Structure of a Plane Shock Layer

The structure of a plane shock wave is discussed and the expected range of applicability of the Navier‐Stokes equations within the shock layer is outlined. The shock profiles are computed using the Bhatnagar‐Gross‐Krook model of the Boltzmann equation and a uniformly converging iteration scheme starting from the Navier‐Stokes solution. It is shown that the Navier‐Stokes solution remains a good approximation in the high‐pressure region of the shock layer up to approximately the point of maximum stress for all shock strengths. In the low‐pressure region, the correct profiles deviate with increasing shock strength from the Navier‐Stokes solution. The physical significance of the kinetic model used and the relation of the present study to previous theoretical and experimental work is discussed

A simple dynamical system that mimics open-flow turbulence

The possible relevance of recent theories concerning the chaotic behavior of nonlinear dynamical systems to turbulence, especially in open flows, has frequently been questioned. Here, the issues that have led to this skepticism are investigated by studying a simple system that has been devised to include, albeit in an impressionistic way, the major mechanisms that are widely considered to operate in a broad class of turbulent flows. The variables in the system seek to represent the amplitudes of large- and small-eddy motion, respectively, and are governed by equations that allow for a Landau–Stuart nonlinear growth, a one-step Richardson cascade, and a specified time-dependent driving force. It is found that the critical value (at the onset of chaos) of the Reynolds-number-like control parameter (nu−1) in the system depends on the character and magnitude of the driving force; and it is analytically demonstrated using the Melnikov technique that, with an appropriate choice of model parameters, chaos can persist at all sufficiently high values of the model Reynolds number (unlike as in most other low-dimensional models). The routes to chaos in the system when the forcing is increased at fixed nu are different from those when nu is decreased at fixed forcing, the latter being found to be more relevant to the case of streamwise-developing flows like a boundary layer. The observed routes are sensitive to the presence of even small stochastic components in the forcing. Computed spectral evolutions in the model show qualitative similarities with observations in boundary layer flow under different disturbance environments. It is concluded that many of the gross features of open-flow turbulence can be understood as dynamical chaos

Molecular Polarisabilities and Orientational Order Parameters od Binary Mesophase Mixtures of Nematic Compounds

Molecular Polarisabilities and Orientational Order Parameters od Binary Mesophase Mixtures of Nematic Compound

Prolonged treatment with vitamin D in postmenopausal women with primary hyperparathyroidism

Introduction/background: Vitamin D deficiency further increases circulating parathyroid hormone (PTH) levels in patients with primary hyperparathyroidism (pHPT), with potential detrimental effects on bone mass. Methods: This was an observational clinical study in consecutive conservatively treated postmenopausal women (n=40) with pHPT and coexistent 25-hydroxyvitamin D deficiency (25OHD ≤50 nmol/l (≤20 ng/ml)). Patients who showed an increase in serum 25OHD above the threshold of vitamin D deficiency (>50 nmol/l; n=28) using treatment with various commonly prescribed vitamin D preparations were, for the purposes of statistical analyses, allocated to the treatment group. Patients who were retrospectively identified as having received no treatment with vitamin D and/or remained vitamin D deficient were considered as non-responders/controls (n=12). Adjusted calcium (adjCa), PTH and 25OHD concentrations were monitored in all subjects up to 54 months (mean observation period of 18±2 months). Results: Prolonged increased vitamin D intake, regardless of the source (serum 25OHD, increase from 32.2±1.7 nmol/l at baseline to 136.4±11.6 nmol/l, P0.73). In contrast, serum PTH remained unchanged (15.8±2.6 vs 16.3±1.9 pmol/l, P=0.64) in patients who remained vitamin D deficient, with a significant difference between groups in changes of PTH (P=0.0003). Intrapartial correlation analyses showed an independent negative correlation of changes in 25OHD with PTH levels (r ic=−0.41, P=0.014). Conclusions: Prolonged treatment with vitamin D in various commonly prescribed preparations appeared to be safe and significantly reduced PTH levels by 21%

Molecular Polarisabilities and Orientational Order Parameters od Binary Mesophase Mixtures of Nematic Compounds

Molecular Polarisabilities and Orientational Order Parameters od Binary Mesophase Mixtures of Nematic Compound

Image processing and statistical analysis of microstructures of as plasma sprayed Alumina–13 wt.% Titania coatings

Plasma spraying of Alumina-13 wt.% Titania coatings in the as sprayed conditions show preferentially stabilized α phase. The morphology of this residual α phase are of two types a partially melted particle type prevailing as rounded or nearly spherical shaped form and the other splats type, a disc shaped caused by the high impact and rapid solidification of the fully molten plume. While the former is totally deleterious to the mechanical properties the latter type of morphology is found to strengthen and toughen the matrix due to the inherent larger stiffness of the residual α phase and also as a result of effective operation of toughening mechanisms such as crack bridging and crack deflection. In this paper an attempt has been made with image analysis to establish the individual constituent features of the complicated as sprayed microstructure. Statistical techniques such as correlation and discriminant analysis were used to group the micro structural features based on the process parameters. Our analysis indicates that for maximum contrast situations in process variables such as extreme values of primary current and widely different substrate material the micro structural features can be easily discriminated and separated into groups. The absence of significant correlation between the micro structural features within a group could also be verified. Our analysis indicates a large negative correlation value for partially melted particles and residual α occurring as splats with the process parameter the primary current of the thermal plasma

Half an hour versus three hour contact of topical steroid (clobetasol propionate)

BACKGROUND: Steroids when left on the skin for longer duration may contribute to the side effects without any additional clinical benefit. The relationship between the duration of topical steroid contact with the skin and its effectiveness has not been established. The ability of the topical steroids to inhibit the size of histamine induced wheal was used to assess their relative efficacy. AIM: To determine whether half an hour contact and three hour contact of a topical steroid, clobetasol propionate, is equally effective in inhibiting the size of the histamine induced wheal. METHODS: On 30 volunteers, 4 squares were marked on flexor aspect of both forearms using a template. One fingertip unit of clobetasol propionate 0.05% was applied on all the areas. Half an hour later all areas of left forearm and last square of right forearm were wiped. Prick testing was done with histamine and size of wheal recorded after 15 minutes. Similarly steroid was wiped from the 1st, 2nd, 3rd square after 1 hr, 2 hr and 3 hrs on right forearm and the corresponding areas prick tested on both forearms. RESULTS: There was statistically significant wheal suppression at the end of 2 hrs and 3hrs as compared to half an hour. CONCLUSION: We conclude that half an hour application of clobetasol propionate is ineffective and that it is effective only after two hours of contact and hence short contact of half an hour will be less effective than relatively prolonged contact of 2 hours