Measurements of recombination of electrons with H3(plus) and H5(plus) ions

The electron-ion recombination coefficients for H3(+) and H5(+) ions were determined by means of a microwave afterglow/mass spectrometer apparatus. Measurements of electron density decays in helium-hydrogen mixtures are correlated with the decay of mass-identified ion currents to the wall of the microwave cavity. At low partial pressures of hydrogen in the mixture, the ion H3(+) dominates the ion composition and the ion wall current tracks the electron density decay curves. From recombination controlled electron density decay curves, the values alpha (H3(+)) = (2.9 + or - 0.3), (2.3 + or - 0.3), and (2.0 + or - 0.2) x 0.0000001 cu cm per sec, are obtained at 205, 300 and 450 K, respectively. At higher partial pressures of hydrogen and low temperatures, where (H5(+)) is the dominant ion, the value alpha (H5(+)) = (3.6 + or - 1.0) x 0.0000001 cu cm per sec is obtained at 205 K. The implications of these results concerning ionization levels in the atmospheres of the outer planets and in the interstellar medium are discussed

Ecological Scale of Bird Community Response to Pinon-Juniper Removal

Pinon (Pinus spp.) and juniper (Juniperus spp.) removal is a common management approach to restore sagebrush (Artemisia spp.) vegetation in areas experiencing woodland expansion. Because many management treatments are conducted to benefit sagebrush-obligate birds, we surveyed bird communities to assess treatment effectiveness in establishing sagebrush bird communities at study sites in Utah, Nevada, Idaho, and Oregon. Our analyses included data from 1 or 2 yr prior to prescribed fire or mechanical treatment and 3 to 5 yr posttreatment. We used detrended correspondence analysis to 1) identify primary patterns of bird communities surveyed from 2006 to 2011 at point transects, 2) estimate ecological scale of change needed to achieve treatment objectives from the relative dissimilarity of survey points to the ordination region delineating sagebrush bird communities, and 3) measure changes in pre- and posttreatment bird communities. Birds associated with sagebrush, woodlands, and ecotones were detected on our surveys; increased dissimilarity of survey points to the sagebrush bird community was characterized by a gradient of increased juniper and decreased sagebrush cover. Prescribed fires burned between 30% and 97% of our bird survey points. However, from 6% to 24% cover of pit-ion-juniper still remained posttreatment on the four treatment plots. We measured only slight changes in bird communities, which responded primarily to current vegetation rather than relative amount of change from pretreatment vegetation structure. Bird communities at survey points located at greater ecological scales from the sagebrush bird community changed least and will require more significant impact to achieve changes. Sagebrush bird communities were established at only two survey points, which were adjacent to a larger sagebrush landscape and following almost complete juniper removal by mechanical treatment. Our results indicate that management treatments that leave residual woodland cover and are not adjacent to extensive sagebrush stands are unlikely to establish sagebrush birds

The effects of prejudicial pre-trial publicity on perceived defendant character and guilt

The “Free Press v. Fair Trial” issue is the one in need of research, yet few students examining its effects have been forthcoming. Those studies that have been made have not adequately isolated the variables in the pre-trial publicity to permit meaningful conclusions. The present study was directed at exploring the effects of prejudicial pre-trial publicity on the defendant’s perceived character and guilt. Sixty-nine undergraduate students were assigned to one of four conditions, receiving either prejudicial or non-prejudicial pre-trial publicity either one or thirty days before they were asked to rule on the defendant’s guilt. A synopsis of evidence was provided in place of a trial. Prejudicial pre-trial publicity has a negative effect on perceived character. Exposure to prejudicial pre-trial publicity one day before trial did not result in lower defendant character ratings at trial than did exposure to prejudicial publicity thirty days before trial. No relationship was found between prejudicial pre-trial publicity and received guilt at trial. A relationship was found between perceived character and perceived guilt

Petri Net Modeling of a Flexible Assembly Station for Printed Circuit Boards

Petri net modeling approaches are presented for a flexible workstation for automatic assembly of printed circuit boards. In order to improve the productivity of such a system, the building of mathematical models is a crucial step. Concentrating on the operational aspects, the authors construct ordinary and temporal Petri net models for the AT&T FWS-200 physical flexible workstation. Three outcomes follow from such models. First, designers can have a better understanding of concurrency, synchronization, mutual exclusion, and sequential relations involved in the system control from the graphical representations of Petri nets. Second, the performance analysis of system operations under different settings can be conducted. Thus, the results can be used to help designers choose the best operational setting on a basis of the system parameters. Third, the models can be used as an aid for automatic generation of real-time control programs and construction of Petri-net-based simulation if needed. The approaches suggested can be generalized to many other applications of multirobot assembly systems

High Precision Solder Droplet Printing Technology: Principle and Applications

Solder droplet printing technology, which is low-cost, noncontact, flexible, data-driven, and environmentally friendly, has emerged as an enabling technology for precisely placing fine solder deposits on a variety of small substrates. It is suitable for a variety of applications including direct chip attach site preparation, 3D substrates, fine line interconnect, substrate via fill, optoelectronics and many others. It enables manufacturing techniques that are impossible or unfeasible with current technology, such as localized replacement of solder on board, depositing solder in different thicknesses on the same board, or using more than one type of solder on the same board. This makes the evaluation of solder droplet printing technology essential for the microelectronics industry. In this paper, the principle of the solder droplet printing technology is described, recent experimental results are included, and potential applications of the technology in the microelectronics industry are evaluated

Amplitude Modulated Droplet Formation in High Precision Solder Droplet Printing

There are many methods used at present to apply solder to wafers, ceramics, laminate and flex circuit boards, and other substrates. Among these, high-precision solder droplet printing technology, which is noncontact, data driven, flexible and environmentally friendly, is a key enabling technology. This technology selectively deposits solder droplets only where required, and therefore needs no mask or secondary resist removal, uses materials more efficiently and creates less waste than other methods. Currently, continuous droplet formation from capillary streams is mainly achieved by application of the well-known Rayleigh instability in which a sinusoidal disturbance is applied to the stream, resulting in evenly spaced and sized droplets. However, changing droplet configurations for various products or varying the size or depth of solder joints is difficult. Amplitude modulated disturbance is employed in this work to generate arbitrary solder stream configurations. The final configuration is mainly determined by several parameters: (1) the degree of modulation of the waveform; (2) the phase difference between the carrier and modulation signals; (3) the charging voltage; and (4) the frequency ratio between the carrier signal and the modulation signal. Many different patterns can be achieved with the proper combination of frequency ratio, phase difference, degree of modulation, and charging voltage. A simulation code was developed to simulate the merging process and determine the parameters needed to achieve certain droplet configuration

Investigation of Part Accuracy and Surface Roughness in Rapid Freeze Prototyping Based Investment Casting

The study as described in this paper is aimed at investigating the dimensional accuracy and surface finish of metal parts made by investment casting with ice patterns generated by rapid freeze prototyping. The process of investment casting with ice patterns is described and contrast with conventional investment casting with wax patterns is made. The selection of binder material for ceramic slurries and the need for an interface agent to separate the ice pattern from the ceramic slurry in the mold making process are discussed. The accuracy and surface finish of ice patterns and of the metal castings are presented and discussed. The parts used in this investigation include cylinders with vertical and slant walls and a turbine impeller.The authors gratefully acknowledge the financial support from the National Science Foundation grants (DMI-0128313 and DMI-0140625) and the Research Board of University of Missouri at Rolla.Mechanical Engineerin

Measurement of Electric Conductivity of Hot Gas in a SF6-circuit Breaker Interrupting Fault Currents

The realization of a new measurement method to determine electric conductivity of hot SF6-gas during interruption fault currents in an original self-blast circuit breaker is presented. The method is based on evaluation of phase shift between sinusoidal kHz-high voltage and current, applied on a sensor. This needs a kHz-resonance voltage generator and adapted sensors as a part of an electromagnetic shielded measurement system to determine time dependent electric conductivity with high resolution