Pre‐Cenomanian vs. Cenozoic folding in the High Atlas revealed by palaeomagnetic data          下载免费PDF全文

Sara Torres‐López  Antonio M. Casas  Juan José Villalaín  Hamidou El Ouardi  Bennacer Moussaid 《地学学报》2016,28(2):110-119

Palaeomagnetic data, and specifically remagnetizations, are used to constrain the geometric reconstruction at 100 Ma of three anticlines cored by gabbroic intrusions and Triassic shales in the Central High Atlas, Morocco. Previous palaeomagnetic results have revealed that the Mesozoic sediments of this region acquired a pervasive remagnetization at the end of the Early Cretaceous. The restoration of palaeomagnetic vectors to the remagnetization stage (100 Ma) allows us to determine the dip of the beds during this period and, thereby, to reconstruct structures during that time and determine the relative contributions of Mesozoic magmatic/diapiric uplift vs. Cenozoic compression to the present‐day dip. Our results indicate that three major anticlines in the Central High Atlas (Tasraft, Tassent and Tissila) were initiated to different degrees before the Late Cretaceous and were reactivated during Cenozoic compression to acquire their present‐day geometry. We also discuss the origin of these structures.  相似文献   

Description and validation of a two-step analogue/regression downscaling method     

J. Ribalaygua  L. Torres  J. Pórtoles  R. Monjo  E. Gaitán  M. R. Pino 《Theoretical and Applied Climatology》2013,114(1-2):253-269

This study describes a two-step analogue statistical downscaling method for daily temperature and precipitation. The first step is an analogue approach: the “n” days most similar to the day to be downscaled are selected. In the second step, a multiple regression analysis using the “n” most analogous days is performed for temperature, whereas for precipitation, the probability distribution of the “n” analogous days is used to define the amount of precipitation. Verification of this method has been carried out for the Spanish Iberian Peninsula and the Balearic Islands. Results show good performance for temperature (BIAS close to 0.1 °C and mean absolute errors around 1.9 °C) and an acceptable skill for precipitation (reasonably low BIAS except in autumn with a mean of ?18 %, mean absolute error lower than for a reference simulation, i.e. persistence and a well-simulated probability distribution according to two non-parametric tests of similarity).  相似文献   

New radial velocities for 30 candidate runaway stars and a possible binary supernova origin for HIP 9470 and PSR J0152–1637     

N. Tetzlaff  G. Torres  A. Bieryla  R. Neuhuser 《Astronomische Nachrichten》2014,335(9):981-991

We report new radial velocity measurements for 30 candidate runaway stars. We revise their age estimates and compute their past trajectories in the Galaxy in order to determine their birthplaces. We find that seven of the stars could be younger than ∼100 Myr, and for five of them we identify multiple young clusters and associations in which they may have formed. For the youngest star in the sample, HIP 9470, we suggest a possible ejection scenario in a supernova event, and also that it may be associated with the young pulsar PSR J0152–1637. Our spectroscopic observations reveal seven of the stars in the sample of 30 to be previously unknown spectroscopic binaries. Orbital solutions for four of them are reported here as well. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

A research program to map the Galactic Emission at low frequencies     

G. De Amici  S. Torres  M. Bensadoun  M. Bersanelli  G. Dall'Oglio  M. Limon  G. Smoot  G. Sironi  T. Villela  C. Witebsky 《Astrophysics and Space Science》1994,214(1-2):151-160

The need for accurate and complete maps of the galaxy at radio frequencies is made evident not only by the importance of the data in the study of galactic dynamics and structure formation but also in the analysis of cosmic background radiation data. A summary of the existing radio surveys of our galaxy is presented along with their limitations. A new program, the Galactic Emission Mapping (GEM) project, to obtain calibrated and complete maps of the galaxy in the 400 to 1400 MHz range, is outlined.Presented at the 2nd UN/ESA Workshop, held in Bogotá, Colombia, 9-13 November, 1992.  相似文献   

Ground response curves for rock masses exhibiting strain‐softening behaviour     

E. Alonso  L. R. Alejano  F. Varas  G. Fdez‐Manin  C. Carranza‐Torres 《国际地质力学数值与分析法杂志》2003,27(13):1153-1185

A literature review has shown that there exist adequate techniques to obtain ground reaction curves for tunnels excavated in elastic‐brittle and perfectly plastic materials. However, for strain‐softening materials it seems that the problem has not been sufficiently analysed. In this paper, a one‐dimensional numerical solution to obtain the ground reaction curve (GRC) for circular tunnels excavated in strain‐softening materials is presented. The problem is formulated in a very general form and leads to a system of ordinary differential equations. By adequately defining a fictitious ‘time’ variable and re‐scaling some variables the problem is converted into an initial value one, which can be solved numerically by a Runge–Kutta–Fehlberg method, which is implemented in MATLAB environment. The method has been developed for various common particular behaviour models including Tresca, Mohr–Coulomb and Hoek–Brown failure criteria, in all cases with non‐associative flow rules and two‐segment piecewise linear functions related to a principal strain‐dependent plastic parameter to model the transition between peak and residual failure criteria. Some particular examples for the different failure criteria have been run, which agree well with closed‐form solutions—if existing—or with FDM‐based code results. Parametric studies and specific charts are created to highlight the influence of different parameters. The proposed methodology intends to be a wider and general numerical basis where standard and newly featured behaviour modes focusing on obtaining GRC for tunnels excavated in strain‐softening materials can be implemented. This way of solving such problems has proved to be more efficient and less time consuming than using FEM‐ or FDM‐based numerical 2D codes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Studies of multiple stellar systems – IV. The triple-lined spectroscopic system Gliese 644     

Tsevi Mazeh  David W. Latham  Elad Goldberg  Guillermo Torres  Robert P. Stefanik  Todd J. Henry †  Shay Zucker  Orly Gnat  Eran O. Ofek 《Monthly notices of the Royal Astronomical Society》2001,325(1):343-357

We present a radial velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.965 5 and 627 d. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. These two orbits together allow us to derive masses for each of the three components in the system: M _A=0.410±0.028 (6.9 per cent), M _Ba=0.336±0.016 (4.7 per cent), and M _Bb=0.304±0.014 (4.7 per cent) M_⊙. We suggest that the relative inclination of the two orbits is very small. Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass–luminosity relation near the bottom of the main sequence, where the relation is poorly determined. These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr. Our radial velocities for Gliese 643 and vB 8, two common proper motion companions of Gliese 644, support the interpretation that all five M stars are moving together in a physically bound group. We discuss possible scenarios for the formation and evolution of this configuration, such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed, versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration.  相似文献   

THERMAP: a mid-infrared spectro-imager for space missions to small bodies in the inner solar system     

O. Groussin  J. Licandro  J. Helbert  J. L. Reynaud  P. Levacher  M. Reyes García-Talavera  V. Alí-Lagoa  P. E. Blanc  E. Brageot  B. Davidsson  M. Delbó  M. Deleuze  A. Delsanti  J. J. Diaz Garcia  K. Dohlen  D. Ferrand  S. F. Green  L. Jorda  E. Joven Álvarez  J. Knollenberg  E. Kührt  P. Lamy  E. Lellouch  J. Le Merrer  B. Marty  G. Mas  C. Rossin  B. Rozitis  J. Sunshine  P. Vernazza  S. Vives 《Experimental Astronomy》2016,41(1-2):95-115

We present THERMAP, a mid-infrared spectro-imager for space missions to small bodies in the inner solar system, developed in the framework of the MarcoPolo-R asteroid sample return mission. THERMAP is very well suited to characterize the surface thermal environment of a NEO and to map its surface composition. The instrument has two channels, one for imaging and one for spectroscopy: it is both a thermal camera with full 2D imaging capabilities and a slit spectrometer. THERMAP takes advantage of the recent technological developments of uncooled microbolometer arrays, sensitive in the mid-infrared spectral range. THERMAP can acquire thermal images (8–18 μm) of the surface and perform absolute temperature measurements with a precision better than 3.5 K above 200 K. THERMAP can acquire mid-infrared spectra (8–16 μm) of the surface with a spectral resolution Δλ of 0.3 μm. For surface temperatures above 350 K, spectra have a signal-to-noise ratio >60 in the spectral range 9–13 μm where most emission features occur.  相似文献   

Rock-magnetic properties of topsoils and urban dust from Morelia (>800,000 inhabitants), Mexico: Implications for anthropogenic pollution monitoring in Mexico’s medium size cities     

Bertha Aguilar Reyes  Francisco Bautista  Avto Goguitchaichvili  Juan Julio Morales Contreras  Julie Battu  Patricia Quintana Owen  Claire Carvallo 《Geofísica Internacional》2013,52(2):121-133

In this work, we investigate the correlation between some magnetic parameters and the level of contamination by heavy metals in urban soils from Morelia city, western Mexico. The magnetic study was carried out on 98 urban soils samples belonging to distinct land uses. Most of analyzed samples contain ferrimagnetic minerals as the responsible for magnetization, most probably corresponding to the titanomagnetites/ titanomaghemites solid solutions. This is inferred from the susceptibility vs. temperature measurements and the isothermal remanent magnetization (IRM) experiments. These measurements also indicate that most of samples are almost completely saturated before 300 mT. Additionally, the S_-200 values (S_-200 = IRM_-200/ SIRM, where IRM_-200= Back-field of 200 mT after magnetic saturation) are between 0.7 and 1.0, characteristic of low coercivity magnetic minerals. The averaged saturation isothermal remanent magnetization (SIRM) curves can be used as an indicator of pollution level, as these curves show different saturation values according to the level of contamination by heavy metals: Cu, Ni, Cr and Sr. These associations of (titano)magnetite with heavy metals were observed by Scanning Electron Microscope revealing some complex aggregates rather than commonly detected spherules.  相似文献   

Archeointensity investigation on pottery vestiges from Puertas de Rolón, Capacha culture: In search for affinity with other Mesoamerican pre-Hispanic cultures     

Juan Morales  Avto Goguitchaichvili  María de los Ángeles Olay Barrientos  Claire Carvallo  Bertha Aguilar Reyes 《Studia Geophysica et Geodaetica》2013,57(4):605-626

We report the results of a rock magnetic and archeointensity study on pottery fragments recovered at the archaeological site of Puertas de Rolón, Capacha culture (Colima), that is considered one of the most important pre-Classic cultural developments of western Mesoamerica, Mexico. Standard rock magnetic experiments were carried out in order to investigate the reliability of the ancient field strength recovered from studied materials. Six out of the seven analyzed fragments gave reliable intensity determinations. The mean archeointensity value obtained in this study is 35.3 ± 3.4 μT. It is in good agreement with another contemporaneous Mesoamerican mean archeointensity of 34.3 ± 1.1 μT obtained for El Opeño. Statistically similar rock-magnetic parameters between ceramics from El Opeño and Puertas de Rolón potsherds appear to be related to clay-sources with similar geological settings and weathering processes. Alternatively, ancient trade or interexchange between western (Capacha Culture) and eastern Mesoamerica locations, as it has been proposed earlier, seem to be supported by results obtained in this study.  相似文献   

Bare soil evaporation under high evaporation demand: a proposed modification to the FAO-56 model     

Enrique A. Torres 《水文科学杂志》2013,58(3):303-315

Abstract

This study evaluates the evaporation component of the FAO-56 model under high evaporation demand. To perform this, two data sets were used as field evaluation, and a second model was used for comparison (a model based on the square root of time, SRT). The results show that although FAO-56, the field data and the SRT model present similar cumulative evaporation over the study period (approximately one month), when the data are analysed daily, FAO-56 overestimated evaporation at the beginning of the process and underestimated it at the end. A correction for FAO-56 is proposed to amend the mismatch between FAO-56 and the field-measured data under high evaporation conditions. Consequently, the parameters used by the FAO-56 evaporation component are discussed.

Citation Torres, E. A. & Calera, A. (2010) Bare soil evaporation under high evaporation demand: a proposed modification to the FAO-56 model. Hydrol. Sci. J. 55(3), 303–315.  相似文献