A general thermodynamic framework for understanding the behaviour of absorption chillers

In this article, a general definition of the process average temperature has been developed, and the impact of the various dissipative mechanisms on 1/COP of the chiller evaluated. The present component-by-component black box analysis removes the assumptions regarding the generator outlet temperature(s) and the component effective thermal conductances. Mass transfer resistance is also incorporated into the absorber analysis to arrive at a more realistic upper limit to the cooling capacity. Finally, the theoretical foundation for the absorption chiller T-s diagram is derived. This diagrammatic approach only requires the inlet and outlet conditions of the chiller components and can be employed as a practical tool for system analysis and comparison. (C) 2000 Elsevier Science Ltd and IIR. All rights reserved.

Understanding Aqueous Dispersibility of Graphene Oxide and Reduced Graphene Oxide through pK(a) Measurements

The chemistry underlying the aqueous dispersibility of graphene oxide (GO) and reduced graphene oxide (r-GO) is a key consideration in the design of solution processing techniques for the preparation of processable graphene sheets. Here, we use zeta potential measurements, pH titrations, and infrared spectroscopy to establish the chemistry underlying the aqueous dispersibility of GO and r-GO sheets at different values of pH. We show that r-GO sheets have ionizable groups with a single pK value (8.0) while GO sheets have groups that are more acidic (pK = 4.3), in addition to groups with pK values of 6.6 and 9.0. Infrared spectroscopy has been used to follow the sequence of ionization events. In both GO and r-GO sheets, it is ionization of the carboxylic groups that is primarily responsible for the build up of charge, but on GO sheets, the presence of phenolic and hydroxyl groups in close proximity to the carboxylic groups lowers the pK(a) value by stabilizing the carboxylate anion, resulting in superior water dispersibility.

Understanding the role of domain-domain linkers in the spatial orientation of domains in multi-domain proteins

Inter-domain linkers (IDLs)' bridge flanking domains and support inter-domain communication in multi-domain proteins. Their sequence and conformational preferences enable them to carry out varied functions. They also provide sufficient flexibility to facilitate domain motions and, in conjunction with the interacting interfaces, they also regulate the inter-domain geometry (IDG). In spite of the basic intuitive understanding of the inter-domain orientations with respect to linker conformations and interfaces, we still do not entirely understand the precise relationship among the three. We show that IDG is evolutionarily well conserved and is constrained by the domain-domain interface interactions. The IDLs modulate the interactions by varying their lengths, conformations and local structure, thereby affecting the overall IDG. Results of our analysis provide guidelines in modelling of multi-domain proteins from the tertiary structures of constituent domain components.

Detailed investigation of contact deformation in ZrN/Zr multiplayer-understanding the role of volume fraction, bilayer spacing, and morphology of interfaces

A systematic study was done to understand the influence of volume fractions and bilayer spacings for metal/nitride multilayer coating using finite element method (FEM). An axisymmetric model was chosen to model the real situation by incorporating metal and substrate plasticity. Combinations of volume fractions and bilayer spacings were chosen for FEM analysis consistent with experimental results. The model was able to predict trends in cracking with respect to layer spacing and volume fraction. Metal layer plasticity is seen to greatly influence the stress field inside nitride. It is seen that the thicker metal induces higher tensile stresses inside nitride and hence leads to lower cracking loads. Thin metal layers < 10 nm were seen to have curved interfaces, and hence, the deformation mode was interfacial delamination in combination with edge cracking. There is an optimum seen with respect to volume fraction similar to 13% and metal layer thickness similar to 30 nm, which give maximum crack resistance.

Understanding Self-Segregation of Immiscible Peripheral Segments in Pseudodendritic Hyperbranched Polydithioacetals: Formation of Improved Janus Structures

Peripherally heterofunctionalized hyperbranched polymers (HBPs) undergo immiscibility-driven self-segregation of the outer segments to form Janus molecular entities (Macromolecules 2012, 45, 2348). In HBPs prepared via AB2 type self-condensation, single-step peripheral heterofunctionalization would lead to random distribution of the two types of terminal units, namely, homofunctionalized (homo-T) and heterofunctionalized (hetero-T) termini. Here, we examine the role of such hetero-T units on the self-segregation of heterofunctionalized pseudodendritic hyperbranched polydithioacetals. Three different heterofunctionalized HB dithioacetals bearing roughly 50 mol % each of docsyl (C-22) and MPEG-350 chains at the periphery were prepared: one of them carried a statistical distribution of homo-T and hetero-T units, and the other carried only two types of homo-T (-TR1R1 and -TR2R2) termini, whereas the third carried largely hetero-T (-TR1R2) termini. Careful examination of DSC and SAXS data reveals that the self-segregation is most effective in HBPs devoid of hetero-T units; interestingly, however, it also showed that randomly heterofunctionalized HBPs self-segregated nearly as effectively.

Understanding the Growth of Interfacial Reaction Product Layers between Dissimilar Materials

When one starts to analyze the evolution of the interfacial reaction product layers between dissimilar materials it is often found out that as the number of interacting species grows, the complexity of the analysis increases extremely rapidly. It may even appear that the task is just too difficult to be completed. In this article we present the thermodynamic-kinetic method, which can be used to rationalize the evolution of interfacial reaction layers and bring back the physics to the analyses. The method is conceptually very simple. It combines energetics-what can happen-with kinetics-how fast things take place. Yet the method is flexible enough that it can utilize quantitative and qualitative data starting from the atomistic simulations up to the experiments carried out with bulk materials. Several examples about how to utilize this method in material scientific problems are given.