Avoiding matrix exponentials for large transition rate matrices.

Exact methods for the exponentiation of matrices of dimension N can be computationally expensive in terms of execution time (N3) and memory requirements (N2), not to mention numerical precision issues. A matrix often exponentiated in the natural sciences is the rate matrix. Here, we explore five methods to exponentiate rate matrices, some of which apply more broadly to other matrix types. Three of the methods leverage a mathematical analogy between computing matrix elements of a matrix exponential process and computing transition probabilities of a dynamical process (technically a Markov jump process, MJP, typically simulated using Gillespie). In doing so, we identify a novel MJP-based method relying on restricting the number of "trajectory" jumps that incurs improved computational scaling. We then discuss this method's downstream implications on mixing properties of Monte Carlo posterior samplers. We also benchmark two other methods of matrix exponentiation valid for any matrix (beyond rate matrices and, more generally, positive definite matrices) related to solving differential equations: Runge-Kutta integrators and Krylov subspace methods. Under conditions where both the largest matrix element and the number of non-vanishing elements scale linearly with N-reasonable conditions for rate matrices often exponentiated-computational time scaling with the most competitive methods (Krylov and one of the MJP-based methods) reduces to N2 with total memory requirements of N.

Long-term heat acclimation training in mice: Similar metabolic and running performance adaptations despite a lower absolute intensity than training at temperate conditions.

This study investigated the impact of long-term heat acclimation (HA) training on mouse thermoregulation, metabolism, and running performance in temperate (T) and hot (H) environments. Male Swiss mice were divided into 1) Sedentary (SED) mice kept in T (22 °C; SED/T), 2) Endurance Trained mice (ET, 1 h/day, 5 days/week, 8 weeks, 60 % of maximum speed) in T (ET/T), 3) SED kept in H (32 °C; SED/H), and 4) ET in H (ET/H). All groups performed incremental load tests (ILT) in both environments before (pre-ET) and after four and eight weeks of ET. In the pre-ET period, H impaired (∼30 %) performance variables (maximum speed and external work) and increased (1.3 °C) maximum abdominal body temperature compared with T. In T, after four weeks, although ET/H exercised at a lower (∼30 %) absolute intensity than ET/T, performance variables and aerobic power (peak oxygen uptake, VO2peak) were similarly increased in both ET groups compared with SED/T. After eight weeks, the external work was higher in both ET groups compared with SED/T. Only ET/T significantly increased VO2peak (∼11 %) relative to its pre-ET period. In H, only after eight weeks, both ET groups improved (∼19 %) maximum speed and reduced (∼46 %) post-ILT blood lactate concentrations compared with their respective pre-ET values. Liver glycogen content increased (34 %) in both ET groups and SED/H compared with SED/T. Thus, ET/H was performed at a lower absolute intensity but promoted similar effects to ET/T on metabolism, aerobic power, and running performance. Our findings open perspectives for applying HA training as part of a training program or orthopedic and metabolic rehabilitation programs in injured or even obese animals, reducing mechanical load with equivalent or higher physiological demand.

Regeneração óssea guiada para aumento horizontal de rebordo utilizando fibrina rica em plaquetas associada a enxertos ósseos: revisão de literatura / Guided bone regenerationfor horizontal bone augmentation using platelet- rich fibrin associated with bone grafts: literature review

Objetivo: revisar a literatura sobre os diferentes tipos de derivados de plaquetas autólogas e o desempenho clínico do uso do sticky bone para aumento ósseo horizontal de rebordo. Materiais e métodos: Para realização dessa revisão foram realizadas buscas nas bases de dados PubMed, Google Scholar e Web of Science, utilizando os seguintes descritores: "platelet-rich fibrin" AND "sticky bone" OR "alveolar bone grafting" AND "sticky bone" OR "guided bone regeneration" AND "sticky bone" AND "alveolar ridge augmentation" OR "Alveolar ridge augmentation" AND "sticky bone". Foram incluídos artigos publicados em inglês, que abordavam conceitos relacionados aos agregados plaquetários e a regeneração óssea guiada para aumento ósseo horizontal de rebordo utilizando fibrina rica em plaquetas associada à enxertos ósseos (sticky bone). Resultados: Após avaliação dos estudos encontrados foram selecionados 11 artigos sobre o uso do sticky bone para aumento horizontal de rebordo. Para compor este trabalho foram selecionados também 14 estudos de revisão e artigos associados ao tema. Por ser de fácil aplicação e obtenção, muitos autores têm estudado as aplicações cirúrgicas do sticky bone e os resultados demonstram que o aumento horizontal do rebordo utilizando essa técnica pode ser realizado de forma previsível. Conclusão: apesar de haver estudos promissores sobre o uso do sticky bone, falta evidência na literatura sobre seu sucesso clínico. Assim, para compreender o potencial regenerativo desta técnica são necessários um maior número de estudos randomizados, com diferentes materiais de enxerto e protocolos padronizados de obtenção do sticky bone.(AU)

Objective: to review the literature on the different types of autologous platelet derivatives and the clinical performance of using sticky bone for horizontal bone ridge augmentation. Materials and methods: In order to conduct this review, it was conducted searches in the PubMed, Google Scholar, and Web of Science databases using the following descriptors: "platelet-rich fibrin" AND "sticky bone" OR "alveolar bone grafting" AND "sticky bone" OR "guided bone regeneration" AND "sticky bone" AND "alveolar ridge augmentation" OR "Alveolar ridge augmentation" AND "sticky bone". It included articles published in English that addressed concepts related to platelet aggregates and guided bone regeneration for horizontal bone augmentation using platelet-rich fibrin associated with bone grafts (sticky bone). Results: After evaluating the studies found, were selected 11 articles on the use of sticky bone for horizontal ridge augmentation. To compose this work, 14 review studies and articles associated with the topic were also selected. Due to its ease of application and availability, many authors have explored the surgical applications of sticky bone, and the results indicate that horizontal ridge augmentation using this technique can be predictably performed. Conclusion: while there are promising studies on the use of sticky bone, the literature lacks evidence regarding its clinical success. Therefore, to fully understand the regenerative potential of this technique, further randomized studies are needed, involving different graft materials and standardized protocols for obtaining sticky bone.(AU)

Information geometry and Bose-Einstein condensation.

It is a long held conjecture in the connection between information geometry (IG) and thermodynamics that the curvature endowed by IG diverges at phase transitions. Recent work on the IG of Bose-Einstein (BE) gases challenged this conjecture by saying that in the limit of fugacity approaching unit-where BE condensation is expected-the curvature does not diverge; rather, it converges to zero. However, as the discontinuous behavior that identifies condensation is only observed at the thermodynamic limit, a study of the IG curvature at a finite number of particles, N, is in order from which the thermodynamic behavior can be observed by taking the thermodynamic limit ( N→∞) posteriorly. This article presents such a study. We find that for a trapped gas, as N increases, the values of curvature decrease proportionally to a power of N, while the temperature at which the maximum value of curvature occurs approaches the usually defined critical temperature. This means that, in the thermodynamic limit, the curvature has a limited value where a phase transition is observed, contradicting the forementioned conjecture.

How many submissions are needed to discover friendly suggested reviewers?

It is common in scientific publishing to request from authors reviewer suggestions for their own manuscripts. The question then arises: How many submissions are needed to discover friendly suggested reviewers? To answer this question, as the data we would need is anonymized, we present an agent-based simulation of (single-blinded) peer review to generate synthetic data. We then use a Bayesian framework to classify suggested reviewers. To set a lower bound on the number of submissions possible, we create an optimistically simple model that should allow us to more readily deduce the degree of friendliness of the reviewer. Despite this model's optimistic conditions, we find that one would need hundreds of submissions to classify even a small reviewer subset. Thus, it is virtually unfeasible under realistic conditions. This ensures that the peer review system is sufficiently robust to allow authors to suggest their own reviewers.

Entropic Dynamics on Gibbs Statistical Manifolds.

Entropic dynamics is a framework in which the laws of dynamics are derived as an application of entropic methods of inference. Its successes include the derivation of quantum mechanics and quantum field theory from probabilistic principles. Here, we develop the entropic dynamics of a system, the state of which is described by a probability distribution. Thus, the dynamics unfolds on a statistical manifold that is automatically endowed by a metric structure provided by information geometry. The curvature of the manifold has a significant influence. We focus our dynamics on the statistical manifold of Gibbs distributions (also known as canonical distributions or the exponential family). The model includes an "entropic" notion of time that is tailored to the system under study; the system is its own clock. As one might expect that entropic time is intrinsically directional; there is a natural arrow of time that is led by entropic considerations. As illustrative examples, we discuss dynamics on a space of Gaussians and the discrete three-state system.

Comment on "Black Hole Entropy: A Closer Look".

In a recent paper (Entropy 2020, 22(1), 17), Tsallis states that entropy-as in Shannon or Kullback-Leiber's definitions-is inadequate to interpret black hole entropy and suggests that a new non-additive functional should take the role of entropy. Here we counterargue by explaining the important distinction between the properties of extensivity and additivity; the latter is fundamental for entropy, while the former is a property of particular thermodynamical systems that is not expected for black holes. We also point out other debatable statements in his analysis of black hole entropy.

Repair with bicortical suspension device restores proximal tibiofibular joint motion.

PURPOSE: Dislocation of the proximal tibiofibular joint is a complex injury that is often overlooked or misdiagnosed. Surgical treatment is recommended for severe acute or for chronic symptomatic instability but there is still no evidence on the optimal reconstruction technique. The purpose of this study is to analyze the motion of the proximal tibiofibular joint after repair with a bicortical suspension device as compared to its normal kinematics. METHODS: Kinematic analysis of the proximal tibiofibular joint was performed during continuous passive motion of the knee and ankle in 7 whole body cadavers in a controlled laboratory study. The 14 knees were measured in four conditions: (1) intact; (2) repair with transarticular bicortical suspension device tensioned to 40 N; (3) the same repair tensioned to 50 N; and (4) the repair tensioned to 50 N after interosseous syndesmotic membrane sectioning. RESULTS: Proximal tibiofibular joint can be successfully repaired by a bicortical suspension device restoring its normal 3D spatial motion. The fixation of the PTFJ with the device tested tensioned to 40 or 50 N could restore the intact joint kinematics for every movement tested except knee internal and external rotation. The fixation to 40 N attained closer values to the intact joint in the movements that evolve the anterior PTFJ ligament. The 50 N fixation is overall more rigid than the intact joint but statistically closer to the normal PTFJ kinematics for the movements more dependent on the posterior PTFJ ligament. Sectioning of the interosseous syndesmotic membrane determined an important loss of stability of the PTFJ during the movements of ankle extension and ankle flexion. Such loss illustrates the relevance of this associated injury when planning PTFJ ligament reconstruction. CONCLUSIONS: This study indicates that the repair of the proximal tibiofibular joint with a transarticular bicortical suspension device tensioned to 40 and 50 N can restore the normal kinematics of this joint. Based on these findings, Surgeons may consider this option as a reliable solution when planning successful treatment for proximal tibiofemoral joint instability.

Kinematics of the proximal tibiofibular joint is influenced by ligament integrity, knee and ankle mobility: an exploratory cadaver study.

PURPOSE: The proximal tibiofibular joint (PTFJ) is a rather unknown articulation. There is little understanding of its anatomy, physiology, and functional role. The objectives of this research are to describe the normal kinematics of the PTFJ and its relation to the ankle and knee movements. METHODS: Fourteen knees of seven adult fresh frozen whole body cadavers were studied. The proximal tibiofibular joint and ligaments were identified, after which we sequentially sectioned the anterior proximal tibiofibular ligament (APTFL), the posterior proximal tibiofibular ligament (PPTFL), and the interosseous syndesmotic membrane. Models with intact and sectioned ligaments were compared, while the unloaded lower limb was manually mobilized in a pre-defined sequence of combined movements of knee, ankle, and proximal tibiofibular joints. The PTFJ spatial displacement was measured by analyzing the length of a distance vector between two 3D coordinate systems settled over the tibia and fibula. RESULTS: On the unaltered PTFJ, direct grasping of the head of the fibula with the hip in 45° of flexion and the knee in 90° of flexion was found to produce an average displacement of 7 mm. Knee movements caused the greatest spatial displacements, almost ten times the ones produced by ankle flexion/extension. Flexion/extension of the knee caused 1.8 times more displacement than single rotations with the knee flexed to 90°. It was found that the APTFL was an important stabilizer of the PTFJ when this joint is tensioned accommodating the movements of ankle extension and foot eversion. The APTFL was not a significant stabilizer of the PTFJ during direct manipulation of the fibular head when imprinting a manual force with posterior direction. The PPTFL was an important accommodator of ankle flexion, foot inversion and knee flexion. The interosseous syndesmotic membrane also proved to be a significant PTFJ stabilizer in rotational movements of the ankle and knee. CONCLUSIONS: This is the first cadaver study to illustrate the PTFJ normal spatial displacement, thereby contributing to a deeper insight of this joint. The contribution of each ligament for PTFJ stability was described and, based on these findings; a new mechanism of injury was suggested. Surgeons can translate the results of this study into the clinical practice.

Exact Renormalization Groups As a Form of Entropic Dynamics.

The Renormalization Group (RG) is a set of methods that have been instrumental in tackling problems involving an infinite number of degrees of freedom, such as, for example, in quantum field theory and critical phenomena. What all these methods have in common-which is what explains their success-is that they allow a systematic search for those degrees of freedom that happen to be relevant to the phenomena in question. In the standard approaches the RG transformations are implemented by either coarse graining or through a change of variables. When these transformations are infinitesimal, the formalism can be described as a continuous dynamical flow in a fictitious time parameter. It is generally the case that these exact RG equations are functional diffusion equations. In this paper we show that the exact RG equations can be derived using entropic methods. The RG flow is then described as a form of entropic dynamics of field configurations. Although equivalent to other versions of the RG, in this approach the RG transformations receive a purely inferential interpretation that establishes a clear link to information theory.

Sex-based effects on immune changes induced by a maximal incremental exercise test in well-trained swimmers.

Studies examining the immune response to acute intensive swimming have shown increased leukocytosis and lymphocyte populations. However, studies concerning mucosal immunity and sex differences remain controversial. The objective of the study was to examine sex differences on the immune response to maximal incremental swimming exercise in well trained swimmers. Participants (11 females, controlled for menstrual cycle phase effects; 10 males) performed a maximal incremental 7x200 m front crawl set. Fingertip capillary blood samples were obtained after each 200 m swim for lactate assessment. Venous blood and saliva samples were collected before and 5 minutes after the swimming test to determine total numbers of leukocytes, lymphocytes and subpopulations, and serum and salivary immunoglobulin A (IgA) levels. IgA secretion rate was calculated. Menstrual cycle phase did not influence the immune response to exercise. As for sex differences, exercise induced an increase in leukocytes, total lymphocytes, CD3(+), CD4(+), CD8(+), and CD16(+)/56(+) in males. In females, only leukocytosis, of a lower magnitude than was observed in males, occurred. CD19(+) increased and CD4(+)/CD8(+) ratio decreased in both groups following exercise whilst IgA, SIgA concentrations, and srIgA did not change. Both males and females finished the incremental exercise very close to the targeted race velocity, attaining peak blood lactate concentrations of 14.6±2.25 and 10.4±1.99 mmol.L(-1), respectively. The effect of a maximal incremental swimming task on immunity is sex dependent and more noticeable in men. Males, as a consequence of higher levels of immunosurveillance may therefore be at a lower risk of infection than females. Key PointsMaximal exercise induces an immune response.This study investigated the influence of sex over the leukocytes subpopulations and mucosal immune responses to maximal swimming.Male swimmers showed a stronger increase of T helper, T cytotoxic and NK lymphocytes than females, suggesting they may be at a lower risk of infection, due to a higher immunosurveillance.Mucosal immunity remained unchanged in both sexes.