Well-defined Pulses Research Articles

Noise-like pulse generation by amplified well-defined pulse in an optical fiber with negative group velocity dispersion

We experimentally and numerically demonstrate that noise-like pulses (NLPs) can be generated by pumping well-defined pulses (WDPs) into an optical fiber amplifier at a wavelength in the region of negative group velocity dispersion. Through investigating the evolution of the optical pulses, it is realized that the output pulses consist of NLPs at the pump wavelength and split solitons at Stokes wavelengths, due to intrapulse Raman scattering followed by the process of soliton fission. Such process of pulse breakup results in the generation of sub-pulses that have peak powers much higher than the unbroken WDPs have, enabling WDPs to strongly induce nonlinear effects. This finding resolves the discrepancy between the experiment and simulation results of supercontinuum generation by using picosecond WDPs in previous research.

Evaluation of a method for time-of-flight, wavelength and neutron flight path calibration for neutron scattering instruments by means of a mini-chopper and standard neutron monitors

Accurate conversion of neutron time-of-flight (TOF) to wavelength is of fundamental importance to neutron scattering measurements in order to ensure the accuracy of the instruments and the experimental results. Equally important in these measurements is the determination of uncertainties, and with the appropriate precision. Especially in cases where instruments are highly configurable, the determination of the absolute wavelength after any change must always be performed (e.g. change of detector position). Inspired by the manner with which neutron spectrometers determine the absolute wavelength, we evaluate for the first time, in the author's knowledge, a commonly used method for converting TOF to neutron wavelength by measuring the neutron flight path length from the source of neutrons to a monitor and we proceed to analytically calculate the uncertainty contributions that limit the precision of the conversion. The method was evaluated at the V20 test beamline at the Helmholtz Zentrum Berlin (HZB), emulating the ESS source with a long pulse of 2.86 ms length and 14 Hz repetition rate, by using a mini-chopper operated at 140 Hz and two portable beam monitors (BMs), as well as accompanied data acquisition infrastructure. The mini-chopper created well-defined neutron pulses and the BM was placed at two positions, enabling the average wavelength of each of the pulses created to be determined. The used experimental setup resulted in absolute wavelength determination at the monitor positions with a δλ mean / λ mean of ∼1.8% for λ > 4 Å. With the use of a thinner monitor, a δλ mean / λ mean of ∼1% can be reached and with a modest increase of the distance between the reference monitor positions a δλ mean / λ mean of below 0.5% can be achieved. Further improvements are possible by using smaller chopper disc openings and a higher rotational speed chopper. The method requires only two neutron measurements and doesn't necessitate the use of crystals or complex fitting with sigmoid functions and multiple free variables, and could constitute a suitable addition to imaging, diffraction, reflectometers and small angle neutron scattering instruments, at spallation sources, that do not normally utilise fast choppers.

Generation of supercontinuum covering 520 nm to [formula omitted] by noise-like laser pulses in an integrated all-fiber system

Supercontinuum (SC) is generated in an integrated all-fiber system, starting with a fiber laser. High-power laser pulses at the 1.56μm center wavelength are pumped into a hybrid nonlinear fiber, which consists of a highly nonlinear fiber (HNLF) fusion-spliced with a photonic crystal fiber (PCF). After the laser pulses propagate through an HNLF with a small dispersion slope of 0.0071 ps/nm2/km at 1.56μm wavelength, a supercontinuum covering a spectral range from 875 nm to 2.2μm is generated. Subsequently, a photonic crystal fiber (PCF) with a zero-dispersion wavelength (ZDW) at 1.04μm is used to expand the SC spectrum to the visible region. The relation between the center wavelength of the pulses and the ZDW of the nonlinear fibers matches the condition that is possible to induce strong soliton-related dynamics. In this study, it is experimentally found that noise-like pulses (NLPs) are more effective to generate ultra-broadband SC spectra than well-defined pulses (WDPs). The SC generated by pumping NLPs into a hybrid nonlinear fiber of an 8 cm HNLF and a 2 m PCF has an average power of 1.9 W and a spectrum covering a wavelength range from 520 nm to 2.25μm. The SC generated by pumping WDPs into the same hybrid nonlinear fiber has an average power of 1.85 W and a spectrum covering a wavelength range from 680 nm to 2.25μm.

Development and evaluation of pulsed – Post column derivatization in liquid chromatography as a concept to minimize reagent consumption

In the current article, we propose an alternative approach to reduce the consumption of the reagents in liquid chromatography coupled to on-line post column derivatization. In our proposal post column reagents do not flow continuously but they are instead introduced as well-defined pulses (at microliter levels) that are merged on-line with the eluted analytes through precise tuning (Pulsed-Post Column Derivatization, Pulsed-PCD). The profiles of the pulses in terms of time and flow rate were investigated “visually” using caffeine as model compound (at 274 nm). The robustness of the procedure was evaluated by Monte Carlo simulations and was verified taking into account the precisions of typically used propulsion systems. As a proof of concept, we selected the determination of histidine in human urine after separation by cation exchange chromatography and Pulsed-PCD derivatization with o-phthalaldehyde. The consumption of the derivatizing reagent was downscaled to the microliter level per run, while the analytical results were within the expected ranges (110 – 1520 µmol L−1) and with good agreement with the corroborative method based on classic HPLC-PCD.

Reassessment of the advertisement call of topotypic Scinax squalirostris (Anura: Hylidae), with an acoustic evaluation of its occurrence in the Serra da Mantiqueira, southeastern Brazil

Reassessment of the advertisement call of topotypic Scinax squalirostris (Anura: Hylidae), with an acoustic evaluation of its occurrence in the Serra da Mantiqueira, southeastern Brazil. Scinax squalirostris (Lutz, 1925) is thought to occur along a broad range in South America. The values reported for calls of topotypes differ substantially among studies. Because vocalizations often play a key role in uncovering cryptic diversity, the call of S. squalirostris is herein redescribed based on a new sample of topotypes. The call of a population from Poços de Caldas, Minas Gerais state, is also described. Topotypic advertisement calls have a dominant frequency between 3970 and 4125 Hz; 13–15 notes emitted at a rate of 24–27/s; call rate of 67/min and duration of 0.52–0.61 s; mid-call notes having 6 or 7 well-defined pulses, and an intra-note pulse rate of 223–266/s. Calls of the Poços de Caldas population have dominant frequency between 4083 and 4358 Hz; 15–18 notes emitted at a rate of 32–34/s; call rate of 64/min and duration of 0.46–0.56 s; mid-call notes having 6 or 8 well-defined pulses, and an intra-note pulse rate of 252–312/s. The advertisement calls of these populations have some differences with each other, and are promptly distinguished from calls of morphologically similar species. Our data to topotypes are inconsistent with some previously reported. A more detailed study of the population from Poços de Caldas is required, and more marked differences may be found in populations more distant from type locality of S. squalirostris.

Broadband nonlinear modeling of RF amplifier-driven systems for multiharmonic predistortion of pulsed output signals

By applying pulsed voltages to particle beams in circular accelerators, the longitudinal distribution of the particles can be controlled. Specifically, so-called barrier bucket systems can be used to enclose the beam between two barrier pulses. The challenge in these barrier bucket systems is, that the high voltage pulses need to be of a certain shape with high signal quality in order to preserve a high beam quality. In order to generate the pulses, frequencies up to 100 times the fundamental frequency are required, leading to high signal distortion caused by frequency-dependent properties of the system and nonlinearities of the power amplifier at high output power. In order to reach the required well-defined output pulses, signal predistortion is indispensable.However, nonlinear PA modeling and signal predistortion tends to focus on modulated signals rather than pulsed voltages as it is mainly used in communication technology. Thus, many previously developed predistortion methods are not applicable for our application or have to be adapted for single voltage pulses. Here, we first define a distortion rate as a quantity for the deviation between the produced signal and the ideal output. In a second step, a Hammerstein model is developed for modeling both, the PA and the driven system together, and finally, the model is tested for two different PAs.

High-power, octave-spanning supercontinuum generation in highly nonlinear fibers using noise-like and well-defined pump optical pulses

High-power, octave-spanning supercontinuum generation through pumping a highly nonlinear fiber with noise-like and well-defined optical pulses is investigated. A two-stage fiber amplifier, consisting of a pre-amplifier and a booster, is used to greatly enhance the average power of noise-like pump pulses from 14 mW to 13.1 W. Owing to the limited coupling efficiency, only a maximum optical power of 4.63 W is launched into the nonlinear fiber. As a result, a supercontinuum spectrum spanning from 940 to 2300 nm with an average power of 3.82 W is achieved with noise-like pump pulses. This is, to the best of our knowledge, the highest average power obtained over such an octave-spanning supercontinuum spectrum using noise-like pump pulses. Supercontinuum generation with a broader spectral range and a higher average power is feasible if the coupling efficiency of the pump pulse power launched into the nonlinear fiber is increased. For the purpose of comparison, well-defined pump pulses with a similar average power at a similar repetition rate are also investigated for similar octave-spanning supercontinuum generation. A supercontinuum spectrum spanning from 950 to 2500 nm with an average power of 3.62 W is obtained with well-defined pump pulses. Even though the spectrum of the resulting supercontinuum using the well-defined pump pulses is broader, a large portion of its optical power is concentrated around the center wavelength, leading to a lower spectral power density at other wavelengths; furthermore, a higher extent of spectral structure appears in its optical spectrum, resulting in a higher power variation among different wavelengths.

Smart Drug Delivery from Electrospun Fibers through Electroresponsive Polymeric Nanoparticles.

Electrospun poly(ε-caprolactone) (PCL) microfibers loaded with poly(3,4-ethylenedioxythiophene) nanoparticles (PEDOT NPs) and curcumin with diameter of 3.9 ± 0.7 μm have been prepared and subsequently characterized using different spectroscopic techniques, scanning electron microscopy, and atomic force microscopy. PEDOT NPs, which are mainly located inside the PCL microfibers, exhibit a diameter of 99 ± 21 nm. PEDOT- and curcumin-containing PCL microfibers behave as extracellular cell matrices, facilitating cell spreading and enhancing cell proliferation because of their heterogeneity and roughness. The release of curcumin from the PCL microfibers by simple diffusion is very slow, external electric stimuli being required to boost and regulate the curcumin delivery process. PEDOT NPs behave as electroactuators upon application of well-defined potential pulses, increasing their diameter by about 17% and migrating from inside the PCL matrix to the surface of the microfibers. This electromechanical actuation mechanism affects the structure of the PCL matrix, promoting the release of curcumin that increases with the number of pulses. Overall, PCL fibers loaded with electroresponsive PEDOT NPs represent a promising and valuable drug delivery system that can be regulated by using pulsatile electrical stimulation.

Retention of intermediate polarization states in ferroelectric materials enabling memories for multi-bit data storage

A homogeneous ferroelectric single crystal exhibits only two remanent polarization states that are stable over time, whereas intermediate, or unsaturated, polarization states are thermodynamically instable. Commonly used ferroelectric materials however, are inhomogeneous polycrystalline thin films or ceramics. To investigate the stability of intermediate polarization states, formed upon incomplete, or partial, switching, we have systematically studied their retention in capacitors comprising two classic ferroelectric materials, viz. random copolymer of vinylidene fluoride with trifluoroethylene, P(VDF-TrFE), and Pb(Zr,Ti)O3. Each experiment started from a discharged and electrically depolarized ferroelectric capacitor. Voltage pulses were applied to set the given polarization states. The retention was measured as a function of time at various temperatures. The intermediate polarization states are stable over time, up to the Curie temperature. We argue that the remarkable stability originates from the coexistence of effectively independent domains, with different values of polarization and coercive field. A domain growth model is derived quantitatively describing deterministic switching between the intermediate polarization states. We show that by using well-defined voltage pulses, the polarization can be set to any arbitrary value, allowing arithmetic programming. The feasibility of arithmetic programming along with the inherent stability of intermediate polarization states makes ferroelectric materials ideal candidates for multibit data storage.

Re-Description of the Advertisement Call of Vitreorana uranoscopa (Müller, 1924) (Anura, Centrolenidae) from the Argentinean Atlantic Forest, with Notes on Natural History

Vitreorana uranoscopa inhabits small or medium-sized streams with rocky bottoms of the Interior Atlantic Forest of eastern Brazil, northeastern Argentina, and likely southeastern Paraguay. Most of the available information originates from Brazilian populations. Only a few populations from Argentina have been reported and information about their natural history is almost unknown. This work re-describes the advertisement call of V. uranoscopa from a new population discovered in the province of Misiones, Argentina, and includes further data about its reproduction, population density and habitat conservation status. On the basis of 11 recorded males, two call types were recorded. Results showed that the typical advertisement call is formed by pulsed notes released singly, in groups, or in combinations of both at an average rate of 13.86 notes/min. Notes lasted 0.013–0.085 s and had 1–5 well-defined pulses lasting 0.003–0.015 s; the pulse repetition rate was 90.9–166.66 pulses/s. The peak of dominant frequency was 4,312.5–4,875.0 Hz with a slight, ascending frequency modulation. These data agree with those reported in previous studies, although some differences in the note duration, intercall interval, number of pulses and harmonics were identified. These differences might be due to either the technological limitations at the time of those studies or interpopulation variation. The second call type (reported for the first time in V. uranoscopa) is formed by 1–2 additional pulses at the beginning of some notes and has lower amplitude than typical calls, but the social context of its emission is still unknown. The calling males perched on the leaves of the marginal vegetation, either alone or occasionally in groups of 2–3 individuals, with a average of 5.5 individuals per 100 m transect. Clutches containing up to 36 eggs or embryos were found on the upper surface of fern fronds. In Argentina, V. uranoscopa occurs only in Araucaria forests of the Interior Atlantic Forest. Thus, the protection of streams with abundant marginal vegetation seems to be essential for the conservation of this species.

Oyster patch reefs as indicators of fossil hydrocarbon seeps induced by synsedimentary faults

The Late Jurassic deposits of the Boulonnais area (N-France) represent the proximal lateral-equivalent of the Kimmeridge Clay Formation; they accumulated on a clastic-dominated ramp subject to synsedimentary faulting as a result of the Atlantic Ocean rifting. In the Gris-Nez Cape area, i.e., close to the northern border fault zone of the Jurassic basin, the Late Jurassic sequence contains small-dimensioned oyster patch reefs (<1 m) that are specifically observed at the base of an abrupt deepening trend in the depositional sequence induced by well-defined pulses of normal fault activity. Petrographic analysis of these patch reefs shows that they are exclusively composed of Nanogyra nana embedded in a microsparitic calcite matrix. ™13C measurements, carried out within both the matrix and the shells, display significantly lower values in the matrix compared to the oyster shells which suggests that the carbonate matrix precipitation was involving a carbon source different from marine dissolved inorganic carbon, most probably related to sulfate reduction, which is evidenced by light ™34S in pyrites. Similarities but also differences with lucinid-rich bioconstructions, namely, the Late Jurassic pseudo-bioherms of Beauvoisin (SE-France) suggest that the patch reefs developed at hydrocarbon seeps are related to synsedimentary faults. The extensional block-faulting segmentation of the northern margin of the Boulonnais Basin in Late Jurassic times is thus believed to have induced a sort of small-dimension hydrocarbon seepage field, recorded by the patch reef distribution.

Research for High-Voltage Nanosecond Rectangular Pulse Generator

In order to calibrate the response characteristic of voltage dividers, the article presents a potable high-voltage nanosecond rectangular pulse generator based on the transmission-line theory. The generator consists of DC high-voltage source, pulse forming line (PFL), special high-voltage switch, pulse transmission line (PTL), resistive load and coaxial voltage divider. The compact charging and discharging circuit is developed coaxially and the interference proof performance is excellent. The voltage amplitude and the pulse width can vary from the output of the DC high-voltage source and the length of PFL respectively. In the article the theory of pulse forming process, the design and the key devices of the generator are investigated theoretically and experimentally. The experimental results demonstrate that the generator can meet the measurement demands and export well-defined rectangular pulses with the rise time less than 751.738ps and the voltage amplitude up to 2kV.

Water and sediment transport of channel-flat systems in a mesotidal mudflat: Willapa Bay, Washington

The muddy tidal flats of southern Willapa Bay, Washington are tidally dominated and receive little direct freshwater input. We use data from instruments deployed in channels of different size and on their adjacent flats to investigate the hydrodynamics and sediment dynamics of each morphological setting under a range of seasonal and meteorological conditions, including rain and wind events. Interaction between the morphology of the channel/flat complex and tidal water-level variations produces well-defined velocity pulses during both flooding and ebbing tides. These pulses represent about 27% of the total along-channel water transport and 35% of the suspended-sediment transport of the system. Maintenance of continuity produces the velocity pulse, and pulse magnitude is determined by tidal range. Wind alters the flow regime in channels and on the flat, enhancing over-flat ebb flow in this study location while decreasing ebb-pulse intensity. Wind speed was positively correlated with minimum suspended-sediment concentration. Precipitation falling directly on flats was found to erode flat sediment, which subsequently formed a temporary deposit in the adjacent channel. Residual along-channel water transport in channels and on nearby flats was flood dominant under all seasonal conditions sampled, and sediment flux was flood dominant during winter and spring deployments.

Thermal response of structured and contaminated carbon surfaces to heat pulses

Experiments involving well-defined heat pulses of laser radiation on the CFC target material NB31 and plasma-exposed CFC-samples with known composition and thickness of the contamination layer have been performed to investigate the thermal properties and behaviour at the surface. Special attention is focussed on the dependence of the surface temperature enhancement and its temporal evolution on the amount of the deposited material. The measured surface temperature excursions are compared with values of analytical and numerical solutions of the heat diffusion equation taking into account a surface region with low thermal conductivity or poor thermal contact to the underlying substrate material.

Capacitive Quenching Measurement Circuit for Geiger-Mode Avalanche Photodiodes

Characterization of Geiger-mode avalanche photodiodes operated in gated mode requires fast rising-edge, well-defined over-bias pulses, and effective avalanche quenching. There has not been a suitable circuit that meets both criteria, thus, making systematic characterization and accurate comparison of these devices difficult. We present a capacitive quenching circuit (CQC) that satisfies both criteria and, thus, offers advantages over existing options such as a gated passive quenching circuit (G-PQC) and gated-mode operation without avalanche quenching. Test results using a commercial Si Geiger-mode avalanche photodiode, together with an experimental comparison between the CQC and the standard G-PQC circuit, are reported. The advantages of the CQC over the G-PQC circuit are demonstrated through comparisons of experimental over-bias pulses, distribution of avalanche current pulses, and dark count rate data. By each metric, the CQC is shown to yield results that are superior to those obtained using a standard G-PQC circuit.

Enhanced performance of a filter–sensor system

In this paper are addressed two important, but seemingly unrelated issues: long term performance of a gas sensing array and performance of an air purification unit. It is shown that when considered together, the system can be regarded as a "smart filter". The enhancement is achieved by periodic differential sampling and measurement of the "upstream" and "downstream" gases of a filter. The correctly functioning filter supplies the "zero gas" from the downstream for the continuous sensor baseline correction. A key element in this scheme is the synthetic jet that delivers well-defined pulses of the two gases. The deterioration of the performance of the "smart filter" can be diagnosed from the response pattern of the sensor. The approach has been demonstrated on removal/sensing of ammonia gas from air.

Reconstructing high-magnitude/low-frequency landslide events based on soil redistribution modelling and a Late-Holocene sediment record from New Zealand

A sediment record is used, in combination with shallow landslide soil redistribution and sediment-yield modelling, to reconstruct the incidence of high-magnitude/low-frequency landslide events in the upper part of a catchment and the history of a wetland in the lower part. Eleven sediment cores were obtained from a dune-impounded wetland at Te Henga, west Auckland, northern New Zealand. Sediment stratigraphy and chronology were interpreted by radiocarbon dating, foraminiferal analysis, and provisional tephrochronology. Gradual impoundment of the wetland began c. 6000 cal yr BP, coinciding with the start of a gentle sea-level fall, but complete damming and initial sedimentation did not begin until c. 1000 cal yr BP. After damming, four well-defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores. For interpreting the sediment pulses, a physically based landslide model was used to determine spatially distributed relative landslide hazard, applicable at the catchment scale. An empirical landslide-soil redistribution component was added and proved able to determine the volumes and spatial pattern of eroded and deposited soil material, sediment delivery ratio and the impact on total catchment sediment yield. Sediment volumes were calculated from the wetland cores and corresponding landslide scenarios are defined through back-analysis of modelled sediment yield output. In general, at least four major high-magnitude landslide events, both natural and intensified by forest clearance activities, occurred in the catchment upstream of Te Henga Wetland during the last c. 1000 years. The spatial distribution of modelled critical rainfall values for the catchment can be interpreted as an expression of shallow landslide hazard. The magnitude of the sediment pulses represented in the wetland can be back-calculated to critical rainfall thresholds representing a shallow landslide model scenario.

Dynamics of magnetic stray fields at initial stage of magnetization reversal of micrometer-sized Co dots

The dynamical evolution of magnetic stray fields has been investigated at the initial stage of magnetization reversal of a microstructured cobalt film (Co dots). Quantitative measurements of the domain magnetization and of the shift of the domain boundaries have been performed at 1 ns intervals. The measurements were performed using an emission electron microscope. The photoelectrons were excited from a sample using well-defined synchrotron-radiation pulses in single bunch operation mode (UE56/1-PGM at BESSY II, Berlin). The magnetization movement was initiated by an external magnetic field pulse, the pulse width being 8 ns. The magnetic field pulse was synchronized with the synchrotron single bunch radiation pulses. The lateral and time resolutions of the applied pulses were 50 nm and 500 ps, respectively.

Cyclic Expression of Class I Alcohol Dehydrogenase in Male Rats Treated with Ethanol

Continuous infusion of ethanol-containing diets has been demonstrated to generate well-defined pulses in blood and urine ethanol concentrations that occur with a frequency of approximately 6 days. The present study aimed to determine if hepatic class I alcohol dehydrogenase was the cause of these cycles. Adult male rats were fed an ethanol-containing diet by continuous intragastric infusion. Hepatic ADH activity, class I ADH mRNA level and rate of class I ADH gene transcription fluctuated in a cyclic pattern that positively correlated with UECs, and inhibition of ADH with 4-methylpyrazole abolished the UEC pulses. These data demonstrate for the first time an ethanol-dependent regulation of rat hepatic class I ADH. The cyclic behavior of the ethanol levels correlates with changes in class I ADH expression and implies adaptability of the ethanol eliminating system to high concentrations of alcohol.

Simple voltage generator for producing well-defined nanosecond pulses of amplitudes in excess of 1 kV

A 50 /spl Omega/ charged coaxial line generator has been developed to produce extremely well-defined single-shot voltage pulses of amplitudes in excess of 1 kV, which are free from overshoot and ringing. The width of the pulses is adjustable from 0.7 ns to 250 ns with estimated rise-times as low as 105 ps. When driving a matched 50 /spl Omega/ load, the amplitude of the first reflected pulse replica is of less than 0.5% of the peak voltage of the main pulse.