46,806 research outputs found
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
Interpolation function of the genocchi type polynomials
The main purpose of this paper is to construct not only generating functions
of the new approach Genocchi type numbers and polynomials but also
interpolation function of these numbers and polynomials which are related to a,
b, c arbitrary positive real parameters. We prove multiplication theorem of
these polynomials. Furthermore, we give some identities and applications
associated with these numbers, polynomials and their interpolation functions.Comment: 14 page
In-plane ferromagnetism in charge-ordering
The magnetic and transport properties are systematically studied on the
single crystal with charge ordering and divergency in
resistivity below 50 K. A long-range ferromagnetic ordering is observed in
susceptibility below 20 K with the magnetic field parallel to Co-O plane, while
a negligible behavior is observed with the field perpendicular to the Co-O
plane. It definitely gives a direct evidence for the existence of in-plane
ferromagnetism below 20 K. The observed magnetoresistance (MR) of 30 % at the
field of 6 T at low temperatures indicates an unexpectedly strong spin-charge
coupling in triangle lattice systems.Comment: 4 pages, 5 figure
Hysteresis and Anisotropic Magnetoresistance in Antiferromagnetic
The out-of-plane resistivity () and magnetoresistivity (MR) are
studied in antiferromangetic (AF) single crystals, which
have three types of noncollinear antiferromangetic spin structures. The
apparent signatures are observed in measured at the zero-field and
14 T at the spin structure transitions, giving a definite evidence for the
itinerant electrons directly coupled to the localized spins. One of striking
feature is an anisotropy of the MR with a fourfold symmetry upon rotating the
external field (B) within ab plane in the different phases, while twofold
symmetry at spin reorientation transition temperatures. The intriguing thermal
hysteresis in and magnetic hysteresis in MR are observed at spin
reorientation transition temperatures.Comment: 4 pages, 4 figure
Thermodynamic properties of tetrameric bond-alternating spin chains
Thermodynamic properties of a tetrameric bond-alternating Heisenberg spin
chain with ferromagnetic-ferromagnetic-antiferromagnetic-antiferromagnetic
exchange interactions are studied using the transfer-matrix renormalization
group and compared to experimental measurements. The temperature dependence of
the uniform susceptibility exhibits typical ferrimagnetic features. Both the
uniform and staggered magnetic susceptibilities diverge in the limit ,
indicating that the ground state has both ferromagnetic and antiferromagnetic
long-range orders. A double-peak structure appears in the temperature
dependence of the specific heat. Our numerical calculation gives a good account
for the temperature and field dependence of the susceptibility, the
magnetization, and the specific heat for Cu(3-Clpy)(N)
(3-Clpy=3-Chloroyridine).Comment: 8 pages, 12 figures; Replaced with final version accepted in Phys.
Rev.
- …