94 research outputs found
Limit on the Fierz Interference Term b from a Measurement of the Beta Asymmetry in Neutron Decay
In the standard model of particle physics, the weak interaction is described
by vector and axial-vector couplings only. Non-zero scalar or tensor
interactions would imply an additional contribution to the differential decay
rate of the neutron, the Fierz interference term. We derive a limit on this
hypothetical term from a measurement using spin polarized neutrons. This method
is statistically less sensitive than the determination from the spectral shape
but features much cleaner systematics. We obtain a limit of b = 0.017(21) at
68.27 C.L., improving the previous best limit from neutron decay by a factor of
four.Comment: Phys. Rev. Lett., https://journals.aps.org/prl
Lytic Water Dynamics Reveal Evolutionarily Conserved Mechanisms of ATP Hydrolysis by TIP49 AAA+ ATPases
SummaryEukaryotic TIP49a (Pontin) and TIP49b (Reptin) AAA+ ATPases play essential roles in key cellular processes. How their weak ATPase activity contributes to their important functions remains largely unknown and difficult to analyze because of the divergent properties of TIP49a and TIP49b proteins and of their homo- and hetero-oligomeric assemblies. To circumvent these complexities, we have analyzed the single ancient TIP49 ortholog found in the archaeon Methanopyrus kandleri (mkTIP49). All-atom homology modeling and molecular dynamics simulations validated by biochemical assays reveal highly conserved organizational principles and identify key residues for ATP hydrolysis. An unanticipated crosstalk between Walker B and Sensor I motifs impacts the dynamics of water molecules and highlights a critical role of trans-acting aspartates in the lytic water activation step that is essential for the associative mechanism of ATP hydrolysis
Characterization of hen phosvitin in aqueous salt solutions: Size, structure, and aggregation
Phosvitins is a key egg yolk protein and can often be found in food emulsions. It is highly phosphorylated and hence phosvitins contain a large number of negatively charged amino acid groups, for pH > pI. Due to the presence of these phophoserines, phosvitins bind to positively charged multivalent ions. Its amphipolar structure makes phosvitin also an efficient emulsion stabilizer. The ion binding and emulsifying abilities of phosvitins are influenced by environmental conditions such as pH and ionic strength. Various physicochemical properties of phosvitins such as size and charge under various conditions, and how they self-assemble via multivalent ions are not well-understood. To gain more insight into these physical characteristics, we performed high brilliance synchrotron small angle X-ray scattering (SAXS) on phosvitin solutions. The structure factor S(q) obtained from the SAXS profiles showed that the double layer interactions between charged phosvitin assemblies are strongly affected by pH and ionic strength of the buffer. The effects of multivalent ions (Mg2+, Fe3+) on the size and structure of phosvitin were also investigated. Our results revealed that the aggregation of phosvitin mediated by metal ions is induced by electrostatic attraction and only occurs beyond a threshold cation concentration, where phosvitin loses long-range electrostatic double layer repulsions. These findings help understanding the effects of metal ions and pH on phosvitin in more complex environments such as food emulsions
Angular X-ray cross-correlation analysis applied to the scattering data in 3D reciprocal space from a single crystal
An application of angular X-ray cross-correlation analysis (AXCCA) to the scattered intensity distribution measured in 3D reciprocal space from a single-crystalline sample is proposed in this work. Contrary to the conventional application of AXCCA, when averaging over many 2D diffraction patterns collected from different randomly oriented samples is required, the proposed approach provides an insight into the structure of a single specimen. This is particularly useful in studies of defect-rich samples that are unlikely to have the same structure. The application of the method is shown on an example of a qualitative structure determination of a colloidal crystal from simulated as well as experimentally measured 3D scattered intensity distributions
Synthetic lethality by targeting the RUVBL1/2-TTT complex in mTORC1-hyperactive cancer cells
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.Despite considerable efforts, mTOR inhibitors have produced limited success in the clinic. To define the vulnerabilities of mTORC1-addicted cancer cells and to find previously unknown therapeutic targets, we investigated the mechanism of piperlongumine, a small molecule identified in a chemical library screen to specifically target cancer cells with a hyperactive mTORC1 phenotype. Sensitivity to piperlongumine was dependent on its ability to suppress RUVBL1/2-TTT, a complex involved in chromatin remodeling and DNA repair. Cancer cells with high mTORC1 activity are subjected to higher levels of DNA damage stress via c-Myc and displayed an increased dependency on RUVBL1/2 for survival and counteracting genotoxic stress. Examination of clinical cancer tissues also demonstrated that high mTORC1 activity was accompanied by high RUVBL2 expression. Our findings reveal a previously unknown role for RUVBL1/2 in cell survival, where it acts as a functional chaperone to mitigate stress levels induced in the mTORC1-Myc-DNA damage axis.NIH 1RO1CA142805National Research Foundation of Korea (NRF) grant (NRF-2017R1C1B1006072
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
Overcoming leakage in scalable quantum error correction
Leakage of quantum information out of computational states into higher energy
states represents a major challenge in the pursuit of quantum error correction
(QEC). In a QEC circuit, leakage builds over time and spreads through
multi-qubit interactions. This leads to correlated errors that degrade the
exponential suppression of logical error with scale, challenging the
feasibility of QEC as a path towards fault-tolerant quantum computation. Here,
we demonstrate the execution of a distance-3 surface code and distance-21
bit-flip code on a Sycamore quantum processor where leakage is removed from all
qubits in each cycle. This shortens the lifetime of leakage and curtails its
ability to spread and induce correlated errors. We report a ten-fold reduction
in steady-state leakage population on the data qubits encoding the logical
state and an average leakage population of less than
throughout the entire device. The leakage removal process itself efficiently
returns leakage population back to the computational basis, and adding it to a
code circuit prevents leakage from inducing correlated error across cycles,
restoring a fundamental assumption of QEC. With this demonstration that leakage
can be contained, we resolve a key challenge for practical QEC at scale.Comment: Main text: 7 pages, 5 figure
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