漆酶在磁性壳聚糖微球上的固定及其酶学性质研究

以磁性壳聚糖微球为载体,戊二醛为交联剂,共价结合制备固定化漆酶。探讨了漆酶固定化的影响因素,并对固定化漆酶的性质进行了研究。确定漆酶固定化适宜条件为50mg磁性壳聚糖微球,加入10mL0.8mgmL漆酶磷酸盐缓冲液(0.1molL,pH7.0),在4℃固定2h。固定化酶最适pH为3.0,最适温度分别为10℃和55℃,均比游离酶降低5℃。在pH3.0,温度37℃时,固定化酶对ABTS的表观米氏常数为171.1μmolL。与游离酶相比,该固定化漆酶热稳定性明显提高,并具有良好的操作和存储稳定性。

具有优良磁性能的新型铁基微晶合金

本文报道了五种铁基微晶合金的研究结果。实验结果表明,用这五种合金均可获得μ_i≥5×10~4的高起始磁导率、Hc≤1.0A/m的低矫顽力,在相当宽的频率范围内的高有效磁导率和低铁损、50Hz下的高幅值磁导率以及窄脉冲条件下的高脉冲磁导率。在f=1KHz和(?)_m=0.4A/m条件下,有效磁导率μ_5′的最佳值为18×10~4,超过了Yoshizawa报道的μ_5′=10×10~4的国际水平。最佳的铁损值为P5/50k=57.9w/kg、P2/100k=30.2w/kg和P3/100k=68w/kg。这也超过了Yoshizawa报道的P2/100k=38.9w/kg的国际水平。实验还证明了,这些合金都具有优良的磁性稳定性。在130℃下保温216小时,起始磁导率不变。

磁化状态对粘结NdFeB磁体磁稳定性影响分析

粘结NdFeB磁体的磁化状态不仅直接决定磁体对外提供的磁场大小,也对磁体的磁稳定性、材料用量有重要影响。通过对不同磁化状态反向退磁一定时间后磁通密度变化率的分析可知,饱和磁化后反向退磁的磁体具有更优的磁稳定性。反向退磁幅度越大,磁体在气隙中磁通密度受外界退磁场导致的损失率越小,磁性能越稳定。反向退磁幅度大于9%时,磁体具有相对较好的磁稳定性;同时,材料用量越多的磁体磁稳定性越好。

黄铜矿半导体DMS的第一原理计算

为了寻找新的高Tc的稀磁半导体(DMS),利用自旋局域密度泛函的第一性原理对 3d过渡金属(TM= V、Cr、Mn、Fe、Co或Ni)掺杂的II IV V2(CdGeP2 和ZnGeP2)以及I III VI2(CuGaS2 和CuGaSe2)黄铜矿半导体的电磁性质进行系统计算.结果发现:V或Cr 掺杂的 II IV V2 将出现铁磁(FM)状态,而 Mn、Fe或者 Co掺杂的 II IV V2 将出现反铁磁(AFM)状态,Ni掺杂时,DMS的磁性非常不稳定;在TM掺杂的 I III VI2 的DMS中,Cr、Mn掺杂的 CuGaS2 和 CuGaSe2将表现为FM状态,而当V、Fe、Co或Ni掺杂时,Cu(Ga,TM)S2 和Cu(Ga,TM)Se2 则表现了AFM性质.Cr掺杂的I IV V 以及 I III VI 黄铜矿半导体将可能出现较高的居里温度(Tc).

Magnetism and Stability of Diluted Magnetic Semiconductor (Ga_(1-x)Fe_x)As

Magnetism and the stability of (Ga 1-xFe x)As are investigated using the first principles LMTO-ASA band calculation by assuming supercell structures.Four concentrations of the 3d impurities are studied (x=1,1/2,1/4,and 1/8).The results show the effect of varying Fe concentration on the magnetic and stable properties.

Thermal stability,crystallization behavior,Vickers hardness and magnetic properties of Fe-Co-Ni-Cr-Mo-C-B-Y bulk metallic glasses

Thermal stability,crystallization behavior,Vickers hardness and magnetic properties of the Fe41Co7-xNixCr15Mo14C15B6Y2（x=0,1,3,5） bulk metallic glasses were investigated.The Fe41Co7-xNixCr15Mo14C15B6Y2（x=0,1,3,5） metallic glasses were fabricated by copper mold casting method.The thermal stability and crystallization behavior of the metallic glass rods were investigated by differential scanning calorimetry and isothermal experiments.Hardness measurements for samples annealed at different temperatures for different time were carried out at room temperature by the Vickers hardness tester,and magnetic measurements were performed at different temperatures by the vibrating sample magnetometer.It is shown that the addition of Ni does not play a positive role for enlarging ΔTx and GFA from parameter γ（=Tx/（Tg＋Tl））,and it can,however,increase the activation energy in the initial stage of crystallization by changing the initial crystallization behavior.The minor addition of Ni can refine the crystal grain obtained from the full crystallization experiment.The primary crystallization causes the decrease of hardness in these alloys,and as the crystallization continues,the hardness in all samples increases instead due to the precipitation of carbide and boride.The annealing temperature has an obvious effect on magnetic properties of these alloys,and the minor addition of Ni can effectively prevent the alloy annealed at high temperature to transform from paramagnetic to ferromagnetic state.

Alloying behavior and characterization of(CoCrFeNiMn)_(90)M_(10)(M=Al,Hf)high-entropy materials fabricated by mechanical alloying

The alloying behavior and microstructures of the(CoCrFeNiMn)_(90)M_(10)(M=Al,Hf)high-entropy alloy(HEA)powders fabricated by mechanical alloying were studied.The CoCrFeNiMn)_(90)Al_(10) powders have duplex solid-solution structures.In contrast,nanocrystalline HfNi_(3) anchoring in amorphous structures is found in the(CoCrFeNiMn)_(90)Hf_(10) powders.The(CoCrFeNiMn)_(90)Al_(10) powders show better ferromagnetic behaviors,mainly explained by the facilitated motion of the magnetic domain induced by the coherent interface between duplex phases.Combined with our previous work,the rules of forming solid-solution and amorphous phase in as-milled HEA powders are preliminarily proposed.It is found that,compared with the as-cast HEA reported previously,the variation range of mixing enthalpy with atomic size difference of the solid-solution formed in as-milled HEA powders is broader.Moreover,the variation ranges between mixing enthalpy and entropy with atomic size difference of the amorphous phase in HEA powder become wider than those of high-entropy bulk metallic glass.

Performance improvement of Fe-6.5Si soft magnetic composites with hybrid phosphate-silica insulation coatings

Fe-6.5Si soft magnetic composites(SMCs)with hybrid phosphate-silica insulation coatings have been designed to improve their comprehensive property via chemical coating combining sol-gel method in this work.The microstructure and magnetic performance of the Fe-6.5Si SMCs with hybrid phosphate-silica insulation coatings were investigated.The hybrid phosphate-silica coatings with high heat resistance and high withstand pressure,formed on the surface of the Fe-6.5Si ferromagnetic powders,were found stable in the composites.Compared with Fe-6.5Si SMCs coated by single phosphate or single silica,Fe-6.5Si SMCs with hybrid phosphate-silica show much higher permeability and lower core loss.The work provides a new way to optimize the magnetic performance of soft magnetic composites.

Effect of phase transition on room temperature ferromagnetism in cerium doped ZnS nanorods

The effects of Ce doping on the structure,optical,oxidation,thermal and magnetic properties of ZnS:Ce nanorods synthesized by a chemical co-precipitation method were reported.The crystalline phase transformation from cubic to hexagonal structure was observed upon doping ZnS with Ce.Magnetic measurements showed the existence of room temperature ferromagnetism in Ce-doped ZnS nanorods.X-ray photoelectron spectroscopic(XPS)measurements provided evidence for Zn-S bonds and oxidation state of Ce in the near-surface region.Raman spectrum provided evidence for the presence of defects as well as hexagonal structure of 5 wt.%Ce doped ZnS nanorods.Ce substitution induced shape evolution was studied by using TEM.DRS spectra further validated the incorporation of Ce^3+ions.The present study reveals that Ce doped ZnS nanorods may find applications in spintronic devices.

Aroma Profile of Myrrh and Its Thermal Variation

The authors examined the thermal change in the aroma profile of myrrh. The fresh odor of raw myrrh and its hexane extract depended on the amount of （E）-13-ocimene. Myrrh was extracted with hexane to avoid inducing changes in the constituents and odor. The main constituent, （E）-L3-ocimene （group A; low boiling point）, and the other constituents （group B; high boiling point） of the hexane extract were separated by bulb-to-bulb distillation. The constituents of groups A and B were analyzed over time by nuclear magnetic resonance analysis and the odors were evaluated. Myrrh＇s odor depended on both the amount of thermally unstable （E）-[3-ocimene, which contributed to the fresh odor, and the constituents of group B （thermally stable）, which contributed to the myrrh-like odor. Six compounds （c^-santalene, （Z）-a-bisabolene, c^-bergamotene, （E）-ct-santalal, c^-photosantalol and campherenol） were isolated from group B. No individual group B component had a myrrh-like odor, although the combined odor of group B was myrrh like. The authors demonstrated that the aroma profile of myrrh depends on the thermal instability of （E）-^-ocimene and a combination of six thermally stable terpenes with similar molecular structures.

Overview on permanent magnetic actuator

Permanent magnetic actuator （PMA）, as a new electronic actuator of vacuum circuit breakers, certainly will be used to replace the traditional mechanical actuator. It has such advantages as simple structure, high reliability, free maintenance, and so on. This paper summarizes the development, structure, magnetic analysis, character analysis, and control strategy of PMA, and also predicts the future trend of PMA development

密度泛函理论研究ZrnCo(n=1-13)团簇的结构和磁性

利用密度泛函理论中的广义梯度近似对ZrnCo(n=1—13)团簇进行了结构优化、能量和频率的计算,研究了ZrnCo团簇的平衡几何结构、稳定性、电子性质和磁性.结果表明:Zr4Co,Zr7Co,Zr9Co和Zr12Co团簇的基态稳定性较高,是幻数团簇,尤其是Zr12Co团簇基态为Ih对称性的二十面体结构且稳定性特别高.ZrnCo团簇的磁矩随尺寸的变化可以分三个阶段:n=1—3有稳定的磁矩,从n=4开始磁矩出现振荡性的猝灭,直至n≥8磁矩完全猝灭.体系的磁矩主要来自局域d电子的贡献,ZrnCo团簇磁矩发生猝灭的主要原因是电荷转移和强烈的spd杂化效应.同时发现,过渡金属掺杂在不同特性材料中所形成的团簇体系,其结构、稳定性和磁性有些非常有意思的相似,如TMX12(TM代表过渡金属Fe或Co,X代表Si和Be)团簇、Zr13TM团簇.对此,值得进一步研究.

密度泛函理论对Zr_nPd团簇结构和性质的研究

用B3LYP/LANL2DZ方法对ZrnPd(n=1—13)团簇的平衡几何结构、能量、频率、电子性质和磁性进行了计算.研究表明,Pd原子位于表面的异构体更为稳定,其中Zr7Pd,Zr12Pd团簇稳定性高,是幻数团簇;此外,相对于ZrnCo与ZrnFe团簇,ZrnPd团簇参与化学反应的能力较弱,化学稳定性更好;通过将Pd原子掺杂到非磁性Zr(n≥5)团簇中,可以使原来没有磁性的团簇转变为高磁性团簇.从Mulliken布居分析结果可知,在ZrnPd(n=1—13)团簇中各原子内、原子间都存在电荷转移,Pd原子总是电子受体。

Magnetically responsive photonic films with high tunability and stability

We demonstrate the fabrication of magnetically assembled one-dimensional chain-like photonic nanostructures with significantly high photonic stability. The key lies in the use of agarose hydrogel to prevent coagulation of the magnetic assemblies. When exposed to an external magnetic field, negatively charged Fe3O4@SiO2 particles can effectively assemble in the hydrogel matrix into one- dimensional chains with internal periodicity and display a fast, fully reversible, and tunable photonic response to the changes in the external field. The steric hindrance and the hydrogen bonding from the agarose network effectively limit the migration of the Fe304@SiO2 particles and their chain-like assemblies. As a result, the system shows remarkable stability in photonic response under external magnetic fields of large gradients, something which has previously been a challenge. The ability to stabilize the magnetic particle assemblies over a long period represents a major stride toward practical applications of such field- responsive photonic materials.

Easily prepared and stable functionalized magnetic ordered mesoporous silica for efficient uranium extraction

Functionalized magnetic Fe_3O_4@SiO_2 composite nanoparticles were prepared by simply embedding iron oxide nanoparticles into MCM-41 through one-step synthesis process, followed by aminopropyls grafting on the mesopore channels, aiming to efficiently and conveniently uptake U(VI) from aqueous solution. The resultant material possesses highly ordered mesoporous structure with large surface area, uniform pore size, excellent thermal stability, quick magnetic response, and desirable acids resistance, confirmed by Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), N_2 adsorption/desorption experiments, powder X-ray diffraction(PXRD), and thermogravimetric analysis(TGA). Detailed U(VI) sorption test indicated that this material is indeed an effective U(VI) sorbent with fast sorption kinetics of less than 2 h, large sorption capacity of 160 mg/g at p H 5.0±0.1, and desirable selectivity towards U(VI) ions over a range of competing metal ions. The absorbed U(VI) can be easily desorbed by 0.01 mol/L or more concentrated HNO_3 solution, and the reclaimed sorbent can be reused with no obvious decrease of sorption capacity even after 4 sorption-desorption cycles. The present results suggest the vast opportunities of this kind of magnetic composite on the solid-phase extraction of U(VI).

On Inherent Irreversibility in a Reactive Hydromagnetic Channel Flow

This study is devoted to investigate the inherent irreversibility and thermal stability in a reactive electrically conducting fluid flowing steadily through a channel with isothermal walls under the influence of a transversely imposed magnetic field.Using a perturbation method coupled with a special type of Hermite-Pade' approximation technique,the simplified governing non-linear equation is solved and the important properties of overall flow structure including velocity field,temperature field and thermal criticality conditions are derived which essentially expedite to obtain expressions for volumetric entropy generation numbers,irreversibility distribution ratio and the Bejan number in the flow field.

Dynamics of Charged Particles Around a Magnetized Black Hole with Pseudo–Newtonian Potential

The linear stability of equilibria of charged particles moving near a compact object with a dipole magnetic field and a pseudo-Newtonian potential is analyzed detalledly. An optimal fourth-order force gradient symplectic method, as a global symplectic integrator that can simultaneously solve both the equations of motion and the variational equations, is used to calculate fast Lyapunov indicators. In this way, dynamical structures are described, and parameter domains for causing chaos are found.

Calculation of Half-Metal, Debye and Curie Temperatures of Co_2 VAl Compound: First Principles Study

By FP-LAPW calculations, the structural, elastic, Debye and Curie temperatures, electronic and magnetic properties of Co2 VAl are investigated. The results indicate that Ferromagnetic （FM） phase is more stable than Anti- Ferromagnetic （AFM） and Non-magnetic （NM） ones. In addition, C11-C12 〉 0, C44 〉 0, and B 〉 0 so Co2 VAl is an elastically stable material with high Debye temperature. Also, the BIG ratio exhibits a ductility behavior. The relatively high Curie temperature provides it as a favorable material for spintronic application. It＇s electronic and magnetic properties are studied by GGA ＋U approach leading to a 100% spin polarization at Fermi level.

Cell surface engineering with polyelectrolyte-stabilized magnetic nanoparticles： A facile approach for fabrication of artificial multicellular tissue-mimicking clusters

Regenerative medicine requires new ways to assemble and manipulate cells for fabrication of tissue-like constructs. Here we report a novel approach for cell surface engineering of human cells using polymer-stabilized magnetic nanoparticles （MNPs）. Cationic polyelectrolyte-coated MNPs are directly deposited onto cellular membranes, producing a mesoporous semi-permeable layer and rendering cells magnetically responsive. Deposition of MNPs can be completed within minutes, under cell-friendly conditions （room temperature and physiologic media）. Microscopy （TEM, SEM, AFM, and enhanced dark-field imaging） revealed the intercalation of nanoparticles into the cellular microvilli network. A detailed viability investigation was performed and suggested that MNPs do not inhibit membrane integrity, enzymatic activity, adhesion, proliferation, or cytoskeleton formation, and do not induce apoptosis in either cancer or primary cells. Finally, magnetically functionalized cells were employed to fabricate viable layered planar （two-cell layers） cell sheets and 3D multicellular spheroids.

Experimental study on the vortex structure and path instability of freely falling annular disks

Bodies freely falling in steady water or air are common scenes encountered in various scientific and engineering fields, including the flapping flight of birds and the reentry of a space shuttle. In this work, the freely falling annular thin disks with small dimensionless moments of inertia f and Reynolds number Re are investigated experimentally in a water tank. We use stereo- scopic vision to record the position and orientation of the disks. The flow structure behind the disks is studied by applying fluorescent dye visualization and PIV method. Varying the geometry dimensionless parameter （the inner to outer diameter ratio η and I＊） of the disks reveals two new falling patterns. When ηcritl=0.6〈η〈ηcrit2=0.8, the disks show a random lateral vibration while falling. For high ηcrit2〉0.8, the circular vortex loops shed frequently from the disk, which causes a lengthways vibration superimposed onto straight vertical motion. We also observe another two falling patterns reported previously： hula-hoop and helical motion. By comparing the wake structure of the two motions, we find that the vortex layer twists more violently in the hula-hoop motion, which is the reason for the different trajectory between them. Further research on flow field reveals that the torque on the disk that causes the vibration is due to the formation, elongation and shedding of the vortex.