Regulation of Microtubule Dynamics in Axon Regeneration: Insights from C. elegans.

The capacity of an axon to regenerate is regulated by its external environment and by cell-intrinsic factors. Studies in a variety of organisms suggest that alterations in axonal microtubule (MT) dynamics have potent effects on axon regeneration. We review recent findings on the regulation of MT dynamics during axon regeneration, focusing on the nematode Caenorhabditis elegans. In C. elegans the dual leucine zipper kinase (DLK) promotes axon regeneration, whereas the exchange factor for Arf6 (EFA-6) inhibits axon regeneration. Both DLK and EFA-6 respond to injury and control axon regeneration in part via MT dynamics. How the DLK and EFA-6 pathways are related is a topic of active investigation, as is the mechanism by which EFA-6 responds to axonal injury. We evaluate potential candidates, such as the MT affinity-regulating kinase PAR-1/MARK, in regulation of EFA-6 and axonal MT dynamics in regeneration

The Role of Microenvironment Reagent Solubility on Reaction Kinetics of 4-Nitrophenol Reduction

The Role of Microenvironment Reagent Solubility on Reaction Kinetics of 4-Nitrophenol Reduction Michael Zeevi1 with Andrew Harrison1 and Christina Tang, PhD1 1Department of Chemical and Life Science Engineering, VCU School of Engineering Introduction: Nanoparticles are of increasing interest due to their high surface area to volume ratio, as well as that they enable fine-tuning of the reaction microenvironment. Through flash nanoprecipitation, core-shell polymer nanoreactors were formed by directed self-assembly. Using the reduction of 4-nitrophenol as a model reduction reaction, we investigated the effect of reagent solubility in the nanoreactor microenvironment’s on nanoreactor kinetics. Methods: The standard reaction was conducted at room temperature, with a 1000-fold excess of sodium borohydride in a quartz cuvette for real-time in situ­ UV-Vis analysis. Reagent concentrations were varied to examine the resulting effect on the calculated reaction rate constant. Reagent solubility limits in the nanoreactor microenvironment were estimated from solubility measurements in solvents with similar Hansen solubility parameters. Ethanol was chosen to represent the hydrophilic poly(ethylene) glycol phase and chloroform was chosen to represent the hydrophobic polystyrene phase. The hydrophilic phase had a visual absorbance at nm, and thus UV-Vis spectrometry was used to determine the saturation concentration. 1H NMR analysis with chloroform-D containing an internal standard (v/v TMS 0.03%) was used to measure the reagent solubility in the hydrophobic phase. Results: 4-nitrophenol solubility in ethanol was determined by UV-Vis spectrometry to be . The solubility in chloroform-D was determined by 1H NMR to be . When 4-nitrophenol concentration is varied independently of sodium borohydride, an inverse relationship is observed with respect to the rate constant. However, when 4-nitrophenol and sodium borohydride concentrations are varied concurrently, no change is witnessed in the rate constant above the standard reaction concentration. Conclusions: This experiment demonstrated that the rate of reaction in polystyrene core nanoreactors is not dependent on the reagent concentrations above the standard concentration. Solubility in each phase was measured in an effort to explain this behavior. The differences in solubility observed between the hydrophobic and hydrophilic phases may serve to explain this behavior if the interior, hydrophobic phase is saturated by 4-nitrophenol at the standard concentration. Future work should include study of concentrations at lower values than the standard concentration to determine when a change in the observed rate constant occurs.https://scholarscompass.vcu.edu/uresposters/1287/thumbnail.jp

Productivity Growth in Service Industries: A Canadian Success Story

The Canadian service sector has performed well in recent years in terms of labour and multifactor productivity growth, both in absolute terms and relative to the United States, offsetting much of the poorer performance of the manufacturing sector. Service sector labour productivity growth has also shown a marked acceleration in both Canada and the United States in recent years relative to earlier periods. The objective of this paper is to identify the factors behind this relative Canadian success story. The sources of the acceleration in service sector labour productivity growth were different in the two countries. In Canada, increased multifactor productivity growth was responsible for 70 per cent of the labour productivity growth acceleration. In the United States, on the other hand, increased capital intensity and intermediate input intensity were the most important contributors to the service sector labour productivity growth acceleration. In Canada, the contribution of capital intensity growth to service sector labour productivity growth actually fell between 1981-1995 and 1995-2000. The factor driving Canada’s superior service sector labour productivity growth has been better multifactor productivity growth, suggesting a productivity convergence to the U.S. level. A faster pace of human capital accumulation relative to the United States, as measured by growth in the proportion of workers with a university degree, fostered the catch-up process of Canadian service industries.Service Sector, Service Industries, Services, Productivity, Productivity Growth, Labour Productivity, Multifactor Productivity, Total Factor Productivity, Growth, Acceleration, Canada, United States

Power-Aware Speed Scaling in Processor Sharing Systems

Energy use of computer communication systems has quickly become a vital design consideration. One effective method for reducing energy consumption is dynamic speed scaling, which adapts the processing speed to the current load. This paper studies how to optimally scale speed to balance mean response time and mean energy consumption under processor sharing scheduling. Both bounds and asymptotics for the optimal speed scaling scheme are provided. These results show that a simple scheme that halts when the system is idle and uses a static rate while the system is busy provides nearly the same performance as the optimal dynamic speed scaling. However, the results also highlight that dynamic speed scaling provides at least one key benefit - significantly improved robustness to bursty traffic and mis-estimation of workload parameters

Stochastic Analysis of Power-Aware Scheduling

Energy consumption in a computer system can be reduced by dynamic speed scaling, which adapts the processing speed to the current load. This paper studies the optimal way to adjust speed to balance mean response time and mean energy consumption, when jobs arrive as a Poisson process and processor sharing scheduling is used. Both bounds and asymptotics for the optimal speeds are provided. Interestingly, a simple scheme that halts when the system is idle and uses a static rate while the system is busy provides nearly the same performance as the optimal dynamic speed scaling. However, dynamic speed scaling which allocates a higher speed when more jobs are present significantly improves robustness to bursty traffic and mis-estimation of workload parameters

Positivity-Preserving Finite Difference WENO Schemes with Constrained Transport for Ideal Magnetohydrodynamic Equations

In this paper, we utilize the maximum-principle-preserving flux limiting technique, originally designed for high order weighted essentially non-oscillatory (WENO) methods for scalar hyperbolic conservation laws, to develop a class of high order positivity-preserving finite difference WENO methods for the ideal magnetohydrodynamic (MHD) equations. Our schemes, under the constrained transport (CT) framework, can achieve high order accuracy, a discrete divergence-free condition and positivity of the numerical solution simultaneously. Numerical examples in 1D, 2D and 3D are provided to demonstrate the performance of the proposed method.Comment: 21 pages, 28 figure