A spectral scheme for Kohn-Sham density functional theory of clusters

Starting from the observation that one of the most successful methods for solving the Kohn-Sham equations for periodic systems -- the plane-wave method -- is a spectral method based on eigenfunction expansion, we formulate a spectral method designed towards solving the Kohn-Sham equations for clusters. This allows for efficient calculation of the electronic structure of clusters (and molecules) with high accuracy and systematic convergence properties without the need for any artificial periodicity. The basis functions in this method form a complete orthonormal set and are expressible in terms of spherical harmonics and spherical Bessel functions. Computation of the occupied eigenstates of the discretized Kohn-Sham Hamiltonian is carried out using a combination of preconditioned block eigensolvers and Chebyshev polynomial filter accelerated subspace iterations. Several algorithmic and computational aspects of the method, including computation of the electrostatics terms and parallelization are discussed. We have implemented these methods and algorithms into an efficient and reliable package called ClusterES (Cluster Electronic Structure). A variety of benchmark calculations employing local and non-local pseudopotentials are carried out using our package and the results are compared to the literature. Convergence properties of the basis set are discussed through numerical examples. Computations involving large systems that contain thousands of electrons are demonstrated to highlight the efficacy of our methodology. The use of our method to study clusters with arbitrary point group symmetries is briefly discussed.Comment: Manuscript submitted (with revisions) to Journal of Computational Physic

Differential Tissue Response to Growth Hormone in Mice

Growth hormone (GH) has been shown to act directly on multiple tissues throughout the body. Historically, it was believed that GH acted directly in the liver and only indirectly in other tissues via insulin‐like growth hormone 1 (IGF‐1). Despite extensive work to describe GH action in individual tissues, a comparative analysis of acute GH signaling in key metabolic tissues has not been performed. Herein, we address this knowledge gap. Acute tissue response to human recombinant GH was assessed in mice by measuring signaling via phospho‐STAT5 immunoblotting. STAT5 activation is an easily and reliably detected early marker of GH receptor engagement. We found differential tissue sensitivities; liver and kidney were equally GH‐sensitive and more sensitive than white adipose tissue, heart, and muscle (gastrocnemius). Gastrocnemius had the greatest maximal response compared to heart, liver, white adipose tissue, and whole kidney. Differences in maximum responsiveness were positively correlated with tissue STAT5 abundance, while differences in sensitivity were not explained by differences in GH receptor levels. Thus, GH sensitivity and responsiveness of distinct metabolic tissues differ and may impact physiology and disease

Beyond a Usage Threshold, NO Form of Energy is Sustainable or Green We are Running Out of “Garbage Dump Space ” To Dissipate “Used ” Energy Into

To date, almost all of the research on green/sustainable energy has been concerned with procurement of ever increasing amounts of energy for human consumption. This singular focus only on the supply-side of the problem completely overlooks what happens to the energy after we use it; thereby implicitly making the dangerously wrong assumption that the earth has unlimited capacity to dissipate energy. In this position paper, we remind the reader that the earth can dissipate only a finite amount of even the greenest of the green forms of energy, while still maintaining thermal equilibria that have evolved over eons. Any long term sustainable energy solution therefore must include a curbing/limiting/controlling our demand for (and consequently, our consumption of) energy. Otherwise, even if and even after all the green-house-effects are fully eliminated, the earth still might eventually experience unnaturally large temperature increase because the amount of energy dissipated is too large

Loop representation of charged particles interacting with Maxwell and Chern-Simons fields

The loop representation formulation of non-relativistic particles coupled with abelian gauge fields is studied. Both Maxwell and Chern-Simons interactions are separately considered. It is found that the loop-space formulations of these models share significant similarities, although in the Chern-Simons case there exists an unitary transformation that allows to remove the degrees of freedom associated with the paths. The existence of this transformation, which allows to make contact with the anyonic interpretation of the model, is subjected to the fact that the charge of the particles be quantized. On the other hand, in the Maxwell case, we find that charge quantization is necessary in order to the geometric representation be consistent.Comment: 6 pages, improved versio

Comparing the Performance of Expert User Heuristics and an Integer Linear Program in Aircraft Carrier Deck Operations

Planning operations across a number of domains can be considered as resource allocation problems with timing constraints. An unexplored instance of such a problem domain is the aircraft carrier flight deck, where, in current operations, replanning is done without the aid of any computerized decision support. Rather, veteran operators employ a set of experience based heuristics to quickly generate new operating schedules. These expert user heuristics are neither codified nor evaluated by the United States Navy; they have grown solely from the convergent experiences of supervisory staff. As unmanned aerial vehicles (UAVs) are introduced in the aircraft carrier domain, these heuristics may require alterations due to differing capabilities. The inclusion of UAVs also allows for new opportunities for on-line planning and control, providing an alternative to the current heuristic-based replanning methodology. To investigate these issues formally, we have developed a decision support system for flight deck operations that utilizes a conventional integer linear program-based planning algorithm. In this system, a human operator sets both the goals and constraints for the algorithm, which then returns a proposed schedule for operator approval. As a part of validating this system, the performance of this collaborative human–automation planner was compared with that of the expert user heuristics over a set of test scenarios. The resulting analysis shows that human heuristics often outperform the plans produced by an optimization algorithm, but are also often more conservative

Essays on Optimal Aid and Fiscal Policy in Developing Economies

Essay I: Which countries receive aid as insurance and why? A theory of optimal aid policy Empirical evidence shows that developing countries with opaque institutions receive procyclical Official Development Aid (ODA) while developing countries with transparent institutions receive acyclical or countercyclical ODA. This paper provides a dynamic equilibrium model of optimal aid policy that quantitatively accounts for this fact. In the model, the donor wants to (a) encourage actions by the aid receiving government that increase output and (b) smooth out economic fluctuations. The transparency of institutions in the country affects the donor's ability to distinguish downturns caused by exogenous shocks, from those caused by government actions. The solution to the donor's mechanism design problem is dependent on the transparency of government actions. If the donor has good information about government actions, aid policy is countercyclical and aid acts as insurance. However, if the donor is unable to infer perfectly the cause of the downturn, aid policy is procyclical to encourage unobservable good actions. The model predicts a similar pattern for ODA commitments for the following year which is supported by the data. For countries with opaque institutions procyclical aid is the result of optimal policies given the information constraints of donors. Essay II: New Evidence on the Relationship Between Aid Cyclicality and Institutions This paper documents a new fact: the correlation between official development assistance (ODA) and GDP is negatively related to the quality of institutions in the receipient country. Differences in institutional indicators that measure corruption, rule of law, government effectiveness and government transparency are particularly important. The results are robust to several modifications. The results hold for both pooled and within regressions specifications and for different sources of institutional quality measures. This fact also reconciles conflicting empirical results about the correlation between ODA and GDP in the literature. For instance, Pallage and Robe (2001) find a positive correlation in two thirds of African economies and half of non-African developing economies, but Rand and Tarp (2002) find no correlation in a different set of developing countries. First, once institutions are accounted for, African economies are not treated differently by donors. Second, the sample in Rand and Tarp (2002) comprises developing economies which have relatively good institutions, therefore, those countries receive acyclical or countercyclical aid. \\ Essay II: Optimal Procyclical Fiscal Policy Without Procyclical Government Spending Procyclical fiscal policy can be caused by either procyclical government expenditure, countercyclical taxes or both. The majority of models which try to explain procyclical fiscal policy as the result of optimal policy have procyclical government expenditures. This paper develops a model which optimally generates procyclical fiscal policy while keeping government expenditures acyclical. Instead, taxes are optimally countercyclical. The model uses endogenous sovereign default to generate an environment where interest rates are lower in booms than in recessions. If household's have insufficient access to financial instruments it is optimal for the government to lower taxes and borrow during booms. This enables impatient households to benefit from the lower interest rates in booms by helping the consumer bring consumption forward