다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

With the cancellation of the Apollo program after Apollo 17 returned from the Moon in 1972, the focus of NASA switched to other areas of the Solar System. Study of the Moon did continue through analysis of the returned samples and remotely sensed data sets (both orbital and surface), as well as through Earth-based telescopic studies. In the 1990s, new orbital data were obtained from several missions (fly-by and orbital), the first being Galileo that allowed the lunar farside to be mapped, followed by global mapping by the Clementine and Lunar Prospector missions. Interest in the Moon started to increase at the beginning of the 21st century as other nations focused their space exploration programs on the Moon. The speech by President Bush in January 2004 put the Moon back into the critical exploration path for NASA, paving the way for humans to return to the lunar surface by 2020. This return will be critical for developing technologies and protocols for the eventual human exploration of other parts of the solar system. At the time of writing (June 2008), the SELENE/Kaguya mission (Japan and Chang’e-1 (China) are orbiting the Moon, with Chandrayaan-1 (India) and Lunar Reconnaissance Orbiter (USA) being scheduled to launch later in 2008. The past (and present) exploration of the Moon begs the question ‘‘what’s left to be done?’’ With the renewed focus on the Moon, now that it is on the pathway for the exploration of Mars (and beyond) a similar question has been raised – what should the astronauts do on the Moon? The publication of the New Views of the Moon book [Jolliff et al., 2006. New Views of the Moon, Reviews in Mineralogy, vol. 60. American Mineralogical Society, 721pp] highlighted a number of important scientific questions that remain unanswered as well as posing many more on the basis of the currently available data. These questions resonated in three Lunar Exploration Analysis Group (LEAG) reports pertinent to this discussion, which were also published (on line) during 2006 (http://www.lpi.usra.edu/leag), and in the National Research Council of the National Academies [2007. The Scientific Context for Exploration of the Moon. National Academies Press, Washington, DC, 112pp] report entitled ‘‘The Scientific Context for Exploration of the Moon’’. This paper synthesizes these recent studies, along with those from the 1980s and 1990s, to emphasize the lunar science questions that remain unanswered. In addition, it summarizes the missions already flown to the Moon along with those that are planned in order to give the reader an idea of exactly what lunar science has been and will be conducted in the hope that it will inspire proposals for missions to address the outstanding science questions. r 2008 Elsevier GmbH. All rights reserved.

/pdf/the-moon-35-years-after-apollo-what-s-left-to-learn-foaasc1vbs.pdf

The Moon 35 years after Apollo: What's left to learn?

Communication Network

We propose and analyse a hybrid numerical–asymptotic hp boundary element method (BEM) for time-harmonic scattering of an incident plane wave by an arbitrary collinear array of sound-soft two-dimensional screens. Our method uses an approximation space enriched with oscillatory basis functions, chosen to capture the high-frequency asymptotics of the solution. We provide a rigorous frequency-explicit error analysis which proves that the method converges exponentially as the number of degrees of freedom N increases, and that to achieve any desired accuracy it is sufficient to increase N in proportion to the square of the logarithm of the frequency as the frequency increases (standard BEMs require N to increase at least linearly with frequency to retain accuracy). Our numerical results suggest that fixed accuracy can in fact be achieved at arbitrarily high frequencies with a frequency-independent computational cost, when the oscillatory integrals required for implementation are computed using Filon quadrature. We also show how our method can be applied to the complementary ‘breakwater’ problem of propagation through an aperture in an infinite sound-hard screen.

/pdf/a-frequency-independent-boundary-element-method-for-3rjcyzbjgn.pdf

A frequency-independent boundary element method for scattering by two-dimensional screens and apertures

Abstract Diffraction of the H $H$- polarized electromagnetic wave by the planar graphene grating in the THz range is considered. The scattering and absorption characteristics are studied. The scattered field is represented in the spectral domain via unknown spectral function. The mathematical model is based on the graphene surface impedance and the method of singular integral equations. The numerical solution is obtained by the Nystrom-type method of discrete singularities.

Modeling of Graphene Planar Grating in the THz Range by the Method of Singular Integral Equations

Wave Diffraction by Periodic Multilayered Structures

Abstract The scattering of the H-polarized plane electromagnetic wave by a finite multilayer graphene strip grating is considered. The properties of the whole structure are obtained from the set of integral equations, which are written in the operator form. The scattering operators of a single layer are used and supposed to be known. Scattering and absorption characteristics as well as diffraction patterns are presented.

Diffraction of the H-polarized plane wave by a finite layered graphene strip grating

The H-polarized plane wave diffraction by the infinite periodic grating with removed strip is considered. In the formulation, the current induced on each strip is divided into two currents, the current on the infinite periodic strip grating and the correction current induced by the removal of a strip. The scattered field is inducted by these currents. The problem is reduced to the dual integral equations with respect to the unknown spectral function of the correction field, and then to the singular integral equation with additional conditions. The singular integral equation of infinite periodic grating is also presented. The near and far fields scattered by the grating are analyzed.

Singular integral equations in diffraction problem by an infinite periodic strip grating with one strip removed

Abstract. Diffraction problem of the TE1nand TM0nmodes by a system of annular slots in the hollow inner conductor of a coaxial waveguide is considered. Inner conductor is of finite thickness. The waveguide is filled with dielectrics with different permittivities. As a key problem the diffraction problem by a circular-to-coaxial waveguide step discontinuity is solved with the mode-matching technique. The obtained solution is used in the analysis of structures with a finite and semiinfinite number of discontinuities. Dependences of the transmission and reflection coefficients of the dominant mode of a circular and coaxial waveguides as functions of wavenumber and distance between slots are analyzed.

Solution of Waves Transformation Problem in Axially Symmetric Structures

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