Time-resolved Emission Research Articles

L-Phenylalanine Partitioning Mechanisms in Model Biological Membranes.

Time-resolved fluorescence spectroscopy in combination with differential scanning calorimetry (DSC) was used to study the chemical interactions that occur when l-phenylalanine is introduced to solutions containing phosphatidylcholine vesicles. Studies reported in this work address open questions about l-Phe's affinity for lipid vesicle bilayers, the effects of l-Phe partitioning on bilayer properties, l-Phe's solvation within a lipid bilayer, and the amount of l-Phe within that local solvation environment. DSC data show that l-Phe reduces the amount of heat necessary to melt saturated phosphatidylcholine bilayers from their gel to liquid-crystalline state but does not change the transition temperature (Tgel-lc). Time-resolved emission shows only a single l-Phe lifetime at low temperatures corresponding to l-Phe remaining solvated in aqueous solution. At temperatures close to Tgel-lc, a second, shorter lifetime appears that is assigned to l-Phe already embedded within the membrane that becomes hydrated as water starts to permeate the lipid bilayer. This new lifetime is attributed to a conformationally restricted rotamer in the bilayer's polar headgroup region and accounts for up to 30% of the emission amplitude. Results reported for dipalmitoylphosphatidylcholine (DPPC, 16:0) lipid vesicles prove to be general, with similar effects observed for dimyristoylphosphatidylcholine (DMPC, 14:0) and distearoylphosphatidylcholine (DSPC, 18:0) vesicles. Taken together, these results create a complete and compelling picture of how l-Phe associates with model biological membranes. Furthermore, this approach to examining amino acid partitioning into membranes and the resulting solvation forces points to new strategies for studying the structure and chemistry of membrane-soluble peptides and selected membrane proteins.

Insights into the Strong Emission Enhancement of Molecular Rotor Thioflavin T in Aqueous Cellulose Nanocrystal Dispersion: White Light Generation in Protein and Micellar Media.

Thioflavin t (THT) is a well-known molecular rotor extensively used to detect amyloid-like structures. But THT shows very weak emission in water. In this article, we have found that THT shows very strong emission in the presence of cellulose nanocrystals (CNCs). Steady-state and time-resolved emission techniques have been used to study the strong emission of THT in aqueous CNC dispersion. The time-resolved study showed that in the presence of CNCs, the lifetime increased by ∼1500 fold compared to pure water (<1 ps). To know the nature of interaction and also the reason for this increase in emission zeta potential, stimuli-dependent and temperature-dependent studies have been carried out. These studies proposed that electrostatic interaction is the main factor for this binding of THT with CNCs. Further, the addition of another anionic lipophilic dye, merocyanine 540 (MC540), with CNCs-THT in both BSA protein (CIE: 0.33, 0.32) and TX-100 micellar (4.5 mM) (CIE: 0.32, 0.30) solutions produced excellent white light emission. Lifetime decay and absorption studies proposed a possible fluorescence resonance energy transfer mechanism in this generation of white light emission.

Population inversion mechanism of optically pumped metastable rare gas based on laser-induced preionization

A 532 nm laser was used to induce ionization of Ar–He mixture, and metastable 4s [3/2]2 level Ar atoms were prepared. The interaction mechanism between laser, Ar atoms, He atoms and free electrons in laser-induced plasma (LIP) was revealed. Through time-resolved atomic emission spectroscopy, two regimes separated by a few microseconds were found during temporal evolution of Ar I 811.5 nm (4p [5/2]3→4s [3/2]2) line. It was demonstrated that the first regime was generated by the “photoexcitation + radiation + collisional relaxation” process, while the second regime was generated by the “ion-electron recombination” process. The above conclusion was confirmed again by the temporal evolution of electron temperature and electron density, and it was also demonstrated that the ionization of Ar atoms induces the ionization of He atoms. A 811.5 nm laser was utilized to excite the metastable 4s [3/2]2 level Ar atoms to the 4p [5/2]3 level, when changing the delay time of the 811.5 nm laser lagging behind the 532 nm laser, the generated 912.3 nm (4p [1/2]1→4s [3/2]2) fluorescence intensity also showed different pattern of variations. The analysis indicated that “photoexcitation + radiation + collisional relaxation”, “ion-electron recombination” and quenching processes will affect the density of metastable 4s [3/2]2 level Ar atoms. Amplified spontaneous emission (ASE) signal at 912.3 nm was obtained along the direction of pump laser. This work verifies the feasibility of optically pumped metastable rare gas laser (OPRGL) based on laser-induced preionization, and provides an alternative scheme for the future development of OPRGL.

SO 2 emissions during the 2021 eruption of La Soufrière, St Vincent, revealed with back-trajectory analysis of TROPOMI imagery

Abstract Determining SO 2 emission time-series from explosive eruptions can provide important insights into the driving magmatic processes, however accurate measurements are difficult to collect. Satellite-based platforms provide SO 2 imagery, however translating this to the altitude- and time-resolved emission history required to unravel volcanic processes is a major challenge. This means SO 2 emission time-series are rarely quantified for major eruptions, producing a gap in our understanding of explosive volcanism. Here, we combine SO 2 imagery collected by the TROPOspheric Monitoring Instrument (TROPOMI) with PlumeTraj, a back-trajectory analysis toolkit, to reconstruct the SO 2 emission prior to, and during, the explosive eruption of La Soufrière volcano, St Vincent, in April 2021. Precursory SO 2 emissions were quantified the day before the eruption, with emission rates in agreement with ground-based measurements. We estimate initial magma sulfur contents by comparing the measured SO 2 emissions with erupted magma volumes, finding that the initial explosion was sulfur poor (730 ppm S) compared to the main eruption phase (up to 3400 ppm S). This suggests that the initial explosion cleared old, previously degassed magma resident in the shallow plumbing system, followed by the eruption of the main, mostly un-degassed magma source.

One-Pot Three Component Synthesis of Quinazolin-4(3H)-One Derivatives: Investigation of Photophysical Properties and FRET Application toward Protein Lysozyme

A one-pot, three-component reaction between isatoic anhydride, 1,3-diketones, and amines/arylhydrazines catalyzed by a combination of molecular I2 and Et3N in open-air affords a series of quinazolin-4(3H)-one derivatives in good yield. The protocol offers an operationally simple, facile, and cost-effective pathway utilizing easily accessible reagents under mild reaction conditions with significant substrate scope. The results of steady state and time-resolved absorption and emission spectroscopy indicate the potential of quinazolin-4(3H)-one derivatives as a fluorescence probe. They exhibit unique photophysical responses in different solvent environments. In addition, they can also act as FRET acceptors during interaction with protein lysozyme. Preliminary biological studies indicate that quinazolin-4(3H)-ones are cell permeable and can be used as a fluorescent probe for bio-imaging of human cervical cancer (HeLa) cells.

Study on luminescent performance of Dy3+-, Tb3+-doped and Tb3+/Dy3+ co-doped TeO2-(Gd,Lu)2O3-WO3 glass scintillators

Three series of Dy3+-, Tb3+-doped and Tb3+/Dy3+ co-doped 40TeO2-20(Gd,Lu)2O3–40WO3 glasses with density of about 6.75 g/cm3 were successfully prepared by high temperature melt-quenching method. The luminescence properties of these rare earth ions doped 40TeO2-20(Gd,Lu)2O3–40WO3 glass were systematically studied by transmittance, photoluminescence (excitation and emission spectra), time-resolved emission spectra (TRES) and X-ray excited luminescence (XEL) spectra, together with the luminescence decay curves. The optimal doping concentration of Dy3+ and Tb3+ ions in 40TeO2-20(Gd,Lu)2O3–40WO3 glasses was determined under UV and X-ray excitation, respectively. It is found there is an efficient energy transfer from Dy3+ to Tb3+ ions in 40TeO2-20(Gd,Lu)2O3–40WO3 glass in photoluminescence spectra. However, it is not true under X-ray excitation due to the complicated physical process.

Non-Phenomenological Description of the Time-Resolved Emission in Solution with Quantum-Classical Vibronic Approaches-Application to Coumarin C153 in Methanol.

We report a joint experimental and theoretical work on the steady-state spectroscopy and time-resolved emission of the coumarin C153 dye in methanol. The lowest energy excited state of this molecule is characterized by an intramolecular charge transfer thus leading to remarkable shifts of the time-resolved emission spectra, dictated by the methanol reorganization dynamics. We selected this system as a prototypical test case for the first application of a novel computational protocol aimed at the prediction of transient emission spectral shapes, including both vibronic and solvent effects, without applying any phenomenological broadening. It combines a recently developed quantum-classical approach, the adiabatic molecular dynamics generalized vertical Hessian method (Ad-MD|gVH), with nonequilibrium molecular dynamics simulations. For the steady-state spectra we show that the Ad-MD|gVH approach is able to reproduce quite accurately the spectral shapes and the Stokes shift, while a ∼0.15 eV error is found on the prediction of the solvent shift going from gas phase to methanol. The spectral shape of the time-resolved emission signals is, overall, well reproduced, although the simulated spectra are slightly too broad and asymmetric at low energies with respect to experiments. As far as the spectral shift is concerned, the calculated spectra from 4 ps to 100 ps are in excellent agreement with experiments, correctly predicting the end of the solvent reorganization after about 20 ps. On the other hand, before 4 ps solvent dynamics is predicted to be too fast in the simulations and, in the sub-ps timescale, the uncertainty due to the experimental time resolution (300 fs) makes the comparison less straightforward. Finally, analysis of the reorganization of the first solvation shell surrounding the excited solute, based on atomic radial distribution functions and orientational correlations, indicates a fast solvent response (≈100 fs) characterized by the strengthening of the carbonyl-methanol hydrogen bond interactions, followed by the solvent reorientation, occurring on the ps timescale, to maximize local dipolar interactions.

Impact of Bidentate Pyridyl-Mesoionic Carbene Ligands: Structural, (Spectro)Electrochemical, Photophysical, and Theoretical Investigations on Ruthenium(II) Complexes.

We present here new synthetic strategies for the isolation of a series of Ru(II) complexes with pyridyl-mesoionic carbene ligands (MIC) of the 1,2,3-triazole-5-ylidene type, in which the bpy ligands (bpy = 2,2'-bipyridine) of the archetypical [Ru(bpy)3]2+ have been successively replaced by one, two, or three pyridyl-MIC ligands. Three new complexes have been isolated and investigated via NMR spectroscopy and single-crystal X-ray diffraction analysis. The incorporation of one MIC unit shifts the potential of the metal-centered oxidation about 160 mV to more cathodic potential in cyclic voltammetry, demonstrating the extraordinary σ-donor ability of the pyridyl-MIC ligand, while the π-acceptor capacities are dominated by the bpy ligand, as indicated by electron paramagnetic resonance spectroelectrochemistry (EPR-SEC). The replacement of all bpy ligands by the pyridyl-MIC ligand results in an anoidic shift of the ligand-centered reduction by 390 mV compared to the well-established [Ru(bpy)3]2+ complex. In addition, UV/vis/NIR-SEC in combination with theoretical calculations provided detailed insights into the electronic structures of the respective redox states, taking into account the total number of pyridyl-MIC ligands incorporated in the Ru(II) complexes. The luminescence quantum yield and lifetimes were determined by time-resolved absorption and emission spectroscopy. An estimation of the excited state redox potentials conclusively showed that the pyridyl-MIC ligand can tune the photoredox activity of the isolated complexes to stronger photoreductants. These observations can provide new strategies for the design of photocatalysts and photosensitizers based on MICs.

Optical and electrical investigation of plasma generated by high-energy self-stabilized spark ignition system

Spark discharge plasma is commonly used for ignition in internal combustion engines. The environmental performance of internal combustion engines with forced ignition is improved when operating under lean mixture conditions. High-energy ignition systems are needed to ensure reliable ignition of lean mixtures. The ignition of a combustible mixture is influenced by several plasma parameters, such as the temperature of its various components, the size of the plasma, and the deposited energy. It is, therefore, beneficial to know these parameters. Here, we present optical and electrical investigation of plasma generated in ambient air by a novel high-energy self-stabilized spark ignition system. The electrical investigation showed two high current pulses, with the current amplitude of ∼40 and ∼150 A. The energy is deposited to the spark gap mainly during the second current pulse, and it is increasing from 213 to 541 mJ with the increasing gap size from 3 to 13 mm. The energy efficiency increases with the gap as well, from around 23% to 58%. Time-resolved emission spectra enabled us to estimate the evolution of the gas temperature, electron excitation temperature, and electron density in the generated plasma. It was found that the highest electron density, 3–4 × 1017 cm−3, correlates with the maximum of the second pulse current. We observed a specific plasma evolution between the two current pulses, with an increase in temperature from 4500 to 7500 K and a contraction of the plasma channel diameter from 3.3 to 0.5 mm.

Time-resolved plasma diagnostics of cathodic cage plasma nitriding system with variable pulsed duty cycle and surface modification of plain carbon steel

Cathodic cage plasma nitriding (CCPN) is an efficient technique to improve the surface properties of metallic and non-metallic materials, including steels. Usually, CCPN is powered by pulsed voltage sources due to additional control of the nitrided layer's thickness and composition as well as the discharge transition to the arc region can be controlled by varying the pulsed duty cycle. As the behavior of pulsed plasma varies with time, it is important to monitor variation in plasma parameters by using time-resolved plasma diagnostics. Unfortunately, the fundamental time-resolved diagnostics of such discharges are still very limited. Here, we report time-resolved measurements of current, voltage, plasma emission, space, and time-resolved emission from a single hole in the cathode as a function of pulsed duty cycle (15–75 %) at constant total current. The results show that the electron temperature is higher if a higher peak current and the shortest 15 % pulsed duty cycle are used. The results obtained from plasma diagnostics are confirmed by treatment of plain carbon steel samples in identical conditions and found that the best hardness, wear, and corrosion resistance is obtained at the lowest pulsed duty cycle. The study suggests that plasma generated at a low pulsed duty cycle and a higher peak discharge current exhibits higher electron temperature and less fluctuations in plasma emission which are more efficient in attaining high surface hardness, better wear, and corrosion resistance to nitride plain carbon steel.

Spin-Momentum Locking and Ultrafast Spin-Charge Conversion in Ultrathin Epitaxial Bi1 - x Sbx Topological Insulator.

The helicity of three-dimensional (3D) topological insulator surface states has drawn significant attention in spintronics owing to spin-momentum locking where the carriers' spin is oriented perpendicular to their momentum. This property can provide an efficient method to convert charge currents into spin currents, and vice-versa, through the Rashba-Edelstein effect. However, experimental signatures of these surface states to the spin-charge conversion are extremely difficult to disentangle from bulk state contributions. Here, spin- and angle-resolved photo-emission spectroscopy, and time-resolved THz emission spectroscopy are combined to categorically demonstrate that spin-charge conversion arises mainly from the surface state in Bi1 - x Sbx ultrathin films, down to few nanometers where confinement effects emerge. This large conversion efficiency is correlated, typically at the level of the bulk spin Hall effect from heavy metals, to the complex Fermi surface obtained from theoretical calculations of the inverse Rashba-Edelstein response. Both surface state robustness and sizeable conversion efficiency in epitaxial Bi1 - x Sbx thin films bring new perspectives for ultra-low power magnetic random-access memories and broadband THzgeneration.

Luminescence properties of Pr3+ doped Bi4Ge3O12 crystal fibers grown by the micro-pulling down technique

The luminescence properties of 0.5%Pr-doped BGO crystals grown by using the micro-pulling down technique were carefully investigated. Room temperature absorption spectra were registered and analyzed within the framework of the Judd-Ofelt formalism and the best fit to the data is obtained by using a modified treatment allowing for the admixture of intensity enabling wave-functions. The results indicate 3P0 and 1D2 radiative lifetimes of about 5.7 μs and 79 μs, in perfect agreement with the time-constants derived from the measured fluorescence decays at room and liquid-nitrogen temperatures. Registration of time-resolved emission and excitation spectra and calibration of the 3P0 emission spectrum in cross section unit clearly indicate that Pr-doped BGO could be the first isotropic crystalline material leading to efficient diode-pumped laser operation at room temperature with laser performances, at least in the deep-red spectral region, comparable to that found with the most important anisotropic Pr-doped fluoride and oxide crystals.

D-Band Hole Dynamics in Gold Nanoparticles Measured with Time-Resolved Emission Upconversion Microscopy.

The performance of photocatalysts and photovoltaic devices can be enhanced by energetic charge carriers produced from plasmon decay, and the lifetime of these energetic carriers greatly affects overall efficiencies. Although hot electron lifetimes in plasmonic gold nanoparticles have been investigated, hot hole lifetimes have not been as thoroughly studied in plasmonic systems. Here, we demonstrate time-resolved emission upconversion microscopy and use it to resolve the lifetime and energy-dependent cooling of d-band holes formed in gold nanoparticles by plasmon excitation and by following plasmon decay into interband and then intraband electron-hole pairs.

Influence of the pulse polarity on micro-hollow cathode helium plasma jet

Helium plasma jets generated by micro-hollow cathode discharge (MHCD) with the square-wave power source of different polarities are investigated in this work. The effects of positive and negative polarity pulses on the MHCD and plasma jet were compared, and the time-resolved optical emission spectra of excited species ( and O) were studied. The results confirm that the electric field is a key factor for the propagation of the jet during the rising edge of the positive current pulse, while the gas expansion is mainly important for the jet propagation during the current stable phase. The time-resolved spectra show that the generation of specie O in the jet-driven by the electric field is more efficient.

Ultrafast multiexciton dynamics in molecular systems: Inclusion of exciton-exciton annihilation

We report simulations of exciton-exciton annihilation (EEA) in dye molecular aggregates with explicit laser pulse excitation in the framework of reduced density matrix theory. We use a supramolecular complex model Hamiltonian, in which each monomer of an aggregate is described by three electronic levels. An expectation value approximation is used to avoid the large amount of matrix elements for various exciton configuration distributions in molecular aggregates. Quantum fluctuations truncation is applied to derive the closed equations of motion for single- and two-site functions. Using these equations, we simulate the laser pulse driven EEA dynamics, and compare it with rate equations to highlight the importance of quantum coherence effects. We also discuss the effects of the aggregate configuration, the molecular transition dipoles and the duration of laser pulses on EEA. Furthermore, we analyze the relation between the coherence time of fusion and the annihilation process. Our study indicates that EEA process is more efficient for coherent excitation at the lowest energy level in J aggregates. Our simulation of the normalized population of the first excited state for various field amplitudes can qualitatively reproduce time-resolved experimental emission spectra. This confirms that the fundamental description of laser pulse induced EEA is correct within our model.

Influence of Thermal Maturity on the Time-Resolved Emission Spectrum (TRES) Fluorescence Lifetime Characteristics of Crude Oils: A Preliminary Study Based on a Thermal Simulation Experiment of Crude Oils

The time-resolved emission spectrum (TRES) fluorescence lifetime characteristics of crude oil have great application potential to classify the oil type and reveal its origin in a multisource petroleum system. However, the influence of thermal maturity on the TRES fluorescence lifetime characteristics of crude oil is still unclear. This study collected typical crude oil samples from deep reservoirs in the Tabei area of the Tarim Basin and obtained a group of pyrolyzed oils with different maturities by a thermal simulation experiment. The TRES average fluorescence lifetime value (τA) and profile pattern (λ–τ) of both pyrolyzed and crude oil samples were investigated. The results indicate that, with increasing maturity, the τA values of pyrolyzed oil slightly increase when EasyRo < 0.90% but decrease when EasyRo > 0.90%. Meanwhile, the λ–τ pattern shows no obvious changes when EasyRo < 1.53% but changes significantly when EasyRo > 1.53%. Based on the TRES fluorescence lifetime characteristics, the deep crude oils in various blocks of the Tabei area are divided into TB-I and TB-II types, which correspond well with their physical properties, diagnostic biomarkers, and carbon isotopic values. The TB-I crude oils are widely distributed in the Shunbei, Hadexun, Repu, and Halahatang blocks. This type of crude oil has a short τA value and exhibits an obvious platform pattern in its λ–τ profile. The TB-II crude oils are distributed only in the Yuke block. This type of crude oil has a long τA value and shows a unimodal pattern in its λ–τ profile. The TRES fluorescence lifetime parameters can effectively classify crude oils with different sources and can further identify the thermal maturity of crude oils with the same sources by combining them with the physical and geochemical parameters of crude oils, which exhibits great application potential to crude oils and individual petroleum inclusions in deep multisource petroleum systems.

Contrasting complexation behaviour of zwitterionic amyloid probe, SYPRO orange with β-cyclodextrin and captisol

The differential complexation studies with cyclodextrins and their charged derivatives have been well studied using cationic, anionic, as well as neutral guest molecules. However, supramolecular complexation with zwitterionic guest molecules is quite limited. Zwitterions are overall neutral molecules with localized charges that can offer additional site-specific electrostatic interaction with cyclodextrins as compared to neutral guest molecules. There is no information on how the different intra- and intermolecular interactions can modulate the binding of a zwitterion with a macrocyclic host. Herein, the supramolecular interactions of biologically important zwitterionic amyloid probe, SYPRO Orange (SO) with β-cyclodextrin (β-CD) and sulfobutylether β-cyclodextrin (SBE-β-CD, Captisol®) have been evaluated and compared using different spectroscopic methods. SO forms inclusion complexes with both β-CD and SBE-β-CD which led to the enhanced fluorescence along with a hypsochromic shift in its emission spectra. It has been shown that the presence of segmental rotation in a guest molecule with charge transfer property favours its association with the macromolecules. The fluorescence enhancement and the binding affinities show contrasting behavior in these two types of host–guest complexes. Time-resolved emission measurements could disentangle the contribution from different inclusion complexes. Ionic strength and temperature variation in the photophysical properties helped to understand the molecular interactions involved in such contrasting behavior.

Tantalum oxide and nitride spectral features from a laser-produced plasma

We report measurements of time-resolved Ta, TaO and TaN emission spectroscopic signatures from a laser-produced plasma. Plasmas were generated using 1064 nm, 6 ns pulses from an Nd:YAG laser focused onto a pure Ta metal target in a gaseous environment with varying percentages of O2/N2 for controlling gas-phase oxidation/plasma chemistry. Time-resolved analysis showed that Ta oxide emission is prominent at later times in plasma evolution, whereas strong atomic emission is present at early times in air. Emission spectral features as a function of O2 partial pressure showed that TaO emission intensity increases, while the peak intensity of TaO appears earlier with increasing O2 availability. We also report emission spectra of TaN, and show that plasma chemistry favors TaO formation instead of TaN when O2 is present in the environment.

Ultrafast motion in a third generation photomolecular motor

Controlling molecular translation at the nanoscale is a key objective for development of synthetic molecular machines. Recently developed third generation photochemically driven molecular motors (3GMs), comprising pairs of overcrowded alkenes capable of cooperative unidirectional rotation offer the possibility of converting light energy into translational motion. Further development of 3GMs demands detailed understanding of their excited state dynamics. Here we use time-resolved absorption and emission to track population and coherence dynamics in a 3GM. Femtosecond stimulated Raman reveals real-time structural dynamics as the excited state evolves from a Franck-Condon bright-state through weakly-emissive dark-state to the metastable product, yielding new insight into the reaction coordinate. Solvent polarity modifies the photoconversion efficiency suggesting charge transfer character in the dark-state. The enhanced quantum yield correlates with suppression of a low-frequency flapping motion in the excited state. This detailed characterization facilitates development of 3GMs, suggesting exploitation of medium and substituent effects to modulate motor efficiency.

Novel Sol-Gel Route to Prepare Eu3+-Doped 80SiO2-20NaGdF4 Oxyfluoride Glass-Ceramic for Photonic Device Applications.

Oxyfluoride glass-ceramics (OxGCs) with the molar composition 80SiO2-20(1.5Eu3+: NaGdF4) were prepared with sol-gel following the "pre-crystallised nanoparticles route" with promising optical results. The preparation of 1.5 mol % Eu3+-doped NaGdF4 nanoparticles, named 1.5Eu3+: NaGdF4, was optimised and characterised using XRD, FTIR and HRTEM. The structural characterisation of 80SiO2-20(1.5Eu3+: NaGdF4) OxGCs prepared from these nanoparticles' suspension was performed by XRD and FTIR revealing the presence of hexagonal and orthorhombic NaGdF4 crystalline phases. The optical properties of both nanoparticles' phases and the related OxGCs were studied by measuring the emission and excitation spectra together with the lifetimes of the 5D0 state. The emission spectra obtained by exciting the Eu3+-O2- charge transfer band showed similar features in both cases corresponding the higher emission intensity to the 5D0→7F2 transition that indicates a non-centrosymmetric site for Eu3+ ions. Moreover, time-resolved fluorescence line-narrowed emission spectra were performed at a low temperature in OxGCs to obtain information about the site symmetry of Eu3+ in this matrix. The results show that this processing method is promising for preparing transparent OxGCs coatings for photonic applications.