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Operando X-ray scattering study of thermoelectric
No full textThe application of thermoelectrics for energy harvesting depends strongly on operational reliability and it is therefore desirable to investigate the structural integrity of materials under operating conditions. We have developed an operando setup capable of simultaneously measuring X-ray scattering data and electrical resistance on pellets subjected to electrical current. Here, operando investigations of β-Zn4Sb3 are reported at current densities of 0.5, 1.14 and 2.3 A mm−2. At 0.5 A mm−2 no sample decomposition is observed, but Rietveld refinements reveal increased zinc occupancy from the anode to the cathode demonstrating zinc migration under applied current. At 1.14 A mm−2 β-Zn4Sb3 decomposes into ZnSb, but pair distribution function analysis shows that Zn2Sb2 units are preserved during the decomposition. This identifies the mobile zinc in β-Zn4Sb3 as the linkers between the Zn2Sb2 units. At 2.3 A mm−2 severe Joule heating triggers transition into the γ-Zn4Sb3 phase, which eventually decomposes into ZnSb, demonstrating Zn ion mobility also in γ-Zn4Sb3 under electrical current
Ligand-Based Design of Allosteric Retinoic Acid Receptor-Related Orphan Receptor γt (RORγt) Inverse Agonists
No full textRetinoic acid receptor-related orphan receptor γt (RORγt) is a nuclear receptor associated with the pathogenesis of autoimmune diseases. Allosteric inhibition of RORγt is conceptually new, unique for this specific nuclear receptor, and offers advantages over traditional orthosteric inhibition. Here, we report a highly efficient in silico-guided approach that led to the discovery of novel allosteric RORγt inverse agonists with a distinct isoxazole chemotype. The the most potent compound, 25 (FM26), displayed submicromolar inhibition in a coactivator recruitment assay and effectively reduced IL-17a mRNA production in EL4 cells, a marker of RORγt activity. The projected allosteric mode of action of 25 was confirmed by biochemical experiments and cocrystallization with the RORγt ligand binding domain. The isoxazole compounds have promising pharmacokinetic properties comparable to other allosteric ligands but with a more diverse chemotype. The efficient ligand-based design approach adopted demonstrates its versatility in generating chemical diversity for allosteric targeting of RORγt
Vibrational properties and cooperativity of the 3D spin crossover network
No full textNuclear inelastic scattering of synchrotron radiation has been used to determine the phonon density of vibrational states (pDOS) for the high-spin and low-spin phases of the hydrated and dehydrated isomer of the spin crossover polymer [Fe(pyrazine)][Pt(CN)4]. Density functional theory calculations have been performed for molecular models of the 3D polymeric system. The models contain 15 Fe(II)/Zn(II) centres and allowed the assignment of the observed bands to the corresponding vibrational modes. Thermodynamic parameters like the mean force constant and the vibrational entropy but also sound velocities of the molecular lattices in both spin states have been derived from the pDOS. Modelling of the low-spin and high-spin centres in the environment or matrix of different spins has revealed the enthalpic and entropic components of the intramolecular cooperativity. In contrast to the 1D spin crossover systems (Rackwitz, et al., Phys. Chem. Chem. Phys., 2013, 15, 15450) based on the rigid 1,2,4-triazole derivatives the distortion of the low-spin iron Fe(II) centre by the matrix of high-spin Fe(II) (modelled as Zn(II)) occurs only in two dimensions, defined by the [M(CN)4]2− sheets, rather than concerning all six Fe–N bonds, as in 1D systems. The enthalpic intramolecular cooperativity has been determined to be 15 kJ mol−1 which is lower than that in 1D systems (20–30 kJ mol−1). Yet, the entropic contribution stabilizes the low-spin state in a low-spin matrix, a behaviour which is opposite to what was found for the 1D systems
A Titanium(IV)-Based Metal-Organic Framework Featuring Defect-Rich Ti-O Sheets as an Oxidative Desulfurization Catalyst
No full textWhile titanium‐based metal–organic frameworks (MOFs) have been widely studied for their (photo)catalytic potential, only a few TiIV MOFs have been reported owing to the high reactivity of the employed titanium precursors. The synthesis of COK‐47 is now presented, the first Ti carboxylate MOF based on sheets of TiIVO6 octahedra, which can be synthesized with a range of different linkers. COK‐47 can be synthesized as an inherently defective nanoparticulate material, rendering it a highly efficient catalyst for the oxidation of thiophenes. Its structure was determined by continuous rotation electron diffraction and studied in depth by X‐ray total scattering, EXAFS, and solid‐state NMR. Furthermore, its photoactivity was investigated by electron paramagnetic resonance and demonstrated by catalytic photodegradation of rhodamine 6G
Probing the Properties of the Pulsar Wind in the Gamma-Ray Binary HESS J0632+057 with NuSTAR and VERITAS Observations
No full textHESS J0632+057 is a gamma-ray binary composed of a compact object orbiting a Be star with a period of about 315 days. Extensive X-ray and TeV gamma-ray observations have revealed a peculiar light curve containing two peaks, separated by a dip. We present the results of simultaneous observations in hard X-rays with NuSTAR and in TeV gamma-rays with VERITAS, performed in 2017 November and December. These observations correspond to the orbital phases phgr ≈ 0.22 and 0.3, where the fluxes are rising toward the first light-curve peak. A significant variation of the spectral index from 1.77 ± 0.05 to 1.56 ± 0.05 is observed in the X-ray data. The multiwavelength spectral energy distributions (SED) derived from the observations are interpreted in terms of a leptonic model, in which the compact object is assumed to be a pulsar and nonthermal radiation is emitted by high-energy electrons accelerated at the shock formed by the collision between the stellar and pulsar wind. The results of the SED fitting show that our data can be consistently described within this scenario, and allow us to estimate the magnetization of the pulsar wind at the location of the shock formation. The constraints on the pulsar wind magnetization provided by our results are shown to be consistent with those obtained from other systems
Gas tungsten arc welding of as-rolled CrMnFeCoNi high entropy alloy
No full textHigh entropy alloys have emerged as novel engineering alloys with remarkable mechanical properties in a widerange of temperatures. Among the several high entropy alloys that were already described, the equiatomicCrMnFeCoNi alloy is the most studied one. In this work, gas tungsten arc welding of as-rolled CrMnFeCoNihigh entropy alloy sheets was performed. The microstructural characterization encompassed the use of electronmicroscopy, including electron backscattered diffraction, synchrotron X-ray diffraction analysis, microhardnesstesting and mechanical evaluation. A comprehensive description of themicrostructural evolution, including textureand microstrain determination, of the joint is presented and discussed. Upon mechanical testing, the jointssystematically failed in the fusion zone due. The large grain size and low hardness of this region justifies the failurelocation. The joints' mechanical behaviour is correlated with the material microstructure
Automated Calculation of N-jet Soft Functions
No full textWe present a systematic framework for the calculation of soft functions that are defined in terms of ≥2 light-like Wilson lines. The formalism represents an extension of a method that we developed earlier for the calculation of dijet soft functions to the general -jet case. We discuss the technical aspects of this generalisation, focussing on SCET-1 soft functions that obey the non-Abelian exponentiation theorem in this contribution. As a first application of our method, we consider the -jettiness observable and present numerical results for the 1-jettiness and 2-jettiness hadron-collider soft functions to next-to-next-to-leading order in the perturbative expansion
High-harmonic generation wave front dependence on a driving infrared wave front
No full textWith high-harmonic generation (HHG), spatially and temporally coherent XUV to soft x-ray (100 nm to 10 nm)table-top sources can be realized by focusing a driving infrared (IR) laser on a gas target. For applications such ascoherent diffraction imaging, holography, plasma diagnostics, or pump–probe experiments, it is desirable to havecontrol over the wave front (WF) of the HHs to maximize the number of XUV photons on target or to tailor the WF.Here, we demonstrate control of the XUV WF by tailoring the driving IR WF with a deformable mirror. The WFsof both IR and XUV beams are monitored with WF sensors. We present a systematic study of the dependence of theaberrations of the HHs on the aberrations of the driving IR laser and explain the observations with propagationsimulations. We show that we can control the astigmatism of the HHs by changing the astigmatism of the drivingIR laser without compromising the HH generation efficiency with a WF quality fromλ/8 toλ/13.3. This allows usto shape the XUV beam without changing any XUV optical element
Superconformal blocks: general theory
No full textIn this work we launch a systematic theory of superconformal blocks for fourpoint functions of arbitrary supermultiplets. Our results apply to a large class of superconformal field theories including 4-dimensional models with any number of supersymmetries. The central new ingredient is a universal construction of the relevant Casimir differential equations. In order to find these equations, we model superconformal blocks as functions on the supergroup and pick a distinguished set of coordinates. The latter are chosen so that the superconformal Casimir operator can be written as a perturbation of the Casimir operator for spinning bosonic blocks by a fermionic (nilpotent) term. Solu tions to the associated eigenvalue problem can be obtained through a quantum mechanical perturbation theory that truncates at some finite order so that all results are exact. We illustrate the general theory at the example of d = 1 dimensional theories with = 2 supersymmetry for which we recover known superblocks. The paper concludes with an outlook to 4-dimensional blocks with = 1 supersymmetry
