基于街景影像和手机信令数据的城市街道安全性研究

城市化进程加快导致街道安全性问题突出,已有研究利用城市视觉要素刻画街道安全感空间分布,忽略了街道真实安全性与安全感间的差异。该文利用街景影像和手机信令数据,结合K-means聚类算法与笛卡尔积运算模型减少“安全感知差异”,以长沙市主城区为研究案例,得到白天、夜晚及总体城市街道安全性分布:1)长沙市主城区安全感指数随圈层数增加呈波动递减趋势,主要原因是建筑视觉要素占比下降较快以及天空视觉要素占比逐步上升;2)长沙市主城区呈双圈层结构,白天高安全性、夜晚低安全性以及总体安全性最低的区域主要分布在主城区中心,具有明显的聚集现象。该研究通过对城市街道安全性和低安全性街道的分析提出街道优化建议,为城市规划提供参考。     

New models of interstellar gas–grain chemistry – I. Surface diffusion rates

In recent years it has become evident that large differences can exist between model results of grain-surface chemistry obtained from a rate equation approach and from a Monte Carlo technique. This dichotomy has led to the development of a modified rate equation method, in which a key element is the artificial slowing down of the diffusion rate of surface hydrogen atoms. Recent laboratory research into the surface diffusion rate of atomic hydrogen suggests that atomic hydrogen moves more slowly on grains than heretofore assumed. This research appears to lessen the need for modifications to the rate equation method. Based on the new laboratory work, we have developed appropriate models of gas-phase and grain-surface chemistry in quiescent dense cloud cores to examine the chemical effects of slowing down the rate at which atomic H can scan over dust surfaces. Furthermore, we have investigated the effect of slowing down the rate at which all species can move over grain surfaces.     

Star formation in NGC 6334 I and I(N)

The northern section of the molecular cloud complex NGC 6334 has been mapped in the CO and CS spectral line emission and in continuum emission at a wavelength of 1300 μm. Our observations highlight the two dominant sources, I and I(N), and a host of weaker sources. NGC 6334 I is associated with a cometary ultracompact H  ii region and a hot, compact core ≤10 arcsec in size. Mid-infrared and CH₃OH observations indicate that it is also associated with at least two protostellar sources, each of which may drive a molecular outflow. For region I we confirm the extreme high-velocity outflow first discovered by Bachiller & Cernicharo and find that it is very energetic with a mechanical luminosity of 390 L_⊙. A dynamical age for the outflow is ∼3000 yr. We also find a weaker outflow originating from the vicinity of NGC 6334 I. In CO and CS this outflow is quite prominent to the north-west, but much less so on the eastern side of I, where there is very little molecular gas. Spectral survey data show a molecular environment at position I which is rich in methanol, methyl formate and dimethyl ether, with lines ranging in energy up to 900 K above the ground state. NGC 6334 I(N) is more dense than I, but cooler, and has none of the high-excitation lines observed toward I. I(N) also has an associated outflow, but it is less energetic than the outflow from I. The fully sampled continuum map shows a network of filaments, voids and cores, many of which are likely to be sites of star formation. A striking feature is a narrow, linear ridge which defines the western boundary. It is unclear if there is a connection between this filament and the many potential sites of star formation, or if the filament existed prior to the star formation activity.     

Interstellar CO towards X Persei (HD 24534) – II. Two-component model

The observations made by the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope ( HST ) of molecular CO in absorbing gas towards X Persei are reported. The two-component statistical equilibrium model incorporating radiative excitation of CO by line emission at the same velocity that originates in nearby molecular clouds has been used to reproduce high-resolution GHRS spectra. Earlier analysis indicates that the cloud has a complex structure and at least a two-component model should be used to obtain accurate results. The spectra obtained from the International Ultraviolet Explorer ( IUE ) were used to complement GHRS data and constrain the space of possible solutions. The new oscillator strengths recommended by Eidelsberg et al. for A–X bands have been used. The results show that one of the components may be attributed to the Perseus OB2 molecular cloud, and the other component to an extension of the Taurus dark cloud. The total CO column density N (CO)=(1.0±0.2)×10¹⁶ cm⁻² has been determined. According to the results about 85 per cent of the observed CO belongs to an extension of the Taurus dark cloud. The CO radiation that originates in nearby molecular clouds may be the dominant excitation mechanism of the observed CO. The early results of ¹³CO line analysis indicate a ¹³CO/¹²CO ratio of about 40.     

The small-scale structure in interstellar H i: a resolvable puzzle

During the past decade or so, measurements of Galactic H  i absorption using VLBI against extragalactic sources, as well as multi-epoch observations in pulsar directions, have detected small-scale transverse variations corresponding to tens of au at the distance of the absorbing matter. Hitherto these measurements have been interpreted as small-scale structure in the H  i distribution with densities n _{H  i} ∼10⁴–10⁵ cm⁻³, orders of magnitude greater than those of the pc-scale structure. Naturally, it is difficult to imagine how such structures could exist in equilibrium with other components of the ISM.
In this paper we show that structure on all scales contributes to the differences on neighbouring lines of sight, and that the observed differences can be accounted for by a natural extension of the distribution of irregularities in the distribution of H  i opacities at larger scales, using a single power law. This, in our opinion, should put an end to the decades-long puzzle of the so-called small-scale structure in H  i and other species in the Galaxy.     

棘皮动物神经肽结构与功能研究进展

神经肽作为一种古老的信号分子,在动物的行为和生理过程中发挥着重要作用.近年来,随着生物信息学和分子生物学技术的发展,大量神经肽得以发掘和揭示,其中海洋生物(棘皮动物)神经肽信号系统及其功能研究亦取得了一定进展.本文对棘皮动物神经肽相关研究进展成果进行了归纳与总结,综述了主要神经肽结构、信号系统、功能及进化地位,并对其今...     

香鱼(Plecoglossus altivelis)脾脏酪氨酸激酶SYK的鉴定及其介导的MAPK信号通路研究

脾脏酪氨酸激酶(SYK)是一种非受体型酪氨酸激酶(non-receptor tyrosine kinase, NRTK)。在哺乳动物中,SYK是重要的细胞信号通路接头分子,其在免疫细胞活化,胞外刺激的信号转导和病原体识别等多种生命过程中扮演重要角色,然而在鱼类中却鲜有报道。本研究以香鱼(Plecoglossus altivelis)为研究对象,探讨了其SYK(PaSYK)在应对病原微生物感染及在活化免疫信号通路中的作用。我们克隆获得了香鱼SYK的cDNA序列,并利用多重序列比对、构建进化树等生物信息学方法分析PaSYK的进化地位;采用实时荧光定量PCR(RT-qPCR)方法分析PaSYK在健康组织及鳗弧菌(Vibrio anguillarum)感染后的表达变化;亚细胞定位检测PaSYK在HEK293T细胞的分布情况;在香鱼头肾单核/巨噬细胞(Monocyte/macrophage,MO/MΦ)中过表达PaSYK,研究其对炎症细胞因子表达的调控作用并在HEK293T细胞及香鱼头肾MO/MΦ中研究PaSYK对MAPK信号通路的活化作用。多重序列比对结果显示,SYK的蛋白质序列和结构域在进化...     

Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction

We relate the equivalent widths of 11 diffuse interstellar bands, measured in the spectra of 49 stars, to different colour excesses in the ultraviolet. We find that most of the observed bands correlate positively with the extinction in the neighbourhood of the 2175-Å  bump. Correlation with colour excesses in other parts of the extinction curve is more variable from one diffuse interstellar band to another; we find that some diffuse bands (5797, 5850 and 6376 Å) correlate positively with the overall slope of the extinction curve, while others (5780 and 6284 Å) exhibit negative correlation. We discuss the implications of these results on the links between the diffuse interstellar band carriers and the properties of the interstellar grains.     

Near-infrared imaging of H2 in molecular outflows from young stars

In an attempt to identify the molecular shocks associated with the entrainment of ambient gas by collimated stellar winds from young stars, we have imaged a number of known molecular outflows in H₂ v=1-0 S(1) and wide-band K. In each flow, the observed H₂ features are closely associated with peaks in the CO outflow maps. We therefore suggest that the H₂ results from shocks associated with the acceleration or entrainment of ambient, molecular gas. This molecular material may be accelerated either in a bow shock at the head of the flow, or along the length of the flow through a turbulent mixing layer.