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231.
Summary Volatile organic compounds (VOC) are present in indoor air at concentrations generally higher than in outdoor air. In this study VOC concentrations in the air of two classrooms differing in insulation, and in the expired air of children in them, were investigated. Qualitative and quantitative determinations were done by gas chromatography-mass spectrometry techniques. Differences in the concentrations of VOC in indoor air and in the expired air of the children were linked to the endogeneous or exogeneous origin of the compounds, to the activities of the children and to the quality of indoor-outdoor air exchanges. 相似文献
232.
Yichuan Zhao 《Statistics & probability letters》2011,81(5):603-610
Accelerated failure time (AFT) models are useful regression tools for studying the association between a survival time and covariates. Semiparametric inference procedures have been proposed in an extensive literature. Among these, use of an estimating equation which is monotone in the regression parameter and has some excellent properties was proposed by Fygenson and Ritov (1994). However, there is a serious under-coverage problem for small sample sizes. In this paper, we derive the limiting distribution of the empirical log-likelihood ratio for the regression parameter on the basis of the monotone estimating equations. Furthermore, the empirical likelihood (EL) confidence intervals/regions for the regression parameter are obtained. We conduct a simulation study in order to compare the proposed EL method with the normal approximation method. The simulation results suggest that the empirical likelihood based method outperforms the normal approximation based method in terms of coverage probability. Thus, the proposed EL method overcomes the under-coverage problem of the normal approximation method. 相似文献
233.
234.
Competitive adsorption on adsorptive solid-phase microextraction (SPME) fibres implies careful determination of operating
conditions for reliable quantitative analysis of VOCs in indoor air. With this objective, two analytical approaches, involving
non-equilibrium and equilibrium extraction, were compared. The average detection limit obtained for GC-MS analysis of nine
VOCs by the equilibrium method is 0.2 μg m−3, compared with 1.9 μg m−3 with the non-equilibrium method. The effect of the relative humidity of the air on the calibration plots was studied, and
shown to affect acetone adsorption only. Hence, the concentrations that can be accurately determined are up to 9 μmol m−3. The methods were then applied to indoor air containing different concentrations of VOCs. The non-equilibrium method, involving
short extraction time, can be used for detection of pollution peaks whereas equilibrium extraction is preferable for measurement
of sub-μg m−3 ground concentration levels.
相似文献
235.
We consider the asymptotic variance of vacancy (AVV) in the high intensity small-grain Boolean model. Subjecting the grains to rotations or, more generally, linear distortions gives rise to a function which maps distortion distributions to the AVV of the corresponding Boolean model. We mainly study continuity properties of this function, where we use the L1 Wasserstein metric on distortion distributions. An important role in the formulation and derivation of our results is played by notions of symmetry commonly used in multivariate analysis and stochastic simulation, such as conjugation-invariance and group models. 相似文献
236.
H.A. Eiselt 《European Journal of Operational Research》2012,216(3):563-572
This paper discusses the location or strengthening of cell phone towers so as to maximize service coverage and minimize the loss of communications if a natural disaster happens. This paper demonstrates that, under a high likelihood of destruction of antennas (towers), the customary method of maximizing coverage provides poor solutions as compared to the proposed method. In addition to the maximization of service coverage, the objectives of our model include the minimization of expected and worst-case losses. The model is applied to a region in the south of Chile that was stricken by one of the most destructive earthquakes registered in history. Computational results are provided for a variety of scenarios. 相似文献
237.
Although the broadcast television (TV) spectrum is currently open for unlicensed operation in the USA, a considerably large geographic area still remains excluded from the unlicensed operation due to potential interference to the licensed users. However, it might be possible to reuse primary spectrum within the protection contour if the frequency reuse occurs inside a building that shields radio signals and reduces interference to the primary system. Interference to outdoor licensed users from the indoor operations can be minimized if the unlicensed users adjust their transmit power according to their locations in the building. This paper presents an analysis and effectiveness evaluation of a novel cognitive radio (CR) system which enables CRs to access the licensed spectrum inside a building in the area within the protection contour. The system utilizes an indoor sensor network for (i) interference sensing, (ii) CR transmit power control, to limit the interference to the outdoor primary receiving antennas. Power control model of the indoor system has been developed to estimate safe transmit power for the indoor users. Two cases have been considered; single-user single-sensor (single indoor user and single sensor), and multi-user multi-sensor. Based on the power control model, a power control algorithm has been developed and its effectiveness is assessed through simulations. The algorithm is effective in realistic propagation scenarios, e.g. when internal partition walls and multipath fading are present. The outage probabilities in these propagation scenarios are found and the procedure of determining the transmit powers for CRs is presented. 相似文献
238.
简要介绍了MDAS组成、基本原理和组网方式;详细对比了MDAS和传统分布系统;详细介绍了MDAS低层建筑和中高层建筑应用场景覆盖方式;以实际案例对MDAS开通前后相关指标及2种建网方案成本分布进行了对比。 相似文献
239.
Indoor radon survey in dwellings of some regions in Yemen 总被引:1,自引:0,他引:1
A. H. Khayrat M. I. Al-Jarallah X. Fazal-ur-Rehman F. Abu-Jarad 《Radiation measurements》2003,36(1-6):449-451
Indoor radon survey in a total of 241 dwellings, distributed in some regions of Yemen was performed, using CR-39 based radon monitors. The objective of this radon survey is to get representative indoor radon data of three regions, namely Dhamar, Taiz and Hodeidah, situated at different altitudes above sea level. The radon concentrations varied from 3 to 270 Bqm−3 with an average of 42 Bqm−3. It was found that the average radon concentration in the surveyed areas increases with altitudes. The highest average radon concentration of 59 Bqm−3 was found in Dhamar city while the lowest average concentration of 8 Bqm−3 was found in Hodeidah city. 相似文献
240.
通过对调频共缆和同一模式下不同传输方式的比较,提出各种调频广播共缆传输方案,各地结合实际,因地制宜,选择适合的传输方案,让农村广播真正落实。 相似文献