Long-wave Band Research Articles

Investigation of the parameters of signals reflected from the ionosphere on the basis of regular radio-field measurements performed in the long-wave band

Diurnal and seasonal variations of the signal reflected from the ionosphere are investigated on the basis of regular measurements of the amplitude and phase of the radio field of a reference radio station operating at a frequency of 50 kHz. The reflected signal is extracted from the mixture of the ground-wavel and reflected-wave fields using a special procedure. Effective parameters of an exponential ionospheric model, which characterize the statistical parameters of the signals in the long-wave band at medium distances, are proposed.

Numerical Experiments of an Advanced Radiative Transfer Model in the U.S. Navy Operational Global Atmospheric Prediction System

AbstractA high-order accurate radiative transfer (RT) model developed by Fu and Liou has been implemented into the Navy Operational Global Atmospheric Prediction System (NOGAPS) to improve the energy budget and forecast skill. The Fu–Liou RT model is a four-stream algorithm (with a two-stream option) integrating over 6 shortwave bands and 12 longwave bands. The experimental 10-day forecasts and analyses from data assimilation cycles are compared with the operational output, which uses a two-stream RT model of three shortwave and five longwave bands, for both winter and summer periods. The verifications against observations of radiosonde and surface data show that the new RT model increases temperature accuracy in both forecasts and analyses by reducing mean bias and root-mean-square errors globally. In addition, the forecast errors also grow more slowly in time than those of the operational NOGAPS because of accumulated effects of more accurate cloud–radiation interactions. The impact of parameterized cloud effective radius in estimating liquid and ice water optical properties is also investigated through a sensitivity test by comparing with the cases using constant cloud effective radius to examine the temperature changes in response to cloud scattering and absorption. The parameterization approach is demonstrated to outperform that of constant radius by showing smaller errors and better matches to observations. This suggests the superiority of the new RT model relative to its operational counterpart, which does not use cloud effective radius. An effort has also been made to improve the computational efficiency of the new RT model for operational applications.

Wavelet-Based Detection of Roughness Progression in Wavebands for Highways in Victoria, Australia

The use of wavelet analysis to locate and assess changes in pavement profile characteristics over time and their links to contributing factors are discussed. This assessment approach was applied to a number of sections from two major freight routes in Victoria, Australia, between 2004 and 2009. Roughness progression rates in the different wavebands for different sites were determined and compared with each other after consideration of the contribution of traffic loading, climatic conditions, pavement composition, and subgrade soil type and the interaction of these factors. Segments within each site that experienced localized progression were also identified. For the sections tested, traffic loading and soil and climate conditions were found to be the most dominant contributors to pavement roughness progression in short and long wavebands. Sites with highly reactive subgrade soils tended to develop higher roughness contents in the longer wavebands and progress at high rates. A distinct localized increase in roughness was observed for all the sites in certain wavebands. Findings of the study confirm that wavelet analysis was a valuable tool for use at the project level in pavement management to locate the problematic segments of any road section and identify the cause of deterioration; these determinations helped in selecting the appropriate treatment method.

Formation of the aggregates of actinocin derivatives containing 4′-benzo-15-crown-5 radicals in amide groups and their interaction with a DNA molecule

Methods of spectrophotometry, spectropolarimetry, and viscometry are used to study the self-organization in the solution of crown-containing actinocin derivative (I) exhibiting antitumor activity and the interaction of the formed aggregates with a DNA molecule. The presence of the 4′-benzo-15-crown-5 radical in the structure of the studied compound determines the observed differences in its complexation with Na+ and K+ ions. The process of aggregation in the presence of K+ ions is accompanied by a shift of the long-wave band in the absorption spectrum to short-wave (the formation of H type aggregates) or long-wave (the formation of J type aggregates) regions depending on the K+ ion concentration in the solution. In the presence of Na+ ions, regardless of their concentration in the solution, J type aggregates form. A scheme of complex formation and their mutual transformations with changes in the ionic composition of the medium is proposed. A study of the interaction of this compound with DNA shows that in the presence of K+ ions it binds to the DNA molecule in the form of monomers and/or dimers without producing large supramolecular aggregates. The H and J structures formed in K+-containing solutions of compound I are broken in the interaction with DNA. If a solution of compound I is added to a DNA solution containing Na+ ions, the J type aggregates are formed directly on the surface of the DNA molecule. At the same type, the J structures originally formed in the Na+-containing solution of compound I practically do not interact with DNA. A study of this system shows that the introduction of the crown group in the compound molecule with a heterocyclic chromophore provides the opportunity to affect its affinity and binding to the DNA molecule by means of the ionic composition of the medium.

New fluorescent 2-(5-acetoacetyl-2-furyl)-benzazoles with prochiral methylene group protons

New fluorescent benzazoles containing prochiral protons in the methylene group have been synthesized. Their spectral-absorption and fluorescent properties have been investigated. Quantum yields of fluorescence were 0.39–0.55. The long-wave absorption band and the emission band in the spectra of the obtained acetoacetyl furylbenzazole derivatives are caused by electronic transition with charge transfer between the benzazole and acetoacetylfuryl fragments.

The wind instability and the resonant interaction of the elastic vibration of a thin plate with a supersonic gas stream

In a supersonic flow, the longwave perturbations running along the stream are stable, whereas the most rapidly growing waves propagate at an angle to the flow velocity. It has been shown that the wind instability of a nonuniform compressible gas flow having a velocity profile can give rise to elastic vibrations of a thin plate at a characteristic wavelength. The dispersion equation and the instability increment showing a maximum in the longwave band have been obtained.

Optical and electrochemical properties of cyclometallated Rh(III) and Pd(II) complexes based on phenyl-substituted pyrazole, pyridine, and pyrimidine with ethylenediamine, 2,2′-bipyridine, and 1,10-phenanthroline

Electrochemical and optical properties of cyclometallated Rh(III) and Pd(II) complexes based on phenyl-substituted pyrazole, pyridine, and pyrimidine with ethylenediamine, 2,2′-bipyridine, and 1,10-phenanthroline chelating ligands were investigated. One-electron reduction waves of the complexes were assigned to ligand-centered processes of electron transfer on π* orbitals of heterocyclic chelating and cyclometallated ligands, whereas irreversible oxidation waves, to the processes involving a mixed phenyl-metal π/d orbital. The long-wave absorption band results from by the spin-allowed optical transition between π/d-HOMO and a π* orbital of a cyclometallated ligand. The character of the optical transition responsible for low-temperature (77 K) phosphorescence of the complexes is defined by the ratio of the energy gap between π* orbitals of chelating and cyclometallated ligands and by the energy of the singlet-triplet splitting of electron-excited states.

Tautomeric composition as a compound characteristic

The electronic absorption spectra (EAS) of organic compounds that are capable of tautomeric transformations, when measured by the different authors, often differ significantly not only in the range of πl,π*bands responsible for the color of the compound, but also in the number of the bands. For example, electronic spectrum in ethanol of a popular reagent for metal analysis, quinalizarin, the 1,2,5,8-tetrahydroxy9,10-anthraquinone, contains by different data 1, 2, 3, or 5 πl,π*-bands, and the position of the longwave band varies from 510 to 550 nm [1]. For a long time no proper significance was attracted to such differences, despite their frequent occurrence: the researchers discarded the published data as erroneous if they were not consistent with their own measurements. However, these substances are not individual compounds, but dynamic mixtures of tautomers and conformers.

Asymmetry in ground and excited states in styryls and methoxystyryls detected by NMR (13C), absorption, fluorescence and fluorescence excitation spectroscopy

Combined quantum-chemical and spectral study of electron structure features of styryls and their oxyanalogues containing benzothiazolium, benzooxazolium, indoleninium, pyridium, quinolinium residues has been fulfilled. It showed that asymmetry degree of molecular geometry and charge distribution in the chromophore of styryls and methoxystyryls considerably differ in the ground and excited states. It was established that two the lowest transitions in styryls are splitting and involve both donor levels, similarly to symmetrical cyanines. If compare with methoxystyryls the long-wave high intensive absorption band is shifted bathochromically due to considerable interaction between the donor quasi-local chromophores. In contrary, because of the low position of a lone electron pair of oxygen in methoxystyryls, only one donor quasi-local chromophore is effective, hence such unsymmetrical dyes absorb appreciably higher.

Spectral and electrochemical properties of mono-, bi-, and tetranuclear cyclopalladized complexes based on 2-(2-thienyl)pyridine and 2-phenylpyridine with pyridine and 4,4′-bipyridyl

Mono-, bi-, and tetranuclear cyclopalladized complexes based on 2-(2-thienyl)pyridine and 2-phenylpyridine with pyridine and 4,4′-bipyridyl were prepared and characterized by the methods of 1H NMR, electron absorption and emission spectroscopy, and also by the voltammetry method. The values of the coordination-induced shifts of proton in the ligands of the complexes were determined; the upfield displacement of chemical shifts of protons of the cyclopalladized ligand nearest to the metal was assigned to the anisotropic action of a ring current of the pyridine rings orthogonal to the coordination plane in 4,4′-bipyridyl and pyridine. Long-wave absorption bands of the complexes were assigned to the spin-allowed optical d-π charge-transfer transitions, and the bands of the low-temperature phosphorescence, to the intraligand π-πNyyC* transitions. Three waves of the reduction of the complexes were assigned to the ligand-centered processes of successive electron transfer on π* orbitals preferentially localized on coordinated pyridine and cyclopalladized ligands.

Research on the novel GeSe2–In2Se3–KBr chalcohalide optic glasses

Abstract (1 − x)(0.75GeSe2–0.25In2Se3) − x(1/3In2Se3–2/3KBr) (x = 0, 0.15, 0.3, 0.45, 0.525) chalcohalide glasses were prepared by traditional melt-quenching method and its glass-forming region was determined. The physical, thermal and optical properties of the GeSe2–In2Se3–KBr ternary glass system are reported. The results show that the GeSe2–In2Se3–KBr glass system has relatively high glass transition temperature (Tg = 286–335 °C) and good thermal stability. With increasing KBr content from 0 to 35 mol%, a blue-shift from 750 to 620 nm at the visible absorbing cutting-off edge is observed. The red-shifting of the transmission cutting-off edge at the long-wave IR band occurs linearly with increasing KBr. The allowed direct transition and indirect transition of samples were calculated according to the classical Tauc equation. The direct optical band gaps and indirect optical band gaps were in the range from 1.649 to 1.931 eV and 1.513 to 1.863 eV, respectively.

Pulsed thermography in multiple infrared spectral bands

Spectrally resolved active thermography by flash pulse excitation was performed in four sub-bands of a mid-wave infrared camera using spectral filtering and in the full long-wave band of a second infrared camera. On zirconia thermal barrier coatings on steel and PVC blocks, spectrally dependent decay rates of the thermal contrast were found. The observed behaviour can be explained by the infrared spectra of the specimens.

Tunable 19 × 10 GHz L-band FP-SOA based multi-wavelength mode-locked fiber laser

We present a multi-wavelength mode-locked fiber ring laser incorporating a semiconductor optical amplifier (SOA) and a Fabry–Perot semiconductor optical amplifier (FP-SOA). Because the gain of the SOA is depleted by an external injection optical signal, the SOA acts as a loss modulator. The FP-SOA serves as a tunable comb filter. The presented laser source can generate 19 synchronized wavelength channels with the extinction ratio of about 21 dB, each mode-locked at 10 GHz, and mode-locked pulse width is about 40 ps. Oscillation wavelengths band can be tuned by adjusting the bias current of the SOA, and wavelength spacing also can be changed by using a tunable optical delay line (ODL) or a temperature controller. The polarization-insensitive devices ensure that the output power is rather stable. This fiber laser has potential applications in longer waveband (L-band) within the low-attenuation window.

Complex formation of verdazyl radicals with verdazilium salts

A number of redox reactions with the participation of stable verdazyl radicals I are known to proceed as autocatalytic processes caused by the generation of verdazylium salt II [1,2]. We found that compounds I and II in solution interact with each other to form a complex compound in a molar ratio 1:1. As compound I we tested 2,4,6-triphenyland 2,3,4,6-tetraphenylverdazyl radicals, while as compound II the respective bromides and also 2,4,6-triphenylver-dazilium hydroxide. The process of the complex formation was studied by the spectrophotometric method monitoring the change in the long-wave absorption bands of verdazilium cations (in the region of 545–550 nm) and verdazyl radicals (in region of 710–720 nm) in anhydrous acetonitrile and acetone, and also in their aqueous solutions. The choice of these solvents was defined by the good solubility and sufficient stability of verdazilium salts in them. Compositions of the complexes were established by the methods of isomolar series and molar ratios. The initial concentrations of reagents was varied within the range of 1.5×10–0.5×10 mol l.

Synthesis and spectral characteristics of a novel heterometallic binuclear complex on the basis of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine

Binuclear bridged complexes [(bpy)2Ru(μ-bptz)Re(CO)3·(Hlg)](X)2 [bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; Hlg = Cl, X = BF4 or Hlg = Br, X = NO3]. Were synthesized and studied by mass spectrometry and infrared and electronic spectroscopy. The complexes give a strong long-wave band in the electronic absorption spectrum. The spectra were interpreted on the basis of TD DFT quantum-chemical calculations.

Effect of acetone vapor treatment on photoluminescence of porous nc-Si–SiOx nanostructures

The effect of treatment in saturated acetone vapors on the spectral composition and intensity of photoluminescence (PL) in porous oblique deposited SiOx films is studied. As a result of this treatment followed by high-temperature annealing at the temperature 930 °C, considerable PL intensity growth and the small blueshift of PL peak position are observed in the porous, column-like structure films containing Si nanocrystals. A more intense shortwave band (peak position - 540-560 nm) appears in the PL spectrum of these structures, in addition to the longwave band (760-780 nm). Both PL bands in treated samples are characterized by monomolecular radiative recombination, which can be attributed to annihilation of excitons in silicon nanocrystals embedded into oxide matrix (longwave band) and in carbon-enriched matrix near surface of oxide nanocolumns (shortwave band). The possibility to control the PL characteristics of the porous structures in a wide spectral range by above treatment is shown.

Absorption Spectra of Estradiol and Tryptophan Constructed by the Statistical and Elongation Methods

The statistical quantum chemical/molecular dynamical method is developed and employed to reproduce optical spectra. This technique includes quantum-mechanical calculations on energy states and photophysical properties of molecular conformers obtained during molecular dynamical simulation. Polycyclic organic molecule estradiol surrounded by solvent particles and protein structure including tryptophan fragment under thermodynamical conditions are considered. A wide absorption spectrum over several excited electronic states of estradiol is constructed. First longwave absorption band of tryptophan-cage mini protein is built involving the elongation method. These statistical spectra reflect the main features of the corresponding experimental ones.

On the Improvement of COAMPS Weather Forecasts Using an Advanced Radiative Transfer Model

Abstract Fu–Liou’s delta-four-stream (with a two-stream option) radiative transfer model has been implemented in the U.S. Navy’s Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS)1 to calculate solar and thermal infrared fluxes in 6 shortwave and 12 longwave bands. The model performance is evaluated at high resolution for clear-sky and overcast conditions against the observations from the Southern Great Plains of the Atmospheric Radiation Measurement Program. In both cases, use of the Fu–Liou model provides significant improvement over the operational implementation of the standard Harshvardhan radiation parameterization in both shortwave and longwave fluxes. A sensitivity study of radiative flux on clouds reveals that the choices of cloud effective radius schemes for ice and liquid water are critical to the flux calculation due to the effects on cloud optical properties. The sensitivity study guides the selection of optimal cloud optical properties for use in the Fu–Liou parameterization as implemented in COAMPS. The new model is then used to produce 3-day forecasts over the continental United States for a winter and a summer month. The verifications of parallel runs using the standard and new parameterizations show that Fu–Liou dramatically reduces the model’s systematic warm bias in the upper troposphere in both winter and summer. The resultant cooling modifies the atmospheric stability and moisture transport, resulting in a significant reduction in the upper-tropospheric wet bias. Overall ice and liquid water paths are also reduced. At the surface, Fu–Liou reduces the negative temperature and sea level pressure biases by providing more accurate radiative heating rates to the land surface model. The error reductions increase with forecast length as the impact of improved radiative fluxes accumulates over time. A combination of the two- and four-stream options results in major computational efficiency gains with minimal loss in accuracy.

Fine Resolution Air Quality Monitoring from a Small Satellite: CHRIS/PROBA.

Current remote sensing techniques fail to address the task of air quality monitoring over complex regions where multiple pollution sources produce high spatial variability. This is due to a lack of suitable satellite-sensor combinations and appropriate aerosol optical thickness (AOT) retrieval algorithms. The new generation of small satellites, with their lower costs and greater flexibility has the potential to address this problem, with customised platform-sensor combinations dedicated to monitoring single complex regions or mega-cities. This paper demonstrates the ability of the European Space Agency's small satellite sensor CHRIS/PROBA to provide reliable AOT estimates at a spatially detailed level over Hong Kong, using a modified version of the dense dark vegetation (DDV) algorithm devised for MODIS. Since CHRIS has no middle-IR band such as the MODIS 2,100 nm band which is transparent to fine aerosols, the longest waveband of CHRIS, the 1,019 nm band was used to approximate surface reflectance, by the subtraction of an offset derived from synchronous field reflectance spectra. Aerosol reflectance in the blue and red bands was then obtained from the strong empirical relationship observed between the CHRIS 1,019 nm, and the blue and red bands respectively. AOT retrievals for three different dates were shown to be reliable, when compared with AERONET and Microtops II sunphotometers, and a Lidar, as well as air quality data at ground stations. The AOT images exhibited considerable spatial variability over the 11 × 11km image area and were able to indicate both local and long distance sources.

Electronic spectra parameters as a tool for studying the structure of the catalytic center and the mechanism of activation of d 0-transition metal complexes in olefin polymerization

The quantum-chemical model formerly designed is described, which explains the high reactivity of the d0-transition metal-carbon σ-bond in concerted reactions including polymerization of olefins. In this model, the energy of transition from the ground singlet state to the excited singlet or triplet state corresponding to the transfer of electron density from the metal-carbon bond to vacant d-atomic orbitals correlates with its relative elongation after which a change in the valence state of a metal begins. This change is caused by the difference in the geometries of valence s-, p-, and d-atomic orbitals having close energies; as a result, at a certain bond elongation, partial uncoupling of electrons involved in bonding takes place so that one of them becomes localized on d-atomic orbital. This process facilitates formation of the reactive state of the bond of the biradical type and leads to a reduction in the energy barrier of the insertion of an olefin molecule into this bond. Lower energies of this barrier correspond to lower values of ΔE(S0 → Sj) and ΔE(S0 → Tj). As shown at the example of zirconocenes Cp2ZrMe2 and Me2CCp2ZrMe2, alongside with a reduction in the energy barrier of olefin insertion into the Zr-Me bond of the cationic complex being formed, the characteristic absorption band in the spectrum of the corresponding neutral derivative shifts to the long-wave region. This band is attributed to the transfer of the electron density from the Zr-Me bond to the Zr atom. Analysis is performed of the causes for bathochromic shifts of the long-wave absorption band for adduct formation in the systems including metallocene and Al-containing cocatalyst.