Showing papers by "Dublin City University published in 2002"

Efficient Algorithms for Pairing-Based Cryptosystems

Abstract: We describe fast new algorithms to implement recent cryptosystems based on the Tate pairing In particular, our techniques improve pairing evaluation speed by a factor of about 55 compared to previously known methods in characteristic 3, and attain performance comparable to that of RSA in larger characteristics We also propose faster algorithms for scalar multiplication in characteristic 3 and square root extraction over Fpm, the latter technique being also useful in contexts other than that of pairing-based cryptography

Standing wave and skin effects in large-area, high-frequency capacitive discharges

Abstract: Large-area capacitive discharges driven at frequencies higher than the usual industrial frequency of 13.56 MHz have attracted recent interest for materials etching and thin film deposition on large-area substrates. Standing wave and skin effects can be important limitations for plasma processing uniformity, which cannot be described by conventional electrostatic theory. An electromagnetic theory is developed for a discharge having two plates of radius R and separation 2l, which accounts for the propagation of surface and evanescent waves from the discharge edge into the centre and the role of capacitive and inductive fields in driving the power absorption. Examples of discharge fields are given having substantial standing wave and/or skin effects. The conditions for a uniform discharge without significant standing wave and skin effects are found to be, respectively, λ0>>2.6(l/s)1/2R and δ>>0.45(dR)1/2, where λ0 is the free space wavelength, s is the sheath width, δ = c/ωp is the collisionless skin depth, with c the speed of light and ωp the plasma frequency, and d = l-s is the plasma half-width. Taking the equality for these conditions for a discharge radius of 50 cm, plate separation of 4 cm, and sheath width of 2 mm, there is a substantial skin effect for plasma densities 1010 cm-3, and there is a substantial standing wave effect for frequencies f70 MHz.

Lipopolysaccharide-induced metastatic growth is associated with increased angiogenesis, vascular permeability and tumor cell invasion.

Abstract: Endotoxin/lipopolysaccharide (LPS), a cell wall component of Gram-negative bacteria, is a potent inflammatory stimulus. We previously reported that LPS increased the growth of experimental metastases in a murine tumor model. Here, we examined the effect of LPS exposure on key determinants of metastasis-angiogenesis, tumor cell invasion, vascular permeability, nitric oxide synthase (NOS) and matrix metalloproteinase 2 (MMP2) expression. BALB/c mice bearing 4T1 lung metastases were given an intraperitoneal (i.p.) injection of 10 microg LPS or saline. LPS exposure resulted in increased lung weight and incidence of pleural lesions. LPS increased angiogenesis both in vivo and in vitro. Vascular permeability in lung tissue was increased 18 hr after LPS injection. LPS increased inducible nitric oxide synthase (iNOS) and MMP2 expression in lung tumor nodules. 4T1 cells transfected with green fluorescent protein (4T1-GFP) were injected via lateral tail vein. LPS exposure resulted in increased numbers of 4T1-GFP cells in mouse lung tissue compared to saline controls, an effect blocked by the competitive NOS inhibitor, N(G) methyl-L-arginine (NMA). LPS-induced growth and metastasis of 4T1 experimental lung metastases is associated with increased angiogenesis, vascular permeability and tumor cell invasion/migration with iNOS expression implicated in LPS-induced metastasis.

Alasdair MacIntyre on Education: In Dialogue with Joseph Dunne

Abstract: This discussion begins from the dilemma, posed in some earlier writing by Alasdair MacIntyre, that education is essential but also, in current economic and cultural conditions, impossible. The potential for resolving this dilemma through appeal to ‘practice’, ‘narrative unity’, and ‘tradition’(three core concepts in After Virtue and later writings) is then examined. The discussion also explores the relationship of education to the modern state and the power of a liberal education to create an ‘educated public’ very different in character from the electorates of contemporary democratic regimes. It concludes with some remarks on the role of education in combating prejudice against certain kinds of human difference.

Sol–gel based optical carbon dioxide sensor employing dual luminophore referencing for application in food packaging technology

Abstract: An optical sensor for the measurement of carbon dioxide in Modified Atmosphere Packaging (MAP) applications has been developed. It is based on the fluorescent pH indicator 1-hydroxypyrene-3,6,8-trisulfonate (HPTS) immobilised in a hydrophobic organically modified silica (ormosil) matrix. Cetyltrimethylammonium hydroxide was used as an internal buffer system. Fluorescence is measured in the phase domain by means of the Dual Luminophore Referencing (DLR) sensing scheme which provides many of the advantages of lifetime-based fluorometric sensors and makes it compatible with established optical oxygen sensor technology. The long-term stability of the sensor membranes has been investigated. The sensor displays 13.5 degrees phase shift between 0 and 100% CO2 with a resolution of better than 1% and a limit of detection of 0.08%. Oxygen cross-sensitivity is minimised (0.6% quenching in air) by immobilising the reference luminophore in polymer nano-beads. Cross-sensitivity towards chloride and pH was found to be negligible. Temperature effects were studied, and a linear Arrhenius correlation between ln k and 1/T was found. The sensor is stable over a period of at least seven months and its output is in excellent agreement with a standard reference method for carbon dioxide analysis.

Constructing elliptic curves with prescribed embedding degrees

Abstract: Pairing-based cryptosystems depend on the existence of groups where the Decision Diffie-Hellman problem is easy to solve, but the Computational Diffie-Hellman problem is hard. Such is the case of elliptic curve groups whose embedding degree is large enough to maintain a good security level, but small enough for arithmetic operations to be feasible. However, the embedding degree for most elliptic curves is enormous, and the few previously known suitable elliptic curves have embedding degree k ≤ 6. In this paper, we examine criteria for curves with larger k that generalize prior work by Miyaji et al. based on the properties of cyclotomic polynomials, and propose efficient representations for the underlying algebraic structures.

Sulfur derivatives of chitosan for palladium sorption

Abstract: Palladium is efficiently extracted from dilute acidic solutions using chitosan derivatives. Sorption performances are enhanced by modification of chitosan through the grafting of sulfur compounds (thiourea, rubeanic acid), which creates new chelating groups, on chitosan backbone using glutaraldehyde as a linker. A comparison of sorption isotherms and sorption kinetics of these two derivatives with those of glutaraldehyde cross-linked chitosan shows that the rubeanic acid derivative of chitosan is the more efficient for the uptake of palladium from dilute solutions. The chemical modification is suspected of bringing chelating functionalities to the ion exchange resin. Sorption capacity is not influenced by the particle size of rubeanic acid derivative of chitosan. Sorption isotherms are described by the Langmuir equation. Increasing the temperature of the solution has little effect on sorption performances. Sorption kinetics are not greatly influenced by the particle size of the sorbent.

Preparation and Characterization of TiO2 Thin Films by Sol-Gel Method

Abstract: Titanium dioxide (TiO2) thin films have been deposited on silicon and glass substrates by the sol-gel process using titanium iso-propoxide [Ti(O-i-C3H7)4]. The bond configuration of the TiO2 thin films was analyzed by using FTIR in the wavenumber range from 400 to 4000 cm−1. The spectral transmittance of as-deposited TiO2 films deposited on fused silica glass was measured in the wavelength range from 200 to 900 nm. X-ray diffraction measurements were performed to determine the crystallinity of the TiO2 films. As-deposited films were amorphous. As the film was annealed at higher temperature, the structure was transformed from amorphous to the anatase crystalline state. The chemical composition of the deposited film was investigated using X-ray photoelectron spectroscopy (XPS). The films are essentially stoichiometric with carbon as the dominant impurity on the surface. Raman spectra show the characteristic of TiO2 anatase phase. The electrical properties of the TiO2 films were measured using capacitance-voltage (C-V) and current-voltage techniques. From C-V measurements, the dielectric constants were calculated to be approximately 26 for the as-deposited films and 75–82 for films annealed at 700°C in different atmosphere. For the as-deposited samples, the breakdown voltage was 2.7 MV/cm, and for an electric field of 1 MV/cm, the leakage current was 5 × 10−5 A/cm2 and the resistivity was 2.2 × 1010 Ω-cm.

Electronic energy transfer and collection in luminescent molecular rods containing ruthenium(II) and osmium(II) 2,2':6',2"-terpyridine complexes linked by thiophene-2,5-diyl spacers.

Abstract: The electronic absorption spectra, luminescence spectra and lifetimes (in MeCN at room temperature and in frozen n-C3H7CN at 77 K), and electrochemical potentials (in MeCN) of the novel dinuclear [(tpy)Ru(3)Os(tpy)]4+ and trinuclear [(tpy)Ru(3)Os(3)Ru(tpy)]6- complexes (3 = 2,5-bis(2,2':6',2''-terpyridin-4-yl)thiophene) have been obtained and are compared with those of model mononuclear complexes and homometallic [(tpy)Ru(3)Ru(tpy)]4+, [(tpy)Os(3)Os(tpy)]4+ and [(tpy)Ru(3)Ru(3)Ru(tpy)]6+ Complexes. The bridging ligand 3 is nearly planar in the complexes, as seen from a preliminary X-ray determination of [(tpy)Ru(3)Ru(tpy)][PF6]4, and confers a high degree of rigidity upon the polynuclear species. The trinuclear species are rod-shaped with a distance of about 3 nm between the terminal metal centres. For the polynuclear complexes, the spectroscopic and electrochemical data are in accord with a significant intermetal interaction. All of the complexes are luminescent (phi in the range 10(-4)-10(-2) and tau in the range 6-340 ns, at room temperature), and ruthenium- or osmium-based luminescence properties can be identified. Due to the excited state properties of the various components and to the geometric and electronic properties of the bridge, Ru --> Os directional transfer of excitation energy takes place in the complexes [(tpy)Ru(3)Os(tpy)]4+ (end-to-end) and [(tpy)Ru(3)Os(3)Ru(tpy)]6+ (periphery-to-centre). With respect to the homometallic case, for [(tpy)Ru(3)Os(3)Ru(tpy)]6+ excitation trapping at the central position is accompanied by a fivefold enhancement of luminescence intensity.

Characterisation of porosity and sensor response times of sol–gel-derived thin films for oxygen sensor applications

Abstract: In recent years, sol–gel-derived films have played a significant role in optical sensor development. This paper focuses on the characterisation of oxygen-sensitive tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS)-based films. Film porosity and sensor response times are reported for a range of films fabricated under different conditions. Porosity data are correlated with predicted film behaviour and also with previous characterisation studies. Oxygen diffusion coefficients are estimated from the response times. The enhanced diffusion coefficient of MTEOS films compared to TEOS films is discussed in terms of the relative oxygen solubility of the films. Comparisons are made with data for oxygen-sensitive polymer films, indicating an enhanced solubility for sol–gel films compared with typical polymer films.

Physical activity intervention: a Transtheoretical Model-based intervention designed to help sedentary young adults become active

Abstract: Physical activity levels in young adults are low. Research supports the use of the Transtheoretical Model of behaviour change (TM) in designing physical activity interventions. This study used a pre-post randomized control design to investigate the effectiveness of a self-instructional intervention for helping sedentary young adults to initiate physical activity. Post-intervention, significantly more of the experimental group (80%), in comparison to the control group (68%), improved their exercise stage of change (SOC) from baseline (P < 0.05). Discriminant analyses revealed that discrimination between stage improvement/non-improvement was possible using the processes of change data. Stage improvers scored significantly higher on all of the behavioral and four out of five of the cognitive processes of change. For stage improvers, the processes of self-re-evaluation and self-liberation were most frequently used, whilst social liberation was used significantly more by the experimental than the control group. This inexpensive, self-instructional intervention, based on the TM and the 'active living message', is an effective method of assisting sedentary young adults to progress through the exercise SOC.

Authenticated ID-based Key Exchange and remote log-in with simple token and PIN number.

Abstract: Authenticated key exchange protocols tend to be either token based or password based. Token based schemes are often based on expensive (and irreplaceable) smart-card tokens, while password-only schemes require that a unique password is shared between every pair of correspondents. The magnetic strip swipe card and associated PIN number is a familiar and convenient format that motivates a combined “two-factor” approach. Finally we suggest an extension of the scheme for use in a client-server scenario.

Cleavage of hemoglobin by hookworm cathepsin D aspartic proteases and its potential contribution to host specificity

Abstract: Hookworms routinely reach the gut of nonpermissive hosts but fail to successfully feed, develop, and reproduce. To investigate the effects of host-parasite coevolution on the ability of hookworms to feed in nonpermissive hosts, we cloned and expressed aspartic proteases from canine and human hookworms. We show here that a cathepsin D-like protease from the canine hookworm Ancylosotoma caninum (Ac-APR-1) and the orthologous protease from the human hookworm Necator americanus (Na-APR-1) are expressed in the gut and probably exert their proteolytic activity extracellularly. Both proteases were detected immunologically and enzymatically in somatic extracts of adult worms. The two proteases were expressed in baculovirus, and both cleaved human and dog hemoglobin (Hb) in vitro. Each protease digested Hb from its permissive host between twofold (whole molecule) and sixfold (synthetic peptides) more efficiently than Hb from the nonpermissive host, despite the two proteases' having identical residues lining their active site clefts. Furthermore, both proteases cleaved Hb at numerous distinct sites and showed different substrate preferences. The findings suggest that the paradigm of matching the molecular structure of the food source within a host to the molecular structure of the catabolic proteases of the parasite is an important contributing factor for host-parasite compatibility and host species range.

Interconnecting carbon nanotubes with an inorganic metal complex.

Abstract: Intermolecular carbon nanotube junctions were formed through amide linkage of amino functionalized multiwall carbon nanotubes and [Ru (dcbpy)(bpy)2](PF6)2, an inorganic metal complex. Nanotube interconnects were visualized using atomic force microscopy. Absorption and emission spectroscopy showed significant changes between starting products and the resulting ruthenium nanotube complex, indicative of successful chemical modification.

Substrate-dependent autoaggregation of Pseudomonas putida CP1 during the degradation of mono-chlorophenols and phenol.

Abstract: A bacterium, CP1, identified as Pseudomonas putida strain, was investigated for its ability to grow on and degrade mono-chlorophenols and phenols as sole carbon sources in aerobic shaking batch culture. The organism degraded up to 1.56 mM 2- and 3-chlorophenol, 2.34 mM 4-chlorophenol and 8.5 mM phenol using an ortho-cleavage pathway. P. putida CP1, acclimated to degrade 2-chlorophenol, was capable of 3-chlorocatechol degradation, while P. putida, acclimated to 4-chlorophenol degradation, degraded 4-chlorocatechol. Growth of P. putida CP1 on higher concentrations of the mono-chlorophenols, >or=1.56 mM 4-chlorophenol and >or=0.78 mM 2- and 3-chlorophenol, resulted in decreases in cell biomass despite metabolism of the substrates, and the formation of large aggregates of cells in the culture medium. Increases in cell biomass with no clumping of the cells resulted from growth of P. putida CP1 on phenol or on lower concentrations of mono-chlorophenol. Bacterial adherence to hydrocarbons (BATH) assays showed cells grown on the higher concentrations of mono-chlorophenol to be more hydrophobic than those grown on phenol and lower concentrations of mono-chlorophenol. The results suggested that increased hydrophobicity and autoaggregation of P. putida CP1 were a response to toxicity of the added substrates.

Temperature-corrected pressure-sensitive paint measurements using a single camera and a dual-lifetime approach

Abstract: The temperature dependence of luminescent coatings which measure surface pressure is a well established problem. Temperature correction of the surface pressure measurement is often carried out by incorporating a second luminescent coating or by co-immobilizing a second luminophore to provide a surface temperature profile. This usually complicates the measurement process by requiring a second camera or sophisticated filtering to distinguish between the two luminescent processes. Here, a single-camera, temperature-corrected PSP (pressure-sensitive paint) system was developed. A new oxygen-permeable sol–gel-based paint, containing both a temperature- and a pressure-sensitive luminophore is described. The fluorescence decay times of the two luminophores are separated by several orders of magnitude. This allows pressure- and temperature-dependent luminescent decay measurements to be separated in the time domain. In addition, the two luminophores were selected such that their absorption and emission spectra occur in similar spectral regions. This avoids the need for different excitation sources or detection filters. Hence a single camera with a gated image intensifier can be used to measure the lifetime of each luminophore within the same cycle. Image alignment issues experienced in dual-camera systems are also avoided. This new PSP has the potential to provide a temperature-corrected surface pressure profile using a single excitation source and detection system.

Curing characteristics of acrylic bone cement

Abstract: Commercial acrylic bone cements are supplied as two components, a polymer powder and a liquid monomer. Mixing of the two components is followed by a progressive polymerization of the liquid monomer to yield a solid mass, a high level of heat being generated during this exothermic reaction. The exposure of bone to high temperatures has led to incidences of bone necrosis and tissue damage, ultimately resulting in failure of the prosthetic fixation. The aim of this study was to determine the thermal properties of two acrylic bone cements as they progress through their polymerization cycles. It was also felt that there was a need to quantify the variations in the curing characteristics as a function of preparing bone cement by different techniques, hand mixing and vacuum mixing. A number of parameters were calculated using the data gathered from the investigation: peak temperature, cure temperature, cure time, and the cumulative thermal necrosis damage index. The results show the temperature profile recorded during polymerization was lowest when the cement was prepared using the Howmedica Mix-Kit I® system: 36 °C for Palacos R® and 41 °C for CMW3® respectively. When the acrylic cements were prepared in any vacuum mixing system there was evidence of an increase in the cure temperature. The main factor that contributed to this rise in temperature was an imbalance in the polymer powder : liquid monomer ratio, there was a high incidence of unmixed powder visible in the mixing barrel of some contemporary vacuum mixing devices. Observing the thermal characteristics of the polymethyl methacrylate (PMMA) bone cements assessed, it was found that particular formulations of bone cements are suited to certain mixing methodologies. It is vital that a full investigation is conducted on a cement mixing/delivery system prior to its introduction into the orthopaedic market.

The Nature of Qualitative Evidence

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K(π, 1) for Artin Groups of Finite Type

Abstract: We construct K(π 1)'s for Artin groups of type C n and D n , using the lattice of elements preceding a Coxeter element in the partial order defined by reflection length.

Motivation and task performance in a task-based web-based tandem project

Abstract: The objective of this paper is to describe a task-based project in tandem via e-mail, and to discuss the effects of motivation on task performance. In this project, a group of Irish students and a group of Spanish students are asked to carry out a series of tasks in collaboration with their tandem partners via e-mail by means of a web page especially designed for the project. Half the message is meant to be written in the student’s native language and half in the target language, and students are also encouraged to correct one another. The goal behind our research is to discuss the effects of motivation on task performance. We argue that resource directing (such as reasoning demands) and resource depleting factors (such as prior knowledge) which belong to task complexity in Robinson’s model (Robinson, 2001) are closely connected to affective variables which, as is the case with motivation, belong to task difficulty. Motivational factors like interest in the meanings to be exchanged, involvement in the decision-making process, students’ expertise in the topic, media and materials used, and the diffusion of outcomes among others have strong effects on task performance, and should therefore be considered together with complexity variables.

Teaching post-editing: a proposal for course content

Abstract: There is a growing demand for translation. To meet this demand, many translation companies are introducing a hybrid technology solution combining translation memory and machine translation. However, few trainee translators receive training in machine translation postediting. This paper asks the question: Why should translator training programmes teach post-editing skills? Is post-editing the same as translation and traditional revision? The skillsets required of a post-editor are listed and the usual list of skills is extended. An outline for a course in post-editing, divided into theoretical and practical components, is proposed. Finally, the question of when such a course should be given to trainee translators is addressed. 1. Why teach post-editing?

Enhanced Fluorescence Sensing Using Sol-Gel Materials

Abstract: The versatility of the sol-gel process with regard to the design of optimized films for fluorescencebased sensing is treated in detail. Sol-gel films are typically used to provide a microporous support matrix in which analyte-sensitive fluorophores are entrapped and into which smaller analyte species may diffuse and interact. The versatility of the process facilitates tailoring of the physicochemical film properties to optimize sensor performance. General principles of sensor optimization are presented. These include issues such as immobilization properties, refractive index control, and sensitivity enhancement. The particular advantages conferred by the use of ormosils are emphasized. In addition, the contribution made by tailored sol-gel films to recent advances in specific fluorescencebased sensor applications is emphasized. This work focuses mainly on results produced in the laboratory of the authors over the past decade.