Pure Absorption Research Articles

Ozone absorption in raw waters

The ozone absorption in raw water entering the main ozonization step at the Belgrade drinking water supply plant was investigated in a continuous stirred tank reactor (CSTR). A slow chemical reaction rate of dissolved ozone and pollutants present in raw water have been experimentally determined. The modified Hatta number was defined and calculated as a criterion which determines whether and to which extent the reactions of ozone and pollutants influence the rate of the pure physical ozone absorption.

Resolution of near-infrared spectral data from distillation of binary mixtures and calculation of band boundaries of feasible solutions for species profiles

In this work, mean centering, ordinary and incomplete rank annihilation based methods were applied to estimate concentration profiles (g/mL) and pure spectra of components from an evolutionary near infrared spectral data for successive condensates from distillation process of binary mixtures. Constraints such as non-negativity, selectivity of some spectral regions and density of condensates were applied during the resolution of some series of data. Fixed size moving window evolving factor analysis (FSMWEFA) and orthogonal projection analysis (OPA) were the applied chemometrics methods for assigning the selective regions. No pure spectrum from any of components or calibration samples was necessary for performing the analysis. Three binary mixtures containing toluene:n-hexane, toluene:cyclohexene and toluene:ethanol were investigated using the proposed method. Band boundaries of feasible solutions for pure absorption spectra and species concentration profiles for the mixture of components were successfully estimated in presence of high spectral overlap. In the first case the solution was unique, but in the second and third distillations a number of acceptable solutions were obtained as band boundaries.

Post-processing of EPR spectra by convolution filtering: Calculation of a harmonics’ series and automatic separation of fast-motion components from spin-label EPR spectra

This communication reports on post-processing of continuous wave EPR spectra by a digital convolution with filter functions that are subjected to differentiation or the Kramers–Krönig transform analytically. In case of differentiation, such a procedure improves spectral resolution in the higher harmonics enhancing the relative amplitude of sharp spectral features over the broad lines. At the same time high-frequency noise is suppressed through filtering. These features are illustrated on an example of a Lorentzian filter function that has a principal advantage of adding a known magnitude of homogeneous broadening to the spectral shapes. Such spectral distortion could be easily and accurately accounted for in the consequent least-squares data modeling. Application examples include calculation of higher harmonics from pure absorption echo-detected EPR spectra and resolving small hyperfine coupling that are unnoticeable in conventional first derivative EPR spectra. Another example involves speedy and automatic separation of fast and broad slow-motion components from spin-label EPR spectra without explicit simulation of the slow motion spectrum. The method is illustrated on examples of X-band EPR spectra of partially aggregated membrane peptides.

Dynamic Molecular Structure and Phase Diagram of DPPC−Cholesterol Binary Mixtures: A 2D-ELDOR Study

This paper is an application of 2D electron-electron double resonance (2D-ELDOR) with the "full Sc- method" to study model membranes. We obtain and confirm the phase diagram of 1,2-dipalmitoyl-sn-glycerophosphatidylcholine (DPPC)-cholesterol binary mixtures versus temperature and provide quantitative descriptions for its dynamic molecular structure using 2D-ELDOR at the Ku band. The spectra from the end-chain 16-PC spin label in multilamellar phospholipid vesicles are obtained for cholesterol molar concentrations ranging from 0 to 50% and from 25 to 60 degrees C. This phase diagram consists of liquid-ordered, liquid-disordered, and gel phases and phase coexistence regions. The phase diagram is carefully examined according to the spectroscopic evidence, and the rigorous interpretation for the line shape changes. We show that the 2D-ELDOR spectra differ markedly with variation in the composition. The extensive line shape changes in the 2D-plus-mixing-time representation provide useful information to define and characterize the membrane phases with respect to their dynamic molecular structures and to determine the phase boundaries. The homogeneous T2's are extracted from the pure absorption spectra and are used to further distinguish the membrane phases. These results show 2D-ELDOR to be naturally suitable for probing and reporting the dynamic structures of microdomains in model membrane systems and, moreover, providing a very detailed picture of their molecular dynamic structure, especially with the aid of the "full Sc- method".

Three-Photon Absorption Cross-Section Enhancement in Two Symmetrical Fluorene-Based Molecules

In this article, we report the pure three-photon absorption effects of two novel symmetrical fluorene-based molecules with 2D-pi-2D [9,9-diethylhexyl-2,7-bis-(N,N-diphenylamine)fluorene] and 2D-D-pi-D-2D [5,5'-(9,9-bis-(2-ethylhexyl)-9H-fluorene-2-yl)bis(N,N-diphenylthiophen-2-amine)] structural motifs. The obtained three-photon absorption cross sections, (4.74 +/- 0.01) x 10(-76) and (6.77 +/- 0.02) x 10(-76) cm(6) s(2) for the 2D-pi-2D and 2D-D-pi-D-2D archetypes, respectively, are rather high. The geometries and electronic excitations of the two molecules were systematically studied by the PM3 and ZINDO/S methods. The influence of the different molecular structures on the three-photon absorption cross section is discussed micromechanically. The experimental and theoretical results demonstrate that the transition dipole moment between the ground and final states is the most definitive factor. A new fitting method that is more accurate than those reported previously was used to obtain the 3PA coefficient.

Spin Resonance Absorption in a 2D Electron Gas

We analyze the power absorption at electron spin resonance excited by the Bychkov{Rashba spin{orbit fleld in a 2D electron gas. We show that, as long as the absorbed power is dissipated by the usual spin lattice relaxation mechanisms, the resonance line shape is expected to be of pure absorption type, i.e., it can be described by the imaginary part of the dynamic magnetic susceptibility. Therefore, the Dysonian line shape observed in ESR of 2D electron gas cannot result from this type of the resonance signal.

Precision measurements with polar molecules: the role of the black body radiation

In the perspective of the outstanding developments of high-precision measurements of fundamental constants using polar molecules related to ultimate checks of fundamental theories, we investigate the possibly counterproductive role of black-body radiation on a series of diatomic molecules which would be trapped and observed for long durations. We show that the absorption of black-body radiation at room temperature may indeed limit the lifetime of trapped molecules prepared in a well-defined quantum state. Several examples are treated, corresponding to pure rotational absorption, pure vibrational absorption or both. We also investigate the role of a black-body radiation-induced energy shift on molecular levels and how it could affect high-precision frequency measurements.

Biselective refocusing pulses and the SERF experiment

The SERF experiment is a variant of the homonuclear J-resolved experiment, in which a single coupling constant is measured. It consists of a single chemical shift selective excitation that is followed by a biselective spin echo. Recent articles mention the existence of artefacts in SERF spectra that are supposedly related to pulse imperfections. This article presents a detailed study of the biselective refocusing pulses. It also reports a method for predicting the position and amplitude of the expected and unexpected 2D spectral peaks in SERF spectra. Artefacts can be partially eliminated by phase cycling or by the introduction of static field gradient pulses in the acquisition sequence. A procedure to obtain of pure absorption peaks in SERF spectra is proposed.

Cascading on extragalactic background light

High-energy gamma-rays propagating in the intergalactic medium can interact with background infrared photons to produce e+e- pairs, resulting in the absorption of the intrinsic gamma-ray spectrum. TeV observations of the distant blazar 1ES 1101-232 were thus recently used to put an upper limit on the infrared extragalactic background light density. The created pairs can upscatter background photons to high energies, which in turn may pair produce, thereby initiating a cascade. The pairs diffuse on the extragalactic magnetic field (EMF) and cascade emission has been suggested as a means for measuring its intensity. Limits on the IR background and EMF are reconsidered taking into account cascade emissions. The cascade equations are solved numerically. Assuming a power-law intrinsic spectrum, the observed 100 MeV - 100 TeV spectrum is found as a function of the intrinsic spectral index and the intensity of the EMF. Cascades emit mainly at or below 100 GeV. The observed TeV spectrum appears softer than for pure absorption when cascade emission is taken into account. The upper limit on the IR photon background is found to be robust. Inversely, the intrinsic spectra needed to fit the TeV data are uncomfortably hard when cascade emission makes a significant contribution to the observed spectrum. An EMF intensity around 1e-8 nG leads to a characteristic spectral hump in the GLAST band. Higher EMF intensities divert the pairs away from the line-of-sight and the cascade contribution to the spectrum becomes negligible.

Effect of bubble contamination on gas–liquid mass transfer coefficient on CO2 absorption in amine solutions

Abstract An electrochemical method was used to follow CO 2 absorption both in water and in alkanolamine solutions in a bubble column (∼1 m tall). This method allows the determination of local mass transfer coefficients along the column. No special care was taken in avoiding trace contaminants. It was found that bubbles contaminate mostly at the gas distributor. Gas–liquid mass transfer coefficient decreases as bubbles rise along the column, taking values closer to those expected for clean bubbles with a mobile surface at the bottom of the column, and values closer to those expected for rigid bubbles, at the top of the column. If this is quantitatively interpreted within the framework of the stagnant cap model, it may be concluded that this decrease is mainly due to bubble shrinkage, which leads to a greater fraction of bubble area being covered by the stagnant cap. Compared with this effect, the effect of further acquisition of contaminant molecules by the bubbles is negligible. The above conclusions can be drawn both for absorption with chemical reaction in amine solutions and for pure absorption of CO 2 in tap water, although in this case the shrinkage effect is less pronounced.

H.E.S.S. observations of LS 5039

Recent observations of the binary system LS 5039 with the High Energy Stereoscopic System (H.E.S.S.) revealed that its Very High Energy (VHE) γ-ray emission is modulated at the 3.9 days orbital period of the system. The bulk of the emission is largely confined to half of the orbit, peaking around the inferior conjunction epoch of the compact object. The flux modulation provides the first indication of γ-ray absorption by pair production on the intense stellar photon field. This implies that the production region size must be not significantly greater than the gamma-gamma photosphere size (∼1 AU), thus excluding the large scale collimated outflows or jets (extending out to ∼1000 AU). A hardening of the spectrum is also observed at the same epoch between 0.2 and a few TeV which is unexpected under a pure absorption scenario and could rather arise from variation with phase in the maximum electron energy and/or the dominant VHE γ-ray production mechanism. This first-time observation of modulated γ-ray emission allows precise tests of the acceleration and emission models in binary systems.

Multiplicity editing including quaternary carbons: improved performance for the 13C‐DEPTQ pulse sequence

An improved version of the DEPTQ experiment yielding the signal and multiplicity information for all carbon types including the signals of quaternary carbons is proposed. It encompasses all the known advantages of the basic DEPT experiment. In comparison to the original version, signals of the sensitivity-limiting quaternary carbons are markedly increased: the initial 13C pulse may be adjusted to the Ernst angle, the NOE build-up period is prolonged by the split relaxation delay and a partial recovery of signal losses due to instrumental imperfections is achieved by the incorporation of composite adiabatic 13C refocussing pulses. Furthermore, pure absorption lineshapes for all carbon types are obtained with only one single scan. These attributes make this experiment attractive for 13C analysis of small molecules (including spectral editing), particularly in high-throughput analysis laboratories.

Lyα emission in high-redshift galaxies

Context. A significant fraction of the high-redshift galaxies show st rong Lyα emission lines. For redshifts z> 5, most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects. Aims. Our aim is to analyse the Lyα emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the Lyα profile and the line strength. Methods. VLT/FORS spectra with a resolution of R≈ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed Lyα profiles are compared with theoretical models. Results. The Lyα lines range from pure absorption (EW = -17 A) to strong emission (EW = 153 A). Most Lyα emission lines show an asymmetric profile, and three galaxies have a double-peaked profile. Both types of profiles can be explained by a uniform mo del consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region. The broad, blueshifted, low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium. We find star-formation r ates of these galaxies ranging from S FRUV = 1.2 to 63.2 M⊙yr −1 uncorrected for dust absorption. Conclusions. The Lyα emission strength of our target galaxies is found to be deter mined by the amount of dust and the kinematics of the outflowing material.

Optical properties of the “clearest” natural waters

Optical measurements within both the visible and near ultraviolet (UV) parts of the spectrum (305–750 nm) were recently made in hyperoligotrophic waters in the South Pacific gyre (near Easter Island). The diffuse attenuation coefficients for downward irradiance, Kd(λ), and the irradiance reflectances, R(λ), as derived from hyperspectral (downward and upward) irradiance measurements, exhibit very uncommon values that reflect the exceptional clarity of this huge water body. The Kd(λ) values observed in the UV domain are even below the absorption coefficients found in current literature for pure water. The R(λ) values (beneath the surface) exhibit a maximum as high as 13% around 390 nm. From these apparent optical properties, the absorption and backscattering coefficients can be inferred by inversion and compared to those of (optically) pure seawater. The total absorption coefficient (atot) exhibits a flat minimum (~ 0.007 m−1) around 410‐420 nm, about twice that of pure water. At 310 nm, atot may be as low as 0.045 m−1, i.e., half the value generally accepted for pure water. The particulate absorption is low compared to those of yellow substance and water and represents only ~15% of atot in the 305‐420‐nm domain. The backscattering coefficient is totally dominated by that of water molecules in the UV domain. Because direct laboratory determinations of pure water absorption in the UV domain are still scarce and contradictory, we determine a tentative upper bound limit for this elusive coefficient as it results from in situ measurements.

Mass transfer and hydrodynamic characteristics of a high aspect ratio self-ingesting reactor for gas–liquid operations

The mass transfer performance of a gas–liquid self-ingesting stirred reactor is reported both for coalescing and non-coalescing systems. The vessel features are a high aspect ratio and a rather narrow multiple-impeller draft tube, through which the gas phase is ingested and led down to the vessel bottom, where it is finely dispersed into the liquid rising in the annular portion of the vessel. Comparison is made between k L a values determined by several variants of the dynamic method, among which pure oxygen absorption in a previously de-gassed liquid phase. Results show that the gas–liquid mass transfer coefficient values obtained with the last approach are remarkably larger than those measured with all other techniques in which nitrogen is initially dissolved in the liquid phase. Possible reasons behind this discrepancy are discussed. The gas–liquid mass transfer performance of the investigated gas inducing contactor is finally compared with literature data on other self-inducing/ingesting devices. Comparison results encourage further development of the investigated apparatus.

Three-photon absorption of a new series of halogenated fluorene derivatives

In this Letter, we report the characterization of the pure three-photon absorption and the measurement of the three-photon absorption cross-section ( σ 3 ′ ) of a new series of halogenated fluorene derivatives. The three-photon absorption of these compounds corresponds to the S 0 → S 1 electronic transition. All four compounds presented here have potential application as photosensitizers in deep photodynamic therapy induced via high order nonlinear absorption. The measurements were done using a tunable OPG pumped by a 25 ps Nd-YAG laser, and performing transmittance vs. input intensity as well as open aperture Z-scan at different wavelengths to determine the highest value of σ 3 ′ .

Spatially varying optical and acoustic property reconstruction using finite-element-based photoacoustic tomography

A finite-element reconstruction algorithm for simultaneous reconstruction of both optical and acoustic properties of heterogeneous media is presented. The algorithm is based on the Helmholtz-like photoacoustic wave equation in the frequency domain. A dual meshing scheme is described and an adjoint sensitivity method is adopted for efficient inverse computation. The algorithm is implemented with the second-order absorbing boundary conditions and with a multireceiving and multifrequency strategy. The algorithm is evaluated using simulated data under various practical cases including different noise levels, varied range of receiving frequency, different contrast levels between the heterogeneity and background region, and multiple targets. The effect of acoustic heterogeneity on conventional pure optical absorption reconstruction is also studied.

Far-Infrared Excited Hydroxyl Lines from Orion KL Outflows

As part of the first far-IR line survey toward Orion KL, we present the detection of seven new rotationally excited OH Λ-doublets (at ~48, ~65, ~71, ~79, ~98, and ~115 μm). Observations were performed with the Long Wavelength Spectrometer Fabry-Pérot on board the Infrared Space Observatory. In total, more than 20 resolved OH rotational lines, with upper energy levels up to ~620 K, have been detected at angular and velocity resolutions of ~80'' and ~33 km s-1, respectively. The OH line profiles show a complex behavior evolving from pure absorption, P Cygni type, to pure emission. We also present a large-scale, 6' declination raster in the OH 2Π3/2 J = 5/2+-3/2- and 2Π3/2 J = 7/2--5/2+ lines (at 119.441 and 84.597 μm) revealing a decrease of excitation outside the core of the cloud. From the observed profiles, mean intrinsic line widths, and velocity offsets between emission and absorption line peaks, we conclude that most of the excited OH arises from Orion outflow(s), that is, the "plateau" spectral component. We determine an averaged OH abundance relative to H2 of χ(OH) = (0.5-1.0) × 10-6, a kinetic temperature of ≳100 K, and a density of n(H2) ≃ 5 × 105 cm-3. Even with these conditions, the OH excitation is heavily coupled with the strong dust continuum emission from the inner "hot core" regions and from the expanding flow itself.

Seaborne measurements of near infrared water-leaving reflectance: The similarity spectrum for turbid waters

Theory and seaborne measurements are presented for the near infrared (NIR: 700‐900 nm) water-leaving reflectance in turbid waters. According to theory, the shape of the NIR spectrum is determined largely by pure water absorption and is thus almost invariant. A ‘‘similarity’’ NIR reflectance spectrum is defined by normalization at 780 nm. This spectrum is calculated from seaborne reflectance measurements and is compared with that derived from laboratory water absorption measurements. Factors influencing the shape of the similarity spectrum are analyzed theoretically and by radiative transfer simulations. These simulations show that the similarity spectrum is valid for waters ranging from moderately turbid (e.g., water-leaving reflectance at 780 nm of order 10 24 or total suspended matter concentration of order 0.3 g m 23 ) to extremely turbid (e.g., reflectance at 780 nm of order 10 21 ). Measurement uncertainties are analyzed, and the air-sea interface correction is shown to be critical for low reflectances. Applications of the NIR similarity spectrum to atmospheric correction of ocean color data and to the quality control of seaborne, airborne, and spaceborne reflectance measurements in turbid waters are outlined.

Optical percolation and nonlinearity of sputtered Ag island films

The fractal dimension Df and the critical parameter nu of the sputtered percolation Ag island films are measured to be about 1.57 and 1.15, respectively. A modified Z-scan method including both transmittance Z-scan and reflection Z-scan is proposed to measure the pure nonlinear absorption of the semi-continuous Ag films near the percolation threshold. As the microstructure of the sputtered Ag films varies from the discontinuous to the continuous, the linear absorbance decreases from 0.97 to 0.58 while the nonlinear absorption coefficient changes from -1.4x10-5m/W to -4.6x10-6m/W at the wavelength of 800nm. The largest nonlinear absorption coefficient beta of the sputtered Ag films is obtained in the discontinuous film near the percolation threshold, which is mainly contributed by the large enhancement of local field of dis-continuous Ag particles.