A QFT-type design methodology for a parallel plant structure and its application in idle speed control

Developed in this paper is a frequency domain design methodology for disturbance rejection in a MISO plant which has a special parallel structure. Shown in this paper is that it is not necessary to close all the parallel loops in order to achieve the hard time domain constraints. The proposed methodology is applied to the idle speed control of a fuel-injected engine.     

Analysis of robot positioning error

Positioning errors of robots used for material handling and assembly can be sufficiently large to cause problems. These errors are due to imperfect repeatability of the robots, and their effects can be ameliorated or exacerbated by tolerances on the workpieces and on the jigs and fixtures. In this paper, a model for characterizing the positioning errors of robots is developed. A statistical analysis of positioning error data is performed to make inferences about the stochastic nature of the robotic system. The basic issue is whether the positioning errors of the robot are state dependent or state invariant.     

Optimal specialization of a maintenance workforce

This article develops an analytical method for determining an optimal specialization strategy for a maintenance workforce. The method assumes that maintenance tasks are generated by a system of statistically identical machines that experience random malfunctions and require periodic service. The impact of alternative workforce structures on system performance is evaluated with a queueing network model. Markov decision analysis is employed to determine an optimal assignment of maintenance personnel to pending tasks as the network status varies over time. A linear programming algorithm is derived to enable simultaneous optimization of specific assignment decisions and the overall workforce structure. A manufacturing example demonstrates the applicability of the method to many industrial contexts. The method is also applied to the problem of maximizing military aircraft sortie generation subject to a constraint on maintenance personnel expenditure.     

GATED COMMUNITIES AND SPATIAL INEQUALITY

ABSTRACT: In this article we analyze gated communities as a nexus of social and spatial relations within the context of urban inequality. We apply Tickamyer's (2000) sociological framework for incorporating space into the study of inequality, which allows us to substantiate the arguments that the process of gating increases urban inequality. The contributions of this article are three: (1) We generate a new systematic theoretical approach toward the study of gated communities, which we consider as middle range theory; (2) We argue that gated communities reproduce the existing levels of social stratification and that they also define a new, permanent differentiation order in the spatial organization of cities in the United States (in this respect we also arrive at six hypotheses, which can be tested in future research); (3) We introduce the term “gating machine,” where the combination of the interests and actions of local governments, real estate developers, the media, and consumers suggest that prevailing structural conditions assure the future proliferation of gated communities.     

HISTAMINE PRODUCTION BY FOOD-BORNE BACTERIAL SPECIES12

A total of 112 bacterial strains representing 38 species were tested for their potential to elicit food poisoning outbreaks via histamine formation in foods. Proteus morganii and Enterobacter aerogenes displayed a quantitative superiority in terms of histamine production on a trypticase-soy broth-histidine (TSBH) medium and a tuna fish infusion broth (TFIB). When bacteria were incubated under standardized conditions in TSBH medium, histamine accumulated to levels exceeding 50 nmoles/ml of media with a total of 23 strains, including 13 of 15 P. morganii strains, 3 of 3 E. aerogenes strains, 3 of 12 Hafnia alvei strains, 1 of 4 Providencia alcalifaciens strains, 1 of 5 Enterobacter cloacae strains, 1 of 1 Proteus rettgeri strains, and 1 of 1 Citrobacter diversus strains. However, only 8 of the 15 P. morganii strains and the 3 E. aerogenes strains were capable of generating histamine in excess of 200 nmoles/ml in the TSBH medium. Of the 23 strains capable of appreciable histamine production in TSBH medium, P. morganii and E. aerogenes were, by far, the most prolific histamine producers in TFIB. Of the organisms tested, only P. morganii and E. aerogenes would appear to have the capability of forming sufficient histamine in scombroid fish products to elicit food poisoning outbreaks.     

The City Crown by Bruno Taut

Translator's Introduction In the early part of the 20th century, Bruno Taut developed an urban concept for the planning and reconfiguration of European cities to overcome national and social differences by means of architecture. A communal center modeled after the medieval cathedral or temple crowned Taut's city. In his anthology Die Stadtkrone ( The City Crown ) (1919), a critical text for the history of European Modernism, Taut championed the use of individual structures to define and affect the planning of an entire city. ¹ Taut's anthology encouraged young architects to envision and build the ideal rather than perpetuate the quotidian. This first English translation of The City Crown maintains Taut's original goal.     

FIRMNESS EVALUATION OF SWEET CHERRIES BY A TRAINED AND CONSUMER SENSORY PANEL

The objective of this study was to examine cherry firmness and the ability of a trained and consumer panel to differentiate between cherries of different firmness values. For the trained panel ( n =  12) and consumer panel ( n =  100) evaluations, two late-maturing, commercially important cherry cultivars were evaluated, "Selah" and "Skeena." For trained panel evaluations, the analytical firmness value of each cherry was determined, although for the consumer panel, cherries were characterized into different firmness categories (low, intermediate and high), after which, a series of paired comparisons were made. "Selah" was the less-firm cultivar by approximately 20 g/mm and consumers could distinguish the more-firm cherry in all comparisons ( P <  0.05). For "Skeena," consumers could only distinguish soft versus firm. Trained panelists were able to distinguish between cherries of a minimum analytical firmness value of ∼40 g/mm. A model was developed to predict sensory firmness from analytical determinations of firmness ( r =  0.63).

PRACTICAL APPLICATIONS

Developing prediction models to estimate sensory response from analytical data will benefit the fruit industry by potentially allowing the use of analytical measurements as a proxy for sensory evaluation. In addition, understanding the importance of firmness on cherry acceptance and knowing the specific firmness values at which individuals can perceive a difference in sensory firmness is useful for cherry growers to produce a cherry with acceptable texture.     

A SURVEY OF HISTAMINE LEVELS IN COMMERCIALLY PROCESSED SCOMBROID FISH PRODUCTS12

Analysis of 100 samples of each of 3 types of commercially processed scombroid fish products obtained at the retail level showed mean histamine concentrations (mg/100 g) of 3.58 for chunk light tuna, 1.50 for albacore tuna, and 2.56 for mackerel. Only 2 samples of chunk light tuna and 2 of mackerel contained greater than 10 mg% histamine. The highest level of histamine found in albacore tuna was 5.35 mg/100 g, while 99% ofthe samples had less than 5 mg% histamine. Chunk light tuna samples contained up to 28.0 mg/100 g, and mackerel samples contained up to 31.5 mg/100 g; 92% of the chunk light tuna and 95% of the mackerel had less than 5% histamine. The histamine levels found in these products were far below any level associated with food poisoning incidents.     

AN EXPERIMENTAL STUDY OF POLYMER DIFFUSION IN CONCENTRATED SOLUTION: IMPLICATIONS FOR DIFFUSION IN POLYMERIZATION

The Trommsdorf or gel effect in free radical polymerization is due to the fact that the termination reaction becomes strongly diffusion controlled above a critical concentration associated with the onset of molecular entanglements. Therefore, an understanding of polymer self-diffusion in entangled systems becomes essential to understanding the Trommsdorf effect. Our group has previously proposed a molecular model for the gel effect which uses a specific theory for polymer diffusion (reptution). The present work represents an experimental attack on the same problem Experimental studies of polymer self-diffusion in entangled systems are scarce. Quasielastic light scattering from ternary systems composed of solvent(l)-polymer(2)-polymer(3), in which species (3) is isorefractive to the solvent (i.e. 0n/0c ₃ = 0), offers an attractive way to study the tracer diffusion coefficient of species (2) in a binary mixture of composition c ₃. In regimes of low momentum transfer (qR _G < 1,) where q is the scattered wave vector and R _G is the polymer radius of gyration, we have shown that the correlation function of the scattered electric field should decay with a single exponential decay time, given by (D₂₂ q ²)^?1 where D ₂₂(c ₂, c ₃) is the main ternary diffusion coefficient of component (2). Extrapolation to zero concentration of 2) at fixed concentration of (3) yields the tracer diffusion coefficient of (2) in the binary mixture of (1) and (3). The systems toluene(l)-polystyrene(2)-polymethylmethacrylate(3) (0n/0c ₃ ≈ 0.007 at 25°C) and toluene(l)-polystyrene(2)-polyvinylmethylether (3) (0n/0c ₃ ≈ 0.012 at 60°C) very nearly satisfy the above criteria. In both systems, we have found that the tracer diffusion coefficient of the polystyrene decreases with increasing concentration of the isorefractive polymer. Further studies have focused upon the dependence of the tracer diffusion coefficient upon polystyrene molecular weight, and upon the effect of incomplete index matching.     

The product cycling problem under increasing yield rates

We investigate the product cycling problem (also known as the common cycle scheduling problem) when there are economies of scale due to increasing yield rates. Increasing yield rates are characteristic of production processes in which the percentage of acceptable parts increases with the duration of the production run, usually owing to adjustments made during the initial portion of the production run. We develop a solution procedure that is optimal for a wide range of production cost functions under very mild conditions. We then compare optimal solutions with those obtained from the commonly used 'fixed-plus-linear' approximation of costs. Computational results suggest that the 'fixed-plus-linear' approximation generally performs well, but may result in substantial errors under certain extreme conditions.