Changes in biomechanical properties of the coronary artery wall contribute to maintained contractile responses to endothelin-1 in atherosclerosis.

AIMS: Our aim was to determine whether alterations in biomechanical properties of human diseased compared to normal coronary artery contribute to changes in artery responsiveness to endothelin-1 in atherosclerosis. MAIN METHODS: Concentration-response curves were constructed to endothelin-1 in normal and diseased coronary artery. The passive mechanical properties of arteries were determined using tensile ring tests from which finite element models of passive mechanical properties of both groups were created. Finite element modelling of artery endothelin-1 responses was then performed. KEY FINDINGS: Maximum responses to endothelin-1 were significantly attenuated in diseased (27±3 mN, n=55) compared to normal (38±2 mN, n=68) artery, although this remained over 70% of control. There was no difference in potency (pD2 control=8.03±0.06; pD2 diseased=7.98±0.06). Finite element modelling of tensile ring tests resulted in hyperelastic shear modulus μ=2004±410 Pa and hardening exponent α=22.8±2.2 for normal wall and μ=2464±1075 Pa and α=38.3±6.7 for plaque tissue and distensibility of diseased vessels was decreased. Finite element modelling of active properties of both groups resulted in higher muscle contractile strain (represented by thermal reactivity) of the atherosclerotic artery model than the normal artery model. The models suggest that a change in muscle response to endothelin-1 occurs in atherosclerotic artery to increase its distensibility towards that seen in normal artery. SIGNIFICANCE: Our data suggest that an adaptation occurs in medial smooth muscle of atherosclerotic coronary artery to maintain distensibility of the vessel wall in the presence of endothelin-1. This may contribute to the vasospastic effect of locally increased endothelin-1 production that is reported in this condition.

A framework for the analysis of thermal losses in reciprocating compressors and expanders

This article presents a framework that describes formally the underlying unsteady and conjugate heat transfer processes that are undergone in thermodynamic systems, along with results from its application to the characterization of thermodynamic losses due to irreversible heat transfer during reciprocating compression and expansion processes in a gas spring. Specifically, a heat transfer model is proposed that solves the one-dimensional unsteady heat conduction equation in the solid simultaneously with the first law in the gas phase, with an imposed heat transfer coefficient taken from suitable experiments in gas springs. Even at low volumetric compression ratios (of 2.5), notable effects of unsteady heat transfer to the solid walls are revealed, with thermally induced thermodynamic cycle (work) losses of up to 14% (relative to the work input/output in equivalent adiabatic and reversible compression/expansion processes) at intermediate Péclet numbers (i.e., normalized frequencies) when unfavorable solid and gas materials are selected, and closer to 10-12% for more common material choices. The contribution of the solid toward these values, through the conjugate variations attributed to the thickness of the cylinder wall, is about 8% and 2% points, respectively, showing a maximum at intermediate thicknesses. At higher compression ratios (of 6) a 19% worst-case loss is reported for common materials. These results suggest strongly that in designing high-efficiency reciprocating machines the full conjugate and unsteady problem must be considered and that the role of the solid in determining performance cannot, in general, be neglected. © 2014 Richard Mathie, Christos N. Markides, and Alexander J. White. Published with License by Taylor & Francis.

Double-wall carbon nanotubes for wide-band, ultrafast pulse generation.

We demonstrate wide-band ultrafast optical pulse generation at 1, 1.5, and 2 μm using a single-polymer composite saturable absorber based on double-wall carbon nanotubes (DWNTs). The freestanding optical quality polymer composite is prepared from nanotubes dispersed in water with poly(vinyl alcohol) as the host matrix. The composite is then integrated into ytterbium-, erbium-, and thulium-doped fiber laser cavities. Using this single DWNT-polymer composite, we achieve 4.85 ps, 532 fs, and 1.6 ps mode-locked pulses at 1066, 1559, and 1883 nm, respectively, highlighting the potential of DWNTs for wide-band ultrafast photonics.

Widely tunable picosecond fiber ring laser mode-locked by a single-wall carbon nanotube (SWNT)-polycarbonate composite film saturable absorber

A widely tunable fiber ring laser, utilising a SWNT/polycarbonate film mode-locker and a 3-nm tunable filter, has been realized. 2.3ps pulse generation over 27nm spectral range is achieved for a constant pump power of 25mW. © 2007 Optical Society of America.

Widely tunable picosecond fiber ring laser mode-locked by a single-wall carbon nanotube (SWNT)-polycarbonate composite film saturable absorber

A widely tunable fiber ring laser, utilising a SWNT/polycarbonate film mode-locker and a 3-nm tunable filter, has been realized. 2.3ps pulse generation over 27nm spectral range is achieved for a constant pump power of 25mW. © 2008 Optical Society of America.

Scaling of velocity fluctuations in off-wall boundary conditions for turbulent flows

A model for off-wall boundary conditions for turbulent flow is investigated. The objective of such a model is to circumvent the need to resolve the buffer layer near the wall, by providing conditions in the logarithmic layer for the overlying flow. The model is based on the self-similarity of the flow at different heights in the logarithmic layer. It was first proposed by Mizuno and Jiménez (2013), imposing at the boundary plane a velocity field obtained on-the-fly from an overlying region. The key feature of the model was that the lengthscales of the field were rescaled to account for the self-similarity law. The model was successful at sustaining a turbulent logarithmic layer, but resulted in some disagreements in the flow statistics, compared to fully-resolved flows. These disagreements needed to be addressed for the model to be of practical application. In the present paper, a more refined, wavelength-dependent rescaling law is proposed, based on the wavelength-dependent dynamics in fully-resolved flows. Results for channel flow show that the new model eliminates the large artificial pressure fluctuations found in the previous one, and a better agreement is obtained in the bulk properties, the flow fluctuations, and their spectral distribution across the whole domain. © Published under licence by IOP Publishing Ltd.

Numerical analyses of tunnel-induced settlement damage to a masonry wall

Settlements due to underground construction represent a risk for the architectural heritage, especially in The Netherlands, because of the combination of soft soil, fragile pile foundation and brittle, un-reinforced masonry façade. Modelling of soil-structure interaction is fundamental to assess the risk of building damage due to tunnelling. This paper presents results of finite element analyses carried out with different models for a simple masonry wall. Focus is paid on the comparison between coupled, uncoupled and semi-coupled analyses, in which the soil-structure interaction is represented in different ways. In particular, the implementation of a soil-structure interface model in the numerical analyses is analysed, in order to asses its validity. The aim of the research project is the development of a damage classification system for different building typologies.