2,523 research outputs found
INSTANTANEOUS AND PROLONGED EFFECTS OF A TRIPLE DENSITY MIDSOLE DURING STANDING AND WALKING TASKS
The purpose of this study was to determine if there were any biomechanical differences between an unstable triple density midsole (TRIPLE) and a stable single density midsole (CONTROL). Twelve females completed 10 walking trials and three static trials followed by a two hour prolonged activity assessment during which participants alternated between standing and walking on a treadmill. Muscle activity, center of pressure, plantar forces and tissue oxygenation were measured for each footwear condition on two separate days. Standing in the TRIPLE condition resulted in better pressure distribution and lower peak forces, while walking in the TRIPLE condition resulted in greater tissue oxygenation. This midsole could be incorporated into other footwear where prolonged exposure to standing and walking tasks are the norm, such as work boots
Muscle tuning and preferred movement path – a paradigm shift
In the last 40 years, the scientific debate around running injuries and running shoes has been dominated by two paradigms, the ‘impact’ and the ‘pronation’ paradigms. However, the development of running shoe technologies aimed at reducing impact forces and pronation has not led to a decline of running-related injuries. This article recommends to abandon the ‘impact’ and ‘pronation’ paradigms due to a lack of biomechanical and epidemiological evidence and instead suggests a shift to new paradigms: ‘Muscle tuning’ and the ‘preferred movement path’. These paradigms represent new approaches to understanding the biomechanical patterns of each individual runner and how they are controlled by the neuromuscular system. Experimental evidence in support of the ‘muscle tuning’ and ‘preferred movement path’ paradigms are presented and discussed regarding their relevance for running performance, injuries, and footwear. Finally, this paper proposes that the concept of ‘functional groups’ should be used and further developed to overcome the challenge that groups of individuals respond differently to footwear interventions. First, groups of individuals who behave similarly (functional groups) should be identified. Second, running shoes should be selected to match the characteristics of the identified functional groups in order to optimize the beneficial effects of running shoes for improving running performance and reducing the risk of running injuries
Quantum capacitance: a microscopic derivation
We start from microscopic approach to many body physics and show the
analytical steps and approximations required to arrive at the concept of
quantum capacitance. These approximations are valid only in the semi-classical
limit and the quantum capacitance in that case is determined by Lindhard
function. The effective capacitance is the geometrical capacitance and the
quantum capacitance in series, and this too is established starting from a
microscopic theory.Comment: 7 fig
IMPACT FORCES AND MOVEMENT CONTROL -TWO NEW PARADIGMS
In the last century, participation in physical activities has developed dramatically. The best documented development was in running with millions of participants (6, 24). Between 1978 and 1983, the number of runners in Canada has more than doubled from 15 % to 31 %, but has decreased in 1988 to about 18 % of the total population (50, 56). The high incidence of injuries in runners has been proposed as one possible reason for this decrease. Between 37 to 56 % of all runners are injured during a year of running (31) and running injuries make up the majority of sport related injuries in the young (31.5 %) and the old (40.5 %) physically active population (29). Major reasons for the development of exercise related injuries proposed in the literature include previous injuries, training errors, excessive impact forces and excessive foot movement or movement control (8, 9, 21, 31). From a biomechanical point of view impact forces and movement control are of interest since they can be influenced with the sport shoe. This paper will concentrate on these two aspects and propose two new paradigms for the functional understanding of impact forces and movement control
Quantum to Classical Transition of the Charge Relaxation Resistance of a Mesoscopic Capacitor
We present an analysis of the effect of dephasing on the single channel
charge relaxation resistance of a mesoscopic capacitor in the linear low
frequency regime. The capacitor consists of a cavity which is via a quantum
point contact connected to an electron reservoir and Coulomb coupled to a gate.
The capacitor is in a perpendicular high magnetic field such that only one
(spin polarized) edge state is (partially) transmitted through the contact. In
the coherent limit the charge relaxation resistance for a single channel
contact is independent of the transmission probability of the contact and given
by half a resistance quantum. The loss of coherence in the conductor is modeled
by attaching to it a fictitious probe, which draws no net current. In the
incoherent limit one could expect a charge relaxation resistance that is
inversely proportional to the transmission probability of the quantum point
contact. However, such a two terminal result requires that scattering is
between two electron reservoirs which provide full inelastic relaxation. We
find that dephasing of a single edge state in the cavity is not sufficient to
generate an interface resistance. As a consequence the charge relaxation
resistance is given by the sum of one constant interface resistance and the
(original) Landauer resistance. The same result is obtained in the high
temperature regime due to energy averaging over many occupied states in the
cavity. Only for a large number of open dephasing channels, describing
spatially homogenous dephasing in the cavity, do we recover the two terminal
resistance, which is inversely proportional to the transmission probability of
the QPC. We compare different dephasing models and discuss the relation of our
results to a recent experiment.Comment: 10 pages, 8 figure
EFFECT OF BASKETBALL SHOES OF DIFFERENT WEIGHTS ON PERFORMANCE IN A GAME-LIKE SCENARIO
Lighter shoes have been shown to improve running economy; however this same phenomenon has not been investigated in basketball shoes. The purpose of this study was to investigate the physiological effects of basketball shoes of different masses during an on-court, game like scenario. Twelve male basketball players participated in this study. One shoe that was modified to have three different masses (Light, Medium, and Heavy) was evaluated in this study. Subjects completed a basketball-specific 20 minute fieldbased work protocol (Basketball-20) in each shoe on three different days while five physiological variables of interest were collected. The light shoe condition resulted in significantly lower oxygen consumption, ventilation, and rate of energy expenditure than the medium and heavy conditions
Hyperentanglement-enabled Direct Characterization of Quantum Dynamics
We use hyperentangled photons to experimentally implement an
entanglement-assisted quantum process tomography technique known as Direct
Characterization of Quantum Dynamics. Specifically, hyperentanglement-assisted
Bell-state analysis enabled us to characterize a variety of single-qubit
quantum processes using far fewer experimental configurations than are required
by Standard Quantum Process Tomography (SQPT). Furthermore, we demonstrate how
known errors in Bell-state measurement may be compensated for in the data
analysis. Using these techniques, we have obtained single-qubit process
fidelities as high as 98.2% but with one-third the number experimental
configurations required for SQPT. Extensions of these techniques to multi-qubit
quantum processes are discussed.Comment: This is part of a joint submission with an implementation with Ions:
"Experimental characterization of quantum dynamics through many-body
interactions" by Daniel Nigg, Julio T. Barreiro, Philipp Schindler, Masoud
Mohseni, Thomas Monz, Michael Chwalla, Markus Hennrich and Rainer Blat
Mesoscopic Capacitance Oscillations
We examine oscillations as a function of Fermi energy in the capacitance of a
mesoscopic cavity connected via a single quantum channel to a metallic contact
and capacitively coupled to a back gate. The oscillations depend on the
distribution of single levels in the cavity, the interaction strength and the
transmission probability through the quantum channel. We use a Hartree-Fock
approach to exclude self-interaction. The sample specific capacitance
oscillations are in marked contrast to the charge relaxation resistance, which
together with the capacitance defines the RC-time, and which for spin polarized
electrons is quantized at half a resistance quantum. Both the capacitance
oscillations and the quantized charge relaxation resistance are seen in a
strikingly clear manner in a recent experiment.Comment: 9 pages, 2 figure
Role of coherence in resistance quantization: Quantum Hall and quantum point versus charge relaxation resistance
The quantization of resistances in the quantum Hall effect and ballistic transport through quantum point contacts is compared with the quantization of the charge relaxation resistance of a coherent mesoscopic capacitor. While the former two require the existence of a perfectly transmitting channel, the charge relaxation resistance remains quantized for arbitrary backscattering. The quantum Hall effect and the quantum point contact require only local phase coherence. In contrast quantization of the charge relaxation resistance requires global phase coherenc
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