Determining production sequences for single-stage multifunctional machining systems based on the tradeoff between fixture cost, re-fixturing and tool replenishment

The main advantage of a Single-Stage Multifunctional machining System (SSMS) is its ability to combine many operations and processes, previously done on different machines in several stages, into a single stage. The flexibility and process variety these machining systems offer have ensured their widespread adoption in industry. As a result SSMSs frequently constitute the bottleneck of a manufacturing system and therefore control system throughput. Hence, it is imperative to use these resources efficiently. This study considers three possible costs and the tradeoffs between them that are pertinent to any job sequence: (i) the Tool Magazine Replenishment (TMR) cost; (ii) the Re-Fixturing (RF) cost; and (iii) the fixture cost. A job sequencing algorithm that minimizes these costs as well as the machine non-operational time, which stems from TMRs and RFs, is developed. The algorithm takes into account the tools and fixture requirements as well as the tool magazine capacity. The algorithm also recommends purchasing additional fixtures when economically justified. The algorithm is used to solve a job sequencing problem that occurs in a real industrial setting.     

Chemorheological changes in crosslinked epoxy resins subjected to large strains

Chemorheological changes in epoxy resins subjected to large strains while heated were observed earlier, but the subject was not treated quantitatively. This paper describes the investigation of an epoxy resin—Epon 826, of known chemical, structure, crosslinked with two different amines. By means of a simple calibrated apparatus, the epoxide samples were subjected to large strains in a non-oxidizing atmosphere and in air. They were heated to different temperatures for various times; the results were compared with data obtained from unstrained samples kept in otherwise the same conditions. The results show a linear-logarithmic relation between the torsion modulus, G₍₁₀₎ and the time of applied strain at a certain temperature and also a linear relation between G₍₁₀₎, and 1/T°K, both above T₍₁₀₎. The results obtained in swelling experiments support the data from 10 sec torsional modulus vs temperature measurements. An increase in the amount of solubles and in M_c is observed on extending the time of heating. A clear difference in properties between the strained and unstrained samples, kept in otherwise the sane conditions, is observed and the contribution of the applied strain to chemorheology has been shown. Both systems of crosslinked Epon 826 showed the same general behavior, although the specific data were different.     

An equivalent pressure source for the heart

A technique is described for the representation of the left ventricle as a one-port source characterized by a generator pressure and an internal impedance. The Fourier components of the pressure and impedance are determined from phasor analysis performed on recorded time-domain functions of pressure and flow under two conditions of loading. One condition is the quiescent state corresponding to normal operation of the circulatory system, and the other is obtained by use of a phase-shift balloon pump situated in the descending thoracic aorta. The use of the balloon pump for determining source parameters is novel. The Fourier components of pressure and impedance are determined for the first five harmonics of the quiescent pulse rate. Heart failure is simulated by ligation of all branches of the anterior descending coronary artery. The source parameters have been found to vary considerably between normal and failing hearts. Valve impedance and the impedance at the root of the aorta were also measured. The generator time-domain pressure waveforms were determined from the Fourier components. Effects of long duration pumping, upon the source parameters were found. The ratio of the calculated magnitudes of internal to external or load impedance indicates the possibility of considering the heart as a pressure source.     

Microwave pulses compressed in a quasi-optical resonator with corrugated mirror

A microwave pulse compressor, representing a three-mirror resonator supplied with a radiation beam reflected from a corrugated mirror, was constructed and experimentally tested. A fivefold compression of microwave pulses with a 70% efficiency was obtained in a 9-mm wavelength range.     

The Aso-Bridge coseismic landslide: a numerical investigation of failure and runout behavior using finite and discrete element methods

The complex coseismic process of the Aso-Bridge landslide during the main shock of the 2016 Kumamoto Earthquake was investigated. Finite element analysis and discrete element analysis considering vertical seismic accelerations (VSA) were conducted to explore the salient features of the prefailure mechanism and postfailure kinematic process of the coseismic landslide associated with the initiation time and kinematic runout behavior, respectively. Two seismic input conditions, one involving only horizontal seismic accelerations (HSA), and the other accounting for both HSA and VSA, were used to assess the influence of VSA from the prefailure to postfailure regimes. First, satisfactory agreement between the study and the published results in terms of landslide initiation time was obtained. As revealed by the rapid change of source displacement (RCSD), VSA did not alter landslide initiation time; however, it significantly increased the RCSD approximately 2-fold, which provided a clear initiation time. At landslide initiation, the estimated average velocities in a vertical direction increased approximately 16-fold (from −0.011 to −0.174 m/s) by accounting for VSA. Second, the results suggested that VSA had a trivial influence on runout behavior in the postfailure regime, given that such behavior was dominated by the collision and free fall during the sliding as well as the terrain features. With an average velocity of 21.34 m/s, the sliding source ultimately reached the riverbank within 21 s. The paper demonstrates that a combination of FEA and DEA can be used to investigate the coseismic process of the Aso-Bridge landslide and lead to satisfactory agreement with the event. Our comprehensive analysis provides insight into the role of VSA in earthquake-induced landslides.

     

Applied bearing pressure beneath a reinforced soil foundation used in a geosynthetic reinforced soil integrated bridge system

Geosynthetic reinforced soil integrated bridge system (GRS-IBS) design guidelines recommend the use of a reinforced soil foundation (RSF) to support the dead loads that are applied by the reinforced soil abutment and bridge superstructure, as well as any live loads that are applied by traffic on the bridge or abutment. The RSF is composed of high-quality granular fill material that is compacted and encapsulated within a geotextile fabric. Current GRS-IBS interim implementation design guidelines recommend the use of design methodologies for bearing capacity that are based around rigid foundation behavior, which yield a trapezoidal applied pressure distribution that is converted to a uniform applied pressure that acts over a reduced footing width for purposes of analysis. Recommended methods for determining the applied pressure distribution beneath the RSF for settlement analyses follow conventional methodologies for assessing the settlement of spread footings, which typically assume uniformly applied pressures beneath the base of the foundation that are distributed to the underlying soil layers in a fashion that can reasonably be modeled with an elastic-theory approach. Field data collected from an instrumented GRS-IBS that was constructed over a fine-grained soil foundation indicates that the RSF actually behaves in a fairly flexible way under load, yielding an applied pressure distribution that is not uniform or trapezoidal, and which is significantly different than what conventional GRS-IBS design methodologies assume. This paper consequently presents an empirical approach to determining the applied pressure distribution beneath the RSF in GRS-IBS construction. This empirical approach is a useful first step for researchers, as it draws important attention to this issue, and provides a framework for collecting meaningful field data on future projects which accurately capture real GRS-IBS foundation behavior.     

Limit state design framework for geosynthetic-reinforced soil structures

Conventional design of geosynthetic-reinforced soil structures is divided into two categories, walls and slopes, based on the batter of its facing system. Internal stability, characterized as sufficient reinforcement anchoring and strength, is performed using earth pressure-based design criteria for reinforced walls while reinforced slopes are founded on limit equilibrium (LE) slope stability analyses. LE analyses are also used to assess the global or compound stability of both types of structures, accounting for the geometry of the reinforced, retained and foundation soils. The application of LE-based methods typically results in determination of a slip surface corresponding to the lowest attained Safety Factor (SF), known as the Factor of Safety (Fs); however, it yields little information about reinforcement loading or connection load. In this study, use of the analyzed spatial distribution of SF known as a Safety Map, is modified to attain a prescribed constant Fs at any location in the reinforced soil mass. This modified framework, implemented through an iterative, top-down procedure of LE slope stability analyses originating from the crest of a reinforced structure and exiting at progressively lower elevations on the facing, enables the determination of a Tension Map that illustrates the required distribution of reinforcement tension to attain a prescribed limit state of equilibrium. This tension map is directly constrained by a pullout capacity envelope at both the rear and front of each reinforcement layer, providing a unified, LE-based approach towards assessing an optimal selection of mutually dependent strength and layout of the reinforcement. To illustrate the utility of the Limit State framework, a series of instructive examples are presented. The results demonstrate the effects of facing elements, closely-spaced reinforcements, secondary reinforcement layers, and is compared to conventional design approaches.     

Implicit leadership theory as a determinant of the factor structure underlying supervisory behavior scales.

Examined implicit leadership theory (preconceptions about the patterning of leadership variables) in 235 college students. Ss completed the Survey of Organizations questionnnaire on a fictitious "Plant X" about which they were given little information. Factor analysis, performed on the items purported to measure 4 leadership factors, resulted in the conceptualized factor structure. Since no information was given regarding supervisory behavior in Plant X, the factor structure was attributed to an implicit leadership theory. Factor analysis on subsamples indicated the factor structure could not be attributed to either experience in organizations or previous instruction in management. It is suggested that responses to questionnaires regarding organizational variables may be contaminated by implicit theory and that multitrait-multimethod procedures may be required to validate questionnaires. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-fulfilling prophecy and gender: Can women be Pygmalion and Galatea?

To date, all published confirmations of the Pygmalion hypothesis among adults have involved men. The few studies among women have had methodological ambiguities. The authors conducted 2 experiments in the Israel Defense Forces to test the Pygmalion hypothesis among women. In both studies, the leaders were led to believe that the trainees randomly assigned to the Pygmalion condition had higher than usual potential. Experiment 1 tested the Pygmalion hypothesis among female officer cadets led by women. Although the treatment did raise expectations, none of the performance measures and none of the mediators or the moderators evidenced any expectancy effects. Experiment 2 tested the Pygmalion hypothesis among women and men taking the same course in gender-segregated platoons. The Pygmalion hypothesis was confirmed among men led by a man and among women led by a man but not among women led by a woman. The authors concluded that the Pygmalion effect can be produced among women but perhaps not by women. Pygmalion research among women leading men is now needed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)