Anisotropic Deformation in the Compressions of Single Crystalline Copper Nanoparticles

Atomistic simulations are performed to probe the anisotropic deformation in the compressions of face-centred-cubic metallic nanoparticles. In the elastic regime, the compressive load-depth behaviors can be characterized by the classical Hertzian model or flat punch model, depending on the surface configuration beneath indenter. On the onset of plasticity, atomic-scale surface steps serve as the source of heterogeneous dislocation in nanoparticle, which is distinct from indenting bulk materials. Under [111] compression, the gliding of jogged dislocation takes over the dominant plastic deformation. The plasticity is governed by nucleation and exhaustion of extended dislocation ribbons in [110] compression. Twin boundary migration mainly sustain the plastic deformation under [112] compression. This study is helpful to extract the mechanical properties of metallic nanoparticles and understand their anisotropic deformation behaviors.Comment: 25 pages, 9 figure

Arte, scienza e storia in un mondo globalizzato: il caso Italia-Cina

Art and science, over the centuries, though starting from different positions, have very often led to the same conclusions. History, on the other hand, establishes identities that derive from our past and allows for exchanges and unity between people of different nationalities, in both a commercial and scientific context, in a world without borders, in spite of obvious contradictions related to this globalized world. The case of Italy-China bears witness to this in a significant way.A case in point is represented by the scientific collaboration between the Alma Mater University of Bologna and Zhejiang University, as well as that between the Salesian Pontifical University of Rome and Fudan University in Shanghai, Zhejiang University and the Foreign Studies University of Beijing.In the first case, the ongoing research project “Historical anamnesis, preservation and valorization of the statues of the Longxing Buddhist Temple of Qingzhou (China)” is being carried out between the Department of Cultural Heritage Diagnostic Laboratory for Cultural Heritage of the University of Bologna and the Cultural Heritage Institute of Zhejiang University. In the second case, collaboration between the Salesian Pontifical University and the Chinese Universities, covers activities relating to the study of philosophy, pedagogy and Latin language and literature.The paper highlights the importance of drawing value of a cultural, conservative, social, identitary nature within the context of the holistic value of cultural heritage and respecting ethical aspects at a personal and interpersonal level, in particular, by offering young people the opportunity to enter the employment market and of which they are currently experiencing all the problematic fluctuations.Arte e scienza, nel corso dei secoli, pur partendo da posizioni iniziali differenti, molto spesso conducono alle stesse conclusioni. D’altra parte la storia stabilisce le identità che nascono dal passato e permette scambi e coesioni fra genti di diversa nazionalità, in campo sia commerciale sia scientifico, in un mondo senza confini. Pur con contraddizioni evidenti riconducibili a questo mondo globalizzato, una significativa testimonianza è rappresentata da Italia-Cina. Al riguardo, si fa riferimento alla collaborazione scientifica fra l’Alma Mater Studiorum Università di Bologna e Zhejiang University nonché fra l’Università Pontificia Salesiana di Roma e Fudan University di Shanghai, Zhejiang University e Beijing Foreign Studies University. Nel primo caso è in atto il progetto di ricerca “Historical anamnesis, preservation and valorization of the statues of the Longxing Buddhist Temple of Qinzhou (Cina)” fra il Dipartimento di Beni Culturali - Laboratorio Diagnostico per i Beni Culturali dell’Università di Bologna e il Cultural Heritage Institute di Zhejiang University. Nel secondo caso la collaborazione fra l’Università Pontificia Salesiana e le Università cinesi riguarda attività relative agli studi di filosofia, pedagogia e lettere latine. Si fa presente l ’importanza di trarre benefici di carattere culturale, conservativo, sociale, identitario nell’ ambito del valore olistico del bene culturale e nel rispetto degli aspetti etici a livello personale e interpersonale, offrendo in particolare ai giovani la possibilità di entrare nel mercato del lavoro del quale vivono le attuali e problematiche fluttuazioni

Research on the Vibration Damping Performance of a Novel Single-Side Coupling Hydro-Pneumatic Suspension

A mine dump truck is exposed to heavy load and harsh working environment. When the truck passes over the road bumps, it will cause the body to tilt and the tires to "jump off the ground" (JOTG), which will affect the stability and safety of the truck, and will cause impact damage to the body and suspension system. To avoid this situation, a kind of Novel Single-side Coupling Hydro-pneumatic Suspension (NSCHs) is presented. NSCHs consists of two cylinders in parallel, which are connected to the accumulator by rubber pipes and mounted on the same side of the dump truck. Theoretical analysis and experimental research were respectively carried out under the road and loading experimental condition. The experimental results show that compared to the conventional single cylinder hydro-pneumatic suspension, under the loading experiment condition, the maximum overshoot pressure of the NSCHs was reduced by 0.4 MPa and the impact oscillation time was shortened by 4.13 s, which plays the effective role in reducing vibration and absorbing energy. Further, it is found that the two cylinders are coupled during the working process, and the NSCHs system can achieve uniform loading and displacement compensation, thus the novel dump truck can avoid the occurrence of the JOTG phenomenon

Trend of near-surface maximum wind speed in China: under a shifted East Asian monsoon scenario

Póster presentado en: EGU General Assembly 2018 celebrada del 8 al 13 de abril en Viena, Austria.The current global climate research has traditionally focused on changes in air temperature and precipitation. As a key climate parameter, changes of winds have a very significant impact on the environment, such as soil wind erosion, air pollution diffusion, wind power energy, etc. In particular, changes of extreme wind speed (i.e., wind gusts) are poorly analyzed and deserve further investigation. In this study we assess trends in máximum wind speed (MWS) across China for 1975-2016, using observed daily wind datasets, and also analyze its relationship with the East Asian monsoon. The raw observed MWS dataset was subject to aquality control and robust homogenization protocol using the Climatol package. The results reveal a statistically significant (p0.10). Even though MWS declines dominated across much of the country through out the year, only as mal number of stations showed statistically significant negative trends in summer (37.7 %) and spring (29.0 %). Our preliminary analyses show that the weakened East Asian monsoon, particularly in winter, positively correlates with the observed changes in MWS. However, statistical significant correlations are too few and further attribution analyses are strongly needed.This research is funded by (i) the National Natural Science Foundation of China (Grant No.41621061); (ii) the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant (Grant No. 703733); and (iii) the Swedish Research Council by the project “Detection and attribution of changes in extreme wind gusts over land” (2017-03780)

Variability of winter haze over the Beijing-Tianjin-Hebei region tied to wind speed in the lower troposphere and particulate sources [Póster]

Póster presentado en: EMS Annual Meeting - European Conference for Applied Meteorology and Climatology 2018, celebrado en Budapest del 3 al 7 de septiembre de 2018.This study analyzes the variability of winter haze days and visibility in the Beijing-Tianjin-Hebei (BTH) region in relation to wind speed changes in the lower troposphere and emissions for 1961-2014. Daily surface meteorological data, NCEP/NCAR atmospheric reanalysis data, and fossil fuel emission data are used in this research. The results reveal a significant increase in winter haze days of +0.8 days decade-1 (p<0.01), and a subsequent decline in visibility of-1.56 km decade-1 (p<0.01). Most interestingly, an accelerated increase in haze days was observed for the last 11-year period (+8.3 days decade-1) of the study (2004-2014). The increase of winter haze occurrence and decrease in visibility are partly attributed to: the significant (p<0.01) declining trend of mean wind speed at the near-surface (-0.19 m s-1 decade-1), 925hPa (-0.23 m s-1 decade-1), and 850hPa (-0.21 m s-1 decade-1); the vertical shear of wind between 1000hPa and 850hPa (-0.07 m s-1 decade-1); and, the declining (dust storm frequency as a proxy,-0.41 days dec-1) surrounding particulate sources and increasing fossil fuel emissions (total carbon emission as a proxy, +4820.6 metric tons dec-1). Specifically, wind speed changes in the lower troposphere explain 41.3% of winter haze days and 71.2% of the visibility variance. These are extended to 51.7% and 81.6% respectively when combined with natural (dust storm frequency) and anthropogenic (fossil fuel emissions) particulate sources. Therefore, the analyses show that wind speed changes in the lower troposphere, together with the varied natural and anthropogenic sources of particulates, play a key role in modulating winter haze and visibility conditions in the BTH area.This research is funded by the National Natural Science Foundation of China (Grant No.41621061), and funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 703733 (STILLING project). This work has been also supported by the VR Project (2017-03780) funded by the Swedish Research Council

Contribution of uneven warming to the observed wind stilling in North China for 1961-2016

This work has been supported by the project “Detection and attribution of changes in extreme wind gusts over land” (2017-03780) funded by the Swedish Research Council

Climatology of near‐surface daily peak wind gusts across Scandinavia: observations and model simulations

An observed daily peak wind gusts (DPWG) dataset over Scandinavia, consisting of time series from 127 meteorological stations across Finland, Norway and Sweden, has been created. This dataset provides high-quality and homogenized near-surface DPWG series for Scandinavia, spanning the longest available time period (1996–2016). The aim of this study is to evaluate the ability of two regional climate models (RCMs) in simulating DPWG winds. According to the observed DPWG climatology, meteorological stations are classified into three regions for which wind conditions are influenced by similar physical processes: coast, inland and mountain. Smaller-scale DPWG features of the three regions are only captured when coarser general circulation models or reanalyses are downscaled by a RCM. Dynamic downscaling is thus needed to achieve more realistic simulations of DPWG when compared to their driving models. The performances of the RCMs are found to be more dependent on model dynamics and physics (such as gust parametrization) than on the boundary conditions provided by the driving models. We also found that the RCMs cannot accurately simulate observed DPWG in inland and mountainous areas, suggesting the need for higher horizontal resolution and/or better representation of relevant boundary-layer processes.It is supported by Swedish Research Council (2017-03780) and Spanish Ministry of Science, Innovation and Universities (RTI2018-095749-A-I00)

Impact of near-surface wind speed variability on wind erosion in the eastern agro-pastoral transitional zone of Northern China, 1982-2016 [Póster]

Póster presentado en: EGU General Assembly 2019 celebrada del 7 al 12 de abril en Viena, Austria.The Wind erosion in arid and semi-arid areas is an important global environmental issue, and changes in wind speed trends over time play a key role in wind erosion dynamics. In a warming climate, scientists have recently observed a widespread decline in wind speed, termed "stilling". Here, we apply the Revised Wind Erosion Equation Model (RWEQ) to simulate the variability of wind erosion and quantify the impact of wind speed changes on soil degradation dynamics over the eastern agro-pastoral transitional zone of Northern China (EANC) from 1982 to 2016. Our results show that a significant (i.e., p<0.05) decrease (-0.007 m s-1 year-1) of near-surface wind speed was observed annually, with significant declining trends in spring (-0.010 m s-1 year-1 ）and autumn (-0.009 m s-1 year-1). At the same time, wind erosion simulations reveal a negative trend for the annual soil loss from wind erosion (SLWE,-6.20 t hectare-2 year-1 , p<0.05; affecting 99.8% of the study region), with significant declining trends in all seasons, particularly in spring (-3.49 t hectare-2 year-1) and autumn (-1.26 hectare-2 year-1). Further, we isolate the effects of wind variability on wind erosion (SLWED) from 1982 to 2016 by the model variable control method. This shows that wind speed variability strongly weakens wind erosion at-8.14 t hectare-2 year-1 (p<0.05) annually, with the strongest stilling recorded in spring leading to major decreases of wind erosion in spring (-4.77 t hectare-2 year-1 , p<0.05). Meanwhile, the weakest stilling in summer had the opposite influence on wind erosion (+0.40 t hectare-2 year-1 , p<0.10). To summarize, our findings have shown a significant impact of wind stilling on the decline of soil erosion rates in Northern China.This research is funded by the National Natural Science Foundation of China (Grant No. 41621061), and funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 703733 (STILLING project). This work has been also supported by the VR Project (2017-03780) funded by the Swedish Research Council

Design, Modeling, and Analysis of a Novel Hydraulic Energy-Regenerative Shock Absorber for Vehicle Suspension

To reduce energy consumption or improve energy efficiency, the regenerative devices recently have drawn the public’s eyes. In this paper, a novel hydraulic energy-regenerative shock absorber (HERSA) is developed for vehicle suspension to regenerate the vibration energy which is dissipated by conventional viscous dampers into heat waste. At first, the schematic of HERSA is presented and a mathematic model is developed to describe the characteristic of HERSA. Then the parametric sensitivity analysis of the vibration energy is expounded, and the ranking of their influences is k1≫m2>m1>k2≈cs. Besides, a parametric study of HERSA is adopted to research the influences of the key parameters on the characteristic of HERSA. Moreover, an optimization of HERSA is carried out to regenerate more power as far as possible without devitalizing the damping characteristic. To make the optimization results more close to the actual condition, the displacement data of the shock absorber in the road test is selected as the excitation in the optimization. The results show that the RMS of regenerated energy is up to 107.94 W under the actual excitation. Moreover it indicates that the HERSA can improve its performance through the damping control

A Non-Equilibrium Sediment Transport Model for Dam Break Flow over Moveable Bed Based on Non-Uniform Rectangular Mesh

The use of multiple-level non-uniform rectangular mesh in coupled flow and sediment transport modeling is preferred to achieve high accuracy in important region without increasing computational cost greatly. Here, a robust coupled hydrodynamic and non-equilibrium sediment transport model is developed on non-uniform rectangular mesh to simulate dam break flow over movable beds. The enhanced shallow water and sediment transport equations are adopted to consider the mass and momentum exchange between the flow phase and sediment phase. The flux at the interface is calculated by the positivity preserving central upwind scheme, which belongs to Godunov-type Riemann-problem-solver-free central schemes and is less expensive than other popular Riemann solvers while still capable of tracking wet/dry fronts accurately. The nonnegative water depth reconstruction method is used to achieve second-order accuracy in space. The model was first verified against two laboratory experiments of dam break flow over irregular fixed bed. Then the quantitative performance of the model was further investigated by comparing the computational results with measurement data of dam break flow over movable bed. The good agreements between the measurements and the numerical simulations are found for the flow depth, velocity and bed changes