Period changes in the pulsating extreme helium stars V652 Her and BX Cir

A new statement of the eigenvalue problem of studying small perturbations in arbitrary integrable self-gravitating systems is presented. An example of such a system, a 2D stellar disc, is considered in detail. The theory, based on the general equation for disc eigenmodes, reveals mechanisms for the formation and growth of global galactic structures. This new point of view specifies the limits of the unified theory of bar-like and spiral modes that was based on the assumption that global galactic structures could be understood in terms of low-frequency disc modes.     

Potential protostars in cloud cores

We present H₂CO observations of young protostar candidates in the Serpens Cloud Core. We find evidence for dense molecular gas in the cores of these objects that is warmer than the surrounding dust. The strong emission and gas properties support the premise that many of these sources may be very young protostars.     

Ultrahigh pressure macro diamonds from Copeton (New South Wales, Australia), based on Raman spectroscopy of inclusions

Mining of Cenozoic alluvial deposits at Copeton and Bingara (Eastern Australia) has produced two million macrodiamonds (0.25 ct median size). Raman spectroscopy is used to identify included minerals within uncut Copeton diamonds, with sealed chamber remnant pressures of 31.7 to 35.6 kbar for coesite, 13.6 and 22.7 kbar for clinopyroxene, and 7.6 kbar for grossular garnet. Assuming elastic behaviour, these values generate inclusion entrapment PT loci which intersect, restricting diamond formation conditions: from 250 °C, 43 kbar to 800 °C, 52 kbar. Larger than error (± 100 °C and ± 4 kbar), this range shows a systematic variation in inclusion composition with diamond zoning and N properties. Published research shows 1) Copeton and Bingara diamonds are unique, and 2) modern alluvium in the Bingara district carries mantle-formed garnet, captured by post-tectonic alkali basalt from an extensive diamondiferous ultrahigh pressure (UHP) terrane that stalled at depth because it is dominated by mafic eclogite. The combined Raman and geological results indicate two sets of subduction UHP diamond formation conditions/protolith are required, firstly cooler oceanic slab and secondly including higher temperature continental crust. The Copeton and Bingara stones are UHP macrodiamonds, and Carboniferous ⁴⁰Ar/³⁹Ar age dates on clinopyroxene inclusions should be interpreted as ages of crystallisation, representing the termination of subduction. The characteristic features of ruptured inclusions and etched percussion marks on Copeton and Bingara diamond indicate volcanic delivery to the earth's surface. Alluvial deposits elsewhere in Eastern Australia may carry similar diamond along with diamond of different origin.     

Impact evaluation on groundwater of the infiltration of an urban wastewater geopurification system placed over a detrital aquifer in a semiarid region (Spain)

Over a period of 4 years and 4 months, the geopurification installations at Dehesas de Guadix (Granada, Spain) were monitored to determine the impact on soil and groundwater of the controlled discharge of urban wastewater, and also to identify the best indicators of the entry of the recharged water into the aquifer. The installations are located in an area where the climate is Mediterranean sub-arid, with an average precipitation of less than 287 mm/year, and a rate of evapotranspiration that is almost three times greater. The system was controlled by determining the balance of majority nutrients and boron in the soil and in the groundwater, both at the points affected directly by the wastewater discharge and at others. The quantity of mass discharged was relatively large (COD 14,656 g/m², NO₃ 85 g/m², NO₂ 4 g/m², NH₄ 2,425 g/m², PO₄ 1,143 g/m², K 1,531 g/m², B 63 g/m²). It was observed that the elimination of nutrients within the soil (COD 97.5%, PO₄ 94.4%, K 59.17%, N _total 18.8%, B 12.69%) was very efficient except for the nitrogen, which nevertheless did not reach the groundwater, as it was eliminated at deep levels of the unsaturated zone. Only 12.69% of the boron was removed, and appreciable, increasing amounts of this element did reach the groundwater. Unexpectedly, none of the majority nutrients behaved as a reliable indicator of the impact on groundwater; despite this, the boron and the bicarbonate did clearly reflect the arrival of the recharged water, and are proposed as the best indicators.     

Mapping susceptibility of rainfall-triggered shallow landslides using a probabilistic approach

To prepare a landslide susceptibility map is essential to identify hazardous regions, construct appropriate mitigation facilities, and plan emergency measures for a region prone to landslides triggered by rainfall. The conventional mapping methods require much information about past landslides records and contributing terrace and rainfall. They also rely heavily on the quantity and quality of accessible information and subjectively of the map builder. This paper contributes to a systematic and quantitative assessment of mapping landslide hazards over a region. Geographical Information System is implemented to retrieve relevant parameters from data layers, including the spatial distribution of transient fluid pressures, which is estimated using the TRIGRS program. The factor of safety of each pixel in the study region is calculated analytically. Monte Carlo simulation of random variables is conducted to process the estimation of fluid pressure and factor of safety for multiple times. The failure probability of each pixel is thus estimated. These procedures of mapping landslide potential are demonstrated in a case history. The analysis results reveal a positive correlation between landslide probability and accumulated rainfall. This approach gives simulation results compared to field records. The location and size of actual landslide are well predicted. An explanation for some of the inconsistencies is also provided to emphasize the importance of site information on the accuracy of mapping results.     

Depths of Partial Crystallization of H2O-bearing MORB: Phase Equilibria Simulations of Basalts at the MAR near Ascension Island (7 11{degrees}S)

Phase equilibria simulations were performed on naturally quenchedbasaltic glasses to determine crystallization conditions priorto eruption of magmas at the Mid-Atlantic Ridge (MAR) east ofAscension Island (7–11°S). The results indicate thatmid-ocean ridge basalt (MORB) magmas beneath different segmentsof the MAR have crystallized over a wide range of pressures(100–900 MPa). However, each segment seems to have a specificcrystallization history. Nearly isobaric crystallization conditions(100–300 MPa) were obtained for the geochemically enrichedMORB magmas of the central segments, whereas normal (N)-MORBmagmas of the bounding segments are characterized by polybariccrystallization conditions (200–900 MPa). In addition,our results demonstrate close to anhydrous crystallization conditionsof N-MORBs, whereas geochemically enriched MORBs were successfullymodeled in the presence of 0·4–1 wt% H₂O in theparental melts. These estimates are in agreement with direct(Fourier transform IR) measurements of H₂O abundances in basalticglasses and melt inclusions for selected samples. Water contentsdetermined in the parental melts are in the range 0·04–0·09and 0·30–0·55 wt% H₂O for depleted and enrichedMORBs, respectively. Our results are in general agreement (within±200 MPa) with previous approaches used to evaluate pressureestimates in MORB. However, the determination of pre-eruptiveconditions of MORBs, including temperature and water contentin addition to pressure, requires the improvement of magma crystallizationmodels to simulate liquid lines of descent in the presence ofsmall amounts of water. KEY WORDS: MORB; Mid-Atlantic Ridge; depth of crystallization; water abundances; phase equilibria calculations; cotectic crystallization; pressure estimates; polybaric fractionation     

Pressures of Crystallization of Icelandic Magmas

Iceland lies astride the Mid-Atlantic Ridge and was createdby seafloor spreading that began about 55 Ma. The crust is anomalouslythick (20–40 km), indicating higher melt productivityin the underlying mantle compared with normal ridge segmentsas a result of the presence of a mantle plume or upwelling centeredbeneath the northwestern edge of the Vatnajökull ice sheet.Seismic and volcanic activity is concentrated in 50 km wideneovolcanic or rift zones, which mark the subaerial Mid-AtlanticRidge, and in three flank zones. Geodetic and geophysical studiesprovide evidence for magma chambers located over a range ofdepths (1·5–21 km) in the crust, with shallow magmachambers beneath some volcanic centers (Katla, Grimsvötn,Eyjafjallajökull), and both shallow and deep chambers beneathothers (e.g. Krafla and Askja). We have compiled analyses ofbasalt glass with geochemical characteristics indicating crystallizationof ol–plag–cpx from 28 volcanic centers in the Western,Northern and Eastern rift zones as well as from the SouthernFlank Zone. Pressures of crystallization were calculated forthese glasses, and confirm that Icelandic magmas crystallizeover a wide range of pressures (0·001 to 1 GPa), equivalentto depths of 0–35 km. This range partly reflects crystallizationof melts en route to the surface, probably in dikes and conduits,after they leave intracrustal chambers. We find no evidencefor a shallow chamber beneath Katla, which probably indicatesthat the shallow chamber identified in other studies containssilica-rich magma rather than basalt. There is reasonably goodcorrelation between the depths of deep chambers (> 17 km)and geophysical estimates of Moho depth, indicating that magmaponds at the crust–mantle boundary. Shallow chambers (<7·1 km) are located in the upper crust, and probablyform at a level of neutral buoyancy. There are also discretechambers at intermediate depths (11 km beneath the rift zones),and there is strong evidence for cooling and crystallizing magmabodies or pockets throughout the middle and lower crust thatmight resemble a crystal mush. The results suggest that themiddle and lower crust is relatively hot and porous. It is suggestedthat crustal accretion occurs over a range of depths similarto those in recent models for accretionary processes at mid-oceanridges. The presence of multiple stacked chambers and hot, porouscrust suggests that magma evolution is complex and involvespolybaric crystallization, magma mixing, and assimilation. KEY WORDS: Iceland rift zones; cotectic crystallization; pressure; depth; magma chamber; volcanic glass     

Room-temperature equation of state of Li<Subscript>2</Subscript>VOSiO<Subscript>4</Subscript> up to 8.5 GPa

High-pressure single-crystal X-ray diffraction measurements of lattice parameters of the compound Li₂VOSiO₄, which crystallises with a natisite-type structure, has been carried out to a pressure of 8.54(5) GPa at room temperature. Unit-cell volume data were fitted with a second-order Birch-Murnaghan EoS (BM-EoS), simultaneously refining V ₀ and K ₀ using the data weighted by the uncertainties in V. The bulk modulus is K ₀ = 99(1) GPa, with K′ fixed to 4. Refinements of third order equations-of-state yielded values of K′ that did not differ significantly from 4. The compressibility of the unit-cell is strongly anisotropic with the c axis (K ₀(c) = 49.7 ± 0.5 GPa) approximately four times more compressible than the a axis (K ₀(a) = 195 ± 3 GPa).     

华南前寒武系基底变质杂岩和中-新生代地幔岩的稀有气体同位素组成及其大地构造意义

对华南前寒武系变质岩浆杂岩稀有气体He、Ne、Ar和Xe的系统研究表明:扬子克拉通基底为含高³He的下地壳"原始岩石层",(³He/⁴He)×10^-6比值为2.8～4.6;而华夏板块基底变质岩浆杂岩则是在缺乏³He、低(³He/⁴He)×10^-8比值(3.15～17.7)的构造环境下形成的大陆中-上地壳变质岩浆杂岩层,反映出两者基底性质迥然不同。华南中-新生代爆破岩筒He同位素组成相反,相对稳定的扬子克拉通(³He/⁴He)×10^-8比值仅0.18～4.22,而郯庐-四会-吴川断裂以东,中-新生代活动地块(太平洋构造域)(³He/⁴He)×10^-8比值高达3.7～20.5。He同位素表明郯庐-四会-吴川断裂带为切割深至地幔的边界深大断裂,是扬子克拉通与华夏板块间的边界且控制了燕山期火山-侵入岩浆向西扩展。Ar同位素组成表明华南大陆中-新生代地幔形成接近"均一"的地幔组份。¹³⁶Xe/¹³⁰Xe-¹²⁹Xe/¹³⁰Xe相关组份表明它们具有地幔柱岩石同位素组成特征。     

Implementing low-cost landslide risk reduction: a pilot study in unplanned housing areas of the Caribbean

Landslides pose a serious physical and environmental threat to vulnerable communities living in areas of unplanned housing on steep slopes in the Caribbean. Some of these communities have, in the past, had to be relocated, at costs of millions of dollars, because of major slides triggered by tropical storm rainfall. Even so, evidence shows that: (1) risk reduction is a marginal activity; (2) there has been minimal uptake of hazard maps and vulnerability assessments and (3) there is little on-the-ground delivery of construction for risk reduction. This article directly addresses these issues by developing a low-cost approach to the identification of the potential pore pressure changes that trigger such slides we seek to address these three commentaries directly. A complex 45–60° slope site in St Lucia, West Indies was selected as a pilot for a modelling approach that uses numerical models (FLAC and CHASM) to verify the need for surface water management to effectively reduce landslide risk. Following the model confirmation, a series of drains were designed and constructed at the site. Post-construction evidence indicates the methodology to be sound, in that the site was stable in subsequent 1-in-1 to 1-in-4 year rainfall events. A critical feature of the approach is that it is community-based from data acquisition through to community members participating in construction.