Green Peak Research Articles

Comparison of Feature Reduction Algorithms for Classifying Tree Species With Hyperspectral Data on Three Central European Test Sites

Tree species information is a basic variable for forest inventories. Knowledge on tree species is relevant for biomass estimation, habitat quality assessment, and biodiversity characterization. Hyperspectral data have been proven to have a high potential for the mapping of tree species composition. However, open questions remain concerning the robustness of existing classification approaches. Here, a number of classification approaches were compared to classify tree species from airborne hyperspectral data across three forest sites to identify a single approach which continuously delivers high classification performances over all test sites. Examined approaches included three feature selection methods [genetic algorithm (GA), support vector machines (SVM) wrapper, and sparse generalized partial least squares selection (PLS)] each combined with two nonparametric classifiers (SVM and Random Forest). Two further setups included classifications applied to the full hyperspectral dataset and to an image transformed with a minimum noise fraction (MNF) transformation. Results showed that SVM wrapper and the GA slightly outperformed the PLS-based algorithm. In most cases, the best classification runs involving a feature selection algorithm outperformed those incorporating the full hyperspectral dataset. However, the best overall results were obtained when using the first 10-20 components of the MNF-transformed image. Selected bands were frequently located in the visual region close to the green peak, at the chlorophyll absorption feature and the red edge rise as well as in three parts of the short-wave infrared region close to water absorption features. These findings are relevant for improving the robustness of tree species classifications from airborne hyperspectral data incorporating feature reduction techniques.

InGaN/GaN core-shell single nanowire light emitting diodes with graphene-based p-contact.

We report on the demonstration of MOVPE-grown single nanowire InGaN/GaN core-shell light emitting diodes (LEDs) with a transparent graphene contact for hole injection. The electrical homogeneity of the graphene-contacted LED has been assessed by electron beam induced current microscopy. By comparing graphene-contacted and metal-contacted nanowire LEDs, we show that the contact layout determines the electroluminescence spectrum. The electroluminescence changes color from green to blue with increasing injection current. High-resolution cathodoluminescence on cleaved nanowires allows the location with high precision of the origin of different emitted wavelengths and demonstrates that the blue peak originates from the emission of the radial quantum well on the m-planes, whereas the green peak arises from the In-rich region at the junction between the m-planes and the semipolar planes. The spectral behavior of the electroluminescence is understood by modeling the current distribution within the nanowire.

Synthesis and cathodoluminescence characteristics of caltrop-like ZnO nanostructures

Novel caltrop-like ZnO nanostructures have been synthesized on Si (100) substrates using a simple carbon thermal method at 1050°C. Structure characterizations indicate that the as-prepared nanostructures have a single crystalline wurtzite structure preferentially oriented in the [0001] direction. Cathodoluminescence measurements of ZnO nanostructures exhibit an intensive ultraviolet peak at 384nm and four broad green peaks (at 492, 504, 524 and 524nm, respectively), which can be attributed to the free exciton emission and the deep level emission, respectively. The prominent optical properties of the caltrop-like ZnO nanostructures make them promising candidates for fabricating optoelectronic nanodevices. A possible growth mechanism is also discussed.

A 1,3‐Indandione‐Functionalized Tetraphenylethene: Aggregation‐Induced Emission, Solvatochromism, Mechanochromism, and Potential Application as a Multiresponsive Fluorescent Probe

A tetraphenylethene (TPE) derivative substituted with the electron-acceptor 1,3-indandione (IND) group was designed and prepared. The targeted IND-TPE reserves the intrinsic aggregation-induced emission (AIE) property of the TPE moiety. Meanwhile, owing to the decorated IND moiety, IND-TPE demonstrates intramolecular charge-transfer process and pronounced solvatochromic behavior. When the solvent is changed from apolar toluene to highly polar acetonitrile, the emission peak redshifts from 543 to 597 nm. IND-TPE solid samples show an evident mechanochromic process. Grinding of the as-prepared powder sample induces a redshift of emission from green (peak at 515 nm) to orange (peak at 570 nm). The mechanochromic process is reversible in multiple grinding-thermal annealing and grinding-solvent-fuming cycles, and the emission of the solid sample switches between orange (ground) and yellow (thermal/solvent-fuming-treated) colors. The mechanochromism is ascribed to the phase transition between amorphous and crystalline states. IND-TPE undergoes a hydrolysis reaction in basic aqueous solution, thus the red-orange emission can be quenched by OH(-) or other species that can induce the generation of sufficient OH(-). Accordingly, IND-TPE has been used to discriminatively detect arginine and lysine from other amino acids, due to their basic nature. The experimental data are satisfactory. Moreover, the hydrolyzation product of IND-TPE is weakly emissive in the resultant mixture but becomes highly blue-emissive after the illumination for a period by UV light. Thus IND-TPE can be used as a dual-responsive fluorescent probe, which may extend the application of TPE-based molecular probes in chemical and biological categories.

UV enhancement in polycrystalline Ag-doped ZnO films deposited by the sol–gel method

Undoped and Ag doped ZnO thin films are deposited by the sol–gel spin coating method. XRD spectra with prominent peaks along (100) (002) (101) show the polycrystalline nature of thin films. The particle size lies between 10 to 28nm as estimated by Debye‐Scherrer method and 10 to 20nm as estimated by WH plot method. Surface topology is studied by atomic force microscopy (AFM). Transmission spectra show that all the films are highly transparent (70–90%) in the visible and IR spectral region and absorption occurs near 370nm. Sharp UV emission at 393nm is observed in photoluminescence spectra of the films along with a broad green emission. Emission intensity of UV peak increases as amount of Ag incorporated into ZnO increases. It is enhanced 7 times by Ag doping in ZnO thin film. The intensity of green peak enhances at higher Ag doping percentage.

적색, 초록, 청색 및 혼합광 LED 조사의 식중독균 저해 효과

The antimicrobial properties of Light-Emitting Diode (LED) are an area of increasing interest. The aim of this study was to evaluate the bactericidal effects of blue (peak at 456 nm), green (peak at 518 nm), red (peak at 654 nm) and blue-green combined (blue 456 nm : green 558 nm = 69:31) LED irradiation to pathogenic bacteria. For this, LED equipment providing power density of <TEX>$10mW/cm^2$</TEX> was installed and plates were exposed to 0.9 or <TEX>$3.0mW/cm^2$</TEX> to irradiate bacteria with 3.2 to <TEX>$259.2mW/cm^2$</TEX> of energy density. As a result, blue and combined LED have shown bactericidal effects on Escherichia coli KCTC 1467 and Listeria monocytogenes ATCC 19115 after irradiation of <TEX>$3.0mW/cm^2$</TEX> for 2 and 4 hr, respectively. Staphylococcus aureus KCTC 1916 was inhibited at 518 nm green LED irradiation. However, red LED irradiation showed no inhibitory effect to the other tested strains. Light technology that utilizes the bactericidal properties of blue (at 456 nm) and blue-green(blue 456 nm : green 558 nm = 69:31) combined LED may have potential applications in the food industry sector.

Fast one-step synthesis of ZnO sub-microspheres in PEG200

ZnO sub-microspheres were synthesized via a new, simple, and one-step method by using zinc acetate dihydrate as a precursor and PEG200 as a solvent and modifier. The effect of temperature (160–210 °C) on the crystallization, surface morphology, and luminescence properties of ZnO spheres was investigated using different characterization techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, and room temperature photoluminescence. The results show that the ZnO crystal has a hexagonal wurtzite structure. The products have monodispersed spherical morphology with diameters in the range of 200–600 nm. They have intensive UV emission peaks at ~380 nm and relatively weak and broad green peaks at ~550 nm. The PEG200 molecules adsorb on the surface of ZnO spheres. On the basis of the experimental results, a mechanism was proposed to elucidate the formation of ZnO sub-micron spheres.

Analysis of the relationship between the spectral characteristics of maize canopy and leaf area index under drought stress

Maize is one of the most widespread grain crops in the world; however, more than 70% of corn in China suffers some degree of drought disaster every year. Leaf area index (LAI) is an important biophysical parameter of the vegetation canopy and has important significance for crop yield estimation. Using the data of canopy spectral reflectance and leaf area index (LAI) for maize plants experiencing different levels of soil moisture from 2011 to 2012, the characteristics of the canopy reflective spectrum and its first derivative, and their relationships to leaf area index, were analyzed. Soil moisture of the control group was about 75% while that of the drought stress treatment was about 45%. In addition, LAI retrieval models for maize were established using vegetation indices (VIs) and principal component analysis (PCA) and the models were tested using independent datasets representing different soil water contents and different developmental stages of maize. The results showed that canopy spectral reflectances were in accordance with the characteristics of green plants, under both drought stress and at different developmental stages. In the visible band, canopy reflectance for both healthy and damaged vegetation had a green-wavelength peak and a red-wavelength valley; reflectance under drought stress, especially in the green peak (about 550nm) and the red valley (about 676nm) was higher than in the control group. In the near-infrared band, the canopy spectral reflectance decreased substantially between 780 and 1350nm under drought stress. Moreover, the red edge of the spectrum was shifted toward blue wavelengths. The first derivative spectrum showed a double peak phenomenon at the edge of the red band at different developmental stages: the main peak appeared between 728 and 732nm and the minor peak at about 718nm. The double peaks become more obvious through the growth and development of the maize, with the most notable effect during the silking and milk stages, after which it gradually decreased. During maize growth, the LAI of all plants, regardless of soil moisture conditions, increased, and the largest LAI also occurred during the silking and milk stages. During those stages, the LAI of plants under different drought stress levels was significantly lower (by 20% or more) than in normal plants with sufficient water supplies. The LAI was highly significantly correlated with canopy spectral reflectance in the bands from 350nm to 510nm, from 571nm to 716nm, and from 1450nm to 1575nm. Also, the LAI was significantly correlated with red edge parameters and several VIs. The Perpendicular Vegetation Index (PVI) had the best correlation with LAI, with a coefficient of determination (R2) of 0.726 for the exponential correlation. Using dependent data, a LAI monitoring model for the maize canopy was constructed using PCA and VI methods. The test results showed that both the VI and PCA methods of monitoring maize LAI could provide robust estimates, with the predicted values of LAI being significantly correlated with the measured values. The model based on PVI showed higher precision under the drought stresses, with a correlation coefficient of 0.893 (n=27), while the model based on PCA was more precise under conditions of adequate soil moisture, with a correlation coefficient of 0.877 (n=32). Therefore, a synthesis of the models based on both VI and PCA could be more reliable for precisely predicting LAI under different levels of drought stresses in maize.

Enhanced Upconversion Luminescence of Erbium–Nitrogen-Doped Zinc Oxide Nano-Wires by Implantation of Ytterbium Ions

ABSTRACT Erbium–nitrogen codoped zinc oxide nanowires of ytterbium-doped are prepared by thermal evaporation and ion implantation methods. Ytterbium ions are doped into nanowires at a fluence of (0, 1, 3, 5, and 9) × 1015 cm−2. Microstructural and optical properties of specimen are investigated by X-ray diffractometer, absorption spectra, Raman, and upconversion photoluminescence examinations. Upconversion photoluminescence emissions at 550 nm and 660 nm are obtained under 980-nm light excitation. Both intensities of green and red peaks are enhanced by the introduction of ytterbium ions. When ytterbium ion fluence is 5 × 1015 cm−2, light emission intensity reaches maximum value. The energy transfer and cross-relaxation processes are responsible for the change of emission intensity.

Research on the structural and optical stability of Ga2O3 films deposited by electron beam evaporation

Ga2O3 films were deposited on c-plane sapphire substrates using electron beam evaporation method with subsequent annealing in oxygen ambient for different time interval. The effect of annealing treatment on the microstructures and optical characteristics of Ga2O3 films were systematically investigated by X-ray diffraction, atomic force microscope, photoluminescence (PL) spectra and optical transmittance spectra, respectively. The results indicated that Ga2O3 films showed a stronger preferred orientation after annealing for 30, 60 and 90 min at 1,000 °C. The diffraction peaks \((\bar{6}01)\) and (403) of the annealed Ga2O3 films increased first and then decreased. We discussed the influence of annealing time interval on the grain sizes and surface morphologies properties of Ga2O3 films. The PL spectra measured at room temperature revealed blue, green and red emissions. Intense green luminescence was obtained from the sample annealed for 60 and 90 min. The crystalline quality of Ga2O3 film was markedly improved after annealing, which caused the intensity of blue peak (~430 nm) and green peak (~513 nm) increasing noticeably. The origin of these emissions was discussed. All annealed Ga2O3 films exhibited a steep absorption edge in deep ultraviolet region, and presented over 70 % transmittance in the visual light region.

Assessing the potential of hyperspectral imagery to map bark beetle-induced tree mortality

Natural hazards caused by insect outbreaks, such as those induced by the European bark beetle (Ips typographus L.), are among the most extensive disturbances affecting forest health in various geographical regions. Accurate and up-to-date knowledge of the spatial distribution of bark beetle-infested trees is critical for forest managers to effectively plan appropriate countermeasures and predict future bark beetle infestation dynamics. In this study, three scenarios for mapping bark beetle-induced tree mortality based on airborne hyperspectral data (HyMap) were examined including combining a genetic algorithm (GA) for feature selection with a supervised support vector machine (SVM) classification. The scenarios differed in how the mortality classes (used to extract the spectral signatures) were defined. Scenario 1 included three mortality classes, while Scenario 2 and 3 each included only one general mortality-related class but with different definitions. The classes, derived from the three scenarios, served as inputs into feature selection facilitated by the GA. The most stable bands, selected by the GA, were then used as input bands for a bootstrapped supervised SVM classification procedure. In two of the three scenarios, the trained classifier was additionally applied to a second independent hyperspectral image to evaluate the stability of the spectral signatures derived from the training samples. The classification procedure was further refined by varying the number of input bands and the input data types, where the bands not only included the original reflectances of the HyMap images but also a first order Savitzky–Golay derivation and continuum-removed spectra.The results of the study indicate that an accurate differentiation of three mortality classes was not possible with the applied methodology. The defined pre-visual “green mortality stage” class in particular was found to be heavily overestimated based on the qualitative analysis of the classified maps and validation statistics (error of commission 65% as shown by the user's accuracy).However, on the other hand, the mapping of dead trees was possible with notably high overall accuracies (OAs) (84%–96%). These results could also be transferred to the second independent hyperspectral image, in which the separation between the healthy trees and the dead trees was possible with OAs of 94%–97%. Somewhat lower but still reasonable OAs (76%–85%) were found when all defined classes were considered. The main confusion occurred between dead trees and sparsely vegetated soil.GA analysis showed that bands that notably contributed to high classification accuracies were frequently located in the visual part of the spectrum, close to the green peak (560nm), as well as around the chlorophyll absorption feature (680nm) and the red edge rise (690nm). In some of the tested cases, additional bands in the SWIR (1532nm) and one in the NIR (1076nm) were stably selected by the GA, which indicated the importance of these bands in the classification process.

Research on Typical Plant Spectral Distinguishable Characteristics by Mann-Whitney U-Test in Wild Duck Lake

Wetlands is a superior way to purify water environment. However monitoring and discriminating among vegetation covers types are critical to understanding population distribution, biogeochemical functioning and the process of wetland recovery. Recently, remote sensing technology has become an important tool to monitor wetland vegetation. Typical wetland plants Bidens Pilosa, Scirpus planiculumis, Phragmites australis and Typha angustifolia in Wild duck wetland were chosen, and Mann-Whitney U-test were used to analyze the spectral characteristics. There were typical vegetation spectral characteristics of dominant species spectral reflectance curve. There are differences among reflective spctral characteristic of species, especially in the green peak and steep reflection. According to the results of Mann-Whitney U-test, the highest frequency bands appeared in702-715732-745747nm, the classification precision of Bidens pilosa , Scirpus planiculumis and Phragmites australis are 100%, 100%, 80%. While It is difficult to distinguish Typha angustifolia from other species effectively using the three spectrum regions.

Effect of growth angle and post-growth annealing on the structural and optical properties of ZnO nanorods grown hydrothermally on p-Si substrate

ZnO nanorods were successfully grown on the p-Si substrate via the hydrothermal method. The influence of growth angle, precursor concentration and post-growth annealing on the structural and optical properties of grown ZnO nanorods were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). Relatively well-aligned ZnO nanorods were obtained under the growth conditions of θ=70° (growth angle) and 0.05M precursor concentration. The PL spectra of ZnO nanorods, annealed in different atmospheres (oxygen, nitrogen and argon), revealed that the intensity of the violet, blue and green peaks were increased by annealing in different atmospheres. The nitrogen atmosphere has the strongest effect on the intensity of PL spectra.

Theoretical Photodynamic Study of the Photoprotolytic Cycle of Firefly Oxyluciferin

Firefly oxyluciferin presents a pH-sensitive fluorescence in aqueous solutions. Its fluorescence spectra are composed of two green peaks at different pH values, despite the enolate anion being the only emitter. A computational approach was used to further elucidate the photoprotolytic cycle of oxyluciferin and investigate its pH sensitivity. It was found that oxyluciferin forms π-π stacking complexes both in the ground and excited states, at basic and acidic/neutral pH. However, at different pH values, these complexes adopt a different conformation, which explains the lower energy of the emission at acidic/neutral pH, in comparison with the emission at basic pH.

Identifying Santa Barbara's urban tree species from AVIRIS imagery using canonical discriminant analysis

In this research, we classify 15 common urban trees in downtown Santa Barbara, California, using crown-level canonical discriminant analysis (CDA) on airborne visible/infrared imaging spectrometer (AVIRIS) imagery. We compare the CDA classification accuracy against results obtained from stepwise discriminant analysis. We also examine the impact of various crown-level aggregation techniques and training sample size on classification results. An overall classification accuracy of 86% was achieved using CDA. Species-specific results were highest for dense crowns with high normalized difference vegetation index values. Bands chosen using forward feature selection spanned AVIRIS full spectral range illustrating a need for retaining a full complement of spectral information. Nevertheless, there is some indication that bands along the green edge, green peak and yellow edge are particularly valuable for discriminating structurally similar urban trees.

DNA stabilized silver nanoclusters for ratiometric and visual detection of Hg2+ and its immobilization in hydrogels

DNA oligomers are particularly interesting templates for making silver nanoclusters (AgNCs) as different emission colors can be obtained by varying the DNA sequence. Many AgNCs have been used as Hg2+ sensors since Hg2+ induces fluorescence quenching. From an analytical chemistry standpoint, however, these ‘light off’ sensors are undesirable. In this work, taking advantage of the fact that some AgNCs are not as effectively quenched by Hg2+, we design a sensor with AgNCs containing two emission peaks. The red peak is strongly quenched by Hg2+ while the green peak shows a concomitant increase, producing an orange-to-green visual fluorescence transformation. Using this AgNC, we demonstrate ratiometric detection with a detection limit of 4nM Hg2+. This sensor is further immobilized in a hydrogel matrix and this gel is also capable of detecting Hg2+ with a visual response.

The evolution behavior of microstructures and optical properties of ZnO films using a Ti buffer layer

Abstract ZnO thin films without and with Ti buffer layer were prepared on Si and glass substrates by radio frequency (RF) magnetron sputtering. The effects of Ti buffer layer with different sputtering time on the microstructure and optical properties of ZnO thin films had been investigated by means of X-ray diffraction (XRD), energy dispersive spectrometer, X-fluorescence spectrophotometer and ultraviolet–visible spectrophotometer. The XRD results showed that the full-width at half-maximum (FWHM) for the ZnO (002) diffraction peak gradually decreased with the increase of sputtering time of Ti buffer layer, indicating that the crystalline quality of ZnO thin films was improved. The UV peak located at 390 nm, two blue peaks located at about 435 and 487 nm, two green peaks located at about 525 and 560 nm were observed from PL spectra. The PL spectra showed that the strongest blue light emission of ZnO films was obtained from Ti buffer layer with the sputtering time of 10 min. Meanwhile, the origins of the emission peaks were discussed through the Gaussian deconvolution. We also studied the optical band gaps.

Tropical phenology: bi‐annual rhythms and interannual variation in an Afrotropical butterfly assemblage

Temporal variation and phenology of tropical insect communities and the role of environmental factors controlling this variation is poorly understood. A better understanding is needed, for example, to predict the effects of climate change on tropical insect communities and to assess the long‐term persistence of tropical communities. We studied seasonal and inter‐annual variation in tropical fruit‐feeding butterflies by exploiting a unique 137‐month abundance time series of &gt;100 species, sampled at 22 locations in the medium altitude montane rain forest of Kibale National Park, western Uganda. Precipitation peaked twice per year, about 20 d after each equinox. Vegetation greenness peaked approximately 33 d later. Species richness and abundance of butterflies peaked about 2 and 3 months, respectively, after the greenness peak. Furthermore, temporal shifts in peaks of butterfly abundances of each 6‐month cycle positively correlated with temporal shifts in peaks of vegetation greenness approximately three months before. The butterfly assemblages of ENSO warm phase years differed significantly from assemblages of the other years. To our knowledge this is the first elucidation of bi‐annual rhythms in butterfly assemblages. Host plant availability could explain the seasonal cycles in butterfly abundance and species richness, because the 3‐month lag observed matches with the egg‐to‐adult development time in the studied species.

Controlled Synthesis of CaWO4 Microcrystalline via Surfactant-Assisted Precipitation Method

CaWO4 microcrystallines have been synthesized via a surfactant-assisted precipitation method using cetyltrimethylammonium bromide (CTAB) and /or Polyvinylalcohol (PVA) as surfactants, respectively. The as-prepared CaWO4 microcrystallines were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectra and photoluminescence spectra (FL). The growth process of these CaWO4 microcrystallines obtained in the presence of CTAB and PVA has been discussed. The structural characterization results indicate that the obtained CaWO4 are ellipsolid-like microcrystallines with the average size of ∼350 nm in short axis and ∼800 nm in long axis, and the CaWO4 microcrystallines possess a pure scheelite structure with a tetragonal symmetry. The FTIR spectra provide the evidence of W–O stretching vibration in [WO4]2− tetrahedrons at 796 cm−1 and W-O bending bands at 438 cm−1. FL spectra reveal that the CaWO4 microcrystallines exhibit the only green peak at 430 nm excited by ultraviolet ray (UV) with the wavelength at 220 nm, 240 nm and 260 nm, respectively. The SEM results indicate that the morphology of the CaWO4 microcrystallines can be affected by the concentration of surfactants.

Crystal structures and optical properties of(Fe, Co)-codoped ZnO thin films

The Fe, Co-codoped Zn0.9FexCo0.1-xO (x=0, 0.03, 0.05, 0.07) thin films are fabricated on the glass substrates by sol-gel method. The surface morphologies, crystal structures, elements and optical properties of the films are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectrum. The XRD results reveal that all the ZnO films are of wurtzite structure. The diffraction peaks of the clusters, oxide or other impurity phase related to Fe and Co are not observed in the samples. This indicates that codoped is beneficial to the improvement on the dispersion of Fe or Co in ZnO. XPS results reveal that Co elements exist as Co2+, Fe elements exist as Fe2+ and Fe3+, but the increase of relative concentration of Fe leads to the increase of Fe3+ content. The ultraviolet emission peak and blue double emission are observed in the PL spectra of all the samples. Compared with the undoped ZnO film, the Co-codoped ZnO film has a blue shift of ultraviolet emission peak of Fe, the unchanged position of the blue double emission peak, and the weakened luminous intensity. Moreover, the green luminescence peak of the doped ZnO film almost disappears. Finally, the luminescence mechanisms of Fe, Co-codoped ZnO films are discussed by combining the microstructures and compositions of the samples.