Excited Surface Research Articles

Molecular Identification of the Transient Species Mediating the Deactivation Dynamics of Solvated Guanosine and Deazaguanosine.

Small structural alterations of the purine/pyrimidine core have been related to important photophysical changes, such as the loss of photostability. Similarly to canonical nucleobases, solute-solvent interactions can lead to a change in the excited state lifetimes and/or to the interplay of different states in the photophysics of these modified nucleobases. To shed light on both effects, we here report a complete picture of the absorption spectra and excited state deactivation of deoxyguanosine and its closely related derivative, deoxydeazaguanosine, in water and methanol through the mapping of the excited state potential energy surfaces and molecular dynamics simulations at the TD-DFT level of theory. We show that the N by CH exchange in the imidazole ring of deoxyguanosine translates into a small red-shift of the bright states and slightly faster dynamics. In contrast, changing solvent from water to methanol implies the opposite, i.e., that the deactivation of both systems to the ground state is significantly hindered.

Tunable Near-Field Radiative Effect in a Td – WTe2 Single Layer

In contrast to artificial metamaterials, natural two-dimensional (2D) hyperbolic materials are able to support higher electromagnetic confinement and stronger photonic density of states. This means natural 2D hyperbolic materials have fascinating potential for applications in thermal photonics. In this work, we investigate mechanisms of near-field thermal radiation (NFTR) in a ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$ single layer at the nanoscale using the fluctuation-dissipation theorem and density-functional theory. The results show that NFTR of ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$ can be 3 orders of magnitude larger than the blackbody limit. By using the photonic tunneling coefficient and the plasmon dispersion, we present a comprehensive study of plasmonic properties of ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$. Moreover, our first-principles calculations predict that application of a certain amount of mechanical stress can trigger topological transition between the elliptic and the hyperbolic surface states by regulating the Fermi surface and interband excitation threshold. Lastly, we systematically exhibit the evolution of surface plasmon polaritons in ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$ under mechanical stress and analyze the performance of using mechanical stress to modulate the corresponding NFTR. Our work explores the great potential of tunable radiative heat flux in ${\mathrm{T}}_{d}$--${\mathrm{WTe}}_{2}$, which is explained here through the peculiar nature of hyperbolic surface plasmons.

Miniature Otto Prism Coupler for Integrated Photonics

AbstractOne of the main issues in integrated photonics is the coupling of free‐space or optical fiber radiation to waveguides on the photonic chip surface. The ideal coupler is miniature, highly efficient, and provides a large number of addressable devices. Here, a new concept of 3D out‐of‐plane coupler is introduced, which is a microscale prism exploiting frustrated total internal reflection in the Otto configuration to excite surface electromagnetic waves or near‐surface waveguide modes. A method for designing the couplers operating at normal incidence is proposed and it is applied to excite Bloch surface waves (BSWs) in 1D photonic crystals. Polymer microprisms are printed using two‐photon laser lithography and allow transferring more than 40% of the incident light energy into BSWs. The couplers enable focusing BSWs simultaneously with their excitation. Advanced design prisms can provide nearly 100% efficiency, making the proposed concept an alternative to actual coupling concepts in integrated photonics.

Comment on “Understanding first-order Raman spectra of boron carbides across the homogeneity range”

The Raman spectra of boron carbide presented by Roma et al. are severely impaired by surface excitations. The reason is the inappropriate energy of the laser used in their spectrometer. Thus, the claimed correlation between point defects in the structure and the resonance peaks in their Raman spectra is highly questionable.

Turbulent flow thermal characteristics in a pipe with ring insert: An experimental and numerical study

Using obstacles inside the tube to improve thermal performance is one of the appropriate and new methods. In most research, stationary inserts have been used, and few studies examined the effect of rotating inserts. In the present work, experimental and numerical study for investigated influence of the obstacle rotational with 10 to 3000 rpm inside the pipe is done. To flow excitation, ring obstacles of complete and 90 ° are placed inside the pipe. Comparison of ring-90 deg with rotating and the complete stationary ring shows an increase of 1.37–1.803 times the coefficient of thermal performance at Re=6000 with the same excitation of the pipe surface. Experimental results showed that ring insert inside the tube at the range of rotating speed 300 to 600 rpm, the coefficient of thermal performance and the Nusselt number compared to the smooth pipe is changed in the range 0.88–2.1 and 2.6–4, respectively. The study demonstrated that using rings with lower angle ratios in rotation mode is an optimal choice and economical and, due to the uniformity of heat flux at the tube surface, better thermal performance than a complete stationary obstacle.

Excited States Computation of Models of Phenylalanine Protein Chains: TD-DFT and Composite CC2/TD-DFT Protocols.

The present benchmark calculations testify to the validity of time-dependent density functional theory (TD-DFT) when exploring the low-lying excited states potential energy surfaces of models of phenylalanine protein chains. Among three functionals suitable for systems exhibiting charge-transfer excited states, LC-ωPBE, CAM-B3LYP, and ωB97X-D, which were tested on a reference peptide system, we selected the ωB97X-D functional, which gave the best results compared to the approximate coupled-cluster singles and doubles (CC2) method. A quantitative agreement for both the geometrical parameters and the vibrational frequencies was obtained for the lowest singlet excited state (a ππ* state) of the series of capped peptides. In contrast, only a qualitative agreement was met for the corresponding adiabatic zero-point vibrational energy (ZPVE)-corrected excitation energies. Two composite protocols combining CC2 and DFT/TD-DFT methods were then developed to improve these calculations. Both protocols substantially reduced the error compared to CC2 and experiment, and the best of both even led to results of CC2 quality at a lower cost, thus providing a reliable alternative to this method for very large systems.

Improved LQG vibration control for multiple inputs of electric vehicle

To improve the ride comfort of electric vehicle, the vertical dynamic model of electric vehicle is established under the excitation of road surface and wheel hub motor. The road excitation is divided into random continuous road and convex road, and the influence of motor electromagnetic excitation on vibration is analyzed. To avoid the empirical value influence of each index weight coefficient on the main vibration control, the weight coefficient is determined by analytic hierarchy process (AHP), the LQG controller of vehicle active suspension is designed by using optimal control theory, and the comprehensive optimization of performance index is realized. The effectiveness of control effect is verified by comparing active and passive control based on single and double excitation.

Photochemistry in a capsule: controlling excited state dynamics via confinement.

Exerting control on excited state processes has been a long-held goal in photochemistry. One approach to achieve control has been to mimic biological systems in Nature (e.g., photosynthesis) that has perfected it over millions of years by performing the reactions in highly organized assemblies such as membranes and proteins by restricting the freedom of reactants and directing them to pursue a select pathway. The duplication of this concept at a smaller scale in the laboratory involves the use of highly confined and organized assemblies as reaction containers. This article summarizes the studies in the author's laboratory using a synthetic, well-defined reaction container known as octa acid (OA). OA, unlike most commonly known cavitands, forms a capsule in water and remains closed during the lifetime of the excited states of included molecules. Thus, the described excited state chemistry occurs in a small space with hydrophobic characteristics. Examples where the photophysical and photochemical properties are dramatically altered, compared to that in organic solvents wherein the molecules are freely soluble, are presented to illustrate the value of a restricted environment in controlling the dynamics of molecules on an excited state surface. While the ground state complexation of the guest and host is controlled by well-known concepts of tight-fit, lock and key, complementarity, etc., free space around the guest is necessary for it to be able to undergo structural transformations in the excited state, where the time is short. This article highlights the role of free space during the dynamics of molecules within a confined, inflexible reaction cavity.

Photoisomerization of phytochrome chromophore models: an XMS-CASPT2 study.

Phytochromes are a superfamily of photoreceptors that harbor linear tetrapyrroles as chromophores. Upon light illumination, the linear tetrapyrrole chromophore undergoes a double bond isomerization which starts a photocycle. In this work, we studied the photoisomerization of chromophore models designed based on the C- and D-rings of the phycocyanobilin (PCB) chromophore. In total, five different models with varying substitutions were investigated. Firstly, the vertical excitation energies were benchmarked using different computational methods to establish the relative order of the excited states. Based on these calculations, we computed the photoisomerization profiles using the extended multi-state (XMS) version of the CASPT2 method. The profiles were obtained for both the clockwise and counterclockwise rotations of the C15C16 bond in the Z and E isomers using a linear interpolation of internal coordinates between the Franck-Condon and MECI geometries. In the minimal chromophore model that lacks the substitutions at the pyrrole rings, the isomerization involves both C14-C15 and C15C16 bonds of the methine bridge between the C- and D-rings, resembling the hula-twist motion. The MECIs are characterized by a partial charge transfer between the two pyrrole rings pointing towards a twisted intramolecular charge transfer. Systematic introduction of substituents leads to an increase in the steric repulsion between the two pyrrole rings causing a pretwist of the dihedral around the C15C16 bond, which creates a preference for the counterclockwise isomerization. An introduction of the carbonyl group at the D-ring increases the extent of charge transfer which changes the isomerization mechanism from hula-twist to one-bond flip.

A computational scheme for evaluating the phosphorescence quantum efficiency: applied to blue-emitting tetradentate Pt(II) complexes.

Phosphorescent organic light-emitting diodes (PhOLEDs) are leading candidates for displays or lighting technologies. Recently, blue phosphorescent tetradentate Pt(II) complexes have been attracting extensive attention due to their high phosphorescence quantum efficiency and numerous chemical structures on account of flexible ligand frames and modifications. Using quantum chemistry coupled with our thermal vibration correlation function (TVCF) formalism, we investigated the triplet excited state energy surface and the decay processes involving both direct vibrational relaxation and minimum energy crossing point (MECP) via the transition state (3TS) to the ground state (S0) for 16 recently experimentally reported blue-emitting tetradentate Pt(II) emitters containing fused 5/6/6 metallocycles. We found that (i) in most cases, the direct vibrational relaxation deactivations dominated the triplet non-radiative decay because either the 3TS is too high or the MECP is not reachable. Hence, results from the TVCF formalism agreed well with the experiments for the phosphorescence quantum efficiency; (ii) only when both 3TS and MECP are low, for instance, for PtON1-oMe, deactivations via MECP dominated the triplet non-radiative decay.

Investigation of the excitations of plasmons and surface exciton polaritons in monoclinic gadolinium sesquioxide by electron energy-loss spectroscopy and plasmon spectroscopic imaging.

The monoclinic gadolinium sesquioxide (denoted as m-Gd2O3) with its lower crystal symmetry exhibits larger dielectric permittivity (κ) than the cubic Gd2O3 (denoted as c-Gd2O3). Recently, a few nanometers thick m-Gd2O3 thin film has been successfully epitaxially grown on a GaN substrate as a promising candidate gate oxide in metal-oxide-semiconductor field-effect transistors (MOSFETs). Thus, it is important to understand the electronic excitations in m-Gd2O3 and investigate them by electron energy loss spectroscopy (EELS) performed with aloof electron beams and electron diffraction to gain the spatial and momentum resolutions. In this study, using scanning transmission electron microscopy combined with EELS (STEM-EELS) in the aloof electron beam setup, we observed low-loss spectral features at 13 eV and 14.5 eV at the specimen edge in a grazing incidence and the material interior, which can be interpreted as a surface plasmon (SP) and a volume plasmon (VP), respectively. Surface exciton polaritons (SEPs), which represents surface resonances associated with excitonic onsets above the bandgap, were also observed at about 7, 10.2, and 36 eV energy loss. Their surface excitation character was confirmed by energy-filtered transmission electron microscopy spectrum imaging (EFTEM-SI) and using relativistic energy versus-momentum (E–k) map calculations. The momentum (q)-dependent EELS indicates that the SEP features near the bandgap represented a function of q and revealed a nondispersive behavior for VP and SEP at 36 eV. The oscillator strengths for VP and SEP at 36 eV dropped at different q values along with different q directions, revealing the anisotropic electronic structures of m-Gd2O3.

Analysis of the track system in bumpy unstructured hard road environment by vibration test

The complex terrain environment in the hilly land directly affects the operational reliability of agricultural robots. In order to study the impact of road irregularity on walking chassis vibration, the 3SYLZ-750 remote-controlled weeding machine which is applied to orchards was taken as the object of study, and the rear roller was selected as the object of observation to reveal the rules under which the vibration of the track chassis changes as there is a sudden change in road surface elevation. A column-type test-to-pass method based on unit excitation was proposed in this study. The excitation behavior and action process were analyzed by category. A critical acceleration prediction model was built and verified by virtual simulation and hard road surface excitation testing. The results showed that at the forward velocity of 0-2.5 km/h and exciter height of 20-100 mm, the vertical vibration acceleration of the target roller was significantly affected by Track Contact Point Centrifugal Acceleration (TCPCA). As TCPCA increased, the change rate of vertical vibration acceleration decreased, reaching a minimum of [−13.8, 28.8]; as TCPCA decreased, the vertical vibration acceleration tended to increase positively at a maximum variation range of [−13.3, 42.2]. The measured and simulated macroscopic change rules were consistent with the theoretical analysis, further verifying the correctness of variable extraction, and providing a research basis for the accurate modification and improvement of the model. The research conclusions can lay a theoretical foundation for analyzing the walking reliability of the track chassis, and provide a design basis and technical support for the development of a tracked agricultural robot chassis for the hilly land in the future. Keywords: track system, unstructured road, vibration test, simulation analysis, hilly land, agricultural robot DOI: 10.25165/j.ijabe.20221504.7249 Citation: Li M T, Li J L, He L, He J, Hu L, Lyu C X. Analysis of the track system in bumpy unstructured hard road environment by vibration test. Int J Agric & Biol Eng, 2022; 15(4): 163–171.

Body Leveling Control Model Establishment and Experiment Analysis

Highlights The vehicle body leveling control model based on tire stiffness and wheel centroid displacement is established in this article.The average pitch angle error is 7.94%, and the tilt angle average error is 4.37%.The body leveling control algorithm developed based on this model can be applied to the automatic leveling control of hilly tractors and cars.Abstract. The body leveling control system is the core part of the attitude control of the hilly mountain tractor. It calculates the body posture in real-time according to the body leveling control model and makes corresponding control strategies. The accuracy of the control model directly affects the vehicle leveling accuracy. This article proposes the leveling control model based on tire stiffness and tire mass displacement. The slope road surface excitation information is collected in the field, and the road surface excitation data is processed appropriately. The accurate road surface excitation information is obtained. The input of the simulation model is displacement data. However, the collected road excitation information is the acceleration signal. Thus, the acceleration signal is converted to the displacement signal through the frequency domain integration method. The comparison between the calculated calculation results and the experimentally acquired attitude data indicates that the average pitch angle error is 7.94%, and the average tilt angle error is 4.37%. Accordingly, the vehicle body leveling control model established in this article is compatible with the experimental results and can accurately output the body posture and develop the body tone. Keywords: Control, Hydraulic, Leveling, Pavement, Road

Nonequilibrium lateral force and torque by thermally excited nonreciprocal surface electromagnetic waves

We show that an isotropic dipolar particle in the vicinity of a substrate made of nonreciprocal plasmonic materials can experience a lateral thermal-fluctuations-induced force and torque when the particle's temperature differs from that of the slab and the environment. We connect the existence of the lateral force to the asymmetric dispersion of nonreciprocal surface polaritons and the existence of the lateral torque to the spin-momentum locking of such surface waves. Using the formalism of fluctuational electrodynamics, we show that the features of lateral force and torque should be experimentally observable using a substrate of doped indium antimonide (InSb) placed in an external magnetic field, and for a variety of dielectric particles. Interestingly, we also find that the directions of the lateral force and the torque depend on the constituent materials of the particles, which suggests a sorting mechanism based on nonequilibrium fluctuational electrodynamics.

Slide-free histological imaging by microscopy with ultraviolet surface excitation using speckle illumination

Microscopy with ultraviolet surface excitation (MUSE) is a promising slide-free imaging technique to improve the time-consuming histopathology workflow. However, since the penetration depth of the excitation light is tissue dependent, the image contrast could be significantly degraded when the depth of field of the imaging system is shallower than the penetration depth. High-resolution cellular imaging normally comes with a shallow depth of field, which also restricts the tolerance of surface roughness in biological specimens. Here we propose the incorporation of MUSE with speckle illumination (termed MUSES), which can achieve sharp imaging on thick and rough specimens. Our experimental results demonstrate the potential of MUSES in providing histological images with ∼ 1 μm spatial resolution and improved contrast, within 10 minutes for a field of view of 1.7 mm × 1.2 mm . With the extended depth of field feature, MUSES also relieves the constraint of tissue flatness. Furthermore, with a color transformation assisted by deep learning, a virtually stained histological image can be generated without manual tuning, improving the applicability of MUSES in clinical settings.

Efficient mid-infrared wavelength converter based on plasmon-enhanced nonlinear response in graphene nanoribbons

Graphene plasmons with enhanced localized electric field have been used for boosting the light–matter interaction in linear optical nano-devices. Meanwhile, graphene is an excellent nonlinear material for several third-order nonlinear processes. We present a theoretical investigation of the mechanism of plasmon-enhanced third-order nonlinearity susceptibility of graphene nanoribbons. It is demonstrated that the third-order nonlinearity susceptibility of graphene nanoribbons with excited graphene surface plasmon polaritons can be an order of magnitude larger than the intrinsic susceptibility of a continuous graphene sheet. Combining these properties with the relaxed phase matching condition due to the ultrathin graphene, we propose a novel plasmon-enhanced mid-infrared (MIR) wavelength converter with arrays of graphene nanoribbons. The wavelength of signal light is in the MIR range, which can excite the tunable surface plasmons polaritons in arrays of graphene nanoribbons. The efficiency of the converter from MIR to near-infrared wavelength can be remarkably improved by 60 times compared with a graphene sheet without graphene plasmons. This work provides a novel idea for the efficient application of graphene in nonlinear optical nano-devices. The proposed MIR wavelength converter is compact, tunable and has promising potential in graphene-based MIR detectors with high detection efficiency.

Efficient Nonlinear Aeroservoelastic Modeling for Morphing Wing with Bilinear Stiffness

In this paper, a novel nonlinear aeroservoelastic modeling methodology for a morphing wing with bilinear stiffnesses in hinge joints is proposed to investigate the nonlinear aeroservoelastic behaviors during the morphing process efficiently. The notable advantage is that the bilinear nonlinearity in hinge joints and the variation of morphing configuration is modeled theoretically using a parameterized fictitious mode approach. The nonlinear, parameter-varying aeroservoelastic system is represented by piecewise-linear modal-based aeroservoelastic equations according to the different combinations of nonlinear parameters in hinge joints. The proposed nonlinear aeroservoelastic modeling methodology can efficiently investigate aeroservoelastic frequency responses, nonlinear aeroservoelastic vibration, and closed-loop stability because the nonlinear aeroservoelastic model is built via the parameterized fictitious modal coordinates, which can represent the bilinear structural stiffness and variation of morphing parameter simultaneously. To demonstrate the modeling accuracy and efficiency of the present method, a folding wing with two bilinear stiffnesses due to backlash in inboard and outboard hinge joints is selected as a test case. The numerical results show that the open-loop and closed-loop nonlinear behaviors of the morphing wing at different folding configurations can be efficiently investigated. Also, the chaotic phenomenon of the morphing wing subject to control surface excitation was firstly found.

Physical and Chemical Properties of Wolf–Rayet Planetary Nebulae

Abstract Wolf–Rayet ([WR]) and weak-emission-line (wels) central stars of planetary nebulae (PNs) have hydrogen-deficient atmospheres, whose origins are not well understood. In the present study, we have conducted plasma diagnostics and abundance analyses of 18 Galactic PNs surrounding [WR] and wels nuclei, using collisionally excited lines (CELs) and optical recombination lines (ORLs) measured with the Wide Field Spectrograph on the Australian National University 2.3 m telescope at the Siding Spring Observatory complemented with optical archival data. Our plasma diagnostics imply that the electron densities and temperatures derived from CELs are correlated with the intrinsic nebular Hβ surface brightness and excitation class, respectively. Self-consistent plasma diagnostics of heavy-element ORLs of N2+ and O2+ suggest that a small fraction of cool (≲7000 K), dense (∼104–105 cm−3) materials may be present in some objects, though with large uncertainties. Our abundance analyses indicate that the abundance discrepancy factors (ADFs ≡ ORLs/CELs) of O2+ are correlated with the dichotomies between forbidden-line and He i temperatures. Our results likely point to the presence of a tiny fraction of cool, oxygen-rich dense clumps within diffuse warm ionized nebulae. Moreover, our elemental abundances derived from CELs are mostly consistent with asymptotic giant branch models in the range of initial masses from 1.5 to 5 M ⊙. Further studies are necessary to understand better the origins of abundance discrepancies in PNs around [WR] and wels stars.

Surface and volume phonon polaritons in a uniaxial hyperbolic material: optic axis parallel versus perpendicular to the surface.

Uniaxial hyperbolic materials enable excitation of phonon polaritons with utrahigh wavevectors that have been shown to be promising for many optical and thermal radiative applications and thus have attracted much attention recently. However, the characteristics of surface and volume phonon polaritons excited with uniaxial hyperbolic materials that exhibit in-plane anisotropy or in-plane isotropy have not been discussed thoroughly and some issues have so far remained elusive. In this paper, we conducted a comprehensive investigation on surface and volume phonon polaritons in a bulk or a thin slab of hexagonal boron nitride (hBN). We clarified the excitation, characteristics and topology of surface and volume phonon polaritons in such a uniaxial hyperbolic material. In particular, we showed that hyperbolic surface phonon polaritons (HSPhPs) can exist in the Type I hyperbolic band of hBN with confined wavevectors when the optic axis (OA) is parallel to the surface. For a thin hBN slab, we revealed a split of HSPhPs and a smooth transition between HSPhPs and HVPhPs in the Type II hyperbolic band. Furthermore, we also identified non-Dyakonov surface phonon polaritons excited without evanescent ordinary waves. These findings may extend the understanding of phonon polaritons in hyperbolic materials and offer new theoretical guidance for the design of infrared optical devices with hyperbolic materials.

Geometric Control Over the Edge Diffraction of Electrically Excited Surface Plasmon Polaritons by Tunnel Junctions

Plasmonic metal–insulator–metal tunnel junctions (MIM-TJs) readily excite surface plasmon polaritons (SPPs) by inelastic electron tunneling, well below the diffraction limit, eliminating the need for bulky optical elements. The highly confined MIM cavity mode (MIM-SPP) excited by the tunneling electrons dominantly outcouples to photons and single-interface SPPs which further outcouple as photons and give characteristic features in the Fourier plane of observation. Here, we employ SPP waveguides, directly integrated with MIM-TJs, to explore the diffraction of single-interface SPPs at the edges of the metal stripe waveguides. In addition to the leakage of the SPP modes through the metal electrodes, SPP edge diffraction presents as an additional channel for SPP outcoupling, not limited by the thickness of the waveguide. Edge diffraction manifests as a straight-line feature in the Fourier plane of the far-field and by systematically varying the width of the waveguides, we show that the in-plane momentum of the SPPs can be controlled, which in turn leads to control over the edge diffraction. We fabricated MIM-TJs with integrated plasmonic stripe waveguides of different widths, and the propagation and confinement of the SPP modes along the edges of the SPP waveguides are directly identified by the experimental back focal plane imaging, which are further corroborated by numerical simulations. Our findings can be exploited for applications ranging from sensing to nonlinear plasmonics, where focusing and localization of SPP fields are necessary.