bluuebunny/crossref_metadata_2025 huggingface dataset:
The development of PTFE (polytetrafluoroethylene)-faced hydrodynamic thrust bearings for hydrogenerator application in the United Kingdom
Authors: Simmons J. E. L. , Knox R. T. , Moss W. O.
Published: October 2002

Polytetrafluoroethylene (PTFE)-faced hydrodynamic thrust bearings have been used for many years in the former Soviet Union and in the People's Republic of China for large hydrogenerator applications. Although there has been some recent interest in other countries, few installations of this sort have previously been reported in Europe or the USA. This paper describes the state of the art and the development and laboratory testing of a prototype set of PTFE pads. Following these trials, a second larger set of thrust pads was designed for use in the pumped-storage hydroelectric power station at Ffestiniog in North Wales. The pads were installed in September 1996 and inspected in May 1997. After nearly 3000 h of operation including 900 separate occasions when the system was started up under load, the pads were found to be in excellent condition. Further hydrogenerator installations of PTFE-faced pads are planned as a result of this successful development.
Application of multi-level multi-integration to contact problems Part 1: Non-Hertzian contact in rolling bearings
Authors: Natsumeda S
Published: October 2002

This paper describes in detail a computer program for the analysis of non-Hertzian contact in rolling bearings using multi-level multi-integration (MLMI), by which any object, i.e. the surface displacement and/or the internal stress component for a given contact pressure distribution, can be obtained in extremely reduced computing time compared with the conventional technique. This paper is composed of three parts: the determination of the values of MLMI parameters so as to make the program adjustable for the wide range of aspect ratios of the mesh rectangle; the development of the numerical procedure solving the contact problem to ensure stable and fast convergence; the application to the contact problems in rolling bearings. By the developed program, the contact analysis can be performed on a personal computer within a few minutes, even if the total number of grid points is more than ten thousand.
Recent advances in engine bearing design analysis
Authors: Xu H
Published: October 2002

A significant advance has been achieved in the development of predictive tools for engine bearing analysis in the last 15 years. Many of these tools have been adopted by vehicle and bearing manufacturers. The use of these tools has helped us to achieve a better understanding of the engine bearing behaviour. Elastohydrodynamic lubrication predictive tools also make it possible to study a bearing as a part of the bearing system. This paper gives a summary of recent advances in the field.
Past, present and future studies in elastohydrodynamics
Authors: Dowson D , Ehret P
Published: October 2002

The development of understanding of the phenomenon of elastohydrodynamic lubrication (EHL) throughout the twentieth century is reviewed. The development of solutions for both line and point contacts is considered for both fully flooded and starved conditions. Particular attention is given to the introduction of non-Newtonian rheological models and numerical methods. Progress in the analysis of impact and general non-steady-state conditions is reviewed, together with the consideration of rough surface and micro-EHL. Attention is drawn to the need to consider realistic models of real surfaces and real fluids in future studies.
The École Centrale de Lyon surface force apparatus: An application overview
Authors: Tonck A , Bec S , Mazuyer D , Georges J-M , Lubrecht A. A.
Published: October 2002

The ECL (École Centrale de Lyon) surface force apparatus (SFA) has been developed and refined over the last two decades. This paper reviews a number of applications of the SFA that are of interest to the tribologist. In order to predict and improve contact performance, the tribologist needs to understand and quantify the basic properties of the lubricant and the solid bodies it is separating. Previously, these important properties were the material bulk properties, or at least these properties were sufficient. This situation is no longer true, and the material properties of the solids and the lubricant are required on a scale which is small or comparable with the film thickness. Nowadays, that means a scale small or comparable with 10−7−10−8 m! It is in this domain that the SFA can provide information on mechanical properties of very thin lubricant films, and on the properties of the solid material close to its surface.
Transverse roughness in elastohydrodynamic lubrication
Authors: Greenwood J. A.
Published: October 2002

The astonishing progress of numerical solutions of the rough surface elastohydrodynamic problem over the last thirty years is reviewed. The state of theoretical understanding of the numerical results is described, and it is shown how from the behaviour of sinusoidal waviness of different wavelengths it is possible to deduce an approximation to the behaviour of real roughness and of isolated ridges and scratches, at least for a Newtonian lubricant. However, it is argued that the lubricant behaviour needed to ensure that theoretical traction coefficients remain of realistic size casts doubt on the use of a Newtonian lubricant for the analysis of rough surfaces, so that the applicability of these predictions to a real elastohydrodynamic lubrication (EHL) contact is somewhat suspect.
Rotor dynamic coefficients of a thrust active magnetic bearing considering runner tilt
Authors: Ho Y. S. , Yu L , Liu H
Published: October 2002

This paper investigates the rotor dynamic coefficients of a thrust active magnetic bearing when runner tilt is taken into account. The influence of runner tilt upon the load capacity and the dynamic forces and moments of a thrust active magnetic bearing is analysed. A total of 24 rotor dynamic coefficients are defined to describe the dynamic behaviour of the thrust active magnetic bearing. A general method is presented to calculate these coefficients, which can be used conveniently for the coupled dynamic analysis when a rotor is supported by both radial and thrust magnetic bearings.
An historical review of studies of polymeric seals in reciprocating hydraulic systems
Authors: Nau B. S.
Published: October 2002

This is a historical review of the literature, outlining the development of our understanding of the factors affecting the performance of reciprocating polymeric seals, rod seals and piston seals, for fluid power systems. Particular attention is paid to early seminal studies many of the findings from which have become an accepted part of the technology while others are sometimes overlooked.
Artificial neural networks for modelling dynamics of impacting bodies and vehicles
Authors: Omar T A , Eskandarian A , Bedewi N E
Published: October 2002

A new approach is demonstrated and tested for modelling the non-linear multi-body dynamics problem of two impacting bodies. An advanced recurrent artificial neural network (ANN) is used to model this highly non-linear dynamic problem. The equations of motion of the dynamic system are used to explain the required inputs for the ANN. The developed networks are trained to predict the acceleration profiles of the impacting objects. Each object is represented by a corresponding ANN. The mutual effect between the two objects, during the impact, is also considered by training the two ANNs simultaneously.

Two numerical examples are used to demonstrate the ability of the new developed approach. The first is the dynamic impact problem of two non-linear lumped systems. The second is two different vehicles in frontal impacts. For each case, the problem is numerically solved for several impact scenarios and the results are used to prepare the data required for training and testing the developed ANNs. The results of the two numerical examples demonstrated the ability of the ANNs to store the non-linear dynamic characteristics of the impacting objects after a successful supervised training. The trained networks are capable of modelling non-linear multi-body dynamics and impact problems.
Relativity: 300 years from a principle to reality
Authors: Rahnejat H
Published: October 2002

This technical note provides a brief background to the historical developments that led to the generalization of Galileo's principle of relativity, leading to Einstein's general theory of relativity. Therefore, its primary purpose is to mark the contributions made in physics of motion on this occasion—the marking of the new Millennium. To keep with the tradition set in this journal, this note contains a new analysis in respect of reported super-luminal observations in gain-assisted light propagation, in particular vis-à-vis their concordance with the general theory of relativity. The incompleteness principle, as an axiom of observation, is introduced here to resolve this issue.
Active damping of the elastodynamic vibrations of a flexible slider-crank mechanism using an energy approach
Authors: Karkoub M A , Zribi M
Published: October 2002

In this paper, the problem of active damping of the elastodynamic vibrations of a flexible slider-crank mechanism is addressed. The slider-crank mechanism is such that the connecting rod is flexible and the crank link is rigid. The slider-crank mechanism system is underactuated since the connecting rod is not directly controlled. A dynamic model for the slider-crank mechanism is derived using the Hamiltonian principle. Then, a control scheme based on an energy approach is proposed. The control scheme uses the passivity of the system to eliminate the vibrations of the flexible connecting rod. Simulation results are given to illustrate the theoretical developments.
Non-linear aspects in the computation of the kinetic parameters for multi-body systems with friction
Authors: Klepp H J
Published: October 2002

Because of the friction laws, the equation for the computation of the kinetic parameters (accelerations and reaction forces) for systems with friction-affected constraints are non-linear. Consequently, the existence and uniqueness of solutions are not assured, and, in general, only numerical and iterative computation methods are applicable. With the help of influence coefficients the kinetic equations are reformulated suitably for the application of trial-and-error based procedures. These procedures extend the cases when closed-form solutions can be determined and, for the general case, show better convergence properties than pure iteration schemes. The meaning of some influence coefficients, the convergence or non-convergence of iteration schemes and the bifurcation of the solutions with increasing friction parameters are illustrated by an example.
Exact, no-transform solution of multi-degree-of-freedom vibrations with non-harmonic, periodic excitation
Authors: Chicurel-Uziel E
Published: October 2002

A procedure is proposed to obtain the steady state displacement solution to linear vibration problems with non-harmonic, periodic, continuous or discontinuous excitation for any finite number of degrees of freedom. The solution obtained is exact, in closed form and in a single equation. The procedure makes no use of any transform. Since the displacement solution is exact, it may be differentiated to obtain the exact velocity and the exact acceleration. An example of a quarter-vehicle suspension model is solved in detail.
An interaction model between flexible structures and piezoelements useful in multi-body modelling
Authors: Braccesi C , Cianetti F
Published: October 2002

In this paper, a general procedure for the synthesis of a reduced dynamic model for the description of flexible structures coupled with piezoelectric sensors and actuators is shown. The authors built an interaction modelling procedure, useful in mechanical system simulation (MSS) software, using a theoretical and finite element modelling (FEM) approach. By modifying and developing an existing modal synthesis method, which is used by most commercial software, a new mode component synthesis methodology was developed. This new procedure allows the simulation of any system containing flexible parts coupled with piezoelectric materials, in linear and non-linear behaviour, under any mechanical and electrical boundary condition both in the frequency and time domain. This is not possible by either the theoretical-analytical or the FEM approach without the involvement of heavy, lengthy computational loads.
On the performance of multi-support spindle-bearing assemblies
Authors: Rahman A K , Aini R , Gohar R
Published: October 2002

A theoretical investigation is undertaken to evaluate the effects of a number of support bearings, bearing settings and preload on the system natural frequencies and amplitudes of vibration of a spindle assembly supported by angular contact ball-bearings. The paper presents a generalized system of non-linear second-order ordinary differential equations for analysing multi-support spindle-bearing assemblies. The ball to raceway contacts are described by the Hertzian equation representing the non-linear elastic deformation of the rolling elements. The results show how significant frequencies and amplitudes vary with number of support bearings, orientations and preload.
Multi-body dynamics in full-vehicle handling analysis
Authors: Hegazy S , Rahnejat H , Hussain K
Published: October 2002

This paper presents a multidegrees-of-freedom non-linear multibody dynamic model of a vehicle, comprising front and rear suspensions, steering system, road wheels, tyres and vehicle inertia. The model incorporates all sources of compliance, stiffness and damping, all with non-linear characteristics. The vehicle model is created in ADAMS (automatic dynamic analysis of mechanical systems) formulation. The model is used for the purpose of vehicle handling analysis. Simulation runs, in-line with vehicle manoeuvres specified under ISO and British Standards, have been undertaken and reported in the paper.
Investigation of the clonk phenomenon in vehicle transmissions—measurement, modelling and simulation
Authors: Biermann J W , Hagerodt B
Published: October 2002

Vehicle drivelines with manual transmissions are exposed to different dynamic engine torques under driving conditions. Besides the excitation through the cyclic irregularity of the combustion engine, there are additional load change excitations, for instance during acceleration and deceleration. With load changes, transient vibrations and noise appear through the contact changes of free-travelling single components of the driveline. In this report a detailed theoretical modelling of the driveline will be presented after a short description of the measurement methods from a test rig. A comparison between the measurement and the calculation results has validated the simulation model. It is shown what effects the loose gears and the toothing clearance have on the angular acceleration of the transmission components. By means of model calculations it has been shown that the vibration behaviour of the test rig correlates well with that under actual driving conditions. Finally remedial measures have been worked out with this simulation tool.
The modelling and simulation of vehicle handling Part 2: Vehicle modelling
Authors: Blundell M V
Published: October 2002

This is the second in a series of four papers looking at the application of computer-based analysis methods to model vehicles and simulate vehicle handling. The material contained in these papers is based on a study carried out in order to investigate the influence of suspension and tyre modelling on the outputs predicted by vehicle handling simulations. The papers deal with analysis methods, vehicle modelling, tyre modelling and handling simulation.

In this paper the methods used to model the vehicle systems relevant to handling simulations using a multi-body systems analysis computer program are described, with the emphasis placed mainly on the modelling of suspension systems. A range of full vehicle models, which use simplified representations of the suspension system, are also described as these models form the basis of a set of comparisons described in Part 4 of this series. Modelling of other vehicle systems such as the steering system and roll bars is also discussed. Tyre modelling is a large topic and as such is covered separately in Part 3 of this series of papers. All of the examples used to illustrate the concepts explained throughout this series of papers have been generated using the ADAMS (Automatic Dynamic Analysis of Mechanical Systems) program.
Magnetorheological fluid devices: Principles, characteristics and applications in mechanical engineering
Authors: Wang J , Meng G
Published: October 2002

Magnetorheological (MR) fluids are a class of new intelligent materials whose rheological characteristics change rapidly and can be controlled easily in the presence of an applied magnetic field. The devices based on MR fluids, including dampers, brakes, clutches, polishing devices and hydraulic valves, etc., have a very promising potential future; some of them have been used commercially in engineering applications such as automobiles, polishing machines, exercise equipment, etc. In this paper, the modes of operation of MR fluid devices are analysed. A comprehensive review is then presented of the principles, characteristics and engineering applications of the MR fluid devices (especially dampers) studied in the last decade. Finally, the application prospects of MR fluid devices are discussed.
Experimental and numerical analyses of the combustion process in a direct injection gasoline engine
Authors: Reissing J , Peters H , Kech J. M. , Spicher U
Published: October 2002

Gasoline direct injection (GDI) spark ignition engine technology is advancing at a rapid rate. The development and optimization of GDI engines requires new experimental methods and numerical models to analyse the in-cylinder processes. Therefore the objective of this paper is to present numerical and experimental methods to analyse the combustion process in GDI engines.

The numerical investigation of a four-stroke three-valve GDI engine was performed with the code KIVA-3V [1]. For the calculation of the turbulent combustion a model for partially premixed combustion, developed and implemented by Kech [4], was used. The results of the numerical investigation are compared to experimental results, obtained using an optical fibre technique in combination with spectroscopic temperature measurements under different engine conditions. This comparison shows good agreement in temporal progression of pressure. Both the numerical simulation and the experimental investigation predicted comparable combustion phenomena.
A methodology for engine design using multi-dimensional modelling and genetic algorithms with validation through experiments
Authors: Senecal P. K. , Montgomery D. T. , Reitz R. D.
Published: October 2002

A methodology for internal combustion engine design has been formulated which incorporates multidimensional modelling and experiments to optimize and simulate direct injection diesel engine combustion and emissions formation. The computer code KIVA-GA performs full-cycle engine simulations within the framework of a genetic algorithm (GA) global optimization code. The methodology is applied to optimize a heavy-duty diesel truck engine. The study simultaneously investigated the effects of six engine input parameters on emissions and performance for a high-speed medium-load operating point. The start of injection (SOI), injection pressure, amount of exhaust gas recirculation (EGR), boost pressure and split injection rate shape were optimized. The convergence of the GA optimization process is demonstrated and the results were compared to those of the experimental optimization study employing a response surface method (RSM), which uses statistically designed experiments to determine an optimum design. In addition, the parameters of the computationally predicted optimum were run experimentally and good agreement was obtained.

The potential for ultra-low emissions levels was assessed through additional computational GA runs that included higher maximum EGR levels (up to 50 per cent). The predicted optimum results in significantly lower soot and NOx emissions together with improved fuel consumption compared to the baseline design. The present results indicate that an efficient design methodology has been developed for optimization of internal combustion engines, one that allows simultaneous optimization of a large number of parameters.
Simulating the homogeneous charge compression ignition process using a detailed kinetic model for n-heptane mixtures
Authors: Kusaka J , Yamamoto T , Daisho Y
Published: October 2002

The homogeneous charge compression ignition (HCCI) combustion has been attracting growing attention in recent years due to its potential for simultaneous improvement of exhaust gas emissions and fuel consumption in diesel engines. For practical application of HCCI to internal combustion (IC) engines, precise control of auto-ignition of pre-mixtures during the compression stroke is inevitable. This paper discusses the auto-ignition processes in an HCCI engine operated with n-heptane/air mixtures using a zero-dimensional combustion model including a detailed kinetics. The model proposed is validated first by a comparison between calculated and experimental pressure diagrams, and then the effects of initial charge conditions, compression ratio and excess air ratio on ignition and combustion are investigated. It was found from the parametric study that HCCI combustion of n-heptane/air mixtures is classified into three types of combustion: complete combustion, only low-temperature reaction and misfire, depending on the compression ratio and excess air ratio at which the engine is operated. Finally, the major paths of the HCCI reaction occurring in the engine cylinder were clarified by a sensitivity analysis of chemical reactions involved in the HCCI reaction scheme.
Particulate matter size distribution and associated polycyclic aromatic hydrocarbon content from indirect and direct injection diesel engines
Authors: Collin F , Gonnord M. F. , Momique J. C. , Monier R , Walter Ch
Published: October 2002

Within the framework of atmospheric aerosol study, evaluation of the contribution of the particle source to global atmospheric pollution is a challenge that requires an improvement in the knowledge of particulate matter. As a part of this knowledge improvement, this study has been focused on particles emitted from diesel vehicles. Two light-duty diesel vehicles were studied for particulate matter size distribution and associated polycyclic aromatic hydrocarbon (PAH) content. A diffusional and inertial spectrometer was used, allowing particles from 7.5 nm to 15 μm to be collected and analysed. Teflon-coated glass fibre filters were employed as collector substrates, and weighed prior to and after sampling. Each of them was extracted with methylene chloride in an accelerated solvent extractor, cleaned on a silica gel micro-column and analysed for PAH by gas chromatography/mass spectrometry using internal standards for quantitation. Both analytical and sampling methods were validated. The highest particle mass was found to be emitted at 0.2 μm for the direct injection engine and 0.07 μm for the indirect injection engine. PAHs were found to be essentially distributed on particles in the accumulation mode, at about 0.2 μm, and high molecular weight PAH distributions were found to be bimodal or trimodal, depending on the engine injection.
Modelling of sprays from high-pressure swirl atomizers
Authors: Gavaises M , Arcoumanis C
Published: October 2002

Aspects of the modelling and experimental validation of transient sprays injected from high-pressure swirl atomizers are presented. The spray model is based on the Lagrangian particle tracking approach where phenomenological submodels are used in order to resolve the various subgrid scale physical processes. Particular attention is given to the effect of the nozzle flow exit conditions on the atomization process of the injected liquid film. This is addressed by employing a linear instability analysis, describing the formation and growth of waves developing on the surface of the liquid, combined with a film movement model which is active until the film's disintegration into ligaments and droplets. The transient variation of the film thickness and its axial and swirl velocity components required as input to the spray model have been estimated from the solution of the flow inside the pressure swirl atomizer using a two-phase computational fluid dynamics (CFD) model. Model predictions are compared with phase Doppler anemometry measurements of the temporal and spatial variation of the droplet size and velocity as well as high-resolution charge coupled device (CCD) spray images. The results confirm that accurate estimation of the nozzle flow exit conditions plays a dominant role in the prediction of sprays injected from pressure swirl atomizers, while the proposed submodels seem to offer significant improvements on the calculated spray structure.
Comparison of in-cylinder coherent anti-Stokes-Raman scattering temperature measurements with predictions from an engine simulation
Authors: Ewart P , Williams R. B. , Lim E. P. , Stone C. R.
Published: October 2002

The objective of this work was to compare the burned gas temperature measured using coherent anti-Stokes-Raman scattering (CARS) with the predictions of a multiple-zone computer simulation of combustion. The tests were at various engine operating conditions with different fuels. Mean cycle modelling was used initially to obtain the appropriate heat transfer tuning parameters for the engine simulation by matching to the cylinder pressure. The predicted mean cycle burned gas temperatures gave good agreement with the measured mean temperatures. Similarly, cycle-by-cycle modelling produced burned gas temperatures that agree with the measured values.

This work showed that the multi-zone computer simulation could accurately predict the burned gas temperature once the fuel burn rate and completeness of combustion have been analysed and the model tuned correctly. The effects of methanol, methane, toluene and iso-octane on the burned gas temperature were investigated. It was found that the fuel burn rate and the adiabatic flame temperature affected the burned gas temperature. Fuels with a high burn rate (such as methanol) have a lower burned gas temperature towards the end of the engine cycle. Toluene has the highest adiabatic flame temperature and hence gave the highest burned gas temperature.
A chemical kinetic modelling study of the mechanism of soot reduction by oxygenated additives in diesel engines
Authors: Nag P , Song K-H , Litzinger T A , Haworth D C
Published: October 2002

Oxygenated fuel additives are effective in reducing soot emissions and breaking the soot/NOx tradeoff in diesel engines. The extent to which molecular structure of the oxygenate plays a role in soot reduction has remained unclear and controversial. It has been suggested in the literature that the rapid breakdown of oxygenates to carbon monoxide (CO) and carbon dioxide (CO2), and subsequent interaction between CO and CO2 with the radical pool, may play a key role. Here a constant-pressure homogeneous reactor model, SENKIN, has been used to simulate the effect of small amounts of CO and CO2 on the formation of polycyclic aromatic hydrocarbons, as surrogates for soot, and other key species such as acetylene (C2H2) using three different detailed chemical mechanisms. The addition of O2 was also studied as a reference case. It is found that polycyclic aromatic hydrocarbon (PAH) and C2H2 decrease with CO addition, and increase slightly with the addition of CO2, regardless of the mechanism used. These results suggest that CO produced by oxygenated additives in diesel fuel is able to effect reduction in PAH as suggested in the literature, but does not confirm a similar effect from CO2.
A study on thermal decomposition of fuels and NOx formation in diesel combustion using a total gas sampling technique
Authors: Miwa K , Mohammadi A , Kidoguchi Y
Published: October 2002

The effects of aromatic components and distillation temperature of diesel fuel on the decomposition of hydrocarbons and NOx formation during diesel combustion were studied at different injection pressures using a rapid compression machine and a total gas sampling device. It was found that fuel injected into hot compressed air is quickly gasified and then thermally cracked, and a large amount of unsaturated light hydrocarbons, mainly C2H4, C2H2 and C3H6, are produced during the ignition delay period. It was also found that the level of the initial rate of heat release is approximately proportional to the amount of light unsaturated hydrocarbons observed. As the injection pressure is increased, both the amount of light hydrocarbons formed and the initial rate of heat release increase, which results in an NOx concentration higher than that at a lower injection pressure. As for the effects of fuel properties, it was revealed that aromatic components in the fuel enhance NOx formation over the combustion period through their higher adiabatic flame temperatures and that a high-distillation temperature of fuel yields a lower rate of heat release and lower NOx formation due to the slower rate of evaporation.
Synthesis and Functionality of Cyclophosphazene-Based Polymers
Authors: Inoue Kenzo , Itaya Tomoyuki
Published: October 2002

Linear poly(organophosphazene)s have been widely investigated, mainly to correlate the structure of inorganic –P=N– backbone bearing organic groups with their properties and functionalites. Our interests have been directed to relatively new types of polymers containing a cyclophosphazene unit in the side chains, main chains, or as central core and end groups. The phosphazene groups in these polymers can serve as modification sites of polymers, leading to new functionalized materials. The six or more reactive sites of cyclophosphazenes are suitable for the preparation of star-shaped polymers or hyperbranched polymers including dendrimers. Recent works related with polymeric self-assembly showed that some organocyclophosphazenes are useful motifs for the construction of supramolecules, reflecting the structural features of the cyclotri(phosphazene)s. In this review, we describe the synthesis and functionalities of polymers containing cyclotri(phosphazene)s.
Catalytic Asymmetric Aldol Reaction of Trimethoxysilyl Enol Ethers Using 2,2′-Bis(di-p-tolylphosphino)-1,1′-binaphthyl·AgF Complex
Authors: Yanagisawa Akira , Nakatsuka Yoshinari , Asakawa Kenichi , Wadamoto Manabu , Kageyama Hiromi , Yamamoto Hisashi
Published: October 2002

Catalytic asymmetric Mukaiyama-type aldol reaction using trimethoxysilyl enol ethers was achieved using 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl (p-Tol-BINAP)·AgF complex as a catalyst. The chiral silver(I) catalyst was easily generated by mixing p-Tol-BINAP and silver(I) fluoride in MeOH at room temperature. High syn- and enantioselectivities were obtained from both the E- and Z-silyl enol ethers. Use of a 1 : 1 mixture of MeOH and acetone as a solvent in the reaction of cyclohexanone-derived trimethoxysilyl enol ethers resulted in higher enantioselectivity.
A Divergent Synthesis of Essentially Enantiopure syn- and anti-Propionate Aldol Adducts Based on the Chiral 1,3,2-Oxazaborolidin-5-one-Promoted Asymmetric Aldol Reaction Followed by Diastereoselective Radical Reduction
Authors: Kiyooka Syun-ichi , Shahid Kazi Abuds
Published: October 2002

Essentially, enantiopure syn- and anti-propionate aldol adducts were divergently synthesized using a novel strategy which utilizes both the highly enantioselective 1,3,2-oxazaborolidin-5-one-promoted aldol reaction with a ketene silyl acetal derived from ethyl 2-bromo propionate and a highly diastereoselective radical debromination reaction. These procedures provide yields that increase to a level available for practical synthesis.
High-Temperature Electrochemical Heat Pump Using a Water Gas Shift Reaction. Electrochemical Reduction of CO2 to CO
Authors: Ishihara Akimitsu , Fujimori Tomotaka , Motohira Naobumi , Ota Ken-ichiro , Kamiya Nobuyuki
Published: October 2002

The electrochemical reduction of CO2 to CO, which is considered to be the key reaction in a new electrochemical heat pump using the water gas shift reaction, was theoretically and experimentally investigated. Thermochemical predictions show that CO2 can be reduced to CO below −0.8 V at 973 K. It was found that the overpotential of the electrochemical reduction of CO2 to CO on a gold electrode was about 0.3 V at 0.01 mA cm−2. Below −1.4 V, in the range where carbon deposition took place, CO could be produced by a chemical reaction between CO2 and carbon. X-ray diffraction showed that the deposited carbon was not amorphous, but graphitized carbon.
The economic value of ensemble forecasts as a tool for risk assessment: From days to decades
Authors: Palmer T. N.
Published: October 2002

Despite the revolutionary development of numerical weather and climate prediction (NWCP) in the second half of the last century, quantitative interaction between model developers and forecast customers has been rather limited. This is apparent in the diverse ways in which weather forecasts are assessed by these two groups: root‐mean‐square error of 500 hPa height on the one hand; pounds, euros or dollars saved on the other.

These differences of approach are changing with the development of ensemble forecasting. Ensemble forecasts provide a qualitative tool for the assessment of weather and climate risk for a range of user applications, and on a range of time‐scales, from days to decades. Examples of the commercial application of ensemble forecasting, from electricity generation, ship routeing, pollution modelling, weather‐risk finance, disease prediction and crop yield modelling, are shown from all these time‐scales.

A generic user decision model is described that allows one to assess the potential economic value of numerical weather and climate forecasts for a range of customers. Using this, it is possible to relate analytically, potential economic value to conventional meteorological skill scores. A generalized meteorological measure of forecast skill is proposed which takes the distribution of customers into account. It is suggested that when customers' exposure to weather or climate risk can be quantified, such more generalized measures of skill should be used in assessing the performance of an operational NWCP system. Copyright © 2002 Royal Meteorological Society.
The influence of aerosol concentrations on the glaciation and precipitation of a cumulus cloud
Authors: Phillips Vaughan T. J. , Choularton Thomas W. , Blyth Alan M. , Latham John
Published: October 2002

The response of the glaciation and precipitation of a multi‐thermal cumulus cloud to changes in the aerosol concentration has been assessed in a series of sensitivity tests with the UMIST Explicit Microphysics Model (EMM). A simulation of this cloud from the Met Office cloud‐resolving model (CRM) has been utilized in these tests. This cumulus cloud was observed by aircraft during the initial stage of its growth over New Mexico on 10 August 1987. The growth of the simulated cloud is divided into two parts: a shallow phase followed by a deep phase. Maximum values of the cloud depth in these two phases were 5 and 9 km, respectively.

In the EMM simulations including only the shallow phase, the precipitation efficiency was found to decrease substantially with increasing atmospheric concentrations of cloud condensation nuclei (CCN). Also, the graupel mixing ratio and total ice concentration were found to decrease as normalized CCN concentrations were increased above typical continental values. These changes are explicable in terms of: (1) the Hallett–Mossop (H–M) process at −3 to −8°C and the freezing of supercooled raindrops in collisions with ice splinters dominating the glaciation; and (2) the warm‐rain process being more significant for the overall precipitation production than the ice process in these particular simulations. The almost complete suppression of precipitation by extreme CCN concentrations corresponding to a forest‐fire plume in the EMM simulation is consistent with the analysis by Rosenfeld of satellite images of Indonesian cumuli engulfed by smoke from biomass burning.

A clear tendency for ice crystals to be smaller and more numerous in the anvil was found with increasing CCN concentrations beyond typical continental values in long‐term simulations that included the deep phase. The sensitivity of the precipitation rate to the normalized CCN concentration was found to be relatively low in these deep cases. Copyright © 2002 Royal Meteorological Society.
The relation of moist symmetric instability and upper‐level potential‐vorticity anomalies to the observed evolution of cloud heads
Authors: Dixon R. S. , Browning K. A. , Shutts G. J.
Published: October 2002

The cloud‐head phenomenon has been known for some time as a precursor of rapid cyclogenesis. Based upon satellite imagery, two stages of cloud‐head development are identified in this study that can be related to early and late stages of the associated cyclone. Weakly convex cloud heads emerge from the baroclinic zone at an early stage in cyclogenesis and strongly convex cloud heads develop in association with the rapid deepening of the cyclone. Trajectories are used to highlight the role of an upper‐level potential‐vorticity (PV) anomaly in the growth of the strongly convex cloud head and the main flow associated with the growth of the strongly convex cloud head is viewed using isentropic analysis. The possible role of moist symmetric instability in the development of both weakly and strongly convex cloud heads is discussed and a new diagnostic for measuring the vertically integrated extent of realizable symmetric (VRS) instability, based on the moist geostrophic PV, is introduced. © Royal Meteorological Society, 2002. G. J. Shutt's contribution is Crown copyright.
Upstream influence of numerically simulated squall‐line storms
Authors: Fovell Robert G.
Published: October 2002

The squall line's impact on its upstream environment is examined using traditional cloud and simplified (parametrized moisture) models. The study was motivated by the need to explain significant differences between the two dynamical frameworks. In both, the first environmental response to the convection consists of a rapidly propagating gravity wave characterized by deep tropospheric subsidence. This gravity wave accelerates the low‐level storm inflow in its wake, with the largest effect seen near the surface.

In the more sophisticated model, however, this wave is eventually followed by a shorter vertical wavelength feature, one possessing lower‐tropospheric ascent. This second gravity wave, absent from the simplified model runs, substantially alters the upstream environment yet again. The gentle low‐level uplift establishes the ‘cool/moist tongue’ of air that has been found to stretch well ahead of the storm in simulations. Between the second wave and the main storm updraught, the accelerated inflow is shifted from the ground to the middle troposphere where it helps to push dry air into the convecting region.

This subsequent environmental adjustment responds to the establishment of a small yet persistent area of weak cooling during the early mature phase. Located in the middle troposphere at the upstream edge of the main cloud mass, this cooling is the combined effect of cloud‐water evaporation and the ascent of subsaturated air. Though the cooling that excites it is of relatively small magnitude (<2 K), this wave's effect is dramatic and significant. A crude fix to the moisture parametrization served to establish a qualitatively similar tongue‐like feature in the simplified model simulations, bringing the results from the two dynamical frameworks more into line. Copyright © 2002 Royal Meteorological Society.
Reputation and Competition
Authors: Höner Johannes
Published: October 2002

This paper shows how competition generates reputation-building behavior in repeated interactions when the product quality observed by consumers is a noisy signal of firms' effort level. There are two types of firms and “good” firms try to distinguish themselves from “bad” firms. Although consumers get convinced that firms which are repeatedly successful in providing high quality are good firms, competition endogenously generates the outside option inducing disappointed consumers to leave firms. This threat of exit induces good firms to choose high effort, allowing good reputations to be valuable, but its uncompromising execution forces good firms out of the market.
Geographic Localization of International Technology Diffusion
Authors: Keller Wolfgang
Published: October 2002

Income convergence across countries turns on whether technological knowledge spillovers are global or local. I estimate the amount of spillovers from R&D expenditures on a geographic basis, using a new data set which encompasses most of the world's innovative activity between 1970 and 1995. I find that technology is to a substantial degree local, not global, as the benefits from spillovers are declining with distance. The distance at which the amount of spillovers is halved is about 1,200 kilometers. I also find that over time, technological knowledge has become considerably more global. Moreover, language skills are important for spillover diffusion.
When Do Research Consortia Work Well and Why? Evidence from Japanese Panel Data
Authors: Branstetter Lee G , Sakakibara Mariko
Published: October 2002

We examine the impact of a large number of Japanese government-sponsored research consortia on the research productivity of participating firms by measuring their patenting in the targeted technologies before, during, and after participation. Consistent with the predictions of the theoretical literature on research consortia, we find consortium outcomes are positively associated with the level of potential R&D spillovers within the consortium and (weakly) negatively associated with the degree of product market competition among consortium members. Furthermore, our evidence suggests that consortia are most effective when they focus on basic research.
Induced Innovation and Energy Prices
Authors: Popp David
Published: October 2002

I use U.S. patent data from 1970 to 1994 to estimate the effect of energy prices on energy-efficient innovations. Using patent citations to construct a measure of the usefulness of the existing base of scientific knowledge, I consider the effect of both demand-side factors, which spur innovative activity by increasing the value of new innovations, and supply-side factors, such as scientific advancements that make new innovations possible. I find that both energy prices and the quality of existing knowledge have strongly significant positive effects on innovation. Furthermore, I show that omitting the quality of knowledge adversely affects the estimation results.
Review of Skidelsky's John Maynard Keynes: Fighting for Britain
Authors: DeLong J. Bradford
Published: October 2002

Skidelsky's three-volume biography of Keynes, of which this is the third, gives us Keynes, entire. The meat of the biography lies in the well-constructed narrative and in the magnificent portraits of Keynes and his age. Robert Skidelsky has given us a superb intellectual biography.
Policy Watch: U.S. Disability Policy in a Changing Environment
Authors: Burkhauser Richard V , Daly Mary C
Published: October 2002

In this paper we provide a context for evaluating the goals and effectiveness of current disability policy. We review the Social Security Disability Insurance and Supplemental Security Income programs and examine trends in disability benefit receipt and employment among working-age people with disabilities. We discuss the difficulties in crafting efficient and equitable programs for this difficult to target, heterogeneous population. We conclude that changes in policy rather than in underlying health are most likely behind the increases in disability benefit receipt and the declines in employment of working-age people with disabilities over the 1990s business cycle.

This feature contains short articles on topics that are currently on the agendas of policymakers, thus illustrating the role of economic analysis in illuminating current debates. Suggestions for future columns and comments on past ones should be sent to C. Eugene Steuerle, c/o Journal of Economic Perspectives, The Urban Institute, 2100 M Street NW, Washington, D.C. 20037.
Competition and Corporate Governance in Transition
Authors: Estrin Saul
Published: October 2002

This paper examines the elements of institutional development critical to the enhancement of company performance in transition economies. This includes initial conditions, forms of privatization, institutional frameworks and the competitiveness of markets. Comparing empirical evidence, the paper concludes that there is a clear distinction in effectiveness of policies followed and their impact between Central Europe and CIS countries. This divergence is attributed to fundamentally different political attitudes toward reform, the need of CIS governments to gain political support for reform and as a consequence of the desire of Central European countries to join European Union.
The Trouble With Electricity Markets: Understanding California's Restructuring Disaster
Authors: Borenstein Severin
Published: October 2002

In June 2000, after two years of fairly smooth operation, California's deregulated wholesale electricity market began producing extremely high prices and threats of supply shortages. The upheaval demonstrated dramatically why most current electricity markets are extremely volatile: demand is difficult to forecast and exhibits virtually no price responsiveness, while supply faces strict production constraints and prohibitive storage costs. This structure leads to periods of surplus and of shortage, the latter exacerbated by sellers' ability to exercise market power. Electricity markets can function much more smoothly, however, if they are designed to support price-responsive demand and long-term wholesale contracts for electricity.
Evolution and Game Theory
Authors: Samuelson Larry
Published: October 2002

Research in noncooperative game theory has focused attention on two questions: Should we expect equilibrium play? If so, which of the multiple equilibria that arise in many games should we expect? This paper summarizes recent approaches to these questions that have been based on evolutionary models.