cssi/SciSciGPT-SciSciNet huggingface dataset:
Random Projections for the Nonnegative Least-Squares Problem

Abstract Constrained least-squares regression problems, such as the Nonnegative Least Squares (NNLS) problem, where the variables are restricted to take only nonnegative values, often arise in applications. Motivated by the recent development of the fast Johnson–Lindestrauss transform, we present a fast random projection type approximation algorithm for the NNLS problem. Our algorithm employs a randomized Hadamard transform to construct a much smaller NNLS problem and solves this smaller problem using a standard NNLS solver. We prove that our approach finds a nonnegative solution vector that, with high probability, is close to the optimum nonnegative solution in a relative error approximation sense. We experimentally evaluate our approach on a large collection of term-document data and verify that it does offer considerable speedups without a significant loss in accuracy. Our analysis is based on a novel random projection type result that might be of independent interest. In particular, given a tall and thin matrix Φ ∈ R n × d ( n ≫ d ) and a vector y ∈ R d , we prove that the Euclidean length of Φ y can be estimated very accurately by the Euclidean length of Φ ∼ y , where Φ ∼ consists of a small subset of (appropriately rescaled) rows of Φ .
Chemical modifications to alter monoamine releasing activity of phenmetrazine analogs as potential treatments of stimulant addiction

and gender, a multiple regression analysis revealed that ACOA status significantly predicted alcohol-related problems (p< .01, R2 = .425). Further, ACOA status moderated the effect between affect lability and problems, B=626, p< .01. Conclusions: Higher affect lability predicted more alcoholrelated problems and this effect was strengthened for those classified as an ACOA, making them more vulnerable to alcoholrelated problems. These results have practical implications on the prevention of risky alcohol use among young adults. Further research is needed to determine the causal mechanisms involved. Financial support: This work was supported by a fellowship from the Society of Public Health Education.
Spatial variations in the rate of sea level rise caused by the present‐day melting of glaciers and ice sheets

The redistribution of surface water mass associated with the melting of glacial ice causes uplift near areas of mass depletion, depression of the seafloors, and changes in the earth's gravitational field which perturb the ocean surface. As a result, local spatial variations exist in the rate of sea level rise. Tide gauges on continental coastlines measure a sea level rise 5% smaller than the global average. Tide gauges in the hemisphere opposite a source of continental mass depletion measure sea level rise 10 to 20% greater than the global average produced by that source while satellites make measurements 10% too low. Because most long duration tide gauges are in the northern hemisphere, if the sources of sea level rise are unbalanced between the two hemispheres, estimates of global sea level rise could be in error by 10 to 20%. Individual tide gauges could be more seriously unrepresentative if they are near regions of significant present-day mass depletion.
First Principles of Instruction

For the past several years the author has been reviewing instructional design theories in an attempt to identify prescriptive principles that are common to the various theries. This paper is a preliminary report of the principles that have been identified by this search. Five first principles are elaborated: (a) Learning is promoted when learners are engaged in solving real-world problems. (b) Learning is promoted when existing knowledge is activated as a foundation for new knowledge. (c) Learning is promoted when new knowledge is demonstrated to the learner. (d) Learning is promoted when new knowledge is applied by the learner. (e) Learning is promoted when new knowledge is integrated into the learner's world. Representative instructional design theories are briefly examined to illustrate how they include these principles. These include: Star Legacy by the Vanderbilt Learning Technology Center, 4-Mat by McCarthy, instructional episodes by Andre, multiple approaches to understanding by Gardner, collaborative problem solving by Nelson, constructivist learning environments by Jonassen, and learning by doing by Schank. It is concluded that, although they use a wide variety of terms, these theories and models do include fundamentally similar principles.
Nonlinear filtering problems with finite-dimensional matrix estimation algebras

Abstract Matrix estimation algebras are Lie algebras that arise naturally in the nonlinear filtering problem for systems with random structure. These are systems that have finitely many modes of operation, where transitions from one mode to another are governed by a finite-state Markov process. Necessary conditions for finite dimensionality of matrix estimation algebras are given. Finite-dimensional filter realizations are constructed for some of the cases for which the matrix estimation algebra is finite dimensional.
ON THE PERILS OF CURVE-OF-GROWTH ANALYSIS: SYSTEMATIC ABUNDANCE UNDERESTIMATES FOR THE GAS IN GAMMA-RAY BURST HOST GALAXIES

We examine the practice of deriving interstellar medium (ISM) abundances from low-resolution spectroscopy of gamma-ray burst (GRB) afterglows. We argue that the multi-ion single-component curve-of-growth analysis technique systematically underestimates the column densities of the metal-line profiles commonly observed for GRBs. This systematic underestimate is accentuated by the fact that many GRB line profiles (e.g., GRB 050730, GRB 050820, GRB 051111) are comprised of "clouds" with a bimodal distribution of column density. Such line profiles may be characteristic of a sight line that penetrates both a high-density star-forming region and more distant, ambient ISM material. Our analysis suggests that the majority of abundances reported in the literature are systematically underestimates and that the reported errors are frequently overoptimistic. Further, we demonstrate that one cannot even report relative abundances with confidence. The implications are profound for our current understanding of the metallicity, dust-to-gas ratio, and chemical abundances of the ISM in GRB host galaxies. For example, we argue that all but a few sight lines allow for the gas to have at least solar metallicity. Finally, we suggest new approaches for constraining the abundances.
A review of cermet-based spectrally selective solar absorbers

Spectrally selective solar absorbers harvest solar energy in the form of heat. Solar absorbers using cermet-based coatings demonstrate a high absorptance of the solar spectrum and a low emittance in the infrared (IR) regime. Extensive work has been done to optimize cermet-based solar absorbers to achieve high performance by exploring different cermet (ceramic–metal composite) materials and film configurations through different preparation techniques such as electrodeposition, sputtering, pulsed laser deposition, and solution-based methods. In this article, we review the progress of cermet-based spectrally selective absorbers with high solar absorptance and low thermal emittance, such as Cr2O3, Al2O3, AlN, SiO2, and ZrO2 based cermets as absorption layers. We also present an outlook for cermet-based spectrally selective absorbers with high thermal stability and high conversion efficiency from sunlight to heat.
Eigenvalues of Hermitian matrices with positive sum of bounded rank

We give a minimal list of inequalities characterizing the possible eigenvalues of a set of Hermitian matrices with positive semidefinite sum of bounded rank. This answers a question of Barvinok.
Location, Location, Location: How Network Embeddedness Affects Project Success in Open Source Systems

The community-based model for software development in open source environments is becoming a viable alternative to traditional firm-based models. To better understand the workings of open source environments, we examine the effects of network embeddedness---or the nature of the relationship among projects and developers---on the success of open source projects. We find that considerable heterogeneity exists in the network embeddedness of open source projects and project managers. We use a visual representation of the affiliation network of projects and developers as well as a formal statistical analysis to demonstrate this heterogeneity and to investigate how these structures differ across projects and project managers. Our main results surround the effect of this differential network embeddedness on project success. We find that network embeddedness has strong and significant effects on both technical and commercial success, but that those effects are quite complex. We use latent class regression analysis to show that multiple regimes exist and that some of the effects of network embeddedness are positive under some regimes and negative under others. We use project age and number of page views to provide insights into the direction of the effect of network embeddedness on project success. Our findings show that different aspects of network embeddedness have powerful but subtle effects on project success and suggest that this is a rich environment for further study.
Magnetocentrifugal launching of jets from discs around Kerr black holes

Strong magnetic fields modify particle motion in the curved space-time of spinning black holes and change the stability conditions of circular orbits. We study conditions for magnetocentrifugal jet launching from accretion discs around black holes, whereby large-scale black hole lines anchored in the disc may fling tenuous coronal gas outwards. For a Schwarzschild black hole, magnetocentrifugal launching requires that the poloidal component of magnetic fields makes an angle less than 60° to the outward direction at the disc surface, similar to the Newtonian case. For prograde rotating discs around Kerr black holes, this angle increases and becomes 90° for footpoints anchored to the disc near the horizon of a critically spinning a = M black hole. Thus, a disc around a critically spinning black hole may centrifugally launch a jet even along the rotation axis.
The EBEX Cryostat and Supporting Electronics

University of Minnesota Ph.D. dissertation. May 2011. Major: Physics. Advisor: Professor Shaul Hanany. 1 computer file (PDF); ix, 81 pages.
Preparation of chiral propargylic alcohols from α,β-unsaturated esters

A series of chiral propargylic alcohols with high enantiomeric excess was prepared by asymmetric dihydroxylation of α,β-unsaturated esters, conversion of the diols to 4-(chloromethyl)-1,3-dioxolane intermediates, and base-induced elimination.
Earnings Management and Derivative Hedging with Fair Valuation: Evidence from the Effects of FAS 133

ABSTRACT: Barton (2001) and Pincus and Rajgopal (2002) show that earnings management through discretionary accruals and derivative hedging are partial substitutes in smoothing earnings before 1999. In this study, we investigate whether Financial Accounting Standard (FAS) 133 regarding hedge accounting in 2000 has influenced the relative merit of the two earnings-smoothing methods. Based on a sample of S&P 500 nonfinancial firms during 1996–2006, we find that the substitution relation between derivative hedging and discretionary accrual is significantly attenuated after FAS 133 implementation. We also document a significant increase in earnings volatility associated with derivative hedging post-FAS 133. These results are robust to the use of various model and method specifications, as well as controlling for contemporaneous macroeconomic and regulatory shocks. Overall, our results suggest that a material change in an accounting rule regarding derivatives can influence the level and volatility of reported e...
Improved quantile inference via fixed-smoothing asymptotics and Edgeworth expansion

To estimate a sample quantile’s variance, the quantile spacing method involves smoothing parameter m. When m,n→∞, the corresponding Studentized test statistic is asymptotically N(0,1). Holding m fixed instead, the asymptotic distribution contains the Edgeworth expansion term capturing the variance of the quantile spacing. Consequently, the fixed-m distribution is more accurate than the standard normal under both asymptotic frameworks. A testing-optimal m is proposed to maximize power subject to size control. In simulations, the new method controls size better than similar methods while maintaining good power. Throughout are results for two-sample quantile treatment effect inference. Code is available online.
Influence of intellectual property, foreign investment, and technological adoption on technology entrepreneurship ☆

Abstract Using a multi-level modeling approach, the present study empirically examines how intellectual property rights, inflow of foreign direct investment and barriers to technological adoption affect the likelihood of individuals' entry into technology entrepreneurship in a sample of 20 emerging economies. The results suggest that regimes with strong intellectual property rights protection combined with high levels of foreign direct investment per capita decrease the likelihood of individuals' entry into technology entrepreneurship, whereas low barriers to technological adoption increase this likelihood. These findings contribute to understanding the influence that national institutions and foreign investment exercise on the entrepreneurial behavior of early-stage technology entrepreneurs in emerging economies, for which the extant literature shows mixed results.
Linking the Price of Agricultural Land to Use Values and Amenities

The recent appreciation in agricultural land values across the United States has raised a number of important questions for farmers, farmland owners, lenders, and policy makers. While traditional economic theory suggests that farmland values are determined by the discounted stream of expected returns, previous research has shown that agricultural land values are actually driven by a complex set of factors. This study leverages the unique characteristics of a national land-based USDA survey on farmland values and cash rents to estimate broad, national-level determinants of the market value of cropland and pastureland. Our results support past research findings that indicate farmland values are only partially explained by agricultural returns. We find that multiple nonagricultural attributes of farmland also contribute to the market value.
Are Coethnics More Effective Counterinsurgents? Evidence from the Second Chechen War

Does ethnicity matter for explaining violence during civil wars? I exploit variation in the identity of soldiers who conducted so-called “sweep” operations (zachistki) in Chechnya (2000–5) as an empirical strategy for testing the link between ethnicity and violence. Evidence suggests that the intensity and timing of insurgent attacks are conditional on who “swept” a particular village. For example, attacks decreased by about 40% after pro-Russian Chechen sweeps relative to similar Russian-only operations. These changes are difficult to reconcile with notions of Chechen solidarity or different tactical choices. Instead, evidence, albeit tentative, points toward the existence of a wartime “coethnicity advantage.” Chechen soldiers, enmeshed in dense intraethnic networks, are better positioned to identify insurgents within the population and to issue credible threats against civilians for noncooperation. A second mechanism—prior experience as an insurgent—may also be at work. These findings suggest new avenues of research investigating the conditional effects of violence in civil wars.
Development of Multiscale Models for Complex Chemical Systems: From H+H2 to Biomolecules (Nobel Lecture)

“Do not go where the path may lead, go instead where there is no path and leave a trail. Ralph Waldo Emerson” Paraphrasing Ralph Waldo Emerson, a 19th century New England philosopher and essayist, I shall try to show in this lecture how I have gone where there was no path and left a trail. It leads from trajectory studies of the reactions of small molecules to molecular dynamics simulations of macromolecules of biological interest. In developing computational methods to study complex chemical systems, the essential element has been to introduce classical concepts wherever possible, to replace the much more time-consuming quantum mechanical calculations. In 1929 Paul Dirac (Nobel Prize in Physics, 1933) wrote (Figure 1) the now familiar statement: “The underlying
Using process technology to control and coordinate software adaptation

We have developed an infrastructure for end-to-end run-time monitoring, behavior/performance analysis, and dynamic adaptation of distributed software. This infrastructure is primarily targeted to pre-existing systems and thus operates outside the target application, without making assumptions about the target's implementation, internal communication/computation mechanisms, source code availability, etc. This paper assumes the existence of the monitoring and analysis components, presented elsewhere, and focuses on the mechanisms used to control and coordinate possibly complex repairs/reconfigurations to the target system. These mechanisms require lower-level effectors somehow attached to the target system, so we briefly sketch one such facility (elaborated elsewhere). Our main contribution is the model, architecture, and implementation of Workflakes, the decentralized process engine we use to tailor, control, coordinate, etc. a cohort of such effectors. We have validated the Workflakes approach with case studies in several application domains. Due to space restrictions we concentrate primarily on one case study, briefly discuss a second, and only sketch others.
What power of two divides a weighted Catalan number

Given a sequence of integers b=(b"0,b"1,b"2,...) one gives a Dyck path P of length 2n the weightwt(P)=b"h"""1b"h"""2...b"h"""n, where h"i is the height of the ith ascent of P. The corresponding weighted Catalan number isC"n^b=@?Pwt(P), where the sum is over all Dyck paths of length 2n. So, in particular, the ordinary Catalan numbers C"n correspond to b"i=1 for all i>=0. Let @x(n) stand for the base two exponent of n, i.e., the largest power of 2 dividing n. We give a condition on b which implies that @x(C"n^b)=@x(C"n). In the special case b"i=(2i+1)^2, this settles a conjecture of Postnikov about the number of plane Morse links. Our proof generalizes the recent combinatorial proof of Deutsch and Sagan of the classical formula for @x(C"n).
Enantioselective Synthesis of 2,2-Disubstituted Tetrahydrofurans: Palladium-Catalyzed [3+2] Cycloadditions of Trimethylenemethane with Ketones

An approach to 2,2-disubstituted 4-methylenetetrahydrofurans has been developed utilizing a cycloaddition of trimethylenemethane with aryl ketones, with formation of the products in up to 96% yield and 95% ee. The reaction is catalyzed by palladium in the presence of a phosphoramidite ligand possessing a stereogenic phosphorus, where only a single epimer at phosphorus yields the active catalyst. The identity of this epimer and the origin of its effect on reactivity are discussed.
School Context and the Gender Gap in Educational Achievement

Today, boys generally underperform relative to girls in schools throughout the industrialized world. Building on theories about gender identity and reports from prior ethnographic classroom observa...
Integrable vs. nonintegrable geodesic soliton behavior

Abstract We study confined solutions of certain evolutionary partial differential equations (PDE) in 1+1 space–time. The PDE we study are Lie–Poisson Hamiltonian systems for quadratic Hamiltonians defined on the dual of the Lie algebra of vector fields on the real line. These systems are also Euler–Poincare equations for geodesic motion on the diffeomorphism group in the sense of the Arnold program for ideal fluids, but where the kinetic energy metric is different from the L2 norm of the velocity. These PDE possess a finite-dimensional invariant manifold of particle-like (measure-valued) solutions we call “pulsons”. We solve the particle dynamics of the two-pulson interaction analytically as a canonical Hamiltonian system for geodesic motion with two degrees of freedom and a conserved momentum. The result of this two-pulson interaction for rear-end collisions is elastic scattering with a phase shift, as occurs with solitons. The results for head-on antisymmetric collisions of pulsons tend to be singularity formation. Numerical simulations of these PDE show that their evolution by geodesic dynamics for confined (or compact) initial conditions in various nonintegrable cases possesses the same type of multi-soliton behavior (elastic collisions, asymptotic sorting by pulse height) as the corresponding integrable cases do. We conjecture this behavior occurs because the integrable two-pulson interactions dominate the dynamics on the invariant pulson manifold, and this dynamics dominates the PDE initial value problem for most choices of confined pulses and initial conditions of finite extent.
Dynamic behavior of the well‐mixed isothermal crystallizer

Under some conditions, continuous crystallization exhibits cyclic changes of the particle size even with constant input conditions. A linearized stability analysis has been performed to determine under what conditions this behavior can be expected. Numerical solutions of the actual nonlinear system equations were carried out to follow the cyclic behavior and to compute the cycle time and the amplitude of the fluctuations. The effect of seeding on the stability limits and product distribution was also evaluated.
A comparative study of the depth of maximum of simulated air shower longitudinal profiles

Abstract A comparative study of simulated air shower longitudinal profiles is presented. An appropriate thinning level for the calculations is first determined empirically. High statistics results are then provided, over a wide energy range (1014.0–1020.5 eV), for proton and iron primaries, using four combinations of the mocca and corsika program frameworks, and the SIBYLL and QGSjet high energy hadronic interaction models. These results are compared to existing experimental data. The way in which the first interaction controls Xmax is investigated, as is the distribution of Xmax.
Traffic exposure near the Los Angeles–Long Beach port complex: using GPS-enhanced tracking to assess the implications of unreported travel and locations

Traffic exposure assessments could misclassify the extent and locations of exposure if traditional recall surveys and self-reported travel diaries do not record all participant activities. The Harbor Communities Time Location Study (HCTLS) examines the nature, extent and implications of underreported locations/ trips in a case study which used portable Global Positioning Systems (GPS) devices to track the diurnal patterns and traffic exposure of 47 residents of communities near the Los Angeles-Long Beach port com- plex. Participants were similar to adults nationwide in time spent indoors, in-vehicle, and outdoors, but spent more time indoors at home (78% vs. 66%). Overall, participants did not report nearly half (49%) of the locations and trips identified in GPS-enhanced data on their activity diaries, resulting in about 3 h/day in unreported locations and 0.6 h/day in unreported trips. The probability of a location/trip being under- reported was systematically correlated with participant and location/trip characteristics. Self-reported data missed about 50 min of heightened air pollution exposures during the 5 h/day on average partici- pants spent in high-traffic areas and about 30 min during the 4 h/day near truck routes. GPS-enhanced methods provide opportunities to more precisely characterize exposure periods and tools to identify facility, roadway, and land use types of the greatest concern for mitigation efforts. Published by Elsevier Ltd.
Stabilizing Cloud Feedback Dramatically Expands the Habitable Zone of Tidally Locked Planets

The habitable zone (HZ) is the circumstellar region where a planet can sustain surface liquid water. Searching for terrestrial planets in the HZ of nearby stars is the stated goal of ongoing and planned extrasolar planet surveys. Previous estimates of the inner edge of the HZ were based on one-dimensional radiative-convective models. The most serious limitation of these models is the inability to predict cloud behavior. Here we use global climate models with sophisticated cloud schemes to show that due to a stabilizing cloud feedback, tidally locked planets can be habitable at twice the stellar flux found by previous studies. This dramatically expands the HZ and roughly doubles the frequency of habitable planets orbiting red dwarf stars. At high stellar flux, strong convection produces thick water clouds near the substellar location that greatly increase the planetary albedo and reduce surface temperatures. Higher insolation produces stronger substellar convection and therefore higher albedo, making this phenomenon a stabilizing climate feedback. Substellar clouds also effectively block outgoing radiation from the surface, reducing or even completely reversing the thermal emission contrast between dayside and nightside. The presence of substellar water clouds and the resulting clement surface conditions will therefore be detectable with the James Webb Space Telescope.
Forecasting Livestock Feed Cost Risks Using Futures and Options

The costs of corn- and soybean-based feeds compose a substantial proportion of the variable costs faced by both mainstream and emergent confined livestock producers. This research develops a method to provide a joint distribution of prices of corn and soybean meal at a future time. Black's 1976 option model and stochastic volatility jump diffusion (SVJD) model are compared in volatility forecasting performance. In general, SVJD is superior to Black's model, though their performance is both commodity-specific and forecasting horizon specific.
A characterization of two classes of locally truncated diagram geometries

Let i = (P;L) be a parapolar space which is locally Ani1;3(K) for some integer n > 6 andK a fleld. There exists a class of 2-convex subspacesD, each isomorphic to D5;5(K), such that every symplecton of i is contained in a unique element of D. Let i = (P;L) be a parapolar space which is locally Ani1;4(K) for n = 7 or an integer n ‚ 9 and some fleld K. Assume that i satisfles the extra condition called the Weak Hexagon Axiom. Then there exists a class of 2-convex subspaces D, each isomorphic to D6;6(K), such that every symplecton of i is contained in a unique element of D. In both of the above cases i is the homomorphic image of a truncated building.
The Value Relevance of Financial Statement Recognition vs. Disclosure: Evidence from SFAS No. 106

This study examines whether the market values financial statement data differently if it is disclosed instead of recognized in the body of the financial statements. We identify a sample of 229 SFAS No. 106 adopters who disclose an estimate of their anticipated liability for retiree benefits other than pensions (PRB) in their financial reports prior to the year of recognition. We then test whether the disclosed estimate of the PRB liability is valued differently by the market than is the subsequently recognized PRB liability. We provide modest and model‐sensitive evidence that the recognized PRB liability receives more weight than the disclosed liability in market value association tests.
Catalytic Enantioselective 1,2-Diboration of 1,3-Dienes: Versatile Reagents for Stereoselective Allylation

More with boron: The development of catalytic enantioselective 1,2-diboration of 1,3-dienes enables a new strategy for enantioselective carbonyl allylation reactions (see scheme). These reactions occur with outstanding levels of stereoselection and can be applied to both monosubstituted and 1,1-disubstituted dienes. The carbonyl allylation reactions provide enantiomerically enriched functionalized homoallylic alcohol products.
NanoSIMS, TEM, AND XANES STUDIES OF A UNIQUE PRESOLAR SUPERNOVA GRAPHITE GRAIN

We report on isotopic and microstructural investigations of a unique presolar supernova (SN) graphite grain, referred to as G6, isolated from the Orgueil CI chondrite. G6 contains complex heterogeneities in its isotopic composition and in its microstructure. Nano-scale secondary ion mass spectrometer isotope images of ultramicrotome sections reveal heterogeneities in its C, N, and O isotopic compositions, including anomalous shell-like structures. Transmission electron microscope studies reveal a nanocrystalline core surrounded by a turbostratic graphite mantle, the first reported nanocrystalline core from a low-density SN graphite grain. Electron diffraction analysis shows that the nanocrystalline core consists of randomly oriented 2-4 nm graphene particles, similar to those in cores of high-density (HD) presolar graphite grains from asymptotic giant branch stars. G6's core also exhibits evidence for planar stacking of these graphene nano-sheets with a domain size up to 4.5 nm, which was unobserved in the nanocrystalline cores of HD graphite grains. We also report on X-ray absorption near-edge structure measurements of G6. The complex isotopic- and micro-structure of G6 provides evidence for mixing and/or granular transport in SN ejecta.
Renal Relevant Radiology: Imaging in Kidney Transplantation

Kidney transplantation can be associated with various complications that vary from vascular complications to urologic disorders to immunologic adverse effects. In evaluating the recipient with graft dysfunction, clinicians can choose among several imaging modalities, including ultrasonography, nuclear medicine studies, computed tomography, and magnetic resonance imaging. This review discusses the evaluation of the kidney transplant recipient using these imaging procedures, emphasizing the clinical diagnostic utility and role of each modality. A kidney biopsy is often required as a gold standard for diagnostic purposes. However, because of the inherent risks of a kidney biopsy, noninvasive imaging in diagnosing causes of graft dysfunction is a highly desired tool used and needed by the transplant community. Because the diagnostic accuracy varies depending on the time course and nature of the transplant-related complication, this review also addresses the advantages and limitations of each modality. The recent advances in kidney transplant imaging techniques and their clinical implications are also discussed.
Three notions of tropical rank for symmetric matrices

We introduce and study three different notions of tropical rank for symmetric and dissimilarity matrices in terms of minimal decompositions into rank 1 symmetric matrices, star tree matrices, and tree matrices. Our results provide a close study of the tropical secant sets of certain nice tropical varieties, including the tropical Grassmannian. In particular, we determine the dimension of each secant set, the convex hull of the variety, and in most cases, the smallest secant set which is equal to the convex hull.
Perpendicular ion heating by low-frequency Alfven-wave turbulence in the solar wind

We consider ion heating by turbulent Alfv?n waves (AWs) and kinetic Alfv?n waves (KAWs) with wavelengths (measured perpendicular to the magnetic field) that are comparable to the ion gyroradius and frequencies ? smaller than the ion cyclotron frequency ?. We focus on plasmas in which ? 1, where ? is the ratio of plasma pressure to magnetic pressure. As in previous studies, we find that when the turbulence amplitude exceeds a certain threshold, an ion's orbit becomes chaotic. The ion then interacts stochastically with the time-varying electrostatic potential, and the ion's energy undergoes a random walk. Using phenomenological arguments, we derive an analytic expression for the rates at which different ion species are heated, which we test by simulating test particles interacting with a spectrum of randomly phased AWs and KAWs. We find that the stochastic heating rate depends sensitively on the quantity ? = ?v ?/v ?, where v ? (v ?) is the component of the ion velocity perpendicular (parallel) to the background magnetic field B 0, and ?v ? (?B ?) is the rms amplitude of the velocity (magnetic-field) fluctuations at the gyroradius scale. In the case of thermal protons, when ? ?crit, where ?crit is a constant, a proton's magnetic moment is nearly conserved and stochastic heating is extremely weak. However, when ?>?crit, the proton heating rate exceeds half the cascade power that would be present in strong balanced KAW turbulence with the same value of ?v ?, and magnetic-moment conservation is violated even when ? ?. For the random-phase waves in our test-particle simulations, ?crit = 0.19. For protons in low-? plasmas, ? ??1/2?B ?/B 0, and ? can exceed ?crit even when ?B ?/B 0 ?crit. The heating is anisotropic, increasing v 2 ? much more than v 2 ? when ? 1. (In contrast, at ? 1 Landau damping and transit-time damping of KAWs lead to strong parallel heating of protons.) At comparable temperatures, alpha particles and minor ions have larger values of ? than protons and are heated more efficiently as a result. We discuss the implications of our results for ion heating in coronal holes and the solar wind.
Evaluation of Transport in the Lower Tropical Stratosphere in a Global Chemistry and Transport Model

Off-line models of the evolution of stratospheric constituents use meteorological information from a general circulation model (GCM) or from a data assimilation system (DAS). Here we focus on transport in the tropics and between the tropics and middle latitudes. Constituent fields from two simulations are compared with each other and with observations. One simulation uses winds from a GCM and the second uses winds from a DAS that has the same GCM at its core. Comparisons of results from the two simulations with observations from satellite, aircraft, and sondes are used to judge the realism of the tropical transport. Faithful comparisons between simulated fields and observations for O3, CH4, and the age-of-air are found for the simulation using the GCM fields. The same comparisons for the simulation using DAS fields show rapid upward tropical transport and excessive mixing between the tropics and middle latitudes. The unrealistic transport found in the DAS fields may be due to the failure of the GCM used in the assimilation system to represent the quasi-biennial oscillation. The assimilation system accounts for differences between the observations and the GCM by requiring implicit forcing to produce consistency between the GCM and observations. These comparisons suggest that the physical consistency of the GCM fields is more important to transport characteristics in the lower tropical stratosphere than the elimination bias with respect to meteorological observations that is accomplished by the DAS. The comparisons presented here show that GCM fields are more appropriate for long-term calculations to assess the impact of changes in stratospheric composition because the balance between photochemical and transport terms is likely to be represented correctly.
A two-stage simulated annealing methodology

We propose a two-stage simulated annealing method. While most previous work has focused on ad hoc constant starting temperatures for the low temperature annealing phase, this paper presents a more formal method for starting temperature determination in two-stage simulated annealing systems. We have successfully applied our method to three optimization problems using both classic and adaptive schedules. We also briefly discuss an alternative stop criterion that experimentally reduces the running time up to an additional ten percent in our problem suite.
Discrete element methods for the plastic analysis of structures subjected to cyclic loading

Discrete element method for plastic analysis of complex built-up structures subjected to cyclic loading causing membrane stress and stress reversal
Coordinated investing with feedback and learning

This paper introduces assets for which the intrinsic value is endogenous to the amount of funding attracted. A rational expectations equilibrium is developed. Additionally, simulations of the model based on bounded rationality explore the different market behavior under fundamental and momentum based investing strategies. Both strategies produce herding characteristics. The herding under the fundamental strategy approximates the optimal investing of a rational central planner. The momentum strategy results in suboptimal economic development.
Metastatic carcinoid tumors--are we making the cut?

BACKGROUND: Although controversial, surgical resection for metastatic carcinoid tumors (MCTs) can potentially prolong survival. METHODS: Patients with MCTs were identified from the Surveillance, Epidemiology and End Results database. Patients undergoing surgery were compared to unresected patients. RESULTS: Surgery was performed in 33% of patients. Predictors of surgery included age ,50 years (odds ratio [OR], 2.4), low grade (OR, 3.1), and the appendix (OR, 36.2) or small intestine (OR, 27.2) as the primary site. Predictors of adverse survival included high grade (hazard ratio, 2.4) and no surgery (hazard ratio, 2.5) or surgery on only primary or distant disease (hazard ratio, 1.5) compared with surgery for both. Survival at 5 years was 5% with no surgery, 28% with surgery on either site, and 46% with surgery at both sites (P , .001). CONCLUSIONS: Surgery for MCTs is more common in younger patients, those with low-grade disease, and those with small bowel or appendiceal primary tumors. Although selection bias cannot be excluded, these data lend support to ‘‘debulking’’ for MCT.
Entrepreneurship, Saving, and Social Mobility

Abstract This paper examines entrepreneurship in order to analyze, first, the degree to which the opportunity to start or own a business affects the household's saving behavior and the implication of this behavior for the distribution of wealth and, second, the relationship between the extent of entrepreneurship in the economy and socioeconomic mobility, that is, the movement of families across wealth classes over time. First, a number of stylized facts based on data from the Panel Study of Income Dynamics and the Survey of Consumer Finances are outlined. They show relevant differences in asset holdings and wealth mobility between entrepreneurs and workers. Second, a dynamic general equilibrium model with an explicit formalization of the entrepreneurial choice is developed. Through the modeling of the entrepreneurial activities, the model generates a concentration of wealth similar to the one observed in the U.S. economy and it replicates the main patterns of wealth mobility in which entrepreneurs experience higher upward mobility than workers. Journal of Economic Literature Classification Numbers: E21, D31, J23
Scaled particle theory for hard sphere pairs. II. Numerical analysis

We use the extension of scaled particle theory presented in the accompanying paper [F. H. Stillinger et al., J. Chem. Phys. 125, 204504 (2006)] to calculate numerically the pair correlation function of the hard sphere fluid over the density range 0⩽ρσ3⩽0.96. Comparison with computer simulation results reveals that the new theory is able to capture accurately the fluid’s structure across the entire density range examined. The pressure predicted via the virial route is systematically lower than simulation results, while that obtained using the compressibility route is lower than simulation predictions for ρσ3⩽0.67 and higher than simulation predictions for ρσ3⩾0.67. Numerical predictions are also presented for the surface tension and Tolman length of the hard sphere fluid.
Knowledge Spillovers and the Optimal Taxation of Multinational Firms

This paper examines a key policy question for many developing countries: Should they allow and even subsidize the entry and operation of multinational …rms? I consider a model in which spillovers drive the formation of productive knowledge, the typical rationale for attracting multinational …rms. I depart from most work on the gains of openness and instead of using simple counterfactual policies (i.e. compare complete openness or complete closedness with each other or with actual policies) I characterize the gains attainable under a Ramsey program, when taxes are set to maximize the welfare of the recipient country subject to the equilibrium behavior of national and foreign agents. I …nd that contrary to laissez-faire, openness under optimal taxation always leads developing countries to catch up with developed countries and improves their welfare. However, in stark contrast with some observed practice, I …nd that a developing country should only subsidize the entry of foreign …rms if the domestic accumulation of know-how is also subsidized.
Millimeter Wave Antenna Technology

Millimeter wave antenna technology has had a long history of development, and as millimeter wave systems evolve through planning to implementation, a significant amount of additional development work will be required. Millimeter wave antennas play a key role in the rationale for millimeter system designs because high spatial resolution can be achieved with modest physical dimensions. Reflector, lens, array, and horn technologies are surveyed. Multiple beam designs and adaptive processing antennas are described because these technologies afford high leverage opportunities to enhance electronic survivability and to extend communication capabilities. Ancillary components, such as radomes, are a necessary part of practical antenna designs and are discussed in some detail.
An empirical model of search with vertically differentiated products

This paper presents a nonsequential search model that allows for vertical product dierentiation. In the unique symmetric equilibrium firms with dierent characteristics draw utilities from a common utility distribution. Because the firms dier in their characteristics this leads to dierent price distributions. The model therefore provides a theoretical rationale for explaining price dispersion as a result of quality dierences and search behavior of consumers together. Using the equilibrium conditions derived from the model, it is shown how to estimate search costs by maximum likelihood using only price data. A data set on prices from Dutch supermarkets reveals that the amount of search has decreased over the sampling period. Moreover, ignoring vertical product dierentiation results in an overestimation of search costs.
Error-Driven Pruning of Treebank Grammars for Base Noun Phrase Identification

Finding simple, non-recursive, base noun phrases is an important subtask for many natural language processing applications. While previous empirical methods for base NP identification have been rather complex, this paper instead proposes a very simple algorithm that is tailored to the relative simplicity of the task. In particular, we present a corpus-based approach for finding base NPs by matching part-of-speech tag sequences. The training phase of the algorithm is based on two successful techniques: first the base NP grammar is read from a "treebank" corpus; then the grammar is improved by selecting rules with high "benefit" scores. Using this simple algorithm with a naive heuristic for matching rules, we achieve surprising accuracy in an evaluation on the Penn Treebank Wall Street Journal.
Techniques for the simulation of large-scale integrated circuits

New techniques for the efficient simulation of large-scale integrated MOS circults are described. These techniques have been implemented in the computer program SPLICE which combines circuit, timing, and logic analyzes in a single package. The use of SOR-Newton methods permits all three forms of analysis to be performed simultaneously, while event-control is used to enhance execution speed. The performance of SPLICE for the simulation of large NMOs circuits is also described.
The impact of firm size and age on knowledge strategies during product development: a study of the drug delivery industry

A successful new product development strategy involves the identification, development, and exploitation of key resources. Such exploitation of a firm's unique knowledge base ultimately leads to successful new products and, in turn, a sustainable competitive advantage. In this paper, we look at a firm's knowledge strategy along three dimensions, and examine the impact of firm size and age on the type of knowledge strategies used to build technological strength and competitive success. The three dimensions of knowledge strategy examined are: extent of emphasis on speed of learning, emphasis on internal versus external sourcing of knowledge, and the development of a broad versus a narrow knowledge base. Using a population of 27 firms from the drug delivery sector of the pharmaceutical industry, we found that firm size and age influenced the success of firm knowledge strategies. Interestingly, we found that the differences in the knowledge strategy dimensions between large and small firms and between old and young firms were not as great as expected. However, we found that firm size and age moderate the relationship between knowledge strategies and technological strength. In other words, firms that used appropriate knowledge strategies for their size and age optimized their technological strength. Concerning size, smaller firms that focused on faster learning and developing a narrow knowledge base were able to optimize technological strength. On the other hand, large firms that developed a broader knowledge base and focused on internal learning achieved similar success. Concerning age, younger firms that maintained connections to external sources of learning and developed a narrower, niche-based knowledge optimized their technological strength.
Procedure for Separating Noise Sources in Measurements of Turbofan Engine Core Noise

The study of core noise from turbofan engines has become more important as noise from other sources like the fan and jet have been reduced. A multiple microphone and acoustic source modeling method to separate correlated and uncorrelated sources has been developed. The auto and cross spectrum in the frequency range below 1000 Hz is fitted with a noise propagation model based on a source couplet consisting of a single incoherent source with a single coherent source or a source triplet consisting of a single incoherent source with two coherent point sources. Examples are presented using data from a Pratt & Whitney PW4098 turbofan engine. The method works well.
Nickel‐Catalyzed Cycloaddition of 1,3‐Dienes with 3‐Azetidinones and 3‐Oxetanones

Both thermodynamic and kinetic forces make C–C bond activation one of the most difficult processes to facilitate.[1] Breaking the strong bond between two carbon atoms is further hampered by the increased steric congestion in C–C bonds relative to C–H and C–X bonds.[1a,b,2] Despite the difficulty associated with C–C bond activation, a handful of transition-metal-catalyzed methods have been developed.[1] In fact, these methods serve as potentially useful technology for the construction of complex molecular architectures from relatively simple starting materials in a highly atom-economical fashion. The C–C bond-activation step in these systems generally occurs by two important processes: 1) oxidative addition of the C–C bond to the transition metal, or 2) β-carbon elimination of transition-metal-alkyl complexes.[1a,j] Furthermore, the use of small cyclic systems wherein the release of inherent strain provides the necessary driving force for C–C bond cleavage has been a central theme of C–C bond activation strategies.[1,3,4]