Submitted Date
Subjects
Authors
Institution
  • Systematic generalization of particle dynamics to the translational reference frame

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-07-18

    Abstract: This paper presents a new development in revealing the nature of the inertial force, a concept that has long stimulated discussion in the history of physics. On this basis, its implications are systematically introduced for the improvement of physics teaching. Firstly, all the theorems in the framework of classical mechanics can be form-invariant generalized to any translational frame of reference, provided that the physical meaning of the force term of the particle in the original formulation is replaced from the total forces to the forces being relatively accounted for. Secondly, in analytical mechanics, since in general the conservative force corresponding to the potential energy is typically a part of the forces acting on the particle, it is enough to ensure that the reference origin is chosen at a position where the vector sum of the conservative forces corresponding to the potential energy is always zero. However, in the case of a general translational reference frame, a correction term for the potential energy due to the forces acting on the reference object must be included in the expression of the Lagrangian and Hamiltonian quantities. Thirdly, the symmetric new equation is applied to the system of particles. The generalized center-of-mass motion theorem and the generalized fixed-axis rotation theorem in the translational reference frame are developed. Finally, for instance, the multi-body dynamics is discussed. In principle, the detour that is introduced by the center-of-mass reference frame can be directly omitted and crossed. To illustrate this, the planetary perturbation equation is demonstrated to be derived in a single step by applying the symmetric new equation of Newtonian dynamics. Besides, the introduction of the symmetric new equation has led to further improvements and refinements in the planetary perturbation equation.

  • Systematic generalization of particle dynamics to the translational reference frame

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-07-16

    Abstract: This paper presents a new development in revealing the nature of the inertial force, a concept that has long stimulated discussion in the history of physics. On this basis, its implications are systematically introduced for the improvement of physics teaching. Firstly, all the theorems in the framework of classical mechanics can be form-invariant generalized to any translational frame of reference, provided that the physical meaning of the force term of the particle in the original formulation is replaced from the total forces to the forces being relatively accounted for. Secondly, in analytical mechanics, since in general the conservative force corresponding to the potential energy is typically a part of the forces acting on the particle, it is enough to ensure that the reference origin is chosen at a position where the vector sum of the conservative forces corresponding to the potential energy is always zero. However, in the case of a general translational reference frame, a correction term for the potential energy due to the forces acting on the reference object must be included in the expression of the Lagrangian and Hamiltonian quantities. Thirdly, the symmetric new equation is applied to the system of particles. The generalized center-of-mass motion theorem and the generalized fixed-axis rotation theorem in the translational reference frame are developed. Finally, for instance, the multi-body dynamics is discussed. In principle, the detour that is introduced by the center-of-mass reference frame can be directly omitted and crossed. To illustrate this, the planetary perturbation equation is demonstrated to be derived in a single step by applying the symmetric new equation of Newtonian dynamics. Besides, the introduction of the symmetric new equation has led to further improvements and refinements in the planetary perturbation equation.

  • Gravitational Lensing of a Static Neutron Star with Magnetic Moment and Magnetic Charge

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-06-14

    Abstract: In this paper, the gravitational lensing of a static neutron star with magnetic moment and magnetic charge is studied. In the spacetime of such a neutron star, the deflection angle of a photon is directly proportional to the neutron star’s magnetic charge and mass-to-distance ratio, while inversely proportional to the magnetic moment of the neutron star. Specifically, when the magnetic charge is 0.5, the deflection angle is constant, independent of changes in the magnetic moment. When both the magnetic moment and the magnetic charge approach zero, all parameters revert to the Schwarzschild case.

  • Prediction of Clock Bias for BeiDou Satellites Using a Combination of Variational Mode Decomposition and Long Short-Term Memory Network

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics Subjects: Information Science and Systems Science >> Basic Disciplines of Information Science and Systems Science submitted time 2024-06-09

    Abstract: The precise estimation of the satellite clock bias (SCB) holds considerable importance in ensuring accurate timekeeping, navigation, and positioning. This studyintroduces a novel SCB prediction approach that integrates variational mode decomposition (VMD) and long short-term memory (LSTM) network techniques, combining signal decomposition with deep learning methodologies. Initially, the raw SCB data undergoespreprocessing, followed by decomposition using the VMD method to generate multiple intrinsic mode functions (IMFs). These decomposed IMFs serve as inputs for LSTM, where several independent LSTM models are established for training and prediction purposes. Subsequently, the predicted outcomes are aggregated and reconstructed to derive the finalSCB prediction. Experimental findings demonstrate notable advancements in clock bias prediction for the spaceborne hydrogen atomic clock for BDS, with prediction accuracies of 0.048 ns, 0.204 ns and 1.397 ns for 6 hours, 3 days and 15 days, respectively. These results exhibit significant enhancements compared to both the LSTM network and the Back Propagation (BP) neural network, with improvements of 56%, 84% and 83% for the aforementioned time intervals in comparison to LSTM, and enhancements of 59%, 82% and 83% relative to the BP neural network. 

  • Closeby Habitable Exoplanet Survey (CHES): an Astrometry Mission for Probing Nearby Habitable Planets

    Subjects: Geosciences >> Space Physics Subjects: Physics >> Geophysics, Astronomy, and Astrophysics Subjects: Astronomy >> Galaxy and Cosmology submitted time 2024-06-02

    Abstract: The Closeby Habitable Exoplanet Survey (CHES) employs state-of-the-art, high-precision astrometry and positioning technology at the microarcsecond level in space. Its primary objective is to conduct a thorough survey of approximately 100 FGK-type stars within the Sun’s proximity (within 10 parsecs), with the goal of detecting potentially habitable Earth-like planets or super-Earths. This pioneering mission involves a detailed census of habitable planets, providing intricate information on their numbers, true masses, and three-dimensional orbits. Notably, CHES marks a historic milestone as the inaugural international space exploration mission exclusively dedicated to the study of terrestrial planets within the nearby habitable zone. CHES’s payload features a cutting-edge optical telescope with a 1.2 m aperture, a field of view measuring 0.44°×0.44°, and a focal length of 36 m. The telescope utilizes a coaxial three-mirror TMA optical imaging system. Impressively, CHES is designed with a positioning measurement accuracy of 1 μas, solidifying its status as the most precise space exploration project globally in terms of positioning accuracy. To achieve the detection objectives of CHES, it is essential to refine and further substantiate the scientific goals through comprehensive argumentation. Overcoming three key technological challenges is crucial: advancing optical systems for large field of view, developing high-quality space telescopes with minimal distortion; breaking through measurement technology for stellar separations at the 10–5 pixel level; and achieving high stability in satellite system attitude control and thermal control precision. CHES stands on the threshold of groundbreaking discoveries, with the exciting prospect of revealing 50 Earth-like planets. This announces a significant leap forward in China’s space science exploration technology.

  • Rutherford’s Atomic Nucleus versus Landau’s Gigantic Nucleus: Does Nature favor flavor symmetry?

    Subjects: Physics >> Nuclear Physics Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-05-29

    Abstract: It is hypothesized that, though atomic nuclei are made of nucleons, strongly interacting matter with baryon number from $A simeq 10^{3-9}$ to $ sim 10^{57}$ would be composed of strangeons if Nature favors always the flavor symmetry of quarks. According to that logic, strangeon matter with $A sim 10^{57}$ could manifest in the form of pulsar-like compact stars, and multi-messenger observations with advanced facilities (e.g., China’s FAST) could eventually provide a disproof/proof. It is worth emphasizing that this point of view, based on established “old physics”, may have particular consequences for understanding our material world, for both normal luminous matter and the dark sector.

  • Non-perturbative corrections to the planetary perturbation equation

    Subjects: Astronomy >> Celestial Mechanics Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-05-16

    Abstract: This paper presents a systematic improvement in celestial dynamics theory by introducing a new symmetric form of particle dynamics equation. For open multi-body systems, the symmetric new equation can be applied to any translational reference frame, thus avoiding the need for inertial reference frame approximations and enhancing the accuracy of theoretical predictions. In the case of bound multi-body systems, applying the symmetric new equation allows for an extremely simplified derivation of the planetary perturbation equation in one step. Furthermore, by considering temporary thrust or impact forces acting on planets, or even considering any external forces acting on the bound system further to enhance the computational precision, a new correction equation is now established for the planetary perturbation that can be further imposed with non-perturbative interactions. This will assist in the prediction of the trajectory of asteroids affected by external forces and in the accurate calculation of the orbit of satellites.

  • Perhaps We Have Misunderstood the Maxwell’s Theory and the Galilean Transformations

    Subjects: Information Science and Systems Science >> Basic Disciplines of Information Science and Systems Science Subjects: Physics >> Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics Subjects: Electronics and Communication Technology >> Optoelectronics and Laser Subjects: Physics >> Geophysics, Astronomy, and Astrophysics Subjects: Physics >> The Physics of Elementary Particles and Fields submitted time 2024-04-08

    Abstract: The Einstein’s theory of special relativity is based on his two postulates. The first is that the laws of physics are the same in all inertial reference frames. The second is that the velocity of light in the vacuum is the same in all inertial frames. The theory of special relativity is considered to be supported by a large number of experiments. This paper revisits the two postulates according to the new interpretations to the exact solutions of moving sources in the laboratory frame. The exact solutions are obtained using the classic Maxwell’s theory, which clearly show that the propagation velocity of the electromagnetic waves of moving sources in the vacuum is not isotropic; the propagation velocity of the electromagnetic waves and the moving velocity of the sources cannot be added like vectors; the transverse Doppler effect is intrinsically included in the fields of the moving sources. The electromagnetic sources are subject to the Newtonian mechanics, while the electromagnetic fields are subject to the Maxwell’s theory. We argue that since their behaviors are quite different, it is not a best choice to try to bind them together and force them to undergo the same coordinate transformations as a whole, like that in the Lorentz transformations. Furthermore, the Maxwell’s theory does not impose any limitations on the velocity of the electromagnetic waves. To assume that all objects cannot move faster than the light in the vacuum need more examinations. We have carefully checked the main experiment results that were considered as supporting the special relativity. Unfortunately, we found that the experimental results may have been misinterpreted. We here propose a Galilean-Newtonian-Maxwellian relativity, which can give the same or even better explanations to those experimental results.

  • PSRDP: A Parallel Processing Method for Pulsar Baseband Data

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: To address the problem of real-time processing of ultra-wide bandwidth pulsar baseband data, we designed and implemented a pulsar baseband data processing algorithm (PSRDP) based on GPU parallel computing technology. PSRDP can perform operations such as baseband data unpacking, channel separation, coherent dedispersion, Stokes detection, phase and folding period prediction, and folding integration in GPU clusters. We tested the algorithm using the J0437-4715 pulsar baseband data generated by the CASPSR and Medusa backends of the Parkes, and the J0332+5434 pulsar baseband data generated by the self-developed backend of the NanShan Radio Telescope. We obtained the pulse profiles of each baseband data. Through experimental analysis, we have found that the pulse profiles generated by the PSRDP algorithm in this paper are essentially consistent with the processing results of Digital Signal Processing Software for Pulsar Astronomy (DSPSR), which verified the effectiveness of the PSRDP algorithm. Furthermore, using the same baseband data, we compared the processing speed of PSRDP with DSPSR, and the results showed that PSRDP was not slower than DSPSR in terms of speed. The theoretical and technical experience gained from the PSRDP algorithm research in this article lays a technical foundation for the real-time processing of QTT (Qi Tai radio Telescope) ultra-wide bandwidth pulsar baseband data.

  • H i in High Gas-phase Metallicity Dwarf Galaxy WISEA J230615.06+143927.9

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: We present resolved Giant Metrewave Radio Telescope H i observations of the high gas-phase metallicity dwarf galaxy WISEA J230615.06+143927.9 (z = 0.005) (hereafter J2306) and investigate whether it could be a Tidal Dwarf Galaxy (TDG) candidate. TDGs are observed to have higher metallicities than normal dwarfs. J2306 has an unusual combination of a blue g − r color of 0.23 mag, irregular optical morphology and high-metallicity (12 + log(O/H) = 8.68 ± 0.14), making it an interesting galaxy to study in more detail. We find J2306 to be an H i rich galaxy with a large extended, unperturbed rotating H i disk. Using our H i data we estimated its dynamical mass and found the galaxy to be dark matter (DM) dominated within its H i radius. The quantity of DM, inferred from its dynamical mass, appears to rule out J2306 as an evolved TDG. A wide area environment search reveals J2306 to be isolated from any larger galaxies which could have been the source of its high gas metallicity. Additionally, the H i morphology and kinematics of the galaxy show no indication of a recent merger to explain the high-metallicity. Further detailed optical spectroscopic observations of J2306 might provide an answer to how a seemingly ordinary irregular dwarf galaxy achieved such a high level of metal enrichment.

  • A Possible γ-Ray Pulsation from PSR J1740−5340B in the Globular Cluster NGC 6397

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: Recently, a new radio millisecond pulsar (MSP) J1740−5340B, hosted in the globular cluster (GC) NGC 6397, was reported with a 5.78 ms spin period in an eclipsing binary system with a 1.97 days orbital period. Based on a modified radio ephemeris updated by tool tempo2, we analyze the ∼15 yr γ-ray data obtained from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and detect PSR J1740−5340B's γ-ray pulsation at a confidence level of ∼4σ with a weighted H-test value of ∼26. By performing a phase-resolved analysis, the γ-ray luminosity in on-pulse interval of PSR J1740−5340B is Lγ ∼ 3.8 × 1033 erg s−1 using NGC 6397's distance of 2.48 kpc. And γ-rays from the on-pulse part of PSR J1740−5340B contribute ∼90% of the total observed γ-ray emissions from NGC 6397. No significant γ-ray pulsation of another MSP J1740−5340A in the GC is detected. Considering that the previous four cases of MSPs in GCs, more data in γ-ray, X-ray, and radio are encouraged to finally confirm the γ-ray emissions from MSP J1740−5340B, especially starving for a precise ephemeris.

  • Periodic Variation Studies of the Two Short Period W UMa-type Eclipsing Binaries: LX Lyn and V0853 Aur

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: In this paper, new light curves (LCs) of contact eclipsing binary (CEB) systems LX Lyn and V0853 Aur are presented and analyzed by using the 2015 version of the Wilson–Devinney (W-D) code. In order to explain their asymmetric LCs, cool starspots on the components were employed. It is suggested that their fill-out degrees are f = 12.0% (LX Lyn) and f = 26.3% (V0853 Aur). At the same time, we found that LX Lyn is a W-type eclipsing binary (EB) with an orbital inclination of i = 8488 and a mass ratio of q = 2.31. V0853 Aur is also a W-type CEB with a mass ratio of q = 2.77 and an orbital inclination of i = 7926. Based on all available times of light minimum, their orbital period changes are studied by using the O − C method. The O − C diagram of LX Lyn reveals a cyclic oscillation with a period of about 14.84 yr and an amplitude of 0.0019 days, which can be explained by the light-travel time effect (LTTE) due to the presence of a third body with a minimum mass of 0.06M⊙. For V0853 Aur, it is discovered that the O − C diagram of the system also shows a cyclic oscillation with a period of 9.64 yr and an amplitude of 0.03365 days. The cyclic oscillation of V0853 Aur can be attributed to the LTTE by means of a third body with a mass no less than 3.77M⊙. The third body may play an important role in the formation and evolution of these systems.

  • The RFI Fast Mitigation Algorithm Based on Block LMS Filter

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: The radio telescope possesses high sensitivity and strong signal collection capabilities. While receiving celestial radiation signals, it also captures Radio Frequency Interferences (RFIs) introduced by human activities. RFI, as signals originating from sources other than the astronomical targets, significantly impacts the quality of astronomical data. This paper presents an RFI fast mitigation algorithm based on block Least Mean Square (LMS) algorithm. It enhances the traditional adaptive LMS filter by grouping L adjacent time-sampled points into one block and applying the same filter coefficients for filtering within each block. This transformation reduces multiplication calculations and enhances algorithm efficiency by leveraging the time-domain convolution theorem. The algorithm is tested using baseband data from the Parkes 64 m radio telescope's pulsar observations and simulated data. The results confirm the algorithm's effectiveness, as the pulsar profile after RFI mitigation closely matches the original pulsar profile.

  • A Rendezvous Mission to the Second Earth Trojan Asteroid 2020 XL5 with Low-Thrust Multi-Gravity Assist Techniques

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: As the second of Earth's Trojan asteroids, 2020 XL5 is worthy of rendezvous and even sample return missions in many aspects. In this paper, a rendezvous mission to Earth's second Trojan asteroid 2020 XL5 is proposed. However, due to its high inclination and large eccentricity, direct impulsive transfer requires large amounts of fuel consumption. To address this challenge, we explore the benefits of electric propulsion and multi-gravity assist techniques for interplanetary missions. These two techniques are integrated in this mission design. The design of a low-thrust gravity-assist (LTGA) trajectory in multi-body dynamics is thoroughly investigated, which is a complex process. A comprehensive framework including three steps is presented here for optimization of LTGA trajectories in multi-body dynamics. The rendezvous mission to 2020 XL5 is designed with this three-step approach. The most effective transfer sequence among the outcomes involves Earth–Venus–Earth–Venus-2020 XL5. Numerical results indicate that the combination of electric propulsion and multi-gravity assists can greatly reduce the fuel consumption, with fuel consumption of 9.03%, making it a highly favorable choice for this rendezvous mission.

  • Simulation of RFI Cancellation Using Subspace Projection Algorithm for PAF Receiver

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: The simulation of radio frequency interference (RFI) cancellation by applying a spatial filtering technique for phased array feed (PAF) is presented. In order to better reflect the characteristics of PAF, a new signal model is to add the coupling coefficient among elements of PAF to the conventional array signal model. Then the subspace projection (SP) algorithm is used to cancel RFI from the correlation matrix of the signal, and finally, the 2D power image is drawn. The power variation of signal-of-interest direction and RFI direction before and after using the SP algorithm is analyzed. The new signal model and simulation strategy can be used to test and verify the beamformer.

  • Low Surface Brightness Galaxies Selected by Different Model Fitting

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: We present a study of low surface brightness galaxies (LSBGs) selected by fitting the images for all the galaxies in α.40 SDSS DR7 sample with two kinds of single-component models and two kinds of two-component models (disk+bulge): single exponential, single sérsic, exponential+deVaucular (exp+deV), and exponential+sérsic (exp+ser). Under the criteria of the B band disk central surface brightness  and the axis ratio b/a > 0.3, we selected four none-edge-on LSBG samples from each of the models which contain 1105, 1038, 207, and 75 galaxies, respectively. There are 756 galaxies in common between LSBGs selected by exponential and sérsic models, corresponding to 68.42% of LSBGs selected by the exponential model and 72.83% of LSBGs selected by the sérsic model, the rest of the discrepancy is due to the difference in obtaining μ0between the exponential and sérsic models. Based on the fitting, in the range of 0.5 ≤ n ≤ 1.5, the relation of μ0 from two models can be written as . The LSBGs selected by disk+bulge models (LSBG_2comps) are more massive than LSBGs selected by single-component models (LSBG_1comp), and also show a larger disk component. Though the bulges in the majority of our LSBG_2comps are not prominent, more than 60% of our LSBG_2comps will not be selected if we adopt a single-component model only. We also identified 31 giant low surface brightness galaxies (gLSBGs) from LSBG_2comps. They are located at the same region in the color–magnitude diagram as other gLSBGs. After we compared different criteria of gLSBGs selection, we find that for gas-rich LSBGs, M⋆ > 1010M⊙ is the best to distinguish between gLSBGs and normal LSBGs with bulge.

  • The Application of Permanent Magnet Synchronous Motor with Small Electrical Time Constant in Fiber Positioner

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: With the development of cutting-edge multi-object spectrographs, fiber positioners located in the focal plane are being scaled down in size, and miniature hollow-cup Permanent Magnet motors are now being considered as a suitable replacement for Faulhaber Precistep stepper motors. However, the small electrical time constant of such coreless motors poses a challenge, as the problem of severe commutation torque ripple in a fiber positioner running a position loop has been tricky. To overcome this challenge, it is advised to increase the Pulse Width Modulation (PWM) frequency as much as possible to mitigate the effects of the current fluctuation. This must be done while ensuring adequate resolution of the PWM generator. By employing a voltage open-loop field-oriented control based on a modulation frequency of 1 MHz, the drive current only costs 25 mA under a 3.3 V power supply. The sine degree of phase current is immaculate, and the repeat positioning accuracy can reach 2 μm. Moreover, it is possible to further shrink the bill of devices and the layout area of the Printed Circuit Board, especially in size-sensitive applications. This device has been developed under the new generation of The Large Sky Area Multi-Object Fiber Spectroscopic Telescope.

  • Spin Evolution of the Magnetar SGR J1935+2154

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: Fast radio bursts (FRBs) are short pulses observed in radio frequencies usually originating from cosmological distances. The discovery of FRB 200428 and its X-ray counterpart from the Galactic magnetar SGR J1935+2154 suggests that at least some FRBs can be generated by magnetars. However, the majority of X-ray bursts from magnetars are not associated with radio emission. The fact that only in rare cases can an FRB be generated raises the question regarding the special triggering mechanism of FRBs. Here we report long time spin evolution of SGR J1935+2154 until the end of 2022. According to ν and , the spin evolution of SGR J1935+2154 could be divided into two stages. The first stage evolves relatively steady evolution until 2020 April 27. After the burst activity in 2020, the spin of SGR J1935+2154 shows strong variations, especially for  . After the burst activity in 2022 October, a new spin-down glitch with Δν/ν = (–7.2 ± 0.6) × 10−6 is detected around MJD 59876, which is the second event in SGR J1935+2154. At the end, spin frequency and pulse profile do not show variations around the time of FRB 200428 and radio bursts 221014 and 221021, which supply strong clues to constrain the trigger mechanism of FRBs or radio bursts.

  • Investigating the Evolution of Amati Parameters with Redshift

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: Gamma-ray bursts (GRBs) are among the brightest objects in the Universe and, hence, can be observed up to a very high redshift. Properly calibrated empirical correlations between intensity and spectral correlations of GRBs can be used to estimate the cosmological parameters. However, the possibility of the evolution of GRBs with redshift is a long-standing puzzle. In this work, we used 162 long-duration GRBs to determine whether GRBs below and above a certain redshift have different properties. The GRBs are split into two groups, and we fit the Amati relation for each group separately. Our findings demonstrate that estimations of the Amati parameters for the two groups are substantially dissimilar. We perform simulations to investigate whether the selection effects could cause the difference. Our analysis shows that the differences may be either intrinsic or due to systematic errors in the data, and the selection effects are not their true origin. However, in-depth analysis with a new data set comprised of 119 long GRBs shows that intrinsic scatter may partly be responsible for such effects.

  • Design and Cryogenic Performance of a Hexapod Platform for a Large Ground-based Wide Field Survey Telescope

    Subjects: Physics >> Geophysics, Astronomy, and Astrophysics submitted time 2024-02-01 Cooperative journals: 《Research in Astronomy and Astrophysics》

    Abstract: The thermal gradient is an important factor that causes degradation to the image quality of telescopes. In order to ensure the accurate alignment of the primary focus unit and the primary mirror, the hexapod platform (as a corrector) is investigated in this paper. First, a ground-based telescope with 2.5 m aperture and 3.5 deg field of view is described. The telescope is under construction, and it is expected to be finished in 2023. Second, the hexapod platform with flexure hinges utilized to adjust the primary focus unit is proposed, which is applied as a corrector. Then, the inverse kinematics of the platform is established and an open-loop control system is built based on it. Finally, the cryogenic performance test for the hexapod platform is performed. The experimental results show that the resolution and repeatability of the translation for the hexapod platform can be achieved at the micrometer level. The resolution and repeatability of the rotation can be achieved at the arc-second level. Therefore, the cryogenic performance of the hexapod platform can meet the optical imaging requirements of the wide-field ground-based telescope. The kinematic analysis and cryogenic performance tests in the paper provide a technical reference for the precise alignment of the primary focus unit and the primary mirror, which can improve the imaging quality of the telescope.