Investigation of water absorption in clay-reinforced polypropylene nanocomposites

The behaviour of polypropylene nanocomposites containing different amounts of commercial nanoclay upon exposure to distilled water and sea water at different temperatures was investigated and compared with that of neat polypropylene. In the initial stages, the weight gain (moisture absorption) follows Fick's second law, but at longer times deviations are observed owing to physical degradation and in some cases a loss of mass. Distilled water diffuses more rapidly than sea water. As the nanoclay content increases, both the rate of moisture absorption and the maximum moisture content increase, owing to the hydrophilic nature of the nanoclay and the added compatibilizing agent. Although the moisture absorption decreases the flexural properties of both the nanocomposites and neat PP, because the unexposed (as-moulded) nanocomposites are significantly superior to the neat PP they remain so even after prolonged exposure.     

New Triterpenes from Gymnema sylvestre

Phytochemical investigation of the aerial parts of Gymnema sylvestre has led to the isolation of seven new triterpenes, six oleane types ( 5, 7 – 11 ) and a new lupane type ( 12 ), and of the six known analogues 1 – 4, 6 , and 13 . The structures and relative configurations of these compounds were elucidated by spectroscopic analyses, including 1D‐ and 2D‐NMR spectroscopy and mass spectrometry, and by the comparison of their NMR data with those of related compounds.     

Minimizing maximum lateness in a flow shop subject to release dates

We consider the problem of minimizing the maximum lateness in a m-machine flow shop subject to release dates. The objective of this paper is to develop a new branch-and-bound algorithm to solve exactly this strongly NP-hard problem. The proposed branch-and-bound algorithm encompasses several features including a procedure for adjusting heads and tails, heuristics, and a lower bounding procedure, which is based on the exact solution of the two-machine flow shop problem with time lags, ready times, and delivery times. Extensive computational experiments show that instances with up to 6000 operations can be solved exactly in a moderate CPU time.     

Reactive layer-by-layer deposition of poly(ethylene imine) and a precursor of TiO2: influence of the sodium chloride concentration on the film growth, interaction with hexacyanoferrate anions, and particle distribution in the film

Films prepared according to a layer-by-layer (LBL) manner find increasing importance in many applications such as coatings with dedicated optical or electronic properties, particularly when including nanomaterials. An alternative way to prepare such hybrid layer-by-layer coatings is to perform sol-gel chemistry in a layer-by-layer manner. In this article, we highlight the importance of the NaCl concentration as a parameter to control the growth as well as the properties of LBL films made from poly(ethylene imine) as the organic counterpart and titanium IV (bisammoniumlactato)dihydroxyde ([Ti(lac)(2)(OH)(2)](2-)) as the precursor of TiO(2). An increase in the sodium chloride concentration leads to the faster growth of the film and to a decrease in the number of hexacyanoferrate anions remaining in the film after a buffer rinse. This may be due to a progressive increase in the fraction of negatively charged TiO(2) as suggested by transmission electron microscopy. In the presence of 0.5 M NaCl, the fraction of TiO(2) is close to 60% in mass. As a surprising finding, the films produced from 0.15 M NaCl are not homogeneously filled with TiO(2) even if the film is produced in an LBL fashion. The increased concentration of TiO(2) at the film-solution interface could constitute a barrier for the incorporation of the negatively charged redox probe.     

Minimising maximum lateness in a two-machine flowshop

The objective of this paper is to develop a branch and bound algorithm for the problem of minimising maximum lateness in a two-machine flowshop, subject to release dates and time lag constraints. The importance of this NP-hard problem is twofold, it arises as a strong relaxation of the classical permutation flowshop problem, and it generalises several well studied two-machine flowshop problems. Computational experiments performed on a large set of randomly generated problems show that our algorithm can solve to optimality large size instances.     

Syntheses and crystal structures of two magnesium–tetrazole compounds in salt and polymeric forms

Two alkaline earth–tetrazole compounds, namely catena‐poly[[[triaquamagnesium(II)]‐μ‐5,5′‐(azanediyl)ditetrazolato‐κ³N¹,N^1′:N⁵] hemi{bis[μ‐5,5′‐(azanediyl)ditetrazolato‐κ³N¹,N^1′:N²]bis[triaquamagnesium(II)]} monohydrate], {[Mg(C₂HN₉)(H₂O)₃][Mg₂(C₂HN₉)₂(H₂O)₆]_0.5·H₂O}_n, (I), and bis[5‐(pyrazin‐2‐yl)tetrazolate] hexaaquamagnesium(II), (C₅H₃N₆)[Mg(H₂O)₆], (II), have been prepared under hydrothermal conditions. Compound (I) is a mixed dimer–polymer based on magnesium ion centres and can be regarded as the first example of a magnesium–tetrazolate polymer in the crystalline form. The structure shows a complex three‐dimensional hydrogen‐bonded network that involves magnesium–tetrazolate dimers, solvent water molecules and one‐dimensional magnesium–tetrazolate polymeric chains. The intrinsic cohesion in the polymer chains is ensured by N—H...N hydrogen bonds, which form R₂²(7) rings, thus reinforcing the propagation of the polymer chain along the a axis. The crystal structure of magnesium tetrazole salt (II) reveals a mixed ribbon of hydrogen‐bonded rings, of types R₂²(7), R₂²(9) and R₂⁴(10), running along the c axis, which are linked by R₂⁴(16) rings, generating a 4,8‐c flu net.     

Influence of anion substitution on hydrogen‐bonding patterns of salt compounds: cytosinium hydrogen sulfate and cytosinium perchlorate

In the two title compounds, cytosinium hydrogen sulfate, C₄H₆N₃O⁺·HSO₄⁻, (I), and cytosinium perchlorate, C₄H₆N₃O⁺·ClO₄⁻, (II), the asymmetric units comprise a cytosinium cation with hydrogen sulfate and perchlorate anions, respectively. The crystal structures of (I) and (II) are similar; that of (I) is characterized by a three‐dimensional N—H...O, O—H...O and C—H...O hydrogen‐bonded network. In (I) and (II), two‐dimensional layers are formed by N—H...O and C—H...O hydrogen bonds and, in the case of (I), they are linked by O—H...O hydrogen bonds where the anion acts as a donor and the cation as an acceptor. The hydrogen‐bonded sheets in (II) form an angle of 87.1°.     

New Acylated Oleanane and Lupane Triterpenes from Gymnema sylvestre

Phytochemical investigation of the aerial parts of Gymnema sylvestre led to the isolation of two known oleanane‐type triterpenes, 1 and 3 , five new acylated derivatives, 2, 4 , and 5 – 7 , and a new lupane‐type triterpene, 8 . The structures and relative configurations of these compounds were elucidated by spectroscopic analyses, including 1D‐ and 2D‐NMR spectroscopy and mass spectrometry, and by the comparison of their NMR data with those of related compounds.     

The two-machine flowshop scheduling problem with sequence-independent setup times: New lower bounding strategies

The two-machine flowshop environment with sequence-independent setup times has been intensely investigated both from theoretical and practical perspectives in the scheduling literature. Nevertheless, very scant attention has been devoted to deriving effective lower bounding strategies. In this paper, we propose new lower bounds for the total completion time minimization criterion. These bounds are based on three relaxation schemes, namely the waiting time-based relaxation scheme, the single machine-based relaxation scheme, and the Lagrangian relaxation scheme. Extensive computational study carried on instances with up to 500 jobs reveals that embedding the waiting time-based bounding strategy within the Lagrangian relaxation framework yields the best performance while requiring negligible CPU time.     

Minimizing the total completion time in a two-machine flowshop with sequence-independent setup times

We consider the problem of minimizing the sum of completion times in a two-machine permutation flowshop subject to setup times. We propose a new priority rule, several constructive heuristics, local search procedures, as well as an effective multiple crossover genetic algorithm. Computational experiments carried out on a large set of randomly generated instances provide evidence that a constructive heuristic based on newly derived priority rule dominates all the proposed constructive heuristics. More specifically, we show that one of our proposed constructive heuristics outperforms the best constructive heuristic in the literature in terms of both error and computational time. Furthermore, we show that one of our proposed local search-based heuristics outperforms the best local search heuristic in the literature in terms of again both error and computational time. We also show that, in terms of quality-to-CPU time ratio, the multiple crossover genetic algorithm performs consistently well.