Search

A novel technique is proposed for refining the spectral regulation of chirped fiber Bragg gratings (CFBGs) during the fabrication process, utilizing an ultraviolet (UV) laser with a chirped phase mask. By incorporating an additional phase into the Hamming window function, a new laser control function is generated. This supplementary phase directly enhances the waveform shift parameter and introduces an extra degree of freedom. Consequently, it becomes easier to accurately control the direct-current component in the photo-induced refractive index change during grating writing, leading to a more precise distribution of the refractive index gradient within the grating. The effectiveness of this method was validated through experiments conducted over a wide bandwidth of 20 nm for the CFBGs. The number of peaks from 1 to 4 were investigated, achieving a contrast of 40 dB. Extensive testing and verification were performed on the peak position shifts within the modulation bandwidth of numerous CFBGs. The results demonstrated that this new approach enables the fabrication of CFBGs with arbitrary waveform spectra. This technique significantly improves the optical performance and application value of CFBGs, offering a means to fabricate high-performance CFBGs using the UV mask method.

Pathogenic oomycetes infect a wide variety of organisms, including plants, animals, and humans, and cause massive economic losses in global agriculture, aquaculture, and human health. Salicylic acid (SA), an endogenous phytohormone, is regarded as an inducer of plant immunity. Here, the potato late blight pathogen Phytophthora infestanswas used as a model system to uncover the inhibitory mechanisms of SA on pathogenic oomycetes. In this research, SA significantly inhibited the mycelial growth, sporulation, sporangium germination, and virulence of P. infestans. Inhibition was closely related to enhanced autophagy, suppression of translation initiation, and ribosomal biogenesis in P. infestans, as shown by multiomics analysis (transcriptomics, proteomics, and phosphorylated proteomics). Monodansylcadaverine (MDC) staining and Western blotting analysis showed that SA promoted autophagy in P. infestansby probably targeting the TOR signaling pathway. These observations suggest that SA has the potential to control late blight caused by P. infestans.

In robotic Chinese calligraphy, the brush stroke training models for Chinese hairy brushes play a crucial role in stroke generation. The method of combining end-to-end techniques and physical models requires further study, however, it is difficult to obtain large amounts of brush strokes for deep learning and training. To overcome this, we propose using a simulated brush model to train a generator based on the Bézier brush stroke model generator (B-BSMG), which was formed by two symmetric cubic Bézier curves according to the physical characteristics and writing posture of the brush. The B-BSMG can generate images for deep learning and training using a dataset simulated by the Bézier brush stroke model. Our renderer is based on parameterized brush strokes, providing a better foundation for deep learning or robotic writing. The results of several experiments prove that the proposed B-BSMG can generate stroke graphics well and outperforms other advanced stroke models.

Graphical abstract:

The advent of the Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Exploration (GOCE) has changed the global contribution in the determination of high-accuracy global geopotential models (GGMs). In this paper, a spectral expansion method is used to determine the combined GGMs, using the high-resolution EGM2008 model and residual terrain model (RTM) to effectively bridge the spectral gap between the satellite and terrestrial data. The accuracy of the combined GGMs shows improvement compared with GOCE/GRACE-based GGMs and EGM2008 in determining the geopotential of the Hong Kong Principal Datum (HKPD). As a result of the DIR_R5/EGM2008/RTM model and GNSS/levelling, the geopotential value of HKPD is estimated to be 62,636,860.52 m2s−2with respect to the global geoid W0 = 62,636,853.4 m2s−2. Therefore, the vertical offset between the HKPD and global geoid is about −72.8 cm, which means that the HKPD is 72.8 cm below the global height datum.

A detailed discussion of the adjustment problems used to combine GNSS/levelling/gravity network data is provided in this paper. The two primary problems inherent to heterogeneous data networks, namely, parametric models that describe the datums and systematic distortions among the available data sets and stochastic models that describe the observational residuals, are described. For parametric models, a relationship between the transformation parameters and the effects of datums and systematic distortions inherent among different height data types is established based on a least squares criterion. For stochastic models, the stochastic errors in GNSS/levelling/gravity data are evaluated, and a Helmert variance component estimation approach is introduced to refine weighting models. Finally, the proposed model is applied to determine the hybrid geoid in Linyi, China. The numerical results validate the capability and effectiveness of the proposed combined adjustment technique for hybrid geoid computations, revealing an achievable external accuracy of ±1.22 cm compared with GNSS/levelling measurements, which can be increased by 0.44 cm compared with classic adjustments of GNSS/levelling/geoid height data.

Based on von Kármán geometric nonlinear theory, the nonlinear ordinary differential equations of motion for axisymmetric free vibration and thermal buckling of simple power-law functionally graded material sandwich circular plates are derived by using Hamilton's principle and Kantorovich averaging procedure. The transverse non-uniform temperature rise and uniform distributed loads were considered in derivation. The geometrically nonlinear two-point boundary value problem posed by the above ordinary differential equations and the clamped boundary conditions is solved with the shooting method. In the case of small amplitude, the effects of the temperature rise at top surface of the plates on the first three-order natural frequencies are investigated. The lowest order thermal post-buckling equilibrium paths and configurations of the plate are obtained. The first three-order out-plane transverse and in-plane radial axisymmetric free vibration mode shapes occurring on the lowest order thermal post-buckling equilibrium configurations of the plate are given. For the pre- and post-buckling plates, the first three-order amplitude frequency dependence of the geometrical nonlinear free vibration is studied. Detailed parametric study is performed in this paper. The present linear and nonlinear frequencies for a degeneration model are good agreement with those in the available literature.

The high-precision local geoid model was computed based on the improved Stokes-Helmert′s boundary value problem and strict integrals of topographic effects. This proposed method involves three steps. First, the mathematical form of Stokes-Helmert′s boundary value problem was derived, and strict computational formulas regarding topographic effects were provided to overcome the disadvantage of planar approximations. Second, a gravimetric geoid model was constructed using the proposed Stokes-Helmert′s scheme with a heterogeneous data set. Third, a least squares adjustment method combined with a multi-surface function model was employed to remove the bias between the gravimetric geoid model and the GNSS/leveling data and to refine the final local geoid model. The accuracy of the final geoid model was evaluated using independent GNSS/leveling data. Numerical results show that an external precision of 1.45 cm is achievable.

A new detection scheme is proposed for an enhanced self-mixing laser Doppler velocimeter (SLDV) using two-photon absorption (TPA), which is based on the TPA-induced quadratic photoconductivity dependence of a photodiode on the incident radiance at 1550 nm with self-mixing interference (SMI). The harmonics of the SMI signal in the frequency spectrum are enhanced simultaneously, as for a fiber-Bragg-grating-based enhanced SLDV. The quadratic response induced by TPA can suppress the undesirable harmonics, making their amplitude into the same level as the noise. From the experimental results presented in this paper, the TPA effect in a commercial Si photodiode implements a sort of ultra-wide bandwidth filter without passively adjusting the cutoff frequencies for an unknown Doppler frequency, which simplifies Doppler signal processing. The signal-to-noise ratio (SNR) is also improved to a considerable level of 15 dB for a Doppler frequency of 4 kHz due to the amplification of an erbium-doped fiber amplifier. This paper provides guidance for the design of the enhanced SLDV with optical filtration.

In this Letter, a novel multiple self-mixing interferometer for a fiber ring laser (FRL) is designed by introducing a circular feedback cavity. A system model is established based on an injection-seeded erbium-doped FRL proposed by Dragic. Owing to the reflection of the collimating lens, the multiplied fringes have different depths, which shows two Doppler frequencies in the spectrum of the self-mixing signal. A double-peak frequency identification algorithm is proposed to extract the Doppler frequency from the unique signal. This technique has the potential to improve the accuracy of fiber self-mixing measurement systems, particularly in Doppler velocimeters.

In some applications in structural health monitoring (SHM), the acoustic emission (AE) detection technology is used in the high temperature environment. In this paper, a high-temperature-resistant AE sensing system is developed based on the fiber Bragg grating (FBG) sensor. A novel high temperature FBG AE sensor is designed with a high signal-to-noise ratio (SNR) compared with the traditional FBG AE sensor. The output responses of the designed sensors with different sensing fiber lengths also are investigated both theoretically and experimentally. Excellent AE detection results are obtained using the proposed FBG AE sensing system over a temperature range from 25 ℃ to 200 ℃. The experimental results indicate that this FBG AE sensing system can well meet the application requirement in AE detecting areas at high temperature.

A novel position-sensitive Fabry–Perot interferometer was constructed with direct phase modulation by a built-in electro-optic modulator. Pure sinusoidal phase modulation of the light was produced, and the first harmonic of the interference signal was extracted to dynamically maintain the interferometer phase to the most sensitive point of the interferogram. Therefore, the minute vibration of the object was coded on the variation of the interference signal and could be directly retrieved by the output voltage of a photodetector. The operating principle and the signal processing method for active feedback control of the interference phase have been demonstrated in detail. The developed vibration sensor was calibrated through a high-precision piezo-electric transducer and tested by a nano-positioning stage under a vibration magnitude of 60 nm and a frequency of 300 Hz. The active phase-tracking method of the system provides high immunity against environmental disturbances. Experimental results show that the proposed interferometer can effectively reconstruct tiny vibration waveforms with subnanometer resolution, paving the way for high-accuracy vibration sensing, especially for micro-electro-mechanical systems/nano-electro-mechanical systems and ultrasonic devices.

Electro-deposition, electrical activation, thermal oxidation, and reactive ion sputtering are the four primary methods to fabricate iridium oxide film. Among these methods, reactive ion sputtering is a commonly used method in standard micro-fabrication processes. In different sputtering conditions, the component, texture, and electrochemistry character of iridium oxide varies considerably. To fabricate the iridium oxide film compatible with the wafer-level processing of neural electrodes, the quality of iridium oxide film must be able to withstand the mechanical and chemical impact of post-processing, and simultaneously achieve good performance as a neural electrode. In this study, parameters of sputtering were researched and developed to achieve a balance between mechanical stability and good electrochemical characteristics of iridium oxide film on electrode. Iridium oxide fabricating process combined with fabrication flow of silicon electrodes, at wafer-level, is introduced to produce silicon based planar iridium oxide neural electrodes. Compared with bare gold electrodes, iridium oxide electrodes fabricated with this method exhibit particularly good electrochemical stability, low impedance of 386 kΩ at 1 kHz, high safe charge storage capacity of 3.2 mC/cm2, and good impedance consistency of less than 25% fluctuation.

ABSTRACTThis study evaluated the synergistic effects of the selective serotonin reuptake inhibitor, fluoxetine, in combination with azoles against Candida albicansboth in vitroand in vivoand explored the underlying mechanism. MICs, sessile MICs, and time-kill curves were determined for resistant C. albicans. Galleria mellonellawas used as a nonvertebrate model for determining the efficacy of the drug combinations against C. albicansin vivo. For the mechanism study, gene expression levels of the SAPgene family were determined by reverse transcription (RT)-PCR, and extracellular phospholipase activities were detected in vitroby the egg yolk agar method. The combinations resulted in synergistic activity against C. albicansstrains, but the same effect was not found for the non-albicans Candidastrains. For the biofilms formed over 4, 8, and 12 h, synergism was seen for the combination of fluconazole and fluoxetine. In addition, the time-kill curves confirmed the synergism dynamically. The results of the G. mellonellastudies agreed with the in vitroanalysis. In the mechanism study, we observed that fluconazole plus fluoxetine caused downregulation of the gene expression levels of SAP1to SAP4and weakened the extracellular phospholipase activities of resistant C. albicans. The combinations of azoles and fluoxetine showed synergistic effects against resistant C. albicansmay diminish the virulence properties of C. albicans.

A birefringent dual-frequency laser with a half-intracavity has been used to develop a laser Doppler velocimeter (LDV). The developed LDV utilizes a new signal-processing method based on a lock-in amplifier to achieve high-resolution velocity measurements and the discrimination of positive and negative velocities. Theoretical analysis and simulation results are presented. The velocity measurement experiments by using a high-precision linear stage are performed to verify the performance of the LDV. Compared with the previous dual-frequency LDVs, the average velocity resolution of the developed LDV is improved from 0.31 mm/s to 0.028 mm/s for a target without the rotational velocity. The measurement results show that our new technique can offer a powerful instrument for metrology sciences.

A novel laser feedback grating interferometer (LFGI) with a phase-generated carrier demodulation technique is proposed in this paper. Laser feedback grating interference occurs when light emitted from a laser is diffracted by the double-diffraction system and re-enters the laser active cavity, thus generating a modulation of the lasing field. In order to improve the displacement measurement resolution, phase modulation is introduced by an electro-optic modulator in the external cavity of the LFGI. Detection of the displacement can be easily achieved by the time-domain orthogonal demodulation, which does not involve any complicated calculation and is insensitive to the sampling error. Experimental results show that the proposed system has a general nanometer-level resolution. It provides a potential displacement sensor with high resolution, simple mechanical structure, and good reliability.

A new signal-processing method based on an electronic frequency down-conversion technique has been introduced into a sinusoidal phase-modulating, self-mixing interferometer. The developed interferometer employs an electro-optical crystal placed in the external cavity of a He–Ne laser to generate the sinusoidal phase modulation with high modulation rate and ultralow insertion loss. Phase quadrature signals which have been amplitude-modulated by the sine and cosine functions, respectively, of the measured displacement can be extracted from the high-density optical fringes through the use of dual-channel multiplier/filter circuits. Therefore, the displacement of the external target can be retrieved from the phase quadrature signals with nanometer resolution and high computational efficiency. Moreover, a much-improved measurement speed from 2.5 to 22  mm/s has been realized owing to the simplified signal-processing method. The performance of the proposed interferometer has been experimentally verified by comparison to an Agilent 5529A dual-frequency laser interferometer. The measurement results from the two instruments agree well, and we therefore expect that our new technique offers a powerful instrument for high-speed metrology sciences.

Hyperspectral reflectance images of healthy and diseased leaves infected with different isolates of Citrus tristeza virus(CTV) including TRL514, CT30, CT32 and CT11A were collected in the visible and near-infrared region of 400–1000 nm. Average reflectance spectrum was generated from each hyperspectral image individually obtained from 60 healthy and 240 CTV-infected leaves. The spectra were transformed with 15-point Savitzky Golay second derivative. Then principal component analysis was performed on the transformed data in order to reduce the dimension of data. Comparative analysis was performed among supervised classification models, including back-propagation neural network (BPNN), linear discriminant analysis (LDA) and Mahalanobis distance (MD). When the second derivative spectra were analyzed, classifier models including BPNN, LDA and MD can discriminate the healthy and CTV-infected leaves with the highest classification accuracies of 100% in the spectral range of 400–1000 nm and 760–1000 nm. Nine optimal wavelengths (405, 424, 920, 947, 957, 972, 978, 980, and 998 nm) selected by stepwise regression resulted in 97.33% total classification accuracy for differentiation of healthy and CTV-infected leaves and showed great potential in CTV diagnosis. However, the overall classification accuracy of different CTV isolates infected leaves resulted in 70% based on the MD model using the selected optimal wavelengths. Further study is required to find out whether the method is suitable for CTV detection under field conditions.

A novel linear microprobe array (LMPA) has been developed by a conventional microfabrication method from silicon. The LMPA leverages the properties of conventional microwire with additional features of naturally formed regular spacing. With the help of periodic microprobe arrays and double-side V-grooves fabricated in advance between each pair of the two microprobes’ rear ends, the number of microprobe units for assembly in one array can be flexibly chosen by cleavage fracture from the LMPA. The fabrication method was demonstrated and the prototype device was assessed by electrochemical impedance spectroscopy (EIS) and in vivotest. The SNR of the spikes recorded was 6.

An electrochemical sensor was explored for recognizing 3,4-dihydroxyphenylalanine (DOPA) enantiomers based on L-cysteine covalently binding with the multi-walled carbon nanotubes functionalized with 3,4,9,10-perylene tetracarboxylic acid (MWCNTs-PTCA-Cys). Here two different ways of square wave voltammetry (SWV) and cyclic voltammetry (CV) were utilized to investigate the stereospecific interaction between the MWCNTs-PTCA-Cys nanocomposite and DOPA enantiomers. The D-DOPA and L-DOPA exhibited different response in both CV and SWV, in addition, the difference in SWV was more obvious and reached to 264.9 uA, suggesting that the enantiomers could be successfully distinguished by MWCNTs-PTCA-Cys nanocomposite, and the selection of electrochemical technique played an important role in enantioselective recognition. Under the optimum conditions, the detection limits of D-DOPA and L-DOPA were 2.5 uM and 4.6 uM (S/N = 3), respectively, with a linear range of 1.0 x 10[?]5 M to 5.0 x 10[?]3 M. This work provided a simple method to recognize and determine DOPA enantiomers with rapid response, excellent recognition ability, high sensitivity and good stability.

Through the amide group of glutamic acid enantiomer and oxygen-containing groups in graphene oxide, chiral functionalized graphene nanosheets were synthesized, which showed good enantioselective recognition of 3,4-dihydroxyphenylalanine enantiomers. These chiral graphene hybrids should be novel promising materials for biological and pharmacological applications.

Micro-displacement measurement based on self-mixing interference using a fiber laser system was demonstrated. The sinusoidal phase modulation technique was introduced into the fiber laser self-mixing interference measurement system to improve the measurement resolution. The phase could be demodulated by the Fourier analysis method. Error sources were evaluated in detail, and the system was experimentally applied to reconstruct the motion of a high-precision commercial piezoelectric ceramic transducer (PZT). The displacement measurement resolution was well beyond a half-wavelength. It provides a practical solution for displacement measurement based on all optical-fiber sensing applications with high precision.

Simple and sensitive chiral interfaces were constructed by assembling l- or d-N-isobutyryl-cysteine (NIBC) on a gold electrode surface through an Au–S bond, and the two chiral interfaces were utilized to interact with l-methotrexate (l-Mtx). The surface characteristics and the process of interaction were explored viacyclic voltammetry (CV). The difference in peak current after l- and d-NIBC interacted with l-Mtx reached 525.3 μA, and a larger current difference was obtained from the l-NIBC interface, suggesting a stereoselective effect between l-Mtx and NIBC enantiomers. Therefore, the chiral NIBC interfaces could not only enhance the electron transfer of l-Mtx, but could also discriminate between NIBC enantiomers.

A chiral platform was designed for enantioselective recognition of naproxen (Nap) enantiomers using BSA biofunctionalized nanosheets of Toluidin blue O (TBO) and reduced graphene oxide (rGO) on the glassy carbon electrode. The novel TBO@rGO nanosheets acting as a supporter for the chiral selector (BSA) and electrochemical signal indicator had plenty of advantages, which were presented and explored via ultraviolet-visible (UV-vis) spectroscopy, scanning electron microscope (SEM) and electrochemical method. Kinetics showed the chiral platform had good redox signal and fast electron transfer. Under optimal conditions, much larger signal discrepancy was obtained after the chiral interface interacted with r-Nap, and a linear electrochemical response to Nap enantiomers was obtained from 5.0 x 10[?]4 mol L[?]1 to 5.0 x 10[?]3 mol L[?]1 with a low detection limit of 3.3 x 10[?]7 mol L[?]1. Meanwhile, quartz crystal microbalance (QCM) for the interactions between BSA and Nap enantiomers further confirmed that r-Nap had a higher affinity with BSA. Furthermore, this simple chiral biosensor with excellent sensitivity and high stability is very expected to have more application in enantioselective recognition.

A sinusoidal phase-modulating He–Ne laser subject to weak optical feedback has been used to develop an interferometer that is capable of performing real-time displacement measurement with nanometer accuracy. The principle and the signal processing method are introduced. A commercial dual-frequency interferometer is included in the displacement measurement in both small and large ranges to evaluate the performance of the developed interferometer. Experimental results show that the average errors and standard deviations of the interferometer are in good agreement with data obtained from the commercial interferometer. The resolution and the multiple feedback effect of the interferometer are discussed in detail. These results show that the development of the interferometer is reasonable and feasible.

The Self-Mixing Interference (SMI) effect of a Vertical-Cavity Surface-Emitting Laser (VCSEL) is studied in this paper. The analysis and experiment are presented to verify the dynamics of the VCSEL. The phenomenon is observed and contrasted with traditional interference phenomenon. The output property of VCSEL is modulated by the change of cavity length and feedback intensity. An interferometer using VCSEL self-mixing based on temporal carrier phase shifting technique is studied. Theoretical analysis and simulation calculations are presented and some errors of this method are discussed.

A new, to the best of our knowledge, method for the measurement of the absolute distance of a remote target based on the laser diode self-mixing interferometry is presented. A double-modulation technique is introduced to improve the measurement resolution. Wavelength modulation of the laser beam is obtained by modulating the injection current of the laser diode. Phase modulation of the laser beam is obtained by an electro-optic crystal in the external cavity. Absolute distance of the external target is determined by the Fourier analysis method. Theoretical analysis and numerical simulations are given. Experimental results show that a resolution of ±0.3 mm can be achieved for absolute distance ranging from 277 to 477 mm.

A fiber in-line Fabry–Pérot interferometer is presented. The sensing head consists of a micro ellipsoidal air cavity and a small section of solid-core photonic crystal fiber. The reflective index (RI) and temperature can be interrogated simultaneously through a fast Fourier transform and by tracing the dip wavelength shift of the reflective spectrum. Experimental results show that the RI amplitude and wavelength sensitivities are 5.30/RIU and 8.46×10^−1??nm/RIU in the range from 1.34 to 1.43, and the temperature amplitude and wavelength sensitivities are 6.8×10^−4/°C and 2.48×10^−3??nm/°C in the range from 15°C to 75°C, respectively. Easy fabrication, a simple system, and simultaneous measurement make it appropriate for dual-parameter sensing application.

Background: Myelodysplastic syndromes (MDS) are defined as a heterogeneous group of clonal hematopoietic stem cell (HSC) malignant disorders which are characterized by bone marrow failure and dysplasia of blood cells. As continually terminated in AML, MDS are treated as the "pre-leukemia" condition. HERG K+channels, being three subtypes: HERG1, HERG.2, HERG3, are expressed transiently at early stages of cells such as progenitor and stem cells, disappearing at later stages of cells like mature cells. Our previous work and others demonstrated that HERG1, as an oncoprotein, was over expressed in AML cells and played crucial roles in SDF-1induced leukemia cell migration. The expression and functional role of HERG1 K+channels in MDS development is not reported. We investigated the HERG1 K+channels expression and explored the functional link between HERG1 K+ channels and MDS progression