Pure Parallel Research Articles

Performance analysis and kinematic design of pure translational parallel mechanism with vertical guide-ways

Performance analysis and kinematic design of the 3-PUU pure translational parallel mechanism with vertical guide-ways are investigated. Two novel performance indices, the critical slider stroke and the main section area of workspace, are defined; The expressions of two other indices, i.e. the global dexterity and global force transfer ratio are revised based on the main section of workspace. Using these indices, performance changes versus the varieties of dimensional parameters of mechanism are investigated in detail and the graphic descriptions of change tendencies of the performance indices are illustrated. By means of these obtained graphic descriptions, kinematic parameters for the 3-PUU pure translational parallel mechanism with better characteristics can be directly acquired.

Cosmic Shear from STIS pure parallels

Following the detection of a cosmic shear signal at the 30 �� scale using archival parallel data from the STIS CCD camera onboard HST in the previous paper of this series, we analyzed a larger data set obtained from an HST GO pure parallel program. Although this data set is considerably larger than the one analyzed previously, we do not obtain a significant detection of the cosmic shear signal. The most likely cause of this null result is that the signal is comparable to (or less than) the random measurement of the noise. We also show that multiple systematics plague the STIS CCD data for its use in cosmic shear programs, and in particular the continuous degradation of the CCD charge transfer efficiency after 4 years in space, which is a source of additional noise that is still difficult to correct for in the absence of physical models.

Parallel versus serial processing and individual differences in high-speed search in human memory

Many mental tasks that involve operations on a number of items take place within a few hundred milliseconds. In such tasks, whether the items are processed simultaneously (in parallel) or sequentially (serially) has long been of interest to psychologists. Although certain types of parallel and serial models have been ruled out, it has proven extremely difficult to entirely separate reasonable serial and limited-capacity parallel models on the basis of typical data. Recent advances in theory-driven methodology now permit strong tests of serial versus parallel processing in such tasks, in ways that bypass the capacity issue and that are distribution and parameter free. We employ new methodologies to assess serial versus parallel processing and find strong evidence for pure serial or pure parallel processing, with some striking apparent differences across individuals and interstimulus conditions.

A New Technique for Clearance Influence Analysis in Spatial Mechanisms

This paper presents a technique for assessing the influence that clearance in the kinematic pairs of a mechanism has on accuracy. The technique works for both planar and spatial, open-, and closed-chain mechanisms, but not for overconstrained mechanisms. It can be defined deterministic, because it precisely determines the actual pose of the link of interest, and does not rely on probability density functions. The most innovative aspect is that, unlike other existing techniques, knowledge of the forces acting on the mechanism is not needed; on the contrary, given a mechanism configuration, the maximum pose error of the link of interest—that is, the maximum displacement of the link of interest caused by clearance take-up—is directly determined. In this way, a problem which is intrinsically kinematic is solved by a kinematic method, rather than by a kinetostatic one as usually done in the literature. This allows for a more general approach to the clearance problem, as it removes one of the inputs (the external load) usually required for a kinetostatic analysis. The numerical effectiveness of the method is shown on a pure translational parallel manipulator.

Position Analysis of a Class of Translational Parallel Mechanisms

The formulation of the forward position analysis of parallel kinematics mechanisms (PMs) is very complex in most cases. The paper proposes a general explicit solution to the problem for a wide class of 3 dof translational architectures, the tetrahedral mechanisms. The class gathers pure translational parallel mechanisms satisfying three hypotheses on geometry and mobility. No assumption is made about symmetry; the actuation can be redundant or nonredundant. Explanatory examples are discussed.

A test of parafoveal‐on‐foveal effects with pairs of orthographically related words

One of the main controversies in the field of eye movements in reading concerns the question of whether the processing of two adjacent words in reading occurs in sequence, or in parallel. To distinguish between these views, the present experiment tested the presence of parafoveal‐on‐foveal effects with pairs of orthographically related words (or neighbours that differed by a single letter) in a controlled but reading‐like situation. Results revealed that fixation times on a foveal target word were shorter when the target was accompanied by an orthographically similar parafoveal word than when the parafoveal word was dissimilar. Furthermore, the size of the effect tended to vary with both the relative frequency of target and parafoveal words, and the position of the critical letter. These results were interpreted in the framework of a pure parallel processing hypothesis, where the processing of adjacent words is only limited by visual acuity, and the respective lexical properties of the foveal and parafoveal words.

Kinematic Condition Analysis of Three-DOF Pure Translational Parallel Manipulators

Several 3-DOF pure translational parallel manipulators have been reported recently. However, kinematic conditions of such translational parallel manipulators have not been studied deeply. Most previously reported translational parallel manipulators were analyzed by considering constraints on the motion of an independent leg. In addition to the constraints of independent legs, the effect of the constraints on an overall mechanism are analyzed in this paper. The overall kinematic constraints are explained by introducing the restriction of motion, which is a constraint that prohibits a manipulator from moving in a certain region or direction, instantaneously. By introducing it, kinematic constraints can be embedded explicitly in the formulation of rate kinematics, and by analyzing it, constraints for a desired motion can be found. This paper derives constraints for pure translational motion in a systematic way. Necessary and sufficient conditions are suggested and several translational parallel manipulators with their kinematic features are provided.

Searching for [CLC][ITAL]z[/ITAL][/CLC] ≃ 6 Objects with the [ITAL]Hubble Space Telescope[/ITAL] Advanced Camera for Surveys: Preliminary Analysis of a Deep Parallel Field

Recent results suggest that z ? 6 marks the end of the reionization era. A large sample of objects at z ? 6, therefore, will be of enormous importance, as it will enable us to observationally determine the exact epoch of the reionization and the sources that are responsible for it. With the Hubble Space Telescope Advanced Camera for Surveys (ACS) coming on-line, we now have a unique opportunity to discover a significant number of objects at z ? 6. The pure parallel mode implemented for the Wide-Field Camera (WFC) has greatly enhanced this ability. We present our preliminary analysis of a deep ACS/WFC parallel field at |b| = 74.?4. We find 30 plausible z ? 6 candidates, all of which have signal-to-noise ratios greater than 7 in the F850LP band. The major source of contamination could be faint cool Galactic dwarfs, and we estimated that they would contribute at most four objects to our candidate list. We derived the cumulative number density of galaxies at 6.0 ? z ? 6.5 as 2.3 arcmin-2 to a limit of 28.0 mag in the F850LP band, which is slightly higher than our prediction. If this is not due to an underestimated contamination rate, it could possibly imply that the faint-end slope of the z ? 6 luminosity function is steeper than ? = -1.6. At the very least, our result suggests that galaxies with L < L* do exist in significant numbers at z ? 6 and that they could be the major sources that contributed the reionizing photons.

VPP Fortran and the design of HPF/JA extensions

AbstractVPP Fortran is a data parallel language that has been designed for the VPP series of supercomputers. In addition to pure data parallelism, it contains certain low‐level features that were designed to extract high performance from user programs. A comparison of VPP Fortran and High‐Performance Fortran (HPF) 2.0 shows that these low‐level features are not available in HPF 2.0. The features include asynchronous inter‐processor communication, explicit shadow, and the LOCAL directive. They were shown in VPP Fortran to be very useful in handling real‐world applications, and they have been included in the HPF/JA extensions. They are described in the paper. The HPF/JA Language Specification Version 1.0 is an extension of HPF 2.0 to achieve practical performance for real‐world applications and is a result of collaboration in the Japan Association for HPF (JAHPF). Some practical programming and tuning procedures with the HPF/JA Language Specification are described, using the NAS Parallel Benchmark BT as an example. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Cosmic shear from STIS pure parallels

We report on the marginal detection of cosmic shear on sub-arcmin scales with archive data from the STIS camera on board HST. For the measurement 121 galaxy fields with a field of view of are used to obtain an rms cosmic shear of ~4% with significance. This value is consistent with groundbased results obtained by other groups on larger scales, and with theoretical predictions for a standard ΛCDM cosmology. To show the suitability of STIS for weak shear measurements we carefully investigated the stability of the PSF. We demonstrate that small temporal changes do not affect the cosmic shear measurement by more than ~10%. We also discuss the influence of various weighting and selection schemes for the galaxy ellipticities.

DYNAMIC RESPONSE OF TWO ROTORS CONNECTED BY RIGID MECHANICAL COUPLING WITH PARALLEL MISALIGNMENT

The effect of parallel misalignment on the lateral and torsional responses of two rotating shafts (Jeffcott rotors) is examined with theoretical and numerical analysis. The general equations of motion are derived and given in dimensionless form to represent the general case. The equations of motion revealed that parallel misalignment couples the translation and angular deflections through the stiffness matrix and the force vector. The non-linear equations are solved numerically using a combination of Newmark and Newton–Raphson methods to determine the dimensionless frequency and transient responses in terms of misalignment magnitude. The numerical results show that the system natural frequencies are excited at transient condition due to the presence of pure parallel misalignment. At steady state condition, the 1×-rotational speed excitation is present in the translation and angular directions, which indicates that parallel misalignment can be a source of both torsional and lateral excitations.

Cosmic shear from STIS pure parallels

Following the second HST servicing mission in 1997 when the STIS instrument was installed and the capability for parallel observations was enhanced, a substantial archive of non-proprietary parallel data has been accumulating. In this paper, we discuss the use of unfiltered STIS imaging data for a project that requires deep observations along as many independent lines-of-sight as possible. We have developed a technique to determine which datasets in the archive can safely be co-added together and have developed an iterative co-addition technique which enabled us to produce 498 high-quality, deep images. The principal motivation for this work is to measure the Cosmic Shear on small angular scales and a value derived from these data will be presented in a subsequent paper. A valuable by-product of this work is a set of high quality combined fields which can be used for other projects. The data are publicly available at http://www.stecf.org/projects/shear/

Thermal Degradation Mechanism of Low-Density Polyethylene Plastic Wastes in Cyclohexane

The thermal LDPE degradation mechanism harnessing a high-pressure autoclave surrounded by a furnace was investigated in this work. Rates of formation of gas, liquid, and solid during degradation of PE plastic wastes in cyclohexane as solvent at 400 and 425°C have been experimentally determined. Four reaction mechanisms have been proposed and tested to estimates of gas, liquid, and solid. Proposed mechanisms are based on the assumption that the reactions are pseudo-first-order with respect to the reacting species. Pseudo-first-order rate constants for each of the indicated mechanistic steps have been calculated by nonlinear regression analysis. The best fit was obtained by model 2 (pure parallel reaction mechanism), and its activation energy was determined.

Disk and Bulge Morphology of WFPC2 Galaxies: The [ITAL]HUBBLE SPACE TELESCOPE[/ITAL] Medium Deep Survey Database

Quantitative morphological and structural parameters are estimated for galaxies detected in Hubble Space Telescope observations of WFPC2 survey fields. A modeling approach based on maximum likelihood has been developed for two-dimensional decomposition of faint undersampled galaxy images into components of disk and bulge morphology. Decomposition can be achieved for images down to F814W (I) ≈ 23.0, F606W (V) ≈ 23.8, and F450W (B) ≈ 23.3 mag in WFPC2 exposures of 1 hr. We discuss details of the fitting procedure and present the observed distributions of magnitude, color, effective half-light radius, disk and bulge axis ratios, bulge-to-(disk+bulge) flux ratio, bulge-to-disk half-light radius ratio, and surface brightness. We also discuss the various selection limits on the measured parameters. The Medium Deep Survey catalogs and images of random pure parallel fields and other similar archival primary WFPC2 fields have been made available via the Internet with a searchable browser interface to the database.

Space Telescope Imaging Spectrograph Parallel Observations of the Planetary Nebula M94‐2011Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under the NASA contract NAS 5‐26555.

ABSTRACTThe planetary nebula M94‐20 in the Large Magellanic Cloud was serendipitously observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope as part of the Hubble Space Telescope Archival Pure Parallel Program. We present spatially resolved imaging and spectral data of the nebula and compare them with ground‐based data, including detection of several emission lines from the nebula and the detection of the central star. We find that the total Hα + [N ii] flux is 7.3 × 10- 15 ergs s−1 cm−2, and we estimate the magnitude of the central star to be mV = 26.0 ± 0.2. Many other Hα sources have been found in M31, M33, and NGC 205 as well. We discuss the use of the parallel observations as a versatile tool for planetary nebula surveys and for other fields of astronomical research.

Models and Scheduling Algorithms for Mixed Data and Task Parallel Programs

An increasing number of scientific programs exhibit two forms of parallelism, often in a nested fashion. At the outer level, the application comprises coarse-grained task parallelism, with dependencies between tasks reflected by an acyclic graph. At the inner level, each node of the graph is a data-parallel operation on arrays. Designers of languages, compilers, and runtime systems are building mechanisms to support such applications by providing processor groups and array remapping capabilities. In this paper we explore how to supplement these mechanisms with policy. What properties of an application, its data size, and the parallel machine determine the maximum potential gains from using both kinds of parallelism? It turns out that large gains can be expected only for specific task graph structures. For such applications, what are practical and effective ways to allocate processors to the nodes of the task graph? In principle one could solve the NP-complete problem of finding the best possible allocation of arbitrary processor subsets to nodes in the task graph. Instead of this, our analysis and simulations show that a simpleswitchedscheduling paradigm, which alternates between pure task and pure data parallelism, provides nearly optimal performance for the task graphs considered here. Furthermore, our scheme is much simpler to implement, has less overhead than the optimal allocation, and would be attractive even if the optimal allocation was free to compute. To evaluate switching in real applications, we implemented a switching task scheduler in the parallel numerical library ScaLAPACK and used it in a nonsymmetric eigenvalue program. Even for fairly large input sizes, the efficiency improves by factors of 1.5 on the Intel Paragon and 2.5 on the IBM SP-2. The remapping and scheduling overhead is negligible, between 0.5 and 5%.

A heat exchanger model for mixtures and pure refrigerant cycle simulations

This paper describes a heat exchanger simulation developed for transient and steady state cycle simulations of mixtures and pure components. The simulation focuses on air to refrigerant condensers and evaporators found in residential heat pumps. The refrigerant differential momentum, continuity, species and energy equations are solved for these components and the steady state results are verified experimentally. Ten different heat transfer correlations for condensation and evaporation are evaluated to determine which best reproduces experimental data. Of those tested Jung and Radermacher's (1989, Int. J. Heat Mass Transfer 32 2435–2446) heat transfer correlation worked the best for evaporation while Dobson et al.'s (1994, ACRC Project 37) correlation worked the best for condensation. The experimentally determined capacity of four cross flow heat exchangers operating as condensers and evaporators with four different refrigerants is compared to the simulation results. The capacities predicted by the simulation agreed with the experimental results within ±8.0%. Furthermore, the simulation is used to quantify the effects of using a zeotropic mixture, R-407C, with cross, parallel and counter flow heat exchangers. As compared to a typical cross flow heat exchanger at typical heat pump operating conditions, the simulation predits that a pure parallel flow heat exchanger can decrease capacity by as much as 8.3% while a pure counter flow heat exchanger can increase performance by up to 4.4%.

Photodissociation of alkyl iodides and CF3I at 304 nm: Relative populations of I(2P1/2) and I(2P3/2) and dynamics of curve crossing

Photodissociation of n-alkyl iodides and CF3I has been studied using state-selective ionization and pulsed-field time-of-flight (TOF) mass spectrometry. The (2+1) resonance-enhanced multiphoton ionization cross-section ratio of I(2P1/2) and I(2P3/2) is measured from I2 photodissociation in the 304 nm region. Using this ratio, the relative populations of I(2P1/2) and I(2P3/2) by a pure parallel excitation to the 3Q0 state of n-alkyl iodides and CF3I are obtained. This method can exclude the effects of clusters and spectrum overlap in different dissociation paths from branching ratio calculations. The product quantum yield of I(2P3/2) obtained from branching ratio reveals the 3Q0–1Q1 curve crossing probability—which increases from 0.70 for CH3I to 0.86 for n-C4H9I (with recoil velocity decrease of fragments at the curve crossing point). The potential energies at the crossing point and the Landau–Zener parameters ζ, calculated from our modified model, are 385 kJ/mol and 1100 m/s for n-alkyl iodides, and 391 kJ/mol and 177 m/s for CF3I, respectively.

スエージング加工した純アルミニウムおよびＡｌ‐２％Ｆｅ合金Ｐ／Ｍ材の再結晶集合組織に及ぼすレーザ照射の影響

A laser shot local melting technique was applied as an artificial nucleation process. Pure aluminum processed through ingot metallurgy and an Al–2%Fe powder metallurgy alloy were cold swaged. The surface layer of specimen cut from the swaged bar parallel or perpendicular to the swaging direction (SD) was melted by one by one shots of laser and then the specimens were annealed. In pure Al shot parallel to SD, [100] oriented grains pre-existing in the unmelted matrix grow continuously by re-solidification and grow back into the matrix by recrystallization, developing a strong [100] recrystallization texture. While this is not the case for pure Al shot perpendicular to SD. In Al–2Fe shot parallel to SD, a [100] solidification texture seems to develop not by growth of matrix grains but by independent nucleation. The re-solidified grains do not grow by recrystallization, leading to the formation of the previously reported [110] texture in the matrix. It is argued that the anisotropic growth behavior of [100] re-solidified grains by recrystallization in pure aluminum may stem from structural characteristics of its deformed matrix, while in the PM alloy compound particles suppress both growth of pre-existing grains by re-solidification and growth of re-solidified grains by recrystallization.

Dynamic shape of the depletion layer of a submillimeter-wave Schottky varactor

Most frequency multipliers at submillimeter wavelengths are based on the Schottky varactor. The main problem of these multipliers is the output power, which remains low at frequencies above 500 GHz. The aim of this work is to help the situation by studying the usability of the conventional equivalent circuit during a fast voltage modulation. The anode edge effects play an important role in this voltage modulation. While the fringing fields, due to the edge effects, reduce the capacitance modulation in small submillimeter-wave varactors, the edge effects also lessen the effect of electron velocity saturation compared with an ideal varactor with a pure parallel plate capacitance. The usefulness of the static model can be estimated by comparing the three-dimensional shape of the depletion layer to the shape given by the dynamic model. The dynamic shape can be obtained by solving the potential and electron conduction currents in the epitaxial layer of the Schottky varactor. In this work the potential and the electron currents have been calculated from simplified device physics by using numerical methods.