Ensemble renormalization group for the random field hierarchical model

The Renormalization Group (RG) methods are still far from being completely understood in quenched disordered systems. In order to gain insight into the nature of the phase transition of these systems, it is common to investigate simple models. In this work we study a real-space RG transformation on the Dyson hierarchical lattice with a random field, which led to a reconstruction of the RG flow and to an evaluation of the critical exponents of the model at T = 0. We show that this method gives very accurate estimations of the critical exponents, by comparing our results with the ones obtained by some of us using an independent method

Statistical mechanics of the spherical hierarchical model with random fields

We study analytically the equilibrium properties of the spherical hierarchical model in the presence of random fields. The expression for the critical line separating a paramagnetic from a ferromagnetic phase is derived. The critical exponents characterising this phase transition are computed analytically and compared with those of the corresponding $D$-dimensional short-range model, leading to conclude that the usual mapping between one dimensional long-range models and $D$-dimensional short-range models holds exactly for this system, in contrast to models with Ising spins. Moreover, the critical exponents of the pure model and those of the random field model satisfy a relationship that mimics the dimensional reduction rule. The absence of a spin-glass phase is strongly supported by the local stability analysis of the replica symmetric saddle-point as well as by an independent computation of the free-energy using a renormalization-like approach. This latter result enlarges the class of random field models for which the spin-glass phase has been recently ruled out.Comment: 23 pages, 2 figure

Cross correlations of the American baby names

The quantitative description of cultural evolution is a challenging task. The most difficult part of the problem is probably to find the appropriate measurable quantities that can make more quantitative such evasive concepts as, for example, dynamics of cultural movements, behavior patterns and traditions of the people. A strategy to tackle this issue is to observe particular features of human activities, i.e. cultural traits, such as names given to newborns. We study the names of babies born in the United States of America from 1910 to 2012. Our analysis shows that groups of different correlated states naturally emerge in different epochs, and we are able to follow and decrypt their evolution. While these groups of states are stable across many decades, a sudden reorganization occurs in the last part of the twentieth century. We think that this kind of quantitative analysis can be possibly extended to other cultural traits: although databases covering more than one century (as the one we used) are rare, the cultural evolution on shorter time scales can be studied thanks to the fact that many human activities are usually recorded in the present digital era.Comment: submitted for consideration to PNA

High storage capacity in the Hopfield model with auto-interactions - stability analysis

Recent studies point to the potential storage of a large number of patterns in the celebrated Hopfield associative memory model, well beyond the limits obtained previously. We investigate the properties of new fixed points to discover that they exhibit instabilities for small perturbations and are therefore of limited value as associative memories. Moreover, a large deviations approach also shows that errors introduced to the original patterns induce additional errors and increased corruption with respect to the stored patterns

High storage capacity in the Hopfield model with auto-interactions - stability analysis

Recent studies point to the potential storage of a large number of patterns in the celebrated Hopfield associative memory model, well beyond the limits obtained previously. We investigate the properties of new fixed points to discover that they exhibit instabilities for small perturbations and are therefore of limited value as associative memories. Moreover, a large deviations approach also shows that errors introduced to the original patterns induce additional errors and increased corruption with respect to the stored patterns

Physiological comparison between competitive and beginner high intensity functional training athletes

Introduction: Among high intensity trainings, high intensity functional training (HIFT) represent one of the most recent developments. The aim of the present study was to investigate the differences between a group of competitive (CMP) HIFT athletes and a group of age- and gender-matched beginner (BGN) HIFT athletes, to clarify the physiological characteristics of each group and the reasons for differences. Methods: 10 BGN (32.5 ± 6.2 years) and 10 CMP (29.0 ± 5.4 years) athletes, were included in the study and were evaluated for anthropometry, VO2peak, lactate threshold, isometric and isokinetic leg maximal power and strength, handgrip and maximal anaerobic power. Results: Compared to BGN athletes, CMP reached higher levels of VO2peak (56.1 ± 2.89 ml·kg-1·min-1 CMP vs. 46.5 ± 6.86 ml·kg-1·min-1 BGN; p .006), while anaerobic capacity did not show significant differences (101.8 ± 9.33 kJ CMP vs. 87.0 ± 28.37 kJ BGN; p = .1). Conclusions: CMP athletes showed greater physiological adaptations in aerobic fitness and strength than BGN. Differences may be attributed to the technical skills acquired by CMP and not only to the physiological adaptations induced by the specific training. The lack of differences in anaerobic capacity is likely due to an early and fast improvement in BGN, compared to other parameters

Physiological profile of high intensity functional training athletes

Introduction: High intensity functional trainings (HIFT) are among the most common and popular training modalities. The aim of the present study was to examine the physiological characteristics of a group of HIFT competitive athletes both in a laboratory and field setting. Methods: Twenty HIFT athletes, 10 men (29 ± 5.3 years) and 10 women (30 ± 3.2 years), were evaluated in the laboratory for anthropometric characteristics, VO2peak, lactate threshold, maximal anaerobic power, maximal voluntary isometric and isokinetic strength, and muscle power during a countermovement jump. Athletes were also monitored in the field by measuring VO2 and lactate during a training session. Results: HIFT competitive athletes reached high levels in VO2peak (52.9 ± 5.67 ml·kg-1·min-1 in men; 52.4 ± 6.17 ml·kg-1·min-1 in women), VO2 at lactate threshold (79.7% of VO2peak in men; 74.5% of VO2peak in women), maximal anaerobic power (7.6 ± 1.32 W·kg-1 in men; 5.0 ± 1.13 W·kg-1 in women; p < .05), maximal voluntary knee extension isometric strength (11.7 ± 1.43 N·kg-1 in men; 9.5 ± 2.25 N·kg-1 in women; p < .05) and isokinetic strength (281.4 ± 31.56 N·kg-1 in men; 243.1 ± 44.13 N·kg-1 in women; p < .05), and muscle power during a countermovement jump (54 ± 5.9 W·kg-1 in men; 40 ± 4.8 W·kg-1 in women; p < .05). VO2peak during the on-field training session (50.6 ± 3.82 ml·kg-1·min-1 in men; 51.9 ± 5.76 ml·kg-1·min-1 in women) and lactate production (10.4 ± 0.69 mmol·l-1 in men; 9.7 ± 0.96 mmol·l-1 in women) revealed the high intensity nature of HIFT. Conclusions: Overall, HIFT athletes show exceptional performances in physiological components that are key to many different sports. The lack of specialization in exclusively one domain of physical fitness reveals the comprehensive nature of this training methodology

No Relationship Between Preoperative and Early Postoperative Strength After ACL Reconstruction

Context: All rehabilitative programs before ACL reconstructive surgery, which are focused on recovery of proprioception and muscular strength, are defined as prehabilitation. While it has shown that prehabilitation positively affects the overall outcome after ACL reconstruction, it is still controversial whether enhancing preoperatively quadriceps strength has some beneficial effect on postoperative strength, mainly during the first period. Objective: To determine whether there is any relationship between pre- and early postoperative quadriceps strength. Design: Case control. Setting: University research laboratory. Participants: Fifty-nine males (18-33 y; age: 23.69 (0.71) y) who underwent ACL reconstruction with patellar-tendon autograft were examined the day before surgery, at 60 and at 90 days after surgery. Main Outcome Measures: The limb-symmetry-index (LSI) was quantified for maximal voluntary isometric contraction (MVIC) of the knee extensor muscles and of the knee flexor muscles at 90° joint angle. K-means analysis was performed on either quadriceps or hamstrings LSI before surgery to classify the patients in high and low preoperative LSI clusters. Differences in postoperative LSI were then evaluated between the high and low preoperative LSI clusters. Results: Following surgery, there were no differences in the quadriceps LSI between patients with high and low preoperative quadriceps LSI. Sixty days after surgery, the hamstrings LSI was higher in patients with high than low preoperative hamstrings LSI (84.0±13.0% vs 75.4±15.9%; P<0.05). Conclusions: Findings suggest that quadriceps strength deficit is related to the ACL injury and increases further after the reconstruction without any correlation between the pre-operative and postoperative values. Therefore, it appears that there is no need to delay surgery in order to increase the preoperative quadriceps strength before surgery