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Mimicking natural botanical/zoological systems has revolutionarily inspired four-dimensional (4D) hydrogel robotics, interactive actuators/machines, automatic biomedical devices, and self-adaptive photonics. The controllable high-freedom shape reconfiguration holds the key to satisfying the ever-increasing demands. However, miniaturized biocompatible 4D hydrogels remain rigorously stifled due to current approach/material limits. In this research, we spatiotemporally program micro/nano (μ/n) hydrogels through a heterojunction geometric strategy in femtosecond laser direct writing (fsLDW). Polyethylene incorporated N-isopropylacrylamide as programmable interactive materials here. Dynamic chiral torsion, site-specific mutation, anisotropic deformation, selective structural coloration of hydrogel nanowire, and spontaneous self-repairing as reusable μ/n robotics were identified. Hydrogel-materialized monolayer nanowires operate as the most fundamental block at nanometric accuracy to promise high freedom reconfiguration and high force-to-weight ratio/bending curvature under tight topological control. Taking use of this biomimetic fsLDW, we spatiotemporally constructed several in/out-plane self-driven hydrogel grippers, diverse 2D-to-3D transforming from the same monolayer shape, responsive photonic crystal, and self-clenched fists at μ/n scale. Predictably, the geometry-modulable hydrogels would open new access to massively-reproducible robotics, actuators/sensors for microenvironments, or lab-on-chip devices.

Rapid fabricating and harnessing stimuli-responsive behaviors of microscale bio-compatible hydrogels are of great interest to the emerging micro-mechanics, drug delivery, artificial scaffolds, nano-robotics, and lab chips. Herein, we demonstrate a novel femtosecond laser additive manufacturing process with smart materials for soft interactive hydrogel micro-machines. Bio-compatible hyaluronic acid methacryloyl was polymerized with hydrophilic diacrylate into an absorbent hydrogel matrix under a tight topological control through a 532 nm green femtosecond laser beam. The proposed hetero-scanning strategy modifies the hierarchical polymeric degrees inside the hydrogel matrix, leading to a controllable surface tension mismatch. Strikingly, these programmable stimuli-responsive matrices mechanized hydrogels into robotic applications at the micro/nanoscale (

The widespread use of stimuli-responsive hydrogels is closely related to their synthesis efficiency. However, the widely used thermal-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels usually require a time-consuming synthesis process to produce (more than 12 h) and exhibit a relatively slow response speed in the field of cryo-polymerization. In this study, a sequence of thawing polymerization after freezing polymerization by a two-step method of free radical polymerization for the efficient synthesis of PNIPAM hydrogels (merely 2 h) with an excellent comprehensive performance is demonstrated. Results show that the overall performance of the as-synthesized PNIPAM hydrogels is at the top level among reported works despite the significantly reduced preparation time. Moreover, after incorporating multi-walled carbon nanotubes (MWNTs), the PNIPAM hydrogels exhibit a rapid near-infrared (NIR) light-response and programmable shape-morphing capability. It is believed that such a viable and time-saving synthetic method for producing PNIPAM hydrogels of high performance will lay a solid foundation for drug delivery and smart actuators.

The characteristics of the runoff hydropower station are to generate power completely according to the natural runoff, and the output and power generation change with the change of the natural flow. The cluster power prediction of the runoff hydropower station is conducive to improving the safety of the power grid operation and improving the utilization rate of hydropower. This paper analyzes the operation characteristics of runoff hydropower stations, summarizes the prediction direction of mainstream runoff hydropower, analyzes the characteristics of the hydrological prediction model represented by the Xin'an River model, and puts forward a study on the power prediction technology of runoff small hydropower cluster based on fusion modeling. Based on the detailed analysis of watershed runoff characteristics, a prediction model based on multi-watershed observation characteristics is proposed, which combines the traditional hydrological model with the LSTM model to form a combined prediction model suitable for runoff hydropower. The method is universal and innovative.

Energy shortage and environmental pollution have become the world's difficult problems, and the development of clean energy has become an inevitable choice. Solving the high proportion of clean energy consumption will become a major issue in the energy field. Various types of energy sources such as hydropower-wind power-photovoltaic power have coupling characteristics in certain geographical areas, and making good use of these coupling properties can better solve its joint prediction problem. This paper first introduces a brief situation of the development of these fields, proposes the main popular computing methods in this field, and conducts targeted analysis for the mainstream methods such as joint prediction, artificial intelligence and clustering algorithm, and finally puts forward the work value and conclusion of multi-energy coupling prediction.

We analysed the plasma expansion characteristics during a laser ablation process and derived dynamics equations to describe the plasma expansion. The equations include the plasma concentration spatial distribution equation, plasma expansion pressure equation and plasma dynamics equation for both the isothermal expansion stage and adiabatic expansion stage. The equations are reasonable, and the required parameters are related only to the laser parameters and materials properties, imparting the model with high versatility and practicability. The models were applied to a numerical simulation of plasma expansion characteristics in the laser ablation of a bronze-bonded diamond grinding wheel. The dimension of plasma isothermal expansion and plasma adiabatic expansion, the expansion velocity of the isothermal plasma, and the contour evolution of plasma expansion were determined. Experiments were then conducted with a high-speed camera to observe the same plasma expansion process for ablating the grinding wheel. A grating spectrometer was used to measure the emission spectrum during the laser ablation process, and the electron temperature and electron density were characterized. The results of the experiments and numerical simulation were found to be essentially consistent, verifying the accuracy and feasibility of the as-developed plasma dynamics equations, with positive implications for optimizing the laser ablation process.

A carrier separating method associated with noise-elimination had been introduced into a sinusoidal phase-shifting self-mixing interferometer. The conventional sinusoidal phase shifting self-mixing interferometry was developed into a more competitive instrument with high computing efficiency and nanometer accuracy of λ / 100 in dynamical vibration measurement. The high slew rate electro-optic modulator induced a sinusoidal phase carrier with ultralow insertion loss in this paper. In order to extract phase-shift quickly and precisely, this paper employed the carrier-separating to directly generate quadrature signals without complicated frequency domain transforms. Moreover, most noises were evaluated and suppressed by a noise-elimination technology synthesizing empirical mode decomposition with wavelet transform. The overall laser system was described and inherent advantages such as high computational efficiency and decreased nonlinear errors of the established system were demonstrated. The experiment implemented on a high precision PZT (positioning accuracy was better than 1 nm) and compared with laser Doppler velocity meter. The good agreement of two instruments shown that the short-term resolution had improved from 10 nm to 1.5 nm in dynamic vibration measurement with reduced time expense. This was useful in precision measurement to improve the SMI with same sampling rate. The proposed signal processing was performed in pure time-domain requiring no preprocessing electronic circuits.

This paper, originally published on 17 May 2019, was withdrawn on 24 July 2019 at the request of the authors.

Integration of phase manipulation and polarization multiplexing was introduced to self-mixing interferometry (SMI) for high-sensitive measurement. Light polarizations were used to increase measuring path number and predict manifold merits for potential applications. Laser source was studied as a microwave-photonic resonator optically-injected by double reflected lights on a two-feedback-factor analytical model. Independent external paths exploited magnesium-oxide doped lithium niobate crystals at perpendicular polarizations to transfer interferometric phases into amplitudes of harmonics. Theoretical resolutions reached angstrom level. By integrating two techniques, this SMI outperformed the conventional single-path SMIs by simultaneous dual-targets measurement on single laser tube with high sensitivity and low speckle noise. In experimental demonstration, by nonlinear filtering method, a custom-made phase-resolved algorithm real-time figured out instantaneous two-dimensional displacements with nanometer resolution. Experimental comparisons to lock-in technique and a commercial Ploytec-5000 laser Doppler velocity meter validated this two-path SMI in micron range without optical cross-talk. Moreover, accuracy subjected to slewing rates of crystals could be flexibly adjusted.

Signals of a self-mixing interferometer established on a semiconductor laser diode are analyzed. Phase is extracted out for decoding measurement which contained in self-mixing fringes. The semiconductor laser diode works as light source and receiver without modulation. By combining Hilbert transform with phase condition of self-mixing interference, micron- displacement is reconstructed by phase information at week or even moderate feedback level. Theoretical analysis and simulation results are presented before verification of experimental measurement. Practical feedback level is estimated by a data fitting technique with a programmable high-resolution PZT. Consistence of the results promises that direct phase extraction on self-mixing interferometer is available for micron-displacement measurement with a nanometer accuracy.