Spectral Peculiarities Research Articles

Peculiarities of 13C NMR Spectra of Benzoylformic Acid and its Esters. 1. Benzoyl Fragment

Peculiarities of 13C NMR spectra of benzoyl fragment of benzoylformic acid and its esters have been investigated and characteristic values of a chemical shift of all five types of fragment atom have been examined. Similar parameters of other benzoyl-containing compounds by general formula Bz–X (X = H, NR2, OR, SR, Cl, Br), as well as those of compounds Bz–C (L)(M)(N) have been compared. It has been shown that spectral peculiarities of a benzoylformates phenyl fragment are defined by the carbonyl, not by the carbalkoxyl group.

AVS-F observations of γ-ray emission during January 20, 2005 solar flare up to 140 MeV

The solar flare of January 20, 2005 (X7.1, 06:36–07:26 UT, maximum at 07:01 UT by the GOES soft X-ray data) was the most powerful one in January 2005 series. The AVS-F apparatus onboard CORONAS-F registered γ-emission during soft X-ray rising phase of this flare in two energy ranges of 0.1–20 MeV and 2–140 MeV. The highest γ-ray energy registered during this flare was ∼140 MeV. Six spectral features were registered in energy spectrum of this solar flare: annihilation + αα (0.4–0.6 MeV), 24Mg + 20Ne + 28Si + neutron capture (1.7–2.3 MeV), 21Ne + 22Ne + 16O + 12С (3.2–5.0 MeV), 16O (5.3–6.9 MeV), one from neutral pions decay (25–110 MeV) and one in energy band 15–21 MeV. Four of them contain typical for solar flares lines – annihilation, nuclear de-excitation and neutron capture at 1H. Spectral feature caused by neutral pions decay was registered during several flares too. Some spectral peculiarities in the region of 15–21 MeV were first observed in solar flare energy spectrum.

Spectroscopic investigation of stars on the lower main sequence

Aims. The aim of this paper is to provide fundamental parameters and abundances with a high accuracy for a large sample of cool main sequence stars. This study is part of wider project, in which the metallicity distribution of the local thin disc is investigated from a complete sample of G and K dwarfs within 25 pc. Methods. The stars were observed at high resolution and a high signal-to-noise ratio with the ELODIE echelle spectrograph. The V sini were obtained with a calibration of the cross-correlation function. Effective temperatures were estimated by the line depth ratio method. Surface gravities (log g) were determined by two methods: parallaxes and ionization balance of iron. The Mg and Na abundances were derived using a non-LTE approximation. Abundances of other elements were obtained by measuring equivalent widths. Results. Rotational velocities, atmospheric parameters (Teff ,l ogg ,[ Fe/H], Vt ), and Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, and Zn abundances are provided for 131 stars. Among them, more than 30 stars are active stars with a fraction of BY Dra and RS CVn type stars for which spectral peculiarities were investigated. We find the mean abundances of the majority of elements in active and nonactive stars to be similar, except for Li, and possibly for Zn and Co. The lithium is reliably detected in 54% of active stars but only in 20% of nonactive stars. No correlation is found between Li abundances and rotational velocities. A possible anticorrelation of log A(Li) with the index of chromospheric activity GrandS is observed. Conclusions. Active and nonactive cool dwarfs show similar dependencies of most elemental ratios vs. [Fe/H]. This allows us to use such abundance ratios to study the chemical and dynamical evolution of the Galaxy. Among active stars, no clear correlation has been found between different indicators of activity for our sample stars.

Deconvoluted Fourier-transform LNT-IR study of coordination copper(II) compounds with dextran derivatives

Deconvoluted Fourier-transform IR spectra, recorded at room and liquid nitrogen temperature, of polysaccharide dextran and its coordination compounds with the copper(II) ion were analyzed in order to find the most specific spectral peculiarities. This allows one to obtain information about the structure and conformation of these polymer compounds. Different influences on the system of intra-and intermolecular interactions were exhibited by analogs recrystallized from D2O. The changes in intensity and width of the IR bands in the region 1450–1050 cm−1 were related to changes in conformation and short-range interactions of the dextran. In the synthesized copper(II)-dextran complexes, the presence of water molecules was confirmed. The results of the FTIR spectroscopy study allowed one to suggest a predominant crystalline form of the copper(II)-dextran complexes.

Clouds, Gravity, and Metallicity in Blue L Dwarfs: The Case of 2MASS J11263991−5003550

Optical and near-infrared spectroscopy of the newly discovered peculiar L dwarf 2MASS J11263991–5003550 are presented. Folkes et al. classified this source as a high proper motion L9±1 dwarf based on its strong H2O absorption at 1.4 μ m . We find that the optical spectrum of 2MASS J1126–5003 is in fact consistent with that of a normal L4.5 dwarf with notably enhanced FeH absorption at 9896 A. However, its near-infrared spectrum is unusually blue, with strong H2O and weak CO bands similar in character to several recently identified L Using 2MASS J1126–5003 as a case study, and guided by trends in the condensate cloud models of Burrows et al. and Marley et al., we find that the observed spectral peculiarities of these sources can be adequately explained by the presence of thin and/or large-grained condensate clouds as compared to normal field L dwarfs. Atypical surface gravities or metallicities alone cannot reproduce the observed peculiarities, although they may be partly responsible for the unusual condensate properties. We also rule out unresolved multiplicity as a cause for the spectral peculiarities of 2MASS J1126–5003. Our analysis is supported by examination of Spitzer mid-infrared spectral data from Cushing et al. which show that bluer L dwarfs tend to have weaker 10 μ m absorption, a feature tentatively associated with silicate oxide grains. With their unique spectral properties, blue L dwarfs like 2MASS J1126–5003 should prove useful in studying the formation and properties of condensates and condensate clouds in low-temperature atmospheres.

On the nature of precursors in the radio pulsar profiles

Abstract In the average profiles of several radio pulsars, the main pulse is accompanied by the preceding component. This so-called precursor is known for its distinctive polarization, spectral and fluctuation properties. Recent single-pulse observations hint that the sporadic activity at the extreme leading edge of the pulse may be prevalent in pulsars. We for the first time propose a physical mechanism of this phenomenon. It is based on the induced scattering of the main pulse radiation into the background. We show that the scattered component is directed approximately along the ambient magnetic field and, because of rotational aberration in the scattering region, appears in the pulse profile as a precursor to the main pulse. Our model naturally explains high linear polarization of the precursor emission, its spectral and fluctuation peculiarities as well as suggests a specific connection between the precursor and the main pulse at widely spaced frequencies. This is believed to stimulate multifrequency single-pulse studies of intensity modulation in different pulsars.

A refined analysis of the remarkable Bp star HR 6000

UVES spectra of the very young (~10^7 years) peculiar B-type star HR 6000 were analyzed in the near-UV and visual spectral regions (3050-9460 A) with the aim to extend to other spectral ranges the study made previously in the UV using IUE spectra. Stellar parameters Teff=12850K, logg=4.10, and xi=0km/s, as determined from H_beta, H_gamma, H_delta Balmer profiles and from the Fe I, Fe II ionization equilibrium, were used to compute an individual abundances ATLAS12 model. We identified spectral peculiarities and obtained final stellar abundances by comparing observed and computed equivalent widths and line profiles. The adopted model fails to reproduce the (b-y) and c color indices. The spectral analysis has revealed: the presence of emission lines for Mn II, Cr II, and Fe II; isotopic anomalies for Hg, Ca; the presence of interstellar lines of Na I at lambda lambda 3302.3, 3302.9, 5890, 5896 A, and of K I at 7665, 7699 A; the presence of a huge quantity of unidentified lines, which we presume to be mostly due to Fe II transitions owing to the large Fe overabundance amounting to [+0.7]. The main chemical peculiarities are an extreme overabundance of Xe, followed by those of Hg, P, Y, Mn, Fe, Be, and Ti. The most underabundant element is Si, followed by C, N, Al, S, Mg, V, Sr, Co, Cl, Sc, and Ni. The silicon underabundance [-2.9] is the lowest value for Si ever observed in any HgMn star. The observed lines of He I can not be reproduced by a single value of the He abundance, but they require values ranging from [-0.8] to [-1.6]. Furthermore, when the observed and computed wings of He I lines are fitted, the observed line cores are much weaker than the computed ones. From the present analysis we infer the presence of vertical abundance stratification for He, Mn, and possibly also P.

X-ray emission from A-type stars

Being fully radiative, stars of spectral type A are not expected to harbor magnetic dynamos and hence such stars are not expected to produce X-ray emission. Indeed, while the X-ray detection rate of such stars in X-ray surveys is low, it is not zero and some of the brighter A-type stars have been detected on different occasions and with different instruments. To study systematically the puzzle of the X-ray emitting A-type stars, we carried out an X-ray study of all A-type stars listed in the Bright Star Catalogue using the ROSAT public data archive. We found a total of 312 bright A-type stars positionally associated with ROSAT X-ray sources; we analyzed the X-ray light curves as well as searched for evidence of RV variations to identify possible late-type companions producing the X-ray emission. In this paper we present a list of X-ray active A-type stars, including the collected data about multiplicity, X-ray luminosity and spectral peculiarities.

FT-IR microimaging spectroscopy: A comparison between healthy and neoplastic human colon tissues

FT-IR microimaging was performed on colon tissues with the aim to characterize spectral ‘markers’ to distinguish healthy from pathological tissues. Evidences of spectral peculiarities were mainly found in the finger print region even in the presence of a low grade adenocarcinoma. The occurrence of inflammation and necrotic states can also be demonstrated. Through statistical analysis as well as custom map procedures it was possible to reconstruct the topological distribution of different biochemical states and to verify results from the histopathological analysis. Preliminary results from FT-NIR analysis are in substantial agreement with those in the mid infrared region.

PHOTOLUMINESCENCE OF A HIGH MOBILITY 2DEG IN THE FRACTIONAL QUANTUM HALL EFFECT REGIME

The magneto-PL spectra of modulation-doped, ultra-high mobility GaAs/AlGaAs single heterojunctions (HJs) were studied under a perpendicularly applied magnetic field up to 33 T and at temperatures of 0.3 and 1.2 K. The spectra show remarkable intensity redistribution between free (bulk) exciton and 2DEG-hole PL channels occurring at electron filling factors, ν = 2 and 1. At 0.3 K, significant 2DEG-hole PL spectral changes are observed near ν = 2/3 and 1/3. Several heterojunctions with 2DEG density in the range of n2D - (1 - 2.7) · 1011 cm -2 display similar features. These spectral peculiarities are attributed to the modification of the 2DEG energy spectrum caused by the e-e interaction, in particular, the recombination of valence hole with the composite (fractionally-charged) particles of the magnetized 2DEG. In HJs with lower n2D < 1011 cm -2, the observed PL evolution at ν < 1 is mainly determined by an intensity redistribution between the σ+ and σ- circularly-polarized free exciton PL components. In this case, the exciton energy is lower than the energy of the 2DEG-hole system, so that the free excitons do not dissociate near the magnetized 2DEG and thus, the 2DEG-hole PL is barely observed.

Positioning of Carbon nanostructures on metal surfaces using laser acceleration and the Raman analyses of the patterns

The laser-induced acceleration of nanoparticles using intense light irradiation was used for positioning and ordering of carbon nanomaterials to form periodical surface structures. Such systems are of interest for different nanotechnology applications. The nanodiamond with averaged size 100 nm, and fullerene (C60) suspended in distilled water were accelerated using high focused laser beam and attached onto metal surface of silver and gold thin films evaporated on Si substrate. The laser was operating both in CW and femtosecond modes with the wavelength of ∼800 nm, pulse duration 150 fs, and average laser power of 300-600 mW. In case of pulse irradiation the repetition rate of 76 MHZ was applied. The nanoparticles were positioned on the metal surface in accordance with a predetermined program to allow patterning of the nanoparticles. The positioning was analyzed for different treatment conditions and compared to the calculated data. To investigate the obtained nanoparticles/metal structures, surface-enhanced Raman scattering (SERS) was used utilizing its high sensitivity on the local properties of the nanostructures. SERS allows the observing of carbon nanostructures with their characteristic peculiarities, such as blinking effect and selective enhancement. Here we try to explain the spectral and spatial peculiarities occurring during the laser acceleration process and the interaction of attached carbon nanostructures with metal surface.

The Spherically Symmetric a2–dynamo and Some of its Spectral Peculiarities

A brief overview is given of recent results on the spectral properties of spherically symmetric MHD α2-dynamos. In particular, the spectra of sphere-confined fluid or plasma configurations with physically realistic boundary conditions (BCs) (surrounding vacuum) and with idealized BCs (super-conducting surrounding) are discussed. The subjects comprise third-order branch points of the spectrum, self-adjointness of the dynamo operator in a Krein space as well as the resonant unfolding of diabolical points. It is sketched how certain classes of dynamos with a strongly localized α-profile embedded in a conducting surrounding can be mode decoupled by a diagonalization ofthe dynamo operator matrix. A mapping of the dynamo eigenvalue problem to that of a quantum mechanical Hamiltonian with energy dependent potential is used to obtain qualitative information about the spectral behavior. Links to supersymmetric Quantum Mechanics and to the Dirac equation are indicated.

Effect of masker type and age on speech intelligibility and spatial release from masking in children and adults

Speech recognition in noisy environments improves when the speech signal is spatially separated from the interfering sound. This effect, known as spatial release from masking (SRM), was recently shown in young children. The present study compared SRM in children of ages 5-7 with adults for interferers introducing energetic, informational, and/or linguistic components. Three types of interferers were used: speech, reversed speech, and modulated white noise. Two female voices with different long-term spectra were also used. Speech reception thresholds (SRTs) were compared for: Quiet (target 0 degrees front, no interferer), Front (target and interferer both 0 degrees front), and Right (interferer 90 degrees right, target 0 degrees front). Children had higher SRTs and greater masking than adults. When spatial cues were not available, adults, but not children, were able to use differences in interferer type to separate the target from the interferer. Both children and adults showed SRM. Children, unlike adults, demonstrated large amounts of SRM for a time-reversed speech interferer. In conclusion, masking and SRM vary with the type of interfering sound, and this variation interacts with age; SRM may not depend on the spectral peculiarities of a particular type of voice when the target speech and interfering speech are different sex talkers.

Dynamics of electron-vibrational excitation of polyphosphazenes containing carbazole and coumarin

In the present work the luminescence properties of polyphosphazenes containing carbazole and coumarine were studied. It was shown that the spectral properties of such systems are determined by the carbazole ore coumarine groups. Some spectral peculiarities connected with the different positions of the phosphor groups are discussed.

The nature of the electronic excitations capturing centres in the DNA

The spectral peculiarities of the DNA, the polynucleotide poly(dAdT) 2, the oligonucleotide d(CCCGGGTTTAAA), the trimer d(ATC) and the low molecular model compounds dGMP, dAMP, dCMP and dTMP were studied. The system of energy sites and electronic processes in the DNA were examined. The lowest excited electronic singlet levels of the DNA were shown to be related with guanine bases, while the lowest excited triplet levels are connected with adenine bases. The nature of the fluorescence and phosphorescence emission centres in the DNA is discussed. It was shown the phosphorescence of the DNA is close to emission of the triplet excitations traps associated with AT-sequences. These centres as well as adenine bases are most photostable. The latter proves to be a successful mechanism for DNA self protection.

Spectral peculiarities of monolayers made of oxidized nanogranules of amorphous copper and their aggregates with high surface concentration

We present results of a theoretical and experimental investigation into monolayers made of oxidized nanogranules of amorphous copper and their aggregates with a high surface concentration. We show theoretically that the packing density of the nanogranules, the size of aggregates, and the thickness and composition of the oxide layer over a Cu nanogranule affect the shift in the plasma resonance. Experimentally we established a non-monotone dependence of the absorption in the plasma resonance band and the UV spectral range with a high surface packing density of copper nanoparticles. The optical measurements indicated a non-uniform oxidation of the granules on the substrate.

Interband optical transitions in GaAs modulation-doped quantum wells: photoreflectance experiment and self-consistent calculations

Photoreflectance spectra of AlGaAs/GaAs/AlGaAs wide quantum wells doped by Si up to Nd = 2 x 1018cm-3 were investigated at room temperature. Three kinds of spectral peculiarities were observed in photoreflectance spectra: a spectral line due to the GaAs band gap (1.42 eV), short-period Frantz–Keldysh oscillations originating from the barrier band gap (1.71 eV) and lines of subbands in the quantum well. The energies of optical transitions are determined by means of the least-squares approximation of experimental data by the sum of Aspnes relations. The experimental results are in good agreement with the self-consistent subband structure calculation. It is shown that with an increase of the doping level the energies of the interband transitions in the quantum well are changed.

Natural, untreated diamonds showing the A, B and C infrared absorptions (“ABC diamonds”), and the H2 absorption

Unusual brown to yellow diamonds of mixed type Ib/IaAB were analyzed. The occurrence of nitrogen in a combination of A, B and C centers directly detectable by IR spectroscopy in natural diamonds is considered to be extremely rare. We propose to call such stones ABC diamonds for short. These diamonds are characterized by a color, luminescence, and anomalous double refraction distribution which results from mixed growth: a center core formed by cuboid growth, rich in nitrogen, covered by an outer rim of “normal” octahedral growth, with much less nitrogen. Nitrogen in the core is present in a more aggregated state than in the rim, which is practically pure type Ib. In the infrared spectra, besides A, B and C 1-phonon absorptions a large number of previously undescribed, tentatively H-related features were identified in some samples; these proposed H-related features were only present in the periphery of the core and the rim of the diamonds, in the core practically no hydrogen was detected. The low temperature Vis/NIR spectra were mainly characterized by two defect-induced centers: the H2 center, and the apparently new 905 nm vibronic absorption with phonon-side bands at 880, 867, 847 nm plus a feature at 806.5 nm. The 905 nm absorption can possibly be attributed to a hydrogen-related center. Although these diamonds present a combination of spectroscopic characteristics (A + B + C center absorptions, H2 absorptions) deemed characteristic of certain HPHT-treated type Ia diamonds, they cannot be confused for such treated diamonds on the basis of their color, color distribution and some spectral peculiarities.

Effect of Dehydration on Photoinduced Transformation in Gelatin Films Made With 14-Fluoro Bacteriorhodopsin Derivatives

Photoinduced transformation in gelatin films made with 14-fluoro bacteriorhodopsin derivatives, both wild-type (WT) and D96N mutant, were studied. Spectral and kinetic peculiarities for these two types of samples were compared over a wide range of relative humidity (9-92%). Analysis of the results considered two existing photoinduced processes that occur in suspensions and films of corresponding pigments. It was demonstrated that there is a range of humidity in which the performance of fluorine WT bacteriorhodopsin gelatin films may offer a technological advantage compared with fluorine D96N bacteriorhodopsin.

Synthesis of soluble meta-linked phenylene-based polymer and the peculiarities in photoluminescence properties

A soluble meta-linked phenylene-based polymer P1 was synthesized by Yamamoto coupling of a 5,5′-dibromo-2,2′-dibutoxy-biphenyl monomer and was characterized by microanalysis, FT-IR, 1H NMR and GPC. The molecular weight of P1 is more than 6000 g/mol. The P1 has good solubility in most organic solvents and good film-formation property. P1 shows the main absorption band at 248 nm with a weak shoulder at 280 nm in solution and the fluorescence emission centered at 374 nm whose intensities strongly depend on the excitation energy localized on both absorption bands. An increase in absorption intensity of 280 nm band and less dependence between fluorescence intensity and excitation energy are found as P1 in film state. The spectral peculiarities are thought to be related to the presence of two stable conformations with twisted angles of 144° and 180° along rotation-permitted axes in polymer chain. The result of theoretical calculations for the absorption spectrum of the model compound is accordant with the proposed conformers in polymer chain.