Ali Demir

A Photovoltaic Fiber Design for Smart Textiles

In this paper, the active photovoltaic fibers consisting of nano-layers of polymer-based organic compounds are presented. A flexible solar cell, including a polymer-based anode, two different nano-materials in bulk heterojunction blends as the light absorbing materials, and a semi-transparent cathode to collect the electrons, was formed by coating these materials onto flexible polypropylene (PP) fibers layer by layer, respectively, to produce electricity. Photovoltaic performances of the fibers were analyzed by measuring current versus voltage characteristics under AM1.5 conditions. The maximum value obtained as the short-circuit current density of photovoltaic fibers was 0.27 mA/cm2. The fabrication issues and also possible smart textile applications of these photovoltaic fibers were discussed.

Effects of Polarity on Electrospinning Process

As one of the nanofiber production processes, the electrospinning process has a conventional configuration consisting of a charged syringe and a grounded collector plate. In this study, the polarities of the electrodes are reversed so that while the collector is charged by power supply, the syringe is grounded. A solution of 7.5 wt % polyvinyl (alcohol)/water is electrospun. The conventional setup and the new inverse setup are compared in terms of production efficiency and the diameter of the nanofibers is produced. Thus, it is aimed to determine which configuration best suits for an extruder-collector system in an industrial context. Results showed that the conventional setup has a noticeably higher nanofiber production efficiency than the new setup due to a lack of Coulombic force acting on the polymer jet in the new setup. Also, nanofiber diameters and web layer pore sizes produced by the conventional setup are much finer and more homogenously distributed than those produced by the new reversed setup.

Photovoltaic textile structure using polyaniline/carbon nanotube composite materials

In this paper, an investigation of flexible electrodes for photovoltaic textile structures utilizing polymer‐based organic materials is presented. The composite structure consisting of a blend of water dispersible carbon nanotube:polyaniline (CNT:PANI) components with poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was applied to be used as the hole collecting electrode in photovoltaic textile applications. Both photovoltaic textiles and conventional solar cells were fabricated by using a blend of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT):(6,6)‐phenyl C61‐butyric acid methyl ester (PCBM). All devices were characterized by measuring current versus voltage characteristics under AM 1.5 conditions. The nanoscale morphology of the photovoltaic structures was investigated using scanning electron microscopy and atomic force microscopy.

Thermal and mechanical properties of composite nanofiber webs and films containing cellulose nanowhiskers

In this study, nanocomposites reinforced with cellulose nanowhiskers (CNWs) were prepared by employing three different fabrication methods. These methods include electrospinning of nanofiber webs using a single-component nozzle, electrospinning of nanofiber webs using a coaxial bi-component nozzle, and film casting followed by compression molding. Maleic anhydride grafted elastomeric polymer was used as the polymer matrix. Nanocomposite samples obtained from these three different systems were characterized in terms of morphology, and mechanical and thermal properties. The processing–structure–property relationships of the nanocomposites are discussed in this paper.

The Effects of Super Absorbent Fibers on the Washing, Dry Cleaning and Drying Behavior of Knitted Fabrics

In this study, water absorption and drying properties of knitted fabrics produced by 100 % polyester staple fibers (PET) yarn, blend of 80 % PET, 20 % super absorbent fibers (SAF) yarn and covered 80—20 % PET-SAF blend yarn, which the surface of the 80—20 % PET-SAF blend yarn has been covered by a monofilament polyester were experimentally examined. The effect of SAF, covering yarn, washing and drying treatment and dry cleaning treatment on the water absorption of the fabrics was analyzed. It was seen that knitted fabric with 80—20 % PET-SAF blend yarn and covered blend yarn always had higher water absorption value and longer drying time than knitted fabric with 100 % PET. However, knitted fabric with covered blend yarn had less water absorption than the fabric with blend yarn. Water absorption values of fabrics did not change too much during repeated water absorption tests. The absorption properties of the fabrics containing SAF decreased dramatically after washing and drying treatment. However, after repeated dry cleaning treatment, there was still considerably high water absorption capacity on the fabric containing SAF with regard to the fabric with 100 % PET.

Water vapor absorption properties of a novel filament composed of maleic anhydride polypropylene, polypropylene and super absorbent polymer

The aim of this study is to develop a prototype filament that can absorb water vapor without creating any feeling of wetness and can be durable against the cleaning processes. A blend of polypropylene (PP) and maleic anhydride polypropylene (MAPP) is used for the outer surface; super absorbent polymer is placed into the cavity of prototype filament. The new prototype filament can absorb water (approximately 23%) without creating any feeling of wetness and dries totally in 20 minutes. Different blend ratios have been investigated for water vapor absorbency after washing treatment and it has been found that 50% MAPP—50% PP blend with high super absorbent polymer has better washing performances.

Design of a Novel Filament with Vapor Absorption Capacity without Creating Any Feeling of Wetness

The aim of this study is to design and develop a novel filament that can absorb water vapor but does not cause any feeling of wetness to the person who touches it. Thus, a polypropylene fiber which absorbs no water vapor (0%) may be used as an outer surface while SAP (super absorbent polymer) may be used as a filler placed into the cavity of the filament in order to absorb the required excessive amount of water vapor. It has been proven that the developed novel filament with SAP filler could absorb water vapor, without creating any feeling of wetness. It has been observed that while a filament with SAP absorbs 8% water vapor providing a dry sense on the outer surface of the filament, a filament without SAP absorbs 0% water vapor. All samples dried in about 20—30 minutes following the first water absorption test. The dry cleaning process caused a decrease in water vapor absorption capacity at a ratio of up to 50%. The amount of SAP, the number of filaments in the filament bundle and the covering density on the filament bundle affected the absorption capacity at statistically significant levels.

Nanofibrous composite air filters

Abstract Airborne particle filtration has become a vitally critical issue, since air pollution severely threatens the public health. Due to the inadequacy of traditional filters to capture extremely fine particles, the nanofibrous composite filters have gained great importance. In order to assess the performance of the nanofibrous filters, pressure drop, capture efficiency, quality factor, uniformity of the filter structure, porosity, packing density, and properties of the turbulent flow through the pores are designated as the important parameters. The nanofibrous filter production techniques can be broadly categorized as the electro- and the nonelectrospinning techniques. Those can be fabricated with sandwich and/or composite form by using these techniques. Either of the approaches can be employed depending on the content and structure of the air filter as composite and biocidal air filter.

Software requirement traceability analysis using text mining methods

In this study, text mining based methods are proposed for requirement traceability analysis which is one of the most essential steps in the software life cycle. It is aimed to automate the requirements traceability process of the software architecture, which is conducted by a data analyst manually, with the proposed methods. For this purpose, besides the tf-idf and Latent Semantic Analysis (LSI/LSA) based approaches which are commonly used in the literature, requirement and design matching activities are realized by using Latent Dirichlet Allocation (LDA) title modelling technique and word2vec models. While the tf-idf based LSI approach achieve the highest classification accuracy, the LDA based approach produces relatively lower classification accuracy than LSI models. The word2vec + tf-idf method which has better classification accuracy than both of the word2vec + BOW and BOW alone models is the method producing the third highest performance.

Cooperative adaptive cruise control using visible light communication

Control of semi/full — autonomous vehicles and visible light communication (VLC) are very hot research topics in their own area of disciplines, and these topics are expected to be more popular in the near future. When it comes to the semi/full — autonomous vehicles, the greatest difference from conventional vehicles is that these vehicles need to communicate with each other in order to maintain the safety of passengers. In this study we had a multidisciplinary approach from communication and control sides and we proposed a communication system with VLC for a cheaper vehicular communication, instead of IEEE 802.11p Wi-Fi protocol. Since VLC can be achieved by using onboard LED lights of current vehicles in market and there is no need for additional hardware (except receiver). In continuation of the study, we implemented a sliding mode control algorithm, and this way the cooperative adaptive cruise controller (CACC) using VLC has been completed. It is observed that distance between two vehicles has been protected in the results of the simulation and study has been successfully concluded.