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X-ray spectral and timing evolution of MAXI J1727-203 with NICER
We present a detailed X-ray spectral and variability study of the full 2018 outburst of MAXI J1727–203 using NICER observations. The outburst lasted approximately four months. Spectral modelling in the 0.3–10 keV band shows the presence of both a soft thermal and a hard Comptonised component. The analysis of these components shows that MAXI J1727–203 evolved through the soft, intermediate, and hard spectral states during the outburst. We find that the soft (disc) component was detected throughout almost the entire outburst, with temperatures ranging from ∼0.4 keV, at the moment of maximum luminosity, to ∼0.1 keV near the end of the outburst. The power spectrum in the hard and intermediate states shows broad-band noise up to 20 Hz, with no evidence of quasi-periodic oscillations. We also study the rms spectra of the broad-band noise at 0.3−10 keV of this source. We find that the fractional rms increases with energy in most of the outburst except during the hard state, where the fractional rms remains approximately constant with energy. We also find that, below 3 keV, the fractional rms follows the same trend generally observed at energies >3 keV, a behaviour known from previous studies of black holes and neutron stars. The spectral and timing evolution of MAXI J1727–203, as parametrised by the hardness–intensity, hardness–rms, and rms–intensity diagrams, suggest that the system hosts a black hole, although we could not rule out a neutron star.
Spin Crossover and Magnetic Properties of Ba-Substituted Cobaltites
The dependence of the properties of the La{sub 0.45}Ba{sub 0.55}CoO{sub 3 – δ} and La{sub 0.4}Ba{sub 0.6}CoO{sub 3 – δ} cobaltites on the oxygen content has been studied. A decrease in the oxygen content leads to the stabilization of cobalt ions in the 3+ oxidation state and to a transition from a conducting state with positive exchange interaction to an antiferromagnetic insulating state with a long range magnetic order with decreasing temperature. Application of a magnetic field gradually transforms the antiferromagnetic state to the ferromagnetic one. The cubic lattice parameter is independent of temperature and an anomalous dependence of the magnetization, electrical conductivity, and magnetoresistance is treated within a spin crossover scenario. It is assumed that the high-temperature conducting phase and ferromagnetic clusters correspond to a collective intermediate spin state of cobalt ions, whereas the low-temperature antiferromagnetic phase corresponds to a mixed high-spin/low-spin state.
Collisional Quenching of Highly Excited H 2 due to H 2 Collisions
Rate coefficients for pure rotational quenching in H 2 ( ν 1 = 0, j 1 ) + H 2 ( ν 2 = 0, j 2 ) collisions from initial levels of j 1 = 2–31 ( j 2 = 0 or 1) to all lower rotational levels are presented. Here, we carried out extensive quantum mechanical close-coupling calculations based on a recently published H 2 –H 2 potential energy surface (PES) developed by Patkowski et al. that has been demonstrated to be more reliable than previous work. Rotational transition cross sections with initial levels of j 1 = 2–14, 18, 19, 24, and 25 were computed for energies ranging from 10 -6 to 1000 cm -1 , while the coupled-states approximation was adopted from 2000 to 20,000 cm -1 . The corresponding rate coefficients were calculated for the temperature range 10 -5 ≤ T ≤ 10,000 K. Scaling methods based on the ultra-cold data (10 -5 –1 K) were used to estimate rate coefficients for all other intermediate rotational states. Comparisons with previous work that adopted different PESs show small discrepancies at high temperatures and in low-energy resonance regions. The astrophysical applications of the current results are briefly discussed, including the rotational H 2 critical densities due to para-H 2 and ortho-H 2 collisions.
Ribosomal targets for antibiotic drug discovery
The present invention relates to methods to identify molecules that binds in the neomycin binding pocket of a bacterial ribosome using structures of an intact bacterial ribosome that reveal how the ribosome binds tRNA in two functionally distinct states, determined by x-ray crystallography. One state positions tRNA in the peptidyl-tRNA binding site. The second, a fully rotated state, is stabilized by ribosome recycling factor (RRF) and binds tRNA in a highly bent conformation in a hybrid peptidyl/exit (P/E) site. Additionally, the invention relates to various assays, including single-molecule assay for ribosome recycling, and methods to identify compounds that interfere with ribosomal function by detecting newly identified intermediate FRET states using known and novel FRET pairs on the ribosome. The invention also provides vectors and compositions with an N-terminally tagged S13 protein.
Active Site Engineering via Optimizing the Heterogeneous Support Structure for Single-Atom Catalysis
Supported single-atom catalysts show a large range of activities and selectivities that depend on the local environment of the catalytic sites. Here a theory-based optimization strategy is presented that is based on a density functional theory determination of the transition states and intermediates for a low-dimensional coordinate representation of the heterogeneity of the active sites. The approach is applied to a vanadium catalyst on an amorphous SiO 2 support that involves a large kinetic network described using a full chemistry model. Without assuming a priori scaling relations or mechanism reduction, the optimal state of heterogeneity is found to lie at atomic configurations where the activation energies for two distinct key chemical processes are equal. It is found a posteriori that the behavior of the system is consistent with linear free energy scaling relations in the randomness parameters. The energetic span theory proves quite useful in reducing the full chemistry model to a small number of key reactions. The use of a nonlinear optimization algorithm in combination with energetic span theory provides significant simplification in treating disordered systems.
Spin-state transition induced half metallicity in a cobaltate from first principles
Half metal is a promising spintronic material. Here, we explore, using first principles calculations, a spin-state transition induced half metallicity in a layered cobaltate via a physical or chemical pressure. Our exemplary first principles study shows that the layered cobaltate Sr{sub 2}CoO{sub 3}F would undergo a transition, under a pressure of 5.4 GPa, from a high-spin antiferromagnetic insulator to an intermediate-spin ferromagnetic half-metal. The former phase is associated with a superexchange in a Mott insulator, and the latter one is due to a broad band formation and a kinetic energy gain of the partially occupied e{sub g} orbital. Note that the above transition could also be induced by a chemical pressure via doping in (Sr{sub 1−x}Ca{sub x}){sub 2}CoO{sub 3}F (x > 0.3). This work suggests that a cobaltate would be of a particular interest if stabilized into an intermediate-spin state.
Tetragonal BaCoO 3 : A Co 4+ Ferromagnetic Mott Insulator
We report the stabilization of the metastable body-centered tetragonal (BCT) phase of BaCoO 3 (BCT-BaCoO 3 ) under high-pressure (15 GPa) and hightemperature (1200 °C) conditions using a mixture precursor. This double perovskite adopts the EuTiO 3 -type structure (space group I4/mcm), as confirmed by powder Xray diffraction and high-resolution STEM. X-ray photoelectron spectroscopy indicates a predominant Co 4+ oxidation state without detectable oxygen vacancies. Magnetization and heat capacity measurements reveal ferromagnetic ordering at T C ∼ 107 K, attributable to the BCT-BaCoO 3 phase. Above this temperature, the mixed-phase sample exhibits Curie−Weiss paramagnetism, a low-spin to high-spin crossover upon cooling, and a possible intermediate-spin state at elevated temperatures. Resistivity data indicates insulating behavior with weak magnetoresistance. DFT and DFT + DMFT calculations suggest that the insulating state originates from an orbitally selective transition sensitive to the nominal valence of the Co-d shell. The metastable BCT-BaCoO 3 phase cannot be retained in pure form at ambient pressure but can be stabilized by embedding it in a disordered mixture, offering a potential route to discover and preserve other high-pressure phases under ambient conditions.
X-ray photoelectron spectroscopy of FeP phosphide
The structure of the outer and inner electron spectra of iron (2p, 3p, 3s, and 3d) and phosphorus (3s and 3p) atoms in FeP monophosphide is studied in detail by the X-ray photoelectron spectroscopy (XPS) method. On the basis of the analysis of the binding energy of electrons, as well as the parameters characterizing the structure of experimental spectra, a conclusion is made that Fe{sup 3+} (d{sup 5}) cations in FeP are stabilized in a state with intermediate value of the total spin (IS, S = 3/2). The range of values of intra-atomic parameters (10Dq, J{sub H}) is established in which the consideration of the high degree of covalence of Fe–P bonds may lead to the stabilization of (FeP{sub 6}){sup 15–} clusters in the IS state.
New insight into the shape coexistence and shape evolution of {sup 157}Yb
High-spin states in {sup 157}Yb have been populated in the {sup 144}Sm({sup 16}O,3n){sup 157}Yb fusion-evaporation reaction at a beam energy of 85 MeV. Two rotational bands built on the {nu}f{sub 7/2} and {nu}h{sub 9/2} intrinsic states, respectively, have been established for the first time. The newly observed {nu}f{sub 7/2} band and previously known {nu}i{sub 13/2} band in {sup 157}Yb are discussed in terms of total Routhian surface methods and compared with the structures in the neighboring N = 87 isotones. The structural characters observed in {sup 157}Yb provide evidence for shape coexistence of three distinct shapes: prolate, triaxial, and oblate. At higher spins, both the {nu}f{sub 7/2} band and {nu}i{sub 13/2} band in {sup 157}Yb undergo a shape evolution with sizable alignments occurring.
Enhanced Nonlinear Double Excitation of He in Intense Extreme Ultraviolet Laser Fields
Nonlinear, three-photon double excitation of He in intense extreme ultraviolet free-electron laser fields ({approx}24.1 eV, {approx}5 TW/cm{sup 2}) is presented. Resonances to the doubly excited states converging to the He{sup +} N=3 level are revealed by the shot-by-shot photoelectron spectroscopy and identified by theoretical calculations based on the time-dependent Schroedinger equation for the two-electron atom under a laser field. It is shown that the three-photon double excitation is enhanced by intermediate Rydberg states below the first ionization threshold, giving a greater contribution to the photoionization yields than the two-photon process by more than 1 order of magnitude.
Kinetic control of tunable multi-state switching in ferroelectric thin films
Deterministic creation of multiple ferroelectric states with intermediate values of polarization remains challenging due to the inherent bi-stability of ferroelectric switching. In this work we show the ability to select any desired intermediate polarization value via control of the switching pathway in (111)-oriented PbZr 0.2 Ti 0.8 O 3 films. Such switching phenomena are driven by kinetic control of the volume fraction of two geometrically different domain structures which are generated by two distinct switching pathways: one direct, bipolar-like switching and another multi-step switching process with the formation of a thermodynamically-stable intermediate twinning structure. Such control of switching pathways is enabled by the competition between elastic and electrostatic energies which favors different types of ferroelastic switching that can occur. As a whole, our work reflects an alternative approach that transcends the inherent bi-stability of ferroelectrics to create non-volatile, deterministic, and repeatedly obtainable multi-state polarization without compromising other important properties, and holds promise for non-volatile multi-state functional applications.
Schrödinger evolution of two-dimensional black holes
This paper systematically treats the evolving quantum state for two-dimensional black holes, with particular focus on the CGHS model, but also elucidating features generalizing to higher dimensions. This is done in Schrödinger picture(s), to exhibit the dynamic evolution of the state at intermediate times. After a review of classical solutions, also connecting to descriptions of higher-dimensional black holes, it overviews the canonical quantum treatment of the full evolution, including gravitational dynamics. Derived in an approximation to this, following conversion to “perturbation picture”, is the evolution of the quantum matter on the background geometry. Features of the evolving matter state are described, based on choice of a time slicing to put the evolution into ADM form. The choices of slicing as well as coordinates on the slices result in different quantum “pictures” for treating the evolution. If such a description is based on smooth trans-horizon slices, that avoids explicit reference to ultra-planckian modes familiar from traditional treatments, and exhibits the Hawking excitations as emerging from a “quantum atmosphere” with thickness comparable to the inverse temperature. Detailed study of the state exhibits the entanglement structure between Hawking quanta and the partner excitations inside the black hole, and the corresponding “missing information”. This explicit description also allows direct study of the evolution and features, e.g. as seen by infalling observers, of these partner excitations, helping to address various puzzles with them. Explicit treatment of the evolving state, and its extension to higher dimensions, provides further connections to information theory and a starting point for study of corrections that can unitarize evolution, arising from new quantum gravity effects — whether wormholes or something entirely different.
Discovery of a nonyrast K{sup {pi}}=8{sup +} isomer in {sup 162}Dy, and the influence of competing K-mixing mechanisms on its highly forbidden decay
The {sup 160}Gd({sup 9}Be,{alpha}3n){sup 162}Dy reaction has been used to study high-spin states in {sup 162}Dy. Pulsed beam conditions were utilized for enhanced isomer sensitivity. An isomer at 2188.1(3) keV with a half-life of 8.3(3) {mu}s has been discovered and assigned K{sup {pi}}= 8{sup +} with a two-quasineutron configuration. Among 11 {gamma}-ray decay branches, an E2, {Delta}K=8 transition to the ground-state band was observed with a reduced hindrance of f{sub {nu}}=35, agreeing well with systematics correlating f{sub {nu}} with the product of the valence neutron and proton numbers (N{sub p}N{sub n}) over an extended N,Z range. Small deviations from N{sub p}N{sub n} dependence are analyzed for a range of two-quasiparticle isomer decays and interpreted as arising from a weak dependence on the isomer excitation energy relative to the yrast line.
Beam Spin Asymmetry Measurements for Two Pion Photoproduction at CLAS
The overarching goal of this analysis, and many like it, is to develop our understanding of the strong force interactions within the nucleon by examining the nature of their excitation spectra. As the resonances of these spectra have very short lifetimes (tau = 1x10 -23 s) and often have very similar masses, it is often impossible to directly observe resonances in the excitation spectra of nucleons. Polarization observables allow us to study the resonances by looking at how they affect the spin state of final state particles. The beam asymmetry is a polarization observable that allows us to detect the sensitivity of these resonances, and other transition mechanisms, to the electric vector orientation of incident photons. Presented in this thesis are first measurements of the beam asymmetries in the resonant region for the reaction channel pgamma p --> p π + π - focusing on the intermediate mesonic states rho^0 and f^0, and the final state pions. The analysis used data from the g8b experiment undertaken at the Thomas Jefferson National Accelerator Facility (JLab), the first experiment at JLab to use a linearly polarized photon beam. Using the coherent Bremsstrahlung facility and the CLAS detector of Hall B at JLab allowed for many multi-channel reactions to be detected and the first measurements of many polarization observables including those presented here. A brief overview of the theoretical framework used to undertake this analysis is given, followed by a description of the experimental details of the facilities used, then a description of the calibration of the Bremsstrahlung tagging facility which the author undertook, and finally the analysis is presented and the resulting measurements.
Energy Scan of the e + e - → h b ( n P ) π + π - ( n = 1 , 2) Cross Sections and Evidence for Υ ( 11020 ) Decays into Charged Bottomoniumlike States
With data collected with the Belle detector at the KEKB asymmetric-energy e + e - collider, we measure the energy dependence of the e + e - → h b ( n P ) π + π - ( n = 1 , 2) cross sections from thresholds up to 11.02 GeV. We find clear Υ ( 10860 ) and Υ ( 11020 ) peaks with little or no continuum contribution. We study the resonant substructure of the Υ ( 11020 ) → h b ( n P ) π + π - transitions and find evidence that they proceed entirely via the intermediate isovector states Z b ( 10610 ) and Z b ( 10650 ) . The relative fraction of these states is loosely constrained by the current data: The hypothesis that only Z b ( 10610 ) is produced is excluded at the level of 3.3 standard deviations, while the hypothesis that only Z b ( 10650 ) is produced is not excluded at a significant state.
Structure changes in {sup 160}Er from low to ultrahigh spin
A spectroscopic investigation of the {gamma} decays from excited states in {sup 160}Er has been performed in order to study the changing structural properties exhibited from low spin up toward ultrahigh spin (I{approx}60({h_bar}/2{pi})). The nucleus {sup 160}Er was populated by the reaction {sup 116}Cd({sup 48}Ca,4n{gamma}) at a beam energy of 215 MeV, and resulting {gamma} decays were studied using the Gammasphere spectrometer. New rotational structures and extensions to existing bands were observed, revealing a diverse range of quasiparticle configurations, which are discussed in terms of the cranked shell model. At spins around 50({h_bar}/2{pi}) there is evidence for oblate states close to the yrast line. Three rotational bands that have the characteristics of strongly deformed triaxial structures are observed, marking a return to collectivity at even higher spin. The high-spin data are interpreted within the framework of cranked Nilsson-Strutinsky calculations.
Photoinduced Reductive Elimination of H 2 from the Nitrogenase Dihydride (Janus) State Involves a FeMo-cofactor-H 2 Intermediate
N 2 reduction by nitrogenase involves the accumulation of four reducing equivalents at the active site FeMo-cofactor to form a state with two [Fe-H-Fe] bridging hydrides (denoted E 4 (4H), the Janus intermediate), and we recently demonstrated that the enzyme is activated to cleave the N≡N triple bond by the reductive elimination (re) of H 2 from this state. We are exploring a photochemical approach to obtaining atomic-level details of the re activation process. We have shown that when E 4 (4H) at cryogenic temperatures is subjected to 450 nm irradiation in an EPR cavity, it cleanly undergoes photoinduced re of H 2 to give a reactive doubly-reduced intermediate, denoted E4(2H)*, which corresponds to the intermediate that would form if thermal dissociative re loss of H 2 preceded N 2 binding. Experiments reported here establish that photoinduced re occurs in two steps. Photolysis of E 4 (4H) generates an intermediate state that undergoes subsequent photoinduced conversion to [E 4 (2H)* + H 2 ]. The experiments, supported by DFT calculation, indicate that the trapped intermediate is an H 2 complex on the ground adiabatic potential energy suface that connects E 4 (4H) with [E 4 (2H)* + H 2 ]. We suggest this complex, denoted E 4 (H 2 ; 2H), is a thermally populated intermediate in the catalytically central re of H 2 by E 4 (4H), and that N 2 reacts with this complex to complete the activated conversion of [E 4 (4H) + N2] into [E 4 (2N2H) + H 2 ].