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A high speed X-Y nanopositioner with integrated optical motion sensing
No full textHigh speed in-plane (X-Y) nanopositioners are of central importance in scanning probe microscopy for performing fast imaging and manipulation. Reducing the size of the nanopositioning stage improves the response speed of the positioner but also introduces challenges in integration of conventional motion sensors. This paper presents the design and development of a novel high speed flexure-guided, piezo-electrically actuated nanopositioner with integrated optical beam deflection-based motion sensing. The sensing strategy eliminates spatial constraints even for small stages. A simple lumped-parameter model is proposed for the nanopositioner. Subsequently, the model is used to design and fabricate the nanopositioner. The measurement system is integrated with the nanopositioning stage and is employed to characterize the quasi-static and dynamic response of the stage. Finally, the in-plane motion measurements are employed to control the stage when it is commanded to track both slow- and fast-varying position signals. In both cases, the use of control is shown to significantly improve the tracking accuracy. © 2019 Author(s)
Linearized ADMM and FAST nonlocal denoising for efficient plug-and-play restoration
No full textIn plug-and-play image restoration, the regularization is performed using powerful denoisers such as nonlocal means (NLM) or BM3D. This is done within the framework of alternating direction method of multipliers (ADMM), where the regularization step is formally replaced by an off-the-shelf denoiser. Each plug-and-play iteration involves the inversion of the forward model followed by a denoising step. In this paper, we present a couple of ideas for improving the efficiency of the inversion and denoising steps. First, we propose to use linearized ADMM, which generally allows us to perform the inversion at a lower cost than standard ADMM. Moreover, we can easily incorporate hard constraints into the optimization framework as a result. Second, we develop a fast algorithm for doubly stochastic NLM, originally proposed by Sreehari et al. (IEEE TCI, 2016), which is about 80� faster than brute-force computation. This particular denoiser can be expressed as the proximal map of a convex regularizer and, as a consequence, we can guarantee convergence for linearized plug-and-play ADMM. We demonstrate the effectiveness of our proposals for super-resolution and single-photon imaging. © 2018 IEEE
Understanding Corona Discharges using Digital Imaging
No full textCorona discharges are unavoidable events in high voltage transmission system due to the existence of concentrated high electric fields. Some of the repercussions include power loss, generation of audio noise, radio frequency interference etc. Corona discharges are also regarded as one of the degradation inducing factors in polymeric insulators. Therefore, detection and analysis of these discharges may greatly help in accessing the severity of the damage on the insulators. The presently available tools include the daytime UV cameras which are expensive and qualitative in nature. However, the commercially available digital single lens reflection (DSLR) camera is equipped to capture these faint discharges with longer exposure time (>1 s) under darker ambience and images may be processed to extract useful information pertinent to the discharge intensity. Exploring the possible use of DSLR camera for corona detection and analysis could emerge as one of the low-cost condition monitoring tools. In the present study, AC corona discharges with voltage levels from 6 kV to 12 kV are generated using a multiple needle corona electrode. The discharge images are captured with a varying exposure time of 20 s, 25 s and 30 s, depending on the over and under saturation of the images. A color thresholding-based image segmentation algorithm is used to extract only the discharge region from the obtained images. A parameter called mean pixel intensity (I avg ) is computed as a quantitative indicator of discharge level and its variation with respect to the applied voltage and the exposure time is studied. A matrix to visualize the sparsity pattern of the I avg is constructed. The matrix entries indicated that, as applied voltage increases the overlapping in the I avg values become more evident. This is attributed to the effect of over saturation in the image pixels. The study shows that images of different voltage level can result in same I avg for the different exposure time and this may be avoided by carefully selecting the camera parameters. © 2018 IEEE
A Nondimensional Model Reveals Alterations in Nuclear Mechanics upon Hepatitis C Virus Replication
No full textMorphology of the nucleus is an important regulator of gene expression. Nuclear morphology is in turn a function of the forces acting on it and the mechanical properties of the nuclear envelope. Here, we present a two-parameter, nondimensional mechanical model of the nucleus that reveals a relationship among nuclear shape parameters, such as projected area, surface area, and volume. Our model fits the morphology of individual nuclei and predicts the ratio between forces and modulus in each nucleus. We analyzed the changes in nuclear morphology of liver cells due to hepatitis C virus (HCV) infection using this model. The model predicted a decrease in the elastic modulus of the nuclear envelope and an increase in the pre-tension in cortical actin as the causes for the change in nuclear morphology. These predictions were validated biomechanically by showing that liver cells expressing HCV proteins possessed enhanced cellular stiffness and reduced nuclear stiffness. Concomitantly, cells expressing HCV proteins showed downregulation of lamin-A,C and upregulation of β-actin, corroborating the predictions of the model. Our modeling assumptions are broadly applicable to adherent, monolayer cell cultures, making the model amenable to investigate changes in nuclear mechanics due to other stimuli by merely measuring nuclear morphology. Toward this, we present two techniques, graphical and numerical, to use our model for predicting physical changes in the nucleus
Energetics of the complex phase diagram of a tunable bilayer graphene probed by quantum capacitance
No full textBilayer graphene provides a unique platform to explore the rich physics in quantum Hall effect. The unusual combination of spin, valley, and orbital degeneracy leads to interesting symmetry-broken states with electric and magnetic field. Conventional transport measurements, like resistance measurements, have been performed to probe the different ordered states in bilayer graphene. However, not much work has been done to directly map the energetics of those states in bilayer graphene. Here, we have carried out the magnetocapacitance measurements with electric and magnetic field in a hexagonal boron nitride encapsulated dual-gated bilayer graphene device. At zero magnetic field, using the quantum capacitance technique we measure the gap around the charge neutrality point as a function of perpendicular electric field and the obtained value of the gap matches well with the theory. In the presence of a perpendicular magnetic field, we observe Landau-level crossing in our magnetocapacitance measurements with electric field. The gap closing and reopening of the lowest Landau level with electric and magnetic field shows the transition from one ordered state to another. Furthermore, we observe the collapsing of the Landau levels near the band edge at higher electric field ((D) over bar > 0.5 V/nm), which was predicted theoretically. The complete energetics of the Landau levels of bilayer graphene with electric and magnetic field in our experiment paves the way to unravel the nature of ground states of the system
Origin of n-type conductivity of monolayer MoS2
No full textMonolayer MoS2 is a promising two-dimensional material for electronic and optoelectronic devices. As-grown MoS2 is an n-type semiconductor, however, the origin of this unintentional doping is still not clear. Here, using hybrid density functional theory, we carried out an extensive study of the often observed native point defects, i.e., V-S, V-Mo, V-S2, V-MoS3, V-MoS6, Mo-S2, and S2(Mo), and found that none of them cause n-type doping. Specifically, the S vacancy (V-S), which has been widely attributed to n-type conductivity, turns out to be an electron compensating center. We report that hydrogen, which is almost always present in the growth environments, is most stable in its interstitial (H-i) and H-S adatom forms in MoS2 and acts as a shallow donor, provided the sample is grown under S-rich condition. Furthermore, they have high migration barriers (in excess of 1 eV), which would ensure their stability even at higher temperatures, and hence lead to n-type conductivity
Synthesis of cobalt-rich alloys with high saturation magnetization: A novel synthetic approach by hydrazine reduction method
No full textCobalt-rich alloys of various compositions (Co33Fe33Ni33, Co40Fe40Ni20, Co50Fe25Ni25 and Co60Fe20Ni20) were synthesized from their respective precursor salts using a novel hydrazine reduction method. The synthesized nanosized powders were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) techniques. XRD phase analysis results revealed that the Co33Fe33Ni33 alloy was formed with a pure FCC phase. Whereas, Co40Fe40Ni20, Co50Fe25Ni25 and Co60Fe20Ni20 alloys were composed of both FCC and BCC phases. The average particle size of the alloys was estimated to be in the range of 107-280 nm. The synthesized cobalt-rich alloys exhibited ferromagnetic properties at room temperature with a high saturation magnetization value up to 138 emu/g. The mixed phase Co40Fe40Ni20 alloy showed higher saturation magnetization and higher coercivity as compared to the other alloy compositions. In mixed phase alloys, the dominance of the BCC phase over the FCC phase seems to has resulted in the enhancement of the saturation magnetization value. The obtained results indicate that the hydrazine reduction method was effective in synthesizing cobalt-rich alloys with excellent soft magnetic properties
Identifying Intermediate States in Prion Protein Folding Pathway: A Possible Precursor to the Misfolded State?
No full textOmnidirectional sub-bandgap photo-detection using functionalized moulded composite flexible platforms
No full textThe substrate is an optically functional component of a thin film organic optoelectronic device. In the well-known context of photovoltaics, the functionality of substrate is relatively simple that of a broadband transmittance which allows almost all the incoming light into the absorber. A less explored idea is that of incorporating other optical functionalities in the substrate bulk. Such unconventional design can help surpass the performance limitations of commonly available optoelectronic materials to achieve novel functionality. Bulk functionalization of substrates is particularly easy when the substrates are made using moldable transparent materials which allow mixing of optically functional materials into a composite substrate bulk. In this paper, the example of photonic-upconversion is considered as a representative optical function, to make organic photo detectors which detect up-converted infrared light. By incorporating this functionality in a composite substrate two advantages are demonstrated in which the composite substrate architecture surpasses the performance of the conventional thin film device design. First, the composite substrate preserves the electronic performance of the device by spatially isolating the optical and the charge transport functions. Second, the composite architecture enables sub-bandgap photo-detection which is invariant with respect to the angle of incidence of the infrared input light, by placing the optical function before the light can encounter optically reflecting interfaces. In summary, the unconventional design employing a composite optically functional substrate can be extended to multiple optical functionalities and represents a key design finding that can enable considerably more efficient optoelectronic device designs
Studying Hemoglobin and a Bare Metal-Porphyrin Complex Immobilized on Functionalized Silicon Surfaces Using Synchrotron X-ray Reflectivity
No full textWe evaluate here, using synchrotron X-ray reflectivity, hemoglobin adsorption characteristics on silicon substrates with varying chemical functionalities. Hemoglobin at isoelectronic point and at negative charge is immobilized on functionalized hydrophilic (hydroxyl, carboxylic, amine) and hydrophobic (alkylated) silicon surfaces for the study. As a control, the bare cofactor hemin (containing only the metal and porphyrin with no amino acid residues) is also studied under similar conditions. Ordered layers (grown using the Langmuir-Blodgett technique) are observed to be less affected by the surface chemistry compared to the multilayers formed by physical absorption. Surface chemistry and charge of the proteins are critical in controlling the protein adsorption characteristics on silicon, such as thickness (correlated to molecule size) and roughness. In this study, this is very well realized by varying both the hydrophobicity and hydrophilicity of the substrate. The fundamental studies discussed here provide us with a set of important guidelines as to how electrode surface functionalization can control molecular conformation/orientation, especially protein adsorption on the substrate. This in turn is expected to have a significant impact on the protein electrochemical function and response of biomolecular devices