Assistive Electro Discharge Machining of AIN Ceramics

Electro discharge machining process experiences limitation due to the non-conductive nature of the workpiece material. However, researchers proposed assistive EDM technique to machine nonconductive materials in the past. These assistive techniques require a minimal thickness of 100 µm conductive coating on the workpiece surface which usually takes longer time to coat the surface using PVD (physical vapor deposition) method. In this paper, a new modified assistive EDM method has been proposed to machine nonconductive Aluminum Nitride ceramics successfully. A three layers coating was used that included silver coating, carbon tape and silver nano-powder on a non-conductive aluminium nitride. This coating aids in conducting EDM operation due to the availability of conductive particles. Apart from the decomposition of dielectric that facilitates carbon particles on top of conductive carbon layer, coating itself also contributes in conductive silver particles. Therefore, carbon as well as silver debris that remains on the ceramics surface aids in continuous spark generation which in turn creates alternative thermal load and thus removes materials.

Ryanodine receptor dispersion disrupts Ca2+ release in failing cardiac myocytes

Reduced cardiac contractility during heart failure (HF) is linked to impaired Ca2+ release from Ryanodine Receptors (RyRs). We investigated whether this deficit can be traced to nanoscale RyR reorganization. Using super-resolution imaging, we observed dispersion of RyR clusters in cardiomyocytes from post-infarction HF rats, resulting in more numerous, smaller clusters. Functional groupings of RyR clusters which produce Ca2+ sparks (Ca2+ release units, CRUs) also became less solid. An increased fraction of small CRUs in HF was linked to augmented ‘silent’ Ca2+ leak, not visible as sparks. Larger multi-cluster CRUs common in HF also exhibited low fidelity spark generation. When successfully triggered, sparks in failing cells displayed slow kinetics as Ca2+ spread across dispersed CRUs. During the action potential, these slow sparks protracted and desynchronized the overall Ca2+ transient. Thus, nanoscale RyR reorganization during HF augments Ca2+ leak and slows Ca2+ release kinetics, leading to weakened contraction in this disease.

Intermittent hypoxia in rats reduces activation of Ca2+ sparks in mesenteric arteries

Ca+ sparks are vascular smooth muscle cell (VSMC) Ca2+-release events that are mediated by ryanodine receptors (RyR) and promote vasodilation by activating large-conductance Ca2+-activated potassium channels and inhibiting myogenic tone. We have previously reported that exposing rats to intermittent hypoxia (IH) to simulate sleep apnea augments myogenic tone in mesenteric arteries through loss of hydrogen sulfide (H2S)-induced dilation. Because we also observed that H2S can increase Ca2+ spark activity, we hypothesized that loss of H2S after IH exposure reduces Ca2+ spark activity and that blocking Ca2+ spark generation reduces H2S-induced dilation. Ca2+ spark activity was lower in VSMC of arteries from IH compared with sham-exposed rats. Furthermore, depolarizing VSMC by increasing luminal pressure (from 20 to 100 mmHg) or by elevating extracellular [K+] increased spark activity in VSMC of arteries from sham rats but had no effect in arteries from IH rats. Inhibiting endogenous H2S production in sham arteries prevented these increases. NaHS or phosphodiesterase inhibition increased spark activity to the same extent in sham and IH arteries. Depolarization-induced increases in Ca2+ spark activity were due to increased sparks per site, whereas H2S increases in spark activity were due to increased spark sites per cell. Finally, inhibiting Ca2+ spark activity with ryanodine (10 μM) enhanced myogenic tone in arteries from sham but not IH rats and blocked dilation to exogenous H2S in arteries from both sham and IH rats. Our results suggest that H2S regulates RyR activation and that H2S-induced dilation requires Ca2+ spark activation. IH exposure decreases endogenous H2S-dependent Ca2+ spark activation to cause membrane depolarization and enhance myogenic tone in mesenteric arteries.

Attract-Repulse Fireworks Algorithm and its CUDA Implementation Using Dynamic Parallelism

Fireworks Algorithm (FWA) is a recently developed Swarm Intelligence Algorithm (SIA), which has been successfully used in diverse domains. When applied to complicated problems, many function evaluations are needed to obtain an acceptable solution. To address this critical issue, a GPU-based variant (GPU-FWA) was proposed to greatly accelerate the optimization procedure of FWA. Thanks to the active studies on FWA and GPU computing, many advances have been achieved since GPU-FWA. In this paper, a novel GPU-based FWA variant, Attract-Repulse FWA (AR-FWA), is proposed. AR-FWA introduces an efficient adaptive search mechanism (AFW Search) and a non-uniform mutation strategy for spark generation. Compared to the state-of-the-art FWA variants, AR-FWA can greatly improve the performance on complicated multimodal problems. Leveraging the edge-cutting dynamic parallelism mechanism provided by CUDA, AR-FWA can be implemented on the GPU easily and efficiently.