Temporal stability and psychological foundations of cooperation preferences

A core element of economic theory is the assumption of stable preferences. We test this assumption in public goods games by repeatedly eliciting cooperation preferences in a fixed subject pool over a period of five months. We find that cooperation preferences are very stable at the aggregate level, but less so at the individual level. Nevertheless, individual preferences are sufficiently stable to predict future behavior fairly accurately. Our results also provide evidence on the psychological foundations of cooperation preferences. The personality dimension 'Agreeableness' is closely related to both the type and the stability of cooperation preferences.Social preferences, preference stability, conditional cooperation, free riding, personality, Big-Five.

Using non-smooth multi-domain dynamics to improve the safety on haul roads in surface mining

The paper presents a preliminary numerical study aimed to improve the safety on haul roads in surface mining. The interaction and collision between granular berms and ultra-class haul trucks are investigated by using non-smooth multi-domain dynamics. The haul truck is modelled as a rigid multibody system and the granular berm as a distribution of rigid particles using the discrete element method. A non-smooth dynamics approach is applied to enable stable and time-efficient simulation of the full system with strong coupling. The numerical model is first calibrated using full-scale data from experimental tests and then applied to investigate the collision between the haul truck and granular berms of different geometry under various approach conditions

Comparison of two DEM strategies for modelling cortical meshes

This work deals with the particle-based modelling of cortical wire meshes. Such meshes are being used in many engineering applications but their modelling is particularly complex because of the common large displacement serviceability conditions, the chance of localized failures, and the intrinsic geometrical and mechanical anisotropies. The discrete element method has proved to be an excellent numerical tool for the investigation of such structures. Here, two modelling strategies are compared using a wire-node description and a wire-cylinder description: in the first the wire mesh is described by a collection of spheres at nodes linked by long-range interaction forces, in the second the wires are represented by means of interconnected cylinders. The force-displacement constitutive model of the interactions is calibrated based on specific tensile tests. The comparison is performed on results of tensile tests and punch tests on a reference mesh panel

Modellazione agli elementi discreti di prove di punzonamento di una rete corticale doppio torta a maglia esagonale

Le reti metalliche sono comunemente usate per la protezione su pendio e la prevenzione del rischio di crolli e distacchi. La loro progettazione \ue8 principalmente basata su considerazioni di carattere empirico, legate all\u2019esperienza del progettista; data l\u2019importanza di tali interventi, e al fine di ottimizzare il progetto, stanno entrando in uso nuovi metodi numerici. In questo lavoro verr\ue0 impiegato il metodo agli elementi discreti (DEM), particolarmente adatto per lo studio di problemi a grande deformazioni, fino alla rottura degli elementi. L\u2019obiettivo \ue8 quello di validare un modello di rete doppio torta a maglia esagonale durante una prova di punzonamento attraverso il raffronto con i risultati sperimentali. In particolare verranno analizzati tre diversi modelli costitutivi e l\u2019influenza delle curve tensione-deformazione relative al filo singolo e a quello doppio torto

INFLUENCE OF ILLUMINATION CHANGES ON IMAGE-BASED 3D SURFACE RECONSTRUCTION

Abstract. The paper investigates the influence of lighting conditions on image-based 3D surface reconstruction, with particular focus on periodic photogrammetric surveys for monitoring and 3D mapping applications. The analyses focus on the accuracy and completeness of each DSM and the daily and hourly repeatability of repeated photogrammetric surveys. Three test sites with rock slopes with a different orientation to the sun and different slope characteristics (slope, pattern, amount of outcropping elements that cast shadows) have been considered to ensure that results can give a general indication of the behaviours in different light conditions. In addition, a simulated virtual test site is included in the study to allow controlled image acquisition and evaluate the effect of the sun's inclination on the DSM accuracy without influence of other weather conditions. The results show that, although there is an optimal time for the acquisitions, if particularly unfavourable light conditions are excluded, the accuracy reduction with time variation is always below 30%. The repeatability analyses by day and by time highlight a good consistence between DEMs belonging to the same day but acquired at different times and, also, between DEMs acquired at the same time but on different days. This suggests that reliable results can be obtained during continuous monitoring of, for instance, rock faces to identify rockfalls

Influence of illumination changes on image-based 3D surface reconstruction

The paper investigates the influence of lighting conditions on image-based 3D surface reconstruction, with particular focus on periodic photogrammetric surveys for monitoring and 3D mapping applications. The analyses focus on the accuracy and completeness of each DSM and the daily and hourly repeatability of repeated photogrammetric surveys. Three test sites with rock slopes with a different orientation to the sun and different slope characteristics (slope, pattern, amount of outcropping elements that cast shadows) have been considered to ensure that results can give a general indication of the behaviours in different light conditions. In addition, a simulated virtual test site is included in the study to allow controlled image acquisition and evaluate the effect of the sun's inclination on the DSM accuracy without influence of other weather conditions. The results show that, although there is an optimal time for the acquisitions, if particularly unfavourable light conditions are excluded, the accuracy reduction with time variation is always below 30%. The repeatability analyses by day and by time highlight a good consistence between DEMs belonging to the same day but acquired at different times and, also, between DEMs acquired at the same time but on different days. This suggests that reliable results can be obtained during continuous monitoring of, for instance, rock faces to identify rockfalls

Photogrammetric digital surface model reconstruction in extreme low-light environments

Digital surface models (DSM) have become one of the main sources of geometrical information for a broad range of applications. Image-based systems typically rely on passive sensors which can represent a strong limitation in several survey activities (e.g., night-time monitoring, underground survey and night surveillance). However, recent progresses in sensor technology allow very high sensitivity which drastically improves low-light image quality by applying innovative noise reduction techniques. This work focuses on the performances of night-time photogrammetric systems devoted to the monitoring of rock slopes. The study investigates the application of different camera settings and their reliability to produce accurate DSM. A total of 672 stereo-pairs acquired with high-sensitivity cameras (Nikon D800 and D810) at three different testing sites were considered. The dataset includes different camera configurations (ISO speed, shutter speed, aperture and image under-/over-exposure). The use of image quality assessment (IQA) methods to evaluate the quality of the images prior to the 3D reconstruction is investigated. The results show that modern high-sensitivity cameras allow the reconstruction of accurate DSM in an extreme low-light environment and, exploiting the correct camera setup, achieving comparable results to daylight acquisitions. This makes imaging sensors extremely versatile for monitoring applications at generally low costs