Differences In Decay Times Research Articles

Time-resolved measurements of dislocation-related photoluminescence bands in silicon

Time decay measurements of dislocation-related PL have been performed for plastically deformed Si samples. Dislocation structures with different spectra were realized by deformation and subsequent thermal treatment. In all cases the decay time of the D1 band is less than that of the D2 band. Intrinsic properties of dislocations may therefore define the difference in decay times between the two bands. We compare this observation with previous results and propose a model of recombination between shallow and deep levels for D1/D2 bands. Different decay times are attributed to different spatial separation of shallow traps from a common deep trap.

Microwave photoconductivity decay characterization of high-purity 4H-SiC substrates

A microwave photoconductivity decay (MPCD) technique, which probes conductivity change in wafers in response to either an above-band-gap or below-band-gap laser pulse, has been used to characterize recombination lifetime in high-purity 4H-SiC substrates produced with three different anneal processes. The above-band-gap (266nm) decay times vary from ∼10ns to tens of microseconds in the 4H-SiC substrates depending on the wafer growth parameters. Wafers produced using the three processes A (as-grown), B (annealed at 2000°C), and C (annealed at 2600°C) have decay times of 10–20ns, 50–500ns, and tens of microseconds, respectively. The differences in decay times are attributed to low, medium, and high densities of recombination centers in process C, B, and A wafers, respectively. The MPCD results correlate with other characterization results such as deep level transient spectroscopy, which also showed that the 2600°C anneal process significantly reduces defect densities, resulting in the enhanced recombination lifetimes. Modeling and one-dimensional simulations indicate a trapping center closer to the conduction band results in a longer MPCD decay transient, but such a trapping based model for the enhanced lifetimes is not compatible with the wide range of experimental characterization results described in this work, which indicate an annealing out of recombination centers at 2600°C.

CLC-3 Channels Modulate Excitatory Synaptic Transmission in Hippocampal Neurons

It is well established that ligand-gated chloride flux across the plasma membrane modulates neuronal excitability. We find that a voltage-dependent Cl(-) conductance increases neuronal excitability in immature rodents as well, enhancing the time course of NMDA receptor-mediated miniature excitatory postsynaptic potentials (mEPSPs). This Cl(-) conductance is activated by CaMKII, is electrophysiologically identical to the CaMKII-activated CLC-3 conductance in nonneuronal cells, and is absent in clc-3(-/-) mice. Systematically decreasing [Cl(-)](i) to mimic postnatal [Cl(-)](i) regulation progressively decreases the amplitude and decay time constant of spontaneous mEPSPs. This Cl(-)-dependent change in synaptic strength is absent in clc-3(-/-) mice. Using surface biotinylation, immunohistochemistry, electron microscopy, and coimmunoprecipitation studies, we find that CLC-3 channels are localized on the plasma membrane, at postsynaptic sites, and in association with NMDA receptors. This is the first demonstration that a voltage-dependent chloride conductance modulates neuronal excitability. By increasing postsynaptic potentials in a Cl(-) dependent fashion, CLC-3 channels regulate neuronal excitability postsynaptically in immature neurons.

Measurement of skin temperature after infrared laser stimulation

Objectives Several types of lasers are available for eliciting laser evoked responses (LEPs). In order to understand advantages and drawbacks of each one, and to use it properly, it is important that the pattern of skin heating is known and duly considered. This study was aimed at assessing the skin temperature during and immediately after irradiation with pulses by Nd:YAP and CO 2 lasers. Materials and Methods The back of the non-dominant hand was irradiated in 8 subjects. Temperatures were measured by a fast analogical pyrometer (5 ms response time). Stimuli were tested on natural colour (white) and blackened skin. Results Nd:YAP pulses yielded temperatures that were correlated with pulse energy, but not with pulse duration; much higher temperatures were obtained irradiating blackened skin than white skin (ranges 100-194 °C vs 35-46 °C). Temperature decay was extremely slow in white skin, reaching its basal value in more than 30 s. CO 2 pulses delivered with power of 3W and 6W yielded temperatures of 69-87 °C on white skin, and 138-226 °C on blackened skin. Temperature decay was very fast (4-8 ms). Conclusions Differences in peak temperatures and decay times between lasers and tested conditions depend on energy and volume of heated skin. The highest temperatures are reached with lesser degree of penetration, as in the case of CO 2 laser and blackened skin. Taking into account the temperature decay time of the skin, the minimum interstimulus interval to get reliable LEPs should be no less than 10 s for Nd:YAP and 100 ms for CO 2 laser. Another important practical consequence of the heating pattern is that the Nd:YAP pulses will activate warmth receptors more easily than CO 2.

Diagnose Parameters of Plasma Induced by Femtosecond Laser Pulse in Quartz and Glasses

Electron plasma induced by a focused femtosecond pulse (130 fs, 800 nm) in quartz, fused silica, K9 glass, and Soda Lime glass was investigated by pump-probe technology. Pump and probe shadow imaging and interferometric fringe imaging have been used to determine plasma density, relaxation time, and electron collision time in the conduction band. In these materials, the electron collision time is about several femtoseconds when the electron density is in the 1019cm−3 range. The electron relaxation processes are different: lifetime is about 170 fs in pure quartz and fused silica, and about 100 ps in K9 and Soda Lime glass. The modified electron band by doped ions is regarded to be responsible for the difference of decay time in these materials.

How Much Afterhyperpolarization Conductance Is Recruited by an Action Potential? A Dynamic-Clamp Study in Cat Lumbar Motoneurons

We accurately measured the conductance responsible for the afterhyperpolarization (medium AHP) that follows a single spike in spinal motoneurons of anesthetized cats. This was done by using the dynamic-clamp method. We injected an artificial current in the neurons that increased the AHP amplitude, and we made use of the fact that the intensity of the natural AHP current at the trough of the voltage trajectory was related linearly to the AHP amplitude. We determined at the same time the conductance and the reversal potential of the AHP current. This new method was validated by a simple theoretical model incorporating AHP and hyperpolarization-activated (Ih) currents and could be applied when the decay time constant of the AHP conductance was at least five times shorter than the estimated Ih activation time. This condition was fulfilled in 33 of 44 motoneurons. The AHP conductance varied from 0.3 to 1.4 microS in both slow- and fast-type motoneurons, which was approximately the same range as the input conductance of the entire population. However, AHP and input conductances were not correlated. The larger AHP in slow-type motoneurons was mainly attributable to their smaller input conductance compared with fast motoneurons. The likeness of the AHP conductance in both types of motoneurons is in sharp contrast to differences in AHP decay time and explains why slow- and fast-type motoneurons have similar gain.

On the influence of background dust on radar scattering from meteor trails

We consider the influence of a possible background of mostly non-visual neutral or positively charged dust, on the diffusion of the ionized meteor trails formed as meteors burn up in the atmosphere. The aim of this is to see if the decay time of such trails, which is used to determine the neutral gas temperature at the trail height, can be affected by a part of the trail electrons being absorbed by dust as they diffuse outward. In our model calculations we consider three different scenarios for the background dust ranging from small but numerous positively charged dust, which is reported being observed by rocket probes, to the larger but well-established population of often visible icy dust particles. We consider the icy dust particles during quiet night conditions when they for the most part will be electrically neutral. We find that the decay of mainly the weaker trails will be affected. For the stronger trails with their larger electron content the limited electron absorption capability of the background dust have a negligible effect on the radar echo decay time. We suggest that systematic investigations at different heights, time of day and year, to look for clear differences in decay times as a function of initial trail echo strength, can give information on a content of the elusive background of dust particles. In such an investigation, the presence of substantial amounts of small positive or neutral dust particles should lead to a significantly smaller apparent decay time for weak trails than for strong trails.

An intra-operative positron probe with background rejection capability for FDG-guided surgery

For radio-guided surgery on tumors using F-18-FDG, detection of annihilation gamma photons emanating from other parts of the body produces background radiation counts and limits its use in clinical situations. To overcome this limitation, we have developed an intra-operative positron probe with background-rejection capability. The positron probe uses a phoswich detector composed of a plastic scintillator and a bismuth germinate (BGO). A positron from a positron emitter such as F-18 is detected by the plastic scintillator and emits annihilation photons. The BGO detects one of the annihilation photons while a photo-multiplier tube (PMT) detects scintillation photons from both scintillators. The decay time differences of these two scintillators are used to distinguish whether the event is a true event where a positron and a following annihilation photon are detected simultaneously, or a background event. In this configuration, only positrons can be selectively detected, even in an environment of high background gamma photon flux. Spatial resolution was 11-mm full width at half maximum (FWHM) 5 mm from the detector surface. Measured sensitivity for the F-18 point source was 2.6 cps/kBq 5 mm from the detector surface. The background count rate was less than 0.5 cps for a 20-cm diameter cylindrical phantom containing 37 MBq of F-18 solution measured on the phantom surface, while the positron count rate was almost linear over a range of approximately 6 kcps. These results indicate that our developed intra-operative positron probe is valuable for radio-guided surgery on tumors using F-18-FDG in a high flux of background annihilation gamma photons.

Amino Acid Residues Responsible for the Meta-III Decay Rates in Rod and Cone Visual Pigments

Vertebrate retinas have two types of photoreceptor cells, rods and cones, which contain visual pigments with different molecular properties. These pigments diverged from a common ancestor, and their difference in molecular properties originates from the difference in their amino acid residues. We previously reported that the difference in decay times of G protein-activating meta-II intermediates between the chicken rhodopsin and green-sensitive cone (chicken green) pigments is about 50 times. This difference only originates from the differences of two residues at positions 122 and 189 (Kuwayama, S., Imai, H., Hirano, T., Terakita, A., and Shichida, Y. (2002) Biochemistry 41, 15245-15252). Here we show that the meta-III intermediates exhibit about 700 times difference in decay times between the two pigments, and the faster decay in chicken green can be converted to the slower decay in rhodopsin by replacing the residues in chicken green with the corresponding rhodopsin residues. However, the inverse directional conversion did not occur when the two residues in rhodopsin were replaced by those of chicken green. Analysis using chimerical mutants derived from these pigments has demonstrated that amino acid residues responsible for the slow rhodopsin meta-III decay are situated at several positions throughout the C-terminal half of rhodopsin. Considering that rhodopsins evolved from cone pigments, it has been suggested that the molecular properties of rhodopsin have been optimized by mutations at several positions, and the chicken green mutants at two positions could be rhodopsin-like pigments transiently produced in the course of molecular evolution.

Fundamental differences in spontaneous synaptic inhibition between deep and superficial layers of the rat entorhinal cortex.

We have previously shown that there are clear differences between spontaneous excitatory synaptic currents recorded in layers V and II of the rat entorhinal cortex (EC) in vitro, and have suggested that these might contribute to a more pronounced susceptibility of the deeper layer to epileptogenesis. In the present study, we have made a detailed comparison of spontaneous synaptic inhibition between the two layers by recording spontaneous inhibitory synaptic currents (sIPSCs) using whole-cell patch-clamp techniques in EC slices. Pharmacological studies indicated that sIPSCs were mediated exclusively by gamma-aminobutyric acid (GABA)(A) receptors. There was little difference in average amplitudes, rise or decay times of sIPSCs in layer II compared with layer V. However, in the former, events occurred at 4-5 times the frequency seen in the latter, and frequencies of </=40 Hz were not uncommon. When activity-independent, miniature IPSCs were isolated in tetrodotoxin (TTX), the frequency in layer V was more than halved, but in layer II only a small reduction was seen, and the frequency remained very high. In terms of kinetics, while averaged sIPSCs in each layer were very similar, detailed comparison of individual sIPSCs within layers revealed distinct differences, possibly reflecting inputs from different subtypes of interneurons or inputs at different somatodendritic locations. In layer V, sIPSCs could be divided into three groups, one with slow rise and decay kinetics and a second with fast rise kinetics, further distinguished into two groups by either fast or slow decay kinetics. The distinction between events in layer II was simpler, one group having both fast rise and decay times and the second with both parameters much slower. Finally, IPSCs could occur in high-frequency bursts in both layers, although these were much more prevalent in layer II. The results are discussed in terms of the overall level of background inhibition in the two layers, as well as how this might relate to their susceptibilities to epileptogenesis.

Dynamical friction in flattened systems: a numerical test of Binney's approach

We carry out a set of self-consistent N-body calculations to investigate how important the velocity anisotropy in non-spherical dark matter haloes is for dynamical friction. For this purpose, we allow satellite galaxies to orbit within flattened and live dark matter haloes (DMHs) and compare the resulting orbit evolution with a semi-analytic code. This code solves the equation of motion of the same satellite orbits with mass loss and assumes the same DMH, but either employs Chandrasekhar's dynamical friction formula, which does not incorporate the velocity anisotropy, or Binney's description of dynamical friction in anisotropic systems. In the numerical and the two semi-analytic models, the satellites are given different initial orbital inclinations and orbital eccentricities, whereas the parent galaxy is composed of a DMH with aspect ratio q h = 0.6.We find that Binney's approach successfully describes the overall satellite decay and orbital inclination decrease for the whole set of orbits, with an averaged discrepancy of less than 4 per cent in orbital radius during the first three orbits. If Chandrasekhar's expression is used instead, the discrepancy increases to 20 per cent. Binney's treatment therefore appears to provide a significantly improved treatment of dynamical friction in anisotropic systems.The velocity anisotropy of the DMH velocity distribution function leads to a significant decrease with time of the inclination of non-polar satellite orbits. But, at the same time, it reduces the difference in decay times between polar and coplanar orbits evident in a flattened DMH when the anisotropic DMH velocity distribution function is not taken into account explicitly. Our N-body calculations furthermore indicate that polar orbits survive about 1.6 times longer than coplanar orbits and that the orbital eccentricity e remains close to its initial value if satellites decay slowly towards the galaxy centre. However, orbits of rapidly decaying satellites modelled with the semi-analytic code show a strong orbital circularization ( $\dot e\gt 0$ ) not present in the N-body computations.

A new technique for multiparameter imaging microscopy: use of long decay time photoluminescent labels enables multiple color immunocytochemistry with low channel-to-channel crosstalk.

In this report, we describe luminescence imaging microscopy using five different photoluminescent dyes in a single specimen. We combined the long decay time luminophores, europium(III) chelate, terbium(III) chelate, palladium(II) coproporphyrin, and platinum(II) coproporphyrin, with a green nuclear stain, Syto 25 trade mark, that emits conventional fast decaying fluorescence. The luminescence emissions from the five different luminophores were separated from each other by the differences in spectra and decay times using time-resolved detection. Applicability of this dye-combination for multiparameter analysis of a biological object was verified in a mixed population of peripheral blood leukocytes. Leukocyte cytocentrifugates were incubated in one step with a cocktail of luminophore-conjugated antibodies recognizing neutrophil- and lymphocyte-specific markers, followed by rapid staining with a mixture of nuclear stain and Pt-porphyrin as an eosinophil stain. The results show that multiple luminescent dyes with long decay time can be used together, and in combination with a conventional fluorophore. The separation of the signals of the long decay time labels was distinctive and enabled reliable identification of different leukocyte types, as well as an automated cell count. The long decay time luminophores together with time-resolved luminescence imaging microscopy (TR-LIM) provide a unique tool for studies of simultaneous expression of multiple antigens at the level of a single cell. In comparison with other multiparameter imaging techniques, the described technique offers increased accuracy of results, simplification of preparation procedure, and dramatic shortening of the total processing time. To our knowledge, this is the first time that simultaneous fivefold labeling/staining and analysis in a single specimen has been performed in the field of immunocytochemistry.

Simultaneous measurement of theB0meson lifetime and mixing frequency withB0→D*−l+νldecays

We measure the B^0 lifetime τ_B^0 and the B0−B0[overbar] oscillation frequency Δm_d with a sample of approximately 14000 exclusively reconstructed B^0→D*−l+ν_l signal events, selected from 23 million BB[overbar] pairs recorded at the Υ(4S) resonance with the BABAR detector at the Stanford Linear Accelerator Center. The decay position of the other B is determined with the remaining tracks in the event, and its b-quark flavor at the time of decay is determined with a tagging algorithm that exploits the correlation between the flavor of the b quark and the charges of its decay products. The lifetime and oscillation frequencies are measured simultaneously with an unbinned maximum-likelihood fit that uses, for each event, the measured difference in decay times of the two B mesons (Δt), the calculated uncertainty on Δt, the signal and background probabilities, and b-quark tagging information for the other B. The results are τ_B^0=(1.523^(+0.024)_(−0.023)±0.022)ps and Δm_d=(0.492±0.018±0.013)ps^(−1). The statistical correlation coefficient between τ_B0 and Δm_d is -0.22.

Prolongation of hippocampal miniature inhibitory postsynaptic currents in mice lacking the GABA(A) receptor alpha1 subunit.

GABA(A) receptors (GABA(A)-Rs) are pentameric structures consisting of two alpha, two beta, and one gamma subunit. The alpha subunit influences agonist efficacy, benzodiazepine pharmacology, and kinetics of activation/deactivation. To investigate the contribution of the alpha1 subunit to native GABA(A)-Rs, we analyzed miniature inhibitory postsynaptic currents (mIPSCs) in CA1 hippocampal pyramidal cells and interneurons from wild-type (WT) and alpha1 subunit knock-out (alpha1 KO) mice. mIPSCs recorded from interneurons and pyramidal cells obtained from alpha1 KO mice were detected less frequently, were smaller in amplitude, and decayed more slowly than mIPSCs recorded in neurons from WT mice. The effect of zolpidem was examined in view of its reported selectivity for receptors containing the alpha1 subunit. In interneurons and pyramidal cells from WT mice, zolpidem significantly increased mIPSC frequency, prolonged mIPSC decay, and increased mIPSC amplitude; those effects were diminished or absent in neurons from alpha1 KO mice. Nonstationary fluctuation analysis of mIPSCs indicated that the zolpidem-induced increase in mIPSC amplitude was associated with an increase in the number of open receptors rather than a change in the unitary conductance of individual channels. These data indicate that the alpha1 subunit is present at synapses on WT interneurons and pyramidal cells, although differences in mIPSC decay times and zolpidem sensitivity suggest that the degree to which the alpha1 subunit is functionally expressed at synapses on CA1 interneurons may be greater than that at synapses on CA1 pyramidal cells.

The surface heat flux feedback. Part II: direct and indirect estimates in the ECHAM4/OPA8 coupled GCM

The surface heat flux feedback in the Atlantic Ocean is estimated in the ECHAM4/OPA8 coupled model. The net heat flux feedback is negative everywhere, mostly ranging between 15 and 35 W m–2 K–1, but reaching up to 50 W m–2 K–1 in the tropics, so that it damps existing sea surface temperature anomalies. The bulk of it is due to the turbulent flux, although in the tropics the radiation feedback also strongly contributes. The turbulent heat flux feedback is strongest in fall and winter at extra-tropical latitudes, and in spring and summer near the equator. At mid-latitudes, the radiation feedback remains small in each season, but it can be strongly negative in parts of the tropics. At extra-tropical latitudes the model feedback compares rather well with estimates derived in Part I from the COADS observations and the NCEP reanalysis, but in the tropical Atlantic the negative heat flux feedback is much too strong. An indirect estimation of the model heat flux feedback is also attempted in regions of small mean surface current, based on the difference in decay time of sea surface temperature and salinity anomalies. The inferred negative heat flux feedback is qualitatively correct, but the seasonal changes in the mixed-layer depth are too large for the method to be accurate at high latitudes.

Measurement of the oscillation frequency for B0– [formula omitted] mixing using hadronic B0 decays

The oscillation frequency of B 0– B 0 mixing ( Δm d ) has been measured using 29.1 fb −1 of data collected with the Belle detector at KEKB. This measurement is made through the distributions of the proper decay time difference of B pairs in events tagged as same- and opposite-flavor decays. In each event, one B is fully reconstructed in a flavor-specific hadronic decay mode, while the flavor of the other is extracted through a likelihood calculated from the b-flavor information carried in its final decay products. We obtain Δm d=(0.528±0.017±0.011) ps −1 , where the first error is statistical and the second error is systematic.

Measurement of theB0−B¯0Oscillation Frequency with Inclusive Dilepton Events

The B0-B-0 oscillation frequency has been measured with a sample of 23 x 10(6) BB- pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both B mesons decay semileptonically and use the charge of the leptons to identify the flavor of each B meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives deltamd = 0.493+/-0.012(stat)+/-0.009(syst) ps-1.

Photoluminescence and Electroluminescence Characterization of In&lt;sub&gt;x&lt;/sub&gt;Ga&lt;sub&gt;1-x&lt;/sub&gt;N/In&lt;sub&gt;y&lt;/sub&gt;Ga&lt;sub&gt;1-y&lt;/sub&gt;N Multiple Quantum Well Light Emitting Diodes

We report on a study of radiative recombination in In0.11Ga0.89N/In.0.01Ga0.99N multiple quantum wells (MQWs). The QWs were nominally undoped, while the InGaN barriers were Si doped. The MQW part is situated in the depletion field of a pn-junction structure with electrical contacts, so that both photoluminescence (PL) and electroluminescence (EL) can be studied as a function of bias. The PL and EL spectra are distinctly different, in particular at low temperatures. The spectral properties and related differences in PL decay times reflect different recombination conditions in the MQW region for the individual QWs.

Measurement of the B(0) and B(+) meson lifetimes with fully reconstructed hadronic final states.

The B(0) and B(+) meson lifetimes have been measured in e(+)e(-) annihilation data collected in 1999 and 2000 with the BABAR detector at center-of-mass energies near the Upsilon(4S) resonance. Events are selected in which one B meson is fully reconstructed in a hadronic final state while the second B meson is reconstructed inclusively. A combined fit to the B(0) and the B(+) decay time difference distributions yields tau(B(0)) = 1.546+/-0.032(stat)+/-0.022(syst) ps, tau(B(+)) = 1.673+/-0.032(stat)+/-0.023(syst) ps, and tau(B(+))/tau(B(0)) = 1.082+/-0.026(stat)+/-0.012(syst).

An acoustical study on double bass bridge height adjusters

A study on double bass bridge height adjusters was made using local and international surveys, a listening test survey, and sound spectrum analysis to learn more about the acoustical properties of various bridge adjusters and their current use. A questionnaire sent via e-mail to members of the International Society of Bassists confirmed that preferences and opinions about adjusters vary widely, though some general tendencies are recognizable. Responses also gave some indications why approximately 60 to 80 bassists use bridge adjusters, while adjusters in central Europe are rarely seen. Computerized listening tests showed that all types of bridge height adjusters cause an audible difference in sound compared to a bridge with no adjusters, and that individual models and materials have unique tonal characteristics. Finally, a digital sound analysis was made comparing a bridge with no adjusters to the same bridge fitted successively with six types of bridge height adjusters. The analysis showed that bridge height adjusters make a significant difference in pizzicato decay time depending on the model and material in question, and FFT spectrum analysis of bowed tones showed the sound characteristics of bridge height adjusters throughout the range of the double bass.