New log-t-based CFAR detectors for a non-homogeneous Weibull Background

Based on new log-t-based detectors, we propose to improve the detection performances of the log-t-Constant False Alarm Rate (log-t-CFAR) detector for a non-homogeneous Weibull background. This paper is twofold. We first resort to the Automatic Constant False Censoring Rate (CFCR) algorithm, which guarantees an accurate rejection of an a priori unknown number of outliers. That is, we introduce two hybrid detectors by coupling the log-t-CFAR algorithm to the Maximum Likelihood-CFCR (MLE-CFCR) algorithm, yielding the H-MLE/log-t-CFAR detector, and to the Weber-Haykin Constant False Censoring Rate (WH-CFCR) algorithm, yielding the H-WH/log-t-CFAR detector. Then, based on the Variability Index (VI) as a background discriminator, we propose the Switching VI-log-t-CFAR (SVI-log-t-CFAR) detector. Thus, depending on the background heterogeneity, this detector has the capability to switch automatically to the appropriate detector; namely, the log-t-CFAR detector, in case of a homogeneous background, either one of the hybrid detectors, in case of the presence of outliers or the Automatic Edge Censoring log-t-CFAR (AEC-log-t-CFAR) detector, in case of the presence of a clutter edge. We assess the efficiency of these detectors through intensive Monte Carlo simulations. We show that, while no additional detection performances are observed in a homogeneous background, the new detectors exhibit a significant CFAR gain with respect to the log-t-CFAR detector in the presence of any inhomogeneity within the reference window.     

Neural and vascular variability and the fMRI-BOLD response in normal aging

Neural, vascular and structural variables contributing to the blood oxygen level-dependent (BOLD) signal response variability were investigated in younger and older humans. Twelve younger healthy human subjects (six male and six female; mean age: 24 years; range: 19–27 years) and 12 older healthy subjects (five male and seven female; mean age: 58 years; range: 55–71 years) with no history of head trauma and neurological disease were scanned. Functional magnetic resonance imaging measurements using the BOLD contrast were made when participants performed a motor, cognitive or a breath hold (BH) task. Activation volume and the BOLD response amplitude were estimated for the younger and older at both group and subject levels. Mean activation volume was reduced by 45%, 40% and 38% in the elderly group during the motor, cognitive and BH tasks, respectively, compared to the younger. Reduction in activation volume was substantially higher compared to the reduction in the gray matter volume of 14% in the older compared to the younger. A significantly larger variability in the intersubject BOLD signal change occurred during the motor task, compared to the cognitive task. BH-induced BOLD signal change between subjects was significantly less-variable in the motor task-activated areas in the younger compared to older whereas such a difference between age groups was not observed during the cognitive task. Hemodynamic scaling using the BH signal substantially reduced the BOLD signal variability during the motor task compared to the cognitive task. The results indicate that the origin of the BOLD signal variability between subjects was predominantly vascular during the motor task while being principally a consequence of neural variability during the cognitive task. Thus, in addition to gray matter differences, the type of task performed can have different vascular variability weighting that can influence age-related differences in brain functional response.     

基坑土钉支护结构多元体系可靠度分析

为了解决岩土介质高度不确定性和变异性引起的工程问题,通过"实用分析法"计算出基坑土钉支护结构各种破坏模式的失效概率,从而应用Stevenson-Moses法得出基坑多元结构体系失稳概率的界限范围,真实地反映了工程的稳定状态。     

Modelling Fruit Characteristics During Apple Maturation: A Stochastic Approach

At present, mathematical models to predict the change of fruit quality attributes during apple maturation are deterministic and do not take into account the large natural variability of fruit quality attributes during the growing season. In this work a stochastic system approach was developed to describe the quality evolution of fruit. The basic dynamics of fruit quality evolution was represented by means of a stochastic system, in which the initial conditions and the model parameters were specified as random variables together with their probability density functions. A fundamental approach from stochastic systems theory was used to compute the propagation of the probability density functions of fruit quality attributes, which requires the numerical solution of the Fokker–Planck equation.     

Development and evaluation of a diffusive gradients in a thin film technique for measuring ammonium in freshwaters

A new diffusive gradients in a thin film (DGT) technique, using Microlite PrCH cation exchange resin, was developed and evaluated for measuring NH₄–N in freshwaters. Microlite PrCH had high uptake (>92.5%) and elution efficiencies (87.2% using 2 mol L⁻¹ NaCl). Mass vs. time validation experiments over 24 h demonstrated excellent linearity (R² ≥ 0.996). PrCH-DGT binding layers had an extremely high intrinsic binding capacity for NH₄–N (∼3000 μg). NH₄–N uptake was quantitative over pH ranges 3.5–8.5 and ionic strength (up to 0.012 mol L⁻¹ as NaCl) typical of freshwater systems. Several cations (Na⁺, K⁺, Ca²⁺ and Mg²⁺) were found to compete with NH₄–N for uptake by PrCH-DGT, but NH₄–N uptake was quantitative over concentration ranges typical of freshwater (up to 0.012 mol L⁻¹ Na⁺, 0.006 mol L⁻¹ K⁺, 0.003 mol L⁻¹ Ca²⁺ and 0.004 mol L⁻¹ Mg²⁺). Effective diffusion coefficients determined from mass vs. time experiments changed non-linearly with electrical conductivity. Field deployments of DGT samplers with varying diffusive layer thicknesses validated the use of the technique in situ, allowed deployment times to be manipulated with respect to NH₄–N concentration, and enable the calculation of the diffusive boundary layer thickness. Daily grab sample NH₄–N concentrations were observed to vary considerably independent of major rainfall events, but good agreements were obtained between PrCH-DGT values and mean grab sample measurements of NH₄–N (C_DGT:C_SOLN 0.83–1.3). Reproducibility of DGT measurements in the field was good (relative standard deviation < 11%). Limit of detection was 0.63 μg L⁻¹ (equivalent to 0.045 μmol L⁻¹) based on 24 h deployments.     

心血管病人的心率变异性

目的研究植物神经系统对心血管功能的影响和作用.方法采用频谱分析的方法进行临床观察.结果给缺血性心脏病病人使用东莨菪硷贴剂24 h后,所有心率变异性参数均显著增加,缺血发作的频率及持续时间均减少.在急性心肌梗死时,频谱中所有的心率变异性指数(LF,HF,VLF和ULF4个区域)均呈典型性降低,其中标准差s<20ms时,致命性室性心律失常发生率显著升高,频谱图上不同的特征改变对心衰的判断预后亦有意义.心率变异性参数分析反映了心血管病人植物神经系统功能状态,副交感神经占优势时,则疾病趋于改善,而交感神经活性增强时则疾病预后不良.结论可将心率变异性的频谱分析法用于临床诊断及疾病的风险评价.     

基于结构面粗糙度随机场表征的抗剪强度变异性

岩体结构面抗剪强度参数具有变异性是客观事实,而受限于室内外直剪试验成本而导致抗剪强度变异性指标获取困难是目前制约岩质边坡可靠度评价发展的主要原因之一。鉴于此,本文提出了一种利用少量实测结构面粗糙度曲线样本和岩块物理力学参数,结合JRC-JCS剪切强度模型、随机场理论和非侵入式离散元数值试验,获取结构面抗剪强度参数变异性指标的方法。将此方法应用于某隧道进口段岩质边坡可靠度评价中,研究发现：（1）该岩质边坡主控结构面粗糙度纵坐标方差为0.012 5 cm2,相关距离为0.75 cm,生成的随机粗糙度曲线与实测样本相似;（2）结构面粘聚力和内摩擦角均值分别为0.427 MPa和54.9°,标准差分别为0.229 MPa和4.47°,变异系数分别为53.63%和8.14%;（3）此边坡稳定性系数服从正态分布,失稳概率为2.8%,可靠度为1.52。     

On a family of risk measures based on proportional hazards models and tail probabilities

In this paper, we explore a class of tail variability measures based on distances among proportional hazards models. Tail versions of some well-known variability measures, such as the Gini mean difference, the Wang right tail deviation and the cumulative residual entropy are, up to a scale factor, in this class. These tail variability measures are combined with tail conditional expectation to generate premium principles that are especially useful to price heavy-tailed risks. We study their properties, including stochastic consistency and bounds, as well as the coherence of the associated premium principles.