**14** Publications

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Plant Phenomics 2020 8;2020:3252703. Epub 2020 Nov 8.

The Pennsylvania State University, Department of Plant Science, Tyson Building, University Park, PA 16802, USA.

A soil coring protocol was developed to cooptimize the estimation of root length distribution (RLD) by depth and detection of functionally important variation in root system architecture (RSA) of maize and bean. The functional-structural model was used to perform soil coring at six locations on three different maize and bean RSA phenotypes. Results were compared to two seasons of field soil coring and one trench. Two one-sided -test (TOST) analysis of data suggests a between-row location 5 cm from plant base (location 3), best estimates whole-plot RLD/D of deep, intermediate, and shallow RSA phenotypes, for both maize and bean. Quadratic discriminant analysis indicates location 3 has ~70% categorization accuracy for bean, while an in-row location next to the plant base (location 6) has ~85% categorization accuracy in maize. Analysis of field data suggests the more representative sampling locations vary by year and species. and field studies suggest location 3 is most robust, although variation is significant among seasons, among replications within a field season, and among field soil coring, trench, and simulations. We propose that the characterization of the RLD profile as a dynamic rhizo canopy effectively describes how the RLD profile arises from interactions among an individual plant, its neighbors, and the pedosphere.

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http://dx.doi.org/10.34133/2020/3252703 | DOI Listing |

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7706327 | PMC |

November 2020

Plant Cell Environ 2021 01 30;44(1):49-67. Epub 2020 Sep 30.

Department of Plant Science, The Pennsylvania State University, University Park, Pennsylvania, USA.

At the genus and species level, variation in root anatomy and architecture may interact to affect strategies of drought avoidance. To investigate this idea, root anatomy and architecture of the drought-sensitive common bean (Phaseolus vulgaris) and drought-adapted tepary bean (Phaseolus acutifolius) were analyzed in relation to water use under terminal drought. Intraspecific variation for metaxylem anatomy and axial conductance was found in the roots of both species. Genotypes with high-conductance root metaxylem phenotypes acquired and transpired more water per unit leaf area, shoot mass, and root mass than genotypes with low-conductance metaxylem phenotypes. Interspecific variation in root architecture and root depth was observed where P. acutifolius has a deeper distribution of root length than P. vulgaris. In the deeper-rooted P. acutifolius, genotypes with high root conductance were better able to exploit deep soil water than genotypes with low root axial conductance. Contrastingly, in the shallower-rooted P. vulgaris, genotypes with low root axial conductance had improved water status through conservation of soil moisture for sustained water capture later in the season. These results indicate that metaxylem morphology interacts with root system depth to determine a strategy of drought avoidance and illustrate synergism among architectural and anatomical phenotypes for root function.

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http://dx.doi.org/10.1111/pce.13875 | DOI Listing |

January 2021

Transl Vis Sci Technol 2019 Jan 28;8(1):25. Epub 2019 Feb 28.

Institute of Neuroscience, Newcastle University, Framlington Place, Newcastle upon Tyne, UK.

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http://dx.doi.org/10.1167/tvst.8.1.25 | DOI Listing |

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6396686 | PMC |

January 2019

R Soc Open Sci 2018 Jan 3;5(1):171446. Epub 2018 Jan 3.

Department of Mathematics, University of Portsmouth, Portsmouth, UK.

We provide a unified mathematical explanation of two classical forms of spatial linguistic spread. The model describes the radiation of linguistic change outwards from a central focus. Changes can also jump between population centres in a process known as . It has recently been proposed that the spatial evolution of dialects can be understood using surface tension at linguistic boundaries. Here we show that the inclusion of long-range interactions in the surface tension model generates both wave-like spread, and hierarchical diffusion, and that it is surface tension that is the dominant effect in deciding the stable distribution of dialect patterns. We generalize the model to allow population mixing which can induce shrinkage of linguistic domains, or destroy dialect regions from within.

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http://dx.doi.org/10.1098/rsos.171446 | DOI Listing |

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5792924 | PMC |

January 2018

Phys Rev E 2016 Dec 30;94(6-1):062319. Epub 2016 Dec 30.

Department of Mathematics, University of Portsmouth, Lion Terrace, Portsmouth PO1 3HF, United Kingdom.

We study the spread of a persuasive new idea through a population of continuous-time random walkers in one dimension. The idea spreads via social gatherings involving groups of nearby walkers who act according to a biased "majority rule": After each gathering, the group takes on the new idea if more than a critical fraction 1-ɛ/2<1/2 of them already hold it; otherwise they all reject it. The boundary of a domain where the new idea has taken hold expands as a traveling wave in the density of new idea holders. Our walkers move by Lévy motion, and we compute the wave velocity analytically as a function of the frequency of social gatherings and the exponent of the jump distribution. When this distribution is sufficiently heavy tailed, then, counter to intuition, the idea can propagate faster if social gatherings are held less frequently. When jumps are truncated, a critical gathering frequency can emerge which maximizes propagation velocity. We explore our model by simulation, confirming our analytical results.

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http://dx.doi.org/10.1103/PhysRevE.94.062319 | DOI Listing |

December 2016

Theor Appl Genet 2017 Feb 18;130(2):419-431. Epub 2016 Nov 18.

Department of Plant Science, The Pennsylvania State University, 221 Tyson Building, University Park, PA, 16802, USA.

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http://dx.doi.org/10.1007/s00122-016-2823-y | DOI Listing |

February 2017

Phys Rev E 2016 Jun 1;93(6):062402. Epub 2016 Jun 1.

Department of Mathematics, University of Portsmouth, Portsmouth, PO1 3HF, United Kingdom.

The songs and calls of many bird species, like human speech, form distinct regional dialects. We suggest that the process of dialect formation is analogous to the physical process of magnetic domain formation. We take the coastal breeding grounds of the Puget Sound white crowned sparrow as an example. Previous field studies suggest that birds of this species learn multiple songs early in life, and when establishing a territory for the first time, retain one of these dialects in order to match the majority of their neighbors. We introduce a simple lattice model of the process, showing that this matching behavior can produce single dialect domains provided the death rate of adult birds is sufficiently low. We relate death rate to thermodynamic temperature in magnetic materials, and calculate the critical death rate by analogy with the Ising model. Using parameters consistent with the known behavior of these birds we show that coastal dialect domain shapes may be explained by viewing them as low-temperature "stripe states."

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http://dx.doi.org/10.1103/PhysRevE.93.062402 | DOI Listing |

June 2016

Phys Rev E Stat Nonlin Soft Matter Phys 2015 Oct 5;92(4):042111. Epub 2015 Oct 5.

Department of Mathematics, University of Portsmouth, Portsmouth PO1 2UP, United Kingdom.

When playing games in groups, it is an advantage for individuals to have accurate statistical information on the strategies of their opponents. Such information may be obtained by remembering previous interactions. We consider a rock-paper-scissors game in which agents are able to recall their last m interactions, used to estimate the behavior of their opponents. At critical memory length, a Hopf bifurcation leads to the formation of stable limit cycles. In a mixed population, agents with longer memories have an advantage, provided the system has a stable fixed point, and there is some asymmetry in the payoffs of the pure strategies. However, at a critical concentration of long memory agents, the appearance of limit cycles destroys their advantage. By introducing population dynamics that favors successful agents, we show that the system evolves toward the bifurcation point.

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http://dx.doi.org/10.1103/PhysRevE.92.042111 | DOI Listing |

October 2015

Plant Methods 2015 2;11:51. Epub 2015 Nov 2.

School of Biology, Georgia Institute of Technology, Atlanta, GA USA ; School of Interactive Computing, Georgia Institute of Technology, Atlanta, GA USA.

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http://dx.doi.org/10.1186/s13007-015-0093-3 | DOI Listing |

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4630929 | PMC |

November 2015

Phys Rev E Stat Nonlin Soft Matter Phys 2015 Sep 14;92(3):032119. Epub 2015 Sep 14.

School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, United Kingdom.

We present a simple game model where agents with different memory lengths compete for finite resources. We show by simulation and analytically that an instability exists at a critical memory length, and as a result, different memory lengths can compete and coexist in a dynamical equilibrium. Our analytical formulation makes a connection to statistical urn models, and we show that temperature is mirrored by the agent's memory. Our simple model of memory may be incorporated into other game models with implications that we briefly discuss.

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http://dx.doi.org/10.1103/PhysRevE.92.032119 | DOI Listing |

September 2015

Phys Rev E Stat Nonlin Soft Matter Phys 2015 Feb 6;91(2):022403. Epub 2015 Feb 6.

Department of Geography, University of Portsmouth, Portsmouth PO1 3HE, United Kingdom.

When corroding or otherwise aggressive particles are incident on a surface, pits can form. For example, under certain circumstances rock surfaces that are exposed to salts can form regular tessellating patterns of pits known as "tafoni." We introduce a simple lattice model in which a gas of corrosive particles, described by a discrete, biased diffusion equation, drifts onto a surface. Each gas particle has a fixed probability of being absorbed and causing damage at each contact. The surface is represented by a lattice of strength numbers which reduce after each absorbtion event, with sites being removed when their strength becomes negative. Regular formations of pits arise spontaneously, with each pit having a characteristic trapezoidal geometry determined by the particle bias, absorbtion probability, and surface strength. The formation of this geometry may be understood in terms of a first order partial differential equation and is a consequence of particle concentration gradients which arise in the pits. By viewing pits as particle funnels, we are able to relate the gradient of pit walls to absorbtion probability and particle bias.

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http://dx.doi.org/10.1103/PhysRevE.91.022403 | DOI Listing |

February 2015

Plant Physiol 2014 Oct 3;166(2):470-86. Epub 2014 Sep 3.

Schools of Biology (A.B., A.D. J.S.W.), Interactive Computing (A.B.), and Physics (J.S.W.), Georgia Institute of Technology, Atlanta, Georgia 30332; andDepartment of Plant Science (J.B., L.M.Y., E.N., J.P.L.) and Intercollege Graduate Degree Program in Ecology (L.M.Y.), Pennsylvania State University, University Park, Pennsylvania 16801.

Current plant phenotyping technologies to characterize agriculturally relevant traits have been primarily developed for use in laboratory and/or greenhouse conditions. In the case of root architectural traits, this limits phenotyping efforts, largely, to young plants grown in specialized containers and growth media. Hence, novel approaches are required to characterize mature root systems of older plants grown under actual soil conditions in the field. Imaging methods able to address the challenges associated with characterizing mature root systems are rare due, in part, to the greater complexity of mature root systems, including the larger size, overlap, and diversity of root components. Our imaging solution combines a field-imaging protocol and algorithmic approach to analyze mature root systems grown in the field. Via two case studies, we demonstrate how image analysis can be utilized to estimate localized root traits that reliably capture heritable architectural diversity as well as environmentally induced architectural variation of both monocot and dicot plants. In the first study, we show that our algorithms and traits (including 13 novel traits inaccessible to manual estimation) can differentiate nine maize (Zea mays) genotypes 8 weeks after planting. The second study focuses on a diversity panel of 188 cowpea (Vigna unguiculata) genotypes to identify which traits are sufficient to differentiate genotypes even when comparing plants whose harvesting date differs up to 14 d. Overall, we find that automatically derived traits can increase both the speed and reproducibility of the trait estimation pipeline under field conditions.

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http://dx.doi.org/10.1104/pp.114.243519 | DOI Listing |

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4213080 | PMC |

October 2014

Phys Rev Lett 2013 Nov 18;111(21):218001. Epub 2013 Nov 18.

Department of Mathematics, University of Portsmouth, PO1 3HF, United Kingdom.

A spatial avalanche model is introduced, in which avalanches increase stability in the regions where they occur. Instability is driven globally by a driving process that contains shocks. The system is typically subcritical, but the shocks occasionally lift it into a near- or supercritical state from which it rapidly retreats due to large avalanches. These shocks leave behind a signature-a distinct power-law crossover in the avalanche size distribution. The model is inspired by landslide field data, but the principles may be applied to any system that experiences stabilizing failures, possesses a critical point, and is subject to an ongoing process of destabilization that includes occasional dramatic destabilizing events.

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http://dx.doi.org/10.1103/PhysRevLett.111.218001 | DOI Listing |

November 2013

Phys Rev E Stat Nonlin Soft Matter Phys 2013 Sep 18;88(3):032124. Epub 2013 Sep 18.

Department of Mathematics, University of Portsmouth, Portsmouth PO1 3HF, United Kingdom.

We propose a model which explains how power-law crossover behavior can arise in a system which is capable of experiencing cascading failure. In our model the susceptibility of the system to cascades is described by a single number, the propagation power, which measures the ease with which cascades propagate. Physically, such a number could represent the density of unstable material in a system, its internal connectivity, or the mean susceptibility of its component parts to failure. We assume that the propagation power follows an upward drifting Brownian motion between cascades, and drops discontinuously each time a cascade occurs. Cascades are described by a continuous state branching process with distributional properties determined by the value of the propagation power when they occur. In common with many cascading models, pure power-law behavior is exhibited at a critical level of propagation power, and the mean cascade size diverges. This divergence constrains large systems to the subcritical region. We show that as a result, crossover behavior appears in the cascade distribution when an average is performed over the distribution of propagation power. We are able to analytically determine the exponents before and after the crossover.

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http://dx.doi.org/10.1103/PhysRevE.88.032124 | DOI Listing |

September 2013