Showing 191 - 200 of 733 Items
Data associated with Walter-McNeill et al. (2021) Oecologia https://doi.org/10.1007/s00442-021-05038-y
Date: 2021-01-01
Creator: Barry Logan
Access: Open access
Sri Lanka in 2018: Seeking a way forward
Date: 2019-02-01
Creator: Sree Padma
Access: Open access
- The highlight of Maithripala Sirisena's presidency came in its very beginning when he ended a decade of autocracy by restoring democracy. And when rivalry with his own prime minister, Ranil Wickremesinghe, devolved into a constitutional crisis, Sirisena was forced to abide by the democratic norms he had restored.
Bilateral consequences of chronic unilateral deafferentation in the auditory system of the cricket gryllus bimaculatus
Date: 2011-04-01
Creator: Hadley Wilson Horch, Elizabeth Sheldon, Claire C. Cutting, Claire R. Williams, Dana M., Riker, Hannah R. Peckler, Rohit B. Sangal
Access: Open access
- The auditory system of the cricket has the unusual ability to respond to deafferentation by compensatory growth and synapse formation. Auditory interneurons such as ascending neuron 2 (AN-2) in the cricket Gryllus bimaculatus possess a dendritic arbor that normally grows up to, but not over, the midline of the prothoracic ganglion. After chronic deafferentation throughout larval development, however, the AN-2 dendritic arbor changes dramatically, and medial dendrites sprout across the midline where they form compensatory synapses with the auditory afferents from the contralateral ear. We quantified the extent of the effects of chronic, unilateral deafferentation by measuring several cellular parameters of 3 different neuronal components of the auditory system: the deafferented AN-2, the contralateral (or nondeafferented) AN-2 and the contralateral auditory afferents. Neuronal tracers and confocal microscopy were used to visualize neurons, and double-label experiments were performed to examine the cellular relationship between pairs of cells. Dendritic complexity was quantified using a modified Sholl analysis, and the length and volume of processes and presynaptic varicosities were assessed under control and deafferented conditions. Chronic deafferentation significantly influenced the morphology of all 3 neuronal components examined. The overall dendritic complexity of the deafferented AN-2 dendritic arbor was reduced, while both the contralateral AN-2 dendritic arbor and the remaining, intact, auditory afferents grew longer. We found no significant changes in the volume or density of varicosities after deafferentation. These complex cellular changes after deafferentation are interpreted in the light of the reported differential regulation of vesicle-associated membrane protein and semaphorin 2a. Copyright © 2011 S. Karger AG, Basel.
Sri Lanka in 2017: Sluggish on many fronts
Date: 2018-01-01
Creator: Sree Padma
Access: Open access
- Sri Lanka's 69-year-old parliamentary democracy continues with power concentrated at the center, and consequently, the country's non-Sinhala-Buddhist minorities on the periphery continue to press for equal rights, while ethnic strife hinders prospects for unified progress. Maithripala Sirisena, president since 2015, promises reconciliation but has received little cooperation from the majority Sinhala Buddhists.
An empirical study of memory sharing in virtual machines
Date: 2019-01-01
Creator: Sean Barker, Timothy Wood, Prashant Shenoy, Ramesh Sitaraman
Access: Open access
- Content-based page sharing is a technique often used in virtualized environments to reduce server memory requirements. Many systems have been proposed to capture the benefits of page sharing. However, there have been few analyses of page sharing in general, both considering its real-world utility and typical sources of sharing potential. We provide insight into this issue through an exploration and analysis of memory traces captured from real user machines and controlled virtual machines. First, we observe that absolute sharing levels (excluding zero pages) generally remain under 15%, contrasting with prior work that has often reported savings of 30% or more. Second, we find that sharing within individual machines often accounts for nearly all (>90%) of the sharing potential within a set of machines, with inter-machine sharing contributing only a small amount. Moreover, even small differences between machines significantly reduce what little inter-machine sharing might otherwise be possible. Third, we find that OS features like address space layout randomization can further diminish sharing potential. These findings both temper expectations of real-world sharing gains and suggest that sharing efforts may be equally effective if employed within the operating system of a single machine, rather than exclusively targeting groups of virtual machines.
The Art Gallery Theorem for Polyominoes
Date: 2012-10-01
Creator: Therese Biedl, Mohammad T. Irfan, Justin Iwerks, Joondong Kim, Joseph S.B., Mitchell
Access: Open access
- We explore the art gallery problem for the special case that the domain (gallery) P is an m-polyomino, a polyform whose cells are m unit squares. We study the combinatorics of guarding polyominoes in terms of the parameter m, in contrast with the traditional parameter n, the number of vertices of P. In particular, we show that ⌊m+1/3⌋ point guards are always sufficient and sometimes necessary to cover an m-polyomino, possibly with holes. When m < 3n/4-4, the sufficiency condition yields a strictly lower guard number than ⌊ n/4⌋, given by the art gallery theorem for orthogonal polygons. © 2012 Springer Science+Business Media, LLC.
Polar oceanography: Engendering students with a sense of place and a sense of time
Date: 2016-06-01
Creator: Collin S. Roesler
Access: Open access
Genetic variation in the serotonin transporter gene influences ERP old/new effects during recognition memory
Date: 2015-11-01
Creator: Robert S. Ross, Paolo Medrano, Kaitlin Boyle, Andrew Smolen, Tim Curran, Erika Nyhus
Access: Open access
- Recognition memory is defined as the ability to recognize a previously encountered stimulus and has been associated with spatially and temporally distinct event-related potentials (ERPs). Allelic variations of the serotonin transporter gene (SLC6A4) have recently been shown to impact memory performance. Common variants of the serotonin transporter-linked polymorphic region (5HTTLPR) of the SLC6A4 gene result in long (l) and short (s) allelic variants with carriers of the s allele having lowered transcriptional efficiency. Thus, the current study examines the effects polymorphisms of the SLC6A4 gene have on performance and ERP amplitudes commonly associated with recognition memory. Electroencephalogram (EEG), genetic, and behavioral data were collected from sixty participants as they performed an item and source memory recognition task. In both tasks, participants studied and encoded 200 words, which were then mixed with 200 new words during retrieval. Participants were monitored with EEG during the retrieval portion of each memory task. EEG electrodes were grouped into four ROIs, left anterior superior, right anterior superior, left posterior superior, and right posterior superior. ERP mean amplitudes during hits in the item and source memory task were compared to correctly recognizing new items (correct rejections). Results show that s-carriers have decreased mean hit amplitudes in both the right anterior superior ROI 1000-1500. ms post stimulus during the source memory task and the left anterior superior ROI 300-500. ms post stimulus during the item memory task. These results suggest that individual differences due to genetic variation of the serotonin transporter gene influences recognition memory. © 2015 Elsevier Ltd.
Learning cognitive maps: Finding useful structure in an uncertain world
Date: 2008-05-22
Creator: Eric Chown, Byron Boots
Access: Open access
- In this chapter we will describe the central mechanisms that influence how people learn about large-scale space. We will focus particularly on how these mechanisms enable people to effectively cope with both the uncertainty inherent in a constantly changing world and also with the high information content of natural environments. The major lessons are that humans get by with a "less is more" approach to building structure, and that they are able to quickly adapt to environmental changes thanks to a range of general purpose mechanisms. By looking at abstract principles, instead of concrete implementation details, it is shown that the study of human learning can provide valuable lessons for robotics. Finally, these issues are discussed in the context of an implementation on a mobile robot. © 2007 Springer-Verlag Berlin Heidelberg.