Production of Metal Prototypes Using a High Powered Laser Machining Centre

The established commercially available rapid prototyping techniques are now well known throughout the manufacturing community. They are able to produce high quality, accurate prototypes, but are limited largely to processing polymer, wax or paper materials. Where a metal part is required, then a further process step, such as investment casting using the prototype part as a pattern is required. As a further point most of the above systems are high capital cost dedicated pieces of equipment. This paper describes the use of laser machining centres as rapid prototyping tools in the areas of, laminated prototyping, using both paper and metal, and laser forming.Mechanical Engineerin

Lagrangian Statistics and Temporal Intermittency in a Shell Model of Turbulence

We study the statistics of single particle Lagrangian velocity in a shell model of turbulence. We show that the small scale velocity fluctuations are intermittent, with scaling exponents connected to the Eulerian structure function scaling exponents. The observed reduced scaling range is interpreted as a manifestation of the intermediate dissipative range, as it disappears in a Gaussian model of turbulence.Comment: 4 pages, 5 figure

Early Atomic Models - From Mechanical to Quantum (1904-1913)

A complete history of early atomic models would fill volumes, but a reasonably coherent tale of the path from mechanical atoms to the quantum can be told by focusing on the relevant work of three great contributors to atomic physics, in the critically important years between 1904 and 1913: J. J. Thomson, Ernest Rutherford and Niels Bohr. We first examine the origins of Thomson's mechanical atomic models, from his ethereal vortex atoms in the early 1880's, to the myriad "corpuscular" atoms he proposed following the discovery of the electron in 1897. Beyond predictions for the periodicity of the elements, the application of Thomson's atoms to problems in scattering and absorption led to quantitative predictions that were confirmed by experiments with high-velocity electrons traversing thin sheets of metal. Still, the much more massive and energetic {\alpha}-particles being studied by Rutherford were better suited for exploring the interior of the atom, and careful measurements on the angular dependence of their scattering eventually allowed him to infer the existence of an atomic nucleus. Niels Bohr was particularly troubled by the radiative instability inherent to any mechanical atom, and succeeded in 1913 where others had failed in the prediction of emission spectra, by making two bold hypotheses that were in contradiction to the laws of classical physics, but necessary in order to account for experimental facts.Comment: 58 Pages + References, 8 Figures. Accepted for publication in the European Physical Journal H (Historical Perspectives on Contemporary Physics). V2 - minor typos corrected and a footnote added to p.2

A Measurement of Time-Averaged Aerosol Optical Depth using Air-Showers Observed in Stereo by HiRes

Air fluorescence measurements of cosmic ray energy must be corrected for attenuation of the atmosphere. In this paper we show that the air-showers themselves can yield a measurement of the aerosol attenuation in terms of optical depth, time-averaged over extended periods. Although the technique lacks statistical power to make the critical hourly measurements that only specialized active instruments can achieve, we note the technique does not depend on absolute calibration of the detector hardware, and requires no additional equipment beyond the fluorescence detectors that observe the air showers. This paper describes the technique, and presents results based on analysis of 1258 air-showers observed in stereo by the High Resolution Fly's Eye over a four year span.Comment: 7 pages, 3 figures, accepted for publication by Astroparticle Physics Journa

Observation of the Ankle and Evidence for a High-Energy Break in the Cosmic Ray Spectrum

We have measured the cosmic ray spectrum at energies above $10^{17}$ eV using the two air fluorescence detectors of the High Resolution Fly's Eye experiment operating in monocular mode. We describe the detector, PMT and atmospheric calibrations, and the analysis techniques for the two detectors. We fit the spectrum to models describing galactic and extragalactic sources. Our measured spectrum gives an observation of a feature known as the ``ankle'' near $3\times 10^{18}$ eV, and strong evidence for a suppression near $6\times 10^{19}$ eV.Comment: 14 pages, 9 figures. To appear in Physics Letters B. Accepted versio

Assembling photoluminescent silicon nanocrystals into periodic mesoporous organosilica

A contemporary question in the intensely active field of periodic mesoporous organosilica (PMO) materials is how large a silsesquioxane precursor can be self-assembled under template direction into the pore walls of an ordered mesostructure. An answer to this question is beginning to emerge with the ability to synthesize dendrimer, buckyball, and polyhedral oligomeric silsesquioxane PMOs. In this paper, we further expand the library of large-scale silsesquioxane precursors by demonstrating that photoluminescent nanocrystalline silicon that has been surface-capped with oligo(triethoxysilylethylene), denoted as ncSi:(CH 2CH 2Si(OEt) 3) nH, can be self-assembled into a photoluminescent nanocrystalline silicon periodic mesoporous organosilica (ncSi-PMO). A comprehensive multianalytical characterization of the structural and optical properties of ncSi-PMO demonstrates that the material gainfully combines the photoluminescent properties of nanocrystalline silicon with the porous structure of the PMO. This integration of two functional components makes ncSi-PMO a promising multifunctional material for optoelectronic and biomedical applications. © 2012 American Chemical Society

Sustainable Harvesting of Tropical Rainforests: Reply to Keto, Scott and Olsen

This paper refutes the Keto et al. proposition that the Queensland selection logging system is neither ecologically nor economically sustainable. The key requirements of this system are: (1) that logging guidelines are sympathetic to the silvicultural characteristics of the forest, ensuring adequate regeneration of commercial species and discouraging invasion by weeds; (2) tree-marking by trained staff specifies trees to be retained, trees to be removed and the direction of felling to ensure minimal damage to the residual stand; (3) logging equipment is appropriate and driven by trained operators to ensure minimal damage and soil disturbance, compaction and erosion; (4) prescriptions ensure that adequate stream buffers and steep slopes are excluded from logging; (5) sufficient areas for scientific reference, feature protection and recreation are identified and excluded from logging; and (6) that deficiencies in an evolving system are recognized and remedied, leading to an improved system. Many studies of the effects of logging in these forests have been published and collectively provide a unique demonstration of one possible approach to sustainable timber harvesting

Avaliação das práticas diferenciais de amamentação: a questão da etnia

Breastfeeding practices in two Brazilian metropolitan areas (S. Paulo and Recife) are described, as part of a study carried out in 1987. In a random sample of healthy 0-8 month old infants, selected from all health care units, higher breastfeeding rates were found in S. Paulo (initiation, prevalence, median and average) than in Recife. The mean duration of breastfeeding, mixed and full, was of 127.5 and 66.6 days, respectively, for S. Paulo, and of 104.4 and 31.7 days for Recife. When data are analysed according to ethnic group, white S. Paulo women breastfeed more than white Recife women. Full breastfeeding rate is more prevalent among white and "mulato" S. Paulo women. However, when the data were analyzed for each city separately, it was found, remarkably, that the non-whites breastfeed more than the whites. In Recife, full breastfeeding is particularly low in whites (of 15.3 days median) and "mulatos" (of 16.7 days), but of 34.5 days in blacks. The study points out the need for greater in-depth investigation of the issue of ethnicity and infant feeding practices, still inadequately understood in world literature.Descreve-se a situação da prática de amamentar em duas áreas metropolitanas brasileiras: São Paulo e Recife, Brasil, em estudos conduzidos em 1987. Em amostras representativas da população de crianças saudáveis de 0-8 meses atendidas pelo sistema de saúde, nota-se que é maior em São Paulo a proporção das mães que iniciam a amamentação e a prevalência de amamentados. A duração média do aleitamento materno total (AM) e quase exclusivo (AE) é respectivamente de 127,5 e 66,6 dias em São Paulo. Em Recife, 104,4 e 31,7 dias, respectivamente, para AM e AE. Estudaram-se também os dados de amamentação conforme a cor da pele da mãe, concluindo que se amamenta mais em São Paulo do que em Recife, significativamente entre brancas. O aleitamento materno quase exclusivo é praticado mais em São Paulo do que em Recife, por brancas e pardas. Observando-se os grupos étnicos em cada uma das cidades, notou-se que são as mulheres não-brancas (pretas e pardas) aquelas que amamentam mais, sendo particularmente baixo o aleitamento quase exclusivo em Recife, maior entre as pretas (34,5 dias de mediana de AE) comparado a 15,3 dias entre brancas e 16,7 entre pardas. O estudo aponta para a necessidade de se elaborar desenhos de pesquisa que levem em conta a questão da etnia e a amamentação, questão não respondida pela literatura em nível mundial

A measurement of the tau mass and the first CPT test with tau leptons

We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV using tau pairs from Z0 decays. To test CPT invariance we compare the masses of the positively and negatively charged tau leptons. The relative mass difference is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.