Cellular communication and “non-targeted effects”: Modelling approaches

During the last decade, a large number of experimental studies on the so-called “non-targeted effects”, in particular bystander effects, outlined that cellular communication plays a significant role in the pathways leading to radiobiological damage. Although it is known that two main types of cellular communication (i.e. via gap junctions and/or molecular messengers diffusing in the extra-cellular environment, such as cytokines, NO etc.) play a major role, it is of utmost importance to better understand the underlying mechanisms, and how such mechanisms can be modulated by ionizing radiation. Though the “final” goal is of course to elucidate the in vivo scenario, in the meanwhile also in vitro studies can provide useful insights. In the present paper we will discuss key issues on the mechanisms underlying non-targeted effects and cell communication, for which theoretical models and simulation codes can be of great help. In this framework, we will present in detail three literature models, as well as an approach under development at the University of Pavia. More specifically, we will first focus on a version of the “State-Vector Model” including bystander-induced apoptosis of initiated cells, which was successfully fitted to in vitro data on neoplastic transformation supporting the hypothesis of a protective bystander effect mediated by apoptosis. The second analyzed model, focusing on the kinetics of bystander effects in 3D tissues, was successfully fitted to data on bystander damage in an artificial 3D skin system, indicating a signal range of the order of 0.7–1 mm. A third model for bystander effect, taking into account of spatial location, cell killing and repopulation, showed dose–response curves increasing approximately linearly at low dose rates but quickly flattening out for higher dose rates, also predicting an effect augmentation following dose fractionation. Concerning the Pavia approach, which can model the release, diffusion and depletion/degradation of candidate signals (e.g. cytokines) travelling in the extra-cellular environment, the good agreement with ad hoc experimental data obtained in our laboratory validated the adopted approach, which in the future can be applied also to other candidate signals.     

Monte Carlo calibration of the response of the University of Chicago’s Cosmic Ray Nuclei Experiment (CRNE) on IMP-8 to electrons above 0.5 MeV

Modern instrument-simulation techniques offer the possibility of increasing the scientific yield from archival space datasets. In this paper, we report on a simulation of the electron response of the University of Chicago’s Cosmic Ray Nuclei Experiment (CRNE) instrument on the IMP-8 satellite. IMP-8/CRNE returned data from 1973 to 2006. The CRNE particle telescope was designed to measure the isotopic composition of Galactic cosmic-ray (GCR) nuclei and has also been used in many studies of protons and ions above 10 MeV/nucleon from solar energetic particle (SEP) events. But CRNE also functions as a highly-capable detector for solar electrons above 0.5 MeV, an energy range that has not been extensively studied. Utilization of the CRNE electron data has heretofore been limited by the fact that CRNE was never calibrated for electrons. We have therefore used the GEANT4 Monte Carlo simulation package to model the CRNE response to electrons and (separately) protons for multiple energies and incident angles. The results were used to compute the energy- and angle-dependence of the effective area and the energy-dependence of the geometric factor. The response to protons, which was already well understood, was used to verify the mass model, the simulation settings, and the post-processing software. Our simulation of the IMP-8/CRNE electron response now allows analysis of hundreds of relativistic solar electron events observed by CRNE over the years, including studies of evolution of electron energy spectra with high time resolution. We show examples of these results and briefly discuss potential applications to future scientific investigations.     

New He neutron monitor for Chilean Cosmic-Ray Observatories from the Altiplanic zone to the Antarctic zone

We present the results of three years of continuous operations and the principal characteristics of our new ³He neutron monitors installed in the Chilean Network of Cosmic-Ray Observatories. During the years 2004 and 2005, we began the construction of this International Geophysical Year (IGY)-type ³He neutron monitor, with the intention of replacing the older proportional tubes of the BF₃. These new monitors are installed in stations at locations ranging from the near-equatorial zone to the Antarctic zone. As a reference system, we used our own BF₃ neutron monitors and previously complemented the collected data with a Monte Carlo simulation for the proton-yield function response of the Putre neutron monitor. Herein, we present for the first time the data obtained from our new high-mountain observatory located in the Altiplanic zone.     

铁磁性纳米线阵列的偏差对磁性的影响

用蒙特卡洛方法对纳米线阵列磁滞回线进行模拟,研究了纳米线排列、长度和直径的偏差对纳米线阵列整体磁学性质的影响。研究结果表明,纳米线位置的标准偏差引起了矫顽力和磁化率降低;长度的标准偏差则仅仅引起饱和磁化强度的增大和剩余磁化强度的减小,而对矫顽力没有影响;直径的的标准偏差对纳米线阵列产生了比较复杂的影响。     

基于贝叶斯模型的长码DS-CDMA信号扩频码与信息序列联合估计

 针对长码直接序列扩频码分多址(DS-CDMA)信号的盲解扩,在信号模型分析的基础上,提出了一种基于可逆跳跃的马尔可夫链蒙特卡罗(RJ-MCMC)扩频码和信息序列联合估计算法。该算法分别对建立的联合后验分布模型进行迭代抽样,并有效地在不同维数的子空间中跳转,从而构造一条马尔可夫链,使其平稳分布为待估参数的后验分布,最终拼接得到每个用户的完整扩频序列和信息序列估计。仿真结果表明:该方法在迭代二十几步时达到收敛;并且在功率相同和不同条件下,当信噪比(SNR)大于-9 dB时,估计序列与真实序列的相似度均超过0.95,信息序列的误码率低于0.01;同时算法对不同用户个数和不同调制样式具有较强的适应性,与Fast-ICA算法相比,估计性能平均提高了约3 dB。     

自适应滤波对提高光电吊舱目标定位精度的研究

针对机载光电吊舱目标定位精度的问题,提出了一种采用LMS自适应噪声抵消技术来提高载机姿态角精度,从而提高目标定位精度的滤波方法。文章介绍了自适应滤波器噪声抵消的工作原理和LMS算法,并给出了LMS算法的Matlab仿真实现的滤波结果,通过分析仿真结果验证了该方法的有效性,并根据蒙特卡罗法计算1000次,得出该方法使经度误差减少了13.2%,纬度误差减少了10.3%,高度误差减少了15.8%。     

交会接近轨迹的闭环斜滑控制算法研究

为了矫正追踪航天器相对接近轨迹的偏离,实现交会轨迹的主动安全控制,在开环斜滑算法的基础上提出了闭环斜滑主动控制方法,包括轨迹控制的闭环斜滑算法和终端控制的闭环斜滑算法。利用某近距离交会接近问题,采用MonteCarlo（蒙特卡洛）打靶仿真,分析比较了开环斜滑算法和2种闭环斜滑算法。结果表明,闭环控制终端偏离明显小于开环情况,同时在较短时间内以较小的速度增量实现了终端状态控制,并且轨迹控制的闭环斜滑算法控制精度小于终端控制算法。     

微波等离子推力器真空羽流模拟计算

粒子节点－直接模拟蒙特卡罗法（DSMC）是求解稀薄气体流动的数值模拟方法，采用轴对称硬球模型、随机取样频率法对微波等离子推力器（MPT）的真空羽流进行了数值模拟计算，为了提高计算效率和节省计算机内存，采用了随机取样频率法（RSF）和加权技术。对MPT真空羽流的浓度、速度和温度分布进行了计算，并对羽流污染进行了分析。计算结果对以后MPT真空羽流场测试和航天器一体化设计提供了参考。     

固体推进剂贮存可靠寿命的Monte Carlo仿真计算

用Monte carlo统计模拟方法对火箭发动机固体推进剂随环境温度变化的力学性能进行了分析,提出了力学性能的可靠寿命仿真计算的方法,并对延伸率的老化可靠寿命进行了计算。     

主动雷达型空空导弹截获概率分析

误差是影响主动雷达型中远距空空导弹武器系统截获得性能的重要因素，通过引入截获目标时间的经验分布函数，提出了基于蒙特卡洛仿真计算导弹截获概率，以及定量评估误差对截获概率影响的方法。仿真结果表明，该方法能够有效分析误差因素对导弹截获得概率的影响，为武器系统误差配置提供计算参考。