Longer Pulse Research Articles

Inhibition of Skeletal Muscle ClC-1 Chloride Channels by Low Intracellular pH and ATP

Skeletal muscle acidosis during exercise has long been thought to be a cause of fatigue, but recent studies have shown that acidosis maintains muscle excitability and opposes fatigue by decreasing the sarcolemmal chloride conductance. ClC-1 is the primary sarcolemmal chloride channel and has a clear role in controlling muscle excitability, but recombinant ClC-1 has been reported to be activated by acidosis. Following our recent finding that intracellular ATP inhibits ClC-1, we investigated here the interaction between pH and ATP regulation of ClC-1. We found that, in the absence of ATP, intracellular acidosis from pH 7.2 to 6.2 inhibited ClC-1 slightly by shifting the voltage dependence of common gating to more positive potentials, similar to the effect of ATP. Importantly, the effects of ATP and acidosis were cooperative, such that ATP greatly potentiated the effect of acidosis. Adenosine had a similar effect to ATP at pH 7.2, but acidosis did not potentiate this effect, indicating that the phosphates of ATP are important for this cooperativity, possibly due to electrostatic interactions with protonatable residues of ClC-1. A protonatable residue identified by molecular modeling, His-847, was found to be critical for both pH and ATP modulation and may be involved in such electrostatic interactions. These findings are now consistent with, and provide a molecular explanation for, acidosis opposing fatigue by decreasing the chloride conductance of skeletal muscle via inhibition of ClC-1. The modulation of ClC-1 by ATP is a key component of this molecular mechanism.

The Effect of Sonification Pulse Rate on Perceived Urgency and Response Behaviors

Emergency signal researchers have devoted considerable energy to understanding the perceived urgency and performance effects of reliable and marginally reliable discrete auditory signals. Relatively little attention has been paid to aspects of continuous auditory displays. The purpose of the current study was to demonstrate and document the effects of sonification presentation rate on perceived urgency and response behaviors during a simulated patient monitoring task. As expected, participants rated shorter interpulse intervals as being significantly more urgent than longer pulse intervals. Participants also responded faster to patient problems when interacting with a sonification system that used shorter pulse intervals.

Coherent orbital waves in the photo-induced insulator–metal dynamics of a magnetoresistive manganite

Photo-excitation can drive strongly correlated electron insulators into competing conducting phases, resulting in giant and ultrafast changes of their electronic and magnetic properties. The underlying non-equilibrium dynamics involve many degrees of freedom at once, whereby sufficiently short optical pulses can trigger the corresponding collective modes of the solid along temporally coherent pathways. The characteristic frequencies of these modes range between the few GHz of acoustic vibrations to the tens or even hundreds of THz for purely electronic excitations. Virtually all experiments so far have used 100 fs or longer pulses, detecting only comparatively slow lattice dynamics. Here, we use sub-10-fs optical pulses to study the photo-induced insulator-metal transition in the magnetoresistive manganite Pr(0.7)Ca(0.3)MnO(3). At room temperature, we find that the time-dependent pathway towards the metallic phase is accompanied by coherent 31 THz oscillations of the optical reflectivity, significantly faster than all lattice vibrations. These high-frequency oscillations are suggestive of coherent orbital waves, crystal-field excitations triggered here by impulsive stimulated Raman scattering. Orbital waves are likely to be initially localized to the small polarons of this room-temperature manganite, coupling to other degrees of freedom at longer times, as photo-domains coalesce into a metallic phase.

Stimulation pulse characteristics and electrode configuration determine site of excitation in isolated mammalian skeletal muscle: implications for fatigue

We examined whether electrical field stimulation with varying characteristics could excite isolated mammalian skeletal muscle through different sites. Supramaximal (20-V, 0.1-ms) pulse stimulation with transverse wire or parallel plate electrodes evoked similar forces in nonfatigued slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles from mice. d-tubocurarine shifted the twitch force-stimulation strength relationship toward higher pulse strengths with both electrode configurations in soleus muscle, suggesting that weaker pulses excite muscle via neuromuscular transmission. With wire stimulation, movement of the recording electrode along the muscle caused a delay between the stimulus artifact and the peak of the action potential, consistent with action potential propagation along the sarcolemma. TTX abolished all contractions evoked with 20-V, 0.1-ms pulses, suggesting that excitation occurred via voltage-dependent Na+ channels and, hence, muscle action potentials. TTX did not prevent force development with > or = 0.4-ms pulses in soleus or 1-ms pulses in EDL muscle. Furthermore, myoplasmic Ca2+ (i.e., the fura 2 ratio) and sarcomere shortening were greater during tetanic stimulation with 2.0-ms than with 0.5-ms pulses in flexor digitorum brevis fibers from rats. TTX prevented all shortening and Ca2+ release with 0.5-ms, but not 2.0-ms, pulses, indicating that longer pulses can directly trigger Ca2+ release. Hence, proper interpretation of mechanistic studies requires precise understanding of how muscles are excited; otherwise, incorrect conclusions can be made. Using this new understanding, we showed that disrupted propagation of action potentials along the surface membrane is a major cause of fatigue in soleus muscle that is focally and continuously stimulated at 125 Hz.

UV-femtosecond laser ablation of SrTiO3 single crystals

We have investigated the ablation behaviour of single crystal SrTiO3 <100> with focus on the influence of the pulse duration at a wavelength of 248 nm. The experiments were performed with KrF-excimer lasers with pulse durations of 34 ns and 500 fs, respectively. Femtosecond-ablation turns out to be more efficient by one order of magnitude and to eliminate the known problem of cracking of SrTiO3 during laser machining with longer pulses [1],[2]. In addition, the cavities ablated with femtosecond pulses display a smoother surface with no indication of melting and well-defined, sharp edges. These effects can be explained by the reduced thermal shock effect on the material by using ultrashort pulses.

Particle balance on HT-7: Error analysis and first results

This paper introduces the utilization and first results of particle balance analysis on HT-7 deuterium retention study. Based on the present measuring system, at the end of a long pulse discharge, more than 90% of the puffed D2 molecules remains inside the vacuum vessel. In the following dozens of seconds, about 30% of the puffed D2 appears as outgassing and is extracted. The permanent D retention is at the level of 60%. More retention happens in longer pulse. Pumping speed is not a decisive factor for D2 retention control.

Simultaneous maximization of cell permeabilization and viability in single-cell electroporation using an electrolyte-filled capillary.

A549 cells were briefly exposed to Thioglo-1, which converts thiols to fluorescent adducts. The fluorescent cells were exposed to short (50-300 ms) electric field pulses (500 V across a 15 cm capillary) created at the tip of an electrolyte-filled capillary. Fluorescence microscopy revealed varying degrees of cell permeabilization depending on the conditions. Longer pulses and a shorter cell-capillary tip distance led to a greater decrease in the cell's fluorescence. Live/dead (calcein AM and propidium iodide) testing revealed that a certain fraction of cells died. Longer pulses and shorter cell-capillary tip distances were more deadly. An optimum condition exists at a cell-capillary tip distance of 3.5-4.5 microm and a pulse duration of 120-150 ms. At these conditions, >90% of the cells are permeabilized and 80-90% survive.

Effect of pulse rise time on charging effects in plasma immersion ion implantation with dielectric substrates with planar and cylindrical geometries

Using a one-dimensional self-consistent fluid model, the effect of pulse rise time on charging effects at dielectric surfaces is investigated during plasma immersion ion implantation (PIII) with planar and cylindrical geometries. The numerical results demonstrate that the pulse rise time plays an important role in PIII process with dielectric substrates. It is found that the charge dose accumulated on the dielectric surface is significant as decreasing pulse rise time, and the surface potential decreases at the later stage of the pulse, which results in the lower ion impact energy. On the other hand, the longer pulse rise time would lead to the lower charge dose accumulated on the dielectric surface and higher ion impact energy at the later stage of the pulse, which would elevate the effective implanted dose and introduce the ions to the depth deep enough for surface modification.

Block by internal Mg2+ causes voltage-dependent inactivation of Kv1.5

Internal Mg2+ blocks many potassium channels including Kv1.5. Here, we show that internal Mg2+ block of Kv1.5 induces voltage-dependent current decay at strongly depolarised potentials that contains a component due to acceleration of C-type inactivation after pore block. The voltage-dependent current decay was fitted to a bi-exponential function (tau(fast) and tau(slow)). Without Mg2+, tau(fast) and tau(slow) were voltage-independent, but with 10 mM Mg2+, tau(fast) decreased from 156 ms at +40 mV to 5 ms at +140 mV and tau(slow) decreased from 2.3 s to 206 ms. With Mg2+, tail currents after short pulses that allowed only the fast phase of decay showed a rising phase that reflected voltage-dependent unbinding. This suggested that the fast phase of voltage-dependent current decay was due to Mg2+ pore block. In contrast, tail currents after longer pulses that allowed the slow phase of decay were reduced to almost zero suggesting that the slow phase was due to channel inactivation. Consistent with this, the mutation R487V (equivalent to T449V in Shaker) or increasing external K+, both of which reduce C-type inactivation, prevented the slow phase of decay. These results are consistent with voltage-dependent open-channel block of Kv1.5 by internal Mg2+ that subsequently induces C-type inactivation by restricting K+ filling of the selectivity filter from the internal solution.

Three-temperature modeling of carrier-phonon interactions in thin GaAs film structures irradiated by picosecond pulse lasers

This article investigates numerically the carrier-phonon interactions in thin gallium arsenide (GaAs) film structures irradiated by subpicosecond laser pulses to figure out the role of several recombination processes on the energy transport during laser pulses and to examine the effects of laser fluences and pulses on non-equilibrium energy transfer characteristics in thin film structures. The self-consistent hydrodynamic equations derived from the Boltzmann transport equations are established for carriers and two different types of phonons, i.e., acoustic phonons and longitudinal optical (LO) phonons. From the results, it is found that the two-peak structure of carrier temperatures depends mainly on the pulse durations, laser fluences, and nonradiative recombination processes, two different phonons are in nonequilibrium state within such lagging times, and this lagging effect can be neglected for longer pulses. Finally, at the initial stage of laser irradiation, SRH recombination rates increases sufficiently because the abrupt increase in carrier number density no longer permits Auger recombination to be activated. For thin GaAs film structures, it is thus seen that Auger recombination is negligible even at high temperature during laser irradiation.

Dependence of calculus retropulsion on pulse duration during HO: YAG laser lithotripsy

The purpose of this study was to investigate the effect of optical pulse duration on stone retropulsion during Ho:YAG (lambda = 2.12 microm) laser lithotripsy. A clinical Ho:YAG laser with pulse durations was employed to fragment calculus phantoms and to evaluate stone phantom retropulsion. At a given pulse energy, optical pulse durations were divided into two discrete conditions: short pulse (tau(p): 120 to approximately 190 microseconds at FWHM) and long pulse (tau(p): 210 to approximately 350 microseconds at FWHM). Plaster of Paris calculus phantoms were ablated at different energy levels using optical fibers of varying diameters (273, 365, and 550 microm in core size). The dynamics of the recoil action of a calculus phantom was monitored using a high-speed camera; the laser-induced craters were evaluated with optical coherent tomography (OCT). Bubble formation and collapse were recorded with a fast flash photography setup, and acoustic transients were measured with a hydrophone. Shorter pulse durations produced more stone retropulsion than longer pulses at any given pulse energy. Regardless of pulse duration, higher pulse energy and larger fibers resulted in larger ablation volume and retropulsion (P<0.05). For shorter pulse durations, more rapid bubble expansion was observed and higher amplitudes of the collapse pressure wave were measured (P<0.05). Less retropulsion and equivalent fragmentation occurred when Ho:YAG pulse duration increased.

Inner Retinal Mechanisms Engaged by Retinal Electrical Stimulation

Retinal prosthetic devices are being developed to bypass degenerated retinal photoreceptors by directly activating retinal neurons with electrical stimulation. However, little is known about retinal activity during such stimulation. Whole cell patch-clamp recordings were obtained from ganglion and bipolar cells in the salamander retinal slice preparation. A stimulating electrode was positioned at the vitreal surface of the slice. Brief pulses of cathodic current evoked transient inward currents in ganglion cells arising from action potentials. Longer pulses (>5 milliseconds) also evoked sustained inward currents in ganglion cells that appeared synaptic in origin because, unlike transient currents, sustained currents were blocked by inhibiting synaptic transmission with Cd2+. These synaptic currents reversed around ECl and were blocked by picrotoxin, strychnine, or both, suggesting they were mediated by GABAa/c and glycine receptors. Synaptic currents were also blocked by the NMDA antagonist MK801 and the KA/AMPA antagonist NBQX, suggesting that epiretinal stimulation evoked glutamate release from bipolar cells, which in turn stimulated the release of GABA and glycine from amacrine cells. Sustained currents were also evoked by epiretinal stimulation in bipolar cells. These currents reversed near ECl and were blocked by picrotoxin, suggesting they arose from GABAa/c receptors. Pulse duration is an important parameter for effective activation of the inner retina by epiretinal stimulation. Brief pulses evoke action potentials only in ganglion cells. However, longer pulses also evoke sustained synaptic currents by stimulating glutamate release from bipolar cell terminals, which, in turn, evokes the release of GABA and glycine from amacrine cells.

Femtosecond laser ablation elemental mass spectrometry

Laser ablation mass spectrometry (LA-MS) has always been an interesting method for the elemental analysis of solid samples. Chemical analysis with a laser requires small amounts of material. Depending on the analytical detection system, subpicogram quantities may be sufficient. In addition, a focused laser beam permits the spatial characterization of heterogeneity in solid samples typically with micrometer resolution in terms of lateral and depth dimensions. With the advent of high-energy, ultra-short pulse lasers, new possibilities arise. The task of this review is to discuss the principle differences between the ablation process of short (>1 ps) and ultra-short (<1 ps) pulses. Based on the timescales and the energy balance of the process that underlies an ablation event, it will be shown that ultra-short pulses are less thermal and cause less collateral damages than longer pulses. The confinement of the pulse energy to the focal region guarantees a better spatial resolution in all dimensions and improves the analytical figures of merit (e.g., fractionation). Applications that demonstrate these features and that will be presented are in-depth profiling of multi-layer samples and the elemental analysis of biological materials.

Treatment of Port Wine Stains With the Pulse Dye Laser

The pulsed dye lasers (PDL) are the gold standard in the treatment of port wine stains (PWS). However, clearance rates vary widely, and many lesions are not completely cleared with laser treatment. This article reviews the use of different types of PDL for the treatment of PWS. Longer pulse durations and higher fluences in conjunction with skin cooling are required for larger vessels. Controversy still exists as to which wavelength induces greater photothermal damage to the blood vessels in PWS. The incomplete response of PWS to the conventional PDL is due to the suboptimal irradiation parameters of energy fluence, pulse duration, and wavelength currently used in clinical settings. New-generation PDL are more effective than conventional PDL, but vessels smaller than 30-50 microm appear resistant to all kinds of PDL treatment.

Laser crystallization — a way to produce crystalline silicon films on glass or on polymer substrates

Laser crystallization of amorphous semiconductor thin films and laser epitaxy, particularly of silicon, are presented. The theoretical background of nucleation and growth is discussed with respect to applications. It is demonstrated that short pulse laser irradiation of amorphous films leads to fine grains in the 10 nm to 1 μm range independent of the semiconductor. With longer pulses in the ms range or by scanning the beam of a cw laser, large crystals in the 100 μm range can be produced in the case Si or Ge on glass substrates. Epitaxial thickening of large-grained Si layers can be achieved by short-pulse laser melting during further deposition of a-Si.

The contribution of tympanic transmission to fine temporal signal evaluation in an ultrasonic moth

In lesser waxmoths Achroia grisella, pair formation and female mate choice involve very fine discrimination of male ultrasonic signals. Female A. grisella prefer male signals with longer pulses and longer ;asynchrony intervals', and evaluate differences in these characteristics in the range of 80-260 mus. The first step in the evaluation of these characteristics is the tympanic transmission of stimuli. We used laser vibrometry to describe the mode of vibration, frequency tuning and stimulus transmission of the tympana of A. grisella. The tympanic response consisted of a rotational mode of vibration, in which the anterior and posterior sections moved out of phase; the posterior section of the tympanum vibrated with all points moving in phase and maximum displacement at the attachment point of the scoloparium that contains the receptor cells. The tympana of A. grisella were tuned to high ultrasonic frequencies and had an estimated time constant (i.e. the limit to their temporal acuity) of about 20-50 mus. Pulse length and all but the shortest asynchrony interval were thus well resolved by the tympanum. We discuss implications for the evaluation of pulse length and asynchrony interval.

In vivo sodium magnetic resonance imaging of the human brain using soft inversion recovery fluid attenuation

Sodium imaging with soft inversion recovery fluid attenuation, which may be advantageous for intracellular weighting, was demonstrated with cerebrospinal fluid (CSF) suppression in five healthy volunteers at 4.7 T. Long rectangular inversion pulses reduce the average power deposition in an inversion recovery sequence, allowing repetition time to be shortened and more averages acquired for a given scan length. Longer pulses also significantly reduce the "depth" of Mz inversion in environments with rapid T1 and T2 relaxation (i.e., brain relative to CSF). Phantom experiments and simulation show a marked SNR increase when using a 10-ms, rather than a 1-ms, rectangular inversion pulse. Images were acquired in 11.1 min with a voxel size of 0.25 cm3 and the SNR in CSF, which is typically approximately 3 times larger than in brain, was reduced to 23% of that in the brain tissue, which had an average SNR of 17.

Elimination of cracking during UV laser ablation of SrTiO 3 single crystals by employing a femtosecond laser

We have performed a comparative study of UV laser ablation of SrTiO 3 with nanosecond- and sub-picosecond sources, respectively. The experiments were performed with lasers at a wavelength of 248 nm and pulse durations of 34 ns and 500 fs. Femtosecond ablation turns out to be more efficient by one order of magnitude and eliminated the known problem of cracking of SrTiO 3 during laser machining with longer pulses. In addition, the cavities ablated with femtosecond pulses display a smoother surface with no indication of melting and well-defined, sharp edges. These effects can be explained by the reduced thermal shock effect on the material by using ultrashort pulses.

The influence of pulse duration on the inactivation of bacteria using monopolar and bipolar profile pulsed electric fields

In recent years, a number of new applications have emerged where pulsed power is being used in the treatment of waste and effluent, foodstuffs, and beverages. One of these emerging applications is pulsed electric field (PEF) inactivation of microorganisms in liquid media. There are several ways in which PEF can be applied, including oscillatory, double exponential, and square wave pulses. Of these, the square-wave pulse is considered to be the most energy-efficient form of PEF delivery. It has been reported that the bipolar square-wave pulse, involving polarity reversal half way through the pulse, provides superior inactivation when compared to the monopolar pulse. However, results from the authors have shown that this is not always the case and that monopolar PEF is at least as effective for bacterial inactivation under the conditions investigated (Beveridge, et al., 2004). Further results are presented here on the effect of changing the pulse duration of the monopolar and bipolar pulse, using total pulse durations of 1, 2, 3, and 4 /spl mu/s. These results, obtained from an improved system, demonstrate how the relative effectiveness of inactivation is a function of the pulse duration. When inactivation is plotted against energy delivered, they show the superiority of monopolar over bipolar pulses for 1- and 2-/spl mu/s pulse profiles. For a pulse duration of around 3 /spl mu/s, there is no significant difference, and with still longer pulses, bipolar pulses appear to be superior to monopolar. It is postulated that electric-field-induced orientation may, in part, be responsible for this effect. These comparative experiments are conducted with complete control of the fluid temperature, which is maintained below 30/spl deg/C.

An analytical modeling of heat transfer for laser-assisted nanoimprinting processes

Laser-assisted direct imprinting (LADI) technique has been proposed to utilize an excimer laser to irradiate and heat up the substrate surface through a highly-transparent quartz mold preloaded on this substrate for micro- to nano-scaled structure fabrications. While the melting depth and molten duration are key issues to achieve a satisfactory imprinting pattern transfer, many material property issues such as crystalline phase alteration, grain size change and induced film stress variation are strongly affected by transient thermal response. With one-dimensional simplification as a model for the LADI technique, the present paper has successfully derived an analytical solution for the arbitrary laser pulse distribution to predict the relevant imprinting parameters during the laser induced melting and solidification processes. The analytical results agree quite well with the experimental data in the literature and hence can be employed to further investigate the effects of LADI technique from laser characteristics (wavelength, fluence and pulse duration) and substrate materials (silicon and copper) on the molten duration, molten depth and temperature distributions. Three kinds of excimer laser sources, ArF (193 nm), KrF (248 nm) and XeCl (308 nm) were investigated in this study. For the silicon substrate, the melting duration and depth were significantly dictated by the wavelength of laser used, indicating that employing the XeCl excimer laser with longer pulse duration (30 ns in the present study) will achieve the longest molten duration and deepest melting depth. As for the copper substrate, the melting duration and depth are mainly affected by the laser pulse duration; however, the wavelength of laser still plays an insignificant role in LADI processing. Meanwhile, the laser fluence should properly be chosen, less than 1.4 J/cm2 herein, so as to avoid the substrate temperature exceeding the softening point of the quartz mold (~1950 K) and to make sure that the mold can still maintain the original features.