Responding changes systematically within sessions during conditioning procedures

When the procedure is held constant within an experimental session, responding often changes systematically within that session. Many of these within-session changes in responding cannot be dismissed as learning curves or by-products of satiation. They have been observed in studies of positive reinforcement, avoidance, punishment, extinction, discrimination, delayed matching to sample, concept formation, maze and alley running, and laboratory analogues of foraging, as well as in the unconditioned substrates of conditioned behavior. When aversive stimuli are used, responding usually increases early in the session. When positive reinforcers are used, responding changes in a variety of ways, including increasing, decreasing, and bitonic functions. Both strong and minimal reinforcement procedures produce within-session decreases in positively reinforced behavior. Within-session changes in responding have substantial theoretical and methodological implications for research in conditioning.     

Ceramic-Metal Composite Produced by Melt Infiltration

A new ceramic-metal composite with continuous interconnected ceramic and metal phases has been fabricated from sintered aluminum nitride infiltrated with aluminum metal. A dense, lightweight, hard material with high strength has been obtained. Advance of the infiltration front was linear with time. The activation energy of the process was very high (330 kJ/mol), suggesting that a chemical interaction rather than viscous flow was rate-controlling. The infiltration rate was observed to be inversely proportional to the pore size. Thermal and mechanical properties of the composite were promising.     

The study of outcomes for CAPD versus hemodialysis patients

Tacrine [1,2,3,4-tetrahydro-9-acridinamine monohydrochloride monohydrate (THA), Cognex] is a potent acetylcholinesterase inhibitor recently approved for treatment of mild-to-moderate Alzheimer's disease. The potential for THA and/or a metabolite of THA to accumulate in brain tissue was investigated by autoradiographic and metabolic profiling techniques in rats given single and multiple doses of [14C]THA. In addition, the brain-to-plasma distribution time course of orally administered 1-hydroxy-THA (1-OH-THA, 24 mg/kg), a primary rat metabolite with anticholinesterase activity, was also examined. Results from a 16 mg/kg single-dose study showed THA to cross the blood-brain barrier readily and concentrate in brain tissue, approximately 5-fold compared with plasma. The metabolite 1-OH-THA was found in much lower amounts relative to THA and when given separately at a similar dose the levels in brain tissue were comparable with plasma concentrations. After multiple-dose administration, THA concentrations in brain tissue were approximately 3-fold higher than those achieved after a single oral dose. However, concentration of 1-OH-THA metabolite increased only 50%. These data suggest a marked difference between the ability of THA and 1-OH-THA to accumulate in brain tissue and may reflect differences in lipophilicity as estimated by calculated log p values. The relevance of THA accumulation in brain tissue to delays observed in THA clinical management of Alzheimer's disease remains to be established.     

Rare carotid-vertebrobasilar anastomoses with notes on the differentiation between proatlantal and hypoglossal arteries

Suspected to be a syndrome rather than an authentic clinical entity, the "desquamative interstitial pneumonia" (DIP) exhibits typical anatomo-pathological aspects of intra-alveolar proliferation of granular pneumocytes, type II pneumocytes, leaving the alveolar interstitium unaffected. In absence of superinfection, it remains almost free of fibrous or inflammatory manifestations. The association of DIP to 4 other fundamental histological varieties of diseases of the pulmonary interstitium (UIP, BIP, LIP, GIP) is at the origin of Liebow's classification. The clinical individualization of these entities is still questioned.