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In this paper, two different models of highly nonlinear bored core photonic crystal fibers (HNL-BCPCF) are presented and compared for attaining an ultra-high negative dispersion coefficient and high nonlinearity. We achieved this dispersion by tailoring a defect into the solid core of the two proposed models and appropriately scaling down the diameter of the neighboring airholes of the core. To investigate the optical transmission properties in the fiber, simulations were carried out employing the finite element method (FEM) having a perfectly matched layer. The simulation results exhibited large negative dispersion coefficients of − 2218 ps/(nm-km) and − 2221 ps/(nm-km) for the two proposed models, respectively, when the wavelength had been tuned to 1550 nm and the corresponding nonlinear coefficients stand out to be 117.6 W−1 km−1 and 118.4 W−1 km−1. The fabrication process had been made much more feasible as the design consists of circular airholes. In our analysis, this geometry of photonic crystal fiber is noticeably more robust for its successful achievement of an ultra-high negative dispersion with high nonlinearity and facilitates optical back propagation applications and dispersion compensation for optical transmission systems.

Ecotourism, a sustainable form of tourism, is increasingly being viewed as a tool that can promote global biodiversity and forest conservation. This study explored the scope of ecotourism in forest conservation practices in the developing context by taking the Sitakunda Botanical Garden and Ecopark (SBGE), Bangladesh’s first ecopark established in 2000, as a case study. Using GIS and remote sensing technology, NDVI analysis revealed that, unlike the anticipated outcomes of the SBGE project, after a brief increase in vegetation coverage of 84.6% from 1995 to 2000, the vegetation coverage fell drastically from 2000 to 2015, wherein 33.4% of vegetation had been completely removed, and much of the dense and medium vegetation had been converted to sparse vegetation or other land uses. Anthropogenic activities, namely, unplanned urbanization, are suggested as the major contributors to this decline. From the period of 2015 to 2020, however, vegetation was seen to regenerate, potentially due to the decelerating urbanization or the possible manifestation of the ‘U’ shape relationship between the changes in vegetation and rates of urbanization. Sustainable land-use policies may help attain the targets of the project and lead the SBGE to emerge as a success story of the Bangladeshi ecotourism industry.

International audience; Biogas production is rising in the context of fossil fuel decline and the future circular economy, yet raw biogas requires purification steps before use. Here, we review biogas upgrading using physical, chemical and biological methods such as water scrubbing, physical absorption, pressure swing adsorption, cryogenic separation, membrane separation, chemical scrubbing, chemoautotrophic methods, photosynthetic upgrading and desorption. We also discuss their techno-economic feasibility. We found that physical and chemical upgrading technologies are near-optimal, but still require high energy and resources. Biological methods are less explored despite their promising potential. High-pressure water scrubbing is more economic for small-sized plants, whereas potassium carbonate scrubbing provides the maximum net value for largesized plants.

The expeditious and world pandemic viral disease of new coronavirus (SARS-CoV-2) has formed a prompt urgency to discover auspicious target-based ligand for the treatment of COVID-19. Symptoms of novel coronavirus disease (COVID-19) typically include dry cough, fever, and shortness of breath. Recent studies on many COVID-19 patients in Italy and the United Kingdom found increasing anosmia and ageusia among the COVID-19-infected patients. SARS-CoV-2 possibly infects neurons in the nasal passage and disrupts the senses of smell and taste, like other coronaviruses, such as SARS-CoV and MERS-CoV that could target the central nervous system. Developing a drug based on the T2Rs might be of better understanding and worth finding better molecules to act against COVID-19. In this research, we have taken a taste receptor agonist molecule to find a better core molecule that may act as the best resource to design a drug or corresponding derivatives. Based on the computational docking studies, the antibiotic tobramycin showed the best interaction against 6LU7 COVID-19 main protease. Aromatic carbonyl functional groups of the molecule established intermolecular hydrogen bonding interaction with GLN189 amino acid and it showed the two strongest carbonyl interactions with receptor protein resulting in a glide score of −11.159. To conclude, depending on the molecular recognition of the GPCR proteins, the agonist molecule can be recognized to represent the cell secondary mechanism; thus, it provides enough confidence to design a suitable molecule based on the tobramycin drug.

In this paper, an asymmetric photonic crystal fiber (PCF) working on surface plasmon resonance (SPR) has been proposed and demonstrated using the wavelength interrogation method and lower birefringence peak method. The proposed sensor contains a D-shaped analyte channel that can detect unknown analytes within the sensing range of 1.42–1.47 refractive index units (RIU) of the analytes. The structural asymmetry induces orthogonal x and y polarization modes. The numerical investigations with the finite element method (FEM) reveal that the sensor has a maximum wavelength sensitivity of 80,000 nm/RIU with a sensor resolution of 1.25 × 10−6 RIU for the y polarization mode and the maximum figure of merit (FOM) is found to be of 370.4 RIU−1. For the x polarization mode, the sensor exhibits a maximum wavelength sensitivity of 53,000 nm/RIU with a resolution of 1.89 × 10−6 RIU, having a maximum figure of merit (FOM) of 351 RIU−1. These results are found by using the wavelength interrogation method via confinement loss. On the other hand, the lower birefringence peak method-based analysis reveals a maximum wavelength sensitivity of 50,000 nm/RIU with a resolution of 2 × 10−6 RIU. As such, it is highly suitable for organic chemical detections and medical diagnostics. In addition, this paper studies the fabrication tolerance on the sensor performance.

In this paper, a highly sensitive miniaturized surface plasmon resonance (SPR) based photonic crystal fiber (PCF) sensor is presented for a wide range of analyte sensing. Gold is selected as the plasmonic metal for its higher chemical stability and titanium oxide works as the adhesive layer for gold attachment on silica. The plasmonic metal and the sensing medium are placed exterior to the surface of the sensor design to make it fitting for practical applications. By a careful arrangement of the periodic arrangement of the refractive index in the design, the generation of the evanescent fields is fine-tuned to obtain the phase matching between the leaky core guided mode and the surface plasmon polariton (SPP) mode. Numerical simulations have been carried out by employing the finite element method (FEM) with the consideration of a perfectly matched layer (PML) to absorb surface radiations. The proposed sensor shows a maximum wavelength sensitivity of 34,000 nm/RIU (refractive index units) and a maximum amplitude sensitivity of 331 RIU−1, investigated by using the wavelength and the amplitude interrogation methods, respectively, for the analyte sensing range of 1.16 to 1.37 RI (refractive index). The sensor also exhibits a wavelength resolution of 2.94×10−6 RIU which indicates a high detection accuracy. On that, the proposed sensor would be an excellent candidate for a wide range of RI detection, applicable for various purposes such as chemical detections, medical diagnostics, bio-sensing, and other low RI analytes.

Arsenic is a highly toxic metalloid that is extensively distributed in soils and water bodies, resulting in a variety of toxicity mechanisms and harmful effects on humans and environmental health. This paper comprehensively reviews the technological development in arsenic (As) removal from wastewater and contaminated soil, and provides insights into the challenges in effective arsenic removal from the environmental compartments. The arsenic removal efficiency of the available technologies is also discussed in terms of their principle of operation, efficiency, advantages, and shortcomings. Many of the existing technologies are not found economically feasible for the regions of interest or are not applicable at the community level. Some of the techniques are often responsible for producing toxic by-products. Overall, the adsorption technique demonstrated high efficiency of almost 100% and a maximum of 95% in removing arsenic from water and soil, respectively. Novel methods such as the application of nanotechnology and polymeric ligand exchangers have also been gaining traction but also seem to possess limitations similar to conventional and non-conventional techniques.

We demonstrate an ultra-low loss photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR)in this paper. In this refractive index (RI) sensor, we explored hexagonal-arrangement of airholes and employed only two different sizes of it. The formation of airholes makes the confinement loss (CL) surprisingly low. The maximum CL is as low as 10.71 and 28.58 dB/cm for x and y-pol modes, respectively within a range of refractive indices 1.33-1.40. The maximum gained amplitude sensitivity is -1212 RIU−1 and -2430 RIU−1, and the maximum figure of merit is as high as 583 and 467 respectively for x and y-polarization (pol) modes respectively. In addition to that, we got a maximum wavelength sensitivity, Sw of 14,000nm/RIU for both x and y-pol modes with a minimum sensor resolution of 7.143x10−6. Gold is preferred over other materials as the plasmonic material for its inert behaviour and higher chemical stability. The analysis was carried out using the finite element method (FEM). This sensor, with its elegant configuration, fabrication feasibility, ultra-low loss, stands out to be an effective and eminent prospect in the current burgeoning SPR sensor realm and also prompts further creative exploration in its hexagonal lattice arrangements.