Non-reactive Mode Research Articles

Quantum dynamical effects of vibrational strong coupling in chemical reactivity

Recent experiments suggest that ground state chemical reactivity can be modified when placing molecular systems inside infrared cavities where molecular vibrations are strongly coupled to electromagnetic radiation. This phenomenon lacks a firm theoretical explanation. Here, we employ an exact quantum dynamics approach to investigate a model of cavity-modified chemical reactions in the condensed phase. The model contains the coupling of the reaction coordinate to a generic solvent, cavity coupling to either the reaction coordinate or a non-reactive mode, and the coupling of the cavity to lossy modes. Thus, many of the most important features needed for realistic modeling of the cavity modification of chemical reactions are included. We find that when a molecule is coupled to an optical cavity it is essential to treat the problem quantum mechanically to obtain a quantitative account of alterations to reactivity. We find sizable and sharp changes in the rate constant that are associated with quantum mechanical state splittings and resonances. The features that emerge from our simulations are closer to those observed in experiments than are previous calculations, even for realistically small values of coupling and cavity loss. This work highlights the importance of a fully quantum treatment of vibrational polariton chemistry.

Investigation of the magnetron balancing effect on the ionized flux fraction and deposition rate of sputtered titanium species for the high-power impulse magnetron sputtering pulses of different lengths

The study is focused on the impact of different magnetic field configurations of a high-power impulse magnetron sputtering (HiPIMS) in a nonreactive mode on the film precursors. Ionized flux fraction and total flux deposited onto the substrate were measured with the magnetic quartz crystal microbalance probe placed in front of the target racetrack. Particularly, we investigated the degree of magnetron balancing and the geometry of the magnetic field above the Ti target surface (4 in. diameter), as crucial factors influencing the thin film deposition, for different HiPIMS pulse lengths. Three unbalanced (II type) magnetron configurations have been chosen for this study: two symmetric geometries—with a regular magnetic field (B parallel to the target about 80 and 35 mT) and one asymmetric (highly unbalanced) magnetron configuration with an intermediate magnetic field (B parallel to the target about 48 mT). The HiPIMS was operated keeping constant the peak current at 43 A for C0-E0 and C10-E0 B-field configurations and a lower value, 33 A, when operating in C10-E10 configuration. In addition to the peak current, the pulse frequency was kept constant at 100 Hz but the pulse length (power on-time, Ton) was varied from 50 up to 100 μs. Obviously, the pulse power and the average power continuously increase with the length of the pulse. The results reveal a significant difference in the trends of the deposition rate and ionized flux fraction reaching the substrate with respect to the degree of balancing of the magnetron. It was found that the ionized fraction of metal arriving at the substrate reaches its maximum for the pulse length between Ton ≈ 70–80 μs in both symmetric cases, with strong and weak magnetic fields. The ionized fraction of Ti atoms in the asymmetric configuration increased in all measured range with the pulse length and the growth rate has a smooth increase.

Tribological properties of ZrN coatings deposited by magnetron sputtering in reactive and non-reactive mode

Zirconium and zirconium nitride coatings were deposited via magnetron sputtering by using high-purity zirconium or zirconium nitride targets. As a particularity, the zirconium nitride coatings were deposited by using a ZrN target via non-reactive mode or by using a Zr target via reactive technique, in argon/nitrogen environment. Depending on the time deposition, coatings with different thicknesses (200, 500 and 1000 nm) have been obtained. Chemical and phase composition, thickness of the coating and morphology of the surfaces were investigated by highly sensitive X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and X-Ray diffraction (XRD). The wear tests have been performed by High Frequency Reciprocating Rig (HFRR). The wear scar diameters decrease with an increase of coatings thickness, while the friction coefficient for the coatings with 500 nm thickness revealed the lowest values for friction coefficients, for all type of coatings

Dynamically Operated Fischer-Tropsch Synthesis in PtL-Part 1: System Response on Intermittent Feed

Society is facing serious challenges to reduce CO2 emissions. Effective change requires the use of advanced chemical catalyst and reactor systems to utilize renewable feedstocks. One pathway to long-term energy storage is its transformation into high quality, low-emission and CO2-neutral fuels. Performance of technologies such as the Fischer-Tropsch reaction can be maximized using the inherent advantages of microstructured packed bed reactors. Advantages arise not only from high conversion and productivity, but from its capability to resolve the natural fluctuation of renewable sources. This work highlights and evaluates a system for dynamic feed gas and temperature changes in a pilot scale Fischer-Tropsch synthesis unit for up to 7 L of product per day. Dead times were determined for non-reactive and reactive mode at individual positions in the setup. Oscillating conditions were applied to investigate responses with regard to gaseous and liquid products. The system was stable at short cycle times of 8 min. Neither of the periodic changes showed negative effects on the process performance. Findings even suggest this technology’s capability for effective, small-to-medium-scale applications with periodically changing process parameters. The second part of this work focuses on the application of a real-time photovoltaics profile to the given system.

Synthesis, Microstructural, and Mechano-Tribological Properties of Self-Lubricating W-S-C(H) Thin Films Deposited by Different RF Magnetron Sputtering Procedures

Carbon-alloyed transition metal dichalcogenide (TMD) coatings have great potential for providing a good tribological response in diverse operating environments. There are different ways to synthesize these coatings by magnetron sputtering, with no clear indication of the best possible route for potential upscaling. In this study, tungsten-sulfur-carbon (W-S-C) coatings were deposited by radio frequency (RF) magnetron sputtering via four different methods. All coatings were sub-stoichiometric in terms of the S/W ratio, with the bombardment of the growing film with backscattered Ar neutrals being the main mechanism governing the S/W ratio. The crystallinity of the films was dependent on the C and S contents. X-ray photoelectron spectroscopy (XPS) revealed W-S and W-C bonding in all coatings. Raman spectroscopy showed the presence of an a-C phase with predominant sp2 bonding. The hardness of the coatings may be related to the C content and the S/W ratio. A friction coefficient of 0.06–0.08 was achieved during sliding in ambient air by the coatings deposited in non-reactive mode with optimal C contents. The results indicate that sputtering in non-reactive mode should be the method of choice for synthesis of these coatings.

Comparison of in-situ oxide formation and post-deposition high temperature oxidation of Ni-aluminides synthesized by cathodic arc evaporation

Thin coatings were synthesized by cathodic arc evaporation of powder metallurgically fabricated Al-Ni targets with the chemical compositions of Al75Ni25, Al67Ni33 and Al52Ni48 atomic percent. The coatings were produced both either from pure metallic vapour or in reactive oxygen atmosphere. Phase transformations and chemical composition at the target surface were investigated by X-ray diffraction (XRD) and by energy-dispersive X-ray spectroscopy (EDS) techniques and compared with the phases composition obtained in the coating. The deposition in non-reactive mode produces intermetallic coatings containing different Ni aluminides. The formation of the aluminides can be controlled by the target composition and is by trend predictable from the Al-Ni phase diagram. The coatings produced in reactive mode are composed of both Al3Ni and Al3Ni2 with the additional formation of AlNi and Al2NiO4 in all the coatings. The coatings composed of intermetallics show high indentation hardness in the range of 10 GPA while the coatings composed of both oxides and intermetallics demonstrate exceptional high hardness of about 30GPa. All coatings have been annealed in ambient air up to 1200°C and were investigated by in-situ XRD analysis in order to follow in detail their oxidation process. For all coatings, the formation of α-Al2O3 and Al2NiO4 could be observed after annealing forming a thin high temperature stable protective layer for remaining AlNi. The coatings deposited in reactive atmosphere contain additional NiO, independently of their original composition.

Simulation of CO 2 concentrations at Tsukuba tall tower using WRF-CO 2 tracer transport model

Simulation of carbon dioxide (CO2) at hourly/weekly intervals and fine vertical resolution at the continental or coastal sites is challenging because of coarse horizontal resolution of global transport models. Here the regional Weather Research and Forecasting (WRF) model coupled with atmospheric chemistry is adopted for simulating atmospheric CO2 (hereinafter WRF-CO2) in nonreactive chemical tracer mode. Model results at horizontal resolution of 27 × 27 km and 31 vertical levels are compared with hourly CO2 measurements from Tsukuba, Japan (36.05°N, 140.13 oE) at tower heights of 25 and 200 m for the entire year 2002. Using the wind rose analysis, we find that the fossil fuel emission signal from the megacity Tokyo dominates the diurnal, synoptic and seasonal variations observed at Tsukuba. Contribution of terrestrial biosphere fluxes is of secondary importance for CO2 concentration variability. The phase of synoptic scale variability in CO2 at both heights are remarkably well simulated the observed data (correlation coefficient >0.70) for the entire year. The simulations of monthly mean diurnal cycles are in better agreement with the measurements at lower height compared to that at the upper height. The modelled vertical CO2 gradients are generally greater than the observed vertical gradient. Sensitivity studies show that the simulation of observed vertical gradient can be improved by increasing the number of vertical levels from 31 in the model WRF to 37 (4 below 200 m) and using the Mellor–Yamada–Janjic planetary boundary scheme. These results have large implications for improving transport model simulation of CO2 over the continental sites.

Reactivity at different levels of cognitive analysis: products versus operations.

C reactivity refers to the extent to which a (mild) negative or sad mood reactivates or triggers negative cognitive factors as observed in clinical depression.1 In this issue, Figueroa and colleagues2 report that cognitive reactivity, as measured by the Leiden Index of Depression Sensitivity (LEIDS), is a long-term predictor of depressive relapse. The authors highlight that 1 important avenue for future research is to examine whether psychological interventions can improve (ie, decrease or reduce) cognitive reactivity scores. I would like to bring to the authors’ and readers’ attention a recent study by Van der Gucht and colleagues,3 which examined that very question while providing preliminary evidence that psychological treatment can indeed reduce cognitive reactivity. In a study that offered a mindfulnessbased intervention to low-income urban adults, cognitive reactivity was measured 4 times using the LEIDS: twice before the intervention (double baseline with 8-week waiting-list period in-between), immediately after the 8-week mindfulness-based intervention (postintervention), and 3 months after treatment completion (follow-up). Cognitive reactivity scores significantly improved from pretreatment to follow-up with a medium effect size (d = 0.69). Importantly, no change in cognitive reactivity scores was observed during the waiting-list interval. That mindfulness-based interventions help reduce cognitive reactivity levels makes sense, as their central aim is to tackle cognitive reactivity by helping people to recognize mood-dependent reactive tendencies and to switch to a nonreactive mode of mind.4 An earlier study by Kuyken and colleagues5 found that mindfulness-based intervention completers showed higher levels of cognitive reactivity than controls, but here, cognitive reactivity was solely assessed postintervention. Also, and most interestingly, the authors used a moodinduction procedure with assessment of pre–post change in dysfunctional cognitions and not the LEIDS to examine cognitive reactivity.5 Figueroa et al2 rightly argue in this issue that a mood-induction procedure might not be a very stable method to assess cognitive reactivity, which would then explain the opposite results as reported by Van der Gucht and

Mechanism and Experimental Observability of Global Switching Between Reactive and Nonreactive Coordinates at High Total Energies.

We present a mechanism of global reaction coordinate switching, namely, a phenomenon in which the reaction coordinate dynamically switches to another coordinate as the total energy of the system increases. The mechanism is based on global changes in the underlying phase space geometry caused by a switching of dominant unstable modes from the original reactive mode to another nonreactive mode in systems with more than 2 degrees of freedom. We demonstrate an experimental observability to detect a reaction coordinate switching in an ionization reaction of a hydrogen atom in crossed electric and magnetic fields. For this reaction, the reaction coordinate is a coordinate along which electrons escape and its switching changes the escaping direction from the direction of the electric field to that of the magnetic field and, thus, the switching can be detected experimentally by measuring the angle-resolved momentum distribution of escaping electrons.

Mathematical modelling of ideal and non-ideal continuous stirred tank bioreactor using simulated solution

BACKGROUND Chemostats are characterized by an increase in viscosity of the reaction broth and are prone to non-ideality. The present study is mainly focused on the identification of non-idealities, namely dead zone and bypassing of a real chemostat or continuous stirred tank bioreactor. RESULTS Experimental studies were conducted in non-reactive mode to study the hydrodynamic characteristics of a real chemostat involving Lactobacillus sp. isolated from Indian curd. The influence of change of relative viscosity on non-ideality parameters was studied. A simulated solution of PVA having the same viscosity range as the growth medium of Lactobacillus sp. were used to understand the hydrodynamic behavior of the reactor by conducting residence time distribution (RTD) experiments in non-reacting mode. Both steady and unsteady state analyses have been carried out with variation of the two main process parameters, namely dilution rate and substrate concentration. CONCLUSION A clear portrait of the comparison between non-ideal and ideal systems has been cited here, and it was observed that the real or non-ideal system lags behind the ideal one in many aspects. The present study adds to the knowledge of biochemically reacting systems. © 2014 Society of Chemical Industry

Taming a wandering attention: short-form mindfulness training in student cohorts

Mindfulness training (MT) is a form of mental training in which individuals engage in exercises to cultivate an attentive, present centered, and non-reactive mental mode. The present study examines the putative benefits of MT in University students for whom mind wandering can interfere with learning and academic success. We tested the hypothesis that short-form MT (7 h over 7 weeks) contextualized for the challenges and concerns of University students may reduce mind wandering and improve working memory. Performance on the sustained attention to response task (SART) and two working memory tasks (operation span, delayed-recognition with distracters) was indexed in participants assigned to a waitlist control group or the MT course. Results demonstrated MT-related benefits in SART performance. Relative to the control group, MT participants had higher task accuracy and self-reported being more “on-task” after the 7-week training period. MT did not significantly benefit the operation span task or accuracy on the delayed-recognition task. Together these results suggest that while short-form MT did not bolster working memory task performance, it may help curb mind wandering and should, therefore, be further investigated for its use in academic contexts.

Bond and mode selectivity in the OH + NH2D reaction: a quasi-classical trajectory calculation

A state-to-state dynamics study was performed to analyze the effects of vibrational excitation on the dynamics of the OH + NH2D gas-phase reaction, which are connected to issues such as bond and mode selectivity. This reaction can evolve along two channels: H-abstraction, H2O(ν) + NHD(ν); and D-abstraction, HOD(ν) + NH2(ν). Based on an analytical potential energy surface previously developed by our group, quasi-classical trajectory calculations and subsequent normal mode analysis were performed. While vibrational excitation of the NH-sym mode of NH2D slightly favours H-abstraction over the D-abstraction, vibrational excitation of the ND mode shows that there is no clear preference for the H- or D-abstraction. These results show that this reaction does not exhibit bond selectivity, suggesting a breakdown of the spectator model. For H-abstraction, vibrational excitation of the non-reactive ND mode is partially retained in the NHD product; and for D-abstraction, excitation of the non-reactive NH mode is also partially retained in the products, indicating that this reaction exhibits mode selectivity only partially. In sum, we rule out bond and mode selectivity for this reaction. All these results were interpreted on the basis of strong coupling between modes along the reaction path, a behaviour which seems to be more the general tendency than the exception in polyatomic reactions.

New liquid chromatography: Mass spectrometry assay for natural phytoestrogens from vegetable extracts

Summary A new liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for the quantification of seven isoflavones (daidzin, genistin, ononin, daidzein, glycitein, genistein, and formononetin) and coumestrol in vegetable extracts was developed. The separation was performed on a Zorbax SB-C18 column with a mixture of methanol (solvent A) and 0.1% (υ/υ) acetic acid in water (solvent B) under gradient conditions at 50°C with a flow rate of 1 mL min−1. The detection of analytes was performed by electrospray ionization, negative ionisation, in non-reactive MS2 mode for aglycons or in reactive MS2 mode for glycosides. The method shows a good linearity (r2 > 0.9948) over the concentration range of 40–4000 ng mL−1 for all analytes, a good precision (CV < 11%) and accuracy (<10%). The method was successfully applied to quantify the isoflavones and coumestrol in vegetable extracts obtained from red clover (Trifolium pratense L., Fabaceae) and dyer's greenweed (Genista tinctoria L., Fabaceae) and can be used in the chemical characterization of vegetables with phytoestrogen content.

Structural and photoelectrochemical properties of Ti1−xWxO2 thin films deposited by magnetron sputtering

W-doped titanium dioxide is a promising candidate material for applications ranging from UV–VIS light photocatalytic reactions to catalyst support in proton-exchange membrane fuel cells, depending on the doping content. The present study reports on the possibility to synthesize substitutional Ti1−xWxO2 thin films with 0≤x≤1 by magnetron co-sputtering from Ti and W metallic targets. Two routes were investigated starting from 1) crystalline titanium tungsten alloys deposited in non-reactive (pure Ar) mode, and 2) amorphous titanium tungsten oxides deposited in reactive (Ar+O2 atmosphere) mode. The structure and phase stability after air annealing at 550°C has been investigated by X-ray Diffraction (XRD). X-ray Reflectivity (XRR) was used to determine the change in film mass density upon annealing. Films of the non-reactive mode series could not be successfully fully oxidized into Ti1−xWxO2 form. For the reactive mode film series, ternary Ti1−xWxO2 oxides were obtained after air annealing and the crystal structure was changed from anatase to rutile with increasing W content in the range 0–33at.%. Films with higher W content (0.33<x≤1) eventually crystallized in the WO3 triclinic structure. Photo-electrodes were elaborated from the deposited thin films on FTO coated glass, and they all showed photo-response when tested in acid solution, under UV–VIS illumination. Among the doped materials, the Ti0.92W0.08O2 thin film showed the highest photo-current.

Study of a HPPMS discharge in Ar/O2 mixture: I. Discharge characteristics with Ru cathode

High power pulsed magnetron sputtering discharges have been actively studied during the last ten years in order to achieve high ionization fraction of sputtered species. These sputtering discharges begin to be well understood in non-reactive mode. However, very few works have been devoted to studying reactive conditions. We report results obtained for these discharges working in an Ar/O2 mixture, with a preionization system to accelerate the current pulse rising. A Ru target was used for deposition of RuO2 conductive oxide. This paper discusses the role played by the presence of oxygen on both the preionization phase and the high current discharge characteristics. A comparison is made of results obtained in an Ar/O2 mixture with those obtained in pure argon. Emphasis is laid on the influence of the O2 flow rate and of the total Ar/O2 mixture pressure. It is observed that the O2 content in the inlet gas mixture strongly affects the preionization phase by the electron attachment to O2 as well as the high current discharge development.

Self-organized localization of macrostates by additive noise in a fast-slow dynamical system: effect of the slow nonreactive mode on the barrier crossing rate of the fast, bistable mode

We have studied the stochastic dynamics of a two-dimensional gradient system composed of a fast, bistable mode and a slow, monotonically decaying mode. The coupling is bidirectional and cooperative. Additive white noise acts on the fast mode only. We find that the noise intensity controls the location of macrostates (shape of the probability density function), the appearance of bimodality in the slow-mode probability distribution and, together with the coupling strength, the rate of fast-mode barrier crossing. These features arise from the interplay of noise, widely separated time scales, and bidirectional, excitatory coupling. They are believed to be generic.

Properties of tungsten and vanadium oxides deposited by MSIP–PVD process for self-lubricating applications

The tungsten and vanadium oxides are known to be usable as solid lubricants at elevated temperatures. So far they have been used mainly as powdery materials for tribological applications or as a component of ceramics. Metal oxides are interesting for tribological insets at atmospheric conditions because of their oxidation stability. This study reports on investigations to find stable process windows for the deposition of tungsten and vanadium oxides in a reactive and non-reactive mode by the magnetron sputter ion plating–PVD-process. One focus of the study is the metal oxide phases generated in the MSIP-process under various conditions and their mechanical and metallographic properties. Coatings were deposited and analyzed by various testing methods to characterize the mechanical and structural properties, such as SEM, scratch-testing, Rockwell test, nanoindentation and XRD. Stable process windows will be presented for the reactive mode as well as the influence of different process parameters to phase generation, microstructure and the material properties. The influence of process-parameters on the deposition rate (d.c. versus r.f. mode, reactive versus non-reactive mode) is of great interest to evaluate the economic relevance. It will be shown that it is possible to deposit vanadium and tungsten oxides despite target contamination effects in wide ranges by adapting the reactive gas-flow, the total gas pressure and the target power.

Activated rate processes in many dimensions: energy diffusion with slow adjustment of a nonreactive mode

Activated rate processes in two dimensions are studied analytically under the condition of weak friction on the reactive mode (energy diffusion) and high friction on the nonreactive coordinate. It is found that the process scenario and, as a consequence, the escape kinetics crucially depend on the strength of the mode coupling. When the coupling is strong the energy diffusion does not manifest itself. The kinetics is single-exponential with a rate constant independent of the friction on the reactive mode. For moderate mode coupling the energy diffusion plays an important role. Different process scenarios and, hence, the kinetics can be realized depending on the strength of friction on the both modes. Both multiexponential decay and single-exponential kinetics are possible. The latter may take place either when particles escape via the saddle on the potential surface (the traditional escape scenario) or when particles escape on a path that avoids the saddle point.

Kramers theory of chemical reactions in a slowly adjusting environment

When describing the reaction dynamics in a slowly relaxing environment, one has to include slow nonreactive modes of the environment in an explicit consideration along with the “chemical” mode intrinsically responsible for the chemical transformation. This is done within the framework of the Kramers approach to condensed phase chemical reaction dynamics. The problem is studied under the condition of high friction of the nonreactive mode (slow adjustment) while friction of the chemical mode covers the whole range from weak to high friction. It is found that the reaction dynamics and, hence, the kinetics depend strongly on the strength of the coupling of the reactive and the nonreactive modes. For strong mode coupling the rate constant monotonically decreases with the increase of the friction of the chemical mode. Such behavior is quite distinctive from one for fast adjustment of the environment when the rate constant demonstrates a turnover behavior. Turnover behavior takes place for moderate strength mode coupling. This case has its own interesting specific features: (1) When friction of the chemical mode tends towards zero, the reaction rate remains finite due to the energy diffusion of the chemical mode induced by the motion of the nonreactive mode. (2) For a certain range of the friction coefficients particles escape the reactant domain on a path that avoids the saddle on the potential surface. This saddle-point avoidance is accompanied by violation of the Arrhenius law in the sense that the activation energy becomes a function of the friction intensity. (3) There is a range of the friction coefficients, where the kinetics is multiexponential. Analytical expressions for the rate constant are obtained for those conditions when the kinetics is single exponential. They show how the rate constant depends on the friction coefficients as well as on the parameters of the potential surface.

Numerical test of Kramers reaction rate theory in two dimensions

The Fokker–Planck–Kramers equation for a system composed by a reactive coordinate x coupled to a solvent coordinate y is employed to study the effect of additional degrees of freedom on the dynamics of reactive events. The system is studied numerically in the diffusional regimes of both coordinates, for different topologies of the bistable potential function and anisotropies of friction. The eigenvalue spectrum is evaluated by representing the time evolution operator over a basis set of orthonormal functions. A detailed analysis of the effect of the explicit consideration of the slow nonreactive mode is carried on to show that a variation of qualitative picture (scenario) of the reaction dynamics occurs when friction along different directions is strongly anisotropic, depending also on the structure of the two-dimensional potential surface. The numerical study supports both the qualitative picture of the reaction dynamics and the rate constant expressions obtained analytically. For those cases where the Langer theory has a restricted range of applicability because of the change in the reaction dynamics scenario, this fact has been numerically demonstrated. Here the Langer expression for the rate constant is replaced by the one obtained as a result of the consideration of the effective one-dimensional problem along the solvent coordinate, characterized by a smaller activation energy than that in the initial problem. All of these facts were confirmed by the numerical test, which shows a satisfactory agreement with the analytical results.