String and M-Theory: Answering the Critics

Using as a springboard a three-way debate between theoretical physicist Lee Smolin, philosopher of science Nancy Cartwright and myself, I address in layman’s terms the issues of why we need a unified theory of the fundamental interactions and why, in my opinion, string and M-theory currently offer the best hope. The focus will be on responding more generally to the various criticisms. I also describe the diverse application of string/M-theory techniques to other branches of physics and mathematics which render the whole enterprise worthwhile whether or not “a theory of everything” is forthcoming.     

Numerical study on incomplete orthogonal factorization preconditioners

We design, analyse and test a class of incomplete orthogonal factorization preconditioners constructed from Givens rotations, incorporating some dropping strategies and updating tricks, for the solution of large sparse systems of linear equations. Comprehensive accounts about how the preconditioners are coded, what storage is required and how the computation is executed for a given accuracy are presented. A number of numerical experiments show that these preconditioners are competitive with standard incomplete triangular factorization preconditioners when they are applied to accelerate Krylov subspace iteration methods such as GMRES and BiCGSTAB.     

Particle dynamics simulations of triboelectric charging in granular insulator systems

Particle dynamics simulations are carried out to study triboelectric charging in granular systems composed of a single insulating material. The simulations implement a model in which electrons trapped in localized high energy states can be transferred during collisions to low energy states in the other particle. It is shown that this effect alone can generate electrostatic charging in the system, and cause net electron transfer from larger particles to smaller particles. The magnitude of charging is small for systems of a single particle size but becomes much greater for a system with polydispersal particle sizes, due to the net electron transfer from larger to smaller particles. The negative charge of smaller particles, and positive charge of larger particles has been observed in field studies and laboratory experiments of granular systems.     

Nonequilibrium accumulation of surface species and triboelectric charging in single component particulate systems

Triboelectric charging occurs in granular systems composed of chemically identical particles even though there is no apparent driving force for charge transfer. We show that such charging can result from nonequilibrium dynamics in which collision-induced electron transfer generates electron accumulation on a particle-size-dependent subset of the system. This idea rationalizes experimental results that suggest that smaller particles charge negatively while the large ones charge positively. This effect occurs generally when there are high energy electrons on a surface that cannot equilibrate to lower energy states on the same surface, but can transfer to lower energy states on other particles during collisions.     

关于K个复相关矩阵相等的检验

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The successive determination of chloride, fluoride and sodium in single samples of orthophosphate minerals by means of ion-sensitive electrodes

A buffer system composed of perchloric acid, citric acid and triethanolamine has been used for the successive determination of chloride, fluoride and sodium in a single sample of an orthophosphate mineral. The conventional sodium-sensitive glass electrode compares favourably with the more expensive Orion sodium-sensitive electrode.     

A model to study the relationship between forecast error,inventory investment,and customer service level in a multiperiod,probabilistic environment

With the advent of Just-In-Time manufacturing strategies, reduction of inventory costs have once again become the focus of all attention. However, efforts to reduce inventory while continuing to live with poor forecasts and unduly high service level requirements, is likely to be futile.This work uses a dynamic programming approach to establish trade-off curves, tying in forecast error, customer service level, and inventory investment. This work applies to realistic, dynamic settings wherein there is uncertainty associated with demand, and lead time could be fixed or probabilistic. This work further assumes form-free probability distributions and thus avoids errors introduced into the analysis from estimating parameters of the distribution from limited data.