Failure mode transition of NbSS phase from cleavage to dimple in Nb-Si based alloys prepared by spark plasma sintering through controlling of NbSS powder size and morphology and alloying

The influence of Nb powder sizes and morphologies (equiaxed and flaky particles) on fracture toughness and fracture modes of Nb-16Si binary alloy and one multi-component Nb-16Si-22Ti-2Al-2Hf-7Cr alloy with an Nb/Nb5Si3 microstructure fabricated by spark plasma sintering (SPS) was investigated. A reduced Nb powder size from 83.8 m to 4.9 m led to an Nb matrix with fine grain (9.9m in size) plus Nb5Si3 islands two-pshase microstructure, which changed the fracture mode of the Nb phase from cleavage (Fig. 1a) to a mixed mode of dimple (arrows A in Fig. 1b), tear (arrows B in Fig. 1b) and cleavage (arrows C in Fig. 1b), and then the fracture toughness of the Nb-16Si binary samples was significantly improved from 8.2 MPa·m1/2 (Fig. 1a) to 12.4 MPa·m1/2(Fig. 1b). A further improvement of the fracture toughness to 15.8 MPa·m1/2 was achieved in the multi-component Nb-16Si-22Ti-2Al-2Hf-7Cr alloy owing to full dimples (Fig. 1c) on the finer fractured Nb grains with a size of 11.2m through addition of the toughening elements of 22 at.% Ti and 2 at.% Hf. It is interesting that when the flaky Nb powders (123.7 m in diameter and 15.2m in thickness) were used to prepare the Nb-16Si binary sample, the Nb grains still adopted the flake morphology and two fracture modes were observed in one fractured Nb grain, i.e., the cleavage mode in radial plane and the dimple or tear mode in axial plane of the flaky Nb grain (Fig. 1d). These kinds of fracture modes in one flaky Nb grain also improved the fracture toughness of the bulk Nb-16Si binary sample to 11.8 MPa·m1/2 (Fig. 1d). Please click Additional Files below to see the full abstract

Limit state analysis on the un-repeated multiple selection bounded confidence model

summary:In this paper, we study the opinion evolution over social networks with a bounded confidence rule. Node initial opinions are independently and identically distributed. At each time step, each node reviews the average opinions of several different randomly selected agents and updates its opinion only when the difference between its opinion and the average is below a threshold. First of all, we provide probability bounds of the opinion convergence and the opinion consensus, are both nontrivial events by analyzing the probability distribution of order statistics. Next, similar analyzing methods are used to provide probability bounds when the selection cover all agents. Finally, we simulate all these bounds and find that opinion fluctuations may take place. These results increase to the understanding of the role of bounded confidence in social opinion dynamics, and the possibility of fluctuation reveals that our model has fundamentally changed the behavior of general DeGroot opinion dynamical processes

Spin-orbit interaction of light induced by transverse spin angular momentum engineering

We report the first demonstration of a direct interaction between the extraordinary transverse spin angular momentum in evanescent waves and the intrinsic orbital angular momentum in optical vortex beams. By tapping the evanescent wave of whispering gallery modes in a micro-ring-based optical vortex emitter and engineering the transverse spin state carried therein, a transverse-spin-to-orbital conversion of angular momentum is predicted in the emitted vortex beams. Numerical and experimental investigations are presented for the proof-of-principle demonstration of this unconventional interplay between the spin and orbital angular momenta, which could provide new possibilities and restrictions on the optical angular momentum manipulation techniques on the sub-wavelength scale. This phenomenon further gives rise to an enhanced spin-direction coupling effect in which waveguide or surface modes are unidirectional excited by incident optical vortex, with the directionality jointly controlled by spin-orbit states. Our results enrich the spin-orbit interaction phenomena by identifying a previously unknown pathway between the polarization and spatial degrees of freedom of light, and can enable a variety of functionalities employing spin and orbital angular momenta of light in applications such as communications and quantum information processing

Spiral Transformation for High-Resolution and Efficient Sorting of Optical Vortex Modes

Mode sorting is an essential function for optical multiplexing systems that exploit the orthogonality of the orbital angular momentum mode space. The familiar log-polar optical transformation provides a simple yet efficient approach whose resolution is, however, restricted by a considerable overlap between adjacent modes resulting from the limited excursion of the phase along a complete circle around the optical vortex axis. We propose and experimentally verify a new optical transformation that maps spirals (instead of concentric circles) to parallel lines. As the phase excursion along a spiral in the wave front of an optical vortex is theoretically unlimited, this new optical transformation can separate orbital angular momentum modes with superior resolution while maintaining unity efficiency

Orbital angular momentum mode-demultiplexing scheme with partial angular receiving aperture

For long distance orbital angular momentum (OAM) based transmission, the conventional whole beam receiving scheme encounters the difficulty of large aperture due to the divergence of OAM beams. We propose a novel partial receiving scheme, using a restricted angular aperture to receive and demultiplex multi-OAM-mode beams. The scheme is theoretically analyzed to show that a regularly spaced OAM mode set remain orthogonal and therefore can be de-multiplexed. Experiments have been carried out to verify the feasibility. This partial receiving scheme can serve as an effective method with both space and cost savings for the OAM communications. It is applicable to both free space OAM optical communications and radio frequency (RF) OAM communications

Compact and high-performance vortex mode sorter for multi-dimensional multiplexed fiber communication systems

With the amplitude, time, wavelength/frequency, phase, and polarization/spin parameter dimensions of the light wave/photon almost fully utilized in both classical and quantum photonic information systems, orbital angular momentum (OAM) carried by optical vortex modes is regarded as a new modal parameter dimension for further boosting the capacity and performance of the systems. To exploit the OAM mode space for such systems, stringent performance requirements on a pair of OAM mode multiplexer and demultiplexer (also known as mode sorters) must be met. In this work, we implement a newly discovered optical spiral transformation to achieve a low-cross-Talk, wide-opticalbandwidth, polarization-insensitive, compact, and robust OAM mode sorter that realizes the desired bidirectional conversion between seven co-Axial OAM modes carried by a ring-core fiber and seven linearly displaced Gaussian-like modes in parallel single-mode fiber channels. We further apply the device to successfully demonstrate high-spectralefficiency and high-capacity data transmission in a 50-km OAM fiber communication link for the first time, in which a multi-dimensional multiplexing scheme multiplexes eight orbital-spin vortex mode channels with each mode channel simultaneously carrying 10 wavelength-division multiplexing channels, demonstrating the promising potential of both the OAM mode sorter and the multi-dimensional multiplexed OAM fiber systems enabled by the device. Our results pave the way for futureOAM-based multi-dimensional communication systems

Quantitative Planar Laser-Induced Fluorescence Technology

Planar laser-induced fluorescence (PLIF) is a highly sensitive and space-time-resolved laser diagnostic technique. It is widely used in the diagnosis of combustion and flow fields to obtain the thermodynamic information of active components and interested molecules in flames. Nowadays, the PLIF technology is developing in two directions: high speed and quantification. In view of the high spatial and temporal resolution characteristics of PLIF technology that other laser diagnostics do not possess, this chapter will focus on the basic principle of laser-induced fluorescence and the current research status of quantitative PLIF technology. In addition, the advantages and disadvantages of various quantitative technologies of component concentration in flames based on laser-induced fluorescence technology are analyzed. At last, the latest works on the quantification of species concentration using planar laser-induced fluorescence in combustion are introduced