cssi/SciSciGPT-SciSciNet huggingface dataset:
Emulating cellular automata in chemical reaction---diffusion networks

Chemical reactions and diffusion can produce a wide variety of static or transient spatial patterns in the concentrations of chemical species. Little is known, however, about what dynamical patterns of concentrations can be reliably programmed into such reaction---diffusion systems. Here we show that given simple, periodic inputs, chemical reactions and diffusion can reliably emulate the dynamics of a deterministic cellular automaton, and can therefore be programmed to produce a wide range of complex, discrete dynamics. We describe a modular reaction---diffusion program that orchestrates each of the fundamental operations of a cellular automaton: storage of cell state, communication between neighboring cells, and calculation of cells' subsequent states. Starting from a pattern that encodes an automaton's initial state, the concentration of a "state" species evolves in space and time according to the automaton's specified rules. To show that the reaction---diffusion program we describe produces the target dynamics, we simulate the reaction---diffusion network for two simple one-dimensional cellular automata using coupled partial differential equations. Reaction---diffusion based cellular automata could potentially be built in vitro using networks of DNA molecules that interact via branch migration processes and could in principle perform universal computation, storing their state as a pattern of molecular concentrations, or deliver spatiotemporal instructions encoded in concentrations to direct the behavior of intelligent materials.
Correlated Random Measures

ABSTRACTWe develop correlated random measures, random measures where the atom weights can exhibit a flexible pattern of dependence, and use them to develop powerful hierarchical Bayesian nonparametric models. Hierarchical Bayesian nonparametric models are usually built from completely random measures, a Poisson-process-based construction in which the atom weights are independent. Completely random measures imply strong independence assumptions in the corresponding hierarchical model, and these assumptions are often misplaced in real-world settings. Correlated random measures address this limitation. They model correlation within the measure by using a Gaussian process in concert with the Poisson process. With correlated random measures, for example, we can develop a latent feature model for which we can infer both the properties of the latent features and their dependency pattern. We develop several other examples as well. We study a correlated random measure model of pairwise count data. We derive an eff...
Empirical Strategies in Labor Economics

Abstract This chapter provides an overview of the methodological and practical issues that arise when estimating causal relationships that are of interest to labor economists. The subject matter includes identification, data collection, and measurement problems. Four identification strategies are discussed, and five empirical examples – the effects of schooling, unions, immigration, military service, and class size – illustrate the methodological points. In discussing each example, we adopt an experimentalist perspective that emphasizes the distinction between variables that have causal effects, control variables, and outcome variables. The chapter also discusses secondary datasets, primary data collection strategies, and administrative data. The section on measurement issues focuses on recent empirical examples, presents a summary of empirical findings on the reliability of key labor market data, and briefly reviews the role of survey sampling weights and the allocation of missing values in empirical research. © 1999 Elsevier Science B.V. All rights reserved.
Computation of the Information Matrix for the Models of Spatial Interactions

I provide algebraic and computational considerations to alleviate the burden of computing the information matrix for models of spatial interaction. Of prime importance, I compute the information matrix without storing an inverse of the spatial differencing operator, a large sparse matrix. To accomplish this efficiently, I developed a version of the conjugate gradient method for the case of sparse matrices and vectors. Performance is demonstrated for various data sets and major types of models of spatial interaction. Its advantages include modest computing resource requirements, suitability for multiprocessing environments, and easily controlled precision. Convergence is guaranteed for all feasible values of the maximum likelihood estimates with the rate of convergence depending on the coefficient of spatial correlation. The efficiency of the proposed method allows complete maximum likelihood estimation of models with very large spatial data sets (one million observations or more).
Duadic Group Algebra Codes

Duadic group algebra codes are a generalization of quadratic residue codes. This paper addresses an open problem raised by Zhu concerning the existence of duadic group algebra codes. These codes can be used to construct degenerate quantum stabilizer codes that have the nice feature that many errors of small weight do not need error correction.
Large Negative Thermal Expansion and Anomalous Behavior on Compression in Cubic ReO3-Type AIIBIVF6: CaZrF6 and CaHfF6

CaZrF6 and CaHfF6 display much stronger negative thermal expansion (NTE) (αL100 K ∼ −18 and −22 ppm·K–1, respectively) than ZrW2O8 and other corner-shared framework structures. Their NTE is comparable to that reported for framework solids containing multiatom bridges, such as metal cyanides and metal–organic frameworks. However, they are formable as ceramics, transparent over a wide wavelength range and can be handled in air; these characteristics can be beneficial for applications. The NTE of CaZrF6 is strongly temperature-dependent, and first-principles calculations show that it is largely driven by vibrational modes below ∼150 cm–1. CaZrF6 is elastically soft with a bulk modulus (K300K) of 37 GPa and, upon compression, starts to disorder at ∼400 MPa. The strong NTE of CaZrF6, which remains cubic to <10 K, contrasts with cubic CoZrF6, which only displays modest NTE above its rhombohedral to cubic phase transition at ∼270 K. CaZrF6 and CaHfF6 belong to a large and compositionally diverse family of materi...
Bounded Verification of Voting Software

We present a case-study in which vote-tallying software is analyzed using a bounded verificationtechnique, whereby all executions of a procedure are exhaustively examined within a finite space given by a bound on the size of the heap and the number of loop unrollings. The technique involves an encoding of the procedure in an intermediate relational programming language, a translation of that language to relational logic, and an analysis of the logic that exploits recent advances in finite model-finding. Our technique yields concrete counterexamples --- traces of the procedure that violate the specification. The vote-tallying software, used for public elections in the Netherlands, had previously been annotated with specifications in the Java Modeling Language and analyzed with ESC/Java2. Our analysis found counterexamples to the JML contracts, indicating bugs in the code and errors in the specifications that evaded prior analysis.
Formal Groups, Elliptic Curves, and Some Theorems of Couveignes

The formal group law of an elliptic curve has seen recent applications to computational algebraic geometry in the work of Couveignes to compute the order of an elliptic curve over finite fields of small characteristic ([2], [6]). The purpose of this paper is to explain in an elementary way how to associate a formal group law to an elliptic curve and to expand on some theorems of Couveignes. In addition, the paper serves as background for [1]. We treat curves defined over arbitrary fields, including fields of characteristic two or three. The author wishes to thank Al Laing for a careful reading of an earlier version of the manuscript and for many useful suggestions.
The reinforcing effects of ethanol within the posterior ventral tegmental area depend on dopamine neurotransmission to forebrain cortico-limbic systems.

Ethanol can be self-infused directly into the posterior ventral tegmental area (pVTA) and these effects involve activation of local dopamine neurons. However, the neuro-circuitry beyond the pVTA involved in these reinforcing effects has not been explored. Intra-pVTA microinjection of ethanol increases dopamine release in the nucleus accumbens (NAC), medial prefrontal cortex (mPFC) and ventral pallidum (VP). The present study tested the hypothesis that the reinforcing effects of ethanol within the pVTA involve the activation of dopamine projections from the pVTA to the NAC, VP and mPFC. Following the acquisition of self-infusions of 200 mg% ethanol into the pVTA, either the dopamine D2 receptor antagonist sulpiride (0, 10 or 100 μM) or the D1 receptor antagonist SCH-23390 (0, 10 or 100 μM) was microinjected into the ipsilateral NAC shell (NACsh), NAC core (NACcr), VP or mPFC immediately prior to the self-infusion sessions to assess the involvement of the different dopamine projections in the reinforcing effects of ethanol. Microinjection of each compound at higher concentration into the NACsh, VP or mPFC, but not the NACcr, significantly reduced the responses on the active lever (from 40-50 to approximately 20 responses). These results indicate that activation of dopamine receptors in the NACsh, VP or mPFC, but not the NACcr, is involved in mediating the reinforcing effects of ethanol in the pVTA, suggesting that the 'alcohol reward' neuro-circuitry consist of, at least in part, activation of the dopamine projections from the pVTA to the NACsh, VP and mPFC.
Machine learning of user profiles: representational issues

As more information becomes available electronically, tools for finding information of interest to users becomes increasingly important. The goal of the research described here is to build a system for generating comprehensible user profiles that accurately capture user interest with minimum user interaction. The research described here focuses on the importance of a suitable generalization hierarchy and representation for learning profiles which are predictively accurate and comprehensible. In our experiments we evaluated both traditional features based on weighted term vectors as well as subject features corresponding to categories which could be drawn from a thesaurus. Our experiments, conducted in the context of a content-based profiling system for on-line newspapers on the World Wide Web (the IDD News Browser), demonstrate the importance of a generalization hierarchy and the promise of combining natural language processing techniques with machine learning (ML) to address an information retrieval (IR) problem.
High Resolution X-Ray Spectra of Supernova Remnants

We review results obtained with the Focal Plane Crystal Spectrometer (FPCS) on the Einstein Observatory. Clear evidence is found for departures from ionization equilibrium in the interior of Puppis A. This comes from the observed weakness of the forbidden lines relative to the resonance lines for the He - like triplets of O VII and Ne IX. However, it is shown that this departure from equilibrium does not alter our conclusion, based on previous FPCS results, that O and Ne are overabundant relative to Fe. The spectrum of N132D shows strong O VIII emission and very weak Fe emission, suggesting an even greater O/Fe abundance enhancement than in Puppis A. In the Cygnus Loop, the O to Ne abundance ratio is approximately solar; we have no information about Fe. The O VII triplet shows clear evidence for departures from ionization equilibrium in the Cygnus Loop. The spectrum of Tycho’s SNR contains lines from ionization stages of Fe XVII through Fe XXIII and XXIV, indicating that a wide range of ionization conditions are present. Cas A and Kepler’s SNR show relatively less emission from the higher ionization stages. For Tycho, we measured the strength of the strong Si XIII lines, and we find that a many-fold overabundance of Si relative to Fe is required regardless of the equilibrium state of the emitting plasma (confirming the Solid State Spectrometer results). On a separate topic, the completed analysis of X-ray Doppler shifts in Cas A suggests that the emitting material is concentrated in a ring that is inclined to the line of sight and is expanding at ~5000 km s-1.
The act of discovery.

The active participation in the learning process by the child might result in the following hypothesized benefits: an increase in intellectual potency so as to make the acquired information more readily viable in problem solving, the enaction of the learning activities in terms of the intrinsic reward of discovery itself (as contrasted with the drive-reduction model of learning), learning the heuristics of discovery, and making material more readily accessible in memory. From Psyc Abstracts 36:01:1FD21B. (PsycINFO Database Record (c) 2010 APA, all rights reserved) (http://psycnet.apa.org/psycinfo/1962-00777-001)
Sound power determination using the sound intensity scanning technique

Sound intensity is the primary quantity required to compute the sound power of sources, which is given by the surface integral of the product of the normal component of the sound intensity and the associated elemental area over any surface fully enclosing the source. In the scanning method, the probe is moved continuously along one or more prescribed paths on the surface. The surface average value of the normal component of sound intensity is obtained in a few scans, instead of independent measurements at several points. This method is relatively quick and easy to perform and gives good results for measurements requiring engineering grades of accuracies. The author examines the range and effect of some of the major parameters associated with the scanning technique, for providing guidance to the user and to the standardization of the procedure
Incentivizing cooperative agreements for sustainable forest management: Experimental tests of alternative structures and institutional rules

Non-industrial private forestland owners (NIPFs) manage the majority of US forestland. But land use conversion is the highest among this group, in part due to the relative paucity of income earned, these agreements can provide opportunities for long term payments from sales of timber and ecosystem services at levels sufficient to reduce the temptation to convert. In this structured well, these agreements can provide opportunities for long term payments from sales of timber and ecosystem services at levels sufficient to reduce the temptation to convert. In this paper we investigate various means of encouraging meaningful participation in cooperative agreements for forests that emphasize conservation. We report on the results obtained through a series of laboratory market experiments in which the participants play the role of NIPFs and make resource allocation decisions facing real financial incentives. Our results shed light on the relative factors that affect the success of these agreements. In particular, we find that when agreements include contribution thresholds (with money back guarantees) coupled with relatively long contract lengths, the groups are able to preserve a significant fraction of forested lands through conservation agreements.
Nature of axial tail instability and bubble-blob formation in near-Earth plasma sheet

[1] Previous global magnetohydrodynamic (MHD) simulations of substorm events have identified the dynamic presence of an axial tail instability that is uniform in the dawn-dusk direction in the near-Earth plasma sheet. The axial tail instability is found to be a major cause of the initial growing MHD force imbalance on closed field lines prior to the subsequent magnetic reconnection and substorm expansion onset processes. In this work, energy principle analysis indicates that a two-dimensional thin current sheet configuration in the magnetotail is typically stable to the axial mode within the framework of ideal MHD model. However, linear resistive MHD calculations find axial tail instabilities on closed field lines in the generalized Harris sheet configurations. The properties of these instabilities are similar to the axial tail modes observed in the global MHD simulations. The axial tail mode is unstable in regimes of low Lundquist number and regions with small normal component of magnetic field. Such resistive axial tail instability would by many researchers be considered as tearing instability in a two-dimensional tail configuration. Unlike the conventional tearing mode of Harris sheet, the linear axial tail instability does not involve any reconnection process. Instead, the nature of the mode is dominantly a slippage process among neighboring flux tubes as facilitated by resistive dissipation. A natural consequence of the axial tail instability is shown to be the formation of bubble-blob pairs in the pressure and entropy profiles in the near-Earth plasma sheet.
Modeling the interaction of HIV with cells of the immune system

Several mathematical models describing the interaction of HIV with T4 lymphocytes and macrophages are presented. The primary problems addressed involve the decline of immunocompetence as mirrored by the T4 cell number, the role of macrophages in the disease process, the interaction in early stages of AIDS, and the fraction of infected circulating T4 cells.
Using the margins command to estimate and interpret adjusted predictions and marginal effects

Many researchers and journals place a strong emphasis on the sign and statistical significance of effects—but often there is very little emphasis on the substantive and practical significance of th...
Real Exchange Rate Uncertainty and Private Investment in Developing Countries

The author examines empirically the link between real exchange rate uncertainty and private investment in developing countries using a large cross country-time series data set. He builds a GARCH-based measure of real exchange rate volatility and finds that it has a strong negative impact on investment, after controlling for other standard investment determinants and taking into account their potential endogeneity. The impact of uncertainty is not uniform, however. There is some evidence of threshold effects, so that uncertainty only matters when it exceeds some critical level. In addition, the negative impact of real exchange rate uncertainty on investment is significantly larger in economies that are highly open and in those with less developed financial systems.
Characterizing Hilbert space frames with the subframe property

We characterize Riesz frames and frames with the subframe property and use this to answer most of the questions from the literature concerning these properties and their relationships to the projection methods etc.
What Is an Institution

The author claims that an institution is any collectively accepted system of rules (procedures, practices) that enable us to create institutional facts. These rules typically have the form of X counts as Y in C, where an object, person, or state of affairs X is assigned a special status, the Y status, such that the new status enables the person or object to perform functions that it could not perform solely in virtue of its physical structure, but requires as a necessary condition the assignment of the status. The creation of an institutional fact is, thus, the collective assignment of a status function. The typical point of the creation of institutional facts by assigning status functions is to create deontic powers. So typically when we assign a status function Y to some object or person X we have created a situation in which we accept that a person S who stands in the appropriate relation to X is such that (S has power (S does A)). The whole analysis then gives us a systematic set of relationships between collective intentionality, the assignment of function, the assignment of status functions, constitutive rules, institutional facts, and deontic powers.
Rising Food Prices Take a Bite Out of Food Stamp Benefits

The Food Stamp Program is designed to provide low-income families with increased food purchasing power to obtain a nutritionally adequate diet. As in most other Federal Government assistance programs, benefits are adjusted in response to rising prices - in this case, rising food prices. The current method of adjustment results in a shortfall between the maximum food stamp benefit and the cost of a nutritionally adequate diet as specified by USDA's Thrifty Food Plan. During fiscal year (FY) 2007, the food purchasing shortfall in the caseload-weighted maximum benefit for the program grew from $7 in October 2006 to $19 in September 2007. In FY 2008, the amount grew from almost $8 in October 2007 to $34 in July 2008 and to $38 in September 2008. In an average month, food stamp households faced shortfalls of over $2 in FY 2003, $12 in FY 2007, and $22 in FY 2008. These losses in food purchasing power account for 1 percent, 4 percent, and 7 percent of the maximum benefit in each respective year. Alternative adjustment methods can reduce the shortfall but will raise program costs.
Semi-automatic Ontology Alignment for Geospatial Data Integration

In geospatial applications with heterogeneous databases, an ontology-driven approach to data integration relies on the alignment of the concepts of a global ontology that describe the domain, with the concepts of the ontologies that describe the data in the local databases. Once the alignment between the global ontology and each local ontology is established, users can potentially query hundreds of databases using a single query that hides the underlying heterogeneities. Using our approach, querying can be easily extended to a new data source by aligning a local ontology with the global one. For this purpose, we have designed and implemented a tool to align ontologies. The output of this tool is a set of mappings between concepts, which will be used to produce the queries to the local databases once a query is formulated on the global ontology. To facilitate the user’s task, we propose semi-automatic methods for propagating such mappings along the ontologies. In this paper, we present the principles behind our propagation method, the implementation of the tool, and we conclude with a discussion of interesting cases and proposed solutions.
Scaling optimistic replication

Replication improves the performance and availability of sharing information in a largescale network. Classical, pessimistic replication incurs network access before any access, in order to avoid conflicts and resulting stale reads and lost writes. Pessimistic protocols assume some central locking site or necessitate distributed consensus. The protocols are fragile in the presence of network failures, partitioning, or denial-of-service attacks. They are safe (i.e., stale reads and lost writes do not occur) but at the expense of performance and availability, and they do not scale well.
SPATIAL PRODUCTION CONCENTRATION UNDER YIELD RISK AND RISK AVERSION

A study of equilibrium acreage allocation decisions at the farm and regional levels under risk aversion, yield uncertainty, and endogenous crop prices is undertaken in a two-crop, two-region setting. The main insight is that a partial specialization in one crop at a regional level may be an equilibrium dominant strategy relative to the more diversified crop mix produced on farm. This is due to the trade-offs among the effects of the "natural hedge" based on the negative price-yield correlation on the probability distributions of crop revenues and whole-farm revenue risk reduction through crop enterprise diversification. Another finding is that equilibrium in which each region grows only one crop is unlikely unless there are comparative advantages in production (or marketing) across regions. Other circumstances under which complete regional specialization is possible include a high level of producer risk aversion along with limited benefits derived through crop enterprise diversification due to high correlation of farm-level yields for different crops, and a low crop price elasticity. This applies to situations in which one can identify growing regions that are possessed of two features. The first feature is that growing conditions are relatively homogenous and farm-level yield co-variability is higher within each region as compared with that across the regions. The second feature is that the sizes of the regions are large enough to have a substantial impact on output prices.
Inference in limited dependent variable models robust to weak identification

Summary We propose tests for structural parameters in limited dependent variable models with endogenous explanatory variables. These tests are based upon the generalized minimum distance principle. They are of the correct size regardless of whether the structural parameters are identified and are especially appropriate for models whose moment conditions are non-linear in the parameters. Moreover, they are computationally simple, allowing them to be implemented using a large number of statistical software packages. We compare our tests to Wald tests in a simulation experiment and use them to analyse the female labour supply and the demand for cigarettes.
Moving the Needle: Making a Contribution When the Easy Questions Have Been Answered

Today’s competitive and research realities are changing. That is, the easy questions have been answered and the easy research has been done. We therefore need to reevaluate our approach to research so that we can help decision makers resolve tomorrow’s challenges. Specifically, to provide nuanced insight, we need to begin to employ multimethod, metaparadigmatic, and longitudinal research more robustly. Of course, given the inherent cost—both time and money—associated with such research, we may need to seek more collaborative research opportunities and reconsider how research contribution is measured. These efforts will help us stay relevant and move the needle forward in an age where decision makers need greater understanding to create value and achieve differential performance.
Miscarriage of Chief Justice: Judicial Power and the Legal Complex in Pakistan under Musharraf

This article explores the struggle for judicial power in Pakistan under Pervez Musharraf focusing on two questions. First, how did pro‐Musharraf regime judges expand judicial power, leading to a confrontation with the regime? Second, how did the bar and the bench mobilize in the struggle for judicial power? The author shows how, instead of blindly supporting economic liberalization in a period of economic growth, the Supreme Court expanded power by scrutinizing questionable urban development, privatization, and deregulation measures in a virtuous cycle of public interest litigation. The author also describes how a politics of reciprocity explains the social mobilization of lawyers as the bench protected the bar from regime penetration, and the bar protected the bench from regime backlash. The Pakistani case questions some of our assumptions about economic liberalization and courts in authoritarian regimes, and the study invites scholars to explore the role of courts in developing judicial support structures and the role of lawyers in social movements.
Dynamic State Tameness

An extension of the idea of state tameness is presented in a dynamic framework. The proposed model for financial markets is rich enough to provide analytical tools that are mostly obtained in models that arise as the solution of SDEs with deterministic coecients. In the presented model the augmentation by a shadow stock of the price evolution has a Markovian character. As in a previous paper, the results obtained on valuation of European contingent claims and American contingent claims do not require the full range of the volatility matrix. Under some additional continuity conditions, the conceptual framework provided by the model makes it possible to regard the valuation of financial instruments of the European type as a particular case of valuation of instruments of American type. This provides a unifying framework for the problem of valuation of financial instruments.
SPACEBORNE CENTRIFUGAL RELAYS FOR SPACECRAFT PROPULSION

Acceleration using centrifugal relays is a recently discovered method for the acceleration of spaceborne payloads to high velocity at high thrust. Centrifugal relays are moving rotors which progressively accelerate reaction mass to higher velocities. One important engineering problem consists of accurately tracking the position of the projectiles and rotors and guiding each projectile exactly onto the appropriate guide tracks on each rotor. The topics of this research are the system kinematics and dynamics and the computerized guidance system which will allow the projectile to approach each rotor with exact timing with respect to the rotor rotation period and with very small errors in lateral positions. Kinematics studies include analysis of rotor and projectile positions versus time and projectile/rotor interactions. Guidance studies include a detailed description of the tracking mechanism (interrupt of optical beams) and the aiming mechanism (electromagnetic focusing) including the design of electromagnetic deflection coils and the switching circuitry.
A complete anytime algorithm for treewidth

In this paper, we present a Branch and Bound algorithm called QuickBB for computing the treewidth of an undirected graph. This algorithm performs a search in the space of perfect elimination ordering of vertices of the graph. The algorithm uses novel pruning and propagation techniques which are derived from the theory of graph minors and graph isomorphism. We present a new algorithm called minor-min-width for computing a lower bound on treewidth that is used within the branch and bound algorithm and which improves over earlier available lower bounds. Empirical evaluation of QuickBB on randomly generated graphs and benchmarks in Graph Coloring and Bayesian Networks shows that it is consistently better than complete algorithms like Quick-Tree [Shoikhet and Geiger, 1997] in terms of cpu time. QuickBB also has good anytime performance, being able to generate a better upper bound on treewidth of some graphs whose optimal treewidth could not be computed up to now.
Audit games with multiple defender resources

Modern organizations (e.g., hospitals, social networks, government agencies) rely heavily on audit to detect and punish insiders who inappropriately access and disclose confidential information. Recent work on audit games models the strategic interaction between an auditor with a single audit resource and auditees as a Stackelberg game, augmenting associated well-studied security games with a configurable punishment parameter. We significantly generalize this audit game model to account for multiple audit resources where each resource is restricted to audit a subset of all potential violations, thus enabling application to practical auditing scenarios. We provide an FPTAS that computes an approximately optimal solution to the resulting non-convex optimization problem. The main technical novelty is in the design and correctness proof of an optimization transformation that enables the construction of this FPTAS. In addition, we experimentally demonstrate that this transformation significantly speeds up computation of solutions for a class of audit games and security games.
REIMR — A Process for Utilizing Liquid Rocket Propulsion‐Oriented ‘Lessons Learned’ to Mitigate Development Risk in Nuclear Thermal Propulsion

This paper is a summary overview of a study conducted at the NASA Marshall Space Flight Center (NASA‐MSFC) during the initial phases of the Space Launch Initiative (SLI) program to evaluate a large number of technical problems associated with the design, development, test, evaluation and operation of several major liquid propellant rocket engine systems (i.e., SSME, Fastrac, J‐2, F‐1). One of the primary results of this study was the identification of the “Fundamental Root Causes” that enabled the technical problems to manifest, and practices that can be implemented to prevent them from recurring in future propulsion system development efforts, such as that which is currently envisioned in the field of nuclear thermal propulsion (NTP). This paper will discus the Fundamental Root Causes, cite some examples of how the technical problems arose from them, and provide a discussion of how they can be mitigated or avoided in the development of an NTP system.
Perfect Matchings and Perfect Powers

In the last decade there have been many results about special families of graphs whose number of perfect matchings is given by perfect or near perfect powers (N. Elkies et al., J. Algebraic Combin. 1 (1992), 111–132s B.-Y. Yang, Ph.D. thesis, Department of Mathematics, MIT, Cambridge, MA, 1991s J. Propp, New Perspectives in Geometric Combinatorics, Cambridge University Press, 1999). In this paper we present an approach that allows proving them in a unified way. We use this approach to prove a conjecture of James Propp stating that the number of tilings of the so-called Aztec dungeon regions is a power (or twice a power) of 13. We also prove a conjecture of Matt Blum stating that the number of perfect matchings of a certain family of subgraphs of the square lattice is a power of 3 or twice a power of 3. In addition we obtain multi-parameter generalizations of previously known results, and new multi-parameter exact enumeration results. We obtain in particular a simple combinatorial proof of Bo-Yin Yang's multivariate generalization of fortresses, a result whose previously known proof was quite complicated, amounting to evaluation of the Kasteleyn matrix by explicit row reduction. We also include a new multivariate exact enumeration of Aztec diamonds, in the spirit of Stanley's multivariate version.
The Transverse Instability of Periodic Waves in Zakharov–Kuznetsov Type Equations

In this paper, we investigate the instability of one-dimensionally stable periodic traveling wave solutions of the generalized Korteweg-de Vries equation to long wavelength transverse perturbations in the generalized Zakharov-Kuznetsov equation in two space dimensions. By deriving appropriate asymptotic expansions of the periodic Evans function, we derive an index which yields sufficient conditions for transverse instabilities to occur. This index is geometric in nature, and applies to any periodic traveling wave profile under some minor smoothness assumptions on the nonlinearity. We also describe the analogous theory for periodic traveling waves of the generalized Benjamin-BonaMahony equation to long wavelength transverse perturbations in the gBBM-Zakharov-Kuznetsov equation.
Determining forecast and decision horizons for reservoir operations under hedging policies

[1] Hedging policies for reservoir operations makes a small deficit in current supply to reduce the probability of a severe water shortage in the future. One of the critical questions for hedging research is how long the forecast period should be so that reliable inflow forecast in the period can be used for decision making under hedging. Decision makers always hope to look further into the future; however, the longer the forecast period, the more uncertain and less reliable the involved information, which will have a diminishing influence on decision making. For dynamic reservoir operation optimization models, the decision horizon (DH) may be defined as the initial periods in which decisions are not affected by forecast data beyond a certain period, defined as the forecast horizon (FH). This paper determines FH with given DH for dynamic reservoir operation problems through both theoretical and numerical analysis. We use order of magnitude analysis and numerical modeling to identify the impact of various factors such as water stress level (the deficit between water availability and demand), reservoir size, inflow uncertainty, evaporation rate, and discount rate. Three types of inflow time series are used: stationary, nonstationary with seasonality, and random walk. Results show that inflow characteristics and reservoir capacity have major impacts on FH when water stress is modest; larger reservoir capacity and the deterministic component of inflow such as seasonality require a longer FH. Economic factors have strong impacts when water stress levels are high.
Local Space-Time Smoothing for Version Controlled Documents

Unlike static documents, version controlled documents are continuously edited by one or more authors. Such collaborative revision process makes traditional modeling and visualization techniques inappropriate. In this paper we propose a new representation based on local space-time smoothing that captures important revision patterns. We demonstrate the applicability of our framework using experiments on synthetic and real-world data.
Income insecurity and underemployment in Indonesia's informal sector

Recent legislation to provide income security to workers in Indonesia covers only those in the formal sector, initially. Workers in the informal sector are at an even greater risk of income loss and are more vulnerable to shocks due to lower average incomes. The author addresses the question of whether there is a rationale for income security schemes for Indonesia's informal sector. Research suggests that, through a range of existing public programs, Indonesia's government already provides important security mechanisms for informal sector workers, and must continue to do so. The author finds no compelling evidence of the need for a nationwide income security scheme for such workers. The author's argument against a new income security scheme is based on three main conclusions. First, only about 12 percent of the informal sector workforce and even less of the formal sector is underemployed. Second, this level of underemployment does not represent compelling empirical evidence of income insecurity. The connection between underemployment and income insecurity is problematic in theory and remains unsubstantiated by national survey data. Third, many mechanisms already exist in Indonesia to mitigate the disruption caused by income insecurity. Households and communities use private strategies to smooth consumption and investment and the government is already active in providing additional income security. Not only does empirical evidence fail to justify a major new policy response, but most evidence suggests that such a response is not presently necessary. The author suggests that any new initiative directed at income insecurity should be limited in scope and should focus on Eastern Indonesia and on remote or isolated areas of Java, areas with below average incomes. If concerns about income insecurity persist, money should be spend finding out where it actually is before implementing a nationwide scheme to deal with it.
Signature jumps and Alexander polynomials for links

We relate the jumps of the signature function of a link to the roots of its first nonzero higher Alexander polynomial.
Streaming algorithms for geometric problems

Computing over data streams is a recent phenomenon that is of growing interest in many areas of computer science, including databases, computer networks and theory of algorithms. In this scenario, it is assumed that the algorithm sees the elements of the input one-by-one in arbitrary order, and needs to compute a certain function of the input. However, it does not have enough memory to store the whole input. Therefore, it must maintain a “sketch” of the data. Designing a sketching method for a given problem is a novel and exciting challenge for algorithm design.
When homomorphism becomes a liability

We show that an encryption scheme cannot have a simple decryption function and be homomorphic at the same time, even with added noise. Specifically, if a scheme can homomorphically evaluate the majority function, then its decryption cannot be weakly-learnable (in particular, linear), even if the probability of decryption error is high. (In contrast, without homomorphism, such schemes do exist and are presumed secure, e.g. based on LPN.) An immediate corollary is that known schemes that are based on the hardness of decoding in the presence of low hamming-weight noise cannot be fully homomorphic. This applies to known schemes such as LPN-based symmetric or public key encryption. Using these techniques, we show that the recent candidate fully homomorphic encryption, suggested by Bogdanov and Lee (ePrint '11, henceforth BL), is insecure. In fact, we show two attacks on the BL scheme: One that uses homomorphism, and another that directly attacks a component of the scheme.
Dynamical tides in eccentric binaries and tidally excited stellar pulsations in Kepler KOI-54

Recent observation of the tidally excited stellar oscillations in the main-sequence binary KOI-54 by the Kepler satellite provides a unique opportunity for studying dynamical tides in eccentric binary systems. We develop a general theory of tidal excitation of oscillation modes of rotating binary stars and apply our theory to tidally excited gravity modes (g-modes) in KOI-54. The strongest observed oscillations, which occur at 90 and 91 times the orbital frequency, are likely due to prograde m= 2 modes (relative to the stellar spin axis) locked in resonance with the orbit. The remaining flux oscillations with frequencies that are integer multiples of the orbital frequency are likely due to nearly resonant m= 0 g-modes; such axisymmetric modes generate larger flux variations compared to the m= 2 modes, assuming that the spin inclination angle of the star is comparable to the orbital inclination angle. We examine the process of resonance mode locking under the combined effects of dynamical tides on the stellar spin and orbit and the intrinsic stellar spindown. We show that KOI-54 can naturally evolve into a state in which at least one m= 2 mode is locked in resonance with the orbital frequency. Our analysis provides an explanation for the fact that only oscillations with frequencies less than 90–100 times the orbital frequency are observed. We have also found evidence from the published Kepler result that three-mode non-linear coupling occurs in the KOI-54 system. We suggest that such non-linear mode coupling may explain the observed oscillations that are not harmonics of the orbital frequency.
Inside the Black Box: the Price Linkage and Transmission between Energy and Agricultural Markets

Motivated by strong comovement and increasing volatility of energy and agricultural prices, we examine dynamic evolutions of ethanol, gasoline, and corn prices over the period of March 2005-March 2011. A structural change is found around March 2008 in the pairwise dynamic correlations between the prices in a multivariate GARCH model. A structural VAR (SVAR) model is then estimated on two subsamples, one before and one after the identified change point. Using the novel method of identification through heteroscedasticity, we exploit the time-varying price volatilities to fully identify the SVAR model. In the more recent period, ethanol, gasoline, and corn prices are found to be more closely linked with a strengthened corn-ethanol relation, which can be largely explained by the new developments of the biofuel industry and related policy instruments. Variance decomposition shows that for each market a significant and relatively large share of the price variation could be explained by the price changes in the other two markets. The results are robust to the inclusion of seasonal dummies and various representative macroeconomic and financial indicators.
Equivocal blind signatures and adaptive UC-security

We study the design of adaptively secure blind signatures in the universal composability (UC) setting. First, we introduce a new property for blind signature schemes that is suitable for arguing security against adaptive adversaries: an equivocal blind signature is a blind signature where there exists a simulator that has the power of making signing transcripts correspond to any message signature pair. Second, we present a general construction methodology for building adaptively secure blind signatures: the starting point is a 2-move "equivocal lite blind signature", a lightweight 2-party signature protocol that we formalize and implement both generically as well as concretely; formalizing a primitive as "lite" means that the adversary is required to show all private tapes of adversarially controlled parties; this enables us to conveniently separate zero-knowledge (ZK) related security requirements from the remaining security properties in the blind signature design methodology. Next, we focus on the suitable ZK protocols for blind signatures. We formalize two special ZK ideal functionalities, single-verifier-ZK (SVZK) and singleprover-ZK (SPZK), both special cases of multi-session ZK that may be of independent interest, and we investigate the requirements for realizing them in a commit-and-prove fashion as building blocks for adaptively secure UC blind signatures. Regarding SPZK we find the rather surprising result that realizing it only against static adversaries is sufficient to obtain adaptive security for UC blind signatures. We instantiate all the building blocks of our design methodology both generically based on the blind signature construction of Fischlin as well as concretely based on the 2SDH assumption of Okamoto, thus demonstrating the feasibility and practicality of our approach. The latter construction yields the first practical UC blind signature that is secure against adaptive adversaries. We also present a new more general modeling of the ideal blind signature functionality.
Air pollution during growth : accounting for governance and vulnerability

New research on urban air pollution casts doubt on the conventional view of the relationship between economic growth and environmental quality. This view holds that pollution automatically increases until societies reach middle-income status because poor countries have neither the institutional capacity nor the political commitment necessary to regulate polluters. Some policymakers and researchers have cited this model (called the "environmental Kuznets curve," or EKC) when arguing that developing countries should "grow first, clean up later." However, new evidence suggests that the EKC model is misleading because it mistakenly assumes that strong environmental governance is not possible for poor countries. As the authors show in this paper, the empirical relationship between pollution and income becomes much weaker when measures of governance are added to the analysis. Their results also suggest that previous research has underestimated the effect of geographic vulnerability (climate and terrain factors) on air quality. The authors find that weak governance and geographic vulnerability alone can account for the crisis levels of air pollution in many developing country cities. When these factors are combined with income and population effects, the authors have a sufficient explanation for the fact that some cities already have air quality comparable to levels in OECD urban areas. To summarize, their results suggest that the maxim "grow first, clean up later" is too simplistic. Appropriate urban growth strategies can steer development toward cities with lower geographic vulnerability, and governance reform can reduce air pollution significantly, long before countries reach middle-income status. This paper - a joint product of the Infrastructure and Environment Team, Development Research Group, the Environment Department, and the Global Environment Facility - is part of a larger effort in the Bank to understand governance and pollution.
β-Amidoaldehydes via oxazoline hydroformylation

4-Substituted oxazolines, which are readily synthesized from naturally occurring α-amino acids, are converted efficiently and stereospecifically to β-amidoaldehydes in the presence of synthesis gas and catalytic dicobalt octacarbonyl.