1,721,062 research outputs found
Deformation mechanisms in rapidly solidified aluminum alloys
No full textThe deformation mechanisms of four rapidly solidified (RS) and hot extruded aluminum alloys were investigated. Al-8.8Fe-3.7Ce (all compositions in wt%) and Al-8.9Fe-6.9Ce alloys produced from RS powders and two Al-8Fe-2Mo alloys one produced from RS ribbons and the other from powders, respectively, were creep tested in the temperature range 250\sp\circC to 350\sp\circC over a range of stresses from 15 to 250 MPa.The Al-8.8Fe-3.7Ce alloy exhibited a diffusional creep region at low stresses and a power law creep region as the stress increased beyond a given transition stress. Coble creep was the deformation mechanism in the diffusional creep region and the strain rates were determined by the size of the RS particulate. In the power law region the creep rates could be predicted by the Sherby and Lin equation.To investigate the influence of the thermal degradation on the creep behavior of the Al-Fe-Ce alloys both alloys were heat-treated for 165 hours at 450\sp\circC, 500\sp\circC and 550\sp\circC, respectively, and creep tested at 300\sp\circC. Both a diffusional and a power law region was observed for both alloys and all heat-treatment temperatures. An increase in the diffusional creep rates was observed for the heat-treated alloys instead of the expected decrease, confirming that the grain size of the material does not determine the creep rates in the diffusional creep region.The Al-8Fe-2Mo ribbon extrusion exhibited a diffusional region at low stresses and a power law region at higher stresses. In the diffusional regime the strain rates were determined by the size of the RS particulate. When the data in the power law regime was plotted as normalized stress versus normalized strain, the Al-8Fe-2Mo data did not exhibit a single slope. The diffusional creep region was totally suppressed in the Al-8Fe-2Mo powder alloy, an observation that is in contrast with the behavior of all other alloys tested in this work. (Abstract shortened with permission of author.)Made available in DSpace on 2011-05-07T13:27:11Z (GMT). No. of bitstreams: 2
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Previous issue date: 1989Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:54:57Z
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The plastic deformation of alloys based on aluminum titanide
No full textThe thermal stability of a dispersion of rare-earth oxide particles in Ti and Ti\sb3Al matrices has been considered analytically and determined experimentally. The solubility product for the formation of erbia (Er\sb2O\sb{3)} in a Ti matrix has been calculated using known thermodynamic data which allows the concentration terms in the Lifshitz, Slyozov and Wagner coarsening equation to be calculated. Predictions show that a dispersion will exhibit a greater thermal stability when in a matrix with an excess concentration of oxygen (with respect to that necessary to form the stoichiometric Er\sb2O\sb3) compared with an excess concentration of erbium. The diffusivity of Er in Ti\sb3Al has been approximated on the basis of known thermodynamic and elastic data. This result has been used to estimate the thermal stability of erbia in Ti\sb3Al. A model has been developed which describes accelerated Ostwald ripening at moving interfaces. Isothermal and isochronal annealing experiments have been executed on rapidly solidified materials with results which are consistent with the presented predictions.Four different Ti\sb3Al alloys have been produced by centrifugal atomization, namely Ti\sb3Al 0.7Er, Ti\sb3Al 2.5Nb, Ti\sb3Al 5Nb and Ti\sb3Al 11Nb (at.%) which have been characterized in the as-rapidly solidified and consolidated (by HIP) condition. A previously unreported Ti-Er-O phase has been identified and characterized using SAD, EDS, EELS and AUGER microanalysis techniques.The four alloys named above have been deformed in compression to 3% strain at room temperature and 650\sp\circC, and the resulting deformation microstructures have been analyzed and the Burgers vector determined by TEM contrast experiments. Stereographic analyses have been used to completely characterize slip systems in the deformed material. These results have been interpreted on the basis of a model of anisotropic charge distribution around atoms in sheets containing only Ti atoms in Ti\sb3Al.Made available in DSpace on 2011-05-07T12:48:23Z (GMT). No. of bitstreams: 2
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Previous issue date: 1989Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:46:03Z
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Defect and deformation studies in transition metal trialuminide compounds
No full textDefect studies have been performed on the intermetallic compounds \rm Al\sb3Ti, \rm Al\sb3V and \rm Al\sb{67}Ni\sb8Ti\sb{25} which were deformed at elevated temperatures. Test materials were prepared via the rapid solidification route. TEM characterizations indicated that the microstructure of the asatomized Al-25at.%Ti alloy powder consisted of primary dendrites of the \rm Al\sb3Ti phase (DO\sb{22} structure) and -aluminum. The as-atomized Al-25at.%V alloy exhibited a microstructure composed of primary \rm Al\sb8V\sb5 dendrites with interdendritic \rm Al\sb3V (DO\sb{22}) and -aluminum. The Al-8at.%Ni-25at.% Ti alloy exhibited dendrites of \rm Al\sb{67}Ni\sb8Ti\sb{25}(L1\sb2) and small \rm Al\sb3Ni\sb2 particles.The consolidated Al-25at.%Ti alloy contained \rm Al\sb3Ti with numerous small particles. Three types of second phases were noted: TiAl particles, oxide streamers at prior particle boundaries; and small TiC particles within certain grains. In the consolidated Al-25at.%V powder, large \rm Al\sb8V\sb5 particles were identified within a matrix of \rm Al\sb3V. The Al-8at.%Ni-25at.%Ti alloy contained \rm Al\sb2NiTi particles (fcc, a\sb0 = 11.94A) in a matrix of \rm Al\sb{67}Ni\sb8Ti\sb{25}.Compression testing was carried out at 300\sp\circC, 600\sp\circC and 800\sp\circC. The weak-beam darkfield technique was employed to determine the Burgers vector, slip plane and dissociation reactions of dislocations responsible for plastic deformation.In \rm Al\sb3Ti, microtwins on the close packed planes formed by the repeated passage of 1/6 111) partial dislocations on successive planes were identified. Partial dislocations with b = 1/2 110) which bound APB's on the (001) plane were also characterized at 300\sp\circC and 600\sp\circC. Dislocations with b = 100) were found to glide on (001) and shown to climb at the higher temperatures (600\sp\circC). \rm Al\sb3V appears to deform by glide of b = 110) dislocation son the planes. At 800\sp\circC, again climbing 100) dislocations were found. In \rm Al\sb{67}Ni\sb8Ti\sb{25}, dislocation glide of the type was identified. At 300\sp\circC, the dislocations were undissociated, while at 600\sp\circC and 800\sp\circC, considerable APB-type dissociation on the planes was noted.Defect structures in the two DO\sb{22} compounds have been explained using a new model of accounting for energies related to the dissociated configurations. This model relies on quantum mechanical calculations for total crystal energies of various other crystal structures, similar to DO\sb{22}, which are present locally within the faulted region of the dissociated dislocations. A possible extrapolation to the case of \rm L1\sb2 compounds is also given.Made available in DSpace on 2011-05-07T13:40:54Z (GMT). No. of bitstreams: 2
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Previous issue date: 1990Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding ([email protected]) on 2011-05-07T14:57:50Z
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Effect of the reproductive cycle on morphology and activity of the ovarian surface epithelium in mammals
Get PDFThe layer of cells lining the outer surface of the mammalian ovary, the
ovarian surface epithelium (OSE), is a constant feature throughout the dynamic
tissue remodeling that occurs throughout the reproductive cycle (follicle growth,
ovulation, corpora lutea formation and pregnancy). Abnormal development of these
cells is responsible for 90% of all epithelial ovarian cancers in women and
epidemiological studies have shown that susceptibility to ovarian cancer is
negatively correlated with increasing pregnancy. Little is known about how OSE
cells are affected at each stage of the cycle, so the main aim of this study was to
determine how the reproductive cycle affected proliferation and degeneration of OSE
cells. This study utilised three animal models each with a different type of
reproductive cycle: a mono-ovular seasonal breeder (Sheep), a mono-ovular
polyoestrous breeder (Cow) and a poly-ovular non human primate (marmoset) to
allow comparisons to be made. Comparison of OSE proliferative activity was made
in sheep and marmoset at each stage of the cycle including pregnancy and
anoestrous. The bovine model was used to investigate apoptotic cell death.
Proliferative activity of somatic cells within the sheep ovary was monitored
throughout the reproductive cycle by detection of cell cycle markers PCNA and Ki67
using immunohistochemistry. The pattern of OSE proliferation was correlated with
the pattern of follicle development at each stage (sheep and marmoset). During
pregnancy cell proliferation was significantly lower in OSE and in granulosa cells,
reflecting a suppression of mature follicle development during these stages whereas
in cycling animals proliferation was increased. Differences in OSE proliferation were
observed in relation to the local underlying tissue environment in both sheep and
marmoset. Epithelial cell rupture and regeneration enhanced the hormonal mitogenic
action on epithelial cells, which showed highest proliferation over corpora lutea in
each animal model.
To test the hypothesis that these changes are mediated by hormones or
growth factors ovine OSE cells were cultured and proliferative activity monitored
after treatment with several factors: fetal calf serum (FCS), follicular fluid from
follicles of varying sizes, corpora lutea extracts, recombinant human IGF-1, oestradiol and progesterone. IGF alone was demonstrated to have an affect on
increasing proliferation of cultured OSE cells. Levels of FSHr and LHr were
monitored by quantitative real- time PCR and it was demonstrated that the
concentration of gonadotrophin receptors in OSE, increased prior to and after
ovulation, at which time the in vivo OSE proliferation also peaked.
The in situ apoptosis index was determined in bovine tissue using TUNEL
throughout the regular cycle, and at mid and late-pregnancy stages. The results
showed that pregnancy induced apoptotic activity in OSE cells and up regulated the
tumour suppressor gene p53. Cultured bovine OSE cells also exhibited an increased
level of apoptosis following progesterone treatment. Since p53/p53 gene expression
in OSE over the corpora lutea producing progesterone also increased, this
progesterone-mediated apoptosis may be mediated through an up-regulation of p53
synthesis.
The effect of pregnancy and low production of gonadotrophins in the
regulation of OSE cell morphology and activity was further investigated in the
marmoset monkey (a non-human primate) treated with GnRH antagonist and infused
with BrdU to monitor proliferative activity. OSE proliferation was correlated to
ovarian events (follicular growth, ovulation and luteinization) and this was
suppressed during pregnancy. Inhibition of gonadotrophin secretion by treatment
with a GnRH antagonist also markedly inhibited OSE proliferation.
Taken together these studies support the hypothesis that pregnancy and
periods of anovulation reduce proliferation of OSE cells and alter the pattern of
apoptotic cell death and that this effect is independent of species and reproductive
pattern. Suppression of gonadotrophins and other growth factors during pregnancy
could enhance p53-mediated apoptosis of damaged and mitogenic cells arising from
repeated ovulations. This effect may partly explain why increasing number of
pregnancies in woman reduces the chance of epithelial ovarian cancers
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