Combining Futures and Spot Markets: A Hybrid Market Approach to Economic Grid Resource Management

Economic forms of resource management in which users can express their valuations for service, offer new possibilities for optimizing resource allocations in Grids. If users are to correctly express these valuations, quality of service guarantees need to be given with respect to the turnaround time of their workloads. Market mechanisms that support bidding and allocations in future time are crucial for delivering such guarantees. To deal with the significant delays that these mechanisms introduce in the allocation process, we present a hybrid market approach in which a low-latency spot market coexists with a higher latency futures market. Based on simulated market scenarios, we show how this combination can significantly increase the total value realized by the Grid infrastructure. We also demonstrate how providers can react to price dynamics in such a hybrid market setting.     

Analysis and comparison of particle tribochargers

Triboelectric separation is a dry electrostatic particle processing technique. A ‘tribocharger’ is used to differentially charge particles of different materials by contact or friction. These are then separated by an electric field. There has been little analytical work done on tribocharger design, slowing the development of this promising technology. One problem is that the fundamental physics of bulk particulate tribocharging have hitherto been poorly understood. We have previously performed experimental and theoretical studies to characterise the charging of bulk particulates in dynamic contact with surfaces. Following from this, a number of tribocharger configurations (sliding trough, vibratory canister and pneumatic cyclone) have been studied and their charging performance and other key parameters compared. An overview of the important results so far is presented, and these are used to demonstrate a general approach to design of tribocharging devices.     

A modeling approach to the effect of resin characteristics on parison formation in extrusion blow molding

The most critical stage in the extrusion blow‐molding process is the parison formation, as the dimensions of the blow‐molded part are directly related to the parison dimensions. The swelling due to stress relaxation and sagging due to gravity are strongly influenced by the resin characteristics, die geometry, and operating conditions. These factors significantly affect the parison dimensions. This could lead to a considerable amount of time and cost through trial and error experiments to get the desired parison dimensions based upon variations in the resin characteristics, die geometry, and operating conditions. The availability of a modeling technique ensures a more accurate prediction of the entire blow‐molding process, as the proper prediction of the parison formation is the input for the remaining process phases. This study considers both the simulated and the experimental effects of various high‐density polyethylene resin grades on parison dimensions. The resins were tested using three different sets of die geometries and operating conditions. The target parison length was achieved by adjusting the extrusion time for a preset die gap opening. The finite element software BlowParison® was used to predict the parison formation, taking into account the swell and sag. Good agreements were found between the predicted parison dimensions and the experimental data. POLYM. ENG. SCI., 2009. Published by Society of Plastics Engineers     

Modelling of abrasive particle energy in water jet machining

A phenomenological model of the three-phase flow inside an abrasive water jet machining cutting head has been developed. Several improvements over previously presented models such as taking into account the abrasive particle size distribution, and the effect of breakage of particles on the energy flux have been made. The model has been validated using an extensive set of experimental data with wide variations in cutting-head geometry, operating pressure, and abrasive mass flow rates. The cross-sectional averaged abrasive particle velocity at the exit of the focussing tube has been predicted with good accuracy over the whole range of experiments. In particular, the Pearson correlation between the model and the experimental results is found to be more than 95%, implying the utility of this model in design.     

Nuclear mubeams: Realization and use as scientific tool

A nuclear mubeam is an ion beam focussed down to a spot of only a few μm in diameter. If such a beam is surrounded by equipment for elemental analysis we have the nuclear muprobe (NMP) suited for elemental analysis with μm spatial resolution and detection limits of a few ppm. The beam focus is achieved by collimation to some 10 μm and further demagnification with the help of an appropriate lens system. The need to fabricate the mechanical parts to a very high precision and to avoid slit scattering at the collimators will be demonstrated and a guide to the optimal design will be given. The different ways of realization are illustrated. Applications in different fields of science are given and the availability of NMPs throughout the world illustrated.     

Flow and heat transfer simulation of injection molding with microstructures

Injection molding has been used for mass production of polymer products with microstructures. Conventional Hele‐Shaw 2.5D midplane simulation is unable to describe the flow pattern correctly. It tends to over‐predict the effects of microstructures on global flow patterns. For the unidirectional flow, an x‐z planar based on the general momentum equation is able to achieve better accuracy and to retrieve more detailed flow and heat transfer information around the microstructures. A hybrid numerical technique is developed, which can significantly reduce the nodes and computation time, and yet provide good flow simulation around the microstructures. The mold‐melt heat transfer coefficient and injection speed are shown to be very important factors in determining the filling depth in microstructures. A decrease of the heat transfer coefficient and the occurrence of wall‐slip are likely in microchannels. Polym. Eng. Sci. 44:1866–1876, 2004. © 2004 Society of Plastics Engineers.