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Distinct chromophore-protein environments enable asymmetric activation of a bacteriophytochrome activated diguanylate cyclase
No full textSensing of red and far-red light by bacteriophytochromes involves intricate interactions between their bilin chromophore and the protein environment. The light-triggered rearrangements of the cofactor configuration and eventually the protein conformation enable bacteriophytochromes to interact with various protein effector domains for biological modulation of diverse physiological functions. Excitation of the holoproteins by red or far-red light promotes the photoconversion to their far-red light–absorbing Pfr state or the red light-absorbing Pr state, respectively. Because prototypical bacteriophytochromes have a parallel dimer architecture, it is generally assumed that symmetric activation with two Pfr state protomers constitutes the signaling-active species. However, the bacteriophytochrome from Idiomarina species A28L (IsPadC) has recently been reported to enable long-range signal transduction also in asymmetric dimers containing only one Pfr protomer. By combining crystallography, hydrogen–deuterium exchange coupled to MS, and vibrational spectroscopy, we show here that Pfr of IsPadC is in equilibrium with an intermediate “Pfr-like” state that combines features of Pfr and Meta-R states observed in other bacteriophytochromes. We also show that structural rearrangements in the N-terminal segment (NTS) can stabilize this Pfr-like state and that the PHY-tongue conformation of IsPadC is partially uncoupled from the initial changes in the NTS. This uncoupling enables structural asymmetry of the overall homodimeric assembly and allows signal transduction to the covalently linked physiological diguanylate cyclase output module in which asymmetry might play a role in the enzyme-catalyzed reaction. The functional differences to other phytochrome systems identified here highlight opportunities for using additional red-light sensors in artificial sensor–effector systems
Experimental observation of κ-phase formation sequences by in-situ synchrotron diffraction
No full textIn-situ annealing experiments using synchrotron diffraction depict the separation of {1 0 0}-superlattice peaks ascribed to C-enrichment of pre-existing, C-lean L′12-ordered structures into C-rich κ-carbides of alike crystal structure during heating of a high-Al lightweight steel. The peak separation is the first experimental in-situ investigation of the transformation sequence during Fe3AlC-phase formation. A detailed analysis of the lattice parameter evolution and thermal expansion behavior was carried out to validate the assignment of phases by comparison with theoretical calculations and available experimental data
Xenon and iodine behaviour in magmas
No full textIodine (I) and xenon (Xe) are two key elements that trace Earth’s differentiation (e.g. atmosphere formation) and dynamics (e.g. volcanism and recycling at subduction zones). Iodine and Xe abundances are linked through the decay of the extinct 129I that produced 129Xe, which is today depleted in the Earth’s atmosphere compared to the composition of the solar system (i.e. chondrites). Iodine and Xe cycles and storage in the deep Earth are almost unknown, which is in large part due to the fact that their behaviour in magmas and fluids, key agents of mass transfer through planetary envelopes, are poorly known. Here, the solubility of Xe and I in melts is measured under high pressure (P) and temperature (T) conditions using large volume presses, and Xe and I behaviour in melts and fluids is monitored in situ under high P-Tconditions using resistive heating diamond anvil cells combined with synchrotron x-ray fluorescence (XRF) and Raman spectroscopy. Xenon, I and H (H2O) contents were measured in quenched glasses by particle x-ray Emission (PIXE) and Elastic Recoil Detection Analysis (ERDA). Solubility, speciation and degassing processes are investigated for two different compositions: haplogranitic melt (HPG analogue for crustal melts) and basaltic melts (MORB and IAB). Experimentally measured solubilities for both elements are much higher than their natural abundances in terrestrial magmas. Xenon solubility at 3.5 GPa reaches 4.00 wt.% in HPG and 0.40 wt.% in basalts. Iodine solubility is 0.46 wt.% at 0.4 GPa on average in HPG, and reaches 1.42 wt.% in basalts at 2 GPa. The in situRaman spectroscopic study shows that I forms I-I bonds in hydrous high P fluids/melts unlike Xe that was previously shown to oxidize in high P melts. The XRF monitoring of I and Xe partitioning between aqueous fluids and silicate melts during decompression (i.e. water degassing) shows that Xe degassing is strongly P-Tdependent and can be retained in the melt at deep crust conditions, while I is totally washed out from the silicate melt by the aqueous phase. Xenon and I degassing processes are based on different mechanisms, which implies that the atmospheric isotopic signature of Xe cannot be inherited from a process involving volcanic water degassing. Instead, 129Xe depletion may originate from a separation of both elements at depth, by deep fluids, a proposition that agrees with a deep storage of Xe in minerals
pinkIndexer – a universal indexer for pink-beam X-ray and electron diffraction snapshots
No full textA crystallographic indexing algorithm, pinkIndexer, is presented for the analysis of snapshot diffraction patterns. It can be used in a variety of contexts including measurements made with a monochromatic radiation source, a polychromatic source or with radiation of very short wavelength. As such, the algorithm is particularly suited to automated data processing for two emerging measurement techniques for macromolecular structure determination: serial pink-beam X-ray crystallography and serial electron crystallography, which until now lacked reliable programs for analyzing many individual diffraction patterns from crystals of uncorrelated orientation. The algorithm requires approximate knowledge of the unit-cell parameters of the crystal, but not the wavelengths associated with each Bragg spot. The use of pinkIndexer is demonstrated by obtaining 1005 lattices from a published pink-beam serial crystallography data set that had previously yielded 140 indexed lattices. Additionally, in tests on experimental serial crystallography diffraction data recorded with quasi-monochromatic X-rays and with electrons the algorithm indexed more patterns than other programs tested
HEJ 2: High Energy Resummation for Hadron Colliders
No full textWe present HEJ 2, a new implementation of the High Energy Jets formalism for high-energy resummation in hadron-collider processes as a flexible Monte Carlo event generator. In combination with a conventional fixed-order event generator, HEJ 2 can be used to obtain greatly improved predictions for a number of phenomenologically important processes by adding all-order logarithmic corrections in . A prime example for such a process is the gluon-fusion production of a Higgs boson in association with widely separated jets, which constitutes the dominant background to Higgs boson production in weak-boson fusion
Inconel-steel multilayers by liquid dispersed metal powder bed fusion: Microstructure, residual stress and property gradients
No full textSynthesis of multi-metal hybrid structures with narrow heat affected zones, limited residual stresses and secondary phase occurrence represents a serious scientific and technological challenge. In this work, liquid dispersed metal powderbed fusion was used to additively manufacture a multilayered structure basedon alternating Inconel 625 alloy (IN625) and 316L stainless steel (316L) layers on a 316L base plate. Analytical scanning and transmission electron microscopies, high-energy synchrotron X-ray diffraction and nanoindentation analysis reveal sharp compositional, structural and microstructural boundaries between alternating 60μm thick alloys’ subregions and unique microstructures at macro-, micro- and nano-scales. The periodic occurrence of IN625 and 316L sub-regions is correlated with a cross-sectional hardness increase and decrease and compressive stress decrease and increase, respectively. The laser scanning strategy induced a growth of elongated grains separated by zig-zag low-angle grain boundaries, which correlate with the occurrence of zig-zag cracks propagating in the growth direction. A sharpfiber texture within the 316L regions turns gradually into afiber texture intheIN625regions.TheoccurrenceoftheC-likestressgradient withapronouncedsurfacetensile stress of about 500MPa is interpreted by the temperature gradient mechanism model. Chemical analysis indicates a formation of reinforcing spherical chromium-metal-oxide nano-dispersoids and demonstrates a possibility for reactive additive manufacturing and microstructural design at the nanoscale, as a remarkable attribute of the deposition process. Finally, the study shows that the novel approach represents an effective tool to combine dissimilar metallic alloys into unique bionic hierarchical microstructures with possible synergetic properties
Scaling and higher twist in the nucleon Compton amplitude
No full textThe partonic structure of hadrons plays an important role in a vast array of high-energy and nuclear physics experiments. It also underpins the theoretical understanding of hadron structure. Recent developments in lattice QCD offer new opportunities for reliably studying partonic structure from first principles. Here we report on the use of the Feynman-Hellmann theorem to study the forward Compton amplitude in the unphysical region. We demonstrate how this amplitude provides direct constraint on hadronic inelastic structure functions. The use of external momentum transfer allows us to study the evolution to explore the onset of asymptotic scaling and reveal higher-twist effects in partonic structure
Search for an excited lepton that decays via a contact interaction to a lepton and two jets in proton-proton collisions at 13 TeV
No full textResults are presented from a search for events containing an excited lepton (electron or muon) produced in association with an ordinary lepton of the same flavor and decaying to a lepton and two hadronic jets. Both the production and the decay of the excited leptons are assumed to occur via a contact interaction with a characteristic energy scale . The branching fraction for the decay mode under study increases with the mass of the excited lepton and is the most sensitive channel for very heavy excited leptons. The analysis uses a sample of proton-proton collisions collected by the CMS experiment at the LHC at 13 TeV, corresponding to an integrated luminosity of 77.4 fb. The four-body invariant mass of the two lepton plus two jet system is used as the primary discriminating variable. No significant excess of events beyond the expectation for standard model processes is observed. Assuming that is equal to the mass of the excited leptons, excited electrons and muons with masses below 5.6 and 5.7 TeV, respectively, are excluded at 95 % confidence level. These are the best limits to date
Combined search for supersymmetry with photons in proton-proton collisions at 13 TeV
No full textA combination of four searches for new physics involving signatures with at least one photon and large missing transverse momentum, motivated by generalized models of gauge-mediated supersymmetry (SUSY) breaking, is presented. All searches make use of proton-proton collision data at 13 TeV, which were recorded with the CMS detector at the LHC in 2016, and correspond to an integrated luminosity of 35.9 fb. Signatures with at least one photon and large missing transverse momentum are categorized into events with two isolated photons, events with a lepton and a photon, events with additional jets, and events with at least one high-energy photon. No excess of events is observed beyond expectations from standard model processes, and limits are set in the context of gauge-mediated SUSY. Compared to the individual searches, the combination extends the sensitivity to gauge-mediated SUSY in both electroweak and strong production scenarios by up to 100 GeV in neutralino and chargino masses, and yields the first CMS result combining various SUSY searches in events with photons at 13 TeV