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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Crystal structures of the high temperature forms of V{sub 8}O{sub 15} and V{sub 9}O{sub 17} and structural trends in the V{sub n}O{sub 2n-1} Magneli series

We report the structure of the metallic high-temperature (ht) form of V{sub 9}O{sub 17}, determined from single crystal X-ray diffraction: space group=P-1 a=5.4219(7) A, b=7.0142(9) A, c=14.5252(19) A, {alpha}=97.0310(10) Degree-Sign , {beta}=90.9900(10) Degree-Sign , {gamma}=108.9630(10) Degree-Sign , V=517.53(12) A{sup 3}, and Z=2. We also report refinement of the structure of metallic ht-V{sub 8}O{sub 15}, space group=P-1, a=5.4315(17) A, b=7.015(2) A, c=13.147(5) A, {alpha}=100.144(4) Degree-Sign , {beta}=95.776(4) Degree-Sign , {gamma}=108.965(3) Degree-Sign , V=459.6(3) A{sup 3}, and Z=2. The structure of metallic V{sub 9}O{sub 17} is interpreted and discussed in the context of the V{sub n}O{sub 2n-1} Magneli phases, yielding trends about how the underlying forces contribute to the metal to insulator transition (MIT). The manner in which structural features of the metallic phases change as a function of n supports previous arguments that there is a turnover in the forces leading to the MIT between n=6 and n=8. - Graphical abstract: Left: The crystal structures of V{sub 8}O{sub 15} and V{sub 9}O{sub 17} shown in context of the crystallographic shear family V{sub n}O{sub 2n-1}. Right: The lattice parameters of V{sub n}O{sub 2n-1} as a function of n. The anamolous trend in b exhibits similar behavior as the metal to insulator (MIT) transition temperature (red). Highlights: Black-Right-Pointing-Pointer Crystal structures of the metallic forms of V{sub 8}O{sub 15} and V{sub 9}O{sub 17}. Black-Right-Pointing-Pointer General trends across the V{sub n}O{sub 2n-1} allow designation of two chain types in all phases. Black-Right-Pointing-Pointer Triclinic b lattice parameter varies anomalously with n, in V{sub n}O{sub 2n-1}. Black-Right-Pointing-Pointer Trend in b matches the metal to insulator transition temperature trend.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Metal ion displacements in noncentrosymmetric chalcogenides La{sub 3}Ga{sub 1.67}S{sub 7}, La{sub 3}Ag{sub 0.6}GaCh{sub 7} (Ch=S, Se), and La{sub 3}MGaSe{sub 7} (M=Zn, Cd)

The quaternary Ga-containing chalcogenides La{sub 3}Ag{sub 0.6}GaS{sub 7}, La{sub 3}Ag{sub 0.6}GaSe{sub 7}, La{sub 3}ZnGaSe{sub 7}, and La{sub 3}CdGaSe{sub 7}, as well as the related ternary chalcogenide La{sub 3}Ga{sub 1.67}S{sub 7}, were prepared by reactions of the elements at 950 °C. They adopt noncentrosymmetric hexagonal structures (space group P6{sub 3}, Z=2) with cell parameters (a=10.2 Å, c=6.1 Å for the sulfides; a=10.6 Å, c=6.4 Å for the selenides) that are largely controlled by the geometrical requirements of one-dimensional stacks of Ga-centered tetrahedra separated by the La atoms. Among these compounds, which share the common formulation La{sub 3}M{sub 1–x}GaCh{sub 7} (M=Ga, Ag, Zn, Cd; Ch=S, Se), the M atoms occupy sites within a stacking of trigonal antiprisms formed by Ch atoms. The location of the M site varies between extremes with trigonal antiprismatic (CN6) and trigonal planar (CN3) geometry. Partial occupation of these sites and intermediate ones accounts for the considerable versatility of these structures and the occurrence of large metal displacement parameters. The site occupations can be understood in a simple way as being driven by the need to satisfy appropriate bond valence sums for both the M and Ch atoms. Band structure calculations rationalize the substoichiometry observed in the Ag-containing compounds (La{sub 3}Ag{sub 0.6}GaS{sub 7}, La{sub 3}Ag{sub 0.6}GaSe{sub 7}) as a response to overbonding. X-ray photoelectron spectroscopy supports the presence of monovalent Ag atoms in these compounds, which are not charge-balanced. - Graphical abstract: Partial occupation of metal atoms in multiple sites accounts for versatility in Ga-containing chalcogenides La{sub 3}M{sub 1–x}GaCh{sub 7} with noncentrosymmetric hexagonal structures. - Highlights: • La{sub 3}M{sub 1–x}GaCh{sub 7} (M =Ga, Ag, Zn, Cd; Ch =S, Se) adopt related hexagonal structures. • Large displacements of M atoms originate from partial occupation of multiple sites. • Bond valence sum arguments give a simple explanation for site preference. • XPS studies confirm presence of monovalent Ag in La{sub 3}Ag{sub 0.6}GaCh{sub 7}. • Substoichiometry in La{sub 3}Ag{sub 0.6}GaCh{sub 7} avoids occupation of Ag–Ch antibonding levels.

36 MATERIALS SCIENCE↗
DOE OSTI2017

On the “alpha-phase” of Ca{sub 2−x}Sr{sub x}MnO{sub 4} and extending the chemistry of Sr{sub 7−y}Ca{sub y}Mn{sub 4}O{sub 15} to y>1

There has been renewed interest in the Ruddlesden-Popper phase (n=2) of composition Ca{sub n+1}Mn{sub n}O{sub 3} {sub n+1} in the light of recent research that has highlighted the nature of the improper ferroelectric ground state, which arises due to the couplings between specific combinations of MnO{sub 6} octahedral rotations and tilts. A fruitful route to control these octahedral degrees of freedom, and hence such desired physical properties, is through chemical substitution on the A–site cation i.e. Ca{sub 2−x}Sr{sub x}MnO{sub 4} for n =1, and in light of this, we have reinvestigated the chemistry of this solid solution. Here we focus on a common impurity phase observed during this synthesis which has been termed the “alpha-phase” in the literature. We show that this impurity phase is actually comprised mainly of a structure related to Sr{sub 7}Mn{sub 4}O{sub 15} but is found here with significantly higher Ca substitution than previously believed possible. Sr{sub 7}Mn{sub 4}O{sub 15} is an interesting structural type in its own right, but has been mainly overlooked to date, exhibiting interesting physics related to low dimensional magnetic ordering and dimer interactions, and we show here that the structural type is a likely candidate for exhibiting a multiferroic ground state. The prospect of being able to tune the lattice and the exchange interactions through further chemical substitution is likely to lead to a renewed interest in this material. - Graphical abstract: Extending the chemistry of Sr{sub 7−y}Ca{sub y}Mn{sub 4}O{sub 15} beyond y>1, revealing highly anisotropic cation ordering and tunable magnetic properties. - Highlights: • Chemistry of the unique structural type Sr{sub 7}Mn{sub 4}O{sub 15} is extended to high Ca concentrations. • Cation occupancy model is determined, showing highly anisotropic solubility of Ca on the 7 unique Sr crystallographic sites. • Anomalies in the magnetic susceptibility data are discussed with reference to symmetry arguments pointing towards a possible novel multiferroic mechanism in this material.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Quaternary rare-earth sulfides RE{sub 3}M{sub 0.5}GeS{sub 7} (RE=La–Nd, Sm; M=Co, Ni) and Y{sub 3}Pd{sub 0.5}SiS{sub 7}

The two metal-deficient series of quaternary Ge-containing sulfides RE{sub 3}M{sub 0.5}GeS{sub 7} (RE = La–Nd, Sm; M = Co, Ni), as well as the related Si-containing sulfide Y{sub 3}Pd{sub 0.5}SiS{sub 7}, were prepared by reactions of the elements at 1050 °C. Single-crystal X-ray diffraction analysis performed on all compounds confirmed noncentrosymmetric hexagonal structures (space group P6{sub 3}, Z =2) with cell parameters in the ranges of a =10.0–10.3 Å and c =5.7–5.8 Å for RE{sub 3}Co{sub 0.5}GeS{sub 7} and RE{sub 3}Ni{sub 0.5}GeS{sub 7}, or a =9.7891(3) Å and c =5.6840(4) Å for Y{sub 3}Pd{sub 0.5}SiS{sub 7}. They are classified as La{sub 3}Mn{sub 0.5}SiS{sub 7}-type structures, with M atoms centred within octahedra (in contrast to La{sub 3}CuSiS{sub 7}-type structures in which M atoms occupy trigonal planar sites) and Ge atoms centred within tetrahedra, both types of polyhedra being arranged in one-dimensional stacks aligned along the c-direction. Charge balance requirements dictate half-occupancy of the M sites. However, bond valence sum arguments indicated that the M atoms are somewhat underbonded within these octahedral sites, so that there is evidence that in some compounds, they can also enter the trigonal planar site at low occupancy (~5%). Magnetic measurements on RE{sub 3}Co{sub 0.5}GeS{sub 7} (RE = Ce, Pr, Sm) revealed paramagnetic behaviour for the Ce and Pr members and apparent antiferromagnetic ordering (T{sub N} =14 K) for the Sm member; fitting to the Curie-Weiss law gave effective magnetic moments consistent with the presence of RE{sup 3+} and Co{sup 2+} species. Band structure calculations on ordered models of La{sub 3}M{sub 0.5}GeS{sub 7} (M = Co, Ni) showed that the Fermi level cuts through M 3d states in the DOS curve and supported the presence of strong M–S and Ge–S bonding interactions. - Graphical abstract: RE{sub 3}M{sub 0.5}GeS{sub 7} (M = Co, Ni) and Y{sub 3}Pd{sub 0.5}SiS{sub 7} contain M atoms partially occupying octahedral and, in some cases, trigonal planar sites within noncentrosymmetric hexagonal structures. - Highlights: • The missing M = Co and Ni series in hexagonal RE{sub 3}M{sub 0.5}GeS{sub 7} have been prepared. • Charge balance is ensured through half occupancy of octahedral M sites. • In some cases, a secondary trigonal planar M site is occupied at very low levels. • Magnetic measurements on RE{sub 3}Co{sub 0.5}GeS{sub 7} support presence of RE{sup 3+} and Co{sup 2+}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Different binding modes of Cu and Pb vs. Cd, Ni, and Zn with the trihydroxamate siderophore desferrioxamine B at seawater ionic strength

The solution speciation in seawater of divalent trace metals (Cd, Cu, Ni, Pb, Zn) is dominated by strong, ostensibly metal-specific organic ligands that may play important roles in microbial metal acquisition and/or detoxification processes. We compare the effective stabilities of these metal-organic complexes to the stabilities of their complexes with a model siderophore, desferrioxamine B (DFOB). While metal-DFOB complexation has been studied in various dilute but often moderately coordinating media, for the purpose of this investigation we measured the stability constants in a non-coordinating background electrolyte at seawater ionic strength (0.7 M NaClO4). Potentiometric titrations of single metals (M) were performed in the presence of ligand (L) at different M:L molar ratios, whereupon the stability constants of multiple complexes were simultaneously determined by non-linear regression of the titration curves with FITEQL, using the optimal binding mode for each metal. Cadmium, Ni, and Zn, like trivalent Fe, sequentially form a bi-, tetra-, and hexadentate complex with DFOB as pH increases, consistent with their coordination number of 6 and regular octahedral geometry. Copper has a Jahn-Teller-distorted square-bipyramidal geometry whereas the geometry of Pb is cryptic, involving a range of bond lengths. Supported by a thermodynamic argument, our data suggest that this impedes binding of the third hydroxamate group and that the hexadentate Cu-DFOB and Pb-DFOB complex identified in earlier reports may instead be a deprotonated tetradentate complex. Absence of the hexadentate complex promotes the formation of a dinuclear (bidentate-tetradentate) complex, M2HL2+, albeit not for Pb in 0.7 M NaCl, evidently due to extensive complexation with chloride. Stabilities of the hexadentate Ni-DFOB, Zn-DFOB, and the tetradentate Pb-DFOB complex are nearly equal, yet about 2 orders of magnitude higher and 4 orders of magnitude lower than those of the hexadentate Cd-DFOB and tetradentate Cu-DFOB complex, respectively. Linear free-energy relations defined by the rare earth elements are able to predict stabilities of the Cd, Zn, and one of the Pb complexes, but underestimate those of the Ni and Cu complexes. The comparison with metal-specific organic ligands detected in seawater yields fair agreement for three of the five metals, implying that they could be siderophore-like. The Cd- and Ni-specific ligands are much stronger and may contain quite different functional groups. Calculations with MINEQL incorporating our new stability constants indicate that very high DFOB concentrations would be required to match the extent of metal-organic complexation observed in seawater, however DFOB may well represent a much broader class of structurally related ligands.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Characterisation of synthesised nickel and cobalt nanoscale oxides

The special features of nano-structured materials have been motivating the search for new synthesis methods for these types of materials. This paper is primarily focused on the characterisation of nickel and cobalt nanoscale oxides synthesised by a method based on the dehydration of their respective metal nitrate solutions. This chemical-based synthesis route is briefly described, and basic thermodynamic arguments are presented to theoretically support the feasibility of obtaining such oxides. In addition, a very homogeneous co-formed Ni and Co oxide compound was obtained by dehydrating a water-based solution of both nitrates. Characterisation was done with by X-ray diffraction and transmission electron microscopy, which revealed, respectively, the presence of oxides and their nanoscale structures, including particle morphology and size distribution. High-resolution electron microscopy (HREM) images indicated that the average particle sizes of the obtained NiO and Co{sub 3}O{sub 4} obtained were approximately 20 nm and 40 nm, respectively. In addition, some particles presented crystalline defects in their inner structure, although those smaller than 5 nm seemed to be defect-free and were spherical or faceted. In addition to being characterised as nano-particle-bearing materials, the co-formed oxides can also be used as the starting material for alloys and nano-composites preparations if they are submitted to complete or partial reduction, respectively. - Highlights: Black-Right-Pointing-Pointer The feasibility in obtaining Ni and Co and their co-formed oxides was evaluated. Black-Right-Pointing-Pointer Ni, Co and Ni and Co co-formed nanostructured oxides were synthesised by the route. Black-Right-Pointing-Pointer XRD, TEM and HREM techniques were used to characterise the obtained nanostructures. Black-Right-Pointing-Pointer The particles sizes of the obtained nanostructures were about 20 nm and 40 nm. Black-Right-Pointing-Pointer The particles smaller than 5 nm were spherical/faceted and seems to be defect-free.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Solid-state reactions to synthesize nanostructured lead selenide semiconductor powders by high-energy milling

Highlights: {yields} PbSe synthesized from PbO instead of Pb powder do not require an inert atmosphere. {yields} During high-energy milling oxygen has to be chemically reduced from the lead oxide. {yields} Solid-state and solid-gas chemical reactions promote both solid and gaseous products. -- Abstract: Both solid-solid and gas-solid reactions have been traced during high-energy milling of Se and PbO powders under vial (P, T) conditions in order to synthesize the PbSe phase. Chemical and thermodynamic arguments are postulated to discern the high-energy milling mechanism to transform PbO-Se micropowders onto PbSe-nanocrystals. A set of reactions were evaluated at around room temperature. Therefore an experimental campaign was designed to test the nature of reactions in the PbO-Se system during high-energy milling.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Preference for a pressure-induced 3D structure after 1T-HfSe 2

Extensive crystal structure prediction searches provide evidence of two 3D structures with orthorhombic (Immm) and monoclinic (C2/m) space groups as reasonable candidates for the first pressure-induced phase of 1T-HfSe 2 . Our candidates are compared with two recent proposals that keep the 2D nature of the ambient conditions phase and display hexagonal (P6 3 /mmc) and monoclinic (C2/m) symmetry, although the latter has a different structure than our proposed C2/m phase. Both of these 2D-like structures are discarded based on simple thermodynamic and kinetic arguments that can be extended to explain the pressure-induced polymorphic sequence of other transition metal dichalcogenides. The computed observables of our orthorhombic phase are fully consistent with the experimental structural and Raman data observed at low and high-pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Omega-Limit Sets and Input-To-State Stability in Power Grids with Switching Equilibria

This paper studies a power transmission system with both conventional generators (CGs) and distributed energy assets (DEAs) providing frequency control. We consider an operating condition with demand aggregating two dynamic components: one that switches between different values on a finite set, and one that varies smoothly over time. Such dynamic operating conditions may result from protection scheme activations, external cyber-attacks, or due to the integration of dynamic loads, such as data centers. Mathematically, the dynamics of the resulting system are captured by a system that switches between a finite number of vector fields - or modes -, with each mode having a distinct equilibrium point induced by the demand aggregation. To analyze the stability properties of the resulting switching system, we leverage tools from hybrid dynamic inclusions and the concept of ..omega.. -limit sets from sets. Specifically, we characterize a compact set that is semi-globally practically asymptotically stable under the assumption that the switching frequency and load variation rate are sufficiently slow. For arbitrarily fast variations of the load, we use a level-set argument with multiple Lyapunov functions to establish input-to-state stability of a larger set and with respect to the rate of change of the loads. The theoretical results are illustrated via numerical simulations on the IEEE 39-bus test system.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2018

Enhanced lithium storage capability of FeF 3 ·0.33H 2 O single crystal with active insertion site exposed

Iron fluoride cathode for lithium batteries intrigues researchers for decades due to high capacity and low cost, but suffers from poor electronic and ionic conductivity. Hierarchical micro/nano construction with preferred orientation growth can shorten ion diffusion pathway and facilitate electron transportation without inducing side reactions. FeF 3 ·0.33H 2 O hierarchical microspheres self-assembled by octagonal single crystal slices are prepared. Benefiting from the artful structure, SAED and XRD characterizations confirm that the octagonal single crystal slices provides more lithium ions intercalation positions (4c sites). Electrochemical tests demonstrate that the well designed FeF 3 ·0.33H 2 O single crystal (FFH-S) delivers 30 mAh g -1 higher capacity (172 mAh g -1 at 0.1C) than the common FeF 3 ·0.33H 2 O polycrystal (FFH-P). In-situ XRD combined with theoretic calculation elucidate the difference in lithium storage capacity. Instructive argument that single crystal octagon slices with [110] oriented growth provide more active sites for lithium ions intercalation contributes to the preparation of high performance iron fluoride cathode materials for rechargeable battery.

25 ENERGY STORAGE↗
DOE OSTI2014

Nuclear Data Sheets for A = 195

Experimental structure and decay data for all nuclides with mass number A=195 (Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, At, Rn) have been revised, updated, and incorporated into the ENSDF data file. All literature available by March 2014 has been considered. This evaluation supersedes the previous one for this mass chain (Zhou Chunmei, Nuclear Data Sheets 86, 645 (1999), 1999Zh11). The detailed level schemes, decay schemes, experimental reaction and decay data on which they are based are summarized and presented here. References, Jπ arguments, and comments are given in the text. No excited state data are yet available for {sup 195}Re and {sup 195}Rn. The adopted levels for {sup 195}At are firstly presented in this evaluation. In addition, Q values have been updated based on 2012Wa38.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Nuclear Data Sheets for A = 198

The 2009 version of Nuclear Data Sheets for A=198 (2009Hu11) has been updated and revised on the basis of the experimental results from various decay and reaction studies before December 2014. The experimental data for all known nuclei with mass number A=198 (Re,Os,Ir,Pt,Au,Hg,Tl,Pb,Bi,Po,At,Rn,Fr) have been revised, updated, and incorporated into the ENSDF data file. The experimental methods, references, Jπ arguments, and necessary comments are given in the text. The adopted levels for 198Re and 198Fr are firstly presented in this evaluation. In addition, Q values have been updated based on 2012Wa38.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

The Scale Method as an Approach for Prompt Fission Neutron Spectra Analysis and Evaluation

The Scale Method was applied for an analysis of experimental and evaluated data of Prompt Fission Neutron Spectra for different isotopes and incident neutron energies below 6 MeV. It was demonstrated that the method describes all experimental data sets in the outgoing neutron energy range 0–7 MeV within uncertainties. Theoretical arguments were provided to support the application of this method. Some important peculiarities connected with the neutron emission mechanism were identified, and proposals for future theoretical and experimental investigations were discussed. It was concluded that the new evaluations completed recently for {sup 235}U systematically overestimate the average energy of experimental prompt fission neutron spectra.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Modeling magnetic fields with helical solutions to Laplace’s equation

The series solution to Laplace's equation in a helical coordinate system is derived and refined using symmetry and chirality arguments. These functions and their more commonplace counterparts are used to model solenoidal magnetic fields via linear, multidimensional curve-fitting. A judicious choice of functional forms, a small number of free parameters and sparse input data can lead to highly accurate, fine-grained modeling of solenoidal magnetic fields, including helical features arising from the winding of the solenoid, with overall field accuracy at better than one part per million.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

The fuzzball nature of two-charge black hole microstates

It has been suggested by A. Sen that the entropy of two-charge supersymmetric bound states in string theory should be accounted for by adding the entropy of source-free horizonless supergravity solutions to the entropy associated with the horizons of small black holes. This would imply that the entropy arises differently depending on the duality frame: in the D1-D5 frame one would count source-free horizonless solutions, while in the NS1-P frame one would compute the area of a horizon. This might lead to the belief that the microstates are described by fuzzball solutions in the D1-D5 duality frame but by a black hole with a horizon in the latter. We argue that this is not the case, and that the microstates are fuzzballs in all duality frames. We observe that the scaling argument used by Sen fails to account for the entropy in the D1-P and other duality frames. We also note that the traditional extremal black hole solution is not a complete string background, since finite-action paths connect the exterior near-horizon extremal throat to the region inside the horizon, including the singularity. The singularity of the traditional black hole solution does not give a valid boundary condition for a fundamental string; correcting this condition by resolving the singularity modifies the black hole to a fuzzball with no horizon. We argue that for questions of counting states, the traditional black hole solution should be understood through its Euclidean continuation as a saddle point, and that the Lorentzian states being counted are fuzzballs in all duality frames.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

On the canonical formulation of gauge field theories and Poincaré transformations

We address the Hamiltonian formulation of classical gauge field theories while putting forward results some of which are not entirely new, though they do not appear to be well known. We refer in particular to the fact that neither the canonical energy momentum vector ( P μ ) nor the gauge invariant energy momentum vector ( P inv μ ) do generate space-time translations of the gauge field by means of the Poisson brackets: In a general gauge, one has to consider the so-called kinematical energy momentum vector and, in a specific gauge (like the radiation gauge in electrodynamics), one has to consider the Dirac brackets rather than the Poisson brackets. Similar arguments apply to rotations and to Lorentz boosts and are of direct relevance to the “nucleon spin crisis” since the spin of the proton involves a contribution which is due to the angular momentum vector of gluons and thereby requires a proper treatment of the latter. We conclude with some comments on the relationships between the different approaches to quantization (canonical quantization based on the classical Hamiltonian formulation, Gupta-Bleuler, path integrals, BRST, covariant canonical approaches).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Detailed comparison of renormalization scale-setting procedures based on the principle of maximum conformality

The Principle of Maximum Conformality (PMC), which generalizes the conventional Gell-Mann-Low method for scale-setting in perturbative QED to non-Abelian QCD, provides a rigorous method for achieving unambiguous scheme-independent, fixed-order predictions for physical observables consistent with the principles of the renormalization group. In addition to the original multi-scale-setting approach (PMCm), two variations of the PMC have been proposed to deal with ambiguities associated with the uncalculated higher order terms in the pQCD series, i.e. the single-scale-setting approach (PMCs) and the procedures based on ``intrinsic conformality" (PMC ∞ ). In this paper, we will give a detailed comparison of these PMC approaches by comparing their predictions for three important quantities R e+e– , R τ , and $Γ(H→b\bar{b}$) up to four-loop pQCD corrections. The PMCs approach determines an overall effective running coupling α s (Q) by the recursive use of the renormalization group equation, whose argument Q represents the actual momentum flow of the process. Our numerical results show that the PMCs method, which involves a somewhat simpler analysis, can serve as a reliable substitute for the full multi-scale PMCm method, and that it leads to more precise pQCD predictions with small residual scale dependence.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Anomalous behavior in high-pressure carbonaceous sulfur hydride

A new experimental study reported behavior in a high-pressure carbon-sulfur-hydrogen system that has been interpreted by the authors as superconductivity at room temperature. The sudden change of electrical resistance at a critical temperature and the change of the R vs. T behavior with an applied magnetic field point to superconductivity. This is a very exciting study in one of the most important areas of science, hence, it is crucial for the community to investigate these findings and hopefully reproduce these results. In this paper, we present calculations that expand upon the arguments put forth, and offer some speculations about physical mechanisms that might explain the observed data. Here, we show that there are errors in the analysis presented in the experimental paper, and with the correct analysis, the reported R vs. T data significantly deviate from the expected behavior. In particular, the extremely sharp change in resistance at the superconducting transition is not consistent with a strongly type II superconductor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗