针对星上微振动主动隔离/抑制的要求,以VCM(voice coil motor)作动器Stewart平台为控制装置,通过对其动力学模型解耦将控制转化为SISO(single input single output)问题;分析了Skyhook控制方法的隔振效果及其对抑振的局限性,在控制系统...针对星上微振动主动隔离/抑制的要求,以VCM(voice coil motor)作动器Stewart平台为控制装置,通过对其动力学模型解耦将控制转化为SISO(single input single output)问题;分析了Skyhook控制方法的隔振效果及其对抑振的局限性,在控制系统中加入了PFF(positive force feedback)控制回路,并引入加速度反馈环节以提高系统的鲁棒稳定性,形成一种振动主动隔离/抑制控制方法;利用Stewart平台的单杆开展了基础扫频激励和负载单频直接干扰共同作用下的S-DOF(single degree of freedom)微振动主动隔离/抑振控制实验,建立了Stewart平台刚/柔混合动力学模型并通过仿真研究了6-DOF振动主动隔离/抑振控制效果。实验和仿真结果表明:该方法可实现良好的振动主动隔离/抑制效果且性能稳定。展开更多
The factors influencing dormancy release in lily bulbs strongly affect commercialization success, but the mechanism of dormancy release is still unclear. Magnetic resonance imaging (MRI) can detect changes in morpholo...The factors influencing dormancy release in lily bulbs strongly affect commercialization success, but the mechanism of dormancy release is still unclear. Magnetic resonance imaging (MRI) can detect changes in morphology and water status in a living plant bulb and aid in investigating release factors. To evaluate whether MRI could be used to detect intra-bulb metabolic changes during the dormant period in Oriental Lilies (Lilium 'Sorbonne'), a series of MRI and sugar concentration measurements were performed weekly on bulbs stored for 11 weeks at 4°C. The image quality of intra-bulb structure obtained using T 1-weighted imaging was superior to that obtained using T 2 -weighted imaging and had a higher signal-to-noise ratio (0.97±0.01). Magnetization transfer ratio values for the bud and basal plate declined during the first eight weeks of cold storage (P>0.05), and were well correlated with concentration of soluble sugar in the bud (R 2 =0.95) and basal plate (R 2 =0.93). Thus, MRI can serve as a valuable tool for observation and analysis of dynamic morphological and metabolic changes in vivo during dormancy release. This information is potentially useful as a guide in the improvement of horticultural product quality.展开更多
Background:Patients with schizophrenia(SCZ)and major depressive disorder(MDD)share significant clinical overlap,although it remains unknown to what extent this overlap reflects shared neural profiles.To identify the s...Background:Patients with schizophrenia(SCZ)and major depressive disorder(MDD)share significant clinical overlap,although it remains unknown to what extent this overlap reflects shared neural profiles.To identify the shared and specific abnormalities in SCZ and MDD,we performed a whole-brain voxel-based meta-analysis using magnetization transfer imaging,a technique that characterizes the macromolecular structural integrity of brain tissue in terms of the magnetization transfer ratio(MTR).Methods:A systematic search based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was conducted in PubMed,EMBASE,International Scientific Index(ISI)Web of Science,and MEDLINE for relevant studies up to March 2022.Two researchers independently screened the articles.Rigorous scrutiny and data extraction were performed for the studies that met the inclusion criteria.Voxel-wise meta-analyses were conducted using anisotropic effect size-signed differential mapping with a unified template.Meta-regression was used to explore the potential effects of demographic and clinical characteristics.Results:A total of 15 studies with 17 datasets describing 365 SCZ patients,224 MDD patients,and 550 healthy controls(HCs)were identified.The conjunction analysis showed that both disorders shared higher MTR than HC in the left cerebellum(P=0.0006)and left fusiform gyrus(P=0.0004).Additionally,SCZ patients showed disorder-specific lower MTR in the anterior cingulate/paracingulate gyrus,right superior temporal gyrus,and right superior frontal gyrus,and higher MTR in the left thalamus,precuneus/cuneus,posterior cingulate gyrus,and paracentral lobule;and MDD patients showed higher MTR in the left middle occipital region.Meta-regression showed no statistical significance in either group.Conclusions:The results revealed a structural neural basis shared between SCZ and MDD patients,emphasizing the importance of shared neural substrates across psychopathology.Meanwhile,distinct disease-specific characteristics could have implic展开更多
AIM: To evaluate the spatial distribution of cerebral abnormalities in cirrhotic subjects with and without hepatic encephalopathy (HE) found with magnetization transfer imaging (MTI).METHODS: Nineteen cirrhotic patien...AIM: To evaluate the spatial distribution of cerebral abnormalities in cirrhotic subjects with and without hepatic encephalopathy (HE) found with magnetization transfer imaging (MTI).METHODS: Nineteen cirrhotic patients graded from neurologically normal to HE grade 2 and 18 healthy control subjects underwent magnetic resonance imaging. They gave institutional-review-board-approved written consent. Magnetization transfer ratio (MTR) maps were generated from MTI. We tested for significant differences compared to the control group using statistical non-parametric mapping (SnPM) for a voxelbased evaluation.RESULTS: The MTR of grey and white matter was lower in subjects with more severe HE. Changes were found in patients with cirrhosis without neurological defi cits in the basal ganglia and bilateral white matter. The loss in magnetization transfer increased in severity and spatial extent in patients with overt HE. Patients with HE grade 2 showed an MTR decrease in white and grey matter: the maximum loss of magnetization transfer effect was located in the basal ganglia [SnPM (pseudo-)t = 17.98, P = 0.0001].CONCLUSION: The distribution of MTR changes in HE points to an early involvement of basal ganglia and white matter in HE.展开更多
Purpose: Recently it was demonstrated that spin-locking (SL) effects can manifest as pseudo magnetization transfer (MT). To our best knowledge the MT models proposed so far cannot distinguish between saturation effect...Purpose: Recently it was demonstrated that spin-locking (SL) effects can manifest as pseudo magnetization transfer (MT). To our best knowledge the MT models proposed so far cannot distinguish between saturation effects caused by the MT preparation pulses and SL phenomena. Therefore a new MT model is proposed. Materials and Methods: A binary spin-bath model for magnetization transfer was extended in that sense that SL effects are considered. The new modified spin bath model was tested for a phantom with different agar concentrates (2%, 4%, 8%) and a MnCl2 (0.3 mM) solution. Results: The mean fitting error is 3.2 times lower for the modified model compared to the original model. Especially the parameter F for the fractional part of the bounded proton pool describes the situation for the MnCl2 (F = 0) better than the original model (F = 0.004). Conclusion: The proposed mathematical modifications of the binary spin-bath model considering SL seem to be a step in the right direction in that sense that the effects associated with SL are not interpreted as magnetization transfer.展开更多
Importance:The process of brain development in children with developmental delay is not well known.Amide proton transfer-weighted(APTw)imaging is a novel molecular magnetic resonance imaging(MRI)technique that can non...Importance:The process of brain development in children with developmental delay is not well known.Amide proton transfer-weighted(APTw)imaging is a novel molecular magnetic resonance imaging(MRI)technique that can noninvasively detect cytosolic endogenous mobile proteins and peptides involved in the myelination process,and may be useful for providing insights into brain development.Objective:To assess the contribution of amide proton transfer-weighted(APTw)imaging and magnetization transfer(MT)imaging to the evaluation of children with developmental delay(DD).Methods:Fifty-one patients with DD were recruited to this study.The patients were divided into two groups according to the state of myelination assessed on conventional magnetic resonance imaging(MRI).Thirty patients(10 girls,20 boys;age range:1-8 months;median age:4 months)in group A showed delayed myelination on MRI,while 21 patients(3 girls,18 boys;age range:12-36months;median age:25months)in group B showed normal myelination on MRI.Fifty-one age-and sex-matched children with normal developmental quotient(DQ)and normal MRI appearance were recruited as normal controls.Three-slice APTw/MT axial imaging was performed at the level of the centrum semiovale,the basal ganglia and the pons.Quantitative data of the MT ratio(MTR)and APTw were analyzed for multiple brain regions.Independent-samplet-tests were used to compare differences in APTw and MTR signals between the two DD groups and normal controls.Analysis of Covariance was conducted to correct the statistical results.The level of statistical significance was set toP<0.05.Results:For group A,the MTR values were lower in all regions(P=0.004-0.033)compared with the normal controls,while the APTw values were higher in the pons,middle cerebellar peduncle,corpus callosum,frontal white matter,occipital white matter and centrum semiovale(P=0.004-0.040).For Group B,the MTR values were slightly reduced,and the APTw values were slightly increased compared with the normal controls,but the differences were not statistic展开更多
The present paper deals with the study of three-dimensional boundary layer flow of biomagnetic Maxwell fluid over a plane horizontal surface stretched linearly along two mutually perpendicular directions. Basic princi...The present paper deals with the study of three-dimensional boundary layer flow of biomagnetic Maxwell fluid over a plane horizontal surface stretched linearly along two mutually perpendicular directions. Basic principles of magnetohydrodynamics (MHD) and ferro-hydrodynamics (FHD) have been employed. The effect of heat generation/absorption has been taken into consideration. The study is theoretical and is conducted by using a combination of approximate and numerical techniques. By using the method of similarity transformation, the governing nonlinear partial differential equations are converted into a set of coupled ordinary differential equations. In the sequel, a suitable numerical method has been developed to solve the coupled differential equations. The accuracy of the numerical method has been checked by comparing the numerical results with those of an earlier study reported in available literatures. Effects of various parameters involved in the study, viz. the magnetohydrodynamic and ferromagnetic parameters, Deborah number, stretching ratio and heat generation on the fluid flow profiles are investigated and the results have been presented graphically. Variations of the skin friction, heat transfer rate and relative wall pressure with change in hydrodynamic and ferromagnetic parameters have also been illustrated. It is found that due to the influence of the Kelvin force, the velocity component in xx-direction is greater than the corresponding one in the hydrodynamic case, but the opposite is true for the velocity component in the yy-direction. We also found that the temperature of the fluid for hydrodynamic flow is greater than that for MHD or FHD flow. It is even greater for BFD flows. The numerical results of the study reveal that the characteristics of blood flow are significantly affected by the presence of a magnetic field.展开更多
目的探讨3DSPGR磁化传递成像(MTI)在鉴别脑脓肿与坏死囊变性胶质瘤和脑转移瘤的应用价值。方法7例经手术病理(3例)或临床随访(4例)证实的脑脓肿、9例经手术病理证实的坏死囊变性胶质瘤和8例经临床证实的坏死囊变性转移瘤在治疗前接受了...目的探讨3DSPGR磁化传递成像(MTI)在鉴别脑脓肿与坏死囊变性胶质瘤和脑转移瘤的应用价值。方法7例经手术病理(3例)或临床随访(4例)证实的脑脓肿、9例经手术病理证实的坏死囊变性胶质瘤和8例经临床证实的坏死囊变性转移瘤在治疗前接受了常规MR和3DSPGR序列MTI检查,测量并计算病灶囊性区、实性区、同层面对侧正常脑白质区和脑脊液的平均磁化传递率(magnetization transfer ratio,MTR)。结果病灶囊性区、实性区、同层面对侧正常脑白质区和脑脊液的MTR分别依次为(0.0803±0.04)、(0.2259±0.03)、(0.3475±0.02)、(-0.1546±0.15);病灶囊性区与脑脊液的MTR之间存在显著性差异,t=8.911,P<0.001,病灶实性区与正常脑白质区的MTR之间存在显著性差异(t=-20.208,P<0.001);脑脓肿与坏死囊变性胶质瘤和脑转移瘤囊性区的MTR均存在显著性差异(F=37.390,P<0.001),其中脑脓肿与胶质瘤存以及脑脓肿与脑转移瘤有显著性差异(P<0.001),胶质瘤和脑转移瘤无明显差异(P=0.179);实性区域的MTR三者之间无差异。结论3DSPGR-MTI以及MTR的测量在鉴别脑脓肿与坏死囊变性胶质瘤和脑转移瘤有重要价值,可作为常规MRI序列的重要补充。展开更多
文摘针对星上微振动主动隔离/抑制的要求,以VCM(voice coil motor)作动器Stewart平台为控制装置,通过对其动力学模型解耦将控制转化为SISO(single input single output)问题;分析了Skyhook控制方法的隔振效果及其对抑振的局限性,在控制系统中加入了PFF(positive force feedback)控制回路,并引入加速度反馈环节以提高系统的鲁棒稳定性,形成一种振动主动隔离/抑制控制方法;利用Stewart平台的单杆开展了基础扫频激励和负载单频直接干扰共同作用下的S-DOF(single degree of freedom)微振动主动隔离/抑振控制实验,建立了Stewart平台刚/柔混合动力学模型并通过仿真研究了6-DOF振动主动隔离/抑振控制效果。实验和仿真结果表明:该方法可实现良好的振动主动隔离/抑制效果且性能稳定。
基金supported by the Special Fund for Agro-scientific Research in the Public Interest (Grant No. 200903020)
文摘The factors influencing dormancy release in lily bulbs strongly affect commercialization success, but the mechanism of dormancy release is still unclear. Magnetic resonance imaging (MRI) can detect changes in morphology and water status in a living plant bulb and aid in investigating release factors. To evaluate whether MRI could be used to detect intra-bulb metabolic changes during the dormant period in Oriental Lilies (Lilium 'Sorbonne'), a series of MRI and sugar concentration measurements were performed weekly on bulbs stored for 11 weeks at 4°C. The image quality of intra-bulb structure obtained using T 1-weighted imaging was superior to that obtained using T 2 -weighted imaging and had a higher signal-to-noise ratio (0.97±0.01). Magnetization transfer ratio values for the bud and basal plate declined during the first eight weeks of cold storage (P>0.05), and were well correlated with concentration of soluble sugar in the bud (R 2 =0.95) and basal plate (R 2 =0.93). Thus, MRI can serve as a valuable tool for observation and analysis of dynamic morphological and metabolic changes in vivo during dormancy release. This information is potentially useful as a guide in the improvement of horticultural product quality.
基金National Key R&D Program of China(No.2022YFC2009904/2022YFC2009900)National Natural Science Foundation(Nos.81621003,81820108018,82027808,and 82001800)Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC001)
文摘Background:Patients with schizophrenia(SCZ)and major depressive disorder(MDD)share significant clinical overlap,although it remains unknown to what extent this overlap reflects shared neural profiles.To identify the shared and specific abnormalities in SCZ and MDD,we performed a whole-brain voxel-based meta-analysis using magnetization transfer imaging,a technique that characterizes the macromolecular structural integrity of brain tissue in terms of the magnetization transfer ratio(MTR).Methods:A systematic search based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines was conducted in PubMed,EMBASE,International Scientific Index(ISI)Web of Science,and MEDLINE for relevant studies up to March 2022.Two researchers independently screened the articles.Rigorous scrutiny and data extraction were performed for the studies that met the inclusion criteria.Voxel-wise meta-analyses were conducted using anisotropic effect size-signed differential mapping with a unified template.Meta-regression was used to explore the potential effects of demographic and clinical characteristics.Results:A total of 15 studies with 17 datasets describing 365 SCZ patients,224 MDD patients,and 550 healthy controls(HCs)were identified.The conjunction analysis showed that both disorders shared higher MTR than HC in the left cerebellum(P=0.0006)and left fusiform gyrus(P=0.0004).Additionally,SCZ patients showed disorder-specific lower MTR in the anterior cingulate/paracingulate gyrus,right superior temporal gyrus,and right superior frontal gyrus,and higher MTR in the left thalamus,precuneus/cuneus,posterior cingulate gyrus,and paracentral lobule;and MDD patients showed higher MTR in the left middle occipital region.Meta-regression showed no statistical significance in either group.Conclusions:The results revealed a structural neural basis shared between SCZ and MDD patients,emphasizing the importance of shared neural substrates across psychopathology.Meanwhile,distinct disease-specific characteristics could have implic
文摘AIM: To evaluate the spatial distribution of cerebral abnormalities in cirrhotic subjects with and without hepatic encephalopathy (HE) found with magnetization transfer imaging (MTI).METHODS: Nineteen cirrhotic patients graded from neurologically normal to HE grade 2 and 18 healthy control subjects underwent magnetic resonance imaging. They gave institutional-review-board-approved written consent. Magnetization transfer ratio (MTR) maps were generated from MTI. We tested for significant differences compared to the control group using statistical non-parametric mapping (SnPM) for a voxelbased evaluation.RESULTS: The MTR of grey and white matter was lower in subjects with more severe HE. Changes were found in patients with cirrhosis without neurological defi cits in the basal ganglia and bilateral white matter. The loss in magnetization transfer increased in severity and spatial extent in patients with overt HE. Patients with HE grade 2 showed an MTR decrease in white and grey matter: the maximum loss of magnetization transfer effect was located in the basal ganglia [SnPM (pseudo-)t = 17.98, P = 0.0001].CONCLUSION: The distribution of MTR changes in HE points to an early involvement of basal ganglia and white matter in HE.
文摘Purpose: Recently it was demonstrated that spin-locking (SL) effects can manifest as pseudo magnetization transfer (MT). To our best knowledge the MT models proposed so far cannot distinguish between saturation effects caused by the MT preparation pulses and SL phenomena. Therefore a new MT model is proposed. Materials and Methods: A binary spin-bath model for magnetization transfer was extended in that sense that SL effects are considered. The new modified spin bath model was tested for a phantom with different agar concentrates (2%, 4%, 8%) and a MnCl2 (0.3 mM) solution. Results: The mean fitting error is 3.2 times lower for the modified model compared to the original model. Especially the parameter F for the fractional part of the bounded proton pool describes the situation for the MnCl2 (F = 0) better than the original model (F = 0.004). Conclusion: The proposed mathematical modifications of the binary spin-bath model considering SL seem to be a step in the right direction in that sense that the effects associated with SL are not interpreted as magnetization transfer.
文摘Importance:The process of brain development in children with developmental delay is not well known.Amide proton transfer-weighted(APTw)imaging is a novel molecular magnetic resonance imaging(MRI)technique that can noninvasively detect cytosolic endogenous mobile proteins and peptides involved in the myelination process,and may be useful for providing insights into brain development.Objective:To assess the contribution of amide proton transfer-weighted(APTw)imaging and magnetization transfer(MT)imaging to the evaluation of children with developmental delay(DD).Methods:Fifty-one patients with DD were recruited to this study.The patients were divided into two groups according to the state of myelination assessed on conventional magnetic resonance imaging(MRI).Thirty patients(10 girls,20 boys;age range:1-8 months;median age:4 months)in group A showed delayed myelination on MRI,while 21 patients(3 girls,18 boys;age range:12-36months;median age:25months)in group B showed normal myelination on MRI.Fifty-one age-and sex-matched children with normal developmental quotient(DQ)and normal MRI appearance were recruited as normal controls.Three-slice APTw/MT axial imaging was performed at the level of the centrum semiovale,the basal ganglia and the pons.Quantitative data of the MT ratio(MTR)and APTw were analyzed for multiple brain regions.Independent-samplet-tests were used to compare differences in APTw and MTR signals between the two DD groups and normal controls.Analysis of Covariance was conducted to correct the statistical results.The level of statistical significance was set toP<0.05.Results:For group A,the MTR values were lower in all regions(P=0.004-0.033)compared with the normal controls,while the APTw values were higher in the pons,middle cerebellar peduncle,corpus callosum,frontal white matter,occipital white matter and centrum semiovale(P=0.004-0.040).For Group B,the MTR values were slightly reduced,and the APTw values were slightly increased compared with the normal controls,but the differences were not statistic
文摘The present paper deals with the study of three-dimensional boundary layer flow of biomagnetic Maxwell fluid over a plane horizontal surface stretched linearly along two mutually perpendicular directions. Basic principles of magnetohydrodynamics (MHD) and ferro-hydrodynamics (FHD) have been employed. The effect of heat generation/absorption has been taken into consideration. The study is theoretical and is conducted by using a combination of approximate and numerical techniques. By using the method of similarity transformation, the governing nonlinear partial differential equations are converted into a set of coupled ordinary differential equations. In the sequel, a suitable numerical method has been developed to solve the coupled differential equations. The accuracy of the numerical method has been checked by comparing the numerical results with those of an earlier study reported in available literatures. Effects of various parameters involved in the study, viz. the magnetohydrodynamic and ferromagnetic parameters, Deborah number, stretching ratio and heat generation on the fluid flow profiles are investigated and the results have been presented graphically. Variations of the skin friction, heat transfer rate and relative wall pressure with change in hydrodynamic and ferromagnetic parameters have also been illustrated. It is found that due to the influence of the Kelvin force, the velocity component in xx-direction is greater than the corresponding one in the hydrodynamic case, but the opposite is true for the velocity component in the yy-direction. We also found that the temperature of the fluid for hydrodynamic flow is greater than that for MHD or FHD flow. It is even greater for BFD flows. The numerical results of the study reveal that the characteristics of blood flow are significantly affected by the presence of a magnetic field.
文摘目的探讨3DSPGR磁化传递成像(MTI)在鉴别脑脓肿与坏死囊变性胶质瘤和脑转移瘤的应用价值。方法7例经手术病理(3例)或临床随访(4例)证实的脑脓肿、9例经手术病理证实的坏死囊变性胶质瘤和8例经临床证实的坏死囊变性转移瘤在治疗前接受了常规MR和3DSPGR序列MTI检查,测量并计算病灶囊性区、实性区、同层面对侧正常脑白质区和脑脊液的平均磁化传递率(magnetization transfer ratio,MTR)。结果病灶囊性区、实性区、同层面对侧正常脑白质区和脑脊液的MTR分别依次为(0.0803±0.04)、(0.2259±0.03)、(0.3475±0.02)、(-0.1546±0.15);病灶囊性区与脑脊液的MTR之间存在显著性差异,t=8.911,P<0.001,病灶实性区与正常脑白质区的MTR之间存在显著性差异(t=-20.208,P<0.001);脑脓肿与坏死囊变性胶质瘤和脑转移瘤囊性区的MTR均存在显著性差异(F=37.390,P<0.001),其中脑脓肿与胶质瘤存以及脑脓肿与脑转移瘤有显著性差异(P<0.001),胶质瘤和脑转移瘤无明显差异(P=0.179);实性区域的MTR三者之间无差异。结论3DSPGR-MTI以及MTR的测量在鉴别脑脓肿与坏死囊变性胶质瘤和脑转移瘤有重要价值,可作为常规MRI序列的重要补充。
