Refractive optical systems for astronomical instruments using infrared arrays in the 0.8 to 2.5 micron bands

As modern infrared arrays evolve towards larger formats and smaller pixel sizes, their use in instruments requires optics of increasingly higher performance. Refractive systems are attractive for many applications because they can accommodate wide fields of view or fast focal ratios while permitting a compact, unobscured layout. We examine design considerations for lenses which can address the entire near-infrared spectral region of 0.8 to 2.5 m. Achromatization over this broad range is a particular challenge. We discuss a systematic study of candidate materials and combinations of materials having useful chromatic properties, with particular emphasis on alkaline earth halides and metallic oxides. We present an example of a practical design being incorporated into an instrument currently under construction.     

V5-2000大地电磁测深仪文件头数据格式研究

V5-2000大地电磁测深仪由于其功能强、轻便、勘探范围大等特点,在国内已得到了广泛应用,但其后期数据解释软件却显得相对薄弱。要想解决解释软件的问题,首先所面临的是测量数据的格式问题。由于其保存的测量数据为特殊格式,为了便于对V5-2000测量数据进行后期处理与分析,这里对V5-2000测量数据的特殊数据格式进行了剖析,并用现今流行的,面向对象化的VB6.0编程语言,编写了相关读取及修改程序,以作为下一步的后期数据解释软件开发之基础。     

基于智能遗传算法和Otsu法的多目标图像分割方法

为了克服传统遗传算法在优化多目标图像分割参数时易陷入局部收敛和搜索效率低的缺陷,本文提出一种基于智能遗传算法和Otsu法的多目标图像分割方法,并将它应用于航空影像的分割。实验结果表明,本文提出的算法比传统遗传算法可以更加快速、更稳定地获取图像分割的最优阈值。     

Site effects close to structural lineaments in eastern Sicily (Italy)

This paper analyses site effects that are applied to compute the H/V spectral ratio close to structural lineaments. Aseismic creep and seismic creep have been examined. The lineaments are located in different types of volcanic soil. The aim of the work is to verify the possibility of fault-guided seismic waves within the structures, which behave as a waveguide for trapped waves.

The measurements of ambient noise were carried out along profiles crossing the structures, and the standard Nakamura technique was applied to calculate the spectral H/V ratio. It was observed that horizontal components of ground motion were found to be significantly amplified within the shear zone.     

关于重力学反问题的几个判定准则─-在某些特定约束下的场源问题

从重力学反问题的基本理论出发,根据处理不适定问题的Tikhonov正则化原理,应用泛函分析概念,从理论上对如何将重力学反问题这一泛定的不适定问题在某些特定约束下转化成具有适定性的定解问题进行讨论．分别推演及刻画出重力场源密度在具有最小位能、最小L2模、最小H1,2模及最小“梯度模”等限定下的性质及表示式．对各种约束及对应的场源特性的数学、物理意义及合理性进行了分析．为重力学反问题研究提供理论判据．     

Mode switching in the nearby Mira-like variable R Doradus

We discuss visual observations spanning nearly 70 years of the nearby semiregular variable R Doradus. Using wavelet analysis, we show that the star switches back and forth between two pulsation modes having periods of 332 d and about 175 d, the latter with much smaller amplitude. Comparison with model calculations suggests that the two modes are the first and third radial overtone, with the physical diameter of the star making fundamental-mode pulsation unlikely. The mode changes occur on a time-scale of about 1000 d, which is too rapid to be related to a change in the overall thermal structure of the star and may instead be related to weak chaos.   The Hipparcos distance to R Dor is 62.4 ± 2.8 pc which, taken with its dominant 332-d period, places it exactly on the period–luminosity (P–L) relation of Miras in the Large Magellanic Cloud. Our results imply first-overtone pulsation for all Miras which fall on the P–L relation. We argue that semiregular variables with long periods may largely be a subset of Miras and should be included in studies of Mira behaviour. The semiregulars may contain the immediate evolutionary Mira progenitors, or stars may alternate between periods of semiregular and Mira behaviour.     

Sakurai's object: the ionized nebula at radio wavelengths

Sakurai's object (V4334 Sgr) is a planetary nebula nucleus which is undergoing its final helium shell flash. This is the first of these rare and important events to be observable with non-optical instruments. We report the first radio detection, using a short (2-h) observation with the Very Large Array (VLA) at 4.86 GHz. The radio emission structure is coincident with the 34-arcsec diameter planetary nebula seen in optical emission lines. We find a statistical distance ∼ 3.8 ± 0.6 kpc, with a range of 1.9 <  D  < 5.3 kpc, depending on the planetary nebula (PN) mass. While we have no direct evidence for a new (post-flash) stellar wind, we estimate an upper limit to the mass-loss rate due to any such wind of 1.7 × 10⁻⁷ M⊙ yr⁻¹. The number of emitting knots in the radio-visible nebula indicates an electron density of ∼ 2 × 10⁸ m⁻³ in those knots, and a total emitting ionized mass of ∼ 0.15 M⊙, at an assumed distance of 3.8 kpc. The radio flux density indicates an Hβ flux of ∼ 6 × 10⁻¹⁶ W m⁻², suggesting an extinction E ( B  −  V ) ∼ 1.15, comparable with reddening estimates in the direction of V4334 Sgr.     

Infrared spectroscopy of Sakurai's object

We present near (ground-based) and far ( ISO ) infrared spectroscopy of Sakurai's object. As in the case of the optical spectrum, between 1996 and 1997 April the near-infrared spectrum underwent a dramatic change to later spectral type, and there is some evidence that the spectrum continued to evolve during 1997. Molecular features of carbon-bearing molecules (CN, C₂, CO) — corresponding to those seen in cool carbon stars — are now prominent in the 1–2.5 μ m range, and the ¹²C/¹³C ratio is low. The ISO data demonstrate the presence of hot circumstellar dust at a temperature of ∼ 680 K. If the dust shell is optically thin, the dust mass is ∼ 2.8 × 10⁻⁸ M⊙.