Showing papers by "University of Luxembourg published in 2005"

Merkle-Damgård revisited: how to construct a hash function

Abstract: The most common way of constructing a hash function (e.g., SHA-1) is to iterate a compression function on the input message. The compression function is usually designed from scratch or made out of a block-cipher. In this paper, we introduce a new security notion for hash-functions, stronger than collision-resistance. Under this notion, the arbitrary length hash function H must behave as a random oracle when the fixed-length building block is viewed as a random oracle or an ideal block-cipher. The key property is that if a particular construction meets this definition, then any cryptosystem proven secure assuming H is a random oracle remains secure if one plugs in this construction (still assuming that the underlying fixed-length primitive is ideal). In this paper, we show that the current design principle behind hash functions such as SHA-1 and MD5 — the (strengthened) Merkle-Damgard transformation — does not satisfy this security notion. We provide several constructions that provably satisfy this notion; those new constructions introduce minimal changes to the plain Merkle-Damgard construction and are easily implementable in practice.

Central limit theorems for sequences of multiple stochastic integrals

Abstract: We characterize the convergence in distribution to a standard normal law for a sequence of multiple stochastic integrals of a fixed order with variance converging to 1. Some applications are given, in particular to study the limiting behavior of quadratic functionals of Gaussian processes.

Against learning. Reclaiming a language for education in an age of learning. [Reprint for 25th Anniversary Issue of Nordisk Pedagogik. Selected as one of the three most significant articles in the 25-year history of the journal.]

Abstract: 54 Ordinary editors’ choice

Online Forums and Deliberative Democracy

Abstract: The Internet is rapidly becoming a part of the everyday lives of a majority of people in the Western world. People perform various activities on the Internet and one of them is discussing politics and society in so-called online forums. In this article, we present an overview of some of the empirical research that evaluates the quality of political conversations in online forums. In the first section, we distinguish research on Usenet groups, web-based political forums and e-consultation forums, and discuss some its findings. In the second section, we elaborate three original categories of variables that attempt to explain differences observed in the quality of deliberation. The third, more extensive section deals with methodological issues. It discusses the operationalisation of deliberative quality and the application of a set of criteria for the idealized public sphere to online conversations. In the conclusion, we present some objections to the previous research and offer some ideas for a more comprehensive approach to online forum analysis.

Prevalence of spondyloarthropathies in France: 2001

Abstract: Objective: To estimate the prevalence of spondyloarthropathies (SpAs) in France in a multiregional representative sample in the year 2001. Methods: A two stage random sample was constituted in seven areas from the national telephone directory and the next birthday method in each household. Interviewers were patient-members of self help groups trained to administer telephone surveys using a validated questionnaire for detecting inflammatory joint disease. Quality of data collection was controlled periodically. SpA was confirmed by the patient’s rheumatologist or by clinical examination. Prevalence estimates after probability sampling correction were standardised for age and sex (1999 national census). Results: Among the 15 219 anonymous telephone numbers selected, 3.6% were places of work or secondary residences and were excluded. The phone interview participation rate ranged across regions from 55.1 to 69.9%. 3554 men and 5841 women were included in the study. Twenty nine cases of SpA were confirmed. All but one fulfilled ESSG criteria. Mean age was 47 years (range 21–78). The overall prevalence standardised for age and sex was 0.30% (95% confidence interval (CI) 0.17 to 0.46). Prevalence was similar in women (0.29% (95% CI 0.14 to 0.49)) and men (0.31 % (95% CI 0.12 to 0.60)). Geographical analysis by department clustering found no significant differences. The prevalence of SpA was as high as that of rheumatoid arthritis. Conclusion: Prevalence of SpA in France was 0.30% in 2001, with no difference between women and men. Ankylosing spondylitis and psoriatic arthritis were the most common SpA subsets.

Prevalence of rheumatoid arthritis in France: 2001

Abstract: Background: Prevalence estimates of rheumatoid arthritis (RA) vary across Europe. Recent estimates in southern European countries showed a lower prevalence than in northern countries. Objectives: To estimate the prevalence of RA in France in a multiregional representative sample in the year 2001. Methods: A two stage random sample was constituted in seven areas (20 counties) from the national telephone directory of households and by the next birthday method in each household. Patient-interviewers, member of self help groups, were trained to administer telephone surveys using a validated questionnaire for case detection of inflammatory rheumatism, and conducted the survey under quality control. All suspected cases of RA were confirmed by their rheumatologist or by clinical examination. Prevalence estimates after probability sampling correction were standardised for age and sex (national census 1999). Results: An average response rate of 64.7% (two stages combined) led to a total of 9395 respondents. Standardised prevalence was 0.31% (95% confidence interval 0.18 to 0.48) for RA, 0.51% in women and 0.09% in men, with a higher age-specific prevalence in the 65–74 year age band. A geographical analysis of county clustering showed significant variation across the country. Conclusion: This national multiregional cooperative study demonstrates the usefulness of working in association with patients of self help groups. It showed a similar prevalence of RA to that of the spondyloarthropathies estimated concomitantly during the survey. It provides a reliable basis for definition of population targets for healthcare delivery and drug treatments.

A talin-dependent LFA-1 focal zone is formed by rapidly migrating T lymphocytes

Abstract: Cells such as fibroblasts and endothelial cells migrate through the coordinated responses of discrete integrin-containing focal adhesions and complexes. In contrast, little is known about the organization of integrins on the highly motile T lymphocyte. We have investigated the distribution, activity, and cytoskeletal linkage of the integrin lymphocyte function associated antigen-1 (LFA-1) on human T lymphocytes migrating on endothelial cells and on ligand intercellular adhesion molecule-1 (ICAM-1). The pattern of total LFA-1 varies from low expression in the lamellipodia to high expression in the uropod. However, high affinity, clustered LFA-1 is restricted to a mid-cell zone that remains stable over time and over a range of ICAM-1 densities. Talin is essential for the stability and formation of the LFA-1 zone. Disruption of the talin–integrin link leads to loss of zone integrity and a substantial decrease in speed of migration on ICAM-1. This adhesive structure, which differs from the previously described integrin-containing attachments displayed by many other cell types, we have termed the “focal zone.”

Cu(InGa)Se2 Solar Cells

Abstract: Cu(In,Ga)Se2 (CIGS) solar cells were characterized in cross section using electron beam induced current (EBIC) and synchrotron based x-ray fluorescence (XRF) measurements. Samples with varying gallium ratios and growth methods were compared. A correlation was observed between the compositional gallium grading profile from XRF and carrier activity seen in EBIC through the thickness of the CIGS layer. Samples with steep back grading showed carrier activity isolated near the CIGS/CdS interface, whereas a more uniform grading resulted in carrier activity seen throughout the absorber layer. 'Notch' grading showed only slight variation in EBIC profile compared to a back graded sample with similar gallium ratios.

Increased Mortality and Aggravation of Heart Failure in Estrogen Receptor-β Knockout Mice After Myocardial Infarction

Abstract: Background— Lower mortality rates among women with chronic heart failure than among men may depend in part on the action of female sex hormones, especially estrogens. The biological effects of estrogens are mediated by 2 distinct estrogen receptor (ER) subtypes (ERα and ERβ). The present study was undertaken to determine the role of ERβ in the development of chronic heart failure after experimental myocardial infarction (MI). Methods and Results— Female ERβ null mice (BERKOChapel Hill) and wild-type littermates (WT) were ovariectomized, given 17β-estradiol, and subjected to chronic anterior MI (MI; BERKO n=31, WT n=30) or sham operation (sham; BERKO n=14, WT n=14). At 8 weeks after MI, both genotypes revealed left ventricular remodeling and impaired contractile function at similar average infarct size (BERKO-MI 32.9±5% versus WT-MI 33.0±4%); however, BERKO mice showed increased mortality (BERKO-MI 42% versus WT-MI 23%), increased body weight and fluid retention (P<0.01), higher ventricular pro-ANP express...

Uncertainty of absolute gravity measurements

Abstract: [1] A total of 96 absolute gravity (AG) measurements at the Membach station and 221 at the Proudman Oceanographic Laboratory (POL) is analyzed for noise content. The lengths of the series were around 10 years (POL) and 8 years (Membach). First the noise at frequencies lower than 1 cpd is studied. This noise consists in setup-dependent offsets and geophysical colored sources. The setup white noise is estimated using continuous relative superconducting gravity (SG) measurements at Membach. The colored environmental noise affecting both AG and SG is estimated using the maximum likelihood estimation technique to fit two types of stochastic models to the SG time series, power law noise, and first-order Gauss Markov (FOGM) noise. We estimate the noise amplitudes of a white noise process plus power law model while simultaneously solving for the spectral index and the noise amplitudes of a white noise process plus FOGM noise model is also estimated. The gravity rate of change and the associated uncertainties as a function of the noise structure are then computed. At frequencies higher than 1 cpd, a time-varying white noise component usually dominates AG time series. Finally, the POL and Membach experiments are applied to estimate the uncertainties for AG campaigns repeated once or twice a year to monitor crustal deformation. Such repeated AG measurements should allow one to constrain gravity rate of change with an uncertainty of 1 nm s−2 yr−1 (or 0.5 mm yr−1) after 14 or 24 years, depending on the noise model. Therefore long-term measurements using absolute gravimeters are appropriate for monitoring slow vertical tectonic deformation.

Diuretic usage in heart failure: a continuing conundrum in 2005.

Abstract: Several large well-designed clinical trials have shown that the use of diuretics is beneficial in patients with hypertension. However, similarly robust data regarding their role in chronic heart failure are lacking. Historically, diuretics were developed for treatment of sodium and water retention in oedematous disorders and clinically, they remain the most potent drugs available to relieve symptoms and eliminate oedema in the congested patient with heart failure. In the non-congested patient, however, diuretics continue to be used on a purely clinical basis without sufficient characterization of benefits, adverse effects, and potential influence on mortality. There are also concerns that chronic diuretic usage can cause adverse vascular effects, unfavourable neuroendocrine activation, electrolyte imbalances, and life-threatening arrhythmias. In this article, we review the limited evidence available regarding the benefits and perils of using diuretics in heart failure.

The estrogen receptor-alpha agonist 16alpha-LE2 inhibits cardiac hypertrophy and improves hemodynamic function in estrogen-deficient spontaneously hypertensive rats

Abstract: Objective : Cardiac mass increases with age and with declining estradiol serum levels in postmenopausal women. Although the non-selective estrogen receptor-α and -β agonist 17β-estradiol attenuates cardiac hypertrophy in animal models and in observational studies, it remains unknown whether activation of a specific estrogen receptor subtype (ERα or ERβ) might give similar or divergent results. Therefore, we analyzed myocardial hypertrophy as well as cardiac function and gene expression in ovariectomized, spontaneously hypertensive rats (SHR) treated with the subtype-selective ERα agonist 16α-LE2 or 17β-estradiol. Methods and Results : Long-term administration of 16α-LE2 or 17β-estradiol did not affect elevated blood pressure, but both agonists efficiently attenuated cardiac hypertrophy and increased cardiac output, left ventricular stroke volume, papillary muscle strip contractility, and cardiac α-myosin heavy chain expression. The observed effects of E2 and 16α-LE2 were abrogated by the ER antagonist ZM-182780. Improved left ventricular function upon 16α-LE2 treatment was also observed in cardiac MRI studies. In contrast to estradiol and 16α-LE2, tamoxifen inhibited cardiac hypertrophy but failed to increase α-myosin heavy chain expression and cardiac output. Conclusions : These results support the hypothesis that activation of ERα favorably affects cardiac hypertrophy, myocardial contractility, and gene expression in ovariectomized SHR. Further studies are required to determine whether activation ERβ mediates redundant or divergent effects.

Targeted Proteolysis Sustains Calcineurin Activation

Abstract: Background— Calcineurin (CnA) is important in the regulation of myocardial hypertrophy. We demonstrated that targeted proteolysis of the CnA autoinhibitory domain under pathological myocardial workload leads to increased CnA activity in human myocardium. Here, we investigated the proteolytic mechanism leading to activation of CnA. Methods and Results— In patients with diseased myocardium, we found strong nuclear translocation of CnA. In contrast, in normal human myocardium, there was a cytosolic distribution of CnA. Stimulation of rat cardiomyocytes with angiotensin (Ang) II increased calpain activity significantly (433±11%; P<0.01; n=6) and caused proteolysis of the autoinhibitory domain of CnA. Inhibition of calpain by a membrane-permeable calpain inhibitor prevented proteolysis. We identified the cleavage site of calpain in the human CnA sequence at amino acid 424. CnA activity was increased after Ang II stimulation (310±29%; P<0.01; n=6) and remained high after removal of Ang II (214±17%; P<0.01; n=6)...

Promoter-hypermethylation is causing functional relevant downregulation of methylthioadenosine phosphorylase ( MTAP ) expression in hepatocellular carcinoma

Abstract: The methylthioadenosine phosphorylase (MTAP) gene is localized in the chromosomal region 9p21. Here, frequently homozygous deletions occur in several kinds of cancer associated with the loss of tumour suppressor genes as p16 and p15. The aim of this study was to analyse MTAP expression in hepatocellular carcinoma (HCC) and to get an insight into the regulation and functional role of MTAP in hepatocancerogenesis. Compared with primary human hepatocytes MTAP expression was markedly downregulated in three different HCC cell lines as determined by real-time PCR and western blotting. This was not due to genomic losses or mutations but to promoter-hypermethylation. Reduced MTAP-expression was confirmed in vivo in HCC compared with non-cancerous liver tissue on both mRNA and protein levels. To study the functional relevance of the downregulated MTAP expression in HCC, MTAP expression was re-induced in HCC cell lines by stable transfection. In these MTAP re-expressing cell clones the invasive potential was strongly reduced, whereas no effects on cell proliferation were observed in comparison with mock transfected cell clones. Furthermore, in MTAP re-expressing cells interferon (IFN)-alpha and IFN-gamma induced a significantly stronger inhibition of cell proliferation than in mock transfected cells. In conclusion, our results suggest a functional role of MTAP inactivation in HCC development and invasiveness. Furthermore, in the light of a recent report revealing an association between MTAP activity and IFN sensitivity, our findings may have clinical significance for therapeutic strategies.

Exploring a spatio-dynamic neighbourhood-based model of residential behaviour in the Brussels periurban area

Abstract: This article proposes a methodology for the construction and the calibration of a micro-economic urban land-use model within an extended Cellular Automata (CA) framework. The methodology is applied to processes of residential spread in a part of the commuting periphery of Brussels. The model hypothesizes that households effect on urban development, through their valuation of neighbourhood externalities. A coarse sensitivity analysis is undertaken in order to explore the relationship between household neighbourhood preferences and emerging spatial morphologies. These macro-structures are measured with different indices in order to parameterize the model.

Predicting the failure of disc surgery by a hypofunctional HPA axis: evidence from a prospective study on patients undergoing disc surgery

Abstract: Patients with postoperative ongoing sciatic pain have been shown to exhibit reduced cortisol levels along with enhanced IL-6 levels. The aim of the present study was to clarify the relationship between a reduced cortisol secretion and enhanced cytokine levels by performing a prospective study on patients with disc herniation. Twenty-two patients were examined before and after their disc surgery. Twelve healthy, pain-free subjects matched for age, education and gender constituted the control group. The preoperative examinations included the assessment of the diurnal pattern of cortisol secretion and the feedback sensitivity of the hypothalamus-pituitary-adrenal (HPA) axis. Patients' subjective stress levels also were assessed during the preoperative examination. The diurnal pattern of cortisol secretion was again assessed during the postoperative examination. Furthermore, blood samples were collected to measure catecholamine, adrenocorticotropic hormone (ACTH)- and interleukin-6 (IL-6) levels before and after measuring the pressure pain thresholds (PPTs). An assessment of the sensitivity of circulating monocytes to the immunosuppressive effects of glucocorticoids was further included in the postoperative examinations. Failed back syndrome (FBS) patients (n=12) showed a reduced cortisol secretion in the morning hours and enhanced feedback sensitivity of the HPA axis. Furthermore, FBS patients displayed an increased in-vitro production of proinflammatory cytokines and a relative glucocorticoid resistance of pro-inflammatory cytokine producing monocytes as compared to non-FBS patients (n=10) and controls. After PPT measurement FBS patients exhibited an increased norepinephrine but decreased epinephrine response, together with lower ACTH levels and a four times higher plasma IL-6 response. These findings suggest that chronically stressed patients are at a higher risk for a poor surgical outcome as their reduced cortisol secretion promotes the postoperative ongoing synthesis of proinflammatory cytokines.

Utile coordination: Learning interdependencies among cooperative agents

Abstract: We describe Utile Coordination, an algorithm that allows a multiagent system to learn where and how to coordinate. The method starts with uncoordinated learners and maintains statistics on expected returns. Coordination dependencies are dynamically added if the statistics indicate a statistically significant benefit. This results in a compact state representation because only necessary coordination is modeled. We apply our method within the framework of coordination graphs in which value rules represent the coordination dependencies between the agents for a specific context. The algorithm is first applied on a small illustrative problem, and next on a large predator-prey problem in which two predators have to capture a single prey.

Effects of Parental Differential Treatment on Relationship Quality with Siblings and Parents: Justice Evaluations as Mediators.

Abstract: Based on equity theory, the present study analyzes to what extent justice evaluations mediate the effects of perceived parental differential treatment (PDT) on relationship quality with siblings and parents as experienced in middle adulthood. Middle-aged adult offspring (N = 709) rated how often they and a sibling received parental recognition, nurturance, and demands for assuming filial responsibility. In addition, they indicated their justice evaluations of PDT and completed measures of relationship quality to sibling and parents. Justice evaluations emerged as either partial or complete mediators between PDT and relationship quality. Moreover, justice evaluations turned out to be more powerful predictors of relationship quality to parents than PDT per se. Implications are discussed concerning factors contributing to justice evaluations and the role of PDT within the context of other justice issues in families.

A formal semantics of timed activity diagrams and its PROMELA translation

Abstract: The lack of a precise semantics for UML activity diagrams makes the reasoning on models constructed using such diagrams infeasible. However, such diagrams are widely used in domains that require a certain degree of confidence. Due to economical interests, the business domain is one of these. To enhance confidence level of UML activity diagrams, this paper provides a formal definition of their syntax and semantics. The main interest of our approach is that we chose UML activity diagrams, which are recognized to be more tractable by engineers, and we extend them with timing constraints. We outline the translation of our semantics into the PROMELA input language of the SPIN model checker which can be used to check several properties.

Robot planning in partially observable continuous domains

Abstract: o We present a value iteration algorithm for learn- ing to act in Partially Observable Markov Decision Processes (POMDPs) with continuous state spaces. Mainstream POMDP research focuses on the discrete case and this complicates its application to, e.g., robotic problems that are naturally modeled using continuous state spaces. The main difculty in dening a (belief-based) POMDP in a continuous state space is that expected values over states must be dened using integrals that, in general, cannot be computed in closed from. In this paper, we provide three main contributions to the literature on continuous- state POMDPs. First, we show that the optimal nite-horizon value function over the continuous innite-dimension al POMDP belief space is piecewise linear and convex, and is dened by a nite set of supporting -functions that are analogous to the -vectors (hyperplanes) dening the value function of a discrete- state POMDP. Second, we show that, for a fairly general class of POMDP models in which all functions of interest are modeled by Gaussian mixtures, all belief updates and value iteration backups can be carried out analytically and exact. Contrary to the discrete case, in a continuous-state POMDP the -functions may grow in size (e.g., in the number of Gaussian components) in each value iteration. Third, we show how the recent point-based value iteration algorithms for discrete POMDPs can be extended to the continuous case, allowing for efcient planning in practical problems. In particular, we demonstrate Perseus, our previously proposed randomized point-based value iteration algorithm, in a simple robot planning problem in a continuous domain, where encouraging results are observed.