Topology Optimization Method of Stamping Structures Based on the Directional Density Field.

The stamping process produces thin-walled structures that, in general, have uniform wall thickness and no enclosed cavity. However, it is difficult to satisfy the above geometric requirements with the current density-based topology optimization method, since configuring the related geometric constraints is challenging. In order to solve this problem, a topology optimization method for stamping structures based on a directional density field is proposed. Specifically, the directional density field is developed to enable the adding and removing of materials only along the stamping direction, so as to avoid internal voids and concave features. The geometric control for uniform wall thickness is realized by tuning the truncation threshold of the Heaviside projection that processes the directional density field into the 0-1 binary field. At the same time, a calibrated filter radius of the truncation thresholds will facilitate the drawing angle control of the stamping ribs. The effectiveness of the established method has been verified by a number of numerical case studies. Results show that the proposed method can perform topology optimization for stamping structures with tunable uniform thickness and drawing angle control of the ribs. No internal voids or undercuts appear in the results. The results also disclose that a constant truncation threshold increment does not guarantee uniform wall thickness, and varying the threshold increments through surface offset and polynomial fitting is necessary.

Printing Ready Topology Optimization for Material Extrusion Polymer Additive Manufacturing.

Additive manufacturing-oriented topology optimization features in the extreme geometric complexity that magnifies the product functional performance. However, the increased geometric complexity makes postprocessing of the designs technically nontrivial and sometimes inefficient because of too many structural details. To address this issue, this article presents a novel printing-ready topology optimization method whereby the topological designs can be directly exported in the format of a printing-ready G-code, which saves the postprocessing efforts of stereo lithograph (STL) model generation, model slicing, and tool path planning. More importantly, the slicing and tool path information can be tracked all the time during optimization to facilitate the evaluation of the tool path-related material constitutive model, for example, the fiber-reinforced composites, so as to improve the numerical analysis accuracy and the design result optimality. Finally, three case studies are performed to test the postprocessing efficiency of the printing-ready approach and the multi-scale design case, which demonstrates the outstanding high efficiency characteristic of the proposed approach.

Redox responsive nanoparticle encapsulating black phosphorus quantum dots for cancer theranostics.

Effective cancer treatment puts high demands for cancer theranostics. For cancer diagnostics, optical coherence tomography (OCT) technology (including photothermal optical coherence tomography (PT-OCT)) has been widely investigated since it induces changes in optical phase transitions in tissue through environmental changes (such as temperature change for PT-OCT). In this report, redox responsive nanoparticle encapsulating black phosphorus quantum dots was developed as a robust PT-OCT agent. Briefly, black phosphorus quantum dots (BPQDs) are incorporated into cysteine-based poly-(disulfide amide) (Cys-PDSA) to form stable and biodegradable nanoagent. The excellent photothermal feature allows BPQD/Cys-PDSA nanoparticles (NPs) as a novel contrast agent for high-resolution PT-OCT bioimaging. The Cys-PDSA can rapidly respond to glutathione and effectively release BPQDs and drugs in vitro and in vivo. And the obtained NPs exhibit excellent near-infrared (NIR) photothermal transduction efficiency and drug delivery capacity that can serve as novel therapeutic platform, with very low chemo drug dosage and side effects. Both of the polymer and BPQD are degradable, indicating this platform is a rare PT-OCT agent that is completely biodegradable. Overall, our research highlights a biodegradable and biocompatible black phosphorus-based nanoagent for both cancer diagnosis and therapy.

Cross-correlation photothermal optical coherence tomography with high effective resolution.

We developed a cross-correlation photothermal optical coherence tomography (CC-PTOCT) system for photothermal imaging with high lateral and axial resolution. The CC-PTOCT system consists of a phase-sensitive OCT system, a modulated pumping laser, and a digital cross-correlator. The pumping laser was used to induce the photothermal effect in the sample, causing a slight phase modulation of the OCT signals. A spatial phase differentiation method was employed to reduce phase accumulation. The noise brought by the phase differentiation method and the strong background noise were suppressed efficiently by the cross-correlator, which was utilized to extract the photothermal signals from the modulated signals. Combining the cross-correlation technique with spatial phase differentiation can improve both lateral and axial resolution of the PTOCT imaging system. Clear photothermal images of blood capillaries of a mouse ear in vivo were successfully obtained with high lateral and axial resolution. The experimental results demonstrated that this system can enhance the effective transverse resolution, effective depth resolution, and contrast of the PTOCT image effectively, aiding the ongoing development of the accurate 3D functional imaging.

Modelling releases of sterile mosquitoes with different strategies.

To prevent the transmissions of malaria, dengue fever, or other mosquito-borne diseases, one effective weapon is the sterile insect technique in which sterile mosquitoes are released to reduce or eradicate the wild mosquito population. To study the impact of the sterile insect technique on disease transmission, we formulate discrete-time mathematical models, based on difference equations, for the interactive dynamics of the wild and sterile mosquitoes, incorporating different strategies in releasing sterile mosquitoes. We investigate the model dynamics and compare the impact of the different release strategies. Numerical examples are given to demonstrate rich dynamical features of the models.