362 research outputs found
Super-slippery Carbon Nanotubes: Symmetry Breaking breaks friction
The friction between the walls of multi-wall carbon nanotubes is shown to be
extremely low in general, with important details related to the specific choice
of the walls. This is governed by a simple expression revealing that the
phenomenon is a profound consequence of the specific symmetry breaking:
super-slippery sliding of the incommensurate walls is a Goldstone mode. Three
universal principles of tribology, offering a recipe for the lubricant
selection are emphasized.Comment: 4 pages, 2 figures, 1 table; pdf available from:
http://www.ff.bg.ac.yu/qmf/qsg_e.ht
Symmetry Based Properties of the Transition Metal Dichalcogenide Nanotubes
The full geometrical symmetry groups (the line groups) of the monolayered,
2Hb and 3R polytypes of the inorganic MoS2 and WS2 micro- and nanotubes of
arbitrary chirality are found. This is used to find the coordinates of the
representative atoms sufficient to determine completely geometrical structure
of tubes. Then some physical properties which can be deduced from the symmetry
are discussed: electron band degeneracies, selection rules, general forms of
the second rank tensors and potentials, phonon spectra.Comment: 6 pages 1 figur
Preparation and characterization of interpenetrating networks based on polyacrylates and poly(lactic acid)
Three different, multifunctional acrylic monomers were photopolymerized in a matrix of poly(lactic acid), PLA, using 2-hydroxy-2-methyl-1-phenyl-propan-1-one as a photoinitiator. The kinetics of the photopolymerization of monomers in PLA, studied with Fourier Transform Infrared Spectroscopy, has been compared to analogous processes of pure monomers under the same conditions (room temperature, air atmosphere). Additionally, poly(ethylene glycol) was added to acrylate/PLA blends as plasticizer.The highly crosslinked networks obtained were characterized by FTIR and optical microscopy. The amount of insoluble gel has been estimated gravimetrically. It was found that the studied systems are characterized by very high polymerization rate, moreover, efficient grafting of polyacrylates on PLA takes place. The observed morphology indicates the heterogeneity of formed networks. The glass transition temperature of PLA in studied blends has been determined by differential scanning calorimetry
Statistical territorial units with purpose of measuring level of development of regions in Serbia
Дан общий обзор существующей классификации статистических территориальных единиц в соответствии с классификацией NSTJ в Сербии. Цель работы - изучить и проанализировать классификации NSTJ в Сербии и определить, соответствует ли она классификации в ЕС. Сформирован перечень возможных мер, которые государство должно предпринять для того, чтобы выровнять степень развития регионов. Рассмотрены возможности использования имеющихся ресурсов. Установлено, что Сербия не имеет региональной политики, целью которой было бы выравнивание регионов и управление их более равномерным развитием в Сербии, как это предусмотрено Конституцией. После распада Югославии в 1991 году Сербия становится одной из европейских стран с крупнейшимими различиями в развитии регионов
Modified group projectors: tight binding method
Modified group projector technique for induced representations is a powerful
tool for calculation and symmetry quantum numbers assignation of a tight
binding Hamiltonian energy bands of crystals. Namely, the induced type
structure of such a Hamiltonian enables efficient application of the procedure:
only the interior representations of the orbit stabilizers are to be
considered. Then the generalized Bloch eigen functions are obtained naturally
by the expansion to the whole state space. The method is applied to the
electronic pi-bands of the single wall carbon nanotubes: together with
dispersion relations, their complete symmetry assignation by the full symmetry
(line) groups and the corresponding symmetry-adapted eigen function are found.Comment: 10 pages 1 figur
Influence of summer temperatures on basic economic and tourism indicators of the middle mediterranean
The Middle Mediterranean is characterized by long, hot, and dry summers, significant historical and cultural values, and the warm Mediterranean sea, making it attractive for coastal tourism. Given these characteristics, the goal of our paper is to analyze the influence of summer temperatures in the region of the Middle Mediterranean on the values of underlying economic and tourism indicators. The method of simple linear correlation and regression was used. Based on the results of testing, we came to the conclusion that the temperatures in the summer months have no significant influence on selected economic and tourism indicators. Also, we conclude that social factors have the greatest influence on these indicators. The coefficients of variation are calculated in the observed period to analyze the variability of the tested values. It could not be identified a statistically significant relationship of indicators with summer temperatures
Single nucleotide polymorphisms and the risk of developing a second primary cancer among head and neck cancer patients: a systematic literature review and meta-analysis
Background: Head and Neck Cancer (HNC) survivors are at increased risk of developing a second primary cancer (SPC). Along with the environmental risk factors, genetic factors have been associated with a potential increased susceptibility to SPC development. We aim to identify the Single Nucleotide Polymorphisms (SNPs) that contribute to SPC development among HNC survivors through a systematic review and meta-analysis. Methods: We searched PubMed, Scopus and ISI Web of Science for eligible studies published in English until January 31st, 2020. We included studies reporting primary data that evaluated the association between SNPs and SPC risk in HNC patients. Data were pooled in a random-effect meta-analyses, when at least two studies on the same SNP evaluated the same genotype model. Heterogeneity was assessed using the χ2-based Q-statistics and the I2 statistics. Quality of the included studies was assessed using the Q-Genie tool. Results: Twenty-one studies, of moderate to good quality, were included in the systematic review. Fifty-one genes were reported across the included studies to have significant associations with an increased SPC risk. Overall, 81 out of 122 investigated SNPs were significantly associated with the SPC risk. Seven studies were included in the meta-analysis, which showed five SNPs associated with an increased risk of SPC: p21C70T, CT + TT (HR = 1.76; 95% CI: 1.28–2.43); FASLG -844C > T, CT + TT (HR = 1.82; 95% CI: 1.35–2.46), P21 C98A, CA + AA (HR = 1.75; 95% CI: 1.28–2.38); FAS -670A > G (HR = 1.84; 95% CI: 1.28–2.66) and GST-M1, Null genotype (HR = 1.54; 95% CI: 1.13–2.10). Conclusions: The identified SNPs in our systematic review and meta-analysis might serve as potential markers for identification of patients at high risk of developing SPC after primary HNC. PROSPERO Registration Number: CRD42019135612
Translational Research: Palatal-derived Ecto-mesenchymal Stem Cells from Human Palate: A New Hope for Alveolar Bone and Cranio-Facial Bone Reconstruction
The management of facial defects has rapidly changed in the last decade. Functional and esthetic requirements have steadily increased along with the refinements of surgery. In the case of advanced atrophy or jaw defects, extensive horizontal and vertical bone augmentation is often unavoidable to enable patients to be fitted with implants. Loss of vertical alveolar bone height is the most common cause for a non primary stability of dental implants in adults. At present, there is no ideal therapeutic approach to cure loss of vertical alveolar bone height and achieve optimal pre-implantological bone regeneration before dental implant placement. Recently, it has been found that specific populations of stem cells and/or progenitor cells could be isolated from different dental resources, namely the dental follicle, the dental pulp and the periodontal ligament. Our research group has cultured palatal-derived stem cells (paldSCs) as dentospheres and further differentiated into various cells of the neuronal and osteogenic lineage, thereby demonstrating their stem cell state. In this publication will be shown whether paldSCs could be differentiated into the osteogenic lineage and, if so, whether these cells are able to regenerate alveolar bone tissue in vivo in an athymic rat model. Furthermore, using these data we have started a proof of principle clinical- and histological controlled study using stem cell-rich palatal tissues for improving the vertical alveolar bone augmentation in critical size defects. The initial results of the study demonstrate the feasibility of using stem cell-mediated tissue engineering to treat alveolar bone defects in humans
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