Geologic reservoirs containing gas hydrate occur beneath permafrost environments and within marine continental slope sediments, representing a potentially vast natural gas source. Numerical ...simulators provide scientists and engineers with tools for understanding how production efficiency depends on the numerous, interdependent (coupled) processes associated with potential production strategies for these gas hydrate reservoirs. Confidence in the modeling and forecasting abilities of these gas hydrate reservoir simulators (GHRSs) grows with successful comparisons against laboratory and field test results, but such results are rare, particularly in natural settings. The hydrate community recognized another approach to building confidence in the GHRS: comparing simulation results between independently developed and executed computer codes on structured problems specifically tailored to the interdependent processes relevant for gas hydrate-bearing systems. The United States Department of Energy, National Energy Technology Laboratory, (DOE/NETL), sponsored the first international gas hydrate code comparison study, IGHCCS1, in the early 2000s. IGHCCS1 focused on coupled thermal and hydrologic processes associated with producing gas hydrates from geologic reservoirs via depressurization and thermal stimulation. Subsequently, GHRSs have advanced to model more complex production technologies and incorporate geomechanical processes into the existing framework of coupled thermal and hydrologic modeling.
This paper contributes to the validation of these recent GHRS developments by providing results from a second GHRS code comparison study, IGHCCS2, also sponsored by DOE/NETL. IGHCCS2 includes participants from an international collection of universities, research institutes, industry, national laboratories, and national geologic surveys. Study participants developed a series of five benchmark problems principally involving gas hydrate processes with geomechanical components. The five problems range from simple geometries with analytical solutions to a representation of the world's first offshore production test of methane hydrates, which was conducted with the depressurization method off the coast of Japan. To identify strengths and limitations in the various GHRSs, study participants submitted solutions for the benchmark problems and discussed differing results via teleconferences. The GHRSs evolved over the course of IGHCCS2 as researchers modified their simulators to reflect new insights, lessons learned, and suggested performance enhancements. The five benchmark problems, final sample solutions, and lessons learned that are presented here document the study outcomes and serve as a reference guide for developing and testing gas hydrate reservoir simulators.
•Code comparisons build confidence in simulators to model interdependent processes.•International hydrate reservoir simulators are compared over five complex problems.•Geomechanical processes significantly impact response of gas hydrate reservoirs.•Simulators yielded comparable results, however many differences are noted.•Equivalent constitutive models are required to achieve agreement across simulators.
We report here on the early stage of the precipitation behavior of aged Al–Li–Cu alloys using transmission electron microscopy. The δ′ phase (Al
3Li, L1
2 structure (Structurbericht)) was found to ...exist in the as-quenched specimen containing 2.4 wt%-Li, whereas no precipitation was observed in the as-quenched specimen with 1.6 wt%-Li. After aging at 100 °C for 3 h, GP-I zones nucleated homogeneously in both specimens; but no δ′ phase was detected in the 1.6 wt%-Li alloy at that stage. As the aging proceeds, the δ′ phase nucleates and grows on the GP-I zones. The composite structure, in which the GP-I zone is flanked by a pair of lenticular δ′ particles, is stable in 180–200 °C. The facing lenticular δ′ particles on a GP-I zone were systematically found to be anti-phase with respect to each other.
Rapid radio brightening of GRB 210702A Anderson, G E; Russell, T D; Fausey, H M ...
Monthly notices of the Royal Astronomical Society,
06/2023, Letnik:
523, Številka:
4
Journal Article
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ABSTRACT
We observed the rapid radio brightening of GRB 210702A with the Australia Telescope Compact Array (ATCA) just 11 h post-burst, tracking early-time radio variability over a 5 h period on ∼15 ...min time-scales at 9.0, 16.7, and 21.2 GHz. A broken power law fit to the 9.0 GHz light curve showed that the 5 h flare peaked at a flux density of 0.4 ± 0.1 mJy at ∼13 h post-burst. The observed temporal and spectral evolution is not expected in the standard internal–external shock model, where forward and reverse shock radio emission evolves on much longer time-scales. The early-time (<1 d) optical and X-ray light curves from the Neil Gehrels Swift Observatory demonstrated typical afterglow forward shock behaviour, allowing us to use blast wave physics to determine a likely homogeneous circumburst medium and an emitting electron population power-law index of p = 2.9 ± 0.1. We suggest that the early-time radio flare is likely due to weak interstellar scintillation (ISS), which boosted the radio afterglow emission above the ATCA sensitivity limit on minute time-scales. Using relations for ISS in the weak regime, we were able to place an upper limit on the size of the blast wave of ≲6 × 1016 cm in the plane of the sky, which is consistent with the theoretical forward shock size prediction of 8 × 1016 cm for GRB 210702A at ∼13 h post-burst. This represents the earliest ISS size constraint on a gamma-ray burst (GRB) blast wave to date, demonstrating the importance of rapid (<1 d) radio follow-up of GRBs using several-hour integrations to capture the early afterglow evolution and to track the scintillation over a broad frequency range.
We herein report a significant improvement of the ductility of AZ31 (Al: 3
wt%, Zn: 1
wt%, balance Mg) sheets processed by differential speed rolling (DSR). The DSR sheets under tension in the ...rolling direction exhibited a plastic strain more than 1.5 times larger than the sheets prepared by conventional rolling (CR), and simultaneous improvements of in-plane isotropy. The origin of these changes has been examined by texture and structural characterizations. The (0
0
0
2) pole intensity of the as-rolled DSR sheet is strongly accumulated in the normal direction, which is preserved after deformation regardless of tensile directions; while that of as-rolled CR sheet show clear splitting, which further broadens after tensile tests. It is suggested that these changes are brought about by the application of a large shear strain to DSR sheets, which resulted in the clear (0
0
0
2) texture, and subsequent ease of the activation of prismatic slip during the deformation.
Structural relaxation behavior of various composition for Zr-Cu-Al ternary bulk amorphous alloys (hyper-eutectic: Zr45Cu45Al10 and Zr49Cu41Al10, eutectic: Zr50Cu40Al10, hypo-eutectic: Zr55Cu35Al10 ...and Zr60Cu30Al10) during isothermal annealing below glass transition temperature (Tg) has been investigated by positron annihilation techniques (positron lifetime and coincidence Doppler broadening (CDB)), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and bulk density measurements. The annealing makes the positron lifetime decrease owing to the relaxation. However, maximum decreasing of positron lifetime after 10 ks annealing for eutectic alloy was observed. And different composition dependence of positron change between hypo- and hyper-eutectic alloys was confirmed. Especially, open-volume in hyper-eutectic alloys is hard to change by the annealing. We found that the trend of positron lifetime change Δτ with Zr concentration is not necessarily correlated with the change in bulk density consistently. On the other hand, the positron lifetime during annealing obeys a stretched exponential relaxation function. Also we found the relaxation parameter β, which indicates the distribution activation energy for open-volume relaxation, varies in Zr concentration.
•The nature of open-volume was classified by hyper- and hypo-eutectic alloy region.•Composition dependence of open-volume relaxation for BA alloys was confirmed.•Relaxation process of open-volume obeys stretched exponential function.•Open-volume relaxation divided into two composition regions essentially.
The atomic structure of CoPt and FePt nanoparticles (with a diameter between 2 and 5 nm) has been studied by transmission electron microscopy. The particles have been produced by a laser vaporization ...cluster source and annealed under vacuum in order to promote chemical ordering. For both alloys, we observe a coexistence of crystalline and multiply twinned particles with decahedral or icosahedral shapes. In addition to particles corresponding to a single L1(0) ordered domain, we put into evidence that even small particles can display several L1(0) domains. In particular, the chemical order can be preserved across twin boundaries which can give rise to spectacular chemically ordered decahedral particles made of five L1(0) domains. The stability of such structures, which had been recently predicted from theoretical simulations, is thus unambiguously experimentally confirmed.
•Fused silica glass was employed as a substrate for vertical GaN nanocolumn growth.•The grown GaN nanocolumns display single crystalline of wurtzite crystal structure.•Few atom layers of zinc-blende ...present at the interface adjacent to the glass.•High GaN optical quality and absence of yellow luminescence are obtained.
We demonstrate GaN nanocolumn growth on fused silica glass by plasma-assisted molecular beam epitaxy. The effect of the substrate temperature, Ga flux and N2 flow rate on the structural and optical properties are studied. At optimum growth conditions, GaN nanocolumns are vertically aligned and well separated with an average diameter, height and density of 72nm, 1.2μm and 1.6×109cm−2, respectively. The nanocolumns exhibit wurtzite crystal structure with no threading dislocations, stacking faults or twinning and grow in the 0001 direction. At the interface adjacent to the glass, there is a few atom layers thick intermediate phase with ABC stacking order (zinc blende). Photoluminescence measurements evidence intense and narrow excitonic emissions, along with the absence of any defect-related zinc blende and yellow luminescence emission.
Context. The BL Lac object S5 0716+714, a highly variable blazar, underwent an impressive outburst in January 2015 (Phase A), followed by minor activity in February (Phase B). The MAGIC observations ...were triggered by the optical flux observed in Phase A, corresponding to the brightest ever reported state of the source in the R-band. Aims.The comprehensive dataset collected is investigated in order to shed light on the mechanism of the broadband emission. Methods. Multi-wavelength light curves have been studied together with the broadband spectral energy distributions (SEDs). The sample includes data from Effelsberg, OVRO, Metsähovi, VLBI, CARMA, IRAM, SMA, Swift-UVOT, KVA, Tuorla, Steward, RINGO3, KANATA, AZT-8+ST7, Perkins, LX-200, Swift-XRT, NuSTAR, Fermi-LAT and MAGIC. Results. The flaring state of Phase A was detected in all the energy bands, providing for the first time a multi-wavelength sample of simultaneous data from the radio band to the very-high-energy (VHE, E > 100 GeV). In the constructed SED, the Swift-XRT+NuSTAR data constrain the transition between the synchrotron and inverse Compton components very accurately, while the second peak is constrained from 0.1 GeV to 600 GeV by Fermi+MAGIC data. The broadband SED cannot be described with a one-zone synchrotron self-Compton model as it severely underestimates the optical flux in order to reproduce the X-ray to γ-ray data. Instead we use a two-zone model. The electric vector position angle (EVPA) shows an unprecedented fast rotation. An estimation of the redshift of the source by combined high-energy (HE, 0.1 GeV < E < 100 GeV) and VHE data provides a value of z = 0.31 ± 0.02stats ± 0.05sys, confirming the literature value. Conclusions. The data show the VHE emission originating in the entrance and exit of a superluminal knot in and out of a recollimation shock in the inner jet. A shock–shock interaction in the jet seems responsible for the observed flares and EVPA swing. This scenario is also consistent with the SED modeling.
In AZ31 (Mg–3Al–1wt% Zn) magnesium alloy sheets rolled by differential speed rolling (DSR) at 423
K, many twins appeared at a low reduction rate of 25%, and fine grains (∼1
μm) having approximately ...the same size dominate at a high reduction rate of 55%. In addition to these microstructural changes, the rolled sheets showed a strong texture characterized by (0
0
0
2) pole tilting about 7 degree from the normal direction (ND) towards the rolling direction (RD) throughout the whole thickness of the DSR sheets. The
(
1
0
1
¯
1
)
pole figure as well as TEM images of the specimen prepared at a reduction rate of 55% indicated that the activation of a prismatic slip played an important role in bringing about dynamical re-crystallization.
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