Cross Sections in the Three-Body Problem

In Dynamical Systems, Birkhoff gave a clear formulation of a cross section, suggested a possible generalization to cross sections with boundary, and raised the question of whether or not such cross sections exist in the three-body problem. In this work, we explicitly develop Birkhoff's notion of a generalized cross section, formulate homological necessary conditions for the existence of a cross section or generalized cross section, and show that these conditions are not satisfied in the three-body problem.     

Needle-like domain structure in Co films deposited on Mo (1 1 0)

Magnetization reversal processes and domain structures have been studied in Mo(1 1 0)/Co(0 0 0 1)/Au(1 1 1) structures grown by molecular beam epitaxy on monocrystalline (11–20) sapphire substrates. Wedge-shaped samples with different Co thickness gradients relative to the Mo [0 0 1] direction were fabricated. Observation of the domain structure was performed at room temperature using Kerr microscopy in a Co thickness range varying from 5 to 50 nm, where the magnetization is oriented in the plane of the sample. A Co thickness-dependent coercivity field was determined through analysis of the domain wall position during the reversal process. A preferential orientation of magnetic domain walls was found, with the domains being needle-like. The orientation, as well as the size of the needles, depends on the Co thickness and the orientation of the magnetic field applied in the sample plane.     

Detection of nitrated benzodiazepines by indirect laser-induced fluorescence detection on a microfluidic device

Recently there has been concern regarding the use of flunitrazepam and other low-dose benzodiazepines in drug-facilitated sexual assault. These compounds are placed in drinks of unsuspecting victims and produce a sedative effect with anterorgrade amnesia. Chip-based microfluidic systems can provide a quick and disposable procedure for the detection of flunitrazepam and other nitrated benzodiazepines used in these crimes. This paper describes the application of indirect quenching of cyanine dye (Cy5) for detection of nitrated benzodiazepines. The separation is performed on a microfluidic device with a separation channel 8 cm long and 50 microm wide and utilizes indirect fluorescence detection with 635 nm laser excitation. The optimization of the separation using micellar electrokinetic chromatography with organic modifiers is described. A borate buffer containing 2.6 microM Cy5 dye, 15 mM sodium dodecyl sulphate (SDS) and 20% methanol is used. Complete separation of four target drugs occurs in under 2 min with limits of detection in the low microg/ml range. Overall the method provides a rapid and simple analysis for the presence of nitrated benzodiazepines in beverages and other similar preparations.     

The analysis of high explosives by liquid chromatography/electrospray ionization mass spectrometry: multiplexed detection of negative ion adducts

The negative ion electrospray ionization mass spectrometric (ESI-MS) detection of adducts of high explosives with chloride, formate, acetate, and nitrate was used to demonstrate the gas-phase interaction of neutral explosives with these anions. The relative intensities of the adduct species were determined to compare the competitive formation of the selected high explosives and anions. The relative stability of the adduct species varies, yielding preferential formation of certain anionic adducts with different high explosives. To exploit this effect, an isocratic high-performance liquid chromatography (HPLC)/ESI-MS method was developed and used for the simultaneous analysis of high explosives using two different techniques for the addition of the anionic additives; pre- and post-column. The results show that the pre-column approach provides similar results with improved selectivity for specific explosives. By detecting characteristic adduct species for each explosive, this method provides a qualitative and quantitative approach for the analysis and identification of high explosives.     

Centred TVD schemes for hyperbolic conservation laws

New first- and high-order centred methods for conservation lawsare presented. Convenient TVD conditions for constructing centredTVD schemes are then formulated and some useful results areproved. Two families of centred TVD schemes are constructedand extended to nonlinear systems. Some numerical results arealso presented.     

Gas-Phase Synthesis of Reactive Molecules Using Adsorbed Reagents

Base-induced elimination reactions have found wide application in the synthesis of strained alkenes. The method is often complicated by a competing process in which the incipient alkene is trapped by nucleophilic addition of the base. Recent studies have shown that the bi-molecular side reactions can be avoided when bases such as potassium tert-but-oxide are supported on an inert surface like silica gel and the reaction is carried out in vacuo. This vacuum gas-solid reaction (VGSR) procedure has the additional advantage that very unstable species may be isolated under conditions that allow detailed studies of their physical and chemical properties. The scope of this procedure has been extended to include the use of fluoride salts supported on glass helices to effect the elimination of β-halosilanes. The fluoride route to strained alkenes is particularly attractive since the reaction may be carried out at very moderate temperatures and the starting materials are readily available. This review describes the development of this vacuum gas-phase procedure and its application in the synthesis and characterization of small-ring alkenes and bicycloalkenes, including methylene-cyclopropene, spiropentadiene, bicyclo-propenyls, 1,2- and 1,3-bridged cyclo-propenes, and other simple cyclo-propenes.