The abundance of HNCO and its use as a diagnostic of environment

Aims. We aim to investigate the chemistry and gas phase abundance of HNCO and the variation of the HNCO/CS abundance ratio as a diagnostic of the physics and chemistry in regions of massive star formation. Methods. A numerical-chemical model has been developed which self-consistently follows the chemical evolution of a hot core. The model comprises of two distinct stages. The first stage follows the isothermal, modified free-fall collapse of a molecular dark cloud. This is immediately followed by an increase in temperature which represents the switch on of a central massive star and the subsequent evolution of the chemistry in a hot, dense gas cloud (the hot core). During the collapse phase, gas species are allowed to accrete on to grain surfaces where they can participate in further reactions. During the hot core phase surface species thermally desorb back in to the ambient gas and further chemical evolution takes place. For comparison, the chemical network was also used to model a simple dark cloud and photodissociation regions. Results. Our investigation reveals that HNCO is inefficiently formed when only gas-phase formation pathways are considered in the chemical network with reaction rates consistent with existing laboratory data. This is particularly true at low temperatures but also in regions with temperatures up to ~200 K. Using currently measured gas phase reaction rates, obtaining the observed HNCO abundances requires its formation on grain surfaces – similar to other “hot core” species such as CH3OH. However our model shows that the gas phase HNCO in hot cores is not a simple direct product of the evaporation of grain mantles. We also show that the HNCO/CS abundance ratio varies as a function of time in hot cores and can match the range of values observed. This ratio is not unambiguously related to the ambient UV field as been suggested – our results are inconsistent with the hypothesis of Martín et al. (2008, ApJ, 678, 245). In addition, our results show that this ratio is extremely sensitive to the initial sulphur abundance. We find that the ratio grows monotonically with time with an absolute value which scales approximately linearly with the S abundance at early times.

Perturbed frequency-selective surfaces fabricated on large thin polymer membranes for multiband infrared applications

The design, fabrication, and characterization of single-screen perturbed frequency-selective surfaces (FSS) at infrared frequencies for single and multiband applications are reported. Single-band FSS based on parallel strips have been perturbed by decreasing the length of every second strip within the array in order to achieve dual band-stop responses. The same principle has been extended to design FSS exhibiting tri- and quadreflection bands. In addition, strip FSSs have been perturbed by replacing every second strip for a metallic ring, resulting in dual-band filters with different polarization responses of the bands. These designs have been fabricated on large thin polyimide membranes using sacrificial silicon wafers. An oxide interlayer between the sacrificial silicon wafer and the polyimide membrane is employed to stop the silicon etching and is wet etched subsequently by a solution of ammonium fluoride and acetic acid that does not attack either the polyimide membrane or the aluminium FSS elements. Fourier transform infrared spectroscopy measurements are presented to validate the predicted responses of the fabricated prototypes.

Reduction of severe bovine serum associated matrix effects on carboxymethylated dextran coated biosensor surfaces

Surface plasmon resonance (SPR) based biosensor technology has been widely used in life science research for many applications. While the advantages of speed, ruggedness, versatility, sensitivity and reproducibility are often quoted, many researchers have experienced severe problem of non-specific binding (NSB) to chip surfaces when performing analysis of biological samples Such as bovine serum. Using the direct measurement of the bovine protein leptin, present in bovine serum samples as a model, a unique buffering system has been developed and optimised which was able to significantly reduce the non-specific interactions of bovine serum components with the carboxymethyl dextran chip (CM5) surface on a Biacore SPR The developed NSB buffering system comprised of HBS-EP buffer, containing 0.5 M NaCl, 0.005% CM-dextran pH 9.0. An average NSB reduction (n = 20) of 85.9% and 87.3% was found on an unmodified CM5 surface and a CM5 with bovine leptin immobilised on the chip surface, respectively. A reduction in NSB of up to 94% was observed on both surfaces. The concentration of the constitutive components and pH of the buffer were crucial in achieving this outcome. (C) 2008 Elsevier B.V. All rights reserved.