Space Charge in Solid Dielectrics (Keynote Lecture)

The importance of space charge in solid dielectrics has been recognized for a long time. Over the years many attempts have been made to observe its dynamics in solid dielectrics. Significant development in measurement techniques has emerged two decades ago. In this paper several popular non-destructive techniques are briefly reviewed, followed by description of some advanced space charge measurement facilities housed in our laboratory. The selected results obtained over the years will be presented. It has been found that the interfaces play important role in space charge formation in addition to the bulk materials. Electrical ageing of polymeric materials under dc condition has been extensively studied and the technique has been extended to XLPE power cables. Recent work on ac ageing of polymeric materials has clearly indicated that ageing under high ac electric field results in the formation of space charge and these charges are very stable, indicating the formation of deep traps due to ac ageing. The impurities in the materials have significant influence on space charge formation and dynamics while the morphological feature of the material however has less effect on space charge. Simulation based on a bipolar charge model shows a good agreement with experimental results

Walking and Wandering: Reconstructing Diasporic Subjectivity in T. C. Huo\u27s Land of Smiles and Lê Thi Diem Thúy’s The Gangster We Are All Looking For

Diaspora has often been defined as the condition of dispersal and displacement in which its members express minimal connections with their host country and always look to return to their ancestral homelands. However, from the literary representations in T. C. Huo’s Land of Smiles and Lê Thi Diem Thúy’s The Gangster We Are All Looking For, it is clear that members of the Southeast Asian diaspora determine to set root in their host country and refuse to be treated as temporary guests. This determination is warranted by their desire to redefine the contentious idea of home beyond cultural ancestry and geopolitical boundaries. Both authors utilize the trope of walking and wandering to debunk the essentialist conception based on the premise that one’s subjectivity is static, especially when it applies to diasporic members’ supposed sense of homelessness and the longing to return to their native countries. Rather than perpetuating the systemic labels onto diasporic members, such as homelessness, passivity, and powerlessness, through walking and wandering, the Southeast Asian refugees in the novels demonstrate the psychosomatic connections with their host country, take part in the pursuit of success, and declare an active, visible presence in their new homeland as fervent subjects who embrace opportunities to obtain material security in the United States

State Taxation of Unitary Businesses

The income taxation of multistate businesses has created problems for tax administrators, primarily with regard to the question of how to divide the income taxation amongst the multiple states. To address this, the concepts of unitary business and formula apportionment have been created. However, the non-uniform state taxation practices create difficulties even with the existence of these concepts. Some states have adopted the Multistate Tax Compact, but for it to be completely effective there still must be a uniform view adopted on what constitutes a unitary business. This note examines the constitutional issues attendant to developing a standard definition of a unitary business, an in-depth analysis of the unitary business concept and its origins, and proposes a workable definition of a unitary business

Weak Continuity and Compactness for Nonlinear Partial Differential Equations

We present several examples of fundamental problems involving weak continuity and compactness for nonlinear partial differential equations, in which compensated compactness and related ideas have played a significant role. We first focus on the compactness and convergence of vanishing viscosity solutions for nonlinear hyperbolic conservation laws, including the inviscid limit from the Navier-Stokes equations to the Euler equations for homentropy flow, the vanishing viscosity method to construct the global spherically symmetric solutions to the multidimensional compressible Euler equations, and the sonic-subsonic limit of solutions of the full Euler equations for multidimensional steady compressible fluids. We then analyze the weak continuity and rigidity of the Gauss-Codazzi-Ricci system and corresponding isometric embeddings in differential geometry. Further references are also provided for some recent developments on the weak continuity and compactness for nonlinear partial differential equations.Comment: 29 page

On the Inverse Problem Relative to Dynamics of the w Function

In this paper we shall study the inverse problem relative to dynamics of the w function which is a special arithmetic function and shall get some results.Comment: 11 page

Local molecular field theory for effective attractions between like charged objects in systems with strong Coulomb interactions

Strong short ranged positional correlations involving counterions can induce a net attractive force between negatively charged strands of DNA, and lead to the formation of ion pairs in dilute ionic solutions. But the long range of the Coulomb interactions impedes the development of a simple local picture. We address this general problem by mapping the properties of a nonuniform system with Coulomb interactions onto those of a simpler system with short ranged intermolecular interactions in an effective external field that accounts for the averaged effects of appropriately chosen long ranged and slowly varying components of the Coulomb interactions. The remaining short ranged components combine with the other molecular core interactions and strongly affect pair correlations in dense or strongly coupled systems. We show that pair correlation functions in the effective short ranged system closely resemble those in the uniform primitive model of ionic solutions, and illustrate the formation of ion pairs and clusters at low densities. The theory accurately describes detailed features of the effective attraction between two equally charged walls at strong coupling and intermediate separations of the walls. New analytical results for the minimal coupling strength needed to get any attraction and for the separation where the attractive force is a maximum are presented.Comment: 8 pages, 5 figures. To be published in PNA

Space Charge Modelling in Solid Dielectrics under High Electric Field Based on Double Charge Injection Model

Present study aims to develop a clear insight on factors that influence space charge dynamics in solid dielectrics through a numerical simulation. The model used for the simulation is proposed by Alison and Hill [1] which describes charge dynamics as a result of bipolar transport with single level trapping. In this model, a constant mobility and no detrapping have been assumed. The simulation results show that carrier mobility, trapping coefficient and Schottky barrier have a significant effect on the space charge dynamics. Many features of space charge profiles observed by experiments have been revealed in despite of over simplistic model. More importantly, the simulation allows us to study the role of each individual parameter in the formation of space charge in solid dielectrics, so that the experimental results can be better understood

Ricci flow on K\"ahler-Einstein manifolds

In our previous paper math.DG/0010008, we develop some new techniques in attacking the convergence problems for the K\"ahler Ricci flow. The one of main ideas is to find a set of new functionals on curvature tensors such that the Ricci flow is the gradient like flow of these functionals. We successfully find such functionals in case of Kaehler manifolds. On K\"ahler-Einstein manifold with positive scalar curvature, if the initial metric has positive bisectional curvature, we prove that these functionals have a uniform lower bound, via the effective use of Tian's inequality. Consequently, we prove the following theorem: Let $M$ be a K\"ahler-Einstein manifold with positive scalar curvature. If the initial metric has nonnegative bisectional curvature and positive at least at one point, then the K\"ahler Ricci flow will converge exponentially fast to a K\"ahler-Einstein metric with constant bisectional curvature. Such a result holds for K\"ahler-Einstein orbifolds.Comment: 49 pages. This is a revised version. Sections 4 and 5 are simplified and streamline

Comparison of the Geometrical Characters Inside Quark- and Gluon-jet Produced by Different Flavor Quarks

The characters of the angular distributions of quark jets and gluon jets with different flavors are carefully studied after introducing the cone angle of jets. The quark jets and gluon jets are identified from the 3-jet events which are produced by Monte Carlo simulation Jetset7.4 in e+e- collisions at $\sqrt s$=91.2GeV. It turns out that the ranges of angular distributions of gluon jets are obviously wider than that of quark jets at the same energies. The average cone angles of gluon jets are much larger than that of quark jets. As the multiplicity or the transverse momentum increases, the cone-angle distribution without momentum weight of both the quark jet and gluon jet all increases, i.e the positive linear correlation are present, but the cone-angle distribution with momentum weight decreases at first, then increases when n > 4 or p_t > 2 GeV. The characters of cone angular distributions of gluon jets produced by quarks with different flavors are the same, while there are obvious differences for that of the quark jets with different flavors.Comment: 13 pages, 6 figures, to be published on the International Journal of Modern Physics