cssi/SciSciGPT-SciSciNet huggingface dataset:
The spectral gap for some spin chains with discrete symmetry breaking

We prove that for any finite set of generalized valence bond solid (GVBS) states of a quantum spin chain there exists a translation invariant finite-range Hamiltonian for which this set is the set of ground states. This result implies that there are GVBS models with arbitrary broken discrete symmetries that are described as combinations of lattice translations, lattice reflections, and local unitary or anti-unitary transformations. We also show that all GVBS models that satisfy some natural conditions have a spectral gap. The existence of a spectral gap is obtained by applying a simple and quite general strategy for proving lower bounds on the spectral gap of the generator of a classical or quantum spin dynamics. This general scheme is interesting in its own right and threfore, although the basic idea is not new, we present it in a system-independent setting. The results are illustrated with a number of examples.
Electron-ion three-body recombination coefficient of argon

Spectroscopic measurements of a 15-kW flowing argon plasma, produced by an atmospheric pressure radio frequency inductively coupled plasma torch, have been made. The plasma is found to be in partial local thermodynamic equilibrium at electronic levels as low as 4p. Ionizational nonequilibrium is observed in the form of an elevated electron density due to the finite three-body electron-ion recombination rate. The flowing plasma is modeled using a two-dimensional axisymmetric flow code, incorporating partial local thermodynamic equilibrium effects, radiative transfer, and ionizational nonequilibrium through the coupled electron continuity equation
Does it pay to beat around the bush? The case of the obfuscating salesperson

Abstract How often do salespeople obfuscate in response to a customer's question? And when and why does obfuscating help or hurt the prospects of a sale? We investigate these questions in three studies, developing and testing a framework based on theory from persuasion, social cognition, and communication theory. The results show that most consumers report having experienced obfuscation in the marketplace and believe that it is more prevalent in professions where people have strong monetary motives to obfuscate. Further, we find that when consumers' prior expectations of a dishonest response to a question are heightened, either because the construct of honesty is chronically salient to the individual or because of the presence of a monetary motive for the salesperson, obfuscation undermines purchase intentions relative to a straightforward “don't know” response. In contrast, when expectations of a dishonest response are low, an obfuscatory response is as persuasive as an admission of lack of knowledge. These effects are mediated by perceived trust in the salesperson. Implications are discussed for persuasion theory, salesperson influence tactics, and consumer welfare.
Tree Diagrams for String Links II: Determining Chord Diagrams

In previous work [7], we defined the intersection graph of a chord diagram associated with a string link (as in the theory of finite type invariants). In this paper, we look at the case when this graph is a tree, and we show that in many cases these trees determine the chord diagram (modulo the usual 1-term and 4-term relations).
Influence of livestock grazing on C sequestration in semi-arid mixed-grass and short-grass rangelands.

Abstract We evaluated the effects of livestock grazing on C content of the plant–soil system (to 60 cm) of two semi-arid grasslands: a mixed-grass prairie (grazed 12 years), and a short-grass steppe (grazed 56 years). Grazing treatments included season-long grazing at heavy and light stocking rates, and non-grazed exclosures. Significantly higher soil C (0–30cm) was measured in grazed pastures compared to non-grazed exclosures, although for the short-grass steppe higher soil C was observed with the heavy grazing treatment only. Excluding grazing caused an immobilization of C in excessive aboveground plant litter, and an increase in annual forbs and grasses which lack dense fibrous rooting systems conducive to soil organic matter formation and accumulation. Our data indicate that higher soil C with grazing was in part the result of more rapid annual shoot turnover, and redistribution of C within the plant–soil system as a result of changes in plant species composition.
The effects of hyperbolic heat conduction around a dynamically propagating crack tip

Abstract Using infrared detectors, Zehnder and Rosakis (1991, J. Mech. Phys. Solids 39(3) , 385), Zehnder and Kallivayalil (1991, SPIE ISS4A , 48) and Mason and Rosakis (1992, SN Report 92-2), have recorded the temperature field around a dynamically propagating crack tip travelling at constant velocity in several metals. At the same time, Tzou (1990a, J. Heat Transfer 112, 21, 1990b, Inst. Heat Mass Transfer 33(5) , 877) has suggested that the temperature field around a propagating crack tip might exhibit some of the characteristics of hyperbolic heat conduction. In this paper a corrected solution of the hyperbolic heat conduction equation for a travelling point source is derived. Then an experimental estimate of the active plastic zone (heat generating zone) at a crack tip is used for various experimental conditions to examine the possible effects of hyperbolic heat conduction around a propagating crack tip. Finally, using the actual experimental conditions of Zehnder and Rosakis (1991) Zehnder and Kallivayalil (1991) and Mason and Rosakis (1992) it is shown that no effects of hyperbolic heat conduction are observed around a propagating crack tip. It is seen that, due to adiabatic conditions at the crack tip during these experiments, the solution of the hyperbolic heat equation is indistinguishable from the solution of the parabolic heat conduction equation for crack propagation in steel.
A new supersymmetric framework for fermion masses

Supersymmetric theories involving a spontaneously broken flavor symmetry can solve the flavor-changing problem while having quark and lepton masses derived from both F and D terms. As an example, a theory of leptons is constructed in which holomorphy constrains the electron to be massless at tree level. The electron flavor symmetries are broken by D terms, leading to flavor mixing in the slepton mass matrices, which allows a radiative electron mass to be generated by the gauge interactions of supersymmetric QED. Such a radiative origin for the electron mass can be probed by searches for τ → eγ, and could be verified or eliminated by measurements o slepton pair production.
Utilizing the PK scale of the MMPI‐2 to detect posttraumatic stress disorder in college students

This study investigated the utility of the PK scale of the MMPI-2 with college students. Results indicated that the PK scale, when combined with DSM IV criteria, does discriminate between college students who obtain a score of 65 or higher and those who score below 65.
THE HOST GALAXIES OF SHORT-DURATION GAMMA-RAY BURSTS: LUMINOSITIES, METALLICITIES, AND STAR FORMATION RATES

The association of some short-duration gamma-ray bursts (GRBs) with elliptical galaxies established that their progenitors, unlike those of long GRBs, belong to an old stellar population. However, the majority of short GRBs appear to occur in star forming galaxies, raising the possibility that some progenitors are related to recent star formation activity. Here, we present optical spectroscopy of these hosts and measure their luminosities, star formation rates, and metallicities. We find luminosities of LB ≈ 0.1-1.5 L *, star formation rates of SFR ≈ 0.2-6 M ☉ yr–1, and metallicities of 12 + log(O/H) ≈ 8.5-8.9 (Z ≈ 0.6-1.6 Z ☉). A detailed comparison to the hosts of long GRBs reveals systematically higher luminosities, lower specific star formation rates (SFR/LB ) by about an order of magnitude, and higher metallicities by about 0.6 dex. The Kolmogorov-Smirnov probability that the short and long GRB hosts are drawn from the same underlying galaxy distribution is only ~10–3. Short GRB hosts exhibit excellent agreement with the specific star formation rates and the luminosity-metallicity relation of field galaxies at z ~ 0.1-1. We thus conclude that short GRB hosts are not dominated by young stellar populations like long GRB hosts. Instead, short GRB hosts appear to be drawn uniformly from the underlying field galaxy distribution, indicating that the progenitors have a wide age distribution of several Gyr.
GAUGE THEORIES FROM ORIENTIFOLDS AND LARGE-N LIMIT

Extending the recent work by M. Bershadsky, Z. Kakushadze and C. Vafa (hep-th/9803076), we consider string perturbative expansion in the presence of D-branes and orientifold planes imbedded in orbifolded space-time. In the α′ → 0 limit the weak coupling string perturbative expansion maps to `t Hooft's large-N expansion. We focus on four-dimensional N = 1, 2, 4 supersymmetric theories, and also discuss possible extensions to N = 0 cases. Utilizing the string theory perturbation techniques we show that computation of any M-point correlation function in these theories reduces to the corresponding computation in the parent N = 4 theory. In particular, we discuss theories (which are rather constrained) with vanishing β-functions to all orders in perturbation theory in the large-N limit. We also point out that in theories with non-vanishing β-functions the gauge coupling running is suppressed in the large-N limit. Introduction of orientifold planes allows to construct certain gauge theories with SO, Sp and SU gauge groups and various matter (only unitary gauge groups with bi-fundamental/adjoint matter arise in theories without orientifold planes).
Mortality of persons with photofluorograms suggestive of cardiovascular disease.

THE advent of photofluorography has made possible the radiologic screening of the chests of millions of persons each year. Although this method has been largely applied to tuberculosis case finding, many cardiovascular abnormalities have also been detected by this procedure. Since diseases of the cardiovascular system are responsible for an increasingly large number of deaths each year, efforts have been made to determine the potential usefulness of chest photofluorography as a means of detecting persons with cardiovascular disease, with the assumption that patients found in routine surveys might be benefited more by appropriate treatment than those seeking medical care because . . .
The search for extrasolar Earth-like planets

Abstract The search for extrasolar Earth-like planets is underway. Over 100 extrasolar giant planets are known to orbit nearby Sun-like stars, including several in multiple-planet systems. These planetary systems are stepping stones for the search for Earth-like planets; the technology development, observational strategies, and science results can all be applied to Earth-like planets. Stars much less massive than the Sun – the most common stars in our Galaxy – are being monitored for the gravitational influence of Earth-like planets. Although Earth-like planets orbiting Sun-like stars are much more difficult to detect, space missions are being built to detect them indirectly due to their effects on the parent star and to quantify fundamental factors such as terrestrial planet frequency, size distribution, and mass distribution. Extremely ambitious space programs are being developed to directly detect Earth-like planets orbiting Sun-like stars, and must tackle the immense technological challenge of blocking out the light of the parent star, which is brighter than the planet by six to ten orders of magnitude. Direct detection of radiation from the planet is necessary for the definitive goal of the search for Earth-like planets: the study of atmospheric spectral signatures for signs of severe disequilibrium chemistry that could be indicative of biological activity. In addition to technological development, a growing flurry of scientific activity has begun to: understand terrestrial planet formation and terrestrial planet frequency; model terrestrial-like planet atmospheres and evolution; articulate the biological signatures of our own Earth; and even study Earth as an extrasolar planet by observation and analysis of the spatially unresolved Earth.
The isomorphism problem for classes of computable fields

Theories of classification distinguish classes with some good structure theorem from those for which none is possible. Some classes (dense linear orders, for instance) are non-classifiable in general, but are classifiable when we consider only countable members. This paper explores such a notion for classes of computable structures by working out several examples. One motivation is to see whether some classes whose set of countable members is very complex become classifiable when we consider only computable members. We follow recent work by Goncharov and Knight in using the degree of the isomorphism problem for a class to distinguish classifiable classes from non-classifiable. For real closed fields we show that the isomorphism problem is Δ11 complete (the maximum possible), and for others we show that it is of relatively low complexity. We show that the isomorphism problem for algebraically closed fields, Archimedean real closed fields, or vector spaces is Π03 complete.
A practical methodology for early buffer and wire resource allocation

As technology scales, interconnect-centric design flows become imperative for achieving timing closure. Preplanning buffers and wires in the layout is critical for such flows. Both buffers and wires must be considered simultaneously, since wire routes determine buffer requirements and buffer locations constrain the wire routes. In contrast to recently proposed buffer-block planning approaches, our novel design methodology distributes a set of buffer sites throughout the design. This allows one to use a tile graph to abstract the buffer planning problem and simultaneously address wire planning. We present a four-stage heuristic called resource allocation for buffer and interconnect distribution for resource allocation that includes a new, efficient technique for buffer insertion using a length-based constraint. Extensive experiments validate the effectiveness of this approach.
Self-adjusting computation

A static algorithm is one that computes the result of a query about the output for a single, fixed input. For example, a static sorting algorithm is one that takes as input a set of keys, and permits queries about the relative order of these keys according to some ordering relation. A dynamic, or incremental, algorithm is one that permits queries about the output to be interleaved with operations that incrementally modify the input. For example, a dynamic sorting algorithm is one that would permit insertion or deletion of keys to be interleaved with queries about their relative ordering. It is often easier to find a static algorithm than a dynamic algorithm for a given problem. There is a large and growing literature on dynamic algorithms for a broad range of problems. Self-adjusting computation is a method for deriving a dynamic algorithm for a problem by "dynamizing" a static algorithm for it. We have studied three main techniques for dynamization: 1. adaptivity 2. selective memoization 3. adaptive memoization.
Exercise Training and Immunosenescence

During the aging process, a decrease in the ability of the immune system to control infection, known as immunosenescence, takes place. Paradoxically, aging also results in chronic low-level inflammation and exaggerated inflammatory responses. A number of studies have investigated the effects of a variety of exercise training interventions on the immune system both in humans and using animal models of aging. Cross-sectional studies that compared masters athletes to untrained, age-matched controls found that the athletes had significantly better immune function, but these studies suffered because of the difficulty in generalizing results from highly trained athletes to a general population of physically active older adults. Prospective studies in humans have attempted to address this, but these studies have resulted in sometimes equivocal findings, possibly as a result of the differences in exercise training programs used. Finally, animal studies, both observational and mechanistic, have almost universally ...
Adiabatic air–water two-phase flow in circular microchannels

Abstract Gas–liquid two-phase flow in microchannels with hydraulic diameters of 100–500 μm exhibits drastically different flow behaviors from its counterpart in conventional macroscopic channels. Of particular interests are the two-phase flow patterns and the two-phase frictional pressure drop for given flow conditions in these microchannels. This paper presents an experimental study of the effects of channel size and superficial phasic velocity on the two-phase flow pattern and pressure drop of air–water mixture in circular microchannels with inner diameters of 100, 180 and 324 μm. Two-phase flow patterns were visualized using high-speed photographic technique. Four basic flow patterns, namely, bubbly flow, slug flow, ring flow and annular flow, were observed. The two-phase flow regime maps were constructed and the transition boundaries between different flow regimes identified. In an effort to unify the flow transition boundary in microchannels of different sizes, a new flow map was developed using the modified Weber numbers as the coordinates. The two-phase frictional pressure gradient in the microchannels was measured and the data were compared with predictions from the separated flow model, the homogeneous flow model and the flow pattern-based phenomenological models. Results show that the flow pattern-based models provide the best prediction of the two-phase pressure drop in the microchannels.
Debt relief and public health spending in heavily indebted poor countries

The Heavily Indebted Poor Countries (HIPC) Initiative, which was launched in 1996, is the first comprehensive effort by the international community to reduce the external debt of the world's poorest countries. The Initiative will generate substantial savings relative to current and past public spending on health and education in these countries. Although there is ample scope for raising public health spending in heavily indebted poor countries, it may not be advisable to spend all the savings resulting from HIPC resources for this purpose. Any comprehensive strategy for tackling poverty should also focus on improving the efficiency of public health outlays and on reallocating funds to programmes that are most beneficial to the poor. In order to ensure that debt relief increases poverty-reducing spending and benefits the poor, all such spending, not just that financed by HIPC resources, should be tracked. This requires that countries improve all aspects of their public expenditure management. In the short run, heavily indebted poor countries can take some pragmatic tracking measures based on existing public expenditure management systems, but in the longer run they should adopt a more comprehensive approach so as to strengthen their budget formulation, execution, and reporting systems.
The MD4 Message-Digest Algorithm

The MD4 message digest algorithm takes an input message of arbitrary length and produces an output 128-bit "fingerprint" or "message digest", in such a way that it is (hopefully) computationally infeasible to produce two messages having the same message digest, or to produce any message having a given prespecified target message digest. The MD4 algorithm is thus ideal for digital signature applications: a large file can be securely "compressed" with MD4 before being signed with (say) the RSA public-key cryptosystem.The MD4 algorithm is designed to be quite fast on 32-bit machines. For example, on a SUN Sparc station, MD4 runs at 1,450,000 bytes/second (11.6 Mbit/sec). In addition, the MD4 algorithm does not require any large substitution tables; the algorithm can be coded quite compactly.The MD4 algorithm is being placed in the public domain for review and possible adoption as a standard.
Uniform Uncertainty Principle and Signal Recovery via Regularized Orthogonal Matching Pursuit

This paper seeks to bridge the two major algorithmic approaches to sparse signal recovery from an incomplete set of linear measurements—L1-minimization methods and iterative methods (Matching Pursuits). We find a simple regularized version of Orthogonal Matching Pursuit (ROMP) which has advantages of both approaches: the speed and transparency of OMP and the strong uniform guarantees of L1-minimization. Our algorithm, ROMP, reconstructs a sparse signal in a number of iterations linear in the sparsity, and the reconstruction is exact provided the linear measurements satisfy the uniform uncertainty principle.
Throwing Good Money After Bad? Cash Infusions and Distressed Real Estate

When a leveraged real estate project experience cash-flow problems, the owner must either inject additional cash or default on the mortgage. We show that it is not optimal for the owner to default as soon as net cash flow becomes negative. Surprisingly, the owner can expropriate some of the mortgage lender's wealth by injecting cash and continuing to pay interest. When the owner has cash constraints, outside investors may be able to extract significant economic rents by financing distressed real estate projects. These results have interesting implications for mortgage lending and the pattern of real estate transaction volume.
Beyond the flow decomposition barrier

We introduce a new approach to the maximum flow problem. This approach is based on assigning arc lengths based on the residual flow value and the residual arc capacities. Our approach leads to an O(min(n2/3, m1/2)m log(n2/m) log U) time bound for a network with n vertices, m arcs, and integral arc capacities in the range [1, …, U]. This is a fundamental improvement over the previous time bounds. We also improve bounds for the Gomory-Hu tree problem, the parametric flow problem, and the approximate s-t cut problem.
Commensurability invariants for nonuniform tree lattices

We study nonuniform lattices in the automorphism groupG of a locally finite simplicial treeX. In particular, we are interested in classifying lattices up to commensurability inG. We introduce two new commensurability invariants:quotient growth, which measures the growth of the noncompact quotient of the lattice; andstabilizer growth, which measures the growth of the orders of finite stabilizers in a fundamental domain as a function of distance from a fixed basepoint. WhenX is the biregular treeXm,n, we construct lattices realizing all triples of covolume, quotient growth, and stabilizer growth satisfying some mild conditions. In particular, for each positive real numberν we construct uncountably many noncommensurable lattices with covolumeν.
Ethical Spillovers in Firms: Evidence from Vehicle Emissions Testing

In this paper, we explore how organizations influence the unethical behavior of their employees. Using a unique data set of over three million vehicle emissions tests, we find strong evidence of ethical spillovers from firms to individuals. When inspectors work across different organizations, they adjust the rate at which they pass vehicles to the norms of those with whom they work. These spillovers are strongest at large facilities and corporate chains, and weakest for the large-volume inspectors. These results are consistent with the economics literature on productivity spillovers from organizations and peers and suggest that managers can influence the ethics of employee behavior through both formal norms and incentives. The results also suggest that employees have persistent ethics that limit the magnitude of this influence. These results imply that if ethical conformity is important to the financial and legal health of the organization, managers must be vigilant in their hiring, training, and monitoring to ensure that employee behavior is consistent with firm objectives.
HEAVY TRUCKS, CONSPICUITY TREATMENT, AND THE DECLINE OF COLLISION RISK IN DARKNESS

Abstract Introduction The influence of amendments to Federal Motor Vehicle Safety Standard (FMVSS) 108, requiring conspicuity treatments on heavy tractors and trailers, was determined in analyses of the odds of fatal collisions in darkness. Method Comparisons were made between crashes in which conspicuity treatment was likely relevant, and those in which it was likely irrelevant. Results Over 23 years, the odds that a fatal collision involving a heavy truck occurred in darkness declined by 58% among relevant crashes, while little decline was observed for irrelevant crashes. Disaggregation into crash types revealed the largest declines occurred in fatal rear-end and angle collisions. A parallel analysis of light vehicles also found declines but no differences among crash type. Similar trends were also observed for nonfatal rear end collisions. Conclusion The results suggest that detection failure may have contributed to the risk of striking a tractor-semitrailer in darkness, and that conspicuity treatments have reduced this risk. Impact on Industry Conspicuity treatments appear to reduce risk of collision into heavy trucks in darkness. It is likely that this benefit would also extend to other vehicles that are not included in the FMVSS 108 regulation (e.g., buses, single unit trucks, recreational vehicles), although many are so equipped, regardless of the regulation.
THE OPPORTUNITY COST OF BEING CONSTRAINED BY THE TYPE OF ASSET: BONDS ONLY OR STOCKS ONLY

I explore investors’ welfare losses when they restrict themselves to invest in either stocks only or bonds only, but not in both. The restriction gives investors sub-optimal asset allocations that result in welfare losses. To measure these welfare losses I compare “only stock indices and Treasury bills” optimal portfolios and “only bond indices and Treasury bills” optimal portfolios with “stock and bond indices and Treasury bills” optimal portfolios using the concept of proportionate opportunity cost along with various CRRA utility functions. The original historical asset returns data set is used with a VAR in generating joint returns distributions for the portfolio formation period. I show that for investors with low levels of risk aversion welfare losses do not exceed 1.8% of initial wealth when they invest sub-optimally. For investors with medium and high levels of relative risk aversion, suboptimal portfolios of only one type of assets, stocks only or bonds only, along with Treasury bills, give expected utility about as high as optimal portfolios that include both types of assets, stocks and bonds.
Islet assessment for transplantation.

Purpose of reviewThere is a critical need for meaningful viability and potency assays that characterize islet preparations for release prior to clinical islet cell transplantation. Development, testing, and validation of such assays have been the subject of intense investigation for the last decade.
Almost Decoupling by Quantitative Feedback Theory

This paper uses almost decoupling theory to obtain a systematic solution to the MIMO-QFT problem by an n times solution of the SISO-QFT sensitivity constraint problem. This is similar to the current MIMO-QFT formulation that requires in principle an n times solution for the elements of the closed-loop transfer matrix. The problem is also in a form where direct comparison with H ∞ control is feasible. However, due to the use of unstructured perturbation description, this design route along with all H ∞ based design methods will invariably produce more conservative (higher bandwidth) controllers than classical QFT
Performance of a model cascade thrust reverser for short-haul applications

Aerodynamic and acoustic characteristics are presented for a cowl-mounted, model cascade thrust reverser suitable for short-haul aircraft. Thrust reverser efficiency was determined from isolated fan-driven models under static and forward velocity conditions. Cascade reverser noise characteristics were determined statically in an isolated pipe-flow test, whereas aerodynamic installation effects were determined with a wind-tunnel, fanpowered airplane model. Application of test results to short-haul aircraft calculations demonstrates that such a cascade thrust reverser may be able to meet both the performance and noise requirements for short-haul aircraft operation. However, aircraft installation effects can be quite significant. a/g bc bs C'D CL C'L d dt fc g N Nd N/Nd P PNL PWL
Competitive Stock Markets: Evidence from Companies’ Dual Listings on the NYSE and NASDAQ

In 2004, NASDAQ launched its dual listing program, which allows NYSE-listed companies to list concurrently on NASDAQ. Investigating this innovation and the impact of competitive interaction between the two markets on both order flow and market liquidity, this study found that dual listing is associated with a significant net growth in aggregate trading volume. Moreover, dual listing narrows the bid–ask spreads on both markets. Overall, dual listing appears to lower transaction costs and improve liquidity for traders on both markets.
Topological equivalences for differential graded algebras

We investigate the relationship between differential graded algebras (dgas) and topological ring spectra. Every dga C gives rise to an Eilenberg?Mac Lane ring spectrum denoted HC. If HC and HD are weakly equivalent, then we say C and D are topologically equivalent. Quasi-isomorphic dgas are topologically equivalent, but we produce explicit counterexamples of the converse. We also develop an associated notion of topological Morita equivalence using a homotopical version of tilting.
WIYN OPEN CLUSTER STUDY. XXXIX. ABUNDANCES IN NGC 6253 FROM HYDRA SPECTROSCOPY OF THE Li 6708 Å REGION

High-dispersion spectra of 89 potential members of the old, super-metal-rich open cluster, NGC 6253, have been obtained with the HYDRA multi-object spectrograph. Based upon radial-velocity measurements alone, 47 stars at the turnoff of the cluster color–magnitude diagram (CMD) and 18 giants are identified as potential members. Five turnoff stars exhibit evidence of binarity while proper-motion data eliminate two of the dwarfs as members. The mean cluster radial velocity from probable single-star members is −29.4 ± 1.3 km s −1 (sd). A discussion of the current estimates for the cluster reddening, derived independently of potential issues with the BV cluster photometry, lead to an adopted reddening of E(B − V ) = 0.22 ± 0.04. From equivalent width analyses of 38 probable single-star members near the CMD turnoff, the weighted average abundances are found to be [Fe/H] = +0.43 ± 0.01, [Ni/H] = +0.53 ± 0.02, and [Si/H] = +0.43 0.03 0.04 , where the errors refer to the standard errors of the weighted mean. Weak evidence is found for a possible decline in metallicity with increasing luminosity among stars at the turnoff. We discuss the possibility that our turnoff stars have been affected by microscopic diffusion. For 15 probable single-star members among the giants, spectrum synthesis leads to abundances of +0.46 0.02 0.03 for [Fe/H]. While NGC 6253 is less than half the age of NGC 6791, it is at least as metal-rich and, within the uncertainties, exhibits the same general abundance pattern as that typified by super-metal-rich dwarfs of the galactic bulge.
Regulation and growth

Why some countries grow faster than others is one of the most important questions in economics. Solving this puzzle has the obvious appeal of improving the living standards for a significant proportion of the world population. We go further towards answering this question by studying a major determinant of growth: regulations governing business activity. Our results also have significant implications for policy. They suggest that countries should put priority on reforming their business regulations when designing growth policies. Measures of institutions currently used in the growth literature indicate the extent of problems but not how to resolve them. By contrast the indicators in the Doing Business database are directly linked to specific reforms. For example the procedures to register a business or property can be cut by combining them at a one-stop shop for businesses. Establishing a credit bureau or reducing mandated severance pay for workers will also improve performance on the business regulations index. Our findings imply that identifying and implementing such reforms can accelerate economic growth.
AN ALGORITHM FOR SEARCHING A POLYGONAL REGION WITH A FLASHLIGHT

We present an algorithm for a single pursuer with one flashlight searching for an unpredictable, moving target in a 2D environment. The algorithm decides whether a simple polygon with n edges and m concave regions can be cleared by the pursuer, and if so, constructs a search schedule of length O(m) in time O(m2+mlogn+n). The key ideas in this algorithm include a representation called "visibility obstruction diagram" and its "skeleton": a combinatorial decomposition based on a number of critical visibility events. An implementation is presented along with a computed example.
Are Physician Executive Pay-for-Performance Programs the Future of Physician Leader Compensation in Canada?

This article explores the growing trend of physician executive pay-for-performance plans in the U.S. and Canada and discusses the underlying principles of incentive-based compensation models. Pay-for-performance plans are becoming increasingly popular with boards of many healthcare organizations across the country. They may offer an opportunity for increased accountability in the context of the 2003 Health Accord. Although there is little current evidence to support the notion that incentive-based compensation has long-term implications for quality improvement, their popularity continues to increase.
Universal Lossless Compression With Unknown Alphabets&#8212;The Average Case

Universal compression of patterns of sequences generated by independent and identically distributed (i.i.d.) sources with unknown, possibly large, alphabets is investigated. A pattern is a sequence of indices that contains all consecutive indices in increasing order of first occurrence. If the alphabet of a source that generated a sequence is unknown, the inevitable cost of coding the unknown alphabet symbols can be exploited to create the pattern of the sequence. This pattern can in turn be compressed by itself. It is shown that if the alphabet size k is essentially small, then the average minimax and maximin redundancies as well as the redundancy of every code for almost every source, when compressing a pattern, consist of at least 0.5log(n/k3) bits per each unknown probability parameter, and if all alphabet letters are likely to occur, there exist codes whose redundancy is at most 0.5log(n/k2) bits per each unknown probability parameter, where n is the length of the data sequences. Otherwise, if the alphabet is large, these redundancies are essentially at least Theta(n-2/3 ) bits per symbol, and there exist codes that achieve redundancy of O(n-1/2) bits per symbol. Two suboptimal low-complexity sequential algorithms for compression of patterns are presented and their description lengths analyzed, also pointing out that the pattern average universal description length can decrease below the underlying i.i.d. entropy for large enough alphabets
Determination of the Central Mass in Active Galactic Nuclei Using Cross-Correlation Lags and Velocity Dispersions

We here estimate the mass M of the central object in five active galactic nuclei (AGNs), using the most recent reverberation data obtained by the AGN Watch Consortium. The cross-correlation function (CCF) centroids of the broad Lyα λ1216 and C IV λ1549 lines are used to estimate the size of the broad-line region (BLR) in these sources. We calculate the velocity dispersions of these lines in the root mean square (rms) spectra and then use our results to estimate M. We argue that our technique of calculating the velocity dispersion should work in the general case of an arbitrary line profile, unlike methods that depend on the measurement of the full-width at half-maximum (FWHM) of the broad line. We also show that our results agree with the FWHM method in the limit of a normal (Gaussian) line profile. The masses calculated here are considerably smaller than those calculated with the previous generation of reverberation data.
Quantifying Parameter Errors Due to the Peculiar Velocities of Type Ia Supernovae

The fitting of the observed redshifts and magnitudes of Type Ia supernovae to what we would see in homogeneous cosmological models has led to constraints on cosmological parameters. However, in performing such fits it is assumed that the sampled supernovae are moving with the Hubble flow, or namely that their peculiar velocities are zero. In reality, peculiar velocities will modify supernova data in a way that can impact best-fit cosmological parameters. We theoretically quantify this effect in the nonlinear regime with a Monte Carlo analysis, using data from semianalytical galaxy catalogs built from the Millennium N-body simulation. We find scaling relations for the errors in best-fit parameters resulting solely from peculiar velocities, as a function of the total number of sources in a supernova survey N and its maximum redshift zmax. For low-redshift surveys, we find that these errors can be of the same order of magnitude as the errors due to an intrinsic magnitude scatter of 0.1 mag. For a survey with N = 2000 and zmax = 1.7, we estimate that the expected peculiar velocity-induced errors in the best-fit cosmological constant density and equation of state can be ?? 0.009 and ?w 0.01, respectively, which are subdominant to the errors due to the intrinsic scatter. We further find that throwing away supernova data below a redshift z 0.01-0.02 can reduce the combined error due to peculiar velocities and the intrinsic scatter, but by only about 10%.
A highly robust and versatile finite element-boundary Integral hybrid code for scattering by BOR objects

A hybrid technique is presented that combines the finite element and boundary integral methods for simulating electromagnetic scattering from body-of-revolution (BOR) objects. This technique correctly models the boundary conditions along the axis of revolution in both the finite element and boundary integral formulations and yields highly accurate solutions. Because of the decoupled computations for the finite element and boundary integral equations, the technique is highly efficient as compared to the method of moments, especially for BORs comprising layered or inhomogeneous materials. It is applicable to a variety of complex, large-size BOR objects consisting of perfect conductors, anisotropic impedance surfaces, anisotropic resistive surfaces, and anisotropic inhomogeneous materials.
The basis problem in many-worlds theories

To fully appreciate the significance of the basis problem mentioned by Zurek, and of the impact of quantum decoherence on fundamental issues, one needs to understand certain subtle aspects of the connection between classical and quantum mechanics. This chapter, which is more technical than the others, explains these aspects, and, with the aid of some pictures, their relevance to the basis and decoherence problems.
Probing the topography of kainate recognition sites: Synthesis of a novel oxetane containing kainic acid analogue.

A short synthesis of the conformationally rigidified spirocyclic-kainic acid analogue 2 is described starting from kainic acid. This relatively conservative change in the structure of kainic acid has been found to lead to a loss of affinity for glutamate recognition sites.
Preparation of pyrrole and pyrrolidine derivatives of pyrimidine. 1‐(2‐pyrimidinyl)pyrrole ‐ an inhibitor of X. phaseoli and X. malvacearum

Pyrrole and pyrrolidine derivatives of pyrimidine were prepared in which the nitrogen atom of the pyrrole or pyrrolidine ring is bonded directly to the 2- or 4-carbon atom of the pyrimidine ring. Pyrrole derivatives were prepared by the dry distillation of an intimate mixture of an aminopyrimidine with mucic acid and by the reaction of a chloropyrimidine with potassium pyrrole. Pyrrolidine derivatives were prepared by the reaction of a chloropyrimidine with pyrrolidine and, in a single instance, by the catalytic hydrogenation of a pyrimidinylpyrrole. At a concentration of 200 mcg/mL, 1-(2-pyrimidinyl)pyrrole inhibited two plant pathogenic bacteria — Xanthomanus phaseoli (pathogenic on the bean plant) and Xanthomanus malvacearum (pathogenic on the cotton plant).
Recursive formulation of operational space control

A recently developed spatial operator algebra approach to modeling and analysis of multibody robotic systems is used to develop O(n) recursive algorithms that compute the op erational space mass matrix and the operational space coriolis/centrifugal and gravity terms of an n-link serial manipulator. These algorithms enable an O(n) recursive im plementation of operational space control.
Prediction of Ligand−Receptor Binding Free Energy by 4D-QSAR Analysis: Application to a Set of Glucose Analogue Inhibitors of Glycogen Phosphorylase

A set of 47 glucose analogue inhibitors of glycogen phosphorylase was investigated using 4D-QSAR analysis. A single significant 4D-QSAR model, having no outliers, was found as a function of alignment and conformational sampling. This 4D-QSAR model consists of six grid cell occupancy descriptors which defines the thermodynamic averaged spatial pharmacophore for this set of analogues. The 4D-QSAR model was validated by aligning it upon the crystal structures of glycogen phosphorylase with some bound inhibitors of the training set. Validation of the 4D-QSAR model was realized by establishing the consistency of the types and locations of the grid cell occupancy descriptors relative to the binding interaction sites of the crystal complex. The loss in binding free energy, due to loss in inhibitor conformational entropy upon binding to the enzyme, was computed and found to be in the 0−2 kcal/mol range for these inhibitors. The “active” conformation of each analogue was also postulated from the 4D-QSAR model.
Marginal modeling of multilevel binary data with time‐varying covariates

We propose and compare two approaches for regression analysis of multilevel binary data when clusters are not necessarily nested: a GEE method that relies on a working independence assumption coupled with a three-step method for obtaining empirical standard errors, and a likelihood-based method implemented using Bayesian computational techniques. Implications of time-varying endogenous covariates are addressed. The methods are illustrated using data from the Breast Cancer Surveillance Consortium to estimate mammography accuracy from a repeatedly screened population.
Multiple Testing. Part I. Single-Step Procedures for Control of General Type I Error Rates

The present article proposes general single-step multiple testing procedures for controlling Type I error rates defined as arbitrary parameters of the distribution of the number of Type I errors, such as the generalized family-wise error rate. A key feature of our approach is the test statistics null distribution (rather than data generating null distribution) used to derive cut-offs (i.e., rejection regions) for these test statistics and the resulting adjusted p-values. For general null hypotheses, corresponding to submodels for the data generating distribution, we identify an asymptotic domination condition for a null distribution under which single-step common-quantile and common-cut-off procedures asymptotically control the Type I error rate, for arbitrary data generating distributions, without the need for conditions such as subset pivotality. Inspired by this general characterization of a null distribution, we then propose as an explicit null distribution the asymptotic distribution of the vector of null value shifted and scaled test statistics. In the special case of family-wise error rate (FWER) control, our method yields the single-step minP and maxT procedures, based on minima of unadjusted p-values and maxima of test statistics, respectively, with the important distinction in the choice of null distribution. Single-step procedures based on consistent estimators of the null distribution are shown to also provide asymptotic control of the Type I error rate. A general bootstrap algorithm is supplied to conveniently obtain consistent estimators of the null distribution. The special cases of t- and F-statistics are discussed in detail. The companion articles focus on step-down multiple testing procedures for control of the FWER (van der Laan et al., 2004b) and on augmentations of FWER-controlling methods to control error rates such as tail probabilities for the number of false positives and for the proportion of false positives among the rejected hypotheses (van der Laan et al., 2004a). The proposed bootstrap multiple testing procedures are evaluated by a simulation study and applied to genomic data in the fourth article of the series (Pollard et al., 2004).
The Origins of Democracy in England

This article uses a rational choice model of the origins of democracy to analyze the political history of medieval England from the Norman conquest to the Hundred Years War. Why did a country just ...
Inequality, Technology, and the Social Contract

Abstract The distribution of human capital and income lies at the center of a nexus of forces that shape a country’s economic, institutional and technological structure. I develop here a unified model to analyze these interactions and their growth consequences. Five main issues are addressed. First, I identify the key factors that make both European-style “welfare state” and US-style “laissez-faire” social contracts sustainable; I also compare the growth rates of these two politico-economic steady states, which are not Pareto-rankable. Second, I examine how technological evolutions affect the set of redistributive institutions that can be durably sustained, showing in particular how skill-biased technical change may cause the welfare state to unravel. Third, I model the endogenous determination of technology or organizational form that results from firms’ tailoring the flexibility of their production processes to the distribution of workers’ skills. The greater is human capital heterogeneity, the more flexible and wage-disequalizing is the equilibrium technology. Moreover, firms’ choices tend to generate excessive flexibility, resulting in suboptimal growth or even self-sustaining technology-inequality traps. Fourth, I examine how institutions also shape the course of technology; thus, a world-wide shift in the technology frontier results in different evolutions of production processes and skill premia across countries with different social contracts. Finally, I ask what joint configurations of technology, inequality and redistributive policy are feasible in the long run, when all three are endogenous. I show in particular how the diffusion of technology leads to the “exporting” of inequality across borders; and how this, in turn, generates spillovers between social contracts that make it more difficult for nations to maintain distinct institutions and social structures.