Ionic liquid-based sodium ion-conducting composite gel polymer electrolytes: effect of active and passive fillers

Journal of Solid State Electrochemistry - We report the studies on composite gel polymer electrolytes (GPEs) comprising 0.5 M solution of sodium trifluoromethane sulfonate (Na-triflate or...     

Structure of Three Related Diphosphorus Ligands: Highlighting the Significance of the Backbone

Abstract  

The three compounds contained in this report—4,6-bis(diphenylphosphino)-10,10-dimethylphenoxasilin (sixantphos), 1; 4,5-bis(diphenylphosphino)-9-isopropylidenexanthene, (isopropxantphos) 2 and bis-(2-diphenylphosphino)-p-tolyl) ether (PTEphos) 3, all contain a common ether-linked diphenylphosphino backbone. These structures are of interest with respect to the intra-molecular P···P distance which is 3.884(2), 4.104(2) and 5.151(2) ? for 1, 2 and 3 respectively. The differences in the P···P distances are as a result of the variations in the backbones. Structure 1 shows a significant roof-like bending of the backbone along the axis of planarity involving the oxygen and Si donor atoms. Compound 2 is also folded with a larger dihedral angle of 35.85(2)° as compared to 24.14(2)° found in 1. The backbone in structure 3 is significantly bent and twisted with a dihedral angle of 67.34(2)°. These data show the effect on the intra-molecular P···P distance of varying the backbone of three xantphos-type ligands, with respect to the nature of the heterocycle donor 1, the substituent on the donor 2 and total loss of xanthene character 3.     

Two-echelon location routing synchronized with production schedules and time windows

Central European Journal of Operations Research - In this paper we study a problem that arose while planning the delivery of perishable goods, such as newspapers or foodstuff, in urban areas. The...     

Retaining positive definiteness in thresholded matrices

Positive definite (p.d.) matrices arise naturally in many areas within mathematics and also feature extensively in scientific applications. In modern high-dimensional applications, a common approach to finding sparse positive definite matrices is to threshold their small off-diagonal elements. This thresholding, sometimes referred to as hard-thresholding, sets small elements to zero. Thresholding has the attractive property that the resulting matrices are sparse, and are thus easier to interpret and work with. In many applications, it is often required, and thus implicitly assumed, that thresholded matrices retain positive definiteness. In this paper we formally investigate the algebraic properties of p.d. matrices which are thresholded. We demonstrate that for positive definiteness to be preserved, the pattern of elements to be set to zero has to necessarily correspond to a graph which is a union of complete components. This result rigorously demonstrates that, except in special cases, positive definiteness can be easily lost. We then proceed to demonstrate that the class of diagonally dominant matrices is not maximal in terms of retaining positive definiteness when thresholded. Consequently, we derive characterizations of matrices which retain positive definiteness when thresholded with respect to important classes of graphs. In particular, we demonstrate that retaining positive definiteness upon thresholding is governed by complex algebraic conditions.     

A Projection Method for the Integer Quadratic Knapsack Problem

In this paper we present a new branch and bound algorithm for solving a class of integer quadratic knapsack problems. A previously published algorithm solves the continuous variable subproblems in the branch and bound tree by performing a binary search over the breakpoints of a piecewise linear equation resulting from the Kuhn-Tucker conditions. Here, we first present modifications to a projection method for solving the continuous subproblems. Then we implement the modified projection method in a branch and bound framework and report computational results indicating that the new branch and bound algorithm is superior to the earlier method.     

Internal magnetic hyperfine fields at Hf nuclei in iron,cobalt and nickel hosts

Integral perturbed angular correlation technique has been used to measure the internal hyperfine magnetic fields at Hf nuclei in Fe, Co and Ni matrices. These represent a consistent set of measurements with diffused sources. The 9+/2 (208 keV) 9?/2 (113 keV) 7?/2 cascade in the decay of¹⁷⁷Lu→¹⁷⁷Hf was used for measurements. The results obtained are: $$\begin{gathered} H_{Fe}^{Hf} = - 266 \pm 47 kG, \hfill \\ H_{Co}^{Hf} = - 116 \pm 18 kG, \hfill \\ H_{Ni}^{Hf} = - 118 \pm 26 kG. \hfill \\ \end{gathered} $$ These measurements are compared with previous results and discussed in terms of methods of source preparation.     

Synthesis and photophysical properties of neutral luminescent rhenium-based molecular rectangles

A series of neutral luminescent molecular rectangles [[Re(CO)(3)(mu-bpy)Br][Re(CO)(3)(mu-L)Br]](2) (1-4) having fac-Re(CO)(3)Br as corners and 4,4'-bipyridine (bpy) as the bridging ligand on one side and other bipyridyl ligands of varying length (L) on the other side have been synthesized and characterized. The crystal structure of 1 shows a rectangular cavity with the dimensions of 11.44 x 7.21 A. When the cavity size is tuned from 1 to 4, a dimension of 11.4 x 20.8 A could be achieved, as revealed by the molecular modeling. These rectangles exhibit luminescence in solution at room temperature. In particular, compound 4 containing 1,4-bis(4'-pyridylethynyl)benzene (bpeb) as bridging ligand shows the excited-state lifetime of 495 ns. Fine-tuning of the cavity size of the rectangles improves their excited-state properties. These properties facilitate the study of excited-state electron-transfer reactions with electron acceptors and donors and host-guest binding. Crystallographic information: 1.6CH(3)COCH(3) is monoclinic, P2(1)/c, with a = 12.0890(2), b = 24.2982(2), and c = 12.8721(2) A, beta = 107.923(1) degrees, and Z = 2.     

The effect of dendritic pendants on the folding of amphiphilic copolymers via supramolecular interactions

The supramolecular folding of amphiphilic heterograft copolymers equipped with dendritic pendants is investigated using a combination of proton nuclear magnetic resonance (¹H NMR) spectroscopy, small‐angle X‐ray scattering, and circular dichroism spectroscopy. Hereto, the linear poly(ethylene glycol) pendants normally used to convey water compatibility are partially substituted with branched analogues. For one set of copolymers, second‐generation polyglycerol dendrons are directly attached to the polymer backbone, while for the other a hydrophilic linker is placed in between. The results show that the branching of the hydrophilic pendants affects the local structure of the folded copolymer but does not influence the overall conformation and single‐chain character of the folded copolymers in solution. All copolymers fold into 4–5 nm single‐chain polymeric nanoparticles with a very compact spherical morphology, independent of the dendritic content of the copolymer. Intriguingly, the incorporation of the dendritic pendants affects the formation of a structured interior even at low incorporation ratios. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 411–421