Ceramic packages for liquid-nitrogen operation

To evaluate their compatibility for use in a liquid-nitrogen computer, metallized ceramic packages with test chips using controlled-collapse solder (Pb-Sn) technology were cycled between 30°C and liquid-nitrogen temperature. Room-temperature electrical resistance measurements were made at regular intervals of cycles to determine whether solder failure accompanied by a significant resistance increase had occurred. For the failed solder joints characterized by the highest thermal shear strain amplitude of 3.3%, it was possible to estimate the number of liquid-nitrogen cycles needed to produce the corresponding failure rate using a room-temperature solder lifetime model. Cross-sectional examination of the failed solder joints using scanning electron microscopy (SEM) and energy-dispersive X-ray analysis indicated solder cracking occurring at the solder-ceramic interface. Chip-pull tests on cycled packages yielded strengths far exceeding the minimal requirement. Mechanisms involving the formation of intermetallics are proposed to account for the observed solder fracture modes after liquid-nitrogen cycling and after chip pull. SEM examination of pulled chips in cycled packages found no apparent sign of cracking in quartz and polyimide for chip insulation     

Characterization of cured polystyrylpyridine by model compounds

The crosslinking or curing reaction of polystyrylpyridine (PSP) has been studied by means of thermal reactions of its model compounds. Compounds 2,6-distyrylpyridine, 4-stilbazole (4-styrylpyridine), and deuterated 4-stilbazole were pyrolyzed at 200–325°C both in air and under vacuum in a sealed tube. The major pyrolysis products were diarylethane and stilbene, and were characterized by gas chromatography-mass spectrometry. Major dimeric products were naphthalene or quinoline derivatives. Mechanisms for the pyrolysis are suggested, and a crosslinked structure for cured PSP is proposed based on the thermal reaction products of model compounds.     

The coincidence counting technique for orders of magnitude background reduction in data obtained with the magnetic recoil spectrometer at OMEGA and the NIF

A magnetic recoil spectrometer (MRS) has been built and successfully used at OMEGA for measurements of down-scattered neutrons (DS-n), from which an areal density in both warm-capsule and cryogenic-DT implosions have been inferred. Another MRS is currently being commissioned on the National Ignition Facility (NIF) for diagnosing low-yield tritium-hydrogen-deuterium implosions and high-yield DT implosions. As CR-39 detectors are used in the MRS, the principal sources of background are neutron-induced tracks and intrinsic tracks (defects in the CR-39). The coincidence counting technique was developed to reduce these types of background tracks to the required level for the DS-n measurements at OMEGA and the NIF. Using this technique, it has been demonstrated that the number of background tracks is reduced by a couple of orders of magnitude, which exceeds the requirement for the DS-n measurements at both facilities.     

Minimizing hierarchical routing error

In hierarchical routing schemes, nodes are grouped into clusters at multiple levels, and a given node sees only a summarized view of the entire network. Hierarchical routing introduces error, which is the difference between the hierarchical path length and the optimal path length using flat routing. Since in practice the routing table size at each node is limited, we formulate the constrained optimization problems of finding a hierarchy structure that minimizes either the worst case or average case routing error. We prove results characterizing solutions of these problems, and present dynamic programming solution algorithms and computational results.     

Getting to the core of the problem: origin of the luminescence from (Mg,Zn)O heterostructured nanowires

We have measured the time-resolved, X-ray excited optical luminescence spectra from two types of MgxZn(1-x)O core-shell, heterostructured nanowires: type I, with a small x, wurtzite core, encased in a larger x, wurtzite sheath; and type II, with a wurtzite core (x approximately 0), encased in a rock-salt sheath (x>0.62). By monitoring the X-ray energy dependence of the various luminescence peaks, we have determined the local environment of the sites where these peaks originate.     

国际化学法规对清洗产品的蕴含

演讲提纲 我将首先简单介绍美国肥皂与洗涤剂协会及我们在化学品管理中所扮演的角色.     

Using passive air samplers to assess urban-rural trends for persistent organic pollutants. 1. Polychlorinated biphenyls and organochlorine pesticides

Passive air samplers were used to investigate urban-rural differences of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) over an integrated time period. Samplers consisting of polyurethane foam (PUF) disks and semi-permeable membrane devices (SPMDs) were housed in protective chambers and deployed at six sites for a 4 month duration in the summer of 2000. The sampling transect originated in downtown Toronto and extended approximately 75 km northward into a rural region. Results for the two types of samplers agreed well with one another. Higher blank levels were encountered for the SPMDs, especially for the OCPs, whereas blanks were very low for the PUF disks. Passive sampler-derived air concentrations were consistent with previous measurements of PCBs and OCPs in the region. The largest urban-rural gradient was observed for PCBs (approximately 5-10 times). Chlordanes also showed an urban-rural gradient, possibly reflecting past usage of chlordane on residential lawns and emissions from treated house foundations. Other OCPs exhibited a rural-urban gradient (dieldrin, endosulfan 1, and DDT isomers), which was attributed either to off-gassing from previously treated agricultural soils (dieldrin and DDTs) or to continued usage in agriculture (endosulfan 1). The results of this study demonstrated the feasibility of using such devices to determine air concentrations of persistent organic pollutants (POPs) and to assess their spatial distribution for time-integrated samples. Data such as this is essential for: model validation and for process research and addressing international monitoring strategies on POPs.