10,400 research outputs found
High strength alloy for immediate temperature, 24 24 to 704 C (75 to 1300 F), applications
Application of prealloyed powder technology to the NASA-TRW-VI-A alloy shows the potential of highly alloyed normally cast superalloys for achieving superior properties at intermediate temperatures
Method of forming articles of manufacture from superalloy powders
A highly alloyed superalloy material is obtained using prealloyed powders. The material is easily shaped at high temperatures when it becomes superplastic because of its particular microstructure
A two-fluid model for tissue growth within\ud a dynamic flow environment
We study the growth of a tissue construct in a perfusion bioreactor, focussing on its response to the mechanical environment. The bioreactor system is modelled as a two-dimensional channel containing a tissue construct through which a flow of culture medium is driven. We employ a multiphase formulation of the type presented by G. Lemon, J. King, H. Byrne, O. Jensen and K. Shakesheff in their study (Multiphase modelling of tissue growth using the theory of mixtures. J. Math. Biol. 52(2), 2006, 571–594) restricted to two interacting fluid phases, representing a cell population (and attendant extracellular matrix) and a culture medium, and employ the simplifying limit of large interphase viscous drag after S. Franks in her study (Mathematical Modelling of Tumour Growth and Stability. Ph.D. Thesis, University of Nottingham, UK, 2002) and S. Franks and J. King in their study (Interactions between a uniformly proliferating tumour and its surrounding: Uniform material properties. Math. Med. Biol. 20, 2003, 47–89).\ud
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The novel aspects of this study are: (i) the investigation of the effect of an imposed flow on the growth of the tissue construct, and (ii) the inclusion of a mechanotransduction mechanism regulating the response of the cells to the local mechanical environment. Specifically, we consider the response of the cells to their local density and the culture medium pressure. As such, this study forms the first step towards a general multiphase formulation that incorporates the effect of mechanotransduction on the growth and morphology of a tissue construct. The model is analysed using analytic and numerical techniques, the results of which illustrate the potential use of the model to predict the dominant regulatory stimuli in a cell population
Method of heat treating a formed powder product material
Heat treating a product material of prealloyed powders after shaping by superplastic deformation restores the ability of the material to resist deformation at high temperatures. Heat treating is accomplished by heating to a temperature between the solidus and liquidus with the application of isostatic pressure to close any voids. This pressure may be simultaneously applied while the material is at the heat treating temperature. The pressure may also be applied when the material cools to a temperature between that at which it is shaped and the solidus
Modelling crystal aggregation and deposition\ud in the catheterised lower urinary tract
Urethral catheters often become encrusted with crystals of magnesium struvite and calcium phosphate. The encrustation can block the catheter, which can cause urine retention in the bladder and reflux into the kidneys. We develop a mathematical model to investigate crystal deposition on the catheter surface, modelling the bladder as a reservoir of fluid and the urethral catheter as a rigid channel. At a constant rate, fluid containing crystal particles of unit size enters the reservoir, and flows from the reservoir through the channel and out of the system. The crystal particles aggregate, which we model using Becker–Döring coagulation theory, and are advected through the channel, where they continue to aggregate and are deposited on the channel’s walls. Inhibitor particles also enter the reservoir, and can bind to the crystals, preventing further aggregation and deposition. The crystal concentrations are spatially homogeneous in the reservoir, whereas the channel concentrations vary spatially as a result of advection, diffusion and deposition. We investigate the effect of inhibitor particles on the amount of deposition. For all parameter values, we find that crystals deposit along the full length of the channel, with maximum deposition close to the channel’s entrance
High-temperature strength of prealloyed-powder products increased by heat/pressure treatment
Heat treatment process involves heating products to a temperature above the solidus, and subsequently applying pressure at a temperature below the solidus. Technique can be modified to one step process involving simultaneous application if both high pressure and heat. Process is not limited to cobalt-base alloys
Application of directional solidification to a NASA nickel-base alloy /TAZ-8B/
Directional solidification of nickel base alloy TAZ-8B to enhance potential for advanced gas turbine engine application
Evaluation of a cobalt-base alloy, HS-31, made by extrusion of prealloyed powders
Evaluation of cobalt base alloy made by extrusion of prealloyed powder
Nonuniqueness in a minimal model for cell motility
Two–phase flow models have been used previously to model cell motility, however these have rapidly become very complicated, including many physical processes, and are opaque. Here we demonstrate that even the simplest one–dimensional, two–phase, poroviscous, reactive flow model displays a number of behaviours relevant to cell crawling. We present stability analyses that show that an asymmetric perturbation is required to cause a spatially uniform, stationary strip of cytoplasm to move, which is relevant to cell polarization. Our numerical simulations identify qualitatively distinct families of travelling–wave solution that co–exist at certain parameter values. Within each family, the crawling speed of the strip has a bell–shaped dependence on the adhesion strength. The model captures the experimentally observed behaviour that cells crawl quickest at intermediate adhesion strengths, when the substrate is neither too sticky nor too slippy
Micron-sized forsterite grains in the pre-planetary nebula of IRAS 17150-3224 - Searching for clues on the mysterious evolution of massive AGB stars
We study the grain properties and location of the forsterite crystals in the
circumstellar environment of the pre-planetary nebula (PPN) IRAS 17150-3224 in
order to learn more about the as yet poorly understood evolutionary phase prior
to the PPN. We use the best-fit model for IRAS 17150-3224 of Meixner et al.
(2002) and add forsterite to this model. We investigate different spatial
distributions and grain sizes of the forsterite crystals in the circumstellar
environment. We compare the spectral bands of forsterite in the mid-infrared
and at 69 micrometre in radiative transport models to those in ISO-SWS and
Herschel/PACS observations. We can reproduce the non-detection of the
mid-infrared bands and the detection of the 69 micrometre feature with models
where the forsterite is distributed in the whole outflow, in the superwind
region, or in the AGB-wind region emitted previous to the superwind, but we
cannot discriminate between these three models. To reproduce the observed
spectral bands with these three models, the forsterite crystals need to be
dominated by a grain size population of 2 micrometre up to 6 micrometre. We
hypothesise that the large forsterite crystals were formed after the superwind
phase of IRAS 17150-3224, where the star developed an as yet unknown hyperwind
with an extremely high mass-loss rate (10^-3 Msol/yr). The high densities of
such a hyperwind could be responsible for the efficient grain growth of both
amorphous and crystalline dust in the outflow. Several mechanisms are discussed
that might explain the lower-limit of 2 micrometre found for the forsterite
grains, but none are satisfactory. Among the mechanisms explored is a possible
selection effect due to radiation pressure based on photon scattering on
micron-sized grains.Comment: Accepted by A&
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