Geometric Placement Research Articles

Geometric leaf placement strategies

Geometric leaf placement strategies for multileaf collimators (MLCs) typically involve the expansion of the beam's-eye-view contour of a target by a uniform MLC margin, followed by movement of the leaves until some point on each leaf end touches the expanded contour. Film-based dose-distribution measurements have been made to determine appropriate MLC margins—characterized through an index d90—for multileaves set using one particular strategy to straight lines lying at various angles to the direction of leaf travel. Simple trigonometric relationships exist between different geometric leaf placement strategies and are used to generalize the results of the film work into d90 values for several different strategies. Measured d90 values vary both with angle and leaf placement strategy. A model has been derived that explains and describes quite well the observed variations of d90 with angle. The d90 angular variations of the strategies studied differ substantially, and geometric and dosimetric reasoning suggests that the best strategy is the one with the least angular variation. Using this criterion, the best straightforwardly implementable strategy studied is a ‘touch circle’ approach for which semicircles are imagined to be inscribed within leaf ends, the leaves being moved until the semicircles just touch the expanded target outline.

The influence of ion beam sputtering geometry on metastable (Ni 81Fe 19)O/Ni 81Fe 19 exchange biased bilayers

Metastable polycrystalline permalloy monoxide films (Ni 81Fe 19)O or PyO, with NiO-type rocksalt crystalline have been fabricated by reactive dual ion beam sputtering (RDIBS). These materials were characterized with high angle X-ray diffraction (HAXRD), X-ray reflectivity (XRR) and vibrating sample magnetometry (VSM). Permalloy monoxide films ranging in thickness from 30 to 100 nm were investigated. The crystalline and magnetic properties of these metastable oxide films are found to depend on (1) the choice of specular versus non-specular RDIBS geometric placement of the ion beam target sputtering source, target and substrate; (2) the use of Ar + (lighter) or Kr + (heavier) sputter ions; and (3) the choice of substrate temperature during sputtering. In addition, the use of modest 500 K post-deposition vacuum anneals in a static magnetic film were also observed to greatly improve the magnetic properties of exchanged biased PyO/Py bilayer structures (Py=Ni 81Fe 19). When optimally processed, RDIBS fabricated permalloy monoxide films can be used to fabricate exchange biased PyO/Py bilayers with improved coercivity characteristics than previously found in equivalent magnetron sputtered PyO/Py or similarly ion beam sputtered NiO/Py bilayer samples.

Self-programmable, self-assembling two-dimensional genetic matter.

Putative two-dimensional coding systems can be constructed from aqueous solutions of purine and pyrimidine nucleic acid bases evaporated at moderate temperatures on the surfaces of inorganic solids. The resultant structures are monolayers which are formed spontaneously by molecular self-assembly and they have been observed with molecular resolution by scanning tunnelling microscopy (STM). When formed from solutions of a single base, the monolayers of adenine and uracil have crystalline characteristics and the STM images can be interpreted in terms of the geometrical placement of planar arranged molecules that interact laterally by intermolecular hydrogen bonding. When formed from solutions containing a mixture of adenine and uracil, the monolayers have aperiodic structures. Small crystalline domains within these monolayers can be interpreted in terms of the single phase configurations of the molecules and the remaining aperiodic structures can presumably be interpreted, geometrically, in terms of the 21 theoretically possible adenine-adenine, uracil-uracil and adenine-uracil hydrogen bonding interactions. We propose that combinatorial arrangements of planar arranged purine and pyrimidine bases could provide the necessary complexity to act as a primitive genetic mechanism and may have relevance to the origin of life.

Static and Low-Velocity Impact Response Characteristics of Pultruded Hybrid Glass-Graphite/Epoxy Composite Beams

The influence of hybridization on the crashworthiness and energy-absorption characteristics of pultruded glass-graphite/epoxy composite beams was investigated. Lowvelocity drop weight instrumented impact tests were conducted on these hybrid composites to determine the load-deformation behavior for evaluating the impact performance in terms of the ductility index, damage initiation, propagation, and total absorbed energies. Three-point static flexural tests were also conducted to compare the static load-deformation characteristics with those of the dynamic low-velocity impact tests. The behavior under both static and dynamic loading conditions was simulated using finite element modeling procedures to identify the failure mechanisms for optimizing the performance of pultruded hybrid composites. Experimental results show that the load and strain to failure of all-graphite/epoxy, all-glass/epoxy and other hybrid composites obtained from impact tests are significantly higher as compared to the static test data. The load-bearing capability of composites after damage initiation (which is dictated by the ductility and failure index) has shown marked improvement for the graphite-outside hybrids when compared with the all-graphite, all-glass, and glass-outside hybrids. The high strain to failure glass fibers absorb considerably higher energy before ultimate failure compared to the brittle graphite fibers; as a result, the fiber content and geometric placement of each type of fiber significantly influenced the energy-absorption characteristics of hybrids. Results indicate that the energy-absorption behavior of pultruded hybrids predicted using finite element modeling is in close agreement with the behavior characterized from experimental impact tests. The effectiveness ofhybridization to improve the impact performance of composites was demonstrated.

Development of High Frequency Terfenol-D Transducer Material

AbstractThe objective of this research and development program is to develop production methods to obtain thin strips of oriented crystalline Terfenol-D and to develop multi-layered driver rods for transducers that will operate over a broad spectrum into the MHz frequency range. To reach this goal, special methods must be used to minimize the amount of mechanical processing, such as machining, as the material is both brittle and expensive. A modified rapid solidification method has been developed to process Terfenol-D to obtain the desired geometric configuration of long thin strips. Currently, sections that are 500 mm long, 2 mm wide and 0.1 mm thick can be produced. In addition, this method enables the crystallographic orientation of the strips of Terfenol-D to be controlled to obtain the preferred orientation that will maximize the magnetostrictive displacement of the material. Magnetostrictive measurements have shown that the samples prepared by this approach have a 62 percent improved magnetostrictive performance when compared to non-oriented Terfenol-D. The ribbons have been consolidated into transducer driver rods. The magnetostrictive performance of the driver rods has been measured to be 60 percent of the as prepared ribbons. The reduction in performance is attributed primarily to the geometric placement of the ribbons inside the driver rods.

Piloted ignition of a slick of oil on a water sublayer: The effect of weathering

Piloted ignition of a slick of oil on a water sublayer has been experimentally studied. The objective of this work is to provide a tool that will serve to assess a fuel's ease to ignite under condition that are representative of oil spills. The fuel is exposed suddenly to external radiation to increase its temperature until ignition occurs. The strength and geometrical placement of the pilot were chosen to minimize gas-phase induction time and heat feedback from the pilot to the fuel surface. Temperature measurements, flow visualization, and ignition delay time are used to characterize piloted ignition, and an existing one-dimensional heat transfer model is used to correlate the experimental results. Two different crude oils and SAE 30W oil were used for these experiments. Crude oils were tested in their natural state and at different levels of weathering. It was observed that the ignition delay time is a strong function of the flow structures formed both in the liquid and gas above the pool. Piloted ignition is inhibited by premature boiling of the water sublayer, and weathering significantly increases the ignition delay time. It was determined that a critical heat flux for ignition could be obtained and better serve as a parameter to characterize the fuel propensity to ignite in the presence of a strong pilot. The minimum heat flux that will permit ignition before boiling of the water sublayer occurs also needs to be considered.

Volume Flow-Rate Measurements and Scaling Laws for a Transverse-Inlet Multiple-Disk Fan

The air moving capacity of a transverse-inlet multiple-disk fan has been measured experimentally and the results successfully collapsed with a simple scaling law. The disk fan studied was an array of several hundred closely spaced plastic disks that rotated about a common axis inside an approximately semicylindrical housing. A splitter plate lying parallel to the axis of rotation and tangent to the disks separated the inflow and outflow streams. The volume flow rate of air per unit length along the axis of rotation was measured using standard LDV techniques. For disk spacings greater than 1 mm, the volume flow rate was found to be essentially proportional to ωhR3, where ω = radian rotation rate of the disks, h = disk spacing, and R = disk radius. This scaling law was derived from a simple force balance for a small fluid element moving between rotating disks. The Reynolds number of the experiments, ωh3R/ν, was varied from 2 × 102 to 103. In addition, the air-moving capability of the disk fan was found to be nearly independent of the geometrical placement of the rotating disks within the fan housing.

Experimental Limitations In Impedance Spectroscopy of Materials Systems

ABSTRACTUsing resistor-capacitor networks, sources of experimental artifacts in impedance spectroscopy were investigated, such sources include machine limitations, rig/cabling contributions at high frequencies, and artifacts due to high impedance reference electrodes and their geometrical placement. In the instance of electrode placement, computer simulations with a pixel-based model were in agreement with the experimental observations. Remedies for these artifacts such as rig shielding/grounding, geometrical adjustments, and null corrections are also discussed.

Stiffness enhancement in aligned, short-fibre composites: A computational and experimental investigation

This communication presents the results of a combined computational and experimental study with the objective of determining the extent to which the alignment of fibres improves the effective tensile modulus of short-fibre-reinforced composite materials. In the computational part, we use the boundary element method (BEM) to model the mechanical response of a fully three-dimensional, multi-particle composite rod consisting of up to 40 individual, rigid, rod-like particles randomly embedded in an elastic matrix. The BEM allows great flexibility in the geometrical placement of the reinforcing particles, thus allowing the numerical investigation of micromechanical, orientational and configurational effects without resorting to the unit cell approximation, as is almost invariably the case with previous work in this area. Besides their volume fraction and aspect ratio, the effective stiffness of the composite rod is found to depend on the relative placement of the reinforcing fibres and is predicted to be highest when the fibres are aligned in the tensile direction. In the experimental part, we apply a hydrodynamic method in order to align, in a small-scale pilot facility, short carbon fibres in an epoxy matrix. Composite samples are prepared and tested two at a time (one with randomly oriented fibres and the other with aligned fibres) and the effect of fibre alignment on mechanical properties is isolated and measured. Experimental results show that aligned fibres are approximately twice as effective than randomly oriented fibres in stiffening the composite in the alignment direction. There is a remarkable agreement between numerical predictions and experimental measurements.

Three Electrode Measurements on Solid Electrolytes

ABSTRACTAC impedance spectroscopy and chronopotentiometry have been used to study solid state ionic conductors. Results obtained using three electrodes are compared to those using a two electrode configuration. The uncompensated resistance was shown to depend strongly on the geometric placement of the electrodes. The optimal configuration is similar to the Luggin capillary arrangement in the liquid phase. The effect of non-negligible geometric capacitance on interpretation of results is discussed.

Introducing global constraints in CHIP

The purpose of this paper is to show how the introduction of new primitive constraints (e.g., among, diffn, cycle) over finite domains in the constraint logic programming system CHIP result in finding very rapidly good solutions for a large class of difficult sequencing, scheduling, geometrical placement and vehicle routing problems. The among constraint allows us to specify sequencing constraints in a very concise way. For the first time, the diffn constraint allows us to express and to solve directly multi-dimensional placement problems, where one has to consider nonoverlapping constraints between n-dimensional objects (e.g., rectangles, parallelepipeds). The cycle constraint makes it possible to specify a wide range of graph partitioning problems that could not yet be expressed by using current constraint logic programming languages. One of the main advantages of all these new primitives is to take into account more globally a set of elementary constraints. Finally, we point out that all the previous primitive constraints enhance the power of the CHIP system significantly, allowing us to solve real life problems that were not within reach of constraint technology before.

New analytical procedure for automatic cell placement in gate-arrays

A fully automated constructive global placement method based on analytical function minimisation is described. It is meant to be applied to the gate-array placement problem, which is known to be a most restrictive one. A penalty function approach is used to convert the problem into an unconstrained optimisation. The objective function is constructed of two parts: the first one, reflecting the attraction criterion, generates the so-called 'relative placement', while the second one assembles the repulsion requirements (in which the essential geometric requirements are incorporated), and generates the so-called 'geometric placement' or 'final placement'. The geometric requirements are introduced sequentially so that a strategy is proposed to enable the final solution (which becomes suboptimal in the sense that a longer interconnection length is obtained) to be kept as near as possible to the relative one. No convergence problems are encountered even for complex examples. Among the introduced penalty functions the most important one is the nonoverlapping penalty function. Here, a new, good approximation of the rectangular module shape is introduced enabling analytical definition of the constraints. It was recognised that, for complex placement problems, the nonoverlapping penalty was not strong enough to ensure nonoverlapping. Hence a new repulsive penalty is introduced which takes into account the module dimensions. Fully automatic row assignment of the modules is ensured by another new penalty. The gate assignment is performed automatically but, in order to avoid integer programming, it is performed as a separate post-processing phase. Examples of complex design were produced utilising 90% of the gate-array central area.

An Approach to Compliance Control of a Parallel Manipulator with Linear Drives

A compliance control approach as applied to parallel manipulators with linear drives is discussed. The desired dynamic manipulator is based on impedance parameters, which can be achieved by adjusting the stiffness and damping of each joint. Impedance parameters can also be changed by an appropriate geometric placement of the linear drive units. A manipulator with two degrees of freedom that includes an anthropomorphic skeleton chain and 3 linear drive units was designed and manufactured. An experiment was carried out on a compliant motion task - fettling of aluminum automobile wheel rims

COMPUTER OPTIMIZING OF ELECTROMAGNETIC DEVICES

The optimization of geometric boundaries and placement of conductors to achieve specific design goals is the principle activity in computational electromagnetics. However the heuristic determination of design variables soon leads to total confusion as the user attempts to wrestle with multiple choices. Even if there are just two states for n parameters there will be, 2n trials. The range of problems posed is vast. One such is the determination of magnet geometries needed to produce an unpolluted uniform field in Magnet Resonance Imaging (MRI) systems, and another application concerns the design of pole shapes in particle accelerators where the higher harmonic distortions must be minimized in dipoles and multipole magnets.

On empty rooms in floorplan graphics: comments on a deficiency in two papers

Floorplan graphs are used in many placement and routing systems for VLSI building-block layout. S. Kimura et al.(ibid., vol. CAD-2, p.285-92, Oct. 1983) and W.M. Dai (ibid., vol.CAD-4, p.189-97, July 1985) proposed algorithms to construct such a graph from a geometrical placement of the building blocks and to define a channel structure from the floorplan graph. In the absence of empty rooms in the floorplan graph the algorithms can correctly derive a channel definition and ordering from the graph. However, in the case that there are empty rooms present in the floorplan graph, neither algorithm can guarantee a correct solution. A counterexample is given to point out the deficiency. A correction to the RRDO algorithm given by Dai et al. is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Flute an Expert Floor Planner for Full-Custom VLSI Design

Flute is a heuristic floorplanner that operates as part of Cadre, a system of cooperating expert agents for converting a hierarchical structural description into full-custom VLSI layout. Flute is modeled on the human floorplanning process and uses a mixture of rule-based programming, state control, and algorithmic operators. Initially, a topological plan is generated by placing modules on a grid graph. From this plan, a constraint graph is prepared. This graph is solved to add geometric size and placement information to the floorplan. Though Flute handles a fairly small number of submodules at a time, it can construct a floorplan of complex VLSI layout using a hierarchical structure of ICs. Flute is implemented in Zeta-lisp on Symbolics Lisp machines.

MULGA-An Interactive Symbolic Layout System for the Design of Integrated Circuits

To aid the design of MOS circuits, a suite of programs residing on the UNIX <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∗</sup> operating system have been designed and written. These programs allow the interactive editing, layout compaction, circuit connectivity extraction, parasitic audit, and timing simulation of MOS ICs within the symbolic domain. The programs make use of an intermediate circuit description language (ICDL), which captures both geometric placement and circuit connectivity. A convenient interface is provided to enable the procedural definition of symbolic layouts in the C programming language. All design may be carried out at a single low-cost work station which incorporates a high-performance color display. In this paper we summarize the operation and use of these programs. In particular, we describe a new compaction algorithm.

Vectorcardiographic studies in infants and children: I. Comparative orthogonal lead studies in the neonatal period

Planar vectorcardiographic QRS loops of 33 normal, term infants were recorded by the Grishman cube, Frank and McFee-Parungao axial lead-placement systems on the first through the third days of life. No changes occurred in direction of loop inscription or in magnitude of the mean and maximal planar and spatial QRS vectors that might reflect changing ventricular loading patterns during the period of transition from the fetal to adult circulation. In this group of infants the orthogonal systems performed quite similarly; the major differences observed among recordings were in the magnitudes of the recorded X, Y and Z deflections, which were greatest for the axial system and smallest for the Frank system. On successive days of life, mean and maximal QRS vectors were of a similar, but not identical, order of magnitude and orientation for a given lead system, but in individual instances wide deviations were observed. In general, in most infants QRS vector directions were right, inferior and anterior, thus reflecting the expected electrical and anatomic preponderance of the right ventricle at this age. The cube system, an unweighted lead system based on geometric placement of skin electrodes, performed in approximation to the orthogonal systems. It was, in general, a technically unsatisfactory system, even though electrode placement seemed to offer the advantage of fewer electrodes. Tracings in general were small, with considerable noise level produced by body tremor; this factor, together with the small signal, produced a small signal to noise ratio. These data will be expanded to encompass measurements from a much larger series of infants, with more detailed, extensive analysis made possible through the use of digital computer technics.

Electromyography in dental research: Part I. Geometric placement of reference electrodes

Electromyography in dental research: Part I. Geometric placement of reference electrodes