Geometric Efficiency Research Articles

Second-generation Micro-Spec: A compact spectrometer for far-infrared and submillimeter space missions

Micro-Spec is a direct-detection spectrometer which integrates all the components of a diffraction-grating spectrometer onto a ≈10-cm2 chip through the use of superconducting microstrip transmission lines on a single-crystal silicon substrate. The second generation of Micro-Spec is being designed to operate with a spectral resolution of at least 512 in the far-infrared and submillimeter (420–540 GHz, 714–555 μm) wavelength range, a band of interest for NASA's experiment for cryogenic large-aperture intensity mapping called EXCLAIM. EXCLAIM will be a balloon-borne telescope that is being designed to map the emission of redshifted carbon monoxide and singly-ionized carbon lines over a redshift range 0<z<3.5 and it will be the first demonstration of the Micro-Spec technology in a space-like environment. This work reviews the status of the Micro-Spec design for the EXCLAIM telescope, with emphasis on the spectrometer's two-dimensional diffractive region, through which light of different wavelengths is focused on kinetic inductance detectors along the instrument focal plane. An optimization process is used to generate a geometrical configuration of the diffractive region that satisfies specific requirements on size, operating spectral range and performance. An initial optical design optimized for EXCLAIM is presented in terms of geometric layout, spectral purity and efficiency.

A GENERIC RIGOROUS SENSOR MODEL FOR PHOTOGRAMMETRIC PROCESSING OF PUSHBROOM PLANETARY IMAGES

Abstract. Currently, each planetary exploration mission team always develops its own software modules to support the photogrammetric processing of planetary images, and as a result of that the main drawbacks are lacking software reusability and the high cost of software development and maintenance. This is mainly due to that there is lack of a highly universal sensor model in the planetary mapping community. This paper presents a generic rigorous sensor model (RSM) for the photogrammetric processing of pushbroom planetary images. The main contributions of this paper include: (1) the implementation details of the generic RSM; (2) the optimized coordinates transformation methods between 3D ground points and 2D image points for linear pushbroom images; (3) a pipeline to acquire exterior orientation (EO) parameters for each planetary image. The generic RSM is developed based on the methodology used in airborne linear scanners ADS40. Specifically, the generic RSM comprises of a camera file and an orientation data file for each image. The camera file stores each detector’s calibrated image coordinates and the orientation data file contains each scan line’s EO parameters, such that the RSM can perform coordinates transformation among pixel coordinates, focal plane coordinates and ground coordinates. Furthermore, the generic RSM supports varying exposure time, summing mode and image distortions, which are typical problems that need to be solved in planetary mapping. We tested the generic RSM with Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC), Chandrayaan-1 Moon Mineralogy Mapper (M3) and Mars Express (MEX) High Resolution Stereo Camera (HRSC) images. The geometric accuracy and computational efficiency of the developed generic RSM were compared with the famous planetary mapping software, namely Integrated System for Imagers and Spectrometers (ISIS). The experimental results demonstrate that the generic RSM has the merits of processing various types of pushbroom planetary images with a unified way and decreasing the software development and maintenance burden. Moreover, the developed generic RSM significantly improves the computational efficiency of orthophoto generation and tie points extraction for pushbroom planetary images.

THIN-WALLED STEEL TUBULAR COLUMNS WITH UNIFORM AND GRADED THICKNESS UNDER CYCLIC LOADING

Thin-walled steel tubular circular columns are widely used as cantilever bridge piers due to their geometric efficiency, aesthetic appearance, and high earthquake resistance. However, local buckling, global buckling, or interaction between both is usually the main reason of significant strength and ductility loss in these columns, which eventually leads to their collapse. This paper investigates the behavior of uniform circular (C) and graded-thickness circular (GC) thin-walled steel tubular columns under constant axial and cyclic lateral loading. The GC column with size and volume of material equivalent to the C column is introduced and analyzed under constant axial and cyclic lateral loading. The analysis carried out using a finite-element model (FEM), which considers both material and geometric nonlinearities. The accuracy of the employed FEM is validated based on the experimental results available in the literature. The results revealed that, significant improvements in strength, ductility, and post-buckling behavior of thin-walled steel columns obtained using the GC column.

The Effects of Radiation and Emitted Light Transport on the Positional Response of 11 cm × 42.5 cm × 5.5 cm NaI(Tl) Detectors.

Experiments were performed with 30 11 cm × 42.5 cm × 5.5 cm NaI(Tl) detectors to better understand their positional response. Spectra were collected using 0.02 to 0.15 MBq point sources of Am, Cs, Co, and Ba positioned on lines parallel and perpendicular to the long axis of the crystal along both the narrow and wide detector faces as well as at different distances from them. A greater density of positions was sampled at the ends of the detector, and repeated measurements were made to examine potential gain drifts during the experiment. Spectroscopic peak counts, spectroscopic pulse heights, and net counts were analyzed. Empirical equations were fit to the aforementioned data for each specific source energy as a function of source position. In addition, a Monte Carlo radiation transport code was used to simulate the expected positionally variable response based solely upon radiation absorption. The simulated radiation transport efficiency functions were compared to the experimental data. The effects of the geometric radiation efficiency, the attenuation and scattering of emitted light within the scintillation crystal, and combined effects such as nonuniformity of the photomultiplier tube, photocathode response, and crystal irregularities were then distinguished. Functions describing each effect were derived. The results suggest potential new corrections to data obtained with large scintillation detectors as well as a novel approach to partial positional gamma-ray detection with minimal collimation, given that the energy resolution is within reason for particular photopeaks.

Comparative study of the optical and economic performance of etendue-conserving compact linear Fresnel reflector concepts

This paper presents a comparative performance investigation of three Compact linear Fresnel collectors; a flat collector, a sun-tracking etendue-conserving collector and an off-peak etendue-conserving collector. A Monte Carlo ray tracing program is used to simulate the fields. The resultant incident radiation on the receiver aperture is used to quantify the geometric intercept factor and optical efficiency of the field. Each field is then optimised for mirror width and the ratio between the mirrors targeting each receiver aperture. The three fields are then compared on the basis of performance. The off-peak etendue-conserving compact linear Fresnel field reaches a peak geometric intercept factor of 92%, while the sun-tracking etendue-conserving field and flat field had a peak geometric intercept factor of 83% and 79% respectively. A maximum total plant cost for the same Levelized Electricity Cost is presented to incorporate a cost comparison.

322. Evaluation of the performance parameters on the Ingenuity TF PET/CT scanner

Purpose To evaluate the performance characteristic of Philips Ingenuity TF PET/CT system with the new Pixelar detector design. A comparison of different image reconstruction protocols for EARL accreditation programme was performed. Methods Performance measurements on PET scanner were performed according to the NEMA NU2-2012 standard. Image quality was extended by accounting for different reconstruction parameters (frame timing, PSF iteration number, PSF regularization). A NEMA Image quality phantom was used for suitable image reconstruction protocol evaluation, according to EARL guideline. Performance measurements on CT scanner were performed according to IAEA No.19 publication. Geometrical efficiency was evaluated by exposure of various beam collimations on radiochromic films. Image quality parameters (MTF, Noise) using all reconstruction filters and iterative reconstruction (IDose) were obtained by Catphan®600 acquisitions. Influence of current modulation on patient dose (DoseRight) was studied using an anthropomorphic phantom. Results Spatial resolutions ranged from 4.6 mm at 1 cm to 6.0 mm at 20 cm. Sensitivity measured in the centre and at 10 cm were 7.58 and 7.43 cps/kBq, respectively. The measured NECR peak was 122.7 kcps at 20.3 kBq/cm3. The scatter fraction was 36.6%. Results of image quality test are reported in table. Manufacturer’s EARL dedicated reconstruction protocol did not perfectly meet accreditation requirements as others reconstructions with PSF. CT acceptance parameters met manufacturers and international guidelines specifications, except from geometrical efficiencies for 5 mm, 2.5 mm and 1 mm beam collimations. Decreasing DoseRight index from 26 to 24 and 16, dose reductions of 19.8% and 67.3% were observed. Conclusions Philips Ingenuity TF PET/CT system has overall good performance characteristics, comparable with similar scanners from other manufacturers. The CT part performance meets manufacturer’s specifications with some discrepancies, which do not have a significant impact on clinical use. Regarding EARL accreditation programme, a better adjustment of reconstruction protocol is needed.

286. Computed Tomography profile analysis with radiochromic films

Purpose This work proposes the use of radiochromic film dosimetry for Multi-Slice Computed Tomography (MSCT) profile analysis along the scanner detector array. For this purpose, Gafchromic® XR-QA2 films were used for single and multiple scans in axial and helical modalities with a MSCT scanner. Methods Radiochromic films were cut into long strips and were irradiated with a MSCT scanner on an air-equivalent block. After irradiation, films were digitized with a commercial flatbed scanner using a resolution of 72 dpi, a colour depth of 48bit and saved in TIFF format. Images were calibrated in kerma in air and profiles were then extracted to obtain information on several parameters. The single scan profile analysis, carried out by maintaining stationary the MSCT couch, allowed to obtain the Radiation Profile Widths (RPWs), overbeaming values and detectors geometric efficiency for different beam collimations (range 1.25–40 mm). The multiple scans profile analysis was carried out for both axial and helical acquisitions, keeping the scan length constant for the different collimations used (20–40 mm). This provided information on the overranging parameter for helical acquisitions and the overbeaming effect in multiple scans. Results The single analysis has allowed to verify that the RPWs measured values coincide with those declared by the manufacturer, as shown in Table 1. In addition, it was possible to verify the extent of the overbeam according to the beam collimation. Finally, it was possible to calculate the geometric efficiency of the detectors as a function of the beam collimation. The multiple scans profile analysis showed that overbeaming effect leads to an overall dose increase in axial CT acquisitions. Regarding the helical modality, the analysis has shown that overranging values depend on the collimation and increases for larger collimations. Conclusions Radiochromic films are suitable for CT applications and allow to obtain information concerning MSCT profiles for single and multiple profile scans and for axial and helical modalities with high spatial resolution.

Trace Elements Analysis by Pixe Spectroscopy

Abstract The trace element analysis system is presented using Proton Induced X-ray Emission (PIXE) analysis at a new Ion Beam Centre in Trnava. Standard PIXE system dedicated to the measurement of thick solid samples was extended by a new application for trace element analysis in aerosol samples. The sample holder was modified with respect to the dimensions of the aerosol filters, and a new sample holder and a Faraday cup (FC) were made. The first results of the PIXE aerosol analysis are presented in this paper. Furthermore, the geometric efficiency of the detection system was verified using 55Fe radioactive source emitting monoenergetic Mn X-ray lines. The measured data were compared with the Monte Carlo simulations regarding/disregarding the X-ray attenuation.

Analytical calculations of the solid angle subtended by a circular disk detector at linear sources

Knowledge of the geometrical solid angle is crucial in all measurements of the assets of radioactive materials and to calibrate detectors. A direct mathematical formalism for the determination of the geometrical solid angle and the geometrical efficiency of a circular disk detector and an arbitrarily positioned line source is deduced. The results have been linked with previous computational treatments. The comparison shows a very satisfactory agreement in all cases.

Geometry, packing, and evolutionary paths to increased multicellular size.

The evolutionary transition to multicellularity transformed life on earth, heralding the evolution of large, complex organisms. Recent experiments demonstrated that laboratory-evolved multicellular "snowflake yeast" readily overcome the physical barriers that limit cluster size by modifying cellular geometry [Jacobeen et al., Nat. Phys. 14, 286 (2018)10.1038/s41567-017-0002-y]. However, it is unclear why this route to large size is observed, rather than an evolved increase in intercellular bond strength. Here, we use a geometric model of the snowflake yeast growth form to examine the geometric efficiency of increasing size by modifying geometry and bond strength. We find that changing geometry is a far more efficient route to large size than evolving increased intercellular adhesion. In fact, increasing cellular aspect ratio is on average ∼13 times more effective than increasing bond strength at increasing the number of cells in a cluster. Modifying other geometric parameters, such as the geometric arrangement of mother and daughter cells, also had larger effects on cluster size than increasing bond strength. Simulations reveal that as cells reproduce, internal stress in the cluster increases rapidly; thus, increasing bond strength provides diminishing returns in cluster size. Conversely, as cells become more elongated, cellular packing density within the cluster decreases, which substantially decreases the rate of internal stress accumulation. This suggests that geometrically imposed physical constraints may have been a key early selective force guiding the emergence of multicellular complexity.

A method to calculate the gamma ray detection efficiency of a cylindrical NaI (Tl) crystal

Given a wide range application of NaI(Tl) detector in industrial and medical sectors, computation of the related detection efficiency in different distances of a radioactive source, especially for calibration purposes, is the subject of radiation detection studies. In this work, a 2in both in radius and height cylindrical NaI (Tl) scintillator was used, and by changing the radial, axial, and diagonal positions of an isotropic 137Cs point source relative to the detector, the solid angles and the interaction probabilities of gamma photons with the detector's sensitive area have been calculated. The calculations present the geometric and intrinsic efficiency as the functions of detector's dimensions and the position of the source. The calculation model is in good agreement with experiment, and MCNPX simulation.

Second-Generation Design of Micro-Spec: A Medium-Resolution, Submillimeter-Wavelength Spectrometer-on-a-Chip

Micro-Spec (µ-Spec) is a direct-detection spectrometer which integrates all the components of a diffraction-grating spectrometer onto a \(\sim \) 10-cm\(^2\) chip through the use of superconducting microstrip transmission lines on a single-crystal silicon substrate. A second-generation µ-Spec is being designed to operate with a spectral resolution of 512 in the submillimeter (500–1000 µm, 300–600 GHz) wavelength range, a band of interest for several spectroscopic applications in astrophysics. High-altitude balloon missions would provide the first test bed to demonstrate the µ-Spec technology in a space-like environment and would be an economically viable venue for multiple observation campaigns. This work reports on the current status of the instrument design and will provide a brief overview of each instrument subsystem. Particular emphasis will be given to the design of the spectrometer’s two-dimensional diffractive region, through which the light of different wavelengths is focused on the detectors along the focal plane. An optimization process is employed to generate geometrical configurations of the diffractive region that satisfy specific requirements on spectrometer size, operating spectral range, and performance. An optical design optimized for balloon missions will be presented in terms of geometric layout, spectral purity, and efficiency.

Probing the fusion of neutron-rich nuclei with re-accelerated radioactive beams

We report the first measurement of the fusion excitation functions for $^{39,47}$K + $^{28}$Si at near-barrier energies. Evaporation residues resulting from the fusion process were identified by direct measurement of their energy and time-of-flight with high geometric efficiency. At the lowest incident energy, the cross-section measured for the neutron-rich $^{47}$K induced reaction is ~6 times larger than that of the $\beta$-stable system. The experimental data are compared with both a dynamical deformation model and coupled channels calculations (CCFULL).

Design and modeling of a spectrum-splitting hybrid CSP-CPV parabolic trough using two-stage high concentration optics and dual junction InGaP/GaAs solar cells

A novel hybrid concentrating solar power/concentrating photovoltaic (CSP/CPV) collector is designed, simulated, and optimized for the purpose of power generation. The two-stage concentrator combines a primary parabolic trough with a secondary compound parabolic concentrator (CPC). Single junction Indium Gallium Phosphide (InGaP) and dual junction (InGaP)/Gallium Arsenide (GaAs) solar cells are examined as spectrally reflective beam splitting solar cells. The secondary CPC profile is optimized to guarantee geometric efficiency despite a non-continuous (i.e. segmented) profile and the final two-stage design achieves a geometric concentration ratio of 50× on the thermal absorber. Optical, thermal, and cell performance models are used to determine net electric production for different configurations of the hybrid collector and combined with cost estimates to calculate $/Wexergy and $/Welectric. The down-selected design incorporates dual junction InGaP/GaAs cells, achieves 40% solar-to-exergy efficiency and 23% solar-to electric-efficiency at 600 °C, with a thermal fraction of 73% and installs for an estimated $2.15/Welectric.

Implementation of a violet Scheimpflug lidar system for atmospheric aerosol studies.

A violet Scheimpflug lidar system employing a 1-W 407-nm multimode laser diode is developed for remote sensing of atmospheric aerosols. The laser beam of the laser diode that is transmitted into atmosphere has been investigated in detail and a cylindrical lens pair is designed to improve the geometrical transmission efficiency. A measurement scheme with automatic exposure as well as a generalized signal processing method are established to optimize the signal-to-noise ratio of lidar signals. The performance of the violet Scheimpflug lidar system has been evaluated during a six-day continuous measurement campaign on a near horizontal path. The maximum measurement distance can reach up to 7 km in sunny clean weathers and to about 2 km during haze with an aerosol extinction coefficient of about 0.9 km. The aerosol extinction coefficient retrieved by the Fernald method is promising and shows good correlation with particle concentrations measured by a local national pollution monitoring station. This work promotes the development of all-time Scheimpflug lidar systems operating at other wavelengths or multiple wavelengths for various atmospheric applications.

Non-tracking East-West XCPC solar thermal collector for 200 celsius applications

The design and development of a commercial-ready medium-temperature solar thermal collector, the external compound parabolic concentrator (XCPC), is presented in which a nonimaging reflector is paired with an evacuated tube absorber for efficient and low-cost heat collection between 100 and 250 °C. The absorber geometry is optimized under the constraint of being assembled with an ultrasonic welding machine, with a final pentagon-shaped absorber selected. The modified absorber shape, gap loss, and truncated reflector result in a geometric efficiency of 93% compared to an ideal CPC. The final prototype has a 4.56 m2 aperture and simulations predict an optical efficiency of 71% and thermal efficiency of 50% at 200 °C. Experimental test results (optical, thermal, stagnation) have confirmed an optical efficiency of 62% and a thermal efficiency near 50% at 200 °C with a final stagnation temperature of 333 °C. A detailed economic analysis reveals the technology can be installed for $0.58/watt and deliver a levelized cost of heat at 3.01 cents per kWh over a 20 year lifetime. This is equivalent to the current cost of natural gas in the United States, which underscores the potential of this technology to assist in decarbonizing the thermal energy sector.

Simulation study of the second-generation MR-compatible SPECT system based on the inverted compound-eye gamma camera design

In this paper, we present simulation studies for the second-generation MRI compatible SPECT system, MRC-SPECT-II, based on an inverted compound eye (ICE) gamma camera concept. The MRC-SPECT-II system consists of a total of 1536 independent micro-pinhole-camera-elements (MCEs) distributed in a ring with an inner diameter of 6 cm. This system provides a FOV of 1 cm diameter and a peak geometrical efficiency of approximately 1.3% (the typical levels of 0.1%–0.01% found in modern pre-clinical SPECT instrumentations), while maintaining a sub-500 μm spatial resolution. Compared to the first-generation MRC-SPECT system (MRC-SPECT-I) (Cai 2014 Nucl. Instrum. Methods Phys. Res. A 734 147–51) developed in our lab, the MRC-SPECT-II system offers a similar resolution with dramatically improved sensitivity and greatly reduced physical dimension. The latter should allow the system to be placed inside most clinical and pre-clinical MRI scanners for high-performance simultaneous MRI and SPECT imaging.

Effects of Varying Matching Between Collimator Hole and Scintillator Pixel on Gamma Camera Image Resolution

A collimator is a key component of gamma cameras, which affects imaging performance significantly. Recently, pixelated scintillator arrays are widely applied in the development of highresolution gamma cameras, instead of monolithic scintillator blocks. Therefore, combining the collimator and the pixelated scintillator has been a crucial factor in achieving good imaging performance. In this study, we investigated the effects of the shape and position of a collimator hole on the image resolution of a gamma camera with a pixelated scintillator. We designed a pixel-matched collimator and a low-energy high-resolution (LEHR) collimator with hexagonal shaped holes that have the same collimator geometrical efficiency. Simulation experiments were performed with a Monte Carlo simulation package (GATE v7.0). For both types of collimator, camera sensitivity was measured for validating the collimator efficiency, and planar images were obtained to measure spatial resolution, with changing the line profile angle based on the septa direction. Camera sensitivities for both collimators were equivalent (difference = 1.76 ± 0.51%). In contrast to the case of the pixel-matched collimator, in the case of the LEHR collimator, as the angle of the line profile varied, the spatial resolution showed a difference at each profile angle. In the case when two collimator holes symmetrically matched with one scintillator pixel, the spatial resolution showed a 64.87% difference in its maximum and a position distortion of 26.06% from the original source position, according to the profile angle, compared to the other unmatched cases. These results showed that using a pixel-matched collimator in gamma camera systems employing a pixelated scintillator is essential for the exact delineation of small regions using high resolution gamma camera imaging

Optimization of three-dimensional modeling for geometric precision and efficiency for healthy and diseased aortas

The study purpose is to optimize modeling parameters, specifically segmentation spacing and centerline extraction, to efficiently construct accurate 3D aortic models. Models are constructed by centerline extraction and orthogonal 2D segmentations. We examine the effect of segmentation interval spacing (2, 1, 0.5, 0.25 cm) and orthogonal segmentation and centerline extraction iteration (one, two, three iterations) for constructing models of Healthy, Tortuous, Aneurysmal, and Dissected human thoracic aortas. Aortic arclength, curvature, and cross-sectional axis ratio were computed to compare variations in modeling parameters. Centerline arclength is precisely characterized for all aortas with a single iteration of centerline extraction (≤1% deviation), however, complex anatomies required 1 cm segmentation intervals whereas the Healthy aorta only required 2 cm intervals. Centerline curvature is more sensitive to modeling methods, requiring 1 cm intervals for ≤5% deviation in peak curvature for the three diseased anatomies, and two iterations of segmentation and centerline extraction for the Aneurysmal and Dissected aortas. Accurate lumen cross-sectional characterization required 1 or 0.5 cm segmentation intervals, and two or three segmentation and centerline iterations, with greater refinement needed for more complex geometries. Depending on the geometric characteristic and complexity of anatomy and pathology, different levels of segmentation interval refinement and iterations of segmentation and centerline extraction are required.

Design and development of a CNC micro blanking machine with mechanical and control validation investigation

The increasing of needs on several industrial fields such as medical, electrical and mechanical field require accurate dimensional and geometrical function and efficiency in a product, one example being the manufacture of micro-hole and micropart products. As one of micromachining processes, CNC micro blanking machine is proposed as basic technology to fabricate the component with miniaturized dimension. In this study, the validation between theoretical input on the program control and mechanical motion is conducted to significantly reduce the gap between actual carriage motion and G-Code motion. The average deviation of actual velocity on post calibration is determined to be 10.8 mm/min, while for carriage displacement for X, Y, and Z axes are -0.0191; -0,0087; and -0.0005 mm, respectively. Based on the analysis has been performed, it can be concluded that the imprecision is caused by the geometrical deviation of carriage (linear guide), so, the carriage movement is hindered by the deviation.