Systematic studies of crystal structures under non-ambient conditions

Variable temperature single crystal X-ray diffraction analysis has been used to study four molecular systems: 4-(p-trlfluoromethyl phenylethynyl) prefluorotoluene (1), 2-methyl-4-(4-trifluoromethyl-phenyl) but-3-yn-2-ol (2), phenylethynyl perfluorotoluene (3) and Zinc Pyromellitate. In the case of the systems (1) - (3), the aim was to analyse the extent of the dynamic disorder in the CF3 groups that are contained in these systems. To this end, segmented rigid body analysis has been employed to estimate forces constants and barriers to rotation of the relevant groups. Complimentary computational methods have been used to obtain further estimates of this barrier to rotation in these systems for both the isolated (gas phase) molecules and for the condensed matter phases for compounds (1) and (3).For Zinc Pyromellitate, variable temperature single crystal X-ray and neutron analysis have been used to probe the behaviour of a proton that sits in a short, strong intramolecular hydrogen bond. The aim here was to discover whether the system exhibits proton migration along the hydrogen bond as a function of temperature and thus gain insights into the energy potential well in which the proton sits. To this end, both computational methods have been used to study the pyromellitate fragment, and variable temperature full crystal structure data so as to gain direct access to information regarding this potential well

Are the Health of the Nation's targets attainable? Postal survey of general practitioners' views

The Health of the Nation's targets were introduced by the government in 1992 as part of a strategic approach to health.1 We aimed, in 1996, to elicit the views of general practitioners on the attainability of these targets

Wolf-Rayets in IC10: Probing the Nearest Starburst

IC10 is the nearest starburst galaxy, as revealed both by its Halpha surface brightness and the large number of Wolf-Rayet stars (WRs) per unit area. The relative number of known WC- to WN-type WRs has been thought to be unusually high (~2), unexpected for IC10's metallicity. In this Letter we report the first results of a new and deeper survey for WRs in IC10. We sucessfully detected all of the spectroscopically known WRs, and based upon comparisons with a neighboring control field, estimate that the total number of WRs in IC10 is about 100. We present spectroscopic confirmation of two of our WR candidates, both of which are of WN type. Our photometric survey predicts that the actual WC/WN ratio is ~0.3. This makes the WC/WN ratio of IC 10 consistent with that expected for its metallicity, but greatly increases the already unusually high number of WRs, resulting in a surface density that is about 20 times higher than in the LMC. If the majority of these candidates are spectroscopically confirmed, IC10 must have an exceptional population of high mass stars.Comment: Accepted by ApJL; only minor correction in this versio

An Analysis of the Physical Properties of Recovered CCA-Treated Wood from Residential Decks

A large volume of CCA-treated wood removed from residential decks is disposed of in landfills every year, and better environmentally conscious alternatives are needed. Recycling CCA-treated wood from the decks could be a feasible alternative, but there is a lack of knowledge regarding the physical properties of the material. This research analyzed the chemical and mechanical properties of spent CCA-treated wood from residential decks to evaluate the material for reuse in other applications. Several of the joists and the decking of removed decks were found to be below the originally stated retention level. The joists had higher retention levels, and length of service was not a factor in level of chemical retention in the decking or joists. The spent decking had similar stiffness properties, but the bending strength was lower than recently treated material. As with the chemical properties, the mechanical properties were not affected by the amount of time the deck was in service. Overall, it was found that the preservative retention properties were lower than expected, the stiffness was equal to, and the strength was lower than, recently CCA-treated wood. This does not indicate that the material is unusable, but aids in determining suitable applications where recycled CCA-treated wood can be used

Recent developments in deuterium oxide tracer approaches to measure rates of substrate turnover: implications for protein, lipid, and nucleic acid research

Purpose of review: Methods that inform on dynamic metabolism that can be applied to clinical populations to understand disease progression and responses to therapeutic interventions are of great importance. This review perspective will highlight recent advances, development, and applications of the multivalent stable isotope tracer deuterium oxide (D2O) to the study of substrate metabolism with particular reference to protein, lipids, and nucleic acids, and how these methods can be readily applied within clinical and pharmaceutical research. Recent findings: Advances in the application of D2O techniques now permit the simultaneous dynamic measurement of a range of substrates (i.e. protein, lipid, and nucleic acids, along with the potential for OMICs methodologies) with minimal invasiveness further creating opportunities for long-term ‘free living’ measures that can be used in clinical settings. These techniques have recently been applied to ageing populations and further in cancer patients revealing altered muscle protein metabolism. Additionally, the efficacy of numerous drugs in improving lipoprotein profiles and controlling cellular proliferation in leukaemia have been revealed. Summary: D2O provides opportunities to create a more holistic picture of in-vivo metabolic phenotypes, providing a unique platform for development in clinical applications, and the emerging field of personalized medicine

Straightening of Thermal Fluctuations in Semi-Flexible Polymers by Applied Tension

We investigate the propagation of a suddenly applied tension along a thermally excited semi-flexible polymer using analytical approximations, scaling arguments and numerical simulation. This problem is inherently non-linear. We find sub-diffusive propagation with a dynamical exponent of 1/4. By generalizing the internal elasticity, we show that tense strings exhibit qualitatively different tension profiles and propagation with an exponent of 1/2.Comment: Latex file; with three postscript figures; .ps available at http://dept.physics.upenn.edu/~nelson/pull.p

A burst chasing x-ray polarimeter

Gamma-ray bursts are one of the most powerful explosions in the universe and have been detected out to distances of almost 13 billion light years. The exact origin of these energetic explosions is still unknown but the resulting huge release of energy is thought to create a highly relativistic jet of material and a power-law distribution of electrons. There are several theories describing the origin of the prompt GRB emission that currently cannot be distinguished. Measurements of the linear polarization would provide unique and important constraints on the mechanisms thought to drive these powerful explosions. We present the design of a sensitive, and extremely versatile gamma-ray burst polarimeter. The instrument is a photoelectric polarimeter based on a time-projection chamber. The photoelectric time-projection technique combines high sensitivity with broad band-pass and is potentially the most powerful method between 2 and 100 keV where the photoelectric effect is the dominant interaction process. We present measurements of polarized and unpolarized X-rays obtained with a prototype detector and describe the two mission concepts; the Gamma-Ray Burst Polarimeter (GRBP) for the U.S. Naval Academy satellite MidSTAR-2, and the Low Energy Polarimeter (LEP) onboard POET, a broadband polarimetry concept for a small explorer mission

Laser optical separation of chiral molecules

The optical trapping of molecules with an off-resonant laser beam involves a forward-Rayleigh scattering mechanism. It is shown that discriminatory effects arise on irradiating chiral molecules with circularly polarized light; the complete representation requires ensemble-weighted averaging to account for the influence of the trapping beam on the distribution of molecular orientations. Results of general application enable comparisons to be drawn between the results for two limits of the input laser intensity. It emerges that, in a racemic mixture, there is a differential driving force whose effect, at high laser intensities, is to produce differing local concentrations of the two enantiomers