Quantum Disordered Regime and Spin Gap in the Cuprate Superconductors

We discuss the crossover from the quantum critical, $z\!=\!1$, to the quantum disordered regime in high-T$_c$ materials in relation to the experimental data on the nuclear relaxation, bulk susceptibility, and inelastic neutron scattering. In our scenario, the spin excitations develop a gap $\Delta\!\sim\!1/\xi$ well above T$_c$, which is supplemented by the quasiparticle gap below T$_c$. The above experiments yield consistent estimates for the value of the spin gap, which increases as the correlation length decreases.Comment: 14 pages, REVTeX v3.0, PostScript file for 3 figures is attached, UIUC-P-93-07-06

Sustainable mining in tropical, biodiverse landscapes: Environmental challenges and opportunities in the archipelagic Philippines

The rising demand for critical metals presents a major economic opportunity for mineral-rich countries. For a sustainable transition to a low-carbon future, it is essential to minimise impacts of mineral resource development to the environment, ecosystems, and societies of these nations. Although there has been considerable progress in the social aspects of the mining sector, environmental metrics are not showing comparable improvement. The Philippines exemplifies this challenge as a country that aims to conserve its exceptional biodiversity to maximise ecosystem services while expanding mining activities for economic growth, in a geographical setting with high mineral potential and vulnerability to natural hazards and climate change. Similar to many mining areas, environmental baselines are mostly non-existent, compounded by a legacy of mining impacts despite an established policy framework. We review issues associated with large- and small-scale mining and identify underlying research challenges and opportunities in the Philippines. Potential environmental research pathways include (i) innovative approaches for catchment scale characterisation and identification of contaminant sources; (ii) quantifying and predicting contaminant transport; (iii) deployment of flexible monitoring devices for larger-scale water quality monitoring programmes; (iv) tailings dam monitoring and management; and (v) resource assessment and metal recovery in ores and tailings. By integrating geomorphological tools with geochemical data, as well as 2D/3D numerical modelling techniques, it becomes possible to predict and understand the behaviour and fate of contaminants across different spatial and temporal scales. The development of cost-effective water quality assessment devices and protocols can help overcome logistical challenges in monitoring a wider range of hydrological conditions. Advanced applications of remote sensing, combined with machine learning, and geophysical monitoring systems provide new opportunities to detect mining footprints and observe change in tailings dams more effectively. Potential impacts of mine wastes can be further minimised by exploring innovative technologies such as the use of metal-accumulating native plant species and environmentally safe solvents to reprocess modern and legacy tailings. Insights from these pathways will enable the realisation of a more sustainable mining future, through the incorporation of findings into existing and future governmental and small- and large-scale mining policy and practice. This will lead to sustainable development for society, particularly in nations that are well positioned to benefit from sustainable mineral resource development

O-17 NMR-SPECTROSCOPY OF MAGNETICALLY ORDERED YBA2CU3O7-X MICROCRYSTALS

open1132sciescopu

NMR studies of PAH/PSS polyelectrolyte multilayers adsorbed onto silica

ABSTRACT: Solid-state NMR spectroscopy is used to monitor the layer-by-layer (L-B-L) growth of polyelectrolyte multilayers on colloidal silica. The dynamics and conformation of polyelectrolyte multilayers comprised of the weak polycation, poly(allylamine) hydrochloride, and the strong polyanion, poly(sodium-4-styrene sulfonate), assembled at pH 7 and pH 10 were studied by a combination of 1H and 13C NMR measurements. NOESY spectra detect the association of water to the polyanion, while relaxation measurements show that the outermost layer and the water content influence the mobility of the polyelectrolytes and the adsorbed water. Differences in mobility for films assembled at high and neutral pH are explained by the conformation of the polycation during the assembly process. Finally, the strong-weak polyelectrolyte multilayers are compared to a previous NMR study of strong-strong polyelectrolyte multilayers