We present a single-step route to generate ordered nanocomposite thin films of secondary phase inclusions (Mn3O4) in a pristine perovskite matrix (LaMnO3) by taking advantage of the complex phase ...diagram of manganese oxides. We observed that in samples grown under vacuum growth conditions from a single LaMnO3 stoichiometric target by Pulsed Laser Deposition, the most favourable mechanism to accommodate Mn2+ cations is the spontaneous segregation of self-assembled wedge-like Mn3O4 ferrimagnetic inclusions inside a LaMnO3 matrix that still preserves its orthorhombic structure and its antiferromagnetic bulk-like behaviour. A detailed analysis on the formation of the self-assembled nanocomposite films evidences that Mn3O4 inclusions exhibit an epitaxial relationship with the surrounding matrix that it may be explained in terms of a distorted cubic spinel with slight (~9º) c-axis tilting. Furthermore, a Ruddlesden-Popper La2MnO4 phase, helping to the stoichiometry balance, has been identified close to the interface with the substrate. We show that ferrimagnetic Mn3O4 columns influence the magnetic and transport properties of the nanocomposite by increasing its coercive field and by creating local areas with enhanced conductivity in the vicinity of the inclusions.
LiNbO3 single crystals were grown by the Czochralski technique in an air atmosphere. The polarized IR and Raman spectra of both poled and unpoled LiNbO3 single crystals were measured and compared. ...The spectra were recorded at different temperatures between 20 and 300 K. In addition, we discussed the phonon anomalies and anharmonicity in both, IR and Raman spectra.
Barium strontium titanate was obtained by hydrothermal treatment of barium strontium titanate citric precursor solution, previously prepared by complex polymerization method. The thermally induced ...phase evolution was followed at various temperatures up to 800 °C using thermogravimetric and differential thermal analysis, X-ray diffraction analysis, and Raman spectroscopy. Microstructural characterization of barium strontium titanate powders was performed by scanning and transmission electron microscopy. The proposed synthesis route has been proven as a better and faster method for barium strontium titanate powder preparation as compared to the conventional complex polymerization route. The method was found efficient for production of low agglomerated, fine, nanosized barium strontium titanate powder with well defined stoichiometry, and sub-micron particle size. The results of structural and microstructural characterization showed the complete crystallization of carbonate-free barium strontium titanate powder at 700 °C with an average size of crystallites below 50 nm.
Raman spectroscopy technique has been successfully used to study the microscopic nature of structural and/or morphological properties of investigated nanopowders. The phonon confinement model has ...been applied for the estimation of nanocrystals dimensions (TiO2 and CeO2), as well as the correlation length (ZnO), from the frequency shift and asymmetrical broadening of Raman optical phonon modes. The particle size distribution in nanopowders has been estimated from the low frequency Raman spectra, using the fact that the acoustic phonon modes in nanosized TiO2 and CeO2 can be well described by the elastic continuum model. In addition, the appearance of surface optical phonon modes has been predicted theoretically by the dielectric functions approach and detected experimentally in the Raman spectra of ZnO nanopowders, whereas the resonant behaviour of the first and second order ZnO Raman modes has been used for estimation of the electron-phonon interaction in this kind of nanomaterial. The optical properties of oxide nanopowders have been investigated by spectroscopic ellipsometry and photoluminescence spectroscopy. It has been shown that bandgap energy, as well as the energies of the other interband electronic transitions in investigated nanopowders can be determined by spectroscopic ellipsometry. On the other side, the existence of the broad bands in visible region of the photoluminescence spectra of TiO2 and ZnO nanopowders points out to the various electronic transitions mediated by defect levels within the bandgap.
Nanocrystalline multilayers from ZnSe/Zn0.6Cd0.4Se with three different layer thicknesses (3.5, 5.0, 10.0 nm) and, for comparison, 400 nm thick Zn0.6Cd0.4Se nanocrystalline single layers have been ...prepared by thermal evaporation of ZnSe and CdSe in vacuum. Raman scattering spectra have been measured in the range 100–1000 cm−1 under excitation with the 488 and 514.5 nm lines of an Ar+ laser. Series of four bands have been seen in the spectra of all samples. They have been related to replicas of the longitudinal optical LO‐phonon in the ZnxCd1−xSe layers and interpreted as an indication for crystallinity of both kinds of samples. A blue shift of the 1 LO maximum has been observed, which has been connected with an increase of the compressive stress in the ternary layers when the layer thickness decreases. It has also been obtained that the ratio of the integrated intensity of the 1 LO band in the spectra taken with the 488 and 514.5 nm lines decreases with decreasing Zn0.6Cd0.4Se layer thickness. The result has been assigned to size‐induced increase of the optical band gap of the layers. This conclusion has been confirmed by spectral photocurrent and optical transmission measurements.
Poljska ljubica (Viola arvensis Murr.) jednogodišnja je vrsta koja zakorovljuje usjeve gustog sklopa te nasade bobičastog voća i povrćarskih kultura. Potječe s prostora Euroazije, a zbog svojstva ...adaptibilnosti proširila se i na ostale kontinente. Često je moguća zamjena s vrstom V. tricolor L. (maćuhica) od koje se razlikuje po boji cvjetova i obliku gornjih listova. Razmnožavanje V. arvensis generativno je. U laboratorijskim uvjetima najveća klijavost ostvaruje se pri temperaturi od 15 °C u trajanju od 8 sati te pri temperaturi od 5 °C u trajanju od 16 sati. Preferira pjeskovita tla reakcije od blago kisele do lužnate. Tolerantna je na zasjenjivanje i sušu. Prezimljuje u formi rozete, a visinom biljka može dosegnuti prosječno 30 cm. Zbog niskog habitusa izravne štete uzrokovane korovnom vrstom V. arvensis nisu toliko značajne koliko neizravne koje se javljaju nakon žetve usjeva kada biljno tkivo zahvaćeno pri žetvi usjeva može utjecati na povećanje vlage sjemena usjeva. V. arvensis vrsta je koja se prilagodila utjecaju čovjeka te se uspješno razvija na obrađivanim tlima. Forma rozete smatra se tolerantnom prema primjeni herbicida te je zbog toga otporna na primjenu kemijskih mjera suzbijanja.
Weeds can be one of the most severe threats to crop production, especially when they are widespread and highly adaptable. Part of the adaptive strategy of plants is the ability to germinate in ...different conditions. Germination is the first developmental phase of plant life and is fundamental for its establishment. In this work, the germination of two populations of Datura stramonium L. at two different sites in Croatia (one cropped, the other non-agricultural) was tested under a wide range of salinity stress, 4, 8, 12, and 16 dS/m, and pH stress, values 1-9, at two temperature ranges of 15-25 °C and 18-30 °C. The results show that this species can tolerate high salinity, with a high number of seeds germinating, even under the highest level of saline stress and especially at higher temperatures: 21.7% of seeds germinated at 15-25 °C and 51.2% at 18-30 °C. D. stramonium also appears to be quite acid tolerant, with a significant reduction in germination only at pH 2, and no germination only at pH 1. Germination was always higher at higher temperatures, independently of abiotic stress. Although there were some differences between the two populations in the final germination percentages, they were similar in their responses to the abiotic stresses.
Rod Panicum obuhvaća veći broj vrsta (370 - 600) raširenih u svijetu, a podrijetlom je iz tropskih i suptropskih krajeva. U RH su prisutne četiri vrste iz ovog roda: Panicum capillare L., Panicum ...dichotomiflorum Michx., Panicum miliaceum L. i Panicum riparium H. Scholz od kojih se prve tri pojavljuju kao korovi okopavinskih usjeva. Panicum capillare i Panicum dichotomiflorum invazivne su vrste na području RH: P. capillare prvi put zabilježen u RH 60-ih godina, Panicum dichotomiflorum 70-ih, a Panicum miliaceum 90-ih godina prošlog stoljeća. Ovisno o različitom vremenu pojave na prostoru RH, u usjevima je kao korovna vrsta najrasprostranjeniji P. capillare kojeg slijedi P. dichotomiflorum te potom P. miliaceum . Navedene su vrste prema životnom ciklusu jednogodišnje te se šire isključivo sjemenom. Sjeme se najčešće širi poljoprivrednim strojevima i oruđem, ali je znatno prisutna epizoohorija te anemohorija . Za razliku od ostalih monokotiledonih korovnih svojti čije sjeme u banci sjemena brzo gubi klijavost, sjeme P. dichotomiflorum može sačuvati klijavost i do 20 godina, čineći perzistentnu banku sjemena u tlu. Sve su navedene vrste kasnoproljetne s temperaturnim minimumom za klijanje od 10 °C i više te optimumom od 30 °C. Suzbijanje vrsta roda Panicum najčešće se provodi herbicidima. Ipak, zbog kasnog nicanja u usporedbi s drugim korovnim travama u kukuruzu, često izbjegnu aplikaciju herbicida, što se potom pogrešno tumači lošom učinkovitosti. No, poznavanjem biologije i ekologije vrsta moguća je uspješna integrirana zaštita te primjena nekemijskih mjera poput zasjenjivanja, odnosno korištenja pokrovnih kultura, smanjenja razmaka sjetve te korištenja plodoreda i obrade tla.
The present study estimated the cracking phenomenon in as-plasma-sprayed hydroxylapatite coatings (HACs) after they were being subjected to the severe cutting conditions in the direction ...perpendicular to the coating/substrate interface. In order to evaluate the effects of substrate preheating on the occurrence of micro-cracks, the HACs were deposited at different initial substrate temperatures (TS = 20, 100 and 200?C). The changes in phase composition and HA splat morphology with TS were observed and were correlated with the cracking occurrence. The results showed that severe cutting conditions introduced a localized cracking in the regions of HACs dominantly attributed to the brittle hydroxyl-deficient amorphous calcium phosphate (ACP) phase. This effect was particularly observable in the HACs deposited without preheating of substrate. On the other hand, the preheating of substrate reduced the presence of micro-cracks and caused insignificant changes in the average local phase composition. In HACs deposited with preheating of substrate, the HA splats (of which HACs are composed) were thinner and recrystallized HA regions seemed smaller in size and more evenly distributed. These results implied potentially important roles of the HA splat formation mechanism on the distribution of ACP and recrystallized HA regions in the as-plasma-sprayed HACs and the cracking resistance of HACs.
Cilj istraživanja bio je utvrditi stupanj morfološke (masa sjemena) i funkcionalne (klijavost, dormantnost, smrtnost sjemena i dinamika klijanja) varijabilnosti unutar dvije populacije sjemena ...korovne vrste Ambrosia artemisiifolia L. (ambrozija) sakupljene u sjeverozapadnom dijelu Hrvatske: Jastrebarsko (45 ° 40'18˝N; 15 ° 39'03˝E), populacija-J i Popovača (45 ° 34´1˝N; 16 ° 40´43˝E), populacija-P. Prikupljeno je sjeme s 20 biljaka/populaciji u listopadu 2014. Rezultati istraživanja ukazuju na slabu varijabilnost (CV-J = 18,2%, CV-P = 29,8%) mase 1 000 sjemenki s prosječnom masom od 4,05 g (J) i 4,54 g (P). Intrapopulacijska varijabilnost bila je relativno visoka za udio mrtvog sjemena u populaciji-J (CV = 67,6%), ali vrlo slaba za udio klijavog (CV = 4,9%) te umjerena za udio dormantnog sjemena (CV = 51,0%). Varijabilnost unutar populacije-P bila je umjerena za udio klijavog i mrtvog sjemena (CV = 34,5%; 34,1%), a relativno slaba za udio
dormantnog sjemena (CV = 14,2%). Dinamika klijanja (T10, T50 i T90) obje populacije bila je slabo ili umjereno varijabilna. Sredina klijanja (T50) bila je relativno slabo varijabilna za obje istraživane populacije (CV - J = 12,0%; CV - P = 22,4%).
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