[en] Silicone polymers are frequently used as cushions and inserts between load bearing parts. In this capacity, they must act to position their associated parts and distribute mechanical force as appropriate. One type of failure is specific to silicones that are filled with high surface area particulates for purposes of tailoring the polymer compressive properties. Additives such as fumed silicon oxide are presumed to have a high degree of surface interaction with the polymer matrix, thus causing the polymer to stiffen and to display greater dimensional stability as a function of temperature. However, it has been observed that the compressive behavior of these materials is not always invariant over long times. There is evidence that suggests changes in humidity and temperature can irreversibly alter the silicone-filler interaction, thereby changing the overall characteristics of parts made from such materials. As before, changes in compressive or shear stability can have serious effects on the ability of these materials to effectively position precision parts or distribute high mechanical loads. We approach the analysis of the filled systems by creating controlled layers of silicone polymers attached to silicon oxide substrates. Straight chain vinyl-silicone polymers identical to those used in the formulation of pads for stockpile systems are chemically appended to a substrate surface, and cross-linked to form a three dimensional network. This type of structure serves as a model of silicone polymer coating a silicon oxide filler particle. We study these model systems first by using Atomic Force Microscopy (AFM) to image the samples with nanometer resolution, and then by measuring the forces of interactions between single model silica filler particles and polymer-coated surfaces. We use normal longitudinal force AFM to measure adhesion, and a relatively newly developed technique, lateral force AFM, to determine the frictional forces between the silica particles and the polymer films. Lateral force AFM is a sophisticated technique that involves observing the torsional deflections of a cantilever that is scanned across a surface perpendicular to the normal mode deflection. For a carefully calibrated system, this gives information on the dynamic frictional component of the particle/polymer interaction. Both force-measuring techniques utilize colloidal silicon oxide probes ranging from 0.6 (micro)m to 2.0 (micro)m in diameter. These probes replace the standard sharp AFM tip on the cantilever with a spherical bead (Figure 1) and are used to examine interactions between the bead material and the sample surface

[en] The design of a fast transverse electromagnetic (TEM) kicker for use in the Bates Pulse Stretcher Ring is described. It provides a 1 mrad/m. kick for a 1GeV electron beam, with transition times below 25 ns. and a 1% flat top. The ± 10 KV driver uses a novel switching technique, based on MOSFET power transistors, which allows complete control over the kicker timing and simplifies the construction greatly. Calculations show that the reliability of such a driver is orders of magnitude better than present designs

[en] This paper presents a critical review of the methods of numerical and physical simulation currently being developed by Electricite de France for evaluating the atmospheric dispersion of gaseous effluents, indicates the newest lines of research and attempts to define their scope and the limit of their respective fields of application. Numerical simulation based on the solution of equations describing the dispersion process (lift and turbulent diffusion) in the atmospheric boundary layer cannot provide a complete solution unless one adopts a certain number of simplifying hypotheses which have to be justified. Physical simulation imposes strict simulation criteria which cannot all be met at the same time; hence the need for a clear definition of the limits within which the simulation is appropriate to the problem in question. Case studies of thermal power station sites demonstrate the complementarity of these methods of simulation (in particular with field observations) with a view to pinpointing the data required for their use and validation

[en] As the nation's nuclear weapons age and the demands placed on them change, significant challenges face the nuclear stockpile. Risks include material supply issues, ever-increasing lifecycle costs, and loss of technical expertise across the weapons complex. For example, non-nuclear materials are becoming increasingly difficult to replace because manufacturing methods and formulations have evolved in such a way as to render formerly available materials unprofitable, unsafe, or otherwise obsolete. Subtle formulation changes in available materials that occur without the knowledge of the weapons community for proprietary reasons have frequently affected the long-term performance of materials in the nuclear weapon environment. Significant improvements in performance, lifetime, or production cost can be realized with modern synthesis, modeling, and manufacturing methods. For example, there are currently supply and aging issues associated with the insensitive high explosive formulations LX-17 and PBX 9502 that are based on triaminotrinitrobenzene (TATB) and Kel-F, neither of which are commercially available today. Assuring the reliability of the stockpile through surveillance and regularly scheduled Life Extension Programs is an increasingly expensive endeavor. Transforming our current stockpile surveillance--a system based on destructive testing of increasingly valuable assets--to a system based on embedded sensors has a number of potential advantages that include long-term cost savings, reduced risk associated with asset transportation, state-of-health assessments in the field, and active management of the stockpile.

[en] A linac beam profile measurement system using wire scanners has been implemented at the Bates Linear Accelerator Center. This facilitates obtaining an optimum linac focusing solution. A nearly non-invasive beam size measurement is made of the two beams which are accelerated simultaneously in the recirculating linac. The wire scanner mechanical accuracy is near one mil. Beam size measurements are reproducible to a few mils. 4 refs., 7 figs

[en] A linac beam profile measurement system using wire scanners has been implemented at the Bates Linear Accelerator Center. This facilitates obtaining an optimum linac focusing solution. A nearly non-invasive beam size measurement is made of the two beams which are accelerated simultaneously in the recirculating linac. The wire scanner mechanical accuracy is near one mil. Beam size measurements are reproducible to a few mils. 4 refs., 7 figs

[en] This paper presents the cooperative design efforts of LBL, SLAC, and LLNL on the magnet power conversion systems for PEP-II. The systems include 900 channels of correction magnet bipolar supplies and 400 unipolar supplies in the range of 5 to 500 kW. We show the decision process and technical considerations influencing the choice of power supply technologies employed. We also show the development of specifications that take maximum advantage of both the resources available and existing facilities while at the same time satisfying tight constraints for cost control, scheduling and coordination of different working groups. Switch-mode power conversion techniques will be used extensively in these systems, from the corrector supplies to the largest units if the dynamic performance specifications demand it. General system descriptions for each of the power supply ranges and for a new common control system interface and regulator are included

[en] This paper reports on the MIT Bates Linear Accelerator Center which is in the process of constructing an electron storage ring. The 190 m ring will be used for internal target experiments with stored beams. It will also be used as a pulse stretcher to provide external beams with high duty factor. The present design incorporates a low beta region with a beta-x of 1 m and a 4.5 m space between ring quadrupoles at the internal target location. The ring will contain up to 80 mA using two turn injection. Extraction using one-half integer resonance will produce up to 50μA with a duty factor over 80%. Injection will occur at 1 kHz. Design extracted beam properties include an energy spread of 0.04% and emittance as low as 0.01 π mm-mr