The Guadalupian-Lopingian boundary stratotype at Penglaitan, and the nearby Tieqiao section, near Laibin, South China, record a series of major environmental changes within the Jiangnan Basin during ...a Mid-Permian biotic crisis. The sequence-stratigraphic, petrographic and palaeontological record of these sections has been studied and the associated strontium isotopic fluctuations have been assayed. Mass extinction of fusulinid foraminifers is most clearly associated in time with onset of volcanism and a relative sea-level fall that led to the establishment of mid-ramp conditions (Laibin Limestone) in settings that were previously dominated by radiolarian mudstones. The regression also coincides with a low point of 87Sr/86Sr ratios. The lowstand deposits contain mafic scoriaceous grains that record pyroclastic volcanism probably centred in the Emeishan flood basalt province 800 km to the west of Laibin. Thus, unusually violent eruptions associated with flood basalts in this province may have contributed to the environmental stresses responsible for the extinction event. Subsequent environmental changes included transgression, spread of dysoxic waters, indicated by populations of small pyrite framboids, and a major negative C-isotope excursion. All these phenomena have been previously related to the end-Guadalupian extinction but they in fact post-date the crisis because a post-extinction fauna of foraminifers is encountered at this time.
New iron selenide superconductors by intercalating smaller-sized alkali metals (Li, Na) and alkaline earths using high-temperature routes have been pursued ever since the discovery of ...superconductivity at about 30 K in KFe2 Se2 , but all have failed so far. Here we demonstrate that a series of superconductors with enhanced Tc = 30∼46 K can be obtained by intercalating metals, Li, Na, Ba, Sr, Ca, Yb, and Eu in between FeSe layers by the ammonothermal method at room temperature. Analysis on their powder X-ray diffraction patterns reveals that all the main phases can be indexed based on body-centered tetragonal lattices with a∼3.755-3.831 Å while c∼15.99-20.54 Å. Resistivities show the corresponding sharp transitions at 45 K and 39 K for NaFe2 Se2 and Ba0.8 Fe2 Se2 , respectively, confirming their bulk superconductivity. These findings provide a new starting point for studying the properties of these superconductors and an effective synthetic route for the exploration of new superconductors as well.
Quark clustering could occur in cold quark matter because of the strong coupling between quarks at realistic baryon densities of compact stars. Although one may still not be able to calculate this ...conjectured matter from the first principles, the intercluster interaction might be analogized to the interaction between inert molecules. Cold quark matter would then crystallize in a solid state if the intercluster potential is deep enough to trap the clusters in the wells. We apply the Lennard-Jones potential to describe the intercluster potential and derive the equations of state, which are stiffer than those derived in conventional models (e.g. MIT bag model). If quark stars are composed of the Lennard-Jones matter, they could have high maximum masses (>2 M⊙) as well as very low masses (<10−3 M⊙). These features could be tested by observations.
This paper presents a numerical approach to the simulation of fluid–solid coupling during the failure of a fractured coal–rock mass taking into consideration the regional geostress characteristics. ...We use the back calculation method to calculate the regional geostress of the study area, and we verify the accuracy of the back calculation method based on the in situ monitoring data. The values of the vertical stress and the minimum principal horizontal stress used in the numerical simulation are 7.057 and 8.085 MPa, respectively. In addition, the maximum principal horizontal stress has a local undulation that is affected by excavation disturbance. With a newly developed mechanical experimental system for digital radiography scanning, the temporal–spatial evolution of the fracture field is also revealed. The main fractures continue to propagate with increased external loading, and the spatial form of the fracture fields is a conjugate pattern and an X-shaped pattern. Based on the COMSOL Multiphysics program, the results indicate that the primary reason for crack propagation and connection is increased external loading, which leads to macroscopic fracturing of the coal–rock mass and incremental changes in the average porosity and permeability. The flow within the maximum velocity region represents the distribution characteristics of the induced cracks. The peak flow velocity is located at the main fracture, and its direction is parallel to that of the water injection pressure. Smaller fractures have a larger hydraulic gradient and larger flow velocities than larger fractures. The water outlet velocity characteristics indicate that the maximum flow velocity in the water outlet is located on the two sides of the model and increases with increasing external loading. All the fluid–solid coupling mechanisms would provide a reliable theoretical basis for optimization of mined-void roof weakening in mining the steeply inclined coal seam.
An advanced backcross population between an accession of Oryza rufipogon (IRGC 105491) and the U.S. cultivar Jefferson ( Oryza sativa ssp. japonica) was developed to identify quantitative trait loci ...(QTLs) for yield, yield components and morphological traits. The genetic linkage map generated for this population consisted of 153 SSR and RFLP markers with an average interval size of 10.3 cM. Thirteen traits were examined, nine of which were measured in multiple environments. Seventy-six QTLs above an experiment-wise significance threshold of P < 0.01 (corresponding to an interval mapping LOD > 3.6 or a composite interval mapping LOD > 3.9) were identified. For the traits measured in multiple environments, 47% of the QTLs were detected in at least two environments. The O. rufipogon allele was favorable for 53% of the yield and yield component QTLs, including loci for yield, grains per panicle, panicle length, and grain weight. Morphological traits related to the domestication process and/or weedy characteristics, including plant height, shattering, tiller type and awns, were found clustered on chromosomes 1 and 4. Comparisons to previous studies involving wild x cultivated crosses revealed O. rufipogon alleles with stable effects in multiple genetic backgrounds and environments, several of which have not been detected in studies between Oryza sativa cultivars, indicating potentially novel alleles from O. rufipogon. Some O. rufipogon-derived QTLs, however, were in similar regions as previously reported QTLs from Oryza sativa cultivars, providing evidence for conservation of these QTLs across the Oryza genus. In addition, several QTLs for grain weight, plant height, and flowering time were localized to putative homeologous regions in maize where QTLs for these traits have been previously reported, supporting the hypothesis of functional conservation of QTLs across the grasses.
•The setups of forming limit testing were developed for meso scale sheet metals.•The forming limit curves (FLC) were developed for pure copper sheets.•The FLC shifts down with the decrease of ...thickness-to-grain-size ratio.•The GTN–Thomason coupled model was extended by considering the size effect.•The FLCs predicted based on the model agree with the experimental ones.
Ductile fracture of metallic materials in micro/meso scale plastic deformation is influenced by geometry and grain sizes and the so-called size effect thus exists. To reveal how the size effect affects the formability of sheet metals in micro/meso scale plastic deformation, the forming limit of sheet metals was studied by experiment and modeling. An extended coupled damage model was first developed based on the Gurson–Tvergaard–Needleman and the Thomason models via considering the geometry and grain size effects on void evolution. In modeling process, the void nucleation was analyzed by taking account the phenomenon that the number of voids decreases with the ratio of thickness to grain size of workpiece. For the void growth, the widely used surface layer model was employed to describe the size effect on the flow stress of material. The grain size effect on void spatial arrangement was also modeled during the coalescence of micro voids. The model was then implemented into finite element simulations and the predicted forming limit curves under different scale factors were constructed. On the other hand, the forming limit experiments were conducted based on the miniaturized Holmberg and Marciniak tests to estimate the formability of sheet metals under different conditions. Both the physical experiments and finite element simulations show a significant size effect on the micro/meso scaled fracture behavior: The forming limit curve shifts down with the decreasing ratio of the thickness to grain size. The simulation results were also corroborated and verified by experiments. In addition, when the ratio is two or less than two, the very scattered limit strain results are observed in the experiments and the strain localization tends to occur at the beginning of deformation. The research conducted advances the understanding of size effect on the formability of micro/meso scaled sheet metals and thus helps the development of the successful and reliable microforming processes.
The rates for endoscopic detection of pancreas divisum at routine endoscopic retrograde cholangiopancreatography (ERCP) vary worldwide, and the sample sizes in the reported studies on endoscopy and ...surgery for pancreas divisum are very small and variable. The aim of this study was to systematically analyze the pooled data and determine endoscopic detection rates for pancreas divisum and pain relief rates in patients with pancreas divisum after endotherapy or surgery.
A search for published data was performed by using the Medline database (1950 to 1st May 2008) with "pancreas divisum" as the keyword. Publications, mainly on endoscopic detection rate, endotherapy, or surgery for pancreas divisum, were deemed relevant, and were further fully reviewed and analyzed.
A total of 615 abstracts were retrieved from Medline; 17 articles on endoscopic detection rate, 15 articles on endotherapy, and 13 articles on surgery were included in the review and analysis. The overall endoscopic detection rate for pancreas divisum was 2.9% (899/31,413), with the rate being significantly higher in the United States (5.8%) and Europe (6.0%) than in Asia (1.5%) (both P < 0.001). The pooled overall response rates (i. e. complete and partial pain relief rates after treatment) to endotherapy (69.4%, 361/520) and surgery (74.9%, 203/271) were similar (P = 0.106). In addition, there were significant differences in the combined response rates (for endotherapy and for surgery) between patients with pancreas divisum of acute recurrent pancreatitis (ARP)-type (81.2 %) compared with chronic pancreatitis-type (68.8%), and between ARP-type and pain-type (53.1%) (both P < 0.05).
The endoscopic detection rate for pancreas divisum is much higher in western countries than in Asian countries. The pooled response rates of patients with pancreas divisum to endotherapy and surgery are similar in the reported series. Patients with ARP-type pancreas divisum respond better to endotherapy or surgery than those with chronic pancreatitis-type and pain-type.
In micro-scaled plastic deformation or micro-forming process, workpiece usually consists of only a few grains in deformation zone. The so-called size effect thus exists and the material deformation ...behaviors are quite different from the conventional ones in macro-scaled. Size effect affects the deformation capability or the forming limit of sheet metals. To explore this effect, uniaxial tensile tests of different-shaped specimens were conducted to obtain the left-hand-side forming limit diagram of sheet metals from macro to micro-scaled. The deformation process was recorded by a digital camera and the limit strains of different deformation conditions were measured using the digital image correlation method. The left-hand-side forming limit diagrams under different thickness-to-grain-size ratio conditions were then constructed. The experimental results show the existence of the significant size effect and the forming limit decreases with the thickness-to-grain-size ratio. However, the scatter of forming limit gets much worse if there are only one or two grains over the thickness of material. To analyze how the size effect affects the ductile fracture in micro-forming, Oyane׳s ductile failure criterion was modified to model the forming limit in micro-scaled plastic deformation. Through calculation, the modified criterion is found to be able to model the decrease of forming limit caused by size effect. The revised Oyane criterion can then be used to analyze the forming limit of sheet metals in micro-scale.
The CRUNCEP V7 dataset was used to drive the Community Land Model version 4.5 (CLM4.5) to simulate the spatiotemporal changes in soil temperature in the Qinghai–Xizang Plateau from 1981 to 2016. The ...simulation results were compared with observations, ERA-Interim, and Global Land Data Assimilation System-Community Land Model (GLDAS-CLM) soil temperature reanalysis data. The results show that (1) the CLM4.5 can accurately reproduce the dynamic changes in the observed soil temperature over time in two soil layers (0–10 cm and 10–50 cm) at most sites, with a significant positive correlation with the observations. (2) The CLM4.5 can depict the spatial distribution of soil temperature in the plateau area, and the distribution characteristics are consistent with those of the reanalysis data. The soil temperature increases from north to south, and the values in the Qaidam Basin are significantly higher than those in the surrounding area. The CLM4.5 results are similar in value to the ERA-Interim product, while the GLDAS-CLM soil temperature values are generally higher. (3) The simulated value shows the trend of ‘increasing–decreasing-increasing–decreasing’ (+ − + −) from the west to the east in summer and autumn, while in winter and spring, the trend is generally increasing, but a decreasing trend is observed in some isolated locations. The temperature variation trends in the ERA-Interim data in winter and the GLDAS-CLM data in the middle of Sanjiangyuan in spring and the Qinghai Plateau in winter are consistent with those of the simulated data. The above results are all tested with 95% confidence. (4) From 1981 to 2016, the soil temperature on the plateau showed a significant upward trend, especially in spring and autumn. The two layers of the plateau have obvious seasonal changes, with the whole year characterised by a ‘single peak shape’. From March to September, the shallow soil temperature is higher than the deep soil temperature, and from October to February, the deep soil temperature is higher than the shallow soil temperature.
ABSTRACT
Glitch is supposed to be a useful probe into pulsar’s interior, but the underlying physics remains puzzling. The glitch activity may reflect a lower limit of the crustal moment of inertia in ...conventional neutron star models. Nevertheless, its statistical feature could also be reproduced in the strangeon star model, which is focused here. We formulate the glitch activity of normal radio pulsars under the framework of starquake of solid strangeon star model, the shear modulus of strangeon matter is constrained to be $\mu \simeq 3\times 10^{34}~\rm erg\,cm^{-3}$, consistent with previous work. Nevertheless, about ten times the shift in oblateness accumulated during glitch interval is needed to fulfill the statistical observations. The fact that typical glitch sizes of two rapidly evolving pulsars (the Crab pulsar and PSR B0540-69) are about two orders of magnitude lower than that of the Vela pulsar, significantly lower than the oblateness change they can supply, indicates probably that only a part of oblateness change is relieved when a pulsar is young. The unreleased oblateness and stress may relax as compensation in the following evolution. The small glitch sizes and low glitch activity of the Crab pulsar can be explained simultaneously in this phenomenological model. Finally, we obtain energy release to be $\Delta E\sim 2.4\times 10^{40}~\rm erg$ and $\Delta E\sim 4.2\times 10^{41}~\rm erg$ for typical glitch size of Δν/ν ∼ 10−6 (Vela-like) and ∼10−8 (Crab-like). The upcoming SKA may test this model through the energy release and the power-law relation between the reduced recovery coefficient $Q/|\dot{\nu }|^{1/2}$ and Δν/ν.
PDF
