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This study investigates the propagation of dark Alfvén solitons in low-β magnetized plasma using Hall-magnetohydrodynamic (Hall-MHD) numerical simulations. The rational solution of the nonlinear Schr o ̈ dinger equation (NLSE) is presented, which is proposed as an effective tool for studying dark envelope solitons in plasma. Our results show a high degree of agreement between numerical simulations and analytical solutions derived from the NLSE via the reductive perturbation method. This agreement validates our modeling and computational approach. In addition, the simulations confirm the existence of dark Alfvén solitons in magnetized plasma. This work demonstrates the effectiveness of Hall-MHD simulations in studying complex plasma phenomena, contributing to the broader understanding of soliton propagation in plasma environments. [ABSTRACT FROM AUTHOR]

A modulational instability of nonlinearly interacting electron whistlers and magnetosonic perturbations is studied in the present paper. For typical parameters, there is no modulational instability. However, modulational instability appears in special cases. For example, when the whistler wavenumber is small enough, there is modulational instability. Its growth rate decreases as the angle between the external magnetic field and the perturbed wave's direction increases, while it increases as the whistler wavenumber increases. It is also found that there is no modulational instability when the whistler wavenumber is larger than a critical value ($k_0 > 0.05$), in which the perturbed wave frequency increases as the angle between the external magnetic field and the perturbed wave's direction increases when the angle between the external magnetic field and the perturbed wave's direction is large enough. Whereas, the perturbed wave frequency first increases as the whistler wavenumber increases, reaches a peak value and then decreases as whistler wavenumber increases. [ABSTRACT FROM AUTHOR]

We conducted a study on the confinement properties of non-neutral proton plasma in an asymmetric magnetic mirror using the three-dimensional (3D) particle-in-cell simulation method. Our findings indicate a close relationship between the ability of the magnetic mirror to confine protons and the incidence orientation of the proton beam. This relationship can only be accurately assessed through 3D simulation, as opposed to two-dimensional simulation. In addition, we observed that a higher velocity parallel to the magnetic field direction results in a shorter confinement time. The electric field at and near the central point of the mirror exhibits quasi-periodic vibrations, attributed to the electrostatic oscillation of the proton and the cyclotron motion. Furthermore, we discovered a drift motion of the confined proton plasma in the direction of the magnetic field gradient. These findings hold implications for the design of magnetic mirrors capable of effectively confining charged particle beams. [ABSTRACT FROM AUTHOR]

The dispersion relation and the speed of linear magnetosonic wave are given in the present paper. Furthermore, an arbitrary amplitude nonlinear magnetosonic solitary wave is studied. It is found that the amplitude of the magnetosonic solitary wave cannot be larger than a critical value. It is found that the maximum speed of the magnetosonic solitary wave is about 1.24 times that of the Alfvén wave speed when the magnetic field is sufficiently strong so that the magnetic pressure is much larger than the fluid pressure. On the other hand, the maximum perturbed magnetic field is just equal to the external magnetic field if the magnetic pressure is much larger than the fluid pressure. It suggest that the variation regime of the perturbed magnetic field is (0 , B 0) , while the variation regime of the speed of magnetosonic solitary wave is (v A , 1.24 v A) in the upstream and downstream regions of the Venusian bow shock. Here B 0 and v A represent the background magnetic field and the Alfvén wave speed, respectively. [ABSTRACT FROM AUTHOR]

The loss rate of ion beams and the non-neutral plasma in an axisymmetric magnetic mirror is investigated in the present paper. It is found that the loss rate increases as the mass of the ions increases for a ion beam confined in a magnetic mirror. Moreover, both the electron loss rate and the ion loss rate are obtained when a non-neutral plasma is confined in a magnetic mirror. It seems that both loss rate remain unchanged in the regime when the electron number density is less than that of the ions. In the other regime that the electron number density is much larger than that of the ion number, the ion loss rate increases with the increase of electron number density, while the electron loss rate decreases as the electron number density increases. This result may help us to devise a mirror to separate the different charged particles by confining these different particles in a magnetic mirror. The electron loss rate and the ion loss rate are obtained when a non-neutral plasma is confined in a magnetic mirror. It seems that both loss rate remain unchanged in the regime when the electron number density is less than that of the ions. In the other regime that the electron number density is much larger than that of the ion number, the ion loss rate increases with the increase of electron number density, while the electron loss rate decreases as the electron number density increases.. [ABSTRACT FROM AUTHOR]

The propagation of dust-acoustic waves in a dusty plasma bounded in finite symmetrical cylindrical geometry has been theoretically investigated. By using the reductive perturbation method, we obtain a quasi-nonlinear Schrödinger equation. It is shown that there is a dark envelope soliton under certain conditions, while its amplitude will decrease with the time. The dependence of both the dispersion relation and group velocity of envelope solitary waves on the radius of cylinder has been given. Moreover, we define the duration time of dark envelope solitons and give the theoretical ones. It is found that the duration time increases as the radius of cylinder increases, while it decreases as the viscosity coefficient of dusty plasmas increases. [ABSTRACT FROM AUTHOR]

We translate three-dimensional magnetohydrodynamic equations describing the bounded plasma into a one-dimensional case and obtain an equivalent damping force that resulted from both the bounded geometry and the viscosity of the plasma by averaging all the physical quantities on the cross section, which is perpendicular to the wave propagation direction. A damping solitary wave propagating in a viscous bounded plasma is also verified by the particle-in-cell simulation method. The results in the present paper may be useful in the study of charged beam and particle acceleration, etc. Moreover, we can devise an experiment to obtain the viscosity coefficient of the plasma by measuring the ratio of two amplitudes at two different points. [ABSTRACT FROM AUTHOR]

We study some nonlinear waves in a viscous plasma which is confined in a finite cylinder. By averaging the physical quantities on the radial direction in some cases, we reduce this system to a simple one-dimensional model. It seems that the effects of the bounded geometry (the radius of the cylinder in this case) can be included in the damping coefficient. We notice that the amplitudes of both Korteweg–de Vries (KdV) solitary waves and dark envelope solitary waves decrease exponentially as time increases from the particle-in-cell (PIC) simulation. The dependence of damping coefficient on the cylinder radius and the viscosity coefficient is also obtained numerically and analytically. Both are in good agreement. By using a definition, we give a condition whether a solitary wave exists in a bounded plasma. Moreover, some of potential applications in laboratory experiments are suggested. [ABSTRACT FROM AUTHOR]

It is well known that the ponderomotive force of a relatively high-frequency magnetosonic wave (HMSW) can excite the low-frequency magnetosonic wave (LMSW). By using the coupled system of dynamical equations of LMSW in the presence of a ponderomotive force of HMSW (pump wave), we have studied the modulational instability of the coupled waves between the HMSW and the LMSW. It is found that there are instabilities for the coupled waves between the HMSW and the LMSW. It is also found that the growth rate depends on several system parameters, such as the frequency of HMSW, the perturbation wave vector, and the background magnetic field. [ABSTRACT FROM AUTHOR]

Evolution of both low-frequency harmonic Alfvén wave train and Alfvén solitary wave is studied by using the compressible MHD fluid model. A critical point is found at which linear wave theory should be replaced by a nonlinear one. A small, but finite amplitude Alfvén solitary wave is numerically found. The head-on collision between an Alfvén wave train and an Alfvén solitary wave is also numerically investigated. An interesting result is that there is no phase shift for both colliding waves which is different from that between two KdV solitary waves. [ABSTRACT FROM AUTHOR]

The finite-amplitude circularly polarized Alfvén envelope solitary waves are numerically studied in the present paper. It is verified that the left-hand polarized Alfvén envelope solitary wave can exist in a magnetized low-β plasma. By comparing the numerical results with the analytical solutions obtained from nonlinear Schrödinger equation, it seems that the analytical result obtained by the reductive perturbation method is reliable if the amplitude of the envelope solitary wave is small enough. Furthermore, the head-on collision between two Alfvén envelope solitary waves is also studied in a magnetized low-β plasma by means of Hall-magnetohydrodynamic numerical simulations. It seems that these two envelope solitary waves remain unchanged after head-on collision, furthermore there is no phase shift for the two waves after head-on collision. [ABSTRACT FROM AUTHOR]

The head-on collision between two dust-acoustic solitary waves in a non-magnetized, collisionless and strongly coupled dust plasma has been studied. The application scope of the analytical solution of the head-on collision is given in the present paper by using the particle-in-cell simulation method. It is noted that the analytical results are valid if the amplitudes of both of the solitary waves are small enough. The effects of the coupling parameters on both the head-on collision and the waveform are also studied in the present paper. [ABSTRACT FROM AUTHOR]

The properties of a high energy short pulse electron beam in a magnetic mirror field are studied numerically by the Particle-in-Cell method. The complex nature of processes studied, and also the need for the calculation of the positions, velocities, and trajectories of billions of particles, required the use of a scalable parallel algorithm. The use of modern supercomputers has allowed us to calculate the plasma dynamics, to determine the electron beam in the magnetic mirror field. Mathematical modeling of non-neutral plasma dynamics at the trap is carried out. The axially integrated radial density profiles, electric field distribution, and phase space distribution of velocity are measured. The axial and radial oscillations of a confined non-neutral plasma are also observed. [ABSTRACT FROM AUTHOR]

A crucial region for China's 'Grain-for-Green Policy' is located within a traditional farmpastoral area, between 2000 to 3000 m above sea level, on the eastern Qinghai-Tibetan Plateau. However, the responses of soil organic carbon (SOC) to different land-use patterns in this region are unclear. Here, we determined the SOC (0-20 cm) content of grasslands and forests that are being converted from farmlands, as well as in abandoned arable land and arable land in this region. The factors influencing the reclaimed lands were analyzed along altitudes from 2030 to 3132 m. Our results showed that SOC content was higher for grassland and abandoned arable land than forest and arable land. The SOC content increased with the increase in altitude for total land-use patterns. Further, the grassland and abandoned arable land had higher SOC content than the forest with almost parallel trends along the increase in altitude. However, the proportion of regulated factors of altitude and species richness varied among forest, grassland, and abandoned arable land. Our results indicated that the land-use pattern of returning farmland to grassland and abandoned arable land was more effective in terms of the SOC storage in the superficial layer in this altitude range in the Qinghai-Tibetan Plateau, thereby being beneficial to optimizing land management in this region. [ABSTRACT FROM AUTHOR]

ABSTRACT A pH-sensitive hydrogel [P(CE- co-DMAEMA- co-MEG)] was synthesized by the free-radical crosslinking polymerization of N,N-dimethylaminoethyl methacrylate (DMAEMA), poly(ethylene glycol) methyl ether methacrylate(MPEG-Mac) and methoxyl poly(ethylene glycol)-poly(caprolactone)-methacryloyl methchloride (PCE-Mac). The effects of pH and monomer content on swelling property, swelling and deswelling kinetics of the hydrogels were examined and hydrogel microstructures were investigated by SEM. Sodium salicylate was chosen as a model drug and the controlled-release properties of hydrogels were pilot studied. The results indicated that the swelling ratios of the gels in stimulated gastric fluids (SGF, pH = 1.4) were higher than those in stimulated intestinal fluids (SIF, pH = 7.4), and followed a non-Fickian and a Fickian diffusion mechanism, respectively. In vitro release studies showed that its release rate depends on different swelling of the network as a function of the environmental pH and DMAEMA content. SEM micrographs showed homogenous pore structure of the hydrogel with open pores at pH 1.4. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40737. [ABSTRACT FROM AUTHOR]

ABSTRACT Stimuli-sensitive hydrogels are one of the most promising and versatile materials with many potential applications. In this article, a pH-sensitive hydrogel [P(AA- co-C8PhEO10Mac)] was synthesized by the free-radical cross-linking polymerization of acrylic acid (AA) and octylphenyl polyoxyethylene methacrylate macromonomer (C8PhEO10Mac). Swelling property, swelling, and deswelling kinetics of the hydrogels in different pH media were studied and hydrogel microstructures were investigated by means of scanning electron microscopy (SEM). Theophylline was chosen as a model drug and the controlled-release properties of hydrogels were pilot studied. The results showed that the P(AA- co-C8PhEO10Mac) hydrogel has a porous structure, both the rapid swelling and deswelling rate, and good pH sensitivity characteristics; The swelling ratios of the gels in stimulated intestinal fluids (SIF, pH = 7.4) were higher than those in stimulated gastric fluids (SGF, pH = 1.4). The in vitro cumulative release data were analyzed using an empirical equation to compute the diffusion exponent ( n), whose values suggest a non-Fickian mode of transport. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1981-1989, 2013 [ABSTRACT FROM AUTHOR]

The adsorption behaviors of three carboxyl hydroxamic acids on diaspore (010) and kaolinite (001) have been studied by density functional theory (DFT) and molecular dynamics (MD) method. The results indicated that carboxyl hydroxamic acids could adsorb on diaspore surface by ionic bonds and hydrogen bonds, and adsorb on kaolinite surface by hydrogen bonds. The models of carboxyl hydroxamic acids adsorbed on diaspore and kaolinite surfaces are proposed. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The author reflects on the documentary film "Our Life Saving Vinegar" which tackles the issue of providing help for sex workers so they can regain their basic labor rights. The abolishment of the licensed prostitute system in Taiwan has made many sex workers unemployed. Some of these women have made a career move by establishing a vinegar production line.

By using particle-in-cell(PIC) simulation method, the proton beam confinement in a magnetic mirror is investigated in the present paper. We define two physical quantities to describe the confinement effects of mirror for proton beam. One is loss rate χ=Nlost/N0, where Nlost is the number of leaked particles from the mirror and N0 is the number of initial particles. The other is confinement time τm. Dependences of loss rate and confinement time on the parameters of both magnetic mirror and proton beam is given. It is found that the larger the mirror ratio, the less the loss rate, and the longer the confinement time. The appropriate proton beam velocity and other parameters of the protons can significantly improve the confinement time of the mirror and the efficiency of confinement. [ABSTRACT FROM AUTHOR]

One-dimensional (1-D) particle-in-cell simulation is used to study the propagation of dark envelop solitons described by the nonlinear Schrödinger equation (NLSE) in electron-ion plasmas. The rational solution of the NLSE is presented, which is proposed as an effective tool for studying the dark envelope soliton in plasma. It is demonstrated by our numerical simulation that there is dark envelope soliton in electron-ion plasmas. The numerical results are in good agreements with the analytical ones from the NLSE which is obtained from the reductive perturbation method. The limitation of the amplitude of dark envelop solitons in plasma is noticed. [ABSTRACT FROM AUTHOR]