Human mobility and COVID-19 initial dynamics

Nonlinear Dynamics - Countries in Europe took different mobility containment measures to curb the spread of COVID-19. The European Commission asked mobile network operators to share on a...     

Synthesis and characterization of chiral poly(alkyl isocyanates) by coordination polymerization using a chiral half‐titanocene complex

A new chiral half‐titanocene complex, [CpTiCl₂(O‐(S)?2‐Bu)], is synthesized and characterized by ¹H and ¹³C NMR spectroscopy. This complex is employed for the coordination polymerization of n‐butyl and n‐hexyl‐ isocyanate leading to chiral polymers, as revealed by their CD spectra. Only the left‐handed helix is produced, due to the chiral (S)?2‐butoxy group, which is bound to the polymer chain end. The polymerization of 3‐(triethoxysilyl)propyl isocyanate produces less soluble polymers. On the other hand, phenyl isocyanate reacts slowly with the complex leading quantitatively and selectively to triphenyl isocyanurate. 2‐Ethylhexyl isocyanate is slowly and selectively cyclotrimerized in the presence of the half‐titanocene complex. However, a statistical copolymer of 2‐ethylhexyl isocyanate and hexyl isocyanate is produced. The reaction of benzyl isocyanate with the complex leads to a mixture of low molecular weight polymer and cyclotrimer. The polymers are characterized using SEC, NMR, and CD spectroscopy and their thermal properties are investigated by TGA/DSC analysis. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2141–2151     

Employing (half-)titanocene complexes as initiators for the synthesis of end-functionalized polylactides by coordination polymerization

Seven (half-)titanocene alkoxide complexes, [Cp₂TiCl(OEt)], [Cp₂TiCl(O-2-Bu)], [Cp₂TiCl(OCH₂CF₂CF₂H)], [CpTiCl₂(OEt)], [CpTiCl₂(O-(S)-2-Bu)], [CpTiCl₂(OCH₂CF₃)], and [Cp₂TiCl(OCH₂CF₃)], were synthesized and employed in lactide coordination polymerization. These organotitanium (IV) compounds proved to be very efficient initiators for the ring-opening polymerization of enantiomeric l -lactide and racemic mixture of rac-lactide, leading to end-functionalized polymers. Kinetic studies illustrated that these compounds produce well-defined polymers in a controlled manner. This was further demonstrated by synthesizing poly(l -lactide-b-hexyl isocyanate) diblock copolymer. The effect of the alkoxy end groups on the thermal behavior of the polymers was also studied by thermogravimetric analysis and differential scanning calorimetry. The polymers were characterized using size exclusion chromatography and proton nuclear magnetic resonance spectroscopy. The optical properties of the diblock copolymer were also investigated. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2192–2202     

The decomposition of global conformal invariants IV: A proposition on local Riemannian invariants

This is the fourth in a series of papers where we prove a conjecture of Deser and Schwimmer regarding the algebraic structure of “global conformal invariants”; these are defined to be conformally invariant integrals of geometric scalars. The conjecture asserts that the integrand of any such integral can be expressed as a linear combination of a local conformal invariant, a divergence and of the Chern-Gauss-Bonnet integrand.The present paper lays out the second half of this entire work: The second half proves certain purely algebraic statements regarding local Riemannian invariants; these were used extensively in the first two papers in this series, see Alexakis (2007, 2009) [2] and [3]. These results may be of independent interest, applicable to related problems.     

In search for mixed transition metal/lanthanide single-molecule magnets: Synthetic routes to NiII/TbIII and NiII/DyIII clusters featuring a 2-pyridyl oximate ligand

Employing the mononuclear complex [Ni{(py)C(Me)NO}₂{(py)C(Me)NOH}] (1) as ‘ligand’ [(py)C(Me)NOH = methyl 2-pyridyl ketone oxime], the use of the ‘metal complexes as ligands’ approach has led to the synthesis of the mixed Ni^II/Ln^III complexes [NiTb{(py)C(Me)NO}₂(NO₃)₃{(py)C(Me)NOH}] (2), [Ni₂Ln₂{(py)C(Me)NO}₆(NO₃)₄] (Ln = Dy, 3; Ln = Tb, 4) and [Ni₂Tb{(py)C(Me)NO}₆](NO₃) (5). The structures of 2, 3, and 5, and the magnetic properties of 2 and 5 are briefly discussed.     

A three-dimensional copper(II) coordination polymer featuring the 2,3-dioxyquinoxalinate(-2) ligand: Preparation,structural characterization and magnetic study

The synthesis, single-crystal X-ray structure and magnetic properties of [Cu₃L₂Cl₂(DMF)₄]_n (1), where L^2? is the 2,3-dioxyquinoxalinate(-2) ligand, are reported. The complex was prepared by the reaction of CuCl₂ and 1,4-dihydro-2,3-quinoxalinedione (H₂L′) under basic conditions using either solvothermal or normal laboratory techniques. Compound 1 is a 3D coordination polymer with an (8².10)-a, lig (LiGe) topology, containing the ligand in a novel 3.1111 (Harris notation) coordination mode. Variable-temperature and variable-field magnetic studies reveal that the ligand L^2? propagates weak antiferromagnetic exchange interactions through its “quinoxaline” part. IR data are discussed in terms of the structural features of 1 and the coordination mode of L^2?.     

Improvement of source and wind field input of atmospheric dispersion model by assimilation of concentration measurements: Method and applications in idealized settings

The problem of correcting the pollutant source emission rate and the wind velocity field inputs in a puff atmospheric dispersion model by data assimilation of concentration measurements has been considered. Variational approach to data assimilation has been used, in which the specified cost function is minimized with respect to source strength and/or wind field. The analyzed wind field satisfied the constraints derived from the conditions of mass conservation and linearized flow equations for perturbations from the first guess wind field. ‘Identical twin’ numerical experiments have been performed for the validation of the method. The first guess estimation errors of source emission rate and wind field were set to a factor of up to 10 and up to 6 m/s respectively. The calculations results showed that in most studied cases an improvement of vector wind difference (VWD) error by about 0.7–1 m/s could be achieved. The resulting normalized mean square error (NMSE) of concentration field was also reduced significantly.