Although vector potentials are more intrinsic physical quantities than magnetic and electric fields, measuring them macroscopically is difficult. A double-nested Helmholtz-type vector potential coil, ...consisting of an elongated solenoid coil wound around a cylinder, and producing a uniform magnetic vector potential, was developed in this study. The coil is carefully designed to reduce the influence of the leakage magnetic field and the scalar potential generated by the coil’s electrical resistance on the measurement. It has the ability to toggle between vector potential and magnetic field generation. We adapted the coil for use in an optically pumped atomic magnetometer. We also developed an optically pumping Rb atomic magnetometer that can calibrate in a zero magnetic field and applied a time-varying magnetic vector potential. We found that the output signal changed with the vector potential even when there was virtually no magnetic field. With increasing frequency, the output voltage decreases for the magnetic signal and increases for the magnetic vector potential signal. The results revealed that the atomic magnetometer is influenced not only by the magnetic field but also by the magnetic vector potential and that the frequency responses are opposite.
A 50-layer stacked InGaAs/GaAs quantum dot solar cell (QDSC) grown on GaAs (100) with a self-organized texture formed on its backside has been fabricated in aim for enhancing the photoabsorption by ...the QD layers. Since doped GaAs substrate has a large free-carrier absorption, a semi-insulating substrate was used for fabricating the QDSC with backside texture. A micrometer-scale texture was formed by a simple wet-etching in a NH4OH solution. The light scattering at the textured backside surface caused a light trapping effect and resulted in an increased effective optical path length by multiple reflection inside QDSC, and this effect was confirmed by the external quantum efficiency (EQE) measurement. The photoabsorption attributed to InGaAs QD layers increased by about 2.4 times compared to QDSC without a textured backside. As a result, the short-circuit current density (Jsc) measured at an air-mass 1.5 global (AM1.5G) spectrum illumination increased from Jsc = 20.9 to 21.5 mA/cm2.
•50-layer InGaAs/GaAs QD solar cell with a self-organized texture on its backside.•Total QD density of 2 × 1012/cm2 was achieved after 50 layer stacks.•Photoabsorption in InGaAs QD layers increased by 2.4 times with light trapping.•Jsc increased from 20.9 to 21.5 mA/cm2 under AM1.5G.
Abstract We report the growth of bulk β-Ga 2 O 3 crystals based on crystal pulling from a melt using a cold container without employing a precious-metal crucible. Our approach, named oxide crystal ...growth from cold crucible (OCCC), is a fusion between the skull-melting and Czochralski methods. The absence of an expensive precious-metal crucible makes this a cost-effective crystal growth method, which is a critical factor in the semiconductor industry. An original construction 0.4–0.5 MHz SiC MOSFET transistor generator with power up to 35 kW was used to successfully grow bulk β-Ga 2 O 3 crystals with diameters up to 46 mm. Also, an original diameter control system by generator frequency change was applied. In this preliminary study, the full width at half maximum of the X-ray rocking curve from the obtained β-Ga 2 O 3 crystals with diameters ≤ 46 mm was comparable to those of β-Ga 2 O 3 produced by edge-defined film fed growth. Moreover, as expected, the purity of the obtained crystals was high because only raw material-derived impurities were detected, and contamination from the process, such as insulation and noble metals, was below the detection limit. Our results indicate that the OCCC technique can be used to produce high-purity bulk β-Ga 2 O 3 single crystalline substrate.
We report, for the first time, about an intermediate band solar cell implemented with InAs/AlGaAs quantum dots whose photoresponse expands from 250 to ∼6000 nm. To our knowledge, this is the ...broadest quantum efficiency reported to date for a solar cell and demonstrates that the intermediate band solar cell is capable of producing photocurrent when illuminated with photons whose energy equals the energy of the lowest band gap. We show experimental evidence indicating that this result is in agreement with the theory of the intermediate band solar cell, according to which the generation recombination between the intermediate band and the valence band makes this photocurrent detectable.
Abstract
Monitoring the behavior of slopes around the sites of hydroelectric power plants and dam reservoirs is important from the viewpoints of their stable operation and a reduction in the risk to ...the local community. Since their facilities are widely located at dam sites, however, it is not easy to efficiently monitor the behavior of them. SAR can be a solution to the problem. On the other hand, there are still difficulties that must be overcome when applying DInSAR as an engineering tool for monitoring in practice, i.e., phase decorrelation, the accuracy and reliability of the results, etc. In particular, the dense vegetation that often covers mountainous areas can prevent the acquisition of precise measurement results. In this paper, DInSAR using ALOS-2 data is applied around a dam basin and the results are compared with the actual ground behavior to confirm the applicability of DInSAR. It is concluded that DInSAR using ALOS-2 data could be a useful tool for monitoring the slope stability of large dam basins, even those covered with dense vegetation.
Crystal growth by micro-pulling-down, Czochralski, and floating zone methods and scintillation properties of Ce:Gd3(Ga,Al)5O12 (Ce:GGAG) multi-component oxide garnets, and Ce:Gd2Si2O7 (Ce:GPS) or ...Ce:(La,Gd)2Si2O7 (Ce:La-GPS) pyro-silicates are reviewed. GGAG crystals demonstrated practically linear dependences of some of the parameters including lattice constant, emission wavelength, and band gap on Ga content. However, emission intensity, light yield and energy resolution showed maxima for intermediate compositions. GGAG crystals had the highest light yield of 56,000photon/MeV for Ga content of 2.7 atoms per garnet formula unit. Similarly the light yield and energy resolution of La-GPS showed the highest values of 40,000photon/MeV and 4.4%@662keV, respectively, for La-GPS containing 10% of La. Moreover, La-GPS demonstrated stable scintillation performance up to 200°C.
We present an experimental method to generate quasiperpendicular supercritical magnetized collisionless shocks. In our experiment, ambient nitrogen (N) plasma is at rest and well magnetized, and it ...has uniform mass density. The plasma is pushed by laser-driven ablation aluminum (Al) plasma. Streaked optical pyrometry and spatially resolved laser collective Thomson scattering clarify structures of plasma density and temperatures, which are compared with one-dimensional particle-in-cell simulations. It is indicated that just after the laser irradiation, the Al plasma is magnetized by a self-generated Biermann battery field, and the plasma slaps the incident N plasma. The compressed external field in the N plasma reflects N ions, leading to counterstreaming magnetized N flows. Namely, we identify the edge of the reflected N ions. Such interacting plasmas form a magnetized collisionless shock.
Several attempts have been carried out to manufacture intermediate band solar cells (IBSC) by means of quantum dot (QD) superlattices. This novel photovoltaic concept allows the collection of a wider ...range of the sunlight spectrum in order to provide higher cell photocurrent while maintaining the open-circuit voltage (VOC) of the cell. In this work, we analyze InAs/GaAsN QD-IBSCs. In these cells, the dilute nitrogen in the barrier plays an important role for the strain-balance (SB) of the QD layer region that would otherwise create dislocations under the effect of the accumulated strain. The introduction of GaAsN SB layers allows increasing the light absorption in the QD region by multi-stacking more than 100 QD layers. The photo-generated current density (JL) versus VOC was measured under varied concentrated light intensity and temperature. We found that the VOC of the cell at 20K is limited by the bandgap of the GaAsN barriers, which has important consequences regarding IBSC bandgap engineering that are also discussed in this work.
•InAs/GaAsN QDs are proposed as a candidate material for the IBSC concept.•The dilute nitrogen in the barrier allows strain-balancing the stacked QD layer structure.•InAs/GaAsN QD cells are designed and fabricated with a large number of QD layers in order to enhance QD absorption.•InAs/GaAsN QD cell and GaAs control cell are subject to JL–VOC concentrated light experiments at low temperature in order to verify the voltage preservation principle.•The maximum VOC of the cell is limited by the GaAsN barrier material at approximately 1.23V.
Abstract
Field monitoring is essential for assessing the stability of natural as well as well-designed slopes to confirm the validity of the design. Many instruments and systems are available for ...monitoring the slope behavior. Interpretation of the monitoring results for assessing the stability of slopes is an important task. Displacements are usually plotted versus time, and their transition and rate of increase are observed and compared with the criteria. This is a common and useful practice, but it is based on an empirical method. Therefore, a method for assessing the stability of slopes on the basis of rock mechanics is required. This paper outlines a back analysis method originally proposed by Sakurai in 1987 to estimate the factor of safety from the measured displacements. Two case studies are demonstrated to confirm the validity of the method. By applying the back analysis method to natural and well-designed slopes, the time transition of the factor of safety can be estimated from the measured displacements. The applicability and limitations of the method are also discussed.
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