The onset of vortex instability in laminar forced convection flow through a horizontal porous channel

The onset of convective instability in a fluid-saturated porous layer between the two horizontal plates heated isothermally from below has been analyzed theoretically by using propagation theory. In the analysis the thermal dispersion coefficient is assumed to be proportional to the streamwise velocity. The results show that both inertia and thermal dispersion stabilize the system.     

Physical Aging of Amorphous Fructose

ABSTRACT: Physical aging of amorphous anhydrous fructose at temperature 5 °C and at 22 °C was studied using differential scanning calorimetry (DSC). The dynamic glass transition temperature, T_g0 for unaged samples was 16 °C and 13.3 °C for heating rate of 10 °C/min and 1 °C/min, respectively. The fictive temperature, T_f0 for unaged samples calculated by Richardson and Savill method was 12 °C, which is close to the dynamic value obtained from the lower DSC heating rate. The fictive temperature T_f of the aged fructose glasses at temperatures both below and above the transition region was fitted well by a non-exponential decay function (Williams-Watts form). Aging above the transition region (22 °C) for 18 d increased both the dynamic glass transition temperature T_g and the fictive temperature T_f. However, aging below the transition region (5 °C) for 1 d increased the dynamic glass transition temperature T_g but decreased the fictive temperature T_f.     

分段控温黄原胶发酵过程

温度是影响黄原胶发酵的重要因素之一。为了优化黄原胶发酵过程的温度控制,在5 L通气式搅拌发酵罐中,非溶氧限制的条件下,对恒温黄原胶发酵过程进行了研究。结果显示,发酵温度为28℃时,在发酵稳定期有较高的菌体浓度,所得黄原胶的丙酮酸含量与表观粘度较高,但有较长的发酵周期。而发酵温度为33℃时,有较短的发酵周期,在发酵稳定期有较高的比产胶速率,但所得黄原胶的丙酮酸含量与表观粘度较低。实验测定了控制黄原胶发酵生长期温度为28℃,稳定期温度为33℃的发酵过程数据。结果表明,与恒温发酵过程相比,通过温度的分段控制可以缩短发酵周期,提高产胶浓度及改善胶的品质,分段控温是黄原胶发酵的一种方便有效的调节手段。     

3D polymeric microfluidic device fabrication via contact liquid photolithographic polymerization (CLiPP)

In this contribution, a new method for the fabrication of complex polymeric microfluidic devices is presented. The technology, contact liquid photolithographic polymerization (CLiPP), overcomes many of the drawbacks associated with other rapid prototyping schemes, such as limited materials choices and time-consuming microassembly protocols. CLiPP shares many traits with other photolithographic methods, but three distinct features: (i) liquid photoresists in contact with the photomask, (ii) readily removed sacrificial materials, and (iii) living radical processes, enable multiple polymeric chemistries and mechanical properties while simultaneously enabling facile fabrication of 3D geometries and surface chemistry control. This contribution details fabrication techniques and methods for the fabrication of high aspect ratio posts covalently bonded to a polymeric substrate, an array of independently stacked bars on top of perpendicular bars, multiple undercut structures fabricated simultaneously, and a complex 3D geometry with intertwined channels.     

Kinetic of CO2 absorption and carbamate formation in aqueous solutions of diethanolamine

The absorption rates of CO₂ into aqueous solutions of Diethanolamine (DEA) with varying concentrations from 0.2 to 4M and temperature range from 293 to 323 K were measured by using a laboratory stirred reactor. The CO₂ partial pressure was varied in a range that the reaction would occur in pseudo first order regime. Experimental data were analyzed and the kinetic parameters associated with the reaction were determined. The activation energy for the deprotonation of the intermediate zwitterion was estimated at about 11.4 kcal/mol. The contribution of carbamate formation to the overall absorbed CO₂ was experimentally evaluated and found to be of the order of 100%.     

11B and 15N solid state NMR investigation of a boron nitride preceramic polymer prepared by ammonolysis of borazine

A poly(aminoborazine), precursor for hexagonal boron nitride (h-BN) obtained by reaction of borazine B₃N₃H₆ with ammonia, and its pyrolysis derivatives have been extensively characterised by ¹⁵N and ¹¹B MAS NMR. The various B and N sites have been identified according to their first neighbouring atoms, as well as to the second ones in the case of ¹⁵N, and have also been quantified. This study demonstrates that a suitable choice of NMR techniques together with the use of isotopic enrichment can lead to a large improvement in spectral resolution, which allows a better understanding of such complex BN preceramic polymer structures and permits to follow the polymer-to-ceramic transformation.