Memory of the Unjamming Transition during Cyclic Tiltings of a Granular Pile

Discrete numerical simulations are performed to study the evolution of the micro-structure and the response of a granular packing during successive loading-unloading cycles, consisting of quasi-static rotations in the gravity field between opposite inclination angles. We show that internal variables, e.g., stress and fabric of the pile, exhibit hysteresis during these cycles due to the exploration of different metastable configurations. Interestingly, the hysteretic behaviour of the pile strongly depends on the maximal inclination of the cycles, giving evidence of the irreversible modifications of the pile state occurring close to the unjamming transition. More specifically, we show that for cycles with maximal inclination larger than the repose angle, the weak contact network carries the memory of the unjamming transition. These results demonstrate the relevance of a two-phases description -strong and weak contact networks- for a granular system, as soon as it has approached the unjamming transition.Comment: 13 pages, 15 figures, soumis \`{a} Phys. Rev.

An adaptive hierarchical domain decomposition method for parallel contact dynamics simulations of granular materials

A fully parallel version of the contact dynamics (CD) method is presented in this paper. For large enough systems, 100% efficiency has been demonstrated for up to 256 processors using a hierarchical domain decomposition with dynamic load balancing. The iterative scheme to calculate the contact forces is left domain-wise sequential, with data exchange after each iteration step, which ensures its stability. The number of additional iterations required for convergence by the partially parallel updates at the domain boundaries becomes negligible with increasing number of particles, which allows for an effective parallelization. Compared to the sequential implementation, we found no influence of the parallelization on simulation results.Comment: 19 pages, 15 figures, published in Journal of Computational Physics (2011

Macro deformation and micro structure of 3D granular assemblies subjected to rotation of principal stress axes

This paper presents a numerical investigation on the behavior of three dimensional granular materials during continuous rotation of principal stress axes using the discrete element method. A dense specimen has been prepared as a representative element using the deposition method and subjected to stress rotation at different deviatoric stress levels. Significant plastic deformation has been observed despite that the principal stresses are kept constant. This contradicts the classical plasticity theory, but is in agreement with previous laboratory observations on sand and glass beads. Typical deformation characteristics, including volume contraction, deformation non-coaxiality, have been successfully reproduced. After a larger number of rotational cycles, the sample approaches the ultimate state with constant void ratio and follows a periodic strain path. The internal structure anisotropy has been quantified in terms of the contact-based fabric tensor. Rotation of principal stress axes densifies the packing, and leads to the increase in coordination numbers. A cyclic rotation in material anisotropy has been observed. The larger the stress ratio, the structure becomes more anisotropic. A larger fabric trajectory suggests more significant structure re-organization when rotating and explains the occurrence of more significant strain rate. The trajectory of the contact-normal based fabric is not centered in the origin, due to the anisotropy in particle orientation generated during sample generation which is persistent throughout the shearing process. The sample sheared at a lower intermediate principal stress ratio (b=0.0) (b=0.0) has been observed to approach a smaller strain trajectory as compared to the case b=0.5 b=0.5 , consistent with a smaller fabric trajectory and less significant structural re-organisation. It also experiences less volume contraction with the out-of plane strain component being dilative

日本人大学生のTOEICのための文法的・語彙的能力に関する考察

本論文は日本人大学生の英語を書くための文法知識と単語力について議論し,近年の外国語教授に関する研究成果をさらに前進させようとするものである。例えば,池田(1990)は日本の大学1年生は附加連結語(additive connectors)(例 also, in addition, furthermore, to begin with, likewise, similarly など)をよく理解できているが,連続連結語(sequential connectors)(例 when, after that, before, prior to など)についてはよく理解できていないと指摘した。また,Lauer(2005)では大学2年生が initial, to grin from ear to ear, price dropped, in the long run などのような表現を上手く使えないと報告している。本研究を通して,勤務校の医学部1年生は次のような文法的・語彙的問題点が顕著であることが分かった。つまり,名詞と動詞の呼応,複文における動詞テンス呼応,複数・冠詞・前置詞の使い方などである。さらに,これらの学生には単語の語尾変化(wide, width, widen など),定型表現(at an all-time high, joint venture など),そしてある特定の単語(bankruptcy, accountable など)に関して,うまく運用ができない状況が散見された。この研究の結果は他の研究で報告された結果と同様に重要である。なぜなら日本人学生の多くがTOEICなどのスコアを上げたいと考えており,もし教師が学生の英語コミュニケーション能力に関して強い部分と弱い部分をよく理解していれば,教師は学生をより効果的に援助し,より良く指導できるからである。(なお,この研究結果をもとに,平成19年には「日本人学生を対象としたオンライン型TOEIC・TOEFL模擬試験」を完成させ,WEB上に公開し学生の利便性を図る予定である

Une nouvelle machine de cisaillement pour l'etude du comportement des milieux granulaires

SIGLEINIST T 75433 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

THE ROLE OF IRAQI LEGISLATIVE AUTHORITY IN DEMOCRATIC TRANSITION DURING THE PERIOD (2003-2021)

Abstract This study aimed to identify the role of the Iraqi legislative authority in the democratic transition during the years (2003-2021), by rising a main hypothesis stated that there is a correlation between the role of the legislative authority and the democratic transition in Iraq. To verify the validity of this hypothesis, and answer its questions, the descriptive analytical approach, the institutional legal approach, the elite theory, the comparative approach, and the systems analysis approach were used. The study concluded that the legislative authority did not contribute to the democratic transformation in Iraq, but rather contributed to perpetuating political backwardness, after the Iraqi parliaments were established on a sectarian basis, and political differences prevailed between political forces within the parliaments, which in turn was reflected in the public mood. Moreover, the legislative authority did not exercise its legislative role, and deliberately obstructed the passage of laws in the interest of the political deals held by the political forces, in addition to the absence of the oversight role of the legislative authority due to the spread of corruption, loyalty to the political bloc, and its preference over the public interest. In light of the results obtained, the study recommended adhering to the national option and defending it to achieve universal citizenship that fuses all subsidiary loyalties within its crucible, formulating joint cooperation between all political forces and currents in a manner that achieves the general interest of all, and working hard to combat all manifestations of widespread administrative and financial corruption very much in Iraq

Organic geochemical records of hydrothermal alteration at Idrija mercury deposit, Slovenia

A combined molecular and stable isotopes (C, N) investigation of the organic matter associated to the Idrija mercury deposit is being used to track the pathway of the mineralizing hydrothermal fluids and their interaction with the organic matter. The studied samples include regional barren rocks, and host rocks and ore from the mine. The Rock-Eval parameters indicate that the organic matter disseminated in regional and mine rocks is mature to post mature. The bitumens from mineralized samples are depleted in aliphatichydrocarbons and enriched in polycyclic aromatic hydrocarbons (PAH), aromatic sulfur compounds (S-PAH) and hydrogenated PAH. The isotopic compositions of kerogens, bitumens,and individual hydrocarbons point to thermal and oxidative degradation of indigenous and migrated bitumens during mineralization and later evolution of the Idrija deposit