A metal dicyanamide cluster with high CO2/N2 selectivity

A new microporous metal dicyanamide cluster, Co(hmt)(dca)2 (hmt: hexamethylenetetramine, dca: dicyanamide), with accessible N-donor sites exhibits high CO2/N2 selectivity, 83 at 295 K and 1 bar, for a mixture with a 15:85 CO2 to N2 ratio. Adsorption studies show that the use of hmt and dca moieties as building blocks for solid adsorbents can enhance the CO2:surface interactions due to N atoms available inside the pores, which is confirmed by X-ray single crystal studies. © 2016 Elsevier Inc. All rights reserved

Online Contextual Influence Maximization in social networks

In this paper, we propose the Online Contextual Influence Maximization Problem (OCIMP). In OCIMP, the learner faces a series of epochs in each of which a different influence campaign is run to promote a certain product in a given social network. In each epoch, the learner first distributes a limited number of free-samples of the product among a set of seed nodes in the social network. Then, the influence spread process takes place over the network, other users get influenced and purchase the product. The goal of the learner is to maximize the expected total number of influenced users over all epochs. We depart from the prior work in two aspects: (i) the learner does not know how the influence spreads over the network, i.e., it is unaware of the influence probabilities; (ii) influence probabilities depend on the context. We develop a learning algorithm for OCIMP, called Contextual Online INfluence maximization (COIN). COIN can use any approximation algorithm that solves the offline influence maximization problem as a subroutine to obtain the set of seed nodes in each epoch. When the influence probabilities are Hölder continuous functions of the context, we prove that COIN achieves sublinear regret with respect to an approximation oracle that knows the influence probabilities for all contexts. Moreover, our regret bound holds for any sequence of contexts. We also test the performance of COIN on several social networks, and show that it performs better than other methods. © 2016 IEEE

Amyloid Inspired Self-Assembled Peptide Nanofibers

Cataloged from PDF version of article.Amyloid peptides are important components in many degenerative diseases as well as in maintaining cellular metabolism. Their unique stable structure provides new insights in developing new materials. Designing bioinspired selfassembling peptides is essential to generate new forms of hierarchical nanostructures. Here we present oppositely charged amyloid inspired peptides (AIPs), which rapidly self-assemble into nanofibers at pH 7 upon mixing in water caused by noncovalent interactions. Mechanical properties of the gels formed by selfassembled AIP nanofibers were analyzed with oscillatory rheology. AIP gels exhibited strong mechanical characteristics superior to gels formed by self-assembly of previously reported synthetic short peptides. Rheological studies of gels composed of oppositely charged mixed AIP molecules (AIP-1 + 2) revealed superior mechanical stability compared to individual peptide networks (AIP-1 and AIP-2) formed by neutralization of net charges through pH change. Adhesion and elasticity properties of AIP mixed nanofibers and charge neutralized AIP-1, AIP-2 nanofibers were analyzed by high resolution force− distance mapping using atomic force microscopy (AFM). Nanomechanical characterization of self-assembled AIP-1 + 2, AIP-1, and AIP-2 nanofibers also confirmed macroscopic rheology results, and mechanical stability of AIP mixed nanofibers was higher compared to individual AIP-1 and AIP-2 nanofibers self-assembled at acidic and basic pH, respectively. Experimental results were supported with molecular dynamics simulations by considering potential noncovalent interactions between the amino acid residues and possible aggregate forms. In addition, HUVEC cells were cultured on AIP mixed nanofibers at pH 7 and biocompatibility and collagen mimetic scaffold properties of the nanofibrous system were observed. Encapsulation of a zwitterionic dye (rhodamine B) within AIP nanofiber network was accomplished at physiological conditions to demonstrate that this network can be utilized for inclusion of soluble factors as a scaffold for cell culture studies. Copyright © 2012 American Chemical Societ

The chicken or the egg; or Who ordered the chiral phase transition?

We draw an analogy between the deconfining transition in the 2+1 dimensional Georgi-Glashow model and the chiral phase transition in 3+1 dimensional QCD. Based on the detailed analysis of the former (hep-th/0010201) we suggest that the chiral symmetry restoration in QCD at high temperature is driven by the thermal ensemble of baryons and anti-baryons. The chiral symmetry is restored when roughly half of the volume is occupied by the baryons. Surprisingly enough, even though baryons are rather heavy, a crude estimate for the critical temperature gives $T_c=180$ Mev. In this scenario the binding of the instantons is not the cause but rather a consequence of the chiral symmetry restoration.Comment: 22 pages, 7 figures, comments about chiral symmetry at finite nuclear density are adde

Encapsulation of a zinc phthalocyanine derivative in self-assembled peptide nanofibers

Cataloged from PDF version of article.In this article, we demonstrate encapsulation of octakis(hexylthio) zinc phthalocyanine molecules by non-covalent supramolecular organization within self-assembled peptide nanofibers. Peptide nanofibers containing octakis(hexylthio) zinc phthalocyanine molecules were obtained via a straight-forward one-step self-assembly process under aqueous conditions. Nanofiber formation results in the encapsulation and organization of the phthalocyanine molecules, promoting ultrafast intermolecular energy transfer. The morphological, mechanical, spectroscopic and non-linear optical properties of phthalocyanine containing peptide nanofibers were characterized by TEM, SEM, oscillatory rheology, UV-Vis, fluorescence, ultrafast pump-probe and circular dichroism spectroscopy techniques. The ultrafast pump-probe experiments of octakis(hexylthio) zinc phthalocyanine molecules indicated pH controlled non-linear optical characteristics of the encapsulated molecules within self-assembled peptide nanofibers. This method can provide a versatile approach for bottom-up fabrication of supramolecular organic electronic devices. © 2012 The Royal Society of Chemistry

A rapid and direct method for half value layer calculations for nuclear safety studies using MCNPX Monte Carlo code

Half Value Layer calculations theoretically need prior specification of linear attenuation calculations, since the HVL value is derived by dividing ln(2) by the linear attenuation coefficient. The purpose of this study was to establish a direct computational model for determining HVL, a vital parameter in nuclear radiation safety studies and shielding material design. Accordingly, a typical gamma-ray transmission setup has been modeled using MCNPX (version 2.4.0) general-purpose Monte Carlo code. The MCNPX code's INPUT file was designed with two detection locations for primary and secondary gamma-rays, as well as attenuator material between those detectors. Next, Half Value Layer values of some well-known gamma-ray shielding materials such as lead and ordinary concrete have been calculated throughout a broad gamma-ray energy range. The outcomes were then compared to data from the National Institute of Standards and Technology. The Half Value Layer values obtained from MCNPX were reported to be highly compatible with the HVL values obtained from the NIST standard database. Our results indicate that the developed INPUT file may be utilized for direct computations of Half Value Layer values for nuclear safety assessments as well as medical radiation applications. In conclusion, advanced simulation methods such as the Monte Carlo code are very powerful and useful instruments that should be considered for daily radiation safety measures. The modeled MCNPX input file will be provided to the scientific community upon reasonable request. © 2022 Korean Nuclear SocietyPrincess Nourah Bint Abdulrahman University, PNU: PNURSP2022R149This work was performed under Princess Nourah bint Abdulrahman University Researchers Supporting Project Number (PNURSP2022R149), Princess Nourah bunt Abdulrahman University, Riyadh, Saudi Arabia. The authors express their sincere gratitude to Princess Nourah bint Abdulrahman University

Binary contributions of Dy3+ ions on the mechanical and radiation resistance properties of oxyfluoroborotellurite Dyx-glasses

5CaF2–5BaF2 – 60B2O3–10TeO2 – (20-x)Na2O – xDy2O3: (0.5 ≤ x ≤ 2.5 mol percent) glasses were studied for their physical, mechanical, and gamma radiation resistance. The density of Dy0.5 and Dy2.5 glass samples containing 0.5 and 2.5 mol of Dy2O3 was changed from 2.98 to 3.09 g/cm3, respectively. The estimated values of longitudinal (LB-C) were altered from 171.085 to 165.390 GPa, bulk (KB–C) from 105.100 to 102.680 GPa, Young's (EB-C) from 128.602 to 122.674 GPa, and shear (SB–C) from 49.612 to 47.150 GPa for mechanical characteristics (GPa). The Poisson's ratio (σB-C) was varied between 0.296 and 0.300. The MCNPX code and Py-MLBUF online calculation platform were used to calculate mass attenuation coefficients for all Dyx-glasses. In terms of quantitative values, the acquired results are in good agreement. For all photon energies, the Dy2.5 glass sample exhibits the highest linear (μ) and mass (μm) attenuation coefficients. All analyzed Dyx-glasses exhibit a similar trend in half-value layer (T1/2) and mean free path (MFP), (T1/2, λ)Dy0.5 > (T1/2, λ)Dy1.0 > (T1/2, λ)Dy1.5 > (T1/2, λ)Dy2.0 > (T1/2, λ)Dy2.5. Over the whole gamma-ray energy range, the Dy2.5 sample has the highest effective atomic number (Zeff) values. Across the whole photon energy and penetration depth range, the Dy2.5 has the lowest EBF and EABF values. Because of the maximum contribution of Dysprosium (III)-oxide, the Dy2.5 sample can be deemed superior in terms of gamma-ray shielding qualities. © 2022 The Author(s)Taif University, TU: TURSP-2020/12The authors thank Taif University Researchers Supporting Project number (TURSP-2020/12), Taif University, Taif, Saudi Arabia

Calculation of NaI(Tl) detector efficiency using 226Ra, 232Th, and 40K radioisotopes: Three-phase Monte Carlo simulation study

Thallium-activated sodium iodide (NaI(Tl)) detectors can be used in gamma cameras, environmental radiation assessments, including radiation emission levels from nuclear reactors, and radiation analysis equipment. This three-phase investigation aimed to model a standard NaI(Tl) detector using the Monte Carlo N-Particle eXtended (MCNPX) general-purpose Monte Carlo simulation techniques. Accordingly, a standard NaI(Tl) detector was designed along with the required properties. Next a validation study of the modelled NaI(Tl) detector has been performed based on the experimental results for absolute detector efficiency values obtained from 226Ra, 232Th, and 40K radioisotopes. Our findings indicate that the obtained absolute detector efficiency values are quite close to used experimental values. Finally, we used the modelled detector for determination of mass attenuation coefficients of Ordinary concrete, Lead, Hematite-serpentine concrete, and Steel-scrap concrete at 186.1, 295.22, 351.93, 609.31, 1120.29, 1764.49, 238.63, 911.2, 2614, and 1460.83 keV gamma-ray energies. Additionally, according to our findings, mass attenuation coefficients obtained from the newly designed detector are compatible with the standard NIST (XCOM) data. To conclude, continuous optimisation procedures are strongly suggested for sophisticated Monte Carlo simulations in order to maintain a high degree of simulation reliability. As a result, it can be concluded that the validation of the simulation model is necessary using measured data. Finally, it can also be concluded that the validated detector models are effective instruments for obtaining basic gamma-ray shielding parameters such as mass attenuation coefficients. © 2022 Huseyin Ozan Tekin et al., published by De Gruyter