35,728 research outputs found
H-Dibaryon from Lattice QCD with Improved Anisotropic Actions
The six quark state(uuddss) called H dibaryon(,) has been
calculated to study its existence and stability. The simulations are performed
in quenched QCD on and anisotropic lattices
with Symanzik improved gauge action and Clover fermion action. The gauge
coupling is and aspect ratio . Preliminary results
indicate that mass of H dibaryon is 2134(100)Mev on lattice and
2167(59)Mev on respectively. It seems that the radius of H
dibaryon is very large and the finite size effect is very obvious
Data assimilation using bayesian filters and B-spline geological models
This paper proposes a new approach to problems of data assimilation, also known as history matching, of oilfield production data by adjustment of the location and sharpness of patterns of geological facies. Traditionally, this problem has been addressed using gradient based approaches with a level set parameterization of the geology. Gradient-based methods are robust, but computationally demanding with real-world reservoir problems and insufficient for reservoir management uncertainty assessment. Recently, the ensemble filter approach has been used to tackle this problem because of its high efficiency from the standpoint of implementation, computational cost, and performance. Incorporation of level set parameterization in this approach could further deal with the lack of differentiability with respect to facies type, but its practical implementation is based on some assumptions that are not easily satisfied in real problems. In this work, we propose to describe the geometry of the permeability field using B-spline curves. This transforms history matching of the discrete facies type to the estimation of continuous B-spline control points. As filtering scheme, we use the ensemble square-root filter (EnSRF). The efficacy of the EnSRF with the B-spline parameterization is investigated through three numerical experiments, in which the reservoir contains a curved channel, a disconnected channel or a 2-dimensional closed feature. It is found that the application of the proposed method to the problem of adjusting facies edges to match production data is relatively straightforward and provides statistical estimates of the distribution of geological facies and of the state of the reservoir
Quasi-energies and Floquet states of two weakly coupled Bose-Einstein condensates under periodic driving
We investigate the quasi-energies and Floquet states of two weakly coupled
Bose-Einstein condensates driven by a periodic force. The quasi-energies and
Floquet states of this system are computed within two different theoretical
frameworks: the mean-field model and the second-quantized model. The mean-field
approach reveals a triangular structure in the quasi-energy band. Our analysis
of the corresponding Floquet states shows that this triangle signals the onset
of a localization phenomenon, which can be regarded as a generalization of the
well-known phenomenon called coherent destruction of tunneling. With the second
quantized model, we find also a triangular structure in the quantum
quasi-energy band, which is enveloped by the mean-field triangle. The close
relation between these two sets of quasi-energies is further explored by a
semi-classical method. With a Sommerfeld rule generalized to time-dependent
systems, the quantum quasi-energies are computed by quantizing semiclassically
the mean-field model and they are found to agree very well with the results
obtained directly with the second-quantized model.Comment: 8pages,12figure
Full Wave Form Inversion for Seismic Data
In seismic wave inversion, seismic waves are sent into the ground and then observed at many receiving points with the aim of producing high-resolution images of the geological underground details. The challenge presented by Saudi Aramco is to solve the inverse problem for multiple point sources on the full elastic wave equation, taking into account all frequencies for the best resolution.
The state-of-the-art methods use optimisation to find the seismic properties of the rocks, such that when used as the coefficients of the equations of a model, the measurements are reproduced as closely as possible. This process requires regularisation if one is to avoid instability. The approach can produce a realistic image but does not account for uncertainty arising, in general, from the existence of many different patterns of properties that also reproduce the measurements.
In the Study Group a formulation of the problem was developed, based upon the principles of Bayesian statistics. First the state-of-the-art optimisation method was shown to be a special case of the Bayesian formulation. This result immediately provides insight into the most appropriate regularisation methods. Then a practical implementation of a sequential sampling algorithm, using forms of the Ensemble Kalman Filter, was devised and explored
Comment on "Novel Convective Instabilities in a Magnetic Fluid"
Comment on the paper "Novel Convective Instabilities in a Magnetic Fluid" by
W. Luo, T. Du, and J. Huang, Phys. Rev. Lett., v.82, p.4134 (1999).Comment: 1 page, 1 figure, To appear in Phys. Rev. Lett. (2001
Microscopy of glazed layers formed during high temperature sliding wear at 750C
The evolution of microstructures in the glazed layer formed during high temperature sliding wear of Nimonic 80A against Stellite 6 at 750 ◦C using a speed of 0.314ms−1 under a load of 7N has been investigated using scanning electron microscopy (SEM), energy dispersive analysis by X-ray (EDX), X-ray diffraction (XRD) analysis, scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM). The results indicate the formation of a wear resistant nano-structured glazed layer. The mechanisms responsible for the formation of the nano-polycrystalline glazed layer are discussed
Kondo effect in carbon nanotube quantum dots with spin-orbit coupling
Motivated by recent experimental observation of spin-orbit coupling in carbon
nanotube quantum dots [F. Kuemmeth \textsl{et al.}, Nature (London) {\bf 452},
448 (2008)], we investigate in detail its influence on the Kondo effect. The
spin-orbit coupling intrinsically lifts out the fourfold degeneracy of a single
electron in the dot, thereby breaking the SU(4) symmetry and splitting the
Kondo resonance even at zero magnetic field. When the field is applied, the
Kondo resonance further splits and exhibits fine multipeak structures resulting
from the interplay of spin-orbit coupling and Zeeman effect. A microscopic
cotunneling process for each peak can be uniquely identified. Finally, a purely
orbital Kondo effect in the two-electron regime is also obtained.Comment: published version, 5 pages, 4 figure
Spin-orbit-induced correlations of the local density of states in two-dimensional electron gas
We study the local density of states (LDOS) of two-dimensional electrons in
the presence of spin-orbit (SO) coupling. Although SO coupling has no effect on
the average density of states, it manifests itself in the correlations of the
LDOS. Namely, the correlation function acquires two satellites centered at
energy difference equal to the SO splitting, , of the electron
Fermi surface. For a smooth disorder the satellites are well separated from the
main peak. Weak Zeeman splitting in a parallel
magnetic field causes an anomaly in the shape of the satellites. We consider
the effect of SO-induced satellites in the LDOS correlations on the shape of
the correlation function of resonant-tunneling conductances at different
source-drain biases, which can be measured experimentally. This shape is
strongly sensitive to the relation between and .Comment: 10 pages, 4 figure
- …