The high flow-rate centrifugal fan needs a three-dimensional impeller to achieve a high efficiency. In this paper, the design procedure of a high-efficiency three-dimensional centrifugal fan is presented. First, the m...The high flow-rate centrifugal fan needs a three-dimensional impeller to achieve a high efficiency. In this paper, the design procedure of a high-efficiency three-dimensional centrifugal fan is presented. First, the main dimensions of the fan were calculated by using the conventional one-dimensional method. Then, the blade loading or the angular momentum distribution along the meridional streamline on the blade surfaces is prescribed. After that, the three-dimensional blade is determined by using the streamline curvature method. With the aid of numerical simulations, the performance of the three-dimensional fan was improved and some of the key influence factors were investigated. The analyses indicate that, as to the high flow-rate centrifugal fan, the Stanitz modified formula is recommended to calculate the separation radius, rb. A proper increase in the separation radius is beneficial for the fan’s performance. It is also indicated that a decrease in the angular momentum on the hub leads to an increase in total pressure efficiency, under the condition of a given constant mean angular momentum at the outlet of the blade. In addition, the installation of a fairing on the hub plate can improve the fan’s efficiency evidently when the streamline curvature method is adopted to design the three-dimensional impeller.展开更多
Background:Outbreaks of coronavirus disease 2019(COVID-19)have been recorded in different countries across the globe.The virus is highly contagious,hence early detection,isolation,and quarantine of infected patients w...Background:Outbreaks of coronavirus disease 2019(COVID-19)have been recorded in different countries across the globe.The virus is highly contagious,hence early detection,isolation,and quarantine of infected patients will play an important role in containing the viral spread.Diagnosis in a mobile lab can aid to find infected patients in time.Methods:Here,we develop a field-deployable diagnostic workflow that can reliably detect COVID-19.Instruments used in this workflow can easily fit in a mobile cabin hospital and also be installed in the community.Different steps from sample inactivation to detection were optimized to find the fastest steps and portable instruments in the detection of COVID-19.Each step was compared to that of the normal laboratory diagnosis setup.Results:From the results,our proposed workflow(80 min)was two times faster compared to that of the normal laboratory workflow(183 min)and a maximum of 32 samples could be detected at each run.Additionally,we showed that using 1%Rewocid WK-30 could inactivate the novel coronavirus directly without affecting the overall detection results.Comparison of our workflow using an in-house assay to that of a commercially acquired assay produced highly reliable results.From the 250 hospital samples tested,there was a high concordance 247/250(98.8%)between the two assays.The in-house assay sensitivity and specificity were 116/116(100%)and 131/134(97.8%)compared to that of the commercial assay.Conclusion:Based on these results,we believe that our workflow is fast,reliable,adaptable and most importantly,field-deployable.展开更多
The combination of cyclopentadiene,β-diketonate and tripyrazoylborate ligands with dysprosium ion afforded five mononuclear compounds:[(Cp)2Dy(Tp∗)](1Dy),[(Cp)Dy(Tp∗)Cl(THF)](2Dy),[(Cp)Dy(Tp)Cl(THF)](3Dy),[(DBM)Dy(Tp...The combination of cyclopentadiene,β-diketonate and tripyrazoylborate ligands with dysprosium ion afforded five mononuclear compounds:[(Cp)2Dy(Tp∗)](1Dy),[(Cp)Dy(Tp∗)Cl(THF)](2Dy),[(Cp)Dy(Tp)Cl(THF)](3Dy),[(DBM)Dy(Tp)Cl(THF)](4Dy),[{(Tp)Dy(DBM)_(2)(H_(2)O)}·THF](5Dy)(Cp=cyclopentadiene;Tp∗=hydrotris(3,5-dimethyl-1-pyrazolyl)borate;Tp=hydrotris(1-pyrazolyl)borate;DBM=dibenzoylmethanoate).Magnetic study revealed that 1Dy and 3Dy exhibited typical butterfly-type hysteresis.AC susceptibility study combined with ab initio calculations indicated that the magnetic relaxation behaviors of 1Dy–4Dy were governed by the Orbach and Raman processes under applied DC field.Moreover,3Dy showed two-step magnetic relaxation,which was attributed to the static disordering of the coordinated THF molecule.Magnetic anisotropy analysis indicated that it was the relative strength of the interactions between DyIII and surrounding ligands that determined the orientation of the magnetic easy axis.展开更多
Persistent memory(PM)promises byte-addressability,large capacity,and durability.Main memory systems,such as key-value stores and in-memory databases,benefit from such features of PM.Due to the great popularity of hash...Persistent memory(PM)promises byte-addressability,large capacity,and durability.Main memory systems,such as key-value stores and in-memory databases,benefit from such features of PM.Due to the great popularity of hash-ing index in main memory systems,a number of research efforts are made to provide high average performance persistent hashing.However,suboptimal tail performance in terms of tail throughput and tail latency is still observed for existing persistent hashing.In this paper,we analyze major sources of suboptimal tail performance from key design issues of persis-tent hashing.We identify the global hash structure and concurrency control as remaining explorable design spaces for im-proving tail performance.We propose Directory-sharing Multi-level Extendible Hashing(Dalea)for PM.Dalea designs an-cestor link-based extendible hashing as well as fine-grained transient lock to address the two main sources(rehashing and locking)affecting tail performance.The evaluation results show that,compared with state-of-the-art persistent hashing Dash,Dalea achieves increased tail throughput by 4.1x and reduced tail latency by 5.4x.Moreover,in order to provide de-sign guidelines for improving tail performance,we adopt Dalea as a testbed to identify different impacts of four factors on tail performance,including fine-grained rehashing,transient locking,memory pre-allocation,and fingerprinting.展开更多
A storage system is the core of a computer,and plays an important role in the sustainable development of emerging strategic industries,such as artificial intelligence,big data,cloud computing,and the Internet of Thing...A storage system is the core of a computer,and plays an important role in the sustainable development of emerging strategic industries,such as artificial intelligence,big data,cloud computing,and the Internet of Things.Storage stack access is a major factor restricting the performance of data-intensive systems because of the increasing performance of processors and network devices.展开更多
The coronavirus disease 2019(COVID-19)pandemic is caused by infection with the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),which is spread primary via respiratory droplets and infects the lungs.Current...The coronavirus disease 2019(COVID-19)pandemic is caused by infection with the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),which is spread primary via respiratory droplets and infects the lungs.Currently widely used cell lines and animals are unable to accurately mimic human physiological conditions because of the abnormal status of cell lines(transformed or cancer cells)and species differences between animals and humans.Organoids are stem cell-derived selforganized three-dimensional culture in vitro and model the physiological conditions of natural organs.Here we showed that SARS-CoV-2 infected and extensively replicated in human embryonic stem cells(hESCs)-derived lung organoids,including airway and alveolar organoids which covered the complete infection and spread route for SARS-CoV-2 within lungs.The infected ceils were ciliated,club,and alveolar type 2(AT2)cells,which were sequentially located from the proximal to the distal airway and terminal alveoli,respectively.Additionally,RNA-seq revealed early cell response to virus infection including an unexpected downregulation of the metabolic processes,especially lipid metabolism,in addition to the well-known upregulation of immune response.Further,Remdesivir and a human neutralizing antibody potently inhibited SARS-CoV-2 replication in lung organoids.Therefore,human lung organoids can serve as a pathophysiological model to investigate the underlying mechanism of SARS-CoV-2 infection and to discover and test therapeutic drugs for COVID-19.展开更多
Measurement of the SO3 concentration in flue gas is important to estimate the acid dew point and to control corrosion of downstream equipment. SO3 measurement is a difficult question since SO3 is a highly reactive gas...Measurement of the SO3 concentration in flue gas is important to estimate the acid dew point and to control corrosion of downstream equipment. SO3 measurement is a difficult question since SO3 is a highly reactive gas, and its concentration is generally two orders of magnitude lower than the SO2 concentration. The SO3 concentration can be measured online by the isopropanol absorption method; however, the reliability of the test results is relatively low. This work aims to find the error sources and to evaluate the extent of influence of each factor on the measurement results. The test results from a SO3 analyzer showed that the measuring errors are mainly caused by the gas–liquid flow ratio, SO2 oxidation, and the side reactions of SO3. The error in the gas sampling rate is generally less than 13%. The isopropanol solution flow rate decreases 3% to 30% due to the volatilization of isopropanol, and accordingly, this will increase the apparent SO3 concentration. The amount of SO2 oxidation is linearly related to the SO2 concentration. The side reactions of SO3 reduce the selectivity of SO42- to nearly 73%. As sampling temperature increases from180 to 300°C, the selectivity of SO42- decreases from 73% to 50%. The presence of H2 O in the sample gas helps to reduce the measurement error by inhibiting the volatilization of the isopropanol and weakening side reactions. A formula was established to modify the displayed value, and the measurement error was reduced from 25%–54% to less than 15%.展开更多
As a respiratory tract virus,SARS-CoV-2 infected people through contacting with the upper respiratory tract first.Previous studies indicated that microbiota could modulate immune response against pathogen infection.In...As a respiratory tract virus,SARS-CoV-2 infected people through contacting with the upper respiratory tract first.Previous studies indicated that microbiota could modulate immune response against pathogen infection.In the present study,we performed metagenomic sequencing of pharyngeal swabs from eleven patients with COVID-19 and eleven Non-COVID-19 patients who had similar symptoms such as fever and cough.Through metagenomic analysis of the above two groups and a healthy group from the public data,there are 6502 species identified in the samples.Specifically,the Pielou index indicated a lower evenness of the microbiota in the COVID-19 group than that in the Non-COVID-19 group.Combined with the linear discriminant analysis(LDA)and the generalized linear model,eighty-one bacterial species were found with increased abundance in the COVID-19 group,where 51 species were enriched more than 8 folds.The top three enriched genera were Streptococcus,Prevotella and Campylobacter containing some opportunistic pathogens.More interestingly,through experiments,we found that two Streptococcus strains,S.suis and S.agalactiae,could stimulate the expression of ACE2 of Vero cells in vitro,which may promote SARS-CoV-2 infection.Therefore,these enriched pathogens in the pharynxes of COVID-19 patients may involve in the virus-host interactions to affect SARS-CoV-2 infection and cause potential secondary bacterial infections through changing the expression of the viral receptor ACE2 and/or modulate the host’s immune system.展开更多
Key-value (KV) stores have become a backbone of large-scale applications in today's data centers. Write- optimized data structures like the Log-Structured Merge-tree (LSM-tree) and their variants are widely used ...Key-value (KV) stores have become a backbone of large-scale applications in today's data centers. Write- optimized data structures like the Log-Structured Merge-tree (LSM-tree) and their variants are widely used in KV storage systems like BigTable and RocksDB. Conventional LSM-tree organizes KV items into multiple, successively larger components, and uses compaction to push KV items from one smaller component to another adjacent larger component until the KV items reach the largest component. Unfortunately, current compaction scheme incurs significant write amplification due to repeated KV item reads and writes, and then results in poor throughput. We propose a new compaction scheme, delayed compaction (dCompaction) that decreases write amplification, dCompaction postpones some compactions and gathers them into the following compaction. In this way, it avoids KV item reads and writes during compaction, and consequently improves the throughput of LSM-tree based KV stores. We implement dCompaction on RocksDB, and conduct extensive experiments. Validation using YCSB framework shows that compared with RocksDB, dCompaction has about 40% write performance improvements and also comparable read performance.展开更多
To clarify the effect of coking dust, sintering dust and fly ash on the activity of activated carbon for various industrial flue gas desulfurization and denitrification, the coupling mechanism of the mixed activated c...To clarify the effect of coking dust, sintering dust and fly ash on the activity of activated carbon for various industrial flue gas desulfurization and denitrification, the coupling mechanism of the mixed activated carbon and dust was investigated to provide theoretical reference for the stable operation. The results show that coking dust had 34% desulfurization efficiency and 10% denitrification efficiency;correspondingly, sintering dust and fly ash had no obvious desulfurization and denitrification activities. For the mixture of activated carbon and dust, the coking dust reduced the desulfurization and denitrification efficiencies by blocking the pores of activated carbon, and its inhibiting effect on activated carbon was larger than its own desulfurization and denitrification activity. The sintering dust also reduced the desulfurization efficiency on the activated carbon while enhancing the denitrification efficiency. Fly ash blocked the pores of activated carbon and reduced its reaction activity. The reaction activity of coking dust mainly came from the surface functional groups, similar to that of activated carbon. The reaction activity of sintering dust mainly came from the oxidative property of Fe_2O _3, which oxidized NO to NO_2 and promoted the fast selectively catalytic reduction(SCR) of NO to form N_2. Sintering dust was activated by the joint action of activated carbon, and both had a coupling function. Sintering dust enhanced the adsorption and oxidation of NO, and activated carbon further promoted the reduction of NO_x by NH_3;thus, the denitrification efficiency increased by 5%-7% on the activated carbon.展开更多
Magneto-luminescent molecules have significant applications in data storage and quantum computing.However,design of these bi-functional molecules coupled with magnetic behavior and photoluminescence is still challengi...Magneto-luminescent molecules have significant applications in data storage and quantum computing.However,design of these bi-functional molecules coupled with magnetic behavior and photoluminescence is still challenging.In this work,we report a metallofullerene DyErScN @In-C80 exhibiting single-molecule magnet (SMM) behavior and near-infrared emission.For DyErScN @Ih-C80,two functional lanthanide metal ions of Dy^3+(SMM function) and Er^3+(luminescent function) are integrated inside a fullerene cage using a trimetallic nitride template,and its structure has been unambiguously characterized by single-crystal X-ray diffraction.Magnetic measurements revealed that DyErScN @Ih-C80 behaves as a SMM with a blocking temperature up to 9 K resulting from the intramolecular magnetic interaction between Dy^3+ and Er^3+ ions.Moreover,DyErScN @In-C80 exhibits temperature-dependent near-infrared emission around 1.5 pm with multiple splitting peaks from Er^3+,which arises from the influence of Dy^3+ ion.This study provides a new strategy to synthesize new magneto-luminescent molecule materials.展开更多
Dear Editor,Severe acute respiratory syndrome coronavirus 2(SARSCoV-2), the etiologic agent of COVID-19, is an enveloped,positive-sense single-stranded RNA virus that first discovered in December 2019 from a seafood m...Dear Editor,Severe acute respiratory syndrome coronavirus 2(SARSCoV-2), the etiologic agent of COVID-19, is an enveloped,positive-sense single-stranded RNA virus that first discovered in December 2019 from a seafood market in Wuhan, China(Zhou et al. 2020).展开更多
文摘The high flow-rate centrifugal fan needs a three-dimensional impeller to achieve a high efficiency. In this paper, the design procedure of a high-efficiency three-dimensional centrifugal fan is presented. First, the main dimensions of the fan were calculated by using the conventional one-dimensional method. Then, the blade loading or the angular momentum distribution along the meridional streamline on the blade surfaces is prescribed. After that, the three-dimensional blade is determined by using the streamline curvature method. With the aid of numerical simulations, the performance of the three-dimensional fan was improved and some of the key influence factors were investigated. The analyses indicate that, as to the high flow-rate centrifugal fan, the Stanitz modified formula is recommended to calculate the separation radius, rb. A proper increase in the separation radius is beneficial for the fan’s performance. It is also indicated that a decrease in the angular momentum on the hub leads to an increase in total pressure efficiency, under the condition of a given constant mean angular momentum at the outlet of the blade. In addition, the installation of a fairing on the hub plate can improve the fan’s efficiency evidently when the streamline curvature method is adopted to design the three-dimensional impeller.
文摘Background:Outbreaks of coronavirus disease 2019(COVID-19)have been recorded in different countries across the globe.The virus is highly contagious,hence early detection,isolation,and quarantine of infected patients will play an important role in containing the viral spread.Diagnosis in a mobile lab can aid to find infected patients in time.Methods:Here,we develop a field-deployable diagnostic workflow that can reliably detect COVID-19.Instruments used in this workflow can easily fit in a mobile cabin hospital and also be installed in the community.Different steps from sample inactivation to detection were optimized to find the fastest steps and portable instruments in the detection of COVID-19.Each step was compared to that of the normal laboratory diagnosis setup.Results:From the results,our proposed workflow(80 min)was two times faster compared to that of the normal laboratory workflow(183 min)and a maximum of 32 samples could be detected at each run.Additionally,we showed that using 1%Rewocid WK-30 could inactivate the novel coronavirus directly without affecting the overall detection results.Comparison of our workflow using an in-house assay to that of a commercially acquired assay produced highly reliable results.From the 250 hospital samples tested,there was a high concordance 247/250(98.8%)between the two assays.The in-house assay sensitivity and specificity were 116/116(100%)and 131/134(97.8%)compared to that of the commercial assay.Conclusion:Based on these results,we believe that our workflow is fast,reliable,adaptable and most importantly,field-deployable.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.22222103,22173015,22025101,21801037,91961114 and 21871039)the Fundamental Research Funds for Central University,China。
文摘The combination of cyclopentadiene,β-diketonate and tripyrazoylborate ligands with dysprosium ion afforded five mononuclear compounds:[(Cp)2Dy(Tp∗)](1Dy),[(Cp)Dy(Tp∗)Cl(THF)](2Dy),[(Cp)Dy(Tp)Cl(THF)](3Dy),[(DBM)Dy(Tp)Cl(THF)](4Dy),[{(Tp)Dy(DBM)_(2)(H_(2)O)}·THF](5Dy)(Cp=cyclopentadiene;Tp∗=hydrotris(3,5-dimethyl-1-pyrazolyl)borate;Tp=hydrotris(1-pyrazolyl)borate;DBM=dibenzoylmethanoate).Magnetic study revealed that 1Dy and 3Dy exhibited typical butterfly-type hysteresis.AC susceptibility study combined with ab initio calculations indicated that the magnetic relaxation behaviors of 1Dy–4Dy were governed by the Orbach and Raman processes under applied DC field.Moreover,3Dy showed two-step magnetic relaxation,which was attributed to the static disordering of the coordinated THF molecule.Magnetic anisotropy analysis indicated that it was the relative strength of the interactions between DyIII and surrounding ligands that determined the orientation of the magnetic easy axis.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No.XDB44030200the Beijing Natural Science Foundation-Haidian Joint Fund for Original Innovation under Grant No.L192038.
文摘Persistent memory(PM)promises byte-addressability,large capacity,and durability.Main memory systems,such as key-value stores and in-memory databases,benefit from such features of PM.Due to the great popularity of hash-ing index in main memory systems,a number of research efforts are made to provide high average performance persistent hashing.However,suboptimal tail performance in terms of tail throughput and tail latency is still observed for existing persistent hashing.In this paper,we analyze major sources of suboptimal tail performance from key design issues of persis-tent hashing.We identify the global hash structure and concurrency control as remaining explorable design spaces for im-proving tail performance.We propose Directory-sharing Multi-level Extendible Hashing(Dalea)for PM.Dalea designs an-cestor link-based extendible hashing as well as fine-grained transient lock to address the two main sources(rehashing and locking)affecting tail performance.The evaluation results show that,compared with state-of-the-art persistent hashing Dash,Dalea achieves increased tail throughput by 4.1x and reduced tail latency by 5.4x.Moreover,in order to provide de-sign guidelines for improving tail performance,we adopt Dalea as a testbed to identify different impacts of four factors on tail performance,including fine-grained rehashing,transient locking,memory pre-allocation,and fingerprinting.
文摘A storage system is the core of a computer,and plays an important role in the sustainable development of emerging strategic industries,such as artificial intelligence,big data,cloud computing,and the Internet of Things.Storage stack access is a major factor restricting the performance of data-intensive systems because of the increasing performance of processors and network devices.
基金This work was supported by grants from National Natural Science Foundation of China(Grant Nos.82070002,82072329,81872511,and 81670093)Frontier Research Program of Bioland Laboratory(Guangzhou Regenerative Medicine and Health Guangdong Laboratory)(2018GZR110105005)+6 种基金National Science and Technology Major Project(2018ZX10301101)the Natural Science Foundation of Guangdong Province(2018A030313455)the Program of Department of Science and Technology of Guangdong Province(2014B020212018)National Key Research and Development Project(2018YFA0507201)the special project for COVID-19 of Guangzhou Regenerative Medicine and Health Guangdong Labo・ratory(2020GZR110106006)the emergency grants for prevention and control of SARS-CoV-2 of Guangdong province(2020B111108001)National Postdoctoral Program for Innovative Talent(BX20190089).
文摘The coronavirus disease 2019(COVID-19)pandemic is caused by infection with the severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),which is spread primary via respiratory droplets and infects the lungs.Currently widely used cell lines and animals are unable to accurately mimic human physiological conditions because of the abnormal status of cell lines(transformed or cancer cells)and species differences between animals and humans.Organoids are stem cell-derived selforganized three-dimensional culture in vitro and model the physiological conditions of natural organs.Here we showed that SARS-CoV-2 infected and extensively replicated in human embryonic stem cells(hESCs)-derived lung organoids,including airway and alveolar organoids which covered the complete infection and spread route for SARS-CoV-2 within lungs.The infected ceils were ciliated,club,and alveolar type 2(AT2)cells,which were sequentially located from the proximal to the distal airway and terminal alveoli,respectively.Additionally,RNA-seq revealed early cell response to virus infection including an unexpected downregulation of the metabolic processes,especially lipid metabolism,in addition to the well-known upregulation of immune response.Further,Remdesivir and a human neutralizing antibody potently inhibited SARS-CoV-2 replication in lung organoids.Therefore,human lung organoids can serve as a pathophysiological model to investigate the underlying mechanism of SARS-CoV-2 infection and to discover and test therapeutic drugs for COVID-19.
基金financial support from the National Natural Science Foundation of China(No.21477131)the Special Research Funding for Public Benefit Industries from the National Ministry of Environmental Protection(No.201509012)
文摘Measurement of the SO3 concentration in flue gas is important to estimate the acid dew point and to control corrosion of downstream equipment. SO3 measurement is a difficult question since SO3 is a highly reactive gas, and its concentration is generally two orders of magnitude lower than the SO2 concentration. The SO3 concentration can be measured online by the isopropanol absorption method; however, the reliability of the test results is relatively low. This work aims to find the error sources and to evaluate the extent of influence of each factor on the measurement results. The test results from a SO3 analyzer showed that the measuring errors are mainly caused by the gas–liquid flow ratio, SO2 oxidation, and the side reactions of SO3. The error in the gas sampling rate is generally less than 13%. The isopropanol solution flow rate decreases 3% to 30% due to the volatilization of isopropanol, and accordingly, this will increase the apparent SO3 concentration. The amount of SO2 oxidation is linearly related to the SO2 concentration. The side reactions of SO3 reduce the selectivity of SO42- to nearly 73%. As sampling temperature increases from180 to 300°C, the selectivity of SO42- decreases from 73% to 50%. The presence of H2 O in the sample gas helps to reduce the measurement error by inhibiting the volatilization of the isopropanol and weakening side reactions. A formula was established to modify the displayed value, and the measurement error was reduced from 25%–54% to less than 15%.
基金financial supports of CAS(project No 153B42KYSB20170004)the Wuhan National Biosafety Lab for this study。
文摘As a respiratory tract virus,SARS-CoV-2 infected people through contacting with the upper respiratory tract first.Previous studies indicated that microbiota could modulate immune response against pathogen infection.In the present study,we performed metagenomic sequencing of pharyngeal swabs from eleven patients with COVID-19 and eleven Non-COVID-19 patients who had similar symptoms such as fever and cough.Through metagenomic analysis of the above two groups and a healthy group from the public data,there are 6502 species identified in the samples.Specifically,the Pielou index indicated a lower evenness of the microbiota in the COVID-19 group than that in the Non-COVID-19 group.Combined with the linear discriminant analysis(LDA)and the generalized linear model,eighty-one bacterial species were found with increased abundance in the COVID-19 group,where 51 species were enriched more than 8 folds.The top three enriched genera were Streptococcus,Prevotella and Campylobacter containing some opportunistic pathogens.More interestingly,through experiments,we found that two Streptococcus strains,S.suis and S.agalactiae,could stimulate the expression of ACE2 of Vero cells in vitro,which may promote SARS-CoV-2 infection.Therefore,these enriched pathogens in the pharynxes of COVID-19 patients may involve in the virus-host interactions to affect SARS-CoV-2 infection and cause potential secondary bacterial infections through changing the expression of the viral receptor ACE2 and/or modulate the host’s immune system.
基金This work is supported by the National Key Research and Development Program of China under Grant No. 2016YFB1000202 and the National Natural Science Foundation of China under Grant Nos. 61303056 and 61379042.
文摘Key-value (KV) stores have become a backbone of large-scale applications in today's data centers. Write- optimized data structures like the Log-Structured Merge-tree (LSM-tree) and their variants are widely used in KV storage systems like BigTable and RocksDB. Conventional LSM-tree organizes KV items into multiple, successively larger components, and uses compaction to push KV items from one smaller component to another adjacent larger component until the KV items reach the largest component. Unfortunately, current compaction scheme incurs significant write amplification due to repeated KV item reads and writes, and then results in poor throughput. We propose a new compaction scheme, delayed compaction (dCompaction) that decreases write amplification, dCompaction postpones some compactions and gathers them into the following compaction. In this way, it avoids KV item reads and writes during compaction, and consequently improves the throughput of LSM-tree based KV stores. We implement dCompaction on RocksDB, and conduct extensive experiments. Validation using YCSB framework shows that compared with RocksDB, dCompaction has about 40% write performance improvements and also comparable read performance.
基金supported by the National Key R&D Program of China (No. 2017YFC0210203)the National Natural Science Foundation of China (No. U1810209 )the Industry School-Research Institution Program of HBIS Group Tangsteel Company。
文摘To clarify the effect of coking dust, sintering dust and fly ash on the activity of activated carbon for various industrial flue gas desulfurization and denitrification, the coupling mechanism of the mixed activated carbon and dust was investigated to provide theoretical reference for the stable operation. The results show that coking dust had 34% desulfurization efficiency and 10% denitrification efficiency;correspondingly, sintering dust and fly ash had no obvious desulfurization and denitrification activities. For the mixture of activated carbon and dust, the coking dust reduced the desulfurization and denitrification efficiencies by blocking the pores of activated carbon, and its inhibiting effect on activated carbon was larger than its own desulfurization and denitrification activity. The sintering dust also reduced the desulfurization efficiency on the activated carbon while enhancing the denitrification efficiency. Fly ash blocked the pores of activated carbon and reduced its reaction activity. The reaction activity of coking dust mainly came from the surface functional groups, similar to that of activated carbon. The reaction activity of sintering dust mainly came from the oxidative property of Fe_2O _3, which oxidized NO to NO_2 and promoted the fast selectively catalytic reduction(SCR) of NO to form N_2. Sintering dust was activated by the joint action of activated carbon, and both had a coupling function. Sintering dust enhanced the adsorption and oxidation of NO, and activated carbon further promoted the reduction of NO_x by NH_3;thus, the denitrification efficiency increased by 5%-7% on the activated carbon.
基金supported by the National Natural Science Foundation of China (Nos.51672281,61227902,5183200& and 51772195)Beijing Natural Science Foundation (No.2162050)+1 种基金the Youth Innovation Promotion Association of CAS (No.2015025)supported by High-performance Computing Platform of Peking University.We thank Dr.
文摘Magneto-luminescent molecules have significant applications in data storage and quantum computing.However,design of these bi-functional molecules coupled with magnetic behavior and photoluminescence is still challenging.In this work,we report a metallofullerene DyErScN @In-C80 exhibiting single-molecule magnet (SMM) behavior and near-infrared emission.For DyErScN @Ih-C80,two functional lanthanide metal ions of Dy^3+(SMM function) and Er^3+(luminescent function) are integrated inside a fullerene cage using a trimetallic nitride template,and its structure has been unambiguously characterized by single-crystal X-ray diffraction.Magnetic measurements revealed that DyErScN @Ih-C80 behaves as a SMM with a blocking temperature up to 9 K resulting from the intramolecular magnetic interaction between Dy^3+ and Er^3+ ions.Moreover,DyErScN @In-C80 exhibits temperature-dependent near-infrared emission around 1.5 pm with multiple splitting peaks from Er^3+,which arises from the influence of Dy^3+ ion.This study provides a new strategy to synthesize new magneto-luminescent molecule materials.
基金supported by the Ministry of Science and Technology of the People’s Republic of China (2020YFC08845600)the National Health Commission of the People’s Republic of China (2018ZX10711001-006)。
文摘Dear Editor,Severe acute respiratory syndrome coronavirus 2(SARSCoV-2), the etiologic agent of COVID-19, is an enveloped,positive-sense single-stranded RNA virus that first discovered in December 2019 from a seafood market in Wuhan, China(Zhou et al. 2020).