Impulse Duration Research Articles

Magnetorheological Fluids Examination for Antivibration Mounts at Impact Loads

In this work the question of magnetorheological fluids usage in damping systems of electromechanical power installations and machinery are studied. The physical backgrounds of magnetic fluids characteristics operation with respect to inner magnetic fields are considered. The processes appearing in magnetorheological fluids at impact loads are looked into. These tasks are solved within the frame of magnetorheological fluid only due to the fact that electromagnetic impulses appear on solenoid windings which are meant to create an inner control magnetic field. The amplitude and the impulses duration is an impact load function. Their influence is to be taken into account when developing magnetorheological dampers.

DEFINITION OF AN INTERVAL OF COHERENT ACCUMULATION OF A PACK OF LONG RADIO IMPULSES AT DETECTION OF THE HIGH-SPEED PURPOSE BY A RADAR STATION WITH ACTIVE PHASED-ARRAY ANTENNA WITH SOLID-STATE DEVICES

Mathematical models of the signals used in radar stations of detection of the high-speed purposes on the big range, working in a decimeter range of wavelength and using solid-state transferring elements are considered. Calculation of correlation function for the pack of radio impulses reflected from the high-speed purpose is resulted. Possibility of application of algorithm of coherent accumulation of a pack of radio impulses of the big duration is considered and the estimation of time of coherent accumulation is made.

Antiknock Performance of Interlayered High-Damping-Rubber Blast Door under Thermobaric Shock Wave

The long duration and high impulse shock wave of thermobaric bomb threatens the security of underground structures. To obtain high resistance blast door against thermobaric shock wave, firstly, the dynamic mechanic property of high damping rubber was studied by split Hopkinson pressure bar (SHPB) equipment and the stress-strain relationship of high damping rubber under average strain rate of 5200/s was obtained. Secondly, the numerical model of interlayered high-damping-rubber blast door was established with ANSYS/LS-DYNA code based on test results, and the antiknock performance of interlayered high-damping-rubber blast door under thermobaric shock wave was analyzed by contrast with ordinary blast door. The results showed that the midspan displacement of the blast door decreased firstly and then increased with the increase of thickness of the high-damping-rubber interlayer, and the optimal thickness of the high-damping-rubber interlayer for energy consuming was 150 mm in the calculation condition of this paper. With the increase of the distance between the interlayer and the front surface of the door, the midspan displacement of the blast door decreased continually. The midspan maximum displacement of interlayered high-damping-rubber blast door decreased 74.5% in comparison to ordinary blast door. It showed that the high-damping-rubber structure can effectively improve the antiknock performance of blast door under thermobaric shock wave.

Working conditions of a converter installation with electromagnetic compatibility

This paper outlines the effect of the switching frequency and the conducting relative duration of a power switch in an impulse convertor on the level of conductive emission by a feed circuit in a frequency range of from 0.15 to 30 MHz. Expansion was performed of the rectangular impulse at frequencies of 50 and 100 kHz in the Fourier series in an LTSpice simulated system. The results of this research allow us to determine the ability to reduce the level of the conductive emission using a lower switching frequency of the power switch. These results are confirmed by full-scale experiments. These experiments are based on imitation of the output block of the impulse convertor. Means of measurement were used that are restricted by GOST (State Standard) to large-scale experiments. It is shown that (1) it is necessary to choose the switching frequency, not only using gross geometry minimization of the device, skin effect, and magnetization reversal of the coil and transformer core, but taking into account of allowable emission level as well, and (2) it is necessary (in the case of nominal power) to provide an open state relative impulse duration close to 50% in the switching PWM convertor.

Investigation of crater form and dimensions evolution during laser treating of materials

Acoustic emission of a zone of the destruction formed during influence of pulse laser radiation on a surface of metal is considered. Dependence of the time form of acoustic fluctuations on parameters of an irradiated material and the law of increase in depth of a crater was estimated. It is revealed, that at action on a surface of the copper sample of a laser impulse duration ∼ 20 µs time of growth of a zone of destruction makes approximately 40 µs. It is shown also that having detected a diffraction picture appearing on incidence of SHF-radiation on the surface of solid and having achieved during the experiment the best coincidence of the experimental and calculated using the computer model data one can define the character of the zone of destruction on the surface of structure being under treatment relief.

청소년의 수면시간과 자살충동 - 평일/주말 수면시간 효과에 대한 성별 분석

청소년의 수면시간과 자살충동 - 평일/주말 수면시간 효과에 대한 성별 분석

Localizing energy in granular materials

A device for absorbing and storing short duration impulses in an initially uncompressed one-dimensional granular chain is presented. Simply stated, short regions of sufficiently soft grains are embedded in a hard granular chain. These grains exhibit long-lived standing waves of predictable frequencies regardless of the timing of the arrival of solitary waves from the larger matrix. We explore the origins, symmetry, and energy content of the soft region and its vibrational modes.

Generation of Electrohydraulic Shock Waves by Plasma-Ignited Energetic Materials: III. Shock Wave Characteristics With Three Discharge Loads

As an important plasma-assisted technology to generate shock waves (SWs), underwater pulsed discharge has drawn much attention in recent years for its complex physical process. Based on three discharge loads, the water gap (WG) load, the electrical wire (EW) load, and the energetic material (EM) load, the discharge processes are briefly introduced and the characteristics of the associated SWs are analyzed. First, the experimental setups were built and typical structures of the three loads were presented. Second, the inherent characteristics of SWs under the three loads, such as their peak pressure, impulse, and time duration of positive pressure and power spectral density (PSD), were studied and compared. Finally, a cracking effect experiment is carried out to study the SW fracturing characteristics. The results show that SWs generated with the WG load have the lowest peak pressure, impulse, and power density, SWs generated with the EW load have a better energy conversion efficiency and the largest peak pressure, and SWs generated with the EM load have the maximum impulse and power density. Furthermore, SW fracturing characteristics are mainly affected by its inherent characteristics. The peak pressure and impulse determine the shock number of fracturing, and the fracture pattern is significantly affected by the PSD.

Fast response co-axial thermocouple for short duration impulse facilities

A fast response Chromel–Alumel (K-type) co-axial thermocouple is designed, fabricated, calibrated and tested in a shock tunnel. The freestream Mach number of 5.75 and the total enthalpy of 0.92 MJ/kg are simulated to study the stagnation point heat flux of a hemi-spherical model through transient temperature trace. The realized K-type co-axial thermocouple of 3 mm in length and 1.6 mm in diameter is flush mounted at the stagnation point of a 7.5 mm radius hemi-spherical model. The achieved response time of the realized K-type co-axial thermocouple is ~3 µs, which is sufficient enough to capture the transient temperature signal. A steady tunnel flow time of 1.8 milliseconds is used to get the average stagnation point heat flux. The measured stagnation point heat flux is 22.96 W/cm2, which is well matched with the Fay–Riddell value within 5.5%. The realized K-type co-axial thermocouple is robust, responds fast, and can be contoured to any type of model surface.

Optical investigations of pulsed sparks in soil near electrode

Experimental results of laboratory investigation of nonlinear processes in moist soil near electrode simulating grounding of electric power facilities are presented. A method of optical recording of spark formation in the soil is developed. Investigations were carried out at voltage of 20-50 kV and current pulse duration of tens of microseconds. The critical electric field and delay of sparks beginning in soil in depending on the electrode construction, moisture and impulse duration are obtained. The images of sparks in soil are obtained for the first time.

The video head impulse test during post-rotatory nystagmus: physiology and clinical implications

The aim of this study was to test the effects of a sustained nystagmus on the head impulse response of the vestibulo-ocular reflex (VOR) in healthy subjects. VOR gain (slow-phase eye velocity/head velocity) was measured using video head impulse test goggles. Acting as a surrogate for a spontaneous nystagmus (SN), a post-rotatory nystagmus (PRN) was elicited after a sustained, constant-velocity rotation, and then head impulses were applied. 'Raw' VOR gain, uncorrected for PRN, in healthy subjects in response to head impulses with peak velocities in the range of 150°/s-250°/s was significantly increased (as reflected in an increase in the slope of the gain versus head velocity relationship) after inducing PRN with slow phases of nystagmus of high intensity (>30°/s) in the same but not in the opposite direction as the slow-phase response induced by the head impulses. The values of VOR gain themselves, however, remained in the normal range with slow-phase velocities of PRN < 30°/s. Finally, quick phases of PRN were suppressed during the first 20-160 ms of a head impulse; the time frame of suppression depended on the direction of PRN but not on the duration of the head impulse. Our results in normal subjects suggest that VOR gains measured using head impulses may have to be corrected for any superimposed SN when the slow-phase velocity of nystagmus is relatively high and the peak velocity of the head movements is relatively low. The suppression of quick phases during head impulses may help to improve steady fixation during rapid head movements.

Urinary incontinence: Clinical observation on 30 patients undergoing treatment with F.R.E.M.S (Frequency Rhythmic Electrical Modulation System).

Urge incontinence is considered to be a dysfunctional pathology of social interest due to the psychological and relational implications of such disability, the elevated number of affected patients and the consequent treatment costs. We propose an innovative non-pharmacological and non-invasive care methodology: Frequency rhythmic electrical modulation system (F.R.E.M.S.) therapy (FT), based on the administration of electric fields of monophasic pulsed, negative, asymmetric current, generated by a neurostimulator with the characteristics of low variable frequency, high voltage and very low impulse duration. 30 patients were studied with urodynamic evaluation and radiological diagnostic techniques, and underwent 2 cycles of 15 days therapy, with a 12 months follow-up. In 93% of cases, we obtained a positive result, with either disappearance or improvement of symptoms. Although the Authors believe that clinical results deserve further neurohistological and immunohistochemical studies, in order to define the anathomophysiological and biochemical changes induced by FT, they propose it as a possible alternative to traditional pharmacological therapy and electrical stimulation.

Investigation of ultrasonic stepping motors and nanomanipulator for scanning probe microscopy

In the following article there is analyzed the designed one coordinate piezoelectronic stepping motor of the scanning probe microscopy (SPM) nanomanipulator, allocated to the positioning. For such a system, apart from the basic parameters: exciting rate and the amplitude of the exciting voltage, there are developed forces and there turns to be significant the motion characteristics of the stepping motor minimal step of SPM nanomanipulator that was determined experimentally. In order to control the positioning equipment accurately, there was designed control software of the SPM nanomanipulator for Linux operating system. Agreeably with its aid it is possible to control the nanomanipulator table under the assigned path, direction and distance, to change the control impulse duration and the number of impulses, necessary for the shift. Applying a computerized research, there was determined the dependence of the table shift on the control impulse duration and the dependence of the table shift on the number of impulses. DOI: http://dx.doi.org/10.5755/j01.mech.21.4.10601

LIAeq100ms, An A-duration adjusted impulsive noise damage risk criterion

Impulsive noise damage risk criteria (DRCs) have been the subject of much debate nationally and internationally for more than 30 years. Several approaches have been used in proposed DRCs including: curves defining exposure based on peak level and A or B duration; auditory hazard units based on the analytical auditory model known as AHAAH; and LAeq metrics based on the equal energy concept. Each of the approaches has positive and negative attributes. One of the issues with LAeq metrics has been the over estimation of hazard with long duration impulses such as those coming from blasts, artillery, large mortars, or shoulder launched missiles. The presentation will describe and discuss the LIAeq100ms impulsive DRC which includes an adjustment based on the A-duration of the impulsive noise and a method of computing protected impulsive noise exposures using impulsive insertion loss data from hearing protectors measured with methods defined in ANSI S12.42.

Characteristics of long air gap discharge current subjected to switching impulse

Measuring the pre-breakdown current of long sparks in air is important for investigating the discharge mechanism. Since the breakdown of long air gaps is conducted by a series of streamer-leader processes, the corresponding current signals cover a bandwidth of 0 to more than 20 MHz. Measurement accuracy of the current from the high voltage side is affected by the displacement current and impulse electromagnetic interference. In this paper, a coaxial current sensor with a DC bandwidth of 74.45 MHz is developed. A displacement current-restrained electrode structure is proposed to reduce the equivalent capacitance between the current sensor and the ground over 30 times. Combined with the digital optical fiber synchronous acquisition unit, a current measurement system for long air gap discharge is established. For the purpose of the UHV system's external insulation optimization design, the discharge current waveform of a 6 m rod-plane air gap under positive switching impulse voltage with 250 μs and 1000 μs time to crest is obtained. Discharge images and stressed voltage are combined to analyze the continuous feature of a current waveform under critical time to crest impulse and discontinuous feature under long front duration impulse. For the purposes of a lightning protection study, the current waveform of a 10 m rod-plane air gap is subjected to negative switching impulse. Finally, the pulse characteristics of the current corresponding to the single channel and branching stepped negative leader are discussed.

Subthreshold High-Frequency Electrical Field Stimulation Induces VEGF Expression in Cardiomyocytes.

Subthreshold electrical stimulation (SES) has been shown to induce an improvement of angiogenesis in ischemic and nonischemic skeletal muscles, mediated by increased VEGF expression. VEGF plays a key role in physiological and pathological angiogenesis. Cardiomyocytes possess the ability to synthesize and secrete VEGF. Thus, we thought to investigate the effect of SES on VEGF regulation in cultured neonatal rat ventricular myocytes (NRVMs), in the aim to reveal new techniques for therapeutic angiogenesis in ischemic heart disease. Cell cultures of NRVMs were electrically stimulated with field strengths below the myocyte depolarization threshold (0.5 V/cm with 1 ms bipolar impulse duration). Frequencies ranging from 5 Hz up to 25, 50, and 99 Hz were applied over a period of 48 h. The expression of VEGF and its receptor KDR was determined with Western blot and ELISA. To reveal the biological activity of the secreted VEGF amount, cultured human coronary artery endothelial cells (HCAECs) were treated with the cell culture supernatant of NRVMs exposed to SES. A dominant effect of SES was observed at 25 Hz. Within this particular frequency the VEGF protein amount in the cytoplasm as well as in the cell culture supernatant increased significantly. In parallel, the protein expression of the KDR receptor decreased in a significant manner. Moreover, cell culture supernatant of NRVMs exposed to SES augmented the growth of HCAECs. Cardiomyocytes respond to SES with an increase in biologically active VEGF expression that promotes cell proliferation of HCAECs. This mechanism may provide new approaches to develop therapeutic angiogenesis in the ischemic heart.

Medium Access Control and Rate Adaptation for Ultrasonic Intrabody Sensor Networks

The use of wirelessly internetworked miniaturized biomedical devices is promising a significant leap forward in medical treatment of many pervasive diseases. Recognizing the limitations of traditional radio-frequency wireless communications in interconnecting devices within the human body, in this paper, we propose for the first time to develop network protocols for implantable devices based on ultrasonic transmissions. We start off by assessing the theoretical feasibility of using ultrasonic waves in human tissues and by deriving an accurate channel model for ultrasonic intrabody communications. Then, we propose a new ultrasonic transmission and multiple access technique, which we refer to as Ultrasonic WideBand (UsWB). UsWB is based on the idea of transmitting information bits spread over very short pulses following a time-hopping pattern. The short impulse duration results in limited reflection and scattering effects, and the low duty cycle reduces the impact of thermal and mechanical effects, which may be detrimental for human health. We then develop a multiple access technique with distributed control to enable efficient simultaneous access by mutually interfering devices based on minimal and localized information exchange and on measurements at the receiver only. Finally, we demonstrate the performance of UsWB through a multiscale simulator that models the proposed communication system at the acoustic wave level, at the physical (bit) level, and at the network (packet) level. We also validate the simulation results by comparing them to experimental results obtained with a software-defined testbed.

Influence of location of the shock absorber on the performance of a shock pulse alarm layout of the drill string

The article, based on the developed nonlinear mathematical and computer models of the work of the drill string with the hammer mechanism, which is used to eliminate sticking drilling tool, conducted research on the location of the shock absorber shock pulse in the place of strike and place of sticking. Produced by numerical calculations of the duration of impact, impact forces and impulses accumulated elastic strain and lost as a result of the impact energy. For different values of the impact mechanism stroke analyzed the influence of the installation site on the performance of the shock absorber.

Air explosion characteristics of a novel TiH2/RDX composite explosive

An explosive mixture of cyclotrimethylenetrinitramine (RDX) and titanium hydride (TiH2) is introduced. To investigate the explosion characteristics of the composite explosive, charges with various contents of the TiH2 powder are prepared and tested in air explosion experiments. Results show that the peak overpressure, positive duration, and positive specific impulse increase as the content of TiH2 increases from 10 to 20%, as compared to passivated RDX. The peak overpressure, duration, and specific impulse have the largest increase of 6, 9, and 23%, respectively, as compared to passivated RDX, when the TiH2 content is 20%. The effect of the TiH2 particle size is also considered. The charge containing the TiH2 powder with a mean particle size of 4.6 μm shows higher values of the three parameters than that containing 45-μm TiH2 particles under the condition of the same content of TiH2. However, the relationship between the detonation velocity and TiH2 content is a linear inverse proportion, and the particle size of TiH2 has a minor effect on it. Solid explosion products of the TiH2/RDX composite explosive are analyzed by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDX). TiO2 is found in explosion products, which is believed to form due to TiH2 oxidation.

Peculiarities of Non-Stationary Temperature Distribution of Optical Non-Transparent Anisotropic Thermoelement at Impulse Ray Excitement

The solutions of the non-stationary equation of thermoconductivity for the optical non-transparent thermoelement at impulse ray excitement are presented in the paper for two-time ranges: when the ray current falls (0&lt;t&lt;tau) and when it stops (t&lt;tau). It is shown that the behavior of temperature distributions essentially depends on the relationship between the impulse duration (tau) and relaxation time (tau0) of temperature shifts over the whole volume of anisotropic thermoelement, arising at the impulse ray excitement. The non-stationary temperature distributions are studied for the long, short and middle impulse excitement.