Ab-initio calculations of spin tunneling through an indirect barrier

We use a fully relativistic layer Green's functions approach to investigate spin-dependent tunneling through a symmetric indirect band gap barrier like GaAs/AlAs/GaAs heterostructure along [100] direction. The method is based on Linear Muffin Tin Orbitals and it is within the Density Functional Theory (DFT) in the Local Density Approximation (LDA). We find that the results of our {\it ab-initio} calculations are in good agreement with the predictions of our previous empirical tight binding model [Phys. Rev. {\bf B}, 075313 (2006)]. In addition we show the $k_{||}$-dependence of the spin polarization which we did not previously include in the model. The {\it ab-initio} calculations indicate a strong $k_{||}$-dependence of the transmission and the spin polarization due to band non-parabolicity. A large window of 25-50 % spin polarization was found for a barrier of 8 AlAs monolayers at $k_{||}$ = 0.03 $2\pi/a$. Our calculations show clearly that the appearance of energy windows with significant spin polarization depends mostly on the location of transmission resonances and their corresponding zeros and not on the magnitude of the spin splitting in the barrier.Comment: 10 pages, 3 figure

Summary of papers presented at the conference "models and monetary policy: research in the tradition of Dale Henderson, Richard Porter, and Peter Tinsley"

On March 26 and 27, 2004, the Federal Reserve Board held a conference in Washington, D.C., on the application of economic models to the analysis of monetary policy issues. The papers presented at the conference addressed several topics that, because they are of interest to central bankers, have been a prominent feature of Federal Reserve research over the years. In particular, the papers represent research in the tradition of work carried out over the past thirty-five years at the Federal Reserve by three prominent staff economists -- Dale W. Henderson, Richard D. Porter, and Peter A. Tinsley. Thus, the conference partly served as a celebration of the contributions made by these individuals to policy-related research since the late 1960s. ; Among the specific topics addressed at the conference were the influence of uncertainty on policymaking; the design of formal rules to guide policy actions; the role of money in the transmission of monetary policy; the determination of asset prices; and econometric techniques for estimating dynamic models of the economy.Monetary policy ; Econometric models

An eclectic credit cycle search : the case of US, Japan and Germany

Credit crunches, quantitative easing and especially international credit cycles are all monetary facets of the still ongoing global economic crisis and financial turmoil. This paper investigates global credit cycle fundamental characteristics, among three leading economies; that is, the USA, Japanese and German. Our statistically sophisticated time series data come from the Bank of International Settlements (BIS) open source. These valuable data cover the period of complete time series, from 1970(Q1) up to 2015(Q1), covering the whole data availability period for these three economic leaders. We indicate that during the 70’s and the first decade of the 21st century, we face significant statistical evidence that credit supply shocks in particular, in economies that lead capitalism globally, affect each other economy quite seriously. The credit data confirm more the presence of an international credit cycle, in the sense that credit growth rates, in these three leading economies in particular, move together over time. We also verify, through classic impulse response analysis, that US credit supply shocks have a stronger effect upon the Japanese and German credit supply variable, for both the 1973 and most significantly the 2008 financial crisis years.peer-reviewe

Cluster Deletion on Interval Graphs and Split Related Graphs

In the Cluster Deletion problem the goal is to remove the minimum number of edges of a given graph, such that every connected component of the resulting graph constitutes a clique. It is known that the decision version of Cluster Deletion is NP-complete on (P_5-free) chordal graphs, whereas Cluster Deletion is solved in polynomial time on split graphs. However, the existence of a polynomial-time algorithm of Cluster Deletion on interval graphs, a proper subclass of chordal graphs, remained a well-known open problem. Our main contribution is that we settle this problem in the affirmative, by providing a polynomial-time algorithm for Cluster Deletion on interval graphs. Moreover, despite the simple formulation of the algorithm on split graphs, we show that Cluster Deletion remains NP-complete on a natural and slight generalization of split graphs that constitutes a proper subclass of P_5-free chordal graphs. Although the later result arises from the already-known reduction for P_5-free chordal graphs, we give an alternative proof showing an interesting connection between edge-weighted and vertex-weighted variations of the problem. To complement our results, we provide faster and simpler polynomial-time algorithms for Cluster Deletion on subclasses of such a generalization of split graphs

Maximizing the Strong Triadic Closure in Split Graphs and Proper Interval Graphs

In social networks the Strong Triadic Closure is an assignment of the edges with strong or weak labels such that any two vertices that have a common neighbor with a strong edge are adjacent. The problem of maximizing the number of strong edges that satisfy the strong triadic closure was recently shown to be NP-complete for general graphs. Here we initiate the study of graph classes for which the problem is solvable. We show that the problem admits a polynomial-time algorithm for two unrelated classes of graphs: proper interval graphs and trivially-perfect graphs. To complement our result, we show that the problem remains NP-complete on split graphs, and consequently also on chordal graphs. Thus we contribute to define the first border between graph classes on which the problem is polynomially solvable and on which it remains NP-complete