Special finite elements: Theoretical background and application

Specijalni konačni elementi (KE) koriste se za modeliranje posebnih fenomena u ponašanju konstrukcija. Izraz "specijalni" označava KE sa specifičnim svojstvima (parametri krutosti, ponašanje pod opterećenjem, itd.) i posebnom ulogom u modeliranju, po čemu se i bitno razlikuju od "standardnih" KE. Postoji više tipova specijalnih KE, ali se najčešće koriste: "nelinearna opruga" KE, "zazor" KE i "veza" KE. Na različitim će primjerima biti pokazane prednosti primjene specijalnih KE, posebno u modeliranju konturnih i prijelaznih uvjeta. Teorijska podloga data je samo u neophodnom obimu, zbog dobrog razumijevanja numeričkih aspekata primjene specijalnih KE.Special finite elements (FEs) are used for modeling of certain phenomena in structural behavior. The term "special" denotes FEs with specific characteristics (stiffness parameters, behavior under load, etc.) and a specific role in modeling, which is their main difference from "common" FEs. There are many types of special FEs, but the following are often used: so-called "nonlinear spring" FE, "gap" FE and "link" FE. Various examples will show many advances in the application of these FEs, especially in modeling of boundary and interface conditions. Theoretical background is given only in the amount necessary for proper understanding of numerical aspects of the application of special FEs

Morphological characteristics of alfalfa genotypes tolerant to low soil ph

In total 76 varieties of alfalfa were collected and sown and 41 alfalfa genotypes showed tolerances to lower soil pH. The selected alfalfa genotypes are then sown in a test field on the soil that belongs to the type of brown soil on the gravel or the cambisol with the soil pH from 5.33 to 5.64. After 5 years, 10 genotypes were selected based on the agronomic properties and the experiment was set up on the soil with the pH from 5.0 to 5.1 in H2O. The following genotypes were used for these tests: G-2, G-11, G-19, G-34, G-39, G-44, G-48, G-51, G-53 and G-100. The following properties were observed: plant height (cm), number of stems per plant, stem thickness (mm), number of internodes per stem, leaf/stem ratio (%), yield of biomass in the I cut (g plant(-1)). During these tests, the highest degree of tolerance towards the lower soil pH was shown by the genotype G-44. Good results were achieved with alfalfa genotypes G-11 and G-48 where the percentage of survivors was over 80%. The highest average plant height during the three-year study (36.9 cm) was recorded in the genotype G-100. The high and stable yield of dry mass per plant have genotypes G-44 and G-19 and they are grouped in group I and are desirable for further breeding. Genotype and year have statistically significant and highly significant influence on the tested parameters, while the significance of the interaction of the genotype x year was determined only for the thickness of the stem

Vascular complications in long COVID are very rare

Depending on the methodology thrombotic events during the acute COVID-19 infection were noted from 20 - 85%. Following the acute phase of the disease, it was noted that a subgroup of patients had various non-specific, prevailing symptoms for weeks, or even months and such a condition was accepted as a long COVID. Having in mind mechanisms of vascular complications in acute COVID infection and pathogenesis of long COVID, one would expect similar presentation and consequences of long COVID on human vasculature. We conducted a wide search of the literature on the topic and after screening of titles and abstracts papers with potential inclusion of the data regarding long COVID and vascular symptoms or complications that occurred during the time span of more than then 4 weeks after COVID infection. Research dealing with long COVID are mostly focused on symptoms and laboratory findings due to the nature of this condition. Data regarding vascular complications in these studies are either missing or the incidence of vascular complications was very low. Very few manifestations were related to cardiovascular system and D-dimer was assessed in only two studies showing increased values from very lot to almost in 30% of patients after COVID infection. Finally, in comparison of vascular complications with other viral infections in Sweden on patients undergoing diagnostic tests for venous thromboembolism increased risk for VTE in COVID-positive patients was proved. In the group of patients with chronic cardiovascular disease, the risk of arterial and venous thrombotic events after COVID infection is substantially higher. In comparison with seasonal influenza burden with coagulation disorders, pulmonary embolism, acute phlebitis, thrombophlebitis or thromboembolism and arterial embolism were higher and cumulative incidence was reported from 0.6 - 5.5% while hazard ration was from 2 - 18. Based on the published literature, vascular complications in the long COVID are very rare. Comparing to a very high rate of thrombotic events in the acute COVID infection and their correlation with severity of clinical presentation of COVID infection, the role and presence of vascular complications in long COVID is without any significance. Future studies focusing on the pathophysiology of long COVID could probably reveal potential mechanisms and explanations for such a difference

Solid-phase extraction as promising sample preparation method for compound of emerging concerns analysis

Today’s environment is under the influence of numerous substances and most of them are not covered by current national and international regulations. Substances that are classified as contaminants of emerging concern, CECs, are not regulated nor systematically controlled in the environment, and they belong to the different chemical classes such as pesticides in current use, pharmaceutically active compounds (PhACs), personal care products, illicit drugs, hormones, micro- and nano-plastics, per- and poly-fluoroalkyl substances (PFAS), and many others. Once released CECs end up in surface water where they can be either accumulated or transported to the other environmental compartments, i.e. soil (by irrigation), underground water, or drinking water. The aim of the research was to investigate the efficiency of different selected solid-phase extraction (SPE) cartridges for preparation of water samples for simultaneous analysis of several CECs. For this purpose, a model mix solution of selected CECs in concentration relevant to environmental appearance was used. The selected CECs (14 PhACs, 11 pesticides in current use, and 4 PFAS) represented emerging contaminants with different properties, including polarities, and varying adverse effect on the environment and human health. Different types of sorbents were investigated: (i) commercial single-layer HLB, (ii) homemade multi-layer I: HLB plus a mix of WAX, WCX, and PPL, and (iii) multi-layer II: mix of WAX, WCX, and PPL plus HLB. The results revealed that the single-layer sorbent showed better efficiency in extraction of the analyzed CECs. Multi-layer sorbent should be further investigated to elucidate the possible reason for the poor extraction of some compounds, as development of a balanced extraction for a wider range of contaminants with different polarities, especially for non-target analysis of chemical residues, is required in order to capture the occurrence of the full profile of micropollutants