Net energy analysis of solar and conventional domestic hot water systems in Melbourne, Australia

It is commonly assumed that solar hot water systems save energy and reduce greenhouse gas emissions. Very rarely has the life-cycle energy requirements of solar hot water systems been analysed, including their embodied energy. The extent to which solar hot water systems save energy compared to conventional systems in Melbourne, Australia, is shown through a comparative net energy analysis. The solar systems provided a net energy saving compared to the conventional systems after 0.5 to 2 years, for electricity and gas systems respectively.<br /

Hypervelocity impact facility for simulating materials exposure to impact by space debris

As a result of man's venturing into space, the local debris contributed by his presence exceeds, at some orbital altitudes, that of the natural component. Man's contribution ranges from fuel residue to large derelect satellites that weigh many kilograms. Current debris models are able to predict the growth of the problem and suggest that spacecraft must employ armor or bumper shields for some orbital altitudes now, and that, the problem will become worse as a function of time. The practical upper limit to the velocity distribution is on the order of 40 km/s and is associated with the natural environment. The maximum velocity of the man-made component is in the 14-16 km/s range. The Long Duration Exposure Facility (LDEF) has verified that the 'high probability of impact' particles are in the microgram to milligram range. These particles can have significant effects on coatings, insulators, and thin metallic layers. The surface of thick materials becomes pitted and the local debris component is enhanced by ejecta from the debris spectrum in a controlled environment. The facility capability is discussed in terms of drive geometry, energetics, velocity distribution, diagnostics, and projectile/debris loading. The facility is currently being used to study impact phenomena on Space Station Freedom's solar array structure, other solar array materials, potential structural materials for use in the station, electrical breakdown in the space environment, and as a means of clarifying or duplicating the impact phenomena on the LDEF surfaces. The results of these experiments are described in terms of the mass/velocity distribution incident on selected samples, crater dynamics, and sample geometry

Masking of aluminum surface against anodizing

Masking material and a thickening agent preserve limited unanodized areas when aluminum surfaces are anodized with chromic acid. For protection of large areas it combines well with a certain self-adhesive plastic tape

Searching for onset of deconfinement via hypernuclei and baryon-strangeness correlations

We argue that the ratio $S_3 =\mathrm{^3_\Lambda H} / (\mathrm{^3He} \times \frac{\Lambda}{p})$ is a good representation of the local correlation between baryon number and strangeness, and therefore is a valuable tool to probe the nature of the dense matter created in high energy heavy-ion collision: quark gluon plasma or hadron gas. A multiphase transport model (AMPT) plus a dynamical coalescence model is used to elucidate our arguments. We find that AMPT with string melting predicts an increase of $S_3$ with increasing beam energy, and is consistent with experimental data, while AMPT with only hadronic scattering results in a low $S_3$ throughout the energy range from AGS to RHIC, and fails to describe the experimental data.Comment: add several sentences in paragraph 2 and 3, one more paragraph (4) and one more reference (11) to address the referee's queries. accepted versio

Quenching of lamellar ordering in an n-alkane embedded in nanopores

We present an X-ray diffraction study of the normale alkane nonadecane C_{19}H_{40} embedded in nanoporous Vycor glass. The confined molecular crystal accomplishes a close-packed structure by alignment of the rod-like molecules parallel to the pore axis while sacrificing one basic principle known from the bulk state, i.e. the lamellar ordering of the molecules. Despite this disorder, the phase transitions observed in the confined solid mimic the phase behavior of the 3D unconfined crystal, though enriched by the appearance of a true rotator phase known only from longer alkane chains.Comment: 7 pages, 3 figure

Differing microstructural properties of 7075-T6 sheet and 7075-T651 extruded aluminium alloy

This paper details an initial study of the differences, if any, in corrosion behaviour between 7075-T6 sheet and 7075-T651 extruded aluminium alloy. The study involved a visual inspection of the grain structure of each material and an analysis of the grain sizes. It was found that there is a significant difference in the grain sizes of the two materials; the extruded material had grains that were approximately 15-20% of the size of the sheet grains. Also, the grains in the sheet material were wider, with a length-to-width aspect ratio of 1.5 (compared with 1.3 for the extruded material). Finally, the grains in the extruded material appeared to form a semi-continuous line of grain boundaries, possibly facilitating the growth of laminar intergranular corrosion; the sheet material contained higher-angle grain boundary junctions which should limit the amount of laminar intergranular corrosion produced and promote networked intergranular corrosion. Further testing will involve corroding specimens and investigating the size, shape and depth of the corrosion produced

Assessment of upper tropospheric HOx sources over the tropical Pacific based on NASA GTE/PEM data: Net effect on HOx and other photochemical parameters

Data for the tropical upper troposphere (8-12 km, 20° N-20° S) collected during NASA's Pacific Exploratory Missions have been used to carry out a detailed examination of the photochemical processes controlling HOx (OH+HO2). Of particular significance is the availability of measurements of nonmethane hydrocarbons, oxygenated hydrocarbons (i.e., acetone, methanol, and ethanol) and peroxides (i.e., H2O2 and CH3OOH). These observations have provided constraints on model calculations permitting an assessment of the potential impact of these species on the levels of HOx, CH3O2, CH2O, as well as ozone budget parameters. Sensitivity calculations using a time-dependent photochemical box model show that when constrained by measured values of the above oxygenated species, model estimated HOx levels are elevated relative to unconstrained calculations. The impact of constraining these species was found to increase with altitude, reflecting the systematic roll-off in water vapor mixing ratios with altitude. At 11-12 km, overall increases in HOx approached a factor of 2 with somewhat larger increases being found for gross and net photochemical production of ozone. While significant, the impact on HOx due to peroxides appears to be less than previously estimated. In particular, observations of elevated H2O2 levels may be more influenced by local photochemistry than by convective transport. Issues related to the uncertainty in high-altitude water vapor levels and the possibility of other contributing sources of HOx are discussed. Finally, it is noted that the uncertainties in gas kinetic rate coefficients at the low temperatures of the upper troposphere and as well as OH sensor calibrations should be areas of continued investigation. Copyright 1999 by the American Geophysical Union

Direct numerical simulations of statistically steady, homogeneous, isotropic fluid turbulence with polymer additives

We carry out a direct numerical simulation (DNS) study that reveals the effects of polymers on statistically steady, forced, homogeneous, isotropic fluid turbulence. We find clear manifestations of dissipation-reduction phenomena: On the addition of polymers to the turbulent fluid, we obtain a reduction in the energy dissipation rate, a significant modification of the fluid energy spectrum, especially in the deep-dissipation range, a suppression of small-scale intermittency, and a decrease in small-scale vorticity filaments. We also compare our results with recent experiments and earlier DNS studies of decaying fluid turbulence with polymer additives.Comment: consistent with the published versio