Analysis of the magnetocaloric effect in Heusler alloys: study of Ni50CoMn36Sn13 by calorimetric techniques

This is an open access article distributed under the Creative Commons Attribution License.Direct determinations of the isothermal entropy increment, −ΔST, in the Heusler alloy Ni50CoMn36Sn13 on demagnetization gave positive values, corresponding to a normal magnetocaloric effect. These values contradict the results derived from heat-capacity measurements and also previous results obtained from magnetization measurements, which indicated an inverse magnetocaloric effect, but showing different values depending on the technique employed. The puzzle is solved, and the apparent incompatibilities are quantitatively explained considering the hysteresis, the width of the martensitic transition and the detailed protocol followed to obtain each datum. The results show that these factors should be analyzed in detail when dealing with Heusler alloys.Financial support from Projects MAT2011-23791, MAT2013-44063-R and MAT2014-53921-R from the Spanish MEC, DGA Consolidated Groups E100 and E34, RFBR 12-07-00676-a, RF President MD-770.2014.2, RSF 14-12-00570 and from the Ministry of Education and Science of the Russian Federation in the framework of the Increase Competitiveness Program of MISiS are acknowledged.We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).Peer Reviewe

Analysis of the magnetocaloric effect in Heusler alloys: Study of Ni50CoMn36Sn13 by calorimetric techniques

Direct determinations of the isothermal entropy increment, -¿ST , in the Heusler alloy Ni50CoMn36Sn13 on demagnetization gave positive values, corresponding to a normal magnetocaloric effect. These values contradict the results derived from heat-capacity measurements and also previous results obtained from magnetization measurements, which indicated an inverse magnetocaloric effect, but showing different values depending on the technique employed. The puzzle is solved, and the apparent incompatibilities are quantitatively explained considering the hysteresis, the width of the martensitic transition and the detailed protocol followed to obtain each datum. The results show that these factors should be analyzed in detail when dealing with Heusler alloys

Theoretical Modelling of Thermoelectric Properties of Fe2Ti1-xVxSn Heusler Alloys

Fe2TiSn is a full-Heusler alloy with 24 valence electrons per formula unit. Its electronic properties, thermal and chemical stability, relatively low cost of constituent elements make it a potential thermoelectric material for practical applications for conversion of waste heat to electricity

Dosimetry for boron neutron capture therapy developed and verified at the accelerator based neutron source VITA

The method of boron neutron capture therapy for malignant tumors, proposed in 1936, is beginning to enter clinical practice. The development of dosimetry tools for characterization of therapeutic mixed neutron-photon beam and assessing the patient’s response to treatment is becoming relevant. In this work, a number of dosimetric techniques have been developed: a compact neutron detector with a pair of cast scintillators, one of which is enriched with boron, to measure the boron dose and the γ-ray dose; cell dosimeter for measuring the sum of the equivalent dose of fast neutrons and the equivalent nitrogen dose; prompt γ-ray spectroscopy for in situ measurement of boron dose in real time; epithermal neutron flux monitor for measuring the epithermal neutron flux. Their verification carried out on the accelerator based neutron source VITA showed that they can become convenient and reliable tools for characterization of neutron beam and assessing the patient’s response to treatment

Radiobiological response of U251MG, CHO-K1 and V79 cell lines to accelerator-based boron neutron capture therapy

In the current article, we provide in vitro efficacy evaluation of a unique accelerator-based neutron source, constructed at the Budker Institute of Nuclear Physics (Novosibirsk, Russian Federation), for boron neutron capture therapy (BNCT), which is particularly effective in the case of invasive cancers. U251MG, CHO-K1 and V79 cells were incubated and irradiated in various concentrations of boric acid with epithermal neutrons for 2–3 h in a plexiglass phantom, using 2.0 MeV proton energy and 1.5–3.0 mA proton current, resulting in a neutron fluence of 2.16 × 1012 cm−2. The survival curves of cells loaded with boron were normalized to those irradiated without boron (to exclude the influence of the fast neutron and gamma dose components) and fit to the linear–quadratic (LQ) model. Colony formation assays showed the following cell survival rates (means ± SDs): CHO-K1: 0.348 ± 0.069 (10 ppm), 0.058 ± 0.017 (20 ppm), 0.018 ± 0.005 (40 ppm); V79: 0.476 ± 0.160 (10 ppm), 0.346 ± 0.053 (20 ppm), 0.078 ± 0.015 (40 ppm); and U251MG: 0.311 ± 0.061 (10 ppm), 0.131 ± 0.022 (20 ppm), 0.020 ± 0.010 (40 ppm). The difference between treated cells and controls was significant in all cases (P < 0.01) and confirmed that the neutron source and irradiation regimen were sufficient for control over cell colony formation. We believe our study will serve as a model for ongoing in vitro experiments on neutron capture therapy to advance in this area for further development of accelerator-based BNCT into the clinical phase

Structure and Raman Spectra of Exotic Carbon Microcrystals from Meteoritic Dust of Chelyabinsk Superbolide

The Chelyabinsk superbolide, the largest in XXI century, which exploded on 15 February 2013 over snowy fields of Southern Urals was a historic event not just only because of its massive scale and explosive power. High-temperature, high-pressure conditions in the front shock wave caused intense ablation of the asteroid material and formation of huge amount of meteoritic dust dispersed in the atmosphere during the flyby. Massive snowfalls just few days before and after the event conserved precipitated meteoritic dust in thin layer of snow which was collected and studied later. The most intriguing and challenging material discovered in the dust was closed-shell 10&ndash;70 &micro;m exotic polygonal graphitic carbon microcrystals of undisclosed nature. Using optical and electron microscopy and Raman spectroscopy the atomic structure of closed-shell microcrystals was thoroughly studied and their graphitic nature was revealed. It was found that some of the particles formed by multilayer graphitic polygonal shells have extensive hollows inside. Comparative microscopic and spectroscopic analysis of meteorite exotic carbon microcrystals with different graphite species, carbon onions, and diamond revealed two distinctively different closed-shell carbon particles. The first type of the particles can be attributed to carbon onions with characteristic graphite nanocrystalline basic structural units (BSU) of 49 nm lateral size and less and, probably, BSU heteroatomic termination necklace with oxygen content comparable to 1.1% and more. It was shown that the second type of unique graphitic carbon particles of a convex shape and perfect hexagonal symmetry with lateral dimensions of 14 &micro;m correspond to multiply twinned closed-shell graphite microcrystals with polyhexacyclooctadecane (&ndash;C18&ndash;)n core wrapped by multiple layers of carbon honeycombs with low (&lt;1%) content of oxygen termination necklace

Chelyabinsk superbolide

On February 15, 2013, the Chelyabinsk meteor sailed over Russian skies in a streak of light that was momentarily brighter than the Sun. The remarkable event and its subsequent shock wave were witnessed and documented by countless local residents, launching a widespread scientific expedition to gather and study the remaining meteoritic fragments. This book chronicles Chelyabinsk’s tale of recovery and discovery from the minds of many of the scientists who studied the superbolide, leading field experiments and collecting meteorites and meteorite dust across the region. The Chelyabinsk superbolide is a complex and multi-aspect phenomenon. The book not only presents the results of the scientific research but also details the firsthand experiences of those involved in such efforts, providing readers with a unique opportunity to look at the "inner workings" of science that are seldom shown to the public. Over the course of their studies, the scientists collected over 200 photographs and a dozen video recordings taken by nearly 40 different eyewitnesses. Many of those never-before-published illustrations and photos can be found in full color in the pages of this book

Nanocomposite Materials Based on Polylactide and Gold Complex Compounds for Absorbed Dose Diagnostics in BNCT

In this study, approaches to the synthesis of complex compound of gold with cysteine [AuCys]n for measuring absorbed dose in boron neutron capture therapy (BNCT) were developed. The dependence of the complex particle size on pH were established. Nanocomposite materials based on polylactide containing [AuCys]n particles with an average size of about 20 nm were obtained using the crazing mechanism. The structure of obtained materials was studied by electron microscopy. The release kinetics of [AuCys]n from polymer matrix were investigated. Release of [AuCys]n from the volume of the polymeric matrix had a delayed start—this process began only after 24 h and was characterized by an effective rate constant of 1 μg/h from a 20 mg composite sample. At the same time, in vitro studies showed that the concentration of 6.25 μg/mL was reliably safe and did not reduce the survival of U251 and SW-620 cells

Study of Lithium Biodistribution and Nephrotoxicity in Skin Melanoma Mice Model: The First Step towards Implementing Lithium Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is one of the promising treatment methods for malignant melanoma. The main issue of this technology is the insufficient selectivity of 10B accumulation in tumor cells. As a result of the neutron absorption by boron, an 84% energy release occurred within the cell by the nuclear reaction 10B (n, α)7Li, which lead to tumor cell death. The use of lithium instead of boron brings a new unique opportunity—local 100% energy release—since all products of the 6Li (n, α)3H reaction have high linear energy transfer characteristics. The aim of this study was to determine the concentrations of Li in the tumor, skin, blood, brain and kidney in experimental animals with B16 melanoma and to analyze the potential Li toxicity after lithium carbonate administration at single doses of 300 and 400 mg/kg. Lithium carbonate was chosen since there is a long-term experience of its use in clinical practice for the treatment of psychiatric disorders. The inductively coupled plasma atomic emission spectrometry was used to evaluate Li concentrations in tissue samples. The accumulation efficiency of Li in the tumor was the highest at a time point of 30 min (22.4 µg/g; at a dose of 400 mg/kg). Despite the high lithium accumulation in the kidneys, the pathological changes in kidney tissues were not found. Thus, lithium may actually be used for the Li-NCT development and future studies can be conducted using 6Li and following irradiation of tumor cells using the schemes of lithium administration tested in this work