According to the characteristics of comprehensive mechanized heading face, established the mathematical model of single-phase air flow with κ-ε two equations model, and have established κ-ε-θ-κp mathematic model...According to the characteristics of comprehensive mechanized heading face, established the mathematical model of single-phase air flow with κ-ε two equations model, and have established κ-ε-θ-κp mathematic model to solve two-phase flow of gas and particles in dust space with eulerian-eulerian method and eulerian-lagrangian method. Numerical solution of gas-particle two-phase flow was put forward based on collocated grid SIMPLE algorithm. Moreover, numerical simulation of dust concentration in fully mechanized caving face was carded out by using Fluent software. Finally, when in forced-exhaust ventilation circumstance, drawer type fan drum have less dust absorption, and most of dust spread to the other site; the dust concentration is inversely proportional to the distance from tunneling head, and the dust concentration has already diffused to decrease below 102 mg/m3 at the position ofx=12 m. Dust are more focused on relative side（in the range about y from 0 to 2 meter） of roadway space of press-ventilated fan drum, especially between tunneling place and drawer type fan drum; the roadway with road header have a higher dust concentration. These conclusions provide reliable theory basis for the dust prevention in comprehensive mechanized heading face.展开更多
Effect of dust charge fluctuations on Kelvin-Helmholtz (K-H) instability driven by sheared dust flow is investigated in magnetised three-component cold dusty plasma. It is found that the dust charge fluctuations have ...Effect of dust charge fluctuations on Kelvin-Helmholtz (K-H) instability driven by sheared dust flow is investigated in magnetised three-component cold dusty plasma. It is found that the dust charge fluctuations have little effect on the tenuous dust plasma in low-frequency perturbation. For a dense dust plasma, the maximum damping rate of the perturbed wave due to dust charge fluctuations will reach the order of dusty charging frequency. It will affect the existence of the K-H instability in the long wave length perturbation.展开更多
Based upon broad-band CCD observation data of comet Hale-Bopp obtained by a 60cm telescope at Xinglong Station of Beijing Astronomical Observatory during March-August, 1996, the photometric results of comet Hale-Bopp ...Based upon broad-band CCD observation data of comet Hale-Bopp obtained by a 60cm telescope at Xinglong Station of Beijing Astronomical Observatory during March-August, 1996, the photometric results of comet Hale-Bopp are reported. Using the photometric results, the dust production rate, radius and mass of nucleus of comet Hale-Bopp are estimated as follows: dM/dt～1.5×10 5 kgs -1, R n～35.5km, and M n～5.65×10 16kg.展开更多
The three measurement periods: the TOMS Nimbus-7 TOMSN7L3 v008 from 1978 to 1993, the TOMS EP TOMSEPL3 v008 from 1996 to 2005 and the OMI OMTO3d v003 from 2004 to 2008 have allowed the presence of dust to be observed ...The three measurement periods: the TOMS Nimbus-7 TOMSN7L3 v008 from 1978 to 1993, the TOMS EP TOMSEPL3 v008 from 1996 to 2005 and the OMI OMTO3d v003 from 2004 to 2008 have allowed the presence of dust to be observed in the 10°North to 20°North latitudinal band (10 - 20 band) of Africa. The 10 - 20 band has a permanent dust presence. The AERONET data show AOD peaks exceeding 2 in Senegal and Niger (on an AOD scale). The statistical study reveals intra-annual relationships in deposition. In Senegal, a significant deposition is observed.展开更多
Based on measurements at the Beijing 325-m Meteorological Tower,this study reports an analysis of atmospheric stability conditions and turbulent exchange during consecutive episodes of particle air pollution in Beijin...Based on measurements at the Beijing 325-m Meteorological Tower,this study reports an analysis of atmospheric stability conditions and turbulent exchange during consecutive episodes of particle air pollution in Beijing(China),primarily due to haze and dust events(15–30 April 2012).Of particular interest were relevant vertical variations within the lower urban boundary layer(UBL).First,the haze and dust events were characterized by different atmospheric conditions,as quite low wind speed and high humidity are typically observed during haze events.In addition,for the description of stability conditions,the bulk Richardson number(RiB) was calculated for three different height intervals: 8–47,47–140,and 140–280 m.The values of RiB indicated an apparent increase in the occurrence frequency of stably-stratified air layers in the upper height interval—for the 140–280-m height interval,positive values of RiB occurred for about 85% of the time.The downward turbulent exchange of sensible heat was observed at 280 m for the full diurnal cycle,which,by contrast,was rarely seen at 140 m during daytime.These results reinforce the importance of implementing high-resolution UBL profile observations and addressing issues related to stably-stratified flows.展开更多
known aridity of the region is a major factor in promoting numerous dust storms. They have many diverse impacts on the environment and the climate of the region. The classification of dust storms and synoptic conditio...known aridity of the region is a major factor in promoting numerous dust storms. They have many diverse impacts on the environment and the climate of the region. The classification of dust storms and synoptic conditions related to their formation in Central Asia are discussed in the content of their diverse impact. We address dust optical properties that are representative of the region. Dust storms significantly reduce visibly and pose a human health threads. They also cause a significant impact on the radiative regime. As a result, dust storms may cause a decrease in temperature during daytime of up to 16℃ and an increase in temperature during night time from up to 7℃ compared to a clear day.展开更多
The equilibrium potential and dust fragmentation criterion of fluffy dust grains in plasma are calculated for comet P/Halley . It is found that the dust grain acquires its largest negative potential and disruptive pro...The equilibrium potential and dust fragmentation criterion of fluffy dust grains in plasma are calculated for comet P/Halley . It is found that the dust grain acquires its largest negative potential and disruptive probability about 50,000km from the comet where the dust mass spectrum measured by the spacecraft took a great change.展开更多
The equilibrium potential of fluffy dust grains in plasma are calculated for comet P/Halley and comet P/G-Z. It is found that the dust equilibrium potential linearly correlates with the logarithm of electron density. ...The equilibrium potential of fluffy dust grains in plasma are calculated for comet P/Halley and comet P/G-Z. It is found that the dust equilibrium potential linearly correlates with the logarithm of electron density. We propose this relationship can also be applied to comet Hale-Bopp.展开更多
The observed linear polarization data of comet Hyakutake are studied at wavelengths λ=0.365 μm,λ=0.485 μm and 0.684μm through simulations using Ballistic Particle-Cluster Aggregate and Ballistic Cluster-Cluster A...The observed linear polarization data of comet Hyakutake are studied at wavelengths λ=0.365 μm,λ=0.485 μm and 0.684μm through simulations using Ballistic Particle-Cluster Aggregate and Ballistic Cluster-Cluster Aggregate aggregates of 128 spherical monomers.We first found that the size parameter of the monomer,x ～ 1.56-1.70,turned out to be the most suitable which provides the best fits to the observed dust scattering properties at three wavelengths：λ=0.365 μm,0.485μm and 0.684μm.Thus,the effective radius of the aggregate （r） lies in the range 0.45 μm ≤ r ≤ 0.49 μm at λ=0.365 μm;0.60 μm ≤ r ≤ 0.66 μm at λ=0.485 μm and 0.88 μm ≤ r ≤ 0.94 μm at λ=0.684 μm.Now using superposition T-MATRIX code and the power-law size distribution,n（r） ～ r-3,the best-fitting values of complex refractive indices are calculated for the observed polarization data at the above three wavelengths.The best-fitting complex refractive indices （n,k） are found to be （1.745,0.095） at λ=0.365 μm,（1.743,0.100） at λ=0.485 μm and （1.695,0.100） at λ=0.684 μm.The refractive indices derived from the present analysis correspond to a mixture of both silicates and organics,which are in good agreement with the in situ measurement of comets by different spacecraft.展开更多
An observational result from March 12 to April 15 for comet Hale-Bopp is given in this paper. During this period a fan-shaped erupted region with angular extent of about 100 degrees near the nucleus was seen continual...An observational result from March 12 to April 15 for comet Hale-Bopp is given in this paper. During this period a fan-shaped erupted region with angular extent of about 100 degrees near the nucleus was seen continually. In addition, a shell structure with at most 5 layers often appeared. It is found that these layers were equal-spaced with a distance of about 2×10 4 km and were moving outward with a speed of about 35 m/s. It is suggested that this phenomenon was possibly a kind of wave created by charged attogram dust grains erupted from the nucleus, which collided with either the solar wind or material of the coma. The propagation period of the wave was about 6 days but the spin of the Comet Hale-Bopp could be very slow and the period was about 3 yr. This spin movement had the opposite direction as its orbital motion.展开更多
Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the d...Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30pc within the initial solid angle of the jet. As the jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results show that a break appears in the light curve of optical afterglow but it extends over a factor of - 80 in time rather than a factor of - 10 in time for the case of strong dust extinction and a factor of - 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.展开更多
基金Supported by the National Natural Science Foundation of China （51074100） the National Natural Science Foundation of Shan dong province （ZR2OIOEM016）
文摘According to the characteristics of comprehensive mechanized heading face, established the mathematical model of single-phase air flow with κ-ε two equations model, and have established κ-ε-θ-κp mathematic model to solve two-phase flow of gas and particles in dust space with eulerian-eulerian method and eulerian-lagrangian method. Numerical solution of gas-particle two-phase flow was put forward based on collocated grid SIMPLE algorithm. Moreover, numerical simulation of dust concentration in fully mechanized caving face was carded out by using Fluent software. Finally, when in forced-exhaust ventilation circumstance, drawer type fan drum have less dust absorption, and most of dust spread to the other site; the dust concentration is inversely proportional to the distance from tunneling head, and the dust concentration has already diffused to decrease below 102 mg/m3 at the position ofx=12 m. Dust are more focused on relative side（in the range about y from 0 to 2 meter） of roadway space of press-ventilated fan drum, especially between tunneling place and drawer type fan drum; the roadway with road header have a higher dust concentration. These conclusions provide reliable theory basis for the dust prevention in comprehensive mechanized heading face.
文摘Effect of dust charge fluctuations on Kelvin-Helmholtz (K-H) instability driven by sheared dust flow is investigated in magnetised three-component cold dusty plasma. It is found that the dust charge fluctuations have little effect on the tenuous dust plasma in low-frequency perturbation. For a dense dust plasma, the maximum damping rate of the perturbed wave due to dust charge fluctuations will reach the order of dusty charging frequency. It will affect the existence of the K-H instability in the long wave length perturbation.
文摘Based upon broad-band CCD observation data of comet Hale-Bopp obtained by a 60cm telescope at Xinglong Station of Beijing Astronomical Observatory during March-August, 1996, the photometric results of comet Hale-Bopp are reported. Using the photometric results, the dust production rate, radius and mass of nucleus of comet Hale-Bopp are estimated as follows: dM/dt～1.5×10 5 kgs -1, R n～35.5km, and M n～5.65×10 16kg.
文摘The three measurement periods: the TOMS Nimbus-7 TOMSN7L3 v008 from 1978 to 1993, the TOMS EP TOMSEPL3 v008 from 1996 to 2005 and the OMI OMTO3d v003 from 2004 to 2008 have allowed the presence of dust to be observed in the 10°North to 20°North latitudinal band (10 - 20 band) of Africa. The 10 - 20 band has a permanent dust presence. The AERONET data show AOD peaks exceeding 2 in Senegal and Niger (on an AOD scale). The statistical study reveals intra-annual relationships in deposition. In Senegal, a significant deposition is observed.
基金funded by the National Basic Research Program of China (Grant No.2014CB447900)Xiaofeng GUO acknowledges the support of the State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry,Institute of Atmospheric Physics,Chinese Academy of Sciences (Grant No.LAPC-KF-2009-02)
文摘Based on measurements at the Beijing 325-m Meteorological Tower,this study reports an analysis of atmospheric stability conditions and turbulent exchange during consecutive episodes of particle air pollution in Beijing(China),primarily due to haze and dust events(15–30 April 2012).Of particular interest were relevant vertical variations within the lower urban boundary layer(UBL).First,the haze and dust events were characterized by different atmospheric conditions,as quite low wind speed and high humidity are typically observed during haze events.In addition,for the description of stability conditions,the bulk Richardson number(RiB) was calculated for three different height intervals: 8–47,47–140,and 140–280 m.The values of RiB indicated an apparent increase in the occurrence frequency of stably-stratified air layers in the upper height interval—for the 140–280-m height interval,positive values of RiB occurred for about 85% of the time.The downward turbulent exchange of sensible heat was observed at 280 m for the full diurnal cycle,which,by contrast,was rarely seen at 140 m during daytime.These results reinforce the importance of implementing high-resolution UBL profile observations and addressing issues related to stably-stratified flows.
文摘known aridity of the region is a major factor in promoting numerous dust storms. They have many diverse impacts on the environment and the climate of the region. The classification of dust storms and synoptic conditions related to their formation in Central Asia are discussed in the content of their diverse impact. We address dust optical properties that are representative of the region. Dust storms significantly reduce visibly and pose a human health threads. They also cause a significant impact on the radiative regime. As a result, dust storms may cause a decrease in temperature during daytime of up to 16℃ and an increase in temperature during night time from up to 7℃ compared to a clear day.
基金theNationalNaturalScienceFoundationofChina (No .196 5 30 0 1)
文摘The equilibrium potential and dust fragmentation criterion of fluffy dust grains in plasma are calculated for comet P/Halley . It is found that the dust grain acquires its largest negative potential and disruptive probability about 50,000km from the comet where the dust mass spectrum measured by the spacecraft took a great change.
基金theNationalNaturalScienceFoundationofChinaUnderGrant (No .199730 18& 196 5 30 0 1)
文摘The equilibrium potential of fluffy dust grains in plasma are calculated for comet P/Halley and comet P/G-Z. It is found that the dust equilibrium potential linearly correlates with the logarithm of electron density. We propose this relationship can also be applied to comet Hale-Bopp.
文摘The observed linear polarization data of comet Hyakutake are studied at wavelengths λ=0.365 μm,λ=0.485 μm and 0.684μm through simulations using Ballistic Particle-Cluster Aggregate and Ballistic Cluster-Cluster Aggregate aggregates of 128 spherical monomers.We first found that the size parameter of the monomer,x ～ 1.56-1.70,turned out to be the most suitable which provides the best fits to the observed dust scattering properties at three wavelengths：λ=0.365 μm,0.485μm and 0.684μm.Thus,the effective radius of the aggregate （r） lies in the range 0.45 μm ≤ r ≤ 0.49 μm at λ=0.365 μm;0.60 μm ≤ r ≤ 0.66 μm at λ=0.485 μm and 0.88 μm ≤ r ≤ 0.94 μm at λ=0.684 μm.Now using superposition T-MATRIX code and the power-law size distribution,n（r） ～ r-3,the best-fitting values of complex refractive indices are calculated for the observed polarization data at the above three wavelengths.The best-fitting complex refractive indices （n,k） are found to be （1.745,0.095） at λ=0.365 μm,（1.743,0.100） at λ=0.485 μm and （1.695,0.100） at λ=0.684 μm.The refractive indices derived from the present analysis correspond to a mixture of both silicates and organics,which are in good agreement with the in situ measurement of comets by different spacecraft.
文摘An observational result from March 12 to April 15 for comet Hale-Bopp is given in this paper. During this period a fan-shaped erupted region with angular extent of about 100 degrees near the nucleus was seen continually. In addition, a shell structure with at most 5 layers often appeared. It is found that these layers were equal-spaced with a distance of about 2×10 4 km and were moving outward with a speed of about 35 m/s. It is suggested that this phenomenon was possibly a kind of wave created by charged attogram dust grains erupted from the nucleus, which collided with either the solar wind or material of the coma. The propagation period of the wave was about 6 days but the spin of the Comet Hale-Bopp could be very slow and the period was about 3 yr. This spin movement had the opposite direction as its orbital motion.
基金Supported by the National Natural Science Foundation of China
文摘Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30pc within the initial solid angle of the jet. As the jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results show that a break appears in the light curve of optical afterglow but it extends over a factor of - 80 in time rather than a factor of - 10 in time for the case of strong dust extinction and a factor of - 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.
