Kinds Of Spectra Research Articles

An Unusual Spectral State of an Ultraluminous Very Soft X-Ray Source during Outburst

We report the results of Chandra and XMM-Newton observations of a new outburst of an ultraluminous X-ray source in M101. During a Chandra monitoring observation of M101, M101 ULX-1 was found to be in outburst in 2004 December, the second outburst in 2004. The peak bolometric luminosity is about 3 × 1040 ergs s-1 (7 × 1039 ergs s-1 in 0.3-7 keV). The outburst spectra are very soft and can generally be fitted with a blackbody model, with temperatures of 40-80 eV, similar to supersoft X-ray sources in the Milky Way and in the Magellanic Clouds. In one Chandra observation, the source spectrum appears to be harder with a temperature of 150 eV. Such a spectral state is rarely seen in M101 ULX-1, and no X-ray source in the Milky Way shows this kind of spectrum. However, such an unusual spectral state very likely belongs to a new class of X-ray sources, quasi-soft X-ray sources, recently discovered in nearby galaxies. M101 ULX-1 returned to supersoft state in a subsequent XMM-Newton observation. Based on the two outbursts in 2004, the extremely high luminosity (Lbol = 1040-1041 ergs s-1), very soft X-ray spectra (kT = 40-150 eV), transient behavior, and state transition provide strong evidence that M101 ULX-1 harbors an intermediate-mass black hole.

PFS-MEX observation of ices in the residual south polar cap of Mars

The Mars Express spacecraft has a highly inclined orbit around Mars and so has been able to observe the south pole of Mars in illuminated conditions at the end of the southern summer ( L s = 330 ). Spectra from the planetary Fourier spectrometer (PFS) short wavelength (SW) channel were recorded over the permanent ice cap to study its composition in terms of CO 2 ice and H 2O ice. Models are fitted to the observed data, which include a spatial mixture of soil (not covered by ice) and CO 2 frost (with a specific grain size and a small amount of included dust and H 2O ice). Two different kinds of spectra were observed: those over the permanent polar cap with almost pure CO 2 ice, negligible water ice, no soil fraction required, and bright; and those over mixed terrain (at the edge of the cap or near troughs) containing a significant soil spatial fraction, more water ice and smaller CO 2 grain size. The amount of water ice given by fits to scaled albedo models is less than 10 ppm by weight. When using multi-stream reflectance models with the appropriate lighting geometry, the water amount must be 2–5 times greater than the albedo fit (less than 50 ppm). At the periphery of the residual polar cap, we found a region almost completely covered by water frost, modeled as a mixture of micron-sized and sub-mm sized grains. Our result using a granular mixture of micron-sized grains of water ice and dust with the CO 2 grains is different from the modeling of OMEGA polar cap observations using molecular mixtures.

Why is the band model not contradictory to molecular theory in organic electroluminescence?

In organic electroluminescence there is a sharp contradiction between the applicability of band model and molecular theory. This contradiction arose from the very beginning of extended study. In this report we studied the blue spectral shift in the newly discovered solid state cathodoluminescence when the applied voltage is increased. There are three different kinds of spectra in three intervals of applied voltage. The reason of this spectral shift is found to be the field ionization of exciton. The switching on of recombination starts only after the beginning of this field ionization. The exciton emission obeys molecular theory and the recombination obeys band model. Thus the demarcation is the appearance of field ionization of excitons. Since the ionization changes with electric field continuously, there is a region of coexistence of these two processes.

Many-body effects in the electronic spectra of cubic boron nitride

We present state of the art first-principles calculations of optical spectra and the loss function of bulk cubic boron nitride $(c\text{\ensuremath{-}}\mathrm{B}\mathrm{N})$, starting from a density functional Kohn-Sham band structure. We investigate the influence of many-body effects beyond the random phase approximation (RPA) on the optical spectra through the inclusion of self-energy and excitonic effects by a GW calculation and the solution of the Bethe-Salpeter equation. For the loss function we only perform RPA calculations, since Bethe-Salpeter results are already available in the literature. We show to which extent, and in which kind of spectra, the description of many-body effects is important for a meaningful comparison with experiment, and when they can be neglected due to mutual cancellation. We also present results obtained within time-dependent density functional theory, both in the adiabatic local density approximation (TDLDA) and using a recently proposed long-range approximation for the exchange-correlation kernel. Our results show that the latter corrects a big part of the error with respect to RPA or TDLDA; however, the corrections are not sufficient to qualify the method for further quantitative predictions, in particular for the study of the optical gap. In fact, since experiments often quote a relatively low (around $6.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) band gap, whereas the calculated optical absorption spectrum already in the random-phase approximation appears blueshifted by more than $2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ with respect to the available experimental curve, we study in particular the question of the optical gap in this material. It turns out that, although there is evidence for a weakly bound exciton in $c\text{\ensuremath{-}}\mathrm{B}\mathrm{N}$, the optical gap of pure monocrystalline cubic BN should be around $11\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, hence significantly bigger than has sometimes been quoted from experiments.

Photoabsorption cross section and ion-yield spectra of helium double-excitation resonances

The photoabsorption cross section and ion-yield spectra of He have been measured in the region of the double-excitation resonances below the $N=2$ threshold. For resonances decaying predominantly by autoionization [the ${2,0}_{n}$ series, low values of $n;$ notation of Herrick and Sinano\ifmmode \check{g}\else \v{g}\fi{}lu, Phys. Rev. A 11, 97 (1975)], the two kinds of spectra yield the same information. For resonances where substantial decay by fluorescence occurs ${(2,1}_{n}$ and $2,\ensuremath{-}{1}_{n}$ series), the ion-yield spectrum differs significantly from the cross section. The ratios of peak intensity of one series to the other are clearly different and the Fano line shape parameter $(q)$ of the ${2,1}_{n}$ series also changes as a function of $n,$ in qualitative agreement with the trends expected when the fluorescence channel is taken into account. These direct measurements confirm the influence of fluorescence on the cross section and agree with previous indirect measurements.

Uniform theory of the Talbot effect with partially coherent light illumination.

A uniform formulation for the self-imaging of gratings with any kind of partially coherent illumination is developed in terms of the cross mutual spectral density of the partial coherence theory. The formulation includes the time diffractive intensity distribution and the averaged diffractive intensity distribution at self-imaging distances and can be applied to both continuous and temporal illuminations with any kind of spectra. It is found that the averaged intensity distribution is related only to the intensity spectrum of illumination. The continuous polychromatic illumination and the ultrashort laser pulses with or without frequency chirp are then studied by a numerical stimulation. It is shown that the ultrashort laser pulse and the continuous polychromatic illuminations have similar averaged self-image distributions. Thus the Talbot effect may help in the study of the temporal and spectral characteristics of ultrashort laser pulses. An experiment with an LED is given, as well.

Impact ofCPphases on neutrinoless double beta decay

We highlight in a model independent way the dependence of the effective Majorana mass parameter, relevant for neutrinoless double beta decay, on the CP phases of the PMNS matrix, using the most recent neutrino data including the cosmological WMAP measurement. We perform our analysis with three active neutrino flavours in the context of three kinds of mass spectra: quasi-degenerate, normal hierarchical and inverted hierarchical. If a neutrinoless double beta decay experiment records a positive signal, then assuming that Majorana masses of light neutrinos are responsible for it, we show how it might be possible to discriminate between the three kinds of spectra.

On theoretical VCD, IR, and Raman spectra of (+)-hexahelicene in the ν(C–H) region

The VCD, IR, and Raman spectra were calculated for the (+)-hexahelicene molecule at the B3PW91/6-31G** level. The geometry was also optimized at the B3PW91/6-311G** level. The assignment and the spectral pattern in the region of the stretching ν(C–H) vibrations is discussed for the three kinds of spectra. The (+)-hexahelicene chirality, connected with the helical twist, can be detected through the stretching ν(C–H) vibrations, however, some VCD bands can compensate the other. The bands of the largest VCD rotational strengths, IR intensity, and Raman activity in the spectra are also mentioned.

Simulated annealing method for powder diffraction pattern decomposition

Simulated annealing algorithm was applied in the decomposition of neutron and x_ray powder diffraction pattern. The method described in this paper has two main advantages: first, the pattern decomposition results do not depend on the starting peak parameters, thus the difficulty in the choice of initial solutions, which occurs in fitting a complex pattern composed of severely overlapped peaks by a conventional least_squares profile fitting method, is overcome; secondly, it has the ability of searching for global other than local optimal solutions, thus can effectively resolve the multi_solution problem mathematically, and this advantage is the most useful when decomposing complex patterns with several local optimal solutions. The computing step is described in detail, the setting of relative parameters is discussed, and the simulated annealing method is compared with a conventional least_squares profile fitting method through both simulated pattern and actual pattern to demonstrate its unique advantage in the decomposition of complex pattern. In principle, the method can also be applied in other kinds of spectra which can be described by profile shape function.

Raman phonons as a probe of disorder, fluctuations, and local structure in doped and undoped orthorhombic and rhombohedral manganites

We present a rationalization of the Raman spectra of orthorhombic and rhombohedral, stoichiometric and doped, manganese perovskites. In particular, we study $R{\mathrm{MnO}}_{3}$ $(R=\mathrm{La},$ Pr, Nd, Tb, Ho, Er, Y, and Ca) and the different phases of Ca- or Sr-doped $R{\mathrm{MnO}}_{3}$ compounds as well as cation deficient $R{\mathrm{MnO}}_{3}.$ The spectra of manganites can be understood as combinations of two kinds of spectra corresponding to two structural configurations of ${\mathrm{MnO}}_{6}$ octahedra and independently of the average structure obtained by diffraction techniques. One type of spectra corresponds to the orthorhombic $\mathrm{Pbnm}$ space group for octahedra with cooperative or dynamic Jahn-Teller distortions, with stretching modes as the main features and whose frequencies correlate to Mn-O distances. The other spectrum is associated to regular but tilted octahedra whose modes can be described in the rhombohedral $R\overline{3}c$ structure, where only bending and tilt modes are observed. The main peaks of compounds with regular ${\mathrm{MnO}}_{6}$ octahedra, such as ${\mathrm{CaMnO}}_{3},$ highly Ca-doped ${\mathrm{LaMnO}}_{3},$ or the metallic phases of Ca- or Sr-doped ${\mathrm{LaMnO}}_{3},$ are bending and tilt ${\mathrm{MnO}}_{6}$ octahedra modes which correlate to $\mathrm{R}\ensuremath{-}\mathrm{O}(1)$ bonds and Mn-O-Mn angles, respectively. In low and optimally doped manganites, the intensity and width of the broad bands are related to the amplitude of the dynamic fluctuations produced by polaron hopping in the paramagnetic insulating regime. The activation energy, which is proportional to the polaron binding energy, is the measure of this amplitude. This study permits to detect and confirm the coexistence, in several compounds, of a paramagnetic matrix with lattice polaron together with regions without dynamic or static octahedron distortions, identical to the ferromagnetic metallic phase. We show that Raman spectroscopy is an excellent tool to obtain information on the local structure of the different microphases or macrophases present simultaneously in many manganites.

Study of the Plasma-Neutral Relaxation in Tore-Supra Edge Plasmas

Passive spectroscopy of the Da line emission is used for the investigation of the Tore-Supra edge plasma in front of a neutralizer plate of the Ergodic Divertor. Two kinds of spectra are observed: symmetric and asymmetric. Symmetric spectra are fitted considering two isotropic populations of deuterium representing the main neutral production mechanisms. The fit of the asymmetric spectra, requires the addition of an anisotropic population resulting from the reflection of ions as neutrals on the V-shaped notches of the neutralizer plate and the inclusion of the relaxation of the deuterium populations through elastic collisions with the plasma ions.

Signatures of Wannier-Stark and surface states in electron tunneling and related phenomena: Electron transmission through a tilted band

Predicted by Wannier in 1960 band states quantization in a constant electric field, $E_n$ = const $\pm n {\cal E}$, where $n =0$, 1, 2, ..., and ${\cal E}$ is proportional to the strength of electric field [this kind of spectrum is commonly referred as the Wannier-Stark ladder (WSL)], implies that the probability of tunneling through a tilted band should have ${\cal E}$ spaced peaks, at least, under the weak coupling of the band states to the source and drain electrodes. It has been shown, however, (Phys. Rev. B {\bf 63}, ..., 2001), that the appearance of the canonical WSL is preceded by WSLs with other level spacing, namely, ${\cal E}_{m'/m}/(1-2m'/m)$, where $m$ and $m'< m/2$ are positive integers specifying certain applied voltage. Here we show that canonical and noncanonical WSLs, in addition to different peak spacing in the transmission spectrum, have other pronouncedly distinctive features. As an example, for the former, the peak and valley tunneling probability decays exponentially with the increase of applied voltage. The corresponding exponents are given by the sum and difference of two Fowler-Nordheim-type exponents implying an anomalous increase of the peak-to-valley ratio. These and other signatures of extended states (es), surface localized states (sls), and Wannier-Stark (WS) states in the through tilted band transmission spectrum are discussed on the basis of (derived for the first time) nearly exact explicit expressions of es-, sls-, and WS states assisted tunneling probability.

Temporal changes in the amino acid contents of particulate organic matter sedimenting in the Bay of Banyuls-sur-Mer (northwestern Mediterranean)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 214:55-65 (2001) - doi:10.3354/meps214055 Temporal changes in the amino acid contents of particulate organic matter sedimenting in the Bay of Banyuls-sur-Mer (northwestern Mediterranean) L. Medernach, A. Grémare*, J. M. Amouroux, J. C. Colomines, G. Vétion Observatoire Océanologique de Banyuls, UMR CNRS No. 7621, BP 44, 66651 Banyuls-sur-Mer Cedex, France *Corresponding author. E-mail: gremare@obs-banyuls.fr ABSTRACT: We monitored gross sedimentation rates (GSR) together with organic carbon, total hydrolysable (THAA) and enzymatically available (EHAA) amino acid contents of the particulate organic matter collected within 2 sediment traps moored during a 4 yr period at a shallow station (18 m) in the Bay of Banyuls-sur-Mer (northwestern Mediterranean). GSRs were between 0.26 and 470.55 g DW m-2 d-1 They were low during spring and summer, and usually higher but much more variable during fall and winter. Organic carbon concentrations were between 1.21 and 6.94% DW, versus 3.36 and 29.16 mg g-1 DW, and 0.54 and 14.44 mg g-1 DW for THAA and EHAA, respectively. EHAA/THAA ratios were between 13.91 and 65.78%. These 4 parameters showed an annual periodicity and correlated negatively with GSR, which supports the role of resuspension in controlling sedimentation. THAA and EHAA spectra were both dominated by glycine, aspartic acid, glutamic acid and alanine. However, there were consistent differences between the 2 kinds of spectra. EHAAs were enriched in threonine, glutamic acid, leucine and aspartic acid; and depleted in arginine, lysine, glycine and histidine. EHAA spectra showed fewer temporal changes than THAA spectra. In all cases but one, significant changes in THAA spectra were related to glycine, aspartic acid, glutamic acid and threonine, and were indicative of the presence of degraded material, probably due to resuspension. We computed degradation indexes based on both THAA and EHAA spectra. THAA degradation index was between -0.318 and 1.363 versus 0.051 and 1.006 for EHAA. Both of these indexes showed an annual periodicity and correlated positively (although weakly) with EHAA/THAA ratios. None of them correlated negatively with GSR. This last result suggests that EHAA/THAA ratios constitute a better index of the lability of particulate organic matter than degradation indexes. KEY WORDS: Particulate organic matter · Amino acids · Bioavailability · Temporal changes · Resuspension Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 214. Online publication date: April 26, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

The dichotomy spectrum for noninvertible systems of linear difference equations *

In this paper we introduce the so—called dichotomy spectrum for nonautonomous linear difference equations , whose coefficient matrices are not supposed to be invertible. This new kind of spectrum is based on the notion of exponential forward dichotomy and consists of at most N+ 1 closed, not necessarily bounded, intervals of the positive real line. If all the matrices A(k) are invertible then the number of spectral intervals is at most N, and if in addition A(k) ≡ A is independent of k then these intervals reduce to the absolut values of the eigenvalues of A. In any case the spectral intervals are associated with invariant vector bundles comprising solutions with a common exponential growth rate. The main result of this paper is a Spectral Theorem which describes all possible forms of the dichotomy spectrum

ESR STUDIES ON GMR RELATED MATERIALS III: ESR OF Mn IN La0.9Ca0.1MnO3

ESR measurements have been done on La 0.9 Ca 0.1 MnO 3 from 4 K up to about 760 K. Two kinds of spectra (the high- and low-field signals) are observed below about 220 K, and clear signals above ≃233 K . The ESR linewidth, ΔH PP , of the high-field signal with g≃2 is nearly proportional to temperature times magnetic moment. The ESR intensity becomes maximum at around 233 K. Above 300 K, ΔH PP is nearly proportional to exp (-600/T), and the intensity follows Curie's law above 600 K, but gradually deviates upward from it with decreasing temperature below about 600 K, presumably due to the "spin-cluster" formation.

ESR STUDIES ON GMR RELATED MATERIALS II: ESR of Mn IN La0.97Ca0.03MnO3

ESR measurements have been carried out for La 0.97 Ca 0.03 MnO 3 at temperatures from 4 K up to 760 K. below ≃243 K , two kinds of spectra, the high-field and low-field signals, are observed down to 96 and 4 K, respectively. They are assumed to be due to Mn 4+ and Mn 3+ ions, respectively. From the g-shifts of the high-field ( Mn 4+) signals, the magnetic interaction coefficient between Mn 4+ and Mn 3+ spins is estimated. Clear single ESR was observed above ≃255 K , and its linewidth and intensity are obtained as a function of temperature. The linewidth nearly follows exp (-550/T), and the intensity gradually deviates from Curie's law below ≃550 K , presumably due to the spin-cluster formation.

Gas sampling glow discharge: a versatile ionization source for gas chromatography time-of-flight mass spectrometry

A gas chromatograph has been coupled to a direct-current gas sampling glow discharge (GSGD) ionization source for the mass spectrometric analysis of halogenated hydrocarbons. The continuous discharge is contained within the first vacuum stage of the differentially pumped spectrometer interface. The discharge can be operated statically or rapidly switched between atomic and molecular ionization modes; both atomic and molecular spectra could be generated in the helium-supported plasma. In the switched configuration, the duty cycle is 50% for each mode. The ionization mode is selected by application of either a positive (molecular) or negative (atomic) potential to the sample introduction electrode, and the two kinds of spectra can be sequentially collected by changing the voltage and current between two preset values. Similar ion-optical voltage settings could be employed for both modes of operation, with the exception of the steering-plate potential, which had to be modulated between two different values (at the plasma switching frequency) to obtain the greatest atomic and molecular signal levels. The source is capable of generating mass spectra resembling those from an electron-impact source while operated in the molecular ionization mode (both static and dynamic). The best atomic detection limits (1-25 fg of analyte/ second) were obtained when the plasma was operated in the static mode with single-channel gated ion counting. Atomic detection limits obtained with boxcar averager data collection were comparable for static and switched operation of the source (1-30 pg/s). Likewise, the molecular detection limits were similar for the static and switched modes and span the range of 7-140 pg/s (boxcar averagers). Precision was better than 7% RSD under all conditions. The atomic and molecular chromatographic peak heights were nearly unchanged over a range of modulation rates from 5 to 100 Hz. The elemental ratio (35Cl+/12C+) for chloroform was also measured over a range of plasma modulation rates (5-90 Hz) and found to be randomly distributed about the sample mean. Several chlorinated hydrocarbons were introduced into the discharge and could be successfully differentiated (or speciated) on the basis of their 35Cl+/12C+ ratios.

Formula omitted]C NMR study of an organic conductor, θ-(BEDT-TTF) 2RbZn(SCN) 4

The compound mentioned in the title is a quasi-two-dimensional organic conductor exhibits a metal–insulator transition accompanied by structural modification at T MI ∼190 K , while the tight-binding band calculation suggests a 3/4 filled band at higher temperatures. The 13 C NMR measurements have been performed on a single crystal to clarify the electronic nature of the metal–insulator transition. At room temperature, the 13 C NMR spectrum indicates that all BEDT-TTF molecules are electronically equivalent. Below T MI, however, it splits into two kinds of spectra with different Knight shifts and spin-lattice relaxation rates. These results show that charge disproportionation occurs below T MI and that long-range Coulomb interaction is important in this system.

Probing colored noise from the index of refraction of strongly driven two-level atoms

We analyze the effects of a reservoir having a generic spectrum (colored noise) on the index of refraction of a system of strongly driven two-level atoms (gas) probed by a weak field. We show that for high Rabi frequencies, $\ensuremath{\Omega},$ a simple analytic expression results for the susceptibility function (with respect to the probe) when $\ensuremath{\nu}\ensuremath{\approx}\ensuremath{\Omega},$ where $\ensuremath{\nu}$ is the detuning between driving and probe fields frequencies. Several distinct features are revealed in that function when compared to the one resulting from a reservoir with a white-noise spectrum (atom-vacuum coupling). We also show that the Mach-Zehnder interferometry could permit distinguishing between the two kinds of spectra and we point out the sensitive dependence of the index of refraction of the atomic gas on $\ensuremath{\Omega}$ and find a signature for the non-Markovian evolution.

Molecular interactions of 4-n-alkyl-4′-cyanobiphenyl detected in vibronic and vibrational spectra

The vibronic absorption and emission spectra of 4-pentyl-4′-cyanobiphenyl in nonpolar, moderately polar and polar solvents, as well as Fourier Transform Infira Red absorption spectra of biphenyl, 4-ethyl-4′-cyanobiphenyl and 4-pentyl-4′-cyanobiphenyl in KBr were measured. In these two kinds of spectra, change of the band shape has been observed for flexible molecules.