Browsing by Subject "Dipole"

Now showing 1 - 6 of 6

Open Access
Dielectrophoresis in microfluidics technology
(2011) Çetin B.; Li, D.
Dielectrophoresis (DEP) is the movement of a particle in a non-uniform electric field due to the interaction of the particle's dipole and spatial gradient of the electric field. DEP is a subtle solution to manipulate particles and cells at microscale due to its favorable scaling for the reduced size of the system. DEP has been utilized for many applications in microfluidic systems. In this review, a detailed analysis of the modeling of DEP-based manipulation of the particles is provided, and the recent applications regarding the particle manipulation in microfluidic systems (mainly the published works between 2007 and 2010) are presented. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Electronic excited states of the CP29 antenna complex of green plants: a model based on exciton calculations
(Springer / Kluwer Academic Publishers, 2000) İşerı, E. İ.; Albayrak, D.; Gülen, D.
We have suggested a model for the electronic excited states of the minor plant antenna, CP29, by incorporating a considerable part of the current information offered by structure determination, site-directed mutagenesis, and spectroscopy in the modeling. We have assumed that the electronic excited states of the complex have been decided by the chlorophyll-chlorophyll (Chl) and Chl-protein interactions and have modeled the Coulombic interaction between a pair of Chls in the point-dipole approximation and the Chl-protein interactions are treated as empirical fit parameters. We have suggested the Qy dipole moment orientations and the site energies for all the chlorophylls in the complex through a simultaneous simulation of the absorption and linear dichroism spectra. The assignments proposed have been discussed to yield a satisfactory reproduction of all prominent features of the absorption, linear and circular dichroism spectra as well as the key spectral and temporal characteristics of the energy transfer processes among the chlorophylls. The orientations and the spectral assignments obtained by relatively simple exciton calculations have been necessary to provide a good point of departure for more detailed treatments of structure-function relationship in CP29. Moreover, it has been discussed that the CP29 model suggested can guide the studies for a better understanding of the structure-function relationship in the major plant antenna, LHCII.
Open Access
Nanoantenna couplers for metal-insulator-metal waveguide interconnects
(SPIE, 2010) Onbasli, M.C.; Okyay, Ali Kemal
State-of-the-art copper interconnects suffer from increasing spatial power dissipation due to chip downscaling and RC delays reducing operation bandwidth. Wide bandwidth, minimized Ohmic loss, deep sub-wavelength confinement and high integration density are key features that make metal-insulator-metal waveguides (MIM) utilizing plasmonic modes attractive for applications in on-chip optical signal processing. Size-mismatch between two fundamental components (micron-size fibers and a few hundred nanometers wide waveguides) demands compact coupling methods for implementation of large scale on-chip optoelectronic device integration. Existing solutions use waveguide tapering, which requires more than 4λ-long taper distances. We demonstrate that nanoantennas can be integrated with MIM for enhancing coupling into MIM plasmonic modes. Two-dimensional finite-difference time domain simulations of antennawaveguide structures for TE and TM incident plane waves ranging from λ = 1300 to 1600 nm were done. The same MIM (100-nm-wide Ag/100-nm-wide SiO2/100-nm-wide Ag) was used for each case, while antenna dimensions were systematically varied. For nanoantennas disconnected from the MIM; field is strongly confined inside MIM-antenna gap region due to Fabry-Perot resonances. Major fraction of incident energy was not transferred into plasmonic modes. When the nanoantennas are connected to the MIM, stronger coupling is observed and E-field intensity at outer end of core is enhanced more than 70 times. © 2010 SPIE.
Open Access
Pd nanocube decoration onto flexible nanofibrous mats of core-shell polymer-ZnO nanofibers for visible light photocatalysis
(Royal Society of Chemistry, 2017) Arslan, O.; Topuz, F.; Eren, H.; Bıyıklı, Necmi; Uyar, Tamer
Plasmonic enhancement for electron-hole separation efficiency and visible light photocatalysis was achieved by Pd nanocube decoration on a ZnO nanolayer coated onto electrospun polymeric (polyacrylonitrile (PAN)) nanofibers. Since exciton formation and sustainable electron-hole separation have a vital importance for realizing better solar energy in photovoltaic and photocatalytic devices, we achieved visible light photocatalysis by Pd nanocube decoration onto well designed core-shell nanofibers of ZnO@PAN-NF. By controlling the cubic Pd nanoparticle size and the thickness of the crystalline ZnO nanolayer deposited onto electrospun PAN nanofibers via atomic layer deposition (ALD), defect mediated visible light photocatalysis efficiency can be increased. By utilizing nanofabrication techniques such as thermal decomposition, electrospinning and ALD, this fabricated template became an efficient, defect mediated, Pd nanocube plasmon enhanced photocatalytic system. Due to the enhanced contact features of the Pd nanocubes, an increase was observed for the visible light photocatalytic activity of the flexible and nanofibrous mat of Pd@ZnO@PAN-NF.
Open Access
Radar cross section (RCS) of perfectly conducting (PEC) thin wires and its application to radar countermeasure: Chaff
(2015) Dalkıran, Rıfat
In electronic warfare, active and passive countermeasures are used to jam threat RF radars. While electronic jamming pods are accepted as an active one, chaff is accepted as a passive countermeasure that consists of millions of perfectly conducting thin metallic wires, dipoles. The aim of this thesis is to first implement Van Vleck’s Methods A and B [1], Tai’s Variational Method [2] and Einarsson’s Direct Method [3] to get radar cross section (RCS) of a dipole and then apply the results to calculate RCS of designed chaff cartridges. The ultimate goal is to suggest more effective passive countermeasure system than commercially available ones. In this thesis, performances of these methods are evaluated. According to these evaluations, Van Vleck’s Method B and Einarsson’s Direct Method are selected for calculating RCS of chaff cartridges. Performance of RR-178 (XN-2) commercial chaff cartridge is compared with three different suggested designs. For each of these designs, 2 to 20 GHz frequency interval is divided into three or six equal sub-frequency intervals and for these intervals particular chaff cartridges with different dipole lengths and numbers are proposed. In terms of total dipole length in the cartridges, instead of 88775 meters dipoles that is used in RR- 178 (XN-2), by using chaff cartridges of third proposed design, in average only 25300 meters dipoles are used while providing more flat and equal average RCS value for 2 to 20 GHz frequency interval. Moreover, for the stated frequency interval, if total dipole length for the chaff cartridges of RR-178 (XN-2) and third proposed design keep equal, about 5.2 dB increase in average RCS value is obtained. Analysis of these results shows that designed chaff cartridges are more effective than commercial ones if the designed ones are used together with compatible Radar Warning Receiver (RWR) and Dispensing System.
Open Access
Role of the environmental spectrum in the decoherence and dephasing of multilevel quantum systems
(The American Physical Society, 2005) Hakioǧlu T.; Savran, K.
We examine the effect of multilevels on decoherence and dephasing properties of a quantum system consisting of a nonideal two level subspace, identified as the qubit, and a finite set of higher energy levels above this qubit subspace. The whole system is under interaction with an environmental bath through a Caldeira-Leggett type coupling. The model that we use is an rf-SQUID under macroscopic quantum coherence and coupled inductively to a flux noise characterized by an environmental spectrum. The model interaction can generate dipole couplings which can be appreciable between the qubit and the high levels. The decoherence properties of the qubit subspace is examined numerically using the master equation formalism of the system's reduced density matrix. We calculate the relaxation and dephasing times as the spectral parameters of the environment are varied. We observe that, these calculated time scales receive contribution from all available frequencies in the noise spectrum (even well above the system's resonant frequency scales) stressing the dominant role played by the nonresonant transitions. The relaxation and dephasing and the leakage times thus calculated, strongly depend on the appreciably interacting levels determined by the strength of the dipole coupling. Under the influence of these nonresonant and multilevel effects, the validity of the two level approximation is dictated not by the low temperature as conveniently believed, but by these multilevel dipole couplings as well as the availability of the environmental modes.