Non-intersecting Channels Research Articles

A Particle Swarm and Clonal Selection Algorithm based Channel Assignment Algorithm in MRMC Wireless Mesh Network

Channel Assignment (CA) in MRMC Wireless Mesh Network (WMN) is an efficient device that exploits numerous non-intersecting channels to reduce the interference and augment the capability of WMN. However, CA could diminish the complete network interference; its consequences might cause certain design issues that impact the efficiency of the network. A good CA in wireless mesh networks could minimize numerous interference co-channels and enhance the throughput. The clonal selection approach is simulated using the rudimentary notion of adaptive immune reply to virus stimulus. The PSO is inspired using the social behaviors of swarms. Motivated by these two optimization methodologies, in this paper, a hybridized particle swarm aided clonal selection approach is introduced for resolving channel assignment issue, i.e., evaluating a lower-interference channel assignment depending on gathered data. Conflict Vector in Conflict Graph known as antigens in clonal selection algorithm having fewer affinity values are improved using the particle swarm optimization update operation. Then the clonal selection and mutation operation is employed iteratively to generate the optimum conflict vectors. The experimental results are carried out using NS2. From the outcomes, it is clearly shown that the suggested approach has better energy efficiency, packet delivery ratio, and less network delay, packet drop compared to existing algorithms.

Adsorption of Polar Enantiomers in Achiral Zeolites

We used molecular simulation techniques to analyze the enantioselective adsorption of chiral polar molecules in achiral zeolites. As a representative chiral molecule, CHClFBr was used in this study. We analyzed the adsorption of racemic and scalemic mixtures of these molecules into different zeolites topologies such as MFI and MEL, both structures with intersecting channels, and FER and TON, frames with nonintersecting channels. In contrast to previous findings on apolar molecules, we found that cations are not essential for imposing heteroselective adsorption, and homoselective adsorption was never observed. We derived the mechanism behind the selectivity, which turns out to be fundamentally different from that observed for apolar adsorbates. Our model is able to explain why apparently similar zeolite topologies can still have strong differences in their adsorption behavior.

Ion exchange as a simple and effective tool for screening possible cation conductors

Although kinetics of the low-temperature cation exchange in mixed oxide materials (aluminates, gallates, titanates, niobates, tantalates, antimonates, phosphates etc.) cannot provide quantitative information on self-diffusion and ionic conductivity in the starting material due to the mixed cation effect, it is the most direct and simple qualitative indication of the cation mobility in the solid state. It does not need using ceramics and single crystals and thus represents a useful tool for rapid selection of prospective cation conductors for subsequent detailed studies of dense samples with electrical methods. Examples of solid electrolytes discovered owing to their ion-exchange properties are reviewed, and rational principles of the ion-exchange testing are discussed. Laws of ion-exchange equilibria are based on ionic size compliance and the principle of hard and soft acids and bases. The former is most important for alkali/alkali exchange and the latter for exchanging cations of similar size but having different electronic structures: those of the rare-gas type and those having 18- or 18 + 2-electron shells, like Na+ and Ag+ or K+ and Tl+. Ion-exchange testing is especially useful for structures with non-intersecting conduction paths. It is shown that the resistivity of crystals with non-parallel and non-intersecting conduction paths cannot be described by the classical tensor formalism. Significant differences between isotope exchange, chemical ion exchange and ion conduction, quasi-one-dimensional and true one-dimensional conductors and single- and multiple-barrelled non-intersecting channels are disclosed and discussed.

Crystal structure of pure-silica ZSM-12 with tetraethylammonium cations from X-ray powder diffraction data

Pure-silica ZSM-12, containing tetraethylammonium cations (TEA) was synthesized using a ‘two-silica’ source strategy and its structure was determined from laboratory X-ray powder diffraction data. This is the first known zeolite structure in which the positions of the TEA cations have been established. The ordered arrangement of TEA cations in the straight nonintersecting channels of the host material, which is reflected in several weak superstructural diffraction peaks, was determined by using the combination of simulated annealing and Rietveld refinement. In accordance with Raman spectroscopy, the calculations confirmed the presence of a tt. tt form of the TEA cations and the absence of the other stable form ( tg. tg) which was also consistent with the dimensions and elliptical cross-section of the channels. Therefore in ZSM-12 structure pore (channels) geometry is directly connected with the conformation of TEA cations. The compound with a moiety formula C 16H 40N 2O 84Si 42 ( M r = 2784.28, Z = 4) crystallizes in the monoclinic Cc space group with unit cell parameters a = 25.2177(9), b = 15.1903(5), c = 24.4754(7) Å, β = 108.516(2)°. The final structure, which resulted in a good agreement between calculated and observed powder diffraction pattern ( R wp = 10.17%), was additionally confirmed by results from thermogravimetric measurements and FTIR spectroscopy.

Three‐Dimensional Framework of Uranium‐Centered Polyhedra with Non‐Intersecting Channels in the Uranyl Oxyvanadates A2(UO2)3(VO4)2O (A: Li, Na).

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Three-dimensional framework of uranium-centered polyhedra with non-intersecting channels in the uranyl oxy-vanadates A2(UO 2) 3(VO 4) 2O ( A=Li, Na)

The uranyl vanadates A 2(UO 2) 3(VO 4) 2O ( A=Li, Na) have been synthesized by solid-state reaction and the structure of the Li compound was solved from single-crystal X-ray diffraction. The crystal structure is built from ∞ 1 [ UO 5 ] 4 - chains of edge-shared U(2)O 7 pentagonal bipyramids alternatively parallel to a ⇒ - and b ⇒ -axis and further connected together to form a three-dimensional (3-D) arrangement. The perpendicular chains are hung on both sides of a sheet ∞ 2 [ ( UO 2 ) ( VO 4 ) 2 ] 4 - parallel to (001), formed by U(1)O 6 square bipyramids connected by VO 4 tetrahedra, and derived from the autunite-type sheet. The resulting 3-D framework creates non-intersecting channels running down the a ⇒ - and b ⇒ -axis formed by empty face-shared oxygen octahedra, the Li + ions are displaced from the center of the channels and occupy the middle of one edge of the common face. The peculiar position of the Li + ion together with the full occupancy explain the low conductivity of Li 2(UO 2) 3(VO 4) 2O compared with that of Na(UO 2) 4(VO 4) 3 containing the same type of channels half occupied by Na + ions in the octahedral sites. Crystallographic data for Li 2(UO 2) 3(VO 4) 2O: tetragonal, space group I41/ amd, a = 7.3303 ( 5 ) Å , c = 24.653 ( 3 ) Å , V = 1324.7 ( 2 ) Å 3 , Z = 4 , ρ mes=5.32(2) g/cm 3, ρ cal=5.36(3) g/cm 3, full-matrix least-squares refinement basis on F 2 yielded, R 1 = 0.032 , w R 2 = 0.085 for 37 refined parameters with 364 independent reflections with I ⩾ 2 σ ( I ) .

A novel open-framework with non-crossing channels in the uranyl vanadates A(UO2)4(VO4)3 (A=Li, Na)

A new sodium uranyl vanadate Na(UO2)4(VO4)3 has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the tetragonal symmetry with space group I41/amd and following cell parameters: a=7.2267(4) Å and c=34.079(4) Å, V=1779.8(2) Å3, Z=4 with ρmes=5.36(3) g/cm3 and ρcal=5.40(2) g/cm3. A full-matrix least-squares refinement on the basis of F2 yielded R1=0.028 and wR2=0.056 for 52 parameters with 474 independent reflections with I⩾2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a CCD detector. The crystal structure is characterized by ∞2[(UO2)2(VO4)] sheets parallel to (001) formed by corner-shared UO6 distorted octahedra and V(2)O4 tetrahedra, connected by V(1)O4 tetrahedra to ∞1[UO5]4− chains of edge-shared UO7 pentagonal bipyramids alternately parallel to the a- and b-axis. The resulting three-dimensional framework creates mono-dimensional channels running down the a- and b-axis formed by face-shared oxygen octahedra half occupied by Na. The powder of Li analog compound Li(UO2)4(VO4)3 has been synthesized by solid-state reaction. The two compounds exhibit high mobility of the alkaline ions within the two-dimensional network of non-intersecting channels.

A novel open-framework with non-crossing channels in the uranyl vanadates A(UO 2) 4(VO 4) 3 ( A=Li, Na)

A new sodium uranyl vanadate Na(UO 2) 4(VO 4) 3 has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the tetragonal symmetry with space group I4 1/ amd and following cell parameters: a=7.2267(4) Å and c=34.079(4) Å, V=1779.8(2) Å 3, Z=4 with ρ mes=5.36(3) g/cm 3 and ρ cal=5.40(2) g/cm 3. A full-matrix least-squares refinement on the basis of F 2 yielded R 1=0.028 and w R 2=0.056 for 52 parameters with 474 independent reflections with I⩾2 σ( I) collected on a BRUKER AXS diffractometer with Mo Kα radiation and a CCD detector. The crystal structure is characterized by ∞ 2[(UO 2) 2(VO 4)] sheets parallel to (001) formed by corner-shared UO 6 distorted octahedra and V(2)O 4 tetrahedra, connected by V(1)O 4 tetrahedra to ∞ 1[UO 5] 4− chains of edge-shared UO 7 pentagonal bipyramids alternately parallel to the a- and b-axis. The resulting three-dimensional framework creates mono-dimensional channels running down the a- and b-axis formed by face-shared oxygen octahedra half occupied by Na. The powder of Li analog compound Li(UO 2) 4(VO 4) 3 has been synthesized by solid-state reaction. The two compounds exhibit high mobility of the alkaline ions within the two-dimensional network of non-intersecting channels.

Structure and properties of the composite zeolite silica-ZSM-12/para-nitroaniline

The pure silica form of zeolite ZSM-12 was loaded with hyper-polarizable para-nitroaniline (pNA) molecules to form a composite material pNA/silica-ZSM-12. 7.6 wt.% of pNA is occluded in the straight non-intersecting channels (free diameter ≈6 Å) of the host material. The composite was characterized by optical microscopy, thermal analysis, NMR- and FTIR-spectroscopy, second harmonic generation (SHG) experiments, molecular modelling and X-ray powder diffraction. The pNA molecules are perfectly aligned with their long axis parallel to the channel direction. The molecules have specific docking sites in the channel, and each molecule uses the channel length of two unit cells. However, the overall symmetry of the composite is centrosymmetric. As indicated by FTIR spectroscopy and thermal analysis, the hydrogen bonds between the sorbate molecules inside the host lattice of silica-ZSM-12 (one-dimensional hydrogen bond system) are weaker as compared to pure pNA crystals (three-dimensional hydrogen bond system). The color of the composite material is yellow. The crystals are dichroitic and change their color in polarized light from colorless to bright yellow. pNA/silica-ZSM-12 shows hardly any SHG. This is in contrast to the composite pNA/AlPO 4-5 which contains the highly polarizable pNA molecules in a non-centrosymmetric arrangement yielding, therefore, strong SHG activity.

Phase transitions and molecular dynamics in the cyclohexane/thiourea inclusion compound

In thiourea inclusion compounds the host structure comprises a hydrogen bonded arrangement of thiourea molecules and contains unidirectional, nonintersecting channels within which guest molecules are located. Structural and dynamic properties of the cyclohexane/thiourea inclusion compound have been studied previously by a wide range of experimental techniques, providing contradictory interpretations. This organic composite crystal displays three thermotropic structural phases on cooling from room temperature, denoted phase I (rhombohedral), phase II (monoclinic), and phase III (monoclinic). However, until now, there has been no attempt to understand the relationship between the dynamics of the guest molecules and the structural and symmetry properties of the composite inclusion compound in the three phases. In the first part of this paper, we determine the space group of each phase from powder x-ray diffraction data. From this knowledge of the symmetry properties of each phase, the phase transitions are described in terms of order parameters defined on the basis of the symmetry principles of Landau theory. Theoretical analysis of the crystal strain occurring at the phase transitions allows a direct comparison between the experimental temperature dependence of the lattice parameters and predictions derived from Landau theory. In the second part of this paper, we report results from powder and single-crystal ${}^{2}\mathrm{H}$ NMR spectroscopy on samples of cyclohexane/thiourea containing perdeuterated cyclohexane guest molecules $({\mathrm{C}}_{6}{\mathrm{D}}_{12}).$ These ${}^{2}\mathrm{H}$ NMR experiments have shown that in phase I, the motionally averaged quadrupole coupling tensor is axially symmetric. On passing from phase I to phase II, the threefold symmetry axis of the $R=3\ifmmode\bar\else\textasciimacron\fi{}c$ space group of phase I is lost, such that the motionally averaged quadrupole interaction tensor is not axially symmetric in phase II. The single crystal ${}^{2}\mathrm{H}$ NMR spectra probe very precisely the relative orientations of the guest molecules, which are consistent with the site symmetry properties of the structure and proposed modes of crystal twinning, and demonstrate that there is only one type of dynamic species of guest molecule in phase II. In phase III, a greater degree of orientational ordering of the cyclohexane molecules is evident. From a detailed consideration of the symmetry properties of the inclusion compound, the dynamics of the guest molecules may be described using simple jump models (i.e., multidimensional pseudospin models) in all three phases. Using these models, the temperature dependence of the order parameter components has been established. These results, in conjunction with x-ray diffraction, provide important information needed to propose a microscopic model for the mechanisms of the phase transitions in the cyclohexane/thiourea inclusion compound.

Investigations of the Phase Transitions in Thiourea Inclusion Compounds with Cycloheptane, Cyclooctane, and Cyclooctanone

Variable temperature single-crystal X-ray diffraction and solid-state NMR experiments have been performed on the thiourea cycloheptane (TC7), cyclooctane (TC8), and cyclooctanone (TCO8) inclusion compounds. Three different phases have been evidenced for TC7 and four for TC8, while only one phase change at high temperature has been found for TCO8. At room temperature, the cyclooctane and cycloheptane adducts exhibit the classical rhombohedral lattice (space group R3̄c). In these structures, the well-resolved host thiourea structure is composed of one-dimensional nonintersecting channels running along the c axis. The guest molecules, located in the center of the channels, are highly disordered as confirmed by the solid-state 13C NMR spectra. Lowering temperature leads to a monoclinic phase resulting from the distortion of the room-temperature lattice where the guest molecules still have some degrees of disorder. Refinement has been performed with a model involving two cycloalkane rings. For TC8, a supplementary phase with a doubling of the b axis is observed below 200 K, having two apparently ordered cyclooctane rings with the same conformation. The cyclooctanone adduct, TCO8, is already monoclinic at room temperature with an ordered guest molecule stabilized within the thiourea channels by a hydrogen bond. Upon heating, a phase change can be detected by solid-sate NMR and X-ray powder diffraction just before decomposition.

A high resolution quasielastic neutron scattering study of the guest molecules dynamics in the cyclohexane/thiourea inclusion compound

In cyclohexane/thiourea inclusion compounds, the host substructure contains uni-directional and non-intersecting channels within which the guest (cyclohexane) molecules are located. There are three thermotropic structural phases in cyclohexane/thiourea: phase I (down to 149 K) is rhombohedral, phase II (149–129 K) is monoclinic and phase III (below 129 K) is also monoclinic . In this paper, we report high resolution (1 μeV) incoherent quasielastic neutron scattering experiments performed in the three phases of the inclusion compound. We show that a quasielastic broadening is observed only in phase III, whereas the dynamics of the guest molecules in phases II and I is too fast to be analysed within the instrumental energy window. In phase III, the cyclohexane molecule undergoes 120° jumps about its three-fold symmetry axis with an activation energy E a=9.6(±0.5) kJ mol −1, the three-fold symmetry axis of cyclohexane being tilted by an angle λ=75° with respect to the channel axis. These experiments confirm the orientational ordering of the guest molecules in phase III of the inclusion compound.

Nitrogen Adsorption Study of MCM-41 Molecular Sieves Synthesized Using Hydrothermal Restructuring

Nitrogen desorption scanning hysteresis loops (DSHLs) for large-pore MCM-41 silicas (pore diameter from 4.0 to 6.5 nm) are reported for the first time. DSHLs for MCM-41 were compared with those of conventional mesoporous silicas and no appreciable differences were found, although hysteresis loops and DSHLs for the latter were usually broader. Since desorption behavior of conventional porous silicas is appreciably influenced by pore connectivity, the observed similarity in hysteresis behavior suggests single-pore “blocking effects” for MCM-41 due to variation of pore diameter along its nonintersecting channels. It was also shown that the steepness of nitrogen desorption branches at relative pressures close to 0.4 often results from proximity of the lower pressure limit of adsorption-desorption irreversibility and consequently it is not justified to consider it as an indication of narrow pore size distribution. Thus, application of desorption data in calculations of pore size distributions may be grossly misleading.

Structural properties of α,ω-dibromoalkane/urea inclusion compounds: a new type of interchannel guest molecule ordering

Structural properties of urea inclusion compounds containing α,ω-dibromoalkanes [Br(CH2)nBr; n= 7–10] as the guest component are reported. In these inclusion compounds, the host (urea) structure contains linear, parallel, non-intersecting channels (tunnels), within which the guest molecules are located. The structural properties of the guest molecules have been determined at room temperature using single-crystal X-ray diffraction techniques (primarily photographic methods), and represent the main focus of this paper.

Structural properties of the guest species in diacyl peroxide/urea inclusion compounds: an X-ray diffraction investigation

In this paper we report single crystal X-ray diffraction studies of urea inclusion compounds containing diacyl peroxides (dioctanoyl peroxide (OP), diundecanoyl peroxide (UP), lauroyl peroxide (LP)) as the guest component. In these inclusion compounds, the host (urea) molecules crystallize in a hexagonal structure that contains linear, parallel, non-intersecting channels (tunnels). The guest (diacyl peroxide) molecules are closely packed inside these channels with a periodic repeat distance that is incommensurate with the period of the host structure along the channel axis. Furthermore, there is pronounced inhomogeneity within the guest structure: within each single crystal, there are regions in which the guest molecules are three-dimensionally ordered, and other regions in which they are only one-dimensionally ordered (along the channel axis). Although it has not proven possible to ‘determine’ the guest structures in the conventional sense, substantial information concerning their average periodicities and their orientational relationships with respect to the host has been deduced from single crystal X-ray diffraction photographs recorded at room temperature. For OP/urea, UP/urea and LP/urea, the guest structure in the three-dimensionally ordered regions is monoclinic, and six types of domain of this monoclinic structure can be identified within each single crystal. The relative packing of diacyl peroxide molecules is the same in each domain, and the different domains are related by 60° rotation about the channel axis. For each of these inclusion compounds, the offset between the ‘heights’ of the guest molecules in adjacent channels is the same ( ca . 4.6 Å (4.6 x 10 -10 m)) within experimental error, suggesting that the relative interchannel packing of the guest molecules is controlled by a property of the diacyl peroxide group. In addition to revealing these novel structural properties, the work discussed in this paper has more general relevance concerning the measurement and interpretation of single crystal X-ray diffraction patterns that are based on more than one three-dimensionally periodic reciprocal lattice. Seven separate reciprocal lattices are required to rationalize the complete X-ray diffraction pattern from each diacyl peroxide/urea crystal studied here.

Structural aspects of urea inclusion compounds and their investigation by X-ray diffraction: a general discussion

Structural aspects of several urea inclusion compounds (differing in the identity of the ‘guest’ species) have been investigated, principally by single-crystal X-ray diffraction. This paper discusses the general structural features that are common to these different systems. Since the structural periodicities of the host (urea) and guest molecules are generally incommensurate, it is convenient to consider the urea inclusion compound to be composed of distinguishable, although not independent, host and guest substructures. The host substructure, for example, is represented in terms of an incommensurately modulated ‘basic host structure’. The basic structure possesses three-dimensional periodicity, and can be treated using conventional crystallographic principles. The incommensurate modulation describes structural perturbations to the basic host structure which arise from host–guest interaction. Similarly, the guest substructure is considered in terms of a ‘basic guest structure’ which experiences an incommensurate modulation mediated by the host substructure. These fundamental structural concepts are developed and used as a basis for rationalizing the X-ray diffraction patterns of urea inclusion compounds.The average basic host structure has been determined from single-crystal X-ray diffraction data measured, at room temperature, via conventional diffractometric techniques. This structure is essentially the same in each compound studied, and contains linear, parallel, non-intersecting channels (tunnels) within which the guest molecules are located. The crystallographic characteristics of the basic guest structure, on the other hand, depend critically upon the identity of the guest. Full structural details of the guest substructures in the different urea inclusion compounds will be given in future publications.

Structural aspects of the chlorocyclohexane/thiourea inclusion system

Halogenocyclohexane/thiourea inclusion compounds are of considerable chemical interest since the halogenocyclohexane molecules included within them are constrained to exhibit uncharacteristic conformational behaviour. Chlorocyclohexane, for example, exists exclusively in the axial conformation within its thiourea inclusion compound. In this paper, various structural aspects of the chlorocyclohexane/thiourea system are considered. The thiourea (host) substructure has been determined from room-temperature single-crystal X-ray diffraction data, and contains linear, infinite, non-intersecting channels (tunnels) within which the chlorocyclohexane (guest) molecules are located. Although the guest molecules are apparently located at certain preferred sites within the channel, the guest substructure is nevertheless substantially disordered. Computational investigations of host–guest interaction in chlorocyclohexane/thiourea corroborate the features of the guest substructure deduced from the room-temperature X-ray diffraction data.

Sorption in zeolites—I: Sorption of single component and binary sorbate systems

Sorption in zeolites with parallel and non-intersecting channels is described by a molecular model. The experiments usually conducted to measure diffusivities at different sorbate concentrations are simulated using a Monte-Carlo type of approach. Simulations depict increase in diffusivity with sorbate concentration which is in quantitative agreement with Darken's equation. The approach permits interpretation of the increase in diffusivity from the kinetic consideration. The model is further extended to simultaneous sorption of two sorbates and the dependence of apparent diffusivities in the binary system on sorbate concentration and intrinsic diffusivities of the sorbates is examined.

Alchemists' Gold, Hg2.86 Asf6; An X-Ray Crystallographic Study of A Novel Disordered Mercury Compound Containing Metallically Bonded Infinite Cations

The compound Hg2.86 AsF6 belongs to the tetragonal space group I41/amd with lattice parameters a = 7.538(4) Å, c = 12.339(5) Å, and Z = 4. The structure was refined using 109 symmetry independent reflections by full matrix least-squares refinement to a final R value of 0.079. The structure may be described as consisting of octahedral AsF6− ions arranged on a lattice which contains linear, non-intersecting channels in two mutually perpendicular directions. Within these channels are infinite chains of mercury atoms, each with a formal charge of +0.35, and with a mercury–mercury distance of 2.64(1) Å.