Clustering of galaxy clusters in cold dark matter universes

We use very large cosmological N -body simulations to obtain accurate predictions for the two-point correlations and power spectra of mass-limited samples of galaxy clusters. We consider two currently popular cold dark matter (CDM) cosmogonies, a critical density model ( τ CDM) and a flat low density model with a cosmological constant (ΛCDM). Our simulations each use 10⁹ particles to follow the mass distribution within cubes of side 2  h ⁻¹ Gpc ( τ CDM) and 3  h ⁻¹ Gpc (ΛCDM) with a force resolution better than 10⁻⁴ of the cube side. We investigate how the predicted cluster correlations increase for samples of increasing mass and decreasing abundance. Very similar behaviour is found in the two cases. The correlation length increases from     for samples with mean separation     to     for samples with     The lower value here corresponds to τ CDM and the upper to ΛCDM. The power spectra of these cluster samples are accurately parallel to those of the mass over more than a decade in scale. Both correlation lengths and power spectrum biases can be predicted to better than 10 per cent using the simple model of Sheth, Mo & Tormen. This prediction requires only the linear mass power spectrum and has no adjustable parameters. We compare our predictions with published results for the automated plate measurement (APM) cluster sample. The observed variation of correlation length with richness agrees well with the models, particularly for ΛCDM. The observed power spectrum (for a cluster sample of mean separation     ) lies significantly above the predictions of both models.     

A numerical study of the r-mode instability of rapidly rotating nascent neutron stars

The first results of numerical analysis of classical r-modes of rapidly rotating compressible stellar models are reported. The full set of linear perturbation equations of rotating stars in Newtonian gravity is solved numerically without the slow rotation approximation. A critical curve of gravitational wave emission induced instability, which restricts the rotational frequencies of hot young neutron stars, is obtained. Taking the standard cooling mechanisms of neutron stars into account, we also show the 'evolutionary curves' along which neutron stars are supposed to evolve as cooling and spinning down proceed. Rotational frequencies of 1.4-M_⊙ stars suffering from this instability decrease to around 100 Hz when the standard cooling mechanism of neutron stars is employed. This result confirms the results of other authors, who adopted the slow rotation approximation.     

Influence of the r-mode instability on hypercritically accreting neutron stars

We have investigated the influence of the r-mode instability on hypercritically accreting neutron stars in close binary systems during their common envelope phases, based on the scenario proposed by Brown et al. On the one hand, neutron stars are heated by the accreted matter at the stellar surface, but on the other hand they are also cooled down by the neutrino radiation. At the same time, the accreted matter transports its angular momentum and mass to the star. We have studied the evolution of the stellar mass, temperature and rotational frequency.
The gravitational-wave-driven instability of the r-mode oscillation strongly suppresses spinning up of the star, the final rotational frequency of which is well below the mass-shedding limit, in fact typically as low as 10 per cent of that of the mass-shedding state. On a very short time-scale the rotational frequency tends to approach a certain constant value and saturates there, as long as the amount of accreted mass does not exceed a certain limit to collapse to a black hole. This implies that a similar mechanism of gravitational radiation to that in the so-called 'Wagoner star' may work in this process. The star is spun up by accretion until the angular momentum loss by gravitational radiation balances the accretion torque. The time-integrated dimensionless strain of the radiated gravitational wave may be large enough to be detectable by gravitational wave detectors such as LIGO II.     

Visibility Characteristics over the South China Sea during 1980–2018 Based on Gridded Data Generated by Artificial Neural Network

This paper generated gridded visibility(Vis) data from 1980 to 2018 over the South China Sea(SCS) based on artificial neural network(ANN), and the accuracy of the generated data was tested. Then, temporal and spatial characteristics of Vis in the area were analyzed based on the generated Vis data. The results showed that Vis in the southern SCS was generally better than that in the northern SCS. In the past 39 years, Vis in both spring and winter has improved, especially in winter at a significant increased speed of 0.37 km decade~(-1). However, Vis in both summer and autumn has decreased, especially in summer with an obvious reduction of 0.84 km decade~(-1). Overall, Vis is best in summer and worst in winter, averaging 31.89 km in summer and 20.96 km in winter, which may be related to the difference of climatic conditions and wind speed in different seasons. At the same time, probability of low Vis in spring is significantly higher than that in other seasons, especially in the northwest of Hainan Island and the northwest of Malaysia.     

云南峨山塔甸地区中元古界黑山头组石英岩矿地质特征

通过1:5万区域地质调查、典型剖面及刻槽采样等研究, 在云南峨山塔甸地区中元古界黑山头组识别出厚104~227 m数层石英岩矿层, 含矿岩性为灰白色、白色、乳白色块-厚层状石英岩, 呈隐晶质-粒状变晶结构, 主要由石英(＞95%)组成; 分析显示样品SiO2含量为95.15%~99.41%, Al2O3含量为0.21%~2.61%, CaO含量为0.008%~0.047%, TFe2O3含量为0.088%~0.47%, K2O含量为0.009%~0.56%, MgO含量为0.010%~ 0.13%, Na2O含量为0.012%~1.4%, TiO2含量为0.011%~0.06%, 部分达到玻璃用、结晶硅用等硅质原料矿工业指标要求, 黑山头组石英岩矿为多层位赋存且单体厚度大的矿体, 层位稳定, 且延伸较远, 为一套滨海相沉积-变质型石英岩矿床, 具有较大潜在价值和经济效益, 有望形成大型石英岩矿原料产地。     

右江盆地富宁地区石炮组化石及顶部凝灰岩年代学特征及意义

通过野外地质调查, 笔者在右江盆地富宁地区中三叠统板纳组与下伏下三叠统石炮组界面之下约100 m采获早三叠世双壳类和菊石等化石, 在T1/T2界面之间新发现一套厚约5 m凝灰岩层, 对其进行LA-ICP-MS U-Pb同位素定年, 自下而上分别获得(249.0±1.9) Ma、(247.9±3.4) Ma、(245.5±1.6) Ma同位素年龄, 在误差范围内一致, 首次获得石炮组顶界年龄为下三叠统奥伦尼克阶。本次新发现的凝灰岩层及化石可作为早—中三叠世等时地层标志进行区域对比, 丰富了右江盆地早三叠世火山岩分布范围, 认为右江盆地滇东南地区T1/T2的划分标志以该套凝灰岩作为标志较为合理。结合前人资料, 这套凝灰岩、生物化石为华南陆块T1/T2界线的划分提供了重要年代学及古生物证据, 认为安尼阶/奥伦尼克阶界线年龄应定为 245.5 Ma, 可能更为合理。     

安徽大别山团岭花岗岩体岩石学特征及成因

团岭花岗岩体侵位于大别山南部超高压变质带变质表壳岩中, 由细粒少斑二长花岗岩和中粒少斑二长花岗岩组成。通过岩石学、岩石化学、地球化学的研究, 确定其为Ｓ 型花岗岩, 源岩可能来自大别山变质杂岩。结合同位素资料, 认为其属燕山期花岗岩, 侵位机制为底辟式强力就位。     

Environmental Geochemistry of Mining Activities in Panzhihua Region, Southwestern China

INTRODUCTIONMining activlties have significant envi ronmenta1 inll)ac'l ssuch as visual intrusions, dust, noise, blasting, trafflc and h}'drology (Kwolek, l999; Ripley et al., l996 ). The l)rot'csst'sof mineral extraction, processing, smelting and refinlng;1rt'never approximate to the environmental neutrality, but tht' affected areas can be ameliorated (KwoIek, l999; Klukanov;1;llltlRapant, 1999). The regions, where mining activities are I,r('sent or continuous for a long tlme, are pote…     

Chemical and Isotopic Characteristics of the Kuroko‐Forming Volcanism

The Miocene northeast Honshu magmatic arc, Japan, formed at a terrestrial continental margin via a stage of spreading in a back‐arc basin (23–17 Ma) followed by multiple stages of submarine rifting (19–13 Ma). The Kuroko deposits formed during this period, with most forming during the youngest rifting stage. The mode of magma eruption changed from submarine basalt lava flows during back‐arc basin spreading to submarine bimodal basalt lava flows and abundant rhyolitic effusive rocks during the rifting stage. The basalts produced during the stage of back‐arc basin spreading are geochemically similar to mid‐ocean ridge basalt, with a depleted Sr–Nd mantle source, whereas those produced during the rifting stage possess arc signatures with an enriched mantle source. The Nb/Zr ratios of the volcanic rocks show an increase over time, indicating a temporal increase in the fertility of the source. The Nb/Zr ratios are similar in basalts and rhyolites from a given rift zone, whereas the Nd isotopic compositions of the rhyolites are less radiogenic than those of the basalts. These data suggest that the rhyolites were derived from a basaltic magma via crystal fractionation and crustal assimilation. The rhyolites associated with the Kuroko deposits are aphyric and have higher concentrations of incompatible elements than do post‐Kuroko quartz‐phyric rhyolites. These observations suggest that the aphyric rhyolite magma was derived from a relatively deep magma chamber with strong fractional crystallization. Almost all of the Kuroko deposits formed in close temporal relation to the aphyric rhyolite indicating a genetic link between the Kuroko deposits and highly differentiated rhyolitic magma.