Study of Ordering in Fe—25%Al—Cr Alloys by Dilatometry, Heat Flow and Mechanical Spectroscopy

It is known that the addition of Cr to the Fe₃Al-based alloys leads to an improvement in their ductility and other properties. In a given work, dilatometric, differential scanning calorimetric (DSC) and internal friction tests are performed to study the ordering process in stoichiometric and overstoichiometric Fe₃Al alloys with Cr addition at a constant heating rate from room temperature up to 1000°C. The results indicate that the addition of Cr slows the D0₃-type ordering process; this can be confirmed by obtained values of activation energy. Cr addition has also an effect on the mechanical properties of studied alloys annealed in D0₃-type order domain. The heights and broadening of three peaks (of X-, Zener-, and Snoek-type) can be changed at the presence of Cr. X-ray diffraction (XRD) and TEM studies are carried out at different temperatures chosen from the obtained DSC curves and affirmed that a rapid quenching just after heat treatment from highest temperature cannot suppress the formation of B2 ordered particles in overstoichiometric Fe₃Al alloys.Відомо, що додавання Cr до стопів на основі Fe₃Al спричиняє поліпшення їх пластичности та інших властивостей. У даній статті виконано дилатометричні випробування та випробування методами диференційної сканівної калориметрії (ДСК) і внутрішнього тертя з метою вивчення процесу впорядкування в стехіометричних та надстехіометричних стопах Fe₃Al з додаванням Cr при сталій швидкості нагрівання від кімнатної температури до 1000°C. Додавання Cr сповільнює процес упорядкування за надструктурним типом D0₃, що підтверджується одержаними значеннями енергії активації. Додавання хрому впливає також на механічні властивості досліджених стопів, відпалених в області D0₃-порядку. Висоти та розширення трьох піків (Зінерового, Снукового та X-типу) можуть змінюватися в присутності Cr. Рентґенодифракційна аналіза та трансмісійна електронна мікроскопія, виконані за різних температур, обраних на підставі одержаних ДСК-кривих, підтвердили, що швидке гартування від самої високої температури зразу після теплового оброблення не може пригнітити формування впорядкованих частинок типу B2 у надстехіометричних стопах Fe₃Al.Известно, что добавление Cr к сплавам на основе Fe₃Al приводит к улучшению их пластичности и других свойств. В данной статье выполнены дилатометрические испытания и испытания методами дифференциальной сканирующей калориметрии (ДСК) и внутреннего трения с целью изучения процесса упорядочения в стехиометрических и сверхстехиометрических сплавах Fe₃Al с добавлением Cr при постоянной скорости нагрева от комнатной температуры до 1000°C. Добавление Cr замедляет процесс упорядочения по сверхструктурному типу D0₃, что подтверждается полученными значениями энергии активации. Добавление хрома влияет также на механические свойства исследуемых сплавов, отжигаемых в области D0₃-порядка. Высоты и уширение трёх пиков (зинеровского, снуковского и X-типа) могут изменяться в присутствии Cr. Рентгенодифракционный анализ и просвечивающая электронная микроскопия, выполненные при различных температурах, выбранных на основании полученных ДСК-кривых, подтвердили, что быстрая закалка от самой высокой температуры сразу после тепловой обработки не может подавить формирование упорядоченных частиц типа B2 в сверхстехиометрических сплавах Fe₃Al

Spin-down of neutron stars by neutrino emission

We study the spin-down of a neutron star during its early stages due to the neutrino emission. The mechanism we consider is the subsequent collisions of the produced neutrinos with the outer shells of the star. We find that this mechanism can indeed slow down the star rotation but only in the first tens of seconds of the core formation, which is when the appropriate conditions of flux and collision rate are met. We find that this mechanism can extract less than 1 % of the star angular momentum, a result which is much less than previously estimated by other authors.Comment: 9 pages, 2 eps figures, RevTeX 4-1. The paper was significantly modified. Now it addresses only the issues of a neutron star spin-down. Version to be published in Phys. Rev.

Novel bimodal TRBD1-TRBD2 rearrangements with dual or absent D-region contribute to TRB V-(D)-J combinatorial diversity

T-cell receptor (TR) diversity of the variable domains is generated by recombination of both the alpha (TRA) and beta (TRB) chains. The textbook process of TRB chain production starts with TRBD and TRBJ gene rearrangement, followed by the rearrangement of a TRBV gene to the partially rearranged D-J gene. Unsuccessful V-D-J TRB rearrangements lead to apoptosis of the cell. Here, we performed deep sequencing of the poorly explored pool of partial TRBD1-TRBD2 rearrangements in T-cell genomic DNA. We reconstructed full repertoires of human partial TRBD1-TRBD2 rearrangements using novel sequencing and validated them by detecting V-D-J recombination-specific byproducts: excision circles containing the recombination signal (RS) joint 5’D2-RS – 3’D1-RS. Identified rearrangements were in compliance with the classical 12/23 rule, common for humans, rats, and mice and contained typical V-D-J recombination footprints. Interestingly, we detected a bimodal distribution of D-D junctions indicating two active recombination sites producing long and short D-D rearrangements. Long TRB D-D rearrangements with two D-regions are coding joints D1-D2 remaining classically on the chromosome. The short TRB D-D rearrangements with no D-region are signal joints, the coding joint D1-D2 being excised from the chromosome. They both contribute to the TRB V-(D)-J combinatorial diversity. Indeed, short D-D rearrangements may be followed by direct V-J2 recombination. Long D-D rearrangements may recombine further with J2 and V genes forming partial D1-D2-J2 and then complete V-D1-D2-J2 rearrangement. Productive TRB V-D1-D2-J2 chains are present and expressed in thousands of clones of human antigen-experienced memory T cells proving their capacity for antigen recognition and actual participation in the immune response

Effect of β-alanine on humoral immune response in low-dose allergy model

At the present time, the efforts of many research groups around the world are aimed at finding new factors triggering the allergic sensitization process linked with IgE synthesis to harmless allergens. According to the recent data, production of tissue cytokines is induced in tissue cells by alarmins, thus, in turn, eliciting pro-allergic immune response. Previously we have shown that β-alanine could be a potential alarmin capable to stimulate production of tissue cytokines. The aim of this work was to determine the impact of β-alanine on humoral immune response in low-dose allergy model. BALB/c mice were immunized by recombinant Asp f 2 protein or commercial ovalbumin (OVA) in the withers 3 times a week with or without β-alanine supplementation. To determine the mechanism of β-alanine effect, α-L-alanine, an isomer which is not MrgD receptor ligand, and β-aminoisobutyrate with β-alanine-like affinity to MrgD ligand, were compared. According to our data, β-alanine stimulated specific IgE and IgG1 production in a short-term course (7 immunizations) and enhanced antibody affinity after long-term (14 immunizations) protocol in the case of low-immunogenic protein Asp f 2. In the case of high-immunogenic OVA protein, the impact of β-alanine was significant only upon antibody affinity. Hence, β-alanine accelerates specific IgE production in the case of low-immunogenic protein. The impact of β-alanine on specific IgE production was not linked to specific MrgD receptor activation, because β-aminoisobutyrate, which is the other ligand of this receptor, did not have a similar effect upon humoral immune response. The effect of β-alanine on IgG1 production seems also independent of MrgD receptor, since the common proteinogenic amino acid α-L-alanine also enhanced specific IgG1 production. The effect of β-alanine on humoral immune response could be linked to its non-specific action, e.g., due to its ability to induce oxidative stress through blocking taurine transporter, or due to its ability to stimulate cellular metabolism

Unique Electron Polarimeter Analyzing Power Comparison and Precision Spin-Based Energy Measurement

Precision measurements of the relative analyzing powers of five electron beam polarimeters, based on Compton, Moller, and Mott scattering, have been performed using the CEBAF accelerator at the Thomas Jefferson National Accelerator Facility ( Jefferson Laboratory). A Wien filter in the 100 keV beam line of the injector was used to vary the electron spin orientation exiting the injector. High statistical precision measurements of the scattering asymmetry as a function of the spin orientation were made with each polarimeter. Since each polarimeter receives beam with the same magnitude of polarization, these asymmetry measurements permit a high statistical precision comparison of the relative analyzing powers of the five polarimeters. This is the first time a precise comparison of the analyzing powers of Compton, Moller, and Mott scattering polarimeters has been made. Statistically significant disagreements among the values of the beam polarization calculated from the asymmetry measurements made with each polarimeter reveal either errors in the values of the analyzing power or failure to correctly include all systematic effects. The measurements reported here represent a first step toward understanding the systematic effects of these electron polarimeters. Such studies are necessary to realize high absolute accuracy (ca. 1%) electron polarization measurements, as required for some parity violation measurements planned at Jefferson Laboratory. Finally, a comparison of the value of the spin orientation exiting the injector that provides maximum longitudinal polarization in each experimental hall leads to an independent and very precise ( better than 10-4) absolute measurement of the final electron beam energy

Space-Time Evolution of Ultrarelativistic Quantum Dipoles in Quantum Electrodynamics

We discuss space-time evolution of ultrarelativistic quantum dipole in QED. We show that the space-time evolution can be described, in a certain approximation, by means of a regularized wave function, whose parameters are determined by the process of the dipole creation by a local current. We derive using these wave functions the dipole expansion law, that is found to coincide parametrically in the leading order with the one suggested by Farrar, Frankfurt,Liu and Strikman.Comment: 15 page

TCRs with segment TRAV9-2 or a CDR3 histidine are overrepresented among nickel-specific CD4+ T cells

Background: Nickel is the most frequent cause of T cell-mediated allergic contact dermatitis worldwide. In vitro, CD4+ T cells from all donors respond to nickel but the involved αβ T cell receptor (TCR) repertoire has not been comprehensively analyzed. Methods: We introduce CD154 (CD40L) upregulation as a fast, unbiased, and quantitative method to detect nickel-specific CD4+ T cells ex vivo in blood of clinically characterized allergic and non allergic donors. Naïve (CCR7+ CD45RA+) and memory (not naïve) CD154+ CD4+ T cells were analyzed by flow cytometry after 5 hours of stimulation with 200 µmol/L NiSO4 ., TCR α- and β-chains of sorted nickel-specific and control cells were studied by high-throughput sequencing. Results: Stimulation of PBMCs with NiSO4 induced CD154 expression on ~0.1% (mean) of naïve and memory CD4+ T cells. In allergic donors with recent positive patch test, memory frequencies further increased ~13-fold and were associated with markers of in vivo activation. CD154 expression was TCR-mediated since single clones could be specifically restimulated. Among nickel-specific CD4+ T cells of allergic and non allergic donors, TCRs expressing the α-chain segment TRAV9-2 or a histidine in their α- or β-chain complementarity determining region 3 (CDR3) were highly overrepresented. Conclusions: Induced CD154 expression represents a reliable method to study nickel-specific CD4+ T cells. TCRs with particular features respond in all donors, while strongly increased blood frequencies indicate nickel allergy for some donors. Our approach may be extended to other contact allergens for the further development of diagnostic and predictive in vitro tests