Diatoms represent an important class of aquatic phototrophs. They are not only one of the major contributors to global carbon fixation, but they also play a key role in the biogeochemical cycling of silica. Molecular identification methods based on conserved DNA sequences, such as internal transcribed spacer (ITS) have revolutionized our knowledge and understanding of conventional taxonomy. In this study, we aimed to compare the conventional identification methods with molecular identification methods. To do so, we isolated 4 diatom samples from the coast at Urla and characterized them using light microscopy (LM) and scanning electron microscopy (SEM) according to morphological features. Then we amplified ITS regions using a conventional polymerase chain reaction (PCR), sequenced the PCR products, and analyzed the sequences using bioinformatic tools. Bioinformatic analysis indicated that the isolated species had high sequence similarity to Pseudo-nitzschia delicatissima, Achnanthes taeniata, Amphora coffeaeformis, and Cylindrotheca closterium. We think that molecular identification methods enable rapid and more reliable identification of diatom species and are crucial for monitoring harmful algal blooms.
Natural diatom frustules composing nanometer size silica particles were heat-treated at temperatures between 600 and 1200℃ for 2 h and used as filler/reinforcing agent (15 wt%) in an epoxy resin. The opal structure of as-received natural diatom frustules was transformed into cristobalite after the heat-treatment above 900℃. The epoxy resin test samples reinforced with heat-treated and as-received frustules and neat epoxy test samples were compression tested at the quasi-static strain rate of 7 × 10−3 s−1. The results showed that the inclusion of the frustules heat-treated at 1000℃ increased the compressive yield strength of the resin by 50%, while the addition of the diatom frustules heat-treated above and below 1000℃ and the as-received frustules increased the strength by ∼25% and 16%, respectively. The heat treatment above 1000℃ decreased the surface area of the frustules from 8.23 m2 g−1 to 3.46 m2 g−1. The cristobalite grains of the frustules heat-treated at 1000℃ was smaller than 100 nm, while the grain size increased to ∼500 nm at 1200℃. The increased compressive stresses of the resin at the specific heat treatment temperature (1000℃) were ascribed to nano size crystalline cristobalite grains. The relatively lower compressive stresses of the epoxy resin filled with frustules heat-treated above 1000℃ were attributed to the micro-cracking of the frustules that might be resulted from higher density of the cristobalite than that of the opal and accompanying reduction of the surface area and the surface pore sizes that might impair the resin-frustule interlocking and intrusion.
A limited number of material models or flow curves are available in commercial finite element softwares at varying temperature and strain rate ranges for plasticity analysis. To obtain more realistic finite element results, flow curves at wide temperature and strain rate ranges are required. For this purpose, a material model for a medium carbon alloy steel material which is used for fastener production was prepared. Firstly, flow curves of the material were obtained at 4 temperatures (20, 100, 200, 400 °C) and 3 strain rates (1, 10, 50 s-1). Then, experimental data was used to construct an artificial neural networks model (ANN) for the material. 75% of the experimental data was used to train the model and the rest was employed for validation and verification. ANN model used in flow curve prediction was developed using the scikit-learn library on Python. Temperature, strain rate and strain were employed as input parameters and flow stress as output parameter in ANN model. In order to increase the accuracy of the ANN model, the number of hidden layers and the number of neurons were also optimized by mean squared error approach. As a result of studies, an ANN-based material model that can be used for wide range of temperature and strain rate values were developed based on the experimental data.
In order to obtain flow curves from compression test results of a cold forging material and predict flow curves of the material at intermediate temperature and strain rate values, a model was developed using Python programming language in this study. The model consists of two parts: Flow curve determination and flow curve prediction. The compression test data including Force-Stroke values was processed to determine the flow curves in the first part, and the flow curve data constructed for certain temperature and strain rate values of the material was used as input for the machine learning algorithms to predict flow curve at desired intermediate temperature and strain rate values in the second part. Moreover, Ludwik material model parameters were estimated by using curve fitting methods in order to define the material model into the simulation software. Machine learning algorithms and various regression models in Python libraries were tested to predict the flow curves. The performances of different machine learning and regression models were compared with respect to the mean squared error and coefficient of determination performance measures. Support vector regression, k-Nearest Neighbour (kNN) and artificial neural network models were used to predict flow curves of cold forging materials and kNN regression model was able to found predictions with the lowest error rate. As a result, a model that can process the compression test data to predict flow curves at intermediate temperature or strain rate values was developed.
Today, there are specially developed fasteners for situations where the need for security and permanent connection is at the forefront. The first thing that comes to mind is the "shear bolt", a fastener that only allows tightening. In this fastener, there is a specially thinned area under the head with machining, and thus, when the bolt reaches a certain torque value, a break occurs in the head part. Thus, a permanent connection is obtained since the hexagon part used only during tightening is eliminated. One of the disadvantages that arise with the use of shear bolts is that there is a significant amount of material used only during tightening and it increases the cost. In addition, uncoated area on the fracture surface makes possible corrosion problems and an extra cost from machining is another disadvantage. The disposal of the broken head part during mass production also appears as an extra cost. In order to prevent these problems, the Norm One Way (NOW®) product, whose patent belongs to Norm Cıvata, has been developed. Thanks to the special head and socket geometry, tightening is done only in one direction and disassembly is not possible. In this study, the effect of increasing the socket depth on the head strength of the bolt was investigated using experimental, analytical and finite element methods. As a result, NOW® product was obtained which is safer, has a head form that will eliminate the possibility of stripping during assembly and at the same time provide maximum weight reduction.
The effects of the Achnanthes taeniata and the diatomaceous earth (diatomite) frustules addition on the compressive strength of an epoxy matrix were investigated experimentally. The Achnanthes taeniata frustules having relatively high length/diameter aspect ratio (2-4) were isolated and cultured in laboratory. While the as-received commercial natural diatomite frustules were non-homogenous in shape and size. The filling epoxy matrix with ~6 wt% of commercial natural diatomite increased the compressive strength from 60 MPa to 67 MPa, while the Achnanthes taeniata frustules addition increased to 79 MPa. The increased compressive strength and modulus of the the Achnanthes taeniata frustules filled epoxy was attributed to the higher aspect ratio and relatively strong bonding with the epoxy matrix. The more effective load transfer from the matrix to the Achnanthes taeniata frustules associated with the enhanced interface bonding was also proved microscopically. The frustules were observed to pull-out on the fracture surface of the Achnanthes taeniata frustules filled epoxy.
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