Electrical and Electronic Engineering - Research Publications
Now showing items 1-12 of 674
Mathematical modelling indicates that lower activity of the haemostatic system in neonates is primarily due to lower prothrombin concentration
(NATURE PUBLISHING GROUP, 2019-03-08)
Haemostasis is governed by a highly complex system of interacting proteins. Due to the central role of thrombin, thrombin generation and specifically the thrombin generation curve (TGC) is commonly used as an indicator of haemostatic activity. Functional characteristics of the haemostatic system in neonates and children are significantly different compared with adults; at the same time plasma levels of haemostatic proteins vary considerably with age. However, relating one to the other has been difficult, both due to significant inter-individual differences for individuals of similar age and the complexity of the biochemical reactions underlying haemostasis. Mathematical modelling has been very successful at representing the biochemistry of blood clotting. In this study we address the challenge of large inter-individual variability by parameterising the Hockin-Mann model with data from individual patients, across different age groups from neonates to adults. Calculating TGCs for each patient of a specific age group provides us with insight into the variability of haemostatic activity across that age group. From our model we observe that two commonly used metrics for haemostatic activity are significantly lower in neonates than in older patients. Because both metrics are strongly determined by prothrombin and prothrombin levels are considerably lower in neonates we conclude that decreased haemostatic activity in neonates is due to lower prothrombin availability.
Conformable Holographic Metasurfaces
(NATURE PUBLISHING GROUP, 2017-07-03)
Metasurface holograms are typically fabricated on rigid substrates. Here we experimentally demonstrate broadband, flexible, conformable, helicity multiplexed metasurface holograms operating in the visible range, offering increased potential for real life out-of-the-lab applications. Two symmetrically distributed holographic images are obtained when circularly polarized light impinges on the reflective-type metasurface positioned on non-planar targets. The two off-axis images with high fidelity are interchangeable by controlling the helicity of incident light. Our metasurface features the arrangement of spatially varying gold nanorods on a flexible, conformable epoxy resist membrane to realize a Pancharatnam-Berry phase profile. These results pave the way to practical applications including polarization manipulation, beam steering, novel lenses, and holographic displays.
High-resolution grayscale image hidden in a laser beam
(CHINESE ACAD SCIENCES, CHANGCHUN INST OPTICS FINE MECHANICS AND PHYSICS, 2018-01-26)
Images perceived by human eyes or recorded by cameras are usually optical patterns with spatially varying intensity or color profiles. In addition to the intensity and color, the information of an image can be encoded in a spatially varying distribution of phase or polarization state. Interestingly, such images might not be able to be directly viewed by human eyes or cameras because they may exhibit highly uniform intensity profiles. Here, we propose and experimentally demonstrate an approach to hide a high-resolution grayscale image in a square laser beam with a size of less than half a millimeter. An image with a pixel size of 300 × 300 nm is encoded into the spatially variant polarization states of the laser beam, which can be revealed after passing through a linear polarizer. This unique technology for hiding grayscale images and polarization manipulation provides new opportunities for various applications, including encryption, imaging, optical communications, quantum science and fundamental physics.
Information-theoretic analysis for transfer learning
Transfer learning, or domain adaptation, is concerned with machine learning problems in which training and testing data come from possibly different distributions (denoted as μ and μ', respectively). In this work, we give an informationtheoretic analysis on the generalization error and the excess risk of transfer learning algorithms, following a line of work initiated by Russo and Zhou. Our results suggest, perhaps as expected, that the Kullback-Leibler (KL) divergence D(μμ') plays an important role in characterizing the generalization error in the settings of domain adaptation. Specifically, we provide generalization error upper bounds for general transfer learning algorithms, and extend the results to a specific empirical risk minimization (ERM) algorithm where data from both distributions are available in the training phase. We further apply the method to iterative, noisy gradient descent algorithms, and obtain upper bounds which can be easily calculated, only using parameters from the learning algorithms. A few illustrative examples are provided to demonstrate the usefulness of the results. In particular, our bound is tighter in specific classification problems than the bound derived using Rademacher complexity.
Contactless, nondestructive determination of dopant profiles of localized boron-diffused regions in silicon wafers at room temperature.
(Nature Publishing Group, 2019-07-18)
We develop a photoluminescence-based technique to determine dopant profiles of localized boron-diffused regions in silicon wafers and solar cell precursors employing two excitation wavelengths. The technique utilizes a strong dependence of room-temperature photoluminescence spectra on dopant profiles of diffused layers, courtesy of bandgap narrowing effects in heavily-doped silicon, and different penetration depths of the two excitation wavelengths in silicon. It is fast, contactless, and nondestructive. The measurements are performed at room temperature with micron-scale spatial resolution. We apply the technique to reconstruct dopant profiles of a large-area (1 cm × 1 cm) boron-diffused sample and heavily-doped regions (30 μm in diameter) of passivated-emitter rear localized-diffused solar cell precursors. The reconstructed profiles are confirmed with the well-established electrochemical capacitance voltage technique. The developed technique could be useful for determining boron dopant profiles in small doped features employed in both photovoltaic and microelectronic applications.
In situ recombination junction between p-Si and TiO2 enables high-efficiency monolithic perovskite/Si tandem cells.
(American Association for the Advancement of Science (AAAS), 2018-12)
Increasing the power conversion efficiency of silicon (Si) photovoltaics is a key enabler for continued reductions in the cost of solar electricity. Here, we describe a two-terminal perovskite/Si tandem design that increases the Si cell's output in the simplest possible manner: by placing a perovskite cell directly on top of the Si bottom cell. The advantageous omission of a conventional interlayer eliminates both optical losses and processing steps and is enabled by the low contact resistivity attainable between n-type TiO2 and Si, established here using atomic layer deposition. We fabricated proof-of-concept perovskite/Si tandems on both homojunction and passivating contact heterojunction Si cells to demonstrate the broad applicability of the interlayer-free concept. Stabilized efficiencies of 22.9 and 24.1% were obtained for the homojunction and passivating contact heterojunction tandems, respectively, which could be readily improved by reducing optical losses elsewhere in the device. This work highlights the potential of emerging perovskite photovoltaics to enable low-cost, high-efficiency tandem devices through straightforward integration with commercially relevant Si solar cells.
Innovative strategies for the elimination of viral hepatitis at a national level: A country case series
Viral hepatitis is a leading cause of morbidity and mortality worldwide, but has long been neglected by national and international policymakers. Recent modelling studies suggest that investing in the global elimination of viral hepatitis is feasible and cost-effective. In 2016, all 194 member states of the World Health Organization endorsed the goal to eliminate viral hepatitis as a public health threat by 2030, but complex systemic and social realities hamper implementation efforts. This paper presents eight case studies from a diverse range of countries that have invested in responses to viral hepatitis and adopted innovative approaches to tackle their respective epidemics. Based on an investment framework developed to build a global investment case for the elimination of viral hepatitis by 2030, national activities and key enablers are highlighted that showcase the feasibility and impact of concerted hepatitis responses across a range of settings, with different levels of available resources and infrastructural development. These case studies demonstrate the utility of taking a multipronged, public health approach to: (a) evidence-gathering and planning; (b) implementation; and (c) integration of viral hepatitis services into the Agenda for Sustainable Development. They provide models for planning, investment and implementation strategies for other countries facing similar challenges and resource constraints.
Short-Term Changes in the Photopic Negative Response Following Intraocular Pressure Lowering in Glaucoma
(ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2020-08-01)
Purpose: To evaluate the short-term changes in inner retinal function using the photopic negative response (PhNR) after intraocular pressure (IOP) reduction in glaucoma. Methods: Forty-seven participants with glaucoma who were commencing a new or additional IOP-lowering therapy (treatment group) and 39 participants with stable glaucoma (control group) were recruited. IOP, visual field, retinal nerve fiber layer thickness, and electroretinograms (ERGs) were recorded at baseline and at a follow-up visit (3 ± 2 months). An optimized protocol developed for a portable ERG device was used to record the PhNR. The PhNR saturated amplitude (Vmax), Vmax ratio, semi-saturation constant (K), and slope of the Naka-Rushton function were analyzed. Results: A significant percentage reduction in IOP was observed in the treatment group (28 ± 3%) compared to the control group (2 ± 3%; P < 0.0001). For PhNR Vmax, there was no significant interaction (F1,83 = 2.099, P = 0.15), but there was a significant difference between the two time points (F1,83 = 5.689, P = 0.019). Post hoc analysis showed a significant difference between baseline and 3 months in the treatment group (mean difference, 1.23 µV; 95% confidence interval [CI], 0.24-2.22) but not in the control group (0.30 µV; 95% CI, 0.78-1.38). K and slope were not significantly different in either group. Improvement beyond test-retest variability was seen in 17% of participants in the treatment group compared to 3% in the control group (P = 0.007, χ2 test). Conclusions: The optimized protocol for measuring the PhNR detected short-term improvements in a proportion of participants following IOP reduction, although the majority showed no change.
Plasmonics-enabled metal-semiconductor-metal photodiodes for high-speed interconnects and polarization sensitive detectors
(SPIE-INT SOC OPTICAL ENGINEERING, 2017-01-01)
Metal-semiconductor-metal (MSM) photodiodes are commonly used in ultrafast photoelectronic devices. Re- cently it was shown that localized surface plasmons can su_ciently enhance photodetector capabilities at both infrared and visible wavelengths. Such structures are of great interest since they can be used for fast, broadband detection. By utilizing the properties of plasmonic structures it is possible to design photodetectors that are sensitive to the polarization state of the incident wave. The direct electrical readout of the polarization state of an incident optical beam has many important applications, especially in telecommunications, bio-imaging and photonic computing. Furthermore, the fact that surface plasmon polaritons can circumvent the di_raction limit, opens up signi_cant opportunities to use them to guide signals between logic gates in modern integrated circuits where small dimensions are highly desirable. Here we demonstrate two MSM photodetectors integrated with aluminum nanoantennas capable of distinguishing orthogonal states of either linearly or circularly polarized light with no additional _lters. The localized plasmon resonances of the antennas lead to selective screening of the un- derlying silicon from light with a particular polarization state. The non-null response of the devices to each of the basis states expands the potential utility of the photodetectors while improving precision. We also demonstrate a design of waveguide-coupled MSM photodetector suitable for planar detection of surface plasmons.
Hot-Carrier Organic Synthesis via the Near-Perfect Absorption of Light
(AMER CHEMICAL SOC, 2018-11-01)
Photocatalysis enables the synthesis of valuable organic compounds by exploiting photons as a chemical reagent. Although light absorption is an intrinsic step, existing approaches rely on poorly absorbing catalysts that require high illumination intensities to afford enhanced efficiencies. Here, we demonstrate that a plasmonic metamaterial capable of near-perfect light absorption (94%) readily catalyzes a model organic reaction with a 29-fold enhancement in conversion relative to controls. The oxidation of benzylamine proceeds via a reactive iminium intermediate with high selectivity at ambient temperature and pressure, using only low-intensity visible irradiation. Control experiments demonstrated that only hot charge carriers produced following photoexcitation facilitate the formation of superoxide radicals, which, in turn, leads to iminium formation. Modeling shows that hot holes with energies that overlap with the highest-occupied molecular orbital (HOMO) of the reactant can participate and initiate the photocatalytic conversion. These results have important implications for hot-carrier photocatalysis and plasmon-hot-carrier extraction.
Output feedback boundary control of heterodirectional semilinear hyperbolic systems
We solve the problem of stabilizing a general class of 1-d semilinear hyperbolic systems with an arbitrary number of states convecting in each direction and with the actuation and sensing restricted to one boundary. The control design is based on the dynamics on the characteristic lines along which the inputs propagate through the domain and the predictability of states in the interior of the domain up to the time they are affected by the inputs. In the context of broad solutions, the state-feedback controller drives systems with globally Lipschitz nonlinearities from an arbitrary initial condition to the origin in minimum time. Alternatively, it is possible to satisfy a tracking objective at the uncontrolled boundary or, for systems with C1-coefficients and initial conditions, to design the control inputs to obtain classical C1-solutions that also reach the origin in finite time. Further, we design an observer that estimates the distributed state from boundary measurements only. The observer combined with the state-feedback controller solves the output-feedback control problem.
Complex Correlation Measure: a novel descriptor for Poincare plot
BACKGROUND: Poincaré plot is one of the important techniques used for visually representing the heart rate variability. It is valuable due to its ability to display nonlinear aspects of the data sequence. However, the problem lies in capturing temporal information of the plot quantitatively. The standard descriptors used in quantifying the Poincaré plot (SD1, SD2) measure the gross variability of the time series data. Determination of advanced methods for capturing temporal properties pose a significant challenge. In this paper, we propose a novel descriptor "Complex Correlation Measure (CCM)" to quantify the temporal aspect of the Poincaré plot. In contrast to SD1 and SD2, the CCM incorporates point-to-point variation of the signal. METHODS: First, we have derived expressions for CCM. Then the sensitivity of descriptors has been shown by measuring all descriptors before and after surrogation of the signal. For each case study, lag-1 Poincaré plots were constructed for three groups of subjects (Arrhythmia, Congestive Heart Failure (CHF) and those with Normal Sinus Rhythm (NSR)), and the new measure CCM was computed along with SD1 and SD2. ANOVA analysis distribution was used to define the level of significance of mean and variance of SD1, SD2 and CCM for different groups of subjects. RESULTS: CCM is defined based on the autocorrelation at different lags of the time series, hence giving an in depth measurement of the correlation structure of the Poincaré plot. A surrogate analysis was performed, and the sensitivity of the proposed descriptor was found to be higher as compared to the standard descriptors. Two case studies were conducted for recognizing arrhythmia and congestive heart failure (CHF) subjects from those with NSR, using the Physionet database and demonstrated the usefulness of the proposed descriptors in biomedical applications. CCM was found to be a more significant (p = 6.28E-18) parameter than SD1 and SD2 in discriminating arrhythmia from NSR subjects. In case of assessing CHF subjects also against NSR, CCM was again found to be the most significant (p = 9.07E-14). CONCLUSION: Hence, CCM can be used as an additional Poincaré plot descriptor to detect pathology.