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- 摘要
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Exploring approximate geometries of minimum energy conical intersections by TDDFT calculations
摘要： An approach is proposed to obtain approximate geometries for minimum energy conical intersections between the ground and first excited singlet electronic states (S0/S1-MECIs) using the time-dependent density functional theory (TDDFT). This approach uses the energy shift method to avoid discontinuities on TDDFT potential energy surfaces around conical intersections. It is shown numerically that the approximate S0/S1-MECIs of benzene and naphthalene obtained by this approach qualitatively reproduce the geometries and energies of the S0/S1-MECIs obtained by multireference theories. Moreover, the performance of the present approach when combined with an automated MECI searching method is examined through applications to benzene and naphthalene.
关键词： energy shift method,time dependent density functional theory,gradient projection,single component artificial force induced reaction,conical intersection,global reaction route mapping
更新于2025-09-23 15:23:52
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Photoinduced collective mode, inhomogeneity, and melting in a charge-order system
摘要： We theoretically investigate photoresponses of a correlated electron system upon stimuli of a pulsed laser light. Real-time dynamics of an interacting spinless fermion model on a one-dimensional chain, as a model of charge order (CO), are numerically simulated using the time-dependent Hartree-Fock method. In particular, we discuss the differences between two situations as the initial state: the homogeneous order and the presence of a domain wall, i.e., a kink structure embedded in the CO bulk. Coherent dynamics are seen in the former case: When the frequency of the pump light ωp is varied, along with single particle excitations across the CO gap (ΔCO), the resonantly-excited collective phase mode near ωp ≈ ΔCO/2 efficiently destabilizes CO. In clear contrast, in the latter case, when ωp is tuned at such in-gap frequencies and the intensity of light is sufficiently large, inhomogeneity spreads out from the kink to the bulk region through kink creations. Moreover, even stronger intensity induces the inhomogeneous melting of CO where the CO gap is destroyed.
关键词： photoinduced phase transition,charge order,collective mode,inhomogeneity,time-dependent Hartree-Fock method
更新于2025-09-23 15:23:52
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Intracortical neural stimulation with untethered, ultrasmall carbon fiber electrodes mediated by the photoelectric effect
摘要： Objective: Neural stimulation with tethered, electrically activated probes is damaging to neural tissue and lacks good spatial selectivity and stable chronic performance. The photoelectric effect, which converts incident light into electric potential and heat, provides an opportunity for a tetherless stimulation method. We propose a novel stimulation paradigm that relies on the photoelectric effect to stimulate neurons around a free-floating, ultrasmall (7-8μm diameter) carbon fiber probe. Methods: A 2-photon microscope induced photo-stimulation with a laser. Chronoamperometry and chronopotentiometry were used to characterize the electrochemical properties of photo-stimulation, while the fluorescence of Rhodamine-B was used to quantify temperature changes. Results: Photo-stimulation caused a local cathodic potential pulse with minimal leakage current. Stimulation induced voltage deflections of 0.05 - 0.4V in vitro, varying linearly with the power of the laser source (5 – 40 mW). Temperature increases in the immediate vicinity of the electrode were limited to 2.5°C, suggesting that this stimulation modality can be used without inducing heat damage. Successful stimulation was supported in vivo by increased calcium fluorescence in local neurons at stimulation onset in a transgenic GCaMP-3 mouse model. Furthermore, cells activated by photo-stimulation were closer to the electrode than in electrical stimulation under similar conditions, indicating increased spatial precision. Conclusion: Our results support the hypothesis that the proposed photoelectric method is effective for neural stimulation. Significance: Photoelectric stimulation is precise and avoids the need for a potentially destructive tether, making it a promising alternative to electrical stimulation.
关键词： GCaMP,electrochemistry,neuromodulation,photovoltaic effect,2-photon microscopy,temperature-dependent,fluorescence
更新于2025-09-23 15:23:52
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Alkyl chains length dependent fluorescence emission and reversible mechanofluorochromism of AIEE-based quinoline derivatives
摘要： Five quinoline derivatives containing different alkyl chains (QLACn, n ? 2, 4, 6, 8, 12) were synthesized to investigate the effect of alkyl chains on their photophysical properties. The ?uorescent properties of the QLACn were affected by the alkyl chains, which indicated obvious blue-shifting trend and ?uorescence emission are alkyl chains length-dependent by grinding-induced spectral shifts (DlMFC). Longer alkyl-length revealed larger DlMFC. Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) measurements indicated that the transformation between microcrystalline and amorphous states upon external stimuli should be responsible for the observed reversible MFC behavior.
关键词： Alkyl chains length-dependent behavior,Quinoline derivatives,Aggregation-induced emission enhancement (AIEE) behavior,Mechano?uorochromism behavior
更新于2025-09-23 15:23:52
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An efficient blind calibration method for nonlinearity mis-matches in <i>M</i>-channel TIADCs
摘要： As gain, offset, and timing mismatches, nonlinearity mismatches also contribute to spurious components which deteriorate TIADC’s performance. This paper proposes an efficient blind calibration method for nonlinearity mismatches in M-channel TIADCs. A modified model for nonlinearity mismatches is established by exploiting binary Hadamard transform (BHT) and differentiator. The calibration is composed of two stages—mismatches compensation and coefficients identification. The principle of mismatches compensation is to reconstruct estimations of the mismatches-induced spurious components and subtract them from the original TIADC’s output. The coefficients identification is performed based on filtered-x least mean square (FxLMS) algorithm. By using improved model and calibration algorithm, the proposed method consumes less computational resource according to the complexity comparison. To tackle the 4-order nonlinearity mismatches in an 16-channel TIADC, the proposed method consumes 23% fewer multipliers than the previous work. Simulation results reveal that both effective resolution and dynamic range improve a lot after calibration.
关键词： frequency-dependent nonlinearity mismatches,TIADC,filtered-x least mean square,binary Hadamard transform,differentiator
更新于2025-09-23 15:23:52
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Angular-Dependent Spontaneous Emission in Cholesteric Liquid Crystal Films
摘要： Due to the presence of a selective reflection band, cholesteric liquid crystals (CLCs) strongly modify the emission of fluorescent guest molecules. While emission along the helical axis is well understood, the emission properties at oblique angles with respect to the cholesteric helix have so far have not been explored in detail. We present a systematic study of the angular-dependent spontaneous emission properties of dye-doped cholesteric films, including a full Stokes analysis of the emitted light. Variation of the cholesteric pitch allows us to probe the effect of the photonic band structure on spontaneous emission in a wide angular range. We find exceptional angular-dependent intensity and polarization variations of the emitted light, and give experimental proof for the splitting of the first-order reflection band as well as its overlap with the second-order band at large detection angles.
关键词： and Hybrid Materials,Optical,Cholesteric Liquid Crystal,Stokes Analysis,Angular-Dependent,Plasmonics,Spontaneous Emission,Magnetic
更新于2025-09-23 15:23:52
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Imaging for Small UAV-Borne FMCW SAR
摘要： Unmanned aerial vehicle borne frequency modulated continuous wave synthetic aperture radars are attracting more and more attention due to their low cost and ?exible operation capacity, including the ability to capture images at different elevation angles for precise target identi?cation. However, small unmanned aerial vehicles suffer from large trajectory deviation and severe range-azimuth coupling due to their simple navigational control and susceptibility to air turbulence. In this paper, we utilize the squint minimization technique to reduce this coupling while simultaneously eliminating intra-pulse motion-induced effects with an additional spectrum scaling. After which, the modi?ed range doppler algorithm is derived for second order range compression and block-wise range cell migration correction. Raw data-based motion compensation is carried out with a doppler tracker. Squinted azimuth dependent phase gradient algorithm is employed to deal with azimuth dependent parameters and inexact deramping, with minimum entropy-based autofocusing algorithms. Finally, azimuth nonlinear chirp scaling is used for azimuth compression. Simulation and real data experiment results presented verify the effectiveness of the above signal processing approach.
关键词： FMCW,intra-pulse motion,Squinted Azimuth-dependent PGA,UAV SAR
更新于2025-09-23 15:23:52
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Dynamical distortions of structural signatures in molecular high-order harmonic spectroscopy
摘要： We study the signature of two-center interferences in molecular high-order harmonic spectra, with an emphasis on the spectral phase. With the help of both ab initio computations based on the time-dependent Schr?dinger equation and the molecular strong-field approximation (SFA) as developed by Chiril? et al. [Phys. Rev. A 73, 023410 (2006)] and Faria [Phys. Rev. A 76, 043407 (2007)], we observe that the phase behavior is radically different for the short and the long trajectory contributions. By means of Taylor expansions of the molecular SFA, we link this effect to the dynamics of the electron in the continuum. More precisely, we find that the value of the electric field at recombination time plays a crucial role in the shape of the destructive interference phase jump.
关键词： molecular spectroscopy,spectral phase,strong-field approximation,two-center interferences,time-dependent Schr?dinger equation,high-order harmonic generation
更新于2025-09-23 15:23:52
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Distance-Range-Oriented Constellation Design for VLC-SCMA Downlink with Signal-dependent Noise
摘要： In this paper, the constellation design for a sparse code multiple access (SCMA) based visible light communication (VLC) downlink is studied. The noise at the receiving avalanche photodiode (APD) is dependent on the signal intensity, and the associated design problems are typically intractable. We point out that for such a system both the minimum Euclidean distance (MED) and Rotated-MED based methods are not the optimal optimization objective, and propose a distance-range-oriented (DRO) modulation, where a linear combination of the minimum and maximum Euclidean distance is considered. We observe in the simulation results that the proposed DRO-based scheme outperform the MED and Rotated-MED based ones across a wide range of signal and noise levels.
关键词： distance range,signal-dependent noise,Constellation design,SCMA,visible light communication
更新于2025-09-23 15:22:29
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Structural, energetic and spectroscopic studies of new luminescent complexes based on 2-(2′-hydroxyphenyl)imidazo[1,2- <i>a</i> ]pyridines and 1,2-phenylenediboronic acid
摘要： Three new blue-luminescent complexes of selected imidazo[1,2-a]pyridine derivatives and 1,2-phenylenediboronic acid have been synthesized and structurally characterized using single-crystal X-ray diffraction. Additionally, the crystal structures of two of the (N,O)-donor compounds have been evaluated for the first time. The crystal packing and molecular motifs observed in the studied crystals have been thoroughly analysed, including computational studies, and are also discussed within the context of analogous systems reported in the literature. It appears that the new compounds form different crystal networks with regard to the asymmetric unit content and packing, although some similarities can be found. In all cases a typical centrosymmetric dimer bound via boronic acid groups is formed, characterized by an interaction energy of about -80 kJ mol-1, while the 2-(2'-hydroxyphenyl)imidazo[1,2-a]pyridine complex and its methoxy derivative form solvate structures, somewhat resembling the previously studied 8-oxyquinolinate analogues. As far as the spectroscopic properties are concerned, the lowest energy excitation observed in the studied complexes is based on the highest occupied molecular orbital–lowest unoccupied molecular orbital transition, and both these molecular orbitals are centred predominantly on the (N,O)-donor species according to the results of time-dependent density functional theory. Thus, the charge transfer observed for the 8-oxyquinolinate equivalents does not occur in these cases. Consequently, the spectroscopic behaviour of the series is very much comparable with that of the parent imidazo[1,2-a]pyridine derivatives, if the excited-state intramolecular proton-transfer process does not take place, as shown by the absorption and emission spectra collected in toluene and acetone solutions. Complexation causes a reduction in the Stokes shift compared with the respective (N,O)-donor molecules.
关键词： periodic calculations,TDDFT,UV–Vis spectroscopy,X-ray diffraction,time-dependent density functional theory,spectroscopic properties,luminescent boron complexes,transferred aspherical atom model (TAAM) refinement
更新于2025-09-23 15:22:29