ARTICLE | doi:10.20944/preprints201807.0018.v1
Subject: Physical Sciences, Mathematical Physics Keywords: dislocation density tensor, thin shells, Riemann curvature tensor
Online: 2 July 2018 (17:08:27 CEST)
The dislocation density tensors of thin elastic shells have been formulated explicitly in terms of the Riemann curvature tensor. The formulation reveals that the dislocation density of the shells is proportional to KA3=2, where K is the Gauss curvature and A is the determinant of metric tensor of the middle surface.
ARTICLE | doi:10.20944/preprints202008.0258.v2
Subject: Materials Science, Nanotechnology Keywords: single nanowires; silicon; dual shells; off-resonance; absorption; photocurrent
Online: 31 August 2020 (08:30:22 CEST)
Single nanowires (NWs) are of great importance for optoelectronic applications, especially solar cells serving as powering nanoscale devices. However, weak off-resonant absorption can limit its light-harvesting capability. Here, we propose a single NW coated with the graded-index dual shells (DSNW). We demonstrate that with appropriate thickness and refractive index of the inner shell, the DSNW exhibits significantly enhanced light trapping compared with the bare NW (BNW), and the NW only coated with the outer shell (OSNW) and the inner shell (ISNW), which can be attributed to the optimal off-resonant absorption mode profiles due to the improved coupling between the reemitted light of the transition modes of the leak mode resonances of the Si core and the nanofocusing light from the dual shells with the graded refractive index. We found that the light absorption can be engineered via tuning the thickness and the refractive index of the inner shell, the photocurrent density is significantly enhanced by 134% (56%, 12%) in comparison with that of the BNW (OSNW, ISNW). This work advances our understanding of how to improve off-resonant absorption by applying graded dual-shell design and provides a new choice for designing high-efficiency single NW photovoltaic devices.
ARTICLE | doi:10.20944/preprints201908.0006.v1
Subject: Biology, Ecology Keywords: chestnut shells; polyphenols; bioactive compounds; apoptosis; cytotoxicity; human cell lines
Online: 1 August 2019 (04:37:49 CEST)
In this study, bioactive compounds present in chestnut shells (CS) - derived from the industrial peeling processing - were extracted through different procedures. The aqueous extracts were characterized and the highest extraction yield and total phenolic content was obtained by Conventional Liquid Extraction (CLE). Gallic and protocatechuic acids were the main simple phenols in the extract with 86.97 and 11.20 mg/g chestnut shells dry extract (CSDE), respectively. Six tumor cell lines (DU 145, PC-3, LNCaP, MDA-MB-231, MCF-7 and Hep G2) and one normal prostate epithelial cell line (PNT2) were exposed to increasing concentration of CSDE (1-100 µg/mL) for 24 h and cell viability was evaluated using MTT assay. A reduced rate in cell viability was observed in DU 145, PC-3, LNCaP and MCF-7 cells while viability of MDA-MB-231 and Hep G2 cells was not affected except for PNT2 cells at a concentration of 100 µg/mL. Furthermore, CSDE-at concentrations of 55.5 and 100 µg/mL- lead to a significant increase of apoptotic cells in DU 145 cells of 28.2% and 61%, respectively. In conclusion, our findings showed that CS might be used for the extraction of several polyphenols that may represent good candidates for alternative therapies or in combination with current chemotherapeutics.
ARTICLE | doi:10.20944/preprints202107.0007.v1
Subject: Materials Science, Biomaterials Keywords: calcium phosphate; monocalcium phosphate; tricalcium phosphate; calcium carbonate; seashell; bivalve shells
Online: 1 July 2021 (10:48:06 CEST)
The search for sustainable resources remains a subject of global interest and the conversion of the abundantly available bivalve shell wastes to advanced materials is an intriguing method. By grinding, each shell of bivalves (cockle, mussel, and oyster) was transformed to the same crystal type of calcite phase of CaCO3, revealed by FTIR and XRD results. Each individual shell powder was reacted with H3PO4 and H2O to prepare Ca(H2PO4)2•H2O giving an anorthic crystal structure. The mixture of each shell powder and its produced Ca(H2PO4)2•H2O was heated at 900 °C for 3 h, giving rhombohedral crystal -Ca3(PO4)2 powder. FTIR and XRD results of the CaCO3, Ca(H2PO4)2•H2O, and Ca3(PO4)2 prepared from each shell powder are quite similar showing no impurities. Thermal behaviors of CaCO3 and Ca(H2PO4)2•H2O produced from each shell are slightly different. Particle sizes and morphologies of all products are significantly different, affected by the kind of shells used. Overall, the bivalve shell wastes were successfully converted to CaCO3, Ca(H2PO4)2•H2O, and Ca3(PO4)2 by a simple, rapid, environmentally benign, and cost-effective approach, which can be a huge potential in many industries providing both economic and ecological benefits according to the Bio-Circular-Green Economy (BCG) model.
ARTICLE | doi:10.20944/preprints202103.0376.v1
Subject: Engineering, Automotive Engineering Keywords: tunnel ventilation shafts; analytical modelling; analytic solution; bending theories; cylindrical shells
Online: 15 March 2021 (11:57:34 CET)
The formulation and analytic solution of a new mathematical model with constitutive curvature for analysis of tunnel ventilation shaft wall is proposed. Based on the Mindlin-Reissner theory for thick shells, this model also takes into account the shell constitutive curvature and considers an expression of the shear correction factor variable (αn) in terms of the thickness (h) and the radius of curvature (R). The main advantage of the proposed model is that it has the possibility to analyze thin, medium and thick tunnel ventilation shafts. As a result, two comparisons were made: the first one, between the new model and the Mindlin-Reissner model without constitutive curvature with the shear correction factor (α_n=6/5) as a constant, and the other, between the new model and the tridimensional numerical models (solids and shells) obtained by finite element method for different slenderness ratios (h/R). The limitation of the proposed model is that it is to be formulated for a general linear-elastic and axial-symmetrical state with continuous distribution of the mass.
ARTICLE | doi:10.20944/preprints202104.0494.v1
Subject: Physical Sciences, Acoustics Keywords: Catenary; surface of revolution; Gauss curvature; minimal surface; shells; deformation; stress; Maple
Online: 19 April 2021 (14:03:24 CEST)
The catenary shells of revolution are widely used in constructions due to their unique mechanics' feature. However, no publications on this type of shells can be found in the literature. To have a better understanding of the deformation and stress of the catenary shells of revolution, we formulate the principal radii for two kinds of catenary shells of revolution and their displacement type governing equations. Numerical simulations are carried out based on both Reissner-Meissner mixed formulations and displacement formulations. Our investigations show that both deformation and stress response of elastic catenary shells of revolution are sensitive to its geometric parameter $c$, and reveal that the mechanics of the catenary shells of revolution does much better than the spherical shells. Two complete codes in Maple are provided.
ARTICLE | doi:10.20944/preprints202103.0617.v1
Subject: Arts & Humanities, Anthropology & Ethnography Keywords: Spondylus shells; archaeomalacology; archaeozoology; pre-Hispanic Ecuador; knowledge representation; formal concept analysis.
Online: 25 March 2021 (13:55:39 CET)
Shells, probably like no other product of nature, have played an important role in the history of mankind. The pre-Hispanic civilizations of Ibero-America also used certain type of shells profusely in their religious ceremonies, in particular, in Ecuador there were two species of main importance, the Spondylus princeps and the Spondylus calcifer broadly employed to manufacture ornaments that possess a strong symbolic, religious and social meaning and that were almost exclusively used by ruling classes. Among these ornaments, the faces carved on the Spondylus shells are little known. In the present study, we chose a total of fifteen (15) pieces from the Pastor Restrepo Lince´s archaeomalacology collection to understand the possible uses of these objects, through the interpretation of the gestures represented on the faces, their dimensions, and their geographical distribution in pre-Hispanic Ecuador. To achieve the proposed objective, we approach the present investigation from the perspective of the formal analysis of concepts, which is a mathematical theory of representation of knowledge, finding that these faces carved in Spondylus, were used daily or in special ceremonial occasions and that its use was common in all the regional cultures of ancient Ecuador, from the oldest such as Valdivia, and for more than 2000 years, indicating a long tradition of the use of Spondylus as an object of great symbolic and economic value until the arrival of the Spanish
ARTICLE | doi:10.20944/preprints201806.0128.v1
Subject: Engineering, Biomedical & Chemical Engineering Keywords: biogas purification; coconut shells; biomass valorization; textural characterization; adsorption isotherms; breakthrough curves.
Online: 7 June 2018 (16:27:12 CEST)
Biomass is a widely distributed and renewable source of carbon. The main objective of this work is to produce an activated carbon from coconut shells with suitable characteristics to separate CO2 from biogas. The textural characterization of the adsorbent has been determined. Pure component adsorption isotherms of CO2 and CH4 at 30, 50 and 70 °C have been measured. Moreover, the performance of the produced activated carbon, as potential adsorbent for CO2 capture from a CO2/CH4 gas mixture has been evaluated under dynamic conditions in a purpose-built fixed-bed setup.
ARTICLE | doi:10.20944/preprints201906.0027.v1
Subject: Physical Sciences, Nuclear & High Energy Physics Keywords: nucleus structure; parameters of external shells; correlation of radii of nuclei and atoms; periodic law.
Online: 4 June 2019 (10:04:44 CEST)
In the work, the nuclei structure was modeled by a system of shells consisting of combinations of spherical and annular vortices. Having connected the spin and the magnetic moments of the nuclei with the dynamics of the outer shell of the nucleus, we determined its type and carried out a semiempirical calculation of the parameters of its structure for stable and unstable nuclear isotopes in the sequence of the order number Z from 1 to 37. Comparison of the obtained nuclear sizes with the radii of the electron shells of atoms made it possible to reveal a definite correlation. On the basis of it, it was concluded that the periodic law of Mendeleyev can determine the patterns in the change in the structure of the atomic nucleus.
ARTICLE | doi:10.20944/preprints201901.0044.v1
Subject: Materials Science, Biomaterials Keywords: microstructure of liquids; water-salt units; salt microcrystals; hydrated shells; coacervates, self – assembly; air pollution.
Online: 4 January 2019 (14:23:37 CET)
It is shown that structuring at the microlevel is the intrinsic property of water and aqueous solutions. At room conditions water (including "ultrapure" one) and aqueous solutions are dispersed systems in which microcrystals of NaCl, surrounded by a layer of hydrated water (average diameter - 10-15 microns), are "elementary microparticles", which form the basis of the dispersed phase. Possible ways of formation of these microparticles and their evolution in the process of evaporation of unstructured part of water - dispersion medium - are considered. It is shown, in particular, that they are present in the air as aerosol contaminants. When the ionic strength of the solution increases, the water-salt particles coagulate, forming a new phase - coacervates, remaining on the substrate after evaporation of the liquid part of the water. The aggregates of coacervate structures, formed in a liquid medium, are disordered during heating, which can cause a change in a number of physicochemical properties of water at the temperatures of 50°-60°C range that have not been correctly explained in the framework of atomic-molecular concepts.
REVIEW | doi:10.20944/preprints202212.0071.v1
Subject: Engineering, Energy & Fuel Technology Keywords: Cashew Nut Shells; Shell Press Cakes; CNS char; Cashew Nut Shell Liquid; CNS Briquettes; Calorific Value
Online: 5 December 2022 (09:15:39 CET)
Cashew nut shells (CNS) are the primary waste produced during the processing of cashew nuts; and needs constant attention to handle or valorize these wastes effectively. As a result, these CNS wastes are processed into solid briquettes citing their significant calorific content, thus making them as a promising renewable biofuel for combustion based applications. In most cases, these wastes are pre-treated either through de-oiling or carbonizing prior to compaction, thus removing the harmful hydrocarbons present in them in form of CNS liquids. Presently, this chapter focus on summarising various data related to these CNS wastes and their briquettes in terms of their availability, chemical characteristics, pre-treatment and processing technique, fuel and combustion properties as reported in various literatures. Here, availability depicts the current trend in global consumption of these snack nuts and the proportionate amount of waste shells produced; while, chemical characteristics focused on discussing their anatomy, proximate, lignocellulosic and elemental compositions. Following this, pre-treatment and processing techniques list out the various practises followed to remove CNSL, process de-oiled CNS cakes into bio-char through carbonization, and briquetting of pre-treated CNS wastes along with their compacting techniques prescribed by various researchers. Lastly, fuel and combustion properties brief out about the fuel traits of developed CNS briquettes along with their burning characteristics; and include parameters like proximate and elemental compositions, density and compressive strength, and results related to their combustion and water boiling tests. Moreover, all the reported results and data in this study were in accordance with the international testing standards; and ranged in between their permissible range.