Decay Time Values Research Articles

Polymer complex solution synthesis of (YxGd1−x)2O3:Eu3+ nanopowders

Yttrium–gadolinium–europium oxide phosphors are regarded promising for many important optical applications, for example in computed tomography medical imaging and plasma displays. In this work, we investigated procedure for (YxGd1−x)2O3:Eu3+ (x= 0, 0.25, 0.5, 0.75 and 1) nanopowder synthesis using polymer complex solution method (PCS) based on polyethylene glycol fuel (PEG). Structural and emission properties of nanopowders are investigated by X-ray diffraction, electron microscopy and photoluminescence measurements. We obtained particles of about 40nm having excellent structural ordering in cubic bixbyte type of structure – space group Ia3 for all mixed oxide compositions. Luminescence emission measurements exposed characteristic transition of the trivalent europium ion incorporated into insulating host. 5D1 and 5D0 decay time values are measured to obtain information on different kinetic processes occurring for these two emitting levels.

Assessing the Acoustical Climate of Underground Stations

Designing a proper acoustical environment—indispensable to speech recognition—in long enclosures is difficult. Although there is some literature on the acoustical conditions in underground stations, there is still little information about methods that make estimation of correct reverberation conditions possible. This paper discusses the assessment of the reverberation conditions of underground stations. A comparison of the measurements of reverberation time in Warsaw’s underground stations with calculated data proves there are divergences between measured and calculated early decay time values, especially for long source–receiver distances. Rapid speech transmission index values for measured stations are also presented.

Asynchronic transmission in the CA3–CA1 hippocampal synapses in the neurological mutant taiep rat

For the taiep rat, a neurological mutant with severe astrogliosis secondary to demyelination, we have described alterations in spinal cord synaptic transmission. Asynchronous responses result from phasic action potential-derived glutamate release in this mutant. To evaluate whether this anomalous transmission is also produced in other regions of the taiep CNS and whether its nature involves a presynaptic or postsynaptic disruption, we studied the CA3-CA1 hippocampal synapses. Excitatory postsynaptic currents (EPSC) evoked by stimulation of Schaffer collaterals were recorded from CA1 pyramidal cells on picrotoxin-treated slices. Initial fast and time-locked EPSCs were evoked by conventional stimulation in both control and taiep neurons, showing similar latency and amplitude values unimodally distributed. In a high percentage of taiep neurons (47%), the initial EPSC was frequently followed by additional asynchronous synaptic currents (EPSC(ASYN)) with latencies ranging from 10 to 300 msec. As with initial EPSCs, EPSC(ASYN) were action potential dependent, sensitive to tetrodotoxin, and blocked by D-2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione. The occurrence probability of these events decayed monoexponentially as a function of poststimulus time. The elevation of extracellular Ca(2+) induced a reduction of amplitudes and a rate increase of EPSC(ASYN), in parallel with a reduction of paired pulse facilitation of initial EPSCs. The presynaptic fiber volley, extracellularly recorded, showed no significant differences between groups, with similar mean values of area and decay time. These findings in hippocampal circuitry suggest that, in taiep, the asynchronous evoked activity represents a rather generalized phenotype of the glutamatergic synapses and that EPSC(ASYN) seems to be determined by presynaptic alterations.

Ti-doped MgAl2O4 spinel single crystals grown by the micro-pulling-down method for laser application: Growth and strong visible blue emission

The photoluminescence spectra of the rod-shaped pure and Ti-doped MgAl 2 O 4 single crystals, grown by the micro-pulling-down (μ-PD) method, have been systematically investigated under high-intensity pulsed Nd 3+ : YAG laser excitation in the ultraviolet (UV) region (266 nm). The chemical properties of the grown crystals under reducing argon atmosphere will be reported and the annealing effect under oxidizing atmosphere will be discussed. The room temperature luminescence properties of Ti-doped MgAl 2 O 4 single crystals were performed before and after annealing as a function of the titanium concentration. Three broad bands absorption in the UV/VIS (visible) spectral regions and a broadband visible blue emission were observed from Ti-doped MgAl 2 O 4 . An estimation of the decay time value of theses emissions was determined from the time-resolved spectra and the energies of the vibrational modes of the MgAl 2 O 4 crystal are obtained from the infrared spectra.

Interpretation of intramolecular stacking effect on the fluorescence intensity decay of 3-methylbenzimidazolyl(5′-5′)guanosine dinucleotides using a model of lifetime distribution

Time-resolved fluorescence of 3-methylbenzimidazole (m(3)B) was used to study stacking interaction between base moieties in di-, tri- and tetra-phosphate analogues of 3-methylbenzimidazolyl(5'-5')guanosine (m(3)Bp( n )G, n = 2, 3, 4), using 5'-triphosphate of 3-methylbenzimidazole riboside (m(3)BTP) as reference. Fluorescence intensity decays of all compounds cannot be satisfactory fitted with single-exponential function. Although an increase of a number of exponents led to better fits, interpretation of the individual exponential terms, i.e. pre-exponential amplitudes and fluorescence lifetimes, cannot be adequately characterized. We show that these fluorescence decays are best fitted by power-like function derived from physically justified distribution of the fluorescence lifetimes, and characterized by the mean value of the excited-state lifetime and relative variance of lifetime fluctuations around the mean value. The latter led to the parameter of heterogeneity and number of decay paths, which depend on the factors responsible for non-radiative decay of the excited state, including base-base stacking interaction. This was studied by means of changes of temperature and the number of phosphate groups in dinucleotides. It was shown that the strongest effect of stacking interactions, characterized by lowest values of both fluorescence mean decay time and relative variance, occurs in the case of m(3)Bp(3)G containing the same number of phosphates as natural mRNA cap. The possible importance of these results for interpretation of the mechanism of function of the mRNA cap structure is discussed.

Some factors determining the PCr recovery overshoot in skeletal muscle

It has been proposed recently that the phosphocreatine (PCr) overshoot (increase above the resting level) during muscle recovery after exercise is caused by a slow decay during this recovery of the direct activation of oxidative phosphorylation taking place during muscle work. In the present article the factors determining the appearance and size of the PCr overshoot are studied using the computer model of oxidative phosphorylation in intact skeletal muscle developed previously. It is demonstrated that the appearance and duration of this overshoot is positively correlated with the value of the characteristic decay time of the direct activation of oxidative phosphorylation. It is also shown that the size of PCr overshoot is increased by low resting PCr/Cr ratio (what is confirmed by our unpublished experimental data), by high intensity of the direct activation of oxidative phosphorylation, by high muscle work intensity and by low rate of the return of cytosolic pH to the resting value during muscle recovery.

Effects of binocular form deprivation on the properties of gamma-aminobutyric acid currents of rat visual cortical neurons

To investigate the effects of binocular form deprivation on the properties of inhibitory synaptic transmission of rat visual cortical neurons during the critical period of visual development. We recorded the postsynaptic currents in visual cortex slices of normal, binocular form deprived and deprivation-removed rats at postnatal days 14, 21 and 28 with the use of whole-cell patch recording, and recorded gamma-aminobutyric acid currents by adding D, L-2-amino-5-phosphonovalerate (50 micromol/L) and 6-cyano-7-nitroquinoxaline-2,3-dione (20 micromol/L) to artificial cerebrospinal fluid. The electrophysiological properties were also analysed. The decay time and peak value of inhibitory postsynaptic currents of normal rat visual cortical neurons became larger with age (P < 0.05), but not in binocular form deprived group (P > 0.05). The decay time and peak value of inhibitory postsynaptic currents became large in deprivation-removed rats at postnatal days 28 (P < 0.05). The rise time did not change markedly in all groups. With visual development, the synaptic transmission of visual cortical neurons in normal rats is strengthened, but it can be inhibited by binocular form deprivation and recovered by visual input.

Use of Individual Flight Corridors to Avoid Vortex Wakes

Vortex wakes of aircraft pose a hazard to following aircraft until the energetic parts of their flow fields have decayed to a harmless level. It is suggested here that in-trail spacings between aircraft can be significantly and safely reduced by designing an individual, vortex-free flight corridor for each aircraft. Because each aircraft will then have its own flight corridor, which is free of vortex wakes while in use by the assigned aircraft, the time intervals between aircraft operations can be safely reduced to the order of seconds. The productivity of airports can then be substantially increased. How large the offset distances between operational corridors need to be to have them vortex free, and how airports need to be changed to accommodate an individual flight-corridor process for landing and takeoff operations, are explored. Estimates are then made of the productivity of an individual flight-corridor system as a function of the in-trail time interval between operations for various values of wake decay time, runway width, and the velocity of a sidewind. The results confirm the need for short time intervals between aircraft operations if smaller offset distances and increased productivity are to be achieved.

Periods of quasi-stationary conditions in interplanetary space according to sequences of SEP events

The values of the characteristic decay time of particle fluxes in SEP events vary, as a rule, considerably from event to event. We point out, however, that at times sequences of events having similar decay times were observed over long time intervals (up to one month, and even longer in a few cases). The values of the decay times, however, differed among different sequences. The constancy of the decay phase in each consecutive event of these series suggests that the interplanetary medium was in steady state during the event series, and, because of solar rotation, its uniformity within sectors extended to 90–180° in heliolongitude. The very rarely observed long series (up to 2–3 solar rotations) indicate the steadiness and homogeneity of the plasma and the interplanetary magnetic field (IMF) in the entire inner solar system in the course of this time span. It is pointed out that the neutral current sheet of the IMF does not represent a substantial obstacle for energetic charged particles. Both hemispheres are (above and below the current sheet), at least during the series of solar events, invariant with time, uniform and alike from the viewpoint of the propagation of charged particles. The investigation of such sequences of events can also be useful for forecasting characteristics of SEP events.

Periods of quasi-stationary conditions in interplanetary space according to sequences of SEP events

The values of the characteristic decay time of particle fluxes in SEP events vary, as a rule, considerably from event to event. We point out, however, that at times sequences of events having similar decay times were observed over long time intervals (up to one month, and even longer in a few cases). The values of the decay times, however, differed among different sequences. The constancy of the decay phase in each consecutive event of these series suggests that the interplanetary medium was in steady state during the event series, and, because of solar rotation, its uniformity within sectors extended to 90–180° in heliolongitude. The very rarely observed long series (up to 2–3 solar rotations) indicate the steadiness and homogeneity of the plasma and the interplanetary magnetic field (IMF) in the entire inner solar system in the course of this time span. It is pointed out that the neutral current sheet of the IMF does not represent a substantial obstacle for energetic charged particles. Both hemispheres are (above and below the current sheet), at least during the series of solar events, invariant with time, uniform and alike from the viewpoint of the propagation of charged particles. The investigation of such sequences of events can also be useful for forecasting characteristics of SEP events.

Statistical properties of sep event flux declines

The interplanetary space is not a passive medium, which merely constitutes a scene for the propagation of previously accelerated energetic particles, but influences the distribution of particles by changing their energies as well due to interactions with magnetic field inhomogeneities. Such processes manifest themselves in the energy spectra of solar energetic particle (SEP) events. In this paper the fluxes of protons with energies of 4–60 MeV are investigated on the basis of two data sets. Both sets are homogeneous, obtained by the CPME instrument aboard the IMP 8 satellite between 1974 and 2001. The first includes all SEP events where the integral fluxes of >4 MeV protons exceeded 2 particle/cm 2 s sr. The other set consists of fluxes recorded in differential energy windows between 0.5 and 48 MeV. Important characteristics of SEP events include the rates of decrease of particle flux, which, as well as peak flux time, is an integral feature of the interplanetary medium within a considerable region, surrounding the observation point. The time intervals selected cover the decay phases of SEP events following flares, CMEs and interplanetary shocks of different origin. Only those parts of declines were selected, that could reasonably be described by exponential dependence, irrespective of the gradual/impulsive character of the events. It is shown that the average values of characteristic decay time, τ , and energy spectral index, γ , are all changing with the solar activity phase. Distributions of τ and γ values are obtained in SEPs with and without shocks and during different phases of events: just after peak flux and late after maximum.

Statistical properties of SEP event flux declines

Abstract The interplanetary space is not a passive medium, which merely constitutes a scene for the propagation of previously accelerated energetic particles, but influences the distribution of particles by changing their energies as well due to interactions with magnetic field inhomogeneities. Such processes manifest themselves in the energy spectra of solar energetic particle (SEP) events. In this paper the fluxes of protons with energies of 4–60 MeV are investigated on the basis of two data sets. Both sets are homogeneous, obtained by the CPME instrument aboard the IMP 8 satellite between 1974 and 2001. The first includes all SEP events where the integral fluxes of >4 MeV protons exceeded 2 particle/cm 2 s sr. The other set consists of fluxes recorded in differential energy windows between 0.5 and 48 MeV. Important characteristics of SEP events include the rates of decrease of particle flux, which, as well as peak flux time, is an integral feature of the interplanetary medium within a considerable region, surrounding the observation point. The time intervals selected cover the decay phases of SEP events following flares, CMEs and interplanetary shocks of different origin. Only those parts of declines were selected, that could reasonably be described by exponential dependence, irrespective of the gradual/impulsive character of the events. It is shown that the average values of characteristic decay time, τ , and energy spectral index, γ , are all changing with the solar activity phase. Distributions of τ and γ values are obtained in SEPs with and without shocks and during different phases of events: just after peak flux and late after maximum.

Activated Dynamics Across Aperiodic Stochastic Potentials†

In recent work, we have developed a new phenomenology allowing us to characterize the dynamics of particles on stochastic bistable surfaces well below the high-friction limit. [Shepherd, T. D.; Hernandez, R. J.Chem.Phys. 2001, 115, 2430.] A generalization of this class of bistable potentials to one-dimensional stochastic aperiodic potentials-viz. potentials which are not periodic in the sense that the barriers separating minima on a regular lattice are of unequal height-is pursued here. Several interesting aspects of the surface diffusion process across aperiodic stochastic potentials are compared to the well-established results for the periodic potential model. In particular, a suppression in the probability of correlated hops and an enhancement in the rate across aperiodic stochastic potentials are observed. Unique features characteristic of bistable stochastic potential models are also exhibited for this multi-barrier model. The most notable is the resonance enhancement of the escape rate (inverse escape time) which reaches a maximum at a nontrivial value of the barrier-correlation decay time.

An Analytic Description of Coronal Proton Trapping

Analytic steady state solutions of the focused diffusion equation are used to deduce proton trapping time, τtrap, an average residence time for all particles injected into the magnetic loop. We take into account the effect of magnetohydrodynamic (MHD) turbulence and the divergence of magnetic field lines in both the corona and chromosphere of the Sun. Numerical simulations of pitch-angle scattering have then been used to check the analytic solutions and to ascertain boundary conditions for the focused diffusion equation. Results are obtained for several different functional forms of B(ζ), the magnetic field as a function of distance along a particular coronal field line. Five cases have been studied, from B constant along the coronal portion of the loop to B(ζ) corresponding to a force-free magnetic structure. The results indicate that a divergence of the magnetic field in the coronal portion of the loop can significantly increase the trapping time, no matter how small the mean free path may be. Derived analytic expressions for τtrap can be used to calculate the intensity of secondary emissions from the loop-top sources. Analytic time-dependent solutions of the focused diffusion equation are considered in the case of constant coronal B to find the basic decay time of the trapped proton number, τdecay, an asymptotic value of the exponential decay time when the time tends to infinity. In the case of variable B in the coronal portion of the loop, Monte Carlo simulations of pitch-angle scattering have been employed to calculate τdecay in a wide range of parameters. However, we have also obtained analytic expressions for how the characteristic time scales with parameters of the magnetic loop. Deduced analytic expressions for τdecay can be used to calculate ion acceleration in the escape-time approximation and to interpret the decay phase of solar gamma-ray flares. Magnetic focusing in the coronal portion of the loop makes acceleration more efficient than would be expected in the approximation without coronal focusing.

Self-association of 8-anilino-1-naphthalene-sulfonate molecules: spectroscopic characterization and application to the investigation of protein folding

It was suggested long ago that the reason for the considerable increase of 8-anilino-1-naphthalene-sulfonate (8-ANS) fluorescence intensity upon the transition from aqueous to organic solvents is the dissociation of 8-ANS associates. To clarify this point the dependence of spectral properties of the dye on concentration and solvent composition was investigated by means of steady-state and time-resolved fluorescence spectroscopy. It was shown that the increase of 8-ANS concentration leads to the changes in the shape of absorption and fluorescence spectra of the dye, accompanied by the decrease in its fluorescence decay time values. Such changes were observed in aqueous and organic solvents for Mg 2+- and NH + 4-salts of 8-anilino-1-naphthalene-sulfonateic acid and reflect the existence of self-association of the dye molecules in both media. However, the decrease in fluorescence intensity induced by the self-association of the probe molecules is too small to explain weak fluorescence of 8-ANS in water. At the same time, it expounds the difference between the decay times of protein-embedded 8-ANS molecules upon interaction of this probe with native and molten globule proteins.

Time-resolved fluorescence spectroscopy of fulvic acid and fulvic acid complexed with Eu 3+ – a comparative study

In this work a systematic characterization of the fluorescence kinetics of fulvic acid by means of a single-photon time correlation technique is reported. The data were extracted from both single decay curves and time-resolved emission spectra and analyzed by the exponential series method. The results strongly suggest the existence of a tri-modal decay time distribution with peak decay time values centred around 0.7, 3 and 10 ns. The relative amplitudes of the decay time distributions were shown to depend on the emission wavelength, indicating a three-species mixture with slightly different emission maxima and widths. As sustained by time-resolved emission spectra the same species of fluorophores are responsible for the fluorescence kinetics behaviour of fulvic acid at all excitation wavelengths used in the experiments. For the first time these techniques and methods were applied in investigating the effects of the Eu 3+ complexation upon fluorescence kinetics of the fulvic acid. Single decay analysis indicates that the peak decay time values are not affected by Eu 3+ addition at all emission and excitation wavelengths used in the experiments. On the contrary, the dependency of relative amplitudes on emission wavelength was greatly reduced in comparison with the uncomplexed fulvic acid. This effect is further evidenced by analysing the barycenter transients of time-resolved emission spectra. Finally, it is also indicated that within the temporal resolution of the experimental set up used the singlet states play no role as donor states in intramolecular energy transfer from the organic fulvic acid ligands to the Eu 3+ energy levels.

Loss factor at the boundary of a single-leaf wall under a vibrational field of diffused bending waves

The internal loss factor (etaint) is an important parameter in the case of calculating the transmission loss of a panel by using SEA (statistical energy analysis). Though energy loss at the edge is fairly large in practical walls, etaint have been ordinarily treated including the edge loss. So it must be necessary to treat quantitatively the energy loss at the boundary of the wall. In this paper, assuming that a panel in excitation is a two-dimensional vibration field of diffused bending waves, a formula of the decay time of a panel is deduced. The subject for experimental study is an aluminum panel mounted in the opening between transmission suite. The panel is excited by a piezoelectric ceramic diaphragm. Vibrational decay time is measured by the impulse response method. The calculation method of the energy absorption coefficient and loss factor at perimeter is indicated by using measured values of decay time and sound radiation.

Early decay times in the Christchurch and Wellington concert halls, New Zealand

The concert halls in Christchurch Town Hall and the Michael Fowler Centre, Wellington, New Zealand, have large suspended reflecting surfaces which provide early lateral reflections to listeners. One objective outcome of this is that measured early decay time (EDT) values are shorter than the reverberation time. EDT values for these two halls published in the book, Auditorium Acoustics and Architectural Design (Spon/Chapman &amp; Hall, London, 1993) are now known to be significantly in error, due to a software fault in the signal analysis program used. Corrected diagrams including the EDT are presented as well as a brief discussion of sound decay in these halls.

Average acoustical characteristics of ten atrium spaces

Extensive acoustical measurements were made in ten different atrium spaces varying in volume from 3 300 to 45 000 m3. Impulse responses were measured at between 18 and 71 combinations of source and receiver position in each atrium depending on the size of the atrium. The computer-based measurement system (RAMSoft-3) used a maximum length sequence signal and a fast Hadamard transform procedure to obtain 5-s-long impulse responses. Octave band values of decay times, sound levels, and energy ratios were calculated for each impulse response. The average values of each quantity in each atrium were used to characterize typical acoustical characteristics of untreated atria. These allow rough estimates of the acoustical conditions in other atria as a function of the volume of the spaces.

Measurement of ion parameters during a forced switching off of current in vacuum

This paper presents the results of ion parameters measured during a forced current commutation of a diffuse vacuum arc, aimed at evaluating the role of ions in discharges occurring rarely after the counterpulse commutation process, in a contact arrangement corresponding to a low-voltage vacuum switch. A sinusoidal half-wave current was interrupted near its amplitude of 400 A with a counterpulse of rise velocities 2.4 and 32 A//spl mu/s. In this way, a forced switching off of dc current was modeled. A retarding field analyzer was used for ion parameter measurements at the forced commutation process. Ion potentials up to 100 V were measured at the current zero moment, and the average decay times of ions after current zero were in the range from a few microseconds up to 30 /spl mu/s as a function of observed ion potential. The measured values of decay times show the rather negligible role of ions in the discharge process after the counterpulse commutation in the examined contact arrangement. The rise time of the countercurrent is proposed as a factor in the successful forced current commutation under these conditions, and values up to a few amperes per microsecond of countercurrent rise velocity can be considered as the limit value.