Browsing by Subject "Wire"

Now showing 1 - 11 of 11

Open Access
Characteristic equations for the lasing Modes of infinite periodic chain of quantum wires
(IEEE, 2008-06) Byelobrov, V. O.; Benson, T. M.; Altıntaş, Ayhan; Nosich, A.I.
In this paper, we study the lasing modes of a periodic open optical resonator. The resonator is an infinite chain of active circular cylindrical quantum wires standing in tree space. Characteristic equations for the frequencies and associated linear thresholds of lasing are derived. These quantities are considered as eigenvalues of specific electromagnetic-field problem with "active" imaginary part of the cylinder material's refractive index - Lasing Eigenvalue Problem (LEP). ©2008 IEEE.
Open Access
Coulomb drag in parallel quantum dots
(Europhysics Letters Association, 2009-07-9) Oldoveanu, V.; Tanatar, Bilal
We study theoretically the electronic transport in parallel few-level quantum dots in the presence of both intradot and interdot long-range Coulomb interaction. Each dot is connected to two leads and the steady-state currents are calculated within the Keldysh formalism using the random-phase approximation for the interacting Green functions. Due to the momentum transfer between the two systems it is possible to get a nonvanishing current through an unbiased Coulomb-blockaded dot, if the other dot is set in the nonlinear transport regime. The transitions between the levels of the passive dot reduce the drag current and lead to negative differential conductance. We also discuss the dependence on temperature and the role of the lead-dot coupling. Copyright (C) EPLA, 2009
Open Access
Dynamic capacity management for voice over packet networks
(2003-06-07) Akar, Nail; Şahin, Cem
In this paper, dynamic capacity management refers to the process of dynamically changing the capacity allocation (reservation) of a pseudo-wire established between two network end points. This process is based on certain criteria including instantaneous traffic load for the pseudo-wire, network utilization, time of day, or day of week. Frequent adjustment of the capacity yields a scalability issue in the form of a significant amount of message processing in the network elements involved in the capacity update process. On the other hand, if the capacity is adjusted once and for the worst possible traffic conditions, a significant amount of bandwidth may be wasted depending on the actual traffic load. There is then a need for dynamic capacity management that takes into account the tradeoff between scalability and bandwidth efficiency. This problem is motivated by voice over packet networks in which end-to-end reservation requests are initiated by PSTN voice calls and these reservations are aggregated into one signal reservation in the core packet network for scalability. In this paper, we introduce a Markov decision framework for an optimal reservation aggregation scheme for voice over packet networks. Moreover, for problems with large sizes, we provide a suboptimal scheme using reinforcement learning. We show a significant improvement in bandwidth efficiency in voice over packet networks using aggregate reservations. © 2003 IEEE.
Open Access
Enhancement of plasmon resonances in the wave scattering by finite grids of circular silver wires
(IEEE, 2010-09) Natarov, D. M.; Benson, T. M.; Altıntaş, Ayhan; Sauleau, R.; Nosich, A. I.
Using the field expansions in local coordinates and addition theorems for cylindrical functions, we consider the problem of the H-polarized plane wave scattered by a finite chain of circular wires. The absorption and scattering cross-sections are found numerically and plasmon and grating-type resonances are studied for the grids of silver nano-size wires. © 2010 IEEE.
Open Access
Experimental observation of true left-handed metamaterial
(IEEE, 2005) Aydın, Koray; Güven, Kaan; Özbay, Ekmel
We report a true left-handed (LH) behavior in composite metamaterials. The magnetic resonance of the SRR structure is demonstrated. Plasma frequency of the LH material is shown to be lower than that of the wires.
Open Access
Hartree-Fock approximation of bipolaron state in quantum dots and wires
(Springer, 2010) Senger, R. T.; Kozal, B.; Chatterjee, A.; Erçelebi, A.
The bipolaronic ground state of two electrons in a spherical quantum dot or a quantum wire with parabolic boundaries is studied in the strong electron-phonon coupling regime. We introduce a variational wave function that can conveniently conform to represent alternative ground state configurations of the two electrons, namely, the bipolaronic bound state, the state of two individual polarons, and two nearby interacting polarons confined by the external potential. In the bipolaron state the electrons are found to be separated by a finite distance about a polaron size. We present the formation and stability criteria of bipolaronic phase in confined media. It is shown that the quantum dot confinement extends the domain of stability of the bipolaronic bound state of two electrons as compared to the bulk geometry, whereas the quantum wire geometry aggravates the formation of stable bipolarons.
Open Access
Lasing modes of infinite periodic chain of quantum wires
(IEEE, 2009-06-07) Byelobrov, V. O.; Benson, T. M.; Sewell, P.; Altıntaş, Ayhan; Nosich, A. I.
In this paper, we study the scattering and eigenvalue problems for a periodic open optical resonator that is an infinite chain of active circular cylindrical quantum wires standing in free space. The scattering problem is solved by the method of partial separation of variables. The eigenvalue problem differs from the first one by the absence of the incident field and presence of "active properties" of cylinders and yields the frequencies and thresholds of lasing. ©2009 IEEE.
Open Access
Modeling of an ac-electro-osmosis based microfluidic mixer
(ASME, 2017) Uslu, H. Dilara; Canpolat, Ç.; Çetin, Barbaros
The purpose of this study is presenting an active micromixer, which is based on AC electro-osmotic flow driven on 3D micro wires. In order to solve governing equations of AC electroosmosis, a commercial software COMSOL Multiphysics® is implemented. Different wire configurations with various imposed electric fields and flow rates are tested for evaluating mixing efficiencies. The analyses show that mixing performance is significantly improved by number of the wires as well as wire orientation. It is also revealed that the degree of mixing can also be controlled by the tuning of the applied voltage for a given flow rate.
Open Access
Simultaneous 3-D motion estimation and wire-frame model adaptation including photometric effects for knowledge-based video coding
(IEEE, 1994) Bozdağı, Gözde; Tekalp, A. M.; Onural, Levent
We address the problem of 3-D motion estimation in the context of knowledge-based coding of facial image sequences. The proposed method handles the global and local motion estimation and the adaptation of a generic wire-frame to a particular speaker simultaneously within an optical flow based framework including the photometric effects of motion. We use a flexible wire-frame model whose local structure is characterized by the normal vectors of the patches which are related to the coordinates of the nodes. Geometrical constraints that describe the propagation of the movement of the nodes are introduced, which are then efficiently utilized to reduce the number of independent structure parameters. A stochastic relaxation algorithm has been used to determine optimum global motion estimates and the parameters describing the structure of the wire-frame model. For the initialization of the motion and structure parameters, a modified feature based algorithm is used. Experimental results with simulated facial image sequences are given.
Open Access
Transmission and reflection properties of composite double negative metamaterials in free space
(IEEE, 2003) Özbay, Ekmel; Aydin, K.; Cubukcu, E.; Bayındır, Mehmet
We report free space transmission and the first reflection measurements of a composite double negative (DNG) metamaterial, also known as a left-handed material (LHM). The metaniaterial composes of the split-ring-resonators and discontinuous thin wires. Very high transmission values of the metamaterial are observed within a frequency range for which both effective permeability and permittivity are expected to be negative.
Open Access
Transmission properties of composite metamaterials in free space
(American Institute of Physics, 2002) Bayındır, Mehmet; Aydin, K.; Özbay, Ekmel; Markoš, P.; Soukoulis, C. M.
We propose and demonstrate a type of composite metamaterial which is constructed by combining thin copper wires and split ring resonators (SRRs) on the same board. The transmission measurements performed in free space exhibit a passband within the stop bands of SRRs and thin wire structures. The experimental results are in good agreement with the predictions of the transfer matrix method simulations. © 2002 American Institute of Physics.