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Tendons exhibit viscoelastic mechanical behavior under tensile loading. The elasticity arises from the collagen chains that form fibrils, while the viscous response arises from the interaction of the water with the solid matrix. Therefore, an understanding of the behavior of water in response to the application of a load is crucial to the understanding of the origin of the viscous response. Three-dimensional MRI mapping of rabbit Achilles tendons was performed at 2.0 T to characterize the response of T1 and T2 relaxation times and the apparent diffusion coefficient (ADC) of water to tensile loading. The ADC was measured in directions both parallel (ADC∥) and perpendicular (ADC⟂) to the long axis of the tendon. At a short diffusion time (5.8 ms) MR parameter maps showed the existence of two regions, here termed 'core' and 'rim', that exhibited statistically significant differences in T1, T2, and ADC⟂ under the baseline loading condition. MR parameter maps were also generated at a second loading condition of ∼1 MPa. At a diffusion time of 5.8 ms, there was a statistically significant increase in the rim region for both ADC⟂ (57.5%) and ADC∥ (20.5%) upon tensile loading. The changes in core ADC(⟂, ∥), as well as the relaxation parameters in both core and rim regions, were not statistically significant. The effect of diffusion time on the ADC(⟂, ∥) values was investigated by creating maps at three additional diffusion times (50.0, 125.0, 250.0 ms) using a diffusion-weighted, stimulated-echo (DW-STE) pulse sequence. At longer diffusion times, ADC(⟂, ∥) values increased rather than approaching a constant value. This observation was attributed to T1 spin-editing during the DW-STE pulse sequence, which resulted in the loss of short- T1 components (with correspondingly lower ADCs) at longer diffusion times (corroborating the results from earlier spectroscopic work). The T1 spin-editing effect was observed both in the core and in the rim regions of the tendon and hence was not solely due to the redistribution of water from the core to the rim upon loading. A measure reflective of the regional change in proton density was noted to be consistent with tensile-load-induced water transport from the central to the peripheral tendon region. Magn Reson Med 53:535-544, 2005. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

When skin is stretched, stimuli experienced by a cutaneous mechanoreceptor neuron are transmitted to the nerve ending through the skin. In these experiments, we tested the hypothesis that the viscoelastic response of the skin influences the dynamic response of cutaneous rapidly adapting (RA) neurons. Cutaneous RA afferent neurons were recorded in 3 species of mice (Tsk, Pallid, and C57BL6) whose skin has different viscoelastic properties. Isolated samples of skin and nerve were stimulated mechanically with a dynamic stretch stimulus, which followed a pseudo Gaussian waveform with a bandwidth of 0-60 Hz. The mechanical response of the skin was measured as were responses of single RA cutaneous mechanoreceptor neurons. For each neuron, the strength of association between spike responses and the dynamic and static components of stimuli were determined with multiple logistic regression analysis. The viscoelastic material properties of each skin sample were determined indirectly, by creating a nonlinear (Wiener-Volterra) model of the stress-strain relationship, and using the model to predict the complex compliance (i.e., the viscoelastic material properties). The dynamic sensitivity of RA mechanoreceptor neurons in mouse hairy skin was weakly related to the viscoelastic properties of the skin. Loss modulus and phase angle were lower (indicating a decreased viscous component of response) in Tsk and Pallid than in C57BL6 mice. However, RA mechanoreceptor neurons in Tsk and Pallid skin did not differ from those in C57 skin with regard to their sensitivity to the rate of change of stress or to the rate of change of incremental strain energy. They did have a decreased sensitivity to the rate of change of tensile strain. Thus the skin samples with lower dynamic mechanical response contained neurons with a somewhat lower sensitivity to dynamic stimuli. [ABSTRACT FROM AUTHOR]

Mechanosensitive nociceptors with unmyelinated axons (C-fibers) were studied in a preparation of isolated skin and nerve from rat. Afferent discharges were recorded while the skin was mechanically stimulated using quantitative stretch (tension) and indentation (compression). The apparatus allowed for generating stimuli of equal magnitudes in both tension and compression. Stimulus–response functions were obtained for individual afferents relating discharge rate to tensile stress or compressive stress. A response threshold and maximal slope were obtained from each function. Thresholds did not differ significantly for compression and tension nor did the maximal slopes. We conclude that C-nociceptors are equally sensitive to tensile and compressive stress. [ABSTRACT FROM AUTHOR]

Objective: To identify computer facilities available in 3 dental schools where 3 different approaches to the use of technology-based learning material have been adopted and assess dental students' perception of their own computer skills and their attitudes towards information technology. Design: Multicentre cross sectional by questionnaire. Subjects: All 181 dental students in their final year of study (1997-8). Results: The overall participation rate was 80%. There were no differences between schools in the students' self assessment of their IT skills but only 1/3 regarded themselves as competent in basic skills and nearly 50% of students in all 3 schools felt that insufficient IT training had been provided to enable them to follow their course without difficulty. There were significant differences between schools in most of the other areas examined which reflect the different ways in which IT can be used to support the dental course. Conclusions: 1. Students value IT as an educational tool. 2. Their awareness of the relevance of a knowledge of information technology for their future careers remains generally low. 3. There is a need to provide effective instruction in IT skills for those dental students who do not acquire these during secondary education. [ABSTRACT FROM AUTHOR]

In a false-twist texturing machine, the yam can be rotated by means of either a pin or a friction twister. Irrespective of the type of twister used, the yarn twist can only be stable when it is numerically equal to the 'speed ratio' (the ratio of rotational to linear speed). When the machine is started up. the yarn has no twist, and a certain length of yam has to be processed before the twist attains its stable value. The nature of this initial development of twist depends on the type of twister used. With a pin twister, the speed ratio is a machine setting and is independent of the yam twist. When the machine is started up, the speed ratio attains its stable value almost instantaneously, and the yarn twist approaches this value exponentially. With a friction twister, the speed ratio is not a machine setting and is inversely related to the yam twist except under certain theoretical limiting conditions, which hardly ever occur in practice. Since the yarn twist equals zero when the machine is started up, the initial value of the speed ratio is higher than its stable value. The subsequent increase in twist is accompanied by a decrease in the speed ratio, and stable conditions are reached when the two quantities have converged to a common value. The difference between the initial and final speed ratios depends on the magnitude of the rotational slip present under stable running conditions. The transition from the initial to the final speed ratio is discontinuous when the longitudinal slip is small or absent. Under these conditions, the development of twist can be calculated by a simple analytical method. When the longitudinal slip is large, the transition from the initial to the final speed ratio is continuous, and the relevant differential equations cannot be solved analytically. For these conditions, numerical solutions are found by means of a computer. [ABSTRACT FROM AUTHOR]

A new method is proposed to appraise the relative energy efficiency of designs for new or refurbished buildings. Based on the development of an energy efficiency index, it is simple to use and understand, and requires no particular expertise. The method offers a straightforward determination of likely energy performance. It addresses the total power rating of plant installed to achieve specified indoor environmental conditions, and the monitoring and control equipment which manages that capacity. Potential applications include appraising performance against established or proposed standards of good practice, testing compliance with energy performance specifications and ranking alternative design choices, either overall or at various stages of design. Inverted, the method offers targets for plant sizing. The strategy offers services designers a more authoritative argument for plant room space early in the design. Despite its simplicity the method promises good field performance. Limited data from six fully air-conditioned buildings reveal a perhaps surprisingly good correlation between the energy efficiency index and observed performance. Once performance data for a wider range of buildings are available, the method can be developed fully for widespread practical application. [ABSTRACT FROM PUBLISHER]

Significantly improved understanding of the energy performance of an existing building can be achieved by investigating the energy consumption for individual end uses (heating, lighting, ventilation etc.) and comparing these consumptions per square metre of floor area with yardstick values for each end use. A method is presented for apportioning metered electricity consumption into end uses, generally without the need for extensive monitoring. Techniques are described for using the results to assess the building in terms of design and performance indices, and presenting the results for building management or research uses. [ABSTRACT FROM PUBLISHER]