Synthesis of Mixed Refrigerant Cascade Cycles

This paper considers the synthesis of refrigeration systems with refrigerant mixtures as working fluids. The employed refrigeration topology encompasses features from industrial liquefaction of natural gas (LNG) systems. This configuration consists of a combination of horizontal and vertical cascades generalizing the vertical cascade of pure refrigerant systems. The key features of mixtures exploited here are their ability to evaporate/condense over a temperature range and their potential to generate streams with different compositions through partial condensation. The synthesis problem is formulated and solved as a nonlinear program. The proposed methodology is illustrated using an example of cooling a methane-rich stream.     

Fe(PyTACN)‐Catalyzed cis‐Dihydroxylation of Olefins with Hydrogen Peroxide

A family of iron complexes with general formula [Fe(II)(^R,Y,XPyTACN)(CF₃SO₃)₂], where ^R,Y,XPyTACN=1‐[2′‐(4‐Y‐6‐X‐pyridyl)methyl]‐4,7‐dialkyl‐1,4,7‐triazacyclononane, X and Y refer to the groups at positions 4 and 6 of the pyridine, respectively, and R refers to the alkyl substitution at N‐4 and N‐7 of the triazacyclononane ring, are shown to be catalysts for efficient and selective alkene oxidation (epoxidation and cis‐dihydroxylation) employing hydrogen peroxide as oxidant. Complex [Fe(II)(^Me,Me,HPyTACN)(CF₃SO₃)₂] ( 7 ), was identified as the most efficient and selective cis‐dihydroxylation catalyst among the family. The high activity of 7 allows the oxidation of alkenes to proceed rapidly (30 min) at room temperature and under conditions where the olefin is not used in large amounts but instead is the limiting reagent. In the presence of 3 mol% of 7 , 2 equiv. of H₂O₂ as oxidant and 15 equiv. of water, in acetonitrile solution, alkenes are cis‐dihydroxylated reaching yields that might be interesting for synthetic purposes. Competition experiments show that 7 exhibits preferential selectivity towards the oxidation of cis olefins over the trans analogues, and also affords better yields and high [syn‐diol]/[epoxide] ratios when cis olefins are oxidized. For aliphatic substrates, reaction yields attained with the present system compare favourably with state of the art Fe‐catalyzed cis‐dihydroxylation systems, and it can be regarded as an attractive complement to the iron and manganese systems described recently and which show optimum activity against electron‐deficient and aromatic olefins.     

Polymers prepared using cleavable initiators: Synthesis, characterization and degradation

Following the great interest in polymers based on degradable monomers and degradable cross-linkers, there is now an increasing activity in the controlled synthesis of polymers using degradable initiators. The degradation of polymers bearing residues of degradable initiators has three unique effects: (a) creation of functional end-groups, (b) controlled reduction in molecular weight, and (c) controlled reduction in the degree of branching. Degradation of such polymers has been done for various reasons, including the production of end-functionalized polymers with freshly prepared thiol end-groups for specific adsorption on to gold surfaces, the transformation of a physical gel to a solution, the conversion of end-linked networks to end-functionalized star polymers and the characterization of their core functionality, and the fabrication of nanoporous membranes by the etching of cylindrical nanophases out of a diblock copolymer film. To date, a variety of labile groups have been employed in these initiators, with most notable example the disulfide, while some other groups are yet to be used.     

Synthesis of Mixed Refrigerant Cascade Cycles

This paper considers the synthesis of refrigeration systems with refrigerant mixtures as working fluids. The employed refrigeration topology encompasses features from industrial liquefaction of natural gas (LNG) systems. This configuration consists of a combination of horizontal and vertical cascades generalizing the vertical cascade of pure refrigerant systems. The key features of mixtures exploited here are their ability to evaporate/condense over a temperature range and their potential to generate streams with different compositions through partial condensation. The synthesis problem is formulated and solved as a nonlinear program. The proposed methodology is illustrated using an example of cooling a methane-rich stream.     

Nonlinear decoupling control in the presence of sensor and actuator deadtimes

This work focuses on synthesizing nonlinear decoupling controllers for multivariable nonlinear systems represented by a state-space model, in the presence of deadtimes. The deadtimes appear in both the inputs and the outputs, but not in the states, and are physically associated with sensors and actuators. Simple sufficient conditions for feasibility of closed-loop deadtimes are derived, which rely only on the structural properties of the system. A control law is then derived so that the closed-loop system is input/output linear and decoupled, with deadtimes equal to the smallest ones that satisfy the feasibility conditions. The proposed method is applied to a chemical process. Its performance is evaluated through simulation in the presence of set-point and disturbance changes.     

Hot melt mixing and foaming of soluplus® and indomethacin

The hot melt mixing (HMM) process was used to dissolve 30 wt% of a model drug, indomethacin (INM), in Soluplus® a water soluble polymer excipient. Comprehensive characterization of the HMM‐prepared samples, using differential scanning calorimetry, X‐ray diffraction, Fourier Transform Infrared spectroscopy, and optical microscopy, strongly suggests that INM was in amorphous state, forming a solid solution with the polymer. Furthermore, to understand the impact of foaming on INM's release profile, the HMM product was foamed in a batch process using supercritical carbon dioxide (CO₂). Dissolution tests of HMM and reference samples were conducted in aqueous solutions with pH 7.4 and 1.2. In all cases INM's release showed strong pH‐dependency; faster release and a greater amount of INM was released at pH 7.4 than at pH 1.2. For pure INM and the physical mixture, the drug's ionizable character results in the observed pH‐dependency. While for the HMM samples it is also a consequence of theformation of hydrogen bonds between Soluplus® and INM which hinder polymer dissolution at pH 1.2. It was observed that the release rate of INM from different sample types at pH 7.4 decreased in the following sequence: foamed HMM > unfoamed HMM > crystalline INM > physical mixture. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Harmonic oscillators realized using current amplifiers and grounded capacitors

New configurations of harmonic oscillators, realized using current amplifier blocks and only grounded capacitors, are introduced in this article. The proposed configurations are based on a grounded inductor simulator scheme and on a loop constructed from first‐order sections, respectively. Comparison with the already published topologies shows that the new configurations have attractive characteristics concerning their implementation in integrated form. Copyright © 2006 John Wiley & Sons, Ltd.     

Selective and localized laser annealing effect for high-performance flexible multilayer MoS2 thin-film transistors

We report the use of ultra-short, pulsed-laser annealed Ti/Au contacts to enhance the performance of multilayer MoS2 field effect transistors （FETs） on flexible plastic substrates without thermal damage. An analysis of the temperature distribution, based on finite difference methods, enabled understanding of the compatibility of our picosecond laser annealing for flexible poly（ethylene naphthalate） （PEN） substrates with low thermal budget （〈 200 ℃）. The reduced contact resistance after laser annealing provided a significant improvement in transistor performance including higher peak field-effect mobility （from 24.84 to 44.84 cm2-V-l.s-1）, increased output resistance （0.42 MΩ at Vgs- Vth = 20 V, a three-fold increase）, a six-fold increase in the self-gain, and decreased sub- threshold swing. Transmission electron microscopy analysis and current-voltage measurements suggested that the reduced contact resistance resulted from the decrease of Schottky barrier width at the MoS2-metal junction. These results demonstrate that selective contact laser annealing is an attractive technology for fabricating low-resistivity metal-semiconductor junctions, providing important implications for the application of high-performance two-dimensional semicon- ductor FETs in flexible electronics.