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Critical Challenge (critical + challenge)
Selected AbstractsScalable Algorithm for Resolving Incorrect Occlusion in Dynamic Augmented Reality Engineering EnvironmentsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 1 2010Amir H. Behzadan As a result of introducing real-world objects into the visualization, less virtual models have to be deployed to create a realistic visual output that directly translates into less time and effort required to create, render, manipulate, manage, and update three-dimensional (3D) virtual contents (CAD model engineering) of the animated scene. At the same time, using the existing layout of land or plant as the background of visualization significantly alleviates the need to collect data about the surrounding environment prior to creating the final visualization while providing visually convincing representations of the processes being studied. In an AR animation, virtual and real objects must be simultaneously managed and accurately displayed to a user to create a visually convincing illusion of their coexistence and interaction. A critical challenge impeding this objective is the problem of incorrect occlusion that manifests itself when real objects in an AR scene partially or wholly block the view of virtual objects. In the presented research, a new AR occlusion handling system based on depth-sensing algorithms and frame buffer manipulation techniques was designed and implemented. This algorithm is capable of resolving incorrect occlusion occurring in dynamic AR environments in real time using depth-sensing equipment such as laser detection and ranging (LADAR) devices, and can be integrated into any mobile AR platform that allows a user to navigate freely and observe a dynamic AR scene from any vantage position. [source] 5.3 Global challenges in research and strategic planningEUROPEAN JOURNAL OF DENTAL EDUCATION, Issue 2002Bruce J. Baum Health sciences research is experiencing dramatic progress. How can dental schools throughout the world best make these research advances relevant for dental students, as well as providing them with the means to assess and utilize the research advances that will occur in the future? This complex question presents a critical challenge to the dental educational community. Research is clearly integral to the mission of dental education. By providing dental students with active learning strategies, dental educators can inculcate the ability for independent scientific thinking and thereby develop reflective as well as technically competent practitioners. However, there is a shortage of well-trained individuals to fill faculty and research positions in certain parts of the world. Global networks for mutual information exchange are imperative to overcome resource limitations in individual institutions, as is dedicated funding for research in the dental educational setting. [source] Mussel-Inspired Polydopamine Coating as a Universal Route to Hydroxyapatite CrystallizationADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Jungki Ryu Abstract Bone tissue is a complex biocomposite material with a variety of organic (e.g., proteins, cells) and inorganic (e.g., hydroxyapatite crystals) components hierarchically organized with nano/microscale precision. Based on the understanding of such hierarchical organization of bone tissue and its unique mechanical properties, efforts are being made to mimic these organic,inorganic hybrid biocomposites. A key factor for the successful designing of complex, hybrid biomaterials is the facilitation and control of adhesion at the interfaces, as many current synthetic biomaterials are inert, lacking interfacial bioactivity. In this regard, researchers have focused on controlling the interface by surface modifications, but the development of a simple, unified way to biofunctionalize diverse organic and inorganic materials remains a critical challenge. Here, a universal biomineralization route, called polydopamine-assisted hydroxyapatite formation (pHAF), that can be applied to virtually any type and morphology of scaffold materials is demonstrated. Inspired by the adhesion mechanism of mussels, the pHAF method can readily integrate hydroxyapatites on ceramics, noble metals, semiconductors, and synthetic polymers, irrespective of their size and morphology (e.g., porosity and shape). Surface-anchored catecholamine moieties in polydopamine enriches the interface with calcium ions, facilitating the formation of hydroxyapatite crystals that are aligned to the c -axes, parallel to the polydopamine layer as observed in natural hydroxyapatites in mineralized tissues. This universal surface biomineralization can be an innovative foundation for future tissue engineering. [source] Reproductive modes in lizards: measuring fitness consequences of the duration of uterine retention of eggsFUNCTIONAL ECOLOGY, Issue 2 2008R. S. Radder Summary 1One of the primary axes of life-history variation involves the proportion of embryonic development for which the offspring is retained within its parent's body; understanding trade-offs associated with prolonging that period thus is a critical challenge for evolutionary ecology. 2Prior to oviposition, most oviparous squamate reptiles retain developing eggs in utero for about one-third of embryogenesis; the strong conservatism in this trait is a major puzzle in reptilian reproduction. To clarify fitness consequences of this prolonged uterine retention, we need to experimentally modify the trait and examine the effects of our manipulation. 3We used transdermal application of corticosterone to induce gravid scincid lizards (Bassiana duperreyi) to lay their eggs ,prematurely', with relatively undeveloped embryos. Corticosterone application induced females to oviposit sooner (mean of 5·41 ± 0·51 days post-treatment) at earlier embryonic developmental stage (27 ± 0·21) than did controls (13·2 ± 1·22 days; embryonic stage 30·4 ± 0·16). 4Corticosterone levels in the egg yolk were unaffected by maternal treatment, so effects of earlier oviposition should not be confounded by endocrine disruption of embryogenesis. Nonetheless, early oviposition reduced hatchling fitness. Hatching success was lower, incubation periods post-laying were increased, and neonates from eggs laid at earlier embryonic stages were smaller and slower. 5These results suggest that retention of developing eggs in utero by oviparous squamates enhances maternal fitness, and does so via modifications to offspring phenotypes rather than (for example) due to accelerated developmental rates of eggs in utero compared to in the nest. 6More generally, our data support optimality models that interpret interspecific variation in the duration of maternal,offspring contact in terms of the selective forces that result from earlier vs. later termination of that maternal investment. [source] Land use/cover changes and their implications on rural livelihoods in the degraded environments of central TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 2009Richard Y. M. KangalaweArticle first published online: 3 FEB 200 Abstract This paper examines the changes in land use/cover types in the degraded environment of central Tanzania over the last 45 years, and how such changes have influenced agricultural and livelihoods sustainability, especially in the Irangi Hills. Changes of land use/cover were measured through aerial photographs interpretations, while local perceptions and description of change were addressed through household interviews and field observations. The results of this study show that there have been variations over the years in terms of both the areas and spatial distribution of cultivated fields. The total land cultivated increased from 31% in the late 1970s to 35% in early 1990s, mainly because of agricultural expansion to sandy watercourses and former grazing areas. Water courses shrank by 55% between late 1970s and early 1990s providing new areas for cultivation. Over the last 45 years, the open and wooded grasslands, and tree-cover types covered about 40% of the total land area, ranging from 29% in 1960 to 43,45% between late 1970s and early 1990s. Spatial and temporal distribution of the cultivated fields and other vegetation cover types were influenced by differences in the scale of land degradation, and the soil-conservation initiatives that have been implemented. With increasing pressure on the land, however, sustaining livelihoods through agricultural production in the area remains a critical challenge. [source] Motivation for Alcohol Becomes Resistant to Quinine Adulteration After 3 to 4 Months of Intermittent Alcohol Self-AdministrationALCOHOLISM, Issue 9 2010Frederic W. Hopf Background:, Continued consumption of alcohol despite deleterious consequences is a hallmark of alcoholism and represents a critical challenge to therapeutic intervention. Previous rat studies showed that enduring alcohol self-administration despite pairing alcohol with normally aversive stimuli was only observed after very long-term intake (>8 months). Aversion-resistant alcohol intake has been previously interpreted to indicate pathological or compulsive motivation to consume alcohol. However, given the time required to model compulsive alcohol seeking in previous studies, there is considerable interest in developing more efficient and quantitative rodent models of aversion-resistant alcohol self-administration. Methods:, Outbred Wistar rats underwent 3 to 4 months or approximately 1.5 months of intermittent, home-cage, two-bottle access (IAA) to 20% alcohol (v/v) or water. Then, after brief operant training, the effect of the bitter-tasting quinine (0.1 g/l) on the motivation to seek alcohol was quantified via progressive ratio (PR). Motivation for quinine-adulterated 2% sucrose under PR was assayed in a separate cohort of 3 to 4 months IAA rats. The effects of quinine on home-cage alcohol consumption in IAA rats and rats with continuous access to alcohol were also examined. Finally, a dose,response for quinine taste preference in IAA and continuous-access animals was determined. Results:, Motivation for alcohol after 3 to 4 months IAA, measured using an operant PR procedure, was not altered by adulteration of alcohol with 0.1 g/l quinine. In contrast, after 3 to 4 months of IAA, motivation for sucrose under PR was significantly reduced by adulteration of sucrose with 0.1 g/l quinine. In addition, motivation for alcohol after only approximately 1.5 months IAA was significantly reduced by adulteration of alcohol with 0.1 g/l quinine. Furthermore, home-cage alcohol intake by IAA rats was insensitive to quinine at concentrations (0.01, 0.03 g/l) that significantly reduced alcohol drinking in animals with continuous access to alcohol. Finally, no changes in quinine taste preference after 3 to 4 months IAA or continuous access to alcohol were observed. Conclusions:, We have developed a novel and technically simple hybrid operant/IAA model in which quinine-resistant motivation for alcohol is evident after an experimentally tractable period of time (3 to 4 months vs. 8 months). Quinine dramatically reduced sucrose and water intake by IAA rats, indicating that continued responding for alcohol in IAA rats despite adulteration with the normally aversive quinine might reflect maladaptive or compulsive motivation for alcohol. This model could facilitate identification of novel therapeutic interventions for pathological alcohol seeking in humans. [source] Complexity Theory and the Philosophy of EducationEDUCATIONAL PHILOSOPHY AND THEORY, Issue 1 2008Mark Mason Abstract Following a brief introduction to complexity theory, this paper considers how various themes in the field relate to the philosophical study of education. Issues and questions introduced include the challenge of complexity theory for the philosophy of education,and, conversely, some critical challenges for complexity theory from educational philosophy; complexity theory and educational continuity and change; the importance that complexity theory places on interpretive perspectives that are transphenomenal, transdisciplinary and transdiscursive; the risks of simplifying complexity to a point that excludes its ambiguities and includes only its dominant usages; the degree of coherence between Dewey's philosophical orientation and that of complexity theory; how Foucault might be read as a complexity theorist; how educational research informed by complexity theory might ask different questions with different analytical perspectives,connectionist, holistic, non-linear, rather than input,output ,black-box' causal modelling, for example; and how curriculum, teaching, the epistemology of schooling, and the ,education of consciousness',understood s an emergent phenomenon,might be different when viewed from the perspective of complexity theory. [source] REVIEW: Consilient research approaches in studying gene × environment interactions in alcohol researchADDICTION BIOLOGY, Issue 2 2010Kenneth J. Sher ABSTRACT This review article discusses the importance of identifying gene-environment interactions for understanding the etiology and course of alcohol use disorders and related conditions. A number of critical challenges are discussed, including the fact that there is no organizing typology for classifying different types of environmental exposures, many key human environmental risk factors for alcohol dependence have no clear equivalents in other species, much of the genetic variance of alcohol dependence in human is not ,alcohol specific', and the potential range of gene-environment interactions that could be considered is so vast that maintaining statistical control of Type 1 errors is a daunting task. Despite these and other challenges, there appears to be a number of promising approaches that could be taken in order to achieve consilience and ecologically valid translation between human alcohol dependence and animal models. Foremost among these is to distinguish environmental exposures that are thought to have enduring effects on alcohol use motivation (and self-regulation) from situational environmental exposures that facilitate the expression of such motivations but do not, by themselves, have enduring effects. In order to enhance consilience, various domains of human approach motivation should be considered so that relevant environmental exposures can be sampled, as well as the appropriate species to study them in (i.e. where such motivations are ecologically relevant). Foremost among these are social environments, which are central to the initiation and escalation of human alcohol consumption. The value of twin studies, human laboratory studies and pharmacogenetic studies is also highlighted. [source] Evaluation policy and evaluation practiceNEW DIRECTIONS FOR EVALUATION, Issue 123 2009William M. K. Trochim The author develops the basic idea of evaluation policy, describes a practical model for development and revision of evaluation policies (including a taxonomy, structure, and set of principles), and suggests critical challenges and opportunities for the future of evaluation policy. An evaluation policy is any rule or principle that a group or organization uses to guide its decisions and actions when doing evaluation. Every entity that engages in evaluation, including government agencies, private businesses, and nonprofit organizations, has evaluation policies. Sometimes they are explicit and written; more often they are implicit and ad hoc principles or norms that have simply evolved over time. Evaluation policies profoundly affect the day-to-day work of all evaluators and ultimately the quality of the programs they evaluate. Many recent and current controversies or conflicts in the field of evaluation can be viewed, at least in part, as a struggle around evaluation policy. Because evaluation policies typically apply across multiple evaluations, influencing policies directly may have systemic and far-reaching effects for practice. Evaluation practice must play a critical role in informing and shaping the development of evaluation policies. © Wiley Periodicals, Inc. [source] | ||||||||||||||||