白噪声,分形噪声与布朗运动

Ｂｒｏｗｎ粒子轨道是一条分形曲线，Ｂｒｏｗｎ运动在电路中产生涨落电压而引起噪声影响仪器质量，本从分形学角度将Ｂｒｏｗｎ运动分为两部分，进而分析了它们对仪器灵敏度的影响，并提出了控制噪声的方法。     

含双噪声源电路的类WKB法研究

本文首次尝试利用ＷＫＢ方法对双噪声原电路的Ｖａｎｄｅｒ Ｐｏｒ方程进行了讨论，并对倍加ＯＵ噪声和可加白噪声下的系统进行了数值计算，所得结果对调节含噪声源的电路有一定指导意义。     

晕核~（11）Li，~（14）Be和~（17）B的进一步研究

在三体模型的基础上，采用汤川作用势，进行变分计算，进一步研究了晕核１１Ｌｉ，１４Ｂｅ和１７Ｂ的基态性质，给出了晕中子密度分布的一个解析表达式．理论计算结果与最新的实验数据一致．     

重离子碰撞两体关联输运理论──Ⅰ．理论模型：相干态表象的构造与基本运动方程

应用相干态表象和两体关联动力学，建立了非相对论重离子碰撞两体关联输运理论ＴＢＣＴＴ（Ｔｗｏ—ＢｏｄｙＣｏｒｒｅｌａｔｉｏｎＴｒａｎｓｐｏｒｔＴｈｅｏｒｙ）．这一理论包括了时间相关的平均场．泡利阻塞和两体碰撞效应，它能够描述重离子碰撞过程中非均匀核物质的演化、涨落效应和碎裂的动力学形成．     

BF3计数管阵列灵敏度标定和X光干扰观测

在黑洞靶实验中，加μｓ高压门和铅屏蔽体后，强Ｘ光辐射对ＢＦ３计数管阵列的干扰得到抑制同时，给出了ＢＦ３计数管阵列灵敏度在位标定结果。     

YBa2Cu3O7膜1／f噪声的测量

建立了一套测量样品电压涨落噪声的频谱分析系统，用此系统观察到超导ＹＢａ２Ｃｕ３Ｏ７取向模在正常态下反常大的１／ｆ噪声，并发现不同结构形貌的样品噪声水平有明显差异。     

HgBCO和PrBCO的正常态的1/f噪声研究

在１００ ～３００Ｋ温度范围内测量了Ｈｇ１２１２ 相块材和薄膜样品的正常态的１／ｆ 噪声,结果显示高质量薄膜的噪声水平为１０４ 量级,已和ＹＢＣＯ 外延膜及单晶相近．还测量了ＰｒＢａ２Ｃｕ３Ｏ７ － δ（ＰｒＢＣＯ） 微桥样品１／ｆ 噪声的尺寸依赖性,发现在ａｂ 面上,存在着与涨落相关的特征尺度,约为１０２μｍ 的量级．样品宽度降到该尺寸以下时,噪声水平急剧下降．在两个体系中,实验结果均和ＤｕｔｔａＨｏｒｎ 热激活模型进行了比较．     

掺Ba的Bi—sr—Cu—O的单晶Raman散射研究

利用Ｒａｍａｎ散射研究了Ｂｉ２Ｓｒ２－ｘＢａｘＣｕＯｙ（ｘ＝０，０．２，０．４）单晶样品的声子振动性质。实验结果表明，在Ｂｉ２Ｓｒ２－ｘＢａｘＣｕＯｙ体的Ｒａｍａｎ谱中主要出现以下几个频率的特征振动模，即１９６，３００，４６０，６２５和６６０ｃｍ＾－１；而频率为１９６，３００，６２５，６６０ｃｍ＾－１的特征峰的强度随着Ｂａ掺杂量的增加而增加。在早期的工作中，我们曾经研究过Ｂａ的掺杂对Ｂｉ２２０１相     

轻丰中子素￣（11）Li，￣（14）Be和￣（17）B的三体动力学

在任中洲、徐躬耦提出的三体模型~［１］基础上，对试探波函数进行了改进。利用关联密度函数研究了~（１１）Ｌｉ，~（１４）Ｂｅ和~（１７）Ｂ的内部结构和粒子关联，定性地找到了支持中子晕结构的证据。     

点噪声源在近程声场中传播损失的仿真研究

在分层介质条件下，用本征声线法仿真计算了点声源这距离噪声场的传播损失曲线，仿真结果表明，其传播损失不仅依赖于声速分布，海区深度，海底反射特性等环境条件，也依赖于声源及接收水听器的深度，声传播损失显著不同于球面波衰减规律，其传播损失率差别可达８ｄＢ，这表明在测量舰船目标的辐射噪声声源级时必要的声场校正测量是必须的。     

A study of noise reduction by acoustic shock waves

I.IntroductionAcousticshockwavcs(ASW)isanimportantphcnomcnoninnonlinearacoustics.Experimentalrcsultshavcshownthatwhenanaircraftcngincinletopcratesneartheson-iccondition,vcrystrongnoisegcncratedbythcfanscanbcreduccdgreat1yowingtothcformationofASWatthcthroatofthcin1etll].ASWisadiscontinuityofacousticvaria-bles,whichisdifTcrcntfromthcshockwavesoccurringinhighspcedsteadyflowinducts.Theformer'sintensityismuch1cssthanthelattcr's.Furthcrmorc,thepositionandintensityofASWisalwayschangedwithtime.l…     

The power spectrum and correlation of flow noise for an axisymmetric body in water

Understanding the physical features of the flow noise for an axisymmetric body is important for improving the performance of a sonar mounted on an underwater platform. Analytical calculation and numerical analysis of the physical features of the flow noise for an axisymmetric body are presented and a simulation scheme for the noise correlation on the hydrophones is given. It is shown that the numerical values of the flow noise coincide well with the analytical values. The main physical features of flow noise are obtained. The flow noises of two different models are compared and a model with a rather optimal fore-body shape is given. The flow noise in horizontal symmetry profile of the axisymmetric body is non-uniform, but it is omni-directional and has little difference in the cross section of the body. The loss of noise diffraction has a great effect on the flow noise from boundary layer transition. Meanwhile, based on the simulation, the noise power level increases with velocity to approximately the fifth power at high frequencies, which is consistent with the experiment data reported in the literature. Furthermore, the flow noise received by the acoustic array has lower correlation at a designed central frequency, which is important for sonar system design.     

Identification of deterministic chaos by an information-theoretic measure of the sensitive dependence on the initial conditions

One of the most difficult problems in the field of non-linear time series analysis is the unequivocal characterization of a measured signal. We present a practicable procedure which allows to decide if a given time series is pure noise, chaotic but distorted by noise, purely chaotic, or a Markov process. Furthermore, the method gives an estimate of the Kolmogorov-Sinai (KS) entropy and the noise level. The procedure is based on a measure of the sensitive dependence on the initial conditions which is called ε-information flow. This measure generalizes the concept of KS entropy and characterizes the underlying dynamics. The ε-information flow is approximated by the calculation of various correlation integrals.     

Structural organization of the needle complex of the type III secretion apparatus of Shigella flexneri

The secretion apparatus known as the needle complex (NC) from the bacterium Shigella flexneri was studied by single particle electron microscopy. The isolated intact NC appears in projection to be composed of a basal body consisting of seven rings and a protruding needle appendage. A comparison of averaged projections of the intact NC and its fragments revealed the organization of the NC into several major subcomplexes. One of these lacks an inner membrane ring of the basal body but still presents the needle appendage attached to four upper rings. The position of the needle appendage within these rings is variable, suggesting that the dissociated component is necessary for stabilizing the needle appendage. Averaged images of the subcomplex lacking the inner membrane basal rings show a thicker extension at the base of the needle appendage, called the socket. This socket was also found to be present in images of the basal body fragment isolated from mutants lacking the mxiH and mxiI genes. This suggests that the socket is not composed of MxiH and MxiI subunits, which form the needle appendage. A symmetry analysis of the basal body top view projections indicated that a peripheral protein component of the inner membrane ring is present in a ring with 24 copies, in contrast to the Salmonella typhimurium NC. A model is presented in which the NC is only associated to the outer- and inner-membranes with its first and seventh ring, respectively.     

Time-delayed phase-control for suppression of the flow-induced noise from an open cavity

A flow over an open cavity causes a cavity resonance, which is a feedback mechanism between the acoustic waves and the pressure fluctuation of the cavity flow. Previous research on the reduction of the cavity resonance has focused on suppressing the flow disturbance. This paper presents a time-delayed phase-control method to reduce the global noise of the cavity. Acoustic feedback of the cavity noise, which amplifies the flow disturbance, can be generally reduced by this control method, regardless of the flow physics. The positions of the sensors and the actuator are determined to increase the control efficiency. Experiments show that this control method reduces the peak of the flow oscillation by suppressing the acoustic feedback.     

开式轴流风扇气动噪声预测

本文采用LES/FW-H的匹配方法,研究了开式轴流风扇内部旋涡流动特征及其与叶片表面干涉引起的气动噪声之间的联系,同时进行了远场噪声预测,探讨了叶轮不同表面辐射噪声时的频谱分布特征.研究结果表明,开式轴流风扇吸力面附近形成的叶尖涡和前缘分离涡在吸力面叶片表面相应位置形成大压力波动,形成主要噪声源;叶片吸力面的辐射噪声可以通过改善吸力面附近的旋涡流动来降低;低速轴流叶轮由叶轮壁面辐射的噪声以宽频成分为主.     

Design of an acoustic enclosure with duct silencers for the heavy duty diesel engine generator set

Diesel engine generator sets in heavy industry plants and residential/official buildings can cause serious noise problems. In this paper, a low noise diesel engine generator set is developed through constructing an acoustic enclosure with ventilation duct silencers that effectively block the acoustic flow but guarantee good thermal flow. Acoustic design of the enclosure, which is initially layout by rule of thumb, is evolved systematically through numerical reanalysis procedure, based on indirect boundary element method (IBFM) with a commercial acoustic analysis code. The cooling performance of the acoustically determined enclosing structure is checked and confirmed through numerical heat flow analysis. The acoustic and cooling performances of the developed low noise diesel engine generator set are confirmed by the experiment.     

Numerical investigation of the interaction of the turbulent dual-jet and acoustic propagation

In order to study the interaction between two independent jets, a three-dimensional(3D) transient mathematical model is developed to investigate the flow field and acoustic properties of the two-stream jets. The results are compared with those of the single-stream jet at Mach number 0.9 and Reynolds number 3600. The large eddy simulation(LES) with dynamic Smagorinsky sub-grid scale(SGS) approach is used to simulate the turbulent jet flow structure. The acoustic field is evaluated by the Ffowcs Williams–Hawkings(FW-H) integral equation. Considering the compressibility of high-speed gas jets, the density-based explicit formulation is adopted to solve the governing equations. Meanwhile, the viscosity is approximated by using the Sutherland kinetic theory. The predicted flow characteristics as well as the acoustic properties show that they are in good agreement with the existing experimental and numerical results under the same flow conditions available in the literature. The results indicate that the merging phenomenon of the dual-jet is triggered by the deflection mechanism of the Coanda effect, which sequentially introduces additional complexity and instability of flow structure. One of the main factors affecting the dual-jet merging is the aperture ratio, which has a direct influence on the potential core and surrounding flow fluctuation. The analysis on the noise pollution reveals that the potential core plays a fundamental role in noise emission while the additional mixing noise makes less contribution than the single jet noise. The overall sound pressure level(OASPL) profiles have a directive property, suggesting an approximate 25° deflection from the streamwise direction, however, shifting toward lateral direction of about 10° to 15° in the dual-jet. The conclusion obtained in this study can provide valuable data to guide the development of manufacturing-green technology in the multi-jet applications.     

Investigation of the spatial correlations of flow noise in vector hydrophone towed linear array

Following the wall pressure spectrum of the turbulent boundary layer developed by Corcos, a method in the frequency-wavenumber space was presented to analyze the flow noise in the vector hydrophone towed linear array. The general forms of the acoustic pressure and particle velocity in the flow noise field were obtained, and the spatial correlations of the flow noise were calculated. The numerical analysis results based on wavenumber integration show that： （1） The spatial correlations of flow noise drops rapidly with increasing axial separation between the elements, so the flow noise received by different vector hydrophones usually sampled in a half-wavelength rate can be considered as independent; （2） The flow noise is highly correlated in the radial direction at low frequency, and only those of high frequency componet can be neglected.