The Injection, Acceleration, and Dynamical Influence of Interstellar Pickup Ions at the Solar Wind Termination Shock

The interaction of interstellar pickup ions with the solar wind termination shock is reviewed and assessed. The pickup ions mass and momentum load the wind and increase its pressure, effects which decrease the strength of the shock and its distance from the Sun. The pickup hydrogen may contribute substantially to the "reflected" ion population, which should provide most of the dissipation at the supercritical quasi-perpendicular shock. A fraction of the pickup ions impinging on the shock is "injected" into the process of diffusive shock acceleration to form the anomalous cosmic ray component. An injection mechanism which accounts for the apparent absence of solar wind ions in the anomalous component is "shock surfing", in which pickup ions which approach the shock slowly may be trapped between the upstream Lorentz force and the shock potential and accelerated in the motional electric field beyond the energy threshold for diffusive shock acceleration. However, the simplest interpretation of shock surfing would favor less massive pickup ion species, in contradiction with Voyager observations of anomalous component composition. A possible extension of the shock surfing mechanism is considered, as well as other injection mechanisms. Finally, the pressure of the anomalous component may modify the structure of the termination shock, which in turn may influence injection rates. This revised version was published online in July 2006 with corrections to the Cover Date.     

The stellar content of a spiral arm of NGC 4321

The effects of the passage of a spiral arm through the disc of the giant Virgo Sc galaxy NGC 4321 are investigated with Hubble Space Telescope WFPC2 images in two colours. Concentrating on a portion of the southern spiral arm of NGC 4321, we have applied a new program to solve for the star formation histories in the arm and interarm regions separately. The observational uncertainties and the variable crowding across the spiral arm are taken into account using the results of artificial star tests. In the interarm regions the data are consistent with a constant star formation rate for the last 50 Myr while the stars in the arm region show a star formation rate four times larger than in the interarm regions in the last 5 Myr.     

Light curves of SN 1998A and comparison with similar unusual SNe

Following the proposal by Damineli that the central object of Eta Carinae may be an early-type binary, we perform numerical simulations of the X-ray emission from colliding stellar winds. A synthetic light curve has been generated which qualitatively agrees with the recent X-ray variability, and provides further support for the binary model. In particular, the model predicts a rise in the observed X-ray emission towards periastron, followed by a sharp drop and subsequent recovery. This is indeed what is seen in the RXTE light curve, although some problems concerning the X-ray spectrum at periastron still need to be explained. The simulations suggest that the width of the periastron dip will provide strong constraints on the binary and stellar wind properties of the components of Eta Car.     

The restricted stability of osumilite under hydrous conditions in the system K2O-MgO–Al2O3–SiO2–H2O

Osumilite_ss was synthesized as a single phase product in the model system K₂O-MgO-Al₂O₃-SiO₂ at 800° C/ 0.5 Kbar water pressure and at 800° to 840° C/1.0 Kbar total pressure with 0.3 in the gas phase. The experimentally determined solid solubility range of synthetic osumilites can be expressed by the formula KMg₂(Al_3-xMg_x) (Al_2–xSi_10+x)O₃₀ with 0x0.4. A survey of sixteen chemical analyses of natural osumilites from eleven occurrences shows a solid solubility characterized by 0x0.6. Reversed stability experiments for the synthetic osumilite KMg₂(Al_2.75Mg_0.25)(Al_1.75Si_10.25)O₃₀ determined at water pressure equal to total pressure demonstrate its restriction to water pressures below 0.8 Kbar (at 0.5 Kbar, the stability range is between 765° and 800° C). At the lower thermal stability limit osumilite+H₂O vapor break down to cordierite+K feldspar+phlogopite_ss+quartz, at the higher one to cordierite+K feldspar+phlogopite+liquid. Reduction of water fugacity will expand the stability field largely by shifting the lower and higher thermal stability limits to lower and higher temperatures, respectively. The dependence of osumilite stability on water fugacity makes osumilite a sensitive indicator mineral for dry conditions in rocks formed at total pressures higher than about 0.8 Kbar.     

Small landslide types and controls in glacial deposits: Lower Skagit river drainage,northern cascade range,Washington

Observations of 167 small, shallow landslides spanning a 22-year period on extensively logged slopes of Quaternary terraces in the lower Skagit and Baker Valleys, Washington, shows that there is a relationship between the common slope failures in this area and the slope angle, stratigraphy, and logging practices. Landslide frequency increases upvalley, as do mean annual precipitation and the frequency of perched water tables. Debris slides are most common, occur on steep slopes (>50%) composed of sand and gravel, and are most abundant in areas previously logged by the clear—cut method. Debris flows occur on shallower slopes (>30%) where the stratigraphy leads to perched water tables. Debris flows larger than 600 m² in area appear to be unrelated to logging practices. Slump flows, described here for the first time, occur on similar slope angles and stratigraphic situations as debris flows. They differ mainly by the presence of semiconsolidated material, usually till, at the slide head. Where till is breached—commonly along road cuts—water infiltration is increased, saturating underlying fine-grained deposits, which then fail by debris flowage. Secondary slumping of till happens when the slope steepens during debris flow failure. Small landslides surrounding Lake Shannon may contribute up to 80% of the total particulate matter yield to the fluvial system at present, increasing lake sedimentation by a rate of 5 mm/yr.     

Origin of granitic magma by crustal remobilisation: Rb-Sr and Pb/Pb geochronology and isotope geochemistry of the late Archaean Qôrqut Granite Complex of southern West Greenland

Rb-Sr and Pb/Pb whole rock isochrons on the Qôrqut Granite Complex yield ages of $\text{2530 ± 30}\text{Myr}\text{(}\text{initial}{}^{87}\text{Sr}{}^{86}\text{Sr}\text{= 0.7081 ± 0.0008)}$ and 2580 ± 80 Myr respectively. A model relating initial Sr and Pb isotopic compositions of the Qôrqut granites to the Sr and Pb isotopic compositions of the Amîtsoq gneisses (ca. 3700 Myr) and Nûk gneisses (ca. 2900 Myr) at 2550 Myr ago, as well as Sr and Pb contents of the gneiss units, suggests that between 40 and 50% of the Qôrqut granite magma was generated by partial melting of Amîtsoq gneisses, and the remainder by partial melting of Nûk gneisses.     

Retail geography and social well-being: A note on the changing distribution of pharmacies in Scotland

Dispensing Chemists represent an important component in the organization of primary medical care in the United Kingdom, as well as providing a basic retail service. Over the past 30 years, the number of dispensing chemists' shops in Scotland has fallen by 40%, a withdrawal of services which has important spatial welfare implications. In this paper the locational dynamics of pharmaceutical retailing are examined, and the pattern of change between 1950 and 1980 is described. It is shown that the major trend, at both regional and intra-urban levels, is centralization. This trend is only weakly related to patterns in population change. Rather, it is the product of a general restructuring of retailing, reinforced by changes in the structure of the health care delivery system.     

Eo-alpine metamorphism in the uppermost unit of the Cretan nappe system — Petrology and geochronology

The uppermost unit of the Cretan nappe system consists of ophiolites on the top, and an ophiolitic mélange at the base.Among the various constituents of the mélange, there are slices of low-P/high-T metamorphics. They form a variegated series consisting of tholeiitic ortho-amphibolites, para-amphibolites, andalusite and sillimanite-cordierite-garnet bearing mica schists, calcsilicate rocks, and marbles. The metamorphic sequence is locally intruded by early tectonic magmatites of gabbroic, dioritic and granitic composition. Critical mineral assemblages lead to a maximum temperature of about 700° C reached during metamorphism, at a total pressure of 4–5 kilobars. K — Ar dating on 6 hornblendes, 7 biotites and 1 muscovite yielded cooling ages of 75–66 m.y. and confirmed earlier results according to which the metamorphism and related magmatism took place in Late Cretaceous times.In order to evaluate the age relationships between the hightemperature metamorphics within the ophiolitic mélange and the ophiolites, hornblendes from ultramafic and mafic rocks of the ophiolite complex were dated by the K — Ar method. Hornblende from one schistose hornblendite forming a constituent of the ophiolites proper yielded 156 m.y. and thus provides a middle Jurassic minimum age for the formation of this piece of oceanic lithosphere. Four hornblendes of calc-alkaline gabbrodiorite dikes within the ophiolite complex gave distinctly lower K — Ar dates of about 140 m.y.. The dikes probably intruded after the detachment of the ophiolites in an island-arc or continental-margin environment.As a consequence, the high-temperature metamorphics and related intrusives in the ophiolitic mélange of Crete are genetically unrelated to the overlying ophiolites. The paleogeographic position of the crystalline terrane, slices of which are now incorporated into the ophiolitic mélange is still open to discussion.     

A possible dependence of tectonic strength on the age of the crust in Asia

In Asia, the intensity and style of active tectonics appears to depend on the age of the last orogenic activity. The shields have remained essentially undeformed during the India-Eurasian collision, but Paleozoic and Mesozoic orogenic belts apparently have been reactivated by this collision, with a suggestion of greater reactivation and more diffuse deformation of the younger belts. If the greater observed heat flow in regions of more recent orogenic activity reflects, at least in part, a greater heat flow from the mantle beneath the younger belts, then the temperatures in the mantle beneath the younger belts should be higher than beneath older belts and shields. Because of the strong dependence on temperature of the creep strength of minerals, particularly of olivine, the crust and mantle beneath the hotter, younger belts should be much weaker than those beneath older belts. This difference in temperature, and consequent difference in strength, may be the cause of the greater reactivation of younger belts.     

The influence of organic debris on channel morphology and bedload transport in a New Zealand forest stream

The behaviour and form of, and bedload sediment transport through, a 3.5 m wide forest stream have been monitored for nearly three years. Bedload transport is highly episodic and spatially variable, and is controlled less by water discharge than by sediment availability. Organic debris in the channel creates temporary base levels and sites at which coarse sediment may remain stored for long periods; collapse or disruption of log and debris jams makes sediment available for transport in only a small proportion of the runoff events that are actually competent to move the material. Even then, sediment travels only a short distance before being redeposited, frequently behind debris accumulations further downstream. Rates of sediment transport during a given runoff event can vary markedly over short distances along the stream, again depending on whether sediment was made available for transport by log jam collapse upstream. Organic debris is therefore a major constraint on the application of physical laws and theories to explaining sediment movement in, and the morphology of, this stream.