Flats and submersions in non-negative curvature

We find constraints on the extent to which O??Neill??s horizontal curvature equation can be used to create positive curvature on the base space of a Riemannian submersion. In particular, we study when K. Tapp??s theorem on Riemannian submersions of compact Lie groups with bi-invariant metrics generalizes to arbitrary manifolds of non-negative curvature.     

Efficient kinetic bioresolution of 2-nitrocyclohexanol

The kinetic bioresolution of 2-nitrocyclohexanol 1 was investigated by screening a range of hydrolases both for enantioselective transesterification and for enantioselective hydrolysis of the corresponding acetate. By appropriate choice of biocatalyst and conditions, both enantiomers of cis and trans 2-nitrocyclohexanol 1 can be accessed in enantiopure form.     

First measurements of the HCFC-142b trend from atmospheric chemistry experiment (ACE) solar occultation spectra

The first measurement of the HCFC-142b (CH₃CClF₂) trend near the tropopause has been derived from volume mixing ratio (VMR) measurements at northern and southern hemisphere mid-latitudes for the 2004–2008 time period from spaceborne solar occultation observations recorded at 0.02 cm⁻¹ resolution with the ACE (atmospheric chemistry experiment) Fourier transform spectrometer. The HCFC-142b molecule is currently the third most abundant HCFC (hydrochlorofluorocarbon) in the atmosphere and ACE measurements over this time span show a continuous rise in its volume mixing ratio. Monthly average measurements at northern and southern hemisphere mid-latitudes have similar increase rates that are consistent with surface trend measurements for a similar time span. A mean northern hemisphere profile for the time span shows a near constant VMR at 8–20 km altitude range, consistent on average for the same time span with in situ results. The nearly constant vertical VMR profile also agrees with model predictions of a long lifetime in the lower atmosphere.     

Eight octads suffice

The following question is answered: What is the minimum number of octads required to define a Steiner system $\text{l}$(5, 8, 24)? A set of octads is said to define a particular Steiner system if it is a subset of the special octads of that system, but of no other. As the title suggests, it is possible to produce a set of eight octads which defines the system, whereas any collection of seven octads is a subset of no Steiner system or of more than one. Note that, given an element of S₂₄, one is now able to decide whether it is in M₂₄ by simply applying it to a defining set of eight octads. If the images are in the system the element must be in M₂₄.     

A broadband polymeric foil transducer

If a 0.001 in (0.025 mm) thick foil of polyethylene teraphthalate is metallized upon one side and a dc voltage is applied to the metallizing, then the foil will adhere firmly by electrostatic attraction to any conducting surface. In acoustic emission experiments with such a foil as a capacitance detector it was observed that by cycling the polarizing voltage it was possible to increase the sensitivity of the device until it was only 30 dB below that of a damped pzt transducer. Such an enhanced response probe has been found to have a frequency response which is flat from 10 kHz to 5 MHz. It also has the advantages of being lightweight; needs no coupling agent when applied to conducting substrates; is stable over long periods; can be made in any shape or array of shapes and will conform to curved surfaces     

Fluorescence of fly ash samples: Implications for in situ and remote detection

A study of the fluorescence spectra of fly ash samples from different sources has shown that each samples has a characteristic fluorescence and excitation spectrum which could be used to identify and monitor its presence. Fluorescence lifetime studies of samples from different sources have demonstrated characteristic features which can be used for identification. The fluorescence method should be useful for in situ and remote monitoring applications.     

Twistors and linearized Einstein theory on plane-fronted impulsive wave backgrounds

The spinor form of linearized gravitation on a curved vacuum background is obtained from the Bianchi identities. There are no Buchdahl constraints to be satisfied, and for a flat background the approach reduces to the usual massless spin 2 theory. The equations are specialized to the plane-fronted impulsive gravitational wave backgrounds which include the ultrarelativistic limit of a moving black hole. Given a solution of the resulting system, it is possible to construct the metric perturbations up to gauge terms. It is shown that this linearized scheme is equivalent to the proposed twistor Hamiltonian formalism. As an example, colliding plane impulsive waves are considered, and the model compares well with the known exact solution. A discussion is given of the application of these methods to ultrarelativistic black-hole encounters.     

Parkin-deficient mice are not more sensitive to 6-hydroxydopamine or methamphetamine neurotoxicity

Background  

Autosomal recessive juvenile parkinsonism (AR-JP) is caused by mutations in the parkin gene which encodes an E3 ubiquitin-protein ligase. Parkin is thought to be critical for protecting dopaminergic neurons from toxic insults by targeting misfolded or oxidatively damaged proteins for proteasomal degradation. Surprisingly, mice with targeted deletions of parkin do not recapitulate robust behavioral or pathological signs of parkinsonism. Since Parkin is thought to protect against neurotoxic insults, we hypothesized that the reason Parkin-deficient mice do not develop parkinsonism is because they are not exposed to appropriate environmental triggers. To test this possibility, we challenged Parkin-deficient mice with neurotoxic regimens of either methamphetamine (METH) or 6-hydroxydopamine (6-OHDA). Because Parkin function has been linked to many of the pathways involved in METH and 6-OHDA toxicity, we predicted that Parkin-deficient mice would be more sensitive to the neurotoxic effects of these agents.