Strong Obstacles Research Articles

Study in Motion Control for Adsorption Type Wall-Climbing Robot with Several Legs

Aiming at the cleaning operation of high-rise building glass wall, a novel pneumatic wall-climbing robot was developed. According to the configuration and the characteristics analysis on the robot, the kinematics equations were derived and PWM / PFM algorithm was proposed based on PID control. The simulation results show that the motion and control for the robot has advantages of fast speed , flexible movement, strong obstacle avoidance ability and simple control features, and so on.

Using Social Media to Measure Conflict Dynamics

The lack of temporal disaggregation in conflict data has so far presented a strong obstacle to analyzing the short-term dynamics of military conflict. Using a novel data set of hourly dyadic conflict intensity scores drawn from Twitter and other social media sources during the Gaza Conflict (2008–2009), the author attempts to fill a gap in existing studies. The author employs a vector autoregression (VAR) to measure changes in Israel’s and Hamas’s military response dynamics immediately following two important junctures in the conflict: the introduction of Israeli ground troops and the UN Security Council vote. The author finds that both Hamas’s and Israel’s response to provocations by the other side increase (both by about twofold) immediately after the ground invasion, but following the UN Security Council vote, Israel’s response is cut in half, while Hamas’s slightly increases. In addition, the author provides a template for researchers to harness social media to capture the micro-dynamics of conflict.

Mapping the microstructure of a friction-stir welded (FSW) Al-Li-Cu alloy

The friction-stir welding (FSW) process induces both heat and deformation which lead to inhomogeneous precipitation microstructures in structural hardening alloys. A map of this microstructure can be obtained by 2D scanning SAXS in alloys where (a) a single phase is precipitating and (b) the precipitates are roughly isotropic. In Al-Li-Cu alloys, these conditions are not fullfilled. Very anisotropic precipitates are forming (T1 and θ′) with aspect ratios in the range 10 to 100. The inhomogeneity in the texture of the material (due to the deformation and recrystallisation) is a strong obstacle to the interpretation of the SAXS signal. This paper is an attempt to apply systematic simple interpretation models to characterise the precipitation microstructure across the weld area. It shows that in certain condition, it is possible to apply simple Guinier-type plot to extract the morphologies (length and thickness) of the particles.

El empleo y la crisis. Precarización y nuevas “válvulas de escape”

At the beginning of 2010, 14 months into the current economic crisis, the most severe in this generation, we must pause briefly to assess employment. It is worth exploring how the occupational panorama has changed with respect to the first three months of the crisis, in which the job market collapse was undoubtedly one of the fastest we have ever experienced. Not only is it necessary to assess the present dynamics of employment, but its relationship to demographics today, characterized by the overwhelming increase of young people entering the workforce. We need to explore the informal sector and labor migration, which in the past decade were the traditional “safety valves” of the labor market and now seem to be encountering strong obstacles that have led to the emergence of new occupational options, some of them highly worrying.

On the correlation between irradiation-induced microstructural features and the hardening of reactor pressure vessel steels

A correlation is attempted between microstructural observations by various complementary techniques, which have been implemented within the PERFECT project and the hardening measured by tensile tests of reactor pressure vessel steel and model alloys after irradiation to a dose of ∼7 × 10 19 n cm −2. This is done, using the simple hardening model embodied by the Orowan equation and applying the most suitable superposition law, as suggested by a parametric study using the DUPAIR line tension code. It is found that loops are very strong obstacles to dislocation motion, but due to their low concentration, they only play a minor role in the hardening itself. For the precipitates, the contrary is found, although they are quite soft (due to their very small sizes and their coherent nature), they still play the dominant role in the hardening. Vacancy clusters are important for the formation of both loops and precipitates, but they will play almost no role in the hardening by themselves.

Minimal Income as Basic Condition for Autonomy

O artigo investiga se uma renda mínima assegurada pelo Estado (que não é a mesma coisa que uma renda básica) é uma condição necessária para que indivíduos (1) atinjam um patamar básico de autonomia e (2) desenvolvam “capabilidades” que os permitam incrementar a sua qualidade de vida. Como embasamento teórico para a minha análise, utilizarei a teoria do reconhecimento de Honneth, a abordagem de “capabilidade” de Sen (também na versão oferecida por Nussbaum) e o conceito de independência de Simmel, como foi desenvolvido em sua Filosofia do Dinheiro. A renda mínima visa garantir não só a sobrevivência dos extremamente pobres (isso também poderia ser realizado através de programas emergenciais), mas também – em cooperação com outros programas do Estado, tais como educação, assistência médica e jurídica etc – permitir que esses indivíduos sejam mais independentes do seu ambiente social, onde muitas vezes a dependência constitui um forte obstáculo ao desenvolvimento da sua autonomia. A inclusão social e política de milhões de pessoas, tanto em países em desenvolvimento quanto nos países pobres, depende da existência de tais programas.

From global paradigms to grounded policies: Local socio‐cognitive constructions of international development policies and implications for development management

AbstractUnderstandings of participatory development require grounding—both in the sense that understandings of the principles must be held by local and international staff working on the ground, and also grounded in the local culture. This article provides documentation of a 10 month ethnographic study of an administrative decentralization support program in Cambodia (Seila), funded through multi‐donor support, in order to examine the agency of local mid‐level staff, asking: How do multiple environments interact to create local understandings of participation in international development environments? Five ‘socio‐cognitive environments’ (SCE) surrounding the program environment were developed to disentangle the factors that influence how one group of local staff negotiates complex cultural and historical realities in juxtaposition to donor conceptualizations of development, providing new understanding of structural factors and other resources employed by embedded agents which promote local staff internalization of democratic governance principles. This study suggests that even in program environments with high degrees of cognitive dissonance due to macro‐historical factors, and where international development mandates tend to create additional cultural and organizational blockages, micro‐programmatic interactions can significantly influence the ability of local staff to surmount strong cognitive obstacles. Copyright © 2010 John Wiley & Sons, Ltd.

Atomic-scale mechanisms of void hardening in bcc and fcc metals

Strengthening due to voids can be a significant effect of radiation damage in metals, but treatment of this by elasticity theory of dislocations is difficult when the mechanisms controlling the obstacle strength are atomic in nature. Results are reported of atomic-scale modelling to compare edge dislocation–void interaction in fcc copper and bcc iron. Voids of up to 6 nm diameter in iron and 8 nm diameter in copper were studied over the temperature range 0 to 600 K at different applied strain rates. Voids in iron are strong obstacles, for the dislocation has to adopt a dipole-like configuration at the void before breaking away. The dipole unzips at the critical stress when the dislocation is able to climb by absorbing vacancies and leave the void surface. Dislocation dissociation into Shockley partials in copper prevents dislocation climb and affects the strength of small and large voids differently. Small voids are much weaker obstacles than those in iron because the partials break from a void individually. Large voids are at least as strong as those in iron, but the controlling mechanism depends on temperature.

Influence of the stress field due to pressurized nanometric He bubbles on the mobility of an edge dislocation in iron

Voids and He bubbles are strong obstacles to dislocation, which induce hardening and loss of ductility. In Fe, molecular dynamics simulation is used to investigate the basic mechanisms of the interaction between a moving edge dislocation and a void or He bubble, as a function of its He content, temperature, interatomic potentials and interaction geometry. Different interatomic potentials for Fe–Fe and Fe–He interactions are used. It appears that temperature eases the dislocation release, due to the increased mobility of the screw segments appearing on the dislocation line upon bowing from the void or He bubble. The mobility includes the cross-slipping of these segments, which leads to the formation of a jog. It appears that the He bubble induces an inhomogeneous stress field in its surroundings, which strongly influences the dislocation passage depending on the geometry of the interaction.

Competing processes in reactions between an edge dislocation and dislocation loops in a body-centred cubic metal

Molecular dynamics simulation was used to investigate reactions of a 1 2 〈 1 1 1 〉 { 1 1 0 } edge dislocation with interstitial dislocation loops of 1 2 〈 1 1 1 〉 and 〈1 0 0〉 type in a model of iron. Whether loops are strong or weak obstacles depends not only on loop size and type, but also on temperature and dislocation velocity. These parameters determine whether a loop is absorbed on the dislocation or left behind as it glides away. Absorption requires glide of a reaction segment over the loop surface and cross-slip of dipole dislocation arms attached to the ends of the segment: these mechanisms depend on temperature and strain rate, as discussed here.

Interrelationship between True Stress–True Strain Behavior and Deformation Microstructure in the Plastic Deformation of Neutron-Irradiated or Work-Hardened Austenitic Stainless Steel

Abstract True stress–true strain relation and deformation microstructure have been examined for high purity Fe-18Cr-12Ni alloy and its alloys doped with 0.7 wt % Si or 0.09 wt % C. In high purity alloy and C-doped alloy irradiated at 240°C up to 3 dpa, the work hardening rate is equivalent to that in unirradiated alloys. These alloys show dislocation channel structure after irradiation and deformation. In irradiated Si-doped alloy, however, the work hardening rate is different from that in unirradiated alloys. This alloy shows fully developed dislocation cell structure after deformation, as seen in unirradiated deformed stainless steels. The cell structure in irradiated Si-doped alloy was much smaller than that in unirradiated Si-doped alloy and in type 316L stainless steel. One of the factors affecting the change in the work hardening rate of irradiated austenitic stainless steel at 240°C is strong obstacles such as γ precipitate that acts as dislocation pining and dislocation loops such as Frank loops that do not act as obstacles.

Mechanisms of hardening due to copper precipitates in α-iron

A comprehensive atomic-level simulation study has been made of interactions between a moving edge dislocation and copper precipitates that are initially coherent with the body-centred-cubic matrix of alpha-iron. Precipitates with diameter, D, in the range 0.7–6 nm have been considered over the temperature range 0–600 K. For some combinations of temperature and D, the critical applied resolved shear stress, τ c, at which the dislocation overcomes a row of precipitates with centre-to-centre spacing, L, is consistent with an elasticity treatment for strong obstacles, e.g. τ c is proportional to L −1 and ln(D). This has a specific atomic-level origin, for the proportionality holds when the dislocation induces a partial transformation of the copper towards the more stable face-centred-cubic phase. The driving force for the transformation increases with decreasing temperature and increasing D, and so τ c has a strong temperature-dependence for large D. The results of these simulations, which employ a set of interatomic potentials of Finnis–Sinclair type, are seen to correspond well with experiments carried out elsewhere.

Hybrid ant colony and immune network algorithm based on improved APF for optimal motion planning

SUMMARYInspired by the mechanisms of idiotypic network hypothesis and ant finding food, a hybrid ant colony and immune network algorithm (AC-INA) for motion planning is presented. Taking the environment surrounding the robot and robot action as antigen and antibody respectively, an artificial immune network is constructed through the stimulation and suppression between the antigen and antibody, and the antibody network is searched using improved ant colony algorithm (ACA) with pseudo- random-proportional rule and super excellent ant colony optimization strategy. To further accelerate the convergence speed of AC-INA and realize the optimal dynamic obstacle avoidance, an improved adaptive artificial potential field (AAPF) method is provided by constructing new repulsive potential field on the basis of the relative position and velocity between the robot and obstacle. Taking the planning results of AAPF method as the prior knowledge, the initial instruction definition of new antibody is initialized through vaccine extraction and inoculation. During the motion planning, once the robot meets with moving obstacles, the AAPF method is used for the optimal dynamic obstacle avoidance. The simulation results indicate that the proposed algorithm is characterized by good convergence property, strong planning ability, self-organizing, self-learning, and optimal obstacle avoidance in dynamic environments. The experiment in known indoor environment verifies the validity of AAPF-based AC-INA, too.

Análisis de necesidades educativas curriculares en la educación primaria dirigida a niños (as) nicaragüenses migrantes en Costa Rica

Recibido 17 de junio 2007 • Aprobado 20 de agosto 2007
 
 
 Con este artículo se pretende dar a conocer las necesidades curriculares identificadas en niñas y niños nicaragüenses migrantes que estudian en la escuela primaria rural Los Ángeles del Cantón Los Chiles de Costa Rica. Ellos y ellas, actualmente, se encuentran en una situación de exclusión, discriminación e indiferencia por parte de las instituciones locales. Existen obstáculos para el aprendizaje efectivo y el desarrollo de actitudes positivas, entre ellos la falta de participación responsable de la comunidad educativa, el procedimiento metodológico utilizado en el aula y la adecuación curricular del modelo pedagógico oficial costarricense; divorciados éstos, de las condiciones socioculturales de esta población educativa, de su familia y de la comunidad rural donde residen.
 Esta situación afecta la motivación de las niñas y niños, quienes no alcanzan las metas educativas: la mayoría de los que se matriculan dejan inconclusa la educación primaria, y los que la completan tienen dificultades académicas para ingresar a secundaria.
 Los sistemas educativos de Nicaragua y de Costa Rica deben plantear estrategias educativas conjuntas, que den respuesta a las necesidades educativas curriculares que presentan los niños nicaragüenses migrantes en las escuelas rurales costarricenses.

Strain rate sensitivity of thermally activated dislocation motion across fields of obstacles of different kind

The thermally activated motion of dislocations across fields of randomly distributed obstacles of two types is studied. The two types have either the same strength and different dependence of the activation energy on the applied force, or different strength but same activation behavior. The objective is to determine how the two sub-populations of obstacles contribute to defining the strain rate sensitivity and the flow stress. Above a threshold stress, dislocation motion undergoes a transition from smooth (“unzipping”) to jerky, i.e. obstacles are bypassed in a correlated manner at high stresses. In the jerky regime, the strain rate sensitivity parameter depends exclusively on the ratio of the applied stress to the mechanical threshold stress of the respective array, the dynamics exhibiting near-critical behavior. This regime appears to be essential for the deformation of real crystals. When obstacles are bypassed in the unzipping mode, the strain rate sensitivity is controlled by the strong obstacles. These results have implications for the finite temperature superposition of contributions of the two types of obstacles to the overall flow stress.

Analysis on the Grating Structure of Si by Using Spectroscopic Ellipsometry

Analysis on the Grating Structure of Si by Using Spectroscopic Ellipsometry S.-H. Han, T. H. Ghong, J. S. Byun and Y. D. Kim Nano Optical Property Laboratory and Department of Physics, Kyung Hee University, Seoul 130-701 Y. Y. Yu and K. C. Park Department of Information Display, Kyung Hee University, Seoul 130-701 (Received 21 October 2007) Spectroscopic ellipsometry (SE) has come to be an important method to determine the critical dimension (CD) of patterned structures by measuring the zeroth-order di raction response at a xed angle of incidence. To investigate the possibility of an in-situ monitoring tool for a complicated multilayer, we performed SE measurements on a one-dimensional patterned c-Si periodic structure with SiO2 hat on Si substrate. Rigorous coupled-wave analysis (RCWA) calculation for the re ected light could explain the measured spectrum quantitatively even when the hat structure on the top acted as a strong obstacle to the probing light. PACS numbers: 78.20.Ci, 78.40.-q, 42.25.Bs

Spectroscopic Ellipsometric Analysis of a Si Grating Pattern Made by Photolithography

We performed spectroscopic ellipsometry (SE) measurements to investigate the possibility of a nondestructive in-situ monitoring tool for determining the critical dimension (CD) of patterned structures. A simple 1D patterned c-Si periodic structure was measured from the zeroth-order diffraction response at a fixed angle of incidence, whose result agreed with the theoretical prediction made by using a rigorous coupled-wave analysis (RCWA) calculation for the reflected light. To investigate the SE’s advantage over atomic force microscopy we also prepared a c-Si periodic structure with a Cr hat on the top. We observed that the theoretical result could also explain the measured spectra quantitatively even when the metallic hat structure on the top acted as a strong obstacle to the probing light.

Toward a New Public Education: Making Globalization Work for Us All

ABSTRACT— Globalization is a long‐term, multidimensional process. If it is to benefit humankind rather than ruining the planet, a number of threats must be urgently addressed, and many global processes must be better managed. This article proposes that managing globalization for the common good requires, inter alia, an enhanced role for democracy, a role supported by a new public education that is inscribed with 6 key values—democracy, critical thinking, relational ethics, creativity, social justice, and solidarity—and is based on a particular image of the child and the school. The article concludes by asking how this new public education might gain ground in the face of strong obstacles and proposes democratic experimentalism and “glocal” networks (the global linking of local experiences) as important elements of positive change that is radical in direction but piecemeal in form.

The transformation of edge dislocation dipoles in aluminium

The transformations of dipoles of dissociated edge dislocations in aluminium are investigated using molecular dynamics for dipole heights ranging from one to ten {1 1 1} interplanar distances and at temperatures up to 900 K. Three types of configurations, hollow, vertical compact and inclined dipoles, are considered and their relative stabilities compared. Hollows are unstable at finite temperature. Dipoles neither annihilate nor form stable hollow cores but transform into height- and temperature-dependent layouts including cores containing ordered free volumes, zigzag faulted dipoles and agglomerated truncated stacking fault tetrahedra (SFT). Small individual SFT are formed at the highest temperatures, attesting to short-range pipe diffusion. These rearranged configurations are strong obstacles to mobile dislocations, thence potential nucleation sites for dislocation entanglement and self-patterning under single slip. A new thermally activated mechanism of SFT formation directly from vacancy clusters resulting from local dipole pinching-off is reported.

Swift-ion-induced hardening and reduction of dislocation mobility in LiF crystals

Ion-induced change in Vickers hardness and arm length of dislocation rosettes created by indentation on the (1 0 0) face of LiF crystals was studied. The irradiations were performed using swift U, Bi and Ni ions with a specific energy of 11 MeV per nucleon at fluences between 106 and 1013 ions cm−2. Remarkable effects of the ion-induced hardening and reduction of dislocation arm length were observed above the threshold fluences of about 109–1010 ions cm−2 and 106–107 ions cm−2, respectively. The products of track core damage and aggregates of single defects in the halo of overlapping tracks are responsible for the effects. The results are analysed using the Orowan's model of dislocation impeding by strong obstacles. The advantages of the dislocation mobility method for the diagnostics of track damage at low-fluence irradiations are demonstrated.