Novel diterpenoid diacylglycerols from marine molluscs: potent morphogens and protein kinase C activators

Five novel 1,2-sn-diacylglycerols with diterpenoid acyl moieties in the sn-1 position were isolated and characterized, together with the corresponding 1,3-sn-diacylglycerols, from three species of dorid nudibranchs molluscs. Their potent activity as morphogens in vivo in the Hydra tentacle regeneration assay and their parallel activity as activators of rat brain protein kinase C (PKC) in vitro are reported here. Our findings promote the use of these compounds as useful molecular probes for both in vivo and in vitro studies on the participation of PKC in cell development.     

Performance model of interactive video-on-demand systems

An interactive video-on-demand (VoD) system allows users to access video services, such as movies, electronic encyclopedia, interactive games, and educational videos from video servers on a broadband network. This paper develops a performance evaluation tool for the system design. In particular, a user activity model is developed to describe the usage of system resources, i.e., network bandwidth and video server usage, by a user as it interacts with the service. In addition, we allow batching of user requests, and the effect of such batching is captured in a batching model. Our proposed queueing model integrates both the user activity and the batching model. This model can be used to determine the requirements of network bandwidth and video server and, hence, the trade-off in communication and storage costs for different system resource configurations     

Improved accuracy of burn wound assessment using laser Doppler

The utility of the laser Doppler for determining burn depth has been questioned because of problems with technology and methodology. This study prospectively evaluates the ability of a new laser Doppler technique to predict burn healing time. Using the Periflux System 4000 laser Doppler, readings were taken on 305 burns (147 patients) on postburn day 3 or 4. Sixty-six wounds were used to derive a predictive function (phase I) and 152 wounds were used to test the function (phase II). Blood flow dynamics (flux), microvascular dilation capacity of the wounds to beat stress, and flow motion wave pattern (vasomotion) were studied using the laser Doppler, and seven parameters were evaluated to determine their relative contribution to the prediction of healing time. These parameters are hyperemic flux (flux value after heating to 42 degrees C), average hyperemic wave amplitude (AHWA), number of average flux units >100(F100), number readings with wave amplitude 75 (A5), average flux change (AFC), percentage of average flux increase, and relative flow capacity (RFC = AFC/average hyperemic flux). After readings were made, the wounds were observed and divided into two groups: those that healed in less than 14 days and those that healed or were grafted after 14 days. A step-wise discriminant analysis was used to assess the relative contribution of the Doppler-derived measures to healing time prediction. AHWA, F100, and RFC were included in the final discriminant function explaining 72% of the healing time variance (Wilks' lambda value 0.28; p value <0.0001). Predicted outcome = 0.05(AHWA) + 0.31(F100) + 5.0(RFC) - 2.3. With this derived function, there is 94% accuracy in the prediction of burn wound healing time compared with a physician predictive accuracy of 70%.     

Dependence of attenuation in a vegetation canopy on frequency andplant water content

Theory is presented to provide insight into the observation that attenuation through vegetation is proportional to vegetation water content. In this analysis, the canopy is modeled as a sparse layer of randomly oriented particles (leaves, stalks, etc.) over a flat, homogeneous ground plane (soil) and an expression is obtained for the “optical depth”. The formulas developed by Ulaby and El Rayes are used to relate this expression to the water content of the canopy. In the low frequency extreme (Rayleigh scatterers), the attenuation varies almost linearly with water content and inversely with wavelength. In contrast, in the high frequency limit, the attenuation is independent of both water content and frequency, in between, geometry dependent “resonances” occur even at the low frequency end of the microwave spectrum (e.g. L-band) making the dependence of attenuation on frequency and water content specific to canopy architecture     

Properties of cast austenitic materials for light water reactors

Primary piping elbows of ligh water reactors are made of cast austeno-ferritic materials (grade CF8 or CF8M) which are susceptible to embrittlement by thermal ageing in service. Ageing kinetics depends on chromium content and on the temperature. The effect of ageing on mechanical properties is determined by the decreasing of Charpy-U energy. It is shown that the rupture of such aged material comes from a combination of cleavage of the ferrite and shearing or ductile tearing of austenite ligaments. The fracture toughness is determined by J-R curves, which exhibit a large scatter related to the solidification macrostructure of the steel. It is shown that J-R curves are independent of the geometry of the specimens.     

Control of calcium hexaluminate grain morphology in in-situ toughened ceramic composites

The influence of processing conditions on the morphology of calcium hexaluminate (CA₆) grains in Al₂O₃: 30 vol% CaO·6Al₂O₃ (CA₆) ceramic composites was investigated. Specimens were prepared by in-situ reaction sintering using precursor powders of alumina, and either calcium carbonate or calcium oxide. In some samples, 1 vol% anorthite glass was added as a sintering aid. X-ray diffraction was used to study the phase development in the as-calcined and sintered states. The resultant microstructures were characterized using both scanning electron microscopy (SEM), and imaging secondary ion mass spectrometry (SIMS). It was found that the CA₆ grains developed a platelike morphology when CaCO₃ was used as the starting calcium-rich powder. In contrast, samples prepared using CaO resulted in equiaxed CA₆ grains. This result was observed to be independent of the anorthite glass addition. The findings are rationalized in terms of distinct CA₆ reaction mechanisms, resulting from differences in the reactivity of the powders during the early stages of calcining.Cement Nomenclature C CaO - A Al₂O₃     

AC measurements of the minimum longitudinal resistance of a QHEsample from 10 Hz to 10 kHz

AC measurements of the longitudinal resistance, R_xx, of a quantum Hall effect (QHE) sample have been made in a frequency range from 10 Hz to 10 kHz. The results show no frequency effect on the minimum value of R_xx corresponding to the quantum numbers i=2 and i=4, within the measurement resolution of 0.5 mΩ. Therefore, the influence of frequency on the value of the quantized Hall resistance, R_H, should not exceed a few parts in 10⁹ . Some unwanted effects detected during the development of the resistance bridge have been pointed out     

Coriolis effects in the dynamics of a rotating elastic structure

Summary Small oscillations of a rotating elasticum with a mass at the free end are investigated with Poincaré-Lindstedt series. It is shown that the mass moves on a figure-eight shaped curve in a direction determined by the sign of the angular velocity and hence that the Coriolis force influences the motion.     

Process optimization and related material properties of silicon films produced by laser-induced chemical vapour deposition from silane

Laser-induced chemical vapour deposition of silicon films on SiO₂/Si (1 0 0) and Si (1 0 0) substrates was studied using ArF laser irradiation of silane/argon gas mixture in parallel to the substrate. The optimal deposition conditions were specified by examination of film morphology at a wide range of irradiation and process parameters. At optimal conditions, specular films were obtained with no powder formation. The effect of deposition parameters, such as laser energy and repetition rate, on the deposition rate and the related film quality, was investigated.