Double Impulses Research Articles

Exponential stability of an alternate control system with double impulses

In this paper, we propose a new system called an alternate control system with double impulses. The present system is a cyclic control system, composed of four parts in a circle: to the first and last halves of each period of the system we add different continuous controls, and at the half-period time and the end of each period of the system we add different impulses. We then investigate the exponential stability of the considered system. An example based on Chua’s circuit is provided to confirm the effectiveness of the theoretical result.

General Dynamic Collapse Criterion for Elastic–Plastic Structures Under Double Impulse as Substitute of Near-Fault Ground Motion

A dynamic collapse criterion for elastic-plastic structures under near-fault ground motions is derived analytically by approximately transforming near-fault ground motions into double impulse and using an energy balance law. A negative post-yield stiffness is introduced to treat the P-delta effect in the single-degree-of-freedom (SDOF) model. The principal part of fling-step near-fault ground motions is modeled by a one-cycle sine wave and then a double impulse. The double impulse enables the efficient use of the energy approach in the derivation of compact expressions of complicated elastic-plastic responses of structures with the negative post-yield stiffness. In contrast to the previous work (Kojima and Takewaki 2016b) for the resonant critical case, a general collapse criterion is provided for the velocity amplitude and the frequency of the double impulse. It is significant that no iteration is needed in the derivation of the dynamic collapse criterion except the solution of transcendental equations. It is shown that discussions on several patterns of dynamic collapse behaviors introduced in the previous critical case are useful for deriving a boundary between the collapse and the non-collapse in the plane of the input velocity and the input frequency. The most important point to be remarked is that the critical state (Kojima and Takewaki 2016b) corresponding to the nonlinear resonance does not necessarily provide the minimum input velocity level with respect to arbitrary impulse timing. The validity of the proposed dynamic collapse criterion is examined by the numerical response analysis for structures under double impulses with collapse or non-collapse parameters.

Presence and Absence of the Shoah in Strasbourg – A Regional Narrative

‘Presence and Absence of the Shoah in Strasbourg – A Regional Narrative’ tells a particularly Alsatian story of the absenting of Jews from the postwar narrative of the city of Strasbourg, and through it, the author explores the tension between regional specificity in a border region with a distinct local identity and a unique history, and a broader national narrative in France. Jews in postwar Strasbourg were absented from the narrative of the war through the double impulse of containment and universalisation. This article uses these double impulses to raise the question of the significance to the postwar of border regions in the making of national narratives.

Experimental investigation on double-impulse phenomenon of hybrid ceramic ball bearing with outer race spall

Abstract Spall is a major fault type in rolling element bearings, which can produce specific vibration signals viz. double impulses. Previous reports indicated that the double impulses consist of two parts, the step response and the impulse response, which can be observed in the vibration generated by a spalled ball bearing. A step and an impulse responses will occur when a rolling element is entering and exiting the spall zone, respectively. Precise measurement of the space between the two parts can be employed to estimate the length of the spall zone along the rotating direction, and provide a possibility to evaluate the remaining useful life (RUL) of faulty bearings under running conditions. However, all the previous works are only concerned with the metal ball bearings. The double-impulse phenomenon generated by faulty hybrid ceramic ball bearings is rarely reported. To address this issue, the double-impulse phenomenon of hybrid ceramic ball bearings with different spall lengths on their outer races will be investigated in this paper. The pre-whitening, kurtogram and squared envelop are employed to extract the two events (the entry and the exit) from the picked vibration. Experimental results indicate that the hybrid ceramic ball bearing with an outer race spall can generate shaper double-impulse phenomenon than that from the faulty metal bearings with almost the same outer race spall length.

Closed-Form Dynamic Stability Criterion for Elastic–Plastic Structures under Near-Fault Ground Motions

A dynamic stability criterion for elastic-plastic structures under near-fault ground motions is derived in closed-form. A negative post-yield stiffness is treated in order to consider the P-delta effect. The double impulse is used as a substitute of the fling-step near-fault ground motion. Since only the free-vibration appears under such double impulse, the energy approach plays a critical role in the derivation of the closed-form solution of a complicated elastic-plastic response of structures with the P-delta effect. It is remarkable that no iteration is needed in the derivation of the closed-form dynamic stability criterion on the critical elastic-plastic response. It is shown via the closed-form expression that several patterns of unstable behaviors exist depending on the ratio of the input level of the double impulse to the structural strength and on the ratio of the negative post-yield stiffness to the initial elastic stiffness. The validity of the proposed dynamic stability criterion is investigated by the numerical response analysis for structures under double impulses with stable or unstable parameters. Furthermore the reliability of the proposed theory is tested through the comparison with the response analysis to the corresponding one-cycle sinusoidal input as a representative of the fling-step near-fault ground motion. The applicability of the proposed theory to actual recorded pulse-type ground motions is also discussed.

Detection and diagnosis of bearing faults using shift-invariant dictionary learning and hidden Markov model

Many existing signal processing methods usually select a predefined basis function in advance. This basis functions selection relies on a priori knowledge about the target signal, which is always infeasible in engineering applications. Dictionary learning method provides an ambitious direction to learn basis atoms from data itself with the objective of finding the underlying structure embedded in signal. As a special case of dictionary learning methods, shift-invariant dictionary learning (SIDL) reconstructs an input signal using basis atoms in all possible time shifts. The property of shift-invariance is very suitable to extract periodic impulses, which are typical symptom of mechanical fault signal. After learning basis atoms, a signal can be decomposed into a collection of latent components, each is reconstructed by one basis atom and its corresponding time-shifts. In this paper, SIDL method is introduced as an adaptive feature extraction technique. Then an effective approach based on SIDL and hidden Markov model (HMM) is addressed for machinery fault diagnosis. The SIDL-based feature extraction is applied to analyze both simulated and experiment signal with specific notch size. This experiment shows that SIDL can successfully extract double impulses in bearing signal. The second experiment presents an artificial fault experiment with different bearing fault type. Feature extraction based on SIDL method is performed on each signal, and then HMM is used to identify its fault type. This experiment results show that the proposed SIDL-HMM has a good performance in bearing fault diagnosis.

Double Impulses Extraction of Faulty Rolling Element Bearing Based on EEMD and Complex Morlet Wavelet

A method for the double impulses extraction of faulty rolling element bearing (REB) is proposed in this paper. In the proposed approach, the (Ensemble Empirical Mode Decomposition) EEMD are employed for filtering the random noise and high-frequency continuous noise without any mode mixing. Then, the extracted signal is filtered with complex Morlet wavelet, which enhanced the double impulses greatly. As a result, clear double impulses can be obtained through the envelope. The effectiveness of the approach is demonstrated by the simulation study.

Thrusters Pairing Guidelines for TrajectoryCorrections of Projectiles

Abstract : A novel method for correcting the trajectory of spin- and fin-stabilized projectiles using pairs of impulse thrusters located away from the center of mass is described in this paper. The impulses are generated from the detonation of a very small quantity of explosive. By locating the impulse thrusters away from the center of mass, it is possible to significantly increase the trajectory correction. This is explained by the fact that, in such a case, the deflection results from the aerodynamic jump due to the projectile oscillation in addition to that of the impulses. An optimal combination of thrusters can be achieved by considering pairs of impulses that have the double objective of maximizing the deflection and minimizing the drag due to the oscillations. In this paper, the linear theory of ballistics is used to develop an analytical model representing the motion of a projectile subjected to impulse thrusters. Using the linearized equations of angular motion and considering ideal cases, the optimization scheme for using double impulses is defined by a set of three rules. The latter are then assessed in the case of actual projectiles, using six-degree- of-freedom computations. The course correction process for a 30-mm fin-stabilized air-defense projectile and a standard 105-mm spin-stabilized artillery shell are presented.

Investigation of Novel Hydrogen/Oxygen Thruster for Orbital Maneuver in Space Station

Hydrogen and oxygen orbital maneuver thruster, based on gas dynamic resonance ignition, is a new liquid rocket propulsion technology, and is especially applicable to space station. By means of theoretic thermodynamic calculation of the hydrogen and oxygen thruster, combined with the experimental exploration on the coaxial hydrogen and oxygen resonance ignition, a scheme of the thruster head configuration is designed as the combination of a coaxial hydrogen/oxygen resonance igniter and an oxygen augmentation injector. Through ignition tests on coaxial hydrogen/oxygen resonance igniter characterization, the thruster head ignition tests have been conducted successfully in sequence of resonance ignition and oxygen augmentation combustion. Finally, the thruster ground tests are successfully carried out informs of single impulse, successive double impulses and 3. 0 seconds continuous running, which verify the reliability and feasibility of the thruster. The response time of the thruster starting is restricted within 0.2 second.

Comparison of Auditory, Somatosensory, and Visually Instructed and Internally Generated Finger Movements: A PET Study

We sought to determine how the pattern of cerebral activation, and in particular in frontal motor areas, during the performance of conditional motor tasks is dependent upon the modality of instruction (visual, auditory, or somatosensory). Regional cerebral blood flow (rCBF) changes with externally instructed movements were also compared with internally generated, self-paced, movements. We used positron emission tomography (PET) with the tracer H215O to measure rCBF in 22 healthy volunteers. External stimuli consisted of the randomized presentation of single or double impulses using a single modality for each condition. In the movement scans, the subjects used the index and middle fingers of their right hands to press a left button for a single and a right button for a double impulse, respectively. In the control scans, subjects were required to covertly distinguish a single from a double stimulus without a motor response. Data were analyzed using conventional subtraction techniques with a statistical threshold of Z > 2.33 with corrections for multiple comparisons. When the activation differences between the three externally instructed movement conditions were statistically compared, nonsignificant trends toward increased rCBF in the sensory cortex of the modality of the cue were observed but no differential activity in cortical motor areas. Internally generated movements, when compared to externally triggered movements, were associated with enhanced activation in bilateral medial and lateral premotor, dorsolateral prefrontal and superior parietal regions, largely confirming previous reports. The data indicate that, on a regional level, modality-specific processing in a conditional motor task does not occur in frontal motor areas and is probably confined to sensory areas.

On re‐excitation of feline motoneurones: its mechanism and consequences.

Conditions required for re-excitation of lumbosacral motoneurones, i.e. for double impulses in the motor axons associated with a single soma-dendritic action potential, were examined in cats anaesthetized with pentobarbitone and paralysed with gallamine triethiodide. Simultaneous recording from a motoneurone (intracellular, and in some experiments also extracellular), and from its axon in a ventral root, was used to assess the relations between the soma and the double axonal action potentials. Action potentials (greater than 70 mV) evoked by brief depolarizing current pulses applied intracellularly were never observed to cause re-excitation. Re-excitation could, however, be regularly induced by procedures which increased the delay between the initial segment and soma-dendritic components of these potentials. Re-excitation could be evoked (i) when brief hyperpolarizing pulses were applied before the onset of the soma-dendritic spikes, (ii) when the depolarizing pulses were applied on a background of long hyperpolarizing pulses or (iii) when two action potentials were evoked in a quick succession (by two brief depolarizing pulses). No relationship was found between the presence of re-excitation of motor axons and the presence of the delayed depolarization which follows the soma-dendritic spikes. Neither re-excitation nor delayed depolarization were found to be dependent upon re-excitation of the initial segment. These observations are thus at variance with previous suggestions that the initial segment spikes induce the re-excitation of motor axons and that the initial segment spikes cause the delayed depolarization following soma-dendritic spikes. Since re-excitation of a motor axon occurred without any signs of a second initial segment spike, it is concluded that it is initiated at the level of the axon, most likely at the first node of Ranvier. Re-excitation of motor axons was also observed during repetitive firing induced by intracellular current injection. However, it occurred then only occasionally, and only under strong depolarizing drive. It is thus not expected to be a common phenomenon under natural conditions of repetitive firing.

Vision and Satire: The Warped Looking Glass in Vanity Fair

AbstractIn Vanity Fair Thackeray moves beyond the inherited traditions of moral and social satire as his vision of society darkens and as he realizes the anarchic potentials of laughter and satire. Examining not the particular ills of a certain society, but the diseased structures inherent in civilization itself, Thackeray creates a world defined by madness and emptiness; in it satire holds little sway. In trying to locate alternatives to or a way out of an apparently inexorable pattern of death and destruction, Thackeray looks, through the image of childhood, toward a pastoral vision, one that assumes various and yet similar configurations for those characters who travel into this visionary landscape. As Charlotte Brontë intuited, Thackeray's novel embodies both the impulses of the moral and social satirist and those of the visionary or prophet. It is the final irreconcilability of these double impulses that accounts for much of the power and haunting quality of Vanity Fair.

The Front Shape of Switching Impulses and its Effect on Breakdown Parameters

A 3-meter rod-plane gap was tested with double exponential switching impulses of different front times. The front of each of the impulses was subsequently modified so that it rose steeply to a certain level of the original front and then followed the basic non-modified impulse. This front modification made it possible to study the influence each region of the front has on the 50% breakdown voltage and the standard deviation of air-gaps. From the results obtained it was possible to detect the region of the front which mainly affects the breakdown parameters. Based on these results, a new definition of the switching-impulse front is proposed providing concrete information about the response of a gap when subjected to an impulse with a given front.

A New Acoustical Phenomenon

WHEN living near Croydon aerodrome during the earlier part of the war, I noticed that the higher-pitched sounds apparently given out from an aeroplane flying nearly overhead varied with the height of my ear above the ground; thus, by bending down to one-half one's normal height, the pitch of this higher note rose an octave. I have on many recent occasions confirmed this result. This phenomenon is most noticeable when standing on a smooth road or lawn, and is scarcely distinguishable on a rougher surface, such as a hayfield; the logical conclusion is therefore that it is due in some manner to reflection from the ground. The pitch of the note varies also with the angle of elevation of the aeroplane, and is not generally audible unless this is more than about 45°. Since the pitch rises continuously as the head is lowered, the apparent explanation is that the note is due to the interval between the arrival of the direct and reflected waves from impulses radiated from the aeroplane—that is to say, no note of this definite pitch comes through the air from the aeroplane, only a regular, or irregular, succession of impulses, the time periods of which have no relation to the observed note, for it is obvious that merely bowing to the aeroplane could not alter the pitch of any note it might be giving out. (It is well known that a note of much lower pitch, due to the engine, is always present, but it is not in this sound that the variation takes place, although it is possible that these are the waves from which the variable high note is produced by reflection.) The pitch of the sound with which we are concerned is thus due to the fixed interval between the arrival of the direct and reflected impulses, and thus depends upon the height of the observer and the angle of elevation of the aeroplane. An interesting deduction from the discovery is that the ear is able to appreciate pitch from a succession of double impulses, if the interval between the elements of each double impulse is constant.