Solar eclipse effects of 22 July, 2009 on the propagation of radio signals

The results of investigation of the variation of radio signal strengths during the solar eclipse on July 22, 2009 are reported in this paper. Observations of the radio signals transmitted from different radio stations at different frequencies and received at a particular observing site indicate a distinct change in signal strength around the time the eclipse umbra passes the propagation paths. The three types of variations in the eclipse day and particularly during its peak period are different from propagation under normal condition. The phenomena of signal variations, the noted “Inverted U-shape“ at one of the frequencies before the occurrence of the eclipse and 13 to 15 minutes time difference between the enhancement of the signal strength and the onset of eclipse are some interesting characteristics. The results are interpreted by ionospheric D-layer behavior at such times.     

American option pricing under stochastic volatility: an efficient numerical approach

This paper develops a new numerical technique to price an American option written upon an underlying asset that follows a bivariate diffusion process. The technique presented here exploits the supermartingale representation of an American option price together with a coarse approximation of its early exercise surface that is based on an efficient implementation of the least-squares Monte–Carlo algorithm (LSM) of Longstaff and Schwartz (Rev Financ Stud 14:113–147, 2001). Our approach also has the advantage of avoiding two main issues associated with LSM, namely its inherent bias and the basis functions selection problem. Extensive numerical results show that our approach yields very accurate prices in a computationally efficient manner. Finally, the flexibility of our method allows for its extension to a much larger class of optimal stopping problems than addressed in this paper.     

An efficient fourth order weighted-Newton method for systems of nonlinear equations

In this paper, we develop a fourth order method for solving the systems of nonlinear equations. The algorithm is composed of two weighted-Newton steps and requires the information of one function and two first Fréchet derivatives. Therefore, for a system of n equations, per iteration it uses n?+?2n ² evaluations. Computational efficiency is compared with Newton’s method and some other recently published methods. Numerical tests are performed, which confirm the theoretical results. From the comparison with known methods it is observed that present method shows good stability and robustness.     

Singular Lagrangian, Hamiltonization and Jacobi last multiplier for certain biological systems

We study the construction of singular Lagrangians using Jacobi’s last multiplier (JLM). We also demonstrate the significance of the last multiplier in Hamiltonian theory by explicitly constructing the Hamiltonian of the Host-Parasite model and a Lotka-Volterra mutualistic system, both of which are well known first-order systems of differential equations arising in biology.     

ESR study of the hydrogenated nanocrystalline silicon thin films

We studied the stability and light-induced paramagnetic centers in hydrogenated nanocrystalline silicon thin films (nc-Si:H) by electron-spin-resonance (ESR) and photothermal-deflection-spectroscopy (PDS). There is no measurable change in defect density upon illumination with white light with a light intensity of 300 mW cm^?2 for 300 h. At low temperatures, upon illumination with sub-bandgap light, a light-induced ESR signal appears. This signal is similar to that in hydrogenated micro-crystalline silicon (μc-Si:H).     

Structure--activity landscape index: identifying and quantifying activity cliffs

A new method for analyzing a structure-activity relationship is proposed. By use of a simple quantitative index, one can readily identify "structure-activity cliffs": pairs of molecules which are most similar but have the largest change in activity. We show how this provides a graphical representation of the entire SAR, in a way that allows the salient features of the SAR to be quickly grasped. In addition, the approach allows us view the SARs in a data set at different levels of detail. The method is tested on two data sets that highlight its ability to easily extract SAR information. Finally, we demonstrate that this method is robust using a variety of computational control experiments and discuss possible applications of this technique to QSAR model evaluation.     

Interaction of chromium with resistant strain Aspergillus versicolor: investigation with atomic force microscopy and other physical studies

The interaction of chromium and a chromate resistant Aspergillus versicolor strain has been studied by atomic force (AFM) and transmission electron (TEM) microscopies. The nanomechanical properties such as cell wall rigidity and elasticity were measured by force spectroscopy and found to be 0.61 +/- 0.08 N/m, and 20.5 +/- 2.1 MPa, respectively. On chromium binding, ultrastuctural changes of the cell wall along with the formation of layered structures on the cell wall were observed. TEM and AFM micrographs demonstrate the accumulation of chromium on the cell wall, which were rough and irregular compared with the smooth pristine mycelia. The surface roughness, cell wall rigidity and elasticity increased to 35.5 +/- 3.5 nm, 0.88 +/- 0.05 N/m, and 62.5 +/- 3.5 MPa, respectively, from the corresponding values of 5.2 +/- 0.68 nm, 0.61 +/- 0.02 N/m, and 20.5 +/- 2.1 MPa for the pristine mycelia. X-ray photoelectron spectroscopy and Fourier transform infrared studies suggest that bound chromium was reduced to its trivalent state by the cell wall components. The reduced chromium species on the cell surface further electrostatically bind chromate ions forming layered structure on the cell wall.     

Chemical data mining of the NCI human tumor cell line database

The NCI Developmental Therapeutics Program Human Tumor cell line data set is a publicly available database that contains cellular assay screening data for over 40 000 compounds tested in 60 human tumor cell lines. The database also contains microarray assay gene expression data for the cell lines, and so it provides an excellent information resource particularly for testing data mining methods that bridge chemical, biological, and genomic information. In this paper we describe a formal knowledge discovery approach to characterizing and data mining this set and report the results of some of our initial experiments in mining the set from a chemoinformatics perspective.     

Web service infrastructure for chemoinformatics

The vast increase of pertinent information available to drug discovery scientists means that there is a strong demand for tools and techniques for organizing and intelligently mining this information for manageable human consumption. At Indiana University, we have developed an infrastructure of chemoinformatics Web services that simplifies the access to this information and the computational techniques that can be applied to it. In this paper, we describe this infrastructure, give some examples of its use, and then discuss our plans to use it as a platform for chemoinformatics application development in the future.