A numerical bifurcation study of friction effects in a slip-controlled torque converter clutch

Friction plays a key role in the efficiency and stability of the slip-controlled torque converter clutches. The effects of friction on the dynamics and stability of a slip-controlled torque converter clutch system using a bifurcation-analysis-based approach is presented in this paper. A three degree-of-freedom nonlinear driveline model with integral feedback action to control the clutch slip speed has been utilized for this study. The clutch interface friction is dependent on the slip speed and is a function of the static friction constant, μ ₀, the low velocity friction constant μ ₁, and the low velocity exponential rate, γ. Using one-parameter numerical continuation, local Hopf bifurcations of the subcritical type are observed as the friction parameters μ ₁ and γ were varied at low slip speeds. The continuation results are verified using simulations of the full nonlinear model. Stick-slip and undesirable oscillations of the model inertia elements are observed for certain parameter values. As the slip speed is increased, the bifurcation instability occurs at an increasingly higher value of μ ₁ signifying an improved tolerance of negative friction gradient at higher slip speeds. Smaller exponential rates γ are tolerated at higher slip speeds before the bifurcation instability occurs. For the range of parameter values considered, no bifurcations occur for a slip speeds higher than 3.4 and 4.5 rad/s with μ ₁ and γ as the continuation parameters, respectively. These values of slip speeds are much lower than the system’s first mode of torsional vibration of 16 Hz (≈100 rad/s).     

Track shapes,etching characteristics and track density distribution on different planes of apatite

Abstract

Studies concerning track shapes, etching characteristics and track density due to spontaneous fission of uranium along various crystallographic planes of apatite are represented. The studies were carried out on large complete crystals as well as on small grains of apatite belonging to various geological origins. Three track types (hexagonal, pyramidal and needle type) have been identified along various crystallographic planes.     

Low cost anisotropic etching of monocrystalline Si (1 0 0): Optimization using response surface methodology

Reduced surface reflectance and enhanced light trapping is required by any high efficiency solar cell. Anisotropic etching was done on silicon (1 0 0) by using tetramethyl ammonium hydroxide TMAH, (CH₃)₄NOH, solution at 85 °C. Process variables considered were solution concentration and time proposed by response surface methodology (RSM). An effective surface texture was resulted with reflectance less than 8% without antireflection coating. The antireflection mechanism was also co-related with the etch rate of Si. Optimized values predicted by RSM for time and TMAH concentration were 5 min and 3.50% respectively. The technique and optimization of parameters by using response surface methodology (RSM) could be valuable in the texturization process for high-efficiency Si solar cells.     

An unprecedented ortho effect in mass spectrometric fragmentation of even-electron negative ions from hydroxyphenyl carbaldehydes and ketones

A mass spectrometric peak for a carboxylate anion is observed in collision-induced dissociation (CID) mass spectra recorded from negative ions derived from ortho isomers of hydroxyphenyl carbaldehydes and ketones. For example, CID spectra of 2-hydroxy derivatives of benzaldehyde, acetophenone, propiophenone, isobutyrophenone, and pivalophenone show peaks at m/z 45, 59, 73, 87, and 101 for the formate, acetate, propionate, isobutyrate, and pivalate anions, respectively.     

Iterative introduction of integral approximations with error bounds in SCF calculations

Another possible application of a previously reported approximation theory for electron repulsion integrals using rigorous error bounds is considered by incorporating the electron density matrix in the approximation scheme. Error bounds are set on the contribution of a given integral to the total energy for a given molecular wave-function; the wave-function is then refined cyclically and additional integrals are computed exactly if necessary until convergence is achieved.     

Triterpenoids from the stembark of Pyrus communis

Three triterpenoids were isolated from the stem bark of Pyrus communis Linn. and identified as lup-20(29)-ene-3alpha, 27-diol (1), lup-20(29)-ene-3alpha-ol (2) and lup-20(29)-ene-3alpha, 28-diol (3) on the basis of spectral and chemical analysis. The Compound (1) is a novel triterpene, being reported first time by us.     

N-acetyl-beta-D-glucosaminidase in acute myocardial infarction

The objective of the study was to investigate whether the lysosomal enzyme, N-Acetyl-beta-D-glucosaminidase (NAG) activity is increased in plasma of patients with acute myocardial infarction (AMI) and to determine if there is any association between plasma levels of NAG and severity of myocardial infarction (MI). NAG activity in plasma was monitored in 69 patients with AMI and 135 normal healthy subjects using a spectrofluorimetric method. A modified Aldrich ST elevation score was used to gauge the severity of MI in terms of size of the infarct. Plasma NAG levels in AMI patients and normal healthy subjects were found to be 10.92+/-7.5 U/l and 6.8+/-2.2 U/l, respectively. These two mean value when compared by Student's t-test were significantly different P = 0.0001. No statistically significant differences in NAG activity were observed in patients in terms of gender, age, location of infarct, time from onset of chest pain to blood sampling in the hospital and size of the infarct.     

Low-energy collision-induced fragmentation of negative ions derived from ortho-, meta-, and para-hydroxyphenyl carbaldehydes, ketones, and related compounds

Collision-induced dissociation (CID) mass spectra of anions derived from several hydroxyphenyl carbaldehydes and ketones were recorded and mechanistically rationalized. For example, the spectrum of m/z 121 ion of deprotonated ortho-hydroxybenzaldehyde shows an intense peak at m/z 93 for a loss of carbon monoxide attributable to an ortho-effect mediated by a charge-directed heterolytic fragmentation mechanism. In contrast, the m/z 121 ion derived from meta and para isomers undergoes a charge-remote homolytic cleavage to eliminate an *H and form a distonic anion radical, which eventually loses CO to produce a peak at m/z 92. In fact, for the para isomer, this two-step homolytic mechanism is the most dominant fragmentation pathway. The spectrum of the meta isomer on the other hand, shows two predominant peaks at m/z 92 and 93 representing both homolytic and heterolytic fragmentations, respectively. (18)O-isotope-labeling studies confirmed that the oxygen in the CO molecule that is eliminated from the anion of meta-hydroxybenzaldehyde originates from either the aldehydic or the phenolic group. In contrast, anions of ortho-hydroxybenzaldehyde and 2-hydroxy-1-naphthaldehyde, both of which show two consecutive CO eliminations, specifically lose the carbonyl oxygen first, followed by that of the phenolic group. Anions from 2-hydroxyphenyl alkyl ketones lose a ketene by a hydrogen transfer predominantly from the alpha position. Interestingly, a very significant charge-remote 1,4-elimination of a H(2) molecule was observed from the anion derived from 2,4-dihydroxybenzaldehyde. For this mechanism to operate, a labile hydrogen atom should be available on the hydroxyl group adjacent to the carbaldehyde functionality.