The objective of this paper is to computationally explore the structural stability and strength of gypsum-protected CFS(cold-formed steel)beam channel sections under non-uniform elevated temperatures when exposed to s...The objective of this paper is to computationally explore the structural stability and strength of gypsum-protected CFS(cold-formed steel)beam channel sections under non-uniform elevated temperatures when exposed to standard fire on one side of the panel and subjected to pure bending.When a CFS member is subjected to fire(or thermal gradients)its material properties change-but this change happens around the cross-section and along the length creating a member which is potentially non-uniform and unsymmetrical in its response even if the apparent geometry is uniform and symmetric.Computational finite element models were analyzed in ABAQUS to establish steady-state thermal gradients of interest.Existing test data were utilized to develop the temperature dependence of the stress-strain response.The time-dependent temperature distribution on the cross-sections obtained from heat transfer analysis was later used in the stability and collapse analyses.The stability of the models was explored to characterize how local,distortional,and global buckling of the member evolves under both uniform and non-uniform temperature distributions.Finally,collapse simulations were performed to characterize the strength under pure bending and explore directly the evolution of strength under the influence of non-uniform temperature.展开更多
Due to operational wear and uneven carbon absorption in compressor and turbine wheels, the unbalance(me) vibration is induced and could lead to sub?synchronous vibration accidents for high?speed turbocharger(TC). Ther...Due to operational wear and uneven carbon absorption in compressor and turbine wheels, the unbalance(me) vibration is induced and could lead to sub?synchronous vibration accidents for high?speed turbocharger(TC). There are very few research works that focus on the magnitude e ects on such induced unbalance vibration. In this paper, a finite element model(FEM) is developed to characterize a realistic automotive TC rotor with floating ring bearings(FRBs). The nonlinear dynamic responses of the TC rotor system with di erent levels of induced unbalance magni?tude in compressor and turbine wheels are calculated. From the results of waterfall and response spectral intensity plots, the bifurcation and instability phenomena depend on unbalance magnitude during the startup of TC. The sub?synchronous component 0.12× caused rotor unstable is the dominant frequency for small induced unbalance. The nonlinear e ects of induced unbalance in the turbine wheel is obvious stronger than the compressor wheel. As the unbalance magnitude increases from 0.05 gbration 1·mm to 0.2 g·mm, the vibration component changes from mainly 0.12× to synchronous vi×. When unbalance increases continuously, the rotor vibration response amplitude is rapidly growing and the 1× caused by the large unbalance excitation becomes the dominant frequency. A suitable un?balance magnitude of turbine wheel and compressor wheel for the high?speed TC rotor with FRBs is proposed: the value of induced un?balance magnitude should be kept around 0.2 g·mm.展开更多
Our newly developed CESE MHD model is used to simulate sun-earth connection event with the well-studied 12 May 1997 CME event as an example. The main features and approximations of our numerical model are as follows：...Our newly developed CESE MHD model is used to simulate sun-earth connection event with the well-studied 12 May 1997 CME event as an example. The main features and approximations of our numerical model are as follows： （1） The modifed conservation element and solution element （CESE） numerical scheme in spherical geometry is implemented in our code. （2） The background solar wind is derived from a 3D time-dependent numerical MHD model by input measured photospheric magnetic fields. （3） Transient disturbances are derived from solar surface by introducing a mass flow of hot plasma. The numerical simulation has enabled us to predict the arrival of the interplanetary shock and provided us with a relatively satisfactory comparison with the WIND spacecraft observations.展开更多
Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, whic...Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, which gives us an opportunity to perform a comparison analysis of these two filaments. The coronal magnetic field extrapolated using our CESE-MHD-NLFFF code reveals that two magnetic flux ropes （MFRs） exist in the same extrapolation box supporting these two filaments, respectively. Analysis of the magnetic field shows that the eruptive MFR contains a bald-patch separatrix surface （BPSS） co- spatial very well with a pre-eruptive EUV sigmoid, which is consistent with the BPSS model for coronal sigmoids. The magnetic dips of the non-eruptive MFRs match Hα observation of the non-eruptive filament strikingly well, which strongly supports the MFR-dip model for filaments. Compared with the non-eruptive MFR/filament （with a length of about 200 Mm）, the eruptive MFR/filament is much smaller （with a length of about 20 Mm）, but it contains most of the magnetic free energy in the extrapolation box and holds a much higher free energy density than the non-eruptive one. Both the MFRs are weakly twisted and cannot trigger kink instability. The AR eruptive MFR is unstable because its axis reaches above a critical height for torus instability, at which the overlying closed arcades can no longer confine the MFR stably. On the contrary, the quiescent MFR is very firmly held by its overlying field, as its axis apex is far below the torus-instability threshold height. Overall, this comparison investigation supports that an MFR can exist prior to eruption and the ideal MHD instability can trigger an MFR eruption.展开更多
Hair has historically reflected material consequences in the Black community; thus, research has begun to investigate how the power/privilege matrix that is propagated throughout the media permeates society and impact...Hair has historically reflected material consequences in the Black community; thus, research has begun to investigate how the power/privilege matrix that is propagated throughout the media permeates society and impacts African-Arnerican women＇s perceptions of hair. This research joins the discussion by exploring how Black hair magazine advertisements influence Black women＇s hair decisions and their percepfious of what constitutes beautiful Black hair. Findings reveal that the images African-American women consume from Black hair magazine advertisements do impact what they consider to be beautiful and, subsequently, influence their day-to-day styling and hair care mechanisms, lending further support to the idea that the media serve as powerful sources of knowledge. This study culminates by theorizing about the constitutive meanings and importance of Black hair as conveyed through magazine advertisements and considers how Black women use social comparisons to make everyday hair decisions to achieve what they identify as good hair.展开更多
This paper presents a comparative“cradle to gate”life cycle assessment(LCA)of 3D printing houses and conventional buildings using SimaPro software,as a tool to model and compare the two alternatives.The study consid...This paper presents a comparative“cradle to gate”life cycle assessment(LCA)of 3D printing houses and conventional buildings using SimaPro software,as a tool to model and compare the two alternatives.The study considered a terraced type of buildings with a floor area of 60 m^(2)(functional unit),which could occupy 2-3 households.The results indicated that 3D printing houses have a smaller environmental impact than conventional buildings in all impact categories except in terrestrial ecotoxicity,in which both alternatives resulted in 172 kg 1,4-DB eq.3D printing houses exhibit a higher climate impact from Timber floorboards,window frames,and Portland cement which are responsible for 7.39×10^(4) kg CO_(2) eq,9.34 ×10^(4) kg CO_(2) eq,and 3.82×10^(4) kg CO_(2) eq respectively.展开更多
While there is overwhelming evidence for dark matter (DM) in galaxies and galaxy clusters, all searches for DM particles have so far proved negative. It is not even clear whether only one particle is involved or a com...While there is overwhelming evidence for dark matter (DM) in galaxies and galaxy clusters, all searches for DM particles have so far proved negative. It is not even clear whether only one particle is involved or a combination of particles, their masses not precisely predicted. This non-detectability raises the possible relevance of modified gravity theories: MOND, MONG, etc. Here we consider a specific modification of Newtonian gravity (MONG) which involves gravitational self-energy, leading to modified equations whose solutions imply flat rotation curves and limitations of sizes of clusters. The results are consistent with current observations including that involving large spirals. This modification could also explain the current Hubble tension. We also consider the effects of dark energy (DE) in terms of a cosmological constant.展开更多
With SDO observations and a data-constrained magnetohydrodynamics （MHD） model, we identify a confined multi-ribbon flare that occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch （BP） ...With SDO observations and a data-constrained magnetohydrodynamics （MHD） model, we identify a confined multi-ribbon flare that occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch （BP） flare with strong evidence. From the photospheric magnetic field observed by SDO/HMI, we find there are indeed magnetic BPs on the polarity inversion lines （PILs） which match parts of the flare ribbons. From the 3D coronal magnetic field derived from an MHD relaxation model constrained by the vector magnetograms, we find strikingly good agreement of the BP separatrix surface （BPSS） footpoints with the flare ribbons, and the BPSS itself with the hot flaring loop system. Moreover, the triggering of the BP flare can be attributed to a small flux emergence under the lobe of the BPSS, and the relevant change of coronal magnetic field through the flare is reproduced well by the pre-flare and post-flare MHD solutions, which match the corresponding pre- and post-flare AIA observations, respectively. Our work contributes to the study of non-typical flares that constitute the majority of solar flares but which cannot be explained by the standard flare model.展开更多
The dynamical behavior of fluids affected by the asymmetric gravity jitter oscillations, in particular, the effect of surface tension on partially-filled rotating fluids in a Dewar tank imposed by time-dependent direc...The dynamical behavior of fluids affected by the asymmetric gravity jitter oscillations, in particular, the effect of surface tension on partially-filled rotating fluids in a Dewar tank imposed by time-dependent directions of background reduced gravity accelerations is investigated. Results show that the greater the components of background reduced gravity in radial and circumferential directions, the greater will be the tendency toward increasing amplitude and degrees of asymmetry of the liquid-vapor interface profiles.展开更多
We present a method of forced-field(i.e., non-force-free field: NFFF) extrapolation of the global magnetic field in the corona, on the basis of single-layer vector magnetogram, by extending an extrapolation technique ...We present a method of forced-field(i.e., non-force-free field: NFFF) extrapolation of the global magnetic field in the corona, on the basis of single-layer vector magnetogram, by extending an extrapolation technique of local magnetic field first developed by Hu et al.(2008). The forced coronal magnetic field is described by a system with the minimum dissipation rate(MDR) which is appropriate for the corona as a forced and open system. The obtained solution of the magnetic field can be decomposed into three components including one potential field and two linear force-free fields(LFFF). Starting from the given single-layer vector magnetogram, the bottom boundary condition for each component is determined with an iterative method to achieve a minimum difference of the transverse component between the extrapolated field and the original magnetogram. The final extrapolated forced field is given by the sum of the three component fields with the obtained bottom boundaries. The method is tested with an analytic magnetohydrostatic(MHS) solution. It is shown that the extrapolated forced field is highly consistent with the MHS solution at least from the solar disk to the heliocentric distance of 1.5 solar radii(R⊙). For instance, the complements of normalized and mean vector errors(E’n, E’m) are as high as ~97% and 95%, respectively. Further comparisons between magnetic strength, force and field line distributions indicate that the MHS solution has been successfully reconstructed.展开更多
Electric power distribution systems are vulnerable to disruption due to severe weather events,especially hurricanes.Such vulnerability is expected to increase over time due to the impact of climate change on hurricane...Electric power distribution systems are vulnerable to disruption due to severe weather events,especially hurricanes.Such vulnerability is expected to increase over time due to the impact of climate change on hurricanes and the decay of wood poles that support the distribution lines.This study investigates the effectiveness of using fiber-reinforced polymer(FRP)sleeve to reinforce wood poles subjected to decay and hurricane hazard to restore their lost strength and extend their effective service life.The potential impact of climate change on the pole decay rate and the intensity and frequency of hurricanes is also considered.The optimal FRP repair time based on the structural reliability of the poles is also determined.Three locations with varying climates are chosen to evaluate and compare the results:Miami,Charleston,and New York City.The results show that in all three locations,the application of the FRP sleeve can more than double the service life of the pole depending on the time of the repair.The results also show that climate change significantly increases the vulnerability of the pole.The probability of failure of the pole at the end of the 21st century under RCP8.5 emission scenario in Miami,Charleston,and New York City increase by about 30%,70%,and 73%,respectively,compared to a no climate change scenario.If climate change is only assumed to affect the decay of the pole,i.e.,no change in hurricane hazard intensity,the corresponding increases in failure probability are 5%,22%,and 20% in Miami,Charleston,and New York City,respectively.This implies that most of the impact of climate change on pole failure risk is due to the increase in hurricane intensity.The impact of climate change on decay is found to be comparatively small.It increases with time as variation in temperature and precipitation becomes more prominent towards the end of the 21st century.The optimization results show that the optimal FRP repair time depends on how the FRP affects the pole's decay rate.If the FRP can significantly slow down the wood decay rate,the optimal time of repair is at the beginning of the pole's life cycle.If the FRP has no impact on the wood decay rate,it is better to repair the pole after significant decay has occurred.展开更多
In recent years remarkable advances have been made in the development of phys-ics based models of various parts of the solar-terrestrial system (see JASTP special issues, October, November 2004; February 2007). In thi...In recent years remarkable advances have been made in the development of phys-ics based models of various parts of the solar-terrestrial system (see JASTP special issues, October, November 2004; February 2007). In this paper, we focus our dis-cussions in a specific region of the Sun to the Earth’s environment (i.e. 1 AU). It is well-known that geomagnetic storms are caused by solar eruptions. The conse-quences of these storms include particle acceleration, solar wind impact on the Earth’s magnetosphere and ionosphere, UV-EUV radiation effects on the lower at-mosphere, etc. One of the main challenges is to predict the arrival time at 1 AU of the solar disturbance. The prospects look good for an accurate, real-time forecast scheme built on the acquisition of solar, heliosphere and the near-Earth data and large-scale models. However, the accuracy of these models still needs improve-ment. We will discuss the present status of the models and challenges to improve the simulation models.展开更多
We present a comparative study of the most advanced three-dimensional time-dependent numerical simulation models of solar wind. These models can be classified into two categories： （I） theoretical, empirical and num...We present a comparative study of the most advanced three-dimensional time-dependent numerical simulation models of solar wind. These models can be classified into two categories： （I） theoretical, empirical and numerically based models and （Ⅱ） self-consistent multi-dimensional numerical magnetohydrodynamic （MHD） models. The models of Category I are used to sep- arately describe the solar wind solution in two plasma flows regions： transonic/trans-Alfvrnic and supersonic/super-Alfvenic, respectively. Models of Category II construct a complete, single, numerical solar wind solution through subsonic/sub-Alfvrnic region into supersonic/super-Alfvrnic region. The Wang-Sheeley-Arge （WSA）/ENLIL in CISM is the most successful space weather model that belongs to Category I, and the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme （BATS-R-US） code in SWMF （Space Weather Modeling Framework） and the solar-interplanetary conservative element solution element MHD （SIP-CESE MHD） model in SWIM （Space Weather Integrated Model） are the most commonly-used models that belong to Category II. We review the structures of their frameworks, the main results for solar wind background studies that are essential for solar transient event studies, and discuss the common features and differences between these two categories of solar wind models. Finally, we conclude that the transition of these two categories of models to operational use depends on the availability of computational resources at reasonable cost and point out that the models＇ prediction capabilities may be improved by employing finer computational grids, incorporating more observational data and by adding more physical constraints to the models.展开更多
How to prevent and control the outbreak of mosquito-borne diseases,such as malaria,dengue fever and Zika,is an urgent worldwide public health problem.The most conventional method for the control of these diseases is t...How to prevent and control the outbreak of mosquito-borne diseases,such as malaria,dengue fever and Zika,is an urgent worldwide public health problem.The most conventional method for the control of these diseases is to directly kill mosquitoes by spraying insecticides or removing their breeding sites.However,the traditional method is not effective enough to keep the mosquito density below the epidemic risk threshold.With promising results international,the World Mosquito Program’s Wolbachia method is helping to reduce the occurrence of diseases transmitted by mosquitoes.In this paper,we introduce a generalized discrete model to study the dynamics of the Wolbachia infection frequency in mosquito populations where infected mosquitoes are impulsively released.This generalized model covers all the relevant existing models since 1959 as some special cases.After summarizing known results of discrete models deduced from the generalized one,we put forward some interesting open questions to be further investigated for the periodic impulsive releases.展开更多
Heating and acceleration of electrons in solar impulsive hard X-ray （HXR） flares are studied according to the two-stage acceleration model developed by Zhang for solar ^3Herich events. It is shown that electrostatic...Heating and acceleration of electrons in solar impulsive hard X-ray （HXR） flares are studied according to the two-stage acceleration model developed by Zhang for solar ^3Herich events. It is shown that electrostatic H-cyclotron waves can be excited at a parallel phase velocity less than about the electron thermal velocity and thus can significantly heat the electrons （up to 40 MK） through landau resonance. The preheated electrons with velocities above a threshold are further accelerated to high energies in the flare-acceleration process. The flareproduced electron spectrum is obtained and shown to be thermal at low energies and power law at high energies. In the non-thermal energy range, the spectrum can be double power law if the spectral power index is energy dependent or related. The electron energy spectrum obtained by this study agrees quantitatively with the result derived from the Reuven Ramaty High Energy Solar Spectroscopic Imager （RHESSI） HXR observations in the flare of 2002 July 23. The total flux and energy flux of electrons accelerated in the solar flare also agree with the measurements.展开更多
Magnetic fields play a fundamental role in the structure and dynamics of the solar corona.As they are driven by their footpoint motions on the solar surface,which transport energy from the interior of the Sun into its...Magnetic fields play a fundamental role in the structure and dynamics of the solar corona.As they are driven by their footpoint motions on the solar surface,which transport energy from the interior of the Sun into its atmosphere,the coronal magnetic fields are stressed continuously with buildup of magnetic nonpotentiality in the form of topology complexity(magnetic helicity)and local electric currents(magnetic free energy).The accumulated nonpotentiality is often released explosively by solar eruptions,manifested as solar flares and coronal mass ejections.展开更多
In this paper we present the results of both evolution of Bibolar Magnetic Regions and flare energy buildup with supergranular diffusion. Based on these results we find (i) MHD processes including diffusion and cyclon...In this paper we present the results of both evolution of Bibolar Magnetic Regions and flare energy buildup with supergranular diffusion. Based on these results we find (i) MHD processes including diffusion and cyclonic of turbulence play a significant role for the development of the complexities of an active region. The meridional flow controls the poleward migration of magnetic field of the active regions, (ii) The diffusion of photosphere field and the magnitude of the shear speed have important effects on the total energy storage in the solar corona.展开更多
The transparent and immutable nature of blockchain provides incentives for organizations wishing to create and implement an open,decentralized governance structure.As members exercise their voting rights,a fault-toler...The transparent and immutable nature of blockchain provides incentives for organizations wishing to create and implement an open,decentralized governance structure.As members exercise their voting rights,a fault-tolerant record accumulates on the blockchain that can be analyzed to diagnose and intercept potential threats to the governing body.To date,there has not been a systematic study of on-chain governance with respect to voting.In this paper,we provide an analysis of blockchain governance through a case study of the first cryptocurrency to adopt on-chain voting,Dash.Our analysis introduces the key characteristics of blockchain governance,steps through a data-driven exploration of Dash's on-chain voting system,and highlights exploitable attack vectors and vulnerabilities for the subversion of Dash's on-chain voting system via a novel network analysis methodology.We then conclude with guidelines for other organizations looking to implement similar blockchain governance solutions while maintaining integrity in their operations.展开更多
文摘The objective of this paper is to computationally explore the structural stability and strength of gypsum-protected CFS(cold-formed steel)beam channel sections under non-uniform elevated temperatures when exposed to standard fire on one side of the panel and subjected to pure bending.When a CFS member is subjected to fire(or thermal gradients)its material properties change-but this change happens around the cross-section and along the length creating a member which is potentially non-uniform and unsymmetrical in its response even if the apparent geometry is uniform and symmetric.Computational finite element models were analyzed in ABAQUS to establish steady-state thermal gradients of interest.Existing test data were utilized to develop the temperature dependence of the stress-strain response.The time-dependent temperature distribution on the cross-sections obtained from heat transfer analysis was later used in the stability and collapse analyses.The stability of the models was explored to characterize how local,distortional,and global buckling of the member evolves under both uniform and non-uniform temperature distributions.Finally,collapse simulations were performed to characterize the strength under pure bending and explore directly the evolution of strength under the influence of non-uniform temperature.
基金National Natural Science Foundation of China(Grant Nos.51575176,11672106,51775030,51875196)Youth Innovative Talents of Hunan Province of China(Grant No.2015RS4043)
文摘Due to operational wear and uneven carbon absorption in compressor and turbine wheels, the unbalance(me) vibration is induced and could lead to sub?synchronous vibration accidents for high?speed turbocharger(TC). There are very few research works that focus on the magnitude e ects on such induced unbalance vibration. In this paper, a finite element model(FEM) is developed to characterize a realistic automotive TC rotor with floating ring bearings(FRBs). The nonlinear dynamic responses of the TC rotor system with di erent levels of induced unbalance magni?tude in compressor and turbine wheels are calculated. From the results of waterfall and response spectral intensity plots, the bifurcation and instability phenomena depend on unbalance magnitude during the startup of TC. The sub?synchronous component 0.12× caused rotor unstable is the dominant frequency for small induced unbalance. The nonlinear e ects of induced unbalance in the turbine wheel is obvious stronger than the compressor wheel. As the unbalance magnitude increases from 0.05 gbration 1·mm to 0.2 g·mm, the vibration component changes from mainly 0.12× to synchronous vi×. When unbalance increases continuously, the rotor vibration response amplitude is rapidly growing and the 1× caused by the large unbalance excitation becomes the dominant frequency. A suitable un?balance magnitude of turbine wheel and compressor wheel for the high?speed TC rotor with FRBs is proposed: the value of induced un?balance magnitude should be kept around 0.2 g·mm.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40621003, 40536029, 40504020, and 40523006, the National Basic Research Programme of China under Grant No 2006CB806304, and the CAS International Partnership Programme for Creative Research Teams. Dr S. T. Wu is supported by AFOSR under Grant No FA 9550-07-1-0468 and NSF ATM036115.
文摘Our newly developed CESE MHD model is used to simulate sun-earth connection event with the well-studied 12 May 1997 CME event as an example. The main features and approximations of our numerical model are as follows： （1） The modifed conservation element and solution element （CESE） numerical scheme in spherical geometry is implemented in our code. （2） The background solar wind is derived from a 3D time-dependent numerical MHD model by input measured photospheric magnetic fields. （3） Transient disturbances are derived from solar surface by introducing a mass flow of hot plasma. The numerical simulation has enabled us to predict the arrival of the interplanetary shock and provided us with a relatively satisfactory comparison with the WIND spacecraft observations.
基金supported by the 973 program under grant 2012CB825601the Chinese Academy of Sciences (KZZD-EW-01-4)+3 种基金the National Natural Science Foundation of China (Nos.41204126,41231068,41274192,41031066 and 41374176)the Specialized Research Fund for State Key Laboratoriessupported by NSFAGS1153323 and AGS1062050support by the Youth Innovation Promotion Association of CAS (2015122)
文摘Solar active region （AR） 11283 is a very magnetically complex region and it has produced many eruptions. However, there exists a non-eruptive filament in the plage region just next to an eruptive one in the AR, which gives us an opportunity to perform a comparison analysis of these two filaments. The coronal magnetic field extrapolated using our CESE-MHD-NLFFF code reveals that two magnetic flux ropes （MFRs） exist in the same extrapolation box supporting these two filaments, respectively. Analysis of the magnetic field shows that the eruptive MFR contains a bald-patch separatrix surface （BPSS） co- spatial very well with a pre-eruptive EUV sigmoid, which is consistent with the BPSS model for coronal sigmoids. The magnetic dips of the non-eruptive MFRs match Hα observation of the non-eruptive filament strikingly well, which strongly supports the MFR-dip model for filaments. Compared with the non-eruptive MFR/filament （with a length of about 200 Mm）, the eruptive MFR/filament is much smaller （with a length of about 20 Mm）, but it contains most of the magnetic free energy in the extrapolation box and holds a much higher free energy density than the non-eruptive one. Both the MFRs are weakly twisted and cannot trigger kink instability. The AR eruptive MFR is unstable because its axis reaches above a critical height for torus instability, at which the overlying closed arcades can no longer confine the MFR stably. On the contrary, the quiescent MFR is very firmly held by its overlying field, as its axis apex is far below the torus-instability threshold height. Overall, this comparison investigation supports that an MFR can exist prior to eruption and the ideal MHD instability can trigger an MFR eruption.
文摘Hair has historically reflected material consequences in the Black community; thus, research has begun to investigate how the power/privilege matrix that is propagated throughout the media permeates society and impacts African-Arnerican women＇s perceptions of hair. This research joins the discussion by exploring how Black hair magazine advertisements influence Black women＇s hair decisions and their percepfious of what constitutes beautiful Black hair. Findings reveal that the images African-American women consume from Black hair magazine advertisements do impact what they consider to be beautiful and, subsequently, influence their day-to-day styling and hair care mechanisms, lending further support to the idea that the media serve as powerful sources of knowledge. This study culminates by theorizing about the constitutive meanings and importance of Black hair as conveyed through magazine advertisements and considers how Black women use social comparisons to make everyday hair decisions to achieve what they identify as good hair.
文摘This paper presents a comparative“cradle to gate”life cycle assessment(LCA)of 3D printing houses and conventional buildings using SimaPro software,as a tool to model and compare the two alternatives.The study considered a terraced type of buildings with a floor area of 60 m^(2)(functional unit),which could occupy 2-3 households.The results indicated that 3D printing houses have a smaller environmental impact than conventional buildings in all impact categories except in terrestrial ecotoxicity,in which both alternatives resulted in 172 kg 1,4-DB eq.3D printing houses exhibit a higher climate impact from Timber floorboards,window frames,and Portland cement which are responsible for 7.39×10^(4) kg CO_(2) eq,9.34 ×10^(4) kg CO_(2) eq,and 3.82×10^(4) kg CO_(2) eq respectively.
文摘While there is overwhelming evidence for dark matter (DM) in galaxies and galaxy clusters, all searches for DM particles have so far proved negative. It is not even clear whether only one particle is involved or a combination of particles, their masses not precisely predicted. This non-detectability raises the possible relevance of modified gravity theories: MOND, MONG, etc. Here we consider a specific modification of Newtonian gravity (MONG) which involves gravitational self-energy, leading to modified equations whose solutions imply flat rotation curves and limitations of sizes of clusters. The results are consistent with current observations including that involving large spirals. This modification could also explain the current Hubble tension. We also consider the effects of dark energy (DE) in terms of a cosmological constant.
基金supported by the National Natural Science Foundation of China (41531073, 41374176, 41574170, 41231068 and 41574171)the Specialized Research Fund for State Key Laboratories
文摘With SDO observations and a data-constrained magnetohydrodynamics （MHD） model, we identify a confined multi-ribbon flare that occurred on 2010 October 25 in solar active region 11117 as a magnetic bald patch （BP） flare with strong evidence. From the photospheric magnetic field observed by SDO/HMI, we find there are indeed magnetic BPs on the polarity inversion lines （PILs） which match parts of the flare ribbons. From the 3D coronal magnetic field derived from an MHD relaxation model constrained by the vector magnetograms, we find strikingly good agreement of the BP separatrix surface （BPSS） footpoints with the flare ribbons, and the BPSS itself with the hot flaring loop system. Moreover, the triggering of the BP flare can be attributed to a small flux emergence under the lobe of the BPSS, and the relevant change of coronal magnetic field through the flare is reproduced well by the pre-flare and post-flare MHD solutions, which match the corresponding pre- and post-flare AIA observations, respectively. Our work contributes to the study of non-typical flares that constitute the majority of solar flares but which cannot be explained by the standard flare model.
文摘The dynamical behavior of fluids affected by the asymmetric gravity jitter oscillations, in particular, the effect of surface tension on partially-filled rotating fluids in a Dewar tank imposed by time-dependent directions of background reduced gravity accelerations is investigated. Results show that the greater the components of background reduced gravity in radial and circumferential directions, the greater will be the tendency toward increasing amplitude and degrees of asymmetry of the liquid-vapor interface profiles.
基金supported by the National Natural Science Foundation of China(Grant Nos.11790303(11790300),41774180,11750110424,11703017)。
文摘We present a method of forced-field(i.e., non-force-free field: NFFF) extrapolation of the global magnetic field in the corona, on the basis of single-layer vector magnetogram, by extending an extrapolation technique of local magnetic field first developed by Hu et al.(2008). The forced coronal magnetic field is described by a system with the minimum dissipation rate(MDR) which is appropriate for the corona as a forced and open system. The obtained solution of the magnetic field can be decomposed into three components including one potential field and two linear force-free fields(LFFF). Starting from the given single-layer vector magnetogram, the bottom boundary condition for each component is determined with an iterative method to achieve a minimum difference of the transverse component between the extrapolated field and the original magnetogram. The final extrapolated forced field is given by the sum of the three component fields with the obtained bottom boundaries. The method is tested with an analytic magnetohydrostatic(MHS) solution. It is shown that the extrapolated forced field is highly consistent with the MHS solution at least from the solar disk to the heliocentric distance of 1.5 solar radii(R⊙). For instance, the complements of normalized and mean vector errors(E’n, E’m) are as high as ~97% and 95%, respectively. Further comparisons between magnetic strength, force and field line distributions indicate that the MHS solution has been successfully reconstructed.
文摘Electric power distribution systems are vulnerable to disruption due to severe weather events,especially hurricanes.Such vulnerability is expected to increase over time due to the impact of climate change on hurricanes and the decay of wood poles that support the distribution lines.This study investigates the effectiveness of using fiber-reinforced polymer(FRP)sleeve to reinforce wood poles subjected to decay and hurricane hazard to restore their lost strength and extend their effective service life.The potential impact of climate change on the pole decay rate and the intensity and frequency of hurricanes is also considered.The optimal FRP repair time based on the structural reliability of the poles is also determined.Three locations with varying climates are chosen to evaluate and compare the results:Miami,Charleston,and New York City.The results show that in all three locations,the application of the FRP sleeve can more than double the service life of the pole depending on the time of the repair.The results also show that climate change significantly increases the vulnerability of the pole.The probability of failure of the pole at the end of the 21st century under RCP8.5 emission scenario in Miami,Charleston,and New York City increase by about 30%,70%,and 73%,respectively,compared to a no climate change scenario.If climate change is only assumed to affect the decay of the pole,i.e.,no change in hurricane hazard intensity,the corresponding increases in failure probability are 5%,22%,and 20% in Miami,Charleston,and New York City,respectively.This implies that most of the impact of climate change on pole failure risk is due to the increase in hurricane intensity.The impact of climate change on decay is found to be comparatively small.It increases with time as variation in temperature and precipitation becomes more prominent towards the end of the 21st century.The optimization results show that the optimal FRP repair time depends on how the FRP affects the pole's decay rate.If the FRP can significantly slow down the wood decay rate,the optimal time of repair is at the beginning of the pole's life cycle.If the FRP has no impact on the wood decay rate,it is better to repair the pole after significant decay has occurred.
基金AFOSR (Grant No. FA9550-07-1-0468)AURA Sub-Award C10569A of NSO’s Cooperative Agreement AST 0132798, and NSF (Grant No. ATM-0754378)CCW is supported by NASA grant NNX07AH85G, FENG is supported by National Natural Science Foundation of China (Grant Nos. 40536029, 40621003, 40374056 and 40574058)
文摘In recent years remarkable advances have been made in the development of phys-ics based models of various parts of the solar-terrestrial system (see JASTP special issues, October, November 2004; February 2007). In this paper, we focus our dis-cussions in a specific region of the Sun to the Earth’s environment (i.e. 1 AU). It is well-known that geomagnetic storms are caused by solar eruptions. The conse-quences of these storms include particle acceleration, solar wind impact on the Earth’s magnetosphere and ionosphere, UV-EUV radiation effects on the lower at-mosphere, etc. One of the main challenges is to predict the arrival time at 1 AU of the solar disturbance. The prospects look good for an accurate, real-time forecast scheme built on the acquisition of solar, heliosphere and the near-Earth data and large-scale models. However, the accuracy of these models still needs improve-ment. We will discuss the present status of the models and challenges to improve the simulation models.
基金Work done by Shi Tsan WU was supported by National Science Foundation of USA(Grant No.AGS 1153323)
文摘We present a comparative study of the most advanced three-dimensional time-dependent numerical simulation models of solar wind. These models can be classified into two categories： （I） theoretical, empirical and numerically based models and （Ⅱ） self-consistent multi-dimensional numerical magnetohydrodynamic （MHD） models. The models of Category I are used to sep- arately describe the solar wind solution in two plasma flows regions： transonic/trans-Alfvrnic and supersonic/super-Alfvenic, respectively. Models of Category II construct a complete, single, numerical solar wind solution through subsonic/sub-Alfvrnic region into supersonic/super-Alfvrnic region. The Wang-Sheeley-Arge （WSA）/ENLIL in CISM is the most successful space weather model that belongs to Category I, and the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme （BATS-R-US） code in SWMF （Space Weather Modeling Framework） and the solar-interplanetary conservative element solution element MHD （SIP-CESE MHD） model in SWIM （Space Weather Integrated Model） are the most commonly-used models that belong to Category II. We review the structures of their frameworks, the main results for solar wind background studies that are essential for solar transient event studies, and discuss the common features and differences between these two categories of solar wind models. Finally, we conclude that the transition of these two categories of models to operational use depends on the availability of computational resources at reasonable cost and point out that the models＇ prediction capabilities may be improved by employing finer computational grids, incorporating more observational data and by adding more physical constraints to the models.
基金supported by National Natural Science Foundation of China(Grant Nos.11971127,12071095 and 11631005)the Changjiang Scholars Program and Program for Innovative Research Team in University(Grant No.IRT 16R16)。
文摘How to prevent and control the outbreak of mosquito-borne diseases,such as malaria,dengue fever and Zika,is an urgent worldwide public health problem.The most conventional method for the control of these diseases is to directly kill mosquitoes by spraying insecticides or removing their breeding sites.However,the traditional method is not effective enough to keep the mosquito density below the epidemic risk threshold.With promising results international,the World Mosquito Program’s Wolbachia method is helping to reduce the occurrence of diseases transmitted by mosquitoes.In this paper,we introduce a generalized discrete model to study the dynamics of the Wolbachia infection frequency in mosquito populations where infected mosquitoes are impulsively released.This generalized model covers all the relevant existing models since 1959 as some special cases.After summarizing known results of discrete models deduced from the generalized one,we put forward some interesting open questions to be further investigated for the periodic impulsive releases.
基金NASA Grant （NNG04GD59G A/C 2-302-14-3380-119） National Science Foundation （ATM 00-70385）.
文摘Heating and acceleration of electrons in solar impulsive hard X-ray （HXR） flares are studied according to the two-stage acceleration model developed by Zhang for solar ^3Herich events. It is shown that electrostatic H-cyclotron waves can be excited at a parallel phase velocity less than about the electron thermal velocity and thus can significantly heat the electrons （up to 40 MK） through landau resonance. The preheated electrons with velocities above a threshold are further accelerated to high energies in the flare-acceleration process. The flareproduced electron spectrum is obtained and shown to be thermal at low energies and power law at high energies. In the non-thermal energy range, the spectrum can be double power law if the spectral power index is energy dependent or related. The electron energy spectrum obtained by this study agrees quantitatively with the result derived from the Reuven Ramaty High Energy Solar Spectroscopic Imager （RHESSI） HXR observations in the flare of 2002 July 23. The total flux and energy flux of electrons accelerated in the solar flare also agree with the measurements.
基金Thiswork is jointly supported by the National Natural Science Foundation of China(NSFC 42174200,41822404,and 41731067)the Fundamental Research Funds for the Central Universities(HIT.OCEF.2021033)+1 种基金the Shenzhen Science and Technology Program(RCJC20210609104422048 and JCYJ20190806142609035)Y.G.is supported by NSFC(11773016 and 11961131002)and 2020YFC2201201.We thank Dr.Aiying Duan for a careful reading of themanuscript.We are very grateful to the six reviewers for helpful comments and suggestions,which improved our manuscript.
文摘Magnetic fields play a fundamental role in the structure and dynamics of the solar corona.As they are driven by their footpoint motions on the solar surface,which transport energy from the interior of the Sun into its atmosphere,the coronal magnetic fields are stressed continuously with buildup of magnetic nonpotentiality in the form of topology complexity(magnetic helicity)and local electric currents(magnetic free energy).The accumulated nonpotentiality is often released explosively by solar eruptions,manifested as solar flares and coronal mass ejections.
文摘In this paper we present the results of both evolution of Bibolar Magnetic Regions and flare energy buildup with supergranular diffusion. Based on these results we find (i) MHD processes including diffusion and cyclonic of turbulence play a significant role for the development of the complexities of an active region. The meridional flow controls the poleward migration of magnetic field of the active regions, (ii) The diffusion of photosphere field and the magnitude of the shear speed have important effects on the total energy storage in the solar corona.
文摘The transparent and immutable nature of blockchain provides incentives for organizations wishing to create and implement an open,decentralized governance structure.As members exercise their voting rights,a fault-tolerant record accumulates on the blockchain that can be analyzed to diagnose and intercept potential threats to the governing body.To date,there has not been a systematic study of on-chain governance with respect to voting.In this paper,we provide an analysis of blockchain governance through a case study of the first cryptocurrency to adopt on-chain voting,Dash.Our analysis introduces the key characteristics of blockchain governance,steps through a data-driven exploration of Dash's on-chain voting system,and highlights exploitable attack vectors and vulnerabilities for the subversion of Dash's on-chain voting system via a novel network analysis methodology.We then conclude with guidelines for other organizations looking to implement similar blockchain governance solutions while maintaining integrity in their operations.
