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排序方式: 共有610条查询结果,搜索用时 31 毫秒
591.
592.
文章运用2010~2014年度沪深两市A股上市公司的相关数据,首先检验了审计意见与内部控制缺陷修正之间的相关性,结果表明上年收到“不清洁”审计意见的企业在当年更有可能进行内控缺陷的整改与修正;进一步通过分组回归发现,高管中具有财务背景特征的成员比例越高,进行缺陷整改的概率更大,一方面表明外部审计非标准审计意见对内部控制治理效用可能赖于管理层的配合,另一方面也折射出高管人力资源有效配置的重要性。而对披露缺陷修正信息的企业进行跟踪研究,发现这类企业在后续年度仍然会收到“不清洁”的审计意见,反映出这些上市公司的缺陷整改可能浮于表面,并不是实施有效的。 相似文献
593.
Julie Sucharová Marie Holá 《International journal of environmental analytical chemistry》2013,93(7):712-727
Moss (Pleurozium schreberi) was investigated as biomonitor of atmospheric polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Samples were collected at a distance of 10, 50 and 100 m from a highway and were seasonally collected in a forest stand near a regional background air pollution station situated approximately 30 km from the highway. The samples from the background area were dried using two different techniques in parallel, air-drying and freeze-drying. Simultaneous pressurised liquid extraction of PAHs and PCBs was performed, followed by purification using gel permeation chromatography of the crude extract. The concentration of the 15 most important Environmental Protection Agency (EPA) PAHs was determined by gas chromatography coupled with ion-trap mass spectrometry with a selected ion storage acquisition programme, and the PCB concentrations were determined using a mass spectrometer operated in tandem mass spectrometry (MS/MS) mode. Acceptable recoveries and quality parameters for PAHs and PCBs were achieved with the use of pressurised liquid extraction followed by gel permeation chromatography. The detection limit was <0.76 ng g?1 for PAHs and <0.04 ng g?1 for PCBs. Possible contamination of the moss samples by 3-ring PAHs and PCBs in the atmosphere was found during air drying. Increased PAH and PCB concentrations caused by car engine exhausts and by asphalt and oil evaporation were found near the highway. Generally, the PAH and PCB concentrations in moss decreased exponentially with distance from the highway. The organic compound concentrations close to the background station showed seasonal fluctuations corresponding to the fluctuations in the local air temperature and particle concentration. 相似文献
594.
Anne-Lise Marie Cédric Przybylski Florence Gonnet Régis Daniel Rémi Urbain Guillaume Chevreux Sylvie Jorieux Myriam Taverna 《Analytica chimica acta》2013
The present study describes a reproducible and quantitative capillary zone electrophoresis (CZE) method, which leads to the separation of nine forms (native, oxidized and glycated) of human serum albumin (HSA). In an attempt to identify the different species separated by this CZE method, the capillary electrophoresis was coupled to mass spectrometry using a sheath liquid interface, an optimized capillary coating and a suitable CE running buffer. CE-MS analyses confirmed the heterogeneity of albumin preparation and revealed new truncated and modified forms such as Advanced Glycation End products (AGEs). Assignment of the CZE peaks was carried out using specific antibodies, carboxypeptidase A or sample reduction before or during the CE separation. Thus, five HSA forms were unambiguously identified. Using this CZE method several albumin batches produced by slightly different fractionation ways could be discriminated. Furthermore, analyses of HSA preparations marketed by five pharmaceutical industries revealed that two therapeutic albumins, including that marketed by LFB, contained the highest proportion of native form and lower levels of oxidized forms. 相似文献
595.
The enantiomers of two acylamine fungicides (metalaxyl and benalaxyl) were separated by EKC using CDs as chiral selectors. The use of 15 mM succinyl-γ-CD for metalaxyl and 5 mM succinyl-β-CD for benalaxyl dissolved in a 50 mM 2-morpholinoethanesulfonic acid buffer (pH 6.5), enabled the chiral separation of metalaxyl enantiomers in 11.5 min with a resolution of 3.1 and the enantiomeric separation of benalaxyl in 7.5 min with a resolution close to 15. Under these conditions, the two enantiomers of each of the chiral compound studied were also separated from folpet, very commonly present in fungicide formulations containing metalaxyl or benalaxyl. The analytical characteristics of the two developed methods were studied in terms of precision, linearity, selectivity, limits of detection (LODs) and limits of quantitation (LOQs) showing their suitability for the determination of these compounds in commercial agrochemical formulations. Finally, the development of an in-capillary preconcentration strategy allowed the detection of enantiomeric impurities up to 1.2% in commercial products labeled as enantiomerically pure in metalaxyl-M. 相似文献
596.
A green analytical method was developed for the analysis of sugar-based depilatories. Three independent partial least squares (PLS) regression models were built for the direct determination of glucose, fructose and maltose without any sample pretreatment based on their attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectra. The models showed adequate prediction capabilities with root-mean-square-errors of prediction ranging from 7.04 to 12.55 mg sugar g−1 sample. As a reference procedure, gradient liquid chromatography with on-line infrared detection, employing background correction based on cubic smoothing splines, was used. The analysis revealed changes in the sugar concentration due to the formulation process as compared to information on the ingredients provided by the manufacturers. Although fructose, glucose and sucrose were declared to be used for the production of depilatories, in the final products only fructose, glucose and maltose were determined. This fact was attributed to pH and temperature conditions employed during the production process as well as to the use of glucose syrup instead of crystalline glucose. The present ATR-FTIR-PLS method enables an accurate, cheap and fast determination without solvent consumption or toxic waste generation and offers therefore a green screening alternative to methods employing chromatographic techniques. 相似文献
597.
We search for isotropic stochastic gravitational-wave background (SGWB) in the International Pulsar Timing Array second data release. By modeling the SGWB as a power-law, we find very strong Bayesian evidence for a common-spectrum process, and further this process has scalar transverse (ST) correlations allowed in general metric theory of gravity as the Bayes factor in favor of the ST-correlated process versus the spatially uncorrelated common-spectrum process is 30 ± 2. The median and the 90% equal-tail amplitudes of ST mode are ${{ \mathcal A }}_{\mathrm{ST}}={1.29}_{-0.44}^{+0.51}\times {10}^{-15}$, or equivalently the energy density parameter per logarithm frequency is ${{\rm{\Omega }}}_{\mathrm{GW}}^{\mathrm{ST}}={2.31}_{-1.30}^{+2.19}\times {10}^{-9}$, at frequency of 1 year−1. However, we do not find any statistically significant evidence for the tensor transverse (TT) mode and then place the 95% upper limits as ${{ \mathcal A }}_{\mathrm{TT}}\lt 3.95\times {10}^{-15}$, or equivalently ${{\rm{\Omega }}}_{\mathrm{GW}}^{\mathrm{TT}}\lt 2.16\times {10}^{-9}$, at frequency of 1 year−1. 相似文献
598.
红外背景抑制与弱小目标的检测算法 总被引:10,自引:1,他引:9
强噪声背景下红外图像中弱小目标的检测一直是研究的重点和难点。根据弱小目标、背景干扰和噪声在红外图像中的差异,研究了三种低信噪比条件下红外图像中弱小目标的检测算法:小波变换、数学形态学、Top—hat算子,分别给出了处理的图像和相应的数据。仿真实验表明:这三种检测算法能十分有效地提高信噪比、增强目标、抑制背景杂波和去除噪声干扰,对信噪比约为2的弱小目标检测能得到很好的结果。三种算法所得结果一致,而且处理速度快,适合于实时图像处理和目标探测。 相似文献
599.
Eckehard W. Mielke 《General Relativity and Gravitation》2008,40(6):1311-1325
The curvature-squared model of gravity, in the affine form proposed by Weyl and Yang, is deduced from a topological action
in 4D. More specifically, we start from the Pontrjagin (or Euler) invariant. Using the BRST antifield formalism with a double
duality gauge fixing, we obtain a consistent quantization in spaces of double dual curvature as classical instanton type background. However,
exact vacuum solutions with double duality properties exhibit a ‘vacuum degeneracy’. By modifying the duality via a scale breaking term, we demonstrate that only Einstein’s equations with an induced cosmological constant emerge for the topology of the macroscopic background. This may have repercussions on the problem of ‘dark energy’ as well as ‘dark matter’ modeled
by a torsion induced quintaxion. 相似文献
600.
Subir Sarkar 《General Relativity and Gravitation》2008,40(2-3):269-284
Several kinds of astronomical observations, interpreted in the framework of the standard Friedmann–Robertson–Walker cosmology,
have indicated that our universe is dominated by a Cosmological Constant. The dimming of distant Type Ia supernovae suggests
that the expansion rate is accelerating, as if driven by vacuum energy, and this has been indirectly substantiated through
studies of angular anisotropies in the cosmic microwave background (CMB) and of spatial correlations in the large-scale structure
(LSS) of galaxies. However there is no compelling direct evidence yet for (the dynamical effects of) dark energy. The precision CMB data can be equally well fitted without dark energy
if the spectrum of primordial density fluctuations is not quite scale-free and if the Hubble constant is lower globally than
its locally measured value. The LSS data can also be satisfactorily fitted if there is a small component of hot dark matter,
as would be provided by neutrinos of mass ∼0.5 eV. Although such an Einstein–de Sitter model cannot explain the SNe Ia Hubble
diagram or the position of the “baryon acoustic oscillation” peak in the autocorrelation function of galaxies, it may be possible
to do so, e.g. in an inhomogeneous Lemaitre–Tolman–Bondi cosmology where we are located in a void which is expanding faster
than the average. Such alternatives may seem contrived but this must be weighed against our lack of any fundamental understanding
of the inferred tiny energy scale of the dark energy. It may well be an artifact of an oversimplified cosmological model,
rather than having physical reality. 相似文献