H. Maezawa

Osaka Prefecture University, Sakai, Ōsaka, Japan

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Publications (125)221.88 Total impact

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    ABSTRACT: Superconducting hot electron bolometer (HEB) mixers have matured as the most sensitive heterodyne detectors for astronomy and atmospheric science in the THz region. The HEB mixer fabrication is based on an ultra thin superconducting film such as Nb, NbN, and NbTiN. In general, the critical temperature (T c) of such thin films is much lower than those of the corresponding bulk materials. In order to improve T c of the thin films, we have employed an AlN film as a buffer layer between a substrate and NbN/NbTiN films. The AlN film is deposited on the quartz or glass substrate in a mixture of Ar and N 2 gas by DC reactive magnetron sputtering. We optimize the Ar and N 2 flow rates to ensure that the X-ray diffraction from the 002 surface of Wurtzite type AlN is dominant. We measure the T c values of the NbN and NbTiN films with the AlN buffer layer (20 nm) deposited on quartz and glass substrates respectively. For the 8 nm NbTiN film on the grass substrate, T c is increased from 8.4 K to 11.0 K by insertion of the AlN buffer layer. For the 10 nm and 6 nm NbN films on the quartz substrate, the T c is increased from 6.9 K to 11.4 K and 6.1 K to 9.8 K respectively. The improvement in Tc would originate from better epitaxial growth of the NbN and NbTiN films on the AlN buffer layer than on the bare substrate. The HEB mixer fabrication using the NbN and NbTiN films with the AlN buffer layer is ongoing.
    12/2023;
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    ABSTRACT: We report temporal variations of the partial column density of nitric oxide (NO) in an altitude range 75–105 km at Syowa Station, Antarctica, from January 2012 to September 2013. We found two patterns of NO temporal variation: (1) a seasonal cycle with a maximum in winter and a minimum in summer, and (2) short-term enhancements on a timeframe of 5–10 days associated with solar activities. In the seasonal cycle, the variation pattern of NO showed good agreement with scotoperiod of solar radiation rather than the downwelling atmospheric transport, suggesting that photodissociation is the main driver of the seasonal variation. To study the short-term enhancements, we compared the NO column density with the proton and electron fluxes obtained by the Polar Orbiting Environmental Satellite/Meteorological Operational (POES/METOP) satellites. There is a weak but significant correlation between the NO and the electron flux, but no correlation between the NO and the proton flux. We also made a detailed comparison of the time series of NO and proton/electron fluxes for 12 selected 25-day timeframes, and found that at least 2 remarkable NO enhancements occurred without any solar proton events (SPEs). During electron precipitation, the NO column density peaked 1–5 days after the commencement of geomagnetic storms, whereas the relationship between NO and the solar proton is not clear because the electron flux also increased at the same time. These results suggest that energetic electron precipitation may be a major cause of NO enhancements above Syowa station in the auroral region, even during SPEs.
    Journal of Geophysical Research: Space Physics. 08/2014;
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    ABSTRACT: The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS ($J_N=4_3-3_2$), HC$_3$N ($J=5-4$), N$_2$H$^+$ ($J=1-0$), and SiO ($J=2-1, v=0$) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely-strong CCS emission is detected. The CCS-to-N$_2$H$^+$ abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different $V_{\rm LSR}$. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few $\times \ 10^5$ yr because CCS is abundant only in such a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is $0.4 \times \ 10^5$ yr, is extremely high as about 70 percent in the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.
    The Astrophysical Journal Letters 07/2014; 791(2). · 6.35 Impact Factor
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    ABSTRACT: We report extreme enhancements of the nitric oxide (NO) column density observed with the ground-based millimeter-wave spectroscopic radiometer installed at Syowa Station, Antarctica, during a large geomagnetic storm in April 2012. From the NO spectrum line shape and NO column density relationship with solar radiation, we concluded that the NO was emitted in the altitude range between 75 km and 100 km. The column density of NO gradually increased during the recovery phase. In addition to variations on a timeframe of several days, we found diurnal variations. The increase of NO was related to precipitated electrons in the energy range of 30–300 keV observed by POES/METOP. We found a rapid response (within one hour) and a one-to-one correspondence between them. For the first time we show that a remarkable increase of the column density of NO is caused by dawn-dusk asymmetry of the plasma sheet electrons.
    Geophysical Research Letters. 03/2014;
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    ABSTRACT: We have made new CO observations of two molecular clouds, which we call "jet" and "arc" clouds, toward the stellar cluster Westerlund 2 and the TeV gamma-ray source HESS J1023-575. The jet cloud shows a linear structure from the position of Westerlund 2 on the east. In addition, we have found a new counter jet cloud on the west. The arc cloud shows a crescent shape in the west of HESS J1023-575. A sign of star formation is found at the edge of the jet cloud and gives a constraint on the age of the jet cloud to be ~Myrs. An analysis with the multi CO transitions gives temperature as high as 20 K in a few places of the jet cloud, suggesting that some additional heating may be operating locally. The new TeV gamma-ray images by H.E.S.S. correspond to the jet and arc clouds spatially better than the giant molecular clouds associated with Westerlund 2. We suggest that the jet and arc clouds are not physically linked with Westerlund 2 but are located at a greater distance around 7.5 kpc. A microquasar with long-term activity may be able to offer a possible engine to form the jet and arc clouds and to produce the TeV gamma-rays, although none of the known microquasars have a Myr age or steady TeV gamma-rays. Alternatively, an anisotropic supernova explosion which occurred ~Myr ago may be able to form the jet and arc clouds, whereas the TeV gamma-ray emission requires a microquasar formed after the explosion.
    The Astrophysical Journal 01/2014; 781(2). · 6.73 Impact Factor
  • 10/2013;
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    ABSTRACT: Stars form out of dense cores in turbulent, magnetized molecular clouds. However, the role of magnetic fields in star formation remains poorly understood both theoretically and observationally. This is in part due to the lack of the observational characterization of the magnetic fields that are associated with the dense cores prior to star formation, or pre-protostellar cores. To shed light on the issue of the magnetic field in the gravitational collapse of pre-protostellar cores, we have started a project of the magnetic field measurements toward pre-protostellar cores using the Zeeman splitting of CCS (JN = 43 - 32) line. We are now developing a new 45GHz band, dual polarization, reciever for the Nobeyama 45m telescope. In this contribution, we summarize a current status of our Zeeman project and future plan.
    10/2013;
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    ABSTRACT: We are developing a new dual polarization receiver at 45GHz band to be installed on the Nobeyama 45 m radio telescope. The purpose of the receiver is to measure the polarization difference caused by the Zeeman effect in magnetized molecular cores, and then we are focusing on the stability of the polarization observations for the development. The magnetic field is considered to play an important role in a star formation process. However, our understanding of the magnetic field in molecular clouds/cores is still very limited, because the measurement of the magnetic field has been quite difficult as it requires very sensitive, stable receiver system. We then plan to develop a new receiver system for measuring the Zeeman effect, and the details about the project is described by Nakamura et al. in this volume. In this presentation, we focus on the development of the new dual polarization receiver.
    10/2013;
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    ABSTRACT: We have developed low-noise waveguide-type superconducting hot electron bolometer (HEB) mixers for astronomical observations in the 0.8-1.0 and 1.3-1.5 THz bands, by using a relatively thick NbTiN superconducting film (10.8 nm). The receiver noise temperature of 350 K (DSB) at 0.81 THz and 490 K at 1.475 THz has been achieved. We have built the 0.8-1.0/1.3-1.5 THz dual band heterodyne receiver using these low noise HEB mixers, and have installed it on the ASTE (Atacama Submillimeter Telescope Experiment) 10 m telescope in Chile in 2011. The 13CO emission (J = 8-7 : 0.8813 THz) has successfully been detected toward the Orion A molecular cloud with our HEB mixer receiver.
    10/2013;
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    ABSTRACT: We have recently observed four hyperfine components of the ground state Λ-doublet-type transition of OH toward several positions in the Taurus Molecular Cloud with the Effelsberg 100 m radio telescope. We have found that the 1612 MHz line appears in absorption toward the eastern position of HCL2, where the [CI](3P1-3P0) emission shows a local peak. Furthermore, the spectrum observed toward the other positions in HCL2 shows two velocity components. The higher velocity component is seen in absorption, whereas the lower velocity component is seen in emission. In order to understand the above results, we have made statistical equilibrium calculations of the OH molecule. It is found that the 1612 MHz line appears in absorption only when the gas kinetic temperature is higher than 40 K. Thus, intensities of the four hyperfine components of OH can be a good thermometer. The combination of emission and absorption observed in HCL2 would reflect a cloud structure like cold dense cores surrounded by a warm less-dense envelope.
    10/2013;
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    ABSTRACT: We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC3603 in the transitions 12CO(J=2-1, J=1-0) and 13CO(J=2-1, J=1-0). We suggest that two molecular clouds at 13 km s-1 and 28 km s-1 are associated with NGC3603 as evidenced by higher temperatures toward the H II region as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ~20 km s-1. We suggest that the two clouds collided with each other a Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster which is as young as a Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along side Westerlund2 where formation may have been triggered by a cloud-cloud collision.
    The Astrophysical Journal 06/2013; · 6.73 Impact Factor
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    ABSTRACT: We present an analysis of the interstellar medium (ISM) toward the γ-ray supernova remnant (SNR) W44. We used NANTEN2 12CO(J = 2-1) and 12CO(J = 1-0) data and Arecibo H I data in order to identify the molecular and atomic gas in the SNR. We confirmed that the molecular gas is located in the SNR shell with a primary peak toward the eastern edge of the shell. We newly identified high-excitation molecular gas along the eastern shell of the SNR in addition to the high-excitation broad gas previously observed inside the shell; the line intensity ratio between the 12CO(J = 2-1) and 12CO(J = 1-0) transitions in these regions is greater than ~1.0, suggesting a kinetic temperature of 30 K or higher, which is most likely due to heating by shock interaction. By comparing the ISM with γ-rays, we find that target protons of hadronic origin are dominated by molecular protons of average density around 200 cm–3, where the possible contribution of atomic protons is 10% or less. This average density is consistent with the recent discovery of the low-energy γ-rays suppressed in 50 MeV-10 GeV as observed with AGILE and Fermi. The γ-ray spectrum differs from place to place in the SNR, suggesting that the cosmic-ray (CR) proton spectrum significantly changes within the middle-aged SNR perhaps due to the energy-dependent escape of CR protons from the acceleration site. We finally derive a total CR proton energy of ~1049 erg, consistent with the SN origin of the majority of the CRs in the Galaxy.
    The Astrophysical Journal 04/2013; 768(2):179. · 6.73 Impact Factor
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    ABSTRACT: We have developed a transportable 30-cm submillimeter-wave telescope to operate at the Dome Fuji station in the Antarctic plateau. Transportability is an important requirement in the design; the telescope can be divided into several subsystems by hands. The maximum weight of the subsystems is restricted to be below 60 kg, so that the telescope can be assembled without a lifting machine. A small 4 K mechanical cryocooler is used for cooling down a SIS mixer. Total power consumption was designed to be less than 2.5 kW. The optical system was designed to satisfy the frequency independent matching condition at the subreflector and the feed horn of the SIS mixer, so we could accommodate a higher frequency receiver without changing mirrors. A quasi-optical filter was employed for the single sideband operation in observations of the CO (J = 4-3) line at 461.04 GHz and the [CI] (3P1-3P0) line at 492.16 GHz. It was equipped with a 1 GHz width spectrometer that covers a velocity width of 600 km/s with a velocity resolution of 0.04 km/s at 461 GHz. We carried out test observations at a 4400-m altitude site in northern Chile during winters of 2010 and 2011. The typical system noise temperature, including atmospheric loss, was 3000 K (SSB) at 461 GHz, that is mainly limited by atmospheric opacity. The beam size of the 30-cm offset Cassegrain antenna at 0.65 mm of wavelength was measured to be 9'.4±0'.4 by cross scanning of the sun. This angular resolution of the 30-cm telescope is same as those of the Columbia-CfA-U. Chile CO (J = 1-0) surveys. We estimated the main beam efficiency to be 87±5% by observing the new moon. We succeeded in mapping Orion Molecular Cloud A and M17 SW in CO (J = 4-3) followed by test observations toward Orion KL in both CO (J = 4-3) and [CI] (3P1-3P0) .
    Terahertz Science and Technology, IEEE Transactions on. 01/2013; 3(1):15-24.
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    ABSTRACT: We have performed ground-based measurements of stratospheric chlorine monoxide (ClO) during the summer in 2009 over the Atacama highland, Chile, a new observing site in the mid-latitude region in the Southern Hemisphere, by using a millimeter-wave spectroscopic radiometer. The radiometer, equipped with a superconducting receiver and a digital Fourier spectrometer, was developed by Nagoya University, and the new observing system provides us high sensitivity and stable performance to measure the very weak ClO lines. The receiver noise temperature of the superconducting receiver is 170 K in DSB. To reveal the diurnal variation of ClO, we retrieved the vertical mixing ratio profiles by the weighted-damped least-squares algorithm applied for the spectral data at 203 GHz obtained between 5 and 16 December 2009. The total error on the retrieval is estimated to be 20% to 30% in an altitude range from 40 km to 50 km. The amplitude of the diurnal variation is estimated as 33% of the daytime average at 40 km. The observed time variation shows a pattern similar to that of the previous works observed in the northern mid-latitude region.
    Atmospheric Measurement Techniques 11/2012; 5(11):2601-2611. · 3.21 Impact Factor
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    ABSTRACT: A mapping observation of the J=1/2 Λ-type doubling transition (3.3GHz) of CH has been conducted toward Heiles Cloud 2 (HCL2) in the Taurus molecular cloud complex to reveal its molecular cloud-scale distribution. The observations were carried out with the Effelsberg 100m telescope. ************************************************************************** * * * The data cube will be available in February 2013 * * * **************************************************************************
    VizieR Online Data Catalog. 10/2012;
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    ABSTRACT: A mapping observation of the $J=1/2$ $\Lambda$-type doubling transition (3.3 GHz) of CH has been conducted toward Heiles Cloud 2 (HCL2) in the Taurus molecular cloud complex to reveal its molecular cloud-scale distribution. The observations were carried out with the Effelsberg 100 m telescope. The CH emission is found to be extended over the whole region of HCL2. It is brighter in the southeastern part, which encloses the TMC-1 cyanopolyyne peak than in the northwestern part. Its distribution extends continuously from the peak of the neutral carbon emission (CI peak) to the TMC-1 ridge, as if it were connecting the distributions of the [C I] and C$^{18}$O emissions. Since CH is an intermediate in gas-phase chemical reactions from C to CO, its emission should trace the transition region. The above distribution of the CH emission is consistent with this chemical behavior. Since the CH abundance is subject to the chemical evolutionary effect, the CH column density in HCL2 no longer follows a linear correlation wit the H$_2$ column density reported for diffuse and translucent clouds. More importantly, the CH line profile is found to be composed of the narrow and broad components. Although the broad component is dominant around the CI peak, the narrow component appears in the TMC-1 ridge and dense core regions such as L1527 and TMC-1A. This trend seems to reflect a narrowing of the line width during the formation of dense cores. These results suggest that the 3.3 GHz CH line is a useful tool for tracing the chemical and physical evolution of molecular clouds.
    Astronomy and Astrophysics 09/2012; · 5.08 Impact Factor
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    ABSTRACT: We have performed ground-based measurements of stratospheric chlorine monoxide (ClO) during the summer in 2009 over the Atacama highland, Chile, a new observing site in the mid-latitude region in the Southern Hemisphere by using a millimeter-wave spectroscopic radiometer. The radiometer equipped with a superconducting receiver and a digital Fourier spectrometer is developed by Nagoya University, and the new system provides us high sensitivity and stable performance to measure the very weak ClO lines. The receiver noise temperature of the superconducting receiver is 170 K in DSB. To reveal the diurnal variation of ClO, we retrieved the vertical mixing ratio profiles by the weighted-damped least squares algorithm applied for the spectral data at 203 GHz obtained between 5 and 16 December 2009. The total error on the retrieval is estimated to be 20% to 30% in an altitude range from 40 to 50 km. The amplitude of the diurnal variation is ±33, ±33, and ±36% at 40, 45, and 50 km, respectively. The time variation curve is basically similar to the previous diurnal variation observed in the northern mid-latitude region but there is a tendency that the increasing rate after the sunrise becomes smaller as the altitude increases.
    Atmospheric Measurement Techniques Discussions. 02/2012; 5(1):1907-1945.
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    ABSTRACT: We have developed the 3.1-THz heterodyne receiver using an NbTiN Hot-Electron Bolometer (HEB) mixer and a THz Quantum Cascade Laser (THz-QCL) as a local oscillator. A quasi optical twin-slot antenna is adopted for the coupling of the RF signal with the mixer. The receiver noise temperature is measured to be 5600 K in DSB. When the optical loss is corrected, it is as low as 2100 K. This result demonstrates that the NbTiN HEB mixer works with the equivalent level of performance at 3.1 THz in comparison with the NbN HEB mixers usually employed in this frequency region.
    Terahertz Science and Technology, IEEE Transactions on. 01/2012; 2(1):22-28.
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    ABSTRACT: Achieving adequate blood pressure (BP) control often requires more than one antihypertensive agent. The purpose of this study was to determine whether a fixed-dose formulation of losartan (LOS) plus hydrochlorothiazide (HCTZ) (LOS/HCTZ) is effective in achieving a greater BP lowering in patients with uncontrolled hypertension. The study was a prospective, multicenter, observational trial exploring the antihypertensive effect of a single tablet of LOS 50 mg/HCTZ 12.5 mg. A total of 228 patients whose BP had previously been treated with more than one antihypertensive agents without having achieved BP goal below 130/80 mmHg enrolled in the study. A significant decrease in systolic and diastolic BP was observed in both clinic and home measurement after switching from the previous treatment to LOS/HCTZ. There was a significant decrease in both B-type natriuretic peptide (BNP) and urinary albumin creatinine (Cr) excretion ratio (ACR), especially in patients with elevated values. In contrast, there was a significant increase in serum Cr concentration in conjunction with a decrease in estimated glomerular filtration rate (eGFR). Overall serum uric acid (UA) concentration increased, whereas in patients with hyperuricemia there was a significant reduction in this value. Switching to LOS/HCTZ provides a greater reduction in clinic and home BP in patients with uncontrolled hypertension. This combination therapy may lead to cardio-, reno protection and improve UA metabolism.
    Clinical and Experimental Nephrology 11/2011; 16(2):269-78. · 1.25 Impact Factor
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    ABSTRACT: We are developing quasi-optical superconducting hot-electron bolometer (HEB) mixer receivers for astronomical and atmospheric remote sensing applications. The microbridge of the HEB mixer was fabricated at room temperature from a 6.8-nm-thick niobium titanium nitride (NbTiN) film deposited on a 20-nm-thick aluminum nitride (AlN) buffer layer, using a helicon sputtering technique at a slow deposition rate. The mixer was cooled to 4.2 K using a closed-cycled mechanical 4 K pulse-tube cryocooler with a temperature fluctuation of ±1.6 mK. The stability of a large-volume NbTiN HEB mixer was studied at 1.47 THz by changing local oscillator (LO) power with the mixer bias voltage fixed. The intermediate frequency (IF) signal measured at 1.5 GHz had a maximum peak at a certain mixer bias current. The receiver noise temperature was lowest at around the IF maximum peak. It was also found that the IF signal was most stable at around the IF maximum peak under conditions in which the instability of LO pumping level, induced by small mechanical vibrations of the cryostat, remained in the optical system.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor

Publication Stats

586 Citations
221.88 Total Impact Points

Institutions

  • 2011–2014
    • Osaka Prefecture University
      • • Graduate School of Science
      • • Department of Physical Science
      Sakai, Ōsaka, Japan
  • 2004–2014
    • National Astronomical Observatory of Japan
      • Astronomy Data Center
      Edo, Tōkyō, Japan
  • 2005–2011
    • Nagoya University
      • Solar-Terrestrial Environment Laboratory
      Nagoya, Aichi, Japan
  • 2000–2009
    • The University of Tokyo
      • • Department of Physics
      • • Department of Astronomy
      Tokyo, Tokyo-to, Japan
  • 1998–2007
    • High Energy Accelerator Research Organization
      • Institute of Materials Structure Science
      Tsukuba, Ibaraki-ken, Japan
  • 1988–2002
    • University of Tsukuba
      • Applied Physics
      Tsukuba, Ibaraki, Japan
  • 1997
    • Institute Energy Economics Japan
      Edo, Tōkyō, Japan