Photonic access concentrator for ATM gigabit switching fabrics

In future broadband communication networks the interest for purely photonic switches is due to the bandwidth mismatch between optical transmission networks and electronic switching nodes. Photonic ATM switching fabrics mainly based on wavelength-switching stages are therefore being studied, to implement high capacity switches with also concentration, multiplexing and demultiplexing functions, using state-of-the-art photonic technology. The architecture of an ATM photonic access concentrator is described in this paper, illustrating the design and implementation of its basic subsystems, the traffic concentrator and the cell multiplexer. The design guidelines are outlined in detail referring to an example, where 128 user lines at 622 Mb/s are given access to 4 outlets at 2.488 Gb/s. The corresponding implementation, based on the systematic use of cell wavelength encoding, makes use either of well-known photonic components, such as Fabry-Perot filters, fiber delay lines, splitters and combiners, either of recently developed devices, like high-speed optical gates and tunable filters and lasers. Finally, the system feasibility is demonstrated presenting the results obtained on a reduced size and speed experimental setup of the cell multiplexer     

Debugging programs that use macro-oriented data abstractions

Enhanced C (EC) is a set-oriented, extensible, C-like language. EC uses data abstractions to define new types. These data abstractions, called clusters, are macro-like devices that perform substitution on the typed syntax tree. Debugging programs that use clusters raise problems that are not encountered in ordinary programming languages. At compile time there is a need to determine and report whether the macro expansion will result in a legal program before this expansion actually takes place. At run-time the problems are how to account for replaced statements and how to handle variables whose types have been established by the clusters, variables that disappear, or variables whose names have been changed. This article presents these problems and their solutions as implemented by the EC compiler and the EC symbolic debugger. Similar debugging problems appear in other languages: The need to handle variables at run time is common to all languages that support data abstraction even if the abstractions are procedure oriented; also, a mild form of the problem of the replaced statement appears in inline procedure substitution of Ada. The solutions developed for the EC debugger apply to these cases as well.     

Modeling Temperature in Coupled Electrical and Thermal Simulations of the Electroconsolidation® Process

Electroconsolidation® is a process for densifying complex-shaped parts by using electrically conductive particulate solids as a pressure-transmitting medium. The part is immersed in a bed of the particulate medium contained in a die chamber. Sintering temperature is achieved by resistive heating of the medium while applying compaction pressure. The process is capable of ultrahigh temperatures and short cycle times and offers the potential for low processing costs.

Control of the process and selection of process conditions require knowledge of the temperatures within the die. Temperature gradients exist because of the high heating rate and because of variations of density and electrical resistivity of the medium due to the presence of the part. Direct measurement of temperature with thermocouples or other conventional means is impractical because of the high temperatures, high currents, and high pressures that are involved. Therefore, a computer model was developed to predict temperature as a function of time and applied voltage for any location in the die. The computer model is composed of three parts: a geometrical model to approximate the density and resistivity variations in the medium, a finite-element model to calculate the rate of resistive heating within each element, and a finite-difference model to calculate the temperature distribution based on solution of the heat-transfer equations. Predicted temperatures have been shown to be in excellent agreement with measurements, and numerical simulation provided encouraging consistency and reasonably accurate predictions of temperature profiles within the die. The model demonstrated the feasibility of a new process to achieve simultaneous application of pressure and heat to powder densification in Electroconsolidation.     

Volume effects and associations in liquid alloys

The regular associated solution model for binary systems has been modified by incorporating the size of the complex as an explicit variable. The thermodynamic properties of the liquid alloy and the interactions between theA _μB type of complex and the unassociated atoms in anA-B binary have been evaluated as a function of relative size of the complex using the activity coefficients at infinite dilution and activity data at one other composition in the binary. The computational procedure adopted for determining the concentration of clusters and interaction energies in the associated liquid is similar to that proposed by Lele and Rao. The analysis has been applied to the thermodynamic mixing functions of liquid Al-Ca alloys believed to contain Al₂Ca associates. It is found that the size of the cluster significantly affects the interaction energies between the complex and the unassociated atoms, while the equilibrium constant and enthalpy change for the association reaction exhibit only minor variation, when the equations are fitted to experimental data. The interaction energy between unassociated free atoms remains virtually unaltered as the size of the complex is varied between extreme values. Accurate data on free energy, enthalpy, and volume of mixing at the same temperature on alloy systems with compound forming tendency would permit a rigorous test of the proposed model.     

Psychosocial factors among members of religious and secular kibbutzim

Mortality in 11 secular kibbutzim between 1970 and 1985 was nearly twice that of 11 matched religious kibbutzim. A cross-sectional study was undertaken in 1991 in 10 of these settlements, 5 religious and 5 secular, to determine whether differences in risk factors could explain the unequal survival. These comprised physical, physiologic and biochemical measurements, health-relevant behaviors and psychosocial variables. This report addresses the psychosocial aspect of the study, which included assessment of sense of coherence, hostility, satisfaction with self, work-related stress, social supports and social contacts using self-administered questionnaires. The response rate among the sample of men and women, aged 35-64 years, was 76% (437 respondents, 208 men and 229 women). Analysis of variance and logistic regression (the latter comparing the upper or lower fourths of the distribution vs. the rest) were used. Religious kibbutz members reported a higher sense of coherence (odds ratio = 1.58, 95% CI 1.02 to 2.46) and a lower level of hostility (odds ratio = 0.49, 95% CI 0.33 to 0.75) than their secular counterparts. Findings for satisfaction with self and work-related stress were inconsistent; there were significant interactions between religious affiliation, sex and age. Younger women reported less satisfaction with self and higher work-related stress than the other age-sex groups in both types of kibbutz. There was no difference in social support or frequency of social contact between religious and secular kibbutzim. Voluntary work was more frequent among the religious kibbutzim. The findings are consistent with an interpretation that Jewish religious observance may enhance the formation of certain protective personality characteristics. Membership in a cohesive religious kibbutz community may increase host resistance to stressors and thereby promote overall well-being and a positive health status. This could reflect an interplay of individual and collective attributes of religion.     

Vitamin C Spray Drying: Study of the Thermal Constraint

Temperature variation in the spray drying method has no effect on the ascorbic acid molecule. No chemical interaction between the colloidal silica and the ascorbic acid could be determined, but a physicochemical interaction “absorption” was determined. Colloidal silica improved the final yield of spray drying in proportion to its concentration. No polymorphic forms could be determined in the spray-dried ascorbic acid. Drug release from the ascorbic acid spray dried was found to be dependent on the Aerosil content: highest release rates were obtained with Aerosil.     

Inside this month

This issue contains a preview of the CFA’s annual trade show, which this year takes place in Anaheim, California. Those of you who also attend the JEC Composites Show in Paris will see a vast difference between these two events, not only in cultural terms but also in focus. CFA is an association for US manufacturers and its show places a high emphasis on education and networking. JEC’s slant is to the end-user and it strives to be a showcase for composites technology. Both of these approaches are to the ultimate benefit of the composites industry, but as companies continue to look at ways of spending their money more effectively, show attendance is one area coming under increasing scrutiny. Many have been saying that it is too expensive to attend JEC every year and now a group of major resin suppliers, including DSM, Reichhold, Ashland and Cray Valley, have taken the step of staying away from next year’s show (see page 64). This will surely dent the show’s profits and it will be interesting to see how the organisers, as well as other exhibitors, will respond to this development.     

Highly potent germination inhibitors in aqueous eluate of fruits of Bishop's weed (Ammi majus L.) and avoidance of autoinhibition

The aqueous eluate from fruits ofAmmi majus (Bishop's weed, Umbelliferae) remarkably inhibited germination of adjacent seeds ofAnastatica hierochuntica, lettuce, or tomato but had no effect on intact fruits ofAmmi. Similar inhibition was found in dark or in light, except that seeds ofA. hierochuntica were significantly more inhibited in the dark than in the light. Xanthotoxin was isolated, identified, and found to account for about a sixth of the inhibitory activity of the eluate. After fruits ofAmmi were submerged in a large volume of water for 4 days, the fruits still exuded enough inhibitors to prevent germination ofA. hierochuntica, lettuce, or tomato. Data support also the proposal that the phytotoxins are compartmentalized between the inner and the outer fruit envelopes. The inner layer excludes inhibitors from the embryo and autotoxicity is thus avoided, whereas the outer one ensures a gradual liberation of the phytotoxic compounds. This, as well as the high reactivity of the eluate, the high densities ofAmmi fruits in nature, and their relatively limited annual germination, suggest chemical inhibition of neighboring plant species other thanAmmi. Hence, in addition to their chemical protection against predators of either lower or higher organisms, furanocoumarins in fruits ofAmmi majus may contribute to its success as a weed.