Significant Relative Motion Research Articles

The examination of operator performance when controlling a shipboard crane anti-sway control system within a virtual-reality simulator

Anti-sway control systems are valuable tools for cranes to prevent unexpected payload sway and undesired motion. However, for shipboard cranes, where the operator moves with the ship, anti-sway control systems can result in significant relative motion between the payload and operator, particularly in rough seas while attempting to align the payload with an ocean-frame target. Therefore, an important question to ask is, do operators actually find anti-sway systems intuitive, or do they feel they have to “fight” the system to achieve their desired performance? To address the question, this paper presents a human factors study designed to evaluate the effectiveness of a shipboard crane anti-sway system with an operator-in-the-loop. Participants completed a series of tests in a virtual-reality simulator, in which they attempted to align the payload of a nine degree-of-freedom shipboard knuckle boom crane with targets in both the ocean/world coordinate frame and ship deck coordinate frame, using an anti-sway system that provided complete motion compensation in both coordinate frames. The study found that there was a statistically significant improvement in the participant’s ability to track a desired payload target with the use of the anti-sway system of up to 49.1%. In addition, as the participant had no knowledge of how the anti-sway system operated, or even if it was active, the results indicate anti-sway control systems can be intuitive for operators to use.

Gaia DR2 distances to Collinder 419 and NGC 2264 and new astrometric orbits for HD 193 322 Aa,Ab and 15 Mon Aa,Ab

Context. On the one hand, the second data release of the Gaia mission (Gaia DR2) has opened a trove of astrometric and photometric data for Galactic clusters within a few kiloparsecs of the Sun. On the other hand, lucky imaging has been an operational technique to measure the relative positions of visual binary systems for a decade and a half. This time is sufficient to apply the results of the technique to the calculation of orbits of some massive multiple systems within ∼1 kpc of the Sun. Aims. As part of an ambitious research program to measure distances to Galactic stellar groups (including clusters) containing O stars, I start with two of the nearest examples: Collinder 419 in Cygnus and NGC 2264 in Monoceros. The main ionizing source for each cluster is a multiple system with an O-type primary: HD 193 322 and 15 Mon, respectively. For each of the two multiple systems, I aim to derive new astrometric orbits for the Aa,Ab components. Methods. First, I present a method that uses Gaia DR2 G + GBP + GRP photometry, positions, proper motions, and parallaxes to obtain the membership and distance of a stellar group and applied these values to Collinder 419 and NGC 2264. Second, I present a new code that calculates astrometric orbits by searching the whole seven-parameter orbit space and apply it to HD 193 322 Aa,Ab and 15 Mon Aa,Ab using, as input, literature data from the Washington Double Star Catalog and the AstraLux measurements recently presented by our group in another paper published this year. Results. I obtain Gaia DR2 distances of 1006+37−34 pc for Collinder 419 and 719 ± 16 pc for NGC 2264; the main contribution to the uncertainties comes from the spatial covariance of the parallaxes. The two NGC 2264 subclusters are at the same distance (within the uncertainties) and show a significant relative proper motion. The distances are shown to be robust. HD 193 322 Aa,Ab follows an eccentric (e = 0.58+0.03−0.04) orbit with a period of 44 ± 1 a and the three stars it contains have a total mass of 76.1+9.9−7.4M⊙. The orbit of 15 Mon Aa,Ab is even more eccentric (e = 0.770+0.023−0.030); it has a period of 108 ± 12 a and a total mass of 45.1+3.6−3.3M⊙ for its two stars.

Studies on Contact Degradation Process and Failure Mechanism of GIB Plug-In Connector

Overheating faults of gas-insulated bus (GIB) plug-in connectors induced by contact degradation seriously threaten the safe operation of equipment and power system. Multiphysics coupled numerical simulations and physical experiments were conducted in this article to reveal contact degradation processes of the GIB plug-in connector. First, electromagnetic-thermal-mechanical coupled finite-element (FE) model was built. Relative motion between contact interfaces was considered by low-velocity Stribeck friction model. FE model was verified by physical experiment. Second, influences of operation current, spring stiffness, and conductor insert depth on contact temperature rise were analyzed. Results show that insufficient conductor could induce overheating on several contact spots then accelerate the degradation process. Third, thermal and motion characteristics under cyclic operation currents and short-circuit (SC) current impact were analyzed. Results show that conductor insert depth could be changed by relative motion between contact elements. Relative motion accumulates gradually under cyclic thermal loading by operation current. Significant relative motion and temperature rise could be induced by SC current impact. Finally, progressive and sudden failure mechanisms of the GIB plug-in connector were discussed. Research result may guide optimal design and field maintenance of GIB equipment, and thus improves its reliability.

Strike-slip tectonics during the Neoproterozoic–Cambrian assembly of East Gondwana: Evidence from a newly discovered microcontinent in the Indian Ocean (Batavia Knoll)

The first dredge samples recovered from the Batavia Knoll in the eastern Indian Ocean demonstrate it is a rifted continental fragment that now lies submerged in 2km of water between the Perth Abyssal Plain and Wharton Basin, ~1600km offshore Western Australia. This knoll is the second microcontinent to have been discovered in this region, lying ~180km to the NE of Gulden Draak Knoll; both knolls rifted from the Indian margin at c. 104–101Ma during the breakup of East Gondwana. Dredged rocks include granite, granodiorite, charnockite and quartz-rich pegmatite, preserving igneous microstructure and biotite-schlieren. The composite nature of many samples suggests derivation from a felsic igneous complex. This basement is at least partly covered by Late Cretaceous sedimentary strata. Zircon grains from five representative granitoid samples primarily display modified oscillatory zoning and U-Pb data that spread along concordia over ~50–70m.y., suggesting protracted magmatism and Pb-loss during the latest Neoproterozoic–early Cambrian (c. 580–530Ma). Despite the span in U-Pb zircon ages, the primary igneous populations exhibit a relatively narrow range of initial Hf isotopic ratios (Hfi=0.281290–0.281814; εHfi=−41.40 to −23.32). This evolved nature of the Hf signature suggests derivation of melts from ancient crust (TDM2=4.05–2.92Ga) with very limited juvenile input. Plate models based on sparse paleomagnetic data imply significant relative motion between India and Australia during the late Neoproterozoic–Cambrian. We suggest the new isotopic data from the Batavia Knoll granitic rocks, coupled with other regional geological constraints, are consistent with magmatic intrusion and subsequent disturbance of U-Pb systems along a late Neoproterozoic–Cambrian sinistral strike-slip margin related to Gondwana assembly.

Constraining the Orbit of the Supermassive Black Hole Binary 0402+379

Abstract The radio galaxy 0402+379 is believed to host a supermassive black hole binary (SMBHB). The two compact-core sources are separated by a projected distance of 7.3 pc, making it the most (spatially) compact resolved SMBHB known. We present new multi-frequency VLBI observations of 0402+379 at 5, 8, 15, and 22 GHz and combine them with previous observations spanning 12 years. A strong frequency-dependent core shift is evident, which we use to infer magnetic fields near the jet base. After correcting for these shifts we detect significant relative motion of the two cores at at . With some assumptions about the orbit, we use this measurement to constrain the orbital period yr and SMBHB mass . While additional observations are needed to confirm this motion and obtain a precise orbit, this is apparently the first black hole system resolved as a visual binary.

Present Velocity Field in the Italian Region by GPS Data: Geodynamic/Tectonic Implications

The analysis of geodetic observations carried out by 478 continuous GPS stations in the Italian region since 2001 has allowed a fairly good definition of the ongoing horizontal velocity field with respect to Eurasia. It is argued that such evidence can provide important insights into the geodynamic context in the central Mediterranean area. Numerous velocity vectors in the Apulia zone coherently indicate that the southern Adriatic domain is moving roughly NE ward. Since no significant decoupling zone between this domain and Nubia has so far been recognized, one could expect that the kinematics of these two plates is compatible. However, this condition is not fulfilled if the Nubia-Eurasia relative motion is taken from the global kinematic models, either deduced by long-term evidence [1] or short-term geodetic data [2] [3]. This problem is considerably reduced if the alternative Nubia-Eurasia rotation pole suggested by [4] is taken into account. This choice is also suggested by other major long-term evidence in the Mediterranean region. The numerous geodetic vectors available in two Adriatic sectors, the Apulia zone and the Venetian plain, would imply an Adria-Eurasia rotation pole incompatible with all Nubia-Eurasia Eulerian poles so far proposed. Since a significant relative motion between these plates is not compatible with the absence of a tectonic decoupling zone, we suppose that the short-term kinematics of Adria might be influenced by a transient non-rigid behaviour of that plate. This hypothesis is compatible with the expected effects (post seismic relaxation) of the major decoupling earthquakes that have occurred along Periadriatic zones in the past tens of years. The compatibility of the GPS kinematic pattern in the Apennine belt, Calabria Arc and Sicily with the implications of the geodynamic/tectonic interpretations so far proposed for the central Mediterranean area is then discussed.

Residual Post-Treatment FDG Avidity in Regional Lymph Nodes Impacts Local-Regional Control in Patients Receiving Definitive Chemoradiation for Non-small Cell Lung Cancer: A Secondary Analysis of ACRIN 6668/RTOG 0235

difficult to validate due to the lack of ground truth. This study aims to investigate a novel method, 3D Hyperpolarized Helium-3 (HP He3) tagging MRI, for evaluating lung ventilations and strains from direct measurements of lung deformation during breathing. Materials/Methods: A three-dimensional (3D) HP He-3 tagging MRI technique was developed for direct measurement of regional lung respiratory motion. Two healthy subjects were imaged under IRB-approved protocol at the end-of-inhalation (EOI) and end-of-exhalation (EOE) phases in a single scan using the HP He-3 MRI tagging technique. The 3D displacement vector field (DVF) of the lung between the EOI and EOE phases was determined by tracking the movements of the center of mass (CM) of the tagging grids in the HP He-3 MR tagging images. The strain tensor, which characterizes the 3D deformation of the grid, was computed from the relative displacements between the CM of each grid and its six nearest neighbors. Ventilations were then calculated using the principal strains (i.e., the eigenvalues of the strain tensor). Results: DVFs and volumetric maps of lung principal strains and ventilation were successfully generated for both subjects. Although Subject #1 had much larger respiratory motion amplitude than Subject #2 (5.8 0.5 cm vs. 3.6 0.5 cm), the first and second principal strains of the two subjects were found to be comparable (e1Z -0.45 0.03, e2Z -0.38 0.03, and e3Z -0.1 0.3 for Subject #1, and e1Z -0.41 0.02, e2Z -0.38 0.01, and e3Z -0.32 0.04 for Subject #2). The average ventilations in the left and the right lungs of two subjects were -73% 6% (left)/-62% 16% (right) and -72% 2% (left)/-71% 1% (right), respectively. Lung fissures were identifiable in the principal strain maps by larger values of e1 (-0.49 0.02), which results from the significant relative motions between lung lobes. Conclusions: A systematic approach was developed to generate 3D functional maps of ventilation and principal strains using HP He-3 tagging MR images obtained at different respiratory phases. This method holds great promise for revealing ground truth information about lung ventilation and strain, which may be applied to validate DIR based calculation, as well as for studying lung biomechanics. Author Disclosure: T. Cui: None. Q. Huang: None. W.G. Miller: None. X. Zhong: None. F. Yin: None. J. Cai: None.

Strain rate effects on the mechanical properties and fracture mode of skeletal muscle

The present study aimed to characterize the mechanical response of beagle sartorius muscle fibers under strain rates that increase logarithmically (0.1mm/min, 1mm/min and 10mm/min), and provide an analysis of the fracture patterns of these tissues via scanning electron microscopy (SEM). Muscle tissue from dogs' sartorius was excised and test specimens were sectioned with a lancet into sections with nominal length, width, and thickness of 7, 2.5 and 0.6mm, respectively. Trimming of the tissue was done so that the loading would be parallel to the direction of the muscle fiber. Samples were immediately tested following excision and failures were observed under the SEM. No statistically significant difference was observed in strength between the 0.1mm/min (2.560±0.37MPa) and the 1mm/min (2.702±0.55MPa) groups. However, the 10mm/min group (1.545±0.50MPa) had a statistically significant lower strength than both the 1mm/min group and the 0.1mm/min group with p<0.01 in both cases. At the 0.1mm/min rate the primary fracture mechanism was that of a shear mode failure of the endomysium with a significant relative motion between fibers. At 1mm/min this continues to be the predominant failure mode. At the 10mm/min strain rate there is a significant change in the fracture pattern relative to other strain rates, where little to no evidence of endomysial shear failure nor of significant motion between fibers was detected.

The kinematics of central-southern Turkey and northwest Syria revisited

Central-southern Turkey, NW Syria, and adjacent offshore areas in the NE Mediterranean region form the boundary zone between the Turkish, African and Arabian plates. A great deal of new information has emerged in recent years regarding senses and rates of active crustal deformation in this region, but this material has not hitherto been well integrated, so the interpretations of key localities by different teams remain contradictory. We have reviewed and synthesised this evidence, combining it with new investigations targeted at key areas of uncertainty. This work has led to the inference of previously unrecognised active faults and has clarified the roles of other structures within the framework of plate motions provided by GPS studies. Roughly one third of the relative motion between the Turkish and Arabian plates is accommodated on the Misis–Kyrenia Fault Zone, which links to the study region from the Kyrenia mountain range of northern Cyprus. Much of this motion passes NNE then eastward around the northern limit of the Amanos Mountains, as previously thought, but some of it splays northeastward to link into newly-recognised normal faulting within the Amanos Mountains. The remaining two thirds of the relative motion is accommodated along the Karasu Valley; some of this component steps leftward across the Amik Basin before passing southward onto the northern Dead Sea Fault Zone (DSFZ) but much of it continues southwestward, past the city of Antakya, then into offshore structures, ultimately linking to the subduction zone bounding the Turkish and African plates to the southwest of Cyprus. However, some of this offshore motion continues southward, west of the Syrian coast, before linking onshore into the southern DSFZ; this component of the relative motion is indeed the main reason why the slip rate on the northern DSFZ, measured geodetically, is so much lower than that on its southern counterpart. In some parts of this region, notably in the Karasu Valley, it is now clear how the expected relative plate motion has been accommodated on active faults during much of the Quaternary: rather than constant slip rates on individual faults, quite complex changes in the partitioning of this motion on timescales of hundreds of thousands of years are indicated. However, in other parts of the region it remains unclear whether additional major active faults remain unrecognised or whether significant relative motions are accommodated by distributed deformation or on the many smaller-scale structures present.

Investigation of crustal motion in Europe by analysing the European VLBI sessions

Since 1990 the International VLBI Service for Geodesy and Astrometry (IVS) has been performing geodetic Very Long Baseline Interferometry (VLBI) observations within the European geodetic VLBI network. In this work, 114 European VLBI sessions from January 1990 to September 2011 are analysed using the Vienna VLBI Software (VieVS). A total of 58 baselines with lengths ranging from 59 m to 4581 km are investigated and the lengths of most of them indicate repeatabilities at the sub-centimetre level. The horizontal station motions which describe the motion of the Eurasian plate are compared to the NUVEL-1A and MORVEL tectonic plate models. Intraplate crustal motions are investigated by estimating the station velocities with respect to Wettzell (Germany), a station on the geodynamically stable part of Eurasia. The northern part of Europe is dominated by the postglacial isostatic rebound, confirmed by four VLBI sites in this region with an uplift from 2.89±0.71 mm/yr (Svetloe, Russia) to 7.23±1.00 mm/yr (Ny-Alesund, Norway) with respect to the central part of the European plate. Besides the vertical uplift, these radio telescopes evidence a horizontal motion from the centre of the former ice sheet towards its border. In the southern part of Europe the motion of the VLBI sites is caused by the collision of the African plate with the Eurasian plate, while the stations on the stable part of Europe do not present any significant relative motions. Our results are compared against those by Haas et al. (J. Geodyn. 35:391–414, 2003) and with velocities of the current reference frame of the International Global Navigation Satellite Systems Service.

Design of High Speed Rotary Valves for Pneumatic Applications

Valves based on rotating geometry have long been sought by designers for their simplicity, compactness, and desirable dynamic properties. Unfortunately, they generally involve tight sealing surfaces with significant relative motion, making them particularly prone to problems of wear, leakage, and seizure. These inherent weaknesses are easily overcome in applications involving low pressures or low actuation speeds but become more significant in applications with high pressures and/or high speeds. In this paper, a new high speed, high pressure rotary valve design for an experimental reciprocating compressor-expander is presented. A physical prototype is created, and leakage and valving experiments are performed. Sealing performance is verified and shown to be on the order of piston ring leakage, making it suitable for compressor use. Although not intended for combustion applications, it is possible that a modified version of this design could function in that capacity. As shown, this design is useful in pneumatic applications in which temperatures are lower and oil leakage is tolerable.

HIGH RESOLUTION Hα IMAGES OF THE BINARY LOW-MASS PROPLYD LV 1 WITH THE MAGELLAN AO SYSTEM

We utilize the new Magellan adaptive optics system (MagAO) to image the binary proplyd LV 1 in the Orion Trapezium at H alpha. This is among the first AO results in visible wavelengths. The H alpha image clearly shows the ionization fronts, the interproplyd shell, and the cometary tails. Our astrometric measurements find no significant relative motion between components over ~18 yr, implying that LV 1 is a low-mass system. We also analyze Large Binocular Telescope AO observations, and find a point source which may be the embedded protostar's photosphere in the continuum. Converting the H magnitudes to mass, we show that the LV 1 binary may consist of one very-low-mass star with a likely brown dwarf secondary, or even plausibly a double brown dwarf. Finally, the magnetopause of the minor proplyd is estimated to have a radius of 110 AU, consistent with the location of the bow shock seen in H alpha.

Kinematics of landslide estimated by repeated GPS measurements in the Avcilar region of Istanbul, Turkey

The aim of this study is to analyze the spatial and temporal behavior of the landslide located in Avcilar region which is situated between Kucukcekmece and Buyukcekmece Lakes in the north-west of Marmara region, Turkey. A network consisting of 10 sites has been surveyed four times from November 2007 to May 2009 using Global Positioning System (GPS). The deformation analysis has been applied to determine the landslide movement parameters of the sites using GPS measurements of the four epochs. The reliable and high precision deformation rates are presented in terms of displacement vectors, velocity vectors and changes of accumulated strain. Landslides of the region are characterized from a regional GPS network. Each site has statistically different temporal behavior and significant relative motions and the region has irregular landslide movements.

A moving mesh algorithm for aero‐thermo‐mechanical modelling in turbomachinery

SUMMARYThis paper describes the development of a mesh deformation method used for aero‐thermo‐mechanical coupling of turbo‐engine components. The method is based on the nonlinear solution of an elastic medium analogy, solved using finite element discretisation and modified to let the boundary nodes be free to slide over the deflected surfaces. This sliding technique relies on a B‐spline reconstruction of the moving boundary and increases the robustness of the method in situations where the boundary deflection field presents significant gradients or large relative motion between two distinct boundaries. The performance of the method is illustrated with the application to an interstage cavity of a turbine assembly, subjected to the deformations computed by a coupled thermo‐mechanical analysis of the engine component. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Visualization of Relative Displacement between Skull and Brain under Occipital Impact Using a 3D Transparent Physical Head Model

A Three dimensional transparent physical model of a human head with real shape was constructed to visualize and measure relative motion between skull and brain in order to clarify the mechanism of acute subdural hematoma. The model consists of a transparent skull, brain made of silicone gel, cerebrospinal fluid to reconstruct relative motion between brain and skull, and meninges which constraints the motion. The shape was based on real-shaped three dimensional CAD data constructed from CT/MRI images of a specific individual. The results of experiments in the cases of impactor collision to the occipital skull showed that shape of impact force pulse applied to the head was not affected on peak bridging vein stretch ratios because significant relative motion between skull and brain occurred by existence of cerebro spinal fluid.

Nonlinear interactions in electrophoresis of ideally polarizable particles

In the classical analysis of electrophoresis, particle motion is a consequence of the interfacial fluid slip that arises inside the ionic charge cloud (or Debye screening layer) surrounding the particle surface when an external field is applied. Under the assumptions of thin Debye layers, weak applied fields, and zero polarizability, it can be shown that the electrophoretic velocity of a collection of particles with identical zeta potential is the same as that of an isolated particle, unchanged by interactions [L. D. Reed and F. A. Morrison, “Hydrodynamic interaction in electrophoresis,” J. Colloid Interface Sci. 54, 117 (1976)]. When some of these assumptions are relaxed, nonlinear effects may also arise and result in relative motions. First, the perturbation of the external field around the particles creates field gradients, which may result in nonzero dielectrophoretic forces due to Maxwell stresses in the fluid. In addition, if the particles are able to polarize, they can acquire a nonuniform surface charge, and the action of the field on the dipolar charge clouds surrounding them drives disturbance flows in the fluid, causing relative motions by induced-charge electrophoresis. These two nonlinear effects are analyzed in detail in the prototypical case of two equal-sized ideally polarizable spheres carrying no net charge, using accurate boundary-element simulations, along with asymptotic calculations by the method of twin multipole expansions and the method of reflections. It is found that both types of interactions result in significant relative motions and can be either attractive or repulsive depending on the configuration of the spheres.

Photometric reconstruction of a dynamic textured surface from just one color image acquisition

Textured surface analysis is essential for many applications. We present a three-dimensional recovery approach for real textured surfaces based on photometric stereo. The aim is to be able to measure the textured surfaces with a high degree of accuracy. For this, we use a color digital sensor and principles of color photometric stereo. This method uses a single color image, instead of a sequence of gray-scale images, to recover the surface of the three dimensions. It can thus be integrated into dynamic systems where there is significant relative motion between the object and the camera. To evaluate the performance of our method, we compare it on real textured surfaces to traditional photometric stereo using three images. We thus show that it is possible to have similar results with just one color image.

Primary Carboniferous and Permian paleomagnetic results from the Yili Block (NW China) and their implications on the geodynamic evolution of Chinese Tianshan Belt

In order to better understand the tectonic role of the Yili Block on the Paleozoic evolution of the Chinese Tianshan Belt, we performed a primary paleomagnetic study on Carboniferous and Permian rocks from different areas in the Yili Block, NW of China. More than 320 sedimentary and volcanic samples were collected from 39 sites. Except for the Ordovician samples showing a weak and unstable magnetic remanence, the majority of this collection presents characteristic remanent magnetization carried by magnetite and hematite. In the study area, though positive fold test has been observed on the Early Carboniferous rocks, a general re-magnetization of these rocks has been identified and attributed to the Late Carboniferous magmatism. Moreover, all Early and Late Carboniferous samples from the interior of the Yili Block yield stable and coherent magnetic directions with exhaustively reverse magnetic polarity. The Late Carboniferous (C 2) is considered as the magnetic remanence age since these rocks are covered or intruded by synchronous magmatic rocks of the Yili arc, which lasted until to ∼ 310 Ma. The C 2 paleomagnetic pole is therefore calculated at 68.6°N, 290.6°E with A 95 = 6.4° and n = 15. The Late Carboniferous rocks located close to a deformation zone present a consistent magnetic inclination but significant different declination with respect to other areas and are suspected to have probably experienced a local rotation. Although no fold test can be performed due to the monoclinal bedding, stable magnetic components are isolated from Late Permian (P 2) red beds in the interior of the Yili Block with also a solo reverse magnetic polarity, the P 2 paleomagnetic pole of the Yili Block has been, therefore, calculated from the characteristic remanent magnetization: 79.7°N, 172.0°E with A 95 = 11.3° and n = 5. Keeping important uncertainties in mind, comparisons of the C 2 and P 2 paleomagnetic poles of the Yili Block with available coeval poles of Junggar, Tarim and Siberia indicate (1) no significant relative motion between the Yili and Junggar blocks since the Late Carboniferous, (2) no significant or weak latitudinal relative motion occurred since the Late Carboniferous among these blocks, but (3) the 46.2° ± 15.1° and the 31.6° ± 15.1° counterclockwise rotations of the Yili–Junggar blocks with respect to Tarim and Siberia took place during C 2 to P 2. These rotations are accommodated by the Permian dextral strike–slip faults along the northern and southern sides of Tianshan Belt and sinistral strike–slip faulting along the Erqishi Fault of Altay Belt, resulting in about 1000 km and 600 km lateral displacements in the Tianshan and Altay belts, respectively.

Toward a self‐consistent, high‐resolution absolute plate motion model for the Pacific

The hot spot hypothesis postulates that linear volcanic trails form as lithospheric plates move relative to stationary or slowly moving plumes. Given geometry and ages from several trails, one can reconstruct absolute plate motions (APM) that provide valuable information about past and present tectonism, paleogeography, and volcanism. Most APM models have been designed by fitting small circles to coeval volcanic chain segments and determining stage rotation poles, opening angles, and time intervals. Unlike relative plate motion (RPM) models, such APM models suffer from oversimplicity, self‐inconsistencies, inadequate fits to data, and lack of rigorous uncertainty estimates; in addition, they work only for fixed hot spots. Newer methods are now available that overcome many of these limitations. We present a technique that provides high‐resolution APM models derived from stationary or moving hot spots (given prescribed paths). The simplest model assumes stationary hot spots, and an example of such a model is presented. Observations of geometry and chronology on the Pacific plate appear well explained by this type of model. Because it is a one‐plate model, it does not discriminate between hot spot drift or true polar wander as explanations for inferred paleolatitudes from the Emperor chain. Whether there was significant relative motion within the hot spots under the Pacific plate during the last ∼70 m.y. is difficult to quantify, given the paucity and geological uncertainty of age determinations. Evidence in support of plume drift appears limited to the period before the 47 Ma Hawaii‐Emperor Bend and, apart from the direct paleolatitude determinations, may have been somewhat exaggerated.

IRAS 16293−2422: Proper Motions, Jet Precession, the Hot Core, and the Unambiguous Detection of Infall

We present high spatial resolution observations of the multiple protostellar system IRAS 16293-2422 using the Submillimeter Array (SMA) at 300 GHz and the Very Large Array (VLA) at frequencies from 1.5 to 43 GHz. This source was already known to be a binary system with its main components, A and B, separated by ~5''. The new SMA data now separate source A into two submillimeter continuum components, which we denote Aa and Ab. The strongest of these, Aa, peaks between the centimeter radio sources A1 and A2, but the resolution of the current submillimeter data is insufficient to distinguish whether this is a separate source or the centroid of submillimeter dust emission associated with A1 and A2. Archival VLA data spanning 18 yr show proper motion of sources A and B of 17 mas yr-1, associated with the motion of the ? Ophiuchi cloud. We also find, however, significant relative motion between the centimeter sources A1 and A2, which excludes the possibility that these two sources are gravitationally bound unless A1 is in a highly eccentric orbit and is observed at periastron, the probability of which is low. A2 remains stationary relative to source B, and we identify it as the protostar that drives the large-scale northeast-southwest CO outflow. A1 is shock-ionized gas that traces the location of the interaction between a precessing jet and nearby dense gas. This jet probably drives the large-scale east-west outflow, and indeed its motion is consistent with the wide opening angle of this flow. The origin of this jet must be located close to A2 and may be the submillimeter continuum source Aa. Thus, source A is now shown to comprise three (proto)stellar components within 1''. Source B, on the other hand, is single, exhibits optically thick dust emission even at 8 GHz, has a high luminosity, and yet shows no sign of outflow. It is probably very young and may not even have begun a phase of mass loss yet. The SMA spectrum of IRAS 16293-2422 reports the first astronomical identification of many lines of organic and other molecules at 300 and 310 GHz. The species detected are typical of hot cores, the emission from which is mainly associated with source A. The abundances of second-generation species, especially of sulphur-bearing molecules, are significantly higher than predicted by chemical models for this source to date, and we suggest that shocks are probably needed to explain these enhancements. The peaks in the integrated emission from molecules having high rotation temperatures coincide with the centimeter source A1, also highlighting the key role of shocks in explaining the nature of hot cores. Finally, we use the high brightness temperature of the submillimeter dust emission from source B to demonstrate the unambiguous detection of infall by observing redshifted SO (77-66) absorption against the emission from its dust disk.