Atmospheric heavy metal pollution in Slovenia derived from results for epiphytic lichens

In 1992, a monitoring survey has been started on the national scale in Slovenia using the epiphytic lichen Hypogymnia physodes (L.) Nyl. The primary aim has been to analyse lichens using the k₀-based INAA method to obtain information about the levels of elements in the atmosphere and to identify significant pollution sources. Monte Carlo-Assisted Factor Analysis was applied to a data set of the 28 elements As, Ag, Ba, Br, Ce, Cd, Co, Cr, Cs, Fe, Ga, Hf, Hg, K, La, Mo, Na, Rb, Sb, Sc, Se, Sr, Sm, Tb, Th, U, W and Zn, which have been selected from the elements determined as the most important ones for the identification of pollution sources. A Monte Carlo approach has been used to give more insight into the uncertainties and significance levels of the factor analysis results. It has been found that concentration patterns in lichens yielded 9 factors (source types) which are presented and discussed in detail. The geographical patterns of the contributions of all factors are also shown.     

The controversy in theγγ →ρρ process: potential scattering or qq\bar q};\bar q}; resonance?; resonance?

Theγγ →ρ ⁰ ρ ⁰ → 4π reaction shows a broad peak at 1.5 GeV in the (J ^P ,J _z )=(2⁺,2) channel which has no counterpart in theρ ⁺ ρ ^? channel. This “resonance” is considered as a candidate for a qq $\bar q$ ; $\bar q$ state in the “s-channel”. We show, however, that it can also be explained by potential scattering ofρ ⁰ ρ ⁰ via theσ- exchange in the “t-channel”.     

Note on list star edge-coloring of subcubic graphs

A star edge-coloring of a graph is a proper edge-coloring without bichromatic paths and cycles of length four. In this paper, we consider the list version of this coloring and prove that the list star chromatic index of every subcubic graph is at most 7, answering the question of Dvořák et al (J Graph Theory, 72 (2013), 313-326).     

Phage display: selecting straws instead of a needle from a haystack

An increasing number of peptides with specific binding affinity to various protein and even non-protein targets are being discovered from phage display libraries. The power of this method lies in its ability to efficiently and rapidly identify ligands with a desired target property from a large population of phage clones displaying diverse surface peptides. However, the search for the needle in the haystack does not always end successfully. False positive results may appear. Thus instead of specific binders phage with no actual affinity toward the target are recovered due to their propagation advantages or binding to other components of the screening system, such as the solid phase, capturing reagents, contaminants in the target sample or blocking agents, rather than the target. Biopanning experiments on different targets performed in our laboratory revealed some previously identified and many new target-unrelated peptide sequences, which have already been frequently described and published, but not yet recognized as target-unrelated. Distinguishing true binders from false positives is an important step toward phage display selections of greater integrity. This article thoroughly reviews and discusses already identified and new target-unrelated peptides and suggests strategies to avoid their isolation.     

Peptide phage display as a tool for drug discovery: targeting membrane receptors

Ligands selected from phage-displayed random peptide libraries tend to be directed to biologically relevant sites on the surface of the target protein. Consequently, peptides derived from library screenings often modulate the target protein's activity in vitro and in vivo and can be used as lead compounds in drug design and as alternatives to antibodies for target validation in both genomics and drug discovery. This review discusses the use of phage display to identify membrane receptor modulators with agonistic or antagonistic activities. Because isolating or producing recombinant membrane proteins for use as target molecules in library screening is often impossible, innovative selection strategies such as panning against whole cells or tissues, recombinant receptor ectodomains, or neutralizing antibodies to endogenous binding partners were devised. Prominent examples from a two-decade history of peptide phage display will be presented, focusing on the design of affinity selection experiments, methods for improving the initial hits, and applications of the identified peptides.     

k0-NAA quality assessment by analysis of different certified reference materials using the KAYZERO/SOLCOI software

A suite of natural matrix reference materials (RMs) were used to assess the quality of analytical results obtained by k ₀-instrumental neutron activation analysis (k ₀-INAA) at the Joef Stefan Institute (IJS). Five certified reference materials (CRMs) from the Institute for Reference Materials and Measurements (IRMM), two standard reference materials (SRMs) from the National Institute of Standards and Technology (NIST), three RMs from the International Atomic Energy Agency (IAEA) and one RM from IJS were analyzed. Altogether, results for twenty-four elements in inorganic matrices and twenty-nine elements in organic matrices, obtained by k ₀-INAA, were compared to certified values. Results obtained show good agreement with certified or assigned values except for Fe, La, Nd, Sm and U in inorganic matrices, and Ag, Al and Cr in organic matrices.     

Simultaneous low-level determination of iodine and manganese in biological materials by radiochemical neutron activation analysis

A new RNAA procedure was developed for simultaneous determination of low levels of I and Mn in biological materials. The procedure is based on sample decomposition by alkaline-oxidative fusion in a mixture of Na₂O₂ + NaOH at 900°C followed by extraction of elementary iodine by chloroform. Subsequently, Mn is separated either by precipitation of hydrated MnO₂ or by extraction of the Mn-diethyldithiocarbamate complex in chloroform. The accuracy of the RNAA procedure developed was proven by analysis of several low-level biological reference materials. Detection limits of I and Mn achievable in both institutes and the degree of interference for the Mn determination due to ⁵⁶Fe(n,p)⁵⁶Mn reaction with fast neutrons are discussed.     

Injective colorings of planar graphs with few colors

An injective coloring of a graph is a vertex coloring where two vertices have distinct colors if a path of length two exists between them. In this paper some results on injective colorings of planar graphs with few colors are presented. We show that all planar graphs of girth ≥ 19 and maximum degree Δ are injectively Δ-colorable. We also show that all planar graphs of girth ≥ 10 are injectively (Δ+1)-colorable, that Δ+4 colors are sufficient for planar graphs of girth ≥ 5 if Δ is large enough, and that subcubic planar graphs of girth ≥ 7 are injectively 5-colorable.