Pressureless sintering of in-situ toughened Yb α-SiAlON ceramics by adding seed crystals prepared by combustion synthesis

Single-phase Yb α-SiAlON ceramics in-situ toughened by elongated grains were prepared by pressureless sintering, with the crystalline powder prepared by combustion synthesis used as seed crystals. The effects of seed addition on the densification, phase transformation, microstructure development, and mechanical properties of the samples were investigated in detail. From the experimental results, it was found that the added seed crystals could promote the phase transformation and facilitate the growth of elongated grains. By adding seed crystals the fracture toughness of the sintered α-SiAlON ceramics was considerably improved, with no obvious degradation in the bulk density and hardness at the same time.     

Distributed parameters for low-frequency dielectric characterization of liquids with open-ended coaxial cell

The theory of distributed parameters is applied at low frequencies to the open-ended coaxial-line dielectric characterization technique. A procedure is proposed to determine the permittivity of liquids when the sample is placed between two dielectric beads to ensure tight closure. The technique leads to a complex transcendental equation that the authors solve. An ad hoc sample holder is built to implement the proposed method. Measurements of both polar and nonpolar liquids demonstrate the adequacy of the method and its advantages with respect to the lumped-circuit theory in the case of polar samples.     

A New Distribution System Reconfiguration Approach Using Optimum Power Flow and Sensitivity Analysis for Loss Reduction

This paper presents a new approach for distribution system reconfiguration (DSR) based on optimum power flow (OPF) in which the branch statuses (open/close) are represented by continuous functions. In the proposed approach, all branches are initially considered closed, and from the OPF results, a heuristic technique is used to determine the next loop to be broken by opening one switch. Then the list of switches that are candidates to be opened is updated, and the above process is repeated until all loops are broken, making the distribution system radial. This paper includes results and comparisons on test systems utilized in three classical papers published in the technical literature, as well as in a previous paper by the authors. Results obtained on a real large-scale distribution system are also presented     

SNR gap approximation for M-PSK-Based bit loading

Adaptive OFDM has the potential of providing bandwidth-efficient communications in hostile propagation environments. Currently, bit loading algorithms use M-ary quadrature amplitude modulation of the OFDM sub-carriers, where the number of bits per symbol modulating each of them is obtained in order to maximize the performance. SNR gap approximation for M-QAM signaling makes the algorithms simpler to implement. However, in some circumstances it may be preferable to use. M-ary phase shift keying. In this letter an approximation is derived for M-PSK similar to the SNR gap of M-QAM so that bit loading algorithms can be extended to this type of modulation. In addition, the performance obtained when using M-PSK is compared to that of M-QAM in a practical situation.     

Pollution Buildup on Road Surfaces

Samples of sediment found on an urban road in Aberdeen (Scotland) were collected by washing designated surfaces. This method, called the “wet” method, was capable of collecting sediment of the smallest particle size range that is normally left behind by traditional sampling techniques using dry vacuuming. Over 17 months (mainly on a weekly basis), 66 samples were collected and analyzed for sediment loading, particle size distribution, concentration of heavy metals (Zn, Cu, Pb, Cd) in four sediment size fractions, and several dissolved pollutants in the effluent collected from washing (NO3?,?SO42?,?PO43?,?Cl?,?F?,?NH4+, total organic carbon, total carbon). Standard statistical methods, including multiple regressions, were used to determine relationships amongst different sediment characteristics. It was found that sediment loading, as well as concentrations of Cl? and SO42?, were highest in the winter months, especially when snow was present on the road surface. It was observed that 66% of total road sediment loading was found within a 0.5 m strip next to the curb. The average sediment particle sizes found were smaller than those previously recorded in the literature. As expected, the concentrations of heavy metals were highest in the smallest particle size fraction analyzed (<63?μm), and this occurred during the summer months when less sediment was available on the street surface. The antecedent dry weather period had a very weak and negative influence on the loading rate of the smallest particle size fraction next to the curb.     

Influence diagnostics in regression with complex designs through conditional bias

One of the areas of Statistics in which the influence analysis has been widely studied is the multiple linear regression model. Nevertheless, the influence diagnostics proposed in this context cannot be applied to regression in complex survey, under randomized inference, since the i.i.d. case does not incorporate any probability weighting or population structure, such as clustering, stratification or measures of size into the analysis. In this paper we introduce some influence diagnostics in regression in complex survey. They are built on the conditional bias concept (Moreno-Rebollo et al., 1999). We emphasize the similarities and differences of the proposed measures with respect to the existing ones for the i.i.d. case. Research partly supported by the Spanish MCYT grant BFM2001-3844 and Spanish MEC grant MTM2004-0111433.     

Parallel Monte Carlo Driver (PMCD)—a software package for Monte Carlo simulations in parallel

Thanks to the dramatic decrease of computer costs and the no less dramatic increase in those same computer's capabilities and also thanks to the availability of specific free software and libraries that allow the set up of small parallel computation installations the scientific community is now in a position where parallel computation is within easy reach even to moderately budgeted research groups. The software package PMCD (Parallel Monte Carlo Driver) was developed to drive the Monte Carlo simulation of a wide range of user supplied models in parallel computation environments. The typical Monte Carlo simulation involves using a software implementation of a function to repeatedly generate function values. Typically these software implementations were developed for sequential runs. Our driver was developed to enable the run in parallel of the Monte Carlo simulation, with minimum changes to the original code that implements the function of interest to the researcher. In this communication we present the main goals and characteristics of our software, together with a simple study its expected performance. Monte Carlo simulations are informally classified as “embarrassingly parallel”, meaning that the gains in parallelizing a Monte Carlo run should be close to ideal, i.e. with speed ups close to linear. In this paper our simple study shows that without compromising the easiness of use and implementation, one can get performances very close to the ideal.     

A new approach to designing reduced scale thermal-hydraulic experiments

Reduced scale experiments are often employed in engineering because they are much cheaper than real scale testing. Unfortunately, though, it is difficult to design a thermal-hydraulic circuit or equipment in reduced scale capable of reproducing, both accurately and simultaneously, all the physical phenomena that occur in real scale and operating conditions. This paper presents a methodology to designing thermal-hydraulic experiments in reduced scale based on setting up a constrained optimization problem that is solved using genetic algorithms (GAs). In order to demonstrate the application of the methodology proposed, we performed some investigations in the design of a heater aimed to simulate the transport of heat and momentum in the core of a pressurized water reactor (PWR) at 100% of nominal power and non-accident operating conditions. The results obtained show that the proposed methodology is a promising approach for designing reduced scale experiments.     

A simulation analysis of the detectability of understory burns in miombo woodlands

The miombo woodlands of southern Africa are one of the most extensively burned biomes in the tropics. The detectability of understory burns in these woodlands was assessed with a sensitivity analysis approach, based on a hybrid geometrical-optical radiative transfer model. Model input data were obtained from a variety of sources, including field biometry and spectroradiometry, and satellite data. The effects of variable tree percent cover, leaf area index, stand density, burn scar age, illumination and observation geometry, and spectral region, were taken into account. Detectability of understory burns was defined as the spectral separability of burned and unburned understory, measured with the Jeffries-Matusita distance, for all possible combinations of the green, red, and near-infrared channels of the Moderate Resolution Imaging Spectrometer (MODIS) sensor. Single channels, or pairwise combinations of channels perform poorly at detecting understory burns, but a large improvement in detectability is obtained for the combination of the three spectral domains. The detectability of understory burns is largely insensitive to the effects of stand structure and illumination/observation geometry, and depends primarily on burn scar age. Our results agree with those of previous satellite-based studies of burns scar detectability in African savanna woodlands.