Evaluation of distortions in laser welded shipbuilding parts using local-global finite element approach

In recognition of the differences of scale between the welding pool and the heat affected zone along the welding line on one hand, and the overall size of the components being welded on the other, a local-global finite element approach was developed for the evaluation of distortions in laser welded shipbuilding parts. The approach involves the tandem use of a 'local' and a 'global' step. The local step involves a three-dimensional finite element model for the simulation of the laser welding process using the Sysweld finite element code, which takes into account thermal, metallurgical, and mechanical aspects. The simulation of the laser welding process was performed using a non-linear heat transfer analysis, based on a keyhole formation model, and a coupled transient thermomechanical analysis, which takes into account metallurgical transformations using the temperature dependent material properties and the continuous cooling transformation diagram. The size and shape of the keyhole used in the local finite element analysis was evaluated using a keyhole formation model and the Physica finite volume code. The global step involves the transfer of residual plastic strains and the stiffness of the weld obtained from the local model to the global analysis, which then provides the predicted distortions for the whole part. This newly developed methodology was applied to the evaluation of global distortions due to laser welding of stiffeners on a shipbuilding part. The approach has been proved reliable in comparison with experiments and of practical industrial use in terms of computing time and storage.

Temperature-induced sex reversal is not responsible for sex-ratio distortions in grayling Thymallus thymallus or brown trout Salmo trutta.

On the basis of the experiments carried out over various years, it was concluded that (1) grayling Thymallus thymallus and brown trout Salmo trutta are resistant to temperature-induced sex reversal at ecologically relevant temperatures, (2) environmental sex reversal is unlikely to cause the persistent sex ratio distortion observed in at least one of the study populations and (3) sex-specific tolerance of temperature-related stress may be the cause of distorted sex ratios in populations of T. thymallus or S. trutta.

The relationship between self-serving cognitive distortions and bullying behaviours among elementary school children /

The purpose ofthe study was to examine the relationshq) between self-serving cognitive distortions and involvement in bullying behaviours. While relationships were e}q)k)red for both bullies and victims, the bully represented the main focus ofthis research. The participants ofthis study were 206 elementary school children in grades 5, 6, 7, and 8 from a school board in South Western Ontario. Participants conq>leted a 2- part self-report questionnaire within a 1-week time period. Part I aimed to measure self-serving cognitive distortions, while Part II was designed to assess selfreports of bullying behaviours. Analyses revealed that a significant direct relationship existed between children's self-serving cognitive distortions and bullying others. More specifically, children's self-serving cognitive distortions were moderately correlated with bullying others (r = .50, p< 0.01). This finding was consistent for both male and female participants. In addition, significant moderate correlations also existed between each ofthe 9 subscales ofself-serving cognitive distortions and bullying others. In regard to the relationship between children's self-serving cognitive distortions and victimization, a low significant direct relationshq) was found (r = .22 p<0.01). This finding was consistent for both male and female participants. The results ofthis study are discussed in terms oftheir theoretical, as well as applied implications.

Spin-Peierls vs Peierls distortions in a family of conjugated polymers

Distortions in a family of conjugated polymers are studied using two complementary approaches: within a many-body valence bond approach using a transfer-matrix technique to treat the Heisenberg model of the systems, and also in terms of the tight-binding band-theoretic model with interactions limited to nearest neighbors. The computations indicate that both methods predict the presence or absence of the same distortions in most of the polymers studied.

Perspectives of auto-correcting lens distortions in mosaic-based underwater navigation

When unmanned underwater vehicles (UUVs) perform missions near the ocean floor, optical sensors can be used to improve local navigation. Video mosaics allow to efficiently process the images acquired by the vehicle, and also to obtain position estimates. We discuss in this paper the role of lens distortions in this context, proving that degenerate mosaics have their origin not only in the selected motion model or in registration errors, but also in the cumulative effect of radial distortion residuals. Additionally, we present results on the accuracy of different feature-based approaches for self-correction of lens distortions that may guide the choice of appropriate techniques for correcting distortions

Distortions and gender-related differences in the perception of mechanical engineering in high school students

Resumen tomado de la publicación

Systematic distortions of perceptual stability investigated using immersive virtual reality

Using an immersive virtual reality system, we measured the ability of observers to detect the rotation of an object when its movement was yoked to the observer's own translation. Most subjects had a large bias such that a static object appeared to rotate away from them as they moved. Thresholds for detecting target rotation were similar to those for an equivalent speed discrimination task carried out by static observers, suggesting that visual discrimination is the predominant limiting factor in detecting target rotation. Adding a stable visual reference frame almost eliminated the bias. Varying the viewing distance of the target had little effect, consistent with observers underestimating distance walked. However, accuracy of walking to a briefly presented visual target was high and not consistent with an underestimation of distance walked. We discuss implications for theories of a task-independent representation of visual space. © 2005 Elsevier Ltd. All rights reserved.

Sample-induced beam distortions in terahertz time domain spectroscopy and imaging systems

It is demonstrated that distortion of the terahertz beam profile and generation of a cross-polarised component occur when the beam in terahertz time domain spectroscopy and imaging systems interacts with the sample under test. These distortions modify the detected signal, leading to spectral and image artefacts. The degree of distortion depends on the optical design of the system as well as the properties of the sample.

Measuring the impacts of distortions in the European Union cotton sector: a partial equilibrium analysis using the ATPSM model framework

The “cotton issue” has been a topic of several academic discussions for trade policy analysts. However the design of trade and agricultural policy in the EU and the USA has become a politically sensitive matter throughout the last five years. This study utilizing the Agricultural Trade Policy Simulation Model (ATPSM) aims to gain insights into the global cotton market, to explain why domestic support for cotton has become an issue, to quantify the impact of the new EU agricultural policy on the cotton sector, and to measure the effect of eliminating support policies on production and trade. Results indicate that full trade liberalization would lead the four West African countries to better terms of trade with the EU. If tariff reduction follows the so-called Swiss formula, world prices would increase by 3.5%.

The effects of longevity and distortions on education and retirement

This article studies the impact of longevity and taxation on life-cycle decisions and long-run income. Individuals allocate optimally their total lifetime between education, working and retirement. They also decide at each moment how much to save or consume out of their income, and after entering the labor market how to divide their time between labor and leisure. The model incorporates experience-earnings profiles and the return-to-education function that follows evidence from the labor literature. In this setup, increases in longevity raises the investment in education - time in school - and retirement. The model is calibrated to the U.S. and is able to reproduce observed schooling levels and the increase in retirement, as the evidence shows. Simulations show that a country equal to the U.S. but with 20% smaller longevity will be 25% poorer. In this economy, labor taxes have a strong impact on the per capita income, as it decreases labor effort, time at school and retirement age, in addition to the general equilibrium impact on physical capital. We conclude that life-cycle effects are relevant in analyzing the aggregate outcome of taxation.

The evolution of TFP in Latin America: high productivity when distortions were high?

Due to widespread government intervention and import-substitution industrialization, there has been a general presumption that Latin America has been much less productive than the leading economies in the last decades. In this paper, however, we show that until the late seventies Latin America had high total factor productivity (TFP) levels relative to the US and other regions. It is only after the late seventies that we observe a fast decrease of relative TFP in Latin America. Results are robust to the use of diferent methodologies and data sources.