Computational design for 4D printing of topology optimized multi-material active composites

Recent efforts on design for four-dimensional(4D)printing have considered the spatial arrangement of smart materials and energy stimuli.The development of multifunctional structures and their desired mechanical/actuation performances require tackling 4D printing from a multi-material design perspective.With the materials distributions there is an opportunity to increase the spectrum of design concepts with computational approaches.The main goal being to achieve the“best”distribution of material properties in a voxelized structure,a computational framework that consists of a finite element analysis-based evolutionary algorithm is presented.It fuses the advantages of optimizing both the materials distribution and material layout within a design space via topology optimization to solve the inverse design problem of finding an optimal design to achieve a target shape change by integrating void voxels.The results demonstrate the efficacy of the proposed method in providing a highly capable tool for the design of 4D-printed active composites.

Pattern formation in 2-μm Tm Mamyshev oscillators associated with the dissipative Faraday instability

We investigate numerically the pattern formation in 2-μm thulium-doped Mamyshev fiber oscillators, associated with the dissipative Faraday instability. The dispersion-managed fiber ring oscillator is designed with commercial fibers, allowing the dynamics for a wide range of average dispersion regimes to be studied, from normal to nearzero cavity dispersion where the Benjamin–Feir instability remains inhibited. For the first time in the 2-μm spectral window, the formation of highly coherent periodic patterns is demonstrated numerically with rates up to ~100 GHz. In addition, irregular patterns are also investigated, revealing the generation of rogue waves via nonlinear collision processes. Our investigations have potential applications for the generation of multigigahertz frequency combs. They also shed new light on the dissipative Faraday instability mechanisms in the area of nonlinear optical cavity dynamics.

Stimulated generation of deterministic platicon frequency microcombs

Dissipative Kerr soliton generation in chip-scale nonlinear resonators has recently observed remarkable advances,spanning from massively parallel communications, to self-referenced oscillators, and to dual-comb spectroscopy.Often working in the anomalous dispersion regime, unique driving protocols and dispersion in these nonlinear resonators have been examined to achieve the soliton and soliton-like temporal pulse shapes and coherent frequency comb generation. The normal dispersion regime provides a complementary approach to bridge the nonlinear dynamical studies, including the possibility of square pulse formation with flattop plateaus, or platicons.Here we report observations of square pulse formation in chip-scale frequency combs through stimulated pumping at one free spectral range and in silicon nitride rings with +55 fs~2∕mm normal group velocity dispersion.Tuning of the platicon frequency comb via a varied sideband modulation frequency is examined in both spectral and temporal measurements. Determined by second-harmonic autocorrelation and cross correlation, we observe bright square platicon pulse of 17 ps pulse width on a 19 GHz flat frequency comb. With auxiliary-laser-assisted thermal stabilization, we surpass the thermal bistable dragging and extend the mode-locking access to narrower 2 ps platicon pulse states, supported by nonlinear dynamical modeling and boundary limit discussions.

Combining infrared and mode synthesizing atomic force microscopy： Application to the study of lipid vesicles inside Streptomyces bacteria

We propose a new analytical approach combining vibrational spectroscopy and acoustic tomography for the detection and characterization of vesicles inside Streptomyces bacteria. Using atomic force microscopy and infrared spectroscopy （AFM-IR）, we detect the presence of triglyceride vesicles. Their sizes in depth are measured with high accuracy using mode synthesizing atomic force microscopy （MS-AFM）. We conducted a comparative study of AFM-IR and MS-AFM, and highlighted the advantages of the coupling of these techniques in having a full characterization （chemical, topographical, and volumetric） of a biological sample. With these complementary techniques, a complete access to the vesicle size distribution has been achieved with an accuracy of less than 50 nm. A 3D reconstruction of bacteria showing the in-depth distribution of vesicles is given to underline the great potential of the acoustic method.

Smart lasers tame complex spatiotemporal cavity dynamics

By associating multimode fibers,optical wavefront manipulation,and a feedback loop controlled by a genetic algorithm,researchers have demonstrated that nonlinear spatiotemporal dynamics can be flexed within the laser cavity to achieve a user-specified objective,such as the lasing wavelength,output power,beam profile or pulsed operation.