Error Assessment in Stereo-based Deformation Measurements

Increasing interest in the use of digital image correlation (DIC) for full-field surface shape and deformation measurements has led to an on-going need for both the development of theoretical formulae capable of providing quantitative confidence margins and controlled experiments for validation of the theoretical predictions. In the enclosed work, a series of stereo vision experiments are performed in a manner that provides sufficient information for direct comparison with theoretical predictions using formulae developed in Part I. Specifically, experiments are performed to obtain appropriate optimal estimates and the uncertainty margins for the image locations/displacements, 3-D locations/displacements and strains when using the method of subset-based digital image correlation for image matching. The uncertainty of locating the 3-D space points using subset-based pattern matching is estimated by using theoretical formulae developed in Part I and the experimentally defined confidence margins for image locations. Finally, the uncertainty in strains is predicted using formulae that involves both the variance and covariance of intermediate variables during the strain calculation process. Results from both theoretical predictions and the experimental work show the feasibility and accuracy of the predictive formulae for estimating the uncertainty in the stereo-based deformation measurements.     

The effect of out-of-plane motion on 2D and 3D digital image correlation measurements

The effect of out-of-plane motion (including out-of-plane translation and rotation) on two-dimensional (2D) and three-dimensional (3D) digital image correlation measurements is demonstrated using basic theoretical pinhole image equations and experimentally through synchronized, multi-system measurements. Full-field results obtained during rigid body, out-of-plane motion using a single-camera vision system with (a-1) a standard f55mm Nikon lens and (a-2) a single Schneider–Kreuznach Xenoplan telecentric lens are compared with data obtained using a two-camera stereovision system with standard f55mm Nikon lenses.Results confirm that the theoretical equations are in excellent agreement with experimental measurements. Specifically, results show that (a) a single-camera, 2D imaging system is sensitive to out-of-plane motion, with in-plane strain errors (a-1) due to out-of-plane translation being proportional to ΔZ/Z, where Z is the distance from the object to the pin hole and ΔZ the out-of-plane translation displacement, and (a-2) due to out-of-plane rotation are shown to be a function of both rotation angle and the image distance Z; (b) the telecentric lens has an effective object distance, Z_eff, that is 50× larger than the 55 mm standard lens, with a corresponding reduction in strain errors from 1250 μs/mm of out-of-plane motion to 25 μs/mm; and (c) a stereovision system measures all components of displacement without introducing measurable, full-field, strain errors, even though an object may undergo appreciable out-of-plane translation and rotation.     

Novel Biocatalysts by Chemical Modification of Known Enzymes: Cross-Linked Microcrystals of the Semisynthetic Peroxidase Seleno-Subtilisin

The linkage of lysine residues on the surfaces of subtilisin crystals (NH₂-Enz; see Scheme) with glutardialdehyde affords an immobilized biocatalyst of high stability and purity. The replacement of the serine OH group in the active site (Enz-OH) by SeO₂H leads to new activity as a peroxidase. Thus for the first time, chemical enzyme engineering has resulted in a biocatalyst with a modified peptide framework as well as a new catalytically active site. This methodology combines reasonable substrate selectivity of a semisynthetic enzyme with the exceptional stability of cross-linked enzyme crystals.     

Valorization of Byproducts of Hemp Multipurpose Crop: Short Non-Aligned Bast Fibers as a Source of Nanocellulose

Nanocellulose was extracted from short bast fibers, from hemp (Cannabis sativa L.) plants harvested at seed maturity, non-retted, and mechanically decorticated in a defibering apparatus, giving non-aligned fibers. A chemical pretreatment with NaOH and HCl allowed the removal of most of the non-cellulosic components of the fibers. No bleaching was performed. The chemically pretreated fibers were then refined in a beater and treated with a cellulase enzyme, followed by mechanical defibrillation in an ultrafine friction grinder. The fibers were characterized by microscopy, infrared spectroscopy, thermogravimetric analysis and X-ray diffraction after each step of the process to understand the evolution of their morphology and composition. The obtained nanocellulose suspension was composed of short nanofibrils with widths of 5–12 nm, stacks of nanofibrils with widths of 20–200 nm, and some larger fibers. The crystallinity index was found to increase from 74% for the raw fibers to 80% for the nanocellulose. The nanocellulose retained a yellowish color, indicating the presence of some residual lignin. The properties of the nanopaper prepared with the hemp nanocellulose were similar to those of nanopapers prepared with wood pulp-derived rod-like nanofibrils.     

Effect of Anions from the Hofmeister Series and Urea on the Binding of the Charged and Uncharged Forms of the Local Anesthetic Tetracaine to Zwitterionic Micelles*

It is widely known that ions in the aqueous phase affect the binding of charged solutes to membranes. Here we report the effect of ions and urea on the interaction of both the charged and uncharged forms of the local anesthetic tetracaine (TTC, an aminoester derivative of ben-zoic acid) to zwitterionic micelles. Binding was monitored by the increase in TTC fluorescence. Shifts in the emission wavelength maximum (δ_max) indicated that the anesthetic was located in an environment of lower polarity. The neutral form of TTC bound to micelles to a larger extent than the protonated form, in agreement with results found for lipid bilayers (Boulanger, Leitch, Schreier and Smith, Can. J. Biochem. 58 , 986–995, 1980). When ions from the Hofmeister series and urea were compared in their ability to affect the partitioning of the anesthetic, binding of both the charged and uncharged forms was found to increase upon addition of SO₄^2– and CI^? but was seen to decrease in the presence of SCN^?, CIO₄^?_- and urea. Solubility measurements revealed that the solubility of uncharged TTC increases in solutions containing the additives in the following order: SO₄^2– < CI^? < CIO₄^?_- < dilute buffer < SCN^? < urea. Spin label EPR spectra indicated that, except for CIO₄^?_-, the ions had little effect on micellar structure. Static light scattering measurements corroborated this result indicating a large increase in micellar molecular weight in the presence of CIO₄^?_- and lesser increases for CI^.- and SCN^?. The results show that, besides affecting the binding of ionic species through an electrostatic mechanism, ions also act by altering water structure and, as a consequence, the water solubility and the tendency to partition into the less polar micellar environment of polar charged or uncharged small organic solutes such as the benzoic acid ester derivative. Moreover, evidence suggests that the ions bind directly to the zwitterionic polar groups of the micelles, leading to changes in structure and size.     

High pressure μSR studies on single crystalline gadolinium

Muon spin rotation data on a single crystalline gadolinium sample have been obtained as function of temperature and hydrostatic external pressure up to 0.6 GPa. In the ferromagnetic state the application of pressure has a strong influence on the whole spin‐turning‐process of the spontaneous magnetization: The onset of the spin‐turning is shifted towards lower temperatures with a rate of approximately dT_st/ dp\approx -50 K/GPa. Higher values of the turning angle up to \vartheta_ext=90^\circ can be reached and stabilized over a wider temperature range. At low temperatures the magnetization turns back again. In the paramagnetic regime the data show a similar behaviour as under ambient pressure: both the Knight‐shift and the muon spin relaxation show deviations from their high temperature behaviour in the critical regime below (T-T_C) < 10 K. So there is no indication of pressure induced effects in this temperature range. This revised version was published online in July 2006 with corrections to the Cover Date.     

Transport through cavities with tunnel barriers: a semiclassical analysis

We study the influence of a tunnel barrier on the quantum transport through a circular cavity. Our analysis in terms of classical trajectories shows that the semiclassical approaches developed for ballistic transport can be adapted to deal with the case where tunneling is present. Peaks in the Fourier transform of the energy-dependent transmission and reflection spectra exhibit a nonmonotonic behaviour as a function of the barrier height in the quantum mechanical numerical calculations. Semiclassical analysis provides a simple qualitative explanation of this behaviour, as well as a quantitative agreement with the exact calculations. The experimental relevance of the classical trajectories in mesoscopic and microwave systems is discussed. Received: 23 October 1997 / Received in final form and Accepted: 11 March 1998     

Generation of narrowband subpicosecond mid-infrared pulses via difference frequency mixing of chirped near-infrared pulses

The widely used setup for the generation of femtosecond infrared (IR) pulses based on parametric amplifiers (OPAs) and difference frequency mixing (DFM) is extended to produce tunable narrowband mid-IR pulses. The insertion of pairs of silicon prisms after the OPA induces adjustable chirp, which leads to the generation of narrowband pulses in the DFM stage. Rapid tunability of the mid-IR wavelength via a computer-controllable actuator can be achieved in a range of approximately 200 cm(-1) at a bandwidth of the IR-pulses between approximately 15 and approximately 50 cm(-1) and pulse energies up to 0.4 microJ. The narrowband mid-IR pulses are well suited for 2D IR spectroscopy.     

Scanning Electron Microscopy for Quantitative Small and Large Deformation Measurements Part II: Experimental Validation for Magnifications from 200 to 10,000

A combination of drift distortion removal and spatial distortion removal are performed to correct Scanning Electron Microscope (SEM) images at both ×200 and ×10,000 magnification. Using multiple, time-spaced images and in-plane rigid body motions to extract the relative displacement field throughout the imaging process, results from numerical simulations clearly demonstrate that the correction procedures successfully remove both drift and spatial distortions with errors on the order of ±0.02 pixels. A series of 2D translation and tensile loading experiments are performed in an SEM for magnifications at ×200 and ×10,000, where both the drift and spatial distortion removal methods described above are applied to correct the digital images and improve the accuracy of measurements obtained using 2D-DIC. Results from translation and loading experiments indicate that (a) the fully corrected displacement components have nearly random variability with standard deviation of 0.02 pixels (≈25 nm at ×200 and ≈0.5 nm at ×10,000) in each displacement component and (b) the measured strain fields are unbiased and in excellent agreement with expected results, with a spatial resolution of 43 pixels (≈54 μm at ×200 and ≈1.1 μm at ×10,000) and a standard deviation on the order of 6 × 10⁻⁵ for each component.