Fourier–Galerkin domain truncation method for Stokes’ first problem with Oldroyd four-constant liquid

AbstractUsing the Fourier–Galerkin method with domain truncation strategy, Stokes’ first problem for Oldroyd four-constant liquid on a semi-infinite interval is studied. It is shown that the Fourier–Galerkin approximations are convergent on the bounded interval. Moreover, an efficient and accurate algorithm based on the Fourier–Galerkin approximations is developed and implemented in solving the differential equations related to the present problem. Also, the effects of non-Newtonian parameters on the flow characteristics are obtained and analyzed. The method developed here is so general that it can be used to study the mathematical models that involve the flow of viscous fluids with shear rate-dependent properties: For example, models dealing with polymer processing, tribology & lubrication, and food processing

An analysis on decentralized adaptive MAC protocols for Cognitive Radio networks

The scarcity of bandwidth in the radio spectrum has become more vital since the demand for more and more wireless applications has increased. Most of the spectrum bands have been allocated although many studies have shown that these bands are significantly underutilized most of the time. The problem of unavailability of spectrum and inefficiency in its utilization has been smartly addressed by the Cognitive Radio (CR) Technology which is an opportunistic network that senses the environment, observes the network changes, and then using knowledge gained from the prior interaction with the network, makes intelligent decisions by dynamically adapting their transmission characteristics. In this paper some of the decentralized adaptive MAC protocols for CR networks have been critically analyzed and a novel adaptive MAC protocol for CR networks, DNG-MAC which is decentralized and non-global in nature, has been proposed. The results show the DNG-MAC out performs other CR MAC protocols in terms of time and energy efficiency

The Current Perspectives of Stem Cell Therapy in Orthopedic Surgery

Context: Musculoskeletal injuries may be painful, troublesome, life limiting and also one of the global health problems. There has been considerable amount of interest during the past two decades to stem cells and tissue engineering techniques in orthopedic surgery, especially to manage special and compulsive injuries within the musculoskeletal system. Evidence Acquisition: The aim of this study was to present a literature review regarding the most recent progress in stem cell procedures and current indications in orthopedics clinical care practice. The Medline and PubMed library databases were searched for the articles related with stem cell procedures in the field of orthopedic surgery and additionally the reference list of each article was also included to provide a comprehensive evaluation. Results: Various sources of stem cells have been studied for orthopedics clinical care practice. Stem cell therapy has successfully used for major orthopedic procedures in terms of bone-joint injuries (fractures-bone defects, nonunion, and spinal injuries), osteoarthritis-cartilage defects, ligament-tendon injuries, femoral head osteonecrosis and osteogenesis imperfecta. Stem cells have also used in bone tissue engineering in combining with the scaffolds and provided faster and better healing of tissues. Conclusions: Large amounts of preclinical studies have been made of stem cells and there is an increasing interest to perform these studies within the human population but preclinical studies are insufficient; therefore, much more and efficient studies should be conducted to evaluate the efficacy and safety of stem cells

Preliminary assessment of microfibres amount in textile wastewater

Textile wastewater is a complex mixture of inorganic compounds, polymers, organic products, dyes, and microfibers (MFs), including microplastics (MPs) and natural fibers. The treatment of textile wastewater, which contains a significant share of MFs, is of great importance to prevent the release of MPs in the environment. MPs analysis requires multiple phases of pretreatment (to eliminate the organic compounds), separation of the MFs from the water, and identification of the MPs among the MFs.This work presents the preliminary results of a research aimed at exploring two issues. Firstly, the pretreatment (through Fenton, H2O2, HCl, KOH and NaOH, applied at 25 °C for 5 days and 60 °C for 6 hours) of artificial textile wastewater, evaluating the effect of the different conditions on the MFs and the MPs. Secondly, the separation of MFs from a real textile wastewater sample through different processes (centrifugation, sink-float & filtration, filtration). The results of the pretreatment tests revealed Fenton, HCl, and H2O2 at 25 °C for 5 days as the best performing chemicals and conditions. Considering the results of the separation tests, filtration gave back the best removal of the MFs from wastewater compared to centrifugation and sink-float and filtration, which left some MFs in the supernatant/float and in the sediment/sink. In conclusion, these preliminary results may be useful to further explore the detection of MFs and MPs in textile wastewater

In-Network Outlier Detection in Wireless Sensor Networks

To address the problem of unsupervised outlier detection in wireless sensor networks, we develop an approach that (1) is flexible with respect to the outlier definition, (2) computes the result in-network to reduce both bandwidth and energy usage,(3) only uses single hop communication thus permitting very simple node failure detection and message reliability assurance mechanisms (e.g., carrier-sense), and (4) seamlessly accommodates dynamic updates to data. We examine performance using simulation with real sensor data streams. Our results demonstrate that our approach is accurate and imposes a reasonable communication load and level of power consumption.Comment: Extended version of a paper appearing in the Int'l Conference on Distributed Computing Systems 200

Effects of process parameters and tool wear on the fatigue life of machined threaded parts

Talaş kaldırılarak tornada açılmış vidalı parçaların yorulma dayanımına imal faktörleri ve koşullarının etkileri, vida diş formundaki çentikli numunelerin yorulma dayanımları ile karşılaştırılarak araştırılmıştır. Vida açmada kesme hızının, radyal ilerlemenin, takım aşınmasının ve iki farklı kesme şemasının vidalı numunenin yorulma dayanımına etkileri bulunmuştur. Deneylerde vidalı numunelerin yorulma dayanımları aynı formdaki çentikli numuneye göre imal faktörlerine bağlı olarak geniş bir dağılım göstermiştir. Vidalı numunenin yorulma dayanımının imal faktörlerine önemli derecede bağlı olduğu ve çentikli numunenin vidayı temsil etmediği görülmüştür. Vidalı numunenin yorulma dayanımında en fazla takım aşınmasının ve kesme hızının daha düşük oranlarda ise kesme şemasının ve radyal ilerlemenin etkili olduğu görülmüştür.  Anahtar Kelimeler: Vida kesme, yorulma, takım aşınması. The effect of the machining parameters on the fatigue life of the threaded parts manufactured by machining were investigated comparing with the endurance limits of same size fine machined notched specimens. To machine precise specimens, rigidity of a universal lathe was improved by an additional slide system, and the final rigidity was measured to make sure of the tight dimensional tolerances. An R. R. Moore four point rotary bending fatigue test machine was designed, manufactured and calibrated. All the specimens were machined from AISI 4340 steel. In both thread and notch machining, uncoated %78 WC, %14 TiC and %8 Co API special tapered pipe thread tools were used. The effects of the cutting force, radial feed, tool wear and two thread cutting feeding methods on the fatigue life of the threaded specimens were determined. Experimental results show that fatigue lives of threaded specimens lie on a large range depending on machining conditions as compared to notched specimens, and thus, notched specimens do not represent fatigue behavior of threaded specimens. According to the experimental results, the most important factors effecting fatigue life of threaded specimens were found to be tool wear and cutting velocity and the effects of the different feeding methods and radial feed were found less significant. Keywords: Thread machining, fatigue, tool wear.

A survey on MAC protocols for complex self-organizing cognitive radio networks

Complex self-organizing cognitive radio (CR) networks serve as a framework for accessing the spectrum allocation dynamically where the vacant channels can be used by CR nodes opportunistically. CR devices must be capable of exploiting spectrum opportunities and exchanging control information over a control channel. Moreover, CR nodes should intelligently coordinate their access between different cognitive radios to avoid collisions on the available spectrum channels and to vacate the channel for the licensed user in timely manner. Since inception of CR technology, several MAC protocols have been designed and developed. This paper surveys the state of the art on tools, technologies and taxonomy of complex self-organizing CR networks. A detailed analysis on CR MAC protocols form part of this paper. We group existing approaches for development of CR MAC protocols and classify them into different categories and provide performance analysis and comparison of different protocols. With our categorization, an easy and concise view of underlying models for development of a CR MAC protocol is provided

Underground Environment Aware MIMO Design Using Transmit and Receive Beamforming in Internet of Underground Things

In underground (UG) multiple-input and multiple-output (MIMO), the transmit beamforming is used to focus energy in the desired direction. There are three different paths in the underground soil medium through which the waves propagates to reach at the receiver. When the UG receiver receives a desired data stream only from the desired path, then the UG MIMO channel becomes three path (lateral, direct, and reflected) interference channel. Accordingly, the capacity region of the UG MIMO three path interference channel and degrees of freedom (multiplexing gain of this MIMO channel requires careful modeling). Therefore, expressions are required derived the degrees of freedom of the UG MIMO interference channel. The underground receiver needs to perfectly cancel the interference from the three different components of the EM-waves propagating in the soil medium. This concept is based upon reducing the interference the undesired components to minimum at UG receiver using the receive beamforming. In this paper, underground environment aware MIMO using transmit and receive beamforming has been developed. The optimal transmit beamforming and receive combin- ing vectors under minimal inter-component interference constraint are derived. It is shown that UG MIMO performs best when all three component of the wireless UG channel are leveraged for beamforming. The environment aware UG MIMO technique leads to three-fold performance improvements and paves the wave for design and development of next generation sensor-guided irrigation systems in the field of digital agriculture

Crystal Reorientation and Amorphization Induced by Stressing Efficient and Stable P-I-N Vacuum-Processed MAPbI3 Perovskite Solar Cells

Herein, the long‐term stability of vacuum‐deposited methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs) with power conversion efficiencies (PCEs) of around 19% is evaluated. A low‐temperature atomic layer deposition (ALD) Al2O3 coating is developed and used to protect the MAPbI3 layers and the solar cells from environmental agents. The ALD encapsulation enables the MAPbI3 to be exposed to temperatures as high as 150 °C for several hours without change in color. It also improves the thermal stability of the solar cells, which maintain 80% of the initial PCEs after aging for ≈40 and 37 days at 65 and 85 °C, respectively. However, room‐temperature operation of the solar cells under 1 sun illumination leads to a loss of 20% of their initial PCE in 230 h. Due to the very thin ALD Al2O3 encapsulation, X‐ray diffraction can be performed on the MAPbI3 films and completed solar cells before and after the different stress conditions. Surprisingly, it is found that the main effect of light soaking and thermal stress is a crystal reorientation with respect to the substrate from (002) to (202) of the perovskite layer, and that this reorientation is accelerated under illumination

Performance Analysis of Receive Diversity in Wireless Sensor Networks over GBSBE Models

Wireless sensor networks have attracted a lot of attention recently. In this paper, we develop a channel model based on the elliptical model for multipath components involving randomly placed scatterers in the scattering region with sensors deployed on a field. We verify that in a sensor network, the use of receive diversity techniques improves the performance of the system. Extensive performance analysis of the system is carried out for both single and multiple antennas with the applied receive diversity techniques. Performance analyses based on variations in receiver height, maximum multipath delay and transmit power have been performed considering different numbers of antenna elements present in the receiver array, Our results show that increasing the number of antenna elements for a wireless sensor network does indeed improve the BER rates that can be obtained