Collaborative Filtering via Group-Structured Dictionary Learning

Structured sparse coding and the related structured dictionary learning problems are novel research areas in machine learning. In this paper we present a new application of structured dictionary learning for collaborative filtering based recommender systems. Our extensive numerical experiments demonstrate that the presented technique outperforms its state-of-the-art competitors and has several advantages over approaches that do not put structured constraints on the dictionary elements.Comment: A compressed version of the paper has been accepted for publication at the 10th International Conference on Latent Variable Analysis and Source Separation (LVA/ICA 2012

Parallel versus Sequential Update and the Evolution of Cooperation with the Assistance of Emotional Strategies

Our study contributes to the debate on the evolution of cooperation in the single-shot Prisoner's Dilemma (PD) played on networks. We construct a model in which individuals are connected with positive and negative ties. Some agents play sign-dependent strategies that use the sign of the relation as a shorthand for determining appropriate action toward the opponent. In the context of our model in which network topology, agent strategic types and relational signs coevolve, the presence of sign-dependent strategies catalyzes the evolution of cooperation. We highlight how the success of cooperation depends on a crucial aspect of implementation: whether we apply parallel or sequential strategy update. Parallel updating, with averaging of payoffs across interactions in the social neighborhood, supports cooperation in a much wider set of parameter values than sequential updating. Our results cast doubts about the realism and generalizability of models that claim to explain the evolution of cooperation but implicitly assume parallel updating

A középkori Lápafő és temploma

A Tolna megye nyugati szélén fekvő Lápafő – a középkorban Vápafő – templomát 1430-ban említi középkori forrás. A település 1348-tól tűnik fel oklevelekben, a 15. század elejétől helyi kisnemeseket is ismerünk. A falu a 16. század végéig szerepel a török defterekben, 1618-tól református lelkészét is említik. A hódoltság után újratelepítése az 1710-es években indult meg. A középkori templomot a 18. században hordhatták szét nyomtalanul. Helye a mai falu református temetőjébe esik, maradványait sírásáskor gyakran megbolygatják. Hozzáférhető részeit 2012-ben tártuk fel a modern sírok között nyitott kutatóárkokkal, illetve a temető nyugati részén két nagyobb szelvénnyel. Az első, román kori periódusban félköríves szentélyzáródású templom épült, szentélyét kőből és téglából alapozták, a hajó alapozását azonban kő- döngölt agyagrétegek váltakoztatásával alakították ki. A későközépkorban nyugat felé 8 méter széles bővítménnyel toldották meg, sarkain egyenes, rövid támpillérekkel, teljes hossza így kb. 18,8 méter lett. A szentélybelsőben talált apró középkori freskótöredékeken többszöri lemeszelés nyomait figyeltük meg, tehát a reformátusok is ezt a templomot használták. A nyugati bővítmény építésével megbolygattak néhány korábbi sírt, amely az Árpád-kori templom temetőjéhez tartozott. Az épület környékét annak pusztulása után is temetőként használták, a bővítmény nyugati falát és a szentély alapozását is újkori sírok vágták át. A középkori falu a Rigói-árok és a Várongi-árok által közrefogott széles dombon feküdt, felszíni nyomait a temető körül találtuk meg, déli irányban a mai falu alá húzódik. A település kerámiaanyaga nem tér el a környező faluhelyekétől, ám a fémtárgyak között akadnak olyan darabok – rombusz- és csillag alakú csatok, sarkantyú, mérlegtöredék (?) –, amelyek talán a 15. század elejétől adatolt helyi nemesek tárgyi hagyatékának tarthatók. Abstract: The church of Lápafő can be found on the western border of Tolna County. It was first mentioned in a Medieval document in 1430. The building was excavated in the Calvinist cemetery of present-day Lápafő in 2012. In the first, Romanesque period a church with a semicircular apse was built from stones, bricks and rammed clay layers. In the Late Middle Ages an annex was added to the church. The full length of the building was about 18,8 meters

Novel Design of a Model Reference Adaptive Controller for Soft Tissue Operations

Model Reference Adaptive Controllers (MRAC) have dual functionality: besides guaranteeing precise trajectory track- ing of the controlled system, they have to provide an “external control loop” with the illusion that it controls a physical system of prescribed dynamic properties, i.e., the “reference system”. The MRACs are designed traditionally by Lyapunov’s 2 nd method that is mathematically complicated, requiring strong skills from the designer. Adaptive controllers alternatively designed by the use of Robust Fixed Point Transformations (RFPT) operate according to Banach’s Fixed Point Theorem , and are normally simple iterative constructions that also have a standard variant for MRAC design. This controller assumes a single actuator that is driven adaptively. Master–Slave Systems form a distinct class of practical applications, in which two arms—the master and the slave—operate simultaneously. The movement of the master must be tracked precisely by the slave in spite of the quite different forces exerted by them. In the present paper, a soft tissue-cutting operation by a master–slave structure is simulated. The master arm has a simple torque–reference friction model, and is driven by the surgeon. The obtained master arm trajectory has to be precisely tracked by the electric DC motor driven slave system, which is in dynamic interaction with the actual tissue under operation. It is shown via simulations that the RFPT-based design can efficiently solve such tasks without considerable mathematical complexity

The effective bandwidth problem revisited

The paper studies a single-server queueing system with autonomous service and $\ell$ priority classes. Arrival and departure processes are governed by marked point processes. There are $\ell$ buffers corresponding to priority classes, and upon arrival a unit of the $k$th priority class occupies a place in the $k$th buffer. Let $N^{(k)}$, $k=1,2,...,\ell$ denote the quota for the total $k$th buffer content. The values $N^{(k)}$ are assumed to be large, and queueing systems both with finite and infinite buffers are studied. In the case of a system with finite buffers, the values $N^{(k)}$ characterize buffer capacities. The paper discusses a circle of problems related to optimization of performance measures associated with overflowing the quota of buffer contents in particular buffers models. Our approach to this problem is new, and the presentation of our results is simple and clear for real applications.Comment: 29 pages, 11pt, Final version, that will be published as is in Stochastic Model

Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations

The main background above 3\,MeV for in-beam nuclear astrophysics studies with $\gamma$-ray detectors is caused by cosmic-ray induced secondaries. The two commonly used suppression methods, active and passive shielding, against this kind of background were formerly considered only as alternatives in nuclear astrophysics experiments. In this work the study of the effects of active shielding against cosmic-ray induced events at a medium deep location is performed. Background spectra were recorded with two actively shielded HPGe detectors. The experiment was located at 148\,m below the surface of the Earth in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data with the same detectors at the Earth's surface, and at depths of 45\,m and 1400\,m, respectively.Comment: Minor errors corrected; final versio

Systematic analysis of the non-extensive statistical approach in high energy particle collisions-experiment vs. theory

The analysis of high-energy particle collisions is an excellent testbed for the non-extensive statistical approach. In these reactions we are far from the thermodynamical limit. In small colliding systems, such as electron-positron or nuclear collisions, the number of particles is several orders of magnitude smaller than the Avogadro number; therefore, finite-size and fluctuation effects strongly influence the final-state one-particle energy distributions. Due to the simple characterization, the description of the identified hadron spectra with the Boltzmann-Gibbs thermodynamical approach is insufficient. These spectra can be described very well with Tsallis-Pareto distributions instead, derived from non-extensive thermodynamics. Using the $q$-entropy formula, we interpret the microscopic physics in terms of the Tsallis $q$ and $T$ parameters. In this paper we give a view on these parameters, analyzing identified hadron spectra from recent years in a wide center-of-mass energy range. We demonstrate that the fitted Tsallis-parameters show dependency on the center-of-mass energy and particle species (mass). Our findings are described well by a QCD (Quantum Chromodynamics) inspired parton evolution ansatz. Based on this comprehensive study, apart from the evolution, both mesonic and baryonic components found to be non-extensive ($q>1$), besides the mass ordered hierarchy observed in the parameter $T$. We also study and compare in details the theory-obtained parameters for the case of PYTHIA8 Monte Carlo Generator, perturbative QCD and quark coalescence models.Comment: 21 pages, 12 figures. This is an extended version of our paper at the 36th International Workshop on Bayesian Inference and Maximum Entropy Methods in Science and Engineering (MaxEnt 2016), 10-15 July 2016, Ghent, Belgiu

Casimir force between planes as a boundary finite size effect

The ground state energy of a boundary quantum field theory is derived in planar geometry in D+1 dimensional spacetime. It provides a universal expression for the Casimir energy which exhibits its dependence on the boundary conditions via the reflection amplitudes of the low energy particle excitations. We demonstrate the easy and straightforward applicability of the general expression by analyzing the free scalar field with Robin boundary condition and by rederiving the most important results available in the literature for this geometry.Comment: 10 pages, 2 eps figures, LaTeX2e file. v2: A reference is added, some minor modifications made to clarify the text. v3: 9 pages, 3 eps figures, LaTeX2e file, revtex style. Paper throughly restructured and rewritten. Much more details are given, but essential results and conclusions are unchanged. Version accepted for publicatio