Counter-examples to Johnson's LQR propriety limits

The question of the range of applicability of the optimal linear regulator results is addressed. In particular, Johnson's recently reported expanded limits are investigated. It is shown that while it may be possible to expand these original limits to some degree, the limits presented by Johnson are too broad and are easily disproved using simple counter-examples.     

On the linear regulator with cross terms in the performance index

The linear regulator theory which is perhaps the most used result of modern control theory is known to apply even when the performance index contains cross terms in control and state. Bryson and Ho (1960) present this result in terms of an equivalent problem. Conditions which guarantee the existence of a solution to the optimal gain equation for the finite and infinite time eases are well known for the equivalent problem. This note presents these conditions in terms of the original problem.     

Performance evaluation of flexible manufacturing systems with blocking

Analytical approximations for the performance of flexible manufacturing systems (FMS) with blocking of machines due to limited local buffers are presented. The approximations are based on a detailed analysis of FMS configurations used in industry. The method proposed uses informations generated by applying the classical closed queueing network (CQN) model to the FMS. The approximations developed are tested against simulation models for a wide variety of FMS configurations. The results presented show that the approximations are very good.     

Measurement of Enzymatic Browning at Cut Surfaces and in Juice of Raw Apple and Pear Fruits

Reflectance procedures were developed to measure the extent of enzymatic browning at cut surfaces and in the raw juice of apple and pear fruits. Reflectance L and a measurements, made at transversely cut surfaces of plugs bored from fruit halves, were linear or bilinear with log time and related to the extent of browning in six apple cultivars. With apple and pear juices, tristimulus values changed linearly with time in samples undergoing browning. Differences between initial and final tristimulus values were better indices of browning than the slopes of time curves. The suitability of these procedures for evaluating the effectiveness of browning inhibitors was demonstrated with SO₂ and ascorbic acid treatments.     

INHIBITION OF LISTERIA MONOCYTOGENES BY NATIVE MICROFLORA OF WHOLE CANTALOUPE1

Fresh‐cut cantalcupe has been recalled due to the possible presence of Listeria monocytogenes. Several studies have reported that naturally occurring microflora of vegetable surfaces may be antagonistic to pathogen attachment, growth or survival. To test this possibility for L. monocytogenes and cantaloupes, whole melon were treated with water, ethanol (70%) or chlorine (200 ppm) to reduce the native microflora on the melon surfaces. Treated or untreated melons were immersed in a six strain cocktail of L. monocytogenes (10⁷ CFU/mL) for 10 min and then allowed to dry for 1 h inside a biosafety cabinet followed by storage at 5, 10 and 20C for 15 days. Fresh‐cut pieces prepared from the treated or untreated melons and directly inoculated with L. monocytogenes (3.48 log CFU/g) were stored under the same conditions listed above. Populations of L. monocytogenes and five classes of native microflora were investigated. Growth of L. monocytogenes in sterile or nonsterile rind and fresh‐cut homogenates was also studied. The population of L. monocytogenes recovered from inoculated (10³ to 10⁸ CFU/mL) whole melons given no disinfection treatment or washed with water was significantly less (P < 0.05) than that recovered from melons treated with chlorine or EtOH. In general, populations of L. monocytogenes declined on the surface of treated and untreated whole melons and on fresh‐cut pieces over the 15 days storage period at the temperatures tested. However, the decline in pathogen populations was less rapid in the presence of reduced populations of native microflora. Higher populations of L. monocytogenes were attained in sterile tissue homogenates than in nonsterile homogenates. Addition of yeast and mold to sterile rind homogenates was highly inhibitory to growth and survival of the pathogen. The results of this study indicate that native microflora of whole cantaloupe inhibited attachment to rind surfaces as well as survival and growth of L. monocytogenes on cantaloupe surfaces and homogenized fresh‐cut pieces. Thus, L. monocytogenes recontamination of melons having a reduced level of native microflora following application of a disinfection treatment may be a food safety concern.     

LARGE ELECTROMAGNETIC PUMPS

ABSTRACT

The development of large electromagnetic pumps for the liquid metal heat transfer systems of fission reactors has progressed for a number of years. Such pumps are now planned for fusion reactors and solar plants as well. The Einstein-Szilard (annular) pump has been selected as the preferred configuration. This paper describes a 54.9 m5/min (14,500 gpm), 1262 kPa (183 psi), 540 °C (1000 °F) test pump and briefly discusses some of the reasons that electromagnetic pumps may be preferred over mechanical pumps and why the annular configuration was selected. A detailed electromagnetic analysis of the annular pump, based on slug flow, is presented. The analysis is then used to explore the implications of large size and power on considerations of electromagnetic skin effect, geometric skin effect, and cylindrical geometry.     

Sugar Composition and Flavor Quality of High Sugar (Shrunken) and Normal Sweet Corn

Soluble sugar composition of the corn kernel in a shrunken (high sugar) variety, ‘Xtra Sweet 77′, and a normal sweet variety, ‘Jubilee’ was determined after freezing a corn-on-cob product at two levels of commercial harvest maturity by HPLC and enzymic methods of analysis. Sucrose, glucose and fructose were found in measurable amounts by both methods. The less mature sample of either variety contained the higher level of each sugar, at a sucrose:glucose:fructose ratio of approximately 15:1:1 in ‘Jubilee’ and 20:1:1 in ‘Xtra Sweet 77′. Sensory evaluation showed ‘Xtra Sweet 77’ which contained nearly twice the total sugars of ‘Jubilee’ to be sweeter. Sweetness differences between maturity samples within a variety were not significant, nor was there a consistent preference shown for the higher sweetness or overall quality of the ‘Xtra Sweet 77’ samples. Sensory perception of sweetness was most highly correlated with sucrose content.     

Engineering Concepts and Communication: A Two‐Quarter Course Sequence

Together the departments of engineering and English designed and implemented a course sequence that sustains first‐year enrollment in engineering while teaching engineering design and fundamental communication skills. The sequence integrates the goals of four formally separate courses: Critical Reading and Writing, Argument and Research, Engineering Concepts I and II. Linking the courses did not detract from the original course goals nor burden the limited time resources of the participating faculty. We found that the linked courses have increased our first to second year retention rate by up to 30 percent.