12C离子束的剂量学研究

研究了L-α-丙氨酸剂量计测量^12C离子辐射的剂量学特性，实验证明丙氨酸剂量计适用于^12C离子辐射的剂量学测量。另外，还研究了^12C离子照射人外周血诱发的染色体畸变（双着丝粒＋着丝粒环）的剂量效应，在0-8．0Gy范围内拟合的最佳回归方程为Y=0．858503D＋0．3615×10^-2D^2。Dosimetric characteristics of L-α-alanine dosemeter used for dosimetry of ^12C ion radiation have been studied. The experimental results indicate that the alanine dosemeter can be used to measure the ^12C ion radiation. In addition, dose effects of chromosome aberration dicentrics and cenric rings were studied after human peripheral blood being irradiated by ^12C ions; the best regression equation, Y = 0. 858 503D ＋ 0. 361 5 ×10^-2D^2, was obtained within 8.0 Gy.     

H0323+022天体的光变特性和黑洞质量研究

从大量文献资料中，收集了BL Lac天体H0323+022光学V波段的大量观测数据，获得了H0323+ 022从1982年至2003年的长期光变曲线.给出了从2000年至2003年，使用云南天文台1米望远 镜和上海天文台的156米望远镜，对H0323+022进行光学波段近4年的监测数据，观测发现 了H0323+022在光学R波段有7min的短时标光变.色指数B—V与V波段的星等值有较强的相关性 ，对H0323+022 CCD测光的结果与Bai（1998）观测的结果ΔR=063 ΔI=081是 一致的.由观测所发现的短时标光变，推算出了BL Lac天体H0323+022的中心黑洞质量和辐射 区域. 关键词： BL Lac天体 光变曲线 短时标光变 辐射区域 中心黑洞质量     

多参考组态相互作用方法计算研究XOn(X=S,Cl；n=0,±1)的解析势能函数和光谱常数

采用从头计算的多参考组态相互作用方法和含扩散基的3个基组aug-cc-PVXZ (X=D,T,Q) 计算了SO和ClO分子及其分子离子的势能曲线，确定了平衡几何结构、离解能，并采用Feller拟合递推方法得到了基函数为无穷大计算水平值. 确定了SO^－，ClO⁺，ClO^-分子离子的基态. 通过Murrell-Sorbie势能函数和最小二乘法拟合得到了解析势能函数. 基于所得的势能函数，通过解核运动的薛定谔方程得到振 关键词： 多参考组态相互作用 势能曲线 解析势能函数 光谱常数     

甲基化抑制剂5-氮杂2′-脱氧胞苷对三维培养A549细胞辐射敏感性的影响

为探讨DNA去甲基化试剂5-氮杂-2′-脱氧胞苷(5-aza-2′-deoxycytidine,5-Aza-CdR)对三维(3D)培养模式下的肺腺癌细胞A549辐射敏感性的作用,开展了系列实验。使用不同浓度5-Aza-CdR处理单层(2D)A549细胞72 h后,MTT法检测其对A549细胞的增殖抑制作用。选取低浓度(2,5μmol/L)5-Aza-CdR预处理2D和3D培养的A549细胞72 h,X射线分别辐照1,2,4,6 Gy,检测微核形成率和克隆存活。实验结果显示,不同浓度的5-Aza-CdR均能抑制2D的A549细胞增殖,且呈剂量依赖性。5μmol/L药物预处理2D与3D细胞并联合辐照后诱导的细胞微核形成率均显著高于相应的对照组,并且细胞存活率显著降低。不过,较低浓度5-Aza-CdR(2μmol/L)预处理的3D培养A549细胞4,6 Gy辐照后微核数目较未用药处理组显著增加,克隆存活率较未用药组显著降低(P0.05),而在2D培养A549细胞中未观测到上述现象。研究结果表明,5-Aza-CdR能抑制A549细胞增殖,3D培养A549细胞药物预处理更能增加其辐射敏感性。结果暗示,为减少对正常细胞的毒性作用,在临床放疗中,可低剂量使用5-Aza-CdR,实现肿瘤的有效靶向治疗。     

HF分子电子基态和激发态的MRCI计算

应用舍Davidson修正的多参考组态相互作用（MRCI）方法,在aug-cc-pVTZ基组水平上对HF基态及最低的多个单重和三重电子激发态进行了势能扫描计算.结合群论原理及分子的离解极限,分析了电子态势能曲线的特征,得出激发态B¹S⁺对应的离解极限为H⁺+F^-（¹S）.基于势能曲线,数值求解核运动的径向Schrodinge方程,得到J=0时束缚电子态X¹S⁺,B¹S⁺,C¹P和D¹S⁺的振动能级和转动常数,继而进行数据拟合得到电子态的光谱常数,基态X¹S⁺:ω_e=4146.94 cm^-1,ω_ez_e=88.08 cm^-1,B_e=21.22 cm^-1,a=0.785 cm^-1;B¹S⁺态:ω_e=1131.37 cm^-1,ω_ex_e=17.28 cm^-1,B_e=3.96 cm^-1,a_e=0.0215 cm^-1,C¹P态:ω_e=2696.37 cm^-1,ω_ex_e=73.43 cm^-1,B_e=15.91 cm^-1,a_e=0.776 cm^-1,D¹S⁺态:ω_e=3104.22 cm^-1,ω_ex_e=118.92 cm^-1,B_e=17.25 cm^-1,a_e=0.992 cm^-1,拟合结果与实验值吻合的较好.     

理论研究OH+离子电子态光谱及跃迁性质

采用高精度的内收缩多参考组态相互作用方法（icMRCI）计算OH⁺离子基态和低激发态的势能曲线和A³П-X³Σ^-跃迁体系的跃迁偶极矩。计算过程中考虑了能量的Davidson修正（+Q）效应和标量相对论修正。根据势能曲线,通过求解核的一维Schrödinger方程得到OH⁺的光谱参数。通过计算A³П-X³Σ^-体系的跃迁偶极矩研究这一跃迁体系的Einstein系数、F-C因子。研究了A³П（ν'=0~6）态的跃迁辐射寿命,结果显示其数量级为10^-6 s。     

离子注入对InAs/GaAs量子点光学效质的影响

研究了低能质子注入诱导的界面混合和快速热退火对量子点发光效率的影响，对其光致发光 峰强进行了拟合计算.研究发现量子点的发光峰强度主要由载流子俘获时间和非辐射复合寿 命决定.由于后退火处理能够部分的消除因质子注入造成的缺陷，量子点中非辐射复合中心 浓度与注入剂量成亚线性关系；退火温度越高，非辐射复合中心被消除越多，亚线性程度越 高.界面混合导致的俘获效率的增加和注入损伤引起的非辐射复合是相互竞争过程，存在一 个临界的注入剂量N_C，当注入剂量N小于N_C，界面混合作 用较为明显，量子点 发光峰强随注入剂量增加而增强；当N大于N_C时，质子注入引起了大量的非 辐射复合 中心，主要表现为注入损伤，量子点的发光峰强随注入剂量增加而迅速减弱.退火温度越高 ，N_C越大. 关键词： 量子点 离子注入 峰强     

AlCl分子X^1∑^+电子态的光谱性质北大核心CSCD

运用耦合簇单双取代三重微扰方法[CCSD(T)]和内收缩多参考组态相互作用方法(MRCI)结合系列相关一致基,aug-cc-pV(n+d)Z(n=D,T,Q,5,6),研究了AlCl(X1∑+)分子的光谱性质.比较了两种理论方法及不同的基组对AlCl(X1∑+)分子的光谱常数的影响.在优选的MRCI/aug-cc-pV(5+d)Z理论水平下于0.05~2.0nm核间距范围内计算了AlCl(X1∑+)分子的势能曲线.拟合势能曲线得到其光谱常数De,D0,Re,ωe,ωexe,Be和αe.它们分别为5.1942eV,5.1644eV,0.21350nm,481.67cm-1,2.1022cm-1,0.2416cm-1和0.0016cm-1.这些结果与已有的实验结果均较为相符.利用这一势能曲线,通过求解双原子分子核运动的径向Schrdinger方程,计算了AlCl分子基态的振转能级.找到了J=0时的全部182个振动态.针对每一振动态,还分别计算了其对应的振动能级、惯性转动常数和离心畸变常数等分子常数.文中的大部分分子常数属首次报导.     

OH,OCl,HOCl(~1A′)的从头算与势能曲线

采用Gassian09程序包中的多种方法对OH,OCl,HOCl分子的基态结构进行优化计算,优选出QCISD/6-311G（2df）,B3P86/6-31 1+G（2df）方法分别对OH（X²∏）,OCl（X²∏）分子进行计算,得到平衡核间距R_OH=0.09696nm,R_OCl=0.1569 nm,谐振频率w（OH）=3745.37 cm^-1,e（OCl）=892.046 cm^-1,与实验结果非常符合.用Murrell-Sorbie势能函数对OH和OCl分子的扫描势能点进行拟合,其扫描点都与四参数Murrell-Sorbie函数拟合曲线符合得很好.优选出QCISD（T）/D95（df,pd）方法对HOCl分子进行计算,得到基态为X¹A’,键长R_OH=0.0966 nm,键角∠HOCl=102.3°,谐振频率w₁（a₁）=738.69 cm^-1,w₂（b2）=1260.25 cm^-1,离解能D_e=2.24 eV.通过比较发现这些结果与实验值符合得很好,并优于文献报道的结果.随后计算出了力常数,在此基础上,推导出HOCl分子的多体展式势能函数.报道了HOCl分子对称伸缩振动势能图中在H+OCl→HOCl反应通道上有一鞍点,H原子需要越过1.74 eV的能垒才能生成HOCl的稳定结构,在Cl+OH→HOCl通道上不存在明显势垒,容易形成稳定的HOCl分子.     

AlCl分子X1Σ+电子态的光谱性质

运用耦合簇单双取代三重微扰方法[CCSD(T)]和内收缩多参考组态相互作用方法(MRCI)结合系列相关一致基, aug-cc-pV(n+d)Z(n = D, T, Q, 5, 6), 研究了AlCl(X1Σ+)分子的光谱性质. 比较了两种理论方法及不同的基组对AlCl(X1Σ+)分子的光谱常数的影响. 在优选的MRCI/aug-cc-pV(5+d)Z理论水平下于0.05-2.0 nm核间距范围内计算了AlCl(X1Σ+)分子的势能曲线. 拟合势能曲线得到其光谱常数De, D0, Re, ωe, ωexe, Be和αe. 它们分别为5.1942 eV, 5.1644 eV, 0.21350 nm, 481.67 cm-1, 2.1022 cm-1, 0.2416 cm-1和0.0016 cm-1. 这些结果与已有的实验结果均较为相符. 利用这一势能曲线, 通过求解双原子分子核运动的径向Schrödinger方程, 计算了AlCl分子基态的振转能级. 找到了J = 0时的全部182个振动态. 针对每一振动态, 还分别计算了其对应的振动能级、惯性转动常数和离心畸变常数等分子常数. 文中的大部分分子常数属首次报导.     

Radiosensitivity of CD3−CD8+CD56+ NK cells

The effect of lower doses (0.5–3.0 Gy) of gamma radiation on radiosensitivity of CD3?/CD8+ NK cells subpopulation isolated from the peripheral blood of healthy volunteers was studied 48 h after the irradiation. Only a subtle increase in terms of induction of apoptosis (A+ cells), was observed in Annexin positive CD3?/CD8+ NK cells. The assessment of the relative presence of CD3^?/CD8⁺ NK cells in Annexin negative populations of lymphocytes considerably contributes to the elimination of individual variability and could be useful in biodosimetry.Living CD3?/CD8+; Annexin negative NK cells were analyzed using five-color flow cytometry 16 h after irradiation by the doses of 1–10 Gy. The study was carried out on NK cells subsets CD3?/CD8? CD16+, CD56 (dim) and CD56 (bright). NK cells characterized with their low-density expression of CD56 (dim) are more cytotoxic and express CD16. Those with high-density expression of CD56 (bright) are known for their capacity to produce cytokines following activation of monocytes but their natural cytotoxicity is low; they are classified as CD16? or CD16 (dim). A dose-depending decrease in the relative presence of CD3?/CD8+ NK cells was observed 16 h after ionizing radiation (1–10 Gy). The decrease was highly pronounced in CD56 (bright) subset of NK cells and this subpopulation was considered as the most radiosensitive one. Unfortunately, the most radiosensitive subpopulation of NK cells – CD56bright cannot be used as a biodosimetric marker due to its insufficient amount in peripheral blood.     

二烯丙基二硫对12C6+离子束辐照损伤小鼠的保护作用研究

研究大蒜素重要活性成分二烯丙基二硫( Diallyl disulfide, 简称DADS) 对12C6+离子束辐照损伤小鼠的保护作用。利用4 Gy 剂量12C6+离子束对不同浓度DADS 预处理的雄性昆明小鼠进行单次全身照射。随后检测骨髓细胞微核率和肝组织中丙二醛(MDA) 含量、蛋白质总羰基含量、总抗氧化能力( TAOC)及谷丙转氨酶(ALT ) 活性。结果显示,与单纯照射组相比,低浓度DADS 预处理组骨髓细胞微核率和肝组织ALT 活性均显著降低(p<0.001),而肝组织T-AOC明显增强( p < 0.05 );中浓度DADS 预处理组肝组织中MDA 含量和蛋白质总羰基含量均显著减少( p < 0.05 )。结果提示,DADS通过抑制氧化应激,有效地保护了脂质、蛋白质和遗传物质免受12C6+离子束辐照引起的损伤。The radioprotective effect of Diallyl disulfide (DADS) on 12C6+ ion irradiation was studied. Pretreated with DADS of different concentration, male Kung-Ming mice were exposed to whole body irradiation with dosage of 4 Gy 12C6+ ion. The animals were sacrificed after irradiation. Then the bone marrow cells micronucleus rate, malondialdehyde (MDA) levels, content of protein carbonylation, total antioxidant capacity ( T-AOC) and alanine aminotransferase ( ALT ) activity were measured. As compared with those in irradiated group, the ratio of micronucleus cells in marrow and the hepatic ALT activity in the pretreatment group with low dose DADS decreased significantly ( p < 0.001 ). Similarly,the content of protein carbonylation and the levels of MDA droped dramatically in the group with middle dose DADS treatment ( p < 0.05 ). On the contrary, the hepatic T-AOC increased markedly in the group of pretreatment with low dose DADS ( p < 0.05 ). The results showed that DADS protect lipoid, protein and genetic material from 12C6+ ion irradiation by right of resisting oxidative stress.     

MR imaging of benign prostatic hypertrophy using a Helmholtz-type surface coil.

MR examinations of the prostate were performed on six healthy volunteers and 18 patients with well-documented symptomatic benign prostatic hypertrophy, using an organ-encompassing Helmholtz-type surface coil at 1.5 T. The healthy volunteers were also imaged with a standard circumferential body coil. The morphologic features and signal intensity characteristics of the prostate and adjacent structures were analyzed in the patient group. Several recognizable patterns of benign prostate hypertrophy were identified including bilaterally symmetrical nodules in the central gland, multiple central gland nodules, and a diffusely heterogeneous central gland without appreciable nodules. The peripheral zone was of moderate to high signal intensity on T2-weighted images, and was diffusely heterogeneous in 78% of patients. The false prostatic capsule, peripheral venous plexus, and seminal vesicles were also characterized. A good correlation was shown between prostatic glandular volume and prostate-specific antigen. Calculated signal-to-noise ratios (S/N) were significantly greater on images acquired with the Helmholtz-type receiver coil than on those acquired with the body coil. We conclude that the hyperplastic prostate gland has a variety of MR appearances, but that recognizable patterns are frequently seen. High resolution imaging with a Helmholtz-type surface coil provides excellent anatomical depiction of the prostate and adjacent structures.     

Investigation of metabolic changes in blood and tissue of mice γ-irradiated with sublethal doses by direct observation of EPR signals from Hb-NO complexes

The metabolic changes in probes of blood and tissue (spleen, liver and kidney) of mice under total γ-irradiation with the doses varied in the interval of 1–10 Gy at the dose rate of 0.073 Gy/min were studied in the early postirradiation period by ex vivo electron paramagnetic resonance (EPR). It was established that the impact with the lower dose rate leads to more intensive nitric monoxide biosynthesis in comparison with higher dose rates. In the early postirradiation period (from 2 up to 6 h), irradiation with doses higher than 2 Gy brings about an increase of the NO concentration and, hence, the appearance of nitrosyl complexes which were registered directly by EPR in blood and spleen. The observed line is identified as the signal from α-(Fe²⁺-NO)₂β(Fe³⁺)₂ or α-(Fe²⁺-NO) α(Fe²⁺)β(Fe³⁺)₂ complexes since the methemoglobin concentration also increases in comparison with the control level. The concentration of Hb-NO complexes in blood and spleen depends on the dose and individual radiosensitivity of the organism. Therefore, the intensity of the Hb-NO signal may serve as a criterion of the radiation injury level during the first hours after the irradiation. 30 h after the impact, the Hb-NO complexes were no longer detected. For the first day, the concentration of Fe³⁺-transferrin in blood increases with the dose and time passed after the irradiation. The intensity of the EPR signal from Fe³⁺-transferrin in blood may also serve as a measure of the radiation injury level.     

Fractional-charge and fractional-spin errors in range-separated density-functional theory

ABSTRACT

We investigate fractional-charge and fractional-spin errors in range-separated density-functional theory (DFT). Specifically, we consider the range-separated hybrid (RSH) method which combines long-range Hartree-Fock (HF) exchange with a short-range semilocal exchange-correlation density functional, and the RSH+MP2 method which adds long-range, second-order Møller-Plesset (MP2) correlation. Results on atoms and molecules show that the fractional-charge errors obtained in RSH are much smaller than in the standard Kohn-Sham (KS) scheme applied with semilocal or hybrid approximations, and also generally smaller than in the standard HF method. The RSH+MP2 method tends to have smaller fractional-charge errors than standard MP2 for the most diffuse systems, but larger fractional-charge errors for the more compact systems. Even though the individual contributions to the fractional-spin errors in the H atom coming from the short-range exchange and correlation density-functional approximations are smaller than the corresponding contributions for the full-range exchange and correlation density-functional approximations, RSH gives fractional-spin errors that are larger than in the standard KS scheme and only slightly smaller than in standard HF. Adding long-range MP2 correlation only leads to infinite fractional-spin errors. This work clarifies the successes and limitations of range-separated DFT approaches for eliminating self-interaction and static-correlation errors.     

重离子周边碰撞和中心碰撞引起的不同裂变行为

本实验同时研究了4 0Ar+209Bi反应中周边碰撞和中心碰撞两者产生的关联裂变碎片,以及其与α粒子的再关联.对裂变碎片质量分布和能量分布随热裂变核初始温度演化的系统分析,发现中心碰撞和周边碰撞所形成的热核存在着不同的裂变行为. Correlated fission fragments from the 40Ar+209Bi reaction and their further correlation with α particles have been studied for peripheral and central collisions simultaneously. The existence of different fission behavior of hot nuclei formed in central and peripheral collisions was found from the systematic analysis of the mass and energy distributions of fission fragments as a function of the initial temperature of hot fissioning nuclei.     

Interference of acute cigarette smoking with [¹³C]methacetin breath test

It is essential to establish whether and how environmental factors affect the reliability of [(13)C]methacetin breath test ((13)C-MBT). In 12 healthy volunteers (smokers), a standard (13)C-MBT with 75 mg [(13)C]methacetin was performed twice in random order: on a control day without smoking and on another day with smoking two cigarettes antecedently. A considerable flattening of the curve of the momentary (13)C recovery within the expiratory air was observed when the (13)C-MBT was performed after smoking. The maximum of the momentary (13)C recovery, D(max), decreased from 37.20±2.58 to 25.39±2.29% dose/h (p=0.00052). Moreover, the time to reach D(max) was prolonged after cigarette smoking (26.5±3.1 vs. 16.5±1.9 min, p=0.0199). The curve of the cumulative (13)C recovery on the cigarette smoking day appeared to be shifted downwards, and statistically significant differences relative to the control situation were found between the 24th and 75th minute following [(13)C]methacetin administration. Smoking cigarettes immediately prior to the (13)C-MBT diminishes the ability of the liver to handle methacetin, and hence a possibility of such an interaction should be excluded in order to interpret the results of the test correctly.     

MRI-induced stimulation of peripheral nerves: dependency of stimulation threshold on patient positioning

Fast gradient systems enable the imaging of moving organs but also restrict imaging possibilities by stimulating the peripheral nerves. Several studies have determined the stimulation thresholds of the peripheral nerves. However, no study has explicitly examined whether stimulation thresholds are dependent on the position of the patient in the MR imager. In this study, combinations of one, two and three gradient axes were switched with sinusoidal wave forms (rise time 300 micros). Stimulation thresholds were determined for five patient positionings: gradient isocenter at the bridge of the nose, jugular fossa, 10 cm cranial of the umbilicus, umbilicus, and 10 cm caudal of the umbilicus. Experiments were performed in two volunteer groups, one for triple gradient switching (17 male, 14 female) and the other for single and double gradient switching (14 male, 11 female). The dependence of the stimulation threshold on the position of the volunteers in the MR imager was statistically significant for most of the gradient combinations, with the highest stimulation thresholds for positions umbilicus+10 and umbilicus at isocenter. Similar patterns of position dependence were obtained for gradient pairs whose axes were axially symmetric to the human body. Mean stimulation thresholds of male volunteers were lower than those of female volunteers. These findings indicate that stimulation thresholds should be defined according to the position of the patient in the MR scanner.     

A shock-capturing methodology based on adaptative spatial filtering for high-order non-linear computations

A shock-capturing methodology is developed for non-linear computations using low-dissipation schemes and centered finite differences. It consists in applying an adaptative second-order filtering to handle discontinuities in combination with a background selective filtering to remove grid-to-grid oscillations. The shock-capturing filtering is written in its conservative form, and its magnitude is determined dynamically from the flow solutions. A shock-detection procedure based on a Jameson-like shock sensor is derived so as to apply the shock-capturing filtering only around shocks. A second-order filter with reduced errors in the Fourier space with respect to the standard second-order filter is also designed. Linear and non-linear 1D and 2D problems are solved to show that the methodology is capable of capturing shocks without providing dissipation outside shocks. The shock detection allows in particular to distinguish shocks from linear waves, and from vortices when it is performed from dilatation rather than from pressure. Finally the methodology is simple to implement and reasonable in terms of computational cost.