cssi/SciSciGPT-SciSciNet huggingface dataset:
Generalized Dix equation and analytic treatment of normal-moveout velocity for anisotropic media*

Despite the complexity of wave propagation in anisotropic media, reflection moveout on conventional common-midpoint (CMP) spreads is usually well described by the normal-moveout (NMO) velocity defined in the zero-offset limit. In their recent work, Grechka and Tsvankin showed that the azimuthal variation of NMO velocity around a fixed CMP location generally has an elliptical form (i.e. plotting the NMO velocity in each azimuthal direction produces an ellipse) and is determined by the spatial derivatives of the slowness vector evaluated at the CMP location. This formalism is used here to develop exact solutions for the NMO velocity in anisotropic media of arbitrary symmetry. For the model of a single homogeneous layer above a dipping reflector, we obtain an explicit NMO expression valid for all pure modes and any orientation of the CMP line with respect to the reflector strike. The contribution of anisotropy to NMO velocity is contained in the slowness components of the zero-offset ray (along with the derivatives of the vertical slowness with respect to the horizontal slownesses) - quantities that can be found in a straightforward way from the Christoffel equation. If the medium above a dipping reflector is horizontally stratified, the effective NMO velocity is determined through a Dix-type average of the matrices responsible for the 'interval' NMO ellipses in the individual layers. This generalized Dix equation provides an analytic basis for moveout inversion in vertically inhomogeneous, arbitrarily anisotropic media. For models with a throughgoing vertical symmetry plane (i.e. if the dip plane of the reflector coincides with a symmetry plane of the overburden), the semi-axes of the NMO ellipse are found by the more conventional rms averaging of the interval NMO velocities in the dip and strike directions. Modelling of normal moveout in general heterogeneous anisotropic media requires dynamic ray tracing of only one (zero-offset) ray. Remarkably, the expressions for geometrical spreading along the zero-offset ray contain all the components necessary to build the NMO ellipse. This method is orders of magnitude faster than multi-azimuth, multi-offset ray tracing and, therefore, can be used efficiently in traveltime inversion and in devising fast dip-moveout (DMO) processing algorithms for anisotropic media. This technique becomes especially efficient if the model consists of homogeneous layers or blocks separated by smooth interfaces. The high accuracy of our NMO expressions is illustrated by comparison with ray-traced reflection traveltimes in piecewise-homogeneous, azimuthally anisotropic models. We also apply the generalized Dix equation to field data collected over a fractured reservoir and show that P-wave moveout can be used to find the depth-dependent fracture orientation and to evaluate the magnitude of azimuthal anisotropy.
Stereotaxy Reduces Cost of Brain Tumor Resection

Abstract Background Health care professionals are under increasing pressure to contain the cost of health care. Simultaneously, medical technology continues to advance. Medical institutions must therefore consider the costs and benefits before using a new technology. Using a direct costing system, we determined the cost efficacy of stereotaxy applied to the resection of brain mass lesions. Methods Twenty-nine patients underwent a stereotactically guided craniotomy and brain tumor resection. Fifteen of them underwent general and fourteen received local anesthesia. Twelve other patients, comprising a historical reference group, underwent a standard craniotomy and brain tumor resection under general anesthesia. Costs were determined for every hospital charge item in all patients. Cost efficiency was then compared between the two groups. Results Patients treated stereotactically incurred additional costs in frame placement and neuroimaging. These costs were offset by savings in operating room time, patient acuity, length of stay, respiratory care, and medications. Savings were greatest for patients who had local anesthesia. Overall, patients treated by stereotactic craniotomy had a total hospitalization cost of $8,495.19, whereas those treated with standard craniotomy incurred a cost of $11,365.23 ( p Conclusion Stereotaxy is cost effective for the surgical treatment of brain tumors. Accurate estimates of cost can justify the use of medical technology. Directly measured cost data is a useful index for any cost containment program.
Parallel simulation of subsonic fluid dynamics on a cluster of workstations

An effective approach of simulating subsonic fluid dynamics on a cluster of non-dedicated workstations is presented. The approach is applied to simulate the flow of air in wind instruments. The use of local-interaction methods and coarse-grain decompositions lead to small communication requirements. The automatic migration of processes from busy hosts to free hosts enables the use of non-dedicated workstations. Simulations of 2D flow achieve 80% parallel efficiency (speedup/processors) using 20 HP-Apollo workstations. Detailed measurements of the parallel efficiency of 2D and 9D simulations are presented, and a theoretical model of efficiency is developed and compared against the measurements. Two numerical methods of fluid dynamics are tested: explicit finite differences, and the lattice Boltzmann method.
Design of charge-balanced time-optimal stimuli for spiking neuron oscillators

In this letter, we investigate the fundamental limits on how the interspike time of a neuron oscillator can be perturbed by the application of a bounded external control input (a current stimulus) with zero net electric charge accumulation. We use phase models to study the dynamics of neurons and derive charge-balanced controls that achieve the minimum and maximum interspike times for a given bound on the control amplitude. Our derivation is valid for any arbitrary shape of the phase response curve and for any value of the given control amplitude bound. In addition, we characterize the change in the structures of the charge-balanced time-optimal controls with the allowable control amplitude. We demonstrate the applicability of the derived optimal control laws by applying them to mathematically ideal and experimentally observed neuron phase models, including the widely studied Hodgkin-Huxley phase model, and by verifying them with the corresponding original full state-space models. This work addresses a fundamental problem in the field of neural control and provides a theoretical investigation to the optimal control of oscillatory systems.
Optimal insurance with adverse selection

We solve the principal–agent problem of a monopolist insurer selling to an agent whose riskiness (loss chance) is private information, a problem introduced in Stiglitz’s ( 1977) seminal paper. For an arbitrary type distribution, we prove several properties of optimal menus, such as efficiency at the top and downward distortions elsewhere. We show that these results extend beyond the insurance problem we emphasize. We also prove that the principal always prefers an agent facing a larger loss and prefers a poorer one if the agent’s risk aversion decreases with wealth. For the standard case of a continuum of types and a smooth density, we show that, under the mild assumptions of a log-concave density and decreasing absolute risk aversion, the optimal premium is backward-S-shaped in the amount of coverage—first concave, then convex. This curvature result implies that quantity discounts are consistent with adverse selection in insurance, contrary to the
Pihef: Plug-In Hybrid Electric Factor

The potential of plug-in hybrid electric vehicles (PHEVs) to operate in electric and hybrid modes and their ability to supplement the energy storage off the grid have made them a front-runner in alternative fuel vehicle development. However, there is currently no widely accepted standard classification that provides an accurate comparison of PHEVs. This paper presents a novel classification for PHEVs: “Pihef: Plug-In Hybrid Electric Factor.” Pihef is the average ratio of the energy provided by the grid to the sum of the energy provided by the grid and fuel. The viability of Pihef is demonstrated via comprehensive simulations and a sensitivity analysis. In addition, the relationship between Pihef and emissions, efficiency, hybridization, and electric range is developed.
Fooling Functions of Halfspaces under Product Distributions

We construct pseudorandom generators that fool functions of halfspaces (threshold functions) under a very broad class of product distributions. This class includes not only familiar cases such as the uniform distribution on the discrete cube, the uniform distribution on the solid cube, and the multivariate Gaussian distribution, but also includes any product of discrete distributions with probabilities bounded away from 0. Our first main result shows that a recent pseudorandom generator construction of Meka and Zuckerman [MZ09], when suitably modifed, can fool arbitrary functions of d halfspaces under product distributions where each coordinate has bounded fourth moment. To eps-fool any size-s, depth-d decision tree of halfspaces, our pseudorandom generator uses seed length O((d log(ds/eps)+log n) log(ds/eps)). For monotone functions of d halfspaces, the seed length can be improved to O((d log(d/eps)+log n) log(d/eps)). We get better bounds for larger eps; for example, to 1/polylog(n)-fool all monotone functions of (log n)= log log n halfspaces, our generator requires a seed of length just O(log n). Our second main result generalizes the work of Diakonikolas et al. [DGJ+09] to show that bounded independence suffices to fool functions of halfspaces under product distributions. Assuming each coordinate satisfies a certain stronger moment condition, we show that any function computable by a size-s, depth-d decision tree of halfspaces is eps-fooled by O(d^4s^2/eps^2)-wise independence.
Building trust in virtual teams

This paper presents a study of trust development in online courses. It reviews the concept of swift trust and examines changes in faculty roles as professors go online. An exploratory content analysis looks at indicators of the development of swift trust in the highest rated of a large number of online courses studied over a three year period, and contrasts these results with one of the poorest rated online courses. Establishing swift trust at the beginning of an online course appears to be related to subsequent course success. Strategies for trust formation are also suggested.
Role of the defect core in energetics of vacancies

Electronic structure calculations at macroscopic scales are employed to investigate the crucial role of a defect core in the energetics of vacancies in aluminium. We find that vacancy core energy is significantly influenced by the state of deformation at the vacancy core, especially volumetric strains. Insights from the core electronic structure and computed displacement fields show that this dependence on volumetric strains is closely related to the changing nature of the core structure under volumetric deformations. These results are in sharp contrast to mechanics descriptions based on elastic interactions that often consider defect core energies as an inconsequential constant. Calculations suggest that the variation in core energies with changing macroscopic deformations is quantitatively more significant than the corresponding variation in relaxation energies associated with elastic fields. Upon studying the influence of various macroscopic deformations, which include volumetric, uniaxial, biaxial and shear deformations, on the formation energies of vacancies, we show that volumetric deformations play a dominant role in governing the energetics of these defects. Further, by plotting formation energies of vacancies and di-vacancies against the volumetric strain corresponding to any macroscopic deformation, we find that all variations in the formation energies collapse on to a universal curve. This suggests a universal role of volumetric strains in the energetics of vacancies. Implications of these results in the context of dynamic failure in metals through shock-induced spalling are analysed.
Exhaustive simulation need not require an exponential number of tests

Simulation is today the most common form of verification. One disadvantage of simulation is the excessive number of tests needed for complete coverage. However, as will be shown, the number of tests may be substantially reduced if test case generation is combined with a structural analysis. The resulting set of test cases for exhaustive simulation may be smaller than exponential, which might make exhaustive simulation feasible. Even if the set of test cases is still too large, choosing tests from this reduced set results in better coverage than otherwise. >
Sterile neutrino search with kaon decay at rest

Monoenergetic muon neutrinos (235.5 MeV) from positive kaon decay at rest are considered as a source for an electron neutrino appearance search. In combination with a liquid argon time projection chamber based detector, such a source could provide discovery-level sensitivity to the neutrino oscillation parameter space ($\ensuremath{\Delta}{m}^{2}\ensuremath{\sim}1\text{ }\text{ }{\mathrm{eV}}^{2}$) indicative of a sterile neutrino. Current and future intense $\ensuremath{\gtrsim}3\text{ }\text{ }\mathrm{GeV}$ kinetic energy proton facilities around the world can be employed for this experimental concept.
Characteristics of Internal Waves in the South China Sea Observed by a Shipboard Coherent Radar

In 2005 and 2007, a coherent X-band radar was deployed in the South China Sea on two different ships. In both cases, the two parabolic antennas of the radar were fixed at grazing angles of approximately 2° looking toward the bow of the ship. The radar transmitted and received through a single antenna but alternated between the two antennas approximately every half second. One antenna was horizontally polarized and the other was vertically polarized. The data were analyzed by computing normalized radar cross sections and scatterer velocities as a function of ground range and time. Surface signatures of internal waves were obvious in both types of image and at both polarizations as regions of enhanced cross sections or scatterer velocities. The collected imagery showed that at least two different types of internal waves exist in the South China Sea: small, nearly sinusoidal trains of waves and large soliton-like waves. These different types traveled at very different speeds and interacted with each other. The small nearly sinusoidal waves traveled at phase speeds near 1 m/s that appeared to increase as the small wave trains were overtaken by the faster solitons. Combined with other shipboard measurements, the radar measurements yielded the widths, maximum velocities, and strain rates of the solitons as well as the dependence of phase speed on amplitude. When the speeds of both the ship and the solitons were removed, the measurements showed that soliton full-widths at half-maximum ranged from about 0.5-4.5 km. These widths showed a dependence on the amplitude of the soliton. The phase speeds of the solitons also depended on their amplitude, reaching 3 m/s in deep water but only about 1.2 m/s in shallow water. CTD profiles were used to estimate an interface depth for a two-layer fluid model of the propagation of the solitons. The phase speeds predicted by this model agreed well with the observed dependence of the soliton phase speed on amplitude in both shallow and deep water.
Experimental determination of the key heat transfer mechanisms in pharmaceutical freeze-drying

ABSTRACT: The study is aimed at quantifying the relative contribution of key heat transfer modes in lyophilization. Measurements of vial heat transfer rates in a laboratory-scale freeze-dryer were performed using pure water, which was partially sublimed under various conditions. The separation distance between the shelf and the vial was systematically varied, and sublimation rates were determined gravimetrically. The heat transfer rates were observed to be independent of separation distance between the vial and the shelf and linearly dependent on pressure in the free molecular flow limit, realized at low pressures ( 120 mTorr), heat transfer rates were independent of pressure and inversely proportional to separation distance. Previous heat transfer studies in conventional freeze-drying cycles have attributed a dominant portion of the total heat transfer to radiation, the rest to conduction, whereas convection has been found to be insignificant. Although the measurements reported here confirm the significance of the radiative and gas conduction components, the convective component has been found to be comparable to the gas conduction contribution at pressures greater than 100 mTorr. The current investigation supports the conclusion that the convective component of the heat transfer cannot be ignored in typical laboratory-scale freeze-drying conditions.
Parameterized micro-benchmarking: an auto-tuning approach for complex applications

Auto-tuning has emerged as an important practical method for creating highly optimized implementations of key computational kernels and applications. However, the growing complexity of architectures and applications is creating new challenges for auto-tuning. Complex applications can involve a prohibitively large search space that precludes empirical auto-tuning. Similarly, architectures are getting more complicated, making it hard to model performance.In this paper, we focus on the challenge to auto-tuning presented by applications with a large number of kernels and kernel instantiations. While these kernels may share a somewhat similar pattern, they differ considerably in problem sizes and the exact computation performed. We propose and evaluate a new approach to auto-tuning which we refer to as parameterized micro-benchmarking. It is an alternative to the two existing classes of approaches to auto-tuning: analytical model-based and empirical search-based. Particularly, we argue that the former may not be able to capture all the architectural features that impact performance, whereas the latter might be too expensive for an application that has several different kernels. In our approach, different expressions in the application, different possible implementations of each expression, and the key architectural features, are used to derive a simple micro-benchmark and a small parameter space. We have evaluated our approach in the context of GPU implementations of tensor contraction expressions.
Turnaround: Retrenchment and recovery

Empirical research was conducted to investigate retrenchment as an integral component of the overall turnaround process. An industry study provided an anchored operational definition of a turnaround situation, indications of its internal and external causes, and an application of an absolute measure of its severity. The research further produced an empirical discrimination between retrenchment as a stand-alone response to financial decline and retrenchment as an initial phase of a turnaround strategy, and an identification of activities that can be used to classify entrepreneurial vs. efficiency emphases in a turnaround firm's recovery response.
Effect of ambipolar plasma flow on the penetration of resonant magnetic perturbations in a quasi-axisymmetric stellarator

A reference equilibrium for the US National Compact Stellarator Experiment is predicted to be sufficiently close to quasi-symmetry to allow the plasma to flow in the toroidal direction with little viscous damping, yet to have sufficiently large deviations from quasi-symmetry that nonambipolarity significantly affects the physics of the shielding of resonant magnetic perturbations by plasma flow. The unperturbed velocity profile is modified by the presence of an ambipolar potential, which produces a broad velocity profile. In the presence of a resonant magnetic field perturbation, nonambipolar transport produces a radial current, and the resulting j × B force resists departures from the ambipolar velocity and enhances the shielding.
Ear-Slicing and Quality Triangulation

Most algorithms for polygon triangulation do not consider the quality of generated triangles. Such algorithms tend to generate low-quality mesh characterized by a large number of thin triangles. We present an approach for modifying the ear-cutting triangulation algorithm so that resulting mesh contains higher proportion of quality triangles. We also propose additional method of polygon decomposition that supports higher quality triangulation.
Improving the validity of activity of daily living dependency risk assessment.

Objectives:Efforts to prevent activity of daily living (ADL) dependency may be improved through models that assess older adults’ dependency risk. We evaluated whether cognition and gait speed measures improve the predictive validity of interview-based models.Method:Participants were 8,095 self-respondents in the 2006 Health and Retirement Survey who were aged 65 years or over and independent in five ADLs. Incident ADL dependency was determined from the 2008 interview. Models were developed using random 2/3rd cohorts and validated in the remaining 1/3rd.Results:Compared to a c-statistic of 0.79 in the best interview model, the model including cognitive measures had c-statistics of 0.82 and 0.80 while the best fitting gait speed model had c-statistics of 0.83 and 0.79 in the development and validation cohorts, respectively.Conclusion:Two relatively brief models, one that requires an in-person assessment and one that does not, had excellent validity for predicting incident ADL dependency but did not signific...
New and Current Evidence on Determinants of Aggregate Federal Personal Income Tax Evasion in the United States

Using the most current data available, this study seeks to identify any new as well as traditional determinants of personal income tax evasion. A variety of empirical estimates find that income tax rates, the IRS audit rate and IRS penalty interest rates, and the unemployment rate all influence tax evasion. In addition, rarely inves- tigated variables including the tax-free interest rate, the public's job approval rating of the president, and the public's dissatisfaction with government, along with previously unstudied variables, namely, the real interest rate yield on Moody's Baa-rated long-term corporate bonds and the real interest rate yield on three-year Treasury notes, also affect income tax evasion.
Specific Impulse Prediction of Solid-Propellant Motors

The methods for the theoretical prediction of delivered specific impulse are relatively well known. They involve computing the losses due to two-phase flow, divergence, boundary layer, kinetics, nozzle submergence, and combustion inefficiency. The largest computed loss in typical aluminized solid propellants is the two-phase flow loss; this computation also has the largest uncertainty because the particle size and distribution are not precisely known. In this paper, a correlation of mean particle diameter vs throat diameter from experimental data was used with the solid-rocket performance prediction program to predict the propellant specific impulse of a number of motors. These predictions are compared to the experimental values. The results indicate that the specific impulse efficiency appears to be an inherent property of the propellant. In addition, the experimental specific impulse and specific impulse efficiency were statistically correlated against motor and propellant variables. These correlations are as accurate as the longer, more expensive, theoretical analysis. In addition to specific impulse prediction, the correlation equations are useful in optimization of motor designs.
What Moves the Mortgage-Backed Securities Market?

Using a vector autoregressive model with monthly data from 1988 through 2001, this study investigates the factors that drive the excess returns on a widely followed mortgage-backed securities (MBS) index. We find that eight important economic variables (industrial productions, new home sales, bond horizon premium, bond quality premium, mortgage rate, refinancing proxy, general stock market index and world bond market index) appear to move the excess returns on MBS. Impulse response analysis and variance decomposition further indicate a strong dynamic relationship between MBS excess returns and changes in these economic variables. Additional analysis of Freddie Mac and Fannie Mae MBS also indicates that the risk of the MBS guarantor is an important determinant of the MBS return dynamics after the creation of the Office of Federal Housing Enterprise Oversight.
Penalized Likelihood Methods for Estimation of Sparse High Dimensional Directed Acyclic Graphs

Directed acyclic graphs are commonly used to represent causal relationships among random variables in graphical models. Applications of these models arise in the study of physical and biological systems where directed edges between nodes represent the influence of components of the system on each other. Estimation of directed graphs from observational data is computationally NP-hard. In addition, directed graphs with the same structure may be indistinguishable based on observations alone. When the nodes exhibit a natural ordering, the problem of estimating directed graphs reduces to the problem of estimating the structure of the network. In this paper, we propose an efficient penalized likelihood method for estimation of the adjacency matrix of directed acyclic graphs, when variables inherit a natural ordering. We study variable selection consistency of lasso and adaptive lasso penalties in high-dimensional sparse settings, and propose an error-based choice for selecting the tuning parameter. We show that although the lasso is only variable selection consistent under stringent conditions, the adaptive lasso can consistently estimate the true graph under the usual regularity assumptions.
In vivo estimation of myocardial infarct size and left ventricular function by prospectively gated computerized transmission tomography.

SUMMARY We evaluated 11 dogs using computerized transmission tomography (CTT); eight were studied after coronary occlusion and three served as sham controls. Ungated scans (1 cm deep) of the left ventricle (LV) were obtained from LV apex to base to determine infarct size (IS). At the middle LV level, prospectively gated scans were obtained to determine LV function. In all infarct dogs, contrast medium enhancement of the entire infarct or the periphery of the infarct occurred. Autopsy IS was compared with the IS by CTT using either the inner (IM) or outer margin (OM) of the contrast-enhanced periphery of the infarcts as the border of the infarct. IS by both CTT techniques correlated well with autopsy IS (r = 0.89 for IM; r = 0.93 for OM). The estimate using OM (26.5 + 12 g) gave IS sizes similar to autopsy values (25.5 + 11.7 g), but IS derived using IM (14.1 8.0 g) underestimated autopsy values by approximately 45% (p < 0.01). From the prospectively gated CTT images, we calculated mid-LV end-diastolic (EDA) and endsystolic areas (ESA) as well as percent area change before and after coronary occlusion. EDA increased from 17.0 + 5.3 cm2 to 23.7 + 7.6 cm2 (p < 0.05). ESA increased from 12.1 + 4.1 cm2 to 18.6 7.2 cm2 (p < 0.05), and percent area change decreased from 29.3 5.0% to 21.7 9.9% (p < 0.05). We conclude that CTT imaging can reliably estimate IS, particularly when the area of rim enhancement of the infarct is included within the presumed infarct region. Estimates of chamber function can be made from gated CTT scans. Anterior myocardial infarctions produce left ventricular dilatation with reduced chamber function, which can be detected by gated CTT scans.
First-principles Study of Electronic and Dielectric Properties of ZrO2 and HfO2

Using density-functional theory with ultrasoft pseudopotentials, we previously investigated the structural and electronic properties of the low-pressure (cubic, tetragonal, and monoclinic) phases of ZrO2 and HfO2, in order to elucidate phonon modes, Born effective charge tensors, and especially the lattice dielectric response in these phases. We now extend this previous work by carrying out similar calculations on the two high-pressure orthorhombic phases, and by providing density-of-states and band-gap information on all polymorphs. Our results show that the electronic structures and dielectric responses are strongly phase-dependent. In particular, the monoclinic phases of ZrO2 and HfO2 are found to have a strongly anisotropic dielectric tensor and a rather small orientational average () compared to the two other low-pressure phases. Our calculations show that is even smaller in the orthorhombic phases.
Instrumentation for interstellar exploration

The time has arrived for designing, building, and instrumenting a spacecraft for a dedicated foray into the galactic environment surrounding our star, the sun. This region was probed in the past by remote techniques and it will be explored in situ by the NASA’s planned Interstellar Probe mission. The mission will significantly advance our understanding of the nature of the local interstellar medium and explore the distant frontier of the solar system by revealing the details of the interaction between the sun and the Galaxy. This mission will also be an important practical step toward interstellar flight of the future. Reaching interstellar space in reasonable time requires high escape velocities and will likely be enabled by non-chemical propulsion such as nuclear-powered electric propulsion or solar sailing. Unusually high spacecraft velocities, enormous distances from the Sun, and non-chemical propulsion will significantly influence design of the mission, spacecraft, and scientific instrumentation. We will review measurement objectives of the first dedicated mission into interstellar space and outline constraints on the instrumentation. Measurement of particles, fields, and dust in the interstellar medium will be complemented by search for complex organic molecules and remote sensing capabilities in various spectral bands. A ‘‘look’’ back at our solar system will also be a glimpse of what a truly-interstellar mission of the distant future would encounter in approaching a target star. The instrumentation for interstellar exploration presents numerous challenges. Mass, telemetry, and power constraints would place a premium on miniaturization and autonomy. There are, however, physical limits on how small the sensors could be. New instrument concepts may be required to achieve the desired measurement capabilities under the stringent constraints of a realistic interstellar mission.
Conducting R&D in Countries with Weak Intellectual Property Rights Protection

Multinational enterprises (MNEs) are increasingly conducting research and development (RD MNEs that possess alternative mechanisms for protecting their intellectual properties will therefore find it attractive to conduct R&D at those locations. A theoretical framework is developed to capture the interaction between firm strategy and the institutional environment. The empirical analysis on a sample of 1,567 U.S.-headquartered innovating firms finds results consistent with the hypotheses that (i) technologies developed in countries with weak IPR protection are used more internally, and (ii) technologies developed by firms with R&D in weak IPR countries show stronger internal linkages. The results suggest that firms may use internal organizations to substitute for inadequate external institutions. By doing so, they are able to take advantage of the arbitrage opportunities presented by the institutional gap across countries.
How far are we from the quantum theory of gravity

I give a pedagogical explanation of what it is about quantization that makes general relativity go from being a nearly perfect classical theory to a very problematic quantum one. I also explain why some quantization of gravity is unavoidable, why quantum field theories have divergences, why the divergences of quantum general relativity are worse than those of the other forces, what physicists think this means and what they might do with a consistent theory of quantum gravity if they had one. Finally, I discuss the quantum gravitational data that have recently become available from cosmology.
Prevention/promotion in America: still spitting on the sidewalk.

Using a metaphor from disease prevention and health promotion efforts from the early 1990s, prevention and promotion efforts of the late 1900s are examined. Primary analyses are made on societal failures to grapple effectively with the major health problems associated with smoking, motor vehicles, and guns. Critical examples are described where American society and decision-makers lack commitment to prevention and promotion ideals and, in these and other situations, have actively encouraged the growth of health problems. The conclusion is drawn that the American society has acquiesced to let the major killers and disablers of children and adults to continue unabated. A stronger commitment to promotion and prevention is encouraged. Language: en
Electrically tunable surface-to-bulk coherent coupling in topological insulator thin films

We study coherent electronic transport in charge-density-tunable microdevices patterned from thin films of the topological insulator (TI) Bi${}_{2}$Se${}_{3}$. The devices exhibit pronounced electric field effect, including ambipolar modulation of the resistance with an on-and-off ratio of 500%. We show that the weak antilocalization correction to conductance is sensitive to the number of coherently coupled channels, which in a TI includes the top and bottom surfaces and the bulk carriers. These are separated into coherently independent channels by the application of gate voltage and at elevated temperatures. Our results are consistent with a model where channel separation is determined by a competition between the phase coherence time and the surface-to-bulk scattering time.
Coherent water transport across the South Atlantic

The role of mesoscale eddies in transporting Agulhas leakage is investigated using a recent technique from nonlinear dynamical systems theory applied on geostrophic currents inferred from the over two decade long satellite altimetry record. Eddies are found to acquire material coherence away from the Agulhas retroflection, near the Walvis Ridge in the South Atlantic. Yearly, one to four coherent material eddies are detected with diameters ranging from 40 to 280 km. A total of 23 eddy cores of about 50 km in diameter and with at least 30% of their contents traceable into the Indian Ocean were found to travel across the subtropical gyre with minor filamentation. Only one eddy core was found to pour its contents on the North Brazil Current. While the ability of eddies to carry Agulhas leakage northwestward across the South Atlantic is supported by our analysis, this is more restricted than suggested by earlier ring transport assessments.
Delta-Decidability over the Reals

Given any collection F of computable functions over the reals, we show that there exists an algorithm that, given any sentence A containing only bounded quantifiers and functions in F, and any positive rational number delta, decides either "A is true", or "a delta-strengthening of A is false". Moreover, if F can be computed in complexity class C, then under mild assumptions, this "delta-decision problem" for bounded Sigma_k-sentences resides in Sigma_k(C). The results stand in sharp contrast to the well-known undecidability of the general first-order theories with these functions, and serve as a theoretical basis for the use of numerical methods in decision procedures for formulas over the reals.
Performance Analysis of CDMA Signature Optimization with Finite Rate Feedback

We analyze the performance of CDMA signature optimization with finite rate feedback. For a particular user, the receiver selects a signature vector from a signature codebook to avoid the interference from other users, and feeds the corresponding index back to this user through a finite rate and error-free feedback link. We assume the codebook is randomly constructed where the entries are independent and isotropically distributed. It has been shown that the randomly constructed codebook is asymptotically optimal. In this paper, we consider two types of signature selection criteria. One is to select the signature vector that minimizes the interference from other users. The other one is to select the signature vector to match the weakest interference directions. By letting the processing gain, number of users and feedback bits approach infinity with fixed ratios, we derive the exact asymptotic formulas to calculate the average interference for both criteria. Our simulations demonstrate the theoretical formulas. The analysis can be extended to evaluate the signal-to-interference plus noise ratio performance for both match filter and linear minimum mean-square error receivers.
Development of Tailored Films and Surfaces for Use in Advanced Chemical Sensors

The microstructure found at the surfaces and interfaces of active sensing materials can strongly affect the performance of solid state chemical sensors. This paper desribes research efforts aimed at improving oxide semiconductor-based gas sensors which utilize changes in conductance and diode current-voltage measurements as detection schemes. Studies of oxide surface modification and the formation of Pd/SnO 2 (110) and Pd/TiO 2 (110) interfaces are discussed as are the electrical changes for these systems induced by H 2 or O 2 adsorption. The fabrication of heteroepitaxial SnO 2 films for use in planar sensing arrays is also reported and the expected advantages of these highly-ordered, uniform films for simplifying the transducing process are described.
Effect of interface style in peer review comments for UML designs

This paper presents our evaluation of using a Tablet-PC to provide peer-review comments in the first year Computer Science course. Our exploration consisted of an evaluation of how students write comments on other students' assignments using three different methods: pen and paper, a Tablet-PC, and a desktop computer. Our ultimate goal is to explore the effect that interface style (Tablet vs. Desktop) has on the quality and quantity of the comments provided.
A SEARCH FOR MULTIPLE EQUILIBRIA IN URBAN INDUSTRIAL STRUCTURE

Theories featuring multiple equilibria are widespread across economics. Yet little empirical work has asked if multiple equilibria are features of real economies. We examine this in the context of the Allied bombing of Japanese cities and industries in World War II. We develop a new empirical test for multiple equilibria and apply it to data for 114 Japanese cities in eight manufacturing industries. The data provide no support for the existence of multiple equilibria. In the aftermath even of immense shocks, a city typically recovers not only its population and its share of aggregate manufacturing, but even the industries it had before.
Constraint qualifications and optimality conditions for nonconvex semi-infinite and infinite programs

The paper concerns the study of new classes of nonlinear and nonconvex optimization problems of the so-called infinite programming that are generally defined on infinite-dimensional spaces of decision variables and contain infinitely many of equality and inequality constraints with arbitrary (may not be compact) index sets. These problems reduce to semi-infinite programs in the case of finite-dimensional spaces of decision variables. We extend the classical Mangasarian–Fromovitz and Farkas–Minkowski constraint qualifications to such infinite and semi-infinite programs. The new qualification conditions are used for exact calculations of the appropriate normal cones to sets of feasible solutions for these programs by employing advanced tools of variational analysis and generalized differentiation. In the further development we derive first-order necessary optimality conditions for infinite and semi-infinite programs, which are new in both finite-dimensional and infinite-dimensional settings.
An analysis of bundle pricing in horizontal and vertical markets: The case of the U.S. cottonseed market

The U.S. cottonseed market has seen the rapid development and adoption of seeds with differing bundles of genetically modified (GM) traits. It has also seen an increase in vertical integration by biotechnology firms. In this article, we investigate the price impacts associated with structural changes in the U.S. cottonseed market from 2002 to 2007. We develop a structural model to examine the substitution/complementarity relationships among cottonseeds sold with different genetic trait bundles and under different vertical arrangements. We examine the price impacts emanating from product differentiation, market concentration, and market size. The econometric investigation finds evidence of subadditive bundle pricing in patented biotech traits. While higher own-market concentrations are found to be associated with higher prices, we also uncover evidence of cross-product complementarity effects that lead to lower prices. Simulations are used to evaluate net price effects, illustrating the usefulness o ft he approach in the analysis of changing market structures.
Potential-based shaping and Q-value initialization are equivalent

Shaping has proven to be a powerful but precarious means of improving reinforcement learning performance. Ng, Harada, and Russell (1999) proposed the potential-based shaping algorithm for adding shaping rewards in a way that guarantees the learner will learn optimal behavior. In this note, we prove certain similarities between this shaping algorithm and the initialization step required for several reinforcement learning algorithms. More specifically, we prove that a reinforcement learner with initial Q-values based on the shaping algorithm's potential function make the same updates throughout learning as a learner receiving potential-based shaping rewards. We further prove that under a broad category of policies, the behavior of these two learners are indistinguishable. The comparison provides intuition on the theoretical properties of the shaping algorithm as well as a suggestion for a simpler method for capturing the algorithm's benefit. In addition, the equivalence raises previously unaddressed issues concerning the efficiency of learning with potential-based shaping.
On the a priori information in sequential estimation problems

In this paper, the effect of errors in the a priori information is studied when the sequential estimations are carried out on the states of linear systems disturbed by white noise. Four theorems are derived to describe the mutual relations among the three covariance matrices, namely the optimum, calculated, and actual covariance matrices, where the last two are based on the incorrect a priori information. By finding the upper bound for the variance of the actual estimate, performance of the Kalman filter is prescribed and the knowledge is utilized for design of the combined system of analog and digital filters. A phase-locked loop receiver is used as an example of analog filter and the considerable improvement on the estimation process is deduced by the theory and it is confirmed by the experimental simulation on the digital computer.
Forced transnationalism: transnational coping strategies and gendered stigma among Jamaican deportees

Once forcibly returned to their countries of citizenship, how and why do deportees engage in transnational relationships? Through analyses of 37 interviews with Jamaican deportees, I approach the question of why deportees engage in transnational practices and reveal that deportees use transnational ties as coping strategies to deal with financial and emotional hardship. This reliance on transnational ties, however, has two consequences: (1) male deportees who rely on transnational strategies to survive face a gendered stigma because they must relinquish the provider role and become dependants; and (2) the transnational coping strategies serve as a reminder of the shame, isolation and alienation that deportees experience because of their deportation. This consideration of the consequences of transnational relationships sheds light on why some migrants are transnational and others are not.
Mixing of asymmetric logarithmic suspension flows over interval exchange transformations

We consider suspension flows built over interval exchange transformations with the help of roof functions having an asymmetric logarithmic singularity. We prove that such flows are strongly mixing for a full measure set of interval exchange transformations.
RESEARCH PRIZES: A MECHANISM TO REWARD INNOVATION IN AFRICAN AGRICULTURE

This paper identifies market failures that limit agricultural R&D for Africa and other resource-poor environments, and proposes a mechanism to help circumvent them with cash prizes for the dissemination of successful innovations. The proposed prize institution would use ex-post experiments and farm surveys to document the value of innovations after their initial diffusion, to avoid pre-specification of technologies. Prizes would be offered in proportion to estimated social benefits, and would buy innovations into the public domain so that innovators with marketable technologies would choose not to apply for prizes. A governance structure to ensure credibility and financial sustainability is proposed.
Reference-Dependent Preferences and Labor Supply: The Case of New York City Taxi Drivers

I develop a model of daily labor supply where preferences are dependent on a reference daily income level, and I apply this model to data on the labor supply of New York City taxi drivers. I find that there may be a reference level of income on a given day that affects labor supply. However, there is substantial day-to-day variation in a given driver's reference level, and most shifts end before reaching the reference income level. This pattern is inconsistent with an important role for reference-dependent preferences.
Estimation of mobile speed and average received power in wireless systems using best basis methods

A new method is presented for estimating the mobile speed and the average received power in general wireless propagation environments. The locally stationary received signal is expanded in a local exponential basis using best basis methods of wavelet analysis. An estimate of the time-varying Doppler power spectrum is obtained together with an estimate of the maximum Doppler frequency, which is proportional to the mobile speed. The average received power is then estimated by integrating the time-varying spectrum. Simulations demonstrate good tracking of variable mobile speed and average received power for a wide range of angular distributions of incident power. The estimator is shown to perform significantly better than an adaptive averaging method described in the literature. The speed and average power estimates are also used to detect the corner effect in urban cellular systems to improve handoff performance and reduce the call dropping rate.