Hasil untuk "Astronomy"

Muhammad Fitrah Alfian Rangga Sakti

We construct the exact stellar configurations that contain an ordinary perfect-fluid matter that interacts minimally with a condensate of gravitons with distinct pressure conditions on the surface. We propose vanishing transverse pressure on the surface for, namely graviton condensate type 1 and vanishing radial pressure on the surface for type 2. The condition for the radial pressure of type 1 requires the existence of a thin shell that will balance the pressure discontinuity while for type 2, the discontinuity on transverse pressure does not require the additional thin shell. It is found that the Buchdahl inequality of the resulting stellar configurations depends on the parameter related to the graviton condensate, such that we can find the ultra-compact regime of the stellar models. Moreover, the echo time and echo frequency within the ultra-compact regime are computed. At the same compactness, it is found that the presence of the graviton condensate will delay the gravitational echoes for type 2 and will expedite the gravitational echoes for type 1 compared to constant density star, τecho2 > τCDS > τecho1. Furthermore, the gravitational perturbation of a massless scalar wave is also investigated to support these results. These results could open more opportunities for the observational study of graviton in the near future, mostly from the compact astrophysical objects.

Akash Kundu, Leopoldo Sarra

Abstract Quantum computing offers exciting opportunities for simulating complex quantum systems and optimizing large-scale combinatorial problems, but its practical use is limited by device noise and constrained connectivity. Designing quantum circuits, which are fundamental to quantum algorithms, is therefore a central challenge in current quantum hardware. Existing reinforcement learning-based methods for circuit design lose accuracy when restricted to hardware-native gates and device-level compilation. Here, we introduce gadget reinforcement learning (GRL) that combines learning with program synthesis to automatically construct composite gates that expand the action space while respecting hardware constraints. We show that this approach improves accuracy, hardware compatibility, and scalability for transverse-field Ising and quantum chemistry problems, reaching systems of up to ten qubits within realistic computational budgets. This framework demonstrates how learned, reusable circuit building blocks can guide the co-design of algorithms and hardware for quantum processors.

Joseph O’Leary, Andrew Melatos, Tom Kimpson et al.

X-ray timing studies of the persistent, Galactic, accretion-powered pulsar 4U 1626−67 reveal torque reversals, during which the pulse frequency ν ( t ) alternates between multiyear episodes of secular acceleration and deceleration, separated by transitions lasting ≲150 days. Here an unscented Kalman filter is applied to track the ν ( t ) fluctuations observed in 22.7 yr (3340 samples) of publicly available Compton Gamma-Ray Observatory and Fermi Gamma-Ray Space Telescope data to test the canonical picture of magnetocentrifugal accretion for consistency with prograde–prograde and retrograde–prograde accretion disk configurations on either side of the 2008 torque reversal. It is found that the retrograde–prograde model is preferred, with a log Bayes factor equal to 0.44 and a maximum a posteriori log likelihood ratio equal to 2.5. The mass accretion rate Q ( t ) and magnetocentrifugal fastness ω ( t ) transition smoothly between episodes of deceleration and acceleration: Q ( t ) shifts by ≤0.34 dex across the reversal, and one measures ω ( t ) ≈ 0.25 and ω ( t ) ≈ 0.30 during deceleration and acceleration, respectively. The angular acceleration $\dot{{\rm{\Omega }}}(t)$ satisfies $-9\,\lesssim \,\dot{{\rm{\Omega }}}(t)/(1{0}^{-12}\,{\rm{rad}}\,{{\rm{s}}}^{-2})\,\lesssim \,-5$ and $2\,\lesssim \,\dot{{\rm{\Omega }}}(t)/(1{0}^{-12}\,{\rm{rad}}\,{{\rm{s}}}^{-2})\,\lesssim \,9$ before and after the 2008 reversal, respectively, compared to $\dot{{\rm{\Omega }}}\approx -3.0\,\times 1{0}^{-12}\,{\rm{rad}}\,{{\rm{s}}}^{-2}$ before reversal and $\dot{{\rm{\Omega }}}\approx 2.5\times 1{0}^{-12}\,{\rm{rad}}\,{{\rm{s}}}^{-2}$ after reversal, as inferred from previous long-term X-ray timing and spectral analysis of 4U 1626−67.

Roger E. Cohen, Kristen B. W. McQuinn, Alessandro Savino et al.

Radial stellar population gradients within dwarf galaxies provide a promising avenue for disentangling the drivers of galaxy evolution, including environment. Within the Local Volume, radial stellar age gradient slopes correlate with interaction history, contrary to model predictions, so dwarfs that are isolated provide a critical control sample. We measure radial stellar age gradients in the relatively isolated gas-rich dwarf irregular Wolf–Lundmark–Melotte Galaxy (WLM), combining JWST NIRCam and NIRISS imaging with six archival Hubble Space Telescope fields over semimajor axis equivalent distances of 0 ≲  R _SMA  ≲ 4 kpc (≲3 R _hl ). Fitting lifetime star formation histories to resolved color–magnitude diagrams, radial age gradients are quantified using τ _90 and τ _50 , the lookback times to form 90% and 50% of the cumulative stellar mass. We find that globally, the outskirts of WLM are older on average, with ( δτ _90 , δτ _50 )/ δ R _SMA  = (0.82 ${}_{-0.10}^{+0.10}$ , 1.60 ${}_{-0.22}^{+0.23}$ ) Gyr kpc ^−1 (stat.), in good agreement with simulations. However, we also detect an azimuthal dependence of radial stellar age gradients, finding that stars on the leading edge of WLM (relative to its proper motion) are both younger and have a flatter age gradient compared to the trailing edge. This difference persists over 0.6 ≲  R _SMA  ≲ 3.2 kpc (∼0.5–2.5 R _hl ) and lookback times up to ∼8 Gyr, and is robust to the assumed stellar evolutionary model. Our results are consistent with star formation triggered by ram pressure stripping from a circumgalactic and/or intergalactic medium, suggested by recent H I observations. If confirmed, processes typifying dense environments, such as ram pressure stripping, may be more relevant to the evolution of isolated galaxies than previously thought.

Biprateep Dey, David Zhao, Brett H Andrews et al.

Key science questions, such as galaxy distance estimation and weather forecasting, often require knowing the full predictive distribution of a target variable Y given complex inputs X . Despite recent advances in machine learning and physics-based models, it remains challenging to assess whether an initial model is calibrated for all x , and when needed, to reshape the densities of y toward ‘instance-wise’ calibration. This paper introduces the local amortized diagnostics and reshaping of conditional densities (LADaR) framework and proposes a new computationally efficient algorithm ( Cal-PIT ) that produces interpretable local diagnostics and provides a mechanism for adjusting conditional density estimates (CDEs). Cal-PIT learns a single interpretable local probability–probability map from calibration data that identifies where and how the initial model is miscalibrated across feature space, which can be used to morph CDEs such that they are well-calibrated. We illustrate the LADaR framework on synthetic examples, including probabilistic forecasting from image sequences, akin to predicting storm wind speed from satellite imagery. Our main science application involves estimating the probability density functions of galaxy distances given photometric data, where Cal-PIT achieves better instance-wise calibration than all 11 other literature methods in a benchmark data challenge, demonstrating its utility for next-generation cosmological analyzes ^9 .

Márcio S. Gomes-Filho, Pablo de Castro, Danilo B. Liarte et al.

The Kardar–Parisi–Zhang (KPZ) equation describes a wide range of growth-like phenomena, with applications in physics, chemistry and biology. There are three central questions in the study of KPZ growth: the determination of height probability distributions; the search for ever more precise universal growth exponents; and the apparent absence of a fluctuation–dissipation theorem (FDT) for spatial dimension <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>d</mi><mo>></mo><mn>1</mn></mrow></semantics></math></inline-formula>. Notably, these questions were answered exactly only for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>1</mn><mo>+</mo><mn>1</mn></mrow></semantics></math></inline-formula> dimensions. In this work, we propose a new FDT valid for the KPZ problem in <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>d</mi><mo>+</mo><mn>1</mn></mrow></semantics></math></inline-formula> dimensions. This is achieved by rearranging terms and identifying a new correlated noise which we argue to be characterized by a fractal dimension <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>d</mi><mi>n</mi></msub></semantics></math></inline-formula>. We present relations between the KPZ exponents and two emergent fractal dimensions, namely <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>d</mi><mi>f</mi></msub></semantics></math></inline-formula>, of the rough interface, and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>d</mi><mi>n</mi></msub></semantics></math></inline-formula>. Also, we simulate KPZ growth to obtain values for transient versions of the roughness exponent <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>, the surface fractal dimension <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>d</mi><mi>f</mi></msub></semantics></math></inline-formula> and, through our relations, the noise fractal dimension <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>d</mi><mi>n</mi></msub></semantics></math></inline-formula>. Our results indicate that KPZ may have at least two fractal dimensions and that, within this proposal, an FDT is restored. Finally, we provide new insights into the old question about the upper critical dimension of the KPZ universality class.

Duo-Duo Chen, Dong-Dong Dong, Xue-Ke Song et al.

Abstract Recently, numerous measures have been proposed for quantifying the quantumness of a given system, and the existence of intrinsic connections among quantum resource measures has been proven. Here, we study the unified relationship between duality, first-order coherence, three-setting linear steering inequality, and maximum average fidelity between two masses due to gravity. Under gravitational inducement, an equivalent relationship was identified between the first-order coherence and duality. The coherence of a system can be controlled by adjusting arm lengths and the distance between the arms of an interferometer. In most cases, the first-order coherence of a system cannot be maximised. Furthermore, a trade-off relationship between gravitationally induced duality and steering violations was derived. We can adjust the arm length and distance between the arms of the interferometer such that the steering violation reaches its maximum at phase $$\pi $$ π . The results show that the value of the steering violation is always greater than 1; that is, the state of the system is steerable. In addition, we explored the intrinsic relationship between duality and the maximal average fidelity due to gravity. In most cases, the maximum average fidelity of the system is greater than 2/3, indicating that the state is useful for quantum teleportation. These results are important for investigating the intrinsic relationships among various quantum resources within the framework of gravity.

Astronomy Editorial Office

High-quality academic publishing is built on rigorous peer review [...]

Farshid Danesh, Samaneh Kesht Karan, Lili Banihashemi et al.

Editorial board members (EBMs) of journals play a pivotal role in authentic international scientific journals. Editorial Board Interlocking (EBI) phenomenon reflects the effectiveness and importance of the scholarly journal's editorial boards in various scientific fields. The primary purpose of this paper is to conduct a Social Network Analysis (SNA) of EBI phenomena from the perspective of astronomy and astrophysics journals. The present study is applied research based on EBI, SNA, and the descriptive-analytical approach. The statistical population of this study consists of the editorial board members of all journals of astronomy and astrophysics indexed in the JCR and official journal websites. There are 1597 job positions in 67 astronomy and astrophysics journals occupied by the 1394 scholars. Data analysis shows EBI for 95 scholars and 79 organizations. "Aleksei A. Starobinsky" from Russia and the Russian Academy of Sciences, "Daniel J. Scheeres" from the United States, and the University of Colorado Boulder have the highest EBI contributions in five journals. "Daniel J. Scheeres," with a centrality of 39, has the highest degree of centrality measurement among the EBMs. The presence of more than five times as many men as women indicates that astronomy and astrophysics journals are considered "masculine" by the editorial board. The EBI phenomenon is observed in astronomy and astrophysics journals due to the limited number of peop le eligible for the editorial board. Due to EBI, a limited number of famous scholars are made macro-policies such as publishing the articles, referees selections, and the reviewing process. Astronomy and astrophysics journals have "elite" academic networks. Gender inequality exists among EBMs, and the majority of them are male. Accordingly, these journals are "men's journals."

Glyn A. Collinson, Heli Hietala, Ferdinand Plaschke et al.

Abstract Shocklets and short large‐amplitude magnetic structures (SLAMS) are steepened magnetic fluctuations commonly found in Earth's upstream foreshock. Here we present Venus Express observations from the 26th of February 2009 establishing their existence in the steady‐state foreshock of Venus, building on a past study which found SLAMS during a substantial disturbance of the induced magnetosphere. The Venusian structures were comparable to those reported near Earth. The 2 Shocklets had magnetic compression ratios of 1.23 and 1.34 with linear polarization in the spacecraft frame. The 3 SLAMS had ratios between 3.22 and 4.03, two of which with elliptical polarization in the spacecraft frame. Statistical analysis suggests SLAMS coincide with unusually high solar wind Alfvén mach‐number at Venus (12.5, this event). Thus, while we establish Shocklets and SLAMS can form in the stable Venusian foreshock, they may be rarer than at Earth. We estimate a lower limit of their occurrence rate of ≳14%.

Yuki Hibiya, Tsuyoshi Iizuka, Hatsuki Enomoto et al.

The short-lived radionuclide, niobium-92 ( ^92 Nb), has been used to estimate the site of nucleosynthesis for p- nuclei and the timing of planetary differentiation, assuming that it was uniformly distributed in the early solar system. Here, we present the internal niobium–zirconium (Nb–Zr) isochron dating of Northwest Africa (NWA) 6704, an achondrite thought to form in the outer protosolar disk due to nucleosynthetic isotope similarities with carbonaceous chondrites. The isochron defines an initial ^92 Nb/ ^93 Nb ratio of (2.72 ± 0.25) × 10 ^−5 at the NWA 6704 formation, 4562.76 ± 0.30 million years ago. This corresponds to a ^92 Nb/ ^93 Nb ratio of (2.96 ± 0.27) × 10 ^−5 at the time of solar system formation, which is ∼80% higher than the values obtained from meteorites formed in the inner disk. The results suggest that a significant proportion of the solar ^92 Nb was produced by a nearby core-collapse supernova (CCSN) and that the outer disk was more enriched in CCSN ejecta, which could account for the heterogeneity of short-lived ^26 Al and nucleosynthetic stable-isotope anomalies across the disk. We propose that NWA 6704 serves as the best anchor for mapping relative Nb–Zr ages of objects in the outer solar system onto the absolute timescale.

Ignatios Antoniadis

Astronomy has a long history over thousands of years, since the creation of ancient civilization [...]

Wonbae Bang, M. T. Kaffash, M. T. Hossain et al.

We report experimental and theoretical studies of spin dynamics in lattice structures of permalloy (Ni80Fe20) nano-ellipses, with four different types of networks including honeycomb and square lattices. The lattices are patterned at the center line of the co-planar wave guide and consist of non-contacting or contacting ellipses. Micromagnetic simulations show excellent agreement with the broadband ferromagnetic resonance (FMR) experimental results. We find the existence of a spin-wave mode localized in the vertex region of the contacting nano-ellipse network. Our finding has important implications when designing an artificial spin ice (ASI) network for functional magnonics.

Francesco Carnazza, Federico Carollo, Dominik Zietlow et al.

Full information about a many-body quantum system is usually out-of-reach due to the exponential growth—with the size of the system—of the number of parameters needed to encode its state. Nonetheless, in order to understand the complex phenomenology that can be observed in these systems, it is often sufficient to consider dynamical or stationary properties of local observables or, at most, of few-body correlation functions. These quantities are typically studied by singling out a specific subsystem of interest and regarding the remainder of the many-body system as an effective bath. In the simplest scenario, the subsystem dynamics, which is in fact an open quantum dynamics, can be approximated through Markovian quantum master equations. Here, we formulate the problem of finding the generator of the subsystem dynamics as a variational problem, which we solve using the standard toolbox of machine learning for optimization. This dynamical or ‘Lindblad’ generator provides the relevant dynamical parameters for the subsystem of interest. Importantly, the algorithm we develop is constructed such that the learned generator implements a physically consistent open quantum time-evolution. We exploit this to learn the generator of the dynamics of a subsystem of a many-body system subject to a unitary quantum dynamics. We explore the capability of our method to recover the time-evolution of a two-body subsystem and exploit the physical consistency of the generator to make predictions on the stationary state of the subsystem dynamics.

N. Satchell, T. Mitchell, P. M. Shepley et al.

Abstract We report on the electrical transport properties of Nb based Josephson junctions with Pt/Co $$_{68}$$ 68 B $$_{32}$$ 32 /Pt ferromagnetic barriers. The barriers exhibit perpendicular magnetic anisotropy, which has the main advantage for potential applications over magnetisation in-plane systems of not affecting the Fraunhofer response of the junction. In addition, we report that there is no magnetic dead layer at the Pt/Co $$_{68}$$ 68 B $$_{32}$$ 32 interfaces, allowing us to study barriers with ultra-thin Co $$_{68}$$ 68 B $$_{32}$$ 32 . In the junctions, we observe that the magnitude of the critical current oscillates with increasing thickness of the Co $$_{68}$$ 68 B $$_{32}$$ 32 strong ferromagnetic alloy layer. The oscillations are attributed to the ground state phase difference across the junctions being modified from zero to $$\pi $$ π . The multiple oscillations in the thickness range $$0.2~\leqslant ~d_\text {CoB}~\leqslant ~1.4$$ 0.2 ⩽ d CoB ⩽ 1.4  nm suggests that we have access to the first zero- $$\pi $$ π and $$\pi $$ π -zero phase transitions. Our results fuel the development of low-temperature memory devices based on ferromagnetic Josephson junctions.

Godelfridus Hadung Lamanepa, Rosenti Pasaribu, Claudia M.M. Maing

<p class="GravityAbstractbody">The purpose of this study was to analyze students' items and abilities—the analysis for mapping test instruments and students' basic concepts regarding optics subjects before lectures are held. The test participants were 35 physics students. The analysis model of item response theory is a one-parameter logistic model or Rasch Model with the scope of analysis of the level of item difficulty, student ability, and statements that fit the item response model. Analysis of item responses and student responses carried out using Winstep version 3.73 software. The results of the qualitative analysis of the test items consisted of memory (C1) analysis (C4). The quantitative analysis using the Rasch model showed that 35% of the total items were difficult category items. For the suitability of test items in the instrument by 85% of items fit or generally function in measurement, more than 57% of students have the geometric optical ability in logit values of 0 to 1. The results of item analysis and student ability become information for teachers to design courses such as method selection, project implementation strategies, and assessments are undertaken.</p><p> </p>

Wolf Thomas J. A., Yang Jie, Sanchez David M. et al.

We resolve the structural dynamics of the ultrafast photoinduced ring opening reaction of 1,3-cyclohexadiene in space and time employing megaelectronvolt gas phase ultrafast electron diffraction. We, furthermore, observe coherent large amplitude motions of the photoproduct.

Pail R., Bamber J., Biancale R. et al.

As changes in gravity are directly related to mass variability, satellite missions observing the Earth’s time varying gravity field are a unique tool for observing mass transport processes in the Earth system, such as the water cycle, rapid changes in the cryosphere, oceans, and solid Earth processes, on a global scale. The observation of Earth’s gravity field was successfully performed by the GRACE and GOCE satellite missions, and will be continued by the GRACE Follow-On mission. A comprehensive team of European scientists proposed the next-generation gravity field mission MOBILE in response to the European Space Agency (ESA) call for a Core Mission in the frame of Earth Explorer 10 (EE10). MOBILE is based on the innovative observational concept of a high-low tracking formation with micrometer ranging accuracy, complemented by new instrument concepts. Since a high-low tracking mission primarily observes the radial component of gravity-induced orbit perturbations, the error structure is close to isotropic. This geometry significantly reduces artefacts of previous along-track ranging low-low formations (GRACE, GRACE-Follow-On) such as the typical striping patterns. The minimum configuration consists of at least two medium-Earth orbiters (MEOs) at 10000 km altitude or higher, and one low-Earth orbiter (LEO) at 350-400 km. The main instrument is a laser-based distance or distance change measurement system, which is placed at the LEO. The MEOs are equipped either with passive reflectors or transponders. In a numerical closed-loop simulation, it was demonstrated that this minimum configuration is in agreement with the threshold science requirements of 5 mm equivalent water height (EWH) accuracy at 400 km wavelength, and 10 cm EWH at 200 km. MOBILE provides promising potential future perspectives by linking the concept to existing space infrastructure such as Galileo next-generation, as future element of the Copernicus/Sentinel programme, and holds the potential of miniaturization even up to swarm configurations. As such MOBILE can be considered as a precursor and role model for a sustained mass transport observing system from space.

M. Bashkanov, S. Kay, D.P. Watts et al.

We report the first large-acceptance measurement of the beam–spin asymmetry for deuteron photodisintegration (γ→d→pn) in the photon energy range 420<Eγ<620MeV. The measurement provides important new constraints on the mechanisms of photodisintegration above the Δ resonance and on the photocoupling of the recently discovered d⁎(2380) hexaquark. Keywords: Hexaquarks, Dibaryon, Deuteron photodisintegration

Li Huang, Lijie Mei, Shixiang Huang

Abstract In this study, we present a novel non-truncated strategy by accompanying the fixed-point iteration with traditional numerical integrators. The proposed non-truncated strategy aims to exactly integrate implicit motion equations that are directly derived from the Lagrangian of the post-Newtonian circular restricted three-body problem. In comparison with the commonly used truncated approach, which cannot exactly but approximately preserve the generalized Jacobian constant (or energy) of the original Lagrangian system, the proposed non-truncated strategy has been determined to preserve this constant well. In fact, the non-truncated strategy and the truncated approach have a difference at second post-Newtonian order. Based on Kolmogorov–Arnold–Moser theory, this difference from the truncation in the equations of motion may lead to destroying the orbital configuration, dynamical behavior of order and chaos, and conservation of the post-Newtonian circular restricted three-body problem. The non-truncated strategy proposed in this study can avoid all these drawbacks and provide highly reliable and accurate numerical solutions for the post-Newtonian Lagrangian dynamics. Finally, numerical results show that the non-truncated strategy can preserve the generalized Jacobian constant in the accuracy of $${\mathscr {O}}(10^{-12})$$ O(10-12) , whereas the truncated approach at the first post-Newtonian (1PN) order only has an accuracy of $${\mathscr {O}}(10^{-3})$$ O(10-3) . Moreover, several orbits are observed to be escaping from the bounded region in the 1PN truncated system via the truncated strategy, but these escaping orbits are unobserved via the non-truncated strategy.