bluuebunny/crossref_metadata_2025 huggingface dataset:
RECONSTRUCTION OF MODIFIED GRAVITY WITH GHOST DARK ENERGY MODELS
Authors: KHODAM-MOHAMMADI A. , MALEKJANI M. , MONSHIZADEH M.
Published: June 2012

In this work, we reconstruct the f(R) modified gravity for different ghost and generalized-ghost dark energy (DE) models in FRW flat universe, which describes the accelerated expansion of the universe. The equation of state and deceleration parameter of reconstructed f(R) gravity have been calculated. The equation of state and deceleration parameter of reconstructed f(R)-ghost/generalized-ghost DE, have been calculated. We show that the corresponding f(R) gravity of ghost/generalized-ghost DE model can behave like phantom or quintessence. Also the transition between deceleration to acceleration regime is indicated by deceleration parameter diagram for reconstructed f(R) generalized-ghost DE model.
HOLOGRAPHIC DARK ENERGY MODEL CHARACTERIZED BY THE CONFORMAL-AGE-LIKE LENGTH
Authors: HUANG ZHUO-PENG , WU YUE-LIANG
Published: June 2012

A holographic dark energy model characterized by the conformal-age-like length scale [Formula: see text] is motivated from the four-dimensional space–time volume at cosmic time t in the flat Friedmann–Robertson–Walker (FRW) universe. It is shown that when the background constituent with constant equation of state wm dominates the universe in the early time, the fractional energy density of the dark energy scales as [Formula: see text] with the equation of state given by [Formula: see text]. The value of wm is taken to be wm≃-1 during inflation, wm = ⅓ in radiation-dominated epoch and wm = 0 in matter-dominated epoch, respectively. When the model parameter d takes the normal value at order one, the fractional density of dark energy is naturally negligible in the early universe, Ω de ≪1 at a ≪1. With such an analytic feature, the model can be regarded as a single-parameter model like the ΛCDM model, so that the present fractional energy density Ω de (a = 1) can solely be determined by solving the differential equation of Ωde once d is given. We further extend the model to the general case in which both matter and radiation are present. The scenario involving possible interaction between the dark energy and the background constituent is also discussed.
FORMING THE FUNCTIONAL TIME IN PROCESS OF BIOCHEMICAL SUBSTANCE EXCHANGE BETWEEN CELLS IN A MULTICELLULAR SYSTEM
Authors: MIHAILOVIĆ DRAGUTIN T. , BALAŽ IGOR
Published: May 2012

In this paper, we shortly summarized current attitudes about time in biology and then we considered the functional time and the way of its emergence. To illustrate that, we chose the simulation of forming the functional time in the process of biochemical substance exchange between three cells in a multicellular system. For that purpose π-cell coordinate system is introduced. Finally, we established a functional time barcode which is a representation of system states through the chronological time, which shows data about the process of intercellular biochemical substance exchange to which it attaches. It represents states by varying the widths and spaces of parallel lines, where system is either synchronized or not.
INTENSITY-BASED MODELS FOR PRICING MORTGAGE-BACKED SECURITIES WITH REPAYMENT RISK UNDER A CIR PROCESS
Authors: WU SEN , JIANG LISHANG , LIANG JIN
Published: June 2012

Under a reduced-form framework, we establish models for pricing mortgage-backed securities with prepayment risk by introducing a stochastic prepayment factor. In the zero-default scenario, the pricing pass-through securities and sequential-pay collateralized mortgage obligation structures are considered. To solve the problems, we introduce a path-dependent variable, from which partial differential equation problems are obtained when the prepayment rate is modeled by a CIR process. Numerical solution to the pricing problem is obtained by developing an explicit characteristics difference scheme.
ASSET ALLOCATION AND ASSET PRICING IN THE FACE OF SYSTEMIC RISK: A LITERATURE OVERVIEW AND ASSESSMENT
Authors: MEINERDING CHRISTOPH
Published: June 2012

This paper provides a detailed overview of the current research linking systemic risk, financial crises and contagion effects among assets on the one hand with asset allocation and asset pricing theory on the other hand. Based on the ample literature about definitions, measurement and properties of systemic risk, we derive some elementary ingredients for models of financial contagion and assess the current state of knowledge about asset allocation and asset pricing with explicit focus on systemic risk. The paper closes with a brief outlook on future research possibilities and some recommendations for the further development of capital market models incorporating financial contagion.
ROBUST MEAN-VARIANCE HEDGING AND PRICING OF CONTINGENT CLAIMS IN A ONE PERIOD MODEL
Authors: TEVZADZE R. , UZUNASHVILI T.
Published: June 2012

In this paper, we consider the mean-variance hedging problem of contingent claims in a financial market model composed of assets with uncertain price parameters. We consider the worst case of model parameters required to solve the minimax problem. In general, such minimax problems cannot be changed to maximin problems. The main approach we develop is the randomization of the parameters, which allows us to change minimax to maximin problems, which are easier to solve. We provide an explicit solution for the robust mean-variance hedging problem in the single-period model for some types of contingent claims.
COOPERATION, CONFLICT AND HIGHER-ORDER STRUCTURES OF SOCIAL NETWORKS
Authors: MALETIĆ SLOBODAN , HORAK DANIJELA , RAJKOVIĆ MILAN
Published: June 2012

Simplicial complexes represent powerful models of complex networks and complex systems in general. We explore the properties of spectra of combinatorial Laplacian operator of simplicial complexes in the context of connectivity of cliques in the simplicial clique complex associated with social networks. The necessity of higher order spectral analysis is discussed and compared with results for ordinary graph spectra. Methods and results are applied using social network of the Zachary karate club and the network of characters from Victor Hugo's novel Les Miserables.
WEYL GEOMETRIES AND TIMELIKE GEODESICS
Authors: FATIBENE L. , FRANCAVIGLIA M.
Published: June 2012

In view of Ehlers–Pirani–Schild formalism, since 1972 Weyl geometries should be considered to be the most appropriate and complete framework to represent (relativistic) gravitational fields. We shall here show that in any given Lorentzian spacetime (M, g) that admits global timelike vector fields any such vector field u determines an essentially unique Weyl geometry ([g], Γ) such that u is Γ-geodesic (i.e. parallel with respect to Γ).
LYAPUNOV FUNCTIONAL AND BLOW-UP RESULTS FOR A CLASS OF PERTURBATIONS OF SEMILINEAR WAVE EQUATIONS IN THE CRITICAL CASE
Authors: HAMZA MOHAMED ALI , ZAAG HATEM
Published: June 2012

We study a class of perturbations for the semilinear wave equation with critical power nonlinearity (in the conformal transform sense). Working in the framework of similarity variables, we introduce a Lyapunov functional for this problem. Using a two-step argument based on interpolation and a critical Gagliardo–Nirenberg inequality, we establish that the blow-up rate of any singular solution is given by the solution of the nonperturbed associated ODE, specifically u″ = up.
UNCONDITIONAL WELL-POSEDNESS FOR WAVE MAPS
Authors: MASMOUDI NADER , PLANCHON FABRICE
Published: June 2012

We prove a uniqueness theorem for solutions to the wave map equation in the natural class, namely (u, ∂tu) ∈ C([0, T); Ḣd/2) × C1([0, T); Ḣd/2-1) in dimension d ≥ 4. This is achieved by estimating the difference of two solutions at a lower regularity level. In order to reduce to the Coulomb gauge, one has to localize the gauge change in suitable cones, as well as to estimate the difference between the frames and connections associated with each solution and to take advantage of the assumption that the target manifold has bounded curvature.
WELL-POSEDNESS FOR THE MASSIVE WAVE EQUATION ON ASYMPTOTICALLY ANTI-DE SITTER SPACETIMES
Authors: HOLZEGEL GUSTAV
Published: June 2012

In this paper, we prove a well-posedness theorem for the massive wave equation (with the mass satisfying the Breitenlohner–Freedman bound) on asymptotically anti-de Sitter spaces. The solution is constructed as a limit of solutions to an initial boundary value problem with boundary at a finite location in spacetime by finally pushing the boundary out to infinity. The solution obtained is unique within the energy class (but non-unique if the decay at infinity is weakened).
ASYMPTOTIC POINTWISE BEHAVIOR FOR SYSTEMS OF SEMILINEAR WAVE EQUATIONS IN THREE SPACE DIMENSIONS
Authors: KATAYAMA SOICHIRO
Published: June 2012

In connection with the weak null condition, Alinhac introduced a sufficient condition for global existence of small amplitude solutions to systems of semilinear wave equations in three space dimensions. We introduce a slightly weaker sufficient condition for the small data global existence, and we investigate the asymptotic pointwise behavior of global solutions for systems satisfying this condition. As an application, the asymptotic behavior of global solutions under the Alinhac condition is also derived.
STABILITY OF STEADY SOLUTIONS TO REACTION-HYPERBOLIC SYSTEMS FOR AXONAL TRANSPORT
Authors: YAN HAO , YONG WEN-AN
Published: June 2012

We are concerned with the stability of steady solutions to the initial and boundary value problem associated with reaction-hyperbolic systems for axonal transport. Under proper structural assumptions, we clarify the relaxation structure of the reaction-hyperbolic systems and establish the large-time asymptotic stability of steady solutions and relaxation boundary-layers.
N-WAVES IN HYPERBOLIC BALANCE LAWS
Authors: DAFERMOS CONSTANTINE M.
Published: June 2012

It is shown that, as time tends to infinity, solutions to the Cauchy problem for a class of genuinely nonlinear scalar balance laws attain N-wave profiles, when the initial data have compact support, or saw-toothed profiles, when the initial data are periodic. The amplitude and length of these waves results from the synergy between flux and source.
Synthesis of extended porphyrins by connection of meso-aryl groups with β-pyrrolic positions
Authors: Pereira Ana M.V.M. , Richeter Sébastien , Jeandon Christophe , Gisselbrecht Jean-Paul , Wytko Jennifer , Ruppert Romain
Published: June 2012

This review focuses on synthetic strategies leading to extended porphyrins, but is limited to examples in which at least one β-pyrrolic carbon is linked to a meso-aryl substituent. Friedel–Crafts reactions are covered first because historically they were the first reactions employed to link β-pyrrolic carbons with meso-aryl groups, thus creating new six-membered fused rings. Other reactions inserting heteroatoms follow. Direct cyclizations between an ortho-carbon and a β-pyrrolic position are presented next. Finally, new highly extended chromophores are described. These compounds are generally obtained in two consecutive reactions. First a Suzuki coupling is used to introduce an aryl group in one or two meso positions. Then the new fused rings are generated by oxidative cyclizations.
Decomposition and Classification of Generic Quantum Markov Semigroups: The Gaussian Gauge Invariant Case
Authors: Fagnola Franco , Hachicha Skander
Published: June 2012

We study the structure of generic quantum Markov semigroups, arising from the stochastic limit of a discrete system with generic Hamiltonian interacting with a Gaussian gauge invariant reservoir. We show that they can be essentially written as the sum of their irreducible components determined by closed classes of states of the associated classical Markov jump process. Each irreducible component turns out to be recurrent, transient or have an invariant state if and only if its classical (diagonal) restriction is recurrent, transient or has an invariant state, respectively. We classify invariant states and study convergence towards invariant states as time goes to infinity.
Recognizing sketched multistroke primitives
Authors: Hammond Tracy , Paulson Brandon
Published: June 2012

Sketch recognition attempts to interpret the hand-sketched markings made by users on an electronic medium. Through recognition, sketches and diagrams can be interpreted and sent to simulators or other meaningful analyzers. Primitives are the basic building block shapes used by high-level visual grammars to describe the symbols of a given sketch domain. However, one limitation of these primitive recognizers is that they often only support basic shapes drawn with a single stroke. Furthermore, recognizers that do support multistroke primitives place additional constraints on users, such as temporal timeouts or modal button presses to signal shape completion. The goal of this research is twofold. First, we wanted to determine the drawing habits of most users. Our studies found multistroke primitives to be more prevalent than multiple primitives drawn in a single stroke. Additionally, our studies confirmed that threading is less frequent when there are more sides to a figure. Next, we developed an algorithm that is capable of recognizing multistroke primitives without requiring special drawing constraints. The algorithm uses a graph-building and search technique that takes advantage of Tarjan's linear search algorithm, along with principles to determine the goodness of a fit. Our novel, constraint-free recognizer achieves accuracy rates of 96% on freely-drawn primitives.
Multimodal approach to affective human-robot interaction design with children
Authors: Okita Sandra Y. , Ng-Thow-Hing Victor , Sarvadevabhatla Ravi K.
Published: June 2012

Two studies examined the different features of humanoid robots and the influence on children's affective behavior. The first study looked at interaction styles and general features of robots. The second study looked at how the robot's attention influences children's behavior and engagement. Through activities familiar to young children (e.g., table setting, story telling), the first study found that cooperative interaction style elicited more oculesic behavior and social engagement. The second study found that quality of attention, type of attention, and length of interaction influences affective behavior and engagement. In the quality of attention, Wizard-of-Oz (woz) elicited the most affective behavior, but automatic attention worked as well as woz when the interaction was short. The type of attention going from nonverbal to verbal attention increased children's oculesic behavior, utterance, and physiological response. Affective interactions did not seem to depend on a single mechanism, but a well-chosen confluence of technical features.
The
SignCom
system for data-driven animation of interactive virtual signers
Authors: Gibet Sylvie , Courty Nicolas , Duarte Kyle , Naour Thibaut Le
Published: June 2012

In this article we present a multichannel animation system for producing utterances signed in French Sign Language (LSF) by a virtual character. The main challenges of such a system are simultaneously capturing data for the entire body, including the movements of the torso, hands, and face, and developing a data-driven animation engine that takes into account the expressive characteristics of signed languages. Our approach consists of decomposing motion along different channels, representing the body parts that correspond to the linguistic components of signed languages. We show the ability of this animation system to create novel utterances in LSF, and present an evaluation by target users which highlights the importance of the respective body parts in the production of signs. We validate our framework by testing the believability and intelligibility of our virtual signer.
Gaze guidance reduces the number of collisions with pedestrians in a driving simulator
Authors: Pomarjanschi Laura , Dorr Michael , Barth Erhardt
Published: June 2012

Our study explores the potential of gaze guidance in driving and analyzes eye movements and driving behavior in safety-critical situations. We collected eye movements from subjects instructed to drive predetermined routes in a driving simulator. While driving, the subjects performed various cognitive tasks designed to divert their attention away from the road. The 30 subjects were equally divided in two groups, a control and a gaze guidance group. For the latter, potentially dangerous events, such as a pedestrian suddenly crossing the street, were highlighted with temporally transient gaze-contingent cues, which were triggered if the subject did not look at the pedestrian. For the group that drove with gaze guidance, eye movements have a reduced variability after the gaze-capturing event and shorter reaction times to it. More importantly, gaze guidance leads to a safer driving behavior and a significantly reduced number of collisions.
Attentive documents
Authors: Buscher Georg , Dengel Andreas , Biedert Ralf , Elst Ludger V.
Published: June 2012

Reading is one of the most frequent activities of knowledge workers. Eye tracking can provide information on what document parts users read, and how they were read. This article aims at generating implicit relevance feedback from eye movements that can be used for information retrieval personalization and further applications.

We report the findings from two studies which examine the relation between several eye movement measures and user-perceived relevance of read text passages. The results show that the measures are generally noisy, but after personalizing them we find clear relations between the measures and relevance. In addition, the second study demonstrates the effect of using reading behavior as implicit relevance feedback for personalizing search. The results indicate that gaze-based feedback is very useful and can greatly improve the quality of Web search. The article concludes with an outlook introducing attentive documents keeping track of how users consume them. Based on eye movement feedback, we describe a number of possible applications to make working with documents more effective.
Gliding and saccadic gaze gesture recognition in real time
Authors: Rozado David , Agustin Javier S. , Rodriguez Francisco B. , Varona Pablo
Published: June 2012

Eye movements can be consciously controlled by humans to the extent of performing sequences of predefined movement patterns, or 'gaze gestures'. Gaze gestures can be tracked noninvasively employing a video-based eye tracking system. Gaze gestures hold the potential to become an emerging input paradigm in the context of human-computer interaction (HCI) as low-cost eye trackers become more ubiquitous. The viability of gaze gestures as an innovative way to control a computer rests on how easily they can be assimilated by potential users and also on the ability of machine learning algorithms to discriminate in real time intentional gaze gestures from typical gaze activity performed during standard interaction with electronic devices. In this work, through a set of experiments and user studies, we evaluate the performance of two different gaze gestures modalities, gliding gaze gestures and saccadic gaze gestures, and their corresponding real-time recognition algorithms, Hierarchical Temporal Memory networks and the Needleman-Wunsch algorithm for sequence alignment. Our results show that a specific combination of gaze gesture modality, namely saccadic gaze gestures, and recognition algorithm, Needleman-Wunsch, allows for reliable usage of intentional gaze gestures to interact with a computer with accuracy rates higher than 95% and completion speeds of around 1.5 to 2.5 seconds per gesture. The optimal gaze gesture modality and recognition algorithm do not interfere with otherwise standard human-computer gaze interaction, generating very few false positives during real time recognition and positive feedback from the users. These encouraging results and the low cost eye tracking equipment used, open up a new HCI paradigm for the fields of accessibility and interaction with smartphones, tablets, projected displays and traditional desktop computers.
Taming Mona Lisa
Authors: Moubayed Samer Al , Edlund Jens , Beskow Jonas
Published: June 2012

The perception of gaze plays a crucial role in human-human interaction. Gaze has been shown to matter for a number of aspects of communication and dialogue, especially for managing the flow of the dialogue and participant attention, for deictic referencing, and for the communication of attitude. When developing embodied conversational agents (ECAs) and talking heads, modeling and delivering accurate gaze targets is crucial. Traditionally, systems communicating through talking heads have been displayed to the human conversant using 2D displays, such as flat monitors. This approach introduces severe limitations for an accurate communication of gaze since 2D displays are associated with several powerful effects and illusions, most importantly the Mona Lisa gaze effect, where the gaze of the projected head appears to follow the observer regardless of viewing angle. We describe the Mona Lisa gaze effect and its consequences in the interaction loop, and propose a new approach for displaying talking heads using a 3D projection surface (a physical model of a human head) as an alternative to the traditional flat surface projection. We investigate and compare the accuracy of the perception of gaze direction and the Mona Lisa gaze effect in 2D and 3D projection surfaces in a five subject gaze perception experiment. The experiment confirms that a 3D projection surface completely eliminates the Mona Lisa gaze effect and delivers very accurate gaze direction that is independent of the observer's viewing angle. Based on the data collected in this experiment, we rephrase the formulation of the Mona Lisa gaze effect. The data, when reinterpreted, confirms the predictions of the new model for both 2D and 3D projection surfaces. Finally, we discuss the requirements on different spatially interactive systems in terms of gaze direction, and propose new applications and experiments for interaction in a human-ECA and a human-robot settings made possible by this technology.
Continuous body and hand gesture recognition for natural human-computer interaction
Authors: Song Yale , Demirdjian David , Davis Randall
Published: June 2012

Intelligent gesture recognition systems open a new era of natural human-computer interaction: Gesturing is instinctive and a skill we all have, so it requires little or no thought, leaving the focus on the task itself, as it should be, not on the interaction modality. We present a new approach to gesture recognition that attends to both body and hands, and interprets gestures continuously from an unsegmented and unbounded input stream. This article describes the whole procedure of continuous body and hand gesture recognition, from the signal acquisition to processing, to the interpretation of the processed signals.

Our system takes a vision-based approach, tracking body and hands using a single stereo camera. Body postures are reconstructed in 3D space using a generative model-based approach with a particle filter, combining both static and dynamic attributes of motion as the input feature to make tracking robust to self-occlusion. The reconstructed body postures guide searching for hands. Hand shapes are classified into one of several canonical hand shapes using an appearance-based approach with a multiclass support vector machine. Finally, the extracted body and hand features are combined and used as the input feature for gesture recognition. We consider our task as an online sequence labeling and segmentation problem. A latent-dynamic conditional random field is used with a temporal sliding window to perform the task continuously. We augment this with a novel technique called multilayered filtering, which performs filtering both on the input layer and the prediction layer. Filtering on the input layer allows capturing long-range temporal dependencies and reducing input signal noise; filtering on the prediction layer allows taking weighted votes of multiple overlapping prediction results as well as reducing estimation noise.

We tested our system in a scenario of real-world gestural interaction using the NATOPS dataset, an official vocabulary of aircraft handling gestures. Our experimental results show that: (1) the use of both static and dynamic attributes of motion in body tracking allows statistically significant improvement of the recognition performance over using static attributes of motion alone; and (2) the multilayered filtering statistically significantly improves recognition performance over the nonfiltering method. We also show that, on a set of twenty-four NATOPS gestures, our system achieves a recognition accuracy of 75.37%.
A multitask approach to continuous five-dimensional affect sensing in natural speech
Authors: Eyben Florian , Wöllmer Martin , Schuller Björn
Published: June 2012

Automatic affect recognition is important for the ability of future technical systems to interact with us socially in an intelligent way by understanding our current affective state. In recent years there has been a shift in the field of affect recognition from “in the lab” experiments with acted data to “in the wild” experiments with spontaneous and naturalistic data. Two major issues thereby are the proper segmentation of the input and adequate description and modeling of affective states. The first issue is crucial for responsive, real-time systems such as virtual agents and robots, where the latency of the analysis must be as small as possible. To address this issue we introduce a novel method of incremental segmentation to be used in combination with supra-segmental modeling. For modeling of continuous affective states we use Long Short-Term Memory Recurrent Neural Networks, with which we can show an improvement in performance over standard recurrent neural networks and feed-forward neural networks as well as Support Vector Regression. For experiments we use the SEMAINE database, which contains recordings of spontaneous and natural human to Wizard-of-Oz conversations. The recordings are annotated continuously in time and magnitude with FeelTrace for five affective dimensions, namely activation, expectation, intensity, power/dominance, and valence. To exploit dependencies between the five affective dimensions we investigate multitask learning of all five dimensions augmented with inter-rater standard deviation. We can show improvements for multitask over single-task modeling. Correlation coefficients of up to 0.81 are obtained for the activation dimension and up to 0.58 for the valence dimension. The performance for the remaining dimensions were found to be in between that for activation and valence.
A hybrid approach for efficient Web service composition with end-to-end QoS constraints
Authors: Alrifai Mohammad , Risse Thomas , Nejdl Wolfgang
Published: June 2012

Dynamic selection of Web services at runtime is important for building flexible and loosely-coupled service-oriented applications. An abstract description of the required services is provided at design-time, and matching service offers are located at runtime. With the growing number of Web services that provide the same functionality but differ in quality parameters (e.g., availability, response time), a decision needs to be made on which services should be selected such that the user's end-to-end QoS requirements are satisfied. Although very efficient, local selection strategy fails short in handling global QoS requirements. Solutions based on global optimization, on the other hand, can handle global constraints, but their poor performance renders them inappropriate for applications with dynamic and realtime requirements. In this article we address this problem and propose a hybrid solution that combines global optimization with local selection techniques to benefit from the advantages of both worlds. The proposed solution consists of two steps: first, we use mixed integer programming (MIP) to find the optimal decomposition of global QoS constraints into local constraints. Second, we use distributed local selection to find the best Web services that satisfy these local constraints. The results of experimental evaluation indicate that our approach significantly outperforms existing solutions in terms of computation time while achieving close-to-optimal results.
Friendship prediction and homophily in social media
Authors: Aiello Luca Maria , Barrat Alain , Schifanella Rossano , Cattuto Ciro , Markines Benjamin , Menczer Filippo
Published: June 2012

Social media have attracted considerable attention because their open-ended nature allows users to create lightweight semantic scaffolding to organize and share content. To date, the interplay of the social and topical components of social media has been only partially explored. Here, we study the presence of homophily in three systems that combine tagging social media with online social networks. We find a substantial level of topical similarity among users who are close to each other in the social network. We introduce a null model that preserves user activity while removing local correlations, allowing us to disentangle the actual local similarity between users from statistical effects due to the assortative mixing of user activity and centrality in the social network. This analysis suggests that users with similar interests are more likely to be friends, and therefore topical similarity measures among users based solely on their annotation metadata should be predictive of social links. We test this hypothesis on several datasets, confirming that social networks constructed from topical similarity capture actual friendship accurately. When combined with topological features, topical similarity achieves a link prediction accuracy of about 92%.
Exact and approximate algorithms for the most connected vertex problem
Authors: Sheng Cheng , Tao Yufei , Li Jianzhong
Published: June 2012

An
(edge) hidden graph
is a graph whose edges are notexplicitly given. Detecting the presence of an edge requires an expensive edge probing query. We consider the
k Most Connected Vertex
(
k
-MCV) problem on hidden bipartite graphs. Given a bipartite graph
G
with independent vertex sets
B
and
W
, the goal is to find the
k
vertices in
B
with the largest degrees using the minimum number of queries. This problem can be regarded as a top-
k
extension of semi-join, and is encountered in several applications in practice.

If
B
and
W
have
n
and
m
vertices, respectively, the number of queries needed to solve the problem is
nm
in the worst case. This, however, is a pessimistic estimate on how many queries are necessary on practical data. In fact, on some inputs, the problem may be settled with only
km
+
n
queries, which is significantly lower than
nm
for
k
≪
n
. The huge difference between
km
+
n
and
nm
makes it interesting to design an adaptive algorithm that is guaranteed to achieve the best possible performance on every input
G
. For
k
≤
n
/2, we give an algorithm that is instance optimal among a broad class of solutions. This means that, for any
G
, our algorithm can perform more queries than the optimal solution (which is unknown) by only a constant factor, which can be shown at most 2.

As a second step, we study an ε-approximate version of the
k
-MCV problem, where ε is a parameter satisfying 0 < ε < 1. The goal is to return
k
black vertices
b
1
, …,

b
k

such that the degree of

b
i

(
i
≤
k
) can be smaller than
t

i

by a factor of at most ε, where
t

i

, …,
t

k

(in nonascending order) are the degrees of the
k
most connected black vertices. We give an efficient randomized algorithm that successfully finds the correct answer with high probability. In particular, for a fixed ε and a fixed success probability, our algorithm performs
o(nm)
queries in expectation for
t

k

= ω(log
n
). In other words, whenever
t

k

is greater than log
n
by more than a constant, our algorithm beats the Ω(
nm
) lower bound for solving the
k
-MCV problem exactly. All the proposed algorithms, despite the complication of their underlying theory, are simple enough for easy implementation in practice. Extensive experiments have confirmed that their performance in reality agrees with our theoretical findings very well.
Online subspace skyline query processing using the compressed skycube
Authors: Xia Tian , Zhang Donghui , Fang Zheng , Chen Cindy , Wang Jie
Published: June 2012

The skyline query can help identify the “best” objects in a multi-attribute dataset. During the past decade, this query has received considerable attention in the database research community. Most research focused on computing the “skyline” of a dataset, or the set of “skyline objects” that are not dominated by any other object. Such algorithms are not appropriate in an online system, which should respond in real time to skyline query requests with arbitrary subsets of the attributes (also called subspaces). To guarantee real-time response, an online system should precompute the skylines for all subspaces, and look up a skyline upon query. Unfortunately, because the number of subspaces is exponential to the number of attributes, such pre computation has very expensive storage cost and update cost. We propose the Compressed SkyCube (CSC) that is much more compact, yet can still return the skyline of any subspace without consulting the base table. The CSC therefore combines the advantage of precomputation in that it can respond to queries in real time, and the advantage of no-precomputation in that it has efficient space cost and update cost. This article presents the CSC data structures, the CSC query algorithm, the CSC update algorithm, and the CSC initial computation scheme. A solution to extend to high-dimensional data is also proposed.
Amdahl's law for predicting the future of multicores considered harmful
Authors: Juurlink B.H.H. , Meenderinck C. H.
Published: June 2012

Several recent works predict the future of multicore systems or identify scalability bottlenecks based on Amdahl's law. Amdahl's law implicitly assumes, however, that the problem size stays constant, but in most cases more cores are used to solve larger and more complex problems. There is a related law known as Gustafson's law which assumes that runtime, not the problem size, is constant. In other words, it is assumed that the runtime on p cores is the same as the runtime on 1 core and that the parallel part of an application scales linearly with the number of cores. We apply Gustafson's law to symmetric, asymmetric, and dynamic multicores and show that this leads to fundamentally different results than when Amdahl's law is applied. We also generalize Amdahl's and Gustafson's law and study how this quantitatively effects the dimensioning of future multicore systems.
About Influence of MEA Compression and Varied Material Properties to the Efficiency of PEMFC's
Authors: Mindt Hans-Wilfried , Megahed Mustafa
Published: June 2012

It is known that the Membrane Electrolyte Assembly (MEA) of a Polymer Electrolyte Membrane Fuel Cell (PEM-FC) will be deformed, during the assembly process. The gas diffusion layers (GDL) will be distorted and squeezed into the gas channels. As a second effect, the material properties of regions between the bars of the bipolar plate will be changed. For certain materials correlations of material properties related to deformations have been found in literature and summarized in this work. Although the properties where measured for specific materials and the correlations has been generalized to provide an initial platform for alternative material investigations. Based on these correlations, the variations of the MEA properties are described in a commercial multi-physics code ACE+ (ESI Group) to determine the influence of the MEA compression and deformation on the PEM-FC performance.
Sulfolane Based Electrolytes for Li-Ion Accumulators
Authors: Štichová Zuzana , Sedlaříková Marie , Vondrák Jiri , Máca Josef
Published: June 2012

The aim of this paper was to verify Walden theorem based on measurements of electrical conductivity and dynamic viscosity in temperature dependence. There are also mentioned the initial measurement from dielectric properties such as permittivity
Review on Electrodes with Extended Surface Area for Supercapacitors
Authors: Vondrák Jiri , Sedlarikova Marie , Dvorak Petr
Published: June 2012

This contribution offers an outline of simplified theories describing processes occurring in porous and nanostructured electrodes, their properties from the view if impedance spectroscopy and their application in electrochemical supercapacitors. Many electrode materials possess multi-level structures starting with macroporosity and ending with nanostructures. Differences as well as similarities between capacitor electrodes and intercalation electrodes will be emphasized. Examples of will be given. Introduction
Reversible Incorporation of Lithium-Ions into Electrodeposited Layers of TiO2
Authors: Jakubis Ivan , Sedlaříková Marie , Vondrák Jiri , Čudek Pavel
Published: June 2012

Thin layers of titanium oxide were deposited electrochemically from potassium titanium oxalate solution on ITO glasses and on QCM sensor. Any treatment at elevated temperature caused mechanical damage of the layers. The thickness of the layers was estimated within 200 - 400 nm. Dry layers were able to incorporate and reversibly released lithium ions from LiClO4 in propylene carbonate; this process was apparent visually by occurrence of brownish color. The material could be used in an electrochromic window or similar device.
LiFePO4 Cathode Nanocomposite with PPy/PEG Conductive Network
Authors: Fedorková Andrea , Oriňáková Renata , Oriňák Andrej , Wiemhöfer Hans-Dieter , Audinot Jean Nicolas , Guillot Jerome
Published: June 2012

The polypyrrole-LiFePO4 composites were synthesized by simple chemical oxidative polymerization of pyrrole (Py) monomer directly on the surface of LiFePO4 particles. Properties of resulting polypyrrole-LiFePO4 (PPy-LiFePO4) samples (especially conductivity) are strongly affected by the preparation technique, polymer additives and conditions during synthesis. The polyethylene glycol (PEG) as additive during polymerization was used to increase the PPy-LiFePO4 conductivity. The electrochemical behaviour of samples was examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and the chemical stability was evaluated using X-ray photoelectron spectrometry (XPS). It was found that PPy-PEG composite polymer decrease particle to particle contact resistance. Impedance measurements showed that the coating of PPy-PEG significantly decreases the charge transfer resistance of LiFePO4 electrodes. Addition of polyethylene glycol (PEG) during PPy polymerisation leads to enhanced electronic conductivities.
Polyvinyl Alcohol Separator Membrane Design for Electrolysers
Authors: Kunovjánek Miroslav
Published: June 2012

Electrolyser needs to solve the problem of separation of products resulting from electrolysis. One way is to use a membrane that separates these products. The requirements for these membranes are especially of high ionic conductivity, impermeability for emerging products and long-term durability in the electrolyte used. These requirements are met by the membrane of cross-linked PVA. In this article there will be compared PVA membrane with membranes 3401 from Celgard Company and Fumapem from Fumatech Company.
Battery Separators
Authors: Pléha David , Dvořák Petr , Kunovjánek Miroslav , Musil Michal , Čech Ondrej
Published: June 2012

Despite the effort of research centers concerning devolopement and production of batteries all over the world, no ideal separator for all types of alkalic batteries is designed. Thanks wide range of offered materials suitable for battery separators, it can be selected the most convenient one for application in our designed alkalic accumulator. Selection depends on plenty specific features: wettability, swelling, ionic conductivity, electric resistivity, mechanical durability, chemical stability, furthermore availabilily on the market and price.
Influence of Different Conditions to the Light Induced Degradation of Solar Cells
Authors: Vanek Jiri , Barinka Radim , Indra Jiri
Published: June 2012

This paper describes study of light induced degradation (LID) in monocrystalline Czochralsky-wafers p-type substrate solar cells during the different test condition. The intensity of light source was 0.5 -1 sun with 1.5 AM spectrum. The temperature of solar cells was controlled in the range of 15 - 70 °C. The samples of solar cells were chosen from nine sets of solar cells produced by variety technologies and with variety parameters. The life time of charge carriers, VA characteristic, electroluminescence characteristic were set up after phosphor diffusion. After light degradation in variety condition was determined again and compare with starting parameters. The samples were regenerated by high temperature with and without light and parameters were measured again. The whole experiment was analyzed and the correlation was made.
Properties of PVA Membranes for Alkaline Fuel Cells
Authors: Chladil Ladislav , Kunovjánek Miroslav , Musil Michal
Published: June 2012

Low-temperature alkaline fuel cells are prospective sources of electric energy. They have large benefits in terms of energy efficiency and environmental protection. Fuel-cell technology is currently at the beginning of practical use in mobile and stationary power equipments. Fuel cells operate in contrast to primary cells in continuous mode, thanks to continual supply of fuel and oxidant to the anode and to the cathode. Commercially produced membranes are usually very expensive, thereby increasing the cost of terminal equipment. One of the alternatives to commercial membranes are PVA membranes, which are suitable for using in low-temperature alkaline fuel cells and also excel with favourable price.
An Apparatus to Measure Efficiency of Hydrogen Energy Storage
Authors: Abraham Pavel , Tošer Pavel , Tonar Karel , Bača Petr
Published: June 2012

This paper deals with creation of new measuring apparatus for students. It also should make them more familiar with renewable resources of energy. Paper also aims to show problems during first measurements of dependencies of hydrogen creation, power, volt-ampere characteristic and basic characteristic of fuel cell.
Effect of Environmental Temperature on the Brittle-Fracture Characteristics under Dynamic Loading and Assessment of Deformation on Low-Alloy Steel
Authors: Binar Tomáš , Kadlec Jaromír , Rejzek Martin , Vlkovský Martin
Published: June 2012

This paper examines the influence of test temperatures, which lead to deformation of brittle-fracture characteristics under dynamic loading of extra-hard low-alloyed steel ARMOX 500T and ARMOX 600T. For the analysis of effects on fracture surfaces a fractographic analysis was used. Temperatures for the experimental investigation were in the temperature range of -80 °C to +100 °C.
Measuring Properties of Manganese Oxides Using Electrochemical Quartz Crystal Microbalance Technique
Authors: Šubarda Jiri , Novák Vitezslav , Pléha David
Published: June 2012

In this paper are described properties of catalyst for fuel cells based on MnOx, which is intended for positive electrode of fuel cells. Mainly is described catalyst in powder form matters obtained by reduction reaction KMnO4 with carbon soot Chezacarb A.
Powerful Fast 16kW-Charger for an Electric Vehicle
Authors: Vorel Pavel , Procházka Petr , Minárik Vladimír
Published: June 2012

This contribution describes a development of a fast-charger for an electric vehicle. Useful modular conception of the power part was chosen. The modules can be serial-parallel reconfigured - for various battery voltage levels. Single-module output parameters are 160 V/16 kW. The charger is based on a DC/DC transistor converter using Cool-MOS transistors and SiC diodes. A non-usual topology of the power circuit is performed. This circuitry was designed (first version), realized and it was just tested. High switching frequency is used at the large output power (80 kHz -16 kW). This way the dimensions of the device are minimised.
Importance of Photovoltaics to Overcome Problems Occurred by Nuclear Power Plant Accident in Japan
Authors: Yamaguchi Masafumi , Ohshita Yoshio
Published: June 2012

The Fukushima nuclear power plant accident generated by earthquake and tsunami occurred in north-east area of Japan on March 11th 2011. This paper presents outline of accidents by the Fukushima nuclear power plan. Such an accidents has given us very important messages such as unclearness for safety and cost effectiveness of nuclear energy and important of clean renewable energies including photovoltaics (PV) instead of nuclear energy. This paper also presents importance of further development of science and technology of PV, government contribution and support to PV and international collaboration and cooperation for PV.
Near-infrared DyeSensitization in Bulk Heterojunction Polymer Solar Cells
Authors: Ito Shinzaburo , Ohkita Hideo , Benten Hiroaki , Honda Satoshi
Published: June 2012

Polymer solar cells with a low-bandgap dye molecule are demonstrated by employing ternary blends of poly(3-hexylthiophene) (P3HT), fullerene derivative (PCBM), and silicon phthalocyanine derivative (SiPc) under different annealing conditions. The solvent annealing induces selective allocation of SiPc molecules at amorphous P3HT domains that would be formed at the interface between P3HT and PCBM crystalline domains, and furthermore effectively suppresses diffusion and aggregation of low molecular weight components which degrade the performance of the thermally annealed devices. As a result, the solvent-annealed ternary blend solar cells exhibited an enhanced power conversion efficiency of 4.5%.
Importance of Molten Salt Electrochemical Processes for Energy Conversion and Storage
Authors: Ito Yasuhiko
Published: June 2012

Various electrochemical processes using molten salt can contribute to the realization of new energy systems directed toward low carbon society. Among these the following two promising processes are selected and described in detail: (1) Electrolytic synthesis of ammonia directly from water and nitrogen, and (2) Electrochemical formation of carbon film. In addition, the expected roles of molten salt electrochemical process in a nuclear field are described.
Alteration of antral and proximal colonic motility induced by chronic psychological stress involves central urocortin 3 and vasopressin in rats
Authors: Ataka Koji , Nagaishi Kanna , Asakawa Akihiro , Inui Akio , Fujimiya Mineko
Published: June 2012

Because of the difficulties in developing suitable animal models, the pathogenesis of stress-induced functional gastrointestinal disorders is not well known. Here we applied the communication box technique to induce psychological stress in rats and then examined their gastrointestinal motility. We measured upper and lower gastrointestinal motility induced by acute and chronic psychological stress and examined the mRNA expression of various neuropeptides in the hypothalamus. Chronic psychological stress disrupted the fasted motility in the antrum and accelerated motility in the proximal colon. mRNA expression of AVP, oxytocin, and urocortin 3 was increased by chronic psychological stress. Intracerebroventricular (ICV) injection of urocortin 3 disrupted the fasted motility in the antrum, while ICV injection of Ucn3 antiserum prevented alteration in antral motility induced by chronic psychological stress. ICV injection of AVP accelerated colonic motility, while ICV injection of SSR 149415, a selective AVP V1b receptor antagonist, prevented alteration in proximal colonic motility induced by chronic psychological stress. Oxytocin and its receptor antagonist L 371257 had no effect on colonic motility in either the normal or chronic psychological stress model. These results suggest that chronic psychological stress induced by the communication box technique might disrupt fasted motility in the antrum via urocortin 3 pathways and accelerates proximal colonic motility via the AVP V1b receptor in the brain.