Oscillatory behaviour of the RBF-FD approximation accuracy under increasing stencil size

When solving partial differential equations on scattered nodes using the Radial Basis Function generated Finite Difference (RBF-FD) method, one of the parameters that must be chosen is the stencil size. Focusing on Polyharmonic Spline RBFs with monomial augmentation, we observe that it affects the approximation accuracy in a particularly interesting way - the solution error oscillates under increasing stencil size. We find that we can connect this behaviour with the spatial dependence of the signed approximation error. Based on this observation we are then able to introduce a numerical quantity that indicates whether a given stencil size is locally optimal.Comment: 8 pages, 6 figures, ICCS 2023 Conference Pape

Renesansa elektroda s ugljikovom pastom; njihove modifikacije i primjene u potenciometrijskim određivanjima farmaceutika

Razvoj elektroda s ugljikovom pastom (CPE, engl. carbon paste electrode) sedamdesetih godina prošlog stoljeća privukao je velik interes znanstvene zajednice budući da je otkriveno da one nude nekoliko prednosti u odnosu na konvencionalne membranske elektrode. Početkom novog tisućljeća dodatni impuls njihovom razvoju dala je primjena ugljikovih nanomaterijala kao novog trenda u njihovu razvoju. Nakon što su uspješno razvijene CPE za potenciometrijsko određivanje više od 70 kemijskih elemenata, te su elektrode privukle dodatno zanimanje za primjenu u farmaciji i medicini. Ovim radom dat je pregled znanstvene literature u posljednjih desetak godina vezan za razvoj CPE za kvantitativno određivanje djelatnih tvari farmaceutika i njihovu primjenu u realnim uzorcima

Oxidation by-products of the C.I. Direct Blue 106 dye after ozonation

Oksidacijski nusprodukti bojila C.I. Direct Blue 106 nakon ozonizacije U radu je istražena oksidacija često upotrebljavanih oksazinskih direktnih bojila C.I. Direct Blue 106 (Direct Dye 106) u vodenim otopinama (600 mg L-1) pomoću ozona. VIS spekti su pokazali degradaciju oksazinskih skupina u početnoj strukturi Direct Dye 106. Oksidacijski nusprodukti, poput sulfata, nitrata, nitrita, kloridnih iona i spojeva fenola su identificirani pomoću MS-MS i LC-MS analiza. Provedena ispitivanja toksičnosti na dafnije (vodenbuhe) nakon ozonizacije otpadne vode koja je sadržala Direct dye 106 je potvrdio da nusprodukti nemaju toksične karakteristike.The oxidation of the often used oxazine direct dye C.I. Direct Blue 106 (Direct Dye 106) in an aqueous solution (600 mg L-1) by ozonation was investigated. VIS spectra showed degradation of the oxazine groups in the initial Direct Dye 106 structure. The oxidation by-products, such as sulphate, nitrate, nitrite, chloride ions and phenolic compounds, were identified by MS-MS and the LC-MS analyses. After ozonation the wastewater containing the Direct Dye 106 showed no toxic characteristics, according to Daphnia magna test (24 h- EC50 > 75%)

Platy limestones. 10 case studies in the Classical Karst

Il progetto RoofOfRock, finanziato nell’ambito del 2° bando di cooperazione transfrontaliera dell’Adriatico IPA 2007-2013 è iniziato nell’ottobre 2012, si concluderà a fine settembre del 2015 e coinvolge 10 partner di 4 nazioni: Slovenia, Italia, Croazia e Bosnia Erzegovina. In qualità di partner associato e stakeholder partecipano le regioni Friuli Venezia Giulia e Veneto. Il progetto RoofOfRock ha tra le sue finalità quelle di proporre un utilizzo del calcare tabulare compatibile con l’ambiente, di favorirne la protezione e la promozione nonché di elaborare delle linee guida utili per una sua valorizzazione come patrimonio naturale e culturale.Pri projektu RoofOfRock, ki je bil izbran za sofinanciranje v okviru 2. poziva Jadranskega čezmejnega programa IPA 2007–2013, sodeluje deset projektnih partnerjev iz štirih držav, in sicer iz Slovenije, Italije, s Hrvaške ter iz Bosne in Hercegovine. Projekt se je začel izvajati oktobra 2012 in se bo zaključil konec septembra 2015. Pri projektu sodelujeta tudi italijanski pokrajini Furlanija - Julijska krajina kot deležnik in Benečija kot pridruženi partner. Namen projekta RoofOfRock je vzpostaviti skupni temelj za trajnostno rabo, zaščito in promocijo ploščastih apnencev ter oblikovati uporabne smernice za trajnostno upravljanje ploščastih apnencev kot skupne naravne in kulturne vrednote na celotnem projektnem prostoru.The RoofOfRock Project is being implemented under 2nd call for ordinary projects of Adriatic IPA CBC Programme 2007, joining 10 partners from 4 countries Slovenia, Italy, Croatia and Bosnia and Herzegovina. It started in October 2012 and is going to be implemented until the end of September 2015. Two Italian Regions Friuli Venezia Giulia and Veneto are participating as stakeholder and associate partner . The RoofOfRock intention is to establish joint platform for platy limestone sustainable use, preservation and promotion, to create the relevant guidelines and to upgrade both individual and joint capacities in preserving such common natural and cultural heritage

Mikrocelični odprtoporozni polistirenski kompoziti iz emulzij

Series of cross-linked polystyrene samples were prepared using an emulsion templating approach, where monomers were contained in the continuous phase of the emulsion, while the droplet aqueous phase induced primary pores, connected with a number of secondary pores. Emulsions with a high fraction of the droplet phase (HIPEs) were used and stabilised with a combination of a surfactant (sorbitan monooleate) and various types of particles (charcoal powder, copper powder and carbon nanopowder). The morphology of the resulting porous polymer depends on the type and amount of the particles added to the emulsionhowever, in all the cases open-cellular morphology was formed. The size of the primary pores (cavities) ranged from 5 µm to 25 µm, while the size of the secondary interconnecting pores was from 1 µm to 5 µm. The materials were investigated using scanning electron microscopy and nitrogen adsorption/desorption.Z uporabo emulzij z visokim deležem notranje faze smo pripravili serijo zamreženih polistirenskih vzorcev. Monomeri so bili vsebovani v kontinuirni fazi emulzije, kapljice notranje vodne faze pa so povzročile poroznost materiala z vrsto primarnih por, povezanih s povezovalnimi porami. Emulzije z visokim deležem notranje faze (HIPE) smo stabilizirali z uporabo surfaktanta v kombinaciji z različnimi delci (oglje v prahu, baker v prahu in ogljikov nanoprah). Na morfologijo pripravljenih odprtoporoznih materialov sta vplivala tako vrsta kot tudi količina dodanih delcev. Velikost primarnih por je bila v območju med 5 µm in 25 µm, medtem ko je bila velikost sekundarnih povezovalnih por v območju med 1 µm in 5 µm. Materiale smo karakterizirali z uporabo vrstičnega elektronskega mikroskopa in adsorpcijo/desorpcijo dušika

Priprava elektrode srebro/srebrov sulfid s kemično obdelavo srebrne žice

The preparation and usability of a sulphide ion selective electrode, prepared by means of chemical pretreatment of silver wire with an ammonium perdisulphate solution, and the sulphidization in an alkaline sulphide solution are described. The electrode is suitable for direct potentiometric measuring of sulphide in alkaline solutions of concentrations down to ▫$1 X 10^{-6} mol/L$▫. The 45 min required for each chemical treatment are enough for the preparation of the described electrode.Opisujemo pripravo sulfidne ionoselektivne elektrode s kemijsko obdelavo srebrne žice v amonijevem peroksodisulfatu in alkalni sulfidni raztopini. Elektroda omogoča direktne potenciometrične meritve koncentracij sulfidnih ionov v alkalnih raztopinah navzdol do ▫$10^{-6} mol/L$▫. Priprava elektrode je enostavna in hitra

Simultaneous GC-MS determination of free and bound phenolic acids in Slovenian red wines and chemometric characterization

Several phenolic acids (PAs), caffeic, vanillic, syringic, p-coumaric and ferulic acid, found in Slovenian red wines were studied using gas chromatography and mass spectrometry (GC-MS). For isolation of the PAs from wine samples, solid phase extraction (SPE) using hydrophilic modified styrene - HLB cartridges was used. The bound PAs were extracted after basic hydrolysis and o-coumaric acid was used as the internal standard (ISTD). The method developed was validated and the linear concentration range for all analytes was from 1 to 100 mg L$^{-1}$ with correlation coefficients above 0.999. We show that the method is repeatable (RSD<2%), recoveries were above 96%, and LOD and LOQ values were acceptable. In all of the wine samples tested, caffeic and p-coumaric acid were determined to be the predominant PAs (17-72 mg L$^{-1}$), while other compounds were found in lower concentrations. Principal Component Analysis (PCA) and Cluster Analysis (CLU) were used to study differences between wines related towards varieties and Slovenian wine regions. The results demonstrate that variety has more influence on PAs content than wine regions in Slovenian red wines.Izbrane fenolne kisline: kavno, vanilinsko, siringinsko, kumarinsko in ferulno smo v različnih rdečih slovenskih vinih analizirali z uporabo GC-MS. Za izolacijo smo uporabljali ekstrakcijski postopek na HLB SPE kolonicah, ki vsebuje hidrofilno modificiran stiren. Pri delu smo vezane fenolne kisline hidrolizirali, kot interni standard pa smo uporabljali orto-kumarinsko kislino. Razvito metodo smo validirali: linearno koncentracijsko območje fenolnih kislin je med 1 in 100 mg L$^{-1}$, korelacijski koeficienti so bili nad 0,999. Potrdili smo dobro ponovljivost, RSD je znašal pod 2%, izkoristke nad 96% in sprejemljive vrednosti LOD ter LOQ. Ugotovili smo, da sta v vzorcih slovenskih vin prevladujoči fenolni spojini kavna in para-kumarna kislina (17–72 mg L$^{-1}$), medtem ko ostale spojine najdemo v nižjem koncentracijskem območju. Metodo glavnih osi (PCA) in analizo klastrov (CLU) smo uporabili za študij podobnosti in razlik med vzorci glede vsebnosti in deležev fenolnih kislin. Potrdili smo korelacijo in večji vpliv sorte grozdja kot vinorodne dežele oziroma regije, iz katere vzorci vin izvirajo

Tungsten - tungsten trioxide electrodes for the long-term monitoring of corrosion processes in highly alkaline media and concrete-based materials

The determination of pH in highly alkaline solutions and concrete materials is extremely important for monitoring or predicting the corrosion processes of reinforced concrete structures and to follow the hydration process of Portland cement, fly-ash, micro silica and other materials used in concrete manufacturing. The corrosion of reinforced concrete structures and the hydration of pozzolanic materials are long-term processes, which means, that appropriate durable, and resilient pH electrodes are needed, for direct implantation regarding solid concrete bodies. The purpose of this work was to characterise the potentiometric and surface properties of tungsten electrodes after exposure to extreme alkaline solutions. The tungsten wire surface was activated at 800 °C for 30 min within an oxygen flow. The formation of homogenous and compact multiple layers of $WO_3$ crystals was observed using X-ray diffraction and scanning electron microscopy. X-ray diffraction of thosetungsten electrodes exposed to saturated calcium hydroxide solution or the pore-water of cement-based materials during 10 months, indicated partly dissolved $WO_3$. Two new compounds appeared on the electrodes surfacespure tungsten and $CaWO_4$. The presence of tungsten was affecting any potentiometric response in acidic pH region (2-5) but in pH 5-12 region the response still remained linear with a slope of 42 2 mV/pH unit. The $W/WO_3$ electrode was suitable for the long-term monitoring of corrosion processes in concrete-basedmaterials according to the pH changes as it has stable and repeatable responses to alkaline solutions (pH > 12). All the tested interferring ions had no significant influence on electrode potential. The $W/WO_3$ electrode is simple, robust, inexpensive, and temperature resistant and can be applied in potentiometric titrations as well as in batch and flow-injection analysis. The prepared electrode is a highly promising pH sensor for the monitoring of pH changes in highly alkaline capillary water of concrete.Merjenje pH v močno alkalnih raztopinah in v betonskih vzorcih je zelo pomembno za napoved korozije armature, kakor tudi za spremljanje drugih hidratacijskih procesov materialov, ki se uporabljajo pri proizvodnji betona. Tovrstni procesi so dologotrajni in zahtevajo robustne, vzdržljive in enostavne pH senzorje, ki omogočajo tudi neposredno namestitev v betonsko matriko. V delu so predstavljene $W/WO_3$ elektrode, ki so bile aktivirane pri 800 °C za 30 minut, pri čemer je na površini nastala homogena in stabilna plast $WO_3$. Tudi dolgotrajna, 10 mesečna izpostavitev v nasičeni raztopini $Ca(OH)_2$, kaže na nespremenjene potenciometrične lastnosti elektrod v območju med pH 5 in 12 z naklonom 42 ± 2 mV/pH. Preizkušeni interferenčni ioni niso imeli signifikantnega vpliva na elektrodni potencial. $W/WO_3$ elektrode so se izkazale kot enostaven, dostopen, temperaturno obstojen in obetaven pH senzor, ki ga lahko uporabljamo tako za klasične potenciometrične titracije kot meritve v pretoku. Še posebej $W/WO_3$ elektrode odlikuje dobro ponovljiv odziv v močno alkalnih raztopinah (pH > 12), kar nakazuje uporabo pri določanju pH vrednosti kapilarne vode ter in-situ meritvah v betonu

Analytical methods for determination of phytic acid and other inositol phosphates

From the early precipitation-based techniques, introduced more than a century ago, to the latest development of enzymatic bio- and nano-sensor applications, the analysis of phytic acid and/or other inositol phosphates has never been a straightforward analytical task. Due to the biomedical importance, such as antinutritional, antioxidant and anticancer effects, several types of methodologies were investigated over the years to develop a reliable determination of these intriguing analytes in many types of biological samplesfrom various foodstuffs to living cell organisms. The main aim of the present work was to critically overview the development of the most relevant analytical principles, separation and detection methods that have been applied in order to overcome the difficulties with specific chemical properties of inositol phosphates, their interferences, absence of characteristic signal (e.g., absorbance), and strong binding interactions with (multivalent) metals and other biological molecules present in the sample matrix. A systematical and chronological review of the applied methodology and the detection system is given, ranging from the very beginnings of the classical gravimetric and titrimetric analysis, through the potentiometric titrations, chromatographic and electrophoretic separation techniques, to the use of spectroscopic methods and of the recently reported fluorescence and voltammetric bio- and nano-sensors