Μs Range Research Articles

Silica sol–gel glasses incorporating dual-luminescent Yb quinolinolato complex: processing, emission and photosensitising properties of the ‘antenna’ ligand

The [Yb(5,7ClQ)(2)(H5,7ClQ)(2)Cl] (1) complex, that exhibits dual-luminescence in the visible (ligand-centered) and in the NIR (Yb-centered), has been incorporated into a silica sol-gel glass obtaining 1-doped glassy material which is optically transparent and homogeneous and with good mechanical properties. The doped sol-gel glass can be considered a "solid state solution" and photophysical studies demonstrate that the emissive properties of the dopant complex are preserved in the silica matrix. Observed NIR decay times fall in the μs range and are likely limited by "second-sphere" matrix interactions. The ligand-to-metal energy transfer mechanism occurs on ultrafast timescale and involves ligand triplet states. The sensitization efficiency of the antenna quinolinolato ligand toward Yb(3+) is estimated to be as high as ~80%. The Yb natural radiative lifetime observed for 1 in MeCN-EtOH solution (τ(rad) = 438 μs) is the shortest reported so far for ytterbium complexes.

Atomistic Simulations of Dominant Pathways in Protein Folding: From a Simple WW Domain to a Complex a Knotted Protein

MD simulations of protein folding using parallel or distributed computing can at most assess small chains with folding times in the μs range. The Dominant Reaction Pathways (DRP) approach now allows to simulate the folding of medium-sized proteins on just few tens of CPUs. We discuss the results of the DRP simulations of the folding of two proteins with different size: the 35 aminoacid WW domain Fip35 and the 83 aminoacid knotted protein YibK. Our results for Fip35 agree with those obtained by Shaw and co-workers, indicating a dominant path in which the first hairpin folds before the second. However, at temperatures below the folding temperature a sub-dominant pathway emerges, in which the order of formation of the hairpins is reversed. This finding can explain the results of the phi-value analysis of Jager and co-workers. Next, we present our results of the folding YibK, a much more complex protein with a self-entangled native structure and we discuss how the dominant folding pathway suggests a precise mechanism for knot formation.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Synthesis, characterization, photophysical studies and interaction with DNA of a new family of Ru(II) furyl- and thienyl-imidazo-phenanthroline polypyridyl complexes

A new family of Ru(II) polypyridyl complexes (C1 to C6) containing furyl- or thienyl-imidazo-phenanthroline ligands (4–6) were synthesized using microwave irradiation and characterized by elemental analysis, 1H NMR, UV–Vis absorption and fluorescence spectroscopy, FAB, ESI-MS and MALDI-TOF-MS spectrometry. On the other hand, the novel furyl- or thienyl-imidazo-phenanthroline derivatives (5–6) were synthesized through the Radziszewski reaction and completely characterized by the usual spectroscopic techniques. The interaction of the complexes with calf thymus DNA in the absence and in the presence of different quenchers (ethidium bromide, potassium hexacyanoferrate(II) and methyl viologen) has been studied by absorption spectroscopy, steady-state and single-photon timing luminescence measurements. Their electronic spectra show visible absorption peaks at 457–463nm, with red luminescence at 603–613nm. The emission quantum yields of these complexes are between 0.006 and 0.016 in air-equilibrated DMSO solution. Luminescence lifetimes in water lie within the 0.4–1.0μs range, with a non-exponential behavior due to aggregation of the probe. Ru(II) complexes C3, C4, C5 and C6 show intrinsic dsDNA-binding constants of 2.74×105, 3.02×105, 1.32×105 and 1.63×105M−1, respectively. The planar extended structure of the imidazo-phenanthroline ligands and the collected spectroscopic data suggest a partial intercalative binding mode of the novel metal probes to double-stranded DNA.

Plasma induced luminescence (PIL)

Laser-induced breakdown spectroscopy (LIBS) is well known tool for elemental analysis of solid, liquid and gaseous materials. The species emission life times in typical plasma are in 10–50 μs range. It is recognized that after this time following plasma formation any useful information does not exist. It is not the case when matrix subjected for plasma excitation is capable to luminescence. In such case UV, visible photons and possibly X-rays created by plasma excite the matrix luminescence, which may be detected after the corresponding delay when plasma emission becomes comparable by its intensity with luminescence. It may be supposed that plasma created by other means, for example, by spark, will also generate luminescence. Evidently it is new luminescence excitation mechanism and correspondingly new luminescence type, plasma induced luminescence (PIL).

Improvement of tribological properties of stainless steel by alloying its surface layer with rare earth elements using high intensity pulsed plasma beams

Austenitic stainless steels are widely used in numerous industrial applications due to their excellent corrosion resistance. However some applications are limited in cases when due to low hardness and poor tribological properties of stainless steel wear is responsible for the durability of a given engineering component.In the present work we have undertaken an attempt to improve the wear resistance of AISI 316L steel by alloying its near surface region with rare earth elements—REE using high intensity pulsed plasma beams in so called deposition by pulse erosion (DPE) mode. Power density of pulses was 106–107W/cm2 with the pulse duration in μs range. Heating and cooling processes were of non-equilibrium type. The near surface layer—thickness in μm range—was melted and simultaneously doped with cerium and lanthanum. Various parameters of the process were set up to get level of doping between 0.3 and 2.8at.% REE.An improvement of tribological properties—linear wear and scratch resistance—with increasing REE concentration as compared to the initial material was observed.

Last developments in diagnostics to follow splats formation during plasma spraying

Plasma sprayed coatings adhesion-cohesion, as well as thermo-mechanical properties depend strongly upon the sprayed particle flattening and solidification, taking place in a few μs and the corresponding splat formation. Sophisticated fast pyrometers (response times of less than 100ns) have been developed for studying the flattening particle temperature evolution when impacting on smooth surfaces. However the signal interpretation is far to be easy without following simultaneously the evolution of the particle shape. As the flattening time is in the μs range and the acquisition frequency of the fastest camera is only one image/μs, it is not possible to follow the flattening particle shape evolution. That is why, different particles considered to have the same impact parameters, were photographed at different flattening times separated by a few hundreds of nanoseconds. In parallel measurements on millimetre-sized drops (metals and ceramics), which flattening time is in the ms range, have been developed because fast cameras (~ 5000 images/s) can be used to follow the flattening phenomena. In this paper are presented the experimental devices developed and impacts of alumina particles in the 40μm and 5mm ranges, but with Weber numbers as close as possible, are compared. Measurements at both scales demonstrate the importance of the substrate preheating control (time and temperature) to achieve disk shaped splats and explain the phenomena induced.

Characterizing the Interaction Among Bullet, Body Armor, and Human and Surrogate Targets

This study used a combined experimental and modeling approach to characterize and quantify the interaction among bullet, body armor, and human surrogate targets during the 10-1000 μs range that is crucial to evaluating the protective effectiveness of body armor against blunt injuries. Ballistic tests incorporating high-speed flash X-ray measurements were performed to acquire the deformations of bullets and body armor samples placed against ballistic clay and gelatin targets with images taken between 10 μs and 1 ms of the initial impact. Finite element models (FEMs) of bullet, armor, and gelatin and clay targets were developed with material parameters selected to best fit model calculations to the test measurements. FEMs of bullet and armor interactions were then assembled with a FEM of a human torso and FEMs of clay and gelatin blocks in the shape of a human torso to examine the effects of target material and geometry on the interaction. Test and simulation results revealed three distinct loading phases during the interaction. In the first phase, the bullet was significantly slowed in about 60 μs as it transferred a major portion of its energy into the body armor. In the second phase, fibers inside the armor were pulled toward the point of impact and kept on absorbing energy until about 100 μs after the initial impact when energy absorption reached its peak. In the third phase, the deformation on the armor's back face continued to grow and energies inside both armor and targets redistributed through wave propagation. The results indicated that armor deformation and energy absorption in the second and third phases were significantly affected by the material properties (density and stiffness) and geometrical characteristics (curvature and gap at the armor-target interface) of the targets. Valid surrogate targets for testing the ballistic resistance of the armor need to account for these factors and produce the same armor deformation and energy absorption as on a human torso until at least about 100 μs (maximum armor energy absorption) or more preferably 300 μs (maximum armor deformation).

Slow and Fast Electron Channels in a Coherent Quantum Dot Mixer

We describe a means to realize slow and fast electron channels by coherent mixing of single-particle levels in quantum dots. The underlying physics, which gives insight into state superposition, can potentially be realized in multi-dot structures with complex gate control. However, we employ vertical double dot structures and in our scheme the mixing of single-particle levels arises because of natural perturbations in the confining potential of the high-symmetry dots. Additionally, because of the intrinsic properties of a Fock–Darwin-like spectrum, we utilize a magnetic field to bring multiple single-particle energy levels into close proximity. We determine single-electron resonant tunneling times (effectively dwell times when on resonance) that are either extended in the slow channel or shortened in the fast channel. Most dramatically, for the slow channel, slow-down factors of ∼10 and single-electron resonant tunneling times extended into the µs range are demonstrated in all systems of two, three, and four mixed single-particle states investigated here.

Measurement of the 90Sr absolute activity using the autocorrelation single-crystal scintillation method

It is shown for the first time that the ASCSTS technique we have introduced several years ago for lifetime measurements can be also used for measuring low level activities. A good example with practical relevance in this respect is 90Sr isotope. In order to apply this technique the radioactive isotope must have an isomeric state with a lifetime spanning the ns–μs range. This method is adequate for measuring weak activities with high detection efficiency in a geometry close to 4π. It is experimentally demonstrated that ASCSTS method is a reliable, high efficiency technique for measuring absolute radioactivity in the long radioactive chains.

Resolving Conformational and Rotameric Exchange in Spin-Labeled Proteins Using Saturation Recovery EPR

The function of many proteins involves equilibria between conformational substates, and to elucidate mechanisms of function it is essential to have experimental tools to detect the presence of conformational substates and to determine the time scale of exchange between them. Site-directed spin labeling (SDSL) has the potential to serve this purpose. In proteins containing a nitroxide side chain (R1), multicomponent electron paramagnetic resonance (EPR) spectra can arise either from equilibria involving different conformational substates or rotamers of R1. To employ SDSL to uniquely identify conformational equilibria, it is thus essential to distinguish between these origins of multicomponent spectra. Here we show that this is possible based on the time scale for exchange of the nitroxide between distinct environments that give rise to multicomponent EPR spectra; rotamer exchange for R1 lies in the ≈0.1-1 μs range, while conformational exchange is at least an order of magnitude slower. The time scales of exchange events are determined by saturation recovery EPR, and in favorable cases, the exchange rate constants between substates with lifetimes of approximately 1-70 μs can be estimated by the approach.

Relaxation of Photogenerated Carriers in P3HT:PCBM Organic Blends

The after-pulse time-resolved microwave conductivity (TRMC) decays observed in P3HT:PCBM blends display a dependence on time close to t(-beta), independent of excitation intensity, in the 10 ns-1 micros range. This is explained in terms of the relaxation of carriers in a Gaussian density of states (DOS). The model is based on a demarcation level that moves with time by thermal release and retrapping of initially trapped carriers. The model shows that when the disorder is large the after-pulse decay of the type t(-beta) is obtained, while at low disorder and large temperature the carrier distribution becomes independent of time. In the measurements different beta values were observed depending on the solvent used for spin-coating: 0.4-0.6 for chlorobenzene and 0.3-0.4 for toluene. The model was applied to extract the shape of the DOS from the TRMC decays, giving a dispersion parameter of about 120 meV for blends with high P3HT content.

Kinetics and thermodynamics of metal-loaded transferrins: transferrin receptor 1 interactions

Transferrin receptor 1 (R) and human serum transferrin (T) are the two main actors in iron acquisition by the cell. R binds TFe(2) (iron-loaded transferrin), which allows its internalization in the cytoplasm by endocytosis. T also forms complexes with metals other than iron. In order to follow the iron-acquisition pathway, these metals should obey at least two essential rules: (i) formation of a strong complex with T; and (ii) interaction of this complex with R. In the present paper, we propose a general mechanism for the interaction of five metal-loaded Ts [Fe(III), Al(III), Bi(III), Ga(III) and Co(III)] with R and we discuss their potential incorporation by the iron-acquisition pathway. With iron- and cobalt-loaded Ts, the interaction of R takes place in two steps: the first is detected by the T-jump technique and occurs in the 100 micros range, whereas the second is slow and occurs in the hour range. Bi(III)- and Ga(III)-loaded Ts interact with R in a single fast kinetic step, which occurs in the 100-500 micros range. No interaction is detected between R and aluminium-saturated T. The fast steps are ascribed to the interaction of the C-lobe of metal-loaded T with the helical domain of R: dissociation constant, K'(1), of 0.50+/-0.07, 0.82+/-0.25, 4+/-0.4 and 1.10+/-0.12 microM for Fe(III), Co(III), Bi(III) and Ga(III) respectively. The second slow steps are ascribed to changes in the conformation of the protein-protein adducts which increase the stability to achieve, at thermodynamic equilibrium, an overall dissociation constant, K(1), of 2.3 and 25 nM for Fe(III) and Co(III) respectively. This last step occurs over several hours, whereas endocytosis takes place in several minutes. This implies that metal-loaded Ts are internalized with only the C-lobe interacting with R. This suggests that, despite a lower affinity for R when compared with TFe(2), some metal-loaded Ts can compete kinetically with TFe(2) for the interaction with R and thus follow the iron-acquisition pathway.

Empirical model description of photon path length for differential path length spectroscopy: combined effect of scattering and absorption

Differential path length spectroscopy (DPS) is a method of reflectance spectroscopy that utilizes a specialized fiber geometry to make the photon path length (tau) insensitive to variations in tissue optical properties over a wide range of absorption (mu(a)) and total scattering (mu(s)) coefficients, which are common within the ultraviolet/visible (UV/VIS) wavelength region. This study extends the description of tau to larger mu(a) and smaller mu(s) values, optical properties that are representative of the near-infrared region (NIR), a region where the DPS path length may be dependent on both coefficients. This study presents a novel empirical relationship between tau and the combined effect of both mu(a) (range: 0.1-12 mm(-1)) and mu(s) (range: 1.5-42 mm(-1)), anisotropy of 0.8, and is applicable to DPS probes containing a wide range of fiber diameters (range: 100-1000 microm). The results indicate that the simple empirical formula, including only one fitted parameter, is capable of accurately predicting tau over a wide range (r=0.985; range: 80-940 microm) and predictions are not biased versus mu(a) or mu(s). This novel relationship is applicable to analysis of DPS measurements of tissue in both the UV/VIS and NIR wavelength regions and may provide information about the wavelength-specific tissue volume optically sampled during measurement.

Concentric needle single fiber electromyography: normative jitter values on voluntary activated Extensor Digitorum Communis

Single fiber electromyography (SFEMG) is the most sensitive clinical neurophysiological test for neuromuscular junction disorders, particularly myasthenia gravis. Normal values for jitter obtained with SFEMG electrode have been published, but there are few publications for concentric needle electrode (CNE). The aim of this study was to discuss the possibilities to analyse the jitter in CNE recordings and to get normal values of jitter for voluntary activated Extensor Digitorum Communis using disposable CNE. Fifty normal subjects were studied, 16 male and 34 female with a mean age of 37.1+/-10.3 years (19-55). The jitter values of action potentials pairs of isolated muscular fibers were expressed as the mean consecutive difference (MCD) after 20 analysed potential pairs. The mean MCD (n=50) obtained was 24.2+/-2.8 micros (range of mean values in each subject was 18-31). Upper 95% confidence limit is 29.8 micros. The mean jitter of all potential pairs (n=1000) obtained was 24.07+/-7.30 micros (range 9-57). A practical upper limit for individual data is set to 46 micros. The mean interpotential interval (MIPI) was 779+/-177 micros (range of individual mean values was 530-1412); there were no potentials with impulse blocking. The present study confirms that CNE is suitable for jitter analysis although certain precautions must be mentioned. Our findings of jitter values with CNE were similar to some other few reports in literature.

Structural and tribological properties of carbon steels modified by plasma pulses containing inert and active ions

It is known that phase transformations into austenite can take place in the surface layer of steels irradiated with intense pulses of laser, ion or plasma beams. Due to the presence of nitrogen and carbon expanded austenite in stainless steel, good corrosion resistance is maintained while the wear resistance is increased. A series of carbon steels with various carbon contents was irradiated with high intensity (5–6 J/cm 2), short (μs range) nitrogen and argon plasma pulses. The pulsed energy was high enough to melt the surface region of the samples. This paper reports the results of investigations of structural and tribological properties of the near surface layer of carbon steels induced by such treatment. The identified phases and wear resistance of the modified layer are presented.

Neural mechanisms for calculation of the interaural intensity difference in the chicken auditory brainstem

Interaural time differences in the envelope of a sound (envelope ITDs) can potentially provide spatial information at high frequencies where interaural phase differences (IPDs) are not available. Interaural intensity differences (IIDs) also provide important spatial information at high frequencies. Both IIDs and envelope ITDs can influence spatial perception at high frequencies, but behavioral and physiological studies suggest that IIDs dominate perception. This study examines envelope ITD sensitivity in the auditory cortex of the pallid bat, a species that uses passive sound localization at the low end of its audible range to find prey. Its auditory system is entirely ‘high-frequency’ in that phase-locking does not occur at the low end of its audible range. If the bat uses ITDs, they must be derived from the envelope of the signal. A previous study of envelope ITD sensitivity in its inferior colliculus (IC) reported that neurons are sensitive to the small ±70 μs range of available ITDs. This study extends these findings to the cortical level to assess the transformation of ITD sensitivity and the binaural response properties that underlie this sensitivity. Two measures of sensitivity were used. The dynamic ITD range measures the range of ITDs over which the maximum response of a neuron decreases by 80%. When presented with square-wave amplitude-modulated tones statically delayed in arrival time, the average dynamic ITD range in the IC is 304 μs, but dropped to 175 μs in auditory cortex. IC neurons average a 38% change in maximum response over the relevant ITD range, while cortical neurons average a 67% change. Also measured were time–intensity trading ratios, which index the extent to which a change in IID can cause a shift the dynamic ITD range. Average trading ratios are approximately the same in the IC and auditory cortex (17.9 μs/dB vs. 16.7 μs/dB, respectively). Binaural interactions changed from the IC to auditory cortex. In IC, ITD sensitivity is an inhibitory, subtractive process in which ITDs reduce the response evoked by contralateral monaural stimulation. In the auditory cortex, both binaural inhibition and facilitation occur. In the majority of cortical neurons, IID and ITD functions were remarkably similar in shape, having stepped, step-peaked or peaked functions. The binaural interactions (inhibition and/or facilitation) evoked by ITDs and IIDs were also typically similar. These results suggest that IIDs and envelope ITDs are having similar effects on output of the same binaural comparator system.

Molecular mobility in model dough systems studied by time-domain nuclear magnetic resonance spectroscopy

The microscopic distribution and dynamic state of water and molecular mobility in various model systems are investigated using time-domain NMR spectroscopy. Starch and gluten showed different continuous distribution populations in T 21 (μsec range, obtained from One pulse experiments) and T 22 (msec range, obtained from CPMG experiments) proving that starch and gluten have different water dynamics and molecular mobility. A starch/gluten mixture (76:12, w/w) and wheat flour dough exhibited similar patterns indicating that water and molecular mobilities in dough tended to be more representative of interactions with starch than gluten, even though both water–starch and water–gluten interactions are occurring in wheat flour dough. Increasing the water content did not influence the continuous distribution pattern of T 21 but affected the relative amount of each fraction in T 21 (i.e. an increase of the more mobile fraction and a decrease of the less mobile fraction with increasing moisture). Added water has an important role in the more mobile fraction but not in the less mobile fraction, which is in μs range. This indicates that model food systems contain multiple microstructural domains with various water and molecular mobilities that show correspondingly different water dynamics. Therefore, the dispersion of various relaxation time constants helped identify the distribution of independent microstructural domains. The manipulation of the composition of the model food system influences the water dynamics and molecular mobility and provides a basis for the application of the microstructural domain concept to real food systems.

Algorithm of Ensemble Pulsar Time

An algorithm of the ensemble pulsar time based on the Wiener filtration method has been constructed. This algorithm has allowed the separation of the contributions of an atomic clock and a pulsar itself to the post-fit pulsar timing residuals. The method has been applied to the timing data of the millisecond pulsars PSR B1855+09 and PSR B1937+21 and allowed to filter out the atomic scale component from the pulsar phase variations. Direct comparison of the terrestrial time TT(BIPM96) and the ensemble pulsar time PTens has displayed that the difference TT(BIPM96) – PTens is within ±0.4 μs range. A new limit of gravitational wave background based on the difference TT(BIPM96) – PTens was established to be Ωgh2~10−10.

Comparison of the internal dynamics of globular proteins in the microcrystalline and rehydrated lyophilized states

Natural abundance solid-state 13C-NMR spin-lattice relaxation experiments in the laboratory ( T 1) and off-resonance rotating ( T 1ρ) frames were applied for qualitative comparison of the internal molecular dynamics of barstar, hen egg white lysozyme and bacteriophage T4 lysozyme in both the microcrystalline and the rehydrated (water content is 50% of the protein mass) lyophilized states. The microcrystalline state of proteins provides a better spectral resolution; however, less is known about the local structure and dynamics in the different states. We found by visual comparison of both T 1 and T 1ρ relaxation decays of various resonance bands of the CPMAS spectra that within the ns–μs range of correlation times there is no appreciable difference in the internal dynamics between rehydrated lyophilized and crystalline states for all three proteins tested. This suggests that the internal conformational dynamics depends weakly if at all on inter-protein interactions in the solid state. Hence, physical properties of globular proteins in a fully hydrated solid state seem to be similar to those in solution. This result at least partly removes concerns about biological relevance of studies of globular proteins in the solid state.

Characterisation of a pulsed rf-glow discharge in view of its use in OES

Pulsed radiofrequency glow discharges are studied in view of their possible advantages for optical emission spectroscopy (GD-OES). The excitation characteristics of a pulsed radiofrequency Grimm-type glow discharge are studied. The effects of a pulsed power supply on the sputtering are investigated and the effect on the emission yield for resonant and non-resonant emission lines is described. The enhancement of the emission yield through rf-power pulsing in the 10 μs range is attributed to a temporal reduction of the self-absorption. The possibility of analysing heat-sensitive non-conductive materials and layers through pulsed rf-GDOES is demonstrated. The work opens several subjects and questions for further research on understanding the plasma processes linked to analytical rf-GD-OES.