3,929 research outputs found
Design sensitivity analysis using EAL. Part 2: Shape design parameters
A numerical implementation of shape design sensitivity analysis of built-up structures is presented, using the versatility and convenience of an existing finite element structural analysis code and its data base management system. This report is a continuation of a previous report on conventional design parameters. The finite element code used in the implementation presented is the Engineering Analysis Language (EAL), which is based on a hybrid analysis method. It has been shown that shape design sensitivity computations can be carried out using the database management system of EAL, without writing a separate program and a separate data base. The material derivative concept of continuum mechanics and an adjoint variable method of design sensitivity analysis are used to derive shape design sensitivity information of structural performances. A domain method of shape design sensitivity analysis and a design component method are used. Displacement and stress functionals are considered as performance criteria
A 2-D oscillating flow analysis in Stirling engine heat exchangers
A two dimensional oscillating flow analysis was conducted, simulating the gas flow inside Stirling heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re(max) = 1920 (Va = 80), 10800 (Va = 272), 19300 (Va = 272), and 60800 (Va = 126). The results are compared with experimental results of previous investigators. Also, predictions of the flow regime on present oscillating flow conditions were checked by comparing velocity amplitudes and phase differences with those from laminar theory and quasi-steady profile. A high Reynolds number k-epsilon turbulence model was used for turbulent oscillating pipe flow. Finally, performance evaluation of the K-epsilon model was made to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis
Design sensitivity analysis using EAL. Part 1: Conventional design parameters
A numerical implementation of design sensitivity analysis of builtup structures is presented, using the versatility and convenience of an existing finite element structural analysis code and its database management system. The finite element code used in the implemenatation presented is the Engineering Analysis Language (EAL), which is based on a hybrid method of analysis. It was shown that design sensitivity computations can be carried out using the database management system of EAL, without writing a separate program and a separate database. Conventional (sizing) design parameters such as cross-sectional area of beams or thickness of plates and plane elastic solid components are considered. Compliance, displacement, and stress functionals are considered as performance criteria. The method presented is being extended to implement shape design sensitivity analysis using a domain method and a design component method
Pairing dynamics in strongly correlated superconductivity
Confirmation of the phononic origin of Cooper pair formation in
superconductors came with the demonstration that the interaction was retarded
and that the corresponding energy scales were associated with phonons. Using
cellular dynamical mean-field theory for the two-dimensional Hubbard model, we
identify such retardation effects in d-wave pairing and associate the
corresponding energy scales with short-range spin fluctuations. We find which
frequencies are relevant for pairing as a function of interaction strength and
doping and show that the disappearance of superconductivity on the overdoped
side coincides with the disappearance of the low energy feature in the
antiferromagnetic fluctuations, as observed in neutron scattering experiments.Comment: LaTeX, 8 pages, 8 figure
Student Responses to Merit Retention Rules
A common justification for HOPE-style merit-aid programs is to promote and reward academic achievement, thereby inducing greater investments in human capital. However, grade-based eligibility and retention rules encourage other behavioral responses. Using the longitudinal records of all undergraduates who enrolled at the University of Georgia (UGA) between 1989 and 1997, we estimate the effects of HOPE on course enrollment, withdrawal and completion, and the diversion of course taking from the academic year to the summer, treating non-residents as a control group. First, we find that HOPE decreased full-load enrollments and increased course withdrawals among resident freshmen. The combination of these responses results in an 11\% lower probability of full-load completion and an annual average reduction in credits completed of 1.0. The latter implies that between 1993 and 1997 Georgia-resident freshmen completed 15,710 fewer credit hours or 3,142 individual course enrollments than non-residents. Second, the scholarship's influence on course-taking behavior is concentrated on students with GPAs on or below the scholarship-retention margin. Third, the effect increased as the income cap was lifted and more students became eligible for the award. Fourth, these freshmen credit-hour reductions represent an intertemporal substitution, not a general slowdown in academic progress. Finally, residents diverted an average of 1.65 more credits from the regular academic year to the first summer term after their matriculation, which amounts to a 72\% rise in summer course taking.Education, Merit-based aid, Education Finance, HOPE Scholarship
Potential-energy (BCS) to kinetic-energy (BEC)-driven pairing in the attractive Hubbard model
The BCS-BEC crossover within the two-dimensional attractive Hubbard model is
studied by using the Cellular Dynamical Mean-Field Theory both in the normal
and superconducting ground states. Short-range spatial correlations
incorporated in this theory remove the normal-state quasiparticle peak and the
first-order transition found in the Dynamical Mean-Field Theory, rendering the
normal state crossover smooth. For smaller than the bandwidth, pairing is
driven by the potential energy, while in the opposite case it is driven by the
kinetic energy, resembling a recent optical conductivity experiment in
cuprates. Phase coherence leads to the appearance of a collective Bogoliubov
mode in the density-density correlation function and to the sharpening of the
spectral function.Comment: 5 pages, 4 figure
Paleoseismology of the Yangsan Fault, southeastern part of the Korean Peninsula
The NNE-trending Yangsan Fault (YSF) is the most prominent fault in the southeastern part of the Korean Peninsula
and has a continuous trace about 200 km long. Activity on this fault was recently investigated using aerial
photographs, topographic analysis, and trenching. The geomorphologic evidence of Late Quaternary faulting is
clearly recognized on both the northern (Yugyeri and Tosung-ri areas) and southern parts (Eonyang to Tongdosa
area) of the fault. The main YSF is marked by a zone of shattered rock that is tens of meters wide and zone of fault
gouge. During the Late Quaternary, right-lateral movement occurred mainly on the southern part, as shown by lowangle
striations on the fault plane, elongation of deformation features in the fault gouge. The estimated vertical slip
rate is about 0.02-0.07 mm/yr, and the lateral slip rate may be several times larger than the vertical rate. The most
recent event occurred prior to deposition of Holocene alluvium. In the northern part, the fault locally changes trend
to almost N-S, dips to the east and has reverse movement. The average vertical slip rate is estimated less than
0.1 mm/yr. The most recent event probably occurred after 1314 cal. years BP (A.D. 536)
Induced local spin-singlet amplitude and pseudogap in high cuprates
In this paper we show that local spin-singlet amplitude with d-wave symmetry,
, can be induced by short-range spin correlations even
in the absence of pairing interactions. Fluctuation theory is formulated to
make connection between pseudogap temperature $T^{*}$, pseudogap size
$\Delta_{pg}$ and . In the present scenario for the
pseudogap, the normal state pseudogap is caused by the induced local
spin-singlet amplitude due to short-range spin correlations, which compete in
the low energy sector with superconducting correlations to make go to
zero near half-filling. Calculated falls from a high value onto the
line and closely follows mean-field N\'{e}el temperature .
The calculated is in good agreement with experimental results. We
propose an experiment in which the present scenario can be critically tested.Comment: 5 pages, 3 figure
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