Time filter

Source Type

Li X.,Beijing Municipal Institute of Labour Protection
Journal of the Acoustical Society of America | Year: 2017

Microperforated panels (MPPs) are efficient sound absorbers featuring microperforations with low porosity. Sound absorption occurs inside the perforations and their vicinity as well, which is represented with an end correction in the transfer impedance of the MPPs. Many empirical models for the end correction were derived from experiment or numerical simulation data. In order to validate these models, this paper presents an analytical solution of the end correction for sharp-edged circular perforations using viscothermal wave theory. The perforations are assumed to be periodically distributed and each perforation is associated with a square duct resulting from a periodic spatial partition. The velocity profile and the temperature field in each perforation are derived from the low reduced frequency model, which pose the boundary conditions to determine the modal coefficients of the acoustic, entropy, and viscous waves in the duct. An impedance end correction model is derived from the asymptotic expansion of the modal solution. It improves the conventional model by introducing a static flow resistance term to describe the energy dissipation due to the acoustic flow distortion outside the perforations. Numerical and experimental examples validate that the proposed model offers better prediction for the transfer impedance and the sound absorption of the MPPs. © 2017 Acoustical Society of America.

Tong D.Q.,National Oceanic and Atmospheric Administration | Tong D.Q.,Chinese Academy of Sciences | Dan M.,National Oceanic and Atmospheric Administration | Dan M.,Beijing Municipal Institute of Labour Protection | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2012

This study introduces an observation-based dust identification approach and applies it to reconstruct long-term dust climatology in the western United States. Long-term dust climatology is important for quantifying the effects of atmospheric aerosols on regional and global climate. Although many routine aerosol monitoring networks exist, it is often difficult to obtain dust records from these networks, because these monitors are either deployed far away from dust active regions (most likely collocated with dense population) or contaminated by anthropogenic sources and other natural sources, such as wildfires and vegetation detritus. Here we propose an approach to identify local dust events relying solely on aerosol mass and composition from general-purpose aerosol measurements. Through analyzing the chemical and physical characteristics of aerosol observations during satellite-detected dust episodes, we select five indicators to be used to identify local dust records: (1) high PM10 concentrations; (2) low PM2.5/PM10 ratio; (3) higher concentrations and percentage of crustal elements; (4) lower percentage of anthropogenic pollutants; and (5) low enrichment factors of anthropogenic elements. After establishing these identification criteria, we conduct hierarchical cluster analysis for all validated aerosol measurement data over 68 IMPROVE sites in the western United States. A total of 182 local dust events were identified over 30 of the 68 locations from 2000 to 2007. These locations are either close to the four US Deserts, namely the Great Basin Desert, the Mojave Desert, the Sonoran Desert, and the Chihuahuan Desert, or in the high wind power region (Colorado). During the eight-year study period, the total number of dust events displays an interesting four-year activity cycle (one in 2000-2003 and the other in 2004-2007). The years of 2003, 2002 and 2007 are the three most active dust periods, with 46, 31 and 24 recorded dust events, respectively, while the years of 2000, 2004 and 2005 are the calmest periods, all with single digit dust records. Among these deserts, the Chihuahuan Desert (59 cases) and the Sonoran Desert (62 cases) are by far the most active source regions. In general, the Chihuahuan Desert dominates dust activities in the first half of the eight-year period while the Sonoran Desert in the second half. The monthly frequency of dust events shows a peak from March to July and a second peak in autumn from September to November. The large quantity of dust events occurring in summertime also suggests the prevailing impact of windblown dust across the year. This seasonal variation is consistent with previous model simulations over the United States. © 2012 Author(s).

Fan W.,Beihang University | Xu Z.,Beijing University of Technology | Xu Z.,Beijing Municipal Institute of Labour Protection | Wang W.-X.,Hong Kong University of Science and Technology
Environmental Pollution | Year: 2014

Jinzhou Bay in Northern China has been seriously contaminated with metals due to the impacts of smelting activities. In this study, we investigated the relationship between metal accumulation in a deposit-feeding polychaete Neanthes japonica and metal concentration and geochemical fractionation (Cd, Cu, Pb, Zn and Ni) in sediments of Jinzhou Bay. Compared with the historical data, metals in the more mobile geochemical fraction (exchangeable and carbonate fractions) were gradually partitioned into the more stable fraction (Fe-Mn oxides) over time. Metal concentration and geochemical fractionation in sediment significantly affected metal bioavailability and accumulation in polychaetes, except for Ni. Metal accumulation in polychaetes was significantly influenced by Fe or Mn content, and to a lesser degree by organic matter. Prediction of metal bioaccumulation in polychaetes was greatly improved by normalizing metal concentrations to Mn content in sediment. The geochemical fractionation of metals in sediments including the exchangeable, organic matter and Fe-Mn oxides were important in controlling the sediment metal bioavailability to polychaetes. © 2014 Elsevier Ltd. All rights reserved.

Li X.,Beijing Municipal Institute of Labour Protection
Journal of the Acoustical Society of America | Year: 2010

This paper is concerned with the ensemble statistics of the dynamic responses of a random system subjected to harmonic excitations. Random point process theory is employed to derive general scaling laws with the Gaussian orthogonal ensemble assumption about the system natural frequencies. A scaled model is built to simulate the high-frequency vibrations of the original system. Specific forms of the scaling laws are presented for a mass-loaded plate regarding the scaling factors for the structural parameters. The ensemble statistics predicted from the scaled model are compared favorably with those obtained from the original system. © 2010 Acoustical Society of America.

Li X.,Beijing Municipal Institute of Labour Protection
Journal of the Acoustical Society of America | Year: 2010

This analysis presents a scaling approach to predict high-frequency mean responses of vibrating systems. The basis of the approach lies in the dynamic similitude between the original systems and the scaled models. A general scaling law is formulated using Skudrzyks mean-value theorem and its specific form is derived for the case of a flexural plate. Modal density is scaled down to reduce the computational cost in the high-frequency mean response prediction. Different scaling procedures are numerically experimented and some insights are given about the accuracy of the scaling approach as compared with a dense finite element analysis. © 2010 Acoustical Society of America.

Wang X.-W.,Zhengzhou University | Wang Z.-F.,Beijing Municipal Institute of Labour Protection
IET Conference Publications | Year: 2012

Current spam filtering algorithm based on artificial immune system considers little regarding to the good word attack, so in this paper, we put forward an immune-based good word attack spam filtering model called GWAIS, which uses the Mutual Information Difference as the evaluation function to discard the good words in the spam and the spam words in the normal email during the generation of the gene library, so that it can improve the quality of the antibody. The experimental results show that GWAIS has better classification performance than that of DTDEF(Danger Theory Based Junk Mail Dynamic Filtering System).

Li X.,Beijing Municipal Institute of Labour Protection
Journal of Sound and Vibration | Year: 2013

A scaling approach is proposed for the vibration analysis of line-coupled plates at high frequencies. It extends earlier scaling approaches for an isolated system to coupled systems. Based on the power flow balance in the plate assembly, a general scaling law is derived and a scaled model is built accordingly. Due to the dynamic similitude in a statistical sense, the scaled model is able to simulate the dynamics of the original system at high frequencies. Numerical examples validate the efficiency of the approach and suggest the application of finite element methods in the high-frequency vibration analysis. © 2013 Elsevier B.V. All rights reserved.

Shusheng B.,Beihang University | Shanshan Z.,Beihang University | Xiaofeng Z.,Beijing Municipal Institute of Labour Protection
Precision Engineering | Year: 2010

An annulus-shaped flexure hinge is composed of three or more beam flexure elements distributed in an annulus suitable for rotational application, such as laser tracking system and cell operation system. The load-deflection property of annulus-shaped flexure hinges can be analyzed by traditional beam deformation expressions or pseudo-rigid-body method accurately and effectively, but methods are incapable to choose the type of hinge and the key parameters in a quick and exact way. In order to avoid laborious design steps, dimensionless design graphs for a novel annulus-shaped flexure hinge and another two types are presented which are based on finite element analysis. Using these graphs as a design tool, designers can determine the optimal geometry, based on the stiffness and demanded rotational properties of annulus-shaped flexure hinge. Between the analyzed flexure hinges, a comparison is made on the basis of equal hinge functionality: rotational properties for different hinges. The result describes the maximum stiffness properties from different hinges in identical situations. The straight-compliant annulus-shaped flexure hinge is preferred for radius stiffness and rotation stiffness. The curved-compliant annulus-shaped flexure hinge has the best axial stiffness. The instances of using dimensionless design graph are given and results indicate that the relative error between dimensionless graph and design demand is below 4%. Using the dimensionless design graph, design process can be reduced in both time and complexity. © 2010 Elsevier Inc. All rights reserved.

Song Y.,Capital Medical University | Tang S.,Beijing Municipal Institute of Labour Protection
TheScientificWorldJournal | Year: 2011

Accumulating studies in animals have shown that nanoparticles could cause unusual rapid lung injury and extrapulmonary toxicity. Whether exposure of workers to nanoparticles may result in some unexpected damage as seen in animals is still a big concern. We previously reported findings regarding a group of patients exposed to nanoparticles and presenting with an unusual disease. The reported disease was characterized by bilateral chest fluid, pulmonary fibrosis, pleural granuloma, and multiorgan damage and was highly associated with the nanoparticle exposure. To strengthen this association, further information on exposure and the disease was collected and discussed. Our studies show that some kinds of nanomaterials, such as silica nanoparticles and nanosilicates, may be very toxic and even fatal to occupational workers exposed to them without any effective personal protective equipment. More research and collaborative efforts on nanosafety are required in order to prevent and minimize the potential hazards of nanomaterials to humans and the environment. Copyright © 2011 Yuguo Song and Shichuan Tang.

Wang Z.,Beijing Jiaotong University | Song B.,University of Science and Technology Beijing | Song B.,Beijing Municipal Institute of Labour Protection | Qin Y.,Beijing Jiaotong University | Jia L.,Beijing Jiaotong University
Physica A: Statistical Mechanics and its Applications | Year: 2012

We propose a cellular automation model to simulate team-moving behavior in bi-directional pedestrian flow. The moving rules for double-pedestrian teaming include the constraint that pedestrians remain on adjacent cells. Phase transition, critical density team number, velocitydensity, and flowdensity relationships are key component parts of the analysis. Simulations show that team-moving produces significant corridor capacity effects, and effects highly depend on the type of teaming behavior. In daily life, pedestrians prefer traverse teaming; under this bias, as teaming pedestrians increase in number, critical density reduces; that means traverse teaming will weaken the capacity of the corridor. The effect of traverse team-moving is nonlinear, and capacity will continually reduce as the team numbers increase; however, reduction rate will decay. We call this phenomenon, "the marginal utility of team-moving. © 2012 Elsevier B.V. All rights reserved.

Loading Beijing Municipal Institute of Labour Protection collaborators
Loading Beijing Municipal Institute of Labour Protection collaborators