Ideal Structural Model Research Articles

Synergistic Etching and Hydrogen Bonding-Induced Self-Assembly of MXene/MOF Hybrid Aerogel for Flexible Room-Temperature Gas Sensing.

Limited by insufficient active sites and restricted mechanical strength, designing reliable and wearable gas sensors with high activity and ductility remains a challenge for detecting hazardous gases. In this work, a thermally induced and solvent-assisted oxyanion etching strategy was implemented for selective pore opening in a rigid microporous Cu-based metal-organic framework (referred to as CuM). A conductive CuM/MXene aerogel was then self-assembled through cooperative hydrogen bonding interactions between the carbonyl oxygen atom in PVP grafted on the surface of defect-rich Cu-BTC and the surface functional hydroxyl group on MXene. A flexible NO2 sensing performance using the CuM/MXene aerogel hybridized sodium alginate hydrogel is finally achieved, demonstrating extraordinary sensitivity (S = 52.47 toward 50 ppm of NO2), good selectivity, and rapid response/recovery time (0.9/4.5 s) at room temperature. Compared with commercial sensors, the relative error is less than 7.7%, thereby exhibiting significant potential for application in monitoring toxic and harmful gases. This work not only provides insights for guiding rational synthesis of ideal structure models from MOF composites but also inspires the development of high-performance flexible gas sensors for potential multiscenario applications.

Pore Size Modulation in Flexible Metal‐Organic Framework Enabling High Performance Gas Sensing

AbstractPore size plays a critical role in determining the performance of metal‐organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore‐size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent‐coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL‐88B. Pore‐size‐dependent gas sensitivity and selectivity were studied for the first time in the MIL‐88B samples. The optimized MIL‐88B‐20 % sample showed one of the best sensing performances among all the reported MOF‐based H2S‐sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore‐size and properties, but also may inspire the development of high‐performance gas sensing materials.

Pore Size Modulation in Flexible Metal-Organic Framework Enabling High Performance Gas Sensing.

Pore size plays a critical role in determining the performance of metal-organic frameworks (MOFs) in catalysis, sensing, and gas storage or separation. However, revealing the pore-size/property relationship remains extremely challenging because ideal structure models possessing different pore sizes but having the same components are lacking. In this work, a solvent-coordination directed structure swelling method was developed for modulating the ratio between the large and narrow pore phases of a flexible MOF, MIL-88B. Pore-size-dependent gas sensitivity and selectivity were studied for the first time in the MIL-88B samples. The optimized MIL-88B-20 % sample showed one of the best sensing performances among all the reported MOF-based H2 S-sensing materials. This work not only provides a method to synthesize ideal structure models for revealing the relationship between pore-size and properties, but also may inspire the development of high-performance gas sensing materials.

Prediction of Thermal Conductivity of a Rock Wool Board by Computer X-Ray Tomography Technique Scanning and Random Generation-Growth Model

Thermal conductivity of rock wool boards was investigated in this study. Although distribution of fibers in a realistic rock wool board is unclear, it can be simulated by computer X-ray tomography technique (CT) followed by rearrangement through the random generation-growth (RGG) model. An ideal CT-RGG structure model of rock wool boards (CT-random generation-growth model) was established by simplifying material properties based on the mesostructure parameters of the RGG model. Thermal conductivity of rock wool boards with different apparent densities and fiber diameters was studied, and the CT-RGG model was analyzed by explicit jump (EJ) diffusion equations solved by the fast Fourier transform method. We found that thermal conductivity of a single rock wool fiber can be successfully determined. Simulation and measurement results show that thermal conductivity increases consistently with the increase of apparent density and fiber diameter, particularly when the apparent density of rock wool board is greater than 140 kg m−3. Compared with the existing theoretical models, the proposed method does not depend on the empirical parameters; therefore, it is useful in designing and optimizing the thermal conductivity of rock wool boards.

MICROSCOPIC DISCONTINUITY DEFORMATION ANALYSIS OF CAPILLARY IN UNSATURATED SOIL

Capillary action is one of significant sources of matric suction in the unsaturated soil. So we propose a new method based on two-dimensional Discontinuous Deformation Analysis(DDA)to simulate the distribution of capillary water and to calculate soil water characteristic curve(SWCC)under different saturation. Firstly,the radius of capillary water meniscus is calculated with iterative algorithm method,and circle center trajectory intersection method is used to determine capillary water distribution in this algorithm. Then,the matric suction,calculated with Young-Laplace equation,is taken into account in the control equation of the original DDA method with the surface tension. Moreover,in order to verify the accuracy of the algorithm,an ideal loess structure model is established. In this model,the soil particles used are mainly coarse particles with high content of loess. The particle size distribution and shape accord with the actual values. And then,the model is used to simulate the distribution of capillary water and to calculate soil water characteristic curve(SWCC). The results show that simulated SWCC contains boundary effect stage,transition stage and residual stage. The distribution of capillary water is simulated at each stage. In addition,the result comparison between the numerical simulation and the experimental data shows the simulation results agree well with experimental data,which suggest that this method is available for simulating capillary action in unsaturated soil.

Synthesis and Electron Microscopy Study of the Quaternary Misfit Layer Chalcogenides {(Bi,Nd)S}1+δCrS2 and {(Pb,Nd)Se}1+δ(NbSe2)2.

In the present work, two compounds, in the Bi-Nd-Cr-S and Pb-Nd-Nb-Se systems, not reported to date were synthesized. The chemical composition and the structural determination of these complex compounds, at atomic resolution, was performed through conventional and aberration-corrected electron microscopy including selected area electron diffraction, high resolution (HR) transmission electron microscopy (TEM), HR scanning TEM, and the analytical associated techniques X-ray energy-dispersive spectroscopy and electron energy-loss spectroscopy. The average compositions are [(Bi0.4,Nd0.6)S]1.25CrS2 and [(Pb0.5,Nd0.5)Se]1.15(Nb1.0Se2)2, respectively. By using these electron microscopy techniques, we confirmed that both compounds can be described in term of two interpenetrated sublattices that fit along a but do not fit along b, giving rise to an incommensurate modulation. A closer inspection along the stacking direction of the subcell has provided an ideal structural model for [(Bi0.4,Nd0.6)S]1.25CrS2 based on the intergrowth of one layer of CrS2, three atoms thick, (111) B1 type, and one layer of (Bi, Nd)Se, two atoms thick, (100) B1 type. In [(Pb0.5,Nd0.5)Se]1.15(Nb1.0Se2)2 we found that two layers of NbSe2, which adopt the 2H-NbSe2 polytype, alternate with one layer of (Pb, Nd)Se B1 type. In addition, crystals showing extended defects, associated with the weak interaction between the layers, were frequently found.

Design and Implementation of Vibration Energy Harvester Based on MSMA Cantilever Beam

Vibration energy exists widely in nature, and the use of intelligent materials to harvest vibration energy to power microelectronic systems is a trend in the field of new energy. In this paper, the inverse effect of magnetic shape memory alloy (MSMA) that is a new intelligent material, is used to design a new kind of vibration energy harvester, which is based on integrated cantilever beam. The structure of cantilever beam and magnetic field loop are optimized, and the ideal structure model of vibration energy harvester is established. The magnetic field is analyzed by using ANSYS finite element software. On the basis of developing the prototype of the harvester, the experimental platform is built and the harvester is tested. The results show that the output voltage of the MSMA vibration energy harvester based on cantilever beam can reach more than 300 mV, which has a wide frequency band of vibration energy harvesting, and possesses a good prospect for development and application.

Theoretical model of personal perception of human by human

The methodological study is devoted to the justification of the cyclical-action strategy and adequate intellectual means of psychological cognition of the personal acceptance of the person by the person as super-complex, substantially rooted and phenomenally numerous, developmentally and functionally dynamic meta-process of the presence in the psycho-spiritual world of the one who is self-analysing this acceptance. The first stage of the research attempt was to create a reliable theoretical platform for building an ideal structural and functional model of personal acceptance as a complete spiral of committing an individual by performing a comparative analysis, on the one hand, the stages of the development of perception as a cognitive process (in particular, categorization and cognition) events, on the other hand, the stages of acceptance as aspects of communication-exchange and at the same time as a multifunctional personal process-micro-stage of ontogeny that were studied by scientists in different recursion theoretical psychological knowledge. The unifying paradigm link and the universal tool for methodologizing this comparative analysis was the logical and structural scheme of actions made by V. Romenet’s, according to which the component cyclic unfolding of mental processes is in the cognitive work of the researcher; a psychological canon, to which tendency moves and under which phenomenology and perception and acceptance are carried out. Therefore, in addition to the regular isolation of situational, motivational, active and post-action periods and their main mechanisms of facilitation (perceptual presence, cognitive presence, thought-study penetration, reflexive absorption), in the multifaceted realization of the personal acceptance inner act, it was given a more detailed, personal and compatible with their existential existence of dominant components (recognition, characterization, interest, intentions), tweaking, deliberation, reflexion, appreciation) and subprocesses (naming, categorization, definition, cognition, comprehension, implementation, conceptualization, living). As a result, the newly created theoretical model, covering two stages – recognition and enrichment, four periods and their basic mechanisms, eight stages and their most necessary mental reconciliation and organization, characterizes the personal acceptance of a person by a person, which is a) virtually complete self-act; b) phenomenally elevates such an act to the level of the psychological canon; c) existentially counts down from the first meeting of a person with a person as a clash of their worlds, consciousnesses and destinies in the situational current of everyday life; d) dialectically unfolds as a complicated process in the framework of the ontogeny of the individual and with a tendency to change the meaning-sense format of the original life of consciousness of both contacts; e) the event ends as a reflexive absorption of the consciousness of another, fragmentarily providing optimization of personal development and cyclic-semantic enrichment of the internal conditions of functioning of the conscious ability of the human-contributor. Therefore, the unprecedented complexity of personal acceptance of such a figure is caused not only by the limited spectrum of phenomenal receptions of interpersonal contact and the presence of hidden belts and links of psycho-spiritual mediation in the general dynamics of its internal development, but also by the fact that the said process unfolds in the life of a particular agent of a social act by a double interpenetrating channel or direction – naturally ontogenetic, that is, as a value-meaning provision of personality, and at the same time unnaturally conscious, that is, as a complement and complication of the living conditions of the conscious flow of a person’s ability to be subjectively present in the world as an inspired personality and universe. Considering this complexity, which is difficult to convey by conventional psychological semantics and the author’s thesaurus and graphic modeling, at the end of the study, figurative analogies and a more metaphorical language for describing the patterns of developmental progress of the psycho-spiritual megamechanism are argued. In particular, the complete complex mechanics of three well-known devices – synthesizer, synchronizer, collider - is projected on the wistful architectonics of the cyclical-factual spiral of personal acceptance, resulting in a depiction of the work-activity of this acceptance as a subjective synthesizer, internally, and internal synthesizer.

Precise and Wide-Ranged Band-Gap Tuning of Ti6-Core-Based Titanium Oxo Clusters by the Type and Number of Chromophore Ligands.

Sensitization with dyes is the most promising option to narrow the band gap and improve visible-light absorption of TiO2. As ideal structure and reaction models of TiO2, titanium oxo clusters (TOCs) with exact crystal structure are beneficial for further understanding the structure-property relationship of TiO2. Most reports mainly focus on the synthesis and properties of TOCs, but research on the band-gap tuning of TOCs at the large range of 3.7-2.0 eV by chromophore ligands (CLs) has been lacking. Herein, six new Ti6-core-based TOCs (Ti6-TOCs) were successfully synthesized by using CLs in a simple and general approach. Each Ti6-TOC structure contains two Ti3(μ3-O) units featuring a flat or pyramidal mode as building blocks. Five Ti6-core structure types were present among the six Ti6-TOCs, which enriched the family of hexanuclear TOCs. To be noted, the band-gap values were tuned at a wide range of 3.41-1.98 eV by controlling the type and number of the CLs 2-hydroxypyridine, salicylaldoxime, and catechol in the structure. Density functional theory calculation revealed that the lowest-energy bands of these Ti6-TOCs are attributed to the CL-to-TiO core charge-transfer bands. This work provides a precise and wide-ranged band-gap tuning method for TOCs. Additionally, the six Ti6-TOCs exhibit good photocurrent response.

Using instability to reconfigure smart structures in a spring-mass model

Multistable phenomenon have long been used in mechanism design. In this paper a subset of unstable configurations of a smart structure model will be used to develop energy-efficient schemes to reconfigure the structure. This new concept for reconfiguration uses heteroclinic connections to transition the structure between different unstable equal-energy states. In an ideal structure model zero net energy input is required for the reconfiguration, compared to transitions between stable equilibria across a potential barrier. A simple smart structure model is firstly used to identify sets of equal-energy unstable configurations using dynamical systems theory. Dissipation is then added to be more representative of a practical structure. A range of strategies are then used to reconfigure the smart structure using heteroclinic connections with different approaches to handle dissipation.

Numerical Simulations of the Lunar Penetrating Radar and Investigations of the Geological Structures of the Lunar Regolith Layer at the Chang’E 3 Landing Site

In the process of lunar exploration, and specifically when studying lunar surface structure and thickness, the established lunar regolith model is usually a uniform and ideal structural model, which is not well-suited to describe the real structure of the lunar regolith layer. The present study aims to explain the geological structural information contained in the channel 2 LPR (lunar penetrating radar) data. In this paper, the random medium theory and Apollo drilling core data are used to construct a modeling method based on discrete heterogeneous random media, and the simulation data are processed and collected by the electromagnetic numerical method FDTD (finite-difference time domain). When comparing the LPR data with the simulated data, the heterogeneous random medium model is more consistent with the actual distribution of the media in the lunar regolith layer. It is indicated that the interior structure of the lunar regolith layer at the landing site is not a pure lunar regolith medium but rather a regolith-rock mixture, with rocks of different sizes and shapes. Finally, several reasons are given to explain the formation of the geological structures of the lunar regolith layer at the Chang’E 3 landing site, as well as the possible geological stratification structure.

Structural Investigation of Zn(II) Insertion in Bayerite, an Aluminum Hydroxide.

Bayerite was treated under hydrothermal conditions (120, 130, 140, and 150 °C) to prepare a series of layered double hydroxides (LDHs) with an ideal composition of ZnAl4(OH)12(SO4)0.5·nH2O (ZnAl4-LDHs). These products were investigated by both bulk techniques (powder X-ray diffraction (PXRD), transmission electron microscopy, and elemental analysis) and atomic-level techniques ((1)H and (27)Al solid-state NMR, IR, and Raman spectroscopy) to gain a detailed insight into the structure of ZnAl4-LDHs and sample composition. Four structural models (one stoichiometric and three different defect models) were investigated by Rietveld refinement of the PXRD data. These were assessed using the information obtained from other characterization techniques, which favored the ideal (nondefect) structural model for ZnAl4-LDH, as, for example, (27)Al magic-angle spinning NMR showed that excess Al was present as amorphous bayerite (Al(OH)3) and pseudoboehmite (AlOOH). Moreover, no evidence of cation mixing, that is, partial substitution of Zn(II) onto any of four Al sites, was observed. Altogether this study highlights the challenges involved to synthesize pure ZnAl4-LDHs and the necessity to use complementary techniques such as PXRD, elemental analysis, and solid-state NMR for the characterization of the local and extended structure of ZnAl4-LDHs.

Octagonal symmetry in low-discrepancy β-manganese.

A low-discrepancy cubic variant of β-Mn is presented exhibiting local octagonal symmetry upon projection along any of the three mutually perpendicular 〈100〉 axes. Ideal structural parameters are derived to be x(8c) = (2-\sqrt{2})\big/16 and y(12d) = 1\big/(4 \sqrt{2}) for the P4132 enantiomorph. A comparison of the actual and ideal structure models of β-Mn is made in terms of the newly devised concept of geometrical discrepancy maps. Two-dimensional maps of both the geometrical star discrepancy D(*) and the minimal interatomic distance dmin are calculated over the combined structural parameter range 0 \leq x(8c) \,\lt\, 1/8 and 1/8 \leq y(12d)\, \lt\, 1/4 of generalized β-Mn type structures, showing that the `octagonal' variant of β-Mn is almost optimal in terms of globally minimizing D(*) while at the same time globally maximizing dmin. Geometrical discrepancy maps combine predictive and discriminatory powers to appear useful within a wide range of structural chemistry studies.

Critical cross-linking to mechanically couple polyelectrolytes and flexible molecules

Molecules cooperate through a variety of mechanical interactions. A fundamental challenge in engineering de novo materials and systems is the identification of molecular structures that define fundamental building blocks – e.g., single structural units. Here, we report a systematic study of the effect and balance of molecular rigidity and variable cross-linking (such as electrostatic or H-bonding) on the resulting cooperative behavior of a molecular complex. Through a simple elastic model, we determine general conditions for mechanical coupling of flexible molecules of finite rigidity via discrete cross-links with finite stiffness. We demonstrate the atomistic mechanism of cooperative deformation (or mechanical coupling) by applying an ideal structural model, derived to solve the representative vibrational modes, and used to extract the effective bending rigidity as a physical metric for complexation. As a case study, we explore the complexation of weak polyelectrolytes used in layer-by-layer assembly, due to their known variation in molecular rigidity and electrostatic cross-linking (as a function of pH). The model is parameterized by previous full atomistic investigations of the constitutive polyelectrolytes: poly(acrylic acid), PAA, and poly(allylamine hydrochloride), PAH, which have persistence lengths on the order of a single nanometer, and are typically considered flexible molecules. We predict the optimal ionization level to induce mechanical coupling and cooperative deformation. Moreover, we indicate a critical regime of allowable cross-link densities which facilitates complexation, for molecules with finite rigidity in general, such as H-bonded polypeptide β-strands, DNA, and collagen. From these results, it is possible to predict when (or if) molecules act as a single mechanical unit.

Synthesis of a layered crystalline AlSPP and reusable catalysts for epoxidation of unfunctionalized olefins

A type of organic–inorganic hybrid material layered crystalline AlSPP (AlSPP) was prepared under simple conditions, completely different to the traditional hydrothermal methods, by the reaction of oligo‐styrenyl phosphonic acid with aluminum acetate and sodium dihydrogen phosphate. The microstructure of AlSPP was characterized by X‐ray diffraction, FT‐IR, atomic absorption spectroscopy, N2 volumetric adsorption, atomic force microscopy, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. Based on the experimental date, the ideal structure model of AlSPP is proposed, which indicated that the layered crystalline AlSPP samples are special lamellar structure with many cavums, holes, channels and ravines on the surface, the interlamellar region and interlayer surfaces of the particles. Therefore AlSPP possesses excellent properties and has potential applications for heterogeneous asymmetric catalyst supports. Copyright © 2012 John Wiley & Sons, Ltd.

Importance of Disordered Polymer Segments to Microstructure-Dependent Photovoltaic Properties of Polymer–Fullerene Bulk Heterojunction Solar Cells

While regulation of the nanoscale microstructure of the active layers in organic bulk heterojunction (BHJ) solar cells, particularly for conjugated polymer–fullerene blend systems, has been shown to be highly important when maximizing power conversion efficiency, little is known about the role of disordered polymer chains in the photovoltaic (PV) behaviors and electrochemical potential drops of polymer–fullerene interfaces. In this study, the microstructural-dependent PV properties of a series of poly(3-hexylthiophene) (P3HT):fullerene (i.e., [6,6]-phenyl-C61-butyric acid methyl ester, or PCBM) blending films with different compositions have been investigated using several experiments (i.e., absorption spectroscopy, Raman spectroscopy, X-ray diffraction, and atomic force microscopy) and theoretical methods (i.e., spectroscopic simulation and quantum mechanical calculations). A strong correlation exists between amorphous P3HT chain properties, characterized by degree of conjugation (Leff), and PV parameters. The impact of Leff of amorphous P3HT on exciton dissociation is addressed, thus providing an ideal structural model for organic BHJ solar cells. Although bigger P3HT and PCBM domains favor carrier transport, the control of disordered P3HT segments and PCBM contact is crucial to exciton dissociation, which can consequently optimize PV performance.

Research on Durability Performance of Novel Double Solution Grouting Material with Metakaolin

At the present, Portland cement-water glass double solution grouting materials have many problems, such as the instability of gelation time and of products, and poor groundwater-corrosion resistance performance, etc. A way to improve the performances of double solution grouting materials was studied by adding metakaolin into the systems. Based on the rapid gelation performance of Portland cement-water glass and the durability of alkali-activated salic cementitious materials, an ideal structural model of the novel anti-aqueous dispersion and anti-aqueous dissolution grouting material (AAGM) was established. Series of experiments were prepared to verify the Na+ solidification and water-corrosion resistance performance of the metakaolin-water glass double solution grouting materials which combined with cement. The results indicated that the compact structure of AAGM was composed of a dominant ingredient of (Na,Ca)-Si-Al-H zeolite gel and a minor part of C-S-H. Moreover, it was shown that the AAGM had hydrated product of low solubility and compact microstructure tested by Fourier transform infrared spectra (FTIR) and transmission electron microscopy (SEM), which proved the well anti-aqueous dispersion and anti-aqueous dissolution performance.

Multiple diffraction in an icosahedral Al-Cu-Fe quasicrystal

In order to reveal its influence on quasicrystal structure analysis, multiple diffraction (MD) effects in an icosahedral Al-Cu-Fe quasicrystal have been investigated in-house on an Oxford Diffraction four-circle diffractometer equipped with an Onyx™ CCD area detector and MoKα radiation. For that purpose, an automated approach for Renninger scans (ψ-scans) has been developed. Two weak reflections were chosen as the main reflections (called P) in the present measurements. As is well known for periodic crystals, it is also observed for this quasicrystal that the intensity of the main reflection may significantly increase if the simultaneous (H) and the coupling (P-H) reflections are both strong, while there is no obvious MD effect if one of them is weak. The occurrence of MD events during ψ-scans has been studied based on an ideal structure model and the kinematical MD theory. The reliability of the approach is revealed by the good agreement between simulation and experiment. It shows that the multiple diffraction effect is quite significant.

Robust efficient method of moments

This paper focuses on the robust efficient method of moments (REMM) estimation of a general parametric stationary process and proposes a broad framework for constructing REMM statistics in this context. This extends the application field of robust statistics to very general time series settings, including situations where the structural and the auxiliary models in the efficient method of moments (EMM) estimating equations are different, models with latent nonlinear dynamics, and models where no closed form expressions for the robust pseudoscore of the given EMM auxiliary model are available. We characterize the local robustness properties of EMM estimators for time series by computing the corresponding influence functions and propose two versions of a REMM estimator with bounded influence function. Two algorithms by which the two versions of a REMM estimator can be implemented are presented. We then show by Monte Carlo simulation that our REMM estimators are very successful in controlling for the asymptotic bias under model misspecification while maintaining a high efficiency under the ideal structural model.

Static bismuth disorder in Bi 2− x(CrTa)O 7− y

The crystal structure of the pyrochlore Bi 2− x (CrTa)O 7− y has been refined by the Rietveld method from powder neutron and synchrotron X-ray diffraction data. Using the ideal pyrochlore structural model, anomalously high atomic displacement parameters (APD), which could not be satisfactorily explained with anisotropic ADP, of both Bi and O′ sites were observed. The structure was successfully refined with a model that incorporated static displacive disorder of both the Bi and O′ atoms. Using this model physically reasonable ADP parameters for both the Bi and O′ atoms, and improvement in the various measure of fit were obtained. The underbonding of the Bi atoms, observed in ideal pyrochlore model, but removed in the disordered structure, is believed to be the main driving force for this disorder.