Designing a fuzzy scheduler for hard real-time systems

In hard real-time systems, tasks have to be performed not only correctly, but also in a timely fashion. If timing constraints are not met, there might be severe consequences. Task scheduling is the most important problem in designing a hard real-time system, because the scheduling algorithm ensures that tasks meet their deadlines. However, the inherent nature of uncertainty in dynamic hard real-time systems increases the problems inherent in scheduling. In an effort to alleviate these problems, we have developed a fuzzy scheduler to facilitate searching for a feasible schedule. A set of fuzzy rules are proposed to guide the search. The situation we are trying to address is the performance of the system when no feasible solution can be found, and therefore, certain tasks will not be executed. We wish to limit the number of important tasks that are not scheduled

Detecting Galaxy-Filament Alignments in the Sloan Digital Sky Survey III

Previous studies have shown the filamentary structures in the cosmic web influence the alignments of nearby galaxies. We study this effect in the LOWZ sample of the Sloan Digital Sky Survey using the "Cosmic Web Reconstruction" filament catalogue. We find that LOWZ galaxies exhibit a small but statistically significant alignment in the direction parallel to the orientation of nearby filaments. This effect is detectable even in the absence of nearby galaxy clusters, which suggests it is an effect from the matter distribution in the filament. A nonparametric regression model suggests that the alignment effect with filaments extends over separations of 30-40 Mpc. We find that galaxies that are bright and early-forming align more strongly with the directions of nearby filaments than those that are faint and late-forming; however, trends with stellar mass are less statistically significant, within the narrow range of stellar mass of this sample.Comment: 14 pages, 13 figures. Accepted to the MNRA

Task-driven influences on fixational eye movements

There is now compelling evidence that the spatiotemporal remapping carried out by fixational eye movements (FEMs) is an essential step in visual processing. Moreover, the overall Brownian-like statistics of FEMs are calibrated to map fine spatial detail into the temporal frequency range to which retinal circuitry is tuned. Here, we tested the hypothesis that the detailed spatial characteristics of FEMs can be adjusted to task demands via cognitive influences that operate even in the absence of a visual stimulus. We examined FEMs in a task that required subjects (N=6) to report which of two letters was displayed. Trials were blocked; in each block, the letter pair was known in advance: H vs. N or E vs. F. The task was demanding: letters were 1.5 deg and embedded in 1/f noise, and had a contrast that yielded ~75% correct performance. Note that the HN discrimination could be accomplished by identification of either a horizontal or oblique contour, but the EF discrimination required identification of a horizontal contour. Thus, in the EF blocks, only a vertical ocular drift would be expected to maximize the neural signal. For each condition, FEM velocity statistics, which were approximately Gaussian, were characterized by their covariance. As predicted, the ratio of velocity variance in the vertical vs. oblique direction was greater in EF trials than in HN trials. This difference was greater when no stimulus was present (20% of trials in each block), indicating open-loop control. We also found that single-trial drift trajectories could be decoded by a simple decoder to identify the task (HN vs. EF) at above-chance levels in most subjects. While the observed covariance patterns showed substantial inter-subject variability, we found that a single transformation, applied with subject-specific strengths, could largely account for all subjects’ findings. Critically, this shared transformation acts holistically on the plane, rather than individually on horizontal and vertical axes. In sum, we find that knowledge of the specific requirements of a visual task exerts fine-tuned open-loop control over ocular drifts, and we characterize the nature of this control

Materials and biological approach to gene delivery in human embryonic stem cells

Gene delivery is an important tool used in the study and manipulation of human pluripotent stem cells for regenerative medicine purposes. However current methods of transient gene delivery are still highly inefficient. Using materials and biologically based concepts, I aim to develop new methods and protocols to enhance the efficiency of gene delivery. For the materials aspect, diblock copolymers consisting of poly(ethylene glycol)-block-poly(γ-4-(((2-(piperidin-1-yl)ethyl)amino)methyl)benzyl-L-glutamate) (PEG-b-PVBLG-8) were synthesized and evaluated for their ability to mediate gene delivery in hard-to-transfect cells, such as IMR-90 human fetal lung fibroblasts and human embryonic stem cells (hESCs). The PEG-b-PVBLG-8 contained a membrane-disruptive, cationic, helical polypeptide block (PVBLG-8) for complexing with DNA and a hydrophilic PEG block to improve the biocompatibility of the gene delivery vehicle. PEG-b-PVBLG-8 diblock polymers with a high degree of polymerization have a greater transfection efficiency and lower toxicity in IMR-90 cells than the commercial reagent Lipofectamine 2000. The usefulness of PEG-b-PVBLG-8 was further demonstrated via the successful transfection of hESCs without a measured loss in cell pluripotency markers. This system proved to be inefficient for hESCs, thus I designed a system that uses the combination of a cell specific and materials approach. Plasmid DNA was condensed with PVBLG-8 to form nanocomplexes, which were further coated with hyaluronic acid. PVBLG-8 has proven to be an effective gene delivery material in certain cell lines, due to its membrane disruptive properties. Yet in more sensitive cell lines, like hESCs, it proves to be toxic and thus ineffective. Hyaluronic acid not only shields the positive charges from the helical peptides, but also acts as a targeting moiety for cell surface receptor CD44, which binds and facilitates the internalization of hyaluronan for degradation. Despite the negative charged surface, the gene transfection of the cells increased by 1.5 fold with reduced toxicity. I demonstrated that the increased transfection efficiency is due to the CD44 mediated targeting delivery of DNA by HA coating nanocomplex. In addition, this nanocomplex system can be further activated through the endosomal specific degradation of HA by hyaluronidase to expose PVBLG-8. From the biological aspect, a small molecule that selectively inhibits the Rho-associated kinase inhibitor (Y-27632) was discovered to transiently alter the hESC morphology to induce spreading and reduced membrane tension. These morphological changes allowed the increase of plasmid transfection, siRNA transfection and nanoparticle uptake to increase substantially. Cells were also able to recover after treatment back to normal pluripotent stem cell morphology and express important pluripotency markers. These new methods expands the field of gene delivery in human pluripotent stem cells, which can be further applied to other biomedical applications