MODIS‐derived visible atmospherically resistant index for monitoring chaparral moisture content

Time series of normalized difference indices (NDIs) derived from MODIS surface reflectance data provide potentially useful information for monitoring fuel moisture content (FMC) for fire risk assessment. The visible atmospherically resistant index (VARI) and normalized difference water index (NDWI) were compared for monitoring live FMC of chaparral shrublands. Regression coefficients are encouraging given disparate spatial resolutions of ground‐based FMC measurements and MODIS‐derived NDIs. VARI exhibited greater temporal co‐variability (0.79>r ²<0.94) and spatial robustness with FMC than NDWI, even though the former is based solely on visible waveband reflectance data.     

Design, fabrication, and testing of VDP MEMS pressure sensors

In this paper, a four-terminal piezoresistive sensor commonly known as a van der Pauw (VDP) structure is presented for its application to MEMS pressure sensing. In a recent study, our team has determined the relation between the biaxial stress state and the piezoresistive response of a VDP structure by combining the VDP resistance equations with the equations governing silicon piezoresistivity and has proposed a new piezoresistive pressure sensor. It was observed that the sensitivity of the VDP sensor is over three times higher than the conventional filament type Wheatstone bridge resistor. To check our theoretical findings, we fabricated several (100) silicon diaphragms with both the VDP sensors and filament resistor sensors on the same wafer so both the sensor elements have same doping concentration. Several diaphragms had VDP sensors of different sizes and orientations to find out their geometric effects on pressure sensitivity. The diaphragms were subjected to known pressures, and the pressure sensitivities of both types of sensors were measured using an in-house built calibration setup. It was found that the VDP devices had a linear response to pressure as expected, and were more sensitive than the resistor sensors. Also, the VDP sensors provided a number of additional advantages, such as its size independent sensitivity and simple fabrication steps due to its simple geometry.     

Design techniques for high-resolution current-mode sigma-deltamodulators

This paper describes techniques for the design of high-resolution oversampling analog-to-digital converters based on current memories. A key point is the reduction of nonlinearities, in particular those introduced by the current switches. A current-memory cell with very high precision and linearity has been designed and used in an experimental third-order Σ-δ modulator in a 0.8-μm digital CMOS process. A linearity of better than 14 b and a maximum signal-to-noise+distortion ratio (SNDR) of 80 dB has been measured for an oversampling ratio (OSR) of 64     

Higher‐order accurate time‐step‐integration algorithms by post‐integration techniques

In this paper, a framework to construct higher‐order‐accurate time‐step‐integration algorithms based on the post‐integration techniques is presented. The prescribed initial conditions are naturally incorporated in the formulations and can be strongly or weakly enforced. The algorithmic parameters are chosen such that unconditionally A‐stable higher‐order‐accurate time‐step‐integration algorithms with controllable numerical dissipation can be constructed for linear problems. Besides, it is shown that the order of accuracy for non‐linear problems is maintained through the relationship between the present formulation and the Runge–Kutta method. The second‐order differential equations are also considered. Numerical examples are given to illustrate the validity of the present formulation. Copyright © 2001 John Wiley & Sons, Ltd.     

Investigation of coated droplets in an optical trap: Raman-scattering, elastic-light-scattering, and evaporation characteristics

Single optically levitated microparticles were investigated by Raman spectroscopy. The particles were composed of di-octyl-phthalate (DOP) and glycerol; these substances are not mixable and form a two-phase droplet. Measurements of the Raman spectrum confirm the formation of droplets containing both chemical species. The spectra show strong input and output structural resonances as expected. If the particle is in resonance, the field inside the particle is enhanced, and most of the inelastically scattered light is emitted from molecules close to the droplet rim. If the particle does not fulfill the resonance condition, the contribution of an individual molecule to the Raman scattering does not depend strongly on the radial position of this molecule. On this basis, the radial distribution of the two components inside the evaporating droplet was determined by time-dependent measurements of the Raman spectrum. Furthermore, elastic-light scattering and the evaporation characteristics of the particles were investigated.     

Shaping Luminescent Properties of Yb3+ and Ho3+ Co‐Doped Upconverting Core–Shell β‐NaYF4 Nanoparticles by Dopant Distribution and Spacing

At the core of luminescence color and lifetime tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the impact of the particle architecture for commonly used sensitizer (S) and activator (A) ions. In this respect, a series of core@shell NaYF₄ UCNPs doped with Yb³⁺ and Ho³⁺ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@…, …@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core–shell NPs. As revealed by quantitative steady‐state and time‐resolved luminescence studies, the relative spatial distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical impact on their luminescence characteristics. Although the increased amount of Yb³⁺ ions boosts UCNP performance by amplifying the absorption, the Yb³⁺ ions can also efficiently dissipate the energy stored in the material through energy migration to the surface, thereby reducing the overall energy transfer efficiency to the activator ions. The results provide yet another proof that UC phosphor chemistry combined with materials engineering through intentional core@shell structures may help to fine‐tune the luminescence features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and display technologies.     

Two-phase heuristic algorithms for full truckloads multi-depot capacitated vehicle routing problem in carrier collaboration

Collaborative transportation, as an emerging new mode, represents one of the major developing trends of transportation systems. Focusing on the full truckloads multi-depot capacitated vehicle routing problem in carrier collaboration, this paper proposes a mathematical programming model and its corresponding graph theory model, with the objective of minimizing empty vehicle movements. A two-phase greedy algorithm is given to solve practical large-scale problems. In the first phase, a set of directed cycles is created to fulfil the transportation orders. In the second phase, chains that are composed of cycles are generated. Furthermore, a set of local search strategies is put forward to improve the initial results. To evaluate the performance of the proposed algorithms, two lower bounds are developed. Finally, computational experiments on various randomly generated problems are conducted. The results show that the proposed methods are effective and the algorithms can provide reasonable solutions within an acceptable computational time.     

EC-EGI: enriched complex EGI for 3D shape registration

Extended Gaussian image (EGI) and complex EGI (CEGI) have been widely used as the representation of 3D shapes for shape recognition and pose estimation. In this work, we extend the representations and present a new representation named enriched complex extended Gaussian image (EC-EGI). The representation follows the same framework of EGI and CEGI, which is to represent each surface patch of the target 3D shape as a weight at the associated spot on the surface of the Gaussian sphere. However, while the original CEGI uses a single complex number as the weight, the new representation uses three complex numbers, which are related to the centroid position of the surface patch in 3D. With the inclusion of more information in the new representation, not only could object pose be determined more accurately, but also some key ambiguities of shape representation that CEGI and EGI have also removed. The translation parameters in the pose estimation application could also be determined in a simpler and more accurate way. In addition, the Gaussian sphere partition problem of CEGI is no longer present. Experimental results on synthetic and real image data are shown to illustrate the performance of the proposed representation in pose estimation.     

Development and validation of an algorithm for registration of serial 3D MR breast data sets

We report on the development of an algorithm to improve the registration of serial 3D MR breast images using combined global translation and rotation with locally varying parameters as geometric transformations. Several phantom and volunteer data sets were acquired and registered using mutual information as a similarity measure of the matching process. After applying a global translation by using a rigid matcher, optimum horizontal and vertical rotation angles were determined. In case of the phantom measurements, angle optimization was performed for each slice of the 3D data set of the phantom, which was deliberately shifted and rotated around different axes. In case of registration of volunteer data, optimum rotation parameters were calculated for preselected equidistant slices of the data set to speed up the calculation time. For slices located between and outside these support slices, the rotation angles were calculated by linear interpolation and extrapolation of the slope of the regression determined by the optimized angles of the support slices. The algorithm improves the registration of serial 3D MR data sets and represents a compromise between a rigid and an elastic 3D matching procedure.