Characterization of excitation beam on second-harmonic generation in fibrillous type I collagen

Following our established theoretical model to deal with the second-harmonic generation (SHG) excited by a linearly polarized focused beam in type I collagen, in this paper, we further quantitatively characterize the differences between SHG emissions in type I collagen excited by collimated and focused beams. The effects of the linear polarization angle (α) and the fibril polarity characterized by the hyperpolarizability ratio ρ on SHG emission has been compared under collimated and focused beam excitation, respectively. In particular, SHG emission components along the i axis \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\left( {I_{2\omega {,}i} } \right)$\end{document} (i = x,y,z), the induced SHG emission deviation angle γij, and the detected SHG signals (I2ω,ij) in the ij plane by rotating the applied polarizer angle φij have been investigated (i = x, x, y; j = y, z, z). Results show that under our simulation model, SHG emission in the xy plane, such as I2ω,x ,I2ω,y ,γxy and I2ω,xy varying as polarization angle (α) under collimated and focused light, presents no significant difference. The reverse of the fibril polarity has induced great impact on I2ω,x ,γxy and I2ω,xy in both collimated and focused light. I2ω,x and γxy show similarity, but I2ω,xy at α = 30° demonstrates a slight difference in focused light to that in collimated light. Under focused light, the reverse of fibril polarity causes obvious changes of the collected SHG intensity I2ω,xz and I2ω,yz at a special polarization angle α = 60° and γxz, γyz along α

Experimental Characterization of Adventitial Collagen Fiber Kinematics Using Second-Harmonic Generation Imaging Microscopy: Similarities and Differences Across Arteries, Species and Testing Conditions

International audienceFibrous collagen networks are well known to play a central role in the passive biomechanical response of soft connective tissues to applied loads. In the current chapter we focus on vascular tissues and share our extensive experience in coupling mechanical loading and multi-photon imaging to investigate, across arteries, species and testing conditions, how collagen fibers move in response to mechanical loading. More specifically, we assess the deformations of collagen networks in rabbit, porcine or human arteries under different loading scenarios: uniaxial tension on flat samples, tension-inflation on tubular samples, bulge inflation on flat samples. We always observe that collagen fibers exhibit a wavy or crimped shape in load-free conditions, and tend to uncrimp when loads are applied, engaging sequentially to become the main load-bearing component. This sequential engagement, which is responsible for the nonlinear mechanical behaviour, is essential for an artery to function normally and appears to be less pronounced for arteries in elderly and aneurysmal patients. Although uncrimping of collagen fibers is a universal mechanism, we also observe large fiber rotations specific to tensile loading, with significant realignment along the loading axis. A unified approach is proposed to compare observations and quantitative analyses as the type of image processing may affect significantly the estimation of collagen fiber deformations. In summary, this chapter makes an important review of the basic roles of arterial microstructure and its deformations on the global mechanical response. Eventually, directions for future studies combining mechanical loading and multi-photon imaging are suggested, with the aim of addressing open questions related to tissue adaptation and rupture

The evaporative cooling system for the ATLAS inner detector

This paper describes the evaporative system used to cool the silicon detector structures of the inner detector sub-detectors of the ATLAS experiment at the CERN Large Hadron Collider. The motivation for an evaporative system, its design and construction are discussed. In detail the particular requirements of the ATLAS inner detector, technical choices and the qualification and manufacture of final components are addressed. Finally results of initial operational tests are reported. Although the entire system described, the paper focuses on the on-detector aspects. Details of the evaporative cooling plant will be discussed elsewhere. © 2008 IOP Publishing Ltd and SISSA

Combined performance tests before installation of the ATLAS Semiconductor and Transition Radiation Tracking Detectors

The ATLAS (A Toroidal LHC ApparatuS) Inner Detector provides charged particle tracking in the centre of the ATLAS experiment at the Large Hadron Collider (LHC). The Inner Detector consists of three subdetectors: the Pixel Detector, the Semiconductor Tracker (SCT), and the Transition Radiation Tracker (TRT). This paper summarizes the tests that were carried out at the final stage of SCT+TRT integration prior to their installation in ATLAS. The combined operation and performance of the SCT and TRT barrel and endcap detectors was investigated through a series of noise tests, and by recording the tracks of cosmic rays. This was a crucial test of hardware and software of the combined tracker detector systems. The results of noise and cross-talk tests on the SCT and TRT in their final assembled configuration, using final readout and supply hardware and software, are reported. The reconstruction and analysis of the recorded cosmic tracks allowed testing of the offline analysis chain and verification of basic tracker performance parameters, such as efficiency and spatial resolution, in combined operation before installation