Showing papers by "University of Cyprus published in 2010"

Hyperbolic geometry of complex networks

Abstract: We develop a geometric framework to study the structure and function of complex networks. We assume that hyperbolic geometry underlies these networks, and we show that with this assumption, heterogeneous degree distributions and strong clustering in complex networks emerge naturally as simple reflections of the negative curvature and metric property of the underlying hyperbolic geometry. Conversely, we show that if a network has some metric structure, and if the network degree distribution is heterogeneous, then the network has an effective hyperbolic geometry underneath. We then establish a mapping between our geometric framework and statistical mechanics of complex networks. This mapping interprets edges in a network as noninteracting fermions whose energies are hyperbolic distances between nodes, while the auxiliary fields coupled to edges are linear functions of these energies or distances. The geometric network ensemble subsumes the standard configuration model and classical random graphs as two limiting cases with degenerate geometric structures. Finally, we show that targeted transport processes without global topology knowledge, made possible by our geometric framework, are maximally efficient, according to all efficiency measures, in networks with strongest heterogeneity and clustering, and that this efficiency is remarkably robust with respect to even catastrophic disturbances and damages to the network structure.

Observation of long-range, near-side angular correlations in proton-proton collisions at the LHC

Abstract: This is the pre-print version of the Published Article, which can be accessed from the link below - Copyright @ 2010 Springer Verlag

Transverse-Momentum and Pseudorapidity Distributions of Charged Hadrons in pp Collisions at root s=7 TeV

Abstract: Charged-hadron transverse-momentum and pseudorapidity distributions in proton-proton collisions at root s = 7 TeV are measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield is obtained by counting the number of reconstructed hits, hit pairs, and fully reconstructed charged-particle tracks. The combination of the three methods gives a charged-particle multiplicity per unit of pseudorapidity dN(ch)/d eta vertical bar(vertical bar eta vertical bar<0.5) = 5.78 +/- 0.01(stat) +/- 0.23(stat) for non-single-diffractive events, higher than predicted by commonly used models. The relative increase in charged-particle multiplicity from root s = 0.9 to 7 TeV is [66.1 +/- 1.0(stat) +/- 4.2(syst)]%. The mean transverse momentum is measured to be 0.545 +/- 0.005(stat) +/- 0.015(syst) GeV/c. The results are compared with similar measurements at lower energies.

Sustaining the Internet with Hyperbolic Mapping

Abstract: Routing packets on the growing and changing underlying structure of the Internet is challenging and currently based only on local connectivity. Here, a global Internet map is devised: with a greedy forwarding algorithm, it is robust with respect to network growth, and allows speeds close to the theoretical best.

Trajectories of pure and co-occurring internalizing and externalizing problems from age 2 to age 12: findings from the National Institute of Child Health and Human Development Study of Early Child Care.

Abstract: How and why do internalizing and externalizing problems, psychopathological problems from different diagnostic classes representing separate forms of psychopathology, co-occur in children? We investigated the development of pure and co-occurring internalizing and externalizing problems from ages 2 to 12 with the use of latent class growth analysis Furthermore, we examined how early childhood factors (temperament, cognitive functioning, maternal depression, and home environment) and early adolescent social and behavioral adjustment variables were related to differential trajectories of pure and co-occurring internalizing and externalizing problems The sample (National Institute of Child Health and Human Development Study of Early Child Care) consisted of 1,232 children (52% male) Mother reports on the Child Behavior Checklist (Achenbach, 1991, 1992) were used to construct the trajectories of externalizing and internalizing problems Analyses identified groups of children exhibiting pure and co-occurring internalizing and externalizing problems Children exhibiting continuous externalizing or continuous co-occurring internalizing and externalizing problems across the 10-year period under investigation were more likely to (a) engage in risky behaviors, (b) be associated with deviant peers, (c) be rejected by peers, and (d) be asocial with peers at early adolescence However, children exhibiting pure internalizing problems over time were only at higher risk for being asocial with peers as early adolescents Moreover, the additive effects of individual and environmental early childhood risk factors influenced the development of chronic externalizing problems, although pure internalizing problems were uniquely influenced by maternal depression Results also provided evidence for the concepts of equifinality and multifinality

microRNAs: a newly described class of encoded molecules that play a role in health and disease.

Abstract: Micro RNAs are evolutionarily conserved, single stranded molecules of about 22 nucleotides in length and function post-transcriptionally by partial binding (partial complementarity) to the mRNA of genes. Binding of a specific miRNA to its target on an mRNA can inhibit its expression by a variety of mechanisms. Although the most common mechanism is translational repression as a result of miRNA binding to the 3’UTR of an mRNA, mechanisms involving mRNA degradation and destabilization have also been described. Micro RNAs are currently considered as “master regulators” of gene expression. Since a single miRNA can bind and consequently regulate the expression of more than 100 different transcripts it has been estimated that miRNAs may be able to regulate up to 30% of the protein-coding genes in the human genome. As a result, miRNAs receive widespread attention on their potential role in complicated biological processes and multifactorial diseases. In this review we are discussing the biogenesis of miRNAs, their mode of action as well as their role in human diseases through genetic variations on their target sites. Hippokratia 2010; 14 (4): 236-240

Antecedents and outcomes of consumer environmentally-friendly attitudes and behaviour

Abstract: With the intensification of problems relating to the environment, a growing number of consumers are becoming more ecologically conscious in their preferences and purchases of goods. This paper presents the results of a study conducted among 500 Cypriot consumers, focusing on the factors that shape consumer environmental attitudes and behaviour, as well as on the resulting outcomes. The findings confirmed that both the inward and outward environmental attitudes of a consumer are positively influenced by his/her degree of collectivism, long-term orientation, political involvement, deontology, and law obedience, but have no connection with liberalism. The adoption of an inward environmental attitude was also found to be conducive to green purchasing behaviour that ultimately leads to high product satisfaction. On the other hand, an outward environmental attitude facilitates the adoption of a general environmental behaviour, which is responsible for greater satisfaction with life. The findings of the study have important implications for shaping effective company offerings to consumers in target markets, as well as formulating appropriate policies at the governmental level to enhance environmental sensitivity among citizens.

Cloud Computing: The New Frontier of Internet Computing

Abstract: Cloud computing is a new field in Internet computing that provides novel perspectives in internetworking technologies and raises issues in the architecture, design, and implementation of existing networks and data centers. The relevant research has just recently gained momentum, and the space of potential ideas and solutions is still far from being widely explored.

Genome-wide association study of recurrent major depressive disorder in two European case–control cohorts

Abstract: Major depressive disorder (MDD) is a highly prevalent disorder with substantial heritability. Heritability has been shown to be substantial and higher in the variant of MDD characterized by recurrent episodes of depression. Genetic studies have thus far failed to identify clear and consistent evidence of genetic risk factors for MDD. We conducted a genome-wide association study (GWAS) in two independent datasets. The first GWAS was performed on 1022 recurrent MDD patients and 1000 controls genotyped on the Illumina 550 platform. The second was conducted on 492 recurrent MDD patients and 1052 controls selected from a population-based collection, genotyped on the Affymetrix 5.0 platform. Neither GWAS identified any SNP that achieved GWAS significance. We obtained imputed genotypes at the Illumina loci for the individuals genotyped on the Affymetrix platform, and performed a meta-analysis of the two GWASs for this common set of approximately half a million SNPs. The meta-analysis did not yield genome-wide significant results either. The results from our study suggest that SNPs with substantial odds ratio are unlikely to exist for MDD, at least in our datasets and among the relatively common SNPs genotyped or tagged by the half-million-loci arrays. Meta-analysis of larger datasets is warranted to identify SNPs with smaller effects or with rarer allele frequencies that contribute to the risk of MDD.

Natural and synthetic antioxidants: An updated overview

Abstract: The current understanding of the complex role of ROS in the organism and pathological sequelae of oxidative stress points to the necessity of comprehensive studies of antioxidant reactivities and interactions with cellular constituents. Studies of antioxidants performed within the COST B-35 action has concerned the search for new natural antioxidants, synthesis of new antioxidant compounds and evaluation and elucidation of mechanisms of action of both natural and synthetic antioxidants. Representative studies presented in the review concern antioxidant properties of various kinds of tea, the search for new antioxidants of herbal origin, modification of tocopherols and their use in combination with selenium and properties of two promising groups of synthetic antioxidants: derivatives of stobadine and derivatives of 1,4-dihydropyridine.

Secondary transfer effects of intergroup contact: Alternative accounts and underlying processes.

Abstract: Although intergroup contact is one of the most prominent interventions to reduce prejudice, the generalization of contact effects is still a contentious issue. This research further examined the rarely studied secondary transfer effect (STE; Pettigrew, 2009), by which contact with a primary outgroup reduces prejudice toward secondary groups that are not directly involved in the contact. Across 3 cross-sectional studies conducted in Cyprus (N = 1,653), Northern Ireland (N = 1,973), and Texas (N = 275) and 1 longitudinal study conducted in Northern Ireland (N = 411), the present research sought to systematically rule out alternative accounts of the STE and to investigate 2 potential mediating mechanisms (ingroup reappraisal and attitude generalization). Results indicated that, consistent with the STE, contact with a primary outgroup predicts attitudes toward secondary outgroups, over and above contact with the secondary outgroup, socially desirable responding, and prior attitudes. Mediation analyses found strong evidence for attitude generalization but only limited evidence for ingroup reappraisal as an underlying process. Two out of 3 tests of a reverse model, where contact with the secondary outgroup predicts attitudes toward the primary outgroup, provide further evidence for an indirect effect through attitude generalization. Theoretical and practical implications of these results are discussed, and directions for future research are identified.

CMS Tracking Performance Results from early LHC Operation.

Abstract: The first LHC pp collisions at centre-of-mass energies of 0.9 and 2.36 TeV were recorded by the CMS detector in December 2009. The trajectories of charged particles produced in the collisions were reconstructed using the all-silicon Tracker and their momenta were measured in the 3.8 T axial magnetic field. Results from the Tracker commissioning are presented including studies of timing, efficiency, signal-to-noise, resolution, and ionization energy. Reconstructed tracks are used to benchmark the performance in terms of track and vertex resolutions, reconstruction of decays, estimation of ionization energy loss, as well as identification of photon conversions, nuclear interactions, and heavy-flavour decays.

Fluctuations in Biological and Bioinspired Electron-Transfer Reactions

Abstract: Central to theories of electron transfer (ET) is the idea that nuclear motion generates a transition state that enables electron flow to proceed, but nuclear motion also induces fluctuations in the donor-acceptor (DA) electronic coupling that is the rate-limiting parameter for nonadiabatic ET. The interplay between the DA energy gap and DA coupling fluctuations is particularly noteworthy in biological ET, where flexible protein and mobile water bridges take center stage. Here, we discuss the critical timescales at play for ET reactions in fluctuating media, highlighting issues of the Condon approximation, average medium versus fluctuation-controlled electron tunneling, gated and solvent relaxation controlled electron transfer, and the influence of inelastic tunneling on electronic coupling pathway interferences. Taken together, one may use this framework to establish principles to describe how macromolecular structure and structural fluctuations influence ET reactions. This framework deepens our understanding of ET chemistry in fluctuating media. Moreover, it provides a unifying perspective for biophysical charge-transfer processes and helps to frame new questions associated with energy harvesting and transduction in fluctuating media.

Assessment of the Risk Factors of Coronary Heart Events Based on Data Mining With Decision Trees

Abstract: Coronary heart disease (CHD) is one of the major causes of disability in adults as well as one of the main causes of death in the developed countries. Although significant progress has been made in the diagnosis and treatment of CHD, further investigation is still needed. The objective of this study was to develop a data-mining system for the assessment of heart event-related risk factors targeting in the reduction of CHD events. The risk factors investigated were: 1) before the event: a) nonmodifiable-age, sex, and family history for premature CHD, b) modifiable-smoking before the event, history of hypertension, and history of diabetes; and 2) after the event: modifiable-smoking after the event, systolic blood pressure, diastolic blood pressure, total cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides, and glucose. The events investigated were: myocardial infarction (MI), percutaneous coronary intervention (PCI), and coronary artery bypass graft surgery (CABG). A total of 528 cases were collected from the Paphos district in Cyprus, most of them with more than one event. Data-mining analysis was carried out using the C4.5 decision tree algorithm for the aforementioned three events using five different splitting criteria. The most important risk factors, as extracted from the classification rules analysis were: 1) for MI, age, smoking, and history of hypertension; 2) for PCI, family history, history of hypertension, and history of diabetes; and 3) for CABG, age, history of hypertension, and smoking. Most of these risk factors were also extracted by other investigators. The highest percentages of correct classifications achieved were 66%, 75%, and 75% for the MI, PCI, and CABG models, respectively. It is anticipated that data mining could help in the identification of high and low risk subgroups of subjects, a decisive factor for the selection of therapy, i.e., medical or surgical. However, further investigation with larger datasets is still needed.

The relation between board size and firm performance in firms with a history of poor operating performance

Abstract: Focusing on a sample of smaller firms with a history of poor operating performance, this paper posits that increases in board size will be associated with better share price performance. Notably, board sizes studied here are, on average, much smaller than those typically studied by prior research. Mostly consistent with predictions, board size is found to be positively correlated with firm value in between-firms tests, and changes in board size are found to be positively associated with annual stock returns. Last, event study results suggest that the market responds favorably to board size increases and unfavorably to large board size decreases. Together, these results identify a setting in which larger board sizes appear to be positively related to shareholder value.

Potential of photovoltaic systems in countries with high solar irradiation

Abstract: Renewable energy sources derived principally from solar energy have been gaining ground over the last few years and are now beginning to contribute to the global energy mix. Solar energy in the form of direct electricity conversion (photovoltaics) is already very popular in countries such as the United States, Germany and Japan. The enormous potential of photovoltaic (PV) technology is also obvious and favourable in countries with high irradiation such as the Mediterranean region. The objective of this paper is to review the different up and coming PV technologies, to explore the potential of different PV systems in countries with high solar irradiation and to compare their performance through the assessment of thirteen different types of PV systems that have been installed side by side in Nicosia, Cyprus and Stuttgart, Germany. Finally useful insight into the performance of the PV systems as a function of the meteorological conditions and location will be highlighted.

Combination of Tevatron searches for the standard model Higgs boson in the W+W- decay mode

Abstract: We combine searches by the CDF and D0 Collaborations for a Higgs boson decaying to W+W-. The data correspond to an integrated total luminosity of 4.8 (CDF) and 5.4 (D0) fb(-1) of p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron collider. No excess is observed above background expectation, and resulting limits on Higgs boson production exclude a standard model Higgs boson in the mass range 162-166 GeV at the 95% C.L.

Indicator dilution models for the quantification of microvascular blood flow with bolus administration of ultrasound contrast agents

Abstract: Indicator dilution methods have a long history in the quantification of both macro- and microvascular blood flow in many clinical applications. Various models have been employed in the past to isolate the primary pass of an indicator after an intravenous bolus injection. The use of indicator dilution techniques allows for the estimation of hemodynamic parameters of a tumor or organ and thus may lead to useful diagnostic and therapy monitoring information. In this paper, we review and discuss the properties of the lognormal function, the gamma variate function, the diffusion with drift models, and the lagged normal function, which have been used to model indicator dilution curves in different fields of medicine. We fit these models to contrast-enhanced ultrasound time-intensity curves from liver metastases and the ovine corpora lutea. We evaluate the models' performance on the image data and compare their predictions for hemodynamic-related parameters such as the area under the curve, the mean transit time, the full-width at half-maximum, the time to the peak intensity, and wash-in time. The models that best fit the experimental data are the lognormal function and the diffusion with drift.

Ethnic minority immigrants and their children in Britain

Abstract: According to the 2001 UK Census ethnic minority groups account for 4.6 million or 7.9 percent of the total UK population. The 2001 British Labour Force Survey indicates that the descendants of Britain’s ethnic minority immigrants form an important part of the British population (2.8 percent) and of the labour force (2.1 percent). In this paper, we use data from the British Labour Force Survey over the period 1979-2005 to investigate educational attainment and economic behaviour of ethnic minority immigrants and their children in Britain. We compare different ethnic minority groups born in Britain to their parent’s generation and to equivalent groups of white native born individuals. Intergenerational comparisons suggest that British born ethnic minorities are on average more educated than their parents as well more educated than their white native born peers. Despite their strong educational achievements, we find that ethnic minority immigrants and their British born children exhibit lower employment probabilities than their white native born peers. However, significant differences exist across immigrant/ethnic groups and genders. British born ethnic minorities appear to have slightly higher wages than their white native born peers. But if British born ethnic minorities were to face the white native regional distribution and were attributed white native characteristics, their wages would be considerably lower. The substantial employment gap between British born ethnic minorities and white natives cannot be explained by observable differences. We suggest some possible explanations for these gaps.