| 1. |
- Morokuma, Tomoki, et al.
(författare)
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OISTER optical and near-infrared monitoring observations of peculiar radio-loud active galactic nucleus SDSSJ110006.07+442144.3
- 2017
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Ingår i: Nippon Tenmon Gakkai obun kenkyu hokoku. - : Oxford University Press (OUP). - 0004-6264. ; 69:5
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Tidskriftsartikel (refereegranskat)abstract
- We present monitoring campaign observations at optical and near-infrared (NIR) wavelengths for a radio-loud active galactic nucleus (AGN) at z = 0.840, SDSSJ110006.07+442144.3 (hereafter, J1100+4421), which was identified during a flare phase in late 2014 February. The campaigns consist of three intensive observing runs from the discovery to 2015 March, mostly within the scheme of the OISTER collaboration. Optical-NIR light curves and simultaneous spectral energy distributions (SEDs) are obtained. Our measurements show the strongest brightening in 2015 March. We found that the optical-NIR SEDs of J1100+4421 show an almost steady shape despite the large and rapid intranight variability. This constant SED shape is confirmed to extend to similar to 5 mu m in the observed frame using the archival WISE data. Given the lack of absorption lines and the steep power-law spectrum of alpha(upsilon) similar to -1.4, where f(v) proportional to v(alpha upsilon), synchrotron radiation by a relativistic jet with no or small contributions from the host galaxy and the accretion disk seemsmost plausible as an optical-NIR emission mechanism. The steep optical-NIR spectral shape and the large amplitude of variability are consistent with this object being a low.peak jet-dominated AGN. In addition, sub-arcsecond resolution optical imaging data taken with Subaru Hyper Suprime-Cam does not show a clear extended component and the spatial scales are significantly smaller than the large extensions detected at radio wavelengths. The optical spectrum of a possible faint companion galaxy does not show any emission lines at the same redshift, and hence a merging hypothesis for this AGN-related activity is not supported by our observations.
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| 2. |
- Bevilacqua, Stella, 1981, et al.
(författare)
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Characterisation and Modeling of MgB2 HEBs IF impedance
- 2016
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Ingår i: Swedish Microwave Days March 15-16, 2016, Linköping, Sweden. ; , s. 55-
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Konferensbidrag (refereegranskat)abstract
- Here we present the method which allows to measure quiteaccurately the HEB impedance employing just one cooling.By knowing the HEB IF impedance a coupling matchingnetwork can be designed for a possible packaged receiver.
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| 3. |
- Bevilacqua, Stella, 1981, et al.
(författare)
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MgB2 Hot-Electron Bolometer Mixers at Terahertz Frequencies
- 2015
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 25:3, s. 2301104-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we compare the performance of MgB2 Hot-Electron Bolometer Mixers operating at Local Oscillator frequencies of 0.6 and 1.63 THz. The minimum noise temperatures that were obtained are 700 and 1150 K for 0.6 and 1.63 THz, respectively. The receiver noise bandwidth is of the order of 2.2-3 GHz for 10-nm-thick HEB devices with a Tc of 8.5 K. Sub-micrometer size HEBs were also fabricated with no degradation of the initial film quality when a 20-nm MgB2 film with a Tc of 22 K was used. In the direct detection mode, the maximum voltage responsivity is in the range of 1-2 kV/W at 1.63 THz and the optimal bias current is around 1/4-1/3 of the Ic at 4.2 K.
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| 4. |
- Bevilacqua, Stella, 1981, et al.
(författare)
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Wideband MgB2 Hot-Electron Bolometer Mixers: IF Impedance Characterisation and Modeling
- 2016
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 26:3, s. 2300105-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a method for low signal S11 parameter vector measurements of a cryogenic device in the microwave frequency range. In particular, the intermediate frequency (IF) impedance of MgB2 Hot-electron Bolometer (HEB) mixers was investigated over a frequency range of 100 MHz to 10 GHz. A new cryogenic calibration technique, which employs the HEB as a calibration kitandrequires two consecutive thermal cycles, was developed for this purpose.The real part of measured IF impedance showed a strong correlationwith the differential resistance (dV/dI) obtained from the dc I-V curves while the imaginary partwas capacitive for almost the entire frequency range.
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| 5. |
- Cherednichenko, Serguei, 1970, et al.
(författare)
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Study of MgB2 HEB mixers vs the LO frequency and the bath temperature
- 2015
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Ingår i: 26th International Symposium on Space Terahertz Technology March 16-18, 2015, Cambridge, United States. ; , s. M2-1
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Konferensbidrag (refereegranskat)abstract
- We investigate the noise and the gain of MgB2 Hot-Electron Bolometer (HEB) mixers at 1.63THz LO. The critical temperature of the HEB was 22K and the film thickness was 20nm. At 4.2K and 12K bath temperatures the lowest obtained receiver noise temperatures are 1700K and 2100K,respectively, with a noise bandwidth of about 4.6GHz. The gain bandwidth is about 3GHz in both cases.
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| 6. |
- Mu, Wangzhong, et al.
(författare)
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Combination of in situ microscopy and calorimetry to study austenite decomposition in inclusion engineered steels
- 2015
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Ingår i: Steel Research International. - : Wiley-VCH Verlagsgesellschaft. - 1611-3683 .- 1869-344X.
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Tidskriftsartikel (refereegranskat)abstract
- In situ high-temperature confocal laser scanning microscopy and differential scanning calorimetry studies of ferrite formation in inclusion engineered (Ti2O3 and TiN) steels have been performed. The applied methodology allows distinction between intragranular ferrite, grain boundary ferrite, and pearlite. The effect of the inclusions and cooling rates on the initiation of phase transformation and the final microstructure is discussed. It is concluded that the applied hybrid methodology could provide vital details of solid-state phase transformations within the field of inclusion engineering.
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| 7. |
- Mu, Wangzhong, et al.
(författare)
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High-Temperature Confocal Laser Scanning Microscopy Studies of Ferrite Formation in Inclusion-Engineered Steels : A Review
- 2018
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Ingår i: JOM. - : Springer. - 1047-4838 .- 1543-1851. ; 70:10, s. 2283-2295
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Forskningsöversikt (refereegranskat)abstract
- The concepts of oxide metallurgy and inclusion engineering can be utilized to improve the properties of low-alloy steels. These concepts aim at controlling the formation of intragranular ferrite (IGF), often a desirable microstructure providing good mechanical properties without the need for expensive alloying elements. IGF formation is stimulated to occur at non-metallic inclusions and form an arrangement of fine, interlocking ferrite grains. A method that has contributed significantly to investigations in this field lately is high-temperature confocal laser scanning microscopy (HT-CLSM). HT-CLSM is suited for in situ studies of inclusion behavior in liquid steel and phase transformations in solid-state steel, where in particular, displacive phase transformations can be studied, since they provide sufficient topographic contrast. The purpose of the present report is to provide a brief review of the state of the art of HT-CLSM and its application for in situ observations of ferrite formation in inclusion-engineered steels. The scientific literature in this field is surveyed and supplemented by new work to reveal the capability of HT-CLSM as well as to discuss the effect of factors such as cooling rate and parent grain size on IGF formation and growth kinetics. The report concludes with an outlook on the opportunities and challenges of HT-CLSM for applications in oxide metallurgy.
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| 8. |
- Novoselov, Evgenii, 1988, et al.
(författare)
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Effect of the Critical and Operational Temperatures on the Sensitivity of MgB2 HEB Mixers
- 2016
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 6:2, s. 238-277
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a study of the noise and thegain of MgB hot-electron bolometer mixers with different critical temperatures and at various operation temperatures. At a local oscillator (LO) frequency of 1.63 THz the minimum input receiver noise temperature was 700 K with a gain of 18 dB for a device with a of 8.5 K. For a device with a of 22.5 K the corresponding values were 1700 K and 19 dB. For the latter device the was 2150 K at a bath temperature of 12 K, which is not achievable with Nb-compound based HEB mixers. We present and compare different methods for measurements of the HEB mixer gain and the output noise.
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| 9. |
- Novoselov, Evgenii, 1988, et al.
(författare)
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Noise measurements of the low Tc MgB2 HEB mixer at 1.6THz and 2.6THz
- 2015
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Ingår i: 26th International Symposium on Space Terahertz Technology March 16-18, 2015, Cambridge, United States. ; , s. P-31
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Konferensbidrag (refereegranskat)abstract
- We present results on MgB2 hot-electron bolometer noise measurements to show reproducibility of achieved results and robustness of the fabricated devices, which being passivated with silicon nitride shows the same performance after 1.5 year storing in nitrogen atmosphere. Noise temperature measurements were performed for the HEB made of 10nm MgB2 thin film on Al2O3 with Tc of 8.5K for 1.6THz LO at 2.7K and 4.2K. The minimum double side band noise temperatures corrected for optical losses for different bath temperatures were 700K and 1150K, whereas the noise bandwidth was 3.2GHz and 3.5GHz, respectively. The mixer output noise temperature and the conversion gain were 26K and -17.7dB, 27K and -14.9dB, respectively. For 2.6THz LO at 2.7K the corresponding values are 1200K and 3.7GHz.
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| 10. |
- Novoselov, Evgenii, 1988, et al.
(författare)
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THz Low Noise Mixers for Sub-mm Astronomy
- 2016
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Ingår i: Swedish Microwave Days March 15-16, 2016, Linköping, Sweden. ; , s. 50-
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Konferensbidrag (refereegranskat)abstract
- In this work we demonstrate that the MgB2 HEB mixer with a Tc of 22K can operate above 12K with just a 25% increase ofthe receiver noise temperature compared to that at 4.2 K. The GBW of 3.5 GHz was archived with a relatively thick film (a typical film thickness for NbN HEB mixers is 3–5 nm).
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