Search Results (4,348)

In this work, we study the time-dependent behavior of quantum correlations of a system of an inverted oscillator governed by out-of-equilibrium dynamics using the well-known Schwinger–Keldysh formalism in the presence of quantum mechanical quench. Considering a generalized structure of a time-dependent Hamiltonian for an inverted oscillator system, we use the invariant operator method to obtain its eigenstate and continuous energy eigenvalues. Using the expression for the eigenstate, we further derive the most general expression for the generating function as well as the out-of-time-ordered correlators (OTOCs) for the given system using this formalism. Further, considering the time-dependent coupling and frequency of the quantum inverted oscillator characterized by quench parameters, we comment on the dynamical behavior, specifically the early, intermediate and late time-dependent features of the OTOC for the quenched quantum inverted oscillator. Next, we study a specific case, where the system of an inverted oscillator exhibits chaotic behavior by computing the quantum Lyapunov exponent from the time-dependent behavior of OTOCs in the presence of the given quench profile. Full article

Percarbonate (SPC) as a promising substitute for liquid H₂O₂ has many advantages in the application of in situ chemical oxidation (ISCO). Developing efficient, cost effective and environmentally friendly catalysts for SPC activation plays the key role in promoting the development of SPC-based ISCO. Herein, the walnut shell biomass was combined with ferric nitrate for the catalytic synthesis of Fe₃C@biochar composite (Fe₃C@WSB), which demonstrated high efficiency in activating SPC for the removal of diclofenac (DCF). The Fe₃C showed average crystallite size of 32.6 nm and the composite Fe₃C@WSB demonstrated strong adsorptivity. The prepared Fe₃C@WSB could activate both SPC and H₂O₂ with high efficiency at ca. pH 3 with extremely low leaching of iron, while in a weak acidic condition, higher efficiency of DCF removal was obtained in the Fe₃C@WSB/SPC process than in the Fe₃C@WSB/H₂O₂ process. Moreover, the Fe₃C@WSB/SPC and Fe₃C@WSB/H₂O₂ processes did not show significant differences when supplied with varying amounts of catalyst or oxidant, but the Fe₃C@WSB/SPC process exhibited stronger capability in dealing with relatively highly concentrated DCF solution. Based on quenching experiments and electron spin resonance (ESR) analysis, heterogeneous activation of SPC was assumed as the dominant route for DCF degradation, and both the oxidation by radicals, including •OH, •O₂⁻ and CO₃^•−, combined with electron transfer pathway contributed to DCF degradation in the Fe₃C@WSB/SPC process. The cycling experiment results also revealed the stability of Fe₃C@WSB. This work may cast some light on the development of efficient catalysts for the activation of SPC. Full article

Encapsulating Cs₄PbBr₆ quantum dots in silicon nano-sheets not only stabilizes the halide perovskite, but also takes advantage of the nano-sheet for a compatible integration with the traditional silicon semiconductor. Here, we report the preparation of un-passivated Cs₄PbBr₆ ellipsoidal nanocrystals and pseudo-spherical quantum dots in silicon nano-sheets and their enhanced photoluminescence (PL). For a sample with low concentrations of quantum dots in silicon nano-sheets, the emission from Cs₄PbBr₆ pseudo-spherical quantum dots is quenched and is dominated with Pb²⁺ ion/silicene emission, which is very stable during the whole measurement period. For a high concentration of Cs₄PbBr₆ ellipsoidal nanocrystals in silicon nano-sheets, we have observed Förster resonance energy transfer with up to 87% efficiency through the oscillation of two PL peaks when UV excitation switches between on and off, using recorded video and PL lifetime measurements. In an area of a non-uniform sample containing both ellipsoidal nanocrystals and pseudo-spherical quantum dots, where Pb²⁺ ion/silicene emissions, broadband emissions from quantum dots, and bandgap edge emissions (515 nm) appear, the 515 nm peak intensity increases five times over 30 min of UV excitation, probably due to a photon recycling effect. This irradiated sample has been stable for one year of ambient storage. Cs₄PbBr₆ quantum dots encapsulated in silicon nano-sheets can lead to applications of halide perovskite light emitting diodes (PeLEDs) and integration with traditional semiconductor materials. Full article

Novel multicomponent glasses with nominal compositions of (50−x)MoO₃:xWO₃:25La₂O₃:25B₂O₃, x = 0, 10, 20, 30, 40, 50 mol% doped with 3 mol % Eu₂O₃ were prepared using a conventional melt-quenching method. Their structure, thermal behavior and luminescent properties were investigated by Raman spectroscopy, differential thermal analysis and photoluminescence spectroscopy. The optical properties of the glasses were investigated by UV–vis absorption spectroscopy and a determination of the refractive index. Physical parameters such as density, molar volume, oxygen molar volume and oxygen packing density were determined. The glasses are characterized by a high glass transition temperature. Raman analysis revealed that the glass structure is built up mainly from tetrahedral (MoO₄)²⁻ and (WO₄)²⁻ units providing Raman bands of around 317 cm⁻¹, 341–352 cm⁻¹, 832–820 cm⁻¹ and 928–935 cm⁻¹. At the same time, with the replacement of MoO₃ with WO₃ some fraction of WO₆ octahedra are produced, the number of which increases with the increasing WO₃ content. A strong red emission from the ⁵D₀ level of Eu³⁺ ions was registered under near-UV (397 nm) excitation using the ⁷F₀ → ⁵L₆ transition of Eu³⁺. Photoluminescence (PL) emission gradually increases with increasing WO₃ content, evidencing that WO₃ is a more appropriate component than MoO₃. The integrated fluorescence intensity ratio R (⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu³⁺ in non-centrosymmetric sites. All findings suggest that the investigated glasses are potential candidates for red light-emitting phosphors. Full article

Controlling the cooling rate experienced by a material during a manufacturing process is a challenge and a major issue. Industrial processing techniques are very diverse and may involve a whole range of cooling rates, which are sometimes extremely high for small and/or thin manufactured parts. For polymers, the cooling rate has consequences on both the microstructure and the time-dependent properties. The common cooling rates associated with conventional calorimetric measurements are generally limited to a few tens of degrees per minute. This work combines several calorimetric techniques (DSC, modulated-temperature DSC, stochastically-modulated DSC and Fast Scanning Calorimetry) to estimate the critical cooling rate required to melt-quench fast-crystallizing polyesters to their fully amorphous state, based on the example of a series of poly(alkylene trans-1,4-cyclohexanedicarboxylate) (PCHs) with a number of methylene groups in the main structure of the repeating unit $n_{C{H}_2}$ varying from 3 to 6. The even-numbered ones require faster cooling rates (about 3000 K s⁻¹ for $n_{C{H}_2}$ = 4, between 500 and 1000 K s⁻¹ for $n_{C{H}_2}$ = 6) compared to the odd-numbered ones (between 50 K min⁻¹ and 100 K s⁻¹ for $n_{C{H}_2}$ = 3, between 10 and 30 K min⁻¹ for $n_{C{H}_2}$ = 5). Full article

The detection of lipopolysaccharide (LPS) has important value for the monitoring of diseases such as sepsis and the impurity control of drugs. In this work, we prepared guanidinylated carbon dots (GQ-CDs) and used them to adsorb 5-carboxyfluorescein (FAM)-labeled single-stranded DNA (ssDNA) to become GQ-CDs/FAM-DNA, resulting in quenched FAM. The quenching efficiency of the FAM-DNA by GQ-CDs in the GQ-CDs/FAM-DNA system was 91.95%, and this quenching was stable over the long term. Upon the addition of LPS, the quenched FAM-DNA in the GQ-CDs/FAM-DNA system regained fluorescence at 520 nm. The mechanism studies found that the addition of LPS promoted the dissociation of FAM-DNA adsorbed on GQ-CDs, thereby restoring fluorescence. The degree of fluorescence recovery was closely related to the content of LPS. Under optimized conditions, the fluorescence recovery was linearly related to LPS concentrations ranging from 5 to 90 μg/mL, with a detection limit of 0.75 μg/mL. The application of this method to plasma samples and trastuzumab injections demonstrated good spiked recoveries and reproducibility. This platform, based on GQ-CDs for the adsorption and quenching of FAM-DNA, enables the detection of LPS through relatively simple mixing operations, showing excellent competitiveness for the determination of actual samples under various conditions. Full article

We discuss local magnetic field quenches using perturbative methods of finite time path field theory (FTPFT) in the following spin chains: Ising and XY in a transverse magnetic field. Their common characteristics are: (i) they are integrable via mapping to a second quantized noninteracting fermion problem; and (ii) when the ground state is nondegenerate (true for finite chains except in special cases), it can be represented as a vacuum of Bogoliubov fermions. By switching on a local magnetic field perturbation at finite time, the problem becomes nonintegrable and must be approached via numeric or perturbative methods. Using the formalism of FTPFT based on Wigner transforms (WTs) of projected functions, we show how to: (i) calculate the basic “bubble” diagram in the Loschmidt echo (LE) of a quenched chain to any order in the perturbation; and (ii) resum the generalized Schwinger–Dyson equation for the fermion two-point retarded functions in the “bubble” diagram, hence achieving the resummation of perturbative expansion of LE for a wide range of perturbation strengths under certain analyticity assumptions. Limitations of the assumptions and possible generalizations beyond it and also for other spin chains are further discussed. Full article

Nd-Fe-C alloys have been reported as hard magnetic materials with a potential higher coercivity than Nd-Fe-B alloys. However, it has been seldom studied since its intrinsic properties were investigated in the last century. Here, we revisited the structure, phase precipitation and magnetic properties of rapidly quenched ternary Nd-Fe-C alloys for further understanding their composition-microstructure-property relationships. The Nd_10+xFe_84−xC₆ (x = −2, 0, 2, 3, 4, 5) alloys with various compositions were prepared by melt spinning. The results show that the hard magnetic Nd₂Fe₁₄C phase can be hardly formed in the as-spun alloys. Instead, the alloys are composed of soft magnetic α-Fe phase and planar anisotropic Nd₂Fe₁₇C_x phase. After annealing above 650 °C, the Nd₂Fe₁₄C phase is precipitated by the peritectoid reaction. All optimally annealed alloys contain Nd₂Fe₁₄C and Nd₂Fe₁₇C_x phases, while the presence and content of α-Fe phase are determined by the alloy composition. The crystallization degree of the as-spun alloys has an effect on their magnetic properties after annealing. After the annealing treatment, partly crystallized as-spun alloys exhibit better magnetic properties than the amorphous alloys. The intrinsic coercivity H_cj = 847 kA/m, remanence J_r = 0.69 T, and maximum energy product (BH)_max = 64.3 kJ/m³ were obtained in the Nd₁₄Fe₈₀C₆ alloy annealed at 725 °C. The formation of the Nd₂Fe₁₄C and Nd₂Fe₁₇C_x phases with the Nd₂O₃ phase precipitated at the triangular grain boundaries is responsible for its relatively good properties. Although the magnetic properties of Nd-Fe-C alloys obtained in this work are inferior to those of Nd-Fe-B, the present results help us to further understand the magnetic behavior of Nd-Fe-C alloys. Full article

The emergence of bio-based carbonaceous materials for various applications has attracted significant attention during the last few years. Here, we report a rapid, efficient, and reproducible microwave-assisted synthesis of graphene quantum dots (GQDs) with identical features irrespective of the nature of biomass waste investigated. The synthesized GQDs were fully characterized by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscopy, and dynamic light scattering. The nanoparticles displayed narrow sizes of 1–2 nm and high solubility in polar solvents such as water and ethanol. The protocol described herein is advantageous in comparison to dealing with the synthesis of GQDs from biomass waste previously reported since our protocol is faster owing to the use of microwave heating and the avoidance of dialysis for the purification step. Furthermore, in solution, the water-soluble particles showed excitation-dependent photoluminescence ranging from blue to orange emission wavelengths. Interestingly, thin films displayed white-light emission under 325 nm UV-light excitation, while aggregation-induced quenching was usually observed, opening the way for their potential use as a phosphor in white-light-emitting diodes. Full article

In this study, Fe, N co-doped biochar (Fe@N co-doped BC) was synthesized by the carbonization–pyrolysis method and used as a carbocatalyst to activate peroxymonosulfate (PMS) for sulfamethoxazole (SMX) removal. In the Fe@N co-doped BC/PMS system, the degradation efficiency of SMX (10.0 mg·L⁻¹) was 90.2% within 40 min under optimal conditions. Radical quenching experiments and electron spin resonance (ESR) analysis suggested that sulfate radicals (SO₄^•−), hydroxyl radicals (^•OH), and singlet oxygen (¹O₂) participated in the degradation process. After the reaction, the proportion of pyrrolic N decreased from 57.9% to 27.1%. Pyrrolic N served as an active site to break the inert carbon network structure and promote the generation of reactive oxygen species (ROS). In addition, pyrrolic N showed a stronger interaction with PMS and significantly reduced the activation energy required for the reaction (∆G = 23.54 kcal/mol). The utilization potentiality of Fe@N co-doped BC was systematically evaluated in terms of its reusability and selectivity to organics. Finally, the intermediates of SMX were also detected. Full article

PDIA3 is a pleiotropic protein primarily located in the endoplasmic reticulum where it is involved in protein folding, catalyzing the formation, breakage, and rearrangement of disulfide bonds. PDIA3 is implicated in numerous pathologies such as cancer, inflammation, and neurodegeneration. Although punicalagin has been proven to be a highly promising PDIA3 inhibitor and can be used as target protein in glioblastoma, it does not have sufficient selectivity for PDIA3 and is a quite-large molecule. With the aim of finding punicalagin derivatives with a simplified structure, we selected punicalin, which lacks the hexahydroxy-diphenic acid moiety. Previous docking studies suggest that this part of the molecule is not involved in the binding with PDIA3. In this study we compared the ability of punicalin to bind and inhibit PDIA3 and PDIA1. Tryptophan fluorescence quenching and disulfide reductase activity (using both glutathione and insulin as substrates) were evaluated, demonstrating the ability of punicalin to bind and inhibit PDIA3 even to a lesser extent compared to punicalagin. On the other hand, punicalin showed a very low inhibition activity towards PDIA1, demonstrating a higher selectivity for PDIA3. Protein thermal shift assay evidenced that both proteins can be destabilized by punicalin as well as punicalagin, with PDIA3 much more sensitive. Additionally, punicalin showed a higher change in the thermal stability of PDIA3, with a shift up to 8 °C. This result could explain the presence of PDIA3 aggregates, evidenced by immunofluorescence analysis, that accumulate within treated cells and that are more evident in the presence of punicalin. The results here obtained show punicalin is able to bind both proteins but with a higher selectivity for PDIA3, suggesting the possibility of developing new molecules with a simplified structure that are still able to selectively bind and inhibit PDIA3. Full article

This study investigates the impact of cooling rate and alloy composition on phase formations and properties of (CoCrCuTi)_100−xFe_x (x = 0, 5, 10, 12.5, 15) high-entropy alloys (HEAs). Samples were synthesized using arc-melting and electromagnetic levitation, followed by quenching through the use of a Cu chill or V-shaped Cu mold. Cooling rates were evaluated by measuring dendrite arm spacings (DASs), employing the relation DAS = k ɛ⁻ⁿ, where constants k = 16 and n = ½. Without Fe addition, a microstructure consisting of BCC1 + BCC2 phases formed, along with an interdendritic (ID) FCC Cu-rich phase. However, with the addition of 5–10% Fe, a Cu-lean C14 Laves phase emerged, accompanied by a Cu-rich ID FCC phase. For cooling rates below 75 K/s, alloys containing 10% Fe exhibited liquid phase separation (LPS), characterized by globular Cu-rich structures within the Cu-lean liquid. In contrast, for the same composition, higher cooling rates of 400–700 K/s promoted a dendritic/interdendritic microstructure. Alloys with 12.5–15 at. % Fe displayed LPS irrespective of the cooling rate, although an increase in uniformity was noted at rates exceeding 700 K/s. Vickers hardness and fracture toughness generally increased with Fe content, with hardness ranging from 444 to 891 HV. The highest fracture toughness (5.5 ± 0.4 K_IC) and hardness (891 ± 66 HV) were achieved in samples containing 15 at. % Fe, cooled at rates of 25–75 K/s. Full article

Simultaneous illumination and communication using solid-state lighting devices like white light-emitting diode (LED) light sources is gaining popularity. The white light LED comprises a single-colored yellow phosphor excited by the blue LED chip. Therefore, color-quality determining parameters like color-rendering index (CRI), correlated color temperature (CCT), and CIE 1931 chromaticity coordinates of generic white LED sources are poor. This article presents the development of multi-color phosphors excited by a blue LED to improve light quality and bandwidth. A multi-layer stacking of phosphor layers excited by a blue LED led to the quenching of photoluminescence (PL) and showed limited bandwidth. To solve this problem, a lens-free, electrically powered, broadband white light source is designed by mounting multi-color phosphor LEDs in a co-planar ring-topology. The CRI, CCT, and CIE 1931 chromaticity coordinates of the designed lamp (DL) were found to be 90, 5114 K, and (0.33, 0.33), respectively, which is a good quality lamp for indoor lighting. CRI of DL was found to be 16% better than that of white LED (WL). Assessment of visible light communications (VLC) feasibility using the DL includes time interval error (TIE) of data pattern or jitter analysis, eye diagram, signal-to-noise ratio (SNR), fast Fourier transform (FFT), and power spectral density (PSD). DL transmits binary data stream faster than WL due to a reduction in rise time and total jitter by 31% and 39%, respectively. The autocorrelation function displayed a narrow temporal pulse for DL. The DL is beneficial for providing high-quality illumination indoors while minimizing PL quenching. Additionally, it is suitable for indoor VLC applications. Full article

Trypsin enzyme has gained recognition as a potential biomarker in several tumors, such as colorectal, gastric, and pancreatic cancer, highlighting its importance in disease diagnosis. In response to the demand for rapid, cost-effective, and real-time detection methods, we present an innovative strategy utilizing the design and synthesis of NIR-sensitive dye–peptide conjugate (SQ-3 PC) for the sensitive and selective monitoring of trypsin activity by fluorescence ON/OFF sensing. The current research deals with the design and synthesis of three unsymmetrical squaraine dyes SQ-1, SQ-2, and SQ-3 along with a dye–peptide conjugate SQ-3-PC as a trypsin-specific probe followed by their photophysical characterizations. The absorption spectral investigation conducted on both the dye alone and its corresponding dye–peptide conjugates in water, utilizing SQ-3 and SQ-3 PC respectively, reveals enhanced dye aggregation and pronounced fluorescence quenching compared to observations in DMSO solution. The absorption spectral investigation conducted on dye only and corresponding dye–peptide conjugates in water utilizing SQ-3 and SQ-3 PC, respectively, reveals not only the enhanced dye aggregation but also pronounced fluorescence quenching compared to that observed in the DMSO solution. The trypsin-specific probe SQ-3 PC demonstrated a fluorescence quenching efficiency of 61.8% in water attributed to the combined effect of aggregation-induced quenching (AIQ) and fluorescence resonance energy transfer (FRET). FRET was found to be dominant over AIQ. The trypsin-mediated hydrolysis of SQ-3 PC led to a rapid and efficient recovery of quenched fluorescence (5-fold increase in 30 min). Concentration-dependent changes in the fluorescence at the emission maximum of the dyes reveal that SQ-3 PC works as a trypsin enzyme-specific fluorescence biosensor with linearity up to 30 nM along with the limit of detection and limit of quantification of 1.07 nM and 3.25 nM, respectively. Full article

The prevalence of multidrug resistance (MDR) and stagnant drug-development pipelines have led to the rapid rise of hard-to-treat antibiotic-resistant bacterial infections. These infectious diseases are no longer just nosocomial but are also becoming community-acquired. The spread of MDR has reached a crisis level that needs immediate attention. The landmark O’Neill report projects that by 2050, mortality rates associated with MDR bacterial infections will surpass mortality rates associated with individuals afflicted with cancer. Since conventional antimicrobials are no longer very reliable, it is of great importance to investigate different strategies to combat these life-threatening infectious diseases. Here, we provide an overview of recent advances in viable alternative treatment strategies mainly targeting a pathogen’s virulence capability rather than viability. Topics include small molecule and immune inhibition of virulence factors, quorum sensing (QS) quenching, inhibition of biofilm development, bacteriophage-mediated therapy, and manipulation of an individual’s macroflora to combat MDR bacterial infections. Full article