声悬浮研究新进展

建立了单轴式声悬浮的参数化模型和边界元算法，对单轴式声悬浮进行了优化设计，可以悬浮起密度高达18．9g/cm^3的金属钨。研究了声悬浮条件下非金属材料和低熔点金属的无容器处理。     

电磁悬浮熔炼的温度特性

利用一般电磁悬浮熔炼感应器，球形试样悬浮情况下，悬浮力和悬浮试样输入功率表达式，建立了不含悬浮感应器电流的悬浮试样输入功率表达式.利用这些表达式，结合自然对流情况下，球形试样在气体介质中的功率耗散模型，建立了悬浮熔炼工艺参量与悬浮熔炼试样温度之间的关系.以(TbDy)Fe2合金在Ar气保护情况下，在一定工艺条件下的电磁悬浮熔炼为例，得到了电磁悬浮熔炼各种工艺参量与悬浮试样温度的关系.通过对计算结果的分析，结合实际电磁悬浮熔炼特点，得到了降低电磁悬浮熔炼试样最低温度的措施：减小悬浮试样的半径；在能够实现悬浮 关键词： 电磁悬浮熔炼 悬浮力 输入功率 耗散功率     

自悬浮定向流法制备纳米铜微粒及其结构表征

 采用自悬浮定向流法制备金属铜纳米微粒，并用TEM，XRD和AES等分析手段研究了铜纳米微粒的形貌、粒度、结构及其表面氧化层特性。结果表明，在一定的参数条件下采用自悬浮定向流法可制备出单晶纳米铜微粒，并且通过工艺参数的调控可达到对微粒粒度的控制。     

声悬浮对超声减摩的影响

考虑了大气中的声悬浮效应,建立起摩擦付的动力学模型。用该模型计算了声悬浮对超声振动减摩的影响。并用已有的实验装置,分别在真空和大气条件下检测了声悬浮对摩擦付间相对接触时间的影响。理论和实验均证明当摩擦付间的预压力较小时,声悬浮的影响是不可忽视的。     

自悬浮定向流纳米金属粉末制备的理论模拟

叙述了自悬浮定向流纳米金属粉末的制备原理，建立了在惰性气体介质中金属液滴表面蒸发 形成悬浮微粒过程的数学模型.描述了蒸发金属液滴表面层的热流动、物质迁移、热扩散、 凝聚相初始核的形成、金属蒸气在粒子表面的凝聚、粒子相互凝聚等过程，考虑了物质迁移 系数等动力学参数对温度的依赖关系.预测了指定粉末尺寸分布下的最佳工艺条件. 关键词： 纳米金属粉末 凝聚理论模拟 自悬浮定向流     

水色要素垂直分布对其遥感反演算法精度的影响

基于辐射传输模型模拟得到叶绿素和悬浮颗粒物在不同垂直分布条件下的遥感反射率数据集,利用该数据集对现有叶绿素、悬浮颗粒物浓度和固有光学量模型进行检验,研究了垂直分布对遥感反演算法反演精度的影响。结果表明：在悬浮颗粒物垂直分布、叶绿素及其垂直分布的影响下,悬浮颗粒物波段比值模型高估的悬浮颗粒物浓度要大于单波段模型;叶绿素波段比值模型和三波段模型能够较好地降低由叶绿素垂直分布、悬浮颗粒物及其垂直分布引起的叶绿素浓度高估的程度。悬浮颗粒物和叶绿素及其垂直分布对固有光学量反演具有双重效应,悬浮颗粒物垂直分布将使得吸收系数和后向散射系数被高估,而叶绿素垂直分布将使得吸收系数和后向散射系数被低估。在悬浮颗粒物和叶绿素共同作用下,固有光学反演结果具有较大的不确定性。     

脉冲磁过滤阴极弧沉积中基片台悬浮电位研究

通过测量脉冲磁过滤阴极弧等离子体沉积系统中的基片台悬浮电位，发现了弧源接地方式对基片台悬浮电位与等离子体电位影响很大。当阳极接地时基片台悬浮电位可达－60V，而弧源悬浮时却只有－5V。因此，要获得相似沉积条件的沉积薄膜，弧源接地方式不同，给基片施加偏压也应有所不同。     

预载对高温超导磁悬浮系统中横向运动引起的悬浮力衰减行为的影响

预载是一种有效抑制高温超导磁悬浮系统中由横向运动引起的悬浮力衰减的方法,但目前研究仅停留在概念验证阶段,尚未对影响预载效果的一些因素进行详细地分析和研究.利用高温超导磁悬浮测试系统,本文通过改变块材的冷却条件(场冷和零场冷)、悬浮高度以及轨道磁场结构、材料性能等实验研究了不同预载高度下YB-CO块材的悬浮力随横向运动次数的变化关系,得到这些因素对预载条件下悬浮力随横向运动变化情况影响的规律.结果表明,预载高度越低,由横向运动引起的悬浮力变化越快地趋于稳定,但悬浮力的稳定值也越小,并且这一现象不随冷却条件、悬浮高度、轨道磁场结构和材料性能等因素的改变而变化.     

声悬浮条件下环己烷液滴的蒸发凝固

采用单轴式声悬浮方法研究了环己烷液滴的蒸发过程,发现环己烷液滴的蒸发可以使自身温度降至熔点以下并发生凝固.高速摄像实时观测表明,环己烷晶核开始形成于液滴赤道附近,并以枝晶方式长大,平均生长速度为12.5-160.4 mm/s.进一步研究发现,声悬浮条件下平均Sherwood数与平均Nusselt数的比值Sh/Nu是在自然对流条件下的1.3倍,这表明声流边界层有效提高了环己烷液滴的蒸发速率而对传热的促进作用相对较小,因而可以使液滴降至更低温度,进而发生凝固.据此,提出了挥发性液体在声悬浮条件下发生蒸发凝固的必要条件. 关键词： 声悬浮 声流 环己烷 蒸发凝固     

自悬浮定向流技术中铜纳米微粒的粒度控制研究

 采用自悬浮定向流技术制备了金属铜纳米微粒，根据TEM的行貌像对样品平均粒度进行标定，并结合样品制备的条件对制备工艺进行了研究。结果表明，自悬浮定向流技术可以方便地制备出不同粒度的金属铜纳米微粒，微粒平均粒径随熔球温度的降低而减小，随冷却气体流速的增大而减小；在1 200℃下微粒平均粒径随惰性气体压强的增大而减小，而在1 300℃时惰性气体压强对微粒平均粒径的影响不再具有规律性。     

Simultaneous effects of pressure and temperature on the binding energy and diamagnetic susceptibility of a laser dressed donor in a spherical quantum dot

Binding energies and diamagnetic susceptibility of an impurity in a spherical GaAs quantum dot under the simultaneous influence of static pressure, temperature and laser radiation are investigated. Pressure- and temperature-dependent dressed potential which is produced by the combined effects of laser radiation and impurity considerably change the energy spectrum and diamagnetic susceptibility of the system. It is shown that binding energies and diamagnetic susceptibility increase with increasing pressure. Moreover, laser radiation effects on the diamagnetic susceptibility are not significant in comparison with its effects on the binding energy.     

Pressure-sensitive blackbody point radiation induced by infrared diode laser irradiation

Ultrabroadband radiation from Yb(2)O(3) at ambient and low air pressures was investigated under the excitation of a 980 nm diode laser. The radiation was confirmed to be blackbody radiation, and it is sensitive to environmental air pressure in the way that the integrated radiation intensity decreases linearly with increasing air pressure. An ideal gas model may be employed to interpret the linear dependence. The pressure-sensitive radiation characteristic provides a potential method for noncontact measurement of air pressure with high accuracy.     

激光诱导Al等离子体连续辐射的时间分布

用Ar作环境气体,压强固定在10kPa,每个激光脉冲能量为115mJ,利用时空分辨技术,采集激光烧蚀Al靶产生的等离子体辐射的时间分辨谱。分析了Al等离子体连续辐射特征。简要讨论了激光诱导等离子体连续辐射的产生机理。提出了原子对激光诱导等离子体连续辐射共振吸收理论。激光诱导等离子体的连续辐射的主要机制是轫致辐射和复合辐射,在激光脉冲作用到靶面瞬间,轫致辐射占主导地位;等离子体演化初期,复合辐射和轫致辐射共同产生等离子体连续辐射;等离子体演化后期,连续辐射主要复合辐射产生的。Al原子对连续辐射的共振吸收是选择性的,这是改变连续辐射按波长“平滑”分布的主要机制。     

Effect of submillisecond radiation of the erbium laser on absorbing liquid

Pressure pulses occurring in water under the effect of submillisecond radiation of the Er³⁺:YAG laser on the free and covered liquid surface were measured. The behavior of pressure pulses is caused by the photoacoustic effect, explosive boiling of the superheated liquid surface layer, and cavitation processes developing after laser exposure.     

Optical breakdown of alkali halide crystals

It is shown that the metallization of a dielectric in the region of its interaction with laser radiation is a substantiated mechanism of laser damage of wide-gap dielectrics. Calculations of the radiation pressure produced by high-power laser radiation and the pressure of external bulk compression at which the dielectric energy-gap width becomes zero and which is calculated on the basis of the self-consistent statistical electron theory of ionic crystals have shown that these pressures are of the same order of magnitude.     

Ion Dynamics in an Atmospheric Source with Photoionization by Radiation of Laser Plasma

Technical Physics - A pulsed source of ions with ionization of the substance under study at atmospheric pressure by the UV radiation of laser plasma is numerically simulated. The calculations are...     

Laser plasmatron for diamond coating deposition

An experimental installation with a laser plasmatron based on a continuous wave CO₂ laser with a radiation power of up to 3.5 kW has been created. The plasmatron design makes it possible to bring out the plasma jet into atmospheric air both along and across the laser beam direction. The spatial temperature distributions on the metal substrate surface heated by the plasma jet are measured. The threshold power for optical discharge maintenance as a function of the gas flow rate and the focal length of the focusing lens are obtained for an Ar and Ar/CH₄/H₂ gas mixture under atmospheric pressure; the radiation spectrum of the discharge plasma is measured. A one-dimensional model of the discharge for estimation of its geometrical parameters in a convergent laser beam with consideration of radiation refraction on the discharge is given.     

光泵THz激光器输出频率稳定特性研究

在太赫兹(THz)成像、雷达探测、相干通信等许多应用领域中,THz辐射源的频率稳定性是直接影响其应用效果的核心问题之一。基于双光子迁移效应建立了光泵THz激光器输出激光频率漂移的物理模型,推导出THz激光频率漂移的解析计算公式。以光泵甲醇(CH₃OH)为例, 给出了不同压强下的甲醇吸收谱线,定量分析了泵浦光频率漂移和泵浦功率对THz激光频率稳定性的影响,并讨论了THz激光腔内工作气体压强对THz激光频率漂移的影响。研究结果表明：随着泵浦光功率的增加,THz激光频率的漂移量逐渐增加;随着THz腔内工作气体压强升高,THz激光的频率漂移逐渐下降;当泵浦光频率漂移量在一定范围时,将出现THz激光的频率漂移量极值,且泵浦光的频率漂移量等于工作气体吸收谱线宽度的1/4时,THz激光输出的频率漂移达到极值。由此可见,在实际工作中,不仅需要合理选择腔内的工作条件(压强、温度),而且还需要采取措施将泵浦光的频率漂移控制在一定范围以内,以提高THz激光的输出频率稳定性。     

Effect of gas pressure on ionization of ambient gas

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Vanadium oxidation as a result of cw CO2 laser irradiation in atmospheric air

New results are reported concerning the vanadium oxidation by cw CO₂ laser irradiation in air at atmospheric pressure. Particular emphasis is paid both to the initial stage and the development of the oxidation process under the action of the laser radiation. Some aspects are finally discussed concerning the quantitative theoretical interpretation of the experimentally recorded data.