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information technology [keywords]
- Ensemble Manifold Rank Preserving for Acceleration-Based Human Activity Recognition. [JOURNAL ARTICLE]
- IEEE Trans Neural Netw Learn Syst 2014 Sep 25.
With the rapid development of mobile devices and pervasive computing technologies, acceleration-based human activity recognition, a difficult yet essential problem in mobile apps, has received intensive attention recently. Different acceleration signals for representing different activities or even a same activity have different attributes, which causes troubles in normalizing the signals. We thus cannot directly compare these signals with each other, because they are embedded in a nonmetric space. Therefore, we present a nonmetric scheme that retains discriminative and robust frequency domain information by developing a novel ensemble manifold rank preserving (EMRP) algorithm. EMRP simultaneously considers three aspects: 1) it encodes the local geometry using the ranking order information of intraclass samples distributed on local patches; 2) it keeps the discriminative information by maximizing the margin between samples of different classes; and 3) it finds the optimal linear combination of the alignment matrices to approximate the intrinsic manifold lied in the data. Experiments are conducted on the South China University of Technology naturalistic 3-D acceleration-based activity dataset and the naturalistic mobile-devices based human activity dataset to demonstrate the robustness and effectiveness of the new nonmetric scheme for acceleration-based human activity recognition.
- Modulation depth estimation and variable selection in state-space models for neural interfaces. [JOURNAL ARTICLE]
- IEEE Trans Biomed Eng 2014 Sep 26.
Rapid developments in neural interface technology are making it possible to record increasingly large signal sets of neural activity. Various factors such as asymmetrical information distribution and across-channel redundancy may, however, limit the benefit of high-dimensional signal sets, and the increased computational complexity may not yield corresponding improvement in system performance. High-dimensional system models may also lead to overfitting and lack of generalizability. To address these issues, we present a generalized modulation depth measure using the state-space framework that quantifies the tuning of a neural signal channel to relevant behavioral covariates. For a dynamical system, we develop computationally efficient procedures for estimating modulation depth from multivariate data. We show that this measure can be used to rank neural signals and select an optimal channel subset for inclusion in the neural decoding algorithm. We present a scheme for choosing the optimal subset based on model order selection criteria. We apply this method to neuronal ensemble spike-rate decoding in neural interfaces, using our framework to relate motor cortical activity with intended movement kinematics. With offline analysis of intracortical motor imagery data obtained from individuals with tetraplegia using the BrainGate neural interface, we demonstrate that our variable selection scheme is useful for identifying and ranking the most information-rich neural signals. We demonstrate that our approach offers several orders of magnitude lower complexity but virtually identical decoding performance compared to greedy search and other selection schemes. Our statistical analysis shows that the modulation depth of human motor cortical single-unit signals is well characterized by the generalized Pareto distribution. Our variable selection scheme has wide applicability in problems involving multisensor signal modeling and estimation in biomedical engineering systems.
- Systematic review and modelling of the cost-effectiveness of cardiac magnetic resonance imaging compared with current existing testing pathways in ischaemic cardiomyopathy. [JOURNAL ARTICLE]
- Health Technol Assess 2014 Sep; 18(59):1-120.
Cardiac magnetic resonance imaging (CMR) is increasingly used to assess patients for myocardial viability prior to revascularisation. This is important to ensure that only those likely to benefit are subjected to the risk of revascularisation.To assess current evidence on the accuracy and cost-effectiveness of CMR to test patients prior to revascularisation in ischaemic cardiomyopathy; to develop an economic model to assess cost-effectiveness for different imaging strategies; and to identify areas for further primary research.Databases searched were: MEDLINE including MEDLINE In-Process & Other Non-Indexed Citations Initial searches were conducted in March 2011 in the following databases with dates: MEDLINE including MEDLINE In-Process & Other Non-Indexed Citations via Ovid (1946 to March 2011); Bioscience Information Service (BIOSIS) Previews via Web of Science (1969 to March 2011); EMBASE via Ovid (1974 to March 2011); Cochrane Database of Systematic Reviews via The Cochrane Library (1996 to March 2011); Cochrane Central Register of Controlled Trials via The Cochrane Library 1998 to March 2011; Database of Abstracts of Reviews of Effects via The Cochrane Library (1994 to March 2011); NHS Economic Evaluation Database via The Cochrane Library (1968 to March 2011); Health Technology Assessment Database via The Cochrane Library (1989 to March 2011); and the Science Citation Index via Web of Science (1900 to March 2011). Additional searches were conducted from October to November 2011 in the following databases with dates: MEDLINE including MEDLINE In-Process & Other Non-Indexed Citations via Ovid (1946 to November 2011); BIOSIS Previews via Web of Science (1969 to October 2011); EMBASE via Ovid (1974 to November 2011); Cochrane Database of Systematic Reviews via The Cochrane Library (1996 to November 2011); Cochrane Central Register of Controlled Trials via The Cochrane Library (1998 to November 2011); Database of Abstracts of Reviews of Effects via The Cochrane Library (1994 to November 2011); NHS Economic Evaluation Database via The Cochrane Library (1968 to November 2011); Health Technology Assessment Database via The Cochrane Library (1989 to November 2011); and the Science Citation Index via Web of Science (1900 to October 2011). Electronic databases were searched March-November 2011.The systematic review selected studies that assessed the clinical effectiveness and cost-effectiveness of CMR to establish the role of CMR in viability assessment compared with other imaging techniques: stress echocardiography, single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Studies had to have an appropriate reference standard and contain accuracy data or sufficient details so that accuracy data could be calculated. Data were extracted by two reviewers and discrepancies resolved by discussion. Quality of studies was assessed using the QUADAS II tool (University of Bristol, Bristol, UK). A rigorous diagnostic accuracy systematic review assessed clinical and cost-effectiveness of CMR in viability assessment. A health economic model estimated costs and quality-adjusted life-years (QALYs) accrued by diagnostic pathways for identifying patients with viable myocardium in ischaemic cardiomyopathy with a view to revascularisation. The pathways involved CMR, stress echocardiography, SPECT, PET alone or in combination. Strategies of no testing and revascularisation were included to determine the most cost-effective strategy.Twenty-four studies met the inclusion criteria. All were prospective. Participant numbers ranged from 8 to 52. The mean left ventricular ejection fraction in studies reporting this outcome was 24-62%. CMR approaches included stress CMR and late gadolinium-enhanced cardiovascular magnetic resonance imaging (CE CMR). Recovery following revascularisation was the reference standard. Twelve studies assessed diagnostic accuracy of stress CMR and 14 studies assessed CE CMR. A bivariate regression model was used to calculate the sensitivity and specificity of CMR. Summary sensitivity and specificity for stress CMR was 82.2% [95% confidence interval (CI) 73.2% to 88.7%] and 87.1% (95% CI 80.4% to 91.7%) and for CE CMR was 95.5% (95% CI 94.1% to 96.7%) and 53% (95% CI 40.4% to 65.2%) respectively. The sensitivity and specificity of PET, SPECT and stress echocardiography were calculated using data from 10 studies and systematic reviews. The sensitivity of PET was 94.7% (95% CI 90.3% to 97.2%), of SPECT was 85.1% (95% CI 78.1% to 90.2%) and of stress echocardiography was 77.6% (95% CI 70.7% to 83.3%). The specificity of PET was 68.8% (95% CI 50% to 82.9%), of SPECT was 62.1% (95% CI 52.7% to 70.7%) and of stress echocardiography was 69.6% (95% CI 62.4% to 75.9%). All currently used diagnostic strategies were cost-effective compared with no testing at current National Institute for Health and Care Excellence thresholds. If the annual mortality rates for non-viable patients were assumed to be higher for revascularised patients, then testing with CE CMR was most cost-effective at a threshold of £20,000/QALY. The proportion of model runs in which each strategy was most cost-effective, at a threshold of £20,000/QALY, was 40% for CE CMR, 42% for PET and 16.5% for revascularising everyone. The expected value of perfect information at £20,000/QALY was £620 per patient. If all patients (viable or not) gained benefit from revascularisation, then it was most cost-effective to revascularise all patients.Definitions and techniques assessing viability were highly variable, making data extraction and comparisons difficult. Lack of evidence meant assumptions were made in the model leading to uncertainty; differing scenarios were generated around key assumptions.All the diagnostic pathways are a cost-effective use of NHS resources. Given the uncertainty in the mortality rates, the cost-effectiveness analysis was performed using a set of scenarios. The cost-effectiveness analyses suggest that CE CMR and revascularising everyone were the optimal strategies. Future research should look at implementation costs for this type of imaging service, provide guidance on consistent reporting of diagnostic testing data for viability assessment, and focus on the impact of revascularisation or best medical therapy in this group of high-risk patients.The National Institute of Health Technology Assessment programme.
- Multivariate Longitudinal Shape Analysis of Human Lateral Ventricles during the First Twenty-Four Months of Life. [JOURNAL ARTICLE]
- PLoS One 2014; 9(9):e108306.
Little is known about the temporospatial shape characteristics of human lateral ventricles (LVs) during the first two years of life. This study aimed to delineate the morphological growth characteristics of LVs during early infancy using longitudinally acquired MR images in normal healthy infants.24 healthy infants were MR imaged starting from 2 weeks old every 3 months during the first and every 6 months during the second year. Bilateral LVs were segmented and longitudinal morphological and shape analysis were conducted using longitudinal mixed effect models.A significant bilateral ventricular volume increase (p<0.0001) is observed in year one (Left: 126±51% and Right: 145±62%), followed by a significant reduction (p<0.02) during the second year of life (Left: -24±27% and Right: -20±18%) despite the continuing increase of intracranial volume. Morphological analysis reveals that the ventricular growth is spatially non-uniform, and that the most significant growth occurs during the first 6 months. The first 3 months of life exhibit a significant (p<0.01) bilateral lengthening of the anterior lateral ventricle and a significant increase of radius (p<0.01) and area (p<0.01) at the posterior portion of the ventricle. Shape analysis shows that the horns exhibit a faster growth rate than the mid-body. Finally, bilateral significant age effects (p<0.01) are observed for the growth of LVs whereas gender effects are more subtle and significant effects (p<0.01) only present at the left anterior and posterior horns. More importantly, both the age and gender effects are growth directionally dependent.We have demonstrated the temporospatial shape growth characteristics of human LVs during the first two years of life using a unique longitudinal MR data set. A temporally and spatially non-uniform growth pattern was reported. These normative results could provide invaluable information to discern abnormal growth patterns in patients with neurodevelopmental disorders.
- Examining Event-Related Potential (ERP) Correlates of Decision Bias in Recognition Memory Judgments. [JOURNAL ARTICLE]
- PLoS One 2014; 9(9):e106411.
Memory judgments can be based on accurate memory information or on decision bias (the tendency to report that an event is part of episodic memory when one is in fact unsure). Event related potentials (ERP) correlates are important research tools for elucidating the dynamics underlying memory judgments but so far have been established only for investigations of accurate old/new discrimination. To identify the ERP correlates of bias, and observe how these interact with ERP correlates of memory, we conducted three experiments that manipulated decision bias within participants via instructions during recognition memory tests while their ERPs were recorded. In Experiment 1, the bias manipulation was performed between blocks of trials (automatized bias) and compared to trial-by-trial shifts of bias in accord with an external cue (flexibly controlled bias). In Experiment 2, the bias manipulation was performed at two different levels of accurate old/new discrimination as the memory strength of old (studied) items was varied. In Experiment 3, the bias manipulation was added to another, bottom-up driven manipulation of bias induced via familiarity. In the first two Experiments, and in the low familiarity condition of Experiment 3, we found evidence of an early frontocentral ERP component at 320 ms poststimulus (the FN320) that was sensitive to the manipulation of bias via instruction, with more negative amplitudes indexing more liberal bias. By contrast, later during the trial (500-700 ms poststimulus), bias effects interacted with old/new effects across all three experiments. Results suggest that the decision criterion is typically activated early during recognition memory trials, and is integrated with retrieved memory signals and task-specific processing demands later during the trial. More generally, the findings demonstrate how ERPs can help to specify the dynamics of recognition memory processes under top-down and bottom-up controlled retrieval conditions.
- An efficient identity-based key management scheme for wireless sensor networks using the bloom filter. [Journal Article]
- Sensors (Basel) 2014; 14(10):17937-51.
With the rapid development and widespread adoption of wireless sensor networks (WSNs), security has become an increasingly prominent problem. How to establish a session key in node communication is a challenging task for WSNs. Considering the limitations in WSNs, such as low computing capacity, small memory, power supply limitations and price, we propose an efficient identity-based key management (IBKM) scheme, which exploits the Bloom filter to authenticate the communication sensor node with storage efficiency. The security analysis shows that IBKM can prevent several attacks effectively with acceptable computation and communication overhead.
- Mobile Healthcare for Automatic Driving Sleep-Onset Detection Using Wavelet-Based EEG and Respiration Signals. [JOURNAL ARTICLE]
- Sensors (Basel) 2014; 14(10):17915-17936.
Driving drowsiness is a major cause of traffic accidents worldwide and has drawn the attention of researchers in recent decades. This paper presents an application for in-vehicle non-intrusive mobile-device-based automatic detection of driver sleep-onset in real time. The proposed application classifies the driving mental fatigue condition by analyzing the electroencephalogram (EEG) and respiration signals of a driver in the time and frequency domains. Our concept is heavily reliant on mobile technology, particularly remote physiological monitoring using Bluetooth. Respiratory events are gathered, and eight-channel EEG readings are captured from the frontal, central, and parietal (Fpz-Cz, Pz-Oz) regions. EEGs are preprocessed with a Butterworth bandpass filter, and features are subsequently extracted from the filtered EEG signals by employing the wavelet-packet-transform (WPT) method to categorize the signals into four frequency bands: α, β, θ, and δ. A mutual information (MI) technique selects the most descriptive features for further classification. The reduction in the number of prominent features improves the sleep-onset classification speed in the support vector machine (SVM) and results in a high sleep-onset recognition rate. Test results reveal that the combined use of the EEG and respiration signals results in 98.6% recognition accuracy. Our proposed application explores the possibility of processing long-term multi-channel signals.
- Design of an Elliptic Curve Cryptography Processor for RFID Tag Chips. [JOURNAL ARTICLE]
- Sensors (Basel) 2014; 14(10):17883-17904.
Radio Frequency Identification (RFID) is an important technique for wireless sensor networks and the Internet of Things. Recently, considerable research has been performed in the combination of public key cryptography and RFID. In this paper, an efficient architecture of Elliptic Curve Cryptography (ECC) Processor for RFID tag chip is presented. We adopt a new inversion algorithm which requires fewer registers to store variables than the traditional schemes. A new method for coordinate swapping is proposed, which can reduce the complexity of the controller and shorten the time of iterative calculation effectively. A modified circular shift register architecture is presented in this paper, which is an effective way to reduce the area of register files. Clock gating and asynchronous counter are exploited to reduce the power consumption. The simulation and synthesis results show that the time needed for one elliptic curve scalar point multiplication over GF(2163) is 176.7 K clock cycles and the gate area is 13.8 K with UMC 0.13 μm Complementary Metal Oxide Semiconductor (CMOS) technology. Moreover, the low power and low cost consumption make the Elliptic Curve Cryptography Processor (ECP) a prospective candidate for application in the RFID tag chip.
- Down-titration and discontinuation strategies of tumor necrosis factor-blocking agents for rheumatoid arthritis in patients with low disease activity. [JOURNAL ARTICLE]
- Cochrane Database Syst Rev 2014 Sep 29.:CD010455.
Anti-tumor necrosis factor (TNF) agents are effective in treating patients with rheumatoid arthritis (RA), but they are associated with (dose-dependent) adverse effects and high costs. To prevent overtreatment, several trials have assessed the effectiveness of down-titration compared with continuation of the standard dose.To evaluate the benefits and harms of down-titration (dose reduction, discontinuation or disease activity guided dose tapering) of anti-TNF agents (adalimumab, certolizumab pegol, etanercept, golimumab, infliximab) on disease activity, functioning, costs, safety and radiographic damage compared with usual care in patients with RA and low disease activity.We searched the Cochrane Central Register of Controlled Trials (CENTRAL), Issue 8, 2013; Ovid MEDLINE (1946 to 8 September 2013); EMBASE (1947 to 8 September 2013); Science Citation Index (Web of Science); and conference proceedings of the American College of Rheumatology (2005 to 2012) and European League against Rheumatism (2005 to 2013). We contacted authors of the seven included studies to ask for additional information on their study; five responded.Randomised controlled trials (RCTs) and controlled clinical trials (CCTs) comparing down-titration (dose reduction, discontinuation, disease activity-guided dose tapering) of anti-TNF agents (adalimumab, certolizumab pegol, etanercept, golimumab, infliximab) to usual care/no down-titration in patients with RA and a low disease activity state.Two review authors independently selected studies, assessed risk of bias and extracted data.Six RCTs and one CCT (total 1203 participants), reporting anti-TNF down-titration, were included. Three studies (559 participants) reported anti-TNF dose reduction compared with anti-TNF continuation. Five studies (732 participants) reported anti-TNF discontinuation compared with anti-TNF continuation (two studies assessed both anti-TNF discontinuation and dose reduction), and one study assessed disease activity-guided anti-TNF dose tapering (137 participants). These studies include only adalimumab and etanercept; controlled data on other anti-TNF agents are absent. Two studies were available in full text; one was assessed as having low risk of bias and the other high risk. Five studies were available only as one or more abstracts. Because data provided in these abstracts were limited, risk of bias was unclear. Clinical heterogeneity between the trials was high.Dose reduction of anti-TNF (etanercept data only) showed no statistically significant or clinical relevant difference in disease activity score in 28 joints (DAS28) (mean difference (MD) 0.10, 95% confidence interval (CI) -0.11 to 0.31) (scale 0.9 to 8; higher score indicates worse disease activity). The proportion of participants who maintained low disease activity was slightly lower among participants given reduced doses of the anti-TNF agent (risk ratio (RR) 0.87, 95% CI 0.78 to 0.98, absolute risk difference (ARD) 9%). Radiographic outcome was slightly worse, but this was not clinically meaningful, compared with continuation of anti-TNF (MD 0.11, 95% CI 0.08 to 0.14) (scale 0 to 448; higher score indicates greater joint damage). Function was not statistically different between anti-TNF dose reduction and continuation (MD 0.10, 95% CI 0.00 to 0.20) (scale 0 to 3; higher score indicates worse functioning). Reinstalment of anti-TNF after failure of dose reduction showed a 5% risk of persistent flare. Data on numbers of serious adverse events (SAEs) (RR 0.58, 95% CI 0.23 to 1.45, ARD -2%) and withdrawals due to adverse events (AEs) (RR 0.57, 95% CI 0.17 to 1,92, ARD -1%) were inconclusive. Most outcomes were based on moderate quality evidence.Participants who discontinued anti-TNF (adalimumab and etanercept data) had higher mean DAS28 (DAS28-erythrocyte sedimentation rate (ESR): MD 1.10, 95% CI 0.86 to 1.34) and DAS28-C-reactive protein (CRP): MD 0.57 95% CI -0.09 to 1.23) and were less likely to maintain a low disease activity state (RR 0.43, 95% CI 0.27 to 0.68, ARD 40%). Also, radiographic and functional outcomes are worse after anti-TNF discontinuation (MD 0.66, 95% CI 0.63 to 0.69, and MD 0.30, 95% CI 0.19 to 0.41, respectively). Data on numbers of SAEs (RR 1.26, 95% CI 0.61 to 2.63, ARD 2%) and withdrawals due to AEs (RR 0.72, 95% CI 0.23 to 2.24, ARD -1%) were inconclusive. Most outcomes were based on moderate quality evidence.The one study comparing disease activity-guided anti-TNF dose tapering (adalimumab and etanercept data) reported no statistically significant differences in functional outcomes (MD 0.20, 95% CI -0.02 to 0.42). Significantly higher mean disease activity was found among participants with tapered anti-TNF at study end (MD 0.50, 95% CI 0.11 to 0.89). No full text of this trial was available for this review. No other major outcomes were reported. All outcomes were based on low quality evidence.We can conclude, mostly based on moderate quality evidence, that non-disease activity guided dose reduction of etanercept 50 mg weekly to 25 mg weekly, after at least three to 12 months of low disease activity, seems as effective as continuing the standard dose with respect to disease activity and functional outcomes, although dose reduction significantly induces minimal and not clinically meaningful differences in radiological progression. Discontinuation (also without disease activity-guided adaptation) of adalimumab and etanercept is inferior to continuation of treatment with respect to disease activity and radiological outcomes and function. Disease activity-guided dose tapering of adalimumab and etanercept seems slightly inferior to continuation of treatment with respect to disease activity, with no difference in function. However the only study investigating this comparison included lower than projected numbers of participants.Caveats of this review are that available data are limited. Also, the heterogeneity between studies and the suboptimal design choices (including absence of disease activity-guided dose reduction and discontinuation and use of superiority designs) limit definitive conclusions. None of the included studies assessed long-term safety and costs, although these factors are specific reasons why clinicians consider lowering the dose or stopping the administration of anti-TNF agents.Future research should include other anti-TNF agents; assessment of disease activity, function and radiographic outcomes after longer follow-up; and assessment of long-term safety, cost-effectiveness and predictors for successful down-titration. Also use of a validated flare criterion, non-inferiority designs and disease activity-guided instead of fixed-dose tapering or stopping would allow researchers to better interpret study findings and generalise the information to clinical practice.
- Radioiodine Biogeochemistry and Prevalence in Groundwater. [JOURNAL ARTICLE]
- Crit Rev Environ Sci Technol 2014 Oct 18; 44(20):2287-2335.
(129)I is commonly either the top or among the top risk drivers, along with (99)Tc, at radiological waste disposal sites and contaminated groundwater sites where nuclear material fabrication or reprocessing has occurred. The risk stems largely from (129)I having a high toxicity, a high bioaccumulation factor (90% of all the body's iodine concentrates in the thyroid), a high inventory at source terms (due to its high fission yield), an extremely long half-life (16M years), and rapid mobility in the subsurface environment. Another important reason that (129)I is a key risk driver is that there is uncertainty regarding its biogeochemical fate and transport in the environment. We typically can define (129)I mass balance and flux at sites, but cannot predict accurately its response to changes in the environment. As a consequence of some of these characteristics, (129)I has a very low drinking water standard, which is set at 1 pCi/L, the lowest of all radionuclides in the Federal Register. Recently, significant advancements have been made in detecting iodine species at ambient groundwater concentrations, defining the nature of the organic matter and iodine bond, and quantifying the role of naturally occurring sediment microbes to promote iodine oxidation and reduction. These recent studies have led to a more mechanistic understanding of radioiodine biogeochemistry. The objective of this review is to describe these advances and to provide a state of the science of radioiodine biogeochemistry relevant to its fate and transport in the terrestrial environment and provide information useful for making decisions regarding the stewardship and remediation of (129)I contaminated sites. As part of this review, knowledge gaps were identified that would significantly advance the goals of basic and applied research programs for accelerating (129)I environmental remediation and reducing uncertainty associated with disposal of (129)I waste. Together the information gained from addressing these knowledge gaps will not alter the observation that (129)I is primarily mobile, but it will likely permit demonstration that the entire (129)I pool in the source term is not moving at the same rate and some may be tightly bound to the sediment, thereby smearing the modeled (129)I peak and reducing maximum calculated risk.