9,525 research outputs found
Spontaneous magnetisation in the plane
The Arak process is a solvable stochastic process which generates coloured
patterns in the plane. Patterns are made up of a variable number of random
non-intersecting polygons. We show that the distribution of Arak process states
is the Gibbs distribution of its states in thermodynamic equilibrium in the
grand canonical ensemble. The sequence of Gibbs distributions form a new model
parameterised by temperature. We prove that there is a phase transition in this
model, for some non-zero temperature. We illustrate this conclusion with
simulation results. We measure the critical exponents of this off-lattice model
and find they are consistent with those of the Ising model in two dimensions.Comment: 23 pages numbered -1,0...21, 8 figure
Refeeding Hypophosphatemia in Adolescents With Anorexia Nervosa: A Systematic Review
The rate of adolescents presenting with anorexia nervosa (AN) is increasing. Medically unstable adolescents are admitted to the hospital for nutrition restoration. A lack of global consensus on appropriate refeeding practices of malnourished patients has resulted in inconsistent refeeding practices. Refeeding hypophosphatemia (RH) is the most common complication associated with refeeding the malnourished patient. This review sought to identify the range of refeeding rates adopted globally and the implication that total energy intake and malnutrition may have on RH while refeeding adolescents with anorexia nervosa. Studies were identified by a systematic electronic search of medical databases from 1980 to September 2012. Seventeen publications were identified, including 6 chart reviews, 1 observational study, and 10 case reports, with a total of 1039 subjects. The average refeeding energy intake was 1186 kcal/d, ranging from 125–1900 kcal/d, with a mean percentage median body mass index (% mBMI) of 78%. The average incidence rate of RH was 14%. A significant correlation between malnutrition (% mBMI) and post-refeeding phosphate was identified (R 2 = 0.6, P = .01). This review highlights the disparity in refeeding rates adopted internationally in treating malnourished adolescents with anorexia nervosa. Based on this review, the severity of malnutrition seems to be a marker for the development of RH more so than total energy intake
A Review of the Erosion of Thermal Barrier Coatings.
The application of thermal barrier coatings (TBCs) to components with internal
cooling in the hot gas stream of gas turbine engines has facilitated a steep
increase in the turbine entry temperature and the associated increase in
performance and efficiency of gas turbine engines. However, TBCs are susceptible
to various life limiting issues associated with their operating environment
including erosion, corrosion, oxidation, sintering and foreign object damage
(FOD). This is a review paper that examines various degradation and erosion
mechanisms of TBCs, especially those produced by electron beam physical vapour
deposition (EB-PVD). The results from a number of laboratory tests under various
impact conditions are discussed before the different erosion and FOD mechanisms
are reviewed. The transitions between the various erosion mechanisms are
discussed in terms of the D/d ratio (contact area diameter/column diameter), a
relatively new concept that relates the impact size to the erosion mechanism.
The effects of ageing, dopant additions and
calciumâ  magnesiumâ  aluminaâ  silicates on the life of TBCs are examined. It
is shown that while ageing increases the erosion rate of EB-PVD TBCs, ageing of
plasma sprayed TBCs in fact lowers the erosion rate. Finally modelling of EB-PVD
TBCs is briefly intr
Erosion, corrosion and erosion-corrosion of EB PVD thermal barrier coatings
Electron beam (EB) physical vapour deposited (PVD) thermal barrier coatings
(TBCs) have been used in gas turbine engines for a number of years. The primary
mode of failure is attributed to oxidation of the bond coat and growth of the
thermally grown oxide (TGO), the alumina scale that forms on the bond coat and
to which the ceramic top coat adheres. Once the TGO reaches a critical
thickness, the TBC tends to spall and expose the underlying substrate to the hot
gases. Erosion is commonly accepted as a secondary failure mechanism, which
thins the TBC thus reducing its insulation capability and increasing the TGO
growth rate. In severe conditions, erosion can completely remove the TBC over
time, again resulting in the exposure of the substrate, typically Ni-based
superalloys. Since engine efficiency is related to turbine entry temperature
(TET), there is a constant driving force to increase this temperature. With this
drive for higher TETs comes corrosion problems for the yttria stabilised
zirconia (YSZ) ceramic topcoat. YSZ is susceptible to attack from molten
calciumâ  magnesiumâ  aluminaâ  silicates (CMAS) which degrades the YSZ both
chemically and micro-structurally. CMAS has a melting point of around 1240 à °C
and since it is common in atmospheric dust it is easily deposited onto gas
turbine blades. If the CMAS then melts and penetrates into the ceramic, the life
of the TBC can be significantly reduced. This paper discusses the various
failure mechanisms associated with the erosion, corrosion and
erosionâ  corrosion of EB PVD TBCs. The concept of a dimensionless ratio D/d,
where D is the contact footprint diameter and d is the column diameter, as a
means of determining the erosion mechanism is introduced and discussed for E
Nano and Micro indentation studies of bulk zirconia and EB PVD TBCs
In order to model the erosion of a material it is necessary to know the material
properties of both the impacting particles as well as the target. In the case of
electron beam (EB) physical vapour deposited(PVD) thermal barrier coatings
(TBCs) the properties of the columns as opposed to the coating as a whole are
important. This is due to the fact that discrete erosion events are on a similar
scale as the size of the individual columns. Thus nano* and micro* indentation
were used to determine the hardness and the Young"s modulus of the
columns. However, care had to be taken to ensure that it was the hardness of the
columns that was being measured and not the coating as a whole. This paper
discusses the differences in the results obtained when using the two different
tests and relates them to the interactions between the indent and the columns of
the EB PVD TBC microstructure. It was found that individual columns had a
hardness of 14 GPa measured using nano indentation, while the hardness of the
coating, using micro indentation decreased from 13 to 2.4 GPa as the indentation
load increased from 0.1 to 3N. This decrease in hardness was attributed to the
interaction between the indenter and a number of adjacent columns and the
ability of the columns to move laterally under indentation
Effect of microstructure and temperature on the erosion rates and mechanisms of modified EB PVD TBCs
Thermal barrier coatings (TBCs) have now been used in gas turbine engines for a
number of decades and are now considered to be an accepted technology. As there
is a constant drive to increase the turbine entry temperature, in order to
increase engine efficiency, the coatings operate in increasingly hostile
environments. Thus there is a constant drive to both increase the temperature
capabilities of TBCs while at the same time reducing their thermal
conductivities. The thermal conductivity of standard 7 wt% yttria stabilized
zirconia (7YSZ) electron beam (EB) physical vapour deposited (PVD) TBCs can be
reduced in two ways: the first by modification of the microstructure of the TBC
and the second by addition of ternary oxides. By modifying the microstructure of
the TBC such that there are more fine pores, more photon scattering centres are
introduced into the coatings, which reduce the heat transfer by radiation. While
ternary oxides will introduce lattice defects into the coating, which increases
the phonon scattering, thus reducing the thermal conductivity via lattice
vibrations. Unfortunately, both of these methods can have a negative effect on
the erosion resistance of EB PVD TBCs. This paper compares the relative erosion
rates of ten different EB PVD TBCs tested at 90à ° impact at room temperature and
at high temperature and discusses the results in term of microstructural and
temperature effects. It was found that by modifying the coating deposition, such
that a low density coating with a highly â  featheredâ  microstructure formed,
generally resulted in an increase in the erosion rate at room temperature. When
there was a significant change between the room temperature and the high
temperature erosion mechanism it was accompanied by a significant decrease in
the erosion rate, while additions of dopents was found to significantly increase
the erosion rate at room and high temperature. However, all the modified
coatings still had a lower erosion rate than a plasma sprayed coatings. So,
although, relative to a standard 7YSZ coating, the modified coatings have a
lower erosion resistance, they still perform better than PS TBCs and their lower
thermal conductivities could make them viable alternatives to 7YSZ for use in
gas turbine en
Erosion of gadolinia doped EB-PVD TBCs
Gadolinia additions have been shown to significantly reduce the thermal
conductivity of EB-PVD TBCs. The aim of this paper is to further the
understanding on the effects of dopants on the erosion resistance of EB-PVD TBCs
by studying the effects of 2 mol% Gd2O3 additions on the room and high
temperature erosion resistance of as received and aged EB-PVD TBCs. Previously
it has been reported that gadolinia additions increased the erosion rate of EB-
PVD TBCs, this is indeed the case for room temperature erosion, however under
high temperature (825 à °C) erosion conditions this is not the case and the doped
TBCs have a slightly lower erosion rate than the standard YSZ EB-PVD TBCs. This
has been attributed to a change in the erosion mechanisms that operate at the
different temperatures. This change in mechanism was not expected under the
impact conditions used and has been attributed to a change in the column
diameter, and how this influences the dynamics of particle impactio
Book Review: Conserving Life on Earth: Conserving Life on Earth, by EhrenfeldDavid W.. Oxford University Press, New York & London: xx + 360 pp., illustr., 23.4 × 16 × 2.6 cm., £4.50, 1972
The Civil Law of Quebec: Some Disjointed Notes for a Lecture
Quebec private law, though not the public law, can be regarded as a reasonably characteristic example of that system of law known as the Civil Law, one of the world\u27s great legal systems; and you live in the province of Prince Edward Island and I of Nova Scotia, where another of the world\u27s great systems flourishes, the Common Law - you will notice that I say another , not the other . It is right and proper that we should attempt to familiarize ourselves with at least one other system of law besides our own, not necessarily with the detailed rules, which may or may not differ from ours, but with the approach of that other system to human problems, its method. For there is no better avenue to improved knowledge of other peoples than through their law, and no one can deny that a better understanding of French Canada in other parts of our country is badly needed
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