[Untersuchungen uber die Harte des Rosawachses im temperaturinvall der fur die Amformung mit der Wachs-Silikon-Methode von bedeutung ist]

Posebno prilagođenim aparatom za ispitivanje tvrdoće bitumenskih materijala ispitivana je tvrdoća ružičastog komercijalnog voska, u pojedinim točkama temperaturnog intervala, od 10°C, do 30°C. Ovaj interval, a osobito područje oko 20°C, važan je u kliničkoj protetskoj praksi, pri upotrebi voska za otiske, u kombinaciji s elastomerima. Utvrđeno je, da je ovo najkritičnije područje i da ružičasti voskovi domaće proizvodnje, u području između 19°C, i 22°C, hlađenjem najbrže stvrdnjavaju i da ovo područje, pri izvođenju otiska voskom i silikonom, treba svakako prijeći pothlađivanjem. Dodatak stearinske kiseline 0,25%— 0,50% ružičastim voskovima, osjetno poboljšava svojstvo tvrdoće, dok veći dodaci nemaju povoljnog učinka.With a modified instrument for the testing bitumen hardness the authors have tested the hardness of the commercial pink wax in a number of temperature intervals ranging from 10CC to 30°C. This range, especially that about 20°C, is important in the prosthetic clinical proctice when the impression wax is used in combination with the elastomeres. It was found that this range is the most critical and that the pink wax produced in our country is most quickly-hardened when cooled between 19°C and 22°C. Therefore this range must be avoided by means of undercooling. Addition of the stearine acid 0,25% — 0,50% to the pink wax significantly improves its hardness properties.Mit speziell eingestelltem Apparat für die Härteprüfung von bituminösen Materialien, wurde der Härtezustand des Rosawachses in den Temperaturintervallen zwischen 10°C und 30°C, gemessen. Dieses Intervall, insbesondere des Gebiet um 20°C, sind in der klinischen Prothetik bei der Verwendung des Abformwachses in Kombination mit Elastomeren, von Bedeutung. Es konnte festgestellt werden, dass Rosawachs heimischer Produktion bei Abkühlung ¡m Temperaturintervall zwischen 19°C und 22°C am schnellsten erhärtet. Dieses Gebiet muss bei der Abkühlung der Wachs-Silikon-Abformung unbedingt durhgegangen werden. Druch Zugabe von 0,25— 0,50%-iger Stearinsäure konnte die Härteeigenschaft des Rosawachses wesentlich verbessert werden, während grössere Zugaben keinen günstigeren Effekt ergeben

Karakterizacija sirodezmina izolovanih iz fitopatogene gljive Leptosphaeria maculans

The pathogenicity of phytopathogenic fungi is associated with phytotoxins, especially with their chemical nature and quantity. Sirodesmins are phytotoxins from the epipolythiodioxopiperazines group, produced by the fungus Leptosphaeria maculans, which are a cause of blackleg and stem canker in oilseed rape (Brassica napus L.). The aim of this work was to obtain a detailed chemical profile of sirodesmins in five fungal isolates (four from Vojvodina, Serbia, and one from the Centre for Agricultural Research, Rothamsted, UK). Sirodesmins showing different phytotoxicity on treated cotyledons of cv. Quinta were separated and detected by thin layer chromatography in all analysed isolates (L.m, C-3, St-5 and S-11) except K-113, which neither contained sirodesmin congeners nor did it exhibit activity. By use of high performance liquid chromatography coupled with tandem mass spectrometer, it was possible to identify total of 10 sirodesmins, together with their precursor-phomamide. It was found that the dominant epipolythiodioxopiperazines of the investigated L. maculans isolates were sirodesmin PL, sirodesmin C, and their de-acetylated derivatives.Patogenost fitopatogenih gljiva povezana je sa fitotoksinima, a naročito sa njihovom hemijskom prirodom i količinom. Sirodezmini su fitotoksini iz grupe epipolitiodioksopiperazina, koje proizvodi gljiva Leptosphaeria maculans, uzročnik suve truleži korena i raka stabla uljane repice. Cilj ovog rada bila je detaljna hemijska karakterizacija sirodezmina u pet izolata gljiva (četiri iz Vojvodine i jedan iz Velike Britanije, Centar za poljoprivredna istraživanja, Rothamsted). Kod svih ispitivanih izolata (L. maculans, C-3, St-3, S-11), osim K-113 (koji nije sadržao sirodezmine niti pokazivao aktivnost) tankoslojnom hromatografijom su razdvojeni i detektovani sirodezmini koji su pokazali različitu fitotoksičnost na tretiranim kotiledonima sorte Quinta. Primenom tečne hromatografije visoke efikasnosti, kuplovane sa tandemskim masenim spektrometrom, bilo je moguće identifikovati ukupno 10 sirodezmina, kao i njihov prekursor - fomamid. Utvrđeno je da su dominantni epipolitio-dioksopiperazini ispitivanih izolata L. maculans sirodezmin PL, sirodezmin C i njihovi deacetilovani derivati

Determination of residues of sulfonylurea herbicides in soil by using microwave-assisted extraction and high performance liquid chromatographic method

A modified method for the analysis of nicosulfuron, rimsulfuron and prosulfuron was developed and validated by using microwave-assisted extraction (MAE) and ultra-performance liquid chromatography with diode array detection in the ultraviolet region (HPLC-UV-DAD). The most important experimental parameters of extraction procedure and HPLC-UV-DAD technique were optimised in respect to those sulfonylurea herbicides. High recoveries of the microwave-assisted extraction were obtained by using a dichloromethane-acetonitrile mixture (2:1 volume ratio) acidified with acetic acid (0.8 vol.%) with the addition of urea. The mean recoveries at three spiking levels ranged from 97.47 to 98.76% for nicosulfuron, 97.88 to 99.17% for rimsulfuron and from 97.91 to 99.83% for prosulfuron. The limits of detection of nicosulfuron, rimsulfuron and prosulfuron were 0.95, 0.91 and 0.89 mu g kg(-1), respectively. The accuracy of the developed method was confirmed by HPLC coupled with tandem mass spectrometry parallel analyses. The developed method was used to investigate the dissipation dynamics of sulfonylurea herbicides in the real field trials in Vojvodina Province, Serbia. The obtained half-lives were 0.05, 0.23 and 0.15 days for recommended dose application of nicosulfuron, rimsulfuron and prosulfuron, respectively. Low residues and short half-life in soil suggested that the risk to sensitive rotational crops after application of those sulfonylurea herbicides is low when they are used in the appropriate dosages

Reconfigurable self-assembly through chiral control of interfacial tension

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 481 (2012): 348–351, doi:10.1038/nature10769.From determining optical properties of simple molecular crystals to establishing preferred handedness in highly complex vertebrates, molecular chirality profoundly influences the structural, mechanical, and optical properties of both synthetic and biological matter at macroscopic lengthscales1,2. In soft materials such as amphiphilic lipids and liquid crystals, the competition between local chiral interactions and global constraints imposed by the geometry of the self-assembled structures leads to frustration and the assembly of unique materials3-6. An example of particular interest is smectic liquid crystals, where the 2D layered geometry cannot support twist, expelling chirality to the edges in a manner analogous to the expulsion of a magnetic field from superconductors7-10. Here, we demonstrate a previously unexplored consequence of this geometric frustration which leads to a new design principle for the assembly of chiral molecules. Using a model system of colloidal membranes11, we show that molecular chirality can control the interfacial tension, an important property of multi-component mixtures. This finding suggests an analogy between chiral twist which is expelled to the edge of 2D membranes, and amphiphilic surfactants which are expelled to oil-water interfaces12. Similar to surfactants, chiral control of interfacial tension drives the assembly of myriad polymorphic assemblages such as twisted ribbons with linear and circular topologies, starfish membranes, and double and triple helices. Tuning molecular chirality in situ enables dynamical control of line tension that powers polymorphic transitions between various chiral structures. These findings outline a general strategy for the assembly of reconfigurable chiral materials which can easily be moved, stretched, attached to one another, and transformed between multiple conformational states, thus enabling precise assembly and nano-sculpting of highly dynamical and designable materials with complex topologies.This work was supported by the National Science Foundation (NSF-MRSEC-0820492, NSF-DMR-0955776, NSF-MRI 0923057) and Petroleum Research Fund (ACS-PRF 50558-DNI7).2012-07-0

New ideas for non-animal approaches to predict repeated-dose systemic toxicity: Report from an EPAA Blue Sky Workshop

© 2020 The Authors The European Partnership for Alternative Approaches to Animal Testing (EPAA) convened a ‘Blue Sky Workshop’ on new ideas for non-animal approaches to predict repeated-dose systemic toxicity. The aim of the Workshop was to formulate strategic ideas to improve and increase the applicability, implementation and acceptance of modern non-animal methods to determine systemic toxicity. The Workshop concluded that good progress is being made to assess repeated dose toxicity without animals taking advantage of existing knowledge in toxicology, thresholds of toxicological concern, adverse outcome pathways and read-across workflows. These approaches can be supported by New Approach Methodologies (NAMs) utilising modern molecular technologies and computational methods. Recommendations from the Workshop were based around the needs for better chemical safety assessment: how to strengthen the evidence base for decision making; to develop, standardise and harmonise NAMs for human toxicity; and the improvement in the applicability and acceptance of novel techniques. “Disruptive thinking” is required to reconsider chemical legislation, validation of NAMs and the opportunities to move away from reliance on animal tests. Case study practices and data sharing, ensuring reproducibility of NAMs, were viewed as crucial to the improvement of non-animal test approaches for systemic toxicity.U.S.Environmental Protection Agency (EPA); Agency for Science, Technology and Research ( A*STAR), Singapor

Finding synergies for the 3Rs – Repeated dose toxicity testing: Report from an EPAA partners' forum

The European Partnership for Alternative Approaches to Animal Testing (EPAA) convened a Partners' Forum on repeated dose toxicity (RDT) testing to identify synergies between industrial sectors and stakeholders along with opportunities to progress these in existing research frameworks. Although RTD testing is not performed across all industrial sectors, the OECD accepted tests can provide a rich source of information and play a pivotal role for safety decisions relating to the use of chemicals. Currently there are no validated alternatives to repeated dose testing and a direct one-to-one replacement is not appropriate. However, there are many projects and initiatives at the international level which aim to implement various aspects of replacement, reduction and refinement (the 3Rs) in RDT testing. Improved definition of use, through better problem formulation, aligned to harmonisation of regulations is a key area, as is the more rapid implementation of alternatives into the legislative framework. Existing test designs can be optimised to reduce animal use and increase information content. Greater use of exposure-led decisions and improvements in dose selection will be beneficial. In addition, EPAA facilitates sharing of case studies demonstrating the use of Next Generation Risk Assessment applying various New Approach Methodologies to assess RDT

Novel devices employing epitaxial wide bandgap semiconductors : physics, electronics and materials characterization

This thesis describes the developments of novel semiconductor devices based on epitaxial wide bandgap semiconductors GaN and ZnS. The number of interesting and exciting results in physics, electronics and materials science of these systems were found in studies motivated by these devices. This thesis consists of three major topics, structural characterization and kinetic growth modeling of the GaNAs/GaAs superlattices, structural and optical characterization and solid phase recrystallization of ZnS thin films grown on GaN and sapphire substrates, and design and fabrication of GaN high power devices as well as measurement of fundamental electronic properties of GaN, such as minority carrier diffusion lengths and lifetimes and critical field for electric breakdown. The set of GaNAs/GaAs superlattices grown by molecular beam epitaxy was analyzed by high resolution X-ray diffraction and cross—sectional transmission electron microscopy. The nitrogen incorporation and GaNAs/GaAs interface sharpness were experimentally found to strongly depend on growth temperature. The activation energies for nitrogen desorption and nitrogen to arsenic segregation were found through simple kinetic model, which is in fine agreement with experimentally obtained results. These fundamental studies provide important insights into growth of GaN on GaAs substrates, which is of significant practical importance for all electronic GaN devices. Zinc sulfide/Gallium nitride heterostructures are potentially interesting system for light emitters in blue and green part of visible spectrum, with DC low power consumption electroluminescent displays being one attractive application of these diodes. Zinc sulfide thin films grown on GaN (0001), GaAs (001) and sapphire (0001) substrates by MBE were characterized by variable temperature photoluminescence and high resolution X-ray diffraction. The structural properties of the films suffered from the large lattice mismatch between ZnS and various substrates which were used. The optical properties of the ZnS films were found to be in direct correlation with structural properties of the films. The ZnS films doped with Al and Ag grown on n and p-type GaN, and sapphire were characterized by low temperature photoluminescence and displayed bright blue luminescence. Fabricated N-ZnS/p-GaN heterostructures were characterized by current-voltage and electroluminescence. Electroluminescence was found to be centered around 390 nm, corresponding to high energy silver band, and it shifted to higher energies with increase in device voltage. Since as grown films suffered from crystalline imperfections, the ZnS thin films on sapphire were recrystallized, by annealing at temperatures above 900 °C at sulfur overpressure of 10 atm. The structural properties of samples significantly improved, indicating more than 10-fold reduction in tilting and excellent crystallinity. The role of sulfur was discussed, and it was found that sulfur is important in preventing film evaporation, increasing boundary migration and providing compliancy to sapphire substrate. The minority carrier diffusion lengths and lifetimes were measured for electrons and holes in unintentionally doped, n and p-type GaN samples grown by several different growth techniques. The experimentally observed diffusion lengths were in the 0.2 — 0.3 µm range for Metal-Organic Chemical Vapor Deposition (MOCVD) and Molecular Beam Epitaxy (MBE) grown samples, and 1 — 2 µm in the case of Halide Vapor Phase Epitaxy (HVPE) grown sample. In the case of MOCVD grown samples, the hole lifetime was estimated to approximately 7 ns, and electron lifetime to approximately 0.1 ns. The same samples were structurally characterized by AFM, and the size of the defect-free regions surrounded by linear dislocations is found to be of the order of measured diffusion length, in qualitative agreement with minority carrier recombination at linear dislocations. A simple model is presented which explains an increase in minority carrier lifetime and diffusion length with a decrease in the dislocation density or increase in the size of defect-free grains. A model which explains why linear dislocations might act as recombination sites is also presented. The important advantage of nitrides and other wide band gap materials for high power devices is a smaller standoff layer thickness for the same standoff voltage, giving smaller ON-state voltage and resistance, smaller power dissipation and larger maximum current density, allowing physically smaller devices for the same power rating. The design rules for nitride based Schottky rectifiers and thyristors are presented. The critical field for electric breakdown and minority carrier recombination lifetimes are found to be important design parameters. Using modeling parameters which are well in the range currently available with GaN, and measured from fabricated devices, design results indicate the possibility of 18 µm thick GaN Schottky rectifiers and 12 µm thick A1GaN thyristors supporting 5 kV standoff voltage. The critical field for electric breakdown was found to be 5 MV/cm from the theoretical studies. The maximum current density for 5 kV thyristors is in the 200 — 400 A/cm^2 range depending on the hole lifetime, and is limited by thermal breakdown. The maximum operating frequency of 5 kV thyristors is in the 1-2 MHz range and also depends on the hole lifetime. Two-terminal GaN Schottky rectifiers were fabricated. The Schottky rectifiers were fabricated on thick GaN layers grown by HVPE and had a standoff voltages in the 450 V to 750 V range, depending on the thickness of the GaN film and contact geometry. Best devices were characterized with reverse current density of 10^(-5)A/cm^2 at reverse bias of 100 V, and 4.2 V ON-state voltage at a forward current density of 100 A/cm^2. Various contact geometries were investigated. It was found that mesa geometry improves ON-state voltage, but causes increase in reverse current density, while that metal field plate geometry significantly reduces reverse current density. The measured critical field for electric breakdown in GaN was found to be (2.5 ± 0.5) MV/cm and it approaches the theoretical estimate of 5 MV/cm. The measured values of critical field are only a lower limit since the reverse breakdown voltage was limited by premature corner and edge breakdown