All to-all communication with minimum start-up costs in 2D/3D toriand meshes

All-to-all communication patterns occur in many important parallel algorithms. This paper presents new algorithms for all-to-all communication patterns (all-to-all broadcast and all-to-all personalized exchange) for wormhole switched 2D/3D torus- and mesh-connected multiprocessors. The algorithms use message combining to minimize message start-ups at the expense of larger message sizes. The unique feature of these algorithms is that they are the first algorithms that we know of that operate in a bottom-up fashion rather than a recursive, top-down manner. For a 2^d×2^d torus or mesh, the algorithms for all-to-all personalized exchange have time complexity of O(2^3d). An important property of the algorithms is the O(d) time due to message start-ups, compared with O(2^d) for current algorithms. This is particularly important for modern parallel architectures where the start-up cost of message transmissions still dominates, except for very large block sizes. Finally, the 2D algorithms for all-to-all personalized exchange are extended to O(2^4d) algorithms in a 2^d×2^d×2^d3D torus or mesh. These algorithms also retain the important property of O(d) time due to message start-ups     

Electrical conduction in polyethylene with semiconductiveelectrodes

The electrical conduction characteristics of polyethylene with semiconductive electrodes have been investigated at electric fields of 10 to 600 kV/cm and at temperatures of 25 to 100°C. It was found that the conduction characteristics of the polyethylene were influenced not only by the constituents of the polyethylene but also the electrode materials. Space-charge-limited conduction was found to be the major conduction mechanism in all cases. Differences between conduction characteristics depending on the constituents of the XLPE are described and their causes are discussed     

Control scheme in hybrid synchronous stationary frame for PWM AC/DC converter under generalized unbalanced operating conditions

This paper proposes a new control scheme of improved transient response for the pulsewidth-modulation ac/dc converter under generalized unbalanced operating conditions. The overall-bandwidth diminishing filter/functional block for extracting positive and negative sequence components has been avoided by employing dual current regulators in positive- and negative-rotating synchronous frames. The steady-state error due to 120-Hz ac signals has been reduced by employing a resonant-gain path in the current regulator. This paper also proposes simplified current-reference calculation scheme in the regulation of instantaneous active/reactive power. Compared to the previous works, the proposed control method has better transient response in compensation for generalized unbalanced operating conditions (unbalanced input supply and unbalanced input impedances) of wide range while still satisfying unity input power-factor correction and ripple-free dc-output-voltage regulation without adding any external hardware. The proposed control system has been analyzed and tuned based on the ac small signal perturbed model under unbalance. Simulation and experimental results confirm the proposed control method under severe unbalanced operating conditions.     

Leaky mode directional coupler for prism coupling interconnection

A leaky mode directional coupler was fabricated with its beam shaped into a Gaussian-like profile and was experimentally demonstrated for suppressing the diffraction of an out-coupled beam. The demonstrated coupler consists of a multilayered waveguide with six layers that are embedded in a symmetric slab waveguide. The out-coupled beam profile was measured to be shaped into a Gaussian function by using the prism coupling method. There was an excellent agreement between the measured and theoretically predicted coupling angles, and it was also confirmed that the diffraction was suppressed.     

Prediction of strain recovery during solid-phase forming of thermoplastics

An approach to predict the strain recovery behavior of polycarbonate (PC) and high impact polystyrene (HIPS) under isothermal and non-isothermal conditions in a solid-phase forming environment is presented in this paper. The constants A and n of a power law relationship of the form ?(t) or δ(t) = Atⁿ, fitted to isothermal creep and stress relaxation data, were determined over a wide range of temperatures for both materials. An expression for isothermal recovery was derived and compared to experimental data. Master curves and the resultant shift factors, obtained by superposing the stress relaxation and creep data (both in tension and compression) were used with the time-temperature super position principle to numerically evaluate uniaxial strain recovery under a specific temperature history. The average temperature history obtained by numerically solving for the temperature distribution in a disc, at an initially high temperature and in contact with a cold metal surface, was used for the non-isothermal case. The theoretical results were compared with recovery data obtained from non-isothermal backward extrusion tests with a temperature history similar to the one described above. Reasonably good agreement was obtained.     

Microencapsulation of a hydrophilic drug into a hydrophobic matrix using a salting-out procedure. II. Effects of adsorbents on microsphere properties

Wax microspheres of the hydrophilic drug guaifenesin were prepared by the congealable disperse-phase method using a salting-out procedure. In order to improve the particle properties of the microspheres, adsorbents (colloidal silica, magnesium stearate, and talc) were used during preparation. The effects of adsorbents on microsphere properties such as the angle of repose (AR), compressibility index (CI), geometric mean diameter (GMD), loading efficiency (LE), and in vitro drug release (DR) were determined. The AR, CI, and GMD of the microspheres were significantly reduced in the presence of the adsorbents. Increase in the concentrations of colloidal silica and magnesium stearate led to lower LE and faster DR, while talc showed no effect, which could be due to the particle diameter and specific surface area of the adsorbents. The microspheres prepared with colloidal silica were chosen to be compressed into tablets since they were smaller, more uniform, and had better flow properties than those made with magnesium stearate and talc. The in vitro drug release profile of the microsphere tablets was compared with that of commercially available Mucinex®, sustained release guaifenesin matrix tablets. Similar release profiles were observed between the two tablets. Scanning electronic microscopy (SEM) studies of the broken tablets revealed that the deformation of the microspheres caused by compression was minimal.     

Rasch fit statistics as a test of the invariance of item parameter estimates

The invariance of the estimated parameters across variation in the incidental parameters of a sample is one of the most important properties of Rasch measurement models. This is the property that allows the equating of test forms and the use of computer adaptive testing. It necessarily follows that in Rasch models if the data fit the model, than the estimation of the parameter of interest must be invariant across sub-samples of the items or persons. This study investigates the degree to which the INFIT and OUTFIT item fit statistics in WINSTEPS detect violations of the invariance property of Rasch measurement models. The test in this study is a 80 item multiple-choice test used to assess mathematics competency. The WINSTEPS analysis of the dichotomous results, based on a sample of 2000 from a very large number of students who took the exam, indicated that only 7 of the 80 items misfit using the 1.3 mean square criteria advocated by Linacre and Wright. Subsequent calibration of separate samples of 1,000 students from the upper and lower third of the person raw score distribution, followed by a t-test comparison of the item calibrations, indicated that the item difficulties for 60 of the 80 items were more than 2 standard errors apart. The separate calibration t-values ranged from +21.00 to -7.00 with the t-test value of 41 of the 80 comparisons either larger than +5 or smaller than -5. Clearly these data do not exhibit the invariance of the item parameters expected if the data fit the model. Yet the INFIT and OUTFIT mean squares are completely insensitive to the lack of invariance in the item parameters. If the OUTFIT ZSTD from WINSTEPS was used with a critical value of | t | > 2.0, then 56 of the 60 items identified by the separate calibration t-test would be identified as misfitting. A fourth measure of misfit, the between ability-group item fit statistic identified 69 items as misfitting when a critical value of t > 2.0 was used. Clearly relying solely on the INFIT and OUTFIT mean squares in WINSETPS to assess the fit of the data to the model would cause one to miss one of the most important threats to the usefulness of the measurement model.     

A study of the development of the stress optic law of photoelastic experiment considering residual stress

Photoelastic experiment has two significant problems. The first problem is manufacturing a model specimen for complicated shapes of structures. The second problem is residual stress contained in the photoelastic model material. In this paper, the stress optic law that can be effecitvely used on photoelastic model materials with residual stress is developed. By using the stress optic law as developed in this research, we can obtain good results in photoelastic experiments using model material in which residual stress is contained. It is assured that the stress optic law developed in this research is useful. Therefore, it is suggested that the stress optic law considering residual stress can be applied to the photoelastic experiment for the stress analysis of the composite materials or bi-materials in which the residual stress is easily contained.     

Extracting information from the molten salt database

Molten salt technology is a catchall phrase that includes some very diverse technologies; electrochemistry, heat transfer, chemical oxidation/reduction baths, and nuclear reactors. All of these technologies are linked by the general characteristics of molten salts that can function as solvents, have good heat-transfer characteristics, function like a fluid, can attain very high temperatures, can conduct electricity, and also may have chemical catalytic properties. The Janz molten salt database is the most comprehensive compilation of property data about molten salts available today and is widely used for both fundamental and applied purposes. Databases are traditionally viewed as “static” documents that are used in a “search and retrieval” mode. These static data can be transformed by informatics and data mining tools into a dynamic dataset for analysis of the properties of the, materials and for making predictions. While this approch has been successful in the chemical and biochemical sciences in searching for and establishing structure-property relationships, it is not widely used in the materials science community. Because the design of the original molten salt database was not oriented toward this informatics goal, it was essential to evaluate this dataset in terms of data mining standards. Two techniques were used—a projection (principal components analysis (PCA)) and a predictive method (partial least squares (PLS))—in conjunction with fundamental knowledge acquired from the long-term practice of molten salt chemistry. This article is based on a presentation made in the symposium entitled “Fourth International Alloy Conference,” which occurred in Kos, Greece, from June 26 to July 1, 2005, and was Sponsored by Engineering Conferences International (ECI) and co-sponsored by Lawrence Livermore National Laboratory and Naval Research Laboratory, United Kingdom.