Two-step phase transitions in Fe(Se,Te)

In the studied crystals of FeSe0.7 Te0.3 , a structural phase transitionoccurs in two stages. At higher temperatures, the electronic subsystemundergoes a reconstruction, leading to a significant increase inelastoresistance. 77 Se NMR data show an abrupt change in the relaxation rateduring this transition. The final transition occurs at a temperature severaldegrees below and is also accompanied by anomalies in the electronicproperties. Thus, in the Fe(Se,Te) series, similarly to the behavior of pureFeSe under pressure, the type of transition changes and intermediate stateappear before the structural transition is suppressed. This similarity betweenthe corresponding phase diagrams is explained by the same deformation of theiron coordination environment in Fe(Se,Te) compounds and in FeSe underpressure. Our findings provide new and significant information on the phasediagram of Fe(Se,Te) compounds and in particular suggest the possible existenceof a triple point near the quantum critical point.

Lamellar Crystal Structure and Haldane Magnetism in NH 4 VPO 4 OH

A novel vanadium hydroxide‐phosphate, NH 4 VPO 4 OH, was synthesized hydrothermally in V 2 O 5 −NH 4 H 2 PO 4 ‐citric acid system at 230 °C. It was characterized by XRD, TG‐DSC, SEM‐EDX, FTIR and NMR spectroscopy. NH 4 VPO 4 OH is isostructural with NH 4 GaPO 4 OH and features edge‐sharing chains of VO 6 octahedra. These chains running along [010] direction of the unit cell are connected by phosphate tetrahedra to form infinite layers parallel to the (100) plane. Ammonium cations are embedded between the heteropolyhedral layers. According to the thermodynamic and NMR measurements supported by the first‐principles calculations, NH 4 VPO 4 OH presents a rare case of Haldane spin system with spin S =1 based on V 3+ ions.

Lamellar Crystal Structure and Haldane Magnetism in NH 4 VPO 4 OH

A novel vanadium hydroxide‐phosphate, NH 4 VPO 4 OH, was synthesized hydrothermally in V 2 O 5 −NH 4 H 2 PO 4 ‐citric acid system at 230 °C. It was characterized by XRD, TG‐DSC, SEM‐EDX, FTIR and NMR spectroscopy. NH 4 VPO 4 OH is isostructural with NH 4 GaPO 4 OH and features edge‐sharing chains of VO 6 octahedra. These chains running along [010] direction of the unit cell are connected by phosphate tetrahedra to form infinite layers parallel to the (100) plane. Ammonium cations are embedded between the heteropolyhedral layers. According to the thermodynamic and NMR measurements supported by the first‐principles calculations, NH 4 VPO 4 OH presents a rare case of Haldane spin system with spin S =1 based on V 3+ ions.

Experimental Determination of the Chiral and Achiral Shape Diagrams of Tellurium Nanocrystals

ABSTRACT The interface between chirality and crystallization and mechanisms by which chirality propagates from crystal structure to overall shapes of crystals are a key topic in crystallography and stereochemistry. Recently, nanocrystals attracted attention as useful model systems for this kind of studies. Specifically, tellurium nanocrystals have been used to address questions on relations between chirality of the crystal structure and that of the overall shape. Previous studies of this system did not offer a comprehensive shape diagram and did not survey all the factors that determine whether shapes that form are chiral or not. In the current report, the distribution of chiral and achiral shapes in this system as a function of different physical and chemical parameters is determined experimentally. It is shown that there is a common logic for formation of chiral shapes, that is, growth at conditions that favor the growth of more reactive nuclei. The experiments also reveal more morphologies than previously encountered, suggesting that a systematic change of conditions in nanocrystal growth is key for identifying morphologies that exist only in a narrow range of conditions.

Vectorization of Gradient Boosting of Decision Trees Prediction in the CatBoost Library for RISC-V Processors

The emergence and rapid development of the open RISC-V instruction setarchitecture opens up new horizons on the way to efficient devices, rangingfrom existing low-power IoT boards to future high-performance servers. Theeffective use of RISC-V CPUs requires software optimization for the targetplatform. In this paper, we focus on the RISC-V-specific optimization of theCatBoost library, one of the widely used implementations of gradient boostingfor decision trees. The CatBoost library is deeply optimized for commodity CPUsand GPUs. However, vectorization is required to effectively utilize theresources of RISC-V CPUs with the RVV 0.7.1 vector extension, which cannot bedone automatically with a C++ compiler yet. The paper reports on our experiencein benchmarking CatBoost on the Lichee Pi 4a, RISC-V-based board, and shows howmanual vectorization of computationally intensive loops with intrinsics canspeed up the use of decision trees several times, depending on the specificworkload. The developed codes are publicly available on GitHub.

Charged-particle production as a function of the relative transverse activity classifier in pp, p–Pb, and Pb–Pb collisions at the LHC

Bilinear Fronsdal currents in the $AdS_{4}$ higher-spin theory

We analyse higher-spin theory with general coupling constant $\eta$ at thesecond order, focusing on the gauge non-invariant vertices$\Upsilon(\omega,\omega)$, $\Upsilon(\Omega,\omega,C)$ and$\Upsilon(\omega,C)$, that are shown to generate nontrivial currents in theFronsdal equations. Explicit expressions for the currents are found in theframe-like formalism counterpart of the TT gauge worked out in the paper. Thenonlinear higher-spin theory is shown to generate all types of Metsaev'scurrents with the coupling constants manifestly expressed via the complexcoupling constant $\eta$ of the higher-spin theory. It is shown that allcurrents in the higher-spin theory are conformal in the TT gauge except forthose bilinear in the higher-spin gauge fields $\omega$.

On massive higher spin supermultiplets in d=4

In this work we discuss the cubic interactions for massless spin 3/2gravitino with massive higher spin supermultiplets using three superblocks(2,3/2), (5/2,2) and (3,5/2) as the first non-trivial examples. We use gaugeinvariant formalism for the massive higher spin fields and, as it common insuch cases, we face an ambiguity related with the possible field redefinitionsdue to the presence of Stueckelberg fields. From one hand, we show how thisambiguity can be used as one more way to classify possible cubic vertices. Wealso note that all these field redefinitions do not change the part of theLagrangian which appears in the unitary gauge (where all Stueckelberg fieldsare set to zero) so we still have some important independent results. From theother hand, we show how using the so-called unfolded formalism one can fixthese ambiguities and obtain consistent deformations for all massive fieldgauge invariant curvatures which is the most important step in theFradkin-Vasiliev formalism. Unfortunately, this works for the massive fieldsonly so the way to construct deformations for the massless field curvatures isstill has to be found.

Low precision preconditioning for solving neutron diffusion eigenvalue problem by finite element method

Application of Backward Differential Formula and Anderson’s method for multigroup diffusion transient equation