Recent discoveries in the search for non-opiate analgetics

A novel phenanthridine, nantradol ( 1 ), resulted from a search to dissect out analgetic activity from the cannabinoid molecule. Nantradol possesses two to seven times greater potency than morphine across a battery of analgetic tests. Despite this morphine-like profile, nantradol does not bind to the opiate receptor. Nantradol has a total of five asymmetric centers and was studied as a 50:50 mixture of two diastereomers, both of which possess the trans 6a, 10a stereochemistry and have β-oriented substituents at positions 6 and 9. Evidence is provided that, in common with the opiates, the analgetic actions of nantradol are stereospecific, the majority of the activity residing in a single levorotatory isomer. The stereospecificity and potency of the analetic effects of the nantradol series suggests a highly specific interaction at an as yet unidentified receptor.     

Identifiability for random translations of Poisson processes

Summary A system in which each point of a stationary Poisson process is subjected to a random displacement, the displacements being independently and identically distributed, is considered. It is shown that the displacement distribution is identifiable if we are given a realization of the original process and the corresponding realization of the displaced process but not the linkage between the two.     

Photoenhanced deposition of silicon oxide thin films using a novel windowless internal nitrogen discharge lamp

This paper reviews the production of silicon oxide thin films using a novel photoenhanced deposition technique incorporating a windowless nitrogen discharge lamp contained within the deposition vessel. This process has the potential to produce better semiconductor/insulator interfaces than those produced using conventional RF glow discharge techniques, since there is no damage to the growing film surface from energetic ions produced in the glow discharge plasma. The use of an internal lamp obviates the need for a window between the lamp and reaction chamber and thus overcomes the problems of attenuation of short wavelength ultraviolet radiation by the window. All the ultraviolet output of the lamp can now directly couple into the reaction gases, so the need for sensitising agents is also removed. Thin films of silicon oxide have been deposited onto single crystal silicon wafers from nitrous oxide-silane gas mixtures. The physical properties are comparable to those of high quality insulator films deposited by plasma enhanced techniques. The results of electrical measurements indicate that this material is of sufficiently high quality to be used as a low temperature deposited gate dielectric for thin film devices. To confirm this, thin film transistors (TFTs) have been fabricated using the material (and an active layer of amorphous silicon deposited in the same system) and characteristics of these TFTs are also presented.     

Nano-powders of Na0.5K0.5NbO3 made by a sol–gel method

Sodium potassium niobate (NKN) nano-particle powders were synthesised through the thermal decomposition of a sol–gel NKN precursor. Powders and gels were characterised by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Hydrated carbonate phases formed as a result of reaction with evolved vapours during organic decomposition, and by reaction of NKN powders with H₂O and CO₂ on exposure to air. The primary particle size of the powders increased from <50 to <250 nm as decomposition temperatures were raised from 500 to 950 °C.     

Giant piezoresistance effects in silicon nanowires and microwires

The giant piezoresistance (PZR) previously reported in silicon nanowires is experimentally investigated in a large number of depleted silicon nano- and microstructures. The resistance is shown to vary strongly with time due to electron and hole trapping at the sample surfaces independent of the applied stress. Importantly, this time-varying resistance manifests itself as an apparent giant PZR identical to that reported elsewhere. By modulating the applied stress in time, the true PZR of the structures is found to be comparable with that of bulk silicon.     

On the Exciton Coupling between Two Chlorophyll Pigments in the Absence of a Protein Environment: Intrinsic Effects Revealed by Theory and Experiment

Exciton coupling between two or more chlorophyll (Chl) pigments is a key mechanism associated with the color tuning of photosynthetic proteins but it is difficult to disentangle this effect from shifts that are due to the protein microenvironment. Herein, we report the formation of the simplest coupled system, the Chl a dimer, tagged with a quaternary ammonium ion by electrospray ionization. Based on action spectroscopic studies in vacuo, the dimer complexes were found to absorb 50–70 meV to the red of the monomers under the same conditions. First‐principles calculations predict shifts that somewhat depend on the relative orientation of the two Chl units, namely 50 and 30 meV for structures where the Chl rings are stacked and unstacked, respectively. Our work demonstrates that Chl association alone can produce a large portion of the color shift observed in photosynthetic macromolecular assemblies.     

Tubular graphite cones with single-crystal nanotips and their antioxygenic properties

Tubular graphite cones (TGCs) with a single-crystal nanotip have been achieved by means of microwave plasma-assisted chemical vapor deposition using in-situ-evaporated Fe catalysts. The absence of the disorder-induced D band in Raman spectra revealed the single-crystalline feature of the nanotip. TGCs were found to stem from Fe catalytic carbon spherules on the order of 100 mum diameter, whose critical role in promoting both nucleation and plasma annealing in the formation of highly crystalline TGCs is discussed. The crystalline quality of such TGCs can be further verified by the investigation of their oxidative stability in air. All TGCs can survive up to 600 degrees C without any structural variations, and a few TGCs still survive with an anisotropic etched and stepped nanotip at temperatures up to 800 degrees C, much better than CNTs. Thus, TGCs with single crystalline nanotips are potential candidates for scanning probes in high-temperature oxygen-containing environments.