Search Results (150)

Atmospheric climate science lacks the capacity to integrate thermodynamics with the gravitational potential of air in a classical quantum theory. To what extent can we identify Carnot’s ideal heat engine cycle in reversible isothermal and isentropic phases between dual temperatures partitioning heat flow with coupled work processes in the atmosphere? Using statistical action mechanics to describe Carnot’s cycle, the maximum rate of work possible can be integrated for the working gases as equal to variations in the absolute Gibbs energy, estimated as sustaining field quanta consistent with Carnot’s definition of heat as caloric. His treatise of 1824 even gave equations expressing work potential as a function of differences in temperature and the logarithm of the change in density and volume. Second, Carnot’s mechanical principle of cooling caused by gas dilation or warming by compression can be applied to tropospheric heat–work cycles in anticyclones and cyclones. Third, the virial theorem of Lagrange and Clausius based on least action predicts a more accurate temperature gradient with altitude near 6.5–6.9 °C per km, requiring that the Gibbs rotational quantum energies of gas molecules exchange reversibly with gravitational potential. This predicts a diminished role for the radiative transfer of energy from the atmosphere to the surface, in contrast to the Trenberth global radiative budget of ≈330 watts per square metre as downwelling radiation. The spectral absorptivity of greenhouse gas for surface radiation into the troposphere enables thermal recycling, sustaining air masses in Lagrangian action. This obviates the current paradigm of cooling with altitude by adiabatic expansion. The virial-action theorem must also control non-reversible heat–work Carnot cycles, with turbulent friction raising the surface temperature. Dissipative surface warming raises the surface pressure by heating, sustaining the weight of the atmosphere to varying altitudes according to latitude and seasonal angles of insolation. New predictions for experimental testing are now emerging from this virial-action hypothesis for climate, linking vortical energy potential with convective and turbulent exchanges of work and heat, proposed as the efficient cause setting the thermal temperature of surface materials. Full article

The spray evaporation process in the boiler desuperheater involves complex droplet behaviors and fluid–thermal coupling, and its temperature distribution characteristics greatly affect the performance and safety of industrial processes. To better understand the process characteristics and develop the optimal desuperheater design, computational fluid dynamics (CFDs) was applied to numerically investigate the flow and thermal characteristics. The Eulerian–Lagrangian approach was used to describe the two-phase flow characteristics. Both primary and secondary droplet breakup, the coupling effect of gas–liquid and stochastic collision and coalescence of droplets were considered in the model. The plain-orifice atomizer model was applied to simulate the atomization process. The numerical model was validated with the plant data. The spray tube structure was found to greatly affect the flow pattern, resulting in the uneven velocity distribution, significant temperature difference, and local reverse flow downstream of the orifices. The velocity and temperature distributions tend to be more uniform due to the complete evaporation and turbulent mixing. Smaller orifices are beneficial for generating smaller-sized droplets, thereby promoting the mass and heat transfer between the steam and droplets. Under the same operating conditions, the desuperheating range of cases with 21, 15, and 9 orifices is 33.7 K, 32.0 K, and 29.8 K, respectively, indicating that the desuperheater with more orifices (i.e., with smaller orifices) shows better desuperheating ability. Additionally, a venturi-type desuperheater was numerically studied and compared with the straight liner case. By contrast, discernible differences in velocity and temperature distribution characteristics can be observed in the venturi case. The desuperheating range of the venturi and straight liner cases is 38.1 K and 35.4 K, respectively. The velocity acceleration through the venturi throat facilitates the droplet breakup and improves mixing, thereby achieving better desuperheating ability and temperature uniformity. Based on the investigation of the spray evaporation process, the complex droplet behaviors and fluid–thermal coupling characteristics in an industrial boiler desuperheater under high temperature and high pressure can be better understood, and effective guidance for the process and design optimizations can be provided. Full article

The separation of particles smaller than 1 µm either by composition or by size is still a challenge. For the separation of SiO₂ and SnO₂, the creation of a selective separation feature and the specific adsorption of salts and surfactants were investigated. The adsorption of various salts, e.g., AlCl₃, ZnCl₂, MnCl₂ and MgCl₂ were therefore analyzed, and the necessary concentration for the charge reversal of the material was determined. It was noticed that the investigated materials differ in their isoelectric point (IEP) and therefore in their adsorption behavior because only ZnCl₂ and MgCl₂ are suitable for a charge reversal of both metal oxides. The phase transfer of the pure material at different pH values with ZnCl₂ or MgCl₂ and sodium dodecyl sulfate (SDS) revealed that the adsorption behavior of the particle has an influence on the phase transfer. As a result, the phase transfer of SiO₂ is pH dependent, whereas the phase transfer of SnO₂ operates over a wider pH range. This allowed the separation of SiO₂ and SnO₂ to be controlled by the salt and surfactant concentration as well as pH. The separation of SiO₂ and SnO₂ was investigated for various parameters such as salt and surfactant concentration, particle concentration and composition of the mixture. Also, pH 8, where a selective phase transfer for SiO₂ occurs, and pH 6, where the greatest difference between the materials exists, were also investigated. By comparing the parameters, it was found that the combination of ZnCl₂/SDS and MgCl₂/SDS enables a selective separation of the materials. Furthermore, it was also found that the concentration of SDS has a significant effect on the separation, as the formation of a bilayer structure is important for the separation, and therefore, higher SDS concentrations are required at higher particle concentrations to increase the separation efficiency. Full article

4H-silicon carbide (4H-SiC) is a cornerstone for next-generation optoelectronic and power devices owing to its unparalleled thermal, electrical, and optical properties. However, its chemical inertness and low dopant diffusivity for most dopants have historically impeded effective doping. This study unveils a transformative laser-assisted boron doping technique for n-type 4H-SiC, employing a pulsed Nd:YAG laser (λ = 1064 nm) with a liquid-phase boron precursor. By leveraging a heat-transfer model to optimize laser process parameters, we achieved dopant incorporation while preserving the crystalline integrity of the substrate. A novel optical characterization framework was developed to probe laser-induced alterations in the optical constants—refraction index ($\mathrm{n}$) and attenuation index ($\mathrm{k}$)—across the MIDIR spectrum (λ = 3–5 µm). The optical properties pre- and post-laser doping were measured using Fourier-transform infrared spectrometry, and the corresponding complex refraction indices were extracted by solving a coupled system of nonlinear equations derived from single- and multi-layer absorption models. These models accounted for the angular dependence in the incident beam, enabling a more accurate determination of $\mathrm{n}$ and $\mathrm{k}$ values than conventional normal-incidence methods. Our findings indicate the formation of a boron-acceptor energy level at 0.29 eV above the 4H-SiC valence band, which corresponds to λ = 4.3 µm. This impurity level modulated the optical response of 4H-SiC, revealing a reduction in the refraction index from 2.857 (as-received) to 2.485 (doped) at λ = 4.3 µm. Structural characterization using Raman spectroscopy confirmed the retention of crystalline integrity post-doping, while secondary ion mass spectrometry exhibited a peak boron concentration of 1.29 × 10¹⁹ cm⁻³ and a junction depth of 450 nm. The laser-fabricated p–n junction diode demonstrated a reverse-breakdown voltage of 1668 V. These results validate the efficacy of laser doping in enabling MIDIR tunability through optical modulation and functional device fabrication in 4H-SiC. The absorption models and doping methodology together offer a comprehensive platform for paving the way for transformative advances in optoelectronics and infrared materials engineering. Full article

Two novel cyclometalated platinum(II) complexes based on 2-phenylpyridine (ppy) and 2,4-difluorophenylpyridine (dfppy) ligands in combination with a benzoylthiourea (4-(decyloxy)-N-((4-(decyloxy)phenyl)carbamothioyl)benzamide, BTU) functionalized with decyloxy alkyl chains as auxiliary ligands were synthesized and characterized for their mechanochromic and photophysical properties. Structural characterization was achieved through IR and NMR spectroscopy, single-crystal X-ray diffraction, and TD-DFT calculations. Both complexes exhibit significant photoluminescence with quantum yields up to 28.3% in a 1% PMMA film. The transitions in solution-phase spectra were assigned to mixed metal-to-ligand (MLCT) and intraligand (ILCT) charge–transfer characteristics. Temperature-dependent studies and thermal analyses confirm reversible phase transitions without mesomorphic behavior despite the presence of the two long alkyl chains. Both complexes displayed reversible mechanochromic and solvatochromic luminescence, with a change in emission color from green to red-orange emissions upon grinding and solvent treatment or heating at 80 °C. Full article

The synchronization of chaotic systems is a fundamental phenomenon in nonlinear dynamics. Most known synchronization techniques suggest that the trajectories of coupled systems converge at an exponential rate. However, this requires transferring a substantial data array to achieve complete synchronization between the master and slave oscillators. A recently developed approach, called time-reversible synchronization, has been shown to accelerate the convergence of trajectories. This approach is based on the special properties of time-symmetric integration. This technique allows for achieving the complete synchronization of discrete chaotic systems at a superexponential rate. However, the validity of time-reversible synchronization between discrete and continuous systems has remained unproven. In the current study, we expand the applicability of fast time-reversible synchronization to a case of digital and analog chaotic systems. A circuit implementation of the Sprott Case B was taken as an analog chaotic oscillator. Given that real physical systems possess more complicated dynamics than simplified models, analog system reidentification was performed to achieve a reasonable relevance between a discrete model and the circuit. The result of this study provides strong experimental evidence of fast time-reversible synchronization between analog and digital chaotic systems. This finding opens broad possibilities in reconstructing the phase dynamics of partially observed chaotic systems. Utilizing minimal datasets in such possible applications as chaotic communication, sensing, and system identification is a notable development of this research. Full article

This paper highlights the transition from traditional procurement systems to the newly introduced eProcurement system in Saudi Arabia, emphasizing the differences and improvements and their implications for sustainable development. The new system aims to enhance transparency, clarify purchasing methodologies, and build trust with the government through effective governance of government purchases and tender management. Guided by Royal Decree, this system aligns with the eProcurement Program to transition into digital processes for proficient bids and government purchases, contributing to more efficient and sustainable procurement practices. While some public agencies have attempted to adopt the new model contract for executing construction projects, it has faced challenges due to its lack of alignment with the best practices and sustainability considerations. The authors argue that many large projects remain exempt from this system, which poses obstacles to achieving the goals of sustainable economic development. The objective of this paper is to explore the newly revised Saudi procurement contracts in comparison with traditional public works contracts, with a focus on how they address socio-economic and environmental sustainability. The research provides an overview of various aspects related to public works contracts (PWCs) in Saudi Arabia, including framework agreements, online reverse auctions, industry localization, knowledge transfer, traditional lump sum contracts, two-phase tenders, and construction project competitions, analyzing their alignment with sustainable development goals. There is limited literature on recent models introduced by the Saudi government, but there are extensive resources on general contract law principles and international public policy. This foundation helps with understanding the legal aspects of public works contracts in Saudi Arabia, their alignment with international standards, and their implications for fostering sustainable development. By examining the literature, researchers can gain insights into the legal and policy framework governing public works contracts in Saudi Arabia and their role in promoting sustainability. The importance of this research lies in its comparative analysis, offering valuable insights into the evolution of procurement practices in Saudi Arabia and their contribution to sustainable socio-economic growth. Full article

Amphiphilic block copolymers are essential for developing advanced polymer nanomaterials with applications in bioimaging, drug delivery, and nanoreactors. In this study, we successfully synthesized functional block copolymer assemblies at high concentrations through redox-initiated reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization of 2-(acetoacetoxy)ethyl methacrylate (AEMA), a β-ketoester functional monomer. Utilizing a redox initiation system at 50 °C, we produced poly(poly(ethylene glycol) methyl ether methacrylate)-b-PAEMA (PPEGMA_n-PAEMA_m). Kinetic studies demonstrated rapid monomer conversion exceeding 95% within 30 min, with distinct polymerization phases driven by micelle formation and monomer depletion. Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) revealed the formation of diverse morphologies, including worm-like, vesicular structures, and spherical micelles, depending on the macro-CTA molecular weight and monomer concentration. Additionally, post-polymerization modification with aggregation-induced emission (AIE) luminogens, such as 1-(4-aminophenyl)-1,2,2-tristyrene (TPE-NH₂), resulted in AIE-active polymer assemblies exhibiting strong fluorescence in aqueous dispersions. These AIE-active polymer assemblies also exhibited good biocompatibility. These findings demonstrate the efficacy of redox-initiated RAFT emulsion polymerization in fabricating functional, scalable block copolymer assemblies with potential applications in the field of life sciences. Full article

The consumption of grape seed extracts is known for its contribution to animal and human health and is associated with its relevant procyanidin content. However, there is a little scientific unanimity whether these properties are due to the procyanidin content or to the length of their polymers. The main reason for this doubt is the technical difficulties related to their separation. Therefore, a preparative separation of grape seed extract was carried out using an integrated ultra/diafiltration procedure with membranes of 300, 30, 5, and 1 kDa molecular mass cut-offs, reverse osmosis and solid-phase extraction to obtain fractions of very high (>300 kDa), high (300–30 kDa), intermediate (30–5 kDa), low molecular mass (5–1 kDa), very-low-mass polar molecules and ions (<1 kDa), and very-low-mass dipole molecules (<1 kDa). Process parameters, mass transfer across the membranes and the quality of separation of each fraction are described and discussed in depth. A high degree of purification was achieved for the higher-molecular-mass fractions (>300, 300–30, and 30–5 kDa), as well as the big majority of procyanidin polymers and oligomers from very-low-molecular-mass species. All fractions were characterized for their procyanidin content by normal phase high-performance liquid chromatography coupled to a photodiode array detector (NP-HPLC-PAD). This analytical technique has shown for the first time that not only do oligomeric procyanidins elute at an increasing order of elution, but polymeric ones also do the same. Full article

Taking the cantilever rotor of a turbine engine as the research object, a dynamic and finite-element model of the cantilever rotor is established, and the effectiveness of the model is verified by the rotor test platform. The transfer function method is used to balance the rotor system under unbalanced excitation, and the experiments prove that the method adopted in this paper has a good balancing effect and effectively reduces the vibration of the unbalanced rotor. On this basis, the experimental tests and simulation analyses of the rotor vibration response under different unbalanced phases and difference combinations are carried out, and the influence of the unbalanced phase’s difference combinations on unbalance and dynamic balance is analyzed. The results show that the vibration response of the system decreases with the increase in the unbalanced phase difference combinations, and the amplitude of the vibration induced by the unbalance of the reverse combination is smaller than that of the in-phase combination. The work in this paper can provide a theoretical basis for the dynamic balance and vibration control of the flexible rotor of an aero-engine. Full article

Porous polymer membranes with highly interconnected open-cellular structure and high toughness are crucial for various application fields. Polymerized high internal phase emulsions (polyHIPEs), which usually exist as monoliths, possess the advantages of high porosity and good connectivity. However, it is difficult to prepare membranes due to brittleness and easy pulverization. Copolymerizing acrylate soft monomers can effectively improve the toughness of polyHIPEs, but it is easy to cause emulsion instability and pore collapse. In this paper, stable HIPEs with a high content of butyl acrylate (41.7 mol% to 75 mol% based on monomers) can be obtained by using a composite emulsifier (30 wt.% based on monomers) consisting of Span80/DDBSS (9/2 in molar ratio) and adding 0.12 mol·L⁻¹ CaCl₂ according to aqueous phase concentration. On this basis, polyHIPE membranes with high open-cellular extent and high toughness are firstly prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization. The addition of the RAFT agent significantly improves the mechanical properties of polyHIPE membranes without affecting open-cellular structure. The toughness of polyHIPE membranes prepared by RAFT polymerization is significantly enhanced compared with conventional free radical polymerization. When the molar ratio of butyl acrylate/styrene/divinylbenzene is 7/4/1, the polyHIPE membrane prepared by RAFT polymerization presents plastic deformation during the tensile test. The toughness modulus reaches 93.04 ± 12.28 kJ·m⁻³ while the open-cellular extent reaches 92.35%, and it also has excellent thermal stability. Full article

Semicarbazide (SEM), a metabolite of nitrofurazone (NFZ), is widely used to detect the illegal application of NFZ in crustaceans. The conventional detection method involves chemical derivatization combined with reversed-phase liquid chromatography–tandem mass spectrometry (RPLC-MS/MS), which is both complex and time-consuming. To address this limitation, a more efficient approach was developed for SEM detection. This study introduces a modified QuEChERS pretreatment method coupled with hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC-MS/MS) for detecting SEM in crustaceans. The proposed method is simple, fast, and highly accurate, making it universally applicable for SEM detection in crustaceans. Additionally, the method was applied to investigate NFZ metabolism in Macrobrachium rosenbergii with a kinetic model. The findings suggested a plausible mechanism for the absorption of NFZ and its subsequent transfer from meat to the shell. In conclusion, this study provides a simple and rapid technique for SEM detection in crustaceans with immense application value. Full article

This study investigates the stability and application of trithiocarbonate-based chain transfer agents (CTAs) in reversible addition–fragmentation chain transfer (RAFT) radical polymerization under harsh conditions. We evaluated the stability of 4-cyano-4-(2-carboxyethylthiothioxomethylthio) pentanoic acid (Rtt-17) and 4-cyano-4-(dodecylsulfanylthiocarbonyl) sulfanylpentanoic acid (Rtt-05) at 60 °C under basic conditions using ¹H NMR and UV–vis absorption spectra, showing that Rtt-05 is more stable than Rtt-17. The greater stability of Rtt-05 is attributed to the hydrophobic dodecyl group, which allows it to form micelles in water, thereby protecting the trithiocarbonate group from the surrounding aqueous phase. In contrast, hydrophilic Rtt-17, without long alkyl chains, cannot form micelles in water. Following the stability assessment, Rtt-17 and Rtt-05 were employed for RAFT polymerization of hydrophilic monomers, such as N,N-dimethylacrylamide (DMA) and 2-(methacryloyloxy)ethyl phosphorylcholine (MPC). DMA can dissolve in both water and organic solvents, and MPC can dissolve in water and polar solvents. Both CTAs successfully controlled the polymerization of DMA, producing polymers with narrow molecular weight distributions (M_w/M_n) less than 1.2. Also, Rtt-17 demonstrated effective control of MPC polymerization, yielding M_w/M_n values of around 1.2. However, during the polymerization of MPC, Rtt-05 failed to maintain control, resulting in a broad M_w/M_n (≥1.9). The inability of Rtt-05 to control MPC polymerization is due to the formation of micelles, which disrupts the interaction between the hydrophilic MPC propagating radicals and the trithiocarbonate group in the hydrophobic core of Rtt-05 micelles. The findings provide critical insights into designing CTAs for specific applications, particularly for biomedical and industrial uses of hydrophilic polymers, highlighting the potential for precise molecular weight control and tailored polymer properties. Full article

Background: N-succinimidyl-[¹⁸F]fluorobenzoate ([¹⁸F]SFB) is commonly prepared through a three-step procedure starting from [¹⁸F]fluoride ion. A number of methods for the single-step radiosynthesis of [¹⁸F]SFB have been introduced recently, including the radiofluorination of diaryliodonium salts and the Cu-mediated ¹⁸F-fluorination of pinacol aryl boronates and aryl tributyl stannanes, but they still have the drawbacks of lengthy product purification procedures. In the present work, two approaches for the direct labeling of [¹⁸F]SFB from diaryliodonium (DAI) salt (4) and pinacol aryl boronate (6) are evaluated, with a major focus on developing a fast and simple SPE-based purification procedure. Methods: DAI salt precursor 6 was labeled employing the common “minimalist” approach with a two-step reaction heating sequence. The Cu-mediated radiofluorination of 4 was accomplished using Bu₄NOTf as a phase transfer catalyst for the elution of [¹⁸F]fluoride, followed by radiofluorination in the same solvent. Several types of SPE cartridges were tested in the elution and SPE procedures. Results: The Cu-mediated ¹⁸F-fluorination of the pinacol aryl boronate precursor afforded a higher RCC of 56 ± 3% (n = 7), making it better suited for the one-pot synthesis of [¹⁸F]SFB. SPE-based purification was achieved using cation exchange and reverse-phase polymer resin cartridges, connected in series. In a full-batch test, [¹⁸F]SFB was obtained with an RCY of 30% (n. d. c.), RCP > 99%, A_m 96–155 GBq/µmol, and a synthesis time of ≤35 min. Conclusions: Compared to other published methods, [¹⁸F]SFB production via the Cu-mediated radiofluorination of pinacol aryl boronate precursor provides significant time and cost savings, coupled with an ease of implementation. Full article

The structural and electronic features of the stimuli-responsive supramolecular inter-ionic charge-transfer material containing electron accepting N-benzylyridinium-4-oxime cation (BPA4⁺) and electron donating hexacyanoferrate (II) are reported. The study of reversible stimuli-induced transformation between hydrated reddish-brown (BPA4)₄[Fe(CN)₆]·10H₂O and anhydrous blue (BPA4)₄[Fe(CN)₆] revealed the origin of observed hydrochromic behavior. The comparison of the crystal structures of decahydrate and anhydrous phase showed that subsequent exclusion/inclusion of lattice water molecules induces structural relocation of one BPA4⁺ that alter the donor-to-acceptor charge-transfer states, resulting in chromotropism seen as reversible reddish-brown to blue color changes. The decreased donor-acceptor distance in (BPA4)₄[Fe(CN)₆] enhanced charge-transfer interaction allowing charge separation via one-electron transfer, as evidenced by in-situ ESR and FTIR spectroscopies. The reversibility of hydrochromic behavior was demonstrated by in-situ HT-XRPD, hot-stage microscopic and in situ diffuse-reflectance spectroscopic analyses. The insight into electronic structural features was obtained with density functional theory calculations, employed to elucidate electronic structure for both compounds. The electrical properties of the phases during dehydration process were investigated by temperature-dependent impedance spectroscopy. Full article