Non-uniform Size Research Articles

Readsynth: short-read simulation for consideration of composition-biases in reduced metagenome sequencing approaches

BackgroundThe application of reduced metagenomic sequencing approaches holds promise as a middle ground between targeted amplicon sequencing and whole metagenome sequencing approaches but has not been widely adopted as a technique. A major barrier to adoption is the lack of read simulation software built to handle characteristic features of these novel approaches. Reduced metagenomic sequencing (RMS) produces unique patterns of fragmentation per genome that are sensitive to restriction enzyme choice, and the non-uniform size selection of these fragments may introduce novel challenges to taxonomic assignment as well as relative abundance estimates.ResultsThrough the development and application of simulation software, readsynth, we compare simulated metagenomic sequencing libraries with existing RMS data to assess the influence of multiple library preparation and sequencing steps on downstream analytical results. Based on read depth per position, readsynth achieved 0.79 Pearson’s correlation and 0.94 Spearman’s correlation to these benchmarks. Application of a novel estimation approach, fixed length taxonomic ratios, improved quantification accuracy of simulated human gut microbial communities when compared to estimates of mean or median coverage.ConclusionsWe investigate the possible strengths and weaknesses of applying the RMS technique to profiling microbial communities via simulations with readsynth. The choice of restriction enzymes and size selection steps in library prep are non-trivial decisions that bias downstream profiling and quantification. The simulations investigated in this study illustrate the possible limits of preparing metagenomic libraries with a reduced representation sequencing approach, but also allow for the development of strategies for producing and handling the sequence data produced by this promising application.

Si,N co-doped carbon quantum dots in mesoporous molecular sieves: A fluorescence sensing platform for Cr(VI) detection

Carbon quantum dots (CQDs) are highly efficient fluorescent probes for metal ion detection; however, they are limited by non-uniform particle size, aggregation, and the inability to facilitate quantitative analysis. Herein, a smart host–guest strategy is utilized, wherein CQDs are immobilized in mesoporous molecular sieves, proving to be an effective method to minimize these drawbacks. Si,N-CQDs@SBA-15 is successfully synthesized by the one-step hydrothermal route using Si,N-CQDs precursor materials as guests and the mesoporous molecular sieve SBA-15 as the host. A good linear relationship between the concentration of Cr(VI) ions and fluorescent intensity is observed from 0 μM to 100 μM (R2 = 0.9986). Thelimitofdetection(LOD) is 0.213 μM, approximately three times lower than that of pristine Si,N-CQDs (0.677 μM). Additionally, Si,N-CQDs@SBA-15 exhibit good detection selectivity for Cr(VI) detection over other metal ions. Moreover, a smartphone-based laboratory device and RGB analysis app are employed to capture and analyze fluorescence images, revealing a LOD for Cr(VI) of 0.201 μM. Förster Resonance Energy Transfer (FRET) is identified as the possible mechanism for the fluorescence quenching of Si,N-CQDs@SBA-15 by Cr(VI) through UV–vis and fluorescence experiments. The practicability of the synthesized fluorescent probes is further validated in river water, yielding satisfactory spiked recoveries ranging from 99.24 % to 106.21 %.

A comparative study on the production of Ni1/3Co1/3Mn1/3C2O4 cathode precursor material for lithium-ion batteries using batch and slug-flow reactors

The intermittent nature of the renewable energy sources drifts research interest towards various electrochemical energy storage devices, such as the lithium ion battery, which offers consistent power supply. The manufacturing cost and electrochemical performance of a battery pack largely depends on the quality of the cathode material, which further depends on the production method and its parameters. However, the traditional stirred tank-based co-precipitation manufacturing process for precursors of lithium nickel manganese cobalt oxide (NCM111) cathode suffers from inhomogeneity in the reaction environment, which leads to non-uniform morphology and particle size distribution (PSD). In this work, slug-flow-based manufacturing platform, which offers a homogeneous reaction environment, is used for the continuous production of NCM111 oxalate precursors. One of the novel features of this work is the comparative study between the quality of batch and slug-flow-derived products. The slug-flow-derived product is found to be better in terms of having bigger particle size, narrower PSD and higher tap density. The study on the single and dual-element precipitation in similar conditions to understand the co-precipitation behavior in the slug-flow manufacturing platform is also a unique feature of this work. Furthermore, the effect of NH4OH concentration and residence time (RT) on the electrochemical performance of cathode were also studied and it is found that the cathode precursors synthesized at a NH4OH concentration of 0.08 M and a RT of 2 minutes followed by lithiation shows a better electrochemical performance of 128 mAh g−1 at 0.1 C with cycling stability of more than 80% both at 0.5 C and 1 C.

Stretched Meshing in a 2D Computational Domain with Elbow Edges for CFD Applications

Mesh generation is critical for obtaining accurate and detailed solutions to mesh-based numerical problems, particularly when capturing specific information within a designated area of the domain. While structured meshes offer consistency, their uniform resolution limits their ability to achieve this. Mesh stretching offers a solution by introducing non-uniform element sizes based on an analytical relationship while preserving the original mesh structure. The objective of this study is to create a hybrid mesh model that leverages the strengths of both structured and stretched meshes. A 2D rectangle with elbow edges serves as the domain. To address the requirements of CFD applications, the domain is refined by increasing element density near the boundaries and corners. Skewness, aspect ratio, and element quality are then assessed to determine the overall mesh quality. The results demonstrate that stretching the structured mesh produced a mesh with quality that meets CFD domain standards.

Effect of particle size distribution variability on the permeability of hydrate-bearing sediments: A CFD study

Natural gas hydrates (NGH) are considered as a future clean energy in the era of carbon neutrality. The seepage behaviour of hydrate-bearing sediment (HBS) and its controlling factors are significant for developing effective production strategies. In this study, we aim to elucidate how the heterogeneous spatial distribution of clayey-silty sediment particles, particularly the non-uniform particle size distribution (PSD) affects the permeability of HBS. An algorithm was developed to generate the heterogeneous spatial distribution of sediment particles based on the PSD of hydrate-bearing cores extracted from Japan Nankai Trough (D50 = 122 μm). A series simulation of fluid flow in porous media based on CFD was conducted for the HBS with varying hydrate saturations (SH). The watershed segmentation algorithm was employed for the identification of pore structure, including pore space and pore throat with a detailed analysis on the pore structure evolution with SH. Host sediments with higher uniformity result in initial high permeability but the permeability reduction with increasing SH is more significant compared with that of lower uniformity. Pore throat width reduced to less than 5 μm with SH above 50% compared with its original width of ∼30 μm. Tortuosity exhibits a linear increase with SH, while permeability decreases exponentially with increasing tortuosity. We propose an improved permeability model (KCpro) based on the classical Kozeny-Carman model accounting for the change in specific surface area for non-uniform PSD in HBS with good agreement. This study confirmed the applicability of CFD modelling as a promising tool to study the seepage behaviour of HBS complementary to classical permeability experimental tests. Results of this study provide fundamental understanding on how permeability evolves in HBS with significant PSD variations in natural gas hydrate reservoirs in nature.

Preparation of silymarin-loaded zein polysaccharide core–shell nanostructures and evaluation of their biological potentials

Abstract Silymarin-loaded zein polysaccharide core–shell nanoparticles (SZPCS-NPs) were synthesized where sodium alginate and pectin offer stability and controlled release qualities to zein, a maize protein, having excellent biocompatibility. The present study is an attempt to develop zein–silymarin polysaccharide core–shell nanostructures to enhance water solubility, thereby improving bioavailability and producing enhanced biological responses in living systems. SZPCS-NPs were prepared using pH-induced antisolvent precipitation method. Five different types of SZPCS-NPs were synthesized using different combinations of sodium alginate and pectin, namely P100–A00 (non-uniform size ranging from 20 to 100 nm), P70–A30 (spherical and uniform size measuring approximately 80 nm in diameter), P50–A50, P30–A70, and P00–A100 exhibited irregular shapes with the presence of some triangular and oval structures and non-uniform size ranging from 20 to 100 nm. The SZPCS-NPs P70–A30 possessed the best results in terms of shape, size, and other characterization studies. Furthermore, the SZPCS-NPs possessed a percent drug loading of 72.5% and entrapment efficiency of 51.7%, respectively. The resulting SZPCS-NPs exhibited an excellent relative bioavailability percentage of 97.4% in comparison to commercial silymarin, having 58.1%, and crude silymarin, having 46.97% bioavailability percentage, correspondingly. In addition, SZPCS-NPs possessed an almost two folds’ increase in antioxidant activity in comparison to crude and commercially available silymarin. Similarly, SZPCS-NPs also showed better stabilization in hepatic biomarker enzymes and possessed better hepatoprotective activity for a period of 6 weeks, in contrast to commercial and crude silymarin formulations.

68Ga]DOTATOC PET-derived radiomics to predict genetic background of head and neck paragangliomas: a pilot investigation.

To investigate the [68Ga]DOTATOC PET radiomic profile of head and neck paragangliomas (HNPGLs) and identify radiomic characteristics useful as predictors of succinate dehydrogenase genes (SDHx) pathogenic variants. Sporadic and SDHx HNPGL patients, who underwent [68Ga]DOTATOC PET/CT, were retrospectively included. HNPGLs were analyzed using LIFEx software, and extracted features were harmonized to correct for batch effects and confronted testing for multiple comparison. Stepwise discriminant analysis was conducted to remove redundancy and identify best discriminating features. ROC analysis was used to define optimal cut-offs. Multivariate decision-tree analysis was performed using CHAID method. 34 patients harboring 60 HNPGLs (51 SDHx in 25 patients) were included. Three sporadic and nine SDHx HNPGLs were metastatic. At stepwise discriminant analysis, both GLSZM-Zone Size Non-Uniformity (ZSNU, reflecting tumor heterogeneity) and IB-TLSRE (total lesion somatostatin receptor expression) were independent predictors of genetic status, with 96.4% of lesions and 91.6% of patients correctly classified after cross validation (p < 0.001). Among non-metastatic patients, GLSZM-ZSNU and IB-TLSRE were significantly higher in sporadic than SDHx HNPGLs (p < 0.001). No differences were revealed in metastatic patients. Decision-tree analysis highlights multifocality and IB-TLSRE as useful variables, correctly identifying 6/9 sporadic and 24/25 SDHx patients. Model failed to classify one SDHA and three sporadic patients (2 metastatic). Radiomics features GLSZM-ZSNU and IB-TLSRE appear to reflect HNPGLs SDHx status and tumor behavior (metastatic vs. non-metastatic). If validated, especially IB-TLSRE might represent a simple and time-efficient radiomic index for SDHx variants early screening and prediction of tumor behavior in HNPGL cases.

Average grain size evaluation using scattering-induced attenuation of coda waves

Grain size is one of the key microstructural factors affecting the mechanical properties of polycrystalline metal materials. In this study, a novel method for grain size evaluation using ultrasonic coda waves is proposed. Different from conventional bulk wave methods that require a point-by-point scanning of the structure, the proposed method allows for a rapid evaluation of the average grain size of the whole part from a single inspection location using one-pass testing data. A piecewise energy attenuation function dealing with different attenuation mechanisms is proposed to obtain the effective attenuation coefficient of coda waves. A power-law model is constructed to correlate the effective attenuation coefficient with the average grain size. Ultrasonic testing on nickel-based superalloy plate specimens with different average grain sizes is performed for model calibration and method verification. The applicability and robustness of the proposed method are further validated using a realistic turbine disk specimen with an irregular shape and non-uniform grain sizes. Results show that the proposed method yields a reliable and accurate estimation of the average grain size with a maximum relative error less than 20 %.

FeNi alloy embedded in three-dimensional nitrogen-doped porous carbon as bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

Iron‑nickel (FeNi) alloy is one of the efficient bifunctional oxygen electrocatalysts for zinc-air batteries (ZABs). However, FeNi alloy nanoparticles prepared by traditional synthesis strategies are easy to agglomerate and have non-uniform sizes, which is not conducive to the improvement of catalytic activity and stability. Here, we have successfully encapsulated two different kinds of nitrogen-rich metal phthalocyanines (MPcs) in situ doping in zeolitic imidazolate framework (ZIF-8) homogeneously by the “double solvents” method. The ligand nitrogen and macrocyclic structure of MPcs encapsulated in ZIF-8 not only helps metal dispersion and enhances the metal-ligand‑nitrogen (M-Nx) structure, but also enhances the graphitisation of three-dimensional (3D) porous carbon after pyrolysis. Thus, a FeNi alloy uniformly embedded in 3D nitrogen-doped porous carbon materials (FeNi@NC) was constructed in the subsequent pyrolysis process and used as an efficient bifunctional oxygen reduction/evolution (ORR/OER) electrocatalyst for rechargeable ZABs. Impressively, the FeNi@NC catalyst carries high half-wave potential (0.850 V) in ORR and the low overpotential (291 mV) in OER, significantly better than Pt/C (0.830 V) and RuO2 (307 mV), respectively. In addition, the rechargeable ZAB assembled with FeNi@NC air cathode has a specific capacity of 649 mW cm−2 and shows no significant degradation after 240 h of charging and discharging cycles. This study provides a new design idea for the manufacture of carbon-supported non-noble metal alloy catalysts with bifunctional oxygen catalytic activity, and verifies the feasibility of regulating the composition of non-noble metals to construct a rechargeable ZABs with excellent performance.

Experimental studies on the impact of adsorbent particle size on the adsorption chiller performance

Adsorption chiller dynamics and its effect on the performance are greatly influenced by the adsorbent particle size because they govern both the micro (intra-particle) and macro (inter-particle) heat and mass transfer resistances within the adsorber bed. The net effect of adsorbent particle size and shape on the overall cooling system performance is addressed here. Initial CFD analysis of columnar adsorber bed with silica gel + water as the working pair, assuming uniform spherical adsorbent, showed increased uptake capacity with smaller sized (0.23 mm radius) particles over bigger sized (0.8 mm radius) ones despite smaller vapor penetration depth of the former. Subsequently, the effect of adsorbent particle size and shape on the overall cooling system performance is investigated experimentally in a single-stage one-bed mode for RD 2060 (0.8 mm radius) and RD 3070 (0.23 mm radius) silica gel specimens. Though the smaller size of RD 3070 is favourable for the adsorption kinetics at the particle level, its non-spherical shape and highly non-uniform size distribution resulted in significantly lower permeability and thermal diffusivity of the packed adsorber bed, thus hindering the cyclic steady state throughput. For the same operating conditions, RD 2060 and RD 3070 yield a cooling capacity (CC) of 107 W and 22 W, respectively. Further, the coefficient of performance (COP) drops by 73% in the case of RD 3070. The present study indicates that the adsorber bed design must consider both the adsorbent size and shape, in addition to other system operational parameters to enhance performance indicators.

Hydrogen-bonding induced assembly of polymer-grafted nanoparticles towards photothermal antibacterial activities

The multiple hydrogen-bond has been introduced as a reversible driving force for directing the assembly of polymer-grafted nanoparticles (PGNPs). The complementary hydrogen-bonds among the polymer ligands lead to the spontaneous aggregation of PGNPs. However, it may also induce the uncontrollable aggregation of PGNPs into assemblies with non-uniform size, even irregular precipitates, due to the immoderate agglomeration associated with the strong interactions of multiple hydrogen-bonds. This severely limits the stable dispersion of PGNP aggregates in a solvent and their applications. In this work, the gold nanoparticles (AuNPs) grafted with thymine-terminated polystyrene (AuNP@PS-Thy) and diaminopyridine-terminated polystyrene (AuNP@PS-Dap) were synthesized, respectively. Their thermal-responsive assembly behavior in an organic solvent was systematically studied. By optimizing the assembly conditions, i.e., the concentration of PGNPs and the incubation time, the assemblies of AuNP@PS-Thy/AuNP@PS-Dap with controllable size were obtained. Interestingly, the assemblies deposited on a solid substrate showed excellent photothermal antimicrobial activities under irradiation of 808 nm and 655 nm lasers. The killing percentage of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) could reach 99 % after irradiating for 10 min. This work establishes an approach for controlling the hydrogen-bonding-induced assembly behavior of PGNPs, which may be extended to construct functional metamaterials with controllable structures.

Improved performance of solar cells using chemically synthesized SnSe nanosheets as light absorption layers

We report the method to fabricate SnSe nanosheet (NSs) coated solar cells with very high performance compared to similar solar cells previously reported using chemically synthesized SnSe nanocrystals. SnSe NSs do not contain toxic metals and are promising materials for the top layer of tandem solar cells. SnSe NSs synthesized using the hot injection method were not suitable for coating as a light absorption layer because of their nonuniform size and tendency to aggregate. The one-pot synthesis produced SnSe NSs with uniform size, making them suitable for fabricating flat and homogeneous films when mixed with conductive polymers. The photoelectric conversion efficiency (PCE) of 4.8% was achieved using films with a sheet coverage of 14.2% of SnSe NSs. The PCE value was nearly two orders of magnitude higher than that of previous similar SnSe-coated solar cells. SnSe NSs coated films, which can be easily produced unlike vapor phase methods, were shown to have the potential to make an important contribution to the field of photovoltaic power generation.

Applications of Cu2+-Loaded Silica Nanoparticles to Photothermal Therapy and Tumor-Specific Fluorescence Imaging.

Copper-based nanomaterials have been employed as therapeutic agents for cancer therapy and diagnosis. Nevertheless, persistent challenges, such as cellular toxicity, non-uniform sizes, and low photothermal efficiency, often constrain their applications. In this study, we present Cu2+-loaded silica nanoparticles fabricated through the chelation of Cu2+ ions by silanol groups. The integration of Cu2+ ions into uniformly sized silica nanoparticles imparts a photothermal therapy effect. Additionally, the amine functionalization of the silica coating facilitates the chemical conjugation of tumor-specific fluorescence probes. These probes are strategically designed to remain in an 'off' state through the Förster resonance energy transfer mechanism until exposed to cysteine enzymes in cancer cells, inducing the recovery of their fluorescence. Consequently, our Cu2+-loaded silica nanoparticles demonstrate an efficient photothermal therapy effect and selectively enable cancer imaging.

Wood chip sound absorbers: Measurements and models

Normal incidence absorption coefficient spectra of samples made from glued wood chips have been measured for various mesh sizes, bulk densities, thicknesses, and air gaps. Increasing thickness introduces additional layer resonance peaks and shifts the initial peak towards lower frequencies. The wood chip samples composed of the smallest mesh sizes were found to offer the highest sound absorption, comparable with that of the same thickness of materials made from synthetic fibers. Measured absorption spectra are compared with predictions of four models for the acoustical properties of rigid porous media. These include a model for slanted parallel identical uniform slits (SS), the Johnson-Champoux-Allard (JCA) and Johnson-Champoux-Allard-Lafarge (JCAL) models for arbitrary pore structures, and model for a non-uniform pore size distribution (NUPSD). Porosity and flow resistivity values have been determined non-acoustically. However, the tortuosity and characteristic lengths required for the JCA model have been obtained by fitting the measured absorption spectra. The thermal permeability required for the JCAL model has been deduced indirectly from the fitted tortuosity through a relationship with standard deviation of the pore size distribution due to the NUPSD model. JCAL and JCA models give the best agreement overall, but predictions of the SS and NUPSD models that use only the fitted tortuosity in addition to measured porosity and flow resistivity are found to give comparable agreement with data for many samples. SS and NUPSD predictions are improved by increasing the tortuosity values compared with those obtained by fitting the JCA model. The study should encourage the creation of sustainable sound-absorbing materials from wood chip wastes.

Formation mechanism of herpetrione self-assembled nanoparticles based on pH-driven method

The self-assembled nanoparticles (SAN) formed during the decoction process of traditional Chinese medicine (TCM) exhibit non-uniform particle sizes and a tendency for aggregation. Our group found that the pH-driven method can improve the self-assembly phenomenon of Herpetospermum caudigerum Wall., and the SAN exhibited uniform particle size and demonstrated good stability. In this paper, we analyzed the interactions between the main active compound, herpetrione (Her), and its main carrier, Herpetospermum caudigerum Wall. polysaccharide (HCWP), along with their self-assembly mechanisms under different pH values. The binding constants of Her and HCWP increase with rising pH, leading to the formation of Her-HCWP SAN with a smaller particle size, higher zeta potential, and improved thermal stability. While the contributions of hydrogen bonding and electrostatic attraction to the formation of Her-HCWP SAN increase with rising pH, the hydrophobic force consistently plays a dominant role. This study enhances our scientific understanding of the self-assembly phenomenon of TCM improved by pH driven method.

An efficient solution of the multi-term multi-harmonic electron Boltzmann equation for use in global models

Solving the electron Boltzmann equation is an essential but costly step in simulating low-temperature plasma kinetics. This work addresses the problem by introducing a solution of the general multi-term multi-harmonic Boltzmann equation (MTMH-BE) optimized for electrons in time-dependent non-equilibrium gases and electric fields. This is accomplished by configuring the numerical Jacobian as the product of a time-independent sparse matrix and an array of time-dependent coefficients. As this approach requires a fixed energy grid, the MTMH-BE is discretized using a finite volume scheme with support for non-uniform cell size, enabling robust solutions across a wide range of reduced field strengths. The new MTMH-BE solver is tested against a range of benchmarks, demonstrating excellent agreement with existing methods. Performance with time-dependent electron energy is evaluated using LoKI-B's pulsed electric field model, with the new solver demonstrating improved wall time scaling and an improvement in grid convergence of over three orders of magnitude. Alternatively, performance with quasi-stationary electrons in an evolving non-equilibrium gas is tested using a nitrogen cross-section set with up to 58 vibrational states and 3,570 processes. Here, the MTMH-BE solver achieves a wall time reduction of up to 99.6% over MultiBolt for error-controlled simulations in the two-term limit, reducing the average solution time from 1-2 seconds to less than 10 ms. These results indicate that the new MTMH-BE solver can improve accuracy and performance in state-to-state global models without the use of grid refinement, cross-section pruning, and other time-saving procedures.

Probabilistic analysis of a sustainable landfill cover considering stress-dependent water retention model and copula-based random fields

Material properties, crucial design parameters in landfill cover systems, can exhibit spatial variability due to non-uniform particle size and uneven compaction, affecting cover performance. Additionally, cover thickness, another key design parameter, can induce stress variation and influence soil-water retention capability. Previous designs always ignored these uncertainties and stress effects, potentially leading to unreasonable design schemes. This study aims to provide design recommendations for a three-layer landfill cover system under heavy rainfall, considering these factors simultaneously by the random finite element method (RFEM). The stress effects are captured using a stress-dependent soil-water retention curve (SDSWRC) and the hysteresis in the SDSWRC is considered in probabilistic analyses. For practical applications, uncertainties in two easily controllable particle size parameters, D10 and D60, are depicted by copula-based cross-correlated random fields. Based on empirical equations, the spatial variability of SDSWRC and water permeability function (WPF) can be further characterised by D10 and D60 random fields. It is found that considering SDSWRC and its spatial variability (e.g., shape) can overestimate percolation by at least 1.7 times compared to deterministic analysis using SWRC. The spatial variability of SDSWRC shape has a more significant impact than spatially variable saturated water permeability on cover system performance. Among candidate copulas, the CClayton copula (survival copula of Clayton copula) yields the most conservative results due to its upper tail dependence. The particle size and thickness of the bottom layer influence the cover system performance more than the upper two layers. A bottom layer with D10≤ 0.009 mm and D60/D10≥ 7.54, and thickness ≥ 0.8 m is recommended to achieve a satisfactory performance level with a 100-year design life.

Cooling Performance Prediction of Particle-Based Radiative Cooling Film Considering Particle Size Distribution.

Here, we present a novel protocol concept for quantifying the cooling performance of particle-based radiative cooling (PBRC). PBRC, known for its high flexibility and scalability, emerges as a promising method for practical applications. The cooling power, one of the cooling performance indexes, is the typical quantitative performance index, representing its cooling capability at the surface. One of the primary obstacles to predicting cooling power is the difficulty of simulating the non-uniform size and shape of micro-nanoparticles in the PBRC film. The present work aims to develop an accurate protocol for predicting the cooling power of PBRC film using image processing and regression analysis techniques. Specifically, the protocol considers the particle size distribution through circle object detection on SEM images and determines the probability density function based on a chi-square test. To validate the proposed protocol, a PBRC structure with PDMS/Al2O3 micro-nanoparticles is fabricated, and the proposed protocol precisely predicts the measured cooling power with a 7.8% error. Through this validation, the proposed protocol proves its potential and reliability for the design of PBRC.

Castor seed-derived luminescent carbon nanoparticles for metal ion detection and temperature sensing applications

In the current study, castor seeds are used as a first-time natural precursor in the hydrothermal process of making carbon nanoparticles. The produced nanoparticles have a non-uniform size distribution with an average diameter of 13 nm and a roughly spherical shape. They comprise a variety of functional groups containing carbon, nitrogen, and oxygen. Their spectra have peaks at 524 nm and 441 nm for their emission and excitation, respectively. They exhibit temperature-sensitive Photoluminescence (PL) behaviour, high quantum yield value (24%), and excitation-dependent emission. In high salt environments, UV radiation, storage time, and fluorescent light they provide exceptional photostability. They have been used in applications for metal ion and thermal sensing. With a limit of detection (LOD) value of 18 μM, they are found to be both sensitive and selective to Fe3+ ions. Additionally, a nanothermosensor with good recovery and a broad temperature range (5 °C–85 °C) has also been demonstrated with a thermal sensitivity of 0.54% °C−1 based on their temperature-sensitive behaviour.

Decentralized Caching Under Nonuniform File Popularity and Size: Memory-Rate Tradeoff Characterization

This paper aims to characterize the memory-rate tradeoff for decentralized caching under nonuniform file popularity and size. We consider a recently proposed decentralized modified coded caching scheme (D-MCCS) and formulate the cache placement optimization problem to minimize the average rate for the D-MCCS. To solve this challenging non-convex optimization problem, we first propose a successive Geometric Programming (GP) approximation algorithm, which guarantees convergence to a stationary point but has high computational complexity. Next, we develop a low-complexity file-group-based approach, where we propose a popularity-first and size-aware (PF-SA) cache placement strategy to partition files into two groups, taking into account the nonuniformity in file popularity and size. Both algorithms do not require the knowledge of active users beforehand for cache placement. Numerical results show that they perform very closely to each other. We further develop a lower bound for decentralized caching under nonuniform file popularity and size as a non-convex optimization problem and solved it using a similar successive GP approximation algorithm. We show that the D-MCCS with the optimized cache placement attains this lower bound when no more than two active users request files at a time. The same is true for files with uniform size but nonuniform popularity and the optimal cache placement being symmetric among files. In these cases, the optimized D-MCCS characterizes the exact memory-rate tradeoff for decentralized caching. For general cases, our numerical results show that the average rate achieved by the optimized D-MCCS is very close to the lower bound.