Full Bandwidth Research Articles

Hofstadter subband ferromagnetism and symmetry-broken Chern insulators in twisted bilayer graphene

In bilayer graphene rotationally faulted to theta=1.1 degrees, interlayer tunneling and rotational misalignment conspire to create a pair of low energy flat band that have been found to host various correlated phenomena at partial filling. Most work to date has focused on the zero magnetic field phase diagram, with magnetic field (B) used as a probe of the B=0 band structure. Here, we show that twisted bilayer graphene (tBLG) in a B as low as 2T hosts a cascade of ferromagnetic Chern insulators with Chern number |C|=1,2 and 3. We argue that the emergence of the Chern insulators is driven by the interplay of the moire superlattice with the B, which endow the flat bands with a substructure of topologically nontrivial subbands characteristic of the Hofstadter butterfly. The new phases can be accounted for in a Stoner picture in which exchange interactions favor polarization into one or more spin- and valley-isospin flavors; in contrast to conventional quantum Hall ferromagnets, however, electrons polarize into between one and four copies of a single Hofstadter subband with Chern number C=-1. In the case of the C=\pm3 insulators in particular, B catalyzes a first order phase transition from the spin- and valley-unpolarized B=0 state into the ferromagnetic state. Distinct from other moire heterostructures, tBLG realizes the strong-lattice limit of the Hofstadter problem and hosts Coulomb interactions that are comparable to the full bandwidth W and are consequently much stronger than the width of the individual Hofstadter subbands. In our experimental data, the dominance of Coulomb interactions manifests through the appearance of Chern insulating states with spontaneously broken superlattice symmetry at half filling of a C=-2 subband. Our experiments show that that tBLG may be an ideal venue to explore the strong interaction limit within partially filled Hofstadter bands.

Detection, Speech Recognition, Loudness, and Preference Outcomes With a Direct Drive Hearing Aid: Effects of Bandwidth.

Direct drive hearing devices, which deliver a signal directly to the middle ear by vibrating the tympanic membrane via a lens placed in contact with the umbo, are designed to provide an extension of audible bandwidth, but there are few studies of the effects of these devices on preference, speech intelligibility, and loudness. The current study is the first to compare aided speech understanding between narrow and extended bandwidth conditions for listeners with hearing loss while fitted with a direct drive hearing aid system. The study also explored the effect of bandwidth on loudness perception and investigated subjective preference for bandwidth. Fifteen adult hearing aid users with symmetrical sensorineural hearing loss participated in a prospective, within-subjects, randomized single-blind repeated-measures study. Participants wore the direct drive hearing aids for 4 to 15 weeks (average 6 weeks) prior to outcome measurement. Outcome measures were completed in various bandwidth conditions achieved by reducing the gain of the device above 5000 Hz or by filtering the stimuli. Aided detection thresholds provided evidence of amplification to 10000 Hz. A significant improvement was found in high-frequency consonant detection and recognition, as well as for speech in noise performance in the full versus narrow bandwidth conditions. Subjective loudness ratings increased with provision of the full bandwidth available; however, real-world trials showed most participants were able to wear the full bandwidth hearing aids with only small adjustments to the prescription method. The majority of participants had either no preference or a preference for the full bandwidth setting.

Modeling of an active suspension system with different suspension parameters for full vehicle

An active suspension system attempts to overcome these compromises so as to provide the best performance for controlling the vehicle. A fully active suspension system aims to control the suspension over the full bandwidth, increase load carrying capacity, handling and ride quality. A model for vehicle’s dynamics while using an active suspension system has been developed. The equations are cast in both the state space form and transfer function forms. To compare the ideal system and a real system, a comparative analysis is also performed by incorporating various sensing and actuation constraints such as time delay and discrete sampling. Simple PID as well as feed-forward controllers is designed and the response is simulated for various disturbances such as road excitations and those arising due to cornering. Parameter studies are also performed to assess the response to various suspension properties. The comparison of the active suspension with respect to the passive suspension indicates significant improvement in performance characteristics such as riding comfort, tendency to rollover and road traction. The studies on the effect of sensing and actuation constraints provide valuable insights into the use of low-cost and/or robust control system elements. Full vehicle model, State space equation, Passive and active suspension system, PID controller, Road profile, MATLAB and SIMULINK

Millimeter-Wave Vertical III-V Nanowire MOSFET Device-to-Circuit Co-Design

Vertical III-V nanowire MOSFETs show potential towards the ultimate transistor scaling. A high transconductance and current density are achieved based on the gate-all-around architecture. This work presents a high-frequency design of such devices, achieving more than 600 GHz cut-off frequencies ( f T, f max), at 20 nm gate length. Furthermore, capacitance design and scaling trends, supported by COMSOL Multiphysics simulations derive state-of-the-art parasitics magnitudes for vertical devices in general, reaching gate-drain capacitance values of 17 aF/wire, corresponding to 0.2 fF/μm. A unique co-designed feedback resonant circuit makes the device unilateral, exhibiting up to 15 dB gain in D-band at 0.5 V supply, and with a current density of 0.5 mA/μm. Finally, a 2-stage low noise amplifier is designed using an optimum matching concept to utilize the full available bandwidth. The resulting circuit performance is independent of transistor gate length, since any decrease in device intrinsic capacitance is assisted by an increase in device overlap capacitances in a setting unique to a current implementation of vertical nanowire MOSFETs. With this approach, amplifiers are designed with more than 20 dB gain and minimum noise figure of 2.5 dB in a simulation environment at 140 GHz. The proposed technology and design platform show a great potential in future low-power communication systems.

Multi-Resonant Frequency Shift Keying: A Novel and Efficient Modulation Scheme for Magnetic Communication

Magnetic communication is a promising technique in harsh environments, such as seawater. To enable efficient communication, transmitting and receiving coils are conventionally operated as part of resonant circuits. However, this results in narrow bandwidths and the associated disadvantages. Thus, most digital modulation schemes cannot be used efficiently on these systems. In this contribution, a mixed hardware/software approach for efficient frequency shift keying is presented. With this energy-efficient modulation concept, the full available bandwidth of a receiver can be utilized for data transmission, while all advantages of using a resonant circuit on the transmitter side can be retained. Towards this goal, a transmitter-side resonant circuit is designed, which supports discrete switching between multiple resonant frequencies. The data symbols are mapped onto these unique resonant frequencies. This prevents the parasitic amplitude modulation associated with conventional frequency shift keying applied to narrow bandwidth circuits, resulting in maximum transmitted magnitude and minimum symbol distortion without need for any further measures. Furthermore, the frequency spacing and/or the cardinality of the symbol alphabet can be increased considerably. At the receiver side, the classical pick-up coil is replaced by a high-sensitivity broadband magnetic field sensor. Numerical results of the mixed hardware/software scheme are provided, and are verified by an experimental setup. This setup is constructed using principles from the field of power electronics and demonstrates, how this modulation concept can be implemented with relatively simple and highly energy efficient electronics and without the use of linear amplifiers in particular.

Equation of motion truncation scheme based on partial orthogonalization

We introduce a general scheme to consistently truncate equations of motion for Green’s functions. Our scheme is guaranteed to generate physical Green’s functions with real excitation energies and positive spectral weights. There are free parameters in our scheme akin to mean field parameters that may be determined to get as good an approximation to the physics as possible. As a test case we apply our scheme to a two-pole approximation for the 2D Hubbard model. At half-filling we find an insulating solution with several interesting properties: it has low expectation value of the energy and it gives upper and lower Hubbard bands with the full non-interacting bandwidth in the large U limit. Away from half-filling, in particular in the intermediate interaction regime, our scheme allows for several different phases with different number of Fermi surfaces and topologies.Graphic abstract

Space-Time Coding Technique for Coherent Frequency Diverse Array

Coherent frequency diverse array (FDA) radar is able to cover all directions with a stable gain by transmitting a single frequency-shifted waveform. However, it is revealed in this work that the range resolution scales linearly with the number of elements, which is limited by the fixed element number. By leveraging the relationship between the beam direction and the signal frequency, we link the sub-bands of the emitted signal to angular sectors. Based on the fact, a novel transmit diversity technique, referred to as two-dimensional (2-D) space-time coding (STC), is proposed to improve the range resolution. For a specific observation direction, the frequency band of each pulse is shifted by STC to synthesize a full bandwidth after the pulse accumulation. Furthermore, the piecewise LFM (linear frequency modulation) waveform design can be combined with the STC technique to synthesize the transmit beampattern flexibly without range resolution degradation for each pulse. Compared with the state-of-the-art technologies, the proposed STC technique has superiorities in range resolution improvement, ultra-low range sidelobe level, interference suppression, and beampattern design capability. In addition, multi-dimensional ambiguity functions are derived to assess the performance in range-angle-Doppler domain, including the range and angle resolutions, the sidelobe level (SLL) and the angular coverage. To satisfy practical demands, the general receive processing procedures are also designed. The proposed method and corresponding theoretical analysis are verified by extensive numerical results.

Configurable Network Protocol Accelerator (COPA)

Today's field-programmable gate arrays (FPGAs) offer not only programmable acceleration capabilities but also include advanced features that are on-par with a mainstream processor platform. However, rather than being deployed as autonomous acceleration nodes, they are generally deployed as second-class citizens under the control of a standard processor platform. The configurable network protocol accelerator (COPA) framework enables FPGAs to support custom inline/lookaside accelerators and attach directly to a 100-Gb/s Ethernet network. The hardware component provides the necessary networking/accelerator infrastructure. The software component supports an open standard API that enables the integrated accelerators to be used with network communication by applications/middleware. COPA enables a truly distributed FPGA accelerator model and has been implemented on variants of Stratix10 FPGAs. The COPA framework along with example accelerator IPs has been validated with microbenchmarks as well as proxy client/server benchmarks and achieves full network bandwidth.

Mainlining databases

The proliferation of modern data processing tools has given rise to open-source columnar data formats. These formats help organizations avoid repeated conversion of data to a new format for each application. However, these formats are read-only, and organizations must use a heavy-weight transformation process to load data from on-line transactional processing (OLTP) systems. As a result, DBMSs often fail to take advantage of full network bandwidth when transferring data. We aim to reduce or even eliminate this overhead by developing a storage architecture for in-memory database management systems (DBMSs) that is aware of the eventual usage of its data and emits columnar storage blocks in a universal open-source format. We introduce relaxations to common analytical data formats to efficiently update records and rely on a lightweight transformation process to convert blocks to a read-optimized layout when they are cold. We also describe how to access data from third-party analytical tools with minimal serialization overhead. We implemented our storage engine based on the Apache Arrow format and integrated it into the NoisePage DBMS to evaluate our work. Our experiments show that our approach achieves comparable performance with dedicated OLTP DBMSs while enabling orders-of-magnitude faster data exports to external data science and machine learning tools than existing methods.

Spectrally sparse optical coherence tomography.

Swept-source optical coherence tomography (OCT) typically relies on expensive and complex swept-source lasers, the cost of which currently limits the suitability of OCT for new applications. In this work, we demonstrate spectrally sparse OCT utilizing randomly spaced low-bandwidth optical chirps, suitable for low-cost implementation with telecommunications grade devices. Micron scale distance estimation accuracy with a resolution of 40 μm at a standoff imaging distance greater than 10 cm is demonstrated using a stepped chirp approach with approximately 23% occupancy of 4 THz bandwidth. For imaging of sparse scenes, comparable performance to full bandwidth occupancy is verified for metallic targets.

Reliable, Intelligent, and Design-Independent Digital Frequency Extraction Methodology for High Bit-Count DIFM Receivers

Frequency extraction is the principal objective and the major function of wideband instantaneous frequency measurement (IFM) receivers. The conventional IFM receivers with several-bit discriminators exhibit fast frequency extraction, but the accuracy and reliability of the extracted frequency have not been main goals and concerns as desired. Increasing the number of discriminators to have a high bit-count (HBC) IFM receiver raises some challenges in the reliability of the frequency extraction that have not been thoroughly solved before. A rigorous practical solution for calculating and assigning a unique correct frequency corresponding to each binary code in HBC IFMs has not been accomplished yet. This article introduces a novel methodology for fast, reliable, and design-independent frequency extraction that intelligently utilizes digital processing to overcome these challenges in HBC digital IFMs (DIFMs). Moreover, compared to the conventional low bit-count IFM receivers, the frequency accuracy is improved. The design methodology to achieve an accurate functional IFM is very robust concerning deviations such as variations in discriminators frequency response, complete failure of a discriminator path, and runtime environmental influences. The proposed methodology, named as read like in-ready (InReDI), has been tested on the fabricated 2-4-GHz 15-bit IFM receiver. The measurement results prove the promising achievement of 11-MHz average frequency rms error in the full frequency bandwidth of 2–4 GHz and in the full dynamic range of 70 dBm. By employing the creatively developed digital processing for generating and using the code-frequency mapping space (CFMS), the designed and fabricated 15-bit IFM achieves 8.3 million pulses per second.

Processing Continuous Active Sonar Transmissions to Achieve an Arbitrarily Fast Update Rate With Full Instantaneous Bandwidth

A processing technique for continuous active sonar (CAS) that uses linear frequency modulation (LFM) waveforms is presented. LFM CAS employs wideband long-duration LFMs with 100% transmit duty cycle. The received signals are typically processed in sub-bands by forming a sequence of matched-filter replicas that correspond to consecutive segments of the full waveform; this increases the update rate of the sonar at the cost of decreased performance in each sub-band due to the decrease in processing bandwidth and duration (energy). The algorithm presented in this article achieves fast updates by forming a sequence of unique matched-filter replicas through a number of circular shifts to the transmitted LFM, resulting in processing across the frequency jump between pings. This approach allows increased processing duration and bandwidth (up to the full duration/bandwidth of the LFM) at the cost of reduced independence between updates. The circular-shift algorithm is mainly considered in the limit where the full duration and bandwidth of the waveform are exploited to provide partially independent detection and ranging opportunities. The update rate can be arbitrarily chosen independent of processing duration. The algorithm is validated with sonar data from the LCAS15 sea trial.

High Gain, Low Noise, Spectral-Gain-Controlled, Broadband Lumped Fiber Raman Amplifier

We demonstrate an 80 nm bandwidth (extending from 1529 to 1609 nm), dual-stage, diode-pumped, lumped Raman amplifier using a relatively short total length (2 km) of highly nonlinear fiber. The impact of Rayleigh back scattering is mitigated and the build-up of thermally generated wavelength dependent noise is controlled by suitably adjusting the spectral gain profile in the two amplifier stages. In this way a high overall gain of 27 dB with 2.6 dB gain flatness and an average noise figure of 5.8 dB with <1 dB variation is achieved across the full amplifier bandwidth.

Performance Evaluation of a Wearable Tattoo Electrode Suitable for High-Resolution Surface Electromyogram Recording.

High-density surface electromyography (HD-sEMG) has been utilized extensively in neuromuscular research. Despite its potential advantages, limitations in electrode design have largely prevented widespread acceptance of the technology. Commercial electrodes have limited spatial fidelity, because of a lack of sharpness of the signal, and variable signal stability. We demonstrate here a novel tattoo electrode that addresses these issues. Our dry HD electrode grid exhibits remarkable deformability which ensures superior conformity with the skin surface, while faithfully recording signals during different levels of muscle contraction. We fabricated a 4 cm×3 cm tattoo HD electrode grid on a stretchable electronics membrane for sEMG applications. The grid was placed on the skin overlying the biceps brachii of healthy subjects, and was used to record signals for several hours while tracking different isometric contractions. The sEMG signals were recorded successfully from all 64 electrodes across the grid. These electrodes were able to faithfully record sEMG signals during repeated contractions while maintaining a stable baseline at rest. During voluntary contractions, broad EMG frequency content was preserved, with accurate reproduction of the EMG spectrum across the full signal bandwidth. The tattoo grid electrode can potentially be used for recording high-density sEMG from skin overlying major limb muscles. Layout programmability, good signal quality, excellent baseline stability, and easy wearability make this electrode a potentially valuable component of future HD electrode grid applications. The tattoo electrode can facilitate high fidelity recording in clinical applications such as tracking the evolution and time-course of challenging neuromuscular degenerative disorders.

Parallel Broadband Femtosecond Reflection Spectroscopy at a Soft X-Ray Free-Electron Laser

X-ray absorption spectroscopy (XAS) and the directly linked X-ray reflectivity near absorption edges yield a wealth of specific information on the electronic structure around the resonantly addressed element. Observing the dynamic response of complex materials to optical excitations in pump–probe experiments requires high sensitivity to small changes in the spectra which in turn necessitates the brilliance of free electron laser (FEL) pulses. However, due to the fluctuating spectral content of pulses generated by self-amplified spontaneous emission (SASE), FEL experiments often struggle to reach the full sensitivity and time-resolution that FELs can in principle enable. Here, we implement a setup which solves two common challenges in this type of spectroscopy using FELs: First, we achieve a high spectral resolution by using a spectrometer downstream of the sample instead of a monochromator upstream of the sample. Thus, the full FEL bandwidth contributes to the measurement at the same time, and the FEL pulse duration is not elongated by a monochromator. Second, the FEL beam is divided into identical copies by a transmission grating beam splitter so that two spectra from separate spots on the sample (or from the sample and known reference) can be recorded in-parallel with the same spectrometer, enabling a spectrally resolved intensity normalization of pulse fluctuations in pump–probe scenarios. We analyze the capabilities of this setup around the oxygen K- and nickel L-edges recorded with third harmonic radiation of the free electron laser in Hamburg (FLASH), demonstrating the capability for pump–probe measurements with sensitivity to reflectivity changes on the per mill level.

Application of A Frequency Chirped RF Intensity Modulated 532 nm Light Source in Underwater Ranging

A radio-frequency (RF) intensity-modulated light source at 532 nm was built for underwater ranging. The intensity of a narrow-linewidth laser at 1064 nm was modulated via a Mach-Zehnder electro-optical modulator. The modulation frequency could be tuned from 10 MHz to 2.1 GHz. The intensity-modulated light was amplified via a 2-stage laser diode-pumped Yb3+ doped large-mode-area fiber amplifier. A 15 mm long magnesium oxide doped periodically-poled lithium niobate (MgO: PPLN) nonlinear crystal was used to convert the 1064 nm light into 532 nm light via frequency doubling. The maximum output power at 532 nm was 2.56 W, the highest efficiency from the fundamental to second harmonic generation (SHG) was 22.6%. The watt level 532 nm light source was applied in underwater ranging experiments. Frequency domain reflectometry (FDR) was applied to retrieve the distances of the objects to the transmitter in a water tank. When the modulation frequency was tuned from 10 MHz to 200 MHz, we obtained ranging accuracy better than 5 cm and ranging resolution smaller than 0.5 cm at 8.6 attenuation length. Two objects spacing by 0.8 m could be resolved simultaneously. The attenuation length at which the object could be detected was limited by the sensitivity of the silicon photodetector. Moreover, we did not use the full bandwidth of the modulation since the lock-in amplifier adopted for data processing had a bandwidth of 200 MHz. Both ranging distance and resolution can be improved if a photomultiplier tube and a high-speed data sampling board were used. Nevertheless, the experimental results showed that the watt level, broadband intensity modulated light source has great potential in underwater detection in terms of ranging accuracy and resolution.

Perceptual Benefits of Extended Bandwidth Hearing Aids With Children: A Within-Subject Design Using Clinically Available Hearing Aids

Purpose The aim of the study was to investigate the achieved audibility with clinically available, modern, high-end, behind-the-ear hearing aids fitted using the Desired Sensation Level v5.0 child prescription for a clinical sample of children with hearing impairment and the effect of the extended bandwidth provided by the hearing aids on several outcome measures. Method The achieved audibility was measured using the maximum audible output frequency method. Twenty-eight children (7-17 years old) with mild to severe hearing losses completed this study. Two hearing aid conditions were fitted for each participant: an extended bandwidth condition, which was fitted to targets as closely as possible, and a restricted bandwidth condition, for which aided output was restricted above 4.5 kHz. Consonant discrimination in noise, subjective preference, aided loudness growth, and preferred listening levels were evaluated in both conditions. Results The extended bandwidth hearing aid fittings provided speech audibility above 4.5 kHz for all children, with an average maximum audible output frequency of 7376 Hz (SD = 1669 Hz). When compared to a restricted bandwidth, the extended bandwidth condition led to an improvement of 5.4% for consonant discrimination in noise scores, mostly attributable to /s/, /z/, and /t/ phoneme perception. Aided loudness results and preferred listening levels were not significantly different across bandwidth conditions; however, 65% of the children indicated a subjective preference for the extended bandwidth. Conclusion The study suggests that providing the full bandwidth available, with modern, behind-the-ear hearing aids, leads to improved audibility, when compared to restricted bandwidth hearing aids, and that it leads to beneficial outcomes for children who use hearing aids, fitted to the Desired Sensation Level v5.0 child prescription, without causing significant increases in their loudness perception.

Assessment of updated low frequency model in delineating bypassed hydrocarbon reservoir: A 4D seismic study of ’X’ - field, offshore, Niger Delta, Nigeria

Aim/objectives: The aim of this research is, to use Time lapse (4D) seismic and investigate the influence of low frequency update in deterministic model-based seismic inversion employed in delineating a prospect saturated with bypassed hydrocarbon accumulation. Method: The dataset employed in this study incorporates 4D seismic volumes with fifteen (15) years production, interval between 2001 baseline and 2016 monitor seismic vintages. The inversion was carried out using full bandwidth of the updated low frequency and bandpass filtered low frequency approaches. The seismic vintages (baseline and monitor) were simultaneously inverted into acoustic impedance volumes for the two approaches. The formation fluid and lithology were discriminated through fluid replacement modelling (FRM) based on the colour separation between brine and gas saturation scenarios. Findings: The two inversion methods employed reveal six (6) zones suspected to be saturated with bypassed hydrocarbons. The delineated bypassed zones are masked in the full bandwidth approach,depicting the effect of the updated low frequency model. Meanwhile, the bandpass filtered approach result presents a better delineated bypassed reservoir as the zones are more pronounced when compared with the full bandwidth approach. Porosity estimate reveals that the bandpass filtered approach is characterized with excellent porosity in the suspected bypassed zones. The results equally gave more reliable and full delineated bypassed zones. Originality and novelty: The dataset employed in this study were obtained from a producing hydrocarbon field which, interest is to maximize the production of oil/gas. The study will bridge the inherent gab observed in using model-based seismic inversion approach to analyse and interpret seismic data in order to delineate hydrocarbon prospects. The research reveals that,the model-based seismic inversion method is still very effective in delineating hydrocarbon prospect when the updated low frequency is bandpass filtered to remove the model effect which influences the inverted acoustic impedance results. Keywords: Porosity; frequency; bypassed; reservoir and impedance

Reference model based discrete time sliding mode control of communication networks

AbstractIn this work, we propose a new sliding mode controller based on a reference model for controlling data transmission rates in a connection‐oriented communication network. In the proposed approach, we build a model of the network, which is controlled by a linear quadratic (LQ) optimal controller. Then, the sliding variable of the real network is forced to follow the reference sliding variable generated by this model. This method enables us to preserve the favorable properties of the optimal controller, such as reducing and smoothing out the initial flow rates. Moreover, once the reference model attains the vicinity of the desired state, the designed sliding mode controller is able to react more rapidly to changes in the available bandwidth, ensuring better robustness. Due to this fact, the considered controller can ensure full bottleneck link bandwidth utilization with smaller memory buffers than the LQ optimal one. This important advantage is shown both analytically, and in computer simulations

Perception of attractive and unattractive face groups is driven by distinct spatial frequencies.

Our visual system is able to extract information on facial attractiveness from groups of faces that contain both coarse and detailed information. This raises the question: What information is extracted from a face group? Is the attractiveness perception of multiple faces driven by high or low spatial frequency that can highlight the local or global information of the faces, respectively? In the first experiment, we adapted participants to four unattractive faces with full bandwidth (FB), high spatial frequency (HSF), and low spatial frequency (LSF). We observed significant aftereffects in the HSF faces adaptation condition, which suggests that the perception of multiple unattractive faces is largely driven by HSF information. In the second experiment, we found a similar but different pattern in the direct-rating tasks, suggesting distinct perception mechanisms in unattractive versus attractive faces. In the third experiment, both the adaptation and direct-rating paradigms suggested that perception of multiple attractive faces is largely driven by LSF information. Overall, results from the three experiments together found that perception of multiple attractive and unattractive faces depends on visual information from different spatial frequencies, suggesting distinctive mechanisms in processing attractive and unattractive groups of faces.