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Reference Frame (reference + frame)
Selected AbstractsHigh power factor ac/dc/ac converter with h-bridge cascade five-level pwm inverterEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2001B.-R. Lin This paper presents an AC/DC/AC converter which consists of a three-phase switch-mode rectifier (SMR) and a three-phase multilevel inverter with separate isolated DC power supplies. Based on a hysteresis current control scheme in the stationary reference frame, the three-phase SMR is controlled to supply sinusoidal currents with high power factor and low current distortion. The separate DC bus voltages are provided by regulated switch-mode DC/DC converters. The series connection of H-bridge cells is adopted to provide multilevel phase voltage. The control scheme of the three-phase multilevel inverter is based on a look-up table with sine-triangular pulse-width-modulation (PWM) method. The voltage unbalance problem between the separate isolated DC bus voltages is improved by using the proposed control scheme. The proposed control algorithm of the AC/DC/AC converter is verified by simulation and experimental results. [source] A semi-analytical estimation of the effect of second-order ionospheric correction on the GPS positioningGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2005H. Munekane SUMMARY We developed a semi-analytical method to evaluate the effect of the second-order ionospheric correction on GPS positioning. This method is based on the semi-analytical positioning error simulation method developed by Geiger and Santerre in which, assuming the continuous distribution of the satellites, a normal equation is formed to estimate the positioning error taking all the contributions of the ranging error by the visible satellites into account. Our method successfully reproduced the averaged time-series of three IGS sites which is comparable to the rigorous simulation. We then evaluated the effect of the ionospheric error on the determination of the reference frame. We evaluated the additional Helmert parameters that are required for the ionospheric effect. We found that the ionospheric effect can lead to annual scale changes of 0.1 ppb, with an offset of 1.8 mm and a semi-annual oscillation of 1 mm in the z -direction. However, these values are too small to explain the current deviations between the GPS-derived reference frame and the ITRF reference frame. Next, we estimated the apparent scale changes due to the ionospheric error in the GEONET coordinate time-series in Japan. We could qualitatively reproduce the observed semi-annual scale changes peaking at the equinoxes and having asymmetrical amplitudes between the vernal and autumnal equinoxes. [source] Optic radiation changes after optic neuritis detected by tractography-based group mappingHUMAN BRAIN MAPPING, Issue 3 2005Olga Ciccarelli Abstract Postmortem data suggest that trans-synaptic degeneration occurs in the lateral geniculate nucleus after optic nerve injury. This study investigated in vivo the optic radiations in patients affected by optic neuritis using fast marching tractography (FMT), a diffusion magnetic resonance imaging (MRI) fiber tracking method, and group mapping techniques, which allow statistical comparisons between subjects. Seven patients, 1 year after isolated unilateral optic neuritis, and ten age and gender-matched controls underwent whole-brain diffusion tensor MR imaging. The FMT algorithm was used to generate voxel-scale connectivity (VSC) maps in the optic radiations in each subject in native space. Group maps of the left and right optic radiations were created in the patient and control group in a standardized reference frame using statistical parametric mapping (SPM99). The reconstructed optic radiations in the patient group were localized more laterally in the posterior part of the tracts and more inferiorly than in the control group. Patients showed reduced VSC values in both tracts compared with controls. These findings suggest that the group mapping techniques might be used to assess changes in the optic radiations in patients after an episode of optic neuritis. The changes we have observed may be secondary to the optic nerve damage. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc. [source] Estimating winter evaporation in boreal forests with operational snow course dataHYDROLOGICAL PROCESSES, Issue 8 2003Angela Lundberg Abstract Snow course measurements from 11 sites located in eastern and northern Finland were used to estimate the total interception evaporation of a winter season for different forest categories. We categorized the sites based on forest density and tree species. Results showed that interception loss from gross precipitation increased with forest density and approached 30% for a forest with the highest density class. Interception loss for the most common forest density class was 11%. Interception losses were slightly larger in spruce forests than in pine, deciduous, or mixed forests. We provide suggestions as to how to design snow surveys to estimate wintertime interception evaporation better. Rough terrain and transition zones between forest and open areas should be avoided. Since evaporation fraction was strongly dependent on tree crown characteristics, snow course data should include direct estimates of canopy closure. Qualitative observations made by different observers should be given a reference frame to ensure comparability of records from different sites. Copyright © 2003 John Wiley & Sons, Ltd. [source] An augmented Lagrange multiplier approach to continuum multislip single crystal thermo,elasto,viscoplasticityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2005C. C. Celigoj Abstract The material and structural behaviour of single crystals is going to be investigated. On the constitutive level the concept of ,generalized standard materials (gsm)' is used to set up the equations for finite deformation multislip single crystal thermo,elasto,viscoplasticity within a continuum slip theory. The only two scalar quantities needed are a thermodynamic potential and a dissipation potential. The resulting evolution equations for the internal (viscoplastic) variables are discretized in time and solved via a backward Euler scheme, using an ,augmented Lagrange multiplier method' for satisfying the multiple constraints, thus circumventing the cumbersome and less robust ,active set strategies'. As a computational reference frame serves the Eulerian setting. The structural behaviour (non-linear coupled thermomechanics) is solved in a staggered algorithm: in an isothermal mechanical phase via q1(displacements)/p0(pressure)/j0(jacobian)-finite elements and in an isogeometric thermal phase via q1(temperatures)-finite elements, followed by an isogeometric and isothermal update phase of the internal variables. Numerical results of the simple isothermal shear test of a single face-centred cubic (fcc) crystal and of the thermomechanical behaviour of a geometrically imperfect strip consisting of initially equally oriented (0/45/30 in Euler angles) fcc-crystals under tension and plane strain conditions are given. Copyright © 2005 John Wiley & Sons, Ltd. [source] Perceptual organization of motions in pigeons (Columba livia)1JAPANESE PSYCHOLOGICAL RESEARCH, Issue 3 2004TOMOKAZU USHITANI Abstract:, We investigated whether pigeons perceived relative motion of more than one object. We trained pigeons to match a white target dot moving vertically at a constant speed to one color and the same dot moving diagonally to another. In Experiment 1, we presented an additional yellow dot (accompanying dot) moving horizontally near the target. We hypothesized that the pigeons would match the diagonal motion to the color for "vertical motion" and vice versa if they perceived relative motion of the target and the accompanying dot. We reduced the size and the speed of the stimuli by half in Experiment 2 and changed the movement pattern of the target to a sine-function in Experiment 3. In Experiment 4, we presented two accompanying dots. However, the results of Experiments 1 to 4 showed no evidence that pigeons perceived relative motion. In Experiment 5, we substituted a moving frame for accompanying dots. The pigeons tended to respond to the color corresponding to the relative motion. These results suggest that pigeons may organize a set of moving objects as one object moving relative to the other in some stimulus displays in which the second object constitutes an explicit reference frame. [source] Locomotor skills and balance strategies in children with internal rotations of the lower limbsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2008Sophie Mallau Abstract The purpose of this study was to investigate the functional effects of a structural deformation, internal rotations (IR) of the lower limbs, on upper body balance strategies used during locomotion in 5,6 year-old and 7,10 year-old children. Balance control was examined in terms of rotation around the longitudinal axis in horizontal plane (yaw) and around the sagittal axis in a frontal plane (roll). Kinematics of foot, pelvis, shoulder, and head rotations were measured with an automatic optical TV image processor and used to calculate angular dispersions and segmental stabilizations. Older children with IR showed a lower gait velocity, particularly in difficult balance conditions than typically developing (TD) children. In younger children, the effect of the local biomechanical deficit remained limited to the lower limbs and did not affect upper body coordination. By contrast, in older children with IR, the development of head stabilization in space was affected. This was demonstrated by an "en bloc" instead of an articulated mode of head-trunk unit systematically adopted by the control group. As pelvic stabilization remains the main reference frame to organize balance control in older children with IR, we conclude that the structural deformity of the legs affect and possibly delay the acquisition of the head stabilization in space strategy. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:117,125, 2008 [source] The 1999 Leonid meteor storm: verification of rapid activity variations by observations at three sitesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2000W. Singer We report observations of an unpredicted fine structure in the activity profile of the Leonid meteor storm of 1999 November 18. Our observations were obtained at three widely separated sites (on the Iberian peninsula, in Germany, and in northern Sweden) and with two totally different techniques (video cameras and meteor radars). The observations clearly show quasi-periodic variations of the meteor rate with temporal separations of individual maxima in the 6- to 9-min range. These temporal variations translate into spatial variations within the dust trail with scales between 10 000 and 30 000 km, depending in which reference frame or direction one chooses to compare. The times for the central three maxima as observed at the three sites agree within 2 min of each other after application of the appropriate topocentric time corrections. We consider a number of potential causes for the observed density variations within the meteor stream. [source] Reliability of measurement of angular movements of the pelvis and lumbar spine during treadmill walkingPHYSIOTHERAPY RESEARCH INTERNATIONAL, Issue 4 2001Nicholas Taylor Abstract Background and Purpose Angular movements of the pelvis and lumbar spine are thought to play an important role in walking. However, little is known about the amount of unpredictable variability in measurement of these movements during human walking. The aim of the present study was to determine the retest reliability of measuring the angular movements of the pelvis and lumbar spine during unimpaired familiarized treadmill walking. Method Retest reliability for 26 subjects without pathology was determined over a one-week interval. Subjects walked on a treadmill at self-selected or a slower speed while measurements of the three-dimensional angular movements were taken with a computer-based video analysis system. Results The frontal plane movements of pelvic list and lumbar lateral flexion (relative to the pelvis) could be measured with high retest reliability at both self-selected and slow walking speeds (intraclass coefficient (ICC) (2,1) , 0.81). In contrast, transverse and sagittal plane movements demonstrated moderate reliability at both speeds (0.37 , ICC (2,1) , 0.76). Averaging the measurement over six strides resulted in increased observed reliability (self-selected walking speed summary Pearson's r = 0.71, slow walking speed summary Pearson's r = 0.79) compared to taking the measurement based on a single stride (self-selected walking speed summary Pearson's r = 0.63, slow walking speed summary Pearson's r = 0.67). Unlike pelvic and lumbar movements (relative to the pelvis), the measurement of lumbar movements (relative to the global reference frame) appeared to depend on whether subjects were walking at self-selected or slow speeds. Conclusions Measurement of pelvic list and lumbar lateral flexion (relative to the pelvis) could be applied with confidence to hypothesis testing about individuals or groups. Movements in the transverse and sagittal planes are unlikely to be appropriate in hypothesis testing about individuals and hence clinical practice, but may still have experimental applications in hypothesis testing about groups. Copyright © 2001 Whurr Publishers Ltd. [source] A direct control scheme based on recurrent fuzzy neural networks for the UPFC series branch,ASIAN JOURNAL OF CONTROL, Issue 6 2009Tsao-Tsung Ma Abstract In this paper, a new control scheme using recurrent fuzzy neural controllers is proposed for the series branch of the unified power flow controller (UPFC) to improve the dynamic performance of real-time power flow control functions with the aim of reducing the inevitable interaction between the real and reactive power flow control parameters. To simplify the theoretical analysis of the coupled dynamics within the UPFC and the controlled power system, the three phase description of a two-bus test power system embedded with a UPFC is transformed into d,q components based on a synchronously rotating reference frame. For control systems with inherent nonlinear coupling features, a feed-forward control scheme based on fuzzy neural controllers is developed to realize the decoupling control objectives. Based on the simulation results, the proposed control scheme is able to overcome the drawbacks of the traditional power flow controllers designed on small disturbance linearizing methods. Comprehensive simulation results on the EMTDC/PSCAD and MATLAB programs are presented and discussed to verify the effectiveness of the proposed control scheme. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] Structures of the B1 domain of protein L from Peptostreptococcus magnus with a tyrosine to tryptophan substitutionACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2001Jason W. O'Neill The three-dimensional structure of a tryptophan-containing variant of the IgG-binding B1 domain of protein L has been solved in two crystal forms to 1.7 and 1.8,Å resolution. In one of the crystal forms, the entire N-terminal histidine-tag region was immobilized through the coordination of zinc ions and its structural conformation along with the zinc coordination scheme were determined. However, the ordering of the histidine tag by zinc does not affect the overall structure of the rest of the protein. Structural comparisons of the tryptophan-containing variant with an NMR-derived wild-type structure, which contains a tyrosine at position 47, reveals a common fold, although the overall backbone root-mean-square difference is 1.5,Å. The Y47W substitution only caused local rearrangement of several side chains, the most prominent of which is the rotation of the Tyr34 side chain, resulting in a 6,Å displacement of its hydroxyl group. A small methyl-sized cavity bounded by ,-strands 1, 2 and 4 and the ,-helix was found in the structures of the Y47W-substituted protein L B1 domain. This cavity may be created as the result of subsequent side-chain rearrangements caused by the Y47W substitution. These high-resolution structures of the tryptophan-containing variant provide a reference frame for the analysis of thermodynamic and kinetic data derived from a series of mutational studies of the protein L B1 domain. [source] Improving k - t SENSE by adaptive regularizationMAGNETIC RESONANCE IN MEDICINE, Issue 5 2007Dan Xu Abstract The recently proposed method known as k - t sensitivity encoding (SENSE) has emerged as an effective means of improving imaging speed for several dynamic imaging applications. However, k - t SENSE uses temporally averaged data as a regularization term for image reconstruction. This may not only compromise temporal resolution, it may also make some of the temporal frequency components irrecoverable. To address that issue, we present a new method called spatiotemporal domain-based unaliasing employing sensitivity encoding and adaptive regularization (SPEAR). Specifically, SPEAR provides an improvement over k - t SENSE by generating adaptive regularization images. It also uses a variable-density (VD), sequentially interleaved k - t space sampling pattern with reference frames for data acquisition. Simulations based on experimental data were performed to compare SPEAR, k - t SENSE, and several other related methods, and the results showed that SPEAR can provide higher temporal resolution with significantly reduced image artifacts. Ungated 3D cardiac imaging experiments were also carried out to test the effectiveness of SPEAR, and real-time 3D short-axis images of the human heart were produced at 5.5 frames/s temporal resolution and 2.4 × 1.2 × 8 mm3 spatial resolution with eight slices. Magn Reson Med 57:918,930, 2007. © 2007 Wiley-Liss, Inc. [source] Electrodynamics in accelerated frames revisitedANNALEN DER PHYSIK, Issue 10 2010J.W. Maluf Abstract Maxwell's equations are formulated in arbitrary moving frames by means of tetrad fields, which are interpreted as reference frames adapted to observers in space-time. We assume the existence of a general distribution of charges and currents in an inertial frame. Tetrad fields are used to project the electromagnetic fields and sources on accelerated frames. The purpose is to study several configurations of fields and observers that in the literature are understood as paradoxes. For instance, are the two situations, (i) an accelerated charge in an inertial frame, and (ii) a charge at rest in an inertial frame described from the perspective of an accelerated frame, physically equivalent? Is the electromagnetic radiation the same in both frames? Normally in the analysis of these paradoxes the electromagnetic fields are transformed to (uniformly) accelerated frames by means of a coordinate transformation of the Faraday tensor. In the present approach coordinate and frame transformations are disentangled, and the electromagnetic field in the accelerated frame is obtained through a frame (local Lorentz) transformation. Consequently the fields in the inertial and accelerated frames are described in the same coordinate system. This feature allows the investigation of paradoxes such as the one mentioned above. [source] | |||||||||||||||||||