Istanbul Technical University

About: Istanbul Technical University is a education organization based out in Istanbul, Turkey. It is known for research contribution in the topics: Fuzzy logic & Large Hadron Collider. The organization has 12889 authors who have published 25081 publications receiving 518242 citations. The organization is also known as: İstanbul Teknik Üniversitesi & Technical University of Istanbul.

Optical MIMO-OFDM With Generalized LED Index Modulation

Abstract: Visible light communications (VLC) is a promising and uncharted new technology for the next generation of wireless communication systems. This paper proposes a novel generalized light emitting diode (LED) index modulation method for multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM)-based VLC systems. The proposed scheme avoids the typical spectrum efficiency losses incurred by time- and frequency-domain shaping in OFDM signals. This is achieved by exploiting spatial multiplexing along with LED index modulation. Accordingly, real and imaginary components of the complex time-domain OFDM signals are separated first, then resulting bipolar signals are transmitted over a VLC channel by encoding sign information in LED indexes. As a benchmark, we demonstrate the performance analysis of our proposed system for both analytical and physical channel models. Furthermore, two novel receiver designs are proposed. Each one is suitable for frequency-flat or selective channel scenarios. It has been shown via extensive computer simulations that the proposed scheme achieves considerably better bit error ratio versus signal-to-noise-ratio performance than the existing VLC-MIMO-OFDM systems that use the same number of transmit and receive units [LEDs and photo diodes (PDs)]. Compared with the single-input single-output (SISO) DC biased optical (DCO)-OFDM system, both spectral efficiency and DC bias can be doubled and removed respectively simply by exploiting a MIMO configuration.

Thermodynamic analysis of wind energy

Abstract: Wind energy is assessed thermodynamically, from resource and technology perspectives The thermodynamic characteristics of wind are considered Wind speed is affected by air temperature and pressure and has an effect on wind turbine performance, based on wind chill effect and Bernoulli's equation The wind chill effect leads to temperature differences that suggest enthalpy and entropy components must be considered in a thermodynamic analysis The wind pressure effect based on Bernoulli's equation affects the entropy of wind These components have not previously been considered in evaluations of wind turbine efficiency for electricity generation A new efficiency formula for wind energy systems is described, which provides important information about the system It is seen that average differences between energy and exergy efficiencies are approximately 40% at low wind speeds and up to approximately 55% at high wind speeds Copyright © 2005 John Wiley & Sons, Ltd

Preparation of ABC miktoarm star terpolymer containing poly(ethylene glycol), polystyrene, and poly(tert‐butylacrylate) arms by combining diels–alder reaction, atom transfer radical, and stable free radical polymerization routes

Abstract: The ABC type miktoarm star terpolymer was prepared utilizing “core-in” and “core-out” methods via combination of Diels–Alder reaction (DA), stable free radical polymerization (SFRP), and atom transfer radical polymerization (ATRP). First, in DA reaction, poly(ethylene glycol)-maleimide (PEG-maleimide) precursor was reacted with succinic acid anthracen-9-ylmethyl ester 3-(2-bromo-2-methyl-propionyloxy)-2-methyl-2-[2-phenyl-2-(2,2,6,6-tetramethyl-piperidin-1-yloxy)-ethoxy-carbonyl]-propyl ester, 8, to give DA adduct, 9, which has appropriate functional groups for SFRP and ATRP. Second, a previously obtained 9 was used as a macroinitiator for SFRP of styrene at 125 °C. As a third step, this PEG-polystyrene (PEG-PSt) precursor with a bromine functionality in the core was employed as a macroinitiator for ATRP of tert-butylacrylate (tBA) in the presence of Cu(I)Br and pentamethyldiethylenetriamine at 80 °C to give ABC type miktoarm star terpolymer (PEG-PSt-PtBA) with controlled molecular weight and low polydispersity (Mw/Mn < 1.27). The obtained polymers were characterized by gel permeation chromatography and 1H NMR. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 499–509, 2006