Andreev reflection in bilayer graphene

We consider the conductance of a normal-superconductor junction in bilayer graphene in the framework of the Dirac-Bogoliubov-De-Gennes equation. A remarkable suppression of the conductance at voltages just below the superconducting gap is found. This can be understood in terms of the spinor structures of the electron and hole excitations, in particular the reflected valence band hole being orthogonal to the incoming electron at normal incidence. Minor changes in response to referee reports, references updated.Comment: 9 pages, 8 figure

Tools for climate change adaptation in water management - inventory and assessment of methods and tools

This report summarizes an inventory of methods and tools for assessing climate change impacts, vulnerability and adaptation options, focusing on the water sector. Two questions are central: What are the opportunities for international applications of Dutch methods and tools? And: Which methods and tools available abroad are suitable for application in The Netherlands

High speed, self-acting shaft seal

A high-speed, self-acting circumferential type shaft seal for use in turbine engines is disclosed. One or more conventional circumferential ring seals having a central aperture are mounted in a housing. In three of the four embodiments of the invention, a helical groove and one or more dam seals are cut in the inner cylindrical surface of the one or more ring seals. In a fourth embodiment, two or more lift pads are disposed in surface contact with the inner cylindrical surface of the seal rings. To the outside of the lift pads, two dam seals are cut in the inner cylindrical surface of two of the ring seals. In each of the embodiments, a net outward radial force was produced during rotation of the turbine causing the ring seals to lift out of contact with the turbine shaft to minimize wear of the ring seals

Shaft seal assembly for high speed and high pressure applications

A seal assembly is provided for reducing the escape of fluids from between a housing and a shaft rotably mounted in the housing. The seal assembly comprises a pair of seal rings resiliently connected to each other and disposed in side-by-side relationship. In each seal ring, both the internal bore surface and the radial face which faces away from the other seal ring are provided with a plurality of equi-spaced recesses. The seal faces referred to are located adjacent a seating surface of the housing. Under normal operating conditions, the seal assembly is stationary with respect to the housing, and the recesses generate life, keep the assembly spaced from the rotating shaft and allow slip therebetween. The seal assembly can seize on the shaft, and slip will then occur between the radial faces and the housing

High-speed, self-acting shaft seal (circumferential type)

Shaft riding circumferential seal is used with turbine engines under high pressure conditions. Construction of seal is discussed and schematic diagram to show operations is provided

Design considerations in mechanical face seals for improved performance. 2: Lubrication

The importance of sealing technology in our industrial, chemical-oriented society in regard to maintenance and environmental contamination is pointed out. It is stated that seal performance (leakage, life) is directly related to seal lubrication. Current thinking in regard to seal lubrication is reviewed; the effect of energy dissipation in the thin lubricating film separating the sealing faces is pointed out, and the results of vaporization due to heating are illustrated. Also, hydrodynamic lubrication is reviewed, and an inherent tendency for the seal to operate with angular misalignment is shown. Recent work on hydrostatic effects is summarized and the conditions for seal instability are discussed. Four different modes of seal lubrication are postulated with the mode type being a strong function of speed and pressure

Design considerations in mechanical face seals for improved performance. 1: Basic configurations

Basic assembly configurations of the mechanical face seal are described and some advantages associated with each are listed. The various forms of seal components are illustrated, and functions pointed out. The technique of seal pressure balancing and its application are described; and the concept of the PV factor, its different forms and limitations are discussed. Brief attention is given to seal lubrication since it is covered in detail in a companion paper. Finally, the operating conditions for various applications of low pressure seals (aircraft transmissions) are listed, and the seal failure mode of a particular application is discussed