The Safety Net as a Network

The lack of a coherent understanding of what is meant by the American safety net made it difficult to have a meaningful discourse on the current condition. This paper proposes an alternative formulation of the social safety net based in network theory to overcome the shortcomings of the previous literature. The first part of the paper describes this approach, attempting to develop an alternative understanding of the safety net grounded in the actions of anti-poverty actors. Next is a list of propositions for measuring five dimensions of a safety net: the frame, structure, positions, influences, and the context. Three policy implications are derived from this new paradigm. First, shifting the level of analysis to network level allows policy makers to broaden the scope of the modern social safety net. Second, quantifying the interaction among actors reveals interdependency, which in turn redefines the power and influence of each actor within the network. Finally, the modern safety net could demonstrate a core-periphery structure. It calls for a new way of thinking about resource distribution and decision making channels of such unique structure.LBJ School of Public Affair

Charge-dependent Azimuthal Correlations in Relativistic Heavy-ion Collisions and Electromagnetic Effects

We propose a scenario where the pattern of the recently observed charge-dependent azimuthal correlations can be understood qualitatively. This is based on the cluster picture and the assumption that the charged hadrons that flow outward from the surface of the overlapping region of the colliding nuclei move primarily parallel to the reaction plane. We also point out the there is a strong electric field induced by the transient magnetic field during the parton production in the initial phase of the relativistic heavy-ion collision and discuss its possible relevance to the scenario.Comment: Revised version to be published in Phys. Rev.

X-shaped radio galaxies as observational evidence for the interaction of supermassive binary black holes and accretion disk at pc scale

A supermassive black hole binary may form during galaxy mergering. we investigate the interaction of the supermassive binary black holes (SMBBHs) and an accretion disk and show that the detected X-shaped structure in some FRII radio galaxies may be due to the interaction-realignment of inclined binary and accretion disk occurred within the pc scale of the galaxy center. We compare in detail the model and observations and show that the configuration is consistent very well with the observations of X-shaped radio sources. X-shaped radio feature form only in FRII radio sources due to the strong interaction between the binary and a standard disk, while the absence of X-shaped FRI radio galaxies is due to that the interaction between the binary and the radiatively inefficient accretion flow in FRI radio sources is negligible. It is suggested that the binary would keep misaligned with the outer disk for most of the life time of FRII radio galaxies and the orientation of jet in most FRII radio galaxies distributes randomly, while the jets in most FRI radio galaxies is expected to be vertical to the accretion disk and thus the major axis of host galaxy. We discuss the relationship of X-shaped and double-double radio galaxies (DDRGs). The model is applied in paticular to two X-shaped radio sources 4C+01.30 and 3C293 and one DDRG source J0116-473 and show that the SMBBHs in the three objects have black hole mass ratios $q \sim 0.1 - 0.3$.Comment: 35 pages, no figure, no table. Accepted for publication in MNRA

Duality and Optimization for Generalized Multi-hop MIMO Amplify-and-Forward Relay Networks with Linear Constraints

We consider a generalized multi-hop MIMO amplify-and-forward (AF) relay network with multiple sources/destinations and arbitrarily number of relays. We establish two dualities and the corresponding dual transformations between such a network and its dual, respectively under single network linear constraint and per-hop linear constraint. The result is a generalization of the previous dualities under different special cases and is proved using new techniques which reveal more insight on the duality structure that can be exploited to optimize MIMO precoders. A unified optimization framework is proposed to find a stationary point for an important class of non-convex optimization problems of AF relay networks based on a local Lagrange dual method, where the primal algorithm only finds a stationary point for the inner loop problem of maximizing the Lagrangian w.r.t. the primal variables. The input covariance matrices are shown to satisfy a polite water-filling structure at a stationary point of the inner loop problem. The duality and polite water-filling are exploited to design fast primal algorithms. Compared to the existing algorithms, the proposed optimization framework with duality-based primal algorithms can be used to solve more general problems with lower computation cost.Comment: 30 pages, 8 figure

Scalar Wave Equation Modeling with Time-Space Domain Dispersion-Relation-Based Staggered-Grid Finite-Difference Schemes

The staggered-grid finite-difference (SFD) method is widely used in numerical modeling of wave equations. Conventional SFD stencils for spatial derivatives are usually designed in the space domain. However, when they are used to solve wave equations, it becomes difficult to satisfy the dispersion relations exactly. Liu and Sen (2009c) proposed a new SFD scheme for one-dimensional (1D) scalar wave equation based on the time-space domain dispersion relation and plane wave theory, which is made to satisfy the exact dispersion relation. This new SFD scheme has greater accuracy and better stability than a conventional scheme under the same discretizations. In this paper, we develop this new SFD scheme further for numerical solution of 2D and 3D scalar wave equations. We demonstrate that the modeling accuracy is second order when the conventional 2M-th-order space-domain SFD and the second order time-domain finite-difference stencils are directly used to solve the scalar wave equation. However, under the same discretization, our 1D scheme can reach 2M-th-order accuracy and is always stable; 2D and 3D schemes can reach 2M-th-order accuracy along 8 and 48 directions, respectively, and have better stability. The advantages of the new schemes are also demonstrated with dispersion analysis, stability analysis, and numerical modeling.National Natural Science Foundation of China 41074100Important National Science & Technology Specific Project of China 2008ZX05024-001Institute for Geophysic

Mixed time integration methods for transient thermal analysis of structures, appendix 5

Mixed time integration methods for transient thermal analysis of structures are studied. An efficient solution procedure for predicting the thermal behavior of aerospace vehicle structures was developed. A 2D finite element computer program incorporating these methodologies is being implemented. The performance of these mixed time finite element algorithms can then be evaluated employing the proposed example problem