Objective: Cocaine-related cues have been hypothesized to perpetuate drug abuse by inducing a craving response that prompts drug-seeking behavior. However, the mechanisms, underlying neuroanatomy, and specificity of this neuroanatomy are not yet fully understood.Method: To address these issues, experienced cocaine users (N=17) and comparison subjects (N=14) underwent functional magnetic resonance imaging while viewing three separate films that portrayed 1 ) individuals smoking crack cocaine, 2) outdoor nature scenes, and 3) explicit sexual content. Candidate craving sites were identified as those that showed significant activation in the cocaine users when viewing the cocaine film. These sites were then required to show significantly greater activation when contrasted with comparison subjects viewing the cocaine film (population specificity) and cocaine users viewing the nature film (content specificity).Results: Brain regions that satisfied these criteria were largely left lateralized and included the frontal lobe (medial and middle frontal gyri, bilateral inferior frontal gyrus), parietal lobe (bilateral inferior parietal lobule), insula, and limbic lobe (anterior and posterior cingulate gyrus). Of the 13 regions identified as putative craving sites, just three (anterior cingulate, right inferior parietal lobule, and the caudate/ lateral dorsal nucleus) showed significantly greater activation during the cocaine film than during the sex film in the cocaine users, which suggests that cocaine cues activated similar neuroanatomical substrates as naturally evocative stimuli in the cocaine users. Finally, contrary to the effects of the cocaine film, cocaine users showed a smaller response than the comparison subjects to the sex film.Conclusions: These data suggest that cocaine craving is not associated with a dedicated and unique neuroanatomical circuitry; instead, unique to the cocaine user is the ability of learned, drug-related cues to produce brain activation comparable to that seen with nondrug evocative stimuli in healthy comparison subjects.

This paper deals with two aspects of the flux law for diffusive convection: (1) the dependence on density ratio, and (2) the dependence on AT. Empirical formulations of the dependence of temperature and salinity fluxes on density ratio are developed using published measurements. At high density ratios (R o > 4) our temperature fluxes agree with those given by Marmorino and Caldwell's (1976) formulation, but at low density ratios (Rp < 2.5) our temperature fluxes are smaller by half. However, it is suggested that any formulation of the 4]3 flux law should be used with caution. A simple convection theory implies that fluxes are not proportional to AT 4/3, as the 4/3 law states, but rather axe proportional to AT raised to an power closer to 5/4. The theory accurately matches measurements of velocity and heat flux in thermal convection. There are insufficient data to test (or even fully formulate) the theory for diffusive convection, but if the thermal convection results carry over to the diffusive case, then the 4/3 flux law overestimates oceanic fluxes by up to about 30%. 1. To present an empirical formulation of the dependence of fluxes on density ratio, using a large data set of published laboratory measurements. This analysis presumes the validity of the traditional 4/3 flux laws. 2. To open discussion of the possibility that the 4/3 flux law (that is, the proportionality between flux and AT 4/a) may be fundamentally wrong and that the exponent on AT may vary between 5/4 and 4]3, depending on the value of the Rayleigh number. Empirical Formulation of C(Ro) Figure 1 shows the flux factor C(Ro) calculated for laboratory experiments made by Turner [1965], Crupper [1975], Marmorino and Caldwell [1976], Newell [1984], and Taylor [1988]. The experimental program typically involves monitoring T and S variations in the layers, using conservation laws to infer the temperature and salinity fluxes, 3365 3366

Small changes in the ways that the ocean transports heat to the overlying ice cover could have a substantial effect on future changes in Arctic ice cover.

The diffusive regime of double-diffusive convection is reviewed, with a particular focus on issues that are holding up the development of large-scale parameterizations. Some of these issues, such as interfacial transports and layer-interface interactions, may be studied in isolation. Laboratory work should help with these. However, we must also face more difficult matters that relate to oceanic phenomena that are not easily represented in the laboratory. These lie beneath some fundamental questions about how double-diffusive structures are formed in the ocean, and how they evolve in the competitive ocean environment.

No abstract