K. Arai

Hirosaki University, Khirosaki, Aomori Prefecture, Japan

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Publications (19)32.86 Total impact

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    ABSTRACT: We report a case of Epstein-Barr virus (EBV)-associated hemophagocytic lymphohistiocytosis (HLH) with clonal karyotype abnormality. A 5-year-old boy was admitted to our hospital with persistent high-grade fever, hepatomegaly, and pancytopenia. Laboratory data disclosed a coagulation abnormality and severe liver damage. Clonal proliferation of EBV-infected cells was detected in the bone marrow by Southern hybridization, and bone marrow cells exhibited clonal chromosomal abnormality. Although the patient was treated with immunochemotherapy according to the HLH94 protocol, the disease recurred during the induction therapy, and the patient died of disseminated intravascular coagulopathy. Considering this aggressive and fatal clinical course, it is important to take intensive therapeutic measures if karyotype abnormality is noted in the treatment of EBV-HLH patients.
    International Journal of Hematology 05/2000; 71(3):263-5. · 1.68 Impact Factor
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    ABSTRACT: A new circuit technology using resonant tunnelling diodes and HEMTs makes the toggle frequency f<sub>toggle</sub> of a static binary frequency divider close to the cutoff frequency f<sub>t</sub> of the used 0.7 μm-gate HEMTs. f<sub>toggle</sub> and f<sub>t</sub> are 34 and 38 GHz, respectively. This technology is promising for use in high-speed logic circuits
    Electronics Letters 02/1998; DOI:10.1049/el:19980103 · 1.07 Impact Factor
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    ABSTRACT: We report a case of myelodysplastic syndrome (MDS) with the 11q23 translocation at its leukemic transformation. Southern blot analysis demonstrated that the MLL gene on chromosome 11 was rearranged during the progression from MDS to acute leukemia. The clinical observation in this case supports the notion that leukemic transformation involves multiple cytogenetic evolutionary progresses, and that MLL gene rearrangement corresponds to the final step of leukemogenesis.
    International Journal of Hematology 02/1998; 67(1):23-6. · 1.68 Impact Factor
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    ABSTRACT: A static frequency divider constructed with resonant tunneling diodes (RTDs) in combination with HEMTs is proposed and demonstrated. The circuit complexity is reduced drastically. The proposed circuit is fabricated using InP-based RTD/HEMT monolithic integration technology. Proper operation is demonstrated at room temperature by a quasi-static test pattern. The circuit includes two sub-circuits which behave like D-latches. Each sub-circuit consists of only three components. This number of components is one fifth of that required to construct a D-latch using conventional SCFL technology. The strong nonlinear I-V characteristics of RTD's are fully utilized for this reduction.
    IEEE Electron Device Letters 12/1997; DOI:10.1109/55.641440 · 3.02 Impact Factor
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    ABSTRACT: A new flip-flop circuit employing a monostable-bistable transition logic element is proposed which was fabricated with resonant tunnelling diodes/HEMT integration technology on an InP substrate. Error free operations up to 18 Gbit/s were demonstrated at room temperature
    Electronics Letters 10/1997; 33(20-33):1733 - 1734. DOI:10.1049/el:19971176 · 1.07 Impact Factor
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    ABSTRACT: Resonant tunneling (RT) devices attract much attention because of their potential for high-speed operation as well as their high functionality, which leads to lower power dissipation. We have developed a highly functional logic gate, called MOBILE (monostable-bistable transition logic element), which exploits the negative differential resistance (NDR) of the RT phenomenon. In this paper, we demonstrate the high-speed operation-up to 18 Gb/s-of the MOBILE flip-flop (FF) circuit at room temperature. The present result indicates the promise of MOBILE-based FF circuits for high-speed digital applications
    Device Research Conference Digest, 1997. 5th; 07/1997
  • K. Arai, M. Yamamoto
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    ABSTRACT: Single peak IV characteristics are experimentally demonstrated by a novel resonant tunneling diode, a resonant tunneling pinch-off diode (RTPD), specially designed to make the coupling between the pinch-off effect and the resonant tunneling effect in the diode itself effective. RTPDs were fabricated using the InGaAs-AlAs-InAlAs material system grown by MBE on semi-insulating InP substrate. Device parameter (emitter width and collector thickness) dependence of the IV characteristics is investigated and compared with previously reported theory. Good agreement between them confirms that the mechanism that brings about the novel characteristics in the RTPD is the above mentioned coupling, and gives guidelines for achieving an RTPD with ideal single peak IV characteristics.
    IEEE Electron Device Letters 11/1996; DOI:10.1109/55.537085 · 3.02 Impact Factor
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    ABSTRACT: High performance InP-based InAlAs/InGaAs enhancement-mode HEMT's are demonstrated using two improved approaches to device structure design and fabrication, i.e., nonalloyed ohmic contacts and Pt-based buried-gate technologies, to reduce the source resistance (R<sub>S</sub>). With specially designed cap layer structures, nonalloyed ohmic contacts to the device channel were obtained providing contact resistance as low as 0.067 Ω·mm. Furthermore, in device fabrication, a Pt-based buried-gate approach is used in which depletion-mode HEMTs are first intentionally fabricated, and then, the Pt-based gate metal is annealed at 250°C, causing the Pt-InAlAs reaction to take place under the gate electrode so that Pt sinks into InAlAs and depletes the channel. As a result, the depletion-mode HEMTs are changed to enhancement-mode, while the channel region between the source and gate electrodes remain undepleted, and therefore, the small R <sub>S</sub> of 0.2 Ω·mm can be maintained. Excellent maximum transconductance of 1170 mS/mm was obtained for a 0.5-μm-gate device. A maximum current-gain cutoff frequency f<sub>T</sub> of 41.2 GHz and maximum unilateral power-gain cutoff frequency f<sub>max</sub> of 61 GHz were demonstrated for a 0.6-μm-gate enhancement-mode HEMT
    IEEE Transactions on Electron Devices 03/1996; DOI:10.1109/16.481725 · 2.36 Impact Factor
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    ABSTRACT: A design for composite-channel structures consisting of an InGaAs channel and an InP subchannel for use as heterostructure field-effect transistors is presented for the first time. This novel channel structure takes advantage of both the high drift velocity and low impact ionization of InP at high electric fields as well as the high electron mobility of InGaAs at low electric fields. It is shown that the doping density of the InP subchannel is the key parameter to realize the advantages of the composite channel. A very high transconductance of 1.29 S/mm and a current gain cutoff frequency of 68.7 GHz are achieved with 0.6 and 0.7 μm gates, respectively. The average velocity of electrons in the composite channel is 2.9×10<sup>7</sup> cm/s. The devices have no kink phenomena in their I-V characteristics possibly due to low impact ionization in the InP subchannel.
    IEEE Transactions on Electron Devices 09/1995; DOI:10.1109/16.398656 · 2.36 Impact Factor
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    ABSTRACT: Acute megakaryoblastic leukaemia (M7) and transient myeloproliferative disorder in Down's syndrome (TMD) are characterized by rapid growth of abnormal blast cells which express megakaryocytic markers. To clarify properties of the blast cells in M7 and TMD cases, we examined erythroid markers expression in blasts from six cases with M7 and seven cases with TMD in this study. Erythroid-specific mRNAs encoding gamma-globin and erythroid delta-aminolevulinate synthase were found to be expressed in blasts from most of these cases, indicating that majorities of the blasts in M7 and TMD cases have erythroid and megakaryocytic phenotypes. We also found that mRNAs encoding GATA-1 and GATA-2 are expressed in all these cases. These results suggest that M7 blasts and TMD blasts correspond to the erythroid/megakaryocytic bipotential progenitor cells.
    British Journal of Haematology 08/1995; 90(3):607-14. · 4.96 Impact Factor
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    ABSTRACT: A newly fabricated three-terminal Josephson junction is coupled with a two-dimensional electron gas (2DEG) in a strained InAs quantum well inserted into an InAlAs/InGaAs modulation-doped structure. The 2DEG is confined in the InAs quantum well and has a maximum mobility of 155000 cm<sup>2</sup>/Vs at a sheet-carrier density of 1.86×10<sup>12</sup> cm<sup>-2</sup> at 10 K. The supercurrent flows through the 2DEG and can be controlled by adjusting the gate voltage. The critical current and normal resistance are measured as a function of the gate voltage, and the sheet-carrier density dependence of the critical current is obtained. We also measure the temperature dependence of the critical current at different gate voltages. The results indicate that, when using this junction, the superconducting characteristics can range between the clean and dirty limits.
    IEEE Transactions on Applied Superconductivity 07/1995; DOI:10.1109/77.403195 · 1.32 Impact Factor
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    ABSTRACT: A new approach to reducing the source resistance in InP-based InAlAs-InGaAs enhancement-mode HEMTs is developed using Pt-based buried-gate technology. Source resistance as small as 0.2 Ωmm is obtained, which results in an excellent transconductance of 1170 mS/mm for a 0.5 μm long gate enhancement-mode HEMT
    Electronics Letters 06/1995; 31(11-31):925 - 927. DOI:10.1049/el:19950603 · 1.07 Impact Factor
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    ABSTRACT: We give a detailed analysis based on Shubnikov-de Haas measurement of the effective mass of 2DEG in an InAs-inserted-channel InAlAs/InGaAs modulation-doped structure. The measured effective mass of the InAs-inserted-channel inverted MD structure was found to be 0.044 m<sub>0</sub>, when n<sub>s</sub>=2.08×10<sup>12</sup> cm<sup>-2 </sup>. The results indicate that almost all of the 2DEG forms in the strained InAs quantum well. They show that the InAs-inserted-channel MD structure improves the electron confinement, since the 2DEG is confined in the InAs quantum well with the thickness of 4 nm. Therefore, it is possible to utilize the excellent transport properties of InAs by the InAs-inserted-channel MD structure
    Indium Phosphide and Related Materials, 1995. Conference Proceedings., Seventh International Conference on; 06/1995
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    ABSTRACT: In this paper, we demonstrate greatly improved R<sub>S</sub> in an E-HEMT structure using non-alloyed ohmic contact and Pt-based buried gate approaches. First, the non-alloyed ohmic contact technique was used to produce very low contact resistance and to provide sharply defined ohmic edges. Second, in the fabrication of our E-HEMT's, we first intentionally fabricated depletion-mode HEMTs (D-HEMTs). Subsequently, by annealing the sample at 250°C, these D-HEMTs were changed to E-HEMTs as a result of the Pt-InAlAs reaction taking place under the gate electrode, while the channel region between source and gate remained undepleted. This allowed a small R<sub>S</sub> to be maintained An excellent transconductance (g<sub>m</sub>) of 1170 mS/mm was achieved for an E-HEMT with a 0.5-μm-gate
    Indium Phosphide and Related Materials, 1995. Conference Proceedings., Seventh International Conference on; 06/1995
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    ABSTRACT: The authors examine the high-frequency performance of a sub-0.1 mu m gate InAlAs/InGaAs HEMT with a thin InAs layer inserted into the InGaAs channel. The transconductance is 2.1 S/mm and the current-gain cutoff frequency is 264 GHz using a 0.08 mu m-long gate.
    Electronics Letters 07/1992; 28(13-28):1230 - 1231. DOI:10.1049/el:19920776 · 1.07 Impact Factor
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    ABSTRACT: An InAlAs/InGaAs HEMT with a thin InAs layer inserted into the InGaAs channel is proposed and its electron transport properties and device performances have been investigated. By optimizing the thickness and the exact point of insertion in the InAs layer, the mobility and electron velocity at 300 K have been increased by 30% and 15%, respectively, compared to the conventional heterostructure. In addition, a maximum intrinsic transconductance of 970 mS/mm and a maximum current gain cutoff frequency of 58.1 GHz have been attained by a 0.6 mu m-gate-length device.< >
    IEEE Electron Device Letters 07/1992; DOI:10.1109/55.145073 · 3.02 Impact Factor
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    ABSTRACT: The authors discuss a novel HEMT (high electron mobility transistor) channel structure, consisting of InGaAs and InP, which can utilize both the high electron mobility of InGaAs at low electric field and InP's high drift velocity at high electric field. HEMTs with 0.6-μm gates, a double channel, and a planar doped carrier supply layer show an extremely high transconductance of 1290 mS/mm. Such a device with a 0.7-μm gate has a cutoff frequency of 68.7 GHz, which exceeds that of conventional InGaAs HEMTs by a factor of 1.3. It is shown that these characteristics may be related to an increase of the effective saturation velocity of electrons in the channel from 2.7×10<sup>7</sup> cm/s to 4.2×10<sup>7</sup> cm/s. Moreover, it is found that there is no kink in the I - V characteristics of double channel devices. These results indicate that InGaAs/In double-channel HEMTs have great potential for application in high-speed and high-power devices
    Indium Phosphide and Related Materials, 1992., Fourth International Conference on; 05/1992
  • T. Enoki, K. Arai, Y. Ishii
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    ABSTRACT: Cutoff frequencies are measured for sub-0.25 mu m-gate InAlAs/InGaAs/InP HEMTs fabricated with a novel T-gate process using ion-beam etching in conjunction with both electron-beam lithography and photolithography. The cutoff frequency of 200 GHz is demonstrated by 0.12 mu m-gate HEMT.
    Electronics Letters 02/1991; 27(2-27):115 - 117. DOI:10.1049/el:19910077 · 1.07 Impact Factor
  • T. Enoki, K. Arai, Y. Ishii
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    ABSTRACT: InAlAs-InGaAs HEMTs with 0.4- to 5- mu m gate lengths have been fabricated and a maximum f/sub T/ of 84 GHz has been obtained by a device with a 0.4- mu m gate length. A simple analysis of their delay times was performed. It was found that gradual channel approximation with a field-dependent mobility model with E/sub c/ of 5 kV/cm holds for long-channel devices (L/sub g/>2 mu m), while a saturated velocity model with a saturated velocity of 2.7*10/sup 7/ cm/s holds for short-channel devices (L/sub g/<1 mu m).< >
    IEEE Electron Device Letters 12/1990; 11(11-11):502 - 504. DOI:10.1109/55.63013 · 3.02 Impact Factor