Economical Alternatives for High Sensitivity in Atomic Spectrometry Laboratory

The most commonly used analytical tools for determination of elements at trace levels are atomic absorption spectrometry (AAS), inductively coupled plasma, optical emission and mass spectrometry (ICP-OES and ICP-MS) and atomic fluorescence spectrometry (AFS). Although sensitive plasma techniques are becoming predominant in most of the western laboratories, AAS keeps its importance in developing countries. Simple and inexpensive ways of enhancing sensitivity will be described for laboratories equipped with only a flame AA spectrometer. Although there are many chemical preconcentration procedures to improve sensitivity of flame AAS, only some atom trapping techniques will be included here. One kind of atom trapping device is a slotted quartz tube (SQT) used for in situ preconcentration of analyte species followed by a rapid revolatilization cycle to obtain an enhanced signal. These devices provide limits of detection at a level of µg L-1. Another kind of atom trapping involves use of vapor generation technique and quartz or tungsten atom trapping surfaces. The analytical steps consist of the generation of volatile species, usually by hydride formation using NaBH4, trapping these species at the surface of an atom trap held at an optimized temperature and finally re-volatilizing analyte species by rapid heating of trap. These species are transported using a carrier gas to an externally heated quartz tube as commonly used in hydride generation AAS systems; a transient signal is formed and measured. These traps have limits of detection in the order of ng L-1

Exact and heuristic approaches to detect failures in failed k-out-of-n systems

This paper considers a k-out-of-n system that has just failed. There is an associated cost of testing each component. In addition, we have apriori information regarding the probabilities that a certain set of components is the reason for the failure. The goal is to identify the subset of components that have caused the failure with the minimum expected cost. In this work, we provide exact and approximate policies that detects components’ states in a failed k-out-of-n system. We propose two integer programming (IP) formulations, two novel Markov decision process (MDP) based approaches, and two heuristic algorithms. We show the limitations of exact algorithms and effectiveness of proposed heuristic approaches on a set of randomly generated test instances. Despite longer CPU times, IP formulations are flexible in incorporating further restrictions such as test precedence relationships, if need be. Numerical results illustrate that dynamic programming for the proposed MDP model is the most effective exact method, solving up to 12 components within one hour. The heuristic algorithms’ performances are presented against exact approaches for small to medium sized instances and against a lower bound for larger instances

Refractive Index Enhancement with Vanishing Absorption in an Atomic Vapor

We report a proof-of-principle experiment where the refractive index of an atomic vapor is enhanced while maintaining vanishing absorption of the beam. The key idea is to drive alkali atoms in a vapor with appropriate control lasers and induce a gain resonance and an absorption resonance for a probe beam in a two-photon Raman configuration. The strength and the position of these two resonances can be manipulated by changing the parameters of the control lasers. By using the interference between these two resonances, we obtain an enhanced refractive index without an increase in the absorption.Comment: 11 pages, 4 figure

Capacidad antioxidante y perfil de ácidos grasos de Centaurea kotschyi (Boiss. & Heldr.) Hayek var. persica (Boiss.) Wagenitz de Turquía

The antioxidant capacity of the methanolic extract and the fatty acid composition of C. kotschyi var. persica were investigated. Six different chemical methods were used to determine the antioxidant capacity. The fatty acid composition was analyzed using gas chromatography. The IC50 value of the extract was determined as 37.09 μg/ml (in the DPPH assay). In the β-carotene/linoleic acid system, the extract exhibited 65.22% inhibition against linoleic acid oxidation. The amount of total phenolic content and total antioxidant capacity were detected as 36.52 mg gallic acid equivalent (GAE)/g and 74.93 mg ascorbic acid equivalent (AE)/g, respectively. The major fatty acid in the composition of C. kotschyi var. persica was found to be C 18:3 ω3 (α-linolenic acid) by GC analysis. The results presented here indicate that C. kotschyi var. persica possess strong antioxidant properties. Therefore, the species can be used as a natural additive in food, cosmetic and pharmaceutical industries.La capacidad antioxidante de extractos metanólicos y composición de ácidos grasos de C. kotschyi var. pérsica fueron investigados. Seis métodos químicos diferentes fueron realizados para la determinación de la capacidad antioxidante. La composición de ácidos grasos fue analizada por cromatografía de gases. Los valores de IC50 de los extractos fueron 37.09 μg/ml (en el ensayo con DPPH). En el sistema β-carotene/ácido linoleico, el extracto mostró un 65.22% de inhibición frente a la oxidación del ácido linoleico. La cantidad total de contenido fenólico y capacidad antioxidante total fueron 36.52 mg equivalentes de ácido gallico (GAE)/g y 74.93 mg equivalentes de ácido ascórbico (AE)/g, respectivamente. El principal ácidos graso encontrado, por análisis de CG, en C. kotschyi var. pérsica fue el C 18:3 ω3 (ácido α-linolenico). Los resultados presentados aquí indican que C. kotschyi var. pérsica posee unas fuertes propiedades antioxidantes. Además, las especies pueden ser usadas como aditivos naturales en los alimentos, en cosmética y en industria farmacéutica

Effects of Piperonyl Butoxide and Tetramethrin Combinations on Biological Activities of Selected Synthetic Pyrethroid Insecticides against Different Housefly (Musca domestica L., Diptera: Muscidae) Populations

Piperonyl butoxide (PBO), a methylenedioxyphenyl compound, is primarily used as a synergist in combination with space spray, residual and admixture products for the control of insect pests in or around domestic and commercial premises, especially food preparation areas. Also, tetramethrin is known as a knockdown agent on target organism and it is generally used with piperonyl butoxide. In this study, effects of piperonyl butoxide and tetramethrin combinations on biological activities of synthetic pyrethroids, cypermethrin, deltamethrin, and permethrin against different housefly (Musca domestica Linnaeus, 1758) populations were evaluated. In addition, the biological efficiency of the insecticides used in the study, insecticide + PBO and insecticide + PBO + tetramethrin combinations, against the WHO standard sensitive housefly population and housefly populations collected from different parts of Turkey were compared. Results showed that PBO extensively promoted the ratio of knockdown and killing effect values of the insecticides. The results also indicated that PBO and PBO + tetramethrin combinations moderately reduced the knockdown effect times of all formulation in all housefly populations. The knockdown effect times were more decreased by insecticide + PBO + tetramethrin combinations than insecticides that are used alone and insecticide + PBO combinations

Coherent Quantum Optical Control with Subwavelength Resolution

We suggest a new method for quantum optical control with nanoscale resolution. Our method allows for coherent far-field manipulation of individual quantum systems with spatial selectivity that is not limited by the wavelength of radiation and can, in principle, approach a few nanometers. The selectivity is enabled by the nonlinear atomic response, under the conditions of Electromagnetically Induced Transparency, to a control beam with intensity vanishing at a certain location. Practical performance of this technique and its potential applications to quantum information science with cold atoms, ions, and solid-state qubits are discussed.Comment: 4 pages, 2 figures. V2: changes in presentation (text, figures, tables) and new references - final version as published in Phys. Rev. Lett

A hybrid reconstruction algorithm for computerized ionospheric tomography

Computerized Ionospheric Tomography (CIT) is a method to reconstruct ionospheric electron density images by using the Global Positioning System data collected by the earth based receivers. In this study, Total Electron Content values obtained from a model based ionosphere and tomographic reconstruction techniques are used together to obtain ionospheric electron density distribution. Algebraic Reconstruction Technique (ART) is one of the most commonly used reconstruction method in medical tomography due to its simplicity in implementation. The performance of ART is independent of basis functions and very sensitive to the initial state. Total Least Squares (TLS) algorithm assumes no regularization and produces the lowest error for Haar basis for a given Latitude interval. The performance of TLS is improved with the number of receivers. If only one receiver is used, TLS algorithm together with Haar basis functions produces a low computational complexity and has a lower reconstruction error compared to Regularized Least Squares Algorithm, When the estimation by TLS is input as the initial state of ART, the overall reconstruction error reduces significantly compared to the reconstruction error of ART only or TLS with Haar basis only. © 2005 IEEE

Algorithms and basis functions in tomographic reconstruction of ionospheric electron density

Computerized ionospheric tomography (CIT) is a method to investigate ionosphere electron density in two or three dimensions. This method provides a flexible tool for studying ionosphere. Earth based receivers record signals transmitted from the GPS satellites and the computed pseudorange and phase values are used to calculate Total Electron Content (TEC). Computed TEC data and the tomographic reconstruction algorithms are used together to obtain tomographic images of electron density. In this study, a set of basis functions and reconstruction algorithms are used to investigate best fitting two dimensional tomographic images of ionosphere electron density in height and latitude for one satellite and one receiver pair. Results are compared to IRI-95 ionosphere model and both receiver and model errors are neglected

Disks Surviving the Radiation Pressure of Radio Pulsars

The radiation pressure of a radio pulsar does not necessarily disrupt a surrounding disk. The position of the inner radius of a thin disk around a neutron star can be estimated by comparing the electromagnetic energy density generated by the neutron star with the kinetic energy density of the disk. Inside the light cylinder, the near zone electromagnetic field is essentially the dipole magnetic field, and the inner radius is the conventional Alfven radius. Far outside the light cylinder, in the radiation zone, $E=B$ and the electromagnetic energy density is $/c \propto 1/r^2$ where $S$ is the Poynting vector. Shvartsman (1970) argued that a stable equilibrium can not be found in the radiative zone because the electromagnetic energy density dominates over the kinetic energy density, with the relative strength of the electromagnetic stresses increasing with radius. In order to check whether this is true also near the light cylinder, we employ global electromagnetic field solutions for rotating oblique magnetic dipoles (Deutsch 1955). Near the light cylinder the electromagnetic energy density increases steeply enough with decreasing $r$ to balance the kinetic energy density at a stable equilibrium. The transition from the near zone to the radiation zone is broad. The radiation pressure of the pulsar can not disrupt the disk for values of the inner radius up to about twice the light cylinder radius if the rotation axis and the magnetic axis are orthogonal. This allowed range beyond the light cylinder extends much further for small inclination angles. We discuss implications of this result for accretion driven millisecond pulsars and young neutron stars with fallback disks.Comment: Accepted by Astrophysical Journal, final version with a minor correctio