To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
We present recent observation results of Sgr A* at millimeter obtained with VLBI arrays in Korea and Japan.
7 mm monitoring of Sgr A* is part of our AGN large project. The results at 7 epochs during 2013-2014, including high resolution maps, flux density and two-dimensional size measurements are presented. The source shows no significant variation in flux and structure related to the G2 encounter in 2014. According to recent MHD simulations by kawashima et al., flux and magnetic field energy can be expected to increase several years after the encounter; We will keep our monitoring in order to test this prediction.
Astrometric observations of Sgr A* were performed in 2015 at 7 and 3.5 millimeter simultaneously. Source-frequency phase referencing was applied and a combined ”core-shift” of Sgr A* and a nearby calibrator was measured. Future observations and analysis are necessary to determine the core-shift in each source.
We have made a CO(J=2-1) observations using the Nobeyama 45m telescope aimed at examining the physical properties of the molecular gas in this object. The upper limit obtained is 1.8 mK (3σ) at a velocity resolution of 100 km s−1, which leads to an upper limit on the molecular gas mass of 5.3 × 1011M⊙, if we assume a line width of 250 km s−1 obtained in the CO(J = 5 - 4) line (rest-frame) and the Galactic CO-to-H2 conversion factor of 4.5 (M⊙ K km s−1 pc2). The line ratio between the 2–1 line and the 5–4 line as well as those from the 7–6 and the 4–3 lines (Omont et al. 1996, Nature, 382, 428) imply that the mean gas density is as high as 103–5 cm−3, which is comparable to that in nearby star burst galaxies (e.g., Solomon et al. 1992, ApJ, 387, L55).
To reveal the origin of the cosmic X-ray background (CXB) in the hard band, we are now conducting a wide (~ 7 deg2) and deep (~ 1 × 10−13 erg sec−1 cm−2 in the 2-10 keV band) survey with the ASCA (the ASCA Large Sky Survey, hereafter LSS). We have detected 83 sources above 4 sigma level in the 0.7-10 keV band with the GIS and resolved ~30% of the CXB in the 2-10 keV band into discrete sources (Ueda 1996). AGNs (type 1 and type 2) and clusters of galaxies are expected to be major contributers to these X-ray sources.
Since the bulk of the energy density of the Cosmic X-ray Background (CXB) resides in the harder energy band than that of the ROSAT band (0.5-2 keV) and since the X-ray sources identified in the ROSAT band have X-ray spectra softer than that of the CXB, investigation of nature of the X-ray sources at the harder energy band is indispensable to solve the origin of the CXB. However, only 2-3% of the CXB in the hard band (2-10 keV) had been resolved into discrete sources (Piccinotti et al. 1982, ApJ 253, 485). We present our preliminary results of optical follow-up observations of the ASCA Lynx deep survey.
We have made a CO (J=2−1) observation using the Nobeyama 45m telescope aimed at examining physical properties of the molecular gas in the object. Upper limit obtained is 1.8 mK (3σ) at a velocity resolution of 100 km s−1, which leads to an upper limit on the molecular gas mass of 5.3 × 1011M⊙, if we assume a line width of 250 km s−1 obtained in J = 5–4 line and the Galactic CO-to-H2 conversion factor of 4.5 M⊙ K km s−1 pc2. The line ratio between 2–1 line and 5–4 line as well as those from 7–6 and 4–3 lines (Omont et al. 1996) imply that the mean gas density is as high as 103–5 cm−3, which is comparable to that in nearby star burst galaxies (e.g., Solomon et al. 1992).
We report the results of near-infrared observations of a type-2 QSO, AX J08494+4454 at z = 0.9 which was identified in our optical follow-up observations of the ASCA Lynx deep survey. This object has a hard X-ray spectrum with an X-ray luminosity of about 1×1044 erg s−1 in 2–10 keV. The optical spectrum shows high-excitation and high-ionization lines but no significant broad Hβ emission. These properties strongly suggest that this object is a “type-2” QSO (Ohta et al. 1996).
We have conducted 1.1 mm ALMA observations of a contiguous 105” × 50” or 1.5 arcmin2 window in the SXDF-UDS-CANDELS. We achieved a 5σ sensitivity of 0.28 mJy, giving a flat sensus of dusty star-forming galaxies with LIR ~6×1011L⊙ (if Tdust=40K) up to z ~ 10 thanks to the negative K-correction at this wavelength. We detected 5 brightest sources (S/N>6) and 18 low-significant sources (5>S/N>4; they may contain spurious detections, though). One of the 5 brightest ALMA sources (S1.1mm = 0.84 ± 0.09 mJy) is extremely faint in the WFC3 and VLT/HAWK-I images, demonstrating that a contiguous ALMA imaging survey uncovers a faint dust-obscured population invisible in the deep optical/near-infrared surveys. We find a possible [CII]-line emitter at z=5.955 or a low-z CO emitting galaxy within the field, allowing us to constrain the [CII] and/or CO luminosity functions across the history of the universe.
The Au-Si liquid phase was obtained by melting the Si surface via Au-Si eutectic reaction, which contributed to the formation of semiconducting iron disilicide (β-FeSi2), on Au-coated Si(100) substrates. By coating a substrate with an Au layer of 60 nm or more, the Au-Si liquid phase covered the entire Si substrate surface, and single-phase β-FeSi2 was grown on Si(100) substrates. A clear photoluminescence spectrum of β-FeSi2 indicated the formation of high-quality crystals with a low density of the non-radiative recombination center in the grains.
The nearby radio galaxy M87 offers a unique opportunity for exploring the connection between γ-ray production and jet formation at an unprecedented linear resolution. However, the origin and location of the γ-rays in this source is still elusive. Based on previous radio/TeV correlation events, the unresolved jet base (radio core) and the peculiar knot HST-1 at >120 pc from the nucleus are proposed as candidate site(s) of γ-ray production. Here we report our intensive, high-resolution radio monitoring observations of the M87 jet with the VLBI Exploration of Radio Astrometry (VERA) and the European VLBI Network (EVN) from February 2011 to October 2012. During this period, an elevated level of the M87 flux is reported at TeV with VERITAS. We detected a remarkable flux increase in the radio core with VERA at 22/43 GHz coincident with the VHE activity. Meanwhile, HST-1 remained quiescent in terms of its flux density and structure at radio. These results strongly suggest that the TeV γ-ray activity in 2012 originates in the jet base within 0.03 pc (projected) from the central supermassive black hole.
We present the results of radio monitoring observations of Sgr A* at 7 mm (i.e. 43 GHz) with the VLBI Exploration of Radio Astrometry (VERA), which is a VLBI array in Japan. VERA provides angular resolution on millisecond scales, resolving structures within 100 Schwarzschild radii of Sgr A* , similar to the Very Large Baseline Array (VLBA). We performed multi-epoch observations of Sgr A* in 2005 - 2008, and started monitoring it again with VERA from 2013 January to trace the current G2 encounter event. Our preliminary results in 2013 show that Sgr A* on mas scales has been in an ordinary state as of August 2013, although some fraction of the G2 cloud already passed the pericenter of Sgr A* in April 2013. We will continue monitoring Sgr A* with VERA and the newly developed KaVA (KVN and VERA Array).
Slow/monoenergetic positron beams and pulsed positron beams have been used as a non-destructive probe to investigate vacancy-type defects in SIMOX substrates which were formed by high - dose oxygen implantation and high-temperature annealing. To obtain depth profiles of vacancy-type defects, a positron beam in the 0–30keV energy range was used. Doppler broadened annihilation spectrum and positron lifetime were measured as a function of incident positron energy. These measurements show the following results; vacancy -type defects exist near the surface of the top silicon layer even if the specimen was analyzed as defect -free Silicon by XTEM, and in the case of the as-implanted specimen, cavities in diameter of about 50–200A are created in the top silicon layer and they include high pressure gases.
A clear PL spectrum was observed from β-FeSi2 grains on gold (Au)-coated (100)Si substrates, and indicated the formation of crystal with the same high quality level as the β-FeSi2 on a copper (Cu)-coated Si substrate. Moreover, the temperature dependence of photoluminescence peak intensities showed lower density of the nonradiative recombination center in β-FeSi2 grains on Au-coated Si substrates than that of β-FeSi2 film on Cu-coated Si. Au was not detected in β-FeSi2 grains by STEM-EDX observation, while Cu was observed in the grains and grain boundaries of β-FeSi2 and rolled as non-radiative recombination center.
We present new, wide, and deep images in the AzTEC/ASTE 1.1 mm continuum and the 12 CO (J = 1–0) emission toward the northern part of the Orion-A GMC. We have found evidence for interactions between molecular clouds and the external forces that may trigger star formation. Two types of possible triggers were revealed: (1) Collisions of the diffuse gas on the cloud surface, particularly at the eastern side of the OMC-2/3 region, and (2) Irradiation of UV on the pre-existing filaments and dense molecular cloud cores. Our wide-field and high-sensitivity imaging has provided the first comprehensive view of the potential sites of triggered star formation in the Orion-A GMC.
Iron silicide thin films were prepared on silicon (Si) and yittria-stabilized zirconia (YSZ) substrates using RF magnetron sputtering and evaporation methods. Epitaxial b-FeSi2 thin films were grown on (100) and (111) planes of Si and YSZ substrates, while noncrystallized films were deposited on (110) plane of both Si and YSZ substrates. The epitaxial relationships between the b-FeSi2 and YSZ were the same as those between b-FeSi2 and Si, in the case of (100) and (111) planes. It is possible that epitaxial b-FeSi2 film can be grown when substrates and b-FeSi2 surfaces consist of either a single element or only cations, while the crystalline film was not shown when either substrate or b-FeSi2 surface consists of a mixture of anions and cations or iron and silicon.
It is important to control the internal stress of the deposited film because the magnetic tape is becoming thinner for attaining higher recording density per volume. Kr gas was used as the working gas in the facing targets sputtering (FTS) system for depositing Co-Cr films. Kr gas has the larger ionization cross section and atomic mass than those of Ar, Co and Cr, so that Kr gas could make stable discharge at lower pressure and the recoiling of Kr atoms on the surface of the Co-Cr target was more effectively suppressed. Therefore, Kr ions seem to be more advantageous as working gas than Ar ions which are the most common working gas. The FTS method with Kr ions could deposit the stress-free Co-Cr films with good crystallinity. Actually, Δθ50 and (Mr/Ms) of Co79Cr21 films deposited on Si wafer by Kr ion sputtering in the pressure range of 10–4 ∼ 5×10−−5 Torr were as small as 4% and 0.1, respectively. The colpressive stress of 1500Å-thick Co79Cr21 films was as small as 108 dyne/cm2, of which the value was smaller than 10% of that by Ar ion sputtering. Therefore, the combination of the FTS method and Kr gas seems to be very convenient for solving the problem of the internal stress.
Tribological troubles and tape-curling of perpendicular magnetic recording tapes are critical for their practical use. Thin films of a wear resistant and electrically conductive Fe-Mo-B based alloy were prepared on plasma-free tape substrates by the facing targets sputtering (FTS) method for applying them as protective layers in the magnetic tapes. The films were perfectly amorphous, very flexible and almost non-magnetic. The alloy targets for these films contained molybdenum atoms at a concentration as high as 24 at%. The Mo atomic weight is higher than that of working gas atoms Ar and Kr. Accordingly, not only Ar but also Kr atoms were recoiled from the target planes and then bombarded the growing layers to cause large compressive stress in the deposited films. Therefore, these protective films must be very thin to avoid tape-curling. Protective films as thin as 100 Å could largely reduce the dynamical friction coefficients of the surfaces of magnetic tapes owing to the hardness of their ceramic phase. In addition to this merit they possessed electrical resistivity as small as 1.2×10-4 Ω·cm. owing to their metallic binder phase. Consequently they are applicable as protective layers of curl-free magnetic tapes.
The production of foamed aluminum has long been considered difficult to realize because of such problems as the low foamability of molten metal, the varying size of cellular structures, solidification shrinkage and so on. Recently these problems have been solved by a number of researches and some manufacturers produce foamed aluminum by their own methods. We have been employing a batch casting process and manufacturing foamed aluminum under the tradename ALPORAS® since 1986. This paper presents the manufacturing process, physical properties and some typical applications of ALPORAS.
TiN films deposited by CVD utilizing TiCl4 and NH3 are widely used in ULSI processes. The residual chlorine in the film is one of the major issues of TiCl4 based chemistry [1–5]. We have examined the kinetics of TiN-CVD using TiCl4 and NH3 as precursors to determine method for controlling the residual chlorine concentration.
We analyzed the deposition rate profiles obtained from a simple tubular isothermal reactor. Deposition was performed over the temperature range from 300°C to 500°C and with varying initial concentrations of TiCl4 and NH3. We found that the deposition rate was independent of the TiCl4 concentration at higher concentrations. The deposition rate was proportional to the TiCl4 concentration in the low concentration range. This phenomenon can be well explained by a Langmuir-Hinshelwood type mechanism. Examination of the deposition rate dependence on the concentration of NH3 showed that both the maximum deposition rate at high TiCl4 concentrations and the first order kinetic rate constant in the lower TiCl4 concentration range were proportional to the NH3 concentration. These results indicate that the deposition was controlled by the Eley-Rideal mechanism. The residual chlorine concentration was found to be proportional to the surface coverage factor of adsorbed TiCl4. We conclude that the best way to obtain good quality TiN films can be obtained theoretically through these kinetic studies.
Migration of protons dissolved in acceptor doped SrZrO3, SrCeO3 and BaCeO3 oxides has been examined under an applied electric potential over a range of temperature from 25 to 220°C. Protons which dissolved in these oxides migrated to the cathode, and they were trapped there when the cathode material had a good ability to getter the migrating hydrogen. The amount of hydrogen accumulated in the cathode could be measured by the ERDA method using a highenergy 4He beam. We measured the amount of hydrogen in the cathode while monitoring the dc current passed through the oxide specimen. The proton transport number was determined from the ratio of the number of hydrogen in the cathode to the total numbers of charge through the specimen. The diffusion coefficient of proton was evaluated using the proton transport number and proton concentration in the specimen.
We have deposited carbon nitride (CNx) films by magnetron sputtering at varying nitrogen pressures and substrate temperatures. The films were deposited on silicon and quartz substrates simultaneously. The incoming ion energy was controlled by a radio frequency power supply. A magnet in front of the substrate holder was used to enhance the plasma density. The films deposited at room temperature (RT) were found to have nitrogen content of ≥ 40%. These films were semiconducting with an optical bandgap of greater than 2 eV and a RT resistivity of 1012 Ω-cm. Films deposited at low nitrogen pressure (< 7 mtorr), at RT and in the presence of a 15 mtesla magnetic field were found to be hard and also exhibited extremely high elastic recovery. The most interesting result we found was that the hard and elastic CN films were also semiconducting with an optical band gap of 1.7 eV, RT resistivity of 107 Ω-cm and an activation energy of 0.8 eV. In all cases the CN films were almost entirely sp2 bonded.