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Measurements from sensor networks consisting of thousands of nodes are often correlated, since nearby sensors observe the same phenomenon. Using Compressed Sensing, that data can be reconstructed with a high probability from a small collection of random linear combinations of those measurements. This opens a new approach to simultaneously extract, transmit and distribute information in wireless sensor networks. Efficient communication schemes well matched to compressive sensing are, nonetheless, needed to realize the full benefits of this approach. We present a simple, practical scheme, called NetCompress, using a novel form of Network Coding. It preserves the reconstruction conditions required for Compressed Sensing and also overcomes the high link-failure rate in wireless sensor networks. NetCompress simultaneously transmits packets of sensor measurements and encodes them to form random projections for Compressed Sensing recovery. A recent result in Compressed Sensing guarantees that the data at all nodes can be accurately recovered with a high probability from a small number of projections, which is much less than the total number of nodes in the network. NetCompress demonstrates this result on both the TOSSIM simulation platform and a testbed comprising 20 micaz and tmote sensor nodes. Our experimental results show that the number of packets that is needed to reconstruct light intensity measurements with reasonable quality is just half the number of nodes in the network.

Background— Atrial fibrillation (AF) is the most common sustained arrhythmia observed in otherwise healthy individuals. Most lone AF cases are nonfamilial, leading to the assumption that a primary genetic origin is unlikely. In this study, we provide data supporting a novel paradigm that atrial tissue–specific genetic defects may be associated with sporadic cases of lone AF. Methods and Results— We sequenced the entire coding region of the connexin 43 (Cx43) gene ( GJA1 ) from atrial tissue and lymphocytes of 10 unrelated subjects with nonfamilial, lone AF who had undergone surgical pulmonary vein isolation. In the atrial tissue of 1 patient, we identified a novel frameshift mutation caused by a single nucleotide deletion (c.932delC) that predicted 36 aberrant amino acids followed by a premature stop codon, leading to truncation of the C-terminal domain of Cx43. The mutation was absent from the lymphocyte DNA of the patient, indicating genetic mosaicism. Protein trafficking studies demonstrated intracellular retention of the mutant protein and a dominant-negative effect on gap junction formation of both wild-type Cx43 and Cx40. Electrophysiological studies revealed no electrical coupling of cells expressing the mutant protein alone and significant reductions in coupling when coexpressed with wild-type connexins. Conclusions— This study reports atrial tissue genetic mosaicism of a novel loss-of-function Cx43 mutation associated with lone AF. These findings implicate somatic genetic defects of Cx43 as a potential cause of AF and support the paradigm that sporadic, nonfamilial cases of lone AF may arise from genetic mosaicism that creates heterogeneous coupling patterns, predisposing the tissue to reentrant arrhythmias.

Stochastic computation, as presented in this paper, exploits the statistical nature of application-level performance metrics, and matches it to the statistical attributes of the underlying device and circuit fabrics. Nanoscale circuit fabrics are viewed as noisy communication channels/networks. Communications-inspired design techniques based on estimation and detection theory are proposed. Stochastic computation advocates an explicit characterization and exploitation of error statistics at the architectural and system levels. This paper traces the roots of stochastic computing from the Von Neumann era into its current form. Design and CAD challenges are described.

The Scisense (London, ON, Canada) micro-manometer pressure sensor is currently being used by investigators to evaluate cardiovascular physiology in mice, but has not been validated to date. The purpose of the current study is to compare the 1.2 F Scisense pressure sensor to the current gold standard produced by Millar Instruments (Houston, TX) (1.4 F). In vitro comparisons were preformed including temperature drift, frequency response analysis up to 250 Hz, and damping coefficient and natural frequency determined via a pop test. The authors also performed in vivo comparisons including pressure drift, dose-response studies to IV isoproterenol, maximum adrenergic stimulation with IV dobutamine, and simultaneous placement of both micro-manometer pressure sensors in the same intact murine hearts. The authors conclude that both sensors are equivalent, and that the Scisense pressure sensor represents an alternative to the current gold standard, the Millar micro-manometer pressure sensor for in vivo pressure measurements in the mouse.

The main drawback of Orthogonal Frequency Division Multiplexing (OFDM) systems is the high peak-to-average power ratio (PAPR), which leads to a significant reduction in performance and power efficiency. Tone injection (TI) is a promising PAPR reduction technique that cyclically extends QAM constellations to allow an alternative encoding with lower PAPR at the transmitter. We present a new efficient complex-baseband algorithm which performs TI by using aggressive clipping to combat large peaks. An approximated-analog PAPR reduction of up to 5.1 dB at a 10–5 symbol-clip probability is obtained for 64-channel 16-QAM OFDM. This is a very fast and practical peak-power reduction method for OFDM systems that essentially achieves the same PAPR as single-carrier modulation for large constellations.

The V-BLAST wireless communication architecture, space-time block code (STBC), and space-frequency block code (SFBC) techniques are strong candidates for achieving very high data rates in 4G broadband wireless communications. This paper extends the efficient Active Constellation Extension Smart Gradient-Project (ACE-SGP) peak-to-average power (PAPR) reduction method to STBC, SFBC, and V-BLAST systems. Simulation results show 4.19 and 3.57 dB of PAPR reduction for the Alamouti STBC and SFBC, respectively.

It has recently been demonstrated that both biphasic and sequential pulse defibrillation shocks are superior to monophasic defibrillation shocks in animals and humans. There is little information directly comparing these two waveforms when pulse characteristics, subject, and total electrode surface area are kept constant. Pigs were randomized in a cross-over design for triplicate determinations of defibrillation threshold using biphasic and sequential pulse shocks and both large and small epicardial electrodes. Anesthetized pigs weighing 18 to 28 kg had sets of defibrillating electrodes (TX-7) with total surface areas of 13 cm2 (group 1, n = 16) and 26 cm2 (group 2, n = 16), respectively, attached to the heart. Leading edge delivered voltage, current, and energy were significantly lower with sequential pulse shocks than with biphasic shocks for both electrode sets (delivered energy means +/- standard error of the mean: 13.3 +/- 1.6 versus 22.4 +/- 3.0 joules, and 9.9 +/- 1.5 versus 14.2 +/- 1.6 joules, respectively). In addition, six of the pigs could not be defibrillated with 900 stored V using biphasic shocks, although all pigs were defibrillated with less than 800 stored V using sequential pulse defibrillation. We conclude that sequential pulse defibrillation using three defibrillating electrodes provides an important current delivery system not matched by biphasic shocks using two electrodes when subject, waveform characteristics, and total electrode surface area are kept constant.

Some antiarrhythmic sodium channel blocking drugs have been found to increase the energy necessary for internal defibrillation. Propafenone is a new drug that has been shown to be efficacious in the therapy of supraventricular and ventricular arrhythmias, and is of potential use in patients with defibrillators. The effects of short-term and prolonged propafenone administration on the internal defibrillation threshold (DFT) were determined in 43 pigs randomized to one of four groups: saline infusion (n = 10); propafenone infusion (n = 10); placebo administration for 8 days (n = 10); or propafenone administration for 8 days (n = 13). Two mesh electrodes were sutured on the right lateral and left lateral epicardial surface and current was delivered from the right electrode to the left electrode. Triplicate DFTs were obtained before and at 40 and 80 minutes after infusion of drug or placebo. In pigs receiving long-term administration, after baseline DFTs were obtained the electrodes were removed and the chest was closed. Following 8 days of drug or placebo administration, DFTs were redetermined. No changes were observed in the short- or long-term control groups. DFTs were lower after propafenone administration: either short-term infusion (20 +/- 6.2 joules at baseline; 15.6 +/- 5 joules at 40 minutes, p less than 0.05; 10.2 +/- 6 joules at 80 minutes, p less than 0.001) or long-term administration (17.8 +/- 2.6 joules at baseline versus 12 +/- 3.2 joules on drug, p less than 0.002). Decreased ventricular cycle lengths were found with acute administration of propafenone. Three pigs died during long-term administration of propafenone.(ABSTRACT TRUNCATED AT 250 WORDS)

Frequency-domain techniques have been extensively investigated for the analysis of high-resolution electrocardiograms (ECGs), although the merit of frequency-domain analysis is still subject to controversy. Time-frequency analysis methods, which estimate the frequency content of a signal as a function of time, potentially provide even more information for improved ECG analysis. Some researchers report impressive results in predicting the outcome of electrophysiologic studies using the short-time Fourier transform (spectrogram). Other time-frequency representations, such as the Wigner distribution, short-time spectral estimators, and the wavelet transform, have also been investigated. The authors present a unified overview of time-frequency representations, showing that only four classes characterize most time-frequency representations. The authors describe the advantages and drawbacks of the various approaches and speculate on their promise for ECG analysis. Very preliminary experiments in applying some of these techniques to the prediction of the outcome of electrophysiologic studies have suggested some possible new research directions.

Transpose-form filter structures have several advantages over direct-form structures for high-speed, parallel implementation of finite impulse response (FIR) filters. Transpose-form least mean square (LMS) adaptive filter architectures are often used in parallel implementations; however, the behavior of these filters differs from the standard LMS algorithm and has not been adequately studied. A method for determining the maximum convergence factor yielding convergence of the mean of the transpose-form LMS adaptive filter taps is developed. The analysis reveals the great similarity of transpose-form LMS adaptive filters to delayed-update LMS adaptive filters, which have been much more fully characterized. >

For real-time monitoring of PCR amplification of DNA, quantitative PCR (qPCR) assays use various fluorescent reporters. DNA binding molecules and hybridization reporters (primers and probes) only fluoresce when bound to DNA and result in the non-cumulative increase in observed fluorescence. Hydrolysis reporters (TaqMan probes and QZyme primers) become fluorescent during DNA elongation and the released fluorophore remains fluorescent during further cycles; this results in a cumulative increase in observed fluorescence. Although the quantification threshold is reached at a lower number of cycles when fluorescence accumulates, in qPCR analysis no distinction is made between the two types of data sets. Mathematical modeling shows that ignoring the cumulative nature of the data leaves the estimated PCR efficiency practically unaffected but will lead to at least one cycle underestimation of the quantification cycle (C(q) value), corresponding to a 2-fold overestimation of target quantity. The effect on the target-reference ratio depends on the PCR efficiency of the target and reference amplicons. The leftward shift of the C(q) value is dependent on the PCR efficiency and with sufficiently large C(q) values, this shift is constant. This allows the C(q) to be corrected and unbiased target quantities to be obtained.

Male frogs and toads call in dense choruses to attract females. Determining the vocal interactions and spatial distribution of the callers is important for understanding acoustic communication in such assemblies. It has so far proved difficult to simultaneously locate and recover the vocalizations of individual callers. Here a microphone-array technique is developed for blindly locating callers using arrival-time delays at the microphones, estimating their steering-vectors, and recovering the calls with a frequency-domain adaptive beamformer. The technique exploits the time-frequency sparseness of the signal space to recover sources even when there are more sources than sensors. The method is tested with data collected from a natural chorus of Gulf Coast toads (Bufo valliceps) and Northern cricket frogs (Acris crepitans). A spatial map of locations accurate to within a few centimeters is constructed, and the individual call waveforms are recovered for nine individual animals within a 9 x 9 m(2). These methods work well in low reverberation when there are no reflectors other than the ground. They will require modifications to incorporate multi-path propagation, particularly for the estimation of time-delays.

Weakly electric fish have the ability to navigate and locate prey in the dark using a unique weak electrosense system. Imitating that ability of electric fish, we develop an electric-field sensing system capable of high-resolution imaging of the surrounding environment, by use of a novel beamforming technique that exploits the sparsity of sources in a scanned space. Both simulation and experimental results show that the sparse beamforming technique accurately images not only a single object but also multiple objects with highly correlated signals.

Load sequence effects on composite material fatigue behavior are due to the difference in residual strength when fatigue occurs, or the 'boundary effect', and the 'material money effect' due to previous loads. The present model, which allows the isolation of the effects of memory from those of boundary, has been investigated through a test program for the case of /+, -35/2s graphite/epoxy laminates under high-low and low-high load sequences which generated statistical residual strength data. As predicted by the model, the memory effect is present and a good correlation is obtained between test results and the theoretical predictions for both median residual strength and the expected percentage of fatigue failures under dual loading. It is noted, however, that the statistical dispersion of the residual strength test results is much smaller than that of the static ultimate strength.

This work evaluates the peak-to-average power ratio (PAPR) performance in a coded orthogonal frequency-division multiplexing (C-OFDM) system using the selective mapping (SLM) approach. Repetition-coded side-information (SI) bits specifying which one of several possible phase sequences is being used are embedded in the data stream at the transmitter before convolutional coding, interleaving, and QAM mapping are applied to the bitstream. The receiver demodulates the received signal using all the possible phase sequences, and then uses the demodulator output in which the demodulated coded SI bits are closest in Hamming distance to the coded SI bits specifying the phase sequence used in that demodulation. It is found that when the number of available phase sequences is four, eight or sixteen, the best performance is obtained when each SI bit is repeated from four to eight times. Our simulation results show that the proposed side-information-embedded SLM C-OFDM system is effective in reducing PAPR.

Minimally invasive beating heart intracardiac surgery is an area of research with many unique challenges. Surgical targets are in constant motion in a blood-filled environment that prevents direct line-of-sight guidance. The restrictive workspace requires compact, yet robust tools for proper therapy delivery. Our novel method for approaching multiple targets inside the beating heart allows their identification and access under augmented reality-assisted image guidance. The surgical platform integrates real-time ultrasound imaging with virtual models of the surgical instruments, along with virtual cardiac anatomy acquired from pre-operative images. Extensive in vitro studies were performed to assess the operator's ability to "deliver therapy" to dynamic intracardiac targets via both transmural and transluminal access, and demonstrated significantly more accurate targeting under augmented reality guidance compared to ultrasound image guidance alone, accompanied by a reduction of procedure time by half. Moreover, preliminary in vivo acute studies on porcine models showed successful prosthesis positioning for beating-heart septal defect repair and mitral valve implantation via direct surgical access. While still in its infancy, this work emphasizes the promise of ultrasound-enhanced model-guided environments for minimally-invasive cardiac therapy, whether delivered via a catheter introduced into the vascular system or a cannula inserted through the heart wall.

The high peak-to-average power ratio (PAPR) of orthogonal frequency multiplexing (OFDM) greatly reduces the transmitter power efficiency. We propose a method that yields significant and consistent PAPR reductions for all numbers of users (receivers) in a beamforming MISOOFDM system, such as WiMAX, by simultaneously exploiting the degrees of freedom in the constellation domain and in the null-space of the channel matrix. We also provide an efficient algorithm that is compatible with various constellation configurations in practical systems. With no sacrifice in data rate or channel efficiency, the proposed method achieves a maximum of 6.59 dB and a minimum of 2.11 dB PAPR reduction in an 8-antenna QPSK beamforming MISO-OFDM scenario.

Some antiarrhythmic drugs may influence the ability of a shock to defibrillate a patient but the effect of lidocaine on defibrillation efficacy has been controversial, suggesting multiple influencing factors. We determined the effects of three doses of lidocaine on defibrillation thresholds, using single and sequential shocks, in 36 open chest halothane-anesthetized pigs. An additional eight pigs were anesthetized with barbiturate and received the highest infusion regime of lidocaine. Shocks were delivered through three mesh electrodes sutured over the anterior right ventricle, posterior right ventricle, and lateral left ventricle for sequential pulse shocks and between a lateral right to a lateral left ventricular mesh electrode for single pulse shocks. Triplicate defibrillation thresholds (DFTs) were obtained before and after lidocaine (n = 32) or saline (n = 12) administration, either with halothane or barbiturate anesthesia. Lidocaine did not alter DFT at any dose with either the single pulse (control 17.4 +/- 3.7 joules [J], highest dose of lidocaine 13.5 +/- 1.7 J, P = NS) or sequential pulse shocks (control 7.6 +/- 0.8 J, highest dose lidocaine 6.6 +/- 0.7 J, P = NS), when halothane anesthesia was used. Similar results were obtained with lower doses. In contrast, lidocaine in pentobarbital anesthetized pigs produced a significant increase of the DFT with single (control 13.7 +/- 1.9, during lidocaine 16.6 +/- 3.1, P less than 0.01) and sequential shocks (control 11.1 +/- 2.2, during lidocaine 14.5 +/- 3.4, P less than 0.01). Interaction between barbiturates and lidocaine, and/or pH may account for the inconsistency in previous studies and must be considered for animal and clinical experiments.

A bus-oriented multiprocessor architecture specialized for computation of the discrete Fourier transform (DFT) of a length N=2/sup M/ sequential data stream is developed. The architecture distributes computation and memory requirements evenly among the processors and allows flexibility in the number of processors and in the choice of a fast Fourier transform (FFT) algorithm. With three buses, the bus bandwidth equals the input data rate. A single time-multiplexed bus with a bandwidth of three times the input data rate can alternatively be used. The architecture requires processors that have identical hardware, which makes it more attractive than the cascade (pipeline) FFT for multiprocessor implementation. >

Our project is the reintroduction of off-pump intracardiac surgery using the Universal Cardiac Introducer (UCI) for safe intracardiac access. The purpose of this study was to evaluate multimodality visualization using three ultrasound modalities and ultrasound augmented with virtual reality. Image guidance was tested on implanting a mitral valve prosthesis via the UCI in 12 pigs. Initially, two-dimensional (2-D) transesophageal echocardiography (TEE) ultrasound, intravascular ultrasound (intracardiac echocardiography [ICE]), and three-dimensional (3-D) epicardial ultrasound were utilized. Ultrasound augmented with virtual reality was used in the last three experiments. A 2-D TEE assisted navigating the prosthesis into the orifice. Positioning was not intuitive and required trial and error method. A 3-D epicardial ultrasound allowed positioning of the valve into the orifice. Positioning of the clip was difficult because of artifacts with multiple reflections and shadowing. Augmented reality displayed the entire prosthesis and the tools without artifacts; provided intuitive information on navigation, positioning, and orientation of tools; and improved significantly image guidance and surgical skill. Augmented virtual reality, with tracked 2-D or 3-D ultrasound imaging, provides guidance that can effectively substitute for direct vision during beating heart intracardiac surgery.

We address the issue of improving information availability in a class of delay-tolerant sensor network applications, where the sensor nodes are deployed in disconnected environments. In such environments, since there is no continuous access to a remote base station, there is a need to leverage the collaborative resources of the sensor network to support in-network storage. The stored data can then be retrieved opportunistically by mobile collectors in the proximity. We have developed a data-centric, in-network storage architecture that partitions the network into storage zones. In such a scheme, some of the storage nodes may be unavailable at the time of storage and retrieval, because they are either sleeping to conserve energy or because they have failed.We present two schemes based on random linear network coding for improving information availability within such a storage architecture. In the centralized scheme, the encoding is performed by the managers in each storage zone, whereas in the decentralized scheme, the encoding is done locally by the zone members. We have implemented the network coding schemes in TinyOS and we present results that show the impact of the zone size, duty cycle, and the degree of encoding on the decoding probability, based on our experiments on a testbed of Micaz motes.

We have developed a visualization environment to assist surgeons with therapy delivery inside the beating heart, in absence of direct vision. This system employs virtual reality techniques to integrate pre-operative anatomical models, real-time intra-operative imaging, and models of magnetically-tracked surgical tools. Visualization is enhanced via 3D dynamic cardiac models constructed from high-resolution pre-operative MR or CT data and registered within the intra-operative imaging environment. In this paper, we report our experience with a feature-based registration technique to fuse the pre- and intra-operative data during an in vivointracardiac procedure on a porcine subject. Good alignment of the pre- and intra-operative anatomy within the virtual reality environment is ensured through the registration of easily identifiable landmarks. We present our initial experience in translating this work into the operating room and employing this system to guide typical intracardiac interventions. Given its extensive capabilities in providing surgical guidance in the absence of direct vision, our virtual environment is an ideal candidate for performing off-pump intracardiac interventions.

The stochastic sensor network-on-chip (SSNOC) was recently proposed as an effective computational paradigm for jointly achieving energy-efficiency and robustness in nanoscale processes. In this paper, we study the trends in energy-efficiency and robustness exhibited by an SSNOC architecture as the feature size scales from 130nm to 32nm for a PN-code acquisition application. The conventional architecture exhibits a 3 orders-of-magnitude loss in detection probability P_{det} due to process variations in the 130nm and smaller technology nodes. At the 130nm and 90nm nodes, the proposed SSNOC architecture recovers from this performance loss, and exhibits a 2 orders-of-magnitude smaller variation in P_det compared to the conventional architecture. However, for the 65nm and 45nm technology nodes, the SSNOC architecture with assistance from circuit level techniques such as adaptive body bias (ABB) and adaptive supply voltage (ASV) shows a 2-3 order-of-magnitude better detection performance. In addition, the SSNOC architecture with ABB/ASV achieves 22% to 31% energy savings. For the 32nm node, the current version of SSNOC with ABB/ASV is not robust enough and thus motivates the need to explore even more powerful versions of SSNOC.

Presented in this paper is an energy-efficient and variation-tolerant PN-code acquisition architecture for the wireless CDMA2000 standard. The architectures is based on the recently proposed stochastic sensor network-on-chip (SSNOC) computational paradigm. The latter employs the principles of statistically similar decomposition and robust estimation theory to compensate for timing errors due to process variations. Performance of the SSNOC-based PN-code acquisition architecture at the slow process corner indicates that the average probability of detection PDet improves by up to 3 orders-of-magnitude over that of the conventional architecture, while the variation in PDet(sigma / mu) is reduced by up to 2 orders-of-magnitude over that of the conventional architecture while simultaneously achieving a power reduction of 39%.

Direction finding of more sources than sensors is appealing in situations with small sensor arrays. Potential applications include surveillance, teleconferencing, and auditory scene analysis for hearing aids. A new technique for time-frequency-sparse sources, such as speech and vehicle sounds, uses a coherence test to identify low-rank time-frequency bins. These low-rank bins are processed in one of two ways: (1) narrowband spatial spectrum estimation at each bin followed by summation of directional spectra across time and frequency or (2) clustering low-rank covariance matrices, averaging covariance matrices within clusters, and narrowband spatial spectrum estimation of each cluster. Experimental results with omnidirectional microphones and colocated directional microphones demonstrate the algorithm's ability to localize 3-5 simultaneous speech sources over 4 s with 2-3 microphones to less than 1 degree of error, and the ability to localize simultaneously two moving military vehicles and small arms gunfire.

Aims: Heart failure (HF) is a major cause of death and morbidity. Connexin 43 (Cx43) content is reduced in the failing myocardium, but regulating factors have not been identified. In HF, inducible nitric oxide synthase (iNOS)-induced high levels of nitric oxide (NO) cause apoptosis and cardiac dysfunction. However, a direct iNOS–Cx43 link has not been demonstrated. We investigated this relationship in mice after myocardial infarction. Methods: Effects of myocardial infarction were evaluated 2 weeks after coronary artery ligation in wild-type C57BL/6 (WT) and iNOS−/− knockout mice. Myocardial Cx43 and Cx45 content were assessed by immunofluorescence confocal imaging and western blotting. Cardiac function was evaluated in anaesthetized mice using a micro pressure-tipped catheter inserted into the left ventricle. Results: Despite similar infarct size, deficiency in iNOS resulted in significantly lower plasma nitrate/nitrite levels, better haemodynamic performance and lower mortality 2 weeks after coronary ligation. Myocardial Cx43, but not Cx45, content was lower in WT mice following ligation. The reduction in Cx43 was less in iNOS−/− compared with WT mice. To assess the direct effect of NO on Cx43 expression, cultured neonatal mouse cardiomyocytes were employed. Incubation with the NO donor, S-nitroso-N-acetylpenicillamine, elicited a dose-dependent decrease in Cx43 content in cultured neonatal cardiomyocytes. Conclusions: Increased NO production from iNOS depressed cardiac performance and contributed to the decreased myocardial Cx43 content 2 weeks after myocardial infarction.

As part of an ongoing theme in our laboratory on reducing morbidity during minimally-invasive intracardiacprocedures, we developed a computer-assisted interventi on system that provides safe access inside the beatingheart and sucient visualization to deliver therapy to intracardiac targets while maintaining the ecacy of theprocedure. Integrating pre-operative information, 2D trans-esophageal ultrasound for real-time intra-operativeimaging, and surgical tool tracking using the NDI Aurora TM magnetic tracking system in an augmented virtualenvironment, our system allows the surgeons to navigate instruments inside the heart in spite of the lack ofdirect target visualization. This work focuses on further enhancing intracardiac visualization and navigation bysupplying the surgeons with detailed 3D dynamic cardiac models constructed from high-resolution pre-operativeMR data and overlaid onto the intra-operative imaging environment. Here we report our experience during an invivo porcine study. A feature-based registration technique previously explored and validated in our laboratorywas employed for the pre-operative to intra-operative mapping. This registration method is suitable for invivo interventional applications as it involves the selection of easily identi“able landmarks, while ensuring a goodalignment of the pre-operative and intra-operative surgical targets. The resulting augmented reality environmentfuses the pre-operative cardiac model with the intra-operative real-time US images with approximately 5 mmaccuracy for structures located in the vicinity of the valvular region. Therefore, we strongly believe that ouraugmented virtual environment signi“cantly enhances intracardiac navigation of surgical instruments, while on-target detailed manipulations are performed under real-time US guidance.Keywords: Image-Guided Cardiac Procedures, Pre-operative Modeling, Intra-operative Imaging, AugmentedVirtual Reality, Data Integration for the Clinic/OR.

Modern integrated circuits (ICs) are designed as massively parallel systems as a consequence of diminishing silicon feature sizes. This has adversely impacted reliability because of increased errors due to process and environmental variations, and particle hits. Viewing hardware errors as analogous to measurement or system noise allows us to borrow results from estimation theory and extend Moore's law. The estimation-theoretic framework provides a design optimization formalization that enables power/reliability trade-off in broad classes of applications. Two applications described here show that specific instantiations of the framework yield significant power savings and system reliability.

An interventional system for minimally invasive cardiac surgery was developed for therapy delivery inside the beating heart, in absence of direct vision. A system was developed to provide a virtual reality (VR) environment that integrates pre-operative imaging, real-time intra-operative guidance using 2D trans-esophageal ultrasound, and models of the surgical tools tracked using a magnetic tracking system. Detailed 3D dynamic cardiac models were synthesized from high-resolution pre-operative MR data and registered within the intra-operative imaging environment. The feature-based registration technique was employed to fuse pre- and intra-operative data during in vivo intracardiac procedures on porcine subjects. This method was found to be suitable for in vivo applications as it relies on easily identifiable landmarks, and hence, it ensures satisfactory alignment of pre- and intra-operative anatomy in the region of interest (4.8 mm RMS alignment accuracy) within the VR environment. Our initial experience in translating this work to guide intracardiac interventions, such as mitral valve implantation and atrial septal defect repair demonstrated feasibility of the methods. Surgical guidance in the absence of direct vision and with no exposure to ionizing radiation was achieved, so our virtual environment constitutes a feasible candidate for performing various off-pump intracardiac interventions.

Electrodes were developed for use in a wireless data-sharing system between hearing aids. Electrodes were placed on the outsides of custom-fit, in-the-ear (ITE) and one-size-fits-all behind-the-ear (BTE) hearing aid shells. Impedance mesurements and gains were collected for six electrode-pair configurations at 21.5, 64.8, 128.3, and 2164.4 MHz for multiple subjects. Electrodes were coated with a standard hearing aid lacquier or with Galxyl-parylene. Preliminary comparisons of impedence values of similar electrodes inserted in subjects' ears showed that for each design, impedance values were fairly constant for all subjects, so mismatch loss variation is not significant across the range of impedances obtained for different subjects. Thus a standard impedance can be chosen for ease of manufacturing hearing aids using this technology. Transducer losses across subjects' heads were generally between 60 and 80 dB at all tested frequencies, but were lower at higher frequencies.

A simple approach to the calculation of dose in cone-collimated electron fields is presented. The method accounts for variations in lateral scatter with field size using a Clarkson Integration. The reduction in output by an irregularly shaped aperture is evaluated based on measurements of the output at various distances from the aperture in a field 2.5 cm in diameter. The first 14 months of clinical use were analysed and it is shown that in 42 out of 600 calculations, the cutout factor was less than 0.95 and that in 77% of these, the calculation method was accurate to ±3%.

Sensor networks provide a convenient way of estimating diffuse fields, but deployment issues and inaccurate clock synchronization may introduce randomness in their behavior. Recently, asynchronous sensor networks (ASN) comprising uncoordinated and randomly placed nodes, have been shown to sustain quasi-stable communication. In order to conserve energy, it is desirable to reduce the number of samples to a minimum. The theory of compressive sensing offers methods of recovering sparse signals from a small set of random measurements. We show that the random space-time sampling in an ASN provides the additional advantage of satisfying the properties required for compressive sensing.

In this paper, we present the sensor network-on-a-chip (SNOC) paradigm for designing robust and energy-efficient systems-on-a-chip (SOC). In this paradigm, computation in the presence of nanometer non-idealities such as process variations, leakage and noise is viewed as an estimation problem. Robust statistical signal processing theory is then employed to recover the performance of the system in the presence of errors especially timing errors. We apply this framework to design an energy-efficient and robust PN-code acquisition system for the wireless CDMA2000 standard. Simulations in IBM's 130 nm CMOS process technology demonstrate up to 30% power savings compared to the conventional architecture for a detection probability of PD = 0.5.

Algorithmic noise tolerance (ANT) techniques have reduced power consumption in many signal-processing applications, but they typically require an error-free estimator block and do not fully exploit the statistical nature of timing errors. By approaching certain computations as estimation problems, we draw inspiration from sensor networks and develop a novel power conservation scheme in which the main computation result is estimated from multiple potentially erroneous sub-computations. The sub-computations are performed by ";sensors"; and a ";fusion center"; acts as a robust estimator. This scheme is shown to offer significant power savings in a PN code acquisition application.

We have developed the Universal Cardiac Introducer (UCI) with the aim of modernizing the off-pump, closed, beating, intracardiac approach. This paper reports our ongoing experience with positioning of a prosthetic MV, under image-guidance, substituting for direct vision. The UCI is comprised of two detachable parts: an attachment-cuff and an airlock-introductory chamber for bulky tools. A prosthetic MV was introduced into the left atrium in 12 pigs via the UCI (LA appendage). Transesophageal and 4D epicardial ultrasound were used for guidance. Limitations of ultrasound imaging prompted the development of a multimodality virtual reality (VR) system introduced in the last three animals. There were no complications associated with cardiac access, while achieving proper valve positioning. TEE contributed to navigating, while 4D epicardial ultrasound was adequate for positioning the prosthesis into the MV orifice. VR provided a 3D context for real-time US imaging with precise navigation and positioning using augmented reality representation of the valve. We demonstrated the feasibility of positioning MV prostheses via the UCI. These results suggest the tremendous potential of virtual reality in making access safe and effective for many intracardiac targets, with the ultimate goal of a safe, versatile, clinical application.

FastICA is a widely-used independent component analysis technique for blindly separating mixtures of instantaneouslymixed, independent sources recorded with multiple sensors. When using FastICA to estimate one source in interference, the unbiased mean-squared error can be bounded from above by the Schniter-Tong bounds on Shalvi-Weinstein estimators. We derive tighter upper bounds by extending both the Schniter-Tong proof and the Schniter-Johnson proof of upper bounds on constant-modulus estimators. These tighter bounds also exist over a wider range of sources and channels; existence gaps of over an order of magnitude of minimum-mean-squared error have been observed.

In an effort to reduce morbidity during minimally- invasive cardiac procedures, we have recently developed an interventional technique targeted towards off-pump cardiac interventions. To compensate for the absence of direct visualization, our system employs a virtual reality environment for image guidance, that integrates pre-operative information with real-time intra-operative imaging and surgical tool tracking. This work focuses on enhancing intracardiac visualization and navigation by overlaying pre-operative cardiac models onto the intra-operative virtual space, to display surgical targets within their specific anatomical context. Our method for integrating pre-operative data into the intra-operative environment is accurate within ~5.0 mm. Thus, we feel that our virtually-augmented surgical space is accurate enough to improve spatial orientation and intracardiac navigation.

Two reasons for the recent rise in radiation exposure from CT are increases in its clinical applicability and the desire to maintain high SNR while acquiring smaller voxels. To address this emerging dose problem, several strategies for reducing patient exposure have already been proposed. One method employed in cardiac imaging is ECG-driven modulation of the tube current between 100% at one time point in the cardiac cycle and a reduced fraction at the remaining phases. In this paper, we describe how images obtained during such acquisition can be used to reconstruct 4D data of consistent high quality throughout the cardiac cycle. In our approach, we assume that the middiastole (MD) phase is imaged with full dose. The MD image is then independently registered to lower dose images (lower SNR) at other frames, resulting in a set of transformations. Finally, the transformations are used to warp the MD frame through the cardiac cycle to generate the full 4D image. In addition, the transformations may be interpolated to increase the temporal sampling or to generate images at arbitrary time points. Our approach was validated using various data obtained with simulated and scanner-implemented dose modulation. We determined that as little as 10% of the total dose was required to reproduce full quality images with a 1 mm spatial error and an error in intensity values on the order of the image noise. Thus, our technique offers considerable dose reductions compared to standard imaging protocols, with minimal effects on the quality of the final data.

Minimally invasive techniques for use inside the beating heart, such as mitral valve replacement and septal defect repair, are the focus of this work. Traditional techniques for these procedures require an open chest approach and a cardiopulmonary bypass machine. New techniques using port access and a combined surgical guidance tool that includes an overlaid two-dimensional ultrasound image in a virtual reality environment are being developed. To test this technique, a cardiac phantom was developed to simulate the anatomy. The phantom consists of an acrylic box filled with a 7% glycerol solution with ultrasound properties similar to human tissue. Plate inserts mounted in the box simulate the physical anatomy. An accuracy assessment was completed to evaluate the performance of the system. Using the cardiac phantom, a 2mm diameter glass toroid was attached to a vertical plate as the target location. An elastic material was placed between the target and plate to simulate the target lying on a soft tissue structure. The target was measured using an independent measurement system and was represented as a sphere in the virtual reality system. The goal was to test the ability of a user to probe the target using three guidance methods: (i) 2D ultrasound only, (ii) virtual reality only and (iii) ultrasound enhanced virtual reality. Three users attempted the task three times each for each method. An independent measurement system was used to validate the measurement. The ultrasound imaging alone was poor in locating the target (5.42 mm RMS) while the other methods proved to be significantly better (1.02 mm RMS and 1.47 mm RMS respectively). The ultrasound enhancement is expected to be more useful in a dynamic environment where the system registration may be disturbed.

Clinical research has been rapidly evolving towards the development of less invasive surgical procedures. We recently embarked on a project to improve intracardiac beating heart interventions. Our novel approach employs new surgical technologies and support from image-guidance via pre-operative and intra-operative imaging (i.e. two-dimensional echocardiography) to substitute for direct vision. Our goal was to develop a versatile system that allowed for safe cardiac port access, and provide sufficient image-guidance with the aid of a virtual reality environment to substitute for the absence of direct vision, while delivering quality therapy to the target. Specific targets included the repair and replacement of heart valves and the repair of septal defects. The ultimate objective was to duplicate the success rate of conventional open-heart surgery, but to do so via a small incision, and to evaluate the efficacy of the procedure as it is performed. This paper describes the software and hardware components, along with the methodology for performing mitral valve replacement as one example of this approach, using ultrasound and virtual tool models to position and fasten the valve in place.

We present results from a new Interagency Language Roundtable (ILR) based comprehension test. This new test design presents questions at multiple ILR difficulty levels within each document. We incorporated Arabic machine translation (MT) output from three independent research sites, arbitrarily merging these materials into one MT condition. We contrast the MT condition, for both text and audio data types, with high quality human reference Gold Standard (GS) translations. Overall, subjects achieved 95% comprehension for GS and 74% for MT, across 4 genres and 3 difficulty levels. Surprisingly, comprehension rates do not correlate highly with translation error rates, suggesting that we are measuring an additional dimension of MT quality. We observed that it takes 15% more time overall to read MT than GS.

By mimicking fish lateral lines and fish sensing behaviors, we constructed an artificial lateral line and employed it for biomimetic flow sensing. Thirteen hot-film anemometers were mounted to the surface of a NACA0015 airfoil to constitute the artificial lateral line. The resulting fish-like platform was maneuvered by a 3-degree-of-freedom robotic arm for two-dimensional mobility in aquatic environments. Assisted with specially developed algorithms, two biologically relevant flow-sensing scenarios have been realized. They were tracking a nearby dipole source in still water by detecting the dipole flow field and tracking a distant stationary source in running water by detecting its hydrodynamic wake.Copyright © 2007 by ASME

Biologists have reported that fish form sensory maps to assist in the imaging of flow disturbances underwater, including those created by predator or prey, using the lateral-line flow-sensing system. Our group has invented artificial lateral-line systems based on both micromachined and commercial hot-wire anemometer sensors. In this paper, we report on the successful application of adaptive beamforming (Capon's method), in conjunction with an artificial lateral line, to visualize flow disturbances, including acoustic dipoles, underwater. Our preliminary results showcase, for the first time, an ability to image an entire region underwater using micro and millimeter scale arrays, thereby mimicking the flow-imaging abilities of fish.

In some chorusing frog species, such as the green treefrog (Hyla cinerea), males can rapidly adjust call-timing with reference to neighbors and avoid acoustic interference while maintaining call-rate. The rules underlying vocal interactions are largely unknown, presumably being species-specific and governed by acoustic and physiological factors. Here, we use a microphone-array technique that can simultaneously localize callers and selectively extract the calls of each frog. This allows us to analyze vocal interactions between individual callers at high spatial and temporal resolutions. We show that green treefrogs can synchronize with one another and prefer to time their calls antiphonally that are on average exactly at one-third and two-thirds of the inter-call intervals of a focal neighbor. When antiphonal calling is not possible, call collision is tolerated even though a continuum of phase positions are available. The communication system in green treefrogs is thus “discrete” with callers capable of rapidly switching between the discrete phase-slots (0, 1/3, and 2/3) in response to changes in a neighbor’s phase. Further, call collision increases and phase-locking decreases, with increasing inter-caller spacing. We conclude that the vocal communication system in green treefrogs is capable of robust maintenance of inter-caller timing so as to maintain chorus synchrony.

An array of whiskers is critical to many mammals to survive in their environment. However, current engineered systems generally employ vision, radar or sonar to explore the surroundings, not having sufficiently benefited from tactile perception. Inspired by the whisking animals, we present here a novel tomography-based tactile fluid-flow imaging technique for the reconstruction of surroundings with an artificial whisker array. The moment sensed at the whisker base is the weighted integral of the drag force per length, which is proportional to the relative velocity squared on a whisker segment. We demonstrate that the 2D cross-sectional mean fluid-flow velocity-field can be successfully mapped out by collecting moment measurements at different angular positions with the whisker array. We use a regularized version of the FOCal underdetermined system solver algorithm with a smoothness constraint to obtain soft-sparse static estimates of the 2D cross-sectional velocity-squared distribution. This new proposed approach has the strong potential to be an alternative environmental sensing technology, particularly in dark or murky environments.

The constant modulus algorithm (CMA), a popular method for performing blind equalization, has the drawback of failing when the input data has a Gaussian distribution or a kurtosis larger than three. This means that source shaping (which is used to increase the shaping gain) can produce data unequalizable by CMA and other important blind equalization techniques. This paper proposes a simple extension of CMA that blindly equalizes many types of shaped constellations, including those shaped by shell mapping.

We present highlights from three experiments that test the readability of current state-of-the art system output from: (1) an automated English speech-to-text (SST) system; (2) a text-based Arabic-to-English machine translation (MT) system; and (3) an audio-based Arabic-to-English MT process. We measure readability in terms of reaction time and passage comprehension in each case, applying standard psycholinguistic testing procedures and a modified version of the standard defense language proficiency test for Arabic called the DLPT*. We learned that: (1) subjects are slowed down by about 25% when reading system STT output; (2) text-based MT systems enable an English speaker to pass Arabic Level 2 on the DLPT*; and (3) audio-based MT systems do not enable English speakers to pass Arabic Level 2. We intend for these generic measures of readability to predict performance of more application-specific tasks.

This work presents results towards realizing a flexible multimodal tactile sensing system for object identification. Using polymer substrates and simple fabrication, robust devices are made that can identify objects based on texture, temperature, as well as material properties such as hardness and thermal conductivity. These capabilities are possible using signal processing techniques and physical models along with individual sensing structures inspired by the specialization found in biological skin. These structures are used to sense various object parameters, and array-wide processing to identify texture using a Maximum Likelihood decision rule. 80% texture classification is achieved. In blind object identification tests, over 90% correct identification was achieved by measurement of material properties.

Little brown bats, Myotis lucifugus, are known for their ability to echolocate and utilize their echolocation system to navigate, and locate and identify prey. Their echolocation signals have been characterized in detail but their communication signals are less well understood despite their widespread use during social interactions. The goal of this study was to develop an automatic classification algorithm for characterizing the communication signals of little brown bats. Sound recordings were made overnight on five individual male bats (housed separately from a large group of captive bats) for 7 nights, using a bat detector and a digital recorder. The spectral and temporal characteristics of recorded sounds were first analyzed and classified by visual observation of a call’s temporal pattern and spectral composition. Sounds were later classified using an automatic classification scheme based on multivariate statistical parameters in MATLAB. Human- and machine-based analysis revealed five discrete classes of bat’s communication signals: downward frequency-modulated calls, steep frequency-modulated calls, constant frequency calls, broadband noise bursts, and broadband click trains.

A modern DSP laboratory course should teach students how to quickly develop efficient applications using a mixture of C and assembly instructions. Since typical irregular DSP microprocessor architectures present some challenges to traditional optimizing compilers, we introduced a novel new interactive optimizing compiler, VISTA, in a DSP laboratory course to teach students about optimizing compilers and the trade-offs between code development in C and assembly. Students generally found VISTA educational and gained improved insight into effective DSP software development.