A model of a liquid droplet impinging on a high-temperature solid surfaces

The paper deals with a model of a liquid droplet vertically impinging on a heated solid surface. The model uses the following assumptions. The value of the wall temperature is taken to be such that the droplet-wall interaction would proceed via gas-vapor interlayer (T 400 °C). The droplet liquid is incompressible and nonviscous. The droplet surface is taken to be free, with its deformation caused by the effect of external pressure distributed over the droplet surface. The pressure is made up by two components, of which the first one is the surface tension pressure due to the curvature of the droplet surface; the second component is the pressure of vapor between the droplet and wall, which is determined by analyzing the process of vapor escape from the vapor interlayer. The motion of liquid within the droplet is taken to be potential and axisymmetric. The equations of droplet motion are solved relative to the potential of the vector field of velocity. The suggested model is used to perform numerical calculations of the droplet collision process, and the obtained results are compared with the data of other authors.Translated from Teplofizika Vysokikh Temperatur, Vol. 42, No. 6, 2004, pp. 921–927.Original Russian Text Copyright © 2004 by A. V. Gulikov, I. I. Berlin, and A. V. Karpyshev.     

Development of chemical sensors based on redox-dependent receptors: N,N'-dimethyldiazapyrenium-modified electrodes

Electrodes modified with Nafion films containing 2,7-dimethyldiazapyrenium (DAP2+) were prepared and characterized with voltammetry by themselves and in the presence of organic substrates. The large, planar, electron-poor aromatic surface in DAP2+ facilitates pi-stacking interactions with other planar aromatic molecules, particularly those that are negatively charged or electron-rich. Previous studies showed that the reduction of DAP2+ decreases the strength of these interactions, making the binding redox-dependent, and resulting in negative shifts in the E(1/2) of DAP2+/+. This study shows that the redox-dependent binding ability of DAP2+ is retained in Nafion, but the selectivity is considerably different. Most significantly, the electron-rich, neutral aromatic compounds that produced small shifts in the E(1/2) of DAP2+/+ in solution cause much larger shifts, up to -110 mV, with the modified electrodes. With indole as a substrate, Nernstian behavior is observed (-60 mV shift per log[indole]) between 10 and 0.5 mM.     

Compiling scientific code using partial evaluation

The partial evaluation approach, which transforms a high-level program into a low-level program that is specialized for a particular application, exposing the parallelism inherent in the underlying numerical computation, is discussed. A prototype compiler that uses partial evaluation is described. Experiments with the compiler have shown that for an important class of numerical programs, partial evaluation can provide marked performance improvements: speedups over conventionally compiled code that range from seven times faster to 91 times faster have been measured. By coupling partial evaluation with parallel scheduling techniques, the low-level parallelism inherent in a computation can be exploited on heavily pipelined or parallel architectures. The approach has been demonstrated by applying a parallel scheduler to a partially evaluated program that simulates the motion of a nine-body solar system     

Influence of chlorhexidine in cavities prepared with ultrasonic or diamond tips on microtensile bond strength

This study evaluated the effect of chlorhexidine (CLX) in cavities prepared with either ultrasound-mounted CVDentUS diamond tips or conventional diamond burs on dentin bond strength after 24 h and 180 days. Forty-eight dentin surfaces from sound third molars were flattened and divided into four groups (n = 12), according to the type of cavity preparation (CVDentUS ultrasound tip or conventional diamond) and with or without 2% CLX (Consepsis) treatment. After application of the adhesive system (Clearfil SE Bond), microhybrid composite resin blocks (Charisma) were made on the dentin surface in increments. After 24 h, the specimens were sectioned into stick-shaped samples with an adhesive interface of approximately 1 mm². From each tooth, half of the sticks were evaluated after 24 h of storage in distilled water and the other half after 180 days, using a universal testing machine. Three-way analysis of variance showed no significant triple interactions (p = 0.722) or double interactions between factors. Higher bond strength values were observed with the use of ultrasonic tips (p = 0.019), irrespective of whether or not CLX was applied in either time period. No difference in bond strength values was observed in terms of CLX application (p = 0.581). No significant difference in bond strength values was shown after storage for 24 h or 180 days (p = 0.302). In conclusion, the ultrasonic tips promoted greater bond strength to dentin, irrespective of whether or not CLX was applied, and storage time.     

Environmental Impact Assessment of Water Projects in Mexico

Mexico is well ahead of many developed and developing countries in many ways, especially in terms of the numbers of water projects constructed, successful transfer of irrigation districts and development of informal markets for groundwater. However, the deterioration of the natural resources of the country, water resources being one of them, due to improper management is not improving the lifestyle of the vast majority of the population in any significant way. Accordingly, extensive modifications in the planning and management processes, including consideration of environmental and social factors and stakeholder participation, are urgently necessary for the water sector. This paper includes an analysis of the environmental impact statements of water projects in Mexico which are under the responsibility of the national water authority. It concludes that the unsatisfactory quality of the EIS of water projects in Mexico represents a serious limitation for developing any post-project evaluation or impact management. The institutional arrangements necessary for implementing the proposed measures are not defined, and the costs of implementing any recommendation are not properly budgeted for in the cost tables. Finally, not only should the reports be critically analysed, but also the whole process of their preparation and approval should be objectively and critically reviewed. This analysis should indicate clearly the shortcomings of the process, and then outline what steps could be taken to overcome them in order to ensure the sustainability of water projects in Mexico. The emphasis should be on producing a streamlined and implementable process .     

Atomic force microscopy studies on whey proteins

β-Lactoglobulin, standard whey protein concentrate (WPC 80) and cold-gelling whey protein concentrate (mWPC 80) were dried onto mica sheets at 0.03-3 μg cm⁻² surface load and imaged with atomic force microscopy (AFM) in tapping mode. β-Lactoglobulin and WPC 80 spread to a fairly even 2.5 nm thick layer at about monolayer surface load, while mWPC showed particle sizes of 20-30 nm laterally. There is little difference in the observed structures between 0.3 and 3 μg cm⁻² apart from the higher surface load. At 0.03 μg cm⁻², β-lactoglobulin spread somewhat more thinly than WPC 80. With the addition of DTT, mWPC spread evenly with only few particles in evidence. AFM appears to be a convenient method for the characterization of aggregation states of sub-micrometer protein particles.