Ice mantles on dust grains: dramatic variation of thickness with grain size

ABSTRACT We compute the desorption rate of icy mantles on dust grains as a function of the size and composition of both the grain and the mantle. We combine existing models of cosmic ray (CR)-related desorption phenomena with a model of CR transport to accurately calculate the desorption rates in dark regions of molecular clouds. We show that different desorption mechanisms dominate for grains of different sizes and in different regions of the cloud. We then use these calculations to investigate a simple model of the growth of mantles, given a distribution of grain sizes. We find that modest variations of the desorption rate with grain size lead to a strong dependence of mantle thickness on grain size. Furthermore, we show that freeze-out is almost complete in the absence of an external ultraviolet (UV) field, even when photodesorption from CR-produced UV is taken into consideration. Even at gas densities of $10^4\, {\rm cm^{-3}}$, less than 30 per cent of the CO remain in the gas phase after 3 × 105 yr for standard values of the CR ionization rate.

Control-theoretic immune tradeoffs explain SARS-CoV-2 virulence and transmission variation

Dramatic variation in SARS-CoV-2 virulence and transmission between hosts has driven the COVID-19 pandemic. The complexity and dynamics of the immune response present a challenge to understanding variation in SARS-CoV-2 infections. To address this challenge, we apply control theory, a framework used to study complex feedback systems, to establish rigorous mathematical bounds on immune responses. Two mechanisms of SARS-CoV-2 biology are sufficient to create extreme variation between hosts: (1) a sparsely expressed host receptor and (2) potent, but not unique, suppression of interferon. The resulting model unifies disparate and unexplained features of the SARS-CoV-2 pandemic, predicts features of future viruses that threaten to cause pandemics, and identifies potential interventions.

Biogeographical venom variation in the Indian spectacled cobra (Naja naja) underscores the pressing need for pan-India efficacious snakebite therapy

Background Snake venom composition is dictated by various ecological and environmental factors, and can exhibit dramatic variation across geographically disparate populations of the same species. This molecular diversity can undermine the efficacy of snakebite treatments, as antivenoms produced against venom from one population may fail to neutralise others. India is the world’s snakebite hotspot, with 58,000 fatalities and 140,000 morbidities occurring annually. Spectacled cobra (Naja naja) and Russell’s viper (Daboia russelii) are known to cause the majority of these envenomations, in part due to their near country-wide distributions. However, the impact of differing ecologies and environment on their venom compositions has not been comprehensively studied. Methods Here, we used a multi-disciplinary approach consisting of venom proteomics, biochemical and pharmacological analyses, and in vivo research to comparatively analyse N. naja venoms across a broad region (>6000 km; seven populations) covering India’s six distinct biogeographical zones. Findings By generating the most comprehensive pan-Indian proteomic and toxicity profiles to date, we unveil considerable differences in the composition, pharmacological effects and potencies of geographically-distinct venoms from this species and, through the use of immunological assays and preclinical experiments, demonstrate alarming repercussions on antivenom therapy. We find that commercially-available antivenom fails to effectively neutralise envenomations by the pan-Indian populations of N. naja, including a complete lack of neutralisation against the desert Naja population. Conclusion Our findings highlight the significant influence of ecology and environment on snake venom composition and potency, and stress the pressing need to innovate pan-India effective antivenoms to safeguard the lives, limbs and livelihoods of the country’s 200,000 annual snakebite victims.

A Field Guide to Eukaryotic Transposable Elements

Transposable elements (TEs) are mobile DNA sequences that propagate within genomes. Through diverse invasion strategies, TEs have come to occupy a substantial fraction of nearly all eukaryotic genomes, and they represent a major source of genetic variation and novelty. Here we review the defining features of each major group of eukaryotic TEs and explore their evolutionary origins and relationships. We discuss how the unique biology of different TEs influences their propagation and distribution within and across genomes. Environmental and genetic factors acting at the level of the host species further modulate the activity, diversification, and fate of TEs, producing the dramatic variation in TE content observed across eukaryotes. We argue that cataloging TE diversity and dissecting the idiosyncratic behavior of individual elements are crucial to expanding our comprehension of their impact on the biology of genomes and the evolution of species.

“Thinking White”: Performing Racial Tension in Blue Collar

By most accounts, as Paul Schrader’s first film as director, Blue Collar was a tension-filled production with the three leading actors coming to blows on multiple occasions. This chapter, will explore the performance styles of Harvey Keitel, Yaphet Kotto, and Richard Pryor with particular focus paid to the latter’s identity as a stand-up comic and movie star during the mid- to late- 1970s. Through casting Pryor, Schrader does not fundamentally alter this comic persona but rather captures a dramatic variation of it, employing it as a defying signifier against the midcentury “realist” acting styles of Keitel and Kotto, who both trained on the New York stage. Through a fostering and challenging of Pryor’s persona and style, Schrader produces a tension between his performers that feels acutely aware of the comedian’s “territorialized” black identity as well as his ability to challenge racial boundaries through his humor. The contrasting styles of Keitel, Kotto, and Pryor provide a dramatic tension attuned to the complicated racial conflicts found in the more integrated work spaces of the 1970s.

Complex Evolutionary History of the Y Chromosome in Flies of the Drosophila obscura Species Group

The Drosophila obscura species group shows dramatic variation in karyotype, including transitions among sex chromosomes. Members of the affinis and pseudoobscura subgroups contain a neo-X chromosome (a fusion of the X with an autosome), and ancestral Y genes have become autosomal in species harboring the neo-X. Detailed analysis of species in the pseudoobscura subgroup revealed that ancestral Y genes became autosomal through a translocation to the small dot chromosome. Here, we show that the Y-dot translocation is restricted to the pseudoobscura subgroup, and translocation of ancestral Y genes in the affinis subgroup likely followed a different route. We find that most ancestral Y genes have translocated to unique autosomal or X-linked locations in different taxa of the affinis subgroup, and we propose a dynamic model of sex chromosome formation and turnover in the obscura species group. Our results suggest that Y genes can find unique paths to escape unfavorable genomic environments that form after sex chromosome–autosome fusions.

Macroevolutionary analysis of discrete traits with rate heterogeneity

Organismal traits show dramatic variation in phylogenetic patterns of origin and loss across the Tree of Life. Understanding the causes and consequences of this variation depends critically on accounting for heterogeneity in rates of trait evolution among lineages. Here, we describe a method for modeling among-lineage evolutionary rate heterogeneity in a trait with two discrete states. The method assumes that the present-day distribution of a binary trait is shaped by a mixture of stochastic processes in which the rate of evolution varies among lineages in a phylogeny. The number and location of rate changes, which we refer to as rate-shift events, are inferred automatically from the data. Simulations reveal that the method accurately reconstructs rates of trait evolution and ancestral character states even when simulated data violate model assumptions. We apply the method to an empirical dataset of mimetic coloration in snakes and find elevated rates of trait evolution in two clades of harmless snakes that are broadly sympatric with dangerously venomous New World coral snakes, recapitulating an earlier analysis of the same dataset. Although the method performed well on many simulated data sets, we caution that overall power for inferring heterogeneous dynamics of single binary traits is low.

Annual Variation of CO2 Absorption and Release in Caotang River of Three Gorges Reservoir

To analyze the annual variation of CO2 absorption and release in Caotang River of Three Gorges Reservoir, this paper selected six sections from the Yangtze River and Caotang River between July 2017 and June 2018, and monitored CO2 emission at the water-gas interface using static closed chamber. The results are as follows: during the investigation, the variation rate of CO2 averaged 0.66-2.05 ppm/Min in Caotang River, and the number was 1.02 ppm/Min and 2.67 ppm/Min in Yangtze River. In November, CO2 in Caotang River experienced dramatic variation as it was released from the water body to the atmosphere. The highest release rate occurred at the CT02 section, which was up to 42.58ppm/min. From July to October of 2017, most sections of the river absorbed CO2 without a fixed pattern in space. From January to March of 2018, the absorption and release rate of CO2 slowed down, with its absolute value between 0.20-2.28 ppm/min. The release or absorption rate of CO2 from April to June was slightly higher than that from January to March.

Quinoline-containing diarylethenes: bridging between turn-on fluorescence, RGB switching and room temperature phosphorescence

Simple structural modifications using oxidation and methylation of a quinoline-containing diarylethene result in dramatic variation of photophysical properties.

Complex evolutionary history of the Y chromosome in flies of the Drosophila obscura species group

The Drosophila obscura species group shows dramatic variation in karyotype, including transitions among sex chromosomes. Members of the affinis and pseudoobscura subgroups contain a neo-X chromosome (a fusion of the X with an autosome), and it was shown that ancestral Y genes of Drosophila have become autosomal in species that contain the neo-X. Detailed analysis in species of the pseudoobscura subgroup revealed a translocation of ancestral Y genes to the small dot chromosome of that group. Here, we show that the Y-dot translocation is restricted to the pseudoobscura subgroup, and translocation of Y genes in the affinis subgroup followed a different route. We find that most ancestral Y genes moved independently to autosomal or X-linked locations in different taxa of the affinis subgroup, and we propose a dynamic model of sex chromosome formation and turnover in the obscura species group. Our results show that Y genes can find unique paths to escape an unfavorable genomic environment.