Impedance characteristics of carbon steel under cathodic protection   总被引：1，自引：0，他引：1  

李言涛  侯保荣 《中国海洋湖沼学报》1998,16(1):60-63

INTRODUCTIONInpraCticalengineeringapplicati0ns,thecormsionofstalundercathodicprotalioncanbecontr0llediftheproodi0np0tenhalisset2O()t03(X)mVnegativewithaspeCttothenatamlcormsi0np0tenial(MasatSugi,l976,Takehiko,l972).Theprotalnp0tentia1edinpraedcalapplicationisbedonexperienceandtheory.Tooru(l985,l986)foundthattheopbocathodicproodionpotentialcoinddedwiththepotentialwhenpolarhati0nresistancemaxndnd,s0thiscoinedencecanbeedt00btainoptbore-sultforcarbonstalundercathodicpronaion.Inthiswork,the…  相似文献   

西安地区部分古遗址考古地磁研究          下载免费PDF全文

孟昭秦 《地质科学》1998,33(4):489-493

通过对陕西耀州窑遗址内4个古窑,临潼兵马俑一号坑,西铜一级公路经过黄堡工地开挖的两个五代窑,以及耀州窑博物馆仓库工地内开挖的一个金代窑和一个春秋窑遗址的古地磁研究,初步得出了西安地区古地磁场变化的规律,为鉴定从春秋到金代西安地区的古遗址、古文物提供了考古地磁学上的一个粗略的标准。  相似文献   

TRES-Ⅰ型多分量瑞利波勘探仪的研究及应用     

李锦飞 《物探与化探》1998,22(2):129-133

提出多分量瑞利波勘探的技术思想和方法,研制成功专用的防爆型多分量瑞利波勘探仪器,建立了在用极化分析对瑞利波勘探记录的多分量信号分析的基础上,用极化滤波提取有效瑞利波信号的方法。在煤矿井下及地面实际应用表明,多分量瑞利波勘探与单分量法比较,信号的信噪比、勘探深度和可靠性均有一定的提高。  相似文献   

Polarization observations of the radio cores of AGN — I. A sample of quasars     

D. J. Saikia  G. F. Holmes  A. R. Kulkarni  C. J. Salter  & S. T. Garrington 《Monthly notices of the Royal Astronomical Society》1998,298(3):877-887

We present total-intensity and linear-polarization observations at a single epoch for a sample of 11 quasars and one BL Lac object. The data were taken with the VLA A array at λλ 20, 18, 6 and 2 cm. We examine the variation of the degree of polarization, p , and polarization position angle, PA, with wavelength, and attempt to determine the rotation measure, RM, of the cores in these sources. The degree of polarization does not exhibit any systematic variation with wavelength, the median values ranging from 2.3 to 3.5 per cent at the different wavelengths. The variation of PA with λ² is not linear over the entire wavelength range. However, for most sources the λλ 20-, 18- and 6-cm PAs do follow such a linear relationship, yielding a median |RM| of about 15 rad m⁻². In contrast, the λλ 6- and 2-cm observations give a median |RM| of about 129 rad m⁻². The long-wavelength emission is likely to originate from a spatially different part of the milliarcsec-scale jet from the λ 2-cm emission, which could turn over at a higher frequency and is likely to be more compact and located closer to the quasar nucleus. We have attempted to obtain linear fits over the entire wavelength range allowing for n  π ambiguities in the PAs, but the fits are not statistically significant. The low values of RM for these core-dominated sources suggest that either the radio emission from the jet intercepts few of the emission-line clouds and their confining medium, or the clouds have a small filling factor and are possibly magnetically confined.  相似文献   

A Polarization Study of Radio Galaxies and Quasars selected from the Molonglo Complete Sample     

C. H. Ishwara-Chandra  D. J. Saikia  V. K. Kapahi  & P. J. McCarthy 《Monthly notices of the Royal Astronomical Society》1998,300(1):269-286

We present total intensity and linear polarization observations made with the Very Large Array at λλ20 and 6 cm of a representative sample of 42 radio galaxies and quasars selected from the Molonglo complete sample. The sources have been chosen to be of large size to probe the depolarizing medium on these scales using our present data and later with observations at lower frequencies with the Giant Metrewave Radio Telescope. The λ20 and 6 cm data are of similar resolutions and show that depolarization between these two wavelengths is seen largely only in those lobes which are within about 300 kpc of the parent galaxy. Examination of the depolarization of the lobes with arm-length asymmetry shows that depolarization is observed predominantly for the lobe which is closer to the nucleus. There is also a trend for the lobe closer to the nucleus to be brighter, consistent with the scenario that the nearer lobe is interacting with a denser environment which is responsible for the higher depolarization and greater dissipation of energy. We have also examined the depolarization asymmetry of the lobes on opposite sides of the nucleus for galaxies and quasars. This shows that the depolarization asymmetry for quasars is marginally higher than that for galaxies. The depolarization properties of our sample are possibly determined by an asymmetric environment as well as the effects of orientation.  相似文献   

60年代末与70年代末中国4个地磁台处Jerk的分析   总被引：5，自引：0，他引：5       下载免费PDF全文

陈伯舫 《地球物理学报》1998,41(1):71-78

外场的影响可以通过一定的方法从地磁月均值中消除,本文用通日月均值资料分析了广州、余山、兰州和北京的Jerk的大小．结果显示,上述4台的X和Y分量都存在二次寻数阶跃．Z分量上Jerk不明显,只有兰州和北京台较易看出60年代末的Jerk．由于本文结果是尽量消除外场影响后的结果,又是中低纬度地区的结果,所以作者认为它可支持Jerk是源于地核的推论,而且认为应将60年代末的Jerk与70年代末的Jerk一并研究．  相似文献   

γ-ray burst ultraviolet/optical afterglow polarimetry as a probe of quantum gravity     

Yi-Zhong Fan †  Da-Ming Wei  Dong Xu 《Monthly notices of the Royal Astronomical Society》2007,376(4):1857-1860

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Constraining the geometry of the neutron star RX J1856.5−3754     

Wynn C. G. Ho 《Monthly notices of the Royal Astronomical Society》2007,380(1):71-77

RX J1856.5−3754 is one of the brightest, nearby isolated neutron stars (NSs), and considerable observational resources have been devoted to its study. In previous work, we found that our latest models of a magnetic, hydrogen atmosphere match well the entire spectrum, from X-rays to optical (with best-fitting NS radius   R ≈ 14  km, gravitational redshift   z _g∼ 0.2  , and magnetic field   B ≈ 4 × 10¹²  G). A remaining puzzle is the non-detection of rotational modulation of the X-ray emission, despite extensive searches. The situation changed recently with XMM–Newton observations that uncovered 7-s pulsations at the     level. By comparing the predictions of our model (which includes simple dipolar-like surface distributions of magnetic field and temperature) with the observed brightness variations, we are able to constrain the geometry of RX J1856.5−3754, with one angle <6° and the other angle     , though the solutions are not definitive, given the observational and model uncertainties. These angles indicate a close alignment between the rotation and the magnetic axes or between the rotation axis and the observer. We discuss our results in the context of RX J1856.5−3754 being a normal radio pulsar and a candidate for observation by future X-ray polarization missions such as Constellation-X or XEUS .  相似文献   

The Dependence of the Geoeffectiveness of Interplanetary Flux Rope on Its Orientation,with Possible Application to Geomagnetic Storm Prediction     

Yuming Wang  Pinzhong Ye  S. Wang 《Solar physics》2007,240(2):373-386

Interplanetary magnetic clouds (MCs) are one of the main sources of large non-recurrent geomagnetic storms. With the aid of a force-free flux rope model, the dependence of the intensity of geomagnetic activity (indicated by Dst index) on the axial orientation (denoted by θ and φ in GSE coordinates) of the magnetic cloud is analyzed theoretically. The distribution of the Dst values in the (θ, φ) plane is calculated by changing the axial orientation for various cases. It is concluded that (i) geomagnetic storms tend to occur in the region of θ<0°, especially in the region of θ≲−45°, where larger geomagnetic activity could be created; (ii) the intensity of geomagnetic activity varies more strongly with θ than with φ; (iii) when the parameters B ₀ (the magnetic field strength at the flux rope axis), R ₀ (the radius of the flux rope), or V (the bulk speed) increase, or |D| (the shortest distance between the flux rope axis and the x-axis in GSE coordinates) decreases, a flux rope not only can increase the intensity of geomagnetic activity, but also is more likely to create a storm, however the variation of n (the density) only has a little effect on the intensity; (iv) the most efficient orientation (MEO) in which a flux rope can cause the largest geomagnetic activity appears at φ∼0° or ∼ 180°, and some value of θ which depends mainly on D; (v) the minimum Dst value that could be caused by a flux rope is the most sensitive to changes in B ₀ and V of the flux rope, and for a stronger and/or faster MC, a wider range of orientations will be geoeffective. Further, through analyzing 20 MC-caused moderate to large geomagnetic storms during 1998 – 2003, a long-term prediction of MC-caused geomagnetic storms on the basis of the flux rope model is proposed and assessed. The comparison between the theoretical results and the observations shows that there is a close linear correlation between the estimated and observed minimum Dst values. This suggests that using the ideal flux rope to predict practical MC-caused geomagnetic storms is applicable. The possibility of the long-term prediction of MC-caused geomagnetic storms is discussed briefly.  相似文献   

Similarity of new palaeomagnetic data from the Santa Rosa Mountains with those from Steens Mountain gives wide regional evidence for a two-stage process of geomagnetic field reversal     

Neil Roberts  Mike Fuller 《Geophysical Journal International》1990,100(3):521-526

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