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

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

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

Spectral scheme for abinitio simulations of clusters

We formulate and implement a spectral scheme designed towards solving the Kohn–Sham equations for clusters in this study. This is motivated by 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. Our spectral solution method allows for efficient calculation of the electronic structure of clusters with high accuracy and systematic convergence properties without the need for any artificial periodicity. The basis functions in our method form a complete orthonormal set and are expressible in terms of spherical harmonics and spherical Bessel functions. We compute the occupied eigenstates of the discretized Kohn–Sham Hamiltonian using a combination of preconditioned block eigensolvers and Chebyshev polynomial filter accelerated subspace iterations. We highlight several algorithmic and computational aspects of our method, including computation of the electrostatics terms and parallelization. We present results from a variety of benchmark calculations employing local and nonlocal pseudopotentials and compare these to the literature. To illustrate the efficacy of our method, we demonstrate computations involving large systems that contain thousands of electrons. Finally, we briefly discuss the use of our method to study clusters with arbitrary point group symmetries

Combination Therapy of Prostate Cancer Utilizing Functionalized Iron Oxide Nanoparticles Carrying TNF-a and Lactonic Sophorolipids

Prostate cancer is one of the most prevalent forms of cancer afflicting men in the United States. In recent years, advances in the field of nanotechnology have allowed for new and innovative ways to treat various types of cancer and various other diseases. Our research focuses on the treatment of the LNCaP line prostate cancer utilizing iron oxide nanoparticles (IONPs) loaded with soluble TNF-a and lactonic sophorolipids (LSLs). TNF-a is a cytokine responsible for apoptosis initiation, while LSLs are naturally-glycolipids shown to alleviate inflammation and improve immune response in certain diseases. We hypothesized that this combination may possess a synergistic effect, displaying greater therapeutic effects than either compound alone. We synthesized polyacrylic acid (PAA)-coated IONPs to serve as a vehicle for these compounds for target-specific delivery. The surface carboxylate groups of the PAA coating can be chemically modified, allowing for binding of ligands to target cell-specific surface receptors or antigens. We conjugated our IONPs with glutamic acid with the aim of targeting the over-expressed glutamate receptors on the surface of the LNCaP cells. This combination therapy showed significant LNCaP cell death within 48 hours of incubation, while healthy cells were unaffected. The therapeutic effects were determined using cytotoxicity, MitoSOX, apoptosis, and migration assays. The results of the combined therapy suggest that these compounds may be a viable alternative to chemotherapeutic drugs in prostate cancer treatment