The impact and rotational light curves of Comet 9P/Tempel 1     

Jean Manfroid  Damien Hutsemékers  Anita L. Cochran  William M. Jackson  Rita Schulz 《Icarus》2007,187(1):144-155

UVES and HIRES high-resolution spectra of Comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C₃, CH, C₂, NH₂, and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact light curves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The impact light curves are consistent with velocities of 400-600 m/s. Their modeling requires a three-step dissociation sequence “Grand-Parent → Parent → Daughter” to produce the observed molecules. The rotational light curve for each species is explained in terms of a single model with three sources. The dust component can however not easily be explained that way.  相似文献   

The western end of the Eoalpine High‐Pressure Belt (Texel unit,South Tyrol / Italy)          下载免费PDF全文

Hannah Pomella  David Flöss  Romed Speckbacher  Peter Tropper  Bernhard Fügenschuh 《地学学报》2016,28(1):60-69

Eclogites in the Texel Unit (Eastern Alps; South Tyrol, Italy) represent the westernmost outcrops of the E–W striking Eoalpine High‐Pressure Belt (EHB). East of the Tauern Window, the EHB forms part of a Cretaceous intracontinental south‐dipping subduction/collision zone; however, the same nappe stack displays a northwest dip at its western end. This prominent change in dip direction gave rise to discussions on the general setting of the Eoalpine collision. Based on our own observations and literature data, we present a new tectonic model for the western end of the EHB. Due to the special situation of this area at the tip of the Southalpine indenter, originally south(east) dipping structures became overturned, and former thrusts appear as normal faults (e.g. Schneeberg fault zone) while former normal faults presently display thrust geometries (e.g. Jaufen fault). Thus, we explain the current configuration with a coherent Eoalpine subduction direction.  相似文献   

Cosmological models with the variable gravitational and cosmological constants     

N. Ibotombi Singh  Anita Sorokhaibam 《Astrophysics and Space Science》2007,310(1-2):131-134

Cosmology with the gravitational and cosmological constants generalized as coupling scalars in Einsteins theory is considered. A general method of solving the field equations is given. Exact solution for Zeldovich fluid satisfying G=G ₀(R/R ₀) ⁿ is given.  相似文献   

Hybrid character and pre-eruptive events of Mt Amiata volcano (Italy) inferred from geochronological,petro-geochemical and isotopic data     

Anita Cadoux  Daniele L. Pinti 《Journal of Volcanology and Geothermal Research》2009,179(3-4):169-190

A new geochronological and geochemical study was carried out to better constrain the petrogenesis and eruptive history of Monte Amiata, a large Pleistocene trachydacitic volcano of Southern Tuscany. Previous studies suggested a magma mixing origin between calc-alkaline silicic melts from the Tuscan Magmatic Province (TMP) and potassic mafic melts like those found in the Roman Magmatic Province (RMP). Two eruptive episodes–the first at ca. 300 kyr, the second at ca. 200 kyr–were distinguished from the few available ages. However, both the involvement of a RMP-like melt as mafic end-member and the timing of volcanic activity remained to be ascertained. The K–Ar ages obtained on plagioclase, sanidine and glass separated from Mt Amiata volcanic rocks demonstrate the sanidine is the most suitable phase for K–Ar dating. Sanidine yields ages of 304–293 kyr for the basal trachydacitic unit (BTC), 298–280 kyr in the domes unit (DLC) and unexpected older ages of 312–308 kyr for the more mafic summit lava unit (OLL). A careful re-examination of the literature ages together with those obtained in this study shows that they tend to a common age of ca. 300 kyr whatever the volcanic unit. We interpret this as a reset of the K–Ar chronometer in response to a consequent recharge of the silicic magma reservoir by hot mafic melts. This recharge most probably triggered the first volcanic eruption of Mt Amiata magmas. In our model, we suppose an initially chemically-stratified magma chamber; the input of deep hot mafic melts reset the crystals clock and probably allowed the eruption of the huge amount of trachydacitic crystal mush. We propose that the controversial BTC unit could have emplaced during a non-explosive eruption if we consider either pre-eruption passive degassing or extrusion of the trachydacites as magmatic foam.First Pb isotopic data of mafic enclaves from the trachydacitic units, together with major and trace elements and new Sr and Nd data support the magma mixing as the dominant process at the origin of the Mt Amiata volcanic rocks. The similar LILE/HFSE ratios evidenced in this contribution between the magmatic enclaves of Mt Amiata and RMP volcanic rocks, together with their comparable Sr, Nd and Pb isotopic compositions, definitively argue for the involvement of a RMP-like melt in the mixing. The Mt Amiata is thus indisputably a hybrid volcano between TMP and RMP in terms of petrogenesis and ages.  相似文献   

龙门山断裂带印支期左旋走滑运动及其大地构造成因   总被引：60，自引：6，他引：60  

王二七  陈智梁等 《地学前缘》2001,8(2):375-384

位于青藏高原东缘的龙门山构造呈北东—南西向将松潘—甘孜褶皱带和华南地块分割开。前者主要是由一套巨厚的三叠纪复理石沉积组成 ,分布在古特提斯海的东缘。后者由前寒武纪基底和上覆的古生代和中生代沉积盖层组成。位于汶川—茂汶断裂以东的前龙门山存在一系列倾向北西的逆掩断层 ,它们将许多由元古宙和古生代岩层组成的断片向南东置于四川盆地的中生代红层之上 ,构成典型的薄皮构造。许多研究由此断定松潘—甘孜褶皱带和四川盆地之间在中生代发生过大规模的北西—南东向挤压。然而 ,汶川—茂汶断裂西侧的松潘—甘孜褶皱带内部的挤压构造线大多是垂直于而不是平形于龙门山断裂带 ,这表明当时的挤压应力不是北西—南东向而是北东—南西向。近年来在龙门山构造带内发现 ,在三叠纪时龙门山断裂带在发生推覆的同时还经历过大规模的北东—南西向的左旋走滑运动 ,协调走滑运动的主要构造为汶川—茂汶断裂。走滑运动的成因与松潘—甘孜褶皱带北东—南西向缩短有关。汶川—茂汶断裂的左旋走滑在龙门山的北东端被古特提斯海沿勉略俯冲带的消减和发生在大巴山的古生代 /中生代岩层的褶皱和冲断作用所吸收 ,在龙门山的南西端被古特提斯海沿甘孜—理塘俯冲带的消减和松潘—甘孜三叠纪复理石的褶皱和冲断作用所吸?  相似文献   

河西内陆河地表水与地下水转化及水资源利用率研究   总被引：16，自引：8，他引：16  

张济世  康尔泗  蓝永超  陈仁升  陈满祥 《冰川冻土》2001,23(4):375-382

河西内陆河水资源产生于祁连山区 ,河流出山以后依次穿越山前洪积扇、走廊南部盆地、北部盆地 ,最后进入尾闾湖 .由于山前洪积扇、南北盆地及河床具有良好的通透性和巨大的蓄水能力使地表水易于转化为地下水 ,出山水量的很大一部分渗入地下避免无效蒸散损耗 ;同时由于特殊的串珠状水文地质盆地构造 ,水资源具有同源性和多次转化特点 ,使水资源的利用率大大提高 .研究表明 ,1999年河西水资源总量为 6 3 79× 10 8m3 ,其中 ,地表水资源量为 5 8 36× 10 8m3 ,地下水资源量为 5 6 39× 10 5m3 ,地表水与地下水重复计算量高达 5 0 96× 10 5m3 .三个流域水资源利用率达到 6 1 4%～ 2 11%  相似文献   

The prism method for terrain corrections using digital computers   总被引：1，自引：0，他引：1  

Dezső Nagy 《Pure and Applied Geophysics》1966,63(1):31-39

Summary In the prism method of making terrain corrections, the topography is approximated by a model consisting of right rectangular prisms. The vertical component of the gravitational attraction of each prism is calculated and the sum of these components gives the terrain correction.The prism method as programmed has no computational limitations. It can be used on all sizes of computers; it can be applied to a large area with any fine grid interval; it can be processed in a single run and yet provides complete flexibility for both research and routine computations. This has been achieved by breaking up larger areas into regions which fit into the computer memory. The contributions of these regions are automatically summed up for each station. While processing each region, various controls may be used at each station to exclude the contribution of a distant part of the area, to use approximate expressions farther from the station, to print out details around the station. There is also provision to refine the model by using smaller prisms around each computation point. Thus full use of elevation control can be made to calculate the terrain correction, the accuracy of which depends only on the quality of the input data.The prism method has been used to calculate terrain corrections for 130 stations in the New Quebec crater area. For five of these stations terrain corrections were also calculated by usingHammer's template. The two independent sets of values differ by less than four per cent.  相似文献   

The Lyngen Gabbro: the lower crust of an Ordovician Incipient Arc     

Astri?J.?S.?KvassnesEmail author  Anita?Hetland?Strand  Heidi?Moen-Eikeland  Rolf?Birger?Pedersen 《Contributions to Mineralogy and Petrology》2004,148(3):358-379

We present evidence for the origin of the Lyngen Gabbro of the Ordovician Lyngen Magmatic Complex in Troms, Northern Norway. The two magmatic suites of the Lyngen Gabbro strike parallel NNE-SSW, and have distinct magmatic signatures. We define these signatures by using major and trace-element analyses together with selected major- and trace-element mineral analyses and ¹⁴³Nd/¹⁴⁴Nd-isotope whole-rock analyses of gabbroic to tonalitic plutonic rocks from seven detailed cross-sections from this large gabbro-complex. The Western suite of the Lyngen Gabbro precipitated from magma that may have been derived from the same system as the associated volcanic rocks. The gabbros have high An-content (An_>90) of their plagioclases relative to co-existing mafic minerals. Together with somewhat high _Nd(t) values (+6), this implies that the parental magmas were hydrous tholeiites similar to those found in back arc basins today. The Eastern suite, on the other hand, consist of cumulates that were precipitated from melts resembling those of ultra-depleted high-Ca boninitic magmas found in fore-arcs. Extremely high-An plagioclases (An_>95) co-exist with evolved mafic minerals and oxides, and the _Nd(t) values are lower (+4) than in the Western suite. The Eastern suite has no volcanic counterpart, but dikes intersecting the suites have compositions that possibly represent its parental magma. The oceanic Rypdalen Shear Zone generally separates the two suites in the north, but several non-tectonic transitions from boninitic to tholeiitic signatures southwards advocate that the magmatism happened concurrently. The magmatic proximity between the suites, the hydrous magmatism and the absence of a silicic or calc-alkaline mature arc section, suggests that the Lyngen Gabbro formed in the Iapetus Ocean under conditions presently found in incipient arcs later emplaced as outer arc highs.  相似文献   

Multi-Wavelength Observations of an Unusual Impulsive Flare Associated with Cme   总被引：1，自引：0，他引：1  

Wahab?UddinEmail author  Rajmal?Jain  Keiji?Yoshimura  Ramesh?Chandra  T.?Sakao  T.?Kosugi  Anita?Joshi  M.?R.?Despande 《Solar physics》2004,225(2):325-336

We present the results of a detailed analysis of multi-wavelength observations of a very impulsive solar flare 1B/M6.7, which occurred on 10 March, 2001 in NOAA AR 9368 (N27 W42). The observations show that the flare is very impulsive with a very hard spectrum in HXR that reveal that non-thermal emission was most dominant. On the other hand, this flare also produced a type II radio burst and coronal mass ejections (CME), which are not general characteristics for impulsive flares. In H we observed bright mass ejecta (BME) followed by dark mass ejecta (DME). Based on the consistency of the onset times and directions of BME and CME, we conclude that these two phenomena are closely associated. It is inferred that the energy build-up took place due to photospheric reconnection between emerging positive parasitic polarity and predominant negative polarity, which resulted as a consequence of flux cancellation. The shear increased to >80 due to further emergence of positive parasitic polarity causing strongly enhanced cancellation of flux. It appears that such enhanced magnetic flux cancellation in a strongly sheared region triggered the impulsive flare.  相似文献   

Size-Resolved Aerosol Characterization for a Polluted Episode at the IfT Research Station Melpitz in Autumn 1997     

A. Plewka  T. Gnauk  E. Brüggemann  C. Neusüss  H. Herrmann 《Journal of Atmospheric Chemistry》2004,48(2):131-156

Inorganic ions, organic carbon (OC), elemental carbon (EC) and a variety of organic single species in airborne particles have been determined at the research station of the Leibniz – Institut für Troposphärenforschung (IfT) in Melpitz (Germany) in autumn 1997.Samples of eight selected measurement events were divided in two groups in order to investigate differences in the chemical composition of particles originating from southwesterly (SW – developed EU countries) or from easterly directions (E – less developed eastern countries). Differences between these two groups were tested statistically by Student's t-test.Five stage cascade impactor samples show nitrate as most abundant in the accumulation mode in the SW group. EC and sulphate show the most abundant mass fractions in the E group. That can be considered as a consequence of domestic coal heating and coal-fired power plant emissions in the region of westerly Poland, northern Czech Republic and easterly Germany. Higher nitrate concentrations in the SW group can be explained by stronger NO _x emissions caused by the leeward plume of the conurbation of Leipzig, as well as by the still higher traffic density in western Germany.The methane sulphonic acid (MSA) mass fraction was higher for SW air masses in accumulation mode particles, probably indicating marine origin. Succinic acid also showed higher mass fractions for the SW group. This could be caused by primary emission in automobile exhaust gases and photochemical formation during transport from SW. Indeed, during SW sampling, solar radiation intensity was higher than during E sampling.The observed differences in the particle composition are an expression of the still existing technology gradient in Europe. Future campaigns could show the development to a joint economy with smaller differences in anthropogenic emissions.  相似文献