14,581 research outputs found
Adaptive Design of Excitonic Absorption in Broken-Symmetry Quantum Wells
Adaptive quantum design is used to identify broken-symmetry quantum well
potential profiles with optical response properties superior to previous ad-hoc
solutions. This technique performs an unbiased stochastic search of
configuration space. It allows us to engineer many-body excitonic wave
functions and thus provides a new methodology to efficiently develop optimized
quantum confined Stark effect device structures.Comment: 4 pages, 3 encapsulated postscript figure
Influence of coating on the thermal resistance of a Ni-Based superalloy
In this paper, the influence of M-CrAlY polycrystalline coating on the thermal fatigue behavior of a Nickel-base superalloy has been investigated. A special device using a rotating bending machine and two thermal sources has been used to perform thermo-mechanical tests. The two thermal sources have been set to obtain temperature variations between 750 and 1120 °C in the central part of the specimens, with a frequency of 0.1 Hz. The results showed a deleterious effect of the coating on the fatigue resistance. Numerical simulations have been carried out on SAMCEF to determine the thermo-mechanical field of the so-tested specimens. Calculated thermo-mechanical cycles of critical sites are associated with microstructure evolution and damage by cracking observed on the specimens. Damage mechanisms related to the presence of coating are discussed
Spatial Besov Regularity for Stochastic Partial Differential Equations on Lipschitz Domains
We use the scale of Besov spaces B^\alpha_{\tau,\tau}(O), \alpha>0,
1/\tau=\alpha/d+1/p, p fixed, to study the spatial regularity of the solutions
of linear parabolic stochastic partial differential equations on bounded
Lipschitz domains O\subset R^d. The Besov smoothness determines the order of
convergence that can be achieved by nonlinear approximation schemes. The proofs
are based on a combination of weighted Sobolev estimates and characterizations
of Besov spaces by wavelet expansions.Comment: 32 pages, 3 figure
Arithmetic complexity via effective names for random sequences
We investigate enumerability properties for classes of sets which permit
recursive, lexicographically increasing approximations, or left-r.e. sets. In
addition to pinpointing the complexity of left-r.e. Martin-L\"{o}f, computably,
Schnorr, and Kurtz random sets, weakly 1-generics and their complementary
classes, we find that there exist characterizations of the third and fourth
levels of the arithmetic hierarchy purely in terms of these notions.
More generally, there exists an equivalence between arithmetic complexity and
existence of numberings for classes of left-r.e. sets with shift-persistent
elements. While some classes (such as Martin-L\"{o}f randoms and Kurtz
non-randoms) have left-r.e. numberings, there is no canonical, or acceptable,
left-r.e. numbering for any class of left-r.e. randoms.
Finally, we note some fundamental differences between left-r.e. numberings
for sets and reals
Triagem de atividade proteolítica em patê de tilápia enlatado.
bitstream/item/91527/1/2009-CTE-0146.pd
Coil Size and Geometric Field Quality in Short Model Dipoles for LHC
We have measured the magnetic field at room temperature and at 1.8 K on more than twenty, 1-m long, single aperture LHC superconducting dipole models. The magnets feature either a 5-block coil geometry or the baseline 6-block geometry foreseen for the LHC. Comparison of warm and cold measurements show that the coil geometry is essentially unchanged during cooldown. We have therefore used mechanical measurements taken on the coil and collars during assembly to estimate the azimuthal coil length. Based on these measurements we show here that the sensitivity of allowed harmonics on coil size is in good agreement with the prediction obtained from the numerical model used for designing the LHC magnets
QCD Tests of the Puzzling Scalar Mesons
Motivated by several recent data, we test the QCD spectral sum rules (QSSR)
predictions based on different proposals (\bar qq, \bar q\bar q qq, and
gluonium) for the nature of scalar mesons. In the I=1 and 1/2 channels, the
unusual (wrong) splitting between the a_0(980) and \kappa(900) and the a_0(980)
width can be understood from QSSR within a \bar qq assignement. However, none
of the \bar qq and \bar q\bar q qq results can explain the large \kappa width,
which may suggest that it can result from a strong interference with
non-resonant backgrounds. In the I=0 channel, QSSR and some low-energy theorems
(LET) require the existence of a low mass gluonium \sigma_B(1 GeV) coupled
strongly to Goldstone boson pairs which plays in the U(1)_V channel, a similar
role than the \eta' for the value of the U(1)_A topological charge. The
observed \sigma(600) and f_0(980) mesons result from a maximal mixing between
the gluonium \sigma_B and \bar qq(1 GeV) mesons, a mixing scheme which passes
several experimental tests. OZI violating J/\psi--> \phi\pi^+\pi^-, D_s--> 3\pi
decays and J/\psi--> \gamma S glueball filter processes may indicate that most
of the I=0 mesons above 1 GeV have important gluonium in their wave functions.
We expect that the f_0(1500), f_0(1710) and f_0(1790) have significant gluonium
component in their wave functions, while the f_0(1370) is mostly \bar qq. Tests
of these results can be provided by the measurements of the pure gluonium
\eta'\eta and 4\pi specific U(1)_A decay channels.Comment: Version to appear in Phys. Rev. D (one previous figure corrupted
- …