Framework Vibrations Research Articles

Advanced vibrant controller results of an energetic framework structure

Abstract This research shows the influence of a new active controller technique on a parametrically energized cantilever beam (PECB) with a tip mass model. This article remains primarily concerned with regulating the system’s response using a novel control mechanism. This study describes a novel control mechanism called the nonlinear proportional-derivative cubic velocity feedback controller (NPDCVFC). The motivation of this article is to design a novel control algorithm in order to mitigate the nonlinear vibrations of a parametrically energized cantilever beam with a tip mass model. The proposed controller NPDCVFC incorporates nonlinearly second- and first-order filters into the system. The system is governed by one nonlinear differential equation having both quadratic and cubic nonlinearities within the parametric force. The controller’s efficiency in reducing framework vibrations, managing nonlinear bifurcations, and calming unstable motion is evaluated using numerical simulations of instantaneous vibrations. The perturbation technique is beneficial for solving the current model under the proposed worst resonance case ( Ω ˆ p = 2 ω ˆ 0 ) \text{(}{\hat{{\Omega }}}_{\text{p}}=2{\hat{{\omega }}}_{0}) . In order to choose the optimal controller, we have also added three more controller approaches to the configuration. Integral resonant control, positive position feedback, and nonlinear integral positive position feedback are the three controller approaches that are applied to the structure under consideration. We determine that the NPDCVFC as a new controller is the most effective for lowering the high vibration amplitudes. Over the investigated model, all numerical results were performed using the MATLAB 18.0 programmer software. The stability analysis and the effects of various elements on the controlled structure have been investigated. A comparison with recently published works of a comparable model has also been prepared. Experiment capacities for a PECB with a tip mass are obtainable to validate the results, and they demonstrate good agreement with analytical and numerical results.

A Temperature Perturbation Infrared Spectroscopy Comparison of HY and NaY Zeolite Dehydration/Rehydration

Temperature step infrared spectroscopy is used to monitor vibrations associated with water molecules and zeolite framework during thermal dehydration and rehydration of HY and NaY. Temperature-dependent HY and NaY infrared spectrum intensity and wavenumber trends for O-H stretching vibrations, H-O-H bending vibrations, and zeolite framework vibrations are compared. Changes in hydroxyl stretching and water bending vibration bands confirm that HY has a stronger hydrogen bonding network. The intensity of a band at 3700 cm−1 in NaY spectra varies with temperature and can be correlated with Na+ migration and zeolite water content. Spectral subtractions reveal complex intensity variations in the framework vibration band wavenumber region. Spectrum differences indicate the presence of at least four overlapping contributions in this wavenumber region. The intensities and wavenumbers of these constituents vary with temperature differently for HY and NaY. For both zeolites, infrared spectrum changes detected during thermal dehydration were mostly reversed when water re-adsorbed to the sample after cooling.

Intrinsic ultralow lattice thermal conductivity in lead-free halide perovskites Cs3Bi2X9 (X = Br, I).

Lead-free halide perovskites have recently garnered significant attention due to their rich structural diversity and exceptionally ultralow lattice thermal conductivity (κL). Here, we employ first-principles calculations in conjunction with self-consistent phonon theory and Boltzmann transport equations to investigate the crystal structure, electronic structure, mechanical properties, and κLs of two typical vacancy-ordered halide perovskites, denoted with the general formula Cs3Bi2X9 (X = Br, I). Ultralow κLs of 0.401 and 0.262 W mK-1 at 300 K are predicted for Cs3Bi2Br9 and Cs3Bi2I9, respectively. Our findings reveal that the ultralow κLs are mainly associated with the Cs rattling-like motion, vibrations of halide polyhedral frameworks, and strong scattering in the acoustic and low-frequency optical phonon branches. The structural analysis indicates that these phonon dynamic properties are closely relevant to the bonding hierarchy. The presence of the extended Bi-X antibonding states at the valence band maximum contributes to the soft elastic lattice and low phonon group velocities. Compared to Cs3Bi2Br9, the face-sharing feature and weaker bond strength in Cs3Bi2I9 lead to a softer elasticity modulus and stronger anharmonicity. Additionally, we demonstrate the presence of wave-like κC in Cs3Bi2X9 by evaluating the coherent contribution. Our work provides the physical microscopic mechanisms of the wave-like κC in two typical lead-free halide perovskites, which are beneficial to designing intrinsic materials with the feature of ultralow κL.

A time-delayed proportional-derivative controller for a dielectric elastomer circular membrane

• In this paper, an internal resonance of a circular DE membrane is investigated within mechanical and electrical excitations in order to find internal resonances for improving its performance for future applications. • This work proposes a time-delayed proportional-derivative (TDPD) controller for decreasing the oscillations of a DE system with quadratic and cubic nonlinearities. • Averaging method is used to solve the controlled system to obtain the first-order approximation solutions and response equations for the DE system. • The TDPD controller is the best control strategy that can reduce the framework vibrations regardless of the excitation frequency. Due to the substantial deformation generated by voltage excitation, the dielectric elastomer (DE) is a new type of functional polymer that can be employed as a smart actuator. In this paper, an internal resonance of a circular DE membrane is investigated within mechanical and electrical excitations in order to find internal resonances for improving its performance for future applications. All programs that contain DE will perform flawlessly if DE is managed. This work proposes a time-delayed proportional-derivative (TDPD) controller for decreasing the oscillations of a DE system with quadratic and cubic nonlinearities. The system is researched and investigated when using a Proportional–derivative (PD) controller to apply time-delayed control on displacement and velocity. Stability is improved, maximum peak overshoot is reduced, settling time is reduced, and the framework transient response is recovered using this control method. The first-order approximation solutions for the DE system are calculated using the averaging method. Simultaneous resonance is regarded as the worst type of resonance. To obtain the dynamic solution of the device with TDPD controllers, analytical and numerical approaches are used. The Routh-Huriwitz approach is used to review and analyze the consistency of the steady state solution in the near-resonance case. The effects of various factors on the steady-state solution are identified and discussed. The effects of time delay are investigated in order to determine the most stable range of time delays for the best performance. The MATLAB software package is used to generate simulation effects. When the results are compared to the numerical simulations, they show that the approximate solution and the control algorithm used in this paper are well validated. At the end, there is a comparison with previously published work. The focus of this paper is on using a TDPD controller to manage the nonlinear dynamic response and probable internal resonances of a circular DE membrane under mechanical and electrical excitations. The approximate solution of a nonlinear system of differential equations is investigated using the averaging technique in the cases of primary and 1:2 internal resonance, which are the worst-case scenarios that should be avoided. To display and compare controller effects at various system settings, several response curves are used. The TDPD controller is used to research nonlinear dynamics control of the DE system with harmonic force. The stability analysis and the effects of parameter behavior are tested using MATLAB program. To examine the controller effect, several response curves are used. The collected findings demonstrated that the TDPD control efficiency in reducing the system's nonlinear oscillations. The frequency response curves of the system were studied at various uncontrolled and regulated coefficients. Before and after control, response curve diagrams employing frequency response equations are created. Finally, validation curves are shown to measure the degree of similarity between analytical and numerical simulation predictions. At the end, there is a comparison with previously published works.

Optimal Raman-scattering signal for estimating the Fe3+ content on the clinozoisite–epidote join

Abstract. To provide a tool for fast estimation of the Fe3+ content in Ca2(Al, Fe3+)3Si3O12(OH) epidote grains, including in thin sections and crude-rock samples, we applied Raman spectroscopy to 33 areas from 15 natural samples with Fe3+ ranging from 0.22 to 1.13 atoms per formula unit (apfu), the chemistry of which was independently determined by wavelength-dispersive electron microprobe analysis (WD-EPMA). The Raman spectra were collected from the very areas subjected to WD-EPMA. We have analysed both the OH-stretching region (3215–3615 cm−1) and the spectral range generated by the framework vibrations (15–1215 cm−1). Similarly to the IR spectra, the Raman peaks in the OH-stretching region shift toward higher wavenumbers with increasing Fe. However, the quantification of Fe3+ based on OH-stretching Raman peaks can be hindered by the multicomponent overlapping and significant intensity variations with the crystal orientation. Among the Raman signals generated by framework vibrations, the position of four peaks (near 250, 570, 600, and 1090 cm−1) exhibit a steady linear regression with the increase in Fe content (in apfu). However, the peak near 250 cm−1 attributed to MO6 vibrations also depends on the crystal orientation and therefore is not always well resolved, which worsens the accuracy in Fe-content determination based on its position. The peaks near 570, 600, and 1090 cm−1 arise from Si2O7 vibrational modes, and although their intensities also vary with the crystal orientation, all three signals are well resolved in a random orientation. However, among the three Si2O7-related signals, the 570 cm−1 peak is the sharpest (peak width <10 cm−1) and is easily recognized as a separate peak. Hence, we propose to use the position of this peak as a highly reliable parameter to estimate the Fe content, via the linear trend given as ω570=577.1(3)-12.7(4)x, where ω is the wavenumber (cm−1) and x is Fe content (apfu), with accuracy ± 0.04 Fe3+ apfu. The peaks near 600 and 1090 cm−1 may be complementarily used for the Fe estimate, based on the following relations: ω600=611.6(2)-13.8(4)x and ω1090=1098.8(3)-13.5(5)x. Analyses of the effect of Sr as a substitution for Ca and Cr at the octahedral sites indicate that contents of Sr <0.12 apfu do not interfere with the quantification of Fe via the ω570 (x) relation, whereas Cr >0.16 apfu leads to overestimation of Fe; Cr presence can be recognized however by the broadening of the peaks near 95 and 250 cm−1.

Quantification of Exchanged Copper Species in Cu‐Chabazite Zeolite using Cryogenic Probe Infrared Spectroscopy

AbstractThe development of a low temperature (−160 °C) NO adsorption technique is disclosed that avoids the chemical conversion of the probe molecule at room temperature. The observed IR peaks for Cu+(NO)2 and Cu2+(NO) species can be used to quantify the amount of exchanged copper species in a broad range of samples, including a wash‐coated honeycomb. Calibration curves for Cu+(NO)2 and Cu2+(NO) are determined for copper loadings up to 3.99 wt% with Silica‐to‐Alumina Ratio (SAR) of 16–22, and quantitative agreement with the complementary hydrogen Temperature Programmed Reduction (H2‐TPR) results is established. This methodology allows to identify different Cu species in Cu‐CHA, such as Z2Cu(II), Z1Cu(II)OH and Cu dimers, based on their distinct IR signatures. In addition, the perturbed T−O−T framework vibration – characterized at 400 °C – can also be used as a complimentary method to quantify Z2Cu(II) species.

Characterization of Natural Precious Opal Using Modern Spectroscopic Techniques in Ethiopia: The Case from Delanta, South Wollo

The purpose of this study was to conduct characterization of the Delanta natural opals obtained from different mining sites. Characteristics of opals mined from different geological locality were examined. Six opal samples were collected from the main mining sites found in different localities from Delanta district and characterized using Fourier infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and inductively coupled plasma optical emission spectroscopy characterization techniques. The scanning electron microscope micrographs showed that all the samples have relatively semi-ordered (semi-crystalline) structural surface morphologies composed of tiny spherical particles. The performed X-ray diffraction analysis showed that the samples have main peaks at 20.0°, 21.72°, 36.9°, 44.0°, and 56.85° with 2 θ values between 10° and 60°. The five diffraction peaks are characteristic peak positions of opal-CT. The Fourier infrared spectroscopy data indicated that the prominent absorption bands for cristobalite at 620 and 520 cm−1 were absent from the spectrum. Instead, three bands in the low frequency region centered at 470, 791, and 1100 cm−1 were observed because of the absorptions of the silicate framework (Si-O) vibrations. red−1−1 Moreover,spectra feature of molecular water and silanol (Si-OH) groups with broadabsorption band centered around 3447 cm-1 andthe O-H stretching vibration of watermolecules and water bending vibration withan absorption band centered around 1634 cm-1were observed.. These values were consistently comparable with literature data. The inductively coupled plasma optical emission spectroscopy analysis showed that four main impurities (>500 parts per million) were Ca (∼1,750–4,730 parts per million), Al (∼1,990–4,319 parts per million, K (∼1,670–3,895 parts per million), and Na (∼595–3,723 parts per million). In general, this study revealed that all opal samples taken from six mining sites in Delanta district were found to be opal-CT as per the results of X-ray diffraction and Fourier infrared spectroscopy investigations.

Synthesis, Characterization, and Antifungal Activity of Cd2SnO4 Nanoparticles Prepared by Sol-Gel Technique

In this study, Cd2SnO4 nanoparticles were produced using a sol-gel technique. X-ray diffraction was used to investigate the Cd2SnO4 nanoparticles. Transmission electron microscope (TEM) with Fourier transform infrared spectrophotometer (FTIR), FE-SEM images show that manufactured Cd2SnO4 nanoparticles have cubic structures with some irregular cubic shaped nanoparticles. XRD patterns of the prepared thin films showed that the nanoparticles have a polycrystalline structure. The wide bands between 551 and 854 cm-1 are attributable to the framework vibrations of the Sn-O bond in SnO2, and the band at 551 cm-1 is also due to cadmium and oxygen in this area, according to the FTIR analysis. The TEM result shows the presence of cubic shaped nanoparticles. The interaction between the cadmium nanoparticles and the cellular contents of the fungi may be the reason for the antifungal effectiveness of Cd2SnO4 nanocomposites.

FRET in Orthogonal, Increasingly Strain‐Rigidified Systems

AbstractThe influence of the geometry factor κ on the efficiency of energy transfer by FRET (Förster resonance energy transfer) was studied by means of dyads of benzoperylene and perylene interlinked by a spacer of the cage bicyclo‐[2.2.2]octane. The electronic transition moments were arranged orthogonally for extinguishing the energy transfer according to Förster's theory. In contrast to the theory energy transfer proceeded unrestrictedly attributed to molecular vibrations. A further rigidifying of the spacer by means of annellation with benzo groups until the very rigid triptycene as a spacer could not hinder the energy transfer so that general strongly coupled molecular framework vibrations seem to be dominant in the energy transfer whereas molecular flexibility seems to be of minor importance. Application such as molecular mirrors are discussed.

Insight into the structural, optical, adsorptive, and photocatalytic properties of MgFe2O4-bentonite nanocomposites

Nanofabrication of magnesium ferrite nanoparticles (MgFe2O4 NPs) and bentonite clay offers a new class of nanocomposites with environmentally safe and non-toxic components. In the present study, MgFe2O4-bentonite clay nanocomposites with four different w/w ratios have been synthesized by a sol–gel auto-combustion method. Their structural, morphological, and magnetic properties have been comparatively analyzed by means of SEM-EDS, TEM, XRD, BET, FTIR, and VSM techniques. The intensity of the FTIR band corresponding to Si-Al-O framework vibration increased linearly with increasing bentonite content, thus confirming successful nanofabrication with different bentonite contents. Magnetization values decreased from 11.4 to 3.7 emu/g with increasing bentonite content. Specific surface areas of the nanocomposites were in the range 48.9–87.0 m2/g, with the highest value for MgFe2O4-bentonite nanocomposite with 1:0.05 (w/w). The synthesized nanocomposites have been used as adsorbents for the sequestration of heavy metal ions from aqueous solution spiked with Pb(II), Ni(II), Zn(II), and Cd(II). Inductively coupled argon plasma-optical emission spectroscopy confirmed NC-I, having the composition 1:0.05, to be the best adsorbent among the synthesized nanocomposites and pristine MgFe2O4 NPs. Maximum removal was observed for Pb(II) ions, followed by Zn(II), Cd(II), and Ni(II) ions, which can be correlated to the radii of the hydrated ions. At optimized adsorbent dose, the removal of heavy metal ions was in the range 92.5–95.2%. NC-I also acted as the best photocatalyst, fully degrading para-nitrophenol within 180 min. The optical band gap of MgFe2O4 NPs is 2.58 eV, and this decreases to 2.26 eV in the NCs. Effective charge separation and a low band gap lead to higher photocatalytic performance. The results correlated with specific surface area. The present studies highlight the immense potential of nanofabrication in tuning the properties of composite materials for environmental applications.

Control of unsteady partial cavitation and cloud cavitation in marine engineering and hydraulic systems

Cavitation is a process of liquid evaporation, bubble or vapor sheet formation, and further collapse of vapor structures, which plays a destructive role in many industrial applications. In marine transport and hydraulic machinery, cavitation usually occurs nearby the surface of a ship propeller and rudder, impeller blades in a pump, and distributor vanes and runner blades in a hydroturbine and causes various undesirable effects such as vibrations of frameworks and/or moving parts, material erosion, and noise enhancement. Based on an extensive literature review, this research is aimed at an experimental investigation of a passive approach to control cavitation on a benchmark hydrofoil using a wedge-type vortex generator in different flow regimes with a high Reynolds number. In this study, we employed a high-speed imaging method to explore the spatial patterns and time evolutions of cavitation structures and utilized a hydroacoustic pressure transducer to record and analyze local pressure pulsations due to the collapse of the cavities in the hydrofoil wake region. The results show that the examined control technique is quite effective and capable of hindering the formation of cloud cavities and reducing the amplitude of pressure pulsations associated with unsteady cavitation dynamics. This study provides important experimental information, which can be useful for improving industrial technologies and for promoting new developments in this particular research field.

A variable temperature infrared spectroscopy study of NaY zeolite dehydration.

Variable temperature diffuse reflection infrared spectroscopy is used to monitor molecular vibration changes associated with water molecules and zeolite framework during thermal dehydration of NaY zeolite. Absorbance bands are assigned to three unique water molecule environments. These three water types exhibit different temperature-dependent band intensity profiles. A band at 3700 cm-1 is assigned to framework acid sites. The intensity of this band was found to vary with temperature in a manner consistent with the occupancy of sodium cations in II' unit cell locations. Specific framework vibrations exhibit temperature-dependent intensity change profiles. Band intensities at 1190, 1060, and 960 cm-1, associated with Si-O-Si and Si-O-Al asymmetric stretching vibrations, are sensitive to water content. Band intensity at 800 cm-1, assigned to Si-O-Si symmetric stretching, is inversely correlated with temperature-dependent unit cell volume changes. All framework band intensity changes detected during heating are reversible after re-hydration during sample cooling.

Support effects in metal catalysis: a study of the behavior of unsupported and silica-supported cobalt catalysts in the hydrogenation of CO2 at atmospheric pressure

Abstract Two 20 wt.% Co/SiO2 catalysts were prepared using silica gel as a support and cobalt acetate and nitrate as precursors, respectively. As a comparison unsupported amorphous cobalt nanoparticles (10–80 nm) were synthesized by decomposing cobalt carbonyl. They were characterized before and after reaction using XRD, IR spectroscopy in the range of framework vibrations, DR-UV–vis-NIR spectroscopies and FE-SEM microscopy. They are active in CO2 methanation at atmospheric pressure. However, unsupported cobalt and the silica-supported catalyst prepared using cobalt acetate deactivate fast at 623–673 K, also due to formation of encapsulating carbon. On the other hand, they retain more stable activity in the reverse water gas shift (rWGS) reaction, producing CO. Methanation and rWGS appear to occur on independent sites. The silica-supported catalyst produced from cobalt nitrate show more stable methanation activity, attributed to the presence of smaller cobalt particles (10–20 nm) that resist deactivation. For both unsupported CoNPs and Co/SiO2, the significant parameters for catalysts deactivation have been determined for CO2 methanation. The differences observed among catalysts produced starting from cobalt acetate and cobalt nitrate, can be associated to the different pH of the impregnating solution.

Nondestructive determination of the amphibole crystal‐chemical formulae by Raman spectroscopy: One step closer

AbstractWe present the results of a comprehensive study linking the crystal‐chemical formulae of amphiboles, a series of extremely complex silicates with the general formula (AB2C5T8O22W2, C5 = M12M22M3) to variations in the peak positions, widths, and intensities of the Raman‐active modes. To this purpose, we have analyzed the Raman scattering generated by the framework vibrations (15–1,215 cm−1) and by the OH‐stretching modes (3,000–4,000 cm−1) of 44 samples, spanning all six major subgroups. We show that, in addition to the information that can be derived from the OH‐stretching range (Leissner et al., Am. Mineral. 2015, 100, 2682), further important features of the amphibole structure, composition, and cationic site population can be directly extracted from the framework Raman spectrum, namely, (a) the distinction between the monoclinic and orthorhombic symmetries; (b) the estimation of TAl content, when TAl > 0.5 apfu; (c) the estimation of CTi content, when CTi > 0.3 apfu; (d) the estimation of CLi content, when CLi > 0.3 apfu; (e) the detection of CAl, when CAl > 0.7 apfu; (f) an estimate of CMg; (g) the estimation of CFe3+ in the case of Na amphiboles; and (h) the estimation of the Fe2+ content at the M2 site in the case of Mg–Fe–Mn amphiboles. Additionally, we point out that the TO4‐ring‐breathing mode near 670 cm−1, which is commonly used to fingerprint various amphibole species, has to be handled with a great care, because it is sensitive to the site population at all crystallographic sites.

Efficiency improvement of loading of potassium ore by means of «Ural-20R» heading-and-winning machine

The paper deals with certain operation features of «Ural-20R» heading-and-winning machines. It has been proven that the efficient capacity field of such excavation machines is limited by the capacity of the subsequent loading equipment: a worm conveyor and a drag-bar reclaim conveyor. The crushing of potassium rock mass by chisels of the operation devices of «Ural-20R» machines is accompanied by intensive circulation and excessive ore degradation during transportation of the rock mass by single cut worms. Intermittent feeding of the ore to the conveyor stipulates considerable framework vibrations and formation of dynamic loads on the elements of the power drive of the reclaim conveyor. When the winning machine is used in mines with negative inclination angles, the capacity of the drag bar reclaim conveyor is drastically reduced. Based on the analysis of structural features of the worms and the conveyor of «Ural-20R», technical proposals have been made as to the efficiency improvement of potassium ore loading.

Hierarchical architectures of ZSM-5 nanocrystalline aggregates with particular catalysis for lager molecule reaction

The spherical self-assemblies of ZSM-5 nanocrystals were hydrothermally synthesized by using organo-functionalized mesoporous silica (MS) as silica source. The prepared materials were well characterized by XRD, FTIR of framework vibration, SEM, TEM, N2 adsorption/desorption and TG analyses, to reveal their hierarchical architectures. The ZSM-5 nano-aggregates are composed of size-tunable nanocrystals, and the size and different morphologies of nanocrystals changed significantly from silanized MS rather than unsilanized MS. Spontaneously stacking of nanocrystals in the zeolitic crystallization based on degrees of silanization on MS surface results in the ZSM-5 samples have high external surface area and mesopore volume from intercrystalline among the nanoparticles. The evaluations of NH3-TPD, pyridine- and 2,6-ditertbutylpyridine-adsorbed FTIR as well as catalytic performances in benzylation reaction of 1,3,5-trimethylbenzene for the ZSM-5 zeolitic samples display the accessibility of acid sites and the catalytic activities for the synthesized hierarchical ZSM-5 zeolites are remarkably enhanced. It is clear that the results can be ascribed to the advantages of hierarchical ZSM-5 zeolites for the catalytic conversion of larger molecule, because of the reduction of the steric limitations and faster diffusion of the reaction species.

Influence of the octahedral cationic-site occupancies on the framework vibrations of Li-free tourmalines, with implications for estimating temperature and oxygen fugacity in host rocks

Tourmalines, XY 3 Z 6 T 6 O 18 (BO 3 ) 3 V 3 W, are excellent petrogenetic indicators as they capture the signature of the host-rock bulk composition. Raman spectra of tourmalines can be used as fingerprints for species identification and crystal-chemical analysis. While Li-bearing species are directly distinguishable by the shape of the OH-stretching vibrations, the discrimination of Mg- and Fe-dominant species can be hindered by the coexistence of at least two types of octahedrally coordinated R n+ cations. Thirty Li-free tourmaline samples comprising 14 different species were studied by Raman spectroscopy and electron microprobe. All nine Fe 3+ -bearing samples were also analyzed by single-crystal X-ray diffraction and Mossbauer spectroscopy. The Raman scattering analysis shows that Mg-dominant species can be immediately distinguished from Fe-dominant species by the shape of the vibrational modes at ~200–240 cm −1 arising from the YO 6 vibrations. Trivalent Fe can be observed and quantified by shifts of the framework vibrations toward lower wavenumbers. The position of the main ZO 6 vibrational mode (275–375 cm −1 ) can be used to determine the Z Fe 3+ content, while the Y Fe 3+ content can be inferred from the position of the peak at ~315 cm −1 . Fits to the data points indicate that the homovalent substitution of Fe 3+ for Al 3+ leads to a considerably larger downward shift of the ZO 6 vibrational mode than the heterovalent substitution Mg 2+ for Al 3+ . The intensity ratio of the two major YO 6 vibrational modes (200–240 cm −1 ) of the fully characterized Fe 3+ -bearing samples reflects the amount of Y-site Mg and thus can be used to deduce the site-occupancy disorder of Mg over the Y and Z site for tourmaline species with Mg ≤2 apfu. By combining the information from framework and OH-stretching vibrations, Raman spectroscopy alone can be used as a micrometer-scale sensitive non-destructive method for the analysis of tourmaline crystal chemistry including trivalent Fe, which is the major tracer for oxygen fugacity and central for intersite geothermometry.

Hierarchical ZSM-5 catalytic performance evaluated in the selective oxidation of styrene to benzaldehyde using TBHP

Hierarchical ZSM-5 catalysts with different Si/Al ratios (20, 60 and 100) were hydrothermally synthesized. The prepared samples were studied by several techniques, including X-ray diffraction (XRD), X-ray fluorescence (XRF) analysis, Fourier transform infrared (FTIR) spectroscopy, N2 adsorption–desorption, high resolution transmission electron microscopy (HR-TEM), high resolution scanning electron microscopy (HR-SEM), and differential scanning calorimetry (DSC) technique. The average crystallite size and crystallinity decreases with increasing Si/Al ratio, which is confirmed by XRD. FTIR analysis further confirms the formation of ZSM-5 by the presence of characteristic bending, stretching and framework vibration. The HR-TEM images showed that all the samples having disc-like nanostructures are assembled by many primary nanocrystals. The as-synthesized ZSM-5 zeolites are thermally stable, which is confirmed by DSC. The catalytic activity of ZSM-5 zeolites was evaluated in the selective oxidation of styrene using tertiary-butyl hydroperoxide (TBHP) as the oxidant. Among the catalysts, ZSM-5(60) catalyst showed significantly higher yield of benzaldehyde at optimum conditions. The catalyst was recovered and recycled three times without a significant loss in activity and selectivity.

РАСЧЕТ ВЫНУЖДЕННЫХ КОЛЕБАНИЙ СТЕРЖНЕВЫХ СИСТЕМ МЕТОДОМ КОНЕЧНЫХ ЭЛЕМЕНТОВ С ПРИМЕНЕНИЕМ ДИНАМИЧЕСКОГО КОНЕЧНОГО ЭЛЕМЕНТА

The analysis of forced vibrations of frameworks using finite element method is considered. The dynamic finite element, the base functions of which represent exact dynamic shapes of structural elements, is used for system discretization. The assessment of errors as a result of classic FEM application is given. The efficiency of application of dynamic finite element for analysis of forced vibrations and dynamic stress-deformed state of structures is shown.

Mechanisms Underlying the Mpemba Effect in Water from Molecular Dynamics Simulations

Experimentally, quenching from warmer water leads to faster freezing than quenching from colder water—the Mpemba effect. Using molecular dynamics, we find that quenching water from 370 K and above leads to a 100 K density of states (DOS) closer to that of ice than quenching from 300 K and below. Especially we find that the biggest difference is for 80–160 cm^(–1) which upon quenching from colder water is much lower than that in ice, while it is much higher than in ice when quenching from warm water. We find that the range of 100–160 cm^(–1) corresponds to framework vibrations within a hexamer, suggesting that the water hexamer serves as a nucleus for crystallization. We tested this by fixing one hexamer and quenching slowly from 370 K, leading to increased correlation with pure ice. We also showed that the structure quenched from 370 K evolves to the ice faster than 300 K case. These results suggest that the higher population of water hexamer states in warm water is responsible for the faster crystallization underlying the Mpemba effect.