Effect of limestone aggregate type and water-cement ratio on concrete strength

This article investigates the effects of water-cement (w-c) ratio and coarse limestone aggregate type on compressive strength of concrete. In this study, Ceyhan (Adana) limestone produced in quarries was used as aggregate material, and its physical, chemical and mechanical properties were determined. The rock was classified due to uniaxial compressive strength, point load index, porosity and Schmidt hammer hardness test method. Concrete samples were produced using crushed limestone. Concrete mixes were designed to have a constant strength and workability for different aggregate gradation using the absolute volume method. Optimum water-cement ratio was determined using vibrating slump for the same concrete mixture proportions. Cylindrical concrete samples were prepared with these fresh mixtures. The concrete produced was cured at 7, 14 and 28 days in water to obtain its compressive strength. It was seen that the compressive strength of concrete depends upon water-cement ratio and aggregate size. (C) 2003 Elsevier B.V. All rights reserved

Orthodontic Materials Interacting with Fifth Generation (5G) Electromagnetic Waves

Objective: Public exposure to radiofrequency (RF) fields from fifth generation (5G) and other sources is known to be below human exposure limits. The interaction of RF fields with the human body has been widely documented, with tissue heating being the primary consequence for RF fields above 100 kHz. This study aimed to reveal possible harm to orthodontic patients associated with 5G electromagnetic waves. The possibility of individuals with orthodontic appliances (metallic braces, porcelain braces, thermoplastic appliances) being more affected by 5G was investigated. Methods: Sixty extracted human teeth were divided into 5 groups. Different types of brackets, arch, and ligature wires were applied to each group. Each group was exposed to 5G electromagnetic waves (3.6 GHz of frequency) for 60 minutes. Temperature measurements were made inside the canine root canals and in saline solution. Results: Exposure to a 5G electromagnetic field increased the temperatures of the root canal of the tooth and sodium chloride (NaCl) solution surrounding samples. Temperature increase in the canals were as follows; metal self-ligating braces > mini metal braces > porcelain braces > clear aligner > control. The temperature change in the NaCl solution at the 60th minute was close to each other in the self-ligating braces and mini metal braces groups. The temperature rise of the NaCl solution in the control group was also minimal. Conclusion: The hypothesis that orthodontic materials alter electromagnetic waves is supported by temperature increases. The ferromagnetic density of the orthodontic materials used was shown to be closely connected to temperature increase

Karaçam (Pinus nigra Arnold.) Odununun Lif Morfolojisi ve Kimyasal Yapısı Üzerine Ağaç Gövde Yüksekliğinin Etkisi

Bu çalışmada, karaçam (Pinus nigra Arnold.) ağacının gövde yüksekliğinin odunun lif morfolojisi ve kimyasal yapısı üzerine etkileri araştırılmıştır. Bu amaçla, karaçam tomruklarının (3 ağaç) 3 farklı kısmından (alt, orta ve üst) odun örnekleri alınmıştır. Örneklerin lif uzunlukları, lif genişlikleri, lümen genişlikleri ve çeper kalınlıkları tespit edilmiştir. Bu lif morfolojik özellikleri kullanılarak liflerin elastiklik oranı, keçeleşme oranı ve Runkel oranı değerleri hesaplanmıştır. Ayrıca, örneklerin holoselüloz, α-selüloz, klason lignini, sıcak ve soğuk su çözünürlükleri ile alkol çözünürlükleri tespit edilmiştir. Elde edilen sonuçlara göre karaçam ağaç gövdesinin alt kısmından alınan örneklerin orta ve üst kısımdan alınan örneklere göre daha esnek liflere sahip olduğu, daha yüksek oranda selüloz, daha düşük oranda lignin içerdiği tespit edilmiştir. Bu yönleri ile karaçam ağaç gövdesinin alt kısmından elde edilen kağıtlar diğer kısımlardan elde edilenlere göre daha yüksek verimli kağıt hamurları, daha sağlam kağıtlar oluşturmaya yatkındır. Buna karşın, özellikle ağacın üst kısmının (ince uç kısım) lif morfolojisinin ve kimyasal yapısının kağıt üretimi için kabul edilebilir ölçüde olduğu da görülmüştür

Coupling the FitzHugh-Nagumo Neuron Model with Memristive Synapse Structure in Neuromorphic Systems Nöromorfik Sistemlerde FitzHugh-Nagumo Nöron Modelinin Memristif Sinaps Yapisi ile Kuplajlanmasi

© 2021 IEEE.In recent years, studies dealing with neuromorphic systems and STDP learning rule; the memristor element, which is introduced as the fourth basic circuit element, is associated with synapse definitions in neural systems. In this study, a pair of neurons defined by the FitzHugh-Nagumo (FHN) neuron model; instead of the classical synapse definitions, a proposed definition for the representation of the memristor element is combined with a configuration in which the synapse is used. The responses of the coupled FHN neurons were observed with numerical simulation results. The numerical results obtained as a result of this coupling process, in which the memristor identification is used, are interpreted by comparing them with the results obtained for the STDP learning rule

On addressing the similarities between STDP concept and synaptic/ memristive coupled neurons by realizing of the memristive synapse based HR neurons

The Spike-Time-Dependent-Plasticity (STDP) learning rule is frequently associated with the memristor structures in the neuromorphic studies, recently. In this study, after two HR neurons are coupled with a memristor based synapse structure as a unidirectional coupling; it is aimed to correlate the STDP learning rule and the memristor based synapse structure. In line of this motivation, two HR neurons (the transmitter and the receiver neurons) have been coupled with a memductance structure. After the current at the output of this memristor based synapse has been applied to the receiver neuron, a phase shift has been induced on the membrane potential of this receiver neuron. Additionally, this phase shift can be controlled by changing the 'Ron' resistance that is a parameter of the windowing function definition of the memristor device similar to the synaptic coupling weight parameter. Since the firing times of these coupled HR neurons can be controlled by changing this 'Ron' resistance, the STDP learning rule, which is based on the instantaneous firing time difference between the coupled neurons, has been validated as an alternative view point in here. The similarity between the pattern of the STDP learning rule and the pattern of two HR neurons coupled with the chemical and the memristor based synapses has been confirmed by comparing the numerical simulation results and it has been seen that the memristor device can be used as an alternative synapse definition in the neuromorphic studies. Finally, two HR neurons coupled with the memristor based synapse have been successfully realized by using the FPGA equipment, so an alternative neuromorphic study, which is associated with the STDP learning rule, memristor synapse and HR neurons, has been presented to the literature with this implementation. (c) 2021 Karabuk University. Publishing services by Elsevier B.V. This is an open access article under the C

Functional emulator designs for a memristor model with programmable analog and digital platforms

Hardware validation and verification studies for emulator circuits of the memristor element usually include either analog or digital realization results. In this study, the implementation stages of a memristor element using the Joglekar window function with programmable and reconfigurable analog and digital platforms are given together in order to observe the characteristic current-voltage relationship, experimentally. Herein, a Joglekar window function-based voltage-controlled memristor has been implemented with the field-programmable analog array (FPAA) platform for the first time. In fact, the FPAA platform has attracted attention thanks to its analog nature, rapid prototyping and low hardware cost specialties, and because different nonlinear functions can be easily constructed on this device. Similarly, the field-programmable gate array (FPGA) platform has recently been recognized for its parallel processing feature in digital signal processing studies. The FPGA-based digital implementation stages of the Joglekar window function-based memristor element are also addressed in this study. Thus, the FPAA and FPGA based memristor emulator designs are presented together in order to contribute the memristor-based analog and digital applications that is required to obtain real-time signals

A New Nonlinear Ion Drift Model of Memristor Element and its Versatile Analog Reconfigurable Realizations

While using polynomial functions to define window functions is an initial approach in studying the memristor element, it is susceptible to generating imaginary results. However, using window functions, including the trigonometric function, is a current field of research on the memristor element. This paper uses the trigonometric Blackman window function to present a new memristor element model and investigates its nonlinear ion drift model properties. The motivation of this study is the usage of the trigonometric Blackman window function, which presents a more detailed definition and leads to more accurate results in windowing operations. The Blackman window function can address the issues of border locking and terminal state. Numerical simulations have verified this proposed structure. Additionally, the analog realizations of the memristor element constructed with the Blackman window function have been achieved on a Field Programmable Analog Array, which offers fast prototyping, serving as an alternative approach for emulating memristors

Extraction and characterization of cellulosic fiber from Centaurea solstitialis for composites

With increasing ecological awareness, researchers around the world seek to make composites reinforced with more eco-friendly natural fibers. In this study,Centaurea solstitialis(yellow star thistle) fibers were characterized as a potential natural fiber reinforcement for green composites. Generally,Centaurea solstitialisplants are undesirable because of their detrimental effect on other plants. In this respect, they are generally considered economically worthless in terms of the economical aspect. From this point of view, characterizingCentaurea solstitialisand using them as a natural fiber reinforcement material can be more appropriate in terms of waste management. To characterize theCentaurea solstitialisfibers, Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis, X-ray Photoelectron Spectroscopy, X-Ray Diffraction Analysis, single fiber tensile test, determinations of density and chemical composition were performed.Centaurea solstitialisfibers have 11.2% hemicellulose and 57.20% cellulose content. The crystallinity index and density of fibers were determined as 71.43% and 1.37 g/cm(3), respectively. Also, fibers exhibited relatively high tensile strength with 111.85 +/- 24.97 MPa and Young's modulus with 3.41 +/- 0.62 GPa. The thermal resistance temperature ofCentaurea solstitialisfibers was found as 273 degrees C. It is suggested thatCentaurea solstitialisfiber is a suitable reinforcement candidate for composites with low density, low cost, abundancy and relatively high tensile strength