3,088 research outputs found
Domain Growth Kinetics in a Cell-sized Liposome
We investigated the kinetics of domain growth on liposomes consisting of a
ternary mixture (unsaturated phospholipid, saturated phospholipid, and
cholesterol) by temperature jump. The domain growth process was monitored by
fluorescence microscopy, where the growth was mediated by the fusion of domains
through the collision. It was found that an average domain size r develops with
time t as r ~ t^0.15, indicating that the power is around a half of the
theoretical expectation deduced from a model of Brownian motion on a
2-dimensional membrane. We discuss the mechanism of the experimental scaling
behavior by considering the elasticity of the membrane
Jet SIFT-ing: a new scale-invariant jet clustering algorithm for the substructure era
We introduce a new jet clustering algorithm named SIFT (Scale-Invariant
Filtered Tree) that maintains the resolution of substructure for collimated
decay products at large boosts. The scale-invariant measure combines properties
of kT and anti-kT by preferring early association of soft radiation with a
resilient hard axis, while avoiding the specification of a fixed cone size.
Integrated filtering and variable-radius isolation criteria block assimilation
of soft wide-angle radiation and provide a halting condition. Mutually hard
structures are preserved to the end of clustering, automatically generating a
tree of subjet axis candidates. Excellent object identification and kinematic
reconstruction for multi-pronged resonances are realized across more than an
order of magnitude in transverse energy. The clustering measure history
facilitates high-performance substructure tagging, which we quantify with the
aid of supervised machine learning. These properties suggest that SIFT may
prove to be a useful tool for the continuing study of jet substructure.Comment: 29 pages, 23 figures, 5 tables, and 5 films (ancillary files
Mitochondrial dysfunction leads to nuclear genome instability: A link through iron-sulfur clusters
Mutations and deletions in the mitochondrial genome (mtDNA), as well as
instability of the nuclear genome, are involved in multiple human diseases. Here we
report that in Saccharomyces cerevisiae, loss of mtDNA leads to nuclear genome
instability, through a process of cell cycle arrest and selection we define as a cellular
crisis. This crisis is not mediated by the absence of respiration, but instead correlates with
a reduction in the mitochondrial membrane potential. Analysis of cells undergoing this
crisis identified a defect in iron-sulfur cluster (ISC) biogenesis, which requires normal
mitochondrial function. We found that down-regulation of non-mitochondrial ISC protein
biogenesis was sufficient to cause increased genomic instability in cells with intact
mitochondrial function. These results suggest mitochondrial dysfunction stimulates
nuclear genome instability by inhibiting the production of ISC-containing protein(s),
which are required for maintenance of nuclear genome integrity
Fission of a multiphase membrane tube
A common mechanism for intracellular transport is the use of controlled
deformations of the membrane to create spherical or tubular buds. While the
basic physical properties of homogeneous membranes are relatively well-known,
the effects of inhomogeneities within membranes are very much an active field
of study. Membrane domains enriched in certain lipids in particular are
attracting much attention, and in this Letter we investigate the effect of such
domains on the shape and fate of membrane tubes. Recent experiments have
demonstrated that forced lipid phase separation can trigger tube fission, and
we demonstrate how this can be understood purely from the difference in elastic
constants between the domains. Moreover, the proposed model predicts timescales
for fission that agree well with experimental findings
Temporal shifts in the distribution of murine rodent body size classes at Liang Bua (Flores, Indonesia) reveal new insights into the paleoecology of Homo floresiensis and associated fauna
Liang Bua, the type locality of Homo floresiensis, is a limestone cave located in the western part of the Indonesian island of Flores. The relatively continuous stratigraphic sequence of the site spans the past ∼190 kyr and contains ∼275,000 taxonomically identifiable vertebrate skeletal elements, ∼80% of which belong to murine rodent taxa (i.e., rats). Six described genera are present at Liang Bua (Papagomys, Spelaeomys, Hooijeromys, Komodomys, Paulamys, and Rattus), one of which, Hooijeromys, is newly recorded in the site deposits, being previously known only from Early to Middle Pleistocene sites in central Flores. Measurements of the proximal femur (n = 10,212) and distal humerus (n = 1186) indicate five murine body size classes ranging from small (mouse-sized) to giant (common rabbit-sized) are present. The proportions of these five classes across successive stratigraphic units reveal two major changes in murine body size distribution due to significant shifts in the abundances of more open habitat-adapted medium-sized murines versus more closed habitat-adapted smaller-sized ones. One of these changes suggests a modest increase in available open habitats occurred ∼3 ka, likely the result of anthropogenic changes to the landscape related to farming by modern human populations. The other and more significant change occurred ∼60 ka suggesting a rapid shift from more open habitats to more closed conditions at this time. The abrupt reduction of medium-sized murines, along with the disappearance of H. floresiensis, Stegodon florensis insularis (an extinct proboscidean), Varanus komodoensis (Komodo dragon), Leptoptilos robustus (giant marabou stork), and Trigonoceps sp. (vulture) at Liang Bua ∼60-50 ka, is likely the consequence of these animals preferring and tracking more open habitats to elsewhere on the island. If correct, then the precise timing and nature of the extinction of H. floresiensis and its contemporaries must await new discoveries at Liang Bua or other as yet unexcavated sites on Flores
Lateral phase separation in mixtures of lipids and cholesterol
In an effort to understand "rafts" in biological membranes, we propose phenomenological models for saturated and unsaturated lipid mixtures, and lipid-cholesterol mixtures. We consider simple couplings between the local composition and internal membrane structure, and their influence on transitions between liquid and gel membrane phases. Assuming that the gel transition temperature of the saturated lipid is shifted by the presence of the unsaturated lipid, and that cholesterol acts as an external field on the chain melting transition, a variety of phase diagrams are obtained. The phase diagrams for binary mixtures of saturated/unsaturated lipids and lipid/cholesterol are in semi-quantitative agreement with the experiments. Our results also apply to regions in the ternary phase diagram of lipid/lipid/cholesterol systems
Molecular motors robustly drive active gels to a critically connected state
Living systems often exhibit internal driving: active, molecular processes
drive nonequilibrium phenomena such as metabolism or migration. Active gels
constitute a fascinating class of internally driven matter, where molecular
motors exert localized stresses inside polymer networks. There is evidence that
network crosslinking is required to allow motors to induce macroscopic
contraction. Yet a quantitative understanding of how network connectivity
enables contraction is lacking. Here we show experimentally that myosin motors
contract crosslinked actin polymer networks to clusters with a scale-free size
distribution. This critical behavior occurs over an unexpectedly broad range of
crosslink concentrations. To understand this robustness, we develop a
quantitative model of contractile networks that takes into account network
restructuring: motors reduce connectivity by forcing crosslinks to unbind.
Paradoxically, to coordinate global contractions, motor activity should be low.
Otherwise, motors drive initially well-connected networks to a critical state
where ruptures form across the entire network.Comment: Main text: 21 pages, 5 figures. Supplementary Information: 13 pages,
8 figure
Training and Onboarding initiatives in High Energy Physics experiments
In this paper we document the current analysis software training and
onboarding activities in several High Energy Physics (HEP) experiments: ATLAS,
CMS, LHCb, Belle II and DUNE. Fast and efficient onboarding of new
collaboration members is increasingly important for HEP experiments as analyses
and the related software become ever more complex with growing datasets. A
meeting series was held by the HEP Software Foundation (HSF) in 2022 for
experiments to showcase their initiatives. Here we document and analyse these
in an attempt to determine a set of key considerations for future experiments
Morphology and Interaction between Lipid Domains
Cellular membranes are a heterogeneous mix of lipids, proteins and small
molecules. Special groupings of saturated lipids and cholesterol form a
liquid-ordered phase, known as `lipid rafts,' serving as platforms for
signaling, trafficking and material transport throughout the secretory pathway.
Questions remain as to how the cell maintains heterogeneity of a fluid membrane
with multiple phases, through time, on a length-scale consistent with the fact
that no large-scale phase separation is observed. We have utilized a
combination of mechanical modeling and in vitro experiments to show that
membrane morphology can be a key player in maintaining this heterogeneity and
organizing such domains in the membrane. We demonstrate that lipid domains can
adopt a flat or dimpled morphology, where the latter facilitates a repulsive
interaction that slows coalescence and tends to organize domains. These forces,
that depend on domain morphology, play an important role in regulating lipid
domain size and in the lateral organization of lipids in the membrane.Comment: 7 pages, 4 figure
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A High-End Estimate of Sea Level Rise for Practitioners
Sea level rise (SLR) is a long-lasting consequence of climate change because global anthropogenic warming takes centuries to millennia to equilibrate for the deep ocean and ice sheets. SLR projections based on climate models support policy analysis, risk assessment and adaptation planning today, despite their large uncertainties. The central range of the SLR distribution is estimated by process-based models. However, risk-averse practitioners often require information about plausible future conditions that lie in the tails of the SLR distribution, which are poorly defined by existing models. Here, a community effort combining scientists and practitioners builds on a framework of discussing physical evidence to quantify high-end global SLR for practitioners. The approach is complementary to the IPCC AR6 report and provides further physically plausible high-end scenarios. High-end estimates for the different SLR components are developed for two climate scenarios at two timescales. For global warming of +2°C in 2100 (RCP2.6/SSP1-2.6) relative to pre-industrial values our high-end global SLR estimates are up to 0.9 m in 2100 and 2.5 m in 2300. Similarly, for a (RCP8.5/SSP5-8.5), we estimate up to 1.6 m in 2100 and up to 10.4 m in 2300. The large and growing differences between the scenarios beyond 2100 emphasize the long-term benefits of mitigation. However, even a modest 2°C warming may cause multi-meter SLR on centennial time scales with profound consequences for coastal areas. Earlier high-end assessments focused on instability mechanisms in Antarctica, while here we emphasize the importance of the timing of ice shelf collapse around Antarctica. This is highly uncertain due to low understanding of the driving processes. Hence both process understanding and emission scenario control high-end SLR
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