Activator-inhibitor system cross

The Brusselator is a cross activator-inhibitor system if b > 1. The trace T and determinant A of the Jacobian are given by... 

The Schnakenberg model is a cross activator-inhibitor system iib > a. The deter-minant of the Jacobian is also always positive, h. = a + b), and no stationary bifurcation can occur. The Hopf threshold b is given by the cubic equation... 

Levodopa, the metabolic precursor of dopamine, is the most effective agent in the treatment of Parkinson s disease but not for drug-induced Parkinsonism. Oral levodopa is absorbed by an active transport system for aromatic amino acids. Levodopa has a short elimination half-life of 1-3 hours. Transport over the blood-brain barrier is also mediated by an active process. In the brain levodopa is converted to dopamine by decarboxylation and both its therapeutic and adverse effects are mediated by dopamine. Either re-uptake of dopamine takes place or it is metabolized, mainly by monoamine oxidases. The isoenzyme monoamine oxidase B (MAO-B) is responsible for the majority of oxidative metabolism of dopamine in the striatum. As considerable peripheral conversion of levodopa to dopamine takes place large doses of the drug are needed if given alone. Such doses are associated with a high rate of side effects, especially nausea and vomiting but also cardiovascular adverse reactions. Peripheral dopa decarboxylase inhibitors like carbidopa or benserazide do not cross the blood-brain barrier and therefore only interfere with levodopa decarboxylation in the periphery. The combined treatment with levodopa with a peripheral decarboxylase inhibitor considerably decreases oral levodopa doses. However it should be realized that neuropsychiatric complications are not prevented by decarboxylase inhibitors as even with lower doses relatively more levodopa becomes available in the brain. 

The system (1.16) is said to be of the cross activator-inhibitor type if the Jacobian has the structure... 

Polyester resins can be cross-linked by a free-radical initiator, usually an organic peroxide. Free radicals may be formed by thermal decomposition of an initiator such as erf-butyl perbenzoate or benzoyl peroxide, by ultraviolet (UV) or visible light decomposition, or by chemical decomposition in ambient temperature applications utilizing activators such as dimethylaniline. Inhibitors such as hydroquinone consume free radicals initially and reaction does not proceed until the inhibitor system is completely consumed. After an induction period the free... 

Consist of a range of chemicals which promote cross-linking can initiate cure by catalysing ( catalysts , hardeners, initiators), speed up and control cure (activators, promoters) or perform the opposite function (inhibitors) producing thermosetting compounds and specialised thermoplastics (e.g. peroxides in polyesters, or amines in epoxy formulations). The right choice of a cure system is dependent on process, process temperature, application and type of resin. 

Osteoclasts are multinucleated cells found on the endosteal surface of bone, in Haversian systems and periosteal surfaces. PTH activates osteoclasts (indirectly via osteoblasts that possess PTH receptors). Calcitonin is a potent inhibitor of osteoclast activity. Local cytokine factors, including interleukin-1 (IL-1), tumour-necrosis factor (TNF), TGF- 0 and interferon-y (INF-y), are important regulators. Osteoclast resorption of bone releases collagen peptides, pyridinoline cross-links and calcium from the bone matrix, through the action of lysosomal enzymes (collagenases and cathepsins). The collagen breakdown products in serum and urine (e.g. hydroxyproline) can be used as biochemical markers. 

The mixed-function oxidase inhibitors aminobenzotriazole and piperonyl butoxide can synergize herbicide activity in resistant Lolium growing in a hydroponic system. This indicates that at least one aspect of cross-resistance in Lolium rigidum may be related to enhanced metabolic activity of mixed-function oxidazes acting to detoxify herbicides. We are now concentrating on direct studies of herbicide metabolism in resistant biotypes. 

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