Moran Process Version of the Tug-of-War Model: Complex Behavior Revealed by Mathematical Analysis and Simulation Studies

In a series of publications McFarland and co-authors introduced the tug-of-warmodel of evolution of cancer cell populations. The model is explaining the joint effect ofrare advantageous and frequent slightly deleterious mutations, which may be identifiable withdriver and passenger mutations in cancer. In this paper, we put the Tug-of-War model inthe framework of a denumerable-type Moran process and use mathematics and simulationsto understand its behavior. The model is associated with a time-continuous Markov Chain(MC), with a generator that can be split into a sum of the drift and selection process partand of the mutation process part. Operator semigroup theory is then employed to prove thatthe MC does not explode, as well as to characterize a strong-drift limit version of the MCwhich displays instant fixation effect, which was an assumption in the original McFarlandsmodel. Mathematical results are fully confirmed by simulations of the complete and limitversions. They also visualize complex stochastic transients and genealogies of clones arising inthe model.

Comparison of polyetheretherketone cables and stainless steel wires for sternal fixation after median sternotomy

Objective To compare the sternal fixation effect of a polyetheretherketone (PEEK) cable product and stainless steel wire after median sternotomy. Methods A multicentre retrospective clinical trial was conducted in patients that underwent median sternotomy for a range of surgical reasons. The sternum was fixed using PEEK sternal cables in the experimental group and stainless steel wires in the control group. The general patient state, product manoeuvrability, bone and wound healing state and blood test results were evaluated at seven visits during the preoperative, surgical and follow-up periods. Results A total of 108 patients (54 in each group) were included in the analysis at the final 180-day follow-up. The sternum was successfully closed using PEEK cables or steel wires in all patients and all healed well. No pathological changes were found on the X-ray imaging. Computed tomography imaging confirmed ideal fracture healing. No significant difference was found between the experimental group and the control group in outcomes. Conclusion PEEK cables are easy to implant and show desirable effectiveness in sternal fixation without any observed side-effects.

The priming effect of competitor product information on advertising creativity

This article examines the manner in which advertising creativity may be influenced by “near” primes in the form of competitor product information that is presented at the briefing stage of engagement with a client. Drawing on the associative theory of creativity and spreading activation theory, this study explores the impact of near primes on both the originality and appropriateness of advertising output and highlights the process mechanism by which it affects overall creativity. Results of a between-subjects experiment indicate that exposing individuals to near primes results in a fixation effect that negatively influences originality but positively influences appropriateness. Associative cognitive flexibility, as measured by the number of “far” analogies accessed during ideation, is shown to be a strong mediator of the relationship between near prime exposure on creativity. Implications for theory and practice are discussed.

Tropical carbon sink accelerated by symbiotic dinitrogen fixation

A major uncertainty in the land carbon cycle is whether symbiotic nitrogen fixation acts to enhance the tropical forest carbon sink. Nitrogen-fixing trees can supply vital quantities of the growth-limiting nutrient nitrogen, but the extent to which the resulting carbon–nitrogen feedback safeguards ecosystem carbon sequestration remains unclear. We combine (i) field observations from 112 plots spanning 300 years of succession in Panamanian tropical forests, and (ii) a new model that resolves nitrogen and light competition at the scale of individual trees. Fixation doubled carbon accumulation in early succession and enhanced total carbon in mature forests by ~10% (~12MgC ha−1) through two mechanisms: (i) a direct fixation effect on tree growth, and (ii) an indirect effect on the successional sequence of non-fixing trees. We estimate that including nitrogen-fixing trees in Neotropical reforestation projects could safeguard the sequestration of 6.7 Gt CO2 over the next 20 years. Our results highlight the connection between functional diversity of plant communities and the critical ecosystem service of carbon sequestration for mitigating climate change.

Biomechanical Investigation about Traditional and Cortical Trajectory Screws of Static and Dynamic Lumbar Fixation

Background To evaluate kinetic and kinematic behavior in both static and dynamic CBT fixation a finite element study was designed. Two types of screw trajectories are commonly used in lumbar surgery. Both traditional trajectory (TT) and cortical bone trajectory (CBT) provide equivalent pull-out strengths of a screw. Dynesys fixation of TT screws, but not dynamization of CBT screws, has been used extensively in lumbar surgery. This study aimed to simulate the biomechanics of CBT-based dynamic system for an evaluation of CBT dynamization.Methods A validated nonlinearly lumbosacral finite-element model was used to simulate four variations of screw fixation. Responses of both implant (screw stress) and tissues (disc motion, disc stress, and facet force) at the upper adjacent (L3-L4) and fixed (L4-L5) segments were used as the evaluation indices. Flexion, extension, bending, and rotation of both TT and CBT screws were simulated in this study for comparison.Results The results showed that the TT static was the most effective stabilizer to the L4-L5 segment, followed by CBT static, TT dynamic, and the CBT dynamic, which was the least effective. Dynamization of the TT and CBT fixators decreased stability of the fixed segment and alleviate adjacent segment stress compensation. The 3.5-mm diameter CBT screw deteriorated stress distribution and rendered it vulnerable to bone-screw loosening and fatigue cracking.Conclusions A systematic analysis of the effects of TT and CBT fixation constructs on kinematic and kinetic responses in a full lumbosacral model is currently lacking. This study examined both the static fixation effect and its dynamic counterpart and identified that dynamization of CBT have slightly inferior structural stiffness than dynamic TT and cautious preoperative evaluation is essential if 3.5-mm diameter CBT screws are used. Therefore, 4.5-mm or 5.5-mm diameter CBT screws, or as big as tolerated, are recommended to avoid loosening and cracking.