An Updated Vision of Continuous-Time Fractional Models

A few days before the end of the revision procedure, my friend J. Tenreiro Machado had a sudden cardio-respiratory arrest and died. Here I want to express my gratitude and tribute to a great man and scientist. He was a very friendly and helpful person, with an unusual work capacity that allowed him to publish interesting articles on a wide range of topics.This paper presents the continuous-time fractional linear systems and their main properties. Two particular classes of models are introduced: the fractional autoregressive-moving average type and the tempered linear system. For both classes, the computations of the impulse response, transfer function, and frequency response are discussed. It is shown that such systems can have integer and fractional components. From the integer component we deduce the stability. The fractional order component is always stable. The initial-condition problem is analyzed and it is verified that it depends on the structure of the system. For a correct definition and backward compatibility with classic systems, suitable fractional derivatives are also introduced. The Grünwald-Letnikov and Liouville derivatives, as well as the corresponding tempered versions, are formulated.authorsversionpublishe

Extraction of reliable information from time-domain pressure and flow signals measured by means of forced oscillation techniques

This paper aims to give a proof-of-concept for the possible application of the forced oscillation lung function test to assess the viscoelastic properties of the airways and tissue. In particular, a novel signal processing algorithm is employed on non-stationary, noisy, (relatively) short time series of respiratory pressure and flow signals. This novel technique is employed to filter the useful information from the signals acquired under two measurement conditions: pseudo-functional residual capacity (PFRC) and pseudo-total lung capacity (PTLC). The PFRC is the measurement performed at lowest lung volume with maximum deflation, and the PTLC is measurement performed at the maximum lung volume under maximum inflation. The results suggest that the proposed technique is able to extract information on the viscoelastic properties of the lung tissue at a macroscopic level. The conclusion of this preliminary study is that the proposed combination of signal processing method and lung function test is suited to be employed on a large database in order to deliver reference values and perform further statistical analysis

Wireless recording of the calls of Rousettus aegyptiacus and their reproduction using electrostatic transducers

Bats are capable of imaging their surroundings in great detail using echolocation. To apply similar methods to human engineering systems requires the capability to measure and recreate the signals used, and to understand the processing applied to returning echoes. In this work, the emitted and reflected echolocation signals of Rousettus aegyptiacus are recorded while the bat is in flight, using a wireless sensor mounted on the bat. The sensor is designed to replicate the acoustic gain control which bats are known to use, applying a gain to returning echoes that is dependent on the incurred time delay. Employing this technique allows emitted and reflected echolocation calls, which have a wide dynamic range, to be recorded. The recorded echoes demonstrate the complexity of environment reconstruction using echolocation. The sensor is also used to make accurate recordings of the emitted calls, and these calls are recreated in the laboratory using custom-built wideband electrostatic transducers, allied with a spectral equalization technique. This technique is further demonstrated by recreating multi-harmonic bioinspired FM chirps. The ability to record and accurately synthesize echolocation calls enables the exploitation of biological signals in human engineering systems for sonar, materials characterization and imaging

A medical information system for monitoring respiratory function and related nonlinear dynamics

In this paper the nonlinear effects in the respiratory systems at low frequencies are measured and evaluated in healthy children and healthy adults. To this aim forced oscillations technique (FOT) has been used to non-invasively measure the lung tissue mechanics. FOT does not require any special effort from the patient in contrast with standardized tests where maneuvers are necessary. Hence, FOT is an ideal lung function test for extreme ages, more specifically children and elderly, given the simpleness of measurement technique. Hitherto, measurements at low frequencies (i.e. close to the breathing frequency similar to 0.3 Hz) have been invasively performed in sacrificed animals and on anesthetized humans. Here we measure in the frequency interval 0.1-2 Hz a total number of 94 volunteers (37 adults with ages between 25-35 years and 57 children with ages between 8-11 years). To evaluate the nonlinear contributions of the respiratory tissue, a novel T-index has been introduced. We have tested the hypothesis whether the nonlinear distortions are changing with growth/development of the respiratory tree and aim to quantify its dependence to biometric values. The results obtained indicate that the proposed index can differentiate between the two analyzed groups and that there is a dependence to age, height and weight. A medical information system may use this information to update predictions of respiratory function and provide aid in decision-making process of drug therapy

Model-free Adaptive Control in Frequency Domain: Application to Mechanical Ventilation

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Theoretical analysis and experimental validation of a simplified fractional order controller for a magnetic levitation system

Fractional order (FO) controllers are among the emerging solutions for increasing closed-loop performance and robustness. However, they have been applied mostly to stable processes. When applied to unstable systems, the tuning technique uses the well-known frequency-domain procedures or complex genetic algorithms. This brief proposes a special type of an FO controller, as well as a novel tuning procedure, which is simple and does not involve any optimization routines. The controller parameters may be determined directly using overshoot requirements and the study of the stability of FO systems. The tuning procedure is given for the general case of a class of unstable systems with pole multiplicity. The advantage of the proposed FO controller consists in the simplicity of the tuning approach. The case study considered in this brief consists in a magnetic levitation system. The experimental results provided show that the designed controller can indeed stabilize the magnetic levitation system, as well as provide robustness to modeling uncertainties and supplementary loading conditions. For comparison purposes, a simple PID controller is also designed to point out the advantages of using the proposed FO controller

Mathematical Modeling and Analysis of Asthma Stability and Severity

Asthma is one of the most common chronic conditions in the United States. Asthma affects about one in fifteen people. It affects children more than adults and blacks more than whites. People with asthma experience attacks of wheezing, breathlessness, chest tightness, and coughing. Asthma can be fatal and the costs for the disease (direct and indirect) are approximated to be tens of billions of dollars each year. There is no cure for asthma. However; for most people if asthma is controlled well they can lead normal, active lives. Therefore asthma controllability is a main factor in clinical practice. In order to control asthma, the disease has to be completely understood. Asthma is very heterogeneous and this makes the exact diagnosis and control procedures difficult. To better evaluate and study asthma, mathematical tools can be very beneficial. In this study we first develop a complete system for lung impedance analysis of laboratory models of asthma. Our designed system is capable of precisely diagnosing the diseased models and predicting the severity of their condition. We also evaluate the treatment progress in mouse models of asthma. We then study an asthma database of humans including measurements of four related laboratory parameters and cluster patients based on inherent properties of the study variables. This mathematical approach clustered patients with specific characteristics and segregated the unstable asthmatic patients in a single group. Our method is very promising in predicting the instability of asthma, which is highly correlated with frequent asthma attacks and increased utilization of care

Foldable all-textile cavity-backed slot antennas for personal UWB localization

An all-textile multimoded cavity-backed slot antenna has been designed and fabricated for body-worn impulse radio ultra-wideband (IR-UWB) operation in the 3,744-4,742.4 MHz frequency band, thereby covering Channels 2 and 3 of the IEEE 802.15.4a standard. Its light weight, mechanical flexibility, and small footprint of 35 mm x 56 mm facilitate integration into textile for radio communication equipment for first aid responders, personal locator beacons, and equipment for localization and medical monitoring of children or the elderly. The antenna features a stable radiation pattern and reflection coefficient in diverse operating conditions such as in free space, when subject to diverse bending radii and when deployed on the torso or upper right arm of a test person. The high isolation toward the wearer's body originates from the antenna's hemispherical radiation pattern with a -3 dB beamwidth of 120 degrees and a front-to-back ratio higher than 11 dB over the entire band. Moreover, the antenna exhibits a measured maximum gain higher than 6.3 dBi and a radiation efficiency over 75%. In addition, orientation-specific pulse distortion introduced by the antenna element is analyzed by means of the System Fidelity Factor (SFF). The SFF of the communication link between two instances of this antenna is higher than 94% for all directions within the antenna's -3 dB beamwidth. This easily wearable and deployable antenna is suitable to support IR-UWB localization with an accuracy in the order of 5 cm