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Search for the chiral magnetic effect at the LHC with the CMS experiment
No full textSearches for the chiral magnetic effect (CME) using charge-dependent azimuthal correlations with respect to event planes are presented in PbPb collisions at 5.02 TeV and pPb collisions at 5.02 and 8.16 TeV, with the CMS experiment at the LHC. The azimuthal correlations with respect to the second- and third-order event planes are explored as a function of pseudorapidity, transverse momentum, and event multiplicity, which provides new insights into the underlying background correlations. By employing an event-shape engineering technique, a linear dependence of charge-dependent correlations on the second-order anisotropy flow (nu(2)) is observed, and the upper limits on the nu(2)-independent fraction, which is directly related to the CME signal, are obtained at 95% confidence level for both pPb and PbPb collisions. These results provide strong constraints on the search for the chiral magnetic effect at LHC energies, and establish new guidelines for searches in future experiments
Highly responsive ZnO/AlN/Si heterostructure-based infrared- and visible-blind ultraviolet photodetectors with high rejection ratio
No full textWe report on the hybrid ZnO/AIN/Si heterostructure-based ultraviolet (UV) photodetectors with infrared- and visible-blind characteristics. The heterostructure was formed by depositing ZnO thin films on Si (111) substrate by introducing an AIN as an intermediate layer. The ZnO film has been grown epitaxially on the underlying substrate with the improved crystallinity and excellent optical properties. The vertical transport properties of the ZnO/AIN/Si heterojunction under dark and light illumination demonstrate the intrinsic infrared- and visible-blind characteristics with excellent ultraviolet responsivity. The heterostructure exhibits a high UV responsivity of 14.5 A/W with UV-to-lnfrared rejection ratio of nearly 4 orders of magnitude. The vertical electrical transport properties across the heterostructure are dominated by the holes in the reverse bias condition, whereas the transport of electrons in the forward bias is hindered at the ZnO/AIN interface due to an existence of huge conduction band offset between ZnO and AIN layers. The AIN intermediate layer acts as an electron blocking layer which allows the hole to transport across the heterostructure in the reverse bias condition. © 2019 IEEE
Rapid formylation of the cellular initiator tRNA population makes a crucial contribution to its exclusive participation at the step of initiation
No full textInitiator tRNAs (i-tRNAs) possess highly conserved three consecutive GC base pairs (GC/GC/GC, 3GC pairs) in their anticodon stems. Additionally, in bacteria and eukaryotic organelles, the amino acid attached to i-tRNA is formylated by Fmt to facilitate its targeting to 30S ribosomes. Mutations in GC/GC/GC to UA/CG/AU in i-tRNACUA/3GC do not affect its formylation. However, the i-tRNACUA/3GC is non-functional in initiation. Here, we characterised an Escherichia coli strain possessing an amber mutation in its fmt gene (fmtam274), which affords initiation with i-tRNACUA/3GC. Replacement of fmt with fmtam274 in the parent strain results in production of truncated Fmt, accumulation of unformylated i-tRNA, and a slow growth phenotype. Introduction of i-tRNACUA/3GC into the fmtam274 strain restores accumulation of formylated i-tRNAs and rescues the growth defect of the strain. We show that i-tRNACUA/3GC causes a low level suppression of am274 in fmtam274. Low levels of cellular Fmt lead to compromised efficiency of formylation of i-tRNAs, which in turn results in distribution of the charged i-tRNAs between IF2 and EF-Tu allowing the plasmid borne i-tRNACUA/3GC to function at both the initiation and elongation steps. We show that a speedy formylation of i-tRNA population is crucial for its preferential binding (and preventing other tRNAs) into the P-site. © The Author(s) 2019. Published by Oxford University Press on behalf of Nucleic Acids Research
Temperature-Dependent Photoluminescence and Energy-Transfer Dynamics in Mn 2+ -Doped (C 4 H 9 NH 3 ) 2 PbBr 4 Two-Dimensional (2D) Layered Perovskite
No full textReported here are the low-temperature photoluminescence (PL), energy-transfer mechanism, and exciton dynamics of Mn 2+ -doped two-dimensional (2D) perovskites that show interesting differences from their three-dimensionally doped counterpart. Dopant emission in 2D system shows increased PL intensity and shortened lifetime with increase of temperature and strong dopant emission even at low temperatures. Transient absorption (TA) spectroscopy reveals the dominant role of "hot" excitons in dictating the fast energy-transfer timescale. The operative dynamics of the generated hot excitons include filling up of existing trap states (shallow and deep) and energy-transfer channel from hot excitons to dopant states. Global analysis and target modeling of TA data provide an estimate of excitons (hot and band edge) to a dopant energy-transfer timescale of �330 ps, which is much faster than the band edge exciton lifetime (�2 ns). Such fast energy-transfer timescale arises due to enhanced carrier exchange interaction resulting from higher exciton confinement, increased covalency, and involvement of hot excitons in the 2D perovskites. In stark contrast to three-dimensional systems, the high energy-transfer rate in 2D system results in high dopant emission intensity even at low temperatures. Increased intrinsic vibronic coupling at higher temperatures further supports efficient Mn 2+ sensitization that ultimately dictates the observed temperature dependence of the dopant emission (intensity, lifetime). © 2019 American Chemical Society
Constraints to vegetation growth reduced by region-specific changes in seasonal climate
No full textWe qualitatively and quantitatively assessed the factors related to vegetation growth using Earth system models and corroborated the results with historical climate observations. The Earth system models showed a systematic greening by the late 21st century, including increases of up to 100 in Gross Primary Production (GPP) and 60 in Leaf Area Index (LAI). A subset of models revealed that the radiative effects of CO 2 largely control changes in climate, but that the CO 2 fertilization effect dominates the greening. The ensemble of Earth system model experiments revealed that the feedback of surface temperature contributed to 17 of GPP increase in temperature-limited regions, and radiation increase accounted for a 7 increase of GPP in radiation-limited areas. These effects are corroborated by historical observations. For example, observations confirm that cloud cover has decreased over most land areas in the last three decades, consistent with a CO 2 -induced reduction in transpiration. Our results suggest that vegetation may thrive in the starkly different climate expected over the coming decades, but only if plants harvest the sort of hypothesized physiological benefits of higher CO 2 depicted by current Earth system models. © 2019 by the authors
The anionic phospholipids in the plasma membrane play an important role in regulating the biochemical properties and biological functions of RecA proteins
No full textEscherichia coli RecA (EcRecA) forms discrete foci that cluster at cell poles during normal growth, which are redistributed along the filamented cell axis upon induction of the SOS response. The plasma membrane is thought to act as a scaffold for EcRecA foci, thereby playing an important role in RecA-dependent homologous recombination. In addition, in vivo and in vitro studies demonstrate that EcRecA binds strongly to the anionic phospholipids. However, there have been almost no data on the association of mycobacterial RecA proteins with the plasma membrane and the effects of membrane components on their function. Here, we show that mycobacterial RecA proteins specifically interact with phosphatidylinositol and cardiolipin among other anionic phospholipids; however, they had no effect on the ability of RecA proteins to bind single-stranded DNA. Interestingly, phosphatidylinositol and cardiolipin impede the DNA-dependent ATPase activity of RecA proteins, although ATP binding is not affected. Furthermore, the ability of RecA proteins to promote DNA strand exchange is not affected by anionic phospholipids. Strikingly, anionic phospholipids suppress the RecA-stimulated autocatalytic cleavage of the LexA repressor. The Mycobacterium smegmatis RecA foci localize to the cell poles during normal growth, and these structures disassemble and reassemble into several foci along the cell after the induction of DNA damage. Taken together, these data support the notion that the interaction of RecA with cardiolipin and phosphatidylinositol, the major anionic phospholipids of the mycobacterial plasma membrane, may be physiologically relevant, as they provide a scaffold for RecA storage and may regulate recombinational DNA repair and the SOS response. © 2019 American Chemical Society
Towards multiscale modeling of the CD8 + T cell response to viral infections
No full textThe CD8 + T cell response is critical to the control of viral infections. Yet, defining the CD8 + T cell response to viral infections quantitatively has been a challenge. Following antigen recognition, which triggers an intracellular signaling cascade, CD8 + T cells can differentiate into effector cells, which proliferate rapidly and destroy infected cells. When the infection is cleared, they leave behind memory cells for quick recall following a second challenge. If the infection persists, the cells may become exhausted, retaining minimal control of the infection while preventing severe immunopathology. These activation, proliferation and differentiation processes as well as the mounting of the effector response are intrinsically multiscale and collective phenomena. Remarkable experimental advances in the recent years, especially at the single cell level, have enabled a quantitative characterization of several underlying processes. Simultaneously, sophisticated mathematical models have begun to be constructed that describe these multiscale phenomena, bringing us closer to a comprehensive description of the CD8 + T cell response to viral infections. Here, we review the advances made and summarize the challenges and opportunities ahead. This article is categorized under: Analytical and Computational Methods > Computational Methods Biological Mechanisms > Cell Fates Biological Mechanisms > Cell Signaling Models of Systems Properties and Processes > Mechanistic Models. © 2019 The Authors. WIREs Systems Biology and Medicine published by Wiley Periodicals, Inc
Modulation of Excited-State Proton-Transfer Dynamics inside the Nanocavity of Microheterogeneous Systems: Microenvironment-Sensitive Förster Energy Transfer to Riboflavin
No full textThe excited-state proton-transfer efficiency of a tetraarylpyrene derivative, 1,3,6,8-tetrakis(4-hydroxy-2,6-dimethylphenyl)pyrene (TDMPP), was investigated thoroughly in the presence of various surfactant assemblies, such as micelles and vesicles. The confined microheterogeneous environments can significantly retard the extent of the excited-state proton-transfer process, resulting in a distinguishable optical signal compared to that in the bulk medium. Physical characteristics of the surfactant assemblies, such as order, interfacial hydration, and surface charge, influence the proton transfer process and allow multiparametric sensing. A higher degree of interfacial hydration facilitates the proton-transfer process, while the positively charged head groups of the surfactants specifically stabilize the anionic form of the probe (TDMPP�O*). Furthermore, Forster energy transfer from the probe to riboflavin was studied in a phospholipid membrane, wherein the relative ratio of the neutral versus anionic forms (TDMPP-OH/TDMPP�O*) was found to influence the extent of energy transfer. Overall, we demonstrate how an ultrafast photophysical process, that is, the excited-state proton transfer, can be influenced by the microenvironment. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei
Reversible defect engineering in graphene grain boundaries
No full textResearch efforts in large area graphene synthesis have been focused on increasing grain size. Here, it is shown that, beyond 1 μm grain size, grain boundary engineering determines the electronic properties of the monolayer. It is established by chemical vapor deposition experiments and first-principle calculations that there is a thermodynamic correlation between the vapor phase chemistry and carbon potential at grain boundaries and triple junctions. As a result, boundary formation can be controlled, and well-formed boundaries can be intentionally made defective, reversibly. In 100 µm long channels this aspect is demonstrated by reversibly changing room temperature electronic mobilities from 1000 to 20,000 cm 2 V �1 s �1 . Water permeation experiments show that changes are localized to grain boundaries. Electron microscopy is further used to correlate the global vapor phase conditions and the boundary defect types. Such thermodynamic control is essential to enable consistent growth and control of two-dimensional layer properties over large areas. © 2019, The Author(s)
Renaissance of Organic Triboluminescent Materials
No full textSolid-state luminescence of organic dyes is an elusive frontier, and understanding and designing solid-state stimuli-responsive materials is not trivial. �Mechanoluminescence� (ML) or �triboluminescence� (TL), which is associated with fracture or force-initiated luminescence from a material, is currently attracting new interest. Fracturing the surfaces of organic crystals ordered in noncentrosymmetric space groups can electronically excite the surface and neighboring molecules through piezo- or pyroelectric effects, and this can result in luminescence when the molecules relax back to their ground states. The combined duration of these two consecutive phenomena leads to force-generated luminescence or TL. Although TL has been known for a very long time, examples of TL-active materials are scarce, but are increasing as synthetic and characterization procedures develop. The question is now whether the relatively rare phenomenon of TL needs to be reevaluated to obtain a broader understanding of the subject. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei