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Powerful concurrency primitives in recent concurrent languages and thread libraries provide great flexibility about implementation of high-level features like concurrent objects. However, they are so low-level that they often make...
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Powerful concurrency primitives in recent concurrent languages and thread libraries provide great flexibility about implementation of high-level features like concurrent objects. However, they are so low-level that they often make it difficult to check global correctness of programs or to perform nontrivial code optimization, such as elimination of redundant communication. In order to overcome those problems, advanced type systems for input-only/output-only channels and linear (use-once) channels have been recently studied, but the type reconstruction problem for those type systems remained open, and there fore, their applications to concurrent programming languages have been limited.
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Distributed generators (DGs) such as fuel cells and solar cells are going to be installed in the demand side of distribution systems. The DGs can reduce distribution loss by appropriate allocation. However, there are several probl...
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Distributed generators (DGs) such as fuel cells and solar cells are going to be installed in the demand side of distribution systems. The DGs can reduce distribution loss by appropriate allocation. However, there are several problems installing DGs such as service restoration of distribution system with DGs and so on. When one bank fault of distribution substation occurs in distribution system, since DGs are simultaneously disconnected from the system, it is not easy to restore isolated load by one bank switching in distribution substation. Therefore, a service restoration method to determine restoration configuration and restoration procedures (switching procedure from normal configuration to restoration configuration) taking into account simultaneous disconnection of DGs is needed. In this paper, the authors propose a computation method to determine the optimal restoration configuration and the restoration procedure considering simultaneous disconnection of DGs by one bank fault of distribution system. In the proposed algorithm, after all of the restoration configuration candidates are effectively enumerated under the operational constraints, the optimal configuration to restore the isolated load is selected among enumerated configuration candidates. After determining the optimal restoration configuration, the optimal restoration procedures are obtained by greedy algorithm. Numerical simulations are carried out for a real scale system model with 237 sectionalizing switches (configuration candidates are 2~(237)) and 21 DGs (total output is 5250 kW which is 3% of total load) in order to examine the validity of the proposed algorithm.
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The standards of the network management system have been established by ISO/IEC and ITU-T in order to efficiently manage and operate proprietary enhanced telecommunication networks. Conforming to these standards, we have developed...
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The standards of the network management system have been established by ISO/IEC and ITU-T in order to efficiently manage and operate proprietary enhanced telecommunication networks. Conforming to these standards, we have developed a network management system which enables to manage and operate various private networks provided to business customers.
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Two-dimensional electron gas (2DEG) transport properties and device characteristics in AlGaN/GaN hetero-structure field-effect transistors (HFETs) have been investigated keeping high-power applications in mind. The 2DEG mobility a...
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Two-dimensional electron gas (2DEG) transport properties and device characteristics in AlGaN/GaN hetero-structure field-effect transistors (HFETs) have been investigated keeping high-power applications in mind. The 2DEG mobility as the function of the 2DEG density at low and above room temperatures has systematically been examined for different Al compositions, revealing that the 2DEG mobility compared at the same 2DEG density is higher for higher Al compositions up to 0.3 above room temperature. This indicates that the high Al composition is favorable not only for high 2DEG densities but also for high 2DEG mobilities. For an HFET (Al = 0.3) with a gate-length (L_g) of 1.5 μm, excellent DC and RF characteristics have been obtained, i.e., a maximum transconductance (g_m) of 180 mS/mm, a cutoff frequency (f_T) of 16 GHz, and a maximum oscillation frequency (f_(max)) of 50 GHz. The selective-area regrowth technique has been applied to reduce the source and drain resistance, and an improved g_m of 215 mS/mm has been obtained in an HFET (L_g = 1.5 μm) as the result of the reduced ohmic resistance (0.3 Ω mm). Moreover, a novel layer structure with the back-doping (BD) design has been proposed where an asymmetric double-heterostructure is employed and the doping is performed also in the backside AlGaN barrier layer. A very high 2DEG density of 2.8 x 10~(13) cm~(-2) with a record value of the mobility-density product (2.4 x 10~(16) (V_s)~(-1)) has been obtained in this structure, proving that the BD design is promising for high-power applications.
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We investigated the effect of In atoms in p-GaN on the damage induced by electron cyclotron resonance etching. After etching the surface of p-GaN without In atoms, the I-V characteristics between two Ni/Au electrodes on the surfac...
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We investigated the effect of In atoms in p-GaN on the damage induced by electron cyclotron resonance etching. After etching the surface of p-GaN without In atoms, the I-V characteristics between two Ni/Au electrodes on the surface showed non-Ohmic behavior. This is ascribed to the damage induced by this etching process, as previously reported. The Ohmic characteristics were much improved for p-GaN doped with In atoms compared with those for p-GaN without In Atoms.
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Hexagonal prism-shaped and triangular prism-shaped GaAs/AlGaAs microcavity lasers using vertical facets as reflectors are proposed and fabricated on a (111)B GaAs substrate by selective area metalorganic vapor phase epitaxy. The m...
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Hexagonal prism-shaped and triangular prism-shaped GaAs/AlGaAs microcavity lasers using vertical facets as reflectors are proposed and fabricated on a (111)B GaAs substrate by selective area metalorganic vapor phase epitaxy. The most important feature of these laser structures is that cavity structures com- posed of the highly symmetrical crystal facets are naturally formed. In this paper, we demonstrate that these laser structures can be controlled three-dimensionally by appropriately choosing the growth conditions and/or the mask pattern.
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GaAs/AlGaAs short-cavity Fabry-Perot lasers and hexagonal prism-shaped and triangular prism-shaped ring-cavity lasers using vertical facets as reflectors are fabricated on a (111) B GaAs substrate by selec- tive area epitaxy. Thes...
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GaAs/AlGaAs short-cavity Fabry-Perot lasers and hexagonal prism-shaped and triangular prism-shaped ring-cavity lasers using vertical facets as reflectors are fabricated on a (111) B GaAs substrate by selec- tive area epitaxy. These lasers surrounded by highly symmetrical crystal facets show single-model lasing at a threshold energy as low as a few picojoules. Single-mode lasing is observed even in a short-cavity Fabry- Perot laser with a 5μm cavity length, In addition, a coupled laser structure of two triangular-prism-shaped lasers with a rectangular optical waveguide is also fabricated.
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The combination of patterned dry etching and selective-area regrowth by MOVPE enables us to fabricate the group Ill-nitride-based lasers of various shapes and sizes and to integrate these lasers on substrates. The vertical cavity ...
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The combination of patterned dry etching and selective-area regrowth by MOVPE enables us to fabricate the group Ill-nitride-based lasers of various shapes and sizes and to integrate these lasers on substrates. The vertical cavity mirrors are formed by selective-area regrowth of the dry-etched inclined facets. No growth occurs on the substrate surface exposed by dry etching. In this method, current-confining structures are self-organizing because of the change in Mg incorporation during the vertical facet formation. The selectively regrown Mg-doped GaN consisted of three regions by the regrowth of top, inclined, and vertical facet surfaces, respectively. These regions exhibited different contrast in scanning electron microscope observation and different cathodeluminescence spectra due to the difference in probability of Mg incorporation into them. This phenomenon was successfully applied to form current-confining structures of the lasers. These lasers lased at room temperature by pulsed current injection.
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The effects of Li_2O doping on TiO_2 nanocrystalline film are investigated to improve the conversion efficiency of dye-sensitized solar cells (DSC), while considering the mechanism of electric conduction in the TiO_2 nanocrystalli...
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The effects of Li_2O doping on TiO_2 nanocrystalline film are investigated to improve the conversion efficiency of dye-sensitized solar cells (DSC), while considering the mechanism of electric conduction in the TiO_2 nanocrystalline film. The temperature dependence of carrier concentration and electric conductivity of Li_2O-doped TiO_2 nanocrystalline film are determined by Hall effect and high-impedance conductivity measurements. At the doping condition of 4.5 ×10~(-5) molar ratio of Li_2O to TiO_2, the electric conductivity at room temperature is maximum, which is almost two orders of magnitude higher than that of the undoped sample. The conduction type and carrier concentration at 500 K are n-type and 1.75×10~(13) cm~(-3), respectively. From the temperature dependence of the electron concentration, the donor depth is estimated as 1.0 eV. By applying Li_2O doping to DSC, the conversion efficiency and open-circuit voltage are maximum at the highest conductivity of the Li_2O-doped TiO_2 layer.
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We investigated the electrical properties of Mg-doped In_xGa_1-xN (0≤x<0.25) grown by metalorganic vapor-phase epitaxy with various growth conditions, such as Mg-doping concentration, growth-rate and growth temperature. The hole concentration depends on the growth-rate, the In mole fraction and the crystal quality of the InGaN layers. ...
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We investigated the electrical properties of Mg-doped In_xGa_1-xN (0≤x<0.25) grown by metalorganic vapor-phase epitaxy with various growth conditions, such as Mg-doping concentration, growth-rate and growth temperature. The hole concentration depends on the growth-rate, the In mole fraction and the crystal quality of the InGaN layers.
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