Design and performance of the angle integrating erenkov array AIROBICC     

A. Karle  M. Merck  R. Plaga  F. Arqueros  V. Haustein  G. Heinzelmann  I. Holl  V. Fonseca  E. Lorenz  S. Martinez  V. Matheis  H. Meyer  R. Mirzoyan  J. Prahal  D. Renker  M. Rozanska  M. Samorski 《Astroparticle Physics》1995,3(4)

An air-shower array consisting of 49 open huts with photomultiplier tubes viewing the night sky over a solid angle of about 1 steradian is described. The array is operating in conjunction with the HEGRA installation. The main objectives of the experiment are VHE to UHE γ-ray astronomy and a determination of the chemical composition of cosmic rays. The design principles, construction and performance in angular resolution, energy threshold and determination of shower parameters are discussed.  相似文献   

Using beryllium-7 to evaluate soil erosion processes in agricultural lands in semiarid regions of Central Argentina     

Juan Pablo de Rosas  Alexander Dario Esquivel  Diego Martinez Heimann  Agustin E. Negri  Flavia Lohaiza  Diego Leonardo Valladares  Alejandro I. Zavala  Hugo Huck  Jimena Juri Ayub 《Environmental Earth Sciences》2018,77(16):587

This work presents the results of a soil erosion study using the ⁷Be technique. This technique estimates the water erosion/deposition from the comparison between ⁷Be soil content of a reference site and an eroded or sedimented site. The soil samples were collected from an agricultural area of the semiarid region of Argentina near San Luis City, which has a marked rainfall season. The area has been used for crop cultivation, being subjected to plowing practices. The ⁷Be in the Reference Site was in the first centimeter of soil, showing the typical exponential decreasing of ⁷Be soil content with depth, with the ⁷Be inventories value being 340?±?50 Bq m^?2 for the dry season and 571?±?48 Bq m^?2 for the rainy season. The ⁷Be technique was applied to a potential eroded site subjected to traditional tillage practices (plowing). A net soil erosion value of 13.5 t ha^?1 (1.35 kg m^?2) was obtained. From the assumptions of the applied technique, we can draw the inference that this erosion was caused by rains produced in the month prior to the date of soil sampling.  相似文献   

Making capitalism in rural China     

Miguel Hidalgo Martinez 《The Australian geographer》2015,46(2):289-290

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Autonomous bathymetry survey system     

Bourgeois  B.S. Martinez  A.B. Alleman  P.J. Cheramie  J.J. Gravley  J.M. 《Oceanic Engineering, IEEE Journal of》1999,24(4):414-423

This paper describes the Autonomous Bathymetry Survey System (AutoSurvey), a system that provides automation of swath sonar bathymetric surveys. This system enables faster surveying of an area through environmentally adaptive techniques while ensuring adequate coverage and data quality. AutoSurvey assesses data quality and coverage in real time and generates next-trackline waypoints based on actual system performance. The need for real-time performance assessment is discussed. A primary factor considered is the effect of the environment on swath bathymetry system performance, which is difficult to predict a priori. The system's features, design, and implementation are discussed in this paper. Simulation and sea trial results are presented, as well as an analysis of the system's ability to reduce survey time  相似文献   

Subglacial clast behaviour and its implication for till fabric development: new results derived from wireless subglacial probe experiments     

Jane K. Hart  Kathryn C. Rose  Kirk Martinez  Royan Ong 《Quaternary Science Reviews》2009,28(7-8):597-607

This study has investigated the three-dimensional movement of clasts within deformation till, using embedded wireless probes. These probes were part of an environmental sensor network, which measured subglacial properties (temperature, water pressure, resistivity, case strain and tilt) six times a day, and relayed that data via radio to the glacier surface, where they were forwarded and broadcast on-line. The system was installed at Briksdalsbreen, Norway and operated from August 2004 until August 2006. Approximately 2000 probe days worth of data were collected, with an increase in performance (41% more readings) during the second year. The probes showed similar patterns of water pressure rises throughout the two years, but with slightly different magnitudes and timings. These changes in water pressure could be related to clast behaviour. The probes decreased their dip over the year, and the rate of change was related to an increase in glacier velocity. After initial changes in dip, the probes experienced changes in orientation, followed by rotation about the a-axis. This continuous rotation was similar to the motion suggested by Jeffery [1922. The motion of ellipsoidal particles immersed in a viscous fluid. Proceedings of the Royal Society of London, Series A 102, 161–179] for the behaviour of clasts within a viscous material. In addition, some probes also showed short, frequent dip oscillations in spring and autumn, which were interpreted to reflect stick-slip events, similar to lodging; and demonstrated how local conditions can interrupt the predicted rotation pattern.Overall, it is demonstrated that when water pressures were high, decoupling occurred associated with basal sliding and dip oscillations; and when water pressures fell, the ice and sediment were coupled and till deformation occurred. These events happened during summer and autumn. It is this combination of “lodgement” and deformation that builds up both a complex (but predictable) fabric and a resultant composite till sedimentology.  相似文献   

Exploring the gamma ray horizon with the next generation of gamma ray telescopes. Part 3: Optimizing the observation schedule of gamma ray sources for the extraction of cosmological parameters     

O. Blanch  M. Martinez   《Astroparticle Physics》2005,23(6):608-615

The optimization of the observation schedule of gamma ray emitters by the new generation of Cherenkov telescopes to extract cosmological parameters from the measurement of the gamma ray horizon at different redshifts is discussed. It is shown that improvements over 35% in the expected cosmological parameter uncertainties can be achieved if instead of equal-observation time, dedicated observation schedules are applied.  相似文献   

Qualitative study of the planar isosceles three-body problem     

Carles Simó  Regina Martinez 《Celestial Mechanics and Dynamical Astronomy》1987,41(1-4):179-251

We consider the particular case of the planar three body problem obtained when the masses form an isosceles triangle for all time. Various authors [1, 2, 12, 8, 9, 13, 10] have contributed in the knowledge of the triple collision and of several families of periodic orbits in this problem. We study the flow on a fixed level of negative energy. First we obtain a topological representation of the energy manifold including the triple collision and infinity as boundaries of that manifold. The existence of orbits connecting the triple collision and infinity gives some homoclinic and heteroclinic orbits. Using these orbits and the homothetic solutions of the problem we can characterize orbits which pass near triple collision and near infinity by pairs of sequences. One of the sequences describes the regions visited by the orbit, the other refers to the behaviour of the orbit between two consecutive passages by a suitable surface of section. This symbolic dynamics which has a topological character is given in an abstract form and after it is applied to the isosceles problem. We try to keep globality as far as possible. This strongly relies on the fact that the intersection of some invariant manifolds with an equatorial plane (v=0) have nice spiraling properties. This can be proved by analytical means in some local cases. Numerical simulations given in Appendix A make clear that these properties hold globally.  相似文献   

Exploring the gamma ray horizon with the next generation of gamma ray telescopes. Part 1: Theoretical predictions     

O. Blanch  M. Martinez   《Astroparticle Physics》2005,23(6):588-597

The physics potential of the next generation of gamma ray telescopes in exploring the gamma ray horizon is discussed. It is shown that a reduction in the gamma ray detection threshold might open a window to use precise determinations of the gamma ray horizon as a function of redshift to either put strong constraints on the extragalactic background light modelling or to obtain relevant independent constraints on the cosmological densities Ω_M and Ω_Λ.  相似文献   

A boundary integral method for steady flow in unsaturated porous media     

M. J. Martinez  D. F. McTigue 《国际地质力学数值与分析法杂志》1992,16(8):581-601

The governing equation for steady flow in a homogeneous, partially saturated, porous medium can be written in a linear form if one adopts a hydraulic conductivity function which varies exponentially with capillary-pressure head. The resulting linear field equation is a steady Fokker–Planck equation and is well-suited to numerical solution by the boundary integral equation method (BIEM). The exponential conductivity function is often used in soil physics and is known to be a reasonable approximation over limited ranges of pressure head. A computer code based on the BIEM for obtaining numerical solutions is described and tested. The BIEM is found to exhibit quadratic convergence with element size reduction on smooth solutions and on singular problems, if mesh grading is used. Agreement between results from the BIEM code and a finite element code that solves the fully non-linear problem is excellent, and is achieved at a substantial advantage in computer processing time. As an illustrative example, the code is applied to determine the distribution of moisture in the vicinity of a tunnel.  相似文献   

Using platforms of opportunity to determine the occurrence and group characteristics of orca (Orcinus orca) in the Hauraki Gulf,New Zealand     

K Hupman  IN Visser  E Martinez  KA Stockin 《新西兰海洋与淡水研究杂志》2013,47(1):132-149

We present the first fine-scale data relating to the occurrence and group characteristics for killer whales (Orcinus orca) in the Hauraki Gulf, New Zealand, as observed from a platform of opportunity (PoP). Group size and composition were examined in relation to water depth and sea surface temperature (SST). From 2000 to 2010, 119 orca encounters were recorded, involving 1 to 18 animals. The encounter rate varied seasonally, being highest in austral spring and lowest in summer. Water depth in which whales were observed was significantly affected by group composition. Sixty-seven percent of groups contained immature animals. Group size was highly skewed towards smaller groups comprising two animals. While this study illustrates that PoPs can be used to indicate the occurrence and group characteristics of highly mobile social species, biases clearly exist. Through identifying such inaccuracies, we present recommendations on how future data should be collected to minimise error and improve datasets for scientific use.  相似文献