Titanium castings using laser-scanned data and selective laser-sintered zirconia molds

Titanium casting molds, made of stabilized and unstabilized zirconium oxide, were created using a combination of selective laser sintering (SLS) and colloidal infiltration. The mold material system was chosen for its thermal shock resistance and low reactivity with molten titanium. The starting material, stabilized zirconia powder mixed with a copolymer binder, was laser sintered into the desired green shape. The binder was removed during pyrolysis and replaced by unstabilized zirconia. As infiltrant weight gain increased, the density, flexural strength, and surface roughness improved to levels adequate for titanium casting trials. A half-scale casting mold for the ball of a human femur bone was produced from laser-scanned data and cast with Ti-6Al-4V alloy. The castings exhibited an as-cast surface roughness (R _a ) of 8 μm and a typical microstructure. This work demonstrates a feasible method of producing complex titanium castings for one-of-a-kind and custom components without the necessity of part-specific tooling or wax patterns.     

Analysis of satellite derived beam and global solar radiation data

Images from the GOES 8 satellite were used along with auxiliary information such as snow cover to produce an hourly solar radiation database on a 0.1° grid for the Pacific Northwest from 1998 through 2002 [Perez, R., Ineichen, P., Moore, K., Kmiecik, M., Chain, C., George, R., Vignola, F. 2002. A new operational satellite-to-irradiance model. Solar Energy 73(5), 307–317]. Both global and beam irradiance values were derived from the satellite images and diffuse values were calculated from the beam and global values. Data from the University of Oregon Solar Radiation Monitoring Network were used to help refine and validate the model used to produce the database from the satellite images.This article presents new and independent tests of this satellite database from one year with high quality data from Kimberly, Idaho that was not used in the original development and testing of the satellite model. The mean bias error of the satellite-derived global and beam irradiance values were 5% and 2% respectively. The standard deviation ranged from 22% for global values to 41% for beam values. The largest discrepancies occur on clear winter days when it is difficult to distinguish between frost or snow on the ground and low lying fog or clouds. It is suggested that ground-based solar or visibility measurements or auxiliary satellite data are needed to augment the satellite cloud cover and snow cover data to reduce errors that can occur during cold winter days.     

A chip multithreaded processor for network-facing workloads

Throughput computing is based on chip multithreading processor design technology. In CMT technology, maximizing the amount of work accomplished per unit of time or other relevant resource, rather than minimizing the time needed to complete a given task or set of tasks, defines performance. By CMT standards, the best processor accomplishes the most work per second of time, per watt of expended power, per square millimeter of die area, and so on (that is, it operates most efficiently). The processor described is a member of Sun's first generation of CMT processors designed to efficiently execute network-facing workloads. Network-facing systems primarily service network clients and are often grouped together under die label "Web servers". The processor's dual-thread execution capability, compact die size, and minimal power consumption combine to produce high throughput performance per watt, per transistor, and per square millimeter of die area. Given the short design cycle Sun needed to create the processor, the result is a compelling early proof of the value of throughput computing.     

Relationships of cognitive components of test anxiety to test performance: Implications for assessment and treatment.

Assessed the degree to which components of test-taking strategies, covert self-statements, and subjective anxiety during an exam provide increments in prediction of test performance over characteristics of ability and gender. Compared to previous research, the study assessed the effectiveness of any test-taking strategies employed on specific questions during an exam in order to directly evaluate the relationship of this problem-solving skill to test performance. 72 college students differing in dispositional test anxiety and college experience studied for and then completed several simulated classroom tests. Test-taking strategies were assessed with the Test Tactics Probe; the Covert Thought Questionnaire was developed to assess self-statements; and subjective anxiety was measured with the Subjective Units of Disturbance Scale. Only test-taking strategies provided a significant increment to multiple-choice and essay test performance but not math test score. Components reflecting internal dialog were more strongly related to each other than to performance, suggesting that these factors may be indirectly related to performance decrements. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thermodynamic treamnts of the CaO-SiO2 system

Thermodynamic data for heat capacity, enthalpy, and activity in the CaO-SiO₂ system have been analyzed using the Redlich-Kister formalism with up to six terms. This system shows both liquid-liquid immiscibility and large negative deviations from ideality due to a strong acid base interaction. We have found it necessary to use separate power series treatments for the acidic and basic regions. A number of different mathematical approaches have been previously used for this system, all giving reasonable calculated phase diagrams. Comparisons of the various treatments show major differences in the enthalpy and free energy of mixing. The known thermodynamic properties of CaSiO₃ and Ca₂SiO₄ provide a more reliable test of the accuracy of computer treatments than does the shape of the calculated phase diagram.     

The Young Manager is Career Planning a Useless Exercise?

Is it worth it in industry to chart a career plan? Will it get a manager where he wants to go any faster? Or will it merely serve as a frustrating reminder of unachieved objectives? Is an executive better off "winging it," letting the chips fall freely? Eight businessmen comment on these and other questions about career planning as well as discuss their own approaches to their careers.     

Initial Sintering of BaTiO3 Compacts

Experimental measurements were made of the rate of initial shrinkage of high-purity BaTiO₃ compacts in air. The time dependence of the shrinkage rate was consistent with a model based on grain boundary vacancy diffusion. The apparent activation energy for the shrinkage rate in the range 700° to 1000°C is 112 ± 9 kcal per mole. Comparison with other data indicates that oxygen ion vacancy diffusion controls the initial sintering rate.     

Effect of Microaerophilic Conditions on Autothermal Thermophilic Aerobic Digestion Process

A pilot-scale, first-stage, autothermal thermophilic aerobic digestion reactor was used to study the effect of microaerophilic conditions on sludge solids destruction, volatile fatty acids (VFA) production, and phosphorus release. For the aeration rates of 0–100 mL∕min and the reactor sludge volume of 72 L, with a primary to secondary sludge ratio of 35:65, the solids destruction efficiency ranged between 19.5 and 23.8%, as measured by total suspended solids (TSS). The maximum increase in VFA concentration (483 mg∕L as acetic acid) occurred at the low airflow rate of 25 mL∕min. The unit VFA production ranged from 0.009 to 0.183 mg of VFA generated∕mg of TSS destroyed, with the dominance of acetic acid. The milligrams of phosphorus released per milligrams of TSS destroyed was from 0.018 to 0.0312, with the maximum measured when no air (nitrogen) was supplied; but the maximum ratio of VFA to PO4 (equal to 8.2) was measured when the air supply was at 25 mL∕min.     

Immediate neighbor scheduling (INS): An adaptive protocol for mobile ad hoc networks using direct-sequence spread-spectrum modulation

We investigate a new approach for scheduling transmissions in a mobile ad hoc network employing direct-sequence spread-spectrum (DSSS). Multiple-access interference may be better tolerated in these systems, allowing higher levels of spatial reuse and a reduction in the overhead required to schedule transmissions. We present a protocol which leverages these features of DSSS to support greater end-to-end throughput and terminal mobility rates. A protocol extension allows terminals to adjust protocol overhead in order to preserve network connectivity in sparse networks. For each transmission, terminals use a combination of common and transmitter-oriented spreading sequences in a format which allows for discovery of nearby terminals and adaptation of transmission rates to maximize throughput. The protocol does not operate over an artificial network graph, nor does it require an initialization phase or two-way exchange of information during a transmission slot. Through simulations, we evaluate the performance of the transmission scheduling protocol in a variety of static and mobile scenarios. For comparison, we also simulate a centralized transmission scheduling protocol with perfect knowledge of topology.     

The Editor's Foreword

My fundamental thesis is that the ultimate task of architecture is to act in favor of humankind: to interpose itself between us and the natural environment in which we find ourselves, in such a way as to remove the gross environmental load from our shoulders. The central function of architecture is thus to lighten the very stress of life. Its purpose is to maximize our capacities by permitting us to focus our limited energies upon those tasks and activities which are the essence of the human experience.

This successful interposition between humanity and its natural environment furnishes the material basis of all great architecture. To wrest the objective conditions for optimal development and well-being from a Nature which only seldom provides it, to satisfy our physiological and psychological requirements at optimal levels—this beyond question is the objective basis of any architecture which is both beautiful and good. To design such a building, as Gropius once so movingly put it, is an authentic act of love.