燃气热水器噪声特性及降噪研究

燃气热水器噪声严重影响居民舒适性。为了了解热水器噪声特性,找到热水器噪声问题并提出针对性降噪方案,本文在半消声室对某型号热水器进行噪声测试,得到原型机的噪声特性,提出顶部进风和增加消声导流罩的降噪方案。通过测试发现:原型机在最大负荷和正常负荷的半球面平均声功率为61.5 d B(A)和58.3 d B(A),且电磁噪声、风机噪声、燃烧系统噪声和空腔共振噪声在热水器腔体相互作用,形成多个峰值频率。进风方式由背面进风改为顶部进风降噪效果明显,其平均半球面声功率在最大负荷和正常负荷降幅分别为5.6 d B(A)和4.7 d B(A)。同时在中低频段声压级降幅明显,高频也有一定降低。增加消声导流罩虽然能降低高频噪声,但是流通面积小,阻力大,使总体降噪效果不明显。     

Electrochemically mediated reduction of horseradish peroxidase by 1,1'-ferrocenedimethanol in organic solvents

Cyclic voltammetry is an efficient means of analyzing the catalytic reduction of H2O2 at immobilized horseradish peroxidase (HRP)-Eastman AQ 55 electrodes in the presence of 1,1'-ferrocenedimethanol as a one-electron reversible cosubstrate. This system was employed to study the kinetics of the reduction of compound II of HRP in a number of organic solvents. An electrocatalytic response was detected in methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, 2-butanone, 1,2-propanediol, acetonitrile, ethyl acetate, and ethylene glycol. Unusual bell-shaped variations of the peak or plateau catalytic current with the substrate concentration were observed in all solvents tested. The results obtained in methanol, acetonitrile, and 1-propanol were analyzed using the model developed by Saveant (Limoges, B.; Saveant, J.-M.; Yazidi, D. J. Am. Chem. Soc. 2003, 125, 9192-9203). The values of k3Gamma0 and K3,M, where k3 = k3,1k3,2/(k3,-1 + k3,2), Gamma0 is the surface concentration of active enzyme, and K3,M = (k3,-1 + k3,2)/k3,1, were determined. The values of k3Gamma0 for the mediated reduction of compound II of HRP in methanol, 1-propanol, and acetonitrile (in the presence of 5% aqueous buffer) were not affected by the solvent dielectric constant but decreased with solvent hydrophobicity. The value of K3,M obtained in methanol was similar to that obtained for [Os(bpy)2pyCl]2+ in aqueous buffer.     

High-precision laser spectroscopy D/H and 18O/16O measurements of microliter natural water samples

Newly available gas analyzers based on off-axis integrated cavity output spectroscopy (OA-ICOS) lasers have been advocated as an alternative to conventional isotope-ratio mass spectrometers (IRMS) for the stable isotopic analysis of water samples. In the case of H2O, OA-ICOS is attractive because it has comparatively low capital and maintenance costs, the instrument is small and field laboratory portable, and provides simultaneous D/H and 16O/18O ratio measurements directly on H2O molecules with no conversion of H2O to H2, CO, or H2/CO2-water equilibration required. Here we present a detailed assessment of the performance of a liquid-water isotope analyzer, including instrument precision, estimates of sample memory and sample mass effects, and instrumental drift. We provide a recommended analysis procedure to achieve optimum results using OA-ICOS. Our results show that, by using a systematic sample analysis and data normalization procedure routine, measurement accuracies of +/-0.8 per thousand for deltaD and +/-0.1 per thousand delta18O are achievable on nanoliter water samples. This is equivalent or better than current IRMS-based methods and at a comparable sample throughput rate.     

Synthesis of graphene soluble in organic solvents by simultaneous ether-functionalization with octadecane groups and reduction

Octadecane-functionalized graphene (OD-G) soluble in organic solvents was produced by combining the Hummers process for graphite oxidation and a simultaneous ether-functionalization and reduction approach with 1-bromooctadecane in pyridine and dimethylformamide (DMF). The exfoliated OD-Gs were testified to be monolayer sheets by transmission electron microscope (TEM) and atomic force microscopy (AFM). The functionalization with octadecane (OD) groups and the effective deoxygenation of graphene oxide (GO) were confirmed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It is proved that the effective reduction and functionalization of GO could be simultaneously completed during the refluxing process. The functionalization with OD groups can effectively prevent the aggregation of GO during the reduction.     

Interfacial stability of graphene-based surfaces in water and organic solvents

The mass production of graphene and graphene oxide (GO) is essential for its use in commercial products. To improve its processing in the solution, dispersion behavior of graphene-based materials and their colloidal stability must be further understood. This study used all-atom molecular dynamics simulations to understand how electrostatics, van der Waals interactions, and hydrogen bonding affect the exfoliation and stability of three-layered graphene as a function of oxidation and solvent. Water, methanol, and ethanol were chosen as solvents due to their various dispersion behaviors. Our study indicated that (1) both surface oxidation level and solvent type can heavily influence the stability and (2) a decrease in interlayer vdW interactions, an increase in GO–solvent electrostatic interactions, and an increase in GO–solvent hydrogen bonding are important factors that can facilitate the dissolution of GO.     

Modified dissolved organic matter fractionation technique for natural water

A technique to fractionate dissolved organic materials (DOMs) from low DOM water (<5mg/l) was developed by using triple columns of DAX-8 adsorption resin, one column of AG-MP-50 cationic resin, and another column of WA 10 weak anionic resin in sequence. The procedure was then applied to fractionate water samples obtained at various sampling locations throughout two surface water treatment plants (WTPs) in central New Jersey to study its effectiveness, DOM occurrence, and variation along treatment units. The treatment plants utilize different treatment methods, hence producing variability in DOM fractions suitable for examining the procedure's effectiveness. This procedure was compared with current fractionation protocols and proved to be accurate in fractionation of low DOM water.     

输气管道气体流经阀门气动噪声产生机理分析

为区分输气管道泄漏音波与阀门噪声,为输气管道音波法泄漏检测提供理论依据及数据库、控制阀门噪声提供解决办法,从音波产生机理角度采用CFD软件耦合专业声学软件方法对输气管道气体流经阀门产生的气动噪声进行研究,建立气动噪声模型,探究气动噪声产生机理及传播、衰减规律。在CFD（Computational Fluid Dynamics）软件中采用大涡湍流模型对气体流经阀门时的瞬态流场求解分析,获得流场分布如脉动压力、脉动速度数据;将CFD计算所得数据导入专业声学软件进行联合仿真,生成气动噪声源项,包括偶极子声源及四极子声源,建立气动噪声产生传播模型,求解输气管道气体流经阀门的气动噪声。     

Absorption of water into organic solvents used for electrochemistry under conventional operating conditions

Many solvents used for electrochemistry can be dried to <1 × 10(-3) M water content by storing the solvents over 3 ? molecular sieves in a nitrogen or argon atmosphere. However, as soon as the solvents are placed in an electrochemical cell, the water content increases significantly. Karl Fischer coulometric titrations were conducted on several predried solvents commonly used for electrochemistry (acetonitrile, dichloromethane, N,N-dimethylformamide, and dimethyl sulfoxide) in a controlled-humidity environment (30%, 50%, and 70% relative humidity) to determine the rate of moisture uptake into the organic solvents when used under typical electrochemical conditions (either in an electrochemical cell under a nitrogen atmosphere or in an electrochemical cell directly exposed to the atmosphere). The results in this study give guidelines for estimating the water content of organic solvents under conventional electrochemical operating conditions.     

Fast and simple reduction of graphene oxide in various organic solvents using microwave irradiation

The fabrication of graphene has been widely studied and chemical reduction is considered the most suitable approach to achieve large-scale production and graphene functionalization due to its versatility of chemical routes. We report here a fast and simple reduction of graphene oxide in various organic solvents using microwave irradiation. The reduction can be completed in several minutes, and the oxygen content and conductivity (10,000 S/m) of the reduced graphene oxide were comparable to the previously reported results which reported between 1 hr and 24 hrs for the reduction. We also found that an amide group containing a solvent like NMP or DMF reduced graphene oxide (GO) more effectively than did other solvents. Further, free radicals generated from NMP significantly enhanced deoxygenation of graphene oxide. Moreover, this approach is a non-toxic and environmentally-friendly method to obtain highly conductive reduced GO for a wide range of applications including graphene-based composites, batteries, and electrodes for super-capacitors.     

用气相色谱法对水中有机磷农药的测定

本文采用固相萃取法预处理,然后用带有火焰光度检测器(FPD)的气相色谱仪测定有机磷农药。结果表明,该法具有简单、快速、准确的持点。     

Engineering manganese oxide/nanocarbon hybrid materials for oxygen reduction electrocatalysis

Manganese oxides are cost-effective and green materials with rich electrochemical properties. Continuous research efforts have been undertaken to obtain MnO _x materials with improved activity and stability for catalyzing the oxygen reduction reaction (ORR). Here, we have developed a novel ORR catalyst by nucleation and growth of Mn₃O₄ nanoparticles on graphene oxide (GO) sheets interconnected by electrically conducting multi-walled carbon nanotubes (MWCNTs). X-ray near edge absorption structure (XANES) spectroscopy revealed the partially reduced nature of GO and strong chemical coupling between the nanoparticles and the GO sheets. Incorporation of MWCNTs was found to improve the activity and stability of the hybrid by imparting higher conductivity to the hybrid material. Furthermore, surface oxidation of the manganese oxide nanoparticles through a calcination step was found to increase the density of ORR active sites. The strongly coupled and electrically interconnected Mn₃O₄/nanocarbon (Mn₃O₄/Nano-C) hybrid is one of the most active and stable manganese oxide-based ORR catalysts and shows promise for electrochemical energy conversion applications.      

On-line analysis of organic components in fine and ultrafine particles by photoionization aerosol mass spectrometry

A new method, photoionization aerosol mass spectrometry (PIAMS), is described for real-time analysis of organic components in airborne particles below approximately 300 nm in diameter. Particles are focused through an aerodynamic lens assembly into the mass spectrometer where they are collected on a probe in the source region. After a sufficient amount of sample has been collected, the probe is irradiated with a pulsed infrared laser beam to vaporize organic components, which are then softly ionized with coherent vacuum ultraviolet radiation at 118 nm (10.5 eV). Since the photon energy is close to the ionization energies of most organic compounds, fragmentation is minimized. Both aliphatic and aromatic compounds of atmospheric relevance are detected and quantified in the low- to midpicogram range. The photoionization signal intensity increases linearly with the amount of material sampled and is independent of particle size. The fragmentation induced by laser desorption is greater than that observed with thermal vaporization, suggesting that the internal energy imparted by the former is greater. Although some molecular fragmentation is observed, mass spectra from common sources of ambient organic aerosol are distinguishable and consistent with previous off-line measurements by gas chromatography/mass spectrometry. These results illustrate the potential of PIAMS for molecular characterization of organic aerosols in ambient and smog chamber measurements.     

Metrological aspects of natural gas analysis by the chromatographic method

We consider the metrological characteristics of the chromatographic method for determination of the component content of natural gas according to GOST 23781- 87. We note the disadvantages inherent in the calibration method recommended by the GOST standard. We present the results of measurements of the composition of natural gas obtained on the high-precision chromatographic system at the All-Union Scientific-Research Institute of Metrology, which makes it possible to solve problems of certification of natural gas samples at the level of primary standards and to transfer the concentration scale for the components in natural gas from the standard chromatographs to working chromatographs. We establish that the figures of merit for the precision of the Institute's apparatus are not inferior to those for the apparatus of the US National Institute of Standards and Technology.Translated from Izmeritel'naya Tekhnika, Vol. 38, No. 4, pp. 62–65, April, 1995.     

H/D exchange- and mass spectrometry-based strategy for the thermodynamic analysis of protein-ligand binding

The equilibrium unfolding properties of four model protein systems were characterized using SUPREX (stability of unpurified proteins from rates of H/D exchange). SUPREX is an H/D exchange- and mass spectrometry-based technique for measuring the free energy (DeltaGf) and m-value (deltaDeltaGf/delta[denaturant]) associated with the folding/unfolding reaction of a protein. The model proteins in this study (calmodulin, carbonic anhydrase II, RmlB, Bcl-xL) were chosen to test the applicability of SUPREX to the thermodynamic analysis of larger (> approximately 15 kDa) or multidomain proteins. In the absence of ligand, DeltaGf and m-values for these proteins could not be evaluated using the conventional data acquisition and analysis methods previously established for SUPREX. However, ligand-bound forms of the proteins were amenable to conventional SUPREX analyses, and it was possible to evaluate reasonably accurate and precise binding free energies of selected ligands. In some cases, protein-ligand dissociation constants (Kd values) could also be ascertained. The SUPREX-derived binding free energies and Kd values evaluated here were in good agreement with those reported on the same complexes using other techniques.