348 research outputs found

    Cortical Dynamics of 3-D Surface Perception: Binocular and Half-Occluded Scenic Images

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    Previous models of stereopsis have concentrated on the task of binocularly matching left and right eye primitives uniquely. A disparity smoothness constraint is often invoked to limit the number of possible matches. These approaches neglect the fact that surface discontinuities are both abundant in natural everyday scenes, and provide a useful cue for scene segmentation. da Vinci stereopsis refers to the more general problem of dealing with surface discontinuities and their associated unmatched monocular regions within binocular scenes. This study develops a mathematical realization of a neural network theory of biological vision, called FACADE Theory, that shows how early cortical stereopsis processes are related to later cortical processes of 3-D surface representation. The mathematical model demonstrates through computer simulation how the visual cortex may generate 3-D boundary segmentations and use them to control filling-in of 3-D surface properties in response to visual scenes. Model mechanisms correctly match disparate binocular regions while filling-in monocular regions with the correct depth within a binocularly viewed scene. This achievement required introduction of a new multiscale binocular filter for stereo matching which clarifies how cortical complex cells match image contours of like contrast polarity, while pooling signals from opposite contrast polarities. Competitive interactions among filter cells suggest how false binocular matches and unmatched monocular cues, which contain eye-of-origin information, arc automatically handled across multiple spatial scales. This network also helps to explain data concerning context-sensitive binocular matching. Pooling of signals from even-symmetric and odd-symmctric simple cells at complex cells helps to eliminate spurious activity peaks in matchable signals. Later stages of cortical processing by the blob and interblob streams, including refined concepts of cooperative boundary grouping and reciprocal stream interactions between boundary and surface representations, arc modeled to provide a complete simulation of the da Vinci stereopsis percept.Office of Naval Research (N00014-95-I-0409, N00014-85-1-0657, N00014-92-J-4015, N00014-91-J-4100); Airforce Office of Scientific Research (90-0175); National Science Foundation (IRI-90-00530); The James S. McDonnell Foundation (94-40

    Cortical Computation of Stereo Disparity

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    Our ability to see the world in depth is a major accomplishment of the brain. Previous models of how positionally disparate cues to the two eyes are binocularly matched limit possible matches by invoking uniqueness and continuity constraints. These approaches cannot explain data wherein uniqueness fails and changes in contrast alter depth percepts, or where surface discontinuities cause surfaces to be seen in depth although they are registered by only one eye (da Vinci stereopsis). A new stereopsis model explains these depth percepts by proposing how cortical complex cells binocularly filter their inputs and how monocular and binocular complex cells compete to determine the winning depth signals.Defense Advanced Research Projects Agency (N00014-92-J-4015); Air Force Office of Scientific Research (90-0175); Office of Naval Research (N00014-91-J-4100); James S. McDonnell Foundation (94-40); Defense Advanced Research Projects Agency and the Office of Naval Research (N00014-95-1-0409, N00014-95-1-0657

    Eradicating the “Fear Environment” in Education That Threatens Free Speech and Emboldens Sexual Discrimination

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    This Article proposes a new conception of sexual harassment that melds the insight of social science with the parameters of sexual harassment established through the Dueling Title IX Conceptions of sexual harassment. This Fear Environment Conception of sexual harassment defines sexual harassing speech as: Speech that creates an environment of fear that interferes with the educational experience of students by causing a reasonable student to believe that (1) they will face similar threats in the future that (2) they cannot avoid, based on the (3) perceived harmful intent of the speaker. This Fear Environment Conception focuses on the education interference that Dueling Title IX Conceptions of sexual harassment identify as the root harm of sexual harassment while utilizing social science to target the fear that creates this education interference. It also uses the critical features of both Dueling Title IX Conceptions of sexual harassment. As with the Hostile Environment Conception, the Fear Environment Conception also assesses speech based on the environment it creates to target speech that produces a harmful educational environment. As with the Objectively Offensive Conception, the Fear Environment Conception creates an objective standard by assessing speech from a reasonable person’s perspective. However, the Fear Environment Conception eliminates the ambiguity that plagues both Dueling Title IX Conceptions by utilizing social science to identify the specific features of speech that cause the fear that leads to education interference and, therefore, the harm associated with sexual harassment. To establish the Fear Environment Conception of sexual harassment, Part II of this Article provides a detailed analysis of the various definitions of sexual harassment offered by Title IX. Part III of this Article discusses the social science research regarding sexual harassment, which demonstrates that fear is the key feature that distinguishes harmful sexual harassment from provocative speech that educational institutions must protect. Finally, Part IV establishes the Fear Environment Conception of sexual harassment that utilizes social science to define sexual harassment based on the fear that creates education interference. Through this Fear Environment Conception, educational institutions will be able to eliminate the culture of fear created when the line between free speech and sexual harassment is blurred. Specifically, it will avoid the overbroad definition of sexual harassment that creates a culture of fear in which students are afraid to express their beliefs. At the same time, it will protect against the culture of fear that arises when educational institutions fail to eliminate the nefarious forms of sexual harassment. Instead, this Fear Environment Conception will enable educational institutions to create a culture of interaction where students are free to express their beliefs and opinions without fear of sexual harassment or speech limits

    Eliminating Rivals, Managing Rivalries: a Comparison of Robert Mugabe and Kenneth Kaunda

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    is article seeks to explore the role that leadership plays in both the perpetration and avoidance of mass atrocities. Many scholars have argued that leadership is pivotal to the outbreak of such violence but there is almost no scholarship which explores the role that political leaders play in mitigating or aggravating the risk of atrocities over time. Why is it that mass atrocities occur in some places but not in others, despite the existence of similar risk factors? By conducting a comparative analysis of Robert Mugabe of Zimbabwe and Kenneth Kaunda of Zambia, this paper investigates the impact that the strategies of each leader had on the risk of mass atrocities. Both countries share similar colonial backgrounds, and display comparable structural risk factors commonly associated with genocide and other mass atrocities. Both Kaunda and Mugabe were key leaders in their countries’ liberation struggles, and both leaders played pivotal roles during the crucial formative years of independence. Yet the two countries have taken dramatically di erent paths – while Zambia has remained relatively stable and peaceful, Zimbabwe has experience mass violence and repression

    Understanding Mass Atrocity Prevention During Periods of Democratic Transition

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    The purpose of this article is to provide a better understanding of why some countries experience mass atrocities dur- ing periods of democratic transition, while others do not. Scholars have long regarded democracy as an important source of stability and protection from mass atrocities such as genocide, crimes against humanity and ethnic cleansing. But democratic transition itself is fraught with the heightened risk of violent conflict and even mass atrocities. Indeed, a number of studies have identified regimes in transition as containing the highest risk of political instability and mass atrocities. What is overlooked is the question of how and why some regimes undergo such transitions without experi- encing mass atrocities, despite the presence of a number of salient risk factors, including state-based discrimination, in- ter-group tension and horizontal inequality. Utilizing a new analytical framework, this article investigates this lacuna by conducting a comparative analysis of two countries—one that experienced atrocities (Burundi) during transition, and one that did not (Guyana). How countries avoid such violence during transition has the potential to yield insights for the mitigation of risk associated with mass atrocity crimes

    The Effects of Dual Tasks on Balance and Gait in Patients with Parkinson’s Disease: A Critically Appraised Topic

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    ● Parkinson’s Disease (PD) is a progressive neurodegenerative disease that affects over 10 million people globally. ● There is evidence to suggest that dual-cognitive tasks negatively impact the gait and balance of patients with PD. ● 19-38% of patients with PD will develop cognitive impairments. ● Higher level cognitive functioning dual tasks exacerbate freezing of gait episodes (FoG). ● Research shows potential improvement with dual-tasks during gait secondary to prioritization of motor task of walking

    Fossilized spermatozoa preserved in a 50-Myr-old annelid cocoon from Antarctica

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    The origin and evolution of clitellate annelids-earthworms, leeches and their relatives-is poorly understood, partly because body fossils of these delicate organisms are exceedingly rare. The distinctive egg cases (cocoons) of Clitellata, however, are relatively common in the fossil record, although their potential for phylogenetic studies has remained largely unexplored. Here, we report the remarkable discovery of fossilized spermatozoa preserved within the secreted wall layers of a 50-Myr-old clitellate cocoon from Antarctica, representing the oldest fossil animal sperm yet known. Sperm characters are highly informative for the classification of extant Annelida. The Antarctic fossil spermatozoa have several features that point to affinities with the peculiar, leech-like 'crayfish worms' (Branchiobdellida). We anticipate that systematic surveys of cocoon fossils coupled with advances in non-destructive analytical methods may open a new window into the evolution of minute, soft-bodied life forms that are otherwise only rarely observed in the fossil record.Facultad de Ciencias Naturales y Muse

    Extraction and Quantification of Sinapinic Acid from Irish Rapeseed Meal and Assessment of Angiotensin-I Converting Enzyme (ACE-I) Inhibitory Activity

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    Phenolic compounds, including phenolic acids, are known to play a protective role against the development of cardiovascular disease. The aim of this work was to generate a phenolic acid extract from Irish rapeseed meal, to determine the quantity of sinapinic acid (SA) in this fraction and to assess the ability of this fraction to inhibit the enzyme angiotensin-I converting enzyme (ACE-I; EC 3.4.15.1). A crude phenolic extract (fraction 1), free phenolic acid containing extract (fraction 2), and an extract containing phenolic acids liberated from esters (fraction 3) were generated from Irish rapeseed meal using a methanol:acetone:water solvent mixture (7:7:6). The total phenolic content (TPC) of each extract was determined and proximate analysis performed to determine the fat, moisture, and protein content of these extracts. Nuclear magnetic resonance (1H NMR) spectroscopy was used to quantify the level of SA in extract 3, which inhibited ACE-I by 91% ± 0.08 when assayed at a concentration of 1 mg/mL, compared to the control, captopril, which inhibited ACE by 97% ± 0.01 when assayed at a concentration of 1 mg/mL

    Animal–plant interactions in a Middle Permian permineralised peat of the Bainmedart Coal Measures, Prince Charles Mountains, Antarctica

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    AbstractEvidence for invertebrate feeding on glossopterid gymnosperms is documented from Middle Permian silicified peats of the Prince Charles Mountains, Antarctica, in the form of coprolites occurring both free in the peat matrix and clustered within excavations in roots, aerial wood and leaves. Observations of coprolites in thin-sections of the peats and from scanning electron microscopy of examples extracted via bulk maceration reveal nine morphotypes distinguished by size, shape, surface texture and contents. These include coprolites with coarse plant debris, spirally ornamented coprolites, coprolites containing spore/pollen remains and fern sporangia, coprolites within Glossopteris leaves, an ellipsoidal morphotype within a fern sporangium, large isolated coprolites between matted leaves, clustered forms filling galleries inside Vertebraria roots and Australoxylon wood, forms with coarse indeterminate constituents and others with fungal contents. Other faunal evidence is limited to indeterminate arthropod exoskeleton fragments. Collectively, the coprolites within the permineralised peat from the Prince Charles Mountains document the presence of diverse feeding behaviours including stem feeding, sporangial feeding, palynivory, root feeding and mycophagy. The first evidence of invertebrate feeding traces in Vertebraria (glossopterid) roots is identified. These findings indicate that herbivory by invertebrates in the high-latitude Permian forest-mire ecosystems of Antarctica was more intense and diverse than previous studies have reported, and affected all parts of the Glossopteris plant, together with components of associated herbaceous taxa
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