Section Of Arc Research Articles

150 GHz NOBA Observations of the Galactic Center Arc

We have used the seven-beam 150 GHz bolometer NOBA installed at the Nobeyama 45-m telescope to map the central section of the Galactic Center Arc. In addition, we mapped Sgr A, which shows Sgr A* and the thermal spiral structure. The results agree with previous mm-observations. South of the thermal “sickle” feature (G0.18-0.04) we observed three regions of enhanced emission along the Arc, which are located slightly offset relative to the most intense vertical filaments seen at low frequencies. This 150 GHz emission is observed at the apparent interacting areas of dense molecular material with the Arc. Another structure is seen south of the molecular cloud, where the Arc's vertical filaments apparently cross a weak filamentary structure running orthogonally in the direction of Sgr A. The 150 GHz results are unexpected in view of previous 32 GHz and 43 GHz results, which indicate a fading of the Arc towards higher frequencies. Cold dust can be ruled out as the origin of the 150 GHz emission. Synchrotron emission from quasi-monoenergetic electrons or an electron distribution with a low-energy cut-off seems to be compatible with the available data. The coincidence of enhanced emission with regions of interacting molecular gas strongly suggests that high-energy electrons are accelerated in those places where the magnetic field is compressed, and subsequently enter and illuminate the Arc.

Alteration and mineralization of an oceanic forearc and the ophiolite‐ocean crust analogy

Mineralogical, chemical, and isotopic (O, C, S, and Sr) analyses were performed on minerals and bulk rocks from a forearc basement section to understand alteration processes and compare with mid‐ocean ridges (MOR) and ophiolites. Ocean Drilling Program Hole 786B in the Izu‐Bonin forearc penetrates 103 m of sediment and 725 m into volcanic flows, breccias, and basal dikes. The rocks comprise boninites and andesites to rhyolites. Most of the section was affected by low‐temperature (<100°C) seawater alteration, with temperatures increasing downward. The rocks are partly (5–25%) altered to smectite, Fe‐oxyhydroxide, calcite, and phillipsite, and exhibit gains of K, Rb, and P, loss of Ca, variable changes in Si, Na, Mg, Fe, Sr, and Y, and elevated δ18O and 87Sr/86Sr. Higher temperatures (∼150°C) in the basal dikes below 750 m led to more intense alteration and formation of chlorite‐smectite, corrensite, albite, K‐feldspar, and quartz (±chlorite). A 5 m thick hydrothermally altered and pyritized zone at 815 m in the basal dikes reacted with mixtures of seawater and hydrothermal fluids to Mg‐chlorite, albite, and pyrite, and gained Mg and S and lost Si and Ca. Focused flow of hydrothermal fluids produced serialization halos (Na‐K sericite, quartz, pyrophyllite, K‐feldspar, and pyrite) along quartz veins at temperatures of 200°–250°C. High 87Sr/86Sr ratios of chloritized (∼0.7055) and sericitized (∼0.7065) rocks indicate involvement of seawater via mixing with hydrothermal fluids. Low δ34S of sulfide (−2 to −5.5‰) and sulfate (12.5‰) are consistent with input of magmatic SO2 into hydrothermal fluids and disproportionation to sulfide and sulfate. Alteration processes were generally similar to those at MORs, but the arc section is more intensively altered, in part because of the presence of abundant glassy rocks and mafic phases. The increase in alteration grade below 750 m and the mineralization in the basal dikes are analogous to changes that occur near the base of the volcanic section in MOR and the Troodos ophiolite.

Crustal assimilation versus subducted sediment input in west Sunda arc volcanics: An evaluation

New geochemical and Sr, Nd, and Pb isotopic analyses of Quaternary to Cretaceous sediments from the northeastern Indian Ocean are used to estimate the composition of the sedimentary material subducted along the Sunda Trench, and to evaluate the effects of crustal contamination versus subducted sediment input in the Quaternary volcanics of the west Sunda arc. Two sediment endmember components are identified: siliceousclastic (SS) and calcareous-organogenic (CS); the latter can be regarded as SS strongly diluted by organogenic material, mainly CaCO3. Siliceous-clastic sediments are characterised by a component isotopically and geochemically similar to “typical” average upper crust. Consequently, LILE and LREE concentrations, LILE/LILE and LILE/LREE values, and Sr, Nd, and Pb isotopic ratios in West Sunda arc volcanics cannot easily distinguish between assimilation of crustal material by uprising magmas and contamination of their mantle source by bulk sediments. Post-Miocene siliceousclastic sediments sampled in the vicinity of the Sunda arc are largely derived from the arc itself, and therefore should not be used to evaluate the extent of sediment contamination of Indonesian arc volcanics. In addition, geophysical evidence suggests that post-Miocene sediments are largely accreted rather than subducted, and existing10Be isotopic data imply that post-Miocene sediments are not recycled by present-day volcanism. As the least contaminated arc volcanics occur in the eastern section of the west Sunda arc, where the highest sediment fluxes have been calculated, subduction of pre-Miocene northeastern Indian Ocean sediments or incorporation of fluids released from them into the sources of west Sunda are volcanics seem unable to reproduce the range and spatial distribution of Sr, Nd, and Pb isotopic values in the arc volcanics. By contrast, assimilation of crustal material by uprising melts derived from Indian Ocean-type mantle wedge, up to a maximum of approximately 10% for the most contaminated arc volcanics, seems better able to account for the Sr, Nd, and Pb isotope systematics of the arc volcanics, and is consistent with the variations in crustal thickness and composition along the arc, and with the spatial distribution of Sr, Nd, and Ph isotope values in mafic arc volcanics. These conclusions are also supported by the low10Be coupled with high B/Be values, and by the positive B/Be-SiO2 and B/Be-87Sr/86Sr correlations in calc-alkaline Sunda arc volcanics.

Abnormal Audiograms and Elevated Acoustic Reflex Thresholds in Obligate Carriers of Autosomal Recessive Non-Syndromic Hearing Loss

Cohen M, Francis M, Coffey R, Pembrey ME, Luxon LM. Abnormal audiograms and elevated acoustic reflex thresholds in obligate carriers of autosomal recessive non-syndromic hearing loss. Acta Otolaryngol (Stockh) 1997; 117: 337-342.Pure-tone audiograms and acoustic reflex thresholds were obtained in 24 presumed obligate carriers of autosomal recessive non-syndromic hearing loss and 30 sex and age appropriate control subjects, with a view to evaluating the prevalence of abnormalities on these tests in the two groups, and a possible link between the findings on the two tests, which may help to localize threshold deficits and/or abnormal configurations to different sections of the reflex arc. Six (25%) of the carriers and one control subject had abnormal audiograms, inferred to be of genetic aetiology through careful exclusion of environmental risk factors. Four additional carriers had acoustic reflex threshold abnormalities. None of the carriers had an abnormality on both tests. The audiometric configurations and acoustic reflex patterns of abnormality were diverse, and may be a reflection of the genetic heterogeneity in ARNSHL.

Control of field uniformity for a large superconducting storage ring magnet

A 1.45 Tesla, 14.2 meter diameter "superferric" magnet is in an advanced stage of construction at Brookhaven National Laboratory. This magnet will be used to store muons for a planned ultra-precise measurement of their anomalous magnetic moment g-2. This measurement requires a magnetic field uniformity of 1 PPM with a knowledge of the field over the muon orbits to 0.1 PPM. The methods built into the design to produce ultra-high field uniformity are described. Large deviations from the ideal circularly symmetric uniform shape of the iron flux path are required to accommodate transfer lines and superconducting current leads, as well as apparatus for beam injection. Shimming methods to correct for the perturbations due to these large holes are presented. The pole pieces consist of 36 closely fitting 10/spl deg/ arc sections butted together to produce a very good approximation to a continuous 360/spl deg/ ring magnet. However, in the case of a possible quench of the superconducting coils, significant eddy currents will be induced which will circulate within the confines of each 10/spl deg/ pole piece. At the great precision required, these eddy currents may leave very small but significant aberrations in the field even after they decay away, because of slight changes in the orientation of the magnetization. Surface coil possibilities to correct for this effect are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Calculations of the radiation doses to the electronic equipment and magnet coil insulation in the PEP-II tunnel

The PEP-II collaboration is a new physics project at SLAC that utilizes an existing tunnel to house two accelerator storage rings; a low-energy positron ring (4 GeV, called the LER) atop a high-energy electron ring (10 GeV, called the HER). Both rings are being designed to permit a high circulating current of 3 A, corresponding to a beam particle number of 1.38 × 10 14. Dose calculations were made to estimate the potential for radiation damages to the electronics and magnet coil insulation in the arc section of the tunnel. An analytical code, SHIELD11, was used to calculate the dose from photon and neutron radiations resulting from beam losses in various modes of operation. Several EGS4 Monte Carlo user codes were developed to calculate the dose from the synchrotron radiation escaping the vacuum chamber in stored beam mode. Two different LER vacuum chamber designs were studied: a 0.35-cm-thick copper wall chamber and a 1-cm-thick aluminum wall chamber with a copper absorber 6 m downstream of every dipole to absorb the synchrotron radiation in a local spot. The HER has a 0.5-cm-thick copper vacuum chamber. Shielding from the 5.4-m-long, C-shaped iron bending magnet for the HER was considered for the beam radiation, while no other structural shielding was assumed for the LER. Furthermore, the dose from all radiations scattering back from the tunnel concrete wall were also estimated using the albedo method or the MORSE code. The results of the dose estimations are presented.

Software architecture of the SSC accelerator systems string test

The software architecture is described for the data acquisition and control systems implemented to support a full cell test of collider arc section lattice components. The discussion is divided into descriptions of the software applications for process controls, operator interfaces, and data acquisition, archiving, and analysis. Specifics are presented for the distributed implementation of the acquisition, archiving, and analysis services, and their integration with a commercial Relational Database Management System (RDBMS). The relational table structure used in the RDBMS is explained. Finally, system performance, lessons learned, and future plans are summarized.

Tectonic evolution of lower crustal rocks in an exposed magmatic arc section in the Hidaka metamorphic belt, Hokkaido, northern Japan

Abstract : The Hidaka metamorphic belt consists of an island‐arc assembly of lower to upper crustal rocks formed during early to middle Paleogene time and exhumed during middle Paleogene to Miocene time. The tectonic evolution of the belt is divided into four stages, D0rs, D1, D2rs, and D3, based on their characteristic deformation, metamorphism, and igneous activity. The premetamorphic and igneous stage (D0) involves tectonic thickening of an uppermost Cretaceous and earliest Tertiary accretionary complex, including oceanic materials in the lower part of the complex. D1 is the stage of prograde metamorphism with increasing temperatures at a constant pressure during an early phase, and with a slight decrease of pressure at the peak metamorphic phase, accompanying flattening of metamorphic rocks and intrusions of mafic to intermediate igneous rocks. At the peak, incipient partial melting of pelitic and psammitic gneisses took place in the amphibolite–granulite facies transition zone, the melt and residuals cutting the foliations formed by flattening. In the deep crust, large amounts of S‐type tonalite magma formed by crustal anatexis, intruded into the granulite facies gneiss zone and also into the upper levels of the metamorphic sequence during the subsequent stage. During D1 stage, mafic and intermediate magmas supplied and transported heat to form the arc‐type crust and at the same time, the magmatic underplating caused extensional doming of the crust, giving rise to flattening and vertical uplifting of the crustal rocks. D2 stage is characterized by subhorizontal top‐to‐the‐south displacement and thrusting of lower to upper crustal rocks, forming a basal detachment surface (décollement) and duplex structures associated with intrusions of S‐type tonalite. Deformation structures and textures of high‐temperature mylonites formed along the décollement, as well as the duplex structures, show that the D2 stage movement occurred under a N‐S trending compressional tectonic regime. The depth of intra‐crustal décollement in the Hidaka belt was defined by the effect of multiplication of two factors, the fraction of partial melt which increases downward, and the fluid flux which decreases downward. The crustal décollement, however, might have extended to the crust‐mantle boundary and/or to the lithosphere and asthenosphere boundary. The subhorizontal movement was transitional to a dextral‐reverse‐slip (dextral transpression) movement accompanied by low‐temperature mylonitization with retrograde metamorphism, the stage defined as D3. The crustal rocks from the basal décollement to the upper were tilted eastward on the N–S axis and exhumed during the D3 stage. During D2 and D3 stages, the intrusion of crustal acidic magmas enhanced the crustal deformation and exhumation in the compressional and subsequent transpressional tectonic regime.

Status of superconducting magnets for the Superconducting Super Collider

The arc sections of the High Energy Booster and the two Collider Rings will need more than 10,000, very large, superconducting dipole and quadrupole magnets. Development work on these magnets was carried out at US/DOE laboratories in a program that began in the mid 1980's. In 1991-95 the technology was transferred to industry and twenty, full-length, Collider dipoles were successfully fabricated and tested. This program, along with HERA and Tevatron experience, has provided industry a data base to use in formulating detailed designs for the prototypes of the accelerator magnets, with an eye to reducing cost and enhancing producibility. Several model magnets from this latest phase of the industrial program have already been tested. The excessive ramp-rate sensitivity of the magnets is understood and solutions are under investigation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Petrochemistry and tectonic significance of Cretaceous island-arc rocks, Cordillera Oriental, Dominican Republic

Cretaceous island-arc rocks of the Caribbean island-arc system have been exposed by Cenozoic faulting in the Cordillera Oriental in eastern Hispaniola. High-K 2O intermediate to felsic volcanic rocks (Loma la Vega volcanics) are interbedded with marine epiclastic sedimentary rocks and tuffs (Las Guajabas tuffs) and unconformably overlie pre-Aptian sedimentary rocks, low-K 2O volcanic rocks (Guamira volcanics) and a granodioritic to tonalitic intrusion (El Valle pluton). The petrology and geochemistry of these units, in conjunction with regional stratigraphic data, are used to speculate on the tectonics of the newly developing Caribbean island-arc system during Early and Late Cretaceous time. The Loma la Vega volcanics are characterized by the presence of large phenocrysts of sanidine, and minor amounts of clinopyroxene, opaque oxides, and rare leucite in a devitrified matrix of chlorite and clay. Although the volcanic rocks have undergone some low-temperature alteration/ metamorphism, which redistributed some major elements and large-ion-litho-phile trace elements, the high-field-strength elements, rare-earth elements, and radiogenic isotopes appear to have been minimally affected. Based on abundances of the relatively immobile elements, trace-element enrichment patterns and isotopic compositions, the Loma la Vega volcanics are considered part of the high-K, calc-alkaline (CA) or shoshonitic island-arc volcanic series. In contrast, pre-Aptian (Early Cretaceous?) volcanic and plutonic rocks of the underlying Los Ranchos Formation have chemical characteristics similar to rocks in the island-arc tholeiitic or “primitive island-arc” (PIA) series that form coeval and along-strike sections of the Early Cretaceous Caribbean island arc in other parts of present-day Hispaniola, Cuba, Puerto Rico and the Virgin Islands. An abrupt and regional change in composition from island-arc tholeiites to high-K, calc-alkaline rocks is coincident with a hypothesized reversal in subduction polarity in pre-Aptian time. As inferred from previously published tectonic models, polarity reversal may have been triggered by attempted subduction of the Caribbean oceanic plateau beneath this segment of the Caribbean island arc. The observed magmatic and tectonic effects of the proposed Cretaceous Caribbean arc reversal are similar to the better documented Neogene subduction reversal event in the Solomon Islands arc in the southwest Pacific.

The tectonostratigraphy and structure of the eastern Nepal Himalaya

Six years of geological research in eastern Nepal has resulted in a new geological map of the eastern Nepal Himalaya which includes the region stretching from the Sikkhim border in the east to the Kathmandu Valley in the west, and from the summits of the Higher Himalaya in the north to the Ganges Plain in the south. This research has permitted the determination of the tectonostratigraphy and structure of one section of the central Himalayan arc. South of the Tibetan Plateau the eastern Nepal Himalaya can be divided into three distinct, thrust‐bound tectonic packages: (1) the Higher Himalayan thrust sheet composed of the Higher Himalayan Crystallines, (2) the Lesser Himalayan thrust sheet composed of the Lesser Himalayan Series, and (3) the Sub‐Himalayan imbricate zone composed of sedimentary rocks belonging to the Siwalik Group. The Higher Himalayan thrust sheet of eastern Nepal has been thrust over the Lesser Himalayan Metasediments a minimum of 140 km, and possibly as much as 175–210 km, along the Main Central Thrust (MCT). The Lesser Himalayan thrust sheet is overlain by the MCT and is underlain by the Main Detachment Fault (MDF) and the Main Boundary Thrust (MBT). Out‐of‐sequence thrust faults in the hanging wall of the MBT have breached and offset the presently inactive MCT. The Sub‐Himalayan imbricate zone is an emergent imbricate fan bounded by the MBT to the north and the Main Frontal Thrust (MFT) to the south and is underlain by the MDF which lies at a depth of between 5 km and 7 km. A balanced cross section constructed across the Higher, Lesser, and Sub‐Himalaya of eastern Nepal shows that the eastern Nepal Himalayan orogenic wedge has undergone a minimum of between 210 and 280 km of horizontal, north‐south tectonic shortening since the initiation of the MCT. The Lesser and Sub‐Himalaya have absorbed 70 km of north‐south shortening by thrusting along the basal MDF, of which the Sub‐Himalayan imbricate zone has accommodated 25 km, the Sun Kosi Thrust has accommodated about 10 km, and the MBT has accommodated the remaining 35 km of shortening. Since the initiation of the MCT between 15 Ma and 25 Ma shortening across the eastern Nepal Himalaya has occurred at an average rate of 8.4–18.6 mm per year. The structural geometry of the eastern Nepal Himalaya suggests an overall “piggyback” sequence of thrusting, with motion transferred from the MCT to the underlying MDF and its emergent splay thrust, the MBT, and with the MBT rotated to its present steep orientation by imbricate thrusting within the Sub‐Himalaya.

Rates and patterns of groundwater flow in the Cascade Range Volcanic Arc, and the effect on subsurface temperatures

The central Oregon section of the Cascade Range volcanic arc is characterized by relatively high Quaternary volcanic extrusion rates and hot‐spring discharge rates, and by high conductive heat flow. However, a large area of near‐ zero near‐surface conductive heat flow occurs in the younger volcanic rocks, due to downward and lateral flow of cold groundwater. Alternate models for the high heat flow observed in older rocks on the flanks of the Cascade Range involve (1) a laterally extensive midcrustal heat source or (2) a narrower, spottier deep heat source that is confined to the Quaternary arc and is flanked by relatively shallow conductive heat flow anomalies caused by regional groundwater flow. We simulated groundwater flow and heat transport through two cross sections west of the Cascade Range crest: one in the Breitenbush area, where there is no major arc‐parallel normal faulting, and one in the McKenzie River drainage, where major graben‐bounding faults exist. Measured temperature profiles, hot‐spring discharge rates, and geochemical inferences constrain the results. The numerical simulations provide some estimates of regional‐scale permeabilities; simulated bulk permeabilities of ∼10−14 m2 in the youngest (0–2.3 Ma) rocks and ∼10−17 m2 in the oldest (18–25 Ma) rocks allow the thermal observations to be matched. In general, permeability decreases downsection, but for rocks of any age, permeability at very shallow (&lt;50 m) depths is probably much higher than the bulk permeability values required by the thermal observations: this is indicated by high recharge rates in 0–7 Ma rocks (&gt;1 m yr−1) and well‐test data from domestic wells in rocks older than 7 Ma (which indicate permeability values of about 10−14 to 10−12 m2). In the simulations, the alternate conceptual models for the deep thermal structure were represented as wide or localized deep heat sources. We found that either model can satisfy the observations. Thermal observations in the Breitenbush area seem to require significant advective heat transfer, whereas the sparser observations in the McKenzie River area can be satisfied with either advection‐ or conduction‐dominated simulations. Available regional gravity, magnetic, and electrical geophysical data do not clearly favor either of the two alternate models. Deep drilling in areas of high heat flow in the older rocks would be the most definitive test. The actual thermal structure is probably more complex than either of the models considered here.

A crustal section of an intra-oceanic island arc: The Late Jurassic-Early Cretaceous Guanajuato magmatic sequence, central Mexico

The Late Jurassic-Early Cretaceous Alisitos-Teloloapan intra-oceanic arc, which extends along the Pacific coast of Mexico, is overlain by the extensive thick calc-alkaline Tertiary volcanics of the Sierra Madre Occidental. In central-southern Mexico this arc can be divided in to two major units. Its base, which is mainly exposed in the Guanajuato-Leon area, consists of a volcano-plutonic assemblage refered to as the Guanajuato magmatic sequence. The top consists of pillowed calc-alkaline basalts and andesites overlain and/or interbedded with a thick volcaniclastic sedimentary pile in which lenses of reworked Albian-Aptian reefal limestones are interlayered. The Guanajuato magmatic sequence represents the crustal section of an intra-oceanic nascent island arc and from top to base is made up of: (1) volcaniclastic sedimentary cover, (2) a predominantly pillowed basaltic sequence, (3) a doleritic and basaltic dyke complex, (4) silicic plutonic rocks and salite diorite, (5) Mg-hornblende diorite, (6) layered cumulate gabbros and, (7) ultramafic-mafic cumulates. Plutonic rocks of intermediate to silicic composition are volumetrically abundant. All the rocks have suffered low-grade metamorphism with magmatic textures preserved. Metamorphic textures do not occur. Mg-rich olivine is restricted to the ultramafic cumulates, whereas Ca-rich clinopyroxene is present in all the rock types, although with the exception of the most differentiated silica rich plutonic rocks. The textural relationships and mineral chemistry of the clinopyroxenes and hornblende in the ultramafic cumulates and in the clinopyroxene gabbros point to an origin by igneous accumulation from a tholeiitic parent magma at shallow levels above the mantle-crust boundary. Al-rich basalts and dolerites belong to a low-K tholeiitic suite. The Nb contents, which are abnormaly high for arc tholeiites, are in the range of N-MORB. Such enrichments have been related to an immature stage of the arc development, the mantle wedge being still enriched. This is in agreement with the evidence that the Guanajuato tholeiitic magma represents the earliest products of the Alisitos-Teloloapan arc magmatic activity. The Guanajuato basic rocks and hornblende diorite show similar high ε Nd ratios which fall in the range of the values of oceanic arcs. The most siliceous plutonic rocks differ from the basic suite by virtue of their slightly lower ε Nd and higher ε Sr ratios, which may be explained by an assimilation-fractional crystallization (AFC) process. The siliceous melts differentiated by crystal fractionation from the tholeiitic mantle magma and assimilated material such as metamorphosed oceanic crust and sediments, which form the wall rocks of the magma chamber. The high ε Sr ratios of the basalts and their feeder dykes are probably related to the polyphase low-grade metamorphism (i.e. hydrothermal oceanic alteration and regional metamorphism) that has affected the uppermost levels of the arc.

Generation and metamorphism of new crust in magmatic arcs: a case study from northern Chile

In a deep section of the Jurassic Andean arc, coastal Cordillera of northern Chile, south of Antofagasta, basic magmas from a mantle source accreted large masses of crust in an early stage of arc development. These gabbroic intrusions were isochemically metamorphosed at moderate pressures (≤ 5 kbar) and high temperatures (∼ 800°C) into uniform garnet-absent dino+ortho-pyroxene gneisses (granulites). Subsequently they were partly transformed into amphibolites (T≤ 700°C) during tectonically controlled access of fluid without major changes in whole rock chemistry. Locally migmatization occurs in the amphibolites. The metamorphic unit was diversified by enduring magmatic activity in the form of chemically distinct gabbroic and quartz dioritic intrusions. Formation and composition of continental crust might be a typical example for the deeper plutonic sections of this continental magmatic arc.

Initial Postcritical Behavior of Thin‐Walled Angle Section Columns

This work deals with the overall flexural instability of an angle section column under axial load, taking into account deformations of the cross section as buckling occurs. A nonlinear differential formulation with two variables is considered. The perturbation method is used to follow the initial postbuckling behavior from the bifurcation point. Deformations of the cross section do not modify the Euler critical load, but they may significantly affect the nature of the postcritical path. Unlike the well-known behavior of columns with solid cross sections, the angle section may exhibit unstable postbuckling deformations typical of the light-gauge sections, as reported in previous studies on thin circular arc sections.

Generalisierte nozifensive Reflexe - I. Methodische Grundlagen

Normal protective and defence reflexes show that the nocifensive system ist intact. Nocifensive reflexes can be modified by various brainstem disturbances, and in the case of lesions the symptoms may appear in the afferent or efferent section of the reflex arc.

Analysis of lubrication characteristics in oil hydraulic vane tip contacts.

The elastohydrodynamic lubrication characteristics of an oil hydraulic vane tip contact with a cam ring have been analyzed numerically under various conditions using a modified Houpert-Hamrock's calculation method provided in the previous paper. Results show that the minimum film thickness in the suction port section is differs little from that in the small arc section and the minimum film thickness in the large arc section is greater than that in the small arc section. Nevertheless the contact load in the suction port section is 2.5 times that in the small arc section for the case of an intravane type and the load in the large arc section is greater than that in the small arc section. The combination of inlet pressure and nonlinear piezoviscous effect causes the increase in oil film thickness in the large arc section. Therefore, it is suggested that the elevating discharge pressure will not cause any lubrication trouble if mineral oil is used as the hydraulic fluid ; the water-based hydraulic fluids present an extreme disadvantage to the vane tip lubrication.

Lubrication modes between vane tip and camring in oil hydraulic vane pumps.

The lubrication modes of line contacts between vane and camring in oil hydraulic vane pumps with and without intravanes have been investigated. First, the variations of the radial acting force of a vane were calculated on the basis of the results measured for the dynamic internal pressure in the four chambers surrounding a vane in addition to the results in the previous paper(4). Next, distinctions of the lubrication modes were made with Hooke's chart which represents an improve-ment over Johnson's. Finally, the influence of the boundary conditions in the lubrication region on the fluid film lubrication was examined by calculating the film pressure distributions. The results show that the high-frequency pressure ripple acts as the force causing separation of vanes from the camring, that the lubrication mode of the vane tip is the rigid-variable-viscosity region, and that discharge pressure higher than 7 MPa exerts a great influence on the oil film pressure in the large arc section because of the Piezo-viscous effect.

Le Complexe d'Ascot des Appalaches du sud du Québec: pétrologie et géochimie

This paper reviews new geochemical data obtained from Ordovician volcanics in the Ascot Complex of the Quebec Appalachians. The Ascot Complex is divided into three distinctive lithotectonic assemblages: the Sherbrooke, Eustis, and Stokes domains. The Sherbrooke Domain includes basalts, pyroclastic breccias, and felsic tuffs. The Eustis Domain is composed of volcanoclastic and pyroclastic rocks. The Stokes Domain is an assemblage of rhyolitic tuffs and basalts. The geochemical composition of the volcanics varies between basaltic and rhyolitic end members. Basaltic rocks are arc tholeiites (La/Yb = 0.5–2). Some basalts found in the Sherbrooke Domain show a composition very close to that of frontal-arc boninites (La/Yb = 1–2) and are depleted of rare-earth elements. Felsic rocks from the Sherbrooke Domain are poorer in light rare-earth elements (La/Yb = 0.5–0.7) than those from the Stokes Domain (La/Yb &gt; 2). All of the felsic rocks are characterized by a negative Eu anomaly (Eu*/Eu = 1.3–3). The Stokes felsites are derived from an enriched magma contaminated by a continental crust component. The Sherbrooke Domain felsites are derived from a source impoverished in incompatible elements and enriched in high-partition-coefficient elements. Volcanic rocks from Sherbrooke and Eustis are thought to represent an incipient intra-oceanic arc. The rocks of the Stokes assemblage represent a more mature section of the same arc, explaining the contamination of generated magmas by continental crust components. The modern architecture of the Ascot Complex is essentially tectonic and may not correspond to the initial internal structure of this Ordovician arc. [Journal Translation]

A helium isotope transect along the Indonesian archipelago

HELIUM isotope studies1,2 have identified the Banda arc section of the Indonesian archipelago as the only circum-Pacific volcanic arc with 3He/4He ratios significantly lower than the common ratio in mid-ocean-ridge basalts (MORB). In eleven of twelve circum-Pacific arcs, MORB-like 3He/4He ratios show that helium in these volcanic terrains is dominantly primordial helium from the mantle wedge above the sinking slab, rather than radiogenic helium from subducting oceanic crust or sediments. Only in the Banda arc have significantly lower ratios been observed, corresponding to as much as 80% radiogenic helium from subducting continental material2. We now report 3He/4He measurements along a 1,800-km section of the Sunda arc, a region of underthrust oceanic lithosphere, showing MORB-like ratios from western Java to a surprisingly sharp transition zone centred on Lomblen Island, where the low ratios of the Banda arc begin. Our results confirm the prediction2 that Sunda arc volcanoes should have MORB-like 3He/4He ratios, with a well-defined transition to the much lower Banda arc ratios near Lewotolo volcano, and demonstrate a remarkable linkage of helium isotope variations with tectonic processes not readily discernible with trace elements or other isotopes.