In this work the high cycle fatigue behavior of a particulate reinforced 2124 aluminum alloy, manufactured by powder metallurgy, is investigated. SiC particles with a size of 3 μm and 300 nm and a ...volume fraction of 5 and 25 vol %, respectively, were used as reinforcement component. The present study is focused on the fatigue strength and the influence of particle size and temperature. Systematic work is done by comparing the unreinforced alloy and the reinforced conditions. All of the material conditions are characterized by electron microscopy and tensile and fatigue testing at room temperature and at 180 °C. With an increase in temperature the tensile and the fatigue strength decrease, regardless of particle size and volume fraction due to the lower matrix strength. The combination of 25 vol % SiC particle fraction with 3 μm size proved to be most suitable to achieve a major fatigue performance at room temperature and at 180 °C. The fatigue strength is increased by 40% when compared to the unreinforced alloy, as it is assumed the interparticle spacing for this condition reaches a critical value then.
The fraction of Compton-thick sources is one of the main uncertainties left in understanding the active galactic nucleus (AGN) population. The Swift Burst Alert Telescope (BAT) all-sky survey for the ...first time gives us an unbiased sample of AGNs for all but the most heavily absorbed sources N H > 1025 cm-2). Still, the BAT spectra (14-195 keV) are time averaged over months of observations and therefore hard to compare with softer spectra from the Swift XRT or other missions. This makes it difficult to distinguish between Compton-thin and Compton-thick models. With Suzaku, we have obtained simultaneous hard (>15 keV) and soft (0.3-10 keV) X-ray spectra for five Compton-thick candidate sources. We report on the spectra and a comparison with the BAT and earlier XMM observations. Based on both flux variability and spectral shape, we conclude that these hidden sources are not Compton thick. We also report on a possible correlation between excess variance and Swift BAT luminosity from the 16 day binned light curves, which holds true for a sample of both absorbed (four sources), unabsorbed (eight sources), and Compton-thick (Circinus) AGNs, but is weak in the 64 day binned BAT light curves.
For the production of aluminum screws, an effective thermomechanical treatment is necessary for enabling high strength combined with good formability. In this study, the influence of pre-aging as ...initial heat treatment prior to following processing steps was investigated for the precipitation hardenable 6056 aluminum alloy. The short-term low temperature pre-aged condition was compared to a naturally aged one representing storage time in manufacturing. As reference, a solution-annealed condition was used. After these initial heat treatments, conventional extrusion and artificial aging followed prior to final thread rolling. The distribution of strain introduced by these forming processes was numerically investigated using finite element simulation. The initial heat treatment had a significant influence on the mechanical properties achievable after the complete thermomechanical processing route. After extrusion and artificial aging, the highest hardness was achieved by the pre-aged condition. Despite its high initial hardness, this condition exhibited the best formability indicated by well-formed threads combined with the highest hardness achieved after thread rolling. Therefore, pre-aging seems to be an advantageous heat treatment for integration in the manufacturing process of screws due to its beneficial effect on the mechanical properties.
We present contemporaneous X-ray, ultraviolet, optical, near-infrared, and radio observations of the black hole binary system, A0620-00, acquired in 2010 March. Using the Cosmic Origins Spectrograph ...on the Hubble Space Telescope, we have obtained the first FUV spectrum of A0620-00 as well as NUV observations with the Space Telescope Imaging Spectrograph. The observed spectrum is flat in the FUV and very faint (with continuum fluxes 1e -- 17 erg cm--2 s--1 A--1). The UV spectra also show strong, broad (FWHM ~ 2000 km s--1) emission lines of Si IV, C IV, He II, Fe II, and Mg II. The C IV doublet is anomalously weak compared to the other lines, which is consistent with the low carbon abundance seen in NIR spectra of the source. Comparison of these observations with previous NUV spectra of A0620-00 shows that the UV flux has varied by factors of 2-8 over several years. We compiled the dereddened, broadband spectral energy distribution (SED) of A0620-00 and compared it to previous SEDs as well as theoretical models. The SEDs show that the source varies at all wavelengths for which we have multiple samples. Contrary to previous observations, the optical-UV spectrum does not continue to drop to shorter wavelengths, but instead shows a recovery and an increasingly blue spectrum in the FUV. We created an optical-UV spectrum of A0620-00 with the donor star contribution removed. The non-stellar spectrum peaks at 3000 A. The peak can be fit with a T = 10,000 K blackbody with a small emitting area, probably originating in the hot spot where the accretion stream impacts the outer disk. However, one or more components in addition to the blackbody are needed to fit the FUV upturn and the red optical fluxes in the optical-UV spectrum. By comparing the mass accretion rate determined from the hot spot luminosity to the mean accretion rate inferred from the outburst history, we find that the latter is an order of magnitude smaller than the former, indicating that ~90% of the accreted mass must be lost from the system if the predictions of the disk instability model and the estimated interoutburst interval are correct. The mass accretion rate at the hot spot is 105 the accretion rate at the black hole inferred from the X-ray luminosity. To reconcile these requires that outflows carry away virtually all of the accreted mass, a very low rate of mass transfer from the outer cold disk into the inner hot region, and/or radiatively inefficient accretion. We compared our broadband SED to two models of A0620-00 in quiescence: the advection-dominated accretion flow model and the maximally jet-dominated model. The comparison suggests that strong outflows may be present in the system, indicated by the discrepancies in accretion rates and the FUV upturn in flux in the SED.
Space weather events produce variations in the electric current in the Earth's magnetosphere and ionosphere. From these high‐altitude atmospheric regions, resulting geomagnetically induced currents ...(GICs) can lead to fluctuations in ground currents that affect the electric power grid and potentially overload transformers during extreme storms. The most extreme geomagnetic storm on record, known as the 1859 Carrington event, was so intense that ground‐based magnetometers were saturated at high magnetic latitudes. The most reliable, unsaturated observation is the hour resolution data from the Colaba Magnetic Observatory in India. However, higher‐frequency components—fluctuations at second through minute time cadence—to the magnetic field can play a significant role in GIC‐related effects. We present a new method for scaling higher‐frequency observations to create a realistic Carrington‐like event magnetic field model, using modern magnetometer observations. Using the magnetic field model and ground conductivity models, we produce an electric field model. This method can be applied to create similar magnetic and electric field models for studies of GIC effects on power grids.
Plain Language Summary
Space weather storms can result in geomagnetically induced currents that can disrupt electric power grids, in the most extreme cases causing blackouts. These extreme storms are rare, but we have on record a case of the 1859 Carrington event which estimates show that if it were to occur today would cause a severe threat to electric power systems. The only reliable magnetic field data from this storm was from an Indian station nearer the equator. Since the effects to power grids are more extreme at higher latitudes, we developed a technique to use magnetic field data from more recent storms along with the 1859 Indian station data to scale the expected magnetic field and electric field from an extreme storm to any latitude. This technique can lead power grid operators to better estimate the effects on their local grids.
Key Points
A new technique is presented for GIC estimates
Magnetometer data are analyzed for major storms
GIC estimates are made for an extreme Carrington‐level storm
In this article, I approach negotiations of belonging by studying the relationship between folklorists and their informants. I examine how young Finnish folklorists on their first collection journeys ...in the early 1920s positioned themselves as scholars by stressing both their identification with and their differences from the informants. The discipline's high status as a "national science" required the collectors to approach the locals as carriers of a national heritage shared between the collectors and informants. On the other hand, the pursuit of scholarly acknowledgement urged the scholars to emphasize their position as experts who could evaluate the authenticity and academic relevance of the information offered by the locals. One effective way to do so was to highlight a temporal distance between the describer and the described, placing the informants in an earlier time of lower social and cultural development than the scholar. I discuss how the alternation between identification and difference can be interpreted as a means for the scholars to negotiate their places in their academic community and to form feasible scholarly personas within it. The article places special focus on how the young collectors performed this negotiation by describing informants in their correspondences with student friends and cooperating to find shared ways of approaching the informants in acceptable ways according to their discipline.
We analysed data from the Cosmic Origins Spectrograph (COS) to characterize the spectral properties and outflows of the active galactic nucleus (AGN), Markarian 1513. Further investigation using ...previous data collected by the Space Telescope Imaging Spectrograph (STIS), Goddard High Resolution Spectrograph (GHRS), and International Ultraviolet Explorer (IUE) was used to examine variability in the outflows along with the AGN emission and continuum luminosity spanning 32 yr. The COS data contained two sets of intrinsic absorption systems. The first, which is associated with an outflow, was observed in Lyman α, N v, Si iv, and C iv, with an outflow velocity of −1521 ± 20 km s−1. This absorption system prevailed through the historical Hubble Space Telescope observations spanning 15 yr, and COS data revealed a previously unobserved Si iv outflow absorption feature. A second absorption system was observed at −17 ± 20 km s−1 in Lyman α, N v, and the blue component of C iv (1548.2 Å), indicating the presence of an intervening cloud, but not necessarily an outflow. Variability was also observed in the continuum levels of the AGN spectrum, which dropped by nearly a factor of 2 in both the power-law index and flux level between the GHRS and COS data.
We use the Swift Burst Alert Telescope (BAT) sample of hard X-ray- selected active galactic nuclei (AGN) with a median redshift of 0.03 and the 2MASS J- and K-band photometry to examine the ...correlation of hard X- ray emission to Eddington ratio as well as the relationship of the J- and K-band nuclear luminosity to the hard X-ray luminosity. The BAT sample is almost unbiased by the effects of obscuration and thus offers the first large unbiased sample for the examination of correlations between different wavelength bands. We find that the near-IR nuclear J- and K-band luminosity is related to the BAT (14-195 keV) luminosity over a factor of 10 super(3) in luminosity and thus is unlikely to be due to dust. We also find that the Eddington ratio is proportional to the X-ray luminosity. This new result should be a strong constraint on models of the formation of the broadband continuum.
For aluminum alloys, anodizing is a common electrochemical surface treatment to allow for protection against corrosion and wear. The produced conversion layers are first sealed in industrial ...processes to further enhance the corrosion protection by closing the coating surface pores. In their lifetime, anodized components often undergo cyclic loadings. However, despite the relevance of a sealing treatment, there is a lack of systematic studies regarding its influence on the fatigue behavior of anodized aluminum components. In this work, a 6082-aluminum alloy was anodized in sulphuric acid and the effect of the anodizing treatment with and without further hydrothermal sealing on the fatigue strength was investigated. The thickness and Martens hardness of the coatings were determined and the coating appearance in non-sealed and sealed conditions was analyzed by scanning electron microscopy prior to and after cyclically loading at R = −1. The fatigue strength was significantly decreased by the anodizing treatment, when compared to the bare substrate. However, hydrothermal sealing had a positive influence as the anodized and sealed condition attained a fatigue strength in the range of the bare aluminum. Distinct differences regarding the coating appearances, thickness, and hardness were not observed when comparing the non-sealed and the sealed conditions. After fatigue loading, numerous pronounced radial cracks were present in the anodic coating, but the number of cracks were significantly lower for the hydrothermally sealed coating. Fatigue failure occurred due to propagation of one crack from the coating towards the substrate, resulting in single-point crack initiation, which was similar to the fatigue fracture behavior of the bare aluminum substrate.
The Swift Burst Alert Telescope (BAT) is discovering interesting new objects while monitoring the sky in the 14-195 keV band. Here we present the X-ray properties and spectral energy distributions ...(SEDs) for two unusual active galactic nucleus sources. Both NVSS 193013+341047 and IRAS 05218-1212 are absorbed, Compton-thin, but heavily obscured (N sub(H) ~ 10 super(23) cm super(-2)), X-ray sources at redshifts <0.1. The SEDs reveal these galaxies to be very red, with high extinction in the optical and UV. A similar SED is seen for the extremely red objects (EROs) detected in the higher redshift universe. This suggests that these unusual BAT-detected sources are a low-redshift (z Lt 1) analog to EROs, which recent evidence suggests are a class of the elusive type II quasars. Studying the multi-wavelength properties of these sources may reveal the properties of their high-redshift counterparts.
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