Investigation of the properties of galactic cosmic rays with the KASCADE-Grande experiment

The properties of galactic cosmic rays are investigated with the KASCADE-Grande experiment in the energy range between 10¹⁴ and 10¹⁸ eV. Recent results are discussed. They concern mainly the all-particle energy spectrum and the elemental composition of cosmic rays.     

A combined interpretation of cosmic ray light nuclei and antiproton measurements

Recently several experiments improved significantly our knowledge of cosmic ray (CR) spectra at high energy. In particular CREAM measured B/C, C/O and N/O ratios up to and PAMELA observed the antiproton-to-proton ratio up to with high accuracy. These results permit to put more stringent constraints on the free parameters involved in the diffusion-loss equation that describes the propagation of CRs in the Galaxy. To this purpose, we perform a new statistical analysis comparing updated experimental data with the predictions of an improved version of our numerical code DRAGON. We obtain well defined ranges of values for the diffusion coefficient normalization and index of the power-law dependence on rigidity as well as for the Alfvén velocity.     

Active Galactic Nuclei and Gamma Ray Bursts: Relativistic shocks and the origin of ultra high energy cosmic rays

The importance of explaining and achieving the highest observed cosmic ray energies by the first order Fermi acceleration mechanism in a given astrophysical environment is a recurring theme in astroparticle physics. In this contribution, we discuss acceleration of cosmic rays in relativistic shock formations, focusing on numerical studies concerning proton acceleration efficiency by subluminal and superluminal shocks, emphasising the dependence of the scattering model, shock Lorentz factor and the angle between the magnetic field and the shock front. We present a diffuse cosmic ray prediction model, where results are compared with the measured flux of cosmic rays at the highest energies. We show that steeper Active Galactic Nuclei spectra provide an excellent fit. Our model explains well the first evidence of a correlation between the cosmic ray flux above 5.7 ×10¹⁰ GeV and the distribution of Active Galactic Nuclei provided by AUGER. On the other hand, Gamma Ray Burst spectra being flatter can hardly explain the highest energy observed flux. We note though that recent Fermi observations of GRB090816c indicate very flat spectra which are expected within our model predictions and support evidence that GRB particle spectra can be flat, when the shock Lorentz factor is of order 1000.     

Studies of the knee of the cosmic rays primary spectrum through measurements in the 10–10 eV energy range

In this contribution I review the most recent results obtained by experiments studying the primary cosmic rays spectrum at energies around the knee, i.e. the change of slope observed at .The main results are: the change of slope has been observed in the spectra of all secondary components of extensive air showers. The primary chemical composition gets heavier above the knee. Almost all experiments, with the exception of TIBET ASγ, attribute the change of slope to the light component of cosmic rays. The arrival directions of cosmic rays are highly isotropic.These results favor an astrophysical explanation of the knee either as the maximum energy achievable in galactic sources or of end of the containment inside galactic magnetic fields. Nevertheless the scenario is neither complete nor univocally accepted and relevant informations can be obtained studying the 10¹⁶–10¹⁸ eV energy range.     

An experiment to detect energetic neutrons and gamma rays from the sun

A payload for the detection and measurement of high energy neutrons and gamma rays from the sun was flown onboard the first Indian satelliteAryabhata. The payload system for this neutron-gamma experiment was designed for detecting energetic neutrons in the energy range 10–500 MeV and gamma rays in the energy range 0.2–20 MeV. The details of the design of the payload, various tests carried out on it as well as the preliminary in-orbit performance are presented.     

Cosmic ray physics with the ARGO-YBJ experiment

Cosmic ray physics in the 10¹²–10¹⁵ eV primary energy range is among the main scientific goals of the ARGO-YBJ experiment. The detector, located at the Cosmic Ray Observatory of Yangbajing (Tibet, P.R. China) at 4300 m a.s.l., is a full coverage Extensive Air Shower array consisting of a carpet of Resistive Plate Chambers of about 6000 m². The apparatus layout, performance and location offer a unique possibility to make a deep study of several characteristics of the hadronic component of the cosmic ray flux in an energy window marked by the transition from direct to indirect measurements. In this work we will focus on the experimental results concerning the measurements of the primary cosmic ray energy spectrum and of the proton-air cross-section. The all-particle spectrum has been measured, by using a bayesian unfolding technique, in the 1–100 TeV energy region. The proton-air cross-section has been measured at the same energies, by exploiting the cosmic ray flux attenuation for different atmospheric depths (i.e. zenith angles). The total proton–proton cross-section has then been estimated at center of mass energies between 70 and 500 GeV, where no accelerator data are currently available.     

Simulation of the cosmic ray Moon shadow in the geomagnetic field

An accurate Monte Carlo simulation of the deficit of primary cosmic rays in the direction of the Moon has been developed to interpret the observations reported in the TeV energy region until now. Primary particles are propagated through the geomagnetic field in the Earth–Moon system. The algorithm is described and the contributions of the detector resolution and of the geomagnetic field are disentangled.     

A method for energy estimation and mass composition determination of primary cosmic rays at the Chacaltaya observation level based on the atmospheric Cherenkov light technique

A new method for energy and mass composition estimation of primary cosmic rays based on the atmospheric Cherenkov light flux in extensive air showers (EAS) is proposed. The Cherenkov light flux in EAS initiated by primary protons and iron nuclei is simulated with the CORSIKA 5.62 code for the Chacaltaya observation level (536 g/cm²) in the energy range 10 TeV–10 PeV. An adequate model for the lateral distribution of Cherenkov light in showers is obtained. Using the model and a solution for the overdetermined system of nonlinear equations based on the Gauss–Newton method with autoregularization, two different detector arrangements are compared. The accuracies in energy and shower axis determination are studied and the corresponding selection criteria are proposed. An approximation with a nonlinear fit is obtained and the energy dependence of the proposed model parameters is studied. A detailed study of the model parameters as a function of the primary energy is made. This permits, taking into account the properties of the proposed method and the strong nonlinearity of the model, a distinction to be made between proton and iron primaries. The detector response for the detector sets is simulated and the accuracies in energy determination are calculated. In addition, the accuracies in shower axis determination are studied and criteria for shower axis position estimation are proposed.     

Energy determination of cosmic ray showers in surface arrays using signal inference at a single distance from the core

In most high energy cosmic ray surface arrays, the primary energy is currently determined from the value of the lateral distribution function at a fixed distance from the shower core, r₀. The value of r₀ is mainly related to the geometry of the array and is, therefore, considered as fixed independently of the shower energy or direction. We argue, however, that the dependence of r₀ on energy and zenith angle is not negligible. Therefore, in the present work we propose a new characteristic distance, which we call r_opt, specifically determined for each individual shower, with the objective of optimizing the energy reconstruction. This parameter may not only improve the energy determination, but also allow a more reliable reconstruction of the shape and position of rapidly varying spectral features. We show that the use of a specific r_opt determined on a shower-to-shower basis, instead of using a fixed characteristic value, is of particular benefit in dealing with the energy reconstruction of events with saturated detectors, which are in general a large fraction of all the events detected by an array as energy increases. Furthermore, the r_opt approach has the additional advantage of applying the same unified treatment for all detected events, regardless of whether they have saturated detectors or not.     

Measurement of the antiproton/proton ratio at TeV energies with the ARGO-YBJ detector

Cosmic ray antiprotons provide an important probe for the study of cosmic-ray propagation in the interstellar space and to investigate the existence of Galactic dark matter. Cosmic rays are hampered by the Moon, therefore a deficit of cosmic rays in its direction is expected (the so-called Moon shadow). The Earth–Moon system acts as a magnetic spectrometer. In fact, due to the geomagnetic field the center of the Moon shifts westward by an amount depending on the primary cosmic ray energy. Paths of primary antiprotons are therefore deflected in an opposite sense in their way to the Earth. This effect allows, in principle, the search of antiparticles in the opposite direction of the observed Moon shadow.The ARGO-YBJ experiment, in stable data taking since November 2007 with an energy threshold of a few 100s of GeV, is observing the Moon shadow with high statistical significance. Using about 1 year data, an upper limit of the flux ratio in the few-TeV energy region is set to a few percent with a confidence level of 90%.     

Identification of the thermal properties of materials using methods of the calculus of variations

A solution of the heat-conduction problem when a linear pulsed source of heat acts in the plane of contact of two semibounded bodies, obtained using methods of the variational-iterational calculus, is presented. The results of tests of a number of heat-insulating materials are given. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 34–36, July, 2007.     

小波变换在密集模态结构参数识别中的应用

系统研究了小波变换在具有低频密集模态的土木工程结构参数识别中的应用。采用Morlet小波，首先阐述了该方法识别模态频率和模态阻尼比的基本原理；分析了其时间和频率分辨率，针对土木工程结构中低频模态密集的情况，提出了选择小波参数的具体方法。通过三自由度结构的数值分析验证了该方法的正确性和优越性。     

Identification of the Orthotropic Elastic Stiffnesses of Composites with the Virtual Fields Method: Sensitivity Study and Experimental Validation

ABSTRACT:  This paper presents the use of a sensitivity study to find the best combinations of free length and fibre angle in an unnotched Iosipescu test processed with the virtual fields method. The sensitivity to noise coefficients arising from the special virtual fields procedure are used to build up a cost function. This function is aimed at balancing out the coefficients of the different orthotropic stiffnesses so that the same confidence level can be reached on all these parameters. Then, experimental validation was performed using a speckled interferometry (ESPI) system. Full-field strains were measured and stiffnesses identified and compared between the usual 0°, 30 mm configuration and an improved 25°, 40 mm configuration. The outcome of the optimisation was confirmed by testing the same specimen several times and comparing scatter between the two configurations. This is a first promising result on the way to the design of a new test for orthotropic stiffness identification on a single specimen from full-field measurements.     

利用模态参数识别技术与分层建模理论修改分析模型

本文根据分层建模理论,在计算机上实现了利用由模态参数识别技术得到的模态参数,对分析模型进行修正。计算结果表明,这一方法很好地反映了实验中的精度问题,不失为联系实验测试与数值分析之间的一座新的桥梁。     

Identification of the elastic and damping properties in sandwich structures with a low core-to-skin stiffness ratio

A mixed numerical–experimental identification procedure for estimating the storage and loss properties in sandwich structures with a soft core is developed. The proposed method uses at the experimental level a precise measurement setup with an electro-dynamic shaker and a scanning laser interferometer, and at the computational level an original structurally damped shell finite element model derived from the higher-order shear deformation theory with piecewise linear functions for the through-the-thickness displacement. The parameter estimation is derived from adequate objective functions measuring the discrepancy between the experimental and numerical modal data. Through a sensitivity analysis it is shown that for sandwich structures with a soft core only one specimen is required for characterizing the dominant properties of both the core and the skins. The procedure is then applied to two test cases for which all the influent elastic properties and the major damping parameters could be estimated with a fairly good precision.