An Analytic and Probabilistic Approach to the Problem of Matroid Representibility

We introduce various quantities that can be defined for an arbitrary matroid, and show that certain conditions on these quantities imply that a matroid is not representable over $\mathbb{F}_q$. Mostly, for a matroid of rank $r$, we examine the proportion of size-$(r-k)$ subsets that are dependent, and give bounds, in terms of the cardinality of the matroid and $q$ a prime power, for this proportion, below which the matroid is not representable over $\mathbb{F}_q$. We also explore connections between the defined quantities and demonstrate that they can be used to prove that random matrices have high proportions of subsets of columns independent

Soilless cultivation of cherry tomato with gutter subirrigationn and reused substrate

Soilless cultivation systems in horticultural production are modern technologies that involve the supply of water and minerals through the nutrient solution and plant growth on media. The soilless cultivation of vegetables ensures higher yields and better quality than with traditional soil crops. When managed in a closed system with irrigation water of good quality soilless cultivation can significantly reduce the environmental impact of nutrient solutions with respect to crops grown in open systems. Compared with drip irrigation, gutter subirrigation simplifies the management of the closed system because disinfection of recirculated nutrient solution and correction of its chemical composition is not necessary. Gutter subirrigation was developed in previous experiments for the cultivation of tomato on fresh substrate. The objective of this work was to evaluate the use of the same substrate after two consecutive crops of tomato and to study the effect of the presence, if any, of previous radical residues with the same cultivar and rootstock. The experiment was conducted in an unheated iron and polycarbonate greenhouse with forced ventilation. Cherry tomato plants were transplanted into pots containing fresh or reused coconut fiber. The following parameters were considered: biomass, production,product quality (electrical conductivity, pH, titratable acidity, dry residue, dissolved solid content) and chemical analysis of recirculated and radical nutrient solution. The results obtained in this experiment reveal no significant differences in production and fruit quality between plants grown on fresh substrate and those grown on reused substrate (marketable yield was 5.4 kg m-2 vs 5.3 kg m-2, respectively)

Litter quality and temperature modulate microbial diversity effects on decomposition in model experiments

The consequences of decline in biodiversity for ecosystem functioning is a major concern in soil ecology. Recent research efforts have been mostly focused on terrestrial plants, while, despite their importance in ecosystems, little is known about soil microbial communities. This work aims at investigating the effects of fungal and bacterial species richness on the dynamics of leaf litter decomposition. Synthetic microbial communities with species richness ranging from 1 to 64 were assembled in laboratory microcosms and used in three factorial experiments of decomposition. Thereafter, the functionality of the different microcosms was determined by measuring their capability to decompose materials with different chemical properties, including two species of litter (Quercus ilex L. and Hedera helix L.), cellulose strips and woody sticks. Incubation was done in microcosms at two temperatures (12°C and 24°C) for 120 days. The number of microbial species inoculated in the microcosms positively affected decomposition rates of Q. ilex and H. helix litters, while relationships found for cellulose and wood were not statistically significant. Diversity effect was greater at higher incubation temperature. We found lower variability of decay rates in microcosms with higher inoculated species richness of microbial communities. Our study pointed out that the relationships between inoculum microbial diversity and litter decomposition is dependent on temperature and litter quality. Therefore, the loss of microbial species may adversely affects ecosystem functionality under specific environmental conditions

Weighting non-covalent forces in the molecular recognition of C60. Relevance of concave–convex complementarity

The relative contributions of several weak intermolecular forces to the overall stability of the complexes formed between structurally related receptors and [60]fullerene are compared, revealing a discernible contribution from concave–convex complementarity.Viruela Martin, Pedro Manuel, [email protected] ; Viruela Martin, Rafael, [email protected] ; Orti Guillen, Enrique, [email protected]

Multiparameter diagnostic sensor measurements in heart failure patients presenting with SARS‐CoV‐2 infection

Aims: Implantable device‐based sensor measurements including heart sounds, markers of ventilation, and thoracic impedance have been shown to predict heart failure (HF) hospitalizations. We sought to assess how these parameters changed prior to COVID‐19 (Cov‐19) and how these compared with those presenting with decompensated HF or pneumonia. Methods and results: This retrospective analysis explores patterns of changes in daily measurements by implantable sensors in 10 patients with Cov‐19 and compares these findings with those observed prior to HF (n = 88) and pneumonia (n = 12) hospitalizations from the MultiSENSE, PREEMPT‐HF, and MANAGE‐HF trials. The earliest sensor changes prior to Cov‐19 were observed in respiratory rate (6 days) and temperature (5 days). There was a three‐fold to four‐fold greater increase in respiratory rate, rapid shallow breathing index, and night heart rate compared with those presenting with HF or pneumonia. Furthermore, activity levels fell more in those presenting with Cov‐19, a change that was often sustained for some time. In contrast, there were no significant changes in 1st or 3rd heart sound (S1 and S3) amplitude in those presenting with Cov‐19 or pneumonia compared with the known changes that occur in HF decompensation. Conclusions: Multi‐sensor device diagnostics may provide early detection of Cov‐19, distinguishable from worsening HF by an extreme and fast rise in respiratory rate along with no changes in S3

A reassessment of the association between azulene and [60]fullerene. Possible pitfalls in the determination of binding constants through fluorescence spectroscopy

We show here that the recently reported surprisingly large association constant (K = 7.6 x 10(4) M-1) between azulene and [60]fullerene is due to experimental artifacts, pointing out potential errors in the characterization of association equilibria by fluorescence spectroscopy, and suggesting the best experimental practices

Rare self-facilitation in terrestrial plants as compared to aquatic sessile organisms: Empirical evidences and causal mechanisms

Species-specificity of facilitative interactions is ecologically relevant for community organization and dynamics. The prevalence of heterospecific facilitation which is found between higher plants seems an evolutionary paradox since beneficiary heterospecifics can compete with, and even replace, their nurse. An extensive review on facilitative interactions for both higher plants and sessile aquatic organisms is presented. The study reports on the occurrence of positive interactions between conspecifics and heterospecifics, in relation to different growth forms and facilitative mechanisms in terrestrial and aquatic environments. Four hypotheses are considered to explain the observed rarity of conspecific compared to heterospecific facilitation: 1) the occurrence of plant-induced unsuitable recruitment conditions (negative conspecific plant-soil feedback and hump-shaped recruitment distribution), 2) higher competition levels between conspecifics, 3) the prevalence of non-facilitated regeneration niche for nurses, and, 4) differences in the research effort. Self-facilitation is reported much more rarely in terrestrial vegetation (5.3% of 1554 cases of facilitiative interactions), than in aquatic ecosystems (36.2%, n = 130). In absolute terms, far more occurrences of heterospecific facilitative interactions are reported for all growth forms. However, when the occurrences of facilitative interactions are expressed as a percentage of the total con- and heterospecific interactions, annual and perennial herbaceous nurse plants show prevailing conspecific interactions, while woody (trees and shrubs) nurse species mostly show heterospecific facilitation. Increase of soil nutrient fertility, improvement of above-ground microclimate, associational refuge and seed trapping are the most common mechanisms of heterospecific interactions. Differently, conspecific facilitation is mostly due to improved soil biotic conditions, changes in fire regimes and reduction of heterospecific competition. Given the frequently reported occurrence of non-facilitated regeneration niche for nurse species, conspecific negative feedback and hump-shaped recruitment distribution in terrestrial plants, these processes are suggested as significantly contributing to explain the observed rarity of conspecific facilitation