Showing papers by "University of Patras published in 2008"

Weight loss, appetite suppression, and changes in fasting and postprandial ghrelin and peptide-YY levels after Roux-en-Y gastric bypass and sleeve gastrectomy: a prospective, double blind study

Abstract: Background:Bariatric surgery is currently the most effective treatment in morbidly obese patients, leading to durable weight loss.Objective:In this prospective double blind study, we aim to evaluate and compare the effects of laparoscopic Roux-en-Y gastric bypass (LRYGBP) with laparoscopic sleeve ga

The variational approximation for Bayesian inference

Abstract: The influence of this Thomas Bayes' work was immense. It was from here that "Bayesian" ideas first spread through the mathematical world, as Bayes's own article was ignored until 1780 and played no important role in scientific debate until the 20th century. It was also this article of Laplace's that introduced the mathematical techniques for the asymptotic analysis of posterior distributions that are still employed today. And it was here that the earliest example of optimum estimation can be found, the derivation and characterization of an estimator that minimized a particular measure of posterior expected loss. After more than two centuries, we mathematicians, statisticians cannot only recognize our roots in this masterpiece of our science, we can still learn from it.

Parametric Image Alignment Using Enhanced Correlation Coefficient Maximization

Abstract: In this work we propose the use of a modified version of the correlation coefficient as a performance criterion for the image alignment problem. The proposed modification has the desirable characteristic of being invariant with respect to photometric distortions. Since the resulting similarity measure is a nonlinear function of the warp parameters, we develop two iterative schemes for its maximization, one based on the forward additive approach and the second on the inverse compositional method. As it is customary in iterative optimization, in each iteration the nonlinear objective function is approximated by an alternative expression for which the corresponding optimization is simple. In our case we propose an efficient approximation that leads to a closed form solution (per iteration) which is of low computational complexity, the latter property being particularly strong in our inverse version. The proposed schemes are tested against the forward additive Lucas-Kanade and the simultaneous inverse compositional algorithm through simulations. Under noisy conditions and photometric distortions our forward version achieves more accurate alignments and exhibits faster convergence whereas our inverse version has similar performance as the simultaneous inverse compositional algorithm but at a lower computational complexity.

VOC oxidation over CuO–CeO2 catalysts prepared by a combustion method

Abstract: CuO–CeO 2 catalysts were prepared via a urea combustion method and their performance in the oxidation of ethanol, ethyl acetate and toluene was evaluated. XRD, H 2 -TPR and N 2 physisorption were employed in catalyst characterization. The specific surface area of mixed materials was higher than the one of single oxides. In ceria-rich materials, crystalline copper oxide phases are absent and segregation of a CuO phase takes place at atomic Cu/(Cu + Ce) ratios higher than 0.25. The mixed oxides get reduced by H 2 at lower temperatures than the corresponding single oxides and copper ions promote reduction of ceria. Ethanol gets more easily oxidized than ethyl acetate, which in turn gets more easily oxidized than toluene. CuO–CeO 2 catalysts of low copper content produce very low amounts of acetaldehyde during ethanol and ethyl acetate oxidation at all conversion levels. This is augmented by the presence of water in the feed. The specific activity of Cu x Ce 1− x catalysts in the oxidation of ethanol, ethylacetate and toluene (specific rate of volatile organic compound (VOC) consumption) is lower than the one of pure CuO and CeO 2 , i.e. combination of the two phases leads to suppression of intrinsic activity. On the other hand, the specific rate of CO 2 production during ethanol and ethyl acetate oxidation is also lower over CuO–CeO 2 than over CeO 2 , but higher than over CuO. The larger surface area of CuO–CeO 2 catalysts counterbalances their smaller specific activity allowing complete VOC conversion at lower temperatures compared to the single oxides.

Biotechnological valorisation of raw glycerol discharged after bio-diesel (fatty acid methyl esters) manufacturing process: Production of 1,3-propanediol, citric acid and single cell oil

Abstract: Raw glycerol, byproduct from bio-diesel production process, is used as carbon substrate in several biotechnological applications. Using Clostridium butyricum F2b, 47.1 g L−1 of 1,3-propanediol was produced in batch anaerobic cultures while substrate uptake rate (rS, expressed in g L−1 h−1) increased with increase in glycerol concentration in the medium. In continuous cultures, microbial behaviour was studied in transitory states after addition of 1,3-propanediol in the chemostat vessel. Microbial growth was not affected by the high 1,3-propanediol (which was added in the chemostat vessel) concentration, while butyric and acetic acids concentrations were increased. In a two-stage continuous culture, 43.5 g L−1 of 1,3-propanediol was produced with a total volumetric productivity of 1.33 g L−1 h−1. Yarrowia lipolytica ACA-DC 50109 was grown in nitrogen-limited aerobic cultures on raw glycerol and it exhibited remarkable biomass production even at high glycerol concentration media, while rS decreased with increase in glycerol concentration. Citric acid was produced after nitrogen depletion in the medium, with the highest quantity of 62.5 g L−1, and yield on glycerol consumed was 0.56 g g−1. Fatty acid analysis of total cellular lipids showed that glycerol concentration increase in the growth medium somehow increased the cellular unsaturated fatty acids content of lipids. Mortierella isabellina ATHUM 2935 exhibited satisfactory growth in nitrogen-limited aerobic cultures with raw glycerol used as sole substrate. When high initial glycerol quantities were employed (e.g. 100 g L−1), 4.4 g L−1 of lipid were accumulated corresponding to around 51% (wt/wt) of lipid in dry weight. rS constantly decreased with increase in glycerol concentration in the medium, and in all cases notable glycerol quantities remained unconsumed in the medium.

Hydrogen Production by Photo-Induced Reforming of Biomass Components and Derivatives at Ambient Conditions

Abstract: Hydrogen can be produced at ambient conditions via an efficient, technologically simple, ecologically benign, and potentially very low-cost process, with the use of a Pt/TiO2 photocatalyst and three abundant and renewable sources: biomass, solar light, and water. The method combines photocatalytic splitting of water and light-induced oxidation of biomass compounds into a single process, able to produce hydrogen at room temperature and atmospheric pressure.

Selective methanation of CO over supported noble metal catalysts: Effects of the nature of the metallic phase on catalytic performance

Abstract: The catalytic performance of Al2O3-supported noble metal catalysts for the methanation of CO, CO2 and their mixture has been investigated with respect to the nature of the dispersed metallic phase (Ru, Rh, Pt, Pd). Experiments have been conducted using feed compositions relevant to those of reformate gas streams, both in the absence and in the presence of water. It has been found that, for all experimental conditions investigated, Ru and Rh are significantly more active than Pt and Pd. Selectivity toward hydrogenation products depends strongly on the noble metal catalyst employed, as well as on whether solo- or co-methanation of CO/CO2 is occuring. For hydrogenation of CO alone, selectivity toward CH4 increases with increasing temperature at the expense of higher hydrocarbons. In presence of water in the feed, catalytic activity of Ru is not affected, while that of Rh is reduced. On the other hand, the performance of Pt and Pd is poor since they promote the undesired water-gas shift (WGS) reaction. In hydrogenation of CO2 alone, selectivity toward higher hydrocarbons is negligible for all catalysts investigated but the reaction is accompanied by production of CO via the reverse WGS reaction. In all cases, addition of water in the feed results in decrease of catalytic activity. In combined hydrogenation of CO/CO2 mixtures, conversion of CO2 is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and approaches 100% when CO2 conversion is initiated. Addition of 30% water vapor in the feed does not affect CO hydrogenation over Ru and Rh catalysts but retards CO2 hydrogenation, thereby expanding the temperature window of operation.

Efficient models for timetable information in public transportation systems

Abstract: We consider two approaches that model timetable information in public transportation systems as shortest-path problems in weighted graphs. In the time-expanded approach, every event at a station, e.g., the departure of a train, is modeled as a node in the graph, while in the time-dependent approach the graph contains only one node per station. Both approaches have been recently considered for (a simplified version of) the earliest arrival problem, but little is known about their relative performance. Thus far, there are only theoretical arguments in favor of the time-dependent approach. In this paper, we provide the first extensive experimental comparison of the two approaches. Using several real-world data sets, we evaluate the performance of the basic models and of several new extensions towards realistic modeling. Furthermore, new insights on solving bicriteria optimization problems in both models are presented. The time-expanded approach turns out to be more robust for modeling more complex scenarios, whereas the time-dependent approach shows a clearly better performance.

The effect of inventory management on firm performance

Abstract: Purpose – Lean management is getting more and more attention in today's highly competitive environment. In this context, the aim of this study is to test the hypothesis that efficient (lean) inventory management leads to an improvement in a firm's financial performance.Design/methodology/approach – Data for the analysis came from the ICAP database, which contains financial information on all medium to large Greek firms. The sample period extended from 2000 to 2002. For each year all manufacturing firms with the corporate form of societes anonyms operating in any one of the three representative industrial sectors in Greece: food, textiles and chemicals were selected.Findings – Preliminary results, obtained by cross‐section linear regressions, reveal that the higher the level of inventories preserved (departing from lean operations) by a firm, the lower its rate of returns. Findings are additionally tested by the use of pseudo‐likelihood ratio test which constitutes a more reliable tool, thus verifying the ...

Computer Architecture Techniques for Power-Efficiency

Abstract: In the last few years, power dissipation has become an important design constraint, on par with performance, in the design of new computer systems. Whereas in the past, the primary job of the computer architect was to translate improvements in operating frequency and transistor count into performance, now power efficiency must be taken into account at every step of the design process. While for some time, architects have been successful in delivering 40% to 50% annual improvement in processor performance, costs that were previously brushed aside eventually caught up. The most critical of these costs is the inexorable increase in power dissipation and power density in processors. Power dissipation issues have catalyzed new topic areas in computer architecture, resulting in a substantial body of work on more power-efficient architectures. Power dissipation coupled with diminishing performance gains, was also the main cause for the switch from single-core to multi-core architectures and slowdown in frequency increase. This book aims to document some of the most important architectural techniques that were invented, proposed, and applied to reduce both dynamic power and static power dissipation in processors and memory hierarchies. A significant number of techniques have been proposed for a wide range of situations and this book synthesizes those techniques by focusing on their common characteristics. Table of Contents: Introduction / Modeling, Simulation, and Measurement / Using Voltage and Frequency Adjustments to Manage Dynamic Power / Optimizing Capacitance and Switching Activity to Reduce Dynamic Power / Managing Static (Leakage) Power / Conclusions

Peripheral nerve damage associated with administration of taxanes in patients with cancer.

Abstract: Peripheral neuropathy is a well recognized toxicity of taxanes, usually resulting to dose modification and changes in the treatment plan. Taxanes produce a symmetric, axonal predominantly sensory distal neuropathy with less prominent motor involvement. A “dying back” process starting from distal nerve endings followed by effects on Schwann cells, neuronal body or axonal transport changes and a disturbed cytoplasmatic flow in the affected neurons is the most widely accepted mechanism of taxanes neurotoxicity. The incidence of taxanes-induced peripheral neuropathy is related to causal factors, such as single dose per course and cumulative dose and risk factors including treatment schedule, prior or concomitant administration of platinum compounds or vinca alcaloids, age and pre-existing peripheral neuropathy of other causes. The most reliable method to assess taxanes neurotoxicity is by clinical examination combined with electrophysiological evaluation. There is currently no effective symptomatic treatment for paclitaxel-associated pain, myalgias and arthralgias. Tricyclic antidepressants and anticonvulsants have been used as symptomatic treatment of neurotoxicity with some measure of success. Therefore, new approaches for prophylaxis against taxanes-induced peripheral neuropathy are needed. Several neuroprotective agents including, thiols, neurotrophic factors, and antioxidants hold promise for their ability to prevent neurotoxicity resulting from taxanes exposure. However, further confirmatory trials are warranted on this important clinical topic. This review critically looks at the pathogenesis, incidence, risk factors, diagnosis, characteristics and management of taxanes-induced peripheral neuropathy. We also highlight areas of future research.

A Nonconvolutional, Split-Field, Perfectly Matched Layer for Wave Propagation in Isotropic and Anisotropic Elastic Media: Stability Analysis

Abstract: A nonconvolutional, split-field, perfectly matched layer, referred to as the multiaxial perfectly matched layer (M-PML), is proposed and implemented. The new formulation is obtained by generalizing the classical perfectly matched layer (PML; as originally proposed by Berenger, [1994]) to a medium in which damping profiles are specified in more than one direction. Under the hypothesis of small damping and using an eigenvalue sensitivity analysis based on first derivatives, we propose a method to study the stability of the M-PML. With this method we demonstrate that the stability of the M-PML is related to the ratios of the specified damping profiles. Recognition of this fact leads to a general procedure for constructing robust, stable M-PML models for anisotropic media. It is also demonstrated that for any anisotropic medium the classical PML exhibits instabilities related to an eigenvalue with zero real part of multiplicity higher than one. Furthermore, we show that exponential growth due to eigenvalues with positive real part can be present in the classical PML for some orthotropic media. The effectiveness of the proposed M-PML and its advantages relative to the classical PML are demonstrated by constructing stable terminations for the aforementioned anisotropic media. The method of stability analysis is developed and demonstrated for two-dimensional elastodynamics problems, but its extension to three-dimensional configurations is straightforward.

CCN activity and droplet growth kinetics of fresh and aged monoterpene secondary organic aerosol

Abstract: The ability of secondary organic aerosol (SOA) produced from the ozonolysis of α-pinene and monoterpene mixtures (α-pinene, β-pinene, limonene and 3-carene) to become cloud droplets was investigated. A static CCN counter and a Scanning Mobility CCN Analyser (a Scanning Mobility Particle Sizer coupled with a Continuous Flow counter) were used for the CCN measurements. Consistent with previous studies monoterpene SOA is quite active and would likely be a good source of cloud condensation nuclei (CCN) in the atmosphere. A decrease in CCN activation diameter for α-pinene SOA of approximately 3 nm hr −1 was observed as the aerosol continued to react with oxidants. Hydroxyl radicals further oxidize the SOA particles thereby enhancing the particle CCN activity with time. The initial concentrations of ozone and monoterpene precursor (for concentrations lower than 40 ppb) do not appear to affect the activity of the resulting SOA. Kohler Theory Analysis (KTA) is used to infer the molar mass of the SOA sampled online and offline from atomized filter samples. The estimated average molar mass of online SOA was determined to be 180±55 g mol −1 (consistent with existing SOA speciation studies) assuming complete solubility. KTA suggests that the aged aerosol (both from α-pinene and the mixed monoterpene oxidation) is primarily water-soluble (around 65%). CCN activity measurements of the SOA mixed with (NH 4 ) 2 SO 4 suggest that the organic can depress surface tension by as much as 10 N m −1 (with respect to pure water). The droplet growth kinetics of SOA samples are similar to (NH 4 ) 2 SO 4 , except at low supersaturation, where SOA tends to grow more slowly. The CCN activation diameter of α-pinene and mixed monoterpene SOA can be modelled to within 10–15% of experiments by a simple implementation of Kohler theory, assuming complete dissolution of the particles, no dissociation into ions, a molecular weight of 180 g mol −1 , a density of 1.5 g cm −3 , and the surface tension of water.

Brain tumor characterization using the soft computing technique of fuzzy cognitive maps

Abstract: The characterization and accurate determination of brain tumor grade is very important because it influences and specifies patient's treatment planning and eventually his life. A new method for characterizing brain tumors is presented in this research work, which models the human thinking approach and the classification results are compared with other computational intelligent techniques proving the efficiency of the proposed methodology. The novelty of the method is based on the use of the soft computing method of fuzzy cognitive maps (FCMs) to represent and model experts' knowledge (experience, expertise, heuristic). The FCM grading model classification ability was enhanced introducing a computational intelligent training technique, the Activation Hebbian Algorithm. The proposed method was validated for clinical material, comprising of 100 cases. FCM grading model achieved a diagnostic output of accuracy of 90.26% (37/41) and 93.22% (55/59) for brain tumors of low-grade and high-grade, respectively. The results of the proposed grading model present reasonably high accuracy, and are comparable with existing algorithms, such as decision trees and fuzzy decision trees which were tested at the same type of initial data. The main advantage of the proposed FCM grading model is the sufficient interpretability and transparency in decision process, which make it a convenient consulting tool in characterizing tumor aggressiveness for every day clinical practice.

Diol-type ligands as central ‘players’ in the chemistry of high-spin molecules and single-molecule magnets

Abstract: The combination of diol-type ligands with paramagnetic transition metal ions has led to the isolation of a host of new homometallic and heterometallic clusters, high-spin molecules and single molecule magnets ranging in nuclearity from two to forty four and with spin ground states as large as S = 61/2. The ligands, whose cluster coordination chemistry is discussed in this article, are 1,3-propanediol and its derivatives, diethanolamine and its derivatives, pyridine-2,6-dimethanol and the gem-diol form of di-2-pyridyl ketone. The structural diversity of the complexes stems from the ability of the ligands to adopt a variety of bridging coordination modes depending on the positions of the two hydroxyl groups in the molecule, the presence/absence of extra donor groups and on the reaction conditions. Examples of ‘true’ reactivity chemistry involving clusters of diol-type ligands are also given. The activation of pyridine-2,6-dimethanol and di-2-pyridyl ketone by 3d-metal centres towards further reactions seems to be an emergent area of synthetic chemistry.