North Carolina State University

About: North Carolina State University is a education organization based out in Raleigh, North Carolina, United States. It is known for research contribution in the topics: Population & Thin film. The organization has 44161 authors who have published 101744 publications receiving 3456774 citations. The organization is also known as: NCSU & North Carolina State University at Raleigh.

A model for development and evolution of complex morphological structures

Abstract: How 'complex' or composite morphological structures like the mammalian craniomandibular region arise during development and how they are altered during evolution are two major unresolved questions in biology. Herein, we have described a model for the development and evolution of complex morphological structures. The model assumes that natural selection acts upon an array of phenotypes generated by variation in a variety of underlying genetic and epigenetic controlling factors. Selection refines the integration of the various morphogenetic components during ontogeny in order to produce a functioning structure and to adapt the organisms to differing patterns of environmental heterogeneity. The model was applied to the development and evolution of the mammalian mandible (which is used as a paradigm of complex morphological structures). The embryology of the mandible was examined in detail in order to identify the fundamental developmental units which are necessary to assemble the final morphological structure. The model is quite general since equivalent units exist for the development of many other biological structures. This model could be applied to many other developing morphological structures as well as other groups of organisms. For example, it can be applied to cell parameters during Drosophila development (Atchley, 1987). The model as discussed in this paper assumes that morphological changes in the mandible result from evolutionary changes in its underlying developmental units. The developmental units relate to characteristics of cellular condensations which are produced from the differentiation of embryonic neural crest cells. The developmental units include: the number of stem cells in preskeletal condensations (n), the time of initiation of condensation formation (t), the fraction of cells that is mitotically active within a condensation (f), the rate of division of these cells (r), and their rate of cell death (d). These units and their derivative structures are discussed in terms of types of tissue differentiation (chondrogenesis, osteogenesis, primary/secondary osteogenesis, intramembranous/endochondral ossification) and growth properties of major morphological regions of the mandible. Variation in these five units provides the developmental basis for ontogenetic and phylogenetic modification of mandibular morphology. We have discussed how these developmental units are influenced by (a) the cell lineage from which they arise, (b) epithelial-mesenchymal (inductive tissue) interactions, (c) regulation of cell differentiation, and (d) extrinsic factors such as muscles, teeth and hormones. Evidence was provided that variation in mandibular morphology is heritable, subject to modification by natural selection, and that divergence among different genetic stocks has apparently occurred through changes in these developmental units and their derivative structures.(ABSTRACT TRUNCATED AT 400 WORDS)

Predicting inter-thread cache contention on a chip multi-processor architecture

Abstract: This paper studies the impact of L2 cache sharing on threads that simultaneously share the cache, on a chip multi-processor (CMP) architecture. Cache sharing impacts threads nonuniformly, where some threads may be slowed down significantly, while others are not. This may cause severe performance problems such as sub-optimal throughput, cache thrashing, and thread starvation for threads that fail to occupy sufficient cache space to make good progress. Unfortunately, there is no existing model that allows extensive investigation of the impact of cache sharing. To allow such a study, we propose three performance models that predict the impact of cache sharing on co-scheduled threads. The input to our models is the isolated L2 cache stack distance or circular sequence profile of each thread, which can be easily obtained on-line or off-line. The output of the models is the number of extra L2 cache misses for each thread due to cache sharing. The models differ by their complexity and prediction accuracy. We validate the models against a cycle-accurate simulation that implements a dual-core CMP architecture, on fourteen pairs of mostly SPEC benchmarks. The most accurate model, the inductive probability model, achieves an average error of only 3.9%. Finally, to demonstrate the usefulness and practicality of the model, a case study that details the relationship between an application's temporal reuse behavior and its cache sharing impact is presented.

Uncovering cryptic genetic variation.

Abstract: Cryptic genetic variation is the dark matter of biology: it is variation that is not normally seen, but that might be an essential source of physiological and evolutionary potential. It is uncovered by environmental or genetic perturbations, and is thought to modify the penetrance of common diseases, the response of livestock and crops to artificial selection and the capacity of populations to respond to the emergence of a potentially advantageous macro-mutation. We argue in this review that cryptic genetic variation is pervasive but under-appreciated, we highlight recent progress in determining the nature and identity of genes that underlie cryptic genetic effects and we outline future research directions.

The Impact of Stereotype Threat on Age Differences in Memory Performance

Abstract: This study investigated the hypothesis that age differences in memory performance may be influenced by stereotype threat associated with negative cultural beliefs about the impact of aging on memory. Recall was examined in 48 young and 48 older adults under conditions varying in the degree of induced threat. Conditions that maximize threat resulted in lower performance in older adults relative to both younger adults and to older adults who did not experience threat. The degree to which threat affected older adults’ performance increased along with the value that these individuals placed on their memory ability. Older adults’ memory performance across experimental conditions was observed to covary with degree of activation of the negative aging stereotype, providing support for the hypothesized relationship between stereotype activation and performance. Finally, stereotype threat also influenced mnemonic strategy use, which in turn partially mediated the impact of threat on recall. These results emphasize the important role played by contextual factors in determining age differences in memory performance.

A survey of simulated annealing as a tool for single and multiobjective optimization

Abstract: This paper presents a comprehensive review of simulated annealing (SA)-based optimization algorithms. SA-based algorithms solve single and multiobjective optimization problems, where a desired global minimum/maximum is hidden among many local minima/maxima. Three single objective optimization algorithms (SA, SA with tabu search and CSA) and five multiobjective optimization algorithms (SMOSA, UMOSA, PSA, WDMOSA and PDMOSA) based on SA have been presented. The algorithms are briefly discussed and are compared. The key step of SA is probability calculation, which involves building the annealing schedule. Annealing schedule is discussed briefly. Computational results and suggestions to improve the performance of SA-based multiobjective algorithms are presented. Finally, future research in the area of SA is suggested.