70,066 research outputs found
Life prediction and constitutive models for engine hot section anisotropic materials program
This report presents the results from a 35 month period of a program designed to develop generic constitutive and life prediction approaches and models for nickel-based single crystal gas turbine airfoils. The program is composed of a base program and an optional program. The base program addresses the high temperature coated single crystal regime above the airfoil root platform. The optional program investigates the low temperature uncoated single crystal regime below the airfoil root platform including the notched conditions of the airfoil attachment. Both base and option programs involve experimental and analytical efforts. Results from uniaxial constitutive and fatigue life experiments of coated and uncoated PWA 1480 single crystal material form the basis for the analytical modeling effort. Four single crystal primary orientations were used in the experiments: (001), (011), (111), and (213). Specific secondary orientations were also selected for the notched experiments in the optional program. Constitutive models for an overlay coating and PWA 1480 single crystal material were developed based on isothermal hysteresis loop data and verified using thermomechanical (TMF) hysteresis loop data. A fatigue life approach and life models were selected for TMF crack initiation of coated PWA 1480. An initial life model used to correlate smooth and notched fatigue data obtained in the option program shows promise. Computer software incorporating the overlay coating and PWA 1480 constitutive models was developed
Skyrme functional from a three-body pseudo-potential of second-order in gradients. Formalism for central terms
In one way or the other, all modern parametrizations of the nuclear energy
density functional (EDF) do not respect the exchange symmetry associated with
Pauli's principle. It has been recently shown that this practice jeopardizes
multi-reference (MR) EDF calculations by contaminating the energy with spurious
self-interactions that, for example, lead to finite steps or even divergences
when plotting it as a function of collective coordinates. As of today, the only
viable option to bypass these pathologies is to rely on EDF kernels that
enforce Pauli's principle from the outset by strictly and exactly deriving from
a genuine, i.e. density-independent, Hamilton operator.
We wish to develop the most general Skyrme-like EDF parametrization
containing linear, bilinear and trilinear terms in the density matrices with up
to two gradients, under the key constraint that it derives strictly from an
effective Hamilton operator. The most general three-body Skyrme-like
pseudo-potential containing up to two gradient operators is constructed to
generate the trilinear part. The present study is limited to central terms.
Spin-orbit and tensor will be addressed in a forthcoming paper.
(See paper for full abstract)Comment: 38 pages revtex, no figur
The Complex Interstellar Na I Absorption toward h and Chi Persei
Recent high spatial and spectral resolution investigations of the diffuse
interstellar medium (ISM) have found significant evidence for small-scale
variations in the interstellar gas on scales less than or equal to 1 pc. To
better understand the nature of small-scale variations in the ISM, we have used
the KPNO WIYN Hydra multi-object spectrograph, which has a mapping advantage
over the single-axis, single-scale limitations of studies using high proper
motion stars and binary stars, to obtain moderate resolution (~12 km/s)
interstellar Na I D absorption spectra of 172 stars toward the double open
cluster h and Chi Persei. All of the sightlines toward the 150 stars with
spectra that reveal absorption from the Perseus spiral arm show different
interstellar Na I D absorption profiles in the Perseus arm gas. Additionally,
we have utilized the KPNO Coude Feed spectrograph to obtain high-resolution (~3
km/s) interstellar Na I D absorption spectra of 24 of the brighter stars toward
h and Chi Per. These spectra reveal an even greater complexity in the
interstellar Na I D absorption in the Perseus arm gas and show individual
components changing in number, velocity, and strength from sightline to
sightline. If each of these individual velocity components represents an
isolated cloud, then it would appear that the ISM of the Perseus arm gas
consists of many small clouds. Although the absorption profiles vary even on
the smallest scales probed by these high-resolution data (~30";~0.35pc), our
analysis reveals that some interstellar Na I D absorption components from
sightline to sightline are related, implying that the ISM toward h and Chi Per
is probably comprised of sheets of gas in which we detect variations due to
differences in the local physical conditions of the gas.Comment: 27 pages text; 8 figure
Binding between two-component bosons in one dimension
We investigate the ground state of one-dimensional few-atom Bose-Bose
mixtures under harmonic confinement throughout the crossover from weak to
strong inter-species attraction. The calculations are based on the numerically
exact multi-configurational time-dependent Hartree method. For repulsive
components we detail the condition for the formation of a molecular
Tonks-Girardeau gas in the regime of intermediate inter-species interactions,
and the formation of a molecular condensate for stronger coupling. Beyond a
critical inter-species attraction, the system collapses to an overall bound
state. Different pathways emerge for unequal particle numbers and intra-species
interactions. In particular, for mixtures with one attractive component, this
species can be viewed as an effective potential dimple in the trap center for
the other, repulsive component.Comment: 10 pages, 10 figure
Optimal uncertainty quantification for legacy data observations of Lipschitz functions
We consider the problem of providing optimal uncertainty quantification (UQ)
--- and hence rigorous certification --- for partially-observed functions. We
present a UQ framework within which the observations may be small or large in
number, and need not carry information about the probability distribution of
the system in operation. The UQ objectives are posed as optimization problems,
the solutions of which are optimal bounds on the quantities of interest; we
consider two typical settings, namely parameter sensitivities (McDiarmid
diameters) and output deviation (or failure) probabilities. The solutions of
these optimization problems depend non-trivially (even non-monotonically and
discontinuously) upon the specified legacy data. Furthermore, the extreme
values are often determined by only a few members of the data set; in our
principal physically-motivated example, the bounds are determined by just 2 out
of 32 data points, and the remainder carry no information and could be
neglected without changing the final answer. We propose an analogue of the
simplex algorithm from linear programming that uses these observations to offer
efficient and rigorous UQ for high-dimensional systems with high-cardinality
legacy data. These findings suggest natural methods for selecting optimal
(maximally informative) next experiments.Comment: 38 page
Life prediction and constitutive models for engine hot section anisotropic materials program
This report presents a summary of results from a 7 year program designed to develop generic constitutive and life prediction approaches and models for nickel-based single crystal gas turbine airfoils. The program was composed of a base program and an optional program. The base program addressed the high temperature coated single crystal regime above the airfoil root platform. The optional program investigated the low temperature uncoated single crystal regime below the airfoil root platform including the notched conditions of the airfoil attachment. Both base and option programs involved experimental and analytical efforts. Results from uniaxial constitutive and fatigue life experiments of coated and uncoated PWA 1480 single crystal material formed the basis for the analytical modeling effort. Four single crystal primary orientations were used in the experiments: group of zone axes (001), group of zone axes (011), group of zone axes (111), and group of zone axes (213). Specific secondary orientations were also selected for the notched experiments in the optional program. Constitutive models for an overlay coating and PWA 1480 single crystal materials were developed based on isothermal hysteresis loop data and verified using thermomechanical (TMF) hysteresis loop data. A fatigue life approach and life models were developed for TMF crack initiation of coated PWA 1480. A life model was developed for smooth and notched fatigue in the option program. Finally, computer software incorporating the overlay coating and PWA 1480 constitutive and life models was developed
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