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Cytotoxic T lymphocytes (CTLs) kill virus-infected and cancer cells through T cell receptor (TCR) recognition. How CTLs terminate signaling and disengage to allow serial killing has remained a mystery. TCR activation triggers membrane specialization within the immune synapse, including the production of diacylglycerol (DAG), a lipid that can induce negative membrane curvature. We found that activated TCRs were shed into DAG-enriched ectosomes at the immune synapse rather than internalized through endocytosis, suggesting that DAG may contribute to the outward budding required for ectocytosis. Budding ectosomes were endocytosed directly by target cells, thereby terminating TCR signaling and simultaneously disengaging the CTL from the target cell to allow serial killing. Thus, ectocytosis renders TCR signaling self-limiting.

Aluminum is the most abundant metal and the third most abundant chemical element in Earth's crust, comprising over 8% of its weight. This chapter reviews the characteristics of aluminum alloys that make them so attractive and note the variety of applications in which they are used. It discusses the wrought alloys and cast alloys. The general corrosion behavior of aluminum alloys depends basically on three factors: (1) the stability of the oxide film, (2) the environment, and (3) the alloying elements. Cutting tool materials for machining aluminum alloys include water-hardening steels, high-speed steels, hard-cast alloys, sintered carbides, and diamonds. The aluminum surface can be finished in more different ways than any other metal. The normal finishing operations fall into four categories: mechanical, chemical, electrochemical, and applied. There are at least two approaches to overviewing important applications of aluminum alloys: by alloy class, and by type of application. Keywords: aluminum alloys; cast alloys; cutting tool materials; wrought alloys

To identify useful sources of materials data, it is important to have clearly in mind at the outset (a) the intended use of data, (b) the type of data required, and (c) the quality of data required. These three factors are key in narrowing a search and improving its efficiency of a search for property data. Therefore, as an introduction to the identification of some specific potentially useful sources of materials data, this chapter discusses those three factors in some detail and describes the options available in types of data sources. The chapter also discusses two fundamental types of materials databases: textual data and numeric data. The two factors affecting data quality and reliability include (a) the manner in which the data were obtained and (b) the statistical reliability of the data presented. The chapter also discusses the variety of platforms available for databases today. Keywords: data quality; data sources; material data; numeric data; statistical reliability; textual data

For developing or verifying material science models and simulation techniques, it is frequently important to have access to reliable material properties in electronic format. New sources of such data are becoming more readily available now, and one notable example of this is the services of STN International. STN is the worldwide scientific and technical information network, operated jointly by the American Chemical Society in the USA, Fachinformationzentrum-Karlsruhe in Europe, and the Japanese Information Center for Science and Technology in Asia. The numeric properties data services available on STN, notably the Material Property Data Network (MPD Network) and the Chemical Property Data Network (CPD Network) are described in some detail below, and their applicability to expert modeling and simulation programs discussed.

Direct and easy-to-use access to a worldwide network of numeric material property databases has been an objective for the past fifteen years, and yet that result remains elusive. In this paper, the authors explore the technical and non-technical issues that have limited it, note some actions that may help meet the objective, and speculate on the nature of the next generation of materials data networks.

As a lead-in to the use of 5083 for liquefied natural gas tanks [1], a special series of fracture tests was ran to substantiate that the alloy has high tear resistance in the relatively thick sections in which it would be used in the structure. These tests were similar in nature to the tear tests which have been made for years [2], but covered a much wider range of variables, viz., (1) much thicker material., (2) specimens from the heat-affected zone as well as the parent metal and the welds, (3) welds made automatically, semiautomatically, and in different positions (flat, vertical, horizontal), and (4) welds in extruded shapes as well as plate. The purposes of this paper are to describe the test procedures, present the results, and discuss their meaning as an indication of the toughness of 5083 for engineering structures.

The mechanical properties of aluminum alioys have been well documented at temperatures down to -320°F for many years [1–3] and, within the past few years, a reasonable amount of information has been developed at -423°F with liquid hydrogen as the cooling agent [4–7]. Nevertheless, little has been known of the properties of aluminum alloys at -452°F, the temperature of liquid helium; only one alloy, 5083, has been thoroughly evaluated prior to 1966 [8].

The explosion of interest in computerized material property data bases and intelligent knowledge systems for flexible manufacturing processes has resulted in two significant developments in the last couple of years: the incorporation of the National Materials Property Data Network, Inc. (MPD Network), and the formation of ASTM Committee E-49 on Computerization of Material Property Data. The MPD Network has the mission of providing engineers and scientists with easy on-line access to worldwide sources of reliable, well-documented material property data. The status of its pilot network and plans for the future are outlined herein. ASTM Committee E-49 has the mission of developing and providing guidelines and standards to aid the builders, maintainers, and suppliers of data bases in meeting the needs of industry and in establishing compatible and consistent sources capable of sharing data. Also reported in this paper is the early progress of the Technical Committee of the MPD Network in establishing guidelines for the evaluation of data, recognizing that there are a number of aspects of data source building and management requiring audit as well as the data itself. It is important that sources of material performance data are well characterized, and that the nature and reliability of the information is conveyed to the user. The further development of guidelines and standard practices in this area will also be dealt with by ASTM Committee E-49. A brief overview of other major material property data base building activities in the United States is also provided.

Fracture-toughness tests have been made of 7075-T6 sheet and -T651 plate and of multi-layered panels of the sheet and plate. The nominal net fracture strength and the critical fracture-toughness parameters (Kc and Gc) of multilayered adhesive-bonded panels are greater than those of sheet or plate of the same total thickness, because the individual layers may fracture independently, each developing shear surfaces. The fracture strength and critical stress intensity factor, Kc, for a 0.5-in. thick panel made up of eight layers of 0.063-in. sheet are approximately twice those of 0.5-in. plate. Multilayered metallurgically bonded panels do not exhibit any advantage over sheet or plate of the same thickness, if the metallurgical bond retards shear-surface formation on the individual layers. The plane-strain stress-intensity factor, determined at pop-in on multi-layered adhesive-bonded or metallurgically bonded panels, is independent of thickness or number of layers.

A tremendous amount of progress has been made in fracture toughness testing over the past 15 years since ASTM Committee E24 was established to focus on the development of fracture test standards [1–6]. From the early leadership of J. R. Low, Jr., and the consistent effort of W. F. Brown, Jr., R. H. Heyer, J. E. Srawley, E. T. Wessel, and many other committee members, several fracture test standards now exist and a number of new methods are being explored for possible standardization. It is the purpose of this chapter to review the available documents, calling attention to those areas of continuing refinement, and to look at new developments likely to lead to new test standards some time in the future.

At present, the 2000(Cu), 5000(Mg), 6000(Mg-Si) series provide most of the aluminum alloys used in cryogenic applications. Established alloys in the 7000(Zn) series, including 7075, 7079, and 7178, are more sensitive to notches than many of the alloys of the above types [1,2] and have not been seriously considered. Recently, several new 7000-series alloys have been introduced with appreciably greater notch toughness than other alloys of this type. It is. expected that these new alloys may be of considerable use in cryogenic applications.

The 'stress-corrosion-fatigue' performance of several high strength- aluminum alloys was investigated by tests of hydraulic cylinders and other types of specimens. Specimens were prepared from forgings and forging stock of alloys 2014-T6, 7075-T6, 7075-T73, 7079-T6, and X7080-T7 and from premium castings of alloy CH70-T7. Alloy 7075-T73 rated best in the corrosion-fatigue tests; no stress-corrosion cracking occurred in this alloy, and the lives of forged cylinders subjected to repeated loadings to 80% of design stress in a corrosive environment were at least 10 times as long for this alloy as for forged cylinders of alloys 2014-T6, 7075-T6, or 7079-T6. Fractographic examination showed that stress-corrosion cracking as well as fatigue cracking occurred in alloys 2014-T6, 7075-T6, and 7079-T6 in the stress-corrosion-fatigue tests. The investigation demonstrated that stress corrosion and fatigue can interact under certain conditions to produce failures in shorter times and fewer cycles than for either phenomenon occurring by itself.

To assist in making the wisest choice of materials for cryogenic applications where fracture toughness is important, a number of investigators have been using tensile tests of smooth and notched specimens to evaluate the notch sensitivity of materials at subzero temperatures[1–6]. There has been little agreement among the investigators as to the design of notch which leads to the most effective comparison of materials although specific choices have been made by some groups.

The tensile properties, plane-strain fracture toughness, axial-stress fatigue properties and fatigue-crack propagation rates, and the resistance to exfoliation and stress-corrosion cracking, were determined for several aluminum alloys. Two thicknesses of X7080-T7E41(T751) and 7178-T651 plate, and two thicknesses of 7075-T6510, 7075-T73510, X7080-T7E42(T7510) and 7178-T6510 extruded shapes, were evaluated.

There are some applications where aluminum alloy castings, because of the ease with which they can be made into relatively complex shapes, would be very desirable for service at cryogenic temperatures. Parts which would require extensive machining from plate or hand forgings and are too intricate for the effective use of die forgings, would be suited ideally for fabrication by casting.

Experience indicates that with the development of materials with higher strengths, the tendency toward catastrophic low-ductility fractures increases, particularly at cryogenic temperatures. Continued efforts to use these higher-strength materials in structural units and yet to ensure against catastrophic low-ductility fractures have markedly increased the efforts aimed at evaluating the resistance of materials to rapid crack propagation. Formerly, coarse qualitative measures were sufficient, but more critical criteria for quantitatively rating materials and for realistically designing with them are now needed.

An impressive amount of literature has been developed to define the tensile properties and notch toughnesses of aluminum alloys at very low cryogenic temperatures [1–3], Data and service experience are consistent in indicating the suitability of many aluminum alloys for cryogenic service, since they retain their relatively high ductility and notch toughness, in addition to having useful strengths at very low temperatures. Although a fair amount of data have been presented on the tensile properties and notch toughness of welds in aluminum alloys [4,5], none have been available for liquid-helium temperature to provide a guide as to which particular combinations of parent and filler alloys might be most desirable for extremely low-temperature service.

Among the readily weldable aluminum alloys showing great promise for cryogenic applications, 2219[1,2] appears to be outstanding. In tests made recently at NASA Lewis Research Laboratories[3], the strengths of both smooth and notched specimens from 2219-T62 sheet (plain, as-welded, and reheat-treated and aged-after-welding) were shown to increase with decrease in temperature to -423°F. The elongations generally remained relatively high. This alloy appears to offer medium-high strength and high toughness similar to that of the high-strength aluminum-magnesium series of alloys plus the advantages of response to postweld thermal treatments.

The interest in the use of aluminum alloys for cryogenic applications has stemmed from the long-recognized increases in tensile properties of these alloys at depressed temperatures [1–4]. The fact that the elongations, as well as the strengths, of most aluminum alloys increase as temperature decreases, and that the reduction of area values are about the same at -320oF as at room temperature, formed the basis for further study of the properties of these alloys at low temperature. Also of importance was the often demonstrated absence of transition in fracture behavior.

Because of the economic advantages in utilizing aluminum alloys for applications at very low temperatures, data were published in 1967 and 1968 for a variety of 2XXX and 5XXX aluminum alloys and for welds in those alloys at -452°F [1’2] showing their high strength, ductility, and toughness. This program has now been extended to include 7XXX alloys in several tempers.

It is well known that the mechanical properties of 301 stainless steel are greatly enhanced by forming at cryogenic temperatures [1,2]. This procedure is sufficiently advantageous that the technique of “cryoforming” stainless steels has become a fairly standard procedure, and such products are available from several suppliers.

No case of eczema due to lemon peel could be found in the literature; hence this report. J. H., a white man, aged 23, was employed by a beverage manufacturing company for four weeks. A week after he began work he was assigned the task of peeling lemons by hand. Itching sensations, followed by an eruption on the hands and forearms, began soon thereafter. In the midst of the peeling operation he would rub both hands and arms to get relief. When first seen, May 2, 1931, he presented an erythematous, vesicular eruption on the dorsum of each hand and on the anterior and posterior aspects of the forearms. A few scattered minute pustules were on the back of the hands. An erythematous vesicular eruption was found on his chin and neck. Contact tests were carried out with fresh lemon peel and lemon juice. These were negative for the lemon