Magnetic properties of misch-metal partially substituted Nd–Fe–B magnets sintered by dual alloy method

The misch-metal(MM) partially substituted Nd–Fe–B sintered magnets were fabricated by the dual alloy method,and the crystal structure, microstructure, and magnetic properties were analyzed comprehensively. X-ray diffraction(XRD)reveals that the increasing content of the MM has an inconsiderable effect on the crystallographic alignment of the magnets.Grains of the two main phases are uniformly distributed, and slightly deteriorate on the grain boundary. Due to the diffusion between the adjacent grains, the MM substituted Nd–Fe–B magnets contain three types of components with different Ce/La concentrations. Moreover, the first-order reversal curve(FORC) diagram is introduced to analyze the magnetization reversal process, coercivity mechanism, and distribution of reversal field in magnetic samples. The analysis indicates that there are two major reversal components, corresponding to the two different main phases. The domain nucleation and growth are determined to be the leading mechanism in controlling the magnetization reversal processes of the magnets sintered by the dual alloy method.     

不同驱动力对Cz硅生长中熔体对流影响的数值模拟研究

为了确定Cz单晶硅生长各种驱动力对熔体对流及固/液界面形状的影响,利用CGSim软件,对典型的Cz单晶硅生长中的熔体对流进行数值模拟.研究了重力、表面张力、平流力、晶转、埚转和氩气剪切力等各种驱动力的大小对熔体对流涡胞、涡胞强度、界面形状、温度分布的影响.结果表明:各种驱动力对熔体对流的影响大小依次为:浮力＞表面张力＞晶转力＞氩气剪切力＞埚转力＞平流力;浮力和表面张力使熔体产生一沿坩埚壁上升、从固/液界面附近下降的涡胞,晶转力和氩气剪切力使熔体产生与前面反方向的涡胞,而埚转力产生多个不同流向的对流涡胞,使熔体混合更加均匀,熔体凝固引起的平流力对熔体对流影响不大;增大埚转,熔体中涡胞数量更多、对流换热更充分、温度梯度更小、熔体内的最高温度更低,有利于减少石英坩埚氧的熔解,但界面更向下凹;增大晶转,熔体内的最高温度无明显变化;固定埚转Ωc=-10 r/min,晶转存在一临界值Ωs(C)=60～ 80 r/min,当Ωs＜Ωs(C)时,增大晶转,固/液界面更向上凹,当Ωs＞Ωs(C)时,增大晶转,固/液界面更向下凹.     

Imaginary Part of the Surface Tension of Water

We report a direct measurement of the imaginary part of the surface tension of water through a dynamic scheme using a thin vertical glass fiber of diameter of 3 tun with one end glued onto a cantilever beam and the other end touching a water-air interface. The frequency dependence of the dissipation factor experienced by the glass fiber is exactly calculated through measuring the phase delay with various frequencies when the glass fiber is forced to oscillate vertically. We find the same intercept at the dissipation factor axis for different frequency dependences of the dissipation factor for different depths by which the glass fiber is dipped into water. This nonzero dissipation factor at zero frequency presents direct evidence of the existence of the imaginary part of surface tension of water and yields a complex surface tension of water σ^＊ = 0.073 ＋ i（0.017 ± 0.002） N/m at room temperature.     

Field—Correlation Effects on Rayleigh—Enhanced Nondegenerate Four—Wave Mixing

We study Rayleigh-enhanced nondegenerate four-wave mixing (NFWM) with time-delayed,correlated fluctuating fields.The importance of the field correlation is revealed in the Rayleigh-enhanced NFWM spectrum when the time delay is varied.The Rayleigh-enhanced NFWM is employed to study the ultrafast processes in the frequency domain.A relaxation time as short as 220 fs was deduced in the Rayleigh-enhanced NFWM experiments in carbon disulphide.     

基于纳米金自组装膜固定辣根过氧化物酶的生物传感研究

将辣根过氧化物酶(HRP)通过纳米技术和自组装技术固定于电极表面,制得了酶修饰电极.纳米金与HRP形成了静电复合物并高效地保持了HRP的生物活性,以对苯二酚作为电子媒介体,差示脉冲伏安法(DPV)研究生物酶电极测定H2O2的线性范围为5.0×10-6～1.0×10-3 mol/L,检测限为2.5×10-6 mol/L,线性方程为△I=0.34765+4.05553CH2O2(mM).酶电极的表观米氏常数(K(app))为0.0675 mmol/L.实验同时证明该生物酶电极具有良好的稳定性和使用寿命.     

降温速率对Ag-SmBCO单畴生长中自发成核的影响

在前期的研究中曾通过Ag掺杂降低Sm123/Sm211体系熔点,利用Nd123冷籽晶技术成功制备出具有理想织构的SmBCO/Ag单畴块材.但在实验结果中发现相比于未掺杂坯体,掺入Ag后的SmBCO坯体生长速率下降,在所考察的慢冷温区里,生长速率呈不断减小趋势,最终因自发成核而无法继续生长,使得SmBCO单畴区域局限于15×15mm2范围内.为了抑制单畴生长中的自发成核现象,本文研究了降温速率对SmBCO/Ag单畴自发成核的影响.在两组不同条件下的降温速率实验中发现,不同的降温速率对体系自发成核的抑制效果是不同的.利用降低降温速率,成功地将掺Ag SmBCO单畴面积从15×15mm2增大至26×26mm2.     

同质冷籽晶技术生长SmBCO/Ag超导单畴块材的研究

在前期的研究中,利用NdBCO123冷籽晶技术成功制备出具有理想织构的SmBCO/Ag单畴块材.但由于高质量的Nd籽晶的供应难以得到保证,从而限制了SmBCO单畴块材的批量化制备.Ag可以降低SmBCO坯体的熔点,这为用SmBCO冷籽晶技术引导SmBCO/Ag坯体生长单畴块材提供了可能性.然而,实验中我们发现,坯体里面的Ag容易向籽晶内部扩散,导致籽晶熔融,对单畴块材的生长产生不利影响.为克服这困难,我们通过在坯体和籽晶之间加入一个SmBCO211缓冲层,有效地阻止坯体里面的Ag向籽晶扩散,成功实现了同质冷籽晶技术生长SmBCO超导单畴块材.     

水泵水轮机开机过程压力脉动的试验研究

水泵水轮机机组的压力脉动是影响机组稳定性的一个非常重要的因素,而转轮与活动导叶之间的无叶区的压力脉动具有振幅最大、振源复杂的特点。本文通过某抽水蓄能电站的真机的试验数据分析,对机组开机过程中无叶区的压力脉动进行了较为深入的研究,获得了水轮机的开机过程及水泵的开机过程中无叶区的压力脉动的幅值和频谱特性,并对其特点进行了分析。     

Atomic coherence in nondegenerate four-wave mixing

Two-photon resonant nondegenerate four-wave mixing (NFWM) with the addition of a coupling field in Ba atomic vapour has been studied. We find that coherence of the atomic level transitions leads to suppression of the NFWM signal, giving rise to a dip with a linewidth that is linearly proportional to the intensity of the coupling field.     

隔水套管波流联合作用下非线性动力响应

考虑流及波流联合作用,研究了深水套管的涡激非线性振动．将套管简化为梁模型,计及Morison非线性流体动力和涡激荷载,建立套管的涡激振动方程．采用Korolov函数求解套管的固有频率和模态,提出了计算涡激非线性动力响应的Galerkin方法,计算了160 m水深中170 m长套管的固有频率和模态,研究了流引起的主共振和波流联合引起的组合共振．计算结果表明波流联合作用下套管的动力响应明显增大,结果也揭示了波流联合激励下套管复杂的动力响应特性．