Weak Restrictions Research Articles

Optimal Bayesian Mechanisms Without Monetary Transfers: A Solution to the Two-Person Implementation Problem

We study the relationship between two-agent implementation problems and the notion of interim efficiency due to Holmstrom and Myerson (1983) in Bayesian environments with private values and independent types. We present a general property, Bayesian efficiency, and show that it is sufficient for implementation of social choice functions. We also show that this condition is sufficient for implementation of social choice sets under a weak domain restriction - in particular, no economic condition is required. As an application, we show that the generalized two-person Nash bargaining solution, due to Myerson (1984), is Bayesian efficient.

Identification and estimation of risk aversion in first-price auctions with unobserved auction heterogeneity

This paper shows point-identification in first-price auctions with risk aversion and unobserved auction heterogeneity, by exploiting multiple bids per auction and variation in the number of bidders. If the exclusion restriction required for point-identification is violated, the recovered primitives are still valid bounds under weaker restrictions. We propose a Sieve Maximum Likelihood Estimator (SMLE). Monte Carlo experiments illustrate that the estimator performs well and that ignoring unobserved auction heterogeneity can bias risk aversion estimates. In an application to timber auctions we find that the bidders are risk-neutral, but we would reject risk-neutrality without accounting for unobserved auction heterogeneity.

Forecasting counting and time statistics of compound Cox processes: a focus on intensity phase type process, deletions and simultaneous events

Compound Cox processes (CCP) are flexible marked point processes due to the stochastic nature of their intensity. This paper states closed-form expressions of their counting and time statistics in terms of the intensity and of the mean processes. They are forecast by means of principal components prediction models applied to the mean process in order to reach attainable results. A proposition proves that only weak restrictions are needed to estimate the probability of a new occurrence. Additionally, the phase type process is introduced, which important feature is that its marginal distributions are phase type with random parameters. Since any non-negative variable can be approximated by a phase-type distribution, the new stochastic process is proposed to model the intensity process of any point process. The CCP with this type of intensity provides an especially general model. Several simulations and the corresponding study of the estimation errors illustrate the results and their accuracy. Finally, an application to real data is performed; extreme temperatures in the South of Spain are modeled by a CPP and forecast.

Методы и средства извлечения данных о персоналиях из авторефератов диссертаций

The problem of extraction of data about a person from scarce data collection is studied. The data collections are public resources on the internet. When these data are collected and parsed they present additional value for users. Collecting such data is problematic because of it’s weak structure restrictions. Thus the system is suggested to automate information gathering and parsing. The initial task is to process personal data from thesis documents publicly available on the internet. This data presents information about scientists which can’t be obtained from other sources. The goal is to be able to make requests to the data having its semantics in mind and not only plain text. The prototype system is developed with PHP and XPath able to collect raw documents from digital repository of National Library of Ukraine by V. I. Vernadskiy. The system also extracts data from the collected documents and stores them locally in RDF data model suitable for specific data and for future exposition to the Semantic Web. The collection of more than 63000 documents was processed to test the system.

Probability-triggered formation control with adaptive roles

ABSTRACT Formation control for a team of robots is investigated in this paper. We consider the case where no communication channels are available. Only sensors with limited ranges can provide the robots with the relative displacements to nearby robots. The robots themselves are fully independent with exchangeable positions in the predefined formations. Thus the robot team is distributed both physically and in their information flow. To deal with the lack of communication, a distributed control strategy is proposed to drive the robots to a potentially flawed formation. Then, a coordination protocol is presented to detect the imperfections such that the locally desired formations are transformed into a globally desired formation. An evaluation method is given to impose a weak restriction on the predefined formation, rendering it almost arbitrary. The minimal local topology is proposed to enhance the robustness. The coordination protocol is then modified by introducing probability to reduce the computation burden and avoid the infinite trajectory loop.

Instrumental variables estimation with competing risk data.

Time-to-event analyses are often plagued by both-possibly unmeasured-confounding and competing risks. To deal with the former, the use of instrumental variables (IVs) for effect estimation is rapidly gaining ground. We show how to make use of such variables in competing risk analyses. In particular, we show how to infer the effect of an arbitrary exposure on cause-specific hazard functions under a semi-parametric model that imposes relatively weak restrictions on the observed data distribution. The proposed approach is flexible accommodating exposures and IVs of arbitrary type, and enabling covariate adjustment. It makes use of closed-form estimators that can be recursively calculated, and is shown to perform well in simulation studies. We also demonstrate its use in an application on the effect of mammography screening on the risk of dying from breast cancer.

Convergence rates of full-implicit truncated Euler–Maruyama method for stochastic differential equations

Motivated by truncated Euler–Maruyama (EM) method established by Mao (J Comput Appl Math 290:370–384, 2015, J Comput Appl Math 296:362–375, 2016), a state-of-the-art scheme named full-implicit truncated EM method is derived in this paper, aiming to use shorter runtime and larger stepsize, as well as to obtain better stability property. Weaker restrictions on truncated functions of full-implicit truncated EM scheme have been obtained, which solve the disadvantage of Mao (2015) requiring the stepsize to be so small that sometimes the truncated EM would be inapplicable. The superiority of our results will be highlighted by the comparisons with the achievements in Mao (2015, 2016) as well as others on the implicit Euler scheme and semi-implicit truncated EM scheme. Numerical examples verify the order of $$L^q$$ -convergence, cheaper computational costs, wider stepsize and better stability.

On Bellman’s and Knuth’s Problems and their Generalizations

Various generalizations of the classical problem of the fastest raising to a power (or the so-called problem on addition chains) are studied in the asymptotic sense. Under weak restrictions, we demonstrate asymptotically tight solutions of the two best known generalizations, namely, Bellman’s problem on the computational complexity (on the minimal number of multiplication operations) of a normed monomial of several variables and Knuth’s problem on the computational complexity of a power system of one variable. We also briefly review some results on the computational complexity for three problems, namely, the computation of p-element systems of normed monomials in q variables, additive computations for systems of p integer linear forms over q variables, and the computation of p-element systems of the free Abelian group with q generators.

Existence and indeterminacy of Markovian equilibria in dynamic bargaining games

The paper studies stationary Markov perfect equilibria in multidimensional models of dynamic bargaining, in which the alternative chosen in one period determines the status quo for the next. We generalize a sufficient condition for existence of equilibrium due to Anesi and Seidmann (2015). We then use this existence result to show that if a weak gradient restriction holds at an alternative, then when players are sufficiently patient, there is a continuum of equilibria with absorbing sets arbitrarily close to that alternative. A sufficient condition for our gradient restriction is that the gradients of all players' utilities are linearly independent at that alternative. When the dimensionality of the set of alternatives is high, this linear independence condition holds at almost all alternatives, and equilibrium absorbing sets are dense in the set of alternatives. This implies that constructive techniques, which are common in the literature, fail to identify many plausible outcomes in dynamic bargaining games.

Decidable models of integer-manipulating programs with recursive parallelism

We study safety verification for multithreaded programs with recursive parallelism (i.e. unbounded thread creation and recursion) as well as unbounded integer variables. Since the threads in each program configuration are structured in a hierarchical fashion, our model is state-extended ground-tree rewrite systems equipped with shared unbounded integer counters that can be incremented, decremented, and compared against an integer constant. Since the model is Turing-complete, we propose a decidable underapproximation. First, using a restriction similar to context-bounding, we underapproximate the global control by a weak global control (i.e. DAGs possibly with self-loops), thereby limiting the number of synchronisations between different threads. Second, we bound the number of reversals between non-decrementing and non-incrementing modes of the counters. Under this restriction, we show that reachability becomes NP-complete. In fact, it is poly-time reducible to satisfaction over existential Presburger formulas, which allows one to tap into highly optimised SMT solvers. Our decidable approximation strictly generalises known decidable models including (i) weakly-synchronised ground-tree rewrite systems, and (ii) synchronisation/reversal-bounded concurrent pushdown systems with counters. Finally, we show that, when equipped with reversal-bounded counters, relaxing the weak control restriction by the notion of senescence results in undecidability.

Linear models for the impact of order flow on prices. II. The Mixture Transition Distribution model

Modelling the impact of the order flow on asset prices is of primary importance to understand the behaviour of financial markets. Part I of this paper reported the remarkable improvements in the description of the price dynamics which can be obtained when one incorporates the impact of past returns on the future order flow. However, impact models presented in Part I consider the order flow as an exogenous process, only characterised by its two-point correlations. This assumption seriously limits the forecasting ability of the model. Here we attempt to model directly the stream of discrete events with a so-called Mixture Transition Distribution (MTD) framework, introduced originally by Raftery [J. R. Stat. Soc. Ser. B, 1985, 528–539]. We distinguish between price-changing and non price-changing events and combine them with the order sign in order to reduce the order flow dynamics to the dynamics of a four-state discrete random variable. The MTD represents a parsimonious approximation of a full high-order Markov chain. The new approach captures with adequate realism the conditional correlation functions between signed events for both small and large tick stocks and signature plots. From a methodological point of view, constraining the MTD within the class of ergodic Markov models, and exploiting the buy–sell symmetry of the data, we propose a weak restriction on the transition matrices which solves the problem of identifiability of mixture models. In spite of the large number of parameters, this translates into a feasible and robust estimation procedure. Out-of-sample analyses demonstrate that the model does not overfit the data.

Expressions for the Drazin inverse of a modified matrix

We present some new expressions for the Drazin inverse of a modified matrix A-CDDB in terms of the Drazin inverse of A and its generalized Shur?s complementD-BADC under weaker conditions. Some results in recent literature are unified and generalized, and most importantly, we obtain new expressions of generalized Sherman-Morrison-Woodbury formula under weaker restrictions.

Explicit formulae for the generalized drazin inverse of block matrices over a Banach algebra

In this paper, we give expressions for the generalized Drazin inverse of a (2,2,0) block matrix over a Banach algebra under certain circumstances, utilizing which we derive the generalized Drazin inverse of a 2x2 block matrix in a Banach algebra under weaker restrictions. Our results generalize and unify several results in the literature.

Large Deviation Principle for Volterra Type Fractional Stochastic Volatility Models

We study fractional stochastic volatility models in which the volatility process is a positive continuous function $\sigma$ of a continuous Gaussian process $\widehat{B}$. Forde and Zhang established a large deviation principle for the log-price process in such a model under the assumptions that the function $\sigma$ is globally Hölder continuous and the process $\widehat{B}$ is fractional Brownian motion. In the present paper, we prove a similar small-noise large deviation principle under weaker restrictions on $\sigma$ and $\widehat{B}$. We assume that $\sigma$ satisfies a mild local regularity condition, while the process $\widehat{B}$ is a Volterra type Gaussian process. Under an additional assumption of the self-similarity of the process $\widehat{B}$, we derive a large deviation principle in the small-time regime. As an application, we obtain asymptotic formulas for binary options, call and put pricing functions, and the implied volatility in certain mixed regimes.

Size and temperature dependence of the energy gaps in Si, SiC and C quantum dots based on tight-binding molecular dynamics simulations

We investigated the size and temperature dependence of the energy gaps in H-terminated Si, SiC, and C quantum dots with diameters ranging from 1 to 10 nm, using tight-binding molecular dynamics (MDs) simulations. For the quantum dots with more than 1000 atoms, the order-N Krylov subspace method was employed. From our results, we formulated the energy gaps of the quantum dots as a function of their size and temperature. Our formula is applicable to the estimation of the energy gaps at any given temperature in the 0–600 K range, for a wide variety of quantum dot sizes (from a small quantum dot to bulk). The calculated energy gaps were in good agreement with the experimentally measured values. The thermal fluctuations of the band gap for a Si quantum dot were also analyzed in detail. We found that, unlike the case of bulk, the decrease in the energy gap at higher temperatures is predominantly caused by an increase in the splitting of the HOMO levels, with only a small contribution from the size expansion effect. For the temperature dependence of the energy gap of Si quantum dots, we also examined the effect of the media surrounding the quantum dots by performing tight-binding MDs simulations at finite temperatures with and without the restriction on the freedom of the motion of the surface H atoms. Our results have clarified that the temperature dependence of the energy gaps of quantum dots in a medium with weak restrictions on the freedom of the surface atomic motion (e.g., in gas or liquid) is larger than in a medium with strong restrictions (e.g., like SiO2), especially in the case of small quantum dots.

Perspectives of alcohol treatment providers and users on alcohol addiction and its facilitating factors in Uganda and Belgium

Background: Although conceptualisation of addiction varies with time and culture, literature on intercultural studies between high and low income countries is scarce. This article uses Diagnostic and Statistical Manual of Mental Disorders (DSM)-5 guidelines on diagnosis of Alcohol Use Disorder (AUD) and the Capability Opportunity Motivation – Behaviour (COM-B) model to explore perspectives on alcohol addiction and its facilitating factors in Uganda and Belgium.Method: Sixty qualitative interviews (40 with service providers and 20 service users) were administered in four alcohol treatment centres, two in Uganda and two in Belgium. Interviews were transcribed and analysed thematically using Nvivo software.Result: While addiction was primarily regarded as a disease enabled by capability factors (affordability and the absence of life and social skills) by Belgian respondents, many Ugandans viewed it as a moral or criminal issue; motivated by the varied roles of informal alcohol use amidst weak restrictions. Opportunity-related factors including; acceptability, availability, media influence, cultural/religious beliefs and practices and peer influence were recognised as facilitating factors in both countries, while stigma was equally prevalent.Conclusion: Interventions in Uganda could explore strengthening legislation and research on utilisation of the well-entrenched religious and cultural institutions to encourage alternatives to alcohol use. In Belgium, promotion of life and social skills, alcohol regulation in educational institutions and other demand reduction strategies seem essential to delay the onset of (mis)use. In both societies; general reduction of opportunities for access, early intervention, programmes for young persons and prevention of stigma through awareness-raising can be explored for mitigation of AUD.

Preventing bank runs

The work of Diamond and Dybvig, 1983 is commonly understood as a theory of bank runs driven by self-fulfilling prophecies. Their contribution may alternatively be interpreted as a theory for preventing these bank runs. Absent aggregate risk over liquidity demand, they show that a simple scheme that suspends withdrawls when a target level of bank reserves is reached implements the efficient allocation as the unique equilibrium. Uniqueness implies that there cannot be a bank-run equilibrium. Unfortunately, this scheme cannot implement the efficient allocation when there is aggregate uncertainty over every possible liquidity demand because any realization of liquidity demand may, in this case, be determined by fundamentals instead of psychology. When there is aggregate risk, Peck and Shell, 2003 demonstrate that the constrained efficient allocation can be implemented by a direct mechanism as an equilibrium. They show that the same mechanism can also implement a bank-run equilibrium, which suggests that Diamond and Dybvig, 1983 can be understood as a theory of bank runs. The use of direct mechanisms, however, imposes a severe restriction on communications. We propose an indirect mechanism that (i) permits depositors to communicate their beliefs, not just their types, (ii) incentivizes depositors to communicate “rumors” of an impending bank run, and (iii) threatens to suspend payments conditional on what is revealed in these communications. We demonstrate that if commitment is possible, then under some weak parameter restrictions our indirect mechanism uniquely implements an allocation that can be made arbitrarily close to the the constrained efficient allocation as an equilibrium. In other words, our mechanism prevents bank runs.

Iterative voting and acyclic games

Multi-agent decision problems, in which independent agents have to agree on a joint plan of action or allocation of resources, are central to artificial intelligence. In such situations, agents' individual preferences over available alternatives may vary, and may try to reconcile these differences by voting.We consider scenarios where voters cannot coordinate their actions, but are allowed to change their vote after observing the current outcome, as is often the case both in offline committees and in online voting. Specifically, we are interested in identifying conditions under which such iterative voting processes are guaranteed to converge to a Nash equilibrium state—that is, under which this process is acyclic. We classify convergence results based on the underlying assumptions about the agent scheduler (the order in which the agents take their actions) and the action scheduler (the actions available to the agents at each step). By so doing, we position iterative voting models within the general framework of acyclic games and game forms.In more detail, our main technical results provide a complete picture of conditions for acyclicity in several variations of Plurality voting. In particular, we show that (a) under the traditional lexicographic tie-breaking, the game converges from any state and for any order of agents, under a weak restriction on voters' actions; and that (b) Plurality with randomized tie-breaking is not guaranteed to converge under arbitrary agent schedulers, but there is always some path of better replies from any initial state of the game to a Nash equilibrium. We thus show a first separation between order-free acyclicity and weak acyclicity of game forms, thereby settling an open question from [7]. In addition, we refute another conjecture of Kukushkin regarding strongly acyclic voting rules, by proving the existence of strongly acyclic separable game forms.

A criterion for the best uniform approximation by simple partial fractions in terms of alternance. II

In the problem of approximating real functions by simple partial fractions of order on closed intervals , we obtain a criterion for the best uniform approximation which is similar to Chebyshev's alternance theorem and considerably generalizes previous results: under the same condition on the poles of the fraction of best approximation, we omit the restriction on the order of this fraction. In the case of approximation of odd functions on , we obtain a similar criterion under much weaker restrictions on the position of the poles : the disc is replaced by the domain bounded by a lemniscate contained in this disc. We give some applications of this result. The main theorems are extended to the case of weighted approximation. We give a lower bound for the distance from to the set of poles of all simple partial fractions of order which are normalized with weight on (a weighted analogue of Gorin's problem on the semi-axis).

Uniqueness results for a boundary value problem in dipolar thermoelasticity to model composite materials

Abstract Composites with microstructure display nonlocal effects and can be effectively modeled through dipolar elasticity. A mixed initial boundary problem is addressed for dipolar thermoelasticity. The basic equations and conditions of the problem are set-up and uniqueness results are proven, which are obtained without introducing definiteness restrictions on the elastic coefficients and, also, without the usual condition imposed to the heat conductivity tensor of being positive definite. An additional result is finally obtained, namely, a reciprocal identity of the Betti's type which underlies another uniqueness result obtained again under weak restrictions.