Processes

As the global population grows and living standards rise, the demand for meat is increasing rapidly, inevitably generating about 100 million metric tonnes of animal bone waste (ABW). This biomass residue is mainly composed of organic collagen and inorganic hydroxyapatite. Therefore, ABW may cause environmental pollution if it is not properly treated, but it can also serve as a valuable resource for the circular economy if appropriately valorized. This comprehensive review aims to focus on thermochemical processes for converting ABW into porous hydroxyapatite-based materials and further summarize their value-added applications (e.g., environmental adsorbents, catalysts or their supports, biomedical materials for bone grafting and tissue engineering, and electrode materials for energy storage). Therefore, the four topics will be covered to echo the targets of this review paper, including the sources and characteristics of ABW, processes for transforming ABW into porous materials, pore property determinations for porous materials derived from ABW, and value-added applications of porous materials derived from ABW. Based on the information gathered in this review, the valorization of ABW and its derived pore materials may facilitate a practical circular economy case in which animal bones are reused as an available resource to produce newly porous materials for a variety of novel and high-value applications like medicine and energy fields.

This paper presents a unified framework for trajectory tracking and static obstacle avoidance of differential-drive mobile robots. A nominal exact-decoupling controller achieves pure exponential longitudinal convergence and globally avoids angular singularities via a stereographic projection; its cascade structure is proved globally asymptotically stable, and a time-scale separation analysis yields an explicit lateral settling-time constant, enabling prescribed convergence design. To handle obstacles, an artificial potential field (APF) correction is superimposed in a structure-preserving manner: the cancellation term responsible for longitudinal decoupling is retained, so the longitudinal error dynamics remain decoupled and are only additively perturbed during avoidance. The perturbed closed loop is modelled as a cascade driven by bounded inputs, and a bounded-input bounded-state (BIBS) analysis guarantees that tracking errors stay bounded during avoidance and recover exponentially with the nominal time constants once the influence zone is left. Quantitative error bounds and a recovery-time estimate enable an explicit safety–performance trade-off. Simulations on circular and figure-eight trajectories with single and multiple static obstacles confirm the predicted recovery behaviour and reduce the total integral squared error (ISE) by factors of 7.4 and 20 relative to a CBF-QP safety filter, with lateral recovery about twice as fast as that of a Kanayama controller augmented by APF.

Efficient atomization of liquid fuels over a broad range of physical properties is important for practical utilization. However, the response of pressure-swirl atomization to substantial variations in liquid viscosity remains insufficiently understood, particularly the transition from a hollow-cone atomization to a degraded atomization regime. A volume-of-fluid numerical method is employed to investigate liquid-film formation and primary breakup in a pressure-swirl nozzle over a range of viscosities and surface tensions of waste-derived pyrolysis oils in this study. The results show that increasing viscosity substantially alters the liquid-film morphology, cone angle, and primary breakup behavior. At high Reynolds numbers, a hollow-cone liquid film develops and undergoes interfacial destabilization and breakup. As the Reynolds number decreases, the hollow-cone morphology is replaced by a spiral-blade morphology. The high-viscosity condition is accompanied by substantially weakened internal swirl and circumferential mixing, allowing the liquid streams originating from individual tangential slots to retain distinct spiral paths. Consequently, centrifugal expansion is suppressed and continuous liquid persists in the central region. These results clarify the flow characteristics associated with the viscosity-dominated transition from hollow-cone to spiral-blade atomization and provide insight into the pressure-swirl atomization of liquids with a broad range of viscosities.