Showing papers by "Wrocław University of Technology published in 2012"

Water Desalination Using Capacitive Deionization with Microporous Carbon Electrodes

Abstract: Capacitive deionization (CDI) is a water desalination technology in which salt ions are removed from brackish water by flowing through a spacer channel with porous electrodes on each side. Upon applying a voltage difference between the two electrodes, cations move to and are accumulated in electrostatic double layers inside the negatively charged cathode and the anions are removed by the positively charged anode. One of the key parameters for commercial realization of CDI is the salt adsorption capacity of the electrodes. State-of-the-art electrode materials are based on porous activated carbon particles or carbon aerogels. Here we report the use for CDI of carbide-derived carbon (CDC), a porous material with well-defined and tunable pore sizes in the sub-nanometer range. When comparing electrodes made with CDC with electrodes based on activated carbon, we find a significantly higher salt adsorption capacity in the relevant cell voltage window of 1.2–1.4 V. The measured adsorption capacity for four materi...

Graphene Oxide vs. Reduced Graphene Oxide as saturable absorbers for Er-doped passively mode-locked fiber laser

Abstract: In this work we demonstrate comprehensive studies on graphene oxide (GO) and reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of Er-doped fiber lasers. The paper describes the fabrication process of both saturable absorbers and detailed comparison of their parameters. Our results show, that there is no significant difference in the laser performance between the investigated SA. Both provided stable, mode-locked operation with sub-400 fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center wavelength. It has been shown that GO might be successfully used as an efficient SA without the need of its reduction to rGO. Taking into account simpler manufacturing technology and the possibility of mass production, GO seems to be a good candidate as a cost-effective material for saturable absorbers for Er-doped fiber lasers.

Graphene Oxide vs. Reduced Graphene Oxide as saturable absorbers for Er-doped passively mode-locked fiber laser

Abstract: In this work we demonstrate comprehensive studies on graphene oxide (GO) and reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of Er-doped fiber lasers. The paper describes the fabrication process of both saturable absorbers and detailed comparison of their parameters. Our results show, that there is no significant difference in the laser performance between the investigated SA. Both provided stable, mode-locked operation with sub-400 fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center wavelength. It has been shown that GO might be successfully used as an efficient SA without the need of its reduction to rGO. Taking into account simpler manufacturing technology and the possibility of mass production, GO seems to be a good candidate as a cost-effective material for saturable absorbers for Er-doped fiber lasers.

Critical thresholds for cerebrovascular reactivity after traumatic brain injury.

Abstract: Pressure-reactivity index (PRx) is a useful tool in brain monitoring of trauma patients, but the question remains about its critical values. Using our TBI database, we identified the thresholds for PRx and other monitored parameters that maximize the statistical difference between death/survival and favorable/unfavorable outcomes. We also investigated how these thresholds depend on clinical factors such as age, gender and initial GCS. A total of 459 patients from our database were eligible. Tables of 2 × 2 format were created grouping patients according to survival/death or favorable/unfavorable outcomes and varying thresholds for PRx, ICP and CPP. Pearson’s chi square was calculated, and the thresholds returning the highest score were assumed to have the best discriminative value. The same procedure was repeated after division according to clinical factors. In all patients, we found that PRx had different thresholds for survival (0.25) and for favorable outcome (0.05). Thresholds of 70 mmHg for CPP and 22 mmHg for ICP were identified for both survival and favorable outcomes. The ICP threshold for favorable outcome was lower (18 mmHg) in females and patients older than 55 years. In logistic regression models, independent variables associating with mortality and unfavorable outcome were age, GCS, ICP and PRx. The prognostic role of PRx is confirmed but with a lower threshold of 0.05 for favorable outcome than for survival (0.25). Results for ICP are in line with current guidelines. However, the lower value in elderly and in females suggests increased vulnerability to intracranial hypertension in these groups.

Neodymium(III) doped fluoride nanoparticles as non-contact optical temperature sensors

Abstract: We report that non-contact optical temperature sensing can be achieved with the use of heavily Nd3+ doped NaYF4 nanoparticles. The temperature evaluation can be realized either by monitoring the absolute luminescence intensity or by measuring the intensity ratio of the two Stark components of the 4F3/2 multiplet in the Nd3+ ions.

Transcranial Doppler Pulsatility Index: What it is and What it Isn’t

Abstract: Background Transcranial Doppler (TCD) pulsatility index (PI) has traditionally been interpreted as a descriptor of distal cerebrovascular resistance (CVR). We sought to evaluate the relationship between PI and CVR in situations, where CVR increases (mild hypocapnia) and decreases (plateau waves of intracranial pressure—ICP).

Sustainable biogas energy in Poland: Prospects and challenges

Abstract: The article investigates prospects and challenges for expanding of sustainable biogas energy in Poland. The number of Polish biogas fuelled power plants and installed electrical power during the 2001–2010 decade is presented. Current economical incentives for biogas energy are discussed. It is emphasized that some revisions to the Polish tradable certificate system are urgently needed in order to encourage energy crop cultivation and the use of best available power technologies. Further, promising, but mostly unexplored feedstocks, such as energy crops, grasses and sorted municipal organic wastes are analyzed. It is also revealed that agrobiogas is characterized by a unique feature of ‘negative net’ CO2 atmospheric emissions and thus the role of agrobiogas in solving Polish CCS dilemmas is discussed. In regard to biogas energy systems it is stressed, that the cost of electricity from biogas is almost independent on the size of agrobiogas CHP power plants in the range of 0.2–5 MWe. Therefore agrobiogas energy is well suited for distributed energy systems involving small-scale agrobiogas power plants offering more green jobs and improved local waste management characteristics. Finally, reliable technologies suitable for biogas energy conversion and upgrading of biogas fuel to marketable gaseous fuels are briefly characterized.

Detergent‐Free Formation and Physicochemical Characterization of Nanosized Lipid–Polymer Complexes: Lipodisq

Abstract: Lipodisq particles are polymer-lipid complexes formed by detergent-free methods Lipodisq particles containing dimyristoylphosphatidylcholine (DMPC) are characterized by increased lipid ordering co

Passive harmonic mode-locking in Er-doped fiber laser based on graphene saturable absorber with repetition rates scalable to 2.22 GHz

Abstract: Passive harmonic-mode locking of erbium-doped fiber laser with atomic multilayer graphene is presented. The laser could operate at several harmonics (from 2nd to 21st) of the fundamental repetition frequency of the ring resonator (106 MHz). The highest achieved repetition rate was 2.22 GHz (which corresponds to the 21st harmonic) with sub-picosecond pulse durations and over 40 dB of the supermode noise suppression. The saturable absorber was formed by multilayer graphene, mechanically exfoliated from pure graphite block through Scotch-tape and deposited on the fiber ferrule.

Nonparametric statistical analysis for multiple comparison of machine learning regression algorithms

Abstract: In the paper we present some guidelines for the application of nonparametric statistical tests and post-hoc procedures devised to perform multiple comparisons of machine learning algorithms. We emphasize that it is necessary to distinguish between pairwise and multiple comparison tests. We show that the pairwise Wilcoxon test, when employed to multiple comparisons, will lead to overoptimistic conclusions. We carry out intensive normality examination employing ten different tests showing that the output of machine learning algorithms for regression problems does not satisfy normality requirements. We conduct experiments on nonparametric statistical tests and post-hoc procedures designed for multiple 1×N and N ×N comparisons with six different neural regression algorithms over 29 benchmark regression data sets. Our investigation proves the usefulness and strength of multiple comparison statistical procedures to analyse and select machine learning algorithms.

Negative carbon intensity of renewable energy technologies involving biomass or carbon dioxide as inputs

Abstract: Conventional fossil fuel-based energy technologies can achieve efficiency in energy conversion but they are usually completely inefficient in carbon conversion because they generate significant CO2 emissions to the atmosphere per unit energy converted. In contrast, some renewable energy technologies characterized by negative carbon intensity can simultaneously achieve efficiency in the conversion of energy and in the conversion of carbon. These carbon negative renewable energy technologies can generate useful energy and remove CO2 from the atmosphere, either by direct capture and recycling of atmospheric CO2 or indirectly, by involving biofuels. Interestingly, the deployment of carbon negative renewable energy technologies can offset carbon emissions from conventional fossil fuel-based energy technologies and thus reduce the overall carbon intensity of energy systems. The current review analyzes two groups of renewable energy technologies involving biomass or CO2 as inputs. The discussions focus on useful techniques which enable to achieve negative carbon intensity of energy while being technologically promising in near-term as well as cost-effective. These analyzes include advanced carbon sequestration concepts such as soil carbon sequestration and CO2 recycling to useful C-rich products such as fuels and fertilizers. The 'drop-in' of renewable energy is achieved by allowing bioenergy and renewable energies in the form of renewable electricity, renewable thermal energy, solar energy, renewable hydrogen, etc. The carbon negative renewable energy technologies are analyzed and perspectives and constraints of each technology are expounded.

GED: the method for group evolution discovery in social networks

Abstract: The continuous interest in the social network area contributes to the fast development of this field. The new possibilities of obtaining and storing data facilitate deeper analysis of the entire network, extracted social groups and single individuals as well. One of the most interesting research topic is the dynamics of social groups, it means analysis of group evolution over time. Having appropriate knowledge and methods for dynamic analysis, one may attempt to predict the future of the group, and then manage it properly in order to achieve or change this predicted future according to specific needs. Such ability would be a powerful tool in the hands of human resource managers, personnel recruitment, marketing, etc. The social group evolution consists of individual events and seven types of such changes have been identified in the paper: continuing, shrinking, growing, splitting, merging, dissolving and forming. To enable the analysis of group evolution a change indicator - inclusion measure was proposed. It has been used in a new method for exploring the evolution of social groups, called Group Evolution Discovery (GED). The experimental results of its use together with the comparison to two well-known algorithms in terms of accuracy, execution time, flexibility and ease of implementation are also described in the paper.

Elemental analysis of teas and their infusions by spectrometric methods

Abstract: A non-alcoholic beverage, tea made from leaves of the Camellia sinensis plant is a potentially rich source of dietary important elements and is consumed by nearly half the worlds population. Of the types of tea, black, oolong and green teas are the most popular, so knowledge about their elemental characteristics is especially important. Habitual drinking of tea infusions may significantly contribute to daily dietary requirements of elements or lead to accumulation of elements and intoxication under overdose conditions. It is especially important that toxic and/or heavy metals, which may be retained by tea plants to a great degree, can have adverse effects on human well-being and health. Accordingly, accurate, precise determination of the mineral content of tea leaves from which tea is made, teas available commercially and their infusions allows us to assess exposure to non-essential elements and to judge the nutritional value of tea reliably. Different instrumental techniques are used for elemental analysis, but atomic and mass spectrometries are preferred most. This review surveys the elemental analysis of teas and their infusions, and the consequences of the presence of various elements in this beverage. We also consider sample-preparation procedures before analysis, the results of analysis and the manner of controlling and assuring the quality of those results. a 2012 Elsevier Ltd. All rights reserved.

Application of computer simulation modeling in the health care sector: a survey

Abstract: This article aims to present examples of computer simulation models that support decision-making processes in the health care sector. The objective of this review is to propose a system of classification of health care topic areas examined with the assistance of simulation methods. The categories described in literature were expanded and a detailed taxonomy for sub-groups was formulated. Usefulness of simulation modeling techniques was investigated and an attempt was made to correlate the simulation approach with a corresponding health care application group from the suggested classification.

Fractional calculus for power functions and eigenvalues of the fractional Laplacian

Abstract: We calculate the fractional Laplacian Δ α/2 for functions of the form u(x) = (1 − |x|2) + and v(x) = x d u(x). As an application, we estimate the first eigenvalues of the fractional Laplacian in a ball.

Regular bipolar fuzzy graphs

Abstract: We introduce the concepts of regular and totally regular bipolar fuzzy graphs. We prove necessary and sufficient condition under which regular bipolar fuzzy graph and totally bipolar fuzzy graph are equivalent. We introduce the notion of bipolar fuzzy line graphs and present some of their properties. We state a necessary and sufficient condition for a bipolar fuzzy graph to be isomorphic to its corresponding bipolar fuzzy line graph. We examine when an isomorphism between two bipolar fuzzy graphs follows from an isomorphism of their corresponding bipolar fuzzy line graphs.

Antiadhesive activity of the biosurfactant pseudofactin II secreted by the Arctic bacterium Pseudomonas fluorescens BD5

Abstract: Background Pseudofactin II is a recently identified biosurfactant secreted by Pseudomonas fluorescens BD5, the strain obtained from freshwater from the Arctic Archipelago of Svalbard. Pseudofactin II is a novel compound identified as cyclic lipopeptide with a palmitic acid connected to the terminal amino group of eighth amino acid in peptide moiety. The C-terminal carboxylic group of the last amino acid forms a lactone with the hydroxyl of Thr3. Adhesion is the first stage of biofilm formation and the best moment for the action of antiadhesive and anti-biofilm compounds. Adsorption of biosurfactants to a surface e.g. glass, polystyrene, silicone modifies its hydrophobicity, interfering with the microbial adhesion and desorption processes. In this study the role and applications of pseudofactin II as a antiadhesive compound has been investigated from medicinal and therapeutic perspectives.

Water Desalination with Wires

Abstract: We show the significant potential of water desalination using a novel capacitive wire-based technology in which anode/cathode wire pairs are constructed from coating a thin porous carbon electrode layer on top of electrically conducting rods (or wires). By alternately dipping an array of electrode pairs in freshwater with and in brine without an applied cell voltage, we create an ion adsorption/desorption cycle. We show experimentally how in six subsequent cycles we can reduce the salinity of 20 mM feed (brackish) water by a factor of 3, while application of a cation exchange membrane on the cathode wires makes the desalination factor increase to 4. Theoretical modeling rationalizes the experimental findings, and predicts that system performance can be significantly enhanced by material modifications. To treat large volumes of water, multiple stacks of wire pairs can be used simultaneously in a “merry-go-round” operational mode.

Optimum Trajectory Control of the Current Vector of a Nonsalient-Pole PMSM in the Field-Weakening Region

Abstract: Industry-proven field-weakening solutions for nonsalient-pole permanent-magnet synchronous motor drives are presented in this paper. The core algorithm relies on direct symbolic equations. The equations take into account the stator resistance and reveal its effect on overall algorithm quality. They establish a foundation for an offline calculated lookup table which secures effective d-axis current reference over entire field-weakening region. The table has been proven on its own and in combination with a PI compensator. Usage recommendations are given in this paper. Functionality of the proposed solutions has been investigated theoretically and in practice. The investigation has been carried out in the presence of motor magnetic saturation and parameter tolerance, taking into account the change of operating temperature. The results and analysis method are included in this paper.

Study of mid-infrared laser action in chalcogenide rare earth doped glass with Dy 3+ , Pr 3+ and Tb 3+

Abstract: We present a study of chalcogenide glass fiber lasers doped with Dy3+, Pr3+ or Tb3+ that would operate in the mid-infrared wavelength range. A set of chalcogenide glass samples doped with different concentrations of rare earth ions is fabricated. The modeling parameters are directly extracted from FTIR absorption measurements of the fabricated bulk glass samples using Judd-Ofelt, Fuchtbauer–Ladenburg theory and McCumber theory. The modeling results show that, for all the dopants considered, an efficient mid-infrared laser action is possible if optical losses are kept at the level of 1dB/m or below.

Development of direct-current, atmospheric-pressure, glow discharges generated in contact with flowing electrolyte solutions for elemental analysis by optical emission spectrometry

Abstract: Direct-current, atmospheric-pressure, glow discharge (dc-APGD) generated in contact with flowing sample solutions is a new, very promising excitation source for analytical optical emission spectrometry, due to its low maintenance requirements and its analytical performance. Since analyzed solutions act as liquid cathodes, this discharge system is useful for the direct determination of elements dissolved in solutions without having to produce their aerosols by pneumatic nebulization. The review presents different systems and designs of dc-APGD generated with the liquid cathode applied to spectrochemical analysis in the past 20 years. We discuss the effect of experimental conditions on analytical response and performance of the discharge. We include analytical figures of merit obtained with different discharge systems and their application to the analysis of environmental and biological samples containing various trace elements.

Electronic properties of gated triangular graphene quantum dots: Magnetism, correlations, and geometrical effects

Abstract: We present a theory of electronic properties of gated triangular graphene quantum dots with zigzag edges as a function of size and carrier density. We focus on electronic correlations, spin, and geometrical effects using a combination of atomistic tight-binding, Hartree-Fock, and configuration interaction methods (TB + HF + CI), including long-range Coulomb interactions. The single-particle energy spectrum of triangular dots with zigzag edges exhibits a degenerate shell at the Fermi level with a degeneracy ${N}_{\mathrm{edge}}$ proportional to the edge size. We determine the effect of the electron-electron interactions on the ground state, the total spin, and the excitation spectrum as a function of a shell filling and the degeneracy of the shell using TB + HF + CI for ${N}_{\mathrm{edge}}l12$ and approximate CI method for ${N}_{\mathrm{edge}}\ensuremath{\geqslant}12$. For a half-filled neutral shell we find spin-polarized ground state for structures up to $N=500$ atoms in agreement with previous ab initio and mean-field calculations and in agreement with Lieb's theorem for a Hubbard model on a bipartite lattice. Adding a single electron leads to the complete spin depolarization for ${N}_{\mathrm{edge}}\ensuremath{\leqslant}9$. For larger structures, the spin depolarization is shown to occur at different filling factors. Away from half-fillings excess electrons(holes) are shown to form Wigner-like spin-polarized triangular molecules corresponding to large gaps in the excitation spectrum. The validity of conclusions is assessed by a comparison of results obtained from different levels of approximations. While for the charge-neutral system all methods give qualitatively similar results, away from the charge neutrality an inclusion of all Coulomb scattering terms is necessary to produce results presented here.