The distinct element method(DEM)has been used successfully for the dynamic analysis of rigid block sys- tems.One of many difficulties associated with DEM is modeling of damping.In this paper,new procedures are propose...The distinct element method(DEM)has been used successfully for the dynamic analysis of rigid block sys- tems.One of many difficulties associated with DEM is modeling of damping.In this paper,new procedures are proposed for the damping modeling and its numerical implementation in distinct element analysis of rigid muhi-block systems.The stiff- ness proportional damping is constructed for the prescribed damping ratio,based on the non-zero fundamental frequency ef- fective during the time interval while the boundary conditions remain essentially constant.At this time interval,the funda- mental frequency can be estimated without complete eigenvalue analysis.The damping coefficients will vary while the damp- ing ratio remains the same throughout the entire analysis.A new numerical procedure is developed to prevent unnecessary energy loss that can occur during the separation phases.These procedures were implemented in the development of the dis- tinet element method for the dynamic analyses of piled multi-block systems.The analysis results |or the single-block and two-block systems were in a good agreement with the analytic predictions.Applications to the seismic analyses of piled four- block systems revealed that the new procedures can make a significant difference and may lead to much-improved results.展开更多
Last year, the State Council issued the Several Opinions on Further Strengthening the Management of Urban Planning. The guideline on urban planning has sparked heated debate among Internet users over opening up gated ...Last year, the State Council issued the Several Opinions on Further Strengthening the Management of Urban Planning. The guideline on urban planning has sparked heated debate among Internet users over opening up gated residential communities to public road system. This paper, based on the analysis of the background and contents of block system reform, explored the problems of the implementation of the block system reform and the impact of the block system reform on the real estate in China from 3 aspects, the selling points of the high-end communities, future property management and the community elderly care model.展开更多
In February 2016, the Central Committee of the Communist Party of China and the State Council of China issued the "Several Opinions of the CPC Central Committee and the State Council on Further Strengthening the ...In February 2016, the Central Committee of the Communist Party of China and the State Council of China issued the "Several Opinions of the CPC Central Committee and the State Council on Further Strengthening the Management of Urban Planning and Construction", stating that, in principle, closed residential areas will no longer be constructed and will be replaced by the promotion of the block system. This change in policy has aroused a great deal of controversy in various circles of society in China. In 2017, Chengdu, the capital city of Sichuan province, made an innovative attempt to implement "small block regulations." In 2018, the first "block system" public rental housing district appeared in Beijing, the capital of China. These innovative practices have promoted the pace of block system reform in China, but in general, the implementation of block system reform is difficult. From the perspective of public opinion, it seems that many citizens misunderstand the block system. This may be due to the complex interactions among community environmental management, public security, privacy, and other factors where individual interests and public interests meet. This article, from the perspective of the protection of civil rights, analyses the advantages and disadvantages of the block system at the value level, distinguishes the differences between the block systems of China, the UK and the US and then puts forward the theory that the block system reforms for newly built and existing residences are different and should be implemented independently. Concerning the key point of the block system reforms, the "greater difficulty in the implementation of the block system reform in the existing residential quarters" is the proposal to expropriate the commonly owned internal roads and appropriately compensate the residents. Finally, to cope with the core issues effectively, this article advocates gradual implementation of the block system reforms in China, including legislation, policy transformation, cultural construction, and pilot trials to promote the success of the implementation.展开更多
Mobile block system is a new type of block technology based on the theory of interval block. This article focuses on the analysis of safety key points, the efficient use of emergency time, the maximum efficiency of mo...Mobile block system is a new type of block technology based on the theory of interval block. This article focuses on the analysis of safety key points, the efficient use of emergency time, the maximum efficiency of mobilizers, to reduce the loss of emergency incidents and casualties.展开更多
The development direction of railways is toward the improvement of capacity and service quality, where the service quality includes safety, schedule, high speed, and comfort. In light of the existing cellular automato...The development direction of railways is toward the improvement of capacity and service quality, where the service quality includes safety, schedule, high speed, and comfort. In light of the existing cellular automaton models, in this paper, we develop a model to analyze the mixed running processes of trains with maximal speeds of 500 km/h and 350 km/h respectively in the moving block system. In the proposed model, we establish some sound rules to control the running processes of a train, where the rules include the departure rules in the intermediate stations, the overtaking rules, and the conditions of speed limitation for a train stopping at a station or passing through a station. With the consideration of the mixed ratio and the distance between two adjacent stations, the properties of the train traffic flow （including capacity and average speed） are simulated. The numerical results show that the interactions among different trains will affect the capacity, and a proper increase of the spatial distance between two adjacent stations can enhance the capacity and the average speed under the moving block.展开更多
Sand production and high water content in oil wells are two major challenges that restrict high and stable production in loose sandstone reservoirs.In this paper,nano SiO_(2),coupling agent triethoxysilane,phenolic re...Sand production and high water content in oil wells are two major challenges that restrict high and stable production in loose sandstone reservoirs.In this paper,nano SiO_(2),coupling agent triethoxysilane,phenolic resin and n-octanol were used to synthesize the main agent SCA-2.Hexamethylenetetramine and vinyl carbonate were selected to prepare the curing agent YGA-1,which was then compounded with SCA-2 to develop a sand fixation and water plugging system.Firstly,single-factor experiments were conducted to determine the optimal concentrations of SCA-2 and YGA-1,subsequently,the system’s sand fixation and water blocking performance were evaluated.Finally,a pilot test was carried out in the mining site.Experimental results showed that the optimal formula composition of the system was 10%SCA-2+5%YGA-1.The gelation time of the system was 180 minutes and the viscosity after gelation could reach 108.4 mPa·s.When the dosage of the drug system was 0.6 PV,the sand production rate remained below 0.08%.Dual-tube parallel experiments showed that the sand fixation and water plugging system had a water flow channel plugging rate of 87.5%,while the oil flow channel plugging rate was only 11.3%,indicating minimal damage to the oil-bearing reservoir.The field test showed that after the measures taken in Well M of X oilfield,the sand free oil recovery period exceeded 360 days,the water content decreased by 5.0%and the cumulative oil production increased by 7092 m^(3).This study provides new ideas for efficient development of loose sandstone reservoirs.展开更多
Nanoscale drug delivery systems(nano-DDSs)have attracted intense interest in tumor chemotherapy in the last decades,to improve antitumor efficacy and minimize toxic and side effects.As a versatile supramolecular build...Nanoscale drug delivery systems(nano-DDSs)have attracted intense interest in tumor chemotherapy in the last decades,to improve antitumor efficacy and minimize toxic and side effects.As a versatile supramolecular building block,cyclodextrins(CDs)have been widely used in the fabrication of the smart nano-DDSs.Besides their multifunctionality,which makes them versatile core in the star(co)polymers for micellar nanomedicines,specific host-vip inclusion complexation via their hydrophobic cavities endows them diversified functions:(i)design of amphiphilic copolymers for micellar nanomedicines,(ii)supramolecular hydrogels and poly(pseudo)rotaxane nano-hydrogels as drug carriers,and(iii)recipient for direct and indirect drug-loading.In the present work,the recent progress of CDs in nano-DDSs for tumor chemotherapy was reviewed,classified by the crucial roles of CD units.Based on the structureperformance relationship,the future perspective was also proposed.展开更多
BACKGROUND Laparoscopic nephrectomy is a preferred surgical approach due to its minimally invasive nature and faster recovery times.However,effective management of postoperative pain remains a significant challenge.Se...BACKGROUND Laparoscopic nephrectomy is a preferred surgical approach due to its minimally invasive nature and faster recovery times.However,effective management of postoperative pain remains a significant challenge.Several traditional methods,including opioid-based analgesia,are commonly used but are associated with side effects such as nausea,vomiting,sedation,and delayed recovery.In recent years,the erector spinae plane block(ESPB)has gained attention as an ultrasoundguided regional anesthesia technique offering promising results in various surgical procedures by reducing opioid requirements and enhancing patient comfort.AIM To evaluate the efficacy and safety of ESPB in comparison to conventional pain management strategies in patients undergoing laparoscopic nephrectomy.METHODS Following PRISMA guidelines,we searched PubMed,EMBASE,Web of Science,and the Cochrane Register for randomized controlled trials(RCTs)comparing ESPB with control for laparoscopic nephrectomy.The Cochrane Risk of Bias tool was employed for quality assessment.The primary outcome was total patient-controlled analgesia(PCA)consumption.Secondary outcomes included hospital discharge time and the incidence of postoperative nausea and vomiting.A random-effects meta-analysis was conducted to calculate pooled mean differences(MD)and odds ratios(OR)with 95%CIs.RESULTS Nine RCTs involving a total of 643 patients(ESPB group=320;control group=323)were included in the analysis.ESPB significantly reduced PCA opioid consumption compared to controls(MD:-14.24,95%CI:-20.66 to-7.83,P<0.0001).Subgroup analysis showed reduced PCA use with ESPB vs morphine(MD:-8.78,95%CI:-15.34 to-2.22,P=0.009),and a non-significant effect compared to other analgesics(MD:-48.26,95%CI:-143.60 to 47.09).No statistically significant differences were observed in discharge time or the incidence of nausea and vomiting.CONCLUSION ESPB demonstrates the potential of reducing PCA in laparoscopic nephrectomy patients;however,its impact on secondary outcomes remains inconclusive.Large-scale RCTs are needed to confirm ESPB's benefits and explore long-term effects.展开更多
For simulating real pasteurization treatments using hot air,hot water,radio frequency and microwave heating,a unique experimental heating block system(HBS)was developed.The stability and uniformity of sample temperatu...For simulating real pasteurization treatments using hot air,hot water,radio frequency and microwave heating,a unique experimental heating block system(HBS)was developed.The stability and uniformity of sample temperatures and heating rates in HBS were determined for studying the thermal resistance of food-borne pathogens.A computer simulation model was also developed to analyze the behavior of thermal process in HBS.The results showed that the required heating rates with various set-temperatures and holding times could be easily and precisely achieved in eight selected food materials.Thermocouple and thermal imaging data showed that the good sample heating uniformity in six cells of HBS was achieved.The real temperature-time histories obtained by radio frequency energy could be approximately done in HBS by setting a number of linear regression curves.The HBS can help in more precisely characterizing the heat resistance of pathogens in foods to further develop pasteurization processes.展开更多
With rapid advancements in Infra-Red (IR) detection techniques, the range from where the IR-guided missiles are able to lock the target aircraft has increased. To avoid the detection and tracking by modern IR-guided m...With rapid advancements in Infra-Red (IR) detection techniques, the range from where the IR-guided missiles are able to lock the target aircraft has increased. To avoid the detection and tracking by modern IR-guided missiles, the aircraft and helicopters also demand progress in its stealth techniques. Hence, study of Infra-Red Signature Suppression (IRSS) systems in aircraft and helicopters has become vital even in design stage. Optical blocking (masking) is one of the effective IRSS techniques used to block the Line- Of-Sight (LOS) of the hot engine parts of the exhaust geometry. This paper reviews the various patents on IR signature suppression systems based on the optical blocking method or a combination of IRSS techniques. The performance penalties generated due to installation of various IRSS methods in aircraft and helicopters are also discussed.展开更多
The paleocontinental margins have frequent and intensive tectonic movement and various ore forming processes. According to their tectono dynamic characteristics, the paleocontinental margins can be classified into t...The paleocontinental margins have frequent and intensive tectonic movement and various ore forming processes. According to their tectono dynamic characteristics, the paleocontinental margins can be classified into three types: the divergent, the convergent and the transformational. Each type has its specific geological geochemical processes and metallogenic system. The paper discusses the tectonic evolution and ore forming features of the North China block margins, puts forward conceptions such as complexity, variety and multi stage development of metallogenic evolution in the paleocontinental margins, and expounds five factors controlling the formation of large superlarge ore deposits in the paleocontinental margins: (1) channelway, (2) rendezvous of fluids, (3) abundance of ore source, (4) thermo dynamic anomaly, (5) long duration of structural activities.展开更多
This feature article summarizes the synthesis of novel olefin block copolymers using fast syndiospecific living homo- and copolymerization of propylene, higher 1-alkene, and norbornene with ansa-fluorenylamidodimethyl...This feature article summarizes the synthesis of novel olefin block copolymers using fast syndiospecific living homo- and copolymerization of propylene, higher 1-alkene, and norbornene with ansa-fluorenylamidodimethyltitanium- based catalyst according to the authors＇ recent results. The catalytic synthesis of monodisperse polyolefin and olefin block copolymer was also described using this living system.展开更多
To date, the high power arc plasma technology is widely used. A next generation high power arc plasma system based on building block structure is presented. The whole arc plasma inverter system is composed of 12 paral...To date, the high power arc plasma technology is widely used. A next generation high power arc plasma system based on building block structure is presented. The whole arc plasma inverter system is composed of 12 paralleled units to increase the system output capability. The hierarchical control system is adopted to improve the reliability and flexibility of the high power arc plasma inverter. To ensure the reliable turn on and off of the IGBT module in each building block unit, a special pulse drive circuit is designed by using pulse transformer. The experimental result indicates that the high power arc plasma inverter system can transfer 300 kW arc plasma energy reliably with high efficiency.展开更多
Objective:Robot-assisted radical prostatectomy(RARP)requires pneumoperitoneum(Pnp)and a steep head-down position that may disturb respiratory system compliance(Crs)during surgery.Our aim was to compare the effects of ...Objective:Robot-assisted radical prostatectomy(RARP)requires pneumoperitoneum(Pnp)and a steep head-down position that may disturb respiratory system compliance(Crs)during surgery.Our aim was to compare the effects of different degrees of neuromuscular block(NMB)on Crs with the same Pnp pressure during RARP.Methods:One hundred patients who underwent RARP were enrolled and randomly allocated to a deep or moderate NMB group with 50 patients in each group.Rocuronium was administered to both groups:in the moderate NMB group to maintain 1–2 responses to train-of-four(TOF)stimulation;and in the deep NMB group to maintain no response to TOF stimulation and 1–2 responses in the post-tetanic count.Pnp pressure in both groups was 10 mm Hg(1 mm Hg=133.3 Pa).Peak inspiratory pressure(Ppeak),mean pressure(Pmean),Crs,and airway resistance(Raw)were recorded after anesthesia induction and at 0,30,60,and 90 min of Pnp and post-Pnp.Surgical space conditions were evaluated after the procedure on a 4-point scale.Results:Immediately after the Pnp,Ppeak,Pmean,and Raw significantly increased,while Crs decreased and persisted during Pnp in both groups.The results did not significantly differ between the two groups at any of the time points.There was no difference in surgical space conditions between groups.Body movements occurred in 14 cases in the moderate NMB group and in one case in the deep NMB group,and all occurred during obturator lymphadenectomy.A significant difference between the two groups was observed.Conclusions:Under the same Pnp pressure in RARP,deep and moderate NMBs resulted in similar changes in Crs,and in other respiratory mechanics and surgical space conditions.However,deep NMB significantly reduced body movements during surgery.展开更多
The major drawback in Orthogonal Frequency Division Multiplexing (OFDM) system is due to the high Peak-to-Average Power Ratio (PAPR), so the performance of the system is significantly degraded by the nonlinearity of a...The major drawback in Orthogonal Frequency Division Multiplexing (OFDM) system is due to the high Peak-to-Average Power Ratio (PAPR), so the performance of the system is significantly degraded by the nonlinearity of a High Power Amplifier (HPA) in the transmitter.In order to mitigate distortion, a block coding scheme for reducing PAPR in OFDM systems with large number of subcarriers based on complementary sequences and predistortion is proposed,which is capable of both error correction and PAPR reduction. Computer simulation results show that the proposed scheme significantly improves Bit Error Rate(BER) performance as compared to an uncoded system when an HPA is employed or a coded system without predistortion.展开更多
Blocker tag attack is one of the denial-of-service(DoS)attacks that threatens the privacy and security of RFID systems.The attacker interferes with the blocked tag by simulating a fake tag with the same ID,thus causin...Blocker tag attack is one of the denial-of-service(DoS)attacks that threatens the privacy and security of RFID systems.The attacker interferes with the blocked tag by simulating a fake tag with the same ID,thus causing a collision of message replies.In many practical scenarios,the number of blocked tags may vary,or even be small.For example,the attacker may only block the important customers or high-value items.To avoid the disclosure of privacy and economic losses,it is of great importance to fast pinpoint these blocked ones.However,existing works do not take into account the impact of the number of blocked tags on the execution time and suffer from incomplete identification of blocked tags,long identification time or privacy leakage.To overcome these limits,we propose a cross layer blocked tag identification protocol(CLBI).CLBI consists of multiple rounds,in which it enables multiple unblocked tags to select one time slot and concurrently verify them by using tag estimation in physical layer.Benefiting from the utilization of most collision slots,the execution time can be greatly reduced.Furthermore,for efficient identification of blocked tags under different proportions,we propose a hybrid protocol named adaptive cross layer blocked tag identification protocol(A-CLBI),which estimates the remaining blocked tag in each round and adjusts the identification strategy accordingly.Extensive simulations show that our protocol outperforms state-of-the-art blocked tags identification protocol.展开更多
A brain-computer interface(BCI)-based electric wheelchair control system was developed, which enables the users to move the wheelchair forward or backward, and turn left or right without any pre-learning. This control...A brain-computer interface(BCI)-based electric wheelchair control system was developed, which enables the users to move the wheelchair forward or backward, and turn left or right without any pre-learning. This control system makes use of the amplitude enhancement of alpha-wave blocking in electroencephalogram(EEG) when eyes close for more than 1 s to constitute a BCI for the switch control of wheelchair movements. The system was formed by BCI control panel, data acquisition, signal processing unit and interface control circuit. Eight volunteers participated in the wheelchair control experiments according to the preset routes. The experimental results show that the mean success control rate of all the subjects was 81.3%, with the highest reaching 93.7%. When one subject's triggering time was 2.8 s, i.e., the flashing time of each cycle light was 2.8 s, the average information transfer rate was 8.10 bit/min, with the highest reaching 12.54 bit/min.展开更多
The symmetric linear system gives us many simplifications and a possibility to adapt the computations to the computer at hand in order to achieve better performance. The aim of this paper is to consider the block bidi...The symmetric linear system gives us many simplifications and a possibility to adapt the computations to the computer at hand in order to achieve better performance. The aim of this paper is to consider the block bidiagonalization methods derived from a symmetric augmented multiple linear systems and make a comparison with the block GMRES and block biconjugate gradient methods.展开更多
Multiple coal seams and interbedded rock assemblages formed in vertical progression due to the influence of multiple stages of sea level transgressions.Based on mercury injection experiment,low temperature liquid nitr...Multiple coal seams and interbedded rock assemblages formed in vertical progression due to the influence of multiple stages of sea level transgressions.Based on mercury injection experiment,low temperature liquid nitrogen experiment,porosity and permeability experiment and breakthrough pressure experiment,the vertical variation characteristics of coal-bearing strata in Gujiao block are explained in detail.The results of the mercury injection and low temperature liquid nitrogen experiments show that the pore structure characteristics fluctuate with increasing depth in the strata,with fewer micropores followed by transition pores.The BET specific surface area and average pore diameter of the Shanxi Formation are generally larger than those of the Taiyuan Formation.Due to the continuous cyclic sequence stratigraphy changes,the porosity,permeability,breakthrough pressure and breakthrough time of the samples show a certain cyclicity.Within the same sequence,the porosity is larger,and the permeability is smaller near the maximum flooding surface.Although the permeability of the sandstone samples is higher,the porosity is lower,and the breakthrough pressure and breakthrough times are greater.The strata in the study area formed in an oxidized environment that was affected by freshwater,and the pore structure of different lithologies is quite different.After the formation of sandstone,the intergranular pores generally underwent filling with secondary quartz,clay minerals and organic matter,resulting in low porosity and permeability.展开更多
This contribution reports an efficient approach for preparing polycarbonate block terpolymers by immortal stepwise copolymerization of CO2 with different epoxides in the presence of enol chain transfer,mediated by rob...This contribution reports an efficient approach for preparing polycarbonate block terpolymers by immortal stepwise copolymerization of CO2 with different epoxides in the presence of enol chain transfer,mediated by robust cobalt catalyst systems consisting of the fluorine substituted salen Co(Ⅲ)NO3 or biphenol-linker bimetallic Co(Ⅲ)complex in conjunction with an ionic cocatalyst,PPNX(PPN=bis(triphenylphosphine)iminium,X=NO3–or 2,4-dinitrophenoxide).Various polycarbonate block terpolymers were obtained in perfectly unimodal distribution of their molecular weights with narrow polydispersity.They all possessed only one broad glass transition temperature,which could be adjusted by altering the length of different polycarbonate segments.展开更多
文摘The distinct element method(DEM)has been used successfully for the dynamic analysis of rigid block sys- tems.One of many difficulties associated with DEM is modeling of damping.In this paper,new procedures are proposed for the damping modeling and its numerical implementation in distinct element analysis of rigid muhi-block systems.The stiff- ness proportional damping is constructed for the prescribed damping ratio,based on the non-zero fundamental frequency ef- fective during the time interval while the boundary conditions remain essentially constant.At this time interval,the funda- mental frequency can be estimated without complete eigenvalue analysis.The damping coefficients will vary while the damp- ing ratio remains the same throughout the entire analysis.A new numerical procedure is developed to prevent unnecessary energy loss that can occur during the separation phases.These procedures were implemented in the development of the dis- tinet element method for the dynamic analyses of piled multi-block systems.The analysis results |or the single-block and two-block systems were in a good agreement with the analytic predictions.Applications to the seismic analyses of piled four- block systems revealed that the new procedures can make a significant difference and may lead to much-improved results.
文摘Last year, the State Council issued the Several Opinions on Further Strengthening the Management of Urban Planning. The guideline on urban planning has sparked heated debate among Internet users over opening up gated residential communities to public road system. This paper, based on the analysis of the background and contents of block system reform, explored the problems of the implementation of the block system reform and the impact of the block system reform on the real estate in China from 3 aspects, the selling points of the high-end communities, future property management and the community elderly care model.
文摘In February 2016, the Central Committee of the Communist Party of China and the State Council of China issued the "Several Opinions of the CPC Central Committee and the State Council on Further Strengthening the Management of Urban Planning and Construction", stating that, in principle, closed residential areas will no longer be constructed and will be replaced by the promotion of the block system. This change in policy has aroused a great deal of controversy in various circles of society in China. In 2017, Chengdu, the capital city of Sichuan province, made an innovative attempt to implement "small block regulations." In 2018, the first "block system" public rental housing district appeared in Beijing, the capital of China. These innovative practices have promoted the pace of block system reform in China, but in general, the implementation of block system reform is difficult. From the perspective of public opinion, it seems that many citizens misunderstand the block system. This may be due to the complex interactions among community environmental management, public security, privacy, and other factors where individual interests and public interests meet. This article, from the perspective of the protection of civil rights, analyses the advantages and disadvantages of the block system at the value level, distinguishes the differences between the block systems of China, the UK and the US and then puts forward the theory that the block system reforms for newly built and existing residences are different and should be implemented independently. Concerning the key point of the block system reforms, the "greater difficulty in the implementation of the block system reform in the existing residential quarters" is the proposal to expropriate the commonly owned internal roads and appropriately compensate the residents. Finally, to cope with the core issues effectively, this article advocates gradual implementation of the block system reforms in China, including legislation, policy transformation, cultural construction, and pilot trials to promote the success of the implementation.
文摘Mobile block system is a new type of block technology based on the theory of interval block. This article focuses on the analysis of safety key points, the efficient use of emergency time, the maximum efficiency of mobilizers, to reduce the loss of emergency incidents and casualties.
基金Project supported by the State Social Science Fund Project, China (Grant No. 11CJY067)the Natural Science Foundation of Gansu Province, China (Grant No. 1107RJYA070)
文摘The development direction of railways is toward the improvement of capacity and service quality, where the service quality includes safety, schedule, high speed, and comfort. In light of the existing cellular automaton models, in this paper, we develop a model to analyze the mixed running processes of trains with maximal speeds of 500 km/h and 350 km/h respectively in the moving block system. In the proposed model, we establish some sound rules to control the running processes of a train, where the rules include the departure rules in the intermediate stations, the overtaking rules, and the conditions of speed limitation for a train stopping at a station or passing through a station. With the consideration of the mixed ratio and the distance between two adjacent stations, the properties of the train traffic flow （including capacity and average speed） are simulated. The numerical results show that the interactions among different trains will affect the capacity, and a proper increase of the spatial distance between two adjacent stations can enhance the capacity and the average speed under the moving block.
文摘Sand production and high water content in oil wells are two major challenges that restrict high and stable production in loose sandstone reservoirs.In this paper,nano SiO_(2),coupling agent triethoxysilane,phenolic resin and n-octanol were used to synthesize the main agent SCA-2.Hexamethylenetetramine and vinyl carbonate were selected to prepare the curing agent YGA-1,which was then compounded with SCA-2 to develop a sand fixation and water plugging system.Firstly,single-factor experiments were conducted to determine the optimal concentrations of SCA-2 and YGA-1,subsequently,the system’s sand fixation and water blocking performance were evaluated.Finally,a pilot test was carried out in the mining site.Experimental results showed that the optimal formula composition of the system was 10%SCA-2+5%YGA-1.The gelation time of the system was 180 minutes and the viscosity after gelation could reach 108.4 mPa·s.When the dosage of the drug system was 0.6 PV,the sand production rate remained below 0.08%.Dual-tube parallel experiments showed that the sand fixation and water plugging system had a water flow channel plugging rate of 87.5%,while the oil flow channel plugging rate was only 11.3%,indicating minimal damage to the oil-bearing reservoir.The field test showed that after the measures taken in Well M of X oilfield,the sand free oil recovery period exceeded 360 days,the water content decreased by 5.0%and the cumulative oil production increased by 7092 m^(3).This study provides new ideas for efficient development of loose sandstone reservoirs.
文摘Nanoscale drug delivery systems(nano-DDSs)have attracted intense interest in tumor chemotherapy in the last decades,to improve antitumor efficacy and minimize toxic and side effects.As a versatile supramolecular building block,cyclodextrins(CDs)have been widely used in the fabrication of the smart nano-DDSs.Besides their multifunctionality,which makes them versatile core in the star(co)polymers for micellar nanomedicines,specific host-vip inclusion complexation via their hydrophobic cavities endows them diversified functions:(i)design of amphiphilic copolymers for micellar nanomedicines,(ii)supramolecular hydrogels and poly(pseudo)rotaxane nano-hydrogels as drug carriers,and(iii)recipient for direct and indirect drug-loading.In the present work,the recent progress of CDs in nano-DDSs for tumor chemotherapy was reviewed,classified by the crucial roles of CD units.Based on the structureperformance relationship,the future perspective was also proposed.
文摘BACKGROUND Laparoscopic nephrectomy is a preferred surgical approach due to its minimally invasive nature and faster recovery times.However,effective management of postoperative pain remains a significant challenge.Several traditional methods,including opioid-based analgesia,are commonly used but are associated with side effects such as nausea,vomiting,sedation,and delayed recovery.In recent years,the erector spinae plane block(ESPB)has gained attention as an ultrasoundguided regional anesthesia technique offering promising results in various surgical procedures by reducing opioid requirements and enhancing patient comfort.AIM To evaluate the efficacy and safety of ESPB in comparison to conventional pain management strategies in patients undergoing laparoscopic nephrectomy.METHODS Following PRISMA guidelines,we searched PubMed,EMBASE,Web of Science,and the Cochrane Register for randomized controlled trials(RCTs)comparing ESPB with control for laparoscopic nephrectomy.The Cochrane Risk of Bias tool was employed for quality assessment.The primary outcome was total patient-controlled analgesia(PCA)consumption.Secondary outcomes included hospital discharge time and the incidence of postoperative nausea and vomiting.A random-effects meta-analysis was conducted to calculate pooled mean differences(MD)and odds ratios(OR)with 95%CIs.RESULTS Nine RCTs involving a total of 643 patients(ESPB group=320;control group=323)were included in the analysis.ESPB significantly reduced PCA opioid consumption compared to controls(MD:-14.24,95%CI:-20.66 to-7.83,P<0.0001).Subgroup analysis showed reduced PCA use with ESPB vs morphine(MD:-8.78,95%CI:-15.34 to-2.22,P=0.009),and a non-significant effect compared to other analgesics(MD:-48.26,95%CI:-143.60 to 47.09).No statistically significant differences were observed in discharge time or the incidence of nausea and vomiting.CONCLUSION ESPB demonstrates the potential of reducing PCA in laparoscopic nephrectomy patients;however,its impact on secondary outcomes remains inconclusive.Large-scale RCTs are needed to confirm ESPB's benefits and explore long-term effects.
基金This research was conducted in the College of Mechanical and Electronic Engineering,Northwest A&F Universitysupported by research grants from General Program of National Natural Science Foundation of China(31371853)National Key Research and Development Program of China(2016YFD0401000).
文摘For simulating real pasteurization treatments using hot air,hot water,radio frequency and microwave heating,a unique experimental heating block system(HBS)was developed.The stability and uniformity of sample temperatures and heating rates in HBS were determined for studying the thermal resistance of food-borne pathogens.A computer simulation model was also developed to analyze the behavior of thermal process in HBS.The results showed that the required heating rates with various set-temperatures and holding times could be easily and precisely achieved in eight selected food materials.Thermocouple and thermal imaging data showed that the good sample heating uniformity in six cells of HBS was achieved.The real temperature-time histories obtained by radio frequency energy could be approximately done in HBS by setting a number of linear regression curves.The HBS can help in more precisely characterizing the heat resistance of pathogens in foods to further develop pasteurization processes.
基金the Indian Institute of Technology Bombay’s Post-Doctoral Research Program, vide appointment no. AO/Admn1/33/2018 dated 10.Aug’2018 for providing funding
文摘With rapid advancements in Infra-Red (IR) detection techniques, the range from where the IR-guided missiles are able to lock the target aircraft has increased. To avoid the detection and tracking by modern IR-guided missiles, the aircraft and helicopters also demand progress in its stealth techniques. Hence, study of Infra-Red Signature Suppression (IRSS) systems in aircraft and helicopters has become vital even in design stage. Optical blocking (masking) is one of the effective IRSS techniques used to block the Line- Of-Sight (LOS) of the hot engine parts of the exhaust geometry. This paper reviews the various patents on IR signature suppression systems based on the optical blocking method or a combination of IRSS techniques. The performance penalties generated due to installation of various IRSS methods in aircraft and helicopters are also discussed.
文摘The paleocontinental margins have frequent and intensive tectonic movement and various ore forming processes. According to their tectono dynamic characteristics, the paleocontinental margins can be classified into three types: the divergent, the convergent and the transformational. Each type has its specific geological geochemical processes and metallogenic system. The paper discusses the tectonic evolution and ore forming features of the North China block margins, puts forward conceptions such as complexity, variety and multi stage development of metallogenic evolution in the paleocontinental margins, and expounds five factors controlling the formation of large superlarge ore deposits in the paleocontinental margins: (1) channelway, (2) rendezvous of fluids, (3) abundance of ore source, (4) thermo dynamic anomaly, (5) long duration of structural activities.
文摘This feature article summarizes the synthesis of novel olefin block copolymers using fast syndiospecific living homo- and copolymerization of propylene, higher 1-alkene, and norbornene with ansa-fluorenylamidodimethyltitanium- based catalyst according to the authors＇ recent results. The catalytic synthesis of monodisperse polyolefin and olefin block copolymer was also described using this living system.
基金supported by National Natural Science Foundation of China (50805051)Guangdong Provincial Science and Technology Project (2008B010400041)
文摘To date, the high power arc plasma technology is widely used. A next generation high power arc plasma system based on building block structure is presented. The whole arc plasma inverter system is composed of 12 paralleled units to increase the system output capability. The hierarchical control system is adopted to improve the reliability and flexibility of the high power arc plasma inverter. To ensure the reliable turn on and off of the IGBT module in each building block unit, a special pulse drive circuit is designed by using pulse transformer. The experimental result indicates that the high power arc plasma inverter system can transfer 300 kW arc plasma energy reliably with high efficiency.
基金Project supported by the Zhejiang Province Public Welfare Technology Application Research Project(No.LGF20H010006),China。
文摘Objective:Robot-assisted radical prostatectomy(RARP)requires pneumoperitoneum(Pnp)and a steep head-down position that may disturb respiratory system compliance(Crs)during surgery.Our aim was to compare the effects of different degrees of neuromuscular block(NMB)on Crs with the same Pnp pressure during RARP.Methods:One hundred patients who underwent RARP were enrolled and randomly allocated to a deep or moderate NMB group with 50 patients in each group.Rocuronium was administered to both groups:in the moderate NMB group to maintain 1–2 responses to train-of-four(TOF)stimulation;and in the deep NMB group to maintain no response to TOF stimulation and 1–2 responses in the post-tetanic count.Pnp pressure in both groups was 10 mm Hg(1 mm Hg=133.3 Pa).Peak inspiratory pressure(Ppeak),mean pressure(Pmean),Crs,and airway resistance(Raw)were recorded after anesthesia induction and at 0,30,60,and 90 min of Pnp and post-Pnp.Surgical space conditions were evaluated after the procedure on a 4-point scale.Results:Immediately after the Pnp,Ppeak,Pmean,and Raw significantly increased,while Crs decreased and persisted during Pnp in both groups.The results did not significantly differ between the two groups at any of the time points.There was no difference in surgical space conditions between groups.Body movements occurred in 14 cases in the moderate NMB group and in one case in the deep NMB group,and all occurred during obturator lymphadenectomy.A significant difference between the two groups was observed.Conclusions:Under the same Pnp pressure in RARP,deep and moderate NMBs resulted in similar changes in Crs,and in other respiratory mechanics and surgical space conditions.However,deep NMB significantly reduced body movements during surgery.
基金Supported in part by the National 863 program of China(No.2001AA123014)
文摘The major drawback in Orthogonal Frequency Division Multiplexing (OFDM) system is due to the high Peak-to-Average Power Ratio (PAPR), so the performance of the system is significantly degraded by the nonlinearity of a High Power Amplifier (HPA) in the transmitter.In order to mitigate distortion, a block coding scheme for reducing PAPR in OFDM systems with large number of subcarriers based on complementary sequences and predistortion is proposed,which is capable of both error correction and PAPR reduction. Computer simulation results show that the proposed scheme significantly improves Bit Error Rate(BER) performance as compared to an uncoded system when an HPA is employed or a coded system without predistortion.
基金This work was supported in part by the National Natural Science Foundation of China under project contracts Nos.61701082,61701116,61601093,61971113 and 61901095in part by National Key R&D Program under project Nos.2018YFB1802102 and 2018AAA0103203+3 种基金in part by Guangdong Provincial Research and Development Plan in Key Areas under project contract Nos.2019B010141001 and 2019B010142001in part by Sichuan Provincial Science and Technology Planning Program under project contracts Nos.2018HH0034,2019YFG0418,2019YFG0120 and 2018JY0246in part by the fundamental research funds for the Central Universities under project contract No.ZYGX2016J004in part by Science and Technology on Electronic Information Control Laboratory.
文摘Blocker tag attack is one of the denial-of-service(DoS)attacks that threatens the privacy and security of RFID systems.The attacker interferes with the blocked tag by simulating a fake tag with the same ID,thus causing a collision of message replies.In many practical scenarios,the number of blocked tags may vary,or even be small.For example,the attacker may only block the important customers or high-value items.To avoid the disclosure of privacy and economic losses,it is of great importance to fast pinpoint these blocked ones.However,existing works do not take into account the impact of the number of blocked tags on the execution time and suffer from incomplete identification of blocked tags,long identification time or privacy leakage.To overcome these limits,we propose a cross layer blocked tag identification protocol(CLBI).CLBI consists of multiple rounds,in which it enables multiple unblocked tags to select one time slot and concurrently verify them by using tag estimation in physical layer.Benefiting from the utilization of most collision slots,the execution time can be greatly reduced.Furthermore,for efficient identification of blocked tags under different proportions,we propose a hybrid protocol named adaptive cross layer blocked tag identification protocol(A-CLBI),which estimates the remaining blocked tag in each round and adjusts the identification strategy accordingly.Extensive simulations show that our protocol outperforms state-of-the-art blocked tags identification protocol.
基金Supported by the National Natural Science Foundation of China(No.81222021,No.30970875,No.90920015,No.61172008 and No.81171423)National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No.2012BAI34B02)Program for New Century Excellent Talents in University of the Ministry of Education of China(No.NCET-10-0618)
文摘A brain-computer interface(BCI)-based electric wheelchair control system was developed, which enables the users to move the wheelchair forward or backward, and turn left or right without any pre-learning. This control system makes use of the amplitude enhancement of alpha-wave blocking in electroencephalogram(EEG) when eyes close for more than 1 s to constitute a BCI for the switch control of wheelchair movements. The system was formed by BCI control panel, data acquisition, signal processing unit and interface control circuit. Eight volunteers participated in the wheelchair control experiments according to the preset routes. The experimental results show that the mean success control rate of all the subjects was 81.3%, with the highest reaching 93.7%. When one subject's triggering time was 2.8 s, i.e., the flashing time of each cycle light was 2.8 s, the average information transfer rate was 8.10 bit/min, with the highest reaching 12.54 bit/min.
基金The research of this author was supported by the National Natural Science Foundation of China,the JiangsuProvince Natural Science Foundation,the Jiangsu Province"333Engineering" Foundation and the Jiangsu Province"Qinglan Engineering" Foundation
文摘The symmetric linear system gives us many simplifications and a possibility to adapt the computations to the computer at hand in order to achieve better performance. The aim of this paper is to consider the block bidiagonalization methods derived from a symmetric augmented multiple linear systems and make a comparison with the block GMRES and block biconjugate gradient methods.
基金the National Natural Science Foundation of China(No.41672149 and No.41672146)the Key Project of the Natural Science Foundation of China(No.41530314)+3 种基金the Application Research Plan of Key Scientific Research Projects in Colleges and Universities of Henan Province(20B610006)Scientific Research Foundation of the Shandong Provincial Key Laboratory of Depositional Mineralization&Sedimentary Mineralsthe Shandong University of Science and Technology(DMSM2017012)the National Science and Technology Major Project(2016ZX05044-002).
文摘Multiple coal seams and interbedded rock assemblages formed in vertical progression due to the influence of multiple stages of sea level transgressions.Based on mercury injection experiment,low temperature liquid nitrogen experiment,porosity and permeability experiment and breakthrough pressure experiment,the vertical variation characteristics of coal-bearing strata in Gujiao block are explained in detail.The results of the mercury injection and low temperature liquid nitrogen experiments show that the pore structure characteristics fluctuate with increasing depth in the strata,with fewer micropores followed by transition pores.The BET specific surface area and average pore diameter of the Shanxi Formation are generally larger than those of the Taiyuan Formation.Due to the continuous cyclic sequence stratigraphy changes,the porosity,permeability,breakthrough pressure and breakthrough time of the samples show a certain cyclicity.Within the same sequence,the porosity is larger,and the permeability is smaller near the maximum flooding surface.Although the permeability of the sandstone samples is higher,the porosity is lower,and the breakthrough pressure and breakthrough times are greater.The strata in the study area formed in an oxidized environment that was affected by freshwater,and the pore structure of different lithologies is quite different.After the formation of sandstone,the intergranular pores generally underwent filling with secondary quartz,clay minerals and organic matter,resulting in low porosity and permeability.
基金financially supported by the National Natural Science Foundation of China (No. 21690073)the Program for Changjiang Scholars and Innovative Research Team in University (No. IRT-17R14)
文摘This contribution reports an efficient approach for preparing polycarbonate block terpolymers by immortal stepwise copolymerization of CO2 with different epoxides in the presence of enol chain transfer,mediated by robust cobalt catalyst systems consisting of the fluorine substituted salen Co(Ⅲ)NO3 or biphenol-linker bimetallic Co(Ⅲ)complex in conjunction with an ionic cocatalyst,PPNX(PPN=bis(triphenylphosphine)iminium,X=NO3–or 2,4-dinitrophenoxide).Various polycarbonate block terpolymers were obtained in perfectly unimodal distribution of their molecular weights with narrow polydispersity.They all possessed only one broad glass transition temperature,which could be adjusted by altering the length of different polycarbonate segments.
