空间光学的发展与波前传感技术

摘要：进入21世纪，国际上一些发达国家和有关部门都已制定了空间发展战略规划，如美国航空航天局（NASA）、欧洲空间局（ESA）和俄罗斯政府相关部门等都提出空间发展战略规划，这些规划提出了今后一段时间内空间科学要解决的问题和发展的方向，而解决这些问题并推进空间技术的发展很大程度上依赖于先进的光学和无线电望远镜及仪器设备。因此，本文介绍本世纪初国际上空间科学应用的大型天文望远镜的发展情况，重点描述了大口径光学望远镜的光学系统以及实现这类天文望远镜的关键技术之一一波前传感技术。     

I=0 toI=1 transition form factors

A method is proposed to extend the hard scattering picture of Brodsky and Lepage to transitions between hadrons with orbital angular momentuml=0 andl=1. The use of covariant spin wave functions turns out to be very helpful in formulating that method. As a first application we construct a light-cone wave function of the nucleon resonance N^*(1535) in the quark-diquark picture. Using this wave function and the extended hard scattering picture, theN-N ^* transition form factors are calculated at large momentum transfer and the results compared to experimental data. As a further application of our method we briefly discuss the- a₁ form factors in an appendix.Supported by the Deutsche Forschungsgemeinschaft.     

Canonical vielbein forms ofD=3 andD=4 gravity

We compare, in bothD=3 andD=4, two vielbein canonical formulations of gravity: that of Deser and Isham which starts with the metric replaced by vielbeins in the ADM action, and that starting directly from first order vielbein action, and compute the functional that generates the canonical transformation between these two formulations. InD=3, the generator thus exhibits the inherent simplicity of the Einstein action, starting from the DI form (which is as complicated as inD=4). InD=4, however, the same procedure, while leads to a somewhat different formulation from the existing ones, does not result in miraculous simplifications.     

The structure ofT=1 levels inA=14 nuclei

States in¹⁴C, populated via the¹¹B(α, p) reaction at 14 MeV bombarding energy, were investigated with the Doppler Shift Attenuation Method (DSAM). The analysis ofpγ coincidence spectra taken in a Ge(Li) detector at 0? and 120? with the particle detector near 0? with respect to the beam direction yielded the following lifetimes and lifetime limits for the states at 6.09, 6.59, 7.01 and 7.34 MeV, respectively, <20 fs, <1,200 fs, <7 fs and 160±60 fs. Shell model calculations using the MSDI and an empirical interaction fitted to nuclear states in 1p and 2s 1d shell nuclei, are shown to account very well for the experimental levels andγ-transition rates of 5 different multipolarities. The structure of the (J ^*,T)=(2⁺, 1) levels is discussed in the light of the experimentally observed T_z-dependence of the 2⁺, 1→0⁺, 1E2 matrix elements.     

Coulomb displacement energies of the T = 1, J = 0 states of A = 42 nuclei

Coulomb displacement energies of the T = 1, J = 0⁺ and 6₁⁺ states of A = 42 nuclei are analyzed with previously known charge dependent forces and effects, and with the available HartreeFock single-particle wave functions. From the study of the Coulomb displacement energies of the 6₁⁺ states, it is found that the present knowledge on the charge dependence, including a phenomenological charge symmetry breaking force previously introduced so as to help explain the Nolen-Schiffer anomaly, gives a sufficient and consistent explanation for both single-particle and twoparticle systems. From the study of the 0⁺ states, we found that the Coulomb displacement energies of the second 0₂⁺ states can be explained with a compensation between the smaller Coulomb energies of the second lowest two-particle state and larger ones of the deformed 4p-2h state.     

Compactification of chiral N = 2, D = 10 supergravity

A general analysis is made for the possible compactifications of chiral N = 2, D = 10 supergravity down to four dimensions.     

Bianchi V models in N=2, D=5 supergravity

We investigate Bianchi V cosmological models containing two interacting scalar fields. These models are derived from a dimensional reduction of theN=2,D=5 supergravity theory. Exact solutions are found.     

N=2 affine superalgebras and Hamiltonian reduction inN=2 superspace

We constructN=2 affine current algebras for the superalgebrassl(n/n-1)⁽¹⁾ in terms ofN=2 supercurrents subjected to nonlinear constraints and discuss the general procedure of the hamiltonian reduction inN=2 superspace at the classical level. We consider in detail the simplest case ofN=2sl(2/1)⁽¹⁾ and show howN=2 superconformal algebra inN=2 superspace follows via the hamiltonian reduction. Applying the hamiltonian reduction to the case ofN=2sl(3/2)⁽¹⁾, we find two new extendedN=2 superconformal algebras in a manifestly supersymmetricN=2 superfield form. Decoupling of four component currents of dimension 1/2 in them yields, respectively,u(2/1) andu(3) Knizhnik-Bershadsky superconformal algebras. We also discuss how theN=2 superfield formulations ofN=2W ₃ andN=2W ₃ ⁽²⁾ superconformal algebras come out in this framework, as well as some unusual extendedN=2 superconformal algebras containing constrainedN=2 stress tensor and/or spin 0 supercurrents.     

Superconformal transformations of theN = 2,D = 4, SSYM

We obtain the superconformal transformation laws for theN=2,D=4 SSYM. The transformations involve Yang-Mills fields and the corresponding field strength tensor is not constrained to be self antidual. We explicitly demonstrate the closure of the superconformal algebra.     

Densitometer for measuring densities in range ofD=0 toD=6

An instrument permitting measurement of the density of a photographic film in a range ofD=0 toD=6 has been designed by simply adapting a normal densitometer. The advantages of this equipment are described as well as the possibilities arising for film dosimetry.     

Superstring effects on D=4, N=1 supergravity

We give a lagrangian and supersymmetry transformation rules for the four-dimensional N=1 supergravity sector of superstring theories with their O(α′) corrections, obtained by the dimensional reduction á la Witten of the effective action of the ten-dimensional heterotic superstring. We also give general forms of O(α′ ″) corrections to supersymmetry transformation rules which arise through an axial vector superfield. Since our system is based on the ten-dimensional superstring without any auxiliary fields, our four-dimensional N=1 supergravity is free of auxiliary fields. Our point-field theory lagrangian is supposed to describe the mass-less fields in the untwisted sector of the ten-dimensional heterotic superstring propagating on orbifolds.     

Model calculations forI=0 andI=2S-wave pion-pion scattering

Several simple models for theS-waves in isospinI=0 andI=2 pion-pion scattering are constructed. These models are based on unitarity, analyticity in the complexq-plane (q=c.o.m. momentum), approximate crossing symmetry, and the assumption that the forces acting in theS-waves are mainly due to exchange ofρ-mesons,fmesons and a strongI=0S-wave. These models contain between one and three parameters, which are being used to obtain a best fit to Walker'sI=0 data. Our best fits are associated with anI=0 scattering lengtha ₀=0.53 μ^?1. Having fixed the parameters from theI=0 data, predictions are obtained for theI=2S-wave. Our predictions are generally characterized by a very small positiveI=2 scattering lengtha ₂? 0.08 μ^?1 and a zero of the phase shift just above threshold, at a total c.o.m. energy of 320 to 360 MeV. The cause for this behaviour is shown to be the strongS-wave in the crossedI=0 channels. Various reasons are discussed, why we might expect this zero to occur at somewhat larger or at smaller energies, even below threshold. Although because of the crudeness of these models the significance of our results is mainly qualitative, certain internal contradictions in the Walker data seem to be indicated.     

New compactifications of Chiral N = 2, d = 10 supergravity

We present a number of new compactifying solutions of chiral N = 2 ten-dimensional supergravity to five dimensions. Several are of the standard Freund-Rubin type; we give a complete classification of such compactifications for which the internal space M⁵ is a coset manifold. In another type of solution M⁵ is a non-Einstein U(1) bundle over a four-dimensional Kähler space, and the complex three-index field strength is nonvanishing in the internal directions. The latter construction gives a solution with SU(3) symmetry when M⁵ is taken to be a stretched five-sphere.     

Breakdown of the Z = 64 shell gap below N = 82

The systematic behavior of 2₁⁺ and 4₁⁺ state energies in GdXe nuclei, below the neutron N = 82 shell gap, are examined in terms of the product of numbers of valence proton and neutron particles, N_pN_n. To produce a smooth dependence of these spectroscopic quantities as functions of N_pN_n, requires that the Z = 64 shell gap disappears for neutron numbers less than, or approximately equal to, N = 78.