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ABSTRACT: This paper presents the image retrieval technique and the analysis of different runs of ImageCLEF 2007 submitted by the CINDI
group. An interactive fusion-based search technique is investigated in both context and content-based feature spaces. For
a context-based image search, keywords from associated annotation files are extracted and indexed based on the vector space
model of information retrieval. For a content-based image search, various global and region-specific local image features
are extracted to represent images at different levels of abstraction. Based on a user’s relevance feedback information, multiple
textual and visual query refinements are performed and weights are adjusted dynamically in a similarity fusion scheme. Finally,
top ranked images are obtained by performing both sequential and simultaneous search processes in the multi-modal (context
and content) feature space.
09/2008: pages 657-664;
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ABSTRACT: The high-Tc ferromagnetic property in Co-doped ZnO (ZCO), mediated by donor impurity band was tested
by controlled introduction of shallow donors (Al) in the Zn0.9−xCo0.1O : Alx (x = 0.005 and 0.01) thin
films. The saturation magnetization for the 10% Co-doped ZnO (4 emu/cc) at 300 K reduces (�0.8 emu/cc)
due to Al doping. The resistivity drops abruptly, from�103 -cm for the ZCO film to 0.033 and 0.02cm
for the 0.5% and 1.0% Al doped ZCO samples, respectively. The XPS measurements did not show any
signature of metallic Co clusters formation in these samples.
Solid State Communications 06/2008; 147:305. · 1.65 Impact Factor
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ABSTRACT: The spin dynamics of dilute paramagnetic impurities embedded in a semiconductor GaAs channel of a conventional lateral spin valve has been investigated. It is observed that the electron spin of paramagnetic Mn atoms can be polarized electrically when driven by a spin valve in the antiparallel configuration. The transient current through the MnAs/GaAs/MnAs spin valve bears the signature of the underlying spin dynamics driven by the exchange interaction between the conduction band electrons in GaAs and the localized Mn electron spins. The time constant for this interaction is observed to be dependent on temperature and is estimated to be 80 ns at 15 K.
Physical Review Letters 05/2008; 100(19):196603. · 7.37 Impact Factor
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ABSTRACT: A tricolor infrared detector with bias-selectable peaks based on tunneling quantum dot infrared photodetector (T-QDIP) architecture is demonstrated. Photoabsorption takes place in In0.4Ga0.6As quantum dots (QDs) and the excited electrons are collected by resonant tunneling across an Al0.2Ga0.8As/In0.1Ga0.9As/Al0.2Ga0.8As double barrier coupled to the QDs. The field dependent tunneling for excited carriers in T-QDIP is used to select the operating wavelength. This T-QDIP detector exhibits three distinct response peaks at 4.5/4.9±0.05, 9.5±0.05, and 16.9±0.1 μm up to 80 K. The peak detectivity is in the range of (1.0–6.0)×1012 Jones at 50 K. Bias polarity allows the selection of either the 9.5 μm or the 16.9 μm peak.
Applied Physics Letters 03/2008; 92(11):111104-111104-3. · 3.84 Impact Factor
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ABSTRACT: A spin-polarized vertical cavity surface emitting laser, with InAs/GaAs self-organized quantum dots as the active gain media, has been fabricated and characterized. Electron spin injection is achieved via a MnAs/GaAs Schottky tunnel contact. The laser is operated at 200 K and, at this temperature, the degree of circular polarization in the output is 8% and the maximum threshold current reduction is 14%. These effects are not observed in identical control devices with nonmagnetic contacts.
Applied Physics Letters 03/2008; 92(9):091119-091119-3. · 3.84 Impact Factor
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ABSTRACT: The effects of two-dimensional spin diffusion on spin extraction in lateral semiconductor spin valves have been investigated experimentally and theoretically. A ferromagnetic collector terminal of variable size is placed between the ferromagnetic electron spin injector and detector of a conventional lateral spin valve for spin extraction. It is observed that transverse spin diffusion beneath the collector terminal plays an important role along with the conventional longitudinal spin diffusion in describing the overall transport of spin carriers. Two-dimensional spin diffusion reduces the perturbation of the channel electrochemical potentials and improves spin extraction.
Applied Physics Letters 01/2008; 92(2):022507-022507-3. · 3.84 Impact Factor
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ABSTRACT: The reduction of the dark current without reducing the photocurrent is a considerable challenge in developing far-infrared
(FIR)/terahertz detectors. Since quantum dot (QD) based detectors inherently show low dark current, a QD-based structure is
an appropriate choice for terahertz detectors. The work reported here discusses multi-band tunnelling quantum dot infrared
photo detector (T-QDIP) structures designed for high temperature operation covering the range from mid-to far-infrared. These
structures grown by molecular beam epitaxy consist of a QD (InGaAs or InAlAs) placed in a well (GaAs/AlGaAs) with a double-barrier
system (AlGaAs/InGaAs/AlGaAs) adjacent to it. The photocurrent, which can be selectively collected by resonant tunnelling,
is generated by a transition of carriers from the ground state in the QD to a state in the well coupled with a state in the
double-barrier system. The double-barrier system blocks the majority of carriers contributing to the dark current. Several
important properties of T-QDIP detectors such as the multi-colour (multi-band) nature of the photoresponse, the selectivity
of the operating wavelength by the applied bias, and the polarization sensitivity of the response peaks, are also discussed.
Opto-Electronics Review 11/2007; 15(4):223-228. · 0.97 Impact Factor
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ABSTRACT: Tunneling quantum dot infrared photodetector (T-QDIP) structures designed for multi-band infrared and terahertz radiation detection are demonstrated. In T-QDIP structures, photoabsorption takes place in InGaAs QDs (due to transition of carriers from the QD ground-state to a QD excited-state) and photoexcited carriers are selectively collected by resonant tunneling, while the dark current is blocked by AlGaAs/InGaAs tunneling barriers. This approach was effectively used to develop terahertz sensors. Characteristics of a room temperature T-QDIP showing two color responses at wavelengths of 6 and 17 mum and a terahertz T-QDIP responding at 6 THz are presented.
Sensors, 2007 IEEE; 11/2007
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ABSTRACT: This paper describes a fully automated method of classifying facial expressions using support vector machines (SVM). Facial expressions are communicated by subtle changes in one or more discrete features such as tightening the lips, raising the eyebrows, opening and closing of the eyes or certain combination of them, which can be identified through monitoring the changes in muscles movement located near about the regions of mouth, eyes and eyebrows. In this work, we have applied an analytic face model using eleven feature points that represent and identify the principle muscle actions as well as provide measurements of the discrete features responsible for each of the six basic human emotions. A multi-detector approach of facial feature point localization has been utilized for identifying these points of interest from the contours of facial components such as eyes, eyebrows and mouth. Feature vectors composed of eleven features are then obtained by calculating the degree of displacement of these eleven feature points from a non-changeable rigid point. Finally, the obtained feature sets are used to train a SVM classifier so that it can classify facial expressions when given to it in the form of a feature set. The method has been tested on two different publicly available facial expression databases and on average, 89.44% and 84.86% of successful recognition rates have been achieved.
Systems, Man and Cybernetics, 2007. ISIC. IEEE International Conference on; 11/2007
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ABSTRACT: Quantum-dot infrared photodetectors have emerged as attractive devices for sensing long wavelength radiation. Their principle of operation is based on absorption of radiation via intersublevel transitions in quantum dots. Multiple layers of self-organized ln(Ga)As/Ga(Al)As quantum dots are generally incorporated in the active region of these devices. Three-dimensional quantum confinement allows normal incidence operation. This paper describes a novel variation in the design of these devices which allows a significant reduction of the dark current, high temperature operation and extension of operation to terahertz frequencies. The principle of operation and operating characteristics of this device - the tunnel quantum-dot intersublevel detector - are described. Operation is demonstrated from 6-80 mum at temperatures up to 300 K with acceptable values of peak responsivity (0.1-0.75 A/W) and specific detectivity (10<sup>7</sup>-10<sup>11</sup>cm ldr Hz<sup>1/2</sup>/W<sup>-1</sup> , depending on temperature and wavelength).
Proceedings of the IEEE 10/2007; · 6.81 Impact Factor
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ABSTRACT: Self-organized In(Ga)As/Ga(Al)As quantum dots have emerged as useful nanostructures that can be epitaxially grown and incorporated in the active region of devices. The near pyramidal dots exhibit properties arising from the three-dimensional quantum confinement and from the coherent built-in strain. The properties and current state-of-the-art characteristics of quantum-dot junction lasers, intersublevel infrared detectors, optical amplifiers, and microcavity devices are briefly reviewed. It is evident that self-organized quantum-dot optoelectronic devices demonstrate properties that are sometimes unique and often surpass the characteristics of existing devices.
Proceedings of the IEEE 10/2007; · 6.81 Impact Factor
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ABSTRACT: This paper presents the techniques and the analysis of different runs submitted by the CINDI group in ImageCLEF 2006. For
the ad-hoc image retrieval from both the photographic and medical image collections, we experimented with cross-modal (image
and text) interaction and integration approaches based on the relevance feedback in the form of textual query expansion and
visual query point movement with adaptive similarity matching functions. For the automatic annotation tasks for both the medical
and object collections, we experimented with a classifier combination approach, where several probabilistic multi-class support
vector machine classifiers with features at different levels as inputs are combined to predict the final probability scores
of each category as image annotation. Analysis of the results of the different runs we submitted for both the image retrieval
and annotation tasks are reported in this paper.
09/2007: pages 715-724;
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ABSTRACT: A ferromagnet/semiconductor based electrically controlled spin-current amplifier using a dual-drain nonlocal lateral spin valve is demonstrated. The spin polarization injected by the source into the channel is amplified at the second drain contact. An amplified current spin polarization of 100% is measured. The controlled variation of amplifier gain with bias is also demonstrated. The observations are explained in the framework of the spin drift-diffusion model.
Applied Physics Letters 08/2007; 91(7):072513-072513-3. · 3.84 Impact Factor
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ABSTRACT: Production of ultra low sulfur diesel through biodesulfurization process has been studied in a trickle bed reactor having a diameter of 0.066 m and a height of 0.6 m. Rhodococcus sp.(no. 2891 NCIM, Pune) in immobilized form has been used to desulfurize hydrotreated diesel having sulfur concentration in the range of 200–540 ppm. The initial substrate concentration, recycle ratio and volumetric flow rate have been chosen as process parameters. Excess biomass accumulation, which is reflected by the increment of pressure drop within the reactor, has been avoided by backwashing technique. Backwashing time has been correlated to volumetric flow rate. A deterministic mathematical model based on the growth kinetic parameters, namely, maximum specific growth rate μmax, saturation constant Ks and yield coefficient YA/B, determined using systematic batch studies has been developed. Simulated data have been compared with the experimental results, which signify that the model predictions can explain the reality satisfactorily. © 2007 American Institute of Chemical Engineers AIChE J, 2007
AIChE Journal 07/2007; 53(8):2188 - 2197. · 2.26 Impact Factor
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ABSTRACT: The dynamics of electron capture and relaxation in an n-doped quantum-dot (QD) infrared detector structure are studied directly in the time domain using ultrafast intraband-pump-interband-probe differential transmission spectroscopy. Femtosecond midinfrared pulses are used to excite electrons from the doped QDs into the conduction band continuum, and the complete electron distribution functions are monitored as a function of time using an interband probe. Because only electrons are excited and no holes are present, the electron-hole scattering which dominates the relaxation in bipolar systems is not present, and the measurement yields the electron dynamics exclusively. Excitation-dependent electron capture times were measured from 40 to <10 ps with increasing pump intensity. Intradot inter-level relaxation times were observed to be ~100 ps, driven by Auger-type electron-electron scattering. Nanosecond-scale dynamics in the n=1 state were also observed and attributed to transport effects. Our results indicate that the phonon bottleneck in the QDs is circumvented by Auger scattering; nevertheless, the electron dynamics in the unipolar device are found to be slower than those observed in bipolar systems, which confirms the significance of the holes in the carrier relaxation in bipolar devices. The results also support the improved operation of QD infrared photodetectors relative to quantum-well-based devices
IEEE Journal of Quantum Electronics 07/2007; · 1.88 Impact Factor
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ABSTRACT: The multi phonon Raman scattering in Mn doped �1%–10%� ZnO was observed at room
temperature using 514.5 nm Ar+ laser. The additional optical modes at 327, 332, 482, 532, and
680 cm−1 in Zn1−xMnxO targets were identified as the second order Raman modes in the disordered
lattice and the precipitation of the secondary phase ZnMn2O4. The crystalline grain sizes of 1%, 3%,
5%, and 10% Mn doped ZnO samples were calculated by phonon confinement model as 31.8, 18.3,
15.9, and 14.1 nm, respectively. The optical band gap was found to be increased �3.27–3.41 eV�
due to the Mn doping.
Applied Physics Letters 06/2007; 90:261903. · 3.84 Impact Factor
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ABSTRACT: The multi phonon Raman scattering in Mn doped (1%–10%) ZnO was observed at room temperature using 514.5 nm Ar+ laser. The additional optical modes at 327, 332, 482, 532, and 680 cm−1 in Zn1−xMnxO targets were identified as the second order Raman modes in the disordered lattice and the precipitation of the secondary phase ZnMn2O4. The crystalline grain sizes of 1%, 3%, 5%, and 10% Mn doped ZnO samples were calculated by phonon confinement model as 31.8, 18.3, 15.9, and 14.1 nm, respectively. The optical band gap was found to be increased (3.27–3.41 eV) due to the Mn doping.
Applied Physics Letters 06/2007; 90(26):261903-261903-3. · 3.84 Impact Factor
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ABSTRACT: A nanosecond-scale recovery component is observed in time-resolved differential transmission spectroscopy experiments on the electron relaxation in n-doped quantum dots. Polarization-dependent measurements show the recovery is not due to Pauli blocking driven by spin relaxation.
Quantum Electronics and Laser Science Conference, 2007. QELS '07; 06/2007
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ABSTRACT: We have studied the linewidth-enhancement factor of 1.3-mum tunnel-injection quantum-dot (QD) lasers utilizing a rate-equation model that takes into account the injection of electrons directly into the QDs from a coupled quantum well, the presence of wetting layer states, and nonequilibrium carrier relaxation in the QDs. In a conventional separate confinement heterostructure QD laser, plasma effects, which result from a large portion of the injected carriers preferably occupying the barrier and wetting layer states, largely determine the values of the linewidth-enhancement factor and lead to a strong dependence of the linewidth-enhancement factor on injection current. In a tunnel-injection QD laser, however, due to the injection of "cold" electrons directly into the lasing states of the QDs, both the values of linewidth-enhancement factor and the dependence on injection current are substantially reduced. The calculated linewidth-enhancement factors of conventional separate confinement heterostructure and tunnel-injection QD lasers are in excellent agreement with reported experimental values. Our analysis elucidates the role of tunnel injection in achieving near-zero alpha-parameter, which would be important in the design of chirp-free high-speed QD lasers
IEEE Journal of Quantum Electronics 06/2007; · 1.88 Impact Factor
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ABSTRACT: We demonstrate multiwavelength lasing of resonant modes in linear (L3) microcavities in a triangular-lattice 2D photonic crystal (PC) slab. The broad spontaneous emission spectrum from coupled quantum dots, modified by the PC microcavity, is studied as a function of the intensity of incident optical excitation. We observe lasing with an ultralow-threshold power of approximately 600 nW and an output efficiency of approximately 3% at threshold. Two other resonant modes exhibit weaker turnon characteristics and thresholds of approximately 2.5 and 200 microW, respectively.
Optics Letters 06/2007; 32(10):1296-8. · 3.40 Impact Factor
