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A compact dual-polarized monostatic antenna (single radiator for transmit and receive modes) is presented with differential receive mode operation to achieve excellent interport isolation for 2.4 GHz single frequency full-duplex or in-band full-duplex applications. The presented antenna comprises three ports radiating element (patch) and a simple 3 dB/180o ring hybrid coupler has been utilized for differentially excited receive mode operation. The 3 dB/180o ring hybrid coupler acts as a self-interference cancellation (SIC) circuit for effective suppression of RF leakage from the transmit port to provide very high interport decoupling between transmit and receive ports. A compact antenna structure has been realized by using two-layered printed circuit board through vias interconnections of both receive ports of the antenna with inputs of SIC circuit. The validation model of proposed antenna offers more than 95 dB peak interport isolation. Moreover, the experimentally measured interport isolation is better than 70 dB throughout the antenna's 10 dB return-loss impedance bandwidth (BW) of 50 MHz (2.38–2.43 GHz). Furthermore, the recorded isolation is more than 80 dB in 20 MHz BW. The implemented antenna has good radiation characteristics including nice gain and low cross-polarization levels as endorsed by measurements. Same antenna structure with microstrip-T feeds can provide DC isolated ports with same interport RF isolation performance for active antenna applications. Such antenna with DC interport isolation will avoid the requirements of additional series capacitors on transmit and receive ports of antenna.
Jessup’s Transnational Law challenges the state as the sole maker of international law. Nevertheless, the doctrine of transnational law advocated for the disrobing of the newly gained sovereignty in Asia and Africa. American corporate lawyers used transnational law to expand their international commercial arbitration practice. Next, in disputes arising from the expropriations by new states of property acquired from concession contracts investors found transnational law profitable. Effectively, Transnational Law, restoring a colonial status quo, facilitated the post-war internationalization of contracts to develop the law of economic protection of aliens. It wantonly focused far too much on “contracts” forgetting conveniently its “concessional” nature. The doctrine of transnational law grew from the McNair-Lauterpacht School of thought that “exploited ungrudgingly and to the full” the “rules” of “private law for the purpose of the development of international law”. The Suez crisis inaugurated the American lawyer's putting of transnational law into practice.
Once the ‘popular plaything of Realpolitiker’ the doctrine of rebus sic stantibus post the 1969 VCLT is often described as an objective rule by which, on grounds of equity and justice, a fundamental change of circumstances may be invoked as a ground for termination of a treaty. Yet recent practice from some States suggests that it is returning with a new livery. They point to an understanding that is premised on vital State interests––a view popular among scholars such as Erich Kaufmann at the beginning of the last century.
This paper presents a two-elements based, dual polarized, single layer, patch antenna array with improved isolation between transmit (Tx) and receive (Rx) ports for 2.4 GHz in-band full duplex (IBFD) or simultaneous transmit and receive wireless applications. The differential feeding deployed at the Rx port effectively suppresses the coupling which is termed as self-interference from the Tx port to achieve high Tx–Rx interport isolation. A simple 3 dB/180° ring hybrid coupler with nice amplitude and phase balance characteristics has been used for differential Rx operation. The mathematical description for a differential feeding based self-interference cancellation mechanism is also presented for the proposed dual polarized IBFD antenna array. The measurement results for the implemented prototype of the antenna array demonstrate very nice levels of Tx–Rx interport isolation. The implemented single layer, compact antenna array presents 10 dB return-loss bandwidth of more than 50 MHz for both Tx and Rx ports. The prototype achieves >80 dB peak interport isolation and 75 dB (65 dB) isolation in 20 MHz (50 MHz) bandwidth.
Polylactic acid (PLA) filament 3D parts printed by fused deposition modeling (FDM) have poor mechanical properties because of weak fusion interfaces. This article shows that SiC-coated PLA filaments are effective means to increase mechanical performance of PLA composites that are microwave heated. Numerical calculations on temperature-rising characteristics and temperature distribution of the interface in the microwave field are shown. 3D-printed specimens of PLA/SiC composites were printed by FDM and heated in a microwave. The experiments show the SiC/PLA composite filaments have better temperature-rising characteristics and temperature distribution at 185 °C for 60 s in the microwave field, and this enabled the 3D-printed specimens to achieve in situ remelting on the interface and increased interface bonding between PLA filaments. The SiC/PLA composite specimens heated using microwave increased by 51% in tensile strength, 42% in tensile modulus, and 18.7% in interlayer breaking stress relative to PLA. These results provided a new approach for the improvement of FDM workpiece strength.
Effects of adding different amounts of SiCp on the microstructure and mechanical properties of the as-cast and as-extruded Mg–7% Zn–1.5% Cu (ZC71) alloys were studied. The as-cast ZC71 alloy consisted of α-Mg phase that encircled with the MgZnCu and Mg(Zn,Cu)2 intermetallics. Hot extrusion has led to a grain-refined structure with distributed intermetallics along the extrusion direction. Adding SiCp decreased the grain size values for the as-extruded composites. The Vickers hardness values increased with SiCp addition for both conditions. The ultimate tensile strength and tensile elongation (El%) values reached the optimum level with 5 wt% SiCp addition. More SiCp additions led to more agglomerations and decrement in strength and elongation. The yield tensile strength also increased with SiC additions. Adding 5 wt% SiCp changed the brittle fracture to the more quasi-cleavage. Hot extrusion altered the fracture mode to more ductile for all composites.
GaN films have been grown on SiC substrates with an AlN nucleation layer by using a metal organic chemical vapor deposition technique. Micro-cracking of the GaN films has been observed in some of the grown samples. In order to investigate the micro-cracking and microstructure, the samples have been studied using various characterization techniques such as optical microscopy, atomic force microscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). The surface morphology of the AlN nucleation layer is related to the stress evolution in subsequent overgrown GaN epilayers. It is determined via TEM evidence that, if the AlN nucleation layer has a rough surface morphology, this leads to tensile stresses in the GaN films, which finally results in cracking. Raman spectroscopy results also suggest this, by showing the existence of considerable tensile residual stress in the AlN nucleation layer. Based on these various observations and results, conclusions or propositions relating to the microstructure are presented.
Deformation and mechanical damage in a three-dimensional braided carbon fiber reinforced carbon and silicon carbide ceramic composite, subjected to compressive loading, has been studied in situ by laboratory X-ray computed tomography. Dimensional change was measured and damage visualized by digital volume correlation analysis of tomographs. Cracks nucleated from defects within the fiber bundles and tended to propagate along the fiber bundle/matrix interface. For longitudinal compression, parallel to the fiber bundles, the initial elastic modulus decreased with increasing compressive strain while significant transverse tensile strains developed due to distributed cracking. For transverse compression, perpendicular to the fiber bundles, the compressive elastic modulus was effectively constant; the tensile strains developed along the fiber direction were small, whereas macroscopic fracture between the fiber bundles caused very large bulk tensile strain perpendicular to the loading. The observations suggest that the mechanical strength might be improved through control of pre-existing defects and application of stitch fibers in the transverse direction.
This study investigated the effects of 1 wt% SiC nanoparticles addition on the microstructures and mechanical properties of Mg9Al–1Si (wt%) alloy subjected to equal channel angular pressing (ECAP). Results showed that addition of SiC nanoparticles could refine matrix grain, Mg17Al12 and Mg2Si phase of as-cast alloy, but the Mg17Al12 phase still exhibited network structure and the morphology of Mg2Si phase was still Chinese-script type. During the ECAP process, network Mg17Al12 and Chinese-script shaped Mg2Si phases were partially broken down into fine particles (∼10 µm) and much finer particles (∼2 µm) respectively. In particular, these Mg17Al12 and Mg2Si particles were uniform distribution in ECAPed Mg9Al–1Si–1SiC composite. The well-distributed particles and the existence of SiC nanoparticles could promote the formation of fine DRXed grains through enhanced grain boundary pinning. During tensile testing at room temperature, ECAPed Mg9Al–1Si–1SiC composite exhibit optimal mechanical properties, the ultimate tensile strength and elongation to failure were reached to 255 MPa and 7.9%, respectively. Furthermore, at elevated temperature of 150 °C, the tensile strength and elongation to failure were considerably increased compared to an ECAPed, SiC-free Mg9Al–1Si alloy.
A chemomechanical coupling model is presented in the temperature range of 1200–1800 °C based on the microstructure during oxidation of ZrB2–SiC. The model includes the interaction of the oxidation rate and the mechanical stress. The stress is generated due to the constraint from the substrate to the lateral growth. The generated stress results in the shrink of the pores in the oxide. At the outer glassy layer surface, the boundary layer evaporation is adopted to describe the evaporation rate. Using the coupling model, the evolutions of the oxide layer thickness, weight gain, pore radius, and stress in both the oxide and substrate are provided, and the theoretical calculated results agree well with the reported experimental results. The results reveal large stress in the oxide layer during the oxidation process. By comparing the results of ZrB2 with different volume fractions of SiC, it is found that ZrB2 with higher volume fraction of SiC has more excellent oxidation resistance and smaller stress.
Surface periodic structures are generated upon irradiation of a silicon carbide (SiC) thin film by the plasma produced by 40 fs pulses from a Ti:Sapphire laser focused onto a thick low density polyethylene (LDPE) foil facing the SiC film. Independently of the number of laser pulses applied, these structures, with average regular periodicity of 710 nm, are evident throughout all irradiated areas. We attribute their formation to the efficient coupling of the unfocused femtosecond laser pulse with the incoherent extreme ultraviolet component of the laser-generated LDPE plasma.
Microstructures of 3C–SiC grown by chemical vapor deposition (CVD) technique on undulant silicon substrate and a further developed technique called switch-back epitaxy (SBE) were studied using transmission electron microscopy (TEM). In case of the CVD sample, the density of the stacking faults was found to be significantly decreasing along growth direction. Sites of collision of stacking faults were observed using high-resolution transmission electron microscopy. Some of the stacking faults were observed to have disappeared after colliding into each other. The stacking faults were identified to be on the same type of plane and had the same type of displacement vector not only in CVD and SBE but also in the epitaxial layer on the SBE SiC samples.
Stability versus change is one of the fundamental debates of the law of treaties. The limits of pacta sunt servanda – under which conditions a state may derogate from treaty obligations when circumstances change – appears as a constant throughout the history of international law. This article examines the limits of pacta sunt servanda in times of fragmentation. It first discusses the mechanisms of general international law – supervening impossibility of performance and fundamental change of circumstances (Articles 61 and 62 VCLT) in the law of treaties and force majeure and the state of necessity (Articles 23 and 25 of the ILC Articles on State Responsibility) in the law of state responsibility. It is argued that they provide only insufficient means to accommodate change. Against that background, derogation is examined in specific treaty regimes, including international human rights law, the law of the sea, and international investment law. Treaty-based termination/withdrawal clauses and emergency exceptions are analysed accordingly. Especially the latter are formulated in a regime-specific way, adapting derogation from treaty obligations to the requirements of the respective treaty regimes. On the basis of an empirical analysis of relevant state practice it is argued that this regime-specificity – a sign of fragmentation – is especially important since there is an increased need for temporary derogation in contemporary international law.
To overcome the low fabrication yield associated with single crystalline 3C–SiC diaphragm-based high temperature capacitive pressure sensors fabricated by wafer bonding, we have developed an alternative based on a polycrystalline SiC-on-Si architecture. The capacitive pressure sensing element, i.e., a thin film diaphragm, was fabricated using low stress and high conductivity low-pressure chemical vapor deposition poly-SiC thin films, and the sensing architecture was formed by wafer bonding a poly-SiC film to a Si substrate using phosphosilicate glass bonding films. With a geometric aspect ratio of up to 800:1 and a maximum deflection load eight times or more to their thickness, the poly-SiC diaphragm-based sensors presented repeatable pressure sensing characteristics up to 500 °C.
To understand the impact that the growth rate has on the residual stress of chemical vapor deposition-grown 3C–SiC heteroepitaxial films on Si substrates, growth experiments were performed. The film thickness was held constant at ∼2.5 μm independent of the growth rate so as to allow for direct film comparison as a function of the growth rate. Stress analysis performed by profilometer curvature measurement, μιχρο-Raman shift analysis and micro-machined freestanding structures, show an apparent disagreement about the stress nature. This incongruity between the experimental data can be explained assuming a strong stress field located in the substrate related to defects generated in the silicon during the growth process.
A technique of controlling growth gas flow rate for adjusting crystal resistivity is presented in this paper. The experimental results showed that high growth gas flow rate could affect SiC crystal resistivity remarkably. The SiC crystal resistivity would get higher and higher with increasing growth gas flow rate. The purifying effect of gas flow rate was contributing to resistivity increase at a relatively low flow rate range. As for the high gas flow rate, increase of resistivity might be explained by the well-known site competition effect. Then, one explanation for reducing nitrogen content in the crystal via increasing gas flow rate was put forward. Namely, the Si component in the gas species may more easily go through the graphite crucible at the initial stage to make the growth ambient C-rich when the gas flow rate is ∼800 sccm or more and hence suppress nitrogen incorporation into carbon site to increase crystal resistivity. This result is very helpful to grow high purity high resistivity SiC ingots.
We reported the surface morphology and electrical property of super-thin Pt films, ∼2 nm thick, deposited on 6H-SiC (0001) substrates and subsequently annealed from 400 to 1000 °C. The surfaces of the films were found to have a feature of islands growth, and the sizes of the islands increased with increasing annealing temperature. Free carbon, produced by selective reactions between Pt and SiC, diffused toward the top surface across the product layers due to low solubility and composition gradient of carbon throughout the reaction zone. A dramatic change of electrical conductivity of the films was observed. A mechanism analysis reveals that the origin came from the contribution of aggregation of islands on the surface and formation of Pt silicides and a thin layer of crystalline graphite.
Crystal structure of 4H-SiC was refined from room-temperature X-ray powder diffraction data using the Rietveld refinement method. The refined lattice constants were determined to be a=b=3.079 93(0) Å, c=10.082 22(2) Å, and the refined overall temperature factor B=0.383(3) Å2. Using the Debye approximation, the Debye temperature was successfully determined to be 1194.8 K.
Les hautes propriétés spécifiques des matériaux composites
à matrice d'alliage de titane renforcée unidirectionnellement par
des filaments de carbure de silicium permettent d'envisager leur emploi pour
des applications aéronautiques. Après une brève description des
constituants et du mode d'élaboration, les principaux mécanismes
d'endommagement sont présentés. Les ruptures de filaments sont
observées dans le cas d'une sollicitation longitudinale tandis que la
rupture de l'interface est mise en évidence dans le cas d'une
sollicitation transverse. Diverses approches multiéchelles destinées
au dimensionnement de pièces en composite SiC/Ti sont ensuite
envisagées. Une analyse basée sur la description du mécanisme de
rupture des filaments permet d'estimer la contrainte à la rupture dans
le cas d'une sollicitation longitudinale. Une méthode de transformation
de champ permet d'obtenir une loi de comportement prenant en compte les
contraintes résiduelles de fabrication. Elle est utilisée pour le
calcul d'un disque de compresseur de turboréacteur renforcé
circonférentiellement par un composite SiC/Ti.
SiC-matrix composites consist of ceramic fibers embedded in a silicon carbide matrix produced by gas-, liquid-, or solid-phase routes, yielding materials that differ in matrix crystallinity, residual porosity, and thermal properties. These composites can be highly engineered in terms of the nature of the reinforcement, the interphase used to control the fiber-matrix bonding, the matrix, and the seal coating used. SiC-matrix composites are refractory ceramics displaying outstanding mechanical and thermal properties at high temperature. Their durability in oxidizing atmospheres and under load exceeds 1000 h at temperatures of up to ∼1200°C. They have been used to fabricate different components of the hot zone of jet engines with significant weight savings and an increase in performance. This article reviews the state of the art in the processing, materials design, and properties of these composites as well as their applications in advanced jet engines.