A microcontroller-based portable electrocardiograph recorder

We describe a low cost portable Holter design that can be implemented with off-the-shelf components. The recorder is battery powered and includes a graphical display and keyboard. The recorder is capable of acquiring up to 48 hours of continuous electrocardiogram data at a sample rate of up to 250 Hz.     

Modeling of defects,dopant diffusion and clustering in silicon

Ion implantation is a very well established technique to introduce dopants in semiconductors. This technique has been traditionally used for junction formation in integrated circuit processing, and recently also in solar cells fabrication. In any case, ion implantation causes damage in the silicon lattice that has adverse effects on the performance of devices and the efficiency of solar cells. Alternatively, damage may also have beneficial applications as some studies suggest that small defects may be optically active. Therefore it is important an accurate characterization of defect structures formed upon irradiation. Furthermore, the technological evolution of electronic devices towards the nanometer scale has driven the need for the formation of ultra-shallow and low-resistive junctions. Ion implantation and thermal anneal models are required to predict dopants placement and electrical activation. In this article, we review the main models involved in process simulation, including ion implantation, evolution of point and extended defects and dopant-defect interactions. We identify different regimes at which each type of defect is more relevant and its inclusion in the models becomes crucial. We illustrate in some examples the use of atomistic modeling techniques to gain insight into the physics involved in the processes as well as the relevance of the accuracy of models.     

Pulse morphology visualization and analysis with applications in cardiovascular pressure signals

We present a new analysis and visualization method for studying the functional relationship between the pulse morphology of pressure signals and time or signal metrics such as heart rate, pulse pressure, and means of pressure signals, such as arterial blood pressure and central venous pressure. The pulse morphology is known to contain potentially useful clinical information, but it is difficult to study in the time domain without the aid of a tool such as the method we present here. The primary components of the method are established signal processing techniques, nonparametric regression, and an automatic beat detection algorithm. Some of the insights that can be gained from this are demonstrated through the analysis of intracranial pressure signals acquired from patients with traumatic brain injuries. The analysis indicates the point of transition from low-pressure morphology consisting of three distinct peaks to a high-pressure morphology consisting of a single peak. In addition, we demonstrate how the analysis can reveal distinctions in the relationship between morphology and several signal metrics for different patients.     

Interpretation of the Lempel-Ziv complexity measure in the context of biomedical signal analysis

Lempel-Ziv complexity (LZ) and derived LZ algorithms have been extensively used to solve information theoretic problems such as coding and lossless data compression. In recent years, LZ has been widely used in biomedical applications to estimate the complexity of discrete-time signals. Despite its popularity as a complexity measure for biosignal analysis, the question of LZ interpretability and its relationship to other signal parameters and to other metrics has not been previously addressed. We have carried out an investigation aimed at gaining a better understanding of the LZ complexity itself, especially regarding its interpretability as a biomedical signal analysis technique. Our results indicate that LZ is particularly useful as a scalar metric to estimate the bandwidth of random processes and the harmonic variability in quasi-periodic signals.     

Interpretation of approximate entropy: analysis of intracranial pressure approximate entropy during acute intracranial hypertension

We studied changes in intracranial pressure (ICP) complexity, estimated by the approximate entropy (ApEn) of the ICP signal, as subjects progressed from a state of normal ICP (< 20-25 mmHg) to acutely elevated ICP (an ICP "spike" defined as ICP > 25 mmHg for < or = 5 min). We hypothesized that the measures of intracranial pressure (ICP) complexity and irregularity would decrease during acute elevations in ICP. To test this hypothesis we studied ICP spikes in pediatric subjects with severe traumatic brain injury (TBI). We conclude that decreased complexity of ICP coincides with episodes of intracranial hypertension (ICH) in TBI. This suggests that the complex regulatory mechanisms that govern intracranial pressure are disrupted during acute rises in ICP. Furthermore, we carried out a series of experiments where ApEn was used to analyze synthetic signals of different characteristics with the objective of gaining a better understanding of ApEn itself, especially its interpretation in biomedical signal analysis.     

Boron pocket and channel deactivation in nMOS transistors with SPER junctions

In this paper, we demonstrate the consequences of extension junction formation by low-temperature solid-phase-epitaxial-regrowth in nMOS transistors. Atomistic simulations, experimental device results, sheet resistance, and scanning spreading resistance microscopy data indicate that the high concentration of silicon interstitials associated with the end-of-range defect band promote the local formation of boron-interstitial clusters, and thus deactivate boron in the pocket and channel. These inactive clusters will dissolve after the high concentration silicon interstitial region of the end-of-range defect band has been annihilated. This nMOS requirement is in direct opposition to the pMOS case where avoidance of defect band dissolution is desired, to prevent deactivation of the high concentration boron extension profile.     

An automatic beat detection algorithm for pressure signals

Beat detection algorithms have many clinical applications including pulse oximetry, cardiac arrhythmia detection, and cardiac output monitoring. Most of these algorithms have been developed by medical device companies and are proprietary. Thus, researchers who wish to investigate pulse contour analysis must rely on manual annotations or develop their own algorithms. We designed an automatic detection algorithm for pressure signals that locates the first peak following each heart beat. This is called the percussion peak in intracranial pressure (ICP) signals and the systolic peak in arterial blood pressure (ABP) and pulse oximetry (SpO2) signals. The algorithm incorporates a filter bank with variable cutoff frequencies, spectral estimates of the heart rate, rank-order nonlinear filters, and decision logic. We prospectively measured the performance of the algorithm compared to expert annotations of ICP, ABP, and SpO2 signals acquired from pediatric intensive care unit patients. The algorithm achieved a sensitivity of 99.36% and positive predictivity of 98.43% on a dataset consisting of 42,539 beats.     

Adaptive modeling and spectral estimation of nonstationary biomedical signals based on Kalman filtering

We describe an algorithm to estimate the instantaneous power spectral density (PSD) of nonstationary signals. The algorithm is based on a dual Kalman filter that adaptively generates an estimate of the autoregressive model parameters at each time instant. The algorithm exhibits superior PSD tracking performance in nonstationary signals than classical nonparametric methodologies, and does not assume local stationarity of the data. Furthermore, it provides better time-frequency resolution, and is robust to model mismatches. We demonstrate its usefulness by a sample application involving PSD estimation of intracranial pressure signals (ICP) from patients with traumatic brain injury (TBI).     

Comparative analysis of the chemical composition and antioxidant activity of red (Psidium cattleianum) and yellow (Psidium cattleianum var. lucidum) strawberry guava fruit

Abstract: Strawberry guava (Psidium cattleianum Sabine) is a native fruit of Brazil widely consumed fresh and used in the food industry. In this context, the present study deals with the chemical characterization and the antioxidant activity of the red (Psidium cattleianum) and yellow (P. cattleianum var. lucidum Hort.) strawberry guava fruits, cultivars Irapuã and Ya‐Cy, respectively. Knowledge of chemical composition is fundamental to human nutrition, contributing to the quality of foods. Phenolic compounds in both fruits were analyzed by HPLC–DAD and the total flavonoid content was determined by the Folin–Ciocalteu assay. The antioxidant activity was evaluated by the total reactive antioxidant (TRAP) method. Psidium cattleianum presented a higher content of polyphenolic compounds than P. cattleianum var. lucidum (501.33 and 292.03 mg/100 g, respectively), with hyperoside being one of the major flavonoids identified for both cultivars. In addition to flavonoids, P. cattleianum presented an anthocyanin, identified as cyanidin. The antioxidant activity varied in a concentration‐dependent manner for both strawberry guava species. The volatile oils in fruits and fatty acids in seeds were quantified by GC‐EM. The analysis of the essential oil of yellow strawberry guava was compared with a previous study on the red cultivar, revealing β‐caryophyllene as the main component in both oils. The fatty acid composition was also quite similar and was especially characterized by the presence of unsaturated fatty acids (86.25% and 76%, respectively), among which linoleic acid as the most abundant. Practical Application: In this study, the chemical characterization and the antioxidant activity of the red (Psidium cattleianum) and yellow (P. cattleianum var. lucidum Hort.) strawberry guava fruits were investigated. This is important for potential application of strawberry guava as functional food. Moreover, it may be the experimental basis for further development and use in food industry.