Decay Time Values Research Articles

Synthesis and photoluminescence properties of Ba2CaZn2Si6O17:Tb3+ green phosphor

Ba2Ca1−xZn2Si6O17:xTb3+ green emitting phosphors with different concentrations (x=0.01, 0.03, 0.06, 0.08, 0.10, 0.15 and 0.20) of Tb3+ ions were synthesized using solid state reaction method. The phase composition of the synthesized phosphors was confirmed by powder X-ray diffraction (PXRD). The morphology was studied using scanning electron microscope (SEM). The excitation and emission spectra were measured to characterize the photoluminescence properties. The optimum Tb3+ concentration in this phosphor was 10mol%. The Tb–Tb critical distance was calculated to be ∼19.6Å. The dipole–dipole interaction dominates in the non-radiative energy transfer between the Tb3+ ions and causes the concentration quenching. The decay time value of the Ba2CaZn2Si6O17:0.10Tb3+ phosphor is about 4.86ms. The CIE coordinates were calculated as x=0.242, y=0.383. The quantum efficiency for x=0.10 sample excited by 240nm is 14.3%.

Influence of SiO2 on the Luminous Properties of Nd3+-Doped Barium Silicophosphate Nanostructured Glasses

Barium phosphate glasses with high glass transition temperature, which belong to alkali-free glasses, are valuable candidates for application in high-power laser glasses. With the introduction of SiO2 content, the thermal properties, refractive index, and mechanical properties of these glasses can be improved, while the effects that silica exerts on the structure and luminous properties of the glasses are still in need of further study. Herein, the structure and the luminous properties, containing transmittance and fluorescence properties, of Nd3+-doped barium silicophosphate glasses are studied. It is notable that both the maximum values of luminous intensity and luminous decay time appear at the composition of 26.7 mol% of SiO2, a composition which also possesses the largest ultraviolet end edge redshift. The maximum percentage of bridging oxygen (BO) is also found at this composition, which is quantified by X-ray photoelectron spectroscopy (XPS). And both the luminous intensity and luminous decay time of these glasses appear in positive correlations with the number of bridging oxygen of the glass matrix. Thus, a method to improve the luminous properties of the barium phosphate glasses through changing the local chemistry state of the dopants by introducing SiO2 content is proposed. The optimized composition found in this paper would be useful throughout the wide field of optics.

Abstract 15489: Altered Biomechanical Properties of PKP2-deficient Hl-1 Cardiac Cells

Arrhythmogenic cardiomyopathy (AC) is a genetic disease caused by mutations in genes encoding the intercalated disk (ID) proteins. ID is a multiprotein complex providing cell-cell junction and connecting the nucleus to the extracellular matrix, and playing a pivotal role for maintaining the structural integrity of the heart tissue. Mutations in PKP2 encoding plakophilin 2 (PKP2) are the most common causes of AC. The objective of this study was to investigate the biomechanical properties of the PKP2-knock down HL-1 mouse cardiac myocytes (PKP2-KD). PKP2 protein levels were reduced by 66 to 75% upon shRNA-targeting of the Pkp2 mRNA. Nuclear stiffness (Young’s modulus) and the force required to deform the nucleus were assessed by atomic force microscopy (AFM). Nuclear stiffness was decreased significantly (5 times) in PKP2-KD HL-1 myocytes as compared to wild-type (WT) myocytes, indicating an increased elasticity and/or susceptibility of the nucleus to be deformed (2 times). Interestingly, cell adhesion was also reduced (10 times) in the PKP2-KD myocytes, indicating a pivotal role of ID proteins in maintaining cell adhesion and mechanical integrity in cardiomyocytes. In the stress-relaxation test, while the decay time value was comparable between WT and PKP2-KD cells, relaxation force and cell deformation values were decreased 3 and 8 times, respectively, in PKP2-KD HL-1 myocytes, confirming the finding in the Young’s modulus. Moreover, the relaxation test revealed a reduced viscosity, highlighting a compromised cytoskeletal stability induced by the PKP2 deficiency. RNA-Sequencing and Ingenuity Canonical Pathway analysis identified integrin, tight junction, and the canonical Wnt signaling, among the most disturbed pathways in the PKP2-KD HL-1 myocytes. The findings indicate that the deficiency of a component of the ID protein markedly affects the whole-cellular biomechanics, which is expected to affect tissue stability, leading to activation of the mechano-transduction pathways.

Spectroscopic and structural properties of polycrystalline Y2Si2O7 doped with Er3+

Powders of yttrium disilicate (Y2Si2O7) doped with Er3+ have been prepared by the sol–gel method. The structure of the obtained powders has been determined. Room temperature emission spectra have been recorded and excited state decay profiles have been analyzed. Differences between the spectroscopic properties of Er3+ in monoclinic α-Y2Si2O7 (space group P-1) and β-Y2Si2O7 (space group C2/m) polymorphs have been investigated and shown. The significant broadening of the emission spectra recorded for the α phase compared to the one for the β phase was discussed in terms of higher number of Y3+ sites (4) present in the α phase with respect to only one Y3+ site in the case of β phase. The higher value of the luminescence decay time of β phase (11.2ms) compared to the α phase (8.5ms) is associated with the higher site symmetry of β-Y2Si2O7. Moreover it was found that Er3+ concentration affects the shape of the 4I13/2→4I15/2 emission band. It results in changes of the relative emission intensities of peaks localized at 1527nm and 1532nm; this indicates changes of the Y3+ sites occupation on increasing the Er3+ concentration. The luminescence lifetime was observed to decrease with the increase of Er3+ concentration. The spectroscopic results have been compared with the ones relative to thin films of Y2Si2O7:Er3+ with a similar composition. The lower value of the luminescence decay time observed for thin films compared to the powder of α phase was explained with the changes of the particles packing resulting in the change of the effective refractive index.

Downconversion in Pr3+–Yb3+ co-doped ZBLA fluoride glasses

Fluorozirconate ZBLA glasses with molar composition 57ZrF4–34BaF2–5LaF3–4AlF3–0.5PrF3–xYbF3 (from x=0 to 10) were synthesized to evaluate the rate of the conversion of visible photons into infrared photons. The emission spectra in the near infrared (NIR) at 950–1100nm and the luminescence decays in the visible and NIR indicate an energy transfer from Pr3+ to Yb3+ upon blue excitation of Pr3+ at 440nm. The energy transfer efficiency increases with Yb3+ concentration to reach 86% with 0.5Pr3+–10Yb3+ co-doping (in mol%). However, the quenching of the Yb3+ emission strongly reduces the efficiency of the downconversion process: the decay time values decrease from 600µs (x=0.5mol%) to 85µs (x=10mol%).

The Lifetime NAD(P)H Fingerprint of Salmonella Infection

The Lifetime NAD(P)H Fingerprint of Salmonella Infection

GCaMP3-Derived Genetically Encoded Probes as Rapid Intracellular Signals for Calcium Dynamics

In intracellular calcium signaling studies genetically encoded probes offer greater intracellular domain specificity than traditional fluorescent signaling molecules, with the ability to be targeted to specific organelles and micro-domains. To this end we evaluated the ability of seven novel mutagenic derivatives of GCaMP3 calcium probe (EF-3, EF-4, EF-34, RS-1, RS-1 EF-3, RS-1 EF-4, and RS-1 EF-34) to rapidly detect intracellular calcium compared to the chemical calcium probe Fura-2 AM. GCaMP3 derived probes were transiently transfected into HEK293T cells which were subsequently incubated in 1 µM Fura-2 AM for 20 minutes prior to experimentation. Fura-2 and GCaMP3-derived probe fluorescence was measured at 380 nm and 488 nm respectively as HEK293T cells were rapidly exposed to 100 µM ATP for 5 s. While mutated probes did not exhibit a greater change in fluorescence than GCaMP3 precursor, mutants EF-3 and EF-4 fluorescence changes were 128.4 and 58.2 % ΔF/Fo respectively, significantly greater than Fura-2 response in the same cells. Additionally, many probes demonstrated faster rise and decay kinetics, with rise time and decay time values up to 150 % faster than Fura-2. Our results suggest that mutations in GCaMP3 can produce genetically encoded probes capable of measuring calcium with equal or larger fluorescence responses as traditional chemical dyes. Additionally, several probes such as GCaMP3 EF-4 demonstrate not only increased fluorescence but dramatically improved kinetic responses - facilitating increasingly sensitive measurements of intracellular calcium signaling.

Robust synchronization of bursting Hodgkin–Huxley neuronal systems coupled by delayed chemical synapses

Synchronized firing of bursting neurons has been found in many real neural systems. In this paper, a modified bursting Hodgkin–Huxley neuronal model is proposed and used to construct neuronal systems with heterogeneous neurons coupled by delayed chemical synapses, then synchronization of the systems is studied in various conditions. First, synchronization for a two-neuron system is explored. It is found that if the synapse is excitatory, the two neurons could achieve burst synchronization easily. If the synapse is inhibitory, they can achieve anti-phase burst synchronization, which is robust to variation of systematic parameters. Second, robust synchronization for a globally coupled neuronal network is investigated. It is found that the robustness of the synchronization is sensitive to the parameter values of synaptic conductance and synaptic delay, but is less sensitive to the parameter values of synaptic decay time. It is also found that the oscillation frequency of the whole network is sensitive to the parameter values of synaptic delay and synaptic decay time, but is less sensitive to the parameter value of synaptic conductance.

Effect of post deposition annealing on thermal evaporated ZnSe:Te towards a scintillator application

ZnSe having a wide but direct bandgap (bulk band gap 2.7eV) is very efficient for detecting nuclear radiations by using its scintillation property. With a high absolute light output and radiation spectra which match well with Si-photodiode spectral sensitivity, ZnSe scintillators have adequately minimized the gap between “scintillator-photodiode” series for modern radiation detectors. Promising features like long decay time and high values of intrinsic radiation absorption make ZnSe based scintillators a very interesting research filed. Here in this report, we investigate an inexpensive and easy method to realize ZnSe:Te film on a quartz substrate. ZnSe:Te film is deposited using a thermal evaporator using ZnSe and ZnTe powders as raw materials to start with. After the deposition, the samples are exposed to a thermal annealing step for 1h. The temperatures are kept at 624, 674 and 724K. We have confirmed presence of a preferred [111] oriented polycrystalline ZnSe:Te thin films by XRD experiments. Photoluminescence experiment using a He:Cd laser at 324nm at low temperature (8K) reports an emission at 2.54eV due to non-equilibrium carrier plasma.

Influence of double confinement on photophysics of 7-(diethylamino)coumarin-3-carboxylic acid in water/AOT/isooctane reverse micelles

The effect of double confinement on the photophysics of 7-(diethylamino)coumarin-3-carboxylic acid (7-DCCA) inside the water pool of water/AOT/isooctane reverse micelles has been reported in this study. At first a supramolecular host–guest complex was formed in water between 2-hydroxypropyl-γ-cyclodextrin (HP-γ-CD) and 7-DCCA. Then the aqueous solution of this complex was used to form reverse micelles at any particular w0 value (w0 = [water]/[surfactant]). We have used sodium dioctyl sulfosuccinate (AOT) as surfactant and isooctane as non-polar solvent to prepare reverse micelles. A comparative study between double confinement system and the single confinement system, where the 7-DCCA molecule was incorporated inside the core of the water/AOT/isooctane reverse micelles, was done. We have used the steady state absorption and fluorescence emission techniques to highlight the significant shift of the spectral behaviour of the 7-DCCA due to the double encapsulation of the dye in the nanopool of the reverse micelles. More affirmation has been achieved by the use of time resolved fluorescence emission spectroscopy. The study of solvation dynamics and rotational relaxation dynamics was used as tools to investigate the effect of double encapsulation on the excited state dynamics of the probe molecule. These excited state dynamics clearly show that even at the highest w0 value studied here, the excited state dynamics of the doubly confined dye are significantly different from those of the single confined dye in the reverse micelle. The higher values of fluorescence emission decay time, rotational relaxation and solvent relaxation times in the doubly confined system compared to those of the single confined system at different w0 values proved the existence of the supramolecular host–guest complex inside the core of the water/AOT/isooctane reverse micelle.

Time-resolved photoluminescence studies of annealed 1.3-μm GaInNAsSb quantum wells

Time-resolved photoluminescence (PL) was applied to study the dynamics of carrier recombination in GaInNAsSb quantum wells (QWs) emitting near 1.3 μm and annealed at various temperatures. It was observed that the annealing temperature has a strong influence on the PL decay time, and hence, it influences the optical quality of GaInNAsSb QWs. At low temperatures, the PL decay time exhibits energy dependence (i.e., the decay times change for different energies of emitted photons), which can be explained by the presence of localized states. This energy dependence of PL decay times was fitted by a phenomenological formula, and the average value of E0, which describes the energy distribution of localized states, was extracted from this fit and found to be smallest (E0 = 6 meV) for the QW annealed at 700°C. In addition, the value of PL decay time at the peak energy was compared for all samples. The longest PL decay time (600 ps) was observed for the sample annealed at 700°C. It means that based on the PL dynamics, the optimal annealing temperature for this QW is approximately 700°C.

Comparative studies of Lu1.95Y0.05SiO5:Ce and Lu0.7Y0.3AlO3:Ce single crystal scintillators for gamma-ray detection

The scintillation characteristics of Lu1.95Y0.05SiO5:Ce (LYSO:Ce) and Lu0.7Y0.3AlO3:Ce (LuYAP:Ce) single crystals were compared for γ-ray detection. The values of scintillation decay time and coincidence time resolution were evaluated. The scintillation decay of LYSO:Ce exhibits approximately a single-exponential component with decay time of 39ns, whereas for LuYAP:Ce an intensity of the fast component with decay time of 21ns is reduced (∼42%) and followed by a high intensity of slower components. The coincidence time resolution for 511keV annihilation quanta of 234 and 894ps was obtained, respectively, for LYSO:Ce and LuYAP:Ce detectors in coincidence experiment using a BaF2-based detector. The time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse.

Speciation of ‘Eu’ in sol–gel derived alkali barium borosilicate glass: Time resolved photoluminescence (TRPL) and Judd—Ofelt analysis

Time resolved photoluminescence spectroscopic (TRPLS) technique was used to investigate the speciation of Eu ion in alkali barium borosilicate glasses prepared via sol–gel method. The metal ion concentration and the annealing temperature were optimized for best signal intensity. It was observed that the presence ofOH groups in the samples reduced the luminescence decay time values. Upon heating the system at higher temperature, the number ofOH groups reduced and the lifetime as well as the intensity increased. At elevated temperatures, it was found that Eu was stabilized in two different asymmetric environments having large site distribution. The overall symmetry around the two metal ion sites was estimated to be C2. Judd—Ofelt intensity parameters for the metal ion were evaluated in all the samples adopting standard procedure. It was observed that, for all the samples, Ω2>Ω4. This indicated the existence of a fair degree of covalency in the metal and ligand bonding.

Microstructure, luminescence and thermal stability properties of NaSrPO4:Tb3+ phosphors with various doping concentrations prepared using conventional solid-state sintering

This paper reports the microstructure, luminescence and thermal stability properties of the NaSr1−xPO4:xTb3+ powders (x=0.008, 0.01, 0.02, 0.04 and 0.06) via the conventional solid-state sintering at 1200°C for 5h. The X-ray diffraction result verifies all diffraction peaks are pure phase of NaSrPO4. The luminescence results show that the NaSrPO4:xTb3+ powders mainly excited at 370nm have a series of the emission-states, related to the typical 4f→4f intra-configuration forbidden transitions of Tb3+, and a major emission peak of around 546nm. The concentration quenching of the NaSr1−xPO4:xTb3+ phosphors is appeared at x=0.02. The decay time values of the NaSr1−xPO4:xTb3+ phosphors for the 5D4 state of the Tb3+ are around 3.30ms to 3.60ms. It is also found the chromaticity coordinate of NaSrPO4:Tb3+ phosphor varies with the increase of the concentration of Tb3+ ions from blue to green. Moreover, the thermal stability of the NaSrPO4:xTb3+ phosphors is slightly better than that of conventional YAG phosphors.

Influence of lutetium content on the scintillation properties in (Lu x Y1−x )AlO3 :Ce single crystals

The absorption, luminescence, and scintillation characteristics of cerium-doped lutetium-yttrium perovskite (LuxY1−x AlO3:Ce; x = 0, 0.3, 0.7) single crystals were investigated. The values of light yield, scintillation decay time, and coincidence time resolution were evaluated. At 662 keV γ-rays (137Cs source), the light yield of 30 700 ph MeV−1 obtained for YAlO3:Ce is much higher than that of 16 200 and 10 600 ph MeV−1 obtained for Lu0.3Y0.7AlO3:Ce and Lu0.7Y0.3AlO3:Ce, respectively. Scintillation decays are dominated by a fast component with decay time value of 16–20 ns, which nearly coincides with the photoluminescence decay time value of 17.5 ns. In scintillation decays the intensity of the fast component becomes reduced and the content of slower components considerably increased with increasing lutetium content in the crystals. The coincidence time spectra for 511 keV annihilation quanta were measured in coincidence experiment using a BaF2-based detector and time resolution was also discussed in terms of a number of photoelectrons and decay time of the scintillation pulse. The photofraction for all the crystals under 662 keV γ-ray excitation was also evaluated and discussed.

Evolution of Sunspot Characteristics in Cycle 23

The aim of this work is to present a statistical study of several parameters (variables) that define sunspot groups. These variables include maximum area, growth and decay times, as well as the evolution families, and solar-cycle phase the groups belong to. We classified group types based on the Zurich classification, which allows us to define a set of families based on their evolution patterns. The time variation of the area of a group was also studied, and a relationship between the maximum area and the growth and decay times was sought. Another study was carried out to find the correlation among different characteristics of the groups, as well as how the probability of a certain value of decay time can vary depending on morphological characteristics defined by these variables. Thus, a program based on a weight matrix combining the variables necessary to classify a group, together with the calculation of the probability for a specific event, has been produced. This approach allows us to predict the future behavior of a group from its historical evolution.

Estimating storage properties of aquifer with magnetic resonance sounding: a field verification in northern Cambodia of the gravitational water apparent cutoff time concept

ABSTRACTMagnetic Resonance Sounding (MRS) has already showed its capability for estimating some aquifer properties, but very little work has been carried out concerning the storage properties used for calculating groundwater reserve and recharge. For unconfined aquifer, this storage property (i.e., the specific yield) is often estimated from the MRS water content. However, a recent study carried out in a poor sandstone aquifer of Northern Cambodia found that the MRS pore‐size related parameter is probably more appropriate because the MRS water content can be dominated by water which does not contribute to the specific yield. A main output of this study is that a threshold value (so‐called apparent cutoff time ACT) of the MRS decay time can be defined for discriminating gravitational water from capillary and bound waters. Since measuring such short MRS signal is quite common, a validation of this result is compulsory to avoid the misuse of the MRS water content.This paper presents an experiment that we set up to check the validity of the ACT approach. We compared two MRS carried out at the same location in a clayey‐sand layer 15 metres thick. The first MRS was carried out with a static water level located at 1.7 metres below the ground level. It revealed a layer with a water content of 3.8% and . According to the ACT approach, this short value of indicates water that is not part of the specific yield and that can not be released by pumping. Thus, we carried out a second MRS after pumping and lowering the water level to an average of 15 metres. As predicted by the ACT approach, we observed that the second MRS signal was the same as the one obtained before pumping.To cross‐check our observation, we carried out a pumping test at the same location. We found a very low value of specific yield, confirming that the main part of the MRS signal is generated by water which was not drained by the pumping. We calculated that the volume of water removed from the aquifer by the pumping was far too low to generate a measurable magnetic resonance signal.From our experiment, we conclude that the ACT approach can be successfully used to estimate the specific yield of poor aquifers, and to avoid a misuse of the MRS water content which can lead to strong overestimates of aquifer reserve and recharge.

Social Computing and the Attention Economy

Social computing focuses on the interaction between social behavior and information, especially on how the latter propagates across social networks and is consumed and transformed in the process. At the same time the ubiquity of information has left it devoid of much monetary value. The scarce, and therefore valuable, resource is now attention, and its allocation gives rise to an attention economy that determines how content is consumed and propagated. Since two major factors involved in getting attention are novelty and popularity, we analyze the role that both play in attracting attention to web content and how to prioritize them in order to maximize it. We also demonstrate that the relative performance of strategies based on prioritizing either popularity or novelty exhibit an abrupt change around a critical value of the novelty decay time, resembling a phase transition.

Transient thermoelectricity in a vibrating quantum dot in Kondo regime

We investigate the time evolution of the thermopower in a vibrating quantum dot suddenly shifted into the Kondo regime via a gate voltage by adopting the time-dependent non-crossing approximation and linear response Onsager relations. Behavior of the instantaneous thermopower is studied for a range of temperatures both in zero and strong electron–phonon coupling. We argue that inverse of the saturation value of decay time of thermopower to its steady state value might be an alternative tool in determination of the Kondo temperature and the value of the electron–phonon coupling strength.

Nonclassicality and decoherence of photon-added squeezed thermal state in thermal environment

Theoretical analysis is given of nonclassicality and decoherence of the field states generated by adding any number of photons to the squeezed thermal state (STS). Based on the fact that the squeezed number state can be considered as a single-variable Hermite polynomial excited state, the compact expression of the normalization factor is derived, a Legendre polynomial. The nonclassicality is investigated by exploring the sub-Poissonian and negative Wigner function (WF). The results show that the WF of single photon-added STS (PASTS) always has negative values at the phase space center. The decoherence effect on PASTS is examined by the analytical expression of WF. It is found that a longer threshold value of decay time is included in single PASTS than in single-photon subtraction STS.