Nearby galaxies. III. Gas–to–dust ratio in the interstellar medium of spiral and dwarf irregular galaxies

The gas-to-dust ratio in the interstellar medium of nearby spiral systems and dwarf irregular galaxies has been obtained by using mainly the compiled data by Schmidt and Boller (1992a). The gas-to-dust ratio of dwarf irregulars is larger by about one order of magnitude than for spiral galaxies, on the average. A relation between the gas-to-dust ratio and the metallicity, represented by the abundance of oxygen, has been detected.     

表现局灶性磨玻璃密度肺癌的CT诊断与随访分析

目的:分析局灶性磨玻璃密度(f GGO)肺癌的CT表现,以提高诊断早期肺癌的准确率。方法:搜集经手术病理证实的、临床及CT资料完整的、表现为磨玻璃密度的肺癌病例34例,作回顾性分析,观察病灶大小、形态、边缘、密度及其他肺癌倾向征象,以及病灶在随访过程中的影像学变化。结果:34例患者中p GGO 7例,m GGO 27例,瘤肺界面清晰,病灶边缘可见分叶、毛刺,病灶内部可见空泡、支气管充气征,病灶周围可见胸膜凹陷征、血管集束征等。f GGO在随访过程中,病灶增大,密度增高,p GGO病灶内部出现实性成分,m GGO病灶内实性成分增多,病灶边缘出现分叶、毛刺,周围出现胸膜凹陷征、血管集束征等恶性征象。结论:f GGO肺癌的CT表现具有一定的特征性,CT随访对f GGO的良恶性鉴别具有较高的价值。     

不良天气条件下妃子笑荔枝螺旋环剥增产效果分析

在妃子笑荔枝将要进入花芽分化期时实施螺旋环剥,观测其各生育期及产量构成要素。结果表明螺旋环剥在不良天气条件下的增产效果明显．其原因是：在秋、冬季气温偏高的天气条件下,螺旋环剥能抑制冬梢抽发,促进花芽分化,有利开花结果;螺旋环剥能推迟花期,有利于避过花期低温连阴雨天气的不良影响;春季气温偏高的天气条件下,螺旋环剥能抑制“...     

Unstable modes of non-axisymmetric gaseous discs

We present a perturbation theory for studying the instabilities of non-axisymmetric gaseous discs. We perturb the dynamical equations of self-gravitating fluids in the vicinity of a non-axisymmetric equilibrium, and expand the perturbed physical quantities in terms of a complete basis set and a small non-axisymmetry parameter ε. We then derive a linear eigenvalue problem in matrix form, and determine the pattern speed, growth rate and mode shapes of the first three unstable modes. In non-axisymmetric discs, the amplitude and the phase angle of travelling waves are functions of both the radius R and the azimuthal angle φ. This is due to the interaction of different wave components in the response spectrum. We demonstrate that wave interaction in unstable discs, with small initial asymmetries, can develop dense clumps during the phase of exponential growth. Local clumps, which occur on the major spiral arms, can constitute seeds of gas giant planets in accretion discs.     

A survey searching for the epoch of assembling of Hubble types

We have started a survey of galaxies at intermediate redshifts using the HST-STIS parallel fields. Our main goal is to analyse the morphology of faint galaxies in order to estimate the epoch of formation of the Hubble classification sequence. The high resolution of STIS images (0.05″) is ideal for this work and enables us to perform a morphological classification and to analyse the internal structures of galaxies. We find that 40% of the 290 galaxies are early types and that there are more irregulars and ellipticals at the fainter magnitudes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Determination of Galaxy Members in Clusters

A new empirical procedure is introduced to determine the confirmed galaxy members of a cluster. The method depends on both the projected distances of galaxies in the cluster field from the cluster centre and their radial velocities. Galaxies of the main body of the cluster are selected first, then the method works iteratively by increasing the standard values of the relative radial distance and velocity until all galaxies belong to the cluster are included. The general apparent shape of the cluster will result from the distribution of the celestial coordinates of the cluster members. This revised version was published online in July 2006 with corrections to the Cover Date.     

早型星系中"黑洞/核球"质量线性关系的解析估计

在“等级式成团”（hierarchical clustering)宇宙学演化框架下,早型星系（E／SO）的形成和演化不是如经典的“整体塌缩”（monolithic collapse)演化模式所描述的是由高红移处的短时间剧烈恒星形成过程一次性完成的;相反,它们可能是在大尺度结构形成过程中由盘星系间的相互合并演化而来,特别是对于质量相当的盘星系间的剧烈合并过程。目前的数值模拟和高分辨成像观测都已证实了这种可能性,而且红移巡天的结果也更多地支持这种演化模式。在此提出一个星系合并过程中核区星暴和中心黑洞共生演化的模型,来解释由空间望远镜（HST）和地面CCD高分辨测光所得的早型星系“黑洞／核球”统计线性相关,也即中心黑洞质量约为其核球体质量的0．6％;同时,该演化模型还可以进一步合理地解释在类星体的近红外成像观测中统计得出的相似的线性相关性,即类星体中心亮度与其母星系质量成正比。并给出此模型计算的极限情况和模型的解析估计。     

Effective Sensitivity of A Non-uniform Phased Array of Short Dipoles

Short dipoles are a key element in new low frequency array antennas as proposed for LOFAR and other astronomical applications. Unfortunately standard texts on short dipole antennas are based on the effective area and do not lead to an astronomically useful sensitivity formulation in a straightforward manner. The concept of maximum effective area is applied to arrays of short dipoles and allows expressing the sensitivity as the ratio of this area over the effective sky brightness temperature as long as the output noise power is dominated by the antenna input radiation. For both quantities we only need to know the array directivity pattern that includes the mutual coupling effects when the actual loading conditions of the array elements are taken into account. Short dipole elements have a constant directivity pattern for frequencies below resonance, but they exhibit strong complex impedance variations that provide only narrow band performance when power matching is applied as required in transmit applications. However, in receive applications voltage or current sensing can be realized, for example with an active balun. Assisted by the steep increase of the sky brightness with wavelength for frequencies below 300 MHz, this can provide sky noise dominated performance over at least a three to one frequency range. Still the low frequency limit is determined by the amplifier noise contribution and the losses in the antenna and in the dielectric ground surrounding the elements. We show that for a sparse array with the elements non-uniformly distributed according to an exponential shell model, a constant sensitivity can be obtained over a frequency range of at least two octaves. In addition, such a configuration has a factor of six greater sensitivity than a rectangular array for a large part of the frequency band.     

NGC 2587: a sparse open cluster projected on to a populous star field

We present CCD photometry in the Johnson U , B and V and Kron–Cousins I passbands for the open cluster NGC 2587. The sample consists of 4406 stars reaching down to   V ∼ 21.0  . We developed a new method to clean statistically the colour–magnitude diagrams. NGC 2587 appears to be a sparse, relatively bright open cluster, with a few tens of members projected on to a populous star field. The comparatively bright F7/8 II type star HD 70927, located close to the cluster centre, seems not to be a member. Our analysis suggests that NGC 2587 is slightly younger than the Hyades and probably of solar metallicity. A cluster radius of roughly 8 arcmin was estimated from the radial stellar density profile. From 18 probable cluster members with measured proper motions, we derive the following mean values for NGC 2587:  μ_α=−4.3 ± 3.6 mas yr⁻¹  and  μ_δ=−2.5 ± 3.4 mas yr⁻¹  . Adopting the theoretical metal content   Z = 0.02  , which provides the best global fit, we derive a cluster age of  500⁺⁶⁰₋₅₀  . Simultaneously, colour excesses   E ( B − V ) = 0.10  and   E ( V − I ) = 0.15  and an apparent distance modulus of   V − M_V = 12.50  are obtained. The interstellar extinction in the cluster direction is found to follow the normal law. NGC 2587 is located at a distance of (2.70 ± 0.70) kpc from the Sun and ∼9.8 kpc from the Galactic centre.     

Microstructural analysis of the classical spiral garnet porphyroblasts of south-east Vermont: evidence for non-rotation

New data strongly suggest that the classical spiral garnet porphyroblasts of south-east Vermont, USA, generally did not rotate, relative to geographical coordinates, throughout several stages of non-coaxial ductile deformation. The continuity of inclusion trails (S_i) in these porphyroblasts is commonly disrupted by planar to weakly arcuate discontinuities, consisting of truncations and differentiation zones where quartz–graphite S_i bend sharply into more graphitic S_i. Discontinuous, tight microfold hinges with relatively straight axial planes are also present. These microstructures form part of a complete morphological gradation between near-orthogonally arranged, discontinuous inclusion segments and smoothly curving, continuous S_i spirals. Some 2700 pitch measurements of well-developed inclusion discontinuities and discontinuous microfold axial planes were taken from several hundred vertically orientated thin sections of various strike, from specimens collected at 28 different locations around the Chester and Athens domes. The results indicate that the discontinuities have predominantly subvertical and subhorizontal orientations, irrespective of variations in the external foliation attitude, macrostructural geometry and apparent porphyroblast-matrix rotation angles. Combined with evidence for textural zoning, this supports the recent hypothesis that porphyroblasts grow incrementally during successive cycles of subvertical and subhorizontal crenulation cleavage development. Less common inclined discontinuities are interpreted as resulting from deflection of anastomosing matrix foliations around obliquely orientated crystal faces prior to inclusion. Most of the idioblastic garnet porphyroblasts have a preferred crystallographic orientation. Dimensionally elongate idioblasts also have a preferred shape orientation, with long axes orientated normal to the mica folia, within which epitaxial nucleation occurred. Truncations and differentiation zones result from the formation of differentiated crenulation cleavage seams against porphyroblast margins, in association with progressive and selective strain-induced dissolution of matrix minerals and locally also the porphyroblast margin. Non-rotation of porphyroblasts, relative to geographical coordinates, suggests that deformation at the microscale is heterogeneous and discontinuous in the presence of undeformed, relatively large and rigid heterogeneities, which cause the progressive shearing (rotational) component of deformation to partition around them. The spiral garnet porphyroblasts therefore preserve the most complete record of the complex, polyphase tectonic and metamorphic history experienced in this area, most of which was destroyed in the matrix by progressive foliation rotation and reactivation, together with recrystallization.