Journal articles: 'Spectral distances'

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Navarro, Silvana G., Romano L. M. Corradi, and Antonio Mampaso. "Distance determination to PNe using the extinction-distance method." Proceedings of the International Astronomical Union 7, S283 (July 2011): 460–61. http://dx.doi.org/10.1017/s1743921312011921.

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AbstractWe present individual distances to three PNe: NGC 6537, NGC 6781 and NGC 7027, determined by the extinction-distance method. These objects are part of a larger sample (35) of PNe that we observed at ORM. In order to apply this method, and to obtain accurate distances, we determined the spectral type of 40 to 60 stars in the line of sight of each PNe. This implied the necessity of classifying few thousands of stellar spectra with S/N ratio between 10 and 60. To solve such need we developed an ANN system to perform automatic spectral classification which could classify spectra with S/N ratio as low as 20 with an accuracy better than 2 spectral subtypes. In this poster we compare the accuracy of such distances with previous distance determinations using other methods. We conclude that it is possible to use this method to obtain the distance of a large number of PNe with better precision.

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Jovanović, Irena, and Zoran Stanić. "Spectral distances of graphs." Linear Algebra and its Applications 436, no. 5 (March 2012): 1425–35. http://dx.doi.org/10.1016/j.laa.2011.08.019.

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Gu, Jiao, Bobo Hua, and Shiping Liu. "Spectral distances on graphs." Discrete Applied Mathematics 190-191 (August 2015): 56–74. http://dx.doi.org/10.1016/j.dam.2015.04.011.

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Chelli, A., and G. Duvert. "Pseudo-photometric distances of 30 open clusters." Astronomy & Astrophysics 619 (November 2018): A132. http://dx.doi.org/10.1051/0004-6361/201833082.

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Aims. We demonstrate that reliable photometric distances of stellar clusters, and more generally of stars, can be obtained using pseudomagnitudes and rough spectral type without having to correct for visual absorption. Methods. We determine the mean absolute pseudomagnitude of all spectral (sub)types between B and K. Distances are computed from the difference between the star’s observed pseudomagnitude and its spectral type’s absolute pseudomagnitude. We compare the distances of 30 open clusters thus derived against the distances derived from TGAS parallaxes. Results. Our computed distances, up to distance modulus 12, agree within 0.1 mag rms with those obtained from TGAS parallaxes, proving excellent distance estimates. We show additionally that there are actually two markedly different distances in the cluster NGC 2264. Conclusions. We suggest that the pseudomagnitude distance estimation method, which is easy to perform, can be routinely used in all large-scale surveys where statistical distances on a set of stars, such as an open cluster, are required.

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Pollacco, D. L., and G. Ramsay. "Reddening Distances for Planetary Nebulae from Broad Band BVIc CCD Imaging." Symposium - International Astronomical Union 155 (1993): 180. http://dx.doi.org/10.1017/s0074180900170421.

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If the zero age main sequence is expressed in the (V–I) versus (B–V)–(V–I) plane the reddening lines are found to lie at a great enough angle to allow reasonably accurate spectral type classification for stars later than ∼ F5. Earlier spectral types can also be identified but with lower accuracy. Comparison with the Q method of UBV photometry and with spectra of some of the program stars shows that the BVIc technique produces reliable results. As late–type stars constitute the most numerous spectral types and are plentiful in all galactic plane directions BVIc reddening distances can be derived close to the desired direction (although to smaller distances than techniques that utilize early type stars). The applicability of the technique is further enhanced by the use of CCDs which generally have a spectral response well suited for BVIc imaging observations. Using the new technique the distance to the PN NGC2440 was found to be (3100 ± 320)pc.

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Cvetkovic, Dragos. "Spectral recognition of graphs." Yugoslav Journal of Operations Research 22, no. 2 (2012): 145–61. http://dx.doi.org/10.2298/yjor120925025c.

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At some time, in the childhood of spectral graph theory, it was conjectured that non-isomorphic graphs have different spectra, i.e. that graphs are characterized by their spectra. Very quickly this conjecture was refuted and numerous examples and families of non-isomorphic graphs with the same spectrum (cospectral graphs) were found. Still some graphs are characterized by their spectra and several mathematical papers are devoted to this topic. In applications to computer sciences, spectral graph theory is considered as very strong. The benefit of using graph spectra in treating graphs is that eigenvalues and eigenvectors of several graph matrices can be quickly computed. Spectral graph parameters contain a lot of information on the graph structure (both global and local) including some information on graph parameters that, in general, are computed by exponential algorithms. Moreover, in some applications in data mining, graph spectra are used to encode graphs themselves. The Euclidean distance between the eigenvalue sequences of two graphs on the same number of vertices is called the spectral distance of graphs. Some other spectral distances (also based on various graph matrices) have been considered as well. Two graphs are considered as similar if their spectral distance is small. If two graphs are at zero distance, they are cospectral. In this sense, cospectral graphs are similar. Other spectrally based measures of similarity between networks (not necessarily having the same number of vertices) have been used in Internet topology analysis, and in other areas. The notion of spectral distance enables the design of various meta-heuristic (e.g., tabu search, variable neighbourhood search) algorithms for constructing graphs with a given spectrum (spectral graph reconstruction). Several spectrally based pattern recognition problems appear in many areas (e.g., image segmentation in computer vision, alignment of protein-protein interaction networks in bio-informatics, recognizing hard instances for combinatorial optimization problems such as the travelling salesman problem). We give a survey of such and other graph spectral recognition techniques used in computer sciences.

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Bronstein, Michael M., and Alexander M. Bronstein. "Shape Recognition with Spectral Distances." IEEE Transactions on Pattern Analysis and Machine Intelligence 33, no. 5 (May 2011): 1065–71. http://dx.doi.org/10.1109/tpami.2010.210.

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da Cunha Lima, A. T., I. C. da Cunha Lima, and M. P. de Almeida. "Analysis of turbulence power spectra and velocity correlations in a pipeline with obstructions." International Journal of Modern Physics C 28, no. 02 (February 2017): 1750019. http://dx.doi.org/10.1142/s012918311750019x.

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We calculate the power spectral density and velocity correlations for a turbulent flow of a fluid inside a duct. Turbulence is induced by obstructions placed near the entrance of the flow. The power spectral density is obtained for several points at cross-sections along the duct axis, and an analysis is made on the way the spectra changes according to the distance to the obstruction. We show that the differences on the power spectral density are important in the lower frequency range, while in the higher frequency range, the spectra are very similar to each other. Our results suggest the use of the changes on the low frequency power spectral density to identify the occurrence of obstructions in pipelines. Our results show some frequency regions where the power spectral density behaves according to the Kolmogorov hypothesis. At the same time, the calculation of the power spectral densities at increasing distances from the obstructions indicates an energy cascade where the spectra evolves in frequency space by spreading the frequency amplitude.

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Jovanovic, Irena, and Zoran Stanic. "Spectral distances of graphs based on their different matrix representations." Filomat 28, no. 4 (2014): 723–34. http://dx.doi.org/10.2298/fil1404723j.

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The investigation of the spectral distances of graphs that started in [3] (I. Jovanovic, Z. Stanic, Spectral distances of graphs, Linear Algebra Appl., 436 (2012) 1425-1435.) is continued by defining Laplacian and signless Laplacian spectral distances and considering their relations to the spectral distances based on the adjacency matrix of graph. Some separate results concerning the defined distances are given, and the initial spectral distances in certain sets of graphs are investigated. Computational data on Laplacian and signless Laplacian spectral distances are provided.

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Baggio, Giacomo, Augusto Ferrante, and Rodolphe Sepulchre. "Conal Distances Between Rational Spectral Densities." IEEE Transactions on Automatic Control 64, no. 5 (May 2019): 1848–57. http://dx.doi.org/10.1109/tac.2018.2855114.

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Boatwright, John. "Regional propagation characteristics and source parameters of earthquakes in northeastern North America." Bulletin of the Seismological Society of America 84, no. 1 (February 1, 1994): 1–15. http://dx.doi.org/10.1785/bssa0840010001.

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Abstract The vertical components of the S wave trains recorded on the Eastern Canadian Telemetered Network (ECTN) from 1980 through 1990 have been spectrally analyzed for source, site, and propagation characteristics. The data set comprises some 1033 recordings of 97 earthquakes whose magnitudes range from M ≈ 3 to 6. The epicentral distances range from 15 to 1000 km, with most of the data set recorded at distances from 200 to 800 km. The recorded S wave trains contain the phases S, SmS, Sn, and Lg and are sampled using windows that increase with distance; the acceleration spectra were analyzed from 1.0 to 10 Hz. To separate the source, site, and propagation characteristics, an inversion for the earthquake corner frequencies, low-frequency levels, and average attenuation parameters is alternated with a regression of residuals onto the set of stations and a grid of 14 distances ranging from 25 to 1000 km. The iteration between these two parts of the inversion converges in about 60 steps. The average attenuation parameters obtained from the inversion were Q = 1997 ± 10 and γ = 0.998 ± 0.003. The most pronounced variation from this average attenuation is a marked deamplification of more than a factor of 2 at 63 km and 2 Hz, which shallows with increasing frequency and increasing distance out to 200 km. The site-response spectra obtained for the ECTN stations are generally flat. The source spectral shape assumed in this inversion provides an adequate spectral model for the smaller events (Mo < 3 × 1021 dyne-cm) in the data set, whose Brune stress drops range from 5 to 150 bars. For the five events in the data set with Mo ≧ 1023 dyne-cm, however, the source spectra obtained by regressing the residuals suggest that an ω2 spectrum is an inadequate model for the spectral shape. In particular, the corner frequencies for most of these large events appear to be split, so that the spectra exhibit an intermediate behavior (where |ü(ω)| is roughly proportional to ω).

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SONG, H., U. C. PAEK, and D. Y. KIM. "WALK-OFF LENGTH LIMITED SPECTRAL BROADENING IN SUPERCONTINUUM GENERATION." Journal of Nonlinear Optical Physics & Materials 18, no. 01 (March 2009): 99–110. http://dx.doi.org/10.1142/s0218863509004464.

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Detailed spectrum broadening mechanisms in supercontinuum (SC) generation are studied with an all-fiber pulsed laser source and a highly nonlinear dispersion-shifted fiber (HN-DSF). Mode-locked fiber laser pulses are stretched to four different pulse widths, and SC spectra are measured with different propagation distances with these pulses. By observing the development of spectral width with distance, we have observed that self-phase modulation (SPM) rather than soliton fission is the dominant process at the beginning of SC generation in our case. We have also confirmed that four-wave mixing (FWM) and its walk-off problem associated with different spectral components are the major limiting factors in efficient wide-band SC generation.

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Kudritzki, Rolf-Peter. "The Wind Momentum – Luminosity Relationship of Blue Supergiants." International Astronomical Union Colloquium 169 (1999): 405–15. http://dx.doi.org/10.1017/s0252921100072304.

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AbstractThe prediction of the Wind Momentum - Luminosity Relationship (WLR) based on the theory of radiation driven winds is verified by quantitative spectroscopy of winds of A-, B- and O-supergiants. The relationship depends on spectral type. New stellar wind calculations are presented reproducing the observed spectral type dependence. The impact of spectral variability on the WLR is investigated by an analysis of some hundred spectra of the luminous A0Ia-supergiant HD92207 obtained within the Heidelberg Spectral Variability Survey and found to be small.Finally, the WLR is discussed as a tool for the determination of extragalactic distances. Recent results obtained for the Galaxy, M31 and M33 are presented. The potential of the method is discussed with the conclusion that it may allow independent distance moduli to be obtained with an accuracy of ten percent out to the Virgo and Fornax clusters of galaxies.

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Houston, Heidi, and Hiroo Kanamori. "Comparison of strong-motion spectra with teleseismic spectra for three magnitude 8 subduction-zone earthquakes." Bulletin of the Seismological Society of America 80, no. 4 (August 1, 1990): 913–34. http://dx.doi.org/10.1785/bssa0800040913.

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Abstract We studied strong-motion spectra observed for three Mw 7.8 to 8.0 earthquakes (the 1985 Michoacán, Mexico; 1985 Valparaíso, Chile; and 1983 Akita-Oki, Japan earthquakes). We determined the decay of spectral amplitude with distance from the station, considering different measures of distance from a finite fault. We compared strong-motion spectra (Fourier acceleration spectra) observed for these three earthquakes with those estimated from the source spectrum determined from teleseismic P waves. We scaled the teleseismic source spectra to produce reference strong-motion spectra at periods from 1 to 10 sec using a simple physical model of far-field S body waves from a point source recorded at the surface of a homogeneous half-space. For all three earthquakes the reference spectral amplitudes at periods of 1 to 5 sec are about half the observed ones at distances of about 50 km. The difference increases as the distance increases. At distances of 200 to 300 km, the reference spectrum is about 1/10 of the observed one. The difference between the reference and the observed spectrum is attributed to the contribution of phases other than direct S waves and to site response. We applied corrections for the finiteness (spatial extent) of the source using a simple model of rupture propagation on a dipping two-dimensional fault. Including the source finiteness did not improve the estimate substantially at periods from 1 to 20 sec, but it modeled significant changes in the signal duration as a function of azimuth for the 1985 Michoacán earthquake. Our results can be used to establish empirical relations between the observed spectra and the half-space responses, depending on the distance and the site condition. If such empirical relations can be established, source spectra determined from teleseismic records may be used to estimate strong motions.

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Gitterman, Yefim, and Torild van Eck. "Spectra of quarry blasts and microearthquakes recorded at local distances in Israel." Bulletin of the Seismological Society of America 83, no. 6 (December 1, 1993): 1799–812. http://dx.doi.org/10.1785/bssa0830061799.

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Abstract In northern Israel, quarry blasts and microearthquakes occur in a region with complicated tectonics. Therefore correct event identification, preferably based on a simple method that can be applied on a routine basis, is essential for accurate and detailed seismotectonic studies. Spectral analysis of quarry blasts and microearthquakes recorded at local distances (5 < Δ < 2000 km) by stations of the Israel Seismograph Network revealed spectral characteristics in the frequency range less than 12.5 Hz that can be used routinely for event identification. Most quarry blasts in northern Israel are ripple-fired, open pit blasts, consequently we chose an event discrimination method based on the recognition of ripple-firing patterns in the signal. A simple model for ripple firing parameters, based on interference theory of linear systems and including random effects, predicts spectral minima at low frequencies identical for different seismic phases. We compared the spectra of complete seismogram signals of 52 events recorded by the ISN at different distances and azimuths, including both microearthquakes and quarry blasts in a selected region of northern Israel. Consistent spectral modulation was found in a band from about 2 to 8 Hz for 18 of 21 reliably identified, i.e., reported, quarry blasts with time delays of 20 to 40 msec. The spectral minima frequencies correspond to those predicted by the theory.

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Davatgari Fami Tafreshi, Mehran, Sanjay Singh Bora, Noorbakhsh Mirzaei, Hadi Ghofrani, and Javad Kazemian. "Spectral models for seismological source parameters, path attenuation and site-effects in Alborz region of northern Iran." Geophysical Journal International 227, no. 1 (June 9, 2021): 350–67. http://dx.doi.org/10.1093/gji/ggab227.

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SUMMARY We analysed 478 three-component strong ground motion time-series from 65 events in the moment magnitude (Mw) 3–6.5 range recorded at 111 stations at distances up to 150 km from 1997 to 2019 in the Alborz region. Non-parametric spectral functions for seismological source, path and site-effects were derived from Fourier amplitude spectra of observed acceleration time-histories using the generalized inversion technique (GIT) for the Alborz region of Iran. To characterize the spectral models in terms of the anelastic attenuation (Q), geometrical spreading, magnitude and stress parameter (Δσ), we fitted non-parametric attenuation and source functions (resulted from inversion) with the standard parametric models. The frequency-dependent non-parametric attenuation function shows a rapid decay at close distances (<60 km) and decreases monotonically at larger distances. The frequency-independent geometrical spreading follows a bilinear hinged model with a crossover distance at 70 km. For hypocentral distances Rhypo < 70 km, the geometrical spreading is ${R^{ - 1.01}}$, and for Rhypo > 70 km it is ${R^{ - 1.37}}$. The corresponding quality factor is $Q\ ( f ) = \ 146{f^{0.91}}$. The non-parametric source spectra were found in a good agreement with Brune's ω-squared model. The stress-parameter (Δσ) values were found to exhibit large variability from 0.36 to 86.7 MPa with no significant magnitude-dependence. The average Δσ was found to be 8.6 MPa. The mean value of the estimated near-surface attenuation (κ0) from high-frequency part of non-parametric source function is 0.032 s (±0.01 s). In general, there is a good agreement between subsoil resonance frequencies and amplification levels estimated from GIT and HVSR (horizontal to vertical spectral ratio). The results of this study provide updated values of seismological source, attenuation and site properties in the Alborz region of northern Iran, which are expected to improve regional seismic hazard analysis studies in the region.

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Garratt, R. C., R. W. Evans, S. S. Hasnain, and P. F. Lindley. "An extended-X-ray-absorption-fine-structure investigation of diferric transferrins and their iron-binding fragments." Biochemical Journal 233, no. 2 (January 15, 1986): 479–84. http://dx.doi.org/10.1042/bj2330479.

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Iron K-edge extended-X-ray-absorption-fine-structure (e.x.a.f.s.) spectra were recorded for diferric human and rabbit serum transferrins and for diferric chicken ovotransferrin in aqueous solution; for ovotransferrin e.x.a.f.s. spectra from the N-terminal and C-terminal domain fragments were also measured. The overall spectral profiles closely resemble one another, indicating similar iron-binding sites. The simulation of the diferric ovotransferrin spectrum suggests a first co-ordination shell consisting of six low-Z ligands (nitrogen/oxygen), two ligands at a distance of approx. 0.185 nm (1.85 A) and four ligands at approx. 0.204 nm (2.04 A). The two shorter distances may correspond to Fe-O (tyrosine), whereas the longer distance is consistent with Fe-N (histidine) and Fe-O (water). Detailed analysis of the spectra of the N-terminal and C-terminal fragments indicates a difference in the short ligand distance.

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Chakraborty, Anwesha, and Biswajit Chakraborty. "Spectral distance on Lorentzian Moyal plane." International Journal of Geometric Methods in Modern Physics 17, no. 06 (May 2020): 2050089. http://dx.doi.org/10.1142/s0219887820500899.

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We present here a completely operatorial approach, using Hilbert–Schmidt operators, to compute spectral distances between time-like separated “events”, associated with the pure states of the algebra describing the Lorentzian Moyal plane, using the axiomatic framework given by [N. Franco, The Lorentzian distance formula in noncommutative geometry, J. Phys. Conf. Ser. 968(1) (2018) 012005; N. Franco, Temporal Lorentzian spectral triples, Rev. Math. Phys. 26(8) (2014) 1430007]. The result shows no deformations of non-commutative origin, as in the Euclidean case, if the pure states are constructed out of Glauber–Sudarshan coherent states.

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Vogl, C., W. E. Kerzendorf, S. A. Sim, U. M. Noebauer, S. Lietzau, and W. Hillebrandt. "Spectral modeling of type II supernovae." Astronomy & Astrophysics 633 (January 2020): A88. http://dx.doi.org/10.1051/0004-6361/201936137.

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There are now hundreds of publicly available supernova spectral time series. Radiative transfer modeling of this data provides insight into the physical properties of these explosions, such as the composition, the density structure, and the intrinsic luminosity, which is invaluable for understanding the supernova progenitors, the explosion mechanism, and for constraining the supernova distance. However, a detailed parameter study of the available data has been out of reach due to the high dimensionality of the problem coupled with the still significant computational expense. We tackle this issue through the use of machine-learning emulators, which are algorithms for high-dimensional interpolation. These use a pre-calculated training dataset to mimic the output of a complex code but with run times that are orders of magnitude shorter. We present the application of such an emulator to synthetic type II supernova spectra generated with the TARDIS radiative transfer code. The results show that with a relatively small training set of 780 spectra we can generate emulated spectra with interpolation uncertainties of less than one percent. We demonstrate the utility of this method by automatic spectral fitting of two well-known type IIP supernovae; as an exemplary application, we determine the supernova distances from the spectral fits using the tailored-expanding-photosphere method. We compare our results to previous studies and find good agreement. This suggests that emulation of TARDIS spectra can likely be used to perform automatic and detailed analysis of many transient classes putting the analysis of large data repositories within reach.

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WALLET, JEAN-CHRISTOPHE. "CONNES DISTANCE BY EXAMPLES: HOMOTHETIC SPECTRAL METRIC SPACES." Reviews in Mathematical Physics 24, no. 09 (October 2012): 1250027. http://dx.doi.org/10.1142/s0129055x12500274.

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We study metric properties stemming from the Connes spectral distance on three types of non-compact non-commutative spaces which have received attention recently from various viewpoints in the physics literature. These are the non-commutative Moyal plane, a family of harmonic Moyal spectral triples for which the Dirac operator squares to the harmonic oscillator Hamiltonian and a family of spectral triples with the Dirac operator related to the Landau operator. We show that these triples are homothetic spectral metric spaces, having an infinite number of distinct pathwise connected components. The homothetic factors linking the distances are related to determinants of effective Clifford metrics. We obtain, as a by-product, new examples of explicit spectral distance formulas. The results are discussed in detail.

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Chen, Jianbo, Qun Zhou, Isao Noda, and Suqin Sun. "Quantitative Classification of Two-Dimensional Correlation Spectra." Applied Spectroscopy 63, no. 8 (August 2009): 920–25. http://dx.doi.org/10.1366/000370209788964520.

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Two-dimensional (2D) correlation spectroscopy, which takes advantage of the apparent enhancement of spectral resolution, is known to be useful in qualitative discrimination of seemingly similar samples. The possibility of quantitative classification of 2D correlation spectra is even more desirable. Two useful parameters, namely Euclidian distance and correlation coefficient between 2D correlation spectra, are introduced for this purpose. Dry and sweet red wine samples are used to demonstrate the utility of these parameters. The distances between the 2D infrared (IR) spectra of sweet and dry red wines are roughly proportional to the differences of sugar contents in them. The result shows that the two parameters are useful measures for the quantitative evaluation of the similarity among the samples and their corresponding 2D correlation spectra.

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Jiang, Xianhua, Lipeng Ning, and Tryphon T. Georgiou. "Distances and Riemannian Metrics for Multivariate Spectral Densities." IEEE Transactions on Automatic Control 57, no. 7 (July 2012): 1723–35. http://dx.doi.org/10.1109/tac.2012.2183171.

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Patané, Giuseppe. "Laplacian spectral distances and kernels on 3D shapes." Pattern Recognition Letters 47 (October 2014): 102–10. http://dx.doi.org/10.1016/j.patrec.2014.04.003.

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Georgiou, T. T. "Distances and Riemannian Metrics for Spectral Density Functions." IEEE Transactions on Signal Processing 55, no. 8 (August 2007): 3995–4003. http://dx.doi.org/10.1109/tsp.2007.896119.

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Fercher, A. F., C. K. Hitzenberger, G. Kamp, and S. Y. El-Zaiat. "Measurement of intraocular distances by backscattering spectral interferometry." Optics Communications 117, no. 1-2 (May 1995): 43–48. http://dx.doi.org/10.1016/0030-4018(95)00119-s.

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Chapman, M. C., G. A. Bollinger, and M. S. Sibol. "Modeling delay-fired explosion spectra at regional distances." Bulletin of the Seismological Society of America 82, no. 6 (December 1, 1992): 2430–47. http://dx.doi.org/10.1785/bssa0820062430.

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Abstract The objectives of this study are to model the observed seismic spectra from large industrial explosions using information obtained from blaster's logs and to compare the explosion spectra with those of small earthquake signals from the same source region. The data set consists of digital waveforms from four mining explosions (200,000 + lb. of explosives each) and two earthquakes (M = 3.5 and 4.0) in eastern Kentucky. The data were recorded on a short-period regional network at distances ranging from 180 to 400 km and have good signal-to-noise ratios at frequencies from 0.5 to 10 Hz. The explosion amplitude spectra differ markedly from those of the earthquakes, by exhibiting strong time-independent amplitude modulations. This spectral modulation is directly attributable to the explosive charge geometry and firing sequence and is largely independent of source-station path and recording site. Modeling of the explosion source spectra shows that the major contributor to the modulated character of the spectra are amplitude minima at frequencies related to the total duration of the explosion sequence. Another important effect is amplitude reinforcement at low frequencies (e.g., 5 Hz) due to the comparatively long delay (0.2 sec) between the firing of individual rows of explosives. These features dominate both Pg and Lg amplitude spectra at frequencies less than 7 Hz. Accurate modeling of the observed spectra at frequencies greater than a few Hertz requires that the azimuth of the recording site be taken into account. Also, the spectra at higher frequencies become sensitive to random variations in the firing times of any of the various subexplosions.

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Wang, Chun, Yang Huang, Haibo Yuan, Huawei Zhang, Maosheng Xiang, and Xiaowei Liu. "The Value-added Catalog for LAMOST DR8 Low-resolution Spectra." Astrophysical Journal Supplement Series 259, no. 2 (March 28, 2022): 51. http://dx.doi.org/10.3847/1538-4365/ac4df7.

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Abstract We present a value-added catalog containing stellar parameters estimated from 7.10 million low-resolution spectra for 5.16 million unique stars with spectral signal-to-noise ratios (S/N) higher than 10 obtained by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Galactic spectroscopic surveys. The catalog presents values of stellar atmospheric parameters (effective temperature T eff, surface gravity log g, metallicity [Fe/H]/[M/H]), α-element to metal abundance ratio [α/M], carbon and nitrogen to iron abundance ratios [C/Fe] and [N/Fe], and 14 bands’ absolute magnitudes deduced from LAMOST spectra using the neural network method. The spectrophotometric distances of those stars are also provided based on the distance modulus. For stars with a spectral S/N larger than 50, precisions of T eff, log g, [Fe/H], [M/H], [C/Fe], [N/Fe], and [α/M] are 85 K, 0.098 dex, 0.05 dex, 0.05 dex, 0.052 dex, 0.082 dex, and 0.027 dex, respectively. The errors of 14 band’s absolute magnitudes are 0.16–0.22 mag for stars with a spectral S/N larger than 50. The spectrophotometric distance is accurate to 8.5% for stars with a spectral S/N larger than 50 and is more accurate than the geometrical distance for stars with a distance larger than 2.0 kpc. Our estimates of [Fe/H] are reliable down to [Fe/H] ∼−3.5 dex, significantly better than previous results. The catalog provides 26,868 unique very metal-poor star candidates ([Fe/H] ≤−2.0). The catalog would be a valuable dataset to study the structure and evolution of the galaxy, especially the solar neighborhood and the outer disk.

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Bozorgnia, Yousef, Mahmoud M. Hachem, and Kenneth W. Campbell. "Ground Motion Prediction Equation (“Attenuation Relationship”) for Inelastic Response Spectra." Earthquake Spectra 26, no. 1 (February 2010): 1–23. http://dx.doi.org/10.1193/1.3281182.

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This paper presents the process and fundamental results of a comprehensive ground motion prediction equation (GMPE, or “attenuation” relationship) developed for inelastic response spectra. We used over 3,100 horizontal ground motions recorded in 64 earthquakes with moment magnitudes ranging from 4.3–7.9 and rupture distances ranging from 0.1–199 km. For each record, we computed inelastic spectra for ductility ranging from one (elastic response) to eight. Our GMPE correlates inelastic spectral ordinates to earthquake magnitude, site-to-source distance, fault mechanism, local soil properties, and basin effects. The developed GMPE is used in both deterministic and probabilistic hazard analyses to directly generate inelastic spectra. This is in contrast to developing “attenuation” relationships for elastic response spectra, carrying out a hazard analysis, and subsequently adopting approximate rules to derive inelastic response from elastic spectra.

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Zlatev, Zlatin. "SPECTRAL INDICES APPLICATION IN THE DETERMINATION OF CROSSBRED LAMBS SLAUGHTER INDICATORS." International Conference on Technics, Technologies and Education, no. 1 (2018): 160–65. http://dx.doi.org/10.15547/ictte.2018.04.007.

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The report describes the data used for slaughter indicators of crossbred lambs. A method is presented of converting color components to spectral characteristics and their second derivative. Methods of selection of informative wavelengths are used by ABC analysis, using an Euclidean distance between the values of reflection at these lengths. The method used for determining spectral indices is presented. The differences in the Euclidean distances between the spectral indexes have been found to show a regularity similar to that of the water absorption coefficient and the tenderness of meat. The proposed spectral indexes will be used in laboratory conditions for the determination of physico-chemical indicators of crossbreed lambs.

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Huang, Yuping, Yutu Yang, Ye Sun, Haiyan Zhou, and Kunjie Chen. "Identification of Apple Varieties Using a Multichannel Hyperspectral Imaging System." Sensors 20, no. 18 (September 8, 2020): 5120. http://dx.doi.org/10.3390/s20185120.

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This paper reports the nondestructive detection of apple varieties using a multichannel hyperspectral imaging system consisting of an illumination fiber and 30 detection fibers arranged at source–detector distances of 1.5–36 mm over the spectral range of 550–1650 nm. Spatially resolved (SR) spectra were obtained for 1500 apples, 500 each of three varieties from the same orchard to avoid environmental and geographical influences. Partial least squares discriminant analysis (PLSDA) models were developed for single SR spectra and spectral combinations to compare their performance of variety detection. To evaluate the effect of spectral range on variety detection, three types of spectra (i.e., visible region: 550–780 nm, near-infrared region: 780–1650 nm, full region: 550–1650 nm) were analyzed and compared. The results showed that the single SR spectra presented a different accuracy for apple variety classification, and the optimal SR spectra varied with spectral types. Spectral combinations had better accuracies for variety detection with best overall classifications of 99.4% for both spectral ranges in the NIR and full regions; however, the spectral combination could not improve the results over the optimal single SR spectra in the visible region. Moreover, the recognition of golden delicious (GD) was better than those of the other two varieties, with the best classification accuracy of 100% for three types of spectra. Overall, the multichannel hyperspectral imaging system provides more spatial-spectral information for the apples, and the results demonstrate that the technique gave excellent classifications, which suggests that the multichannel hyperspectral imaging system has potential for apple variety detection.

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Baring, Matthew G. "Gamma-Ray Burst Spectral Breaks and Source Beaming." International Astronomical Union Colloquium 142 (1994): 899–903. http://dx.doi.org/10.1017/s0252921100078283.

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AbstractThe principal discovery of the ComptonGamma-Ray Observatory(GRO) concerning gamma-ray bursts is that these sources are isotropic but with a comparative deficiency of fainter sources, suggesting that they are probably cosmological in origin. If they are at such large distances from Earth then they are extremely luminous and compact. A consequence of this is that two-photon pair production attenuation of the gamma-ray continuum cannot be avoided unless the source radiation is substantially beamed. Most sources do not display gamma-ray turnovers although a few GRB detected byGROexhibit distinct spectral breaks in the MeV range. A derivation of the relationship defining of the degree of beaming in burst sources with spectral breaks due toγ-γattenuation, as a function of source spectral index and break energy, is presented. It is found that sources at distances of ~1 Gpc must typically be beamed with bulk Lorentz factors of around 103-104, indicating powerful bulk acceleration in bursts, although these Lorentz factors are reduced markedly for steep source spectra. Since the source spectra are not strongly Comptonized, such beaming will blueshift the γ-γ attenuation breaks to energies much higher than 1 MeV; an absolute lower bound to the source bulk Lorentz factor is determined from this additional constraint. This blueshifting suggests that those sources with MeV breaks may not be cosmological, or that their breaks are produced by a mechanism that dominates γ-γ attenuation at these energies.Subject headings:gamma-rays: bursts — radiation mechanisms: nonthermal

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Kollatschny, W., M. W. Ochmann, M. Zetzl, M. Haas, D. Chelouche, S. Kaspi, F. Pozo Nuñez, and D. Grupe. "Broad-line region structure and line profile variations in the changing look AGN HE 1136-2304." Astronomy & Astrophysics 619 (November 2018): A168. http://dx.doi.org/10.1051/0004-6361/201833727.

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Aims. A strong X-ray outburst was detected in HE 1136-2304 in 2014. Accompanying optical spectra revealed that the spectral type has changed from a nearly Seyfert 2 type (1.95), classified by spectra taken 10 and 20 years ago, to a Seyfert 1.5 in our most recent observations. We seek to investigate a detailed spectroscopic campaign on the spectroscopic properties and spectral variability behavior of this changing look AGN and compare this to other variable Seyfert galaxies. Methods. We carried out a detailed spectroscopic variability campaign of HE 1136-2304 with the 10 m Southern African Large Telescope (SALT) between 2014 December and 2015 July. Results. The broad-line region (BLR) of HE 1136-2304 is stratified with respect to the distance of the line-emitting regions. The integrated emission line intensities of Hα, Hβ, He I λ5876, and He II λ4686 originate at distances of 15.0−3.8+4.2, 7.5−5.7+4.6, 7.3−4.4+2.8, and 3.0−3.7+5.3 light days with respect to the optical continuum at 4570 Å. The variability amplitudes of the integrated emission lines are a function of distance to the ionizing continuum source as well. We derived a central black hole mass of 3.8 ± 3.1 × 107 M⊙ based on the linewidths and distances of the BLR. The outer line wings of all BLR lines respond much faster to continuum variations indicating a Keplerian disk component for the BLR. The response in the outer wings is about two light days shorter than the response of the adjacent continuum flux with respect to the ionizing continuum flux. The vertical BLR structure in HE 1136-2304 confirms a general trend that the emission lines of narrow line active galactic nuclei (AGNs) originate at larger distances from the midplane in comparison to AGNs showing broader emission lines. Otherwise, the variability behavior of this changing look AGN is similar to that of other AGN.

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Anderson, John, Roberto Quaas, Quigbin Chen, David Almora, Ricardo Vázquez, Juan Velasco, Citlali Pérez, and Gerardo Castro. "CHARACTERISTICS OF EARTHQUAKES IN THE MEXICAN SUBDUCTION ZONE ON STRONG MOTION ACCELEROGRAMS." Revista de Ingeniería Sísmica, no. 54 (December 19, 1996): 17. http://dx.doi.org/10.18867/ris.54.234.

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Aceelerograms recorded on the Guerrero, Mexico, strong motion accelerograph network illustrate the dependence of strong ground motion on the magnitude and the hypocenter distance. These data suppport the hipothesis that complexity in accelerograms at short distances arises from complexity at the source. The duration of strong shaking is controlled by the source dimension at short distances, and extended by wave porpagation effects as distance increases. Peak amplitudes (peak acceleration, velocity) saturate at different magnitudes at different distances. This change in shape of attenuation curves as magnitude increases can be explained by the trnasition of Green's functions from simple, short pulses at short distances to longer duration wave trains at large distances. Spectral amplitudes demonstrate scalin relations in which loe frequency amplitudes are proportional to seismic moment but high frecuencies increase much less rapidly. The beginnings of large earthquakes look like small earthquakes, consistent with a cascade model for the growth of large events. The mostrecent large earthquake, on sept. 14,995 (Mw=7.4) shows surprisingly weak peak accelerations.

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Ouahada, Khmaies, and Hendrik C. Ferreira. "New Distance Concept and Graph Theory Approach for Certain Coding Techniques Design and Analysis." Communications in Applied and Industrial Mathematics 10, no. 1 (January 1, 2019): 53–70. http://dx.doi.org/10.1515/caim-2019-0012.

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Abstract A New graph distance concept introduced for certain coding techniques helped in their design and analysis as in the case of distance-preserving mappings and spectral shaping codes. A graph theoretic construction, mapping binary sequences to permutation sequences and inspired from the k-cube graph has reached the upper bound on the sum of the distances for certain values of the length of the permutation sequence. The new introduced distance concept in the k-cube graph helped better understanding and analyzing for the first time the concept of distance-reducing mappings. A combination of distance and the index-permutation graph concepts helped uncover and verify certain properties of spectral null codes, which were previously difficult to analyze.

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Stahl, Benjamin E., Thomas de Jaeger, WeiKang Zheng, and Alexei V. Filippenko. "The snapshot distance method: estimating the distance to a Type Ia supernova from minimal observations." Monthly Notices of the Royal Astronomical Society 505, no. 2 (May 13, 2021): 2300–2308. http://dx.doi.org/10.1093/mnras/stab1367.

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ABSTRACT We present the snapshot distance method (SDM), a modern incarnation of a proposed technique for estimating the distance to a Type Ia supernova (SN Ia) from minimal observations. Our method, which has become possible owing to recent work in the application of deep learning to SN Ia spectra (we use the deepSIP package), allows us to estimate the distance to an SN Ia from a single optical spectrum and epoch of 2 + passband photometry – one night’s worth of observations (though contemporaneity is not a requirement). Using a compilation of well-observed SNe Ia, we generate snapshot distances across a wide range of spectral and photometric phases, light-curve shapes, photometric passband combinations, and spectrum signal-to-noise ratios. By comparing these estimates to the corresponding distances derived from fitting all available photometry for each object, we demonstrate that our method is robust to the relative temporal sampling of the provided spectroscopic and photometric information, and to a broad range of light-curve shapes that lie within the domain of standard width–luminosity relations. Indeed, the median residual (and asymmetric scatter) between SDM distances derived from two-passband photometry and conventional light-curve-derived distances that utilize all available photometry is $0.013_{-0.143}^{+0.154}$ mag. Moreover, we find that the time of maximum brightness and light-curve shape (both of which are spectroscopically derived in our method) are only minimally responsible for the observed scatter. In a companion paper, we apply the SDM to a large number of sparsely observed SNe Ia as part of a cosmological study.

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Sugiura, Makoto, and Ushio Saitoh. "Spectral analysis on urban silhouettes from differeny visual distances." Journal of the City Planning Institute of Japan 35 (2000): 787–92. http://dx.doi.org/10.11361/journalcpij.35.787.

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Zeune, Leonie, Guus van Dalum, Leon W. M. M. Terstappen, Stephan A. van Gils, and Christoph Brune. "Multiscale Segmentation via Bregman Distances and Nonlinear Spectral Analysis." SIAM Journal on Imaging Sciences 10, no. 1 (January 2017): 111–46. http://dx.doi.org/10.1137/16m1074503.

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Kamm, C., and D. Kahn. "Relationship between LP‐residual spectral distances and phonetic judgments." Journal of the Acoustical Society of America 78, S1 (November 1985): S82. http://dx.doi.org/10.1121/1.2023022.

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Robila, S. A. "Using spectral distances for speedup in hyperspectral image processing." International Journal of Remote Sensing 26, no. 24 (December 20, 2005): 5629–50. http://dx.doi.org/10.1080/01431160500168728.

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Patané, Giuseppe. "A unified definition and computation of Laplacian spectral distances." Pattern Recognition 93 (September 2019): 68–78. http://dx.doi.org/10.1016/j.patcog.2019.04.004.

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Zapata, Félix, María López-López, José Manuel Amigo, and Carmen García-Ruiz. "Multi-spectral imaging for the estimation of shooting distances." Forensic Science International 282 (January 2018): 80–85. http://dx.doi.org/10.1016/j.forsciint.2017.11.025.

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Yili Li and Kon Max Wong. "Riemannian Distances for Signal Classification by Power Spectral Density." IEEE Journal of Selected Topics in Signal Processing 7, no. 4 (August 2013): 655–69. http://dx.doi.org/10.1109/jstsp.2013.2260320.

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Sharrock, D. S., I. G. Main, and A. Douglas. "Observations of Q from the northwest Pacific subduction zone recorded at teleseismic distances." Bulletin of the Seismological Society of America 85, no. 1 (February 1, 1995): 237–53. http://dx.doi.org/10.1785/bssa0850010237.

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Abstract Twenty-seven earthquakes in the northwest Pacific, with mb ≧ 5.4, are used to study upper-mantle attenuation. The data were recorded at seismometer arrays in Australia, Canada, India, and Scotland. The short-period instruments used in the arrays are sufficiently broadband, and the signal-to-noise enhancement resulting from beamforming the data is good enough, that seismic noise is above system noise out to between 3 and 5 Hz, and in some cases to 8 Hz. The instrument response has been removed and a power law (ω−2) farfield source correction has been assumed and applied. The remaining fall-off in the spectra above 1 Hz (which is above the corner frequency fc) is assumed to be due to attenuation, including losses due both to anelasticity and to scattering. An ω−3 spectral fall-off, preferred by some, would result in lower estimates of attenuation. Conservative estimates of the average attenuation along the whole path have been made from the spectral fall-off. Despite the imperfect knowledge of the source spectra, the high sensitivity of spectral amplitudes to attenuation at high frequencies yields quite reliable and stable attenuation estimates. The scatter in the data is small, resulting in estimates of mean t* (tAV*) with an average standard error of only 21%, where tAV* is defined as the ratio of the travel time T to the effective mean quality factor QAV. Only 14 of the 64 measurements show a tAV* above 0.5 sec within the given error bounds. All estimates of tAV* and QAV refer to P-wave attenuation only. The results for tAV* from the northwest Pacific subduction zone cannot be explained simply by the traditional high-Q subducting slab in a low-Q upper mantle. A low-Q region in the uppermost 100 km (approximately) of the subduction zone has been identified. Source-corrected tAV* yield upper-mantle QAV estimates of about 1200 for predominantly oceanic paths (Australia and India) and 1500 for mixed continental and oceanic paths (Canada and Scotland).

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Shin, T. C., and R. B. Herrmann. "Lg attenuation and source studies using 1982 Miramichi data." Bulletin of the Seismological Society of America 77, no. 2 (April 1, 1987): 384–97. http://dx.doi.org/10.1785/bssa0770020384.

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Abstract Using data from earthquakes in the 1982 Miramichi earthquake source zone, spectral excitation and attenuation of the Lg phase are studied. With data in the distance range of 135 to 994 km, interpretation is complicated by the presence of high-frequency Sn and Pn waves which interfere with the Lg wave. At the larger distances, the signal at frequencies above 7 Hz is completely dominated by the non-Lg arrivals. A frequency-dependent Lg-Q is determined which rises from 300 at 0.5 Hz to about 1400 at 10 Hz, at which it flattens at higher frequency. The Sn coda apparent Q rises above 3000 at frequencies higher than 10 Hz. Seismic moment and corner frequency estimates are made using Lg-Q corrected spectra. The moment estimates compare well with those obtained from long-period surface waves and short distance spectral estimates. The Lg corner frequency estimates are substantially lower than the short distance estimates. This discrepancy is the subject of discussion, but the Lg moment-corner frequency estimates do model observed data well using a Brune (1970) source model and the derived attenuation relation.

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Yashchuk, V. M., I. V. Lebedyeva, and O. M. Navozenko. "Manifestations of triplet electronic excitations migration in π-electron containing polymers." Bulletin of Taras Shevchenko National University of Kyiv. Series: Physics and Mathematics, no. 1 (2019): 242–45. http://dx.doi.org/10.17721/1812-5409.2019/1.55.

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The results of spectral studies of polymers with aromatic side groups are considered and analyzed. In particular, the phosphorescence spectra of polyvinylcarbazole (PVCa) polyvinyl-7-benzocarbazole (PV7BK) polypropylcarbazole (PEPC) are presented and analyzed. The phosphorescence of these polymers has been shown to be related to the migration of triplet excitons in macromolecules. The phosphorescence of PVC is determined at 77by deep traps (oxides), at 4.2 -shallow traps (monomer units of PVCa). The spreading length of triplet excitons in PVCa macromolecules is 600 A – that corresponds to the average distances between adjacent traps in the macromolecule. There are no such traps in PV7BK macromolecules. The boundary conditions for triplet excitons in macromolecules of PV7BCa were used for evaluation the excitons spreading length. With this aim the dependence of phosphorescence spectra on molecular weihgt were studied The effect of changing of spectral positions of phosphorescence bands when exciton rich the end macromolecular cell was used. The average trip length of triplet excitons is approximately 1000 A. This distance is in fact limited by the probability of the meeting of triplet excitons in the macromolecule and their annihilation at a given excitation intensity.

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Silva, Walter J., and Robert K. Green. "Magnitude and Distance Scaling of Response Spectral Shapes for Rock Sites with Applications to North American Tectonic Environment." Earthquake Spectra 5, no. 3 (August 1989): 591–624. http://dx.doi.org/10.1193/1.1585542.

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Response spectral shapes (Sa/a) computed from the BLWN (Band Limited White Noise) ground motion model combined with RVT (Random Vibration Theory) compare favorably with shapes computed from WNA (Western North American) earthquakes recorded at rock sites. The comparisons are made at close distances and for moment magnitudes 4 1/2, approximately 5, 6, and 6 1/2. Predicted spectral shapes for the ENA (Eastern North America) show reasonably good agreement with empirical results at frequencies of 1 and 10 Hz and with other random process models at frequencies of 0.5, 1, 2, 5, 10, and 20 Hz. Magnitude dependence of Sa/a is predicted to be significant for periods greater than 0.2 seconds in WNA and for periods greater than 0.1 seconds in ENA and increases with increasing period. Distance scaling appears to be significant only in WNA and at distances exceeding 50 km.

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Little, Alex D., Donald H. Mershon, and Patrick H. Cox. "Spectral Content as a Cue to Perceived Auditory Distance." Perception 21, no. 3 (June 1992): 405–16. http://dx.doi.org/10.1068/p210405.

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Changes in the spectral content of wide-band auditory stimuli have been repeatedly implicated as a possible cue to the distance of a sound source. Few of the previous studies of this factor, however, have considered whether the cue provided by spectral content serves as an absolute or a relative cue. That is, can differences in spectral content indicate systematic differences in distance even on their first presentation to a listener, or must the listener be able to compare sounds with one another in order to perceive some change in their distances? An attempt to answer this question and simultaneously to evaluate the possibly confounding influence of changes in the sound level and/or the loudness of the stimuli are described in this paper. The results indicate that a decrease in high-frequency content (as might physically be produced by passage through a greater amount of air) can lead to increases in perceived auditory distance, but only when compared with similar sounds having a somewhat different high-frequency content, ie spectral information can serve as a relative cue for auditory distance, independent of changes in overall sound level.

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Usanov, D. A., A. V. Skripal, E. I. Astakhov, I. S. Kostuchenko, and S. Yu Dobdin. "SELF-MIXING INTERFEROMETRY FOR DISTANCE MEASUREMENT USING A SEMICONDUCTOR LASER WITH CURRENT-MODULATED WAVELENGTH." Computer Optics 42, no. 1 (March 30, 2018): 54–59. http://dx.doi.org/10.18287/2412-6179-2018-42-1-54-59.

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The capabilities of the method of current-modulated laser wavelength are shown to be extended by using harmonic modulation. Advantages of the sawtooth modulation method associated with using the frequency measurements of the interference signal as an information parameter have been researched. Advantages of the harmonic-type modulation based on the use of measurement results for spectral component amplitudes of the interference signal for distance determination have also been investigated. A comparative analysis of methods for absolute distance measurements at the existing capabilities of semiconductor laser wavelength modulation has demonstrated the benefits of the harmonic modulation of laser diode current for distances under 30 cm, showing the sawtooth current modulation to work better for distances greater than 50 cm.

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Zdziarski, Andrzej A. "Variable jet Lorentz factors can explain soft self-absorbed radio spectra of accreting black holes." Monthly Notices of the Royal Astronomical Society: Letters 489, no. 1 (August 14, 2019): L58—L62. http://dx.doi.org/10.1093/mnrasl/slz127.

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Abstract We study the effect of variable jet bulk Lorentz factors, i.e. either jet acceleration or deceleration, on partially synchrotron self-absorbed radio spectra from cores of radio-loud active galactic nuclei and black hole binaries in the hard state. In about a half of quasars and radio galaxies, their core radio spectra are observed to be soft, i.e. have the spectral index of α < 0. If they are emitted by jets with constant Lorentz factors, that softness implies deposition of large amounts of energy at large distances from the centre. We show here that such soft spectra can be explained without that energetic requirement by emission of jets with the Doppler factor increasing with the distance. This can happen for either jet acceleration or deceleration, depending on the jet viewing angle. We find our model can explain the quiescent radio to X-ray spectra of the BL Lac objects Mrk 421 and Mrk 501.

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Jain, Richa N., R. K. Choudhary, Anil Bhardwaj, Umang Parikh, Bijoy K. Dai, and M. V. Roopa. "A study on the solar coronal dynamics during the post-maxima phase of the solar cycle 24 using S-band radio signals from the Indian Mars Orbiter Mission." Monthly Notices of the Royal Astronomical Society 511, no. 2 (January 13, 2022): 1750–56. http://dx.doi.org/10.1093/mnras/stac056.

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ABSTRACT Radio signals from India’s Mars Orbiter Mission (MOM) have been used to study turbulence in the solar plasma during the post-maximum phase of solar cycle 24. S-band (2.29 GHz) radio carrier downlink signals from MOM were received at the Indian Deep Space Network, Bangalore, and frequency residuals were spectrally analysed to obtain coronal turbulence spectra at heliocentric distances ranging between 4 and 20 R⊙, corresponding to coronal regions where the solar wind is primarily accelerated. The frequency fluctuation spectrum relates to the turbulence regime in the near-Sun region. The turbulence power spectrum (the temporal spectrum of frequency fluctuations) at smaller heliocentric distances (<10 R⊙) reveals flattening in lower-frequency regions, with a spectral index αf ∼ 0.3−0.5, which corresponds to the solar wind acceleration region. For larger heliocentric distances (>10 R⊙), the curve steepens with a spectral index αf ∼ 0.7−0.8, a value close to 2/3 and indicative of a developed Kolmogorov-type turbulence spectrum. The findings are consistent with earlier results. Plausible explanations to support the theory of coronal heating by magnetohydrodynamic waves and the acceleration of the solar wind are presented. An insight into the feeble maximum of solar cycle 24 is discussed.

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Journal articles on the topic 'Spectral distances'

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