Guest Positions Research Articles

Research on the Folk "Deacon" in Dongtun Town, Xinxiang City, Henan Province—Initial Investigation Report on Entering into Marriage Rituals

With the continuous development of society, tremendous changes have occurred in rural areas in terms of culture, society, and economy, and rural marriage rituals have also undergone changes. The work of wedding organizers and "deacons" who assist in the ceremony has been impacted by the transformation of new-style marriage rituals. When the master of ceremonies of the new-style wedding enters the rural wedding, how do the "deacon" and the master of ceremonies cooperate to hold the wedding successfully? This article aims to explore what is the folk "deacon" and its changes, selecting Dongtun Town, Xinxiang City, Henan Province as the field survey point, and trying to present what is the folk "deacon" and explore the universal law of its changes through this case study by switching between different perspectives of the host and guest positions.

Phase transitions and guest positions state in the nanodisperse TiO2 caused by laser irradiation

Phase transitions and guest positions state in the nanodisperse TiO2 caused by laser irradiation

Electrical properties of clathrate formed on the basis of a p-type semiconductor with 2D guest positions filled with ferroelectric and propolis

The paper presents findings on the characteristics of GaSe fourfold-expanded matrix with propolis and sodium nitrite (NaNO2), intercalated in between matrix layers. The nature of changes of impedance frequency behavior, electric loss tangent, and dielectric permittivity under normal conditions, when illumination is applied, and in a constant magnetic field of synthesized intercalate GaSe < NaNO2 > and bi-intercalate GaSe < NaNO2 + Propolis > has been identified. The extraordinary effects have been obtained, indicating that clathrate GaSe < NaNO2 > has immense values of photo- and magneto-capacitive effects while a current–voltage (I–V) characteristic of clathrate GaSe < NaNO2 + Propolis > exhibits the hysteresis behavior typical of memristor structures. The memory effect related to pseudo-capacitive charge accumulation has been found and shown to be due to oxidation–reduction reactions.

Confinement of Luminescent Guests in Metal-Organic Frameworks: Understanding Pathways from Synthesis and Multimodal Characterization to Potential Applications of LG@MOF Systems.

This review gives an authoritative, critical, and accessible overview of an emergent class of fluorescent materials termed “LG@MOF”, engineered from the nanoscale confinement of luminescent guests (LG) in a metal–organic framework (MOF) host, realizing a myriad of unconventional materials with fascinating photophysical and photochemical properties. We begin by summarizing the synthetic methodologies and design guidelines for representative LG@MOF systems, where the major types of fluorescent guest encompass organic dyes, metal ions, metal complexes, metal nanoclusters, quantum dots, and hybrid perovskites. Subsequently, we discuss the methods for characterizing the resultant guest–host structures, guest loading, photophysical properties, and review local-scale techniques recently employed to elucidate guest positions. A special emphasis is paid to the pros and cons of the various methods in the context of LG@MOF. In the following section, we provide a brief tutorial on the basic guest–host phenomena, focusing on the excited state events and nanoscale confinement effects underpinning the exceptional behavior of LG@MOF systems. The review finally culminates in the most striking applications of LG@MOF materials, particularly the “turn-on” type fluorochromic chemo- and mechano-sensors, noninvasive thermometry and optical pH sensors, electroluminescence, and innovative security devices. This review offers a comprehensive coverage of general interest to the multidisciplinary materials community to stimulate frontier research in the vibrant sector of light-emitting MOF composite systems.

Effectiveness of a Chairside Acrylic Adjustment Cabinet in Reducing Dental Acrylic Debris and Aerosols

AbstractPurposeChairside prosthesis adjustment procedures generate contaminated acrylic particle debris that include visible splatter (particles &gt;50 μm) as well as invisible aerosols (&lt;50 µm). The purpose of this study was to evaluate the effectiveness of a chairside acrylic adjustment cabinet (CAAC) in reducing airborne aerosol particles (&lt;10 µm) and visible acrylic debris, time required for airborne aerosols to return to baseline levels after an acrylic adjustment procedure, and the effect on operatory turnover time.Materials and methodsA total of 40 acrylic adjustment procedures were carried out in a simulated setting with (experiment) and without (control) a CAAC. Standardized acrylic samples of self‐polymerized, and heat polymerized polymethylmethacrylate resins, Triad™ and Fastray™ custom tray materials were evaluated. Airborne aerosol measurements were done using a handheld Lase.r Particle Counter for absolute particle counts of sizes 0.3, 0.5, 1.0, 2.5, 5.0, and 10.0 μm before, during, and immediately after adjustment and 10 minutes postadjustment. Spread of aerosols was assessed at three distinct locations within the dental operatory specific to the provider, the patient, and the caregiver/guest. Visible acrylic debris and operatory turnover time were evaluated immediately postadjustments by a blinded investigator. Repeated measures ANOVA was used to estimate group effect, time effect and interaction between group and time for air particle analysis. Independent samples T‐tests were used for group differences between operatory turnover time, and time for aerosols to return to baseline. Chi‐square test was used for visible surface analysis.ResultsIn the control group, total aerosol particle counts increased from 6542.7 ± 162.6 particles at baseline to 598378.7 ± 586363.2 and 367569.9 ± 432220.8 particles during and immediately postadjustment, respectively. Adjustments made in the experiment group led to significantly reduced aerosol counts during (97738.9 ± 97866.5) and immediately postadjustment (19786.5 ± 14004.9; F = 17.8, p = 0.006). Similar trends were noted for the patient and guest positions. Time for aerosol particles to return to baseline was significantly lower in the experiment group (20.56 ± 14.5 minutes) compared to the control group (37.9 ± 31.96 minutes; p = 0.03). Visible acrylic debris analysis showed a significant decrease of 78% in the experiment group (p &lt; 0.001). No significant differences were noted in operatory turnover time between the two groups (p = 0.61).ConclusionsAcrylic adjustment procedures generated aerosols of particle sizes less than 10 µm and were measured in significant quantities throughout the dental operatory for up to 115 minutes. Chairside acrylic adjustment cabinets significantly decreased airborne aerosols, visible acrylic particle debris, and reduced the time for airborne aerosols to return to baseline levels.

Language and (in)hospitality

AbstractBased on a long-term ethnography of Sub-Saharan African migrants in Cape Town, South Africa, this article examines how language as ideology and practice shapes the rules of guesting and hosting and helps (re)configure the on-going positionalities of both the nation-state-defined-host and the foreigner-guest, making murky the distinction between the two. The key notion ofhospitalitydeveloped here is examined aspracticesrather than asidentities.I argue that this theoretical shift makes it possible to unsettle the host and guest positions by not positing them a priori or conceptualizing them as immutable. It likewise makes it possible to deconstruct the categories imposed by the State and by which scholars and policy makers alike abide, such as the dichotomy betweenmigrantsandlocals. At a broader level, the paper draws attention to the Occidentalism that has plagued academia, particularly in the work done on migration. I show how the South African case challenges many scholarly assumptions on language and migration overwhelmingly based on the examination of South-to-North migrations, which do not adequately represent worldwide migrations.

The Smaller the Better: Hosting Trivalent Rare-Earth Guests in Cu–P Clathrate Cages

Summary The most striking difference between the trivalent rare-earth cations and their alkali and alkaline-earth peers is the presence of localized 4 f electrons. Placing trivalent rare-earth cations inside fullerene molecules or in between blocks of intermetallics has given rise to a plethora of fascinating properties and materials. A long-sought-after yet undiscovered material is a semiconducting compound with rare-earth cations situated inside the oversized polyhedral cages of a three-dimensional framework. In this work, we present a synthesis of unconventional clathrates, Ba 8−x R x Cu 16 P 30 , with the smallest pentagonal dodecahedral cages encapsulating La 3+ and Ce 3+ . Their composition and crystal structure were unambiguously determined by a combination of synchrotron powder diffraction, time-of-flight neutron powder diffraction, scanning transmission electron microscopy, and electron energy-loss spectroscopy. Our quantum-mechanical calculations and experimental characterizations show that the incorporation of the rare-earth cations significantly enhances hole mobility and reduces hole concentration, resulting in a drastic (700%) increase in the thermoelectric performance.

The anomalous halogen bonding interactions between chlorine and bromine with water in clathrate hydrates.

Clathrate hydrate phases of Cl2 and Br2 guest molecules have been known for about 200 years. The crystal structure of these phases was recently re-determined with high accuracy by single crystal X-ray diffraction. In these structures, the water oxygen-halogen atom distances are determined to be shorter than the sum of the van der Waals radii, which indicates the action of some type of non-covalent interaction between the dihalogens and water molecules. Given that in the hydrate phases both lone pairs of each water oxygen atom are engaged in hydrogen bonding with other water molecules of the lattice, the nature of the oxygen-halogen interactions may not be the standard halogen bonds characterized recently in the solid state materials and enzyme-substrate compounds. The nature of the halogen-water interactions for the Cl2 and Br2 molecules in two isolated clathrate hydrate cages has recently been studied with ab initio calculations and Natural Bond Order analysis (Ochoa-Resendiz et al. J. Chem. Phys. 2016, 145, 161104). Here we present the results of ab initio calculations and natural localized molecular orbital analysis for Cl2 and Br2 guests in all cage types observed in the cubic structure I and tetragonal structure I clathrate hydrates to characterize the orbital interactions between the dihalogen guests and water. Calculations with isolated cages and cages with one shell of coordinating molecules are considered. The computational analysis is used to understand the nature of the halogen bonding in these materials and to interpret the guest positions in the hydrate cages obtained from the X-ray crystal structures.

Crystal engineering the clathrate hydrate lattice with NH4F

There have been very few attempts to apply crystal engineering approaches to modify the clathrate lattice with the aim of modifying structure and properties. To this end, solutions of ammonium fluoride in water were used to prepare clathrate hydrates with ammonium fluoride replacing water molecules in the hydrate lattice. Both modified structure I Xe and structure II tetrahydrofuran/Xe hydrates were prepared, with the hydrate lattices consisting of NH4F-water solid solutions containing up to ~19 and 25 mole% NH4F, respectively. The lattice constants for both hydrates decreased with increase of the amount of NH4F incorporated, and guest positions and cage occupancies were determined from the PXRD patterns with direct space methods and Rietveld analysis. The 129Xe NMR spectra for Xe in the small cavities of each hydrate showed NH4F concentration-dependent fine structure, not evident in the pure water clathrates, and characteristic of the presence of cage configurations with different distributions of ions. Analysis of the spectra along with density functional theory calculations of the chemical shifts allowed reasonable assignments to be made of the ion distribution. As a test of the altered function of the clathrate upon modification, a clathrate of methanol was prepared, something which has not been possible to do with a pure water clathrate. Structural analysis of the PXRD pattern by direct space methods showed that the methanol OH was hydrogen-bonded to one or both of the NH4+ and F− ions in the lattice, a conclusion corroborated by the absence of molecular motion (except for methyl group rotation) of the methanol guest in the clathrate cages, as determined by static 2H NMR and molecular dynamics simulations. The stability of the modified methanol clathrate can be attributed to the strong methanol CH3OH⋯F− or CH3OH⋯NH4+ hydrogen bonding which leaves the water–water hydrogen bonding network intact, as opposed to the situation in a pure water clathrate where the methanol–water hydrogen bonding disrupts the lattice and a stable clathrate cannot be made.

Water–Halogen Interactions in Chlorine and Bromine Clathrate Hydrates: An Example of Multidirectional Halogen Bonding

There are unresolved questions in our understanding of the clathrate hydrates with halogen molecule guests. In this work, we describe the synthesis and single crystal X-ray structural determination of cubic structure I (sI) Cl2, tetragonal structure III (sIII) Br2, and mixed cubic sI Cl2–Br2 clathrate hydrate phases. Unlike the previous X-ray structural determination of the pure chlorine clathrate hydrate by Pauling and Marsh (Proc. Nat. Acad. Sci. USA1952, 38, 112), we report that 32.5% of the clathrate small cages are occupied by Cl2 molecules. Pure Br2 produces the unique tetragonal sIII clathrate hydrate whose structure is refined from single-crystal measurements, identifying disordered Br2 guest positions in cages and giving structural details not previously identified. In mixed sI clathrate hydrate of Cl2 and Br2, we observed that Br2 guests fit into the large sI cages. The introduction of Br2 in the Cl2 hydrate lattice causes severe distortions because of strong Br···OH2 interactions. In these three hydrate structures, based on accepted van der Waals radii, the effective diameters of the clathrate hydrate cages are smaller than the size of the Cl2 and Br2 guest molecules. The accommodation of these guests in the cages and the short O···Cl and O···Br contact distances reveal halogen bonding between the water oxygen atoms and the dihalogen guests. The X-ray structural determinations of the length of the Cl–Cl and Br–Br bonds of the Cl2 and Br2 guests show significant librational shortening compared to free Cl2 and Br2 molecules.

Homo- and Heterovalent Substitutions in the New Clathrates I Si30P16Te8–xSex and Si30+xP16–xTe8–xBrx: Synthesis, Crystal Structure, and Thermoelectric Properties

The new cationic clathrates I Si(30)P(16)Te(8-x)Se(x) and Si(30+x)P(16-x)Te(8-x)Br(x) were synthesized by the standard ampule technique. The Si(30)P(16)Te(8-x)Se(x) (x = 0-2.3) clathrates crystallize in the cubic space group Pm3̅n with the unit cell parameter a ranging from 9.9382(2) to 9.9696(1) Å. In the case of the Si(30+x)P(16-x)Te(8-x)Br(x) (x = 1-6.4) clathrates, the lattice parameter varies from 9.9720(8) to 10.0405(1) Å; at lower Si/P ratios (x = 1-3) the ordering of bromine atoms induces the splitting of the guest positions and causes the transformation from the space group Pm3n to Pm3. Irrespective of the structure peculiarities, the normal temperature motion of the guest atoms inside the oversized cages of the framework is observed. The title clathrates possess very low thermal expansion coefficients ranging from 6.6 × 10(-6) to 1.0 × 10(-5) K(-1) in the temperature range of 298-1100 K. The characteristic Debye temperature is about 490 K. Measurements of the electrical resistivity and thermopower showed typical behavior of p-type thermally activated semiconductors, whereas the temperature behavior of the thermal conductivity is glasslike and in general consistent with the PGEC concept. The highest value of the thermoelectric figure of merit (ZT = 0.1) was achieved for the Br-bearing clathrate Si(32.1(2))P(13.9(2))Te(6.6(2))Br(1.0(1)) at 750 K.

Welcoming the World: Governing Hospitality in London’s 2012 Olympic Bid1

Bulley, Dan and Debbie Lisle. (2012) Welcoming the World: Governing Hospitality in London’s 2012 Olympic Bid. International Political Sociology, doi: 10.1111/j.1749-5687.2012.00158.x © 2012 International Studies Association London’s successful bid for the 2012 Olympic Games presented a diverse, cosmopolitan city opening its arms and “welcoming the world.” This article explores the apparently benign gesture of hospitality contained in London’s official candidature files submitted in 2004 and asks how such a promise of inclusiveness is managed. We argue that London’s depiction of itself as hospitable to every kind of visitor relies on subtle techniques of governmentality in which the subject positions of “host” and “guest” are imagined and produced in ways that make them more governable. By this, we are not referring to acts of authority, coercion, or discipline that exclude subjects or render them docile bodies within a rigid panoptical city. Rather, we are referring to the delicate ways in which the official bid document imagines and produces the ideal subject positions of host and guest and in so doing enables, encourages, and incentivizes certain behaviors. This analysis of urban welcoming takes us beyond reductive oppositions of hospitality and hostility, inclusion and exclusion, self and other. It focuses instead on how London’s inclusive welcome produces a variety of host and guest positions (for example, the “Olympic Family,” volunteers, guest workers), segregates them within the city, and then “conducts their conduct” in the areas of planning, security, transport, accommodation, education, and training. By analyzing the techniques of governmentality at work in London’s 2004 bid document, this article foregrounds the enabling form of power driving the city’s inclusive welcome and exposes its inherent micropolitics.

On the crystal structure of the germanium-based cationic clathrates [Ge38.3Sb7.7]I7.44, [Ge38.1P7.9]I8, and [Ge30.5Sn7.7P7.75]I7.88

Compounds [Ge38.3Sb7.7]I7.44, [Ge38.1P7.9]I8, and [Ge30.5Sn7.7P7.75]I7.88 with the clathrate type-I structure were synthesized. They crystallize in the cubic space group \(Pm\bar 3n\) with the unit cell parameter a = 10.8592(9), 10.4983(12), and 10.7210(10) A (Z = 1), respectively. Their crystal structure represents the germanium(tin)-pnictogen framework, capturing the guest iodine anions in its cavities. All compounds have no vacancies in the host substructure; however, two of them show vacancies in the guest positions. The atomic distribution over the framework sites is of the most interest as it follows trends associated with the relative electronegativities of the atoms composing the framework. The results of the band structure calculations and application of the Zintl counting scheme are also discussed in relation to potential thermoelectric properties.

Synthesis and clathrate-type crystal structure of a solid solution in the Sn-In-P-Br system

The solid solution of the general formula Sn24−x In x P19.2+0.2x Br8 (x ≤ 10) was synthesized in the Sn-In-P-Br system, and its crystal structure was determined for the composition with x = 7.8. This solid solution crystallizes in the cubic system, the space group Pm \(\bar 3\) n, and has a type-I clathrate structure, in which the clathrate framework is composed of tin, indium, and phosphorus atoms, whereas bromine atoms occupy two types of guest positions. The unit cell parameter a increases with increasing indium content, two linear regions with different increments being observed in the a(x) plot. The crystal structure of the solid solution is characterized by a complicated disorder manifested in the partial occupancy of three closely spaced positions by tin and indium atoms. The application of the Zintl formalism to the rationalization of the composition of the solid solution is discussed, and its structure is compared with the iodide analogs of similar composition but showing differences in structural details.

Semiclathrates of the Ge–P–Te System: Synthesis and Crystal Structures

Novel compounds [Ge(46-x) P(x) ]Te(y) (13.9≤x≤15.6, 5.92≤y≤7.75) with clathrate-like structures have been prepared and structurally characterized. They crystallize in the space group Fm ̅3 with the unit cell parameter changing from 20.544(2) to 20.698(2) Å (Z=8) on going from x=13.9 to x=15.6. Their crystal structure is composed of a covalently bonded Ge-P framework that hosts tellurium atoms in the guest positions and can be viewed as a peculiar variant of the type I clathrate superstructure. In contrast to the conventional type I clathrates, [Ge(46-x) P(x) ]Te(y) contain tricoordinated (3b) atoms and no vacancies in the framework positions. As a consequence of the transformation of the framework, the majority of the guest tellurium atoms form a single covalent bond with the host framework and thus the title compounds are the first representative of semiclathrates with covalent bonding. A comparison is made with silicon clathrates and the evolution of the crystal structure upon changing the tellurium content is discussed.

Bulk and Surface Structure and High‐Temperature Thermoelectric Properties of Inverse Clathrate‐III in the Si‐P‐Te System

The creation of thermoelectric materials for waste heat recovery and direct solar energy conversion is a challenge that forces the development of compounds that combine appreciable thermoelectric figure-of-merit with high thermal and chemical stability. Here we propose a new candidate for high-temperature thermoelectric materials, the type-III Si(172-x)P(x)Te(y) cationic clathrate, in which the framework is composed of partially ordered silicon and phosphorus atoms, whereas tellurium atoms occupy guest positions. We show that the utmost stability of this clathrate (up to 1500 K) in air is ensured by the formation of a nanosized layer of phosphorus-doped silica on the surface, which prevents further oxidation and degradation. As-cast (non-optimized) Si-P-Te clathrates display rather high values of the thermoelectric figure-of-merit (ZT=0.24-0.36) in the temperature range of 700-1100 K. These ZT values are comparable to the best values achieved for the properly doped transition-metal-oxide materials. The methods of the thermoelectric efficiency optimization are discussed.

Cleave and capture chemistry illustrated through bimetallic-induced fragmentation of tetrahydrofuran

The cleavage of ethers is commonly encountered in organometallic chemistry, although rarely studied in the context of new, emerging bimetallic reagents. Recently, it was reported that a bimetallic sodium-zinc base can deprotonate cyclic tetrahydrofuran under mild conditions without opening its heterocyclic (OC(4)) ring. In marked contrast to this synergic sedation, herein we show that switching to the more reactive sodium-magnesium or sodium-manganese bases promotes cleavage of at least six bonds in tetrahydrofuran, but uniquely the ring fragments are captured in separate crystalline complexes. Oxide fragments occupy guest positions in bimetallic, inverse crown ethers and C(4) fragments ultimately appear in bimetallated butadiene molecules. These results demonstrate the special synergic reactivity that can be executed by bimetallic reagents, which include the ability to capture and control, and thereby study, reactive fragments from sensitive substrates.

Cationic Clathrate I Si46-xPxTey (6.6(1) ≤ y ≤ 7.5(1), x ≤ 2y): Crystal Structure, Homogeneity Range, and Physical Properties

A new cationic clathrate I Si(46-x)P(x)Te(y) (6.6(1) < or = y < or = 7.5(1), x < or = 2y at 1375 K) was synthesized from the elements and characterized by X-ray powder diffraction, thermal analysis, scanning electron microscopy, wavelength dispersive X-ray spectroscopy (WDXS), neutron powder diffraction, and (31)P NMR spectroscopy. The thermal behaviors of the magnetic susceptibility and resistivity were investigated as well. Si(46-x)P(x)Te(y) reveals a wide homogeneity range due to the presence of vacancies in the tellurium guest positions inside the smaller cage of the clathrate I structure. The vacancy ordering in the structure of Si(46-x)P(x)Te(y) causes the change of space group from Pm3n (ideal clathrate I) to Pm3 accompanied by the redistribution of P and Si atoms over different framework positions. Neutron powder diffraction confirmed that P atoms preferably form a cage around the vacancy-containing tellurium guest position. Additionally, (31)P NMR spin-spin relaxation experiments revealed the presence of sites with different coordination of phosphorus atoms. Precise determination of the composition of Si(46-x)P(x)Te(y) by WDXS showed slight but noticeable deviation (x < or = 2y) of phosphorus content from the Zintl counting scheme (x = 2y). The compound is diamagnetic while resistivity measurements show activated behavior or that of heavily doped semiconductors. Thermal analysis revealed high stability of the investigated clathrate: Si(46-x)P(x)Te(y) melts incongruently at approximately 1460 K in vacuum and is stable in air against oxidation up to 1295 K.

Surface and interlayer structure of vermiculite intercalated with methyl viologen

Molecular modeling using empirical force field revealed the differences between the surface and interlayer arrangement of the dye guest molecules in vermiculite intercalated with the divalent methyl viologen cation (MV(2+)). Conformation and anchoring of MV(2+) cations on the silicate layer in the interlayer space of vermiculite host structure is different from that on the crystal surface. A preferential position has been found for the anchoring of guests on the silicate layer. Anyway the arrangement of guests in the interlayer space as well as on the crystal surface exhibits a high degree of disorder due to a certain flexibility in guest molecules arrangement and first of all due to the presence of water molecules in the interlayer space. The presence of water disturbs not only the regularity in guest positions and orientations but also in conformation of guest molecules in the interlayer space of the host structure.

Molecular Recognition in Cyclodextrin Complexes of Amino Acid Derivatives: The Effects of Kinetic Energy on the Molecular Recognition of a Pseudopeptide in a Nonconstraining Host Environment as Revealed by a Temperature-Dependent Crystallographic Study

The crystal structure of a triclinic 2:2 inclusion complex of beta-cyclodextrin with N-acetyl-L-phenylalanine methyl ester has been determined at several temperatures between 298 and 20 K to further study molecular recognition using solid-state supramolecular beta-cyclodextrin complexes. The study reveals kinetic energy dependent changes in guest molecule conformations, orientations, and positions in the binding pocket presented by the crystal lattice. Accompanying these changes are observable differences in guest-guest interactions and hydrogen-bonding interactions in the binding pocket that involve guest molecules, water of hydration molecules, and beta-cyclodextrin molecules. On the basis of the differences observed in the crystal structures, we present a solid-state example of a system that displays the properties of both classical and quantum chemical models. At higher temperatures, the structure conforms to a classical mechanical model with dynamic disorder. At lower temperatures, the observations conform to examples in which there is static disorder representative of models in which quantum states differing in conformation, position, and orientation of components in the crystal structure are occupied. Ab initio theoretical calculations on the different guest molecule conformations have been carried out. Superpositions of theoretical electrostatic surface potential diagrams on the observed molecular positions in the complexes provide confidence that the deconvolution of the guest molecule disorder is acceptable. Temperature-dependent solid-state magic angle spinning deuteron NMR measurements provide evidence for large-amplitude, diffusive motion on a microsecond time scale in the complex.