Finite sample properties of estimators of spatial autoregressive models with autoregressive disturbances

The article investigates the finite sample properties of estimators for spatial autoregressive models where the disturbance terms may follow a spatial autoregressive process. In particular we investigate the finite sample behavior of the feasible generalized spatial two-stage least squares (FGS2SLS) estimator introduced by Kelejian and Prucha (1998), the maximum likelihood (ML) estimator, as well as that of several other estimators. We find that the FGS2SLS estimator is virtually as efficient as the ML estimator. This is important because the ML estimator is computationally burdensome, and may even be forbidding in large samples, while the FGS2SLS estimator remains computationally feasible in large samples. Received: 20 January 2001 / Accepted: 31 August 2001     

High-speed path-length scanning with a multiple-pass cavity delay line

Techniques for high-speed delay scanning are important for low-coherence interferometry, optical coherence tomography, pump probe measurements, and other applications. We demonstrate a novel scanning delay line using a multiple-pass cavity. Differential delays are accumulated with each pass so that millimeter delays can be generated with tens of micrometer mirror displacements. With special design criteria, misalignment sensitivity can be dramatically reduced. The system is demonstrated to scan 6 m/s at 2-kHz repetition rates. Real-time optical coherence tomography imaging with 500 pixel images at four frames/s is performed. Using a Cr:forsterite laser source, we obtained axial image resolutions of 6 microm with 92-dB sensitivity.     

Benecol®—一种有效、安全降低血清胆固醇水平的独特食品配料

在世界范围内,心血管疾病——冠心病(CHD)、中风、周围动脉疾病的患病数量正在增加.据世界卫生组织(WHO)统计估计,每年大约有1600万人死于各种形式的心血管疾病.高血清胆固醇是导致各种心血管疾病的主要危险因素之一.近来,通过饮食方法如功能食品来降低胆固醇水平已经引起了极大关注.植物甾醇和植物甾烷醇是动物胆固醇的植物等价物,因为它们在植物细胞中的作用与胆固醇在动物细胞中的作用是一样的.如果在日常的饮食当中含有足量的植物甾醇或植物甾烷醇,则它们可以有效地降低胃肠道中对胆固醇的吸收量,从而降低血清胆固醇浓度.植物甾烷醇酯是世界上第一个基于植物甾醇的降低胆固醇的商业食品配料.1995年芬兰首次生产出添加植物甾烷醇酯的降胆固醇食品.如今,在全世界的24个国家销售Benecol品牌的各种植物甾烷醇酯强化食品,包括植物黄油、酸奶、牛奶、橙汁、通心粉等.Benecol食品含有植物甾烷醇酯,专门针对想通过饮食方法降低血清胆固醇水平的人群.植物甾烷醇酯的安全性已经得到了严格的安全性测试,并得到了40多项人体临床研究的证实.国际专业团体已经充分肯定了植物甾烷醇酯食品的降低胆固醇的功效.     

A consistent modelling methodology for secondary settling tanks in wastewater treatment

The aim of this contribution is partly to build consensus on a consistent modelling methodology (CMM) of complex real processes in wastewater treatment by combining classical concepts with results from applied mathematics, and partly to apply it to the clarification-thickening process in the secondary settling tank. In the CMM, the real process should be approximated by a mathematical model (process model; ordinary or partial differential equation (ODE or PDE)), which in turn is approximated by a simulation model (numerical method) implemented on a computer. These steps have often not been carried out in a correct way. The secondary settling tank was chosen as a case since this is one of the most complex processes in a wastewater treatment plant and simulation models developed decades ago have no guarantee of satisfying fundamental mathematical and physical properties. Nevertheless, such methods are still used in commercial tools to date. This particularly becomes of interest as the state-of-the-art practice is moving towards plant-wide modelling. Then all submodels interact and errors propagate through the model and severely hamper any calibration effort and, hence, the predictive purpose of the model. The CMM is described by applying it first to a simple conversion process in the biological reactor yielding an ODE solver, and then to the solid-liquid separation in the secondary settling tank, yielding a PDE solver. Time has come to incorporate established mathematical techniques into environmental engineering, and wastewater treatment modelling in particular, and to use proven reliable and consistent simulation models.     

Reduction of a single granule drying model: An essential step in preparation of a population balance model with a continuous growth term

The development of a Population Balance Model (PBM) for a pharmaceutical granule drying process requires a continuous growth term; the latter actually represents the drying process as the moisture content is the internal coordinate of the PBM. To establish such a PBM, a complex drying model for a single granule needs reduction in complexity. The starting point is a detailed model that describes the drying behavior of single pharmaceutical granules. A Global Sensitivity Analysis (GSA) was performed to detect the most sensitive degrees of freedom in the model as these need to be retained in the reduced model. Simulations of the complex drying model were, in a next phase, used to develop the reduced model, which describes the decrease of the moisture content in function of the gas temperature. The developed reduced model was then included in a Population Balance Equation (PBE) to describe the drying behavior of a population of granules. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1127–1138, 2013     

Behavior Measurement, Analysis, and Regime Classification in Car Following

This paper first reports a data acquisition method that the authors used in a project on modeling driver behavior for microscopic traffic simulations. An advanced instrumented vehicle was employed to collect driver-behavior data, mainly car-following and lane-changing patterns, on Swedish roads. To eliminate the measurement noise in acquired car-following patterns, the Kalman smoothing algorithm was applied to the state-space model of the physical states (acceleration, speed, and position) of both instrumented and tracked vehicles. The denoised driving patterns were used in the analysis of driver properties in the car-following stage. For further modeling of car-following behavior, we developed and implemented a consolidated fuzzy clustering algorithm to classify different car-following regimes from the preprocessed data. The algorithm considers time continuity of collected driver-behavior patterns and can be more reliably applied in the classification of continuous car-following regimes when the classical fuzzy C-means algorithm gives unclear results     

EXAFS study on the reactions between iron and fulvic acid in acid aqueous solutions

Iron(III) competes with trace metals for binding sites on organic ligands. We used X-ray absorption fine structure (EXAFS) spectroscopy to determine the binding mode and oxidation state of iron in solutions initially containing only iron(III) and fulvic acid at pHs 2 and 4. EXAFS spectra were recorded at different times after sample preparation. Iron was octahedrally configured with inner-sphere Fe-O interactions at 1.98-2.10 A, depending on the oxidation state of iron. Iron(III) formed complexes with fulvic acid within 15 min. Iron(III) was reduced to iron(II) with time at pH 2, whereas no significant reduction occurred at pH 4. No signs of dimeric/trimeric hydrolysis products were found in any of the solution samples (<0.45 microm). However, the isolated precipitate of the pH 2 sample (>0.45 microm) showed Fe...Fe distances, indicating the presence of tightly packed iron(III) trimers and/or clusters of corner-sharing octahedra. It is suggested that the binding mode of iron(III) to fulvic acid at low pH may be phase-dependent: in solution mononuclear complexes predominate, whereas in the solid phase hydrolyzed polynuclear iron(III) complexes form, even at very low pH values. The observed pH dependence of iron(III) reduction was consistent with expected results based on thermodynamic calculations for model ligands.     

A seamless ground truth detection for enhancing localization on mobile robots

Robot localization mechanism is an essential feature to determine the position of the corresponding robot within an environment, particularly in the field of Standard Platform League (SPL) at the RoboCup. Despite the available input from the onboard sensors, the ground truth information is necessary for a real-time localization system. This study proposes an efficient color-based segmentation scheme using an overhead projective camera with an autonomous calibration procedure. This enhances the system robustness against lighting changes and different labeling setups for the field environment. The experimental results show that the proposed method localizes and recognizes objects with a detection rate of 96.4%.