Almost positive links are strongly quasipositive

We prove that any link admitting a diagram with a single negative crossing is strongly quasipositive. This answers a question of Stoimenow’s in the (strong) positive. As a second main result, we give a simple and complete characterization of link diagrams with quasipositive canonical surface (the surface produced by Seifert’s algorithm). As applications, we determine which prime knots up to 13 crossings are strongly quasipositive, and we confirm the following conjecture for knots that have a canonical surface realizing their genus: a knot is strongly quasipositive if and only if the Bennequin inequality is an equality.

Object Coreference in German: The Reflexive sich as a Problem for Derivational Approaches to Binding

Despite Grewendorf’s well-known German binding data with the double-object verb zeigen ‘show’, where one object reflexively binds the other and which suggests that the direct object (DO) is generated higher than the indirect object (IO), this paper argues for the canonical surface order of IO > DO as base order. We highlight the exceptional status of Grewendorf’s examples, build on scope facts as well as a quantitative acceptability rating study, and exploit the fact that zeigen can also be used as inherently reflexive with idiomatic meaning. Appealing to the base configuration of the pieces of idiomatic expressions and considering different Spell-Out possibilities of coreferential objects in German, we show that the case, number, and gender underspecification of the anaphor sich poses a previously unnoticed problem for derivational approaches to binding.

Socialization of Providencia stuartii enables resistance to environmental insults.

Providencia stuartii is a highly-social pathogen responsible for nosocomial chronic urinary tract infections. The bacterium indeed forms floating communities of cells (FCC) besides and prior-to canonical surface-attached biofilms (SAB). Within P. stuartii FCC, cells are riveted one to another owing to by self-interactions between its porins, viz. Omp-Pst1 and Omp-Pst2. In pathophysiological conditions, P. stuartii is principally exposed to high concentrations of urea, ammonia, bicarbonate, creatinine and to large variations of pH, questioning how these environmental cues affect socialization, and whether formation of SAB and FCC protects cells against those. Results from our investigations indicate that FCC and SAB can both form in the urinary tract, endowing cells with increased resistance and fitness. They additionally show that while Omp-Pst1 is the main gateway allowing penetration of urea, bicarbonate and ammonia into the periplasm, expression of Omp-Pst2 enables resistance to them.

Irreversible Alteration of Extracellular Vesicle and Cell-Free Messenger RNA Profiles in Human Plasma Associated With Ex Vivo Platelet Activation

The discovery and utility of clinically relevant circulating biomarkers depend on standardized methods that minimize preanalytical errors. Here, we examined the preanalytical variations of extracellular vesicles (EVs) and cell-free mRNA (cf-mRNA) profiles in human plasma and how post-freeze/thaw processing removes and retains EVs and cf-mRNA subtypes. Using multiparametric nanoscale flow cytometric analysis, which utilized forward light scatter, side scatter, and fluorescence intensity, we characterized the effect of specific preanalytical variables on vesicle subpopulations in human plasma. Cf-mRNA levels were measured by multiplexed RT-qPCR with a panel including housekeeping, platelet, and tissue-specific genes. We found that blood processing centrifugation and temperature strongly impacted the levels of residual platelets and platelet microvesicles. Intriguingly, exosome-sized events were more resistant to processing methods. We also examined the morphology of quiescent and activated platelets and platelet-derived EVs by electron microscopy. We demonstrated that platelet activation and fragmentation generated ex vivo vesicles similar to EVs in size, morphology, and canonical surface markers. Critically, freezing plasma containing residual platelets yielded irreversible ex vivo generation of new EV subpopulations and cf-mRNA transcripts, which were not removable by additional processing after freeze-thaw. In summary, we identified distinct subpopulations of EVs and cf-mRNA in human plasma that are differentially influenced by platelet activation and fragmentation during sample collection, processing, and banking via post freeze/thaw processing.

The Dual Complex of a Semi-log Canonical Surface

Semi-log canonical varieties are a higher-dimensional analogue of stable curves. They are the varieties appearing as the boundary $\Delta $ of a log canonical pair $(X,\Delta )$ and also appear as limits of canonically polarized varieties in moduli theory. For certain three-fold pairs $(X,\Delta ),$ we show how to compute the PL homeomorphism type of the dual complex of a dlt minimal model directly from the normalization data of $\Delta $.

An image analysis method to survey the dynamics of polar protein abundance in the regulation of tip growth

ABSTRACTTip growth is critical for the lifestyle of many walled cells. In yeast and fungi, this process is typically associated with the polarized deposition of conserved tip factors, including landmarks, Rho GTPases, cytoskeleton regulators, and membrane and cell wall remodelers. Because tip growth speeds may vary extensively between life cycles or species, we asked whether the local amount of specific polar elements could determine or limit tip growth speeds. Using the model fission yeast, we developed a quantitative image analysis pipeline to dynamically correlate single tip elongation speeds and polar protein abundance in large data sets. We found that polarity landmarks are typically diluted by growth. In contrast, tip growth speed is positively correlated with the local amount of factors related to actin, secretion or cell wall remodeling, but, surprisingly, exhibits long saturation plateaus above certain concentrations of those factors. Similar saturation observed for Spitzenkörper components in much faster growing fungal hyphae suggests that elements independent of canonical surface remodelers may limit single tip growth. This work provides standardized methods and resources to decipher the complex mechanisms that control cell growth.This article has an associated First Person interview with Sarah Taheraly, joint first author of the paper.

Binding German (In)direct Objects: Spell-Out Strategies for Disambiguation

Despite Grewendorf’s (1988) well-known German binding data with the double-object verb zeigen ‘show’, which suggests that the direct object (DO) is generated higher than the indirect object (IO), this paper argues for the canonical surface order of IO>DO as base order. Highlighting the exceptional status of Grewendorf's examples, building on Featherston & Sternefeld’s (2003) quantitative acceptability rating study, and exploiting the fact that zeigen can also be used as inherently reflexive with idiomatic meaning, and we appeal to Bruening's (2010) theory of idiom formation as well as the Encyclopedia within Distributed Morphology (Marantz 1997, Embick & Noyer 2007) and propose a flexible Spell-Out mechanism within a derivational approach to binding (e.g. Hornstein 2001 and Zwart 2002) that can override narrow syntactic case licensing by realizing nominals with different morphological case.