体电子密度对术后宫颈癌放射治疗计划剂量精确度的影响研究

目的通过在放疗计划系统手动赋予以CT图像为基础的肿瘤组织及危及器官准确的均匀体电子密度,研究其对剂量精确性的影响。方法回顾性选取20例术后宫颈癌放疗计划,从国际辐射单位与测量委员会(ICRU)46号报告导出相应器官的体电子密度,转化为相对电子密度后植入计划系统(Monaco5.11,Sweden)的危及器官模块,包括膀胱、直肠、小肠、肾脏、脊髓、股骨头、髂骨,其他组织以人体的平均电子密度代替。原始计划为双弧容积旋转调强(360°VMAT),采用蒙特卡罗算法,计算网格为0.3 cm×0.3 cm×0.3 cm,最小子野宽度为0.6 cm。保持原始计划通量不变,重新计算剂量生成新计划。通过剂量学参数以及剂量-体积直方图(DVH)二维曲线比较两种计划的区别。结果植入体电子密度后生成的计划中(Plan_(RED)),患者绝大部分的靶区剂量参数与原始计划(Plan_(ref))之间的偏差<2%,所有靶区D_(2)、D_(98)、D_(mean)的平均偏差<0.7%,180个数据中只有2个数值在2%~3%。膀胱、直肠、小肠的V_(20)、V_(30)、D_(1 cm^(3))、D_(mean)、Plan_(ref)的平均偏差<0.6%,240个数据中有4个数值>2%。Plan_(RED)的平均跳数比Plan_(ref)高0.9%,子野总数不变。手动赋予电子密度生成的计划剂量偏高,但符合临床要求。DVH图中靶区、危及器官的二维曲线几乎完全重合。两组计划剂量参数的差异无统计学意义(P>0.05)。结论通过在计划系统中手动赋予人体电子密度来生成的术后宫颈癌计划与原始计划剂量整体偏差<2%,符合临床要求,为实现MRI直接用来进行放疗计划设计和剂量计算提供了参考。

电子密度模体插件自动定位方法

目的探讨基于深度卷积神经网络(DCNN)对电子密度模体(CIRS 062)插件自动定位的方法。方法首先基于DCNN模型分割CIRS 062的吸气态肺、呼气态肺、松质骨和密质骨4个插件;之后采用摩尔邻域追踪算法处理插件边缘;最后根据几何特征定位其他4个插件。结果基于DCNN分割结果的戴斯相似性系数均>0.85,精确度均>0.81,综合评价指标均>0.61。结论基于DCNN方法可实现插件自动定位。

CT-电子密度转换曲线的采集校正及对治疗计划剂量计算的影响

目的:为提高放疗精度,建立CT-电子密度转换曲线,确定对放射治疗计划剂量计算的影响。方法:利用CT电子密度模体,对模拟定位CT机的CT值进行检测。比较人体不同组织的CT值,建立CT-电子密度转换曲线。根据各组织的相对电子密度对组织不均匀性剂量进行校正,并分析照射剂量MU数值的变化。结果:在同一定位扫描参数下,不同位置的等效密度组织CT值均有变化:高密度组织CT值变化较大,近床面的等效密度组织CT值变化均大于远床面的等效密度组织。不同的CT-电子密度转换曲线其MU数值相差均<20%,调强放疗(intensity modulated radiation therapy,IMRT)较大,三维适形放射治疗(3-dimensional conformal radiation therapy,3DCRT)和调强放疗各偏差值相同。结论:对治疗计划系统数据进行采集录入时,应正确合理地输入一条CT-电子密度转换曲线,以保证治疗计划剂量计算的精度。

电离层闪烁功率谱及不均匀体漂移速度反演

从Rytov理论出发,给出了弱起伏下一般平静电离层电波传播的闪烁指数。研究表明:尺度为第一菲涅耳带的电子密度不均匀体对电离层电波闪烁的贡献应起主要作用。进而在Shkarofsky不均匀体幂率谱基础上,给出了闪烁的功率谱,并对影响闪烁功率谱的主要因素作了具体分析。同时,在给定不均匀体离地高度的情况下,通过对闪烁功率谱函数振荡部分出现第一极小值时的频率和总功率谱曲线出现第一极小值时频率的比对,反演得到了不均匀体的漂移速度。最后实验分析表明:在误差范围内,该结果能正确反映电离层不均匀体的真实漂移速度。

电磁脉冲信号电离层传播的时间特性

研究背景电离层以及分布于其中的电子密度不规则性结构的变化,对穿越于其中电磁脉冲信号的传播时间产生的影响.基于积分方程迭代法得到的时间矩和双频、双点互相干函数的解析解,从理论分析和数值模拟,探讨电磁脉冲信号穿过电离层随机介质传播的时延特性,并基于极区背景电离层参数,模拟分析脉冲信号的附加时延随电离层电子密度不规则体谱指数,内、外尺度以及电子密度起伏方差等的变化.理论和数值模拟表明,电离层脉冲信号传播的时延取决于背景电离层以及相应的群速传播项的影响,而电离层不规则体的色散、散射作用对电磁脉冲信号附加时延的影响相对较小,两者在数量级上相差数十倍.

Inverse Halogen Bonds Interactions Involving Br Atom in the Electronic Deficiency Systems of CH3＋… Br-Y （Y--H, CCH, CN, NC）

Inverse halogen bonds interactions involving Br in the electronic deficiency systems of CH3＋...Br-Y （Y=H, CCH, CN, NC） have been investigated by B3LYP/6- 311＋＋G（d, p） and MP2/6-311＋＋G（d, p） methods. The calculated interaction energies with basis set super-position error correction of the four IXBs complexes are 218.87, 219.48, 159.18, and 143.05kJ/mol （MP2/6-311＋＋G（d, p））, respectively. The relative stabilities of the four complexes increased in the order： CH3＋ … BrCN〈CH3＋…- BrNC〈CH3＋… BrH≈CH3＋ …BrCCH. Natural bond orbital theory analysis and the chemical shifts calculation of the related atoms revealed that the charges flow from Br-Y to CH3e. Here, the Br of Br-Y acts as both a halogen bond donor and an electron donor. Therefore, compared with conventional halogen bonds, the IXBs complexes formed between Br-Y and CH3＋. Atoms-in-molecules theory has been used to investigate the topological properties of the critical points of the four IXBs structures which have more covalent content.

基于星载SAR信号的TEC反演新方法

由于星载合成孔径雷达(SAR)系统工作于电离层之上,其信号不可避免地将受到电离层的影响.背景电离层以及电离层电子密度不规则体多重散射效应可引起距离向图像质量的下降,在强起伏情况下,多重散射效应对信号的延迟影响不可忽略.针对此问题,本文提出了一种基于SAR回波信号的三频相位自适应TEC反演新方法,利用反演的结果对电离层的影响进行校正.给出了校正前后的点目标成像仿真,结果显示此方法充分考虑了多重散射效应引起的TEC估计误差,可以有效地补偿电离层对距离向成像的影响,提高了距离向点目标图像质量.

Structures and Electronic Properties of Cu_N (N≤13) Clusters

A systematic study on the structures and electronic properties of copper clusters has been performed using the density functional theory. In the calculation, there are many isomers near the ground state for small copper clusters. Our results show that the three-dimensional isomers of copper clusters start from Cu7 cluster and then show a tendency to form more compact structures. The results of the formation energy and the second derivative of binding energy with duster size show that besides N = 8, N =11 is also a magic number. Furthermore, it is the first time to find that the ground state of 11-atom clusters is a biplanar structure as same as the 13-atom cluster. The clear odd-even alternation as cluster size for the formation energy indicates the stability of electronic close shell existed in the range studied.

Time Evolution of the Multicomponent Laser Plasma Parameters

The emission of CulnSe2-based laser ablation plasma has been investigated at a distance of I mm from the target surface. The plasma was formed by radiation of the neodymium laser （5 ×10^8 W.cm^-2; 1,064 nm; 20 ns; 12 Hz）. The temporal dynamics have been obtained for the plasma parameters, such as the population of excited states of atoms, electron temperature and density. Two peaks were observed in the temporal profile of the population of excited states. The temporal dependence of electron temperature was singly peaked. During the time interval of 0-300 ns, the electron temperature varied in the range of 1.6-1.2 eV and the density of electrons varied in the range of 1.3 × 10^16 cm^-3 to 9 × 10^14 cm^-3. It has been established that at the selected conditions of plasma formation saved ratio of copper and indium, which correspond to stoichoimetric target composition.

Electronic and Optical Properties of Rock-Salt A1N under High Pressure via First-Principles Analysis

Electronic and optical properties of rock-salt AIN under high pressure are investigated by first-principlesmethod based on the plane-wave basis set.Analysis of band structures suggests that the rock-salt AIN has an indirectgap of 4.53 eV,which is in good agreement with other results.By investigating the effects of pressure on the energygap,the different movement of conduction band at X point below and above 22.5 GPa is predicted.The opticalproperties including dielectric function,absorption,reflectivity,and refractive index are also calculated and analyzed.Itis found that the rock-salt AIN is transparent from the partially ultra-violet to the visible light area and hardly does thetransparence affected by the pressure.Furthermore,the curve of optical spectrum will shift to high energy area (blueshift) with increasing pressure.

The Effect of Defects on the Mobility of HEMT Transistors Based on AIGaN/GaN

A phenomenological low-filed mobility model is developed to describe the dependence ot the carrier molgmty on me gate to source bias applied for AIGaN/GaN high electron mobility transistor. The results show excellent agreement with experimental data, when compared thereby proving the validity of the model. In the proposed work the temporal evolution of the mobility degradation shows a sharp decline in emission rates below 456 s-1. We also note a sharp decline for large defects densities.

A first-principles study of the structural,electronic and elastic properties of solid nitromethane under pressure

The structural,electronic and elastic properties of solid nitromethane are investigated under pressure by performing first-principles density functional theory(DFT)calculations within the generalized gradient approximation(GGA)and the local density approximation(LDA).The obtained ground state structure properties are found to be consistent with existing experimental and theoretical results.The pressure-induced variations of structure parameters(a,b,c and V)indicate that the solid nitromethane has an anisotropic compressibility,and the compression along the c direction is more difficult than along a and b directions.From the vibration curves of intermolecular bond length and bond angle,we find that the C—N bond is the most sensitive among these bonds under pressure,suggesting that the C—N bonds may be broken first under external loading.The influence of pressure on the electronic properties of solid NM has been studied,indicating that solid NM is an insulating compound with a large indirect band gap and tends to be a semiconductor with increasing pressure.Finally,we predict the elastic constants and their pressure dependence for the solid NM with the bulk modulus,Young’s modulus,shear modulus and the Poisson’s ratio derived.

The global star formation law of galaxies revisited in the radio continuum

We study the global star formation law, the relation between the gas and star formation rate （SFR） in a sample of 130 local galaxies with infrared （IR） luminosities spanning over three orders of magnitude （109-1012 Lo）, which includes 91 normal spiral galaxies and 39 （ultra）luminous IR galaxies [（U）LIRGs]. We derive their total （atomic and molecular） gas and dense molecular gas masses using newly available HI, CO and HCN data from the literature. The SFR of galaxies is determined from total IR （8-1000 μm） and 1.4 GHz radio continuum （RC） luminosities. The galaxy disk sizes are defined by the de-convolved elliptical Gaussian FWHM of the RC maps. We derive the galaxy disk-averaged SFRs and various gas surface densities, and investigate their relationships. We find that the galaxy disk-averaged surface density of dense molecular gas mass has the tightest correlation with that of SFR （scatter -0.26 dex）, and is linear in log-log space （power-law slope of N=1.03±0.02） across the full galaxy sample. The correlation between the total gas and SFR surface densities for the full sample has a somewhat larger scatter （-0.48 dex）, and is best fit by a power-law with slope 1.45±0.02. However, the slope changes from -1 when only normal spirals are considered, to -1.5 when more and more （U）LIRGs are included in the fitting. When different CO-to-H2 conversion factors are used to infer molecular gas masses for normal galaxies and （U）LIRGs, the bi-modal relations claimed recently in CO observations of high-redshift galaxies appear to also exist in local populations of star-forming galaxies.

Novel ionic liquid based electrolyte for double layer capacitors with enhanced high potential stability

Developing electrolyte with high electrochemical stability is the most effective way to improve the energy density of double layer capacitors(DLCs), and ionic liquid is a promising choice. Herein, a novel ionic liquid based high potential electrolyte with a stabilizer, succinonitrile, was proposed to improve the high potential stability of the DLC. The electrolyte with 7.5 wt% succinonitrile added has a high ionic conductivity of 41.1 m S cm^(-1) under ambient temperature, and the DLC adopting this electrolyte could be charged to 3.0 V with stable cycle ability even under a discharge current density of 6 A g^(-1). Moreover, the energy density could be increased by 23.4% when the DLC was charged to 3.0 V compared to that charged to 2.7 V.

Fast and reliable identification of atomically thin layers of TaSe2 crystals

Deposition of clean and defect-free atomically thin two-dimensional crystalline flakes on surfaces by mechanical exfoliation of layered bulk materials has proven to be a powerful technique, but it requires a fast, reliable and non-destructive way to identify the atomically thin flakes among a crowd of thick flakes. In this work, we provide general guidelines to identify ultrathin flakes of TaSe2 by means of optical microscopy and Raman spectroscopy. Additionally, we determine the optimal substrates to facilitate the optical identification of atomically thin TaSe2 crystals. Experimental realization and isolation of ultrathin layers of TaSe2 enables future studies on the role of the dimensionality in interesting phenomena such as superconductivity and charge density waves.

A New Approach to Energy Integral for Investigation of Dust-Ion Acoustic(DIA)Waves in Multi-Component Plasmas with Quantum Effects in Inertia Less Electrons

Dust-ion acoustic waves are investigated in this model of plasma consisting of negatively charged dusts, cold ions and inertia less quantum effected electrons with the help of a typical energy integral. In this case, a new technique is applied formulating a differential equation to establish the energy integral in case of multi-component plasmas which is not possible in general. Dust-ion acoustic （DIA） compressive and rarefactive, supersonic and subsonic solitons of various amplitudes are established. The consideration of smaller order nonlinearity in support of the newly established quantum plasma model is observed to generate small amplitude solitons at the decrease of Mach number. The growths of soliton amplitudes and potential depths are found more sensitive to the density of quantum electrons. The small density ratio r（= 1 - f） with a little quantized electrons supplemented by the dust charges Zu and the in-deterministic new quantum parameter C2 are found responsible to finally support the generation of small amplitude solitons admissible for the model.

GaN-based LEDs for light communication

Rapid improvement in the efficiency of GaN-based LEDs not only speed up its applications for general illumination, but offer the possibilities for data transmission. This review is to provide an overview of current progresses of GaN-based LEDs for light communications. The modulation bandwidth of GaN-based LEDs has been first improved by optimizing the LED epilayer structures and the modulation bandwidth of 73 MHz was achieved at the driving current density of 40 A/cm2 by changing the multi-quantum well structures. After that, in order to increase the current density tolerance, different parallel flip-chip micro-LED arrays were fabricated. With a high injected current density of ~7900 A/cm2, a maximum modulation bandwidth of ~227 MHz was obtained with optical power greater than 30 mW. Besides the increase of carrier concentrations, the radiative recombination coefficient B was also enhanced by modifying the photon surrounding environment based on some novel nanostructures such as resonant cavity, surface plasmon, and photonic crystals. The optical 3 dB modulation bandwidth of GaN-based nanostructure LEDs with Ag nanoparticles was enhanced by 2 times compared with GaN-based nanostructure LEDs without Ag nanoparticles.Our results demonstrate that using the QW-SP coupling can effectively help to enhance the carrier spontaneous emission rate and also increase the modulation bandwidth for LEDs, especially for LEDs with high intrinsic IQE. In addition, we discuss the progress of the faster color conversion stimulated by GaN-based LEDs.

The effects of proton irradiation on the electrical properties of NbAlO/AlGaN/GaN MIS-HEMT

AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistors （MIS-HEMTs） with atomic layer deposited （ALD） NbA10 gate dielectric were investigated using 3 MeV proton irradiation at a fluence of 1015 p/crn2. It was found that the proton irradiation damage caused degradation in DC performance and a flatband voltage shift in the capacitance-voltage curve. Gate-drain conductance measurements indicated that new traps were introduced in GaN from the irradiation, and the trap densities increased from 1.18×10^12 cm-2.eV-1 to 1.82×10^12 cm-2.eV-1 in MIS-HEMTs after irradiation. However, these increases in trap densities caused by irradiation in MIS-HEMT are less than those in HEMT, which can be attributed to the protection of the A1GaN surface by the NbA10 dielectric layer.

Theoretical investigation of substitution and end-group effects on poly(p-phenylene vinylene)s

Semi-empirical AM1 and ZINDO/S,as well as density function theory(DFT)method B3LYP/6-31G(d)quantum chemical calculations were carried out to study the electronic structures and optical properties of poly(p-phenylene vinylene)derivatives(PPVs)with 10 and 11 phenylene rings in the backbone.The calculations suggest that the assembly of alternate incorporation of CN and alkoxy substituted phenylene rings in the PPV backbone could be a good way to construct organic semiconductors with low HOMO/LUMO energy band-gaps.The effect of the end-group on the electronic structures and optical properties of the conjugated polymer was investigated by the calculated UV-Vis and UPS spectra.It was demonstrated that the aldehyde and phosphate end-groups have limited effects on the photophysical properties in the UV-Visible range.

Energy loss of tens keV charged particles traveling in the hot dense carbon plasma

The energy loss of charged particles, including electrons, protons, and α-particles with tens keV initial energy E0, traveling in the hot dense carbon(C) plasma for densities from 2.281 to 22.81 g/cm3 and temperatures from 400 to 1500 eV is systematically and quantitatively studied by using the dimensional continuation method. The behaviors of different charged particles are readily distinguishable from each other. Firstly, because an ion is thousands times heavier than an electron, the penetration distance of the electron is much longer than that of proton and α-particle traveling in the plasma. Secondly, most energy of electron projectile with E0 < 100 keV deposits into the electron species of C plasma, while for the cases of proton and α-particle with E0 < 100 keV,about more than half energy transfers into the ion species of C plasma. A simple decreasing law of the penetration distance as a function of the plasma density is fitted, and different behaviors of each projectile particle can be clearly found from the fitted data.We believe that with the advanced progress of the present experimental technology, the findings shown here could be confirmed in ion-stopping experiments in the near future.