| 1. |
- Cheng, Zhaowei, et al.
(författare)
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Using deep learning to accelerate magnetic resonance measurements of molecular exchange
- 2023
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 159:5
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Tidskriftsartikel (refereegranskat)abstract
- Real-time monitoring and quantitative measurement of molecular exchange between different microdomains are useful to characterize the local dynamics in porous media and biomedical applications of magnetic resonance. Diffusion exchange spectroscopy (DEXSY) is a noninvasive technique for such measurements. However, its application is largely limited by the involved long acquisition time and complex parameter estimation. In this study, we introduce a physics-guided deep neural network that accelerates DEXSY acquisition in a data-driven manner. The proposed method combines sampling pattern optimization and physical parameter estimation into a unified framework. Comprehensive simulations and experiments based on a two-site exchange system are conducted to demonstrate this new sampling optimization method in terms of accuracy, repeatability, and efficiency. This general framework can be adapted for other molecular exchange magnetic resonance measurements.
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| 2. |
- Han, SongTao, et al.
(författare)
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Fringe fitting and group delay determination for geodetic VLBI observations of DOR tones
- 2019
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Ingår i: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 63:5, s. 1754-1767
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Tidskriftsartikel (refereegranskat)abstract
- Extracting the group and phase delays of interferometric observations produced in the Very Long Baseline Interferometry (VLBI) measurement concept requires a special fringe fitting and delay search algorithm for the recorded bandwidth. While fringe fitting is in use routinely for several megahertz wide channels in geodetic and astrometric VLBI with quasar observations, fringe fitting for artificial tones of very small bandwidth of artificial signals for Differential One-way Ranging (DOR) requires a different way of handling. In a project called Observing the Chang’E-3 Lander with VLBI (OCEL), the DOR tones emitted by the Chang’E-3 lander were observed in a standard geodetic VLBI mode with 8 or 4 MHz wide channels to maintain compatibility with the corresponding quasar observations. For these observations, we modified the existing fringe fitting program of the Haystack Observatory Processing Software (HOPS), fourfit, to properly handle narrow band DOR tones. The main motivations are that through this modification, the data of quasars and artificial radio sources can be processed in the existing geodetic analysis pipeline, and that the algorithm can be used for similar projects as well. In this paper, we describe the algorithm and show that the new algorithm produces much more reliable group delay results than using the standard fourfitalgorithm. This is done by a simulation test and in particular by processing of real observations. It is shown that in many cases, systematic deviations of several nanoseconds, which are seen with the standard fourfit algorithm, can be avoided. The ultimate benefit of the new procedure is demonstrated by reducing the errors in delay triangle closures by at least a factor of 3, which, in the OCEL case, is from ∼300 to ∼100 ps.
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| 3. |
- Klopotek, Grzegorz, 1990, et al.
(författare)
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Position determination of the Chang’e 3 lander with geodetic VLBI
- 2019
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Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 71:1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We present results from the analysis of observations of the Chang’e 3 lander using geodetic Very Long Baseline Interferometry. The applied processing strategy as well as the limiting factors to our approach is discussed. We highlight the current precision of such observations and the accuracy of the estimated lunar-based parameters, i.e., the lunar lander’s Moon-fixed coordinates. Our result for the position of the lander is 44.1219 3 ∘ N , -19.51159∘E and -2637.3 m, with horizontal position uncertainties on the lunar surface of 8.9 m and 4.5 m in latitude and longitude, respectively. This result is in good agreement with the position derived from images taken by the Narrow Angle Camera of the Lunar Reconnaissance Orbiter. Finally, we discuss potential improvements to our approach, which could be used to apply the presented concept to high-precision lunar positioning and studies of the Moon.[Figure not available: see fulltext.].
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| 4. |
- Luo, Lei, et al.
(författare)
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Convergence angle and dimple shape effects on the heat transfer characteristics in a rotating dimple-pin fin wedge duct
- 2019
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 74:10, s. 1611-1635
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Tidskriftsartikel (refereegranskat)abstract
- A numerical method is employed to study effects of convergence angle and dimple shape on flow structure and heat transfer under a rotating frame. The investigated convergence angles are 0.0°, 6.3°, and 12.7°. The dimple shapes are circular, streamwise-elliptical, and spanwise-elliptical. The rotation number ranges from 0.0 to 0.4. Computed flow structures and heat transfer are compared. Higher rotation number generates better heat transfer in the dimple-pin wedge duct. The rotation direction also affects the flow structure and heat transfer. The spanwise-elliptical dimple shape shows best heat transfer augmentation as it generates the strongest vortex structure and turbulent kinetic energy in the dimples. Larger convergence angles exhibit larger Nusselt numbers and better heat transfer enhancement. Effects of the Coriolis force are considered as this force has favorable effects on enhancing the heat transfer on the surface it acts on.
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| 5. |
- Sun, Jing, et al.
(författare)
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VLBI observations to the APOD satellite
- 2018
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Ingår i: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 61:3, s. 823-829
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Tidskriftsartikel (refereegranskat)abstract
- The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10 cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1 s integration time of the correlator output is on the level of 0.1 ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype.
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| 6. |
- Wang, Songtao, et al.
(författare)
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Heat transfer characteristics of a dimpled/protrusioned pin fin wedge duct with different converging angles for turbine blades
- 2019
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Ingår i: Numerical Heat Transfer; Part A: Applications. - : Informa UK Limited. - 1040-7782 .- 1521-0634. ; 76:5, s. 369-392
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Tidskriftsartikel (refereegranskat)abstract
- A numerical method is utilized to investigate the converging angle effects on the flow structure and heat transfer of a pin fin wedge duct with dimples/protrusions. The studied converging angles are 0:0°; 6:3°; and 12:7° The results show that a pin fin-dimple wedge duct with larger converging angle produces higher heat transfer enhancement due to flow acceleration, increase of the impingement region, and shrinkage of the flow recirculation region, but it is also accompanied with a much larger friction factor. A pin fin-protrusion wedge duct with larger converging angle yields higher heat transfer augmentation due to flow acceleration and more intense impingement on the protrusion but it is also associated with larger pressure penalty.
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| 7. |
- Yan, Han, et al.
(författare)
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Flow structure and heat transfer characteristics in a ribbed two-pass channel with varying divider inclination angle
- 2021
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Ingår i: International Journal of Thermal Sciences. - : Elsevier BV. - 1290-0729. ; 166
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Tidskriftsartikel (refereegranskat)abstract
- A numerical method is utilized in this paper to study the effects of varying divider inclination angle on the flow structure and heat transfer characteristics in a ribbed two-pass channel for Reynolds number varying from 10,000 to 50,000. The studied divider inclination angles are −3°,−2°,−1°,0°, +1°, +2° and +3°. The ribs have an orientating angle of 45°. The results show that the heat transfer in the bend region and in the passage upstream the bend is enhanced significantly and the heat transfer in the passage downstream the bend is reduced compared to a channel with a straight divider wall as the divider wall inclination angle varies from −3° to +3°. Channels with inclined divider wall produce higher pressure drop and friction factors than a channel with straight divider wall. According to the results, a channel with −1° inclined divider shows the best thermal performance among all the channels investigated. The flow structure and heat transfer characteristics for all the channels are depicted in detail and discussed in this study.
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| 8. |
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