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Wavelength Shift (wavelength + shift)

Distribution by Scientific Domains
Physics and Astronomy28%

Selected Abstracts

Porous Silicon-Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and Specificity

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2010
Anne M. Ruminski
Abstract Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub-millimeter porous silicon-based sensor elements is demonstrated in the concentration range 50,800 ppm. The sensor elements are prepared as one-dimensional photonic crystals (rugate filters) by programmed electrochemical etch of p++ silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane-modified materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fibers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifications display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fiber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full-scale activated carbon respirator cartridge simulator is demonstrated. [source]

Desensitizing models using covariance matrix transforms or counter-balanced distortions

JOURNAL OF CHEMOMETRICS, Issue 4 2005
Rocco DiFoggio
Abstract This paper presents a generalization of the Lagrange multiplier equation for a regression subject to constraints. It introduces two methods for desensitizing models to anticipated spectral artifacts such as baseline variations, wavelength shift, or trace contaminants. For models derived from a covariance matrix such as multiple linear regression (MLR) and principal components regression (PCR) models, the first method shows how a covariance matrix can be desensitized to an artifact spectrum, v, by adding ,2v,,,v to it. For models not derived from a covariance matrix, such as partial least squares (PLS) or neural network (NN) models, the second method shows how distorted copies of the original spectra can be prepared in a counter-balanced manner to achieve desensitization. Unlike earlier methods that added random distortions to spectra, these new methods never introduce any accidental correlations between the added distortions and the Y -block. The degree of desensitization is controlled by a parameter, ,, for each artifact from zero (no desensitization) to infinity (complete desensitization, which is the Lagrange multiplier limit). Unlike Lagrange multipliers, these methods permit partial desensitization so we can individually vary the degree of desensitization to each artifact, which is important when desensitization to one artifact inhibits desensitization to another. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A simple method for simultaneous measurement of the tilt angle and temperature

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2007
Jinhua Yan
Abstract A simple and compact sensor for simultaneous measurement of the tilt angle and temperature is presented. The sensor is composed of a fiber taper and a fiber Bragg grating. The tilt angle is measured by monitoring the tilt-induced loss of the taper. The grating is used for enhancing the tilt angle sensitivity as well as monitoring the wavelength shift induced by the temperature variation. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2248,2250, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22701 [source]

Perturbation analysis of fiber surface plasma resonance sensor

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2006
F. G. Sun
Abstract Perturbation method is used to calculate the resonance wavelength shift and the sensitivity of fiber surface plasma resonance sensor. We show that the resonance wavelength always shifts to long wavelength direction as the sensed medium dielectric index increases. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2425,2427, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21956 [source]

An optimized H, index for disentangling stellar population ages

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
J. L. Cervantes
ABSTRACT We have defined a new H, absorption index definition, H,o, which has been optimized as an age indicator for old and intermediate age stellar populations. Rather than using stellar spectra, we employed for this purpose a library of stellar population spectral energy distributions of different ages and metallicities at moderately high resolution. H,o provides us with improved abilities for lifting the age,metallicity degeneracy affecting the standard H, Lick index definition. The new index, which has also been optimized against photon noise and velocity dispersion, is fully characterized with wavelength shift, spectrum shape, dust extinction and [,/Fe] abundance ratio effects. H,o requires spectra of similar qualities as those commonly used for measuring the standard H, Lick index definition. Aiming at illustrating the use and capabilities of H,o as an age indicator we apply it to Milky Way globular clusters and to a well selected sample of early-type galaxies covering a wide range in mass. The results shown here are particularly useful for applying this index and understand the involved uncertainties. [source]

High-fidelity spectroscopy at the highest resolutions

ASTRONOMISCHE NACHRICHTEN, Issue 5 2010
D. Dravins
Abstract High-fidelity spectroscopy presents challenges for both observations and in designing instruments. High-resolution and high-accuracy spectra are required for verifying hydrodynamic stellar atmospheres and for resolving intergalactic absorption-line structures in quasars. Even with great photon fluxes from large telescopes with matching spectrometers, precise measurements of line profiles and wavelength positions encounter various physical, observational, and instrumental limits. The analysis may be limited by astrophysical and telluric blends, lack of suitable lines, imprecise laboratory wavelengths, or instrumental imperfections. To some extent, such limits can be pushed by forming averages over many similar spectral lines, thus averaging away small random blends and wavelength errors. In situations where theoretical predictions of lineshapes and shifts can be accurately made (e.g., hydrodynamic models of solar-type stars), the consistency between noisy observations and theoretical predictions may be verified; however this is not feasible for, e.g., the complex of intergalactic metal lines in spectra of distant quasars, where the primary data must come from observations. To more fully resolve lineshapes and interpret wavelength shifts in stars and quasars alike, spectral resolutions on order R = 300 000 or more are required; a level that is becoming (but is not yet) available. A grand challenge remains to design efficient spectrometers with resolutions approaching R = 1 000 000 for the forthcoming generation of extremely large telescopes (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Synthesis and Evaluation of Dual Wavelength Fluorescent Benzo[b]thiophene Boronic Acid Derivatives for Sugar Sensing

CHEMICAL BIOLOGY & DRUG DESIGN, Issue 4 2007
Senol Akay
Cell surface glycoproteins have been known to play very important roles in various physiologic and pathologic processes. Small molecule compounds capable of carbohydrate recognition can be very useful for the development of sensing, diagnostic, and therapeutic agents. Along this line, we are interested in developing water-soluble fluorescent boronic acid compounds for carbohydrate recognition. As such, a series of benzo[b]thiophene boronic acid derivatives have been synthesized and their fluorescent properties analyzed at physiologic pH. Benzo[b]thiophene derivatives were found to be a new type of fluorescent reporter compounds capable of dual fluorescent emission under physiologic pH conditions. Compounds 1, 3, 4, 5, and 6 showed unusual emission wavelength shifts upon binding of sugars. These boronic acids will be useful tools for building glycoprotein biosensors for biologic applications. [source]