Using a combination of a seed layer, low-growth rates, and different growth temperatures, we have produced InAs/GaAs quantum dots ͑QD's͒ that emit at very long wavelengths ͑up to 1.39 m at 293 K͒ with an ultranarrow inhomogeneous broadening ͑full width at half maximum of 14 meV at 10 K͒. The results are discussed in terms of strain relaxation and reduced In/Ga intermixing in the second layer. These two phenomena are interrelated and their control is crucial for achieving long wavelength emission. The QD structures also exhibit interlayer electronic coupling effects. Finally, combining this method with the use of InGaAs in the barrier instead of GaAs, emission wavelengths around 1.5 m at 293 K have been achieved.

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A group of four patients with RA were examined to test the hypothesis that there is a change in the endogenous opioid system in the brain during inflammatory pain. Regional cerebral opioid receptor binding was quantified using the opioid receptor antagonist [11C] diprenorphine and positron emission tomography (PET). In the four patients studied in and out of pain, significant increases in [11C]diprenorphine binding were seen in association with a reduction in pain. Increases were seen in most of the areas of the brain that were sampled apart from the occipital cortex. Significant region-specific increases over and above the more generalized changes were also seen in the frontal, cingulate and temporal cortices in addition to the straight gyrus. These findings are consistent with the hypothesis that there are substantial increases in occupancy by endogenous opioid peptides during inflammatory pain.

Positron emission tomography was used to measure alveolar gas volume, pulmonary blood volume (VB), regional alveolar ventilation (VA), and the regional ventilation-to-perfusion ratio (VA/Q) in a transaxial slice at midheart level in eight supine subjects and one prone normal subject during quiet breathing. These relationships allow regional blood flow (Q) to be calculated as VA/(VA/Q). No significant differences between right and left lung were found. Within the volume studied, which excluded the peripheral 2 cm of the lung, there was an exponential increase in Q by 11%/cm from 1.2 ml.min-1.cm-3 in the upper (ventral) to 3.5 ml.min-1.cm-3 in the lower (dorsal) lung regions, explaining 61% of the total variation within groups, whereas the horizontal gradient only explained 7% (right lung; supine subjects). Similar gravitational gradients were found in the single prone subject. VA and Q were well matched except at the dorsal lung thoracic border where low values of VA/Q due to a reduction in ventilation were occasionally found even in these normal subjects. VB and Q were reasonably well matched, implying that variations in vascular transit time due to gravity are kept to a minimum. The coefficient of local variation of peripheral vascular transit times (VB/Q) (33%) was, therefore, less than would have been expected if VB and Q were uncorrelated (57%).

Scanning tunneling microscopy has been used to study the transition in surface structure between the As-terminated 2ϫ4 and c͑4ϫ4͒ reconstructions on both GaAs͑001͒ and InAs͑001͒, as a function of surface temperature under an As 2 flux. For both materials, two-phase surface reconstructions exist through the transition regime. On GaAs, the two-phase surface consists of disordered ͑2ϫ4͒-like structures plus a c͑4ϫ4͒-like phase terminating one monolayer below the 2ϫ4 surface. On InAs, a disordered asymmetric 1ϫ3 phase occurs ͕a͑1ϫ3͖͒ in addition to the main phases, one monolayer below each main phase. In both cases, simple addition of As via As-on-As chemisorption cannot account for the formation of the c͑4ϫ4͒ reconstruction from the 2ϫ4 surface. The c͑4ϫ4͒ phase is inherently multilayered, which explains how the structure can form without the addition or removal of the group III component and still maintain its layering registry with the residual 2ϫ4 or a͑1ϫ3͒ phase. One result of this formation process is the necessary intermixing of group III and group V species in the second layer of the c͑4ϫ4͒ reconstruction. Direct evidence of species intermixing on the top layer of the InAs͑001͒-a͑1ϫ3͒ structure is also shown and models for all of these reconstructions are proposed.

Studies performed on 18 patients with Parkinson's disease and 6 control subjects have shown that acute administration of L-DOPA in clinically effective doses gives rise to a diffuse increase in regional cerebral blood flow without accompanying stimulation of regional oxygen utilization. The data suggest that this rise in rCBF is caused by vasodilatation due to a direct action of the drug on the cerebral blood vessels. The effect of L-DOPA on rCBF did not correlate with the degree of clinical improvement seen in each patient after treatment. The therapeutic effect of L-DOPA in the brain was not reflected in any change of regional cerebral oxygen utilization as measured by our technique. We suggest that the pharmacological actions of L-DOPA in the brain take place on at least two different levels.