Effect of Dzyaloshinski-Moriya interaction on spin-polarized neutron scattering

For magnetic materials containing many lattice imperfections (e.g., nanocrystalline magnets), the relativistic Dzyaloshinski-Moriya (DM) interaction may result in nonuniform spin textures due to the lack of inversion symmetry at interfaces. Within the framework of the continuum theory of micromagnetics, we explore the impact of the DM interaction on the elastic magnetic small-angle neutron scattering (SANS) cross section of bulk ferromagnets. It is shown that the DM interaction gives rise to a polarization-dependent asymmetric term in the spin-flip SANS cross section. Analysis of this feature may provide a means to determine the DM constant.Comment: 10 pages, 7 figure

Sotsiaaltöötajate ja sotsiaalkomisjonide koostöö vallasotsiaaltöö korraldamisel

Minu töö eesmärgiks oli uurida sotsiaaltöötajate ja sotsiaalkomisjonide koostööd valla sotsiaaltöö korraldamisel. Läbiviidud intervjuudest laekus piisavalt materjali, mis võimaldas leida vastused püstitatud uurimisküsimustele. Eestis ei ole varem sotsiaaltöötajate ja sotsiaalkomisjonide koostööd ning sotsiaalkomisjoni rolli maasotsiaaltöö korraldajana uuritud. Andmeid analüüsides said kinnitust ka varasemad maasotsiaaltööalased uurimused, kuid lisandusid uued vaatenurgad maasotsiaaltöö korraldamises. Maasotsiaaltöötajale olulised koostööpartnerid on üldiselt kaasatud ka sotsiaalkomisjoni, kuid sotsiaaltöötajad ei ole osanud sotsiaalkomisjoni, kui kollegiaalset organit ja kootööpartnerit enda jaoks teadvustanud. Sotsiaalkomisjon oli nende jaoks oluline tööriist, kes aitab vastu võtta otsuseid ja jagab ühiselt vastutust kogukonna ees. Analüüsi tulemusena võib välja tuua, te sotsiaalkomisjonide liikmed ei ole tavaliselt sotsiaaltööharidusega ja seetõttu jääb ka nende professionaalne tugi sotsiaaltöötajale nõrgaks. Suuremat tähelepanu tuleks pöörata nii volikogude kui sotsiaalkomisjonide liikmete koolitamisele, et neist oleks abi väikese valla sotsiaaltöötajatele. Kuid komisjonide liikmed on olulised informatsiooniallikad, kes tunnevad kohalikke olusid ja traditsioone ning kellel on teadmisi teistelt elualadelt ning täiendavad sellega sotsiaaltöötaja teadmisi. Intervjuudest selgus, et komisjonilt oodatakse kohaliku elu ja inimeste tundmist, erialane asjatundmine ei ole nii oluline. Sotsiaalkomisjoni roll väikeses vallas on kindlasti erinev linnade ja suuremate omavalitsuste omast. Suuremas omavalitsuses on suurem võimalus sotsiaalkomisjoni töösse erialaspetsialiste kaasata. Seeläbi tõuseb ka professionaalne tase. Maapiirkonnad on oma olemuselt suhteliselt sarnased ja intervjueeritavates valdades olid teineteisest sõltumatult tekkinud üsna sarnased mustrid sotsiaalkomisjonide töö korraldamisel. Tõenäoliselt on see kohalikke olusid arvestades parim võimalik ja vajalik viis valla sotsiaaltööd teha. Peamiselt tegelesid sotsiaalkomisjonid igapäevase sotsiaaltöö korraldamise ning klienditööga, tagasihoidlikuks jäi kohaliku sotsiaalpoliitika kujundamise osa. Selleks puudusid komisjoni liikmetel ka oskused, teadmised ja ambitsioon. Pean oluliseks teadvustada maasotsiaaltöötaja partneri ja maasotsiaaltöö tegijana ka valla sotsiaalkomisjoni. Sotsiaalkomisjoni liige maakogukonnas võiks olla ka piirkonna sotsiaalpoliitika kujundaja ja uute teenuste ellukutsuja. Selleks, et parandada sotsiaalkomisjonide tööd ja tõsta sotsiaalkomisjonide mainet, tuleks nii sotsiaaltöötajatele kui komisjonide liikmetele komisjonide rolli ja võimaluste mõistmiseks läbi viia koolitusi.http://www.ester.ee/record=b4498545*es

Identification of colistin resistance mechanisms in pmrC-, pmrA-, and pmrB-deficient Acinetobacter baumannii

Acinetobacter baumannii is a menacing nosocomial pathogen that readily develops resistance to antibiotics. Colistin, a polymyxin, is currently the last-line choice for treating infections caused by multidrug-resistant A. baumannii. This cationic peptide is attracted to the negatively charged lipopolysaccharide (LPS) on Gram-negative bacterial membranes and acts by destabilizing and permeabilizing it. Unfortunately, there is a disturbing trend of strains developing resistance to colistin in recent years. A. baumannii is known to modify its LPS in order to interrupt the initial charge interaction with colistin. The most common mechanism implicated in this resistance strategy is the upregulation of the pmrAB genes encoding a two-component regulatory system, which in turn upregulates pmrC that encodes phosphoethanolamine transferase. PmrAB have also been shown to be global regulators of cellular growth processes and virulence. Gain-of-function mutations in pmrAB are the most commonly reported colistin resistance mechanism. However, it is not known if and how A. baumannii strains deficient in any of the pmrCAB genes develop colistin resistance. We therefore aim to determine secondary mechanisms of colistin resistance in pmrCAB-deficient strains. Using A. baumannii strain AB5075 and inactivation mutants of pmrC, -A, and -B, we generated genetically stable colistin-resistant mutants on agar containing increasing colistin concentrations. We conducted whole genome sequencing to identify genetic changes responsible for colistin resistance. We also characterized their phenotypes, including resistance profiles to Gram-positive antimicrobials, LPS structure, in vitro growth fitness, and in vivo virulence using a Galleria mellonella model. Colistin-resistant mutants possessed mutations in lpx and mla genes, which are involved in lipid biosynthesis and membrane composition, respectively. Most mutants were susceptible to Gram-positive antimicrobial agents, likely resulting from severely compromised outer membranes. Furthermore, colistin-resistant mutants displayed reduced fitness in vitro and decreased virulence in vivo. A. baumannii is adept at evading colistin by modifying its membrane structure, even outside of the control of pmrCAB. However, mutations that disrupt membrane integrity are costly and unlikely to persist in clinical settings. Therefore, colistin-resistant mutants with such mutations seemingly carry low public health significance. Even if these mutants do emerge in the clinic, various Gram-positive agents can be included as treatment options

Magnetic small-angle neutron scattering on bulk metallic glasses

The present PhD thesis is devoted to the exploration of the use of the magnetic small-angle neutron scattering (SANS) technique for analyzing the magnetic microstructure of bulk magnetic materials. More specifically, magnetic-field-dependent SANS has been utilized to study the magnetic microstructure of bulk metallic glasses (BMGs). The magnetic scattering is compared for soft magnetic and hard magnetic compositions in different mechanically treated states. On the basis of the continuum theory of micromagnetics, the correlation function of the spin-misalignment SANS cross section is computed and analyzed as a function of various external and material parameters. Analysis of the experimental correlation functions of the BMG reveals the existence of field-dependent anisotropic long-wavelength magnetization fluctuations on a scale of a few tens of nanometers. As a second aspect of this PhD work, we have explored the impact of the Dzyaloshinski-Moriya interaction on the elastic magnetic SANS cross section of microstructural-defect-rich materials. The effect was demonstrated by measuring polarized SANS on a nanocrystalline terbium sample and on a cold-rolled polycrystalline cobalt sample

Anisometric mesoscale nuclear and magnetic texture in sintered Nd-Fe-B magnets

By means of temperature and wavelength-dependent small-angle neutron scattering (SANS) experiments on sintered isotropic and textured Nd-Fe-B magnets we provide evidence for the existence of an anisometric structure in the microstructure of the textured magnets. This conclusion is reached by observing a characteristic cross-shaped angular anisotropy in the total unpolarized SANS cross section at temperatures well above the Curie temperature. Comparison of the experimental SANS data to a microstructural model based on the superquadrics form factor allows us to estimate the shape and lower bounds for the size of the structure. Subtraction of the scattering cross section in the paramagnetic regime from data taken at room temperature provides the magnetic SANS cross section. Surprisingly, the anisotropy of the magnetic scattering is very similar to the nuclear SANS signal, suggesting that the nuclear structure is decorated by the magnetic moments via spin-orbit coupling. Based on the computation of the two-dimensional correlation function we estimate lower bounds for the longitudinal and transversal magnetic correlation lengths

Microwave spectroscopy of the low-temperature skyrmion state in Cu2OSeO3

In the cubic chiral magnet Cu2OSeO3 a low-temperature skyrmion state (LTS) and a concomitant tilted conical state are observed for magnetic fields parallel to . In this work, we report on the dynamic resonances of these novel magnetic states. After promoting the nucleation of the LTS by means of field cycling, we apply broadband microwave spectroscopy in two experimental geometries that provide either predominantly in-plane or out-of-plane excitation. By comparing the results to linear spin-wave theory, we clearly identify resonant modes associated with the tilted conical state, the gyrational and breathing modes associated with the LTS, as well as the hybridization of the breathing mode with a dark octupole gyration mode mediated by the magnetocrystalline anisotropies. Most intriguingly, our findings suggest that under decreasing fields the hexagonal skyrmion lattice becomes unstable with respect to an oblique deformation, reflected in the formation of elongated skyrmions

The Comparison of Direct and Indirect Methods for Determining the Magnetocaloric Parameters in the Heusler Alloy Ni50Mn34.8In14.2B

The magnetocaloric properties of the Ni50Mn34.8In14.2B Heusler alloy have been studied by direct measurements of the adiabatic temperature change (ΔTAD(T,H)) and indirectly by magnetization (M(T,H)), differential scanning calorimetry, and specific heat (C(T,H)) measurements. The presence of a first-order ferromagnetic-paramagnetic transition has been detected for Ni50Mn34.8In14.2B at 320 K. The magnetocaloric parameters, i.e., the magnetic entropy change (ΔSM = (2.9-3.2) J/kgK) and the adiabatic temperature change (ΔTAD = (1.3-1.52) K), have been evaluated for ΔH = 1.8 T from CP(T,H) and M(T,H) data and from direct ΔTAD(T,H) measurements. The extracted magnetocaloric parameters are comparable to those of Gd

Microstructural-defect-induced Dzyaloshinskii-Moriya interaction

The antisymmetric Dzyaloshinskii?Moriya interaction (DMI) plays a decisive role for the stabilization and control of chirality of skyrmion textures in various magnetic systems exhibiting a noncentrosymmetric crystal structure. A less studied aspect of the DMI is that this interaction is believed to be operative in the vicinity of lattice imperfections in crystalline magnetic materials, due to the local structural inversion symmetry breaking. If this scenario leads to an effect of sizable magnitude, it implies that the DMI introduces chirality into a very large class of magnetic materials?defect-rich systems such as polycrystalline magnets. Here, we show experimentally that the microstructural-defect-induced DMI gives rise to a polarization-dependent asymmetric term in the small-angle neutron scattering (SANS) cross section of polycrystalline ferromagnets with a centrosymmetric crystal structure. The results are supported by theoretical predictions using the continuum theory of micromagnetics. This effect, conjectured already by Arrott in 1963, is demonstrated for nanocrystalline terbium and holmium (with a large grain-boundary density), and for mechanically deformed microcrystalline cobalt (with a large dislocation density). Analysis of the scattering asymmetry allows one to determine the defect-induced DMI constant, D=0.45±0.07mJ/m2 for Tb at 100K. Our study proves the generic relevance of the DMI for the magnetic microstructure of defect-rich ferromagnets with vanishing intrinsic DMI. Polarized SANS is decisive for disclosing the signature of the defect-induced DMI, which is related to the unique dependence of the polarized SANS cross section on the chiral interactions. The findings open up the way to study defect-induced skyrmionic magnetization textures in disordered materials

Интерференционный множитель Земли

The article is devoted to the pattern propagation factor of the Earth enabling for more precise determination of the radar station visibility range in case there are reflections from underlying surface. The article provides analytical solution in general form taking into account the Earth sphericity. It enables to obtain the results in the wide-band and altitude range of the observed objects by means of computer simulation. The article gives analytical expression for the Earth multiplier under the flat approximation assumption, free of restrictions common for research literature. Besides, the article defines boundaries in which it is permissible to view the Earth as a flat surface. In addition, the article provides examples to illustrate graphical estimate of the error of all approximations both with respect to the general case of the Earth sphericity and relative to each other.Рассмотрена задача учета интерференционного множителя Земли, позволяющего более точно определить зону видимости радиолокационной станции при наличии отражений от подстилающей поверхности. Представлено аналитическое решение этой задачи в общем виде с учетом сферичности Земли, позволяющее получить результат в широком диапазоне дальностей и высот целей с использованием компьютерного моделирования. Получено аналитическое выражение для множителя Земли в условиях “плоского приближения” без ограничений, обычно встречающихся в литературе. Определены границы допустимости “плоского приближения Земли”. На примерах дается графическая оценка погрешности всех приближений как по отношению к общему случаю сферичности Земли, так и относительно друг друга

β-Cell Proliferation, but Not Neogenesis, Following 60% Partial Pancreatectomy Is Impaired in the Absence of FoxM1

OBJECTIVE—This study was designed to determine whether the transcription factor FoxM1 was required for regeneration of β-cell mass via proliferation and/or neogenesis in the adult after 60% partial pancreatectomy (PPx)