SUMMARYA stabilized ®nite element formulation is employed to study incompressible¯ows past a pair of cylinders at Reynolds numbers 100 and 1000 in tandem and staggered arrangements. Computations are carried out for three sets of cylinder arrangements. In the ®rst two cases the cylinders are arranged in tandem and the distance between their centres is 2Á5 and 5Á5 diameters. The third case involves the two cylinders in staggered arrangement. The distance between their centres along the¯ow direction is 5Á5 diameters, while it is 0Á7 diameter in the transverse direction. The results are compared with¯ows past a single cylinder at corresponding Reynolds numbers and with experimental observations by other researchers. It is observed that the qualitative nature of thē ow depends strongly on the arrangement of cylinders and the Reynolds number. In all cases, when the¯ow becomes unsteady, the downstream cylinder, which lies in the wake of the upstream one, experiences very large unsteady forces that may lead to wake-induced¯utter. The Strouhal number, based on the dominant frequency in the time history of the lift coef®cient, for both cylinders attains the same value. In some cases, even though the near wake of the two cylinders shows temporal periodicity, the far wake does not.

The synthesis, structure, and magnetic properties of four Dy coordination compounds isolated as [Dy (LH ) (μ -η :η -Piv)]Cl⋅2 MeOH⋅H O (1), [Dy (LH) (μ -OH) (Piv) (MeOH) ]⋅4 MeOH⋅2 H O (2), [Dy (LH ) (tfa) (O PtBu)(Cl) ]Cl ⋅15.5 H O⋅4 MeOH⋅5 CHCl (3) and [Dy (L) (LH) (tfa) ]Cl ⋅15 H O⋅7 MeOH⋅12 CHCl (4) are reported (Piv=pivalate, tfa=1,1,1-trifluoroacetylacetone, O PtBu=tert-butylphosphonate). Among these, 3 displays an equilateral triangle topology with a side length of 9.541 Å and a rare pentagonal-bipyramidal Dy environment, whereas complex 4 exhibits a single-stranded nanowheel structure with the highest nuclearity known for a homometallic lanthanide cluster structure. A tentative model of the dc magnetic susceptibility and the low-temperature magnetization of compounds 1 and 2 indicates that the former exhibits weak ferromagnetic intramolecular exchange interaction between the Dy ions, whereas in the latter both intramolecular ferromagnetic and antiferromagnetic magnetic exchange interactions are present. Compounds 1, 3, and 4 exhibit frequency-dependent ac signals below 15 K at zero bias field, but without exhibiting any maximum above 2 K at frequencies up to 1400 Hz. The observed slow relaxation of the magnetization suggests that these compounds could exhibit single molecule magnet (SMM) behavior with either a thermal energy barrier for the reversal of the magnetization that is not high enough to block the magnetization above 2 K, or there exists quantum tunneling of the magnetization (QTM).

The synthesis, structure, and magnetic properties of three DyIII complexes of different nuclearity, [Dy2(H2L)2(NO3)] [NO3]·2H2O·CH3OH (1), [Dy4(HL)2(piv)4(OH)2] (2), and [Dy6(H2L)3(μ3–OH)­(μ3–CO3)3(CH3OH)4(H2O)8] 5Cl·3H2O (3) [(H4L) = 6-((bis­(2-hydroxyethyl)­amino)-N′-(2-hydroxybenzylidene)­picolinohydrazide)], are described. This variety of complexes with the same ligand could be obtained by playing with the metal-to-ligand molar ratio, the type of DyIII salt, the kind of base, and the presence/absence of coligand. 1 is a dinuclear complex, while 2 is a tetranuclear assembly with a butterfly-shaped topology. 3 is a homometallic hexanuclear complex that exhibits a propeller-shaped topology. Interestingly, in this complex 3, three atmospheric carbon dioxide molecules are trapped in the form of carbonate ions, which assist in holding the hexanuclear complex together. All of the complexes reveal a slow relaxation of magnetization even in zero applied field. Complex 1 is a zero-field SMM with an effective energy barrier (U eff) of magnetization reversal equal to 87(1) K and a relaxation time of τ0 = 6.4(3) × 10–9 s. Under an applied magnetic field of 0.1 T, these parameters change to U eff = 101(3) K, τ0 = 2.5(1) × 10–9 s. Complex 2 shows zero-field SMM behavior with U eff = 31(2) K, τ0 = 4.2(1) × 10–7 s or τ01 = 2(1) × 10–7 s, U eff1 = 37(8) K, τ02 = 5(6) × 10–5 s, and U eff2 = 8(4) by considering two Orbach relaxation processes, while 3, also a zero-field SMM, shows a double relaxation of magnetization [U eff1 = 62.4(3) K, τ01 = 4.6(3) × 10–8 s, and U eff1 = 2(1) K, τ02 = 4.6(2) × 10–5 s]. The ab initio calculations indicated that in these complexes, the Kramer’s ground doublet is characterized by an axial g-tensor with the prevalence of the m J = ±15/2 component, as well as that due to the weak magnetic coupling between the metal centers, the magnetic relaxation, which is dominated by the single DyIII centers rather than by the exchange-coupled states, takes place via Raman/Orbach or TA-QTM. Moreover, theoretical calculations support a toroidal magnetic state for complex 2.

Four new dinuclear complexes, [Co­(μ-L)­(μ-CCl3COO)­Y­(NO3)2]·2CHCl3·CH3CN·2H2O (1), [Co­(μ-L)­(μ-CH3COO)­Y­(NO3)2]·CH3CN (2), [Co­(μ-L)­(μ-PhCOO)­Y­(NO3)2]·3CH3CN·2H2O (3), and [Co­(μ-L)­(μ-tBuCOO)­Y­(NO3)2]·CHCl3·2H2O (4), having a CoIIYIII core, have been synthesized by employing a ferrocene based compartmental ligand which was synthesized by the reaction of diacetyl ferrocene with hydrazine hydrate followed by a condensation reaction with o-vanillin. A general synthetic protocol was employed to synthesize complexes 1–4, where the metallic core was kept the same with changing the bridging carboxylate groups. In all the complexes, the main structural motif is kept similar by only slightly varying the substitution on the bridging acetate groups. This variation has resulted in a small but subtle influence on the magnetic relaxation of all these four compounds. Ab initio CASSCF/NEVPT2 calculations were carried out to assess the effect of the different substitutions of the bridging ligands on the magnetic anisotropy parameters and on orbital arrangements. Ab initio calculations yield a very large positive D value, which is consistent with the geometry around the CoII ion and easy plane anisotropy (g xx , gyy > g zz ), with the order of the calculated D in the range of 72.4 to 91.7 cm–1 being estimated in this set of complexes. To ascertain the sign of zero-field splitting in these complexes, EPR spectra were recorded, which support the sign of D values estimated from ab initio calculations.

in Wiley Online Library (wileyonlinelibrary.com).Most of the published studies have focused on the thermal integration of nonreactive distillation columns. The key limitation of reactive distillation (RD) technology is that the necessary conditions (such as pressure and temperature) for the reaction must match those of distillation. Owing to this constraint, the reaction conversion may be adversely affected at the elevated pressure in the reactive section of an internally heat integrated distillation column (HIDiC). This fact forces us to adopt an external heat integration approach for an industrial heterogeneously catalyzed ethyl tert-butyl ether (ETBE) RD column. The direct vapor recompression column (VRC) is an external heat integration scheme that is successfully used as an energy efficient scheme for separating a close-boiling mixture. Interestingly, there exists a large temperature difference between the two ends of the representative ETBE column, and it makes the external heat integration more challenging. Aiming to improve the thermal efficiency of the ETBE column under the VRC framework, various heat pump arrangements with intermediate reboiler(s) (IR(s)) are explored and analyzed with performing a comparative study in terms of energy consumption and economics. To improve further the thermal efficiency, in this contribution, a novel multistage vapor recompression RD column with IRs is introduced addressing a number of practical concerns. An algorithm for the proposed column is formulated showing the sequential steps involved in heat integration. It is inspected that the proposed multistage vapor recompression RD system appears overwhelmingly superior to the classical vapor recompression RD and its conventional stand alone column providing a significant savings in energy as well as cost.