119 research outputs found
Incorporating Statistical Strategy into Image Analysis to Estimate Effects of Steam and Allyl Isocyanate on Weed Control
Weeds are the major limitation to efficient crop production, and effective weed management is necessary to prevent yield losses due to crop-weed competition. Assessments of the relative efficacy of weed control treatments by traditional counting methods is labor intensive and expensive. More efficient methods are needed for weed control assessments. There is extensive literature on advanced techniques of image analysis for weed recognition, identification, classification, and leaf area, but there is limited information on statistical methods for hypothesis testing when data are obtained by image analysis (RGB decimal code). A traditional multiple comparison test, such as the Dunnett-Tukey-Kramer (DTK) test, is not an optimal statistical strategy for the image analysis because it does not fully utilize information contained in RGB decimal code. In this article, a bootstrap method and a Poisson model are considered to incorporate RGB decimal codes and pixels for comparing multiple treatments on weed control. These statistical methods can also estimate interpretable parameters such as the relative proportion of weed coverage and weed densities. The simulation studies showed that the bootstrap method and the Poisson model are more powerful than the DTK test for a fixed significance level. Using these statistical methods, three soil disinfestation treatments, steam, allyl-isothiocyanate (AITC), and control, were compared. Steam was found to be significantly more effective than AITC, a difference which could not be detected by the DTK test. Our study demonstrates that an appropriate statistical method can leverage statistical power even with a simple RGB index
Evaluation of a Steam Application by a Mobile Applicator for Soil Disinfestation in Strawberry Nurseries
Soil disinfestation with steam has been evaluated in strawberry fruiting fields as a nonchemical method of soil disinfestation; however, little is known about the use of steam for field production of strawberry daughter plants. The objective of this study was to compare daughter plant production in soils previously treated with steam compared to those treated with standard methyl bromide (MB) and chloropicrin (Pic) treatments. A prototype field steam applicator and a self-propelled diesel-fueled steam generator and applicator were tested at two high-elevation nurseries near Macdoel, CA, in Sept. 2018 and Aug. 2020, respectively. The steam application heated the soil above 60â°C for â60 minutes to a depth of 25 cm at both nurseries. The pest control efficacy of the steam applications against weeds, Verticillium spp., Tylenchulus semipenetrans, and Pythium ultimum were similar to that of MB:Pic. The stolons and daughter plants densities in fields with steam treatment were similar to those in fields with MB:Pic treatment. Therefore, we suggest that soil disinfestation with steam may be a viable method of producing healthy strawberry plants. However, more research is needed to verify plant sanitation and quality
Interlayer Registry Determines the Sliding Potential of Layered Metal Dichalcogenides: The case of 2H-MoS2
We provide a simple and intuitive explanation for the interlayer sliding
energy landscape of metal dichalcogenides. Based on the recently introduced
registry index (RI) concept, we define a purely geometrical parameter which
quantifies the degree of interlayer commensurability in the layered phase of
molybdenum disulphide (2HMoS2). A direct relation between the sliding energy
landscape and the corresponding interlayer registry surface of 2H-MoS2 is
discovered thus marking the registry index as a computationally efficient means
for studying the tribology of complex nanoscale material interfaces in the
wearless friction regime.Comment: 13 pages, 7 figure
Nanomechanical Properties and Phase Transitions in a Double-Walled (5,5)@(10,10) Carbon Nanotube: ab initio Calculations
The structure and elastic properties of (5,5) and (10,10) nanotubes, as well
as barriers for relative rotation of the walls and their relative sliding along
the axis in a double-walled (5,5)@(10,10) carbon nanotube, are calculated using
the density functional method. The results of these calculations are the basis
for estimating the following physical quantities: shear strengths and diffusion
coefficients for relative sliding along the axis and rotation of the walls, as
well as frequencies of relative rotational and translational oscillations of
the walls. The commensurability-incommensurability phase transition is
analyzed. The length of the incommensurability defect is estimated on the basis
of ab initio calculations. It is proposed that (5,5)@(10,10) double-walled
carbon nanotube be used as a plain bearing. The possibility of experimental
verification of the results is discussed.Comment: 14 page
TIF film, substrates and nonfumigant soil disinfestation maintain fruit yields
A 5-year project to facilitate the adoption of strawberry production systems that do not use methyl bromide initially focused on fumigant alternatives and resulted in increased use of barrier films that reduce fumigant emissions. The focus shifted in year 3 to evaluating and demonstrating nonfumigant alternatives: soilless production, biofumigation, anaerobic soil disinfestation (ASD) and disinfestation with steam. In the 2010â2011 strawberry production season, fruit yields on substrates were comparable to fruit yields using conventional methods. Anaerobic soil disinfestation and steam disinfestation also resulted in fruit yields that were comparable to those produced using conventionally fumigated soils. Additional work is in progress to evaluate their efficacy in larger-scale production systems in different strawberry production districts in California
Hindered rolling and friction anisotropy in supported carbon nanotubes
Carbon nanotubes (CNTs) are well known for their exceptional thermal,
mechanical and electrical properties. For many CNT applications it is of the
foremost importance to know their frictional properties. However, very little
is known about the frictional forces between an individual nanotube and a
substrate or tip. Here, we present a combined theoretical and experimental
study of the frictional forces encountered by a nanosize tip sliding on top of
a supported multiwall CNT along a direction parallel or transverse to the CNT
axis. Surprisingly, we find a higher friction coefficient in the transverse
direction compared with the parallel direction. This behaviour is explained by
a simulation showing that transverse friction elicits a soft 'hindered rolling'
of the tube and a frictional dissipation that is absent, or partially absent
for chiral CNTs, when the tip slides parallel to the CNT axis. Our findings can
help in developing better strategies for large-scale CNT assembling and sorting
on a surface.Comment: 8 pages, 5 figure
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