Theoretical Prediction of CHn Crystal Structures under High Pressures

CHn is the precursor unit for graphene synthesis. We have theoretically predicated a series of CHn structures with n = 1, 2, 4, 6, 8, 10, and 12 at elevated pressures (ambient pressure, 50, 100, 200, 300, 350, and 400 GPa) using evolutionary algorithms. The predicted CH and CH2 structures are graphane-type and polyethylene over the whole considered pressure range, respectively. The molecular crystalline methane is predicted for the stoichiometry of CH4. The combination of methane and H2 for CH6, CH8, CH10, and CH12 up to 300 GPa are obtained. At 400 GPa, the mixture of polymer and H2 for CH6, CH10, and CH12 comes into play. From the computed enthalpy, higher pressure and more hydrogen concentration contributed to the decomposition (to carbon and H2) of CHn systems. The total density of states for these CHn structures show that only the CH12 phase is metallic above 300 GPa. The rotational properties are traced in H2 and the CHn structures. The CH4 rotation is more sensitive to the pressure. The H2 units are nearly freely rotational. Other structures of CHn, including fcc-type and experimentally known structures, are not competitive with the structures predicted by evolutionary algorithms under high pressure region. Our results suggest that the CHn (n > 4) system is a potential candidate for hydrogen storage where H2 could be released by controlling the pressure.

ABOUT CONICAL CUMULATION IN STORAGE AMPOULES

Conical cumulation in storage ampoules consists of a periodically repeating wave pattern - the formation of an axial high-pressure region as a result of the focusing of oblique waves and its unloading. In this case, the convergence of the oblique wave is accompanied by a loss of stability - protrusions appear at the wave front, the collision of which leads to an increase in pressure. The expansion of the high-pressure region is accompanied by the formation of an axial crack and continues until its pressure becomes lower than the pressure of the incoming oblique waves, after which the flow pattern is repeated.

Biomass Burning and Gas Flares create the extreme West African Aerosol Plume which perturbs the Hadley Circulation and thereby changes Europe’s winter climate

Europe’s winter climate has experienced three significant changes recently: increased UK flooding; Iberian drought; and warmer temperatures north of the Alps. The literature links all three to a persistent, significant increase in sea level pressure over the Mediterranean and Iberia which changes the atmospheric circulation system by: forcing cold fronts north away from Iberia; and creating a south westerly flow around the high-pressure region bringing warmer, moist air from the subtropical Atlantic to Europe which increases UK precipitation and European temperatures. Here I show, using modelled, reanalysis and measured data, that: the extreme, anthropogenic, West African aerosol Plume (WAP) which exists from late December to early April perturbs the northern, regional Hadley Circulation creating the high-pressure region; and that the WAP has only existed in its extreme form in recent decades as the major sources of the aerosols: biomass burning; and gas flaring have both increased significantly since 1950 due to: a four-fold increase in population (United Nations); and gas flaring rising from zero to 7.4 billion m3/annum (Global Gas Flaring Reduction Partnership). I also suggest that the WAP can be eliminated and Europe’s winter climate returned to its natural state after the crucial first step of recognising the cause of the changes is taken.

Spreading or contraction of viscous drops between plates: single, multiple or annular drops

The behaviour of a viscous drop squeezed between two horizontal planes (a squeezed Hele-Shaw cell) is treated by both theory and experiment. When the squeezing force $F$ is constant and surface tension is neglected, the theory predicts ultimate growth of the radius $a\sim t^{1/8}$ with time $t$. This theory is first reviewed and found to be in excellent agreement with experiment. Surface tension at the drop boundary reduces the interior pressure, and this effect is included in the analysis, although it is negligibly small in the squeezing experiments. An initially elliptic drop tends to become circular as $t$ increases. More generally, the circular evolution is found to be stable under small perturbations. If, on the other hand, the force is reversed ($F<0$), so that the plates are drawn apart (the ‘contraction’, or ‘lifting plate’, problem), the boundary of the drop is subject to a fingering instability on a scale determined by surface tension. The effect of a trapped air bubble at the centre of the drop is then considered. The annular evolution of the drop under constant squeezing is still found to follow a ‘one-eighth’ power law, but this is unstable, the instability originating at the boundary of the air bubble, i.e. the inner boundary of the annulus. The air bubble is realised experimentally in two ways: first by simply starting with the drop in the form of an annulus, as nearly circular as possible; and second by forcing four initially separate drops to expand and merge, a process that involves the resolution of ‘contact singularities’ by surface tension. If the plates are drawn apart, the evolution is still subject to the fingering instability driven from the outer boundary of the annulus. This instability is realised experimentally by levering the plates apart at one corner: fingering develops at the outer boundary and spreads rapidly to the interior as the levering is slowly increased. At a later stage, before ultimate rupture of the film and complete separation of the plates, fingering spreads also from the boundary of any interior trapped air bubble, and small cavitation bubbles appear in the very low-pressure region, far from the point of leverage. This exotic behaviour is discussed in the light of the foregoing theoretical analysis.

Plantar Pressure Distribution during Standing in Female Patients with Hip Osteoarthritis Who Underwent Total Hip Arthroplasty

Introduction: Assessment of plantar pressure indicates the manner in which the plantar region contacts the ground as the first point in a leg-linked kinetic chain, and receives force from the ground. However, few studies have examined the changes in plantar pressure distribution in patients who underwent Total Hip Arthroplasty (THA) before and after THA, or compared plantar pressure distribution between THA patients and healthy adults. Objective: Plantar pressure distribution in patients with end-stage hip osteoarthritis who undergo THA may be adjusted to that in healthy adults by correcting leg length discrepancy. Herein, our objective was to find out if the plantar pressure distribution during standing differs before and after THA, and between healthy adults and THA patients. Design: Case control study. Setting: Single orthopedic clinic in Japan. Participants: THA patients (n=58; THA group) and healthy adults (n=53; control group). Interventions: Not applicable. Main outcome measure(s): The maximum plantar pressure under each foot measured during standing for 20 s was assessed for location, symmetry, and leg length discrepancy. Results: The distribution plantar pressure in the THA group differed preand postoperatively. The maximum plantar pressure region was the heel in approximately 80% of the patients three months after THA; it was not different in THA patients three months postoperatively and in healthy adults. Patients with asymmetrical maximum plantar pressure regions were those whose postoperative maximum plantar pressure region in the affected leg was the forefoot and those whose maximum plantar pressure region in the affected leg shifted to the heel. The leg length discrepancies decreased significantly after THA. Conclusions: The plantar pressure distribution during standing in female patients adjusted to that in healthy adults after THA. Patients with asymmetrical distribution of maximum plantar pressure may benefit from balance assessment and physical therapy.

Sensitivity Analysis of Tunable Equation of State Material Model In Pulsed Mercury Target Simulation

A pulsed neutron spallation target is subjected to very short but intense loads from repeated proton pulses. Approximately 60% of the energy from each proton pulse is deposited into the mercury target material and the stainless-steel target structure, leading to a high-pressure region in both the stationary target structure and the flowing mercury. The high-pressure region propagates and leads to fluid-structure interaction. The resultant loading on the target structure containing liquid mercury is difficult to predict, although various simulation approaches and material models for the mercury have been tried. To date, the best match of simulation to experimental data is obtained by using an equation of state (EOS) material model with a specified tensile cutoff pressure, which simulates the cavitation threshold. The inclusion of a threshold to represent cavitation is key to the successful predictions of stress waves triggered by the high-energy pulse striking the mercury and vessel. However, recent measurements of target structure strain show that significant discrepancies remain between the measured and simulated strain values in the EOS mercury model. These differences grow when noncondensable helium gas is intentionally injected into the flowing mercury to reduce the loading on the structure. An EOS-based proportional–integral–derivative (PID) mercury model has been proposed to reduce the gap between the measured and simulated vessel strain responses for targets with gas injection. The conceptual and numerical description and initial investigation of the PID model are presented in previous work. Further studies of this PID model — including the sensitivity of the structure’s strain response to model parameters (the tensile cutoff, PID parameters Kp, Ki, and Kd) — are reported in this article. Results show the strain response is more sensitive to changes in the tensile cutoff value than to changes in the model parameters Kp, Ki, and Kd. These results will aid in future work where the model parameters will be optimized to match simulation data to strain measurements.

Investigation on Dynamic Characteristics of the Reed Valve in Compressors Based on Fluid-Structure Interaction Method

The flow in the gap between the reed and the valve seat has a significant influence on the dynamic characteristics of the reed valve used in reciprocating compressors. The fluid–structure interaction (FSI) method is an effective method for studying reciprocating compressors. A three-dimensional FSI model of a reciprocating compressor with a reed valve is established in this paper, which has an important influence on the flow rate characteristic of reciprocating compressors. Furthermore, an experimental investigation is implemented to verify the FSI model. Based on the established FSI model, the pressure distribution on the reed valve surface is identified by varying the height of the suction valve limiter and the rotational speed of the compressor, which has an important effect on the dynamic characteristics of the reed valve. Although the low-pressure region, due to the Bernoulli effect on the surface of the reed, hinders the rapid opening of the valve to some extent, it is obviously beneficial to the timely closure of the valve and increases the volumetric efficiency of the compressor. Moreover, the optimal height of the valve limiter and the appropriate rotational speed of the compressor are obtained.

Development of converging-diverging multi-jet nozzles for molten smelt shattering in kraft recovery boilers

The effective shattering of molten smelt is highly desired in recovery boiler systems. Ideally, shatter jet nozzle designs should: i) generate high shattering energy; ii) create a wide coverage; and iii) minimize steam consumption. This study proposes a novel converging-diverging multi-jet nozzle design to achieve these goals. A laboratory setup was established, and the nozzle performance was evaluated by generating jet pressure profiles from the measurement of a pitot tube array. The results show that the shatter jet strength is greater with a large throat diameter, high inlet pressure, and a short distance between the nozzle exit and impingement position. Increasing the number of orifices generates a wider jet coverage, and the distance between the orifices should be limited to avoid the formation of a low-pressure region between the orifices. The study also demonstrates that an optimized converging-diverging multi-jet nozzle significantly outperformed a conventional shatter jet nozzle by achieving higher energy and wider coverage while consuming less steam.