scholarly journals Dual-high-frequency VLBI study of blazar-jet brightness-temperature gradients and collimation profiles

2021 ◽  
Author(s):  
P. R. Burd ◽  
M. Kadler ◽  
K. Mannheim ◽  
A.-K. Back ◽  
J. Ringholz ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
High Frequency ◽  
Temperature Gradients

Thermal Fatigue Evaluation Method Based on Power Spectrum Density Functions Against Fluid Temperature Fluctuation

2005 ◽  
Author(s):  
Naoto Kasahara ◽  
Nobuyuki Kimura ◽  
Hideki Kamide
Keyword(s):  
Thermal Stress ◽  
Power Spectrum ◽  
High Frequency ◽  
Thermal Stresses ◽  
Evaluation Method ◽  
Power Spectrum Density ◽  
Temperature Gradients ◽  
Fluid Temperature ◽  
Spectrum Density ◽  
Fatigue Evaluation

Fluid temperature fluctuates at an incomplete mixing area of high and low temperature fluids in nuclear components. It induces random variations of local temperature gradients in structural walls, which lead to cyclic thermal stresses. When thermal stresses and cycle numbers are large, there are possibilities of fatigue crack initiations and propagations. It is recognized that there are attenuation factors depending on fluctuation frequency in the transfer process from fluid temperature to thermal stresses. If a frequency of fluctuation is very low, whole temperature of the wall can respond to fluid temperature, because thermal diffusivity homogenizes structural temperature. Therefore, low frequency fluctuations do not induce large thermal stress due to temperature gradients in structures. On the other hand, a wall surface cannot respond to very high frequency fluctuation, since a structure has a time constant of thermal response. High frequency fluctuations do not lead to large thermal stress. Paying attention to its attenuation mechanism, Japan Nuclear Cycle Development Institute (JNC) has proposed a fatigue evaluation method related to frequencies. The first step of this method is an evaluation of Power Spectrum Density (PSD) on fluid, from design specifications such as flow rates, diameters of pipes and materials. In the next step, the PSD of fluid is converted to PSD of thermal stress by the frequency transfer function. Finally, the PSD of thermal stress is transformed to time history of stress under an assumption of random phase. Fatigue damage factors can be evaluated from stress ranges and cycles obtained by the rain flow wave count method. Proposed method was applied to evaluate fatigue damage of piping junction model tests conducted at Oarai Engineering Center. Through comparison with direct evaluation from measurements and predictions by conventional methods, the accuracy of the proposed method was validated.

Measured Variation of High Frequency Sound Absorption in Porous Metals Subject to Changes in Temperature and Temperature Gradient

2013 ◽  
Author(s):  
Weihua Chen ◽  
Tianning Chen ◽  
Xiaopeng Wang ◽  
Zhiping Ying
Keyword(s):  
Temperature Gradient ◽  
High Frequency ◽  
Sound Absorption ◽  
Porous Metal ◽  
Temperature Gradients ◽  
High Frequency Range ◽  
Frequency Range ◽  
Porous Metals ◽  
Testing Module ◽  
Peak Value

Porous metal, as a new acoustic material, bears the general metal properties, such as good conductivity, ductibility, heat transfer and high specific stiffness and intensity, and meanwhile exhibits good performance in sound absorption. Thus, it enjoys a growing popularity in industrial and civilian sound-absorbing applications where non-metallic materials are impracticable. Therefore it is of great significance to explore the sound-absorption properties of porous metals. The existing studies mainly focus on the low frequency range and are under uniform temperature assumption. In this paper, an experimental setup was built up to investigate the sound absorption of porous metals subject to temperature gradients, and much concern was paid to that of high frequency range. The setup is composed of five modules: I. heating module; II. cooling module; III. temperature controlling & testing module; IV. spectrum analyzer and V. impedance tube testing module. Based on this setup, the sound absorption of a hard-backed porous metal in a high-frequency range (2000–4000Hz)and under different temperature gradients (+2°C/mm, +4°C/mm and +6°C/mm) are measured, and results show that: 1) The sound absorption of porous metal is significantly influenced by temperature gradients; 2) The peak of sound absorption curve moves to a higher frequency range as the temperature gradient increases in the frequency range 2000∼4000Hz but the peak value decreases slightly; 3) The peak value of sound absorption curve enlarges as the temperature gradient increases but the frequency of peak value is fixed.

scholarly journals Microwave signatures of ice hydrometeors from ground-based observations above Summit, Greenland

2015 ◽  
Vol 15 (23) ◽  
pp. 34497-34532
Author(s):  
C. Pettersen ◽  
R. Bennartz ◽  
M. S. Kulie ◽  
A. J. Merrelli ◽  
M. D. Shupe ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Temperature Difference ◽  
Liquid Water ◽  
High Frequency ◽  
Passive Microwave ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Cloud Radar ◽  
Brightness Temperatures ◽  
High Frequency Microwave

Abstract. Multi-instrument, ground-based measurements provide unique and comprehensive datasets of the atmosphere for a specific location over long periods of time and resulting data compliments past and existing global satellite observations. This paper explores the effect of ice hydrometeors on ground-based, high frequency passive microwave measurements and attempts to isolate an ice signature for summer seasons at Summit, Greenland from 2010–2013. Data from a combination of passive microwave, cloud radar, radiosonde, and ceilometer were examined to isolate the ice signature at microwave wavelengths. By limiting the study to a cloud liquid water path of 40 g m−2 or less, the cloud radar can identify cases where the precipitation was dominated by ice. These cases were examined using liquid water and gas microwave absorption models, and brightness temperatures were calculated for the high frequency microwave channels: 90, 150, and 225 GHz. By comparing the measured brightness temperatures from the microwave radiometers and the calculated brightness temperature using only gas and liquid contributions, any residual brightness temperature difference is due to emission and scattering of microwave radiation from the ice hydrometeors in the column. The ice signature in the 90, 150, and 225 GHz channels for the Summit Station summer months was isolated. This measured ice signature was then compared to an equivalent brightness temperature difference calculated with a radiative transfer model including microwave single scattering properties for several ice habits. Initial model results compare well against the four years of summer season isolated ice signature in the high-frequency microwave channels.

scholarly journals Solutions for thermally mismatched brazing operations for ceramic tokamak magnetic sensor

2016 ◽  
Vol 2016 (CICMT) ◽  
pp. 000058-000063 ◽  
Author(s):  
Caroline Jacq ◽  
Thomas Maeder ◽  
Benoit R. Ellenrieder ◽  
Philipp Windischhofer ◽  
Xinyue Jiang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Thermal Stability ◽  
Low Temperature ◽  
High Frequency ◽  
Thermal Stresses ◽  
Magnetic Sensor ◽  
Temperature Gradients ◽  
Ceramic Technology ◽  
Vacuum Vessel ◽  
Main Substrate

Abstract To monitor high-frequency fluctuations of the equilibrium magnetic field in tokamaks, a 3D magnetic sensor has been developed. The sensor, which is positioned inside the vacuum vessel behind the protective tiles of the tokamak and is exposed to potential temperatures up to 400°C, is based on thick-film and LTCC (low-temperature co-fired ceramic) technology. To connect the sensor to the cabling that runs inside the vacuum vessel, mineral-insulated cables have to be brazed to the sensor to ensure electrical connection together with mechanical robustness and sufficient thermal stability. As the brazing temperature is about 600°C, direct brazing to the alumina sensor substrate can cause failure by cracking induced by thermal stresses. It arises both by temperature gradients stemming from the localised heating and by the high thermal mismatch of alumina with the braze and wire materials. In previous work, high stresses from temperature gradients were efficiently decoupled by brazing indirectly to alumina beams attached to the main substrate, and local thermal stresses between alumina and braze/wire by using a porous metallisation. However, as the slender alumina beams protruding out of the substrate are somewhat cumbersome and fragile, three alternatives were studied in the present work: 1) testing shorter and more robust beams, 2) replacing the alumina beam by a silver wire, and 3) depositing a porous temperature- and stress-decoupling dielectric to enable direct brazing on the main alumina substrate. These solutions are characterised with respect to their mechanical robustness and of the degree of thermal decoupling with the substrate they provide.

scholarly journals Combined Radiometer–Radar Microphysical Profile Estimations with Emphasis on High-Frequency Brightness Temperature Observations

2003 ◽  
Vol 42 (4) ◽  
pp. 476-487 ◽  
Author(s):  
Gail M. Skofronick-Jackson ◽  
James R. Wang ◽  
Gerald M. Heymsfield ◽  
Robbie Hood ◽  
Will Manning ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
High Frequency ◽  
Temperature Observations

Jupiter's Temperate Belt/Zone Contrasts at Depth Revealed By Juno

2020 ◽  
Author(s):  
Leigh N. Fletcher ◽  
Fabiano Oyafuso ◽  
Michael Allison ◽  
Andrew Ingersoll ◽  
Liming Li ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Negative Correlation ◽  
Temperature Gradients ◽  
Kinetic Temperature ◽  
Zone Structure ◽  
Strong Negative Correlation ◽  
Zonal Flows ◽  
Upper Troposphere ◽  
Zonal Winds ◽  
California Institute Of Technology

<p><strong>Introduction:</strong>  The locations of Jupiter’s cloud-top east-west jets are relatively constant over time and define the cyclonic belts and their neighbouring anticyclonic zones.  Thermal-infrared observations of the upper troposphere reveal cool temperatures, elevated abundances of condensate and disequilibrium gases, and enhanced cloud opacity over the zones, and the opposite over the belts (Gierasch et al., 1986, doi:10.1016/0019-1035(86)90125-9).  This distribution implies upwelling motions in zones and subsidence in belts. However, this picture has been called into question by the observed eddy-momentum flux convergence into the eastward jets (and divergence from the westward jets), which suggests a compensating flow in the opposite direction, from belts into zones, which is partially supported by the distribution of lightning at low latitudes (Little et al., 1999, doi:10.1006/icar.1999.6195).  It is possible that two different atmospheric regimes exist:  a deep regime where eddies are able to drive the zonal flows, and a higher-altitude regime where those zonal flows decay with height. Reconciling this apparent inconsistency remains a key challenge for the understanding of Jupiter’s atmosphere, and Juno observations of the deeper atmosphere shed important light on this issue. </p> <p><strong>Methodology:</strong>  Juno’s Microwave Radiometer (MWR) examines the vertical structure of Jupiter’s belts and zones below the clouds by sounding in six channels from 1.4 to 50 cm, sensing from the cloud-tops at ~0.7 bar to pressures greater than 300 bar. Initial results (Li et al. 2017, doi:10.1002/2017GL073159) revealed contrasts at depth that bore a potential resemblance to the belt/zone structure in the upper troposphere.  We report on progress in our analysis of averaged nadir microwave brightness and its emission-angle dependence from the first two years of Juno’s mission.  We investigate the correlation between the meridional gradient of the brightness temperature at all emission angles and the cloud-top zonal winds.  These brightness temperature gradients reflect changes in gaseous opacity (e.g., ammonia and water), kinetic temperature, or both. We explore the implications of the contrasts observed between belts and zones as a function of depth sounded by MWR.</p> <p><strong>Preliminary Results:</strong>  Meridional brightness temperature gradients above the clouds (p<1 bar) were measured by the VLT/VISIR mid-infrared instrument in 2016, alongside the 1.37-cm MWR channel sensing temperatures and ammonia at p~0.7 bar. The gradients show a strong negative correlation with the cloud-tracked zonal winds and suggest a combination of zonal jet decay with altitude in the upper troposphere (e.g., Pirraglia et al., 1981, doi:10.1038/292677a0), along with depletion of volatiles (ammonia) within cyclonic belts.  MWR observations suggest that this negative correlation persists as deep as ~1.5 – 3.5 bar for both the tropical and temperate jets.  For the strong eastward jet near 6<sup>o</sup>N, this is broadly consistent with results from both the Galileo Probe (Atkinson et al., 1998, doi:10.1029/98JE00060) and Cassini cloud-tracking (Li et al., 2006, doi:10.1029/2005JE002556), which suggested that the jet decayed with height from the ~5-bar level to the 0.5-bar level by more than 90 m/s.  We will report on our initial exploration of how these correlations change at deeper pressure levels by looking at MWR wavelengths beyond 10 cm, probing well below the expected condensation level of Jupiter’s water clouds.</p> <p><strong>Acknowledgements:</strong>  Fletcher was supported by a Royal Society Research Fellowship and European Research Council Consolidator Grant (under the European Union's Horizon 2020 research and innovation programme, grant agreement No 723890) at the University of Leicester.  Levin, Orton, and Oyafuso were supported by the National Aeronautics and Space Administration through funds distributed to the Jet Propulsion Laboratory, California Institute of Technology.</p>

scholarly journals The Linear Polarization of Radiation from Jupiter at 6 cm Wavelength

1968 ◽  
Vol 21 (3) ◽  
pp. 337 ◽  
Author(s):  
D Morris ◽  
JB Whiteoak ◽  
F Tonking
Keyword(s):  
Synchrotron Radiation ◽  
Brightness Temperature ◽  
Linear Polarization ◽  
High Frequency ◽  
Central Meridian ◽  
Thermal Component ◽  
Nonthermal Radiation ◽  
Polarization Of Radiation ◽  
The Mean ◽  
Direction Of Polarization

At a wavelength of 6 cm the degree of linear polarization of the radiation from Jupiter is 0�076�0�002. The variation of the direction of polarization with longitude of the central meridian is consistent with the increased period of rotation determined by Komesaroff and McCulloch (1967). There is evidence of an asymmetricl beaming of the nonthermal radiation with longitude in addition to the latitude asymmetry that was detected previously by Roberts and Komesaroff (1965). The mean flux density normalized to a distance of 4�04 a.u. is 1O�7�0�2 f.u. The small nonthermal contribution (3'7 f.u.) is further evidence for a high frequency cutoff in the synchrotron radiation; the thermal component corresponds to a brightness temperature of about 250oK.

Spatial and temporal analysis of high-frequency internal gravity wave signatures in brightness temperature satellite images

2021 ◽  
Author(s):  
Robert Vicari
Keyword(s):  
Water Vapor ◽  
Brightness Temperature ◽  
Gravity Wave ◽  
Gravity Waves ◽  
High Frequency ◽  
Satellite Images ◽  
Internal Gravity Wave ◽  
Internal Gravity Waves ◽  
Small Scale ◽  
Wave Patterns

<p>Highly idealized model studies suggest that convectively generated internal gravity waves in the troposphere with horizontal wavelengths on the order of a few kilometers may affect the lifetime, spacing, and depth of clouds and convection. To answer whether such a convection-wave coupling occurs in the real atmosphere, one needs to find corresponding events in observations. In general, the study of high-frequency internal gravity wave-related phenomena in the troposphere is a challenging task because they are usually small-scale and intermittent. To overcome case-by-case studies, it is desirable to have an automatic method to analyze as much data as possible and provide enough independent and diverse evidence.<br>Here, we focus on brightness temperature satellite images, in particular so-called satellite water vapor channels. These channels measure the radiation at wavelengths corresponding to the energy emitted by water vapor and provide cloud-independent observations of internal gravity waves, in contrast to visible and other infrared satellite channels where one relies on the wave impacts on clouds. In addition, since these water vapor channels are sensitive to certain vertical layers in the troposphere, combining the images also reveals some vertical structure of the observed waves.<br>We propose an algorithm based on local Fourier analyses to extract information about high-frequency wave patterns in given brightness temperature images. This method allows automatic detection and analysis of many wave patterns in a given domain at once, resulting in a climatology that provides an initial observational basis for further research. Using data from the instrument ABI on board the satellite GOES-16 during the field campaign EUREC<sup>4</sup>A, we demonstrate the capabilities and limitations of the method. Furthermore, we present the respective climatology of the detected waves and discuss approaches based on this to address the initial question.</p>

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