A simple proof for visibility paths in simple polygons

The purpose of this note is to give a simple proof for a necessary and sufficient condition for visibility paths in simple polygons. A visibility path is a curve such that every point inside a simple polygon is visible from at least one point on the path. This result is essential for finding the shortest watchman route inside a simple polygon specially when the route is restricted to curved paths

Query-points visibility constraint minimum link paths in simple polygons

We study the query version of constrained minimum link paths between two points inside a simple polygon $P$ with $n$ vertices such that there is at least one point on the path, visible from a query point. The method is based on partitioning $P$ into a number of faces of equal link distance from a point, called a link-based shortest path map (SPM). Initially, we solve this problem for two given points $s$, $t$ and a query point $q$. Then, the proposed solution is extended to a general case for three arbitrary query points $s$, $t$ and $q$. In the former, we propose an algorithm with $O(n)$ preprocessing time. Extending this approach for the latter case, we develop an algorithm with $O(n^3)$ preprocessing time. The link distance of a $q$-$visible$ path between $s$, $t$ as well as the path are provided in time $O(\log n)$ and $O(m+\log n)$, respectively, for the above two cases, where $m$ is the number of links

A Viscoplastic Constitutive Model For Cyclic Clay Behavior

«RÉSUMÉ: Les séismes peuvent avoir des conséquences désastreuses en termes de pertes humaines et matérielles. Parmi les phénomènes géotechniques qui peuvent mener à des pertes pendant un tremblement de terre, la liquéfaction des sols granulaires a été le plus étudié, bien que l’amollissement cyclique des argiles puisse générer des dommages significatifs. Par exemple, le tremblement de 1964 en Alaska a déclenché un glissement de terrain majeur le long de la 4ième avenue à Anchorage, dont la cause principale était l’amollissement cyclique. Pour étudier l'impact de tels phénomènes, des simulations numériques dynamiques non linéaires peuvent être utilisées. Ces simulations s'appuient sur des modèles constitutifs qui sont formulés pour capturer le déclenchement de la liquéfaction ou de l’amollissement cyclique. L'utilisation de ces modèles nécessite une connaissance de leur formulation et des essais et erreurs fastidieux pour calibrer leurs nombreux paramètres d'entrée. La calibration difficile a rendu difficile l'utilisation de modèles constitutifs avancés pour les applications géotechniques sismiques. En conséquence, les modèles constitutifs avancés n'ont pas été largement adoptés dans la pratique malgré l'attention significative qu'ils ont reçue ces dernières années.» et «----------ABSTRACT: Earthquakes can have dire consequences both in terms of loss of human lives and properties. Among the geotechnical phenomena that can induce losses during an earthquake, liquefaction of granular soils is the most well-studied but cyclic softening of clays is also capable of producing significant damages. For instance, the 1964 Alaska earthquake triggered a major landslide along the 4th avenue in Anchorage, attributed to cyclic softening. To study the impact of such phenomena, numerical dynamic nonlinear simulations can be used. These simulations rely on constitutive models that are formulated to capture the triggering of liquefaction or cyclic softening. The use of these models requires knowledge of their formulation, and time-consuming trial and error efforts to calibrate their numerous input parameters. The arduous calibration has rendered the use of advanced constitutive models for earthquake geotechnical applications in practice challenging. As a results advanced constitutive models have not been widely adopted in practice despite the significant attention they have received in recent years.

Efficacy of IANB and Gow-Gates Techniques in Mandibular Molars with Symptomatic Irreversible Pulpitis: A Prospective Randomized Double Blind Clinical Study

Introduction: The aim of the present study was to compare the efficacy of the inferior alveolar nerve block (IANB) and Gow-Gates techniques in mandibular molars with symptomatic irreversible pulpitis. Methods and Materials: In this randomised, double-blind clinical trial, 80 patients referred to Mashhad Dental School, were randomly divided into two groups: IANB and Gow-Gates anaesthetic techniques using 2% lidocaine with 1:100000 epinephrine. After injection, if pain during caries/dentin removal and access cavity preparation was reported in each group, the patients once again were randomly allocated to receive buccal or lingual supplementary infiltration. Pain severity was evaluated using a visual analogue scale. The rates of positive aspiration and changes in heart rate were compared between the IANB and Gow-Gates. Paired and individual t-tests and the Mann-Whitney U-test were used to compare the reduction in pain severity. The level of significance was set at 0.05. Results: The success rates of anaesthesia in the Gow-Gates and IANB techniques were 50% and 42.5%, respectively with no significant difference (P=0.562). Supplementary infiltrations significantly reduced pain severity in all subgroups (P<0.05). Lingual infiltration resulted in a significantly greater reduction in pain severity in the IANB group than in the Gow-Gates group (P<0.05). No significant difference in heart rate or positive aspiration results was observed between groups (P>0.05). Conclusions: In the present study, the efficacy of the IANB and Gow-Gates techniques was comparable in mandibular molars with symptomatic irreversible pulpitis. Supplementary buccal and lingual infiltration significantly reduced pain severity. Keywords: Buccal Infiltration; Gow-Gates Technique; Inferior Alveolar Nerve Block; Irreversible Pulpitis; Lingual Infiltratio

Dental Pulp Reaction to Exposure at Different Time Intervals in Open Apex Canine Teeth of Cats

INTRODUCTION: Open-apex teeth with irreversible pulpitis require complex and difficult treatment. Providing the right environment for apexogenesis and pulp protection is vital for their long term prognosis. The young pulp of open apex tooth, however, is better equipped against irritation and assault. The aim of this study was to evaluate pulp inflammation in open apex canine teeth of cats. MATERIALS AND METHODS: In this in vivo study, twelve cats with open apex canines were used. Pulps were iatrogenically exposed and the animals were sacrificed at one, seven, thirty and ninety days after pulp exposure. Samples were prepared for histological evaluations. RESULTS: During the first and seventh day, changes were limited to acute inflammation in the coronal pulp. During the first month pulp changes in 45.5% of samples were similar to the seventh day. In the other samples necrosis and abscess spread to the end of the root, and internal resorption and periapical abscess were observed. In 45.5% of samples in the apical region vital tissue was barely observed (during 90 days); in 54.5% of samples however, complete pulp necrosis, internal resorption and a large periapical lesion was observed. CONCLUSION: In one and seven-day periods pulp tissue was vital; however, in the thirty and ninety-day periods, minority of the pulp samples were vital

Defluoridation of water via Light Weight Expanded Clay Aggregate (LECA): Adsorbent characterization, competing ions, chemical regeneration, equilibrium and kinetic modeling

International audienceNatural, H2O2 and MgCl2 - modified Light Weight Expanded Clay Aggregate (LECA) were used as fluoride adsorbents. Characterization of LECA and its modified forms was done by infra-red, X-ray diffraction, scanning electron microscope and X-ray fluorescence studies. The specific surface area of HML and MGML was 3.34 and 3.97 times greater than that of NL (11.72 m2/g). Improved chemical composition of Magnesium (as oxide) to 15.6% by 2 M MgCl2 solution was ascertained through XRF results. The fluoride levels were reduced (within the safe limit of WHO: 0.5-1.5 mg/L−1) to 0.39 mg/L, 1.0 mg/L and 0.075 mg/L respectively using natural (NL), H2O2 (HML) and MgCl2 - modified LECA (MGML) at a pH of 6.0 and initial fluoride concentration of 10 g/L for an equilibrium time of 120 min. The sorption capacities of 8.53 mg/g, 17.83 mg/g and 23.86 mg/g were determined for NL, HML and MGML respectively. Validation of kinetic and isotherm models was checked for the present fluoride sorption dynamics. The thermodynamic data revealed that the present fluoride sorption was spontaneous, exothermic and ends up with decrease in randomness. Prediction of fluoride sorption mechanism for onto natural and modified LECA forms was also elucidated. Chloride and sulfate were the highly competing species against fluoride sorption. Regeneration efficiency of the spent LECA materials prompted the ability of MGML even after five cycles of adsorption-regeneration processes