multi-stage modeling

  • 文章类型: Journal Article
    我们定义并解释了用于电和磁刺激的场建模的准静态近似(QSA)。神经调节分析管道包括离散阶段,当计算给定刺激剂量在组织中产生的电场和磁场时,特别应用QSA。QSA简化了建模方程以支持易于处理的分析,增进理解,和计算效率。QSA在神经调制中的应用基于四个基本假设:(A1)在组织中没有波传播或自感应,(A2)线性组织特性,(A3)纯电阻组织,和(A4)非分散组织。由于这些假设,每个组织被分配一个固定的电导率,和简化的方程(例如,拉普拉斯方程)求解场的空间分布,它与字段的时间波形分离。认识到组织的电特性可能更复杂,我们解释了如何将QSA嵌入并行或迭代管道中,以对电导率的频率依赖性或非线性进行建模。我们调查了QSA在特定应用中的历史和有效性,比如微刺激,深部脑刺激,脊髓刺激,经颅电刺激,和经颅磁刺激.在使用QSA模型或测试其极限时,QSA在神经调节中的精确定义和解释对于严格至关重要。
    We define and explain the quasistatic approximation (QSA) as applied to field modeling for electrical and magnetic stimulation. Neuromodulation analysis pipelines include discrete stages, and QSA is applied specifically when calculating the electric and magnetic fields generated in tissues by a given stimulation dose. QSA simplifies the modeling equations to support tractable analysis, enhanced understanding, and computational efficiency. The application of QSA in neuromodulation is based on four underlying assumptions: (A1) no wave propagation or self-induction in tissue, (A2) linear tissue properties, (A3) purely resistive tissue, and (A4) non-dispersive tissue. As a consequence of these assumptions, each tissue is assigned a fixed conductivity, and the simplified equations (e.g. Laplace\'s equation) are solved for the spatial distribution of the field, which is separated from the field\'s temporal waveform. Recognizing that electrical tissue properties may be more complex, we explain how QSA can be embedded in parallel or iterative pipelines to model frequency dependence or nonlinearity of conductivity. We survey the history and validity of QSA across specific applications, such as microstimulation, deep brain stimulation, spinal cord stimulation, transcranial electrical stimulation, and transcranial magnetic stimulation. The precise definition and explanation of QSA in neuromodulation are essential for rigor when using QSA models or testing their limits.
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  • 文章类型: Journal Article
    评估暴露于低水平苯的职业人群的白血病风险。
    使用线性化多阶段(LMS)模型拟合来自中国苯队列研究的白血病发病率数据。个别苯暴露水平,尿S-苯基巯基尿酸(S-PMA)和反式,反式粘康酸(t,t-MA)是对来自中国工厂的98名接触苯的工人进行测量的。通过四舍五入累积苯浓度的四分位数(<3、3-5、5-12、≥12mg/m3·年,分别)。使用LMS模型评估苯诱发白血病的风险,并使用EPA模型和新加坡半定量风险评估模型对结果进行了验证。
    LMS模型显示,在四个暴露组中,白血病风险与累积浓度的增加呈正相关(额外的白血病风险分别为4.34、4.37、4.44和5.52×10-4;Ptrend<0.0001)。我们还发现,使用尿t估计的白血病风险,与S-PMA相比,LMS模型中的t-MA与空气中的苯估计的t-MA更相似。LMS模型估计的白血病风险在所有浓度下与新加坡半定量风险评估模型一致,在高浓度下(5-12,≥12mg/m3·年)与EPA模型一致,在低浓度(<3和3-5mg/m3·年)时超过EPA模型。然而,在所有四个苯暴露组中,这三种模型估计的白血病风险超过了EPA设定的致癌风险的最低可接受限值1×10-6.
    这项研究证明了源自中国苯队列的LMS模型在评估与低水平苯暴露相关的白血病风险方面的实用性,并提示在累积浓度低于3mg/m3·年时可能发生白血病风险。
    UNASSIGNED: To assess leukemia risk in occupational populations exposed to low levels of benzene.
    UNASSIGNED: Leukemia incidence data from the Chinese Benzene Cohort Study were fitted using the Linearized multistage (LMS) model. Individual benzene exposure levels, urinary S-phenylmercapturic acid (S-PMA) and trans, trans-muconic acid (t, t-MA) were measured among 98 benzene-exposed workers from factories in China. Subjects were categorized into four groups by rounding the quartiles of cumulative benzene concentrations (< 3, 3-5, 5-12, ≥12 mg/m3·year, respectively). The risk of benzene-induced leukemia was assessed using the LMS model, and the results were validated using the EPA model and the Singapore semi-quantitative risk assessment model.
    UNASSIGNED: The leukemia risks showed a positive correlation with increasing cumulative concentration in the four exposure groups (excess leukemia risks were 4.34, 4.37, 4.44 and 5.52 × 10-4, respectively; Ptrend < 0.0001) indicated by the LMS model. We also found that the estimated leukemia risk using urinary t, t-MA in the LMS model was more similar to those estimated by airborne benzene compared to S-PMA. The leukemia risk estimated by the LMS model was consistent with both the Singapore semi-quantitative risk assessment model at all concentrations and the EPA model at high concentrations (5-12, ≥12 mg/m3·year), while exceeding the EPA model at low concentrations (< 3 and 3-5 mg/m3·year). However, in all four benzene-exposed groups, the leukemia risks estimated by these three models exceeded the lowest acceptable limit for carcinogenic risk set by the EPA at 1 × 10-6.
    UNASSIGNED: This study demonstrates the utility of the LMS model derived from the Chinese benzene cohort in assessing leukemia risk associated with low-level benzene exposure, and suggests that leukemia risk may occur at cumulative concentrations below 3 mg/m3·year.
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    文章类型: Preprint
    我们定义并解释了用于电和磁刺激的场建模的准静态近似(QSA)。神经调节分析管道包括离散阶段,当计算给定刺激剂量在组织中产生的电场和磁场时,特别应用QSA。QSA简化了建模方程以支持易于处理的分析,增进理解,和计算效率。QSA在神经调节中的应用基于四个基本假设:(A1)在组织中没有波传播或自感应,(A2)线性组织特性,(A3)纯电阻组织,和(A4)非分散组织。由于这些假设,每个组织被分配一个固定的电导率,和简化的方程(例如,拉普拉斯方程)求解场的空间分布,它与字段的时间波形分离。认识到组织的电特性可能更复杂,我们解释了如何将QSA嵌入并行或迭代管道中,以对电导率的频率依赖性或非线性进行建模。我们调查了QSA在特定应用中的历史和有效性,比如微刺激,深部脑刺激,脊髓刺激,经颅电刺激,和经颅磁刺激.在使用QSA模型或测试其极限时,QSA在神经调节中的精确定义和解释对于严格至关重要。
    We define and explain the quasistatic approximation (QSA) as applied to field modeling for electrical and magnetic stimulation. Neuromodulation analysis pipelines include discrete stages, and QSA is applied specifically when calculating the electric and magnetic fields generated in tissues by a given stimulation dose. QSA simplifies the modeling equations to support tractable analysis, enhanced understanding, and computational efficiency. The application of QSA in neuro-modulation is based on four underlying assumptions: (A1) no wave propagation or self-induction in tissue, (A2) linear tissue properties, (A3) purely resistive tissue, and (A4) non-dispersive tissue. As a consequence of these assumptions, each tissue is assigned a fixed conductivity, and the simplified equations (e.g., Laplace\'s equation) are solved for the spatial distribution of the field, which is separated from the field\'s temporal waveform. Recognizing that electrical tissue properties may be more complex, we explain how QSA can be embedded in parallel or iterative pipelines to model frequency dependence or nonlinearity of conductivity. We survey the history and validity of QSA across specific applications, such as microstimulation, deep brain stimulation, spinal cord stimulation, transcranial electrical stimulation, and transcranial magnetic stimulation. The precise definition and explanation of QSA in neuromodulation are essential for rigor when using QSA models or testing their limits.
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  • 文章类型: Journal Article
    Collecting and sharing information about affected areas is an important activity for optimal decision-making in relief processes. Defects such as over-sending some items to affected areas and mistakes in transferring injured people to medical centers in accidents are due to improper management of this information. Because cloud computing as a processing and storage platform for big data is independent of the device and location and can also perform high-speed processing, its use in disasters has been highly regarded by researchers. In this environment, a three-stage dynamic procedure for evacuation operations and logistics issues is presented. The first stage of the proposed model is image processing and tweet mining in a cloud center in order to determine the disaster parameters. In stage II, a mixed-integer multi-commodity model is presented for the relief commodity delivery, wounded people transportation with capacity constraints, and locating of the possible on-site clinics and local distribution centers near disaster areas. In stage III, by using a system of equations, detailed vehicle load/unload instructions are obtained. Finally, the effectiveness of the proposed model on the data of an earthquake disaster in Iran is investigated. The results of comparing the proposed approach with a two-stage algorithm show that the total number of unsatisfied demand for all types of commodities in the proposed approach was better than the other. Also, the number of survivors in the three-stage model is significantly higher than in the two-stage one. The better performance of the proposed algorithm is due to the fact that online data is continuously available and that decisions such as sending relief items and dispatching are made more effectively.
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