The inevitable formation of a Mach disk at the central axis of a convergent conical shock wave may suffer from fundamental changes when the flow deviates from the axisymmetric condition. In this paper, the behaviours of near-conical shocks, which are generated by a circular ring wedge of $10^{\circ }$ at typical angles of attack (AoAs), are investigated at a free stream Mach number of 6 in a shock tunnel. To reveal the characteristics and mechanism of the flow, numerical analyses are carried out under the same conditions. The results indicate that when the flow deviates from axial symmetry, the circumferential non-uniformity is remarkably intensified as the shock converges downstream. The converging centre shifts against the inclination of the incoming flow and moves to the leeward side. For a sufficiently small AoA, the formation of a Mach disk remains similar to that in the axisymmetric case, although the Mach disk shrinks in size and is slightly flattened. As the circumferential non-uniformity of the shock increases at an AoA of approximately $3^{\circ }$, a pair of kinks separate the shock surface into two discontinuous segments with the stronger shock segment on the windward side and the weaker shock segment on the leeward side. When the AoA increases further, the shrinkage of the Mach disk continuously occurs, and the Mach disk is eventually replaced by a regular reflection. The discontinuity of a convergent shock with flattening on the separated shock segments and the insufficient strength increase during the subsequent convergence are responsible for the appearance of regular reflection.

A new enantiornithine bird is described on the basis of a well preserved partial skeleton from the Upper Cretaceous Qiupa Formation of Henan Province (central China). It provides new evidence about the osteology of Late Cretaceous enantiornithines, which are mainly known from isolated bones; in contrast, Early Cretaceous forms are often represented by complete skeletons. While the postcranial skeleton shows the usual distinctive characters of enantiornithines, the skull displays several features, including confluence of the antorbital fenestra and the orbit and loss of the postorbital, evolved convergently with modern birds. Although some enantiornithines retained primitive cranial morphologies into the latest Cretaceous Period, at least one lineage evolved cranial modifications that parallel those in modern birds.

A combination of shock tunnel experiments, numerical simulations and theoretical analyses is conducted on V-shaped blunt leading edges (VBLEs) with a wide range of geometric parameters at a free stream Mach number of 6. The interactions between the shock waves induced by the two straight branches and the crotch of the VBLEs set up intriguing wave structures with increases in $R/r$ (i.e. the crotch radius $R$ over the leading edge radius $r$) and $\beta$ (i.e. the half-span angle between the two straight branches), including regular reflection (RR), Mach reflection (MR) and regular reflection from the same family (sRR). These wave structures are observed in shock tunnel experiments and are reproduced by numerical simulations. Of great interest, transitions of shock interactions from RR to MR and from MR to sRR are identified with variation in $R/r$ or $\beta$. It is revealed that the specific geometric constraints of VBLEs, rather than the classic detachment and von Neumann criteria, govern the transitions of shock interactions. From theoretical analyses of the relative geometric positions of the shock structures near the crotch, transition criteria of the shock interactions on VBLEs are established. These theoretical transition criteria achieve good agreement with the numerical and experimental results for a wide range of $R/r$ and $\beta$ and thus show great potential for practical engineering applications, such as the selection of geometric parameters for the cowl lip of a hypersonic inlet.

This paper characterizes the geometry of converging near-elliptic shock waves at a Mach number of 6. The converging shocks are produced by elliptic conical surfaces with shapes made up from adjacent straight generators, each deflected a constant angle from the free-stream direction. Combined shock tunnel experiments and numerical analyses are conducted to depict the evolution of the converging shock waves for several elliptic entry aspect ratios $AR$s (i.e. the ratio of the major axis to the minor axis). It is revealed that the deviation from axial symmetry is amplified as the shock front approaches the centreline, which results in different shock interaction types compared with the axisymmetric case. Three typical shock interaction types are classified depending on various ARs. For a small AR, faster shock strengthening in the major plane dominates, although a Mach reflection (type A) that resembles the axisymmetric flow field is formed. However, for a sufficiently large AR, the shock strengthening is eventually terminated by the intersection of the weaker shocks in the minor plane owing to their smaller off-centre distances, which results in a regular reflection (type B). Between these two interaction patterns, there is a critical AR for which both the shock fronts in the major and minor planes intersect at the centreline coincidentally, and this critical intersection (type C) exhibits an extreme case of a shock front converging to a singular point. This study indicates that deviation from axial symmetry affects the evolution of the shock structures in converging flow.

The Richtmyer–Meshkov instability on a three-dimensional single-mode light/heavy interface is experimentally studied in a converging shock tube. The converging shock tube has a slender test section so that the non-uniform feature of the shocked flow is amply exhibited in a long testing time. A deceleration phenomenon is evident in the unperturbed interface subjected to a converging shock. The single-mode interface presents three-dimensional characteristics because of its minimum surface feature, which leads to the stratified evolution of the shocked interface. For the symmetry interface, it is quantitatively found that the perturbation amplitude experiences a rapid growth to a maximum value after shock compression and finally drops quickly before the reshock. This quick reduction of the interface amplitude is ascribed to a significant Rayleigh–Taylor stabilization effect caused by the deceleration of the light/heavy interface. The long-term effect of the Rayleigh–Taylor stabilization even leads to a phase inversion on the interface before the reshock when the initial interface has sufficiently small perturbations. It is also found that the amplitude growth is strongly suppressed by the three-dimensional effect, which facilitates the occurrence of the phase inversion.

We study the one-pot facile hydrothermal growth of ultralong silver–carbon (Ag–C) nanocables with Ag nanowires as the cores and carbon as the sheaths through the mediation of H2SO4 and without using an organic surfactant. In the investigation, Ag–C nanostructures were systematically and extensively examined as a function of both temperature and H2SO4 concentration to locate the optimal conditions for preparing ultralong, robust, and uniform Ag–C coaxial nanocables at T = 180 °C and 0.5 M H2SO4. The characterization clearly demonstrated a simple, efficient, and surfactant-free synthesis of Ag–C nanocables. In the hydrothermal process, glycerol acts as both reducing agent and carbon source, while H2SO4 mediates the directional growth of the silver nanowire core and assists the deposition of carbon. Moreover, the nanocables manifest unusual ferromagnetism at room temperature and a plausible mechanism of forming Ag–C nanocables was proposed as a result of the chain-like hydrogen sulfate compounds owing to the H2SO4 mediation.

The physical properties of the layered iron superconductors and related phases are discussed starting from first principles calculations. The electronic structure is described as that of metallic Fe2+ square lattice sheets with substantial direct Fe-Fe hopping and interactions with the neighboring anionic pnictogens or chalcogens. The materials have a semi-metallic band structure, and in particular the Fermi surface consists of small cylindrical electron sections centered at the zone corner, and compensating hole sections at the zone boundary. The density of states N(EF) is high placing the materials near itinerant magnetism in general, and furthermore the small Fermi surface sections are well nested leading to a tendency towards a spin density wave. Comparison of experimental and density functional results imply the presence of exceptionally strong spin fluctuations in these materials. Superconductivity is discussed within this context.

In this paper, we demonstrate a multi-phase genetic programming (MPGP) approach to an autonomous robot learning task, where a sumo wrestling robot is required to execute specialized pushing maneuvers in response to different opponents' postures. The sumo robot used has a very simple, minimalist hardware configuration. This example differs from the earlier studies in evolutionary robotics in that the former is carried out on-line during the performance of a robot, whereas the latter is concerned with the evolution of a controller in a simulated environment based on extended genetic algorithms. As illustrated in several sumo maneuver learning experiments, strategic maneuvers with respect to some possible changes in the shape and size of an opponent can readily emerge from the on-line MPGP learning sessions.

The advent of inlaid Cu interconnects has presented new challenges for the industry to fill high aspect ratio dual inlaid features. CVD Cu offers advantages for excellent step coverage and is a technique extendible for future generations of devices. We have developed a robust CVD Cu process and a CVD/PVD reflow integration scheme. In this paper, we present results of an extensive study on CVD Cu process development and integration. The effects of various precursors, carrier gases (H2, He and N2) and barrier layers including CVD TiN, PVD Ta, PVD TaN, PVD Ta-Si-N, and a hybrid barrier, on the CVD Cu film properties and device electrical properties are discussed. The extendibility and challenges of current CVD Cu processing will also be discussed.

A process has been developed for the deposition of amorphous Ti-Si-N films using reactive ion sputtering of a TiSi target. The Ti-Si-N films have been extensively characterized over a wide range of process parameters. Resistivities of the films less than 300 μΩ-cm have been achieved. Stress measurements on Ti-Si-N films indicate that the film stress changes from tensile to compressive as the nitrogen composition is increased. Near-zero film stresses were achieved by choice of optimum nitrogen N2 flow. SIMS analysis of Cu diffusion through blanket PVD Ti-Si-N (300Å) after an anneal at 390°C/3 hour showed a near overlap of the Cu profile compared to the profile of an unannealed SiO2/PVD Ti-Si-N /Cu film stack, indicating that the Cu did not diffuse significantly through the barrier after anneal. Low contact resistance (0.8 Ω) and low (< 10−11 A) leakage were obtained using a dual inlaid structure with a 300 Å Ti-Si-N processed with optimized conditions. These results showed that Ti-Si-N could be used as a potential barrier for copper metallization.

La1−xSrxCoO3 (LSCO) and La1−xCaxMnO3 (LCMO) are a class of magnetic oxides exhibiting the colossal magnetoresistance (CMR) effect. However, the CMR ratio of LSCO is much lower than that of LCMO. Microstructure studies were carried out to understand this difference. In La0.5Sr0.5CoO3 (LSCO), an ordered, anisotropic perovskite-type structure n-LSCO was observed. The ordered structure has a tetragonal cell with a La-Co-Sr-Co- [001] layered atom distribution along the c-axis. This new structure is intrinsic for the LSCO system and is a direct result of the lattice substitution between La and Sr. The entire film is composed of [001], [010] and [100] anisotropic domains with sizes on the order of 30–200 nm. The La0 7Ca0.3MnO3 (LCMO) film, however, does not exhibit a domain structure. It is concluded that the domain structure may have negative effect on the CMR ratio.

MgAl2O4 films have been grown epitaxially on both Si(100) and MgO(100) by a novel single source metal-organic chemical vapor deposition (MOCVD) process. A single molecular source reagent [magnesium dialuminum isopropoxide, MgAl2(OC3H7)8] having the desired Mg: Al ratio was dissolved in a liquid solution and flash-vaporized into the reactor. Both thermal and plasma-enhanced MOCVD were used to grow epitaxial MgAl2O4 thin films. The Mg: Al ratio in the deposited films was the same as that of the starting compound (Mg: Al = 1:2) over a wide range of deposition conditions. The deposition temperature required for the formation of crystalline spinel was found to be significantly reduced and crystallinity was much improved on Si by using a remote plasma-enhanced MOCVD process. The epitaxial nature of the MgAl2O4 films was established by x-ray pole figure analysis.

Thin film heterostructures of BaTiO3/YBa2Cu3O7-x (YBCO) and BaTiO3/LaxSrl-xCoO3 (LSCO) have been prepared by a novel single liquid source plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) process. Both YBCO and LSCO are conductive oxides with perovskite structure and lattice parameters closely matched to BaTiO3. YBCO films were found to deteriorate after the deposition of BaTiO3 under the PE-MOCVD conditions as revealed by X-ray diffraction and electrical characterization. LSCO thin films prepared by PE-MOCVD have a mirror-like surface, exhibit low electrical resistivity (p = 200 μΩ-cm at room temperature) and are robust to BaTiO3 deposition. These characteristics make LSCO a promising electrode material for ferroelectric capacitors.

YBa2Cu3O7−x thin films have been grown in-situ on Si (100) with a composite buffer layer of Pt/Ta/ONO (ONO stands for a S1O2 / Si3N4 /SiO2 trilayer) by plasma enhanced metal organic chemical vapor deposition (PE-MOCVD). X-ray diffraction measurements indicate that c-axis oriented YBa2Cu3O7−x films are formed in-situ at substrate temperatures as low as 650 °C on Pt/Ta/ONO/Si. The composite P/Ta/ONO provided an adherent metallic interlayer and effectively prevented the interaction between YBa2Cu3O7−x and Si. Four probe resistivity measurements indicate the onset of superconductivity at 92 K and achieved zero resistance at 65 K.

Films of the Tl‐Ba‐Ca‐Cu‐O high‐Tc superconductor can be prepared by several organometallic chemical vapor deposition routes. Two of these involve Ba‐Ca‐Cu‐0 films that are first prepared using the volatile metal‐organic precursors Ba(heptafluorodimethyloctanedionate)2, Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2‐ Deposition is carried out at a pressure of 5 Torr with argon as the carrier gas and water vapor as the reactant gas. Thallium is next incorporated into these films either by organometallic chemical vapor deposition using Tl(cyclopentadienide) as the source, or by vapor diffusion using bulk Tl‐Ba‐Ca‐Cu‐O as the source. Thallium deposition is carried out at atmospheric pressure with an argon carrier and water‐saturated oxygen reactant gas, followed by rapid thermal annealing. Both procedures yield films that consist primarily of the TlBa2Ca2Cu3Ox phase, have preferential orientation of the Cu‐O planes parallel to the substrate surface, and exhibit onset of superconductivity at ∼125 K with zero resistance by 100 K.