捷总理谈捷克改革的经验教训

俄罗斯《消息报》1994年第63期刊载捷总理克劳斯对该报的谈话。克劳斯说,他讲话的目的旨在叙述“我们经济改革最初几年的经验教训。”他认为捷克的经济和社会改革在“所有后共产主义世界里跑得较快。” 克劳斯总结的经验教训共有10条: 1.没有单纯的经济解决办法 他指出,在大规模的、全社会的根本改革中不可能采取单纯的经济解决办法,他认为,一些“社会工程师们”提出的“系统转轨”的想想是错误的、骗人的和危险的。某些理论家对某些单个改革理论的分析也只有理论意义而没有实践意义,因为现在和将来的现实都是另一回事。在改革中会有不可避免的阻力、形形色色的垄断性、各类群体的政治和社会压力。

城市农行加快发展的战略探讨

随着酝酿已久的农村金融体制改革付诸实施,农业银行真正改变了“一身三任”的角色,从此进入集中精力办好商业银行的新阶段。办好商业银行的突破口在哪里?我们认为,考虑到城市农行的特殊地缘优势,以及从其对当前整个农行系统所作的贡献来看,可以断言,城市农行将成为全国农行系统转轨的先导,并将起到决定性影响。因此,城市农行必须加快发展,为系统转轨提供新鲜经验及打好物质基础。需要指出的是,本文所定义的城市是指在一定区域中具有影响和决定该区域经济发展水平、规模和进程的大中城市。

Modeling of miner track system during steering motion

Equipment for deep sea mining has risen from a position of virtual non-existence to a major industrial significance and in deep sea bed mining, the miner is the key equipment of the whole system that charges with the most complex and dangerous task.Evaluation of trafficability for tracked vehicles for deep sea mining is essential. Rare earth elements(REEs) are used in a wide range of modern applications. These applications are highly specific and substitutes are inferior or unknown. One possible source of the REE could be the poly-metallic nodule, at present explored in the tropical part of the Pacific Ocean. In developing miners of high performance, dynamic behaviour should be investigated under various traveling conditions. The mechanics of tracked vehicles is of continuing interest to organizations and agencies that specify design and operate tracked vehicles. Most works done are on the complete track vehicle system but in this work the research activity is aimed only at the track system with the basic aim of optimizing the track system design so that it can be manufactured by using the minimum resources. Equations and models are developed for the track system of a miner during steering motion. These equations and models could further be used for design optimization of the track system.

丘吉尔与一战时的英国海军

丘吉尔与一战时的英国海军刘波人们所熟知的丘吉尔是一位在二战中力挽狂澜、使英国免遭法西斯涂炭的著名政治家和外交家。但是，对于在一战时任海军大臣的丘吉尔则知之甚少。长期以来，学术界一直认为，“两强标准”是战前英国海军的发展战略，这有失偏颇。因为丘吉尔出任...

Analytic approach on geometric structure of invariant manifolds of the collinear Lagrange points

An analytical method is proposed to find geometric structures of stable,unstable and center manifolds of the collinear Lagrange points.In a transformed space,where the linearized equations are in Jordan canonical form,these invariant manifolds can be approximated arbitrarily closely as Taylor series around Lagrange points.These invariant manifolds are represented by algebraic equations containing the state variables only without the help of time.Thus the so-called geometric structure of these invariant manifolds is obtained.The stable,unstable and center manifolds are tangent to the stable,unstable and center eigenspaces,respectively.As an example of applicability,the invariant manifolds of L 1 point of the Sun-Earth system are considered.The stable and unstable manifolds are symmetric about the line from the Sun to the Earth,and they both reach near the Earth,so that the low energy transfer trajectory can be found based on the stable and unstable manifolds.The periodic or quasi-periodic orbits,which are chosen as nominal arrival orbits,can be obtained based on the center manifold.

Fuel consumption for interplanetary missions of solar sailing

The orbits of solar sails can be changed by adjusting the sail’s attitude through external control torques.The resulting momentum will be changed,either provided by a typical attitude control subsystem or by a propellantless device.This paper investigates the extra momentum input and fuel consumption for a typical attitude control subsystem.The minimum-time transfer trajectories are designed for two rendezvous missions using both indirect and direct methods,generating continuous and discrete attitude histories,respectively.The results show that the momentum variation is almost wholly due to the solar radiation pressure.The feasibility of using tip-mounted microthrusters for attitude control is evaluated.The results show that less than0.1 kg of propellant are required for an interplanetary transfer mission when pulsed plasma thrusters with a specific impulse of700 s and a thrust of 150 mN are mounted at the tip of a 20 m square solar sail.The fuel consumptions of two transfer missions indicate that a tip-mounted pulsed plasma thruster is a viable technique for the attitude control of a solar sail.

A novel method of periodic orbit computation in circular restricted three-body problem

Periodic orbits are fundamental keys to understand the dynamical system of circular restricted three-body problem, and they play important roles in practical deep-space exploration. Current methods of periodic orbit computation need a high-order analytical approximate solution to start the iteration process, thus making the computation complicated and limiting the types of periodic orbits that can be obtained. By utilizing the symmetry of the restricted three-body problem, a special kind of flow function is constructed, so as to map a state on the plane of symmetry to another state that also lies in this plane. Based on this flow function, a new method of periodic orbit computation is derived. This method needs neither a starting analytic approximation nor the state transition matrix to be computed, so it can be conveniently implemented on a computer. Besides, this method is unaffected by the nonlinearity of the dynamical system, allowing a large set of periodic orbits which have x-z plane symmetry to be computed numerically. As examples, some planar periodic orbits (e.g. Lyapunov orbit) and spatial periodic orbits (e.g. Halo orbit) are computed. By further combining with a differential correction process, the method introduced here can be used to design resonant orbits that can jump between different resonant frequencies. One such resonant orbit is given in this paper, verifying the efficiency of this method.