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The CERN PS accelerator complex has been pro gressively converted to full computer controls without interrupting its full-time operation (more than 6000 hours per year with on average not more than 1% of the total down-time due to controls). The application soft ware amounts to 120 man-years and 45O*OOO instructions: it compares with other large software projects, also outside the accelerator world: e.g. Skylab's ground support software.1 This paper outlines the application software structure which takes into account technical requirements and constraints (resulting from the compl exity of the process and its operation) and economical and managerial ones. It presents the engineering and management techniques used to promote implementation, testing and commissioning within budget, manpower and time constraints and concludes with experience gained.

Computer assisted controls at the 28 GeV PS made their entry in 1967 and today around 80% of the processes are included in various styles. Beam intensity has since increased two orders of magnitude and interleaved cycles of different beam properties are now serving SPS, ISR and the 28 GeV experimental area. This came about by substantial additions to the accelerator equipment, the main one being the Booster and Linac. Plans up to the end of 1980 include: addition of the Antiproton Accumulation Ring, acceleration of antiprotons in the CPS, the concomitant beam transfer and switching, and multibatch filling of the SPS, requiring cycles times down to 0.65 sec. The improvement programme for controls aims to alleviate the operational and maintenance problems ensuing from this explosive expansion and to create a framework for further growth.2. Introduction The importance of efficient controls in the machine studies which led up to and accompanied the improvements and new projects, can hardly be overestimated. Machine studies and even routine operation indeed find themselves growingly impaired by shortcomings, diversity in presentation and underlying logic and by the disjointed nature of the controls that followed the expansion. The upkeep and improvement of hardware and software are scattered over a number of groups and are often only known to one single specialist, hence vulnerability and hard to a6ses total use of resources.Recent trends make a life cycle of another 10 to 15 years highly probable and further growth cannot be ruled out. It was thus decided to build an integrated and user-oriented control systeml that can cope with growth, taking the SPS philosophy2 as a starting point. Users aspects(i) Operators and machine experimenters wish to see a virtual machine, i.e. an apparent structure, following the actions on and the behaviour of the beam, hardware and control intricacies being hidden. As attributes they wish, efficiency, simultaneity, and flexibility for machine experiments, a trustworthy surveyand-alarm system for routine operation.The process is thus divided up so that operationally relevant subsets may be selected through a tree structure from the touch-panels. There are separate trees for different contexts, e.g. starting-up, settingup and machine study, normal operation, probably also a hardware tree and a controls specialist tree. Operations have further specified the applications programs, in particular interactions and displays and they have participated in the choice of console hardware and facilities. A structured naming scheme for process variables and interactions has been divisionally accepted.(ii) Process equipment engineers expect assistance for maintenance and improvements of their hardware. The main consoles being essentially reserved for operation, there is a need for local access through terminals at several levels and facilities for engineers, to develop, load and run their own detailed diagnostic programs for process-hardware off-line or on-line tests. Operators must be able to call fi...

Given a beam in elastic equilibrium whose mean fibre is a continuous curve and which is acted upon by couples of arbitrarily directed axes, the problem which we set is to determine: I. The system of forces acting on any section normal to the mean fibre. II. The stresses existing in this section and the limiting of those stresses. Determination of the forces acting on a section.-We first consider a section ABC of a plane curved beam represented in Fig. 1, by its mean fibre, with a torsional moment applied at A in a plane normal to the mean fibre. The moment applied at A is represented by the vector AA' following the ordinary conventions of mechanics. To determine the forces acting on a Section B normal to the mean fibre at B, we prolong AA' until it intersects the trace BD of the section. At D we carry DD' = AA' which we decompose, in conformity with the de St. Venant principle of elastic equivalence of statically equivalent systems, into its components DD' and DD"', tangential and normal, respectively, to the trace BD. Then the vectors

Part 1Given a beam in elastic equilibrium whose mean fibre is a continuous curve and which is acted upon by couples of arbitralily directed axes, the problem which we set is to determine:I. The system of forces acting on any section normal to the mean fibre.II. The stresses existing in this section and the limiting of those stresses.I. Determination of the forces acting on a section. We first consider a section ABC of a plane curved beam represented in Fig. 1 by its mean fibre, with a torsional moment applied Fig. 1 at A in a plane normal to the mean fibre. The moment applied at A is represented by the vector AA' following the ordinary *Read by title at the meeting of the National Academy of Sciences, Nov. 10, 1924. Abstract in The Proc. Nat. Acad. Sc., Jan. 1925. tMassachusetts Institute of Technology, Cambridge, Mass., U. S. A. tUniversity of Ghent, Ghent, Belgium.