17 research outputs found
Lower limb stiffness estimation during running: the effect of using kinematic constraints in muscle force optimization algorithms
The focus of this paper is on the effect of muscle force optimization algorithms on the human lower limb stiffness estimation. By using a forward dynamic neuromusculoskeletal model coupled with a muscle short-range stiffness model we computed the human joint stiffness of the lower limb during running. The joint stiffness values are calculated using two different muscle force optimization procedures, namely: Toque-based and Torque/Kinematic-based algorithm. A comparison between the processed EMG signal and the corresponding estimated muscle forces with the two optimization algorithms is provided. We found that the two stiffness estimates are strongly influenced by the adopted algorithm. We observed different magnitude and timing of both the estimated muscle forces and joint stiffness time profile with respect to each gait phase, as function of the optimization algorithm used
Liouville Correlation Functions from Four-dimensional Gauge Theories
We conjecture an expression for the Liouville theory conformal blocks and
correlation functions on a Riemann surface of genus g and n punctures as the
Nekrasov partition function of a certain class of N=2 SCFTs recently defined by
one of the authors. We conduct extensive tests of the conjecture at genus 0,1.Comment: 32 pages, 8 figures; v2: minor corrections, published versio
Altered hip muscle forces during gait in people with patellofemoral osteoarthritis
Objectives: The study aimed to (1) assess whether higher vasti (VASTI), gluteus medius (GMED), gluteus maximus (GMAX) and gluteus minimus (GMIN) forces are associated with participant characteristics (lower age, male gender) and clinical characteristics (lower radiographic disease severity, lower symptom severity and higher walking speed); and (2) determine whether hip and knee muscle forces are lower in people with patellofemoral joint (PFJ) osteoarthritis (OA) compared to those without PFJ OA. Design: Sixty participants with PFJ OA and 18 (asymptomatic, no radiographic OA) controls ≥40 years were recruited from the community or via referrals. A three-dimensional musculoskeletal model was used in conjunction with optimisation theory to calculate lower-limb muscle forces during walking. Associations of peak muscle forces with participant and clinical characteristics were conducted using Pearson's r or independent t-tests and between-group comparisons of mean peak muscle forces performed with walking speed as a covariate. Results: Peak muscle forces were not significantly associated with participant, symptomatic or radiographic-specific characteristics. Faster walking speed was associated with higher VASTI muscle force in the PFJ OA (r = 0.495; P < 0.001) and control groups (r = 0.727; P = 0.001) and higher GMAX muscle force (r = 0.593; P = 0.009) in the control group only. Individuals with PFJ OA (N = 60) walked with lower GMED and GMIN muscle forces than controls (N = 18): GMED, mean difference 0.15 [95% confidence interval (CI): 0.01 to 0.29] body weight (BW); GMIN, 0.03 [0.01 to 0.06] BW. No between-group differences were observed in VASTI or GMAX muscle force: VASTI, 0.10 [-0.11 to 0.31] BW; GMAX, 0.01 [-0.11 to 0.09] BW. Conclusion: Individuals with PFJ OA ambulate with lower peak hip abductor muscle forces than their healthy counterparts
The index of the overlap Dirac operator on a discretized 2d non-commutative torus
The index, which is given in terms of the number of zero modes of the Dirac
operator with definite chirality, plays a central role in various topological
aspects of gauge theories. We investigate its properties in non-commutative
geometry. As a simple example, we consider the U(1) gauge theory on a
discretized 2d non-commutative torus, in which general classical solutions are
known. For such backgrounds we calculate the index of the overlap Dirac
operator satisfying the Ginsparg-Wilson relation. When the action is small, the
topological charge defined by a naive discretization takes approximately
integer values, and it agrees with the index as suggested by the index theorem.
Under the same condition, the value of the index turns out to be a multiple of
N, the size of the 2d lattice. By interpolating the classical solutions, we
construct explicit configurations, for which the index is of order 1, but the
action becomes of order N. Our results suggest that the probability of
obtaining a non-zero index vanishes in the continuum limit, unlike the
corresponding results in the commutative space.Comment: 22 pages, 8 figures, LaTeX, JHEP3.cls. v3:figures 1 and 2 improved
(all the solutions included),version published in JHE
Rock Varnish on Hualalai and Mauna Kea Volcanoes, Hawai'i
Tropical rock varnishes found on Hualalai and Mauna Kea
Volcanoes, Hawai'i, vary systematically with time and environment. Radiocarbon
dating of encapsulated organic matter, (K+ + Ca2+)/Ti4+ ratios, and Zn,
Cu, and Ni trace element concentrations in rock varnish are consistent with lava
flowages established by K-Ar and 14C dating, where samples are collected from
arid microsites well away from the soil surface. However, inaccurate ages are
obtained from rock varnish in subsurface locations and from sites with abundant
lichens, cyanobacteria, and fungi that chemically erode varnish. In contrast with
continental deserts, Hawaiian varnishes commonly interfinger with and are less
common than rock coatings of amorphous silica. Laboratory experiments on
Hawaiian rock varnishes indicate that K and Ca are preferentially leached
relative to Ti over time and at higher temperatures. The location of in situ
leaching has been identified in Hawaiian varnishes as porous textures without
abundant detrital grains