1,316 research outputs found
Cyclic creep and fatigue of TD-NiCr (thoria-dispersion-strengthened nickel-chromium), TD-Ni, and NiCr sheet at 1200 C
The resistance of thin TD-NiCr sheet to cyclic deformation was compared with that of TD-Ni and a conventional nickel-chromium alloy. Strains were determined by a calibration technique which combines room-temperature strain gage and deflection measurements with high-temperature deflection measurements. Analyses of the cyclic tests using measured tensile and creep-rupture data indicated that the TD-NiCr and NiCr alloy specimens failed by a cyclic creep mechanism. The TD-Ni specimens, on the other hand, failed by a fatigue mechanism
Motion of condensates in non-Markovian zero-range dynamics
Condensation transition in a non-Markovian zero-range process is studied in
one and higher dimensions. In the mean-field approximation, corresponding to
infinite range hopping, the model exhibits condensation with a stationary
condensate, as in the Markovian case, but with a modified phase diagram. In the
case of nearest-neighbor hopping, the condensate is found to drift by a
"slinky" motion from one site to the next. The mechanism of the drift is
explored numerically in detail. A modified model with nearest-neighbor hopping
which allows exact calculation of the steady state is introduced. The steady
state of this model is found to be a product measure, and the condensate is
stationary.Comment: 31 pages, 9 figure
Laser application to measure vertical sea temperature and turbidity, design phase
An experiment to test a new method was designed, using backscattered radiation from a laser beam to measure oceanographic parameters in a fraction of a second. Tyndall, Rayleigh, Brillouin, and Raman scattering all are utilized to evaluate the parameters. A beam from a continuous argon ion laser is used together with an interferometer and interference filters to gather the information. The results are checked by direct measurements. Future shipboard and airborne experiments are described
From the zero-field metal-insulator transition in two dimensions to the quantum Hall transition: a percolation-effective-medium theory
Effective-medium theory is applied to the percolation description of the
metal-insulator transition in two dimensions with emphasis on the continuous
connection between the zero-magnetic-field transition and the quantum Hall
transition. In this model the system consists of puddles connected via saddle
points, and there is loss of quantum coherence inside the puddles. The
effective conductance of the network is calculated using appropriate
integration over the distribution of conductances, leading to a determination
of the magnetic field dependence of the critical density. Excellent
quantitative agreement is obtained with the experimental data, which allows an
estimate of the puddle physical parameters
Autonomous decision-making against induced seismicity in deep fluid injections
The rise in the frequency of anthropogenic earthquakes due to deep fluid
injections is posing serious economic, societal, and legal challenges to
geo-energy and waste-disposal projects. We propose an actuarial approach to
mitigate this risk, first by defining an autonomous decision-making process
based on an adaptive traffic light system (ATLS) to stop risky injections, and
second by quantifying a "cost of public safety" based on the probability of an
injection-well being abandoned. The ATLS underlying statistical model is first
confirmed to be representative of injection-induced seismicity, with examples
taken from past reservoir stimulation experiments (mostly from Enhanced
Geothermal Systems, EGS). Then the decision strategy is formalized: Being
integrable, the model yields a closed-form ATLS solution that maps a risk-based
safety standard or norm to an earthquake magnitude not to exceed during
stimulation. Finally, the EGS levelized cost of electricity (LCOE) is
reformulated in terms of null expectation, with the cost of abandoned
injection-well implemented. We find that the price increase to mitigate the
increased seismic risk in populated areas can counterbalance the heat credit.
However this "public safety cost" disappears if buildings are based on
earthquake-resistant designs or if a more relaxed risk safety standard or norm
is chosen.Comment: 8 pages, 4 figures, conference (International Symposium on Energy
Geotechnics, 26-28 September 2018, Lausanne, Switzerland
Idealized digital models for conical reed instruments, with focus on the internal pressure waveform
International audienceTwo models for the generation of self-oscillations of reed conical woodwinds are presented. They use the fewest parameters (of either the resonator or the ex-citer), whose influence can be quickly explored. The formulation extends iterated maps obtained for loss-less cylindrical pipes without reed dynamics. It uses spherical wave variables in idealized resonators, with one parameter more than for cylinders: the missing length of the cone. The mouthpiece volume equals that of the missing part of the cone, and is implemented as either a cylindrical pipe (first model) or a lumped element (second model). Only the first model adds a length parameter for the mouthpiece and leads to the solving of an implicit equation. For the second model, any shape of nonlinear characteristic can be directly considered. The complex characteristics impedance for spherical waves requires sampling times smaller than a round trip in the resonator. The convergence of the two models is shown when the length of the cylindrical mouthpiece tends to zero. The waveform is in semi-quantitative agreement with experiment. It is concluded that the oscillations of the positive episode of the mouthpiece pressure are related to the length of the missing part, not to the reed dynamics
An Efficient Data Structure for Dynamic Two-Dimensional Reconfiguration
In the presence of dynamic insertions and deletions into a partially
reconfigurable FPGA, fragmentation is unavoidable. This poses the challenge of
developing efficient approaches to dynamic defragmentation and reallocation.
One key aspect is to develop efficient algorithms and data structures that
exploit the two-dimensional geometry of a chip, instead of just one. We propose
a new method for this task, based on the fractal structure of a quadtree, which
allows dynamic segmentation of the chip area, along with dynamically adjusting
the necessary communication infrastructure. We describe a number of algorithmic
aspects, and present different solutions. We also provide a number of basic
simulations that indicate that the theoretical worst-case bound may be
pessimistic.Comment: 11 pages, 12 figures; full version of extended abstract that appeared
in ARCS 201
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