Arginine (2-amino-5-guanidino pentanoic acid) was shown in 1895 by Hedin to be present in the proteins of horn. Metabolic nitrogen balance studies, conducted in 1957 by Rose in human adults and in 1959 by Snyderman an...Arginine (2-amino-5-guanidino pentanoic acid) was shown in 1895 by Hedin to be present in the proteins of horn. Metabolic nitrogen balance studies, conducted in 1957 by Rose in human adults and in 1959 by Snyderman and coworkers in young infants, revealed that a dietary source of this amino acid was not an obligatory requirement for growth and maintenance of nitrogen homeostasis in healthy individuals. Hence, It was initially classified as a non-essential (dispensable) amino acid and, perhaps, for reasons of this classification arginine did not receivc the earlier atteniion it now deserves, in relation to an understanding of the nutritional biochemistry and physiology of its metabolism in humans subjects. However, there is currently a considerable interest in the cellular and tissue functions, as well as clinical, therapeutic significance, of arginine. In this paper we review the multiple functions of arginlne, including its role in the L-arginine-nitric oxide pathway,cellular regeneration, immune function, protein synthesis and protein breakdown. We then consider some in vivo aspects of the physiology of arginine metabolism, which varies greatly among eukaryotes, with particular reference to humans. Against this background, studies of arginine in the nutrition of humans under various pathophysiological conditions are reviewed briefly. Finally, a new, updated concept for the metabolic basis for the 'conditional essentiality' of arginine is proposed展开更多
Two coaxial vertical cylinders-one is a riding hollow cylinder and the other a solid cylinder of greater radius at some distance above an impermeable horizontal bottom,were considered.This problem of diffraction by th...Two coaxial vertical cylinders-one is a riding hollow cylinder and the other a solid cylinder of greater radius at some distance above an impermeable horizontal bottom,were considered.This problem of diffraction by these two cylinders,which were considered as idealization of a buoy and a circular plate,can be considered as a wave energy device.The wave energy that is created and transferred by this device can be appropriately used in many applications in lieu of conventional energy.Method of separation of variables was used to obtain the analytical expressions for the diffracted potentials in four clearly identified regions.By applying the appropriate matching conditions along the three virtual boundaries between the regions,a system of linear equations was obtained,which was solved for the unknown coefficients.The potentials allowed us to obtain the exciting forces acting on both cylinders.Sets of exciting forces were obtained for different radii of the cylinders and for different gaps between the cylinders.It was observed that changes in radius and the gap had significant effect on the forces.It was found that mostly the exciting forces were significant only at lower frequencies.The exciting forces almost vanished at higher frequencies.The problem was also investigated for the base case of no plate arrangement,i.e.,the case having only the floating cylinder tethered to the sea-bed.Comparison of forces for both arrangements was carried out.In order to take care of the radiation of the cylinders due to surge motion,the corresponding added mass and the damping coefficients for both cylinders were also computed.All the results were depicted graphically and compared with available results.展开更多
A hydraulic exciting system with a wave exciter has been constructed in order to study the hydraulic vibra- tion law. The system consists of an oil source, wave-exciter and oil cylinder, and is controlled by a wave-ex...A hydraulic exciting system with a wave exciter has been constructed in order to study the hydraulic vibra- tion law. The system consists of an oil source, wave-exciter and oil cylinder, and is controlled by a wave-exciter. The working principle of the hydraulic exciting system and wave exciter has been analyzed, and its excitation process has been illustrated. The law of every pipe＇s pressure fluctuation of the system is obtained by experiment. The theo- retical analysis and experimental data prove that the pipeline pressure periodically changes and the pipeline pressure fluctuation frequency is independently controlled by the excitation frequency of the wave-exciter. Every pipelinc＇s pressure wave is produced by system flow fluctuation and water hammer coupling. The pressure fluctuation rules of the system provide a theoretical basis for the study of the associated liberation system.展开更多
In this paper, the homology of four radio bursts occuring on August 28, 1989 are discussed in time domain, in frequency domain and in their exciting functions.From the discussions, it may be possible that if two radio...In this paper, the homology of four radio bursts occuring on August 28, 1989 are discussed in time domain, in frequency domain and in their exciting functions.From the discussions, it may be possible that if two radio bursts are homologus, then their ratios of the duration time for rising phases, decaying phases and total bursts are similar in time domain, so do their exciting functions. Therefore they resemble each other in their Fourier apectra.展开更多
Ground-borne vibrations caused by vibration sources such as road traffic and construction exhibit complicated properties during propagation from the vibration source to the inside of a building. In the present paper, ...Ground-borne vibrations caused by vibration sources such as road traffic and construction exhibit complicated properties during propagation from the vibration source to the inside of a building. In the present paper, a numerical analysis technique for the system of vibration source and propagation path of ground vibration is developed in order to systematically determine the propagation properties of the vibration as part of developing a predictive technique for exposure evaluations by vibrations in three directions at receiving points of vibration in the human body. First, the exciting forces in three directions for input into the numerical computation are inversely-estimated by using the measured acceleration rec- ords of the measurement points, which are near the vibration source. The thin-layered element method is used for numerical computation of the ground vibration. Then, the calculation results for the ground vibration obtained by using the estimated exciting force are compared with the measured results, and the influence of the stratified structure of the ground on the exciting force and the propagation properties of the ground vibration are studied. From these results, in a prediction of the ground vibration in three directions, it is emphasized that it is necessary to consider the influence of horizontal exciting force, although attention has been paid to only the vertical exciting force for simulating ground vibration.展开更多
The uniform speed of the magnetic field is directly influenced by the quality of the exciting signals for time grating sensors,which determines the measurement accuracy of the time grating sensors.Therefore,the highqu...The uniform speed of the magnetic field is directly influenced by the quality of the exciting signals for time grating sensors,which determines the measurement accuracy of the time grating sensors.Therefore,the highquality exciting signals are of great significance to the measurement accuracy improvement of the time grating sensors.Regarding the high requirements on quadrature exciting signal sources for linear time grating sensors,a direct digital frequency synthesis technique is employed to design the quadrature exciting signals.In addition,an active band-pass filter is designed to eliminate the interference and improve the signal quality.The frequency and the phase of the proposed quadrature exciting signal sources can easily adjust,and the precision of the signals is high.The exciting signal sources and the signal processing circuits are integrated into one FPGA chip,which greatly decrease the size of the circuit board and improve the reliability.Simulation and experiment results prove the validity.This design method can be widely applied into many applications which require high quality of exciting signal sources.展开更多
One Wednesday morning 1 eleven o'clock, Tom was walking down Main Street. 2 he heard the sound of gun (手枪), he 3 the sound must come from the bank. He ran to the bank and 4 a man coming out of the bank.
One Wednesday morning 1 eleven o'clock, Tom was walking down Main Street. 2 he heard the sound of gun (手枪), he 3 the sound must come from the bank.He ran to the bank and 4 a man coming out of the bank. The man w...One Wednesday morning 1 eleven o'clock, Tom was walking down Main Street. 2 he heard the sound of gun (手枪), he 3 the sound must come from the bank.He ran to the bank and 4 a man coming out of the bank. The man was 5 and fat 6 red hair.What's more,he carried a bag and a gun in his hand. Before Tom could do _7_,he had run into the street and disappeared(消失)among people.展开更多
The vibration response formulas of the mechanical system under the affect of thevari-frequency exciting force are deduced. It is proved by the theoretical analysis and experimentalresults that the vibration response a...The vibration response formulas of the mechanical system under the affect of thevari-frequency exciting force are deduced. It is proved by the theoretical analysis and experimentalresults that the vibration response amplitude of the mechanical system under the affect of thevari-frequency exciting force is far smaller than that under the affect of the constant frequency exciting force on condition that the exciting force amplitudes are just the same;while the vari-fre-quency rate a increases to 5 Hz per second the vibration amplitude will decrease to 10% only as lowas that under the affect of the constant frequency exciting force. All these conclusions will be of significance for revealing the mechanism of suppressing chatter in van-speed cutting and analyzing theexperimental results of sine-wave scanning exciting test.展开更多
Chaoyang Theatre is famous for presenting acrobatic shows in Beijing. For Sichuan Suining Acrobatic Troupe, the performance here in the theatre is as usually-fully seated and most audiences are tourists from abroad. H...Chaoyang Theatre is famous for presenting acrobatic shows in Beijing. For Sichuan Suining Acrobatic Troupe, the performance here in the theatre is as usually-fully seated and most audiences are tourists from abroad. However,展开更多
"Teacher, what are we going to do next class?" This is an exciting question which I often hear from my students. As an English conversation teacher, I can make the learning of English either a dull and borin..."Teacher, what are we going to do next class?" This is an exciting question which I often hear from my students. As an English conversation teacher, I can make the learning of English either a dull and boring duty, or an exciting adventure. It is very important that I make my students hate missing my class, and keep them guessing just what will happen the next time! Let us consider some important ways that any teacher can help his other students want to do展开更多
Vibration cementing is a new technique that can significantly improve the bond strength of cementing interface.To popularize this technique,it is necessary to solve the key problem of how to make cementing string gene...Vibration cementing is a new technique that can significantly improve the bond strength of cementing interface.To popularize this technique,it is necessary to solve the key problem of how to make cementing string generate downhole radial vibration in the WOC stage.For this purpose,an electric vibrator was developed.With this vibrator,electric energy is converted into mechanical energy by means of a high-temperature motor vibration unit.The motor vibration unit rotates the eccentric block through an output shaft to generate an exciting source,which produces an axial-rotating exciting force at the bottom of the casing string.Then,the vibration characteristics of vertical well casing string under the exciting force were analyzed by using the principal coordinate analysis method,and the response model of casing string to an electric vibrator was developed.Finally,the effects of casing string length,exciting force and vibration frequency on the vibration amplitude at the lowermost of the casing string were analyzed based on a certain casing program.It is indicated that the casing string length and the square of vibration frequency are inversely proportional to the vibration amplitude at the lowermost of the casing string,and the exciting force is proportional to the vibration amplitude at the lowermost of the casing string.These research results provide a theoretical support for the application of vibration cementing technology to the cementing sites with different requirements on well depth and amplitude.展开更多
Due to the dynamical character of electromagnetic exciter and the coupling between structure and exciter(s),the actual output force acting on the structure is usually not equal to the exact value that is supposed to b...Due to the dynamical character of electromagnetic exciter and the coupling between structure and exciter(s),the actual output force acting on the structure is usually not equal to the exact value that is supposed to be,especially when multi-exciters are used as actuators to precisely actuate large flexible structure.It is necessary to consider these effects to ensure the force generated by each exciter is the same as required.In this paper,a robust control method is proposed for the multi-input and multi-output(MIMO)structural vibration control system to trace the target actuating force of each exciter.A special signal is designed and put into the coupled mul-ti-exciter-structure system,and the input and output signals of the system are used to build a dynamic model involving both the dynamical characters of the exciters and the structure using the subspace identification method.Considering the uncertainty factors of the multi-exciter/structure system,an H-infinity robust controller is designed to decouple the coupling between structure and exciters based on the identified system model.A MIMO vibration control system combined with a flexible plate and three electromagnetic exciters is adopted to demonstrate the proposed method,both numerical simulation and model experiments showing that the output force of each exciter can trace its target force accurately within the requested frequency band.展开更多
Ⅰ. INTRODUCTION By using degenerate four-wave mixing (DFWM) method, the third-order nonlinear optical susceptibility of transparent media can be conventionally measured. Nonlinear properties of media in ground state ...Ⅰ. INTRODUCTION By using degenerate four-wave mixing (DFWM) method, the third-order nonlinear optical susceptibility of transparent media can be conventionally measured. Nonlinear properties of media in ground state are well known, but those in exciting state are less studied. When a medium absorbs incident radiation, a part of population can be excited into high exciting state. In DFWM this resonant enhancement effect can be used to increase the third-展开更多
The living world remains a mystery with many exciting discoveries awaiting scientists. My interest in observing living phenomena dates back to my childhood. I was lucky enough to enter Peking University to study biolo...The living world remains a mystery with many exciting discoveries awaiting scientists. My interest in observing living phenomena dates back to my childhood. I was lucky enough to enter Peking University to study biology and have been on a journey of life science research ever since. Along the way, I have made stops at many scientific journals to report my discoveries. When I was a postgraduate student.展开更多
Epilepsy is a leading cause of disability and mortality worldwide. However, despite the availability of more than 20 antiseizure medications, more than one-third of patients continue to experience seizures. Given the ...Epilepsy is a leading cause of disability and mortality worldwide. However, despite the availability of more than 20 antiseizure medications, more than one-third of patients continue to experience seizures. Given the urgent need to explore new treatment strategies for epilepsy, recent research has highlighted the potential of targeting gliosis, metabolic disturbances, and neural circuit abnormalities as therapeutic strategies. Astrocytes, the largest group of nonneuronal cells in the central nervous system, play several crucial roles in maintaining ionic and energy metabolic homeostasis in neurons, regulating neurotransmitter levels, and modulating synaptic plasticity. This article briefly reviews the critical role of astrocytes in maintaining balance within the central nervous system. Building on previous research, we discuss how astrocyte dysfunction contributes to the onset and progression of epilepsy through four key aspects: the imbalance between excitatory and inhibitory neuronal signaling, dysregulation of metabolic homeostasis in the neuronal microenvironment, neuroinflammation, and the formation of abnormal neural circuits. We summarize relevant basic research conducted over the past 5 years that has focused on modulating astrocytes as a therapeutic approach for epilepsy. We categorize the therapeutic targets proposed by these studies into four areas: restoration of the excitation–inhibition balance, reestablishment of metabolic homeostasis, modulation of immune and inflammatory responses, and reconstruction of abnormal neural circuits. These targets correspond to the pathophysiological mechanisms by which astrocytes contribute to epilepsy. Additionally, we need to consider the potential challenges and limitations of translating these identified therapeutic targets into clinical treatments. These limitations arise from interspecies differences between humans and animal models, as well as the complex comorbidities associated with epilepsy in humans. We also highlight valuable future research directions worth exploring in the treatment of epilepsy and the regulation of astrocytes, such as gene therapy and imaging strategies. The findings presented in this review may help open new therapeutic avenues for patients with drugresistant epilepsy and for those suffering from other central nervous system disorders associated with astrocytic dysfunction.展开更多
In order to realize the comprehensive utilization of industrial solid waste rice husk ash and heavy metal cadmium contaminated soil,rice husk ash-based geopolymer prepared by alkaline activator was used to modify cadm...In order to realize the comprehensive utilization of industrial solid waste rice husk ash and heavy metal cadmium contaminated soil,rice husk ash-based geopolymer prepared by alkaline activator was used to modify cadmium contaminated soil.The main physical and chemical properties of rice husk ash were clarified by SEM,XRF and X-ray diffraction.The unconfined compressive strength test and toxicity leaching test were carried out on the modified soil.Combined with FTIR and TG micro-level,the solidification mechanism of rice husk ash-based geopolymer solidified cadmium contaminated soil was discussed.The results show that the strength of geopolymer modified soil is significantly higher than that of plain soil,and the unconfined compressive strength at 7 d age is 4.2 times that of plain soil.The strength of modified soil with different dosage of geopolymer at 28 d age is about 36% to 40% higher than that of modified soil at 7 d age.Geopolymer has a significant effect on the leaching of heavy metals in contaminated soil.When the cadmium content is 100 mg/kg,it meets the standard limit.In the process of complex depolymerization-condensation reaction,on the one hand,geopolymers are cemented and agglomerated to form a complex spatial structure,which affects the macro and micro characteristics of soil.On the other hand,it has significant adsorption,precipitation and replacement effects on heavy metal ions in soil,showing good strength and low heavy metal leaching toxicity.展开更多
The concept of the brain cognitive reserve is derived from the well-acknowledged notion that the degree of brain damage does not always match the severity of clinical symptoms and neurological/cognitive outcomes.It ha...The concept of the brain cognitive reserve is derived from the well-acknowledged notion that the degree of brain damage does not always match the severity of clinical symptoms and neurological/cognitive outcomes.It has been suggested that the size of the brain(brain reserve) and the extent of neural connections acquired through life(neural reserve) set a threshold beyond which noticeable impairments occur.In contrast,cognitive reserve refers to the brain's ability to adapt and reo rganize stru cturally and functionally to resist damage and maintain function,including neural reserve and brain maintenance,resilience,and compensation(Verkhratsky and Zorec,2024).展开更多
For many decades,Alzheimer's disease research has primarily focused on impairments within cortical and hippocampal regions,which are thought to be related to cognitive dysfunctions such as memory and language defi...For many decades,Alzheimer's disease research has primarily focused on impairments within cortical and hippocampal regions,which are thought to be related to cognitive dysfunctions such as memory and language deficits.The exact cause of Alzheimer's disease is still under debate,making it challenging to establish an effective therapy or early diagnosis.It is widely accepted that the accumulation of amyloid-beta peptide in the brain parenchyma leads to synaptic dysfunction,a critical step in Alzheimer's disease development.The traditional amyloid cascade model is initiated by accumulating extracellular amyloid-beta in brain areas essential for memory and language.However,while it is possible to reduce the presence of amyloid-beta plaques in the brain with newer immunotherapies,cognitive symptoms do not necessarily improve.Interestingly,recent studies support the notion that early alterations in subcortical brain regions also contribute to brain damage and precognitive decline in Alzheimer's disease.A body of recent evidence suggests that early Alzheimer's disease is associated with alterations(e.g.,motivation,anxiety,and motor impairment)in subcortical areas,such as the striatum and amygdala,in both human and animal models.Also,recent data indicate that intracellular amyloid-beta appears early in subcortical regions such as the nucleus accumbens,locus coeruleus,and raphe nucleus,even without extracellular amyloid plaques.The reported effects are mainly excitatory,increasing glutamatergic transmission and neuronal excitability.In agreement,data in Alzheimer's disease patients and animal models show an increase in neuronal synchronization that leads to electroencephalogram disturbances and epilepsy.The data indicate that early subcortical brain dysfunctions might be associated with non-cognitive symptoms such as anxiety,irritability,and motivation deficits,which precede memory loss and language alterations.Overall,the evidence reviewed suggests that subcortical brain regions could explain early dysfunctions and perhaps be targets for therapies to slow disease progression.Future research should focus on these non-traditional brain regions to reveal early pathological alterations and underlying mechanisms to advance our understanding of Alzheimer's disease beyond the traditionally studied hippocampal and cortical circuits.展开更多
文摘Arginine (2-amino-5-guanidino pentanoic acid) was shown in 1895 by Hedin to be present in the proteins of horn. Metabolic nitrogen balance studies, conducted in 1957 by Rose in human adults and in 1959 by Snyderman and coworkers in young infants, revealed that a dietary source of this amino acid was not an obligatory requirement for growth and maintenance of nitrogen homeostasis in healthy individuals. Hence, It was initially classified as a non-essential (dispensable) amino acid and, perhaps, for reasons of this classification arginine did not receivc the earlier atteniion it now deserves, in relation to an understanding of the nutritional biochemistry and physiology of its metabolism in humans subjects. However, there is currently a considerable interest in the cellular and tissue functions, as well as clinical, therapeutic significance, of arginine. In this paper we review the multiple functions of arginlne, including its role in the L-arginine-nitric oxide pathway,cellular regeneration, immune function, protein synthesis and protein breakdown. We then consider some in vivo aspects of the physiology of arginine metabolism, which varies greatly among eukaryotes, with particular reference to humans. Against this background, studies of arginine in the nutrition of humans under various pathophysiological conditions are reviewed briefly. Finally, a new, updated concept for the metabolic basis for the 'conditional essentiality' of arginine is proposed
文摘Two coaxial vertical cylinders-one is a riding hollow cylinder and the other a solid cylinder of greater radius at some distance above an impermeable horizontal bottom,were considered.This problem of diffraction by these two cylinders,which were considered as idealization of a buoy and a circular plate,can be considered as a wave energy device.The wave energy that is created and transferred by this device can be appropriately used in many applications in lieu of conventional energy.Method of separation of variables was used to obtain the analytical expressions for the diffracted potentials in four clearly identified regions.By applying the appropriate matching conditions along the three virtual boundaries between the regions,a system of linear equations was obtained,which was solved for the unknown coefficients.The potentials allowed us to obtain the exciting forces acting on both cylinders.Sets of exciting forces were obtained for different radii of the cylinders and for different gaps between the cylinders.It was observed that changes in radius and the gap had significant effect on the forces.It was found that mostly the exciting forces were significant only at lower frequencies.The exciting forces almost vanished at higher frequencies.The problem was also investigated for the base case of no plate arrangement,i.e.,the case having only the floating cylinder tethered to the sea-bed.Comparison of forces for both arrangements was carried out.In order to take care of the radiation of the cylinders due to surge motion,the corresponding added mass and the damping coefficients for both cylinders were also computed.All the results were depicted graphically and compared with available results.
基金supported by National Natural Science Foundation of China under Grant No.50775154Shanxi Province Science Foundation of China under Grant No.2011011026-2
文摘A hydraulic exciting system with a wave exciter has been constructed in order to study the hydraulic vibra- tion law. The system consists of an oil source, wave-exciter and oil cylinder, and is controlled by a wave-exciter. The working principle of the hydraulic exciting system and wave exciter has been analyzed, and its excitation process has been illustrated. The law of every pipe＇s pressure fluctuation of the system is obtained by experiment. The theo- retical analysis and experimental data prove that the pipeline pressure periodically changes and the pipeline pressure fluctuation frequency is independently controlled by the excitation frequency of the wave-exciter. Every pipelinc＇s pressure wave is produced by system flow fluctuation and water hammer coupling. The pressure fluctuation rules of the system provide a theoretical basis for the study of the associated liberation system.
文摘In this paper, the homology of four radio bursts occuring on August 28, 1989 are discussed in time domain, in frequency domain and in their exciting functions.From the discussions, it may be possible that if two radio bursts are homologus, then their ratios of the duration time for rising phases, decaying phases and total bursts are similar in time domain, so do their exciting functions. Therefore they resemble each other in their Fourier apectra.
基金supported in part by the Minis-try of the Environment of Japan
文摘Ground-borne vibrations caused by vibration sources such as road traffic and construction exhibit complicated properties during propagation from the vibration source to the inside of a building. In the present paper, a numerical analysis technique for the system of vibration source and propagation path of ground vibration is developed in order to systematically determine the propagation properties of the vibration as part of developing a predictive technique for exposure evaluations by vibrations in three directions at receiving points of vibration in the human body. First, the exciting forces in three directions for input into the numerical computation are inversely-estimated by using the measured acceleration rec- ords of the measurement points, which are near the vibration source. The thin-layered element method is used for numerical computation of the ground vibration. Then, the calculation results for the ground vibration obtained by using the estimated exciting force are compared with the measured results, and the influence of the stratified structure of the ground on the exciting force and the propagation properties of the ground vibration are studied. From these results, in a prediction of the ground vibration in three directions, it is emphasized that it is necessary to consider the influence of horizontal exciting force, although attention has been paid to only the vertical exciting force for simulating ground vibration.
基金funded by National Natural Science Foundation of China(No.51775075)Natural Science Foundation of Chongqing(No.cstc2016jcyj A0505)
文摘The uniform speed of the magnetic field is directly influenced by the quality of the exciting signals for time grating sensors,which determines the measurement accuracy of the time grating sensors.Therefore,the highquality exciting signals are of great significance to the measurement accuracy improvement of the time grating sensors.Regarding the high requirements on quadrature exciting signal sources for linear time grating sensors,a direct digital frequency synthesis technique is employed to design the quadrature exciting signals.In addition,an active band-pass filter is designed to eliminate the interference and improve the signal quality.The frequency and the phase of the proposed quadrature exciting signal sources can easily adjust,and the precision of the signals is high.The exciting signal sources and the signal processing circuits are integrated into one FPGA chip,which greatly decrease the size of the circuit board and improve the reliability.Simulation and experiment results prove the validity.This design method can be widely applied into many applications which require high quality of exciting signal sources.
文摘One Wednesday morning 1 eleven o'clock, Tom was walking down Main Street. 2 he heard the sound of gun (手枪), he 3 the sound must come from the bank. He ran to the bank and 4 a man coming out of the bank.
文摘One Wednesday morning 1 eleven o'clock, Tom was walking down Main Street. 2 he heard the sound of gun (手枪), he 3 the sound must come from the bank.He ran to the bank and 4 a man coming out of the bank. The man was 5 and fat 6 red hair.What's more,he carried a bag and a gun in his hand. Before Tom could do _7_,he had run into the street and disappeared(消失)among people.
文摘The vibration response formulas of the mechanical system under the affect of thevari-frequency exciting force are deduced. It is proved by the theoretical analysis and experimentalresults that the vibration response amplitude of the mechanical system under the affect of thevari-frequency exciting force is far smaller than that under the affect of the constant frequency exciting force on condition that the exciting force amplitudes are just the same;while the vari-fre-quency rate a increases to 5 Hz per second the vibration amplitude will decrease to 10% only as lowas that under the affect of the constant frequency exciting force. All these conclusions will be of significance for revealing the mechanism of suppressing chatter in van-speed cutting and analyzing theexperimental results of sine-wave scanning exciting test.
文摘Chaoyang Theatre is famous for presenting acrobatic shows in Beijing. For Sichuan Suining Acrobatic Troupe, the performance here in the theatre is as usually-fully seated and most audiences are tourists from abroad. However,
文摘"Teacher, what are we going to do next class?" This is an exciting question which I often hear from my students. As an English conversation teacher, I can make the learning of English either a dull and boring duty, or an exciting adventure. It is very important that I make my students hate missing my class, and keep them guessing just what will happen the next time! Let us consider some important ways that any teacher can help his other students want to do
文摘Vibration cementing is a new technique that can significantly improve the bond strength of cementing interface.To popularize this technique,it is necessary to solve the key problem of how to make cementing string generate downhole radial vibration in the WOC stage.For this purpose,an electric vibrator was developed.With this vibrator,electric energy is converted into mechanical energy by means of a high-temperature motor vibration unit.The motor vibration unit rotates the eccentric block through an output shaft to generate an exciting source,which produces an axial-rotating exciting force at the bottom of the casing string.Then,the vibration characteristics of vertical well casing string under the exciting force were analyzed by using the principal coordinate analysis method,and the response model of casing string to an electric vibrator was developed.Finally,the effects of casing string length,exciting force and vibration frequency on the vibration amplitude at the lowermost of the casing string were analyzed based on a certain casing program.It is indicated that the casing string length and the square of vibration frequency are inversely proportional to the vibration amplitude at the lowermost of the casing string,and the exciting force is proportional to the vibration amplitude at the lowermost of the casing string.These research results provide a theoretical support for the application of vibration cementing technology to the cementing sites with different requirements on well depth and amplitude.
基金supported by the National Natural Science Foundation of China(Grant Nos.11072198,11102162)111 Project of China(Grant No.B07050)
文摘Due to the dynamical character of electromagnetic exciter and the coupling between structure and exciter(s),the actual output force acting on the structure is usually not equal to the exact value that is supposed to be,especially when multi-exciters are used as actuators to precisely actuate large flexible structure.It is necessary to consider these effects to ensure the force generated by each exciter is the same as required.In this paper,a robust control method is proposed for the multi-input and multi-output(MIMO)structural vibration control system to trace the target actuating force of each exciter.A special signal is designed and put into the coupled mul-ti-exciter-structure system,and the input and output signals of the system are used to build a dynamic model involving both the dynamical characters of the exciters and the structure using the subspace identification method.Considering the uncertainty factors of the multi-exciter/structure system,an H-infinity robust controller is designed to decouple the coupling between structure and exciters based on the identified system model.A MIMO vibration control system combined with a flexible plate and three electromagnetic exciters is adopted to demonstrate the proposed method,both numerical simulation and model experiments showing that the output force of each exciter can trace its target force accurately within the requested frequency band.
文摘Ⅰ. INTRODUCTION By using degenerate four-wave mixing (DFWM) method, the third-order nonlinear optical susceptibility of transparent media can be conventionally measured. Nonlinear properties of media in ground state are well known, but those in exciting state are less studied. When a medium absorbs incident radiation, a part of population can be excited into high exciting state. In DFWM this resonant enhancement effect can be used to increase the third-
文摘The living world remains a mystery with many exciting discoveries awaiting scientists. My interest in observing living phenomena dates back to my childhood. I was lucky enough to enter Peking University to study biology and have been on a journey of life science research ever since. Along the way, I have made stops at many scientific journals to report my discoveries. When I was a postgraduate student.
基金supported by the National Key Research and Development Program of China,No. 2023YFF0714200 (to CW)the National Natural Science Foundation of China,Nos. 82472038 and 82202224 (both to CW)+3 种基金the Shanghai Rising-Star Program,No. 23QA1407700 (to CW)the Construction Project of Shanghai Key Laboratory of Molecular Imaging,No. 18DZ2260400 (to CW)the National Science Foundation for Distinguished Young Scholars,No. 82025019 (to CL)the Greater Bay Area Institute of Precision Medicine (Guangzhou)(to CW)。
文摘Epilepsy is a leading cause of disability and mortality worldwide. However, despite the availability of more than 20 antiseizure medications, more than one-third of patients continue to experience seizures. Given the urgent need to explore new treatment strategies for epilepsy, recent research has highlighted the potential of targeting gliosis, metabolic disturbances, and neural circuit abnormalities as therapeutic strategies. Astrocytes, the largest group of nonneuronal cells in the central nervous system, play several crucial roles in maintaining ionic and energy metabolic homeostasis in neurons, regulating neurotransmitter levels, and modulating synaptic plasticity. This article briefly reviews the critical role of astrocytes in maintaining balance within the central nervous system. Building on previous research, we discuss how astrocyte dysfunction contributes to the onset and progression of epilepsy through four key aspects: the imbalance between excitatory and inhibitory neuronal signaling, dysregulation of metabolic homeostasis in the neuronal microenvironment, neuroinflammation, and the formation of abnormal neural circuits. We summarize relevant basic research conducted over the past 5 years that has focused on modulating astrocytes as a therapeutic approach for epilepsy. We categorize the therapeutic targets proposed by these studies into four areas: restoration of the excitation–inhibition balance, reestablishment of metabolic homeostasis, modulation of immune and inflammatory responses, and reconstruction of abnormal neural circuits. These targets correspond to the pathophysiological mechanisms by which astrocytes contribute to epilepsy. Additionally, we need to consider the potential challenges and limitations of translating these identified therapeutic targets into clinical treatments. These limitations arise from interspecies differences between humans and animal models, as well as the complex comorbidities associated with epilepsy in humans. We also highlight valuable future research directions worth exploring in the treatment of epilepsy and the regulation of astrocytes, such as gene therapy and imaging strategies. The findings presented in this review may help open new therapeutic avenues for patients with drugresistant epilepsy and for those suffering from other central nervous system disorders associated with astrocytic dysfunction.
基金Funded by Central Guiding Local Science and Technology Development Special Fund Project(No.ZYYD2023B02)Innovation and Entrepreneurship Training Program for College Students in Xinjiang Uygur Autonomous Region(No.S202410994015)+2 种基金China University of Mining and Technology Coal Fine Exploration and Intelligent Development National Key Laboratory Xinjiang Engineering College Joint Fund(No.SKLCRSM-XJIE24KF001)Basic Research Funds for Autonomous Region Universities(No.XJEDU2024P082)National Natural Science Foundation of China(No.41662017)。
文摘In order to realize the comprehensive utilization of industrial solid waste rice husk ash and heavy metal cadmium contaminated soil,rice husk ash-based geopolymer prepared by alkaline activator was used to modify cadmium contaminated soil.The main physical and chemical properties of rice husk ash were clarified by SEM,XRF and X-ray diffraction.The unconfined compressive strength test and toxicity leaching test were carried out on the modified soil.Combined with FTIR and TG micro-level,the solidification mechanism of rice husk ash-based geopolymer solidified cadmium contaminated soil was discussed.The results show that the strength of geopolymer modified soil is significantly higher than that of plain soil,and the unconfined compressive strength at 7 d age is 4.2 times that of plain soil.The strength of modified soil with different dosage of geopolymer at 28 d age is about 36% to 40% higher than that of modified soil at 7 d age.Geopolymer has a significant effect on the leaching of heavy metals in contaminated soil.When the cadmium content is 100 mg/kg,it meets the standard limit.In the process of complex depolymerization-condensation reaction,on the one hand,geopolymers are cemented and agglomerated to form a complex spatial structure,which affects the macro and micro characteristics of soil.On the other hand,it has significant adsorption,precipitation and replacement effects on heavy metal ions in soil,showing good strength and low heavy metal leaching toxicity.
文摘The concept of the brain cognitive reserve is derived from the well-acknowledged notion that the degree of brain damage does not always match the severity of clinical symptoms and neurological/cognitive outcomes.It has been suggested that the size of the brain(brain reserve) and the extent of neural connections acquired through life(neural reserve) set a threshold beyond which noticeable impairments occur.In contrast,cognitive reserve refers to the brain's ability to adapt and reo rganize stru cturally and functionally to resist damage and maintain function,including neural reserve and brain maintenance,resilience,and compensation(Verkhratsky and Zorec,2024).
文摘For many decades,Alzheimer's disease research has primarily focused on impairments within cortical and hippocampal regions,which are thought to be related to cognitive dysfunctions such as memory and language deficits.The exact cause of Alzheimer's disease is still under debate,making it challenging to establish an effective therapy or early diagnosis.It is widely accepted that the accumulation of amyloid-beta peptide in the brain parenchyma leads to synaptic dysfunction,a critical step in Alzheimer's disease development.The traditional amyloid cascade model is initiated by accumulating extracellular amyloid-beta in brain areas essential for memory and language.However,while it is possible to reduce the presence of amyloid-beta plaques in the brain with newer immunotherapies,cognitive symptoms do not necessarily improve.Interestingly,recent studies support the notion that early alterations in subcortical brain regions also contribute to brain damage and precognitive decline in Alzheimer's disease.A body of recent evidence suggests that early Alzheimer's disease is associated with alterations(e.g.,motivation,anxiety,and motor impairment)in subcortical areas,such as the striatum and amygdala,in both human and animal models.Also,recent data indicate that intracellular amyloid-beta appears early in subcortical regions such as the nucleus accumbens,locus coeruleus,and raphe nucleus,even without extracellular amyloid plaques.The reported effects are mainly excitatory,increasing glutamatergic transmission and neuronal excitability.In agreement,data in Alzheimer's disease patients and animal models show an increase in neuronal synchronization that leads to electroencephalogram disturbances and epilepsy.The data indicate that early subcortical brain dysfunctions might be associated with non-cognitive symptoms such as anxiety,irritability,and motivation deficits,which precede memory loss and language alterations.Overall,the evidence reviewed suggests that subcortical brain regions could explain early dysfunctions and perhaps be targets for therapies to slow disease progression.Future research should focus on these non-traditional brain regions to reveal early pathological alterations and underlying mechanisms to advance our understanding of Alzheimer's disease beyond the traditionally studied hippocampal and cortical circuits.
