Noise reduction in commercial refrigerators - a practical approach

An Adande refrigeration unit originally designed for use in the commercial catering industry was redesigned for use in households. This sector is more sensitive to refrigeration noise, following the introduction of the EU noise labelling directive. A practical noise control ap-proach was taken consisting of benchmarking the existing commercial unit, diagnosing the primary noise sources, redesigning the system components without affecting the refrigera-tion performance and assessing improvements. The aim was to reduce noise emissions and improve sound quality to those of frost free household refrigerators. Value engineering was used to optimise the performance gains such that the new unit suitable for the domestic mar-ket would be also used in the commercial sector. The sound power reduction achieved was greater than 4 dB. The sound quality of both the existing standard refrigerator and the opti-mised prototype unit were evaluated by a jury in a real living environment. The subjective exercise showed that the optimised prototype was perceived as being quieter and of im-proved sound quality compared to the standard refrigerator

Predicted Infrared and Raman Spectra for Neutral Ti_8C_12 Isomers

Using a density-functional based algorithm, the full IR and Raman spectra are calculated for the neutral Ti_8C_12 cluster assuming geometries of Th, Td, D2d and C3v symmetry. The Th pentagonal dodecahedron is found to be dynamically unstable. The calculated properties of the relaxed structure having C3v symmetry are found to be in excellent agreement with experimental gas phase infrared results, ionization potential and electron affinity measurements. Consequently, the results presented may be used as a reference for further experimental characterization using vibrational spectroscopy.Comment: 6 pages, 5 figures. Physical Review A, 2002 (in press

Detailed Analysis of Scatter Contribution from Different Simulated Geometries of X-ray Detectors.

Scattering is one of the main issues left in planar mammography examinations, as it degrades the quality of the image and complicates the diagnostic process. Although widely used, anti-scatter grids have been found to be inefficient, increasing the dose delivered, the equipment price and not eliminating all the scattered radiation. Alternative scattering reduction methods, based on postprocessing algorithms using Monte Carlo (MC) simulations, are being developed to substitute anti-scatter grids. Idealized detectors are commonly used in the simulations for the purpose of simplification. In this study, the scatter distribution of three detector geometries is analyzed and compared: Case 1 makes use of idealized detector geometry, Case 2 uses a scintillator plate and Case 3 uses a more realistic detector simulation, based on the structure of an indirect mammography X-ray detector. This paper demonstrates that common configuration simplifications may introduce up to 14% of underestimation of the scatter in simulation results

Free standing modulation doped core-shell GaAs/AlGaAs hetero-nanowires

Modulation doped AlGaAs/GaAs core-shell nanowire structures were grown by molecular beam epitaxy. A Si delta-doping was introduced in the AlGaAs shell around the {110} facets of the GaAs core. The wires are typically highly resistive at low temperatures. However, they show a pronounced persistent photoconductivity effect indicating activation of free carriers from the delta-doped shell to the GaAs core. The n-type character of the channel is demonstrated by applying a back-gate voltage. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Burkholderia pseudomallei in a lowland rice paddy: seasonal changes and influence of soil depth and physico-chemical properties.

Melioidosis, a severe infection with the environmental bacterium Burkholderia pseudomallei, is being recognised increasingly frequently. What determines its uneven distribution within endemic areas is poorly understood. We cultured soil from a rice field in Laos for B. pseudomallei at different depths on 4 occasions over a 13-month period. We also measured physical and chemical parameters in order to identify associated characteristics. Overall, 195 of 653 samples (29.7%) yielded B. pseudomallei. A higher prevalence of B. pseudomallei was found at soil depths greater than the 30?cm currently recommended for B. pseudomallei environmental sampling. B. pseudomallei was associated with a high soil water content and low total nitrogen, carbon and organic matter content. Our results suggested that a sampling grid of 25 five metre square quadrats (i.e. 25?×?25?m) should be sufficient to detect B. pseudomallei at a given location if samples are taken at a soil depth of at least 60?cm. However, culture of B. pseudomallei in environmental samples is difficult and liable to variation. Future studies should both rely on molecular approaches and address the micro-heterogeneity of soil when investigating physico-chemical associations with the presence of B. pseudomallei

Evidence of high-n hollow ion emission from Si ions pumped by ultraintense x-rays from relativistic laser plasma

We report on the first observation of high-n hollow ions (ions having no electrons in the K or L shells) produced in Si targets via pumping by ultra-intense x-ray radiation produced in intense laser-plasma interactions reaching the radiation dominant kinetics regime. The existence of these new types of hollow ions in high energy density plasma has been found via observation of highly-resolved x-ray emission spectra of silicon plasma, and confirmed by plasma kinetics calculations, underscoring the ability of powerful radiation sources to fully strip electrons from the inner-most shells of light atoms. Hollow ions spectral diagnostics provide a unique opportunity to characterize powerful x-ray radiation of laboratory and astrophysical plasmas

Stability, Electronic Structure and Vibrational Modes of Ti_8C_12 Dimer

We present our density functional results of the geometry, electronic structure and dissociation energy of Ti_8C_12 dimer. We show that as opposed to the currently held view that Ti_8C_12 are highly stable monodispersed clusters, the neutral Ti_8C_12 clusters form covalent bonds and form stable dimers. We determine that the Ti atoms bond weakly (0.9 eV/bond) to organic ligands such as ammonia. Alternatively the Met-Car dimer has a cohesive energy of 4.84 eV or approximately 1.2 eV per bond. While Met-Car dimers are stable, formation of these dimers may be quenched in an environment that contains a significant population of organic ligands. The ionization and dissociation energies of the dimer are of same order which prevents the observation of the dimer in the ion mass spectroscopy. The analysis of the vibrational frequencies show the lowest-energy structure to be dynamically stable. We also present infrared absorption and Raman scattering spectra of the Ti_8C_12 dimer.Comment: 5 pages, 3 figures (Better quality figures available on request). Physical Review B (Rapid Communication) (2002, in press