| 1. |
- Gong, Hanmo, et al.
(författare)
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Gold nanoparticle transfer through photothermal effects in a metamaterial absorber by nanosecond laser
- 2014
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 6080-
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Tidskriftsartikel (refereegranskat)abstract
- A non-complicated, controllable method of metallic nanoparticle fabrication at low operating light power is proposed. The method is based on laser-induced forward transfer, using a metamaterial absorber as the donor to significantly enhance the photothermal effect and reduce the operating light fluence to 35 mJ/cm(2), which is much lower than that in previous works. A large number of metallic nanoparticles can be transferred by one shot of focused nanosecond laser pulses. Transferred nanoparticles exhibit good size uniformity and the sizes are controllable. The optical properties of transferred particles are characterized by dark-field spectroscopy and the experimental results agree with the simulation results.
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| 2. |
- Chen, Fu qiang, et al.
(författare)
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Turbulent compressible flow analysis on multi-stage high pressure reducing valve
- 2018
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Ingår i: Flow Measurement and Instrumentation. - : Elsevier BV. - 0955-5986. ; 61, s. 26-37
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Tidskriftsartikel (refereegranskat)abstract
- Pressure reducing valve plays an important role in thermodynamic systems. Under extreme operating conditions, greater demands are requested on pressure reducing systems. In this paper, a novel multi-stage high pressure reducing valve (MSHPRV) is proposed, which can achieve multi-stage pressure reducing processes, improve the flow characteristics and deal with complex conditions. Here, the effects of different structural parameters on turbulent compressible flow inside MSHPRV are numerically investigated to achieve low valve noise and energy consumption. Mach number is taken as the parameter to reflect the fluid compressibility. Higher Mach number can cause serious aerodynamic noise and large amount of energy consumption. Based on this, transmission loss of MSHPRV is also studied to achieve better noise control performances. Meanwhile, larger turbulent dissipation rate means larger degree of energy consumption, so it is with the exergy loss. Thus, numerical models with different valve openings, perforated plate diameters, chamfer radii of perforated plates, pressure ratios and stages of perforated plates are established, and the effects of these structural parameters on the compressible turbulent flow and energy consumption of MSHPRV are investigated. Results show that different structural parameters have significant impacts on compressible turbulent flow and energy consumption performance in MSHPRV. The best noise control and least energy consumption of MSHPRV is achieved with such parameters as pressure ratio 7, perforated plate diameter 4 mm and 4 stage plates. This work can benefit the further research work on energy saving and multi-stage design of pressure reducing devices.
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| 3. |
- Lu, R.S., et al.
(författare)
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A ring-like accretion structure in M87 connecting its black hole and jet
- 2023
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 616:7958, s. 686-690
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Tidskriftsartikel (refereegranskat)abstract
- The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation1,2. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted as gravitationally lensed emission around a central black hole3. Here we report images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High-resolution imaging shows a ring-like structure of [Formula: see text] Schwarzschild radii in diameter, approximately 50% larger than that seen at 1.3 mm. The outer edge at 3.5 mm is also larger than that at 1.3 mm. This larger and thicker ring indicates a substantial contribution from the accretion flow with absorption effects, in addition to the gravitationally lensed ring-like emission. The images show that the edge-brightened jet connects to the accretion flow of the black hole. Close to the black hole, the emission profile of the jet-launching region is wider than the expected profile of a black-hole-driven jet, suggesting the possible presence of a wind associated with the accretion flow.
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| 4. |
- Tang, Wankai, et al.
(författare)
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Path Loss Modeling and Measurements for Reconfigurable Intelligent Surfaces in the Millimeter-Wave Frequency Band
- 2022
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Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 70:9, s. 6259-6276
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Tidskriftsartikel (refereegranskat)abstract
- Reconfigurable intelligent surfaces (RISs) provide an interface between the electromagnetic world of wireless propagation environments and the digital world of information science. Simple yet sufficiently accurate path loss models for RISs are an important basis for theoretical analysis and optimization of RIS-assisted wireless communication systems. In this paper, we refine our previously proposed free-space path loss model for RISs to make it simpler, more applicable, and easier to use. The impact of the antenna's directivity of the transmitter, receiver, and the unit cells of the RIS on the path loss is explicitly formulated as an angle-dependent loss factor. The refined model gives more accurate estimates of the path loss of RISs comprised of unit cells with a deep sub-wavelength size. Based on the proposed model, the properties of a single unit cell are evaluated in terms of scattering performance, power consumption, and area, which allows us to unveil fundamental considerations for deploying RISs in high frequency bands. Two fabricated RISs operating in the millimeter-wave (mmWave) band are utilized to carry out a measurement campaign. The measurement results are shown to be in good agreement with the proposed path loss model. In addition, the experimental results suggest an effective form to characterize the power radiation pattern of the unit cell for path loss modeling.
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| 5. |
- Chen, Fu qiang, et al.
(författare)
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Pressure analysis on two-step high pressure reducing system for hydrogen fuel cell electric vehicle
- 2017
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 42:16, s. 11541-11552
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen fuel cell electric vehicle (FCEV) can achieve zero exhaust emission and zero pollution. In order to make FCEV reach a farther travel distance, greater demands are put on its pressure reducing system. In this paper, a two-step high pressure reducing system for FCEV is proposed. The system is made up of two parts, a new high multi-stage pressure reducing valve (HMSPRV) and a multi-stage muffler. As a new system, its feasibility has to be verified. Since the valve opening condition has a great effect on hydrogen flow, pressure reduction and energy consumption, different valve opening conditions are taken as the research point. The flow field analysis of the new HMSPRV is conducted on three aspects: pressure field, velocity field and energy consumption. It can be found that both the pressure reducing and velocity increasing gradients mainly reflect at those throttling components for all valve openings. For energy consumption, in the comprehensive study of flow vortexes and turbulent dissipation rate, it can be found that the larger of the valve opening, the larger of energy consumption. Then, a thermo-fluid-solid coupling analysis is conducted on the new HMSPRV, and it is concluded that the new system meets strength requirement. Furthermore, as the second step of the high pressure reducing system, the flow and pressure fields of multi-stage muffler are investigated. The five-stage muffler is exactly designed to complete the whole pressure reducing process. This study can provide technological support for achieving pressure regulation in the hydrogen transport system of FCEV when facing complex conditions, and it can also benefit the further research work on energy saving and multi-stage flow of pressure reducing devices.
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| 6. |
- Pang, Zhibo, et al.
(författare)
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Global Fresh Food Tracking Service Enabled by Wide Area Wireless Sensor Network
- 2010
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Ingår i: 2010 IEEE Sensors Applications Symposium, SAS 2010. - : IEEE Sensors Council. ; , s. 6-9
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Konferensbidrag (refereegranskat)abstract
- A global fresh food tracking service is presented, in which a set of primary environmental conditions for transport of fresh fruits and vegetables, including global position, temperature, relative humidity, concentrations of CO2, O2 and ethylene gases and 3-axis acceleration, is collected through mobile and remotely controllable wireless sensor nodes. Real time monitoring, tracking, alarming, close-loop controlling and information sharing could therefore be provided as WEB services with service oriented architecture. Fully functioned hardware modules, protocols and system software have been developed. A 50-day field test has been successfully carried out, proving the system concept and the robustness of hardware and software designed. Due to its worldwide deploy-ability and added-values to fresh food supply chain, it is feasible to establish a practical fresh food tracking service business.
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| 7. |
- Boström, Ola, et al.
(författare)
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Writing a handbook of vehicle safety measures
- 2013
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Ingår i: Proceedings of the 16th International Conference Road Safety on Four Continents. - Linköping : Statens väg- och transportforskningsinstitut.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper describes the development of a handbook intended to increase the common Chinese knowledge of safety features in today’s cars. The handbook is the result of the joint effort of China based CATARC and Autoliv China as well as Sweden based Chalmers University and Autoliv Research. The origin and basis of the handbook is the master thesis work by the Chalmers student Jing Li.It is known from the introduction section that road traffic safety is a big issue at global levels for it is a leading factor for fatalities. The problem in China is serious since the number of vehicles on the roads grows fast, which means it is more likely to be exposed to road accidents and the safety countermeasures and people’s safety awareness fail to catch up with the increasing traffic. This project work is done following the methods of literature review, telephone interviews with Chinese people, accident data research, and Madymo simulations for common but dangerous situations. It is to combine the techniques and the real situations, which are totally different from Sweden, to make the techniques serve more people. Through these methods, the handbook of vehicle safety measures is developed.
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| 8. |
- Chen, Fu qiang, et al.
(författare)
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Thermo-mechanical stress and fatigue damage analysis on multi-stage high pressure reducing valve
- 2017
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549. ; 110, s. 753-767
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Tidskriftsartikel (refereegranskat)abstract
- A multi-stage high pressure reducing valve (MSHPRV) is proposed. It can achieve a multi-stage pressure reducing way. Valve failure mainly occurs under high pressure and high temperature conditions, thus it is necessary to investigate the strength of MSHPRV under those complex conditions. In this paper, the mathematical model of MSHPRV is established and Computational Fluid Dynamics (CFD) method is employed to simulate its flow fields and thermo-mechanical stress. Next, the stress of MSHPRV under different opening time and the fatigue damage of MSHPRV under different valve openings are studied. Finally, two changes are provided on geometry of MSHPRV and the geometrical factors are optimized. The results show that, the radial direction from inner wall to outer wall is the main heat transfer direction for valve body. At opening time 50 s, the working condition of MSHPRV is dangerous condition. Meanwhile, the maximum value of thermal stress is 487 MPa, which is located at the upper end face of valve chamber region B3. There is a lag effect of stress distribution with respect to temperature distribution. The combined stress of valve body is composed of thermal stress and mechanical stress, in which thermal stress holds the dominant position. Moreover, with the increasing of valve opening, the fatigue damage of valve body increases correspondingly. It can be concluded that MSHPRV can cope with complex conditions like high pressure and high temperature. In the optimization design of MSHPRV, it can be found that the best strength of MSHPRV is achieved with such geometrical factors as angle 15, diameter 4 mm and 2 stage plates. Besides, radian design as the improved structure is recommended. This work can benefit the further research work on the regulation performance and safe operation of high pressure reducing valve.
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| 9. |
- Eatough, Ralph P., et al.
(författare)
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Verification of Radiative Transfer Schemes for the EHT
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 897:2
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Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) Collaboration has recently produced the first resolved images of the central supermassive black hole in the giant elliptical galaxy M87. Here we report on tests of the consistency and accuracy of the general relativistic radiative transfer codes used within the collaboration to model M87∗ and Sgr A∗. We compare and evaluate (1) deflection angles for equatorial null geodesics in a Kerr spacetime; (2) images calculated from a series of simple, parameterized matter distributions in the Kerr metric using simplified emissivities and absorptivities; (3) for a subset of codes, images calculated from general relativistic magnetohydrodynamics simulations using different realistic synchrotron emissivities and absorptivities; (4) observables for the 2017 configuration of EHT, including visibility amplitudes and closure phases. The error in total flux is of order 1% when the codes are run with production numerical parameters. The dominant source of discrepancies for small camera distances is the location and detailed setup of the software "camera"that each code uses to produce synthetic images. We find that when numerical parameters are suitably chosen and the camera is sufficiently far away the images converge and that for given transfer coefficients, numerical uncertainties are unlikely to limit parameter estimation for the current generation of EHT observations. The purpose of this paper is to describe a verification and comparison of EHT radiative transfer codes. It is not to verify EHT models more generally.
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| 10. |
- Georgiev, Boris, et al.
(författare)
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A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT.
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