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Skarphagen, Helge, David Banks, Bjørn S. Frengstad e Harald Gether. "Design Considerations for Borehole Thermal Energy Storage (BTES): A Review with Emphasis on Convective Heat Transfer". Geofluids 2019 (22 de abril de 2019): 1–26. http://dx.doi.org/10.1155/2019/4961781.
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Borehole thermal energy storage (BTES) exploits the high volumetric heat capacity of rock-forming minerals and pore water to store large quantities of heat (or cold) on a seasonal basis in the geological environment. The BTES is a volume of rock or sediment accessed via an array of borehole heat exchangers (BHE). Even well-designed BTES arrays will lose a significant quantity of heat to the adjacent and subjacent rocks/sediments and to the surface; both theoretical calculations and empirical observations suggest that seasonal thermal recovery factors in excess of 50% are difficult to obtain. Storage efficiency may be dramatically reduced in cases where (i) natural groundwater advection through the BTES removes stored heat, (ii) extensive free convection cells (thermosiphons) are allowed to form, and (iii) poor BTES design results in a high surface area/volume ratio of the array shape, allowing high conductive heat losses. The most efficient array shape will typically be a cylinder with similar dimensions of diameter and depth, preferably with an insulated top surface. Despite the potential for moderate thermal recovery, the sheer volume of thermal storage that the natural geological environment offers can still make BTES a very attractive strategy for seasonal thermal energy storage within a “smart” district heat network, especially when coupled with more efficient surficial engineered dynamic thermal energy stores (DTES).
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Gamisch, Sebastian, Stefan Gschwander e Stefan J. Rupitsch. "Numerical and Experimental Investigation of Wire Cloth Heat Exchanger for Latent Heat Storages". Energies 14, n.º 22 (11 de novembro de 2021): 7542. http://dx.doi.org/10.3390/en14227542.
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Latent thermal energy storages (LTES) offer a high storage density within a narrow temperature range. Due to the typically low thermal conductivity of the applied phase change materials (PCM), the power of the storages is limited. To increase the power, an efficient heat exchanger with a large heat transfer surface and a higher thermal conductivity is needed. In this article, planar wire cloth heat exchangers are investigated to obtain these properties. They investigated the first time for LTES. Therefore, we developed a finite element method (FEM) model of the heat exchanger and validated it against the experimental characterization of a prototype LTES. As PCM, the commercially available paraffin RT35HC is used. The performance of the wire cloth is compared to tube bundle heat exchanger by a parametric study. The tube diameter, tube distance, wire diameter and heat exchanger distance were varied. In addition, aluminum and stainless steel were investigated as materials for the heat exchanger. In total, 654 variants were simulated. Compared to tube bundle heat exchanger with equal tube arrangement, the wire cloth can increase the mean thermal power by a factor of 4.20 but can also reduce the storage capacity by a minimum factor of 0.85. A Pareto frontier analysis shows that for a free arrangement of parallel tubes, the tube bundle and wire cloth heat exchanger reach similar performance and storage capacities.
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Svoboda, Roman, Nicola Koutná, Daniela Košťálová, Miloš Krbal e Alena Komersová. "Indomethacin: Effect of Diffusionless Crystal Growth on Thermal Stability during Long-Term Storage". Molecules 28, n.º 4 (6 de fevereiro de 2023): 1568. http://dx.doi.org/10.3390/molecules28041568.
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Differential scanning calorimetry and Raman spectroscopy were used to study the nonisothermal and isothermal crystallization behavior of amorphous indomethacin powders (with particle sizes ranging from 50 to 1000 µm) and their dependence on long-term storage conditions, either 0–100 days stored freely at laboratory ambient temperatures and humidity or placed in a desiccator at 10 °C. Whereas the γ-form polymorph always dominated, the accelerated formation of the α-form was observed in situations of heightened mobility (higher temperature and heating rate), increased amounts of mechanically induced defects, and prolonged free-surface nucleation. A complex crystallization behavior with two separated crystal growth modes (originating from either the mechanical defects or the free surface) was identified both isothermally and nonisothermally. The diffusionless glass–crystal (GC) crystal growth was found to proceed during the long-term storage at 10 °C and zero humidity, at the rate of ~100 µm of the γ-form surface crystalline layer being formed in 100 days. Storage at the laboratory temperature (still below the glass transition temperature) and humidity led only to a negligible/nondetectable GC growth for the fine indomethacin powders (particle size below ~150 µm), indicating a marked suppression of GC growth by the high density of mechanical defects under these conditions. The freely stored bulk material with no mechanical damage and a smooth surface exhibited zero traces of GC growth (as confirmed by microscopy) after >150 days of storage. The accuracy of the kinetic predictions of the indomethacin crystallization behavior was rather poor due to the combined influences of the mechanical defects, competing nucleation, and crystal growth processes of the two polymorphic phases as well as the GC growth complex dependence on the storage conditions within the vicinity of the glass transition temperature. Performing paired isothermal and nonisothermal kinetic measurements is thus highly recommended in macroscopic crystallization studies of drugs with similarly complicated crystal growth behaviors.
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Raj, Sarath, Bibin K.S. e Reby Roy K.E. "OpenFOAM Analysis on the Comparison of Safety Requirements Provided for Water-Air and LOX-He Storage Systems". International Journal of Occupational Safety and Health 14, n.º 4 (1 de outubro de 2024): 436–48. http://dx.doi.org/10.3126/ijosh.v14i4.57612.
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Introduction: In storage vessels filled with cryogenic liquids thermal destratification can be effectively done by the continuous supply of bubble movements. Therefore, the pressure builds up subsequent blasting of such containers can be avoided and cryogenic storage vessels can be used safely. The Volume of Fluid (VOF) approach is utilized in the current computational analysis to examine the safety precautions, dynamics of bubble creation, and subsequent collapse of the free liquid surface in both vertically and horizontally aligned rectangular containers. Methods: In the present work, using the Volume of Fluid (VOF) method, numerically investigated the sloshing behavior within a rectangular container with a 15% free air space with double gas inlets. Results: The impact of inlet gas velocity on sloshing rate due to bubbling is investigated numerically. Also, comparative studies are carried out to investigate the variations of bubble diameter, detachment time, and bubble detachment frequencies considering water-air and LOX-He systems. The mixing behaviors in LOX due to helium bubble formation under different inlet gas velocities were also numerically investigated. The numerical results show that the average deformation index increased by 23.83% when the water-air system was replaced with the LOX-He system. Hence, it can be understood that for the storage vessels filled with cryogenic liquids more safety precautions have to be considered to avoid thermal stratification. The safety precautions include increasing the gas flow rate and including more number gas flow inlets. Conclusion: The present analysis concludes that under a given condition the free liquid surface deformation is more for the case where storage vessels filled with LOX-He. Hence, it can be understood that for the storage vessels filled with cryogenic liquids more safety precautions have to be considered to avoid thermal stratification. The safety precautions include increasing the gas flow rate and including more number gas flow inlets.
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Raj, Sarath, K. S. Bibin, K. E. Reby Roy, Bibin Prasad e J. S. Jayakumar. "Analysis of free liquid surface deformation and thermal destratification in liquid storage tanks using OpenFOAM". Journal of Energy Storage 102 (novembro de 2024): 113848. http://dx.doi.org/10.1016/j.est.2024.113848.
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Serebrov, A. P., E. A. Kolomensky, A. K. Fomin, I. A. Krasnoschekova, A. V. Vassiljev, D. M. Prudnikov, I. V. Shoka et al. "New Neutron Lifetime Measurements with the Big Gravitational Trap and Review of Neutron Lifetime Data". KnE Energy 3, n.º 1 (9 de abril de 2018): 121. http://dx.doi.org/10.18502/ken.v3i1.1733.
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Neutron lifetime is one of the most important physical constants which determines parameters of the weak interaction and predictions of primordial nucleosynthesis theory. In our experiment we measure the storage time of UCN in the material trap coated with a hydrogen-free fluorine-containing polymer (Fomblin grease UT-18). The stability of this coating to multiple thermal cycles between 80 K and 300 K was tested. The achieved storage time is only 1.5% less than free neutron lifetime. Using additional surface, which can be plunged into the trap to change the collision frequency of UCN with walls, we calculate free neutron lifetime by extrapolation to zero collision frequency. The result of the measurements with this new experimental setup is
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Shen, Zhenzhen, Kun Fang, Mike Hamilton, R. Wayne Johnson, Erica Snipes e Michael Bozack. "Lead-free Solder Attach for 200°C Applications". Additional Conferences (Device Packaging, HiTEC, HiTEN, and CICMT) 2013, HITEN (1 de janeiro de 2013): 000260–67. http://dx.doi.org/10.4071/hiten-wa18.
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Conventional SAC lead-free solders have a melting point of 217°C to 227°C, limiting their suitability for applications at 200°C. AgBiXTM solder has potential for 200°C applications because of its ~260°C solidus temperature. BiAgX paste has been used to assemble SiC test die to ceramic substrates with direct bond copper (DBC), reactive brazed CuMo, thick film Au, thick film PtAu, thick film PdAg and thick film Ag. Surface mount chip resistors have also been attached to thick film metallized substrates. The assembly process and initial shear strength test results are presented. Assemblies have also been subjected to thermal testing: thermal cycling (−55°C to +195°C) and high temperature (200°C) storage. The shear strength of these assemblies after thermal testing are presented and compared to initial results.
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Pan, Chao, Ran Ding, Li Dong, Jing Wang e Yucai Hu. "Horseradish Peroxidase-Carrying Electrospun Nonwoven Fabrics for the Treatment of o-Methoxyphenol". Journal of Nanomaterials 2015 (2015): 1–6. http://dx.doi.org/10.1155/2015/616879.
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The carboxyl-functionalized polystyrene (poly(styrene-co-methacrylic acid), PSMAA) nanofibers with average diameters of 250 ± 20 nm was prepared by electrospinning. PSMAA nanofibrous membrane were employed for immobilization of horseradish peroxidase (HRP) enzyme on the fibrous surface by a chemical method. The parameters about immobilizing HRP on the PSMAA nanofibers were studied and the influence on the activity of the HRP is discussed. This study showed that soap-free emulsion method is an ideal technology to modify the polystyrene surface and ultimately achieve enzyme immobilization on electrospun PSMAA nanofibers surfaces. Compared with free HRP, the acid-base stability, thermal stability, and storage stability of HRP were increased after the immobilization. The immobilized HRP maintained about 60% of its initial activity during a 20-day storage period. However, the free HRP maintained only 40% of its initial activity. The removal percentages of o-methoxyphenol (OMP) reached 80.2% after 120 min for immobilized HRP. These results suggest that the proposed scheme for immobilization of HRP has potential in industrial applications for the treatment of phenolic wastewater.
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Menchaca-Campos, Carmina, Gonzalo Martínez-Barrera, Héctor López-Valdivia, Héctor Carrasco e Alberto Álvarez-Castillo. "Post-irradiation effects on gamma-irradiated nylon 6,12 fibers". Journal of Polymer Engineering 33, n.º 9 (1 de dezembro de 2013): 823–28. http://dx.doi.org/10.1515/polyeng-2013-0070.
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Abstract Post-irradiation effects on nylon 6,12 crystalline fibers gamma-irradiated 6 years previously (6YI) were studied, including thermal stability and morphology; their relationship with storage time was also studied. The results of these studies were compared with those obtained for non-irradiated (NI) and namely freshly irradiated (FI) crystalline fibers. The results include analyses like thermogravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM) and optical images for (6YI and FI) both kinds of nylon 6,12 fibers. The results showed that the most prominent effect is related to the reaction progress. The chain scission and/or crosslinking mechanisms, as well as the free radicals, allow proceeding with the reaction, and consequently, changes on the properties of the FI samples. The melting point, degree of crystallinity, degradation temperature and morphology prove that additional chemical reactions and surface modifications keep occurring in the fibers long after the irradiation process has ended. With storage time, the surface becomes rougher, the color turns yellowish, the melting point diminishes and the degree of crystallinity increases.
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Atta, Ayman, Mahmood Abdullah, Hamad Al-Lohedan e Nermen Mohamed. "Coating Sand with New Hydrophobic and Superhydrophobic Silica/Paraffin Wax Nanocapsules for Desert Water Storage and Transportation". Coatings 9, n.º 2 (17 de fevereiro de 2019): 124. http://dx.doi.org/10.3390/coatings9020124.
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Paraffin wax emulsions have gained immense attention as a cheap, environment-friendly, and aroma-free material for preparing superhydrophobic coatings. In this work, paraffin wax (PWs) capsules consisting of hydrophobic silica nanoparticles were used for coating desert sand. Different types of the hydrophobic silica nanoparticles, modified with new oleylamino- and oleylamide silane precursors, were prepared in the presence and absence of paraffin waxes. The particle sizes, surface charges, thermal stability, surface morphologies, and wetting characteristics of these nanoparticles were investigated. The combination of these superhydrophobic silica nanoparticles and desert sand, showed excellent water repellency; stable water droplets remained on the sand surface, without any wetting or permeation. Furthermore, the mixing of the superhydrophobic sand with untreated sand (mixing ratio 1:10 wt %), with a thickness of 2 cm, sustained a great water-holding capacity with a water column height of 35 cm. The good thermal stability of the PWs capsules containing hydrophobic silica nanoparticles, along with their good water-holding capacity, make them potential candidates for developing superhydrophobic sand for desert water storage and transportation.
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Mongibello, Luigi, Nicola Bianco, Martina Caliano e Giorgio Graditi. "Numerical Simulation of an Aluminum Container including a Phase Change Material for Cooling Energy Storage". Applied System Innovation 1, n.º 3 (4 de setembro de 2018): 34. http://dx.doi.org/10.3390/asi1030034.
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Thermal energy storage systems can be determinant for an effective use of solar energy, as they allow to decouple the thermal energy production by the solar source from thermal loads, and thus allowing solar energy to be exploited also during nighttime and cloudy periods. The current study deals with the modelling and simulation of a cooling thermal energy storage unit consisting of an aluminum container partially filled with a phase change material (PCM). Two unsteady models are implemented and discussed, namely a conduction-based model and a conduction-convection-based one. The equations systems relative to both the models are solved by means of the Comsol Multiphysics finite element solver, and results are presented in terms of temporal variation of temperature in different points inside the PCM, of the volume average liquid fraction, and of the cooling energy stored and released through the aluminum container external surface during the charge and discharge, respectively. Moreover, the numerical results obtained by the implementation of the above different models are compared with experimental ones obtained with a climatic chamber. The comparison between numerical and experimental results indicate that, for the considered cooling energy storage unit, free convection plays a crucial role in the heat transfer inside the liquid PCM and cannot be neglected.
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Zhang, Jin Song, e Jian Hua Zhang. "Estimation of Whiskers Growth on Sn Coating of Cu-Leads in Different Accelerated Tests". Advanced Materials Research 160-162 (novembro de 2010): 1575–81. http://dx.doi.org/10.4028/www.scientific.net/amr.160-162.1575.
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With the ban of Sn-Pb alloys coated on Cu leads in electronic devices, the electronic packaging industry uses Pb-free Sn alloys as the coating materials. This replacement meets a widely concern that Pb-free Sn alloys have a stronger propensity to grow whiskers on the surface of the coating. The experimental samples have been plated a pure Sn coating on Cu leads by an industrial plating process before the accelerated tests. The study executed three different environment conditions to estimate whiskers growth on the Sn coating of Cu leads. They were Room Temperature/Humidity Storage (RS), High Temperature/Humidity Storage (TH) and Temperature Cycling (TC). No whisker had been found in the samples during the RS tests since this environment condition had not destroyed the surface continuity to promote whiskers grow out of the Sn coating. In the TH tests, the moisture degraded the coating surface to produce the electrochemical corrosion on some local areas. Sn whiskers were easy prone to grow from the corroded areas on the coating surface with a high rate. In the TC tests, Sn whiskers grew from the cracks on the coating surface with a high density based on the mechanism of the thermal fatigue. The alternating stress in the coating surface induced by the temperature fluctuation tore the Sn oxide grains to form cracks and provide a growth path for Sn whiskers on the coating surface.
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Comanescu, Cezar. "Graphene Supports for Metal Hydride and Energy Storage Applications". Crystals 13, n.º 6 (27 de maio de 2023): 878. http://dx.doi.org/10.3390/cryst13060878.
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Energy production, distribution, and storage remain paramount to a variety of applications that reflect on our daily lives, from renewable energy systems, to electric vehicles and consumer electronics. Hydrogen is the sole element promising high energy, emission-free, and sustainable energy, and metal hydrides in particular have been investigated as promising materials for this purpose. While offering the highest gravimetric and volumetric hydrogen storage capacity of all known materials, metal hydrides are plagued by some serious deficiencies, such as poor kinetics, high activation energies that lead to high operating temperatures, poor recyclability, and/or stability, while environmental considerations related to the treatment of end-of-life fuel disposal are also of concern. A strategy to overcome these limitations is offered by nanotechnology, namely embedding reactive hydride compounds in nanosized supports such as graphene. Graphene is a 2D carbon material featuring unique mechanical, thermal, and electronic properties, which all recommend its use as the support for metal hydrides. With its high surface area, excellent mechanical strength, and thermal conductivity parameters, graphene can serve as the support for simple and complex hydrides as well as RHC (reactive hydride composites), producing nanocomposites with very attractive hydrogen storage properties.
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Gage, Samuel, Prashant Sharan, Craig Turchi e Judy Netter. "Evaluation of Formate Salt PCM’s for Latent Heat Thermal Energy Storage". Energies 14, n.º 3 (1 de fevereiro de 2021): 765. http://dx.doi.org/10.3390/en14030765.
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This work examines formate salts as potential phase change materials (PCMs) for middle-high temperature (≤250 °C) latent heat thermal energy storage applications. The thermophysical properties of three formate salts were characterized: pure sodium formate and binary blends of sodium/potassium formate and sodium/calcium formate. The stability of formate PCM’s was evaluated by thermal cycling using differential scanning calorimetry where sodium formate and sodium/potassium formate appeared stable over 600 cycles, while sodium/calcium formate exhibited a monotonic decrease in heat of fusion over the test period. A longer test with sodium formate led to gas release and decomposition of the salt. FTIR analysis of the PCM showed degradation of formate to oxalate. T-history experiments with 50-g PCM quantities demonstrated a bulk supercooling of only 2–3 °C for these salts. Thermal conductivity enhancement of over 700% was achieved by embedding aluminum in the solid PCM. Finally, mild carbon steel was immersed in molten sodium formate for up to 2000 h. Sodium formate was found to be non-corrosive, as calculated by mass loss and confirmed by cross-sectional high-resolution microscopy. FTIR analysis of the PCM after 2000 h shows oxidation at the free surface, while the bulk PCM remained unchanged, further indicating a need to protect the formate from atmospheric exposure when used as a PCM.
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Afzaal, Muhammad, Farhan Saeed, Huda Ateeq, Yasir Abbas Shah, Muzzamal Hussain, Ahsan Javed, Ali Ikram et al. "Effect of Cellulose–Chitosan Hybrid-Based Encapsulation on the Viability and Stability of Probiotics under Simulated Gastric Transit and in Kefir". Biomimetics 7, n.º 3 (10 de agosto de 2022): 109. http://dx.doi.org/10.3390/biomimetics7030109.
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Encapsulation comprises a promising potential for the targeted delivery of entrapped sensitive agents into the food system. A unique combination of cellulose/chitosan (Cl-Ch)-based hybrid wall material was employed to encapsulate L. plantarum by emulsion technique. The developed beads were further subjected to morphological and in vitro studies. The viability of free and encapsulated probiotics was also evaluated in kefir during storage. The developed beads presented porous spherical structures with a rough surface. A 1.58 ± 0.02 log CFU/mL, 1.26 ± 0.01 log CFU/mL, and 1.82 ± 0.01 log CFU/mL reduction were noticed for Cl-Ch hybrid cells under simulated gastro-intestinal and thermal conditions, respectively. The encapsulated cells were found to be acidic and thermally resistant compared to the free cells. Similarly, encapsulated probiotics showed better viability in kefir at the end of the storage period compared to free cells. In short, the newly developed Cl-Ch hybrid-based encapsulation has a promising potential for the targeted delivery of probiotics, as career agents, in gastric transit, and in foods.
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Texter, John, Zhiming Qiu, Joe Byrom e Rene Crombez. "Reactive Nanofluids for Tuning Resin Hardness". MRS Advances 4, n.º 2 (2019): 125–31. http://dx.doi.org/10.1557/adv.2018.678.
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ABSTRACTPolyurea resins derived from tolyldiisocyante (TDI) and a reactive solvent-free nanofluid (NF-NH2) surface-decorated with propylamines can be tuned over three to five orders of magnitude in storage modulus (10 MPa to 10 GPa) and hardness modulus (6 kPa to 4 GPa) by varying weight fractions of components. The thermal properties of this NF-NH2 are similar to several other nanofluids reported using the same bulky anionic counterion that also imparts liquidity in the absence of any solvent. This tuning suggests applications ranging from opaque protective coatings to clearcoats to sealants to adhesives.
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Jo, Wonhyuk, Yong Chan Cho, Seongheun Kim, Eric Carl Landahl e Sooheyong Lee. "Reduced Thermal Conductivity in Ultrafast Laser Heated Silicon Measured by Time-Resolved X-ray Diffraction". Crystals 11, n.º 2 (14 de fevereiro de 2021): 186. http://dx.doi.org/10.3390/cryst11020186.
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We investigate the effect of free carrier dynamics on heat transport in bulk crystalline Silicon following femtosecond optical excitation of varying fluences. By taking advantage of the dense 500 MHz standard fill pattern in the PLS-II storage ring, we perform high angular-resolution X-ray diffraction measurements on nanosecond-to-microsecond time-scales with femtometer spatial sensitivity. We find noticeably slowed lattice recovery at increasingly high excitation intensities. Modeling the temporal evolution of lattice displacements due to the migration of the near surface generated heat into the bulk requires reduced thermal diffusion coefficients. We attribute this pump-fluence dependent thermal transport behavior to two separate effects: first, the enhanced nonradiative recombination of free carriers, and, second, reduced size of the effective heat source in the material. These results demonstrate the capability of time-resolved X-ray scattering as an effective means to explore the connection between charge carrier dynamics and macroscopic transport properties.
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Casaburi, Gustavo Belmiro, Marcos Henrique Ramos Da Silva, Lourenço Correr Sobrinho e Rafael Leonardo Xediek Consani. "Electric Current as an Alternative Method for Surface Treatment of Acid-Sensitive Ceramics". European Journal of Dental and Oral Health 4, n.º 3 (7 de junho de 2023): 8–14. http://dx.doi.org/10.24018/ejdent.2023.4.3.257.
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Objectives: The aim of this study was to evaluate the silane application with electric current as an alternative method for surface treatment of acid-sensitive ceramic. Materials and Methods: IPS E.max Press ceramic discs applied with silane, associated or not with hydrofluoric acid, electric current and storage time in water were divided in the groups (n=10) AE+CF (Acid etching + electric current free); AE+CA (Acid etching + electric current); AF+CF (Acid etching free + electric current free); AF+CA (Acid free + electric current); AE+CF +T (Acid etching + electric current free + thermal cycling); AE+CA+T (Acid etching + electric current + thermal cycling); AF+CF+T (Acid free + electric current free + thermal cycling) and AF+CA-T (Acid etching free + electric current + thermal cycling. In the conditioned groups, 10% hydrofluoric acid was applied for 20s. The silane was applied with microbrush in the AE+CF-T, AE+CA-T, AF+CF-T and AE+CA-T groups and in the other groups it was replaced by a metal tip conductor of electric current. Cylindrical silicone matrices with three holes (12 mm in diameter and 1mm thick) were placed on the ceramic. The resin cement RelyX U200 was inserted into the holes of the matrix, subjected to a static load of 250mg for 2min and photoactivated for 20s. After removing the matrix, the sample with resin cement cylinder adhered to the ceramic was stored in an oven at 37 ºC for 24h. The 24-h samples and those thermocycled with 10,000 cycles in vats with water at temperatures of 5±1 ºC and 55±1 ºC were submitted to microshear resistance test, fracture analysis, SEM analysis and contact angle. Data were submitted to one-way ANOVA and Tukey’s test (α=0.05). Results: At 24h, AE+CA showed the highest value in bond resistance and AF+CF at the lowest, both different from AE+CF while AF+CA was intermediate. After thermocycling, with higher values AE+CA+T and AE+CF-T were similar, as well as AF+CF+T and AF+CA+T with lower values. AE+CF+T and AE+CA+T differed statistically from AF+CF+T and AF+CA+T. Adhesive failure was predominant in all groups with or without thermocycling. At 24h, there was cohesive failures in mixed resin cement in the AE+CA and AF+CF. After thermocycling, there were mixed failures in the AE+CA+T and cohesive failures in resin cement for the AE+CF+T and AF+CA+T. The greater contact angle vas observed in the AE+CF. Conclusions: The association of hydrofluoric acid etching, application of silane with electric current and storage times promoted different values of bond strength, types of failures and contact angles in samples of resin cement bonded to acid-sensitive ceramics. Clinical Relevance: The application of silane with an electric current is a promising method to improve the adhesive bond between resin cement and ceramics, especially when associated with hydrofluoric acid etching.
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Puszka, Andrzej, e Janusz W. Sikora. "Synthesis and Characterization of New Polycarbonate-Based Poly(thiourethane-urethane)s". Polymers 14, n.º 14 (20 de julho de 2022): 2933. http://dx.doi.org/10.3390/polym14142933.
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The new segmented poly(thiourethane-urethane)s (PTURs) based on 1,1′-methanediylbis(4-isocyanatocyclohexane) (HMDI, Desmodur W®), polycarbonate diol (PCD, Desmophen C2200) and (methanediyldibenzene-4,1-diyl)dimethanethiol were synthesized by one-step melt polyaddition method. The obtained PTURs, with a content of 30–60 wt% of the hard segments (HS), were tested in which the influence of changes in the HS content on their properties was determined. The polymers were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), thermal analysis (DSC, TGA) and thermomechanical analysis (DMTA). Additionally, tensile strength, optical (refractive index, UV-VIS and color) and surface properties of the obtained polymers (contact angle and surface free energy) and adhesion to copper were examined. FTIR analysis verified the supposed structure of the polymers obtained and showed a complete conversion of the isocyanate groups. TGA analysis confirmed the relatively good thermal stability of the polymers. On the other hand, after performing the DSC analysis, it was possible to state that the obtained materials were partially or completely amorphous, and the microphase separation decreased with increasing HS content in the polymer. Similar observations were made from the DMTA data. In addition, the hardness, tensile strength, modulus of elasticity, storage modulus, adhesion to copper, refractive index and total free surface energy increased with increasing HS content in the polymer.
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R, Kumaravelrajan, Swetha M e Suba V. "Characterization of Immobilized β-Amylase Enzyme Isolated from Sweet Potato and prepared by Entrapment Method". International Journal of Pharmaceutical Sciences and Nanotechnology(IJPSN) 15, n.º 6 (16 de dezembro de 2022): 6196–203. http://dx.doi.org/10.37285/ijpsn.2022.15.6.2.
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Aim: This study attempted to isolate β-amylase from sweet potato and enzyme immobilized by encapsulation method, and characterized with various parameters.
Methods: The enzyme β-amylase was isolated with phosphate-buffered saline and purified by centrifugation with ammonium sulfate. The purified enzyme was immobilized on chitosan (0.25 g) and sodium alginate (0.25 g) polymers by entrapment method in the presence of calcium chloride (0.5 M). The immobilized enzyme was characterized by a starch hydrolysis test, the optimal pH and temperature were studied and the stability of the immobilized enzyme was also determined. SEM analysis was performed and Vm and Km were also found.
Results: The starch hydrolysis test showed positive results on the starch agar plates for immobilized enzymes. The thermal inactivation showed a severe loss in the activity of the free enzymes (49.3 %) while the temperature profile of the immobilized enzymes was much broader (84.55 %) at higher temperatures (80° C). The optimal pH and stability indicated that the immobilized enzyme has higher stability in the pH range of 5-8. The Km and Vmax value of free and immobilized enzyme was 7.67 mmol, 21.15 µmol (R2 0.8880), and 4.72 mmol,16.79 µmol (R2 0.8446) respectively. The storage of free and immobilized enzymes for one month showed that 83.5 % and 40 % of free enzymes and 11.6 % and 8.6 % of immobilized enzymes lost activity at 25° C and 4° C, respectively. SEM analysis shows the smooth, porous surface.
Conclusion: Immobilized enzymes (natural polymers) exhibit higher thermal stability the optimal pH and stability indicate immobilized enzyme has higher stability in the pH range of 5-8, and achieves a relative activity of 69.7 %. After 6 uses, the reuse efficiency of the immobilized enzyme decreased from 99.8 % to 52.3 %. The storage of the immobilized enzyme showed much higher stability than the found-free enzyme.
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Moreno-Insertis, F., M. Schüssler e A. Ferriz-Mas. "Storage of Magnetic Flux in the Overshoot Region". Symposium - International Astronomical Union 157 (1993): 41–44. http://dx.doi.org/10.1017/s0074180900173838.
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The combined action of the subadiabatic ambient stratification in the overshoot region below the convection zone and the inertial forces associated with the solar rotation is shown to lead to the suppression of the escape of magnetic flux in the form of toroidal flux tubes both toward the surface and toward higher latitudes. We show that a flux ring initially in thermal equilibrium with its environment and rotating with the ambient angular velocity moves radially and latitudinally towards an equilibrium configuration of lower internal temperature and larger internal rotation rate with respect to the surrounding, field-free gas. We conclude that flux rings with B≲ 105 G can be kept within the overshoot region if the superadiabaticity is sufficiently negative, i.e. δ = ▿ – ▿ad≲–10−5; below that field strength the poleward drift is also reduced to a latitudinal oscillation of moderate amplitude, δθ ≲ 20 deg. Flux rings with significantly larger field strength cannot be kept in the equatorial parts of the overshoot region: their equilibrium configuration is located at high latitudes far outside the solar activity belts and, at any rate, requires unrealistic values of δ.
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Chiriac, Adriana Petronela, Mariana-Dana Damaceanu, Mihai Asandulesa, Daniela Rusu e Irina Butnaru. "Optimization of Nanocomposite Films Based on Polyimide–MWCNTs towards Energy Storage Applications". Energies 16, n.º 9 (27 de abril de 2023): 3739. http://dx.doi.org/10.3390/en16093739.
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In order to obtain polyimide-based composite materials for energy storage applications, four synthetic methods towards a polyimide matrix with 2 wt.% pristine or acid-functionalized MWCNTs have been developed. The polyimide is derived from a nitrile aromatic diamine and a fluorene-containing dianhydride which allowed the formation of flexible free-standing nanocomposite films. The films were thoroughly characterized by means of structural identification, morphology, mechanical, thermal and dielectric behavior, as well as the charge storage performance. The obtained data indicated higher homogeneity of the composites loaded with acid-functionalized MWCNTs that enabled significantly increased dielectric properties compared to the matrix. To assess the electrical charge storage capability, cyclic voltammetry and galvanostatic charge–discharge measurements were employed in a three-electrode cell configuration. Due to the higher conductivity of pristine MWCNTs compared to acid-functionalized ones, increased capability to store charges was achieved by the nanocomposites containing these fillers, despite their lower homogeneity. An attempt to increase the carbonaceous material content was made by applying a thin carbon layer onto the nanocomposite film surface, which led to higher capacitance.
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Moszczyńska, Julia, Xinying Liu e Marek Wiśniewski. "Non-Thermal Ammonia Decomposition for Hydrogen Production over Carbon Films under Low-Temperature Plasma—In-Situ FTIR Studies". International Journal of Molecular Sciences 23, n.º 17 (25 de agosto de 2022): 9638. http://dx.doi.org/10.3390/ijms23179638.
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Due to easy storage and transportation, liquid hydrogen carriers will play a significant role in diversifying the energy supply pathways by transporting hydrogen on a large scale. Thus, in this study, amorphous carbonaceous materials have been employed for hydrogen production via ammonia decomposition under non-thermal plasma (NTP) conditions. The adsorption and splitting of ammonia over carbons differing in the chemical structure of surface functional groups have been investigated by in situ spectral studies directly under NTP conditions. As a result of NH3 physical and chemical sorption, surface species in the form of ammonium salts, amide and imide structures decompose immediately after switching on the plasma environment, and new functionalities are formed. Carbon catalysts are very active for NH3 splitting. The determined selectivity to H2 is close to 100% on N-doped carbon material. The data obtained indicate that the tested materials possess excellent catalytic ability for economical, COx-free hydrogen production from NH3 at a low temperature.
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Rong, Junhui, Yun Wang, Liang Ni, Wenli Zhang, Chunmei Li, Juan Han e Zijuan Zhou. "Immobilization of Horseradish Peroxidase on Multi-Armed Magnetic Graphene Oxide Composite". Food technology and biotechnology 57, n.º 2 (2019): 260–71. http://dx.doi.org/10.17113/ftb.57.02.19.5832.
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In this study, a novel type of multi-armed polymer (poyltehylene glycol, PEG) magnetic graphene oxide (GO) composite (GO@Fe3O4@6arm-PEG-NH2) has been synthesized as a support for immobilization of horseradish peroxidase (HRP) for the first time. The loading amount of HRP was relatively high (186.34 mg/g) due to the surface of carrier material containing a large amount of amino groups from 6arm-PEG-NH2, but degradation rate of phenols was also much higher (95.4 %), which is attributed to the synergistic effect between the free HRP (45.4 %) and the support material of GO@Fe3O4@6arm-PEG-NH2 (13.6 %). Compared with the free enzyme, thermal, storage and operational stability of the immobilized HRP improved. The immobilized HRP still retained over 68.1 % activity after being reused 8 times. These results suggest that the multi-armed magnetic composite has good application prospect for enzyme immobilization.
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Namba, Kazuhiro, Shohei Ogura, Satoshi Ohno, Wen Di, Koichi Kato, Markus Wilde, Ivo Pletikosić, Petar Pervan, Milorad Milun e Katsuyuki Fukutani. "Acceleration of hydrogen absorption by palladium through surface alloying with gold". Proceedings of the National Academy of Sciences 115, n.º 31 (13 de julho de 2018): 7896–900. http://dx.doi.org/10.1073/pnas.1800412115.
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Enhancement of hydrogen (H) absorption kinetics improves the performance of hydrogen-purifying membranes and hydrogen-storage materials, which is necessary for utilizing hydrogen as a carbon-free energy carrier. Pd–Au alloys are known to show higher hydrogen solubility than pure Pd. However, the effect of Au on the hydrogen penetration from the surface into the subsurface region has not been clarified so far. Here, we investigate the hydrogen absorption at Pd–Au surface alloys on Pd(110) by means of thermal desorption spectroscopy (TDS) and hydrogen depth profiling with nuclear reaction analysis (NRA). We demonstrate that alloying the Pd(110) surface with submonolayer amounts of Au dramatically accelerates the hydrogen absorption. The degree of acceleration shows a volcano-shaped form against Au coverage. This kinetic enhancement is explained by a reduced penetration barrier mainly caused by a destabilization of chemisorbed surface hydrogen, which is supported by density-functional-theory (DFT) calculations. The destabilization of chemisorbed surface hydrogen is attributed to the change of the surface electronic states as observed by angle-resolved photoemission spectroscopy (ARPES). If generalized, these discoveries may lead to improving and controlling the hydrogen transport across the surfaces of hydrogen-absorbing materials.
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Zhu, Quan Yao, Fei Wu e Wen Chen. "Influence of Network Structure on Dynamic Mechanical Properties of Cross-Linked Polystyrene / Glass Fiber Composites". Advanced Materials Research 79-82 (agosto de 2009): 151–54. http://dx.doi.org/10.4028/www.scientific.net/amr.79-82.151.
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The cross-linked polystyrene prepolymer was synthesized with divinylbenzene (DVB) as crosslinker via free-radical crosslinking copolymerization (FCC) and used as the matrix materials for E-glass fiber reinforced composites. The surface modification was performed by treatment of E-glass fiber with γ-methacryloylpropyl trimethoxysilane (MPS) solution. Fourier transform infrared spectroscopy (FTIR) was used to identify the functional groups on the surface modified glass fibers. Dynamic mechanical thermal analysis (DMTA) of these composites revealed that the dynamic storage modulus (E′) was gradually enhanced with the increasing content of DVB (0~3.0 wt %) whereas the damping parameter (tanδ) peaks are lower and broader, indicating better load bearing capacity. Moreover, the Tg was shifted to higher temperature corresponding to the increasing of crosslinking density. Morphology of fracture surfaces for these composites showed different fiber-matrix interfacial adhesion which was mainly attributed to the variation of crosslinking network structure in the interface.
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Miranda, Michele, Daniele Urioste, Livia T. Andrade Souza, Adriano A. Mendes e Heizir F. de Castro. "Assessment of the Morphological, Biochemical, and Kinetic Properties for Candida rugosa Lipase Immobilized on Hydrous Niobium Oxide to Be Used in the Biodiesel Synthesis". Enzyme Research 2011 (16 de agosto de 2011): 1–10. http://dx.doi.org/10.4061/2011/216435.
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Lipase from Candida rugosa (CRL) was immobilized by covalent attachment on hydrous niobium oxide. The matrix could effectively be attached to the enzyme with high retention of activity and prevent its leakage. Following immobilization, CRL exhibited improved storage stability and performed better at higher incubation temperatures. In addition, the enzyme retained most of its catalytic efficiency after successive operational cycles. The immobilized derivative was also fully characterized with respect to its morphological properties: particle size, surface specific area, and pore size distribution. Structural integrity and conformational changes, such as surface cavities in the support, set by the lipase procedure, were observed by Scanning Electron Microscopy. Additionally, a comparative study between free and immobilized lipases was provided in terms of pH, temperature, and thermal stability. CRL derivative was evaluated for the synthesis of biodiesel employing babassu oil and short chain alcohols. The process was feasible only for oil and butanol reaction system.
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Dolinina, Ekaterina S., Elizaveta Yu Akimsheva e Elena V. Parfenyuk. "Development of Novel Silica-Based Formulation of α-Lipoic Acid: Evaluation of Photo and Thermal Stability of the Encapsulated Drug". Pharmaceutics 12, n.º 3 (4 de março de 2020): 228. http://dx.doi.org/10.3390/pharmaceutics12030228.
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Powerful antioxidant α-lipoic acid (LA) is easily degraded under light and heating. This creates difficulties in its manufacture, storage and reduces efficiency and safety of the drug. The purpose of this work was to synthesize novel silica-based composites of LA and evaluate their ability to increase photo and thermal stability of the drug. It was assumed that the drug stabilization can be achieved due to LA-silica interactions. Therefore, the composites of LA with unmodified and organomodified silica matrixes were synthesized by sol-gel method at the synthesis pH below or above the pKa of the drug. The effects of silica matrix modification and the synthesis pH on the LA-silica interactions and kinetics of photo and thermal degradation of LA in the composites were studied. The nature of the interactions was revealed by FTIR spectroscopy. It was found that the rate of thermal degradation of the drug in the composites was significantly lower compared to free LA and mainly determined by the LA-silica interactions. However, photodegradation of LA in the composites under UV irradiation was either close to that for free drug or significantly more rapid. It was shown that kinetics of photodegradation was independent of the interactions and likely determined by physical properties of surface of the composite particles (porosity and reflectivity). The most promising composites for further development of novel silica-based formulations were identified.
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Pan, Lina, Xiyu Liu, Dianfa Fan, Zhangbo Qian, Xinjun Sun, Pan Wu e Liping Zhong. "Study of Oncolytic Virus Preservation and Formulation". Pharmaceuticals 16, n.º 6 (5 de junho de 2023): 843. http://dx.doi.org/10.3390/ph16060843.
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In recent years, oncolytic viruses (OVs) have emerged as an effective means of treating cancer. OVs have multiple oncotherapeutic functions including specifically infecting and lysing tumor cells, initiating immune cell death, attacking and destroying tumor angiogenesis and triggering a broad bystander effect. Oncolytic viruses have been used in clinical trials and clinical treatment as drugs for cancer therapy, and as a result, oncolytic viruses are required to have long-term storage stability for clinical use. In the clinical application of oncolytic viruses, formulation design plays a decisive role in the stability of the virus. Therefore, this paper reviews the degradation factors and their degradation mechanisms (pH, thermal stress, freeze–thaw damage, surface adsorption, oxidation, etc.) faced by oncolytic viruses during storage, and it discusses how to rationally add excipients for the degradation mechanisms to achieve the purpose of maintaining the long-term stability of oncolytic viral activity. Finally, the formulation strategies for the long-term formulation stability of oncolytic viruses are discussed in terms of buffers, permeation agents, cryoprotectants, surfactants, free radical scavengers, and bulking agent based on virus degradation mechanisms.
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Lebedev, Vladimir, Andrey Deev e Konstantin Deev. "Method for Calculating Heat Transfer in a Heat Accumulator Using a Phase Change Material with Intensification Due to Longitudinal Fins". Energies 17, n.º 21 (24 de outubro de 2024): 5281. http://dx.doi.org/10.3390/en17215281.
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One of the challenges in energy supply for isolated power systems is maintaining a steady balance between generated and consumed energy. The application of energy storage systems and flexible energy sources is the most preferable approach for these systems. Small- and medium-sized nuclear power plants are promising, carbon-free options for energy supply to isolated power systems. However, these plants have low maneuverability. To solve this problem, this article discusses the use of a thermal accumulator using a phase change material (solar salt) to heat feedwater. Tubes with longitudinal fins are used to intensify heat transfer in the storage system. This paper presents a method for calculating heat transfer along the entire heat exchange surface of such an accumulator. A series of 2D simulations were conducted to study the solidification process of solar salt around a heat exchange tube at various temperatures on the inner wall surface. The regression dependences of heat transfer on the temperature of the inner surface of the wall and the thickness of the solid PCM layer were determined. Using the presented method and the obtained regression dependencies, we determined the time graphs of the temperature change in the heat transfer fluid at the outlet of the accumulator during discharge. Based on the results presented, it was found that an accumulator with 72.7 tons of solar salt (dimensions: 6 × 3.71 × 2.15 m) can replace a high-pressure heater №1 at a low-power nuclear power plant (50 MW) during 3450 s.
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Zhang, Hanyue, Hong Chen, Xu Gao, Xi Pan, Qingmiao Huang, Junlong Xie e Jianye Chen. "Numerical Study on Behaviors of the Sloshing Liquid Oxygen Tanks". Energies 15, n.º 17 (4 de setembro de 2022): 6457. http://dx.doi.org/10.3390/en15176457.
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In marine storage and transportation, the sloshing of liquid oxygen disturbs the thermodynamic equilibrium and induces stress on tank walls. Numerous problems are associated with the sloshing mechanism and demand a detailed investigation. In this study, a numerical model is developed by coupling the Eulerian framework and the algebraic interface area density (AIAD) method while considering the interphase drag force to investigate the thermal behavior of sloshing liquid oxygen. The effect of the sloshing frequency on the evaporation performance of liquid oxygen is studied. Moreover, anti-sloshing is conducted by employing a T-shaped baffle. The results show that the sloshing induced a vapor explosion phenomenon due to the invalidation of the surface impedance and thermal destratification to enhance free convection, resulting in rapid depressurization and increased evaporation loss. In addition, maximum evaporation loss occurred under the vapor–liquid coupling excitation condition. The T-shaped baffle has an excellent anti-sloshing effect because of the generating tip vortices and the enhanced shearing effect of the walls, which are regarded as motion damping factors.
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Vasu, B., Atul Kumar Ray e Rama SR Gorla. "Free convective heat transfer in Jeffrey fluid with suspended nanoparticles and Cattaneo–Christov heat flux". Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanomaterials, Nanoengineering and Nanosystems 234, n.º 3-4 (4 de maio de 2020): 99–114. http://dx.doi.org/10.1177/2397791420912628.
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Free convection flow of Jeffrey nanofluid past a vertical plate with sinusoidal variations of surface temperature and species concentration is presented. The study of heat transfer and nanofluid transport has been done by employing Cattaneo–Christov heat flux model and Buongiorno model, respectively. Equations governing the flow are non-dimensionalized using appropriate transformations. Furthermore, the method of local similarity and local non-similarity is used to reduce the equations into non-linear coupled system of equations which are then solved by homotopy analysis method. The obtained results are validated by comparing with the existing results available in the literature. The numerical results are found to be in good agreement. The effects of varying the physical parameters such as Deborah Number, Prandtl number, Schmidt number, thermophoresis parameter, Brownian motion parameter and buoyancy ratio parameter are obtained and presented graphically. The effect of sinusoidal variation of surface temperature and species concentration on the skin friction coefficient, Nusselt number and Sherwood number is also shown. Velocity for Jeffrey nanofluid is more than the Newtonian nanofluid while temperature and nanoparticle concentration for Jeffrey nanofluid is less than the Newtonian nanofluid. Raising value of thermal relaxation times leads to an increase in the heat transfer coefficient. It is observed that temperature of Cattaneo–Christov heat flux model is less than that in classical Fourier’s model away from the vertical wall. These types of boundary layer flow problems are found in vertical film solar energy collector, grain storage, transportation and power generation, thermal insulation, gas production, petroleum resources, geothermal reservoirs.
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Dive, Aniruddha, Yiran Xiao, Liwen Wan e Francesco Fornasiero. "Evaluating Li Ion Storage Mechanism in Carbon Nanotubes (CNT) Anodes for High Energy Density Li-Ion Batteries: An Atomistic Perspective". ECS Meeting Abstracts MA2024-02, n.º 11 (22 de novembro de 2024): 1507. https://doi.org/10.1149/ma2024-02111507mtgabs.
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Current Lithium-ion batteries (LIBs) are limited to energy densities of ~150 Wh/kg and pose safety issues associated with dendrite formation and the use of flammable liquid electrolytes that can result in the common battery failure known as thermal runaway and explosion. Lithium metal is an ideal anode for high energy density LIBs due to its high theoretical capacity (3860 mAh/g) but is dangerous due to its propensity to form dendrites. Carbon nanotubes (CNTs) with superior electronic, mechanical, and structural properties provide an exciting alternative as anode for high energy density LIBs. LIBs with vertically aligned CNTs forest help achieve the capacity retention > 80% and superior efficiency over 1000 charging-discharging cycles. However, a fundamental understanding of Li+ ion storage within CNT anodes is largely unexplored and lacking. Experimental characterization of Li+ ion storage in CNT anodes is expensive and challenging. Previous theoretical studies have evaluated storage mechanism for isolated Li+ ions within small diameter CNTs (< 1.5 nm) forest. In common organic liquid electrolytes, Li+ ions prefer to be solvated and therefore isolated Li+ ions cannot accurately describe the Li+ storage mechanism especially in large diameter CNTs. In the current study, we carefully investigated the de-solvation mechanisms for Li+ ions in EC: EMC (3/7 w/w) 1.2 M LiPF6 liquid electrolytes both inside and outside of pristine CNT. The calculated de-solvation energies for Li+ ion adsorption onto the outside surface (~0.4-0.5 eV) of CNTs show relatively lower energies as compared to inside surface (~ 0.9-1.0 eV) of CNTs. We therefore claim that the Li+ ion storage strongly occurs on the outside surface of pristine defect-free CNTs. We further employ classical molecular dynamics simulations to investigate the Li+ ion storage on the outside of CNTs. The classical molecular dynamics simulations reveal a capacitive-type storage mechanism for pristine CNTs forest. Recent experimental reports suggest a large fraction of storage mechanism in CNT anode to be capacitive type (> 55 %) which supports the findings from atomistic modeling. Introducing structural defects (n-membered C-C rings), functional groups (-OH, =O, -COOH) etc... can lead to intercalation or plating-type Li ion storage in CNT forest which would result in higher capacity as well as energy density. However, for pristine CNTs we report the Li+ ion storage mechanism to be purely capacitive and therefore would serve as potential supercapacitor rather than battery. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
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Lv, Xifeng, Huan Cao, Rui Zhang, Xuehua Shen, Xiaodong Wang e Fang Wang. "Waste Plastic Polypropylene Activated Jujube Charcoal for Preparing High-Performance Phase Change Energy Storage Materials". Nanomaterials 13, n.º 3 (29 de janeiro de 2023): 552. http://dx.doi.org/10.3390/nano13030552.
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The research on the high-value utilization of biomass has good application prospects and is conducive to sustainable development. In this paper, three different types of activators (potassium hydroxide, phosphoric acid, and polypropylene) were used to carbonize jujube branches at high temperatures of 600 °C and 800 °C, and then the PEG/jujube charcoal composite phase change materials (PCM) were prepared by vacuum impregnation of polyethylene glycol (PEG). The results showed that the carbon support activated by polypropylene (PP) had a richer pore size distribution than the other two activation methods, and the 800 °C carbonization carrier loaded PEG had a higher phase change enthalpy than the composite material at 600 °C. The mesoporous and macroporous structures were staggered with PP-activated jujube charcoal at 800 °C, with a specific surface area of 1082.2 m²/g, the melting enthalpy of the composite material reached 114.92 J/g, and the enthalpy of solidification reached 106.15 J/g after PEG loading. The diffraction peak of the composite phase change material was the superposition of PEG and carbon matrix, which proved that the loading process was physical adsorption. After 200 thermal cycles, the melting enthalpy and crystallization enthalpy were only reduced by 4.3% and 4.1%, respectively, and they remained stable and leak-free at the melting point of PEG for 2 h, demonstrating good thermal stability of the composite phase change materials. In summary, PP has obvious advantages over traditional activation, and the carbon-supported PEG phase change composite after PP activation is a biochar energy storage material with excellent performance.
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Hamieh, Tayssir. "Exploring the Application of Advanced Chromatographic Methods to Characterize the Surface Physicochemical Properties and Transition Phenomena of Polystyrene-b-poly(4-vinylpyridine)". Molecules 29, n.º 20 (11 de outubro de 2024): 4812. http://dx.doi.org/10.3390/molecules29204812.
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The linear diblock copolymer polystyrene-b-poly(4-vinylpyridine) (PS-P4VP) is an important copolymer recently used in many applications such as optoelectronics, sensors, catalysis, membranes, energy conversion, energy storage devices, photolithography, and biomedical applications. (1) Background: The surface thermodynamic properties of PS-P4VP copolymers are of great importance in many chemical and industrial processes. (2) Methods: The inverse gas chromatography (IGC) at infinite dilution was used for the experimental determination of the retention volumes of organic solvents adsorbed on copolymer surfaces as a function of temperature. This led to the variations in the free energy of interaction necessary to the evaluation of the London dispersive and polar acid–base surface energies, the polar enthalpy and entropy, the Lewis acid–base constants, and the transition temperatures of the PS-P4VP copolymer. (3) Results: The application of the thermal Hamieh model led to an accurate determination of the London dispersive surface energy of the copolymer that showed non-linear variations versus the temperature, highlighting the presence of two transition temperatures. It was observed that the Lewis acid–base parameters of the copolymer strongly depend on the temperature, and the Lewis base constant of the solid surface was shown to be higher than its acid constant. (4) Conclusions: An important effect of the temperature on the surface thermodynamic properties of PS-P4VP was proven and new surface correlations were determined.
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Alothman, Othman Y. "Processing and Characterization of High Density Polyethylene/Ethylene Vinyl Acetate Blends with Different VA Contents". Advances in Materials Science and Engineering 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/635693.
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Different series of high density Polyethylene/Ethylene Vinyl Acetate (HDPE/EVA) blends were prepared via melt blending in a corotating intermeshing twin screw extruder. The effects of VA percentage and EVA loading ratio on the thermal, rheological viscoelastic, mechanical, and fracture toughness of the blends were analyzed. The results showed that the addition of EVA to HDPE reduces the thermal, elastic, and viscoelastic properties of the blends. The microscopic examination of the fracture surface confirmed the ductile fracture of HDPE/EVA blends for all blend ratios and VA percentages. Increasing the EVA ratio and VA content caused a significant reduction in the blend crystallinity but had no significant effect on melting temperature. The complex viscosity increased with increasing the percentage of EVA due to the restriction of molecular mobility and reduction of free volume, induced by the addition of EVA. The storage modulus decreased with increasing the EVA ratio and temperature, while it increased with increasing the frequency. Young’s modulus, yield strength, and fracture strain decreased with increasing the EVA ratio. Similarly, the fracture toughness decreased proportional to the EVA percentage. Finally the results indicated that the VA content has significant effects on the mechanical, thermal, and dynamic properties of HDPE/EVA blends.
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Shen, Ming-Yuan, Chen-Feng Kuan, Hsu-Chiang Kuan, Chia-Hsun Chen, Jia-Hong Wang, Ming-Chuen Yip e Chin-Lung Chiang. "Preparation, Characterization, Thermal, and Flame-Retardant Properties of Green Silicon-Containing Epoxy/Functionalized Graphene Nanosheets Composites". Journal of Nanomaterials 2013 (2013): 1–10. http://dx.doi.org/10.1155/2013/747963.
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In this investigation, silane was grafted onto the surface of graphene nanosheets (GNSs) through free radical reactions, to form Si-O-Et functional groups that can undergo the sol-gel reaction. To improve the compatibility between the polymer matrix and the fillers, epoxy monomer was modified using a silane coupling agent; then, the functionalized GNSs were added to the modified epoxy to improve the thermal stability and strengthen the flame-retardant character of the composites. High-resolution X-ray photoelectron spectrometry reveals that when the double bonds in VTES are grafted to the surfaces of GNSs. Solid-state 29Si nuclear magnetic resonance presents that the distribution of the signal associated with the T3structure is wide and significant, indicating that the functionalization reaction of the silicone in the modified epoxy and VTES-GNSs increases the network-like character of the structures. Thermal gravimetric analysis, the integral procedure decomposition temperature, and limiting oxygen index demonstrate that the GNSs composites that contained silicon had a higher thermal stability and stronger flame-retardant character than pure epoxy. The dynamic storage modulus of all of the m-GNSs containing composites was significantly higher than that of the control epoxy, and the modulus of the composites increased with the concentration of m-GNSs.
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Bahk, Je-Hyeong, Oluwasegun Isaac Akinboye, Vamsi Krishna Reddy Kondapalli e Vesselin Shanov. "(Invited) Electron Transport in Nanocarbon Networks for Energy Conversion and Storage Applications". ECS Meeting Abstracts MA2024-01, n.º 7 (9 de agosto de 2024): 792. http://dx.doi.org/10.1149/ma2024-017792mtgabs.
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Carbon nanostructures have attracted great attention in recent years as novel electrode materials in batteries with increased capacity and conductivity as well as enhanced material stability. In these nanostructures, nanocarbons such as carbon nanotubes and graphene nanoplatelets are interconnected to construct their three-dimensional networks around the host materials for Li deposition. This work focuses on the study of electron transport phenomena in these nanocarbon networks with two model material systems: (1) single-walled carbon nanotube (SWCNT) networks co-embedded with silica microparticles (Fig. (a)), and (2) free-standing three-dimensional graphene (3DG) structures with polymeric surface modifications (Fig. (b)). We characterize the materials for electrical conductivity and thermopower with varying material contents in the composites to reveal several key factors determining their energy-dependent carrier transport characteristics. It is found that in these three-dimensional nanocarbon networks, carrier tunneling at the junctions between nanocarbons along with the network morphology predominantly determines the transport properties. Simultaneous increase in electrical conductivity and thermopower is achieved for SWCNT networks co-embedded with silica microparticles by increasing silica content up to 40 w.t.% at a fixed CNT content. The enhanced electron transport is attributed to the reduced junction distances due to the intimate network formation on the surface of silica particles with a polymer binder. Our transport theory based on the Landauer formalism for junction tunneling reveals that the junction modification with polymer can alter the potential barrier heights for both electrons and holes at the junction to significantly change the transport properties of the composite. Doping of nanocarbons is also investigated for their impacts on the junction transport and the geometric factor of the networks. Finally, we also investigate the use of these carbon nanostructures in solid-state thermoelectric (TE) energy harvesters and ionic TE capacitors to harvest thermal energy from temperature gradients and fluctuations. Figure 1
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Johan, Ummie Umaiera Mohd, Raja Noor Zaliha Raja Abd Rahman, Nor Hafizah Ahmad Kamarudin, Wahhida Latip e Mohd Shukuri Mohamad Ali. "Immobilization of Hyperthermostable Carboxylesterase EstD9 from Anoxybacillus geothermalis D9 onto Polymer Material and Its Physicochemical Properties". Polymers 15, n.º 6 (9 de março de 2023): 1361. http://dx.doi.org/10.3390/polym15061361.
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Carboxylesterase has much to offer in the context of environmentally friendly and sustainable alternatives. However, due to the unstable properties of the enzyme in its free state, its application is severely limited. The present study aimed to immobilize hyperthermostable carboxylesterase from Anoxybacillus geothermalis D9 with improved stability and reusability. In this study, Seplite LX120 was chosen as the matrix for immobilizing EstD9 by adsorption. Fourier-transform infrared (FT-IR) spectroscopy verified the binding of EstD9 to the support. According to SEM imaging, the support surface was densely covered with the enzyme, indicating successful enzyme immobilization. BET analysis of the adsorption isotherm revealed reduction of the total surface area and pore volume of the Seplite LX120 after immobilization. The immobilized EstD9 showed broad thermal stability (10–100 °C) and pH tolerance (pH 6–9), with optimal temperature and pH of 80 °C and pH 7, respectively. Additionally, the immobilized EstD9 demonstrated improved stability towards a variety of 25% (v/v) organic solvents, with acetonitrile exhibiting the highest relative activity (281.04%). The bound enzyme exhibited better storage stability than the free enzyme, with more than 70% of residual activity being maintained over 11 weeks. Through immobilization, EstD9 can be reused for up to seven cycles. This study demonstrates the improvement of the operational stability and properties of the immobilized enzyme for better practical applications.
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Cristoforides, P., R. Amaral, L. G. May, M. A. Bottino e L. F. Valandro. "Composite Resin to Yttria Stabilized Tetragonal Zirconia Polycrystal Bonding: Comparison of Repair Methods". Operative Dentistry 37, n.º 3 (1 de maio de 2012): 263–71. http://dx.doi.org/10.2341/11-193-l.
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SUMMARY Purpose The purpose of the current study was to evaluate different approaches for bonding composite to the surface of yttria stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics. Methods One hundred Y-TZP blocks were embedded in acrylic resin, had the free surface polished, and were randomly divided into 10 groups (n=10). The tested repair approaches included four surface treatments: tribochemical silica coating (TBS), methacryloxydecyldihidrogenphosphate (MDP)–containing primer/silane, sandblasting, and metal/zirconia primer. Alcohol cleaning was used as a “no treatment” control. Surface treatment was followed by the application (or lack thereof) of an MDP-containing resin cement liner. Subsequently, a composite resin was applied to the ceramic surface using a cylindrical mold (4-mm diameter). After aging for 60 days in water storage, including 6000 thermal cycles, the specimens were submitted to a shear test. Analysis of variance and the Tukey test were used for statistical analyses (α=0.05). Results Surface treatment was a statistically significant factor (F=85.42; p<0.0001). The application of the MDP-containing liner had no effect on bond strength (p=0.1017). TBS was the only treatment that had a significantly positive effect on bond strength after aging. Conclusion Considering the evaluated approaches, TBS seems to be the best surface treatment for Y-TZP composite repairs. The use of an MDP-containing liner between the composite and Y-TZP surfaces is not effective.
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Alami, Abdul Hai, Kamilia Aokal, Mhd Adel Assad, Di Zhang, Hussain Alawadhi e Bilal Rajab. "One-step synthesis and deposition of few-layer graphene via facile, dry ball-free milling". MRS Advances 2, n.º 15 (2017): 847–56. http://dx.doi.org/10.1557/adv.2017.245.
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ABSTRACTGraphene is a 2-D carbon material showing considerable prominence in a wide range of optoelectronics, energy storage, thermal and mechanical applications. However, due to its unique features which are typically associated with difficulty in handling (ultra-thin thickness and hydrophobic surface, to name a few), synthesis and subsequent deposition processes are thus critical to the material properties of the prepared graphene films. While existing synthesis approaches such as chemical vapor deposition and epitaxial growth can grow graphene with high degree of order, the costly high temperature and/or high vacuum process prohibit the widespread usage, and the subsequent graphene transfer from the growth substrates for deposition proves to be challenging. Herein, a low-cost one-step synthesis and deposition approach for preparing few-layer graphene (FLG) on flexible copper substrates based on dry ball-free milling of graphite powder is proposed. Different from previous reports, copper substrates are inserted into the milling crucible, thus accomplishing simultaneous synthesis and deposition of FLG and eliminating further deposition step. Furthermore, while all previously reported high energy milling processes involve using balls of various sizes, we adopt a ball-free milling process relying only on centrifugal forces, which significantly reduces the surface damage of the deposition substrates. Sample characterization indicates that the process yields FLG deposited uniformly across all tested specimens. Consequently, this work takes graphene synthesis and deposition a step closer to full automation with simple and low-cost process.
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Tsujimoto, A., WW Barkmeier, T. Takamizawa, TM Wilwerding, MA Latta e M. Miyazaki. "Interfacial Characteristics and Bond Durability of Universal Adhesive to Various Substrates". Operative Dentistry 42, n.º 2 (1 de março de 2017): E59—E70. http://dx.doi.org/10.2341/15-353-l.
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SUMMARY Objective: This study investigated the interfacial characteristics and bond durability of universal adhesives to various substrates. Methods and Materials: Two universal adhesives were used: 1) Scotchbond Universal and 2) G-Premio Bond. The substrates used were bovine enamel and dentin with or without phosphoric acid etching, resin composite, lithium disilicate and leucite-reinforced glass ceramics, zirconia, and metal alloys. The surface free energy and the parameters of various substrates and of substrates treated by adhesive after light irradiation were determined by measuring the contact angles of three test liquids. Resin composite was bonded to the various substrates to determine shear bond strength after 24 hours water storage and 10,000 thermal cycles. A one-way analysis of variance (ANOVA) and the Tukey post hoc test were used for the surface free energy data, and a two-way ANOVA and the Tukey post hoc test were used for analysis of shear bond strength data (α=0.05). Results: The interfacial characteristics of the various substrates show significant differences depending on the type of substrate, but the interfacial characteristics of substrate treated by adhesive after light irradiation did not show any significant differences regardless of the substrate used. The bond durability of two universal adhesives to various substrates differs depending on the type of substrate and the adhesive. Conclusions: The results of this study suggest that universal adhesives modify the interfacial characteristics of a wide range of substrates and create a consistent surface, but the bond durability of universal adhesive to various substrates differs depending on the type of substrate and the adhesive.
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Kirchner-Burles, Charlie Rodney, Michael Johnson, Mark Buckwell, Gareth Hinds, Paul Robert Shearing, Rhodri Jervis e James B. Robinson. "Investigating Low Temperature Degradation and Its Impact on the Performance and Safety of Lithium-Ion Batteries". ECS Meeting Abstracts MA2024-02, n.º 4 (22 de novembro de 2024): 512. https://doi.org/10.1149/ma2024-024512mtgabs.
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Lithium-ion batteries are at the forefront of facilitating the modern-day industrial revolution: a transition from petrochemical energy storage to specialised carbon-free energy storage. Batteries hold a crucial role in storing energy generated by renewables outside of peak energy demands, whilst also enabling an extended portable energy supply for applications such as electronic devices, aerospace applications and electric vehicles. Increasing the energy densities of our batteries is one of the main avenues these technologies are taking to ensure the demands of the green transition are met. In recent years, numerous high-profile failures of lithium-ion batteries have been reported1, contributing to wider concerns about the safety of high energy density cells. Inadequate management of such systems can be costly for both human health and financial damages. To accommodate these more energy-dense cells, manufacturers need to provide better assurances in safe cell operations. Apprehensions in cell safety can mainly be attributed to a cell’s ability to enter thermal runaway, a process that is most often caused by an internal short circuit (ISC). Such an event can be triggered by three different modes of abuse: thermal, mechanical, and electrical. At the anode, metallic lithium can precipitate onto the surface via three main conditions: overcharge, high charging currents, and low charging temperatures. Each of which creates a saturation of intercalated lithium-ions in the crystallographic active sites near the anode surface. This lowers the anodes surface potential until it is sufficiently low enough for lithium plating to occur. This work investigates cell function at low temperatures and how the resulting degradation affects their response to abusive conditions. Various ageing regimes were applied to a set of commercial lithium-ion cells and, by monitoring their electrochemical behaviour, carrying out ex-situ characterisation of the aged negative electrodes, and employing X-ray computed tomography (CT), this work evaluates the decline in performance observed at low temperatures. Subsequent accelerated rate calorimetry (ARC) and operando ultra-high-speed synchrotron tomography studies highlight the diminished thermal stability these aged cells possess as the states of degradation become more advanced and reveal the mechanisms through which failure occurs. These findings demonstrate why improved cell architecture and real-time management systems are necessary to realise commercial success in future battery applications. Figure 1
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Vranić, Edina, Odon Planinšek, Andrijana Tivadar, Sabira Hadžović e Stanko Srčič. "Physico-Chemical Characterisation Of Different Clindamycin Phosphate Samples". Bosnian Journal of Basic Medical Sciences 7, n.º 2 (20 de maio de 2007): 182–89. http://dx.doi.org/10.17305/bjbms.2007.3078.
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For the majority of the pharmaceutical dosage forms, the substances that are used maintain solid state under the standard storage conditions, i.e. powders. The interactions of pharmaceutical powders (active ingredient(s) and excipients) with liquids and vapors (particularly aqueous solutions and their vapors) occur almost always during the production process. From the physical point of view, the interactions among individual components may differ from the expected because chemically identical substances obtained from different producers vary very much. These differences influence either the production process and/or the pharmaceutical form properties. In order to overcome these problems it is necessary to establish a control over the physico-chemical properties of the used materials.The aim of this work was to determine physico-chemical properties of three powder clindamycin phosphate samples (labeled as sample S1, S2 and S3) acquired through different suppliers. All the analysis were made for the purpose of establishing possible differences among the tested samples that showed variable physical stability in the solution: recrystallization of the S3 sample in the aqueous solution has been established during storage under standard conditions. On the basis of the obtained data it was possible to recognize the differences among the tested clindamycin phosphate samples and to explain the anomalous behavior of one sample.The surface free energy components for the investigated clindamycin phosphate samples were determined using Wu and Goodvan Oss method. The investigated clindamycin phosphate samples exhibit certain differences in surface free energy values as well as in surface morphology and thermal behavior. Comparison of γ+ and γ- values leads to the conclusion that all three clindamycin phosphate samples perform as monopolar, more electron acceptors, i.e. Lewis acids. However, an important difference exists between samples S1 and S2 on one and S3 on the other side. Sample S3 exhibits stronger acidic behavior, what could be connected with its recrystallization during the storage.The samples S1, S2 and S3 have different melting points e.g. “onset” temperatures. When the melting points move towards 200oC, the width of the “onset” temperature peak is especially important. In the case of wider peak, the potential for recrystallization seems to be higher.According to the stated, the sample S1 would be the “sample of choice” for the formulation of the stable pharmaceutical dosage form and has not shown any recrystallization tendencies during the storage period.
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Botticelli, Simone, Giovanni La Penna, Germano Nobili, Giancarlo Rossi, Francesco Stellato e Silvia Morante. "Modelling Protein Plasticity: The Example of Frataxin and Its Variants". Molecules 27, n.º 6 (17 de março de 2022): 1955. http://dx.doi.org/10.3390/molecules27061955.
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Frataxin (FXN) is a protein involved in storage and delivery of iron in the mitochondria. Single-point mutations in the FXN gene lead to reduced production of functional frataxin, with the consequent dyshomeostasis of iron. FXN variants are at the basis of neurological impairment (the Friedreich’s ataxia) and several types of cancer. By using altruistic metadynamics in conjunction with the maximal constrained entropy principle, we estimate the change of free energy in the protein unfolding of frataxin and of some of its pathological mutants. The sampled configurations highlight differences between the wild-type and mutated sequences in the stability of the folded state. In partial agreement with thermodynamic experiments, where most of the analyzed variants are characterized by lower thermal stability compared to wild type, the D104G variant is found with a stability comparable to the wild-type sequence and a lower water-accessible surface area. These observations, obtained with the new approach we propose in our work, point to a functional switch, affected by single-point mutations, of frataxin from iron storage to iron release. The method is suitable to investigate wide structural changes in proteins in general, after a proper tuning of the chosen collective variable used to perform the transition.
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Askadskii, Andrey, Tatyana Matseevich e Andrey Matseevich. "Newest models and calculation schemes for quantitative analysis of physical properties of polymers". MATEC Web of Conferences 251 (2018): 01043. http://dx.doi.org/10.1051/matecconf/201825101043.
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New models and calculation schemes have been developed for the quantitative analysis of a number of physical properties of polymers — glass transition temperature, flow temperature of polymer nanocomposites, thermal conductivity, boiling point of polymer solutions, water absorption and water permeability of polymers and nanocomposites, strength, viscosity, storage and losses moduli, refractive index and dielectric constant. All calculation schemes are based on the structure of linear and cross-linked polymers; their degree of crystallinity, free volume, the effect of temperature, the composition of copolymers and homogeneous mixtures of polymers, the concentration of nanoparticles, their shape, size distribution, orientation angles, the structure of polar groups grafted to the surface of nanoparticles, the energy of intermolecular interactions are taken into account. All computational schemes are computerized and allow calculations to be carried out automatically after the introduction of the structure of a repeating unit of polymer unit into the computer, as well as the shape and size of nanofillers.
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Bianco, Simona, Muhammad Hasan, Ashfaq Ahmad, Sarah-Jane Richards, Bart Dietrich, Matthew Wallace, Qiao Tang, Andrew J. Smith, Matthew I. Gibson e Dave J. Adams. "Mechanical release of homogenous proteins from supramolecular gels". Nature 631, n.º 8021 (17 de julho de 2024): 544–48. http://dx.doi.org/10.1038/s41586-024-07580-0.
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AbstractA long-standing challenge is how to formulate proteins and vaccines to retain function during storage and transport and to remove the burdens of cold-chain management. Any solution must be practical to use, with the protein being released or applied using clinically relevant triggers. Advanced biologic therapies are distributed cold, using substantial energy, limiting equitable distribution in low-resource countries and placing responsibility on the user for correct storage and handling. Cold-chain management is the best solution at present for protein transport but requires substantial infrastructure and energy. For example, in research laboratories, a single freezer at −80 °C consumes as much energy per day as a small household1. Of biological (protein or cell) therapies and all vaccines, 75% require cold-chain management; the cost of cold-chain management in clinical trials has increased by about 20% since 2015, reflecting this complexity. Bespoke formulations and excipients are now required, with trehalose2, sucrose or polymers3 widely used, which stabilize proteins by replacing surface water molecules and thereby make denaturation thermodynamically less likely; this has enabled both freeze-dried proteins and frozen proteins. For example, the human papilloma virus vaccine requires aluminium salt adjuvants to function, but these render it unstable against freeze–thaw4, leading to a very complex and expensive supply chain. Other ideas involve ensilication5 and chemical modification of proteins6. In short, protein stabilization is a challenge with no universal solution7,8. Here we designed a stiff hydrogel that stabilizes proteins against thermal denaturation even at 50 °C, and that can, unlike present technologies, deliver pure, excipient-free protein by mechanically releasing it from a syringe. Macromolecules can be loaded at up to 10 wt% without affecting the mechanism of release. This unique stabilization and excipient-free release synergy offers a practical, scalable and versatile solution to enable the low-cost, cold-chain-free and equitable delivery of therapies worldwide.
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Ouchi, H., T. Takamizawa, K. Tsubota, A. Tsujimoto, A. Imai, WW Barkmeier, MA Latta e M. Miyazaki. "The Effects of Aluminablasting on Bond Durability Between Universal Adhesives and Tooth Substrate". Operative Dentistry 45, n.º 2 (1 de março de 2020): 196–208. http://dx.doi.org/10.2341/18-170-l.
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SUMMARY The aim of this study was to determine the effect of aluminablasting on the bond durability of universal adhesives and adherent surface characteristics. Adhese Universal (Ivoclar Vivadent), All-Bond Universal (Bisco), Bondmer Lightless (Tokuyama Dental), G-Premio Bond (GC), and Scotchbond Universal (3M ESPE) were used in self-etch mode. The prepared bovine enamel and dentin specimens were divided into two groups based on whether they received an aluminablasting prior to application of the universal adhesives. The resin composite bonded specimens were stored in distilled water at 37°C for 24 hours, following which the shear bond strength (SBS) of half of the specimens was measured (24-hour group). The other half was subjected to 30,000 thermal cycles between 5 and 55°C before SBS measurement (TC group). Surface roughness (Ra) and surface free energy (SFE) of the adherent surfaces were also measured, and scanning electron microscopy observation and scanning electron microscopy/energy-dispersive X-ray analysis were carried out. Most of the adhesives did not show any significant differences in enamel SBS values between the two pretreatment groups, regardless of the storage condition. However, the dentin SBS values were significantly lower in specimens that underwent aluminablasting compared with those that did not, irrespective of their storage conditions. Significantly higher Ra and SFE values were observed in the enamel and dentin of specimens that underwent aluminablasting. Although aluminablasting increased the Ra and SFE values of enamel and dentin, its effect on the SBS value was dependent on the tooth substrate. In addition to C, O, Na, Mg, P, and Ca, the element Al was detected in the enamel and dentin of samples that had undergone aluminablasting. These results suggest that although aluminablasting of the tooth surface is thought to be effective for modification of the adherent surface, it may not enhance enamel bond performance and may also adversely affect the dentin bond effectiveness of the universal adhesives.
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Pergal, Marija, Sanja Ostojic, Milos Steinhart, Ivan Stefanovic, Lato Pezo e Milena Spírková. "Nanocomposites made from thermoplastic linear poly(urethane-siloxane) and organoclay: Composition impact on the properties". Journal of the Serbian Chemical Society, n.º 00 (2022): 36. http://dx.doi.org/10.2298/jsc220223036p.
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Thermoplastic poly(urethane-siloxane)/organoclay nanocomposites (TPU NCs) with different hard segment content (20-55 wt.%) were prepared by in situ polymerization in the presence of organically modified montmorillonite as a nanofiller (Cloisite 30B; 1 wt.%). Hydroxyl-terminated ethoxypropyl-poly(dime-thylsiloxane) was used as soft segment, while 4,4'-methylenediphenyl diisocyanate and 1,4-butanediol were the hard segment components. The study of the influence of the hard segment content on the functional properties of TPU NCs was performed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffract-tometry (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic mechanical thermal analyses (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), water contact angle and water absorption tests. The results revealed that TPU NCs with increasing hard segment content exhibit higher values of degree of microphase separation, melting temperature of the hard segments, degree of crystallinity, storage modulus (except for TPU NC-55), but lower thermal stability and hydrophobicity. TPU NC films were hydrophobic and their free surface energy was in the range from 17.7 to 24.9 mJ m-2. This work highlights how the composition of TPU NCs would mani-pulate their functional properties and provide an additional composition handle for designing advanced TPU NC materials for special biomedical applications.
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Choi, Moonhyun, Maeng Gi Kim, Kevin Injoe Jung, Tae Hee Lee, Miran Ha, Woochan Hyung, Hyun Wook Jung e Seung Man Noh. "Reactivity and Curing Efficiency of Isocyanate Cross-Linkers with Imidazole-Based Blocking Agents for Low-Temperature Curing of Automotive Clearcoats". Coatings 10, n.º 10 (13 de outubro de 2020): 974. http://dx.doi.org/10.3390/coatings10100974.
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For the application of low-temperature curing on automotive clearcoats, isocyanate cross-linkers blocked with imidazole derivatives were newly synthesized. The effect of the alkyl groups in the imidazole derivatives on the deblocking behavior and curing kinetics was investigated. The free isocyanate groups exposed by the deblocking of imidazole-based blocking agents were monitored by real-time Fourier-transform infrared spectroscopy. The bond dissociation energy, activation energy of deblocking, and H–N distance were interpreted through density functional theory simulation of various imidazole-based blocked isocyanates. To evaluate their applicability to automotive clearcoats, the synthesized imidazole-based blocked isocyanates were mixed with a polyol binder containing hydroxyl groups, and the clearcoat samples were cured at relatively low curing temperatures (100, 110, and 120 °C). The real-time storage modulus was measured using a rotational rheometer to elucidate the thermal curing dynamics by the blocking agents. In addition, the surface hardness of the cured clearcoat layers, which is affected by the chemical structure of the imidazole derivatives, was evaluated by nanoindentation test. In-depth analyses of the deblocking behaviors and thermal curing properties of clearcoats using imidazole-based blocked isocyanates demonstrated that the newly developed coating system could be suitably applied for the development of low-temperature curing technology.