cssi/SciSciGPT-SciSciNet huggingface dataset:
HIGHLY VARIABLE OBJECTS IN THE PALOMAR-QUEST SURVEY: A BLAZAR SEARCH USING OPTICAL VARIABILITY

We identify 3113 highly variable objects in 7200 deg^2 of the Palomar-QUEST (PQ) Survey, which each varied by more than 0.4 mag simultaneously in two broadband optical filters on timescales from hours to roughly 3.5 years. The primary goal of the selection is to find blazars by their well-known violent optical variability. Because most known blazars have been found in radio and/or X-ray wavelengths, a sample discovered through optical variability may have very different selection effects, elucidating the range of behavior possible in these systems. A set of blazars selected in this unusual manner will improve our understanding of the physics behind this extremely variable and diverse class of active galactic nucleus (AGN). The object positions, variability statistics, and color information are available using the PQ CasJobs server. The time domain is just beginning to be explored over large sky areas; we do not know exactly what a violently variable sample will hold. About 20% of the sample has been classified in the literature; over 70% of those objects are known or likely AGNs. The remainder largely consists of a variety of variable stars, including a number of RR Lyrae and cataclysmic variables.
Associated Legendre Functions and Spherical Harmonics of Fractional Degree and Order

Trigonometric formulas are derived for certain families of associated Legendre functions of fractional degree and order, for use in approximation theory. These functions are algebraic, and when viewed as Gauss hypergeometric functions, belong to types classified by Schwarz, with dihedral, tetrahedral, or octahedral monodromy. The dihedral Legendre functions are expressed in terms of Jacobi polynomials. For the last two monodromy types, an underlying ‘octahedral’ polynomial, indexed by the degree and order and having a nonclassical kind of orthogonality, is identified, and recurrences for it are worked out. It is a (generalized) Heun polynomial, not a hypergeometric one. For each of these families of algebraic associated Legendre functions, a representation of the rank-2 Lie algebra $$\mathfrak {so}(5,\mathbb {C})$$ is generated by the ladder operators that shift the degree and order of the corresponding solid harmonics. All such representations of $$\mathfrak {so}(5,\mathbb {C})$$ are shown to have a common value for each of its two Casimir invariants. The Dirac singleton representations of $$\mathfrak {so}(3,2)$$ are included.
Magnetic inhibition of convection and the fundamental properties of low-mass stars - III. A consistent 10 Myr age for the Upper Scorpius OB association

When determining absolute ages of identifiably young stellar populations, results strongly depend on which stars are studied. Cooler (K, M) stars typically yield ages that are systematically younger than warmer (A, F, G) stars by a factor of two. I explore the possibility that these age discrepancies are the result of magnetic inhibition of convection in cool young stars by using magnetic stellar evolution isochrones to determine the median age of the Upper Scorpius subgroup of the Scorpius-Centaurus OB association. A median age of 10 Myr consistent across spectral types A through M is found, except for a subset of F-type stars that appear significantly older. Agreement is shown for ages derived from the Hertzsprung-Russell (HR) diagram and from the empirical mass-radius relationship defined by eclipsing multiple-star systems. Surface magnetic field strengths required to produce agreement are approximately 2.5 kG and are predicted from a priori estimates of thermal equipartition values. A region in the HR diagram is identified that plausibly connects stars whose structures are weakly influenced by the presence of magnetic fields with those whose structures are strongly influenced by magnetic fields. The models suggest that this region is characterized by stars with rapidly thinning outer convective envelopes where the radiative core mass is greater than 75% of the total stellar mass. Furthermore, depletion of lithium predicted from magnetic models appears in better agreement with observed lithium equivalent widths than predictions from non-magnetic models. These results suggest that magnetic inhibition of convection plays an important role in the early evolution of low-mass stars and that it may be responsible for noted age discrepancies in young stellar populations.
The Advanced Spectral Library (ASTRAL): Reference Spectra for Evolved M Stars

The HST (Hubble Space Telescope) Treasury Program Advanced Spectral Library Project: Cool Stars was designed to collect representative, high-quality ultraviolet spectra of eight evolved F-M type cool stars. The Space Telescope Imaging Spectrograph (STIS) echelle spectra of these objects enable investigations of a broad range of topics, including stellar and interstellar astrophysics. This paper provides a guide to the spectra of the two evolved M stars, the M2 Iab super giant alpha Ori and the M3.4 giant gamma Cru, with comparisons to the prototypical K1.5 giant alpha Boo. It includes identifications of the significant atomic and molecular emission and absorption features and discusses the character of the photospheric and chromospheric continua and line spectra. The fluorescent processes responsible for a large portion of the emission-line spectrum, the characteristics of the stellar winds, and the available diagnostics for hot and cool plasmas are also summarized. This analysis will facilitate the future study of the spectra, outer atmospheres, and winds, not only of these objects but of numerous other cool, low-gravity stars, for years to come.
A General Metric for Riemannian Manifold Hamiltonian Monte Carlo

Markov Chain Monte Carlo (MCMC) is an invaluable means of inference with complicated models, and Hamiltonian Monte Carlo, in particular Riemannian Manifold Hamiltonian Monte Carlo (RMHMC), has demonstrated success in many challenging problems. Current RMHMC implementations, however, rely on a Riemannian metric that limits their application. In this paper I propose a new metric for RMHMC without these limitations and verify its success on a distribution that emulates many hierarchical and latent models.
Outlier Robust Mean Estimation with Subgaussian Rates via Stability

We study the problem of outlier robust high-dimensional mean estimation under a finite covariance assumption, and more broadly under finite low-degree moment assumptions. We consider a standard stability condition from the recent robust statistics literature and prove that, except with exponentially small failure probability, there exists a large fraction of the inliers satisfying this condition. As a corollary, it follows that a number of recently developed algorithms for robust mean estimation, including iterative filtering and non-convex gradient descent, give optimal error estimators with (near-)subgaussian rates. Previous analyses of these algorithms gave significantly suboptimal rates. As a corollary of our approach, we obtain the first computationally efficient algorithm with subgaussian rate for outlier-robust mean estimation in the strong contamination model under a finite covariance assumption.
Atomistic Subsemirings of the Lattice of Subspaces of an Algebra

Let A be an associative algebra with identity over a field k. An atomistic subsemiring R of the lattice of subspaces of A, endowed with the natural product, is a subsemiring which is a closed atomistic sublattice. When R has no zero divisors, the set of atoms of R is endowed with a multivalued product. We introduce an equivalence relation on the set of atoms such that the quotient set with the induced product is a monoid, called the condensation monoid. Under suitable hypotheses on R, we show that this monoid is a group and the class of k1 A is the set of atoms of a subalgebra of A called the focal subalgebra. This construction can be iterated to obtain higher condensation groups and focal subalgebras. We apply these results to G-algebras for G a group; in particular, we use them to define new invariants for finite-dimensional irreducible projective representations.
Proof of factorization of fragmentation function in non-equilibrium QCD

Abstract In this paper, we prove factorization of fragmentation function in non-equilibrium QCD by using Schwinger–Keldysh closed-time path integral formalism. We use the background field method of QCD in a pure gauge in path integral approach to prove factorization of fragmentation function in non-equilibrium QCD. Our proof is valid in any arbitrary gauge fixing parameter α . This may be relevant to study hadron production from quark-gluon plasma at high energy heavy-ion colliders at RHIC and LHC.
Revisiting the classifications of 6d SCFTs and LSTs

Gauge-theoretic anomaly cancellation predicts the existence of many 6d SCFTs and little string theories (LSTs) that have not been given a string theory construction so far. In this paper, we provide an explicit construction of all such “missing” 6d SCFTs and LSTs by using the frozen phase of F-theory. We conjecture that the full set of 6d SCFTs and LSTs is obtained by combining the set of theories constructed in this paper with the set of theories that have been constructed in earlier literature using the unfrozen phase of F-theory. Along the way, we demonstrate that there exist SCFTs that do not descend from LSTs via an RG flow.
Gaussian ensemble for quantum integrable dynamics

Abstract We propose a Gaussian ensemble as a description of the long-time dynamics of isolated quantum integrable systems. Our approach extends the Generalized Gibbs Ensemble (GGE) by incorporating fluctuations of integrals of motion. It is asymptotically exact in the classical limit irrespective of the system size and, under appropriate conditions, in the thermodynamic limit irrespective of the value of Planck’s constant. Moreover, it captures quantum corrections near the classical limit, finite size corrections near the thermodynamic limit, and is valid in the presence of non-local interactions. The Gaussian ensemble bridges the gap between classical integrable systems, where a generalized microcanonical ensemble is exact even for few degrees of freedom, and GGE, which requires thermodynamic limit. We illustrate our results with examples of increasing complexity.
Meridional almost normal surfaces in knot complements

Suppose K is a knot in a closed 3–manifold M such that M−N(K) is irreducible. We show that for any integer n there exists a triangulation of M−N(K) such that any weakly incompressible bridge surface for K of n bridges or fewer is isotopic to an almost normal bridge surface.
Energy-Aware Virtual Machine Management in Inter-Datacenter Networks Over Elastic Optical Infrastructure

Datacenters (DCs), deployed in a large scale to support the ever increasing demand for data processing applications, consume tremendous energy. Powering DCs with renewable energy can effectively reduce the brown energy consumption. Owing to geographically distributed deployment of DCs, the renewable energy generation and the data processing demands usually vary in different DCs. Migrating virtual machines (VMs) among DCs according to the availability of renewable energy helps match the energy demands and the renewable energy generation in DCs, and thus maximizes the utilization of renewable energy. We first elicit the renewable energy-aware inter-DC (inter-DC) VM migration problem in an inter-DC network over the elastic optical infrastructure, present it as a many-manycast communications problem, and then formulate it as an integer linear programming problem. The objective is to minimize the total cost of the brown energy consumption of DCs in such inter-DC network via VM migration. We use CVX and Gurobi to solve this problem for small network configurations, and we propose a few heuristic algorithms that approximate the optimal solution for large network configurations. Through extensive simulations, we show that the proposed algorithms, by migrating VM among DCs, can reduce up to 19.7% cost of the brown energy consumption.
The earliest phase transition

Abstract The question of a phase transition in exiting the Planck epoch of the early universe is addressed. An order parameter is proposed to help decide the issue, and estimates are made concerning its behavior. Our analysis is suggestive that a phase transition occurred.
On the existence of exotic matter in classical Newtonian mechanics

According to Newton’s law of gravitation, the force between two particles depends upon their inertial, as well as their active and passive gravitational masses. For ordinary matter, all three of th...
An Optimization Principle for Deriving Nonequilibrium Statistical Models of Hamiltonian Dynamics

A general method for deriving closed reduced models of Hamiltonian dynamical systems is developed using techniques from optimization and statistical estimation. Given a vector of resolved variables, selected to describe the macroscopic state of the system, a family of quasi-equilibrium probability densities on phase space corresponding to the resolved variables is employed as a statistical model, and the evolution of the mean resolved vector is estimated by optimizing over paths of these densities. Specifically, a cost function is constructed to quantify the lack-of-fit to the microscopic dynamics of any feasible path of densities from the statistical model; it is an ensemble-averaged, weighted, squared-norm of the residual that results from submitting the path of densities to the Liouville equation. The path that minimizes the time integral of the cost function determines the best-fit evolution of the mean resolved vector. The closed reduced equations satisfied by the optimal path are derived by Hamilton-Jacobi theory. When expressed in terms of the macroscopic variables, these equations have the generic structure of governing equations for nonequilibrium thermodynamics. In particular, the value function for the optimization principle coincides with the dissipation potential that defines the relation between thermodynamic forces and fluxes. The adjustable closure parameters in the best-fit reduced equations depend explicitly on the arbitrary weights that enter into the lack-of-fit cost function. Two particular model reductions are outlined to illustrate the general method. In each example the set of weights in the optimization principle contracts into a single effective closure parameter.
The extremely high peak energy of GRB 110721A in the context of a dissipative photosphere synchrotron emission model

The Fermi observations of GRB 110721A have revealed an unusually high peak energy ~15 MeV in the first time bin of the prompt emission. We find that an interpretation is unlikely in terms of internal shock models, and confirm that a standard blackbody photospheric model also falls short. On the other hand, we show that dissipative photospheric synchrotron models ranging from extreme magnetically dominated to baryon dominated dynamics are able to accommodate such high peak values.
Biochemical patterns of antibody polyreactivity revealed through a bioinformatics-based analysis of CDR loops

To defend itself against bacteria and viruses, the body depends on a group of proteins known as antibodies. Each subset of antibodies undergoes a rigorous training regimen to ensure it recognizes a single epitope well – that is, one specific region on the surface of foreign, harmful organisms. Most antibodies stick extremely tightly to their one unique epitope, but some can also weakly bind to molecules that are vastly different from their main trained targets. This feature – known as polyreactivity – can in some cases help the immune system fight against multiple strains of viruses. On the other hand, when antibodies are designed in the laboratory to treat diseases, this characteristic can sometimes lead to the failure of pre-clinical trials. Yet it is currently unclear why some antibodies are polyreactive when others are not. To investigate this question, Boughter et al. compared over 1,000 polyreactive and non-polyreactive antibody sequences from a large database, revealing differences in the physical properties of the region of the antibodies that attaches to epitopes. Using these defining features, Boughter et al. went on to design a new piece of freely available, automated software that could predict which antibodies would be polyreactive more than 75% of the time. Such software could ultimately help to guide the design of antibody-based treatments, while bypassing the need for costly laboratory tests.
Decidable verification of uninterpreted programs

We study the problem of completely automatically verifying uninterpreted programs—programs that work over arbitrary data models that provide an interpretation for the constants, functions and relations the program uses. The verification problem asks whether a given program satisfies a postcondition written using quantifier-free formulas with equality on the final state, with no loop invariants, contracts, etc. being provided. We show that this problem is undecidable in general. The main contribution of this paper is a subclass of programs, called coherent programs that admits decidable verification, and can be decided in Pspace. We then extend this class of programs to classes of programs that are k-coherent, where k ∈ ℕ, obtained by (automatically) adding k ghost variables and assignments that make them coherent. We also extend the decidability result to programs with recursive function calls and prove several undecidability results that show why our restrictions to obtain decidability seem necessary.
Novel graph processor architecture, prototype system, and results

Graph algorithms are increasingly used in applications that exploit large databases. However, conventional processor architectures are inadequate for handling the throughput and memory requirements of graph computation. Lincoln Laboratory's graph-processor architecture represents a rethinking of parallel architectures for graph problems. Our processor utilizes innovations that include a sparse matrix-based graph instruction set, a cacheless memory system, accelerator-based architecture, a systolic sorter, high-bandwidth multidimensional toroidal communication network, and randomized communications. A field-programmable gate array (FPGA) prototype of the new graph processor has been developed with significant performance enhancement over conventional processors in graph computational throughput.
A Bayesian Inference Framework for Procedural Material Parameter Estimation

Procedural material models have been gaining traction in many applications thanks to their flexibility, compactness, and easy editability. We explore the inverse rendering problem of procedural material parameter estimation from photographs, presenting a unified view of the problem in a Bayesian framework. In addition to computing point estimates of the parameters by optimization, our framework uses a Markov Chain Monte Carlo approach to sample the space of plausible material parameters, providing a collection of plausible matches that a user can choose from, and efficiently handling both discrete and continuous model parameters. To demonstrate the effectiveness of our framework, we fit procedural models of a range of materials---wall plaster, leather, wood, anisotropic brushed metals and layered metallic paints---to both synthetic and real target images.
On connectivity-dependent resource requirements for digital quantum simulation of d-level particles

A primary objective of quantum computation is to efficiently simulate quantum physics. Scientifically and technologically important quantum Hamiltonians include those with spin-s, vibrational, photonic, and other bosonic degrees of freedom, i.e. problems composed of or approximated by d-level particles (qudits). Recently, several methods for encoding these systems into a set of qubits have been introduced, where each encoding's efficiency was studied in terms of qubit and gate counts. Here, we build on previous results by including effects of hardware connectivity. To study the number of SWAP gates required to Trotterize commonly used quantum operators, we use both analytical arguments and automatic tools that optimize the schedule in multiple stages. We study the unary (or one-hot), Gray, standard binary, and block unary encodings, with three connectivities: linear array, ladder array, and square grid. Among other trends, we find that while the ladder array leads to substantial efficiencies over the linear array, the advantage of the square over the ladder array is less pronounced. These results are applicable in hardware co-design and in choosing efficient qudit encodings for a given set of near-term quantum hardware. Additionally, this work may be relevant to the scheduling of other quantum algorithms for which matrix exponentiation is a subroutine.
DFT-Spread-OFDM-Based Chirp Transmission

In this study, we propose a framework for chirp-based communications by exploiting discrete Fourier transform-spread orthogonal frequency division multiplexing (DFT-s-OFDM). We show that a well-designed frequency-domain spectral shaping (FDSS) filter for DFT-s-OFDM can convert its single-carrier nature to a linear combination of chirps circularly translated in the time domain. Also, by exploiting the properties of the Fourier series and Bessel function of the first kind, we analytically obtain the FDSS filter for an arbitrary chirp. We theoretically show that the chirps with low ripples in the frequency domain result in a lower bit-error ratio (BER) via less noise enhancement. We also address the noise enhancement by exploiting the repetitions in the frequency. The proposed framework offers a new way to efficiently synthesize chirps that can be used in Internet-of-Things (IoT), dual-function radar and communication (DFRC) or wireless sensing applications with existing DFT-s-OFDM transceivers.
Finite temperature auxiliary field quantum Monte Carlo in the canonical ensemble

Finite temperature auxiliary field-based quantum Monte Carlo methods, including determinant quantum Monte Carlo and Auxiliary Field Quantum Monte Carlo (AFQMC), have historically assumed pivotal roles in the investigation of the finite temperature phase diagrams of a wide variety of multidimensional lattice models and materials. Despite their utility, however, these techniques are typically formulated in the grand canonical ensemble, which makes them difficult to apply to condensates such as superfluids and difficult to benchmark against alternative methods that are formulated in the canonical ensemble. Working in the grand canonical ensemble is furthermore accompanied by the increased overhead associated with having to determine the chemical potentials that produce desired fillings. Given this backdrop, in this work, we present a new recursive approach for performing AFQMC simulations in the canonical ensemble that does not require knowledge of chemical potentials. To derive this approach, we exploit the convenient fact that AFQMC solves the many-body problem by decoupling many-body propagators into integrals over one-body problems to which non-interacting theories can be applied. We benchmark the accuracy of our technique on illustrative Bose and Fermi–Hubbard models and demonstrate that it can converge more quickly to the ground state than grand canonical AFQMC simulations. We believe that our novel use of HS-transformed operators to implement algorithms originally derived for non-interacting systems will motivate the development of a variety of other methods and anticipate that our technique will enable direct performance comparisons against other many-body approaches formulated in the canonical ensemble.
Targeting weather insurance markets

The suitability of insurance products often depends greatly on individual circumstances. This paper examines the challenges of heterogeneity in a relatively new product, weather‐indexed insurance. This index insurance product has been launched in over a dozen countries, with the goal of enabling households engaged in agricultural activity a means to manage risk. Using data from a large‐scale field experiment, we build and calibrate a model which accounts for household investment decisions, including the scope for self‐insurance via labor markets to (risky) wage work. Our results show that insurance is most valuable to households with reduced access to wage labor, or to those who face wages that are sensitive to rainfall risk. These findings have important implications for areas where index insurance is most effective.
Creating optimal conditions for reproducible data analysis in R with ‘fertile’

The advancement of scientific knowledge increasingly depends on ensuring that data-driven research is reproducible: that two people with the same data obtain the same results. However, while the necessity of reproducibility is clear, there are significant behavioral and technical challenges that impede its widespread implementation, and no clear consensus on standards of what constitutes reproducibility in published research. We present fertile, an R package that focuses on a series of common mistakes programmers make while conducting data science projects in R, primarily through the RStudio integrated development environment. fertile operates in two modes: proactively (to prevent reproducibility mistakes from happening in the first place), and retroactively (analyzing code that is already written for potential problems). Furthermore, fertile is designed to educate users on why their mistakes are problematic and how to fix them.
Online Decentralized Decision Making With Inequality Constraints: An ADMM approach

We discuss an online decentralized decision making problem where the agents are coupled with affine inequality constraints. Alternating Direction Method of Multipliers (ADMM) is used as the computation engine and we discuss the convergence of the algorithm in an online setting. To be specific, when decisions have to be made sequentially with a fixed time step, there might not be enough time for the ADMM to converge before the scenario changes and the decision needs to be updated. In this case, a suboptimal solution is employed and we analyze the optimality gap given the convergence condition. Moreover, in many cases, the decision making problem changes gradually over time. We propose a warm-start scheme to accelerate the convergence of ADMM and analyze the benefit of the warm-start. The proposed method is demonstrated in a decentralized multiagent control barrier function problem with simulation.
The Story of the Real Exchange Rate

The real exchange rate (RER) measures relative price levels across countries, capturing deviations from purchasing power parity (PPP). RER is a key variable in international macroeconomic models as...
Counteracting Inequality in Markets via Convex Pricing

We study market mechanisms for allocating divisible goods to competing agents with quasilinear utilities. For linear pricing (i.e., the cost of a good is proportional to the quantity purchased), the First Welfare Theorem states that Walrasian equilibria maximize the sum of agent valuations. This ensures efficiency, but can lead to extreme inequality across individuals. Many real-world markets – especially for water – use convex pricing instead, often known as increasing block tariffs (IBTs). IBTs are thought to promote equality, but there is a dearth of theoretical support for this claim.
Practical Compositional Fairness: Understanding Fairness in Multi-Component Recommender Systems

How can we build recommender systems to take into account fairness? Real-world recommender systems are often composed of multiple models, built by multiple teams. However, most research on fairness focuses on improving fairness in a single model. Further, recent research on classification fairness has shown that combining multiple "fair" classifiers can still result in an "unfair" classification system. This presents a significant challenge: how do we understand and improve fairness in recommender systems composed of multiple components? In this paper, we study the compositionality of recommender fairness. We consider two recently proposed fairness ranking metrics: equality of exposure and pairwise ranking accuracy. While we show that fairness in recommendation is not guaranteed to compose, we provide theory for a set of conditions under which fairness of individual models does compose. We then present an analytical framework for both understanding whether a real system's signals can achieve compositional fairness, and improving which component would have the greatest impact on the fairness of the overall system. In addition to the theoretical results, we find on multiple datasets---including a large-scale real-world recommender system---that the overall system's end-to-end fairness is largely achievable by improving fairness in individual components.
Arithmetic properties of the sum of divisors

Abstract The divisor function σ ( n ) denotes the sum of the divisors of the positive integer n. For a prime p and m ∈ N , the p-adic valuation of m is the highest power of p which divides m. Formulas for ν p ( σ ( n ) ) are established. For p = 2 , these involve only the odd primes dividing n. These expressions are used to establish the bound ν 2 ( σ ( n ) ) ≤ ⌈ log 2 ⁡ ( n ) ⌉ , with equality if and only if n is the product of distinct Mersenne primes, and for an odd prime p, the bound is ν p ( σ ( n ) ) ≤ ⌈ log p ⁡ ( n ) ⌉ , with equality related to solutions of the Ljunggren-Nagell diophantine equation.
Atypical Molecular Basis for Drug Resistance to Mitochondrial Function Inhibitors in Plasmodium falciparum.

The continued emergence of drug-resistant Plasmodium falciparum parasites hinders global attempts to eradicate malaria, emphasizing the need to identify new antimalarial drugs. Attractive targets for chemotherapeutic intervention are the cytochrome (cyt) bc 1 complex, which is an essential component of the mitochondrial electron transport chain (mtETC) required for ubiquinone recycling and mitochondrially localized dihydroorotate dehydrogenase (DHODH) critical for de novo pyrimidine synthesis. Despite the essentiality of this complex, resistance to a novel acridone class of compounds targeting cyt bc 1 was readily attained, resulting in a parasite strain (SB1-A6) that was panresistant to both mtETC and DHODH inhibitors. Here, we describe the molecular mechanism behind the resistance of the SB1-A6 parasite line, which lacks the common cyt bc 1 point mutations characteristic of resistance to mtETC inhibitors. Using Illumina whole-genome sequencing, we have identified both a copy number variation (∼2×) and a single-nucleotide polymorphism (C276F) associated with pfdhodh in SB1-A6. We have characterized the role of both genetic lesions by mimicking the copy number variation via episomal expression of pfdhodh and introducing the identified single nucleotide polymorphism (SNP) using CRISPR-Cas9 and assessed their contributions to drug resistance. Although both of these genetic polymorphisms have been previously identified as contributing to both DSM-1 and atovaquone resistance, SB1-A6 represents a unique genotype in which both alterations are present in a single line, suggesting that the combination contributes to the panresistant phenotype. This novel mechanism of resistance to mtETC inhibition has critical implications for the development of future drugs targeting the bc 1 complex or de novo pyrimidine synthesis that could help guide future antimalarial combination therapies and reduce the rapid development of drug resistance in the field.
Simulating dust grain-radiation coupling on a moving mesh

We present a model for the interaction between dust and radiation fields in the radiation hydrodynamic code AREPO-RT, which solves the moment-based radiative transfer equations on an unstructured moving mesh. Dust is directly treated using live simulation particles, each of which represent a population of grains that are coupled to hydrodynamic motion through a drag force. We introduce methods to calculate radiation pressure on and photon absorption by dust grains. By including a direct treatment of dust, we are able to calculate dust opacities and update radiation fields self-consistently based on the local dust distribution. This hybrid scheme coupling dust particles to an unstructured mesh for radiation is validated using several test problems with known analytic solutions, including dust driven via spherically-symmetric flux from a constant luminosity source and photon absorption from radiation incident on a thin layer of dust. Our methods are compatible with the multifrequency scheme in AREPO-RT, which treats UV and optical photons as single-scattered and IR photons as multi-scattered. At IR wavelengths, we model heating of and thermal emission from dust. Dust and gas are not assumed to be in local thermodynamic equilibrium but transfer energy through collisional exchange. We estimate dust temperatures by balancing these dust-radiation and dust-gas energy exchange rates. This framework for coupling dust and radiation can be applied in future radiation hydrodynamic simulations of galaxy formation.
Kinetics of aging process on reduced Ag exchanged mordenite in dry air and humid air

Aging effects of off-gas streams including dry air and humid air on reduced silver exchanged mordenite (Ag0Z) were studied. Aged Ag0Z was prepared by exposing Ag0Z to dry air and humid air at different aging temperatures, time, and water vapor concentrations. Iodine loading capacity on the aged Ag0Z was obtained through a continuous-flow adsorption system. Significant iodine loading capacity losses were observed after the Ag0Z was exposed to dry air and humid air. Physical and chemical analyses were conducted to observe the physical and chemical changes of Ag0Z after being aged. From iodine adsorption data and sample analyses, it was found that iodine loading capacity on the aged Ag0Z in dry air and humid air decreases with increasing aging temperatures, time and water vapor concentrations. The pseudo reaction model describes experimental data well and the oxidation of Ag0 is the rate determining step in the aging process.
Cash Flow Hedging and Liquidity Choices

This article studies the interaction between corporate hedging and liquidity policies. We present a theoretical model that shows how corporate hedging facilitates greater reliance on cost-effective, externally provided liquidity in lieu of internal resources. We test the model’s predictions by employing a new empirical approach that separates cash flow hedging from other hedging instruments. Using detailed, hand-collected data, we find that cash flow hedging reduces the firm’s precautionary demand for cash and allows it to rely more on bank lines of credit. Furthermore, we find a significant positive effect of cash flow hedging on firm value, where prior evidence is mixed.
The Wrongheaded and Dangerous Campaign to Criminalize Good Faith Legal Advice

I argue in this brief essay that the increasingly fervent insistence on criminal punishment of the Bush administration lawyers for their legal advice on interrogation policy is both wrong-headed and dangerous. It is wrong-headed because the insistence on criminal prosecution of attorneys based solely upon their good faith interpretation of the law is highly unlikely to succeed as a matter of both U.S. and international law. It is dangerous because, at least with respect to U.S. law, prosecuting good faith legal advice is (and should be) a violation of those attorneys’ constitutional rights under the U.S. Constitution’s First Amendment and broader norms of free expression. Insisting on prosecuting lawyers for their good-faith legal advice, or even threatening prosecution, will chill the ability of future government lawyers to give legal advice on complex and important questions implicating U.S. national security.
The Value‐Added Tax in Ghana

Ghana's Parliament enacted a value-added tax (VAT) in December 1994, with collection to begin on March 1, 1995. The short preparation period proved fatal for the tax. However, the nation's fiscal problems continue and the government is resolved to reintroduce the tax in 1998. This article reviews the structure of the failed tax, showing how it would have been a more effective general consumption tax than the system it would have replaced, examines the reasons for its untimely demise, and considers prospects for a successful reintroduction of the tax. Ghana's experience with the VAT can hold important lessons for countries contemplating the introduction of such a tax.
Resource allocation challenges in South African universities: a management accounting perspective

This paper makes a critical appraisal of the resource allocation process in a South African university that attempts to improve its rating in international benchmarks. Using the University of the Witwatersrand as a case study, the paper documents its challenges, and develops a balanced scorecard for one of its professional academic units. The paper contributes to the literature on higher education management, and indicates that decentralisation reduces the problem of attraction and retention of academic staff, and examines the tensions between teaching and research on one hand, and professional schools and senior management on the other hand.
Feeling Inadequate?: The Struggle to Define the Savings Clause in 28 U.S.C. § 2255

Federal prisoners who wish to mount a collateral challenge to their conviction or sentence are generally prohibited from making their claim via the writ of habeas corpus and are forced to proceed under a similar procedure set out in 28 U.S.C. § 2255. After the passage of the Antiterrorism and Effective Death Penalty Act (AEDPA), which added significant restrictions to § 2255 review but not to habeas review, that prohibition can be the difference between freedom and incarceration for a federal prisoner serving a term of incarceration based on an illegal conviction or sentence. There is, however, a provision within § 2255, known as the savings clause, that contains an exception to the habeas bar where the remedy provided by § 2255 is “inadequate or ineffective to test the legality of the detention.” The courts of appeals have split on the proper test to govern the application of the savings clause. This Note examines each of the tests that has been adopted by the circuits and shows how each is problematic when analyzed in light of the text of § 2255, the legislative intent behind the passage of the AEDPA, and the constitutional considerations inherent in post-conviction review. This Note goes on to posit a new test for the application of the savings clause that more effectively navigates those competing interests.
Police Relations with Black and White Youths in Different Urban Neighborhoods

Much of the research on police—citizen relations has focused on adults, not youth. Given that adolescents and particularly young males are more likely than adults to have involuntary and adversarial contacts with police officers, it is especially important to investigate their experiences with and perceptions of the police. This article examines the accounts of young Black and White males who reside in one of three disadvantaged St. Louis, Missouri, neighborhoods— one predominantly Black, one predominantly White, and the other racially mixed. In-depth interviews were conducted with the youths, and the authors' analysis centers on the ways in which both race and neighborhood context influence young males' orientations toward the police.
Where do capabilities come from and how do they matter? A study in the software services industry

Recent years have witnessed a surge of interest in the notion of capabilities as an important source of competitive advantage. This recognition has, in turn, placed emphasis on the question of where and how these capabilities emerge and how they influence firm performance. The present paper is an attempt to address this question. Using a large sample of detailed project-level data from a leading firm in the global software services industry, we attempt to empirically study the importance of capabilities. We find that two broad classes of capabilities are significant. The first class, which we label client-specific capabilities, is a function of repeated interactions with clients over time and across different projects. This learning from repeated interactions with a given client reduces project execution costs and helps improve project contribution. The second class, termed project management capabilities, is acquired through deliberate and persistent investments in infrastructure and systems to improve the firm's software development process. Our empirical results suggest that the marginal returns to acquiring different capabilities may be different and an understanding of such trade-offs can improve firm decisions to improve and/or acquire such capabilities. We discuss the key contributions of our paper and the implications for future research on capabilities. Copyright © 2004 John Wiley & Sons, Ltd.
Endogenous Insurance and Informal Relationships

A rich literature seeks to explain the distinctive features of equilibrium institutions arising in risky environments which lack formal insurance and credit markets. I develop a theory of endogenous matching between heterogeneously risk-averse individuals who, once matched, choose both the riskiness of the income stream they face (ex ante risk management) as well as how to share that risk (ex post risk management). I …nd a clean condition on the fundamentals of the model for unique positive-assortative and negative-assortative matching in risk attitudes. From this, I derive an intuitive falsi…ability condition, discuss support for the theory in existing empirical work, and propose an experimental design to test the theory. Finally, I demonstrate the policy importance of understanding informal insurance as the risk-sharing achieved within the equilibrium network of partnerships, rather than within a single, isolated partnership. A hypothetical policy which reduces aggregate risk is a strict Pareto improvement if the matching is unchanged, but can be seen to harm the most risk-averse individuals and to exacerbate inequality when the endogenous network response is taken into account: the least risk-averse individuals abandon their roles as informal insurers in favor of entrepreneurial partnerships. This results in an increase in the risk borne by the most risk-averse agents, who must now
Civil Disobedience and the Lawyer's Obligation to the Law

The purpose of this essay is to propose and justify a theory of the proper role of the lawyer faced with issues involving civil disobedience. Given the assumption that civil disobedience sometimes is morally proper, the more difficult question concerns whether civil disobedience might be proper in certain circumstances for general (nonlawyer) citizens, yet still improper for the lawyer, either as individual or as counselor. As described in Part IA, by becoming a member of the legal profession the lawyer takes on special responsibilities, which require the lawyer to make certain personal and professional sacrifices. As described in Part IB, our American legal system, with its Constitution, Bill of Rights, and emphasis on democracy, causes many people to see a close correlation between the rule of law (the notion that there are certain principles of justice with which both governments and individuals must comply) and positive law (the pronouncements of legislatures, courts, and administrative entities). Part IC sets out why, in light of this close identification between positive law and the rule of law, lawyers have a special obligation to act in accordance with the law. Part II of this article discusses the lawyer as counselor. When serving as a counselor, the lawyer provides both raw information and discussion to help the client make a fully informed decision. The lawyer's role as counselor includes informing the client of his or her options within the law. In order to fulfill this responsibility, the lawyer must be able to have a wide ranging discussion with the client. Any limitations on the lawyer's discussion come from according proper respect for the client's autonomy.
Converting social conflict: Focal points and the evolution of cooperation

We examine the ability of focal points to transform situations of potential conflict into situations of cooperation. In performing this function, focal points convert “worst-case scenarios” into “better-case scenarios,” which are easier for political economic systems to handle. Focal points thus contribute to the ability of political economies to perform well in the face of less than ideal conditions, enhancing systemic robustness.
From Here to Eternity: Environmental Law and Future Generations

In formulating environmental regulation, policy makers must often consider tradeoffs between current costs and benefits far in the future. One controversial technique for weighing future consequences is exponential discounting, which is used to convert future benefits into their equivalent present-day values. In this article, Professor Farber assesses the appropriateness of using exponential discounting to place a present-day value on future harms, which often may have the effect of minimizing catastrophic events far in the future. Professor Farber concludes that some form of discounting is appropriate, given that society cannot allocate finite resources equally over an infinite number of future time periods. Professor Farber reaches this conclusion through a model which relies on three simple assumptions. The first is that we are always willing to invest something to obtain a future benefit. The second is that the value of a future time period is the sum of its parts. And finally, that the relative appeal of permanent versus temporary solutions remains the same. Based on these assumptions, Professor Farber argues that exponential discounting necessarily follows. Professor Farber then considers several other factors that can affect this model, such as the perpetuation value of environmental resources and the use of hyperbolic discounting, where the discount rate itself declines over time.
The Role of Alcohol and Drug Consumption in Determining Physical Fights and Weapon Carrying by Teenagers

The purpose of this study is to examine the question of whether alcohol or drug use causes teenagers to engage in violent behaviors as measured by physical fighting, carrying a gun, or carrying other types of weapons. Simple OLS estimation of the effects of drug and alcohol consumption on violence may be biased because of the possibility that both behaviors are determined by unmeasured individual traits. Two-stage least squares estimates are employed to establish causality. This method first predicts consumption using the prices of beer, marijuana and cocaine and then enters predicted consumption in the violence equation. This technique allows the consumption measures to be purged of their correlation with unobserved characteristics. Data come from the National School-Based Youth Risk Behavior Surveys, which are nationally representative samples of high school students. Results indicate that beer and marijuana consumption do cause teens to engage in more physical fights, while cocaine use appears to have no relationship. None of the substances lead to increased probabilities of carrying a gun or other weapon.
Does Advertising Overcome Brand Loyalty? Evidence from the Breakfast‐Cereals Market

In differentiated product markets where consumer preferences are characterized by brand loyalty, an important role for advertising may be to overcome brand loyalty by encouraging consumers to switch to less familiar brands. Using a scanner panel dataset of breakfast-cereal purchases, I find evidence consistent with the hypothesis that advertising counteracts the tendencies of brand loyalty toward repeat purchasing. Equivalently, advertising reduces switching costs in this market. Furthermore, counterfactual experiments demonstrate that in markets with brand loyalty, advertising is an attractive and effective option—relative to alternative promotional activities, such as price discounts—of stimulating demand for a brand.