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1999

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Articles 331 - 360 of 456

Full-Text Articles in Physics

Butt-Coupling Loss Of 0.1 Db/Interface In Inp/Ingaas Multi-Quantum-Well Waveguide-Waveguide Structures Grown By Selective Area Chemical Beam Epitaxy, C. A. Verschuren, M. R. Leys, H. Vonk, J. H. Wolter, P. J. Harmsma, Y. S. Oei Jan 1999

Butt-Coupling Loss Of 0.1 Db/Interface In Inp/Ingaas Multi-Quantum-Well Waveguide-Waveguide Structures Grown By Selective Area Chemical Beam Epitaxy, C. A. Verschuren, M. R. Leys, H. Vonk, J. H. Wolter, P. J. Harmsma, Y. S. Oei

Turkish Journal of Physics

The lateral coupling of waveguiding structures in both [011] and [0\bar{1}1] directions is studied using embedded selective area epitaxy by Chemical Beam Epitaxy. All growth steps are carried out under the same growth conditions on (100) lnP substrates misoriented by 0.5° towards (111)B. Both planar and selectively grown material exhibits bright luminescence and narrow PL line widths (8 meV FWHM at 4K), up to the lateral junction. Moreover, no degradation of the original material properties is observed after regrowth. SEM images show very flat layers and excellent lateral coupling for all four types of junctions. After reactive ion etching of …

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Silicon-Based Optoelectronics: Progress And Challenges, Tamim P. Sidiki, Clivia M. Sotomayor Torres Jan 1999

Silicon-Based Optoelectronics: Progress And Challenges, Tamim P. Sidiki, Clivia M. Sotomayor Torres

Turkish Journal of Physics

We review the status of silicon-based optoelectronics with emphasis on light emitting diodes. Erbium-doped Si, por-Si and silicon-based superlattices and nanostructures are discussed. The origin behind light emission in silicon with feature sizes below about 60 nm still remains poorly understood.

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3 \Mu M Intersubband Quantum Well Photodetector (Qwip), Rita Gupta, A. L. Y. Wong, S. K. Haywood Jan 1999

3 \Mu M Intersubband Quantum Well Photodetector (Qwip), Rita Gupta, A. L. Y. Wong, S. K. Haywood

Turkish Journal of Physics

In recent years photodetectors operating in the mid- to far infrared region of 3-15 \mu m have been designed based on electron and hole intersubband transitions in multiple quantum wells and superlattices. In general, QWIPs based on electron transitions show greater detectivity compared to the hole-based photodetectors. However, selection rules for electron intersubband transitions usually forbid the TE mode operation, associated with normal light incidence; Therefore, special coupling structures/geometries have been employed to couple light into the device. The spectral region 3-5 \mu m is of interest for a variety of applications such as environmental gas sensing, thermal imaging etc. …

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Hellish-Vcsel: A Hot Electron Laser, A. Obrien-Davies, N. Balkan, A. Boland-Thoms, M. J. Adams, J. Roberts Jan 1999

Hellish-Vcsel: A Hot Electron Laser, A. Obrien-Davies, N. Balkan, A. Boland-Thoms, M. J. Adams, J. Roberts

Turkish Journal of Physics

Hot Electron Light emission and Lasing In Semiconductor Heterostructures (HEL-LISH-1) is a novel hot electron surface emitter consisting of a GaAs QW on the n side of an Ga_{1-x}Al_xAs p-n junction. It utilises hot electron transport parallel to the junction plane. The injection of hot electron hole pairs into the QW is achieved via tunnelling and thermionic emission processes. Recently this structure has been modified by the incorporation of an upper and lower DBR defining a VCSEL (HELLISH-VCSEL). This has been shown to lase at room temperature with a Full Width at Half Maximum (FWHM) of 1.5 nm. In this …

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Single Si \Delta-Doped Gaas Investigations By New Photothermal Wavelength Modulated Photocurrent Technique, Fi̇kret Hajiev, Yener Özkan, M. Çeti̇n Arikan Jan 1999

Single Si \Delta-Doped Gaas Investigations By New Photothermal Wavelength Modulated Photocurrent Technique, Fi̇kret Hajiev, Yener Özkan, M. Çeti̇n Arikan

Turkish Journal of Physics

New Photothermal Wavelength Modulated Photocurrent (PWMPC) technique is reported. This technique is used for investigation of the MBE grown p-GaAs sample in which a single Si-layer was embedded with a \delta-type profile. Two spectral features were observed at 1.5137 eV and 1.5115 eV at 20 K. These peaks were attributed to the (D°,X) and (A°,X)-excitons bound to neutral donors and acceptors, respectively. We studied the temperature dependence of these excitonic peaks positions at temperatures between 20-90 K. Additionally, we demonstrate a blue shift of photocurrent spectra under a low level illumination intensity. PWMPC technique and the nature of the registered …

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Semiconductor And Dielectric Microcavity Spectroscopy, Ali̇ Serpengüzel Jan 1999

Semiconductor And Dielectric Microcavity Spectroscopy, Ali̇ Serpengüzel

Turkish Journal of Physics

Semiconductor and dielectric microcavities are used for the localization of photons as well as the enhancement of photon density of states. The enhancement of photoluminescence, electroluminescence, and lasing by the use of microcavities leads to novel active and passive optoelectronic and photonic devices such as channel droppping filters, semiconductor lasers, and resonant cavity enhanced devices. Experimental results showing photoluminescence enhancement in active planar, lasing in active ellipsoidal microcavities as well as light scattering in passive and spherical microcavities are presented.

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Characterization Of Inas/Gaas Qd Structures By Hrem And Pl Spectroscopy, Y. Ati̇ci̇, D. Cherns, A. Polimeni, M. Henini, L. Eaves Jan 1999

Characterization Of Inas/Gaas Qd Structures By Hrem And Pl Spectroscopy, Y. Ati̇ci̇, D. Cherns, A. Polimeni, M. Henini, L. Eaves

Turkish Journal of Physics

No abstract provided.

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Experimental Separation Of Phonon And Extrinsic Scattering In 2d Carrier Gases In Gaas, F. F. Ouali, H. R. Francis, H. C. Rhodes Jan 1999

Experimental Separation Of Phonon And Extrinsic Scattering In 2d Carrier Gases In Gaas, F. F. Ouali, H. R. Francis, H. C. Rhodes

Turkish Journal of Physics

A new method which separates phonon scattering from extrinsic scattering in 2D gases in GaAs is presented. In contrast to previous ones, the technique makes no assumptions about the temperature dependence of the extrinsic scattering. The preliminary measurements of the phonon limited mobility \mu_{ph} on two electron gas samples show a Bloch-Grüneisen regime in the temperature range 1.2-4.5K and the results agree reasonably well with other experimental and theoretical work.

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Stability Of Quasi-Two-Dimensional Bipolarons, R. Tuğrul Senger, Ati̇lla Erçelebi̇ Jan 1999

Stability Of Quasi-Two-Dimensional Bipolarons, R. Tuğrul Senger, Ati̇lla Erçelebi̇

Turkish Journal of Physics

The stability criteria of quasi-two-dimensional dimensional bipolarons have been studied within the framework of strong coupling and path-integral theories. It is shown that the critical values of the electron-phonon coupling constant (\alpha), and the ratio of dielectric constants (\eta = \epsilon_{\infty}/\epsilon_{0}) exhibit some non-trivial features as the effective dimensionality is tuned from three to two.

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The Extended Hybrid Model For Optical Phonon Confinement, C. R. Bennett, B. K. Ridley, N. A. Zakhleniuk, M. Babiker Jan 1999

The Extended Hybrid Model For Optical Phonon Confinement, C. R. Bennett, B. K. Ridley, N. A. Zakhleniuk, M. Babiker

Turkish Journal of Physics

The theory of optical phonons and their confinement in heterostructures is reviewed with analogies made to the theory of acoustic phonons. The dielectric continuum (DC) model is obtained when bulk dispersion is ignored and the hybrid model is found when dispersion is included. The issue of boundary conditions is investigated and the solutions are shown with comparisons made using electron-phonon scattering.

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Wigner Crystalization In Semiconductor Quantum Wires, I. Al-Hayek, B. Tanatar, M. Tomak Jan 1999

Wigner Crystalization In Semiconductor Quantum Wires, I. Al-Hayek, B. Tanatar, M. Tomak

Turkish Journal of Physics

We study the Wigner crystallization in semiconductor quantum wires within the density functional approach. As the density of electrons in quasi-one-dimensional structures is lowered, we find that the system favors the crystalline phase as envisioned by Wigner.

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The Effect Of Non-Equilibrium Acoustic Phonons On The Tunnel Current In Gaas/Alas Superlattices, S. A. Cavill, F. F. Ouali, L. J. Challis, A. J. Kent, M. Henini, A. V. Akimov Jan 1999

The Effect Of Non-Equilibrium Acoustic Phonons On The Tunnel Current In Gaas/Alas Superlattices, S. A. Cavill, F. F. Ouali, L. J. Challis, A. J. Kent, M. Henini, A. V. Akimov

Turkish Journal of Physics

We present the first study of the effect of ballistic acoustic phonons generated by a heated metal film on the tunnel current in GaAs/AlAs superlattices. The phonon-induced increase of the tunnel current as a function of applied voltage has a maximum at a voltage that varies linearly with heater temperature both in zero and applied magnetic field. The behaviour is consistent with phonon-assisted tunnelling by stimulated phonon emission. The system acts as a phonon spectrometer in the < 1THz frequency region with a resolution of approximately 200 GHz.

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Optimisation Of The Tunable Wavelength Hot Electron Light Emitter, Ali̇ Teke, Naci̇ Balkan Jan 1999

Optimisation Of The Tunable Wavelength Hot Electron Light Emitter, Ali̇ Teke, Naci̇ Balkan

Turkish Journal of Physics

We report on the optimization of the hot electron tunable wavelength surface light emitting device developed by us. The device consists of a p-GaAs, and n-Ga_{1-x}Al_xAs heterojunction containing an inversion layer on the p- side, and GaAs quantum wells on the n- side, and is referred to as HELLISH-2 (Hot Electron Light Emitting and Lasing in Semiconductor Heterojunction). The device utilises hot electron longitudinal transport and, therefore, light emission is independent of the polarity of the applied voltage. In order to optimise the operation of the device a theoretical model that calculates the tunnelling and the thermionic components of the …

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Binding Energies Of Excitons In Symmetric And Asymmetric Coupled Double-Quantum Well Structures In A Magnetic Field, Esi̇n Kasapoğlu, Hüseyi̇n Sari, Yüksel Ergün, Sezai̇ Elagöz, Naci̇ Balkan, İsmai̇l Sökmen Jan 1999

Binding Energies Of Excitons In Symmetric And Asymmetric Coupled Double-Quantum Well Structures In A Magnetic Field, Esi̇n Kasapoğlu, Hüseyi̇n Sari, Yüksel Ergün, Sezai̇ Elagöz, Naci̇ Balkan, İsmai̇l Sökmen

Turkish Journal of Physics

The binding energy of excitons in the symmetric and asymmetric coupled double GaAs/Ga_{1-x}Al_xAs quantum wells is calculated by using variational approach. Results have been obtained as a function of the potential symmetry, the size of the quantum well, and the coupling parameter of the wells in the presence of a magnetic field applied parallel to the growth direction. The role of the asymmetric barriers, magnetic field, barrier and well width in determining the tunability of the excitonic binding parameters of the GaAs/Ga_{1-x}Al_xAs system is discussed.

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Band-Gap Renormalization In Quantum Wires, K. Güven, C. R. Bennett, B. Tanatar Jan 1999

Band-Gap Renormalization In Quantum Wires, K. Güven, C. R. Bennett, B. Tanatar

Turkish Journal of Physics

Improved techniques in semiconductor fabrication increased the interest in quantum wire structures, because of their opto-electronic device application possibilities. Many-body interactions among the electrons and holes in the wire lead to the band-gap renormalization (BGR), which in turn affect the optical properties of the system. We study the BGR within the random-phase approximation incorporating the dynamical effects, and investigate the density dependence.

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Improvement In Electroabsorption And The Effect Of The Electric Field In The Tuneable Wavelength Converter, Hüseyi̇n Sari, Esi̇n Kasapoğlu, Yüksel Ergün, İsmai̇l Sökmen Jan 1999

Improvement In Electroabsorption And The Effect Of The Electric Field In The Tuneable Wavelength Converter, Hüseyi̇n Sari, Esi̇n Kasapoğlu, Yüksel Ergün, İsmai̇l Sökmen

Turkish Journal of Physics

The numerical results of the study of a novel wavelength converter which can be tuned with the application of an external field are presented. For this device, exciton binding energies, radiuses and the absorption coefficient are numerically analysed as a function of electric field. We showed that the interband transition energy and the overlap function between electron and hole changes abruptly when an electric field is applied. This phenomenon can be used the increase the change in the absorption coefficient and reduce the on-state transmission loss in electroabsorption modulators.

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A Gainasp/Inp Vertical Cavity Surface Emitting Laser For 1.5 \Mu M Operation, R. Sceats, N. Balkan, M. J. Adams, J. Masum, A. J. Dann, S. D. Perrin, I. Reid, J. Reed, P. Cannard, M. A. Fisher, D. J. Elton, M. J. Harlow Jan 1999

A Gainasp/Inp Vertical Cavity Surface Emitting Laser For 1.5 \Mu M Operation, R. Sceats, N. Balkan, M. J. Adams, J. Masum, A. J. Dann, S. D. Perrin, I. Reid, J. Reed, P. Cannard, M. A. Fisher, D. J. Elton, M. J. Harlow

Turkish Journal of Physics

We present the results of our studies concerning the pulsed operation of a bulk GaInAsP/InP vertical cavity surface emitting laser (VCSEL). The device is tailored to emit at around 1.5 \mu m at room temperature. The structure has a 45 period n-doped GaInAsP/InP bottom distributed Bragg reflector (DBR), and a 4 period Si/Al_2O_3 dielectric top reflector defining a 3-\lambda cavity. Electroluminescence from a 16 \mu m diameter top window was measured in the pulsed injection mode. Spectral measurements were recorded in the temperature range between 125K and 240K. Polarisation, lasing threshold current and linewidth measurements were also carried out at …

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An Investigation Of Electrical Properties Of Porous Silicon, G. Algün, M. Ç. Arikan Jan 1999

An Investigation Of Electrical Properties Of Porous Silicon, G. Algün, M. Ç. Arikan

Turkish Journal of Physics

In this work, electrical properties of porous silicon structures, formed with electrochemical anodization in HF acid solution under two different current densities, were investigated. In these experiments, Sb doped (111)-oriented n-type silicon samples with 0.006-0.015 \Omega cm resistivity was used. Samples were anodized in a solution of 38% HF and 99% C_2H_2OH at 1:1 ratio for 15 minutes. After anodization, the structures that formed at low current density (J = 5 mA/cm^2) was compared with structures that formed at high current density (J = 30 mA/cm^2). Both structures and electrical properties were investigated.

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Light Emission From Travelling Space Charge Domains, M. Hostut, N. Balkan Jan 1999

Light Emission From Travelling Space Charge Domains, M. Hostut, N. Balkan

Turkish Journal of Physics

We report light emission from n-doped GaAs epilayers associated with impact ionization when the device is biased in the negative difference resistance (NDR) regime (F > 3.5 kV cm^{-1}). Spectral distribution of the emitted light (electroluminescence) has been measured to identify the energy distribution of the recombining electron-hole pairs. Electron temperatures, calculated from the high energy tail of the electroluminescence spectra, show that the light emission is due to the recombination of the impact ionized holes with the background, channel, and the travelling space charge electrons. The range of the electron temperatures obtained indicate that the contribution to the light emission …

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Electronic Energy Spectrum In A Dqws Within A Tilted Magnetic Field, S. Elagöz, H. Sari, Y. Ergün, P. Karasu, İ. Sökmen Jan 1999

Electronic Energy Spectrum In A Dqws Within A Tilted Magnetic Field, S. Elagöz, H. Sari, Y. Ergün, P. Karasu, İ. Sökmen

Turkish Journal of Physics

The analytical solution of the Schrödinger equation for a DQWS subjected to an externally applied tilted magnetic field are obtained and the results are discussed. The dependency of energy spectrum of the system on the applied magnetic field direction is also given.

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The Orbit Center Dependence Of The Energy Levels In A Multiple Quantum Wells Under External Tilted Magnetic And Electric Fields, R. Amca, Y. Ergün, H. Sari, S. Elagöz, İ. Sökmen Jan 1999

The Orbit Center Dependence Of The Energy Levels In A Multiple Quantum Wells Under External Tilted Magnetic And Electric Fields, R. Amca, Y. Ergün, H. Sari, S. Elagöz, İ. Sökmen

Turkish Journal of Physics

An analytical solution to the Schrödinger equation for a multiple quantum well system subjected to an externally applied electric field the growth direction and an externally applied tilted magnetic field are obtained and the results are discussed. The energy dependence energy spectrum of the system as a function of the external electric field and the orbit center is also discussed.

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Carrier Transport And Band Offsets In Two Dimensional Heterostructures, Hi̇lmi̇ Ünlü Jan 1999

Carrier Transport And Band Offsets In Two Dimensional Heterostructures, Hi̇lmi̇ Ünlü

Turkish Journal of Physics

Advances in the low dimensional heterojunction device technology cannot be complete without adequate and reliable analytic model for determining interface properties such as band offsets needed to study the carrier transport and to evaluate the device performance at high temperatures and pressures. In this article, using the extended universal tight binding model of semiconductors, a new way of determining the band offsets in heterostructures is presented. In this model the band offsets are first determined by aligning the vacuum level, defined relative to valence band maximum which is screened by optical dielectric constant of semiconductors, at the interface at absolute …

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Interference Of Charged Particles In A Vector Potential With Vanishing Magnetic Field, İsmai̇l Hakki Duru Jan 1999

Interference Of Charged Particles In A Vector Potential With Vanishing Magnetic Field, İsmai̇l Hakki Duru

Turkish Journal of Physics

An interference experiment in a magnetic field free region with non vanishing vector potential created by two perpendicularly intersecting planes carrying uniform currents is discussed. The relation of this configuration to the Aharonov-Bohm potential is examined. An experimental set up which is finite in the direction of electronic motion is studied.

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Multitime Generalization Of Maxwell Electrodynamics And Gravity, Vladilen Barashenkov Jan 1999

Multitime Generalization Of Maxwell Electrodynamics And Gravity, Vladilen Barashenkov

Turkish Journal of Physics

System of equations of motion for interacting electromagnetic field and charged bodies is derived by means of an action principle in six-dimensional space with a three-dimensional time vector. The influence of the additional (hidden) components of time on the body motion is considered. Macroscopic experiments and astrophysical observations which can reveal the time multi-dimensionality are discussed. At present there are no facts which would be in contradiction with the hypothesis of the multi-dimensionality of time.

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The Concept Of Free Electromagnetic Field In Quantum Domain, Alexander Shumovsky, Özgür Müstecaplioğlu Jan 1999

The Concept Of Free Electromagnetic Field In Quantum Domain, Alexander Shumovsky, Özgür Müstecaplioğlu

Turkish Journal of Physics

By virtue of the consideration of polarization and phase properties of dipole radiation in the quantum domain, it is shown that the concept of free electromagnetic field should be considered as a quite risky approximation in the description of quantum fluctuations of some physical observables.

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Quantum Mechanics Of The Electric Charge, Andrzej Staruszkiewicz Jan 1999

Quantum Mechanics Of The Electric Charge, Andrzej Staruszkiewicz

Turkish Journal of Physics

The Author summarizes the evidence that his quantum theory of the electric charge depends in a nontrivial way on the numerical value of the fine structure constant.

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Elementary Charges In Classical Electrodynamics, Edward Kapuscik, Maciej Widomski Jan 1999

Elementary Charges In Classical Electrodynamics, Edward Kapuscik, Maciej Widomski

Turkish Journal of Physics

In the framework of classical electrodynamics elementary particles are treated as capacitors. The electrostatic potentials satisfy equations of the Schrödinger type. An interesting "quantization condition" for elementary charges is derived.

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Two-Level Atom In A Squeezed Vacuum, Ryszard Tanas Jan 1999

Two-Level Atom In A Squeezed Vacuum, Ryszard Tanas

Turkish Journal of Physics

The master equation for a two-level atom interacting with a strong coherent field and damped into a reservoir formed by a finite bandwidth squeezed vacuum is derived. The master equation extends the Yeoman and Barnett approach to a non-zero detuning of the driving field from the atomic resonance and allows to discuss the role of squeezing bandwidth and the detuning in the level shifts, widths and intensities of spectral lines. The approach is valid for arbitrary values of the Rabi frequency and detuning but for the squeezing bandwidths larger than the natural linewidth in order to satisfy the Markov approximation.

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Medium-Dependent Metric In Electrostatics, Bernard Jancewicz Jan 1999

Medium-Dependent Metric In Electrostatics, Bernard Jancewicz

Turkish Journal of Physics

The use of differential forms allows the formulation of the principal equations of electrodynamics in a metric-independent way. The metric is needed only for finding the solutions. Various metrics can be introduced, depending on the medium. A special metric, connected with the electric permittivity tensor, allows us to reduce all electrostatic problems in anisotropic media to those in in isotropic one.

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Bands Of Localized Electromagnetic Waves In Random Collections Of Dielectric Particles, Marian Rusek, Arkadiusz Orlowski Jan 1999

Bands Of Localized Electromagnetic Waves In Random Collections Of Dielectric Particles, Marian Rusek, Arkadiusz Orlowski

Turkish Journal of Physics

Anderson localization of electromagnetic waves in random arrays of dielectric cylinders is studied. An effective theoretical approach based on the finite size scaling analysis of transmission is developed. The disordered dielectric medium is modeled by a system of randomly distributed 2D electric dipoles. The appearance of the band of localized waves emerging in the limit of an infinite medium is discovered. It suggests deeper insight into existing experimental and theoretical results.

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