Low-frequency acoustic scatterings from a finite cylindrical shell are numerically analyzed by FEM. The simulation results show that the acoustic-scattering field in waveguide has lots of frequency-related sidelobes, while no sidelobes exist in free space at low frequencies. The simulation also indicates that the module value in waveguide can be almost 20 dB larger than that in free space at low frequency, which is caused by the ocean boundaries. We also demonstrate that when the incident wave direction is normal to the target at low frequency, the target strength will be maximum and the distribution of the acoustic-scattering field is axisymmetric about the incident waving direction. Meanwhile, the acoustic-scattering field is also related to the impedance of the seabed, and the change of the impedance makes just a little contribution to the scattering field. Finally, the influence of different target locations is analyzed, including the targets near the sea surface, seabed and the middle region of the ocean waveguide, respectively. From simulation results, it is evident that the distribution of the acoustic-scattering field at low frequency has a little difference, which is smaller than 0.5 dB with various target locations, and the change is frequency and boundary-related.
Abstract Lithospheric thinning occurred in the North China Craton (NCC) that resulted in extensive Mesozoic magmatism, which has provided the opportunity to explore the mechanism of the destruction of the NCC. In this study, new zircon U–Pb ages, geochemical and Lu–Hf isotopic data are presented for Early Cretaceous adakitic rocks in the Liaodong Peninsula, with the aim of establishing their origin as well as the thinning mechanism of the NCC. The zircon U–Pb data show that crystallization occurred during 127–120 Ma (i.e. Early Cretaceous). These rocks are characterized by high Sr (294–711 ppm) content and Sr/Y ratio (38.5–108), low Yb (0.54–1.24 ppm) and Y (4.9–16.4 ppm) contents, and with no obvious Eu anomalies, implying that they are adakitic rocks. They are enriched in large-ion lithophile elements (e.g. Ba, K, Pb and Sr) and depleted in high-field-strength elements (e.g. Nb, Ta, P and Ti). These adakitic rocks have negative zircon ϵ Hf ( t ) contents (−28.9 to −15.0) with two-stage Hf model ages ( T DM2 ) of 3004–2131 Ma. Based on the geochemical features, such as low TiO 2 and MgO contents, and high La/Yb and K 2 O/Na 2 O ratios, these adakites originated from the partial melting of thickened eclogitic lower crust. They were in an extensional setting associated with the slab rollback of the Palaeo-Pacific Ocean. In combination with previous studies, as a result of the rapid retracting of the Palaeo-Pacific Ocean during 130–120 Ma, the asthenosphere upwelled and modified the thickened lithospheric mantle, which lost its stability, resulting in the lithospheric delamination and thinning of the NCC.
Mechanical grinding (MG) is an effective method to regulate the pore structure and surface properties of mineral material.Grinding diatomite samples were prepared by horizontal sander under different grinding time.The pore structure and surface properties of grinding samples were characterized systematically by the particle size analysis, low temperature nitrogen adsorption, MIP, fractal theory, XRD, SEM, TEM, FTIR and surface hydroxyl density analysis.The humidity control performance (HCP) of grinding diatomite was tested under different temperature and relative humidity.The relationship among pore structure, surface properties and HCP was analyzed.The results show that macroporous is more easily damaged by mechanical force than mesoporous, and the internal blind holes structure can be opened.The HCP of diatomite is positively correlated with the specific surface area, mesoporous volume, the inhomogeneity of macroporous structure and the number of hydroxyl groups, while negatively correlated with the proportion of macroporous volume.
In the present scenarios of globalization, product life-cycle has become shorter and more frequent. of the Supply chain members' behavior will affect effectiveness and revenue of supply chain. In our study, the fairness preference was introduced into the model for two-level supply chain with stochastic demand depending on promotional effort. Firstly, we find the condition that is able to achieve channel coordination. Then we design a combined contract with the buyback and sales reward and penalty contract to solve the problem. We find that the supply chain can be coordinated with the combine contract properly designed. Finally, we use a numerical example to reveal the effectiveness of the combine contract and gain more insights.
The East Kunlun Orogen (EKO) is located in the western part of the Central Asian Orogenic Belt of China, and has witnessed the Late Permian-Triassic tectonic evolution involving the subduction and extinction of the Paleo-Tethys Ocean. In this study, geochronology, geochemistry, and Hf isotope analysis of Late Permian-Triassic granitoids in the EKO were carried out, and previous data were collated to determine a new model for the closure mode of the Paleo-Tethys Ocean. The zircon U-Pb ages of granodiorites and monzonitic granites in the Dachagou area (DCG) in the western part of the EKO (W-EKO) were found to be 233.4 ± 1.1 and 225.8 ± 1.2 Ma, respectively. The DCG granodiorites and monzonitic granites are characterized by low values of multiple characteristics: 10, 000 Ga/Al ratios (1.75-2.06 and 1.42-1.60), Zr + Nb + Ce + Y values (111.30-200.31 ppm and 88.86-96.40 ppm), Zr saturation temperature (730-775℃ and 703-710℃), and P2O5 contents (0.04-0.07% and 0.01%), similar to those of I-type granite. The Hf isotopic composition εHf (t) of zircons in the DCG granodiorites and monzonitic granites ranged from -2.4 to +0.1 and -3.0 to +0.2, with two-stage model ages (tDM2) of 1413–1254 and 1447–1245 Ma, respectively. They were probably generated by the mixing of Mesoproterozoic lower-crust-derived and mantle-derived melts. The zircon U-Pb age of quartz diorite in the Lalingzaohuo (LLZH) area was 244.5 ± 2.6 Ma its Nb/Ta ratios (13.73-15.35) and εHf(t) values (-0.7-+2.5; tDM2 = 1314-1113 Ma) indicate the origin of crust-mantle mixing. In addition, zircon U-Pb ages for granodiorites and monzonitic granites of the Nagengkangqieer area (NGKQE) in the eastern part of the EKO (E-EKO) were found to be 250.1 ± 2.8 and 238.9 ± 2.2 Ma, respectively. These rocks are also characterized by low 10, 000 Ga/Al ratios (2.37-2.66 and 2.49-2.63), Zr + Nb + Ce + Y values (337.59-363.3 ppm, 301.43-332.44 ppm), Zr saturation temperature (774-784℃, 788-804℃), and A/CNK ratios (0.88-0.91, 1.00-1.08), again similar to I-type granite. The ratios of La/Nb (1.60-1.94, 1.86-2.01), Ce/Pb (3.51-5.65, 2.89-3.38), and Nb/U (8.52-20.39, 4.81-6.77), as well as εHf(t) (-3.9--0.4, -3.3--1.1) in these samples indicate that the magma was mainly derived from the partial melting of crustal materials. Along with contemporaneous rocks, the DCG and NGKQE granodiorites and the LLZH quartz diorites are inferred to have formed in a subduction environment. In contrast, the DCG and NGKQE monzonitic granites formed in a collision environment. Based on the results of this study, the closure time of the W-EKO and E-EKO of the Paleo-Tethys Ocean had a difference of ~15 Ma, and W-EKO was later than the E-EKO, hence the closure mode of the Paleo-Tethys Ocean should be a “scissor-type” closure.
Large areas of intermediate-acid intrusive rocks are widely exposed in the Eastern Kunlun Orogenic Belt (EKOB), which is an ideal place to study crustal reworking and growth and the tectonic setting and evolution of the Paleo-Tethys Ocean. Petrographic research shows that intermediate-acid intrusive rocks are mainly composed of diorite, diorite porphyry, granodiorite, and monzogranite, and their zircon U-Pb ages are 260.8 ± 1.5 Ma, 250.7 ± 1.8 Ma, 242.6 ± 0.7 Ma, 239.8 ± 1.2 Ma, 235.2 ± 0.9 Ma, and 230.2 ± 1.0 Ma. They are generally divided into granite, quartz monzonite and monzodiorite series in the QAP diagram. The granite series (HRGLG and LMR monzogranites and BLGX granodiorite) has high SiO2 contents and calc-alkaline features; it has low P2O5 and Zr+Nb+Ce+Y (75–267 ppm) contents, showing affinities to I-type granite, which reflects reworking of Mesoproterozoic lower crust. The quartz monzonite series (KEQK and DDKD diorites) has medium SiO2 and lower MgO contents (1.63–2.59 wt.%) than mantle-derived magmas and has crustal Nb/U and Ce/Pb ratios but mantle-like Nb/Ta ratios. Their geochemistry with binary properties related to both crust and mantle indicate that they probably originated from an AFC process involving mantle-derived melts and provide an important growth model of the continental crust in the EKOB. The monzodiorite series (BLGX diorite porphyry) has medium SiO2 and high MgO contents and Mg# values (59–61) and contains high-Mg diorites. They are enriched in LILEs and depleted in HFSEs; furthermore, strikingly high enrichments in Rb/Y ratios and Ba contents but a narrow range of Nb/Y ratios suggest that they originated from partial melting of hydrous mantle peridotites affected by fluids from the subducted slab. In conclusion, we suggest that the 261–235 Ma intermediate-acid intrusions represent the sustained subduction of the Paleo-Tethys Ocean slab and that the 230 Ma BLGX diorite porphyry records the breakoff of the Paleo-Tethys Ocean slab.
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