Stevens Institute of Technology

About: Stevens Institute of Technology is a education organization based out in Hoboken, New Jersey, United States. It is known for research contribution in the topics: Cognitive radio & Wireless network. The organization has 5440 authors who have published 12684 publications receiving 296875 citations. The organization is also known as: Stevens & Stevens Tech.

Ownership confinement ensures representation independence for object-oriented programs

Abstract: Representation independence formally characterizes the encapsulation provided by language constructs for data abstraction and justifies reasoning by simulation. Representation independence has been shown for a variety of languages and constructs but not for shared references to mutable state; indeed it fails in general for such languages. This article formulates representation independence for classes, in an imperative, object-oriented language with pointers, subclassing and dynamic dispatch, class oriented visibility control, recursive types and methods, and a simple form of module. An instance of a class is considered to implement an abstraction using private fields and so-called representation objects. Encapsulation of representation objects is expressed by a restriction, called confinement, on aliasing. Representation independence is proved for programs satisfying the confinement condition. A static analysis is given for confinement that accepts common designs such as the observer and factory patterns. The formalization takes into account not only the usual interface between a client and a class that provides an abstraction but also the interface (often called “protected”) between the class and its subclasses.

Why copper is preferred over iron for oxygen activation and reduction in haem-copper oxidases

Abstract: Haem-copper oxidase (HCO) catalyses the natural reduction of oxygen to water using a haem-copper centre. Despite decades of research on HCOs, the role of non-haem metal and the reason for nature's choice of copper over other metals such as iron remains unclear. Here, we use a biosynthetic model of HCO in myoglobin that selectively binds different non-haem metals to demonstrate 30-fold and 11-fold enhancements in the oxidase activity of Cu- and Fe-bound HCO mimics, respectively, as compared with Zn-bound mimics. Detailed electrochemical, kinetic and vibrational spectroscopic studies, in tandem with theoretical density functional theory calculations, demonstrate that the non-haem metal not only donates electrons to oxygen but also activates it for efficient O-O bond cleavage. Furthermore, the higher redox potential of copper and the enhanced weakening of the O-O bond from the higher electron density in the d orbital of copper are central to its higher oxidase activity over iron. This work resolves a long-standing question in bioenergetics, and renders a chemical-biological basis for the design of future oxygen-reduction catalysts.

Esterification and transesterification of waste cooking oil over Amberlyst 15 and modified Amberlyst 15 catalysts

Abstract: Biodiesel production via the simultaneous esterification and transesterification reactions of waste cooking oil (WCO) with methanol was investigated. A batch reflux reactor was used in conjunction with acidic ion-exchange catalysts, i.e., Amberlyst 15 and modified Amberlyst 15. The activity of the Amberlyst 15 catalysts could be altered via heat treatment at temperatures that are ≥493 K, as a consequence of the reduction of the active surface ( SO3H). The hydrogen ion-exchange capacities of the catalysts ranged from 2.5 meq H+/g to 5.1 meq H+/g. The reaction parameters included the molar ratio of alcohol to oil (6:1–15:1), reaction temperature (298–338 K), catalyst concentration (1–9 wt.%), reaction time (1–72 h) and the free fatty acid content (1.04–8.04%). It was observed that the activities of the Amberlyst 15 and modified Amberlyst 15 catalysts increased linearly with increasing hydrogen ion-exchange capacities of the catalysts. Amberlyst 15 exhibited the highest hydrogen ion-exchange capacity and consequently generated the highest biodiesel yield of (78 ± 3.39%). The esterification reaction of excess fatty acids was also investigated. When the esterification and transesterification reactions were carried out simultaneously, the water generated from the esterification of free fatty acids led to the hydrolysis of triglycerides and reduced the biodiesel yield emphasizing the necessity for the removal of the water during concomitant esterification of excess fatty free acids present and the transesterification of the triglycerides for biodiesel production.

Hydrodynamics of Ship Propellers

Abstract: This book deals with flows over propellers operating behind ships, and the hydrodynamic forces and moments which the propeller generates on the shaft and on the ship hull. The first part of the book is devoted to fundamentals of the flow about hydrofoil sections and wings, propellers in uniform flow and pragmatic design guides for analysis and performance. The second part covers the development of unsteady section and blade forces arising from operation in non-uniform hull wakes. The problem of a non-cavitating, wide-bladed propeller in a wake is treated by a new and completely developed theory. A final chapter discusses the optimisation of efficiency of compound propulsors. The authors have taken great care to clearly describe physical concepts and mathematical steps. An appendix provides a concise introduction to (or reprise of) the mathematical techniques used.