ODS+Hf and AISI 316L steel surface variations at high laser intensity, 1013 W/cm2, in air and vacuum: comparative study

The behavior of Oxide Dispersion Strengthened (ODS) steel with addition of hafnium, as well as AISI 316L steel, at high laser intensity of ~1013 W/cm2 in ambiences of air and vacuum, was studied. Irradiation source was Ti:Sapphire laser operating at 804 nm and pulse length of ~65 fs. Morphological and chemical studies were considered, thus that: (i) given laser intensity induced damages on both steels with the damage being more prominent on AISI 316L steel; (ii) various surface features were present, such as coral-like structure and Laser Induced Periodic Surface Structures (LIPSS), with LIPSS being dominant on the surface; (iii) the interaction was accompanied by generation of plasma above the target, and (iv) chemical analysis has shown that surface elemental content also depends on the ambience used.SPIG 2022 : 31st Summer School and International Symposium on the Physics of Ionized Gases : Contributed papers and abstracts of invited lectures, topical invited lectures and progress reports; September 5-9,2022, Belgrad

Planar carbon nanotube-graphene hybrid films for high-performance broadband photodetectors

Graphene has emerged as a promising material for photonic applications fuelled by its superior electronic and optical properties. However, the photoresponsivity is limited by the low absorption cross section and ultrafast recombination rates of photoexcited carriers. Here we demonstrate a photoconductive gain of $\sim$ 10$^5$ electrons per photon in a carbon nanotube-graphene one dimensional-two dimensional hybrid due to efficient photocarriers generation and transport within the nanostructure. A broadband photodetector (covering 400 nm to 1550 nm) based on such hybrid films is fabricated with a high photoresponsivity of more than 100 AW$^{-1}$ and a fast response time of approximately 100 {\mu}s. The combination of ultra-broad bandwidth, high responsivities and fast operating speeds affords new opportunities for facile and scalable fabrication of all-carbon optoelectronic devices.Comment: 21 pages, 3 figure

Cyclic Delay-Doppler Shift: A Simple Transmit Diversity Technique for Delay-Doppler Waveforms in Doubly Selective Channels

Delay-Doppler waveform design has been considered as a promising solution to achieve reliable communication under high-mobility channels for the space-air-ground-integrated networks (SAGIN). In this paper, we introduce the cyclic delay-Doppler shift (CDDS) technique for delay-Doppler waveforms to extract transmit diversity in doubly selective channels. Two simple CDDS schemes, named time-domain CDDS (TD-CDDS) and modulation-domain CDDS (MD-CDDS), are proposed in the setting of multiple-input multiple-output (MIMO). We demonstrate the applications of CDDS on two representative delay-Doppler waveforms, namely orthogonal time frequency space (OTFS) and affine frequency division multiplexing (AFDM), by deriving their corresponding CDDS matrices. Furthermore, we prove theoretically and experimentally that CDDS can provide OTFS and AFDM with full transmit diversity gain on most occasions

Mechanical and tribological properties of aluminium incorporated with amorphous Ni60Nb40 particles

844-852In this paper, development and characterization of pure aluminium (Al) reinforced with metallic amorphous Ni60Nb40 particles has been presented. Ni60Nb40 amorphous alloy reinforcement powder has been incorporated within Al-metal powder to produce Al-Ni60Nb40 composite. The composite has been sintered using bidirectional microwave sintering technique. Structure, indentation/tensile/compressive behaviour and tribological properties of the produced Al-10% Ni60Nb40 have been evaluated. It has been found that the: (i) reinforcement have retained the amorphous structure, (ii) reinforcement have distributed uniformly in the matrix and (iii) interface between the Al-matrix and the amorphous reinforcement has been free of reactive products. Upon comparison of mechanical properties with pure aluminium, the synthesized composite has showed significant enhancement in microhardness, tensile and compressive yield strengths. Under dry sliding wear condition, the composite has showed lower wear rates and lower coefficient of friction. The observed improvement in the composite behaviour has been explained using the processing-microstructure-mechanical properties correlation

Mathematical Modeling of the Concentrated Energy Flow Effect on Metallic Materials

Numerous processes take place in materials under the action of concentrated energy flows. The most important ones include heating together with the temperature misdistribution throughout the depth, probable vaporization on the surface layer, melting to a definite depth, and hydrodynamic flotation; generation of thermo-elastic waves; dissolution of heterogeneous matrix particles; and formation of nanolayers. The heat-based model is presented in an enthalpy statement involving changes in the boundary conditions, which makes it possible to consider melting and vaporization on the material surface. As a result, a linear dependence of penetration depth vs. energy density has been derived. The model of thermo-elastic wave generation is based on the system of equations on the uncoupled one-dimensional problem of dynamic thermo-elasticity for a layer with the finite thickness. This problem was solved analytically by the symbolic method. It has been revealed for the first time that the generated stress pulse comprises tension and compression zones, which are caused by increases and decreases in temperature on the boundary. The dissolution of alloying elements is modeled on the example of a titanium-carbon system in the process of electron beam action. The mathematical model is proposed to describe it, and a procedure is suggested to solve the problem of carbon distribution in titanium carbide and liquid titanium-carbide solution in terms of the state diagram and temperature changes caused by phase transitions. Carbon concentration vs. spatial values were calculated for various points of time at diverse initial temperatures of the cell. The dependence of carbon particle dissolution on initial temperature and radius of the particle were derived. A hydrodynamic model based on the evolution of Kelvin-Helmholtz instability in shear viscous flows has been proposed to specify the formation of nanostructures in materials subjected to the action of concentrated energy flows. It has been pointed out for the first time that, for certain parameters of the problem, that there are two micro-and nanoscale peaks in the relation of the decrement to the wavelength of the interface disturbance

Microstructure and Mechanical Properties of Magnesium-Aluminium (Mg-Al) Alloys with High Aluminium Content (Al =10, 15, 20 wt. %)

184-189Magnesium-Aluminium (Mg-Al) alloys containing zinc or manganese are preferred choice in automobile and aerospace sectors. Aluminium, the major strengthening element in Mg-alloys is always added below its solid solubility limit of 12.5 wt.%. In the current study, Mg-Al binary systems with Al-content just below and above the solubility limit (Al = 10, 15 and 20 wt.%,) were developed and examined for their microstructural and mechanical behaviour. Microstructural studies showed the importance of Al-content in determining: (i) grain size reduction and (ii) distribution and amount of inter metallic phase. Mechanical property evaluation showed that the hardness increase was linearly dependent on Al-content, with Mg-20Al showing > 250% increase in hardness than commercial AZ91alloy. Mg-10Al showed 215% and 130% increase in yield and ultimate strengths respectively, and exhibited the best properties in terms of work of fracture, which is representative of the alloy’s toughness

Research advances in acute-on-chronic liver failure

Acute-on-chronic liver failure (ACLF) is a severe liver disease with high mortality in China. Early diagnosis could reduce complications and improve the survival rate. In the present review, the definition, etiology, and pathogenesis related to inflammatory response, reactive oxygen species, and metabolism are reviewed. Also, the new approaches to the treatment of ACLF and prognostic factors are summarized. Generally, the development of ACLF is considered to be life-threatening for patients. Therefore, a universal definition of ACLF should be proposed, which would provide good guidance and standard for the clinical diagnosis and treatment of ACLF in China. In addition, the risk factors for ACLF in patients with chronic liver diseases need to be determined by prospective studies

Urban green spaces in Guangzhou (China): attitude, preference, use pattern and assessment

published_or_final_versionGeographyDoctoralDoctor of Philosoph

Overview of Cross-eye Jamming Research

Cross-eye jamming is an effective angular deception jamming technique used for countering monopulse radars. With the need of countermeasure against active radar seekers, the research on cross-eye jamming becomes a hot research topic in electronic war. This study overviews the cross-eye jamming with regard to jamming theories, equipment, application problems, and current research trends to offer comprehensive knowledge and future research ideas

Ambiguity Resolution for Phase-Based 3-D Source Localization under Fixed Uniform Circular Array

Under fixed uniform circular array (UCA), 3-D parameter estimation of a source whose half-wavelength is smaller than the array aperture would suffer from a serious phase ambiguity problem, which also appears in a recently proposed phase-based algorithm. In this paper, by using the centro-symmetry of UCA with an even number of sensors, the source’s angles and range can be decoupled and a novel algorithm named subarray grouping and ambiguity searching (SGAS) is addressed to resolve angle ambiguity. In the SGAS algorithm, each subarray formed by two couples of centro-symmetry sensors can obtain a batch of results under different ambiguities, and by searching the nearest value among subarrays, which is always corresponding to correct ambiguity, rough angle estimation with no ambiguity is realized. Then, the unambiguous angles are employed to resolve phase ambiguity in a phase-based 3-D parameter estimation algorithm, and the source’s range, as well as more precise angles, can be achieved. Moreover, to improve the practical performance of SGAS, the optimal structure of subarrays and subarray selection criteria are further investigated. Simulation results demonstrate the satisfying performance of the proposed method in 3-D source localization