Long-term reading experiment on a photorefractive holographic memory with the hologram sustainment technique by optical feedback

We demonstrate a long-term continuous readout of a two-dimensional image in a photorefractive holographic memory with a BaTiO₃ crystal. A considerable extension of reading time is achieved by use of a hologram sustainment technique with an optical feedback circuit. Hologram rewritings by the simultaneous illumination of the reading beam and the feedback beam, which is incident on a crystal from the opposite direction to the reading beam, contribute to all-optical hologram sustainment without any fixing technique. In this paper, the effectiveness of the hologram sustainment technique is explained by the analysis of the temporal property of the amplitude of the index grating in a crystal. By calculating the temporal properties of the reconstructed beam intensity, we reveal the feedback rate and the coupling strength for high output efficiency. We perform an experiment on two-dimensional image reading and writing with a 45° cut BaTiO₃ crystal and show that a recorded image can be reconstructed over 20?min without critical image degradation whereas a reconstructed image fades away within 20?s in the conventional readout technique.     

Deterministic Magnetization Switching Using Lateral Spin–Orbit Torque

Current-induced magnetization switching by spin–orbit torque (SOT) holds considerable promise for next generation ultralow-power memory and logic applications. In most cases, generation of spin–orbit torques has relied on an external injection of out-of-plane spin currents into the magnetic layer, while an external magnetic field along the electric current direction is generally required for realizing deterministic switching by SOT. Here, deterministic current-induced SOT full magnetization switching by lateral spin–orbit torque in zero external magnetic field is reported. The Pt/Co/Pt magnetic structure is locally annealed by a laser track along the in-plane current direction, resulting in a lateral Pt gradient within the ferromagnetic layer, as confirmed by microstructure and chemical composition analysis. In zero magnetic field, the direction of the deterministic current-induced magnetization switching depends on the location of the laser track, but shows no dependence on the net polarization of external out-of-plane spin currents. From the behavior under external magnetic fields, two independent mechanisms giving rise to SOT are identified, i.e., the lateral Pt–Co asymmetry as well as out-of-plane injected spin currents, where the polarization and the magnitude of the SOT in the former case depends on the relative location and the laser power of the annealing track.     

Effects of the writing process and crosstalk on the timing accuracy of pulses in NRZ digital recording

The position at which a NRZ transition is recorded is dependent on the write current, the effect of increasing the current being to shift the recorded position beyond the trailing gap edge. The shift is more marked with a thick medium than a thin coating, and is worsened if the write head pole tips are approaching saturation. If the recording field changes magnitude when reversed, positive pulses become displaced relative to negative, and pulse pairing occurs. When recording different patterns on adjacent tracks, peak shifts can occur due to writing crosstalk aiding or opposing the head field and the shifts may well impose an upper limit to track density.     

External bit field analyses

Three-dimensional external bit fields emanating from single and multiple magnetic transitions with a finite track width have been calculated. The magnetic field interferences between tracks have been also simulated. The results show that the fields have a large component in the track width direction near the transition edges. This contributes to field extension in the neighboring track direction. The amount of extension decreases with bit density increase. The results of our calculations are backed up by Lorentz microscopy observation of films in which bit fields are transcribed.     

Terahertz radiation from a shallow incidence-angle InAs emitter in a magnetic field irradiated with femtosecond laser pulses

The optimized incidence angle and magnetic field direction geometry of an InAs terahertz radiation emitter irradiated with femtosecond laser pulses in a magnetic field is reported. The optimum geometric layout is the magnetic field direction parallel to the semiconductor surface and at an incidence angle that is slightly larger than the Brewster angle. Additionally, we also observed a center frequency shift of terahertz radiation spectrum by changing the incidence angle of the excitation laser.     

Oscillation Characteristics of Levitation Force of YBCO Bulk Exposed to AC Magnetic Field above NdFeB Guideway

In the present High Temperature Superconducting (HTS) maglev vehicle system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material property of the NdFeB magnet. In order to investigate the influence of the nonuniformity on the levitation performance of the HTS bulk, the experiment involved an electromagnet, which is supplying AC current to simulate the nonuniformity of the external magnetic field. The levitation force of the HTS bulk is measured when applying AC current on the electromagnet coils. The results indicate that the levitation force abruptly changes and oscillates after applying AC external magnetic field. The effect of the amplitude of the AC magnetic field on the levitation force is studied; the result shows that the oscillation amplitude of the levitation force increases with the amplitude of the AC external magnetic field and is independent of the Field Cooling Height (FCH) of the bulk.     

Photo-rewritable flexible LCD using indium zinc oxide/polycarbonate substrates

This work presents a photo-rewritable transmissive flexible-LCD based on the alignment effect of the photo-induced adsorption of azo dye on flexible indium zinc oxide/polycarbonate (IZO/PC) substrates. Images can be displayed without applying an external field and rewritten by changing the direction of the writing laser beam while the cell temperature is controlled. By using IZO/PC substrates, the writing and erasing processes can be achieved within 1 min with a high contrast.     

Effect of AC Magnetic Field on the Levitation Force of YBCO Bulk above NdFeB Guideway

In the present High Temperature Superconducting (HTS) maglev vehicle system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneous of the material property of the NdFeB magnet. In order to investigate the influence of the nonuniformity on the levitation performance of the HTS bulk, an electromagnet supplied by AC current is used to simulate the nonuniformity of the external magnetic field. The levitation force of the HTS bulk is measured when applying AC currents to the electromagnet coils. Experimental results indicate that the levitation force changes abruptly and then oscillates after applying AC external magnetic field, and the levitation force is attenuated by the AC magnetic field after withdrawing the AC field. Moreover, the oscillation amplitude and the attenuation rate of the levitation force increase with the amplitude of the AC external magnetic field.     

Decay Characteristics of Levitation Force of YBCO Bulk Exposed to AC Magnetic Field above NdFeB Guideway

The superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material property of the NdFeB magnet. So it is required to study the characteristics of levitation force of the bulks affected by the non-uniform applied magnetic fields along the moving direction. In this paper, we will study the characteristics of the levitation force relaxation between the HTS bulk and the NdFeB guideway by an experiment in which AC external magnetic field generated by an electromagnet is used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway. From the experimental results, it has found that the levitation force is decreasing with the application of the AC external magnetic field, and the decay increasing with the amplitude of the applied magnetic field and is almost independent of the frequency.     

Dynamical use of different sources of information in heading judgments from retinal flow.

The optic flow arising in the eyes of an observer during self-motion is influenced by the occurrence of eye movements. The determination of heading during eye movements may be based on the pattern of retinal image motion (the retinal flow) or on an additional use of an extraretinal eye-movement signal. Previous research has presented support for either of these hypotheses, depending on the movement geometry and the layout of the visual scene. A special situation in which all previous studies unequivocally have agreed that an extra-retinal signal is required occurs when the visual scene consists of a single frontoparallel plane. In this situation eye movements shift the center of expansion on the retina to a location that does not correspond to the direction of self-movement. Without extraretinal input, human observers confuse the center of expansion with their heading and show a systematical heading estimation error. We reexamined and further investigated this situation. We presented retinal flow stimuli on a large projection screen in the absence of extra-retinal input and varied stimulus size, presentation duration, and orientation of the plane. In contrast to previous studies we found that in the case of a perpendicular approach toward the plane, heading judgments can be accurate. Accurate judgments were observed when the field of view was large (90 degrees x 90 degrees) and the stimulus duration was short (< or = 0.5 s). For a small field of view or a prolonged stimulus presentation, a systematic and previously described error appeared that is related to the radial structure of the flow field and the location of the center of expansion. An oblique approach toward the plane results in an ambiguous flow field with two mathematically possible solutions for heading. In this situation, when the stimulus duration was short, subjects reported a perceived heading midway between these two solutions. For longer flow sequences, subjects again chose the center of expansion. Our results suggest a dynamical change in the analysis or interpretation of retinal flow during heading perception.     

The influence of moving domain walls on the appearance of the second harmonic in the magnetoimpedance spectrum of a cobalt-based amorphous microwire

We have studied the influence of moving domain walls (DWs) on the magnetoimpedance of a cobalt-based amorphous microwire. A model describing the DW motion in the electric field of an alternating current in the absence of a skin effect is proposed. When the current amplitude exceeds a certain threshold value, the DW motion leads to the appearance of a second harmonic component in the frequency spectrum of the sample response voltage. The second harmonic amplitude has been studied as a function of the external longitudinal magnetic field, the current frequency, and the angle of deviation of the microwire anisotropy axis from the circular direction. The sensitivity of the second harmonic to the external magnetic field can be significantly higher than that of the first harmonic.     

Electric-field multiplexing of volume holograms in paraelectric crystals

Electric-field multiplexing (EFM) results from the tuning of the effective wavelength of the light beam inside a photorefractive crystal. This tuning results from the application of an external electric field to the crystal during holographic recording. We demonstrate the high Bragg selectivity of this multiplexing technique in paraelectric crystals and compare it with the selectivity obtained in the ferroelectric phase. The effects of the two major physical parameters of working in the paraelectric phase, the temperature and the external electric field applied during the writing stage, are investigated. Experimental results of the EFM of three image-bearing holograms recorded in reflection geometry are presented along with a qualitative analysis of the Bragg selectivity in paraelectric crystals.     

Novel Asymmetric Critical State in YBa2Cu3O7−δ with Columnar Defects

We studied the critical state field profile using magneto-optical technique in YBa ₂ Cu ₃ O _7– with columnar defects (CDs) when the field is tilted away from CDs. We observed an asymmetric critical state field profile with the current discontinuity line (d-line) considerably away from the center of the sample. The shift of the d-line from the center (y) has symmetric hysteresis loop with respect to H = 0. When the field sweep direction is changed, the previous d-line disappears and a new d-line is generated at the opposite side. The shift of the d-line is parallel to the tilting plane of H and toward the direction of the misalignment of H from CDs. We interpret this asymmetry as caused by the in-plane magnetization, which is originated from the alignment of vortices to CDs. The field dependence of y is discussed in relation with the correlation length of vortices along CDs.     

Correction of amplitude distortions for truncated Bessel beam and SER estimation for 4ASK

Abstract

We apply amplitude corrections to a truncated Bessel beam that has propagated through turbulent atmosphere modelled by random phase screens. These corrections are realized via transmitting an unmodulated beam in parallel to the one carrying the 4 amplitude shift keying (ASK) modulated message signal. On the receiver side, the amplitude corrections are obtained by dividing the intensity of the unmodulated beam by its free space equivalence. The corrections are then used to restore the amplitude distortions of the beam carrying the 4ASK modulated message signal and in the determination of decision boundaries for the received 4ASK symbols. The success of the system is visually inspected by comparing the received intensity profiles before and after the application of corrections. Furthermore, simulation analysis of symbol error rate (SER) is made, where the proposed set-up is found to be quite insensitive to wavelength difference between the unmodulated and modulated beams. On the other hand, the difference in the structure constant values of these two beams seems to have profound effect on system performance.     

Behavior of acoustic axes and internal conical refraction in LiNbO (3) and SrTiO(3) crystals placed in an external electric field

The behavior of acoustic axes and conical refraction are analyzed for lithium niobate and strontium titanate crystals, which are either mechanically squeezed or mechanically free and placed in an external electric field. Relying on numerical calculation, field dependencies of the acoustic axis shift and splitting angles have been elaborated, which are compared with the results obtained previously in the context of the theory of perturbations. External electric fields with the intensity E<10(7) V/m have yielded small (<1 degrees ) angles of acoustic axis splitting and shift; however, for greater field intensities, E>/=10(7) V/m, the rearrangement of the crystal's acoustic axes with respect to its initial position (E=O) assumes a "macroscopic nature". In particular, degeneracies having Poincare indexes with opposite signs may merge and "annihilate". We also first examined the variation of the conical refraction parameters versus the external electric field with transverse elastic waves which propagate along the acoustic axes of conical degeneracy in the above-mentioned materials. With actually achievable field strengths, the direction of energy velocity can be altered by several degrees. It is sufficient for the development of highly effective modulators, switchers, and acoustic wave gates to be used in various logic elements and other signal processing units.     

Integrating Writing Instruction into Engineering Courses: A Writing Center Model

Engineering students often have difficulty learning how to write laboratory reports in their field. To assist students with this learning process and teach them writing strategies that will prove helpful in the workplace, a writing center was established in the Electrical and Computer Engineering (ECE) Department at the University of South Carolina. There, consultants trained in technical writing work closely with ECE faculty members and teaching assistants to create a supportive network for students as they draft reports, including discussions during recitation periods, team consultations, and individual consultations. This paper presents a theoretical framework for the writing center program, as well as specific writing strategies that have proven helpful. Assessment methods and feedback from faculty and students about the success of the program are presented as well.     

Mechanico-electromagnetic waves in elastic dielectric crystals in a magnetic field

The mechanico-electromagnetic coupled waves under an external magnetic field are theoretically investigated, where elastic dielectric crystals with higher symmetry are taken into consideration. There are three types of the coupled waves: the predominantly electromagnetic waves, the predominantly mechanical transverse and longitudinal waves. Their propagation velocities, and the amplitude ratios of the polarization, the mechanical vibration, and the electromagnetic fields are obtained, which depend not only on the material constants but also on the suppressed magnetic intensity and its direction relative to the propagation direction.     

Dependence of the Bragg condition on an external electric field for a polymeric photorefractive material

We investigated the effect of an applied electric field on the Bragg condition of degenerate four-wave mixing a polymeric photorefractive material with a low glass-transition temperatue. For a polymeric photorefractive material the application of an external electric field is necessary for photorefractivity leads to birefringence of the material by poling of the nonlinear optical chromophore. Because the propagation vectors of the pumping and reading beams inside the material are influenced by the refractive index of the material, the Bragg condition depends on the magnitude of the external field. Using an oriented gas model and the-coupled-mode theory, we numerically analyzed the Bragg-mismatch effect that causes a reduction in diffraction efficiency as a function of an external field. We present the boundary conditions for sample thickness and grating spacing for which the Bragg-mismatch effect must be taken into account.     

Research and Application for the Regularity of Distribution about Curvature Radius and Curvature Center of the Linkage Point Track in a Link Mechanism

It is illustrated that there exists an inflection circle on the linkage rigid body by the principle of relative motion. Confirmed methods of the inflection circle, curvature radius and curvature center of the point track on the linkage rigid body are given in the case of the different contact type of move instantaneous center line and static instantaneous center line. The regularity of distribution of curvature radius and curvature center of the point track is researched. The identification methods called determination parameters and auxiliary vertical line of the diameter and direction of the inflection circle in the four bar mechanism are pointed out. A design method of the crane hoisting mechanism is discussed in the end of this paper.     

Effect of tangential magnetic field on ecton processes in cathode spot of vacuum arc

Emission and erosion processes involved in the final stage of the cathode spot cell operation in vacuum arc in the presence of an external magnetic field have been numerically simulated. It is established that the application of a magnetic field leads to asymmetry in the distributions of current density and heat flux, so that their maxima shift in the “anti-Ampere” direction. For more detailed analysis of the phenomenon of retrograde motion of the cathode spot in a magnetic field, it is necessary to study the behavior of a liquid metal phase in the spot.