Deflection of laser-produced ions in laser-induced thermal-desorption/fourier-transform mass spectrometry for surface analysis

A method for deflecting ions, such as K⁺, produced outside a Fourier-transform mass spectrometer cell during laser-induced thermal desorption, is described. This technique has been shown to deflect laser-generated K and Ti ions from two Ti foil samples (biomedical implant model surfaces), yielding mass spectra of coadsorbed organic species. Further studies characterizing the laser desorption/deflection parameters have shown that ion deflection improves with higher deflection voltages and greater sample to Fourier-transform mass spectrometry cell separation. Higher laser power densities resulted in greater surface ion production; hence higher deflection voltages were necessary. A 6% increase in laser power necessitated a fourfold increase in deflection voltage for the Ti sample.     

Advanced Optical Network

The following article describes an advanced dense wavelength division multiplexing (DWDM) Optical Network developed by L-3 Photonics. The network, configured as an amplified optical bus, carries traffic simultaneously in both directions, using multiple wavelengths. As a result, data distribution is of the form peer-to-multi-peer, it is protocol independent, and it is scalable. The network leverages the rapid growth in commercial optical technologies, including wavelength division multiplexing (WDM), and when applied to military and commercial platforms such as aircraft, ships, unmanned and other vehicles, provides a cost-effective, low-weight, high-speed, and high noise-immune data distribution system.     

Selenium speciation in soil extracts using LC-ICP-MS

Selenium (Se) speciation in soil affects its bioavailability to crops. An analytical procedure for the determination of inorganic Se species (selenite and selenate) in soil extracts by anion-exchange liquid chromatography (LC) with ICP-MS detection has been developed, with 10-fold higher sensitivity than existing HGAAS-based soil Se measurements. A comparison of phosphate extraction solutions on agricultural soils amended with 20?µg?kg^–1 selenate or selenite was carried out, and a 0.016?M?KH₂PO₄ extraction solution is recommended. Recovery of selenate was >91%; however, selenite recovery ranged between 18.5% and 46.1%, due to rapid binding to the soil. Soil preparation did not have a significant (p?>?0.05) effect on the extractability of the selenate or selenite amendments. The stability of Se species in the phosphate extracts was variable, depending on temperature and storage time. Therefore, immediate (<1?h) analysis of the soil extracts is preferable. The method developed was applied to the determination of extractable Se from six arable soils in the UK. Extractable Se levels in these soils ranged between 6 and 13?µg?kg^–1 consisting of selenite and some soluble organic Se.     

Asymmetry of velocity distributions in peripheral reactions with heavy ions at Fermi energies

The asymmetry of velocity distributions of projectile-like fragments produced in heavy ion collisions is considered. The calculations performed in the transport model approach (Vlasov kinetic equation with the collision term) are compared with the experimental data for the ²²Ne (40MeV/nucleon) + ⁹Be and ¹⁸O (35 MeV/nucleon) + ⁹Be(¹⁸¹Ta) reactions. It is found that the velocity distributions contain two components: a direct component centered at the beam velocity and a dissipative component at lower energies, leading to asymmetry of velocity distributions. The direct component is interpreted empirically within the Goldhaber model, and the centroids and widths σ₀ of the distributions for each fragment are extracted. It is found that value of σ₀ derived from experimental data is smaller by a factor of 2 than the theoretical one. The dissipative (also called deep inelastic) component is described well by the transport calculations. It is shown that the ratio of yields of direct and dissipative components, which determines the asymmetry of velocity distributions, depends on shape of the deflection function. Original Russian Text ? T.I. Mikhailova, B. Erdemchimeg, G. Kaminski, A.G. Artyukh, M. Colonna, M. Di Toro, I.N. Mikhailov, Yu.M. Sereda, H.H. Wolter, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 6, pp. 898–903.     

Filling Length in Finitely Presentable Groups

We study the filling length function for a finite presentation of a group , and interpret this function as an optimal bound on the length of the boundary loop as a van Kampen diagram is collapsed to the basepoint using a combinatorial notion of a null-homotopy. We prove that filling length is well behaved under change of presentation of . We look at 'AD-pairs' (f,g) for a finite presentation : that is, an isoperimetric function f and an isodiametric function g that can be realised simultaneously. We prove that the filling length admits a bound of the form [g+1][log (f+1)+1] whenever (f,g) is an AD-pair for . Further we show that (up to multiplicative constants) if is an isoperimetric function ( ) for a finite presentation then ( ) is an AD-pair. Also we prove that for all finite presentations filling length is bounded by an exponential of an isodiametric function.Partially supported by NSF grant DMS-9800158Supported by EPSRC Award No. 98001683 and Corpus Christi College, Oxford.     

Use of labelled nitrogen to measure gross and net rates of mineralization and microbial activity in permanent pastures following fertilizer applications at different time intervals

Measurements of some of the main internal N-cycling processes in soil were obtained by labelling the inorganic N pool with the stable isotope of nitrogen ((15)N). The (15)N mean pool dilution technique, combined with other field measurements, enabled gross and net N-mineralization rates to be resolved in grassland soils, which had previously either received fertilizer N (F), or had remained unfertilized (U) for many years. The two soils were subdivided into plots that received N at different time intervals (over 3 weeks), prior to (15)N measurements being made. By this novel approach, possible 'priming' effects over time were investigated to try to overcome some of the temporal problems of isotopic labelling of soil N (native plus fertilizer) and to identify possible changes in a range of primary N-transformation processes. The results suggested that an overall stimulation of microbially mediated processes occurred with all N treatments, but there were inconsistencies associated with the release of N, both in the timing and the degree to which different processes responded to the application of fertilizer N. The rates of these processes were, however, within the range of previously reported data and the (15)N measurements were not adversely affected by the differences in N pools created by the treatments. Thus, the mean pool dilution technique was shown to be applicable to agricultural soils, under conditions relevant to grass swards receiving fertilizer. For example, between the U and F treatments, the size of inorganic N pools increased by five-fold and gross rates of mineralization reached 3.5 and 4.8 microg N g(-1) (dry soil) d(-1), respectively, but did not vary greatly with the timing of N applications. A correlation (r(2) = 0.57) was found between soil respiration (which is relatively simple to measure) and net mineralization (which is more time consuming), suggesting that the former might be used as an indicator of the latter. Although this relationship was stronger in previously unfertilized soils, the similarities found with fertilized soils suggest that this approach could be used to obtain information of wider agronomic value and would, therefore, warrant further work under a range of soil conditions.     

Electrophoresis in the presence of gradients: I. Viscosity gradients

In many cases, the resolution provided by capillary electrophoresis systems approaches that predicted for diffusion-limited separations. Once all device-related sources of band broadening have been eliminated or minimized, only thermal diffusion remains. In principle, peaks can be sharpened using gradients of various system characteristics such as gel concentration, buffer viscosity and electric field. However, it is not clear whether this can actually increase the resolution of the system. In this article, we focus our attention on viscosity gradients and we examine both continuous and step-like variations. Our results indicate that the performance of electrophoretic systems cannot be improved by viscosity gradients. They may provide extra stacking, and thus improve the resolution, when the injection width is non-negligible. However, for the systems considered here, the best resolution is obtained when the viscosity is uniform and the stacking is entirely performed at injection. We conclude by discussing the link between these results, the fundamental laws of thermodynamics, the nature of the detection process and the importance of having nonlinear effects in nonuniform systems.     

Total synthesis of the mycolactones

[structure: see text] The first total synthesis of the mycolactones is reported. This work unambiguously confirms our earlier relative and absolute stereochemical assignment of the mycolactones.