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One-way quantum finite automata are reversible in nature, which greatly reduces its accepting property. In fact, the set of languages accepted by one-way quantum finite automata is a proper subset of regular languages. In this paper, we replace the tape head of one-way quantum finite automata with DNA double strand and name the model Watson–Crick quantum finite automata. The non-injective complementarity relation of Watson–Crick automata introduces non-determinism in the quantum model. We show that this introduction of non-determinism increases the computational power of one-way quantum finite automata significantly. Watson–Crick quantum finite automata can accept all regular languages and also accepts some languages which are not accepted by any multi-head deterministic finite automata. Exploiting the superposition property of quantum finite automata, we show that Watson–Crick quantum finite automata accept the language L = {ww|w ∈ {a, b}*}.

Multiple-input single-output two-dimensional magnetic recording gain in a magnetic tape system was studied under the condition where the bit aspect ratio is 22%–37% compared to current tape systems. The performance was mainly evaluated in terms of signal-to-noise ratio (SNR) cross-track profile utilizing a 2-D read-back signal synthesized from the waveform acquired with a conventional single-reader tape head. The results show that, depending on the reader pitch selected, either significant gain in tracking margin up to 215% compared to the traditional 1-D signal-processing scheme or an additional SNR gain accompanied with a moderate increase in approximately 30% in tracking margin can be achieved by utilizing the 2-D equalization.

The recording performance of a new prototype magnetic tape based on perpendicularly oriented strontium ferrite particles is investigated using a 29 nm wide tunneling magnetoresistive reader. At a linear density of 702 kbpi, a post-detection byte-error rate of 2.8e-2 is demonstrated based on measured recording data and a software read channel. The read channel uses a 64-state implementation of an extended version of a data-dependent noise-predictive maximum-likelihood detection scheme that tracks the first and second order statistics of the data-dependent noise. At the demonstrated post-detection byte-error rate, a post-error-correction-coding byte-error rate of less than 1e-20 can be achieved using an iterative decoding architecture. To facilitate aggressive track-density scaling, we made multiple advances in the area of track following. First, we developed a new timing-based servo pattern and implemented a novel quad channel averaging scheme. Second, we developed a new field programmable gate array prototyping platform to enable the implementation of quad channel averaging. Third, we enhanced our low disturbance tape transport with a pair of 20 mm diameter air bearing tape guides and a prototype track-following actuator. Fourth, we developed a novel low friction tape head and finally, we designed a set of tape speed optimized track-following controllers using the model-based H∞ design framework. Combining these technologies, we achieved a position error signal (PES) characterized by a standard deviation ≤ 3.18 nm over a tape speed range of 1.2 to 4.1 m/s. This magnitude of PES in combination with a 29 nm wide reader enables reliable recording at a track width of 56.2 nm corresponding to a track density of 451.9 ktpi, for an equivalent areal density of 317.3 Gb/in2.

In situ consolidation of thermoplastic composites by Automated Tape Placement (ATP) is challenging. High quality ATP grade pre-preg material and tape head equipped with an efficient heat sources like lasers offer an opportunity towards high deposition rates and improved mechanical properties of composite materials. In this study uni-directional carbon fiber/ polyphenylene sulfide (UD tape prepreg CF/PPS), carbon fiber/polyetheretherketone (UD tape prepreg CF/PEEK) as well as blend of carbon fiber/polyetheretherketone/polyphenylene sulfide (UD tapes prepregs CF/PEEK/PPS) laminates are compared in terms of their properties after beeing processed by ATP technology. CF/PPS, CF/PEEK and blend CF/PPS/PEEK laminate specimens were processed using in-situ laser-assisted ATP (LATP) process. LATP processing parameters used in this study were chosen based on a preliminary trials; the results provide a basis for refinement of these parameters and prepreg material with an optimal and balanced set of final mechanical properties. This study showed an attempt how to manage the processing parameters for LATP process and to obtain composite materials with tailored properties. The process for production of thermoplastic plates with LATP head in general is a process that is governed by many parameters such as: laser power, angle of incidence, roller pressure and temperature, placement speed, tool temperature, then types of the roller material and the tool material. These parameters are not subject of discussing in this paper; they are kept constant, and the goal of the paper is to manage the crystallinity level within the composite thermoplastic material during annealing step at different temperatures after LATP process. Also, the void content during the production process could be controlled. More particularly, the authors showed that composites based on PPS matrix manufactured with LATP process possess higher flexural strength, with less void content compared to samples based on PEEK matrix. These samples showed also higher crystallinity after annealing step. Keywords: thermoplasts, laser-assisted automated tape placement (LATP), degree of crystallinity, void content, flexural strength.

A prototype perpendicularly oriented sputtered tape sample was investigated using a prototype high-moment tape write head and a 48 nm-wide tunneling magnetoresistive hard disk drive read head. A linear density of 818 kbpi with a post-detection byte-error rate $\sigma $ -PES) ≤ 6.5 nm was also demonstrated over a tape speed range of 1.2–4.1 m/s. This magnitude of PES in combination with a 48 nm-wide reader enables reliable recording at a track width of 103 nm corresponding to a track density of 246.2 ktpi, for an equivalent areal density of 201.4 Gb/in2.

Nearly all air enters the stratosphere through the tropical tropopause layer (TTL). The TTL therefore exerts a control on stratospheric chemistry and climate. The hemispheric meridional overturning (Brewer–Dobson) circulation spreads this TTL influence upward and poleward. Stratospheric water vapor concentrations are set near the tropical tropopause and are nearly conserved in the lowermost stratosphere. The resulting upward propagating tracer transport signal of seasonally varying entry concentrations is known as the tape recorder signal. Here, we study the roles of vertical and horizontal mixing in shaping the tape recorder signal in the tropical lowermost stratosphere, focusing on the 80 hPa level. We analyze the tape recorder signal using data from satellite observations, a reanalysis, and a chemistry–climate model (CCM). By modifying past methods, we are able to capture the seasonal cycle of effective vertical transport velocity in the tropical lowermost stratosphere. Effective vertical transport velocities are found to be multiple times stronger than residual vertical velocities for the reanalysis and the CCM. We also study the tape recorder signal in an idealized 1-D transport model. By performing a parameter sweep, we test a range of different strengths of transport contributions by vertical advection, vertical mixing, and horizontal mixing. By introducing seasonality into the transport strengths, we find that the most successful simulation of the observed tape recorder signal requires vertical mixing at 80 hPa that is multiple times stronger compared to previous estimates in the literature. Vertical mixing is especially important during boreal summer when vertical advection is weak. Simulating the reanalysis tape recorder requires excessive amounts of vertical mixing compared to observations but also to the CCM, which hints at the role of spurious dispersion due to data assimilation. Contrasting the results between pressure and isentropic coordinates allows for further insights into quasi-adiabatic vertical mixing, e.g., associated with overshooting convection or breaking gravity waves. Horizontal mixing, which takes place primarily along isentropes due to Rossby wave breaking, is captured more consistently in isentropic coordinates. Overall, our study emphasizes the role of vertical mixing in lowermost tropical stratospheric transport, which appears to be as important as vertical advection by the residual mass circulation. This questions the perception of the tape recorder as a manifestation of slow upward transport as opposed to a phenomenon influenced by quick and intense transport through mixing, at least near the tape head. However, due to the limitations of the observational dataset used and the simplicity of the applied transport model, further work is required to more clearly specify the role of vertical mixing in lowermost stratospheric transport in the tropics.

Magnetic tape heads are ubiquitously used to read and record on magnetic tapes in technologies as diverse as old VHS tapes, modern hard-drive disks, or magnetic bands on credit cards. Their design highlights the ability to convert electric signals into fluctuations of the magnetic field at very high frequencies, which is essential for the high-density storage demanded nowadays. Here, we twist this conventional use of tape heads to implement one in a magnetic tweezers design, which offers the unique capability of changing the force with a bandwidth of [Formula: see text] 10 kHz. We calibrate our instrument by developing an analytical expression that predicts the magnetic force acting on a superparamagnetic bead based on the Karlqvist approximation of the magnetic field created by a tape head. This theory is validated by measuring the force dependence of protein L unfolding/folding step sizes and the folding properties of the R3 talin domain. We demonstrate the potential of our instrument by carrying out millisecond-long quenches to capture the formation of the ephemeral molten globule state in protein L, which has never been observed before. Our instrument provides the capability of interrogating individual molecules under fast-changing forces with a control and resolution below a fraction of a piconewton, opening a range of force spectroscopy protocols to study protein dynamics under force.

We examine the behaviors of various models of k-limited automata, which naturally extend Hibbard’s [Inf. Control, vol. 11, pp. 196–238, 1967] scan limited automata, each of which is a linear-bounded automaton satisfying the k-limitedness requirement that the content of each tape cell should be modified only during the first k visits of a tape head. One central model is k-limited probabilistic automaton (k-lpa), which accepts an input exactly when its accepting states are reachable from its initial state with probability more than 1/2. We further study the behaviors of one-sided-error and bounded-error variants of such k-lpa’s as well as deterministic and nondeterministic models. We discuss fundamental properties of those machine models and obtain inclusions and separations among language families induced by these machine models. In due course, we study special features—the blank skipping property and the closure under reversal—which are keys to the robustness of k-lpa’s.

A new tape–head design with surface cavities is presented as an alternative to the conventional skiving-edge flat-profile head design. The new head design is referred to as the vacuum head, inspired by the sub-ambient air pressure that develops in the surface cavities during operation. Two prototype head modules, a writer and a reader, were fabricated by modifying commercial tape–head modules and are compared with unmodified reference modules. A finite-element model is presented to simulate the head–tape interface and aid in the surface topography design of the vacuum head prototypes. The modeling results correspond qualitatively with experimental data from interferometer measurements of the shape of tape as it passes over the vacuum heads. The vacuum heads are operated successfully in data read/write experiments, with a slightly reduced signal-to-noise ratio performance compared with the reference heads. An indirect measure of head friction is obtained from tape velocity spectra that show a much reduced friction-induced compressional wave tape resonance for the vacuum modules compared with that for the reference modules. The results presented in this paper show that the new vacuum head design is a promising candidate for future heads with low friction, enabling the use of very smooth media for reduced magnetic spacing and increased areal densities.

Magnetic tape heads are ubiquitously used to read and record on magnetic tapes in technologies as diverse as old VHS tapes, modern hard drive disks, or magnetic bands on credit cards. Their design highlights the ability to convert electric signals into fluctuations of the magnetic field at very high frequencies, which is essential for the high density storage demanded nowadays. Here, we twist this conventional use of tape heads to implement one in a new magnetic tweezers design, which offers the unique capability of changing the force with a bandwidth of ~ 10 kHz. We calibrate our instrument by developing an analytical expression that predicts the magnetic force acting on a superparamagnetic bead based on the Karlqvist approximation of the magnetic field created by a tape head. This theory is validated by measuring the force dependence of protein L unfolding/folding step sizes, and the folding properties of the R3 talin domain. We demonstrate the potential of our instrument by carrying out millisecond-long quenches to capture the formation of the ephemeral molten globule state in protein L, which has never been observed before. Our instrument provides for the first time the capability of interrogating individual molecules under fast-changing forces with a control and resolution below a fraction of a pN, opening a range of novel force spectroscopy protocols to study protein dynamics under force.

The resolution limits of tape head lateral position estimates derived from timing-based servo (TBS) patterns preformatted on perpendicularly oriented barium ferrite tape media are investigated. A set of four new TBS patterns with azimuth angles ranging from 15° to 24° but having, otherwise, identical parameters are compared. Measurements of the standard deviation of the closed-loop position-error signal are compared with resolution estimates based on: 1) the noise floor of the power spectral density of the lateral tape motion measured from the servo pattern during open or closed-loop track-following and 2) an analytical lower bound on the mean-squared estimation error, which depends on the servo readback signal shape and the signal-to-noise ratio. All four servo patterns are shown to achieve nanoscale resolution under realistic operating conditions. The 24° pattern was found to provide the highest performance with a position estimation resolution better than 3.8 nm for a single channel, and better than 2.6 nm when the estimates of two channels are combined.

In this paper, we study the mechanical interface between a hard-disk drive (HDD) head and magnetic recording tape to enable the use of HDD heads to investigate future tape operating points. Tape surface height measurements were obtained using an interferometer microscope for varying wrap angle configurations, tape velocities, and tape tensions. Simultaneously, the readback signal from the read element of the HDD head was captured to study the quality of the contact between the tape and the head. The signal-to-noise ratio (SNR) and bit-error rate (BER) performance of pseudorandom bit sequence (PRBS) data readback experiments are presented. An analytical model is described for estimating the magnetic spacing from the PRBS readback spectrum. In contrast to current commercial tape heads, the HDD head surface has a pronounced topography containing cavities. When tape passes in close proximity, subambient pressures are formed inside these cavities and the resulting pressure differences force the tape toward the head and deform the tape into remarkable shapes. For the topography of the HDD head used, the shape of tape is predominantly determined by the leading and trailing wrap angles. Readback was obtained only in the backward direction (i.e., opposite to the direction of operation in an HDD), with positive leading but negative trailing wrap angles. Better readback is obtained for shallow wrap angles, lower tape velocity, and higher tape tension. Good readback is obtained for leading and trailing wrap angles $\sim 0.3^{\circ }$ and −0.2°, respectively. Fits of the analytical model to the spectrum of the readback signal of PRBS data lead to a magnetic spacing estimate of $\sim 30$ nm. At 600 kb/in linear density, we measured 11 dB SNR and $7\times 10^{-3}$ BER for PRBS data on perpendicularly oriented particulate barium–ferrite tape.

Results of experiments in which hard-disk drive (HDD) tunnel valve (TV) sensors were run in continuous contact with magnetic recording tape are presented. In one mode, suspended HDD sliders were run against tape backed by a supporting air film in a novel configuration. In another, tape was run in an air-skiving mode over HDD rowbars mounted on support beams, similar to the way tape wraps a conventional tape head. The data indicate that HDD TV sensors can successfully operate in continuous contact with running tape media. Measurements show that roughness of older generation metal particle tape limits the signal-to-noise ratio achievable using existing narrow HDD TV sensors. However, TV sensors optimized for running on smoother barium ferrite tape are now a viable candidate for future high areal density tape recording platforms.

The friction and magnetic spacing between magnetic tape and a recording head are measured as a function of the wrap angle at several tape speeds and tape tensions for two tape samples with different roughnesses. An increase in friction and a decrease in magnetic spacing are measured for: 1) increasing wrap angle; 2) decreasing tape speed; and 3) increasing tape tension. The relation between the magnetic spacing and friction is fixed when varying the tape tension or wrap angle. For the rougher tape sample, reducing the tape speed (and adjusting the tape tension and wrap angle accordingly) reduces the magnetic spacing without increasing the friction. Although the smoother tape experiences more friction for a fixed wrap angle and tape tension, a smaller magnetic spacing at a specified friction is measured for it than for the rougher tape.

Ultra-precise positioning of the recording head over the data tracks is required to achieve the aggressive track density scaling envisioned for future tape storage systems. The track-follow control system is responsible for reducing the misalignment between the tape and the head created primarily by lateral motion of the flexible medium. The challenge of improving the track-following accuracy becomes even more difficult in the presence of external vibration disturbances. Typically, position error signal (PES) information is measured at the tape head using pre-formatted servo information and is used in a feedback controller during track-following to maintain the position of the read/write elements at the desired position during tape transport. In this paper, a track-follow scheme is introduced in which a high-bandwidth low-noise position sensor is used in conjunction with the position information read back by the head from preformatted servo patterns on the tape. A cascade control configuration is proposed, in which first an inner loop is designed based on the actuator position information provided by the sensor. The high-bandwidth and low-noise characteristics of the sensor enable a high closed-loop bandwidth of the inner system that effectively compensates for external vibration disturbances. Subsequently, using a cascade structure, a PES-based controller is designed that compensates for the lateral tape motion disturbances. Simulation and experimental results are presented that illustrate the performance of the proposed scheme compared to a conventional PES-based track-follow control system.

Reliable and precise tape transport is of fundamental importance to achieve larger volumetric recording densities in tape storage systems. The performance of the tape transport control system, which is affected by variations in the tape velocity and tension, impacts the write and read quality of the data tracks and eventually the achievable areal recording density. During operation in cruise velocity mode, disturbances in velocity and tension may be induced for example by tape reel eccentricities. This problem is particularly serious when the reel rotation frequencies are close to the resonance frequency determined by the tape path. Typically, the tape velocity is estimated at the tape head from a servo signal, which is obtained by reading pre-formatted servo information, and used for tape transport control during cruise mode. In such a scheme, velocity disturbances observed at the head cannot be attributed to an individual reel. Hence no targeted disturbance suppression can take place at the individual tape reels. However, Hall sensors are typically included in tape drives to obtain additional tape velocity information from the individual reels. This information is used to achieve proper tape transport operation in the absence of valid velocity estimates from the pre-formatted servo information, for example during tape acceleration. In this paper, we present a novel control scheme for tape transport that uses velocity measurements from three sources, the Hall sensors at the tape reels and the servo channel that yields velocity estimates at the head. Specifically, characterization of the multiple-input multiple-output (MIMO) tape transport system provides an accurate system model and enables an optimized two-sensor control design. Furthermore, H∞ filtering is employed to perform sensor fusion and the resulting state estimates are used in the feedback control of the two reels. Experimental results are presented to illustrate the behavior and performance of the proposed tape transport control system.

Aggressive track-density scaling in linear magnetic tape recording has been identified as a key means of sustaining capacity scaling. As the reader width decreases, the relative signal contribution of the written track region outside the lateral extent of the reader increases. We model, analyze and quantify side-reading effects of shielded magneto-resistive read heads reading narrow tracks on perpendicular-oriented tape media. We compare results from extended analytical models with experimental data. An understanding of these effects will be important in designing track misregistration budgets and SNR margins for future operating points of parallel-channel tape recording systems.