In this study, the length scaling for the boundary layer separation induced by two incident shock waves is experimentally and analytically investigated. The experiments are performed in a Mach 2.73 flow. A double-wedge shock generator with two deflection angles ($\alpha _1$ and $\alpha _2$) is employed to generate two incident shock waves. Two deflection angle combinations with an identical total deflection angle are adopted: ($\alpha _1 = 7^\circ$, $\alpha _2 = 5^\circ$) and ($\alpha _1 = 5^\circ$, $\alpha _2 = 7^\circ$). For each deflection angle combination, the flow features of the dual-incident shock wave–turbulent boundary layer interactions (dual-ISWTBLIs) under five shock wave distance conditions are examined via schlieren photography, wall-pressure measurements and surface oil-flow visualisation. The experimental results show that the separation point moves downstream with increasing shock wave distance ($d$). For the dual-ISWTBLIs exhibiting a coupling separation state, the upstream interaction length ($L_{int}$) of the separation region approximately linearly decreases with increasing $d$, and the decrease rate of $L_{int}$ with $d$ increases with the second deflection angle under the condition of an identical total deflection angle. Based on control volume analysis of mass and momentum conservations, the relation between $L_{int}$ and $d$ is analytically determined to be approximately linear for the dual-ISWTBLIs with a coupling separation region, and the slope of the linear relation obtained analytically agrees well with that obtained experimentally. Furthermore, a prediction method for $L_{int}$ of the dual-ISWTBLIs with a coupling separation region is proposed, and the relative error of the predicted $L_{int}$ in comparison with the experimental result is $\sim$10 %.

The sequential occurrence of three layers of smooth muscle layers (SML) in human embryos and fetus is not known. Here, we investigated the process of gut SML development in human embryos and fetuses and compared the morphology of SML in fetuses and neonates. The H&E, Masson trichrome staining, and Immunohistochemistry were conducted on 6–12 gestation week human embryos and fetuses and on normal neonatal intestine. We showed that no lumen was seen in 6–7th gestation week embryonic gut, neither gut wall nor SML was developed in this period. In 8–9th gestation week embryonic and fetal gut, primitive inner circular SML (IC-SML) was identified in a narrow and discontinuous gut lumen with some vacuoles. In 10th gestation week fetal gut, the outer longitudinal SML (OL-SML) in gut wall was clearly identifiable, both the inner and outer SML expressed α-SMA. In 11–12th gestation week fetal gut, in addition to the IC-SML and OL-SML, the muscularis mucosae started to develop as revealed by α-SMA immune-reactivity beneath the developing mucosal epithelial layer. Comparing with the gut of fetuses of 11–12th week of gestation, the muscularis mucosae, IC-SML, and OL-SML of neonatal intestine displayed different morphology, including branching into glands of lamina propria in mucosa and increased thickness. In conclusions, in the human developing gut between week-8 to week-12 of gestation, the IC-SML develops and forms at week-8, followed by the formation of OL-SML at week-10, and the muscularis mucosae develops and forms last at week-12.

Intestinal atresia (IA), a common cause of neonatal intestinal obstruction, is a developmental defect, which disrupts the luminal continuity of the intestine. Here, we investigated (i) the process of lumen formation in human embryos; and (ii) how a defective lumen formation led to IA. We performed histological and histochemical study on 6–10 gestation week human embryos and on IA septal regions. To investigate the topology of embryonic intestine development, we conducted 3D reconstruction. We showed that a 6–7th gestation week embryonic gut has no lumen, but filled with mesenchyme cells and vacuoles of a monolayer of epithelial cells. A narrow gut lumen was formed by gestation week-9, the gut was filled with numerous vacuoles of different sizes, some vacuoles were merging with the developing embryonic gut wall. At gestation week-10, a prominent lumen was developed, only few vacuoles were present and were merging with the intestine wall. At IA septal regions, vacuoles were located in the submucous layer, covered by a single layer of epithelium without glandular structure, and surrounded with fibrous tissue. The mucosal epithelium was developed with lamina propria and basement membrane, but the submucosa and the longitudinal smooth muscle layers were not properly developed. Hence, the vacuoles in IA septum could represent a remnant of vacuoles of embryonic gut. In conclusion, the fusion of vacuoles with the developing intestine wall associates with the disappearance of vacuoles and gut lumen formation in human embryos, and perturbation of these developmental events could lead to IA.

The study of the petrogenesis of some magmatic rocks with special geochemical attributes provides effective information for us to explore the deep geodynamic background of their formation. A series of granitic porphyry dykes have been found in the mélange zone of the Asa region in southern Tibet, whose genesis may be closely related to the evolution of the Meso-Tethyan Ocean. Regional geodynamic evolution is investigated by whole-rock geochemical analysis, zircon U–Pb dating and Lu–Hf isotopic analysis of two porphyritic granites. The Asa porphyritic granites have high SiO2 (74.29–78.65 wt %) and alkalis (Na2O + K2O = 6.51–9.35 wt %) contents, and low Al2O3 (11.60–14.51 wt %), CaO (0.04–0.19 wt MgO (0.01–0.10 wt %) contents. They are enriched in Zr, Nb, Ce, Y and Hf and depleted in Ti, Ba, Sr and P, consistent with A-type granites. The samples are relatively rich in LREEs, with LREE/HREE ratios of 1.73–3.04. They display negative Eu anomalies (Eu/Eu* = 0.24–0.28) and obvious Ce anomalies in some samples. Zircon U–Pb analyses show that the porphyritic granites formed in late Early Cretaceous time, 107.4 to 105.5 Ma. Zircon εHf(t) values are in the range of 6.9 to 12.0. These data indicate that the porphyritic granites were sourced from interaction between mantle-derived and juvenile lower crust-derived melts, with the addition of oceanic sediment-derived melts. This occurred when the subducting Bangong–Nujiang oceanic crust split to create a slab window. Rising asthenosphere triggered re-melting of lower crust basalts, resulting in the formation of the late Early Cretaceous A-type granites around Asa.

Tomographic particle image velocimetry (TPIV) measurement with six high-resolution charge-coupled device (CCD) cameras is conducted to investigate flow structures over a finite circular cylinder with an aspect ratio of 2 ($h/d=2$). This short wall-mounted cylinder is fully immersed in a thick turbulent boundary layer ($\unicode[STIX]{x1D6FF}/h=1.025$). Focus is placed on the three-dimensional instantaneous vortex structures and their dynamic characteristics in the wake flow fields. Based on the present results, a refined topological model of the mean wake field behind the finite circular cylinder is proposed, where the spatial locations of the typical vortex structures and their interactions are described in more detail. Among the reported typical vortex structures (i.e. the horseshoe, tip, base, trailing and arch vortex), emphasis is laid on discussion of the tip and arch vortex. The instantaneous 3D M-shape arch vortex and an alternating large-scale streamwise vortex are first found in the present experiment, and their developments are also discussed. Therefore, it is suggested that the instantaneous finite-cylinder wake is dominated by the arch vortex system and the large-scale streamwise vortices. Moreover, in the instantaneous volumetric flow fields, both the antisymmetric and the symmetric wake behaviours are observed. With proper orthogonal decomposition (POD) analysis, the dynamic characteristics of the wake field are clarified. Different from the flow around an infinite cylinder without control, the third and fourth POD modes are characterized by low-frequency symmetric shedding. The low-frequency feature shown in the second mode pair is observed and associated with the occurrence of instantaneous symmetric 3D wake behaviour triggered by the low-aspect-ratio effect and the extension of the separated shear layer. The low frequency seems be attributed to the flapping phenomenon, i.e. oscillation of the recirculation in the backward-facing step flow. It is found that the flapping motion has a modulating effect on the occurrence of the antisymmetric shedding vortex and thus the large-scale streamwise vortex.

The conventional process for preparing dry spinnable regenerated silk fibroin (RSF) aqueous solution needs not only an addition of Ca2+ but also an adjustment of pH value. In this work, an RSF dry spinning dope was prepared by using a simplified method with solely adding Ca2+. Compared with the conventional RSF solution, the simply prepared aqueous solution showed similar content of β-sheet conformation and diameter of RSF aggregates but lower viscosity. Furthermore, the posttreated RSF fiber dry-spun from this simply prepared solution showed higher crystallinity and crystalline orientation, smaller crystallite size, and better mechanical properties. It could be concluded that Ca2+ played a much more important role than pH value in improving the structures and properties of RSF spinning solution and fibers. Therefore, the step of adjusting pH value could be excluded in the process of preparing high performance RSF fibers.

In this work, the silk fibroin/sericin (SF/SS) blend aqueous solutions with different SF/SS mass ratios (100/0, 90/10, 85/15, 75/25, and 65/35) were prepared and electrospun to get regenerated fibers. It was found that the addition of SS in the SF solution could increase the apparent viscosity of the solution and improve its electrospinnability so that the fine uniform electrospun SF/SS fibers could be obtained. The quantitative analysis result of Raman spectroscopy showed that the presence of SS facilitated the conformational transition of SF from random coil/α-helix structure to β-sheet structure. Combined with the differential scanning calorimetry result, it was further hypothesized that SS could affect the structural change of SF by dehydrating SF and inducing the formation of hydrogen bonds between SF molecules. Consequently, SS also played an important and positive role in the thermal and mechanical properties of the resultant SF/SS fibers.

Formation of intermetallic compounds (IMCs) at the interface between two metals during soldering processing exerts much influence on the electrical and mechanical performance of integrate circuits (ICs). Considering both of the thermodynamic and kinetic factors (including nucleation and growth) on phase formation, a new model capable of predicting phase formation sequence at the interface between two metals with different structures has been proposed in this work. Application of this new model on the interfacial reactions between pure elemental pairs of metals such as Ni/Sn, Cu/In, Cu/Sn, and Co/Sn at different temperatures shows good agreement between predictions by this model and experimental observations.

Spatial ordering of InAs quantum dots was attained by using misfit dislocations generated in a metastable InGaAs layer by means of thermal annealing. Influence of quantum dot positional ordering and dot proximity to dislocation arrays on carrier dynamics was studied by timeresolved photoluminescence. Substantially narrower inhomogeneous broadening from the ordered quantum dots was observed. Excitation intensity dependence of the photoluminescence intensity and carrier lifetime indicates stronger influence of nonradiative recombination for the ordered quantum dot structures. Numerical simulations allow estimating electron and hole capture rates from the quantum dots to traps located either at the quantum dot interfaces or in the vicinity of the quantum dots.

Poly Si1−xGex films have been suggested as a promising alternative to the currently employed poly-Si gate electrode for CMOS technology due to lower resistivity, less boron penetration, and less gate depletion effect than those of poly Si gates. We investigated the formation of poly Si1−xGex films grown by UHV CVD using Si2H6 and GeH4 gases, and studied their microstructures as well as their electrical characteristics. The Ge content of the Si1−xGex films increased linearly with the flux of the GeH4 gas up to x=0.3, and saturated above x=0.45. The deposition rate of the poly Si1−xGex films increased linearly with the flux of the GeH4 gas up to x=0.1, above which it is slightly changed. The resistivity of the Si1−xGex films decreased as the Ge content increased, and was about one half of that of poly-Si films at the Ge content of 45%. The C-V measurements of the MOSCAP structures with poly Si1−xGex gates demonstrated that the flat band voltage of the poly Si1−xGex films was lower than that of poly-Si films by 0.2V.

We report the highly reflecting (>99.9%) In0.53Al0.14Ga0.33As/In0.52Al0.48As 30.5 pairs distributed Bragg reflector (DBR) and the In0.53Ga0.47As/ In0.52Al0.48As active cavity layer grown at high temperature by low pressure metal organic chemical vapor deposition with in-situ double beam laser reflectometry. One of the laser wavelengths selected for in-situ measurement was same as the DBR wavelength. The growth temperature was 750 °C. Good surface morphology of the multi-layer stacks was achieved by the temperature ramping of the InP buffer layer at the beginning of a multi-layer stacks. The width of stop band edge of the DBR reflectivity spectrum was found to be 1000Å.

We report application of in-situ laser reflectometry in monitoring InAl1−xAs (0 ≤ x ≤1) epitaxial layers grown on a GaAs substrate by low pressure metal-organic chemical vapor deposition. Two different lasers were used simultaneously: One was a He-Ne laser operating at 0.6328 μm and the other was a diode laser operating at 1.53 μm. The two laser beams were incident on the growing layer at an angle of 71° from the surface normal, and the reflected beams were detected by Si and Ge photovoltaic detectors, respectively. Since the epitaxial layer of InxAl1−xAs (0 ≤ x ≤1) has a wide range of index of refraction, the reflected signals showed a variety of patterns. The optical constants of the InxAl1−xAs epitaxial layers were obtained for the entire range of composition.

In this paper, under certain conditions on the orthogonal distribution T0, we give a characterization of real hypersurfaces of type A in a complex space form Mn(c), c ≠ 0.