Influence of rotational darkening on ultraviolet interstellar extinction

Der Einfluß der Rotationsverdunklung schnell rotierender Sterne wird einer Neudiskussion unterzogen. Dafür werden filterphotometrische Helligkeiten vom Satelliten ANS herangezogen. Von schwach verfärbten B Sternen (E(B - V) 0.1 mag) wurden die Helligkeiten vom Einfluß der interstellaren Extinktion befreit. Die Verleilung der Sterne im Rotationsgeschwindigkeits-Farbenindex-Diagramm weist eine Streuung auf, die den Betrag der photometrischen Fehler übersteigt. Die Lage der Sterne im Rotationsgeschwindigkeits-Farbenindex-Diagramm befindet sich in qualitativer Übereinstimmung mit entsprechenden theoretischen Resultaten. Bei der Diskussion von individuell abweichenden Verläufen der interstellaren Extinktion vom durchschnittlichen Extinktionsgesetz sollte der Einfluß der Rotationsverdunklung als eine mögliche Quelle für die Abweichungen in Betracht gezogen und geprüft werden.     

Excitation of whistler waves by reflected auroral electrons

Excitation of electron cyclotron waves and whistlers by reflected auroral electrons which possess a loss-cone distribution is investigated. Based on a given magnetic field and density model, the instability problem is studied over a broad region along the auroral field lines. This region covers altitudes ranging from one quarter of an Earth radius to five Earth radii. It is found that the growth rate is significant only in the region of low altitude, say below the source region of the auroral kilometric radiation. In the high altitude region the instability is insignificant either because of low refractive indices or because of small loss cone angles.     

The interstellar 2200 Å band: A second catalogue of equivalent widths and preliminary statistical analysis (Mitteilungen der Universitäts-Sternwarte zu Jena Nr. 162)

A second catalogue of equivalent widths of the interstellar 2200 Å band is presented. It is based on spectrophotometric data obtained with the TD-1 satellite and supplements a catalogue already published (paper I). Both catalogues list a total of 779 stars. The reliability of the derived parameters is analysed. There is a satisfying agreement with spectrophotometric data obtained with the OAO-2 satellite. The relationship between the equivalent width of the 2200-Å band and and the colour excess is discussed, making use of additional data for more strongly reddened stars obtained with OAO-2 and IUE.     

Silicon carbide and the infrared excess of carbon stars

This paper reports laboratory investigations on the absorption spectrum of SiC particles in the 10 μm region. The particles had a mean diameter of 0.31 μm. Our experimental results indicate that a large part of the infrared excess observed in carbon stars may be caused by SiC.     

Source parameters of intermediate-depth Vrancea (Romania) earthquakes from empirical Green's functions modeling

Several source parameters (source dimensions, slip, particle velocity, static and dynamic stress drop) are determined for the moderate-size October 27th, 2004 (M_W = 5.8), and the large August 30th, 1986 (M_W = 7.1) and March 4th, 1977 (M_W = 7.4) Vrancea (Romania) intermediate-depth earthquakes. For this purpose, the empirical Green's functions method of Irikura [e.g. Irikura, K. (1983). Semi-Empirical Estimation of Strong Ground Motions during Large Earthquakes. Bull. Dis. Prev. Res. Inst., Kyoto Univ., 33, Part 2, No. 298, 63–104., Irikura, K. (1986). Prediction of strong acceleration motions using empirical Green's function, in Proceedings of the 7th Japan earthquake engineering symposium, 151–156., Irikura, K. (1999). Techniques for the simulation of strong ground motion and deterministic seismic hazard analysis, in Proceedings of the advanced study course seismotectonic and microzonation techniques in earthquake engineering: integrated training in earthquake risk reduction practices, Kefallinia, 453–554.] is used to generate synthetic time series from recordings of smaller events (with 4 ≤ M_W ≤ 5) in order to estimate several parameters characterizing the so-called strong motion generation area, which is defined as an extended area with homogeneous slip and rise time and, for crustal earthquakes, corresponds to an asperity of about 100 bar stress release [Miyake, H., T. Iwata and K. Irikura (2003). Source characterization for broadband ground-motion simulation: Kinematic heterogeneous source model and strong motion generation area. Bull. Seism. Soc. Am., 93, 2531–2545.] The parameters are obtained by acceleration envelope and displacement waveform inversion for the 2004 and 1986 events and MSK intensity pattern inversion for the 1977 event using a genetic algorithm. The strong motion recordings of the analyzed Vrancea earthquakes as well as the MSK intensity pattern of the 1977 earthquake can be well reproduced using relatively small strong motion generation areas, which corresponds to small asperities with high stress drops (300–1200 bar) and high particle velocities (3–5 m/s). These results imply a very efficient high-frequency radiation, which has to be taken into account for strong ground motion prediction, and indicate that the intermediate-depth Vrancea earthquakes are inherently different from crustal events.     

On the use of JMA intensity in earthquake early warning systems

The estimation of strength of shaking at a site from the initial P-wave portion of ground motion is the key problems for shortening the alert time of the earthquake Early Warning (EEW). The most of the techniques proposed for the purpose utilize (a) ground motion models based on the estimated magnitude and hypocentral distance, or (b) the interim proxies, such as initial vertical displacement P _d . We suggest the instrumental Japan Meteorological Agency (JMA) intensity (JMA_I) as a characteristic for fast estimation of damage potential in the EEW systems. We investigated the scaling relations between JMA_I measured using the whole earthquake recordings (overall intensity) and using particular time intervals of various duration (2.0–8.0 s) starting from the P-wave arrival (preliminary intensity). The dataset included 3,660 records (K-NET and the KiK-net networks) from 55 events (M _W 4.1–7.4) occurred in 1999–2008 in Japan. We showed that the time interval of 4–5 s from the P-wave arrival can be used for reliable estimations of the overall intensity with the average standard error of about 0.5 JMA units. The uncertainty in the prediction may be reduced by consideration of local site conditions or by development of the station-specific models.     

Integration of stress testing with graph theory to assess the resilience of urban road networks under seismic hazards

Transportation networks daily provide accessibility and crucial services to societies. However, they must also maintain an acceptable level of service to critical infrastructures in the case of disruptions, especially during natural disasters. We have developed a method for assessing the resilience of transportation network topology when exposed to environmental hazards. This approach integrates graph theory with stress testing methodology and involves five basic steps: (1) establishment of a scenario set that covers a range of seismic damage potential in the network, (2) assessment of resilience using various graph-based metrics, (3) topology-based simulations, (4) evaluation of changes in graph-based metrics, and (5) examination of resilience in terms of spatial distribution of critical nodes and the entire network topology. Our case study was from the city of Kathmandu in Nepal, where the earthquake on April 25, 2015, followed by a major aftershock on May 12, 2015, led to numerous casualties and caused significant damage. Therefore, it is a good example for demonstrating and validating the developed methodology. The results presented here indicate that the proposed approach is quite efficient and accurate in assisting stakeholders when evaluating the resilience of transportation networks based on their topology.     

A new solid state diffusion model applied to inverse zoning and diffusion rims in minerals

Any oxide and silicate mineral which is nominally anhydrous but crystallized in the presence of H₂O incorporates traces of H₂O in solid solution. In the case of MgO it can be shown that OH^? pairs convert into H₂+O ₂ ^2? . If the H₂ molecules are lost, the O ₂ ^2? remain in the lattice as excess oxygen stabilized by excess cation vacancies. When the O ₂ ^2? anions decay either thermally or by decompression unbound O^? states (positive holes) are generated which lead to surface charges and subsurface space charge layers. Calculated space charge profiles are presented. O^? concentrations as small as 10–20 ppm suffice to create electric surface fields of the order of 4·10⁷ V·m^?1. The diffusion mechanism which derives from these premises incorporates novel features: the cation diffusion is coupled to the counterdiffusion of unbound and vacancy-bound O^? states. The cation diffusion is predicted to be very fast because first, it is field-enhanced (electrochemically driven) and second, it is not rate-limited by the intrinsic cation vacancy concentration nor by the counter-diffusion of other cations. The model may apply to cases of inverse zoning and diffusion rim formation in minerals under certain P-T conditions.     

A deuterium-hydrogen fractionation mechanism in magnesium oxide

Water dissolved in a nominally anhydrous oxide like MgO forms not only OH^? ions, as is usually assumed, but also molecular H₂ and peroxy anions O₂^2?. The specific lattice site where this reaction occurs has been identified for the model-type MgO structure: it is the fully OH^? compensated cation vacancy. In partially deuterated synthetic MgO, molecular D₂ forms preferentially to H₂, by a factor of the order of 4. Three methods have been used to study this very large D/H fractionation experimentally: mass spectrometry, electron spin resonance and infrared spectroscopy. All give consistent results and confirm that internal D/H fractionation occurs and is a function of the temperature. Theoretically the D/H fractionation is explained by the lower zeropoint energy of D₂ with respect to H₂, amplified by secondary processes through which the molecular hydrogen species become mobilized and eventually lost via diffusion. The possible consequences of such internal D/H fractionation processes are indicated for the interpretation of water and hydrogen release patterns, with varying D/H ratios, from terrestrial and extraterrestrial samples.     

On the modeling of ground-motion field for assessment of multiple-location hazard,damage, and loss: example of estimation of electric network performance during scenario earthquake

Consideration of within-earthquake ground-motion correlation is essential for the estimation of seismic hazards, damage, and loss for spatially distributed systems. In many seismically active regions, the strong motion data of real engineering significance are completely unavailable or very scarce. The absence of necessary data does not allow developing regional empirical correlation models, and the models obtained for other regions should be used with correspondent sensitivity analysis. The level of within-earthquake correlation may vary in broad range; therefore, development of correspondent criteria for selection from available models is important. In this paper, we analyzed the performance of a system of critical elements of electric power network (substations) depending on variations in within-earthquake correlation. The performance is described as probability of different levels of non-functionality, i.e., percentage of area suffering power outage, and probability of expected number of customers without power. We have shown that the proper choice of the within-earthquake correlation model is critical in comprehensive estimations of functionality of substations in electrical power system. Skipping the ground-motion variability and within-earthquake correlation may lead to unreliable results. Relevance of geology-based within-earthquake correlation models has been demonstrated, and a scheme, which allows reducing uncertainty in the choice of realistic correlation, has been proposed.