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A mass shift method using ICP-MS/MS with O 2 reaction gas is used for ultra-trace determinations of U and Th in samples containing W, Ir, Pt, and Au derived polyatomic interferants without the need for extensive chemical sample preprocessing.
Measurements of the 182 W(n, 2n) 181 W cross section have been performed in the neutron energy range between 8 and 15 MeV using the activation technique. Such data are needed to help interpret results of laser shots at the National Ignition Facility using a new DT capsule design, featuring a high-Z inner shell, with tungsten as the favored material, and an outer shell made of a low-Z material. Our data are in very good agreement with the previous data of Frehaut et al., which are based on a different technique, and in fair agreement with the ENDF/B-VIII.0 and the JEFF-3.3 evaluations.
A search for Higgs boson pair (HH) production with one Higgs boson decaying to two bottom quarks and the other to two W bosons are presented. The search is done using proton-proton collisions data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$^{−1}$ recorded by the CMS detector at the LHC from 2016 to 2018. The final states considered include at least one leptonically decaying W boson. No evidence for the presence of a signal is observed and corresponding upper limits on the HH production cross section are derived. The limit on the inclusive cross section of the nonresonant HH production, assuming that the distributions of kinematic observables are as expected in the standard model (SM), is observed (expected) to be 14 (18) times the value predicted by the SM, at 95% confidence level. The limits on the cross section are also presented as functions of various Higgs boson coupling modifiers, and anomalous Higgs boson coupling scenarios. In addition, limits are set on the resonant HH production via spin-0 and spin-2 resonances within the mass range 250–900 GeV.[graphic not available: see fulltext]
By means of first-principles density-functional theory calculations, we investigate the role of hydrostatic pressure in the electronic structure of the T d (Pmn2 1 ) and 1T" (Pm) phases of the Weyl semimetal Mo 0.5 W 0.5 Te 2 , which is a promising material for phase-change memory technology and superconductivity. We particularly focus on changes occurring in the distribution of the gapless Weyl points (WPs) within the 0 to 45 GPa pressure range. Here we further investigate the structural phase transition and lattice dynamics of the T d and 1T" phases within the aforementioned pressure range. Our calculations suggest that both the T d and 1T" phases of Mo 0.5 W 0.5 Te 2 host four WPs in their full Brillouin zone at zero pressure. The total number of WPs increases to 44 (36) with increasing pressure via pair creation up to 20 (15) GPa for the T d (1T") phase, and beyond this pressure pair annihilation of WPs starts occurring, leaving only 16 WPs at 45 GPa in both phases. The enthalpy versus pressure data reveal that the 1T" phase is more favorable below the critical pressure of 7.5 GPa; however, beyond this critical pressure the T d phase becomes enthalpically favorable. We also provide the calculated x-ray diffraction spectra along with the calculated Raman- and infrared-active phonon frequencies to facilitate the experimental identification of the studied phases
Interactions between well-mixed fine powders of As 2 O 3 , P 2 O 5 , MoO 3 , WO 3 and Nb 2 O 5 at different stoichiometry in quartz ampoules under vacuum at ~1000 °C in the presence of metallic molybdenum (or niobium), over several weeks, led to shiny dichroic crystalline materials being formed in cooler parts of the reaction vessel. An addition of small quantities of metals-Mo or Nb-was made with the aim of partially reducing their highly oxidized Mo(VI), W(VI) or Nb(V) species to corresponding Mo(V), W(V) and Nb(IV) centers, in order to form mixed valence solids. Sublimed crystals of four new compounds were investigated using a variety of techniques, with prime emphasis on the X-ray analysis, followed by spectroscopy (diffusion reflectance, IR, Raman and EPR), second harmonic generation (SHG), thermal analysis under N 2 and air atmosphere, and single crystals electrical conductivity studies. The results evidenced the formation of new complex solids of previously unknown compositions and structures. Three out of four compounds crystallized in non-centrosymmetric space groups and represent layered 2D polymeric puckered structures that being stacked on each other form 3D lattices. All new solids exhibit strong second-harmonic-generation (SHG effect; based on YAG 1064 nm tests with detection of 532 nm photons), and a rare photosalient effect when crystals physically move in the laser beam. Single crystals’ electrical conductivity of the four new synthesized compounds was measured, and the results showed their semiconductor behavior. Values of band gaps of these new solids were determined using diffusion reflectance spectroscopy in the visible region. Aspects of new solids’ practical usefulness are discussed.
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Two additions impacting tables 3 and 4 in ref. [1] are presented in the following. No significant impact is found for other results or figures in ref. [1].
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W crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. there are ten inequivalent W sites. In the first W site, W is bonded to eight W atoms to form distorted WW8 hexagonal bipyramids that share corners with six WW8 hexagonal bipyramids, corners with two WW7 hexagonal pyramids, edges with twenty-two WW8 hexagonal bipyramids, and edges with two WW7 hexagonal pyramids. There are a spread of W–W bond distances ranging from 2.63–3.04 Å. In the second W site, W is bonded to eight W atoms to form distorted WW8 hexagonal bipyramids that share corners with five WW8 hexagonal bipyramids, corners with three WW7 hexagonal pyramids, edges with twenty-three WW8 hexagonal bipyramids, and an edgeedge with one WW7 hexagonal pyramid. There are a spread of W–W bond distances ranging from 2.63–3.06 Å. In the third W site, W is bonded to eight W atoms to form distorted WW8 hexagonal bipyramids that share corners with seven WW8 hexagonal bipyramids, edges with nineteen WW8 hexagonal bipyramids, and edges with five WW7 hexagonal pyramids. There are a spread of W–W bond distances ranging from 2.63–3.04 Å. In the fourth W site, W is bonded to eight W atoms to form distorted WW8 hexagonal bipyramids that share corners with six WW8 hexagonal bipyramids, corners with two equivalent WW7 hexagonal pyramids, edges with seventeen WW8 hexagonal bipyramids, and edges with six WW7 hexagonal pyramids. There are a spread of W–W bond distances ranging from 2.63–3.01 Å. In the fifth W site, W is bonded to eight W atoms to form distorted WW8 hexagonal bipyramids that share corners with six WW8 hexagonal bipyramids, a cornercorner with one WW7 hexagonal pyramid, edges with eighteen WW8 hexagonal bipyramids, and edges with six WW7 hexagonal pyramids. There are a spread of W–W bond distances ranging from 2.63–3.00 Å. In the sixth W site, W is bonded to eight W atoms to form distorted WW8 hexagonal bipyramids that share corners with five WW8 hexagonal bipyramids, corners with three WW7 hexagonal pyramids, edges with sixteen WW8 hexagonal bipyramids, and edges with seven WW7 hexagonal pyramids. There are a spread of W–W bond distances ranging from 2.63–2.97 Å. In the seventh W site, W is bonded to seven W atoms to form distorted WW7 hexagonal pyramids that share corners with five WW8 hexagonal bipyramids, corners with six WW7 hexagonal pyramids, edges with thirteen WW8 hexagonal bipyramids, and edges with four WW7 hexagonal pyramids. There are a spread of W–W bond distances ranging from 2.63–2.67 Å. In the eighth W site, W is bonded to seven W atoms to form distorted WW7 hexagonal pyramids that share corners with four WW8 hexagonal bipyramids, corners with seven WW7 hexagonal pyramids, edges with thirteen WW8 hexagonal bipyramids, and edges with four WW7 hexagonal pyramids. There are a spread of W–W bond distances ranging from 2.63–2.67 Å. In the ninth W site, W is bonded to eight W atoms to form distorted WW8 hexagonal bipyramids that share corners with five WW8 hexagonal bipyramids, corners with two equivalent WW7 hexagonal pyramids, edges with twelve WW8 hexagonal bipyramids, and edges with eleven WW7 hexagonal pyramids. There are a spread of W–W bond distances ranging from 2.63–3.05 Å. In the tenth W site, W is bonded to seven W atoms to form distorted WW7 hexagonal pyramids that share corners with four WW8 hexagonal bipyramids, corners with seven WW7 hexagonal pyramids, edges with twelve WW8 hexagonal bipyramids, and edges with five WW7 hexagonal pyramids. Both W–W bond lengths are 2.63 Å.
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Abstract Initially, vanadium dioxide seems to be an ideal first-order phase transition case study due to its deceptively simple structure and composition, but upon closer inspection there are nuances to the driving mechanism of the metal-insulator transition (MIT) that are still unexplained. In this study, a local structure analysis across a bulk powder tungsten-substitution series is utilized to tease out the nuances of this first-order phase transition. A comparison of the average structure to the local structure using synchrotron x-ray diffraction and total scattering pair-distribution function methods, respectively, is discussed as well as comparison to bright field transmission electron microscopy imaging through a similar temperature-series as the local structure characterization. Extended x-ray absorption fine structure fitting of thin film data across the substitution-series is also presented and compared to bulk. Machine learning technique, non-negative matrix factorization, is applied to analyze the total scattering data. The bulk MIT is probed through magnetic susceptibility as well as differential scanning calorimetry. The findings indicate the local transition temperature ( $$T_c$$ T c ) is less than the average $$T_c$$ T c supporting the Peierls-Mott MIT mechanism, and demonstrate that in bulk powder and thin-films, increasing tungsten-substitution instigates local V-oxidation through the phase pathway VO $$_2\, \rightarrow$$ 2 → V $$_6$$ 6 O $$_{13} \, \rightarrow$$ 13 → V $$_2$$ 2 O $$_5$$ 5 .
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