234 research outputs found
Molecular ferroelectric contributions to anomalous hysteresis in hybrid perovskite solar cells
We report a model describing the molecular orientation disorder in
CH3NH3PbI3, solving a classical Hamiltonian parametrised with electronic
structure calculations, with the nature of the motions informed by ab-initio
molecular dynamics. We investigate the temperature and static electric field
dependence of the equilibrium ferroelectric (molecular) domain structure and
resulting polarisability. A rich domain structure of twinned molecular dipoles
is observed, strongly varying as a function of temperature and applied electric
field. We propose that the internal electrical fields associated with
microscopic polarisation domains contribute to hysteretic anomalies in the
current--voltage response of hybrid organic-inorganic perovskite solar cells
due to variations in electron-hole recombination in the bulk.Comment: 10 pages; 4 figures, 2 SI figure
ClaimChain: Improving the Security and Privacy of In-band Key Distribution for Messaging
The social demand for email end-to-end encryption is barely supported by
mainstream service providers. Autocrypt is a new community-driven open
specification for e-mail encryption that attempts to respond to this demand. In
Autocrypt the encryption keys are attached directly to messages, and thus the
encryption can be implemented by email clients without any collaboration of the
providers. The decentralized nature of this in-band key distribution, however,
makes it prone to man-in-the-middle attacks and can leak the social graph of
users. To address this problem we introduce ClaimChain, a cryptographic
construction for privacy-preserving authentication of public keys. Users store
claims about their identities and keys, as well as their beliefs about others,
in ClaimChains. These chains form authenticated decentralized repositories that
enable users to prove the authenticity of both their keys and the keys of their
contacts. ClaimChains are encrypted, and therefore protect the stored
information, such as keys and contact identities, from prying eyes. At the same
time, ClaimChain implements mechanisms to provide strong non-equivocation
properties, discouraging malicious actors from distributing conflicting or
inauthentic claims. We implemented ClaimChain and we show that it offers
reasonable performance, low overhead, and authenticity guarantees.Comment: Appears in 2018 Workshop on Privacy in the Electronic Society
(WPES'18
Clonal interference and Muller's ratchet in spatial habitats
Competition between independently arising beneficial mutations is enhanced in
spatial populations due to the linear rather than exponential growth of clones.
Recent theoretical studies have pointed out that the resulting fitness dynamics
is analogous to a surface growth process, where new layers nucleate and spread
stochastically, leading to the build up of scale-invariant roughness. This
scenario differs qualitatively from the standard view of adaptation in that the
speed of adaptation becomes independent of population size while the fitness
variance does not. Here we exploit recent progress in the understanding of
surface growth processes to obtain precise predictions for the universal,
non-Gaussian shape of the fitness distribution for one-dimensional habitats,
which are verified by simulations. When the mutations are deleterious rather
than beneficial the problem becomes a spatial version of Muller's ratchet. In
contrast to the case of well-mixed populations, the rate of fitness decline
remains finite even in the limit of an infinite habitat, provided the ratio
between the deleterious mutation rate and the square of the
(negative) selection coefficient is sufficiently large. Using again an analogy
to surface growth models we show that the transition between the stationary and
the moving state of the ratchet is governed by directed percolation
MLN51 Stimulates the RNA-Helicase Activity of eIF4AIII
The core of the exon-junction complex consists of Y14, Magoh, MLN51 and eIF4AIII, a DEAD-box RNA helicase. MLN51 stimulates the ATPase activity of eIF4AIII, whilst the Y14-Magoh complex inhibits it. We show that the MLN51-dependent stimulation increases both the affinity of eIF4AIII for ATP and the rate of enzyme turnover; the K (M) is decreased by an order of magnitude and k (cat) increases 30 fold. Y14-Magoh do inhibit the MLN51-stimulated ATPase activity, but not back to background levels. The ATP-bound form of the eIF4AIII-MLN51 complex has a 100-fold higher affinity for RNA than the unbound form and ATP hydrolysis reduces this affinity. MLN51 stimulates the RNA-helicase activity of eIF4AIII, suggesting that this activity may be functionally important
Electrons in High-Tc Compounds: Ab-Initio Correlation Results
Electronic correlations in the ground state of an idealized infinite-layer
high-Tc compound are computed using the ab-initio method of local ansatz.
Comparisons are made with the local-density approximation (LDA) results, and
the correlation functions are analyzed in detail. These correlation functions
are used to determine the effective atomic-interaction parameters for model
Hamiltonians. On the resulting model, doping dependencies of the relevant
correlations are investigated. Aside from the expected strong atomic
correlations, particular spin correlations arise. The dominating contribution
is a strong nearest neighbor correlation that is Stoner-enhanced due to the
closeness of the ground state to the magnetic phase. This feature depends
moderately on doping, and is absent in a single-band Hubbard model. Our
calculated spin correlation function is in good qualitative agreement with that
determined from the neutron scattering experiments for a metal.Comment: 21pp, 5fig, Phys. Rev. B (Oct. 98
Aneuploidy Drives Genomic Instability in Yeast
Aneuploidy decreases cellular fitness, yet it is also associated with cancer, a disease of enhanced proliferative capacity. To investigate one mechanism by which aneuploidy could contribute to tumorigenesis, we examined the effects of aneuploidy on genomic stability. We analyzed 13 budding yeast strains that carry extra copies of single chromosomes and found that all aneuploid strains exhibited one or more forms of genomic instability. Most strains displayed increased chromosome loss and mitotic recombination, as well as defective DNA damage repair. Aneuploid fission yeast strains also exhibited defects in mitotic recombination. Aneuploidy-induced genomic instability could facilitate the development of genetic alterations that drive malignant growth in cancer
Spatiotemporal mortality and demographic trends in a small cetacean: Strandings to inform conservation management
With global increases in anthropogenic pressures on wildlife populations comes a responsibility to manage them effectively. The assessment of marine ecosystem health is challenging and often relies on monitoring indicator species, such as cetaceans. Most cetaceans are however highly mobile and spend the majority of their time hidden from direct view, resulting in uncertainty on even the most basic population metrics. Here, we discuss the value of long-term and internationally combined stranding records as a valuable source of information on the demographic and mortality trends of the harbour porpoise (Phocoena phocoena) in the North Sea. We analysed stranding records (n = 16,181) from 1990 to 2017 and demonstrate a strong heterogeneous seasonal pattern of strandings throughout the North Sea, indicative of season-specific distribution or habitat use, and season-specific mortality. The annual incidence of strandings has increased since 1990, with a notable steeper rise particularly in the southern North Sea since 2005. A high density of neonatal strandings occurred specifically in the eastern North Sea, indicative of areas important for calving, and large numbers of juvenile males stranded in the southern parts, indicative of a population sink or reflecting higher male dispersion. These findings highlight the power of stranding records to detect potentially vulnerable population groups in time and space. This knowledge is vital for managers and can guide, for example, conservation measures such as the establishment of time-area-specific limits to potentially harmful human activities, aiming to reduce the number and intensity of human-wildlife conflicts
Scans for signatures of selection in Russian cattle breed genomes reveal new candidate genes for environmental adaptation and acclimation
Domestication and selective breeding has resulted in over 1000 extant cattle breeds. Many of these breeds do not excel in important traits but are adapted to local environments. These adaptations are a valuable source of genetic material for efforts to improve commercial breeds. As a step toward this goal we identified candidate regions to be under selection in genomes of nine Russian native cattle breeds adapted to survive in harsh climates. After comparing our data to other breeds of European and Asian origins we found known and novel candidate genes that could potentially be related to domestication, economically important traits and environmental adaptations in cattle. The Russian cattle breed genomes contained regions under putative selection with genes that may be related to adaptations to harsh environments (e.g., AQP5, RAD50, and RETREG1). We found genomic signatures of selective sweeps near key genes related to economically important traits, such as the milk production (e.g., DGAT1, ABCG2), growth (e.g., XKR4), and reproduction (e.g., CSF2). Our data point to candidate genes which should be included in future studies attempting to identify genes to improve the extant breeds and facilitate generation of commercial breeds that fit better into the environments of Russia and other countries with similar climates
Is the central-marginal hypothesis a general rule? Evidence from three distributions of an expanding mangrove species, Avicennia germinans (L.)
The central-marginal hypothesis (CMH) posits that range margins exhibit less genetic diversity 16 and greater inter-population genetic differentiation compared to range cores. CMH predictions 17 are based on long-held ‘abundant-centre’ assumptions of a decline in ecological conditions and 18 abundances towards range margins. Although much empirical research has confirmed CMH, 19 exceptions remain almost as common. We contend that mangroves provide a model system to 20 test CMH that alleviates common confounding factors and may help clarify this lack of 21 consensus. Here, we document changes in black mangrove (Avicennia germinans) population 22 genetics with 12 nuclear microsatellite loci along three replicate coastlines in the United States 23 (only 2 of 3 conform to underlying ‘abundant-centre’ assumptions). We then test an implicit 24 prediction of CMH (reduced genetic diversity may constrain adaptation at range margins) by 25 measuring functional traits of leaves associated with cold tolerance, the climatic factor that 26 controls these mangrove distributional limits. CMH predictions were confirmed only along the 27 coastlines that conform to ‘abundant-centre’ assumptions and, in contrast to theory, range margin 28 A. germinans exhibited functional traits consistent with greater cold tolerance compared to range 29 cores. These findings support previous accounts that CMH may not be a general rule across 30 species and that reduced neutral genetic diversity at range margins may not be a constraint to 31 shifts in functional trait variation along climatic gradients
The CCR4-NOT Complex Is Implicated in the Viability of Aneuploid Yeasts
To identify the genes required to sustain aneuploid viability, we screened a deletion library of non-essential genes in the fission yeast Schizosaccharomyces pombe, in which most types of aneuploidy are eventually lethal to the cell. Aneuploids remain viable for a period of time and can form colonies by reducing the extent of the aneuploidy. We hypothesized that a reduction in colony formation efficiency could be used to screen for gene deletions that compromise aneuploid viability. Deletion mutants were used to measure the effects on the viability of spores derived from triploid meiosis and from a chromosome instability mutant. We found that the CCR4-NOT complex, an evolutionarily conserved general regulator of mRNA turnover, and other related factors, including poly(A)-specific nuclease for mRNA decay, are involved in aneuploid viability. Defective mutations in CCR4-NOT complex components in the distantly related yeast Saccharomyces cerevisiae also affected the viability of spores produced from triploid cells, suggesting that this complex has a conserved role in aneuploids. In addition, our findings suggest that the genes required for homologous recombination repair are important for aneuploid viability
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