cssi/SciSciGPT-SciSciNet huggingface dataset:
Scaffolding cooperative multi-device activities in an informal learning environment

Informal learning environments, e.g. children's science museums, provide special challenges for educational software design: the software must (1) be immediately accessible, (2) convey educational content within short episodes of use, and (3) should allow multiple users to participate at the same time. While mobile technology allows for multiple simultaneous users, significant scaffolding is required to allow groups to walk up and productively use it. Using a design experiment approach, my research focuses on the design and evaluation of distributed scaffolds that enable informal learners to use mobile technology effectively.
HYDROLOGIC TEST SYSTEM FOR FRACTURE FLOW STUDIES IN CRYSTALLINE ROCK

. A hydrologic test system has been designed to measure the intrinsic permeabilities of individual fractures in crystalline rock. This report contains the design schematics and specifications necessary to build and/or modify this test system for other similar field applications. This system is used to conduct constant pressure/declining flow rate and pressure pulse hydraulic tests. The system is composed of four distinct units: (1) The Packer System, (2) Injection System, (3) Collection System, and (4) Electronic Data Acquisition System. The apparatus is built in modules so it can be easily transported and reassembled. It is also designed to operate over a wide range of pressures (0–300 psig) and flow rates (0.2–1.0 gal/min). This system has proved extremely effective and versatile in its use at the Climax Facility, Nevada Test Site.
Synthesis of Novel 7α-Thiol-Bridged Progesterone Derivatives

Abstract Novel synthetic routes to the formation of progesterone derivatives are of interest due to their potential role in the treatment of breast cancer. This multi-step synthesis proceeds via the dehydrogenation of the endocyclic ketone moiety of the steroid, affording the resulting α,β–γ,δ-unsaturated system. This is followed by 1,6-conjugate addition of p-aminothiophenol, affording the C7 thiol-bridged progesterone analog. The resulting compound was then subjected to a selection of isocyanates affording a variety of novel progesterone derivatives for their medicinal evaluation.
Chiral Metal as a Heisenberg Ferromagnet

The two-dimensional surface of an integer quantum hall multilayer is mapped onto a Heisenberg spin chain with ferromagnetic coupling. Using this mapping it is shown nonperturbatively that the surface states constitute a very anisotropic metal in the infinite size limit. For multilayers of finite size, two diffusive mesoscopic regimes are identified and the conductance fluctuations are calculated perturbatively for both. The Heisenberg spin-chain representation is used to study the directed wave problem and the exact result is obtained that the mean-square deflection of a directed wave grows as the square root of the propagation distance.
Hydrothermal Synthesis of Er-Doped Luminescent TiO2 Nanoparticles

Here we report the synthesis and characterization of a stable suspension of fluorescent erbium-doped titania nanoparticles and their assembly into thin films and photonic crystals. The nanoparticles were synthesized through a sol−gel process followed by peptization with tetramethylammonium hydroxide and hydrothermal treatment. As expected, following the hydrothermal treatment, X-ray diffraction shows the particles to be exclusively anatase. The nanoparticles form a stable suspension in water and were cast into 2- and 20-μm-thick films and formed into an inverse opal structure through templating with a colloidal crystal. As synthesized, only a faint fluorescence at 1532 nm was observed from the particles when pumped with 795-nm laser radiation; however, heat treatment at temperatures as low as 100 °C resulted in a significant increase in the fluorescence. The fluorescence was observed to increase further with annealing up to 500 °C, perhaps due to removal of hydroxyl groups and other surface species. Throu...
Imitation in a non-scale R&D growth model

Abstract Motivated by recent empirical evidence this paper extends a non-scale R&D growth model to allow for technological imitation in addition to innovation. It is shown that a simple modification of the standard R&D equation results in a more general model that can explain not only the growth process of developed countries that mostly innovate, but also the growth process of developing countries that mostly imitate.
Planet Migration and Gap Formation by Tidally Induced Shocks

Gap formation in a gas disk triggered by disk-planet tidal interaction is considered. Density waves launched by the planet are assumed to be damped as a result of their nonlinear evolution leading to shock formation and its subsequent dissipation. As a consequence, wave angular momentum is transferred to the disk, leading to evolution of its surface density. Planetary migration is an important ingredient of the theory; effects of the planet-induced surface density perturbations on the migration speed are considered. A gap is assumed to form when a stationary solution for the surface density profile is no longer possible in the frame of reference migrating with the planet. An analytical limit on the planetary mass necessary to open a gap in an inviscid disk is derived. The critical mass turns out to be smaller than the mass M1 for which the planetary Hill radius equals the disk scale height by a factor of at least Q5/7 (Q is the Toomre stability parameter), depending on the strength of the migration feedback. In viscous disks the critical planetary mass could vary from ~0.2M1 to M1, depending on the disk viscosity. This implies that a gap could be formed by a planet with mass of 2-15 M⊕, depending on the disk aspect ratio, viscosity, and the planet's location in the nebula.
An integer programming approach for linear programs with probabilistic constraints

Linear programs with joint probabilistic constraints (PCLP) are difficult to solve because the feasible region is not convex. We consider a special case of PCLP in which only the right-hand side is random and this random vector has a finite distribution. We give a mixed-integer programming formulation for this special case and study the relaxation corresponding to a single row of the probabilistic constraint. We obtain two strengthened formulations. As a byproduct of this analysis, we obtain new results for the previously studied mixing set, subject to an additional knapsack inequality. We present computational results which indicate that by using our strengthened formulations, instances that are considerably larger than have been considered before can be solved to optimality.
Coherent State Quantization of Constraint Systems

We study the quantization of systems with general first- and second-class constraints from the point of view of coherent state phase-space path integration, and show that all such cases may be treated, within the original classical phase space, by using suitable path-integral measures for the Lagrange multipliers which ensure that the quantum system satisfies the appropriate quantum constraint conditions. Unlike conventional methods, our procedures involve no {delta}-functionals of the classical constraints, no need for dynamical gauge fixing of first-class constraints nor any average thereover, no need to eliminate second-class constraints, no potentially ambiguous determinants, as well as no need to add auxiliary dynamical variables expanding the phase space beyond its original classical formulation, including no ghosts. Additionally, our procedures have the virtue of resolving differences between suitable canonical and path-integral approaches, and thus agree with previous results obtained by other methods for such cases. Several examples are considered in detail. {copyright} 1997 Academic Press, Inc.
ON THE EVOLUTION OF THE CO SNOW LINE IN PROTOPLANETARY DISKS

CO is thought to be a vital building block for prebiotic molecules that are necessary for life. Thus, understanding where CO existed in a solid phase within the solar nebula is important for understanding the origin of life. We model the evolution of the CO snow line in a protoplanetary disk. We find that the current observed location of the CO snow line in our solar system, and in the solar system analog TW Hydra, cannot be explained by a fully turbulent disk model. With time-dependent disk models we find that the inclusion of a dead zone (a region of low turbulence) can resolve this problem. Furthermore, we obtain a fully analytic solution for the CO snow line radius for late disk evolutionary times. This will be useful for future observational attempts to characterize the demographics and predict the composition and habitability of exoplanets.
Capacity choice in a two-stage problem under uncertainty

Abstract When choosing production capacity, a firm may not know which among mutually exclusive projects will be most profitable. It may be possible to await more information before committing given capacity to a project. We identify when shifts in project profitability and firm pecking order increase ex ante optimal capacity choice.
Smooth interpolation of lattice gauge fields by signal processing methods

We digitally filter the Fourier modes of the link angles of an abelian lattice gauge field which produces the Fourier modes of a continuum Aμ(x) that exactly reproduces the lattice links through their definition as phases of finite parallel transport. The constructed interpolation is smooth (C∞), free from transition functions, and gauge equivariant. After discussing some properties of this field, we discuss the non-abelian generalization of the method.
Automated aids fob reliable software

Recent investigations on the use of automation to realize the twin objectives of cost reduction and reliability improvement for computer programs developed for the U. S. Air Force are reported. The concepts of reliability and automation as they pertain to software are explained. Then, over twenty automated tools and techniques (aids) identified by this investigation are described and categorized. Based on the information reviewed, an assessment of the state of the technology is made. Finally, specific recommendations which try to give direction to future efforts are offered.
Mock Catalogs for the DEEP2 redshift survey

We present a set of mock redshift catalogs, constructed from N-body simulations, designed to mimic the DEEP2 survey. Galaxies with a range of luminosities are placed within virialized halos in the simulation using a variant of the halo model. The halo model parameters are chosen to reproduce local clustering and abundance data and are assumed to be independent of redshift. This allows us to predict the luminosity function, two-point correlation function, luminosity- and scale-dependent bias, redshift space distortions, and so on, of our galaxies at higher redshifts. We show that the low-order clustering properties are consistent with preliminary DEEP2 data. The catalogs can be used to evaluate the selection effects of the survey and to test new algorithms and statistics that are to be used in the analysis of DEEP2 data.
Iodobenzene diacetate on alumina: Rapid oxidation of alcohols to carbonyl compounds in solventless system using microwaves☆

Abstract In an environmentally benign solventless system, alcohols are rapidly oxidized to carbonyl compounds using alumina-supported iodobenzene diacetate (IBD) as an oxidant under microwave irradiation.
The “Silent Majority” in Black and White Invisibility and Imprecision in the Historiography of Mass Incarceration

Over the past decade, mass incarceration has received much scholarly attention from historians, social scientists, and legal scholars. Despite the substantive contributions of this research, the ov...
Mechanism for surface waves in vibrated granular material

We use molecular-dynamics simulations to study the formation of surface waves in vertically vibrated granular material. We find that the horizontal movements of particles, which are essential for the formation of the waves, consist of two distinct processes. First, the movements sharply increase while the particles are colliding with a bottom plate, where the duration of the collisions is very short compared to the period of the vibration. Next, the movements gradually decrease between the collisions, during which the particles move through the material. We also find that the horizontal velocity field after the collisions is strongly correlated to the surface profile before the collisions.
Partonic picture of nuclear shadowing at small x

Abstract We find that coherent multiple scatterings of the partonic fluctuations of the virtual photon with the nucleons inside the nucleus result in the large nuclear shadowing effect for parton distributions in nuclei. We predict the gluon shadowing effect at small x and for Q 2 ≥ 3GeV 2 .
Atomistic modeling of amorphous silicon carbide: an approximate first-principles study in constrained solution space

Localized basis ab initio molecular dynamics simulation within the density functional framework has been used to generate realistic configurations of amorphous silicon carbide (a-SiC). Our approach consists of constructing a set of smart initial configurations that conform to essential geometrical and structural aspects of the materials obtained from experimental data, which is subsequently driven via a first-principles force field to obtain the best solution in a reduced solution space. A combination of a priori information (primarily structural and topological) along with the ab initio optimization of the total energy makes it possible to model a large system size (1000 atoms) without compromising the quantum mechanical accuracy of the force field to describe the complex bonding chemistry of Si and C. The structural, electronic and vibrational properties of the models have been studied and compared to existing theoretical models and available data from experiments. We demonstrate that the approach is capable of producing large, realistic configurations of a-SiC from first-principles simulation that display its excellent structural and electronic properties. Our study reveals the presence of predominant short range order in the material originating from heteronuclear Si-C bonds with a coordination defect concentration as small as 5% and a chemical disorder parameter of about 8%.
Interactions Between Moderate- and Long-Period Giant Planets: Scattering Experiments for Systems in Isolation and with Stellar Flybys

The chance that a planetary system will interact with another member of its host star's nascent cluster would be greatly increased if gas giant planets form in situ on wide orbits. In this paper, we explore the outcomes of planet-planet scattering for a distribution of multi-planet systems that all have one of the planets on an initial orbit of 100 AU. The scattering experiments are run with and without stellar flybys. We convolve the outcomes with distributions for protoplanetary disk and stellar cluster sizes to generalize the results where possible. We find that the frequencies of large mutual inclinations and high eccentricities are sensitive to the number of planets in a system, but not strongly to stellar flybys. However, flybys do play a role in changing the low and moderate portions of the mutual inclination distributions, and erase dynamically cold initial conditions on average. Wide-orbit planets can be mixed throughout the planetary system, and in some cases, can potentially become hot Jupiters, which we demonstrate using scattering experiments that include a tidal damping model. If planets form in situ on wide orbits, then there will be discernible differences in the proper-motion distributions of a sample of wide-orbit planets compared withmore » a pure scattering formation mechanism. Stellar flybys can enhance the frequency of ejections in planetary systems, but autoionization is likely to remain the dominant source of free-floating planets.« less
Structure in the classical knot concordance group

We provide new information about the structure of the abelian group of topological concordance classes of knots in S 3 . One consequence is that there is a subgroup of infinite rank consisting entirely of knots with vanishing Casson-Gordon invariants but whose non-triviality is detected by von Neumann signatures.
Stopping single photons in one-dimensional circuit quantum electrodynamics systems

We propose a mechanism to stop and time reverse single photons in one-dimensional circuit quantum electrodynamics systems. As a concrete example, we exploit the large tunability of the superconducting charge quantum bit (charge qubit) to predict one-photon transport properties in multiple-qubit systems with dynamically controlled transition frequencies. In particular, two qubits coupled to a waveguide give rise to a single-photon transmission line shape that is analogous to electromagnetically induced transparency in atomic systems. Furthermore, by cascading double-qubit structures to form an array and dynamically controlling the qubit transition frequencies, a single photon can be stopped, stored, and time reversed. With a properly designed array, two photons can be stopped and stored in the system at the same time. Moreover, the unit cell of the array can be designed to be of deep subwavelength scale, miniaturizing the circuit.
On a problem of Yau regarding a higher dimensional generalization of the Cohn–Vossen inequality

We show that a problem asked by Yau (Open problems in geometry. Chern–a great geometer of the twentieth century, pp. 275–319, 1992) cannot be true in general. The counterexamples are constructed based on the recent work of Wu and Zheng (Examples of positively curved complete Kahler manifolds. Geometry and Analysis, vol. 17, pp. 517–542, 2010).
Cyclic Voltammetric Study of Electroreduction of Dichlorosilanes

The electroreduction of organo-substituted dichlorosilanes, Me 2 SiCl 2 , MeEtSiCl 2 , MePrSiCl 2 , MeHexSiCl 2 , Me(c-Hex)SiCl 2 , MePhSiCl 2 , and Ph 2 SiCl 2 in THF, is reported. A two-step reduction scheme (E 1 : RR'SiCl 2 ⇄ [RR'SiCl 2 ]- and E 2 : [RR'SiCl 2 ]- ⇄ [RR'SiCl 2 ] = ) is suggested in which the redox potentials E 1 and E 2 are separated by ∼110 mV. A simulation of the irreversible voltammograms indicates multiple pathways in producing silyl anion, among them the decomposition of dianion and/or the disproportionation of silyl anion radicals, which is further corroborated by low-temperature cyclic voltammetric measurements. Subsequently, silyl anion undergoes S N 2 nucleophilic attack on another chlorosilane molecule to form Si-Si bonds. Taft substituent constants have been applied and proved effective in correlating the substituent effect on the reduction of dichlorosilanes. For dialkyl-substituted chlorosilanes, the Taft analysis of the polar contribution of substituents to the cathodic peak shift gives a positive ρ* ∼ 2.4, which indicates an S N 2 nucleophilic reaction in the formation of silyl dianion intermediate. The steric effect of substituents, however, is largely responsible for the stability of the S N 2 transition state.
Comparison of rural and urban ambulance crashes in Pennsylvania.

Objective. To describe andcompare the characteristics of, andassociated injuries caused by, ambulance crashes that occur in rural versus urban areas. Methods. Crash data collected by the Pennsylvania Department of Transportation were obtained for ambulance crashes from 1997 to 2001. Crash demographics (e.g., location of crash, road conditions, andintersection type) andinjuries reported by police were analyzed to determine differences, if any, between crashes occurring in rural andurban areas. Results. 311 rural and1,434 urban ambulance crashes were identified. Day andtime of crash, light conditions, androad type were similar. Rural crashes were more likely to occur on snowy roads (13% vs. 5%) andat nighttime without street lighting (25% vs. 4%). Operator error was the most common cause of crashes (75% for rural; 93% for urban), whereas vehicle or environmental conditions more frequently affected rural drivers (25% vs. 7%). Urban crashes were more likely to involve angled collisions with other vehicles (54...
Flügge’s Conjecture: Dissipation- versus Deflection-Induced Pavement–Vehicle Interactions

AbstractThe dissipation occurring below a moving tire in steady-state conditions in contact with a viscoelastic pavement is expressed using two different reference frames: a fixed observer attached to the pavement and a moving observer attached to the pavement–tire contact surface. The first approach is commonly referred to as dissipation-induced pavement–vehicle interaction (PVI), the second as deflection-induced PVI. Based on the principle of frame independence, it is shown that both approaches are strictly equal, from a thermodynamic point of view, and thus predict the same amount of dissipated energy. This equivalence is illustrated through application to two pavement systems: a viscoelastic beam and a viscoelastic plate both resting on an elastic foundation. The amount of dissipated energy in the pavement structure needs to be supplied by the vehicle to maintain constant speed, thus contributing to the rolling resistance, associated excess fuel consumption, and greenhouse gas emissions. The model her...
Synthesis and reactivity of 6-(fluoromethyl)indole and 6-(difluoromethyl)indole

Abstract The N-1 BOC protected precursors of 6-(fluoromethyl)indole and 6-(difluoromethyl)indole were prepared and deprotected via flash vacuum thermolysis. The stability of these newly prepared, unprotected indole derivatives has been characterized and compared to that of a previously known compound, 6-(trifluoromethyl)indole.
Wall-crossing, open BPS counting and matrix models

We consider wall-crossing phenomena associated to the counting of D2-branes attached to D4-branes wrapping lagrangian cycles in Calabi-Yau manifolds, both from M-theory and matrix model perspective. Firstly, from M-theory viewpoint, we review that open BPS generating functions in various chambers are given by a restriction of the modulus square of the open topological string partition functions. Secondly, we show that these BPS generating functions can be identified with integrands of matrix models, which naturally arise in the free fermion formulation of corresponding crystal models. A parameter specifying a choice of an open BPS chamber has a natural, geometric interpretation in the crystal model. These results extend previously known relations between open topological string amplitudes and matrix models to include chamber dependence.
Equilibrium model for ion exchange between multivalent cations and zeolite-A in a molten salt

A two-site equilibrium model that previously only accommodated monovalent cations has been extended to include divalent and trivalent cations for ion exchange between zeolite-A and molten chloride salts, a process being considered for concentrating nuclear fission products into high level waste forms. Equilibrium constants were determined by fitting the model to equilibrium data sets for ion exchange between zeolite-A and Cs ternary salt (CsCl-LiCl-KCl), Rb ternary salt (RbCl-LiCl-KCl), Na ternary salt (NaCl-LiCl-KCl), Sr ternary salt (SrCl2-LiCl-KCl), and U ternary salt (UCl3-LiCl-KCl). The results reveal a good fit between the experimental data sets and the model. The two ion exchange sites, framework sites and occluded sites, demonstrate different relative selectivities for the cations. It was found that Sr2+ is the preferred cation in the ion exchange site, and Cs+ is the preferred cation in the occlusion site. Meanwhile, Li+ has the highest combined selectivity when both ion exchange and occlusion sites are considered. Interestingly, divalent and trivalent species are more preferred in the ion exchange site than the monovalent species with the exception of Li+. © 2006 American Institute of Chemical Engineers AIChE J, 2006
In memoriam: Ivan Daskalov: 1933–2004

Ivan Daskalov [1933–2004] was a friend who will be missed by many. Neither the quality of a man nor the concept of a friendship can be defined with words. We may only say that both will be missed.
Ab-initio study of SrTiO3 surfaces

Abstract We present first-principles total-energy calculations of (001) surfaces of SrTiO3. Both SrO-terminated and TiO2-terminated surfaces are considered, and the results are compared with previous calculations for BaTiO3 surfaces. The major differences are in the details of the relaxed surface structures. Our calculations argue against the existence of a large ferroelectric relaxation in the surface layer, as had been previously proposed. We do find some indications of a weak surface ferroelectric instability, but so weak as to be easily destroyed by thermal fluctuations, except perhaps at quite low temperatures. We also compute surface relaxation energies and surface electronic band structures, obtaining results that are generally similar to those for BaTiO3.
MR Imaging of Pediatric Arthritis

The role of MR imaging in pediatric arthritis is to detect early manifestations of arthritis, evaluate the extent of disease, and monitor disease activity during treatment. More specifically, MR imaging can characterize the pediatric arthropathy based on typical imaging findings, detect early signs of synovitis and erosions, stage the severity of joint involvement, demonstrate associated internal derangement, monitor disease progression or treatment response, and evaluate for complications. This article discusses MR imaging findings of juvenile idiopathic arthritis, enthesis-related arthritis, juvenile psoriatic arthritis, and articular findings in collagen vascular diseases, septic arthritic, hemophilia, neuroarthropathy, and pseudoarthridities.
Multilevel Latent Gaussian Process Model for Mixed Discrete and Continuous Multivariate Response Data

We propose a Bayesian model for mixed ordinal and continuous multivariate data to evaluate a latent spatial Gaussian process. Our proposed model can be used in many contexts where mixed continuous and discrete multivariate responses are observed in an effort to quantify an unobservable continuous measurement. In our example, the latent, or unobservable measurement is wetland condition. While predicted values of the latent wetland condition variable produced by the model at each location do not hold any intrinsic value, the relative magnitudes of the wetland condition values are of interest. In addition, by including point-referenced covariates in the model, we are able to make predictions at new locations for both the latent random variable and the multivariate response. Lastly, the model produces ranks of the multivariate responses in relation to the unobserved latent random field. This is an important result as it allows us to determine which response variables are most closely correlated with the latent variable. Our approach offers an alternative to traditional indices based on best professional judgment that are frequently used in ecology. We apply our model to assess wetland condition in the North Platte and Rio Grande River Basins in Colorado. The model facilitates a comparison of wetland condition at multiple locations and ranks the importance of in-field measurements.
Mixed convection in an inclined channel with a discrete heat source

Abstract The effects of laminar forced flow on buoyancy-induced natural convection cells throughout the regions of natural, mixed, and forced convection have been numerically investigated for a parallel planes channel with a discrete heat source. Emphasis is placed on the influence of the inlet flow velocity and the inclination angle of the channel, and the local buoyancy induced by the discrete source. The results indicate that the overall Nusselt number of the source strongly depends on the inclination angle (γ) in the natural and mixed convection regimes when γ > 45° . On the other hand, the changes in Nu and θ s.max are negligible when the channel is from 0 to 45°, i.e. there is no significant penalty in heat transfer due to the inclination of the channel up to γ = 45° . As Gr increases at a fixed Re, the entrainment of the air from the downstream exit is observed for the case of aiding flow.
A discretized Fourier orthogonal expansion in orthogonal polynomials on a cylinder

We study the convergence of a discretized Fourier orthogonal expansion in orthogonal polynomials on B^2x[-1,1], where B^2 is the closed unit disk in R^2. The discretized expansion uses a finite set of Radon projections and provides an algorithm for reconstructing three-dimensional images in computed tomography. The Lebesgue constant is shown to be of asymptotic order m(log(m+1))^2, and convergence is established for functions in C^2(B^2x[-1,1]).
Formal assessment of problem-solving and planning processes in preschool children☆

Abstract While much is known about adult problem-solving, the materials, analyses, and theoretical issues from the adult literature rarely make contact with the tasks typically used to investigate children's thinking. This paper examines the behavior of 4-, 5-, and 6-year-old children attempting to solve a novel variant of the Tower of Hanoi task. Problems varied in difficulty (one to seven moves for the minimum path solution) and in goal type: tower (all objects on one peg) or flat (all pegs occupied). For each problem, children gave verbal statements of their complete solution plan. The Plan Analysis examined performance as a function of goal type and age. Better performance was observed for tower ending problems, and among older children. The Error Analysis revealed that specific error propensities were related to both age and goal type. The Strategic Analysis compared the first move profiles of 6-year-olds to those of several plausible move selection models, and a high degree of correspondence was obtained between specific models and individual children. Young children appear to have rudimentary forms of many of the problem-solving processes previously identified in adults, but they may differ in encoding and representational processes.
Two-body Problems with Confining Potentials

A formalism is presented that allows an asymptotically exact solution of non-relativistic and semi-relativistic two-body problems with infinitely rising confining potentials. We consider both linear and quadratic confinement. The additional short-range terms are expanded in a Coulomb-Sturmian basis. Such kinds of Hamiltonians are frequently used in atomic, nuclear, and particle physics.
High contrast metastructures for silicon photonics

A new class of planar optics has emerged using near-wavelength gratings with a large refractive index contrast. We will review how this seemingly simple structure lends itself to extraordinary properties, which can be designed top-down based for integrated optics on a silicon substrate.
A Matching Model on the Use of Immigrant Social Networks and Referral Hiring

Using a simple search model, with urn-ball derived matching function, this paper investigates the effect of firm owner’s and coworkers’ nativity on hiring patterns and wages. In the model, social networks reduce search frictions and wages are derived endogenously as a function of the efficiency of the social ties of current employees. As a result, individuals with more efficient connections tend to receive higher wages and lower unemployment rate. However, because this efficiency depends on matching with same-type owners and coworkers, there is also a differential effect among workers’ wages in the same firm. This analysis highlights the potential importance of social connections and social capital for understanding employment opportunities and wage differentials between these groups.
Computer science and game theory

Game theory has been playing an increasingly visible role in computer science, in areas as diverse as artificial intelligence, theory, distributed systems, and other areas. I take stock of where most of the action has been in the past decade or so, and suggest that going forward, the most dramatic interaction between computer science and game theory could be around what might be called game theory pragmatics.
REGIO- AND DIASTEREOSELECTIVE MICHAEL ADDITIONS BY UNSYMMETRICAL ALLYLIC ANIONS UPON ETHYL PROPIOLATE

Abstract A convenient and efficient procedure for regio- and diastereoselective addition of prenyl and geranyl anions to ethyl propiolate is reported. This 1,4-addition reaction produces exclusively the trans isomer at the double bond deriving from the triple bond of ethyl propiolate without rearrangement of the starting primary, allylic carbanion nucleophile.
The Complexity of Approximating Vertex Expansion

We study the complexity of approximating the vertex expansion of graphs G = (V, E), defined as ΦV def = minSCV n . |N(S)|/(|S||V\S). We give a simple polynomialtime algorithm for finding a subset with vertex expansion O(√(ΦV log d)) where d is the maximum degree of the graph. Our main result is an asymptotically matching lower bound: under the Small Set Expansion (SSE) hypothesis, it is hard to find a subset with expansion less than C(√(ΦV log d)) for an absolute constant C. In particular, this implies for all constant e > 0, it is SSE-hard to distinguish whether the vertex expansion <; e or at least an absolute constant. The analogous threshold for edge expansion is √Φ with no dependence on the degree (Here Φ denotes the optimal edge expansion). Thus our results suggest that vertex expansion is harder to approximate than edge expansion. In particular, while Cheeger's algorithm can certify constant edge expansion, it is SSE-hard to certify constant vertex expansion in graphs.
Controlling Vibrational Chaos of a Curved Structure

Nonlinear response of a flexible curved panel exhibiting bifurcation to fully developed chaos is demonstrated along with the sensitivity to small perturbations from the initial forcing. The response is determined from the measured time series at two fixed points. The panel is forced by an external nonharmonic multifrequency and monofrequency sound field. Using a low-power time-continuous control, carefully tuned to each initial forcing condition, produces large long-term effects on the dynamics toward taming chaos. Without knowledge of the initial forcing, control may be achieved by destructive interference. In this case, the control power is proportional to the loading power. Calculation of the correlation dimension and the estimation of positive Lyapunov exponents, in practice, are the proof of chaotic response.
Using Hicksian Surplus Measures to Examine Consistency of Individual Preferences: Evidence from a Field Experiment

This paper pits neoclassical theory against prospect theory by investigating several clean tests of the competing hypotheses. Consistent with previous work, the field experimental data suggest that prospect theory adequately organizes behavior among inexperienced consumers, whereas consumers with intense market experience behave largely in accordance with neoclassical predictions. The data indicate that the convergence in values occurs entirely because of lower Hicksian equivalent surplus values.
Palladium-Catalyzed Synthesis of Vinyl Phosphines from Ketones.

Abstract The palladium-catalyzed conversion of vinyl triflates to vinyl phosphines is reported. This process allows for the synthesis of vinyl phosphines from ketones. Selective enolization of a variety of ketones followed by trapping of the enolate as the vinyl triflate is reported. The vinyl triflates are then converted to the corresponding vinyl phosphine through palladium catalysis. The resulting vinyl phosphines can then be reduced to give alkyl phosphines.
Retrieving the Complex Intracavity Pump Field of a Kerr Comb from the Through Port Data

A method of retrieving the complex intracavity pump field from the through port is proposed, and verified through characterizing the time-domain waveform of a mode-locked comb related to dark soliton formation in a normal-dispersion microresonator.
Elasticities of rate schedule parameters

The rate schedules for services provided by regulated industries are often not defined in terms of simple per-unit charges but as multipart tariffs. For example, in the case of block price rates, the rate parameters are the definition of the block limits and the per-unit charges in each block. The analysis of these rates is complicated by the fact that most econometric models provide only per-unit or marginal-cost-based elasticities. This paper presents a technique for determining the rate schedule elasticities from elasticities for functions of the rate schedule parameters such as per-unit price elasticities. Also presented are methods for determining elasticities for combinations of service characteristics and the price schedule parameter elasticities for an entire service market. Examples are given for block water rates and Hopkinson and time-of-day electricity rates.
PTHALOS: a fast method for generating mock galaxy distributions

Current models of galaxy formation applied to understanding the large-scale structure of the Universe have two parts. The first is an accurate solution of the equations of motion for the dark matter caused by gravitational clustering. The second consists of making physically reasonable approximations to the behaviour of baryons inside dark matter haloes. The first uses large, computationally intensive, N-body simulations. We argue that because the second step is, at least at present, uncertain, it is possible to obtain similar galaxy distributions without solving the first step exactly. We describe an algorithm that is several orders of magnitude faster than N-body simulations, but that is, nevertheless, rather accurate. The algorithm combines perturbation theory with virialized halo models of the non-linear density and velocity fields. For two- and three-point statistics the resulting fields are exact on large scales, and rather accurate well into the non-linear regime, particularly for two-point statistics in real and redshift space. We then show how one can use this algorithm to generate mock galaxy distributions from halo occupation numbers. As a first application, we show that it provides a good description of the clustering of galaxies in the PSCz survey. We also discuss applications to the estimation of non-Gaussian contributions to the error bars and the covariance matrix of the power spectrum, in real and redshift space, for galaxies and dark matter. The results for the latter show good agreement with simulations, supporting the use of our method for constraining cosmological parameters from forthcoming galaxy surveys.
Heat and Dust in Active Layers of Protostellar Disks

Requirements for magnetic coupling and accretion in the active layer of a protostellar disk are re-examined, and some implications for thermal emission from the layer are discussed. The ionization and electrical conductivity are calculated following the general scheme of Ilgner and Nelson but with an updated UMIST database of chemical reactions and some improvements in the grain physics, and for the minimum-mass solar nebula rather than an alpha disk. The new limits on grain abundance are slightly more severe than theirs. Even for optimally sized grains, the layer should be at least marginally optically thin to its own thermal radiation, so that narrow, highly saturated emission lines of water and other molecular species would be expected if accretion is driven by turbulence and standard rates of ionization prevail. If the grain size distribution extends broadly from well below a micron to a millimeter or more, as suggested by observations, then the layer may be so optically thin that its cooling is dominated by molecular emission. Even under such conditions, it is difficult to have active layers of more than 10 g cm-2 near 1 AU unless dust is entirely eliminated or greatly enhanced ionization rates are assumed. Equipartition-strength magnetic fields are then required in these regions of the disk if observed accretion rates are driven by magnetorotational turbulence. Wind-driven accretion might allow weaker fields and less massive active layers but would not heat the layer as much as turbulence and therefore might not produce emission lines.
Synthesis and reactivity of 1,2- and 1,4-dihydroxyarene complexes of chromium tricarbonyl

Abstract Direct reaction of Me3Si protected 1,2- or 1,4-dihydroxyarenes with Cr(CO)6 affords fair to good yields of the corresponding Cr(CO)3 complexes (1a–4a) which were characterized by 1H and 13C NMR and IR spectroscopic measurements. Removal of the Me3Si protecting groups with KF·2H2O or HBF4·Et2O afforded the 1,2- or 1,4-dihydroxyarene complexes 1b–4b which were characterized in solution but their instability and air-sensitivity precluded their isolation. Proton transfer reactions were monitored by IR spectroscopy. The crystal structure of 2,3-(Me3Si)2C10H6Cr(CO)3 was determined in the space group P21/c with a = 11.019(4), b = 17.613(9), c = 11.843(4) A, β = 105.11(3)°, V = 2219.0 A3, Z = 4. This synthetic route provides access to the π-coordination chemistry of 1,2-dihydroxyarenes which cannot be prepared by direct interaction of the arene with Cr(CO)6.
A Newcomer′s Guide to Peptide Crystallography

Here we provide a guide for adapting the tools developed for protein X-ray crystallography to study the structures and supramolecular assembly of peptides. Peptide crystallography involves selecting a suitable peptide, crystallizing the peptide, collecting X-ray diffraction data, processing the diffraction data, determining the crystallographic phases and generating an electron density map, building and refining models, and depositing the crystallographic structure in the Protein Data Bank (PDB). Advances in technology make this process easy for a newcomer to adopt. This paper describes techniques for determining the X-ray crystallographic structures of peptides: incorporation of amino acids containing heavy atoms for crystallographic phase determination, commercially available kits to crystallize peptides, modern techniques for X-ray crystallographic data collection, and free user-friendly software for data processing and producing a crystallographic structure.
Self-energy of decuplet baryons in nuclear matter

Abstract We calculate, in chiral perturbation theory, the change in the self-energy of decuplet baryons in nuclear matter. These self-energy shifts are relevant in studies of meson-nucleus scattering and of neutron stars. Our results are leading order in an expansion in powers of the ratio of characteristic momenta to the chiral symmetry-breaking scale (or the nucleon mass). Included are contact diagrams generated by 4-baryon operators, which were neglected in earlier studies for the Δ isomultiplet but contribute to the self-energy shifts at this order in chiral perturbation theory.
Controlling spike timing and synchrony in oscillatory neurons

We describe an algorithm to control synchrony between two periodically firing neurons. The control scheme operates in real-time using a dynamic clamp platform. This algorithm is a low-impact stimulation method that brings the neurons toward the desired level of synchrony over the course of several neuron firing periods. As a proof of principle, we demonstrate the versatility of the algorithm using real-time conductance models and then show its performance with biological neurons of hippocampal region CA1 and entorhinal cortex.
Propagation of sound through a real jet flowfield

The sound propagation of harmonic disturbances through a real jet flowfield which contains mean flow gradients in pressure and velocities, has been studied. A finite-differe nce approximation for the equations which govern the acoustic disturbance is obtained for a subsonic axisymmetric jet in terms of acoustic pressure and acoustic energy flux. Experimental results are used to describe the mean flowfield of a model jet. The equations are solved numerically using a Newton-type iterative scheme. The directivity at various distances from a point source located at two jet diameters downstream of the jet exit on its centerline compared qualitatively well with the numerical result of Schubert 7 and with the experimental result of Grande. 15 The computations are made for acoustic energy density flux crossing an ideal plane at the smallest possible distance from the jet, in the area where the homogeneous wave equation is reasonably well satisfied. This result also compared qualitatively well with the experiment of Maestrello.1
Critical behavior of the Kramers escape rate in asymmetric classical field theories

We introduce an asymmetric classical Ginzburg–Landau model in a bounded interval, and study its dynamical behavior when perturbed by weak spatiotemporal noise. The Kramers escape rate from a locally stable state is computed as a function of the interval length. An asymptotically sharp second-order phase transition in activation behavior, with corresponding critical behavior of the rate prefactor, occurs at a critical length l c , similar to what is observed in symmetric models. The weak-noise exit time asymptotics, to both leading and subdominant orders, are analyzed at all interval lengthscales. The divergence of the prefactor as the critical length is approached is discussed in terms of a crossover from non-Arrhenius to Arrhenius behavior as noise intensity decreases. More general models without symmetry are observed to display similar behavior, suggesting that the presence of a “phase transition” in escape behavior is a robust and widespread phenomenon.
Supersymmetric M5-branes with H-field

Abstract In this paper we investigate the form of calibrated M5-branes in the presence of a nonvanishing 3-form field H. We discuss the influence of the H-field on the deformation of supersymmetric n-cycles (in particular SLAG submanifolds in R n ). In addition we argue for a construction which relates calibrated M5-branes of different “curved” dimensions to each other.
QSO envelopes: optically thin, low density, and normal abundances

Consideration of a family of photoionization models which are optically thin to the ionizing radiation, have low enough density that collisional de-excitation is unimportant, and have normal (cosmic) chemical abundances. The line ratios from all such models with a given form of the ionizing spectrum can be derived by means of a scaling law from a single numerical calculation and expressed as a function of one physical parameter. The value of the parameter is uniquely determined from the observed line ratios. The resulting model is in reasonably good agreement with the typical or composite QSO spectrum and with line intensities for two recently observed individual QSOs. It is therefore suggested that much of the emission may come from optically thin gas, although some of the observational evidence (especially the strength of Mg II 2800 A) indicates that thick gas may also be present in some objects.
Eating More Beef: Market Structure and Firm Behavior in the Pacific Basin Beefpacking Industry

Abstract New GATT/WTO regulations have enhanced the power of competitive strategies implemented by the transnational corporations which now dominate the production and distribution of packaged beef in the Pacific Basin. The political actions that have facilitated these economic changes are illustrative of a wider globalization project sponsored by the US and transnational capital. Here I explain the replacement of “national beef sectors” in Australia, New Zealand and the United States with a new industry structure focused on exports to East Asia that features key attributes of the emergent third (global) food regime (after McMichael, 1995 ).
Improved formal preparation of enantiomerically pure anti-benzo[a]pyrene diol epoxide

Abstract We report an improved, economical formal route to enantiomerically pure anti -benzo[ a ]pyrene diol epoxide (BPDE). A trimethylaluminum catalyzed regio- and stereoselective opening of racemic 7,8-epoxy-7,8,9,10-tetrahydrobenzo[ a ]pyrene with Mosher's acid delivers benzylic esters exclusively. This step is a significant improvement over the lack of regioselectivity of standard procedures. We also show that modification of the subsequent chemical steps further shortens the preparation of enantiomerically pure anti -BPDE.