The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hy...The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hydraulic shearing.This study first analyzed the crack deflection theory of layered rock.The semi-circle bending test under asymmetric loading is performed,and the four-dimensional Lattice Spring Model(4D-LSM)is established to examine how the bedding parameters affect coal crack propagation under mode Ⅱ dominant loads.The 4D-LSM results are comparable to the coal loading test results under quasi-mode Ⅱ and the analytical prediction of crack deflection theory.During mode Ⅱ loading,the coal crack propagation is greatly influenced by the angle,strength,and elastic modulus of the bedding plane,while the effects of thickness and spacing of bedding are insignificant.The crack of coal tends to propagate towards the bedding,following a decrease in bedding angle,a decrease in bedding strength,and an increase in elastic modulus.With higher bedding strength,spacing,and thickness,the peak load on the coal sample is higher.The influences of bedding strength,elastic modulus,spacing,and thickness on the peak load of coal samples and its anisotropy gradually decrease.It is proved that compared with the tangential stress ratio and traditional energy release ratio theories,the corrected energy release ratio criterion can more accurately predict the direction of crack deflection of coal,especially under mode Ⅱ loading.The results can provide assistance in the design of initiation pressure and fracturing direction in coal seam hydraulic fracturing.展开更多
Different components of deep-sea submersibles,such as the pressure hull,are usually subjected to intermittent loading,dwell loading,and unloading during service.Therefore,for the design and reliability assessment of s...Different components of deep-sea submersibles,such as the pressure hull,are usually subjected to intermittent loading,dwell loading,and unloading during service.Therefore,for the design and reliability assessment of structural parts under dwell fatigue loading,understanding the effects of intermittent loading time on dwell fatigue behavior of the alloys is essential.In this study,the effects of the intermittent loading time and stress ratio on dwell fatigue behavior of the titanium alloy Ti-6 Al-4 V ELI were investigated.Results suggest that the dwell fatigue failure modes of Ti-6 Al-4 V ELI can be classified into three types,i.e.,fatigue failure mode,ductile failure mode,and mixed failure mode.The intermittent loading time does not affect the dwell fatigue behavior,whereas the stress ratio significantly affects the dwell fatigue life and dwell fatigue mechanism.The dwell fatigue life increases with an increase in the stress ratio for the same maximum stress,and specimens with a negative stress ratio tend to undergo ductile failure.The mechanism of dwell fatigue of titanium alloys is attribute to an increase in the plastic strain caused by the part of the dwell loading,thereby resulting in an increase in the actual stress of the specimens during the subsequent loading cycles and aiding the growth of the formed crack or damage,along with the local plastic strain or damage induced by the part of the fatigue load promoting the cumulative plastic strain during the dwell fatigue process.The interaction between dwell loading and fatigue loading accelerates specimen failure,in contrast to the case for individual creep or fatigue loading alone.The dwell fatigue life and cumulative maximum strain during the first loading cycle could be correlated by a linear relationship on the log–log scale.This relationship can be used to evaluate the dwell fatigue life of Ti alloys with the maximum stress dwell.展开更多
By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation beha...By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation behavior of the laser welded joint specimens of TC4 titanium alloy. The results showed that for the unmodified specimens, the yield phenomenon occurs first in the region of the joint, but the undercut value has an effect on the stress and strain of starting to yield phenomenon, and a great effect on the plastic deformation behavior.When the undercut is less than a certain value, the large plastic deformation occurs in the base metal region and the plasticity of the specimen is comparable to that of the base metal, but the larger undercut defect results in a concentrated plastic deformation in the joint region and rapidly failed in this region. But the double-sided dressing specimen is significantly different. The physical yield is no longer concentrated in the joint region, but at the same time occurs in the several regions including joint and the base metal. And the plastic deformation mainly occurs in the base material area, similar to that of the base material.展开更多
A novel 2D/2D Bi_(2)MoO_(6)/g-C_(3)N_(4) step-scheme(S-scheme)composite by loading Au as cocatalyst was successfully fabricated using a photoreduction and hydrothermal route.The obtained Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au ...A novel 2D/2D Bi_(2)MoO_(6)/g-C_(3)N_(4) step-scheme(S-scheme)composite by loading Au as cocatalyst was successfully fabricated using a photoreduction and hydrothermal route.The obtained Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au photocatalysts were characterized by X-ray diffraction(XRD),transmission electron microscope(TEM),X-ray photo-electron spectroscopy(XPS),UV–vis diffuse reflectance spectra(UV–vis),Fourier transform infrared spectroscopy(FTIR),photoluminescence(PL),photocurrent response(I-t),and electrochemical impedance spectroscopy(EIS).The HRTEM images revealed that an intimate interface in composites were formed.The optimum photocatalytic activity of Rhodamine B degradation over Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au was about 9.7 times and 13.1 times as high as those of Bi_(2)MoO_(6) and g-C_(3)N_(4),respectively.The notably improved photocatalytic activity of Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au could be mainly ascribed to the abundant active sites and the enhanced separation efficiency of photogenerated carriers in Bi_(2)MoO_(6)/g-C_(3)N_(4) S-scheme system.Notably,Au nanoparticles could act as a co-catalyst to further promote electron transfer and separation from the conduction band of g-C_(3)N_(4).Additionally,a possible step-scheme photocatalytic reaction mechanism of Rh B degradation over Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au was tentatively proposed.PL and transient photocurrent analysis implied that Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au photocatalysts possessed the lower recombination rate of photogenerated carriers compared with pure Bi_(2) MoO_(6) and g-C_(3)N_(4),respectively.The present work is expected to provide useful information in designing 2D/2D S-scheme heterojunction photocatalysts.展开更多
Mesoporous LiFePO4/C composites containing 80 wt% of highly dispersed LiFePO4 nanoparticles(4-6 nm) were fabricated using bimodal mesoporous carbon(BMC) as continuous conductive networks. The unique pore structure of ...Mesoporous LiFePO4/C composites containing 80 wt% of highly dispersed LiFePO4 nanoparticles(4-6 nm) were fabricated using bimodal mesoporous carbon(BMC) as continuous conductive networks. The unique pore structure of BMC not only promises good particle connectivity for LiFePO4, but also acts as a rigid nano-confinement support that controls the particle size. Furthermore, the capacities were investigated respectively based on the weight of LiFePO4 and the whole composite. When calculated based on the weight of the whole composite, it is 120 mAh·g-1at 0.1 C of the high loading electrode and 42 mAh·g-1at 10 C of the low loading electrode. The electrochemical performance shows that high LiFePO4 loading benefits large tap density and contributes to the energy storage at low rates, while the electrode with low content of LiFePO4 displays superior high rate performance, which can mainly be due to the small particle size, good dispersion and high utilization of the active material, thus leading to a fast ion and electron diffusion.展开更多
The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investi-gated under proportional and nonproportional multiaxial loading.The fatigue tests were conducted usin...The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investi-gated under proportional and nonproportional multiaxial loading.The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments,at room temperature in air.Two fatigue tests were conducted:one for proportional loading and one for nonproportional loading.The proportional loading was represented by a push-pull strain path(PP)and the nonproportional loading by a circle strain path(Cl).The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects.However,the sizes of the defects were measured,and the defects were found not to cause a reduction in fatigue strength above a critical size.The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths.Different fracture patterns were recognized for each strain paths;however,both showed retention of the crack propagation,despite the presence of numerous defects,probably because of the interaction of the defects.The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components.展开更多
This work studied CuO/CeO2-Co3O4 with wt% Ce:Co ratio 95:5 for selective CO oxidation with effect of? wt% Cu loading. The catalysts were prepared by co-precipitation. Characterizations of catalysts were carried out by...This work studied CuO/CeO2-Co3O4 with wt% Ce:Co ratio 95:5 for selective CO oxidation with effect of? wt% Cu loading. The catalysts were prepared by co-precipitation. Characterizations of catalysts were carried out by XRD and BET techniques. The results showed a good dispersion of CuO for 5 wt% Cu loading catalysts and showed high specific surface area of catalyst. For selective CO oxidation, both 5CuO and 30CuO catalysts could remove completely CO in the presence of excess hydrogen at 423 K and 20CuO could eliminate CO completely at 443 K. Moreover, considering the selectivity to CO oxidation, the 5CuO catalyst has shown the highest selectivity of 85% while the 30CuO catalyst obtains the selectivity of 65% at the reaction temperature of 423 K.展开更多
The conventional discrete wavelet transform （DWT） introduces artifacts during denoising of images containing smooth curves. Finite ridgelet transform （FRIT） solved this problem by mapping the curves in terms of sm...The conventional discrete wavelet transform （DWT） introduces artifacts during denoising of images containing smooth curves. Finite ridgelet transform （FRIT） solved this problem by mapping the curves in terms of small curved ridges. However, blind application of FRIT all over an image is computationally heavy. Finite curvelet transform （FCT） selectively applies FRIT only to the tiles containing small portions of a curve. In this work, a novel curvelet transform named as 4-quadrant finite curvelet transform （4QFCT） based on a new concept of 4-quadrant finite ridgelet transform （4QFRIT） has been proposed. An image is band pass filtered and the high frequency bands are divided into small non-overlapping square tiles. The 4QFRIT is applied to the tiles containing at least one curve element. Unlike FRIT, the 4QFRIT takes 4 sets of radon projections in all the 4 quadrants and then averages them in time and frequency domains after denoising. The proposed algorithm is extensively tested and benchmarked for denoising of images with Gaussian noise using mean squared error （MSE） and peak signal to noise ratio （PSNR）. The results confirm that 4QFCT yields consistently better denoising performance quantitatively and visually.展开更多
Bimetallic oxides composites have received an increasing attention as promising adsorbents for aqueous phosphate (P) removal in recent years. In this study, a novel magnetic composite MZLCO was prepared by hybridizing...Bimetallic oxides composites have received an increasing attention as promising adsorbents for aqueous phosphate (P) removal in recent years. In this study, a novel magnetic composite MZLCO was prepared by hybridizing amorphous Zr-La (carbonate) oxides (ZLCO) with nano-FeOthrough a one-pot solvothermal method for efficient phosphate adsorption. Our optimum sample of MZLCO-45 exhibited a high Langmuir maximum adsorption capacity of 96.16 mg P/g and performed well even at low phosphate concentration. The phosphate adsorption kinetics by MZLCO-45 fitted well with the pseudo-second-order model, and the adsorption capacity could reach 79% of the ultimate value within the first 60 min. The phosphate adsorption process was highly p H-dependent, and MZLCO-45 performed well over a wide p H range of 2.0-8.0. Moreover, MZLCO-45 showed a strong selectivity to phosphate in the presence of competing ions (Cl^(-), NO_(3)^(-), SO_(4)^(2-), HCO_(3)^(-), Ca^(2+), and Mg^(2+)) and a good reusability using the eluent of Na OH/Na Cl mixture, then 64% adsorption capacity remained after ten recycles. The initial 2.0 mg P/L in municipal wastewater and surface water could be efficiently reduced to below 0.1mg P/L by 0.07 g/L MZLCO-45, and the phosphate removal efficiencies were 95.7% and 96.21%, respectively. Phosphate adsorption mechanisms by MZLCO-45 could be attributed to electrostatic attraction and the inner-sphere complexation via ligand exchange forming Zr/La-O-P, -OH and CO_(3)^(2-)groups on MZLCO-45 surface played important roles in the ligand exchange process. The existence of oxygen vacancies could accelerate the phosphate absorption rate of the MZLCO-45 composites.展开更多
A cross-sectional study was conducted at the “Centre de l’Appui Psycho-Médico-Social (APMS)” which is a centre for Psychological and Medical Support in N'Djamena (Chad) from January to March 2014. The aim ...A cross-sectional study was conducted at the “Centre de l’Appui Psycho-Médico-Social (APMS)” which is a centre for Psychological and Medical Support in N'Djamena (Chad) from January to March 2014. The aim of this study was to evaluate the correlation between asymptomatic bacteriuria (ASB) and viral load level and CD4 count in seventy-six (76) HIV-1 infected pregnant women on antiretroviral therapy (ART). Urine culture and bacteria identification were performed by using a chromogenic culture medium (UriselectR4). T CD4+ lymphocytes count and viral load measurement were done respectively on PIMATM test and Abbott m2000 RealTime HIV-1. In this study, 25 (32.9%) pregnant women were carrying ASB and major bacteria;Escherichia coli and Streptococcus agalactiae known to cause neonatal meningitis to newborns were identified. Bacteria were isolated mainly in women with CD4 lymphocytes 3log (70%) (19/25). Besides the prevention of mother to child transmission of HIV, which remains a goal, it is important to prevent also the transmission of other microorganisms causing neonatal infections. Our findings support the needs to do bacteriological analysis of urine in every HIV-infected pregnant woman at least in late pregnancy.展开更多
In Sub-Saharan Africa, HIV affects lots of women of childbearing age;without prevention they can transmit the virus to their child. A cross-sectional study was conducted in the center of Psycho Medico-Social Support (...In Sub-Saharan Africa, HIV affects lots of women of childbearing age;without prevention they can transmit the virus to their child. A cross-sectional study was conducted in the center of Psycho Medico-Social Support (APMS) in N’Djamena, Chad from January 2014 to March 2015. Our sampling concerned HIV-1 infected pregnant women followed up for PMTCT and their newborn. CD4+ lymphocytes and HIV-1 viral load were tested respectively with PIMATM and Abbott m2000 Real Time in mothers. Early infant diagnosis of HIV-1 was done in Children using PCR tool (Abbott m2000 Real Time). Pregnant women included in the study had a median age of 25 years (IQR, 22 - 30 years). Most of them (75.6%) (34/45), were under combination ART (TDF + 3TC or FTC + EFV). The median duration on ART was 4 month (IQR [3 - 5 months]). Nevirapine syrup was administrated to newborns as prophylaxis at least for the first six weeks of life until EID was done. At ART initiation, mothers’ LTCD4+ median was 249 cells/mm3 (IQR: 95 - 674 cells/mm3). After a median duration of 4 months on ART, LTCD4+ median was 530 cells/mm3 (IQR [263 - 1220 cells/mm3]). Viral load assessment in mothers showed that 15.5% (7/45) were undetectable, 75.6% (34/45) were detectable with a VL < 3log copies/ml and 8.8% (4/45) at virologic failure (VL > 3log copies/ ml). Four (11.4%) of 35 children included were tested positive at EID for HIV-1. Antiretroviral treatment management in pregnant women can improve their health and reduce the risk of MTCT. Availability of virologic monitoring in routine is essential for pregnant women in resources limited setting for preventing HIV transmission to their new-born and keep them alive.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52225402,U1910206)the National Key Research and Development Project of China(Grant No.2022YFC3004602).
文摘The fracture network of hydraulic crack is significantly influenced by the bedding plane in coalbed methane extraction.Under mode Ⅱ loading,crack deflection holds a key position in hydraulic cracking,especially in hydraulic shearing.This study first analyzed the crack deflection theory of layered rock.The semi-circle bending test under asymmetric loading is performed,and the four-dimensional Lattice Spring Model(4D-LSM)is established to examine how the bedding parameters affect coal crack propagation under mode Ⅱ dominant loads.The 4D-LSM results are comparable to the coal loading test results under quasi-mode Ⅱ and the analytical prediction of crack deflection theory.During mode Ⅱ loading,the coal crack propagation is greatly influenced by the angle,strength,and elastic modulus of the bedding plane,while the effects of thickness and spacing of bedding are insignificant.The crack of coal tends to propagate towards the bedding,following a decrease in bedding angle,a decrease in bedding strength,and an increase in elastic modulus.With higher bedding strength,spacing,and thickness,the peak load on the coal sample is higher.The influences of bedding strength,elastic modulus,spacing,and thickness on the peak load of coal samples and its anisotropy gradually decrease.It is proved that compared with the tangential stress ratio and traditional energy release ratio theories,the corrected energy release ratio criterion can more accurately predict the direction of crack deflection of coal,especially under mode Ⅱ loading.The results can provide assistance in the design of initiation pressure and fracturing direction in coal seam hydraulic fracturing.
基金the National Key Research and Development Program of China(No.2017YFC0305500)。
文摘Different components of deep-sea submersibles,such as the pressure hull,are usually subjected to intermittent loading,dwell loading,and unloading during service.Therefore,for the design and reliability assessment of structural parts under dwell fatigue loading,understanding the effects of intermittent loading time on dwell fatigue behavior of the alloys is essential.In this study,the effects of the intermittent loading time and stress ratio on dwell fatigue behavior of the titanium alloy Ti-6 Al-4 V ELI were investigated.Results suggest that the dwell fatigue failure modes of Ti-6 Al-4 V ELI can be classified into three types,i.e.,fatigue failure mode,ductile failure mode,and mixed failure mode.The intermittent loading time does not affect the dwell fatigue behavior,whereas the stress ratio significantly affects the dwell fatigue life and dwell fatigue mechanism.The dwell fatigue life increases with an increase in the stress ratio for the same maximum stress,and specimens with a negative stress ratio tend to undergo ductile failure.The mechanism of dwell fatigue of titanium alloys is attribute to an increase in the plastic strain caused by the part of the dwell loading,thereby resulting in an increase in the actual stress of the specimens during the subsequent loading cycles and aiding the growth of the formed crack or damage,along with the local plastic strain or damage induced by the part of the fatigue load promoting the cumulative plastic strain during the dwell fatigue process.The interaction between dwell loading and fatigue loading accelerates specimen failure,in contrast to the case for individual creep or fatigue loading alone.The dwell fatigue life and cumulative maximum strain during the first loading cycle could be correlated by a linear relationship on the log–log scale.This relationship can be used to evaluate the dwell fatigue life of Ti alloys with the maximum stress dwell.
基金Project was supported by National Defense Basic Scientific Research Program of China (JCKY2016205A001)。
文摘By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation behavior of the laser welded joint specimens of TC4 titanium alloy. The results showed that for the unmodified specimens, the yield phenomenon occurs first in the region of the joint, but the undercut value has an effect on the stress and strain of starting to yield phenomenon, and a great effect on the plastic deformation behavior.When the undercut is less than a certain value, the large plastic deformation occurs in the base metal region and the plasticity of the specimen is comparable to that of the base metal, but the larger undercut defect results in a concentrated plastic deformation in the joint region and rapidly failed in this region. But the double-sided dressing specimen is significantly different. The physical yield is no longer concentrated in the joint region, but at the same time occurs in the several regions including joint and the base metal. And the plastic deformation mainly occurs in the base material area, similar to that of the base material.
基金financially supported by the Fundamental Research Funds for the Central Universities(No.JUSRP51716A)the National Natural Science Foundation of China(Nos.21203077 and 21773099)the financially support from the Qing Lan Project of Jiangsu Province。
文摘A novel 2D/2D Bi_(2)MoO_(6)/g-C_(3)N_(4) step-scheme(S-scheme)composite by loading Au as cocatalyst was successfully fabricated using a photoreduction and hydrothermal route.The obtained Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au photocatalysts were characterized by X-ray diffraction(XRD),transmission electron microscope(TEM),X-ray photo-electron spectroscopy(XPS),UV–vis diffuse reflectance spectra(UV–vis),Fourier transform infrared spectroscopy(FTIR),photoluminescence(PL),photocurrent response(I-t),and electrochemical impedance spectroscopy(EIS).The HRTEM images revealed that an intimate interface in composites were formed.The optimum photocatalytic activity of Rhodamine B degradation over Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au was about 9.7 times and 13.1 times as high as those of Bi_(2)MoO_(6) and g-C_(3)N_(4),respectively.The notably improved photocatalytic activity of Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au could be mainly ascribed to the abundant active sites and the enhanced separation efficiency of photogenerated carriers in Bi_(2)MoO_(6)/g-C_(3)N_(4) S-scheme system.Notably,Au nanoparticles could act as a co-catalyst to further promote electron transfer and separation from the conduction band of g-C_(3)N_(4).Additionally,a possible step-scheme photocatalytic reaction mechanism of Rh B degradation over Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au was tentatively proposed.PL and transient photocurrent analysis implied that Bi_(2)MoO_(6)/g-C_(3)N_(4)/Au photocatalysts possessed the lower recombination rate of photogenerated carriers compared with pure Bi_(2) MoO_(6) and g-C_(3)N_(4),respectively.The present work is expected to provide useful information in designing 2D/2D S-scheme heterojunction photocatalysts.
基金supported by the National Natural Science Foundation of China (NSFC 21103184)the Ph.D.Programs Foundation (20100041110017) of Ministry of Education of Chinathe Fundamental Research Funds for the Central Universities
文摘Mesoporous LiFePO4/C composites containing 80 wt% of highly dispersed LiFePO4 nanoparticles(4-6 nm) were fabricated using bimodal mesoporous carbon(BMC) as continuous conductive networks. The unique pore structure of BMC not only promises good particle connectivity for LiFePO4, but also acts as a rigid nano-confinement support that controls the particle size. Furthermore, the capacities were investigated respectively based on the weight of LiFePO4 and the whole composite. When calculated based on the weight of the whole composite, it is 120 mAh·g-1at 0.1 C of the high loading electrode and 42 mAh·g-1at 10 C of the low loading electrode. The electrochemical performance shows that high LiFePO4 loading benefits large tap density and contributes to the energy storage at low rates, while the electrode with low content of LiFePO4 displays superior high rate performance, which can mainly be due to the small particle size, good dispersion and high utilization of the active material, thus leading to a fast ion and electron diffusion.
基金Supported by Japan Society for the Promotion of Science KAKENHI(Grant No.18H05256).
文摘The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investi-gated under proportional and nonproportional multiaxial loading.The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments,at room temperature in air.Two fatigue tests were conducted:one for proportional loading and one for nonproportional loading.The proportional loading was represented by a push-pull strain path(PP)and the nonproportional loading by a circle strain path(Cl).The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects.However,the sizes of the defects were measured,and the defects were found not to cause a reduction in fatigue strength above a critical size.The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths.Different fracture patterns were recognized for each strain paths;however,both showed retention of the crack propagation,despite the presence of numerous defects,probably because of the interaction of the defects.The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components.
文摘This work studied CuO/CeO2-Co3O4 with wt% Ce:Co ratio 95:5 for selective CO oxidation with effect of? wt% Cu loading. The catalysts were prepared by co-precipitation. Characterizations of catalysts were carried out by XRD and BET techniques. The results showed a good dispersion of CuO for 5 wt% Cu loading catalysts and showed high specific surface area of catalyst. For selective CO oxidation, both 5CuO and 30CuO catalysts could remove completely CO in the presence of excess hydrogen at 423 K and 20CuO could eliminate CO completely at 443 K. Moreover, considering the selectivity to CO oxidation, the 5CuO catalyst has shown the highest selectivity of 85% while the 30CuO catalyst obtains the selectivity of 65% at the reaction temperature of 423 K.
文摘The conventional discrete wavelet transform （DWT） introduces artifacts during denoising of images containing smooth curves. Finite ridgelet transform （FRIT） solved this problem by mapping the curves in terms of small curved ridges. However, blind application of FRIT all over an image is computationally heavy. Finite curvelet transform （FCT） selectively applies FRIT only to the tiles containing small portions of a curve. In this work, a novel curvelet transform named as 4-quadrant finite curvelet transform （4QFCT） based on a new concept of 4-quadrant finite ridgelet transform （4QFRIT） has been proposed. An image is band pass filtered and the high frequency bands are divided into small non-overlapping square tiles. The 4QFRIT is applied to the tiles containing at least one curve element. Unlike FRIT, the 4QFRIT takes 4 sets of radon projections in all the 4 quadrants and then averages them in time and frequency domains after denoising. The proposed algorithm is extensively tested and benchmarked for denoising of images with Gaussian noise using mean squared error （MSE） and peak signal to noise ratio （PSNR）. The results confirm that 4QFCT yields consistently better denoising performance quantitatively and visually.
基金supported by the Beijing Municipal Science and Technology Project (No. Z181100005518007)the National Key Research and Development Program of China (No. 2017YFC0505303)+1 种基金the National Natural Science Foundation of China (Nos. 51978054 and 51678053)Beijing Municipal Education Commission through the Innovative Transdisciplinary Program ‘Ecological Restoration Engineering’ (No. GJJXK210102)。
文摘Bimetallic oxides composites have received an increasing attention as promising adsorbents for aqueous phosphate (P) removal in recent years. In this study, a novel magnetic composite MZLCO was prepared by hybridizing amorphous Zr-La (carbonate) oxides (ZLCO) with nano-FeOthrough a one-pot solvothermal method for efficient phosphate adsorption. Our optimum sample of MZLCO-45 exhibited a high Langmuir maximum adsorption capacity of 96.16 mg P/g and performed well even at low phosphate concentration. The phosphate adsorption kinetics by MZLCO-45 fitted well with the pseudo-second-order model, and the adsorption capacity could reach 79% of the ultimate value within the first 60 min. The phosphate adsorption process was highly p H-dependent, and MZLCO-45 performed well over a wide p H range of 2.0-8.0. Moreover, MZLCO-45 showed a strong selectivity to phosphate in the presence of competing ions (Cl^(-), NO_(3)^(-), SO_(4)^(2-), HCO_(3)^(-), Ca^(2+), and Mg^(2+)) and a good reusability using the eluent of Na OH/Na Cl mixture, then 64% adsorption capacity remained after ten recycles. The initial 2.0 mg P/L in municipal wastewater and surface water could be efficiently reduced to below 0.1mg P/L by 0.07 g/L MZLCO-45, and the phosphate removal efficiencies were 95.7% and 96.21%, respectively. Phosphate adsorption mechanisms by MZLCO-45 could be attributed to electrostatic attraction and the inner-sphere complexation via ligand exchange forming Zr/La-O-P, -OH and CO_(3)^(2-)groups on MZLCO-45 surface played important roles in the ligand exchange process. The existence of oxygen vacancies could accelerate the phosphate absorption rate of the MZLCO-45 composites.
文摘A cross-sectional study was conducted at the “Centre de l’Appui Psycho-Médico-Social (APMS)” which is a centre for Psychological and Medical Support in N'Djamena (Chad) from January to March 2014. The aim of this study was to evaluate the correlation between asymptomatic bacteriuria (ASB) and viral load level and CD4 count in seventy-six (76) HIV-1 infected pregnant women on antiretroviral therapy (ART). Urine culture and bacteria identification were performed by using a chromogenic culture medium (UriselectR4). T CD4+ lymphocytes count and viral load measurement were done respectively on PIMATM test and Abbott m2000 RealTime HIV-1. In this study, 25 (32.9%) pregnant women were carrying ASB and major bacteria;Escherichia coli and Streptococcus agalactiae known to cause neonatal meningitis to newborns were identified. Bacteria were isolated mainly in women with CD4 lymphocytes 3log (70%) (19/25). Besides the prevention of mother to child transmission of HIV, which remains a goal, it is important to prevent also the transmission of other microorganisms causing neonatal infections. Our findings support the needs to do bacteriological analysis of urine in every HIV-infected pregnant woman at least in late pregnancy.
文摘In Sub-Saharan Africa, HIV affects lots of women of childbearing age;without prevention they can transmit the virus to their child. A cross-sectional study was conducted in the center of Psycho Medico-Social Support (APMS) in N’Djamena, Chad from January 2014 to March 2015. Our sampling concerned HIV-1 infected pregnant women followed up for PMTCT and their newborn. CD4+ lymphocytes and HIV-1 viral load were tested respectively with PIMATM and Abbott m2000 Real Time in mothers. Early infant diagnosis of HIV-1 was done in Children using PCR tool (Abbott m2000 Real Time). Pregnant women included in the study had a median age of 25 years (IQR, 22 - 30 years). Most of them (75.6%) (34/45), were under combination ART (TDF + 3TC or FTC + EFV). The median duration on ART was 4 month (IQR [3 - 5 months]). Nevirapine syrup was administrated to newborns as prophylaxis at least for the first six weeks of life until EID was done. At ART initiation, mothers’ LTCD4+ median was 249 cells/mm3 (IQR: 95 - 674 cells/mm3). After a median duration of 4 months on ART, LTCD4+ median was 530 cells/mm3 (IQR [263 - 1220 cells/mm3]). Viral load assessment in mothers showed that 15.5% (7/45) were undetectable, 75.6% (34/45) were detectable with a VL < 3log copies/ml and 8.8% (4/45) at virologic failure (VL > 3log copies/ ml). Four (11.4%) of 35 children included were tested positive at EID for HIV-1. Antiretroviral treatment management in pregnant women can improve their health and reduce the risk of MTCT. Availability of virologic monitoring in routine is essential for pregnant women in resources limited setting for preventing HIV transmission to their new-born and keep them alive.
