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247 results on '"Liu, L.X."'

15. Quasi-Monochromatic Gamma Beam Modulation at Slegs

Author

Hao, Zirui, primary, Fan, G.T., additional, Xu, Hanghua, additional, Liu, L.X., additional, Zhang, Y., additional, Wang, Hongwei, additional, Yang, Yuxuan, additional, Jin, Sheng, additional, Chen, K.J., additional, Sun, Q.K., additional, and Wang, Z.W., additional

Published
2024
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27. A method for the measurement of elastic scattering angular distribution at HIRFL-RIBLL

Author

Yang, Y.Y., Wang, J.S., Wang, Q., Ma, J.B., Huang, M.R., Han, J.L., Ma, P., Jin, S.L., Bai, Z., Hu, Q., Jin, L., Chen, J.B., Wada, R., Sun, Z.Y., Chen, R.F., Zhang, X.Y., Hu, Z.G., Yuan, X.H., Cao, X.G., Xu, Z.G., Xu, S.W., Zhen, C., Chen, Z.Q., Chen, Z., Chen, S.Z., Du, C.M., Duan, L.M., Fu, F., Gou, B.X., Hu, J., He, J.J., Lei, X.G., Li, S.L., Li, Y., Lin, Q.Y., Liu, L.X., Shi, F.D., Tang, S.W., Xu, G., Xu, X., Zhang, L.Y., Zhang, X.H., Zhang, W., Zhao, M.H., Zhang, Y.H., and Xu, H.S.

Published
2013
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31. Food system resilience and governance:a pork story in China

Author

Bruce, Donald, Bruce, Ann, Zhang, J., Liu, L.X., Tyfield, D., Bruce, Donald, Bruce, Ann, Zhang, J., Liu, L.X., and Tyfield, D.

Abstract

Given the leading role of pork in China’s meat diet, the stability of pork supply alongside the sustainability of pork production had been priorities in the pork system governance. The central government thus began the environmental protection campaign (EPC) of the pork system in 2014, aiming at optimising the regional layout of pig breeding and the producers’ competence. However, such efforts have been interrupted and challenged by the outbreak of African swine fever (ASF) in 2018, with domestic pork yield falling sharply in 2019 and pork prices and imports soaring consequently. By applying an empirical and in-depth observational analysis with the driver-pressure-state-impact-response (DPSIR) model of these two significant events (EPC and ASF) in China’s pork system, this paper examines how governance may influence food system resilience. This analysis demonstrates the crucial role of governance in China’s pork system – as a pressure source for EPC by proactively facilitating systemic transformation or as partners with the pork industry to fight ASF shocks. The pork-related policy priorities have experienced a swing between environmental sustainability and production recovery, particularly as manifested in adjusting the regional layout of pig breeding. Advocacy and preferential policies for large-scale breeding have resulted in factual inequalities and accelerated the withdrawal of small producers from the pig production system. Public authorities’ weighing of sustainability and resilience across different stages has also led to contrasting views on policy formulation and implementation. From the perspective of resilience, this paper illustrates that pursuing reorientation of the pork system during the EPC has undermined the systemic robustness to cope with the ASF, while dedicated policies on recovery have further compromised the original goals of systemic reorientation. By exploring the sharing of risks and benefits among multi-jurisdictional and multi-level poli

Published
2022

32. Organisational resilience and COVID lockdown:a multi-case study from restaurants in Wuhan, China

Author

Bruce, Donald, Bruce, Ann, Zhang, J., Liu, L.X., Tyfield, D., Bruce, Donald, Bruce, Ann, Zhang, J., Liu, L.X., and Tyfield, D.

Abstract

At the beginning of 2020, Wuhan was attacked by the outbreak of Covid-19 and experienced severe lockdowns lasting for 76 days. Along with its supply chains, the urban food system has survived COVID, but many businesses in the food system were significantly impacted, and the restaurant industry was among the most impacted ones with a 65.8% annual revenue reduction. In this study, we look into the organisational resilience of SMEs in the restaurant business. Nine semi-structured interviews were conducted one year after the lockdown was lifted, covering a wide range of restaurant types and scales. By examining the experiences of restaurants via the theoretical lens of dynamic capabilities, we focus on whether and how they sensed the threats and opportunities around the outbreak of Covid-19, seized opportunities by absorbing threats and adapting during and managed threats and transformed after the lockdown. The analysis highlights that reconfiguring resources to react rapidly has compensated for unpreparedness, which relies heavily on the operators’ ability to access resources and collaborate with traditional and non-traditional supply chain actors. The cumulative effects of dynamic capabilities on organisational resilience at the sensing, seizing and transforming phase further underline the significance of keeping up and responding promptly to developments. However, inequality in access to resources has affected the dynamic capabilities of restaurants, with self-employed and independent restaurants tending to absorb the change and maintain the status quo, while restaurants with professional management are more willing to seize opportunities and transform. These findings reflect several worrying aspects around the recovery and transformation of China’s urban restaurant sector in the post-Covid age. From an ethical view, the environment for independent restaurants has generally deteriorated, with prominent players gaining overwhelming advantages over small competitors in

Published
2022

33. Organisational resilience and COVID lockdown : a multi-case study from restaurants in Wuhan, China

Author

Bruce, Donald, Bruce, Ann, Zhang, J., Liu, L.X., Tyfield, D., Bruce, Donald, Bruce, Ann, Zhang, J., Liu, L.X., and Tyfield, D.

Abstract

At the beginning of 2020, Wuhan was attacked by the outbreak of Covid-19 and experienced severe lockdowns lasting for 76 days. Along with its supply chains, the urban food system has survived COVID, but many businesses in the food system were significantly impacted, and the restaurant industry was among the most impacted ones with a 65.8% annual revenue reduction. In this study, we look into the organisational resilience of SMEs in the restaurant business. Nine semi-structured interviews were conducted one year after the lockdown was lifted, covering a wide range of restaurant types and scales. By examining the experiences of restaurants via the theoretical lens of dynamic capabilities, we focus on whether and how they sensed the threats and opportunities around the outbreak of Covid-19, seized opportunities by absorbing threats and adapting during and managed threats and transformed after the lockdown. The analysis highlights that reconfiguring resources to react rapidly has compensated for unpreparedness, which relies heavily on the operators’ ability to access resources and collaborate with traditional and non-traditional supply chain actors. The cumulative effects of dynamic capabilities on organisational resilience at the sensing, seizing and transforming phase further underline the significance of keeping up and responding promptly to developments. However, inequality in access to resources has affected the dynamic capabilities of restaurants, with self-employed and independent restaurants tending to absorb the change and maintain the status quo, while restaurants with professional management are more willing to seize opportunities and transform. These findings reflect several worrying aspects around the recovery and transformation of China’s urban restaurant sector in the post-Covid age. From an ethical view, the environment for independent restaurants has generally deteriorated, with prominent players gaining overwhelming advantages over small competitors in

Published
2022

34. Food system resilience and governance : a pork story in China

Author

Bruce, Donald, Bruce, Ann, Zhang, J., Liu, L.X., Tyfield, D., Bruce, Donald, Bruce, Ann, Zhang, J., Liu, L.X., and Tyfield, D.

Abstract

Given the leading role of pork in China’s meat diet, the stability of pork supply alongside the sustainability of pork production had been priorities in the pork system governance. The central government thus began the environmental protection campaign (EPC) of the pork system in 2014, aiming at optimising the regional layout of pig breeding and the producers’ competence. However, such efforts have been interrupted and challenged by the outbreak of African swine fever (ASF) in 2018, with domestic pork yield falling sharply in 2019 and pork prices and imports soaring consequently. By applying an empirical and in-depth observational analysis with the driver-pressure-state-impact-response (DPSIR) model of these two significant events (EPC and ASF) in China’s pork system, this paper examines how governance may influence food system resilience. This analysis demonstrates the crucial role of governance in China’s pork system – as a pressure source for EPC by proactively facilitating systemic transformation or as partners with the pork industry to fight ASF shocks. The pork-related policy priorities have experienced a swing between environmental sustainability and production recovery, particularly as manifested in adjusting the regional layout of pig breeding. Advocacy and preferential policies for large-scale breeding have resulted in factual inequalities and accelerated the withdrawal of small producers from the pig production system. Public authorities’ weighing of sustainability and resilience across different stages has also led to contrasting views on policy formulation and implementation. From the perspective of resilience, this paper illustrates that pursuing reorientation of the pork system during the EPC has undermined the systemic robustness to cope with the ASF, while dedicated policies on recovery have further compromised the original goals of systemic reorientation. By exploring the sharing of risks and benefits among multi-jurisdictional and multi-level poli

Published
2022

35. Precision isochronous mass measurements at the storage ring CSRe in Lanzhou

Author

Tu, X.L., Wang, M., Litvinov, Yu.A., Zhang, Y.H., Xu, H.S., Sun, Z.Y., Audi, G., Blaum, K., Du, C.M., Huang, W.X., Hu, Z.G., Geng, P., Jin, S.L., Liu, L.X., Liu, Y., Mei, B., Mao, R.S., Ma, X.W., Suzuki, H., Shuai, P., Sun, Y., Tang, S.W., Wang, J.S., Wang, S.T., Xiao, G.Q., Xu, X., Xia, J.W., Yang, J.C., Ye, R.P., Yamaguchi, T., Yan, X.L., Yuan, Y.J., Yamaguchi, Y., Zang, Y.D., Zhao, H.W., Zhao, T.C., Zhang, X.Y., Zhou, X.H., and Zhan, W.L.

Published
2011
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41. High-shear granulation : an investigation into granule breakage rates

Author

de Koster, S.A.L., liu, L.X., Litster, J., and Smith, R.M.

Abstract

Granule breakage is an important rate process in wet granulation that promotes product uniformity and controls product size and strength. In this work, a model to predict granule breakage is proposed and experimentally validated. The model assumes exponential of the surviving granules, dependent on a probability of breakage; a function of powder and binder properties, as well as operating parameters. Validation experiments were performed with a breakage-only granulator, filled with cohesive, non-granulating sand. Premade pellets made from lactose monohydrate and silicone oils were granulated at several impeller speeds, and the number of survivors was observed over time. The results revealed that the number of granules did indeed decay exponentially. It was found that the overall probability of breakage was inversely proportional to the capillary number. Moreover, the pore saturation played an important role in determining the probability of breakage, with higher pore saturations reducing breakage overall. A comparison with experimental data from literature revealed that the developed models agrees qualitatively with the experimental data, but is unable to fully capture the effect of powder properties and powder-binder interaction.

Published
2021

42. High-speed operation of a gas-bearing supported MEMS-air turbine

Author

Teo, C.J., Liu, L.X., Li, H.Q., Ho, L.C., Jacobson, S.A., Ehrich, F.F., Epstein, A.H., and Spakovszky, Z.S.

Subjects
Bearings (Machinery) -- Usage, Bearings (Machinery) -- Mechanical properties, Gas-turbines -- Speed, Gas-turbines -- Electric properties, Gas-turbines -- Mechanical properties, Science and technology
Abstract

Silicon based power micro-electro-mechanical system (MEMS) applications require high-speed microrotating machinery operating stably over a large range of operating conditions. The technical barriers to achieving stable high-speed operation with micro-gas-bearings are governed by (1) stringent fabrication tolerance requirements and manufacturing repeatability, (2) structural integrity of the silicon rotors, (3) rotordynamic coupling effects due to leakage flows, (4) bearing losses and power requirements, and (5) transcritical operation and whirl instability issues. To enable high-power density the micro-turbomachinery must be run at tip speeds comparable to conventional scale turbomachinery. The rotors of the micro-gas turbines are supported by hydrostatic gas journal and hydrostatic gas thrust bearings. Dictated by fabrication constraints the location of the gas journal bearings is at the outer periphery of the rotor The high bearing surface speeds (target nearly 10 x [10.sup.6] mm rpm), the very low bearing aspect ratios (L/D

Published
2009

44. Effects of bearing stiffness anisotropy on hydrostatic micro gas journal bearing dynamic behavior

Author

Liu, L.X. and Spakovszky, Z.S.

Subjects
Anisotropy -- Measurement, Journal bearings -- Design and construction, Journal bearings -- Mechanical properties, Hydrostatics -- Research, Gas-turbines -- Research, Elasticity -- Evaluation, Engineering and manufacturing industries, Science and technology
Abstract

The high-speed microhydrostatic gas journal bearings used in the high-power density MIT microengines are of very low aspect ratio with an L/D of less than 0.1 and are running at surface speeds of order 500 m/s. These ultra-short high-speed bearings exhibit whirl instability limits and a dynamic behavior much different from conventional hydrostatic gas bearings. The design space for stable high-speed operation is confined to a narrow region and involves singular behavior (Spakovszky and Liu, 2005, 'Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings,' ASME J. Vibr. Acoust., 127(3), pp. 254-261). This together with the limits on achievable fabrication tolerance, which can be achieved in the silicon chip manufacturing technology, severely affects bearing operability and limits the maximum achievable speeds of the microturbomachinery. This paper introduces a novel variation of the axial-flow hydrostatic micro gas journal bearing concept, which yields anisotropy in bearing stiffness. By departing from axial symmetry and introducing biaxial symmetry in hydrostatic stiffness, the bearing 's top speed is increased and fabrication tolerance requirements are substantially relieved making more feasible extended stable high-speed bearing operation. The objectives of this work are: (i) to characterize the underlying physical mechanisms and the dynamic behavior of this novel bearing concept and (ii) to report on the design, implementation, and test of this new microbearing technology. The technical approach involves the combination of numerical simulations, experiment, and simple, first-principles-based modeling of the gas bearing flow field and the rotordynamics. A simple description of the whirl instability threshold with stiffness anisotropy is derived explaining the instability mechanisms and linking the governing parameters to the whirl ratio and stability limit. An existing analytical hydrostatic gas bearing model is extended and modified to guide the bearing design with stiffness anisotropy. Numerical simulations of the full nonlinear governing equations are conducted to validate the theory and the novel bearing concept. Experimental results obtained from a microbearing test device are presented and show good agreement between the theory and the measurements. The theoretical increase in achievable bearing top speed and the relief in fabrication tolerance requirements due to stiffness anisotropy are quantified and important design implications and guidelines for micro gas journal bearings are discussed. [DOI: 10.1115/1.2180813]

Published
2007

46. Scaling laws for ultra-short hydrostatic gas journal bearings

Author

Spakovszky, Z.S. and Liu, L.X.

Subjects
Bearings (Machinery) -- Research, Rotors -- Research, Vibration -- Research, Science and technology
Abstract

The journal bearings of the MIT micro-devices are located at the outer periphery of the rotor and are designed to operate at rotational speeds of order two million rpm in order to enable high-power densities with turbomachinery tip speeds near 500 m/s. These journal bearings are very short compared to their relatively large bearing diameters such that the bearing L/D is typically less than 0.1, that is at least one order of magnitude smaller than in conventional gas bearings. Thus, the ultra-short micro gas journal bearings essentially act as short annular seals and operate at Reynolds numbers of order 300, two orders of magnitude lower than conventional annular seals. The concepts that hold for turbulent flow, large scale annular seals do not apply to micro bearings and the laminar flow regime sets new challenges in the design, implementation and operation of ultra-short, high-speed gas bearings. In order to reach the goal of operating the MIT micro devices at full design speed, the micro-bearing design must be improved and engineering solutions need to be found to overcome the challenges of high-speed bearing operation. This paper is the first to derive the scaling laws for the dynamics of ultra-short hydrostatic gas journal bearings. The theory is established from first principles and enables a physics based characterization of the dynamic behavior of ultra-short hydrostatic gas bearings. The derived scaling laws for natural frequency and damping ratio show good agreement with experimental data. A simple criterion for whirl instability is found that only depends on bearing geometry. The scaling laws together with this criterion are used to delineate engineering solutions critical for stable high-speed bearing operation. Design charts are developed which provide the link between fabrication tolerances, bearing performance, and the tolerable level of rotor unbalance for a minimum required whirl ratio.

Published
2005

47. Hydrostatic gas journal bearings for micro-turbomachinery

Author

Liu, L.X., Teo, C.J., Epstein, A.H., and Spakovszky, Z.S.

Subjects
Integrated circuit fabrication -- Research, Microelectromechanical systems -- Research, Vibration -- Research, Integrated circuit fabrication, Science and technology
Abstract

Several years ago an effort was undertaken at MIT to develop high-speed rotating MEMS (Micro Electro-Mechanical Systems) using computer chip fabrication technology. To enable high-power density the micro-turbomachinery must be run at tip speeds of order 500 m/s, comparable to conventional scale turbomachinery. The high rotating speeds (of order 2 million rpm), the relatively low bearing aspect ratios (L/D

Published
2005

50. An international comparison of 50/60 Hz power

Author

Oldham Nile, Nelson, Tom, Bergeest, R., Ram, G., Carranza, R., Corney, A.C., Gibbes, M., Kryiazis, G., Laiz, H.M., Liu, L.X., Pogliano, U., Rydler, K.E., Shapiro, E., So, Eddy, Temba, M., and Wright, O.

Subjects
Power transmission -- Research
Published
2001

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