Anatomy, morphology and evolution of the patella in squamate lizards and tuatara (Sphenodon punctatus)

The patella (kneecap) is the largest and best-known of the sesamoid bones, postulated to confer biomechanical advantages including increasing joint leverage and reinforcing the tendon against compression. It has evolved several times independently in amniotes, but despite apparently widespread occurrence in lizards, the patella remains poorly characterised in this group and is, as yet, completely undescribed in their nearest extant relative Sphenodon (Rhynchocephalia). Through radiography, osteological and fossil studies we examined patellar presence in diverse lizard and lepidosauromorph taxa, and using computed tomography, dissection and histology we investigated in greater depth the anatomy and morphology of the patella in 16 lizard species and 19 Sphenodon specimens. We have found the first unambiguous evidence of a mineralised patella in Sphenodon, which appears similar to the patella of lizards and shares several gross and microscopic anatomical features. Although there may be a common mature morphology, the squamate patella exhibits a great deal of variability in development (whether from a cartilage anlage or not, and in the number of mineralised centres) and composition (bone, mineralised cartilage or fibrotendinous tissue). Unlike in mammals and birds, the patella in certain lizards and Sphenodon appears to be a polymorphic trait. We have also explored the evolution of the patella through ancestral state reconstruction, finding that the patella is ancestral for lizards and possibly Lepidosauria as a whole. Clear evidence of the patella in rhynchocephalian or stem lepidosaurian fossil taxa would clarify the evolutionary origin(s) of the patella, but due to the small size of this bone and the opportunity for degradation or loss we could not definitively conclude presence or absence in the fossils examined. The pattern of evolution in lepidosaurs is unclear but our data suggest that the emergence of this sesamoid may be related to the evolution of secondary ossification centres and/or changes in knee joint conformation, where enhancement of extensor muscle leverage would be more beneficial.Sophie Regnault, Marc E. H. Jones, Andrew A. Pitsillides, John R. Hutchinso

Linear Momentum Density in Quasistatic Electromagnetic Systems

We discuss a couple of simple quasistatic electromagnetic systems in which the density of electromagnetic linear momentum can be easily computed. The examples are also used to illustrate how the total electromagnetic linear momentum, which may also be calculated by using the vector potential, can be understood as a consequence of the violation of the action-reaction principle, because a non-null external force is required to maintain constant the mechanical linear momentum. We show how one can avoid the divergence in the interaction linear electromagnetic momentum of a system composed by an idealization often used in textbooks (an infinite straight current) and a point charge.Comment: 22 pages, 5 figures, to appear in Eur. J. Phy

Typical properties of optimal growth in the Von Neumann expanding model for large random economies

We calculate the optimal solutions of the fully heterogeneous Von Neumann expansion problem with $N$ processes and $P$ goods in the limit $N\to\infty$. This model provides an elementary description of the growth of a production economy in the long run. The system turns from a contracting to an expanding phase as $N$ increases beyond $P$. The solution is characterized by a universal behavior, independent of the parameters of the disorder statistics. Associating technological innovation to an increase of $N$, we find that while such an increase has a large positive impact on long term growth when $N\ll P$, its effect on technologically advanced economies ($N\gg P$) is very weak.Comment: 8 pages, 1 figur

Inspiratory muscle training reduces blood lactate concentration during volitional hyperpnoea

Although reduced blood lactate concentrations ([lac−]B) have been observed during whole-body exercise following inspiratory muscle training (IMT), it remains unknown whether the inspiratory muscles are the source of at least part of this reduction. To investigate this, we tested the hypothesis that IMT would attenuate the increase in [lac−]B caused by mimicking, at rest, the breathing pattern observed during high-intensity exercise. Twenty-two physically active males were matched for 85% maximal exercise minute ventilation (V˙Emax) and divided equally into an IMT or a control group. Prior to and following a 6 week intervention, participants performed 10 min of volitional hyperpnoea at the breathing pattern commensurate with 85% V˙Emax

Dinámica folicular durante el ciclo estral natural en búfalas (Bubalus bubalis)

The aim of the study was to monitor the follicular dynamics of the natural estrous cycle in the domestic buffalo in Colombia. Patterns of growth and regression of ovarian follicles in two consecutive oestrus cycles in 11 buffalos were evaluated. Ultrasound examination of the ovaries were conducted every second day to establish patterns of follicular waves, number of waves, emergency day, number of follicles recruited, and characteristics of the dominant follicle (DF) and of the corpus luteum (CL). Progesterone (P4) concentration was determined by radioimmunoassay. Seventeen normal cycles (2, 11 and 4 estrous cycles with one, two and three follicular waves, respectively) were evaluated. The inter ovulatory interval was 12.5 ± 2.7, 20.5 ± 1.2 and 28.8 ± 1.9 days for cycles with 1, 2 and 3 follicular waves, respectively. Follicular waves emerged on days 0 ± 2.3 for cycles with 1 wave, on days 2.3 ± 1.0 and 10.5 ± 1.0 in cycles with two waves and on days 1.6 ± 1.25, 8.0 ± 1.9 and 20.8 ± 1.6 (mean ± e.e.) in cycles with the waves. The concentration of P4 on the day of maximum diameter of CL on average was 7.2 ± 6.6 ng/ml. In conclusion, follicular dynamics of the Colombian buffalo is characterized by patterns of one, two and three follicular waves, with predominance of two-wave cycles.El objetivo del estudio fue monitorear la dinámica folicular del ciclo estral natural de hembras bufalinas en Colombia. Se evaluaron los patrones de crecimiento y regresión de folículos ováricos de 11 búfalas durante dos ciclos estrales. Se realizaron exámenes ecográficos interdiarios de los ovarios para establecer patrones de ondas foliculares, número de ondas, día de emergencia, número de folículos reclutados, y características del folículo dominante (FD) y del cuerpo lúteo (CL). Las concentraciones de progesterona (P4) se determinaron por radioinmunoensayo. Se evaluaron 17 ciclos normales (2, 11 y 4 ciclos con una, dos y tres ondas foliculares, respectivamente). El intervalo inter-ovulatorio fue de 12.5 ± 2.7, 20.5 ± 1.2 y 28.8 ± 1.9 días para los ciclos con 1, 2 y 3 ondas foliculares, respectivamente. Las ondas foliculares emergieron los días 0 ± 2.3 en ciclos de una onda, los días 2.3 ± 1.0 y 10.5 ± 1.0 en ciclos de dos ondas y los días 1.25 ± 1.6, 8.0 ± 1.9 y 20.8 ± 1.6 (promedio ± e.e.) en ciclos de tres ondas. El diámetro máximo (cm) alcanzado por el FD fue de 1.2 ± 0.4 en ciclos de una onda, de 1.02 ± 0.2 y 1.3 ± 0.3 en ciclos de dos ondas, y de 1.2 ± 0.3, 1.3 ± 0.3 y 1.2 ± 0.3 en ciclos de tres ondas. La concentración de P4 en el día de máximo diámetro del CL en promedio fue de 7.2 ± 6.6 ng/ml. Se concluye que la dinámica folicular de la búfala colombiana se caracteriza por presentar patrones de una, dos y tres ondas foliculares, con predominio de ciclos de dos ondas

An empirical eigenvalue-threshold test for sparsity level estimation from compressed measurements

Compressed sensing allows for a significant reduction of the number of measurements when the signal of interest is of a sparse nature. Most computationally efficient algorithms for signal recovery rely on some knowledge of the sparsity level, i.e., the number of non-zero elements. However, the sparsity level is often not known a priori and can even vary with time. In this contribution we show that it is possible to estimate the sparsity level directly in the compressed domain, provided that multiple independent observations are available. In fact, one can use classical model order selection algorithms for this purpose. Nevertheless, due to the influence of the measurement process they may not perform satisfactorily in the compressed sensing setup. To overcome this drawback, we propose an approach which exploits the empirical distributions of the noise eigenvalues. We demonstrate its superior performance compared to state-of-the-art model order estimation algorithms numerically. © 2014 EURASIP