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Finite Element Convergence for State-Based Peridynamic Fracture Models

Communications on Applied Mathematics and Computation 2020年第1期2卷 93-128页

作者： prashant k.jha Robert Lipton Department of Mathematics Louisiana State UniversityBaton RougeLAUSA

We establish the a priori convergence rate for finite element approximations of a class of nonlocal nonlinear fracture *** consider state-based peridynamic models where the force at a material point is due to both the strain between two points and the change in volume inside the domain of the nonlocal *** pairwise interactions between points are mediated by a bond potential of multi-well type while multi-point interactions are associated with the volume change mediated by a hydrostatic strain *** hydrostatic potential can either be a quadratic function,delivering a linear force–strain relation,or a multi-well type that can be associated with the material degradation and *** first show the well-posedness of the peridynamic formulation and that peridynamic evolutions exist in the Sobolev space *** show that the finite element approximations converge to the H2 solutions uniformly as measured in the mean square *** linear continuous fi nite elements,the convergence rate is shown to be Ct Δt+Csh2/ε2,where𝜖is the size of the horizon,his the mesh size,and Δt is the size of the time *** constants Ct and Cs are independent of Δt and h and may depend on ε through the norm of the exact *** demonstrate the stability of the semi-discrete *** stability of the fully discrete approximation is shown for the linearized peridynamic *** present numerical simulations with the dynamic crack propagation that support the theoretical convergence rate.

关键词： Nonlocal fracture models Peridynamic State-based peridynamic Numerical analysis Finite element approximation

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Depletion of an Artificial Seed Bank of Palmer Amaranth (<i>Amaranthus palmeri</i>) over Four Years of Burial

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American Journal of Plant Sciences 2014年第11期5卷 1599-1606页

作者： prashant jha Jason k. Norsworthy Josefina Garcia Department of Crop Soil and Environmental Sciences University of Arkansas Fayetteville USA Southern Agricultural Research Center Montana State University Huntley USA

An artificial seed bank study was conducted at Pendleton, SC, USA, to investigate the persistence of Palmer amaranth seeds buried uniformly across a 10-cm depth in soil inside polyvinyl chloride (PVC) cylindrical pipes over 4 years. The experiment was conducted using a split-plot design, with year as the main plot factor and with or without soil disturbance (shallow tillage to a depth of 10 cm) as the subplot factor. Annual soil disturbance through tillage in the spring stimulated emergence during the first and second year after burial. A total of 0.5% to 0.8% of the seed bank emerged during the 4-yr burial period, and 99% or more of the 4-yr total emergence occurred during the first two years of burial. Seeds retrieved from 0 to 5 cm and 5 to 10 cm depths did not differ in viability. Soil disturbance influenced the decline of the artificial seed bank at least in the first year, with fewer viable seeds remaining in annually-disturbed plots. Regardless of soil disturbance, a small fraction of seeds (0.01% to 0.03% of original seed bank) remained viable in the soil after four years of burial. In conclusion, Palmer amaranth seeds buried across a 10 cm soil depth in the artificial seed bank had low persistence, which implies that burial may aid management of the weed seed bank.

关键词： Burial Dormancy Persistence Soil Seed Bank Seedling Emergence Tillage

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Using Pyroxasulfone for Downy Brome (<i>Bromus tectorum</i>L.) Control in Winter Wheat

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American Journal of Plant Sciences 2017年第10期8卷 2367-2378页

作者： Vipan kumar prashant jha Amit J. jhala Department of Research Centers Southern Agricultural Research Center Montana State University Bozeman MT USA Department of Agronomy and Horticulture University of Nebraska-Lincoln Lincoln NE USA

Downy brome is one of the most troublesome weeds in no-till wheat production systems of the US Great Plains. Pyroxasulfone is a relatively new, soil-applied residual herbicide (root/shoot growth inhibitor) labeled for use in wheat. Multiple field experiments were conducted near Huntley, MT from 2012 through 2016 to determine the efficacy of pyroxasulfone to control downy brome in imidazolinone (IMI)-tolerant (Clearfield™) winter wheat. Pyroxasulfone did not cause any injury to wheat in any of the three studies. Downy brome injury with pyroxasulfone preemergence (PRE) only program did not differ between 89 or 178 g·ai (active ingredient)·ha-1 rates, and averaged 82% and 84% in 2 separate studies. In a preplant (PP) burndown program, the addition of pyroxasulfone (178 g·ai·ha-1) to glyphosate improved downy brome end-season injury from 15% to 74%. In a separate study, the end-season injury with pyroxasulfone was greater when applied PRE (84%) compared to the delayed PRE (DPRE) timing (74%). In addition, the water dispersible granule (WDG) formulation of pyroxasulfone performed slightly better than the suspension concentrate (SC) formulation for downy brome injury. Pyroxasulfone applied PRE in the fall at a rate of 89 g·ai·ha-1 followed by (fb) imazamox (44 g·ai·ha-1 rate) applied postemergence (POST) in the spring effectively controlled downy brome (99% end-season injury). Furthermore, the injury was consistent with the standard program comprising of propoxycarbazone (29 g·ai·ha-1) PRE fb imazamox POST in IMI-tolerant winter wheat. In conclusion, pyroxasulfone applied PRE in the fall can be effectively utilized in conjunction with a standard acetolactate synthase (ALS)-inhibitor-based POST herbicide program for a season-long downy brome management in winter wheat.

关键词： Downy Brome Pyroxasulfone Soil-Applied Herbicide Herbicide Rate Application Timing Formulation Wheat

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Evaluation of Preemergence Herbicides for Crop Safety and Weed Control in Safflower

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American Journal of Plant Sciences 2017年第10期8卷 2358-2366页

作者： prashant jha Vipan kumar Charlemagne A. Lim Ramawatar Yadav Southern Agricultural Research Center Department of Research Centers Montana State University Bozeman MT USA

Weed management in safflower (Carthamus tinctorious L.) is a major challenge for growers due to very limited herbicide options available, particularly for broadleaf weed control. Field experiments were conducted at the Montana State University Southern Agricultural Research Center (MSU-SARC) near Huntley, MT in 2015 and 2016 to evaluate preemergence (PRE) soil-residual herbicides for crop safety and season-long broadleaf weed control in safflower. Among all herbicide programs tested, only sulfentrazone (105 g·ai·ha-1) alone or with pendimethalin (1064 g·ai·ha-1) caused 4% to 12% early-season visible injury to safflower, although the injury was not evident beyond 30 DAT. Sulfentrazone alone or with pendimethalin and pyroxasulfone (59 g·ai·ha-1) with pendimethalin had a season-long residual activity on kochia [kochia scoparia (L.) Schrad] and Russian-thistle (Salsola tragus L), with 89% to 99% control at 60 DAT, and up to 98% reduction in weed density compared with dimethenamid-P (213 g·ai·ha-1) and S-metolachlor (433 g·ai·ha-1) at 65 DAT. Pyroxasulfone (59 or 118 g·ai·ha-1) alone or dimethenamid-P with pendimethalin provided a moderate to good control (65% to 79% at 60 DAT) of kochia and Russian-thistle. However, the end-season control of kochia or Russian-thistle was inadequate ( S-metolachlor alone program. Safflower grain yield with sulfentrazone alone or with pendimethalin, pyroxasulfone alone or with pendimethalin, and dimethenamid-P with pendimethalin averaged 3559 kg·ha-1, which was 195% higher compared with the nontreated check. In conclusion, sulfentrazone and pyroxasulfone or dimethenamid-P in combination with pendimethalin will be effective PRE herbicide programs for kochia and Russian-thistle control in safflower.

关键词： Safflower Weed Control Preemergence Herbicide kochia Russian-Thistle

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