Characteristics of air and water velocity fields during natural convection

Air and water velocity fields have been simulated during natural convection, using a two-dimensional volume of fluid (VOF) model. The results have shown that during unstable thermal stratification, the root-mean-square (RMS) airside velocities are an order of magnitude higher than the RMS waterside velocities, whereas, during the stable thermal stratification, the velocity magnitudes are comparable for air and water sides. Furthermore, the magnitude of the air velocity changed more rapidly with the change in the bulk air–water temperature difference than the water velocity, indicating that the air velocities are more sensitive to the bulk air and water temperature difference than the water velocities. A physical model of the heat and mass transfer across the air–water interface is defined. According to this model, the vortices on the air and water sides play an important role in enhancing the heat and mass transfer. Due to the significance of the flow velocities in the transport process, it has been proposed that the correlations for the heat and mass transfer during natural convection should be improved by incorporating the flow velocity as a parameter.     

Isolation of CeLu2N@Ih‐C80 through a Non‐Chromatographic,Two‐Step Chemical Process and Crystallographic Characterization of the Pyramidalized CeLu2N within the Icosahedral Cage

By combining two chemical methods of purification, 4 mg of purified CeLu₂N@C₈₀ was readily isolated from 500 mg of carbon soot extract without the use of recycling HPLC, a method which has previously been necessary to obtain pure samples of endohedral fullerenes. In stage 1, CeLu₂N@C₈₀ was selectively precipitated by virtue of its low first oxidation potential (+0.01 V) and the judicious choice of MgCl₂ as the Lewis acid precipitant. For stage 2, we used a stir and filter approach (SAFA), which employed the electron‐rich NH₂ groups immobilized on silica gel to selectively bind residual endohedrals and higher cage fullerenes that were contaminants from stage 1. Crystallographic analysis of CeLu₂N@C₈₀ in the co‐crystal CeLu₂N@I_h‐C₈₀ ? Ni(octaethylporphyrin) ? 2(toluene) reveals that the I_h‐C₈₀ cage is present with a pyramidalized CeLu₂N unit inside.     

Synthesis and Structure of LaSc2N@Cs(hept)‐C80 with One Heptagon and Thirteen Pentagons

The synthesis and single‐crystal X‐ray structural characterization of the first endohedral metallofullerene to contain a heptagon in the carbon cage are reported. The carbon framework surrounding the planar LaSc₂N unit in LaSc₂N@C_s(hept)‐C₈₀ consists of one heptagon, 13 pentagons, and 28 hexagons. This cage is related to the most abundant I_h‐C₈₀ isomer by one Stone–Wales‐like, heptagon/pentagon to hexagon/hexagon realignment. DFT computations predict that LaSc₂N@C_s(hept)‐C₈₀ is more stable than LaSc₂N@D_5h‐C₈₀, and suggests that the low yield of the heptagon‐containing endohedral fullerene may be caused by kinetic factors.     

Investigation of the fluid temperature field inside a flat-plate solar collector

An experimental study was conducted to investigate fluid temperature fields inside a flat-plate solar collector tube. The results show the highest fluid temperature at the upper end of the tube which decreased gradually to the lowest value at the bottom end of the tube, whereas, the temperature field in the horizontal plane is symmetric about the centerline. The vertical temperature gradients vary with the axial distance. The local fluid temperature increased nonlinearly along the collector length and its magnitude decreased with an increase in the Reynolds number. The local Rayleigh number increased with the axial distance and at a given location, its magnitude increased with a decrease in the Reynolds number, whereas, the local Nusselt number trends in flat-plate collector tube are in general similar to that in the conventional laminar channel flows. The local fluid temperature increased with an increase in the incident heat flux at a given collector orientation but decreased for the inclined collectors. The results show that over the given Reynolds number range, the fluid in a flat-plate collector tube is stably stratified over most of the fluid cross-sectional domain and the convective currents are suppressed and restricted to a thin layer adjacent to the lower tube wall. The results from the present study provide the physical explanation for the heat transfer enhancement by insert devices. That is, the insert devices disrupt the stably stratified layer and induce mixing which enhances the heat transfer.     

Effect of two sonochemical procedures on achieving to different morphologies of lead(II) coordination polymer nano-structures

Micro and nano-structures of a lead(II) coordination polymer, [Pb₂(2-Me-8-Hq)₂(MeOH)₂]_n (1), [2-Me-8-HqH = 2-methyl-8-hydroxyquinoline]_, were synthesized by two sonochemical methods. These new micro and nano-structures were characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. Compound 1 was structurally characterized by single-crystal X-ray diffraction and consists of primary dimeric unit of [Pb₂(2-Me-8-Hq)₂(MeOH)₂]. Self assembly between the dimmeric units of [Pb₂(2-Me-8-Hq)₂(MeOH)₂] from Pb-O bonds results in formation of a one-dimensional lead(II) coordination polymer. The Pb^II-ion in compound 1 has PbO₆N₁ coordination sphere with a stereo-chemically ‘active’ electron lone pair on the metals. By a reversible solid-state structural transformation, we successfully prepared [Pb₂(2-Me-8-Hq)₂]_n (2) by thermal desolvation of 1. Thermal stability of compound 1 was studied by thermo gravimetric and differential thermal analyses. In addition nano-structure of PbO was prepared from calcination process of compound 1 at 873 K.     

The electrochemical detection of droplets in microfluidic devices

This paper presents a new electrochemical method for the detection and characterisation of aqueous droplets in an organic carrier fluid (1,2-dichloroethane) formed in flow-focusing microfluidic devices. The devices consist of a conventional flow-focusing channel 250 microm wide and 250 microm deep cast out of poly(dimethylsiloxane) (PDMS) which is sealed onto a glass substrate containing a set of microelectrodes 100 microm long. Chronoamperometric analysis of a suitable electrolyte contained in the organic phase is presented for characterising the droplet frequency and size. This chronoamperometric method is then extended to a dual working electrode approach in order to determine the velocity of the droplet. Good agreement between experimental measurements and theory was observed.     

The nature of synergistic effects in transition metal oxides/in-situ intermediate-hydroxides for enhanced oxygen evolution reaction

Oxygen evolution reaction is highly important for hydrogen production via water splitting but requires ～0.22 V onset overpotential, resulting in at least 15% extra energy consumption even utilized with the benchmark hetero-doped transition-metal hydroxide catalysts. The lack of fundamental understanding on catalyst behaviour and on synergistic mechanisms limit the breakthrough for material design. Here, we systematically summarise a variety of investigations and arguments on the mechanism from the microscale (optimal octahedral intermediate with six M?O coordination) to atomic scale (the active site behaviour). The electron–orbital scale (e_g) is further described for the intrinsic OER activity. The synergistic effect may also lead to a short-cut pathway of lattice-oxygen-mediated mechanism to achieve a smaller overpotential. This review provides a theoretical reference for the design of advanced catalysts.     

Importance of explicit vectorization for CPU and GPU software performance

Much of the current focus in high-performance computing is on multi-threading, multi-computing, and graphics processing unit (GPU) computing. However, vectorization and non-parallel optimization techniques, which can often be employed additionally, are less frequently discussed. In this paper, we present an analysis of several optimizations done on both central processing unit (CPU) and GPU implementations of a particular computationally intensive Metropolis Monte Carlo algorithm. Explicit vectorization on the CPU and the equivalent, explicit memory coalescing, on the GPU are found to be critical to achieving good performance of this algorithm in both environments. The fully-optimized CPU version achieves a 9× to 12× speedup over the original CPU version, in addition to speedup from multi-threading. This is 2× faster than the fully-optimized GPU version, indicating the importance of optimizing CPU implementations.     

Influence of a rectangular baffle on the downstream flow structure

An experimental study was conducted to investigate the impact of a rectangular baffle inside a square channel. PIV was used to measure the two-dimensional velocity fields. The measurements were conducted for two Reynolds numbers in the fully turbulent regime. The changes to the flow structure due to the insertion of a baffle were quantified by a direct comparison with the flow structure in the absence of a baffle, under similar conditions. Results show that the turbulent velocities are enhanced by a factor of two to three and the rates of energy production and dissipation are enhanced by more than an order of magnitude when a baffle is inserted in the channel. Significant enhancement of turbulence was observed in a region up to two times the baffle height immediately downstream of the baffle and the thickness of this layer increased to three times the baffle height further downstream of the baffle.     

Vanishing of the top local cohomology modules over Noetherian rings

Let R be a (not necessarily local) Noetherian ring and M a finitely generated R-module of finite dimension d. Let be an ideal of R and denote the intersection of all prime ideals . It is shown that