Effect of confinement on heat transfer characteristics of a microscale impinging jet

This study experimentally investigates the local heat transfer characteristics of a microscale confined impinging air jet on a heated plate. The experimental parameters included the Reynolds number (Re_D = 1600–5600), the nozzle-to-plate spacing (H/D = 1–10), and the degree of confinement of the nozzle (D_C/D = 3, 6, 9, 12, 24, 48). The degree of confinement of the nozzle is a novel parameter. A reduction in the heat transfer rate was found for nozzles whose D_C/D values were 6, 9, 12, 24, and 48 as a result of the confinement effect at small nozzle-to-plate spacings. The confinement effect disappeared beyond H/D values of 2, 3, 4, 8, and 17 for D_C/D values of 6, 9, 12, 24, and 48, respectively. Flow characteristics were investigated by measuring pressure distributions along the wall. Subatmospheric pressure, which is evidence of the confinement effect, was observed for the confined nozzles. Correlations of the stagnation and average Nusselt numbers are proposed on the basis of the experimental results. Finally, a contour map that depicts the ratio of the Nusselt numbers of the unconfined and confined jets is presented. The contour map confirms that the confined jets have a smaller Nusselt number than the unconfined jets whenever the degree of confinement of the nozzle is large and the nozzle-to-plate spacing is small.     

Wettability manipulation of magnetic transition metal nanorod arrays by X-ray irradiation

Wettability manipulation of glancing angle deposited Fe/Co/Ni nanorod arrays was realized by X-ray irradiation in ultra-high vacuum chamber. Reversible transition was also purchased by alternating ethanol immersion and X-ray irradiation. Alkyl group adsorption–desorption mechanism and corresponding morphology dependence of wettability manipulation were revealed.     

Aromatic–aromatic interaction between metallacycle and phenyl ring

The X-ray crystal structure of [CuL₂]ClO₄ where L is the 1:1 condensate of benzil-monohydrazone and 2-pyridinecarboxaldehyde, reveals unprecedented π–π interaction between the metallacycles and phenyl rings. The interaction is intramolecular.     

Synthesis and characterization of a Keggin-type V(V)-substituted isopolytungstate, (n-C3H7)5[H4VW11O40]

A new V(V)-substituted isopolytungstate, (n-C₃H₇)₅[H₄VW₁₁O₄₀], with Keggin structure was synthesized in an acidic aqueous–CH₃CN solution and characterized by elemental analysis, FT-IR, Raman, ¹H NMR, and cyclic voltammetry.     

The temperature effect on swelling of shales under cyclic wetting and drying

Swelling rock such as shale can generate uplift force below foundations often resulting in structure deformation. The expansive upward force can be reduced, however, if the rock undergoes cycles of hydration and dehydration. An effort was attempted to measure the changes of swelling potentials (i.e. pressure and strain) of shales while the samples underwent two cycles of wetting-and-drying treatments at different temperatures between −10 and 23°C. Two sets of twenty-five shale samples collected from one coal mine in interior Alaska and two mines in southwestern Pennsylvania were tested under confined and free swelling conditions. The maximum swelling pressure and strain developed within the shales were related to three factors: shale moisture susceptibility, testing temperature, and initial tempering air humidity. As a result of the first cycle swelling tests, 76% of the samples failed (i.e. cracked) in the confined test and 56% of samples similarly failed in the free swelling tests. Samples that did not fail were brought back to their initial state of water saturation. The second cycle swelling tests were next performed on those samples. This attempt allowed measurements of a reduction of swelling pressure and strain of the shale samples. Swelling pressure and strain of the samples decreased considerably in the second cycle of tests. The reduction in swelling potential was likely caused by the growth of microcracks in the samples during the first cycle of swelling test. The swelling pressure and strain measured in the second cycle test were noted to have strong correlation with the swelling potentials measured in the first cycle.     

Theory and Experiments on Enclosing Control of Multi-Agent Systems

This paper proposes a control strategy called enclosing control. This strategy can be described as follows: the followers design their control inputs based on the state information of neighbor agents and move to specified positions. The convex hull formed by these followers contains the leaders. We use the single-integrator model to describe the dynamics of the agents and proposes a continuous-time control protocol and a sampled-data based protocol for multi-agent systems with stationary leaders with fixed network topology. Then the state differential equations are analyzed to obtain the parameter requirements for the system to achieve convergence. Moreover, the conditions achieving enclosing control are established for both protocols. A special enclosing control with no leader located on the convex hull boundary under the protocols is studied, which can effectively prevent enclosing control failures caused by errors in the system. Moreover, several simulations are proposed to validate theoretical results and compare the differences between the three control protocols. Finally, experimental results on the multi-robot platform are provided to verify the feasibility of the protocol in the physical system.      

Steering rigidified nonplanar conjugation based perylene diimide supramolecular for enhancing photocatalytic activity

π-Conjugated supramolecular with higher delocalization of electrons has attracted considerable attention in enhancing the charge transfer in photocatalysis. However, those conjugated macromolecules often possess varied rotational geometries, which will significantly deteriorate charge mobility but still inexplicitly. Herein, we reported diversified PDI polymers with intramolecular angles of 94.7°, 149.7° and 176.3° to explore the role of π-conjugated non-planar molecules. Density functional theory (DFT) calculations and experimental results show that vertical structural PDIMH has antibonding in anisotropic polarizable monomer to generate a macro-dipole, which greatly expands the built-in electric field and facilitates charge transfer and exciton dissociation. On the other hand, the vertical angle is favorable for the face-to-face overlap of the homogeneous molecules, which will create a carrier migration channel and promote carrier separation. Notably, PDIMH exhibited highly effective photocatalytic sterilization (near 100% in 2 h) and benzylamine oxidation (conversion rate up to 300 mmol g⁻¹h⁻¹), which is superior to other ever reported catalysts. This work provides a new interpretation for regulating molecular geometry in developing highly efficient photocatalyst to solve future sustainable issues.     

Ce incorporated pyrochlore Pr2Zr2O7 solid electrolytes for enhanced mild-temperature NO2 sensing

NO₂ sensor has attracted extensive attention due to its important application in environment monitor. Conventional NO₂ sensors based on the yttria-stabilized zirconia (YSZ) electrolyte possess fast response, high sensitivity and good stability, whereas its ionic conductivity decreases significantly at low- and intermediate-temperature, limiting the practical application in motor vehicles. In this work, a pyrochlore-phase A₂B₂O₇ solid electrolyte, Pr₂Zr_2−xCe_xO_7+δ (PZC), was applied for the first time to construct the amperometric-type NO₂ sensor. Ce incorporated significantly improved the sensing performance of the PZC NO₂ sensor with NiO as the sensing electrode. The effect of Ce-doped concentration and operating temperature on the sensitivity, selectivity, stability, response and recovery characteristics were investigated in detail. The results showed that the optimal sensor based on the Pr₂Zr_1.9Ce_0.1O_7+δ substrate gave high sensitivity, excellent selectivity and quick response-recovery behavior to NO₂ gas. The gas-sensing mechanism was also discussed. The PZC sensors are well established effective for sensing NO₂ at mild-temperature working window of 500–700 °C, and thus exhibit the promising application in motor vehicles.