Secondary Extinction Research Articles

Evidence of extinction in strongly textured high-purity copper

In order to test the influence of extinction on texture measurements, pole figures of four copper samples were measured using neutron diffraction with three different wavelengths. The copper samples had previously been cold rolled to different extents and partially annealed. Therefore, three of the samples presented a relatively strong texture and the fourth sample a relatively weak texture. In this study, the results from equivalent pole figures were compared between the different samples. These investigations showed that, in general, except for the sample with weak texture, the 222 reflection showed higher pole density maxima than the 111 reflection. Since all measuring conditions were the same for both reflections, this difference was attributed to extinction. The pole density maxima of strong reflections also revealed a slight tendency to lower values with decreasing wavelengths. This phenomenon is attributed to the fact that more reflections exist at shorter wavelengths and therefore an increase in secondary extinction is measurable at these wavelengths.

Microstructure Characterization of Textured Materials Considering Extinction Phenomenon

Texture is defined by the measured polar figure (PF) obtained from the integrated intensity of diffracted X-rays. The integrated intensity can be affected both by the pole density (PD) and by the phenomenon of extinction that reduces the PD and cannot be avoided. PF does not contain information about grain microstructure, but parameters of the primary and secondary extinction are related to the crystal microstructural features. Recently an original X-ray diffraction method was proposed for correction of PD and separation and determination of the primary and secondary extinction parameters for characterization of textured aluminum samples. This problem was solved using some assumptions. The parameter of the primary extinction can be used for calculation of domain size. The secondary extinction parameter is related to the average domain disorientation angle that depends on dislocation density in domain boundaries. Extinction parameters were used for microstructure evaluation of cold rolled nickel with and without annealing at 600°C. The validity of the proposed assumption for nickel samples was evaluated in terms of the extinction length. The corrected pole density and the parameters of primary and secondary extinction were calculated using the first order reflection for two different wavelengths (Cu and Co) and the second order reflection for one of the used wavelengths. In annealed samples the primary and secondary extinction were presented simultaneously. According to the obtained parameters of extinction the microstructure of textured nickel was evaluated.

Microstructure Characterization of Textured Nickel Using Parameters of Extinction

AbstractX ray diffraction (XRD) is the common technique for texture analysis by means of pole figure (PF) measurement. PF reflects the grains orientation distribution but contains no information about grain microstructure. The reflected intensity can be affected by the extinction phenomenon that reduces the pole density (PD). The parameters of extinction are related to the crystal microstructure. The parameter of the primary extinction is connected with domain size and parameter of the secondary extinction is related to the angle of domains disorientation that depends on dislocation density in domain boundary. An original XRD method is proposed for correction of PD, considering extinction phenomenon, and separation of the extinction parameters in the case of textured aluminum. The problem is solved under some assumptions. In the present work cold rolled nickel with and without annealing at 600 °C is investigated. The validity of the proposed assumptions for Ni is evaluated in terms of the extinction length. The corrected PD in the maximum of PF and the parameters of the primary and secondary extinction are calculated using the first order reflection for CuKα- and CoKα- radiations and the second order reflection for one of the used wavelengths. Both in cold rolled sample without annealing and in the annealed sample the primary and secondary extinctions are present simultaneously. According to the obtained parameters of extinction the microstructure of textured nickel is evaluated and their modification at the annealing process is demonstrated.

New approach to adaptive single pole auto-reclosing of power transmission lines

In this study, a novel digital algorithm is introduced for recognition of arcing (transient) faults and determination of dead time for adaptive auto-reclosing. The algorithm distinguishes between arcing and permanent faults by using the zero sequence voltage measured at the relaying point. If the fault is recognised as an arcing fault, then the third harmonic of the zero sequence voltage is used to evaluate the extinction time of secondary arc and to initiate reclosing signal. The proposed algorithm uses an adaptive threshold level and therefore no significant adjustment is needed for different transmission systems. Moreover, its performance is independent to fault location, line parameters and the system pre-fault operating conditions. The algorithm has been successfully tested for various faults and operating conditions on a 400 kV overhead line using the electro-magnetic transient program (EMTP). The test results have demonstrated validity of the algorithm in determining the secondary arc extinction time and blocking unsuccessful automatic reclosing during permanent faults.

Electron density distribution in hexagonal cobalt: Aγ-ray diffraction study

The electron density distribution of ferromagnetic hexagonal cobalt is studied at room temperature using high-quality single-crystal diffraction data measured up to $\text{sin}\text{ }\ensuremath{\theta}/\ensuremath{\lambda}=1.9\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$ with 316.5 keV gamma radiation. A highly anisotropic mosaic-block orientation was found. The ensuing anisotropy in secondary extinction could be fairly well described by the Thornley-Nelmes formalism, with adjusted mosaicities close to the directly observed ones. The structure factors have been analyzed by a multipole expansion model within the Hartree-Fock framework. Thermal mean-square atomic amplitudes are distinctly different along the $a$ and $c$ axes. The total $3d$ charge exhibits appreciable anisotropy with an excess of density in the singlet ${a}_{\text{g}}$ along the $c$ axis and a deficiency in the two doublet ${e}_{\text{g}}$ orbitals. The $3d$ shell in the metal shows a slight contraction of 1.2% relative to the free atom. Agreement with low-order form factors from critical-voltage electron diffraction reaches 0.1%. No difference of $d$-electron count is found between metal and atom. A $3{d}^{7}$ configuration implies incomplete filling of the majority-spin band. The directed metallic bonds are characterized in terms of the electron density topology.

CCD PHOTOMETRY OF STANDARD STARS AT MAIDANAK ASTRONOMICAL OBSERVATORY IN UZBEKSTAN: TRANSFORMATIONS AND COMPARISONS

Observation of standard stars is of crucial importance in stellar photometry. We have studied the standard transformation relations of the UBVRI CCD photometric system at the Maidanak Astronomical Observatory in Uzbekistan. All observations were made with the AZT-22 1.5m telescope, SITe 2k CCD or Fairchild 486 CCD, and standard Bessell UBVRI filters from 2003 August to 2007 September. We observed many standard stars around the celestial equator observed by SAAO astronomers. The atmospheric extinction coefficients, photometric zero points, and time variation of photometric zero points of each night were determined. Secondary extinction coefficients and photometric zero points were very stable, while primary extinction coefficients showed a distinct seasonal variation. We also determined the transformation coefficients for each filter. For B, V, R, and I filters, the transformation to the SAAO standard system could be achieved with a straight line or a combination of two straight lines. However, in the case of the U filter and Fairchild 486 CCD combination, a significant non-linear correction term - related to the size of Balmer jump or the strength of the Balmer lines - of up to 0.08 mags was required. We found that our data matched well the SAAO photometry in V, B-V, V-I, and R-I. But in U-B, the difference in zero point was about 3.6 mmag and the scatter was about 0.02 mag. We attribute the relatively large scatter in U-B to the larger error in U of the SAAO photometry. We confirm the mostly small differences between the SAAO standard UBVRI system and the Landolt standard system. We also attempted to interpret the seasonal variation of the atmospheric extinction coefficients in the context of scattering sources in the earth's atmosphere.

The precision of XRD apparatus can be assessed by accounting for secondary extinction of a single reflection

The precision of XRD apparatus can be assessed by accounting for secondary extinction of a single reflection

Parasites reduce food web robustness because they are sensitive to secondary extinction as illustrated by an invasive estuarine snail

A robust food web is one in which few secondary extinctions occur after removing species. We investigated how parasites affected the robustness of the Carpinteria Salt Marsh food web by conducting random species removals and a hypothetical, but plausible, species invasion. Parasites were much more likely than free-living species to suffer secondary extinctions following the removal of a free-living species from the food web. For this reason, the food web was less robust with the inclusion of parasites. Removal of the horn snail, Cerithidea californica, resulted in a disproportionate number of secondary parasite extinctions. The exotic Japanese mud snail, Batillaria attramentaria, is the ecological analogue of the native California horn snail and can completely replace it following invasion. Owing to the similarities between the two snail species, the invasion had no effect on predator–prey interactions. However, because the native snail is host for 17 host-specific parasites, and the invader is host to only one, comparison of a food web that includes parasites showed significant effects of invasion on the native community. The hypothetical invasion also significantly reduced the connectance of the web because the loss of 17 native trematode species eliminated many links.

Technical requirements for UHV substation equipment

AbstractCIGRE Study Committee A3 established WG A3.22 ‘Technical requirements for substation equipment exceeding 800 kV’ to review the state‐of‐the‐art technical specifications for substation equipment exceeding 800kV in accordance with a request from IEC SC 17A. WG A3.22 conducted the initial surveys and submitted the first Technical Brochure on technical specifications for substation equipment such as gas circuit breaker (GCB), disconnecting switches (DS), earthing switches (ES), high‐speed grounding switches (HSGS) and metal oxide surge arrester (MOSA) applied to 800 kV and 1100/1200 kV networks. The investigations include the insulation level, first‐pole‐to‐clear factor, DC time constants, transient recovery voltage (TRV), line surge impedance and secondary arc extinction time. WG A3.22 will provide the technical background of all aspects of the available specifications with the intention of identifying the best practice for ultra high voltage (UHV) transmission systems. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Trophically Unique Species Are Vulnerable to Cascading Extinction

Understanding which species might become extinct and the consequences of such loss is critical. One consequence is a cascade of further, secondary extinctions. While a significant amount is known about the types of communities and species that suffer secondary extinctions, little is known about the consequences of secondary extinctions for biodiversity. Here we examine the effect of these secondary extinctions on trophic diversity, the range of trophic roles played by the species in a community. Our analyses of natural and model food webs show that secondary extinctions cause loss of trophic diversity greater than that expected from chance, a result that is robust to variation in food web structure, distribution of interactions strengths, functional response, and adaptive foraging. Greater than expected loss of trophic diversity occurs because more trophically unique species are more vulnerable to secondary extinction. This is not a straightforward consequence of these species having few links with others but is a complex function of how direct and indirect interactions affect species persistence. A positive correlation between a species’ extinction probability and the importance of its loss defines high‐risk species and should make their conservation a priority.

Trophically Unique Species Are Vulnerable to Cascading Extinction

Understanding which species might become extinct and the consequences of such loss is critical. One consequence is a cascade of further, secondary extinctions. While a significant amount is known about the types of communities and species that suffer secondary extinctions, little is known about the consequences of secondary extinctions for biodiversity. Here we examine the effect of these secondary extinctions on trophic diversity, the range of trophic roles played by the species in a community. Our analyses of natural and model food webs show that secondary extinctions cause loss of trophic diversity greater than that expected from chance, a result that is robust to variation in food web structure, distribution of interactions strengths, functional response, and adaptive foraging. Greater than expected loss of trophic diversity occurs because more trophically unique species are more vulnerable to secondary extinction. This is not a straightforward consequence of these species having few links with others but is a complex function of how direct and indirect interactions affect species persistence. A positive correlation between a species' extinction probability and the importance of its loss defines high-risk species and should make their conservation a priority.

Thickness Measurement of Thin Textured Films by a Novel X-Ray Diffraction Method Accounting for Secondary Extinction

Accounting for secondary extinction (SE) of the intensities measured from a textured film by means of conventional X-ray diffractometer, a new X-ray diffraction method is described for determination of film thickness. Physically, the problem is restricted to using a reflection pair corresponding to the main component of the texture. As model sample a vacuum-deposited silver thin film is used.

Secondary extinction correction used in a novel method for improved XRD characterizations of textured materials: The case of thin films

Secondary extinction correction used in a novel method for improved XRD characterizations of textured materials: The case of thin films

Secondary extinction correction used in a novel method for improved XRD characterizations of textured materials: The case of thin films

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Analysis of X‐ray extinction in crystals with inhomogeniously distributed dislocations

AbstractThe secondary extinction theory of Zachariasen for mosaic crystals as well as the formalism of Becker&amp;Coppens have been used for substructure analysis (lattice disorientations, block size, density of excess dislocations, etc.) in crystals with inhomogeniously distributed dislocations in the Bragg case of diffraction geometry. In the case of large crystals DS ≫ Λhkl the mean total density ρD of randomly distributed dislocations was also estimated taking into account additionally the primary X‐ ray extinction treatment. In this connection two cases are considered: I) pure secondary extinction related to arrangement of dislocation walls and II) mixed extinction in crystals with large subgrains related to randomly distributed dislocations and arrangement of dislocation walls. In order to check the considerations, the experimental and calculated data were compared for Be (model I) and Cu (model II) single crystals. The weakly distorted single crystals of Be and Cu were experimentally investigated in the Bragg case of diffraction geometry using Cu Kα1 radiation by means of double crystal diffractometer. A new experimental procedure was proposed. Using alternative technique for substructure analysis (for instance EBSD) the reliability of analysis based on extinction phenomenon in weakly distorted single crystals has been checked. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Sequencing events across the Permian–Triassic boundary, Guryul Ravine (Kashmir, India)

The Permian–Triassic boundary (PTB) section at Guryul Ravine (Kashmir, India) comprises a > 100-m-thick, apparently conformable succession of mixed siliciclastic–carbonate sediments deposited in a deep-shelf or ramp setting. This section, although long important in debates concerning placement of the PTB, has not previously been the focus of an integrated chemostratigraphic study. In the present study, samples from a 20-m-thick interval straddling the PTB were analyzed for major- and trace-element concentrations, TOC-TIC, REEs, and organic δ 13C– δ 15N to investigate contemporaneous environmental changes. The Guryul Ravine section exhibits a sequence of discrete events that provide potentially important information about the character and cause(s) of the PTB. Two transient negative C-isotopic excursions within the upper changxingensis zone predate the Late Permian event horizon (LPEH, i.e., the global mass extinction event) by ∼ 200–400 kyr and are associated with the onset of a major eustatic rise and with secondary extinction peaks. These excursions may record minor environmental disturbances prior to the main end-Permian crisis, supporting an intrinsic mechanism such as volcanism and climate change rather than an extrinsic mechanism such as a bolide impact. The onset of a large (∼ − 4.0 to − 4.5‰), sustained negative C-isotope shift marks the LPEH, which is located at the Zewan–Khunamuh formation contact ∼ 260 cm below the biostratigraphically defined PTB. The Guryul Ravine section exhibits a stepwise extinction pattern, with the largest peak between the LPEH and PTB and a secondary peak just above the PTB, a pattern similar to that observed in the Meishan D GSSP.

New Digital Algorithm for Adaptive Reclosing Based on the Calculation of the Faulted Phase Voltage Total Harmonic Distortion Factor

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a new numerical algorithm suitable for determining adaptive dead time, and blocking automatic reclosing during permanent faults on overhead lines. It is based on terminal voltage input data processing. The decision if it is safe or not to reclose is determined by the voltage signal of faulted and tripped line phase using the total harmonic distortion factor calculated by discrete Fourier transform. The algorithm was successfully tested using signals recorded on the real power system. The tests demonstrate the ability of the presented algorithm to determine the secondary arc extinction time and to block unsuccessful automatic reclosing of high-voltage lines with permanent fault. </para>

Numerical Algorithm for Adaptive Single Pole Autoreclosure Based on Determining the Secondary Arc Extinction Time

This article presents a new numerical algorithm suitable for defining recloser reclaim time and blocking automatic reclosing during permanent faults on overhead lines. It is based on terminal voltage input data processing. The decision if it is safe or not to reclose is determined from the voltage signal of faulted and tripped line phase using fundamental and third harmonic calculated by discrete Fourier transform. The algorithm was successfully tested using signals recorded on the real power system. The tests demonstrate the ability of presented algorithm to determine the secondary arc extinction time and to block unsuccessful automatic reclosing of HV lines with permanent fault.

Early onset of secondary extinctions in ecological communities following the loss of top predators

The large vulnerability of top predators to human-induced disturbances on ecosystems is a matter of growing concern. Because top predators often exert strong influence on their prey populations their extinction can have far-reaching consequences for the structure and functioning of ecosystems. It has, for example, been observed that the local loss of a predator can trigger a cascade of secondary extinctions. However, the time lags involved in such secondary extinctions remain unexplored. Here we show that the loss of a top predator leads to a significantly earlier onset of secondary extinctions in model communities than does the loss of a species from other trophic levels. Moreover, in most cases time to secondary extinction increases with increasing species richness. If local secondary extinctions occur early they are less likely to be balanced by immigration of species from local communities nearby. The implications of these results for community persistence and conservation priorities are discussed.

Extinction cascades and catastrophe in ancient food webs

A model is developed to explore the potential responses of paleocommunities to disruptions of primary production during times of mass extinction and ecological crisis. Disruptions of primary production are expected to generate bottom-up cascades of secondary extinction, and these are predictable given species richnesses, functional diversity, and trophic link distributions. If, however, consumers are permitted to compensate for the loss of trophic resources by increasing the intensities of their remaining biotic interactions, top-down driven catastrophic increases of secondary extinction emerge from the model. Both bottom-up and top-down effects are themselves controlled by the geometry of the food webs. The general Phanerozoic trends of increasing taxonomic and ecological diversities, as well as the varying strengths of biotic interactions, have led to food webs of increasing complexity. The frequency of catastrophic secondary extinction increases as food web complexity increases, but increased complexity also serves to dampen the magnitude of the secondary extinctions. When intraguild competitive interactions are included in the model, competitively inferior taxa are observed to possess greater probabilities of survival if the guilds are embedded in simple subnetworks of the overall food web. The result is the emergence of postextinction guilds dominated by those inferior taxa. These results are congruent with empirical observations of “disaster taxa” dominance after some mass extinction events, and provide a mechanism for the reorganization of ecosystems that is observed after those events. The model makes the testable prediction that dominance by disaster taxa, however, should be observed only when bottom-up disruptions have caused ecosystems to collapse catastrophically.