Color constancy for landmark detection in outdoor environments

European Workshop on Advanced Mobile Robots (EUROBOT), 2001, Lund (Suecia)This work presents an evaluation of three color constancy techniques applied to a landmark detection system designed for a walking robot, which has to operate in unknown and unstructured outdoor environments. The first technique is the well-known image conversion to a chromaticity space, and the second technique is based on successive lighting intensity and illuminant color normalizations. Based on a differential model of color constancy, we propose the third technique, based on color ratios, which unifies the processes of color constancy and landmark detection. The approach used to detect potential landmarks, which is common to all evaluated systems, is based on visual saliency concepts using multiscale color opponent features to identify salient regions in the images. These regions are selected as landmark candidates, and they are further characterized by their features for identification and recognition.This work was supported by the project 'Navegación autónoma de robots guiados por objetivos visuales' (070-720).Peer Reviewe

Indexing and efficient instance-based retrieval of process models using untanglings

Process-Aware Information Systems (PAISs) support executions of operational processes that involve people, resources, and software applications on the basis of process models. Process models describe vast, often infinite, amounts of process instances, i.e., workflows supported by the systems. With the increasing adoption of PAISs, large process model repositories emerged in companies and public organizations. These repositories constitute significant information resources. Accurate and efficient retrieval of process models and/or process instances from such repositories is interesting for multiple reasons, e.g., searching for similar models/instances, filtering, reuse, standardization, process compliance checking, verification of formal properties, etc. This paper proposes a technique for indexing process models that relies on their alternative representations, called untanglings. We show the use of untanglings for retrieval of process models based on process instances that they specify via a solution to the total executability problem. Experiments with industrial process models testify that the proposed retrieval approach is up to three orders of magnitude faster than the state of the art

Photodesorption of CO ice

At the high densities and low temperatures found in star forming regions, all molecules other than H2 should stick on dust grains on timescales shorter than the cloud lifetimes. Yet these clouds are detected in the millimeter lines of gaseous CO. At these temperatures, thermal desorption is negligible and hence a non-thermal desorption mechanism is necessary to maintain molecules in the gas phase. Here, the first laboratory study of the photodesorption of pure CO ice under ultra high vacuum is presented, which gives a desorption rate of 3E-3 CO molecules per UV (7-10.5 eV) photon at 15 K. This rate is factors of 1E2-1E5 larger than previously estimated and is comparable to estimates of other non-thermal desorption rates. The experiments constrains the mechanism to a single photon desorption process of ice surface molecules. The measured efficiency of this process shows that the role of CO photodesorption in preventing total removal of molecules in the gas has been underestimated.Comment: 5 pages, 4 figures, accepted by ApJ

The non-Abelian gauge theory of matrix big bangs

We study at the classical and quantum mechanical level the time-dependent Yang-Mills theory that one obtains via the generalisation of discrete light-cone quantisation to singular homogeneous plane waves. The non-Abelian nature of this theory is known to be important for physics near the singularity, at least as far as the number of degrees of freedom is concerned. We will show that the quartic interaction is always subleading as one approaches the singularity and that close enough to t=0 the evolution is driven by the diverging tachyonic mass term. The evolution towards asymptotically flat space-time also reveals some surprising features.Comment: 29 pages, 8 eps figures, v2: minor changes, references added: v3 small typographical changes

A General Definition of "Conserved Quantities" in General Relativity and Other Theories of Gravity

In general relativity, the notion of mass and other conserved quantities at spatial infinity can be defined in a natural way via the Hamiltonian framework: Each conserved quantity is associated with an asymptotic symmetry and the value of the conserved quantity is defined to be the value of the Hamiltonian which generates the canonical transformation on phase space corresponding to this symmetry. However, such an approach cannot be employed to define `conserved quantities' in a situation where symplectic current can be radiated away (such as occurs at null infinity in general relativity) because there does not, in general, exist a Hamiltonian which generates the given asymptotic symmetry. (This fact is closely related to the fact that the desired `conserved quantities' are not, in general, conserved!) In this paper we give a prescription for defining `conserved quantities' by proposing a modification of the equation that must be satisfied by a Hamiltonian. Our prescription is a very general one, and is applicable to a very general class of asymptotic conditions in arbitrary diffeomorphism covariant theories of gravity derivable from a Lagrangian, although we have not investigated existence and uniqueness issues in the most general contexts. In the case of general relativity with the standard asymptotic conditions at null infinity, our prescription agrees with the one proposed by Dray and Streubel from entirely different considerations.Comment: 39 pages, no figure

COVID-19 Outbreak: Effect of an Educational Intervention Based on Health Belief Model on Nursing Students' Awareness and Health Beliefs at Najran University, Kingdom of Saudi Arabia

This study aimed to investigate the effect of an educational intervention based on the health belief model (HBM) about COVID-19 on nursing  students' awareness and health beliefs. A true-experimental research design was conducted at nursing college, Najran University, KSA. A  comprehensive sampling was followed to include all female students at the colleges (164 students). The sample was divided randomly into  intervention (82) and control group (82). The educational intervention was designed and conducted based on the HBM through four sequential phases: assessment, planning, implementation, and evaluation. The current study results indicated no statistically significant differences between intervention and control groups concerning their demographic characteristic, awareness, and health beliefs before intervention. After intervention, significant differences (p< 0.05) were observed between intervention and control groups in their awareness and all HBM constructs regarding COVID19. There were positive, statistically significant correlations (P< 0.05) between participants' total HBM score and their total awareness score. This study concluded that HBM is effective in increasing nursing students' awareness regarding COVID-19. It also increases their perceived  susceptibility, severity, and benefits. Besides, it may increase their self-efficacy to overcome perceived barriers to practice protective and preventive actions while dealing with COVID-19. Keywords: Awareness, COVID-19, Health belief model, Nursing students, Saudi Arabia   Cette étude visait à étudier l'effet d'une intervention éducative basée sur le modèle de croyance en santé (HBM) à propos du COVID-19 sur la sensibilisation des étudiants en soins infirmiers et leurs croyances en matière de santé. Une conception de recherche véritablement expérimentale a été menée au collège d'infirmières de l'Université de Najran, en Arabie Saoudite. Un échantillonnage complet a été suivi pour inclure toutes les étudiantes des collèges (164 étudiantes). L'échantillon a été divisé au hasard en groupe d'intervention (82) et groupe témoin (82). L'intervention éducative a été conçue et menée sur la base du HBM à travers quatre phases séquentielles: évaluation, planification, mise en oeuvre et évaluation. Les résultats de l'étude actuelle n'ont indiqué aucune différence statistiquement significative entre les groupes d'intervention et de contrôle concernant leurs caractéristiques démographiques, leur sensibilisation et leurs croyances en matière de santé avant l'intervention. Aprèsl'intervention, des  différences significatives (p <0,05) ont été observées entre les groupes d'intervention et de contrôle dans leur connaissance et tutes les constructions HBM concernant COVID19. Il y avait des corrélations positives et statistiquement significatives (P <0,05) entre le score HBM total des participants et leur score total de sensibilisation. Cette étude a conclu que HBM est efficace pour sensibiliser les étudiants en sciences infirmières au COVID-19. Cela augmente également leur sensibilité, leur gravité et leurs avantages perçus. En outre, cela peut augmenter leur efficacité personnelle pour surmonter les obstacles perçus à la pratique d'actions de protection et de prévention tout en traitant le COVID-19. Mots-clés: Sensibilisation, COVID-19, modèle de croyance en matière de santé, étudiants en sciences infirmières, Arabie saoudit