2,388 research outputs found
Wave-current force on bridge foundation
Many cross-sea bridges have been constructed or in construction in the Chinese coastal areas, such as Hangzhou Bay Bridge, East China Sea Bridge and Hong Kong-Zhuhai-Macau Bridge, etc. Usually the foundations of cross-sea bridges will bear the load of wave and current simultaneously, the extreme value of which is an important factor for bridge design. It is quite difficult to estimate the extreme wave-current forces on bridge foundations due to their complex form, for example a polygonal platform pier shape on piles. In this paper, we use a combination method to calculate wave-current force on such complex bridge foundation. The Morison equation is applied to calculation wave-current load on piles with small diameters (D/L<0.2) and the effect of wave phase difference between piles is considered when calculating the total force on all piles. For bridge foundation strctures of large diameters (D/L>0.2), wave force and curent force are calculated seperately and then added together, i.e. wave force is calculated by Boundary Element Method based on wave diffraction theory, while current force is calculated by the drag force formula. Some physical model tests are conducted for different types of bridge foudations, and wave-current forces are measured by force sensors. The calculation method is verified by the physical model and good agreement is obtained between calculation results and model tests data. It is revealed that the nonlinear wave-current interaction effect on force is not significant in large diameter stucture case, but the wave parameters used in the wave force model should be the ones affected by the current
Relations as executable specifications: taming partiality and non-determinism using invariants
Comunicação publicada em "Lecture Notes in Computer Science", vol. 7560 (2012), pag. 146-161The calculus of relations has been widely used in program specification and reasoning. It is very tempting to use such specifications as running prototypes of the desired program, but, even considering finite domains, the inherent partiality and non-determinism of relations makes this impractical and highly inefficient. To tame partiality we prescribe the usage of invariants, represented by coreflexives, to characterize the exact domains and codomains of relational specifications. Such invariants can be used as pre-condition checkers to avoid runtime errors. Moreover, we show how such invariants can be used to narrow the non-deterministic execution of relational specifications, making it viable for a relevant class of problems. In particular, we show how the proposed techniques can be applied to execute specifications of bidirectional transformations, a domain where partiality and non-determinism are paramount.Fundação para a Ciência e a Tecnologi
Theory for Metal Hydrides with Switchable Optical Properties
Recently it has been discovered that lanthanum, yttrium, and other metal
hydride films show dramatic changes in the optical properties at the
metal-insulator transition. Such changes on a high energy scale suggest the
electronic structure is best described by a local model based on negatively
charged hydrogen (H) ions. We develop a many-body theory for the strong
correlation in a H ion lattice. The metal hydride is described by a large
-limit of an Anderson lattice model. We use lanthanum hydride as a prototype
of these compounds, and find LaH is an insulator with a substantial gap
consistent with experiments. It may be viewed either as a Kondo insulator or a
band insulator due to strong electron correlation. A H vacancy state in LaH
is found to be highly localized due to the strong bonding between the electron
orbitals of hydrogen and metal atoms. Unlike the impurity states in the usual
semiconductors, there is only weak internal optical transitions within the
vacancy. The metal-insulator transition takes place in a band of these vacancy
states.Comment: 18 pages, 16 figures and 6 tables. Submitted to PR
Statistical properties of power-law random banded unitary matrices in the delocalization-localization transition regime
Power-law random banded unitary matrices (PRBUM), whose matrix elements decay
in a power-law fashion, were recently proposed to model the critical statistics
of the Floquet eigenstates of periodically driven quantum systems. In this
work, we numerically study in detail the statistical properties of PRBUM
ensembles in the delocalization-localization transition regime. In particular,
implications of the delocalization-localization transition for the fractal
dimension of the eigenvectors, for the distribution function of the eigenvector
components, and for the nearest neighbor spacing statistics of the eigenphases
are examined. On the one hand, our results further indicate that a PRBUM
ensemble can serve as a unitary analog of the power-law random Hermitian matrix
model for Anderson transition. On the other hand, some statistical features
unseen before are found from PRBUM. For example, the dependence of the fractal
dimension of the eigenvectors of PRBUM upon one ensemble parameter displays
features that are quite different from that for the power-law random Hermitian
matrix model. Furthermore, in the time-reversal symmetric case the nearest
neighbor spacing distribution of PRBUM eigenphases is found to obey a
semi-Poisson distribution for a broad range, but display an anomalous level
repulsion in the absence of time-reversal symmetry.Comment: 10 pages + 13 fig
Modeling realistic Earth matter density for CP violation in neutrino oscillation
We examine the effect of a more realistic Earth matter density model which
takes into account of the local density variations along the baseline of a
possi ble 2100 km very long baseline neutrino oscillation experiment. Its
influence to the measurement of CP violation is investigated and a comparison
with the commonly used global density models made. Significant differences are
found in the comparison of the results of the different density models.Comment: 16 pages, 8 figure
On the nature of the z=0 X-ray absorbers: I. Clues from an external group
Absorption lines of OVII at redshift zero are observed in high quality
Chandra spectra of extragalactic sightlines. The location of the absorber
producing these lines, whether from the corona of the Galaxy or from the Local
Group or even larger scale structure, has been a matter of debate. Here we
study another poor group like our Local Group to understand the distribution of
column density from galaxy to group scales. We show that we cannot yet rule out
the group origin of z=0 systems. We further argue that the debate over Galactic
vs. extragalactic origin of z=0 systems is premature as they likely contain
both components and predict that future higher resolution observations will
resolve the z=0 systems into multiple components.Comment: Submitted to ApJ
Temperature dependence of current self-oscillations and electric field domains in sequential tunneling doped superlattices
We examine how the current--voltage characteristics of a doped weakly coupled
superlattice depends on temperature. The drift velocity of a discrete drift
model of sequential tunneling in a doped GaAs/AlAs superlattice is calculated
as a function of temperature. Numerical simulations and theoretical arguments
show that increasing temperature favors the appearance of current
self-oscillations at the expense of static electric field domain formation. Our
findings agree with available experimental evidence.Comment: 7 pages, 5 figure
Strange quark matter in a chiral SU(3) quark mean field model
We apply the chiral SU(3) quark mean field model to investigate strange quark
matter. The stability of strange quark matter with different strangeness
fraction is studied. The interaction between quarks and vector mesons
destabilizes the strange quark matter. If the strength of the vector coupling
is the same as in hadronic matter, strangelets can not be formed. For the case
of beta equilibrium, there is no strange quark matter which can be stable
against hadron emission even without vector meson interactions.Comment: 19 pages, 8 figure
Transforming data by calculation
Thispaperaddressesthefoundationsofdata-modeltransformation.A catalog of data mappings is presented which includes abstraction and representa- tion relations and associated constraints. These are justified in an algebraic style via the pointfree-transform, a technique whereby predicates are lifted to binary relation terms (of the algebra of programming) in a two-level style encompassing both data and operations. This approach to data calculation, which also includes transformation of recursive data models into “flat” database schemes, is offered as alternative to standard database design from abstract models. The calculus is also used to establish a link between the proposed transformational style and bidi- rectional lenses developed in the context of the classical view-update problem.Fundação para a Ciência e a Tecnologia (FCT
Beam Test Results of the BTeV Silicon Pixel Detector
The results of the BTeV silicon pixel detector beam test carried out at
Fermilab in 1999-2000 are reported. The pixel detector spatial resolution has
been studied as a function of track inclination, sensor bias, and readout
threshold.Comment: 8 pages of text, 8 figures, Proceedings paper of Pixel 2000:
International Workshop on Semiconductor Pixel Detectors for Particles and
X-Rays, Genova, June 5-8, 200
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