Read Head Research Articles

Effects of illuminance and contrast on the reading of Chinese text by myopes

Twenty-four young adults with myopia in both eyes and no anisometropia participated in this study. Observers were instructed to read one A4-sized page of Chinese text at different levels of illuminance and text contrast, while their reading distance, head tilt angle and reading speed were recorded using an electromagnetic motion tracking system. Four illuminances (3, 30, 300 and 600 lx) and two text contrast levels (90% and 45%) were tested in randomised order. Observers tended to shorten their reading distance and increase their head tilt angle when reading at low illuminance. In addition, their reading speed was markedly slower at low illuminance and low contrast. These effects were found for both text contrast conditions but were greater at low contrast. Illuminance and text contrast play a critical role in myope’s reading behaviour. An illuminance of 300 lx or more with high-contrast text allows for good reading posture and rapid reading of Chinese text.

The Common Basis of Memory and Consciousness: Understanding the Brain as a Write-Read Head Interacting With an Omnipresent Background Field.

The main goal of this article consists in addressing two fundamental issues of consciousness research and cognitive science, namely, the question of why declarative memory functions are inextricably linked with phenomenal awareness and the question of the physical basis of memory traces. The presented approach proposes that high-level cognitive processes involving consciousness employ a universal mechanism by means of which they access and modulate an omnipresent background field that is identified with the zero-point field (ZPF) specified by stochastic electrodynamics (SED), a branch of physics that deals with the universal principles underlying quantum systems. In addition to its known physical properties and memory capacities, the ZPF is hypothesized to be an immanently sentient medium. It is propounded that linking up to a particular field mode of the ZPF activates a particular phenomenal nuance, implying that the phase-locked coupling of a set of field modes, i.e., the formation of a so-called ZPF information state, constitutes an appropriate mechanism for the amalgamation of elementary shades of consciousness into a complex state of consciousness. Since quantum systems rest exactly on this mechanism, conscious memory processes in the brain are expected to differ from unconscious processes by the presence of the typical features of many-body quantum systems, particularly long-range coherence and attractor formation, which is supported by a huge body of empirical evidence. On this basis, the conceptual framework set out in this article paves the way for a new understanding of the brain as a write–read head interacting with the ZPF, leading to self-consistent interpretations of the neural correlates of memory formation and memory retrieval and explaining why these memory processes are closely intertwined with phenomenal awareness. In particular, the neural correlates suggest that the brain produces consciously perceived memory traces by writing sequences of information states into the ZPF and retrieves consciously experienced memory traces by reading sequences of information states from the ZPF. Using these theoretical foundations, altered states of consciousness and memory disorders can be traced back to impairments of the ZPF write–read mechanism. The mechanism should reveal itself through characteristic photon emissions, resulting in testable predictions.

On deterministic sensing $$5'\rightarrow 3'$$ Watson–Crick finite automata: a full hierarchy in 2detLIN

Watson–Crick (abbreviated as WK) finite automata are working on double stranded DNA molecule that is also called Watson–Crick tape. Subsequently, these automata have two reading heads, one for each strand. While in traditional WK automata both heads read the whole input in the same physical direction, in $$5'\rightarrow 3'$$ WK automata the heads start from the two extremes (say $$5'$$ end of the strands) and read the input in opposite direction. In sensing $$5'\rightarrow 3'$$ WK automata the process on the input is finished when the heads meet. Since the heads of a WK automaton may read longer strings in a transition, in previous models a so-called sensing parameter took care for the proper meeting of the heads (not allowing to read the same positions of the input in the last step). Recently a new model is investigated, which works without the sensing parameter. In this paper, the deterministic counterpart is studied and is proven to accept the language class 2detLIN defined by the deterministic variant of the earlier version. However, using some of the restricted variants, e.g, all-final automata, the classes of the accepted languages are changed showing a finer hierarchy inside the class of linear context-free languages.

Thickness Dependence of Degree of B2 Order of Polycrystalline Co <sub>2</sub>(Mn <sub>0.6</sub>Fe <sub>0.4</sub>)Ge Heusler Alloy Films Measured by Anomalous X-Ray Diffraction and its Impacts on Current-Perpendicular-To-Plane Giant Magnetoresistance Properties

We investigated the degree of B2 order (SB2) of 4-10 nm-thick polycrystalline Co2(Mn0.6Fe0.4)Ge (CMFG) Heusler alloy films using anomalous X-ray diffraction (AXRD) and its correlation to the magnitude of current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) effect. We found that SB2 of the CMFG films is degraded for the film thickness below 6 nm, which is an issue for practical applications of CPP-GMR devices such as read head sensors. Since SB2 has a thickness-dependence, the bulk spin polarization (β) of the CMFG layers is also expected to vary depending on the thickness; thus, the deduction of β using the Valet-Fert model, where β is assumed to be thickness-independent, is not valid for the CPP-GMR devices with polycrystalline CMFG layers.

A Novel ITI Suppression Technique for Coded Dual-Track Dual-Head Bit-Patterned Magnetic Recording Systems

Generally, an intertrack interference (ITI) is a critical problem in bit-patterned magnetic recording (BPMR) systems that can attain an areal density (AD) up to 4 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Unavoidably, at high ADs, a very narrow track width must be employed, leading to severe ITI and unacceptable system performance. To tackle the ITI; therefore, this article introduces a novel ITI suppression technique for coded dual-track dual-head (DTDH) BPMR systems. At the first turbo iteration, the weighted readback signal of the adjacent track served as an estimated ITI signal is utilized for subtracting from the target readback signal to subside the ITI effect, before passing the refined readback signal to a turbo equalizer. Nonetheless, for the second turbo iteration onwards, the estimated ITI signal generated by the soft information obtained from a decoder at each turbo iteration will be then employed to subtract from the target readback signal during the turbo decoding process. Computer simulation results demonstrate that the proposed system can provide better performance than the DTDH system using a hard ITI suppression technique as well as the conventional system using one read head to decode one data track for all ADs, because the proposed technique can estimate the ITI signal well. Furthermore, when considering the recording system under the effects of media noise and track mis-registration, we also found that the proposed system is more robust than other systems.

Unstable Playback Response of CPP-GMR Read Head Induced by Electromagnetic Interference: Structural Dependence

Although several studies have claimed that the current perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) technology is the most attractive technology to achieve ultrahigh capacities of data storage applications, there are still recent studies indicating the inaccuracy of the reading head response caused by the electromagnetic interference (EMI). To improve the precision of the head response, we report a dependence of the physical dimension of CPP-GMR read head on the readback signal distortion due to the EMI. The simulations were based on micromagnetic modeling. The EMI impacts on the head response were analyzed as a function of structural parameters of the head, including the length of stripe height (SH) and read width (RW). Then, the readback characteristics of the head, including the spin-transfer induced noise, power spectral density, and bit-error-rate (BER), were discussed. It was found that an alternation of either SH or RW influences the noise profile. Adjusting the length of RW demonstrates a more influential impact on the noise than that of SH. The frequency spectrum of the head response was also carried out. The physical explanations regarding the results found in this article were given through the behavior of the demagnetization field. The effects of bias current on the head output were additionally investigated. Moreover, the BER of the head with varying the head dimensions was characterized. From findings, the appropriate sizing of the CPP-GMR sensors for an areal density of 1 Tb/in2 was predicted. The results can be utilized to design CPP-GMR read heads at ultrahigh areal densities.

Measurement and determination of encoder disc surface parameters in x-z planes using a conventional optical disc reading head

Non-contact surface measurement methods as well as roughness parameter determination methods are analyzed in the paper. While most of the modern non-contact surface inspection methods require advanced instrumentation and a big budget, this study looks into a novel approach to non-contact encoder disc roughness measurements by using the proposed system attached to the rotary table with an implemented optical disc pick up head and the reference angle encoder. Application of a conventional optical disc laser reading system resulted in a cost effective and compact solution for a non-destructive angle encoder disc surface inspection. Assets and shortcomings as well as detailed analysis of the measurement procedure are explained in the paper. The experimental setup and the measurement results are presented within this article.

Ultra-giant magnetoresistance in graphene-based spin valves with gate-controlled potential barriers

Pursuing larger tunnel magnetoresistance is a significant work to develop attractive spin-valve devices for high-performance read heads of hard disk drives, magnetic random access memories, and transistors. Here, we propose an ultra-giant magnetoresistance reaching higher than 40 000% at room temperature by using a spin valve of an armchair graphene nanoribbon with double gate-controlled potential barriers. The ultra-giant magnetoresistance approximately 60 times larger than that of traditional MgO-barrier spin valves is caused by an extraordinary current suppression in the antiparallel mode. Moreover, owing to the concept of the gate-voltage barrier, the proposed system provided not only lower complexity of the fabricating standard but also longer endurance of the operation than traditional spin-valve devices.

Highly accurate, absolute optical encoder using a hybrid-positioning method.

An absolute optical encoder with nanometric positioning repeatability is introduced and investigated. The encoder consists of an improved scale grating and a compact two-probe reading head. The scale grating contains multiple unevenly spaced distance marks that are superimposed onto grating grooves. The two probes, which are located in the sensor head, read the marks and the grating grooves to determine the position and displacement simultaneously. For one of the two probes, a mask with the same code design with the marks on the scale grating generates a pulse signal to locate the position of the marks approximately-with an accuracy of less than about half a grating period (0.5μm). For the other probe, light beams are configured for grating interferometry to measure displacement with nanometer-scale resolution. In this Letter, high-quality sinusoidal signals of grating interferometry are used to accurately locate the marks on the scale grating, with stable 100-subdivision phase information. The testing results show that the positioning repeatability can reach 10nm for a motion range of several tens of millimeters.

Material Development of Perpendicular Recording for High Areal Density Hard Disk Drives

This review paper provides a survey of material development of perpendicular recording (or perpendicular magnetic recording, PMR) as it relates to the ‘areal density’ of hard disk drives (HDDs) with high amounts of information stored per unit area. Conventional longitudinal recording has reached its limits in terms of increasing the areal density. Hence, perpendicular recording promises to achieve high areal density, which is the current goal for both the academic and industrial sectors. Development of perpendicular recording can be considered in terms of the 3 primary parts of HDDs: the medium, write head and read head. Experimentation and computer simulations were used to optimize the parameters for improving the areal density of HDDs.

Ultra-wideband 1–20 GHz Non-contact FMR Test System for TMR HGA

The read sensor of hard disk drive abnormality at the bar level is detected by a ferromagnetic resonant analyzer (FMRA) system requiring a galvanic contact to the sensor. After the read head is assembled to the slider, a quasistatic tester is used to check the slider functionality. At this stage, the FMR information of the read sensor cannot be easily accessed since there is no suitable measurement technique available. In this research, an innovative non-contact ferromagnetic resonant (FMR) measurement for the read head sensor quality control at slider level is reported for the first time. The proposed test system is designed for detecting the FMR from 1 to 20 GHz. The FMR is interpreted from the peak of read sensor resistance over the frequency span. This new measurement technique has been applied to a model of tunneling magnetoresistance (TMR) sensor and compared with the FMRA. The FMR frequency at 5.4 GHz can be detected by the proposed measurement system with only 1 MHz difference from the value obtained from conventional FMRA. The higher effective stiffness field of the read sensor is also observed from the lower FMR resistance in the shorter stripe height head.

A High-Reliable and High-Precision Algorithm of Angle Measurement for UAV Airborne Photoelectrical Detection System

In order to achieve high-reliable and high-precision target measurement for UAV photoelectric detection system without increasing any costs, an algorithm of angle measurement is proposed. Firstly, by analyzing the character of grating grid image’s edge, a fast method using three gradient points to establish a parabolic function is applied for automatic grating image sub-pixel edge detection. Coarse code decoding is improved by OTSU’s method to reduce bit error rate (BER) as well as manufacturing difficulty, and a high-precision subdivision method based on observed image of grating lines is introduced to calculate subdivision angle. Secondly, simulation of BER and precision analysis show that proposed algorithm is robust in both processes of coarse code decoding and subdivision. Finally, experiment results show that BER is no more than 0.02%, the standard deviation of proposed algorithm is 1.8″ and the standard deviation of error is only 7.1″ with one reading head, indicating that proposed algorithm is robust, reliable and precise.

Layer-selective detection of magnetization directions from two layers of antiferromagnetically-coupled magnetizations by ferromagnetic resonance using a spin-torque oscillator

We use micromagnetic simulation to demonstrate layer-selective detection of magnetization directions from magnetic dots having two recording layers by using a spin-torque oscillator (STO) as a read device. This method is based on ferromagnetic resonance (FMR) excitation of recording-layer magnetizations by the microwave field from the STO. The FMR excitation affects the oscillation of the STO, which is utilized to sense the magnetization states in a recording layer. The recording layers are designed to have different FMR frequencies so that the FMR excitation is selectively induced by tuning the oscillation frequency of the STO. Since all magnetic layers interact with each other through dipolar fields, unnecessary interlayer interferences can occur, which are suppressed by designing magnetic properties of the layers. We move the STO over the magnetic dots, which models a read head moving over recording media, and show that changes in the STO oscillation occur on the one-nanosecond timescale.

Pushing down the lateral dimension of single and coupled magnetic dots to the nanometric scale: Characteristics and evolution of the spin-wave eigenmodes

Planar magnetic nanoelements, either single- or multi-layered, are exploited in a variety of current or forthcoming spintronic and/or ICT devices, such as read heads, magnetic memory cells, spin-torque nano-oscillators, nanomagnetic logic circuits, magnonic crystals and artificial spin-ices. The lateral dimensions of the elemental magnetic components have been squeezed down during the last decade to a few tens of nanometers, but they are still an order of magnitude larger that the exchange correlation length of the constituent materials. This means that the spectrum of spin-wave eigenmodes, occurring in the GHz range, is relatively complex and cannot be described within a simple macrospin approximation. On the other hand, a detailed knowledge of the dynamical spectrum is needed to understand or to predict crucial characteristics of the devices. With this focused review we aim at the analysis and the rationalization of the characteristics of the eigenmodes spectrum of magnetic nanodots, paying special attention to the following key points: (i) Consider and compare the case of in-plane and out of-plane orientation of the magnetization, as well as of single- and multi-layered dots, putting in evidence similarities and diversities, and proposing a unifying nomenclature and labelling scheme; (ii) Underline the evolution of the spectrum when the lateral size of magnetic dots is squeezed down from hundreds to tens of nanometers, as in current devices, with emphasis given to the occurrence of soft modes and to the change of spatial localization of the fundamental mode for in-plane magnetized dots; (iii) Extend the analysis from isolated elements to twins of dots, as well as to dense arrays of dipolarly interacting dots, showing how the discretized eigenmodes distinctive of the single element transform in finite-width frequency bands of spin waves propagating through the array.

An Iterative Two-Head Two-Track Detection Method for Staggered Bit-Patterned Magnetic Recording Systems

One of the major problems in bit-patterned magnetic recording (BPMR) systems is an inter-track interference (ITI) that can significantly degenerate the system performance, especially at high areal densities (ADs). Generally, the BPMR system with staggered islands experiences less ITI effect than that with regular islands. Therefore, we propose an iterative two-head two-track detection method for a staggered BPMR system to further reduce the ITI effect, which employs two read heads to read two adjacent tracks and decodes them simultaneously. To lessen the ITI, the weighted readback signal of one track, serving as an ITI signal, is subtracted from the readback signal of the other track, and vice versa, before passing the refined readback signal to an iterative decoding process. Hence, the decoded data will be utilized to estimate the ITI signal for the next global iteration, $N_{\mathrm{ G}}$ . Supposing that the refined readback signal has only one-side ITI effect. We also present the design of the $2{\times }3$ target and its compatible equalizer that will be employed in the proposed system. Results demonstrate that the proposed system not only is superior to the conventional system but also has low complexity. Specifically, the proposed system can perform close to the conventional system whose readback signal encounters only one-side ITI effect when $N_{\mathrm{ G}} = 2$ , 3 and 5 iterations for $\text {AD} = 2$ , 2.5, and 3 Tb/in2, respectively.

Characteristics of magnetic sensor with assembly errors in a rotary recording system

A magnetic position sensing system consists of a magnetic rotary ring with polarities magnetized on its radial surface and a position sensor made of magnetoresistance. Two quadrature sinusoidal output signals from sensor are processed into position information for motion control application. Magnetoresistance varies with the angle between magnetization (M) of external field and flow current (I) inside the sensor patterns. Therefore, the assembly error either in sensor or rotary ring would cause distorted signal. The assembly error between sensor and the medium such as offset, pitch, roll, yaw error and eccentricity between scale and stage of motion centre of read head would be discussed in this paper. Experimental and analytical parameter studies were conducted in this paper to discuss the accuracy error and variation of output quadrature signal caused by assembly error. Through the parameter studies, the data under various conditions can then be used to serve as a baseline.

Anisotropic and Controllable Gilbert-Bloch Dissipation in Spin Valves.

Spin valves form a key building block in a wide range of spintronic concepts and devices from magnetoresistive read heads to spin-transfer-torque oscillators. We elucidate the dependence of the magnetic damping in the free layer on the angle its equilibrium magnetization makes with that in the fixed layer. The spin pumping-mediated damping is anisotropic and tensorial, with Gilbert- and Bloch-like terms. Our investigation reveals a mechanism for tuning the free layer damping insitu from negligible to a large value via the orientation of fixed layer magnetization, especially when the magnets are electrically insulating. Furthermore, we expect the Bloch contribution that emerges from the longitudinal spin accumulation in the nonmagnetic spacer to play an important role in a wide range of other phenomena in spin valves.

Properties of right one-way jumping finite automata

Right one-way jumping finite automata (ROWJFAs), were recently introduced in H. Chigahara et al. (2016) [3] and are jumping automata that process the input in a discontinuous way with the restriction that the input head reads deterministically from left-to-right starting from the leftmost letter in the input and when it reaches the end of the input word, it returns to the beginning and continues the computation. We characterize the family of permutation closed languages accepted by ROWJFAs in terms of Myhill-Nerode equivalence classes. Using this, we investigate closure and non-closure properties as well as inclusion relations to families of the Chomsky-hierarchy and related families. We also give more characterizations of languages accepted by ROWJFAs in the case that the language is given as the concatenation of two languages.

A Design Study of a Heat Flow-Type Reading Head for a Linear Encoder Based on a Micro Thermal Sensor

A new concept of reading head for a linear encoder, in which graduations on a scale grating are read by using a micro thermal sensor composed of a thin film resistor, is proposed to realize a compact encoder system. In the proposed reading head, measurement of the in-plane relative displacement between the micro thermal sensor and the scale grating will be carried out in such a way that the graduations on a scale grating are read by the micro thermal sensor through the change in the heat flow between the sensor and the scale grating surface. In this paper, as the first step of research, theoretical calculations based on the theory of heat flow between the sensor and scale interface are carried out. In addition, basic experiments are carried out to search for the possibility of realizing the proposed concept of the reading head based on the micro thermal sensor.

Mark Twain's life-long fascination with phrenology.

Samuel Langhorne Clemens (Mark Twain; 1835-1910), American humorist and writer, followed scientific and medical developments, and relished exposing questionable practices and ideas. In his youth, he pondered how phrenologists were assessing character, and in 1855 he copied sections of a phrenology book and a skull diagram into a notebook. Later, in London, he had two phrenological examinations by Lorenzo Fowler-one without and the other after identifying himself. Following his "test," which produced contrasting results, he began to ridicule phrenologists and phrenology in Tom Sawyer, Huckleberry Finn, and other works. He underwent at least two more head readings in the United States, and in Eddypus, an unfinished work from 1901 to 1902, he maintained that phrenologists base their insights primarily on how people dress and answer questions. Although now lampooning the craniological tenets of phrenology, Twain never seemed to reject the idea of distinct faculties of mind associated with specialized brain organs.