A heuristic approach for the stochastic optimization of mine production schedules

Traditionally, mining engineers plan an open pit mine considering pre-established conditions of operation of the plant(s) derived from a previous plant optimization. By contrast, mineral processing engineers optimize the processing plants by considering a regular feed from the mine, with respect to quantity and quality of the materials. The methods implemented to optimize mine and metallurgical plans simultaneously are known in the mining industry as global or simultaneous optimizers. The development of these methods has been of major concern for the mining industry over the last decade. Some algorithms are available in commercial mining software packages however, these algorithms ignore the inherent geological uncertainty associated with the deposit being considered, which leads to shortfalls in production, quality, and expected cashflows. This paper presents a heuristic method to generate life-of-mine production schedules that consider operating alternatives for processing plants and incorporate geological uncertainty. The method uses iterative improvement by swapping periods and destinations of the mining blocks to generate the final solution. The implementation of the method at a copper deposit shows its ability to control mine and processing capacities while increasing the expected net present value by 30% when compared with a solution generated using a standard industry practice.     

Nonuniform exponential dichotomies and Lyapunov functions

For the nonautonomous dynamics defined by a sequence of bounded linear operators acting on an arbitrary Hilbert space, we obtain a characterization of the notion of a nonuniform exponential dichotomy in terms of quadratic Lyapunov sequences. We emphasize that, in sharp contrast with previous results, we consider the general case of possibly noninvertible linear operators, thus requiring only the invertibility along the unstable direction. As an application, we give a simple proof of the robustness of a nonuniform exponential dichotomy under sufficiently small linear perturbations.     

Fluid dynamics of self-propelled microorganisms,from individuals to concentrated populations

Nearly close-packed populations of the swimming bacterium Bacillus subtilis form a collective phase, the “Zooming BioNematic” (ZBN). This state exhibits large-scale orientational coherence, analogous to the molecular alignment of nematic liquid crystals, coupled with remarkable spatial and temporal correlations of velocity and vorticity, as measured by both novel and standard applications of particle imaging velocimetry. The appearance of turbulent dynamics in a system which is nominally in the regime of Stokes flow can be understood by accounting for the local energy input by the swimmers, with a new dimensionless ratio analogous to the Reynolds number. The interaction between organisms and boundaries, and with one another, is modeled by application of the methods of regularized Stokeslets.     

The Vortex Filament Equation as a Pseudorandom Generator

In this paper, we consider the evolution of the so-called vortex filament equation (VFE),

$$\mathbf{X}_t = \mathbf{X}_s\wedge\mathbf{X}_{ss}, $$

taking a planar regular polygon of M sides as initial datum. We study VFE from a completely novel point of view: that of an evolution equation which yields a very good generator of pseudorandom numbers in a completely natural way. This essential randomness of VFE is in agreement with the randomness of the physical phenomena upon which it is based.

     

Multifunctional microgel magnetic/optical traps for SERS ultradetection

We report on the fabrication of a SERS substrate comprising magnetic and silver particles encapsulated within a poly(N-isopropylacrylamide) (pNIPAM) thermoresponsive microgel. This colloidal substrate has the ability to adsorb analytes from solution while it is expanded (low temperature) and reversibly generate hot spots upon collapse (high temperature or drying). Additionally, the magnetic functionality permits concentration of the composite particles into small spatial regions, which can be exploited to decrease the amount of material per analysis while improving its SERS detection limit. Proof of concept for the sequestration of uncommon molecular systems is demonstrated through the first SERS analysis of pentachlorophenol (PCP), a chlorinated ubiquitous environmental pollutant.     

Microwave assisted extraction for mercury speciation analysis

The application of microwave-assisted extraction (MAE) to the work-up of environmental and biological samples in the study of mercury speciation analysis has increased in recent years and is now increasingly accepted as a standard approach. The review provides a brief theoretical background of microwave heating and the basic principles of microwave energy used for extraction. The advantages and disadvantages of (a) MAE techniques, (b) the influence of the main parameters affecting the extraction, (c) statistical optimization approaches, and (d) strategies for method validation also are highlighted. Recent applications of MAE to mercury species analyses in biological samples, soils, sediments, and crude oil samples are surveyed and critically reviewed. In addition, comparisons of its use with other well-established extraction procedures are discussed.

Application of NMR methods to the study of the interaction of natural products with biomolecular receptors

In this review, we present applications of NMR spectroscopy as a potent tool for the study of molecular interactions. It is clear that a variety of NMR methods may be employed to deduce key features of ligand–receptor molecular recognition processes, looking at the process from the perspective of the receptor or the ligand. We have not provided an exhaustive review, but we have tried to focus on describing the different aspects within this research topic. We have therefore selected examples accordingly, depending on the particular problem under study or the application/development of protocols to circumvent the technical problems that may be found when working in this field.