Kinetics of desorption of ions from quartz and mica surfaces

As part of an investigation concerning the fate of²²⁶Ra during uranium ore milling and long-term taillings storage we have investigated the kinetics of the desorption of alkaline earth, lead and sulfate ions from quartz and mica surfaces into water and dilute nitric acid using a radio-tracer technique. The retention times are sufficiently long to permit the growth of the surface deposits hypothesized in the HILEMAN-SNODGRASS model. The kinetics of desorption of most of these ions is found to agree with the model for rate-limiting desorption proposed by CEREFOLINI. In the case of the desorption of Ba²⁺ from mica surfaces the data suggest some degree of integration of the Ba²⁺ into the mica.     

Poly(perfluoroalkylation) of metallic nitride fullerenes reveals addition-pattern guidelines: synthesis and characterization of a family of Sc3N@C80(CF3)n (n = 2-16) and their radical anions

A family of highly stable (poly)perfluoroalkylated metallic nitride cluster fullerenes was prepared in high-temperature reactions and characterized by spectroscopic (MS, (19)F NMR, UV-vis/NIR, ESR), structural and electrochemical methods. For two new compounds, Sc(3)N@C(80)(CF(3))(10) and Sc(3)N@C(80)(CF(3))(12,) single crystal X-ray structures are determined. Addition pattern guidelines for endohedral fullerene derivatives with bulky functional groups are formulated as a result of experimental ((19)F NMR spectroscopy and single crystal X-ray diffraction) studies and exhaustive quantum chemical calculations of the structures of Sc(3)N@C(80)(CF(3))(n) (n = 2-16). Electrochemical studies revealed that Sc(3)N@C(80)(CF(3))(n) derivatives are easier to reduce than Sc(3)N@C(80), the shift of E(1/2) potentials ranging from +0.11 V (n = 2) to +0.42 V (n = 10). Stable radical anions of Sc(3)N@C(80)(CF(3))(n) were generated in solution and characterized by ESR spectroscopy, revealing their (45)Sc hyperfine structure. Facile further functionalizations via cycloadditions or radical additions were achieved for trifluoromethylated Sc(3)N@C(80) making them attractive versatile platforms for the design of molecular and supramolecular materials of fundamental and practical importance.     

Rapid and Inexpensive Method for the Spectroscopic Determination of Innate Immune Activity of Crocodilians

We have employed a spectroscopic assay based on the hemolysis of sheep red blood cells (SRBCs) to assess the immune system of the American alligator (Alligator mississippiensis). The assay is based on the hemolytic disruption of the SRBCs by the immunological proteins in the crocodilian serum. Incubation of 1% SRBCs (v/v) with alligator serum resulted in hemolysis that was measured at 540 nm in a microtiter plate reader. The hemolysis was concentration‐, time‐, and temperature‐dependent. This assay is rapid, inexpensive, easy to perform, requires small sample volumes, and is useful for evaluating the humoral immune response of crocodilians.     

Bounds for the least squares distance using scaled total least squares

Summary. The standard approaches to solving overdetermined linear systems construct minimal corrections to the data to make the corrected system compatible. In ordinary least squares (LS) the correction is restricted to the right hand side c, while in scaled total least squares (STLS) [14,12] corrections to both c and B are allowed, and their relative sizes are determined by a real positive parameter . As , the STLS solution approaches the LS solution. Our paper [12] analyzed fundamentals of the STLS problem. This paper presents a theoretical analysis of the relationship between the sizes of the LS and STLS corrections (called the LS and STLS distances) in terms of . We give new upper and lower bounds on the LS distance in terms of the STLS distance, compare these to existing bounds, and examine the tightness of the new bounds. This work can be applied to the analysis of iterative methods which minimize the residual norm, and the generalized minimum residual method (GMRES) [15] is used here to illustrate our theory. Received July 20, 2000 / Revised version received February 28, 2001 / Published online July 25, 2001     

Practical use of the symmetric Lanczos process with re-orthogonalization

Several extreme eigenvalues and vectors of large symmetric matrices can often be found to machine accuracy by carrying out far less than the full number of steps of the Lanczos process. To prove the accuracy of such results a rounding error analysis of the process with re-orthogonalization is given here. It is found that a stopping criterion has to be introduced to obtain a priori error bounds.     

A study of fibrous long spacing collagen ultrastructure and assembly by atomic force microscopy

Fibrous long spacing collagen (FLS) fibrils are collagen fibrils that display a banding with periodicity greater than the 67nm periodicity of native collagen. FLS fibrils can be formed in vitro by addition of alpha(1)-acid glycoprotein to an acidified solution of monomeric collagen, followed by dialysis of the resulting mixture. We have investigated the ultrastructure of FLS fibrils formed in vitro using the atomic force microscope (AFM). The majority of the fibrils imaged showed typical diameters of approximately 150nm and had a distinct banding pattern with a approximately 250nm periodicity. However, we have also observed an additional type of FLS fibril, which is characterized by a secondary banding pattern surrounding the primary bands. These results are compared with those obtained in past investigations of FLS ultrastructure carried out using the transmission electron microscope (TEM). The importance of the fibril's surface topography in TEM staining patterns is discussed. Images of FLS fibrils in various stages of assembly have also been collected, and the implications of these images in determining the mechanism of assembly and the formation of the characteristic banding pattern of the fibrils is discussed.     

铸造铝青铜合金Cu-14Al-4Fe-Mn的摩擦磨损性能

用往复式摩擦磨损试验机考察了新型高强度、高耐磨性铸造铝青铜合金Cu-14Al-4Fe-Mn(代号HSWAB)的摩擦磨损性能,利用形貌扫描电子显微镜观察分析了合金磨损表面形貌,探讨了其磨损机理.结果表明,HSWAB合金在干摩擦和油润滑条件下的摩擦磨损性能及磨损机理存在明显差异.在干摩擦条件下,合金中脱落的硬质点及氧化物等磨粒导致较为严重的磨粒磨损,摩擦系数高、磨损率大,主要磨损机理为磨粒磨损、粘着磨损、氧化磨损及疲劳磨损.在油润滑条件下,摩擦系数和磨损率均显著降低,疲劳磨损和氧化磨损受到抑制,主要磨损机理为磨粒磨损和粘着磨损.Cu-14Al-4Fe-Mn合金在油润滑条件下的摩擦系数低达0.08,磨损率低达3.7×10-6g/m,是一种优良的耐磨材料.     

An Ensemble and Single-molecule Fluorescence Spectroscopy Investigation of Calcium Green 1, a Calcium-ion Sensor

The calcium-ion indicator dye, Calcium Green 1 (CG-1), has been characterized using a combination of ensemble and single-molecule optical spectroscopy measurements. In terms of ensemble measurements, CG-1 demonstrated a strong increase in fluorescence emission as a function of increasing [Ca²⁺]. This was accompanied by a change in the relative proportions of two chemical forms of the dye, each with a different fluorescence lifetime, which were found to co-exist in solution. From single-molecule fluorescence measurements, it was found that the fluorescence intensity and photobleaching time (on-time) of each CG-1 molecule was invariant with [Ca²⁺] and that changes in ensemble fluorescence intensity simply correlates with the number of fluorescent molecules in solution. These results are compared with that of the related system, Calcium Green 2 (CG-2), and the mechanisms of operation of these two indicator dyes are discussed.     

Structural and compositional mapping of a phase-separated Langmuir-Blodgett monolayer by atomic force microscopy

The structure and composition of a phase-separated arachidic acid (C19H39COOH) (AA) and perfluorotetradecanoic acid (C13F27COOH) (PA) Langmuir-Blodgett monolayer film was characterized by several different types of atomic force microscopic measurements. At the liquid-air interface, surface pressure-area isotherms show that mixtures of the two acids follow the additivity rule expected from ideal mixtures. Topographic images of the deposited monolayer indicate that the surfactants are oriented normal to the substrate surface, and that the acids undergo phase separation to form a series of discontinuous, hexagonal domains separated by a continuous domain. A combination of lateral force (friction) imaging and adhesion force measurements show that the discontinuous domains are enriched in AA, whereas the surrounding continuous domain is a mixture of both AA and PA. This was further verified by selective, in situ dissolution of AA by n-hexadecane, followed by high-resolution topographical imaging of the discontinuous domains.