Fast Fourier Optimization: Sparsity Matters

Many interesting and fundamentally practical optimization problems, ranging from optics, to signal processing, to radar and acoustics, involve constraints on the Fourier transform of a function. It is well-known that the {\em fast Fourier transform} (fft) is a recursive algorithm that can dramatically improve the efficiency for computing the discrete Fourier transform. However, because it is recursive, it is difficult to embed into a linear optimization problem. In this paper, we explain the main idea behind the fast Fourier transform and show how to adapt it in such a manner as to make it encodable as constraints in an optimization problem. We demonstrate a real-world problem from the field of high-contrast imaging. On this problem, dramatic improvements are translated to an ability to solve problems with a much finer grid of discretized points. As we shall show, in general, the "fast Fourier" version of the optimization constraints produces a larger but sparser constraint matrix and therefore one can think of the fast Fourier transform as a method of sparsifying the constraints in an optimization problem, which is usually a good thing.Comment: 16 pages, 8 figure

Optimized energy calculation in lattice systems with long-range interactions

We discuss an efficient approach to the calculation of the internal energy in numerical simulations of spin systems with long-range interactions. Although, since the introduction of the Luijten-Bl\"ote algorithm, Monte Carlo simulations of these systems no longer pose a fundamental problem, the energy calculation is still an O(N^2) problem for systems of size N. We show how this can be reduced to an O(N logN) problem, with a break-even point that is already reached for very small systems. This allows the study of a variety of, until now hardly accessible, physical aspects of these systems. In particular, we combine the optimized energy calculation with histogram interpolation methods to investigate the specific heat of the Ising model and the first-order regime of the three-state Potts model with long-range interactions.Comment: 10 pages, including 8 EPS figures. To appear in Phys. Rev. E. Also available as PDF file at http://www.cond-mat.physik.uni-mainz.de/~luijten/erikpubs.htm

On the Tractability of (k, i)-Coloring

In an undirected graph, a proper ( k, i )-coloring is an assign- ment of a set of k colors to each vertex such that any two adjacent vertices have at most i common colors. The ( k, i )-coloring problem is to compute the minimum number of colors required for a proper ( k, i )- coloring. This is a generalization of the classic graph colo ring problem. Majumdar et. al. [CALDAM 2017] studied this problem and show ed that the decision version of the ( k, i )-coloring problem is fixed parameter tractable (FPT) with tree-width as the parameter. They aske d if there exists an FPT algorithm with the size of the feedback vertex s et (FVS) as the parameter without using tree-width machinery. We ans wer this in positive by giving a parameterized algorithm with the size o f the FVS as the parameter. We also give a faster and simpler exact algo rithm for ( k, k − 1)-coloring, and make progress on the NP-completeness of sp ecific cases of ( k, i )-colorin

Challenging the obesity paradox: Extreme obesity and COPD mortality in the SUMMIT Trial

Populations with COPD demonstrate higher survival in overweight and obese compared with normal weight; the “obesity paradox”. Relationships in less-severe COPD are unclear, as is the impact of cardiovascular risk, and few studies include individuals at extremes of obesity.  We examined the relationship between body mass index (BMI; defined as underweight: 40 kg·m−2, suggesting that obesity may not remain protective at the extremes in this population

Characterization of Arabidopsis ABCG11/WBC11, an ATP binding cassette (ABC) transporter that is required for cuticular lipid secretion

Summary ABCG11/WBC11, an ATP binding cassette (ABC) transporter from Arabidopsis thaliana, is a key component of the export pathway for cuticular lipids. Arabidopsis wbc11 T-DNA insertional knock-out mutants exhibited lipidic inclusions inside epidermal cells similar to the previously characterized wax transporter mutant cer5, with a similar strong reduction in the alkanes of surface waxes. Moreover, the wbc11 knock-out mutants also showed defects not present in cer5, including post-genital organ fusions, stunted growth and a reduction in cutin load on the plant surface. A mutant line previously isolated in a forward genetics screen, called permeable leaves 1 (pel1), was identified as an allele of ABCG11/WBC11. The double knock-out wbc11 cer5 exhibited the same morphological and biochemical phenotypes as the wbc11 knock-out. A YFP-WBC11 fusion protein rescued a T-DNA knock-out mutant and was localized to the plasma membrane. These results show that WBC11 functions in secretion of surface waxes, possibly by interacting with CER5. However, unlike ABCG12/ CER5, ABCG11/WBC11 is important to the normal process of cutin formation

Lack of cyclophilin D protects against the development of acute lung injury in endotoxemia.

Sepsis caused by LPS is characterized by an intense systemic inflammatory response affecting the lungs, causing acute lung injury (ALI). Dysfunction of mitochondria and the role of reactive oxygen (ROS) and nitrogen species produced by mitochondria have already been proposed in the pathogenesis of sepsis; however, the exact molecular mechanism is poorly understood. Oxidative stress induces cyclophilin D (CypD)-dependent mitochondrial permeability transition (mPT), leading to organ failure in sepsis. In previous studies mPT was inhibited by cyclosporine A which, beside CypD, inhibits cyclophilin A, B, C and calcineurin, regulating cell death and inflammatory pathways. The immunomodulatory side effects of cyclosporine A make it unfavorable in inflammatory model systems. To avoid these uncertainties in the molecular mechanism, we studied endotoxemia-induced ALI in CypD-/- mice providing unambiguous data for the pathological role of CypD-dependent mPT in ALI. Our key finding is that the loss of this essential protein improves survival rate and it can intensely ameliorate endotoxin-induced lung injury through attenuated proinflammatory cytokine release, down-regulation of redox sensitive cellular pathways such as MAPKs, Akt, and NF-kappaB and reducing the production of ROS. Functional inhibition of NF-kappaB was confirmed by decreased expression of NF-kappaB-mediated proinflammatory genes. We demonstrated that impaired mPT due to the lack of CypD reduces the severity of endotoxemia-induced lung injury suggesting that CypD specific inhibitors might have a great therapeutic potential in sepsis-induced organ failure. Our data highlight a previously unknown regulatory function of mitochondria during inflammatory response

A five-year review of burn injuries in Irrua

<p>Abstract</p> <p>Background</p> <p>The management of burns remains a challenge in developing countries. Few data exist to document the extent of the problem. This study provides data from a suburban setting by documenting the epidemiology of burn injury and ascertaining outcome of management. This will help in planning strategies for prevention of burns and reducing severity of complications.</p> <p>Methods</p> <p>A total of 72 patients admitted for burns between January 1st, 2002 and December 31st, 2006 at the Irrua specialist teaching hospital were studied retrospectively. Sources of information were the case notes and operation registers. Data extracted included demographics as well as treatment methods and outcome</p> <p>Results</p> <p>The results revealed male to female ratio of 2.1:1. Over 50% of the injuries occurred at home. There was a seasonal variation with over 40% of injuries occurring between November and January. The commonest etiologic agent was flame burn from kerosene explosion. There were 7 deaths in the series.</p> <p>Conclusion</p> <p>Burns are preventable. We recommend adequate supply of unadulterated petroleum products and establishment of burn centers.</p