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Showing papers by "University of Electro-Communications published in 2009"


Journal ArticleDOI
TL;DR: The strategies for depositing CdSe quantum dots on nanostructured mesoporous TiO(2) electrodes are summarized and the methods that facilitate improvement in the performance and stability of QDSCs are discussed.
Abstract: Quantum dot sensitized solar cells (QDSCs) have attracted significant attention as promising third-generation photovoltaic devices. In the form of quantum dots (QDs), the semiconductor sensitizers have very useful and often tunable properties; moreover, their theoretical thermodynamic efficiency might be as high as 44%, better than the original 31% calculated ceiling. Unfortunately, the practical performance of these devices still lags behind that of dye-sensitized solar cells. In this Account, we summarize the strategies for depositing CdSe quantum dots on nanostructured mesoporous TiO2 electrodes and discuss the methods that facilitate improvement in the performance and stability of QDSCs. One particularly significant factor for solar cells that use polysulfide electrolyte as the redox couple, which provides the best performance among QDSCs, is the passivation of the photoanode surface with a ZnS coating, which leads to a dramatic increase of photocurrents and efficiencies. However, these solar cells us...

739 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of the lattice structure on spin-fluctuation-mediated superconductivity in the iron pnictides was studied and a random phase approximation was applied to the models to solve the Eliashberg equation.
Abstract: We study the effect of the lattice structure on the spin-fluctuation-mediated superconductivity in the iron pnictides adopting the five-band models of several virtual lattice structures of LaFeAsO, as well as actual materials such as NdFeAsO and LaFePO obtained from the maximally localized Wannier orbitals. Random phase approximation is applied to the models to solve the Eliashberg equation. This reveals that the gap function and the strength of the superconducting instability are determined by the cooperation or competition among multiple spin-fluctuation modes arising from several nestings among disconnected pieces of the Fermi surface, which is affected by the lattice structure. Specifically, the appearance of the Fermi surface $\ensuremath{\gamma}$ around $(\ensuremath{\pi},\ensuremath{\pi})$ in the unfolded Brillouin zone is sensitive to the pnictogen height ${h}_{\text{Pn}}$ measured from the Fe plane, where ${h}_{\text{Pn}}$ is shown to act as a switch between high-${T}_{c}$ nodeless and low-${T}_{c}$ nodal pairings. We also find that reduction in the lattice constants generally suppresses superconductivity. We can then combine these to obtain a generic superconducting phase diagram against the pnictogen height and lattice constant. This suggests that NdFeAsO is expected to exhibit a fully gapped, sign-reversing $s$-wave superconductivity with a higher ${T}_{c}$ than in LaFeAsO, while a nodal pairing with a low ${T}_{c}$ is expected for LaFePO, which is consistent with experiments.

539 citations


Journal ArticleDOI
TL;DR: The proposed sum of squares (SOS) approach for modeling and control of nonlinear dynamical systems using polynomial fuzzy systems is presented, and the derived stability and stabilizability conditions are represented in terms of SOS and can be numerically solved via the recently developed SOSTOOLS.
Abstract: This paper presents a sum of squares (SOS) approach for modeling and control of nonlinear dynamical systems using polynomial fuzzy systems. The proposed SOS-based framework provides a number of innovations and improvements over the existing linear matrix inequality (LMI)-based approaches to Takagi-Sugeno (T-S) fuzzy modeling and control. First, we propose a polynomial fuzzy modeling and control framework that is more general and effective than the well-known T--S fuzzy modeling and control. Secondly, we obtain stability and stabilizability conditions of the polynomial fuzzy systems based on polynomial Lyapunov functions that contain quadratic Lyapunov functions as a special case. Hence, the stability and stabilizability conditions presented in this paper are more general and relaxed than those of the existing LMI-based approaches to T-S fuzzy modeling and control. Moreover, the derived stability and stabilizability conditions are represented in terms of SOS and can be numerically (partially symbolically) solved via the recently developed SOSTOOLS. To illustrate the validity and applicability of the proposed approach, a number of analysis and design examples are provided. The first example shows that the SOS approach renders more relaxed stability results than those of both the LMI-based approaches and a polynomial system approach. The second example presents an extensive application of the SOS approach in comparison with a piecewise Lyapunov function approach. The last example is a design exercise that demonstrates the viability of the SOS-based approach to synthesizing a stabilizing controller.

420 citations


Journal ArticleDOI
TL;DR: Several factors cooperate to improve the performance of quantum-dot-sensitized solar cells: an open structure of the wide bandgap electron collector, which facilitates a higher covering of the internal surface with the sensitizer, a surface passivation of TiO2 to reduce recombination and improved counter electrode materials.
Abstract: Solar cells based on a mesoporous structure of TiO2 and the polysulfide redox electrolyte were prepared by direct adsorption of colloidal CdSe quantum dot light absorbers onto the oxide without any particular linker. Several factors cooperate to improve the performance of quantum-dot-sensitized solar cells: an open structure of the wide bandgap electron collector, which facilitates a higher covering of the internal surface with the sensitizer, a surface passivation of TiO2 to reduce recombination and improved counter electrode materials. As a result, solar cells of 1.83% efficiency under full 1 sun illumination intensity have been obtained. Despite a relatively large short circuit current (J(sc) = 7.13 mA cm(-2)) and open circuit voltage (V(oc) = 0.53 V), the colloidal quantum dot solar cell performance is still limited by a low fill factor of 0.50, which is believed to arise from charge transfer of photogenerated electrons to the aqueous electrolyte.

387 citations


Journal ArticleDOI
TL;DR: In this paper, a quantitative rescattering theory for high-order harmonic generation (HHG) by intense laser pulses is presented, which can be expressed as a product of a returning electron wave packet and the photorecombination differential cross section of the laser free continuum electron back to the initial bound state.
Abstract: The quantitative rescattering theory (QRS) for high-order harmonic generation (HHG) by intense laser pulses is presented. According to the QRS, HHG spectra can be expressed as a product of a returning electron wave packet and the photorecombination differential cross section of the laser-free continuum electron back to the initial bound state. We show that the shape of the returning electron wave packet is determined mostly by the laser. The returning electron wave packets can be obtained from the strong-field approximation or from the solution of the time-dependent Schr\"odinger equation (TDSE) for a reference atom. The validity of the QRS is carefully examined by checking against accurate results for both harmonic magnitude and phase from the solution of the TDSE for atomic targets within the single active electron approximation. Combining with accurate transition dipoles obtained from state-of-the-art molecular photoionization calculations, we further show that available experimental measurements for HHG from partially aligned molecules can be explained by the QRS. Our results show that quantitative description of the HHG from aligned molecules has become possible. Since infrared lasers of pulse durations of a few femtoseconds are easily available in the laboratory, they may be used for dynamic imaging of a transient molecule with femtosecond temporal resolutions.

274 citations


Proceedings ArticleDOI
11 Mar 2009
TL;DR: A hypervisor architecture, called parapass-through, designed to minimize the code size of hypervisors by allowing most of the I/O access from the guest operating system (OS) to pass-through the hypervisor, while the minimum access necessary to implement security functionalities is completely mediated by thehypervisor.
Abstract: Virtual machine monitors (VMMs), including hypervisors, are a popular platform for implementing various security functionalities. However, traditional VMMs require numerous components for providing virtual hardware devices and for sharing and protecting system resources among virtual machines (VMs), enlarging the code size of and reducing the reliability of the VMMs.This paper introduces a hypervisor architecture, called parapass-through, designed to minimize the code size of hypervisors by allowing most of the I/O access from the guest operating system (OS) to pass-through the hypervisor, while the minimum access necessary to implement security functionalities is completely mediated by the hypervisor. This architecture uses device drivers of the guest OS to handle devices, thereby reducing the size of components in the hypervisor to provide virtual devices. This architecture also allows to run only single VM on it, eliminating the components for sharing and protecting system resources among VMs.We implemented a hypervisor called BitVisor and a parapass-through driver for enforcing storage encryption of ATA devices based on the parapass-through architecture. The experimental result reveals that the hypervisor and ATA driver require approximately 20 kilo lines of code (KLOC) and 1.4 KLOC respectively.

204 citations


Proceedings ArticleDOI
07 Nov 2009
TL;DR: This paper proposes an automatic food image recognition system for recording people's eating habits and uses the Multiple Kernel Learning (MKL) method to integrate several kinds of image features such as color, texture and SIFT adaptively.
Abstract: Since health care on foods is drawing people's attention recently, a system that can record everyday meals easily is being awaited. In this paper, we propose an automatic food image recognition system for recording people's eating habits. In the proposed system, we use the Multiple Kernel Learning (MKL) method to integrate several kinds of image features such as color, texture and SIFT adaptively. MKL enables to estimate optimal weights to combine image features for each category. In addition, we implemented a prototype system to recognize food images taken by cellular-phone cameras. In the experiment, we have achieved the 61.34% classification rate for 50 kinds of foods. To the best of our knowledge, this is the first report of a food image classification system which can be applied for practical use.

195 citations


Journal ArticleDOI
TL;DR: In this article, the effect of strain rate and its discontinuous changes on the deformation and microstructural behavior of a coarse-grained 7475 Al alloy were studied in multidirectional forging at 763 K.

186 citations


Journal ArticleDOI
01 Apr 2009
TL;DR: The design approach discussed in this paper is more general than that based on the existing LMI approaches to T-S fuzzy control system designs and provides more relaxed design results than theexisting LMI approach.
Abstract: This paper presents the guaranteed cost control of polynomial fuzzy systems via a sum of squares (SOS) approach. First, we present a polynomial fuzzy model and controller that are more general representations of the well-known Takagi-Sugeno (T-S) fuzzy model and controller, respectively. Second, we derive a guaranteed cost control design condition based on polynomial Lyapunov functions. Hence, the design approach discussed in this paper is more general than the existing LMI approaches (to T-S fuzzy control system designs) based on quadratic Lyapunov functions. The design condition realizes a guaranteed cost control by minimizing the upper bound of a given performance function. In addition, the design condition in the proposed approach can be represented in terms of SOS and is numerically (partially symbolically) solved via the recent developed SOSTOOLS. To illustrate the validity of the design approach, two design examples are provided. The first example deals with a complicated nonlinear system. The second example presents micro helicopter control. Both the examples show that our approach provides more extensive design results for the existing LMI approach.

165 citations


Proceedings ArticleDOI
14 Nov 2009
TL;DR: The present method calculates the O(N log N) treecode and O (N) fast multipole method (FMM) on the GPUs with unprecedented efficiency and demonstrates the performance of the method by choosing one standard application -a gravitational N-body simulation- and one non-standard application -simulation of turbulence using vortex particles.
Abstract: As an entry for the 2009 Gordon Bell price/performance prize, we present the results of two different hierarchical N-body simulations on a cluster of 256 graphics processing units (GPUs). Unlike many previous N-body simulations on GPUs that scale as O(N2), the present method calculates the O(N log N) treecode and O(N) fast multipole method (FMM) on the GPUs with unprecedented efficiency. We demonstrate the performance of our method by choosing one standard application --a gravitational N-body simulation-- and one non-standard application --simulation of turbulence using vortex particles. The gravitational simulation using the treecode with 1,608,044,129 particles showed a sustained performance of 42.15 TFlops. The vortex particle simulation of homogeneous isotropic turbulence using the periodic FMM with 16,777,216 particles showed a sustained performance of 20.2 TFlops. The overall cost of the hardware was 228,912 dollars. The maximum corrected performance is 28.1TFlops for the gravitational simulation, which results in a cost performance of 124 MFlops/$. This correction is performed by counting the Flops based on the most efficient CPU algorithm. Any extra Flops that arise from the GPU implementation and parameter differences are not included in the 124 MFlops/$.

138 citations


Journal ArticleDOI
TL;DR: The proposed algorithm for active noise control of impulsive noise modeled using non-Gaussian stable processes achieves the best performance among the existing algorithms, and at the same computational complexity as that of FxLMS algorithm.

Journal ArticleDOI
TL;DR: The results demonstrate the excellent functions of the intercity optical fiber link and the great potential of optical lattice clocks for use in the redefinition of the second.
Abstract: We demonstrate a precision frequency measurement using a phase-stabilized 120 km optical fiber link over a physical distance of 50 km. The transition frequency of the 87Sr optical lattice clock at the University of Tokyo is measured to be 429228004229874.1(2.4) Hz referenced to international atomic time. The results demonstrate the excellent functions of the intercity optical fiber link and the great potential of optical lattice clocks for use in the redefinition of the second.

Journal ArticleDOI
TL;DR: A comprehensive quantitative rescattering (QRS) theory for describing the production of high-energy photoelectrons generated by intense laser pulses is presented in this article, where the momentum distributions of these electrons can be expressed as the product of a returning electron wave packet with the elastic differential cross sections (DCS) between free electrons with the target ion.
Abstract: A comprehensive quantitative rescattering (QRS) theory for describing the production of high-energy photoelectrons generated by intense laser pulses is presented. According to the QRS, the momentum distributions of these electrons can be expressed as the product of a returning electron wave packet with the elastic differential cross sections (DCS) between free electrons with the target ion. We show that the returning electron wave packets are determined mostly by the lasers only and can be obtained from the strong field approximation. The validity of the QRS model is carefully examined by checking against accurate results from the solution of the time-dependent Schr\"odinger equation for atomic targets within the single active electron approximation. We further show that experimental photoelectron spectra for a wide range of laser intensity and wavelength can be explained by the QRS theory, and that the DCS between electrons and target ions can be extracted from experimental photoelectron spectra. By generalizing the QRS theory to molecular targets, we discuss how few-cycle infrared lasers offer a promising tool for dynamic chemical imaging with temporal resolution of a few femtoseconds.

Journal ArticleDOI
TL;DR: The light-color modulation mechanism of firefly (beetle) bioluminescence is proposed, where the light emitter is the excited singlet state of OL(-) [(1)(OL(-))*], and light emission is modulated by the polarity of the active-site environment of a luciferase and the degree of covalent character of the O8'...H bond between 1-O(-) and its ion-pair models.
Abstract: To reveal the light-color modulation mechanism of firefly (beetle) bioluminescence, we investigated the spectroscopic properties of the phenolate anion 1-O(-) generated from 5,5-dimethyloxyluciferin (1-OH) using various base/solvent combinations. Phenolate anion 1-O(-) is a model compound for the keto form of wild-type oxyluciferin phenolate anion (OL(-)), which is postulated to be the emitter of the bioluminescence. The fluorescence maxima of 1-O(-) were found to depend on the base/solvent combination used, and they varied in the range 541-640 nm, which covers the almost whole range of the bioluminescence emission maximum. In a polar solvent, where (1)(1-O(-))* and the countercation (the conjugate acid of a base) make a solvent-separated ion pair or a free ion couple, the emission maxima of 1-O(-) were found to be modulated by the solvent polarity. In a less polar solvent, where (1)(1-O(-))* and the countercation are formed as a contact ion pair, the strength of the covalent character of the O8'...H bond between (1)(1-O(-))* and the countercation is operative. The effect of the base/solvent combination on the emission properties of (1)(1-O(-))* was also verified using fluorescence lifetime measurements and density functional theory calculations on 1-O(-) and its ion-pair models. On the basis of these results, we propose the following light-color modulation mechanism: (1) the light emitter is the excited singlet state of OL(-) [(1)(OL(-))*], and (2) light emission from (1)(OL(-))* is modulated by the polarity of the active-site environment of a luciferase and the degree of covalent character of the O8'...H bond between (1)(OL(-))* and a protonated basic moiety in the active site. Mechanisms for variation of the bioluminescence colors and their applications are discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors used massive molecular dynamics simulations of protein-ligand conformations obtained by molecular docking in order to improve the enrichment performance of molecular docking and employed the molecular mechanics/Poisson Boltzmann and surface area method to estimate the binding free energies.
Abstract: Virtual compound screening using molecular docking is widely used in the discovery of new lead compounds for drug design. However, this method is not completely reliable and therefore unsatisfactory. In this study, we used massive molecular dynamics simulations of protein-ligand conformations obtained by molecular docking in order to improve the enrichment performance of molecular docking. Our screening approach employed the molecular mechanics/Poisson-Boltzmann and surface area method to estimate the binding free energies. For the top-ranking 1,000 compounds obtained by docking to a target protein, approximately 6,000 molecular dynamics simulations were performed using multiple docking poses in about a week. As a result, the enrichment performance of the top 100 compounds by our approach was improved by 1.6–4.0 times that of the enrichment performance of molecular dockings. This result indicates that the application of molecular dynamics simulations to virtual screening for lead discovery is both effective and practical. However, further optimization of the computational protocols is required for screening various target proteins.

Journal ArticleDOI
TL;DR: In this paper, a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 49-ps 11mJ Nd:YLF laser, was used to ascertain the true amplified seed energy and the parametric superfluorescence levels.
Abstract: We produce carrier-envelope-phase-stable 15.7-fs (2-cycle) 740-μJ pulses at the 2.1-μm carrier wavelength, from a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 49-ps 11-mJ Nd:YLF laser. A novel seed pulse spectral shaping method is used to ascertain the true amplified seed energy and the parametric superfluorescence levels.

Book ChapterDOI
02 Dec 2009
TL;DR: In this article, a meet-in-the-middle preimage attack was proposed for SHA-256 and SHA-512 compression functions, which uses a range of novel techniques to split the function into two independent parts and then match them in a birthday-style phase.
Abstract: In this paper, we present preimage attacks on up to 43-step SHA-256 (around 67% of the total 64 steps) and 46-step SHA-512 (around 57.5% of the total 80 steps), which significantly increases the number of attacked steps compared to the best previously published preimage attack working for 24 steps. The time complexities are 2251.9, 2509 for finding pseudo-preimages and 2254.9, 2511.5 compression function operations for full preimages. The memory requirements are modest, around 26 words for 43-step SHA-256 and 46-step SHA-512. The pseudo-preimage attack also applies to 43-step SHA-224 and SHA-384. Our attack is a meet-in-the-middle attack that uses a range of novel techniques to split the function into two independent parts that can be computed separately and then matched in a birthday-style phase.

Journal ArticleDOI
TL;DR: To the authors' knowledge, these are the highest output powers generating from active photonic bandgap fibers, as well as from ytterbium-doped fiber lasers at these wavelengths.
Abstract: Ytterbium-doped solid-core photonic bandgap fiber amplifiers operating at the long-wavelength edge of the ytterbium gain band are reported. The low-loss bandgap transmission window is formed in the very low gain region, whilst outside the bandgap, large attenuation inhibits the exponential growth of amplified spontaneous emission in the huge-gain 1030-1100 nm region. Hence parasitic-lasing-free, high-power amplification with a marked efficiency is enabled. A 32 W output at 1156 nm with a 66% slope efficiency and 30 W output at 1178 nm with a 58% slope efficiency were successfully obtained. To our knowledge, these are the highest output powers generating from active photonic bandgap fibers, as well as from ytterbium-doped fiber lasers at these wavelengths.

Journal ArticleDOI
TL;DR: In this article, the anomalous Hall effect was used to detect the domain wall motion induced by electric current in a Co/Ni nano-wire with perpendicular magnetic anisotropy, where the minimum threshold current density of approximately 5×1011 A/m2 was observed for the wire width of 70 nm.
Abstract: The authors show experimental results on domain wall motion induced by electric current in a Co/Ni nano-wire with perpendicular magnetic anisotropy. The motion was detected electrically by using the anomalous Hall effect. Threshold current density for the domain wall motion was found to decrease with decreasing the wire width, where the minimum threshold current density of approximately 5×1011 A/m2 was observed for the wire width of 70 nm.

Journal ArticleDOI
TL;DR: The proposed adaptive fuzzy logic control based on physical properties of wheeled inverted pendulums makes use of a fuzzy logic engine and a systematic online adaptation mechanism to approximate the unknown dynamics.

Proceedings ArticleDOI
06 Mar 2009
TL;DR: This paper proposes a low-latency router architecture that predicts an output channel being used by the next packet transfer and speculatively completes the switch arbitration in the prediction routers, and analyzes the prediction hit rates of six prediction algorithms on meshes, tori, and fat trees.
Abstract: Network-on-Chips (NoCs) are quite latency sensitive, since their communication latency strongly affects the application performance on recent many-core architectures. To reduce the communication latency, we propose a low-latency router architecture that predicts an output channel being used by the next packet transfer and speculatively completes the switch arbitration. In the prediction routers, incoming packets are transferred without waiting the routing computation and switch arbitration if the prediction hits. Thus, the primary concern for reducing the communication latency is the hit rates of prediction algorithms, which vary from the network environments, such as the network topology, routing algorithm, and traffic pattern. Although typical low-latency routers that speculatively skip one or more pipeline stages use a bypass datapath for specific packet transfers (e.g., packets moving on the same dimension), our prediction router predictively forwards packets based on a prediction algorithm selected from several candidates in response to the network environments. In this paper, we analyze the prediction hit rates of six prediction algorithms on meshes, tori, and fat trees. Then we provide three case studies, each of which assumes different many-core architecture. We have implemented a prediction router for each case study by using a 65nm CMOS process, and evaluated them in terms of the prediction hit rate, zero load latency, hardware amount, and energy consumption. The results show that although the area and energy are increased by 6.4–15.9% and 8.0–9.5% respectively, up to 89.8% of the prediction hit rate is achieved in real applications, which provide favorable trade-offs between the modest hardware/energy overheads and the latency saving.

Journal ArticleDOI
TL;DR: Diode-pumped mode-locked laser operation based on Yb(3+):Sc(2)O(3) and Yb-3+:Y( 2)O (3) multi-gain-media oscillator has been demonstrated and the optical-to-optical efficiency was 18.8%.
Abstract: Diode-pumped mode-locked laser operation based on Yb(3+):Sc(2)O(3) and Yb(3+):Y(2)O(3) multi-gain-media oscillator has been demonstrated. 66-fs pulse duration with an average power of 1.5 W and 53-fs pulse duration with an average power of 1 W under 8-W laser diode pumping were achieved. The optical-to-optical efficiency was 18.8%. Additionally, 68-fs pulse duration with an average power of 540 mW from Yb(3+):Y(2)O(3) ceramic was also obtained.

Journal ArticleDOI
TL;DR: It is concluded that a specific form of yoga can generate controlled high-frequency gamma waves, and that applying the same methodology to other meditation recordings might yield an improved understanding of the neurocorrelates of meditation.

Journal ArticleDOI
TL;DR: In this paper, the authors present midlatitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with a Super Dual Auroral Radar Network (SuperDARN) HF radar at around 10 MHz in Hokkaido, Japan, in combination with a 630-nm all-sky imager and a GPS network (GEONET) that provides total electron content (TEC) data.
Abstract: [1] We present midlatitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with a Super Dual Auroral Radar Network (SuperDARN) HF radar at around 10 MHz in Hokkaido, Japan, in combination with a 630-nm all-sky imager and a GPS network (GEONET) that provides total electron content (TEC) data. MSTIDs propagating southward from high latitudes are detected at first with the HF radar and then with the imager and GEONET. We analyze two MSTID events, one in winter (event 1) and the other in summer (event 2), to find that MSTIDs appear simultaneously, at least, at 55°–25°N. It is shown that nighttime MSTIDs propagate toward the southwest over a horizontal distance of about 4000 km, and daytime MSTIDs do so toward the southeast. Daytime radar echoes are due to ground/sea surface (GS) scatter, while nighttime echoes in event 1 return from 15-m-scale F region field-aligned irregularities (FAIs) and those in event 2 are due to GS scatter. Doppler velocities of the nighttime F region FAI echoes in event 1 are negative (motion away from the radar) within strong echo regions and are positive (motion toward the radar) within weak echo regions. This fact suggests that the strong (weak) echoes return from suppressed (enhanced) airglow/TEC areas, in line with previous observations over central Japan. The nighttime MSTIDs in events 1 and 2 are often accompanied by concurrent coherent echoes from FAIs in sporadic E (Es) layers. The Es echo areas in event 2 rather coincide with suppressed airglow/TEC areas in the F region that are connected with the echo areas along the geomagnetic field, indicating the existence of E and F region coupling at night.

Journal ArticleDOI
TL;DR: In this paper, a negative group delay (NGD) circuit was employed to equalize a group delay variation in a broadband ultra wideband (UWB) InGaP/GaAs heterojunction bipolar transistor (HBT) monolithic microwave integrated circuit (MMIC) amplifier.
Abstract: A negative group delay (NGD) circuit has been employed to equalize a group delay variation in a broadband ultra-wideband (UWB) InGaP/GaAs heterojunction bipolar transistor (HBT) monolithic microwave integrated circuit (MMIC) amplifier. Using the NGD circuit, a part of a salient group delay characteristic in the operation band of broadband amplifiers can be suppressed without an increase of the entire group delay. The MMIC amplifier has a steep group delay increase in the lower frequency region of the full-band UWB band (3.1-10.6 GHz) due to the sum of phase variations near the cutoff frequencies of the HBTs. The NGD circuit has been inserted to reduce this increase of the group delay in the UWB band. By adding a three-cell NGD circuit while considering input and output matching at the input side of the MMIC amplifier, the group delay variation is decreased by 78%. However, gain was also decreased by insertion of the multistage NGD circuit. In an attempt to avoid this decrease in gain, a one-cell NGD circuit was inserted into the feedback loop of the MMIC amplifier, and as a result, we were able to decrease the group delay variation by 79%, with minimal gain deterioration.

Journal ArticleDOI
TL;DR: In this article, the collapse dynamics of dipolar Bose-Einstein condensates of chromium atoms in different harmonic trap geometries, from prolate to oblate, were investigated.
Abstract: We experimentally investigate the collapse dynamics of dipolar Bose–Einstein condensates of chromium atoms in different harmonic trap geometries, from prolate to oblate. The evolutions of the condensates in the unstable regime are compared with three-dimensional simulations of the Gross–Pitaevskii equation including three-body losses. In order to probe the phase coherence of collapsed condensates, we induce the collapse in several condensates simultaneously and let them interfere.

Proceedings ArticleDOI
10 Oct 2009
TL;DR: This paper proposes LDA-based framework for multimodal categorization and words grounding for robots and provides a relevance measure that encodes the degree of connection between words and modalities.
Abstract: In this paper we propose LDA-based framework for multimodal categorization and words grounding for robots. The robot uses its physical embodiment to grasp and observe an object from various view points as well as listen to the sound during the observing period. This multimodal information is used for categorizing and forming multimodal concepts. At the same time, the words acquired during the observing period are connected to the related concepts using multimodal LDA. We also provide a relevance measure that encodes the degree of connection between words and modalities. The proposed algorithm is implemented on a robot platform and some experiments are carried out to evaluate the algorithm. We also demonstrate a simple conversation between a user and the robot based on the learned model.

Journal ArticleDOI
TL;DR: In this article, the spontaneous emission of an atom near a nanofiber with two fiber-Bragg-grating (FBG) mirrors was studied and it was shown that up to 94% of spontaneous emission from the atom can be channeled into the guided modes in the overdamped-cavity regime.
Abstract: We study spontaneous emission of an atom near a nanofiber with two fiber-Bragg-grating (FBG) mirrors. We show that the coupling between the atom and the guided modes of the nanofiber can be significantly enhanced by the FBG cavity even when the cavity finesse is moderate. We find that, when the fiber radius is 200 nm and the cavity finesse is about 30, up to 94% of spontaneous emission from the atom can be channeled into the guided modes in the overdamped-cavity regime. We show numerically and analytically that vacuum Rabi oscillations and strong coupling can occur in the FBG cavity even when the cavity finesse is moderate (about 30) and the cavity length is large (on the order of 10 cm to 1 m), unlike the case of planar and curved Fabry-Perot cavities.

Journal ArticleDOI
TL;DR: Degradation modeling of InGaP/GaAs/Ge triple-junction (3J) solar cells subjected to proton irradiation is performed with the use of a one-dimensional optical device simulator, PC1D.

Journal ArticleDOI
TL;DR: In this paper, the VLF/LF radio signals method for studying preseimic activity is applied to the Abruzzo earthquake (M=6.3, 6 April 2009).
Abstract: . The VLF/LF radio signals method for studying preseimic activity is applied to the Abruzzo earthquake (M=6.3, 6 April 2009). The data collected by three receivers located in Moscow (Russia), Graz (Austria) and Bari (Italy) at about 3000 km, 1000 km and 500 km from the epicenter were used. The signals received from the Sardinia (20.27 kHz) and the Sicily (45.9 kHz) transmitters, both located in Italy, were compared with those received from the Iceland (37.5 kHz), the Great Britain (19.58 kHz) and the Germany (23.4 kHz) transmitters. The propagation paths of the two Italian transmitters cross the epicentral area (seismic paths) unlike the paths of the other three signals (control paths). Using two different analyses, that are the study of the night-time signal and the research of shifts in the evening terminator times, clear anomalies were revealed 2–8 days before the occurrence of the Abruzzo earthquake in the seismic paths, while no anomalies have been found in the control paths.