72,100 research outputs found
The role of LAI and leaf chlorophyll on NDVI estimated by UAV in grapevine canopies
No full textDespite the wide use of the Normalized Difference Vegetation Index (NDVI) in precision viticulture, there are no studies aimed at discriminating the contribution of plant biomass from that of leaf chlorophyll on canopy NDVI. Leaf area index (LAI) and leaf chlorophyll (Chl) were concomitantly monitored by ground measurements and projected canopy area (PCA), canopy volume (CV) and NDVI by high resolution UAV multispectral images in fully productive "Sangiovese" grapevines either grown in containers or in the field and subjected to different irrigation regimes over two consecutive years. NDVI values calculated from only vine canopy pixels (NDVIUAV) and NDVI obtained from mixed ground-canopy pixels (simulated Satellite NDVI, NDVISAT) were both evaluated as potential predictor of LAI and leaf Chl concentration.The seasonal patterns of LAI and leaf Chl concentration were affected by irrigation, showing differences depending on field vs container-grown conditions. In situations where a decoupling between LAI and leaf Chl occurred, NDVIUAV and NDVISAT showed different responses: NDVIUAV patterns strictly followed the leaf Chl ones, whereas NDVISAT was more affected by LAI. The coefficient of determination between NDVIUAV and leaf Chl ranged between 0.51 and 0.78, that between NDVIUAV and leaf Chl from 0.01 to 0.76, depending on the irrigation-growing conditions combination. NDVISAT was a better predictor of LAI (R-2=0.69) than NDVIUAV (R-2=0.42). In field-grown vines the relationships between NDVI (both UAV and SAT) and LAI was stronger than in potted ones. The relationships between LAI and PCA (R-2=0.44) or LAI and canopy volume (R-2=0.77) were both significant. The results allowed to confirm the two main hypotheses behind this experiment: i) leaf Chl concentration had a greater impact than LAI on NDVI values obtained from vine canopy pixels (NDVIUAV), whereas NDVISAT was more affected by LAI; ii) The canopy volume from UAV images was a better predictor of LAI than NDVI and the resulting relationship showed a better temporal stability
Supplemental material for publication JAAD-D-19-02389 (Chun-Yu Lai et al. Association between bullous pemphigoid and ischemic heart diseases: A systematic review and meta-analysis. J Am Acad Dermatol. 2020)
No full textSupplemental material for publication JAAD-D-19-02389 (Chun-Yu Lai et al. Association between bullous pemphigoid and ischemic heart diseases: A systematic review and meta-analysis. J Am Acad Dermatol. 2020
The theory and practice of utopia in our troubled times : a conversation with author Larissa Lai and critic Sherryl Vint
No full textAmid current global crises, the international conference “The Knock at the Door: Utopian Dreams for Post-Covid Times,” jointly organized by the University of Huelva (Spain) and the University of Calgary (Canada) on May 21–24, 2023, at the University of Huelva, provided a forum for reflecting upon the role played by speculative fiction in (re)imagining better futures, while remaining vigilant to possible threats and dangers. The title of the conference, borrowed from philosopher John Rajchman,1 is intentionally ambiguous. Lying behind that door could be total liberation for all—or it could be secret police who lead us toward genocides, deportation, rapes, and mass graves. Taking this dichotomous trope, “the knock at the door,” as a point of departure, professors Larissa Lai (University of Toronto, Canada; recipient of a Maria Zambrano fellowship at the University of Huelva at the time of the interview) and Sherryl Vint (University of California Riverside, USA) engaged...Depto. de Estudios Ingleses: Lingüística y LiteraturaFac. de Ciencias Económicas y EmpresarialesTRUEpu
An automated procedure for estimating the leaf area index (LAI) of woodland ecosystems using digital imagery, MATLAB programming and its application to an examination of the relationship between remotely sensed and field measurements of LAI
No full text© CSIRO 2008Leaf area index (LAI) is one of the most important variables required for modelling growth and water use of forests. Functional–structural plant models use these models to represent physiological processes in 3-D tree representations. Accuracy of these models depends on accurate estimation of LAI at tree and stand scales for validation purposes. A recent method to estimate LAI from digital images (LAID) uses digital image capture and gap fraction analysis (Macfarlane et al. 2007b) of upward-looking digital photographs to capture canopy LAID (cover photography). After implementing this technique in Australian evergreen Eucalyptus woodland, we have improved the method of image analysis and replaced the time consuming manual technique with an automated procedure using a script written in MATLAB 7.4 (LAIM). Furthermore, we used this method to compare MODIS LAI values with LAID values for a range of woodlands in Australia to obtain LAI at the forest scale. Results showed that the MATLAB script developed was able to successfully automate gap analysis to obtain LAIM. Good relationships were achieved when comparing averaged LAID and LAIM (LAIM = 1.009 – 0.0066 LAID; R2 = 0.90) and at the forest scale, MODIS LAI compared well with LAID (MODIS LAI = 0.9591 LAID – 0.2371; R2 = 0.89). This comparison improved when correcting LAID with the clumping index to obtain effective LAI (MODIS LAI = 1.0296 LAIe + 0.3468; R2 = 0.91). Furthermore, the script developed incorporates a function to connect directly a digital camera, or high resolution webcam, from a laptop to obtain cover photographs and LAI analysis in real time. The later is a novel feature which is not available on commercial LAI analysis softwares for cover photography. This script is available for interested researchers.Sigfredo Fuentes, Anthony R. Palmer, Daniel Taylor, Melanie Zeppel, Rhys Whitley and Derek Eamu
Optical instruments for measuring leaf area index in low vegetation : application in Arctic ecosystems
No full textAuthor Posting. © Ecological Society of America, 2005. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 15 (2005): 1462–1470, doi:10.1890/03-5354.Leaf area index (LAI) is a powerful diagnostic of plant productivity. Despite the fact that many methods have been developed to quantify LAI, both directly and indirectly, leaf area index remains difficult to quantify accurately, owing to large spatial and temporal variability. The gap-fraction technique is widely used to estimate the LAI indirectly. However, for low-stature vegetation, the gap-fraction sensor either cannot get totally underneath the plant canopy, thereby missing part of the leaf area present, or is too close to the individual leaves of the canopy, which leads to a large distortion of the LAI estimate. We set out to develop a methodology for easy and accurate nondestructive assessment of the variability of LAI in low-stature vegetation. We developed and tested the methodology in an arctic landscape close to Abisko, Sweden.
The LAI of arctic vegetation could be estimated accurately and rapidly by combining field measurements of canopy reflectance (NDVI) and light penetration through the canopy (gap-fraction analysis using a LI-COR LAI-2000). By combining the two methodologies, the limitations of each could be circumvented, and a significantly increased accuracy of the LAI estimates was obtained. The combination of an NDVI sensor for sparser vegetation and a LAI-2000 for denser vegetation could explain 81% of the variance of LAI measured by destructive harvest. We used the method to quantify the spatial variability and the associated uncertainty of leaf area index in a small catchment area.This research was funded by U.S. National Science Foundation
grant DEB0087046
On Reading and Writing: an Interview with Larissa Lai
No full textCultural activist, author and Creative Writing Professor Larissa Lai is interviewed by Spanish critic Sonia Villegas López
Pseudorandomness Analysis of the Lai-Massey Scheme
No full textAt Asiacrypt’99, Vaudenay modified the structure in the IDEA cipher to a new scheme, which they called as the Lai-Massey scheme. It is proved that 3-round Lai-Massey scheme is sufficient for pseudorandomness and 4-round Lai-Massey scheme is sufficient for strong pseudorandomness. But the author didn’t point out whether three rounds and four rounds are necessary for the pseudorandomness and strong pseudorandomness of the Lai-Massey Scheme. In this paper we find a two round pseudorandomness distinguisher and a three-round strong pseudorandomness distinguisher, thus prove that three rounds is necessary for the pseudorandomness and four rounds is necessary for the strong pseudorandomness
Novel microwave dielectric LTCCs based upon V2O5 doped M2+Cu2Nb2O8 compounds (M2+ = Zn, Co, Ni, Mg and Ca)
No full textThe copper-niobates, M2+Cu2Nb2O8 (M2+ = Zn, Co, Ni, Mg or Ca) have good microwave dielectric properties when sintered between 985-1010 °C and 1110 °C for CaCu2Nb2O8. Therefore, they would be potential dielectric LTCC materials if they could be made to sinter below 960 °C (melting point of silver). To this end, additions of 3 wt.% V2O5 were made to ZnCu2Nb2O8, CoCu2 Nb2O8, NiCu2Nb2O8, MgCu2Nb2O8 and CaCu2 Nb2O8, and their sintering and dielectric behaviour was investigated for samples fired between 800 and 950 °C. Doping lowered sintering temperatures to below the 960 °C limit in all cases. Doping had the general effect of reducing εr, density, Qf and τf, although doped CaCu2 Nb2O8 had a Qf value of 9300 GHz, nearly four times that of the best undoped sample. Doped ZnCu2 Nb2O8 fired to 935 °C had Qf = 10,200 GHz, and for doped CoCu2Nb2O8 fired to 885 °C Qf = 7500 GHz. When doped and undoped samples all fired to 935 °C were compared, all doped samples had greater εr and density, and all except ZnCu2Nb2O8 had a smaller τf. All doped samples had a more linear relationship between frequency and temperature in the range 250-300 K. © 2005 Elsevier Ltd. All rights reserved
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