Effect of magnesium content on the ageing behaviour of water-chilled Al-Si-Cu-Mg-Fe-Mn (380) alloy castings

A study of the effect of magnesium concentration on the ageing behaviour as measured by the hardness of 380 alloy was conducted for three levels of magnesium, namely 0.06 (base alloy), 0.33 and 0.5 wt%, for water-chilled castings (dendrite arm spacing ∼ 10–15 μm). Differential scanning calorimetry analysis of as-cast samples was carried out to determine the changes in the reactions of the phases obtained during alloy solidification, employing heating rates of 0.1 and 1.0°Cs⁻¹, up to approximately 700°C. Two heat treatments were applied to the as-cast alloys: T5 comprising ageing at 25 (room temperature), 155, 180, 200 and 220°C, for times up to 200 h, and T6 comprising solution heat treatment at 480 °C or 515°C for 8 h, followed by quenching in warm water at 60°C, followed by immediate artificial ageing at 155 or 180°C for varying times up to 100h. The results show that the higher hardness values obtained with T6 treatment can be explained by the excess precipitation of magnesium-containing phases in the as-solidified alloys. This precipitation could be eliminated under the high cooling-rate conditions prevalent in die-casting operations so that T5 treatment may be used to replace T6 treatment to produce the same hardness values. In addition, solution heat treatment in the low-temperature range (480–515°C) is adequate to produce the required changes in silicon morphology and dissolution of magnesium in the matrix. No significant difference in hardness behaviour was observed when the magnesium content was increased beyond 0.3 wt%.     

Minimal communication cost software construction in the Internet environment

This paper investigates the issue of building software in the Internet environment, where local area network (LAN) based systems are interconnected by links with different bandwidth and do not share file systems. The software is modeled as a directed acyclic graph. Each node in the graph represents a logical step in processing the software while the edges describe the order of execution. The problem is to construct the software at a particular LAN with minimum Internet communication cost. An optimal polynomial algorithm, SOFTCON, with time complexity is presented, where and are the number of nodes and edges in the graph describing the software respectively, is the number of LANs in the Internet environment, and is the time complexity of the network flow algorithm on the flow network with nodes and edges transformed from the directed acyclic graph of the software. Received: 6 December 1995 / 1 May 1996     

Spinal abscess of Haemophilus paraphrophilus. A case report

STUDY DESIGN: A case of paraspinal abscess formation from Haemophilus paraphrophilus is presented. OBJECTIVES: To describe a case of paraspinal abscess formation from H. paraphrophilus, a fastidious commensal organism of the mouth and pharynx. A precise bacteriologic identification can be difficult; techniques for such identification are discussed. SUMMARY OF BACKGROUND DATA: Spinal abscess caused by H. paraphrophilus is unusual and can be very difficult to diagnose. METHODS: The etiology, clinical presentation, technical examinations, and treatment are reviewed. RESULTS: Prolonged antibiotic treatment was curative, although surgery was considered. CONCLUSIONS: Bacteriologic diagnoses in these rare infections are difficult. Antibiotic therapy was curative in the patient described.     

Autoxidation of ubiquinol-6 is independent of superoxide dismutase

Ubiquinone (Q) is an essential, lipid soluble, redox component of the mitochondrial respiratory chain. Much evidence suggests that ubiquinol (QH2) functions as an effective antioxidant in a number of membrane and biological systems by preventing peroxidative damage to lipids. It has been proposed that superoxide dismutase (SOD) may protect QH2 form autoxidation by acting either directly as a superoxide-semiquinone oxidoreductase or indirectly by scavenging superoxide. In this study, such an interaction between QH2 and SOD was tested by monitoring the fluorescence of cis-parinaric acid (cPN) incorporated phosphatidylcholine (PC) liposomes. Q6H2 was found to prevent both fluorescence decay and generation of lipid peroxides (LOOH) when peroxidation was initiated by the lipid-soluble azo initiator DAMP, dimethyl 2,2'-azobis (2-methylpropionate), while Q6 or SOD alone had no inhibitory effect. Addition of either SOD or catalase to Q6H2-containing liposomes had little effect on the rate of peroxidation even when incubated in 100% O2. Hence, the autoxidation of QH2 is a competing reaction that reduces the effectiveness of QH2 as an antioxidant and was not slowed by either SOD or catalase. The in vivo interaction of SOD and QH2 was also tested by employing yeast mutant strains harboring deletions in either CuZnSOD and/or MnSOD. The sod mutant yeast strains contained the same percent Q6H2 per cell as wild-type cells. These results indicate that the autoxidation of QH2 is independent of SOD.     

A 1000 A/20 kV/25 kHz-500 kHz Volt-Ampere-Wattmeter for loads withpower factors from 0.001 to 1.00

Many industrial processes and scientific experiments utilize large amounts of ac power at frequencies from 3 kHz to 500 kHz. The phase angle and the impedances of these loads often vary over a wide range. This paper describes an instrument to provide an accurate measurement of currents (1 A to 1000 A), voltages (100 V to 20 kV), and powers (100 W to 20 MW) over the frequency range from 25 kHz to 500 kHz. It deals with loads having power factors down to nearly zero and with load impedances from 10 Ω to 20 kΩ. The paper contains practical details of both the design and the calibration of the front-end voltage and current transducers. The characteristics of a nearly ideal broadband current transducer are presented. Overall instrument calibration, verification and traceability problems are considered in detail     

New and used temporal models: An issue of time

TheSpecial Issue on Applications of Temporal Models raises many issues of time: What are the important properties of time? How can time be best represented? How can one reason about time-dependent properties? What are the important directions of temporal research? This introductory piece very briefly surveys the current wide variety of temporal models, temporal reasoning methods, and applications to time-varying phenomena. Promising areas of investigation such as the verification of concurrent systems, knowledge-base representation methods, and dealing with theFrame Problem pass in fleeting review. Brief introductions to each of the works in the volume close the section.     

Effect of alloying elements on the solidification characteristics and microstructure of Al- Si- Cu- Mg- Fe 380 alloy

The effect of varying the major alloying elements within the limits of specification on the solidification behavior, fluidity, and microstructure of a 380 alloy has been studied at two cooling rates. The thermal analysis technique has been used to study the solidification behavior. The alloying elements investigated ranged from 3.22 to 4.09 pct copper, 1.01 to 1.70 pct iron, 0.06 to 0.50 pct magnesium, 1.69 to 3.00 pct zinc, and 0.16 to 0.46 pct manganese. The results show that the solidification behavior of the 380 alloys is complicated, and the cooling curve at 0.4 ‡C/s indicates six reactions taking place during the process of solidification. Cooling curves obtained for each of the alloying element additions, their analysis, and the resultant microstructures are discussed.     

Tracking trajectories of the cart-pendulum system

The problem of tracking a periodic trajectory of the well-known cart-pendulum system is solved. After a change of coordinates and a change of feedback, the equations of this system are nonlinear but feedforward. This property is extensively used to carry out for this system the design of uniformly asymptotically stabilizing time-varying state feedbacks by using the forwarding approach.     

Polymerase chain reaction in the diagnosis of tuberculosis. Comparison of two target sequences for amplification

Amplification of a 340 bp sequence of the 38 kDa protein gene of Mycobacterium tuberculosis by the polymerase chain reaction has been developed. The sensitivity of this PCR was shown to be 10 fg both by agarose gel electrophoresis and Southern blot hybridisation being equivalent to 2-3 organisms and highly specific to M. tuberculosis and excluding even M. tuberculosis H37Ra and Mycobacterium bovis BCG. Sputum samples from patients with pulmonary tuberculosis gave a positivity rate of 45%. PCR was also performed using pt8 and pt9 primers which amplified a 541 bp sequence of IS6110. 41% of the above samples gave positive amplification. Three samples that were positive for 38 kDa sequence were negative for IS6110.     

Validity of psychological assessment: Validation of inferences from persons' responses and performances as scientific inquiry into score meaning.

The traditional conception of validity divides it into three separate and substitutable types: content, criterion, and construct validities. This view is fragmented and incomplete, especially because it fails to take into account both evidence of the value implications of score meaning as a basis for action and the social consequences of score use. The new unified concept of validity interrelates these issues as fundamental aspects of a more comprehensive theory of construct validity that addresses both score meaning and social values in test interpretation and test use. That is, unified validity integrates considerations of content, criteria, and consequences into a construct framework for the empirical testing of rational hypotheses about score meaning and theoretically relevant relationships, including those of an applied and a scientific nature. Six distinguishable aspects of construct validity are highlighted as a means of addressing central issues implicit in the notion of validity as a unified concept. These are content, substantive, structural, generalizability, external, and consequential aspects of construct validity. In effect, these six aspects function as general validity criteria or standards for all educational and psychological measurement, including performance assessments, which are discussed in some detail because of their increasing emphasis in educational and employment settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)