水下吸声覆盖层声管测试的背衬研究

在吸声覆盖层水声声管测试的实验研究中，覆盖层背衬的选择对测量结果有重大影响。在我们二维理论研究的基础上，建立了吸声覆盖层声学特性的传递函数模型，分析比较了不同背衬对吸声覆盖层声学性能的影响。结果表明，不同背衬对吸声覆盖层吸声性能的影响具有明显不同的特性。背衬为双层壳体时，水层对吸声覆盖层的吸声系数曲线有明显的调制现象。背衬为单层壳体或双层壳体时，从整体上讲，吸声系数更趋近于刚性背衬而非软背衬的情况。在实验室小样品声管测试中，以较厚的钢柱作为背衬的测试数据来衡量吸声覆盖层性能更为合适，且易于实现。     

机电耦合系数和复阻抗对压电换能器脉冲波形的影响

在地震模型实验中,需要指向性均匀、脉冲持续时间短的低频压电换能器。实验发现,具有匹配背衬的换能器发射脉冲的视周期总是比无背衬的长;向水中辐射的脉冲波形比向细棒中辐射的复杂。但没见过对这些现象的详细解释。 本文仅从基本压电万程和梅森等效电路出发,计算了长度模压电换能器的传递函数,并用数值方法计算了机电耦合系数k_(33)和复阻抗对长度模压电换能器脉冲波形的影响。结果表明具有匹配背衬的换能器k_(33)越大,其“单极”脉宽越宽;且复阻抗使脉冲波形变复杂。我们进行了复阻抗对脉冲波形影响的实验,计算和实验基本符合。在一定的近似条件下,可作为设计和使用脉冲压电换能器的参考。     

阿秒范围电子动力学的直接观测

为研究一个系统的动力学过程，通常采用激光脉冲抽运实验的方法．实验中，用可见波长的抽运脉冲激光来激发该系统，并使用第二个探测脉冲对系统演化与脉冲问延迟的关系进行跟踪．在这种实验中，可达到的时间分辨依赖于激光脉冲的时间精度，但是这些脉冲通常要持续几个飞秒（fs，lfs=10^-15s），因此不能用于研究更快的过程．最近一项很有希望的进展是将脉冲压缩到了200as（as为阿秒，1as=10^-18s）．     

超声换能器辐射特性的优化*

匹配层和背衬层是换能器的重要组成部分,对换能器特性有重要影响。针对发射型换能器,基于有/无匹配层和空气/树脂背衬两种条件组合,该文研究了匹配层与背衬层对换能器辐射特性的影响。结果表明,负载材料为水时,空气背衬换能器相较于树脂背衬换能器声能辐射效率更高;匹配层可以提高换能器的主瓣能量,抑制旁瓣能量及旁瓣数量。因此,针对发射型换能器的设计,背衬材料的选择应遵循与压电材料的阻抗差异越大越优的原则;匹配层的合理设计不仅可以提高超声换能器的声能辐射效率,还可以提高主瓣旁瓣峰值比,使声能更集中。     

环氧-钨粉背衬工艺及其应用

本文实现一种用真空抽吸环氧法制成背衬的工艺。声阻抗率可达30×10~6Pas/m。背衬棒用于低超声频换能器,可以得到单极或双极的声脉冲。     

采用光谱展宽技术的钛宝石飞秒激光放大器

报道了飞秒激光啁啾脉冲放大器中的激光脉冲光谱展宽技术，实验中使用了几种光谱展宽元件，结果表明使用激光光谱展宽元件能有效地将飞秒激光脉冲 光谱展宽，抑制了飞秒激光放大器中常见的激光脉冲光谱增益窄化现象，从飞秒放大系统的振荡级输出28fs种子脉冲，放大后得到了重复频率为10Hz、峰值功率为1．6TW、脉冲宽度37．5fs的超短强飞秒激光脉冲 。     

单脉冲和再加热正交双脉冲激光诱导击穿光谱对比研究

为了提高激光诱导击穿光谱技术(LIBS)的检测灵敏度和辐射光谱特性,采用再加热正交双脉冲结构对样品中的4种元素Fe,Pb,Ca和Mg以及含有不同浓度重金属元素Cr的土壤样品进行分析。研究了4条特征谱线FeⅠ：404.581 nm,PbⅠ：405.78 nm,CaⅠ：422.67 nm和MgⅠ：518.361 nm的光谱强度和信背比随两激光脉冲之间时间间隔的变化关系,获得了两激光脉冲之间最佳的时间间隔为1.0 μs。在单脉冲和双脉冲条件下,得到了4条特征谱线FeⅠ：404.581 nm,PbⅠ：405.78 nm,CaⅠ：422.67 nm和MgⅠ：518.361 nm光谱强度的增强倍数分别为2.23,2.31,2.42和2.10;分析了特征谱线FeⅠ：404.581 nm和CaⅠ：422.67 nm谱线强度随时间的演化特性以及4条特征谱线信背比随光谱采集延时的变化关系,双脉冲能有效延长光谱强度的衰减时间以及提高特征谱线的信背比;比较分析了等离子体温度和电子密度随时间的演化特性,在双脉冲条件下,等离子体温度最大升高了730 K,电子密度最大增加了1.8×1016 cm-3。单脉冲和双脉冲条件下获得重金属元素Cr的检测限分别为38和20 μg·g-1,再加热正交双脉冲技术使元素检测限下降近2倍。以上结果表明：再加热正交双脉冲能有效地提升LIBS技术的检测灵敏度和光谱特性,为进一步降低元素的检测限提供了有效的方法。     

自由空间中超短啁啾洛仑兹脉冲光束的空间奇异性

给出了超短啁啾洛仑兹脉冲光束在自由空间中的传输方程，研究了啁啾对洛仑兹脉冲光束空间奇异性的影响．理论及数值模拟的结果表明，由于啁啾的作用，对于脉冲宽度大于一个光波振荡周期的洛仑兹脉冲光束同样存在空间奇异性．在初始位置，啁啾洛仑兹脉冲光束的空间奇异性出现在脉冲的前沿或后沿．当洛仑兹脉冲光束传输以后，啁啾洛仑兹脉冲光束的空间奇异性将更加强烈．     

PB-1型窄脉冲压电薄膜可逆式换能器

本文著者研制成PB-1型PVDF可逆式压电换能器。它的通频带较宽,中心频率500—900KHz,通带Q值1.5,发送电压响应[级]148.9dB(re:1μPa/V),灵敏度-210dB(re:1V/μPa)。在水中声脉冲持续时间7—10μs,并有足够的声功率输出,电声效率约10％。 本文介绍了该换能器的结构、理论分析、测量结果及应用效果。证明了理论与实验的一致性。可供电声、水声、超声等其它PVDF传感器设计时参考。     

快速光脉冲藻类光合作用测量方法的激发条件研究（英文）

激发光强和激发持续时间是快速光脉冲藻类光合作用测量方法的关键实验条件.通过光脉冲激发实验,定量分析了不同平均激发光强下还原态初级电子受体的比例和发生再氧化的初级电子受体的比例.结果表明:快速光脉冲激发的最佳平均光强为30 000μmol quanta·m-2·s-1,最佳激发持续时间为70μs;30 000μmol quanta·m-2·s-1平均激发光强能够在70μs内还原96.08%的初级电子受体,且仅9.81%的初级电子受体发生了再氧化.     

PZT-95/5压电陶瓷的冲击波活化改性研究

 研究了冲击波对PZT-95/5压电陶瓷的活化改性作用，对PZT-95/5粉末及块状材料进行动态冲击波加载。实验表明：在合适的条件下，冲击波作用可提高样品的密度ρ，压电应变常数d₃₃，介电常数ε，降低介电耗损系数tg δ%。通过对样品进行X射线衍射，扫描电镜SEM、透射电镜TEM和X射线光电子能谱XPS等微观测试分析，揭示了冲击波改性的机理主要是：晶粒细化，晶界破坏，孔隙增多，缺陷增多，相变产生等，从而达到对样品改性的作用。     

Tuning of pnicogen and chalcogen bonds by an aerogen-bonding interaction: a comparative ab initio study

Using high-level ab initio calculations, the cooperativity effects between an aerogen-bonding and a pnicogen- or chalcogen-bonding interactions are studied in ternary Y···PH₂CN···ZO₃ and Y···SHCN···ZO₃ complexes (Y?=?NH₃, N₂ and Z?=?Ar, Kr, Xe). A detailed analysis of the structures, interaction energies and bonding properties is performed on these systems. For each set of the complexes, a favourable cooperativity is observed between Z···N and P/S···N interactions, especially in complexes involving NH₃ and XeO₃ molecules. It is found that for a given Y or Z, the amount of cooperativity effects in Y···PH₂CN···ZO₃ complexes are important than Y···SHCN···ZO₃ ones. For each ternary complex considered, the effect of a Z···N aerogen bond on a P/S···N bond is more pronounced than that of a P/S···N bond on a Z···N bond. The mechanism of the cooperativity effects in the ternary complexes is studied by electron density difference, quantum theory of atoms in molecules and natural bond orbital analyses. The solvent effects are also studied on the interaction energy and cooperativity of Z···N and P/S···N bonds in the ternary systems.     

The strengthening effect of a hydrogen or lithium bond on the Z···N aerogen bond (Z = Ar,Kr and Xe): a comparative study

An ab initio study is performed on O₃Z···NCM···NCX (Z = Ar, Kr and Xe; M = H and Li; X = H, F and CH₃) complexes to investigate cooperativity effects between aerogen and hydrogen or lithium bonding interactions in these systems. To understand the cooperative effects, a detailed analysis of the binding distances, interaction energies and bonding properties is performed on these complexes. The results indicate that all Z···N and H/Li···N binding distances in the ternary complexes are shorter than those of corresponding binary systems. For a given M or X, cooperative energies increase as Z = Xe > Kr > Ar. Moreover, O₃Z···NCLi···NCX complexes exhibit a larger cooperative energy than O₃Z···NCH···NCX ones. The non-covalent interaction (NCI) index analysis indicates that the formation of an H/Li···N interaction in the ternary complexes shifts the location of the spike associated with the Z···N interaction towards the negative λ₂ρ values. This indicates that NCI analysis can be regarded as a useful tool for the study of cooperative effects between two different non-covalent interactions. Also, cooperative effects in O₃Z···NCM···NCX complexes make a decrease in ¹⁴N nuclear quadrupole coupling constants of NCH or NCLi molecule.     

弛豫铁电单晶弯曲梁矢量水听器研究

研制了一种弛豫铁电单晶(PMNT)二维矢量水听器,矢量通道和声压通道分别由两个正交压电单晶复合弯曲梁振子和PZT-5压电陶瓷圆管组成。基于弹性力学理论和水下质点振速测量原理对弯曲梁矢量水听器进行建模,推导给出了接收电压灵敏度表达式,分析了弯曲梁应力分布对矢量水听器接收性能的影响以及PMNT压电单晶材料与弯曲梁结构的匹配问题。在理论分析的基础上,研制了PMNT压电单晶和PZT、-5压电陶瓷矢量水听器样品并进行测试。测试结果表明:压电单晶矢量水听器与压电陶瓷矢量水听器相比,接收电压灵敏度提高11 dB,自噪声降低3 dB,测试结果与理论结果相符。      

Chalcogen bonds tuned by an N–H···π or C–H···π interaction: investigation of substituent,cooperativity and solvent effects

In the present work, ab-initio calculations are performed to investigate cooperativity effects between chalcogen bond and H···π interactions in XHY···NCH···C₆H₆ and XHY···CNH···C₆H₆ complexes, where X = F, Cl, Br, CN, NC, and Y = S, Se. The nature of these interactions and the mechanism of cooperativity are studied by means of quantum theory of atoms in molecules, noncovalent interaction index, many-body analysis of interaction energy and electron density shift analysis. For each ternary complex, the shortening of the Y···N(C) distance is more pronounced than that of the H···π. The cooperative energies of these complexes are all negative which demonstrate a positive cooperativity between the Y···N(C) and H···π interactions. The many-body analysis of interaction energy reveals that the two-body energy term has the largest contribution to the total interaction energies of ternary complexes. A good linear correlation is established between the three-body energy and cooperative energy values in the ternary systems. The cooperative energies of XHY···CNH···C₆H₆ complexes indicate a larger sensitivity on the polarity of solvent than XHY···NCH···C₆H₆ ones.     

Enhancement of the magnetoelectric coupling in an A-line shape magnetostrictive/piezoelectric structure

In this study, a new kind of magnetoelectric (ME) structure is designed with Terfenol-D, PZT-5A and nonmagnetic and nonelectric trestle. The configuration of this ME structure presents “A-line” type, PZT-5A and Terfenol-D are respectively bonded with the trestles, which adopt the knuckle joint assembly. Differently from the conventional ME layered structure, in the new structure, the deformation of the PZT-5A of larger size is driven by a Terfenol-D layer of smaller size at an external magnetic field. Since the driven force is applied at the ends of piezoelectric layer through the trestles, the whole piezoelectric layer can be completely stretched or compressed, and the larger voltage should be induced. For the new ME structure with mica trestle, the maximum value of ${\alpha }_E$ is twice higher than that for the conventional laminated ME structure. Furthermore, a wider range of response frequency is also observed in this structure. For the new ME structure with ABS trestle, the experimental results indicate that the maximum ME voltage coefficient is measured as high as 31.85 V/cm?Oe at 405 Oe.     

Cooperativity of tetrel bonds tuned by substituent effects

Substituent effects on cooperativity between N···X and C···X interactions are studied in the 4-Z-Py···XH₃(NC)···XH₃(NC) complexes, where X = C, Si; Z = H, F, OH, CH₃, NH₂, F, NC, CN, NO₂ and Py = pyridine. All N···X and C···X binding distances in the ternary complexes are always shorter than those in the corresponding binary complex. This indicates that the formation of the N···X interaction strengthens C···X bond in these complexes and vice versa. Our results reveal that the strength of N···X and C···X interactions in the ternary complexes considerably depends on the nature of X and Z substituents. For a given aromatic system, the shortening of N···X and C···X distances is more important for SiH₃(NC) complexes than CH₃(NC) counterparts. The mechanism of cooperative effects in the ternary complexes is unveiled by electrostatic potential analyses and natural bond theory.     

Theoretical evaluation to improve the performance of composite wax powder: cooperativity effects involving the strong Na+···π/σ and weak hydrogen-bonding interactions in the complex of graphene oxide with Na+ and CH4

ABSTRACT

To provide a reasonable design scheme to improve the performance of composite wax powder, the ternary complex Na⁺···graphene oxide (GO)···CH₄ was selected as a model system to evaluate the cooperativity effect between the Na⁺···σ/π and H-bonding interactions in the composite wax powder doped with GO at the M06-2X/6-311++G(2d,p) and MP2/6-311++G(2d,p) levels. The cooperativities in GO···(CH₄)_n (n?=?1～10) and thermodynamic cooperativity effects in Na⁺···GO···CH₄ were also investigated. Although the changes of the absolute values of H-bonding interactions were slight, from those of relative values, the influence of the Na⁺···π or Na⁺···O interaction on the C–H···π, O–H···C or C–H···O interaction was notable upon the formation of ternary systems. The anti-cooperativity effect was found in the cyclic structure, while the cooperativity effect appeared in the linear conformation. The Na⁺···σ/π and H-bonding interactions as well as cooperativities in Na⁺···GO···CH₄ were stronger than those in Na⁺···coronene···CH₄. The formation of Na⁺···GO···CH₄ is a thermodynamic cooperativity process driven by the enthalpy change. Therefore, it could be inferred that, when graphite powder or carbon black was replaced by GO, the compatibilities could be strengthened among various components, and thus the performance of casting moulds could be improved. Atoms-in-molecules (AIM) and reduced density gradient (RDG) analyses confirmed the cooperativity effect and revealed the nature of the improved performance of composite wax powder with GO. The GO···(CH₄)_n (n?=?1～3) are positively cooperative, while the negative cooperativity is shown when n?=?4～10.     

The strengthening effect of a halogen,chalcogen or pnicogen bonding on halogen–π interaction: a comparative ab initio study

The aim of this work is to study the possible cooperative effects between Z···N and X···π interactions (Z = Cl, S, P and X = Cl, Br) in some model complexes, where both these interactions coexist. The nature of the interactions in these complexes is characterised by means of molecular electrostatic potential, electron localisation function, quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses. According to the results, the formation of an Z···N interaction in these systems makes a significant shortening of X···π distance. The cooperative enhancement of the X···π bonding in the ternary complexes depend on the strength of the Z···N interaction, and it becomes larger in the order Z = Cl > S > P. The mechanism of the cooperativity between the Z···N and X···π interactions is studied using the parameters derived from the QTAIM and NBO analyses.     

Tuning of tetrel bonds interactions by substitution and cooperative effects in XH3Si···NCH···HM (X = H,F, Cl,Br; M = Li,Na, BeH and MgH) complexes

In this work, the interplay between the tetrel bond and the dihydrogen bond is investigated in ternary XH₃Si···NCH···HM complexes, where X = H, F, Cl, Br and M = Li, Na, BeH, MgH. The nature of Si···N and H···H interactions is studied by molecular electrostatic potential (MEP), noncovalent interaction and electron localisation function analyses. All binding distances in the ternary complexes are shorter than those of isolated XH₃Si···NCH and NCH···HM systems. That is, the two types of interactions have a cooperative effect on each other. The results of the MEP analysis indicate that the enhancement of the Si···N and H···H bonds can mainly be attributed to the electrostatic interaction. The plot of the reduced density gradient versus sign (λ₂)ρ indicates that the location of the spike associated with each interaction in the ternary systems moves slightly towards the negative (λ₂)ρ values with respect to the binary systems. This confirms that both Si···N and H···H interactions in the ternary complexes are strengthened by the presence of other. Besides, cooperative effects lead to a considerable change in the ¹⁴N nuclear quadrupole coupling constant values of the ternary complexes relative to the XH₃Si···NCH complexes.