62 research outputs found
Glycans as receptors for influenza pathogenesis
No full textInfluenza A viruses, members of the Orthomyxoviridae family, are responsible for annual seasonal influenza epidemics and occasional global pandemics. The binding of viral coat glycoprotein hemagglutinin (HA) to sialylated glycan receptors on host epithelial cells is the critical initial step in the infection and transmission of these viruses. Scientists believe that a switch in the binding specificity of HA from Neu5Acα2-3Gal linked (α2-3) to Neu5Acα2-6Gal linked (α2-6) glycans is essential for the crossover of the viruses from avian to human hosts. However, studies have shown that the classification of glycan binding preference of HA based on sialic acid linkage alone is insufficient to establish a correlation between receptor specificity of HA and the efficient transmission of influenza A viruses. A recent study reported extensive diversity in the structure and composition of α2-6 glycans (which goes beyond the sialic acid linkage) in human upper respiratory epithelia and identified different glycan structural topologies. Biochemical examination of the multivalent HA binding to these diverse sialylated glycan structures also demonstrated that high affinity binding of HA to α2-6 glycans with a characteristic umbrella-like structural topology is critical for efficient human adaptation and human-human transmission of influenza A viruses. This review summarizes studies which suggest a new paradigm for understanding the role of the structure of sialylated glycan receptors in influenza virus pathogenesis.National Institute of General Medical Sciences (U.S.) (Glue Grant U54 GM62116)National Institutes of Health (U.S.) (Grant GM57073)Singapore-MIT Alliance for Research and Technolog
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Extraordinary Magnetoresistance in Two and Three Dimensions: Geometrical Optimization
No full textThe extraordinary magnetoresistance (EMR) in metal-semiconductor hybrid structures was first demonstrated using a van der Pauw configuration for a circular semiconductor wafer with a concentric metallic inclusion in it. This effect depends on the orbital motion of carriers in an external magnetic field, and the remarkably high magnetoresistance response observed suggests that the geometry of the metallic inclusion can be optimized to significantly enhance the EMR. Here we consider the theory and simulations to achieve this goal by comparing both two-dimensional as well as three-dimensional structures in an external magnetic field to evaluate the EMR in them. Examples of structures that are compatible with present day technological capabilities are given together with their expected responses in terms of EMR. For a 10 micron 2D square structure with a square metallic inclusion, we see a MR up to 10^7 percent for an applied magnetic field of 1 Tesla
Use of Nasal Non-Invasive Ventilation with a RAM Cannula in the Outpatient Home Setting
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Background:
Nasal non-invasive-ventilation (Nasal NIV) is a mode of ventilatory support providing positive pressure to patients via a nasal interface. The RAM Cannula is an oxygen delivery device that can be used as an alternative approach to deliver positive pressure. Together they have been successfully used to provide respiratory support in neonatal in-patient settings.
Objective:
To describe the outpatient use of Nasal NIV/RAM Cannula as a feasible alternative for home respiratory support in children with chronic respiratory failure.
Methods:
We performed a retrospective case series of 18 children (4 months to 19 years old) using the Nasal NIV/RAM Cannula in the Pediatric Pulmonary Clinic at the McGovern Medical School, UTHealth (2014-16). Consideration for Nasal NIV/RAM Cannula utilization included: inability to wean-off in-patient respiratory support, comfort for dyspnea, intolerability of conventional mask interfaces and tracheostomy avoidance.
Results:
Average age was 7 years. 50% were Caucasian, 38% African-American and 11% Hispanics. Pulmonary disorders included: chest wall weakness (38%), central control abnormalities (33%), obstructive lung disease (16%) and restrictive lung disease (11%). Indications for Nasal NIV/RAM Cannula initiation included: CPAP/BPAP masks intolerability (11%), dyspnea secondary to chest wall weakness (38%) and tracheostomy avoidance (50%). Average length of use of Nasal NIV/RAM Cannula was 8.4 months. Successful implementation of Nasal NIV/Ram Cannula was 94%. One patient required a tracheostomy following the use of Nasal NIV/RAM Cannula. Significant decrease in arterial PaCO2 pre and post Nasal NIV/RAM cannula initiation was notable (p=0.001).
Conclusion:
Outpatient use of Nasal NIV/RAM Cannula may prove to be a feasible and save treatment alternative for children with chronic respiratory failure, chest wall weakness, dyspnea and traditional nasal/face mask intolerance to avoid tracheostomy.
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The Adiabatic Bond Charge Model of Phonons
No full textThe dispersion relation between frequency and wavevector of atomic vibrations, or phonons, can be succinctly described by the adiabatic bond charge model, first developed by Weber. The model employs as few as four parameters to fit experiment. We investigated this model in order to better unify the description of the technologically relevant group IV elemental semiconductors (e.g. diamond, silicon, germanium, and gray tin) by replacing an ad hoc parameter introduced by Weber with one arising from quadrupolar interactions between the bond charges, and by fitting the parameters to density functional theory calculations. We also illustrate constant frequency surfaces embedded in wavevector space for the various modes of vibration for the first time. The bond charge model allows for rapid calculation of various quantities related to the interaction of phonons with electrons and photons as compared to density functional theory, especially in structures with little symmetry and for macroscopic structures, thus enabling the design of complicated electronic and photonic devices much more accurately
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Finite Element Method Modeling of Optoconductance in Metal-Semiconductor Hybrid Devices
No full textA numerical description of the extraordinary optoconductance (EOC) effect is presented using two separate models. Extraordinary optoconductance is part of a general class of EXX geometric effects involving the external perturbation of the properties of a 2D electron gas in a macroscopic semiconductor or metal-semiconductor hybrid structure. The addition of metallic inclusions, has been shown to increase the sensitivity of devices relying on EXX effects. Following the discovery of the first EXX effect, extraordinary magneto-resistance (EMR), an optical equivalent was suggested. Unlike EMR, where the external perturbation is an applied magnetic field, EOC results from the modification of the local charge density in the semiconductor by a focused laser.
The first model assumes Gaussian charge densities for the photo-generated electron-hole pairs while the second model directly solves the semiconductor drift-diffusion equations using the finite element method (FEM). Results from both models are shown to agree with experimental EOC data, both as a function of the laser spot position and temperature. The FEM model has the ability to describe EOC in more complex geometries making it useful in designing EOC devices geared for particular applications
Machine Learning Driven Simulation in the Automotive Industry
No full textThe current thesis investigates data-driven simulation decision-making with field-quality consumer data. This is accomplished by outlining the benefits and uses of combining machine learning and simulation in the literature and by locating barriers to the use of machine learning (ML) in the simulation subsystems at a case study organization. Additionally, an implementation is carried out to demonstrate how Scania departments can use this technology to analyze their current data and produce results that support the exploration of the simulation space and the identification of potential design issues so that preventative measures can be taken during concept development. The thesis' findings provide an overview of the literature on the relationship between machine learning and simulation technologies, as well as limitations of using machine learning in simulation systems at large scale manufacturing organizations. Support vector machines, logistic regression, and Random Forest classifiers are used to demonstrate one possible use of machine learning in simulation
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Studies on the Emergence of Order in Out-of-equilibrium Systems
No full textA challenge in fundamental physics and especially in thermodynamics is to understand emergent order in far-from-equilibrium systems. While at equilibrium, temperature plays the role of a key thermodynamic variable whose uniformity in space and time defines the equilibrium state the system is in, this is not the case in a far-from-equilibrium driven system. When energy flows through a finite system at steady-state, temperature takes on a time-independent but spatially varying character. In this study, the convection patterns of a Rayleigh-Bénard fluid cell at steady-state is used as a prototype system where the temperature profile and fluctuations are measured spatio-temporally. The thermal data is obtained by performing high-resolution real-time infrared calorimetry on the convection system as it is first driven out-of-equilibrium when the power is applied, achieves steady-state, and then as it gradually relaxes back to room temperature equilibrium when the power is removed. This work provides new experimental data on the non-trivial nature of thermal fluctuations when stable complex convective structures emerge. The thermal analysis of these convective cells at steady-state further yield local equilibrium-like statistics as the temperature manifold bifurcates into regions of emergent order (sources) and disorder (sink). These localized domains which coexist together, reveal equilibrium-like fluctuations for the temperature scalar. We extend these experimental results to derive a thermodynamic equation of state for a driven system with emergent order from the first principles. We present a field theoretic formalism by defining the Lagrangian density as a function of a generic thermodynamic scalar. Our definition of the thermodynamic Lagrangian density involves two components, the internal work or the coherent part which gives rise to emergent order, and the internal dissipation or the incoherent part which acts as the internal sink. The salient feature of this formulation is that it takes into account the spatial and temporal gradients of the thermodynamic scalar as the system is driven out-of-equilibrium, similar to the Rayleigh-Bénard system. The action functional defined on this scalar manifold connects local equilibrium-like domains. On minimizing the action and solving the Euler-Lagrange equation, we obtain a generalized thermodynamic equation of state for a driven system with emergent order. In conclusion, these results correlate the spatial ordering of the convective cells with the evolution of the system's temperature manifold
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Non-Asymptotic Quantum Scattering Theory for Low-Dimensional Materials
No full textOver the past few decades, solid-state devices have steered the field of nanoelectronics. The advancement in semiconductor technology has led to the development of classical integrated circuits, which follows the trend defined by Moore’s law. However, in order to achieve the next generation of computing circuits, one requires to go beyond the limits of Moore’s law. This has led to a revolution in the development of new quantum materials, and harnessing their physical properties. This new class of quantum materials constitutes low-dimensional systems such as semiconductor heterostructures and atomically thin two-dimensional (2D) materials. Tunability of the physical properties offered by these structures, makes them ideal candidates to host high performance nanoelectronic circuits and quantum information platforms. In this thesis, we develop a scalable first-principles informed quantum transport theory to investigate the carrier transport properties of low-dimensional materials, and reveal their novel electronic and thermoelectric properties.
While first-principles calculations effectively determine the atomistic potentials associated with defects and impurities, they are ineffective for direct modeling of carrier transport properties at length scales relevant for device applications. Traditionally, scattering properties are obtained by applying the asymptotic boundary conditions. However, these boundary conditions do not account for the decaying evanescent mode contributions, that are crucial while determining the transport properties of low-dimensional systems. Here, we develop a novel non-asymptotic quantum scattering theory to obtain the transport properties in proximity to the scattering centers, for confined as well as open domain in one-, two- and three-dimensional systems. We then bridge this scattering theory and the k.p perturbation theory, with inputs from ab-initio electronic structure calculations, to construct a versatile multiscale formalism. The continuum nature of the formalism enables us to model realistic meso- and nano-scale devices.
The given formalism is applied to study electron scattering in quantum waveguides. Several interesting phenomena are revealed through our analysis. The Fano resonance profile for the transmission spectrum of both propagating and evanescent modes is observed. An enhancement of power factor far beyond the earlier proposed limits is obtained by embedding attractive impurities within the waveguide. A current rectification device is simulated, which is expected to find applications in quantum transport.
We further apply this formalism to reveal the novel electronic and thermoelectric properties of monolayer lateral transition-metal dichalcogenide (TMDC) heterostructures. We show that material inclusions in such heterostructures leads to enhancement of electron mobility by an order of magnitude larger than pristine TMDCs. The band alignment between the materials also enhances the thermoelectric figure-of-mertit (ZT) and power factor far beyond the pristine TMDCs. Our study opens new avenues for constructing ultra-efficient in-plane thermoelectric devices using lateral TMDC heterostructures
Determinants of Glycan Receptor Specificity of H2N2 Influenza A Virus Hemagglutinin
Get PDFThe H2N2 subtype of influenza A virus was responsible for the Asian pandemic of 1957-58. However, unlike other subtypes that have caused pandemics such as H1N1 and H3N2, which continue to circulate among humans, H2N2 stopped circulating in the human population in 1968. Strains of H2 subtype still continue to circulate in birds and occasionally pigs and could be reintroduced into the human population through antigenic drift or shift. Such an event is a potential global health concern because of the waning population immunity to H2 hemagglutinin (HA). The first step in such a cross-species transmission and human adaptation of influenza A virus is the ability for its surface glycoprotein HA to bind to glycan receptors expressed in the human upper respiratory epithelia. Recent structural and biochemical studies have focused on understanding the glycan receptor binding specificity of the 1957-58 pandemic H2N2 HA. However, there has been considerable HA sequence divergence in the recent avian-adapted H2 strains from the pandemic H2N2 strain. Using a combination of structural modeling, quantitative glycan binding and human respiratory tissue binding methods, we systematically identify mutations in the HA from a recent avian-adapted H2N2 strain (A/Chicken/PA/2004) that make its quantitative glycan receptor binding affinity (defined using an apparent binding constant) comparable to that of a prototypic pandemic H2N2 (A/Albany/6/58) HA.National Institute of General Medical Sciences (U.S.) (GM57073)National Institute of General Medical Sciences (U.S.) (U54 GM62116)Singapore. Agency for Science, Technology and ResearchSingapore-MIT Alliance for Research and Technolog
Nonclassical Structures within the N-qubit Pauli Group
No full textStructures that demonstrate nonclassicality are of foundational interest in quantum mechanics, and can also be seen as resources for numerous applications in quantum information processing- particularly in the Hilbert space of N qubits. The theory of entanglement, quantum contextuality, and quantum nonlocality within the N-qubit Pauli group is further developed in this the-sis. The Strong Kochen-Specker theorem and the structures that prove it are introduced and explored in detail. The pattern of connections between structures that show entanglement, contextuality, and nonlocality is explained. Computational search algorithms and related tools were developed and used to perform complete searches for minimal nonclassical structures within the N-qubit Pauli group up to values of N limited by our computational re-sources. Our results are surveyed and prescriptions are given for using the elementary nonclassical structures we have found to construct more complex types of such structures. Families of nonclassical structures are presented for all values of N, including the most compact family of projector-based parity proofs of the Kochen-Specker theorem yet discovered in all dimensions of the form 2N, where N ≥ 2. The applications of our results and their connection with other work is also discussed
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