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排序方式: 共有176条查询结果,搜索用时 15 毫秒
71.
P. Álvarez-Iglesias M. F. Araújo A. Gouveia T. Drago 《Journal of Radioanalytical and Nuclear Chemistry》2009,281(2):237-240
Two sediment cores (~30 m long) were retrieved at the mouth of the Minho Estuary to assess its palaeoenvironmental evolution
for the last millennia. Samples were characterized by Energy-Dispersive X-Ray Fluorescence Spectrometry and Instrumental Neutron
Activation Analysis, complemented by sedimentological analyses. Provenance of major and trace element contents (lithogenic
or biogenic, continental or marine) is assessed. The influence of grain size effect on total element concentration is discussed.
Most of the samples present a negative Eu anomaly. Sedimentological and geochemical parameters allow differentiating four
geological units––fluvial, marine, estuarine and sand barrier––which reflects the temporal evolution of the Minho Estuary. 相似文献
72.
Christos Levcopoulos Drago Krznaric 《Journal of Algorithms in Cognition, Informatics and Logic》1998,27(2):303-338
This article settles the following two longstanding open problems:
- • What is the worst case approximation ratio between the greedy triangulation and the minimum weight triangulation?
- • Is there a polynomial time algorithm that always produces a triangulation whose length is within a constant factor from the minimum?
73.
Antonio Drago 《Fresenius' Journal of Analytical Chemistry》1990,337(2):220-224
Summary An new insight into the history of chemistry is outlined. The underlying mathematical principles are discussed and the specific tradition of analytical chemistry is emphasized. 相似文献
74.
A. R. Osborne L. Bergamasco M. Serio L. Bianco L. Cavaleri M. Drago L. Iovenitti D. Viezzoli 《Il Nuovo Cimento C》1996,19(1):151-176
Summary We study nonlinear interactions in measured surface wave trains obtained in the Northern Adriatic Sea about 16 kilometres
from Venice, Italy.Nonlinear Fourier analysis is discussed in terms of the exact spectral solution to the Korteweg-deVries (KdV) equation as given by theinverse scattering transform (IST). For the periodic and/or quasi-periodic boundary conditions assumed herein, the approach may be viewed as a nonlinear,
broad-banded generalization of the ordinary, linear Fourier transform. In particular, we study solition interactions, their
properties and the nonlinear dynamics of the radiation (or oscillation) modes as found from the inverse scattering transform
analysis. We also conduct a number of computer experiments in which measured wave trains are numerically propagated forward
in time toward shallow water and backward in time into deep water in order to assess how the nonlinear wave dynamics are influenced
by propagation over variable bathymetry. On this basis we develop a scenario for the evolution of nonlinear wave trains, initially
far offshore in deep water, as they propagate into shallow water regions. The deep-water waves have a small Ursell number
and are hence not very nonlinear; as they propagate toward shallow water, the Ursell number gradually increases in the numerical
experiments by about an order of magnitude. A useful parameterization of nonlinearity in these studies is the ?spectral modulus,?
a number between 0 and 1, which is associated with each IST spectral frequency. Small values of the modulus mean that a particular
spectral component is linear (a sine wave); large values of the modulus (≈1) indicate that the component is nonlinear (a soliton).
There is a systematic increase of the modulus as the waves propagate into shallow water where nonlinear effects predominate;
we describe how the modulus varies as a function of spectral frequency during this shoaling process. The results suggest that
the effect of increasing nonlinearity ?saturates? the IST spectrum (i.e. the modulus ≈1 for all frequencies) to that virtually all spectral components become solitons in sufficiently shallow water. 相似文献
75.
76.
Phase relations in the system Bi2O3CdO were studied in the composition range from 90-30 mole% Bi2O3. A new phase, Bi2O3 · CdO, was found to exist up to 925 K. At this temperature it decomposes to form CdO and the 5Bi2O3 · 3CdO phase. The 5Bi2O3 · 3CdO phase is stable between 925 and 963 K and melts incongruently. Below 925 K it decomposes to Bi2O3 · CdO and 6Bi2O3 · CdO. The phase 5Bi2O3 · 3CdO has cubic symmetry. The Sillenite-type bcc phase 6Bi2O3 · CdO forms above 897 K from oxide mixtures in the solid state or from fused oxide mixtures, but the compound could never be prepared as a single phase. 相似文献
77.
Letters in Mathematical Physics - The existence of a real linear space structure on the set of observables of a quantum system—i.e., the requirement that the linear combination of two... 相似文献
78.
A model-based optimisation of the process of printed circuit board laser structuring is presented. For this purpose, a comprehensive theoretical model of the interaction between the travelling pulsed laser beam and conductive layer, as well as between the laser beam and the induced plasma plume is employed. The model is used to calculate process speed. Based on the process speed determined, the influence of pulse power, duration, and frequency on process speed is analysed. In addition, an optimal range of process parameters with respect to process speed and quality is defined. 相似文献
79.
Iftimie D. Filho M.C. Lopes Lopes H.J. Nussenzveig 《Communications in Mathematical Physics》2003,237(3):441-469
In this article we study the long-time behavior of incompressible ideal flow in a half plane from the point of view of vortex
scattering. Our main result is that certain asymptotic states for half-plane vortex dynamics decompose naturally into a nonlinear
superposition of soliton-like states. Our approach is to combine techniques developed in the study of vortex confinement with
weak convergence tools in order to study the asymptotic behavior of a self-similar rescaling of a solution of the incompressible
2D Euler equations on a half plane with compactly supported, nonnegative initial vorticity.
Received: 28 June 2002 / Accepted: 6 January 2003
Published online: 5 May 2003
RID="⋆"
ID="⋆" Research supported in part by CNPq grant 300.962/91-6
RID="⋆⋆"
ID="⋆⋆" Research supported in part by CNPq grant 300.158/93-9
Communicated by P. Constantin 相似文献
80.
Güneş Erdoğan Mohamed Haouari Melda Örmeci Matoglu Okan Örsan Özener 《The Journal of the Operational Research Society》2015,66(10):1742-1754
Airline companies seek to solve the problem of determining an assignment of crews to a pre-determined flight schedule with minimum total cost, called the Crew Pairing Problem (CPP). Most of the existing studies focus on the CPP of North American airlines, which widely differs from that of most European airline companies in terms of the objective function, the flight structure, and the planning horizon. In this study, we develop an optimization-driven heuristic algorithm that can efficiently handle large-scale instances of the CPP that must be solved on a monthly basis. We perform computational experiments using flight schedules of an European airline company to test the performance of the solution method. Our computational results demonstrate that our algorithm is able to provide high-quality solutions to monthly instances with up to 27?000 flight legs. 相似文献