Search

The technology of arranging particles by ultrasound has matured. In recent years, this technology has been used as a basis for arranging particles in a photocurable resin for stereolithography (SL). In order to process the resin doped with particles to obtain a variety of particle arrangement patterns, most of the previous work chose to use different polygonal containers to obtain single-layer fiber angles. In this adjustment mode, the selectivity of the fiber angle is very poor, usually 45°, 90° and other common angles. In this work, we designed and manufactured a new ultrasound-assisted 3D printing platform that can flexibly adjust the thickness of the sandwich and the rotation angle of the sandwich. We will introduce the basic working principle and matching usage of the device, and show some basic print samples.

Extrusion-based printing technology has a promising development in the field of tissue engineering scaffold. Researchers package cells/particles in biomaterials and then extrude them through a nozzle and solidify to get a scaffold. This method can achieve uniform distribution of cells/particles in biomaterials or the addition of particles in biomaterials to enhance the mechanical properties of the scaffold. Sodium alginate is a kind of polysaccharide biomaterial which has a wide range of applications in the field of bioprinting. However, the diameter of the nozzle determines the accuracy of the cells/particles position in the alginate scaffold. A method of ultrasonic-assisted 3D bioprinting a composite of alginate and particles is proposed. The acoustic pressure can concentrate cells/particles to the center of the nozzle, which can achieve a more precise positioning than the diameter of the nozzle, and facilitate the purpose of depositing specific cells/particles to the determined location of the biomaterial.

Extrusion-based bioprinting is one of the most common biomanufacturing methods. The bioink composed of biomaterials and living cells is extruded into cylindrical filaments. The filaments are deposited on the substrate and stacked layer by layer to form a three-dimensional structure. During the extrusion process, the ink tends to accumulate at the nozzle, which clogs the nozzle and increases extrusion pressure, resulting in the decrease of cell survival rate. Here, we propose a method of using ultrasound to manipulate cells to assist the bioprinting process, which can alleviate nozzle clogging. The ceramic piezoelectric plate(PZT) is used to drive the nozzle to generate structural resonance, and the ultrasonic standing wave generated by the vibration make the cells/particles in the ink gather at the center of the nozzle, thereby reducing the risk of clogging of the nozzle. In this paper, we first analyze the mechanism of the standing wave generated in the cylindrical elastic nozzle and drive the cells to move under the PZT drive, and then use the finite element software to simulate the standing wave drive process. The results show that this method can be solved by a simple and low-cost device. The results indicate that this method has the possibility of using simple and low-cost equipment to solve the problem of nozzle clogging in bioprinting.

The magnetic phase transitions in MnNiGe1 − xGax (x = 0.0725, 0.080, and 0.085) compounds were investigated by dc magnetization measurements. Due to the introduction of Ga, all the compounds crystallized in Ni2In-type structure at room temperature instead of TiNiSi-type structure for their parent compound MnNiGe. With increasing temperature, each compound goes through two magnetic phase transitions, i.e. magnetostructural phase transitions from antiferromagnetic (AFM) TiNiSi-type phase to ferromagnetic (FM) Ni2In-type phase and ferromagnetic to paramagnetic (FM–PM) transition of Ni2In-type phase. It was found that the magnetostructural phase transition temperatures Tt decreased with the increase of Ga content, while the FM–PM transition temperature TC almost did not change. Large inverse magnetic entropy ΔSM in the vicinity of Tt following a conventional one around TC was observed for each sample.

Magnetic critical behavior of Mn5Ge3 ribbons was investigated by dc magnetization measurements. The critical exponents were obtained by a modified Arrott plot technique and the Kouvel–Fisher method. Finally, β = 0.372 ± 0.003 and γ = 1.05 ± 0.01 were determined. The exponent δ = 3.88 ± 0.02 obtained from the magnetization isotherm of TC fulfills the Widom scaling relation δ = 1 + γ/β. Moreover, with these exponents, the magnetization curves collapse into two independent curves following a single equation around TC. These results confirm the reliability of the obtained critical exponents. However, this set of exponents belongs to none of the classical theoretical models. This phenomenon is probably caused by the anisotropy of the Mn ions.

A quantitative model for calculation of the lifetime of quasibound states, including the Γ‐X transfer, in a AlAs‐GaAs‐AlAs double‐barrier structure is presented. When device is designed that a Γ‐like energy level approaches to an X‐like energy level, anticrossing of the Γ‐X transition occurs and the lifetime of the state can be several orders larger than that of a pure Γ system.

A Green's-function approach is employed to calculate the electron tunneling through a double-barrier device for infrared-radiation detection. Electrons photoexcited by an ir beam undergo transitions to a resonant channel, so that the transmission coefficient for tunneling substantially increases by several orders of magnitude compared with the dark state. This photon-induced resonant tunneling can be switched and controlled by a change of the applied static voltage. Such a system is ideal for ir photodetectors.

The proper treatment of the electron‐phonon coupling between electrons confined to two dimensions (2‐D) by phonons traveling freely in three dimensions (3‐D) requires special care because phonon heating produces a bottleneck in the rate of transfer of energy from the carriers to the phonons. Because the carriers interact with phonons primarily when the latter are close to the quantum well, the latter should be described, not by plane waves, but by packets adapted to the shape of the carrier confinement. A quasi‐equilibrium technique that retains off‐diagonal elements in the phonon wave‐vector permits an unrestricted treatment of the density operator equation. That in turn leads to a choice of wave packet that comes from solving the integrodifferential equations rather than by imposition. Moreover, if the carrier distribution is assumed in quasi‐equilibrium with a given drift and temperature, the coupled partial differential equations are reduced to coupled ordinary differential equations that can be solved with modest computer power. Comparison with experimental results for steady flow of energy from carriers to phonons, and for time‐dependent relaxation yields quantitative agreement.

Mn5Ge3−xAlx ribbons with x=0,0.5, and 1 were prepared by single roller melt-spinning method. Textured structures were observed in these ribbons as a result of fast cooling, with highly ordered columnar grains perpendicular to the surface. The magnetocaloric effect and critical behavior were investigated by dc magnetization measurement. Curie temperatures decrease from 297 K to 283 K as the Al content increases, and the peak entropy changes also decrease from 4.92 J/kg K to 3.0 J/kg K under an external magnetic field change of 3 T. Critical exponents were obtained by modified Arrott plots technique, Kouvel-Fisher method, and critical isothermal analysis. Similar values of exponents of β∼0.37, γ∼1, and δ∼3.8 were obtained for all of the compositions. Moreover, rescaled entropy data for all compositions collapse into a universal curve, revealing universal behavior for the magnetocaloric effect in this series of compounds.

The crystal structure, magnetic properties and magnetostriction of polycrystalline magnetostrictive alloys Nd(Fe1−xCox)1.9 were investigated. It was found that the single cubic Laves phase can only be obtained in the samples with x>0.4 by a traditional annealing method. In contrast, the cubic Laves phase exists over the entire composition range studied in the samples annealed under high pressure. Both the Curie temperature and saturation magnetization increase with increasing Co concentration to a maximum at x = 0.2 and then decrease with further increasing x, which could be understood in the frame of rigid band model. The spin phase diagram for Nd(Fe1−xCox)1.9 is constructed to illustrate the arrangement for the easy magnetization direction and crystal structure. The magnetostriction of Nd(Fe1−xCox)1.9 increases with increasing Co concentration and peaks at x = 0.1 and then presents an anomalous behavior when 0.2≤x≤0.6. It is suggested that the external-field-induced lattice strain should be responsible ...

We study the transport of the photoexcited quasi-2D electron-hole (e-h) plasma in a p-doped semiconductor quantum well, where electrons are a minority. Using the drifted temperature model for both electrons and holes and introducing a coordinate transformation to the center-of-mass system, separately, for electrons and holes, we obtain a set of coupled equations for the drift velocities and the temperatures of electrons and holes. We show that negative absolute mobility for minority electrons occurs at low temperature and under a weak electric field due to the electron-hole drag. In a strong electric field and at room bath temperature, our results show that the electrons are heated much more than the holes. The electron mobility is smaller in the presence of the hole plasma than in the absence of holes. These results are in agreement with experiments.