An Experimental Study of Micro-Dimpled Texture in Friction Control under Dry and Lubricated Conditions

Friction control is a vital technology for reaching sustainable development goals, and surface texturing is one of the most effective and efficient techniques for friction reduction. This study investigated the performance of a micro-dimpled texture under varying texture densities and experimental conditions. Reciprocating sliding tests were performed to evaluate the effects of the micro-dimpled texture on friction reduction under different normal loads and lubrication conditions. The results suggested that a micro-dimpled texture could reduce the coefficient of friction (CoF) under dry and lubricated conditions, and high dimple density results in a lower CoF. The dominant mechanism of the micro-dimpled texture’s effect on friction reduction was discussed, and surface observation and simulation suggested that a micro-dimpled texture could reduce the contact area at the friction interface, thereby reducing CoF.

The mechanics of snow friction as revealed by micro-scale interface observations

The mechanics of snow friction are central to competitive skiing, safe winter driving and efficient polar sleds. For nearly 80 years, prevailing theory has postulated that self-lubrication accounts for low kinetic friction on snow: dry-contact sliding warms snow grains to the melting point, and further sliding produces meltwater layers that lubricate the interface. We sought to verify that self-lubrication occurs at the grain scale and to quantify the evolution of real contact area to aid modeling. We used high-resolution (15 μm) infrared thermography to observe the warming of stationary snow under a rotating polyethylene slider. Surprisingly, we did not observe melting at contacting snow grains despite low friction values. In some cases, slider shear failed inter-granular bonds and produced widespread snow movement with no persistent contacts to melt (μ < 0.03). When the snow grains did not move and persistent contacts evolved, the slider abraded rather than melted the grains at low resistance (μ < 0.05). Optical microscopy revealed that the abraded particles deposited in air pockets between grains and thereby carried heat away from the interface, a process not included in current models. Overall, our results challenge whether self-lubrication is indeed the dominant mechanism underlying low snow kinetic friction.

Ivabradine-sensitive incessant atrial tachycardia during pregnancy: a case report

Background Automaticity is the dominant mechanism in maternal focal atrial tachycardia (FAT) during pregnancy and if incessant, can cause tachycardia-induced cardiomyopathy. Medication failure for FATs is common, however, for the subgroup due to increased automaticity ivabradine sensitivity has been described and may represent a valuable treatment option. Little data are available regarding the safety profile of ivabradine during pregnancy. Case Summary We report the case of a 38-year-old woman with background of peripartum cardiomyopathy and incessant atrial tachycardia with deteriorating ventricular function during her second pregnancy unresponsive to betablockade and demonstrating the immediate successful rate-controlling effect of ivabradine. Discussion Early recognition of persistent maternal FAT is essential due to its frequent association with tachycardia-mediated cardiomyopathy. Our case report highlights the challenges of providing an equally safe and effective treatment of these notoriously difficult to treat arrhythmias during pregnancy. Ivabradine in combination with a betablocker can be effective for abnormal automaticity but its safety profile during pregnancy remains uncertain.

From Power to Legitimacy—Explaining Historical and Contemporary Water Conflict at Yesa Reservoir (Spain) and Gross Reservoir (USA) Using Path Dependency

Conflict over new dams and reservoirs is well-studied, but less is known about controversies over the reoperation of existing water infrastructure. This paper presents two cases of reoperation that have been embroiled in conflict: the Gross Reservoir Expansion Project in Colorado, United States, and the Yesa Reservoir Regrowth project in Aragon and Navarra, Spain. A historical analysis of each of the cases relies on process tracing, reaching back to their construction in the 1950s up to present day, and a cross-case comparison distills findings on the causes of historical and contemporary conflict. The paper adds empirical evidence to the phenomenon of path dependency, and argues that a transition of the dominant mechanism of institutional reproduction occurs in the cases—from power to legitimacy—which in turn informs us about the historical and present-day conflicts. We find that through the contemporary reoperation, water service providers are experiencing a legitimacy crisis related to the quickly-evolving values of water users, and their access to competing sources of knowledge and expertise.

Pathophysiology of Takotsubo Cardiomyopathy: Reopened Debate

Takotsubo cardiomyopathy (TTC), a persistently obscure dysfunctional condition of the left ventricle, is uniquely transient but nevertheless dangerous. It features variable ventricular patterns and is predominant in women. For 30 years, pathophysiologic investigations have progressed only slowly and with inadequate focus. It was initially proposed that sudden-onset spastic obliteration of coronary flow induced myocardial ischemia with residual stunning and thus TTC. Later, it was generally accepted without proof that, in the presence of pain or emotional stress, the dominant mechanism for TTC onset was a catecholamine surge that had a direct, toxic myocardial effect. We think that the manifestations of TTC are more dynamic and complex than can be assumed from catecholamine effects alone. In addition, after reviewing the recent medical literature and considering our own clinical observations, especially on spasm, we theorize that atherosclerotic coronary artery disease modulates and physically opposes obstruction during spasm. This phenomenon may explain the midventricular variant of TTC and the lower incidence of TTC in men. We continue to recommend and perform acetylcholine testing to reproduce TTC and to confirm our theory that coronary spasm is its initial pathophysiologic factor. An improved understanding of TTC is especially important because of the condition's markedly increased incidence during the ongoing COVID-19 pandemic.

Sustainable Cationic Cellulose for Highly Efficient Flocculation of Suspended Particles

Sustainable, cationic cellulose bio-flocculants with various amino group contents were successfully prepared by a feasible chemical crosslinking with polyethyleneimine (PEI). The flocculation performances of diverse PEI-grafting cellulose (CE-PEI)were evaluated topurify sewage sludge treatment. Further, the preparation conditions and flocculation mechanismof CE-PEI were investigated. Benefiting from the high surface positive charges and the supramolecular structure of PEI, the results indicate that CE-PEI could remove the turbid Kaolin suspension effectively. The efficiency of CE-PEI for removing the turbid in Kaolin suspension is 98.2%.Flocculation kinetic results indicated that charge neutralization was the dominant mechanism for the flocculation process. And then, the small Kaolin particles agglomerate together to form large flocs by the function of adsorbing, gathering, and enwrapping. Thus, this work not only exploits a promising application of cellulose as a bio-flocculantbut also provides a feasible approach to efficiently purify high turbidity wastewater.

Breakdown Phase in the GOLEM Tokamak and Its Impact on Plasma Performance

The effect of the breakdown phase on subsequent plasma parameters in GOLEM tokamak is investigated remotely. The dependence of the breakdown voltage and the breakdown time on the time delay between the switchings-on of a toroidal magnetic field Bt and a toroidal electric field Et for different groups of the pressure magnitudes is built. The performed experiments have shown that, for GOLEM tokamak, the shorter the temporal delay, the better are the mean plasma parameters. In addition, the breakdown phase is discussed in more details. In the discussion, the avalanche phase of the breakdown is analyzed. The dominant mechanism of particle losses during the avalanche phase, future steps, and tasks are discussed and set. The experiments on studying the breakdown phase have been carried out remotely on GOLEM tokamak by undergraduate students of V.N. Karazin Kharkiv National University.