基于声压-振速测量的平面近场声全息实验研究

常规的近场声全息均是采用全息面声压或质点振速作为输入量求解,由于采用单一输入量无法分离来自全息面背向声波的干扰,因此要求所有声源均位于全息面的同一侧,即测量声场为自由声场,这种要求大大限制了近场声全息的实际应用.基于声压-速度测量的近场声全息以全息面上声压和质点振速同时作为输入量,通过建立和求解两侧声源在全息面上的声压和质点振速耦合关系,可以实现全息面两侧声波的分离,从而解决上述问题.文中在前期对声场分离技术研究的基础上,基于欧拉公式和有限差分近似,推导了新的基于声压-速度测量的平面近场声全息理论公式.随后通过实验检验了该方法在有背景源干扰情况下实现声场分离和重建的有效性.     

水听器线列阵近场声压测量误差实验研究

本文介绍了用于近场声压的测量水听器中阵元水听器测量声压的可靠性检验方法和实验结果,提出了元水听器测量球面波场中声传播衰减的曲线与现想球面波声场中场传播衰减的曲线对比的检验,要用球面声源声中心测量值对收发距离进行修正的方法,实验水池中对线列阵上十元水吸器在球形声源水池中进行了传播衰减曲线的测量分析,验证了基阵的弱散散射性能,表明线阵可用于距离小至1／7波长的极近场的扫描测量。     

双全息面分离声场技术及其在声全息中的应用

提出双全息面分离声场技术,克服以往近场声全息(NAH)和基于声强测量的宽带声全息(BAHIM)的应用局限。以往方法的局限在于:全息面一侧的声场必须是自由声场,即要求所有的声源仅能位于全息面的另一侧;而在实际测量的情况下,这个要求是很难达到的。本文提出的声场分离技术利用波场的外推理论,建立起在波数域声场分离的公式,然后通过二维Fourier逆变换,便得到了全息面一侧声源产生的声压,从而达到声场分离的目的。原理的推导理论上论证该技术正确性,数值仿真显示了方法的可行性和有效性。     

基于平面声全息的全空间场变换:Ⅱ.水下大面积平面发射声基阵的近场声全息实验

研制了一套多通道水声声全息测量系统,解决了多通道系统的校准及弱散射水听器接收线阵的设计等问题。在非消声水池内,利用该系统对水下大面积平面发射声基阵进行了近场声全息实验,给出了声基阵表面的声强分布、声基阵各阵元及全阵的辐射声功率、基阵远场空间指向性图和指向性参数等。实验结果证明脉冲法和分区扫描数据合成的测量方法是可行的,实验系统的设计与实施方法可用于更大规模的声全息系统。     

近场头相关传输函数的多声源快速测量系统设计与验证

近场头相关传输函数(HRTF)是双耳听觉科学研究和虚拟听觉重放应用的重要基础数据。近场HRTF测量系统要求具有高的测量效率、精度和重复性,以至于目前未见文献解决真人受试者的近场HRTF测量困难。本文研究并实现了一种计算机控制的近场HRTF的高效测量系统,并提出系统的快速校准方法,首先实现了真人受试者的近场HRTF测量。通过声学、机械与电子硬件和软件的综合设计,提高了测量效率。通过准确校准声源、受试者和双耳传声器的位置,提高了测量精确度和重复性。系统可用于1.0 m范围内不同声源距离的真人受试者以及人工头的近场HRTF测量,单个声源距离的全空间近场HRTF测量时间减少至20 min以内。测量结果表明,系统测量精度满足实际需求,可用于科学研究和个性化近场HRTF测量及数据库建立。      

基于反射系数估算的半空间边界阻抗和声源直接辐射重构

半空间中声源直接辐射声场重构的实施需要构造以边界声阻抗为参量的半空间基函数,边界声阻抗的获取则通常需要借助原位测量方法.基于半空间球面波基函数叠加的声场重构方法,通过在声源近场布置全息测量面和一支参考传声器采集声压,并以参考传声器声压重构误差取得最小值为准则,估算各全息测点的声压反射系数,就能在边界阻抗未知条件下实现声源直接辐射声压的重构,从而摆脱了常规方法对声阻抗原位测量技术的依赖.本文的目的是对这一方法进行详细的参数讨论,并在估算声压反射系数的基础上,进一步对边界声阻抗加以重构,提出一种基于近场声全息的声阻抗测量方法.以球形声源为例,对声阻抗和声源直接辐射声压的重构进行了仿真,定量地分析参考传声器坐标、边界有效流阻率和边界孔隙度随深度的降低率等参数对重构精度的影响.     

基于声强测量的近场声全息及其在水下声源声辐射分析中的应用

基于声强测量的宽带声全息（ＢＡＨＩＭ）是一种新的有效的声场重建技术，在获得了测量面（全息面）上两个切向声强分量后，利用ＢＡＨＩＭ可以预报声源的辐射场及噪声源定位。本文给出了不同声源和参数下ＢＡＨＩＭ数值分析结果，井利用自行研制的双通道自动扫描声强测量系统进行了水下声源近场声辐射的ＢＡＨＩＭ实验，结果证实了该方法的有效性，它增强了分析和识别噪声源的能力。     

电子束光刻-近场全息法制作平焦场光栅的误差分析及补偿方法

在激光等离子体诊断等领域中,以平焦场光栅为核心器件的软X射线光谱仪发挥着重要作用。利用电子束光刻-近场全息法制作的平焦场光栅兼具电子束光刻线密度变化灵活,以及全息光栅低杂散光、抑制高次谐波等的特点。采用光线追迹方法分析电子束光刻-近场全息法制作平焦场光栅的主要制作误差对其光谱成像特性的影响。结果表明:电子束光刻制备熔石英掩模和近场全息图形转移过程的制作误差均会导致谱线展宽;以目前应用较多的软X射线平焦场光栅(中心线密度为2400line/mm、工作波段在0.8~6.0nm)为例,当熔石英掩模在光栅矢量方向的长度为50mm时,电子束光刻分区数目应保证在1500以上;熔石英掩模线密度偏差引入的谱线展宽可以通过调整近场全息制作参数来消除;确定了近场全息中的两个主要影响因素——熔石英掩模与光栅基底的间距和夹角;近场全息中各误差因素之间有相互补偿的效果,故除了尽可能消除制备过程中的每一种制作误差外,也可以通过优化不同误差之间的分配来降低制备误差。本研究对优化电子束直写掩模策略、降低掩模制作难度、设计和调整近场全息光路有重要帮助。     

浅海鼓虾噪声声源级测量方法

鼓虾噪声是声源级高、频带宽的冲激噪声,对浅海高频声呐和水下通信系统有很强干扰。本文针对实地测量鼓虾噪声声源级存在的多径传播和随机多声源问题,提出一种自动测量实际海域中鼓虾噪声声源级的方法。基于匹配场思想,在一个大孔径垂直线阵上对近场的大量鼓虾噪声进行自动定位。利用鼓虾噪声的强冲激特性,使用阈值检测的方法获得鼓虾信号的到达时间,同时将其幅度进行归一化,解决了各声源幅度动态范围相差大的问题。利用射线理论计算近场直达波到达时间作为拷贝场,对数据进行球面波波束形成,解决近场多途多声源定位问题。通过定位结果将接收鼓虾信号的峰峰值声压换算到距离声源1 m处,计算峰峰值声源级。在东海测量的结果显示,该海域的鼓虾噪声峰峰值声源级平均值为173 dB re: 1μPa@1 m,50%的测量值在168~175 dB re: 1μPa@1 m之间。      

阵列式双水听器平面扫描声强分布测量和声功率计算实验研究

根据双水听器法测量声强的基本原理，本文提出了基阵在湖中的布放及测量声强分布的实施步骤。通过对试验数据的处理与分析，给出了声强分布的三维力和等值曲线图，并利用扫描平面上的声强分布。计算出声源辐射的声功率。实验表明，本文提出的用列阵式双水听器声强测量系统，作平面扫描测量声强分布的方案是合理的；利用所测得的双平面近场声强分布来计算源的辐射也是可行的。     

关于"太阳在银河系中所受引力与到银心距离r的关系"的讨论

讨论了银道面内的引力场强分布和太阳在银河系中所受引力与到银心距离r的关系，指出引力场强g并不是与r的平方成反比，这是由于银河系的大小和形状不能忽略造成的．强调了万有引力定律的适用条件．     

On the predictability of the positions of the convergence zones in the ocean

The disagreement between the experimental and calculated positions of the first convergence zone are known from many publications. The most probable cause for such a disagreement, namely, the incorrect specification of the input data for the calculations, is considered. The lack of simultaneity between the hydrological surveys of the region and the acoustic experiments is emphasized. The experimental data obtained by the author in five ocean regions are presented. These data characterize the diurnal variability of the distance from the source to the nearest boundary of the convergence zone. The relations proposed by different researchers for calculating the sound speed from the temperature, salinity, and hydrostatic pressure are analyzed. It is shown that these relations lead to a substantial difference in the estimated depth dependence of the hydrostatic gradient of the sound speed. The position of the first convergence zone is calculated for the propagation conditions determined by vertical temperature and salinity profiles with the subsequent recalculation of these profiles into sound speed profiles by using eight different formulas known from the literature. It is shown that different formulas lead to different values of the distance to the first zone; this difference is substantially greater than that between the calculations and experiment. The necessity of improving the recalculation relations in view of the experimental data on sound propagation in natural oceanic waveguides, including the data on the actual positions of the convergence zones, is emphasized.     

On the calculation of the bremsstrahlung in the region of the plasma frequency

On the basis of the classical theory of radiation produced in incomplete Coulomb interaction, a formula is derived for the coefficient of the bremsstrahlung of fully ionized plasma. In the region of rectilinear approximation a comparison is made with the results of the quantum formula derived from the Born approximation. Furthermore, the influence of dispersion upon the emission coefficient is taken into account; some relations for the region of dispersion are given.     

Dependence of the Intensity of the Spectral Lines and the Composition of the Sample and the Plasma Parameters of the Unipolar Arc

The investigation was made of the dependence of the intensity of Tl, Ga, Mo, Mg, Mn, Sn, Bi, Ni, Zn, Pt and Au spectral lines and the plasma parameters (temperature T, electron concentration n_e, degree of 6 ionnization α) from concentration of lithium additive.     

Extracting the wavefunction of the LSP at the LHC

We consider associated production of squarks and gluinos with the lightest supersymmetric particle (LSP), or states nearly degenerate in mass with it. Though sub-dominant to pair production of color SU(3)-charged superpartners, these processes are directly sensitive to the wavefunction composition of the lightest neutralinos. Exploiting event-shape variables - including some introduced here for the first time - we are able to identify the composition of the LSP by selecting events involving a single high-pT jet recoiling against missing transverse energy. We illustrate the proposed technique on a set of benchmark cases and propose methods for applying these results in more realistic experimental environments.     

On the Question of the Source of the Apokamp

Technical Physics - The object of this work is the apokamp—a new type of plasma jet, which is formed from a bright offshoot emerging at the bending point of a channel of a high-voltage...     

Set the controls for the heart of the Sun

In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.