Magnetic iron oxide nanoparticles as MRI contrast agents - a comprehensive physical and theoretical study

Magnetite nanoparticles, especially superparamagnetic iron oxide nanoparticles, are established contrast agents for magnetic resonance imaging. Magnetosomes, which are magnetite nanoparticles of biological origin, have been shown to have better contrast properties than current formulations possibly because of their larger size and high monodispersity. Here, we present an integrated study of magnetosomes and synthetic magnetite nanoparticles of varying size, hence, magnetic properties. We investigate not only the relaxation times as a measure for the contrast properties of these particles, but also their cytotoxicity and demonstrate the higher contrast of the larger particles. A theoretical model is presented that enables us to simulate the R2=R1 ratio of a contrast agent and con�rm that larger particles offer higher contrast. The results from this study illustrate the possibility to obtain colloidal stability of large magnetic nanoparticles for magnetic resonance imaging applications and serve as an impetus for a more quantitative description of the contrast effect as a function of the size

Interferometer for nanometric displacement sensing

Bakalaura darbā aplūkotas interferometrisko metožu pielietošanas iespējas mazu pārvietojumu mērīšanai, paskaidroti dažāda tipa interferometru darbības principi, optisko interferences signālu reăistrēšanas un apstrādes metodes. Darba rezultātā ar pieejamo aparatūru LU CFI Segnetoelektriėu fizikas laboratorijā nodemonstrēts daudzstaru kompensēta diferenciālā interferometra darbības princips, parādot, kā iespējams veikt mazu deformāciju mērījumus ar augstu izšėiršanu. Izskaidrots divu optisko detektoru (kvadratūras) reăistrācijas metodes pielietojums joslu dalīšanai un modulācijas metodes pielietojums Ĝoti augstas izšėiršanas sasniegšanai. Ar darba rezultātiem ir parādīts, ka izveidotais interferometra prototips un piedāvātās datu reăistrācijas un apstrādes metodes dod iespēju ar nanometrisku precizitāti veikt segnetoelektrisku materiālu parauga virsmas pārvietojumu mērījumus.The work considers methods for small displacement sensing with nanometric resolution using double pass differential interferometer. Various types of interferometers have been discussed as well as methods of optical interference signal registration and processing. As a result of this work the working principle of many-beam compensated differential interferometer has been demonstrated in Ferroelectrics laboratory of UL ISSP. It has been shown how to realize measurements of small deformations with high resolution and explained how to use two optical detector (quadrature) registration for fringe subdivision. Also it has been shown how to use modulation method to gain very high resolution. Results have proved that this interferometer prototype and methods of data registration and processing gives the ability to make nenometric precision measurements of surface displacement of ferroelectric materials

Electromechanical Properties of Ferroelectric Relaxors

Segnetoelektriskie materiāli tiek plaši pielietoti ļoti daudzās tehnoloģijās, un pēdējās desmitgadēs aktuāla ir kļuvusi bezsvina segnetoelektriķu pētīšana. Nātrija bismuta titanāts NaBiTiO3 (NBT) ir aktuāls bezsvina segnetoelektrisks materiāls, jo uzrāda labas elektromehāniskās īpašības. Maģistra darba "Segnetoelektrisku relaksoru elektromehāniskās īpašības" mērķis ir veicināt LU Cietvielu fizikas institūtā sākto jaunu NBT cieto šķīdumu turpmāku pētniecību. Darba gaitā ir izveidota eksperimentālā iekārta segnetoelektrisku materiālu paraugu deformācijas mērīšanai atkarībā no pieliktā elektriskā lauka un paraugā inducētās polarizācijas. Ir izveidota datorprogramma, kas spēj ar augstu izšķirtspēju izmērīt interferences ainas pārvietošanos. Ir veikti pirmie mērījumi NBT ternārajiem cietajiem šķīdumiem ar stroncija titanātu un svina titanātu.Ferroelectric materials have wide range applications in a lot of fields. Research on lead-free ferroelectrics has become actual in the last decades. Sodium bismuth titanate NaBiTiO3 (NBT) is an actual lead-free ferroelectric because it shows good electromechanical properties. The objective of Masters thesis "Electromechanical properties of ferroelectric relaxors" is to develop research on new NBT solid solutions that has been started in Institute of solid state physics (University of Latvia). An experimental setup has been made in the course of this work to measure deformation of ferroelectric material samples in dependence of applied electric field and induced polarization. A computer program has been made that can measure interference pattern movement with high accuracy. First measurements of NBT ternary solid solutions with strontium titanate and lead titanate has been made

Diatom communities in lakes and streams of varying salinity from south-west Western Australia : distribution and predictability

The distribution pattern of diatoms from lakes and streams of varying salinity in the south-west of Western Australia was investigated. A total of 95 water bodies were sampled and separated into freshwater (50 ppt). The south-west and specifically the inland wheatbelt region has been severely influenced by secondary salinisation, due to clearing of native vegetation for agriculture. There has been little research on diatom communities from salt-affected systems, with this data providing the basis for the development of an inference model based on species optima and tolerance limits to salinity.Physico-chemical variables measured from the study sites were collated and assessed. Salinity ranged from freshwater (0.04) to hypersaline (156.80 ppt), and pH ranged from acidic (2.90) to alkaline (10.51). Dissolved oxygen levels were recorded from 1.11 to 18.67 mgL[superscript]-1, water temperature from 6.30 to 28.10 ºC and peripheral vegetation scores from 1 (little or no cover) to 5 (dense cover). Analysis of variance (ANOVA) showed that salinities were significantly higher in standing waters located further inland, compared to flowing waters in high rainfall areas. Hypersaline wetlands displayed significantly lower dissolved oxygen levels, higher water temperatures and reduced peripheral vegetation, compared to freshwaters. The pH of hypersaline sites was also significantly lower, associated with surrounding land use or underlying geology. The data collected provides important baseline information, with implications for aquatic biota.The community structure of diatoms in relation to varying salinity concentration was explored. An artificial substrate collector (JJ periphytometer) was used to standardise sampling and ensure diatom assemblages were representative of ambient water quality. A total of 217 taxa were identified with the highest diversity observed in freshwater sites (up to 33 species), and limited to less than 15 in hypersaline waters. According to BIOENV, salinity was the key factor influencing diatom community structure. SIMPER analysis found a number of discriminating taxa between salinity ranges, specifically between assemblages from freshwater and hypersaline sites. Taxa such as Achnanthidium minutissimum and Gomphonema parvulum were indicative of freshwaters. In comparison, Amphora coffeaeformis and Nitzschia ovalis were associated with hypersaline water bodies.Diatom community structure was also examined from 20 hypersaline wetlands in the wheatbelt region with varying pH. Characteristic taxa including Amphora coffeaeformis, Hantzschia sp. aff. baltica and Nitzschia ovalis showed a wide tolerance to salinity and pH, or hypersaline acidic conditions. BIOENV analysis found there were no observable differences between diatom assemblages in relation to salinities above 50 ppt and that pH was highly correlated to species composition. The increasing occurrence of acid saline lakes is of concern and is most likely attributable to deep drainage practices and continued use of fertilisers in agricultural areas.A diatom-based transfer function was developed from the south-west dataset, to document species optima and tolerance limits to salinity. CCA analysis showed that salinity accounted for a significant and independent amount of variation in the diatom data enabling an inference model to be derived. The most successful model was generated using tolerance-downweighted weighted averaging, with a high coefficient of determination and low prediction errors that remained high after jackknifing. The optima of freshwater diatoms were similar to those reported from other regions of the world, although the optima of hypersaline species tended to be higher. Comparatively, the model performed very well, with the potential to be applied in future paleolimnological studies.In conclusion, this study has shown diatoms to be effective biomonitoring tools, providing the basis for future sampling strategies that assess the biodiversity of salt-affected water bodies in Western Australia. Potential indicator species from different salinity ranges were identified and the sensitivity of diatoms allowed for the development of a statistically robust inference model for the south-west. The reported optima and tolerance limits of important taxa may be further explored to evaluate the success of remediation measures implemented for secondary salinised systems in this region

Conditioned inhibition in flavour aversion learning : odor as a conditioned inhibitor

Two experiments were performed which demonstrated that an olfactory stimulus can become associated with toxicosis over long CS-US delays and, more importantly, that an olfactory stimulus can become a conditioned inhibitor in a feeding situation. In Experiment 1, hooded rats were allowed to drink water while a stream of amyl acetate vapour was directed towards the end of the drinking spout. Toxicosis was then induced via the injection of lithium chloride after delays of 0, 0.5, 1, 4, and 12 hours for different groups. When compared with no-toxicosis controls, it was found that significant aversions were obtained for all groups except the 12 hr delay group. In Experiment 2, hooded rats were given conditioned inhibition training in which the taste of saccharin alone was always followed by induced illness, but the taste of saccharin plus the odor of amyl acetate was not. In a series of three subsequent tests - summation, enhancement of conditioning, and retardation - it was demonstrated that the odor had acquired active inhibitory properties. The results paralleled those obtained with more traditionally studied stimuli and techniques and hence were found to be readily predictable from a recent model of conditioning set forth by Rescorla & Wagner (1972)