ibc and SNe II. This confirms that both of these types of objects have similar (massive) progenitors. The present data show that, in order to understand the dependence of supernova type on host-galaxy population, it is more important to obtain accurate morphological classifications than it is to increase the size of the data sample.

The Efficiency of Noble Metals in Reducing the Corrosion Potential in the Primary Coolant Circuits of Boiling Water Reactors Operating under Hydrogen Water Chemistry Operation

Abstract In order to promote the effectiveness of hydrogen water chemistry (HWC) and to achieve a more effective reduction in electrochemical corrosion potential (ECP) in the primary coolant circuits of boiling water reactors (BWRs), the technology of noble metal chemical addition (NMCA) was brought into practice about 10 years ago. NMCA aims at enhancing the oxidation of hydrogen on metal surfaces and lowering the concentrations of the oxidants (oxygen and hydrogen peroxide) via recombination with hydrogen on the catalyzed surfaces, and therefore reducing the corrosion potentials of the structural alloys in a BWR primary heat transport circuit. Previous research indicates that the effectiveness of NMCA in combination with a low HWC might be evaluated via model predictions of the hydrogen-to-oxidant molar ratio (MH/O) in the primary coolant circuit. If the MH/O at a certain location is calculated to be greater than 2, it is justified that the NMCA would be effective in reducing the ECP to much below the critical potential for Intergranular Stress Corrosion Cracking (IGSCC), EIGSCC, of --0.23 VSHE. However, this statement is true only when the recombination efficiency of hydrogen with oxygen and/or hydrogen peroxide at the location of interest is 100%. Otherwise, significant amounts of oxidants may still be present, even with a stoichiometric MH/O of greater than 2. With the aid of a computer model DEMACE, we explored the impact of incomplete recombination and found that the ECP might be reduced under given circumstances, but not to a great extent, and might remain well above EIGSCC. Accordingly, considerable caution should be exercised upon using the MH/O as a sole indicator for evaluating the effectiveness of NMCA with low HWC as a means of mitigating IGSCC in a BWR. An important finding of this study is that it is necessary to quantify the recombination efficiencies of hydrogen with oxygen and/or hydrogen peroxide on the noble metal treated stainless steel surfaces in order to qualify the use of MH/O as an indicator for NMCA effectiveness in the primary coolant circuit of a BWR. KEYWORDS: noble metal chemical additioncorrosion potentialintergranular stress corrosion crackingboiling water reactor

Text-mined dataset of gold nanoparticle synthesis procedures, morphologies, and size entities

Abstract Gold nanoparticles are highly desired for a range of technological applications due to their tunable properties, which are dictated by the size and shape of the constituent particles. Many heuristic methods for controlling the morphological characteristics of gold nanoparticles are well known. However, the underlying mechanisms controlling their size and shape remain poorly understood, partly due to the immense range of possible combinations of synthesis parameters. Data-driven methods can offer insight to help guide understanding of these underlying mechanisms, so long as sufficient synthesis data are available. To facilitate data mining in this direction, we have constructed and made publicly available a dataset of codified gold nanoparticle synthesis protocols and outcomes extracted directly from the nanoparticle materials science literature using natural language processing and text-mining techniques. This dataset contains 5,154 data records, each representing a single gold nanoparticle synthesis article, filtered from a database of 4,973,165 publications. Each record contains codified synthesis protocols and extracted morphological information from a total of 7,608 experimental and 12,519 characterization paragraphs.

Pupillary Reactivity to Emotional Information in Child and Adolescent Depression: Links to Clinical and Ecological Measures

Depressed children exhibit a dynamic change in cognitive-affective resources devoted to processing negative emotional words, with more dramatic decreases than in comparison children after a negative word is initially processed, a pattern that differs markedly from that observed in depressed adults. Diminished late pupil dilation in children with major depression could be a marker for problems in emotional reactivity and/or regulation associated with pediatric depression.

Constitutive modeling of Ni–Mn–Ga ferromagnetic shape memory alloys under biaxial compression

Ferromagnetic shape memory alloys are a type of shape memory alloys that exhibit inelastic strains when subjected to magnetic fields. So far, several constitutive models have been proposed to predict ferromagnetic shape memory alloys’ behaviors under the application of a magnetic field and a compressive stress. In this article, an available constitutive model in a continuum framework is used to investigate the behaviors of Ni–Mn–Ga under biaxial compressive stresses. Since the required model parameters in the original approach are not unique for all loading conditions, the model is modified so that a unique set of model parameters suffices to study different loading conditions. Loading history is also considered in an improved way, and two-dimensional phase diagram is generalized to three-dimensional phase diagram, called reorientation surface in this work, to directly enter the effects of loading history on reorientation start conditions. The orthogonality property of a surface and its gradient vector are used to obtain the general conditions which must be satisfied to ensure continuation of reorientations.

ChemInform Abstract: Superconducting MgB₂ Nanowires.

Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Building and characterization of catalysts on single crystal surfaces

SN 2016iyc: a Type IIb supernova arising from a low-mass progenitor

ABSTRACT In this work, photometric and spectroscopic analyses of a very low-luminosity Type IIb supernova (SN) 2016iyc have been performed. SN 2016iyc lies near the faint end among the distribution of similar supernovae (SNe). Given lower ejecta mass (Mej) and low nickel mass (MNi) from the literature, combined with SN 2016iyc lying near the faint end, one-dimensional stellar evolution models of 9–14 M⊙ zero-age main-sequence (ZAMS) stars as the possible progenitors of SN 2016iyc have been performed using the publicly available code mesa. Moreover, synthetic explosions of the progenitor models have been simulated, using the hydrodynamic evolution codes stella and snec. The bolometric luminosity light curve and photospheric velocities produced through synthetic explosions of ZAMS stars of mass in the range of 12–13 M⊙ having a pre-supernova radius R0 = (204–300) R⊙, with Mej = (1.89–1.93) M⊙, explosion energy Eexp = (0.28–0.35) × 1051 erg, and MNi &amp;lt; 0.09 M⊙, are in good agreement with observations; thus, SN 2016iyc probably exploded from a progenitor near the lower mass limits for SNe IIb. Finally, hydrodynamic simulations of the explosions of SN 2016gkg and SN 2011fu have also been performed to compare intermediate- and high-luminosity examples among well-studied SNe IIb. The results of progenitor modelling and synthetic explosions for SN 2016iyc, SN 2016gkg, and SN 2011fu exhibit a diverse range of mass for the possible progenitors of SNe IIb.

On the pitfalls of geographic face routing

Geographic face routing algorithms have been widely studied in the literature [1, 8, 13]. All face routing algorithms rely on two primitives: planarization and face traversal. The former computes a planar subgraph of the underlying wireless connectivity graph, while the latter defines a consistent forwarding mechanism for routing around "voids." These primitives are known to be provably correct under the idealized unit-disk graph assumption, where nodes are assumed to be connected if and only if they are within a certain distance from each other.In this paper we classify the ways in which existing planarization techniques fail with realistic, non-ideal radios. We also demonstrate the consequences of these pathologies on reachability between node pairs in a real wireless testbed. We then examine the various face traversal rules described in the literature, and identify those [12, 16] that are robust to violations of the unit-disk graph assumption.

Chloride-Assisted Corrosion of Copper and Protection by Benzotriazole

The structure and composition of copper surfaces in aqueous solutions of benzotriazole (BTAH) and NaCl was investigated by sum frequency vibrational spectroscopy as a function of concentration and bias during cyclic voltammetry experiments. We found that the protection provided by the BTAH films formed at the copper surface is effective for negative bias voltages below the open circuit potential (OCP) but not at positive voltages where Cl^- displaces BTAH. By measuring the Gibbs adsorption energy of BTAH and Cl^-, we found that a particularly stable Cl^- structure is formed around the OCP, suggesting that electronegative additives that move the OCP to higher negative values can improve BTAH protection, which we confirmed by the addition of a negatively charged sodium dodecyl sulfate surfactant.

On chaos in digital filters: Case b = -1

The authors extend the symbolic analysis of digital filters with overflow nonlinearity to all values of the parameter a. While the behavior of digital filters for mod a mod <or=2 is not chaotic, it is completely chaotic for mod a mod >2.<<ETX>>

2016 International Land Model Benchmarking (ILAMB) Workshop Report

As Earth system models become increasingly complex, there is a growing need for comprehensive and multi-faceted evaluation of model projections. To advance understanding of biogeochemical processes and their interactions with hydrology and climate under conditions of increasing atmospheric carbon dioxide, new analysis methods are required that use observations to constrain model predictions, inform model development, and identify needed measurements and field experiments. Better representations of biogeochemistry–climate feedbacks and ecosystem processes in these models are essential for reducing uncertainties associated with projections of climate change during the remainder of the 21st century.