Absolute Extinction Research Articles

Imaging and Absolute Extinction Cross-Section Measurements of Nanorods and Nanowires through Polarization Modulation Microscopy

This paper describes an experimental technique for measuring the extinction cross-section of anisotropic nanomaterials. The experiments are performed by focusing a laser beam to a diffraction-limited spot under an optical microscope, and using a photoelastic modulator (PEM) to rotate the polarization of the light beam. Monitoring the transmitted beam with a lock-in amplifier referenced to twice the resonant frequency of the PEM yields the difference in extinction for light polarized parallel and perpendicular to the optical axis of the nanostructure. These experiments are the single particle analog of polarization modulation microscopy (PMM). Experimental results for gold nanorods and CdSe nanowires are presented that demonstrate the sensitivity and properties of this technique. In particular, we show that by collecting images at two laser polarizations separated by 45° it is possible to construct an extinction cross-section image. The advantages and disadvantages of the PMM technique compared to existing ways of measuring the extinction of nanoparticles (photothermal heterodyne imaging and spatial modulation spectroscopy) are discussed. Results from experiments where we collected simultaneous absorption and emission images are also presented for different shaped CdSe nanowires. These measurements provide insight into how the structure of the nanowire affects its photophysics.

Absolute optical extinction measurements of single nano-objects by spatial modulation spectroscopy using a white lamp

This article describes a high sensitivity spectrophotometer designed to detect the overall extinction of light by a single nanoparticle (NP) in the 10(-4)-10(-5) relative range, using a transmission measurement configuration. We focus here on the simple and low cost scheme where a white lamp is used as a light source, permitting easy and broadband extinction measurements (300-900 nm). Using a microscope, in a confocal geometry, an increased sensitivity is reached thanks to a modulation of the NP position under the light spot combined with lock-in detection. Moreover, it is shown that this technique gives access to the absolute extinction cross-sections of the single NP provided that the incident electromagnetic field distribution experienced by the NP is accurately characterized. In this respect, an experimental procedure to characterize the light spot profile in the focal plane, using a reference NP as a probe, is also laid out. The validity of this approach is discussed and confirmed by comparing experimental intensity distributions to theoretical calculations taking into account the vector character of the tightly focused beam. The calibration procedure permitting to obtain the absolute extinction cross-section of the probed NP is then fully described. Finally, the force of the present technique is illustrated through selected examples concerning spherical and slightly elongated gold and silver NPs. Absolute extinction measurements are found to be in good consistency with the NP size and shape independently obtained from transmission electron microscopy, showing that spatial modulation spectroscopy is a powerful tool to get an optical fingerprint of the NP.

Peering through the veil: near-infrared photometry and extinction for the Galactic nuclear star cluster

Context. The nuclear star cluster of the Galaxy is an important template for understanding its extragalactic counterparts, which can currently not be resolved into individual stars. Important drawbacks of observations of the Galactic center are, however, the presence of strong and spatially highly variable interstellar extinction and extreme crowding of the sources, which makes the use of adaptive optics techniques necessary. Both points pose serious obstacles to precise photometry that is needed for analyzing the stellar population.Aims. The aims of this work are to provide accurate photometry in multiple near-infrared broadband filters, to determine the power-law index of the extinction-law toward the central parsec of the Galaxy, to provide measurements of the absolute extinction toward the Galactic center, and finally to measure the spatial variability of extinction on arcsecond scales.Methods. We use observations of the central parsec of the Milky Way that were obtained with the near-infrared camera and adaptive optics system NAOS/CONICA at the ESO VLT unit telescope 4. The photometric method takes into account anisoplanatic effects and limits the corresponding systematic uncertainties to ≲ 2%. Absolute values for the extinction in the H , , and L' -bands as well as of the power-law indices of the H to and to L' extinction-laws are measured based on the well-known properties of red clump stars. Extinction maps are derived based on and colors.Results. We present -band photometry for ~7700 stars, and additionally photometry for stars detected in the H and/or L' -bands. From a number of recently published values we compute a mean distance of the Galactic center of kpc, which has an uncertainty of just . Based on this and on the RC method, we derive absolute mean extinction values toward the central parsec of the Galaxy of mag, mag, and mag. We estimate values of the power-law indices of the extinction-law of and . A -band extinction map for the Galactic center is computed based on this extinction law and on stellar colors. Both its statistical and systematic uncertainties are estimated to be 10%. Extinction in this map derived from stellar color excesses is found to vary on arcsecond scales, with a mean value of mag. Mean extinction values in a circular region with 0.5'' radius centered on Sagittarius A* are , , and .

Fourier transform infrared spectroscopy of 1-cyclohexyluracil aggregates in CDCl3 solutions

We reinvestigated the self-aggregation of 1-cyclohexyluracil (1CHU) in CDCl(3) solutions. Wavelength dependent absolute extinction coefficients of the monomer and of dimers are presented on the basis of a simple deconvolution method. Two isomeric dimer structures coexist in a solution with similar abundance. Our results are supported by RI-B3LYP/TZVP calculations within the conductorlike screening model framework to account for solvent effects in the ab initio calculations.

Surface Plasmon Resonance of Single Gold Nanodimers near the Conductive Contact Limit

We have studied the spectral response of individual pairs of gold nanoparticles chemically synthesized and stabilized on a transparent thin film. Very thin interspacing distances are explored by taking advantage of a residual layer of surfactant molecules at the metal surface. Absolute extinction cross section measurements by the spatial modulation spectroscopy technique are correlated to the corresponding high magnification images independently obtained from transmission electron microscopy. The signature of a transition from isolated to conductively coupled particles is evidenced in the optical spectra and is discussed in relation with their morphology. The strength of the electromagnetic coupling is controlled not only by their spacing but also by the shape of their opposite surfaces in the gap region.

The complex, variable near-infrared extinction towards the Nuclear Bulge

Using deep J-, H- and K S -band observations, we have studied the near-infrared extinction of the Nuclear Bulge, and find significant, complex variations on small physical scales. We have applied a new variable near-infrared colour excess (V-NICE) method to measure the extinction; this method allows for variation in both the extinction law parameter a and the degree of absolute extinction on very small physical scales. We see significant variation in both these parameters on scales of 5 arcsec. In our observed fields, representing a random sample of sight lines to the Nuclear Bulge, we measure a to be 2.64 ± 0.52, compared to the canonical 'universal' value of 2. Our measured levels of A KS are similar to previously measured results (1 ≤ A KS ≤ 4.5); however, the steeper extinction law results in higher values for A J (4.5 ≤ A J ≤ 10) and A H (1.5 ≤ A H ≤ 6.5). Only when the extinction law is allowed to vary on the smallest scales can we recover self-consistent measures of the absolute extinction at each wavelength, allowing accurate reddening corrections for field star photometry in the Nuclear Bulge. The steeper extinction law slope also suggests that previous conversions of near-infrared extinction to A V may need to be reconsidered. Finally, we find that the measured values of extinction are significantly dependent on the filter transmission functions of the instrument used to obtain the data. This effect must be taken into account when combining or comparing data from different instruments.

Absolute extinction cross-section of individual magnetic split-ring resonators

We measure the absolute extinction cross section spectra of individual split-ring resonators (fundamental magnetic resonance at 1.4-mum wavelength). The experiments are compared with a simple electric-circuit model and with microscopic calculations.

Structural assignment of adenine aggregates in CDCl3

We reinvestigated the self-association of 9-substituted adenine derivatives in CDCl3 solutions and present the infrared spectra of 9-ethyladenine and N-methyl-9-ethyladenine and its aggregates in the spectral regions between 1500 and 1800 cm(-1) and between 2700 and 3600 cm(-1). Wavelength dependent absolute extinction coefficients of the monomer and dimers are presented on the basis of a simple deconvolution method. Comparison of the deconvoluted dimer spectra with quantum chemical calculations allows for a structural assignment of the two dimer structures that coexist in 9-ethyladenine/CDCl3 solutions. In contrast, the dimer spectrum of N-methyl-9-ethyladenine is dominated by a single isomer.

Correlation between the Extinction Spectrum of a Single Metal Nanoparticle and Its Electron Microscopy Image

The absolute extinction cross-section spectrum of a single nanoparticle measured using spatial modulation spectroscopy (SMS) is correlated with its transmission electron microscopy (TEM) image. The sizes of quasi-spherical particles obtained by the two methods are found to be in good quantitative agreement. The possibilities opened up by combination of these methods for precise correlation of the optical response of a nanoobject with its geometry are illustrated in the case of a pair of interacting nanoparticles (dimer).

Spectroscopic and photometric observations of selected Algol-type binaries – I. V1665 Aquilae and AG Arietis

We present the first radial velocities and ground-based photometric observations of V1665 Aql and AG Ari. These double-lined eclipsing binaries have eccentric orbits with eccentricities of 0.24 and 0.09, respectively. New UBV photometric data and radial velocities were analysed using a modified version of the Wilson-Devinney program for the parameters of the systems. Good phase coverage and relatively small scatter both in the light and in the radial-velocity curves meant that the eccentricity and the argument of periastron as well as orbital and stellar parameters could be determined. Our solutions indicate that AG Ari includes a third light with a considerable amount of 5.6 per cent in U, 6.4 per cent in B, and 9 per cent in V. By comparing its light contribution with the total light we classified it as an F-type star. The components in each system are of very nearly equal mass, temperature, and luminosity. Their absolute parameters were compared with those of stars belonging to well-studied detached eclipsing binaries. The components lie well inside the main-sequence band. In addition, the apsidal motion rates of the system have been determined from an analysis of all the photometric observations obtained by space missions and by us. We determined the preliminary apsidal motion periods of the systems to be 449 ± 34 yr for V1665 Aql and 155 ± 6 yr for AG Ari. Because well-detached eclipsing binaries are optimal distance indicators, we estimated the distances to V1665 Aql and AG Ari to be 477 ± 40 and 292 ± 18 pc from the determined absolute visual magnitudes and interstellar extinction. A comparison with evolutionary tracks indicates that the primary component of V1665 Aql has an age of about 1.6 x 10 8 yr and is near the main-sequence terminal age. The components of AG Ari are intermediate-mass main-sequence stars with an age of about 5.6 × 10 8 yr.

In situ infrared aerosol spectroscopy for a variety of nerve agent simulants using flow-through photoacoustics

We present newly measured results of an ongoing experimental program established to measure optical cross sections in the mid- and long-wave infrared for a variety of chemically and biologically based aerosols. For this study we consider only chemically derived aerosols, and in particular, a group of chemical compounds often used as simulants for the detection of extremely toxic organophosphorus nerve agents. These materials include: diethyl methylphosphonate (DEMP), dimethyl methylphosphonate (DMMP), diisopropyl methylphosphonate (DIMP), and diethyl phthalate (DEP). As reported in a prior study [Appl. Opt. 44, 4001 (2005)], we combine two optical techniques well suited for aerosol spectroscopy [i.e., flow-through photoacoustics and Fourier transform infrared (FTIR) emission spectroscopy], to measure in situ the absolute extinction and absorption cross sections over a variety of wavelengths spanning the IR spectral region from 3 to 13 mum. Aerosol size distribution(s), particle number density, and dosimetric measurements are recorded simultaneously in order to present optical cross sections that are aerosol mass normalized, i.e., m(2)/gram. Photoacoustic results, conducted at a series of CO(2) laser lines, compare well with measured broadband FTIR spectral extinction. Both FTIR and photoacoustic data also compare well with Mie theory calculations based on measured size distributions and previously published complex indices of refraction.

High-resolution discrete absorption spectrum of α-methallyl free radical in the vapor phase

The α-methallyl free radical is formed in the flash photolysis of 3-methylbut-1-ene, and cis-pent-2-ene in the vapor phase, and then subsequent reactions have been investigated by kinetic spectroscopy and gas–liquid chromatography. The photolysis flash was of short duration and it was possible to follow the kinetics of the radicals’ decay, which occurred predominantly by bimolecular recombination. The measured rate constant for the α-methallyl recombination was (3.5 ± 0.3) × 10 10 mol −1 l s −1 at 295 ± 2 K. The absolute extinction coefficients of the α-methallyl radical are calculated from the optical densities of the absorption bands. Detailed analysis of related absorption bands and lifetime measurements in the original α-methallyl high-resolution discrete absorption spectrum image were also carried out by image processing techniques.

Extinction Coefficients and Purity of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) hold great promise for advanced applications in aerospace, electronics and medicine, yet these industries require materials with rigorous quality control. There are currently no accepted standards for quality assurance or quality control among the commercial suppliers of SWNTs. We briefly discuss the applicability of various techniques to measure SWNT purity and review, in detail, the advantages of near infrared (NIR) spectroscopy for the quantitative assessment of the bulk carbonaceous purity of SWNTs. We review the use of solution phase NIR spectroscopy for the analysis and characterization of a variety of carbon materials, emphasizing SWNTs produced by the electric arc (EA), laser oven (LO) and HiPco (HC) methods. We consider the applicability of Beer's law to carbon materials dispersed in dimethylformamide (DMF) and the effective extinction coefficients that are obtained from such dispersions. Analysis of the areal absorptivities of the second interband transition of semiconducting EA-produced SWNTs for a number of samples of differing purities has lead to an absolute molar extinction coefficient for the carbonaceous impurities in EA-produced SWNT samples. We conclude that NIR spectroscopy is the clear method of choice for the assessment of the bulk carbonaceous purity of EA-produced SWNTs, and we suggest that an absolute determination of the purity of SWNTs is within reach. Continued work in this area is expected to lead to a universal method for the assessment of the absolute bulk purity of SWNTs from all sources--such a development will be of great importance for nanotube science and for future customers for this product.

Study of the Extinction Coefficients of Single-Walled Carbon Nanotubes and Related Carbon Materials

The measurement of the bulk purity of single-walled carbon nanotubes (SWNTs) is an important outstanding problem. We report a solution-phase near-IR (NIR) spectroscopic study of a range of carbon materials with an emphasis on SWNTs, and we show that NIR spectroscopy is an extremely powerful tool in the assessment of the carbonaceous purity of SWNTs. We demonstrate the applicability of Beer's law for all of the carbon materials included in this study within a range of concentrations in dimethylformamide (DMF), and we are able to solve for the effective extinction coefficients. By analyzing the areal absorptivities of the second interband transition of semiconducting SWNTs for a number of samples of differing purities, we are able to derive an absolute molar extinction coefficient for the carbonaceous impurities in SWNT samples. We demonstrate significant progress toward the establishment of an absolute scale for the bulk carbonaceous purity of SWNTs.

Current Issues of Religious Studies in Ukraine

In our literature, following Professor D. Ugrinovich, it is still customary to divide religious studies into theoretical and historical ones. It even found its name in the name of some religious departments, institutes. We will not discuss here the issue of the legitimacy of such a division. To me, the philosophy of religion is one of the disciplinary entities of religious studies, as is the history of religion. The main specificity of religious studies (as opposed to the study of religious phenomena by individual sciences) is that it studies religion not as a whole, but as a whole, in the organic totality of all its components and functions. Religion appears to him not as a static phenomenon, but as a dynamic phenomenon. The subject of religious studies is a functioning religion, and this functioning occurs through the interaction and interplay of all its components, and not with the absolute extinction of something in it in the change of historical eras, because religion has a prehistoric meaning.

The T 1←S 0 Absorption Spectrum of Gaseous 4H-Pyran-4-thione

The T 1←S 0 absorption spectrum of 4H-pyran-4-thione (PT) was measured in a static cell at room temperature (550–620 nm) and in a seeded cold supersonic jet (580–600 nm) using the cavity ring-down (CRD) method. In the static cell absolute extinction coefficients were determined between 573 and 610 nm with an accuracy of ∼±5%. In this region 22 harmonic sequences and 18 hot bands were observed. The energetically lowest ground state vibration at 167.5 cm −1 was identified as the promoting mode in the static PT gas. The mode in the triplet state was found at 152.3 cm −1. The CRD absorption spectra of static PT gas and jet-cooled PT are compared with the phosphorescence excitation spectrum of isolated PT. The weak S 1, 0←S 0, 0 absorption was tentatively assigned to a transition at ∼17433 cm −1.

High resolution electronic absorption spectra of anisole and phenoxyl radical

High resolution absorption spectra of anisole and phenoxyl radical has been recorded in the vapor phase at room temperature by flash photolysis technique, and subsequent reactions have been investigated by kinetic spectroscopy. It was possible to follow the kinetics of the radical's decay which occurred predominantly by bimolecular recombination. The concentration of the phenoxyl radical calculated from the concentration of diphenoxyl molecules formed in the reaction cell during the optical pumping. The absolute extinction coefficient of this radical was measured from the absorption band at 291 nm, and found to be 0.95×10 +4 mol −1 l cm −l.

Does Revelation 14:11 Teach Eternal Torment? Examining a Proof-text on Hell

This article examines a text (Rev. 14: 11) that is usually cited to support the doctrine of hell as eternal torment. A new exegetical interpretation of Revelation 14: 11 is proposed, suggesting that the traditional reading of the elements of this verse misses the inverted parallelistic structure of the unit Revelation 14:9-11. When the chiasm is discerned, the meaning of the text is seen to give no confirmation to ‘eternal torment’. Rather, this text fits well into the Conditional Immortality interpretation. This view holds that God will finally and fully bring his enemies to judgement, with absolute destruction and extinction as the result. This text is also discussed in the context of the Revelation to John, and the general teaching of the New Testament on the destiny of the unsaved. Some concluding comments of the function of interpretative doctrinal grids are offered.

Determination of RV towards galactic O stars

We present new measurements of the interstellar reddening parameter towards 35 O stars. The results are combined with measurements from the literature for 60 stars to study the behaviour of R V with heliocentric distance. R V is the single basic parameter which characterizes the interstellar extinction from the near-infrared to the far-UV spectral region. The absolute extinction A V , from which R V is derived, is best determined by optical and near-infrared photometry (Cardelli et al. [CITE]). We consider important the derivation of R V with the same technique in the direction of as many as possible galactic O stars.

Estimating the Effect on Soil Organisms of Exceeding No-Observed Effect Concentrations (NOECs) of Persistent Toxicants

In estimating the effects of toxic substances on ecosystems we generally lack information on the sensitivity (expressed as a no-observed effect concentration, NOEC) of individual species in the field, and have to rely on information from laboratory test species, expressed as a frequency distribution of NOECs. In this case we can express toxic stress as the fraction of organisms that is exposed above its NOEC: the potentially affected fraction (PAF). This paper describes a model of the soil food web and the effect of toxic stress by persistent pollutants. The model predicts that in the absence of competition, individual species disappear from the foodweb at toxic concentrations 3–5 times their NOEC. With competition present, species affected by toxic stress are replaced by less sensitive ones. This has a twofold effect: species disappear from the foodweb at a lower concentration because loss of competitiveness occurs well before absolute extinction, but the replacement of disappearing species implies that the effect on total biomass and diversity becomes only noticeable at a PAF level near 100%. Model predictions are in good agreement with observations on nematode communities in experimental fields contaminated with copper and zinc. The model serves to illustrate why overall measures of ecosystem functioning (total biomass, production, diversity) are affected by toxic stress only at high levels of pollution, which is particularly true for systems with a high diversity. This apparent robustness masks a considerable genetic ‘erosion’, i.e. the disappearance of sensitive species or genotypes. The PAF is a good indicator of the latter effect.