Control of a pulse combustion reactor with thermoacoustic phenomena

We have developed a novel way of controlling parameters in reactors using flue gases from pulse combustion as a direct source of heat and as a means of transport of particulate materials synthesized in a slightly reductive environment or oxidative environment. The reactor is used for a spray pyrolysis synthesis of materials or the sintering of different ceramic powders. The reactor is heated directly, which means reduced energy losses, and the enhanced drying reported using pulse combustion is implemented for faster reaction. A slightly reductive atmosphere is maintained by combusting a stoichiometric fuel and air mixture and adding acetylene to the flue gas flow. Reaction conditions must be carefully controlled; this is achieved by influencing the characteristic times of the pulse combustion and changing the frequency of combustion and with it the temperature and flue gas composition in the reactor. The frequency is changed by nitrogen dilution of burning gas, influencing the mixing of the combustible mixture with hot flue gases and damping of frequencies with a secondary Helmholtz resonator. The frequency of pressure oscillations in the combustor should be the same as one of the harmonic frequencies of the reactor pipe to reach an acoustic resonance. In this work, the frequency of pulse combustion was altered in such a way that resonance was established with the reactor pipe and that a suitable reaction environment was obtained. With good control over all parameters, we were able to synthesize different Li-ion cathode materials, such as LiFePO₄ and Li(Ni_xMn_yCo_z)O_2.     

Extended energy approach to chaotic elastic-plastic response to impulsive loading

The paper supplements and extends an energy approach which helps to interpret elastic-plastic dynamic responses of a two-degree-of-freedom beam model whose ends are fixed, so that shallow arch action prevails, and chaotic as well as quasi-periodic vibrations may occur. For a problem of short pulse loading, a characteristic diagram is derived in which the energies at the stationary points (equilibria) of the elastic strain energy function V(w₁, w₂) are plotted against the pulse force, taken as the single loading parameter of the problem. Here w₁, w₂ are the displacements, and the function V contains the set of plastic strains as parameters, generated during the response. An alternative viewpoint is also introduced in which the plastic strains and the total available energy are regarded as specified parameters, and the problem is one of elastic response to arbitrary initial values of displacements and velocities.     

A Modified Method for Measuring the Spin Relaxation in Nuclear Quadrupole Resonance

A simple and rather efficient method for measuring the spin–spin relaxation time T ₂ in nuclear quadrupole resonance (NQR) is proposed. The method uses the phase cycling (or alternation) technique and is rather efficient in measuring short T ₂ times. Results on the use of this method for detecting NQR signals on nuclei of nitrogen ¹⁴N in a (CH₂)₆H₄ polycrystal are presented. The application of modified pulse sequences enables rather accurate measurements of the T ₂ time for this compound.     

CO2 laser cutting of stained glass

This paper covers the CO₂ laser cutting of stained glass using a Ferranti MF400 CNC laser cutting machine. The report examines the various laser cutting parameters required to generate a cut surface in glass which will require minimal post-treatment to be carried out, and also investigates the degree of geometrical intricacy that can be attempted, together with the associated limitations, in cutting 2D glass components. The experimental procedure used to obtain the necessary information for a preliminary database on the laser cutting of stained glass is also detailed. Finally, the implications and applications of the investigative work are examined for commercial situations through construction of a simple 2D test artefact.Notation f pulse frequency (Hz) - k thermal conductivity (W/mK) - P laser beam power (W) - Pl pulse duration (10^–5 s) - Pr pulse ratio - Ps pulse separation (10^–5 s) - P shield gas pressure (bar) - R _a surface roughness (m) - t _s substrate thickness (mm) - V cutting speed (mm/min) - V _opt optimum cutting speed (mm/min) - w kcrf width (mm) - angle of deviation (deg.) - wavelength (m) - d perforation depth (mm)     

CO2 laser emission modes to control enamel erosion

Considering the importance and prevalence of dental erosion, the aim of this in vitro study was to evaluate the influence of different modes of pulse emission of CO₂ laser associated or not to acidulated phosphate fluoride (APF) 1.23% gel, in controlling enamel erosion by profilometry. Ninety‐six fragments of bovine enamel were flattened and polished, and the specimens were subjected to initial erosive challenge with hydrochloric acid (pH = 2). Specimens were randomly assigned according to surface treatment: APF 1.23% gel and gel without fluoride (control), and subdivided according to the modes of pulse CO₂ laser irradiation: no irradiation (control), continuous, ultrapulse, and repeated pulse (n = 12). After surface treatment, further erosive challenges were performed for 5 days, 4 × 2 min/day. Enamel structure loss was quantitatively determined by a profilometer, after surface treatment and after 5 days of erosive challenges. Two‐away ANOVA revealed a significant difference between the pulse emission mode of the CO₂ laser and the presence of fluoride (P ≤ 0.05). The Duncan's test showed that CO₂ laser irradiation in continuous mode and the specimens only received fluoride, promoted lower enamel loss than that other treatments. A lower dissolution of the enamel prisms was observed when it was irradiated with CO₂ laser in continuous mode compared other groups. It can be concluded that CO₂ laser irradiation in continuous mode was the most effective to control the enamel structure loss submitted to erosive challenges with hydrochloric acid. Microsc. Res. Tech. 78:654–659, 2015. © 2015 Wiley Periodicals, Inc.     

A method of controllable pulse-heating for investigation of properties of short-lived liquids

A method of controlled pulse heating of low-inertia thermal probe immersed into the liquid under study with a temperatureT ₀ is described. The control system provides a “temperature plateau”-type heating mode, which consists in a rapid (t ₁∼10 μs) increase in the mass-average probe temperature to a chosen valueT _pl ≫T ₀ and maintains this value for a certain time interval (t ₂∼10³–10² μs) to within 1 K. Thermal effusivity of the substance, in relative units, is determined from the value of its internal heat flux. Sensitivity to changes in the thermal effusivity of a reference substance was 10⁻⁴. Due to the short pulse length and fine tuning of theT _pl value, the method allows one to conduct step-by-step scanning of “instantaneous” thermal properties of a substance in the region of its short-lived states.     

Effect of a pulsed electromagnetic field on the surface roughness in superfinishing EDM

It is shown and confirmed that the behaviour of a pulsed electromagnetic field influences the surface roughness especially in superfinishing electrodischarge machining (EDM). In accordance with technological experiments, instrumental measuring and theoretical analysis, some principles of the microenergy EDM process are discovered. An effective method concerning the generator and conducts is proposed to ensure that all discharges occur with desired pulse parameters. A best surface roughness of 0.04 μm R_a is achieved.     

Transient torsional vibrations of a rigid mass connected to an elastic half-space by an elastic circular rod

Applying Laplace transformations with respect to time and numerical inverse Laplace transformations, the transient torsional vibrations of a rigid mass connected to an elastic half-space by an elastic rod are analyzed under two specific incident pulse loads. The time histories of the rigid mass rotation are presented. Application of the numerical inverse Laplace transformations enables us to obtain the time histories of the rigid mass rotation accurately and fairly quickly by utilizing a digital computer. This method is applicable to the transient problem of a rigid mass connected to a half-space by an elastic medium or a finite elastic medium on a half-space, e.g. machines such as a press or a pile driver footed on a foundation, if the shape of the incident pulse is not very complicated and the maximum time T_max is not too long. When the slenderness ratio of the rod is small, the damping effect of the half-space on the rigid mass rotation due to waves radiating to infinity is small, regardless if the shear modulus ratio of the half-space and the rod is large or not. The amplitude of the rigid mass roation increases and its period lengthens as the shear modulus ratio increases.     

Sources of High-Power Ultrawideband Radiation Pulses with a Single Antenna and a Multielement Array

Sources of high-power ultrawideband electromagnetic pulses are described. They consist of a generator of single-polarity pulses, a bipolar pulse former, and a radiating system, for which either a single antenna or a 16-element antenna array is used. The values of the effective potential E _p R = 440 kV for the single antenna and 1.7 MV for an array excited by a bipolar pulse with a duration of 2 ns and a repetition rate of 100 Hz are obtained.__________Translated from Pribory i Tekhnika Eksperimenta, No. 3, 2005, pp. 46–54.Original Russian Text Copyright © 2005 by Gubanov, Efremov, Koshelev, Koval’chuk, Korovin, Plisko, Stepchenko, Sukhushin.     

Automated focusing in bright-field microscopy for tuberculosis detection

Pulsed‐laser atom‐probe tomography is used to compare the field‐evaporation mass spectrum and spatial distribution of molecular fragments from various poly(3‐alkylthiophene) films deposited on sharpened aluminium specimen carriers using two different deposition methods. Films deposited via a modified solution‐cast methodology yield small fragments with a uniform structural morphology whereas films deposited via an electrospray ionization methodology yield a wide range of fragments with a very non‐uniform structural morphology. The main field‐evaporated chemical species identified for both deposition types were, in order of typical relative abundance, C₂H₅⁺, CH₃⁺, C₂H₄⁺, followed by C₃H_7,8⁺/SC⁺ and SCH⁺. Thick electrospray depositions allowed investigation of the influence of laser‐pulse energy on the analysis. Evidence is presented supporting the presence of a critical laser‐pulse energy whereby changes in film morphology are signalled by the appearance of a new mass fragment at 190 Da.     

Efficiency of Pulsed Regimes for Enhancing the Breakdown Strength of Vacuum Insulation

Processing the experimental data on breakdown delay time in a vacuum was used to obtain the function K (t _p) of the relative change in the field gain factor at microscopic inhomogeneities of the cathode surface resulting from the realization of optimum pulse conditioning regimes. It is shown that over the range of pulse durations 10^–8 t _p 10^–6 s, the relative change in the state of the cathode surface corresponds to the relative changes in the breakdown strength of all-metal electrodes and to the voltage of the appearance of local flashes in a system of evaporated electrodes—a microchannel plate and the screen of an image intensifier. Applying optimum regimes for conditioning the surface with pulses of durations t _p < 10^–8 s makes it possible to achieve the limiting breakdown strength determined by the cathode mechanism of breakdown initiation.     

Determining the Current-Compensation Factor for a High-Current Relativistic Electron Beam in the Presence of an External Liner

The current-compensation factor f _m of a high-current relativistic electron beam (REB) with an energy E _e = 1.1 MeV, a current I _b = 24 kA, and a pulse duration t _p = 60 ns was investigated. The beam traveled in a metallic drift pipe filled with air at a pressure of 1 to 760 Torr. The dependence of the current compensation of the REB on the resistance of an external liner and the gas pressure was determined by two methods: using Rogowski loops placed around the transport channel or resistive back-current shunts inserted in the breaks of the drift pipe. It was ascertained that f _m of the high-current REB slightly varied with the gas pressure and was virtually independent of the resistance of the external liner. It was shown that the current compensation could be correctly determined by measuring the total current with the Rogowski loops placed inside the drift pipe and not with resistive shunts.     

Ion processes in a liquid-xenon ionization chamber under high-intensity pulsed irradiation

The current of positive ions in a liquid-xenon ionization chamber was studied under intense pulsed irradiation of the chamber with bremsstrahlung from a microtron. The dose absorbed in xenon during a radiation pulse was varied from 0.1 to 1.3 × 10⁴ μGy. It has been revealed that, in the dependence of the current on the irradiation dose, a deviation from a simple linear dependence is observed at a pulse dose of ∼4 μGy (∼0.2D _cr). Calculations show that recombination is the main cause of such deviation. A space charge appearing in the chamber under high irradiation intensities leads to a decrease in the electric field. The manifestation of the effects of a space charge becomes substantial when the field in a certain part of the chamber drops almost to zero. Under particular irradiation conditions, the space charge manifested itself in this study beginning with doses in a pulse of ∼50 μGy. The joint effect of the recombination and the space charge resulted in a dependence of the type of i ∼ D ^1/3. The influence of the ion current on the energy resolution of the ionization spectrometer is calculated for γ quanta detected during intervals between irradiation pulses. It is shown that a substantial impairment of the resolution begins at doses appreciably lower than the critical dose. The influence of the ion current becomes greater, as the dimensions of the chamber increase.     

Picosecond mid-IR laser induced surface damage on Gallium Phosphate (GaP) and Calcium Fluoride(CaF<Subscript>2</Subscript>)

Picosecond mid-IR USPL induced surface damage on a Gallium Phosphate (GaP) and Calcium Fluoride (CaF₂) is reported. A semiconductor GaP and a dielectric material CaF₂, that are transparent over3–10μm, were exposed to one picosecond mid-IR light (4.7μm) to investigate laser-induced surface morphological changes on the target The initiation of damage along the polishing scratch line of GaP and the random location of damage digs on the CaF₂ suggests that the mid-IR picosecond laser-induced damage on targets started from intrinsic surface defects. Multiple pulse irradiations produced periodic corrugated surface structures (ripples) perpendicular to the polarization of light on both GaP and CaF₂. In terms of the orientation and the spacing between ripples, observed ripples have common features with previously reported ripples.     

A General Program For Computer Controlled Pulsed Nmr Relaxation Studies

ABSTRACT

A general program is described which provides a variety of nuclear relaxation measurements on an NMR pulse spectrometer under control of a minicomputer. The common pulse sequences for T₁ T₂ and T_1ρ. are included. A field gradient coil was added to the probe and provided with a constant-current power supply to make possible homogeneity spoiling, self-diffusion measurements and a series of pulse sequences useful for simultaneous measurement of T₁ and T₂ and for measurement of long relaxation times.     

A Gas-Discharge Source of Quasi-monochromatic Ultrasoft X-rays

The results of a study of radiation characteristics of a high-current pinch discharge of the plasma-focus type in the region of soft and ultrasoft X-rays are presented. Experiments were performed at a moderate energy of discharges in a mixture of H₂ and Ne. It was shown that a comparatively narrow spectrum region of the generated radiation, which corresponds to the line emission of lithium-like ions Ne⁷⁺ with an average effective quantum energy E _eff 0.16 keV, can be selected. The Ne⁷⁺ emission fluence was (0.2–1.0) × 10¹² quant/cm² per pulse with a duration _0.5 = 40–100 ns. The results obtained demonstrate the feasibility of using such discharges in laboratories as pulse sources of quasi-monochromatic ultrasoft X-rays.     

THE EFFECTS OF EMISSION LIGHT PULSE WIDTH ON NON INVASIVE OPTICAL PLETHYSMOGRAPHIC DEVICES

Projecting pulsed light on biological tissue facilitates capturing in-depth optical plethysmographs to inspect micro-vascular blood flow. However, it remains unclear how the pulse width of light emission (t _pw) affects human tissue. In this study, alternating red and infrared light emitting diodes from a finger clip probe were set at 512 Hz. After conducting optical receiver sampling and digital filtering, the logarithmic ratio of the red and infrared light was used to examine their relationship to the pulse width. The pulse width varied from 70–1000 µs, yielding no observable effects on the ratios. These findings suggest that reducing the illumination time of optical components may reduce the amount of power consumed by the equipment and extend the lifetime of the power supply.     

Soft X-ray contact microscopy with nanosecond exposure times

High resolution (better than 20 nm) contact micrographs have been produced with exposure times of about a nanosecond. The illuminating source was a short-lived carbon plasma produced by focusing a single short (～1 ns) 100 J pulse from the Vulcan laser at the Rutherford Appleton Laboratory (RAL) to a 300 μm spot on a graphite target. This plasma emits strongly in the soft X-ray region, particularly at the CVI (3.37 nm) and CV (4.03 nm) lines. The specimens were behind a 100 nm thick Si₃N₄ window, at atmospheric pressure in an environmental cell. The images of diatoms recorded on X-ray resist showed features down to the limit of resolution of the SEM used to view the developed resist, which was about 20 nm.     

A Programmable Device for Experiments Employing a Superheated Probe in the Pulsed Operation Mode

A device was developed for experiments on the controlled heating of a thin wire probe immersed in the substance being analyzed, with penetration into the region of short-lived (superheated) states of the substance. The thermostabilization of the probe, pulse-heated to the selected temperature T _pl(t > t _pl), is described. Using the iteration method, the software fits the coefficients of the heating function to reproduce the required temperature regime with an error of <0.5% over 10–20 cycles. The length of the stabilization pulse in the experiments was 1–10 ms at probe temperatures as high as 1000 K. The sensitivity of the compensation technique of relative measurements to relative changes in the thermophysical properties of a superheated substance was 10^–3 at a characteristic time of 10 s.     

Experimental Investigation on Electrical Discharge Drilling of Ti-6Al-4V Alloy

This article describes the experimental investigation related to creation of holes in aerospace titanium alloy workpiece using static electrode machining and electrical discharge drilling (EDD) process. Special attachment for holding and rotating the tool electrode was developed and installed on electrical discharge machining (EDM) machine by replacing the original conventional tool holder provided on die sinking EDM. The effect of input parameters such as gap current, pulse on-time, duty factor and RPM of tool electrode on output parameters for average hole circularity (C_a) and average surface roughness (R_a) have been studied. It is observed that the effect of rotating electrode machining has considerable influence on the output parameters over stationary electrode machining. The micro-graphs and photographs of few selected samples were taken by SEM and metallurgical microscope, which also commensurate with the findings of the study.