Microdosimetric characteristics of the clinical proton beams at JINR,Dubna

High-energy proton radiotherapy beams give rise to secondary heavy charged particles with elevated linear energy transfer (LET), which contribute to the dose in a patient. This contribution to the characteristics of radiotherapy proton beams was experimentally studied by means of a LET spectrometer based on a track detector. The spectrometer permits LET spectra to be established in the region above 10 keV.micron-1 in tissue. Sets of track detectors were exposed in the various depths of a phantom irradiated with protons of two energies, 150 and 205 MeV. It was observed that the contribution of particles with the values of LET mentioned increases with the depth, representing from about 2 (at the surface) up to few tens% close to Bragg peak region of the total dose. There, some of primary protons contribute also above 10 keV.micron-1. Using the 'biological weighted function' proposed, the clinical RBE was calculated, it could approach 1.3. This effect has to be taken into account during the clinical beam production and the radiotherapy.     

Microdosimetric characteristics of proton beams from 50 keV to 200 MeV

Proton beams are of growing interest for radiation therapy due to their special physical and radiobiological properties. Microdosimetric characteristics of proton beams have strong influence on the relative biological effectiveness for each biological system. This study focused on the microdosimetric characteristics of monoenergetic protons from 50 keV to 200 MeV. Monte Carlo techniques were used to simulate track segments of protons in water. Dose mean lineal energies were derived to characterise proton beams with changing kinetic energy and changing radiation qualities at various depths and within spread-out Bragg peaks of clinic interests.     

Microdosimetric analysis for high LET radiation

For short range high linear energy transfer (LET) radiation therapy the biological effects are strongly affected by the heterogeneity of the specific energy (z) distribution delivered to tumour cells. Three-dimensional (3-D) dosimetry information at the cellular level is required for this study. An ideal approach would be the reconstruction of the cell and the radiation source microdistribution from sequential autoradiographic sections, which is, however, not a practical solution. In this paper, a novel microdosimetry analysis method, which obtains the specific energy (z) distribution directly from the morphological information in individual autoradiographic sections, is applied to human glioblastoma multifore (GBM) and normal brain tissue specimens in boron neutron capture therapy. The results are consistent with Monte Carlo simulation and demonstrate a uniform radiation source distribution in both GBM and normal brain tissues. We also hypothesise a biophysical model based on specific energy for survival analysis. The specific energy distributions to cell nuclei were calculated with a uniform radiation source distribution. By combining this microdosimetric analysis with measured cell survival data at the low dose region, a cell survival curve at high doses is predicted, which is consistent with the commonly used simple exponential curve model for high LET radiation.     

Microdosimetric measurements for neutron-absorbed dose determination during proton therapy

This work presents microdosimetric measurements performed at the Midwest Proton Radiotherapy Institute in Bloomington, Indiana, USA. The measurements were done simulating clinical setups with a water phantom and for a variety of stopping targets. The water phantom was irradiated by a proton spread out Bragg peak (SOBP) and by a proton pencil beam. Stopping target measurements were performed only for the pencil beam. The targets used were made of polyethylene, brass and lead. The objective of this work was to determine the neutron-absorbed dose for a passive and active proton therapy delivery, and for the interactions of the proton beam with materials typically in the beam line of a proton therapy treatment nozzle. Neutron doses were found to be higher at 45° and 90° from the beam direction for the SOBP configuration by a factor of 1.1 and 1.3, respectively, compared with the pencil beam. Meanwhile, the pencil beam configuration produced neutron-absorbed doses 2.2 times higher at 0° than the SOBP. For stopping targets, lead was found to dominate the neutron-absorbed dose for most angles due to a large production of low-energy neutrons emitted isotropically.     

Microdosimetric investigation at the therapeutic proton beam facility of CATANA

Proton beams (62 Mev) are used by the Laboratori Nazionali del Sud of the Italian Institute of Nuclear Physics to treat eye melanoma tumours at the therapeutic facility called CATANA. A cylindrical slim tissue-equivalent proportional counter (TEPC) of 2.7 mm external diameter has been used to compare the radiation quality of two spread-out Bragg peaks (SOBP) at the CATANA proton beam.     

短切炭纤维增强沥青基C/C复合材料的组织特征

利用新型、高效的模压半炭化成型工艺，在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料制品，并借助光学显做镜和扫描电镜对其微观组织和断口形貌进行了观察。通过分析，解释了短切炭纤维增强沥青基C／C复合材料中炭纤维损伤的形成机制，提出了作为增强体相的短切炭纤维和焦炭颗粒与基体炭之间独特的界而结构模型。研究还表明：复合材料中明显存在着基体相和颗粒相一基体相的显微结构不仅呈层片状，而且层片状的结构好像数层桔子皮，将颗粒相包裹起来，这种“桔皮包裹”式的结构与炭纤维表面的POG结构基本相似。     

Vibration damping characteristics of carbon fiber-reinforced composites containing multi-walled carbon nanotubes

Vibration damping characteristic of nanocomposites and carbon fiber reinforced polymer composites (CFRPs) containing multiwall carbon nanotubes (CNTs) have been studied using the free and forced vibration tests. Several vibration parameters are varied to characterize the damping behavior in different amplitudes, natural frequencies and vibration modes. The damping ratio of the hybrid composites is enhanced with the addition of CNTs, which is attributed to sliding at the CNT-matrix interfaces. The damping ratio is dependent on the amplitude as a result of the random orientation of CNTs in the epoxy matrix. The natural frequency shows negligible influence on the damping properties. The forced vibration test indicates that the damping ratios of the CFRP composites increase with increasing CNT content in both the 1st and 2nd vibration modes. The CNT-epoxy nanocomposites also show similar increasing trends of damping ratio with CNT content, indicating the enhanced damping property of CFRPs arising mainly from the improved damping property of the modified matrix. The dynamic mechanical analysis further confirms that the CNTs have a strong influence on the composites damping properties. Both the dynamic loss modulus and loss factor of the nanocomposites and the corresponding CFRPs show consistent increases with the addition of CNTs, an indication of enhanced damping performance.     

Microdosimetric comparison of scanned and conventional proton beams used in radiation therapy

Multiple groups have hypothesised that the use of scanning beams in proton therapy will reduce the neutron component of secondary radiation in comparison with conventional methods with a corresponding reduction in risks of radiation-induced cancers. Loma Linda University Medical Center (LLUMC) has had FDA marketing clearance for scanning beams since 1988 and an experimental scanning beam has been available at the LLUMC proton facility since 2001. The facility has a dedicated research room with a scanning beam and fast switching that allows its use during patient treatments. Dosimetric measurements and microdosimetric distributions for a scanned beam are presented and compared with beams produced with the conventional methods presently used in proton therapy.     

Adsorptive and structural characteristics of carbon sorbents

This paper describes the adsorptive, structural, and textural characteristics of carbon sorbents of various origins: OU-A activated charcoal powder (unmodified and modified with a cellulose polyelectrolyte), AUT-MI fibrous activated carbon, and expanded graphite intercalated with sulfuric acid. In accordance with their pore structure parameters and specific surface area, the highest adsorption capacity for water-soluble markers (iodine and methylene blue) and anionic surfactants is offered by the activated charcoal and fibrous carbon. Surface modification with an anionic polymer increases the adsorption of positively charged methylene blue molecules.     

炭毡传感特性研究

通过对炭毡进行拉伸、循环加载等试验,研究了其电阻随变形而改变的规律.结果表明:在弹性范围内,拉伸加载时,电阻值呈可逆性增加;卸载时,电阻值则为可逆性减小.炭毡具有良好的电阻-变形敏感性,且有满意的线性度和良好的重复性.炭毡通电处理后,其电阻值更加稳定,在循环载荷下,重复性比未通电前好.炭毡作为一种新型的传感元件,可用于监测工程结构的服役状况.     

Flow characteristics of carbon fibre moulding compounds

This paper presents the development of a low-cost carbon fibre moulding compound using an automated spray deposition process. Directed Fibre Compounding (DFC) is used to produce charge packs directly from low cost carbon fibre tows and liquid epoxy resin. A range of material and process related parameters have been studied to understand their influence on the level of macroscopic charge flow, in an attempt to produce a carbon fibre moulding compound with similar flow characteristics to conventional glass fibre SMCs.Charge packs covering just 40% of the mould can be effectively used to process DFC, without detrimentally affecting void content, fibre distribution and mechanical properties. Tensile stiffness and strength values of 36 GPa and 320 MPa are reported for isotropic materials (100% charge coverage), which increase to 46 GPa and 408 MPa with flow induced alignment (50% charge coverage) at 50% fibre volume fraction.     

Hygrothermal characteristics of carbon fibre reinforced plastics

Journal of Materials Science - The following account describes investigations of the moisture absorption characteristics of specimens prepared from a unidirentionally reinfonced sheet of carbon...     

I-V characteristics of carbon black-loaded crystalline polyethylene

The I-V characteristics of carbon black-loaded crystalline polyethylene were investigated at room temperature and at few degrees above the melting temperature, T _m. The material was chemically cross-linked using silane. It had a large carbon black content of 28 parts per hundred by weight and displayed a strong positive temperature coefficient of resistance (PTCR) effect with a resistivity jump of four orders of magnitude. Logarithmic current-voltage plots were found to be linear with unity slopes at temperatures above and below T _m, indicating good ohmic behaviour. This is in contrast with previous theories which explain the PTCR effect on the basis of electron tunnelling as the current conduction mechanism. A new model capable of explaining both the PTCR effect and the steep reduction in resistance above T _m is presented, according to which the PTCR effect is the result of the co-operative effect of changes in crystallinity and volume expansion.     

碳纳米管与活性炭超级离子电容器的频率响应

分别采用碳纳米管和活性炭作用超级离子电容器的电极材料，应用交流阻抗频谱法，研究了两类超级离子电容器的频率响应特性。结果表明，用碳纳米管作电极，超级离子电容器地频率250mHz以下出现“电荷饱和”；而用活性炭作电极，超级离子电容器在频率为100mHz时仍未出现“电荷饱和”，说明碳纳米管超级离子电容器的频率响应特性优于活性炭超级离子电容器的频率响应特性，但是上述两类超级离子电容器的频率响应特性均比传统介质电容器的频率响应特性差。