Luminescence and laser action of coumarin dyes doped in silicate and aluminosilicate glasses prepared by the sol-gel technique

Coumarin dyes are encapsulated in silicate and aluminosilicate polymeric glasses synthesized by the sol-gel technique. The coumarin dyes retain their luminescent properties in all of the aged gels and in many of the dried gels (xerogels). The luminescence spectra of the new optical materials are reported. The luminescence of coumarin 4 provides a probe at the molecular level of the changes which occur during the gelation and drying. The spectral changes are studied and discussed in detail. Gels and xerogels doped with coumarin 460, 480, and 540A exhibit optical gain and laser action. The laser properties of these new solid-state dye laser materials are reported and discussed.     

The effect of field modifier blocks on the fast photoneutron dose equivalent from two high-energy medical linear accelerators

High-energy linear accelerators (linacs) have several advantages, including low skin doses and high dose rates at deep-seated tumours. But, at energies more than 8 MeV, photonuclear reactions produce neutron contamination around the therapeutic beam, which may induce secondary malignancies. In spite of improvements achieved in medical linac designs, many countries still use conventional (non-intensity-modulated radiotherapy) linacs. Hence, in these conventional machines, fitting the beam over the treatment volume may require using blocks. Therefore, the effect of these devices on neutron production of linacs needs to be studied. The aim of this study was to investigate the effect of field shaping blocks on photoneutron dose in the treatment plane for two high-energy medical linacs. Two medical linacs, a Saturn 43 (25 MeV) and an Elekta SL 75/25 (18 MeV), were studied. Polycarbonate (PC) films were used to measure the fluence of photoneutrons produced by these linacs. After electrochemical etching of the PC films, the neutron dose equivalent was calculated at the isocentre and 50 cm away from the isocentre. It was noted that by increasing the distance from the centre of the X-ray beam towards the periphery, the photoneutron dose equivalent decreases rapidly for both the open and blocked fields. Increasing the energy of the photons causes an increase in the amount of photoneutron dose equivalent. At 25 MeV photon energy, the lead blocks cause a meaningful increase in the dose equivalent of photoneutrons. In this research, a 30% increase was seen in neutron dose contribution to central axis dose at the isocentre of a 25 MeV irregular field shaped by lead blocks. It is concluded that lead blocks must be considered as a source of photoneutron production when treating irregular fields with high-energy photons.     

Hybrid Computational Simulation and Study of Terahertz Pulsed Photoconductive Antennas

A photoconductive antenna (PCA) has been numerically investigated in the terahertz (THz) frequency band based on a hybrid simulation method. This hybrid method utilizes an optoelectronic solver, Silvaco TCAD, and a full-wave electromagnetic solver, CST. The optoelectronic solver is used to find the accurate THz photocurrent by considering realistic material parameters. Performance of photoconductive antennas and temporal behavior of the excited photocurrent for various active region geometries such as bare-gap electrode, interdigitated electrodes, and tip-to-tip rectangular electrodes are investigated. Moreover, investigations have been done on the center of the laser illumination on the substrate, substrate carrier lifetime, and diffusion photocurrent associated with the carriers temperature, to achieve efficient and accurate photocurrent. Finally, using the full-wave electromagnetic solver and the calculated photocurrent obtained from the optoelectronic solver, electromagnetic radiation of the antenna and its associated detected THz signal are calculated and compared with a measurement reference for verification.     

Synthesis and characterization of polyethylene glycol mediated silver nanoparticles by the green method

The roles of green chemistry in nanotechnology and nanoscience fields are very significant in the synthesis of diverse nanomaterials. Herein, we report a green chemistry method for synthesized colloidal silver nanoparticles (Ag NPs) in polymeric media. The colloidal Ag NPs were synthesized in an aqueous solution using silver nitrate, polyethylene glycol (PEG), and β-D-glucose as a silver precursor, stabilizer, and reducing agent, respectively. The properties of synthesized colloidal Ag NPs were studied at different reaction times. The ultraviolet-visible spectra were in excellent agreement with the obtained nanostructure studies performed by transmission electron microscopy (TEM) and their size distributions. The Ag NPs were characterized by utilizing X-ray diffraction (XRD), zeta potential measurements and Fourier transform infrared (FT-IR). The use of green chemistry reagents, such as glucose, provides green and economic features to this work.     

Hydrophobicity of fluorocarbon-finished electrospun poly (acrylonitrile) nanofibrous webs

This article reports the hydrophobicity of fluorocarbon-finished nanofibrous webs composed of electrospun poly (acrylonitrile) nanofibers with fiber diameter in the range of about 100–3000 nm. The results obtained from sliding angle and contact angle measurements tests are reported. It was found that the contact angle of unfinished samples with average fiber diameters of about 700, 980 , and 3050 nm lies between 132° and 134°, indicating a rather high and at the same time not much different hydrophobicity for the webs. However, after finishing the electrospun nano- and microfibrous webs, the contact angle increased by a considerable amount to 138°–157° for the webs with average fiber diameter in the range of about 100–3050 nm, respectively. Sliding angle test of the finished nanofibrous webs showed a minimum angle of about 3° for the web with average fiber diameter of 3055 nm. To the best of authors’ knowledge, the rolling angle of 3° is the smallest rolling angle ever reported in the literature. The result of this work showed also that sliding angle test may be more sensitive than contact angle test. It was also ascertained that none of the Wenzel model and Cassie–Baxter model can represent the superhydrophobicity of the fluorocarbon-finished nano- and microfibrous webs.     

Creep analysis of an earth embankment on soft soil deposit with and without PVD improvement

In this paper, an anisotropic creep constitutive model, namely Creep-SCLAY1S is employed to study the installation effects of prefabricated vertical drains (PVDs) on the behavior of a full scale test embankment, namely Haarajoki embankment in Finland. The embankment was constructed on a natural soft soil with PVD installed to improve the drainage under one half of it. The Creep constitutive model used in this study, incorporates the effects of fabric anisotropy, structure and time within a critical state based framework. For comparison, the isotropic modified Cam clay (MCC) model and the rate-independent anisotropic S-CLAY1S model are also used for the analyses. The numerical predictions are compared with field measurements and the results indicate that the creep model provides an improved approximation of field settlements, and excess pore pressure build-up and dissipations. In addition, the application of two commonly used permeability matching techniques for two dimensional (2D) plane-strain analysis of the PVD problem is studied and the results are discussed highlighting their limitations and advantages.     

Prediction of the durability of limestone aggregates using computational techniques

Neural Computing and Applications - The durability of aggregates is an important factor that is used as an input parameter in desirable engineering properties along with resistance to exposure...     

Selective etching of polylactic acid in poly(styrene)‐block‐poly(d,l)lactide diblock copolymer for nanoscale patterning

Self‐assembled thin films of a lamellar forming polystyrene‐block‐poly(d,l )lactide (PS‐b‐PLA) block copolymer (BCP) contain a “reactive” block that can be readily removed to provide a template for substrate pattern formation. Various methods of PLA removal were studied here with a view to develop the system as an on‐chip etch mask for substrate patterning. Solvo‐microwave annealing was used to induce microphase separation in PS‐b‐PLA BCP with a periodicity of 34 nm (L_o) on silicon and silicon on insulator (SOI) substrates. Wet etches based on alkaline and enzymatic solutions were studied in depth. Fourier transform‐infrared (FT‐IR) analysis showed that basic hydrolysis using sodium hydroxide (NaOH) or ammonium hydroxide (NH₄OH) solutions resulted in greater PLA removal in comparison to an enzymatic approach using Proteinase K in a Tris‐HCl buffer solution. However, in the enzymatic approach, the characteristic self‐assembled fingerprint patterns were retained with less damage. Comparison to a dry etch procedure using a reactive ion etch (RIE) technique was made. A detailed study of the etch rate of PS and PLA homopolymer and PS‐b‐PLA shows depending on DC bias, the etch selectivity of PLA and PS can be almost doubled from 1.7 at DC bias 145 V to 3 at DC bias 270 V. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40798. Together with Krebs et al., J. Appl. Polym. Sci. (2014) 131 , 40795, doi: 10.1002/app.40795 , this article is part of a Special Issue on Polymers for Microelectronics. The remaining articles appear in J. Appl. Polym. Sci. (2014) volume 131 , issue 24. This note was added on 1st July 2014.     

Autophagy,Unfolded Protein Response,and Neuropilin-1 Cross-Talk in SARS-CoV-2 Infection: What Can Be Learned from Other Coronaviruses

The COVID-19 pandemic is caused by the 2019–nCoV/SARS-CoV-2 virus. This severe acute respiratory syndrome is currently a global health emergency and needs much effort to generate an urgent practical treatment to reduce COVID-19 complications and mortality in humans. Viral infection activates various cellular responses in infected cells, including cellular stress responses such as unfolded protein response (UPR) and autophagy, following the inhibition of mTOR. Both UPR and autophagy mechanisms are involved in cellular and tissue homeostasis, apoptosis, innate immunity modulation, and clearance of pathogens such as viral particles. However, during an evolutionary arms race, viruses gain the ability to subvert autophagy and UPR for their benefit. SARS-CoV-2 can enter host cells through binding to cell surface receptors, including angiotensin-converting enzyme 2 (ACE2) and neuropilin-1 (NRP1). ACE2 blockage increases autophagy through mTOR inhibition, leading to gastrointestinal complications during SARS-CoV-2 virus infection. NRP1 is also regulated by the mTOR pathway. An increased NRP1 can enhance the susceptibility of immune system dendritic cells (DCs) to SARS-CoV-2 and induce cytokine storm, which is related to high COVID-19 mortality. Therefore, signaling pathways such as mTOR, UPR, and autophagy may be potential therapeutic targets for COVID-19. Hence, extensive investigations are required to confirm these potentials. Since there is currently no specific treatment for COVID-19 infection, we sought to review and discuss the important roles of autophagy, UPR, and mTOR mechanisms in the regulation of cellular responses to coronavirus infection to help identify new antiviral modalities against SARS-CoV-2 virus.