A search for H i in some peculiar faint dwarf galaxies

We present a deep Giant Metrewave Radio Telescope (GMRT) search for H  i 21-cm emission from three dwarf galaxies, viz. POX 186, SC 24 and KKR 25. Based, in part, on previous single-dish H  i observations, these galaxies have been classified as a blue compact dwarf (BCD), a dwarf irregular and a transition galaxy, respectively. However, in conflict with previous single-dish detections, we do not detect H  i in SC 24 or KKR 25. We suggest that the previous single-dish measurements were probably confused with the local Galactic emission. In the case of POX 186, we confirm the previous non-detection of H  i but with substantially improved limits on its H  i mass. Our derived upper limits on the H  i mass of SC 24 and KKR 25 are similar to the typical H  i mass limit for dwarf spheroidal (dSph) galaxies, whereas in the case of POX 186, we find that its gas content is somewhat smaller than is typical of BCD galaxies.     

海底地震数据记录器

海底地震数据记录器是一种大动态、宽频带数字仪器，能用 于海底或陆地边远地区记录地震数据. 它体积小、重量轻、操作简单，采用两个缓存存 储器控制PC/104嵌入式计算机，能在低功耗、长时间连续记录地震数据. 记录器的关键部件 是PC/104嵌入式计算机，能保证记录器工作可靠. 它使用硬盘存储数据，2GB的硬盘能容纳 19998 GB的地震数据，记录地震数据多长时间由抽样率决定.     

Low-frequency variability and binarity of the δ Scuti star XX Pyx

We analyse 147 h of single-site CCD time series photometry of the multiperiodic low-amplitude δ Scuti star XX Pyx with the aim of investigating variability at low frequencies. Part of the data were obtained in the context of the 1998 multisite campaign on XX Pyx, the results of which were described by Handler et al. We find that periodic low-frequency variations are present in the XX Pyx light curves, and we detect two frequencies at f _A=0.8695 cycle d⁻¹ and f _B=1.7352 cycle d⁻¹ , respectively, with amplitudes of 4.5 and 5.4 mmag. The low-frequency variability is intrinsic to XX Pyx, and cannot be attributed to instrumental or atmospheric effects. The near 2:1 ratio of the frequencies leads us to suggest that XX Pyx is a δ Scuti star in a binary system, with a possible binary period of 27.6 h. This is strongly supported by the detection of radial velocity variations from the re-analysis of echelle spectra obtained by Handler et al. However, in the absence of a spectroscopic period, alternative explanations of the photometric variability involving pulsation are also possible; the variations occur close to possible combination frequencies of the short-period ( δ Scuti) variations, but high Q values of 0.57 and 0.28 d suggest that the variations are not a result of normal (p-)modes. They could possibly be due to g-modes excited to observable amplitudes as a result of resonance effects. Surface features (spots) are unlikely to be the cause of the variations.
We searched for combination frequencies (  f _i − f _j ) , f being the normal δ Scuti frequencies detected by Handler et al., but failed to detect any.     

The micro-glitch in PSR B1821−24: a case for a strange pulsar?

The single glitch observed in PSR B1821−24, a millisecond pulsar in M28, is unusual on two counts. First, the magnitude of this glitch is at least an order of magnitude smaller  (Δν/ν∼ 10⁻¹¹)  than the smallest glitch observed to date. Secondly, all other glitching pulsars have strong magnetic fields with   B ≳ 10¹¹ G  and are young, whereas PSR B1821−24 is an old recycled pulsar with a field strength of  2.25 × 10⁹ G  . We have earlier suggested that some of the recycled pulsars could actually be strange quark stars. In this work, we argue that the crustal properties of such a strange pulsar are just right to give rise to a glitch of this magnitude, explaining the scarcity of larger glitches in millisecond pulsars.     

Maximum-likelihood TOA Estimation of X-ray Pulsar Signals on the Basis of Poison Model

The cycle-stationary Poison model for the photon arrival of X-ray pulsars and the estimation of the pulse's time of arrival (TOA) are discussed. Based on this model, the maximum likelihood estimation (MLE) of the TOA, as well as the Cramer-Rao boundary (CRB), are presented, especially the approximate formulation of the likelihood function and the Cramer-Rao boundary are derived for the low-R_SN (signal-to-noise ratio) cases. By using the analytical pulse profile, we have made the Monte-Carlo simulation on the TOA estimation of PSR B1821-24, discussed the estimate error for different observation times and signal-to-noise ratios, and presented the corresponding R_SN-thresholds. The results show that this method of data analysis can estimate effectively the timing accuracy of X-ray pulsar pulses and help to evaluate the corresponding performances in other applications.     

中国东部第三系陆相沉积中的甲藻甾烷：海侵指相的标志物？

通过对我国东部盆地洪泽凹陷和临清坳限德州凹陷第三系相沉积泥岩中生物标志物分析，检测到了丰富的甲藻甾烷异构体和２４－正丙基胆甾烷。结合它们的分布特征与产出的地层微体古生物资料，笔者推断它们可能是海侵作用的产物。     

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Geometric characterization of the Arjuna orbital domain

Arjuna‐type orbits are characterized by being Earth‐like, having both low‐eccentricity and low‐inclination. Objects following these trajectories experience repeated trappings in the 1:1 commensurability with the Earth and can become temporary Trojans, horseshoe librators, quasi‐satellites, and even transient natural satellites. Here, we review what we know about this peculiar dynamical group and use a Monte Carlo simulation to characterize geometrically the Arjuna orbital domain, studying its visibility both from the ground and with the European Space Agency Gaia spacecraft. The visibility analysis from the ground together with the discovery circumstances of known objects are used as proxies to estimate the current size of this population. The impact cross‐section of the Earth for minor bodies in this resonant group is also investigated. We find that, for ground‐based observations, the solar elongation at perigee of nearly half of these objects is less than 90°. They are best observed by space‐borne telescopes, but Gaia is not going to improve significantly the current discovery rate for members of this class. Our results suggest that the size of this population may have been underestimated by current models. On the other hand, their intrinsically low encounter velocities with the Earth induce a 10–1000‐fold increase in the impact cross‐section with respect to what is typical for objects in the Apollo or Aten asteroid populations. We estimate that their probability of capture as transient natural satellites of our planet is about 8 %. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

内转塔式单点系泊系统设计方法研究

以南中国海恩平24-2油田开发工程为背景,针对南中国海海域恶劣环境条件,提出了新建单点系泊系统的总体方案规划与设计方法,为工程总承包(EPCI)提供技术支持,并确定了适用于恩平24-2油田开发的单点形式——带解脱装置内转塔式永久单点系泊系统。首先针对恩平24-2油田海域特征,规划出最适宜的单点总体布置,然后根据油田环境参数,提出了内转塔式单点系泊系统(包括浅水系泊系统、动态立管和动态电缆)的设计方法并对其系泊系统进行分析。研究结果可以看出内转塔式单点系泊系统设计方法对于环境恶劣海况下的单点设计具有指导意义,并能为国内单点的技术发展积累设计经验。