192 research outputs found
Direct Selective Laser Sintering of Tool Steel Powders to High Density: Part B -The Effect on Microstructural Evolution
This paper describes recent progress on the Direct Selective Laser Sintering of M2 [Fe6W-5Mo-4Cr-2V-0.8C] high speed steel (HSS) and H13 [Fe-5Cr-1V-1Si-1.5Mo-0.4C] tool steel
powders. Part B will focus on the microstructural evolution of laser scanned powder beds. It has
been found that H13 powders are more amenable to Direct Selective Laser Sintering than M2
powders. Densities up to 90% are possible with H13 powder compared with 70% for M2. The
relationship between alloy composition, microstructure, post-scanned density and scan
conditions will be discussed for single track, single layer and multi-layer constructions.The research reported in this paper is a joint project between the Universities of Bradford, Leeds
and Liverpool, funded by the UK Engineering and Physical Sciences Research Council under
Grant Number GR/R32222.Mechanical Engineerin
Direct Selective Laser Sintering of Tool Steel Powders to High Density: Part A - Effects of Laser Beam Width and Scan Strategy
This paper describes progress on the Direct Selective Laser Sintering of M2 and H13 tool
steel powders, comparing this with previous and further observations on stainless steel powders.
The distinguishing feature is the melting of single tracks and layers in deep powder beds. The
paper focuses on changing characteristics of the melt pool (mass, volume, aspect ratio, stability)
and laser-powder interactivity as the laser beam width, power and scan speed change. It also
compares the melt pool of neighbouring tracks during single layer construction. Simulations
from a computer model to predict melt pool shape and dimension show reasonable agreement
with experimental results at low scan speeds (0.5mm/s). But unexpected increases in melt depth
above 1.0mm/s have been observed, suggesting higher values and more variability in laser
absorptivity than expected, even approaching 1.0 for the CO2 laser radiation used in this work.Mechanical Engineerin
EYM equations in the presence of q-stars
We study Einstein-Yang-Mills equations in the presence of gravitating
non-topological soliton field configurations, of q-ball type. We produce
numerical solutions, stable with respect to gravitational collapse and to
fission into free particles, and we study the effect of the field strength and
the eigen-frequency to the soliton parameters. We also investigate the
formation of such soliton stars when the spacetime is asymptotically anti de
Sitter.Comment: 11 pages, to appear in Phys. Rev.
On paraquaternionic submersions between paraquaternionic K\"ahler manifolds
In this paper we deal with some properties of a class of semi-Riemannian
submersions between manifolds endowed with paraquaternionic structures, proving
a result of non-existence of paraquaternionic submersions between
paraquaternionic K\"ahler non locally hyper paraK\"ahler manifolds. Then we
examine, as an example, the canonical projection of the tangent bundle, endowed
with the Sasaki metric, of an almost paraquaternionic Hermitian manifold.Comment: 13 pages, no figure
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
Interactions between cell surface protein disulphide isomerase and S-nitrosoglutathione during nitric oxide delivery
In this study, we investigated the role of protein disulphide isomerase (PDI) in rapid metabolism of S-nitrosoglutathione (GSNO) and S-nitrosoalbumin (albSNO) and in NO delivery from these compounds into cells. Incubation of GSNO or albSNO (1 μM) with the megakaryocyte cell line MEG-01 resulted in a cell-mediated removal of each compound which was inhibited by blocking cell surface thiols with 5,5′-dithiobis 2-nitrobenzoic acid (DTNB) (100 μM) or inhibiting PDI with bacitracin (5 mM). GSNO, but not albSNO, rapidly inhibited platelet aggregation and stimulated cyclic GMP (cGMP) accumulation (used as a measure of intracellular NO entry). cGMP accumulation in response to GSNO (1 μM) was inhibited by MEG-01 treatment with bacitracin or DTNB, suggesting a role for PDI and surface thiols in NO delivery. PDI activity was present in MEG-01 conditioned medium, and was inhibited by high concentrations of GSNO (500 μM). A number of cell surface thiol-containing proteins were labelled using the impermeable thiol specific probe 3-(N-maleimido-propionyl) biocytin (MPB). Pretreatment of cells with GSNO resulted in a loss of thiol reactivity on some but not all proteins, suggesting selective cell surface thiol modification. Immunoprecipitation experiments showed that GSNO caused a concentration-dependent loss of thiol reactivity of PDI. Our data indicate that PDI is involved in both rapid metabolism of GSNO and intracellular NO delivery and that during this process PDI is itself altered by thiol modification. In contrast, the relevance of PDI-mediated albSNO metabolism to NO signalling is uncertain
Dilatonic Black Holes with Gauss-Bonnet Term
We discuss black holes in an effective theory derived from a superstring
model, which includes a dilaton field, a gauge field and the Gauss-Bonnet term.
Assuming U(1) or SU(2) symmetry for the gauge field, we find four types of
spherically symmetric solutions, i.e., a neutral, an electrically charged, a
magnetically charged and a ``colored'' black hole, and discuss their
thermodynamical properties and fate via the Hawking evaporation process. For
neutral and electrically charged black holes, we find critical point and a
singular end point. Below the mass corresponding to the critical point,
nosolution exists, while the curvature on the horizon diverges and anaked
singularity appears at the singular point. A cusp structure in the mass-entropy
diagram is found at the critical point and black holes on the branch between
the critical and singular points become unstable. For magnetically charged and
``colored" black holes, the solution becomes singular just at the end point
with a finite mass. Because the black hole temperature is always finite even at
the critical point or the singular point, we may conclude that the evaporation
process will not be stopped even at the critical point or the singular point,
and the black hole will move to a dynamical evaporation phase or a naked
singularity will appear.Comment: 31pages, 11figures, LaTex styl
A Likelihood Method for Measuring the Ultrahigh Energy Cosmic Ray Composition
Air fluorescence detectors traditionally determine the dominant chemical
composit ion of the ultrahigh energy cosmic ray flux by comparing the averaged
slant depth of the shower maximum, , as a function of energy to the
slant depths expect ed for various hypothesized primaries. In this paper, we
present a method to make a direct measurement of the expected mean number of
protons and iron by comparing the shap es of the expected
distributions to the distribution for data. The advantages of this method
includes the use of information of the full distribution and its ability to
calculate a flux for various cosmic ray compositi ons. The same method can be
expanded to marginalize uncertainties due to choice of spectra, hadronic models
and atmospheric parameters. We demonstrate the technique with independent
simulated data samples from a parent sample of protons and iron. We accurately
predict the number of protons and iron in the parent sample and show that the
uncertainties are meaningful.Comment: 11 figures, 22 pages, accepted by Astroparticle Physic
Alternative Methods to Finding Patterns in HiRes Stereo Data
In this paper Ultra High Energy Cosmic Rays UHECRs data observed by the HiRes
fluorescence detector in stereo mode is analyzed to search for events in the
sky with an arrival direction lying on a great circle. Such structure is known
as the arc structure. The arc structure is expected when the charged cosmic
rays pass through the galactic magnetic field. The arcs searched for could
represent a broad or a small scale anisotropy depending on the proposed source
model for the UHECRs. The Arcs in this paper are looked for using Hough
transform were Hough transform is a technique used to looking for patterns in
images. No statistically significant arcs were found in this study
- …