Search results for "Kulta"
showing 10 items of 67 documents
Kultakmeņi Latvijas teritorijā kā arheoloģiskās izpētes objekts: funkcionalitāte un izmantošanas hronoloģija
2022
Pētījumā, izmantojot triangulācijas pieeju, akmeņu folklora salīdzināta ar arheoloģisko materiālu, rakstiskajos avotos rodamo informāciju un ikonogrāfisko materiālu, identificējot vairākas kultakmeņu funkcijas, kas var pārklāties laikā. Ziedošana uzskatāma par sekundāru funkciju kultakmeņiem, kuru primārā funkcija saistīta ar apbedīšanas rituāliem vai depozītu sargāšanu. Savukārt krustakmeņiem, kuru primārā funkcija saistīta ar kristīgās telpas robežu iezīmēšanu ainavā, sekundārā funkcija saistīta ar upurēšanu. Kultakmeņu funkcijas korelē ar dabas objektu situējumu ainavā. Kultakmeņi situēti tiešā kopienas apdzīvotās teritorijas tuvumā vai ir tās ainavas sastāvdaļa. Veicot Grīžu Velna beņķa…
Kultakmeņi Daugavas lejtecē: identifikācija un izmantošanas hronoloģija
2019
Līdz šim lielākoties notikusi kultakmeņu apzināšana un tipoloģizēšana pēc to vizuālajām pazīmēm. Kulta vietu arheoloģiskajā izpētē iegūtais arheoloģiskais materiāls ir mazskaitlīgs un vienveidīgs, un līdz šim ne vienmēr ļāvis identificēt un datēt kultakmeņus. Bakaulara darbā, analizējot ar kultakmeņu identifikāciju un izmantošanas hronoloģiju saistīto problemātiku, identificēti Daugavas kultakmeņu marķieri. Lai pārbaudītu 3D vizualizācijas iespējas Daugavas kultakmeņu interpretācijā un identifikācijā, kas līdz šim nav darīts, veikta Mārtiņsalas akmens elku 3D vizuālizācija. Lai precizētu kultakmeņu izmantošanas hronoloģiju, veikta kultakmeņu un iespējamo kultakmeņu situēšana ar senvietām, i…
Cubic aromaticity in ligand-stabilized doped Au superatoms
2021
The magnetic response of valence electrons in doped gold-based [M@Au8L8]q superatoms (M = Pd, Pt, Ag, Au, Cd, Hg, Ir, and Rh; L = PPh3; and q = 0, +1, +2) is studied by calculating the gauge including magnetically induced currents (GIMIC) in the framework of the auxiliary density functional theory. The studied systems include 24 different combinations of the dopant, total cluster charge, and cluster structure (cubic-like or oblate). The magnetically induced currents (both diatropic and paratropic) are shown to be sensitive to the atomic structure of clusters, the number of superatomic electrons, and the chemical nature of the dopant metal. Among the cubic-like structures, the strongest arom…
Binding Behavior of Carbonmonoxide to Gold Atoms on Ag(001)
2020
AbstractThe adsorption behavior of single CO molecules at 4 K bound to Au adatoms on a Ag(001) metal surface is studied with scanning tunneling microscopy (STM) and inelastic electron tunneling spectroscopy (IETS). In contrast to earlier observations two different binding configurations are observed—one on top of a Au adatom and the other one adsorbed laterally to Au on Ag(001). Moreover, IETS reveals different low-energy vibrational energies for the two binding sites as compared to the one for a single CO molecule bound to Ag(001). Density functional theory (DFT) calculations of the adsorption energies, the diffusion barriers, and the vibrational frequencies of the CO molecule on the diffe…
Gold Nanoparticles on 3D-Printed Filters : From Waste to Catalysts
2019
Three-dimensionally printed solid but highly porous polyamide-12 (PA12) plate-like filters were used as selective adsorbents for capturing tetrachloroaurate from acidic solutions and leachates to prepare PA12–Au composite catalysts. The polyamide-adsorbed tetrachloroaurate can be readily reduced to gold nanoparticles by using sodium borohydride, ascorbic acid, hydrogen peroxide, UV light, or by heating. All reduction methods led to polyamide-anchored nanoparticles with an even size distribution and high dispersion. The particle sizes were somewhat dependent on the reduction method, but the average diameters were typically about 20 nm. Particle sizes were determined by using a combination of…
How many gold atoms make gold metal?
2015
It is well known that a piece of gold is an excellent metal: it conducts heat and electricity, it is malleable to work out for jewellery or thin coatings, and it has the characteristic golden colour. How do these everyday properties – familiar from our macroscopic world – change when a nanometre-size chunk of gold contains only 100, 200 or 300 atoms? nonPeerReviewed
Metal Doping of Au25(SR)18- Clusters : Insights and Hindsights
2019
The structure, properties, and applications of atomically precise gold nanoclusters are the object of active research worldwide. Over the last few years, research has been also focusing on selective doping of metal nanoclusters through introduction of foreign-metal atoms. Doping has been studied for several clusters, especially the atomically precise Au25(SR)18. Doping has been carried out with noble metals, such as platinum, and less noble metals, such as cadmium and mercury, also because of the ease by which monodoping can be achieved with these metals. Previous studies, which relied extensively on the use of mass spectrometry and single crystal X-ray crystallography, led to assign the sp…
Kullan talteenotto sähkö- ja elektroniikkaromusta
2017
Tutkielman kirjallisessa osassa käydään läpi yleisesti kiertotaloutta ja metallien osuutta kiertotaloudessa. Lisäksi kirjallisessa osassa keskitytään sähkö- ja elektroniikkaromun kasvavaan määrään ja sen kierrätyksen tärkeyteen sekä kierrätyksen ongelmiin. Työssä käydään läpi yleiset kullan talteenottotavat, hydrometallurgia, pyrometallurgia sekä fysikaalinen ja mekaaninen erottelu, joita on tutkittu sähkö ja elektroniikkaromun kierrätykseen. Myös yleisimmät kullan analysoinnissa käytetyt menetelmät käydään läpi kirjallisen osan loppuvaiheessa. Kullan talteenotolle kehitettiin menetelmä, jonka avulla kulta pystyttiin ottamaan talteen jopa yli 99 % puhtaudella ja 60–70 % saannoilla liuotetus…
Population of a low-spin positive-parity band from high-spin intruder states in 177Au: The two-state mixing effect
2020
The extremely neutron-deficient isotopes 177,179Au were studied by means of in-beam ?-ray spectroscopy. Specific tagging techniques, ?-decay tagging in 177Au and isomer tagging in 179Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2d3/2 and 3s1/2 proton-hole configurations, from the 1i13/2 proton-intruder configuration was observed in 177Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state. © 2020
Ligand Ratio Plays a Critical Role in the Design of Optimal Multifunctional Gold Nanoclusters for Targeted Gastric Cancer Therapy
2021
Nanodrug delivery systems (NDDSs) based on water-soluble and atomically precise gold nanoclusters (AuNCs) are under the spotlight due to their great potential in cancer theranostics. Gastric cancer (GC) is one of the most aggressive cancers with a low early diagnosis rate, with drug therapy being the primary means to overcome its increasing incidence. In this work, we designed and characterized a set of 28 targeted nanosystems based on Au144(p-MBA)60 (p-MBA = para-mercaptobenzoic acid) nanocluster to be potentially employed as combination therapy in GC treatment. The proposed multifunctional AuNCs are functionalized with cytotoxic drugs (5-fluorouracil and epirubicin) or inhibitors of diffe…