1,770 research outputs found
Analytical and numerical analyses of the micromechanics of soft fibrous connective tissues
State of the art research and treatment of biological tissues require
accurate and efficient methods for describing their mechanical properties.
Indeed, micromechanics motivated approaches provide a systematic method for
elevating relevant data from the microscopic level to the macroscopic one. In
this work the mechanical responses of hyperelastic tissues with one and two
families of collagen fibers are analyzed by application of a new variational
estimate accounting for their histology and the behaviors of their
constituents. The resulting, close form expressions, are used to determine the
overall response of the wall of a healthy human coronary artery. To demonstrate
the accuracy of the proposed method these predictions are compared with
corresponding 3-D finite element simulations of a periodic unit cell of the
tissue with two families of fibers. Throughout, the analytical predictions for
the highly nonlinear and anisotropic tissue are in agreement with the numerical
simulations
Investigation of grain orientations of melt-textured HTSC with addition of uranium oxide, Y2O3 and Y2BaCuO5
Local grain orientations were studied in melt-textured YBCO samples processed with various amounts of depleted uranuim oxide (DU) and Y 2O3 by means of electron backscatter diffraction (EBSD) analysis. The addition of DU leads to the formation of Ucontaining nanoparticles (Y2Ba4CuUOx) with sizes of around 200 nm, embedded in the superconducting Y-123 matrix. The orientation of the Y 2BaCuO5 (Y-211) particles, which are also present in the YBCO bulk microstructure, is generally random as is the case in other melttextured Y-123 samples. The presence of Y-211 particles, however, also affects the orientation of the Y-123 matrix in these samples
Cosmological Parameter Extraction from the First Season of Observations with DASI
The Degree Angular Scale Interferometer (\dasi) has measured the power
spectrum of the Cosmic Microwave Background anisotropy over the range of
spherical harmonic multipoles 100<l<900. We compare this data, in combination
with the COBE-DMR results, to a seven dimensional grid of adiabatic CDM models.
Adopting the priors h>0.45 and 0.0<=tau_c<=0.4, we find that the total density
of the Universe Omega_tot=1.04+/-0.06, and the spectral index of the initial
scalar fluctuations n_s=1.01+0.08-0.06, in accordance with the predictions of
inflationary theory. In addition we find that the physical density of baryons
Omega_b.h^2=0.022+0.004-0.003, and the physical density of cold dark matter
Omega_cdm.h^2=0.14+/-0.04. This value of Omega_b.h^2 is consistent with that
derived from measurements of the primordial abundance ratios of the light
elements combined with big bang nucleosynthesis theory. Using the result of the
HST Key Project h=0.72+/-0.08 we find that Omega_t=1.00+/-0.04, the matter
density Omega_m=0.40+/-0.15, and the vacuum energy density
Omega_lambda=0.60+/-0.15. (All 68% confidence limits.)Comment: 7 pages, 4 figures, minor changes in response to referee comment
Monitoring method for carbon nanotubes (CNT): Personal sampler and corresponding reading device
At present, CNT and other nanofiber materials in air can only be detected by deposition on a substrate and the use of off-line imaging analysis such as scanning electron microscopy. The majority of techniques suitable for the quasi- real-time measurement of engineered nanoparticles such as electrical low pressure impactor, condensation particle counter, optionally combined with a scanning mobility particle sizer (SMPS) can not distinguish between nanoparticles in general and airborne nanofibres in particular. In common workplace settings the considerable background of fine and ultrafine particles thus poses a challenge for these instruments. Furthermore, a true portability of the present devices is not given due to their size and power consumption. However, there is an urgent need due to the expected toxicity of nanofibres to control workplace environments with a robust and mobile device to ensure the safety of the working personnel as soon as possible. To meet these challenges, a suitable personal sampler together with a corresponding reading device is under development in the NANODEVICE-project, funded by the European Commission under grant agreement FP7-211464-2. A pre-prototype personal sampler for CNT sampling, the used Raman-spectroscopic inspection of deposited CNTs and a possible approach in determining the qualitative presence of CNTs will be shown. Additionally, it seems even possible to distinguish between carbon nanofibers from different manufacturers based on Raman spectroscopy and data analysis
Epitaxial LaFeAsOF thin films grown by pulsed laser deposition
Superconducting and epitaxially grown LaFeAsOF thin films were successfully
prepared on (001)-oriented LaAlO3 substrates using pulsed laser deposition. The
prepared thin films show exclusively a single in-plane orientation with
epitaxial relation (001)[100] parallel to (001)[100] and a FWHM value of 1deg.
Furthermore, resistive measurement of the superconducting transition
temperature revealed a Tc90 of 25K with a high residual resistive ratio of 6.8.
The applied preparation technique, standard thin film pulsed laser deposition
at room temperature in combination with a subsequent post annealing process, is
suitable for fabrication of high quality LaFeAsO1-xFx thin films. A high upper
critical field of 76.2 T was evaluated for magnetic fields applied
perpendicular to the c-axis and the anisotropy was calculated to be 3.3
assuming single band superconductivity.Comment: 6 pages, 4 Figure
Anisotropic behaviour of human gallbladder walls
Inverse estimation of biomechanical parameters of soft tissues from non-invasive measurements has clinical significance in patient-specific modelling and disease diagnosis. In this paper, we propose a fully nonlinear approach to estimate the mechanical properties of the human gallbladder wall muscles from in vivo ultrasound images. The iteration method consists of a forward approach, in which the constitutive equation is based on a modified Hozapfel–Gasser–Ogden law initially developed for arteries. Five constitutive parameters describing the two orthogonal families of fibres and the matrix material are determined by comparing the computed displacements with medical images. The optimisation process is carried out using the MATLAB toolbox, a Python code, and the ABAQUS solver. The proposed method is validated with published artery data and subsequently applied to ten human gallbladder samples. Results show that the human gallbladder wall is anisotropic during the passive refilling phase, and that the peak stress is 1.6 times greater than that calculated using linear mechanics. This discrepancy arises because the wall thickness reduces by 1.6 times during the deformation, which is not predicted by conventional linear elasticity. If the change of wall thickness is accounted for, then the linear model can used to predict the gallbladder stress and its correlation with pain. This work provides further understanding of the nonlinear characteristics of human gallbladder
Trapping and ground-state cooling of
We demonstrate co-trapping and sideband cooling of a ion
pair in a cryogenic Paul trap. We study the chemical lifetime of and
its dependence on the apparatus temperature, achieving lifetimes of up to
at 10 K. We demonstrate cooling of translational motion to an
average phonon number of 0.07(1), corresponding to a temperature of . Our results provide a basis for quantum logic spectroscopy experiments of
, as well as other light ions such as , , and
- …