单座容积超大型厅堂顶部材料吸声效率的研究

单座容积超过国家标准推荐上限值两倍及以上的厅堂定义为超大型厅堂,这类厅堂在观演建筑中越来越多。在超大型厅堂的音质设计中,为了控制厅堂内的混响时间,顶部往往需要布置吸声材料。借助厅堂音质计算机模拟分析软件,以三个超大型厅堂模型的混响时间为例,探讨了吸声材料布置在顶部时的吸声效率。研究结果表明,顶部材料的吸声效率与声源到顶面的距离和声源的频率均呈负相关,而材料自身的吸声系数对顶部吸声效率的影响较小。     

EASE3．0高级运用之声场设计

声场设计的主要内容 声场设计是电声设计的核心。当我们绘制好模型，确立好了厅堂基本的吸声材料之后，就可以进行声场设计了。通常，声场设计的主要内容是根据各种厅堂的结构类型进行音箱的选型和分布形式的设计，后期还要根据声场的不同情况对建声环境和装饰材料做最终调整。     

小型流动演出的扩声系统设计

小型流动]出的特点小型流动]出的声场条件优劣难测,]出环境千差万别。在设备运输和安装方面还经常受指定时间的制约,如此等等都给流动]出的音响设计提出了很多挑战性的难题。为适应环境变化,需要音响师思维敏捷、动作迅速,选择合适的工作地点组织设备安装,做到有条不紊、忙中不乱。还要认真对周围的声场环境观察分析,利用现场的实验手段准确判断出声场的缺陷,努力运用电声设备的功能去弥补声场的不足。例如用混响器人为地调整混响时间,用均衡器去消除反馈点来提升总的增益,调整音箱位置与方向以保证最佳的声场均匀度。如遇较大的]出场地,流…     

厅堂音质评价的新参量MTF与IACC

一、引言 厅堂音质评价参量可以以为是介于主观听觉感受与客观的可测量的声场参数之间的一座“桥梁”,它的发展不仅取决于心理声学进展,而且还与新技术新方法的应用有关。在进行厅堂传输特性的研究方面,近年来所发展的MTF调制传输函数方法已经得到了广泛的重视,它能够对厅堂内的语言传输特性作快速的定量分析,这种分析不仅包括了厅堂中各种因素如背景噪声、混响声等对语言清晰度的影响,而且对11个国家的语言特性均有良好的一致性,使得厅堂音质的定量化评价又多了一个有力的工具。另一方面,多重相关因子分析技术在厅堂音质研究中的应用,已…     

厅堂音质辅助设计方法的应用研究

对厅堂音质辅助设计方法的发展历程、研究现状、基础理论和发展趋势进行了概述和讨论,介绍了厅堂的音质要求和设计参量,指出为确保厅堂音质达到设计预定的客观参量,在厅堂声学方案设计完成后,还需采用计算机模拟技术和(或)声学缩尺模型等辅助手段,对声场进行预测,以此为依据对方案不足之处进行修正,并举例说明;同时指出,由于声场复杂性和实验设备及过程的局限性,具体应用时,还需结合理论分析和工程实践进行判断。     

厅堂声场的有源控制

本文对利用电声方法的厅堂声场控制技术进行阐述，着重论述了声场支援的方法和系统，最后好几种典型的声场控制系统的实例。     

影院建筑声学标准与测量(下)

2.声场分布及声缺陷的测量: 在影院及其它厅堂中,为使观(听)众区内任意位置都能清楚地听到对白、语言、音乐、动效等内容,故声场分布的均匀性也极为重要。 在相关标准中规定“在观众区内各测试点间声压级的最大值与最小值之差不大于6dB,最大值与平均值之差不大于3dB。”     

一种高仿真度的采样混响效果器

为逼真地模仿著名音乐厅和教堂的声场效果,人们设计了采样混响效果器。首先对这些厅堂进行实地测试,使脉冲声信号将其声场的反射声阵列采集下来,然后再通过数字信号处理器将其逼真地模拟出来,这就是采样混响的基本原理。由于真实厅堂的声场的反射声阵列十分密集,早期的数字信号处理器运算速度较低,无法处理如此海量的数据。所以,逼真地实时模仿厅堂的混响效果在电脑插件上很难完成,即使有一些专业级的硬件混响器能做到,价位也非常昂贵。     

孔隙分布不均匀性对陶瓷材料强度的影响

由于工艺特殊性,一些陶瓷材料中不可避免地存在孔隙、夹杂等缺陷,且孔隙、夹杂大多分布不均匀,而这种不均匀性对陶瓷材料力学性能有较大影响.根据分布不均匀性特点,以陶瓷材料中孔隙分布为例,定义了均匀度对孔隙分布的不均匀性进行量化,提出了利用图像处理确定均匀度的方法.根据图像处理结果,将材料分为富含孔隙的等效基体相和不含孔隙的等效颗粒相,利用相互作用直推估计(IDD)法研究了材料强度随均匀度的变化关系.结果表明:孔隙分布均匀度对材料强度有较大影响,孔隙分布的均匀度越小,材料强度越低,并且在均匀度低于0.2时造成强度的剧烈降低,当均匀度大于0.5时,对材料强度的影响很小.     

颐和园德和园大戏楼修缮前后声场对比测试与分析

为促进德和园大戏楼声场真实性的保护,在修缮前后分别对大戏楼声场的混响时间、脉冲响应、声场不均匀度进行了测试。通过修缮前后的数据对比分析,探明了看戏廊封闭及临时看台对大戏楼声场的影响;对德和园声学真实性的修缮效果给出评价结果;也为史料记载的观演行为提供了科学佐证。     

More on the reaction of graphite/potassium with water

The first stage intercalation compound of graphite with K°, C₈K, will react with water at room temperature to yield a solid product containing graphite inserted with potassium cations and water molecules. Temperature-variant ¹H NMR shows that both T₁ and T₂ decrease as temperature decreases from 298 K to 213 K (T₁ > T₂ at these temperatures) with an activation energy of 0.25 eV.

Starting with a C₈K/D₂O product, one can isotopically exchange with H₂O to yield a product with 17% H₂O after 48 hours at room temperature, showing the inserted species are not kinetically “encapsulated.” X-ray diffraction, thermogravimetric analysis, and nuclear magnetic resonance are used to distinguish the graphite compound from a mixture of graphite and hydrates of potassium hydroxide.     

Ab initio calculation on fullerene C32 and Its Derivative

In this paper, we studied the equilibrium geometries, the electronic structures and the binding energies of fullerene C₃₂ as well as its hydrogenates and fluorides interactions by the SCF Hartree-Fock calculations using the latest version of GAMESS of ab initio programs. The fullerene C₃₂ is found to have a ¹A₂' closed-shell ground state in D_3d symmetry or a ¹E_U singlet state in D_3h symmetry. It is predicted to be easy to add some hydrogen or fluorine atoms to the C₃₂ cage and to produce a series of derivatives C₃₂H_2n,C₃₂F_2n (n=l, 3, 6), in which C₃₂H₂,C₃₂F₂ (D_3d), C₃₂H₆^a,C₃₂F₆^c(D_3h) are more stable. We suggest that this implies that the vertex of triplet pentagons of the C₃₂ cage is an activation site for addition.     

Conformations and Electronic Structure of Fullerene C24 and C26 Molecules

The quantum mechanical investigations of fullerene C₂₄, C₂₆, C₂₈ molecule conformers are performed in the framework of the point set group theory and semiempirical PM3 configuration interaction and the MNDO, AMI methods. The main criterion of stability of calculated fiillerene molecules we state the lowest total energy of various isomers and conformers that appears due to the Jahn-Teller distortion. The most stable occurs C₂₄ (D₆ symmetry) conformation with term¹A₁ and open shell C₂₆ (D_3h) conformation with term⁵A₁.     

Molecular orbital studies on the rings composed of D2d C36 cages

The structures and electronic properties of the rings composed of D_2d C₃₆ cages are investigated using the semi-empirical AM1 molecular orbital method with full geometric optimization. It is found that most of the converged structures are more stable after the rings are formed. Strain plays an important role in the stability of the fullerene rings. Other factors influencing the stability are also discussed, such as the type of the bonded carbon atoms and the size of retained aromatic domains. Comparison of the structures and electronic properties are made between the C₃₆-rings and those composed of D_6h C₃₆ isomers.     

Computations of metal-covered C60 and C70

Semiempirical quantum-chemical PM3 calculations are reported for a new class of exohedral metallo-fullerenes – metal-coated or metal-covered fullerenes: C₆₀M_n and C₇₀M_n. The exohedral species have been observed in gas phase, however, their geometrical and electronic structures are not known yet. Relatively-even metal-atom distributions over the fullerene rings are considered – such regular forms are computed for M = Be, Mg, Al. Three selected types of stoichiometries are treated in particular: C₆₀M₁₂/C₇₀M₁₂ (metal atoms above all pentagons), C₆₀M₂₀/C₇₀M₂₅ (metal atoms above all hexagons), and C₆₀M₃₂/C₇₀M₃₇ (metal atoms above all rings). If an odd number of electrons should result (Al), the related cation is computed, or one metal atom added or removed. This interesting arrangement above the rings is possible only for some types of atoms, while other elements are localized above bonds or atoms, or inside the cage, or even react and destroy the cage. Other limitation comes from the parametrization of the computational technique used – the PM3 semiempirical method is parametrized only for some selected metals. Metal-layer atomization heats are suggested as a stability measure. Structural characteristics are also presented and interesting reductions of the cage symmetry are found. Their relationship to Jahn–Teller effect is discussed. The metal covered fullerenes can represent models for metal catalysis in the nanotube synthesis and could eventually lead to new interesting materials.     

A STUDY ON THE THERMAL STABILITY TO 1000°C OF VARIOUS CARBON ALLOTROPES AND CARBONACEOUS MATTER BOTH UNDER NITROGEN AND IN AIR

The thermal behavior of graphite, C₆₀ fullerene, fullerene black (carbon soot containing fullerenes), extracted fullerene black and diamond has been analyzed to 1000°C by TGA-DTA (thermogravimetric analysis and differential thermal analysis) under a nitrogen flow at a heating rate of 20°C/min. Very small weight losses have been recorded in the case of graphite and diamond. Furthermore no diamond graphitization has been observed. The sublimation of pure C₆₀ and the fullerene fraction of fullerene black (both pristine and extracted) has been observed and discussed.

The combustion reaction in air flow of graphite, C₆₀ and C₇₀ fullerenes, fullerene black (both unextracted and extracted), carbon nanotubes and diamond has been studied by TGA-DTA at a heating rate of 20°C/min. C₇₀ fullerene and fullerene black have been found to be the most reactive carbon materials with O₂. The role played by C₇₀ in the degradation of fullerites has been discussed. Among the carbon materials examined, the best resistance to O₂ attack has been shown by diamond and carbon nanotubes. The behavior of graphite is intermediate between diamond and fullerene blacks. The behavior of C₆₀ fullerene appears closer to that of graphite although it appears to be more reactive with O₂. Samples of graphite and carbon blacks N375 and N234 have been studied by TGA-DTA in air flow before and after a radiation treatment with neutrons or γ radiation. The effect of the radiation damage in the combustion reaction of these carbon materials has been discussed.     

Crystal Structure of C60 and C70 Compounds

Fullerene intercalated compounds are the most intensively examined molecular materials to exhibit superconducting, ferromagnetic, optical non-linear and other properties. the fullerene C₆₀ or C₇₀ serve usually as electron acceptors in these materials. Although the electron acceptor properties of the fullerene are similar to those of the weak organic acceptors, the fullerene forms various C₆₀-based materials, namely clathrates, charge-transfer complexes and weak, molecular complexes. the search for cation species for fullerene-based materials is one of the routes towards progress in the design of materials with interesting physical properties.

Physical properties of the fullerene-derived molecular compounds are determined mainly by their crystal structure packing. Relatively large cavities in the fullerene solid can easily accommodate small units like solvent molecules or electron-donor organic compounds. An intercalation with these species is usually accompanied either by a lowering in crystal symmetry or by a change in the stacking arrangement of the C₆₀ spheres. These factors influence the interactions between fullerene (host) and an organic molecule (guest). Charge transfer between the electron donor molecule and the fullerene is usually weak and is hindered by unfavourable steric factors; it does not correlate with the ionization potential of the donor.

In this paper we present characteristic structures of one-, two-, and three-component fullerene compounds or else the structures of fullerene clathrates, neutral (van der Waals) complexes and ionic charge-transfer complexes. One can conclude that the stability and properties of the fullerene-based derivatives are defined by the steric compatibility between the three-dimensional donor and the spherical or elongated fullerene.     

吸声材料布置对报告厅声场的影响

目前我国有大量报告厅面临声学改造,而吸声材料的不同布置位置会对室内音质造成较大影响。文章以重庆大学建卒厅为例,对5个声学改造阶段的室内混响时间、声压级、语言传输指数进行了模拟与实测,研究了吸声材料的布放位置对报告厅内声场分布特征及大厅典型声学参数的影响。在该报告厅内,相同吸声材料布放在吊顶的不同区域,模拟的中频混响时间下降值可相差13.8%。在侧墙安装吸声材料后,各接收点声压级衰减的最大差值可达3.2 dB(A),且语言清晰度受混响时间与早期反射声的影响较大。未来报告厅的声学设计应优化吸声材料的布放位置,合理控制声场不均匀度。     

Which Fullerene Is Appropriate to Host C20? A Molecular Modeling Study

Molecular mechanics (MM) and molecular dynamics (MD) study of fullerene complexes of the short-lived “smallest fullerene” C₂₀ with icosahedral C₆₀, C₈₀, C₁₄₀, C₁₈₀, and C₂₄₀ of I_h, I_h, I, I_h, I_h symmetry, respectively, using CVFF and ESFF forcefields revealed that the most stable complexes can be formed only if the intershell distance between fullerenes is similar to that in graphite or in experimentally observed buckyonions. The fullerenes C₁₄₀ and C₁₈₀ are the smallest suitable candidates to form such complexes with C₂₀. Similarly to the stabilization of short-lived cyclobutadiene or benzyne in hemicarcerands, C₂₀ is expected to be stabilized inside the C₁₄₀ and C₁₈₀ cages which would enable a deeper understanding of the highly nonplanar system of conjugated bonds of this exotic molecule.     

Preparation of Fullerene Derivatives by Resistive Heating With Graphite Crucible

We report here the preparation of both endohedral fullerenes (La°C₈₂, La₂°C₈₀) and exohedral fullerenes (C₆₀ (C_mO_n)) by the resistive heating with graphite crucible filled with lanthanum oxide.