Molten salt electrosynthesis of silicon carbide nanoparticles and their photoluminescence property

A one-step molten salt electrochemical strategy was proposed to synthesize SiC nanoparticles from ultra-fine silicon dioxide/carbon(SiO_(2)/C)mixtures.The electrosynthesis process and physicochemical properties of the synthesized products were systematically analyzed via X-ray diffraction,electron microscopy,Raman spectroscopy and photoluminescence spectroscopy,etc.A combined chemical/electrochemical reaction,electrochemical deoxidation,and in-situ carbonization reaction mechanism was proposed to reveal the electrochemical synthesis process of SiC nanoparticles from SiO_(2)/C in molten CaCl_(2).The as-prepared SiC with particle size ranging from 8 to 14 nm possesses a polycrystalline structure.In addition,the SiC nanoparticles demonstrate obvious photoluminescence property due to the synergetic size effect and microstructural characteristics.

The Influence of Cap and Defect Layer on Interface Optical-Phonon Modes in Finite Superlattices

Employing the transfer matrix method, we investigate the property of the interface optical-phonon modes （IOPMs） in a finite superlattice with a cap layer and a structural defect layer in the dielectric continuum approximation. In the present structure, there exist two types of defect IOPMs： localized modes and surface modes. The evolution of extended, localized and surface IOPMs can be clearly tracked with the thickness of the defect or cap layer. In some cases, degeneracy between surface IOPMs may occur, but the conservation of the total number of the IOPMs is always kept for every value of the transversal wave number. These results show that the spectra of these localized or surface IOPMs can be engineered by adjusting structural parameters.

Saturable Absorption Enchantment of Au Nanorods Based on Energy Transfer between Longitudinal and Transverse Energy Levels

Four kinds of Au nanorods（NRs）with different aspect ratios are designed to adjust the relationship between resonance energy level of longitudinal（L）and transverse（T）modes.During the femto-second Z-scan experiments,huge saturable absorption phenomena are observed while the energy level T is located between one to two times of the energylevel L.This means that the energy may transfer between longitudinal and transverse energylevels in the same and/or different Au NRs.It effectively depresses the production of revised saturated absorption and increases the saturable absorption efficiency.This method is significant for the preparation of high-efficiency saturable absorption devices.

Left and Right Inverse Eigenpairs Problem of Orthogonal Matrices

In this paper, the left and right inverse eigenpairs problem of orthogonal matrices and its optimal approximation solution are considered. Based on the special properties of eigenvalue and the special relations of left and right eigenpairs for orthogonal matrices, we find the equivalent problem, and derive the necessary and sufficient conditions for the solvability of the problem and its general solutions. With the properties of continuous function in bounded closed set, the optimal approximate solution is obtained. In addition, an algorithm to obtain the optimal approximation and numerical example are provided.

Evolution and Trend of Deep Learning in Agriculture: A Bibliometric Approach

Deep Learning has recently gained a great deal of attention. From this, resulted many applications in a variety of industries, including agriculture. An essential study goal is to understand what has been done in the use of deep learning in agriculture (DLA) thus far in order to establish a robust research agenda to address its future challenges. The present state of research on the DLA with special attention to Africa was evaluated in this study using bibliometric analysis. A search of documents dealing with DLA was realized in the Web of Science database, a world-leading publisher-independent global citation database. A bibliometric program named Bibliometrix was used to examine the data after the search yielded 3207 items. Key findings are highlighted and discussed, and then some directions for potential future research are suggested.

Two Families of Multipoint Root-Solvers Using Inverse Interpolation with Memory

In this paper, a general family of derivative-free n + 1-point iterative methods using n + 1 evaluations of the function and a general family of n-point iterative methods using n evaluations of the function and only one evaluation of its derivative are constructed by the inverse interpolation with the memory on the previous step for solving the simple root of a nonlinear equation. The order and order of convergence of them are proved respectively. Finally, the proposed methods and the basins of attraction are demonstrated by the numerical examples.

THE GENERALIZED REFLEXIVE SOLUTION FOR A CLASS OF MATRIX EQUATIONS (AX-B,XC=D)

In this article, the generalized reflexive solution of matrix equations （AX = B, XC = D） is considered. With special properties of generalized reflexive matrices, the necessary and sufficient conditions for the solvability and the general expression of the solution are obtained. Moreover, the related optimal approximation problem to a given matrix over the solution set is solved.

Runge-Kutta method, finite element method, and regular algorithms for Hamiltonian system

The symplectic algorithm and the energy conservation algorithm are two important kinds of algorithms to solve Hamiltonian systems. The symplectic Runge- Kutta （RK） method is an important part of the former, and the continuous finite element method （CFEM） belongs to the later. We find and prove the equivalence of one kind of the implicit RK method and the CFEM, give the coefficient table of the CFEM to simplify its computation, propose a new standard to measure algorithms for Hamiltonian systems, and define another class of algorithms --the regular method. Finally, numerical experiments are given to verify the theoretical results.

Electrolytic production of Ti-Ge intermetallics from oxides in molten CaCl_2-NaCl

Titanium germanium intermetallics （TixGey）were directly prepared from titanium oxide （TiO2） and germanium oxide（GeO2） powders mixture by using an electrodeoxidation process. The electrochemical experiment was carried out in a molten fluxCaCl2-NaCl at 800℃ with a potential of 3.0 V. The results show that monolithic germanide Ti5Ge3 intermetallic can be directlyproduced from TiO2-GeO2 or CaTiO3-GeO2 precursors （both molar ratios are 5：3）, and the obtained Ti5Ge3 powders exhibithomogenous particle structure. In addition, the phase composition of the final product can be dramatically affected by the initialmolar ratio of TiO2 to GeO2. The reaction mechanism of the electrodeoxidation process was discussed based on the experimentalresults. It is suggested that the electrodeoxidation process is an environmentally friendly method for the preparation of Ti-Geintermetallics.

Switching and Fano resonance via exciton–plasmon interaction

We fnrther study theoretically the properties of switching and Fano resonance in a hybrid nanosystem consisting of two quantum dots （QDs） and a metal nanowire via exciton-plasmon interaction. The transmission of the single plasmon can be switched on or off in a wide-frequency region by adjusting the transition frequencies of the QDs and the phase of the propagating plasmon. Specifically, the dynamical mechanism of Fano-type transmission is further revealed and analyzed in detail.

Role of localised surface plasmon polaritons coupling in optical transmission through double-layer metal apertures

In this paper, we investigate the optical properties of the double-layer metal films perforated with single apertures by analysing the coupling of localized surface plasmon polaritons （LSPPs）. It is found that the amplitude and the wavelength of transmission peak in such a structure can be adjusted by changing the longitudinal interval D between two films and the lateral displacements dx and dy which are parallel and perpendicular to the polarization direction of incident light, respectively. The variation of longitudinal interval D results in the redshift of transmission peak due to the change of coupling strength of LSPPs near the single apertures. The amplitude of transmission peak decreases with the increase of dy and is less than that in the case of dx, which originates from the difference in coupling manner between LSPPs and the localized natures of LSPPs.

Least Squares Symmetrizable Solutions for a Class of Matrix Equations

In this paper, we discuss least squares symmetrizable solutions of matrix equations (AX = B, XC = D) and its optimal approximation solution. With the matrix row stacking, Kronecker product and special relations between two linear subspaces are topological isomorphism, and we derive the general solutions of least squares problem. With the invariance of the Frobenius norm under orthogonal transformations, we obtain the unique solution of optimal approximation problem. In addition, we present an algorithm and numerical experiment to obtain the optimal approximation solution.

Standing Shocks in the Inner Slow Solar Wind

We examine whether the flow tube along the edge of a coronal streamer supports standing shocks in the inner slow wind by solving an isothermal wind model in terms of the Lambert W function.It is shown that solutions with standing shocks do exist and they exist in a broad area in the parameter space characterizing the wind temperature and flow tube.In particular,streamers with cusps located at a heliocentric distance(≥)3.2R⊙can readily support discontinuous slow winds with temperatures barely higher than 1 MK.

Drought Forecasting: A Bibliometric Analysis and Future Research Directions

Droughts represent one of the most dangerous natural disasters in the world, due to their ability to progressively spread over large areas up to continental scale, as well as their adverse environmental, human and socio-economic effects. Unfortunately, these effects are increasingly accentuated under the influence of climate change. One of the main challenges today is to mitigate the damage associated with droughts by developing tools capable of predicting the occurrence of such events in advance. Many solutions have been implemented for this purpose. But with the great progress in artificial intelligence, many scientists propose the use of Machine Learning to provide more optimal solutions to the problem related to droughts. In the present study, a bibliometric analysis was conducted to assess the current level of research on forecasting and monitoring of droughts in the world in general, particularly in West Africa through different methods based on the artificial intelligence. A search for articles on the topic was performed in the Web of Science (WoS) database, which is a global, publisher-independent citation database. The search identified a total of 3284 documents and the collected data was analyzed using a bibliometric tool called Bibliometrix. The main results are presented and discussed, followed by some potential avenues for research.

A New Modification of Newton Method with Cubic Convergence

Newton’s method is used to find the roots of a system of equations f (x) = 0. It is one of the most important procedures in numerical analysis, and its applicability extends to differential equations and integral equations. Analysis of the method shows a quadratic convergence under certain assumptions. For several years, researchers have improved the method by proposing modified Newton methods with salutary efforts. A modification of the Newton’s method was proposed by McDougall and Wotherspoon [1] with an order of convergence of 1+ √2. On a new type of methods with cubic convergence was proposed by H. H. H. Homeier [2]. In this article, we present a new modification of Newton method based on secant method. Analysis of convergence shows that the new method is cubically convergent. Our method requires an evaluation of the function and one of its derivatives.

Controllable Nucleation of Nanobubbles at a Modified Graphene Surface

The properties of nanoscale gas bubbles at the solid/water interface have been investigated for more than 20 years. However, the stability of nanobubbles remains far from being understood. How to control the formation of nanobubbles is the key issue for understanding their long lifetime. In this work, using molecular dynamics simulations we modify the substrate （graphene） with charge dipoles in which the local properties of the surface could be changed. Nanobubbles could be stabilized on the local hydrophobic area and modified area with the hydrophilic boundary where gas nuclei are deposited beforehand. Those results provide two methods to control the nucleation of gas nanobubbles and fix them on a target area.

Floquet control of the gain and loss in a PT-symmetric optical coupler

Controlling the balanced gain and loss in a PT-symmetric system is a rather challenging task. Utilizing Floquet theory, we explore the constructive role of periodic modulation in controlling the gain and loss of a PT-symmetric optical coupler. It is found that the gain and loss of the system can be manipulated by applying a periodic modulation. Purther, such an original non-Hermitian system can even be modulated into an effective Hermitian system derived by the high-frequency Floquet method. Therefore, compared with other PT- symmetry control schemes, our protocol can modulate the unbroken PT-symmetric range to a wider parameter region. Our results provide a promising approach for controlling the gain and loss of a realistic system.

Low-Temperature Thermal Conductance in Superlattice Nanowire with Structural Defect

Using the scattering-matrix cascading method, we investigate the effect of structural defect on the acoustic phonon transmission and thermal conductance in the superlattice nanowire at low temperatures. In the present system, the phonon transmissions exhibit quite complex oscillatory behaviour. It is found that a lateral defect in an otherwise periodic structure significantly decrease the thermal conductance and completely washes away the transmission quantization. However, the appreciable transmission quantization survives in the presence of a longitudinal defect whereas a good quantization plateau of thermal conductance emerges below the universal level in a wide temperature range with the lateral defect.

Enhanced optical transmission by V-shaped nanoslit in metal film

In this paper, we reveal that the enhanced transmission through a perforated metal film can be further boosted up by a V-shaped nanoslit, which consists of two connected oblique slits. The maximum transmission at resonance can be enhanced significantly by 71.5% in comparison with the corresponding vertical slit with the same exit width. The value and position of transmission resonance peak strongly depend on the apex angle of the V-shaped slit. The optimum apex angle, at which the transmission is maximal, is sensitive to the slit width. Such phenomena can be well explained by a concrete picture in which the incident wave drives free electrons on the slit walls. Moreover, we also simply analyze the splitting of the transmission peak in the symmetry broken V-shaped slit, originating from the resonances of different parts of the V-shaped slit. We expect that our findings will be used to design the nanoscale light sources based on the metal nanoslit structures.

Quenching Fluorescence of Quantum Dots by Using Gold Nanocrystals in Quantum and Classical Size Regime

This paper investigates the factors which can influence the quenching effect from the perspective of energy transfer.The quenched fluorescence of the Cd Se semiconductor quantum dots(SQDs)by using plasmonic Au nanocrystals(p-AuNCs)and molecule-like Au nanocrystals(m-AuNCs)in aqueous suspensions and spin-coated films is comparatively investigated.In the aqueous suspensions,the p-AuNCs have larger quenching effect than the m-AuNCs.In the spin-coated films,the p-AuNCs and m-AuNCs have comparable quenching factor.Furthermore,the experiments show that the p-AuNCs simultaneously enhance the radiative and nonradiative rates.But the m-Au NCs only enhance the nonradiative rate of the SQDs,which reveals the difference of quenching process between the p-AuNCs and m-AuNCs.This result of the research has guiding significance for the detection technique based on the fluorescence quenching.