11,088 research outputs found
Time domain computational modelling of 1D arterial networks in monochorionic placentas
Published versio
From soft harmonic phonons to fast relaxational dynamics in CHNHPbBr
The lead-halide perovskites, including CHNHPbBr, are
components in cost effective, highly efficient photovoltaics, where the
interactions of the molecular cations with the inorganic framework are
suggested to influence the electronic and ferroelectric properties.
CHNHPbBr undergoes a series of structural transitions
associated with orientational order of the CHNH (MA) molecular
cation and tilting of the PbBr host framework. We apply high-resolution
neutron scattering to study the soft harmonic phonons associated with these
transitions, and find a strong coupling between the PbBr framework and
the quasistatic CHNH dynamics at low energy transfers. At higher
energy transfers, we observe a PbBr octahedra soft mode driving a
transition at 150 K from bound molecular excitations at low temperatures to
relatively fast relaxational excitations that extend up to 50-100 meV.
We suggest that these temporally overdamped dynamics enables possible indirect
band gap processes in these materials that are related to the enhanced
photovoltaic properties.Comment: (main text - 5 pages, 4 figures; supplementary information - 3 pages,
3 figures
Cell competition and tumor heterogeneity
Cancers exhibit a remarkable degree of intratumoral heterogeneity (ITH), which results from complex cellular interactions amongst various cell types. This phenomenon provides an opportunity for clonal selection and growth advantages to aggressive cancer cell types, resulting in worse prognosis and challenges to anti-cancer therapy. Cell competition is a conserved mechanism operational in cellular and organ systems, which allows neighboring cells to compare their relative fitness levels and results in the elimination of viable but suboptimal cells. By abuse of this conserved homeostasis mechanism, aggressive cancer cell types gain an advantage over normal cell types by achieving traits like increased proliferation, de-differentiation, and stemness. This review presents recent evidence that cell competition mechanisms actively participate in the regulation of intratumoral cell-cell interactions and thus contribute to ITH, and this process is essential for cancer development and progression
From the UV to the static-field limit: rates and scaling laws of intense-field ionization of helium
Phylogenetic relationships of African Caecilians (Amphibia: Gymnophiona): insights from mitochondrial rRNA gene sequences
Africa (excluding the Seychelles) has a diverse caecilian fauna, including the endemic family Scolecomorphidae and six endemic genera of the more cosmopolitan Caeciliidae. Previous molecular phylogenetic studies have not included any caecilians from the African mainland. Partial 12S and 16S mitochondrial gene sequences were obtained for two species of the endemic African Scolecomorphidae and five species and four genera of African Caeciliids, aligned against previously reported sequences for 16 caecilian species, and analysed using parsimony, maximum likelihood, Bayesian and distance methods. Results are in agreement with traditional taxonomy in providing support for the monophyly of the African Caeciliid genera Boulengerula and Schistometopum and for the Scolecomorphidae. They disagree in indicating that the Caeciliidae is paraphyletic with respect to the Scolecomorphidae. Although more data from morphology and/or molecules will be required to resolve details of the interrelationships of the African caecilian genera, the data provide strong support for at least two origins of caecilians in which the eye is reduced and covered with bone, and do not support the hypotheses that the caecilian assemblages of Africa, and of East and of West Africa are monophyletic
Evolutionary game dynamics in phenotype space
Evolutionary dynamics can be studied in well-mixed or structured populations.
Population structure typically arises from the heterogeneous distribution of
individuals in physical space or on social networks. Here we introduce a new
type of space to evolutionary game dynamics: phenotype space. The population is
well-mixed in the sense that everyone is equally likely to interact with
everyone else, but the behavioral strategies depend on distance in phenotype
space. Individuals might behave differently towards those who look similar or
dissimilar. Individuals mutate to nearby phenotypes. We study the `phenotypic
space walk' of populations. We present analytic calculations that bring
together ideas from coalescence theory and evolutionary game dynamics. As a
particular example, we investigate the evolution of cooperation in phenotype
space. We obtain a precise condition for natural selection to favor cooperators
over defectors: for a one-dimensional phenotype space and large population size
the critical benefit-to-cost ratio is given by b/c=1+2/sqrt{3}. We derive the
fundamental condition for any evolutionary game and explore higher dimensional
phenotype spaces.Comment: version 2: minor changes; equivalent to final published versio
The scale dependence and structure of convergence fields preceding the initiation of deep convection
Links between convergence and convection are poor in global models, and poor representation of convection is the source of many model biases in the tropics. State-of-the-art convection-permitting simulations allow us to analyze realistic convection statistically. The analysis of fractal dimension is used to show that in convection-permitting simulations (grid spacings 1.5, 4, and 12 km) of the West African monsoon, 50% of deep convective initiations occur in the near vicinity of low-level boundary layer convergence lines that are orientated along the mean wind. In these simulations, more than 80% of the initiations occur within large-scale (300 × 300 km) convergence, with some 20% in large-scale divergence, and almost all cases occur within local scale (60 × 60 km) convergence. The behavior alters in a simulation with a convection scheme and a grid spacing of 12 km; initiation is less frequent over convergence lines, and there is less dependency on high-magnitude low-level local convergence. Key Points Fifty percent of storms initiate along convergence lines Most initiations occur in large and local scale convergence Parameterized convection exhibits a weaker dependence on strong convergence ©2014. American Geophysical Union. All Rights Reserved
Semiclassical charged black holes with a quantized massive scalar field
Semiclassical perturbations to the Reissner-Nordstrom metric caused by the
presence of a quantized massive scalar field with arbitrary curvature coupling
are found to first order in \epsilon = \hbar/M^2. The DeWitt-Schwinger
approximation is used to determine the vacuum stress-energy tensor of the
massive scalar field. When the semiclassical perturbation are taken into
account, we find extreme black holes will have a charge-to-mass ratio that
exceeds unity, as measured at infinity. The effects of the perturbations on the
black hole temperature (surface gravity) are studied in detail, with particular
emphasis on near extreme ``bare'' states that might become precisely zero
temperature ``dressed'' semiclassical black hole states. We find that for
minimally or conformally coupled scalar fields there are no zero temperature
solutions among the perturbed black holes.Comment: 19 pages; 1 figure; ReVTe
Genome-Wide RNAi Screen Identifies Regulators of Cardiomyocyte Necrosis
Regulation of cellular death is central to nearly all physiological routines and is dysregulated in virtually all diseases. Cell death occurs by two major processes, necrosis which culminates in a pervasive inflammatory response and apoptosis which is largely immunologically inert. As necrosis has long been considered an accidental, unregulated form of cellular death that occurred in response to a harsh environmental stimulus, it was largely ignored as a clinical target. However, recent elegant studies suggest that certain forms of necrosis can be reprogrammed. However, scant little is known about the molecules and pathways that orchestrate calcium-overload-induced necrosis, a main mediator of ischemia/reperfusion (IR)-induced cardiomyocyte cell death. To rectify this critical gap in our knowledge, we performed a novel genome-wide siRNA screen to identify modulators of calcium-induced necrosis in human muscle cells. Our screen identified multiple molecular circuitries that either enhance or inhibit this process, including lysosomal calcium channel TPCN1, mitophagy mediatorTOMM7, Ran-binding protein RanBP9, Histone deacetylase HDAC2, chemokine CCL11, and the Arp2/3 complex regulator glia maturation factor-γ(GMFG). Notably, a number of druggable enzymes were identified, including the proteasome β5 subunit (encoded by PSMB5 gene), which controls the proteasomal chymotrypsin-like peptidase activity. Such findings open up the possibility for the discovery of pharmacological interventions that could provide therapeutic benefits to patients affected by myriad disorders characterized by excessive (or too little) necrotic cell loss, including but not limited to IR injury in the heart and kidney, chronic neurodegenerative disorders, muscular dystrophies, sepsis, and cancers
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