3D MERGE与3D SPACE STIR序列在腰椎间盘突出症检查中的应用比较

目的:对比三维多回波恢复梯度回波(3D MERGE)、三维可变反转角快速自旋回波(3D SPACE STIR)序列在腰椎间盘突出症(LDH)检查中的应用效果。方法:选择2020年1月~2022年11月收治的135例LDH患者,回顾性分析患者临床和磁共振成像(MRI)资料,所有患者均接受常规MRI扫描及3D MERGE、3D SPACE STIR序列扫描,对比3D MERGE、3D SPACE STIR序列测量神经根直径的一致性,评价两种序列的图像质量参数[信噪比(SNR)、对比噪声比(CNR)]、图像清晰度评分。结果:3D MERGE和3D SPACE STIR序列测量的L3~S1神经根直径比较差异无统计学意义(P>0.05),且两组序列测量的L3、L4、L5和S1直径均显示出较高相关性(r=0.957,0.986,0.975,0.972,P<0.05);3D MERGE序列的SNR及CNR均高于3D SPACE STIR序列,神经根显示分级、图像清晰度评分优于3D SPACE STIR序列,差异有统计学意义(P<0.05)。结论:3D MERGE、3D SPACE STIR序列在LDH神经根直径测量中具有极高一致性,3D MERGE序列较3D SPACE STIR序列能够更清晰显示神经跟的解剖形态,图像质量更好。

Effects of Root-Growing Space on Its Absorbing Characteristics

Influences of root-growing space of maize upon root physiological characteristics, nutrient uptake and crop yields were studied under conditions with and without supply of water and N. Results showed that limitation of the root-growing space greatly affected root growth, decreased total root-absorbing area and TTC-reductive amounts. However, it obviously increased the root active-absorbing area, specific absorbing area(absorbing area per gram root weight)and specific active-absorbing area(actively absorbing area per gram root weight)in addition to promoting the TTC-reductive intensity. This clearly showed that plants were not passively tolerant to stress, but actively regulated their physiological metabolic processes, and strengthened their absorbing ability to increase water and nutrient uptake so that root injury by the environmental stress could be reduced. Supply of water and N stimulated root growth, increased root-absorbing area and activity. promoted nutrient uptake, and therefore increased crop yield and decreased the detrimental effects resulting from the limitation of roots-growing space.

Root phosphatase activity is a competitive trait affiliated with the conservation gradient in root economic space

Background:The diversity of resource acquisition strategies of plant roots determines the species coexistence patterns to a certain extent.However,few root physiological traits have been investigated,such as root phosphatase activity(PA)that affects plant phosphorus(P)uptake.Methods:Root PA and classical root functional traits were investigated for 21 coexisting species in a deciduous broad-leaved forest in warm temperate-subtropical transition zone,China.We analyzed the root order variation of absorptive fine root PA,clarified the attribution of root PA in root economic space(RES)and the different P acquisition strategies of co-occurring species based on the multidimensional RES theory,and determined the dominant factors affecting interspecific variation in root PA.Results:There was no distinct pattern of PA variation with root order in the first three root orders of absorptive fine roots,and root PA was constrained by phylogeny.Root PA is a competitive trait affiliated with the conservation gradient in RES.The tight linkages among root PA,mycorrhizal colonization,diameter,specific root length,and nitrogen concentration suggested trade-offs among P acquisition strategies of co-occurring species,i.e.species with long and fine roots acquire inorganic P by actively exploring the soil and secreting phosphatase to mineralize and hydrolyze organic P,while species with short and thick roots obtain P mainly by investing C in mycorrhizal partners.Conclusions:Collectively,our study provides an insight into the forest species coexistence in climatic transition zones,i.e.species coexistence mechanisms based on diverse phosphorus acquisition strategies.

Genetic analysis of the human hair roots as a tool for spaceflight experiments

The use of hair roots as experimental samples has been a research focus for understanding the effects of spaceflight on astronauts, because it has many advantages, one of which is the fact that hair matrix cells actively divide in a hair follicle and sensitively reflect the physical conditions of the human body. In 2009, a research program focusing on the analysis of astronauts’ hairs was initiated to examine the effects of long-term spaceflight on the gene expression and mineral metabolism in the human body. Since the number of samples per astronaut is limited to 5 strands of hairs at each sampling point, due to the ethical viewpoint of astronauts or limited resources in space, it is important to develop an effective method for the molecular analysis of small amounts of hair roots. In this study, mRNA successfully extracted from 1, 5, and 10 hair follicles was amplified and subjected to the DNA microarray analysis to compare the gene expression within subjects. The results indicated that (1) it was possible to perform the genetic analysis on hair samples stored at -80℃, even without a fixation buffer and (2) the newly modified method of mRNA extraction and analysis was effective in detecting differential gene expression in samples containing only 5 hairs. In conclusion, RNA was efficiently extracted from 5 hair roots, which is the same number of hair roots used in the space experiment;therefore, this method can be applied to genetically analyze astronauts’ hair samples.

APPROXIMATE SOLUTION OF A p-th ROOT FUNCTIONAL EQUATION IN NON-ARCHIMEDEAN (2,β)-BANACH SPACES

In this paper, using the Brzdek's fixed point theorem [9,Theorem 1] in non-Archimedean(2,β)-Banach spaces, we prove some stability and hyperstability results for an p-th root functional equation ■where p∈{1, …, 5}, a_1,…, a_k are fixed nonzero reals when p ∈ {1,3,5} and are fixed positive reals when p ∈{2,4}.

磁共振SPACE序列在诊断极外侧椎间盘突出中的临床应用

目的：探讨磁共振不同序列在极外侧椎间盘突出上的表现及诊断价值。方法：对经手术证实的5例极外侧椎间盘突出患者的磁共振常规扫描图像、SPACE序列图像及临床资料进行回顾性分析。结果：本组5例均为男性，年龄32～53岁，平均34岁。椎间孔内侧型2例，椎间孔外侧型2例，混合型1例。极外侧椎间盘突出在平扫矢状位椎间孔层面上表现为椎间孔内和（或）外软组织肿块信号，形态多呈圆形、卵圆形或不规则形，T2WI轴位呈等或混杂信号，边缘不清，T2WI冠状位呈位于孔内和（或）外软组织肿块信号，硬膜囊受压，强化扫描呈中央不强化，周边环状强化信号；SPACE序列冠状位椎间孔周围出现异常低信号，呈圆形、卵圆形或不规则形并与线状马尾神经根相交；SPACE—STIR序列显示受压移位的神经根与突出的椎间盘呈“腋下网球”样征象。结论：在磁共振SPACE序列上能直观地显示神经根与椎间盘之间空间关系，具有一定的特征性，对临床的定性及定位诊断有重要参考价值。

3.0T-MRI 3D-SPACE序列显示神经根与骶管囊肿的关系

目的观察3T磁共振3D-SPACE(sampling perfection with application-optimized contrasts by using differentflip angle evolutions,SPACE)序列在显示神经根与骶管囊肿关系的应用价值。方法对19例神经根囊肿患者行3T磁共振常规扫描及3D-SPACE序列扫描,并在工作站对原始图像沿神经根走形进行冠状位、横轴位重建,分析常规序列及3D-SPACE序列重建图像MRI征象。结果 19例患者3D-SPECE序列冠状位重建图像均清晰的显示出神经根与骶管囊肿的关系,其中神经根中央型9例,神经根周围型7例,灯笼状3例。结论磁共振3D-SPACE序列具有扫描层面薄和多方位重建优势,能够清晰的显示囊肿的解剖部位以及囊肿与神经根的关系,为临床诊断提供更多信息。

3D MEDIC和3D SPACE磁共振神经成像在腰骶丛神经根的一致性对比研究

目的验证三维多回波数据联合成像(three dimensional multi-echo data imagine combination with selective water excitation,3D MEDIC WE)和三维快速自旋回波成像(three dimensional sampling perfection with application optimized contrasts by using different flip angle evolution,3D SPACE STIR)序列在腰骶丛神经根成像中的可行性和重复性。方法将55例受试者分为腰椎无异常表现的正常对照组(20例)、单纯性腰椎间盘突出症(lumbar disc herniation,LDH)组(20例)和慢性炎性脱髓鞘性多发性神经根神经病症(chronic inflammatory demyelinating polyradiculoneuropathy,CIDP)组(15例),分别应用两种腰骶丛神经根成像,评价图像质量参数信噪比(signal to noise ratio,SNR)、对比噪声比(contrast to noise ratio,CNR)和对比度(contrast ratio,CR),并验证正常对照组、CIDP组和LDH组测量神经根直径的一致性。结果两序列测得神经根直径的一致性较高(正常组r=0.95,CIDP组r=0.99,LDH组r=0.97,P<0.001),图像质量评价指标显示,3D SPACE STIR序列在SNR、CNR和CR三项指标中占优,3D MEDIC WE定性评估图像质量评分较高。两序列均能清晰显示正常腰骶丛神经根、病变所致的弥漫性形态增粗神经根以及间盘突出受挤压变形的神经根。结论3D MEDIC WE和3D SPACE STIR序列可应用于腰骶丛神经根成像,两序列对正常和异常形态、走行的神经根评估具备很高的可行性和重复性。综合考量临床图像的定性、定量评价,可择优选择恰当的序列为腰骶丛神经根成像提供影像支持。

波束域Root-MUSIC算法的进一步降阶处理

研究了波束域降阶Root-MUSIC算法,在子阵分解降阶的基础上,进一步将多项式的求根阶次降到与源数目相同,提出了求解降阶多项式的方法。该方法最大程度地减少了求根多项式的阶次和求解多项式的次数,并保持了Root-MUSIC算法的优良性能。显著降低运算量是其最大优点,仿真结果验证了降阶算法的有效性,并比较了不同阶次波束域Root-MUSIC算法的估计性能。

磁共振SPACE-STIR序列在腰骶神经根病变中的应用

目的探讨磁共振SPACE-STIR序列在腰骶神经根病变中应用价值。方法回顾性分析了190例因腰腿痛进行磁共振检查患者的常规磁共振(CMRI)及SPACE-STIR扫描图像,根据磁共振诊断对190例患者做病因学统计;对手术证实的56例60个椎间盘,比较CMRI和SPACE-STIR诊断阳性率、统计常规分型;对手术证实的57个有神经根受累椎间盘,行SPACE-STIR分型与手术分型比较。采用SPSS 13.0统计学软件对CMRI和SPACE-STIR诊断阳性率进行配对资料的卡方检验,一致性资料采用Kappa一致性检验。结果190例腰腿痛患者中椎间盘突出139例,占73.16%,为腰腿痛的主要病因。CMRI与CMRI+SPACE诊断阳性率分别是87.5%、93.3%,差异具有统计学意义(P=0.016)。SPACE-STIR分型与手术分型具有很好的符合性(kappa=0.906,P=0.000)。结论 SPACE-STIR序列使得病灶与神经鞘的解剖关系更加明确,对腰骶神经根病变的病因诊断、诊断阳性率的提高以及临床制定恰当的治疗方案提供了重要的信息。

iRoot SP用于直根管桩腔预备后根尖封闭性的研究

目的:评价iRoot SP对直根管桩腔预备的根尖封闭效果。方法:选取73颗离体直根管牙随机分为8组。A1和B1、A2和B2、A4组分别用AH Plus、iRoot SP、ZOE+热牙胶根充,A3组iRoot SP+单尖根充。C、D组为阳、阴性对照。A1-A4组行即刻桩腔预备; B1、B2组行延迟桩腔预备。染色后透明牙技术评价根尖微渗漏情况。结果:各组染料渗透深度比较A1、A2、A3组间,A1与B1,A2与B2组间比较无统计学意义(P> 0. 05),A4组和C组渗透长度大于A2组(P <0. 05)。结论:iRootSP和AH Plus的根尖封闭性能相同; iRoot SP结合热牙胶充填和结合单尖充填后即刻桩腔预备的根尖封闭性无明显差异。

Effects of clump spacing on nutrient distribution and root activity of Dendrocalamus strictus in the humid region of Kerala,peninsular India

The humid agroclimatic conditions of Kerala,India permit the cultivation of an array of bamboo species of which Dendrocalamus strictus Roxb.(Nees.) is an important one on account of its high growth rate and multiple uses. Stand density, a potential tool in controlling the productivity of woody ecosystems, its effect on growth and root distribution patterns may provide a better understanding of productivity optimization especially when bamboo-based intercropping options are considered.Growth attributes of 7-year-old bamboo(D. strictus) stands managed at variable spacing(4×4 m, 6×6 m, 8×8 m,10×10 m, 12×12 m) were studied. Functional root activity among bamboo clumps were also studied using a radio tracer soil injection method in which the radio isotopeP was applied to soil at varying depths and lateral distances from the clump. Results indicate that spacing exerts a profound influence on growth of bamboo. Widely spaced bamboo exhibited higher clump diameters and crown widths while clump heights were better under closer spacing. Clump height was 30% lower and DBH 52%higher at the widest spacing(12×12 m) compared to the closest spacing(4×4 m). With increasing soil depth and lateral distance, root activity decreased significantly. Root activity near the clump base was highest(809 counts per minute, cpm; 50 cm depth and 50 cm lateral distance) at 4×4 m. Tracer study further showed wider distribution of root activity with increase in clump spacing. It may be concluded that the intensive foraging zone of bamboo is within a 50-cm radius around the clump irrespective of spacing. N, P and K content in the upper 20 cm was 2197,21, and 203 kg/ha respectively for the closely spaced bamboo(4×4 m) which were significantly higher than corresponding nutrient content at wider spacings. About 50% of N, P and K were present within the 0–20 cm soil layer, which decreased drastically beyond the 20 cm depth.The results suggest that stand management practices through planting density regulation can modify the resource acquisition patterns of D. strictus which in turn can change growth and productivity considerably. Such information on root activities, spatial and temporal strategies of resource sharing will be helpful in deciding the effective nutrition zone for D. strictus. Further, the study throws light on the spatial distribution of non-competitive zones for productivity optimization yields, especially when intercropping practices are considered.

Comparing growth and fine root distribution in monocultures and mixed plantations of hybrid poplar and spruce

Disease prevention, biodiversity, productivity improvement and ecological considerations are all factors that contribute to increasing interest in mixed plantations. The objective of this study was to evaluate early growth and productivity of two hybrid poplar clones, P. balsamifera x trichocarpa （PBT） and P. maximowiczii x balsamifera （PMB）, one improved family of Norway spruce （Picea glauca （PA）） and one improved family of white spruce （Picea abies （PG）） growing under different spacings in monocultures and mixed plots. The plantations were established in 2003 in Abitibi-Témiscamingue, Quebec, Canada, in a split plot design with spacing as the whole plot factor （1 × 1 m, 3 × 3 m and 5 × 5 m） and mixture treatments as subplot factor （pure： PBT, PMB, PA and PG, and 1：1 mixture PBT：PA, PBT：PG, PMB：PA and PMB：PG）. Results showed a beneficial effect of the hybrid poplar-spruce mixture on diameter growth for hybrid poplar clones, but not for the 5 × 5 m spacing because of the relatively young age of the plantations. Diameter growth of the spruces decreased in mixed plantings in the 1 × 1 m, while their height growth increased, resulting in similar aboveground biomass per tree across treatments. Because of the large size differences between spruces and poplars, aboveground biomass in the mixed plantings was generally less than that in pure poplar plots. Leaf nitrogen concentration for the two spruce families and hybrid poplar clone PMB was greater in mixed plots than in monocultures, while leaf nitrogen concentration of clone PBT was similar among mixture treatments. Because of its faster growth rate and greater soil resources demands, clone PMB was the only one showing an increase in leaf N with increased spacing between trees. Fine roots density was greater for both hybrid poplars than spruces. The vertical distribution of fine roots was insensitive to mixture treatment.

基于频率超前校正的VSG并联系统有功振荡抑制策略

针对虚拟同步发电机(virtual synchronous generator,VSG)在外界扰动时存在的有功暂态振荡问题,提出一种基于频率超前校正的VSG并联系统有功振荡抑制策略。首先,建立VSG并联系统有功环小信号模型,分析负载功率突变时的VSG有功振荡机理。然后,基于微分超前校正思想并结合VSG有功环控制结构,将有功功率反馈至频率偏差之上,从而增大系统阻尼程度并抑制VSG并联系统有功暂态振荡。接下来,建立改进型VSG并联系统状态空间模型,通过根轨迹分析系统动态响应性能。最后,通过Matlab/Simulink仿真和实验验证了该方案能够有效抑制VSG并联系统有功暂态振荡,并且不影响其稳态有功特性。

有限维单李代数的伴随表示分解

利用有限维单李代数根空间分解,给出复数域上有限维单李代数的根链;利用复数域上不可约sl(2,C)-模的分类,给出有限维单李代数g在伴随作用下分解成g的不可约sl(2,C)-子模直和的分解式.

调亏灌溉对滴灌核桃树根系空间分布特征的影响

【目的】分析小于2 mm的根系滴灌核桃有效吸水根系分布特性,建立有效根长密度函数,研究不同调亏灌溉对核桃树根系空间分布特性,为滴灌核桃精准调亏灌溉提供理论依据。【方法】以14年生温185核桃树为试材,采用30 cm×20 cm×20 cm的分段分层法,取样分析有效吸水根系(d<2 mm)分布特征,研究调亏灌溉对滴灌核桃树有效根系空间分布的影响。【结果】在不同调亏灌溉处理中,W_(0)、W_(3)、W_(4)的核桃树有效总根长分布总体变化趋势表现为单峰曲线,且各个调亏处理在20~40 cm有效总根长最大,分别为50959、74067、55678 cm。不同处理下垂直方向根长密度一维符合指数分布,且水平方向根长密度符合多项式分布。W_(0)、W_(3)、W_(4)各处理有效根长均表现出土层深度在20~40 cm,在距离核桃树行向30~60 cm处最大,分别为11794、22753、14119 cm。【结论】不同调亏灌溉处理下,滴灌核桃树根系有效生长密度表现为W_(3)>W_(4)>W_(0),调亏滴灌灌溉模式使核桃吸水根系更靠近地表生长。

考虑长距离输电缆特性的逆变器并网系统谐波不稳定分析及抑制

长距离输电缆(LTC)与并网逆变器交互作用易引发系统谐波不稳定的风险,且忽略线路频变特性可能会导致稳定性误判。文中计及输电线路的分布参数特性和频变特性,研究如何评估这类逆变器并网系统的稳定性。首先,基于矢量匹配法对含LTC的交流系统进行等值,同时考虑逆变器的内外环控制、锁相环、控制延时等环节,建立dq旋转坐标系下逆变器并网系统高频状态空间模型;其次,采用参与因子分析方法辨识出导致谐波不稳定的关键影响环节,并基于根轨迹方法分析了LTC频变特性、延迟时间、控制器参数、电缆长度和电网阻抗对系统稳定性的影响;再次,提出了基于参数灵敏度分析和矩阵相似变换的系统稳定性改善方法,并对改进后系统的谐波稳定性进行分析;最后,基于RT-LAB构建硬件在环实验平台进行了验证,实验结果验证了理论分析的正确性。

国家授时中心西安卫星激光测距系统进展

卫星激光测距技术是目前精度最高的测距手段之一,其观测数据可用于卫星精密定轨、地球参考框架的建立与维持以及地球自转参数的解算等研究。中国科学院国家授时中心在中国载人航天工程专项项目的支持下,在西安市长安区国家授时中心航天基地园区建成了一套卫星激光测距系统,且已成功实现了对中国空间站以及其他激光卫星的激光测距。详细介绍了该套卫星激光测距系统的设备参数情况以及当前观测情况,并对部分观测数据进行了详细分析,为之后开展长期观测以及稳定运行提供参考,也为利用卫星激光测距数据开展激光时间比对和其他研究奠定基础。

基于SGP4模型的空间站轨道精度分析

针对在地面站天线对空间站观测任务中,通常基于卫星工具包(satellite tool kit,STK)软件规划出天线对空间站的方位角和俯仰角,实现天线对空间站的自动跟踪.为了保证天线跟踪的准确性和可靠性,需要定期计算出准确的空间站轨道和天线的方位俯仰角,并更新规划任务.因此科学分析与评估空间站两行轨道根数(two line elements,TLE)长期预报精度,对地面站实现空间站的精准跟踪具有重要意义.本文以中国空间站(China Space Station,CSS)梦天实验舱为例,基于TLE数据,利用STK软件提供的简化常规摄动规模型(simplified general perturbations4,SGP4)模型计算空间站轨道以及空间站相对于西安地面站的方位角和俯仰角,并分析不同策略下的精度效果.试验结果表明:在第二天更新空间站的TLE,可以获得较好的轨道结果,从而更好地保障天线的跟踪精度.

基于TRU系统的深圳城市绿地优势观花树种根系空间分布特征

为促进城市绿地优势观花树种健康管理,以深圳城市绿地优势观花树种为研究对象,采用树木雷达系统(Tree radar unit,TRU)检测方法,对火焰木Spathodea campanulata、凤凰木Delonix regia、美丽异木棉Ceiba speciosa、黄花风铃木Handroanthus chrysanthus进行根系检测,探寻不同树种、不同立地下根系分布特征。结果表明,(1)整体而言,根系水平分布的特征为距离树干越远,根系密度越小。不同树种水平根系分布密度存在显著差异(P<0.05)。(2)垂直方向根系分布以20~40 cm土层密度最高,而0~20 cm、40~60 cm土层范围根密度较小,绝大多数根系分布在0~60 cm范围土层中。(3)不同树种总体垂直分布密度差异显著(P<0.05),随土层深度增加呈先增加后减小规律,通常于20~40 cm土层范围内达到峰值。(4)道路立地与硬质铺装环境根系相比于草坪绿地具有更明显的胁迫响应,根系为应对胁迫普遍采取侧重于分支生长的策略,具体表现为道路立地与硬质铺装环境下相同树种水平与垂直根系密度远高于草坪绿地,且在表层土壤根系形成聚集效应,表层土壤范围内根系含量相比草坪绿地显著增加(P<0.05)。总体根系密度呈道路立地>硬质铺装>草坪绿地。(5)在城市硬质环境胁迫下,各树种根系横向扩张能力呈凤凰木>火焰木>美丽异木棉>黄花风铃木。为了改善城市绿地树木的根系发育,建议采用土壤改良、生根剂施用、新型基质换填和菌根形成诱导等方法,并结合引根管、隔根挡板、树池和绿化带的工程技术改造,以促进根系健康发展。