Multi-objective optimization of cortical bone grinding parameters based on particle swarm optimization.

Grinding is a fundamental operation in craniotomy. Suitable grinding parameters will not only reduce force damage, but also ensure grinding efficiency. In this study, the regression equations of material removal rate and grinding force were obtained based on the theory of cortical bone grinding and full factorial test results, a multi-objective optimization based on the particle swarm algorithm was proposed for optimizing the grinding parameters: spindle speed, feed speed, and grinding depth in the grinding process. Two conflicting objectives, minimum grinding force and maximum material removal rate, were optimized simultaneously. The results revealed that the optimal grinding parameter combination and optimization results were as follows: spindle speed of 5000 rpm, feed rate of 60 mm/min, grinding depth of 0.6 mm, grinding force of 15.1 N, and material removal rate of 113.8 mm3/min. The parameter optimization result can provide theoretical guidance for selecting cortical bone grinding parameters in actual craniotomy.

Cortical bone grinding mechanism modeling and experimental studyfor damage minimization in craniotomy.

Craniotomy, as a part of neurosurgery, implies a safe opening of the skull with mechanical equipment. Grinding is a traditional machining method that can accurately and efficiently remove bone tissue. Aiming at low-damage and high-efficiency bone grinding, this study analyzed the kinematic law of a single abrasive grain during the grinding process. The theoretical model of grinding force was established based on the calculation of specific energy and friction force. The grinding test platform was set up, and the full factorial experimental design was performed to link the grinding force evolution with different processing parameters. The experimental results obtained on porcine femurs validated the model predictions where the grinding force grew with feed speed and grinding depth; it exhibited a decreasing trend with rotation speed, followed by increasing one.

Research progress of adsorption and removal of heavy metals by chitosan and its derivatives: A review.

Chitosan has received widespread attention as an adsorbent for pollutants because of its low cost and great adsorption potentials. Chitosan has abundant hydroxyl and amino groups that can bind heavy metal ions. However, it has defects such as sensitivity to pH, low thermal stability, and low mechanical strength, which limit the application of chitosan in wastewater treatment. The functional groups of chitosan can be modified to improve its performance via crosslinking and graft modification. The porosity and specific surface area of chitosan in powder form are not ideal, therefore, physical modification has been attempted to generate chitosan nanoparticles and hydrogel. Chitosan has also been integrated with other materials (e.g. graphene, zeolite) resulting in composite materials with improved adsorption performance. This review mainly focuses on reports about the application of chitosan and its derivatives to remove different heavy metals. The preparation strategy, adsorption mechanism, and factors affecting the adsorption performance of adsorbents for each type of heavy metal are discussed in detail. Recent reports on important organic pollutants (dyes and phenol) removal by chitosan and its derivatives are also briefly discussed.

Surface quality and pullout strength of ultrasonically-assisted drilling cortical bone.

Bone surgery is a complex process involving sustainable and healthy human recuperation, but poor surface quality and loose implant fixtures can affect the recovery time of orthopedic patients. However, it has been demonstrated that the application of ultrasonic vibration during drilling procedures can improve the success of bone remediation procedures. The focus of the present paper was on the investigation of surface quality and pullout strength of drilled holes. After analyzing the special kinematic characteristics of the ultrasonically-assisted drilling (UAD), UAD testing using fresh cortical bone was carried out and compared with the results obtained after conventional drilling (CD) procedures. Surface roughness measurements and microscope examination were used to evaluate surface quality, and an electro-mechanical tensile machine was used to measure pullout resistance. The test findings indicated that surface roughness was reduced by 17-68.7% when using UAD; the axial pullout strength of screws inserted into UAD holes was significantly increased by 4.28-30.1% compared to that of CD. It was found also that low spindle speeds and high feed rates reduced surface quality and the stability of the inserted cortical screws. The findings demonstrated that UAD produced better surface quality and higher pullout strengths, which could provide greater stability for implants and improved post-operative recovery.

Covariant Bethe-Salpeter approximation in models of strongly correlated electron systems.

Strongly correlated electron systems are generally described by tight-binding lattice Hamiltonians with strong local (onsite) interactions, the most popular being the Hubbard model. Although the half-filled Hubbard model can be simulated by Monte Carlo (MC), physically more interesting cases beyond half-filling are plagued by the sign problem. One therefore should resort to other methods. It was demonstrated recently that a systematic truncation of the set of Dyson-Schwinger equations for correlators of the Hubbard, supplemented by a "covariant" calculation of correlators leads to a convergent series of approximants. The covariance preserves all the Ward identities among correlators describing various condensed matter probes. While first-order (classical), second-order (Hartree-Fock or Gaussian), and third-order (Cubic) covariant approximation were worked out, the fourth-order (quartic) seems too complicated to be effectively calculable in fermionic systems. It turns out that the complexity of the quartic calculation in local interaction models,is manageable computationally. The quartic (Bethe-Salpeter-type) approximation is especially important in 1D and 2D models in which the symmetry-broken state does not exists (the Mermin-Wagner theorem), although strong fluctuations dominate the physics at strong coupling. Unlike the lower-order approximations, it respects the Mermin-Wagner theorem. The scheme is tested and exemplified on the single-band 1D and 2D Hubbard model.

Ultrahigh Energy Efficiency and Large Discharge Energy Density in Flexible Dielectric Nanocomposites with Pb0.97La0.02(Zr0.5SnxTi0.5-x)O3 Antiferroelectric Nanofillers.

Flexible dielectric capacitors have been widely studied recently on account of their fast charge-discharge speed, high power density, and superior wearable characteristics. Inorganic ferroelectric fillers/polymer matrix composites combining large maximum electric displacement (Dmax) of ferroelectric materials with good flexibility and high electric breakdown strength (Eb) of the polymer are regarded as the most promising materials for preparing flexible dielectric capacitors with superior energy storage properties. However, simultaneously achieving large discharge energy density (Wd) and high energy efficiency (η) in these composites remains challenging on account of a large remnant electric displacement (Dr) and low Dmax - Dr values of ferroelectric fillers. In contrast, antiferroelectrics (AFEs) exhibit near zero Dr and larger Dmax - Dr values and are thus attractive composite fillers to simultaneously achieve large Wd and high η. On the basis of these factors, in this report, we design and prepare Pb0.97La0.02(Zr0.5SnxTi0.5-x)O3 (PLZST) AFE nanoparticles (NPs)/poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposites and investigate the effects of the Sn and AFE NPs contents on the energy storage capacity of the nanocomposites. Through reasonable adjustment of the Sn content and the PLZST AFE fillers content, because of the large Dmax - Dr value of 7.75 µC/cm2 and small Dr value of 0.26 µC/cm2 at the Eb as high as 3162 kV/cm, the Pb0.97La0.02(Zr0.5Sn0.38Ti0.12)O3 AFE NPs/P(VDF-HFP) polymer nanocomposite with 7 wt % fillers exhibits the most superior energy storage properties with an ultrahigh η of 93.4% and a large Wd of 12.5 J/cm3. These values are superior to those of the recently reported dielectric nanocomposites with a single-layer structure containing ferroelectric nanowires, nanofibers, nanobelts, nanotubes, and nanosheets or core-shell structure fillers, which are prepared via a very complicated method. This work not only shows that, in principle, the polarization characteristics of the composites depend mainly on those of the inorganic fillers but also demonstrates a convenient, effective, and scalable way to fabricate dielectric capacitors with superior flexibility and energy storage capacities.