375 research outputs found
A Generic Circular Source Distribution for solving potential problems using Meshless Methods
No full textApproximate solutions to the potential equation “2U = 0 in a simply-connected 2-dimensional
domain D are found using the Method of Fundamental Solutions (MFS) with sources placed on a
circle. Previous research has shown that a few discrete points sources placed a large distance from
D can give good numerical accuracy. The discrete source distribution can be random, and a circular
source distribution is one which could be used for any domain. Several domains are considered, and
an attempt is made to determine an optimal radius for the source distribution and number of sources
required in order to give sufficient accuracy. Simple configurations for D give results whose
accuracy depends in an ordered and predictable way on the source radius and the number of sources.
With more complex domains the source radius and the number of sources have a crucial impact on
accuracy
SEA/WOMAN
No full textA new laboratory research performance by Anna Furse, Athletes of the Heart, UK) in collaboration with Maja Mitic (DAH Teatar, Serbia) and Antonella Diana (Teatret OM, Denmark) based on Henrik Ibsen's 'The lady from the sea' (1888).
The project is an AHRC/ACE funded project as part of the Pinter Centre for Performance and Creative Writing's Fractured Narratives project. It has been touring in the UK and to Beirut, Lebanon
The method of meshless fundamental solutions with sources at infinity
No full textThe method of external source collocation is used to solve a discretised boundary value problem, ∇2U = 0, where U is the potential in a two-dimensional simply-connected region D, subject to a mixture of Neumann and Dirichlet boundary conditions. Numerical analysis has, to date, been hindered by an accumulation of round-off error, which has made it impossible to investigate accuracy of the Meshless Fundamental Solutions method unless sources are near the boundary. Symbolic analysis allows a full investigation of ill-conditioned systems in which sources can be placed "at infinity". This analysis provides an indication of how many sources must be used and where they should be placed
Supplementary material for: "Secondary metabolites from endemic species Iris adriatica Trinajstic ex Mitic (Iridaceae)"
No full textExperimental data: Plant material; Extract preparation; Extract separation; General. Table S1. Silica gel column separation program. Isolation. Figure S1. The main HMBC correlations in both types of Iris adriatica isofavonoids; A - nigricin-type, B - tectorigenin-type. 1H and 13C NMR spectra of all isolated compounds.This is Supplementary material for: Bukvicki, D., Novaković, M., Ab, G. N., Marin, P. D.,& Asakawa, Y. (2018). Secondary metabolites from endemic species Iris adriatica Trinajstic ex Mitic (Iridaceae). Natural Product Research, Taylor and Francis, 32(15), 1849-1852.[ https://doi.org/10.1080/14786419.2017.1402309]The published version of the article: [https://cer.ihtm.bg.ac.rs/handle/123456789/2438
Seasonal "Windows of opportunity" in Alpine headwaters: implication for diatom assemblages
No full textIn the European Alps, around 80% of glacier volume is predicted to vanish within the end of this century because of global warming. The progressing glacier retreat is affecting the Alpine hydrological dynamics as well as the distribution and biodiversity of glacier-fed streams. Within this scenario of vanishing glaciers, mountain permafrost is becoming increasingly significant since the thawing of its subsurface ice occurs at a slower rate in comparison to surface glacier ice. The most common evidence of mountain permafrost are the rock glaciers, i.e., creeping rocky landforms made of rock fragments that host subsurface ice. Springs and streams emerging from intact (containing ice) and relict (not containing ice) rock glaciers are increasingly considered as a climate-resistant source of cold water, as well as ecological refugia for cold-stenothermic aquatic organisms. Nonetheless, the knowledge of benthic biodiversity and dynamics in relation to the seasonal changes of habitat and water chemical setting is still patchy and incomplete. Ecological Windows of Opportunity (WOs) are defined as seasonal periods of mild environmental conditions supporting the development of benthic primary producers, especially diatoms, in Alpine glacial streams. The primary WO occurs in autumn when glacier ablation is reduced, and glacier-fed streams have stable channels and less turbid waters. Differently, the spring WO more strongly depends on stochastic meteorological factors and is more irregularly paralleled by benthic growth. Although WOs have been conceptually modelled based on field surveys of primary producers in glacial streams of the European Alps, much scarcer field evidence is available for headwaters of different origin. In particular, the seasonal development of diatom biomass and diversity in Alpine headwaters fed by rock-glaciers and in non-glacial reference streams (i.e., not influenced by permafrost and glaciers) in the present context of Alpine deglaciation is poorly known. Here we present the first results of a two-year investigation on seasonal development of diatom biomass and diversity in headwater streams of different origin in two deglaciating catchments of the Italian Central- Eastern Alps. The study has been conducted within the Euregio project “Rock-me” (2022-2025, https://rock-glaciers-euregio.fmach.it/) by investigating physical (temperature, turbidity) and chemical (nutrients, major ions, and trace elements) parameters of water, organic and chlorophyll-a content of epilithic biofilm, as well as density and taxonomic composition of epilithic diatoms in streams fed by glaciers and rock glaciers, and in non-glacial reference streams in both catchments. We found different patterns of seasonal WOs, outlined by higher diatom density and biofilm chlorophyll content, either in early or late summer, in headwaters of different origin in relation to differing hydrological dynamics and habitat settings. The early summer WO appears to be more pronounced in headwaters fed by glaciers or rock glaciers, as a possible effect of the climate-related hydrological dynamics in deglaciating Alpine catchments. On the other hand, non-glacial springs and streams with more stable water discharge are characterised by a more evident late summer WO. Seasonal changes of diatom biodiversity seem to be related to differing hydrological dynamics at catchment scal
Benthic diatom communities in two proglacial lakes with different glacial influence (Cevedale glacier, Italy).
No full textClimatic changes induce cascadeeffects on high mountain headwaters. Due to the current deglaciation, proglacial lakes increased worldwide in number and volume in the last decades, thus becoming more represented ecosystems in high mountain landscapes. With the progression of glacier retreat, proglacial lakes rapidly evolve from ice contact conditions towards ice distal conditions. The final evolution stage is a clear water mountain lake, with no glacial influence. In the European Alps, ice distal proglacial lakes represent the largest proportion of high mountain lakes, in comparison with ice contact ones and clear lakes. Glacial runoff is typically cold and contains large amounts of inorganic suspended solids (so called “glacial flour”). Due to low water temperature and high turbidity, proglacial lakes are highly selective habitats, where planktonic communities are taxonomically simplified and quantitatively scarce. Nonetheless, littoral habitat conditions may sustain algal growth. However, benthic assemblages have been scarcely addressed by studies on Alpine proglacial lakes regarding qualitative and especially quantitative aspects. Here, we provide a first characterisation of the littoral diatom assemblages of two Alpine proglacial lakes with different glacial influence and discuss differences in community composition between the ice contact and the ice distal lake habitat. The two lakes are located between 2700 and 2900 m a.s.l. in the Martello Valley (Stelvio National Park, Province of Bolzano, Italy). They formed in the past decades in the depressions of the land surface shaped by the retreat of the Cevedale glacier and are both dammed by moraines. The ice contact lake (CL) receives glacial runoff flowing on debris-covered ice. The ice distal lake (DL) is about 500 m downstream and hydrologically connected to CL. In the ice-free seasons 2022 and 2023, we collected quantitative diatom samples from colonised substrata (stones or cohesive sediment) during the different stages of the Alpine glacial summer (snow melt, glacier ablation and base flow). In parallel, we collected water samples to analyse chemical habitat conditions and installed temperature dataloggers in the water column to calibrate a 2D laterally-averaged hydrodynamic model that allowed to reconstruct lake thermal dynamics. The two lacustrine habitats differed mainly in water turbidity, littoral water temperature and thermal dynamics, i.e., stratification patterns. In addition, we found differences in the benthic diatom communities of the two proglacial lakes. Alpha diversity was higher in the ice distal lake (DL), where we found species that were not observed in the ice contact lake (CL). In CL, diatom density peaks corresponded to the increase of Achnanthidium minutissimum s.l. (Kützing) Czarnecki, which was the numerically dominant species in all the samples in this lake. Density peaks in DL were characterised by different dominant species during the Alpine summer and the community composition showed a species succession. Furthermore, in DL, we observed a stable population of Pinnularia bullacostae Krammer & Lange-Bertalot. At the best of out knowledge, this is the first record of the species in the European Alp
Subfossil diatoms of Perialpine lakes reveal early lake responses to climate warming and human impact in the 20th century
No full textThe majority of Perialpine lakes suffered from nutrient enrichment since the early 1960s because of the demographic growth and the economic boom that followed World War II. However, limnological surveys have remained scattered and irregular for both large and small Perialpine lakes during the early stages of nutrient enrichment, while regular monitoring programs started mainly during the most acute anthropogenic eutrophication or in conjunction with the launching of lake restoration measures. As a result, the early-stage responses of Perialpine lakes to major human-related perturbations occurred during Anthropocene can only be reconstructed based on information preserved in deep lake sediment records. Subfossil diatoms are among the most reliable biological remains in lake sediments and have been extensively used for the reconstruction of the trophic evolution of temperate lakes at secular scale. In this contribution we provide evidence of the capacity of subfossil diatoms to provide information on indirect effects of early global warming occurred in the first half of the 20th century in both large and small Perialpine lakes. We present results of subfossil diatom studies conducted during the last ca. 10 years on sediment cores from a set of large Perialpine, and two additional smaller mid altitude lakes, located on both the northern and southern Alpine slopes. Diatom based environmental reconstructions show that lake biological responses to major changes in lake nutrient availability during the post-war economic development was particularly rapid and coherent in different lake types north and south of the Alps. In addition, these studies reveal that first changes in the diatom species composition occurred already during the first half of the 20th century in several lakes. Although the investigated lakes differ in location, morphology (e.g. altitude, size, depth), and exposition to direct and indirect human impacts, subfossil diatoms first relevant changes mainly occurred between the 1930s and the 1940s. In most of the lakes early diatom changes consist in the rapid substitution of small centric taxa by pennate taxa mainly belonging to the genera Asterionella and Fragilaria. These changes could be interpreted as indirect community response to the first documented climate warming after the end of the Little Ice Age, that mimicked nutrient enrichment effects although being mediated by lake-specific hydrological and thermal dynamics. The interpretation of the observed changes is difficult for some lakes due to the combination of climate related effects with superimposed and simultaneous anthropogenic perturbations that ranged from early eutrophication to hydroelectric exploitation. These results underscore: a) the importance of the paleolimnological approach for complementing and expanding limnological surveys and for predicting future lake ecological trends based on the understanding of past lake responses; b) the potential of subfossil sediment diatoms as a proxy to understand indirect effects of climate change on the planktonic lake biota
Chemometric insights into grape stems: antioxidant capacity, phenolic composition, and mineral profile
No full textThe primary objective of this investigation was to assess the total polyphenolic content (TPC), identify and quantify individual polyphenols, and evaluate their radical scavenging activity (RSA), as well as determine the mineral composition in stem extracts from nine distinct Vitis vinifera varieties. The total phenolic content in grape stem extracts ranged from 34.87 to 76.95 mg gallic acid equivalents (GAE) per gram of dry weight (d.w.). These extracts exhibited significant free radical scavenging activity, ranging from 0.344 to 0.898 mmol Trolox equivalents (TE) per gram d.w. Stem extracts were predominantly characterized by flavan-3-ols, flavonols, and phenolic acids. Catechin and quercetin-3-glucuronide were identified as the most abundant components, with concentrations of up to 1.858 mg/g d.w. and 1.315 mg/g d.w., respectively. Potassium (K) emerged as the most abundant element in all samples, with content ranging from 7.297 mg/g d.w. to 16.695 mg/g d.w., followed by calcium (Ca), phosphorus (P), and magnesium (Mg)
Diatom diversity of five thermal springs in Serbia
No full textDue to their high water temperature and special water chemistry, thermal springs offer unique ecological conditions for microbial communities. They are considered to be very interesting and important habitats for the study of algal flora, including diatom biodiversity. However, their occurrence in Serbian thermal springs is scarcely investigated. The aim of this study was to assess the diversity of the diatom community in five
thermal springs in central Serbia (Vrujci spa, Bukovička spa, Omoljica, Ovčanska spa and Poljane). Samples were collected from natural thermal springs except from Bukovička spa, where they were taken
from the tap. In Vrujci spa, samples were collected both from the tap and from the natural spring. During the autumn and winter in 2023, a total of 11 biofilm samples were collected with a sterile scalpel. The
samples were treated with HCl and KMnO4 in the laboratory, afterwards permanent diatom slides were made. The Carl Zeiss AxioImager.M1 light microscope with DIC optics, AxioCam MRc5 and AxioVision4.9
software were used for microscopic analysis. During survey, in total 82 diatom taxa belonging to 33 genera were identified. The most taxon-rich genera were Nitzschia and Navicula with 13 and 10 taxa, respectively. Our preliminary results show that the samples from the Vrujci spa have
the highest diatom diversity (62 taxa) and from Bukovička the lowest (5 taxa). In the Vrujci spa, 40 taxa were identified in the natural thermal spring, while 22 were recorded at the tap. The highest temperature
(25.1°C) was measured at this site compared to the other thermal springs. The dominant taxa were Staurosira venter and Achnanthidium straubianum, which distinguishes this natural thermal spring from the others. At the tap in Vrujci, the dominance of Navicula veneta, Nitzschia palea and Achnanthidium microcephalum showed that the communities at natural and artificial sites differ greatly. In Bukovička spa, the most abundant taxa included N. palea and N. veneta. In the Omoljica thermal spring, 19 taxa were identified with dominance of N. palea, followed by Gomphonema parvulum and N. veneta with slightly lower abundances. In Poljane, N. palea and A. microcephalum were dominant from 11 recorded taxa. In Ovčanska spa, Nitzschia thermaloides was found to be predominant. In addition, the other 18 taxa found at this thermal spring occur with very low abundances. Additional taxonomic insights are required to more precisely define the diatom communities and the ecology of the taxa inhabiting thermal springs. Besides, occurrence of rare species can be expected in this types of extreme habitats.Levkov Z, Mitic Kopanja D, Zaova D, editors. Book of abstracts: 15th European Diatom Meeting; 2024 May 7-9; Ohrid, North Macedonia. Skopje: Faculty of Natural Sciences and Mathematics; 2024. 154-5
Ultrafast tangential micro-mixers for the study of biochemical reactions on the microsecond time scale
No full textDetailed understanding of chemical and enzyme catalysis constitutes a main focus of current biochemical research. Fundamental insight in how (bio)catalysts function, requires knowledge of their three dimensional structure and a wide range of time resolved experiments that monitor the reaction progress. The ultimate aim is the determination of the molecular structure of transition and transient states during the chemical bond-breaking and bond-making step that occurs as part of the overall reaction. Chemists claim to have observed transient or transition states with lifetimes as short as 100-500 femtoseconds. Single steps in enzyme catalysis are usually slower than this, although electron transfer and proton transfer can occur in picoseconds or nanoseconds, respectively. The movements of protein domains which are critical to drive enzyme catalysis because they directly promote the breaking and reforming of chemical bonds, occur at a longer time scale of ~0.1-1 µs. This time range can thus be regarded as the fastest in which formation of enzyme catalytic intermediates occur or protein domains can fold into the native structure of the active enzyme.To study catalytic mechanisms of enzymes and chemical reactions in detail, the reaction should be initiated so rapidly that the subsequent formation and decay of all reaction intermediates can in fact be detected. Even the fastest present-day continuous-flow mixing equipment is too slow (~45 µs) to monitor the very beginning of enzyme catalysis. In order to design a general kinetic instrument with a much shorter dead-time to mix reactants and observe the reaction progress both the mixer and observation cell need to be miniaturized to micrometer dimensions (~100 µm) while maintaining high mixing efficiency and good optical quality. This thesis deals with the design and development of a new kinetic instrument that can perform, observe and detail, on the μs time scale, the catalytic mechanism of enzymes, in particular those of the oxidoreductases
- …
