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1.
水下吸声覆盖层声管测试的背衬研究   总被引:2,自引:1,他引:2       下载免费PDF全文
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。  相似文献   

2.
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。  相似文献   

3.
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。  相似文献   

4.
对熔体急冷法制备的非晶合金Fe52Co34HfTB6Cu1进行了不同频率的中频磁脉冲处理,用透射电子显微镜、穆斯堡尔谱、正电子湮没寿命谱等方法研究了处理前后试样的微观结构及结构缺陷变化.结果表明,经中频磁脉冲处理后,样品发生了部分纳米晶化,晶化量随磁脉冲频率增加而增加,当磁脉冲频率为2000Hz时,晶化量达33.1%:在淬态非晶样品中,正电子在类单空位中的湮没寿命t1为150.5ps,强度,1为77.7%,在微孔洞中的湮没寿命仡为349.7ps,强度I2为22.3%;随磁脉冲频率的增加,t1,t2值呈现减小的变化趋势,与淬态非晶相比,I1有所增加,如下降,t1,t2的平均值亍大幅降低.  相似文献   

5.
环氧-钨粉背衬工艺及其应用   总被引:1,自引:0,他引:1       下载免费PDF全文
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。  相似文献   

6.
张小强  赵光义  周林  姜占兴  梁川  李名加  王真 《强激光与粒子束》2018,30(2):025004-1-025004-6
高能量亚纳秒脉冲X射线可用于精确定标辐射探测系统的时间响应特性和探测灵敏度,对于脉冲辐射场诊断技术研究具有重要意义。研制了一种小型化、可移动的亚纳秒脉冲X射线源,装置占地区域尺寸为1.2 m×40 cm,重142 kg。设计了双锥形绕组同轴结构变压器,采用新颖的三谐振变压技术,将纳秒脉冲形成线充电至520 kV,通过油介质自击穿开关放电,输出370 kV,3.8 ns的高压脉冲。设计了多级过匹配传输线提升输出电压,并利用油介质peaking-chopping开关进行脉冲压缩,产生了峰值520 kV、半高宽0.5 ns、功率1.8 GW的高压脉冲。基于Child-Langmuir定理,设计了刀刃阴极X光管,在520 kV电压下的运行阻抗为150 Ω,管前20 cm处的X射线峰值能量注量率约为1×1016 MeV·cm-2·s-1,累积照射量为4.1 mR。  相似文献   

7.
树华 《物理》2005,34(12):943-943
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).  相似文献   

8.
为实现对环向场电流的高效准确控制,提高中国环流器二号M托卡马克装置的实验效率,开展了针对300 MV·A六相脉冲发电机组向环向场脉冲放电的仿真研究。从300 MV·A六相脉冲发电机组向聚变装置环向场供电系统的拓扑出发,以等效处理分析为基础建立了仿真模型并进行脉冲放电动态过程仿真。通过对比分析仿真波形与300 MV·A六相脉冲发电机组向HL-2A装置供电的实际波形,验证了仿真模型的可靠性和合理性。在此基础上进行了300 MV·A六相脉冲发电机组向HL-2M环向场供电过程仿真研究,根据不同的环向场电流平顶值,得到了其对应的300 MV·A六相脉冲发电机组励磁电压控制波形,可以作为下阶段装置高参数实验实际控制的重要参考和先进控制策略研究平台。  相似文献   

9.
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:404.581nm,PbⅠ:405.78nm,CaⅠ:422.67nm和MgⅠ:518.361nm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1.0μs。在单脉冲和双脉冲条件下,得到了4条特征谱线FeⅠ:404.581nm,PbⅠ:405.78nm,CaⅠ:422.67nm和MgⅠ:518.361nm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:404.581nm和CaⅠ:422.67nm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730K,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20μg·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。  相似文献   

10.
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 。  相似文献   

11.
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.  相似文献   

12.
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.  相似文献   

13.
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.  相似文献   

14.
PZT-95/5压电陶瓷的冲击波活化改性研究   总被引:5,自引:0,他引:5       下载免费PDF全文
 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。  相似文献   

15.
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.  相似文献   

16.
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.  相似文献   

17.
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.  相似文献   

18.
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.  相似文献   

19.
We performed a systemic investigation of the substitution and cooperative effects on the O–H···O and N–H···O H-bonds in the complexes of 2-pyridone and its derivatives with oxalic acid. Generally, the electron-withdrawing substituent in 2-pyridone weakens the O–H···O H-bond but strengthens the N–H···O H-bond, while the opposite effect is for the electron-donating group. In addition, the substitution effect is associated with its substitution position in 2-pyridone. The total interaction energy of a chainlike trimer with oxalic acid as a middle molecule exhibits some additivity. When oxalic acid combines with two 2-pyridone/2-pyridinethione molecules, the O–H···O/S H-bond is weakened but the N–H···O H-bond is enhanced. When three oxalic acid molecules are linked by the double O–H···O H-bonds, one H-bond with the middle oxalic acid as the proton donor is weakened and the other H-bond with the middle oxalic acid as the proton acceptor is strengthened.  相似文献   

20.
The nuclear magnetic shielding, electric dipole moment and electric field gradient at the nuclei were studied by ab initio computations as a function of the one-dimensional proton transfer coordinate in BrH ··· NH3. The properties are vibrationally averaged along this reaction coordinate for BrH ··· NH3 and BrD ··· NH3. The effect of a matrix has been approximated, as in previous calculations, by surrounding BrH ··· NH3 with three argon atoms.  相似文献   

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