788 research outputs found
Direct electrochemical production of pseudo-binary Ti–Fe alloys from mixtures of synthetic rutile and iron(III) oxide
Combining the FFC-Cambridge process with field-assisted sintering technology (FAST) allows for the realisation of an alternative, entirely solid-state, production route for a wide range of metals and alloys. For titanium, this could provide a route to produce alloys at a lower cost compared to the conventional Kroll-based route. Use of synthetic rutile instead of high purity TiO2 offers further potential cost savings, with previous studies reporting on the reduction of this feedstock via the FFC-Cambridge process. In this study, mixtures of synthetic rutile and iron oxide (Fe2O3) powders were co-reduced using the FFC-Cambridge process, directly producing titanium alloy powders. The powders were subsequently consolidated using FAST to generate homogeneous, pseudo-binary Ti–Fe alloys containing up to 9 wt.% Fe. The oxide mixture, reduced powders and bulk alloys were fully characterised to determine the microstructure and chemistry evolution during processing. Increasing Fe content led to greater β phase stabilisation but no TiFe intermetallic phase was observed in any of the consolidated alloys. Microhardness testing was performed for preliminary assessment of mechanical properties, with values between 330–400 Hv. Maximum hardness was measured in the alloy containing 5.15 wt.% Fe, thought due to the strengthening effect of fine α phase precipitation within the β grains. At higher Fe contents, there was sufficient β stabilisation to prevent α phase transformation on cooling, leading to a reduction in hardness despite a general increase from solid solution strengthening
Variational Monte Carlo Calculations of H and He with a relativistic Hamiltonian - II
In relativistic Hamiltonians the two-nucleon interaction is expressed as a
sum of , the interaction in the rest frame,
and the ``boost interaction'' which depends upon the
total momentum and vanishes in the rest frame. The
can be regarded as a sum of four terms: , ,
and ; the first three originate from the
relativistic energy-momentum relation, Lorentz contraction and Thomas
precession, while the last is purely quantum. The contributions of and have been previously calculated with the
variational Monte Carlo method for H and He. In this brief note we
report the results of similar calculations for the contributions of and . These are found to be rather small.Comment: 7 pages, P-94-09-07
A Model for Dark Energy decay
We discuss a model of non perturbative decay of dark energy into hot and cold
dark matter. This model provides a mechanism from the field theory to realize
the energy transfer from dark energy into dark matter, which is the requirement
to alleviate the coincidence problem. The advantage of the model is the fact
that we accommodate a mean life compatible with the age of the universe. We
also argue that supersymmetry is a natural set up, though not essential.Comment: 5 pages to be published in Physics Letters
Composite vertices that lead to soft form factors
The momentum-space cut-off parameter of hadronic vertex functions
is studied in this paper. We use a composite model where we can measure the
contributions of intermediate particle propagations to . We show that
in many cases a composite vertex function has a much smaller cut-off than its
constituent vertices, particularly when light constituents such as pions are
present in the intermediate state. This suggests that composite
meson-baryon-baryon vertex functions are rather soft, i.e., they have \Lambda
considerably less than 1 GeV. We discuss the origin of this softening of form
factors as well as the implications of our findings on the modeling of nuclear
reactions.Comment: REVTex, 19 pages, 5 figs(to be provided on request
The Nuclear Sigma Term in the Skyrme Model: Pion-Nucleus Interaction
The nuclear sigma term is calculated including the nuclear matrix element of
the derivative of the NN interaction with respect to the quark mass,
. The NN potential is evaluated in the
skyrmion-skyrmion picture within the quantized product ansatz. The contribution
of the NN potential to the nuclear sigma term provides repulsion to the
pion-nucleus interaction. The strength of the s-wave pion-nucleus optical
potential is estimated including such contribution. The results are consistent
with the analysis of the experimental data.Comment: 16 pages (latex), 3 figures (eps), e-mail: [email protected] and
[email protected]
On a Testing Methodology for the Mechanical Property Assessment of a New Low-Cost Titanium Alloy Derived from Synthetic Rutile
Mechanical property data of a low-cost titanium alloy derived directly from synthetic rutile is reported. A small-scale testing approach comprising consolidation via field-assisted sintering technology, followed by axisymmetric compression testing, has been designed to yield mechanical property data from small quantities of titanium alloy powder. To validate this approach and provide a benchmark, Ti-6Al-4V powder has been processed using the same methodology and compared with material property data generated from thermo-physical simulation software. Compressive yield strength and strain to failure of the synthetic rutile-derived titanium alloy were revealed to be similar to that of Ti-6Al-4V
Experimental vertical stability studies for ITER performance and design
Operating experimental devices have provided key inputs to the design process for ITER axisymmetric control. In particular, experiments have quantified controllability and robustness requirements in the presence of realistic noise and disturbance environments, which are difficult or impossible to characterize with modelling and simulation alone. This kind of information is particularly critical for ITER vertical control, which poses the highest demands on poloidal field system performance, since the consequences of loss of vertical control can be severe. This work describes results of multi-machine studies performed under a joint ITPA experiment (MDC-13) on fundamental vertical control performance and controllability limits. We present experimental results from Alcator C-Mod, DIII-D, NSTX, TCV and JET, along with analysis of these data to provide vertical control performance guidance to ITER. Useful metrics to quantify this control performance include the stability margin and maximum controllable vertical displacement. Theoretical analysis of the maximum controllable vertical displacement suggests effective approaches to improving performance in terms of this metric, with implications for ITER design modifications. Typical levels of noise in the vertical position measurement and several common disturbances which can challenge the vertical control loop are assessed and analysed.United States Department of Energy (DE-FC02-04ER54698, DEAC52- 07NA27344, and DE-FG02-04ER54235
A fault identification and classification scheme for an automobile door assembly process
A process fault identification and classification scheme for an automobile door assembly process is presented based on multivariate in-line dimensional measurements and principal component factor analysis. First, the door assembly process and the dimensional measurement system are briefly introduced. Second, the technique of principal component factor analysis is presented for process fault identification. Process faults are summarized based on off-line identified case studies. Finally a machine classification scheme based on principal components and principal factors is presented and evaluated, using the pattern knowledge obtained off-line. This scheme is shown to be effective in classifying process faults using production data.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45569/1/10696_2005_Article_BF01324797.pd
Magnetic Phase transitions in Plasmas and Transport Barriers
A model of magnetic phase transitions in plasmas is presented: plasma blobs
with pressure excess or defect are dia- or para-magnets and move radially under
the influence of the background plasma magnetisation. It is found that magnetic
phase separation could be the underlying mechanism of L to H transitions and
drive transport barrier formation. Magnetic phase separation and associated
pedestal build up, as described here, can be explained by the well known
interchange mechanism, now reinterpreted as a magnetisation interchange which
remains relevant even when stable or saturated. A testable necessary criterion
for the L to H transition is presented.Comment: 3 figures, 9 pages, equations created with MathType To be published
in Nuclear Fusion, accepted August 201
Adubos verdes e seus efeitos no rendimento da cana-de-açúcar em sistema de plantio direto.
O objetivo deste trabalho foi avaliar adubos verdes e seus efeitos no rendimento da cana-de-açúcar em sistema de plantio direto (SPD). O trabalho foi realizado em Campos dos Goytacazes (RJ), no período de dezembro de 2003 a julho de 2005. O delineamento experimental foi em blocos casualizados, com quatro repetições. Os tratamentos foram: feijão-de-porco (Canavalia ensiformis), mucuna-preta(Mucuna aterrimum), crotalária (Crotalária juncea) em plantio direto e vegetação espontânea em preparo convencional (testemunha). Com crotalária aos 35 dias após emergência (DAE) houve maior taxa de cobertura do solo – 87% – e, aos 92 DAE produziu 17.852 kg ha-1 de matéria seca, respectivamente, 41%, 78% e 407% superior ao feijão-de-porco, mucuna e vegetação espontânea, além de superá-las em acúmulos de K, Mg, S, Zn e Fe. O feijão-de-porco e a mucuna proporcionaram o maior teor de N na parte aérea. Com feijão-de-porco, os teores de P e Ca foram maiores que a crotalária e a mucuna. Com vegetação espontânea, o maior teor de K foi na parte aérea. As leguminosas acumularam maiores quantidades de N e Cu do que a vegetação espontânea. A crotalária e o feijão-de-porco acumularam 66% a mais de P na parte área que a mucuna. O SPD utilizando a adubação verde contribuiu significativamente para a maior produtividade de cana-de-açúcar, 135.863 kg ha-1, sendo 37% superior ao PC com a vegetação espontânea
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