Asymmetric Vibration Research Articles

Iterative universal state selective correction for the Brillouin-Wigner multireference coupled-cluster theory.

As a further development of the previously introduced a posteriori Universal State-Selective (USS) corrections [K. Kowalski, J. Chem. Phys. 134, 194107 (2011); J. Brabec et al., ibid. 136, 124102 (2012)], we suggest an iterative form of the USS correction by means of correcting effective Hamiltonian matrix elements. We also formulate USS corrections via the left Bloch equations. The convergence of the USS corrections with excitation level towards the full configuration interaction (FCI) limit is also investigated. Various forms of the USS and simplified diagonal USS corrections at the singles and doubles and perturbative triple levels are numerically assessed on several model systems and on the ozone and tetramethyleneethane molecules. It is shown that the iterative USS correction can successfully replace the previously developed a posteriori Brillouin-Wigner coupled cluster size-extensivity correction, while it is not sensitive to intruder states and performs well also in other cases when the a posteriori one fails, like, e.g., for the asymmetric vibration mode of ozone.

Ultrafast 2DIR spectroscopy of ferric azide precursors for high-valent iron. Vibrational relaxation, spectral diffusion, and dynamic symmetry breaking

Femtosecond mid-infrared pump-probe and two-dimensional mid-infrared spectroscopy have been used to investigate the dynamics of vibrational relaxation and vibrational spectral diffusion of the asymmetric N3-stretching vibration of pseudo-octahedral azidoiron(III) complexes, [L6-nFe(N3)n](+) with n = 1 or 2 and L being an auxiliary ligand of denticity 6-n, in acetonitrile at room temperature. Compared to the free azide anion in acetonitrile solution, the vibrational relaxation dynamics are considerably accelerated. Vibrational energy transfer to the solvent is accelerated by virtue of a resonance with an overtone transition of the solvent. Intramolecular vibrational redistribution is found to be accelerated by virtue of a coupling between the initial azide stretching vibration and the torsional modes involving the axial ligands. Vibrational spectral diffusion within the asymmetric N3-stretching resonance was found to be insensitive to solvent fluctuations because the axial azide ligands are only partially accessible to the solvent. The particular role of intramolecular structural relaxations of the complex for shaping the linear and nonlinear two-dimensional infrared spectra is discussed in terms of ultrafast symmetry-breaking torsional fluctuations and on the basis of density functional theory calculations.

Analysis of flow-induced instability in a redesigned steam control valve

Industrial steam turbines represent one of the largest fractions of prime movers. Regardless of the steam-turbine application being considered, speed and/or load control will be required. Speed control is the primary control loop for all turbine applications, industrial as well as utility. The inlet of industrial steam turbine is usually controlled by a single valve, or a series of valves (multi-valve assembly) working in concert. These valves are required to operate under wide ranges of valve openings and pressure ratios. As a turbine governing valve, the venturi valve, has been widely used in steam turbines to regulate inlet flow in the last 40 years. But as turbine output power become larger, a number of valve failure incidences started to be reported and improving the valve designs became a high priority. Despite numerous investigations to eliminate valve failure, the attempts were not fully successful due to the complicated nature of the fluid–structure interaction mechanisms, and the basic mechanism causing valve vibration and failure is still far from being fully understood. As a continuation of previous valve studies, a newly designed valve has been investigated experimentally and. This paper presents detailed experimental investigations to clarify the mechanisms of valve instability caused by unsteady flows around the valve. A result of the asymmetric unstable flow, noise and vibration characteristics of the valve together with an overall performance assessment of the valve is presented.

Free and forced vibration characteristics of bimodular composite laminated circular cylindrical shells

The free and forced vibration characteristics of bimodular cross-ply laminated clamped–clamped circular cylindrical shells are studied using Bert’s and a recently proposed model considering first order shear deformation theory. The free vibration frequencies in positive and negative half cycles are found to be same for all asymmetric modes and for axisymmetric modes with even number of axial half waves, and different for axisymmetric modes with odd number of axial half waves. However, the negative half cycle amplitude is significantly greater than the positive half cycle amplitude due to the local stiffness of bimodular cylindrical shells being different for positive and negative half cycles even though the natural frequencies are same for positive and negative half cycles of asymmetric vibrations. The relative difference of positive and negative half cycle frequencies is very less for single layer orthotropic shells, and it is significant for cross-ply shells for axisymmetric mode of vibration. The vibration characteristics predicted using proposed and Bert’s constitutive models are quite close except for the transverse to the fiber direction normal stress.

Development of a Vibrational Hydration Ruler

Amino acids covalently modified with spectroscopic reporters offer the potential to probe local protein hydration with high spatial and temporal resolution when coupled with the appropriate spectroscopic technique. Three azidophenylalanine residues have been synthesized and, in combination with the commercially available 4-azido-L-phenylalanine, form a series of unnatural amino acids (UAAs) containing the azide vibrational reporter at varying distances from the aromatic ring of phenylalanine. The azide vibrational reporter was selected due to the position, sensitivity and extinction coefficient of the azide asymmetric stretch vibration. The sensitivity of the azide reporters for these UAAs was investigated in solvents that mimic distinct local protein environments. Three of the four azido modified phenylalanine residues were successfully genetically incorporated into a surface site in superfolder green fluorescent protein (sfGFP) utilizing an engineered, orthogonal aminoacyl-tRNA synthetase in response to an amber codon with high efficiency and fidelity. The site-specific incorporation of these UAAs was verified by SDS-PAGE and ESI-Q-TOF mass analysis. IR spectroscopy was then utilized to probe the protein hydration state for the azide group in these sfGFP constructs.

ATR-FTIR spectroscopy reveals involvement of lipids and proteins of intact pea pollen grains to heat stress tolerance.

With climate change, pea will be more frequently subjected to heat stress in semi-arid regions like Saskatchewan during flowering. The pollen germination percentage of two pea cultivars was reduced by heat stress (36°C) with an important decrease in cultivar ‘CDC Golden’ compared to ‘CDC Sage.’ Lipids, protein and other pollen coat compositions of whole intact pollen grains of both pea cultivars were investigated using mid infrared (mid-IR) attenuated total reflectance (ATR)–Fourier transform infrared (FTIR) spectroscopy. Curve fitting of ATR absorbance spectra in the protein region enabled estimation and comparison of different protein secondary structures between the two cultivars. CDC Sage had relatively greater amounts of α-helical structures (48.6–43.6%; band at 1654 cm-1) and smaller amounts of β-sheets (41.3–46%) than CDC Golden. The CDC Golden had higher amounts of β-sheets (46.3–51.7%) compared to α-helical structures (35.3–36.2%). Further, heat stress resulted in prominent changes in the symmetrical and asymmetrical CH2 bands from lipid acyl chain, ester carbonyl band, and carbohydrate region. The intensity of asymmetric and symmetric CH2 vibration of heat stressed CDC Golden was reduced considerably in comparison to the control and the decrease was higher compared to CDC Sage. In addition, CDC Golden showed an increase in intensity at the oxidative band of 3015 cm-1. These results reveal that the whole pollen grains of both pea cultivars responded differently to heat stress. The tolerance of CDC Sage to heat stress (expressed as pollen germination percentage) may be due to its protein richness with α-helical structures which would protect against the destructive effects of dehydration due to heat stress. The low pollen germination percentage of CDC Golden after heat stress may be also due to its sensitivity to lipid changes due to heat stress.

Reaction of the C3(X1Σg+) carbon cluster with H2S(X1A1), hydrogen sulfide: Photon-induced formation of C3S, tricarbon sulfur

In this paper we report on the neutral-neutral reaction of the C3 carbon cluster with H2S in solid inert argon at 12 K, conditions that mimic, in part, the surfaces of interstellar grains. In the first step of the reaction, a C3•H2S complex is formed via an almost barrierless entrance addition mechanism. This complex, stabilized by an estimated 7.45 kJ/mol (CCSD(T)/aug-cc-pVTZ//B3LYP/6-311++G(d,p) level), is formed by the interaction of a terminal carbon of C3 with a hydrogen in H2S. This con-covalent complex displays a band at 2044.1 cm(-1) observed via Fourier transform infrared absorption spectroscopy. With the help of the MP2/aug-ccpVDZ level method, this band is assigned to the CC asymmetric vibration mode. When the complex is exposed to UV-visible photons (hν < 5.5 eV) the tricarbon sulfur C3S molecule is identified, based on the appearance of a characteristic CC stretching band at 2047.5 cm(-1). Calculated ground-state potential energy surfaces also confirm the concomitant formation of molecular H2. This facile reaction pathway involves an attainable transition state of 174.4 kJ/mol. Conversely, competing lower-energy reaction pathways that would lead to the generation of H2C3S (propadienethione), or C2H2 (acetylene) and CS, involve much more complex, multi-stage pathways, and are not observed experimentally.

Synthesis and Characterizations of Metal Oxide-Sulfonic Acid Functionalized ZSM-5 for Photocatalytic Degradation and Adsorption of Dimethylarsenic Acid

TiO2 and ZnO were incorporated into ZSM-5 using titanium tetrachloride and zinc nitrate as the precursors respectively. The functional group of ZSM-5 was further modified using mercaptopropyl trimethoxysilane (MPTS). This method was used to produce a two-in-one composite namely TiO2-ZSM5-SH and ZnO-ZSM5-SH which holds the abilities to degrade organic pollutants as well as to remove them from the environment. Determination of the composition and morphology of all synthesized catalyst complexes were characterized using Fourier Transformed Infrared (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HR-TEM). Results obtained indicated that the average diameters for TiO2-ZSM5-SH particles are 2.398 μm, slightly larger than the diameter of ZnO-ZSM5-SH particles with an average of 1.8067 μm. Both TiO2-ZSM5-SH and ZnO-ZSM5-SH appeared as sphere-like shape and amorphous since both metal oxides were incorporated into the ZSM-5 pores. The compositions of these complexes were proven by the presence of a strong silica absorption band showing the existence of Si-O stretching vibrations and SiO2 asymmetric vibrations in the synthesized complexes. For TiO2-ZSM5-SH, the Ti-O stretching vibration can be seen at 3467.29 cm-1 and at 1637.86 cm-1 while Zn-O absorption band appeared at 455.52 cm-1 in ZnO-ZSM5-SH. The symmetric and asymmetric vibrations of –CH2 and –CH3 indicate the existence of alkyl groups in the ZSM-5. The ability of catalyst complexes synthesized as photocatalyst were applied and tested on the photodegradation of dimethylarsenic acid (DMA) under ultra violet (UV) radiation which showed that these catalyst complexes are proven be able to degrade DMA into less toxic intermediates and are able to adsorb the remaining arsenic species from the aqueous solutions.

Infrared spectroscopy and density functional theory investigation of calcite, chalk, and coccoliths--do we observe the mineral surface?

We have measured infrared spectra from several types of calcite: chalk, freshly cultured coccoliths produced by three species of algae, natural calcite (Iceland Spar), and two types of synthetic calcite. The most intense infrared band, the asymmetric carbonate stretch vibration, is clearly asymmetric for the coccoliths and the synthetic calcite prepared using the carbonation method. It can be very well fitted by two peaks: a narrow Lorenzian at lower frequency and a broader Gaussian at higher frequency. These two samples both have a high specific surface area. Density functional theory for bulk calcite and several calcite surface systems allows for assignment of the infrared bands. The two peaks that make up the asymmetric carbonate stretch band come from the bulk (narrow Lorenzian) and from a combination of two effects (broad Gaussian): the surface or near surface of calcite and line broadening from macroscopic dielectric effects. We detect water adsorbed on the high surface area synthetic calcite, which permits observation of the chemistry of thin liquid films on calcite using transmission infrared spectroscopy. The combination of infrared spectroscopy and density functional theory also allowed us to quantify the amount of polysaccharides associated with the coccoliths. The amount of polysaccharides left in chalk, demonstrated to be present in other work, is below the IR detection limit, which is 0.5% by mass.

Two-step transfer function calculation method and asymmetrical piecewise-linear vibration isolator under gravity

Piecewise-linear isolators are widely used in spacecraft for satisfying ever more stringent vibration requirements of high precision payloads. This paper focuses on ground tests of such isolators, with special consideration of gravitational asymmetry and mount flexibility. With asymmetrical equivalent isolator parameters derived with the extended equivalent linearization method, a two-step transfer function calculation method is proposed for enhancing the computation efficiency in dealing with studies where huge amount of computations are required, such as design parameter studies. The asymmetrical effect due to the gravity is presented by the movement of dynamic equilibrium positions as well as the softening and hardening characteristics of frequency responses. The effects and differences of the rigid mount and flexible mount, which respectively correspond to the shake table test and the whole spacecraft structure ground test, are studied with various design parameters. Numerical results show that the preload is an important factor in determining such effects and differences.

VIBRATION OF THE CIRCULAR ANNULAR PLATE WITH AN INTERNAL FREE EDGE

Whole and with opening elliptic membranes meet as elements of machines of devices: diaphragms, winders. Results of calculations of frequency parameter for the symmetric vibrations of such membranes at the different values of excentricity are presented in background literature and based on one of works. In scientific literature there are not experimental information on determination of frequencies of vibrations of such plates, which would enable to estimate exactness of the presented results. Absent calculations of frequency parameter of asymmetrical vibrations, and also results of calculation frequency the parameter of elliptic membrane with opening. A whole elliptic membrane is stretched by equipartition forces. Worked out an equation of eigentones in the rectangular system of coordinates. The formulas of transformation of rectangular co-ordinates are entered to elliptic and equalization of eigentones is determined in the set elliptic system of coordinates. The decision of this system is given through the ordinary and modified Mathieu function of the first family. Worked out a frequency equation and his decision is found for symmetric vibrations and asymmetrical vibrations at different. For an elliptic membrane with opening to the decision the Mathieu function of the second family is added on the basis of Floquet theorem. Resulted decisions of frequency equalization at the different values of excentricity of internal and external ellipse it is Necessary to conduct experimental researches of tasks on determination of frequency parameter of symmetric and asymmetrical whole with opening of membranes. .

Asymmetric vibration characteristics of two-cylinder four-stroke single-piston hydraulic free piston engine

The structure and working principle of a two-cylinder four-stroke single-piston hydraulic free piston engine (HFPE) were introduced. The basic vibration equation of free piston assembly (FPA) was established based upon the energy conversion between the injected fuel and the friction together with the load. Both the theoretical and numerical results show that the vibration system of FPA is a nonlinear conservative autonomous system in one cycle. The FPA vibration is symmetric with constant amplitude when FPA is only driven by the compression pressure in the compression accumulator and that in the combustion chamber. When considering the friction and load, FPA could still achieve a stable vibration after a few cycles’ adjustment whether the input energy is equal to the consumed energy or not. The vibration characteristics are different when FPA vibrates in the compression stroke and the expansion stroke, which is the unique feature of the single-piston HFPE.

Effects of adding alcohols on ZSM-12 synthesis

This work systematically studies on adding alcohols to alter the crystal growth behavior of ZSM-12, using 1-propanol (1P), 2-propanol (2P), ethylene glycol (EG), 1,3-propanediol (PD), 1,6-hexanediol (HD), diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (TTEG) as co-solvents. The effects of co-solvent content, temperature, and excess mineralizer content were studied as well. Except 2P, all other co-solvents are observed to tune the crystal morphology into a discrete round-shape. Except DEG and TTEG, all other co-solvents promote the crystallization rate of MTW phase, verified by larger zeolite crystal size in SEM images. The observation is corroborated with the formation of cristobalite, possibly via Ostwald ripening mechanism. The finding enlightens us using a lower synthesis temperature to attain high purity MTW phase, with an adequate amount of co-solvents. It is noteworthy that using HD as co-solvent facilitate the anisotropic growth of MTW crystals along the b-axis (2θ of 8.5°), possibly due to the effect of co-solvent’s hydrophobicity as well as the backbone length. The blue shift of symmetric and asymmetric Si-O vibration modes in FTIR spectra implies that TEG and HD are incorporated within the ZSM-12 pore structure. This work provides potential synthetic route to form anisotropic ZSM-12 membranes with preferred orientation.

Coherent electron hole dynamics near a conical intersection.

The coherent evolution of an electron hole in a photoionized molecule represents an unexplored facet of charge transfer phenomena occurring in complex systems. Using ultrafast extreme ultraviolet spectroscopy, we investigate the real-time dynamics of an electron hole wave packet created near a conical intersection in CO_{2}. We resolve the oscillation of the electron hole density between σ and π character, driven by the coupled bending and asymmetric stretch vibrations of the molecule. We also quantify the mixing between electron hole configurations and find that the wave packet coherence diminishes with time due to thermal dephasing.

Dimorphic cerium(III) oxoarsenate(III) Ce[AsO3

Colourless, water- and air-stable single crystals of cerium(III) oxoarsenate(III) Ce[AsO3] were prepared by the reaction of cerium metal (Ce) and arsenic sesquioxide (As2O3) in the presence of cesium chloride (CsCl) as fluxing agent at 750 °C in an evacuated silica ampoule. Ce[AsO3] crystallizes monoclinically (a = 902.89(8), b = 782.54(7), c = 829.68(7) pm, β = 103.393(3)°, Z = 8) in the space group P21/c and is isotypic with α-Pb[SeO3]. There are two crystallographically different Ce3+ positions. (Ce1)3+ is coordinated by nine oxygen atoms (d(Ce–O) = 244–286 pm) and (Ce2)3+ by only eight (d(Ce–O) = 239–273 pm). Both crystallographically different As3+ cations form discrete ψ1 tetrahedra [AsO3]3− (d(As–O) = 174–179 pm), which are attached to the Ce3+ cations via edges and corners. The second monoclinic modification of Ce[AsO3] with the lattice parameters a = 439.32(4), b = 529.21(5), c = 617.34(6) pm and β = 105.369(3)° with Z = 2 was obtained by high-pressure synthesis (11 GPa, 1200 °C) and has both a higher density (6.31 vs. 6.13 g · cm−3) and a higher calculated Madelung part of the lattice energy (15,155 vs. 15,132 kJ · mol−1). It adopts the space group P21/m, crystallizing isotypically with La[AsO3], β-Pb[SeO3], Pb[SO3] (scotlandite) or K[ClO3] and exhibits nine-fold coordinated Ce3+ cations exclusively (d(Ce–O) = 254–287 pm) along with tripodal [AsO3]3− anions (d(As–O) = 175–176 pm). Raman spectroscopy on both phases of Ce[AsO3] shows stretching vibrations between 769 and 731 cm−1 as well as asymmetric vibrations in the range of 659–617 cm−1. The symmetric bending mode vibrations emerge in an interval from 340 to 410 cm−1 and the asymmetric bending modes range between 230 and 290 cm−1.

Spectroscopy and picosecond dynamics of aqueous NO2

We investigate the formation of aqueous nitrogen dioxide, NO2 formed through femtosecond photolysis of nitrate, NO₃⁻ and nitromethane CH3NO2(aq). Common to the experiments is the observation of a strong induced absorption at 1610 ± 10 cm(-1), assigned to the asymmetric stretch vibration in the ground state of NO2. This assignment is substantiated through isotope experiments substituting (14)N by (15)N, experiments at different pH values, and by theoretical calculations and simulations of NO2-D2O clusters.

Autonomous Magnetoelastic Biosentinels for the Detection and Capture of Invasive Pathogens

This paper investigates the use of self-propelled magnetoelastic (ME) biosentinels to seek out and capture pathogenic bacteria in a stagnant liquid. These ME biosentinels are composed of an asymmetric-shaped ME resonator coated with a filamentous landscape phage that specifically binds with the pathogen of interest. When a time-varying magnetic pulse is applied, the ME biosentinels can be placed into mechanical resonance by magnetostriction. The resultant asymmetric vibration then generates a net force on the surroundings and hence generates autonomous motion in the liquid. As soon as the biosentinels find and bind with the target pathogen through the phage-based biomolecular recognition, a change in the biosentinel’s resonant frequency occurs, and thereby the presence of the target pathogen can be detected. In order to actuate the ME biosentinels into mechanical resonance of a desired mode, modal analysis using the three-dimensional finite element method was first performed, followed by determination of the resonant frequency. In addition, the net force due to the asymmetric vibration was calculated, and the resultant motion of the biosentinels was simulated. Both dynamic simulation and experimental results showed that the ME biosentinels can move autonomously through the liquid and actively bind with the target pathogen.

Lattice thermal expansion of the solid solutions (La1 − xSmx)2Ce2O7

A series of solid solutions with the general formula (La1−xSmx)2Ce2O7 (0.0≤x≤1.0) were prepared by the coprecipitation–calcination method. The products obtained were characterized by powder X-ray diffraction for phase purity. It was observed that La3+ and Sm3+ can form complete solid solution in (La,Sm)2Ce2O7 with defect-fluorite-type phase. The unit cell parameters of these solutions were calculated by a least squares method and the lattice parameters decreased linearly as x increased. The lattice thermal expansion behavior of (La1−xSmx)2Ce2O7 (0.0≤x≤1.0) was investigated by high-temperature X-ray diffraction in the temperature range 298–1623K. The lattice parameters aT of all the solutions at different temperature can be expressed as aT=a+bT+cT2. As x<1, the thermal expansion has a sudden decrease at ca. 473K. The coefficients of lattice thermal expansion of Sm2Ce2O7 were 10.2–13.6×10−6K−1 from 298 to 1623K, and without the thermal contraction at low temperature. The materials show positive or negative thermal expansion due to the asymmetric anharmonic vibration.

Collective vibrations of water-solvated hydroxide ions investigated with broadband 2DIR spectroscopy

The infrared spectra of aqueous solutions of NaOH and other strong bases exhibit a broad continuum absorption for frequencies between 800 and 3500 cm(-1), which is attributed to the strong interactions of the OH(-) ion with its solvating water molecules. To provide molecular insight into the origin of the broad continuum absorption feature, we have performed ultrafast transient absorption and 2DIR experiments on aqueous NaOH by exciting the O-H stretch vibrations and probing the response from 1350 to 3800 cm(-1) using a newly developed sub-70 fs broadband mid-infrared source. These experiments, in conjunction with harmonic vibrational analysis of OH(-)(H2O)n (n = 17) clusters, reveal that O-H stretch vibrations of aqueous hydroxides arise from coupled vibrations of multiple water molecules solvating the ion. We classify the vibrations of the hydroxide complex by symmetry defined by the relative phase of vibrations of the O-H bonds hydrogen bonded to the ion. Although broad and overlapping spectral features are observed for 3- and 4-coordinate ion complexes, we find a resolvable splitting between asymmetric and symmetric stretch vibrations, and assign the 2850 cm(-1) peak infrared spectra of aqueous hydroxides to asymmetric stretch vibrations.

Substituent effect on supramolecular motifs in series of succinimide polycyclic keto derivatives – Spectroscopic, theoretical and crystallographic studies

The substituent effect on the supramolecular arrangement in a series of polycyclic monoimide keto derivatives crystals was studied. Single crystal X-ray diffraction and IR spectroscopic experiments were performed for seven related compounds, as well as the Hirshfeld surface analysis and quantum chemical calculations at HF and DFT levels in vacuo, in solution and for small clusters. The presence of CO group at the bridge of the main hydrocarbon skeleton implied the catemer motif of the NimideH⋯Oimide hydrogen bond in case of smaller substituents (H, MeO, EtO). For more voluminous groups (iBuO) or additional hydrogen bond acceptors (AcO, O) the steric hindrance increased and the imide⋯imide interactions were no longer present in the solid state. The NimideH⋯Oketo or NimideH⋯Oester hydrogen bonds were formed instead. The binding energy per one NH⋯O interaction calculated for supramolecular clusters at HF/6-31G(d,p) level was ca. 20kJmol−1, indicating moderate strength of this hydrogen bond. The solvation free energies and induced dipole moments were computed at B3LYP/6-311+G(d,p) level using the integral equation formalism model (IEF PCM) considering three solvents of various polarity: non-polar chloroform, polar aprotic dimethyl sulfoxide (DMSO) and polar protic water. The relations between the vibrational spectra and the crystal structure have been discussed. The following sequence of carbonyl stretching modes in IR spectra has been derived from quantum chemical calculations: (1) at the highest frequencies – the symmetric vibration of two imide CO bonds, (2) the vibrations of keto CO bonds attached directly to the polycyclic hydrocarbon skeleton, (3) the asymmetric vibration of two imide CO bonds, and (4) at the lowest frequencies – the vibration of ester CO group. The characteristic peaks observed in imide experimental IR spectra at about 3080cm−1 have been explained as overtone and combination bands of νCO stretching and γNH out-of-plane bending vibrations.