Thermal Design and Verification of Spherical Scientific Satellite Q-SAT

Small satellites have gradually become an important mean of space scientific exploration. The Tsinghua University developed a spherical small satellite, Q-SAT, which is aimed at detecting the Earth gravity and atmosphere parameters. In the current paper, thermal control for Q-SAT is discussed. For heat exchange between the satellite and the environment, radiation plays the main part. Different from traditional cuboid satellites, the current spherical satellite has no individual heat input and output plane which brings challenges to the thermal design of the satellite. In addition, the cost of small satellites is required to be as low as possible. A passive thermal control solution based on integrated spherical structure is employed on the Q-SAT. The combination of two integrated hemispheres is designed to facilitate the heat conduction. Different materials are utilized to control the heat transfer path. Firstly, a set of numerical simulations demonstrate that the current design can be well adapted to complex flight environment. Next, the thermal design is verified by thermal tests. As the traditional heat radiation lamps cannot meet the test requirements of the spherical satellite, an external heat flow test method which is based on distributed heaters is proposed. Results from numerical simulations agree well with the experimental test results. Both results show that the thermal system can guarantee the functions of the satellite. Q-SAT was successfully launched into orbit on August 6, 2020. The telemetry data from Q-SAT verified the effectiveness of the satellite thermal system. The thermal design and test method proposed in present paper can potentially be adopted to other small scientific satellites as well.

Simultaneous and independent capture of multiple Rayleigh dielectric nanospheres with sine-modulated Gaussian beams

This study investigates the propagation properties and radiation forces on Rayleigh dielectric particles produced by novel sine-modulated Gaussian beams (SMGBs) because of the unique focusing properties of four independent light intensity distribution centers and possessing many deep potential wells in the output plane of the target laser. The described beams can concurrently capture and manipulate multiple Rayleigh dielectric spheres with high refractive indices without disturbing each other at the focus plane. Spheres with a low refractive index can be guided or confined in the focus but cannot be stably trapped in this single beam trap. Simulation results demonstrate that the focused SMGBs can be used to trap particle in different planes by increasing the sine-modulate coefficient g. The conditions for effective and stable capture of high-index particles and the threshold of detectable radius are determined at the end of this study.

Simplified Geometric Approach to Freeform Beam Shaper Design

Beam of light shaping process can be considered ultimate, if both irradiance and wavefront spatial distributions are under control and both can be shaped arbitrarily. In order to keep these two quantities determined simultaneously, it is required to apply at least two powered refractive or reflective surfaces. In this paper, a fully geometric design method of double-freeform beam shapers is discussed briefly. The presented algorithm is based on two stages. First, integrable input-output ray mapping is calculated by the application of the novel GATMA (Geometric Approach to Monge–Ampere equation) method. It allows us to determine the shape of the first freeform surface. Then, according to the condition of constant optical path length between input and output plane, corrected by wavefront phases at those planes, the second surface is determined. GATMA algorithm combines advantages of Monge–Ampere (MA) equation and ray-tracing efficient apparatus. Compared to the state-of-the-art freeform design methods, GATMA does not need to solve MA equation directly but uses this equation as an error function. Such approach makes the computation algorithm simpler and more robust and convergent. The application of the proposed method in a challenging design example of a beam shaper, transforming uniform collimated beam into a beam having a triangular cross section and flat wavefront, is presented as a case study.

Misalignment resilient diffractive optical networks

As an optical machine learning framework, Diffractive Deep Neural Networks (D2NN) take advantage of data-driven training methods used in deep learning to devise light–matter interaction in 3D for performing a desired statistical inference task. Multi-layer optical object recognition platforms designed with this diffractive framework have been shown to generalize to unseen image data achieving, e.g., >98% blind inference accuracy for hand-written digit classification. The multi-layer structure of diffractive networks offers significant advantages in terms of their diffraction efficiency, inference capability and optical signal contrast. However, the use of multiple diffractive layers also brings practical challenges for the fabrication and alignment of these diffractive systems for accurate optical inference. Here, we introduce and experimentally demonstrate a new training scheme that significantly increases the robustness of diffractive networks against 3D misalignments and fabrication tolerances in the physical implementation of a trained diffractive network. By modeling the undesired layer-to-layer misalignments in 3D as continuous random variables in the optical forward model, diffractive networks are trained to maintain their inference accuracy over a large range of misalignments; we term this diffractive network design as vaccinated D2NN (v-D2NN). We further extend this vaccination strategy to the training of diffractive networks that use differential detectors at the output plane as well as to jointly-trained hybrid (optical-electronic) networks to reveal that all of these diffractive designs improve their resilience to misalignments by taking into account possible 3D fabrication variations and displacements during their training phase.

Fractional Fourier Transform for Digital Image Recognition

In the image recognition field, there are several techniques that allow identifying patterns in digital images, correlation being one of them. In a correlation, you have to obtain an output plane that is as clean as possible. To measure the sharpness of the correlation peak and the cleanliness of the output plane, a performance metric called Peak to Correlation Energy (PCE) is used. In this paper, the fractional correlation is applied to recognize real phytoplankton images. This fractional correlation guarantees a higher PCE compared to the conventional correlation. The results of PCE are two-orders of magnitude higher than those obtained with the conventional correlation and manage to identify 91.23% of the images, while the conventional correlation only manages to identify 87.42% of them. This methodology was tested using images in salt and pepper or Gaussian noise, and the fractional correlation output plane always is cleaner and generates a better-defined correlation peak when compared with the classical correlation.

A Spiral-Phase Rear Mounted Triple Masking for Secure Optical Image Encryption Based on Gyrator Transform

Background: A spiral phase rear mounted masked scheme is proposed based on Gyrator Transform (GT) to enhance the security contribution of second lens of the existing Double Random Phase Encoding (DRPE) system by modulating the phase of the output obtained in output plane. An additional third layer of Spiral Phase Mask (SPM) is included in the output plane in the same 4f system. Objective: To develop a symmetric cryptosystems to enhance the security potential of the second lens and to prevent the comfortable realization of the cipher-image in the transform domain. Methods: The original image is first scrambled using Arnold transform with frequency and then is convoluted with a secret random phase mask, RPM in GT and then obtained result is convoluted with another secret RPM in inverse GT. The obtained result is then finally convoluted with SPM. Results: It verifies the sensitivity and achieves better performance in terms of recovering a high quality image. Results show the security, performance and quality analysis on the basis of correlation coefficient, occlusion attack, key sensitivity and noise attack, entropy and histogram. Conclusion: It enhances the security potential of second lens in DRPE and introduces diffusion in the system. The system is simulated for binary and greyscale image and achieves better performance as compared to existing DRPE variants. Key sensitivity is more secure and cannot recover original image without knowing all the parameters. Correlation coefficient are also weakly correlated and does not reveals relevant information. Simulation result demonstrates the feasibility and robustness of cryptosystem.

Development of mathematical methods for calculation of the pubic arch angle

Hypothesis/aims of study. The frequency of adverse intranatal outcomes is significantly increased when the pubic arch angle (PAA) is less than 90°. The accuracy of the manual method for determining PAA depends on a large number of parameters, such as obesity of a woman, as well as stereometric sensation and the experience of a doctor. Determination of PAA using ultrasound and X-ray pelviometry is generally available and reliable; however, it requires special training. The aim of this study was to develop mathematical methods for calculation of PAA. Study design, materials and methods. The study included a retrospective and prospective analysis of 120 birth histories based on the Regional Clinical Hospital Perinatal Center (the Chita city, the years 2017/2018), which were divided into three equal groups. Group 1 consisted of patients with body weight deficit, group 2 included patients with normal body mass index, and group 3 comprised patients with alimentary constitutional obesity. On the eve of the birth, external pelviometry, the manual method for determining PAA, and ultrasound pelviometry by translabial access were performed. Results. PAA determined by the manual method was 99.6 ± 11.3° in group 1, 100.1 ± 14.2° in group 2, and 98.2 ± 10.7° in group 3. When ultrasound pelviometry was performed, the value of PAA was 97.4 ± 10.7° in group 1, 104.8 ± 13.8° in group 2, and 104.1 ± 12.3° in group 3. The error of the manual method was 2.2% in group 1, 4.5% in group 2, and 7.6% in group 3. On the basis of mathematical modeling of external pelviometry data, a pattern is defined, which is expressed by the formula: PAA = 180° – arccos (0,5 ∙ S1S2/S1P) – arccos (0,5 ∙ B1B2/(B2S1 – S1P), where PAA is the pubic arch angle (°); S1S2, Distantia spinarum; S1P, the distance between the anterior superior spine of the ilium to the lower edge of the symphysis; B2S1, the distance between the anterior superior spine of the ilium to the tuberosity of the opposite ischium; B1B2, the transverse size of the output plane. The coefficient of determination (R-squared) is 0.82. Thus, mathematical modeling allows determining PAA with a high degree of reliability.

Double-grating monochromatic beamline with ultrafast response for FLASH2 at DESY

The preliminary design of a monochromatic beamline for FLASH2 at DESY is presented. The monochromator is tunable in the 50–1000 eV energy range with resolving power higher than 1000 and temporal response below 50 fs over the whole energy range. A time-delay-compensated configuration using the variable-line-spacing monochromator design with two gratings is adopted: the first grating disperses the radiation on its output plane, where the intermediate slit performs the spectral selection; the second grating compensates for the pulse-front tilt and for the spectral dispersion due to diffraction from the first grating.