Taboo search: an approach to the multiple minima problem.

Described here is a method, based on Glover's taboo search for discrete functions, of solving the multiple minima problem for continuous functions. As demonstrated by model calculations, the algorithm avoids entrapment in local minima and continues the search to give a near-optimal final solution. Unlike other methods of global optimization, this procedure is generally applicable, easy to implement, derivative-free, and conceptually simple.

5-coordinate si compounds as intermediates in the synthesis of silicates in nonaqueous media.

Sodium silicoglycolate, an organosilicon compound in which silicon is in 5-coordination with respect to oxygen, is shown to be a reaction intermediate in the synthesis of a purely siliceous sodalite with ethylene glycol as solvent. The presence of silicon-29 nuclear magnetic resonances at -105.5 +/- 0.3 parts per million in solution and -102.7 parts per million in the solid state as well as x-ray powder diffraction patterns demonstrate that 5-coordinate silicon is intimately involved in the synthesis. Silicon compounds of the 5-coordinate type are highly reactive and are promising starting materials for the synthesis of novel silicone polymers, molecular sieves, glasses, semiconductors, and ceramics. We have used sodium silicoglycolate to prepare the molecular sieve silicalite as well as sodalites of different compositions.

Transport of radioactive oxygen, nitrogen and xenon into the rabbit thoracic aorta in situ.

An in situ preparation of the rabbit thoracic aorta has been used to study the transport of short-lived radioactive isotopes of oxygen (15O16O), nitrogen (13N14N) and an isotope of xenon (133Xe) from 0.9% NaCl into the artery wall. At a luminal hydrostatic pressure of 2 kPa the uptake of all three isotopes by the intima-media increased with time in experiments of up to 15 min duration. Uptake of labelled oxygen was an order of magnitude higher than that of xenon and almost two orders of magnitude higher than nitrogen uptake. Adventitial uptake was similar for all three species. For a perfusion time of 2 1/2 min, the intimal-medial uptake of all three gases increased by almost an order of magnitude as luminal pressure increased from 2 to 13 kPa. Adventitial uptake increased rapidly and at a similar rate for all three gases. The studies were limited in depth and accuracy by the small quantities of isotope available.

Surface chemistry and biological pathogenicity of silicates: an X-ray photoelectron spectroscopic study.

We extend our electron spectroscopy for chemical analysis studies of the chemistry of silicates to provide direct surface chemical information on the interactions involved in silicate-induced lung and tissue pathology. A total of five fibrous and non-fibrous silicate minerals, primarily amphiboles, have been studied: anthophyllite, tremolite, cummingtonite, hornblende and actinolite. We have followed the 'inlattice' surface chemistry of these materials and monitored features such as the simultaneous presence of four- and six-coordinate (with respect to oxygen) structural aluminium, and the presence of iron in the M4 octahedral positions. In vitro experiments involving contact of the silicate with cultured murine Ehrlich cells have identified modifications in the surface chemistry of Al, Mg and Fe in the silicates and changes in cellular iron content.

Oxidative damage in Alzheimer's dementia, and the potential etiopathogenic role of aluminosilicates, microglia and micronutrient interactions.

While evidence implicating free radical oxidative processes in the etiopathogenesis of Alzheimer's dementia is accumulating, the specific cellular and biochemical mechanisms involved remain to be identified. The potential pathogenic role of microglial cells in neurodegenerative processes is indicated by the finding that purified murine microglial cells exposed in vitro to various model aluminosilicate particles stimulate the generation of tissue-injurious free radical reactive oxygen metabolites. Analogous inorganic aluminosilicate deposits have been reported to occur in the core of the characteristic senile plaques found in the brains of Alzheimer disease subjects. The possible modulation of free radical oxidative activity by antioxidant micronutrients and pharmacological agents, provides a rational basis for further preventative and therapeutic clinical investigations.

Dynamics of HIV infection and AIDS in central African cities.

A detailed stochastic model of HIV infection and AIDS for large cities in central Africa is described, which reproduces past events in Kinshasa, Zaire and projects rapid future spread of the disease, consistent with recent findings for Nairobi, Kenya. Most of the parameters used describe the behaviour of individuals, and it is therefore possible to look at the effects of changes in such behaviour, and thus to test various strategies aimed at providing effective public health policies. The model demonstrates that, if the spread of infection is to be controlled, changes in the behaviour of the major risk groups are essential. With appropriate modifications, this model could be adapted for use elsewhere in Africa.

Cephaloconiosis: a free radical perspective on the proposed particulate-induced etiopathogenesis of Alzheimer's dementia and related disorders.

By analogy to the etiology of the pneumoconioses, exogenous dust-induced diseases of the lung, and endogenous crystal-induced arthropathies such as gout, it is proposed that Alzheimer's dementia and allied disorders are causally related to the accumulation of fibriform inorganic deposits within the brain. Hence the neonosological term 'Cephaloconiosis'. It is proposed that: 1) either by the extrinsic migration or intrinsic formation and deposition of insoluble and persistent inorganic reactive nidi, the particle-induced generation of tissue-damaging free-radical oxygen metabolites by stimulated brain glial macrophage-type and allied phagocytic cells, provides a rationale for the etiopathogenesis of neurodegenerative processes; 2) the modulation of the injurious oxidative metabolic reaction by micronutrient and pharmacological antioxidant agents is a rational and potentially feasible strategy for future therapeutic clinical investigations.

Transverse relaxation times of spin 3/2 nuclei in the quadrupole nutation NMR experiment.

Transverse relaxation times in the rotating frame of quadrupolar nuclei with half-integer spins are inversely proportional to the linewidth of quadrupole nutation NMR spectra. We apply fictitious spin -1/2 operators to I = 3/2 nuclei to derive correlations between the transitions of a multi-level system which affect nuclear relaxation. When omega rf << omega Q, all possible multiple-quantum transitions contribute to the transverse quadrupolar relaxation time in the rotating frame T2Qp. When omega rf >> omega Q, two of the three single-quantum transitions do not contribute. In the low-temperature region (outside the extreme narrowing limit), the contribution of double- and triple-quantum coherences to T2Qp goes through a minimum for omega rf << omega Q, while the triple-quantum coherence appears at zero frequency and corresponds to a short transverse relaxation time for omega rf >> omega Q.

Two-dimensional J-resolved and SUPERCOSY NMR experiments in the solid state.

Two 2D experiments, novel to solid-state NMR, are demonstrated using the trimethylsilyl ester of cubic octameric silicate (Q8M8). J-Resolved 13C NMR with BLEW-12 proton homonuclear decoupling reveals the scalar 13C-1H couplings and 29Si SUPERCOSY the connectivities of silicon atoms in the distorted Q8 cube.

Powder MAS NMR lineshapes of quadrupolar nuclei in the presence of second-order quadrupole interaction.

We derive a complete analytical solution for the powder magic angle spinning (MAS) nuclear magnetic resonance (NMR) lineshape in the presence of second-order quadrupole interaction, considering a radiofrequency (rf) pulse of finite width, a finite MAS frequency, and a non-zero asymmetry parameter. (Ix) is calculated using two approaches. The first applies time-dependent perturbation theory in the presence of the rf pulse and stationary perturbation theory (SPT) in its absence. The second is based on the Magnus expansion of the density matrix in the interaction representation during the pulse and SPT in its absence. We solve the problem in the laboratory frame using the properties of the Fourier transform and spin operators. Diagonalisation is not required. Both approaches agree well with each other under all conditions and also with the transition probability approach for the central transition. The Magnus expansion exists at all times and the effect of the non-secular terms is negligible. We describe an analytical method of averaging (Ix) over the Euler angles and simulate the 11B MAS NMR lineshapes for crystalline and vitreous B2O3. A critical analysis is given of all earlier calculations of the MAS NMR lineshape.

Alzheimer's disease: a pathogenic role for aluminosilicate-induced phagocytic free radicals.

The occurrence of aluminosilicate deposits within the cerebral plaques in Alzheimer's senile dementia sufferers has prompted further consideration of the possible role of such materials in the aetiology and pathogenesis of the disease. We have monitored the ability of various natural and synthetic model aluminosilicate particulates of differing morphological and chemical composition to stimulate the generation of phagocyte-derived free radical reactive oxygen metabolites (ROM) using an in vitro chemiluminescent technique on purified human blood-derived polymorphonuclear leukocytes (PMN). The results indicate that an enhanced chemiluminescent response is produced by calcium-bearing fibriform particulates. It is proposed that an analogous in vivo particle-induced and phagocyte-mediated oxidative stress could provide a potential pathogenic mechanism in the development of Alzheimer's disease.

Aluminosilicates and the ageing brain: implications for the pathogenesis of Alzheimer's disease.

Senile plaques are a neuropathological feature of the ageing brain and consist of abnormal neuritic and glial processes surrounding an extracellular core of material with fibrillary ultrastructure. Present at low densities in the cerebral cortex of most aged individuals, they occur in large numbers in Alzheimer's disease, the major form of senile dementia. Energy-dispersive X-ray microprobe analysis of isolated cores and plaques in situ from patients with Alzheimer's disease or Down's syndrome and from normal controls has shown co-localization of high concentrations of aluminium (4-19%) and silicon (6-24%) at the centre of the core. The presence of these elements as aluminosilicates has been confirmed using solid-state 27Al nuclear magnetic resonance. These findings provide a link with the other major neuropathological feature of Alzheimer's disease, the neurofibrillary tangle-bearing neurons, where high intracellular levels of Al and Si have also been reported. The focal deposition of these elements may be an early and essential factor in the pathogenesis of Alzheimer-type changes, reflecting an increased exposure to aluminium.

Solid-state 27Al NMR studies of aluminophosphate molecular sieves. Enhanced resolution by quadrupole nutation and double-rotation.

Solid-state 27Al NMR spectra of several aluminophosphate molecular sieves have been recorded with conventional magic-angle spinning (MAS), double-rotation (DOR) and quadrupole nutation with fast MAS. Enhanced resolution was obtained in the quadrupole nutation experiment at certain radiofrequency pulse strengths. This extra resolution can be comparable to that attainable using DOR, and does not introduce spinning sidebands.

23Na NMR studies of Na-DNA in the solid state.

23Na MAS, CP/MAS and quadrupole nutation NMR spectra and the 23Na spin-lattice relaxation times in Na-DNA with and without competing species (Mg2+, ethidium bromide and [Ru(phen)3]2+) reveal the presence of two sodium sites with different NMR parameters. While in the presence of Mg2+, sodium resides far from the surface of the DNA molecule, ethidium bromide and [Ru(phen)3]2+ displace sodium closer towards the surface.

Extraction of nitric oxide and nitrogen dioxide from an oxygen carrier using molecular sieve 5A.

Nitric oxide (NO) is effective in the management of pulmonary hypertension and shunt-related hypoxia. Nitrogen dioxide (NO2) is formed when the gas is delivered with oxygen. Both oxides of nitrogen have well recognized adverse effects. The scavenging properties of several forms of soda lime have been investigated. A gas flow containing NO 70 ppm and NO2 5 ppm in oxygen was introduced into a vertically mounted Waters' canister containing: (i) 125 g of molecular sieve 5A (a calcium aluminosilicate zeolite) and (ii) 135 g of soda lime containing a potassium permanganate marker. NO and NO2 concentrations were measured at hourly intervals at the entry and exit points using an electrochemical analyser. Extraction ratios (gradient/ inlet x 100) were calculated for a 24-h period. High extraction ratios (in excess of 90%) of NO and NO2 were observed with both compounds for up to 1 h but these declined rapidly after this time with soda lime. In contrast, the molecular sieve produced extraction ratios in excess of 98% for both gases over the 24-h period. We conclude that the molecular seive 5A is a highly effective scavenger of NO and NO2.

Aluminosilicates and senile plaque formation in Alzheimer's disease.

Aluminium and silicon were found to be colocalised in the central region of senile plaque cores in studies with energy dispersive X-ray microanalysis. The distribution of these elements was similar in cores isolated from the cerebral cortex of patients with senile dementia of the Alzheimer type and in cores studied in situ from tissue sections from the cerebral cortex of presenile and senile patients with Alzheimer's disease, and elderly, mentally normal patients. High-resolution solid-state nuclear magnetic resonance techniques showed aluminium and silicon to be present as aluminosilicates. The presence of aluminosilicates at the centre of senile plaque cores contrasts with the distribution of other inorganic constituents and suggests that they may be involved in the initiation or early stages of senile plaque formation.