In this study, knowledge, attitude and perception (KAP) of maritime workers’ towards COVID-19 during the rapid outbreak in Nigeria and the UK were examined. The study participants completed a self-developed online KA...In this study, knowledge, attitude and perception (KAP) of maritime workers’ towards COVID-19 during the rapid outbreak in Nigeria and the UK were examined. The study participants completed a self-developed online KAP questionnaire prepared by the convenience sampling method. The knowledge questionnaire comprised questions regarding the clinical characteristics and prevention of COVID-19. The assessments regarding the maritime workers’ attitudes and perceptions towards COVID-19 included questions on preventive measures such as wearing masks on the ships and the attitude towards continuous trade with the Chinese communities. A multiple logistic regression analysis was done using SPSS Statistics version 23.0 to analyse the results of the two groups. The three explanatory variables, gender, residence and age used in the two models applied were not significant predictors of the participants’ knowledge, attitude and perception about COVID-19. The odds ratio was small, except for the age group, which was 6.72 in the first model. This implies that the odds of having knowledge about COVID-19 during the pandemic were 6.72 times higher for the older age group. The odds ratios were generally low for attitude and perception about COVID-19, as shown in Table 4. Participants had considerable knowledge about COVID-19 and could stay healthy during the first wave of the novel coronavirus in 2019 because of the policies and measures imposed by the governments of Nigeria and the United Kingdom to curtail the spread of COVID-19.展开更多
Background: The use of chest imaging in COVID-19 can be especially useful for patients with moderate to severe symptoms or comorbidities. Objective: This study aimed to demonstrate the high resolution computed tomogra...Background: The use of chest imaging in COVID-19 can be especially useful for patients with moderate to severe symptoms or comorbidities. Objective: This study aimed to demonstrate the high resolution computed tomography (CT) findings observed among the coronavirus disease 2019 (COVID-19) patients presented with pneumonia and to reveal the most frequent infiltration and distribution patterns of the disease. Methodology: This was a retrospective study. This study was performed in the Department of Radiology & Imaging at Kurmitola General Hospital, Dhaka, Bangladesh. This was the first dedicated COVID-19 hospital with a bed capacity of 500 and well-equipped ICU facilities. The recorded HRCT scan data were collected in the period from April 2020 up to May 2020 during the first wave of COVID-19 in Bangladesh. As this was a retrospective study, verbal or written consent was not obtained from all potential participants or guardians. The available demographic data as well as the medical history of all data were collected and thoroughly reviewed from the record book. These patients were RT-PCR confirmed cases of COVID-19 patients presented with pneumonia and were admitted to Kurmitola General Hospital, Dhaka, Bangladesh. All these patients underwent HRCT scans of the chest. Result: A total number of 155 COVID-19 patients with HRCT scan were evaluated. The mean age with SD of the study population was 58.03 ± 14.08 years with the range of 22 to 97 years. The male and female ratio was 2.04:1. Fibrosis of the lungs and thickening of pleura were found in 38 (24.5%) cases and 33 (21.3%) cases respectively. The involvement of both lungs was found in 32 (20.6%) cases. The presence of pneumonitis and bronchiectasis were detected in 77 (49.7%) cases and 5 (3.2%) cases respectively. Left-sided mild pleural effusion was also noted in 6 (3.9%) cases. Ground glass opacity was found in different forms. The most common form was the presence of only ground glass opacities which was 63 (40.6%) cases. Bilateral ground-glass opacities were detected in 63 (40.6%) cases. Conclusion: In conclusion, HRCT scan of the chest shows the bilateral ground-glass opacities and fibrosis of the lungs with pneumonitis in most of the COVID-19 hospital admitted patients.展开更多
R-wave detection is the main approach for heart rate variability analysis and clinical application based on R-R interval. The maximum first derivative plus the maximum value of the double search algorithm is applied o...R-wave detection is the main approach for heart rate variability analysis and clinical application based on R-R interval. The maximum first derivative plus the maximum value of the double search algorithm is applied on electrocardiogram(ECG) of MIH-BIT Arrhythmia Database to extract R wave. Through the study of algorithm's characteristics and R-wave detection method, data segmentation method is modified to improve the detection accuracy. After segmentation modification, average accuracy rate of 6 sets of short ECG data increase from 82.51% to 93.70%, and the average accuracy rate of 11 groups long-range data is 96.61%. Test results prove that the algorithm and segmentation method can accurately locate R wave and have good effectiveness and versatility, but may exist some undetected problems due to algorithm implementation.展开更多
According to the freely linear Rossby wave theory, global 1°×1°climatology of Rossby deformation radius and phase speed are studied under the fiat bottom fluid approximation. Geographical variations in ...According to the freely linear Rossby wave theory, global 1°×1°climatology of Rossby deformation radius and phase speed are studied under the fiat bottom fluid approximation. Geographical variations in the contours of the phase speed are very similar to those of the Rossby radius of formation, which are mainly affected by stratification, rotation, water depth, topography, etc. The basin-crossing time of the first baroclinic Rossby wave is obtained and analyzed in the global ocean basins. The results are useful to learn the importance of Rosaby wave and the adiabatic adjustment of large-scale ocean circulation.展开更多
The present paper is aimed to study the effect of Gaussian laser light on first and second sound waves in superfluid helium theoretically using optoacoustic method. The mechanism applied in this study is electrostrict...The present paper is aimed to study the effect of Gaussian laser light on first and second sound waves in superfluid helium theoretically using optoacoustic method. The mechanism applied in this study is electrostriction mechanism. This study considers crystal parts of superfluid helium with a zero absorption coefficient applying electrostriction mechanism. Affecting Gaussian laser light on these crystal parts, a spectrum of cylindrical first and second sound waves and cylindrical slow and rapid waves is obtained. Meanwhile, frequency of waves amplitudes proportionate to time period of laser light is calculated.展开更多
In seismic exploration, it is common practice to separate the P-wavefield from the S-wavefield by the elastic wavefield decomposition technique, for imaging purposes. However, it is sometimes difficult to achieve this...In seismic exploration, it is common practice to separate the P-wavefield from the S-wavefield by the elastic wavefield decomposition technique, for imaging purposes. However, it is sometimes difficult to achieve this, especially when the velocity field is complex. A useful approach in multi-component analysis and modeling is to directly solve the elastic wave equations for the pure P- or S-wavefields, referred as the separate elastic wave equa- tions. In this study, we compare two kinds of such wave equations： the first-order （velocity-stress） and the second- order （displacement-stress） separate elastic wave equa- tions, with the first-order （velocity-stress） and the second- order （displacement-stress） full （or mixed） elastic wave equations using a high-order staggered grid finite-differ- ence method. Comparisons are given of wavefield snap- shots, common-source gather seismic sections, and individual synthetic seismogram. The simulation tests show that equivalent results can be obtained, regardless of whether the first-order or second-order separate elastic wave equations are used for obtaining the pure P- or S-wavefield. The stacked pure P- and S-wavefields are equal to the mixed wave fields calculated using the corre- sponding first-order or second-order full elastic wave equations. These mixed equations are computationallyslightly less expensive than solving the separate equations. The attraction of the separate equations is that they achieve separated P- and S-wavefields which can be used to test the efficacy of wave decomposition procedures in multi-com- ponent processing. The second-order separate elastic wave equations are a good choice because they offer information on the pure P-wave or S-wave displacements.展开更多
Objective:To evaluate patient demographic characteristics and risk factors for mortality during the first and the second wave among COVID-19 patients in a tertiary care hospital of India.Methods:Data were taken from t...Objective:To evaluate patient demographic characteristics and risk factors for mortality during the first and the second wave among COVID-19 patients in a tertiary care hospital of India.Methods:Data were taken from the hospital’s electronic system for COVID-19 patients from August 2020 to December 2020,and the second from January 2021 to May 2021.The mortality rate,demographic and clinical characteristics,laboratory profile,and reasons for the death of the two waves were retrieved and compared,and the risk factors of the two waves were determined.Results:In the first wave,1177 COVID-19 cases visited the hospital and 96(8.2%)died.In comparison,the death rate in the second wave was significantly higher(244/2038,12.0%)(P<0.001).No significant difference in age[60(50-69)vs.60.5(53-70),P=0.11]or gender(P=0.34)was observed between the two waves.Compared to the first wave.there were significantly more cases with fever,cough,weakness,loss of taste and smell,and sore throat during the second wave(P<0.05),but significantly fewer cases with kidney disease(6.6%vs.13.5%,P=0.038)and diabetes mellitus(35.7%vs.50.0%,P=0.015).Besides,during the second wave,more patients had abnormal X-ray findings,higher levels of lymphocytes and serum ferritin(P<0.05).In addition,there were significant differences in the rate of death cases with acidosis,septic shock,acute kidney injury,diabetes mellitus,cardiovascular events,hypothyroidism(P<0.05).Multivariate regression showed that during the first wave,age(OR:1.10;95%CI:1.02-1.21),diabetes mellitus(OR:3.16;95%CI:2.08-3.53),and abnormal X-ray(2.67;95%CI:2.32-2.87)were significant independent risk factors of mortality;while in the second wave,age(OR:1.13;95%CI:1.12-1.28),diabetes mellitus(OR:8.98;95%CI:1.79-45.67),abnormal X-ray(OR:12.83;95%CI:2.32-54.76),high D-dimer(OR:10.89;95%CI:1.56-134.53),and high IL-6(OR:7.89;95%CI:1.18-47.82)were significant independent risk factors of mortality.Conclusion:Overall mortality and incidence of severe diseases are higher in the second wave than the first wave.Demographic characteristics,co-morbidities,and laboratory inflammatory parameters,especially D-dimer and IL-6,are significant risk facors of mortality during the COVID-19 pandemic.展开更多
The quantum object is in general considered as displaying both wave and particle nature. By particle is understood an item localized in a very small volume of the space, and which cannot be simultaneously in two disjo...The quantum object is in general considered as displaying both wave and particle nature. By particle is understood an item localized in a very small volume of the space, and which cannot be simultaneously in two disjoint regions of the space. By wave, to the contrary, is understood a distributed item, occupying in some cases two or more disjoint regions of the space. The quantum formalism did not explain until today the so-called “collapse” of the wave-function, i.e. the shrinking of the wave-function to one small region of the space, when a macroscopic object is encountered. This seems to happen in “which-way” experiments. A very appealing explanation for this behavior is the idea of a particle, localized in some limited part of the wave-function. The present article challenges the concept of particle. It proves in the base of a variant of the Tan, Walls and Collett experiment, that this concept leads to a situation in which the particle has to be simultaneously in two places distant from one another—situation that contradicts the very definition of a particle. Another argument is based on a modified version of the Afshar experiment, showing that the concept of particle is problematic. The concept of particle makes additional difficulties when the wave-function passes through fields. An unexpected possibility to solve these difficulties seems to arise from the cavity quantum electrodynamics studies done recently by S. Savasta and his collaborators. It involves virtual particles. One of these studies is briefly described here. Though, experimental results are needed, so that it is too soon to conclude whether it speaks in favor, or against the concept of particle.展开更多
随着柔性直流电网的发展,其边界结构将发生改变,从“有边界电网”转变为“无边界电网”。如果在配置保护时,能够在原理上尽量适用于两种边界结构,则可以大大降低电网结构变化时保护验证的繁复性、提升保护应用的经济性。为提升线路行波...随着柔性直流电网的发展,其边界结构将发生改变,从“有边界电网”转变为“无边界电网”。如果在配置保护时,能够在原理上尽量适用于两种边界结构,则可以大大降低电网结构变化时保护验证的繁复性、提升保护应用的经济性。为提升线路行波保护对不同边界结构的适用性,该文提出一种新型的行波保护方案。该保护方案主要通过非故障极电流首行波积分(first current integration of non-fault pole,FCINP)实现。基于FCINP在不同边界结构电网下的距离特性和边界特性,可有效地提升保护在有边界电网和无边界电网下的故障识别性能,从而提升保护适用性。所提保护在基于PSCAD/EMTDC直流电网仿真模型中进行了性能验证。展开更多
In this paper, the travelling wave solutions for the generalized Burgers-Huxley equation with nonlinear terms of any order are studied. By using the first integral method, which is based on the divisor theorem, some e...In this paper, the travelling wave solutions for the generalized Burgers-Huxley equation with nonlinear terms of any order are studied. By using the first integral method, which is based on the divisor theorem, some exact explicit travelling solitary wave solutions for the above equation are obtained. As a result, some minor errors and some known results in the previousl literature are clarified and improved.展开更多
Elastic properties of three high pressure polymorphs of CaCO_3 are investigated based on first principles calculations.The calculations are conducted at 0 GPa–40 GPa for aragonite, 40 GPa–65 GPa for post-aragonite, ...Elastic properties of three high pressure polymorphs of CaCO_3 are investigated based on first principles calculations.The calculations are conducted at 0 GPa–40 GPa for aragonite, 40 GPa–65 GPa for post-aragonite, and 65 GPa–150 GPa for the P2_1/c-h-CaCO_3 structure, respectively. By fitting the third-order Birch–Murnaghan equation of state（EOS）, the values of bulk modulus K_0 and pressure derivative K~＇_0 are 66.09 GPa and 4.64 for aragonite, 81.93 GPa and 4.49 for post-aragonite, and 56.55 GPa and 5.40 for P2_1/c-h-CaCO_3, respectively, which are in good agreement with previous experimental and theoretical data. Elastic constants, wave velocities, and wave velocity anisotropies of the three highpressure CaCO_3 phases are obtained. Post-aragonite exhibits 25.90%–32.10% V_P anisotropy and 74.34%–104.30% V_S splitting anisotropy, and P2_1/c-h-CaCO_3 shows 22.30%–25.40% V_Panisotropy and 42.81%–48.00% V_S splitting anisotropy in the calculated pressure range. Compared with major minerals of the lower mantle, CaCO_3 high pressure polymorphs have low isotropic wave velocity and high wave velocity anisotropies. These results are important for understanding the deep carbon cycle and seismic wave velocity structure in the lower mantle.展开更多
文摘In this study, knowledge, attitude and perception (KAP) of maritime workers’ towards COVID-19 during the rapid outbreak in Nigeria and the UK were examined. The study participants completed a self-developed online KAP questionnaire prepared by the convenience sampling method. The knowledge questionnaire comprised questions regarding the clinical characteristics and prevention of COVID-19. The assessments regarding the maritime workers’ attitudes and perceptions towards COVID-19 included questions on preventive measures such as wearing masks on the ships and the attitude towards continuous trade with the Chinese communities. A multiple logistic regression analysis was done using SPSS Statistics version 23.0 to analyse the results of the two groups. The three explanatory variables, gender, residence and age used in the two models applied were not significant predictors of the participants’ knowledge, attitude and perception about COVID-19. The odds ratio was small, except for the age group, which was 6.72 in the first model. This implies that the odds of having knowledge about COVID-19 during the pandemic were 6.72 times higher for the older age group. The odds ratios were generally low for attitude and perception about COVID-19, as shown in Table 4. Participants had considerable knowledge about COVID-19 and could stay healthy during the first wave of the novel coronavirus in 2019 because of the policies and measures imposed by the governments of Nigeria and the United Kingdom to curtail the spread of COVID-19.
文摘Background: The use of chest imaging in COVID-19 can be especially useful for patients with moderate to severe symptoms or comorbidities. Objective: This study aimed to demonstrate the high resolution computed tomography (CT) findings observed among the coronavirus disease 2019 (COVID-19) patients presented with pneumonia and to reveal the most frequent infiltration and distribution patterns of the disease. Methodology: This was a retrospective study. This study was performed in the Department of Radiology & Imaging at Kurmitola General Hospital, Dhaka, Bangladesh. This was the first dedicated COVID-19 hospital with a bed capacity of 500 and well-equipped ICU facilities. The recorded HRCT scan data were collected in the period from April 2020 up to May 2020 during the first wave of COVID-19 in Bangladesh. As this was a retrospective study, verbal or written consent was not obtained from all potential participants or guardians. The available demographic data as well as the medical history of all data were collected and thoroughly reviewed from the record book. These patients were RT-PCR confirmed cases of COVID-19 patients presented with pneumonia and were admitted to Kurmitola General Hospital, Dhaka, Bangladesh. All these patients underwent HRCT scans of the chest. Result: A total number of 155 COVID-19 patients with HRCT scan were evaluated. The mean age with SD of the study population was 58.03 ± 14.08 years with the range of 22 to 97 years. The male and female ratio was 2.04:1. Fibrosis of the lungs and thickening of pleura were found in 38 (24.5%) cases and 33 (21.3%) cases respectively. The involvement of both lungs was found in 32 (20.6%) cases. The presence of pneumonitis and bronchiectasis were detected in 77 (49.7%) cases and 5 (3.2%) cases respectively. Left-sided mild pleural effusion was also noted in 6 (3.9%) cases. Ground glass opacity was found in different forms. The most common form was the presence of only ground glass opacities which was 63 (40.6%) cases. Bilateral ground-glass opacities were detected in 63 (40.6%) cases. Conclusion: In conclusion, HRCT scan of the chest shows the bilateral ground-glass opacities and fibrosis of the lungs with pneumonitis in most of the COVID-19 hospital admitted patients.
基金supported by the National Natural Science Foundation of China(Nos.61271082,61201029,81201161)
文摘R-wave detection is the main approach for heart rate variability analysis and clinical application based on R-R interval. The maximum first derivative plus the maximum value of the double search algorithm is applied on electrocardiogram(ECG) of MIH-BIT Arrhythmia Database to extract R wave. Through the study of algorithm's characteristics and R-wave detection method, data segmentation method is modified to improve the detection accuracy. After segmentation modification, average accuracy rate of 6 sets of short ECG data increase from 82.51% to 93.70%, and the average accuracy rate of 11 groups long-range data is 96.61%. Test results prove that the algorithm and segmentation method can accurately locate R wave and have good effectiveness and versatility, but may exist some undetected problems due to algorithm implementation.
基金This study was supported by the National Natural Science Foundation of China under contract No.40576020the Youth Innovative Foundation Project of Polar Reasearch Institute of China under contract No.J0D 200601.
文摘According to the freely linear Rossby wave theory, global 1°×1°climatology of Rossby deformation radius and phase speed are studied under the fiat bottom fluid approximation. Geographical variations in the contours of the phase speed are very similar to those of the Rossby radius of formation, which are mainly affected by stratification, rotation, water depth, topography, etc. The basin-crossing time of the first baroclinic Rossby wave is obtained and analyzed in the global ocean basins. The results are useful to learn the importance of Rosaby wave and the adiabatic adjustment of large-scale ocean circulation.
文摘The present paper is aimed to study the effect of Gaussian laser light on first and second sound waves in superfluid helium theoretically using optoacoustic method. The mechanism applied in this study is electrostriction mechanism. This study considers crystal parts of superfluid helium with a zero absorption coefficient applying electrostriction mechanism. Affecting Gaussian laser light on these crystal parts, a spectrum of cylindrical first and second sound waves and cylindrical slow and rapid waves is obtained. Meanwhile, frequency of waves amplitudes proportionate to time period of laser light is calculated.
基金partially supported by China National Major Science and Technology Project (Subproject No:2011ZX05024-001-03)
文摘In seismic exploration, it is common practice to separate the P-wavefield from the S-wavefield by the elastic wavefield decomposition technique, for imaging purposes. However, it is sometimes difficult to achieve this, especially when the velocity field is complex. A useful approach in multi-component analysis and modeling is to directly solve the elastic wave equations for the pure P- or S-wavefields, referred as the separate elastic wave equa- tions. In this study, we compare two kinds of such wave equations： the first-order （velocity-stress） and the second- order （displacement-stress） separate elastic wave equa- tions, with the first-order （velocity-stress） and the second- order （displacement-stress） full （or mixed） elastic wave equations using a high-order staggered grid finite-differ- ence method. Comparisons are given of wavefield snap- shots, common-source gather seismic sections, and individual synthetic seismogram. The simulation tests show that equivalent results can be obtained, regardless of whether the first-order or second-order separate elastic wave equations are used for obtaining the pure P- or S-wavefield. The stacked pure P- and S-wavefields are equal to the mixed wave fields calculated using the corre- sponding first-order or second-order full elastic wave equations. These mixed equations are computationallyslightly less expensive than solving the separate equations. The attraction of the separate equations is that they achieve separated P- and S-wavefields which can be used to test the efficacy of wave decomposition procedures in multi-com- ponent processing. The second-order separate elastic wave equations are a good choice because they offer information on the pure P-wave or S-wave displacements.
文摘Objective:To evaluate patient demographic characteristics and risk factors for mortality during the first and the second wave among COVID-19 patients in a tertiary care hospital of India.Methods:Data were taken from the hospital’s electronic system for COVID-19 patients from August 2020 to December 2020,and the second from January 2021 to May 2021.The mortality rate,demographic and clinical characteristics,laboratory profile,and reasons for the death of the two waves were retrieved and compared,and the risk factors of the two waves were determined.Results:In the first wave,1177 COVID-19 cases visited the hospital and 96(8.2%)died.In comparison,the death rate in the second wave was significantly higher(244/2038,12.0%)(P<0.001).No significant difference in age[60(50-69)vs.60.5(53-70),P=0.11]or gender(P=0.34)was observed between the two waves.Compared to the first wave.there were significantly more cases with fever,cough,weakness,loss of taste and smell,and sore throat during the second wave(P<0.05),but significantly fewer cases with kidney disease(6.6%vs.13.5%,P=0.038)and diabetes mellitus(35.7%vs.50.0%,P=0.015).Besides,during the second wave,more patients had abnormal X-ray findings,higher levels of lymphocytes and serum ferritin(P<0.05).In addition,there were significant differences in the rate of death cases with acidosis,septic shock,acute kidney injury,diabetes mellitus,cardiovascular events,hypothyroidism(P<0.05).Multivariate regression showed that during the first wave,age(OR:1.10;95%CI:1.02-1.21),diabetes mellitus(OR:3.16;95%CI:2.08-3.53),and abnormal X-ray(2.67;95%CI:2.32-2.87)were significant independent risk factors of mortality;while in the second wave,age(OR:1.13;95%CI:1.12-1.28),diabetes mellitus(OR:8.98;95%CI:1.79-45.67),abnormal X-ray(OR:12.83;95%CI:2.32-54.76),high D-dimer(OR:10.89;95%CI:1.56-134.53),and high IL-6(OR:7.89;95%CI:1.18-47.82)were significant independent risk factors of mortality.Conclusion:Overall mortality and incidence of severe diseases are higher in the second wave than the first wave.Demographic characteristics,co-morbidities,and laboratory inflammatory parameters,especially D-dimer and IL-6,are significant risk facors of mortality during the COVID-19 pandemic.
文摘The quantum object is in general considered as displaying both wave and particle nature. By particle is understood an item localized in a very small volume of the space, and which cannot be simultaneously in two disjoint regions of the space. By wave, to the contrary, is understood a distributed item, occupying in some cases two or more disjoint regions of the space. The quantum formalism did not explain until today the so-called “collapse” of the wave-function, i.e. the shrinking of the wave-function to one small region of the space, when a macroscopic object is encountered. This seems to happen in “which-way” experiments. A very appealing explanation for this behavior is the idea of a particle, localized in some limited part of the wave-function. The present article challenges the concept of particle. It proves in the base of a variant of the Tan, Walls and Collett experiment, that this concept leads to a situation in which the particle has to be simultaneously in two places distant from one another—situation that contradicts the very definition of a particle. Another argument is based on a modified version of the Afshar experiment, showing that the concept of particle is problematic. The concept of particle makes additional difficulties when the wave-function passes through fields. An unexpected possibility to solve these difficulties seems to arise from the cavity quantum electrodynamics studies done recently by S. Savasta and his collaborators. It involves virtual particles. One of these studies is briefly described here. Though, experimental results are needed, so that it is too soon to conclude whether it speaks in favor, or against the concept of particle.
文摘随着柔性直流电网的发展,其边界结构将发生改变,从“有边界电网”转变为“无边界电网”。如果在配置保护时,能够在原理上尽量适用于两种边界结构,则可以大大降低电网结构变化时保护验证的繁复性、提升保护应用的经济性。为提升线路行波保护对不同边界结构的适用性,该文提出一种新型的行波保护方案。该保护方案主要通过非故障极电流首行波积分(first current integration of non-fault pole,FCINP)实现。基于FCINP在不同边界结构电网下的距离特性和边界特性,可有效地提升保护在有边界电网和无边界电网下的故障识别性能,从而提升保护适用性。所提保护在基于PSCAD/EMTDC直流电网仿真模型中进行了性能验证。
基金supported by the Research Foundation of Education Bureau of Hubei Province,China (Grant No Z200612001)the Natural Science Foundation of Yangtze University (Grant No 20061222)
文摘In this paper, the travelling wave solutions for the generalized Burgers-Huxley equation with nonlinear terms of any order are studied. By using the first integral method, which is based on the divisor theorem, some exact explicit travelling solitary wave solutions for the above equation are obtained. As a result, some minor errors and some known results in the previousl literature are clarified and improved.
基金supported by the National Natural Science Foundation of China(Grant Nos.41174071,41373060,41374096,and 41403099)the Seismic Fund of Institute of Earthquake Science,China Earthquake Administration(CEA)(Grant Nos.2012IES0408,2014IES0407,and 2016IES0101)
文摘Elastic properties of three high pressure polymorphs of CaCO_3 are investigated based on first principles calculations.The calculations are conducted at 0 GPa–40 GPa for aragonite, 40 GPa–65 GPa for post-aragonite, and 65 GPa–150 GPa for the P2_1/c-h-CaCO_3 structure, respectively. By fitting the third-order Birch–Murnaghan equation of state（EOS）, the values of bulk modulus K_0 and pressure derivative K~＇_0 are 66.09 GPa and 4.64 for aragonite, 81.93 GPa and 4.49 for post-aragonite, and 56.55 GPa and 5.40 for P2_1/c-h-CaCO_3, respectively, which are in good agreement with previous experimental and theoretical data. Elastic constants, wave velocities, and wave velocity anisotropies of the three highpressure CaCO_3 phases are obtained. Post-aragonite exhibits 25.90%–32.10% V_P anisotropy and 74.34%–104.30% V_S splitting anisotropy, and P2_1/c-h-CaCO_3 shows 22.30%–25.40% V_Panisotropy and 42.81%–48.00% V_S splitting anisotropy in the calculated pressure range. Compared with major minerals of the lower mantle, CaCO_3 high pressure polymorphs have low isotropic wave velocity and high wave velocity anisotropies. These results are important for understanding the deep carbon cycle and seismic wave velocity structure in the lower mantle.
