Stable Configuration Research Articles

Numerical analysis of the bistable propagation of lean premixed hydrogen flames

Premixed hydrogen-air flames that propagate in slender channels have been recently found to be bistable in the limit of fuel-lean mixtures and non-negligible heat losses. Specifically, two stable configurations conformed by either a circular or a double-cell flame front arise for the same combination of controlling parameters (fuel mixture, heat transfer). Nevertheless, this multiplicity of solutions lacks a satisfactory explanation that predicts the formation of either one or another structure given a particular ignition transient. In this work, the analysis of a set of numerical simulations is offered to unveil the underlying physics controlling the bistable behavior. The formulation employed here proves that simplified one-step Arrhenius reaction and quasi-two-dimensional equations suffice to reproduce the complex dynamics, rendering three-dimensional effects and detailed chemical kinetics as second-order contributions that may be important, however, to provide exact quantitative results. Specifically, the initial temperature profiles and subsequent expansion of the flow field prescribe the growth of the flame front leading to different curvatures and sizes of the kernel that control the evolution into one of the canonical structures. Moreover, the achievement of double-cell flames require splitting and reorientation processes prior to pairing of isolated flames, which call for specific initialization conditions that enable these transient dynamics.

Insights into dynamical evolution and stability of thin-shell configurations through acoustic black holes

The main goal of this work is to use the cut and paste method to match the inner flat and outer acoustic Schwarzschild black holes to examine the geometry of a thin-shell. Moreover, the study uses the Klein–Gordon equation and the equation of motion to examine the dynamical evolution of a thin-shell composed of massive as well as massless scalar field. The results of the study show that the collapsing behavior is exhibited by the potential function of a massless scalar shell while the effective potential of a massive scalar shell first collapses and then progressively increases. Additionally, the researchers have analyzed the stable configuration for the phantom-type equation of state encompassing dark energy, quintessence and phantom energy by applying the linearized radial perturbations. As a result, the research suggests that thin-shell Schwarzschild black holes are less stable than acoustic Schwarzschild black holes.

Mathematical modeling of early processes of morphogenesis of epithelial tissues

Studying morphogenetic processes through traditional methods, such as observa-tion and experimentation, can be highly complex and laborious. Utilizing mathematical modeling methods makes it possible to analyze big data and uncover patterns that may be unnoticed when employing traditional approaches. In this study, a vertex mathemati-cal model of squamous epithelial tissue morphogenesis is proposed. The elementary unit of the system is the cell, which can dynamically change its shape and size. We in-troduce a new potential that accounts not only for the elasticity of cell perimeters and areas but also for the elasticity of their internal angles. Additionally, we introduce an inte-gral equation of chemical signaling, which allows for the consideration of chemo-mechanical cell-cell interactions. In addition to the above, the model incorporates im-portant processes of real epithelia, such as cell proliferation and intercalation. Based on the simulation results, a diagram of the system's principal states was constructed as a function of control parameters. A parameter range is identified within which the cellular system adopts the most energetically favorable and stable configurations. Furthermore, two processes occur in the early stages of morphogenesis, namely morula formation and blastula formation. This paper provides a detailed physical and mathematical description of these processes. The obtained results can be utilized in developing methods for influ-encing morphogenetic processes in medical applications.

Reticular poly(pyrrole methylene)s synthesized by synchronous-cross-linking process for the capture of Hg(ll) from water: Adsorption performance and mechanism

The development of novel high-capacity porous materials is critical to advancing the treatment of mercury-containing wastewater. In this study, two reticular poly(pyrrole methylene) adsorbent materials (PPB2E and PPD2E) were synthesized by a synchronous cross-linking method and successfully employed for Hg(II) adsorption in water. Their adsorption performance on Hg(II) in water was investigated. The results showed that PPB2E and PPD2E have large specific surface areas (535.43 m2/g and 523.23 m2/g, respectively) and are abundant microporous, with the molecular chains partially cross-linked and partially oxidized to form a conjugated structure. The adsorption of Hg(II) by the two adsorbents could reach equilibrium within 120 min, and the adsorption behavior followed the pseudo-second-order model. The adsorption isotherms were more in line with the Langmuir model, and the maximum adsorption capacities of PPB2E and PPD2E for Hg(II) were up to 1537.46 mg/g and 1511.94 mg/g (298 K, pH = 4), respectively. The two adsorbents exhibited excellent adsorption selectivity for Hg(II) in mixed metal salt solutions with good cycling stability. The primary adsorption mechanism of the synthesized materials for Hg(II) was jointly verified by characterization and DFT calculations: Hg(OH)2 molecules were adsorbed by forming hydrogen bonds with pyrrole N and carboxyl O in the adsorbents. Compared with other metal ions, the materials have more active sites for Hg(II) adsorption, higher utilization, and easier formation of stable adsorption configurations, thus exhibiting highly selective adsorption.

Metastability for the degenerate Potts Model with positive external magnetic field under Glauber dynamics

We consider the ferromagnetic q-state Potts model on a finite grid graph with non-zero external field and periodic boundary conditions. The system evolves according to Glauber-type dynamics described by the Metropolis algorithm, and we focus on the low temperature asymptotic regime. We analyze the case of positive external magnetic field associated to one spin value. In this energy landscape there is one stable configuration and q−1 metastable states. We study the asymptotic behavior of the first hitting time from any metastable state to the stable configuration as β→∞ in probability, in expectation, and in distribution. We also identify the exponent of the mixing time and find an upper and a lower bound for the spectral gap. Finally, we identify all the minimal gates and the tube of typical trajectories for the transition from any metastable state to the unique stable configuration by giving a geometric characterization.

Adsorption and formation energies of nucleobase–Fullerene: A first-principles simulation

A computational study was conducted using the density functional theory (DFT) method to determine the energy stability of a system composed of deoxyribonucleic acid/ribonucleic acid (DNA/RNA) nucleobase molecules on Fullerene C[Formula: see text] as a potential gene delivery system. The feasibility of the system for gene delivery and nanomedicine applications was assessed by examining the strong geometric bonds formed between Adenine, Cytosine, Guanine, Thymine, and Uracil nucleobases and C[Formula: see text]Si molecules in close proximity to Fullerene. The bonding affinities of each nucleobase with Fullerene were observed to follow the order Uracil > Guanine > Cytosine > Thymine > Adenine. Furthermore, calculations of adsorption and formation energies were performed to determine the most stable configuration within the Fullerene structure. Guanine demonstrated the highest stability, indicating its potential as an efficient carrier for the delivery of guanine-based genetic material into cells. Additionally, the Fullerene surface exhibited a high propensity for Cytosine adherence, as evidenced by the lowest adsorption energy observed for the interaction between Cytosine and Fullerene. The potential application of Si-doped Fullerene C60 as a gene delivery system was highlighted, based on the strong interactions observed with DNA/RNA nucleobase molecules. These valuable insights will contribute to the development of efficient gene delivery strategies and offer promising prospects for advancing gene therapy and nanomedicine.

A theoretical approach to the corrosion inhibition of iron in acidic solution by a green formulation derived from Nigella sativa L seeds oil

A theoretical approach combining density functional theory (DFT) computation, Monte Carlo (MC) methods, and molecular dynamics (MD) simulations was used to investigate and validate the iron corrosion inhibition performances in the acidic medium of a green formulation based on the oil extracted from Nigella sativa L. DFT calculations allowed to determine the energetic, global, and local chemical reactivity parameters. The most stable adsorption configuration of the fatty acids components of the Nigella sativa L. formulation was determined by the Monte Carlo methods with the adsorption locator module and by molecular dynamics simulations. Results indicated that all the compounds are absorbed with a totally flat orientation on the first layer of the metal surface.The active sites of molecules were effectively established by using DFT through the analysis of frontier molecular orbitals (FMO), the Hirshfeld population analysis (HPA), the electrostatic potential (ESP), molecular electron density analysis (MED), and Fukui indices (FI). The solvent effect was investigated by using the conductor-like polarizable continuum model (CPCM). Protonation effects were also analysed through the protonation energy (PE), the proton affinity (PA), and the absolute gas phase basicity (GB). The formation of a coating on the iron surface validated the good protective action of the green formulation derived from Nigella sativa L.The computational and theoretical approaches substantiate our experimental electrochemical and spectroscopic studies [1].

Electronic structure, magnetic and adsorption properties of monolayer chromium disulfide adsorbed by (non)-metals: A first-principles study

In this paper, the changes in the electronic structure, magnetic and adsorption properties induced by the adsorption of nine nonmetals (NMs) and twelve transition metals (TMs) on the monolayer CrS2 system have been investigated in the context based on the GGA+U methodology under the density-functional theory. The corresponding energetically most stable configurations were determined by calculating the formation energies for the four high-symmetry sites of each adsorption system. The atom adsorption induces a tunable electronic structure of the system, changing the surface structure and metallic properties of the monolayer CrS2. The system is made to show a wide variety of spintronic properties, such as narrow forbidden band semiconductors and semi-metals. Magnetically, the adsorbed atoms caused the redistribution of the electronic orbitals of the system, which formed local magnetic moments of different sizes at the adsorption sites and further caused the enhancement of the total magnetic moment of the system. The atom adsorption is expected to make monolayer CrS2 a potential spintronic material, which promotes the application of this material in nanoelectronics and spintronics.

The pragmatic cycle of knowledge work: Unlocking cross-domain collaboration in open innovation spaces

Collaborating is increasingly characterized by working across domains and organizations. Teams rapidly form and dissolve, actors and settings frequently change, yet most academic research focuses on stable organizations and team configurations with familiar domains. This leads to the question: how do people successfully collaborate across domains and organizations in circumstances where there is little shared knowledge? We explored this question within the nascent digital health sector when Hacking Health—a non-profit organization—used an open innovation approach to bring together actors from different domains and organizations in temporary spaces to spur new collaborations. We found that actors faced many challenges and engaged in four interconnected types of knowledge work to address them: exploring, complementing, mapping, and modeling. This article reveals how Hacking Health’s open innovation approach used different kinds of temporary spaces to progressively orient actors in their knowledge work to develop sustainable collaborations to create digital health solutions.

Toward boosted alkaline hydrogen evolution reaction: Covalent organic framework-derived N-doped carbon for highly dispersed cobalt nanoparticles

The preparation of renewable hydrogen via electrocatalytic water splitting is a burgeoning strategy in developing sustainable energy. However, it is still a great challenge to prepare an efficient non-precious metal based electrocatalyst for hydrogen evolution in alkaline electrolysis. Herein, we describe a functional hydrogen evolution reaction (HER) electrocatalyst by the combination of soaking metal ions in covalent organic framework (COF) and high temperature calcination. Especially, the 2Co-NC-700 catalyst possesses large specific surface area, appropriate defective nature and structural distortion, thus it embodies outstanding HER catalytic activity with only an overpotential of 303 mV at the current density of 10 mA cm−2 in the solution of 1.0 M KOH. Moreover, the kinetics and durability are also confirmed. Theoretical calculations not only indicates that the stable configuration combined small-sized cobalt nanoparticles and nitrogen-doped carbon but also reveals the synergistic effect of multiple active sites, while the optimal active location that shows the lowest hydrogen adsorption free energy is a major contributor for excellent HER. This work not only offers a highly efficient HER catalyst in alkaline environment but also provides a novel approach to develop non-precious metal nitrogen-doped carbon materials derived from COF as HER electrocatalysts in alkaline media.

Point defects, doping and the path to n-type SnTe

Point defects in SnTe were studied using first-principles modeling. Sn vacancies were found to be spontaneously formed in SnTe and make it intrinsically a p-type semiconductor, in excellent accord with experiments. The calculated electronic structure for Sn vacancy reveals that the Fermi level is shifted down into the valence band and presents p-type behavior. In contrast, the Fermi level shifts near the conduction band minimum (CBM) for Te vacancy and presents an n-type behavior. All the interstitial sites were considered for a comprehensive intrinsic point defect study. The body-centered (tetrahedral) site was found to be a stable interstitial configuration for Sn, whereas the split<111> interstitial was preferred for Te. We found that the electronic structures due to the interstitial configurations were distinct. Sn interstitials defects, Fermi level was shifted inside the conduction band for body interstitial, near to CBM for split 111 interstitial, whereas inside the bandgap for the base and split 110 interstitial defects. Contrary results were obtained for Te interstitial defects; the Fermi level was found inside the valence band for body interstitial, close to VBM for split 111, while the Fermi level was obtained inside the bandgap for base and split 110 interstitial defects. In addition, extrinsic oxygen impurities and other possible dopants that can transform SnTe to n-type were investigated. Interstitial oxygen was found to be stable at the body-interstitial site and is incorporated easily into the material in both Sn- and Te-rich environments, leading the material to p-type. The Fermi level was obtained inside the bandgap for oxygen substituted in Te vacancy and showed no preferred conductivity behavior. Finally, we find that Sb, Bi, and halogens (in Sn-rich conditions) can significantly improve electron concentrations and be promising dopants to transform the material's intrinsic conductivity from p-type to n-type. Notably, the sample should be prevented from incorporating oxygen impurities while doping sample n-type.

Highly efficient separation of phenol with tetraethylammonium chloride-based deep eutectic solvents: Experiments and theoretical calculations

To gain more insight into the mechanism of the separation of phenols by deep eutectic solvents (DESs), four DESs: tetraethylammonium chloride (TEAC)-ethylene glycol (EG), TEAC-diethylene glycol (DEG), TEAC-triethylene glycol (TEG) and TEAC-tetraethylene glycol (TTEG) were prepared for the extraction of phenols from model oil. Experimental parameter optimization results indicated that four DESs were effective in extracting phenols, and TEAC-EG had the highest extraction efficiency (EE), with EE up to 98.95%. Subsequently, the formation mechanism of DESs and the extraction mechanism were revealed at the molecular/atomic level by quantum calculations using density functional theory (DFT). The most stable configurations, hydrogen bonding lengths, and interaction energies of DESs and corresponding systems have been calculated, and the weak interactions in the systems were visualized and further analyzed. The results showed that DESs formation were mainly due to a combined effect of hydrogen bonding and van der Waals (vdW) forces. Besides, hydrogen bonding and vdW forces between DESs and phenol were the main forces acting to extract phenol, and the hydrogen bonding within DESs was weakened when DESs interacted with phenol.

Multiple retinal isomerizations during the early phase of the bestrhodopsin photoreaction

Bestrhodopsins constitute a class of light-regulated pentameric ion channels that consist of one or two rhodopsins in tandem fused with bestrophin ion channel domains. Here, we report on the isomerization dynamics in the rhodopsin tandem domains of Phaeocystis antarctica bestrhodopsin, which binds all-trans retinal Schiff-base (RSB) absorbing at 661 nm and, upon illumination, converts to the meta-stable P540 state with an unusual 11-cis RSB. The primary photoproduct P682 corresponds to a mixture of highly distorted 11-cis and 13-cis RSB directly formed from the excited state in 1.4 ps. P673 evolves from P682 in 500 ps and contains highly distorted 13-cis RSB, indicating that the 11-cis fraction in P682 converts to 13-cis. Next, P673 establishes an equilibrium with P595 in 1.2 µs, during which RSB converts to 11-cis and then further proceeds to P560 in 48 µs and P540 in 1.0 ms while remaining 11-cis. Hence, extensive isomeric switching occurs on the early ground state potential energy surface (PES) on the hundreds of ps to µs timescale before finally settling on a metastable 11-cis photoproduct. We propose that P682 and P673 are trapped high up on the ground-state PES after passing through either of two closely located conical intersections that result in 11-cis and 13-cis RSB. Co-rotation of C11=C12 and C13=C14 bonds results in a constricted conformational landscape that allows thermal switching between 11-cis and 13-cis species of highly strained RSB chromophores. Protein relaxation may release RSB strain, allowing it to evolve to a stable 11-cis isomeric configuration in microseconds.

Electronic structure of CeCu4In from band structure calculations and X-ray photoelectron spectroscopy

We present a combined new experimental and theoretical study of the electronic structure for the heavy fermion CeCu4In based on X-ray photoelectron spectroscopy (XPS) data and ab-initio band structure calculations. The compound crystallizes in the orthorhombic CeCu4.38In1.62 type of structure (space group Pnnm). Below the Fermi energy the total density of states contains mainly 3d–states of Cu atoms that hybridized with the Ce 4f electronic states. The Ce core-level XPS spectra point to a stable trivalent configuration of Ce atoms in CeCu4In, consistently with the magnetic susceptibility data. For more detailed information about electronic states the fully relativistic band structure was calculated within the density functional theory (DFT) for the first time. Based on these calculations we present calculated photoemission spectra, which very well reproduce the experimental ones. The Fermi level is located at a deep decrease in the density of electronic states and reaches a value of 3.69 states/(eV f.u.). This value is much smaller than the one obtained experimentally, which indicates the importance of many-body effects, which are not properly taken into account in ab-initio calculations. The valence band is formed mainly by Cu(3d) electrons with a small contribution of Ce(4f) electrons in the immediate vicinity of the Fermi level.

Periodic DFT calculations for the heterogeneous formation of 2-chlorothiophenoxy radical from 2-chlorothiophenol on Cu(111) surface in fly ash

Copper plays a crucial role in the heterogenous dissociation of chlorothiophenols (CTPs) to form chlorothiophenoxy radicals (CTPRs), which is the initial and critical step in the formation of polychlorinated thianthrenes/dibenzothiophenes (PCTA/DTs). Here, first-principles calculations were performed to investigate the activity of Cu(111) surface towards the formation of adsorbed 2-CTPR from 2-CTP. The interaction between 2-CTP and Cu(111) surface was explored to find stable adsorption configurations. Besides, the decomposition routes of 2-CTP on the Cu(111) surface were further explored. Moreover, the effects of water on the formation of absorbed 2-CTPR on the Cu(111) surface were examined. Our results demonstrate that the flat adsorption of 2-CTP on the surface with adsorption energy in the range of −33.21 kcal/mol to −28.37 kcal/mol is more stable than the vertical adsorption with adsorption energy ranging from −23.53 kcal/mol to −13.38 kcal/mol. The Cu(111) surface catalyzes the conversion of 2-CTP into the adsorbed 2-CTPR with a modest energy barrier of 9.46 kcal/mol. Furthermore, water molecules exhibit stronger catalytic activity in this process with a decreased energy barrier of 5.87 kcal/mol through “water bridge” and hydrogen bonding. Specifically, the water accepts the hydrogen atom from 2-CTP and donates another hydrogen to the surface via “water bridge”. This research provides a molecular-level understanding of the heterogeneous formation of PCTA/DTs by fly ash, suggesting novel approaches for control strategy and legislation of dioxin analogues.

Symmetries of the Large Scale Structures of the Universe as a Phenomenology of a Fractal Turbulence: The Role of the Plasma Component

We present a new perspective on the symmetries that govern the formation of large-scale structures across the Universe, particularly focusing on the transition from the seeds of galaxy clusters to the seeds of galaxies themselves. We address two main features of cosmological fluid dynamics pertaining to both the linear and non-linear regimes. The linear dynamics of cosmological perturbations within the Hubble horizon is characterized by the Jeans length, which separates stable configurations from unstable fluctuations due to the gravitational effect on sufficiently large (and therefore, massive enough) overdensities. On the other hand, the non-linear dynamics of the cosmological fluid is associated with a turbulent behavior once the Reynolds numbers reach a sufficiently high level. This turbulent regime leads to energy dissipation across smaller and smaller scales, resulting in a fractal distribution of eddies throughout physical space. The proposed scenario suggests that the spatial scale of eddy formation is associated with the Jeans length of various levels of fragmentation from an original large-scale structure. By focusing on the fragmentation of galaxy cluster seeds versus galaxy seeds, we arrived at a phenomenological law that links the ratio of the two structure densities to the number of galaxies in each cluster and to the Hausdorff number of the Universe matter distribution. Finally, we introduced a primordial magnetic field and studied its influence on the Jeans length dynamics. The resulting anisotropic behavior of the density contrast led us to infer that the main features of the turbulence could be reduced to a 2D Euler equation. Numerical simulations showed that the two lowest wavenumbers contained the major energy contribution of the spectrum.

Influence of structural modifications on mechanical and magnetic properties of Co2FeGa full Heusler alloys: A comparative study on L21 and XA structures

In this study we are investigating the effect of pressure and tetragonal distortion of Co2FeGa full Heusler compound in L21 and XA structures on the elastic, magnetic and thermomagnetic properties. Our approach for this is by using density functional theory (DFT) and Monte Carlo (MC) simulation. Our result reveals a significant effect of pressure on the magnetization and Curie temperature on both prototypes. The elastic constants calculated here determine the stable configuration on both structures. The exchange interaction is also influenced by the pressure. The same sort of behavior of the effect of tetragonal distortion is seen on the elastic constants, magnetization, and exchange interaction. Therefore, a detailed significant effect is found in this work and compared to previous studied.

A DFT investigation of hydrazine nitrate dissociation mechanism on MoN(0 0 1)

Hydrazine nitrate (HN) is an important additive for hydrazine-based monopropellant. In this work, density functional theory (DFT) was adopted to calculate the decomposition process of HN components on MoN (001) catalyst surface. Firstly, two stable adsorption configurations of hydrazine nitrate were identified and determined the catalytic decomposition pathway of the thermodynamically favorable configuration. Pathway analysis revealed that the nitric acid group preferentially decomposes in all pathways. Moreover, due to the high activation and desorption energies, H2O molecules are more likely to be generated in the gas phase rather than preferentially adsorbed on the surface. By calculating the activation energies of each elementary reaction, it can be concluded that the cleavage of the NO bond in NO3– with the barrier energy of 0.32 eV plays a decisive role in the decomposition of the HN molecule.

Mechanical logic gate design based on multi-stable metamaterial with multi-step deformation

Mechanical metamaterials exhibit remarkable design versatility, enabling a series of unconventional mechanical properties via structural modifications. However, it is worth noting that many existing mechanical metamaterials either possess a singular deformation path or only multi-step deformation paths without reusability. This study proposes a novel multi-step deformation metamaterial that possesses multiple stable configurations. This metamaterial produces a unique two-step deformation mode under displacement loading, where the curved beams of the unit cells undergo snap-through and the vertical beams buckling. The influence of geometrical parameters on the multistability of the structure is thoroughly examined, and a theoretical prediction model for the buckling load is formulated. To validate the accuracy of the model, experimental tests and finite element simulations are conducted on the two-step deformation mode of periodic array of the unit cell. Additionally, a bi-material design approach for the unit cell is further introduced to enhance the specific energy absorption of the structure while reinforce the negative stiffness effect. Leveraging the multistable characteristics of the structure, mechanical logic gates such as AND, OR, NOT and NAND are conceptualized and experimentally validated. Through the implementation of rational designs and combinatorial connections within the logic gate structure, more complex logic operations can be realized.

Systematic study of the structure-property relationship of C24N24 nanoclusters for the detection and electrochemical sensing of chemical warfare agents: Molecular modelling at DFT level

Chemical warfare agents (CWAs) are highly poisonous and dangerous to all forms of life. Their rapid discovery and removal are crucial for the protection of people and the environment. Current technology still falls short of the 100 % efficiency threshold. Therefore, we make use of the efficient three-dimensional C24N24-nanostructured material for the rapid detection and electrochemical sensing of CWAs phosgene (COCl2) and thiophosgene (CSCl2) by employing benchmark DFT and TD-DFT investigations. Nine stable configurations of C24N24 nanocluster were quantum chemically designed facing through chlorine, oxygen, sulphur atoms of phosgene and thiophosgene and with their planar orientations on the large and small cavities of the nanocluster. Optimization of geometry, FMO, adsorption energies, NBO, QTAIM, and NCI, were the methods for evaluating the interaction between chemical warfare agents and the nanocluster. Fine-tuning of electronic properties; recovery time (∼3 × 10−14s−1), electrical conductivity (∼1.84 × 109), sensitivity (∼0.050), electrophilicity index (1.76–1.68 eV), hardness (3.52–3.37 eV), softness (∼0.15 eV), energy gap (2.85–2.55 eV), and interaction distance (4.274±1.245A0), values ascertain the elevated reactivity and an imperishable sensitivity of the C24N24 nanocluster towards the investigated CWAs. The energy gap, QTAIM, NCI, sensitivity, and recovery time analysis confirmed that the Pl*@C24N24-SC nanostructured material developed as the most suited surface for the effective finding of phosgene and Pl@C24N24-LC for thiophosgene. Adsorption energies of −8.490 and -8.507 kcal/mol for the Pl*@C24N24-SC and Pl@C24N24-LC complexes, respectively, were the deciding factors. The C24N24 nanocluster has the highest sensitivity and shortest recovery time for S@C24N24-LC and Pl@C24N24-LC complex with the value of 0.0509 and 3.23 × 10−14s−1 which shows the potential of C24N24 nanocluster as a promising influential sensing material to monitor CWAs phosgene and thiophosgene. This theoretical framework will assist experimentalists in detecting toxic CWAs by using C24N24 nanocluster-based sensor.