Configuration Transition Research Articles

Interactions investigated by the spectroscopic, microscopic and molecular docking studies for liquid crystal-based biosensor

ABSTRACT The interactions between liquid crystal (LC) 4´-pentyl-4-biphenylcarbonitrile and protein bovine serum albumin are investigated to develop an LC-based biosensor. Various techniques, such as polarising optical microscopy, Raman spectroscopy, and molecular docking method, are used for analysing these interactions. The change in the alignment of LC molecules in the presence of bovine serum albumin results in the director configuration transition. This transfiguration of the director of LC molecules, when it undergoes a change from radial to bipolar configuration, confirms the detection of albumins under polarising optical microscopy. The limit of detection is also determined from this study. The Raman spectra are deconvoluted to calculate the spectral parameters, namely peak position, linewidth, and integrated intensity. The variation of these parameters with concentration and temperature is discussed, pertaining to the changes in orientational ordering and inter/intramolecular interactions. The active binding sites, active residues and binding energy are calculated by molecular docking analysis. The active binding residues of albumins involved in the docking with liquid crystal are further confirmed using Raman spectroscopy.

Application of environmentally friendly amphoteric polyacrylamide hydrophobically modified with plant oil as additive in water-based drilling fluid

Hydrophobic associating polymers show great potential in formulation of high-performance drilling fluids, due to their hydrophobic associative ability in high-temperature and high-salt conditions. Herein, a novel amphoteric polyacrylamide of poly(acrylamide/2-acrylamido-2-methyl-1-propanesulfonic acid/methylacrylethyl trimethylammonium chloride) hydrophobically modified with epoxidized soybean oil denoted as PAADE was prepared and applied in water-based drilling fluid, and one without hydrophobic modification (PAAD) was also used for comparison. Compared with PAAD, PAADE displayed characteristic association behavior with a critical association concentration (CAC) of 0.3 w/v%, and a salt thickening phenomenon over 3 w/v% NaCl concentration. The impacts of PAADE and PAAD on rheological and filtration properties of bentonite-based drilling fluid (BTDF) were evaluated under different salinity. The fitted Herschel-Bulkley rheological parameters indicated that BTDF containing PAADE showed stronger yield stress, easier flowability and better salt resistance at a reasonable concentration below CAC. Meanwhile, PAADE largely reduced the fluid loss of BTDF before and after thermal aging at 150°C, showing high temperature tolerance. The addition of NaCl promoted larger reduction of filtration. The superior properties of PAADE in BTDF were revealed to be the competitive results of salt-induced hydrophobic association and inter-particles configuration transition. Moreover, the incorporation of epoxidized soybean oil improved the biodegradability of PAADE.

Singularity Loci, Bifurcated Evolution Routes, and Configuration Transitions of Reconfigurable Legged Mobile Lander From Adjusting, Landing, to Roving

AbstractThis paper presents the reconfigurable legged mobile lander (ReLML) with its modes from adjusting, landing, to roving. Based on the invented metamorphic variable-axis revolute hinge, the actuated link has three alternative phases of rotating around either of two orthogonal topological axes or locking itself to the base as a rigid body. This property enables the ReLML to switch among three modes and within two driving states (as the adjusting and roving modes are active mechanisms driven by motors, while the landing truss is regarded as a passive mechanism driven by the touchdown impact force exerted on footpad). The unified differential kinematics for the ReLML is established by the screw-based Jacobian modeling, unifying both active and passive operation phases throughout all modes. Afterward, the distributions of workspaces and singularity loci in three modes are discussed for the multi-solution sake, and the selection principle of the practicable solution pattern is proposed to obtain the actual workspace, singularity loci, and configurations. The results stemming from the Jacobian-matrix-based method and the Grassmann-geometry-based method give mutual authentication. Finally, as prospects for promising applications, four bifurcated evolution routes and configuration transitions are figured out and compared.

Bottom-Up Assembled Photonic Crystals for Structure-Enabled Label-Free Sensing.

Photonic crystals (PhCs) display photonic stop bands (PSBs) and at the edges of these PSBs transport light with reduced velocity, enabling the PhCs to confine and manipulate incident light with enhanced light–matter interaction. Intense research has been devoted to leveraging the optical properties of PhCs for the development of optical sensors for bioassays, diagnosis, and environmental monitoring. These applications have furthermore benefited from the inherently large surface area of PhCs, giving rise to high analyte adsorption and the wide range of options for structural variations of the PhCs leading to enhanced light–matter interaction. Here, we focus on bottom-up assembled PhCs and review the significant advances that have been made in their use as label-free sensors. We describe their potential for point-of-care devices and in the review include their structural design, constituent materials, fabrication strategy, and sensing working principles. We thereby classify them according to five sensing principles: sensing of refractive index variations, sensing by lattice spacing variations, enhanced fluorescence spectroscopy, surface-enhanced Raman spectroscopy, and configuration transitions.

On the compound sessile drops: configuration boundaries and transitions

Abstract

Sapphire α−Al2O3 puzzle: Joint μSR and density functional theory study

Sapphire $(\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3})$ has been investigated by the muon spin rotation $(\ensuremath{\mu}\mathrm{SR})$ method in several experiments in the past. The main $\ensuremath{\mu}\mathrm{SR}$ component is a diamagnetic-like signal with a fast relaxation. Because of this diamagnetic-like behavior, the signal was assigned to either positively charged muonium $({\mathrm{Mu}}^{+})$ or negatively charged muonium $({\mathrm{Mu}}^{\ensuremath{-}})$, but neither of the two assignments was satisfactory (the so-called ``sapphire puzzle''). We have proposed that the signal is due to a weakly paramagnetic muonium configuration (transition state) which is formed during the reaction of muonium with the host lattice. In the present paper, we report new experimental data on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ and discuss these and earlier data in the ${\mathrm{Mu}}^{\ensuremath{-}}$ and in the transition state model. Calculations based on density functional theory were also performed with detailed findings on the energetics of the different muonium configurations and their migration energies. We conclude that the transition state model is more plausible than the ${\mathrm{Mu}}^{\ensuremath{-}}$ model, but the ${\mathrm{Mu}}^{\ensuremath{-}}$ interpretation cannot be excluded completely. In addition, the evidence is presented that the bare muon performs local motion but no long-range diffusion below room temperature in the microsecond time range.

Online reconfiguration of regularity-based resource partitions in cyber-physical systems

We consider the problem of resource provisioning for real-time cyber-physical applications in an open system environment where there does not exist a global resource scheduler that has complete knowledge of the real-time performance requirements of each individual application that shares the resources with the other applications. Regularity-based Resource Partition (RRP) model is an effective strategy to hierarchically partition and assign various resource slices among the applications. However, RRP model does not consider changes in resource requests from the applications at run time. To allow for the run time adaptation to resource requirement changes, we consider in this paper the issues in online resource partition reconfiguration, including semantics issues that arise in configuration transitions that may cause application failures. Based on the reconfiguration semantics, we study the online resource reconfigurability problem under the RRP model where the availability factors of resource partitions may be reconfigured at run time. We formalize and solve the Dynamic Partition Reconfiguration (DPR) problem for uniform environment where the minimal intervals assigned to each task for execution on each resource are the same. Extensive experiments have been conducted to evaluate the performance of the proposed approaches in different scenarios. We also present a case study using the autonomous F1/10 model car; the controller of the F1/10 car requires resource adaptation to satisfy the computing needs of its PID controller and vision system under different operating conditions. Our implementation demonstrates the effectiveness and benefit of online resource partition reconfiguration using the proposed approach in a real-world cyber-physical system.

Enhancement of electromagnetically induced transparency and absorption signals in 85Rb atomic vapor medium by using a small external magnetic field

In the present work, a theoretical and experimental study to enhance electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) signals in an 85 R b atomic vapor medium at room temperature is conducted. Also, switching from EIT to EIA signal at a particular value of the magnetic field is observed. Further, by using circularly polarized coupling light, the dispersion profile of the linearly polarized probe signal is investigated theoretically and experimentally. The nine-level system of 85 R b D2 transition in a ladder-type configuration is fully solved by using the density matrix theory. The simulated results are found in good qualitative agreement with experimental observations. Hence, an experimental setup is developed for (1) achieving enhanced EIT and EIA signal, (2) switching from EIT to EIA, and (3) dispersion measurement. These observations have potential applications towards measurement of the group velocity of light, quantum memory, quantum information, and optical switching.

Influence of failure mechanism on seismic bearing capacity factors for shallow foundations near slopes

The bearing capacity of shallow foundations may decrease when located near slopes, particularly under seismic conditions. However, there is limited work that isolates the destabilising influences of seismicity and finite slope geometry on ultimate bearing capacity in terms of conventional bearing capacity factors. Herein, analytical solutions based on upper-bound kinematic limit analysis are used to isolate both the mechanism of failure and bearing capacity factors (Nc, Nγ and Nq) for shallow foundations near slopes subject to seismic action without using principles of superposition. The analytical solutions of ultimate seismic bearing capacity show good agreement and accuracy compared with numerical results. Seismic bearing capacity factors are assessed considering transitions in failure mechanism, soil properties and finite configurations of slope and footing geometry. The results presented demonstrate significant non-linearity in bearing capacity factors that have not been previously demonstrated, primarily owing to the transition in governing mechanism with geometry, shear strength or seismic loading. This study shows that the isolation of bearing capacity factors without superposition is possible considering slope and footing geometry, and is greatly influenced by the failure mechanism.

Packing of stiff rods on ellipsoids: Geometry.

We suggest a geometrical mechanism for the ordering of slender filaments inside nonisotropic containers, using cortical microtubules in plant cells and the packing of viral genetic material inside capsids as concrete examples. We show analytically how the shape of the cell affects the ordering of phantom elastic rods that are not self-avoiding (i.e., self-crossing is allowed). We find that for oblate cells, the preferred orientation is along the equator, while for prolate spheroids with an aspect ratio close to 1, the orientation is along the principal (long axis). Surprisingly, at a high enough aspect ratio, a configurational phase transition occurs and the rods no longer point along the principal axis, but at an angle to it, due to high curvature at the poles. We discuss some of the possible effects of self-avoidance using energy considerations. These results are relevant to other packing problems as well, such as the spooling of filament in the industry or spider silk inside water droplets.

Atomic vibration as an indicator of the propensity for configurational rearrangements in metallic glasses.

In a metallic glass (MG), the propensity for atomic rearrangements varies spatially from location to location in the amorphous solid, making the prediction of their likelihood a major challenge. One can attack this problem from the "structure controls properties" standpoint. But all the current structure-centric parameters are mostly based on local atomic packing information limited to short-range order, hence falling short in reliably forecasting how the local region would respond to external stimuli (e.g., temperature and/or stress). Alternatively, one can use indicators informed by physical properties to bridge the static structure on the one hand, and the response of the local configuration on the other. A sub-group of such physics-informed quantities consists of atomic vibration parameters, which will be singled out as the focus of this article. Here we use the Cu64Zr36 alloy to systematically demonstrate the following two points, all using a single model MG. First, we show in a comprehensive manner the interrelation among common vibrational parameters characterizing the atomic vibrational amplitude and frequency, including the atomic mean square displacement, flexibility volume, participation fraction in the low-frequency vibrational modes and boson peak intensity. Second, we demonstrate that these vibrational parameters fare much better than purely static structural parameters based on local geometrical packing in providing correlation with the propensity for local configurational transitions. These vibrational parameters also share a correlation length similar to that in structural rearrangements induced by external stimuli. This success, however, also poses a challenge, as it remains to be elucidated as to why short-time dynamical (vibrational) behavior at the bottom of the energy basin can be exploited to project the height of the energy barrier for cross-basin activities and in turn the propensity for locally collective atomic rearrangements.

The first order L-G phase transition in liquid Ag and Ag-Cu alloys is driven by deviatoric strain

An undercooled liquid-phase (L-phase) can undergo a first order configurational phase transition to either a crystal phase (X-phase) or a metastable, configurationally heterogeneous, rigid glassy phase (G-phase). To investigate the underlying mechanism of the L-G transition, we employ molecular dynamics simulations to study G-phase formation in a binary Cu-Ag system. We find that G-phase formation is driven by the reduction of local distortion energy arising from deviatoric strains in the liquid phase and demonstrate its local distribution. Reduction of distortion energy contributes over 80% of the latent heat of the L-G transition, suggesting that condensation of spatially varying random elastic fields in the liquid is primarily responsible for the first order L-G transition. By applying this analysis to crystallization and G-phase formation in elementary Ag, we show that deviatoric strain energy is the dominant driving force for the L-G and L-X transition also in the case of the pure metal.

Magnetic ground state of the ordered double-perovskite Sr2YbRuO6 : Two magnetic transitions

Comprehensive muon spin rotation/relaxation (muSR) and neutron powder diffraction (NPD) studies supported via bulk measurements have been performed on the ordered double perovskite Sr2YbRuO6 to investigate the nature of the magnetic ground state. Two sharp transitions at TN1 ~ 42 K and TN2 ~ 36 K have been observed in the static and dynamic magnetization measurements, coinciding with the heat capacity data. In order to confirm the origin of the observed phase transitions and the magnetic ground state, microscopic evidences are presented here. An initial indication of long-range magnetic ordering comes from a sharp drop in the muon initial asymmetry and a peak in the relaxation rate near TN1. NPD confirms that the magnetic ground state of Sr2YbRuO6 consists of an antiferromagnetic (AFM) structure with interpenetrating lattices of parallel Yb3+ and Ru5+ moments lying in the ab-plane and adopting a A-type AFM structure. Intriguingly, a small but remarkable change is observed in the long-range ordering parameters at TN2 confirming the presence of a weak spin reorientation (i.e. change in spin configuration) transition of Ru and Yb moments, as well as a change in the magnetic moment evolution of the Yb3+ spins at TN2. The temperature dependent behaviour of the Yb3+ and Ru5+ moments suggests that the 4d-electrons of Ru5+ play a dominating role in stabilizing the long range ordered magnetic ground state in the double perovskite Sr2YbRuO6 whereas only the Yb3+ moments show an arrest at TN2. The observed magnetic structure and the presence of a ferromagnetic interaction between Ru- and Yb- ions are explained with use of the Goodenough-Kanamori-Anderson (GKA) rules. Possible reasons for the presence of the second magnetic phase transition and of a compensation point in the magnetization data are linked to competing mechanisms of magnetic anisotropy.

Parameter-correlation study on shock–shock interaction using a machine learning method

To predict the maximum heating load induced by shock–shock interaction more reliably and accurately, the geometrical scale of the overall wave configuration of shock–shock interaction is very useful. However, it is hard to be solved with traditional shock theory due to its complexity. The results of numerical and experimental studies are case-by-case. Concise formulas correlating the geometrical scales of shock–shock interaction with the given flow parameters are desired but still unavailable. In the present work, a set of correlative formulas for the triple-points' coordinates of type IVa, IV, and III shock–shock interaction are derived by multilevel block building algorithm, a functional machine learning method. The key flow structure of shock–shock interaction, i.e., the supersonic impinging jet, can be determined with the help of shock theories and the formulas. In addition, the transition criteria respectively for the overall wave configuration transitions of type IVa ↔ type IV and type IV ↔ type III shock–shock interaction can be obtained by the machine learning based method.

Protein Microgel-Stabilized Pickering Liquid Crystal Emulsions Undergo Analyte-Triggered Configurational Transition.

Herein, we report a novel approach that involves Pickering stabilization of micometer-sized liquid crystal (LC) droplets with biocompatible soft materials such as a whey protein microgel (WPM) to facilitate the analysis of analyte-induced configurational transition of the LC droplets. The WPM particles were able to irreversibly adsorb at the LC-water interface, and the resulting WPM-stabilized LC droplets possessed a remarkable stability against coalescence over time. Although the LC droplets were successfully protected by a continuous network of the WPM layer, the LC-water interface was still accessible for small molecules such as sodium dodecyl sulfate (SDS) that could diffuse through the meshes of the adsorbed WPM network or through the interfacial pores and induce an LC response. This approach was exploited to investigate the dynamic range of the WPM-stabilized LC droplet response to SDS. Nevertheless, the presence of the unadsorbed WPM in the aqueous medium reduced the access of SDS molecules to the LC droplets, thus suppressing the configuration transition. An improved LC response to SDS with a lower detection limit was achieved after washing off the unadsorbed WPM. Interestingly, the LC exhibited a detection limit as low as ∼0.85 mM for SDS within the initial WPM concentration ranging from 0.005 to 0.1 wt %. Furthermore, we demonstrate that the dose-response behavior was strongly influenced by the number of droplets exposed to the aqueous analytes and the type of surfactants such as anionic SDS, cationic dodecyltrimethylammonium bromide (DTAB), and nonionic tetra(ethylene glycol)monododecyl ether (C12E4). Thus, our results address key issues associated with the quantification of aqueous analytes and provide a promising colloidal platform toward the development of new classes of biocompatible LC droplet-based optical sensors.

Coherent forward-scattering spectra of Cs I 852.1-nm with a light-emitting diode and a diode laser in a Voigt configuration

The coherent forward scattering (CFS) spectra of Cs I 852.1-nm line was measured using a CFS spectrometer in a Voigt configuration with an electromagnet and temperature-controlled Cs gas cell. A light-emitting diode (LED) and a diode laser (DL) were used as broadband and narrowband light sources, respectively. The relation of the CFS intensity and external magnetic field (B) was log–log plotted. Results showed that the CFS signal intensities depend on B to the power of 1.69 ± 0.38 and 1.51 ± 0.06 for DL and LED, respectively. A higher external magnetic field should be favorable when a broadband light source is used. However, the CFS signal decreased with an LED source as B approached 300 mT. To explain this observation, the hyperfine Paschen–Back splitting pattern of the Cs I 852.1-nm transition was calculated. The decrease in the CFS signal was caused by the level-crossing of π- and σ-components of the Cs I 852.1-nm transition in a Voigt configuration.

A DFT Study of N2O Homogeneous and Heterogeneous Reduction Reaction by the Carbon Monoxide

ABSTRACT The mechanism of N2O homogeneous and heterogeneous reactions with CO were investigated using density functional theory (DFT). The M06-2X method with the 6–311 G(d) basis set were adopted for geometry optimization and energy calculations of each configuration (reactants, intermediates, transition states and products). Thermodynamic and kinetic analyzes were also conducted to study the influence of temperature on the reaction process. Calculation results showed that there are two channels for the homogeneous reaction between N2O and CO. In addition, the heterogeneous reduction reaction of N2O and CO has two possible reaction pathways due to the different adsorption configurations of CO on char surface. From thermodynamic analysis, the enthalpy difference (ΔH) and Gibbs free energy difference (ΔG) of the homogeneous and heterogeneous reactions are both negative, which indicates that the reaction of N2O and CO is an exothermic process and can take place spontaneously. For the both homogeneous and heterogeneous reactions between N2O and CO, the equilibrium constant of the N2O and CO reaction is always higher than 105 at 800 ~ 1800 K, suggesting that the reaction can be carried out completely. From the kinetic analysis, activation energy of the heterogeneous reaction (137.26 kJ/mol) is much lower than that of the homogeneous reactions (224.53 kJ/mol and 215.89 kJ/mol), which indicates that the reduction reaction of N2O with CO is more likely to take place on char surface. The calculation results explain the reaction mechanism of N2O and CO, which can provide a theoretical foundation for N2O emission.

Preparation and controlled properties of temperature/photo dual sensitive polymers by facile Ugi reaction

In this investigation, we described a facile preparation of temperature/photo dual sensitive polymers (PGABs) by Ugi four-component polymerization (Ugi-4CP) at room temperature in “one-pot” method using glutaraldehyde, 4-amido-azobenzene, t-butyl isocyanide and carboxyl-end-capped polyethylene glycols (S-PEG) as monomers. PGABs were found to be reversibly sensitive to the temperature in salt solution, and their lower critical solution temperatures (LCST) can be tuned to the range of 17.2–68.4 °C by changing the structure of PGABs, sort and concentration of salt. The configuration transition of PGABs between cis-form and trans-form was reversibly induced by the alternating radiation at 365 and 254 nm. The rate and conversion of isomerization showed a remarkable dependence on the chemical structure of PGAB. By the photosensitivity, the LCST of PGAB-800 is further regulated in 1.0 °C change because of the hydrophilicity difference of cis-trans-azobenzene moiety. Through the combination of the thermosensitivity and photosensitivity, the particles of PGABs with nano/μm dimension were successfully controlled by the light radiation and temperature change.

Oxidation State Assignments in the Organoplatinum One‐Electron Redox Series [(N^N)PtMes2]n, n = +,0, –,2‐

The neutral complexes [(N^N)PtMes2], N^N = bis(1‐methyl‐2‐imidazolyl)ketone (bik) or N,N'‐disubstituted 1,2‐bis‐iminoacenaphthenes (R‐BIAN), Mes = mesityl, were obtained and characterized as PtII species with planar N2PtC2 configuration and charge transfer transitions in the visible. Reversible one‐electron reduction produces radical anion complexes with the spin predominantly localized in the N^N ligand, according to EPR, UV/Vis‐IR spectroelectrochemistry, DFT and TD‐DFT studies. Reversible one‐electron oxidation was also possible, attributed to the steric and electronic influence from the mesityl ligands. The EPR silent cation [(bik)PtMes2]+ was characterized by UV/Vis‐NIR spectroscopy and TD‐DFT calculations as a system with spin density contributions from Pt (31 %) and two mesityl groups (69 %).

Mechanism, Chemoselectivity, and Stereoselectivity of NHC‐Catalyzed Asymmetric Desymmetrization of Enal‐Tethered Cyclohexadienones

Density functional theory calculations were performed to study the mechanism, chemoselectivity, and stereoselectivity for the N‐heterocyclic carbene (NHC)‐catalyzed asymmetric desymmetrization of enal‐tethered cyclohexadienones. The results showed that the whole reaction includes nucleophilic addition, homoenolate intermediate generation, Michael addition, protonation, esterification, and catalyst elimination. Protonation and esterification were demonstrated to be mediated by AcOH/AcO–, in stark contrast to the experimental speculation that MeOH provided the proton. The Michael addition step determined the chemoselectivity and stereoselectivity. The observed β‐chemoselectivity was attributed to the hydrogen‐bond and favorable π–π interaction in the β‐addition transition states. Moreover, the β‐addition transition state with (S,R,S)‐configuration was most stable, in agreement with the experimental results that the product derived from this structure was preferentially generated. Further noncovalent interaction analysis showed that stronger π–π interaction between cyclohexadienones and the NHC catalyst, as well as C–H···π interactions, made the (S,R,S)‐configuration transition state the most energetically favored.