Solving the mystery of human sleep schedules one mutation at a time.

Sleep behavior remains one of the most enigmatic areas of life. The unanswered questions range from "why do we sleep?" to "how we can improve sleep in today's society?" Identification of mutations responsible for altered circadian regulation of human sleep lead to unique opportunities for probing these territories. In this review, we summarize causative circadian mutations found from familial genetic studies to date. We also describe how these mutations mechanistically affect circadian function and lead to altered sleep behaviors, including shifted or shortening of sleep patterns. In addition, we discuss how the investigation of mutations can not only expand our understanding of the molecular mechanisms regulating the circadian clock and sleep duration, but also bridge the pathways between clock/sleep and other human physiological conditions and ailments such as metabolic regulation and migraine headaches

Particle Acceleration and Plasma Dynamics during Magnetic Reconnection in the Magnetically-dominated Regime

Magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. The energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. We carry out two- and three-dimensional kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. The simulations focus on electron-positron plasmas starting with a magnetically dominated, force-free current sheet ($\sigma \equiv B^2/(4\pi n_e m_e c^2) \gg 1$). For this limit, we demonstrate that relativistic reconnection is highly efficient at accelerating particles through a first-order Fermi process accomplished by the curvature drift of particles along the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra $f \propto (\gamma-1)^{-p}$ and approaches $p = 1$ for sufficiently large $\sigma$ and system size. Eventually most of the available magnetic free energy is converted into nonthermal particle kinetic energy. An analytic model is presented to explain the key results and predict a general condition for the formation of power-law distributions. The development of reconnection in these regimes leads to relativistic inflow and outflow speeds and enhanced reconnection rates relative to non-relativistic regimes. In the three-dimensional simulation, the interplay between secondary kink and tearing instabilities leads to strong magnetic turbulence, but does not significantly change the energy conversion, reconnection rate, or particle acceleration. This study suggests that relativistic reconnection sites are strong sources of nonthermal particles, which may have important implications to a variety of high-energy astrophysical problems.Comment: 18 pages, 13 figures, slightly modified after submitted to Ap

PREVENTION AND REHABILITATION OF NON-CONTACT ACL INJURY: NEW INFORMATION IN RECENT STUDIES

Anterior cruciate ligament (ACL) injury is one of the most common injuries in sports. Tremendous efforts have been made to prevent this devastating injury. Recent studies provided new information understanding ACL injury and the prevention and rehabilitation of the injury. Anterior translation of the tibia is the primary mechanism of the injury. Small knee flexion angle in landing tasks is a primary risk factor of the injury. Gender differences in movement patterns are likely due to differences in training and skill levels. New prevention programs need to be developed to improve compliance to prevention programs. Movement patterns may need to be evaluated in actual game conditions

Integrating Functional Synthesis

Design couples synthesis and analysis in iterative cycles, alternatively generating solutions, and evaluating their validity. The accuracy and depth of evaluation has increased markedly because of the availability of powerful simulation tools and the development of domain-specific knowledge bases. Efforts to extend the state of the art in evaluation have unfortunately been carried out in stovepipe fashion, depending on domain-specific views both of function and of what constitutes “good” design. Although synthesis as practiced by humans is an intentional process that centers on the notion of function, computational synthesis often eschews such intention for sheer permutation. Rather than combining synthesis and analysis to form an integrated design environment, current methods focus on comprehensive search for solutions within highly circumscribed subdomains of design. This paper presents an overview of the progress made in representing design function across abstraction levels proven useful to human designers. Through an example application in the domain of mechatronics, these representations are integrated across domains and throughout the design process

Injury rate, mechanism, and risk factors of hamstring strain injuries in sports: A review of the literature

Hamstring strains are one of most common sports injuries. The purpose of this literature review is to summarize studies on hamstring strain injury rate, mechanism, and risk factors in the last several decades with a focus on the prevention and rehabilitation of this injury. Hamstring injury commonly occurs in sporting events in which high speed sprinting and kicking are frequently performed, such as Australian football, English rugby, American football, and soccer. Basic science studies have demonstrated that a muscle strain injury occurs due to excessive strain in eccentric contraction instead of force, and that elongation speed and duration of activation before eccentric contraction affect the severity of the injury. Hamstring strain injury is likely to occur during the late swing phase and late stance phase of sprint running. Shortened optimum muscle length, lack of muscle flexibility, strength imbalance, insufficient warm-up, fatigue, lower back injury, poor lumbar posture, and increased muscle neural tension have been identified as modifiable risk factors while muscle compositions, age, race, and previous injuries are non-modifiable risk factors. The theoretical basis of some of these risk factors, however, is lacking, and the results of clinical studies on these risk factors are inconsistent. Future studies are needed to establish the cause-and-effect relationships between those proposed risk factors and the injury

Effect of different types of fibers on the microstructure and the mechanical behavior of Ultra-High Performance Fiber-Reinforced Concretes

International audienceThis study investigates the effect of adding different types of fibers on the microstructure and the mechanical behavior of cementitious composites, in particular on UHPC. These fibers were distinguished mainly by their differing nature (steel, mineral and synthetic), their dimensions (macroscopic or microscopic), and their mechanical properties. The microstructure of the specimens was examined by using SEM observation and by measuring the porosity, the intrinsic permeability and the P-wave velocity. The mechanical behavior under loading has been studied using a uni-axial compression test which combines the gas permeability and the acoustic emission (AE) measurement. This work focuses on the cracking process under mechanical loading. The experimental results show that the fiber has a relatively slight influence on the compressive strength and elastic modulus of concrete, except for the steel fiber which improves the strength because of its intrinsic rigidity. However, The addition of fiber significantly reduces the lateral strain at peak loading and increases the threshold of initial cracking (σk-ci) and that of unstable cracking (σk-pi). Therefore, the fibers clearly restrain the cracking process in concrete under the mechanic loadin