Effect of Cr spacer on structural and magnetic properties of Fe/Gd multilayers

In this work we analyse the role of a thin Cr spacer between Fe and Gd layers on structure and magnetic properties of a [Fe(35A)/Cr(tCr)/Gd(50A)/Cr(tCr)]x12 superlattice. Samples without the Cr spacer (tCr=0) and with a thin tCr=4A are investigated using X-ray diffraction, polarized neutron and resonance X-ray magnetic reflectometry, SQUID magnetometery, magneto-optical Kerr effect and ferromagnetic resonance techniques. Magnetic properties are studied experimentally in a wide temperature range 4-300K and analysed theoretically using numerical simulation on the basis of the mean-field model. We show that a reasonable agreement with the experimental data can be obtained considering temperature dependence of the effective field parameter in gadolinium layers. The analysis of the experimental data shows that besides a strong reduction of the antiferromagnetic coupling between Fe and Gd, the introduction of Cr spacers into Fe/Gd superlattice leads to modification of both structural and magnetic characteristics of the ferromagnetic layers

Bacterial formate dehydrogenase. Increasing the enzyme thermal stability by hydrophobization of alpha-helices

AbstractNAD+-dependent formate dehydrogenase (EC 1.2.1.2, FDH) from methylotrophic bacterium Pseudomonas sp.101 exhibits the highest stability among the similar type enzymes studied. To obtain further increase in the thermal stability of FDH we used one of general approaches based on hydrophobization of protein α-helices. Five serine residues in positions 131, 160, 168, 184 and 228 were selected for mutagenesis on the basis of (i) comparative studies of nine FDH amino acid sequences from different sources and (ii) with the analysis of the ternary structure of the enzyme from Pseudomonas sp.101. Residues Ser-131 and Ser-160 were replaced by Ala, Val and Leu. Residues Ser-168, Ser-184 and Ser-228 were changed into Ala. Only Ser/Ala mutations in positions 131, 160, 184 and 228 resulted in an increase of the FDH stability. Mutant S168A was 1.7 times less stable than the wild-type FDH. Double mutants S(131,160)A and S(184,228)A and the four-point mutant S(131,160,184,228)A were also prepared and studied. All FDH mutants with a positive stabilization effect had the same kinetic parameters as wild-type enzyme. Depending on the position of the replaced residue, the single point mutation Ser/Ala increased the FDH stability by 5–24%. Combination of mutations shows near additive effect of each mutation to the total FDH stabilization. Four-point mutant S(131,160,184,228)A FDH had 1.5 times higher thermal stability compared to the wild-type enzyme

Magnetization and ferromagnetic resonance in a Fe/Gd multilayer: Experiment and modelling

Static and dynamic magnetic properties of a [Fe(35 Å<rf)/Gd(50 Å)]12 superlattice are investigated experimentally in the temperature range 5-295 K using SQUID magnetometery and the ferromagnetic resonance (FMR) technique at frequencies 7-38 GHz. The obtained magnetization curves and FMR spectra are analysed theoretically using numerical simulation on the basis of the effective field model. At every given temperature, both static and resonance experimental data can be approximated well within the proposed model. However, a considerable temperature dependence of the effective field parameter in gadolinium layers has to be taken into account to achieve reasonable agreement with the experimental data in the entire temperature range studied. To describe the peculiarities of experimental FMR spectra, a non-local diffusion-type absorption term in Landau-Lifshitz equations is considered in addition to the Gilbert damping term. Possible reasons for the observed effects are discussed. © 2017 IOP Publishing Ltd

Ant-aphid relations in Costa Rica, Central America (Hymenoptera: Formicidae; Hemiptera: Aphididae)

We present the first catalogue of ant-aphid associations (Hymenoptera: Formicidae / Hemiptera: Aphididae) of Costa Rica. 29 species of ants and 18 species of aphids establish 48 relationships. Those interactions seem not to be rare in Costa Rica

The Association between ATM IVS 22-77 T>C and Cancer Risk: A Meta-Analysis

BACKGROUND AND OBJECTIVES: It has become increasingly clear that ATM (ataxia-telangiectasia-mutated) safeguards genome stability, which is a cornerstone of cellular homeostasis, and ATM IVS 22-77 T>C affects the normal activity of ATM proteins. However, the association between the ATM IVS 22-77 T>C genetic variant and cancer risk is controversial. Therefore, we conducted a systematic meta-analysis to estimate the overall cancer risk associated with the polymorphism and to quantify any potential between-study heterogeneity. METHODS: A total of nine studies including 4,470 cases and 4,862 controls were analyzed for ATM IVS 22-77 T>C association with cancer risk in this meta-analysis. Heterogeneity among articles and their publication bias were also tested. RESULTS: Our results showed that no association reached the level of statistical significance in the overall risk. Interestingly, in the stratified analyses, we observed an inverse relationship in lung and breast cancer. CONCLUSION: Further functional research on the ATM mechanism should be performed to explain the inconsistent results in different cancer types

The ultrasound use of simulators, current view, and perspectives: Requirements and technical aspects (WFUMB state of the art paper)

Simulation has been shown to improve clinical learning outcomes, speed up the learning process and improve learner confidence, whilst initially taking pressure off busy clinical lists. The World Federation for Ultrasound in Medicine and Biology (WFUMB) state of the art paper on the use of simulators in ultrasound education introduces ultrasound simulation, its advantages and challenges. It describes different simulator types, including low and high-fidelity simulators, the requirements and technical aspects of simulators, followed by the clinical applications of ultrasound simulation. The paper discusses the role of ultrasound simulation in ultrasound clinical training, referencing established literature. Requirements for successful ultrasound simulation acceptance into educational structures are explored. Despite being in its infancy, ultrasound simulation already offers a wide range of training opportunities and likely holds the key to a broader point of care ultrasound education for medical students, practicing doctors, and other health care professionals. Despite the drawbacks of simulation, there are also many advantages, which are expanding rapidly as the technology evolves

Sample Handling and Chemical Kinetics in an Acoustically Levitated Drop Microreactor

Accurate measurement of enzyme kinetics is an essential part of understanding the mechanisms of biochemical reactions. The typical means of studying such systems use stirred cuvettes, stopped-flow apparatus, microfluidic systems, or other small sample containers. These methods may prove to be problematic if reactants or products adsorb to or react with the container’s surface. As an alternative approach, we have developed an acoustically-levitated drop reactor eventually intended to study enzyme-catalyzed reaction kinetics related to free radical and oxidative stress chemistry. Microliter-scale droplet generation, reactant introduction, maintenance, and fluid removal are all important aspects in conducting reactions in a levitated drop. A three capillary bundle system has been developed to address these needs. We report kinetic measurements for both luminol chemiluminescence and the reaction of pyruvate with nicotinamide adenine dinucleotide, catalyzed by lactate dehydrogenase, to demonstrate the feasibility of using a levitated drop in conjunction with the developed capillary sample handling system as a microreactor

Cellular Radiosensitivity: How much better do we understand it?

Purpose: Ionizing radiation exposure gives rise to a variety of lesions in DNA that result in genetic instability and potentially tumorigenesis or cell death. Radiation extends its effects on DNA by direct interaction or by radiolysis of H2O that generates free radicals or aqueous electrons capable of interacting with and causing indirect damage to DNA. While the various lesions arising in DNA after radiation exposure can contribute to the mutagenising effects of this agent, the potentially most damaging lesion is the DNA double strand break (DSB) that contributes to genome instability and/or cell death. Thus in many cases failure to recognise and/or repair this lesion determines the radiosensitivity status of the cell. DNA repair mechanisms including homologous recombination (HR) and non-homologous end-joining (NHEJ) have evolved to protect cells against DNA DSB. Mutations in proteins that constitute these repair pathways are characterised by radiosensitivity and genome instability. Defects in a number of these proteins also give rise to genetic disorders that feature not only genetic instability but also immunodeficiency, cancer predisposition, neurodegeneration and other pathologies. Conclusions: In the past fifty years our understanding of the cellular response to radiation damage has advanced enormously with insight being gained from a wide range of approaches extending from more basic early studies to the sophisticated approaches used today. In this review we discuss our current understanding of the impact of radiation on the cell and the organism gained from the array of past and present studies and attempt to provide an explanation for what it is that determines the response to radiation

Linkage disequilibrium pattern of the ATM gene in breast cancer patients and controls; association of SNPs and haplotypes to radio-sensitivity and post-lumpectomy local recurrence

<p>Abstract</p> <p>Background</p> <p>The ATM protein is activated as a result of ionizing radiation, and genetic variants of the <it>ATM </it>gene may therefore affect the level of radiation-induced damage. Individuals heterozygous for <it>ATM </it>mutations have been reported to have an increased risk of malignancy, especially breast cancer.</p> <p>Materials and methods</p> <p>Norwegian breast cancer patients (272) treated with radiation (252 of which were evaluated for radiation-induced adverse side effects), 95 Norwegian women with no known history of cancer and 95 American breast cancer patients treated with radiation (44 of which developed ipsilateral breast tumour recurrence, IBTR) were screened for sequence variations in all exons of the <it>ATM </it>gene as well as known intronic variants by denaturating high performance liquid chromatography (dHPLC) followed by sequencing to determine the nature of the variant.</p> <p>Results and Conclusion</p> <p>A total of 56 variants were identified in the three materials combined. A borderline significant association with breast cancer risk was found for the 1229 T>C (Val>Ala) substitution in exon 11 (P-value 0.055) between the Norwegian controls and breast cancer patients as well as a borderline significant difference in haplotype distribution (P-value 0.06). Adverse side effects, such as: development of costal fractures and telangiectasias, subcutaneous and lung fibrosis, pleural thickening and atrophy were evaluated in the Norwegian patients. Significant associations were found for several of the identified variants such as rs1800058 (Leu > Phe) where a decrease in minor allele frequency was found with increasing level of adverse side effects for the clinical end-points pleural thickening and lung fibrosis, thus giving a protective effect. Overall our results indicate a role for variation in the <it>ATM </it>gene both for risk of developing breast cancer, and in radiation induced adverse side effects. No association could be found between risk of developing ipsilateral breast tumour recurrence and any of the sequence variants found in the American patient material.</p