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1. Quasi‐polynomial mixing of critical two‐dimensional random cluster models

   https://doi.org/10.1002/rsa.20868  

   Gheissari, Reza ; Lubetzky, Eyal ( June 2019 , Random Structures & Algorithms)

   We study the Glauber dynamics for the random cluster (FK) model on the toruswith parameters (p,q), forq ∈ (1,4] andpthe critical point p_c. The dynamics is believed to undergo acritical slowdown, with its continuous‐time mixing time transitioning fromforp ≠ p_cto a power‐law innatp = p_c. This was verified atp ≠ p_cby Blanca and Sinclair, whereas at the criticalp = p_c, with the exception of the special integer pointsq = 2,3,4 (where the model corresponds to the Ising/Potts models) the best‐known upper bound on mixing was exponential inn. Here we prove an upper bound ofatp = p_cfor allq ∈ (1,4], where a key ingredient is bounding the number of nested long‐range crossings at criticality.

    

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2. Paludicola gen. nov. and Revision of the Species Formerly in Batrachospermum Section  Turfosa (Batrachospermales, Rhodophyta)

   https://doi.org/10.1111/jpy.13001  

   Vis, Morgan L. ; Lee, Janina ; Eloranta, Pertti ; Chapuis, Iara S. ; Lam, Daryl W. ; Necchi, Jr., Orlando ; Oliveira, ed., M. C. ( May 2020 , Journal of Phycology)

   Since the first phylogenetic study of the order Batrachospermales,Batrachospermumwas shown to be paraphyletic. Subsequently, sections of the genus have been methodically investigated usingDNAsequences and morphology in order to propose new genera and delineate species.BatrachospermumsectionTurfosais the last section with multiple species yet to be examined. New sequence data of specimens from Europe and the United States were combined with the sparse sequence data already available. Phylogenetic analyses usingrbcL andCOI‐5P sequences showed this section to be a well‐supported clade, distinct fromBatrachospermumsectionBatrachospermumand its segregate genera. Section Turfosais raised to the generic rank asPaludicolagen. nov. Substantial genetic variation within the genus was discovered and 12 species are recognized based onDNAsequence data as well as morphological characters and geographic distribution. The following morphological characters were applied to distinguish species: branching pattern (pseudodichotomous or irregular), whorl size (reduced or well developed), primary fascicles (curved or straight), spermatangia origin (primary or secondary fascicles), and carposporophyte arrangement (loose or dense). Previously published species were transferred to the new genus:P. turfosa,P. keratophyta,P. orthosticha,P. phangiae,andP. periploca. Seven new species are proposed as follows:P. groenbladiifrom Europe;P. communis,P. johnhallii, andP. leafensisfrom North America; andP. aquanigra,P. diamantinensis, andP. turfosiformisfrom Brazil. In addition, three unsequenced species in the section,P. bakarensis,P. gombakensis, andP. tapirensis, were transferred to the new genus.

    

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3. Relationship between local-scale topography and vegetation on the invasive C 4 perennial bunchgrass buffelgrass ( Pennisetum ciliare ) size and reproduction

   https://doi.org/10.1017/inp.2023.9  

   Hovanes, Katherine A. ; Lien, Aaron M. ; Baldwin, Elizabeth ; Li, Yue M. ; Franklin, Kim ; Gornish, Elise S. ( March 2023 , Invasive Plant Science and Management)

   Buffelgrass [Pennisetum ciliare(L.) Link] is an invasive C₄perennial bunchgrass that is a threat to biodiversity in aridlands in the Americas and Australia. Topography influencesP. ciliareoccurrence at large spatial scales, but further investigation into the relationship between local-scale topography andP. ciliaregrowth and reproduction would be beneficial. Further, density-dependent effects onP. ciliaregrowth and reproduction have been demonstrated in greenhouse experiments, but the extent to which density dependence influencesP. ciliarein natural populations warrants further investigation. Here we present a study on the relationships between local-scale topography (aspect and slope gradient) and vegetation characteristics (shrub cover,P. ciliarecover, andP. ciliaredensity) and their interactions on individualP. ciliareplant size and reproduction. We measured slope gradient, aspect, shrub cover,P. ciliarecover,P. ciliaredensity, and the total number of live culms and reproductive culms of 10P. ciliareplants in 33 4 by 4 m plots located in 11 transects at the Desert Laboratory at Tumamoc Hill, Tucson, AZ, USA. We modeled the relationships at the local scale of (1)P. ciliarecover and density with aspect and slope gradient and (2)P. ciliaresize and reproduction with abiotic (slope gradient and aspect) and biotic (P. ciliarecover and density and native shrub and cacti cover) characteristics. Aspect and slope gradient were poor predictors ofP. ciliarecover and density in already invaded sites at the scale of our plots. However, aspect had a significant relationship withP. ciliareplant size and reproduction.Pennisetum ciliareplants on south-facing aspects were larger and produced more reproductive culms than plants on other aspects. Further, we found no relationship betweenP. ciliaredensity andP. ciliareplant size and reproduction. Shrub cover was positively correlated withP. ciliarereproduction. South-facing aspects are likely most vulnerable to fast spread and infilling by newP. ciliareintroductions.

    

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4. Variation in the SSUrDNA of the Genus Protostelium Leads to a New Phylogenetic Understanding of the Genus and of the Species Concept for Protostelium mycophaga (Protosteliida, Amoebozoa)

   https://doi.org/10.1111/jeu.12476  

   Shadwick, John D. L. ; Silberman, Jeffery D. ; Spiegel, Frederick W. ( November 2017 , Journal of Eukaryotic Microbiology)

   Members of the genusProtostelium(includingP. mycophaga,P. nocturnum, andP. okumukumu) are protosteloid amoebae commonly found in terrestrial habitats on dead plant matter. They, along with the closely allied nominal genusPlanoprotostelium, containing the single speciesPl. aurantium, all have an amoeboid trophic stage with acutely pointed subpseudopodia and orange lipid droplets in the granuloplasm. These amoebae form stalked fruiting bodies topped with a single, usually deciduous spore. The species are identified based on their fruiting body morphologies except forPl. aurantiumwhich looks similar toP. mycophagain fruiting morphology, but has amoebae that can make flagella in liquid medium. We built phylogenetic trees using nuclear small subunit ribosomalDNAsequences of 35 isolates from the generaProtosteliumandPlanoprotosteliumand found that (1) the nonflagellatedP. nocturnumandP. okumukumubranch basally in the genusProtostelium, (2) the flagellate,Pl. aurantiumfalls within the genusProtosteliumin a monophyletic clade with the nominal variety,P. mycophagavar.crassipes, (3) the cultures initially identified asProtostelium mycophagacan be divided into at least three morphologically recognizable taxa,P. aurantiumn. comb.,P. apiculatumn. sp., andP. m. rodmanin. subsp., as well as a paraphyletic assemblage that includes the remainder of theP. mycophagamorphotype. These findings have implications for understanding the ecology, evolution, and diversity of these amoeboid organisms and for using these amoebae as models for other amoeboid groups.

    

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5. Statistics of Energy in Isothermal Supersonic Turbulence

   https://doi.org/10.3847/1538-4357/ad5008  

   Rabatin, Branislav ; Collins, David_C ( July 2024 , The Astrophysical Journal)

   Supersonic isothermal turbulence is a common process in astrophysical systems. In this work, we explore the energy in such systems. We show that the conserved energy is the sum of the kinetic energy (K) and Helmholtz free energy (F). We develop analytic predictions for the probability distributions,P(F) andP(K), as well as their nontrivial joint distribution,P(F,K). We verify these predictions with a suite of driven turbulence simulations, finding excellent agreement. The turbulence simulations were performed at Mach numbers ranging from 1 to 8, and three modes of driving: purely solenoidal, purely compressive, and mixed. We find thatP(F) is discontinuous atF= 0, with the discontinuity increasing with Mach number and compressive driving.P(K) resembles a lognormal with a negative skew. The joint distribution,P(F,K), shows a bimodal distribution, with gas either existing at highFand highKor at lowFand lowK.

    

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