Showing papers by "Dublin City University published in 1995"
01 Sep 1995
TL;DR: This work considers queueing systems where the workload process is assumed to have an associated large deviation principle with arbitrary scaling and there exist increasing scaling functions (at,vt,teE+) and a rate function / such that if (Wt,teR+) denotesThe workload process, then limi;^ 1 \ogP(Wt/at > w) = — I(w)
Abstract: We consider queueing systems where the workload process is assumed to have an associated large deviation principle with arbitrary scaling: there exist increasing scaling functions (at, vt, t∈R+) and a rate function I such that if (Wt, t∈R+) denotes the workload process, thenon the continuity set of I. In the case that at = vt = t it has been argued heuristically, and recently proved in a fairly general context (for discrete time models) by Glynn and Whitt[8], that the queue-length distribution (that is, the distribution of supremum of the workload process Q = supt≥0Wt) decays exponentially:and the decay rate δ is directly related to the rate function I. We establish conditions for a more general result to hold, where the scaling functions are not necessarily linear in t: we find that the queue-length distribution has an exponential tail only if limt→∞at/vt is finite and strictly positive; otherwise, provided our conditions are satisfied, the tail probabilities decay like
485 citations
TL;DR: Ecconomies of scale are obtainable for highly bursty traffic expected in ATM multiplexing for heterogeneous superpositions, Gaussian processes, Markovian additive processes and Poisson processes.
Abstract: We analyse the queueQ
L at a multiplexer withL inputs. We obtain a large deviation result, namely that under very general conditions
$$\mathop {\lim }\limits_{L \to \infty } L^{ - 1} \log P\left[ {Q^L > Lb} \right] = - I(b)$$
provided the offered load is held constant, where the shape functionI is expressed in terms of the cumulant generating functions of the input traffic. This provides an improvement on the usual effective bandwidth approximation
$$P\left[ {Q^L > b} \right] \approx e^{ - \delta b}$$
replacing it with
$$P\left[ {Q^L > b} \right] \approx e^{ - LI(b/L)}$$
, The differenceI(b)−δb determines the economies of scale which are to be obtained in large multiplexers. If the limit
$$
u = - \lim _{t \to \infty } t\lambda _t (\delta )$$
exists (here λt, is the finite time cumulant of the workload process) then
$$\lim _{b \to \infty } (I(b) - \delta b) =
u$$
. We apply this idea to a number of examples of arrivals processes: heterogeneous superpositions, Gaussian processes, Markovian additive processes and Poisson processes. We obtain expressions forv in these cases,v is zero for independent arrivals, but positive for arrivals with positive correlations. Thus ecconomies of scale are obtainable for highly bursty traffic expected in ATM multiplexing.
270 citations
TL;DR: The chemical and genetic strategies are complementary and have been combined to stabilize cytochrome c by metal-mediated cross-linking following site-specific mutagenesis and the beneficial effects of certain additives on protein stability are summarized.
229 citations
TL;DR: It is concluded that yeasts have contributed significantly to the understanding of the metal uptake process and suggest directions for future work.
Abstract: This review addresses metal uptake specifically by yeast. Metal uptake may be passive, active or both, depending on the viability of the biomass, and is influenced by a number of environmental and experimental factors. Uptake is typically accompanied by a degree of ion exchange and, under certain conditions, may be enhanced by the addition of an energy source, Intracellularly accumulated metal is most readily associated with the cell wall and vacuole but may also be bound by other cellular organelles and biomolecules. The intrinsic biochemical, structural and genetic properties of the yeast cell along with environmental conditions are crucial for its survival when exposed to toxic metals. Conditions of pH, temperature and the presence of additional ions, amongst others, have varying effects on the metal uptake process. We conclude that yeasts have contributed significantly to our understanding of the metal uptake process and suggest directions for future work.
213 citations
TL;DR: In this article, an overview of the state-of-the-art of optical sensors employing sol-gel-derived coatings is presented, which is particularly suited to the side-coating of optical fibres or waveguides in evanescent-wave sensors.
Abstract: In this paper an overview is presented of the state-of-the-art of optical sensors employing sol-gel-derived coatings. The technique is particularly suited to the side-coating of optical fibres or waveguides in evanescent-wave sensors because precise control of sensitivity-determining parameters, such as the coating thickness and length, is achievable. Sensors based on entrapped organic and inorganic dyes, enzymes and other biomolecules have been reported. The main features of the process are illustrated by examples of chemical sensors and biosensors from the literature. In particular, the development of an oxygen sensor based on the quenching of fluorescence from a sol-gel-entrapped ruthenium complex and an absorption-based pH sensor are described. Issues that require further investigation before this technology can proceed to the stage of industrial development are also highlighted.
174 citations
TL;DR: There is a powerful heating mechanism associated with pressure effects that arise during the expansion and contraction of sheaths during low-pressure capacitively coupled rf discharges.
Abstract: Collisionless heating in low-pressure capacitively coupled rf discharges is usually attributed to a stochastic interaction between electrons and the oscillating sheath. We show that this explanation is not complete---there is a powerful heating mechanism associated with pressure effects that arise during the expansion and contraction of sheaths.
167 citations
TL;DR: In this article, the authors examined how subordinates' reaction to control systems is influenced by the leadership behaviour of supervisors and found that a leadership style characterized by high structure and low consideration was associated with the highest level of dysfunctional behaviour for all behaviours examined.
Abstract: Prior research has highlighted the problem of dysfunctional reactions to control systems. Studies carried out in auditing firms have revealed high levels of budget pressure leading to a variety of dysfunctional behaviours which can be difficult to control. This study examines how subordinates' reaction to control systems is influenced by the leadership behaviour of supervisors. Data were collected by means of a questionnaire sent to all audit seniors in three Big Six audit firms. Two forms of dysfunctional behaviour were measured: under-reporting of time and audit quality reduction behaviour. A leadership style characterized by high structure and low consideration was found to be associated with the highest level of dysfunctional behaviour for all behaviours examined, while the lowest level of dysfunctional behaviour was associated with a style depicting low structure and high consideration. Perceived environmental uncertainty was found to moderate these relationships, and to exercise a stronger moderating effect for audit quality reduction behaviour than for under-reporting of time.
166 citations
TL;DR: In this paper, a surface roughness model for the end milling of 190 BHN steel was developed in terms of cutting speed, feed, and axial depth of cut.
137 citations
TL;DR: In this paper, the potential of the test ions to displace preloaded borderline metals ions from the biomass increased with increasing covalent index, except for Pb 2+, which totally displaced the preloaded Sr 2+.
134 citations
TL;DR: Solver, an analysis tool incorporated into Microsoft Excel V 5.0 for Windows, has been evaluated for solving non-linear equations and the results suggest that solver can be successfully used for modelling data obtained in many analytical situations.
130 citations
TL;DR: Two standard features in the electron energy distribution function (EEDF) have been proposed as a test of the ability of a probe system to resolve features, first the transition from a low temperature bi-Maxwellian distribution to a Druyveysten distribution and the “hole” in the EEDF at 2 eV to 4 eV in nitrogen plasmas.
Abstract: The use of a Langmuir probe system in two GEC cells is reviewed. The major problems associated with probe diagnostics in a GEC cell are outlined and discussed. While the data base is still insufficient to give definitive values for many parameters, a number of standard measurements are put forward. The plasma density in argon is 9×109 cm-3 (±20 %) at an applied rf voltage of 250 V (500 V peak to peak) and a gas pressure of 13.3 Pa (100 mTorr). The electron density scales linearly with applied voltage. The plasma to ground sheath resistance is shown to be very important with a value of 810 Ω in argon at a pressure of 13.3 Pa (100 mTorr) and discharge current of 0.1 A. The value of plasma to ground resistance scales inversely with discharge current and sublinear with pressure. Two standard features in the electron energy distribution function (EEDF) have been proposed as a test of the ability of a probe system to resolve features, first, the transition from a low temperature (<1 eV) bi-Maxwellian distribution to a Druyveysten distribution (3 eV) at 13.3 Pa (100 mTorr) in argon, and the "hole" in the EEDF at 2 eV to 4 eV in nitrogen plasmas.
TL;DR: The conventional assumption in the theory of superparamagnetism, that except in the very early stages of relaxation to equilibrium the only appreciable time constant is the one associated with the smallest nonvanishing eigenvalue, is no longer true when an applied constant magnetic field exceeds a certain critical value.
Abstract: The relaxation behavior of an assembly of noninteracting single-domain ferromagnetic particles in the presence of a constant magnetic field is studied by solving the corresponding Fokker-Planck equation. The analysis is performed by first converting that equation into a hierarchy of differential-recurrence relations by expanding the solution in Legendre polynomials. The spectrum of eigenvalues and their associated amplitudes is then determined by matrix methods where all the desired physical quantities such as the magnetization correlation time and complex magnetic susceptibility may be computed numerically. In order to ensure the accuracy of the results obtained this solution is compared with an exact solution derived in terms of matrix continued fractions. It is shown that the conventional assumption in the theory of superparamagnetism, that except in the very early stages of relaxation to equilibrium the only appreciable time constant is the one associated with the smallest nonvanishing eigenvalue, is no longer true when an applied constant magnetic field exceeds a certain critical value. The breakdown of this assumption manifests itself in (a) a dramatically large deviation of the magnetization correlation time (area under the curve of the decay of the magnetization) from the inverse of the lowest eigenvalue, and (b) in the presence of relatively strong high-frequency modes superimposed on the N\'eel one usually assigned to the lowest eigenvalue. The results are compared with available experimental data.
TL;DR: In this article, an intrinsic fiber-optic oxygen sensor based on phase fluorimetry is presented. But the performance of the intrinsic oxygen sensor in real-time measurement mode is reported.
Abstract: In this paper we report preliminary results from an intrinsic fibre-optic oxygen based on phase fluorimetry. Phase fluorimetry is a method of measuring the luminescence lifetime of a fluorophore and, where suitable, has many advantages over other reported optical sensing techniques such as absorption and fluoresecnece intensity monitoring. Lifetime measurements are absolute quantities, which offer the possibility of inherent referencing, and are usually independent of indicator concentration, photobleaching the excitation source intensity. The long excited-state lifetime of ruthenium polypyridyl complexes are efficiently quenched by oxygen. Sol-gel immobilization of the ruthenium complex (Ru II -tri(4,7-diphenyl-1,10-phenanthroline)) on a multimode optical fibre yields highly durable, inert, microporous claddings which exhibit almost complete quenching under evanescent-wave excitation. The fluorophore decay curve exhibits a double exponential behaviour consisting of a fast and a slow component, both of which undergo quenching on exposure to oxygen. These data are used to model and expected behaviour of the sensor in phase fluorimetric mode. The predictions are in close agreement with experimental measurements performed with the coated fibre under blue light-emitting diode (LED) excitation. An optimum modulation frequency is identified and the performance of the intrinsic oxygen sensor in real-time measurement mode is reported. The use of an inexpensive light source, combined with a simple fabrication technique and the advantages of the phase fluorimetric method, facilitates the production of low cost, high performance optical oxygen sensors.
TL;DR: In this article, the possibility of grinding thermosets and thermoplastics using an open grinding wheel is discussed with reference to bond type, grit type, and grit size and porosity.
TL;DR: In this paper, the effect of a constant magnetic field, applied at an angle to the easy axis of magnetization, on the N\'eel relaxation time of a single domain ferromagnetic particle with uniaxial anisotropy was studied by calculating the lowest nonvanishing eigenvalue of the appropriate Fokker-Planck equation using matrix methods.
Abstract: The effect of a constant magnetic field, applied at an angle $\ensuremath{\psi}$ to the easy axis of magnetization, on the N\'eel relaxation time $\ensuremath{\tau}$ of a single domain ferromagnetic particle (with uniaxial anisotropy) is studied by calculating the lowest nonvanishing eigenvalue ${\ensuremath{\lambda}}_{1}$ (the escape rate) of the appropriate Fokker-Planck equation using matrix methods. The effect is investigated by plotting ${\ensuremath{\lambda}}_{1}$ versus the anisotropy parameter $\ensuremath{\alpha}$ for various values of $\ensuremath{\psi}$, and the ratio $h=\frac{\ensuremath{\xi}}{2\ensuremath{\alpha}}$, where $\ensuremath{\xi}$ is the external field parameter and ${\ensuremath{\lambda}}_{1}$ versus $\ensuremath{\psi}$ for various $h$ values (for rotation of the magnetization vector M both in a plane and in three dimensions). If M rotates in a plane the curve of ${\ensuremath{\lambda}}_{1}$ versus $\ensuremath{\psi}$ is symmetric about $\ensuremath{\psi}=\frac{\ensuremath{\pi}}{4}$ in the range $0l\ensuremath{\psi}l\frac{\ensuremath{\pi}}{2}$ and significant decrease in $\ensuremath{\tau}$ with increasing $\ensuremath{\psi}$ is predicted for large $\ensuremath{\xi}$ and $\ensuremath{\alpha}$. The maximum decrease in $\ensuremath{\tau}$ occurs at $\ensuremath{\psi}=\frac{\ensuremath{\pi}}{4}$ whereupon $\ensuremath{\tau}$ increases again to the $\ensuremath{\psi}=0$ value at $\ensuremath{\psi}=\frac{\ensuremath{\pi}}{2}$. For rotation of M in three dimensions, the curve of ${\ensuremath{\lambda}}_{1}$ versus $\ensuremath{\psi}$ ($0l\ensuremath{\psi}l\ensuremath{\pi}$) is symmetric about $\ensuremath{\psi}=\frac{\ensuremath{\pi}}{2}$. Thus the maximum decrease in $\ensuremath{\tau}$ again occurs at $\ensuremath{\psi}=\frac{\ensuremath{\pi}}{4}$ with maximum increase to a value exceeding that at $\ensuremath{\psi}=0$ (i.e., with the field applied along the polar axis with that axis taken as the easy axis), at $\ensuremath{\psi}=\frac{\ensuremath{\pi}}{2}$ (field applied along the equator), the $\ensuremath{\psi}=0$ value being again attained at $\ensuremath{\psi}=\ensuremath{\pi}$. The results are shown to be consistent with the behavior predicted by the Kramers theory of the rate of escape of particles over potential barriers. This theory when applied to the potential barriers for the equatorial orientation of the field for rotation in three dimensions yields a simple approximate formula for the escape rate which is in reasonable agreement with the exact ${\ensuremath{\lambda}}_{1}$ calculated from the Fokker-Planck equation. Pfeiffer's approximate formula for the barrier height as a function of $\ensuremath{\alpha}$ [H. Pfeiffer, Phys. Status Solidi 122, 377 (1990)] is shown to be in reasonable agreement with our results.
TL;DR: A cDNA encoding a Schistosoma japonicum aspartic proteinase was cloned, sequenced, and found to encode a zymogen of 380 amino acid residues, and identity comparisons showed that the enzyme was most closely related to the cathepsin Ds.
TL;DR: In this paper, the pharmacology, metabolism, and chemistry of Clofazimine were discussed and a review of the drug's properties was given, including its properties and properties.
Abstract: (1995). The Pharmacology, Metabolism, and Chemistry of Clofazimine. Drug Metabolism Reviews: Vol. 27, No. 4, pp. 591-614.
TL;DR: Capillary electrophoresis with electrochemical detection (CEEC) is evaluated for the determination of tryptophan and kynurenine in microdialysis samples obtained from rat brain following systemic administration of tryPTophan.
TL;DR: It is argued that a feedback signal in the form of a variable price for network service is a workable tool to aid network operators in controlling Internet traffic and suggested that these prices should vary dynamically based on the current utilization of network resources.
Abstract: The Internet continues to evolve as it reaches out to a wider user population. The recent introduction of user-friendly navigation and retrieval tools for the World Wide Web has triggered an unprecedented level of interest in the Internet among the media and the general public, as well as in the technical community. It seems inevitable that some changes or additions are needed in the control mechanisms used to allocate usage of Internet resources. In this paper, we argue that a feedback signal in the form of a variable price for network service is a workable tool to aid network operators in controlling Internet traffic. We suggest that these prices should vary dynamically based on the current utilization of network resources. We show how this responsive pricing puts control of network service back where it belongs: with the users.
TL;DR: A novel detection system for the determination of glucose in the presence of clinically important interferents, based on the use of dual sensors and flow-injection analysis (FIA), is described.
TL;DR: The presence of a prolyl endopeptidase activity in the particulate fractions of bovine brain, which is distinct from that in the cytoplasm, is reported.
Abstract: Prolyl endopeptidase, which has long been recognised for its importance in the degradation of several neuropeptides such as thyroliberin, luteinising hormone releasing hormone, angiotensin, substance P and neurotensin, has been widely characterised as a cytosolic enzyme. However, in this paper, we report the presence of a prolyl endopeptidase activity in the particulate fractions of bovine brain, which is distinct from that in the cytoplasm. This previously uncharacterised activity was found to reside in the synaptosomal membranes, a location which is highly significant for the inactivation of neuropeptides in brain. Following vigorous salt washing and osmotic shock, the prolyl endopeptidase activity was released from the membranes by treatment with the detergent Triton X-100, and was partially purified by gel filtration on a Sephacryl S-200HR column. This prolyl endopeptidase activity was shown to have a molecular mass (87 kDa) higher than the cytosolic prolyl endopeptidase but, from initial investigation, appears to demonstrate a similarly broad substrate specificity towards proline-containing neuropeptides. The partially purified enzyme was inhibited by certain thiol-protease inhibitors and was also found to be sensitive to the metal chelator 1,10-phenanthroline.
TL;DR: It is argued that a cathepsin L proteinase recently identified in their laboratory as the predominant cysteine proteinase activity of Schistosoma mansoni may play the leading role in haemoglobin digestion.
18 Jun 1995
TL;DR: In this paper, the authors discuss the implications of self similar models for the problem of estimating loss probabilities in networks, and their validity, and examine the experimental basis for self-similar modelling.
Abstract: We discuss the implications of self similar models for the problem of estimating loss probabilities in networks, and their validity. We present the tail asymptotics in a queue serviced at constant rate and whose input process has long-range dependence, for example, fractional Brownian motion (FBM) with Hurst parameter H>1/2. Some heterogeneous superpositions of such sources are also treated. We examine the experimental basis for self-similar modelling. If fluctuations in traffic levels can be accounted for by variations in time-dependent external parameters, rather than statistically through parsimonious modelling by FBM, then quality of service predictions may be achieved by applications of techniques familiar for short-range dependent traffic.
TL;DR: In this article, three types of glucose sensors were prepared by electrochemical deposition of glucose oxidase (GOD), [Os(bpy)2(PVP)10Cl]Cl (Os-polymer) (bpy = 2,2'-bipyridyl, PVP = poly(4-vinylpyridine)) within polyphenol (PPh) films on a platinum electrode.
TL;DR: It was observed that individual batches of waste biomass produced from different fermentation runs had consistent metal uptake capacities and the implications of the above results on the use of waste yeast biomass for treatment of metal-containing effluents are discussed.
Abstract: Three strains ofSaccharomyces cerevisiae and one strain of aCandida sp. obtained from different industrial sources were screened for uptake of silver and copper. Considerable differences in metal uptake capacities were found between the different strains ofS. cerevisiae and betweenS. cerevisiae and theCandida sp. used. Copper uptake capacities ranged from 0.05 mmol g−1 dry wt to 0.184 mmol g−1 dry wt while values of 0.034 mmol Ag g−1 dry wt and 0.193 mmol Ag g−1 dry wt biomass were observed. Use of ion-selective electrodes (ISEs) enabled the detection of copper complexing agents (possibly proteins and carbohydrates) released by yeasts into the surrounding medium. In contrast, these compounds had no silver complexation abilities. Langmuir and Scatchard transformations of metal adsorption isotherms suggested differences in the mechanisms involved in metal uptake by the various yeasts. The differences between strains ofS. cerevisiae were due possibly to differences in cell wal composition. Different methods of preparation of biomass (fresh, air, oven and freeze-dried) had little effect on metal uptake in comparison with fresh biomass. Storage of fresh waste biomass at 4°C for 20 days had no effect on metal biosorption capacities. It was also observed that individual batches of waste biomass produced from different fermentation runs had consistent metal uptake capacities. The implications of the above results on the use of waste yeast biomass for treatment of metal-containing effluents are discussed.
TL;DR: A cathepsin L proteinase secreted by the parasitic helminth Fasciola hepatica can cleave fibrinogen and produce a fibr in clot with a specific activity of 4.7 National Institutes of Health thrombin-equivalent U/mg.
Abstract: A cathepsin L proteinase secreted by the parasitic helminth Fasciola hepatica can cleave fibrinogen and produce a fibrin clot with a specific activity of 4.7 National Institutes of Health thrombin-equivalent U/mg. This is the first report of a fibrinogen-clotting activity aside that of thrombin and the snake venom proteinases, which are all serine proteinases. Clot formation by cathepsin L is not inhibited by the thrombin inhibitor hirudin or by the anti-polymerant H-Gly-Pro-Arg-Pro-OH. The enzyme exerts its activity on fibrinogen in a unique manner. Although the cleavage of fibrinogen may involve the initial removal of fibrinopeptides, additional proteolysis of the alpha, beta and gamma fibrinogen polypeptides takes place. SDS/PAGE analysis of the cathepsin-L-produced clots revealed that cleavage of the alpha polypeptide (66 kDa) precedes that of the beta (52 kDa) and gamma (46.5 kDa) polypeptides. Concurrent with the cleavage of these polypeptides is the appearance of components of 120, 100 and 25 kDa. The appearance of higher molecular-sized components in the cathepsin L clots suggests that polymerisation involves the formation of molecular interactions that are resistant to boiling in mercaptoethanol and SDS.
TL;DR: In this article, the effect of post-weld heat-treatment on the mechanical properties and residual stresses of I-beam welded box-sections in structural steel material has been evaluated.
TL;DR: A haemoprotein released in vitro by adult Fasciola hepatica was purified by gel filtration chromatography on Sephacryl S-200 and ion-exchange Chromatography on DEAE-Sepharose and found to contain a haem group and has absorption spectra characteristics similar to heamoglobins.
Abstract: A haemoprotein released in vitro by adult Fasciola hepatica was purified by gel filtration chromatography on Sephacryl S-200 and ion-exchange chromatography on DEAE-Sepharose. The molecule, with an apparent molecular weight of > 200 kDa, contains a haem group and has absorption spectra characteristics similar to haemoglobins. N-terminal amino acid sequence analysis revealed no similarity between the F. hepatica haemoglobin and other vertebrate or invertebrate haemoglobins. Antibodies to the haemoglobin molecule can be detected in the sera of F. hepatica-infected bovines as early as 1 week after infection.
TL;DR: In this paper, a study of tool deterioration in the end milling of Inconel 718 using uncoated tungsten carbide inserts under dry conditions is presented.