Damage function for poly(vinyl chloride) in heritage collections

Yellowing of plastic objects as a consequence of chemical degradation is a common heritage conservation challenge. In the case of poly(vinyl chloride) elimination of hydrogen chloride leads to the formation of polyene sequences that act as chromophores. The objective of this work was to quantitatively evaluate the rate of degradation observed as yellowing, as relevant to room conditions during long-term storage of heritage collections. Degradation was quantified as increase in the b* colour coordinate during accelerated degradation at 50 and 70 °C as a function of temperature, relative humidity, plasticizer content, and polymer molecular weight. The significance of each variable was investigated with multiple linear regression. Lower temperature, lower relative humidity, higher polymer molecular weight and higher plasticizer content were associated with lower degradation rates. The activation energy of 86 kJ/mol was calculated. The concept of ‘1- °C-equivalent’ is introduced to enable variable prioritisation from a heritage management aspect. The resulting model can be used to shape environmental management guidelines and identify the most vulnerable objects in heritage collections

Control of posture with FES systems

One of the major obstacles in restoration of functional FES supported standing in paraplegia is the lack of knowledge of a suitable control strategy. The main issue is how to integrate the purposeful actions of the non-paralysed upper body when interacting with the environment while standing, and the actions of the artificial FES control system supporting the paralyzed lower extremities. In this paper we provide a review of our approach to solving this question, which focuses on three inter-related areas: investigations of the basic mechanisms of functional postural responses in neurologically intact subjects; re-training of the residual sensory-motor activities of the upper body in paralyzed individuals; and development of closed-loop FES control systems for support of the paralyzed joints

Machine learning-assisted non-destructive plasticizer identification and quantification in historical PVC objects based on IR spectroscopy

Non-destructive spectroscopic analysis combined with machine learning rapidly provides information on the identity and content of plasticizers in PVC objects of heritage value. For the first time, a large and diverse collection of more than 100 PVC objects in different degradation stages and of diverse chemical compositions was analysed by chromatographic and spectroscopic techniques to create a dataset used to construct classification and regression models. Accounting for this variety makes the model more robust and reliable for the analysis of objects in museum collections. Six different machine learning classification algorithms were compared to determine the algorithm with the highest classification accuracy of the most common plasticizers, based solely on the spectroscopic data. A classification model capable of the identification of di(2-ethylhexyl) phthalate, di(2-ethylhexyl) terephthalate, diisononyl phthalate, diisodecyl phthalate, a mixture of diisononyl phthalate and diisodecyl phthalate, and unplasticized PVC was constructed. Additionally, regression models for quantification of di(2-ethylhexyl) phthalate and di(2-ethylhexyl) terephthalate in PVC were built. This study of real-life objects demonstrates that classification and quantification of plasticizers in a general collection of degraded PVC objects is possible, providing valuable data to collection managers

The mechanism of caesium intercalation of graphene

Properties of many layered materials, including copper- and iron-based superconductors, topological insulators, graphite and epitaxial graphene can be manipulated by inclusion of different atomic and molecular species between the layers via a process known as intercalation. For example, intercalation in graphite can lead to superconductivity and is crucial in the working cycle of modern batteries and supercapacitors. Intercalation involves complex diffusion processes along and across the layers, but the microscopic mechanisms and dynamics of these processes are not well understood. Here we report on a novel mechanism for intercalation and entrapment of alkali-atoms under epitaxial graphene. We find that the intercalation is adjusted by the van der Waals interaction, with the dynamics governed by defects anchored to graphene wrinkles. Our findings are relevant for the future design and application of graphene-based nano-structures. Similar mechanisms can also play a role for intercalation of layered materials.Comment: 8 pages, 7 figures in published form, supplementary information availabl

Transfer of Aflatoxin M1 From the Contaminated Milk Into Cheese and Whey

Aflatoxin M1 is a major metabolite of aflatoxin B1 which is formed when animals ingest contaminated feed. Aflatoxin B1, when ingested by an animal, is rapidly absorbed in the gastrointestinal tract and transformed into a metabolite aflatoxin M1, appearing in the blood after 15 minutes and then secreted in the milk from the mammary gland. Aflatoxin B1 shows hepatotoxic and carcinogenic effects and aflatoxin M1 has a distinct genotoxicity, carcinogenicity and cytotoxicity. The resistance to heat treatment and mild acidic conditions used in the production of cheese or other dairy products (such as, for example, yogurt, cream, butter, and ice cream) has been accounted for the contamination of such products. It is known that aflatoxin M1 is bound to milk proteins, mainly casein, and therefore the toxin is more concentrated in the cheese than in the milk used in cheese production. In practice, aflatoxin M1 can be found in dairy products at levels that are 2-5 times higher than in milk. As a result of the binding of aflatoxin M1 to milk proteins the toxin is distributed more in curd than in whey. Control of samples of milk from the Vojvodina market was conducted during March and April of 2014, in the Dairy Laboratory and Laboratory for the Analysis of Animal Feed and Animal Products, the Department of Animal Science, Faculty of Agriculture, Novi Sad. The method used was HPLC with fluorescence detection with pre-treatment of milk on immunoaffinity columns. The analysis of milk was performed on milk of 12 dairies whose products can be found on the Vojvodina market. The manufacturer with the highest levels of aflatoxin M1 in milk was chosen and a semi-hard cheese was made of such milk. The results showed the expected increase of concentration of aflatoxin M1 in cheese and whey. Since Serbia has no regulation that determines the minimum allowable level of aflatoxin M1 in cheese and other dairy products, the results were compared with acceptable values for cheese in some European countries

Protest event data for Croatia, Portugal, Serbia and Spain: Focus on strike data

‘Disobedient Democracy: A Comparative Analysis of Contentious Politics in the European Semi-periphery’ is a research project implemented by the Faculty of Political Science of the University of Zagreb, in the period 2016-2021, led by Principal Investigator Danijela Dolenec and funded by the Swiss National Science Foundation (IZ11Z0_166540 – PROMYS). The overall objective of the project is to explore how protest politics advances democracy by collecting and analyzing data on protest mobilizations in four countries: Portugal, Spain, Croatia and Serbia.‎info:eu-repo/semantics/publishedVersio

Discrete solvent effects on the effective interaction between charged colloids

Using computer simulations of two charged colloidal spheres with their counterions in a hard sphere solvent, we show that the granular nature of the solvent significantly influences the effective colloidal interaction. For divalent counterions, the total effective force can become attractive generated by counterion hydration, while for monovalent counterions the forces are repulsive and well-described by a solvent-induced colloidal charge renormalization. Both effects are not contained in the traditional "primitive" approaches but can be accounted for in a solvent-averaged primitive model.Comment: 4 pages, 3 figure

Hysteresis in Two-Dimensional Liquid Crystal Models

We make a numerical study of hysteresis loop shapes within a generalized two-dimensional Random Anisotropy Nematic (RAN) model at zero temperature. The hysteresis loops appear on cycling a static external ordering field. Ordering in these systems is history dependent and involves interplay between the internal coupling constant J, the anisotropy random field D, and the ordering external field H. Here the external field is represented by a traceless tensor, analogous to extension-type fields in continuum mechanics. The calculations use both a mean field approach and full lattice simulations. Our analysis suggests the existence of two qualitatively different solutions, which we denote as symmetric and symmetry breaking. For the set of parameters explored, only the symmetric solutions are stable. Both approaches yield qualitatively similar hysteresis curves, which are manifested either by single or double loops. But the quantitative differences indicate that mean field estimates are only of limited predictive value