An experimental investigation of flow parameters inside a spherical swirl pre-chamber of a diesel engine under motoring condition

 The main aim of the present investigation is to experimentally study the flow parameters inside a spherical combustion chamber of an indirect injection diesel engine. For this a spherical chamber has been fitted in the cylinder head. Using a constant temperature hot-wire anemometer, measurements have been made under non-firing condition at 400 and 500 rpm during compression stroke. Mean velocity and turbulence intensity values are evaluated from the hot-wire signal. Measurements are made at three axial planes, six angular locations and four radial positions. Large variations of mean velocity and turbulence intensity have been observed within the chamber. From the measurements, the mean velocity and turbulence intensity are found to be maximum at 30° before compression TDC and these values are found to decrease towards the centre of the pre-chamber. The mean velocity and turbulence intensity distribution with respect to various locations and crank angles are presented and discussed. Received: 7 November 1995/Accepted: 26 October 1997     

Student Difficulties with Accessing and Using Mathematical Knowledge

This article examines the issue of why students fail to activate and use mathematical knowledge during problem solving when it is known that they possess the required knowledge. This issue is explored by analyzing problem-solving attempts of a high-achieving student and a low-achieving student in the domain of plane geometry. On the basis of these data and other literature, three major sources of mathematical knowledge-access difficulties are identified that might be considered by classroom teachers, including a student's (1) dispositional state, (2) management of the problem-solving process, and (3) state of organization of his or her mathematical knowledge. It is argued that teaching practices that place emphasis on careful management of problem-solving activity could help students activate and extend the use of mathematical knowledge acquired in lesson activities.     

Synthesis,characterization and biological evaluation of manganese(II), cobalt(II), nickel(II), copper(II), and cadmium(II) complexes with monobasic (NO) and neutral (NN) Schiff bases

New complexes of Mn^II, Co^II, Ni^II, Cu^II, and Cd^II with bis(acetophenone) ethylenediamine and 5-chlorosalicylideneaniline or 5-bromosalicylideneaniline have been prepared and characterized on the basis of elemental analyses, thermogravimetric analyses, magnetic measurements, electronic and i.r. spectra. The antimicrobial activities of the complexes, ligands, control (dimethyl formamide) and metal salts were tested against Salmonella typhi (bacteria), Saccharomyces cerevisae (yeast), and two fungal species Lasiodiplodia theobromae and Fusarium oxysporum. The results are discussed.     

The quasi-equilibrium phase of nonlinear chains

We show that time evolution initiated via kinetic energy perturbations in conservative, discrete, spring-mass chains with purely nonlinear, non-integrable, algebraic potentials of the formV(x _i − x _i +1) ∼ (x _i − x _i+1 ) ²ⁿ ,n ≥ 2 and an integer, occurs via discrete solitary waves (DSWs) and discrete antisolitary waves (DASWs). Presence of reflecting and periodic boundaries in the system leads to collisions between the DSWs and DASWs. Such collisions lead to the breakage and subsequent reformation of (different) DSWs and DASWs. Our calculations show that the system eventually reaches a stable ‘quasi-equilibrium’ phase that appears to be independent of initial conditions, possesses Gaussian velocity distribution, and has a higher mean kinetic energy and larger range of kinetic energy fluctuations as compared to the pure harmonic system withn = 1; the latter indicates possible violation of equipartition.     

Compensation differences between male and female CEOs for publicly traded firms: a nonparametric analysis

A recent article in the popular press suggested that gender is one determining factor of corporate executives' pay. The average compensation for the top 20 men was more than 10 times larger than for the top 20 women. We would expect, however, that direct compensation from salary and bonuses would be similar for both genders given the public nature of the data. There have been few academic articles on the topic of gender pay differences among top executives. One paper found marginally significant statistical evidence that women CEOs are paid more than their male counterparts. In this paper, we extend the literature by looking at compensation differences of male and female CEOs. Our sample includes over 40 female CEOs for publicly traded companies and matched pairs of comparable male CEOs. In addition, we use data envelopment analysis to derive a gap measure representing the difference between male and female compensation. The results suggest that there is a statistical difference between male and female potential compensation.     

Spline Approximation Method for Solving Self-Adjoint Singular Perturbation Problems on Non-Uniform Grids

A numerical method based on cubic spline with adaptive grid is given for the self-adjoint singularly perturbed two point boundary value problems. The scheme derived in this method is second order accurate. Numerical examples are given to support the predicted theory.     

A mathematical model to describe the change in the constitutive character of blood due to platelet activationUn modèle mathématique décrivant le changement du caractère constitutif du sang dû à l'activation des plaquettes

Though a minor component by volume, platelets can have a profound influence on the flow characteristics of blood and thereby have serious consequences with regard to cardiovascular functions. Platelets are extremely sensitive to chemical agents as well as mechanical inputs and platelet activation is a necessary precursor to many life threatening medical conditions such as acute myocardial infarction, most strokes, acute arterial occlusion, venous thrombosis and pulmonary embolism. In cardiovascular devices such as ventricular assist devices and prosthetic heart valves, high shear stresses can trigger platelet activation. Moreover, such devices have artificial surfaces that are thrombogenic, the thrombotic deposition contributing to the failure of the device. Thus, there is a need to develop a mathematical model for the flow of blood that takes into account platelet activation, no such model being available at the moment. While there has been considerable amount of work in blood rheology, the role of platelets in the flow characteristics of blood has been largely ignored. This study addresses this lacuna. To cite this article: M. Anand, K.R. Rajagopal, C. R. Mecanique 330 (2002) 557–562.     

Oxidation of cinnamic acid derivatives: A pulse radiolysis and theoretical study

We introduce an algorithm to solve the secular equation that arises in the time independent multimode expansion of the quadratic vibronic coupling problem in parallel. The implementation can handle expansions of arbitrary length, with the open-ended character of the algorithm achieved through the use of fine grained parallelism to partition the trial vectors. The characteristics of the algorithm are discussed and its utility is illustrated by determining a model photoelectron spectrum of the ethoxy radical (C₂H₅O) using a vibronic expansion involving more than 1 billion vibronic basis states. This calculation also represents the first determination of a photoelectron spectrum obtained using a diabatic Hamiltonian obtained with a recently introduced ab initio surface reshaping procedure.     

Quantitative TLC Analysis of Sterol (24β-Ethylcholesta-5,22E,25-triene-3β-ol) in Agnimantha (Clerodendrum phlomidis Linn)

A quantitative method using silica gel 60F₂₅₄ high performance thin layer chromatography plates, automated bandwise sample application, and automated visible mode densitometric method has been developed for the determination of 24β-ethylcholesta-5,22E,25-triene-3β-ol (ECTO) in the aerial part of Clerodendrum phlomidis. ECTO was used as a chemical marker for the standardization of C. phlomidis plant extracts. The separation was performed on silica gel 60F₂₅₄ TLC plates using chloroform-methanol (98.5: 1.5, v/v) as mobile phase. The quantitation of ECTO was carried out using the densitometric reflection/absorption mode at 650 nm after post chromatographic derivatization with anisaldehyde reagent. A precise and accurate quantification can be performed in the linear working concentration range of 150–400 ng band⁻¹ with good correlation (r ² = 0.996). The method was validated for peak purities, precision, robustness, limit of detection (LOD) and quantitation (LOQ), etc. as per ICH guidelines.     

Medium-Chain Fatty Acids (MCFA) Production Through Anaerobic Fermentation Using <Emphasis Type="Italic">Clostridium kluyveri</Emphasis>: Effect of Ethanol and Acetate

Medium-chain fatty acids (MCFA) are saturated monocarboxylic acids and can be used as antimicrobials, corrosion inhibitors, precursors in biodiesel, and bioplastic production. In the present study, MCFA production was evaluated with acetate and ethanol using the bacteria Clostridium kluyveri. Effects of substrate, electron donor, and methane inhibitor on MCFA production were evaluated. Bacteria successfully converted the ethanol and acetate to butyrate (C4), caproate (C6), and caprylate (C8) by chain elongation process. The highest concentrations of butyrate (4.6 g/l), caproate (3.2 g/l), and caprylate (0.5 g/l) were obtained under methane inhibition conditions than other conditions. The productions of butyrate and caproate were 1.6 and 1.48 times higher under methane inhibition conditions, respectively. Results denoted that the bacteria C. kluyveri can be used for conversion of acetate and ethanol into useful products like butyrate and caproate.