52 resultados para ESR DOSIMETRY
Resumo:
This study describes the utilization of deep eutectic solvents (DESs) based on the mixture of the N-methylacetamide (MAc) with a lithium salt (LiX, with X = bis[(trifluoromethyl)sulfonyl]imide, TFSI; hexafluorophosphate, PF6; or nitrate, NO3) as electrolytes for carbon-based supercapacitors at 80 °C. The investigated DESs were formulated by mixing a LiX with the MAc (at xLi = 0.25). All DESs show the typical eutectic characteristic with eutectic points localized in the temperature range from −85 to −52 °C. Using thermal properties measured by differential scanning calorimetry (DSC), solid–liquid equilibrium phase diagrams of investigated LiX–MAc mixtures were then depicted and also compared with those predicted by using the COSMOThermX software. However, the transport properties of selected DESs (such as the conductivity (σ) and the fluidity (η–1)) are not very interesting at ambient temperature, while by increasing the temperature up to 80 °C, these properties become more favorable for electrochemical applications, as shown by the calculated Walden products: w = ση–1 (mS cm–1 Pa–1 s–1) (7 < w < 16 at 25 °C and 513 < w < 649 at 80 °C). This “superionicity” behavior of selected DESs used as electrolytes explains their good cycling ability, which was determined herein by cyclic voltammetry and galvanostic charge–discharge methods, with high capacities up to 380 F g–1 at elevated voltage and temperature, i.e., ΔE = 2.8 V and 80 °C for the LiTFSI–MAc mixture at xLi = 0.25, for example. The electrochemical resistances ESR (equivalent series resistance) and EDR (equivalent diffusion resistance) evaluated using electrochemical impedance spectroscopy (EIS) measurements clearly demonstrate that according to the nature of anion, the mechanism of ions adsorption can be described by pure double-layer adsorption at the specific surface or by the insertion of desolvated ions into the ultramicropores of the activated carbon material. The insertion of lithium ions is observed by the presence of two reversible peaks in the CVs when the operating voltage exceeds 2 V. Finally, the efficiency and capacitance of symmetric AC/AC systems were then evaluated to show the imbalance carbon electrodes caused by important lithium insertion at the negative and by the saturation of the positive by anions, both mechanisms prevent in fact the system to be operational. Considering the promising properties, especially their cost, hazard, and risks of these DESs series, their introduction as safer electrolytes could represent an important challenge for the realization of environmentally friendly EDLCs operating at high temperature.
Resumo:
The synthesis and characterization of 2-dodecylcyclobutanone is described. Solvent extraction techniques for the isolation of this compound from irradiated minced chicken meat and its detection by selected ion monitoring are outlined. The compound was not detected in either raw or cooked nonirradiated minced chicken meat by the methods used, but its presence was confirmed in the irradiated samples. 2-Dodecyclobutanone was detectable for 20 days postirradiation. The dose (4.7 kGy) of irradiation applied was below the recommended upper limit for food (10 kGy), and this compound may have potential as a marker for irradiated chicken meat and for other foods containing lipid.
Resumo:
Stem cells are fundamental to the development of any tissue or organism via their ability to self-renew, which is aided by their unlimited proliferative capacity and their ability to produce fully differentiated offspring, often from multiple lineages. Stems cells are long lived and have the potential to accumulate mutations, including in response to radiation exposure. It is thought that stem cells have the potential to be induced into a cancer stem cell phenotype and that these may play an important role in resistance to radiotherapy. For radiation-induced carcinogenesis, the role of targeted and non-targeted effects is unclear with tissue or origin being important. Studies of genomic instability and bystander responses have shown consistent effects in haematopoietic models. Several models of radiation have predicted that stem cells play an important role in tumour initiation and that bystander responses could play a role in proliferation and self-renewal.
Resumo:
PURPOSE: To evaluate the permanent prostate brachytherapy (PPB) learning curve using postimplant multisector dosimetric analysis and to assess the correlation between sector -specific dosimetry and patient-reported outcome measures (PROMs).
METHODS AND METHODS: First 200 patients treated with (125)I PPB monotherapy (145 Gy) at a single institution were assessed. Postimplant dosimetry (PID) using CT was evaluated for whole prostate (global) and 12 sectors, assessing minimum dose to 90% of prostate (D90) and dose to 0.1 cm(3) of rectum (D0.1cc). Global and sector PID results were evaluated to investigate changes in D90 with case number. Urinary and bowel PROMs were assessed using the International Prostate Symptom Score and the Expanded Prostate Cancer Index Composite questionnaire. The correlation between global and individual sector PID and urinary/bowel PROMs was also evaluated.
RESULTS: Linear regression confirmed a significant improvement in global D90 with case number (r(2) = 0.20; p = 0.001) at a rate of 0.11 Gy/case. Postimplant D90 of base sectors increased at a rate of 0.11-0.15 Gy/case (p = 0.0001) and matched global improvement. The regression lines of midgland and apex sectors were significantly different from global D90 (p = 0.01). Posterior midgland sectors showed a significant reduction in D90 with case number at a rate of 0.13-0.19 Gy/case (p = 0.01). Dose to posterior midgland sectors correlated with rectal D0.1cc dose but not bowel PROMs. Dose to posterior midgland sectors correlated with urinary International Prostate Symptom Score change, which was not apparent when global D90 alone was considered.
CONCLUSIONS: Sector analysis provided increased spatial information regarding the PPB learning curve. Furthermore, sector analysis correlated with urinary PROMs and rectal dose.
Resumo:
The use of high linear energy transfer radiations in the form of carbon ions in heavy ion beam lines or alpha particles in new radionuclide treatments has increased substantially over the past decade and will continue to do so due to the favourable dose distributions they can offer versus conventional therapies. Previously it has been shown that exposure to heavy ions induces pan-nuclear phosphorylation of several DNA repair proteins such as H2AX and ATM in vitro. Here we describe similar effects of alpha particles on ex vivo irradiated primary human peripheral blood lymphocytes. Following alpha particle irradiation pan-nuclear phosphorylation of H2AX and ATM, but not DNA-PK and 53BP1, was observed throughout the nucleus. Inhibition of ATM, but not DNA-PK, resulted in the loss of pan-nuclear phosphorylation of H2AX in alpha particle irradiated lymphocytes. Pan-nuclear gamma-H2AX signal was rapidly lost over 24h at a much greater rate than foci loss. Surprisingly, pan-nuclear gamma-H2AX intensity was not dependent on the number of alpha particle induced double strand breaks, rather the number of alpha particles which had traversed the cell nucleus. This distinct fluence dependent damage signature of particle radiation is important in both the fields of radioprotection and clinical oncology in determining radionuclide biological dosimetry and may be indicative of patient response to new radionuclide cancer therapies.
Resumo:
OBJECTIVE: This work investigates the delivery accuracy of different Varian linear accelerator models using log-file derived MLC RMS values.
METHODS: Seven centres independently created a plan on the same virtual phantom using their own planning system and the log files were analysed following delivery of the plan in each centre to assess MLC positioning accuracy. A single standard plan was also delivered by seven centres to remove variations in complexity and the log files were analysed for Varian TrueBeams and Clinacs (2300IX or 2100CD models).
RESULTS: Varian TrueBeam accelerators had better MLC positioning accuracy (<1.0mm) than the 2300IX (<2.5mm) following delivery of the plans created by each centre and also the standard plan. In one case log files provided evidence that reduced delivery accuracy was not associated with the linear accelerator model but was due to planning issues.
CONCLUSIONS: Log files are useful in identifying differences between linear accelerator models, and isolate errors during end-to-end testing in VMAT audits. Log file analysis can rapidly eliminate the machine delivery from the process and divert attention with confidence to other aspects. Advances in Knowledge: Log file evaluation was shown to be an effective method to rapidly verify satisfactory treatment delivery when a dosimetric evaluation fails during end-to-end dosimetry audits. MLC RMS values for Varian TrueBeams were shown to be much smaller than Varian Clinacs for VMAT deliveries.
