Procedures utilizing Chelex100 chelating resin have been developed for extracting DNA from forensic-type samples for use with the PCR. The procedures are simple, rapid, involve no organic solvents ...and do not require multiple tube transfers for most types of samples. The extracion of DNA from semen and very small blood stains using Chelex 100 is as efficient or more efficient than using proteinase K and phenol-chloroform extraction. DNA extracted from bloodstains seems less prone to contain PCR inhibitors when prepared by this method. The Chelex method has been used with amplification and typing at the HLA DQα locus to obtain the DQα genotypes of many different types of samples, including whole blood, bloodstains, seminal stains, buccal swabs, hair and post-coital samples. The results of a concordance study are presented in which the DQα genotypes of 84 samples prepared using Chelex or using conventional phenol-chloroform extraction are compared. The genotypes obtained using the two different extraction methods were identical for all samples tested.
This study conducts experimental and numerical studies on the progressive damage occurring during the drilling of composite laminates. In particular, this work focuses on push-out delamination, which ...occurs at the interface around the drill-exit and is the most critical damage suffered during the drilling process. To investigate the damage progression mechanisms, penetration and interruption drilling tests are performed on composite laminate consisting of quasi-isotropic CFRP plies and fabric GFRP ply (bottom side). After drilling tests, the damage evolution is evaluated using X-ray computed tomography and optical microscopy. Based on the experimental results, a simplified simulation model is established, and damage progression simulation is performed using an explicit dynamic finite element method. The results show that the bending deformation in the bottom two plies triggers the propagation of push-out delamination. Therefore, the extent of delamination is significantly affected by the thickness and the material properties of the bottom plies.
Display omitted
This study seeks to establish a high-fidelity mesoscale simulation methodology that can predict the progressive damage and resultant failure of carbon fiber reinforced plastic laminates (CFRPs). In ...the proposed scheme, the plastic behavior (i.e., pre-peak nonlinear hardening in the local stress-strain response) is characterized through the pressure-dependent elasto-plastic constitutive law. The evolution of matrix cracking and delamination, which result in post-peak softening in the local stress-strain response, is modeled through cohesive zone models (CZM). The CZM for delamination is introduced through an interface element, but the CZM for matrix cracking is introduced through an extended finite element method (XFEM). Additionally, longitudinal failure, which is dominated by fiber breakage and typically depends on the specimen size, is modeled by the Weibull criterion. The validity of the proposed methodology was tested against an off-axis compression (OAC) test of unidirectional (UD) laminates and an open-hole tensile (OHT) test of quasi-isotropic (QI) laminates. Finally, sensitivity studies were performed to investigate the effect of plasticity and thermal residual stress against the prediction accuracy in the OHT simulation.
A micro-scale simulation scheme is developed in this study to evaluate in-situ damage and strength properties of CFRP laminates with various ply thicknesses. To capture both the initiation and ...propagation of transverse cracks, the microscopic random fiber configuration and the constraint effect from neighboring plies should be carefully considered. This study considers the representative volume element (RVE), consisting of the 'inhomogeneous' ply in which the solid elements individually modeled the fiber and matrix, and the 'homogenized' plies, homogeneously modeled by the shell elements. Matrix damage and debonding between fiber and matrix were modeled in the inhomogeneous ply to reproduce transverse crack propagation. Furthermore, in the RVE simulation, the key degree of freedom method was incorporated to evaluate the in-situ properties of each ply effectively. The validity of the proposed tool was examined by comparing the predicted cracking behavior with the results of unidirectional tensile tests on cross-ply laminates having different 90º ply thicknesses. The effects of ply thickness on the in-situ damage and strength properties of cross-ply laminates were numerically investigated, and the continuum damage mechanics model for thin-ply laminate was proposed based on the numerical results.
The aim of this study is to investigate the mechanical properties of noncircular carbon fiber reinforced plastics (CFRPs). For an efficient study of various CFRP microstructures, this study combines ...an extended finite element method (XFEM), a homogenization method, and a Monte Carlo method and establishes XFEM-based computational micromechanics. This scheme made it possible to simulate CFRPs having various microstructure without remeshing and resetting boundary conditions. In the verification against general circular CFRPs, it was revealed that the developed scheme has a sufficient accuracy for the prediction of the homogenized elastic constants including their stochastic nature. Finally, the effects of the cross-sectional fiber shape on the macroscopic CFRP properties were examined. Among the five fiber shapes (circular, elliptical, two-lobed, triangular, and square), the square CFRP exhibited the best transverse mechanical properties. Therefore, it was concluded that the noncircular carbon fibers have a potential to enhance the macroscopic mechanical performance of CFRPs.
Progressive damages in the open-hole compression (OHC) tests of composite laminates were experimentally and numerically studied. In the experiment, the failure mechanisms were investigated via in ...situ microscopy observation, digital image correlation, X-ray radiography, and X-ray computed tomography. Three layups were tested to examine the dependence of progressive damages on the layups. Additionally, numerical simulation was conducted to comprehensively examine the failure mechanisms. In the numerical studies, the simulation scheme, considering the plasticity, kink-band failure, multiple intra-laminar cracks, and delamination, was developed. From the experiment and simulation, it is clarified that the kink-band is initiated and propagated by the combined stress states consisting of longitudinal compression and in-plane shear around the intra-laminar cracks. Therefore, for the high-fidelity OHC simulation in various layups, it is necessary to capture the interaction between kink-band and intra-laminar cracks by considering the combined stress state in the kink-band failure criteria and modeling the multiple intra-laminar cracks.
•This study focused on the high-velocity impact on composite laminates.•Phenomenological mesomodeling based on the experiment was presented.•In the experiment, diffuse matrix cracks and dominant ...matrix cracks were observed.•The presented mode used continuous and discrete damage models for two crack types.•The presented mode was more accurate and efficient than the conventional models.
This study presents both experimental testing and phenomenological mesomodeling for composite laminates under high-velocity impact. First, we conducted high-velocity impact tests on CFRP laminates and investigated the penetration and damage behaviors. Three kinds of internal damage were observed: fiber breakage, matrix cracking, and delamination. The observed matrix cracks were classified into two categories: multiple (diffuse) cracks around the impact point and large (dominant) cracks on the bottom ply. A phenomenological mesomodel was then developed based on these experiment observations. In the presented model, both continuous and discrete damage models were implemented for modeling two crack configurations. For comparison, we presented two conventional models (one using only the discrete damage model, and the other using only the continuous damage model). To validate the presented model, high-velocity impact simulations were performed, and the predicted results were compared with experiment and conventional models in terms of the damage area and distribution.
The Byzantine Empire has bequeathed to us a rich legacy of Christian churches, many of which possess historical and cultural significance. Unfortunately, the majority of these structures are ...currently undergoing a process of decay, having not received adequate preservation efforts. Moreover, the absence of collaboration between researchers in the various fields, each with their own focus on the study of Byzantine churches, presents a pressing need for dialogue and a collective response from these researchers. The region of Laconia, located in the south of Greece, is particularly in need of immediate attention, given the abundance of churches located therein. To address these challenges, the authors propose a novel approach involving the documentation of these churches in a digital format through the presentation of 3D models as scholarly editions that incorporate all available data sets in a multimedia format. This paper delineates several requisite specifications for 3D scholarly editions, which hold the key to solving the twin problems faced by Byzantine churches, namely, their protection and the scarcity of interdisciplinary collaboration amongst researchers. With 3D scholarly editions based on multimedia resources and adequate information management, it will be possible to facilitate collaboration and research between various fields of Byzantine studies, and beyond. Such efforts will serve to ensure that cultural heritage passed down from previous generations will be transmitted to future ones.
Polyaniline-based atomic switches are material building blocks whose nanoscale structure and resultant neuromorphic character provide a new physical substrate for the development next-generation, ...nanoarchitectonic-enabled computing systems. Metal ion-doped devices consisting of a Ag/metal ion doped polyaniline/Pt sandwich structure were fabricated using an in situ wet process. The devices exhibited repeatable resistive switching between high (ON) and low (OFF) conductance states in both Ag
+
and Cu
2+
ion-doped devices. The threshold voltage for switching was>0.8 V and average ON/OFF conductance ratios (30 cycles for 3 samples) were 13 and 16 for Ag
+
and Cu
2+
devices, respectively. The ON state duration was determined by the decay to an OFF state after pulsed voltages of differing amplitude and frequency. The switching behaviour is analagous to short-term (STM) and long-term (LTM) memories of biological synapses. Memristive behaviour and evidence of quantized conductance were also observed and interpreted in terms of metal filament formation bridging the metal doped polymer layer. The successful realization of these properties within physical material systems indicate polyaniline frameworks as suitable neuromorphic substrates for in materia computing.
Resistance in neuromorphic nanowire networks can be decreased when activated by voltage as multiple pathways of low resistance interconnected nanowires form, increasing nanowire to nanowire ...connectivity. We show that high connectivity regions are retained for a few minutes after the energy source is switched off. We have used this property to devise an associative device. With a multielectrode array, we send current through the network to connect together areas that are spatially associated with a given electrode combination forming a pattern. We correctly retrieve the stored patterns by passing a small current through the network at a later time even when we input a faulty or incomplete pattern as the network groups stored patterns into cluster of high associativity, in analogy with semantic memory association in the human brain.
PDF
