Imaging Bundle Research Articles

Curvature strict positivity of direct image bundles associated to pseudoconvex families of domains

Curvature strict positivity of direct image bundles associated to pseudoconvex families of domains

Aerial Hybrid Adjustment of LiDAR Point Clouds, Frame Images, and Linear Pushbroom Images

In airborne surveying, light detection and ranging (LiDAR) strip adjustment and image bundle adjustment are customarily performed as separate processes. The bundle adjustment is usually conducted from frame images, while using linear pushbroom (LP) images in the bundle adjustment has been historically challenging due to the limited number of observations available to estimate the exterior image orientations. However, data from these three sensors conceptually provide information to estimate the same trajectory corrections, which is favorable for solving the problems of image depth estimation or the planimetric correction of LiDAR point clouds. Thus, our purpose with the presented study is to jointly estimate corrections to the trajectory and interior sensor states in a scalable hybrid adjustment between 3D LiDAR point clouds, 2D frame images, and 1D LP images. Trajectory preprocessing is performed before the low-frequency corrections are estimated for certain time steps in the following adjustment using cubic spline interpolation. Furthermore, the voxelization of the LiDAR data is used to robustly and efficiently form LiDAR observations and hybrid observations between the image tie-points and the LiDAR point cloud to be used in the adjustment. The method is successfully demonstrated with an experiment, showing the joint adjustment of data from the three different sensors using the same trajectory correction model with spline interpolation of the trajectory corrections. The results show that the choice of the trajectory segmentation time step is not critical. Furthermore, photogrammetric sub-pixel planimetric accuracy is achieved, and height accuracy on the order of mm is achieved for the LiDAR point cloud. This is the first time these three types of sensors with fundamentally different acquisition techniques have been integrated. The suggested methodology presents a joint adjustment of all sensor observations and lays the foundation for including additional sensors for kinematic mapping in the future.

Development Of An Endoscopic, Absorption Corrected And Calibrated OH Laser Induced Fluorescence Probe System for High Pressure Combustion Diagnostics

We present the design and preliminary results of an endoscopic OH laser-induced fluorescence (LIF) system that is capable of acquiring 1D-line measurements in high pressure combustion processes within large-scale test facilities. The system can be exploited to acquire line-of-sight OH-chemiluminescence images and absorption corrected absolute OH-species concentration from which additionally temperature distribution can be extracted in case of lean mixtures in chemical equilibrium. Different critical components, such as light guides for high power UV laser pulses and flexible UV image guides, were first tested and characterized in a laboratory setup. Optimization regarding pulse energy and beam quality led to the selection of an 1m long hollow core fiber for laser light delivery as a central element for the experimental setup despite high losses caused by bending the fiber. The image transfer is accomplished by a 7m long flexible UV image bundle, which is preferred to the use of a rigid borescope in harsh environments. We designed the endoscopic UV optics using readily available parts and achieved an approximated image resolution of 21.6 line pairs/mm. Additionally, post-processing methods, such as flat-field correction, can improve the image quality substantially and remove the pixilation effect of the fiber bundle structure nearly completely. To validate the complete system, probe-based qualitative OH-LIF measurements were performed in a well-known laminar flame of a matrix burner, which serves as a mock-up for anticipated applications in an industrial test environment with a technology readiness level (TRL) greater than 4. The final step consists of the integration of the miniaturized optics into a cooled probe system which protects the sensitive optics against the harsh environment of an aero-engine sector combustor. For this purpose, two probe systems were designed to include, on the one hand, the endoscope optics together with the fiber image bundle end tip and, on the other hand, the laser emitting and receiving system for performing an absorption measurement needed to quantify the recorded LIF signal.

Improved resolution in fiber bundle inline holographic microscopy using multiple illumination sources.

Recent work has shown that high-quality inline holographic microscopy images can be captured through fiber imaging bundles. Speckle patterns arising from modal interference within the bundle cores can be minimized by use of a partially-coherent optical source such as an LED delivered via a multimode fiber. This allows numerical refocusing of holograms from samples at working distances of up to approximately 1 mm from the fiber bundle before the finite coherence begins to degrade the lateral resolution. However, at short working distances the lateral resolution is limited not by coherence, but by sampling effects due to core-to-core spacing in the bundle. In this article we demonstrate that multiple shifted holograms can be combined to improve the resolution by a factor of two. The shifted holograms can be rapidly acquired by sequentially firing LEDs, which are each coupled to their own, mutually offset, illumination fiber. Following a one-time calibration, resolution-enhanced images are created in real-time at an equivalent net frame rate of up to 7.5 Hz. The resolution improvement is demonstrated quantitatively using a resolution target and qualitatively using mounted biological slides. At longer working distances, beyond 0.6 mm, the improvement is reduced as resolution becomes limited by the source spatial and temporal coherence.

Sensing of Magnetic-Field Gradients with Nanodiamonds on Optical Glass-Fiber Facets.

We demonstrate a photonic sensor of the magnetic field and its gradients with remote readout. The sensor is based on optically detected magnetic resonance (ODMR) in nanodiamonds with nitrogen-vacancy color centers that are covalently attached as a thin film on one facet of an optical fiber bundle. By measuring ODMR signals from a group of individual fibers in an ∼0.5-mm-wide imaging bundle, differences of local magnetic field strengths and magnetic field gradients are determined across the plane of the bundle facet. The measured gradients are created by direct electric currents flowing in a wire placed near the nanodiamond film. The measurement enabled the determination of the net magnetic field corresponding to various current directions and their corresponding magnetic field gradients. This demonstration opens up a perspective for compact fiber-based endoscopy, with additional avenues for remote and sensitive magnetic field detection with submicrometer spatial resolution under ambient conditions.

Novel Design and Application of High-NA Fiber Imaging Bundles for In Vivo Brain Imaging with Two-Photon Scanning Fluorescence Microscopy.

Here, we provide experimental verification supporting the use of short-section imaging bundles for two-photon microscopy imaging of the mouse brain. The 8 mm long bundle is made of a pair of heavy-metal oxide glasses with a refractive index contrast of 0.38 to ensure a high numerical aperture NA = 1.15. The bundle is composed of 825 multimode cores, ordered in a hexagonal lattice with a pixel size of 14 μm and a total diameter of 914 μm. We demonstrate successful imaging through custom-made bundles with 14 μm resolution. As the input, we used a 910 nm Ti-sapphire laser with 140 fs pulse and a peak power of 9 × 104 W. The excitation beam and fluorescent image were transferred through the fiber imaging bundle. As test samples, we used 1 μm green fluorescent latex beads, ex vivo hippocampal neurons expressing green fluorescent protein and cortical neurons in vivo expressing the fluorescent reporter GCaMP6s or immediate early gene Fos fluorescent reporter. This system can be used for minimal-invasive in vivo imaging of the cerebral cortex, hippocampus, or deep brain areas as a part of a tabletop system or an implantable setup. It is a low-cost solution, easy to integrate and operate for high-throughput experiments.

On the positivity of direct image bundles

In the present paper, we obtain an equivalent relation between the log-plurisubharmonicity of the relative Bergman kernel, the Griffiths and Nakano positivity for the direct image with the natural $L^2$ metric, by finding a converse of Berndtsson's theorem on the direct image. A converse of Berndtsson's generalization of Kiselman minimal principle is also obtained. Bibliography: 30 titles.

On the positivity of direct image bundles

In the present paper, we obtain an equivalent relation between the log-plurisubharmonicity of the relative Bergman kernel, the Griffiths and Nakano positivity for the direct image with the natural $L^2$ metric, by finding a converse of Berndtsson's theorem on the direct image. A converse of Berndtsson's generalization of Kiselman minimal principle is also obtained.

Application of a Thoracic CT Decision Rule in the Evaluation of Injured Children: A Quality Improvement Initiative.

Differences in injury patterns in children suggest that life-threatening chest injuries are rare. Radiation exposure from computed tomography increases cancer risk in children. Two large retrospective pediatric studies have demonstrated that thoracic computed tomography can be reserved for patients based on mechanism of injury and abnormal findings on chest radiography. Implement a decision rule to guide utilization of thoracic computed tomography in the evaluation of pediatric blunt trauma, limiting risk of unnecessary radiation exposure and clinically significant missed injuries. A protocol for thoracic computed tomography utilization in pediatric blunt trauma was implemented using a Plan-Do-Study-Act cycle at our Level I pediatric trauma center, reserving thoracic computed tomography for patients with (1) mediastinal widening on chest radiography or (2) vehicle-related mechanism and abnormal chest radiography. We modified our resuscitation order set to limit default imaging bundles. The medical record and trauma registry data were reviewed for all pediatric blunt trauma patients (younger than 18 years) over a 30-month study period before and after protocol implementation (May 2017 to July 2018 and February 2019 to April 2020), allowing for a 6-month implementation period (August 2018 to January 2019). During the study period, 1,056 blunt trauma patients were evaluated with a median (range) Injury Severity Score of 5 (0-58). There were no significant demographic differences between patients before and after protocol implementation. Thoracic computed tomography utilization significantly decreased after implementation of the protocol (26.4% [129/488] to 12.7% [72/568; p < .05]), with no increase in clinically significant missed injuries. Protocol compliance was 88%. Application of decision rules can safely limit ionizing radiation in injured children. Further limitations to thoracic computed tomography utilization may be safe and warrant continued study due to the rarity of significant injuries.

3D Structure from 2D Dimensional Images Using Structure from Motion Algorithms

Natural disasters and human interference have endangered heritage structures around the world. Therefore, 3D modeling of buildings is important for historical preservation, particularly in low-income and war-affected countries. The majority of 3D structure surveying acquisition approaches, terrestrial laser scanning (TLS), total station measurements, or traditional photogrammetry require either high-cost technologies or professional user supervision. Structure from motion (SfM) approaches address both of these issues by allowing a non-expert user to produce a dense point cloud for real structures by taking a few 2D photographs with a digital camera and processing them with highly automated and freely available data processing tools. The state of the art for the SfM technique is presented in this paper. Agisoft Metashape, VisualSFM, and Regard3D, three well-known types of SfM software, were examined and compared. The 3D point cloud was scaled and transformed into a local coordinates system using total station instruments that were used to obtain some ground control points (GCPs). Ninety-six 2D digital photographs for the historical Emara Palace in Najran, Saudi Arabia, were obtained as data input, and the image matching, bundle adjustment (BA), completeness, and accuracy of three used packages were calculated and compared.

Research on Parameter Design and Simulation of Infrared Optical Fiber Imaging System Based on Error Theory

As the microlens array is attached to the infrared optical fiber imaging bundle, forming a rigid assemble is a new method to optimize the imaging quality of the infrared optical fiber imaging system. The alignment accuracy of the assembly is essential to the overall imaging quality of the system. To ensure that the assembly can still produce quality images under a certain alignment error, the imaging system model of assembly was established. Then introduced the concept of error margin and error margin coefficient to analyze the alignment error types and corresponding error effects of the assembly. Based on these concepts, the parameter design of the optical fiber imaging system was started. The limiting alignment errors were calculated at the error margin factor ξ = 1.25: transverse δx = 9 μm, longitudinal dz = 50 μm, and deflection angle γ = 1.5°. Lastly, a ZEMAX simulation study was carried out. The simulation results showed that: under a certain alignment error, the light did not leak but be completely coupled into the core of the fiber, which confirmed the accuracy of error analysis and parameter design. And the assembly was realized in certain high-quality imaging under an alignment error. So the error analysis and parameters were designed correctly, and high imaging quality transfer of the system with a certain alignment error was achieved for the assembly.

Research on the Coupled Modulation Transfer Function of the Discrete Sampling System with Hexagonal Fiber-Optic Imaging Bundles

In this study, we developed a numerical model of the coupled modulation transfer function (coupled-MTF) based on the discrete sampling system from the perspective of optical system imaging quality evaluation for coupled two-dimensional discrete sampling characteristics of the hexagonally aligned fiber-optic imaging bundles and CCD image elements. The results show that when the spatial frequency of the input target signal deviates from the Nyquist frequency by 1%, an increase in the number of fibers leads to a faster convergence of the oscillation of the coupled-MTF, and the coupled-MTF converges to a stable value when the number of fibers reaches 1000 × 1000. The deviation of the spatial frequency of the input target signal from the Nyquist frequency is within 1%, and the oscillatory convergence of the coupled-MTF accelerates with increasing deviation. The coupled-MTF oscillates with the deviation period of the wave peak of the input target signal from the initial position of the fiber center, and the theoretical oscillation spatial period is twice the fiber diameter. This study produces important guidelines for the selection of the number of fibers, input spatial frequency, and initial position deviation of the hexagonally arranged fiber imaging bundles.

POSITIVELY CURVED FINSLER METRICS ON VECTOR BUNDLES

AbstractWe construct a convex and strongly pseudoconvex Kobayashi positive Finsler metric on a vector bundle E under the assumption that the symmetric power of the dual $S^kE^*$ has a Griffiths negative $L^2$ -metric for some k. The proof relies on the negativity of direct image bundles and the Minkowski inequality for norms. As a corollary, we show that given a strongly pseudoconvex Kobayashi positive Finsler metric, one can upgrade to a convex Finsler metric with the same property. We also give an extremal characterization of Kobayashi curvature for Finsler metrics.

Photonic waveguide bundles using 3D laser writing and deep neural network image reconstruction.

In recent years, three-dimensional (3D) printing with multi-photon laser writing has become an essential tool for the manufacturing of three-dimensional optical elements. Single-mode optical waveguides are one of the fundamental photonic components, and are the building block for compact multicore fiber bundles, where thousands of single-mode elements are closely packed, acting as individual pixels and delivering the local information to a sensor. In this work, we present the fabrication of polymer rectangular step-index (STIN) optical waveguide bundles in the IP-Dip photoresist, using a commercial 3D printer. Moreover, we reduce the core-to-core spacing of the imaging bundles by means of a deep neural network (DNN) which has been trained with a large synthetic dataset, demonstrating that the scrambling of information due to diffraction and cross-talk between fiber cores can be undone. The DNN-based approach can be adopted in applications such as on-chip platforms and microfluidic systems where accurate imaging from in-situ printed fiber bundles suffer cross-talk. In this respect, we provide a design and fabrication guideline for such scenarios by employing the DNN not only as a post-processing technique but also as a design optimization tool.

Correlative cryo-imaging of the cellular universe with soft X-rays and laser light used to track F-actin structures in mammalian cells.

Imaging of actin filaments is crucial due to the integral role that they play in many cellular functions such as intracellular transport, membrane remodelling and cell motility. Visualizing actin filaments has so far relied on fluorescence microscopy and electron microscopy/tomography. The former lacks the capacity to capture the overall local ultrastructure, while the latter requires rigorous sample preparation that can lead to potential artefacts, and only delivers relatively small volumes of imaging data at the thinnest areas of a cell. In this work, a correlative approach utilizing in situ super-resolution fluorescence imaging and cryo X-ray tomography was used to image bundles of actin filaments deep inside cells under near-native conditions. In this case, fluorescence 3D imaging localized the actin bundles within the intracellular space, while X-ray tomograms of the same areas provided detailed views of the local ultrastructure. Using this new approach, actin trails connecting vesicles inthe perinuclear area and hotspots of actin presence within and around multivesicular bodies were observed. The characteristic prevalence of filamentous actin in cytoplasmic extensions was also documented.

Combined Block Adjustment for Optical Satellite Stereo Imagery Assisted by Spaceborne SAR and Laser Altimetry Data

To ensure the accuracy of large-scale optical stereo image bundle block adjustment, it is necessary to provide well-distributed ground control points (GCPs) with high accuracy. However, it is difficult to acquire control points through field measurements outside the country. Considering the high planimetric accuracy of spaceborne synthetic aperture radar (SAR) images and the high elevation accuracy of satellite-based laser altimetry data, this paper proposes an adjustment method that combines both as control sources, which can be independent from GCPs. Firstly, the SAR digital orthophoto map (DOM)-based planar control points (PCPs) acquisition is realized by multimodal matching, then the laser altimetry data are filtered to obtain laser altimetry points (LAPs), and finally the optical stereo images’ combined adjustment is conducted. The experimental results of Ziyuan-3 (ZY-3) images prove that this method can achieve an accuracy of 7 m in plane and 3 m in elevation after adjustment without relying on GCPs, which lays the technical foundation for a global-scale satellite image process.

Curvature Formulas Related to a Family of Stable Higgs Bundles

In this paper, we investigate the geometry of the base complex manifold of an effectively parametrized holomorphic family of stable Higgs bundles over a fixed compact K\"{a}hler manifold. The starting point of our study is Schumacher-Toma/Biswas-Schumacher's curvature formulas for Weil-Petersson-type metrics, in Sect. 2, we give some applications of their formulas on the geometric properties of the base manifold. In Sect. 3, we calculate the curvature on the higher direct image bundle, which recovers Biswas-Schumacher's curvature formula. In Sect. 4, we construct a smooth and strongly pseudo-convex complex Finsler metric for the base manifold, the corresponding holomorphic sectional curvature is calculated explicitly.

On deformations of Fano manifolds

In this paper, we provide new necessary and sufficient conditions for the existence of Kahler–Einstein metrics on small deformations of a Fano Kahler–Einstein manifold. We also show that the Weil–Petersson metric can be approximated by the Ricci curvatures of the canonical $$L^2$$ metrics on the direct image bundles. In addition, we describe the plurisubharmonicity of the energy functional of harmonic maps on the Kuranishi space of the deformation of compact Kahler–Einstein manifolds of general type.

The asymptotic of curvature of direct image bundle associated with higher powers of a relatively ample line bundle

Let pi :mathcal {X}rightarrow M be a holomorphic fibration with compact fibers and L a relatively ample line bundle over mathcal {X}. We obtain the asymptotic of the curvature of L^2-metric and Qullien metric on the direct image bundle pi _*(L^kotimes K_{mathcal {X}/M}) up to the lower order terms than k^{n-1}, for large k. As an application we prove that the analytic torsion tau _k(bar{partial }) satisfies partial bar{partial }log (tau _k(bar{partial }))^2=o(k^{n-1}), where n is the dimension of fibers.

Phonon imaging in 3D with a fibre probe

We show for the first time that a single ultrasonic imaging fibre is capable of simultaneously accessing 3D spatial information and mechanical properties from microscopic objects. The novel measurement system consists of two ultrafast lasers that excite and detect high-frequency ultrasound from a nano-transducer that was fabricated onto the tip of a single-mode optical fibre. A signal processing technique was also developed to extract nanometric in-depth spatial measurements from GHz frequency acoustic waves, while still allowing Brillouin spectroscopy in the frequency domain. Label-free and non-contact imaging performance was demonstrated on various polymer microstructures. This singular device is equipped with optical lateral resolution, 2.5 μm, and a depth-profiling precision of 45 nm provided by acoustics. The endoscopic potential for this device is exhibited by extrapolating the single fibre to tens of thousands of fibres in an imaging bundle. Such a device catalyses future phonon endomicroscopy technology that brings the prospect of label-free in vivo histology within reach.