Magnetic properties of the selected nanoparticles and their influence on superconductivity of magnesium diboride

Istraživali smo magnetska svojstva odabranih nanočestica (nanočestica nikal-kobaltbor slitine, NiCoB, neoklopljenih i oklopljenih u SiO2 omotač, i nanočestica nikla, Ni, oklopljenih ugljikom) te elektromagnetska svojstva žica supravodiča magnezij diborida, MgB2, nedopiranog i dopiranog istim nanočesticama. Neoklopljene i oklopljene NiCoB nanočestice amorfne su strukture i veličine 15 − 20 nm. Na niskim temperaturama vrijeme relaksacije magnetizacije NiCoB čestica dulje je od vremena mjerenja magnetizacije te se njihovo magnetsko ponašanje može opisati modelom jednodomenskih čestica kod kojih magnetski moment čestice mijenja smjer termičkom aktivacijom preko barijere anizotropije. Superparamagnetsko ponašanje na sobnoj temperaturi, relativno velika magnetizacija na niskoj temperaturi i u visokom polju te relativno malo koercitivno polje promatranih čestica (NiCoB i Ni) pogodni su za magnetsko zapinjanje magnetskih vrtloga u supravodiču. Elektromagnetska svojstva MgB2 dopiranog magnetskim česticama rezultat su natjecanja negativnog utjecaja magnetskih primjesa u supravodiču i poboljšanja zapinjanja vrtloga koje se ostvaruje dopiranjem nanočesticama. Iako je temperatura prijelaza, Tc, niža u dopiranim uzorcima, na niskim temperaturama i visokim poljima dopirani uzorci imaju veće vrijednosti gustoće kritične struje, Jc. U području malih polja ireverzibilno polje, Birr, uzoraka dopiranih Ni česticama povećano je u odnosu na čisti MgB2 što se može povezati s poboljšanjem zapinjanja vrtloga do kojeg dolazi zbog privlačnog magnetskog medudjelovanja čestica i vrtloga u supravodiču.We have investigated magnetic properties of the selected nanoparticles (nanoparticles of the nickel-cobalt-boron, NiCoB, alloy, uncoated and coated with SiO2 and nanoparticles of nickel, Ni, coated with carbon) and electromagnetic properties of the superconducting magnesium diboride, MgB2, wires, undoped and doped with these nanoparticles. Uncoated and coated NiCoB nanoparticles are in an amorphous state and size of the particles is 15 − 20 nm. Relaxation time of magnetization of the NiCoB particles is longer than time of the measurement of magnetization at low temperature. The magnetic behaviour of the particles is described within the model of singledomain particles with thermal activation of the magnetic moment of the particle over the anisotropy barrier. Superparamagnetic behaviour of the particles at room temperature, relatively high magnetization at low temperature and in high field, as well as relatively small coercive field of the selected particles (NiCoB i Ni) are favourable for magnetic pinning of the magnetic vortices in superconductor. Electromagnetic properties of the MgB2 doped with magnetic particles are the result of the competition of the negative influence of the magnetic particles inside superconductor and enhancement of the flux pinning, which is achieved by nanoparticle doping. Although transition temperature, Tc, is lower in doped samples, higher values of the critical current density, Jc, are achieved in doped samples at low temperatures and high filed region. At low field region, the irreversibility field, Birr of the samples doped with Ni nanoparticles is enhanced with respect to undoped sample, which can be related to the flux pinning enhancement via attractive magnetic interaction between particles and vortices in superconductor

Composition and Morphology Investigation of NiCoB Nanoparticles, as-Prepared and Coated by SiO2

NiCoB nanoparticles, as-prepared and coated by SiO2, were synthesized by chemical reduction of metallic salts. The as-prepared samples were additionally annealed at 650 for 1 hour in argon atmos-phere. All samples (the as-prepared and annealed ones) were investigated by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). According to FE-SEM observations each of the investigated samples was composed of nearly spherical nanoparticles with average dimension smaller than 30 nm. Also, tendency of formation of irregular agglomerates was present in both cases of the as-prepared and annealed investigated samples. XRD measurements of as-prepared samples revealed fully amorphous structure. In case of annealed samples, crystallization of different phases was confirmed (as a consequence of heat treatment at 650 C). The existence of these phases was also observed from FE-SEM micrographs as different morphologies present in the samples.(doi: 10.5562/cca2234

The Influence of CuFe2O4 Nanoparticles on Superconductivity of MgB2

AbstractThe influence of CuFe2O4 nanoparticle doping on superconducting properties of Fe-sheated MgB2 wires has been studied. The wires containing 0, 3 and 7.5wt.% of monodisperse superparamagnetic nanoparticles (∼7nm) were sintered at 650°C or 750°C for 1 hour in the pure argon atmosphere. X-ray diffraction patterns of doped samples showed very small maxima corresponding to iron boride and an increase in the fraction of MgO phase indicating some interaction of nanoparticles with Mg and B. Both magnetic and transport measurements (performed in the temperature range 2–42K and magnetic field up to 16 T) showed strong deterioration of the superconducting properties upon doping with CuFe2O4. The transition temperatures, Tc, of doped samples decreased for about 1.4K per wt.% of CuFe2O4. Also, the irreversibility fields Birr(T) decreased progressively with increasing doping. Accordingly, also the suppression of Jc with magnetic field became stronger. The observed strong deterioration of superconducting properties of MgB2 wires is at variance with reported enhancement of critical currents at higher temperatures (determined from magnetization) in bulk MgB2 samples doped with Fe3O4 nanoparticles. The probable reason for this discrepancy is briefly discusse

Size distribution of FeNiB nanoparticles

Two samples of amorphous nanoparticles FeNiB, one of them with SiO2 sheath around the core and one without, were investigated by transmission electron microscopy and magnetic measurements. The coating gives mean particle diameters of 4.3 nm compared to 7.2 nm for the uncoated particles. Magnetic measurements prove superparamagnetic behaviour above 160 K (350 K) for the coated (uncoated) sample. With use of effective anisotropy constant Keff – determined from hysteresis loops – size distributions are determined both from ZFC curves, as well as from relaxation measurements. Both are in good agreement and are very similar for both samples. Comparison with the size distribution determined from TEM pictures shows that magnetic clusters consist of only few physical particles

Microstructural Features of Magnetic NiCoB Nanoparticles Addition to MgB2 Precursor Powders

Magnesium diboride (MgB2) is a superconductor characterized by interesting properties like rather high superconducting transition temperature Tc = 39 K, long coherence length and low anisotropy. In addition, it has a very simple crystal structure and low density. Those properties make the MgB2 an ideal candidate for a wide range of applications. To improve the electromagnetic properties of MgB2, magnetic nickel-cobalt-boron (NiCoB) nanoparticles (mean grain size 17 ± 3 nm) were added to Mg and B precursor powders and sintered at 650 °C, i.e. the temperature of MgB2 superconductor formation. The nearly spherical NiCoB nanoparticles, as-prepared by the chemical reduction of metallic salts, were amorphous according to previous study. The resulting MgB2 sample, formed after the sintering at 650 °C, was subjected to detailed microstructural analysis which included the application of various experimental methods: XRD, FE-SEM, EDS, elemental mapping, TEM and SAED. The methods confirmed the formation of new crystal CoNi phase (due to heat treatment at 650C), consisting of spherical nanoparticles (~ 6 nm) with tendency to spherical agglomerates formation. Those nanosized magnetic particles (characterized by the single domain magnetic structure and blocking temperature TB below room temperature), located at MgB2 grain boundaries, could serve as effective magnetic pinning centers in MgB2, thus improving its electromagnetic properties. This work is licensed under a Creative Commons Attribution 4.0 International License

CARDIORENAL SYNDROME TYPE 2 – LITERATURE REVIEW

U srpnju 2013. godine proveli smo pretraživanje literature u bazi podataka Pubmed. Ključna riječ je bila kardiorenalni sindrom tip 2, a pretraživanje ograničeno na radove koji su napisani na engleskom jeziku i koje se odnose na ljude. U ovaj pregled literature nismo uključili reference u postupku objave i sažetke. Iako je u posljednjem desetljeću postignut velik napredak u shvaćanju kardiorenalnog sindroma (KRS) točan patogenetski slijed njegova postanka i razvoja još nije do kraja razjašnjen. Samim time niti do sada poznata terapija ne može u potpunosti anulirati konektore u KRS. Uz standardnu terapiju koja je za sada nedovoljnog učinka u sprječavanju progresije KRS, obećavajući učinak imaju novi lijekovi poput levosimendana, antagonista adenozin A1 receptora i tezosentana.We performed literature search in the Pubmed database in July 2013. The key word used for search was cardiorenal syndrome type 2, limited to English language and humans. Over the last decade, a significant advance in the understanding of the cardiorenal syndrome has been achieved. However, precise pathogenesis remains to be clarified. Current treatment in postponing progression of cardiorenal syndrome type 2 is not efficient, although novel drugs like levosimendan and tezosentan seem promising. Future research is necessary to determine their role in the treatment of cardiorenal syndrome type 2

Synthesis, Structural Characterization and Magnetic Properties of Iron Boride Nanoparticles with or without Silicon Dioxide Coating

Nanoparticles of iron boride (Fe2B, Fe2B coated in SiO2, FexCo2−xB coated in SiO2) were synthesized using the reduction of metal ions by sodium borohydride. X-ray diffraction confirms the amorphicity of the coated compounds and scanning electron microscope imaging revealed the nanoparticulated structure of all compounds. The splitting between zero-field-cooled and field-cooled temperature dependent magnetization curves point to the blocking of superparamagnetic particles magnetization. Magnetic hysteresis loops are however consistent with the combined effects of blocked superparamagnetic and ferromagnetic (multidomain) particles. The observed quite complex magnetic behaviour is in accordance with structural studies, where additional phases and broad distribution of particle sizes were identified

Synthesis, Structural Characterization and Magnetic Properties of Iron Boride Nanoparticles with or without Silicon Dioxide Coating

Nanoparticles of iron boride (Fe2B, Fe2B coated in SiO2, FexCo2−xB coated in SiO2) were synthesized using the reduction of metal ions by sodium borohydride. X-ray diffraction confirms the amorphicity of the coated compounds and scanning electron microscope imaging revealed the nanoparticulated structure of all compounds. The splitting between zero-field-cooled and field-cooled temperature dependent magnetization curves point to the blocking of superparamagnetic particles magnetization. Magnetic hysteresis loops are however consistent with the combined effects of blocked superparamagnetic and ferromagnetic (multidomain) particles. The observed quite complex magnetic behaviour is in accordance with structural studies, where additional phases and broad distribution of particle sizes were identified

Should we be afraid of ticks?

Krpelji su artropodi i pripadaju rodu Artropoda, razredu paučnjaka (Arachnida), podrazredu Acaria, redu Parasitiformes, te se dijele u dvije dobro opisane obitelji: čvrsti krpelji (Ixodidae) i meki krpelji (Argasidae). Opisana je i treća obitelj, Nuttalliellidae, međutim s obzirom da pripadnici te vrste već duže nisu uzrokovani, nije poznata njena točna filogenetska povezanost s ostale dvije obitelji. Obitelj mekih krpelja (Argasidae) sastoji se od 193 vrste. Obitelj čvrstih krpelja (Ixodidae) sastoji se od 702 vrste svrstane u 14 rodova. Mnoge vrste krpelja igraju važnu ulogu u humanoj i veterinarskoj medicini kao vektori zaraznih bolesti poput: krpeljnog meningoencefalitisa (KME), Lyme borelioze, tularemije, erlihioze, mediteranske pjegave groznice, krimsko-kongoanske hemoragijske vrućice, itd. Europski centar za prevenciju i nadzor bolesti (ECDC) prati kretanje i distribuciju krpelja i njihovih vrsta. U Europi se putem VectorNet mreže prate kretanja sljedećih vrsta krpelja: Dermacentor reticulatus, Hyalomma marginatum, Ixodes persulcatus, Ixodes ricinus, Ornithodorus spp i Rhipicephalus sanguineus. Ixodes ricinus vrlo je rasprostranjen, a njegova distribucija seže od Portugala do Rusije, sjeverne Afrike do Skandinavije. Može preživjeti u različitim okolišnim uvjetima. Njegova distribucija se promijenila u mnogim zemljama posljednjih godina, tako da se može pronaći i na višim nadmorskim visinama i geografskim širinama. Krpelj vrste Ixodes ricinus uključen je u prijenos bolesti KME i Lyme borelioze. U Republici Hrvatskoj je prema podacima Hrvatskog zavoda za javno zdravstvo u razdoblju od 2004. do 2017. godine, registrirano ukupno 5.834 slučajeva Lyme borelioze (godišnji prosjek 417 slučajeva), dok je u istom razdoblju na području grada Zagreba registrirano 1.774 slučajeva (godišnji prosjek 127 slučajeva). U promatranom razdoblju u Republici Hrvatskoj registrirano je ukupno 376 slučajeva KME (godišnji prosjek 27 slučajeva), dok je u istom razdoblju na području grada Zagreba registrirano 27 slučajeva KME (godišnji prosjek 2 slučaja). Podaci o oboljelim osobama dobiveni su iz službenih prijava zaraznih bolesti kao sastavnog dijela sustava obveznog prijavljivanja zaraznih bolesti u Republici Hrvatskoj. Cijepljenje protiv KME i mjere osobne zaštite (odjeća, repelenti) imaju veliku važnost u individualnoj zaštiti osoba protiv bolesti koje prenose krpelji.Ticks are arthropods from the Phylum Arthropoda, Class Arachnida, Subclass Acaria, order Parasitiformes, divided in two Families: hard ticks (Ixodidae) and soft ticks (Argasidae). Phylogenetic link of the third family (Nuttalliellidae) to other families remains unknown, as, although well described, it has not been sampled for a long time. The family of soft ticks (Argasidae) counts 193 species, and that of hard ticks (Ixodidae) counts 702 species divided in 14 classes. Many tick species have an important role in human and veterinary medicine as vectors of infectious diseases such as: tick-borne encephalitis (TBE), Lyme borreliosis, tularemia, ehrlichiosis, boutonneuse fever, Crimean-Congo haemorrhagic fever, etc. The European Centre for Disease Prevention and Control (ECDC) monitors the movement and distribution of ticks and their species. Tick species Dermacentor reticulatus, Hyalomma marginatum, Ixodes persulcatus, Ixodes ricinus, Ornithodorus spp. and Rhipicephalus sanguineus are monitored in Europe via VectorNet network. The distribution of Ixodes ricinus tick is very wide (from Portugal to Russia; from North Africa to Scandinavia); and therefore it can survive in different environmental surroundings. The geographical distribution of Ixodes ricinus tick has changed in many countries in the past years, so it can be found on higher altitudes and geographical latitudes and longitudes. Ixodes ricinus tick is involved in the transmission of TBE and Lyme borreliosis. According to data from the Croatian Institute of Public Health obtained from the national communicable disease reporting system, there were 5834 (annual average 417) cases of Lyme borreliosis (LB) registered in the Republic of Croatia in the period from 2004 till 2017, with 1774 (annual average 127) of them in the city of Zagreb. In the same period, there were 376 cases (annual average 27) of TBE registered in the Republic of Croatia, with 27 cases (annual average 2) in the city of Zagreb. Vaccination against TBE and personal protective measures (adequate clothing, repellents) play an important role in the prevention of tickborne diseases