198 research outputs found
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Compatibility of structural materials with liquid lead-bismuth and mercury
Both liquid Hg and Pb-Bi eutectic have been proposed as possible target materials for spallation neutron sources. During the 1950s and 1960s, a substantial program existed at BNL as part of the Liquid Metal Fuel Reactor program on compatibility of Bi, Pb, and their alloys with structural materials. Subsequently, compatibility studies of Hg with structural materials were performed in support of development of Rankine-cycle Hg turbines for nuclear applications. This paper reviews our understanding of the corrosion/mass-transfer reactions of structural materials with these liquid-metal coolants. Topics discussed include the basic solubility relations of Fe, Cr, Ni, and refractory metals in these liquid metals, results of inhibition studies, role of oxygen on corrosion, and specialized topics such as cavitation corrosion and liquid-metal embrittlement. Emphasis is on utilizing the understanding gained in this earlier work on the development of heavy-liquid-metal targets in spallation neutron sources
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Examination of turbine discs from nuclear power plants
Investigations were performed on a cracked turbine disc from the Cooper Nuclear Power Station, and on two failed turbine discs (governor and generator ends) from the Yankee-Rowe Nuclear Power Station. Cooper is a boiling water reactor (BWR) which went into commercial operation in July 1974, and Yankee-Rowe is a pressurized water reactor (PWR) which went into commercial operation in June 1961. Cracks were identified in the bore of the Cooper disc after 41,913 hours of operation, and the disc removed for repair. At Yankee-Rowe two discs failed after 100,000 hours of operation. Samples of the Cooper disc and both Yankee-Rowe disc (one from the governor and one from the generator end of the LP turbine) were sent to Brookhaven National Laboratory (BNL) for failure analysis
Large scale directional anomalies in the WMAP 5yr ILC map
We study the alignments of the low multipoles of CMB anisotropies with
specific directions in the sky (i.e. the dipole, the north Ecliptic pole, the
north Galactic pole and the north Super Galactic pole). Performing
random extractions we have found that: 1) separately quadrupole and octupole
are mildly orthogonal to the dipole but when they are considered together, in
analogy to \cite{Copi2006}, we find an unlikely orthogonality at the level of
0.8% C.L.; 2) the multipole vectors associated to are unlikely aligned
with the dipole at C.L.; 3) the multipole vectors associated to
are mildly orthogonal to the dipole but when we consider only maps
that show exactly the same correlation among the multipoles as in the observed
WMAP 5yr ILC, these multipole vectors are unlikely orthogonal to the dipole at
C.L..Comment: 12 pages, 10 figures, 3 tables. Accepted for publication in JCAP. Few
references added and some typos correcte
Simulating Cosmic Microwave Background maps in multi-connected spaces
This article describes the computation of cosmic microwave background
anisotropies in a universe with multi-connected spatial sections and focuses on
the implementation of the topology in standard CMB computer codes. The key
ingredient is the computation of the eigenmodes of the Laplacian with boundary
conditions compatible with multi-connected space topology. The correlators of
the coefficients of the decomposition of the temperature fluctuation in
spherical harmonics are computed and examples are given for spatially flat
spaces and one family of spherical spaces, namely the lens spaces. Under the
hypothesis of Gaussian initial conditions, these correlators encode all the
topological information of the CMB and suffice to simulate CMB maps.Comment: 33 pages, 55 figures, submitted to PRD. Higher resolution figures
available on deman
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Experience with stress corrosion cracking and materials compatibility at the High Flux Beam Reactor
Searching for hidden mirror symmetries in CMB fluctuations from WMAP 7 year maps
We search for hidden mirror symmetries at large angular scales in the WMAP 7
year Internal Linear Combination map of CMB temperature anisotropies using
global pixel based estimators introduced for this aim. Two different axes are
found for which the CMB intensity pattern is anomalously symmetric (or
anti-symmetric) under reflection with respect to orthogonal planes at the
99.84(99.96)% CL (confidence level), if compared to a result for an arbitrary
axis in simulations without the symmetry. We have verified that our results are
robust to the introduction of the galactic mask. The direction of such axes is
close to the CMB kinematic dipole and nearly orthogonal to the ecliptic plane,
respectively. If instead the real data are compared to those in simulations
taken with respect to planes for which the maximal mirror symmetry is generated
by chance, the confidence level decreases to 92.39 (76.65)%. But when the
effect in question translates into the anomalous alignment between normals to
planes of maximal mirror (anti)-symmetry and these natural axes mentioned. We
also introduce the representation of the above estimators in the harmonic
domain, confirming the results obtained in the pixel one. The symmetry anomaly
is shown to be almost entirely due to low multipoles, so it may have a
cosmological and even primordial origin. Contrary, the anti-symmetry one is
mainly due to intermediate multipoles that probably suggests its
non-fundamental nature. We have demonstrated that these anomalies are not
connected to the known issue of the low variance in WMAP observations and we
have checked that axially symmetric parts of these anomalies are small, so that
the axes are not the symmetry ones.Comment: 18 pages, 10 figures, 2 tables. Consideration and discussion
expanded, 5 figures and 1 table added, main conclusions unchange
Fluctuations and Intrinsic Pinning in Layered Superconductors
A flux liquid can condense into a smectic crystal in a pure layered
superconductors with the magnetic field oriented nearly parallel to the layers.
If the smectic order is commensurate with the layering, this crystal is {\sl
stable} to point disorder. By tilting and adjusting the magnitude of the
applied field, both incommensurate and tilted smectic and crystalline phases
are found. We discuss transport near the second order smectic freezing
transition, and show that permeation modes lead to a small non--zero
resistivity and large but finite tilt modulus in the smectic crystal.Comment: 4 pages + 1 style file + 1 figure (as uufile) appended, REVTEX 3.
Cosmic microwave background anisotropies in multi-connected flat spaces
This article investigates the signature of the seventeen multi-connected flat
spaces in cosmic microwave background (CMB) maps. For each such space it
recalls a fundamental domain and a set of generating matrices, and then goes on
to find an orthonormal basis for the set of eigenmodes of the Laplace operator
on that space. The basis eigenmodes are expressed as linear combinations of
eigenmodes of the simply connected Euclidean space. A preceding work, which
provides a general method for implementing multi-connected topologies in
standard CMB codes, is then applied to simulate CMB maps and angular power
spectra for each space. Unlike in the 3-torus, the results in most
multi-connected flat spaces depend on the location of the observer. This effect
is discussed in detail. In particular, it is shown that the correlated circles
on a CMB map are generically not back-to-back, so that negative search of
back-to-back circles in the WMAP data does not exclude a vast majority of flat
or nearly flat topologies.Comment: 33 pages, 19 figures, 1 table. Submitted to PR
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Design and analysis of a 20 MW propulsion power train
The electric ship research program at the University of Texas at Austin focuses on the development of power system technology for future electric ships. The main goal of the on-going research activity is to identify critical, high pay-off technology development needed to enable major improvement, in size and functionality, of navy ships power systems. Initial efforts were directed towards the establishment of a baseline power train which highlights various constraints and provides a basis for later optimization efforts. A 20 MW power train system was chosen for such a baseline, and all components, from fuel to propulsion motor, were considered and their impact on the whole power system assessed. The baseline design consists of a 25 MVA/3600 rpm radial flux permanent magnet generator, a 22 MVA PWM converter, and a 20 MW/150 rpm radial flux permanent magnet motor, along with the amount of fuel sized for an assumed mission profile, and the widely used LM2500 gas turbine. The analysis shows that fuel is by far the dominant component contributing to weight and volume and, consequently, overall efficiency of power train components is the most relevant parameter to reduce weight and volume. The 3600 rpm generator is the smallest component. The 150 rpm motor is the heaviest component, other than fuel, weighing close to 100 tonnes.Center for Electromechanic
Monte Carlo Methods for Estimating Interfacial Free Energies and Line Tensions
Excess contributions to the free energy due to interfaces occur for many
problems encountered in the statistical physics of condensed matter when
coexistence between different phases is possible (e.g. wetting phenomena,
nucleation, crystal growth, etc.). This article reviews two methods to estimate
both interfacial free energies and line tensions by Monte Carlo simulations of
simple models, (e.g. the Ising model, a symmetrical binary Lennard-Jones fluid
exhibiting a miscibility gap, and a simple Lennard-Jones fluid). One method is
based on thermodynamic integration. This method is useful to study flat and
inclined interfaces for Ising lattices, allowing also the estimation of line
tensions of three-phase contact lines, when the interfaces meet walls (where
"surface fields" may act). A generalization to off-lattice systems is described
as well.
The second method is based on the sampling of the order parameter
distribution of the system throughout the two-phase coexistence region of the
model. Both the interface free energies of flat interfaces and of (spherical or
cylindrical) droplets (or bubbles) can be estimated, including also systems
with walls, where sphere-cap shaped wall-attached droplets occur. The
curvature-dependence of the interfacial free energy is discussed, and estimates
for the line tensions are compared to results from the thermodynamic
integration method. Basic limitations of all these methods are critically
discussed, and an outlook on other approaches is given
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