High-level ab initio potential energy surfaces and vibrational energies of H2CS

Six-dimensional (6D) potential energy surfaces (PESs) of H(2)CS have been generated ab initio using the recently proposed explicitly correlated (F12) singles and doubles coupled cluster method including a perturbational estimate of connected triple excitations, CCSD(T)-F12b [T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys. 127, 221106 (2007)] in conjunction with F12-optimized correlation consistent basis sets. Core-electron correlation, high-order correlation, scalar relativistic, and diagonal Born-Oppenheimer terms were included as additive high-level (HL) corrections. The resulting 6D PESs were represented by analytical functions which were used in variational calculations of the vibrational term values below 5000 cm(-1). The best PESs obtained with and without the HL corrections, VQZ-F12(*HL) and VQZ-F12?, reproduce the fundamental vibrational wavenumbers with mean absolute deviations of 1.13 and 1.22 cm(-1), respectively. A detailed analysis of the effects of the HL corrections shows how the VQZ-F12 results benefit from error cancellation. The present purely ab initio PESs will be useful as starting points for empirical refinements towards an accurate "spectroscopic" PES of H(2)CS.     

Application of denoising methods to regularizationof ill-posed problems

Linear systems of equations and linear least-squares problems with a matrix whose singular values “cluster” at the origin and with an error-contaminated data vector arise in many applications. Their numerical solution requires regularization, i.e., the replacement of the given problem by a nearby one, whose solution is less sensitive to the error in the data. The amount of regularization depends on a parameter. When an accurate estimate of the norm of the error in the data is known, this parameter can be determined by the discrepancy principle. This paper is concerned with the situation when the error is white Gaussian and no estimate of the norm of the error is available, and explores the possibility of applying a denoising method to both reduce this error and to estimate its norm. Applications to image deblurring are presented.     

Towards Jaffe and Taubes Conjectures in the strongly repulsive limit

 We consider the abelian Yang-Mills-Higgs Action on all of ℝ² for large coupling constants (the strongly repulsive case). The homotopy classes of configurations are defined in a weak sense under the assumption of finite action only. We prove that the homotopy classes which admit a global minimizer for the YMH Action are exactly the +1, -1 and 0 degree classes. Finally we prove that any global minimizer in one of these homotopy classes is the axially symmetric solution (modulo gauge action) in the corresponding class. Received: 4 September 1999 / Revised version: 4 February 2002     

Dual/scram-mode combustion limits of ethylene and surrogate endothermically-cracked hydrocarbon fuels at Mach 8 equivalent high-enthalpy conditions

This paper examines the scram/dual-mode combustion limits of hydrocabon fuels within a Mach 8, scramjet combustor. Flight-equivalent flows were delivered to the axisymmetric, cavity combustor via a reflected shock tunnel. Two scramjet fuels were examined: ethylene and a surrogate mixture representing endothermically cracked n-dodecane. Combustion modes were examined via static pressure sensors and through both chemiluminescence imaging, and planar laser induced fluorescence (PLIF) of the OH combustion radical in the combustor exhaust plume. Ethylene-fuelled experiments developed scram-mode combustion under reduced fuelling conditions, experiencing shock wave dominated flowfields. OH PLIF diagnostics indicated such combustion modes developed a ring-like structure of combustion products, primarily axisymmetrically adjacent to the combustor wall. Increased fuelling anchored combustion downstream of the fuel injector, while further increases instigated dual-mode combustion. In this mode, subsonic combustion regions combine with the supersonic coreflow to permit the transfer of information upstream with substantially increased pressure encountered. Optical diagnostics indicate broadly asymmetric, unsteady combustion features. The surrogate mixture representing endothermically cracked n-dodecane experienced rapid onset from no-combustion (optically confirmed) to fully developed dual-mode combustion at critical fuelling rates. OH PLIF signals and chemiluminescence of this fuel were weaker than comparable ethylene cases, indicating potential differences in combustion pathways.     

Nonuniqueness of Weak Solutions to the SQG Equation

We prove that weak solutions of the inviscid SQG equations are not unique, thereby answering Open Problem 11 of De Lellis and Székelyhidi in 2012. Moreover, we also show that weak solutions of the dissipative SQG equation are not unique, even if the fractional dissipation is stronger than the square root of the Laplacian. In view of the results of Marchand in 2008, we establish that for the dissipative SQG equation, weak solutions may be constructed in the same function space both via classical weak compactness arguments and via convex integration. © 2019 Wiley Periodicals, Inc.     

Nickel‐Catalyzed Inter‐ and Intramolecular Aryl Thioether Metathesis by Reversible Arylation

A nickel‐catalyzed aryl thioether metathesis has been developed to access high‐value thioethers. 1,2‐Bis(dicyclohexylphosphino)ethane (dcype) is essential to promote this highly functional‐group‐tolerant reaction. Furthermore, synthetically challenging macrocycles could be obtained in good yield in an unusual example of ring‐closing metathesis that does not involve alkene bonds. In‐depth organometallic studies support a reversible Ni⁰/Ni^II pathway to product formation. Overall, this work not only provides a more sustainable alternative to previous catalytic systems based on Pd, but also presents new applications and mechanistic information that are highly relevant to the further development and application of unusual single‐bond metathesis reactions.     

Transient dynamics of cold-rolled and subsequently thermally rejuvenated atactic-polystyrene using broadband dielectric spectroscopy

The effect of plastic deformation on the molecular dynamics of atactic polystyrene (a-PS) was studied by broadband dielectric relaxation spectroscopy (BDRS), Fourier-transform infrared spectroscopy (FTIR) and polarized-light microscopy. Sheets of a-PS have been subjected to cold rolling, that is, mechanical rejuvenation, followed by a quenching step and fast heating above its glass-transition temperature, resulting in thermal rejuvenation. Cold rolling revealed, in addition to the known α- and γ(I)-relaxations, four hitherto unknown relaxation processes (II, III, IV and V). Using the framework of craze formation and multiplicity of the glass transition (E. Donth, G. H. Michler, Colloid Polym. Sci. 1989, 267, 557–567), supported by an activation-enthalpy/entropy analysis (Starkweather, W. Howard, Macromolecules 1981, 14, 1277–1281), the following physical picture emerges: (a) processes I and II represent local conformation transitions γ referring to chains of two different degrees of stretching (T/G-ratio); and (ii) processes III and IV were identified as helix-inversion processes of T₂G₂ helices as reported earlier for syndiotactic-rich PS—an assignment supported by FTIR results. Finally, the relaxation V could be attributed to the onset of the fibrillar glass transition (within crazes), leading to stress release by collapse of the fibrils and hence dying out of process V. Polarized-light microscopy confirmed the creation of oriented structures and internal stresses upon cold rolling, and their removal upon thermal rejuvenation.     

Synthesis,Crystal Structures,and Properties of Mn(NCS)2 Coordination Compounds with 4-Picoline as Coligand and Crystal Structure of Mn(NCS)2

Reaction of Mn(NCS)₂ with 4-picoline (4-methylpyridine) leads to the formation of [Mn(NCS)₂(4-picoline)₄] · 0.67 · 4-picoline · 0.33 · H₂O ( 1 - Mn ) reported in literature, Mn(NCS)₂(4-picoline)₂(H₂O)₂ ( 2-Mn/H₂O ), and of [Mn(NCS)₂(4-picoline)₂]_n ( 2-Mn/I ). 1-Mn and 2-Mn/H₂O consist of discrete complexes, in which the metal cations are octahedrally coordinated, whereas in 2-Mn/I the metal cations are linked by pairs of μ-1,3-bridging thiocyanate anions into corrugated chains. Measurements using thermogravimetry and differential scanning calorimetry as well as temperature dependent X-ray powder diffraction on 1-Mn and 2-Mn/H₂O reveal that upon heating both compounds transform into [Mn(NCS)₂(4-picoline)]_n ( 3-Mn ) via 2-Mn/I as intermediate. 3-Mn shows a very rare chain topology in which the metal cations are linked by μ-1,3,3 (N,S,S) coordinating anionic ligands which was never observed before with Mn^II. From these investigations there is no hint that a further modification of 2-Mn can be prepared as recently observed for [M(NCS)₂(4-picoline)₂]_n (M = Fe, Cd) and such a form is also not available if the metastable forms of the Fe^II or Cd^II compounds were used as template during thermal decomposition. Magnetic investigations on 2-Mn/H₂O show only paramagnetic behavior, whereas for 2-Mn/I antiferromagnetic ordering is observed. Finally, the crystal structure of Mn(NCS)₂ was determined from XRPD data, which shows that it is strongly related to that of 3-Mn .     

Fluorescent hydroxyflavone-zeolite nanoparticles: ship-in-a-bottle synthesis and photophysical properties.

3-Hydroxyflavone (3-OHF) was incorporated in zeolite micropores by ship-in-a-bottle synthesis. This strategy consists of constructing the molecule by reaction of small precursors within the cavity. 3-OHF molecules exhibit excited-state intramolecular proton transfer (ESIPT) and a tautomeric equilibrium between the 3-OHF-excited structures N* and T*exists. This equilibrium is strongly affected by the protic nature and polarity of the surrounding medium. The textural and spectroscopic characterization of the dye-loaded zeolite colloids enabled the study of the correlation between the optical properties of the dye and the zeolite micropore environment.