Pulse Delay Time Research Articles

Modified Microwave Sampling Beamformer for Fast Weighting Control and Image Rejection

A modified microwave sampling beamformer (MSBF) for fast weight control and image replica rejection is presented. In the MSBF, each element weight is modified by controlling the corresponding switch using a pulse train with adjusted pulse width and time delay. A new limit for the sampling frequency is obtained as a function of the signal bandwidth and the pulse train duration. The image replica is introduced and techniques to lower its effect or to reject it are proposed. The relation between the sampling frequency and the pulse train duration, the effect of the image replica, and the effectiveness of the rejection technique are verified by simulating the new structure in the time domain.

Global attractivity and permanence of a SVEIR epidemic model with pulse vaccination and time delay

In this study, we propose a new SVEIR epidemic disease model with time delay, and analyze the dynamic behavior of the model under pulse vaccination. Pulse vaccination is an effective strategy for the elimination of infectious disease. Using the discrete dynamical system determined by the stroboscopic map, we obtain an ‘infection-free’ periodic solution. We also show that the ‘infection-free’ periodic solution is globally attractive when some parameters of the model under appropriate conditions. The permanence of the model is investigated analytically. Our results indicate that a large vaccination rate or a short pulse of vaccination or a long latent period is a sufficient condition for the extinction of the disease.

Experimental Analysis for the Low-Temperature Growth of Poly-Si Films by Using Double Excimer Laser

This paper is to investigate a double splitting excimer laser technique for making poly Si films. In this research, a KrF excimer laser of 248 nm in wavelength is used to irradiate a-Si films of 0.1 m in thickness on glass substrate to produce poly-Si ones. The control parameters are laser intensity (200~500 mJ/cm2), laser pulse number (1~2 shots) and delay time between two shots (one nanosecond). Average grain sizes from SEM photos are used to analyze the effects of these parameters. Firstly, in the excimer laser experiment, different laser fluences are utilized to study the effect on the microstructure of the silicon film. Purely from the viewpoint of heat transfer, the Si film obtains more energy has the slower cooling or solidification rate, which results in the larger grain. From the experimental results, it can be found that the grain size increases until the laser fluence increases up to the critical value of complete melting, which limits the grain growth method of energy increase. In this work, a double-splitting-laser method is proposed. In the method, a laser pulse from an excimer laser is divided into two pulses by a beam splitter. The cyclic optical path is used to control the delay time of the second pulse. Optical mirrors and optical attenuators are utilized to adjust the energy density of these two laser pulses. The delay time between these two pulses is changeable and controlled in the order of nanosecond. The second pulse is applied when the Si film is solidifying after the irradiation of the first one. This could enhance the solidification time and enlarge the grain size of the poly-Si film.

Time domain reflectrometry measurements using a movable obstacle for the determination of dielectric profiles

Abstract. Microwave techniques for the measurement of the permittivity of soils including the water content of soils and other materials, especially TDR (time domain reflectometry), have become accepted as routine measurement techniques. This summary deals with an advanced use of the TDR principle for the determination of the water content of soil along a probe. The basis of the advanced TDR technique is a waveguide, which is inserted into the soil for obtaining measurements of the effective soil permittivity, from which the water content is estimated, and an obstacle, which can mechanically be moved along the probe and which acts as a reference reflection for the TDR system with an exactly known position. Based on the known mechanical position of the reference reflection, the measured electrical position can be used as a measure for the effective dielectric constant of the environment. Thus, it is possible to determine the effective dielectric constant with a spatial resolution given by the step size of the obstacle displacement. A conventional industrial TDR-system, operating in the baseband, is used for the signal generation and for the evaluation of the pulse delay time of the obstacle reflection. Thus, a cost effective method for the acquisition of the dielectric measurement data is available.

Design and analysis of coherent OCDM en/decoder based on photonic crystal

The design and performance analysis of a new coherent optical en/decoder based on photonic crystal (PhC) for optical code -division -multiple (OCDM) are presented in this paper. In this scheme, the optical pulse phase and time delay can be flexibly controlled by photonic crystal phase shifter and time delayer by using the appropriate design of fabrication. According to the PhC transmission matrix theorem, combination calculation of the impurity and normal period layers is applied, and performances of the PhC-based optical en/decoder are also analyzed. The reflection, transmission, time delay characteristic and optical spectrum of pulse en/decoded are studied for the waves tuned in the photonic band-gap by numerical calculation. Theoretical analysis and numerical results indicate that the optical pulse is achieved to properly phase modulation and time delay, and an auto-correlation of about 8dB ration and cross-correlation is gained, which demonstrates the applicability of true pulse phase modulation in a number of applications.

Phase space modulation of laser produced protons with a double-foil target generation of quasimonoenergetic proton beams

It is shown by one-dimensional particle-in-cell simulation that quasimonoenergetic protons can be generated from a double-solid-foil target irradiated by two ultrashort intense laser pulses. In this approach, one uses the first laser pulse irradiating on the first foil to generate the energetic protons, and one uses the second laser pulse irradiating on the second foil to generate an electrostatic field, which modulates the energy spectrum of protons from the first foil. Quasimonoenergetic protons with tunable energy peaks can be obtained by controlling the time delay and intensity of the second pulse as well as the distance between the two foils. It is also found that a preplasma on the second foil increases the peak energy. The dependence of the proton beam quality on the laser and target parameters is also discussed.

Proteomics and Glycomics Analyses of N-Glycosylated Structures Involved in Toxoplasma gondii-Host Cell Interactions

The apicomplexan parasite Toxoplasma gondii recognizes, binds, and penetrates virtually any kind of mammalian cell using a repertoire of proteins released from late secretory organelles and a unique form of gliding motility (also named glideosome) that critically depends on actin filaments and myosin. How T. gondii glycosylated proteins mediate host-parasite interactions remains elusive. To date, only limited evidence is available concerning N-glycosylation in apicomplexans. Here we report comprehensive proteomics and glycomics analyses showing that several key components required for host cell-T. gondii interactions are N-glycosylated. Detailed structural characterization confirmed that N-glycans from T. gondii total protein extracts consist of oligomannosidic (Man(5-8)(GlcNAc)2) and paucimannosidic (Man(3-4)(GlcNAc)2) sugars, which are rarely present on mature eukaryotic glycoproteins. In situ fluorescence using concanavalin A and Pisum sativum agglutinin predominantly stained the entire parasite body. Visualization of Toxoplasma glycoproteins purified by affinity chromatography followed by detailed proteomics and glycan analyses identified components involved in gliding motility, moving junction, and other additional functions implicated in intracellular development. Importantly tunicamycin-treated parasites were considerably reduced in motility, host cell invasion, and growth. Collectively these results indicate that N-glycosylation probably participates in modifying key proteins that are essential for host cell invasion by T. gondii.

Steering dissociation of Br2 molecules with two femtosecond pulses via wave packet interference

The dissociation dynamics of Br2 molecules induced by two femtosecond pump pulses are studied based on the calculation of time-dependent quantum wave packet. Perpendicular transition from X 1Sigma g+ to A 3Pi 1u+ and 1Pi 1u+ and parallel transition from X 1Sigma g+ to B 3Pi 0u+, involving two product channels Br (2P3/2)+Br (2P3/2) and Br (2P3/2)+Br* (2P1/2), respectively, are taken into account. Two pump pulses create dissociating wave packets interfering with each other. By varying laser parameters, the interference of dissociating wave packets can be controlled, and the dissociation probabilities of Br2 molecules on the three excited states can be changed to different degrees. The branching ratio of Br*/(Br+Br*) is calculated as a function of pulse delay time and phase difference.

Single-frequency coherent terahertz-wave generation using two Cr:forsterite lasers pumped using one Nd:YAG laser

We have developed a compact terahertz-wave generator using two small Cr:forsterite lasers with single Nd:YAG laser pumping based on difference frequency generation in a GaP crystal. A Cr:forsterite laser was constructed with diffraction gratings, by which the pulse duration and delay time of the Cr:forsterite laser depend on the Cr:forsterite laser energy and the cavity length. The Cr:forsterite laser energy was tuned using the optical alignment and pumping energy. Temporal overlap of two Cr:forsterite laser pulses was realized at the GaP crystal. A single-frequency terahertz wave was generated at energy of 4.7 pJ around 2.95 THz using a 30-cm-long Cr:forsterite laser system.

Measurements of the plasma density in the FTU tokamak by a pulsed time-of-flight X-wave refractometer

On-line control over the plasma density in tokamaks (especially, in long-term discharges) requires reliable measurements of the averaged plasma density. For this purpose, a new method of density measurements—a pulsed time-of-flight plasma refractometry—was developed and tested in the T-11M tokamak. This method allows one to determine the averaged density from the measured time delay of nanosecond microwave pulses propagating through the plasma. For an O-wave, the measured time delay is proportional to the line-averaged density and is independent of the density profile (f≫fp) τo ≈ ko\( \tfrac{1} {{f^2 }}\mathop \smallint \limits_l \)N(xdx. A similar formula is valid for an X-wave: τX = ≈ kx\( \tfrac{{f^2 + f_c^2 }} {{(f^2 - f_c^2 )^2 }}\mathop \smallint \limits_l \)N(x)dx. Here, f is the frequency of the probing wave, fp is the plasma frequency, l= 4 a is the path length for two-pass probing in the equatorial plane, a is the plasma minor radius, kO and kX are numerical factors, fc is the electron-cyclotron frequency at the axis of the plasma column, and fp≫fc, f. Measurements of the time delay provide the same information as plasma interferometry, though they do no employ the effect of interference. When the conditions fp≫fc, f are not satisfied, the measured time delay depends on the shape of the density profile. In this case, in order to determine the average density regardless of the density profile, it is necessary to perform simultaneous measurements at several probing frequencies in order to determine the average density. In ITER (Bt ∼ 5T), a spectral window between the lower and upper cutoff frequencies in the range of 50–100 GHz can be used for pulsed time-of-flight X-wave refractometry. This appreciably simplifies the diagnostics and eliminates the problem of the first mirror. In this paper, the first results obtained in the FTU tokamak with a prototype of the ITER pulsed time-of-flight refractometer are presented. The geometry and layout of experiments similar to the planned ITER experiments are described. The density measured by pulsed time-of-flight refractometry is shown to agree well with the results obtained in FTU with a two-frequency scanning IR interferometer. The results obtained are analyzed, and the future experiments are discussed.

Quantum computing based on one-photon polarisation states of light pulses propagating in a doped resonance medium

The propagation of one-photon light pulses in optical media doped with rare-earth atoms is considered under conditions close to the atomic optical resonance. The four-beam polarisation interaction M-scheme with two probe pulses and two pump pulses is analysed. The regimes of induced cross-interaction between probe optical pulses are studied and the conditions are found for controlling efficiently their group velocities in the medium, which is determined by the tunings of the atomic optical resonance. An algorithm is proposed for quantum information processing by coding and controlling the time delays of one-photon light pulses in this system.

DLC film properties obtained by a low cost and modified pulsed-DC discharge

Surface and bulk properties of diamond-like carbon (DLC) films prepared by using different techniques and under different conditions have been of great concern. The main focus is to reach low total stress, high hardness, high adherence, and low friction coefficient, including the deposition in large area at high growth rate. In this work, DLC films were obtained by using a low cost modified pulsed-DC discharge technique. Different pulse bursts with different pulse widths and delay times were considered. Studies have been carried out in order to match the best set of parameters as mentioned above for different applications, as required in the frame work of our project. The DLC films were deposited onto Si(100) and 304 stainless steel substrates. A thin amorphous silicon interlayer was used to reduce the DLC film's total stress and to improve the films' adhesion to the substrates. A summary of the deposition rates, structural, mechanical, and tribological properties as functions of the pulsed-DC voltage and pulse characteristics will be presented. The results show that the adhesion of the DLC coatings on stainless steel using a thin amorphous silicon interlayer could be improved significantly.

Propagation Characteristics of Infrared Pulse Waves through Windblown Sand and Dust Atmosphere

The physics characteristics of the windblown sand and dust atmosphere at the sand bench of Yellow River in China are discussed. The pulse distortion and time delay of infrared nanosecond pulse propagating through the atmosphere having sand and dust particles are investigated at 1.06 and 3.8 μm, respectively. It is shown that the delay of 10 ns laser pulse propagating through 5 km windblown sand and dust atmosphere are over 1 ns and 10 ns at 1.06 and 3.8 μm, respectively. The pulse spread increases slightly with wavelength increase. The pulse spread of a 10 ns laser pulse is over 40 ns at 3.8 μm. The pulse delay and spread increase rapidly with the sand particle density increasing in atmosphere. The narrower the pulse width is, the more the pulse distortion is. Hence, at infrared band, for a laser pulse propagating in sand and dust atmosphere, the pulse delay and spread are quite severe and need be taken into account for a narrower pulse laser system.

Ultrashort pulsed complex argument Sinc-Gaussian beams

By using slowly-varying envelope approximation, a family of solutions of the paraxial wave equation are found in theory, which represents a new family of ultrashort pulsed beams called ultrashort pulsed complex argument Sinc-Gaussian beams. These pulsed beams with a certain frequency have a nearly complex argument Gaussian profile, a sinc function temporal shape. The ultrashort pulsed complex argument Sinc-Gaussian beams and their propagation properties in free space are studied detailedly, such as intensity on the axis, transversal intensity distribution of the pulsed beams, polarity reversal, pulse time delay, etc..

Isolation and characterization of a novel uronic acid-containing acidic glycosphingolipid from the ascidian Halocynthia roretzi

A novel uronic acid-containing glycosphingolipid (UGL-1) was isolated from the ascidian Halocynthia roretzi. UGL-1 was prepared from chloroform-methanol extracts and purified by the use of successive column chromatography on DEAE-Sephadex, Florisil, and Iatrobeads. Chemical structural analysis was performed using methylation analysis, gas chromatography, gas chromatography-mass spectrometry, matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry, and 1H-NMR spectra. The chemical structure of UGL-1 was determined to be a glucuronic acid-containing glycosphingolipid, Galbeta1-4(Fucalpha1-3)GlcAbeta1-1Cer. The ceramide component was composed of C16:0 and C18:0 acids and C16-, C17-, and C18-phytosphingosines as major components.

C 60 in intense short pulse laser fields down to 9fs: Excitation on time scales below e-e and e-phonon coupling

The interaction of C60 fullerenes with 765-797 nm laser pulses as short as 9 fs at intensities of up to 3.7 x 10(14) W cm(-2) is investigated with photoion spectroscopy. The excitation time thus addressed lies well below the characteristic time scales for electron-electron and electron-phonon couplings. Thus, energy deposition into the system is separated from energy redistribution among the various electronic and nuclear degrees of freedom. Insight into fundamental photoinduced processes such as ionization and fragmentation is obtained from the analysis of the resulting mass spectra as a function of pulse duration, laser intensity, and time delay between pump and probe pulses, the latter revealing a memory effect for storing electronic energy in the system with a relaxation time of about 50 fs. Saturation intensities and relative abundances of (multiply charged) parent and fragment ions (C60(q+), q=1-6) are fingerprints for the ionization and fragmentation mechanisms. The observations indicate that for final charge states q>1 the well known C60 giant plasmon resonance is involved in creating ions and a significant amount of large fragments even with 9 fs pulses through a nonadiabatic multielectron dynamics. In contrast, for energetic reasons singly charged ions are generated by an essentially adiabatic single active electron mechanism and negligible fragmentation is found when 9 fs pulses are used. These findings promise to unravel a long standing puzzle in understanding C60 mass spectra generated by intense femtosecond laser pulses.

Nondispersive delay line on magnetostatic waves

A new approach to the design of a nondispersive delay line on magnetostatic waves is proposed, whereby the cascades operating on the surface waves and the backward volume waves have a common passband in the same magnetic system due to a difference in the crystallogrphic orientations of ferrite waveguides cut from a {100} yttrium iron garnet film. The possibility to obtain a pulse delay time of up to 113 ± 3 ns in a 300-MHz-wide frequency band is experimentally demonstrated. The central frequency of this band can be tuned within 4–6 GHz by changing the applied magnetic field.

A wide-angle magnetic spectrograph of a novel design

At the 5MV tandem accelerator of the CMAM we install a UHV magnetic spectrograph for the detection of scattered and recoiled ions. Its special feature is that the ions emerging from the sample are passing through a 4nm thick DLC foil before entering the spectrograph. The secondary electrons emerging from this foil upon passage of an ion are focused on a two-dimensional position sensitive multi-channel plate (MCP) detector with delay-line read-out. From their impact position on this detector the direction of the ion is determined with a precision of 0.15° within an elliptical cone of 6°×9°. The spectrograph, consisting of a 115° sector magnet with special shaped pole faces, focuses the ions onto a one-dimensional position sensitive MCP detector, also with delay-line read-out, in the focal plane of the magnet. The time delay of the coincident pulses in the first and second detector is measured so that the velocity v of the ion is known in addition to the magnetic rigidity mv/q, allowing determination of m/q. The energy resolution is determined by the straggling in the foil and amounts to ΔE/E≈10−3 for 2MeV α particles. Blocking patterns of scattered or recoiled ions can be measured in one run. Because of the ion identification implied in the system, recoil spectra can be generated with light ions used as projectile.

Dynamics of the collective excitations of the quantum Hall system

Using the non linear optical technique of 3-pulse 4-wave mixing, we study the dynamics of the collective excitations of the quantum Hall system. We excite the system with 100 fs pulses propagating in directions k 1 and k 3 and then probe its time evolution with a delayed pulse k 2. We measure the non-linear optical response from the lowest Landau level along the direction k 1+ k 2− k 3. As function of the time delay of pulse k 2, this signal shows striking beats for short time delays (∼500 fs), followed by a rise (∼20 ps) and then a decay (∼100 ps). We identify the microscopic origin of this dynamics by extending the standard theory of ultra fast nonlinear optics to include the effects of the correlations.

Making ultracold molecules in a two-color pump-dump photoassociation scheme using chirped pulses

This theoretical paper investigates the formation of ground state molecules from ultracold cesium atoms in a two-color scheme. Following previous work on photoassociation with chirped picosecond pulses [Luc-Koenig et al., Phys. Rev. A, 70, 033414 (2004)], we investigate stabilization by a second (dump) pulse. By appropriately choosing the dump pulse parameters and time delay with respect to the photoassociation pulse, we show that a large number of deeply bound molecules are created in the ground triplet state. We discuss (i) broad-bandwidth dump pulses which maximize the probability to form molecules while creating a broad vibrational distribution as well as (ii) narrow-bandwidth pulses populating a single vibrational ground state level, bound by $113\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The use of chirped pulses makes the two-color scheme robust, simple, and efficient.