Heating rate profiles in galaxy clusters

In recent years, evidence has accumulated suggesting that the gas in galaxy clusters is heated by non-gravitational processes. Here, we calculate the heating rates required to maintain a physically motivated mass flow rate, in a sample of seven galaxy clusters. We employ the spectroscopic mass deposition rates as an observational input along with temperature and density data for each cluster. On energetic grounds, we find that thermal conduction could provide the necessary heating for A2199, Perseus, A1795 and A478. However, the suppression factor of the classical Spitzer value is a different function of radius for each cluster. Based on the observations of plasma bubbles, we also calculate the duty cycles for each active galactic nucleus (AGN), in the absence of thermal conduction, which can provide the required energy input. With the exception of Hydra-A, it appears that each of the other AGNs in our sample requires duty cycles of roughly 10⁶–10⁷ yr to provide their steady-state heating requirements. If these duty cycles are unrealistic, this may imply that many galaxy clusters must be heated by very powerful Hydra-A type events interspersed between more frequent smaller scale outbursts. The suppression factors for the thermal conductivity required for combined heating by AGN and thermal conduction are generally acceptable. However, these suppression factors still require 'fine-tuning' of the thermal conductivity as a function of radius. As a consequence of this work, we present the AGN duty cycle as a cooling flow diagnostic.     

On viscosity, conduction and sound waves in the intracluster medium

Recent X-ray and optical observations of the Perseus cluster indicate that a combination of weak shocks at small radii  (≳20  kpc)  and viscous and conductive dissipation of sound waves at larger radii is responsible for heating the intracluster medium and can balance radiative cooling of cluster cores. We discuss this mechanism more generally and show how the specific heating and cooling rates vary with temperature and radius. It appears that this heating mechanism is most effective above  10⁷  K  , which allows for radiative cooling to proceed within normal galaxy formation but stifles the growth of very massive galaxies. The scaling of the wavelength of sound waves with cluster temperature and feedback in the system are investigated.     

Statistical approach to determine the salinized ground water flow path and hydrogeochemical features around the underground LPG cavern,Korea

The ground water flow path of the coastal area in the Yellow Sea, Korea, was interpreted using both the cross‐correlation analysis of hydraulic properties and the principal component analysis (PCA) of ground water chemistry. Data was obtained from observation wells in the underground liquefied petroleum gas (LPG) cavern constructed in the coastal area of Pyeongtaek. Cross‐correlation results showed that the operating pressure became more influenced on artificial factors for the variation of the groundwater level of the study area (45–66% of correlation coefficient) even though its affecting area was limited to the region with fractures or faults, and also showed that the delay time from the variation of operating pressure to the fluctuation of ground water level were relatively long periods (28–31 days). Three hydrogeochemical events (encrusted cement dissolution, host rock dissolution, and seawater intrusion), which were dominantly influenced on ground water quality, could be induced from the result of PCA. Quantitative evaluation for these events using the mixed equation with principal component scores suggest that the dissolution of encrusted cement materials was the predominant factor (39·0% of the total mixed proportion) to change the chemical composition of the seepage water during the ground water flow from the observation wells to the cavern. Integration of the statistical results also imply that ground water flow and hydrogeochemistry were predominantly affected by artificial factors such as cavern operation pressure and dissolution of encrusted cement materials, which were interdependent factors on the observation wells with high cross‐correlation coefficients and pH. Copyright © 2007 John Wiley & Sons, Ltd.     

Petrology and retrograde P-T path in granulites of the Kanskaya formation, Yenisey range, Eastern Siberia

The Kanskaya formation in the Yenisey range, Eastern Siberia is a newly studied example of retrogression of granulite facies rocks. The formation consists of two stratigraphical units: the lower Kuzeevskaya group and the upper Atamanovskaya group. Rocks from both of these units show rare reaction textures such as replacement of cordierite by garnet, sillimanite and quartz, silimanite coronas around spinel and corundum, and garnet rims around plagioclase in metabasites, while plagioclase rims around garnet can be seen in associated metapelites. The paragenesis quartz + orthopyroxene + sillimanite is a feature of the Kuzeevskaya group. In many samples, chemical zoning of garnet and cordierite shows an increase in Mg from core to rim as well as the reverse.
Biotite-garnet-cordierite-sillimanite-quartz as well as spinel±biotite-garnet°Cordierite±sillimanite-quartz assemblages were studied using geothermometers and geobarometers based on both exchange and net-transfer reactions (Perchuk & Lavrent'eva, 1983; Aranovich & Podlesskii, 1983; Gerya & Perchuk, 1989). Detailed investigation of 10 samples including 1000 microprobe analyses revealed decompression (first stage) followed by the near isobaric cooling of the granulites. From geological studies, the 7 km total thickness of the sequence closely corresponds to the pressure difference (∼ 2.2kbar) measured by geobarometers in the samples taken from different levels in the sequence. Individual samples yield P-T paths ranging from 100°C/kbar to 140°C/kbar depending on their locations with respect to the large Tarakskiy granite pluton. In places the 100°C/kbar path changed to the 140°C/kbar due to the influence of the intrusion. In a P-T diagram these trajectories are subparallel lines, whose P-T maxima define the Archaean geotherm between 3.1 and 2.7 Ga, determined isotopically. A petrological model for P-T evolution of the Kanskaya formation is proposed.     

Kinetics of phosphate adsorption by iron oxyhydroxides in aqueous systems

The rate of uptake of phosphate onto synthetic Fe(III)- and Fe(II)-derived oxyhydroxides has been studied using reaction conditions similar to those encountered in natural waters. Kinetic analyses were carried out on the adsorption profiles and both first-order and second-order conditional rate constants were obtained. The temperature dependence of some of the rate constants was investigated and corresponding apparent activation energies calculated. Similar experiments and analyses were undertaken using Fe from natural sources and in general the conditional rate constants obtained in seawater were in agreement with the synthetic ones. The results of this study are of value when comparing the time scales of adsorption processes in natural waters with the time scales of mixing and advection.     

Late Proterozoic High-pressure granulite facies meta-morphism in the north-east Ox inlier, north-west Ireland

Abstract High-pressure granulite-facies gneisses in the NE Ox inlier in NW Ireland have undergone extensive Caledonian retrogression. In the local area of Slishwood, however, reworking was negligible and the gneisses (psammites, semipelites, pelites, metabasites and ultramafites) preserve evidence of P–T changes at high grade which mainly post-date pre-Caledonian polyphase deformation. Temperatures reached 850–900°C (based on garnet-clinopyroxene geothermometry and the presence of mesoperthite) during and after decompression from earlier eclogite-facies conditions (inferred from textural evidence of plagioclase release in sieve-textured augite). Subsequent cooling at high pressure is inferred from the unequivocal replacement of sillimanite by kyanite.
A Sm–Nd mineral isochron (gt–cpx–plag–WR) of 605 ± 37 Ma is taken to date a point on the cooling path, and confirms the hitherto suspected pre-Caledonian age of the high-grade metamorphism. Geochemical and Sm–Nd isotopic data indicate that the protoliths were probably late Proterozoic arkosic sediments and tholeiites. Following metamorphism they apparently came to reside near the base of the crust where they slowly cooled. The eventual exhumation of these gneisses is attributed to Caledonian crustal imbrication, followed by rapid isostatic recovery.     

Metamorphic evolution of granulites in the Minto Block, northern Québec: extraction of peak P-T conditions taking account of late Fe-Mg exchange

In the central Minto Block of northern Québec, the Lake Minto and Goudalie domains are dominated, respectively, by orthopyroxene-bearing plutonic suites (granite-granodiorite and diatexite) and a tonalitic gneiss complex, both of which contain scattered remnant paragneisses. Two main granulite-grade mineral assemblages are observed in the paragneiss: garnet (Grt)-orthopyroxene (Opx)-plagioclase-quartz (GOPQ) and garnet (Grt)-cordierite (Crd)-sillimanite-plagioclase-quartz (GCSPQ). These show distinct lithological associations, with the GCSPQ assemblages occurring exclusively within the diatexite in the Lake Minto domain. Petrogenetic grid considerations demonstrate that the GOPQ rocks are higher grade than the GCSPQ rocks. Maximum temperatures for GOPQ rocks, obtained from equilibria based on Al solubility in orthopyroxene in equilibrium with garnet, range from 950 to 1000d? C, significantly higher than garnet-orthopyroxene Fe-Mg exchange temperatures of 700 ± 50d? C, the latter probably representing a closure temperature below peak conditions. The Al temperatures were corrected for late cation exchange by adjusting the Fe/(Fe + Mg) ratios in garnet and orthopyroxene, to achieve internal consistency between the GOPQ thermometers and barometers. Grt-Crd thermometry records temperatures of 750±50d? C. Peak P-T conditions range from 5-6 kbar and 750-800d? C in the Goudalie and eastern Lake Minto domains, to 7-10 kbar and 950-1000d? C in the western and central Lake Minto domain. This variability contrasts with the uniform crustal pressures of 5 ± 1 kbar recorded by the GCSPQ assemblages in the diatexites and the hornblende granodiorites (c. 4-5 kbar) across the same area. The GOPQ rocks are inferred to record earlier P-T conditions that prevailed before the formation of GCSPQ assemblages and the intrusion of the granodiorites. Partial P-T paths in GOPQ rocks from both domains, based on net transfer equilibria corrected for Fe-Mg resetting, document cooling of 100-250d? C from thermal-peak conditions, concomitant with a modest pressure decrease of 2-3 kbar. Although textures diagnostic of isobaric cooling are not developed, the paths are consistent with a tectonic model in which granulite metamorphism and crustal thickening in the Minto Block were consequences of magmatic underplating. The progression from higher P-T conditions recorded by GOPQ assemblages to lower P-T conditions recorded by GCSPQ assemblages is attributed to variable amounts of synmagmatic uplift and cooling in a single, continuous thermal event in the Minto crust, associated with protracted crustal magmatism. In the Goudalie and eastern Lake Minto domains, where GOPQ and GCSPQ rocks and Hbl granodiorites have similar P-T conditions of equilibration, the crust may not have been thickened as much as further west, where GOPQ P-T conditions are significantly higher than those of the hornblende granodiorites and the GCSPQ rocks.     

细基江篱繁枝变种在不同水层中的栽培试验

本文报道了为改变我国华南沿海目前在半咸淡水塘中进行地播式裁培细基江篱繁枝变种单产低的状况而进行的不同水层夹苗栽培和施肥增产试验,证明了越靠近水面江篱藻体生长越快,越接近底部藻钵生长越差,提出如果在水塘中单纯裁培江篱则水塘深度应保持20～30厘米,如果水深超过1米以上,则应采用浮筏式夹苗栽培,并在水中混养鱼虾等。浸泡施肥试验证明,在短短的40天裁培过程施肥藻体比不施肥藻体增产23％,说明了施肥的重要性。     

Age, Origin and Cooling History of the Coronel Joao Sa Pluton, Bahia, Brazil

In north-east Brazil, Archean and Paleoproterozoic cratonicblocks are enclosed within a network of Brasiliano-age (0·7–0·55Ga) metasedimentary foldbelts. The unfoliated Coronel JoãoSá granodiorite pluton, which contains magmatic epidoteand strongly resorbed clinopyroxene, intrudes the SergipanoFoldbelt. Zircons yield a concordant U–Pb crystallizationage of 625 ± 2 Ma; titanite ages are approximately 621Ma. Discordant zircons suggest inheritance from at least twomagma sources of ages <1·8 and >2·2 Ga.Model calculations based on diffusion parameters and Rb–Srisotope data from separated minerals indicate that the plutoncooled at a rate of 36°C/Myr. Whole-rock element compositionsand initial Sr–Nd isotopic compositions that are heterogeneouson all length scales suggest magma mixing. Trace-element concentrationsand Nd isotope data argue against a contribution from a contemporaneousmantle-derived magma. Values of magmatic _Nd (at 625 Ma) resemblecontemporary _Nd for local supracrustal rocks and basement, compatiblewith anatexis of a crustal source. In north-east Brazil, cratonicblocks could have amalgamated with foldbelts that originatedas: (1) a mosaic of island arcs and arc basins (traditionalallochthonous model), or as (2) extensional continental sedimentarybasins (but not oceanic crust) later involved in collision (autochthonousmodel). The Coronel João Sá isotopic and chemicaldata support an autochthonous origin. KEY WORDS: Brasiliano Orogeny; granodiorite pluton; Rb–Sr isotopes, Sm–Nd isotopes; U–Pb isotopes, magma cooling rate     

Effects of Volcanic Ash on Computers and Electronic Equipment

Computers and electronic equipment are an important component of the infrastructure of our modern environment. It is therefore essential that we know the effects of volcanic ash on such equipment. This paper presents the results of a pilot study to test computers and cooling fans in an ash-charged environment to assess their vulnerability. In the experiment, ash was poured on to computers and cooling fans in a sealed 0.216 m³ perspex box, with the effects on both the ash and the equipment monitored. Three different types of ash (1996 Ruapehu andesitic ash, Sakurajima andesitic ash and Kaharoa rhyolitic ash) were used in the experiments.In the first experiment each type of ash was photographed by Scanning Electron Microscope (SEM), then passed through the bearing unit of a cooling fan and photographed again afterwards. The bearings within the cooling fan continued to work even after 720 h of testing and there was no significant abrasion of the fan-shaft bearing. The ash was however fragmented, suggesting that the brittle ash shattered to fine dust, which caused significantly less abrasion to the bearings or shaft than expected. Three computers were then tested in the sealed box. Ash was introduced at increasing rates to simulate catastrophic entry of ash into a work environment, and computers were tested throughout using the BURNIN^® testing programme. Failure times ranged from 100 to 150 h; most failures occurring when humidity was increased by spraying water mist into the airflow. If dried out the computers continued to operate again if failure was not catastrophic. Card slot edge connectors proved to be one of the weakest links, as a bridge of ash formed across the gap. They were also subject to abrasion with some of the gold plating being removed. This did not however cause operating difficulties.The conclusions are that computers are more resilient than originally thought, unless the ash is moist. Simple low-tech procedures should be adequate to protect computers from small amounts of dry and moist ash contamination.