Image Correlation for Shape, Motion and Deformation Measurements provides a comprehensive overview of data extraction through image analysis. Readers will find and in-depth look into various single- ...and multi-camera models (2D-DIC and 3D-DIC), two- and three-dimensional computer vision, and volumetric digital image correlation (VDIC). Fundamentals of accurate image matching are described, along with presentations of both new methods for quantitative error estimates in correlation-based motion measurements, and the effect of out-of-plane motion on 2D measurements. Thorough appendices offer descriptions of continuum mechanics formulations, methods for local surface strain estimation and non-linear optimization, as well as terminology in statistics and probability. With equal treatment of computer vision fundamentals and techniques for practical applications, this volume is both a reference for academic and industry-based researchers and engineers, as well as a valuable companion text for appropriate vision-based educational offerings.
Fragile X-associated tremor ataxia syndrome (FXTAS) results from a CGG repeat expansion in the 5′ UTR of FMR1. This repeat is thought to elicit toxicity as RNA, yet disease brains contain ...ubiquitin-positive neuronal inclusions, a pathologic hallmark of protein-mediated neurodegeneration. We explain this paradox by demonstrating that CGG repeats trigger repeat-associated non-AUG-initiated (RAN) translation of a cryptic polyglycine-containing protein, FMRpolyG. FMRpolyG accumulates in ubiquitin-positive inclusions in Drosophila, cell culture, mouse disease models, and FXTAS patient brains. CGG RAN translation occurs in at least two of three possible reading frames at repeat sizes ranging from normal (25) to pathogenic (90), but inclusion formation only occurs with expanded repeats. In Drosophila, CGG repeat toxicity is suppressed by eliminating RAN translation and enhanced by increased polyglycine protein production. These studies expand the growing list of nucleotide repeat disorders in which RAN translation occurs and provide evidence that RAN translation contributes to neurodegeneration.
•CGG repeats in the 5′ UTR of FMR1 elicit AUG-independent (RAN) translation•This produces an aggregation-prone polyglycine protein found in patients•CGG RAN translation explains pathologic differences in FXTAS mice•CGG RAN translation is critical for CGG repeat toxicity in fly disease models
CGG repeat expansions underlie the neurodegenerative disorder fragile X-associated tremor ataxia syndrome. Todd et al. describe how CGG repeats trigger non-AUG-initiated translation, producing a polyglycine protein that accumulates in FXTAS brains and contributes to toxicity in model systems.
Although normothermic machine perfusion of donor livers may allow assessment of graft viability prior to transplantation, there are currently no data on what would be a good parameter of graft ...viability. To determine whether bile production is a suitable biomarker that can be used to discriminate viable from non-viable livers we have studied functional performance as well as biochemical and histological evidence of hepatobiliary injury during ex vivo normothermic machine perfusion of human donor livers. After a median duration of cold storage of 6.5 h, twelve extended criteria human donor livers that were declined for transplantation were ex vivo perfused for 6 h at 37 °C with an oxygenated solution based on red blood cells and plasma, using pressure controlled pulsatile perfusion of the hepatic artery and continuous portal perfusion. During perfusion, two patterns of bile flow were identified: (1) steadily increasing bile production, resulting in a cumulative output of ≥ 30 g after 6 h (high bile output group), and (2) a cumulative bile production <20 g in 6 h (low bile output group). Concentrations of transaminases and potassium in the perfusion fluid were significantly higher in the low bile output group, compared to the high bile output group. Biliary concentrations of bilirubin and bicarbonate were respectively 4 times and 2 times higher in the high bile output group. Livers in the low bile output group displayed more signs of hepatic necrosis and venous congestion, compared to the high bile output group. In conclusion, bile production could be an easily assessable biomarker of hepatic viability during ex vivo machine perfusion of human donor livers. It could potentially be used to identify extended criteria livers that are suitable for transplantation. These ex vivo findings need to be confirmed in a transplant experiment or a clinical trial.
Considerable evidence suggests that the formation of long-term memories requires a critical period of new protein synthesis. Recently, the notion that some of these newly synthesized proteins ...originate through local translation in neuronal dendrites has gained some traction. Here, we review the experimental support for this idea and highlight some of the key questions outstanding in this area.
Livers derived from donation after circulatory death (DCD) are increasingly accepted for transplantation. However, DCD livers suffer additional donor warm ischemia, leading to biliary injury and more ...biliary complications after transplantation. It is unknown whether oxygenated machine perfusion results in better preservation of biliary epithelium and the peribiliary vasculature. We compared oxygenated hypothermic machine perfusion (HMP) with static cold storage (SCS) in a porcine DCD model.
After 30 min of cardiac arrest, livers were perfused in situ with HTK solution (4°C) and preserved for 4 h by either SCS (n = 9) or oxygenated HMP (10°C; n = 9), using pressure-controlled arterial and portal venous perfusion. To simulate transplantation, livers were reperfused ex vivo at 37°C with oxygenated autologous blood. Bile duct injury and function were determined by biochemical and molecular markers, and a systematic histological scoring system.
After reperfusion, arterial flow was higher in the HMP group, compared to SCS (251±28 vs 166±28 mL/min, respectively, after 1 hour of reperfusion; p = 0.003). Release of hepatocellular enzymes was significantly higher in the SCS group. Markers of biliary epithelial injury (biliary LDH, gamma-GT) and function (biliary pH and bicarbonate, and biliary transporter expression) were similar in the two groups. However, histology of bile ducts revealed significantly less arteriolonecrosis of the peribiliary vascular plexus in HMP preserved livers (>50% arteriolonecrosis was observed in 7 bile ducts of the SCS preserved livers versus only 1 bile duct of the HMP preserved livers; p = 0.024).
Oxygenated HMP prevents arteriolonecrosis of the peribiliary vascular plexus of the bile ducts of DCD pig livers and results in higher arterial flow after reperfusion. Together this may contribute to better perfusion of the bile ducts, providing a potential advantage in the post-ischemic recovery of bile ducts.
Efficient memory formation relies on the establishment of functional hippocampal circuits. It has been proposed that synaptic connections are refined by neural activity to form functional brain ...circuitry. However, it is not known whether and how hippocampal connections are refined by neural activity in vivo. Using a mouse genetic system in which restricted populations of neurons in the hippocampal circuit are inactivated, we show that inactive axons are eliminated after they develop through a competition with active axons. Remarkably, in the dentate gyrus, which undergoes neurogenesis throughout life, axon refinement is achieved by a competition between mature and young neurons. These results demonstrate that activity-dependent competition plays multiple roles in the establishment of functional memory circuits in vivo.
► A genetic system to dissect the role of activity in the memory circuit is established ► Activity-dependent competition refines the hippocampal circuit in vivo ► A unique form of competition between mature and young DG neurons refines their axons
•Dynamic fracture initiation toughness using cylindrical specimen with spiral crack.•A torsional Hopkinson bar is used to effectively generate a Mode-I fracture failure.•Interaction integral method ...is used to extract the dynamic stress intensity factors.
An experimental and numerical approach is proposed to determine the dynamic fracture initiation toughness of materials from a cylindrical specimen with spiral surface crack subjected to dynamic torsional load using a torsional Hopkinson bar apparatus. The torsion load creates predominantly tensile stress perpendicular to the spiral crack of the specimen, resulting in nominally Mode I conditions. The torque applied to the specimen is measured by strain gages attached to the bar and the time at which the crack propagation initiated is measured using stereo imaging and stereo digital image correlation. Using the measured torque and the time of fracture as input, a commercial FE package, ABAQUS, is utilized to analyze the spiral crack and numerically extract the dynamic fracture parameters. A 3D format of the dynamic interaction integral method is utilized to calculate the three components of the applied dynamic stress intensity factors. The result demonstrates that the spiral crack-torsional loading configuration indeed generates nominally Mode I conditions and can be used to measure the dynamic fracture initiation toughness. To demonstrate the proposed method, three aluminum alloys; Al 7050-T6, Al 2024-T3, and Al 6061-T6, were experimentally studied. The results are consistent, repeatable and in good agreement with literature data.
In the second half of the twentieth century France played the greatest role - even greater than Germany's - in shaping what eventually became the European Union. By the early twenty-first century, ...however, in a hugely transformed Europe, this era had patently come to an end. This comprehensive history shows how France coupled the pursuit of power and the furtherance of European integration over a sixty-year period, from the close of the Second World War to the hesitation caused by the French electorate's referendum rejection of the European Union's constitutional treaty in 2005.
•A geometry factor is proposed for extracting the Mode I stress intensity factor from experimental data obtained during torsional loading of spirally-cracked solid and tubular cylindrical ...specimen.•The proposed spirally cracked specimen can be used to study the plane strain fracture toughness of all engineering materials, including in the case when there is no sufficient material volume to make thick, standard samples required to approximately establish plane strain conditions.•The method works for both shallow and deep surface cracks so that one can obtain nominally plane strain Mode I fracture toughness results for a broad range of industrially relevant fracture geometries.
A geometry factor is proposed for extracting the Mode I stress intensity factor from experimental data obtained during torsional loading of solid and tubular cylindrical specimens with a spiral crack on the surface. Using torque at fracture and specimens geometry as an input, the stress intensity factor at the corresponding fracture load was determined using a finite element analysis based on interaction integral method. The computed Mode-I stress intensity factor and the measured fracture load are used to quantify the geometry factor for different depths of spiral crack in cylindrical specimens following Benthem’s circumferential crack solution approach. The proposed model was validated by testing a polycarbonate specimen and compared it with a conventional three-point bending method. The difference between results from the proposed formula and the standard method was about 1.7% and 4.1% for solid and tubular specimens respectively. Furthermore, the fracture toughness value of different materials in the open literature was compared to the results recalculated by using the proposed formula. The result is in good agreement with different materials considered with a maximum difference of less than 6%.
•Viscoelastic behavior of uncured tows determined experimentally in relevant temperature range.•Measurements show tow obeys time temperature superposition principle (TTSP)•WLF and Arrhenius models ...are excellent fits to data.•TTSP for WLF model provide results over 9 decades of time.•Data shows tow is elastic during wrinkle formation in AFP manufacturing of thermoset composite components.
In support of computational modeling of tow placement at elevated temperature, the creep response of IM7/8552 uncured prepreg slit tape material during 3-point bend loading at different temperatures is measured using an RSA III dynamic mechanical analyzer. Short term creep experiments were conducted for a duration of 1000 s at ten different temperatures ranging from −5°C (below Tg of 0 °C) to 40 °C, with the latter being the nominal processing temperature for the tow. Results show that the tow material obeys the time-temperature superposition principle (TTSP) in the temperature range selected for the creep experiments. Using the TTSP, creep compliance master curve spanning more than eight logarithmic decades is obtained for the nominal processing temperature of 40 °C. The time–temperature shift factor is observed to follow closely the William-Landel-Ferry (WLF) model, with the WLF parameters obtained by least square fitting of the experimentally determined shift factors utilizing closed form shifting algorithm (CFS). The WLF model for the material is used to extend the master curve to a range of temperatures above glass transition temperature (Tg) of the material. The creep compliance data is further employed to obtain the retardation spectra of the material using an algorithm based on the work of a co-author and applied recently to a different material system by the authors. Details for extraction of the retardation spectra from the creep compliance results are provided. Results from these studies demonstrate that the creep compliance reconstructed from the retardation spectra accurately represent the experimental results while providing baseline data to quantify the importance of viscoelastic behavior in wrinkle formation during advanced manufacturing of aerospace components.
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