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Determination of output factors and absorbed dose profiles for Leksell gamma knife
No full textStereotaktička radiokirurgija sve je popularnija metoda za liječenje patoloških procesa unutar mozga, a Leksellov gama nož je jedan od vodećih uređaja koji pokazuje izvrsne rezultate u tom području. Uređaj koristi 192 uska fotonska snopa fotona koji nastaju u raspadu radioaktivnih izvora 60Co. Snopovi se pomoću stereotaktičkog okvira precizno usmjeravaju u leziju i sijeku se u zajedničkoj točki koju nazivamo izocentar. U zračenju se predaje jednokratna visoka doza zračenja, što za rezultat daje približno sfernu raspodjelu apsorbirane doze. Za izračun apsorbirane doze koristi se računalni algoritam, a osnovu za izračun predstavljaju točno određeni izlazni faktori i profili apsorbirane doze koji su u ovom radu eksperimentalno određeni. Uz navedene veličine, osnovu za točan račun doze čini i brzina apsorbirane doze određena u referentnim uvjetima, što nije predmet ovog diplomskog rada. Sva mjerenja izložena u ovom radu provedena su na Odjelu za stereotaksiju, funkcijsku neurokirurgiju i radioneurokirurgiju, Klinike za neurokirurgiju KBC-a Zagreb. Profili i izlazni faktori određeni su pomoću EBT3 radiokromskog filma i ionizacijskih komora PinPoint3D i PinPoint za sve širine fotonskih snopova gama noža dobivenih kolimatorima veličine 4 mm, 8 mm i 16 mm. Sva mjerenja su provedena u tkivo-ekvivalentnom fantomu Solid Water.
Pune širine na pola maksimuma i širine polusjena profila dobivenih EBT3 filmom su u vrlo dobrom slaganju s referentnim vrijednostima dobivenim Monte Carlo simulacijama, dok vrijednosti izlaznih faktora dobivene filmom odstupaju od referentnih vrijednosti, posebice za najmanje polje gama noža veličine 4 mm. Analizom profila dobivenih ionizacijskim komorama PinPoint3D i PinPoint utvrđeno je širenje polusjena za polje veličine 4 mm i 8 mm, dok vrijednosti širina na pola maksimuma ne odstupaju značajno od referentnih vrijednosti. Vrijednosti izlaznih faktora dobivenih ionizacijskim komorama značajno odstupaju za malo polje veličine 4 mm, dok su vrijednosti za polje veličine 8 mm u skladu s referentnim vrijednostima. Širenje polusjena profila i veliko odstupanje izlaznih faktora za malo polje veličine 4 mm prisutno je zbog izraženog volumnog učinka usrednjavanja signala karakterističnog za ionizacijske komore i narušenja lateralne elektronske ravnoteže koje se može javiti u malim fotonskim poljima. Razlog velikog volumnog učinka usrednjavanja signala leži u neodgovarajućem odnosu veličina aktivnog mjernog volumena ionizacijske komore i fotonskih snopova. Zbog navedenog, EBT3 film je preporučeni dozimetar za određivanje profila doza [16], ali ne i za određivanje izlaznih faktora, a male ionizacijske komore su preporučeni dozimetri za određivanje apsorbirane doze u referentnim uvjetima, ali ne i za relativnu dozimetriju, za određivanje profila i izlaznih faktora.Stereotactic radiosurgery is an increasingly popular method for treating pathological processes within the brain, and the Leksell Gamma Knife is one of the leading irradiators or machines that shows excellent results in this field. The device uses narrow photon beams generated by the radioactive 60Co sources, which are precisely directed at the lesion using a stereotactic frame. The photon beam axes intersect at a common point called the isocenter. During irradiation, a high dose can be delivered, resulting in an approximately spherical distribution of the absorbed dose. A computer algorithm is used to calculate the absorbed dose, and the calculation is based on precisely determined output factors, and absorbed dose profiles, which were experimentally determined in this study. Additionally, the basis for accurate dose calculation is also the absorbed dose rate determined in the reference conditions, which is not the subject of this thesis. All measurements presented in this study were conducted at the Division of Stereotaxy, Functional Neurosurgery, and Radiosurgery of the Department of Neurosurgery, University Hospital Center Zagreb. Profiles and output factors were determined using EBT3 radiochromic film and PinPoint3D and PinPoint ionization chambers for all widths of the gamma knife photon beams obtained with collimators of sizes 4 mm, 8 mm, and 16 mm. All measurements were performed in a tissue-equivalent phantom, Solid Water.
The full width at half maximum (FWHM) and penumbra widths of the profiles obtained with EBT3 film are in very good agreement with the reference values obtained from Monte Carlo simulations, while the output factor values obtained with the film deviate from the reference values, especially for the smallest gamma knife field size of 4 mm. Analysis of the profiles obtained with the PinPoint3D and PinPoint ionization chambers revealed a broadening of the penumbra for the field sizes of 4 mm and 8 mm, while the FWHM values do not significantly deviate from the reference values. The output factor values obtained with the ionization chambers significantly deviate for the small field size of 4 mm, while the values for the 8 mm field size are in line with the reference values. The broadening of the penumbra and significant deviation of output factors for the small 4 mm field are due to the pronounced volume averaging effect characteristic of ionization chambers and the disruption of lateral electronic equilibrium that can occur in small fields. The reason for the significant volume averaging effect lies in the inappropriate ratio between the active measuring volume of the ionization chamber and the photon beams. Therefore, the EBT3 film is the recommended dosimeter for dose profile determination [16], but not for determining output factors, while small ionization chambers are the recommended dosimeters for determining absorbed dose under reference conditions, but not for relative dosimetry, such as determining profiles and output factors
Morphological and genetic characterization of the Mediterranean killifish population Aphanius fasciatus (Teleostei, Aphaniidae) in the Šćuza Bay
No full textObrvan, Aphanius fasciatus, je eurihalina vrsta koja naseljava vodna tijela kojima su svojstvene ekstremne vrijednosti saliniteta i temperature. Svi zabilježeni lokaliteti rasprostranjenosti međusobno su odvojeni zbog malog broja pogodnih staništa što uz značajke biologije vrste, različite pritiske i ugroze te izostanak protoka gena između populacija dovodi opstanak lokalnih populacija u pitanje. Ciljevi ovog istraživanja bili su opisati morfološke karakteristike i gensku raznolikost populacije u uvali Šćuza, utvrditi filogenetski položaj i srodstvene odnose u odnosu na druge populacije ove vrste te predložiti konzervacijske mjere za opstanak populacije. Za proučavanje morfologije koristila se deskriptivna statistika, a t-testom je istraživana razlika u morfometrijskim karakteristikama mužjaka i ženki. Kako bi se utvrdili srodstveni odnosi među populacijama, provedena je filogenetska rekonstrukcija na temelju sekvenci gena za citokrom b pomoću metode najveće parsimonije, metode najveće vjerojatnosti i metode susjednog povezivanja. Uz to analizom vijabilnosti populacije utvrđeno je koje prijetnje imaju najveći učinak na opstanak populacije. Dobiveni rezultati smještaju istraživanu populaciju u sjevernojadransku grupu populacija obrvana. Utvrđena je umjerena genska raznolikost, no nešto viša nego u drugim populacijama na istočnoj obali Jadrana. Kao najveća prijetnja opstanku populacije prepoznata je degradacija staništa.The Mediterranean killifish, Aphanius fasciatus, is a euryhaline species that inhabits water bodies characterized by extreme values of salinity and temperature. All recorded localities of distribution are separated from each other due to the small number of suitable habitats, which in addition to the features of the species' biology, different pressures and threats and the absence of gene flow between populations leads local populations to extinction. The aim of this study was: describe the morphological characteristics and genetic diversity of the population in the Šćuza bay, determine the phylogenetic position and relationships in relation to other populations of this species, and to propose conservation measures for the survival of the population. Descriptive statistics was used to study the morphology, and the difference in the morphometric characteristics of males and females was investigated using the t-test. To determine relationships between populations, a phylogenetic reconstruction was used, based on cytochrome b gene sequences using the maximum parsimony, maximum likelihood and median joining. In addition, a population viability analysis determined which threats have the biggest effect on the population survival. The results place the researched population in the northern Adriatic group of Mediterranean killifish populations. Moderate genetic diversity was found, but somewhat higher than in other populations on the eastern coast of the Adriatic. Habitat degradation is recognized as the biggest threat to the survival of the population
Euclidean domains
No full textTeorem o dijeljenju s ostatkom kaže da za dane cijele brojeve i postoje jedinstveni cijeli brojevi i takvi da je i . Klasa integralnih domena, to jest komutativnih prstena s jedinicom bez djelitelja nule, koji posjeduju svojstvo analogno teoremu o dijeljenju s ostatkom, nazivaju se euklidske domene. Štoviše, euklidske domene dopuštaju oblik Euklidova algoritma za određivanje najvećeg zajedničkog djelitelja. U ovom diplomskom radu pokazujemo neka svojstva euklidskih domena te primjere primjere iz klase prstena oblika i .The quotient-remainder theorem says that for given integers and , there exist unique integers and such that i . A class of integer domains, i.e. commutative rings with unity that has no zero divisors, that posseses a property analogous to the quotient-remainder theorem are called Euclidean domains. Moreover, Euclidean domains admits a form of the Euclidean algorithm for calculating the greatest common divisor. In this thesis, we show some properties of Euclidean domains and give some examples in the class of rings of the form and
Interactions between the gut microbiome and the immune system
No full textCrijevo je jedno od najvećih imunoloških organa koje svojom sluznicom djeluju kao barijera protiv
prodora patogena, istovremeno esencijalno je za održavanje komunikacije imunološkog sustava i
crijevnog mikrobioma. Crijevni mikrobiom zajednica je brojnih bakterija, virusa i gljivica koji na
razne načine utječu na imunološki odgovor. Bakterije svojim metabolitima reguliraju proliferaciju,
diferencijaciju i funkcionalnost imunoloških stanica. Svojim utjecajem na imunološki sustav
promiču homeostazu crijeva ili pogoršavaju upalne procese. Jedna vrsta bakterijskih metabolita,
kratkolančane masne kiseline (eng. short-chain fatty acids, dalje: SCFA), pokazale su se kao važni
medijatori upalnih procesa. SCFA-producirajuće bakterije dominiraju zdravim crijevom. Međutim,
različiti čimbenici uzrokuju promjene u sastavu mikrobioma, gdje se povećava kolonizacija
patogena, što dovodi do disbioze crijeva. Disbioza crijeva povezana je s patogenezom različitih
bolesti i povećanoj podložnosti zarazama. S obzirom na to da se svakim novim istraživanjem
interakcije crijevnog mikrobioma i imunološkog sustava pokazuju esencijalnim za zdravlje cijelog
organizma, istraživanje ovog područja vrlo je važno za proučavanje patogeneze bolesti povezanih
s disbiozom i razvojem novih lijekova i tretmana.The intestine is one of the largest immune organs, its mucosa acts as a barrier against the
penetration of pathogens. It is also essential for maintaining communication between the immune
system and the gut microbiome. The gut microbiome is a big community of bacteria, viruses and
fungi that influence the immune response in various ways. Bacteria regulate the proliferation,
differentiation and functionality of immune cells with their metabolites. Through their influence
on the immune system, they promote gut homeostasis or worsen inflammatory processes. One type
of bacterial metabolites, short-chain fatty acids (SCFA), have shown to be important mediators of
inflammatory processes. SCFA-producing bacteria dominate the healthy gut, however various
factors cause changes in the composition of the microbiome where pathogen colonization increases
causing gut dysbiosis. Gut dysbiosis is associated with the pathogenesis of various diseases and
increased susceptibility to infections. New studies show that the interaction between the gut
microbiome and the immune system is essential for the health of the whole organism, research in
this area is critical for the understanding of the pathogenesis of dysbiosis-related diseases and the
development of new drugs and treatments
Magnetic resonance study of rare-earth titanates
No full textWe present an electron spin resonance (ESR) and nuclear magnetic resonance (NMR) study of rare-earth titanates derived from the spin-1/2 Mott insulator YTiO3. Measurements of single-crystalline samples of (Y, Ca, La)TiO3 in a wide range of isovalent substitution (La) and hole doping (Ca) reveal several unusual features in the paramagnetic state of these materials. ESR of the unpaired Ti electron shows broad resonance lines at all temperatures and substitution/doping levels, which we find to be caused by short electronic spin-lattice relaxation times. We model the relaxation as an Orbach process that involves a low-lying electronic excited state, which enables the determination of the excited-state gap from the temperature dependence of the ESR linewidths. We ascribe the small gap to Jahn-Teller splitting of the two lower Ti 2 orbitals. The value of the gap closely follows the Curie temperature . 89Y NMR demonstrates a clear discrepancy between the static and dynamic local magnetic susceptibilities, with deviations from Curie-Weiss behavior at temperatures far above , consistent with the electronic gap detected with ESR. No significant changes are observed by NMR close to , but suppression of fluctuations is detected in the NMR spin-lattice relaxation time at temperatures of about 3×. Additionally, the nuclear spin-spin relaxation rate shows an unusual peak in dependence on temperature for all samples. These results provide insight into the interplay between orbital and spin degrees of freedom in rare-earth titanates and indicate that full orbital degeneracy lifting is associated with ferromagnetic order
Evolucije elektroničkih i kristalnih struktura spojeva europija u ovisnosti o tlaku
No full textIn this thesis, I present results of evolution of electronic and crystal structures of non-centrosymmetric EuTGe3 (T = Co, Rh and Ir) under hydrostatic pressure. Since the discovery of the first heavy-fermion superconductor CeCu2Si2, more than 30 systems have been discovered that exhibit unconventional f -electron superconductivity. Most of them belong to Ce and U compounds, and their phase diagrams are often discussed by using the Doniach model. The ground state is characterized by the competition between the Kondo effect and the Ruderman Kittel-Kasuya-Yosida (RKKY) interaction, which originates from the interaction of localized f -electrons with conduction electrons. The Kondo effect screens the magnetic moments, while the RKKY interactions stabilize the magnetic ordering. Superconductivity tends to appear near the magnetic quantum critical point (QCP). Recently, pressure induced heavy-fermion superconductors have been discovered among CeTX3 (T = Co, Rh, Ir; X = Si, Ge) with the BaNiSn3-type (I4mm) structure which does not possess inversion symmetry. They have attracted much attention due to the possible coexistence of spin-singlet and -triplet Cooper channels initiated by antisymmetric spin-orbit interaction as well as strong correlations.U disertaciji su predstavljeni rezultati evolucije elektronske i kristalne strukture necentrosimetričnih EuTGe3 (T = Co, Rh i Ir) sustava pod hidrostatskim tlakom. Od otkrića prvog teškofermionskog supravodiča CeCu2Si2, otkriveno je više od 30 sustava koji pokazuju nekonvencionalnu f-elektronsku supravodljivost. Većina njih pripada spojevima Ce i U, a njihovi fazni dijagrami često se diskutiraju u okviru Doniachovog modela. Osnovno stanje karakterizirano je natjecanjem Kondo efekta i Ruderman-Kittel-Kasuya-Yosida (RKKY) interakcije. Obje interakcije proizlaze iz interakcije lokaliziranih f -elektrona s metaličnim elektronima. Kondo efekt zasjenjuje magnetske momente, dok RKKY interakcija stabilizira magnetsko uređenje. Supravodljivost se obično pojavljuje blizu magnetske kvantne kritične točke (QCP). Nedavno je otkrivena tlakom inducirana supravodljivost u teškofermionskom sustavu CeTX3 (T = Co, Rh, Ir; X = Si, Ge) s BaNiSn3-tipom (I4mm) strukture koja ne posjeduje inverzijsku simetrije. Ovi sustavi su privukli veliku pažnju zbog moguće koegzistencije spinsingletnih i -tripletnih Cooperovih kanala iniciranih antisimetričnom spin-orbit interakcijom, kao i jakim korelacijama
The role of retinoic acid in mammalian stem cell differentiation
No full textU ovom su radu prikazana dosadašnja istraživanja i saznanja o učincima retinoične kiseline koji potiču diferencijaciju matičnih stanica kod sisavaca. Retinoična kiselina je morfogen koji ima širok raspon funkcija tijekom embrionalnog razvoja organizma. Na diferencijaciju matičnih stanica može djelovati na razini genoma ili preko izvangenomskih mehanizama. Također ima velik potencijal u primjeni u terapijske svrhe protiv teških i malignih bolesti. No poznat je i njen oprečni utjecaj na stimulaciju proliferacije stanica. Cilj ovog rada bio je obuhvatiti nove zaključke u ovom širokom području i otvoriti pitanja za buduća istraživanja ključna za bolje razumijevanje mehanizama retinoične kiseline i njene suradnje s drugim molekulama u staničnom mikrookolišu koje oblikuju staničnu sudbinu.This paper presents the current research and findings on the effects of retinoic acid that promote the differentiation of stem cells in mammals. Retinoic acid is a morphogen with a wide range of functions during the embryonic development of an organism. It can influence stem cell differentiation at the genomic level or through non-genomic mechanisms. Additionally, it holds significant potential for therapeutic applications against severe and malignant diseases. However, its contradictory impact on the stimulation of cell proliferation is also well-known. The aim of this paper was to encompass new conclusions in this broad field and to raise questions for future research crucial for a better understanding of the mechanisms of retinoic acid and its interactions with other molecules in the cellular microenvironment that shape cell fate
Bioactive compounds and biological effects of Brassica microgreens extracts
No full textZbog klimatskih promjena i ubrzanog rasta svjetske populacije, potrebno je pronaći nove izvore hrane koji zadovoljavaju nutritivne zahtjeve te se mogu uzgajati na brz i jednostavan način, uz što manje učinke na okoliš. Mikropovrće, mlade jestive biljke koje sadrže stabljiku, kotiledone i nekoliko pravih listova, pokazalo se kao obećavajuća nova „funkcionalna hrana“ koja odgovara tim uvjetima. Rod Brassica ističe se kao jedan od najčešće uzgajanih za ljudsku prehranu i stoga najdostupnijih za proizvodnju mikropovrća. Povrće ovog roda poznato je po visokim koncentracijama za organizam čovjeka korisnih nutrijenata i fitokemikalija, a mikropovrće se pokazalo kao još bogatiji izvor nekih od njih, poput različitih vitamina, minerala, pigmenata, polifenola i glukozinolata. Mnogi od tih bioaktivnih spojeva imaju izrazito pozitivne učinke na ljudsko zdravlje, zahvaljujući svojim antioksidacijskim, antiupalnim, antidijabetičkim i antikancerogenim svojstvima, stoga se konzumacija mikropovrća bogatog istima predlaže kao učinkovit način prevencije i liječenja niza kroničnih bolesti. Ovaj rad predstavlja pregled informacija o fitokemijskom i nutritivnom sastavu mikropovrća roda Brassica, posebice bioaktivnim spojevima i njihovim učincima u ljudskom organizmu, kako bi se pokazao potencijal mikropovća kao nove „superhrane“.Due to climate change and rapid growth in global population, it is necessary to find new food sources that satisfy nutritional needs and can be cultivated in a fast and simple way, with minimal environmental effects. Microgreens, young plants containing the stem, cotyledons and the emerging first true leaves, have proven to be a promising new „functional food“ that meets those conditions. The Brassica genus stands out as one of the most commonly grown for human consumption and thus one of the most readily available for the production of microgreens. Vegetables of this genus are known for their high concentrations of nutrients and phytochemicals useful for the human organism, and microgreens turn out to be an even richer source of some of them, such as different vitamins, pigments, polyphenols and glucosinolates. Many of these bioactive compounds have extremely positive effects on human health, thanks to their antioxidant, anti-inflammatory, antidiabetic and anticancer properties, which is why consumption of microgreens rich in them is proposed as an effective mean of preventing and treating various chronic diseases. This paper presents an overview of information about the phytochemical and nutritional composition of Brassica microgreens, especially bioactive compounds and their effects in the human organism, in order to show the potential of microgreens as the new „superfood“
Ugađanje plazmoničkih svojstava metala legiranjem – računalno istraživanje
No full textAlloying is a potentially very effective way of tuning the plasmonic properties by optimizing them for desired purposes. Methods based on DFT have a great potential for studying the connection between structure and properties of alloys because they enable prediction of properties and provide insight into the fundamental nature of materials thus enabling understanding of the structure-properties dependence. In this paper, a computational framework suitable for efficiently performing a large number of calculations is presented, and the GLLB-SC functional is highlighted as a superior option to standard GGA functionals. A database of predicted optical properties was created, trends were explained on based on the electronic structure changes, and emergent properties of alloys were highlighted. A method for calculating energy distribution of hot carriers is also presented, and the results are explained based on the electronic structure of alloys. These insights enable rational engineering of hot carrier energy distribution.Legiranje je potencijalno veoma učinkovit način ugađanja plazmoničkih svojstava metala u svrhu optimizacije za željenu funkciju. Metode temeljene na DFT-u imaju velik potencijal za proučavanje povezanosti strukture i svojstava legura jer omogućuju predviđanje svojstava i daju uvid u fundamentalna svojstva tvari čime produbljuju razumijevanje ovisnosti svojstava o strukturi. U ovom radu predstavljen je računalni okvir prilagođen učinkovitoj provedbi velikog broja računa te je GLLB-SC funkcional predstavljen kao opcija superiorna standardno korištenim GGA funkcionalima. Stvorena je baza predviđenih optičkih svojstava binarnih legura, opaženi trendovi su objašnjeni na temelju promjena u elektronskoj strukturi, te su istaknuta emergentna svojstva legiranja. Predstavljena je i metoda za računanje distribucije energija vrućih nosioca naboja, a dobiveni rezultati objašnjeni su na temelju elektronske strukture legura. Dobivene spoznaje daju temelj za racionalni inženjering distribucije energija vrućih nosioca naboja
The influence of glaciations on loess deposition
No full textLes ili prapor je pleistocenski sediment nastao djelovanjem vjetra na periglacijalnim prostorima. Različit horizontalni i vertikalni razvoj lesa je rezultat mnogih čimbenika. Porijeklo lesa se najprije traži u istraživanom području, a onda i u širim okolnim područjima. Kriofrakcija, glacijalna i fluvijalna erozija te prijenos i padinski procesi modeliranjasu dali osnovnu masu prašinastog materijalaiz kojegse kasnije dijagenezom razvio les i njemu slični sedimenti. Akumulaciju prašinastog materijala eolskog porijekla su izvršili prvenstveno sjeverni te sjeveroistočni vjetrovi tokom razdoblja maksimuma posljednjeg glacijala. Les je vrlo važan jer se nakon posljednjeg glacijala, na njemu razvio debeli sloj izuzetno plodna tla. Radi se o laganim, poroznim tlima koja su kasnije, u neolitiku, s početkom poljoprivrede bila vrlo povoljna za razvoj poljoprivrede. Neolitske su zajednice, zbog primitivnih tehnika, ovisile o prirodnoj osnovi koja je direktno utjecala na geografsku raspodjelu stanovništva i naseljenosti. Upravo iz tih razloga je neolitska poljoprivreda bila najrazvijenija na lesnim zaravnima s plodnim tlom. Također, lesne zaravni imaju izuzetnu važnost i vrijednost za današnju poljoprivredu.Loess is a Pleistocene sediment formed by the action of wind in periglacial areas. The different horizontal and vertical development of loess is the result of many factors. The origin of loess is first sought in the studied area, and then in the wider surrounding areas. Cryo fracturing, glacial and fluvial erosion, as well as transport and slope processes, provided the basic mass of dusty material from which loess and similar sediments later developed through diagenesis. The accumulation of dusty material of aeolian origin was primarily caused by northern and northeastern winds during the peak of the last glacial period. Loess is very important a thick layer of extremely fertile soils developed on it after the last ice age. These are light, porous soils which later, in the Neolithic period, with the beginning of agriculture, were very favorable for the development of farming. Neolithic communities were dependent on the natural base due to their primitive techniques, which had a direct impact on geographical distribution of the population and settlements. For these reasons, Neolithic agriculture was most developed on loess plateaus with fertile soil. Loess plateaus are also of extraordinary importance and value for today's agriculture