Experimental and mathematical studies of natural convection for solid-salt dissolution in water

The phenomena of natural convection caused by a concentration gradient usually creates currents as a result of buoyancy forces. These forces are formed from the combined effect of a fluid density gradient and the body force (gravitational force). The above phenomenon was studied experimentally in a circular glass column of 0.08 m diameter and 1 m length. This column was erected vertically and filled with distilled water with a salt bag placed on top of it and partially immersed in water. The dissolution mechanism was then modelled and a finite difference method was used to solve the formulated equations by using the implicit scheme of MacCormack (Anderson et al., 1984). The experimental results and the numerical predictions are represented graphically and give compatible agreement.     

A study of neutron and gamma radiation effects on transmission of various types of glasses, optical coatings, cemented optics and fiber

A study of radiation effects on various types of glasses, dielectric optical coatings, cemented optics and fiber was undertaken with a view to select them for extreme radiation environments. Samples were exposed to different radiation doses in the Pakistan Research Reactor-I (PARR-I) for neutron and Cobalt 60 source for gamma irradiation. Transmissions were measured before and after irradiation. The dielectric coatings were subjected to additional tests (adhesion, abrasion and humidity, etc.) as per MIL-M-13508C and MIL-C-675C. All 15 glasses studied showed varying amounts of transmission loss as expected, with negligible degradation for three types. Recovery of transmissions with time/ageing was also studied, with more or less complete recovery with temperature annealing. A faster bleaching of darkened/brown glasses was achieved by using UV lamps or UV laser. The dielectric coatings (HR, AR) and one of the two commercial optical cements showed excellent resistance to neutrons and gamma radiations, and could be good candidates for the fabrication and utilization of optical components in extreme radiation environments. The data allowed several Chinese glasses to be studied for the first time.     

Isolation and characterization of cellulose nanowhiskers from Acacia caesia plant

Acacia caesia (L.) Willd (soap bark) fiber is an abundant natural resource, that is rich in cellulose. The study reports the effective utilization of underutilized Acacia caesia fiber for the isolation of nanocellulose whiskers. The nanocellulose whiskers were isolated successfully from Acacia caesia fibers by following alkali, bleaching, and sulfuric acid treatment. The obtained nanocellulose whiskers were carefully investigated for its chemical composition, structure, morphology, crystallinity, and thermal stability. The chemical composition and Fourier transform infrared spectra of nanocellulose whiskers showed the elimination of the non-cellulosic parts present in the raw Acacia caesia fibers. The X-ray diffraction analysis showed an upsurge in the crystallinity of the cellulose fibers after the chemical treatments. The isolation of nanocellulose whiskers from Acacia caesia raw fiber was confirmed by electron microscopy analysis. The thermogravimetric analysis showed remarkably high char residue for the nanocellulose whiskers compared to raw fibers. Based on the properties of nanocellulose whiskers, it can be concluded that the nanocellulose whiskers produced from Acacia caesia raw fibers are potential reinforcing material for developing high-performance green composites.     

A survey and taxonomy on energy efficient resource allocation techniques for cloud computing systems

In a cloud computing paradigm, energy efficient allocation of different virtualized ICT resources (servers, storage disks, and networks, and the like) is a complex problem due to the presence of heterogeneous application (e.g., content delivery networks, MapReduce, web applications, and the like) workloads having contentious allocation requirements in terms of ICT resource capacities (e.g., network bandwidth, processing speed, response time, etc.). Several recent papers have tried to address the issue of improving energy efficiency in allocating cloud resources to applications with varying degree of success. However, to the best of our knowledge there is no published literature on this subject that clearly articulates the research problem and provides research taxonomy for succinct classification of existing techniques. Hence, the main aim of this paper is to identify open challenges associated with energy efficient resource allocation. In this regard, the study, first, outlines the problem and existing hardware and software-based techniques available for this purpose. Furthermore, available techniques already presented in the literature are summarized based on the energy-efficient research dimension taxonomy. The advantages and disadvantages of the existing techniques are comprehensively analyzed against the proposed research dimension taxonomy namely: resource adaption policy, objective function, allocation method, allocation operation, and interoperability.     

Entering the field in qualitative field research: a rite of passage into a complex practice world

The concept of ‘the field’ is significant in ethnographic research as well as qualitative research methods more generally. However, how a field researcher enters the field is usually taken for granted after gaining access to the field. We suggest that entrance is a distinct phase of fieldwork that differs from negotiating access. Entrance is not a trivial event; rather, it is a rite of passage into a complex practice world and marks a critical field moment. Drawing on our ethnography and insights from hermeneutics and anthropology, we show that a practical understanding of the field represents a fusion of horizons where a fieldworker is thrown. The concept of thrownness highlights the fact that the fieldworkers' own historicity and prejudices affect their entrance into the field; hence, entrance into the field orientates an ethnographer in the field and influences the entire period of fieldwork that follows. Our theorizing is intended as a contribution towards advancing the discussion of qualitative research methods.     

The effect of hydrogen in the mechanism of aluminum-induced crystallization of sputtered amorphous silicon using scanning Auger microanalysis

The metal-induced crystallization (MIC) of hydrogenated sputtered amorphous silicon (a-Si:H) using aluminum has been investigated using X-ray diffraction (XRD) and scanning Auger microanalysis (SAM). Hydrogenated, as well as non-hydrogenated, amorphous silicon (a-Si) films were sputtered on glass substrates, then capped with a thin layer of Al. Following the depositions, the samples were annealed in the temperature range 200 °C to 400 °C for varying periods of time. Crystallization of the samples was confirmed by XRD. Non-hydrogenated films started to crystallize at 350 °C. On the other hand, crystallization of the samples with the highest hydrogen (H₂) content initiated at 225 °C. Thus, the crystallization temperature is affected by the H₂ content of the a-Si. Material structure following annealing was confirmed by SAM. In this paper, a comprehensive model for MIC of a-Si is developed based on these experimental results.     

Graph Pangenomes Track Genetic Variants for Crop Improvement

Global climate change and the urgency to transform crops require an exhaustive genetic evaluation. The large polyploid genomes of food crops, such as cereals, make it difficult to identify candidate genes with confirmed hereditary. Although genome-wide association studies (GWAS) have been proficient in identifying genetic variants that are associated with complex traits, the resolution of acquired heritability faces several significant bottlenecks such as incomplete detection of structural variants (SV), genetic heterogeneity, and/or locus heterogeneity. Consequently, a biased estimate is generated with respect to agronomically complex traits. The graph pangenomes have resolved this missing heritability and provide significant details in terms of specific loci segregating among individuals and evolving to variations. The graph pangenome approach facilitates crop improvements through genome-linked fast breeding.     

Polylactide‐perylene derivative for blue biodegradable organic light‐emitting diodes

In this work we demonstrate, for the first time, the use of polylactic acid (PLA) as a biodegradable host matrix for the construction of the active emissive layer of organic light‐emitting diode (OLED) devices for potential use in bioelectronics. In this preliminary study, we report a robust synthesis of two fluorescent PLA derivatives, pyrene‐PLA ( AH10 ) and perylene‐PLA ( AH11 ). These materials were prepared by the ring opening polymerisation of l ‐lactide with hydroxyalkyl‐pyrene and hydroxyalkyl‐perylene derivatives using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene as catalyst. OLEDs were fabricated from these materials using a simple device architecture involving a solution‐processed single‐emitting layer in the configuration ITO/PEDOT:PSS/PVK:OXD‐7 (35%): AH10 or AH11 (20%)/TPBi/LiF/Al (ITO, indium tin oxide; PEDOT:PSS, poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonic acid); PVK, poly(vinylcarbazole); OXD‐7, (1,3‐phenylene)‐bis‐[5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole]; TPBi, 2,2′,2″‐(1,3,5‐benzenetriyl)tris(1‐phenyl‐1H‐benzimidazole)). The turn‐on voltage for the perylene OLED at 10 cd m^–2 was around 6 V with a maximum brightness of 1200 cd m^–2 at 13 V. The corresponding external quantum efficiency and device current efficiency were 1.5% and 2.8 cd A^–1 respectively. In summary, this study provides proof of principle that OLEDs can be constructed from PLA, a readily available and renewable bio‐source. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.     

A new application of giant reed waste material for ammonium removal

Excess nitrogen is one of the main causes of eutrophication in water bodies. In this study, the undesirable agricultural lignocellulosic material giant reed was used to remove ammonium ions from aqueous solutions. Batch experiments were conducted to investigate the effect of various parameters such as contact time, initial ammonium concentration, adsorbent dosage, pH, particle size, agitation rate and phosphate coexisting during the ammonium adsorption process. The ammonium sorption capacity of fibrous giant reed (FGR) at equilibrium was 12.49?mg?N/g with a maximum removal efficiency of 76% observed within 30?min at pH range of 6.5–9.5. Results revealed that the Freundlich isotherm model fitted better with the sorption process than the Langmuir model, and the adsorption process was well described by pseudo-second-order kinetic model. FT-IR analyses indicated that complexation and ion exchange could be the main mechanisms for the ammonium removal by FGR. Results revealed that FGR has a sorption capacity comparable to that of other natural sorbents with the advantage of greater availability with no cost.     

Ultra low loss (Mg1 − xCax)2SiO4 dielectric ceramics (x = 0 to 0.15) for millimeter wave applications

(Mg_{1 − x}Ca_x)₂SiO₄ dense ceramics (x ≥ 0.15) were prepared, and their microwave dielectric characteristics were investigated together with the structure evolution. The sintering temperature for Mg₂SiO₄ ceramics was reduced significantly with Ca²⁺substitution. (Mg_{1 − x}Ca_x)₂SiO₄ ceramics exhibited a small increase in dielectric constant (ε_r) correlated with increased crystallite size, and ultra-high quality factor Qf value was achieved throughout the compositional range. Temperature coefficient of resonant frequency (τ_f) was considerably tuned from −70 ppm/°C to −33 ppm/°C, and this improvement was deeply linked with the decreased bond valance. At x = 0.075, (Mg_{1 − x}Ca_x)₂SiO₄ ceramics exhibited the best combination of microwave dielectric characteristics: ε_r = 7.2, Qf = 199,800 GHz at 26 GHz, τ_f = −33 ppm/°C. The present ceramics could be expected as promising candidate of dielectric materials for millimeter wave applications.