Design rules for scalability in spin-orbit electronics.

Spin-orbit electronics (spin-orbitronics) has been widely discussed for enabling nonvolatile devices that store and process information with low power consumption. The potential of spin-orbitronics for memory and logic applications has been demonstrated by perpendicular anisotropy magnetic devices comprised of heavy-metal/ferromagnet or topological-insulator/ferromagnet bilayers, where the heavy metal or topological insulator provides an efficient source of spin current for manipulating information encoded in the bistable magnetization state of the ferromagnet. However, to reliably switch at room temperature, spin-orbit devices should be large to reduce thermal fluctuations, thereby compromising scalability, which in turn drastically increases power dissipation and degrades performance. Here, we show that the scalability is not a fundamental limitation in spin-orbitronics, and by investigating the interactions between the geometry of the ferromagnetic layer and components of the spin-orbit torque, we derive design rules that lead to deeply scalable spin-orbit devices. Furthermore, employing experimentally verified models, we propose deeply scaled spin-orbit devices exhibiting high-speed deterministic switching at room temperature. The proposed design principles are essential for design and implementation of very-large-scale-integration (VLSI) systems that provide high performance operation with low power consumption.

Evaluating the Validity of an Automated Device for Asthma Monitoring for Adolescents: Correlational Design.

BACKGROUND: Symptom monitoring is a cornerstone of asthma self-management. Conventional methods of symptom monitoring have fallen short in producing objective data and eliciting patients' consistent adherence, particularly in teen patients. We have recently developed an Automated Device for Asthma Monitoring (ADAM) using a consumer mobile device as a platform to facilitate continuous and objective symptom monitoring in adolescents in vivo. OBJECTIVE: The objectives of the study were to evaluate the validity of the device using spirometer data, fractional exhaled nitric oxide (FeNO), existing measures of asthma symptoms/control and health care utilization data, and to examine the sensitivity and specificity of the device in discriminating asthma cases from nonasthma cases. METHODS: A total of 84 teens (42 teens with a current asthma diagnosis; 42 without asthma) aged between 13 and 17 years participated in the study. All participants used ADAM for 7 consecutive days during which participants with asthma completed an asthma diary two times a day. ADAM recorded the frequency of coughing for 24 hours throughout the 7-day trial. Pearson correlation and multiple regression were used to examine the relationships between ADAM data and asthma control, quality of life, and health care utilization at the time of the 7-day trial and 3 months later. A receiver operating characteristic (ROC) curve analysis was conducted to examine sensitivity and specificity based on the area under the curve (AUC) as an indicator of the device's capacity to discriminate between asthma versus nonasthma cases. RESULTS: ADAM data (cough counts) were negatively associated with forced expiratory volume in first second of expiration (FEV1) (r=-.26, P=.05), forced vital capacity (FVC) (r=-.31, P=.02), and overall asthma control (r=-.41, P=.009) and positively associated with daily activity limitation (r=.46, P=.01), nighttime (r=.40, P=.02) and daytime symptoms (r=.38, P=.02), and health care utilization (r=.61, P<.001). Device data were also a significant predictor of asthma control (ß=-.48, P=.003), quality of life (ß=-.55, P=.001), and health care utilization (ß=.74, P=.004) after 3 months. The ROC curve analysis for the presence of asthma diagnosis had an AUC of 0.71 (95% CI 0.58-0.84), which was significantly different from chance (χ(2) 1=9.7, P=.002), indicating the device's discriminating capacity. The optimal cutoff value of the device was 0.56 with a sensitivity of 51.3% and a specificity of 72.7%. CONCLUSIONS: This study demonstrates validity of ADAM as a symptom-monitoring device in teens with asthma. ADAM data reflect the current status of asthma control and predict asthma morbidity and quality of life for the near future. A monitoring device such as ADAM can increase patients' awareness of the patterns of cough for early detection of worsening asthma and has the potential for preventing serious and costly future consequences of asthma.

Automated Cough Assessment on a Mobile Platform.

The development of an Automated System for Asthma Monitoring (ADAM) is described. This consists of a consumer electronics mobile platform running a custom application. The application acquires an audio signal from an external user-worn microphone connected to the device analog-to-digital converter (microphone input). This signal is processed to determine the presence or absence of cough sounds. Symptom tallies and raw audio waveforms are recorded and made easily accessible for later review by a healthcare provider. The symptom detection algorithm is based upon standard speech recognition and machine learning paradigms and consists of an audio feature extraction step followed by a Hidden Markov Model based Viterbi decoder that has been trained on a large database of audio examples from a variety of subjects. Multiple Hidden Markov Model topologies and orders are studied. Performance of the recognizer is presented in terms of the sensitivity and the rate of false alarm as determined in a cross-validation test.

Preamplifiers for non-contact capacitive biopotential measurements.

Non-contact biopotential sensing is an attractive measurement strategy for a number of health monitoring applications, primarily the ECG and the EEG. In all such applications a key technical challenge is the design of a low-noise trans-impedance preamplifier for the typically low-capacitance, high source impedance sensing electrodes. In this paper, we compare voltage and charge amplifier designs in terms of their common mode rejection ratio, noise performance, and frequency response. Both amplifier types employ the same operational-transconductance amplifier (OTA), which was fabricated in a 0.35 um CMOS process. The results show that a charge amplifier configuration has advantages for small electrode-to-subject coupling capacitance values (less than 10 pF--typical of noncontact electrodes) and that the voltage amplifier configuration has advantages for electrode capacitances above 10 pF.

Non-contact ECG sensing employing gradiometer electrodes.

Noncontact, capacitive electrocardiogram (ECG) measurements are complicated by motion artifacts from the relative movement between the ECG electrodes and the subject. To compensate for such motion we propose to employ first and second order gradiometer electrode designs. A MATLAB-based simulation tool to enable assessment of different electrode configurations and placements on human subjects has been developed to guide the refinement of electrode designs. Experimental measurements of the sensitivity, motion artifact cancellation, and common mode rejection for various prototype designs were conducted with human subjects. Second order gradiometer electrode designs appear to give the best performance as measured by signal to noise plus distortion ratio. Finally, both gradiometer designs were compared with standard ECG recording methods and showed less than 1% beat detection mismatch employing an open source beat detection algorithm.

A low noise, non-contact capacitive cardiac sensor.

The development of sensitive, non-contact electric field sensors to measure weak bioelectric signals will be useful for the development of a number of unobtrusive health sensors. In this paper we summarize our recent work on a number of specific challenges in the development of non-contact ECG sensors. First, we considered the design of a low noise sensor preamplifier. We have adapted circuit designs that incorporate a double feedback loop to cancel the input transistor leakage current while providing stable operation, fast settling time and good low frequency response without the need for ultrahigh value resistors. The measured input referred noise of the preamplifier in the frequency band 0.05-100 Hz is 0.76 µV(rms), which is several times lower than existing ECG preamplifiers.

Optimal spread spectrum watermark embedding via a multistep feasibility formulation.

We consider optimal formulations of spread spectrum watermark embedding where the common requirements of watermarking, such as perceptual closeness of the watermarked image to the cover and detectability of the watermark in the presence of noise and compression, are posed as constraints while one metric pertaining to these requirements is optimized. We propose an algorithmic framework for solving these optimal embedding problems via a multistep feasibility approach that combines projections onto convex sets (POCS) based feasibility watermarking with a bisection parameter search for determining the optimum value of the objective function and the optimum watermarked image. The framework is general and can handle optimal watermark embedding problems with convex and quasi-convex formulations of watermark requirements with assured convergence to the global optimum. The proposed scheme is a natural extension of set-theoretic watermark design and provides a link between convex feasibility and optimization formulations for watermark embedding. We demonstrate a number of optimal watermark embeddings in the proposed framework corresponding to maximal robustness to additive noise, maximal robustness to compression, minimal frequency weighted perceptual distortion, and minimal watermark texture visibility. Experimental results demonstrate that the framework is effective in optimizing the desired characteristic while meeting the constraints. The results also highlight both anticipated and unanticipated competition between the common requirements for watermark embedding.