Search results for " stiffness"
showing 10 items of 299 documents
Stretch-shortening cycle: a powerful model to study normal and fatigued muscle.
2000
Stretch-shortening cycle (SSC) in human skeletal muscle gives unique possibilities to study normal and fatigued muscle function. The in vivo force measurement systems, buckle transducer technique and optic fiber technique, have revealed that, as compared to a pure concentric action, a non-fatiguing SSC exercise demonstrates considerable performance enhancement with increased force at a given shortening velocity. Characteristic to this phenomenon is very low EMG-activity in the concentric phase of the cycle, but a very pronounced contribution of the short-latency stretch-reflex component. This reflex contributes significantly to force generation during the transition (stretch-shortening) pha…
ASSOCIATION OF SERUM URIC ACID WITH AORTIC STIFFNESS IN UNTREATED HYPERTENSIVE SUBJECTS.
2013
INTRODUCTION: Recent studies have reported an association between serum uric acid (SUA) and reduced arterial elasticity. However, in these studies arterial elastic properties have been assessed chiefly by measuring brachial-ankle pulse wave velocity (PWV) or peripheral PWV and only sometimes by using aortic PWV, that is considered the gold standard for measuring arterial stiffness. Moreover, the studies exploring the influence of SUA on aortic distensibility in subjects with arterial hypertension yielded conflicting results. AIM: The purpose of our study was to evaluate the relationships between SUA and aortic stiffness in a group of essential hypertensive patients. METHODS: We enrolled 222…
Microstructural manipulation of electrospun scaffolds for specific bending stiffness for heart valve tissue engineering
2012
Biodegradable thermoplastic elastomers are attractive for application in cardiovascular tissue construct development due to their amenability to a wide range of physical property tuning. For heart valve leaflets, while low flexural stiffness is a key design feature, control of this parameter has been largely neglected in the scaffold literature where electrospinning is being utilized. This study evaluated the effect of processing variables and secondary fiber populations on the microstructure, tensile and bending mechanics of electrospun biodegradable polyurethane scaffolds for heart valve tissue engineering. Scaffolds were fabricated from poly(ester urethane) urea (PEUU) and the deposition…
Experimental Survey on Dry Asphalt Rubber Concrete for Sub-ballast Layers
2012
The railway traffic through a town or near built-up areas causes heavy effects such as noise and vibration on surroundings. In order to minimize the level of these impacts the railway companies with researchers and practitioners seek suitable solutions especially in the field of the rail-track because the main source of the ground borne vibrations and noise is the bad wheel-track contact. In particular, a big effort is addressed to new materials with high mechanical and environmental performance that can be utilized within the sub-ballast layer. This paper presents the results of an experimental survey on the potential application of Dry Asphalt Rubber Concrete (DARC) in sub-ballast layers …
DAMPING AND MECHANICAL PROPERTIES OF DRY ASPHALT RUBBER FOR SUB-BALLAST LAYERS
2011
The passage of railway lines through a town or near built-up areas poses serious environmental problems such as noise and vibration. Consequently railway companies have shown an increasing interest in developing new materials with high mechanical and environmental performance. This paper presents the results of an experimental research on the potential application of Dry Asphalt Rubber (DAR) in sub-ballast layers by measuring its damping and mechanical properties. An experimental survey based on four point bending and Marshall tests was carried to measure the stiffness modulus and damping ratio both of a standard bituminous mixture and of dry asphalt rubber mixture with a rubber content equ…
Performance improvements of asphalt mixtures by dry addition of polymeric additives
2017
This paper shows the results of an experimental study concerning the development and optimization of asphalt mixtures for binder and base courses, improved with specifically engineered additives. The focus was on the mechanical improvements of the mixtures as achievable via dry modification with polymeric additives by making use of aggregate and bitumen of average quality, as locally available, in order to limit the consumption of virgin materials. The results allowed interesting conclusions to be drawn about the use of polymeric additives for these mixtures. In particular, the modified mixtures proved to have better performance in terms of both permanent deformation resistance and stiffnes…
Hardening structures isolated by double sliding devices: Seismic reliability-based design approach
2019
This study deals with seismic reliability-based design (SRBD) relationships in terms of behavior factors and displacement demands for hardening structures equipped with double friction pendu-lum system (DFPS) bearings. An equivalent 3dof system having a hardening post-yield slope is adopted to describe the superstructure behavior, whereas velocity-dependent laws are assumed to model the responses of the two surfaces of the DFPS. The yielding characteristics of the super-structures are defined for increasing behavior factors in compliance with the seismic hazard of L’Aquila site (Italy) and with NTC18 assuming a lifetime of 50 years. Considering several natural seismic records and building p…
4. Inflammation, Endothelial Dysfunction and Arterial Stiffness as Therapeutic Targets in Cardiovascular Medicine.
2016
In the last decades, many factors thought to be associated with the atherosclerotic process and cardiovascular events have been studied, and some of these have been shown to correlate with clinical outcome, such as arterial stiffness, endothelial dysfunction and immunoinflammatory markers. Arterial stiffness is an important surrogate marker that describes the capability of an artery to expand and contract in response to pressure changes. It can be assessed with different techniques, such as the evaluation of PWV and AIx. It is related to central systolic pressure and it is an independent predictor of cardiovascular morbidity and mortality in hypertensive patients, type 2 diabetes, end-stage…
Buckling of Elastic Beam Under Unilateral Constraint
1988
ABSTRACT A criterion is proposed to calculate the critical load of a continuous beam under unilateral constraint. The beam is assumed to be built in at the ends and to rest on equally spaced elastic supports, that have equal stiffness. The problem is solved by determining the length of the half-wave of the buckled shape, the number of supports involved, and their position with respect to the end of the half-wave. The analysis model thus defined is determined in relation to the geometry of the beam and to the ratio between the stiffness of the supports and the shearing stiffness of the generic span. It is shown that there exists a limiting value of this ratio, below which the critical load i…
Mechanical and neural stretch responses of the human soleus muscle at different walking speeds
2009
During human walking, a sudden trip may elicit a Ia afferent fibre mediated short latency stretch reflex. The aim of this study was to investigate soleus (SOL) muscle mechanical behaviour in response to dorsiflexion perturbations, and to relate this behaviour to short latency stretch reflex responses. Twelve healthy subjects walked on a treadmill with the left leg attached to an actuator capable of rapidly dorsiflexing the ankle joint. Ultrasound was used to measure fascicle lengths in SOL during walking, and surface electromyography (EMG) was used to record muscle activation. Dorsiflexion perturbations of 6 deg were applied during mid-stance at walking speeds of 3, 4 and 5 km h(-1). At eac…