Hasil untuk "Astronomy"

Tanagodchaporn Inyanya, Youn Kil Jung, Hongjing Yang et al.

Planet-formation theories suggest the presence of free-floating planets (FFPs) that are ejected from their formation sites. While these planets emit very little light, they can be identified through gravitational microlensing. Here, we report the discovery of a FFP candidate in the microlensing event KMT-2024-BLG-3237. The observed light curve exhibits strong finite-source effects characterized by a small amplitude (≲0.9 mag) and a short timescale (≲3 days). The analysis yields an Einstein timescale of t _E  = 0.54 ± 0.02 days and an angular Einstein radius of θ _E  = 6.30 ± 0.48 μ as. The measurements make it possible to estimate the lens mass as $M\,\simeq 102\,{M}_{\oplus }\,{({\pi }_{{\rm{rel}}}/16\,\mu {\rm{as}})}^{-1}$ , where π _rel is the relative lens-source parallax. Depending on the unknown π _rel , the lens could be a Neptune-mass planet ( π _rel  ≃ 0.1 mas) or a Saturn-mass planet ( π _rel  ≃ 16 μ as). A Bayesian analysis yields the lens mass $M={67.3}_{-42.5}^{+103.2}\,{M}_{\oplus }$ and the lens distance ${D}_{{\rm{L}}}={7.34}_{-2.11}^{+0.96}\,{\rm{kpc}}$ . This lens is thirteenth isolated microlens with a measurement of θ _E  < 10 μ as. We find that additional searches for possible signatures of a lens host do not show significant evidence for the host.

Jingyan Li, Yan Niu, Dan Yu et al.

Facial information carries key personal privacy, and it is crucial to ensure its security through encryption. Traditional encryption for portrait images typically processes the entire image, despite the fact that most regions lack sensitive facial information. This approach is notably inefficient and imposes unnecessary computational burdens. To address this inefficiency while maintaining security, we propose a novel dual-region encryption model for portrait images. Firstly, a Multi-task Cascaded Convolutional Network (MTCNN) was adopted to efficiently segment facial images into two regions: facial and non-facial. Subsequently, given the high sensitivity of facial regions, a robust encryption scheme was designed by integrating a CNN-based key generator, the proposed three-dimensional Multi-module Nonlinear Feedback-coupled Chaotic System (3D-MNFC), DNA encoding, and bit reversal. The 3D-MNFC incorporating time-varying parameters, nonlinear terms and state feedback terms and coupling mechanisms has been proven to exhibit excellent chaotic performance. As for non-facial regions, the Logistic map combined with XOR operations is used to balance efficiency and basic security. Finally, the encrypted image is obtained by restoring the two ciphertext images to their original positions. Comprehensive security analyses confirm the exceptional performance of the regional model: large key space (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mn>2</mn><mn>536</mn></msup></semantics></math></inline-formula>) and near-ideal information entropy (7.9995), NPCR and UACI values of 99.6055% and 33.4599%. It is worth noting that the model has been verified to improve efficiency by at least 37.82%.

Jiaxiang Tian, Yulong Zhong, Yingchun Shen et al.

The Global Navigation Satellite System (GNSS) is vital for monitoring terrestrial water storage (TWS). However, effectively extracting hydrological load deformation from GNSS observations poses a significant challenge. This study proposes a novel strategy; the seasonal hydrological load signals are removed from the raw data, and the remaining signals use principal component analysis (PCA). Simulation results from Yunnan Province demonstrate that the spatial distribution of the root mean square error (RMSE) is improved by approximately 15 % compared with traditional PCA extraction from raw data. From January 2013 to December 2022, TWS was inverted from 24 GNSS stations in Yunnan Province. The spatial distribution and time series of TWS inverted from GNSS align well with those TWS inferred from the Gravity Recovery and Climate Experiment (GRACE), GRACE Follow-On (GFO), and the Global Land Data Assimilation System (GLDAS) land surface model. However, the amplitude of the GNSS-inverted TWS is slightly higher. Since GNSS ground stations are more sensitive to hydrological load signals, they show correlations with precipitation data that are 8.6 % and 6.0 % higher than those of GRACE and GLDAS, respectively. In the power spectral density analysis of GRACE/GFO, GLDAS, and GNSS, the signal strength of GNSS is much higher than that of GRACE/GFO and GLDAS in the June and February cycles. These findings suggest that the new data extraction strategy can capture higher frequency hydrological signals in TWS, and GNSS observations can help address limitations in GRACE/GFO observations. This study demonstrates the potential of GNSS TWS in capturing higher-frequency hydrological signals and climate extremes application.

Yisheng Tu, Zhi-Yun Li, Zhaohuan Zhu et al.

Jets and outflows are commonly observed in young stellar objects, yet their origins remain debated. Using 3D nonideal magnetohydrodynamic (MHD) simulations of a circumstellar disk threaded by a large-scale open poloidal magnetic field, we identify three components in the disk-driven outflow: (1) a fast, collimated jet, (2) a less collimated, slower laminar disk wind, and (3) a magneto-rotational instability (MRI)-active turbulent disk wind that separates the former two. At high altitudes, the MRI-active wind merges with the laminar disk wind, leaving only the jet and disk wind as distinct components. The jet is powered by a novel mechanism in the star formation context: a lightly mass-loaded outflow driven by toroidal magnetic pressure in the low-density polar funnel near the system’s rotation axis. A geometric analysis of the magnetic field structure confirms that magnetic tension does not contribute to the outflow acceleration, with magnetic pressure acting as the dominant driver. While the outflow in our model shares similarities with the magneto-centrifugal model—such as angular momentum extraction from the accreting disk—centrifugal forces play a negligible role in jet acceleration. In particular, the flow near the jet base does not satisfy the conditions for magneto-centrifugal wind launching. Additionally, the jet in our simulation exhibits strong spatial and temporal variability. These differences challenge the applicability of rotation–outflow velocity relations derived from steady-state, axisymmetric magneto-centrifugal jet models for estimating the jet’s launching radius. For the slower disk wind, vertical motion is driven by toroidal magnetic pressure, while centrifugal forces widen the wind’s opening angle.

C.-I. Björnsson

The evolution of SN 1993J is unlikely to be self-similar. Spatially resolved very long baseline interferometry observations show that the velocity of the outer rim of the radio emission region breaks at a few hundred days. The reason for this break remains largely unknown. It is argued here that it is due to the transition between an initial piston phase to a later phase, which is described by the standard model. The properties of the reverse shock are quite different for a piston phase as compared to the standard self-similar model. This affects the expected X-ray emission; for example, the reverse shock becomes transparent to X-ray emission much earlier in the piston phase. Furthermore, it is shown that the observed box-like emission line profiles of H α and other optical lines are consistent with an origin from the transition region between the envelope and the core. It is also pointed out that identifying the observed, simultaneous breaks at ≈3100 days in the radio and X-ray light curves with the reverse shock reaching the core makes it possible to directly relate the mass-loss rate of the progenitor star to observables.

Mingyang Wang, Peng Liu, Jianping Yuan et al.

We report the detection of an antiglitch with a fractional frequency change of Δ ν / ν  = −3.46(6) × 10 ^−9 in the rotation-powered pulsar PSR J1835−1106 at MJD 55813(9), based on timing observations collected with the Nanshan 26 m and Parkes 64 m radio telescopes from 2000 January to 2022 July. A comparison of the average pulse profiles within ±300 days of the event reveals no significant morphological changes. We also estimate the angular velocity lag between the normal and superfluid components at the time of the glitch, showing that one of the superfluid glitch models is incompatible with PSR J1835−1106 due to its insufficient spin-down rate and angular velocity lag. The wind braking scenario offers a viable alternative, consistent with the observed spin-down behavior, glitch amplitude, and postglitch recovery. High-cadence, high-sensitivity monitoring of similar events is essential to distinguish between internal (superfluid) and external (wind-related) glitch mechanisms.

J. Tacza, G. Li, J.‐P. Raulin

Abstract The suppression of high‐energy cosmic rays, known as Forbush decreases (FDs), represents a promising factor in influencing the global electric circuit (GEC) system. Researchers have delved into these effects by examining variations, often disruptive, of the potential gradient (PG) in ground‐based measurements taken in fair weather regions. In this paper, we aim to investigate deviations observed in the diurnal curve of the PG, as compared to the mean values derived from fair weather conditions, during both mild and strong Forbush decreases. Unlike the traditional classification of FDs, which are based on ground level neutron monitor data, we classify FDs using measurements of the Alpha Magnetic Spectrometer (AMS‐02) on the International Space Station. To conduct our analysis, we employ the superposed epoch method, focusing on PGs collected between January 2010 and December 2019 at a specific station situated at a low latitude and high altitude: the Complejo Astronómico El Leoncito (CASLEO) in Argentina (31.78°S, 2,550 m above sea level). Our findings reveal that for events associated with FDs having flux amplitude (A) decrease ≤10%, no significant change in the PG is observed. However, for FDs with A > 10%, a clear increase in the PG is seen. For these A > 10% events, we also find a good correlation between the variation of Dst and Kp indices and the variation of PG.

Adam Ingram, Niek Bollemeijer, Alexandra Veledina et al.

We report on an observational campaign on the bright black hole (BH) X-ray binary Swift J1727.8–1613 centered around five observations by the Imaging X-ray Polarimetry Explorer. These observations track for the first time the evolution of the X-ray polarization of a BH X-ray binary across a hard to soft state transition. The 2–8 keV polarization degree decreased from ∼4% to ∼3% across the five observations, but the polarization angle remained oriented in the north–south direction throughout. Based on observations with the Australia Telescope Compact Array, we find that the intrinsic 7.25 GHz radio polarization aligns with the X-ray polarization. Assuming the radio polarization aligns with the jet direction (which can be tested in the future with higher-spatial-resolution images of the jet), our results imply that the X-ray corona is extended in the disk plane, rather than along the jet axis, for the entire hard intermediate state. This in turn implies that the long (≳10 ms) soft lags that we measure with the Neutron star Interior Composition ExploreR are dominated by processes other than pure light-crossing delays. Moreover, we find that the evolution of the soft lag amplitude with spectral state does not follow the trend seen for other sources, implying that Swift J1727.8–1613 is a member of a hitherto undersampled subpopulation.

Michael M. Foley, Alyssa Goodman, Catherine Zucker et al.

Barnard’s Loop is a famous arc of H α emission located in the Orion star-forming region. Here, we provide evidence of a possible formation mechanism for Barnard’s Loop and compare our results with recent work suggesting a major feedback event occurred in the region around 6 Myr ago. We present a 3D model of the large-scale Orion region, indicating coherent, radial, 3D expansion of the OBP-Near/Briceño-1 (OBP-B1) cluster in the middle of a large dust cavity. The large-scale gas in the region also appears to be expanding from a central point, originally proposed to be Orion X. OBP-B1 appears to serve as another possible center, and we evaluate whether Orion X or OBP-B1 is more likely to have caused the expansion. We find that neither cluster served as the single expansion center, but rather a combination of feedback from both likely propelled the expansion. Recent 3D dust maps are used to characterize the 3D topology of the entire region, which shows Barnard’s Loop’s correspondence with a large dust cavity around the OPB-B1 cluster. The molecular clouds Orion A, Orion B, and Orion λ reside on the shell of this cavity. Simple estimates of gravitational effects from both stars and gas indicate that the expansion of this asymmetric cavity likely induced anisotropy in the kinematics of OBP-B1. We conclude that feedback from OBP-B1 has affected the structure of the Orion A, Orion B, and Orion λ molecular clouds and may have played a major role in the formation of Barnard’s Loop.

Z. Wang, A. Vaivads, H. S. Fu et al.

Magnetic flux ropes or magnetic islands are important structures responsible for electron acceleration and energy conversion during turbulent reconnection. However, the evolution of flux ropes and the corresponding electron acceleration process still remain open questions. In this paper, we present a comparative study of flux ropes observed by the Magnetospheric Multiscale mission in the outflow region during an example of turbulent reconnection in Earth's magnetotail. Interestingly, we find the farther the flux rope is away from the X-line, the bigger the size of the flux rope and the slower it moves. We estimate the power density converted at the observed flux ropes via the three fundamental electron acceleration mechanisms: Fermi, betatron, and parallel electric field. The dominant acceleration mechanism at all three flux ropes is the betatron mechanism. The flux rope that is closest to the X-line, having the smallest size and the fastest moving velocity, is the most efficient in accelerating electrons. Significant energy also returns from particles to fields around the flux ropes, which may facilitate the turbulence in the reconnection outflow region.

Mohammed El Amine Monir, Zohra Bahnes, Houaria Riane et al.

The first principle calculations on the structural, electronic structure as well as the magnetic properties of Ruddlesden-Popper Nd2MO4 (M = Sc and Y) compounds were accomplished by using the full-potential linearized augmented plane waves with local orbitals (FP-LAPW + lo) method within the spin-polarized density functional theory (spin-DFT) and implemented in the WIEN2k package. The exchange and correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural properties. Moreover, the PBE-GGA + U approximation (where U is the Hubbard correlation term) is used to treat “d” and “f” electrons for the electronic and magnetic properties of these compounds. The equilibrium structural parameters such as: lattice constants (a0 and c0), bulk modulus (B0) and the first pressure-derivative of bulk modulus (B’), are optimized for all these alloys. The calculations of the electronic properties for the Ruddlesden-Popper Nd2MO4 (M = Sc and Y) compounds at their equilibrium lattice parameters disclose that the both compounds are half-metallic materials. The magnetic properties show that the total magnetic moment for the two Nd2ScO4 and Nd2YO4 compounds is found in integer value. The magnetic moment of Nd is reduced from its free space charge value of 4μB, whereas small magnetic moments are produced on the nonmagnetic O1 and O2 sites.

Abdulrahim Al Balushi, Zhencheng Wang, Donald Marolf

Abstract We generalize the Gao-Jafferis-Wall construction of traversable two-sided wormholes to multi-boundary wormholes. In our construction, we take the background spacetime to be multi-boundary black holes in AdS3. We work in the hot limit where the dual CFT state in certain regions locally resembles the thermofield double state. Furthermore, in these regions, the hot limit makes the causal shadow exponentially small. Based on these two features of the hot limit, and with the three-boundary wormhole as our main example, we show that traversability between any two asymptotic regions in a multi-boundary wormhole can be triggered using a double-trace deformation. In particular, the two boundary regions need not have the same temperature and angular momentum. We discuss the non-trivial angular dependence of traversability in our construction, as well as the effect of the causal shadow region.

Sharon Aol, Stephan Buchert, Edward Jurua

Abstract Ionospheric irregularities can affect satellite communication and navigation by causing scintillations of radio signals. The scintillations are routinely measured using ground-based networks of receivers. This study presents observations of ionospheric irregularities by Langmuir probes on the Swarm satellites. They are compared with amplitude scintillation events recorded by the Global Positioning System-Scintillation Network and Decision Aid (GPS-SCINDA) receiver installed in Mbarara (Lat: $$0.6^{\circ }\hbox {S}$$ 0 . 6 ∘ S , Lon: $$30.8^{\circ }\hbox {E}$$ 30 . 8 ∘ E , Mag. lat: $$10.2^{\circ }\hbox {S}$$ 10 . 2 ∘ S ). The study covers the years from 2014 to 2018 when both data sets were available. It was found that the ground-based amplitude scintillations were enhanced when Swarm registered ionospheric irregularities for a large number of passes. The number of matching observations was greater for Swarm A and C which orbited at lower altitudes compared to Swarm B. However, some counterexamples, i.e., cases when in situ electron density fluctuations were not associated with any observed L-band amplitude scintillation and vice versa, were also found. Therefore, mismatches between observed irregularity structures and scintillations can occur just over a few minutes and within distances of a few tens of kilometers. The amplitude scintillation strength, characterized by the S4 index was estimated from the electron density data using the well-known phase screen model for weak scattering. The derived amplitude scintillation was on average lower for Swarm B than for A and C and less in accordance with the observed range. Irregularities at an altitude of about 450 km contribute strongly to scintillations in the L-band, while irregularities at about 510-km altitude contribute significantly less. We infer that in situ density fluctuations observed on passes over or near Mbarara may be used to indicate the risk that ionospheric radio wave scintillations occur at that site.

Hussein Abdulrahman Hussein , Sangar Abdalla Rasul

This research concentrates on the condition of in the land of Kurds between (6-9 Hi|12-15 AC). In other words, this research demonstrates the role of scientists and scientific institutions in the development of mental sciences. The significance of this research is in displaying the position of the land of Kurds within the mentioned historical period. That is because this field has somehow been ignored and the researchers have mostly focused on the political and military developments. We have found it is necessary to open a gate for conducting researchs on this subject. in order to determine the role of the scientists in the paties sciences. This research consists of three parts. In the first part, we discuss the Christian religion; its institutions, and impacts on the Kurds. In the second part, we discuss the role of scientists in the land of Kurds and their publications about history and philosophy. In the third part, we discuss the the role of the scientists in the of Kurds about the sciences such as accountancy, chemistry, astronomy, medicine.

Man Xie, Shu-Yi Wei, Guang-You Qin et al.

Abstract We study the suppressions of high transverse momentum single hadron and dihadron productions in high-energy heavy-ion collisions based on the framework of a next-to-leading-order perturbative QCD parton model combined with the higher-twist energy loss formalism. Our model can provide a consistent description for the nuclear modification factors of single hadron and dihadron productions in central and non-central nucleus–nucleus collisions at RHIC and the LHC energies. We quantitatively extract the value of jet quenching parameter $$\hat{q}$$ q^ via a global $$\chi ^2$$ χ2 analysis, and obtain $${\hat{q}}/{T^3} = 4.1$$ q^/T3=4.1 –4.4 at $$T = 378$$ T=378  MeV at RHIC and $${\hat{q}}/{T^3} = 2.6$$ q^/T3=2.6 –3.3 at $$T = 486$$ T=486  MeV at the LHC, which are consistent with the results from JET Collaboration. We also provide the predictions for the nuclear modification factors of dihadron productions in Pb + Pb collisions at $$\sqrt{s_\mathrm{{NN}}}$$ sNN = 5.02 TeV and in Xe + Xe collisions at $$\sqrt{s_\mathrm{{NN}}}$$ sNN = 5.44 TeV.

Xiaowen Zhang, Xingzhao Liu

In this paper, the problem of cognitive radar (CR) waveform optimization design for target detection and estimation in multiple extended targets situations is investigated. This problem is analyzed in signal-dependent interference, as well as additive channel noise for extended targets with unknown target impulse response (TIR). To address this problem, an improved algorithm is employed for target detection by maximizing the detection probability of the received echo on the promise of ensuring the TIR estimation precision. In this algorithm, an additional weight vector is introduced to achieve a trade-off among different targets. Both the estimate of TIR and transmit waveform can be updated at each step based on the previous step. Under the same constraint on waveform energy and bandwidth, the information theoretical approach is also considered. In addition, the relationship between the waveforms that are designed based on the two criteria is discussed. Unlike most existing works that only consider single target with temporally correlated characteristics, waveform design for multiple extended targets is considered in this method. Simulation results demonstrate that compared with linear frequency modulated (LFM) signal, waveforms designed based on maximum detection probability and maximum mutual information (MI) criteria can make radar echoes contain more multiple-target information and improve radar performance as a result.

Márton Lendvay

The aim of this paper is to test whether the concept of resilience can be applied to rural communities in postsocialist transition countries such as Hungary. Resilience, a concept engaged with the dynamics of change, has gained popularity in recent years following the post-2008 crisis and has become a core theme of academic, policy and lay discourses in the Anglo-Saxon world. The ongoing processes of socio-economic transition within the post-socialist environment have also att racted wide attention in the past decades, although not within the frameworks of resilience thinking. The concept of resilience is missing from post-socialist discourses and has not been applied to rural communities before in an Eastern European context, although the nature of post-socialist transition characterised by complexity, cross-scalar processes and multiplicity of actors involved make it an especially suitable field for resilience studies. In this paper, we aim to flag the potential directions and successful application of the concept of resilience both as a research topic and as a tool for researchers of the post-socialist space while we caution for the potential pitfalls and misuses of the concept and critically analyse aspects that attracted wide debates. We illustrate how rural community resilience may be conceptualised on the example of the watermelon producing community of Medgyesegyháza, Hungary.

Jun-Yi Ge, Vladimir N. Gladilin, Jacques Tempere et al.

Scanning tunneling microscope (STM) is a powerful tool but local control of superconductivity with the STM tip is still lacking. Here, Geet al. show the use of an STM tip to control the local pinning in a superconductor through the heating effect, allowing to manipulate single superconducting vortex at nanoscale.

S. Kulkarni, C. Heiles

J. M. Bailey, T. Slater