ADV-MAC: Analysis and optimization of energy efficiency through data advertisements for wireless sensor networks

Several Medium Access Control (MAC) protocols have been proposed for wireless sensor networks with the objective of minimizing energy consumption. For example, Sensor-MAC (S-MAC) was proposed to reduce energy consumption by introducing a duty cycle. However, S-MAC cannot handle variable loads because of its static duty cycle. Timeout-MAC (T-MAC) introduced an adaptive duty cycle to handle variable traffic loads. However, nodes that do not take part in data exchange waste energy because of continuous renewal of their timeout values. To eliminate this energy waste, we propose ADV-MAC, a MAC protocol for wireless sensor networks that introduces the concept of advertising for data contention. ADV-MAC minimizes the energy lost in idle listening while maintaining an adaptive duty cycle to handle variable loads. Additionally, ADV-MAC enables energy efficient MAC-level multicasting. We derive an analytical model for the packet delivery ratio and the energy consumption of the protocol. We verify the analytical model with simulations and use the model to choose an optimal value of the advertisement period. Simulations show that the optimized ADV-MAC provides substantial energy gains (50–70% less than T-MAC and S-MAC for the scenarios investigated) while faring as well as T-MAC in terms of packet delivery ratio and latency.     

Stress delocalization in crack tolerant electrospun nanofiber networks

The fracture toughness of a noncontinuum fibrous network produced by electrospinning polyamide 6 nanofibers is investigated. The mechanical properties of the nanofiber network is observed to be independent of various incorporated macroscopic crack lengths, resulting in an apparent increase in fracture toughness with increasing crack length as evaluated using conventional fracture mechanics. Strain mapping of the nanofiber network indicates stress delocalization mechanisms operating around these macroscopic cracks in the network. The deformation behavior of the nanofiber network will therefore depend on the volume of fibers being loaded in the network and not the number of fibers in the cross-sectional width defining continuum sample mechanics. These results indicate a propensity for both the synthetic electrospun nanofibrous network in this work and potentially other nanofibrous networks to resist failure from macroscopic cracks incorporated within the material.     

Adenylate Kinase 4—A Key Regulator of Proliferation and Metabolic Shift in Human Pulmonary Arterial Smooth Muscle Cells via Akt and HIF-1α Signaling Pathways

Increased proliferation of pulmonary arterial smooth muscle cells (PASMCs) in response to chronic hypoxia contributes to pulmonary vascular remodeling in pulmonary hypertension (PH). PH shares numerous similarities with cancer, including a metabolic shift towards glycolysis. In lung cancer, adenylate kinase 4 (AK4) promotes metabolic reprogramming and metastasis. Against this background, we show that AK4 regulates cell proliferation and energy metabolism of primary human PASMCs. We demonstrate that chronic hypoxia upregulates AK4 in PASMCs in a hypoxia-inducible factor-1α (HIF-1α)-dependent manner. RNA interference of AK4 decreases the viability and proliferation of PASMCs under both normoxia and chronic hypoxia. AK4 silencing in PASMCs augments mitochondrial respiration and reduces glycolytic metabolism. The observed effects are associated with reduced levels of phosphorylated protein kinase B (Akt) as well as HIF-1α, indicating the existence of an AK4-HIF-1α feedforward loop in hypoxic PASMCs. Finally, we show that AK4 levels are elevated in pulmonary vessels from patients with idiopathic pulmonary arterial hypertension (IPAH), and AK4 silencing decreases glycolytic metabolism of IPAH-PASMCs. We conclude that AK4 is a new metabolic regulator in PASMCs interacting with HIF-1α and Akt signaling pathways to drive the pro-proliferative and glycolytic phenotype of PH.     

Effect of different turbulence models on combustion and emission characteristics of hydrogen/air flames

This paper aims to present modeling results of hydrogen/air combustion in a micro-cylindrical combustor. Modeling studies were carried out with different turbulence models to evaluate performance of these models in micro combustion simulations by using a commercially available computational fluid dynamics code. Turbulence models implemented in this study are Standard k-ε, Renormalization Group k-ε, Realizable k-ε, and Reynolds Stress Transport. A three-dimensional micro combustor model was built to investigate impact of various turbulence models on combustion and emission behavior of studied hydrogen/air flames. Performance evaluation of these models was executed by examining combustor outer wall temperature distribution; combustor centerline temperature, velocity, pressure, species and NO_x profiles. Combustion reaction scheme with 9 species and 19 steps was modeled using Eddy Dissipation Concept model. Results obtained from this study were validated with published experimental data. Numerical results showed that two equation turbulence models give consistent simulation results with published experimental data by means of trend and value. Renormalization Group k-ε model was found to give consistent simulation results with experimental data, whereas Reynolds Stress Model was failed to predict detailed features of combustion process.