Cyclic behavior and microstructural stability of ultrafine-grained AA6060 under strain-controlled fatigue

AbstractThe strain-controlled fatigue behavior of AA6060, a precipitation hardening aluminum alloy, was investigated in ultrafinegrained (UFG) conditions after severe plastic deformation (SPD) by equal-channel angular pressing (ECAP). Two as-processed conditions, representing different stages of strain hardening and grain refinement as well as a ductility-optimized condition, achieved by a combined ECAP and aging treatment were considered. Low-voltage scanning transmission electron microscopy on samples stopped at characteristic stages of the fatigue process was applied to investigate the microstructural development. The as-processed as well as the optimized condition showed cyclic softening, which was found to be dependent on the amount of prestrain induced by ECAP processing. This is linked to dynamic recovery processes in the microstructure, indicated by a clearer distinction of grain boundaries and a reduction of dislocations in the grain interior. For all applied plastic strain amplitudes, ranging from Δεpl/2=1×10−3 to 5×10−3, the fatigue life of the ductility-optimized condition did not reach that of the severely work-hardened counterpart. For explaining this unexpected result, the differing (size-dependent) effectiveness of precipitates for the pinning of dislocations during cyclic loading was considered

Comparison of Emissions Inventories of Anthropogenic Air Pollutants in China

Anthropogenic air pollutant emissions have been increasing rapidly in China. Modelers use emissions inventories to assess temporal and spatial distribution of these emissions to estimate their impacts on regional and global air quality. However, large uncertainties exist in emissions estimates and assessing discrepancies in these inventories is essential for better understanding of the trends in air pollution over China. We compare five different emissions inventories estimating emissions of carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), particulate matter with an aerodynamic diameter of 10 um or less (PM10) from China. The emissions inventories analyzed in this paper include Regional Emissions inventory in ASia v2.1 (REAS); Multi-resolution Emission Inventory for China (MEIC); Emission Database for Global Atmospheric Research v4.2 (EDGAR); the inventory by Yu Zhao (ZHAO); and the Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS). We focus on the period between 2000 and 2008 during which the Chinese economic activities have more than doubled. In addition to the national total, we also analyzed emissions from four source sectors (industry, transportation, power, and residential) and within seven regions in China (East, North, Northeast, Central, Southwest, Northwest, and South) and found that large disagreements (~ seven fold) exist among the five inventories at disaggregated levels. These discrepancies lead to differences of 67 ug/m3, 15 ppbv, and 470 ppbv for monthly mean PM10, O3, and CO, respectively, in modelled regional concentrations in China. We also find that MEIC inventory emissions estimates create a VOC-limited environment that produces much lower O3 mixing ratio in the East and Central China compared to the simulations using REAS and EDGAR estimates. Our results illustrate that a better understanding of Chinese emissions at more disaggregated levels is essential for finding an effective mitigation measure for reducing national and regional air pollution in China

How Many CMEs Have Flux Ropes? Deciphering the Signatures of Shocks, Flux Ropes, and Prominences in Coronagraph Observations of CMEs

We intend to provide a comprehensive answer to the question on whether all Coronal Mass Ejections (CMEs) have flux rope structure. To achieve this, we present a synthesis of the LASCO CME observations over the last sixteen years, assisted by 3D MHD simulations of the breakout model, EUV and coronagraphic observations from STEREO and SDO, and statistics from a revised LASCO CME database. We argue that the bright loop often seen as the CME leading edge is the result of pileup at the boundary of the erupting flux rope irrespective of whether a cavity or, more generally, a 3-part CME can be identified. Based on our previous work on white light shock detection and supported by the MHD simulations, we identify a new type of morphology, the `two-front' morphology. It consists of a faint front followed by diffuse emission and the bright loop-like CME leading edge. We show that the faint front is caused by density compression at a wave (or possibly shock) front driven by the CME. We also present high-detailed multi-wavelength EUV observations that clarify the relative positioning of the prominence at the bottom of a coronal cavity with clear flux rope structure. Finally, we visually check the full LASCO CME database for flux rope structures. In the process, we classify the events into two clear flux rope classes (`3-part', `Loop'), jets and outflows (no clear structure). We find that at least 40% of the observed CMEs have clear flux rope structures. We propose a new definition for flux rope CMEs (FR-CMEs) as a coherent magnetic, twist-carrying coronal structure with angular width of at least 40 deg and able to reach beyond 10 Rsun which erupts on a time scale of a few minutes to several hours. We conclude that flux ropes are a common occurrence in CMEs and pose a challenge for future studies to identify CMEs that are clearly not FR-CMEs.Comment: 26 pages, 9 figs, to be published in Solar Physics Topical Issue "Flux Rope Structure of CMEs

The new ALEPH Silicon Vertex Detector

The ALEPH collaboration, in view of the importance of effective vertex detection for the Higgs boson search at LEP 2, decided to upgrade the previous vertex detector. Main changes were an increased length (±20 cm), a higher granularity for rφ view (50 µm), a new preamplifier (MX7 rad hard chip), a polymide (upilex) fan-out on z side to carry the signals from the strips to the front-end electronics outside the fiducial region reducing consequently the passive material in the central region by a factor of two. The detector, the running experience and its performance will be described

The new ALEPH Silicon Vertex Detector

The ALEPH collaboration, in view of the importance of effective vertex detection for the Higgs boson search at LEP 2, decided to upgrade the previous vertex detector. Main changes were an increased length (±20 cm), a higher granularity for rφ view (50 µm), a new preamplifier (MX7 rad hard chip), a polymide (upilex) fan-out on z side to carry the signals from the strips to the front-end electronics outside the fiducial region reducing consequently the passive material in the central region by a factor of two. The detector, the running experience and its performance will be described