LOCALLY NONLINEAR STOCHASTIC ANALYSIS OF OFFSHORE STRUCTURES

This paper' presents a simple method for the stochastic dynamic analysis of some offshore platforms with localized nonlinearity. The transfer function of the platform with initial linear stiffness is first determined, and the nonlinear iteration is performed on the condensed stiffness matrix only. Computational efforts are reduced. This method can be used to analyze a fixed platform on nonlinear foundation and a guyed tower platform having nonlinear guylines.     

Polycyclic aromatic hydrocarbons in the atmospheres of Titan and Jupiter

Polycyclic aromatic hydrocarbons (PAHs) are important components of the interstellar medium and carbonaceous chondrites, but have never been identified in the reducing atmospheres of the outer solar system. Incompletely characterized complex organic solids (tholins) produced by irradiating simulated Titan atmospheres reproduce well the observed UV/visible/IR optical constants of the Titan stratospheric haze. Titan tholin and a tholin generated in a crude simulation of the atmosphere of Jupiter are examined by two-step laser desorption/multiphoton ionization mass spectrometry. A range of two- to four-ring PAHs, some with one to four alkylation sites are identified, with net abundance approximately 10(-4) g g-1 (grams per gram) of tholins produced. Synchronous fluorescence techniques confirm this detection. Titan tholins have proportionately more one- and two-ring PAHs than do Jupiter tholins, which in turn have more four-ring and larger PAHs. The four-ringed PAH chrysene, prominent in some discussions of interstellar grains, is found in Jupiter tholins. Solid state 13C NMR spectroscopy suggests approximately equal to 25% of the total C in both tholins is tied up in aromatic and/or aliphatic alkenes. IR spectra indicate an upper limit in both tholins of approximately equal to 6% by mass in benzenes, heterocyclics, and PAHs with more than four rings. Condensed PAHs may contribute at most approximately 10% to the observed detached limb haze layers on Titan. As with interstellar PAHs, the synthesis route of planetary PAHs is likely to be via acetylene addition reactions.     

The IRS 1 circumstellar disk, and the origin of the jet and CO outflow in B5

We report the discovery of the inner edge of the high velocity CO outflow associated with the bipolar jet originating from IRS 1 in Barnard 5 and the first ever resolution of its circumstellar disk in the 2.6 mm dust continuum and C18O. From high spatial resolution observations made with the Owens Valley Millimeter Array we are able to locate the origin of the outflow to within approximately 500 AU on either side of IRS 1 and apparently at the edge of, or possibly within, its circumstellar disk. The orientation of the continuum disk is perpendicular to the highly collimated jet outflow recently seen in optical emission at much farther distances. The disk has been detected in C18O giving a disk mass approximately 0.16 M (solar). Our HCO+ and HCN maps indicate significant chemical differentiation in the circumstellar region on small scales with HCO+ tracing an extended disk of material. The 12CO interferometer maps of the outflow show two conelike features originating at IRS 1, the blue one fanning open to the northeast and the red one to the southwest. The vertices of the cones are on either side of the circumstellar disk and have a projected opening angle of about 90 degrees. The intrinsic opening angle is in the range of 60 degrees-90 degrees which leads to significant interaction between outflow and infall.     

Homochirality as the signature of life: the SETH Cigar

A characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. It is therefore suggested that a search for extra-terrestrial life can be approached as a Search for Extra-Terrestrial Homochirality (SETH). A novel miniaturized space polarimeter, called the SETH Cigar, is described which could he used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. It is believed that homochirality will be found in the subsurface layers on Mars as a relic of extinct life.     

一次地震导致另一次地震

在本期(Nature,375卷,1995年5月18日)的221页上,Harris,Simpson和Reasenberg考察了南加州相邻地震间可能存在的联系。作者发现在一个大于等于5级地震震后的前18个月内,任一个邻近地区发生的后续大震(M≥5)几乎总是发生在一条被首震引起的静应力场变化所加载趋于破裂的断层上。如果是这样的话,它对于地震危险性评价意味着什么呢? 一次地震能够用一个弹性介质内的有限位错     

震后一分钟：强震图,有效震中和有效震级

本文报道了台湾实时地震监测的最新进展,尤其是台湾中心气象局遥测地震台网(CWBSN)的实时强震监测。该项工作旨在大震发生后迅即速报。如果速报能在强振动到来之前完成,那么地震早期警报将成为可能。CWBSN已能在大震发生后一分钟内给出强度图、震中和震级。速报和早期警报主要适用于大震(M>>5);不限幅波形记录的需要促使CWBSN在1995年将强震探测仪(如力平衡加速度计)并入其遥测地震监测系统中。将时间域递归处理应用于多道输入地震信号,通过一组联网微机生成强度图。通过等值线,能迅速识别出位于强度图最大等值线(通常为100gal)中央的有效震中。有效震级也能迅速由最大等值线(通常为100gal)覆盖的表面积确定。对于具有有限破裂面的大震,如此得出的震中和震级是更适当的震源位置和破坏强度的估算值。有效震中给出了破坏区域的中心,与传统的震中定位比较,后者仅给出了破裂形成的初始位置。有效震级所反映的更接近地震破坏的潜能,而不是强调总能量释放的传统震级。CWBSN已能在一分钟内获取上述震源的关键信息。这一时间将会进一步缩短至30s以内,如本文中举例描述的那样,地震早期警报的确是一个可能达到的目标。速报和早期警报信息将电传给用户,以采取人为或无人干予的快速反应行动。     

球粒陨石冲击脉体冷却速率对(Mg,Fe)_2SiO_4多型转变的制约

发生在寺巷口陨石冲击脉体的较大冷却速率 ( >1 0 0 0 0℃·s-1)使得橄榄石(α 相 )的高压多型γ相被保存了下来 ;冷却速率中等的和平河陨石冲击脉体 ( 1 0 0 0～ 2 0 0 0℃·s-1) ,γ相部分逆转为β相 ,但β相向α相的进一步逆转受阻 ,脉体保存了β相 ;冷却速率较慢的蒙巴喇陨石冲击脉体 ( <5 0 0℃·s-1) ,γ相几乎全部逆转为α相 .冲击脉体的热散失滞后于陨石母体冲击压缩阶段 ,发生在陨石母体崩解成碎块以后 .脉体的冷却速率制约了 (Mg ,Fe) 2 SiO4高压多型的逆向转变过程 .