bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of the multiple organ injury and dysfunction caused by endotoxemia in 5-lipoxygenase knockout mice and by the 5-lipoxygenase inhibitor zileuton
Authors: Collin Marika , Rossi Antonietta , Cuzzocrea Salvatore , Patel Nimesh S A , Di Paola Rosanna , Hadley Julia , Collino Massimo , Sautebin Lidia , Thiemermann Christoph
Published: August 2004

The role of 5-lipoxygenase (5-LOX) in the pathophysiology of the organ injury/dysfunction caused by endotoxin is not known. Here, we investigate the effects of treatment with 5-LOX inhibitor zileuton in rats and targeted disruption of the 5-LOX gene in mice (5-LOX−/−) on multiple organ injury/dysfunction caused by severe endotoxemia. We also investigate the expression of β2-integrins CD11a/CD18 and CD11b/CD18 on rat leukocytes by flow cytometry. Zileuton [3 mg/kg intravenously (i.v.)] or vehicle (10% dimethyl sulfoxide) was administered to rats 15 min prior to lipopolysaccharide (LPS; Escherichia coli, 6 mg/kg i.v.) or vehicle (saline). 5-LOX−/− mice and wild-type littermate controls were treated with LPS (E. coli, 20 mg/kg intraperitoneally) or vehicle (saline). Endotoxemia for 6 h in rats or 16 h in mice resulted in liver injury/dysfunction (increase in the serum levels of aspartate aminotransferase, alanine aminotransferase, γ-glutamyl transferase, alkaline phosphatase, bilirubin), renal dysfunction (creatinine), and pancreatic injury (lipase, amylase). Absence of functional 5-LOX (zileuton treatment or targeted disruption of the 5-LOX gene) reduced the multiple organ injury/dysfunction caused by endotoxemia. Polymorphonuclear leukocyte infiltration (myeloperoxidase activity) in the lung and ileum as well as pulmonary injury (histology) were markedly reduced in 5-LOX−/− mice. Zileuton also reduced the LPS-induced expression of CD11b/CD18 on rat leukocytes. We propose that endogenous 5-LOX metabolites enhance the degree of multiple organ injury/dysfunction caused by severe endotoxemia by promoting the expression of the adhesion molecule CD11b/CD18 and that inhibitors of 5-LOX may be useful in the therapy of the organ injury/dysfunction associated with endotoxic shock.
Millennial-scale variability of Holocene hydrography in the southwestern Okhotsk Sea: diatom evidence
Authors: Shimada Chieko , Ikehara Ken , Tanimura Yoshihiro , Hasegawa Shiro
Published: August 2004

Diatom analysis of two submarine cores off eastern Hokkaido Island, northern Japan, provides insights into the Holocene palaeoenvironmental history of the southwestern Okhotsk Sea. Diatom flora was mainly composed of open-water and/or high-productivity-related Thtalassionema nitzschioides, Neodenticula semninae and sea-ice-related species such as Bacterosira fragilis and Fragilariopsis cylindrus, suggesting millennial-scale alternation of dominant hydrographic regimes. Great abundances of T. nitzschioides and N. seminae, in particular, together with the ice-related species, from the early Holocene onward show that this biota was the major contributor to productivity in the southwestern Okhotsk Sea. On the other hand, faint but important occurrences of warm-water species such as Fragilariopsis doliolus were observed during 6.3-5.5, 4.2-2.7 and 1. l-0.2 ka. Such rhythmic occurrences of warm-water species as a sensitive indicator of the Soya Warm Current and the terminal branch of the subtropical Kuroshio Current reflect this history. The presence of this warm species is probably in tune with pulses of the Tsushima Warm Current that have been documented in Holocene sediments of the Japan Sea. These floral results, which might imply the millennially paced variability in palaeoclimate regimes in both Subarctic and subtropical regions, are well documented in these cores from the southwestem Okhotsk Sea.
Vegetation structure and pollen source area
Authors: Bunting M. J. , Gaillard M.-J. , Sugita S. , Middleton R. , Broström A.
Published: August 2004

In this paper we use a simulation approach to explore the effect of variation in taxon parameters and landscape patterning on relevant source area of pollen. We use the Prentice-Sugita model, assume constant atmospheric conditions and basin morphology, and take a reductionist approach to explore the behaviour of pollen dispersal and deposition in a simple landscape scenario. Individual factors within the scenario (pollen fall speed, relative pollen productivity, size of basic unit in the landscape mosaic, patch size, rarity of individual taxa and overall number of taxa present in the landscape) are varied while all other parameters are kept constant. thus pennitting exploration of the role of different components of the system. These simulations suggest that, for basins of given size under fixed atmospheric conditions, the relevant source area of pollen is primarily an expression of the patterning of the different vegetation elements within the landscape. This has important implications for the interpretation of palaeoecological records and reconstruction of past environments. Reconstruction, especially quantitative reconstruction, requires some estimate of past relevant source area of pollen. If, as our results suggest, vegetation patterning is an important determinant of this, then it must also be taken into account when attempting to reconstruct past vegetation communities.
A 6000-year high-resolution climatic record from a stalagmite in Xiangshui Cave, Guilin, China
Authors: Zhang Meiliang , Yuan DaoXian , Lin Yushi , Qin Jiaming , Bin Li , Cheng Hai , Edwards R. Lawrence
Published: August 2004

Middle-to late-Holocene palaeoclimate change has been reconstructed at high resolution by the analysis of the carbon and oxygen isotopes from a thermal ionization mass spectrometric (TIMS) U/Th dated stalagmite from Xiangshui Cave, near Guilin, Guangxi Province, China. The carbon and oxygen isotopic records from the stalagmite suggest that changes in the Asian monsoon since the middle Holocene (6000 BP) can be divided into two periods: (1) an interval from 6000 to 3800 BP when a strong East Asian summer monsoon gradually weakened and climate was relatively warm and humid; (2) a cool period from 3800 to 373 BP when the East Asian summer monsoon was relatively weak and the winter monsoon was probably relatively strong. This cooler interval was interspersed with a number of short warm periods. A This interpretation is largely based upon the general increase in 6180 values of the stalagmite between 6000 and 3800 BP and shifts in 6180 about a relatively heavy mean value between 3800 and 373 BP. The 6000 to 3800 BP trend is probably associated with decrease in precipitation and temperature subsequent to the mid-Holocene climatic optimum.
Tephrostratigraphy of An Loch Mór, Inis Oírr, western Ireland: implications for Holocene tephrochronology in the northeastern Atlantic region
Authors: Chambers Frank M. , Daniell John R.G. , Hunt John B. , Molloy Karen , O'Connell Michael
Published: August 2004

Twelve definable cryptotephra layers younger than c. 8600cal. BP are reported from lacustrine core material taken from An Loch Mór, Inis Oírr, Aran Islands, western Ireland. The geochemistry of these shard layers, which represent more Holocene tephras than previously geochemically characterized from any European site outside the proximal volcanic influence of Italy or Iceland, is presented. Of these tephras, four may correlate with known Iceland-derived tephra horizons (Vo 1477, HI, Lairg A and H5); one appears to have two possible named correlatives (Hoy;‘Lairg B’ at Sluggan Bog, N Ireland); another has a plausible correlative (AD 860A); but two others represent Icelandic tephras apparently not previously reported on Iceland itself, including a tephra that has geochemistry very similar to Hl (AD 1104) but which dates to c. cal. AD 840. Four tephras that date from the period c. AD 40-1400 have a distinct geochemical signature that relates to Jan Mayen, 750km to the northeast of Iceland and some 1800km distant from An Loch Mór. The results contribute substantially to the chronology of the sediments from An Loch Mór and, at the international level, to the tephrostratigraphy of the northeast Atlantic region. The well-attested Icelandic H4 tephra (from a Hekla eruption of c. 4260cal. BP) was not recorded; it is suggested that An Loch Mór lies south of its recordable distribution in this part of the northeast Atlantic region. Taken together with work at other sites, the findings point to a wealth of potential tephra isochrons in Holocene deposits of the northeast Atlantic seaboard. It is clear also that calcareous lake sediments can be as fruitful a source of tephras as peats. Potential problems relating to dating and geochemical fingerprinting of tephra layers in individual sites are highlighted with reference to the Lairg tephras as recorded in Scotland and Northern Ireland, and to the Hoy tephra that has been described from Orkney.
Palaeoecology of human impact during the historic period: palynology and geochemistry of a peat deposit at Abbeyknockmoy, Co. Gaiway, Ireland
Authors: Lomas-Clarke Sarah H. , Barber Keith E.
Published: August 2004

Understanding the present condition of the cultural landscape requires a palaeoecological perspective with a particular emphasis on the growing intensity of human impact over the last few centuries. Detailed palynological investigations of the uppermost metre of peat at Abbeyknockmoy Bog were supplemented by silicon and titanium analyses to give additional proxy records for the intensity of human impact on the local landscape. The AMS radiocarbon chronology for this profile is constrained by the presence of the Hekla-l tephra isochron of AD 1104. The palaeoenvironmental evidence correlates closely to the local historical and archaeological records. The results indicate a late Iron Age lull in human impact in the early centuries AD, which is followed by increasing agricultural activity during the early Christian A period. The establishment of the Cistercian monastery of Abbeyknockmoy in the twelfth century AD had a significant impact upon the landscape. A peak in deforestation and farming activity is registered in the seventeenth and eighteenth centuries AD. The silicon and titanium records correlate strongly with the pollen indicators for increased human disturbance.
Unstable early-Holocene climatic and environmental conditions in northwestern Russia derived from a multidisciplinary study of a lake-sediment sequence from Pichozero, southeastern Russian Karelia
Authors: Wohlfarth Barbara , Schwark Lorenz , Bennike Ole , Filimonova Ludmila , Tarasov Pavel , Björkmanj Leif , Brunnberg Lars , Demidov Igor , Possnert Goran
Published: August 2004

A sediment core from Lake Pichozero (6146'; N, 3725'; E 118 m a.s.l.) provides information on the environmental and climatic conditions in southeastern Russian Karelia during the Lateglacial and early Holocene (12 800-9300 cal. BP). The chronology of the sequence is constrainied by varve counting and AMS 14C measurement of terrestrial plant macrofossils. Multiproxy analyses (magnetic susceptibility, grain size, TOC, TN, TS, Rock Eval, pollen and macrofossils) imply that cold and dry regional climatic conditions with sparse Arctic vegetation prevailed prior to 11500 cal. BP. Coincident with the transition to the Holocene at 11 500 cal. BP, air temperatures and lake productivity increased and Betula pubescens and Populus treinula started to migrate into the area, followed by Picea abies at 10 750 cal. BP. Although lake productivity decreased at around 11 000 cal. BP and remained low until 9600 cal. BP, pollen-based climate reconstructions imply variable climatic conditions in the region over time. Drier and colder summers prevailed from 11 200 to 10900 cal. BP, followed by an interval of higher annual temperatures and precipitation from 10900 to 10750 cal. BP. Lower annual temperatures and drier conditions existed from 10750 to 10200 cal. BP, and higher temperatures and precipitation are inferred between 10200 and 10000 cal. BP. Finally, declining temperatures and precipitation occurred from 10 000 cal. BP onwards, with a minimum at around 9600 cal. BP. These climatic shifts are temporally coincident with those recorded in North Atlantic terrestrial, marine and ice-core archives and indicate that relatively minor climate signals were transmitted further to the east.
Stable isotopic analyses of modern benthic foraminifera from seasonally stratified shelf seas: disequilibria and the 'seasonal effect'
Authors: Scourse J. D. , Kennedy H. , Scott G. A. , Austin W. E.N.
Published: August 2004

Previously published stable isotopic data on benthic foraminiferal species from a Holocene sequence in the Celtic Sea have been interpreted in terms of the progressive replacement of a tidally mixed by a stratified water mass. Offsets in the δ18O data between Ammonia batavus and Quinqueloculina seminulum were attributed to a ‘seasonal effect’ in which these two species were hypothesized to have calcified at different times of the year. The aims of this study were to test the hypotheses (1) that benthic foraminiferal stable isotope records from across the Celtic Sea front reflect seasonal stratification and (2) that offsets in the oxygen isotope record between different species are the result of the postulated seasonal effect. Hypothesis 1 was tested through investigation of live and dead benthic foraminiferal and bottom-water δ18O and δ13C sampled in transects across the Celtic Sea front from mixed through frontal to stratified water masses. Measurements of bottom-water salinity enabled a mixing-line equation to be developed for this area enabling quantitative reconstructions of bottom-water temperature from the isotopic data. Samples from stratified settings are characterized by heavier δ18Oforam and lighter δ13Cforam values than the mixed samples. Offsets in δ18Oforam between A. batavus and Q. seminum support the notion of the seasonal effect. A. batavus produces values close to equilibrium while Q. seminulum overestimates temperature by up to 2°C and this might explain some of the offset observed between the two species observed in the palaeodata. Comparison of the δ18Ofoarm data with measured seasonal temperature cycles from mixed and stratified localities in the Celtic Sea demonstrates that, while most foraminifera calcify during the summer months, different species calcify at, or are preserved from, different times within this warm part of the seasonal cycle; Q. seminulum calcifies during September when peak bottom-water temperatures occur, while A. batavus calcifies during September in stratified localities, but during spring or early summer in mixed localities. This study confirms the interpretation of the δ18O palaeodata from the Celtic Sea as a palaeostratification record and demonstrates that δ18O data from shelf-sea cores can be used to supplement benthic foraminiferal assemblages as a tool for reconstructing the long-term dynamics of seasonal stratification.
REE3+ and Mn2+ activated cathodoluminescence in lateglacial and Holocene stalagmites of central Europe: evidence for climatic processes?
Authors: Richter Detlev K. , Gotte Thomas , Niggemann Stefan , Wurth Georg
Published: August 2004

Combined visual cathodoluminescence (CL) and spectral analyses of CL reveals periodic enrichments of rare earth elements (REE3+) and manganese (Mn2+) within the laminations of eight calcitic lateglacial to postglacial stalagmites. In the annual layers, the enrichment of trace elements can be correlated with the autumn/winter laminae, which are strongly pigmented and rich in organic carbon. During the Holocene, they occur especially in the Atlantic stage and in subrecent/recent times. The enrichment of REE3+ and Mn + reflects times of more intense weathering, which presumably prevailed during the Atlantic warm and humid climate. In subrecent/recent times, especially the last 100 years, these enrichments may have been at least partially anthropogenically induced.
New dates for first millennium BC tephra isochrones in Ireland
Authors: Plunkett Gill M. , Pilcher Jonathan R. , McCormac F. Gerry , Hall Valerie A.
Published: August 2004

Three distinct, first millennium BC tephras (BMR-190, OMH-185, GB4-150) have been recognized in Irish peat deposits, including a previously undated ash (BMR-190). We present the results of a programme of high-precision 14C wiggle-matching on a peat profile containing all three tephras from Glen West, County Fermanagh, Northern Ireland. The wiggle-match provides highly refined dates of 705-585cal. BC for BMR-190, 755-680cal. BC for OMH-185 and 800-758cal. BC for GB4-150. The tephras constitute valuable, widespread isochrones for palaeoecological research across the first millennium BC, when a prolonged 14C calibration plateau between 750 and 400 cal. BC presents a major problem to dating and correlating palaeoenvironmental events from multisite, multiproxy studies of the period.
The influence of biotic drivers on North American palaeorecords: alternatives to climate
Authors: Crainel Joseph M. , McLauchlan Kendra K.
Published: August 2004

Biotic causes of changes in palaeorecords are discussed as a counterbalance to the (over) emphasis on climatic drivers in the interpretation of palaeoecological change. Biotic and climatic drivers are considered as competing hypotheses with particular reference to the importance of early-Holocene drought in the northern central grassland region of North America. It is concluded that the observed patterns are explained better by grazers than by the direct effects of climatic variation. The elevation of biotic factors as competing hypotheses with climate will require new conceptual and methodological approaches to palaeoecology in North America.
Research on the reliability of a scroll compressor in a heat pump system
Authors: Zhao Y , Li L , Wu H , Shu P , Shen J
Published: August 2004

The scroll compressor is used in heat pump and refrigeration system equipment because of important features such as its compact size, high efficiency, low vibration and noise level, etc. In the refrigeration cycle the scroll compressor runs smoothly and perfectly, but in the heat pump cycle some problems appear because of deterioration in the working condition. The effect of different factors such as atmospheric condition, electric voltage fluctuation, the configuration of the scroll compressor, etc., on the running reliability of the heat pump system are discussed in this paper, thermodynamic behaviour is examined and some basic design concepts for running reliability of the scroll compressor in the heat pump system are pointed out. Experimental results show that the temperature difference is about 10 K between the gas discharged from the outlet of the compressor and the wound wire of the motor in a high-pressure shell compressor. Calculated and test results show good agreement. The wound wire temperature of the motor in a low-pressure shell is much lower than that in a high-pressure shell scroll compressor. Hence, the low-pressure shell scroll compressor has higher running reliability than the high-pressure one.
Examination of the performance envelope of combined Rankine, Brayton and two parallel inverse Brayton cycles
Authors: Alabdoadaim M A , Agnew B , Alaktiwi A
Published: August 2004

The study presented in this paper investigated the performance of a proposed system constructed from Brayton, two parallel inverse Brayton and Rankine cycles. It has been carried out by varying the Brayton cycle pressure ratio for different values of expansion pressures of the two inverse Brayton cycles using variable inlet pressures, above atmospheric. The results revealed that the best theoretical performance could be achieved when the system was simulated with a high value of expansion pressure of the second inverse Brayton cycle. Also, it was shown that, as a result of altering the expansion pressure of the second inverse Brayton cycle, the range of the upper cycle pressure ratio increased and the system attained a high thermal efficiency (54 per cent).
Exergetic analysis of cogeneration-based district energy systems
Authors: Rosen M A , Le M N , Dincer I
Published: August 2004

Energy and exergy analyses are investigated for cogeneration-based district energy systems. In the analyses, exergy methods, in addition to the more conventional energy analysis, are employed to evaluate overall and component efficiencies and to identify and assess thermodynamic losses. Exergy analysis provides an enhanced understanding of the characteristics of energy systems and can assist design and improvement efforts. A case study is presented to highlight the importance of district energy systems and to illustrate how exergy analysis can be efficiently and effectively applied to such systems to determine system and component efficiencies. The results should assist in the enhancement of both cogeneration-based district energy systems and simulation techniques for building energy systems.
Simulation of fluid flow in a high compression ratio reciprocating internal combustion engine
Authors: Sridhar G , Paul P J , Mukunda H S
Published: August 2004

This paper discusses the detailed three-dimensional modelling of a reciprocating engine geometry comprising a flat cylinder head and a bowl-in-piston combustion chamber, simulating the motoring or non-firing conditions. The turbulence is modelled using a standard k-ɛ model and the results are compared against experimental results from the literature. Computed velocity profiles at time steps close to top centre (TC) are presented. The effect of squish and reverse squish becomes significant in a high compression ratio reciprocating engine. This enhanced fluid movement during a reverse squish regime could have an effect on burn rate, particularly in a spark ignition engine fuelled with biomass-derived producer gas, which has optimum ignition timing close to TC.
Low flowrate effects in a centrifugal pump impeller
Authors: Rose M G
Published: August 2004

This paper reports on an experiment in a centrifugal pump at low flowrates. A variety of measurement techniques was used: laser Doppler anemometry (LDA), impeller vane surface static pressure, a three-hole pneumatic probe and time-resolved static pressure. Some light is shed on the flow mechanisms present in the impeller off design. Evidence is found of a recirculation vortex, at 49 per cent of design flow-rate, in the impeller flow passages. From design flowrate down to 46 per cent of design flowrate there is no evidence of rotating stall, which first appears at 43 per cent. The most likely interpretation of this result is that there is a three-cell rotating stall system with the cells rotating at approximately 43 per cent of the impeller rotational speed. At 20 per cent of the design flowrate, the fluid in the inlet pipe ‘prerotates’ with no time mean flow reversal, interpreted as a developed stall cell system.
Effective gas-to-gas heat exchanger by means of energy conversion between gas enthalpy and thermal radiation
Authors: Nassab Gandjalikhan S A
Published: August 2004

This paper presents the heat transfer characteristics of a new type of gas-to-gas heat exchanger that operates on the basis of energy conversion between gas enthalpy and thermal radiation. A theoretical analysis is conducted for the one-dimensional system where convection and radiation take place simultaneously in three porous layers. In the high-temperature section, the enthalpy of gas flow converts to thermal radiation and the reverse direction of this process occurs in two recovery sections. The porous medium is assumed to be a homogeneous continuum that absorbs, emits and scatters thermal radiation. In order to investigate the thermal behaviour of gas flows and porous layers, the coupled energy equations for the gas and porous media, based on a two-flux radiation model, are solved numerically using an iterative method. Computational results show that this type of heat exchanger has a very high efficiency, especially when the porous layers have a high optical thickness and a low scattering coefficient. To confirm the validity of the present analysis, the numerical results for a simple energy recovery system are compared with theoretical results of other investigators and reasonable agreement is found.
Liquid metal systems for gasification-based power generation
Authors: Warner N A
Published: August 2004

A closed-loop liquid metal system is proposed for the simultaneous quenching and desulphurization at elevated temperature of raw fuel gas from commercial gasifiers. Besides its origins in a recently conceived liquid metal transport gasifier, application to the oxygen-blown Shell gasifier and the air-blown Mitsui-Babcock gasifier is discussed. The quenched fuel gas is filtered at relatively low temperature before being reheated to 750 °C or above by direct contact heat exchange with liquid metal in advance of partial precombustion to raise the temperature (1735 and 1194 °C respectively). Ammonia is reduced and equilibrium established prior to massive superheated steam injection, utilizing all available steam, and then rapid transmission to the can-annular combustors of a 1500 °C Class gas turbine at 870 °C, where autoignition of the highly preheated fuel gas is predicted. NOx emissions as low as 2 ppmv are anticipated. Mercury is projected to be recovered in elemental form, while other air toxics are prevented from discharging into the environment. Water recovery at 99 per cent appears feasible in a low-pressure drop system, and visible plume discharge is avoided by reheating the condenser off-gas in direct contact with a passivated liquid metal surface. Parallels are drawn with the molten tin based float glass process.
Elasto-plastic hemispherical contact models for various mechanical properties
Authors: Quicksall J. J. , Jackson R. L. , Green I
Published: August 2004

This work uses the finite element technique to model the elastoplastic deformation of a hemisphere contacting a rigid flat for various material properties typical of aluminium, bronze, copper, titanium and malleable cast iron. Additionally, this work conducted parametric finite element method (FEM) tests on a generic material in which the elastic modulus and Poisson's ratio are varied independently while the yield strength is held constant. A larger spectrum of material properties are covered in this work than in most previous studies. The results from this work are compared with two previously formulated elastoplastic models simulating the deformation of a hemisphere in contact with a rigid flat. Both of the previously formulated models use carbon steel mechanical properties to arrive at empirical formulations implied to pertain to various materials. While both models considered several carbon steels with various yield strengths, they did not test materials with various Poisson's ratios or elastic moduli. The previously generated elastoplastic models give fairly good predictions when compared with the FEM results for various material properties from the current work, except that one model produces more accurate predictions overall, especially at large deformations where other models neglect important trends due to decreases in hardness with increasing deformation.
Morphological effect of epitaxial Ag films with thickness of the order of nanometres on the tribological properties of a single-crystal silicon surface in an ultra-high-vacuum environment
Authors: Goto M , Nakahara T , Honda F
Published: August 2004

The tribological properties of thin Ag films deposited on an Si (111) 7 × 7 surface have been studied in sliding contact with a diamond as a function of the film thickness ranging from 0.4 to 170nm in an ultra-high-vacuum environment. Observations by scanning tunnelling microscopy (STM) and atomic force microscopy on the morphology of the epitaxial Ag film showed three kinds of structure as the thickness increased: an island structure (at 1.5 nm or less), a network structure (between 1.5 and 20 nm) and a continuous rough film (thicker than 20 nm). The coefficient of friction reached at 0.007 for an Ag film thickness of 5 nm with the network structure, and it increased as the film thickness increased more than 5 nm. The coefficient of friction was 0.06 for a thickness of 170 nm; therefore, the coefficient of friction correlates with the morphology of the film. Observations by means of STM and reflection high-energy electron diffraction showed that the fine Ag (111) sheets with the network structure were sheared and rotated by sliding of the diamond surface. The high lubricity of the thin Ag film was attributed to a perfect film without shearing in spite of the nanometric thickness and much lower shear strength of the film than that of the Si substructure, and the lubricity was influenced by the morphology of the film.
The effect of particle concentration in a magneto rheological suspension on the performance of a boundary lubricated contact
Authors: Leung W. C. , Bullough W. A. , Wong P. L. , Feng C
Published: August 2004

The tribological effects of several different concentrations of the same solid particle in a magnetorheological suspension (MRS) were examined on an apparatus operating in the boundary lubricated regime, using two different base fluids. The choice of optimum magnetorheological (MR) particle concentration is nominally restricted by the provision of desirable rheological effects in the fluid mix, such as the yield strength responsiveness to an applied magnetic field and low zero excitation viscosity. However, the aim of the present work is to identify the desirable range of particle concentrations for magnetorheological suspensions from a tribological viewpoint alone for one readily available particle type and two smooth bearing surfaces, one relatively hard and the other soft. The results provide a useful reference towards the formulation of an MRS and the prediction of friction and wear when the MRS is used between slipping surfaces.

Experimental studies were carried out in order to understand and uncover the boundary lubricated wear mechanisms of the MRS with different particle concentrations. The friction and wear that occur in seals and bearings that have to cope with such fluids can be a major impediment to application should they be operated in unduly adverse conditions. Generally these sliding surfaces operate outside of the area affected by the rheology controlling magnetic field, with one or two exceptions. Hence, the tests have been undertaken in unexcited conditions.

Considering that the carbonyl iron powders used in the MRS are relatively high in concentration, their effect on a boundary lubricated contact of two smooth steel surfaces may or may not be adequately described by the typical three-body abrasive wear mechanism since the particles are also comparatively soft and pass through an extremely small gap (nominally smaller than the typical dimension of the MR particles). This scenario is not well-addressed by tribologists whose concerns traditionally involve low concentrations of particles of higher hardness than surfaces such as wear debris. Would the damaging effect be controlled by controlling the particle concentration of the MRS? Two different base oils were used to mix with carbonyl iron powders, which were extracted from a commercial MR fluid from Lord Corporation, as different specimen fluids. The two different base oils are a pure mineral oil and a hydraulic oil with extreme pressure (EP) additives.
Adhesion experiment on a wheel/rail system and its numerical analysis
Authors: Jin X. S. , Zhang W. H. , Zeng J , Zhou Z. R. , Liu Q. Y. , Wen Z. F.
Published: August 2004

The experiment on the adhesion coefficient of a wheel-rail system has been carried out by means of a full-scale test facility under the condition of different axle loads and rolling speeds. The effects of the condition of the wheel-rail contact surfaces, such as a clean and dry surface, water and oil contamination and slip, on the adhesion coefficient have been investigated in the experiment. The experimental results show that, when the rolling speed of the wheelset increases, the adhesion coefficient decreases under the condition of the constant creepage and water contamination on the contact surfaces, but it increases for oil contamination. Using the data obtained by statistics and analysis of the experimental results and Kalker's rolling contact theory with Hertzian form modified by the present authors, a numerical analysis concerning the effect of wheelset rolling speed on the adhesion coefficient and the distribution of the stick-slip area in the contact area has been made. The numerical results are in good agreement with those obtained by experiment. They are very useful in designing the traction power of a locomotive at higher speeds.
Measurement of running torque of tapered roller bearings
Authors: Blake J. J. , Truman C. E.
Published: August 2004

A novel experimental arrangement is proposed which allows fast and repeatable measurements of the running torque of tapered roller bearings under combined axial and radial loading. Its principles of operation are explained and experimental results presented over a large range of speeds and under different lubrication conditions. By permitting direct torque readings, this arrangement allows rapid comparison between the performance of tapered roller bearings and developmental bearings for which there are no current theoretical torque formulae available. Comparisons are made between the results and a standard torque prediction model for tapered roller bearings. Limited agreement is observed.
A non-linear model for pre-rolling friction force in precision positioning
Authors: Mekid S
Published: August 2004

Ultra-precision positioning is contaminated by the non-linearities and hysteresis caused by Hertzian contact at pre-rolling due to the absence of accurate models that could be implemented by positioning controllers to compensate for it. In this paper an attempt is made to model such behaviour at low speed and dry conditions while taking into account the mechanical characteristics of the bodies in contact. The proposed model simulates the non-linear behaviour, called non-linear spring behaviour (NSB), from pre-rolling to the steady state rolling without a transitional function. The model is compared to experimental measurements performed with several materials.
Wittig Type Methylenation of Ketones with Bis(iodozincio)methane and Ionic Liquid
Authors: Yoshino Hideaki , Kobata Masami , Yamamoto Yuhei , Oshima Koichiro , Matsubara Seijiro
Published: August 2004

Ketones were transformed into alkenes via methylenation with bis(iodozincio)methane and ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) in the absence of additional metal salt such as titanium chlorides.
Searching for Good Multiple Recursive Random Number Generators via a Genetic Algorithm
Authors: Tang Hui-Chin , Kao Chiang
Published: August 2004

In designing ideal multiple recursive random number (RN) generators (MRGs), the best set of multipliers, in terms of the lattice structure of the RNs produced, is sought. As the order of the MRG increases, the number of possible sets of multipliers to be examined grows exponentially. This paper proposes a genetic algorithm for designing good MRGs. The set of multipliers associated with the MRG is encoded as a binary string. Via the operations of reproduction, crossover, and mutation, new sets of multipliers are generated. The spectral values of the MRGs are calculated to guide the search process. As an illustration, the proposed algorithm is employed to find good sets of multipliers for MRGs of orders three and four. The results are better than those derived from other studies. To conclude, this paper not only finds better MRGs of orders three and four, but also develops an algorithm for designing MRGs of higher orders.
Exploiting Tabu Search Memory in Constrained Problems
Authors: Kulturel-Konak Sadan , Norman Bryan A. , Coit David W. , Smith Alice E.
Published: August 2004

This paper puts forth a general method to optimize constrained problems effectively when using tabu search. An adaptive penalty approach is used that exploits the short-term memory structure of the tabu list along with the long-term memory of the search results. It is shown to be effective on a variety of combinatorial problems with different degrees and numbers of constraints. The approach requires few parameters, is robust to their setting, and encourages search in promising regions of the feasible and infeasible regions before converging to a final feasible solution. The method is tested on three diverse NP-hard problems, facility layout, system reliability optimization, and orienteering, and is compared with two other penalty approaches developed explicitly for tabu search. The proposed memory-based approach shows consistent strong performance.
Testing the Nearest Kronecker Product Preconditioner on Markov Chains and Stochastic Automata Networks
Authors: Langville Amy N. , Stewart William J.
Published: August 2004

This paper is the experimental follow-up to Langville and Stewart (2002), where the theoretical background for the nearest Kronecker product (NKP) preconditioner was developed. Here we test the NKP preconditioner on both Markov chains (MCs) and stochastic automata networks (SANs). We conclude that the NKP preconditioner is not appropriate for general MCs, but is very effective for a MC stored as a SAN.
A General Heuristic for Production Planning Problems
Authors: Pochet Yves , Van Vyve Mathieu
Published: August 2004

We consider production planning problems with the restriction that all integer variables model setups. Since finding a feasible solution of such problems is in general NP-complete, the classical approaches have been the use of heuristics to find good feasible solutions on the one hand, or branch and cut on the other hand. In the case of the former, a dual bound is not available, and there is no guarantee of solution quality. For the latter, the accent has been on improving the dual bound and only the simplest schemes have been used to find good feasible solutions.

Here we first show that such simple schemes may run into trouble, even when applied to very simple problems. This motivates the proposed heuristic, IPE, which is designed to be used within a branch-and-cut approach. We test the performance of the heuristic on various published lot-sizing and network-design problems, with and without tightened reformulations. We compare these results with other heuristics and with time truncated branch-and-bound searches. IPE appears to be the best choice for large problems with weak formulations.
The Constraint Consensus Method for Finding Approximately Feasible Points in Nonlinear Programs
Authors: Chinneck John W.
Published: August 2004

This paper develops a method for moving quickly and cheaply from an arbitrary initial point at an extreme distance from the feasible region to a point that is relatively near the feasible region of a nonlinearly constrained model. The method is a variant of a projection algorithm that is shown to be robust, even in the presence of nonconvex constraints and infeasibility. Empirical results are presented.
DNA Sequencing—Tabu and Scatter Search Combined
Authors: Błażewicz Jacek , Glover Fred , Kasprzak Marta
Published: August 2004

In this paper, a tabu-search algorithm enhanced by scatter search is presented. The algorithm solves the DNA sequencing problem with negative and positive errors, yielding outcomes of high quality. We compare the new method with two other metaheuristic approaches: a previous tabu-search method and a hybrid genetic algorithm, and also with an old branch-and-bound approach.
The [Pht/Pht/∞]K Queueing System: Part II—The Multiclass Network
Authors: Nelson Barry L. , Taaffe Michael R.
Published: August 2004

We demonstrate a numerically exact method for evaluating the time-dependent mean, variance, and higher-order moments of the number of entities in the multiclass [Pht/Pht/∞]K queueing network system, as well as at the individual network nodes. We allow for multiple, independent, time-dependent entity classes and develop time-dependent performance measures by entity class at the nodal and network levels. We also demonstrate a numerically exact method for evaluating the distribution function and moments of virtual sojourn time through the network for virtual entities, by entity class, arriving to the system at time t. We include an example using software that we have developed and have put in downloadable form in the Online Supplement to this paper on the journal's website.
Opportunities for Combinatorial Optimization in Computational Biology
Authors: Greenberg Harvey J. , Hart William E. , Lancia Giuseppe
Published: August 2004

This is a survey designed for mathematical programming people who do not know molecular biology and want to learn the kinds of combinatorial optimization problems that arise. After a brief introduction to the biology, we present optimization models pertaining to sequencing, evolutionary explanations, structure prediction, and recognition. Additional biology is given in the context of the problems, including some motivation for disease diagnosis and drug discovery. Open problems are cited with an extensive bibliography, and we offer a guide to getting started in this exciting frontier.
Geometric and Subexponential Asymptotics of Markov Chains of M/G/1 Type
Authors: Takine Tetsuya
Published: August 2004

This paper considers the steady-state solution of Markov chains of M/G/1 type. We first derive the matrix product-form solution of the steady-state probability. This formula is considered as a natural generalization of the matrix-geometric solution of quasi birth-and-death processes to Markov chains of M/G/1 type. Based on this formula, we study the asymptotics of the tail distribution. For the light-tailed case, we show a sufficient condition for the geometric asymptotics of the tail distribution, employing the Markov key renewal theorem. Contrary to the previous works, some periodic characteristics of transitions in upper levels are explicitly taken into account and a new geometric asymptotic formula is established. Furthermore, for the heavy-tailed case, we show a subexponential asymptotics formula for the tail distribution under a mild condition.
The Preservation of Continuity and Lipschitz Continuity by Optimal Reward Operators
Authors: Laraki Rida , Sudderth William D.
Published: August 2004

We give necessary and sufficient conditions for certain optimal reward operators to preserve continuity and Lipschitz continuity.
Online Scheduling of a Single Machine to Minimize Total Weighted Completion Time
Authors: Anderson Edward J. , Potts Chris N.
Published: August 2004

This paper considers the online scheduling of a single machine in which jobs arrive over time, and preemption is not allowed. The goal is to minimize the total weighted completion time. We show that a simple modification of the shortest weighted processing time rule has a competitive ratio of two. This result is established using a new proof technique that does not rely explicitly on a lower bound on the optimal objective function value. Because it is known that no online algorithm can have a competitive ratio of less than two, we have resolved the open issue of determining the minimum competitive ratio for this problem.
Coordinating Inventory Control and Pricing Strategies with Random Demand and Fixed Ordering Cost: The Infinite Horizon Case
Authors: Chen Xin , Simchi-Levi David
Published: August 2004

We analyze an infinite horizon, single-product, periodic review model in which pricing and production/inventory decisions are made simultaneously. Demands in different periods are identically distributed random variables that are independent of each other, and their distributions depend on the product price. Pricing and ordering decisions are made at the beginning of each period, and all shortages are backlogged. Ordering cost includes both a fixed cost and a variable cost proportional to the amount ordered. The objective is to maximize expected discounted, or expected average, profit over the infinite planning horizon. We show that a stationary (s, S, p) policy is optimal for both the discounted and average profit models with general demand functions. In such a policy, the period inventory is managed based on the classical (s, S) policy, and price is determined based on the inventory position at the beginning of each period.
On Constraint Sampling in the Linear Programming Approach to Approximate Dynamic Programming
Authors: de Farias Daniela Pucci , Van Roy Benjamin
Published: August 2004

In the linear programming approach to approximate dynamic programming, one tries to solve a certain linear program—the ALP—that has a relatively small number K of variables but an intractable number M of constraints. In this paper, we study a scheme that samples and imposes a subset of m≪M constraints. A natural question that arises in this context is: How must m scale with respect to K and M in order to ensure that the resulting approximation is almost as good as one given by exact solution of the ALP? We show that, given an idealized sampling distribution and appropriate constraints on the K variables, m can be chosen independently of M and need grow only as a polynomial in K. We interpret this result in a context involving controlled queueing networks.
Hard Equality Constrained Integer Knapsacks
Authors: Aardal Karen , Lenstra Arjen K.
Published: August 2004

We consider the following integer feasibility problem: Given positive integer numbers a0, a1,…,an, with gcd(a1,…,an) = 1 and a = (a1,…,an), does there exist a vector x ∈ ℤn≥0 satisfying a x = a0? We prove that if the coefficients a1,…,an have a certain decomposable structure, then the Frobenius number associated with a1,…,an, i.e., the largest value of a0 for which a x = a0 does not have a nonnegative integer solution, is close to a known upper bound. In the instances we consider, we take a0 to be the Frobenius number. Furthermore, we show that the decomposable structure of a1,…,an makes the solution of a lattice reformulation of our problem almost trivial, since the number of lattice hyperplanes that intersect the polytope resulting from the reformulation in the direction of the last coordinate is going to be very small. For branch-and-bound such instances are difficult to solve, since they are infeasible and have large values of a0/ai, 1 ≤ i ≤ n. We illustrate our results by some computational examples.
Potential, Consistency, and Cost Allocation Prices
Authors: McLean Richard P. , Pazgal Amit , Sharkey William W.
Published: August 2004

In a typical cost allocation problem, a decision maker must allocate the joint cost of producing a specified vector of goods or services using prices. In earlier work, Billera, Heath, and Raanan applied the theory of values of nonatomic games of Aumann and Shapley to develop a pricing mechanism called Aumann-Shapley pricing. The Aumann-Shapley value for nonatomic games has an axiomatic foundation that was adapted to the cost allocation context by Billera and Heath and Mirman and Tauman. In this paper, we develop the notions of “reduced cost function,” “consistency,” and “potential” for cost allocation problems and we provide a new axiomatic characterization of symmetric and weighted Aumann-Shapley pricing in terms of consistency.
Error Bounds for Perturbing Nonexponential Queues
Authors: van Dijk Nico M. , Miyazawa Masakiyo
Published: August 2004

A general framework is provided to derive analytic error bounds for the effect of perturbations and inaccuracies of nonexponential service or arrival distributions in single- and multiserver queues. The general framework is worked out in detail for the three types of finite or infinite buffer queues: GI/G/1/N, M/G/c/N, and GI/M/c/N.

First, for the standard GI/G/1/N queue, it is illustrated how the general error bound result can lead to error bounds for different performance measures like the throughput, mean queue length, and stationary queue length distribution. Next, for the M/G/c/N queue, an error bound and monotonicity result are established for the throughput. M/G/c/N queues can so be compared even when hazard rates are not ordered. Finally, for the GI/M/c/N queue, a similar result is obtained with a perturbation of the interarrival time distribution.

The error bound results are supported by asymptotic expressions for the M/M/c/N queue and numerical results for the GI/G/1/N queue.