Search

A biodegradable UV-cured resin has been fabricated via stereolithography apparatus (SLA). The formulation consists of a commercial polyurethane resin as an oligomer, trimethylolpropane trimethacrylate (TEGDMA) as a reactive diluent and phenylbis (2, 4, 6-trimethylbenzoyl)-phosphine oxide (Irgacure 819) as a photoinitiator. The tensile strength of the three-dimensional (3D) printed specimens is 68 MPa, 62% higher than that of the reference specimens (produced by direct casting). The flexural strength and modulus can reach 115 MPa and 5.8 GPa, respectively. A solvent-free method is applied to fabricate graphene-reinforced nanocomposite. Porous bone structures (a jawbone with a square architecture and a sternum with a round architecture) and gyroid scaffold of graphene-reinforced nanocomposite for bone tissue engineering have been 3D printed via SLA. The UV-crosslinkable graphene-reinforced biodegradable nanocomposite using SLA 3D printing technology can potentially remove important cost barriers for personalized biological tissue engineering as compared to the traditional mould-based multistep methods.

Microstructures, elevated temperature mechanical properties and fracture mechanisms of the as-extruded ZM61-xSn (x=2, 4, 8, wt%) alloys were investigated by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and high temperature tensile tests. The results reveal that the addition of Sn can refine microstructures and the refinement effect increases with the increase of Sn content. The average grain sizes of the as-extruded ZM61-xSn (x=2, 4, 8) alloys are 11, 8 and 4 μm, respectively. With the increasing of Sn amount, the strength of experimental alloys increases at first and decreases afterward. ZM61-4Sn alloy shows the highest strength, whose ultimate tensile strength and yield strength are 216 and 173 MPa tested at 180 °C, respectively. The ductility increases with the content of Sn increasing, and the elongation of as-extruded ZM61-xSn (x=2, 4, 8) alloys are 183.8%, 235.8% and 258.6%, respectively, when tensile temperature reaches 300 °C. The ZM61-4Sn alloy has the optimal coalescence of strength and ductility. The localized necking leads to the final fracture of the specimens and the micro-void coalescence is the main fracture mechanism. Incomplete dynamic recrystallization occurs when tensile tests are carried out at 260 and 300 °C.

This paper investigated the effect of aging treatment before extrusion on microstructure and mechanical properties of AZ80 magnesium alloy. Fractural microstructures of the test specimens were also analyzed by scanning electron microscopy. Results show that aging treatment before extrusion can remarkably promote grain refinement; the dispersed Mg17Al12 particles precipitated from the matrix during aging treatment before extrusion distribute in the grain boundaries; during the subsequent extrusion process these particles can pin grain boundaries migration and lead to fine microstructure; however, with prolonging the aging time, the grain refinement effect is weakened. After aging treatment and subsequent extrusion, the yield strength, tensile strength and elongation are increased. Based on fracture surface analysis, the premature cracks occur around big particles in grain boundaries lead to loss of elongation. The strengthening effect of aging before extrusion in AZ80 magnesium alloy proven in this paper provides a new method for the design of the relatively high-performance magnesium alloys.

High molecular weight (HMW) polyethylenimine (PEI) is one of the most versatile nonviral gene vectors that was extensively investigated over the past two decades. The cytotoxic profile of HMW PEI, however, encouraged a search for safer alternatives. Because of lack of cytotoxicity of low molecular weight (LMW) PEI, enhancing its performance via hydrophobic modifications has been pursued to this end. Since the performance of modified PEIs depends on the nature and extent of substituents, we systematically investigated the effect of hydrophobic modification of LMW (1.2 kDa) PEI with a short propionic acid (PrA). Moderate enhancements in PEI hydrophobicity resulted in enhanced cellular uptake of polyplexes and siRNA-induced silencing efficacy, whereas further increase in PrA substitution abolished the uptake as well as the silencing. We performed all-atom molecular dynamics simulations to elucidate the mechanistic details behind these observations. A new assembly mechanism was observed by the presence of hydrophobic PrA moieties, where PrA migrated to core of the polyplex. This phenomenon caused higher surface hydrophobicity and surface charge density at low substitutions, and it caused deleterious effects on surface hydrophobicity and cationic charge at higher substitutions. It is evident that an optimal balance of hydrophobicity/hydrophilicity is needed to achieve the desired polyplex properties for an efficient siRNA delivery, and our mechanistic findings should provide valuable insights for the design of improved substituents on nonviral carriers.

In the phase shift modulation type optical components constructed by traditional dielectric waveguides with the low refractive index constant based on the total inner reflection mechanism,the length of the modulation region is usually millimeter or centimeter order of magnitude,while their horizontal size is micrometer of order of magnitude,therefore,the most typical characteristics of optical waveguide devices are long and narrow.Reducing the size of optical waveguide devices is a hard problem in the development of highly dense integrated optical circuits.The emergence of photonic crystals provides a new approach to develop highly dense integrated optical circuits.The plane wave expansion method is used to calculate the dispersion curves of the line-defect type photonic crystal waveguides.It is observed that there is a large change of wave prorogation constant near the guided-wave band edge,corresponding to a little change of refractive index of the material.If the work frequency is selected near the guided-wave band edge,the phase shift modulation length is expected to largely reduce.The finite-difference time-domain method is used to demonstrate the results above.Calculated results indicate that there is strong enhancement effect of refractive index phase shift modulation near guided-wave band edge: for the refractive index change of 0.46%,the phase shift modulation length in these waveguides is only 11.7% of that in conventional uniform dielectric material.This enhancement effect is originated from the special flat dispersion properties near the guide-wave band edge,and it is expected to be applied to high dense photonic integrated circuits after further research.

Residual distortion is a serious problem associated with welding thin aluminum alloy plates. As a distortion control technique static thermal tensioning has been used for many years. Owing to the insufficient understanding of its control mechanism and parameter influence, its application cannot always yield ideal results. So finite element analysis was performed. Based on the simulation results, presetting a saddle-shaped temperature field during welding can significantly reduce longitudinal inherent shrinkage strain in the weld and its adjacent zones, which will then reduce residual stresses and distortion. Temperature difference between the side and central zones is a key parameter and with its increase distortion reduction can be improved. Postweld thermal tensioning can cause certain plastic tensioning, but its effect cannot compare to that of a preset one. These numerical simulation findings were verified finally by experimental investigation.

The magnetization behavior of the layered anisotropic high-Tc superconductor in the mixed state Hc1 H Hc2 has a feature that when the angle between the applied magnetic field H and the CuO plane (a-b plane) is less than a critical value ( L), the vortex lattice is converted from three-dimensional structure into two-dimensional structure, forming a phenomenon so called the lock-in transition, where the flux lines are completely parallel to the a-b plane, and the vertical component of the magnetic induction B丄 (perpendicular to the a-b plane) is consequently zero. So far, there have still existed the differences in the physical explanation of the lock-in phenomenon. For the lock-in phenomenon occurring in the region between the CuO planes, it can be considered to be caused by the transverse Meissner effect. However, for the one occurring in other extended correlated defect areas, such as twin boundaries in YBa2Cu3O7- (YBCO) crystal, this phenomenon is believed to be the results of the energy linearization of the vortices trapped in the defect channels. Many theoretical and experimental studies have revealed the existence of the lock-in behaviors related to the microstructure properties of the superconductor crystals. Therefore, the research of the lock-in transition behavior will be helpful to understand the intrinsic pinning properties of the layered anisotropic superconductors, and the phase transition process in the vortex system. In this paper, we systematically measure the magnetic torque signal in melt texture growth YBCO (MTG-YBCO) bulk and observe an abnormal lock-in transition behavior in the vortex system. The critical angle of the lock-in transition is found to be directly proportional to the strength of the magnetic field, which is contrary to the observations in the common cases. According to the framework of the Ginzburg-Landau theory and the kink structure model of the vortex line, we discuss the abnormal phenomenon, and propose that there is a type of extend-correlated defect structure, which is parallel to the a-b plane, in the MTG-YBCO crystal. The relationship between the critical angle of the lock-in transition to the temperature and the magnetic field is established theoretically, and the theoretical results coincide well with the torque measurements.

We study the photo-detachment interference patterns of a hydrogen negative ion in the magnetic field near different dielectric surfaces with a semi-classical open orbit theory. We give a clear physical picture describing the photo-detachment of H− in this case. The electron flux distributions are calculated at various dielectric surfaces with unchanged magnetic field strength. It is found that the electron flux distributions of H− are very different in a magnetic field near different dielectric surfaces, namely the dielectric surface has a great influence on the photo-detachment interference pattern of the negative ion. Therefore, the interference pattern in the detached-electron flux distribution can be controlled by changing the dielectric constant. We hope that our studies may guide the future experimental research in photo-detachment microscopy.

In this work, using three-state model and time-dependent wave packet method, the wave packet dynamic process and time-resolved photoelectron spectrum of NaLi molecule in femtosecond pump-probe intense laser field are investigated and the relation between the parameter of the femtosecond laser and time-resolved photoelectron spectrum is obtained. It is found that the vibrational periods of wave packet are different for different laser wavelengths and the photoelectron spectra are different for different pump-probe delay times. The height and position of the peak of the photoelectron spectrum change with pump-probe delay time. When 1=352 nm and t=400 fs, the corresponding signal in the outer well (0.5 eV) is obviously smaller than that in the inner well (1.35 eV). The result reveals that the time-resolved photoelectron spectrum reflects the information about the wave packet dynamic of the excited state 41+ The results may be useful for realizing the optical control of molecule and the process of quantum manipulation of molecule experimentally, and provide some important basis for further theoretical research in this respect.

The photodetached electron flux of H- in magnetic field near a metal surface is studied with a semi-classical open theory, and the relation between the electron flux distribution and classical trajectory is also revealed. The electron flux distributions are calculated at various magnetic field strengths, with a ion-surface distance given. The results show that with the increase of magnetic field strength, the interference pattern in the flux distribution becomes much more complicated because the number of the classical trajectories of the detached electrons contributing to the electron flux distribution increases. In addition, we find that as the energy of detached electron changes, the detached-electron flux distribution changes accordingly. Therefore, the interference pattern in the detached-electron flux distribution can be controlled by adjusting the magnetic field strength and the energy of detached electron. Our study will provide a new understanding of photo-detachment microscopy of anion in external field and surface, and can be used to guide the future experimental research on the anion photo-detachment microscopy.

According to the semi-classical theory, we study the photodetachment microscopy of H− in the electric field near a metal surface. During the photodetachment, the electron is photo-detached by a laser and the electron is drawn toward a position-sensitive detector. The electron flux distribution is measured as a function of position. Two classical paths lead the ion to any point in the classically allowed region on the detector, and waves traveling along these paths produce an interference pattern. If the metal surface perpendicular to the electric field is added, we find that the interference pattern is related not only to the electron energy and the electric-field strength, but also to the ion-surface distance. In addition, the laser polarization also has a great influence on the electron flux distribution. We present calculations predicting the interference pattern that may be seen in experiment. We hope that our study can provide a new understanding of the electron flux distribution of negative ions in an external field and surface, and can guide future experimental research on negative ion photo-detachment microscopy.

Using the closed orbit theory, we study the photo-detachment of H- in a magnetic field near a dielectric surface. The photo-detachment cross section of this system is also derived and calculated. It is found that the photo-detachment cross section is not only related to the magnetic field strength, but also depends on the dielectric constant. For a given ion-surface distance and dielectric constant, with the increase of the magnetic field strength, the number of the closed orbits increases greatly and the oscillatory structure in the photo-detachment cross section becomes much more complicated. On the other hand, for a given magnetic field strength, the dielectric constant also has a great influence on the photo-detachment process of negative ion. Above the ionization threshold, the photo-detachment cross section becomes oscillatory. With the increase of the dielectric constant, the oscillatory structure in the cross-section becomes much more complicated. Therefore we can control the photo-detachment of negative ion by changing the magnetic field strength and the dielectric constant. This study provides a new understanding of the photo-detachment process of negative ion in the presence of external fields and surfaces.

Z_scan experiments are performed on the azobenzene polymer (DR_13_PMMA) films with He_Ne laser. It is found that the relation between the cha nge of refractive index of the sample and the light intensity behaves like a sat u rable effect, whose relative parameters are alterable with light intensity. It i s also found that the change of refractive index induced by linearly polarized l ight is distinctly greater than that induced by circularly polarized light. The phenomena are explained by using the theory based on the effect of angular hole burning of photoisomerization.

The microstructural evolution and the mechanical properties of Mg-6Zn-1Mn-4Sn-0.5Y wrought alloy extruded at 360 and 420 °C were investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), electron back scattered diffraction (EBSD) and tensile test. The results show that the phase compositions of as-cast and extruded alloys consist of α-Mg, Mn, Mg7Zn3, Mg2Sn, and MgSnY phases. As the extrusion temperature increases from 360 °C to 420 °C, dynamic recrystallization completes and grain growth occurs. The yield strength, the ultimate tensile strength and the elongation decrease from 259 MPa, 350 MPa and 18.3% to 239 MPa, 332 MPa and 12.5%, respectively. The theoretical calculations combined with the experimental results reveal that fine grain strengthening and solid solution strengthening play the dominating role in the enhancement of yield strength.