bluuebunny/crossref_metadata_2025 huggingface dataset:
An Evolutionary Approach for Multi-Pass Turning Operations
Authors: Singh G , Choudhary A K , Karunakaran K P , Tiwari M K
Published: June 2006

Owing to the significant role that machining parameters play in performing successful and efficient machining operations, the determination of optimum machining parameters is a subject of high importance. The problems are well-known complex puzzles and are treated as a strongly non-deterministic polynomial (NP)-hard problem. In this research, a multi-pass turning problem has been modelled, taking into consideration several technological constraints pertaining to force, power, chip-tool interface temperature, tool life, stable cutting region, etc.; while aiming to satisfy the objective of minimizing the unit production cost. The solution of such a problem, even one of modest size, is marked by excessive computational complexity and therefore random search optimization techniques are needed in order to resolve the problem. In this paper, a heuristic has been developed to determine the number of passes and a new kind of genetic algorithm (GA), incorporating the features of chromosome differentiation and simulated annealing, has been developed and applied to address multi-pass turning problems. The proposed algorithm overcomes the drawbacks of simple GAs and the methodology adopted here has the capability of achieving a better balance between exploration and exploitation, and of escaping from local minima. The proposed algorithm has been tested on various case studies adopted from the literature, as well as on ten simulated data sets. Intensive computational experiments revealed its superiority over earlier approaches.
Computer Simulation of Casting Process of Aluminium Wheels - A Case Study
Authors: Hsu Yeh-Liang , Yu Chia-Chieh
Published: June 2006

Aluminium disc wheels intended for normal use in passenger cars are commonly produced by gravity casting. If the cooling process and the initial temperature of the mould are not well controlled, shrinkage cavity will occur after solidification, causing leakage in the disc wheel. In this research, a casting simulation software is used to simulate the casting process of aluminium wheels. The casting simulation is done iteratively until the mould temperature converges to a stable temperature. A ‘shrinkage index’ (SI) is defined to provide a quantified index of casting quality of aluminium wheels, based on the phenomenon of liquid entrapped at the joints of rim and spokes of the wheel where shrinkage cavity usually happens. This shrinkage index shows good correlation with the aluminium wheel leakage test results. This paper also discusses the influence of cooling process parameters on SI, including initial mould temperature, and geometry of the wheel, which verifies engineers' empirical data. This iterative simulation process and SI can be used to predict the casting quality of aluminium wheels and to find the optimal parameters of the casting process.
Tool-Life Modelling of Carbide and Ceramic Cutting Tools Using Multi-Linear Regression Analysis
Authors: Amaitik S M , Taşgin T T , Kiliç S E
Published: June 2006

This paper presents a study for the development of tool-life models for machining operations by means of a statistical approach called multi-linear regression analysis. The study was applied to a milling process for machining SAE 121 cast iron in a factory without interrupting the mass production. Different cutting tool materials under dry conditions were used in the cutting tests. Several machining experiments were performed and mathematical models for tool life have been postulated by using least-square regression analysis. The analysis was based on a first-order model in which the tool life is expressed as a function of two independent variables; cutting speed and feed rate. Analysis of variance was applied to check the adequacy of the mathematical models and their respective parameters. In order to demonstrate the usefulness of the developed models, tool-life contours have been generated and presented in different plots.
Formation of Micromoulds via UV Lithography of SU8 Photoresist and Nickel Electrodeposition
Authors: Thian S , Tang Y , Fuh J Y H , Wong Y S , Loh H T , Lu L , Tee D Z S
Published: June 2006

Current lithography methods for creating micromoulds, other than LIGA, often use glass or silicon wafer as substrates. Since they are nonconductive, a metallic seed layer is required to be deposited over the substrate for electrodeposition to take place. This paper demonstrates a new method of creating a micromould directly onto a metal substrate, which can then be immediately utilized for microinjection moulding after nickel electrodeposition. The selected metal brass substrate is machined by a single-point diamond turning process to achieve a nanosurface of 12 nm. Standard UV lithography using SU8 photoresist was then employed to create a microgear onto the brass. At approximately 20 μm depth, nickel microcavity gear of 1 mm diameter was successfully created directly onto the brass substrate, after electrodeposited in nickel solution. A pulse current deposition method at a current density of 400 A/m2 was used for the deposition process.
A Novel Method for the Rapid Production of Inexpensive Dies and Moulds with Surfaces Made by Incremental Sheet Forming
Authors: Allwood J M , Bramley A N , Ridgman T W , Mileham A R
Published: June 2006

The choice of processing routes for parts is often strongly influenced by high tooling costs that can only be justified when large batches are required. This paper describes a novel system for producing inexpensive dies and moulds. The system exploits the recently developed ‘incremental sheet forming’ process to produce a die surface, which is then supported by a reinforcement and used as a conventional die or mould. A demonstrator die pair has been designed, constructed and tested, and the results show that even with a temporary reinforcement such as sand, the dies retain geometric accuracy. The use of this system allows more widespread application of incremental sheet forming than has been envisaged to date, as it expands the potential process applicability beyond prototypes and small batches by allowing manufacture, validation, and adjustment of dies and moulds for conventional mass production processes.
Research on the Flow and Cavitation Characteristics of Multi-Stage Throttle in Water-Hydraulics
Authors: Yinshui Liu , Yousheng Yang , Zhuangyun Li
Published: June 2006

In water-hydraulic power systems cavitation is more likely to happen than in oil-hydraulic power systems because of the high vaporous pressure of water. A multi-stage throttle, which consists of two or more orifices in a throttle, is an effective way to avoid or reduce cavitation damage. In this research, the cavitation characteristics of two-stage throttles are analysed theoretically and compared with a single-stage. Then, experiments are conducted to investigate the flow and cavitation characteristics of multi-stage throttles including two kinds of two-stage throttles and one of a three-stage kind. All the experiments are carried out under the two cases with and without backpressure, respectively. The working medium is tap water. Experimental results show that the shape of the multi-stage throttle and operating conditions have remarkable effects on the flow and cavitation characteristics.
Prediction of the Collapse Time of a Process Storage Vessel Due to Internal Steam Condensation
Authors: Cronin K , Baker S
Published: June 2006

Thin-walled, storage tanks are prone to vacuum collapse because of the development of a net external pressure. Condensation of steam inside the vessel can cause the rapid development of this mode of failure. External atmospheric conditions also affect the process. An expression to predict the time taken for collapse to occur is developed. The formula is validated by a series of experimental tests on a variety of laboratory scale drums and at a number of different air flow conditions. A parameter study indicates the relative importance of the input variables used.
Neural network for structural stress concentration factors in reliability-based optimization
Authors: Zhang Y M , Zhang L , Zheng J X , Wen B C
Published: June 2006

Stress concentration damage is one of the most troublesome problems in practical engineering structures. In order to reduce damage, it is very important to determine stress concentration factors accurately. An artificial neural network (NN) technique has been used in this article to simulate the relationship between basic random variables and stress concentration factors, and the explicit expression of the stress concentration factors can be obtained directly. The expression of the stress concentration and the reliability theory have been combined to solve the structural reliability problems; then, the corresponding methods of reliability analysis and optimization design have been presented.
α ↔ β changes in Ti-6A1-2Sn-4Zr-2Mo-Si alloy: Characterization, microstructure, and mechanical properties
Authors: Tarín P , Rodríguez M C , Simón A G , Piris N M , Badía J M , Antoranz J M
Published: June 2006

In a Ti-6Al-2Sn-4Zr-2Mo-Si alloy, α ↔ β transformation kinetics and other transformation characteristics and its influence on subsequent cooling transformations have been evaluated by differential and dilatometric thermal analysis, hardness and conductivity measurements, and metallographic observation, after performing controlled thermal treatments. Starting from the mill annealed condition, samples were heated at temperatures between 650 and 1060 °C for 1 h, then water quenched, and subsequently heated at 565 °C for 8 h, air cooled. The mechanical properties of samples heat treated as indicated have also been obtained. Finally, the validity of hardness and conductivity measurements and tensile test results as a control method for the correct solution treatment (and the primary α percentage) has been studied.
Measurements in the wake of an airfoil with regular roughness on the upper surface near the leading edge
Authors: Kim S , Kim J S , Park J , Choi J
Published: June 2006

The incompressible flow in the near wake of a NACA0012 airfoil is measured when the artificial roughness of a sandpaper strip is attached on the upper surface parallel to the leading edge. The strip location and the angle of attack are varied under constant roughness size and the fixed Reynolds number. The wake shape factor increases because of roughness, when compared with the smooth surface case regardless of the angle of attack. Its magnitude is larger when the strip is placed at the leading edge than that of the other cases. The velocity defect in the wake increases by the surface roughness. However, the turbulent intensity and the absolute value of the turbulent shear stress are reduced by the roughness.
Examination of the Performance of an Unconventional Combination of Rankine, Brayton, and Inverse Brayton Cycles
Authors: Alabdoadaim M. A. , Agnew B , Potts I
Published: June 2006

The study presented in this article examined the thermodynamic performance of a proposed system constructed from Brayton, inverse Brayton, and steam Rankine cycles. The theoretical examination was performed by varying the Brayton cycle pressure ratio for different values of inlet pressure and expansion pressures of the inverse Brayton cycle and for different ratios of the inverse Brayton power turbine mass flow to the gas generator mass flow. The results indicated that for the three values of mass flow ratio examined, better performance could be achieved when the proposed system is operated at high Brayton cycle pressure ratio (high maximum system temperature and the highest value of inverse Brayton cycle expansion pressure). It was revealed that in the case of the mass flow equal to 0.25, the proposed system achieved the highest value of Brayton cycle pressure ratio and attained a maximum thermal efficiency of 57.7 per cent.
Effects of Shear Stress Forces to Rotordynamic Coefficients in Staggered Labyrinth Seals
Authors: Dereli Y , Eser D
Published: June 2006

In this article, shear stresses in calculating the rotordynamic coefficients of staggered labyrinth seals are presented. Differences in the values of these coefficients are observed and quantified. The results of the present article are compared with the results of earlier formulations that neglect the effect of shear stresses for various geometries and operating conditions.
Fluid Flow in the Squish-Jet Combustion Chamber
Authors: Lappas P , Evans R. L.
Published: June 2006

Fluid flow characteristics near top dead centre (TDC) were measured in three different combustion chambers designed to generate squish flow and to enhance turbulence generation in internal combustion engines. One of the combustion chambers was a plain bowl-in-piston type, whereas the remaining two were different configurations of the squishjet chamber, which has a unique geometry for forming jets that converge radially inwards as TDC is approached. Both particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) were used to measure mean velocities and turbulent fluctuations near to TDC. To accurately and consistently set the initial and boundary conditions, the University of British Columbia Rapid Intake and Compression Machine (UBC-RICM) was used. The microscopic particles used for PIV and LDV seeding were introduced into the cylinder by a novel system developed to suit the momentary flow in the UBC-RICM. The experimental study led to a greater understanding of the flow processes inside these complex combustion chambers. The results also indicated that squish-jet chambers tend to generate higher levels of turbulence than plain bowl-in-piston chambers do, even though they may generate lower mean squish velocities. These results will also be used in a future study to assess the validity of squish flow predictions made by the computational fluid dynamic code, KIVA-3V.
New Method for Comparing Flow in Spring-Loaded Valves
Authors: Zhang Z
Published: June 2006

Spring-loaded valves possesses a dynamic operating range, in which the moving element is balanced by the flow and the spring forces. This feature means that the valve performance, including the pressure drop coefficient and the valve gaps, cannot be fully described only by using the Reynolds number without considering the spring properties. In this article, the theoretical analysis of the flow in spring-loaded valves was made to unify the flow and the spring forces. A new dimensionless number named the Zhang number was defined, with which the valve gaps and thus the pressure drop coefficient in the dynamic operating range can be clearly described. The similarity of flows in the valve loaded by different spring sets is then ensured. The significance of this similarity has been excellently demonstrated by an industrial compressor valve. Specifically, once a valve loaded by a set of springs is characterized, the valve characteristics using other spring sets can be directly obtained from the existing characteristic. No additional calibration of valve flows is necessary.
Tribo-assisted reorientation of nanometre-thick Ag film in ultrahigh vacuum environment
Authors: Goto M , Akimoto K , Honda F , Nakahara T
Published: June 2006

The tribo-assisted reorientation of the 5-nm-thick Ag film with polycrystalline structure has been studied in an ultrahigh vacuum (UHV) environment. The film was prepared on an Si (1 1 1) √3 × √3-Ag surface in a UHV condition at a pressure less than 4 × 10−8 Pa. The friction coefficient of the film was 0.07 at the beginning of the sliding and decreased to 0.02 as the reciprocal sliding cycle proceeded. Reflection high-energy electron diffraction observation showed that the crystallographic orientation of the film surface was changed by the mechanical rubbing motion of the diamond pin. Scanning tunnelling microscopy observation showed that the Ag (1 1 1) plane on the worn surfaces of the film oriented parallel to the substrate surface. Synchrotron orbital-radiated X-ray diffraction showed that the Ag (1 1 1) domains in the layer increase as the number of slidings increase, which corresponded to the friction reduction process. This study has clarified the reorientation process of the Ag film with nanometric thickness.
Effects of soot on wear in elastohydrodynamic lubrication contacts
Authors: Kaneta M , Irie T , Nishikawa H , Matsuda K
Published: June 2006

Diesel engines produce soot, i.e. particulates as a residue of the combustion process. Lubricants contaminated with soot may result in an increased rate of wear. Numerous investigations have, therefore, been conducted to elucidate the mechanism of soot wear from different viewpoints. However, this important and complicated problem is still being debated. In this article, the mechanism of soot wear is discussed on the basis of the direct observations of soot behaviour among contact surfaces, the wear pattern obtained with a four-ball tester, and the wear mode observed with a newly developed two-roller testing machine. It is consequently proved that soot acts as an abrasive.
High-pressure chamber measurements
Authors: Jacobson B. O.
Published: June 2006

Results from the design of a high-pressure chamber and its components, recently developed at the Lund Institute of Technology, are presented. The results show that at high pressures, when the lubricants have solidified, the density varies linearly with the pressure and the shear strength also increases nearly linearly with pressure. This is also true for the investigated gasses when they are compressed through the liquid into the solid state. Also waxes, which are solid at room pressure and temperature, show the same type of linearity.

The high-pressure chamber has been used for pressures up to 3.3 GPa for a large number of compression experiments in the present form. It has been used for compressibility, shear strength, and viscosity measurements, and gasses, liquids, semi-solids (greases), and solids have been investigated.
Adaptive high-order finite element solution of transient elastohydrodynamic lubrication problems
Authors: Lu H , Berzins M , Goodyer C. E. , Jimack P. K. , Walkley M
Published: June 2006

This article presents a new numerical method to solve transient line contact elastohydrodynamic lubrication (EHL) problems. A high-order discontinuous Galerkin (DG) finite element method is used for the spatial discretization, and the standard Crank-Nicolson method is employed to approximate the time derivative. An h-adaptivity method is used for grid adaptation with the time-stepping, and the penalty method is employed to handle the cavitation condition. The roughness model employed here is a simple indentation, which is located on the upper surface. Numerical results are presented comparing the DG method to standard finite difference (FD) techniques. It is shown that micro-EHL features are captured with far fewer degrees of freedom than when using low-order FD methods.
Investigations on power losses in high-speed gears
Authors: Diab Y , Ville F , Velex P
Published: June 2006

Power losses in high-speed gears come from the friction between the teeth (sliding and rolling), the lubrication process (dip or jet lubrication), the pumping of a gas-lubricant mixture during the meshing, and the losses associated with windage effects. The authors have developed different approaches to analyse the contribution of each power loss source, namely:

(a) the windage losses based on simplified air flow models neglecting the influence of the lubricant, which compare well with the experimental evidence from a specific test bench; (b) an original model of gas trapping in the intertooth time-varying spaces, which has been validated using the experimental findings on a spur gear test rig in which pressure transducers have been placed at the bottom of the space between two teeth; (b) tooth friction, by introducing into a three-dimensional dynamic model of gears a new traction law based on measurements from a two-disc machine which accounts for lubricant properties and surface finish.

The combination of the three models allows for the prediction of gear efficiency over a wide range of speeds and loads for jet-lubricated geared units. This approach also makes it possible to improve tooth geometry and gearbox design to minimize power losses and heat generation. The procedure is illustrated in several industrial applications.
Influence of vibrations and noise on experimental results of lubricated non-conformal contacts
Authors: Ciulli E , Bassani R
Published: June 2006

Dynamic effects are present in both simulated and real contacts. The influence of vibrations and other interferences on experimental results of lubricated non-conformal point contacts have been investigated. Tests with theoretically constant speed and load have been carried out. Friction force and speed signals have been analysed in particular. Signals have been analysed in the time and frequency domains by investigating first some preliminary aspects such as the influence of the sample rate. Peaks in the frequency domain of the measured quantities have been compared with the theoretical ones calculated considering possible defects of moving elements. The analysis has evidenced the presence of some misalignments and bearing problems. The friction fluctuations have been put in relation to the film thickness variations revealed by the interference images recorded by a new high-speed camera. The presence of a part of the friction force generated by dynamic forces directly acting on the load cell, and therefore not related to the lubricated contact, is revealed, evidencing the usefulness of studies combining different methodologies. The detection of the sources of the different signal variations can indicate the ways of possible reduction of the unwanted effects that can also be separated from the effects relevant to the real contacts by opportune filtering methods.
Extraction and tribological investigation of top piston ring zone oil from a gasoline engine
Authors: Lee P. M. , Priest M , Stark M. S. , Wilkinson J. J. , Smith Lindsay J. R. , Taylor R. I. , Chung S
Published: June 2006

With tightening emission regulations, increased expected fuel economy, and longer drain intervals impacting on lubricant formulation, greater understanding of how oil degrades in an automotive engine is becoming ever more important. Equally significant is the effect that this degraded lubricant has on the tribological operation of the engine, particularly its overall internal friction and component wear

In a previous paper, four tests to degrade oil in a single cylinder engine were reported [1]. These tests were set up such that the lubricating oil was degraded in the ring pack before returning to the sump, where it was sampled and chemical and rheological analysis undertaken. This paper reports the extension of this work using the same Hydra engine and describes how oil has additionally been extracted from the rear of the top piston ring during engine operation. This extracted oil has then been subjected to similar analysis as the sump oil samples in the previous tests, along with additional analysis to look at the tribological properties of the oil using tribometers.

The results clearly show significant differences in the rheological, tribological, and chemical properties of the fresh oil and used sump oil samples when compared with the top ring zone (TRZ) oil samples, particularly the effect of load on the levels of volatiles present in the TRZ samples and their effect on traction and friction coefficient values during tribological testing.
Investigation into the effect of a sandwich acetabular cup upon lubricant film thickness in metal-on-metal total hip replacements
Authors: Liu F , Jin Z. M. , Dowson D
Published: June 2006

The development of a large lubricant film thickness generally depends upon the large elastic deformations of the bearing surfaces from the elastohydrodynamic lubrication (EHL) point of view. The deformation of the bearing surfaces of total hip joint replacements can be influenced by the material properties as well as the structural supports. A conceptual sandwich cup, which consists of a hemispherical metallic bearing shell bonded to a polyethylene backing, together with a solid metallic femoral head was considered in an EHL analysis for quasi-static conditions of load and speed to investigate the effect of the sandwich cup upon lubricant film thickness in total hip replacements. It was found that a reduction in the cup wall thickness of the metallic shell and an increase in the polyethylene thickness resulted in an increase in the predicted lubricant film thickness and a decrease in the hydrodynamic pressure. A general relationship was found between the film thickness and the metallic inlay thickness.
Effect of start-up conditions on elastohydrodynamic lubrication of metal-on-metal hip implants
Authors: Jalali-Vahid D , Jin Z. M. , Dowson D
Published: June 2006

Lubrication plays an important role in the wear and friction of metal-on-metal bearings for artificial hip joints. It is generally known that both load and speed can influence the lubrication mechanism. This is particularly important in hip implants, which experience many intermittent start-ups and stops, which may adversely affect the lubrication and increase wear in metal-on-metal hip implants. The effect of start-up and gait initiation upon elastohydrodynamic lubrication (EHL) in a typical metal-on-metal hip implant has been investigated in the present study. A simple ball-on-plane model was used for a full transient EHL analysis under assumed start-up conditions represented by linear variations in both load and speed, but with different development time periods. It was shown that the duration of the start-up period had little effect on the predicted lubrication film thickness during either the start-up or the steady cyclic conditions. It was found that only two to three steps were required to establish a continuous steady cyclic variation of the predicted lubricant film thickness. This suggests that intermittent motions associated with start-up and stop may have only a small effect on the wear of metal-on-metal hip implants.
Approximate model for unsteady finite porous journal bearings fluid film force calculation
Authors: D'Agostino V , Ruggiero A , Senatore A
Published: June 2006

This article focuses on an analytical approximate fluid film pressure solution in finite porous journal bearings. Exploring the dynamic behaviour of a rotor on porous bearings, such as the fluid film force, the authors find in an analytical model an effective approach to provide a more readable description of the interaction between rotor and bearings. Furthermore, this kind of method for analysing the behaviour of a system is more effective than a numerical procedure and allows covering not only the individual case, but also the whole class to which the system in question belongs.

The proposed model provides a quick analytical calculation of the fluid film force for different values of the permeability factor, aspect ratio, and eccentricity ratio in the whole domain of dynamic states. The results are in good agreement with those achieved using the numerical solutions.
Simulated fuel dilution and friction-modifier effects on piston ring friction
Authors: Smith O , Priest M , Taylor R. I. , Price R , Cantlay A , Coy R. C.
Published: June 2006

Government legislation, customer requirement, and pressure from the original equipment manufacturers (OEM) continually pushes the issue of increased vehicle fuel economy to the forefront. Lubricant manufacturers responded by creating low viscosity lubricants with complex additive packages capable of reducing total engine friction while maintaining the useful life of the engine. An important component in the lubricant additive package is the friction modifier, whose job is to reduce the sliding friction of components operating in the boundary lubrication regime.

It is widely agreed that 40-60 per cent of mechanical friction can be attributed to the piston/ring/cylinder wall interface, much of which is as a result of the compression ring whose lubrication is kept purposely minimal to control exhaust emissions. A logical progression to research suggests utilizing fuel to administer friction modifier directly to the top ring zone of the engine, the area where its effects are most beneficial. This article describes a series of tests conducted using a Plint TE-77 reciprocating tribometer to investigate the synergy of lubricant and fuel containing friction modifier at the top ring zone. A computational model has been modified and utilized to further investigate the potential impact of administering friction modifier at the top ring zone via the fuel.
Influence of Cutting Edge Radius on the Wear Resistance of Powder Metallurgy High-Speed Steel Milling Inserts
Authors: Rech J , Schaff M-J
Published: June 2006

The wear behaviour of powder metallurgy high-speed steel (PM-HSS) milling inserts is investigated experimentally. Cutting inserts with different cutting edge radii tested at various feed rates and cutting speeds were examined. The radii have been obtained either by microsandblasting or by honing. The initiation and progress of the tool wear was analysed with scanning electron microscopy (SEM) of the cutting edges. The experimental results exhibit quantitatively the effect of tool radius on the performance of milling inserts. A radius on the cutting edge prevents fast and unpredictable wear, and can lead to a great improvement of the tool life.
Catalysis on Electron Transfer and the Mechanistic Insight into Redox Reactions
Authors: Fukuzumi Shunichi
Published: June 2006

Both thermal and photoinduced electron transfer reactions from one-electron reductants to various organic oxidants such as carbonyl compounds are catalyzed by the presence of acids and metal ions. The acceleration of rates of electron transfer is ascribed to the thermodynamic stabilization of products of electron transfer by the protonation or complexation with metal ions, which results in the positive shift of the reduction potentials of oxidants. In the case of Mg2+-catalyzed electron transfer reduction of p-benzoquinone derivatives, the formation of 1 : 1 and 1 : 2 complexes between semiquinone radical anion and Mg2+ is confirmed by the transient absorption spectra as well as by the ESR spectra. From the spectral change at different Mg2+ concentrations is determined the formation constant (K2) of the 1 : 2 complex. The K2 values of various semiquinone anions determined from the direct detection of the Mg2+ complexes agree well with those estimated from the kinetic analysis on the Mg2+-catalyzed electron transfer reactions. The direct spectroscopic detection of complexes between the semiquinone radical anions and Mg2+, combined with the kinetic analysis of the catalytic effects of Mg2+ on not only the electron transfer reactions but also on various reactions involving p-benzoquinone derivatives such as Mg2+-catalyzed Diels–Alder reactions of anthracenes with p-benzoquinone derivatives, provides a confirmative basis for delineating the catalytic mechanisms of Mg2+ on various types of reactions. A remarkable increase in the reactivity of the photoexcited states of carbonyl compounds in the electron transfer reactions is also found by the complexation with Mg2+. The photoexcitation of the Mg2+ complex results in strong fluorescence in contrast with the nonfluorescent excited states of uncomplexed carbonyl compounds. Thus, various redox reactions of carbonyl compounds via photoinduced electron transfer are made possible by the catalysis of metal ions which form complexes with carbonyl compounds. The fundamental concept and the scope of catalysis on electron transfer are reviewed in this account to provide some insight into the mechanistic viability.
The Electrical Behavior of Charge-Transfer Salts Based on an Unsymmetrical Donor Bis(ethylenedithio)diselenadithiafulvalene (STF): Disorder Effect on the Transport Properties
Authors: Naito Toshio , Kobayashi Hayao , Kobayashi Akiko
Published: June 2006

The hybrid donor between bis(ethylenedithio)tetrathiafulvalene and -tetraselenafulvalene (ET and BETS, respectively) has been synthesized and the electrical properties together with the crystal structures of its cation radical salts investigated. All of the crystals studied by X-ray structural analysis turned out to have an orientational disorder at the donor site. Although some of the charge-transfer salts were found to be isostructural with the corresponding ET and/or BETS salts, not all of their electrical properties are parallel to them; some are similar, others are significantly different from those of the parent donor salts. Such a trend indicates that the effect of the disorder on the electrical behavior might not be always equal, and should depend on some factor(s) yet to be clarified.
Thermodynamic Study of the Effects of Monovalent Cations on Dimerization of a Dianionic Azo Dye, 2-[(2-Hydroxy-1-naphthyl)azo]-5-[(4-sulfonatophenyl)azo]benzenesulfonate, in Aqueous Salt Solution
Authors: Murakami Kiyofumi , Kimura Yuko , Saito Masahiko
Published: June 2006

Thermodynamics of the dimerization of 2-[(2-hydroxy-1-naphthyl)azo]-5-[(4-sulfonatophenyl)azo]benzenesulfonate in the presence of 0.05 mol dm−3 alkali metal cations and tetralkylammonium cations has been studied spectrophotometrically. From the dimerization constant and its temperature dependence, the values of standard enthalpy change and entropy change of dimerization have been calculated. The results show that both of them increase in the order of K+ < Li+ < Na+ < Rb+ < Cs+ and NH4+ < (CH3)4N+ < (C2H5)4N+ < (C3H7)4N+, and further, an enthalpy–entropy compensation relation with the compensation temperature of 300 K does hold. Dimer structure has also been examined using exciton theory. The angle between long molecular axes of monomers in the dimer lies in 43—44° for Na+, K+, Rb+, and Cs+, and is about 52° for Li+, but, that for tetralkylammonium cations has a tendency to increase with an increase in the size of the alkyl chain up to tetraethylammonium ion and somewhat decreases for tetrapropylammonium ion, i.e., 38° (NH4+) < 41° ((CH3)4N+) < 59° ((C2H5)4N+) > 46° ((C3H7)4N+). These results clearly show the participation of the cations in the thermodynamic and structural properties of the dimerization. By comparing the data with those in the absence of added salt, the results have been interpreted in terms of the condensation of cations around the dimer and the hydration structure of cations.
Rayleigh Light-Scattering Spectroscopy: Application to the Determination of Proteins Using Bromopyrogallol Red
Authors: Ma Chun Qi , Li Ke An , Tong Shen Yang
Published: June 2006

A method for the quantitation of proteins in aqueous solution involving the binding of bromopyrogallol red to proteins under acidic conditions has been developed. The binding of the dye to proteins is accompanied by an enhancement of Rayleigh light scattering at 332 nm; the scattering intensity is linear over the range 0.136—6.80 μg ml−1. The reaction is completed immediately after mixing dye and protein solutions, and the scattering signal is stable for at least 3 h. There are very few interference with the method, most of which can be minimized by dilution.
Distribution Study of the Hydration of Nitric Acid in Dodecane
Authors: Naganawa Hirochika , Tachimori Shoichi
Published: June 2006

The hydration of nitric acid in dodecane was determined on the basis of the acid and water distribution between aqueous acid solutions and dodecane at 298 K. By analyzing the distribution data, mono- and decahydrate of nitric acid in addition to the anhydrous acid were found in dodecane. The solvent influence on the formation of the acid hydrates in dodecane was also compared with the results obtained in benzene.
Reactions of Molybdenocene and Tungstenocene Derivatives with Cobalt Carbonyls and the Related Compounds
Authors: Nakamura Takashi , Minato Makoto , Ito Takashi , Tanaka Masako , Osakada Kohtaro
Published: June 2006

Reactions of molybdenocene and tungstenocene derivatives [M(Cp)2(H)2], [M(Cp)2H(OTs)], or [{M(Cp)2H(μ-Li)}4] (M = Mo, W) with [Co2(CO)8] or [Co(CO)4]− gave [M(Cp)2H(CO)]+[Co(CO)4]− and [M(Cp)2(μ-H)(μ-CO)Co(CO)3] depending on the reaction conditions employed. These ionic heterobimetallic complexes were characterized by IR and NMR, as well as by X-ray diffraction analyses. A possible mechanism for the formation of the complexes is proposed.
Efficient Synthesis of Selenocarbonyl Compounds by Treating Carbonyl Compounds with Bis(1,5-cyclooctanediylboryl) Selenide
Authors: Shimada Kazuaki , Jin Norikazu , Kawaguchi Michiko , Dobashi Kumiko , Nagano Yumi , Fujimura Manabu , Kudoh Eiichi , Kai Tomonari , Saito Noboru , Masuda Jun-ichi , Iwaya Masaki , Fujisawa Hiroyuki , Aoyagi Shigenobu , Takikawa Yuji
Published: June 2006

Selenoaldehydes and selenoketones were generated in situ, by treating aldehydes or ketones, respectively, with bis(1,5-cyclooctanediylboryl) selenide; the resulting selenocarbonyl compounds were trapped with 2,3-dimethyl-1,3-butadiene to give the corresponding [4+2] cycloadducts. The treatment of amides, an ester, and ketones possessing bulky substituents with the reagent also afforded the corresponding selenoamides, a selenoester, and sterically protected selones, respectively, in modest yields. On the other hand, a similar treatment of cinnamaldehyde with the reagent gave the 2,3-dihydroselenophene derivative, which originated from a [4+2]-type self-dimerization of in situ generated 3-phenyl-2-propeneselenal.
Useful Intermediates, 3-C-Dichloromethyl Furanose Derivatives, for the Synthesis of Branched-Chain Functionalized Sugars
Authors: Sato Ken-ichi , Suzuki Katsuhiko , Ueda Miyuki , Kajihara Yasuhiro , Hori Hiroyuki
Published: June 2006

A few novel branched-chain functionalized sugars, which have important functions such as hydroxy, hydro, chloro, or azido at the quaternary carbon, were stereoselectively prepared in good yield via the same intermediary 3-C-,3-O-chloromethylene- or 3-C-dichloromethyl-1,2 : 5,6-di-O-isopropylidene-α-d-furanose derivatives.
Synthesis and Mercurophilic Properties of 2,2′-Oxybis(ethylenethio)ditropone and α-[2-(2-Troponylthio)ethyl]-ω-(2-troponylthio)oligo(oxyethylene)
Authors: Kubo Kanji , Mori Akira , Takeshita Hitoshi
Published: June 2006

The condensation reactions of 2-(p-tolylsulfonyloxy)tropone with 2,2′-oxydiethanethiol and its α-(2-sulfanylethyl)-ω-sulfanyloligo(oxyethylene) derivatives afforded 2,2′-oxybis(ethylenethio)ditropone and α-[2-(2-troponylthio)ethyl]-ω-(2-troponylthio)oligo(oxyethylene). Reflecting the acyclic nature of the polyethylene glycol moiety, they formed the complexes with various metal ions. Among them, mercury(II) salts were exclusively transported through a liquid membrane at least under the conditions used.
Effects of Solvent Fluctuations on the Rate of the Thermal Z/E Isomerization of N-Benzylideneanilines in a Highly Viscous Liquid Hydrocarbon
Authors: Asano Tsutomu , Matsuo Kohei , Sumi Hitoshi
Published: June 2006

The effects of the solvent viscosity on the thermal Z/E isomerization of three substituted N-benzylideneanilines were studied in a nonpolar aprotic solvent, 2,4-dicyclohexyl-2-methylpentane. By increasing the pressure to several hundred megapascals, the viscosity of the reaction system was raised high enough to retard the isomerization. The viscosity dependence of the observed rate constant was analyzed by assuming a two-step mechanism based on the two-dimensional reaction-coordinate model proposed by one of the present authors. The rate constant of this mechanism is given by 1/(kTST−1 + kf−1), where kTST represents the rate constant expected from the transition state theory, while kf (>0) represents the part controlled by a solvent rearrangement during thermal fluctuations. The kf values were inversely proportional to a fractional power of the viscosity, in agreement with the theory. It was also found that, compared at the same temperature and viscosity, the kf values in the present solvent are larger than those in a polar aprotic solvent, glycerol triacetate, and in a polar protic solvent, 2-methyl-2,4-pentanediol, reported earlier.
Generation and Trapping of Bis(dialkylamino)silylenes: Experimental Evidence for Bridged Structure of Diaminosilylene Dimers
Authors: Sakamoto Kenkichi , Tsutsui Shinobu , Sakurai Hideki , Kira Mitsuo
Published: June 2006

Reduction of dichlorobis(diisopropylamino)silane and dichlorobis(cis-2,6-dimethylpiperidino) silane by alkali metals gave the corresponding bis(diisopropylamino)silylene and bis(cis-2,6-dimethylpiperidino)silylene, respectively. These were successfully trapped by toluene and benzene as well as by hydrosilane, olefin, and acetylene. As the first evidence for the existence of the bridged-dimer of the diaminosilylenes, we have found scrambling of the amino-substituents on a silicon atom during the simultaneous generation of two different bis(dialkylamino)silylenes in benzene. Diaminosilyenes generated thermally from the other new precursors designed here gave no evidence for the bridged dimer, due to the high temperature required for the generation.
The Catalytic Fries Rearrangement and o-Acylation Reactions Using Group 3 and 4 Metal Triflates as Catalysts
Authors: Kobayashi Shu , Moriwaki Mitsuhiro , Hachiya Iwao
Published: June 2006

Group 3 and 4 metal triflates (Sc(OTf)3, TiCl(OTf)3, Zr(OTf)4, and Hf(OTf)4) were found to be efficient catalysts in the Fries rearrangement of phenyl or 1-naphthyl acylates. It was also found that the o-acylation (direct acylation) reactions of phenols and 1-naphthols with acid chlorides proceeded smoothly in the presence of the triflates. Both reactions were successfully carried out using small amounts of the triflates (catalytically), and comparison of catalytic activities of these metal triflates in these reactions is discussed.
Living Radical Polymerization of Styrene in the Presence of 4-Hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, and Radical Transformation of the Resulting Polymer by Other Radicals
Authors: Yoshida Eri , Okada Yasushi
Published: June 2006

Radical polymerization of styrene was performed by benzoyl peroxide (BPO) as an initiator, in the presence of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (HTEMPO) at 95 °C for 3.5 h, and then continued at 125 °C for another designated period. The polymerization was found to proceed in the accordance with a living mechanism, because the molecular weight of the polystyrene was in proportion to the conversion and was in inverse proportion to the initial concentration of HTEMPO. Further, it was found that all the resulting polystyrene had the HTEMPO moiety at their chain ends and that the initial concentration of HTEMPO determined the molecular weight of the polymer produced, from 1H NMR analysis. The radical transformation of the HTEMPO-modified polystyrene by 4-methoxy-TEMPO (MTEMPO), was also performed. The transformation proceeded to give the polystyrene with MTEMPO moiety at the chain end, although the degree of the transformation decreased over time. It was found that decomposition of the MTEMPO-modified polystyrene obtained by the reaction occurred during the reaction.
Preparation of SiO2–ZrO2–Na2O Porous Glass Supports
Authors: Tsurita Yasushi , Wada Keisuke
Published: June 2006

A new method for preparing porous supports was investigated by heating a sol-gel-derived SiO2–ZrO2 and SiO2–TiO2 microspherical gel in the presence of NaCl. In the SiO2–ZrO2 system, the surface of the products comprised a sponge-like structure similar to the porous glasses manufactured by the phase-separation method. Their pore volume ranged from 1.48 to 3.18 cm3 g−1 and the surface area ranged from 10 to 48 m2 g−1. They contained a significant amount of Na2O, whereas the Cl content was less than 0.1 wt%. The alkaline durability was excellent, as was expected from the composition of SiO2–ZrO2–Na2O. On the contrary, a heat treatment of the sol-gel-derived SiO2–TiO2 microspherical gel, together with NaCl, caused crystallization of titania and silica, and the formation of glassy mixed oxide was not observed.
Conformational Studies of Some 1-Hetera-2,6-diphenylcyclohexan-4-one Oximes Using NMR Spectra-Evidence for Boat Form Contributions to trans-2,6-Diphenyl Systems
Authors: Gurumani Venkataraman , Pandiarajan Karuppiah , Swaminathan Meenakshisundaram
Published: June 2006

1H NMR spectra have been recorded for cis- and trans-2,6-diphenyltetrahydrothiopyran-4-ones (1 and 5), cis- and trans-2,6-diphenyltetrahydropyran-4-ones (2 and 6), 3-methyl- and 3-ethyl-2,6-diphenyltetrahydropyran-4-ones (3 and 4) and their oximes (7 — 12) at 270 MHz. For the oximes, 13C NMR spectra have also been recorded. The coupling constants suggest that the oximes 7, 8, 9, and 10, which have the phenyl groups in cis orientation, largely exist in chair conformations with equatorial disposition of the substituents. Analysis of the vicinal coupling constants of trans-2,6-diphenyltetrahydrothiopyran-4-one oxime (11) suggests that boat forms 11c and 11d must make significant contributions to it. Moreover, chair conformation 11a, which has the axial phenyl group in the syn-side, should be more populated than chair conformation 11b, which has the axial phenyl group in the anti-side. These conclusions are corroborated using 13C chemical shifts. The NOESY spectrum of 11 gives definite evidence for the contribution of 11c. The coupling constants of 12 suggest that the chair conformation 12a with axial phenyl group in the syn-side should be more populated than chair conformation 12b with the axial phenyl group in the anti-side. By analogy boat form should contribute to 12 also.
Conformational Studies Using Molecular Mechanics on Model Peptides with 1-Aminocycloalkane 1-Carboxylic Acid Residues
Authors: Rao Shashidhar N , Chan Ming Fai , Balaji Vitukudi N
Published: June 2006

Peptides with conformationally restricted 1-aminocyclopropane-1-carboxylic acid (Acc3) moieties were previously shown to exhibit preference for γ-turn structures in the solution phase and solid phase. We present conformational energy calculations on model compounds containing 1-aminocycloalkane carboxylic acid with 4, 5, and 6-membered rings using molecular mechanics methods. The low-energy models adopt conformations characteristic of a variety of regular structures, such as the α-helix, γ-turn, and polyproline-II-type three- and four-fold helices. The energetically most favored models adopt the γ-turn (2.27 helix) conformation in the model peptide of 1-aminocyclobutane-1-carboxylic acid (Acc4), similar to Acc3 peptides, while they adopt the α-/310-helical conformation (of either handedness) in the corresponding compounds with cyclopentane (Acc5) and cyclohexane (Acc6). The salient features of our investigations are qualitatively consistent with the crystal structures of peptide analogs containing Acc4, Acc5, and Acc6 and the previously reported solution phase and conformational studies on peptides containing Acc5. Our results have implications for the design of γ-turn and α-/310-helical peptidomimetics.
Surface Enhanced Raman Spectroscopic Study of 2- and 3-Bromothiophenes in Silver Hydrosol
Authors: Mukherjee Kana M , Misra T N
Published: June 2006

Surface enhanced Raman spectra (SERS) of 2- and 3-bromothiophene molecules in silver sol are compared with those of molecules in acetonitrile solution. The experimental results suggest that the 2-isomer is adsorbed on the metal surface through both the sulfur and the bromine atoms, with the thiophene molecular plane almost normal to the surface, whereas the 3-isomer is adsorbed principally through the sulfur atom. The Raman excitation profile of the molecules in the surface adsorbed state follows surface plasmon resonance frequency, reflecting the contribution of classical electromagnetic effect to SERS in silver sol. The observed “first layer effect”, i.e. maximum enhancement on a monomolecular layer formation on the metal surface, suggests charge transfer contribution to SERS of these molecules. Further, appearance of Ag–Br and Ag–S stretching modes in the SER spectra of 2-isomer indicates chemisorption of the adsorbate molecules on the metal surface.