Initial steps of the metal-catalysed degradation of L-dehydroascorbic acid in acidic aqueous solutions

The initial steps of the degradation of L-de- hydroascorbic acid (L-DHA) in acidic aqueous solutions and the catalytic effect of different transition metal ions on this reaction were studied. The main product was identified as 3,6-furanosido-2,3-hexodiulosonic acid-2-hydrate (compound I) by GLC-MS and ¹³C-NMR, formed by lactone hydrolysis and hydration of the carbonyl group in the C-2 position of L-dehydroascorbic acid. In addition, number of other compounds were detected; they are formed from compound I by simple enolisation, lactonisation, hydration and dehydration reactions as well as by cleavage and formation of cyclic half acetal bonds. The chemical structures of these compounds were tentatively deduced by the mass spectra of their TMS derivatives and a reaction scheme for their formation is proposed. The velocity and the direction of the reactions were found to be strongly influenced by the presence of catalytic amounts of different transition metal ions. It was concluded that in acidic medium, in contrast to the situation in neutral and alkaline solutions, the opening of the lactone ring of L-DHA is, to a certain degree, a reversible reaction.     

A ¹⁸F-labeled fluorobutyl-substituted spirocyclic piperidine derivative as a selective radioligand for PET Imaging of sigma₁ receptors

In this study, we synthesized and evaluated a new spirocyclic piperidine derivative 3 , containing a 4‐fluorobutyl side chain, as a PET radioligand for neuroimaging of σ₁ receptors. In vitro, compound 3 displayed high affinity for σ₁ receptors (K_i=1.2 nM ) as well as high selectivity. [¹⁸F] 3 radiosynthesis was performed from the corresponding tosylate precursor, with high radiochemical yield (45–51 %), purity (>98 %), and specific activity (>201 GBq μmol^?1). Metabolic stability of [¹⁸F] 3 in the brain of CD‐1 mice was verified, and no penetration of peripheral radiometabolites into the cerebral tissue was observed. Results of ex vivo autoradiography revealed that the distribution of [¹⁸F] 3 in the brain corresponded to regions with high σ₁ receptor density. The highest region‐specific total‐to‐nonspecific ratio was determined in the facial nucleus (4.00). Biodistribution studies indicated rapid and high levels in brain uptake of [¹⁸F] 3 (2.2 % ID per gram at 5 min p.i.). Pre‐administration of haloperidol significantly inhibited [¹⁸F] 3 uptake into the brain and σ₁ receptor‐expressing organs, further confirming in vivo target specificity.     

Oscillation Susceptibility Analysis along the Path of the Longitudinal Flight Equilibriums in ADMIRE Model

Our goal is the oscillation susceptibility analysis in the framework of a nonlinear mathematical model in the so-called ADMIRE or Aero Data Model in a Research Environment. First, we analyze the oscillation susceptibility along the path of the longitudinal flight equilibriums when the flight control system (FCS) is decoupled. After that, a similar analysis is undertaken in the case when the FCS is coupled. For decoupled FCS, it is shown that on the path of the longitudinal flight equilibriums there exists a saddle-node where stability is lost and fold bifurcation occurs. Maneuvers are simulated showing the effect of an instantaneous change of the elevator angle, and the evolution of the unstable equilibriums (due to the maneuvers) to the corresponding exponentially stable equilibriums. It is shown numerically that at the saddle-node oscillations occur when the elevator angle is less than the critical value and the start is from the saddle-node. More precisely, it is shown that if the plane state parameters coincide with the saddle-node coordinates and the elevator angle is changed instantaneously from the critical value to a value which is less than this value, then two of the state parameters (α,q) begin to oscillate with the same period and the third parameter (θ) increases, tending to infinity. Thus, the orbit of the system evolves spiraling. It is shown also, that if the elevator angle is reset, the plane returns to a stable equilibrium. Therefore, a soft or no catastrophic stability loss takes place. When the FCS is coupled, the plane for every value of the amplification factor has a unique equilibrium which is exponentially stable and attracts all the equilibriums which exist in decoupled case. In this case, there are no bifurcation points on the equilibrium path. The dependence of the equilibrium and of the relaxation period on the amplification factor value is found numerically. Finally, it is concluded that when the FCS is decoupled, then along the path of the longitudinal equilibriums oscillations can occur, but when the FCS is coupled and the pilot can modify (instantaneously) only the amplifier factor value, then the vehicle, defined by the considered numerical data, is not anymore susceptible to oscillation.     

Instrumental geometry

For two decades, the individual members of the SmartGeometry Group have pioneered innovative computer-aided design (cad) techniques and technologies. Now that they are situated in key positions in internationally renowned companies, the group is involved in developing a new generation of parametric design software. Here, Robert Aish (Director of Research at Bentley Systems), Lars Hesselgren (Director of Research and Development, kpf London), J Parrish (Director of ArupSport) and Hugh Whitehead (Project Director of the Specialist Modelling Group, Foster and Partners, London) discuss with Achim Menges the group's instrumental approach to geometry and their unique collaboration spanning the world of practice and software development. Copyright © 2006 John Wiley & Sons, Ltd.     

Nichtlinearer Bettungsansatz von Besler bei Baugrubenwänden

Besler's nonlinear subgrade reaction approach for excavation walls. It is investigated how the displacements of the foot of the wall in service states can be described close to the real behaviour. Thereby Besler's non linear approach for the subgrade reaction is used. The main points of the paper are the numerical implementation and the influence of the flexibility and preloading by the weight of the excavation on the displacements. Finally recommendations are given for the use in practice.