Normative EMG activation patterns of school-age children during gait

Gait analysis is widely used in clinics to study walking abnormalities for surgery planning, definition of rehabilitation protocols, and objective evaluation of clinical outcomes. Surface electromyography allows the study of muscle activity non-invasively and the evaluation of the timing of muscle activation during movement. The aim of this study was to present a normative dataset of muscle activation patterns obtained from a large number of strides in a population of 100 healthy children aged 6-11 years. The activity of Tibialis Anterior, Lateral head of Gastrocnemius, Vastus Medialis, Rectus Femoris and Lateral Hamstrings on both lower limbs was analyzed during a 2.5-min walk at free speed. More than 120 consecutive strides were analyzed for each child, resulting in approximately 28,000 strides. Onset and offset instants were reported for each observed muscle. The analysis of a high number of strides for each participant allowed us to obtain the most recurrent patterns of activation during gait, demonstrating that a subject uses a specific muscle with different activation modalities even in the same walk. The knowledge of the various activation patterns and of their statistics will be of help in clinical gait analysis and will serve as reference in the design of future gait studie

Structural determination of archaeal UDP-N-acetylglucosamine 4-epimerase from Methanobrevibacter ruminantium M1 in complex with the bacterial cell wall intermediate UDP-N-acetylmuramic acid

The crystal structure of UDP-N-acetylglucosamine 4-epimerase (UDP-GlcNAc 4-epimerase; WbpP; EC 5.1.3.7), from the archaeal methanogen Methanobrevibacter ruminantium strain M1, was determined to a resolution of 1.65 Å. The structure, with a single monomer in the crystallographic asymmetric unit, contained a conserved N-terminal Rossmann fold for nucleotide binding and an active site positioned in the C-terminus. UDP-GlcNAc 4-epimerase is a member of the short-chain dehydrogenase/reductase superfamily, sharing sequence motifs and structural elements characteristic of this family of oxidoreductases and bacterial 4-epimerases. The protein was co-crystallized with coenzyme NADH and UDP-N-acetylmuramic acid, the latter an unintended inclusion and well known product of the bacterial enzyme MurB and a critical intermediate for bacterial cell wall synthesis. This is a non-native UDP sugar amongst archaea and was most likely incorporated from the Eschericha coli expression host during purification of the recombinant enzyme

Geometry of quantum observables and thermodynamics of small systems

The concept of ergodicity---the convergence of the temporal averages of observables to their ensemble averages---is the cornerstone of thermodynamics. The transition from a predictable, integrable behavior to ergodicity is one of the most difficult physical phenomena to treat; the celebrated KAM theorem is the prime example. This Letter is founded on the observation that for many classical and quantum observables, the sum of the ensemble variance of the temporal average and the ensemble average of temporal variance remains constant across the integrability-ergodicity transition. We show that this property induces a particular geometry of quantum observables---Frobenius (also known as Hilbert-Schmidt) one---that naturally encodes all the phenomena associated with the emergence of ergodicity: the Eigenstate Thermalization effect, the decrease in the inverse participation ratio, and the disappearance of the integrals of motion. As an application, we use this geometry to solve a known problem of optimization of the set of conserved quantities---regardless of whether it comes from symmetries or from finite-size effects---to be incorporated in an extended thermodynamical theory of integrable, near-integrable, or mesoscopic systems

Two-Particle Microrheology of quasi-2D Viscous Systems

We study the correlated motions of colloidal particles in a quasi-2D system (Human Serum Albumin (HSA) protein molecules at an air-water interface) for different surface viscosities $\eta_{s}$. We observe a transition in the behavior of the correlated motion, from 2-D interface dominated at high $\eta_{s}$ to bulk fluid-dependent at low $\eta_{s}$. The correlated motions can be scaled onto a master curve which captures the features of this transition. This master curve also characterizes the spatial dependence of the flow field of a viscous interface in response to a force. From the flow field and the correlated particle motions, we calculate a two-particle MSD (mean square displacement) for direct comparison with rheological measurements.Comment: 4 pages, 4 figures, submitted to PR

Thermodynamics of an one-dimensional ideal gas with fractional exclusion statistics

We show that the particles in the Calogero-Sutherland Model obey fractional exclusion statistics as defined by Haldane. We construct anyon number densities and derive the energy distribution function. We show that the partition function factorizes in the form characteristic of an ideal gas. The virial expansion is exactly computable and interestingly it is only the second virial coefficient that encodes the statistics information.Comment: 10pp, REVTE