Growth-Led Tourism and the Role of Exchange Rate: Empirical Evidence from Sri Lanka

We re-visit the growth-led tourism hypothesis to examine the role of the exchange rate in the nexus. Using yearly data on Sri Lanka from 1995 to 2018, preliminary tests reveal a long-run association between tourism receipts, economic growth, and the official exchange rate. Consistent robustness results from a battery of econometric techniques validate that the connection holds autonomously and interactively. Conclusions drawn from the linear models suggest that a percentage change in economic growth increases tourism by 0.8% to 1.2%. Likewise, the exchange rate boosts tourism by 0.006% to 0.008%, on average, ceteris paribus. For the most part, the interaction of the exchange rate with economic growth upholds the "growth-led tourism" hypothesis. We also find that the results hold across the conditional distribution of tourism. Additional evidence from the margin plot reveals that the effect of economic growth on tourism is positive as the Sri Lankan Rupee depreciates. The upward trend of the plot within the 95% confidence interval shows that currency depreciation enhances the impact of economic growth on tourism. These are novel contributions to the literature as it suggests that currency depreciation in Sri Lanka is pro-tourism. Policy recommendations are discussed

Antimicrobial modification of PLA scaffolds with ascorbic and fumaric acids via plasma treatment

An optimal medical scaffold should be biocompatible and biodegradable and should have adequate mechanical properties and scaffold architecture porosity, a precise three-dimensional shape, and a reasonable manufacturing method. Polylactic acid (PLA) is a natural biodegradable thermoplastic aliphatic polyester that can be fabricated into nanofiber structures through many techniques, and electrospinning is one of the most widely used methods. Medical fiber mat scaffolds have been associated with inflammation and infection and, in some cases, have resulted in tissue degradation. Therefore, surface modification with antimicrobial agents represents a suitable solution if the mechanical properties of the fiber mats are not affected. In this study, the surfaces of electrospun PLA fiber mats were modified with naturally occurring L-ascorbic acid (ASA) or fumaric acid (FA) via a plasma treatment method. It was found that 30 s of radio-frequency (RF) plasma treatment was effective enough for the wettability enhancement and hydroperoxide formation needed for subsequent grafting reactions with antimicrobial agents upon their decomposition. This modification led to changes in the surface properties of the PLA fiber mats, which were analyzed by various spectroscopic and microscopic techniques. FTIR-ATR confirmed the chemical composition changes after the modification process and the surface morphology/topography changes were proven by SEM and AFM. Moreover, nanomechanical changes of prepared PLA fiber mats were investigated by AFM using amplitude modulation-frequency modulation (AM-FM) technique. A significant enhancement in antimicrobial activity of such modified PLA fiber mats against gram-positive Staphylococcus aureus and gram-negative Escherichia coli are demonstrated herein. © 2020 The AuthorsQatar National Research Fund (a member of The Qatar Foundation) [22-076-1-011]; Qatar University Collaborative Grant [QUCG-CAM-20/21-3]; Czech Science FoundationGrant Agency of the Czech Republic [19-16861S

Novel Slippery Liquid-Infused Porous Surfaces (SLIPS) based on electrospun polydimethylsiloxane/polystyrene fibrous structures infused with natural blackseed oil

Hydrophobic fibrous slippery liquid-infused porous surfaces (SLIPS) were fabricated by electrospinning polydimethylsiloxane (PDMS) and polystyrene (PS) as a carrier polymer on plasma-treated polyethylene (PE) and polyurethane (PU) substrates. Subsequent infusion of blackseed oil (BSO) into the porous structures was applied for the preparation of the SLIPS. SLIPS with infused lubricants can act as a repellency layer and play an important role in the prevention of biofilm formation. The effect of polymer solutions used in the electrospinning process was investigated to obtain well-defined hydrophobic fibrous structures. The surface properties were analyzed through various optical, macroscopic and spectroscopic techniques. A comprehensive investigation of the surface chemistry, surface morphology/topography, and mechanical properties was carried out on selected samples at optimized conditions. The electrospun fibers prepared using a mixture of PDMS/PS in the ratio of 1:1:10 (g/g/mL) using tetrahydrofuran (THF) solvent showed the best results in terms of fiber uniformity. The subsequent infusion of BSO into the fabricated PDMS/PS fiber mats exhibited slippery behavior regarding water droplets. Moreover, prepared SLIPS exhibited antibacterial activity against Staphylococcus aureus and Escherichia coli bacterium strains.RP/CPS/2022/001, RP/CPS/2022/002; Qatar National Research Fund, QNRFQatar National Research Fund (a member of The Qatar Foundation) [NPRP13S-0123-200153, JSREP 07-022-3-010]; Ministry of Education, Youth and Sports of the Czech Republic DKRVO [RP/CPS/2022/001, RP/CPS/2022/002

Slippery liquid-infused porous polymeric surfaces based on natural oil with antimicrobial effect

Many polymer materials have found a wide variety of applications in biomedical indus-tries due to their excellent mechanical properties. However, the infections associated with the bio-film formation represent serious problems resulting from the initial bacterial attachment on the polymeric surface. The development of novel slippery liquid-infused porous surfaces (SLIPSs) repre-sents promising method for the biofilm formation prevention. These surfaces are characterized by specific microstructural roughness able to hold lubricants inside. The lubricants create a slippery layer for the repellence of various liquids, such as water and blood. In this study, effective antimi-crobial modifications of polyethylene (PE) and polyurethane (PU), as commonly used medical pol-ymers, were investigated. For this purpose, low-temperature plasma treatment was used initially for activation of the polymeric surface, thereby enhancing surface and adhesion properties. Subse-quently, preparation of porous microstructures was achieved by electrospinning technique using polydimethylsiloxane (PDMS) in combination with polyamide (PA). Finally, natural black seed oil (BSO) infiltrated the produced fiber mats acting as a lubricating layer. The optimized fiber mats’ production was achieved using PDMS/PA mixture at ratio 1:1:20 (g/g/mL) using isopropyl alcohol as solvent. The surface properties of produced slippery surfaces were analyzed by various microscopic and optics techniques to obtain information about wettability, sliding behavior and surface morphology/topography. The modified PE and PU substrates demonstrated slippery behavior of an impinged water droplet at a small tilting angle. Moreover, the antimicrobial effects of the produced SLIPs using black seed oil were proven against Gram-positive Staphylococcus aureus (S. au-reus) and Gram-negative Escherichia coli (E. coli). © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Qatar National Research Fund ( Qatar Foundation) [JSREP07-022-3-010]; Qatar University [QUCG-CAM-20/21-3]; Ministry of Education, Youth and Sports of the Czech Republic DKRVO [RP/CPS/2020/001]Qatar National Research Fund, QNRF; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT: RP/CPS/2020/001; Qatar University, QU: QUCG-CAM-20/21-

Designing of polyethylene-based material modified by plasma discharge for water/oil separation

Produced water (PW) from petrochemical industries is one of the largest wastewaters generated in Qatar. Soluble and insoluble oil contaminants occur in this water and must be removed if water will be used or discharged into the land or sea. Adsorption is a common procedure used in the industry for a wastewater treatment and oily components removal. It is a simple, cost effective process. Currently there are many available natural and synthetic, particularly polymeric adsorbents. Polyolefins are pure hydrocarbon polymers, which due to an appropriate sorption efficiency of lowmolecular weight hydrocarbons can be used as suitable sorbents. However, polyolefins' based sorbents are commercially used only for removal of free oil. In this work, we have investigated a potential use of polyethylene as a filtration media in tertiary filtration of emulsified oil/water mixtures with respect to key parameters determining their adsorption ability. Polyethylene powders of various size and physical treatment were used. Emulsion formed from distilled water and commercial Diesel oil (DO) with a concentration below 200 ppm was used as a model of PW. The emulsions were prepared without emulsifier, and emulsification was insured by ultrasonication. The relationships between the sorption properties and surface composition and morphology of modified and unmodified PE powders were evaluated. Characterizations include the neat oil sorption, and sorption from emulsions, scanning electron microscopy, and profilometry. The PE adsorbents were further characterized by Brunauer-Emmett Teller surface area analysis, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed in order to characterize the porosity, crystallinity and chemical composition of PE, respectively. Sorption experiments were carried out as a function of different weight dosage, initial oil concentrations, and contact time to obtain the optimum conditions for the adsorption process. The results showed that LDPE powder, at a dosage of 3 g treated with plasma, using initial oil concentration of 100 ppm and 720 min of contact time presented the most suitable conditions for the adsorption of oil from emulsified DO. The adsorption process renders LDPE a suitable adsorbent for the removal of oil from diluted oil emulsions with an oil removal efficiency exceeding 93.5%. Equilibrium studies have been carried out to determine the sorption capacity of LDPE for the adsorption of oil from diluted DO emulsions using the optimum conditions. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherms. Equilibrium data were fitted very well with the Freundlich model. The pseudo first- and second-order kinetic models were used to describe the kinetic data and the rate constants of sorption were evaluated. The experimental data were fitted well with the pseudo-second-order kinetic model. The study confirmed the feasibility of using oil adsorbents based on plasma treated PE powders as potential adsorbents media for the removal of oil contaminants from P

The Separation of Emulsified Water/Oil Mixtures through Adsorption on Plasma-Treated Polyethylene Powder

This work addresses the preparation and characterization of efficient adsorbents for tertiary treatment (oil content below 100 ppm) of oil/water emulsions. Powdered low-density polyethylene (LDPE) was modified by radio-frequency plasma discharge and then used as a medium for the treatment of emulsified diesel oil/water mixtures in the concentration range from 75 ppm to 200 ppm. Plasma treatment significantly increased the wettability of the LDPE powder, which resulted in enhanced sorption capability of the oil component from emulsions in comparison to untreated powder. Emulsions formed from distilled water and commercial diesel oil (DO) with concentrations below 200 ppm were used as a model of oily polluted water. The emulsions were prepared using ultrasonication without surfactant. The droplet size was directly proportional to sonication time and ranged from 135 nm to 185 nm. A sonication time of 20 min was found to be sufficient to prepare stable emulsions with an average droplet size of approximately 150 nm. The sorption tests were realized in a batch system. The effect of contact time and initial oil concentrations were studied under standard atmospheric conditions at a stirring speed of 340 rpm with an adsorbent particle size of 500 microns. The efficiency of the plasma-treated LDPE powder in oil removal was found to be dependent on the initial oil concentration. It decreased from 96.7% to 79.5% as the initial oil concentration increased from 75 ppm to 200 ppm. The amount of adsorbed oil increased with the increasing contact time. The fastest adsorption was observed during the first 30 min of treatment. The adsorption kinetics for emulsified oils onto sorbent followed a pseudo-second-order kinetic model

Preparation of slippery liquid infused porous surfaces on polymeric substrates

Many polymers have been found in bio-science paralleling with advancement in a technology sector. A selection of suitable polymers for using in a biomedical sector is based on many factors such as chemical nature, surface free energy or morphology, which influence cell-polymer surface interactions. However, these materials suffering from infections represent serious issues for their applications. These infections closely relate with biofilm formation, whereby microorganisms are strongly attached to surface forming strong attached multicellular communities. Therefore, a preparation of slippery liquid infused porous surfaces (SLIPS) using low-temperature plasma technique in combination with electrospinning technique was utilized in this research. A multistep physicochemical approach was carried out for this purpose. The first step includes the pre-treatment of polyethylene (PE) and polyurethane (PU) substrates using low-temperature plasma to activate the surface for an adhesion improvement. Subsequently, the 3D porous network consisted of superhydrophobic fiber mats was fabricated on the plasma activated substrates using electrospinning technique. Final step consisted of the infusion of naturally oils with emphasis on their antimicrobial effect. This complex strategy led to the effective antimicrobial modification of the PE and PU surface potentially applicable in the biomedical field

Effect of humidity on the electrical properties of the silver-polyaniline/polyvinyl alcohol nanocomposites

Polymer-metal nanocomposites with enhanced mechanical, optical, electrical, dielectric, and antimicrobial properties are currently in high demand for many industrial applications. Here, we study and present the effect of UV-reduced silver nanoparticles on the synthesis of polyaniline-polyvinyl alcohol-silver nanocomposites (PPVA-Ag) and utilize them to make a humidity sensor and antimicrobial agent. A thorough study of the surface morphology of the prepared films using SEM, AFM, and profilometry is performed; it is found that uniform film is formed in all these cases. These studies show that an increase in Ag concentration leads to an increase in the surface micro roughness of the PPVA-Ag film. XPS determines the chemical composition of the prepared PPVA-Ag nanocomposites. At different humidity conditions, the electrical resistivity of the PPVA-Ag nanocomposites is measured. The results show uniform changes in resistivity with an increase in humidity and good repeatability. These polymer-metal nanocomposites are found to have exhibited antimicrobial abilities making them useful for biomedical applications as well. © 2019 Elsevier B.V.Qatar University Student Grant [QUST-2-CAM-2018-4]; Czech Science Foundation [17-05095S

Fabrication of polyaniline-graphene/polystyrene nanocomposites for flexible gas sensors

This research work presents the fabrication of polyaniline (PANI) and graphene-polyaniline (graphene-PANI) nanocomposite-coated polystyrene (PS) nanofibre mats, as well as their application in flexible and highly sensitive gas sensors. The surface morphology of the flexible films is investigated using a number of techniques. The profilometry studies confirmed that the electrospun fibres are evenly distributed over a large surface area and there was no visible difference between coated and uncoated fibres. The SEM morphology studies revealed that a nanocomposite consisting of 10 nm PANI nanofibres and graphene forms a uniform coating around 3 m diameter PS fiber. AFM showed differences in the 3D surface topography between plain PS nanofibres and coated ones, which showed an increased roughness. Moreover, conductive AFM has indicated an increase in the electrical current distribution from picoamperes to nanoamperes of the PS samples coated with PANI and graphene-PANI because of the applied voltage to the AFM tip that contacted the sample surface. The chemical properties of all the samples are analysed by Fourier transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD), which revealed the presence of chemical interactions between the nanocomposites and the polymeric backbones. The TGA study indicated that graphene-PANI coated fibres have the highest thermal stability compared to the pure fibres. The addition of the nanocomposite layer to the PS fibre significantly increased the electrical conductivity. Therefore, nanocomposite-coated flexible membranes are used to fabricate carbon dioxide gas sensors (sensing range: 20-100 ppm). Due to the higher surface area of the nanocomposite coated fibre the availability of adsorption area is also higher, which leads to an increase in sensitivity to carbon dioxide gas. The sensitivity increases with the increase in gas concentration. The average response time of the sensor is calculated to be 65 seconds, with good and uniform repeatability.The authors express their deep sense of gratitude to students of Al-Bairaq for their contribution in the experimental work. Authors would also like to acknowledge the Office of Vice President for Research and Centre for Advanced Materials for the constant support during this research work. Qatar University Student Grant number QUST-2-CAM-2018-4 made this work possible. The authors would like to express their gratitude to the Qatar National Library for nancial support to pay open access charges for this publication.Scopu

Development of PLA Fibers as an Antimicrobial Agent with enhanced infection resistance using electrospinning/plasma technology

Humans are vulnerable and easily prone to all kind of injuries, diseases, and traumas that can be damaging to their tissues (including its building unit, cells), bones, or even organs. Therefore, they would need assistance in healing or re-growing once again. Medical scaffolds have emerged over the past decades as one of the most important concepts in the tissue engineering field as they enable and aide the re-growth of tissues and their successors. An optimal medical scaffold should be addressing the following factors: biocompatibility, biodegradability, mechanical properties, scaffold architecture/porosity, precise three-dimensional shape and manufacturing technology. There are several materials utilized in the fabrication of medical scaffolds, but one of the most extensively studied polymers is polylactic acid (PLA). PLA is biodegradable thermoplastic aliphatic polyester that is derived from naturally produced lactic acid. PLA is characterized with its excellent mechanical properties, biodegradability, promising eco-friendly, and excellent biocompatibility. PLA can be fabricated into nanofibers for medical scaffolds used through many techniques; electrospinning is one of the widely used methods for such fabrication. Electrospinning is a favorable technique because in the preparation of scaffolds, some parameters such as fiber dimensions, morphology, and porosity are easily controlled. A problem that is associated with medical scaffolds, such as inflammation and infection, was reported in many cases resulting in a degradation of tissues. Therefore, a surface modification was thought of as a needed solution which mostly focuses on an incorporation of extra functionalities responsible for the surface free energy increase (wettability). Therefore, plasma technique was a favorable solution for the surface treatment and modification. Plasma treatment enables the formation of free radicals. These radicals can be easily utilized for grafting process. Subsequently, ascorbic acid (ASA) could be incorporated as anti-inflammatory and anti-infection agent on the plasma pretreated surface of scaffolds