bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of titanium carbide particles addition on the forging behaviour of powder metallurgy composite steels
Authors: Senthilkumar V , Narayanasamy R
Published: November 2008

This paper evaluates some of the cold-forging features of composite steel preforms of varying titanium carbide contents during cold upsetting under triaxial stress state conditions. A complete experimental investigation is carried out on composite steel preforms of varying titanium carbide contents, namely, 3%TiC and 4%TiC with different lubricating conditions; namely, graphite and zinc stearate and no lubrication. Cylindrical compacts with aspect ratios of 0.42, 0.67, and 1.0 were prepared, sintered, and upset forged at room temperature. The measured barrel radius of curvature is found to have a circular arc because the above relationship is a straight-line one. A relationship is established between the measured barrel radius and the stress ratio parameters of (σθ/σz), (σz/σm), and (σeff/σz) determined under triaxial stress state conditions for both composite steels of varying titanium carbide content. The effect of titanium carbide particle addition in the composite steel, initial preform geometry, and lubricating conditions on the deformation behaviour has been studied, together with the densification route of the composite steel preforms during the deformation.
Modelling and optimization of machining conditions for the multi-pass dry turning process
Authors: Wang Y-C , Chen T
Published: November 2008

The determination of the optimal cutting parameters that are able to satisfy specific technological and economic conditions is one of the most important elements in the process planning of metal cutting operations. For multi-pass turning operations, solving the problem of machining economics by optimizing the key cutting parameters including the number of roughing cuts, cutting speeds, depth of cuts, and feed rates has been an important research topic for at least the last two decades. Numerous cutting constraints considering tool life, cutting force, power, stable cutting region, chip—tool interface temperature, and roughing and finishing parameter relations complicate the machining optimization problem. However, no paper in the existing literature has taken into account the influence of the use of lubricants. In recent years, many researchers and experts have urged the minimization (and in same cases total elimination) at the use of lubricants in machining operations to avoid causing environmental and human health problems. Some studies indicate that in fact the purchase costs of lubricants and the costs associated with their use are frequently higher than the costs of the cutting tools. Therefore, metal cutting without fluids has become a new field for technological innovation. This paper presents an evolutionary-strategy-based optimization technique to optimize the cutting conditions in a multi-pass turning process under dry cutting conditions.
Selection of decoupling points in supply chains using a knowledge-based approach
Authors: Kundu S , McKay A , de Pennington A
Published: November 2008

As consumer affluence and desire for customized products and services at affordable prices and shorter lead times continue to accelerate, supply chain operators are facing increasing challenges of becoming both physically efficient (to enable the delivery of low cost) and flexible (to enable market-responsiveness). In order to meet these challenges, organizations are devising supply chain operation strategies that enable them to gain the benefits of physical efficiency of mass production and the customer focus of mass customization. A key to gaining these benefits lies in the selection of appropriate decoupling points in the supply chain. Decoupling points lie on the push—pull boundary. The selection of decoupling points requires knowledge from a range of different experts. The research reported in this paper used knowledge-based techniques to bring together knowledge from the viewpoints of different experts in the selection of decoupling points in supply chains. A knowledge model in the form of a network of production rules is presented. Results derived from applying the knowledge model to the case studies show similar trends to published literature.
Investigation of the cutting conditions in milling operations using image texture features
Authors: Gadelmawla E S , Eladawi A E , Abouelatta O B , Elewa I M
Published: November 2008

Texture is an important image feature in image analysis, which is related to qualitative properties of surfaces and corresponds to both brightness value and pixel locations. Image texture has been introduced into a wide range of applications such as metal surface analysis, textiles characterization, ultrasonic images processing, and food qualities evaluation. One of the most common methods for texture analysis is the grey level co-occurrence matrix (GLCM), which has a large number of texture features. In this work, an investigation of the relationship between GLCM texture features and the cutting conditions in milling operations (typically, feed, speed, and depth of cut) has been carried out. A vision system was employed to capture images for specimens with various known cutting conditions; then, the images were analysed by a software, which has been fully developed in-house to calculate 22 texture features. The relationship between each texture feature and the three cutting conditions are discussed and the correlation coefficients are introduced. The results showed that 15 texture features have good correlations with the feed, nine have good correlations with the speed, while only two have good correlations with the depth of cut.
An investigative study of the interface heat transfer coefficient for finite element modelling of high-speed machining
Authors: Iqbal S A , Mativenga P T , Sheikh M A
Published: November 2008

This paper is concerned with the development of an experimental set-up and finite element (FE) modelling of dry sliding of metals to estimate the interface heat transfer coefficient. Heat transfer between the chip, the tool, and the environment during the metal-machining process has an impact on the temperatures and on the wear mechanisms, and hence on the tool life and on the accuracy of the machined component. For modelling of the metal-machining process, the interface heat transfer coefficient is an important input parameter to quantify the transfer of heat between the chip and the tool and to predict the temperature distribution accurately within the cutting tool. In previous studies involving FE analysis of the metal-machining process, the heat transfer coefficient has been assumed to be between 10 kW/m2 °C and 100 000 kW/m2 °C, with a background from metal-forming processes (especially forging). Based on the operating characteristics, metal-forming and metal-machining processes are different in nature. Hence there was a need to develop a procedure close to the metal-machining process, to estimate this parameter in order to increase the reliability of FE models. To this end, an experimental set-up was developed in which an uncoated cemented carbide pin was rubbed against a steel workpiece while the later was rotated at speeds similar to the cutting tests. This modified pin-on-disc set-up was equipped with temperature and force-monitoring equipment. An FE model was constructed for heat generation and frictional contact. The experimental and modelling results of the dry sliding process yield the interface heat transfer coefficient for a range of rubbing speeds.
Parameter correlation study of cylinder liner roughness for production and quality control
Authors: Rosen B-G , Anderberg C , Ohlsson R
Published: November 2008

Surface roughness plays an important role in the control of emissions and friction losses in the cylinder liner—piston ring system as well as securing economically favourable manufacturing. A number of different commercial cylinder liner types have been characterized using traditional two-dimensional stylus and ISO parameters together with the latest three-dimensional characterization. The results highlight the weak and strong correlations between different families of parameters traditionally used for liner surface specifications. The bearing curve based Rxq and Rk parameter families have been evaluated and show systematic and consistent differences when characterizing the same surface features when trying to establish independent characterization of the highly stratified, two-process cylinder liner surfaces. No significant improvement in discrimination results from using ensemble averages. Presentation of correlations in the form of topological diagrams helps to show when parameters with a high intrinsic variability can be effectively replaced by other more robust parameters with which they have a high correlation. Plateau parameters are in general more highly correlated than valley parameters. Three-dimensional parameters show high internal correlations and also correlate highly with some corresponding two-dimensional parameters.
A multi-objective disassembly planning approach with ant colony optimization algorithm
Authors: Lu C , Huang H Z , Fuh J Y H , Wong Y S
Published: November 2008

This paper proposes a multi-objective disassembly planning approach with an ant colony optimization algorithm. The mechanism of ant colony optimization in disassembly planning is discussed, and the objectives to be optimized in disassembly planning are analysed. In order to allow a more effective search for feasible non-dominated solutions, a multi-objective searching algorithm with uniform design is investigated to guide the ants searching the routes along the uniformly scattered directions towards the Pareto frontier; based on the above searching algorithm, an ant colony optimization algorithm for disassembly planning is developed. The results of a case study are given to verify the proposed approach.
The effect of shielding gas composition in CO2 laser—gas metal arc hybrid welding
Authors: Chae H-B , Kim C-H , Kim J-H , Rhee S
Published: November 2008

In carbon dioxide (CO2) laser—gas metal arc hybrid welding, a shielding gas is supplied to isolate the molten metal from the ambient air, suppress the laser-induced plasma, remove the plume out of the keyhole, and stabilize the metal transfer. In this study, a shielding gas consisting of helium, argon, and CO2 was used, and its effects on the composition of the welding phenomena, such as behaviours of laser-induced plasma generation, molten pool flow, and droplet transfer in gas metal arc welding, were investigated. High-speed video observation was used to investigate the welding phenomena inside the arc regime. Consequently, helium was found to have a dominant role in suppressing laser-induced plasma; minimum helium content at a laser power of 8 kW was suggested for laser autogenous and hybrid welding. Argon and CO2 govern the droplet transfer and arc stability. A 12 per cent addition of CO2 stabilizes the metal transfer and eliminates undercut caused by insufficient wetting of molten metal.
Productivity rate of rotor-type automated lines and optimization of their structure
Authors: Usubamatov R , Abdulmuin M Z , Nor A M , Murad M N
Published: November 2008

Rotor-type production lines are used in many areas of industry. Existing analytical approaches that utilize productivity rate data of the rotor-type lines do not reflect reliable technical parameters. This paper presents a new analytical approach for calculating the productivity rate of a rotor-type automatic machine and automated lines with parallel—sequential action and optimization of its structure as a number of serial and parallel stations using the criterion of maximal productivity rate.
The effect of axial charge stratification and exhaust gases on combustion ‘development’ in a homogeneous charge compression ignition engine
Authors: Aleiferis P G , Charalambides A G , Hardalupas Y , Taylor A M K P , Urata Y
Published: November 2008

A high-swirl low-compression-ratio, optically accessed engine that was able to produce a stratified charge was used to investigate the differences in homogeneous charge compression ignition (HCCI) combustion and in the propagation of the autoignition front between a non-stratified and a stratified charge. Natural-light images were acquired using a fast camera to visualize HCCI combustion and to quantify the location of autoignition, the apparent ‘propagation speed’ of the autoignition front, and its variations between closed-valve injection timing (leading to a nearly homogeneous charge) and open-valve injection timing (leading to a strongly axially stratified charge), owing to temperature inhomogeneities that were introduced by utilizing a camshaft which allowed 40 per cent internal exhaust gas recirculation (iEGR).

Experimental results show that, in the case without exhaust gas recirculation (EGR) and with closed-valve injection timing, autoignition started under the primary intake valve near the cylinder wall, while, in the case without EGR and with open-valve injection timing, autoignition started between the exhaust valve and the secondary intake valve, closer to the centre of the piston. With 40 per cent iEGR and closed-valve injection timing, autoignition started between the exhaust valve and the primary intake valve near the cylinder wall. These differences can be explained by the difference in the location of hot gases due to the injection timing or due to iEGR. Finally, without EGR, a ‘uniform’ autoignition front of HCCI combustion from the original sites of autoignition was observed compared with a more ‘random development’ of the autoignition front with 40 per cent iEGR. Strong local inhomogeneities (possibly a very rich mixture at a low temperature) could be present with 40 per cent iEGR.
Older drivers' perceptions, responses, and driving behaviours during complex traffic conditions at a signalized intersection
Authors: Hong I , Kurihara T , Iwasaki M
Published: November 2008

In Japan, drivers over the age of 65 years are classified as ‘older drivers’. On 1 October 2006, people over the age of 65 years comprised 20.8 per cent of the population, and 13.1 per cent of these are licensed drivers. Ageing causes a decrease in both physical and psychomotor abilities. Older drivers tend to cause traffic accidents owing to complex traffic conditions. The major goals of this study are to investigate the characteristics of older drivers' eye fixation movement and responses under heavy traffic volume at an intersection with a traffic signal. A personal-computer-based driving simulator was used to evaluate driver behaviours and to reproduce unexpected roadway hazards and realistic four-step traffic volume. An eye position recorder on a near-infrared system was used to collect eye movement data. The drivers' initial cognition ability was determined on the basis of reaction time tests under three different conditions. The older driver group in this study shows the following characteristics: first, as the task complexity increases, the reaction time increases (i.e. a slowed reaction); second, as the drivers become older, the time interval between recognition of a hazard and avoidance of the hazard increases; third, as the traffic volume increases, the driver has fewer eye fixations, shorter mean fixation time, and slower fixation speed compared with the younger drivers' group; fourth, traffic volume is one of the most important factors that complicates the driving task and causes hesitation in decision making. These results provide basic data to improve traffic services to make them suitable for older drivers in an ageing society.
The mechanical hybrid vehicle: An investigation of a flywheel-based vehicular regenerative energy capture system
Authors: Diego-Ayala U , Martinez-Gonzalez P , McGlashan N , Pullen K R
Published: November 2008

Capturing braking energy by regeneration into an onboard energy storage unit offers the potential to reduce significantly the fuel consumption of vehicles. A common technique is to generate electricity in the motors of a hybrid electric vehicle when braking, and to use this to charge an onboard electrochemical battery. However, such batteries are costly, bulky, and generally not amenable to fast charging as this affects battery life and capacity. In order to overcome these problems, a mechanical energy storage system capable of accepting and delivering surges of power is proposed and investigated. A scale physical model of the system, based around a flywheel, a planetary gear set, and a brake, was built and operated in a laboratory. Tests showed that the proposed system could be used to store and provide braking energy between a flywheel and a vehicle, the latter emulated by an air-drag dynamometer. This validated the operating principle of the system and its computational model. Further, a computational analysis of a full-size vehicle incorporating the mechanical energy storage system was conducted. The results showed that the utilization of this system in a vehicle, when compared with a conventional vehicle, led to reductions in emissions and fuel consumption.
Probability density diagnostic metric for an integrated three-way catalyst controller and monitor
Authors: Muske K R , Jones J C Peyton , Kirschman J S , Frey J C , Makki I H , Uhrich M J , Howse J W
Published: November 2008

An integrated model-based methodology for three-way automotive catalyst control and diagnostic monitoring is presented in this work. The catalyst controller and monitor both utilize a limited integrator catalyst oxygen storage model with an adaptive integral gain. This adaptive catalyst gain, which is a measure of the catalyst oxygen storage capacity, is used by the controller to provide information on the dynamic catalyst behaviour and by the diagnostic monitor to provide information on long-term catalyst deactivation and short-term emission control device failure. A statistical classification technique based on the fraction of time that the catalyst gain values in a moving window are within a threshold of zero is employed as the test metric for on-board diagnostic monitoring. The performance of the catalyst monitor is demonstrated with experimental vehicle test data from a 4.6 l ULEV II gasoline engine operated over a series of Environmental Protection Agency Federal Test Procedure drive cycles with differently aged catalysts. Preliminary results indicate that it is possible to perform very accurate discrimination between catalyst operation, even near the on-board diagnostic detection threshold, using this technique.
The application of power-based transfer path analysis to passenger car structure-borne noise
Authors: Han X , Guo Y-J , Zhao Y-E , Lin Z-Q
Published: November 2008

Structure-borne noise in a passenger car is usually transmitted through multiple and/or multi-dimensional paths. Therefore, identification and control of these transfer paths are effective measures for noise reduction. A power-based transfer path analysis methodology is proposed for this purpose. First, the power flow of each transfer path is estimated with an equivalent-uncoupled-system method based on linear network theory and the Thevenin equivalent theorem. Next, the correlation between the power flow of each transfer path and the sound pressure in the passenger compartment is established; then the contribution of each transfer path is ranked; meanwhile the dominant paths and their key parameters are identified through the equations of power flow calculation. Finally, these key parameters can be analysed and then improved to reduce the structure-borne noise. An illustration of this methodology is given with a passenger car model containing a power plant, three mounts, a compliant car body, and an enclosed acoustic cavity. It is demonstrated that the methodology is effective to analyse and control the structure-borne noise transfer paths.
Analysis and optimization of gel-cast ceramic foam diesel particulate filter performance
Authors: Williams A M , Garner C P , Binner J G P
Published: November 2008

Gel-cast ceramic foams potentially offer a more robust configurable alternative filtration medium to monolithic wall flow filters (WFFs) for the reduction in particulate matter (PM) emissions from diesel internal combustion engines. The fundamental back pressure and filtration efficiency characteristics of gel-cast ceramic foam diesel particulate filters (DPFs) have been investigated. Methodology is developed for the first time that allows the calculation of the effect of local PM loading on the pressure drop characteristics from experimental data without problems caused by the non-uniform PM loading in the filter that can be applied to all depth bed filtration media. The back pressure and filtration efficiency relationships were used to develop graphical design spaces to aid development of application-specific DPFs. Effects of PM distribution on the pressure drop of the filter are presented. Filters with a non-even distribution of PM were found to have lower pressure drops than filters with an evenly distributed PM for the same average specific PM loadings. The predictions showed that gel-cast ceramic foams can achieve comparable back pressure, filtration volume, and PM holding capacity with WFFs with a lower filtration efficiency of about 80 per cent. The model demonstrated that greater than 90 per cent filtration efficiency can be achieved with filter volumes of about 0.6 times the volume of a WFF with a lower PM holding capacity.
Experimental investigation of combustion and heat transfer in a direct-injection spark ignition engine via instantaneous combustion chamber surface temperature measurements
Authors: Cho K-W , Assanis D , Filipi Z , Szekely G , Najt P , Rask R
Published: November 2008

An experimental study was performed to provide the combustion and in-cylinder heat transfer characteristics resulting from different injection strategies in a direct-injection spark ignition (DISI) engine. Fast-response thermocouples were embedded in the piston top and cylinder head surface to measure the instantaneous combustion chamber surface temperature and heat flux, thus providing critical information about the combustion characteristics and a thorough understanding of the heat transfer process.

Two distinctive operating modes, homogeneous and stratified, were considered and their effect on combustion and heat transfer in a DISI engine was investigated. The stratified operating mode yielded significantly higher spatial variations of heat flux than the homogeneous mode. This behaviour is directly caused by the main features of stratified combustion, i.e. vigorous burning of a close-to-stoichiometric mixture near the spark, and a cool, extremely lean mixture at the periphery. The cooling effect of the spray impinging on the piston surface when the fuel is injected late in compression could be detected too. The local phenomena change with varying speed and injection parameters.

Comparison between the calculated global heat fluxes and measured local heat fluxes were performed in order to assess the behaviour of classic heat transfer models. Comparisons between the global and local heat fluxes provide additional insight into spatial variations, as well as indications about the suitability of different classic models for investigations of the heat transfer aspect of DISI engines. Special consideration is required when applying classic heat transfer correlations to stratified DISI operation as heat flux values are lower by more than 30 per cent when compared with homogeneous operation of the same engine at the same load.
Structural optimization of an automobile roof structure using equivalent static loads
Authors: Jeong S-B , Yi S-I , Kan C-D , Nagabhushana V , Park G-J
Published: November 2008

In a vehicle rollover accident, the strength of the roof structure is an important factor of security in order to reduce the death and injury rates. The National Highway Traffic Safety Administration proposed strength requirements of the roof structure on roof crush resistance in the Federal Motor Vehicle Safety Standard (FMVSS) 216. Recently, there have been many structural optimization studies that design the structure of a vehicle to satisfy this safety regulation. Most previous studies used approximation methods such as the response surface method (RSM) as a crash problem has high non-linearity and difficulty in sensitivity calculation. However, the solution from the RSM may not be accurate and has a limit on the number of design variables. In this research, non-linear dynamic (transient) response optimization using equivalent static loads (ESLs) is proposed to design the structure of a vehicle to satisfy the safety regulation. ESLs for linear response analysis are made to generate the same displacement field as that from non-linear dynamic loads at each time step of non-linear dynamic analysis. A dynamic load is transformed to a set of ESLs. The static loads are used as the multiple loading conditions for linear response optimization, which are not costly in the linear response optimization process. Size optimization using ESLs is performed to reduce the structural mass while the FMVSS 216 regulation is satisfied. The optimum results using ESLs are compared with those from the RSM. As a result, the proposed method is very efficient and derives good solutions. Non-linear analysis is performed using the commercial code LS-DYNA. NASTRAN is used in calculating the ESL and linear response optimization. LS-OPT is utilized for structural optimization using the RSM.
Development of a driving simulator for telematics human—machine interface studies
Authors: Koo T-Y , Bae C-H , Kim B-Y , Rowland Z , Suh M-W
Published: November 2008

Driving simulators are useful tools not only to test the components of future cars but also to evaluate the telematics service and human—machine interface (HMI). However, driving simulators available at present cannot be implemented to test and evaluate the telematics service system as the global positioning system (GPS), which contains basic functional support for the telematics module, does not work in the virtual reality environment. In this paper, a GPS simulator is developed which is able to emulate GPS satellite signals, consisting of the NMEA-0183 protocol and RS232C communication standards, and thereby presenting a method of implementing a telematics service for a driving simulator. It is expected that the driving simulator, together with the GPS simulator, can be used to study the HMI for evaluation of commercial telematics systems in order to realize the human-in-the-loop evaluation systems.
Friction and camber influences on the static stiffness properties of a racing tyre
Authors: Gruber P , Sharp R S , Crocombe A D
Published: November 2008

Investigation of the stationary load—deflection behaviour of tyres reveals many details of the structure and the rubber-to-road friction properties. These characteristics are fundamental to the understanding of the behaviour of both the stationary and the rolling tyre. In connection with racing, tyre static stiffness characteristics are of interest as they reflect on the controllability of the vehicle to which they are fitted.

In this paper, the construction of a finite element (FE) model capable of predicting the static tyre behaviour in great detail is presented. The model is validated against extensive experimental data, including contact pressure distributions and load—deflection characteristics. Static loading tests, which involve variations in the friction rules coupling tread rubber with the ground surface, and in wheel camber angle, are simulated with the tyre model. The results of the simulations reveal that a friction coefficient of 0.5 is sufficient to prevent sliding in static loading tests for this particular tyre. Lower levels of friction lead to tread sliding and reduced vertical tyre stiffness. Sliding is primarily lateral, leading to narrowing of the contact patch of the tyre. Narrowing also increases the local sidewall curvature, which is part of the softening mechanism for both upright and cambered tyres.
Study on the collapse of tapered tubes subjected to oblique loads
Authors: Hosseini-Tehrani P , Pirmohammad S , Golmohammadi M
Published: November 2008

In this work, several antisymmetric tapered tubes with an inner stiffener under axial and oblique loading are studied and optimum dimensions of the tapered tube are derived from a crashworthiness point of view. The importance of detecting these dimensions is optimizing the weight while the crashworthiness of tube is not damaged. By using an internal stiffener, crashworthiness is improved against oblique loads, and the sensitivity of tubes with respect to oblique loads and bending deformation is diminished. The numerical models have been developed using the explicit finite element code LS-DYNA. The crashworthiness of the optimized tapered tube is compared with that of an octagonal-cross-section tube which is known as the best energy absorber model in the literature. It is shown that an optimized tapered tube has an average of 29.3 per cent less crushing displacement in comparison with octagonal-section tube when both tubes have the same weights and the same peaks of crushing load. Finally, the orientation of loading is changed and the best orientation is proposed.
Towards the use of diamond-like carbon solid lubricant coatings in vacuum and space environments
Authors: Fontaine J
Published: November 2008

Owing to the increasing demand in tribological performance for vacuum- and space-related applications, development of new solid lubricant coatings is necessary. Diamond-like carbon (DLC) coatings have been successfully used in many conventional mechanical applications to reduce both friction and wear. The potential use of these new solid lubricants under vacuum becomes then a critical question, which this article will attempt to address. DLC deposition, structure, and properties are first introduced to the reader. The exceptional tribological behaviour of DLC coatings is also discussed, in comparison with other tribological coatings. Attention is focused on the vacuum tribology of DLC films, pointing out the very low friction and wear that may be achieved with these materials. Phenomena accounting for establishment and lifetime of such low-friction regime are proposed. Finally, some open issues concerning vacuum- and space-related applications are discussed.
Tribological aspects of a strain wave gearing system with specific reference to its space application
Authors: Ueura K , Kiyosawa Y , Kurogi J , Kanai S , Miyaba H , Maniwa K , Suzuki M , Obara S
Published: November 2008

Strain wave gearing (SWG), also known as harmonic drive gear, has been used in many space applications. In 2003, a development of grease-lubricated-type SWG for space flight applications was begun. The life tests of the SWG exposed to vibration test and thermal vacuum test were performed in vacuum. The life test results showed that the in-vacuum operating life of the SWG was significantly short compared with the in-atmosphere life, which is normally corresponding to a rolling fatigue life of wave generator bearing. This may be mainly caused by the severe wear at the wave generator—flexspline interface, where the lubricant is not supplied easily into the clearance in vacuum.
Kinetic Investigation of Reaction of Ascorbate and Hydroxyl Radical Adduct of DMPO (5,5-Dimethyl-1-pyrroline N-Oxide) Studied by Stopped-flow ESR
Authors: Sakurai Yasuhiro , Sanuki Hodaka , Komatsu-Watanabe Rushiru , Ideguchi Tomoko , Yanagi Naoki , Kawai Kiyoshi , Kanaori Kenji , Tajima Kunihiko
Published: November 2008

By means of a stopped-flow electron spin resonance (ESR) method, the second-order rate constant, defined for reduction of the hydroxyl radical adduct of 5,5-dimethyl-1-pyrroline N-oxide (DMPO/OH) by ascorbic acid at pH 7.4, was evaluated to be 5.2±0.2×103 M−1 s−1, which was at least 700 times faster than that of 2,2,6,6-tetramethyl-4-hydroxylpiperidine-N-oxyl (TEMPOL) radical (7 M−1 s−1).
Template-free Preparation of Hollow Hexagonal Fluorapatite Nanoprisms
Authors: Chen Min , Jiang Deli , Xie Jimin , Zhu Jianjun , Wu Yunlong
Published: November 2008

Hollow hexagonal fluorapatite (FHAp) nanoprisms have been successfully prepared via a template-free method with the assistance of Na2EDTA/citric acid (CA) mixed chelating reagent. These novel hollow FHAp nanoprisms have an outer length of about 1 μm, an average outer diameter of 150 nm, and a shell thickness of about 50 nm. The effects of reaction temperature and chelating reagent on the formation of final products were studied. A possible formation mechanism for the hollow FHAp nanoprisms is proposed.
Identification and characterization of a short 2′–3′ bond-forming ribozyme
Authors: Smith Duncan J. , Konarska Maria M.
Published: November 2008

A large number of natural and artificial ribozymes have been isolated since the demonstration of the catalytic potential of RNA, with the majority of these catalyzing phosphate hydrolysis or transesterification reactions. Here, we describe and characterize an extremely short ribozyme that catalyzes the positionally specific transesterification that produces a 2′–3′ phosphodiester bond between itself and a branch substrate provided in trans, cleaving itself internally in the process. Although this ribozyme was originally derived from constructs based on snRNAs, its minimal catalytic motif contains essentially no snRNA sequence and the reaction it catalyzes is not directly related to either step of pre-mRNA splicing. Our data have implications for the intrinsic reactivity of the large amount of RNA sequence space known to be transcribed in nature and for the validity and utility of the use of protein-free systems to study pre-mRNA splicing.
Stalling of spliceosome assembly at distinct stages by small-molecule inhibitors of protein acetylation and deacetylation
Authors: Kuhn Andreas N. , van Santen Maria A. , Schwienhorst Andreas , Urlaub Henning , Lührmann Reinhard
Published: November 2008

The removal of intervening sequences from a primary RNA transcript is catalyzed by the spliceosome, a large complex consisting of five small nuclear (sn) RNAs and more than 150 proteins. At the start of the splicing cycle, the spliceosome assembles anew onto each pre-mRNA intron in an ordered process. Here, we show that several small-molecule inhibitors of protein acetylation/deacetylation block the splicing cycle: by testing a small number of bioactive compounds, we found that three small-molecule inhibitors of histone acetyltransferases (HATs), as well as three small-molecule inhibitors of histone deacetylases (HDACs), block pre-mRNA splicing in vitro. By purifying and characterizing the stalled spliceosomes, we found that the splicing cycle is blocked at distinct stages by different inhibitors: two inhibitors allow only the formation of A-like spliceosomes (as determined by the size of the stalled complexes and their snRNA composition), while the other compounds inhibit activation for catalysis after incorporation of all U snRNPs into the spliceosome. Mass-spectrometric analysis of affinity-purified stalled spliceosomes indicated that the intermediates differ in protein composition both from each other and from previously characterized native A and B splicing complexes. This suggests that the stalled complexes represent hitherto unobserved intermediates of spliceosome assembly.
Leakage and slow allostery limit performance of single drug-sensing aptazyme molecules based on the hammerhead ribozyme
Authors: de Silva Chamaree , Walter Nils G.
Published: November 2008

Engineered “aptazymes” fuse in vitro selected aptamers with ribozymes to create allosteric enzymes as biosensing components and artificial gene regulatory switches through ligand-induced conformational rearrangement and activation. By contrast, activating ligand is employed as an enzymatic cofactor in the only known natural aptazyme, the glmS ribozyme, which is devoid of any detectable conformational rearrangements. To better understand this difference in biosensing strategy, we monitored by single molecule fluorescence resonance energy transfer (FRET) and 2-aminopurine (AP) fluorescence the global conformational dynamics and local base (un)stacking, respectively, of a prototypical drug-sensing aptazyme, built from a theophylline aptamer and the hammerhead ribozyme. Single molecule FRET reveals that a catalytically active state with distal Stems I and III of the hammerhead ribozyme is accessed both in the theophylline-bound and, if less frequently, in the ligand-free state. The resultant residual activity (leakage) in the absence of theophylline contributes to a limited dynamic range of the aptazyme. In addition, site-specific AP labeling shows that rapid local theophylline binding to the aptamer domain leads to only slow allosteric signal transduction into the ribozyme core. Our findings allow us to rationalize the suboptimal biosensing performance of the engineered compared to the natural aptazyme and to suggest improvement strategies. Our single molecule FRET approach also monitors in real time the previously elusive equilibrium docking dynamics of the hammerhead ribozyme between several inactive conformations and the active, long-lived, Y-shaped conformer.
The use of simple model systems to study spliceosomal catalysis
Authors: Valadkhan Saba , Manley James L.
Published: November 2008

Since direct analysis of many aspects of spliceosomal function is greatly hindered by the daunting complexity of the spliceosome, the development of functionally validated simple model systems can be of great value. The critical role played by a base-paired complex of U6 and U2 snRNAs in splicing in vivo suggests that this complex could be a suitable starting point for the development of such a simple model system. However, several criteria must be satisfied before such a snRNA-based in vitro system can be considered a valid model for the spliceosomal catalytic core, including similarities at the level of reaction chemistry and cationic and sequence requirements. Previous functional analyses of in vitro assembled base-paired complexes of human U2 and U6 snRNAs have been promising, providing insight into catalysis. Furthermore, they strongly suggest that with further optimization, these RNAs might indeed be able to recapitulate the function of the spliceosomal catalytic core, thus opening the door to several lines of study not previously possible.
Complementarity Among Vertical Integration Decisions: Evidence from Automobile Product Development
Authors: Novak Sharon , Stern Scott
Published: November 2008

This paper examines complementarity among vertical integration decisions in automobile product development. Though most research assumes that contracting choices are independent of each other, contracting complementarity arises when the returns to a single vertical integration decision are increasing in the level of vertical integration associated with other contracting choices. First, effective coordination may depend on the level of (noncontractible) effort on the part of each agent; contracting complementarity results if coordination efforts are interdependent and vertical integration facilitates a higher level of noncontractible effort. Second, effective coordination may require the disclosure of proprietary trade secrets, and the potential for expropriation by external suppliers may induce complementarity among vertical integration choices. We provide evidence for complementarity in product development contracting by taking advantage of a detailed data set that includes the level of vertical integration and the contracting environment for individual automobile systems in the luxury automobile segment. Using an instrumental variables framework that distinguishes complementarity from unobserved firm-level factors, the evidence is consistent with the hypothesis that contracting complementarity is an important driver of vertical integration choices. The findings suggest that contracting complementarity may be particularly important when coordination is important to achieve but difficult to monitor.
Change of the Refractive Index of Illite Particles by Reduction of the Fe Content of the Octahedral Sheet
Authors: Friedrich Frank , Steudel Annett , Weidler Peter G.
Published: November 2008

Sub-micrometer clay particles are of interest in clay-polymer applications, especially when transparency is important. The scattering of light can be reduced by the adjustment of the refractive index (RI) of the clays to that of the matrix. In this study, the RI of sub-micrometer illite particles was changed by treatment with 5 M HCl for treatment times ranging between 2 and 24 h. The dissolution of Fe leads to a decrease in the RI of illite from 1.587 for the unaltered material to 1.502 after 24 h. The layer structure of the illite particles was preserved during the treatment. The RI of the sub-micrometer illite particles was determined by means of a photospectrometer measuring the light intensity passing through suspensions containing the clay particles, with varying refractive indices.
Some Physicochemical Properties of the White Sepiolite Known as Pipestone From Eskişehir, Turkey
Authors: Önal Müşerref , Yilmaz Hamza , Sarikaya Yüksel
Published: November 2008

Various physicochemical characteristics of a sepiolite sample from the Eskişehir area, Turkey, were investigated to help in making predictions about possible uses of the material. The sample was examined by chemical analysis (CA), thermal analysis (DTA/TGA), X-ray diffraction (XRD) analysis, particle-size analysis (PSA), linear dilatometry (LD), scanning electron microscopy (SEM), mercury porosimetry (Hg-Por.), and low-temperature nitrogen adsorption/desorption (N2-AD) techniques. The CA and XRD data indicated that the sepiolite contains only 6% dolomite by mass. The XRD patterns showed that sepiolite anhydride, enstatite, diopside, and opal-CT form upon heating the sepiolite above 600, 800, 900, and 1200°C, respectively. The maximum rate of endothermic changes in the DTA and TGA curves were observed at 82, 287, and 491°C, corresponding to the loss of external, zeolitic, and bound water from the sepiolite, respectively. Dehydroxylation and recrystallization of the sepiolite were fastest at 845°C and 862°C, respectively. The LD curve indicated that the shrinkage began at 800°C and reached 4.0% at 1000°C. The proportion of particles with diameters of <2 µm, and the external surface area of the long-term (24 h) water-treated sepiolite were determined by PSA as 79% by volume, and 8 m2g−1, respectively. The SEM view revealed discrete bundles of sepiolite fibers of various lengths. The specific surface area found from adsorption data was 316 m2g−1. The specific micro-, meso-, macro-, and total-pore volumes obtained from the combination of Hg-Por. and N2-AD results were 0.16, 0.21, 0.45, and 0.82 cm3g−1, respectively. The average macropore and micro-mesopore radii in the sepiolite were estimated (using the Hg-Por. and N2-AD data) tobe 35 and 2.4 nm, respectively.
Representations of relatedness with parents and friends and autonomous academic motivation during the late adolescence–early adulthood period: Reciprocal or unidirectional effects?
Authors: Guay Frédéric , Marsh Herbert W. , Senécal Caroline , Dowson Martin
Published: November 2008

Background The literature on the determinants of academic motivation indicates that social and affective processes connected to students' interpersonal relationships are central elements in understanding students' academic motivation and other school‐related outcomes.

Aims The aim of this study was to answer the following questions: Does autonomous motivation drive representations of relatedness, do representations of relatedness drive autonomous motivation, or are these constructs reciprocally related over time?

Sample The sample consists of 834 adolescents aged 18 years (SD = 1.88) who participated in a 3‐year longitudinal study.

Results Results from the structural equation models provided good support for the effect of representations of relatedness with parents on autonomous academic motivation but no convincing support for the effect of motivation on representations of relatedness with parents. In addition, no significant effect in either direction was found between representations of relatedness with friends and autonomous academic motivation.

Conclusion It might be important to inform parents that they may still have an influence on their adolescent's representations of relatedness and subsequently on his/her autonomous academic motivation even during the late adolescence–early adulthood period, a period when some parents may be tempted to believe that they can do little to motivate their offspring.
Assessment of Apoptosis by Immunohistochemistry to Active Caspase-3, Active Caspase-7, or Cleaved PARP in Monolayer Cells and Spheroid and Subcutaneous Xenografts of Human Carcinoma
Authors: Bressenot Aude , Marchal Sophie , Bezdetnaya Lina , Garrier Julie , Guillemin François , Plénat François
Published: November 2008

Immunohistochemistry to active caspase-3, recently recommended for apoptosis detection, is inappropriate to detect apoptosis involving caspase-7. Cleavage of poly-ADP-ribose polymerase 1 (PARP-1), a major substrate of both caspases, is a valuable marker of apoptosis. Apoptosis evaluation induced in vitro either by paclitaxel or by photodynamic treatment (PDT) with Foscan in HT29 or KB monolayer cells and HT29 spheroids yielded a close percentage of labeled cells whatever the antibody used, whereas in control specimens, cleaved PARP (c-PARP) immunostaining failed to detect apoptosis as efficiently as active caspase-3 or −7 immunostaining. Studies in MDA-MB231 monolayer cells and HT29 xenografts either subjected or not subjected to Foscan-PDT resulted in a significant higher number of active caspase-3–labeled cells, although immunofluorescence analysis showed c-PARP and active caspase-3 perfectly colocalized in tumors. A restricted expression of c-PARP was obvious in the greater part of caspase-3 expressing cells from control tumor, whereas photosensitized tumors showed a higher number of cells expressing large fluorescent spots from both active caspase-3 and c-PARP. These results support the assumption that c-PARP expression was dependent on treatment-induced apoptosis. The absence of caspase-7 activation in some caspase-3–expressing cells undergoing Foscan-PDT shows the relevance of using antibodies that can discriminate caspase-dependent apoptotic pathways.
Residual Fluid as a Source of Error in Bubble Point Testing
Authors: Elton David , Hayes David
Published: November 2008

The bubble point test (ASTM D6767) is a method of calculating the pore size distribution of geotextiles. ASTM D6767 allows a variety of wetting fluids to be used in the test. However, different fluids are found to produce different pore size distributions, even though relevant fluid properties are supposedly accounted for in the data reduction (Elton, D. J., Hayes, D. W., Adanur, S., Geotech. Test. J., Vol. 30, No. 1, 2007, pp. 9–16). The ASTM D6767 data reduction is found to be theoretically incorrect. The effect of residual wetting fluid on the pore size distribution is examined. Residual fluid is defined as fluid that remains on the walls of a previously saturated pore after the critical pressure for the fluid in the pore has been reached (after the bubble point pressure is reached). Since the phenomenon of residual fluid is not considered in ASTM D6767, it presents a source of error. Bretherton’s law suggests residual fluid errors will be reduced by using fluids with a small viscosity to surface tension ratio.