cssi/SciSciGPT-SciSciNet huggingface dataset:
Supernova 1998S at 14 years postmortem: continuing circumstellar interaction and dust formation

We report late-time spectroscopic observations of the Type IIn supernova (SN) 1998S, taken 14 years after explosion using the Large Binocular Telescope. The optical spectrum exhibits strong, broad emission features of [O i], [O ii] and Hα, in addition to weaker features of [O iii], Hβ and [Fe ii]. The last decade of evolution has exhibited a strengthening of the oxygen transitions relative to Hα, evidence that the late-time emission is powered by increasingly metal-rich SN ejecta crossing the reverse shock. The Hα luminosity of ≈8000 L⊙ requires that SN 1998S is still interacting with relatively dense circumstellar material (CSM), probably produced by the strong wind of a red supergiant progenitor at least ∼103 years before explosion. The emission lines exhibit asymmetric blueshifted profiles, which implies that the receding hemisphere of the SN is obscured by dust. The [O iii] λ5007 line, in particular, exhibits a complete suppression of its red wing. This could be the result of the expected wavelength dependence for dust extinction or a smaller radial distribution for [O iii]. In the latter case, the red wing of [O iii] could be absorbed by core dust, while both the blue and red wings are absorbed by dust within the cool dense shell between the forward and reverse shocks; this interpretation could explain why late-time [O iii] emission from SNe is often weaker than models predict. The [O i] line exhibits double-peaked structure on top of the broader underlying profile, possibly due to emission from individual clumps of ejecta or ring-like structures of metal-rich debris. The centroids of the peaks are blueshifted and lack a red counterpart. However, an archival spectrum obtained on day 1093 exhibits a third, redshifted peak, which we suspect has become extinguished by dust that formed over the last decade, after day 1093. This implies that the ‘missing’ red components of multi-peaked oxygen profiles observed in other SNe might be obscured by varying degrees of dust extinction.
Presentations of self and the status dynamics of psychotherapy and supervision.

This article explores basic issues in the status dynamics of psychotherapy and supervision. Self-presentation and status markers create a dynamic that affects the participants in psychotherapy and ...
Credit constraints and international financial crises

Abstract A version of the Kiyotaki and Moore (J. Political Econom. 105 (1997) 211) model of credit cycles is used to examine the extent to which a crisis in a country can spread to another seemingly unrelated country. The model features two small open economies that face credit constraints and produce a differentiated commodity which they export to a large country. A productivity shock to one of the small open economies triggers an adverse terms of trade shock to the other which is then amplified by credit constraints. The paper provides a new perspective on the relationship between terms of trade shocks and the balance of payments that differs from existing models which focus on risk sharing and consumption smoothing. In particular, it is shown that if financial frictions are present, a temporary terms of trade shock can trigger capital outflows and a rapid deterioration in the current account.
The Expected Rate of Credit Losses on Banks' Loan Portfolios

ABSTRACT Estimating expected credit losses on banks' portfolios is difficult. The issue has become of increasing interest to academics and regulators with the FASB and IASB issuing new regulations ...
How Effective Is Internal Control Reporting under SOX 404? Determinants of the (Non‐)Disclosure of Existing Material Weaknesses

We study determinants of internal control reporting decisions under Section 404 of the Sarbanes-Oxley Act (SOX 404) using a sample of restating firms whose original misstatements are linked to underlying control weaknesses. We find that only a minority of these firms acknowledge their existing control weaknesses during their misstatement periods, and that this proportion has declined over time. Further, the probability of reporting existing weaknesses is negatively associated with external capital needs, firm size, non-audit fees, and the presence of a large audit firm; it is positively associated with financial distress, auditor effort, previously reported control weaknesses and restatements, and recent auditor and management changes. These results provide evidence that detection and disclosure incentives play a role in whether existing material weaknesses are reported, which has implications for the effectiveness of SOX 404 in providing investors with advance warning of potential accounting problems.
The linearized classical Boussinesq system on the half‐line

The linearization of the classical Boussinesq system is solved explicitly in the case of nonzero boundary conditions on the half-line. The analysis relies on the unified transform method of Fokas and is performed in two different frameworks: (i) by exploiting the recently introduced extension of Fokas's method to systems of equations; (ii) by expressing the linearized classical Boussinesq system as a single, higher-order equation which is then solved via the usual version of the unified transform. The resulting formula provides a novel representation for the solution of the linearized classical Boussinesq system on the half-line. Moreover, thanks to the uniform convergence at the boundary, the novel formula is shown to satisfy the linearized classical Boussinesq system as well as the prescribed initial and boundary data via a direct calculation.
Contemporaneous Loan Stress and Termination Risk in the CMBS Pool: How “Ruthless” is Default?

∗∗∗ This study analyzes the impact of contemporaneous loan stress on the termination of loans in the commercial mortgage-backed securities pool from 1992 to 2004 using a novel measure, based on changes in net operating incomes and property values at the metropolitan statistical area-property-type-year level. Employing a semi-parametric competing risks model for a variety of specifications, we find that the probability of default is extremely low even at very high levels of stress, although the coefficient estimates of greatest interest are very statistically significant. These results suggest substantial lender forbearance and are consistent with previous research that models default as a “gradual dynamic process” rather than a “ruthless” exercise once “in the money.” The period from 1980 to 2004 saw significant fluctuations in commercial property markets across the country: recession and collapse during the late 1980s and early 1990s, recovery in the late 1990s, and downturn yet again with the events of September 11. During much of this period, default rates on commercial loans have moved strongly with these market trends: soaring in the late 1980s and early 1990s and then falling steadily with market recovery in the 1990s. As documented in Lancaster and Butler (2006), they remained remarkably low from 2000 to 2004 despite the market stress after September 11. So how does one go about explaining this phenomenon? The first explanation argues that levels of loan stress in the last decade have simply been unusually low. As markets recovered even poorly originated loans remained relatively free from stress, and the Federal Reserve Board’s liquid monetary policy after 2002 kept asset prices from reacting to the recession. An alternative explanation is that borrowers and lenders have become more accommodative to loan distress in recent years and that default has become a slowly evolving dynamic game—rather than the “ruthless” exercise of an option.
Triangulating the World Trade Organization

One of the biggest challenges facing the World Trade Organization is to determine its own mission. The failure to launch new trade talks at the WTO’s Ministerial Conference at Seattle in late 1999 was due, in large part, to disagreements between members about what “new” issues should be placed on the negotiating agenda. These problems continued to stymie the WTO in the run-up to the Doha ministerial meeting in 2001.
Can the Euro Ever Challenge the Dollar

Can the euro ever challenge the dollar as an international currency? This article argues that Europe's new money is fated to remain a distant second to America's greenback, for four reasons. First is the persistent inertia of monetary behaviour, which will inhibit any rapid switch to the euro. Second is the cost of doing business in euros, which is unlikely to decline below transactions costs for the greenback. Third is an anti-growth bias built into EMU, which will limit returns on euro-denominated assets. And fourth is the ambiguous governance structure of EMU, which sows doubt among prospective euro users.
The IDEA Eligibility Mess

The Individuals with Disabilities Education Act (IDEA) guarantees students with disabilities a free public education appropriate to their needs, but students must meet the definition of “child with a disability” to be eligible for that entitlement. The law governing special education eligibility, however, is charitably characterized as a mess. There are several sources of the current eligibility confusion. First, recent court cases have reached conflicting conclusions about how much adverse educational impact the child’s disabling condition must have, what constitutes a sufficient need for special education, and when children with emotional disabilities are eligible. Second, long-established methods for assessing learning disabilities have withered under criticism from educational experts, and a new method of approaching learning disabilities, response-to-intervention, is being touted by the United States Department of Education. Nevertheless, that innovation remains largely unproven and may be impossible to implement at scale. Third, Congress and others have focused long-overdue attention on the disproportionate percentage of African-Americans who are found eligible for special education under the disability categories of mental retardation and emotional disturbance, but neither Congress nor anyone else appears to have a promising idea about how to address the situation. This Article analyzes and critiques the recent cases, describes and comments on the new learning disability assessment methodology, and evaluates competing ideas about how to respond to ethnic disproportion. It concludes that the solution to the entire set of problems is not a redefinition of special education eligibility under IDEA, but rather a renewed attention to the actual terms of the statute and the goal of full educational opportunity. This step will promote what might be called “not-quite-so-special education,” that is, an entitlement for a broad class of children to high quality special education supports provided in the regular educational environment. * Vincent dePaul Professor of Law, DePaul University. B.A. Columbia, J.D. Yale. Thanks to Robert Garda, Andrea Kaufman, Michael Perlin, and Paul Secunda for their comments on an earlier draft. Thanks also to Kim Brown, David King, and Christopher Cook for their research assistance. Author contact: mweber@depaul.edu; 312/362-8808.
Ranking, Unemployment Duration, and Wages

It explores the implication of one central assumption: when firms receive multiple acceptable applications, they hire the worker who has been unemployed for the least amount of time. This assumption ("ranking") is contrasted with the assumption of random hiring ("no-ranking"). By embodying this assumption in a model of the labour market with job creation/destruction and matching, the joint behaviour of unemployment, the distribution of unemployment durations, and wages are characterized. The implication that the re-employment prospects of employed workers, were they to become unemployed, are better than those of the currently unemployed appears to have been an important feature of European unemployment experience in the 1980's. This paper examines the effects of the composition of unemployment on wage determination. It explores one central assumption: when firms receive multiple acceptable applications, they hire the worker who has been unemployed for the least amount of time. We refer to this assumption as "ranking" and contrast it throughout to the assumption of random hiring, or "no-ranking". By embodying this assumption in a model of the labour market with job creation/destruction and matching, we characterize the joint behaviour of unemployment, the distribution of unemployment durations, and wages. "Ranking" has a number of important implications. First, in addition to the obvious result that the exit rate from unemployment is a decreasing function of duration, we show that the effect of duration is stronger the higher the rate of unemployment. Second, with the wage depending on the distributions of prospective unemployment durations, the presence of long-term unemployed, per se, has little effect on wages. Third, looking at the relation between the wage and the aggregate level of unemployment, and comparing ranking to the case of no-ranking, the wage moves less with the level of unemployment, but more with the change in unemployment. Put simply, ranking and no-ranking models show exactly the same aggregate unemployment, slightly different long-run responses of wages to unemployment, and sharply different wage dynamics. The paper is organized as follows. Section I characterizes the matching process and derives a matching function based on an urn-ball process, with vacancies as urns and applications by unemployed workers as balls. Thus the distribution of applications per vacancy depends on aggregate unemployment and vacancies. Vacancies with at least one acceptable application are filled. When a vacancy receives more than one acceptable application, firms use a rule to choose among applicants. Thus, the rule determines who is hired but does not affect the number of hires. Section II uses this matching function in a model of the labour market with continual job creation and destruction and characterizes the equilibrium values of unemployment, vacancies and hires.
A Theory of Bank Capital

Banks can create liquidity precisely because deposits are fragile and prone to runs. Increased uncertainty makes deposits excessively fragile, creating a role for outside bank capital. Greater bank capital reduces the probability of financial distress but also reduces liquidity creation. The quantity of capital influences the amount that banks can induce borrowers to pay. Optimal bank capital structure trades off effects on liquidity creation, costs of bank distress, and the ability to force borrower repayment. The model explains the decline in bank capital over the last two centuries. It identifies overlooked consequences of having regulatory capital requirements and deposit insurance. DOES BANK CAPITAL STRUCTURE MATTER, and if so, how should it be set? Most work on the subject extrapolates an answer from prior work on the capital structure of industrial firms. But bank assets and functions are not the same as those of industrial firms. In fact, one strand of the banking literature suggests banks have a role precisely because they do not suffer the asymmetric information costs of issuance faced by industrial firms (see Gorton and Pennacchi (1990)). Therefore, to really understand the determinants of bank capital structure, we should start by modeling the essential functions banks perform, and then ask what role capital plays. Using this approach, we can see that a bank's capital structure affects its liquiditycreation and credit-creation functions in addition to its stability. The consequent trade-offs imply an optimal bank capital structure. Because customers rely to different extents on liquidity and credit, bank capital structure also determines the nature of the bank's clientele. Our approach will help us better understand the impact of regulations such as minimum capital requirements, and also help suggest the consequences of different recapitalization policies in a banking crisis. We start by describing the functions a bank performs. Consider a world where a number of entrepreneurs each has a project in need of funding. Each entrepreneur has specific abilities vis 'a vis his project so that the cash flows he can generate exceed what anyone else can generate from it. An entrepreneur cannot commit his human capital to the project, except on a
Lending Relationships and Information Rents: Do Banks Exploit Their Information Advantages?

In the process of lending to a firm, a bank acquires proprietary firm-specific information that is unavailable to nonlenders. This asymmetric evolution of information between lenders and prospective lenders grants the former an information monopoly. This article empirically investigates whether relationship banks exploit this advantage by charging higher interest rates than those that would prevail were all banks symmetrically informed. My identification strategy hinges on the notion that large information shocks that level the playing field among banks erode the relationship bank's information monopoly. I use the borrower's initial public offering (IPO) as such an information-releasing event, and build a panel dataset in which the unit of observation is a firm's lending relationships before and after its IPO. Prior to a firm's IPO, I find a U-shaped relation between borrowing rates and relationship intensity. After the IPO, interest rates are decreasing in relationship intensity. Furthermore, mean interest rates drop after an IPO. The results are robust to firm and loan-year fixed effects, and to controls for firm leverage pre- and post-IPO. Thus, the reported interest rate pattern is clean of any confounding effects that might arise from changes in financial risk. The Author 2009. Published by Oxford University Press on behalf of The Society for Financial Studies. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org, Oxford University Press.
The Base Closure and Realignment Commission: A Rational or Political Decision Process?

This article examines the Base Closure and Realignment Commission's (BRAC) decision process. It uses as a case study the BRAC's reversal of the Defense Department's recommendation concerning the east coast air mobility wing. The analysis reviews decision theory, the rational and political decision models, and the financial implications of the reversal decision.
What Can Account for Fluctuations in the Terms of Trade

This paper studies the sources of terms of trade volatility. We decompose the terms of trade into two components. The ‘goods price’ component stems from differences in the composition of import and export baskets, while the ‘country price’ component stems from deviations from the law of one price. Countries are classified according to their major import and export goods: commodities, manufactured goods and fuels. Except fuel exporters, there is roughly equal importance of goods price vs country price volatility. These results suggest that there may be a role for reducing terms of trade volatility through diversification of a country's exports.
Marginal Cost Pricing and Eminent Domain

There are three separate strands of literature in economics that are related to the efficiency of takings under eminent domain: one addresses the question of optimal compensation for properties that are taken, the second inquires how governments might learn the values of properties that they consider taking, while the third analyzes solutions to the problem of land assembly. This essay reviews these strands of literature and argues that the principle of marginal cost pricing can be used as a unifying principle for integrating them.
On Kamisar, killing, and the future of physician-assisted death.

Tens perhaps hundreds of thousands of trees could have been spared over the last forty-five years had opponents of physicianassisted death only been content to let Yale Kamisar be their exclusive spokesperson. Their movement would have lost no significant substance or persuasive force, for Kamisar's 1958 article Some NonReligious Views Against Proposed 'Mercy-Killing' Legislation'presaged the shape and content of the subsequent forty-five year debate over legalizing physician-assisted death ("PAD").2 Kamisar's article preceded by years the development of a whole jurisprudence relating to the withholding/withdrawing of life-sustaining medical treatment ("LSMT") and the administration of pain-relief substances alleviating physical suffering while risking accelerated death.3 That article demonstrated remarkable prescience and intellectual honesty while shaping the content of opposition to PAD. Kamisar continued to participate in the debate for decades thereafter,4 always exhibiting remarkable intellectual honesty and
Two Kinds of Criminal Wrongs

I distinguish two kinds of criminal wrongs. A wrongdoer who acts in defiance of his conscience is guilty of what I call a wicked wrong. A wrongdoer who does not act in defiance of his conscience is...
A Maximum Entropy Joint Demand Estimation and Capacity Control Policy

We propose a tractable, data-driven demand estimation procedure based on the use of maximum entropy (ME) distributions, and apply it to a stochastic capacity control problem motivated from airline revenue management. Specifically, we study the two fare class “Littlewood” problem in a setting where the firm has access to only potentially censored sales observations; this is also known as the repeated newsvendor problem. We propose a heuristic that iteratively fits an ME distribution to all observed sales data, and in each iteration selects a protection level based on the estimated distribution. When the underlying demand distribution is discrete, we show that the sequence of protection levels converges to the optimal one almost surely, and that the ME demand forecast converges to the true demand distribution for all values below the optimal protection level. That is, the proposed heuristic avoids the “spiral down” effect, making it attractive for problems of joint forecasting and revenue optimization problems in the presence of censored observations.
Law as Design: Objects, Concepts and Digital Things

This Article initiates an account of “things” in the law, including both conceptual things and material things. Human relationships matter to the design of law. Yet things matter too. To an increasing extent, and particularly via the advent of digital technology, those relationships are not only considered ex post by the law but are designed into things, ex ante, by their producers. This development has a number of important dimensions. Some are familiar, such as the reification of conceptual things as material things, so that computer software is treated as a good. Others are new, such as the characterization of material things as conceptual things, so that digital goods become licensable. The regulatory consequences of the thing are increasingly built into the construction of the thing. These developments appear to be poised to envelop things beyond the digital sphere. It may no longer be apt to divide the world cleanly into conceptual and material objects. “Things” combine features of both. As a result, they can no longer be viewed solely as passive backgrounds against which relation-based legal analysis unfolds. To ensure that society maintains the ability to regulate as broadly as it deems legitimate, law must account for the creation and design of the “things” that increasingly dominate developments across a variety of legal domains, from intellectual property law to antitrust law to commercial law. The Article describes how things exercise the authority that characterizes classic legal regulation, and it reviews the different mechanisms that legal institutions have used to recognize and differentiate things. Understanding those mechanisms is a step toward appreciating the nature of the regulatory landscape in which both legal institutions and
Effect of Technology on Sales Performance: Progressing from Technology Acceptance to Technology Usage and Consequence

Technology plays an ever-increasing role in personal selling and customer relationship management (CRM). Over the past decade, many models examining the acceptance of technology have been proposed and refined, contributing significantly to our knowledge of technology adoption. An implicit assumption made in such models is that increasing the usage of technology is better—that is, more usage is better than less usage. This is a critical assumption that has not been tested in the literature. What if technology has diminishing returns? We propose that it is time to progress to a Technology Performance Usage Model (TPUM) and to look for usage levels that lead to optimum effect on performance. Our model is tested using a sample of 131 salespeople in an operational CRM context. Results show a curvilinear relationship between a salesperson’s prime task performance (measured as sales percent to quota) and their usage of the “enabling” CRM technology. Initially, the CRM technology is enabling on sales performance,...
Testing the Effects of Sale Method Restrictions in Municipal Bond Issuance: The Case of New Jersey

Can state governments save money by restricting the practice of selling tax-exempt bonds through negotiation, or do such regulations impose additional costs? Circumstances in New Jersey recently created a natural experiment to test this proposition. This study finds significant cost savings for those issues sold through competition both before and after such restrictions were put in place. All else equal, issues sold competitively after the policy change did not have significantly higher interest costs, despite a shift in volume toward competitive sales, suggesting that there exists room for increased use of competitive sales without incurring a cost penalty.
Probability Elicitation, Scoring Rules, and Competition Among Forecasters

Probability forecasters who are rewarded via a proper scoring rule may care not only about the score, but also about their performance relative to other forecasters. We model this type of preference and show that a competitive forecaster who wants to do better than another forecaster typically should report more extreme probabilities, exaggerating toward zero or one. We consider a competitive forecaster's best response to truthful reporting and also investigate equilibrium reporting functions in the case where another forecaster also cares about relative performance. We show how a decision maker can revise probabilities of an event after receiving reported probabilities from competitive forecasters and note that the strategy of exaggerating probabilities can make well-calibrated forecasters (and a decision maker who takes their reported probabilities at face value) appear to be overconfident. However, a decision maker who adjusts appropriately for the misrepresentation of probabilities by one or more forecasters can still be well calibrated. Finally, to try to overcome the forecasters' competitive instincts and induce cooperative behavior, we develop the notion of joint scoring rules based on business sharing and show that these scoring rules are strictly proper.
Say at home, or stay at home? Policy implications on female labor supply and empowerment

This paper develops a theory of female labor supply in a general equilibrium framework in the context of a developing economy. In stage 1, men and women decide whether to get married foreseeing the power and market dynamics in stage 2. Single people make their own decisions whereas married couples make decisions together, the power distribution among partners is determined endogenously. It is shown that female labor supply can take different shapes due to structural differences between economies and multiple equilibria might occur, causing low female labor force participation trap. As for policy implications, we find that tax-break to the employers can give a huge boost to female employment and may reduce the wage-gap. However, tax-benefit to women may widen the wage-gap although both these policies empower women. We also conclude that true empowerment should come with the freedom of choice (to work); increasing female labor force participation does not necessarily empower women. Results found here resonate well with previous empirical findings and suggest additional testable implications.
The Effect of Measurement Task Transparency on Preference Construction and Evaluations of Personalized Recommendations

Abstract Marketing activities frequently involve personalizing product offers to consumers' individually measured preferences. Because preferences are often ill-defined, responses to customized offers may depend on how easy it is for consumers to identify the preferences they stated in the measurement task. A series of experiments shows that the likelihood of choosing a personalized recommendation that matches measured preferences most closely is greater with measurement tasks that allow consumers to identify their stated preferences more easily (i.e., transparent tasks). However, this difference in choice likelihood due to task transparency is observed only for novices (versus experts), and making the identification of stated preferences more difficult eliminates the effect by decreasing the choice likelihood following more (versus less) transparent tasks. The author identifies consumers' understanding of their own preferences as the mechanism underlying the task transparency effect. The findings provide...
Agroecosystem modeling and optimal economic decisions: Implications for sustainable agriculture

We adapt a biogeochemical model of an agroecosystem to account for optimal economic behavior on the part of agricultural producers. Two institutional management regimes are considered: one in which a representative producer does not account for stock pollution caused by use of agricultural inputs, and one in which the externality is internalized. Comparative statics of the steady state of the former problem are analyzed in order to gain insight into the effects of potential policy and technological changes. Results show that a more realistic ecosystem component that includes nutrient cycling can qualitatively change optimal management practices relative to a one-state representation, potentially rendering systems ‘unsustainable’ under some criteria and leading to policy instruments that exacerbate, rather than mitigate, external damages or the resource base. Moreover, the qualitative effect of changes in model parameters are not necessarily uniform across different agricultural systems, implying that a prescription for the so-called ‘sustainable’ management under one system may have unintended consequences under another system. Copyright © 2007 John Wiley & Sons, Ltd.
Calendar rotations: A new approach for studying the impact of timing using earnings announcements

Abstract We develop a novel methodology for studying the causal impact of announcement timing. Our methodology uses firms’ earnings announcements and leverages quasi-exogenous variation attributable to the specific day-of-week on which a calendar month begins. We refer to the resulting variation in announcement timing as “calendar rotations,” which are uncorrelated with proxies for announcement content. In applying our methodology, we show announcements moved forward by calendar rotations receive heightened media and investor attention, and experience greater earnings announcement premia. Taken together, our study details a method for studying how the timing of information flows impacts outcomes of interest to financial economists.
Periodicity in the cohomology of finite general linear groups via $q$-divided powers

We show that $\bigoplus_{n \ge 0} {\mathrm H}^t({\bf GL}_n({\bf F}_q), {\bf F}_\ell)$ canonically admits the structure of a module over the $q$-divided power algebra (assuming $q$ is invertible in ${\bf F}_{\ell}$), and that, as such, it is free and (for $q \neq 2$) generated in degrees $\le t$. As a corollary, we show that the cohomology of a finitely generated ${\bf VI}$-module in non-describing characteristic is eventually periodic in $n$. We apply this to obtain a new result on the cohomology of unipotent Specht modules.
Quantum Behavior of a Classical Particle Subject to a Random Force

We give a partial answer to the question whether the Schrodinger equation can be derived from the Newtonian mechanics of a particle in a potential subject to a random force. We show that the fluctuations around the classical motion of a one dimensional harmonic oscillator subject to a random force can be described by the Schrodinger equation for a period of time depending on the frequency and the energy of the oscillator. We achieve this by deriving the postulates of Nelson’s stochastic formulation of quantum mechanics for a random force depending on a small parameter. We show that the same result applies to small potential perturbations around the harmonic oscillator. We also show that the noise spectrum can be chosen to obtain the result for all oscillator frequencies for fixed mass. We discuss heuristics to generalize the result for a particle in one dimension in a potential where the motion can be described using action-angle variables. The main motivation of this paper is to provide a step for constructing a Newtonian theory which would approximately reproduce quantum mechanics both in unitary evolution and measurement regimes.
Synchronization of clocks and metronomes: A perturbation analysis based on multiple timescales.

In 1665, Huygens observed that two pendulum clocks hanging from the same board became synchronized in antiphase after hundreds of swings. On the other hand, modern experiments with metronomes placed on a movable platform show that they often tend to synchronize in phase, not antiphase. Here, we study both in-phase and antiphase synchronization in a model of pendulum clocks and metronomes and analyze their long-term dynamics with the tools of perturbation theory. Specifically, we exploit the separation of timescales between the fast oscillations of the individual pendulums and the much slower adjustments of their amplitudes and phases. By scaling the equations appropriately and applying the method of multiple timescales, we derive explicit formulas for the regimes in the parameter space where either antiphase or in-phase synchronization is stable or where both are stable. Although this sort of perturbative analysis is standard in other parts of nonlinear science, surprisingly it has rarely been applied in the context of Huygens’s clocks. Unusual features of our approach include its treatment of the escapement mechanism, a small-angle approximation up to cubic order, and both a two- and three-timescale asymptotic analysis.
Robot-Based Assessment of HIV-Related Motor and Cognitive Impairment for Neurorehabilitation

There is a pressing need for strategies to slow or treat the progression of functional decline in people living with HIV. This paper explores a novel rehabilitation robotics approach to measuring cognitive and motor impairment in adults living with HIV, including a subset with stroke. We conducted a cross-sectional study with 21 subjects exhibiting varying levels of cognitive and motor impairment. We tested three robot-based tasks – trajectory tracking, N-back, and spatial span – to assess if metrics derived from these tasks were sensitive to differences in subjects with varying levels of executive function and upper limb motor impairments. We also examined how well these metrics could estimate clinical cognitive and motor scores. The results showed that the average sequence length on the robot-based spatial span task was the most sensitive to differences between various cognitive and motor impairment levels. We observed strong correlations between robot-based measures and clinical cognitive and motor assessments relevant to the HIV population, such as the Color Trails 1 ( rho = 0.83), Color Trails 2 ( rho = 0.71), Digit Symbol – Coding ( rho = 0.81), Montreal Cognitive Assessment – Executive Function subscore ( rho = 0.70), and Box and Block Test ( rho = 0.74). Importantly, our results highlight that gross motor impairment may be overlooked in the assessment of HIV-related disability. This study shows that rehabilitation robotics can be expanded to new populations beyond stroke, namely to people living with HIV and those with cognitive impairments.
Design and Experiments with LoCO AUV: A Low Cost Open-Source Autonomous Underwater Vehicle*

In this paper we present the LoCO AUV, a Low-Cost, Open Autonomous Underwater Vehicle. LoCO is a general-purpose, single-person-deployable, vision-guided AUV, rated to a depth of 100 meters. We discuss the open and expandable design of this underwater robot, as well as the design of a simulator in Gazebo. Additionally, we explore the platform’s preliminary local motion control and state estimation abilities, which enable it to perform maneuvers autonomously. In order to demonstrate its usefulness for a variety of tasks, we implement a variety of our previously presented human-robot interaction capabilities on LoCO, including gestural control, diver following, and robot communication via motion. Finally, we discuss the practical concerns of deployment and our experiences in using this robot in pools, lakes, and the ocean. All design details, instructions on assembly, and code will be released under a permissive, open-source license.
The Fact-Law Distinction: Strategic Factfinding and Lawmaking in a Judicial Hierarchy

A fundamental but understudied procedural institution of American law is that appellate courts defer more to trial courts’ findings of fact than to their conclusions of law. I formally model this procedural institution, showing how trial courts use factfinding to achieve their preferred outcome and how appellate courts craft rules in anticipation of trial courts’ strategic factfinding. Trial courts do not always report facts truthfully. Appellate courts do not commit to consistent rules, but consistent rules may emerge in equilibrium, creating a misleading appearance of judicial commitment to legal consistency. Preference divergence between trial and appellate courts has a nonmonotonic effect on factfinding. Fact deference can explain suboptimal rulemaking and reversals even when there is no uncertainty about the likelihood of review or the reviewing court’s ideal rule. The model is also useful in understanding why the institution of fact deference persists. Applications to policing and other domains are discussed. (JEL K40, K41, D02)
Data Analysis Using Representation Theory and Clustering Algorithms

This work aims to expand the knowledge of the area of data analysis through persistence homology and representations of directed graphs. To be specific, we looked for how we can analyze homology cluster groups using agglomerative Hierarchical Clustering algorithms and methods. Additionally, the Wine data, which is offered in R studio, was analyzed using various cluster algorithms such as Hierarchical Clustering, K-Means Clustering, and PAM Clustering. The goal of the analysis was to find out which cluster's method is proper for a given numerical dataset. We tried to find the agglomerative hierarchical clustering method by testing the data that will be the optimal clustering algorithm among these three; K-Means, PAM, and Random Forest methods. By comparing each model's accuracy value with cultivar coefficients, we concluded that K-Means methods are the most helpful when working with numerical variables. On the other hand, PAM clustering and Gower with Random Forest are the most beneficial approaches when using categorical variables. These tests can determine the optimal number of clustering groups, given the data set, and by doing the proper analysis. Using those the project, we can apply our method to several industrial areas such that clinical, business, and others. For example, people can make different groups based on each patient who has a common disease, required therapy, and other things in the clinical society. Additionally, people can expect to get several clustered groups based on the marginal profit, marginal cost, or other economic indicators for the business area.
The effect of differential victim crime reporting on predictive policing systems

Police departments around the world have been experimenting with forms of place-based data-driven proactive policing for over two decades. Modern incarnations of such systems are commonly known as hot spot predictive policing. These systems predict where future crime is likely to concentrate such that police can allocate patrols to these areas and deter crime before it occurs. Previous research on fairness in predictive policing has concentrated on the feedback loops which occur when models are trained on discovered crime data, but has limited implications for models trained on victim crime reporting data. We demonstrate how differential victim crime reporting rates across geographical areas can lead to outcome disparities in common crime hot spot prediction models. Our analysis is based on a simulation1 patterned after district-level victimization and crime reporting survey data for Bogota, Colombia. Our results suggest that differential crime reporting rates can lead to a displacement of predicted hotspots from high crime but low reporting areas to high or medium crime and high reporting areas. This may lead to misallocations both in the form of over-policing and under-policing.
Efficacy of the radial pair potential approximation for molecular dynamics simulations of dense plasmas

Macroscopic simulations of dense plasmas rely on detailed microscopic information that can be computationally expensive and is difficult to verify experimentally. In this work, we delineate the accuracy boundary between microscale simulation methods by comparing Kohn–Sham density functional theory molecular dynamics (KS-MD) and radial pair potential molecular dynamics (RPP-MD) for a range of elements, temperature, and density. By extracting the optimal RPP from KS-MD data using force matching, we constrain its functional form and dismiss classes of potentials that assume a constant power law for small interparticle distances. Our results show excellent agreement between RPP-MD and KS-MD for multiple metrics of accuracy at temperatures of only a few electron volts. The use of RPPs offers orders of magnitude decrease in computational cost and indicates that three-body potentials are not required beyond temperatures of a few eV. Due to its efficiency, the validated RPP-MD provides an avenue for reducing errors due to finite-size effects that can be on the order of ∼ 20 %.
Asymptotically Optimal Strategies for Online Prediction with History-Dependent Experts

We establish sharp asymptotically optimal strategies for the problem of online prediction with history dependent experts. The prediction problem is played (in part) over a discrete graph called the d dimensional de Bruijn graph, where d is the number of days of history used by the experts. Previous work Drenska and Kohn ( arXiv:2007.12732 , 2020) established $$O(\varepsilon )$$ optimal strategies for $$n=2$$ experts and $$d\le 4$$ days of history, while Drenska and Kohn (J Nonlinear Sci 30. 30(1), 137–173, 2020) established $$O(\varepsilon ^{1/3})$$ optimal strategies for all $$n\ge 2$$ and all $$d\ge 1$$ , where the game is played for N steps and $$\varepsilon =N^{-1/2}$$ . In this paper, we show that the optimality conditions over the de Bruijn graph correspond to a graph Poisson equation, and we establish $$O(\varepsilon )$$ optimal strategies for all values of n and d.
Structure for Regular Inclusions. II: Cartan envelopes, pseudo-expectations and twists

Abstract We introduce the notion of a Cartan envelope for a regular inclusion ( C , D ) . When a Cartan envelope exists, it is the unique, minimal Cartan pair into which ( C , D ) regularly embeds. We prove a Cartan envelope exists if and only if ( C , D ) has the unique faithful pseudo-expectation property and also give a characterization of the Cartan envelope using the ideal intersection property. For any covering inclusion, we construct a Hausdorff twisted groupoid using appropriate linear functionals and we give a description of the Cartan envelope for ( C , D ) in terms of a twist whose unit space is a set of states on C constructed using the unique pseudo-expectation. For a regular MASA inclusion, this twist differs from the Weyl twist; in this setting, we show that the Weyl twist is Hausdorff precisely when there exists a conditional expectation of C onto D . We show that a regular inclusion with the unique pseudo-expectation property is a covering inclusion and give other consequences of the unique pseudo-expectation property.
Static Optimality and Dynamic Search-Optimality in Lists and Trees

Adaptive data structures form a central topic of on-line algorithms research. The area of Competitive Analysis began with the results of Sleator and Tarjan showing that splay trees achieve static optimality for search trees, and that Move-to-Front is constant competitive for the list update problem [ST1], [ST2]. In a parallel development, powerful algorithms have been developed in Machine Learning for problems of on-line prediction [LW], [FS]. This paper is inspired by the observation made in [BB] that if computational decision-making costs are not considered, then these ``weighted experts'' techniques from Machine Learning allow one to achieve a 1+e ratio against the best static object in hindsight for a wide range of data structure problems.
Evaluating risk detection methods to uncover ontogenic-mediated adverse drug effect mechanisms in children.

Identifying adverse drugs effects (ADEs) in children, overall and within pediatric age groups, is essential for preventing disability and death from marketed drugs. At the same time, however, detection is challenging due to dynamic biological processes during growth and maturation, called ontogeny, that alter pharmacokinetics and pharmacodynamics. As a result, methodologies in pediatric drug safety have been limited to event surveillance and have not focused on investigating adverse event mechanisms. There is an opportunity to identify drug event patterns within observational databases for evaluating ontogenic-mediated adverse event mechanisms. The first step of which is to establish statistical models that can identify temporal trends of adverse effects across childhood. Using simulation, we evaluated a population stratification method (the proportional reporting ratio or PRR) and a population modeling method (the generalized additive model or GAM) to identify and quantify ADE risk at varying reporting rates and dynamics. We found that GAMs showed improved performance over the PRR in detecting dynamic drug event reporting across child development stages. Moreover, GAMs exhibited normally distributed and robust ADE risk estimation at all development stages by sharing information across child development stages. Our study underscores the opportunity for using population modeling techniques, which leverage drug event reporting across development stages, as biologically-inspired detection methods for evaluating ontogenic mechanisms.