47 research outputs found
Rapid motion adaptation reveals the temporal dynamics of spatiotemporal correlation between on and off pathways
No full textAt the early stages of visual processing, information is processed by two major thalamic pathways encoding brightness increments (ON) and decrements (OFF). Accumulating evidence suggests that these pathways interact and merge as early as in primary visual cortex. Using regular and reverse-phi motion in a rapid adaptation paradigm, we investigated the temporal dynamics of within and across pathway mechanisms for motion processing. When the adaptation duration was short (188 ms), reverse-phi and regular motion led to similar adaptation effects, suggesting that the information from the two pathways are combined efficiently at early-stages of motion processing. However, as the adaption duration was increased to 752 ms, reverse-phi and regular motion showed distinct adaptation effects depending on the test pattern used, either engaging spatiotemporal correlation between the same or opposite contrast polarities. Overall, these findings indicate that spatiotemporal correlation within and across ON-OFF pathways for motion processing can be selectively adapted, and support those models that integrate within and across pathway mechanisms for motion processing. © The Author(s) 2016
Clock distribution network techniques
No full textClock distribution networks are essential to synchronous systems. The design of these networks affects the system performance dramatically and sometimes determines whether the chip can function properly or not. This thesis first describes in detail how a synchronous system works. Based on the design metrics such as the clock skew requirement and power requirement, different clock distribution network topologies are then presented, including the popular H tree, grid and serpentine structures. Finally, commonly used techniques for improving clock skew, jitter and power are discussed and conclusions are offered.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2022-08-01The student, Shuang Chen, accepted the attached license on 2020-06-26 at 16:40.The student, Shuang Chen, submitted this Thesis for approval on 2020-06-26 at 16:50.This Thesis was approved for publication on 2020-06-29 at 15:08.DSpace SAF Submission Ingestion Package generated from Vireo submission #15473 on 2020-10-02 at 15:49:41Made available in DSpace on 2020-10-07T22:48:09Z (GMT). No. of bitstreams: 2
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The role of molecular length scale on the viscoplastic response of amorphous polymer nanofibers in the glassy state
No full textPolymeric nanostructures are quite distinct because of the large ratio of surface-to-volume macromolecules which result in very different physical and mechanical behavior compared to bulk. Of special interest are nanostructures in which the constituent polymer is in its glassy state to provide structural and dimensional stability against surface forces that are particularly strong at the micron and submicron scales. The majority of existing literature on the mechanical properties of ultra-small volumes of polymers in their glassy state focuses on ultra-thin films and is limited to small deformations and the viscoelastic regime. Experiments with composite materials encapsulating polystyrene (PS) thin films and in their glassy state at room temperature have demonstrated shear yielding and large deformations that are not possible at the macroscale where PS fails at small strains due to crazing. This dissertation research focused on direct experiments with atactic PS nanofibers to elucidate and quantify the unusual viscoplastic response of ultra-small volumes of PS as a function of the underlying molecular and structural length scales. PS is an ideal polymer for this study because it is amorphous and its glass transition temperature, Tg, is much higher (100C) than room temperature.
The objective of this research was to understand the synergistic coupling between the material length scale as defined by macromolecular size, and the specimen size as defined by the fiber diameter, which can result in extreme ductility and simultaneous strengthening and toughening for fiber diameters at the submicron scale. To this goal, PS fibers with diameters 150–5,000 nm were electrospun from monodisperse PS powders with molecular weights, MW, in the range 13,000–9,000,000 g/mol. Individual nanofibers were tested using a surface micromachined device for nanofiber testing at the quasi-static strain rate of 10-2 s-1. Unlike the brittle behavior of bulk PS, the engineering stress vs. stretch ratio of individual nanofibers with several combinations of MW and diameter displayed very repeatable post-yield behavior including necking and pronounced strain-hardening. Specifically, the ratio of the structural length scale (fiber diameter) to the intrinsic macromolecular length scale (root-mean-square end-to-end chain distance), Dnorm, was shown be an excellent scaling parameter to determine the occurrence and evolution of necking and strain hardening in submicron scale PS fibers. This interplay between molecular and structural length scales in glassy PS fibers was favorably exploited to harness a ~3,000% increase in toughness along with simultaneous increase in tensile strength: the highest fiber strength was achieved for Dnorm = 3–5, whereas increasing Dnorm resulted in gradual decline in strength. Bulk-like brittle behavior took place for Dnorm > 18. It was shown that the effects of molecular and structural lengths scales on large deformation behavior of fibers could be collapsed onto a single master curve as long as the MW was larger than the critical value for constant inter-chain entanglement length. Furthermore, it was shown that the pronounced hardening in PS nanofibers is not a result of post yield necking, but part of the material constitutive response: experiments on individual poly(lactide-co-glycolic acid) (PLGA) nanofibers showed that unlike in bulk specimens, nanoscale imperfections and specimen irregularities are rather benign and strong post-yield strain hardening occurs even when necking is suppressed.
The viscous component of the large deformation response in PS nanofibers was assessed by tensile experiments with PS nanofibers with MW = 123,000 – 2,000,0000 g/mol and diameters of 200 – 750 nm in the range of strain rates 10-4 - 102 s-1. For fibers with Dnorm 10, i.e. fibers without significant post-neck hardening. For all PS fibers, the rate dependent stress vs. stretch ratio curves scaled with yield stress. Therefore, a normalized stress vs. strain curve could be generated to combine size effects and temporal effects on the mechanical behavior of PS nanofibers at room temperature.Item withdrawn by Laura Spradlin ([email protected]) on 2014-12-04T13:49:47Z
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University of Illinois Theses & Dissertations (ID: 1)
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Spatially regulated β-actin translation in epithelia: analysis of adherens junction assembly, membrane cytoskeletal dynamics and tissue function
No full textThe β-actin mRNA contains a 28 nucleotide sequence in the 3′UTR termed the zipcode which, along with a trans acting factor called the Zipcode Binding Protein-1 (ZBP-1/IMP-1), regulates the spatio-temporal expression pattern of the β-actin. This mode of post-transcriptional gene regulation is required for several cellular processes including cell migration, cell-cell adhesion, and cell-matrix adhesion. Adding to the list of signaling cascades such as RhoA and Src, work in this thesis demonstrates E-cadherin endocytosis, and plausibly gene expression pathways regulating cell proliferation, converge on spatially regulated β-actin translation. E-cadherin endocytosis and recycling has been shown to be important during the maintenance of epithelial adherens junctions. However in this thesis, endocytosis of E-cadherin is shown to negatively regulate adherens junction assembly, while spatially regulated β-actin translation balances this by promoting actin filament anchoring of cadherin complexes. Mislocalization of β-actin translation impairs adherens junction maturation in epithelial cells following de novo cell-cell contact. These results have implications in development and disease where the assembly and maintenance of epithelial adherens junctions is essential. In order to quantify the extent of adherens junction assembly defects in epithelial cells following de novo contact, a Fluorescence Covariance Index based on calculating Pearson’s Correlation Coefficients was developed and validated using several components of the adherens junction complex. In addition to quantitating the morphological effects of mislocalizing β-actin translation on adherens junctions, the FCI analysis showed correlation of these morphological defects with loss of epithelial barrier function. Lastly, inhibiting dynamin mediated endocytosis rescued adherens junction structure and epithelial barrier function in cells with partially mislocalized β-actin. Using Matrigel embedded 3D cyst cultures of MDCK cells, spatially regulated β-actin translation was shown to have an effect on cell shape, size and proliferation during epithelial morphogenesis. These defects in assembling a normal 3D epithelium along with disorganized acto-myosin and tight junctions, point to a role for compartmentalized β-actin translation in regulating a mechanosensitive module – plausibly Hippo and/or YAP/TAZ pathways. Finally, collective cell migration, an important paradigm in several biological processes such as wound repair and development, was used to determine the role of spatially regulated β-actin translation in epithelial wound repair. Spatially regulated β-actin translation is shown to regulate actin flux at cell-cell adhesions in leader-follower cell pairs to control tissue migration rates. Although cells with partially mislocalized β-actin translation have a more active leading edge, this increased protrusive activity fails to translate into increased migratory rate. These data taken together suggest that collective cell migration in epithelial sheets is an emergent property of both single cell dynamics and cell-cell interactions.Ph.D.Includes bibliographical referencesby Pavan Vedul
Give me your wired and your highly skilled: measuring the impact of immigration policy on employers and shareholders
No full textThis paper links finance theory to labor economics in the context of migration and immigration policy. Using event analysis, I measure the impact of immigration policy on the firm profits, in particular the American Competitiveness and Workforce Improvement Act (ACWIA) of 1998 nearly doubled the available number of H-1B visas for skilled foreign workers in FY 1999. The empirical results show that top H-1B visa user industries enjoyed significant and positive excess returns with the passage of the Act, while industries with little need for H-1B visas experienced no significant changes. Several robustness checks support the results.Skilled immigrants, immigration policy, employers, shareholders, event study, H-1B visa
Nutritional status in edentulous people as compared to age matched dentate individuals-a cross-sectional study
No full textObjectives: To assess the nutritional status in completely edentulous subjects and to compare with age matched dentate individuals. Materials and Method: The study was carried out in 60 individuals divided into two groups. Group one consisted of 30 edentulous subjects and 30 dentate individuals formed the second group Body Mass Index (BMI), serum albumin and hemoglobin values were analyzed in both the groups. Independent sample t- test was employed to check for the difference between the groups and Pearson′s correlation was done to ascertain the association between the variables within the groups. Results: There was a significant difference in all the biomarkers evaluated in between the groups. The values were negatively correlated with the period of edentulism within the groups. Conclusion: Edentulous people had lower nutritional values than their dentate counterparts and maintaining a healthy and normal dentition may have significant bearing on the overall health of an individual. body mass index, serum albumin, malnutrition, edentulous, dental statu
Analytical evaluation of performance of a small scale horizontal axis wind turbine rotor blade
No full textAge group, location or pedagogue: factors affecting parental choice of kindergartens in Hungary
No full textHungary has experienced significant political, economic, demographic and social changes since the end of Soviet domination in the 1990s. The gradual move towards liberal-democracy has been accompanied by growing emphasis on individualism, choice and diversity. Universal kindergarten provision for 5-6 year olds is a long established feature of the Hungarian education system, but little is known about parental choice (Török, 2004). A case study (Yin, 2004) of factors influencing parental choice and satisfaction was undertaken in one Hungarian town. This was based on a survey of 251 parents of children attending both mixed-age and same-age groups across 12 kindergartens. Parents suggested that the most important influences were geographical location and the individual pedagogue(s). Given that traditionally each pedagogue follows ‘their’ cohort from kindergarten entry to primary school, their influence appears heightened. Although generally satisfied with their chosen arrangement, parents from same-age groups expressed significantly more confidence and satisfaction, particularly in relation to cognitive development and preparation for school. Parents appear less convinced about the trend towards mixed-age groups and questions are raised about sufficiency of evidence of their benefits in a Hungarian context and the driving factors behind change
