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A nanostructured silicon/porous carbon spherical composite was prepared by a simple hydrothermal method using glucose as a carbon source and Pluronic F127 as a soft template/pore forming agent in the presence of silicon nanoparticles, and a subsequent carbonization process. In this composite, silicon nanoparticles were individually and separately coated with a porous carbon shell with a thickness of 15-20 nm and a pore size of 3-5 nm. The composite electrode exhibited excellent cycling stability and rate capability, delivering a stable capacity of 1607 mA h g À1 at a current density of 0.4 A g À1 after 100 cycles, and a reversible capacity of 1050 mA h g À1 even at a high current density of 10 A g À1 . Detailed analysis of cyclic voltammetry and electrochemical impedance spectroscopy revealed that the composite showed favorable electrochemical kinetics due to the nano-sized porous carbon shell, which facilitated the formation of a solid electrolyte interface film and the transportation of Li ions and electrons, and decreased the charge transfer resistance, thus significantly improving the electrochemical performance compared with the bare nano-Si electrode.

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Thiolic compounds are important metal-complexing ligands as well as important components of the global sulfur biogeochemical cycle. A lack of information on the concentration and distribution of thiols in natural waters, especially in the dissolved fraction, is still a major impediment to a complete understanding of the role of thiols in these biogeochemical processes. The concentrations of dissolved, colloidal, and particulate thiols were measured along a salinity gradient in estuarine waters off of Galveston Bay, Texas. The majority of thiols were present in the dissolved fraction, although more thiolic species were detected in the particulate phase. Dissolved glutathione was present at higher concentrations (0.23 to 6.23 nM) than was the particulate glutathione (0.094 to 0.72 nM). Most ␥-glutamylcysteine was present in the particulate phase, with concentrations as high as 2.24 nM in the middle of the estuary. Phytochelatin-2 was ubiquitous in surface waters, with chlorophyll a-normalized concentrations of up to 6.3 mol g Chl a Ϫ1 . A major thiol peak was present in Lower Galveston Bay and a minor peak in Upper Galveston Bay, and in both regions, 5-6 mol of ␥-glutamylcysteine were produced per mole of glutathione. This bimodal distribution indicates in situ production of thiols from two different phytoplankton communities in Galveston Bay during this period.Sulfur is an essential element and is required for protein synthesis by all organisms. The metabolic studies of sulfurcontaining species in natural waters have branched into two major areas, which are concerned with the following: (1) the global biogeochemical cycle of volatile sulfur species, such as dimethyl sulfide (DMS), carbonyl sulfide (OCS), and related compounds (Watts 2000) and (2) the detoxification properties of thiolic compounds, such as glutathione (GSH), cysteine (Cys), and sulfide, for ameliorating oxidative stress caused by trace metals, radicals, and other xenobiotic compounds (Grill et al. 1985;Giovanelli 1987). These two research areas are related at the molecular level in organisms during the synthesis and transformation of amino acids. Production of DMS is closely related to methylation reactions during methionine synthesis (Grone and Kirst 1992) and to the detoxification processes involved in GSH transformation (Meister and Anderson 1983). In water, organic matter-mediated photoreactions of dissolved organic sulfur compounds lead to the formation of OCS and related compounds (Zepp and Andreae 1995).GSH, as one of the most abundant low-molecular weight (LMW) thiols in animals, plants, and bacteria, has been shown to play an important role in protecting cells against oxidative stress, radiation damage, and elevated levels of heavy metals (Giovanelli 1987). The use of GSH (rather than Cys) as the major active reduced sulfur species is thought to have evolved when organisms adapted to the oxic atmo-1 Corresponding author (tangd@tamug.tamu.edu). AcknowledgmentsThis manuscript greatly benefited from discussions with J. Pinckney about...

In X-ray crystallography, a least-squares structure refinement is used to two purposes: to prove the correctness of the proposed model and to improve it. In electron crystallography, the same tool would be desirable. However, the standard programs for least-squares structure refinement used in X-ray diffraction may give wrong results using electron diffraction data because the kinematically calculated diffracted intensity is not valid for the interaction of electrons and crystals thicker than about 20 A for strong scatterers. In this paper, a new approach is presented that overcomes this problem and in addition takes into account all the advantages contained in dynamic scattering. The multislice method, well known in high-resolution electron microscopy (HREM), was combined with a least-squares algorithm, resulting in the multislice least-squares (MSLS) procedure. Experiments show that the atomic positions obtained by the new procedure are of the same accuracy as those obtained from single-crystal X-ray diffraction. However, the size of the single crystals used is much smaller (diameters down to +100 A). Also, light-atom positions can be determined with high precision by using data sets from crystal areas with different thicknesses. The multislice refinement gave good results up to 150 to 400A depending on the composition of the crystal, with R values based on the intensities of less than 5%. An additional advantage of the approach is that some extra quantities (e.g. crystal thickness, crystal orientation) can be refined at the same time. Acta Co'stallographica Section A

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