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Qingfeng Wu Qiang Li Xiaodong Jin Xinguo Liu Zhongying Dai 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(2):153-158
Although radiation-induced bystander effects have been well documented in a variety of biological systems, whether irradiated cells have the ability to generate bystander signaling persistently is still unclear and the clinical relevance of bystander effects in radiotherapy remains to be elucidated. This study examines tumor cellular bystander response to autologous medium from cell culture irradiated with high-linear energy transfer (LET) heavy ions at a therapeutically relevant dose in terms of clonogenic cell survival. In vitro experiments were performed using human hepatoma HepG2 cell line exposed to 100 keV/μm carbon ions at a dose of 2 Gy. Two different periods (2 and 12 h) after irradiation, irradiated cell conditioned medium (ICCM) and replenished fresh medium were harvested and then transferred to unirradiated bystander cells. Cellular bystander responses were measured with the different medium transfer protocols. Significant higher survival fractions of unirradiated cells receiving the media from the irradiated cultures at the different times post-irradiation than those of the control were observed. Even replenishing fresh medium for unirradiated cells which had been exposed to the ICCM for 12 h could not prevent the bystander cells from the increased survival fraction. These results suggest that the irradiated cells could release unidentified signal factor(s), which induced the increase in survival fraction for the unirradiated bystander cells, into the media sustainedly and the carbon ions triggered a cascade of signaling events in the irradiated cells rather than secreting the soluble signal factor(s) just at a short period after irradiation. Based on the observations in this study, the importance of bystander effect in clinical radiotherapy was discussed and incorporating the bystander effect into the current radiobiological models, which are applicable to heavy ion radiotherapy, is needed urgently. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(3):224-232
In order to ascertain the accuracy and applicability of the method which was developed in the previous paper for evaluating the dose equivalent in a single-burst and mixed radiation field, a comparison with two other ones has been carried out. One is based on the measurement of the neutron energy spectrum with TOF system and the separate measurement of the absorbed doses with twin chambers. In the other, a tissue-equivalent proportional counter is used for measuring the LET distribution of the absorbed dose. The average quality factor has been evaluated in a pulsed and mixed field generated by an electron linear accelerator. A good agreement has been found among these methods. A problem about the experimental determination of the dose equivalent index has also been discussed. It was pointed out that the average quality factor as a function of the depth in tissue could be regarded as characteristic of the mixed radiation field. 相似文献
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本文从综合考虑ODMRP协议转发组的有效性和健壮性出发,提出了一种基于LET(Link Expiration Time)预测和转发组成员数的组播路由协议LETFG-ODMRP(Optimal Multicast Protocol with LET and FGs based on ODMRP).LETFG-ODMRP通过对网络中传输路径保持连接时间LET的预测,得知路径的稳定度,然后结合考虑转发组成员数,建立一种新的路由选择标准PathMetric.采用此种路由选择标准,LETFG-ODMRP可调节权重在候选路由集中选择稳定或有效的传输路径构成转发组.模拟仿真结果证实LETFG-ODMRP提高了组播协议健壮性、有效性及自适应能力. 相似文献
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对LiF热释光探测器(TLD)的响应对致电离粒子的LET的依赖性进行了初步实验研究。用作实验研究的粒子主要是中子,包括热中子和由^7Li(p,n)^7Be、T(p,n)^3He核反应生成的中能中子、快中子(0.018-0.945MeV)及14MeV中子。实验结果表明:LiF(Mg、Cu、P)-TLD的响应对致电离粒子LET的依赖性是显著的。对于较高能量的中子,由LiF-TLD产生的热释光量仅与^6Li、^7Li在LiF-TLD中导致的吸收剂量相对应,这与某些文献的报道相一致。 相似文献
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D. Zhou E. Semones R. Gaza S. Johnson N. Zapp M. Weyland 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2007,580(3):1283-1289
Radiation in low Earth orbit (LEO) is mainly from Galactic Cosmic Rays (GCR), solar energetic particles and particles in South Atlantic Anomaly (SAA). These particles’ radiation impact to astronauts depends strongly on the particles’ linear energy transfer (LET) and is dominated by high LET radiation. It is important to investigate the LET spectrum for the radiation field and the influence of radiation on astronauts. At present, the best active dosimeters used for all LET are the tissue equivalent proportional counter (TEPC) and silicon detectors; the best passive dosimeters are thermoluminescence dosimeters (TLDs) or optically stimulated luminescence dosimeters (OSLDs) for low LET and CR-39 plastic nuclear track detectors (PNTDs) for high LET. TEPC, CR-39 PNTDs, TLDs and OSLDs were used to investigate the radiation for space mission Expedition 12 (ISS-11S) in LEO. LET spectra and radiation quantities (fluence, absorbed dose, dose equivalent and quality factor) were measured for the mission with these different dosimeters. This paper introduces the operation principles for these dosimeters, describes the method to combine the results measured by CR-39 PNTDs and TLDs/OSLDs, presents the experimental LET spectra and the radiation quantities. 相似文献
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移动网络结构日趋复杂,网络场景多样化,影响用户体验的因素也越来越难以判断。结合SEQ平台系统,通过调整上行调度算法参数中"上行HARQ最大传输次数"参数,增大UE配置的最大传输次数,提高数据包传输成功率,降低信道编码率,提高解码效果,以降低HTTP页面打开时延。通过试验区优化验证,该措施能有效降低HTTP页面的各项时延。 相似文献
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S. Vinodh Kumar B. Ghadei P. K. Jal K. Dey J. B. M. Krishna A. Saha 《应用聚合物科学杂志》2006,101(3):1591-1597
Polyethersulphone (PES) was irradiated with 4 MeV proton, 3.6 MeV C+, and 145 MeV Ne6+ ions at different ion fluences. The linear energy transfer dependence on ion‐induced spectral changes was analyzed by ultraviolet–visible, Fourier transform infrared spectroscopy and fluorescence spectroscopy. The gradual red shift with the increase in optical absorption was observed in the region of 350–500 nm for proton and 400–800 nm for C+ and Ne6+ ions irradiated PES. The gradual shift in absorption may be attributed to the formation of carbonaceous clusters. The gradual decrease in optical band gap indicates increase in cluster sizes. When PES was irradiated with protons, loss in fluorescence emission intensity at 440 nm was observed, although there was no change in spectral shape. In contrast, C+ and Ne6+ ion irradiated PES showed blue shift with concomitant loss in intensity and the formation of new peak at 575 nm. In fact, heavier ions are found to be more effective in inducing physicochemical modifications in PES. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1591–1597, 2006 相似文献
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J. Pearson 《溶剂提取与离子交换》2013,31(6):584-600
Tributyl Phosphate (TBP), used in chemical separation processes for used nuclear fuel, is susceptible to radiolysis causing losses in process performance. We have studied its degradation by exposing dry 1M TBP/n-dodecane solutions to gamma radiation from a cesium-137 source and in a mix of low and high linear energy transfer (LET) radiation by irradiating samples in the UC Irvine TRIGA® reactor and utilizing the 10B(n,α)7Li reaction. In a 1 M solution of TBP in n-dodecane the degradation of TBP (G?TBP) was found to be 0.36 and 0.14 μmol/J for low and high LET radiation, respectively. The formation of dibutyl phosphoric acid, DBP, (G+DBP) in this solution was found to be 0.18 and 0.047 μmol/J for low and high LET radiation, respectively. In samples exposed to low LET as well as a mix of low and high LET a variety of TBP degradation products containing phosphorus were observed indicating that other degradation products than DBP and the monobutyl diacid (MBP) were formed. Our results for both low and high LET radiation compare well with previous studies on these systems indicating that high LET degrades TBP to a lesser extent than gamma radiation. Available data for high LET is not as abundant as for low LET making such comparisons challenging. Nevertheless, our method yields a value for G+DBP that agrees well with previous alpha radiolysis studies indicating that our method shows promise for studying high LET radiolysis in liquid-liquid extraction systems. 相似文献