A simple control scheme for the manipulation of a particle by means of optical tweezers

We present a simple control scheme for changing the position of a microscopic particle immersed in a viscous medium and trapped by optical tweezers. We derive a simple feedback controller under the consideration that the particle mass is so small that it can be discarded from the motion equations. This approximation is well justified in practice, since the inertial force produced by the motion of a micron‐scaled trapped particle is completely dominated by the medium viscous drag force. Finally, we formally prove that the obtained controller is able to globally asymptotically stabilize the system when the particle mass is considered, if some suitable values of some control parameter are used. The stability analysis of the controlled system was carried out by using the standard Lyapunov stability theory. Also, by means of numerical simulations, we show that the obtained closed‐loop system is robust when random thermal noise is presented. Copyright © 2010 John Wiley & Sons, Ltd.     

基于实时系统的多功能微波自动测量仪研制

分析了现有的自动测量线的优缺点。在传统测量线的基础上,基于美国国家仪器(NI)的实时处理系统sbRIO-9642,通过LabVIEW开发了具备实时远程控制功能的多功能微波自动测量仪。实现了测量对象的实时控制,以及测量过程的远程控制。在测量大驻波比的终端负载时,改进了K倍最小法,提高了测量精度。同时,从理论上探究了利用传统测量线实现多频率测量的方法,该方法可以用于检测多路未知信号的频率,具有较强的实用性和创新性。     

Highly sensitive detection of HCl gas using a thin film of meso-tetra(4-pyridyl)porphyrin coated glass slide by optochemical method

The meso-tetra(4-pyridyl)porphyrin (MTPyP) deposited on glass slide by dip coating was used as a solid state sensor for HCl gas detection by optochemical method. Exposure of MTPyP coated glass slide to HCl gas results in the formation of protonated meso-tetra(4-pyridyl)porphyrin (PMTPyP). UV-vis and fluorescence spectral methods were used to study the protonation of MTPyP both in solution and on solid state. The absorption spectrum of MTPyP modified glass slide shows an intense Soret band at 427 nm, which is shifted to 470 nm upon exposure to HCl gas. The concentration of HCl gas was monitored from the absorbance changes of Soret band of PMTPyP at 470 nm. The detection limit of the solid state sensor was found to be 0.01 ppm. The recovery rate of the solid state was very fast and it was monitored by UV-vis and fluorescence techniques with successive exposure to HCl gas and ammonia vapor with nitrogen gas. The planarity and energy of the molecule have changed after exposed to HCl gas which was confirmed by ab-intio calculation using Gaussian software. The response of the solid state sensor towards HCl gas was highly stable for several months.     

Flexible H2 sensor fabricated by layer-by-layer self-assembly of thin films of polypyrrole and modified in situ with Pt nanoparticles

A novel flexible H₂ gas sensor was fabricated by the layer-by-layer (LBL) self-assembly of a polypyrrole (PPy) thin film on a polyester (PET) substrate. A Pt-based complex was self-assembled in situ on the as-prepared PPy thin film, which was reduced to form a Pt-PPy thin film. Microstructural observations revealed that Pt nanoparticles formed on the surface of the PPy film. The sensitivity of the PPy thin film was improved by the Pt nanoparticles, providing catalytically active sites for H₂ gas molecules. The interfering gas NH₃ affected the limit of detection (LOD) of a targeted H₂ gas in a real-world binary gas mixture. A plausible H₂ gas sensing mechanism involves catalytic effects of Pt particles and the formation of charge carriers in the PPy thin film. The flexible H₂ gas sensor exhibited a strong sensitivity that was greater than that of sensors that were made of Pd-MWCNTs at room temperature.     

Spatial and temporal dynamics of river channel migration and vegetation in central Amazonian white-water floodplains by remote-sensing techniques

We investigated spatial and temporal migration of the Solimões, the Japurá, and the Aranapu River channels in western Brazilian Amazonia with Landsat TM imagery over a 21-year period. Additionally, we classified and monitored how channel migrations affect the distribution of pioneer vegetation and old-growth forest. The cloud-free study area was 153,032 ha — open water plus 3 km inland on each margin. The channel migration rates, expressed as percent dislocation of the open water body of the river year^− 1, were lowest in the Japurá River (1.2%), and highest in the Aranapu channel (2.5%), the point bars at river confluence being the most affected landforms subject to geomorphic changes. Annual rates of lateral erosion and accretion of vegetated land along the three rivers were well-balanced. They averaged 0.79 and 0.83% of the cloud-free channel area over the 21 years. The Solimões River was more dynamic than the Japurá River, which can be traced to higher water discharge and sediment load. During the 21 years, the area covered by pioneer vegetation increased by 5.8% of the study area, while late-succession areas decreased by a similar amount (5.5%). According to local biomass estimates of the different vegetation types, these values suggest that C-releases by alluvial erosion would be much higher than C-sequestration caused by the creation of areas suitable for colonization by pioneer vegetation at our study site.     

Step sequence planning for a biped robot by means of a cylindrical shape model and a high-resolution 2.5D map

A novel step sequence planning (SSP) method for biped-walking robots is presented. The method adopts a free space representation custom-designed for efficient biped robot motion planning. The method rests upon the approximation of the robot shape by a set of 3D cylindrical solids. This feature allows efficient determination of feasible paths in a 2.5D map, comprising stepping over obstacles and stair climbing. A SSP algorithm based on A^∗-search is proposed which uses the advantages of the aforementioned environment representation. The efficiency of the proposed approach is evaluated by a series of simulations performed for eight walking scenarios.     

Band depth analysis of CHRIS/PROBA data for the study of a Mediterranean natural ecosystem. Correlations with leaf optical properties and ecophysiological parameters

The absorption feature approach was used in CHRIS multiangular hyperspectral data in order to investigate its potential for ecosystem remote sensing. For that purpose, CHRIS images in mode 1 were acquired throughout a two-year period for a Mediterranean ecosystem dominated by the semi-deciduous shrub Phlomis fruticosa. During each acquisition, coincident in situ Leaf spectra and ecophysiological measurements (Leaf Area Index, leaf pigment content and leaf water potential) were conducted. After data preprocessing, absorption feature information was calculated for both CHRIS and Leaf spectra for the whole spectrum. Three common characteristic absorption features within the spectral areas 450-550 nm, 550-750 nm and 900-1000 nm were detected. Each spectral area was then examined separately and four characteristic parameters were calculated that described the pattern, magnitude and position of the maximum absorption. Correlations between CHRIS and Leaf spectra for each date and viewing angle (VA) were then conducted. All correlations, either on full continuum removed spectra or on spectral areas, showed high coefficients of determination, especially (i) in higher observation angles (VA + 55), (ii) during the wet season and (iii) in strong absorptions such as the “red absorption”. Subsequently, correlations between CHRIS and Leaf absorption parameters of selected spectral areas with field-measured ecophysiological parameters were examined. Ecophysiological parameters proved to be highly correlated to CHRIS and Leaf absorption parameters in magnitude and/or pattern of the absorption feature and less in wavelength of the maximum absorption. CHRIS VAs +/− 36 showed the highest correlations although the type of relation, linear or nonlinear, was not conclusive. Finally, a first comparison between narrowband spectral indices and absorption features in correlations with ecophysiological parameters showed that both methods provide significant and comparable results, with oblique angles showing best performance. However, ecophysiological parameters are generally better predicted linearly by narrowband spectral indices issued from CHRIS, with most significant differences appearing on pigments absorbing mainly within 450-550 nm.     

Estimation of orientation of a textured planar surface using projective equations and separable analysis with M-channel wavelet decomposition

Estimation of the orientation of a textured planar surface is one of the basic tasks in the area of “shape from texture”. For the solution of this task, many successful approaches were proposed. In this paper, we have examined a few unaddressed questions: First, is there a mathematical formulation that relates the spectral characteristics of the texture pattern and the orientation of an inclined planar surface in a polar-coordinate system? Second, is there a good wavelet-based approach that produces an accurate estimate of the orientation angle of the textured planar surface by analyzing the spectral behavior of one single uncalibrated image?To answer these questions at first we present the formulation of a “texture projective equation”, which relates the depth and orientation of an inclined planar surface in a polar coordinate system with the spectral properties of its image texture. A suitable imaging geometry has been considered to enable separable analysis of the effect of inclination of the texture surface. Next, a method for shape from texture is presented based on discrete wavelet analysis to estimate the orientation of the planar surface. This approach although designed mainly for M-channel wavelets, is also applicable for dyadic wavelet analysis. Texture characteristics in the subbands of wavelet decomposition are analyzed using scalograms, and quantitatively evaluated based on texture projective equations. The proposed method of estimation of the orientation of a planar texture surface is evaluated using a set of simulated and real world textured images.     

Preparation and characterization of nanocrystalline α-Fe2O3 by a sol-gel process

α-Fe₂O₃ ultra-fine powder with an average particle size of 6–26nm has been prepared by a sol-gel process. Thermal analysis, X-ray diffraction and transmission electron microscope were used to study its formation process and micro-structure. The temperature dependence of the electric conductance of the elements made of nanocrystalline α-Fe₂O₃ shows that the gas-sensing properties are strongly related to its surface. The elements exhibited good sensitivity and selectivity to ethyl alcohol, indicating it is a promising alcohol-sensing material.     

Estimating aboveground carbon in a catchment of the Siberian forest tundra: Combining satellite imagery and field inventory

This study was part of an interdisciplinary research project on soil carbon and phytomass dynamics of boreal and arctic permafrost landscapes. The 45 ha study area was a catchment located in the forest tundra in northern Siberia, approximately 100 km north of the Arctic Circle.The objective of this study was to estimate aboveground carbon (AGC) and assess and model its spatial variability. We combined multi-spectral high resolution remote sensing imagery and sample based field inventory data by means of the k-nearest neighbor (k-NN) technique and linear regression.Field data was collected by stratified systematic sampling in August 2006 with a total sample size of n = 31 circular nested sample plots of 154 m² for trees and shrubs and 1 m² for ground vegetation. Destructive biomass samples were taken on a sub-sample for fresh weight and moisture content. Species-specific allometric biomass models were constructed to predict dry biomass from diameter at breast height (dbh) for trees and from elliptic projection areas for shrubs.Quickbird data (standard imagery product), acquired shortly before the field campaign and archived ASTER data (Level-1B product) of 2001 were geo-referenced, converted to calibrated radiances at sensor and used as carrier data. Spectral information of the pixels which were located in the inventory plots were extracted and analyzed as reference set. Stepwise multiple linear regression was applied to identify suitable predictors from the set of variables of the original satellite bands, vegetation indices and texture metrics. To produce thematic carbon maps, carbon values were predicted for all pixels of the investigated satellite scenes. For this prediction, we compared the kNN distance-weighted classifier and multiple linear regression with respect to their predictions.The estimated mean value of aboveground carbon from stratified sampling in the field is 15.3 t/ha (standard error SE = 1.50 t/ha, SE% = 9.8%). Zonal prediction from the k-NN method for the Quickbird image as carrier is 14.7 t/ha with a root mean square error RMSE = 6.42 t/ha, RMSE_r = 44%) resulting from leave-one-out cross-validation. The k-NN-approach allows mapping and analysis of the spatial variability of AGC. The results show high spatial variability with AGC predictions ranging from 4.3 t/ha to 28.8 t/ha, reflecting the highly heterogeneous conditions in those permafrost-influenced landscapes. The means and totals of linear regression and k-NN predictions revealed only small differences but some regional distinctions were recognized in the maps.     

Phytoplankton biomass distribution and identification of productive habitats within the Galapagos Marine Reserve by MODIS, a surface acquisition system, and in-situ measurements

The Galapagos Marine Reserve (GMR) is one of the most diverse ecosystems in the world. Phytoplankton are the base of the ecosystem food chain for many higher trophic organisms, so identifying phytoplankton biomass distribution is the first step in understanding the dynamic environment for effective management of the GMR. Moderate Resolution Imaging Spectroradiometer (MODIS) and hyperspectral surface acquisition system derived chlorophyll, in-situ chlorophyll fluorescence, nitrate, salinity, and temperature were collected from March 2005 to the onset of a mild El Niño in November 2006. Islands in the eastern GMR, such as San Cristobal and Espanola, are the first to experience impacts of El Niño and southern migration of the Equatorial Front. Productive habitats were defined as surface waters with salinities > 34, temperatures < 24 °C, and chlorophyll a > 0.4 mg m^− 3. Six temporally variable productive habitats identified were: west of Isabela Island, southwest of Floreana Island, south of Santa Cruz, between Santiago and Santa Cruz Islands, and on the eastern side near San Cristobal Island. Model results coupled with surface acquisition system derived chlorophyll indicated productive habitats may also occur for short periods and at a distance from islands such as when the Equatorial Undercurrent (EUC) and South Equatorial Current (SEC) collide over the seamounts north of Isabela Island. All productive habitats were related to topographic upwelling from the EUC into surface waters.