Bayesian comparison of latent variable models: Conditional vs marginal likelihoods

Typical Bayesian methods for models with latent variables (or random effects) involve directly sampling the latent variables along with the model parameters. In high-level software code for model definitions (using, e.g., BUGS, JAGS, Stan), the likelihood is therefore specified as conditional on the latent variables. This can lead researchers to perform model comparisons via conditional likelihoods, where the latent variables are considered model parameters. In other settings, however, typical model comparisons involve marginal likelihoods where the latent variables are integrated out. This distinction is often overlooked despite the fact that it can have a large impact on the comparisons of interest. In this paper, we clarify and illustrate these issues, focusing on the comparison of conditional and marginal Deviance Information Criteria (DICs) and Watanabe-Akaike Information Criteria (WAICs) in psychometric modeling. The conditional/marginal distinction corresponds to whether the model should be predictive for the clusters that are in the data or for new clusters (where "clusters" typically correspond to higher-level units like people or schools). Correspondingly, we show that marginal WAIC corresponds to leave-one-cluster out (LOcO) cross-validation, whereas conditional WAIC corresponds to leave-one-unit out (LOuO). These results lead to recommendations on the general application of the criteria to models with latent variables.Comment: Manuscript in press at Psychometrika; 31 pages, 8 figure

Analysis of Linkage-Friendly Genetic Algorithms

Evolutionary algorithms (EAs) are stochastic population-based algorithms inspired by the natural processes of selection, mutation, and recombination. EAs are often employed as optimum seeking techniques. A formal framework for EAs is proposed, in which evolutionary operators are viewed as mappings from parameter spaces to spaces of random functions. Formal definitions within this framework capture the distinguishing characteristics of the classes of recombination, mutation, and selection operators. EAs which use strictly invariant selection operators and order invariant representation schemes comprise the class of linkage-friendly genetic algorithms (lfGAs). Fast messy genetic algorithms (fmGAs) are lfGAs which use binary tournament selection (BTS) with thresholding, periodic filtering of a fixed number of randomly selected genes from each individual, and generalized single-point crossover. Probabilistic variants of thresholding and filtering are proposed. EAs using the probabilistic operators are generalized fmGAs (gfmGAs). A dynamical systems model of lfGAs is developed which permits prediction of expected effectiveness. BTS with probabilistic thresholding is modeled at various levels of abstraction as a Markov chain. Transitions at the most detailed level involve decisions between classes of individuals. The probability of correct decision making is related to appropriate maximal order statistics, the distributions of which are obtained. Existing filtering models are extended to include probabilistic individual lengths. Sensitivity of lfGA effectiveness to exogenous parameters limits practical applications. The lfGA parameter selection problem is formally posed as a constrained optimization problem in which the cost functional is related to expected effectiveness. Kuhn-Tucker conditions for the optimality of gfmGA parameters are derived

Hash-based signatures for the internet of things

While numerous digital signature schemes exist in the literature, most real-world system rely on RSA-based signature schemes or on the digital signature algorithm (DSA), including its elliptic curve cryptography variant ECDSA. In this position paper we review a family of alternative signature schemes, based on hash functions, and we make the case for their application in Internet of Things (IoT) settings. Hash-based signatures provide postquantum security, and only make minimal security assumptions, in general requiring only a secure cryptographic hash function. This makes them extremely flexible, as they can be implemented on top of any hash function that satisfies basic security properties. Hash-based signatures also feature numerous parameters defining aspects such as signing speed and key size, that enable trade-offs in constrained environments. Simplicity of implementation and customization make hash based signatures an attractive candidate for the IoT ecosystem, which is composed of a number of diverse, constrained devices

PDFS: Practical Data Feed Service for Smart Contracts

Smart contracts are a new paradigm that emerged with the rise of the blockchain technology. They allow untrusting parties to arrange agreements. These agreements are encoded as a programming language code and deployed on a blockchain platform, where all participants execute them and maintain their state. Smart contracts are promising since they are automated and decentralized, thus limiting the involvement of third trusted parties, and can contain monetary transfers. Due to these features, many people believe that smart contracts will revolutionize the way we think of distributed applications, information sharing, financial services, and infrastructures. To release the potential of smart contracts, it is necessary to connect the contracts with the outside world, such that they can understand and use information from other infrastructures. For instance, smart contracts would greatly benefit when they have access to web content. However, there are many challenges associated with realizing such a system, and despite the existence of many proposals, no solution is secure, provides easily-parsable data, introduces small overheads, and is easy to deploy. In this paper we propose PDFS, a practical system for data feeds that combines the advantages of the previous schemes and introduces new functionalities. PDFS extends content providers by including new features for data transparency and consistency validations. This combination provides multiple benefits like content which is easy to parse and efficient authenticity verification without breaking natural trust chains. PDFS keeps content providers auditable, mitigates their malicious activities (like data modification or censorship), and allows them to create a new business model. We show how PDFS is integrated with existing web services, report on a PDFS implementation and present results from conducted case studies and experiments.Comment: Blockchain; Smart Contracts; Data Authentication; Ethereu

Energy benefits and emergent space use patterns of an empirically parameterized model of memory-based patch selection

Many species frequently return to previously visited foraging sites. This bias towards familiar areas suggests that remembering information from past experience is beneficial. Such a memory-based foraging strategy has also been hypothesized to give rise to restricted space use (i.e. a home range). Nonetheless, the benefits of empirically derived memory-based foraging tactics and the extent to which they give rise to restricted space use patterns are still relatively unknown. Using a combination of stochastic agent-based simulations and deterministic integro-difference equations, we developed an adaptive link (based on energy gains as a foraging currency) between memory-based patch selection and its resulting spatial distribution. We used a memory-based foraging model developed and parameterized with patch selection data of free-ranging bison Bison bison in Prince Albert National Park, Canada. Relative to random use of food patches, simulated foragers using both spatial and attribute memory are more efficient, particularly in landscapes with clumped resources. However, a certain amount of random patch use is necessary to avoid frequent returns to relatively poor-quality patches, or avoid being caught in a relatively poor quality area of the landscape. Notably, in landscapes with clumped resources, simulated foragers that kept a reference point of the quality of recently visited patches, and returned to previously visited patches when local patch quality was poorer than the reference point, experienced higher energy gains compared to random patch use. Furthermore, the model of memory-based foraging resulted in restricted space use in simulated landscapes and replicated the restricted space use observed in free-ranging bison reasonably well. Our work demonstrates the adaptive value of spatial and attribute memory in heterogeneous landscapes, and how home ranges can be a byproduct of non-omniscient foragers using past experience to minimize temporal variation in energy gains

Electrohidráulica : colección de ejercicios con soluciones. Nivel básico

La presente colección de problemas forma parte del sistema para enseñanza de Electrohidráulica de FESTO DIDACTIC. La colección de ejercicios está pensada para orientación del profesor. Cada problema contiene en forma resumida indicaciones sobre el: ámbito material, objetivo didáctico, planteamiento del problema. El planteamiento del problema queda ilustrado con un plano de situación, observaciones, tablas y esquemas ayudan en la solución del problema. Las soluciones adjuntas a cada problema permiten una evaluación rápida del problema resueltoThe present collection of problems is part of the system for teaching Electrohydraulics of FESTO DIDACTIC. The collection of exercises is intended for teacher guidance. Each problem contains in summary form indications on the: material scope, didactic objective, approach of the problem. The problem statement is illustrated with a situation plan, observations, tables and schemata help in solving the problem. The solutions attached to each problem allow a rapid evaluation of the problem solvedEstación elevadora -- Selección de piezas sobre una cinta transportadora -- Dispositivo de doblar -- Dispositivo de prensar -- Máquina de estampar -- Mando de una puerta – Unidad de cepillado -- Avance para la ladradora – Prensa -- Dispositivo alimentador – Dispositivo de montaje – Dispositivo elevador para paquetes – Maquina de serra

Electrohidráulica : colección de ejercicios con soluciones. Nivel avanzado

Colección de ejercicios concebida como nivel avanzado para el juego de elementos TP 601 y TP 602 del sistema para enseñanza de la técnica de automatización electrohidráulica de FESTO DIDACTIC, Cada uno de los ejercicios comprende datos resumidos sobre, ámbito material, objetivo didáctico, planteamiento del ejercicio y hoja de soluciónCollection of exercises conceived as advanced level for the set of elements TP 601 and TP 602 of the system for teaching the electrohydraulic automation technique of FESTO DIDACTIC, Each of the exercises comprises summary data on, material scope, didactic objective, approach of the exercise And solution sheetEjercicio 1: Válvula de cierre -- Ejercicio 2: Taladradora -- Ejercicio 3: Dispositivo escariador -- Ejercicio 4: Dispositivo de sujeción -- Ejercicio 5: Fresadora -- Ejercicio 6: Prensa para contrachapados -- Ejercicio 7: Torno automático para piezas de plástico -- Ejercicio 8: Prensa dobladora -- Ejercicio 9: Brechadora -- Ejercicio 10: Máquina operadora -- Ejercicio 11 : Horno secador continuo -- Ejercicio 12: Pulidora -- Ejercicio 13: Fundidora por inyección para plásticos -- Ejercicio 14: Troqueladora -- Ejercicio 15: Moldeadora de piezas -- Ejercicio 16: Campana rectificadora por fricción -- Ejercicio 17: Prensa de embutición profunda -- Ejercicio 18: Cadena transfer -- Ejercicio 19: Máquina estampadora -- Ejercicio 20: Dispositivo alimentado

Hidráulica: colección de ejercicios con soluciones: nivel básico

Ofrece medios didácticos y equipos para ejercicios, comprobados y fiables, útiles para la formación y el perfeccionamiento profesional, orientados a la práctica. La colección de ejercicios TP501, en combinación con el manual TP501, ofrece conocimientos básicos sobre los circuitos más importantes de la técnica de automatización hidráulica. Cada uno de los ejercicios contiene, de modo resumido, las siguientes informaciones: el objetivo didáctico, el planteamiento del ejercicio, una descripción del ejercicio y un plano de situación y una propuesta de solución.It offers didactic means and equipment for exercises, proven and reliable, useful for training and professional development, oriented to practice. The TP501 exercise collection, in combination with the TP501 manual, offers basic knowledge about the most important circuits of the hydraulic automation technique. Each of the exercises contains, in a summarized way, the following information: the didactic objective, the approach of the exercise, a description of the exercise and a situation plan and a solution proposal.Torno automático -- Elevador de paquetes, Válvula limitadora de presión -- Prensa de embutición -- Calandria para rollos de papel -- Horno de templado -- Portón de caldera -- Sistema estabilizador de cadena transportadora -- Cabina de esmaltado -- Transfer automática para varias operaciones -- Estampadora -- Rectificadora plana -- Taladradora -- Portón de guillotina -- Tronzadora -- Volquete de contenedores -- Prensa para encolado -- Equipo de montaje -- Fresadora -- Cuba volcable para virutas.naConvenio SENA-Festo160 página

Keyword-Based Delegable Proofs of Storage

Cloud users (clients) with limited storage capacity at their end can outsource bulk data to the cloud storage server. A client can later access her data by downloading the required data files. However, a large fraction of the data files the client outsources to the server is often archival in nature that the client uses for backup purposes and accesses less frequently. An untrusted server can thus delete some of these archival data files in order to save some space (and allocate the same to other clients) without being detected by the client (data owner). Proofs of storage enable the client to audit her data files uploaded to the server in order to ensure the integrity of those files. In this work, we introduce one type of (selective) proofs of storage that we call keyword-based delegable proofs of storage, where the client wants to audit all her data files containing a specific keyword (e.g., "important"). Moreover, it satisfies the notion of public verifiability where the client can delegate the auditing task to a third-party auditor who audits the set of files corresponding to the keyword on behalf of the client. We formally define the security of a keyword-based delegable proof-of-storage protocol. We construct such a protocol based on an existing proof-of-storage scheme and analyze the security of our protocol. We argue that the techniques we use can be applied atop any existing publicly verifiable proof-of-storage scheme for static data. Finally, we discuss the efficiency of our construction.Comment: A preliminary version of this work has been published in International Conference on Information Security Practice and Experience (ISPEC 2018