Report on the 2012 Proficiency Test on pyrrolizidine alkaloids in honey and hay

The purpose of this proficiency test was to investigate the current measurement capacities of testing laboratories for pyrrolizidine alkaloids in honey and plant materials. The scheme consisted of two parts: Benchmarking performance of laboratories against known estimates of pyrrolizidine alkaloids in the samples and checking for methodological differences while measuring naturally contaminated materials. Twenty-eight laboratories expressed their will to participate and analysed multiple analytes in several test samples of honey and plant material. The analysis of spiked honey showed no statistical differences between determining a common sum parameter for alkaloids and individual determination. A significant difference has been found however for of naturally contaminated materials. Individual alkaloid determination showed significantly lower results, possibly because of the presence of substances contributing to the sum parameter that were not in the scopes of the methods applied as well as lack of standard materials available on the market. Satisfactory performance for all of analytes has been achieved by more than half of participants analysing for both: sum parameter, and alkaloids analysed individually.JRC.D.5-Standards for Food Bioscienc

Altered Proliferation, Synthetic Activity, and Differentiation of Cultured Human sebocytes in the Absence of Vitamin A and Their Modulation by Synthetic Retinoids

Human sebocytes maintained in medium containing delipidized serum were studied for ultrastructural characteristics, cell proliferation, lipid synthesis, immunophenotype, and keratin expression before and after the addition of the synthetic retinoids isotretinoin and acitretin (10-8 - 10-5 M).Compared to the properties of sebocytes cultured in normal sebocyte medium (1–2 × 10-7 M vitamin A), the use of delipidized serum (undetectable amounts of vitamin A) resulted in prominent decrease of i) proliferation; ii) number of intracellular lipid droplets and synthesis of total lipids, especially triglycerides, squalene, and wax esters; and iii) labeling with monoclonal antibodies identifying progressive and late-stage sebocyte differentiation. Intercellular spaces narrowed and cell-to-cell contacts were established by abundant desmosomes. Lanosterol was induced. Keratins 14, 16, 17, and 18 were upregulated and the keratin 16: keratin 4 ratio, negatively correlating with sebocyte differentiation, increased.Addition of isotretinoin and acitretin exerted a biphasic effect. At concentrations ≤ 10-7 M, both compounds enhanced sebocyte proliferation and synthesis of total lipids, especially triglycerides and cholesterol, and decreased Ianosterol, keratin 16, and the keratin 16: keratin 4 ratio. In contrast, retinoid concentrations > 10-7 M inhibited sebocyte proliferation in a dose-dependent manner.Our findings indicate that vitamin A is essential for proliferation, synthetic activity, and differentiation of human sebocytes in vitro. Synthetic retinoids partially reinstate the altered functions of sebocytes maintained in medium containing delipidized serum. In contrast to the previously shown isotretinoin-specific response of cultured sebocytes in the presence of vitamin A, similar effects of isotretinoin and acitretin were obtained in its absence. This suggests different interactions of synthetic retinoids with vitamin A, possibly influencing their efficacy on the sebacceous gland

Genes Encoding Structural Proteins of Epidermal Cornification and S100 Calcium-Binding Proteins Form a Gene Complex (“Epidermal Differentiation Complex”) on Human Chromosome 1q21

Chromosome 1 reveals in region 1q21 a most remarkable density of genes that fulfill important functions in terminal differentiation of the human epidermis. These genes encode the cornified envelope precursors loricrin, involucrin, and small proline-rich proteins (SPRR1, SPRR2, and SPRR3), the intermediate filament-associated proteins profilaggrin and trichohyalin, and several S100A calcium-binding proteins. Extending and refining our previous physical map of 1q21 we have now mapped two additional S100A genes as well as the three SPRR subfamilles and resolved the arrangement of involucrin, SPRRs, and loricrin. All genes are linked within 1.9 Mbp of human genomic DNA in the order: S100A10, trichohyalin, profilaggrin, involucrin, SPRR3, SPRR1B, SPRR2A, loricrin, S100A9, S100A8, S100A6. Co-localization of genes expressed late during maturation of epidermal cells together with genes encoding calcium-binding proteins is particularly intriguing since calcium levels tightly control the differentiation of epithelial cells and the expression of genes encoding epidermal structural proteins. Accounting for the close functional cooperation among these structurally and evolutionary related genes, we conclude that these loci constitute a gene complex, for which we propose the name epidermal differentiation complex

Correlations of Heavy Quarks Produced at Large Hadron Collider

We study the correlations of heavy quarks produced in relativistic heavy ion collisions and find them to be quite sensitive to the effects of the medium and the production mechanisms. In order to put this on a quantitative footing, as a first step, we analyze the azimuthal, transverse momentum, and rapidity correlations of heavy quark-anti quark ($Q\overline{Q}$) pairs in $pp$ collisions at $\cal{O}$($\alpha_{s}^{3}$). This sets the stage for the identification and study of medium modification of similar correlations in relativistic collision of heavy nuclei at the Large Hadron Collider. Next we study the additional production of charm quarks in heavy ion collisions due to multiple scatterings, {\it viz.}, jet-jet collisions, jet-thermal collisions, and thermal interactions. We find that these give rise to azimuthal correlations which are quite different from those arising from prompt initial production at leading order and at next to leading order.Comment: 26 pages, 15 figures. Three new figures added, comparison to experimental data included, abstract and discussion expande

Direct growth of graphene on GaN via plasma-enhanced chemical vapor deposition under N₂ atmosphere

One of the bottlenecks in the implementation of graphene as a transparent electrode in modern opto-electronic devices is the need for complicated and damaging transfer processes of high-quality graphene sheets onto the desired target substrates. Here, we study the direct, plasma-enhanced chemical vapor deposition (PECVD) growth of graphene on GaN-based light-emitting diodes (LEDs). By replacing the commonly used hydrogen (H2) process gas with nitrogen (N2), we were able to suppress GaN surface decomposition while simultaneously enabling graphene deposition at lt;800 °C in a single-step growth process. Optimizing the methane (CH4) flow and varying the growth time between 0.5 h and 8 h, the electro-optical properties of the graphene layers could be tuned to sheet resistances as low as ∼1 kΩ/D with a maximum transparency loss of ∼12. The resulting high-quality graphene electrodes show an enhanced current spreading effect and an increase of the emission area by a factor of ∼8 in operating LEDs. © 2020 The Author(s)

Anomalous mass dependence of radiative quark energy loss in a finite-size quark-gluon plasma

We demonstrate that for a finite-size quark-gluon plasma the induced gluon radiation from heavy quarks is stronger than that for light quarks when the gluon formation length becomes comparable with (or exceeds) the size of the plasma. The effect is due to oscillations of the light-cone wave function for the in-medium $q\to gq$ transition. The dead cone model by Dokshitzer and Kharzeev neglecting quantum finite-size effects is not valid in this regime. The finite-size effects also enhance the photon emission from heavy quarks.Comment: 8 pages, 3 figure

The time-dependent expression of keratins 5 and 13 during the reepithelialization of human skin wounds

The time-dependent reepithelialization of 55 human surgical skin wounds with a wound age between 8h and more than 2 months was investigated by the immunohistochemical localization of cytokeratins 5 and 13. A complete, rebuilt epidermal layer over the wound area was first detectable in a 5-day-old wound, while all wounds of more than 18 days duration contained a completely reepithelialized wound area. Between 5 and 18 days the basal layer of keratinocytes showed — in contrast to normal skin — only some cells positive for cytokeratin 5. In some, but not all lesions with a wound age of 13 days or more, a basal cell layer completely staining for cytokeratin 5 was demonstrable. This staining pattern was found in all skin wounds with a wound age of more than 23 days. The immunohistochemical detection of cytokeratin 13 which can be observed regularly in non-cornifying squamous epithelia provides no information for the time-estimation of human skin wounds, since no significant temporary expression of this polypeptide seems to occur during the healing of human skin wounds