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[en] Due to its low fractionation sensitivity, also known as “alpha/beta ratio,” in relation to its surrounding organs at risk, prostate cancer is predestined for hypofractionated radiation schedules assuming an increased therapeutic ratio compared to normofractionated regimens. While moderate hypofractionation (2.2–4 Gy) has been proven to be non-inferior to normal fractionation in several large randomized trials for localized prostate cancer, level I evidence for ultrahypofractionation (>4 Gy) was lacking until recently. An accumulating body of non-randomized evidence has recently been strengthened by the publication of two randomized studies comparing ultrahypofractionation with a normofractionated schedule, i.e., the Scandinavian HYPO-RT trial by Widmark et al. and the first toxicity results of the PACE‑B trial. In this review, we aim to give a brief overview of the current evidence of ultrahypofractionation, make an overall assessment of the level of evidence, and provide recommendations and requirements that should be followed before introducing ultrahypofractionation into routine clinical use.
[en] Mediastinal radiotherapy (RT), especially when combined with bleomycin, may result in substantial pulmonary morbidity and mortality. The use of modern RT techniques like intensity-modulated radiotherapy (IMRT) is gaining interest to spare organs at risk. We evaluated 27 patients who underwent RT for Hodgkin’s lymphoma between 2009 and 2013 at our institution. For each patient, three different treatment plans for a 30-Gy involved-field RT (IFRT) were created (anterior-posterior-posterior-anterior setup [APPA], 5‑field IMRT, and 7‑field IMRT) and analyzed concerning their inherent “normal tissue complication probability” (NTCP) for pneumonitis and secondary pulmonary malignancy. The comparison of different radiation techniques showed a significant difference in favor of standard APPA (p < 0.01). The risk of lung toxicity was significantly higher in plans using 7‑field IMRT than in plans using 5‑field IMRT. The absolute juxtaposition showed an increase in risk for radiation pneumonitis of 1% for plans using 5‑field IMRT over APPA according to QUANTEC (Quantitative Analyses of Normal Tissue Effects in the Clinic) parameters (Burman: 0.15%) and 2.6% when using 7‑field IMRT over APPA (Burman: 0.7%) as well as 1.6% when using 7‑field IMRT over 5‑field IMRT (Burman: 0.6%). Further analysis showed an increase in risk for secondary pulmonary malignancies to be statistically significant (p < 0.01); mean induction probability for pulmonary malignoma was 0.1% higher in plans using 5‑field IMRT than APPA and 0.19% higher in plans using 7‑field IMRT than APPA as well as 0.09% higher in plans using 7‑field IMRT than 5‑field IMRT. During a median follow-up period of 65 months (95% confidence interval: 53.8–76.2 months), only one patient developed radiation-induced pneumonitis. No secondary pulmonary malignancies have been detected to date. Radiation-induced lung toxicity is rare after treatment for Hodgkin lymphoma but may be influenced significantly by the RT technique used. In this study, APPA RT plans demonstrated a decrease in potential radiation pneumonitis and pulmonary malignancies. Biological planning using NTCP may have the potential to define personalized RT strategies.
[en] A 300 MeV electron linac is constructed in 1967 at Tohoku University for advanced research on nuclear physics, radiochemistry and neutron science. A very high beam repetition rate of 300 pps is employed to achieve a duty factor of more than 0.1%. Although substantial parts of the linac sadly collapsed as a result of the Great East Japan earthquake occurred in 2011, the low-energy part of the linac still supplies high-intensity beams. To expand current research activities, the introduction of a versatile accelerator system that employs superconducting radiofrequency (SRF) cavities have been considered. Because the low surface resistance on these SRF cavities decreases the power dissipated to the cavity walls, the beams can be accelerated with a duty factor as high as 100%. However, the SRF cavities, which are manufactured from niobium (Nb), need to be operated at cryogenic temperatures of 2 K with a considerably large cryogenic system. Recently it is pointed out that the large heat load could be greatly lowered by replacing the standard Nb cavities with those coated with high-temperature superconductors. The possibility of developing simple and low-cost SRF accelerators based on conduction cooling with a 4 K refrigerator system is anticipated. (© 2020 Wiley‐VCH GmbH)
[en] Recently, Fe-based superconductors have shown promising properties of high critical temperature and high upper critical fields, which are prerequisites for applications in high-field magnets. Critical temperature, T, is an important characteristic correlated with crystallographic and electronic structures. By doping with foreign ions in the crystal structure, T can be modified, which however requires significant manpower and resources for materials synthesis and characterizations. In this study, we develop the Gaussian process regression model to predict T of doped Fe-based superconductors based on structural and topological parameters, including the lattice constants, volume, and bonding parameter topological index H. The model is stable and accurate, contributing to fast T estimations.
[en] HANARO has been actively utilized since attaining first criticality in 1995. In 2009, the cold neutron source was installed inside the reflector tank. The main utilization fields of HANARO are neutron beam applications, nuclear fuel and material test, radioisotope production, neutron activation analysis and neutron transmutation doping. After the Fukushima accident, HANARO had been requested to evaluate the seismic margin for the reactor’s main components, and the seismic margin assessment led to the reinforcement of HANARO’s wall. In December 2017, HANARO started operating after overcoming many issues for about a 3 year-shutdown. For the period of long-term shutdown, the circumstances surrounding HANARO, such as research reactor regulation and new research reactor construction project, has been drastically changed. To meet the expectations of HANARO to produce world-class science and to respond to the rapidly changing environment, a strategic plan for HANARO was prepared, and 4 missions were re-established. They are 1) advancement of neutron science and technology, 2) not only meeting but also creating the needs of the industry, 3) contributions to the national society issues, and 4) safe and stable operation of the facility. To achieve the missions, all members involved in the HANARO shared their same perception that the stable operation of HANARO is the most important. HANARO is trying hard to give the confidence for its sustainability and excellence through the various activities. (author)
[en] The well-known yttrium founded polycrystalline superconductors named cuprates with high critical temperature (TC) and arrangement of pure YBaCuO (shortened-Y358) and YBaCuO (shortened-Y123) accompany with various (0.00, 0.40, and 0.50 wt%) nanoparticles Tin-doped (SnO2) composites were manufactured by solid-state response method. The X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX) apparatuses were used to analyse the micro-features and morphological structures of the synthetic mixtures. The XRD associated with the pure Y358 compares to the Y123 specimen shown alike structures for both samples with approximately three times longer lattice parameter c. The SEM images related to the pure compounds exhibited different intergrowth crystals from the doped ones. The EDX diagrams display all the compositional components in appropriate quantities. Electrical resistivity ρ(T) measurements were performed to evaluate not only superconducting transition temperatures (T), (T) and (T) but also critical parameters such as critical magnetic field B(0) and critical current density J(0) in pure and SnO2 added YBCO specimens. The data correlated to Y123 and Y358 compounds shown that rising SnO2 nanoparticle insertion into these samples triggered the enhancement of critical parameters which describes better flux pinning. Comparing these data regarding application and superconducting properties point of view confirmed that the sample Y358 with 0.50 wt% nano-sized (SnO2) inclusion is superior among them.
[en] Turkey’s desire to gain knowledge on the peaceful uses of nuclear technologies led to the signing of an ‘Atoms for Peace’ agreement with the United States of America (USA) in May 1955. After this cooperation Agreement, Turkey established the Atomic Energy Commission as the nuclear regulatory body with Law no. 6821 on 27 August 1956 and started the studies to build a nuclear research centre and a research reactor and become one of the founding members of IAEA in 1957. Turkey's first research reactor TR-1 reached criticality on 6 February 1962 in Çekmece Nuclear Research and Training Centre in Istanbul. Later, this reactor was replaced with TR-2 in 1981. General Directorate of Electrical Power Resources Survey and Development Administration (EIEI) started the first studies in 1965 for the installation of a nuclear power plant. A report was prepared by a foreign consortium suggesting the installation of a 400 MWe pressurized heavy water reactor. After establishment of Turkish Electricity Authority (TEK) in 1970 studies for site selection were commenced in 1974 and TEK gained a site license in 1976 for Akkuyu Site in southern Turkey at the Mediterranean coast. Atomic Energy Commission evolved to become Turkish Atomic Energy Authority in 13 July 1982 with the Law no. 2690. This law was the main nuclear law in the country until July 2018. After several attempts without success in previous decades, the Government decided on starting the nuclear programme with Russian Federation. The ‘Agreement Between the Government of the Republic of Turkey and the Government of the Russian Federation on Cooperation in Relation to the Construction and Operation of a Nuclear Power Plant at the Akkuyu Site in the Republic of Turkey’ (the Akkuyu Agreement) was signed on 12 May 2010. According to the Akkuyu Agreement a project company will be established by a Russian Consortium to install the NPP. Every completed unit of the NPP will enjoy 15 years of guaranteed electricity sale at a fixed average price over this period. 70% of the electricity produced by the first two units and 30% of the electricity produced for the remaining two units will be purchased by the Government owned Turkish Electricity Trading and Contracting Company (TETAŞ). The rest will be sold by the project company to the free electricity market. At the end of the contract period all the electricity produced will be sold to the free electricity market.
[en] Motivated by the recent experimental discovery of the high-critical-temperature superconductor LaH (250-260 K at high pressures 170-190 GPa), the influence of H isotope substitution on the phonon spectra, electron-phonon interactions, and thermodynamic properties of superconducting LaHD (x = 0 , 2 , 5 , 8 , 10) at 250 GPa are studied. On the basis of first-principles calculations, it is found that all investigated systems are dynamically stable in a clathrate structure with space group Fmm and exhibit high superconducting critical temperatures T ranging from 169 to 234 K. The dominant role of hydrogen in enhancing T is examined by numerically solving the Eliashberg equations. The estimated critical temperature, superconducting energy gap, specific heat, and thermodynamic critical field demonstrate that the underlying mechanism of superconductivity in lanthanum hydride is conventional electron-phonon coupling, which manifests itself in terms of isotope effect. (© 2020 Wiley‐VCH GmbH)
[en] The present work concerns the use of 1995 CHF table for uniformly heated round tubes, developed jointly by Canadian and Russian researchers, for the prediction of critical heat flux in rod bundles geometries. Comparisons between measured and calculated critical heat fluxes indicate that this table can be applied to rod bundles provided that a suitable correction factor is employed. The tolerance limits associated with the departure from nucleate boiling ratio (DNBR) are evaluated by using statistical analysis. (author)
[en] The intensity of defect-related photoluminescence (PL) in semiconductors changes with temperature, and it usually decreases exponentially above some critical temperature, a process called the PL quenching. Herein, main mechanisms of PL quenching are reviewed. Most examples are given for defects in GaN as the most studied modern semiconductor, which has important applications in technology. Peculiarities of defect-related PL in I-VII, II-VI, and III-V compounds are also reviewed. Three basic mechanisms of PL quenching are distinguished. Most examples of PL quenching can be explained by the Schön-Klasens mechanism, whereas very few or even no confirmed cases can be found in support of the Seitz-Mott mechanism. Third mechanism, the abrupt and tunable quenching, is common for high-resistivity semiconductors. Temperature dependence of capture coefficients and a number of other reasons may affect the temperature dependence of PL intensity. The ''negative quenching'' or a significant rise in PL intensity with temperature is explained by a competition between recombination channels for minority carriers. (© 2020 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)