68,824 research outputs found
Incorporation of TiC particles on AlSi 4340 low alloy steel surfaces via tungsten inert gas melting
Surface cladding utilizes a high energy input to deposit a layer on substrate surfaces providing protection against wear and corrosion. In this work, TiC particulates were incorporated by melting single tracks in powder preplaced onto AISI 4340 low alloy steel surfaces using a Tungsten Inert Gas (TIG) torch with a range of processing conditions. The effects of energy input and powder content on the melt geometry, microstructure and hardness were investigated. The highest energy input (1680J/mm) under the TIG torch produced deeper (1.0 mm) and wider melt pools, associated with increased dilution, compared to that processed at the lowest energy (1008J/mm). The melt microstructure contained partially melted TiC particulates associated with dendritic, cubic and globular type carbides precipitated upon solidification of TiC dissolved in the melt; TiC accumulated more near to the melt-matrix interface and at the track edges. Addition of 0.4, 0.5 and 1.0 mg/mm2 TiC gave hardness values in the resolidified melt pools between 750 to over 1100Hv, against a base hardness of 300 Hv; hardness values are higher in tracks processed with a grcater TiC addition and reduced energy input
Energy input is primary controller of methane bubbling in subarctic lakes
Emission of methane (CH4) from surface waters is often dominated by ebullition (bubbling), a transport mode with high‐spatiotemporal variability. Based on new and extensive CH4 ebullition data, we demonstrate striking correlations (r2 between 0.92 and 0.997) when comparing seasonal bubble CH4 flux from three shallow subarctic lakes to four readily measurable proxies of incoming energy flux and daily flux magnitudes to surface sediment temperature (r2 between 0.86 and 0.94). Our results after continuous multiyear sampling suggest that CH4 ebullition is a predictable process, and that heat flux into the lakes is the dominant driver of gas production and release. Future changes in the energy received by lakes and ponds due to shorter ice‐covered seasons will predictably alter the ebullitive CH4 flux from freshwater systems across northern landscapes. This finding is critical for our understanding of the dynamics of radiatively important trace gas sources and associated climate feedback
Energy input and HI spin temperatures in low pressure regions
Two recent (unpublished) HI emission/absorption studies carried out with good sensitivity using the Arecibo 21 cm beam are discussed. One study (Colgan, Salpeter and Terzian) looked for high velocity clouds of our own Galaxy in absorption in the directions of 63 of the brightest continuum sources reachable with the Arecibo telescope. HI emission mapping in the neighborhood of these directions was also carried out. The other study (Corbelli and Schneider) looked for absorption along lines of sight to about 50 weaker sources which pass within a few diameters of nearby disk galaxies. Neither study detected any absorption
Directed transport in a ratchet with internal and chemical freedoms
We consider mechanisms of directed transport in a ratchet model comprising,
besides the external freedom where transport occurs, a chemical freedom that
replaces the familiar external driving by an autonomous dynamics providing
energy input, and an internal freedom representing a functional mode of a motor
molecule. The dependence of the current on various parameters is studied in
numerical simulations of our model. In particular, we point out the role of the
internal freedom as a buffer between energy input and output of mechanical work
that allows a temporary storage of injected energy and can contribute to the
efficiency of current generation.Comment: 7 pages, 9 figure
Superbubble evolution in disk galaxies, I. Study of blow-out by analytical models
Galactic winds are a common phenomenon in starburst galaxies in the local
universe as well as at higher redshifts. Their sources are superbubbles driven
by sequential supernova explosions in star forming regions, which carve out
large holes in the interstellar medium and eject hot, metal enriched gas into
the halo and to the galactic neighborhood. We investigate the evolution of
superbubbles in exponentially stratified disks. We present advanced analytical
models for the expansion of such bubbles and calculate their evolution in space
and time. With these models one can derive the energy input that is needed for
blow-out of superbubbles into the halo and derive the break-up of the shell,
since Rayleigh-Taylor instabilities develop soon after a bubble starts to
accelerate into the halo. The approximation of Kompaneets is modified in order
to calculate velocity and acceleration of a bubble analytically. Our new model
differs from earlier ones, because it presents for the first time an analytical
calculation for the expansion of superbubbles in an exponential density
distribution driven by a time-dependent energy input rate. The time-sequence of
supernova explosions of OB-stars is modeled using their main sequence lifetime
and an initial mass function. We calculate the morphology and kinematics of
superbubbles powered by three different kinds of energy input and we derive the
energy input required for blow-out as a function of the density and the scale
height of the ambient interstellar medium. The Rayleigh-Taylor instability
timescale in the shell is calculated in order to estimate when the shell starts
to fragment and finally breaks up. Analytical models are a very efficient tool
for comparison to observations, like e.g. the Local Bubble and the W4 bubble
discussed in this paper, and also give insight into the dynamics of superbubble
evolution.Comment: 18 pages, 11 figure
Response of Farm Energy Input Prices to World Crude Oil Prices
Farm Management, Resource /Energy Economics and Policy,
- …