Showing papers by "University of Luxembourg published in 2008"

”Aggregation Functions”, Cambridge University Press

Abstract: There is given a short overview of the monograph rdquoAggregation Functionsrdquo (M. Grabisch, J. L. Marichal, R. Mesiar, E. Pap), Cambridge University Press (in press).

A review of methods for capacity identification in Choquet integral based multi-attribute utility theory: Applications of the Kappalab R package

Abstract: The application of multi-attribute utility theory whose aggregation process is based on the Choquet integral requires the prior identification of a capacity. The main approaches to capacity identification proposed in the literature are reviewed and their advantages and inconveniences are discussed. All the reviewed methods have been implemented within the Kappalab R package. Their application is illustrated on a detailed example.

Anomalous harmonics in the spectra of GPS position estimates

Abstract: Prior studies of the power spectra of GPS position time series have found pervasive seasonal sig- nals against a power-law background of flicker noise plus white noise. Dong et al. (2002) estimated that less than half the observed GPS seasonal power can be explained by redistributions of geophysical fluid mass loads. Much of the residual variation is probably caused by unidentified GPS technique errors and analysis arti- facts. Among possible mechanisms, Penna and Stewart (2003) have shown how unmodeled analysis errors at tidal frequencies (near 12- and 24-hour periods) can be aliased to longer periods very efficiently. Signals near fortnightly, semiannual, and annual periods are expected to be most seriously affected. We have examined spectra for the 167 sites of the International GNSS (Global Navigation Satellite Systems) Service (IGS) network having more than 200 weekly measurements during 1996.0-2006.0. The non-linear residuals of the weekly IGS solutions that were included in ITRF2005, the latest version of the International Terrestrial Reference Frame (ITRF), have been used. To improve the detection of common-mode signals, the normalized spectra of all sites have been stacked, then boxcar smoothed for each local north (N), east (E), and height (H) component. The stacked, smoothed spectra are very similar for all three components. Peaks are evident at harmonics of about 1 cycle per year (cpy) up to at least 6 cpy, but the peaks are not all at strictly 1.0 cpy intervals. Based on the 6th harmonic of the N spectrum, which is among the sharpest and largest, and assuming a linear overtone model, then a common fundamental of 1.040 ± 0.008 cpy can explain all peaks well, together with the ex- pected annual and semiannual signals. A flicker noise power-law continuum describes the background spectrum down to periods of a few months, after which the residuals become whiter. Similar sub-seasonal tones are not apparent in the residuals of available satellite laser ranging (SLR) and very long baseline interferometry (VLBI) sites, which are both an order of magnitude less numerous and dominated by white noise. There is weak evidence for a few isolated peaks near 1 cpy harmonics in the spectra of geophysical loadings, but these are much noisier than for GPS positions. Alternative expla- nations related to the GPS technique are suggested by the close coincidence of the period of the 1.040 cpy frequency, about 351.2 days, to the ''GPS year''; i.e., the interval required for the constellation to repeat its inertial orientation with respect to the sun. This could indicate that the harmonics are a type of systematic error related to the satellite orbits. Mechanisms could involve orbit modeling defects or aliasing of site-dependent position- ing biases modulated by the varying satellite geometry.

New routes to sustainable photovoltaics: evaluation of Cu2ZnSnS4 as an alternative absorber material

Abstract: Thin film heterojunction solar cells based on chalcopyrites such as Cu(In,Ga)Se2 have achieved impressive efficiencies. However concern about the long term sustainability of photovoltaics based on scarce or expensive raw materials has prompted the search for alternative absorber materials. In this work, films of the p-type absorber Cu2ZnSnS4 (CZTS) were prepared by electroplating metallic precursors sequentially onto a molybdenum-coated glass substrate followed by an nealing in a sulfur atmosphere. The polycrystalline CZTS films were characterized by photoelectrochemical methods, which showed films were p-type with doping densities of the order of 1016 cm–3 and a band gap of 1.49 eV, close to the optimum value for terrestrial solar energy conversion. Preliminary results obtained for solar cells fabricated with this material are promising. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Covariance between psychological and endocrine responses to pharmacological challenge and psychosocial stress: a question of timing.

Abstract: Objective: To test if the covariance of hypothalamus-pituitary-adrenal (HPA) axis and subjective-psychological responses to stress is dependent on different dynamics of these systems. Although stress theories typically assume substantial correlations of psychological and endocrine stress responses, studies have produced inconsistent results. One reason for this might be imperfect coupling of the different stress response systems. However, inconsistent correlations might also be a result of different on-/offsets of these stress responses, i.e., specific dynamics of the systems. Methods: HPA axis indicators and subjective-psychological states were repeatedly and synchronously measured in a pharmacological challenge test (injection of corticotropin-releasing hormone and infusion of arginine vasopressin; Study 1; n = 42) and a psychosocial stress situation (Trier Social Stress Test; Study 2; n = 219). Cross-correlation analysis was used to test for lag effects in HPA axis reactivity and psychoendocrine responses. Results: Analyses revealed high cross-correlations of adrenocorticotropic hormone with cortisol responses (up to r = .80 in Study 1 and r = .56 in Study 2) and positive associations of psychological with endocrine stress responses (up to r = .48 in Study 1 and r = .54 in Study 2) at nonzero lags. Subjective-psychological responses preceded HPA axis responses. Moreover, high levels of cortisol were associated with lower later levels of anxiety and activation. Conclusions: The findings suggest that psychoendocrine stress responses are more closely coupled than previous studies suggested. Due to different dynamics of the systems, endocrine responses lag behind psychological responses.

Stochastic Calculus of Variations in Mathematical Finance

Abstract: Gaussian stochastic calculus of variations.- Pathwise propagation of Greeks in complete elliptic markets.- Market equilibrium and price-volatility feedback rate.- Multivariate conditioning and regularity of laws.- Non-elliptic markets and instability in HJM models.- Insider trading.- Rates of weak convergence and distribution theory on Gaussian spaces.-Fourier series method for the measurement of historical volatilities.

Encountering Foucault in lifelong learning

Abstract: 1. Mobilizing Foucault in studies of lifelong learning Katherine Nicoll and Andreas Fejes Section 1: Governing policy subjects 2. Actively seeking subjects? Richard Edwards 3. Understanding the mechanisms of neoliberal control: lifelong learning flexibility and knowledge capitalism Mark Olssen 4. Our 'will to learn' and the assemblage of a learning apparatus Maarten Simons and Jan Masschelein 5. The operation of knowledge and construction of the lifelong learning subject Ulf Olsson and Kenneth Petersson 6. The reason of reason: cosmopolitanism, social exclusion and lifelong learning Thomas S. Popkewitz 7. Historicizing the lifelong learner: governmentality and neoliberal rule Andreas Fejes Section 2: Governing pedagogical subjects 8. Self-governance in the job search: regulative guidelines in job seeking Marinette Fogde 9. Adult learner identities under construction Katarina Sipos Zackrisson and Liselott Assarsson 10. Recognition of prior learning as a technique of governing Per Andersson 11. Pathologizing and medicalizing lifelong learning: a deconstruction Gun Berglund 12. Motivation theory as power in disguise Helene Ahl 13. Discipline and e-learning Katherine Nicoll 14. Academic work and adult education: a site of multiple subjects Nicky Solomon Section 3: Governing subjects 15. Encountering Foucault in lifelong learning Gert Biesta

Regulation of superoxide production in neutrophils: role of calcium influx.

Abstract: Upon stimulation, activation of NADPH oxidase complexes in neutrophils produces a burst of superoxide anions contributing to oxidative stress and the development of inflammatory process. Store-operated calcium entry (SOCE), whereby the depletion of intracellular stores induces extracellular calcium influx, is known to be a crucial element of NADPH oxidase regulation. However, the mechanistic basis mediating SOCE is still only partially understood, as is the signal-coupling pathway leading to modulation of store-operated channels. This review emphasizes the role of calcium influx in the control of the NADPH oxidase and summarizes the current knowledge of pathways mediating this extracellular calcium entry in neutrophils. Such investigations into the cross-talk between NADPH oxidase and calcium might allow the identification of novel pharmacological targets with clinical use, particularly in inflammatory diseases.

DICKKOPF-4 is induced by TCF/β-catenin and upregulated in human colon cancer, promotes tumour cell invasion and angiogenesis and is repressed by 1α,25-dihydroxyvitamin D3

Abstract: Aberrant activation of the Wnt/β-catenin signaling pathway is a hallmark of colon cancer. We show that the Wnt antagonist DICKKOPF-4 (DKK-4) gene is repressed by 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) in human colon cancer cells. This effect correlated with the inhibition of the DKK-4 promoter. Chromatin immunoprecipitation assays revealed that 1,25(OH)2D3 induces early and transient binding of the vitamin D receptor (VDR) and the SMRT corepressor to the region adjacent to the transcription start site of DKK-4. Additionally, we demonstrate that the DKK-4 gene is a new downstream target of TCF/β-catenin. Remarkably, expression of DKK-4 messenger RNA (mRNA) was not detected in a series of 29 human normal (N) colon biopsies but expression was upregulated in all the matched tumour (T) tissues. An inverse correlation existed between the expression of DKK-4 and VDR RNA in the Ts. Ectopic DKK-4 expression increased the migration and invasion properties of colon cancer cells and conditioned media (CM) from DKK-4-expressing cells enhanced the capacity to migrate and form capillary-like tubules of human primary microvascular endothelial cells. In conclusion, DKK-4 is upregulated in colon cancer and is associated with the acquisition of malignant properties by neoplastic cells. DKK-4 downregulation is a novel effect of 1,25(OH)2D3 that may contribute to its anticancer action.

The emergent curriculum: navigating a complex course between unguided learning and planned enculturation

Abstract: The emergent curriculum: Navigating a complex course between unguided learning and planned enculturation

A Likelihood-Based Analysis for Relaxing the Exclusion Restriction in Randomized Experiments with Imperfect Compliance

Abstract: This paper examines the problem of relaxing the exclusion restriction for the evaluation of causal effects in randomized experiments with imperfect compliance. Exclusion restriction is a relevant assumption for identifying causal effects by the nonparametric instrumental variables technique, in which the template of a randomized experiment with imperfect compliance represents a natural parametric extension. However, the full relaxation of the exclusion restriction yields likelihood functions characterized by the presence of mixtures of distributions. This complicates a likelihood-based analysis because it implies partially identified models and more than one maximum likelihood point. We consider the model identifiability when the outcome distributions of various compliance states are in the same parametric class. A two-step estimation procedure based on detecting the root closest to the method of moments estimate of the parameter vector is proposed and analyzed in detail under normally distributed outcomes. An economic example with real data on return to schooling concludes the paper.

The Random Oracle Model and the Ideal Cipher Model Are Equivalent

Abstract: The Random Oracle Model and the Ideal Cipher Model are two well known idealised models of computation for proving the security of cryptosystems. At Crypto 2005, Coron et al.showed that security in the random oracle model implies security in the ideal cipher model; namely they showed that a random oracle can be replaced by a block cipher-based construction, and the resulting scheme remains secure in the ideal cipher model. The other direction was left as an open problem, i.e.constructing an ideal cipher from a random oracle. In this paper we solve this open problem and show that the Feistel construction with 6 rounds is enough to obtain an ideal cipher; we also show that 5 rounds are insufficient by providing a simple attack. This contrasts with the classical Luby-Rackoff result that 4 rounds are necessary and sufficient to obtain a (strong) pseudo-random permutation from a pseudo-random function.

A combined extended finite element and level set method for biofilm growth

Abstract: This paper presents a computational technique based on the extended finite element method (XFEM) and the level set method for the growth of biofilms. The discontinuous-derivative enrichment of the standard finite element approximation eliminates the need for the finite element mesh to coincide with the biofilm–fluid interface and also permits the introduction of the discontinuity in the normal derivative of the substrate concentration field at the biofilm–fluid interface. The XFEM is coupled with a comprehensive level set update scheme with velocity extensions, which makes updating the biofilm interface fast and accurate without need for remeshing. The kinetics of biofilms are briefly given and the non-linear strong and weak forms are presented. The non-linear system of equations is solved using a Newton–Raphson scheme. Example problems including 1D and 2D biofilm growth are presented to illustrate the accuracy and utility of the method. The 1D results we obtain are in excellent agreement with previous 1D results obtained using finite difference methods. Our 2D results that simulate finger formation and finger-tip splitting in biofilms illustrate the robustness of the present computational technique. Copyright © 2007 John Wiley & Sons, Ltd.

Introduction to the special issue on normative multiagent systems

Abstract: This special issue contains four selected and revised papers from the second international workshop on normative multiagent systems, for short NorMAS07 (Boella et al. (eds) Normative multiagent systems. Dagstuhl seminar proceedings 07122, 2007), held at Schloss Dagstuhl, Germany, in March 2007. At the workshop a shift was identified in the research community from a legal to an interactionist view on normative multiagent systems. In this editorial we discuss the shift, examples, and 10 new challenges in this more dynamic setting, which we use to introduce the papers of this special issue.

Review: Familial Parkinson's disease--genetics, clinical phenotype and neuropathology in relation to the common sporadic form of the disease.

Abstract: The identification of the first gene in familial Parkinson's disease (PD) only 10 years ago was a major step in the understanding of the molecular mechanisms in neurodegeneration. Alpha-synuclein aggregation was not only recognized as a key event in neurodegeneration in patients carrying mutations in this gene, but it turned out to be the most consistent marker to define Lewy body pathology also in non-heritable idiopathic PD (IPD). Subsequent comprehensive pathoanatomical studies of IPD brains led to a novel concept of an ascending pathological process in variable stages that are reflected by alpha-synuclein aggregation at specific predilection sites. To date, more than seven genes are known to cause familial PD. The fact that these genetic forms of Parkinsonism present with clinical features indistinguishable from IPD, but may display neuropathological features that are not consistent with IPD, underscores the need of a more differentiated approach to familial and sporadic forms of Parkinsonism. Indeed, in distinct populations, mutations in one single gene were found to cause the disease in up to 40% of patients formerly described as 'idiopathic' cases. These findings indicate that IPD, as defined by a late-onset disorder with no (apparent) genetic contribution, is part of a clinical syndrome that becomes more and more heterogeneous in terms of aetiology, with overlapping clinical and pathoanatomical features. Thus in the present review, we discuss clues from familial PD to our understanding of the molecular pathogenesis of neurodegeneration with special consideration of the variable clinical and neuropathological aspects.

Attacks on RFID Protocols

Abstract: This document consists of a description of attack methodologies and a collection of detailed attacks upon RFID protocols. It is meant to serve as a quick and easy reference and it will be updated as new attacks are found. Currently the only attacks on protocols shown in full detail are the authors’ original attacks with references to similar attacks on other protocols. The main security properties considered are authentication, untraceability, and desynchronization resistance.

Paradigm and Ideology in Educational Research: Social Functions of the Intellectual

Abstract: I accept much that Popkewitz says in his impressive book. I wish I didn't! He writes with great elegance and power on many issues of current interest: the social and cultural location of research activities; the relationship between theory, research and practice; the social role of the intellectual and the epistemological and social assumptions inherent in professional practice. I read the book with a degree of elation, inwardly nodding and saying to myself: Yes, yes, yes. And yet after finishing it I experienced a certain post-reading tristesse. The analysis of the nature of educational research, strategies of educational change, the process of evaluation and problems of educational consultancy is trenchant but the question with which one is left is not: What is the future for these activities? but: Have these activities any future? Popkewitz's discussion of different research paradigms will be familiar to most readers who are already university teachers or members of the research community, but it constitutes a very clear and sophisticated introduction for students coming fresh to the discussion of conflicting methodologies. He is fair to all perspectives, but his own position is quite clear. In stating that the purpose of this book is to probe 'how social assumptions, cultural location and political interests become inextricably tied to conceptual procedures and design questions' it is clear that the idea of rational, objective, value-free educational science isn't going to come out on top. And so it proves. However, though a critique of Western liberal-bourgeois objectivist social science will be familiar to many, Popkewitz's chapter on Soviet pedagogical sciences may well cover unfamiliar ground. The point which he elaborates is that the Western emphasis on schooling as a psychological problem and the Soviet emphasis on schooling as a pedagogical problem have to be seen not simply as differing in their utilitarian purposes but as rooted in the different historical and social circumstances in which educational goals are decided. Soviet research is based on Marxist analysis underpinned by the philosophical assumptions of dialectical materialism, but Popkewitz explores various contradictions and the challenges made by a number of Soviet educationists.

Die Untersuchung des professionellen Wissens deutscher Mathematik-Lehrerinnen und -Lehrer im Rahmen der COACTIV-Studie

Abstract: In der COACTIV-Studie wurden die Mathematiklehrkrafte der PISA-Klassen 2003/04 befragt und getestet. Zentraler Bestandteil von COACTIV sind die Tests zum fachdidaktischen Wissen und zum Fachwissen von Mathematiklehrkraften der Sekundarstufe. Die vorliegende Publikation stellt Konzeptualisierung und Operationalisierung der beiden Wissensbereiche erstmals umfassend vor und beschreibt die Testkonstruktion ausfuhrlich, wobei zur Illustration auch auf bislang noch unveroffentlichtes Itemmaterial zuruckgegriffen wird. Unter anderem die folgenden wichtigen Fragen werden mit den Tests untersucht: Welche Unterschiede gibt es hinsichtlich der Schulformen? Wie hangen fachdidaktisches Wissen und Fachwissen mit der Berufserfahrung zusammen? Welche Zusammenhange bestehen zwischen den beiden Wissensbereichen und subjektiven Uberzeugungen der Lehrkrafte sowie Aspekten des Unterrichts? Inwieweit tragt das professionelle Wissen einer Mathematiklehrkraft zum Lernfortschritt der Schulerinnen und Schuler bei?

Opportunistic DTN routing with window-aware adaptive replication

Abstract: This paper presents ORWAR, a resource-efficient protocol for opportunistic routing in delay-tolerant networks. Our approach exploits the context of mobile nodes (speed, direction of movement and radio range) to estimate the size of a contact window. This knowledge is exploited to make better forwarding decisions and to minimize the probability of partially transmitted messages. As well as optimizing the use of bandwidth during overloads it helps to reduce energy consumption since partially transmitted messages are useless and waste transmission power. Another feature of the algorithm is the use of a differentiation mechanism based on message utility. This allows allocating more resources for high utility messages. More precisely, messages are replicated in the order of highest utility first, and removed from the buffers in the reverse order. To illustrate the benefit of such a scheme the global accumulated utility is used as a system-wide performance metric. Simulations illustrate the benefit of our model and show that ORWAR provides lower overhead and higher delivery rate, as well as higher accumulated utility compared to a number of well-known algorithms (including Maxprop and SprayAndWait).

Will present day glacier retreat increase volcanic activity? Stress induced by recent glacier retreat and its effect on magmatism at the Vatnajökull ice cap, Iceland

Abstract: Global warming causes retreat of ice caps and ice sheets. Can melting glaciers trigger increased volcanic activity? Since 1890 the largest ice cap of Iceland, Vatnajokull, with an area of similar to 8000 km(2), has been continuously retreating losing about 10% of its mass during last century. Present-day uplift around the ice cap is as high as 25 mm/yr. We evaluate interactions between ongoing glacio-isostasy and current changes to mantle melting and crustal stresses at volcanoes underneath Vatnajokull. The modeling indicates that a substantial volume of new magma, similar to 0.014 km(3)/yr, is produced under Vatnajokull in response to current ice thinning. Ice retreat also induces significant stress changes in the elastic crust that may contribute to high seismicity, unusual focal mechanisms, and unusual magma movements in NW-Vatnajokull.

Cryptanalysis of EC-RAC, a RFID Identification Protocol

Abstract: At RFID'08, Lee et al. have proposed a RFID scheme based on elliptic curve cryptography. This scheme, called Elliptic Curve Random Access Control (EC-RAC) has been conceived in order to be implemented on an efficient security processor designed for RFID tags. The aim of this scheme is to enable a fast, secure and private identification scheme. Security arguments are given to prove that RFID tags implementing this scheme are neither traceable nor cloneable. We here show how tags can be tracked if one has eavesdropped the same tag twice and we show that a tag can be impersonated if it has been passively eavesdropped three times. We propose a new scheme based on a modification of the Schnorr scheme as efficient as the initial scheme. We prove that this scheme is zero-knowledge, sound against active adversaries. Moreover, our proposal is private under the Decisional Diffie-Hellman assumption.

Stein's method and normal approximation of Poisson functionals

Abstract: We combine Stein's method with a version of Malliavin calculus on the Poisson space. As a result, we obtain explicit Berry-Ess\'een bounds in Central Limit Theorems (CLTs) involving multiple Wiener-It\^o integrals with respect to a general Poisson measure. We provide several applications to CLTs related to Ornstein-Uhlenbeck L\'evy processes.