Articoli di riviste: "Astrophysics Technique"

1

Shen, Yang-Ping, Bing Guo e Wei-Ping Liu. "An indirect technique in nuclear astrophysics: alpha-cluster transfer reaction". EPJ Web of Conferences 260 (2022): 01001. http://dx.doi.org/10.1051/epjconf/202226001001.

Testo completo

Abstract (sommario):

Helium(4He, or α)is the second most abundant element in the observable Universe. The α-particle induced reactions such as(α, γ), (α, n) and (α, p) play a crucial role in nuclear astrophysics, especially for understanding stellar heliumburning. Because of the strong Coulomb repulsion, it is greatly hindered to directly measure the cross sections for these α-capture reactions at stellar energies. Alpha-cluster transfer reaction is a powerful tool for investigation of astrophysical(α, γ), (α, n)and(α, p)reactions since it can preferentially populate the natural-parity states with an α-cluster structure which dominantly contribute to these astrophysical α-capture reactions during stellar heliumburning. In this paper, we reviewthe theoretical scheme, theexperimental technique, astrophysical applications and the future perspectives of such approach based on α-cluster transfer reactions.

Gli stili APA, Harvard, Vancouver, ISO e altri

2

Rahma, Siti Nur, Suliyanah Suliyanah e Abdul Halim. "How do Astrophysics and the Qur'an Perceive the Extraterrestrial Life? A Qualitative Study". Jurnal Pendidikan Fisika 10, n. 2 (20 aprile 2022): 107–22. http://dx.doi.org/10.26618/jpf.v10i2.7433.

Testo completo

Abstract (sommario):

The topic of extraterrestrial life is still only a theory and the truth is still being investigated. Therefore, this research aims to analyze the beginning formation of the universe according to astrophysics and the Qur’an, astrophysics discoveries about extraterrestrial life, and letters in the Qur’an that hint at extraterrestrial life, as well as analyzing the relationship between astrophysics and letters in the Qur’an related to extraterrestrial life. This research is qualitative research with a method consisting of library research and interviews. The primary data of this research comes from scientific articles of previous research, relevant books, and interpretations of Qur’an verses. The secondary data were obtained through the results of interviews with experts. The data analysis technique in this study was adapted from the analysis technique of Miles Huberman, while the verses of the Qur’an used the Kemenag interpretation with a scientific interpretation style. The results show that in line with the astrophysical discoveries, the creation of the universe and the existence of extraterrestrial life are also hinted at in the Qur'an. In addition, the alleged presence of water on other planets also supports the signs in the Qur'an. Based on the results, it can be concluded that there is no dichotomy between astrophysical discoveries and signs in the Qur'an regarding extraterrestrial life.

Gli stili APA, Harvard, Vancouver, ISO e altri

3

Longair, Malcolm. "Radio astronomy and the rise of high-energy astrophysics two anniversaries". International Journal of Modern Physics D 28, n. 02 (gennaio 2019): 1930004. http://dx.doi.org/10.1142/s0218271819300040.

Testo completo

Abstract (sommario):

This paper celebrates the 100th anniversary of the birth of Martin Ryle and the 50th anniversary of the discovery of pulsars by Jocelyn Bell and Antony Hewish. Ryle and Hewish received the 1974 Nobel Prize in Physics, the first in the area of astrophysics. Their interests strongly overlapped, one of the key papers on the practical implementation of the technique of aperture synthesis being co-authored by Ryle and Hewish. The discovery of pulsars and the roles played by Hewish and Bell are described. These key advances were at the heart of the dramatic rise of high-energy astrophysics in the 1960s and led to the realization that general relativity is central to the understanding of high-energy astrophysical phenomena.

Gli stili APA, Harvard, Vancouver, ISO e altri

4

Mukhamedzhanov, A. M., L. D. Blokhintsev, B. F. Irgaziev, A. S. Kadyrov, M. La Cognata, C. Spitaleri e R. E. Tribble. "Trojan Horse as an indirect technique in nuclear astrophysics". Journal of Physics G: Nuclear and Particle Physics 35, n. 1 (13 dicembre 2007): 014016. http://dx.doi.org/10.1088/0954-3899/35/1/014016.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

5

Spitaleri, Claudio. "Trojan Horse technique to measure nuclear astrophysics rearrangement reactions". Journal of Physics: Conference Series 420 (25 marzo 2013): 012137. http://dx.doi.org/10.1088/1742-6596/420/1/012137.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

6

Tumino, A., C. Spitaleri, S. Cherubini, V. Crucillà, C. Fu, Z. Elekes, Z. Fülöp et al. "The trojan horse method as indirect technique in nuclear astrophysics". Journal of Physics: Conference Series 111 (1 maggio 2008): 012033. http://dx.doi.org/10.1088/1742-6596/111/1/012033.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

7

Minier, Vincent, Gilles Durand, Pierre-Olivier Lagage e M. Talvard. "CAMISTIC: THz/submm astronomy at Dome C in Antarctica". Proceedings of the International Astronomical Union 2, n. 14 (agosto 2006): 709–10. http://dx.doi.org/10.1017/s1743921307012367.

Testo completo

Abstract (sommario):

Submillimetre (submm) astronomy is the prime technique to unveil the birth and early evolution of a broad range of astrophysical objects. It is a relatively new branch of observational astrophysics which focuses on studies of the cold Universe, i.e., objects radiating a significant – if not dominant – fraction of their energy at wavelengths ranging from ∼ 100 μm to ∼ 1 mm. Submm continuum observations are particularly powerful to measure the luminosities, temperatures and masses of cold dust emitting objects. Examples of such objects include star-forming clouds in our Galaxy, prestellar cores and deeply embedded protostars, protoplanetary disks around young stars, as well as nearby starburst galaxies and dust-enshrouded high-redshift galaxies in the early Universe.

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Bukvić, S., Dj Spasojević e V. Žigman. "Advanced fit technique for astrophysical spectra". Astronomy & Astrophysics 477, n. 3 (12 novembre 2007): 967–77. http://dx.doi.org/10.1051/0004-6361:20065969.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

9

Crossland, Tom, Pontus Stenetorp, Sebastian Riedel, Daisuke Kawata, Thomas D. Kitching e Rupert A. C. Croft. "Towards machine-assisted meta-studies: the Hubble constant". Monthly Notices of the Royal Astronomical Society 492, n. 3 (23 dicembre 2019): 3217–28. http://dx.doi.org/10.1093/mnras/stz3400.

Testo completo

Abstract (sommario):

ABSTRACT We present an approach for automatic extraction of measured values from the astrophysical literature, using the Hubble constant for our pilot study. Our rules-based model – a classical technique in natural language processing – has successfully extracted 298 measurements of the Hubble constant, with uncertainties, from the 208 541 available arXiv astrophysics papers. We have also created an artificial neural network classifier to identify papers in arXiv which report novel measurements. From the analysis of our results we find that reporting measurements with uncertainties and the correct units is critical information when distinguishing novel measurements in free text. Our results correctly highlight the current tension for measurements of the Hubble constant and recover the 3.5σ discrepancy – demonstrating that the tool presented in this paper is useful for meta-studies of astrophysical measurements from a large number of publications.

Gli stili APA, Harvard, Vancouver, ISO e altri

10

SINNIS, GUS. "TeV ASTROPHYSICS WITH THE MILAGRO AND HAWC OBSERVATORIES". International Journal of Modern Physics D 22, n. 11 (settembre 2013): 1360010. http://dx.doi.org/10.1142/s0218271813600109.

Testo completo

Abstract (sommario):

Ground-based gamma-ray astronomy has historically implemented two dramatically different techniques. One method employs Imaging Atmospheric Cherenkov Telescope(s) (IACT) that detect the Cherenkov light generated in the atmosphere by extensive air showers. The other method employs particle detectors that directly detect the particles that reach ground level — known as Extensive Air Shower (EAS) arrays. Until recently, the IACT method had been the only technique to yield solid detections of TeV gamma-ray sources. Utilizing water Chernkov technology, Milagro, was the first EAS array to discover new gamma-ray sources and demonstrated the power of and need for an all-sky high duty cycle instrument in the TeV energy regime. The transient nature of many TeV sources, the enormous number of potential sources, and the existence of TeV sources that encompass large angular areas all point to the need for an all-sky, high duty-factor instrument with even greater sensitivity than Milagro. The High Altitude Water Cherenkov (HAWC) Observatory will be over an order of magnitude more sensitive than Milagro. In this paper we will discuss the results from Milagro and the design of the HAWC instrument and its experimental sensitivity.

Gli stili APA, Harvard, Vancouver, ISO e altri

11

de la Fuente, Eduardo, Juan Carlos Díaz–Vélez, Paolo Desiati, Jose Luis García–Luna, Janet Torrealba e Ricardo Gúzman–Alcála. "Information Technologies on High-Energy Astrophysics: Cosmic Ray Anisotropy using HAWC Observatory". EPJ Web of Conferences 208 (2019): 03005. http://dx.doi.org/10.1051/epjconf/201920803005.

Testo completo

Abstract (sommario):

The detection of astroparticles, specially at high energies (>100 GeV), requires special techniques and instruments (telescopes or observatories), for example, those that use the Water Cherenkov radiation technique. In this paper we show an example of how Information Technologies can be used to perform maps and produce high impact results. The latter case is illustrated in the summary of the generation of a high statistics map of cosmic rays at 10 TeV in the northern sky with data collected by the High Altitude Water Cherenkov (HAWC) observatory.

Gli stili APA, Harvard, Vancouver, ISO e altri

12

Devorkin, David H. "Takamine and Saha: Contacts with Western Astrophysics". Highlights of Astronomy 11, n. 2 (1998): 732–33. http://dx.doi.org/10.1017/s1539299600018621.

Testo completo

Abstract (sommario):

In the fall of 1920 two young scholars happened to meet in London and found they had many interests in common in laboratory spectroscopy and astrophysics. One was an Indian and the other a Japanese, and their paths crossed as they visited American and European centers to learn the tools and techniques of the quantum theory. The young Japanese scholar, T. Takamine, whose home base was then the Institute of Physical and Chemical Research in Tokyo, was delighted to have met Meghnad Saha, from Calcutta, who was just putting the finishing touches on his fourth paper on ionization equilibrium in the atmospheres of the sun and stars. When they met, Takamine and Saha spoke of Sommerfeld’s theories, and pledged to keep in touch. Thus began a correspondence that lasted for some twenty years, as Takamine returned to Japan from his long visits to American and European observatories and spectroscopic laboratories, and Saha returned to India. Of the two, Takamine had stayed the longer time in the West, mainly at Mount Wilson where he was in residence through much of 1919 working with John Anderson and A. S. King, and published on the ”The Stark Effect for Metals.” Takamine also returned to Mount Wilson in 1924, and toured many spectroscopic laboratories in the United States continuing to hone his interests and technique. Elsewhere I have examined Saha’s contacts with western astrophysics. Here I examine briefly how Takamine established and maintained contacts in the West and why he did so.

Gli stili APA, Harvard, Vancouver, ISO e altri

13

Okuda, Haruyuki, Gunther Hasinger, M. D. Arnaud, S. Bludman, J. Braga, N. Brosch, L. Gurvits et al. "Commission 44: Space & High Energy Astrophysics". Proceedings of the International Astronomical Union 1, T26A (dicembre 2005): 319–26. http://dx.doi.org/10.1017/s1743921306004777.

Testo completo

Abstract (sommario):

Division XI was born by merging Commission 44 “Space and High Energy Astrophysics” and Commission 48 “High Energy Astrophysics” by the decision at the IAU General Assembly in The Hague (1994). As the naming of space astronomy is technique oriented, i.e. astronomy from space, it covers quite a wide range of astronomy, almost all branches of astronomy are included by the progress of space observations. Historically, it started from high energy astronomy, UV, X, and gamma rays astronomy, somewhat including cosmic ray physics. However, in these days, space observations have expanded to low energy astronomy, such as optical, infrared, submillimeter and even radio waves(Space VLBI).

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Meyers, Patrick M., Tanner Prestegard, Vuk Mandic, Victor C. Tsai, Daniel C. Bowden, Andrew Matas, Gary Pavlis e Ross Caton. "A Linear Inversion Approach to Measuring the Composition and Directionality of the Seismic Noise Field". Remote Sensing 13, n. 16 (5 agosto 2021): 3097. http://dx.doi.org/10.3390/rs13163097.

Testo completo

Abstract (sommario):

We develop a linear inversion technique for measuring the modal composition and directionality of ambient seismic noise. The technique draws from similar techniques used in astrophysics and gravitational-wave physics, and relies on measuring cross-correlations between different seismometer channels in a seismometer array. We characterize the sensitivity and the angular resolution of this technique using a series of simulations and real-world tests. We then apply the technique to data acquired by the three-dimensional seismometer array at the Homestake mine in Lead, SD, to estimate the composition and directionality of the seismic noise at microseism frequencies. We show that, at times of low-microseism amplitudes, noise is dominated by body waves (P and S), while at high-microseism times, the noise is dominated by surface Rayleigh waves.

Gli stili APA, Harvard, Vancouver, ISO e altri

15

Dhiman, Gaurav, e Vijay Kumar. "Astrophysics inspired multi-objective approach for automatic clustering and feature selection in real-life environment". Modern Physics Letters B 32, n. 31 (10 novembre 2018): 1850385. http://dx.doi.org/10.1142/s0217984918503852.

Testo completo

Abstract (sommario):

In this paper, a novel astrophysics-based approach is proposed for automatically finding the clusters and features simultaneously. A novel agent encoding scheme is used to encode both the number of clusters and features. A novel dynamic threshold technique is proposed for an efficient searching. The validation of proposed technique is tested on eight real-life data sets. The statistical significance of proposed technique is attributed by statistical tests. It is also applied on solving image segmentation and microarray data analysis problems. Experimental results reveal that the proposed technique outperforms the other competitive approaches.

Gli stili APA, Harvard, Vancouver, ISO e altri

16

Deniz, Sinan, e Necdet Bildik. "A new analytical technique for solving Lane - Emden type equations arising in astrophysics". Bulletin of the Belgian Mathematical Society - Simon Stevin 24, n. 2 (aprile 2017): 305–20. http://dx.doi.org/10.36045/bbms/1503453712.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Bigg, Charlotte. "Travelling Scientist, Circulating Images and the Making of the Modern Scientific Journal". Nuncius 30, n. 3 (2015): 675–98. http://dx.doi.org/10.1163/18253911-03003002.

Testo completo

Abstract (sommario):

The early astrophysicist Norman Lockyer was both editor of the journal Nature from its creation in 1869 and for the following five decades, and an early practioner of the new astronomy. He frequently used the journal to expound his scientific theories, report on his work and send news home while on expeditions. I look into the particular visual culture of astrophysics developed by Lockyer in Nature, its evolution at a time of rapid development both of the techniques of astrophysical observation and visualization and of the techniques of image reproduction in print. A study of the use and reuse of visual materials in different settings also makes it possible to sketch the circulating economy of Lockyer’s images and the ways in which he put himself forward as a scientist, at a time when he was advocating the State support of research and scientists and helping create the modern scientific journal.

Gli stili APA, Harvard, Vancouver, ISO e altri

18

Ma, Wen-Xiu, Mohamed M. Mousa e Mohamed R. Ali. "Application of a new hybrid method for solving singular fractional Lane–Emden-type equations in astrophysics". Modern Physics Letters B 34, n. 03 (19 dicembre 2019): 2050049. http://dx.doi.org/10.1142/s0217984920500499.

Testo completo

Abstract (sommario):

In this research, a hybrid numerical method combining cosine and sine (CAS) wavelets and Green’s function approach is created to acquire the arrangements of fractional Lane–Emden Problem. The suggested methodology for detecting the solution of nonlinear equations dependent on variations of germinal algorithms is applied on nonlinear fractional Lane–Emden Problem under some smooth conditions and results in an iterative scheme of nonlinear equations Because of its efficiency, this technique is applied on a large variety of equations from the boundary value problems to the optimization. This paper is extending the suggested methodology technique for fractional Lane–Emden Problem. Moreover, the feature of the present novel method is utilized to convert the problem under observance into a system of algebraic equations that can be illuminated by suitable algorithms. A rapprochement of results has likewise been obtained using the present strategy and those reported using other techniques seem to indicate the precision and computational efficiency to establish the suitability of the Green-CAS wavelet method.

Gli stili APA, Harvard, Vancouver, ISO e altri

19

Barrett, Jim W., Ilya Mandel, Coenraad J. Neijssel, Simon Stevenson e Alejandro Vigna-Gómez. "Exploring the Parameter Space of Compact Binary Population Synthesis". Proceedings of the International Astronomical Union 12, S325 (ottobre 2016): 46–50. http://dx.doi.org/10.1017/s1743921317000059.

Testo completo

Abstract (sommario):

AbstractAs we enter the era of gravitational wave astronomy, we are beginning to collect observations which will enable us to explore aspects of astrophysics of massive stellar binaries which were previously beyond reach. In this paper we describe COMPAS (Compact Object Mergers: Population Astrophysics and Statistics), a new platform to allow us to deepen our understanding of isolated binary evolution and the formation of gravitational-wave sources. We describe the computational challenges associated with their exploration, and present preliminary results on overcoming them using Gaussian process regression as a simulation emulation technique.

Gli stili APA, Harvard, Vancouver, ISO e altri

20

MOTOBAYASHI, TOHRU. "NUCLEAR STRUCTURE AND NUCLEAR ASTROPHYSICS STUDIES WITH FAST HEAVY-ION BEAMS". International Journal of Modern Physics E 18, n. 10 (novembre 2009): 1965–69. http://dx.doi.org/10.1142/s0218301309014093.

Testo completo

Abstract (sommario):

Collaboration between France and Japan on studies with fast RI (radioactive isotope) beams and related technical developments started in 1980s, when the GANIL accelerators and RIKEN cyclotron complex started operation and RI beam production technique was developed. Several examples of collaboration on nuclear physics and nuclear astrophysics experiments including related technical development are discussed.

Gli stili APA, Harvard, Vancouver, ISO e altri

21

Rastorguev, Alexey S., Andrey K. Dambis, Marina V. Zabolotskikh, Leonid N. Berdnikov e Natalia A. Gorynya. "The Baade–Becker–Wesselink technique and the fundamental astrophysical parameters of Cepheids". Proceedings of the International Astronomical Union 8, S289 (agosto 2012): 195–202. http://dx.doi.org/10.1017/s1743921312021382.

Testo completo

Abstract (sommario):

AbstractThe Baade–Becker–Wesselink (BBW) method remains one of most often used tools to derive a full set of Cepheid astrophysical parameters. The surface brightness version of the BBW technique was preferentially used during the past few decades to calculate Cepheid radii and to improve period–luminosity–colour relations. Its implementation requires a priori knowledge of Cepheid reddening values. We propose a new version of the BBW technique, which allows one to independently determine the colour excess and the intrinsic colour of a radially pulsating star, in addition to its radius, luminosity and distance. The new technique is a generalization of the Balona light curve-modelling approach. The method also allows calibration of the function F(CI0) = BC(CI0) + 10 log [Teff (CI0)] for the class of pulsating stars considered. We apply this technique to a number of classical Cepheids with very accurate light and radial-velocity curves. The new technique can also be applied to other pulsating variables, e.g., RR Lyrae stars. We also discuss the possible dependence of the projection factor on the pulsation phase.

Gli stili APA, Harvard, Vancouver, ISO e altri

22

Wang, Ru-Yue, Jian-Fu Zhang, Alex Lazarian, Hua-Ping Xiao e Fu-Yuan Xiang. "Gradient measurement of synchrotron polarization diagnostic: Application to spatially separated emission and Faraday rotation regions". Monthly Notices of the Royal Astronomical Society 505, n. 4 (17 giugno 2021): 6206–16. http://dx.doi.org/10.1093/mnras/stab1708.

Testo completo

Abstract (sommario):

ABSTRACT Considering the spatially separated polarization radiation and Faraday rotation regions to simulate complex interstellar media, we study synchrotron polarization gradient techniques’ measurement capabilities. We explore how to trace the direction of projected magnetic field of emitting-source region at the multifrequency bands, using the gradient technique compared with the traditional polarization vector method. Furthermore, we study how Faraday rotation density in the foreground region, i.e. a product of electron number density and parallel component of magnetic fields along the line of sight, affects the measurement of projected magnetic field. Numerical results show that synchrotron polarization gradient technique could successfully trace projected magnetic field within emitting-source region independent of radio frequency. Accordingly, the gradient technique can measure the magnetic field properties for a complex astrophysical environment.

Gli stili APA, Harvard, Vancouver, ISO e altri

23

Eesa, Bushra. "Modified Hermite Operational Matrix Method for Nonlinear Lane-Emden Problem". Al-Qadisiyah Journal Of Pure Science 25, n. 3 (27 giugno 2020): 71–79. http://dx.doi.org/10.29350/qjps.2020.25.3.1128.

Testo completo

Abstract (sommario):

Nonlinear Lane –Emden equations are significant in astrophysics and mathematical physics. The aim of this paper is submitted a new approximate method for finding solution to nonlinear Lane-Emden type equations appearing in astrophysics based on modified Hermite integration operational matrix. The suggest technique is based on taking the truncated modified Hermite series of the solution function in the nonlinear Lane-Emden equation and then changed into a matrix equation with the given conditions. Nonlinear system of algebraic equation using collection points is obtained. The present method is applied on some relevant physical problems as nonlinear Lane-Emden type equations.

Gli stili APA, Harvard, Vancouver, ISO e altri

24

Mirzoyan, Razmik. "Technological Novelties of Ground-Based Very High Energy Gamma-Ray Astrophysics with the Imaging Atmospheric Cherenkov Telescopes". Universe 8, n. 4 (29 marzo 2022): 219. http://dx.doi.org/10.3390/universe8040219.

Testo completo

Abstract (sommario):

In the past three decades, the ground-based technique of imaging atmospheric Cherenkov telescopes has established itself as a powerful discipline in science. Approximately 250 sources of very high gamma rays of both galactic and extra-galactic origin have been discovered largely due to this technique. The study of these sources is providing clues to many basic questions in astrophysics, astro-particle physics, physics of cosmic rays and cosmology. The currently operational generation of telescopes offer a solid performance. Further improvements of this technique led to the next-generation large instrument known as the Cherenkov Telescope Array. In its final configuration, the sensitivity of CTA will be several times higher than that of the currently best instruments VERITAS, H.E.S.S., and MAGIC. This article is devoted to outlining the technological developments that shaped this technique and led to today’s success.

Gli stili APA, Harvard, Vancouver, ISO e altri

25

GRUN, J., M. LAMING, C. MANKA, D. W. DONNELLY, B. C. COVINGTON, R. P. FISCHER, A. VELIKOVICH e A. KHOKHLOV. "Laser–plasma simulations of astrophysical phenomena and novel applications to semiconductor annealing". Laser and Particle Beams 21, n. 4 (ottobre 2003): 529–34. http://dx.doi.org/10.1017/s0263034603214087.

Testo completo

Abstract (sommario):

At the frontier of plasma physics and technology are applications of laser-generated plasmas to laboratory simulations of astrophysical phenomena and to industrial processing. This article presents work at the Naval Research Laboratory in both of these areas. We show how laser plasmas are used to measure a blast wave corrugation overstability important in astrophysics. Detailed atomic physics calculations of radiative cooling within the blast front are used to develop a criterion of the existence of the overstability and are used to explain the experimental results. The criterion depends on quantities such as element abundances, densities, temperatures, and blast wave velocities—quantities which can be measured spectroscopically—and therefore used to infer whether astrophysical blast wave nonuniformities are the result of this instability. In other experiments, high-velocity jets are formed in the laboratory using miniature hollow cones. Jets produced by these cones are used to study the physics of jets occurring in supernovae and in star-forming accretion disks. In industrial semiconductor processing, annealing, that is, removing crystal damage and electrically activating the semiconductor, is a critical step. Industrial annealing techniques most often utilize heat generated by an oven, flash lamps, or a low-power laser. During such heating dopants within the semiconductor lattice diffuse and spread. This degrades the performance of circuits in which the individual circuit elements are very close to each other. We are developing an annealing technique in which shock or sound waves generated by a laser plasma are used to anneal the semiconductor. We have demonstrated that the method works over small areas and that it does not lead to significant dopant diffusion.

Gli stili APA, Harvard, Vancouver, ISO e altri

26

Heald, George. "The Faraday rotation measure synthesis technique". Proceedings of the International Astronomical Union 4, S259 (novembre 2008): 591–602. http://dx.doi.org/10.1017/s1743921309031421.

Testo completo

Abstract (sommario):

AbstractWe discuss practical aspects of the novel Faraday Rotation Measure Synthesis technique, first described by Burn (1966), and recently extended and implemented by Brentjens & de Bruyn (2005). The method takes advantage of the excellent spectral coverage provided by modern radio telescopes to reconstruct the intrinsic polarization properties along a line of sight, using a Fourier relationship between the observed polarization products and a function describing the intrinsic polarization (the Faraday dispersion function). An important consequence of the Fourier relationship and discrete frequency sampling is the need, in some cases, to deconvolve the sampling response from the reconstructed Faraday dispersion function. Practical aspects of the deconvolution procedure are discussed. We illustrate the use of the technique by summarizing a recent investigation carried out with the WSRT. We conclude by briefly describing the applicability to future programs which will be carried out with the next generation of radio telescopes such as LOFAR.

Gli stili APA, Harvard, Vancouver, ISO e altri

27

Shannon, Ryan. "Constraining the nanohertz gravitational wave background with the Parkes Pulsar Timing Array". Proceedings of the International Astronomical Union 8, S291 (agosto 2012): 177. http://dx.doi.org/10.1017/s174392131202354x.

Testo completo

Abstract (sommario):

AbstractThe direct detection of gravitational waves will usher in a new era of astrophysics, enabling the study of regions of the universe opaque to electromagnetic radiation or electromagnetically quiet. An ensemble of pulsars (referred to as a pulsar timing array) provides a set of clocks distributed across the Galaxy sensitive to gravitational waves with periods on the order of five years (frequencies of many nanohertz). Plausible source of gravitational waves in this frequency band include massive black hole binaries in the throes of mergers and oscillating cosmic strings. The stochastic gravitational wave background, the sum of gravitational waves emitted throughout the universe, is the most likely signal to be detected by a pulsar timing array.While the detection of gravitational waves will be a milestone in pulsar astronomy, a constraining limit on the strength of the gravitational wave background can be used to constrain cosmological models and early Universe physics. Here we present a new algorithm that can be used to constrain the strength of the GWB with a pulsar timing array. We then apply this technique to Parkes Pulsar Timing Array observations and place a new limit on the strength of the GWB. We conclude by discussing the astrophysical implications of this limit and the prospects for detecting gravitational waves with pulsars.

Gli stili APA, Harvard, Vancouver, ISO e altri

28

Alves, João, Marco Lombardi e Charles Lada. "Insights on molecular cloud structure". Proceedings of the International Astronomical Union 6, S270 (maggio 2010): 99–102. http://dx.doi.org/10.1017/s1743921311000238.

Testo completo

Abstract (sommario):

AbstractStars form in the densest regions of clouds of cold molecular hydrogen. Measuring structure in these clouds is far from trivial as 99% of the mass of a molecular cloud is inaccessible to direct observation. Over the last decade we have been developing an alternative, more robust density tracer technique based on dust extinction measurements towards background starlight. The new technique does not suffer from the complications plaguing the more conventional molecular line and dust emission techniques, and when used with these can provide unique views on cloud chemistry and dust grain properties in molecular clouds. In this brief communication we summarize the main results achieved so far using this technique.

Gli stili APA, Harvard, Vancouver, ISO e altri

29

Casali, G., L. Magrini, A. Frasca, A. Bragaglia, G. Catanzaro, V. D’Orazi, R. Sordo et al. "Stellar Population Astrophysics (SPA) with TNG". Astronomy & Astrophysics 643 (27 ottobre 2020): A12. http://dx.doi.org/10.1051/0004-6361/202039176.

Testo completo

Abstract (sommario):

Context. Open clusters are excellent tracers of the chemical evolution of the Galactic disc. The spatial distribution of their elemental abundances, through the analysis of high-quality and high-resolution spectra, provides insight into the chemical evolution and mechanisms of element nucleosynthesis in regions characterised by different conditions (e.g. star formation efficiency and metallicity). Aims. In the framework of the Stellar Population Astrophysics (SPA) project, we present new observations and spectral analysis of four sparsely studied open clusters located in the solar neighbourhood, namely Collinder 350, Gulliver 51, NGC 7044, and Ruprecht 171. Methods. We exploit the HARPS-N spectrograph at the TNG telescope to acquire high-resolution optical spectra for 15 member stars of four clusters. We derive stellar parameters (Teff, log g, [Fe/H] and ξ) using both the equivalent width (EW) analysis and the spectral fitting technique. We compute elemental abundances for light, α-, iron-peak, and n-capture elements using the EW measurement approach. We investigate the origin of the correlation between metallicity and stellar parameters derived with the EW method for the coolest stars of the sample (Teff < 4300 K). The correlation is likely due to the challenging continuum setting and to a general inaccuracy of model atmospheres used to reproduce the conditions of very cool giant stars. Results. We locate the properties of our clusters in the radial distributions of metallicity and abundance ratios, comparing our results with clusters from the Gaia-ESO and APOGEE surveys. We present the [X/Fe]−[Fe/H] and [X/Fe]−RGC trends for elements in common between the two surveys. Finally, we derive the C and Li abundances as a function of the evolutionary phase and compare them with theoretical models. Conclusions. The SPA survey, with its high-resolution spectra, allows us to fully characterise the chemistry of nearby clusters. With a single set of spectra, we provide chemical abundances for a variety of chemical elements, which are comparable to those obtained in two of the largest surveys combined. The metallicities and abundance ratios of our clusters fit very well in the radial distributions defined by the recent literature, reinforcing the importance of star clusters to outline the spatial distribution of abundances in our Galaxy. Moreover, the abundances of C and Li, modified by stellar evolution during the giant phase, agree with evolutionary prescriptions (rotation-induced mixing) for their masses and metallicities.

Gli stili APA, Harvard, Vancouver, ISO e altri

30

Landolt, Arlo U., Peter Martinez, Pierre Bastien, Sergei N. Fabrika, Ronald L. Gilliland, Frank Grundahl, Carme Jordi e Ulisse Munari. "COMMISSION 25: STELLAR PHOTOMETRY AND POLARIMETRY". Proceedings of the International Astronomical Union 3, T26B (dicembre 2007): 192–94. http://dx.doi.org/10.1017/s1743921308024071.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

31

Mantovani Sarti, Valentina. "Hyperon-nucleon femtoscopy, nuclear production and bearing on astrophysics". EPJ Web of Conferences 259 (2022): 05003. http://dx.doi.org/10.1051/epjconf/202225905003.

Testo completo

Abstract (sommario):

The presence of hyperons in the inner core of neutron stars is still an open issue in astrophysics and the so-called hyperon puzzle is far away from being solved. A complete understanding of how the interaction between hyperons and nucleons, at the level of two- and three-body, behaves in vacuum and at finite baryon density is a key requirement in order to build a realistic Equation of State for matter inside the core of neutron stars. Recently, measurements of hadron-hadron correlation functions with the femtoscopy technique in small colliding systems delivered a large amount of precise data on several hyperonnucleon pairs. Several interactions relevant for the physics of neutron stars, such as pΛ and pΞ, have been compared to the femtoscopic data and the effects on the corresponding Equation of State have been investigated. The extension to the three-body forces with the measurement of correlations involving triplets and proton-deuteron pairs will provide for the first time access to the genuine three-body interaction and shed light on the hyperon-puzzle.

Gli stili APA, Harvard, Vancouver, ISO e altri

32

Li, T. P. "Imaging in Hard X-ray Astronomy". Symposium - International Astronomical Union 214 (2003): 70–83. http://dx.doi.org/10.1017/s0074180900194173.

Testo completo

Abstract (sommario):

The energy range of hard X-rays is a key waveband to the study of high energy processes in celestial objects, but still remains poorly explored. In contrast to direct imaging methods used in the low energy X-ray and high energy gamma-ray bands, currently imaging in the hard X-ray band is mainly achieved through various modulation techniques. A new inversion technique, the direct demodulation method, has been developed since early 90s. with this technique, wide field and high resolution images can be derived from scanning data of a simple collimated detector. The feasibility of this technique has been confirmed by experiment, balloon-borne observation and analyzing simulated and real astronomical data. Based the development of methodology and instrumentation, a high energy astrophysics mission – Hard X-ray Modulation Telescope (HXMT) has been proposed and selected in China for a four-year Phase-A study. The main scientific objectives are a full-sky hard X-ray (20–200 keV) imaging survey and high signal-to-noise ratio timing studies of high energy sources.

Gli stili APA, Harvard, Vancouver, ISO e altri

33

Kashem, Bushra Esaa, e Suha SHIHAB. "Approximate solution of Lane-Emden problem via modified Hermite operation matrix method". Samarra Journal of Pure and Applied Science 2, n. 2 (22 settembre 2021): 57–67. http://dx.doi.org/10.54153/sjpas.2020.v2i2.113.

Testo completo

Abstract (sommario):

Lane-Emden equations are singular initial value problems and they are important in mathematical physics and astrophysics. The aim of this present paper is presenting a new numerical method for finding approximate solution to Lane-Emden type equations arising in astrophysics based on modified Hermite operational matrix of integration. The proposed technique is based on taking the truncated modified Hermite series of the solution function in the Lane-Emden equation and then transferred into a matrix equation together with the given conditions. The obtained result is system of linear algebraic equation using collection points. The suggested algorithm is applied on some relevant physical problems as Lane-Emden type equations.

Gli stili APA, Harvard, Vancouver, ISO e altri

34

Valbusa Dall'Armi, Lorenzo, Angelo Ricciardone e Daniele Bertacca. "The dipole of the astrophysical gravitational-wave background". Journal of Cosmology and Astroparticle Physics 2022, n. 11 (1 novembre 2022): 040. http://dx.doi.org/10.1088/1475-7516/2022/11/040.

Testo completo

Abstract (sommario):

Abstract One of the main pillars of the ΛCDM model is the Cosmological Principle, which states that our Universe is statistically isotropic and homogeneous on large scales. Here we test this hypothesis using the Astrophysical Gravitational Wave Background (AGWB) expected to be measured by the Einstein Telescope-Cosmic Explorer network; in particular we perform a numerical computation of the AGWB dipole, evaluating the intrinsic contribution due to clustering and the kinematic effect induced by the observer motion. We apply a component separation technique in the GW context to disentangle the kinematic dipole, the intrinsic dipole and the shot noise (SN), based on the observation of the AGWB at different frequencies. We show how this technique can also be implemented in matched-filtering to minimize the covariance which accounts for both instrumental noise and SN. Since GW detectors are essentially full-sky, we expect that this powerful tool can help in testing the isotropy of our Universe in the next future.

Gli stili APA, Harvard, Vancouver, ISO e altri

35

Trudu, Matteo, Maura Pilia, Gregory Hellbourg, Pierpaolo Pari, Nicolò Antonietti, Claudio Maccone, Andrea Melis, Delphine Perrodin e Alessio Trois. "Performance analysis of the Karhunen–Loève Transform for artificial and astrophysical transmissions: denoizing and detection". Monthly Notices of the Royal Astronomical Society 494, n. 1 (13 marzo 2020): 69–83. http://dx.doi.org/10.1093/mnras/staa694.

Testo completo

Abstract (sommario):

ABSTRACT In this work, we propose a new method of computing the Karhunen–Loève Transform (KLT) applied to complex voltage data for the detection and noise level reduction in astronomical signals. We compared this method with the standard KLT techniques based on the Toeplitz correlation matrix and we conducted a performance analysis for the detection and extraction of astrophysical and artificial signals via Monte Carlo (MC) simulations. We applied our novel method to a real data study-case: the Voyager 1 telemetry signal. We evaluated the KLT performance in an astrophysical context: our technique provides a remarkable improvement in computation time and MC simulations show significant reconstruction results for signal-to-noise ratio (SNR) down to −10 dB and comparable results with standard signal detection techniques. The application to artificial signals, such as the Voyager 1 data, shows a notable gain in SNR after the KLT.

Gli stili APA, Harvard, Vancouver, ISO e altri

36

Khozov, G. V. "Photometric technique for selecting cool carbon stars". Astrophysics 35, n. 2-3 (1992): 378–80. http://dx.doi.org/10.1007/bf01003991.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

37

Chen, Zhaoting, Laura Wolz, Marta Spinelli e Steven G. Murray. "Extracting H i astrophysics from interferometric intensity mapping". Monthly Notices of the Royal Astronomical Society 502, n. 4 (11 febbraio 2021): 5259–76. http://dx.doi.org/10.1093/mnras/stab386.

Testo completo

Abstract (sommario):

ABSTRACT We present a new halo model of neutral hydrogen (H i) calibrated to galaxy formation simulations at redshifts z ∼ 0.1 and z ∼ 1.0 that we employ to investigate the constraining power of interferometric H i intensity mapping on H i astrophysics. We demonstrate that constraints on the small-scale H i power spectrum can break the degeneracy between the H i density $\Omega _{\rm H\, \small {I}}$ and the H i bias $b_{\rm H\, \small {I}}$. For z ∼ 0.1, we forecast that an accurate measurement of $\Omega _{\rm H\, \small {I}}$ up to 6 per cent level precision and the large-scale H i bias $b_{\rm H\, \small {I}}^0$ up to 1 per cent level precision can be achieved using Square Kilometre Array (SKA) pathfinder data from MeerKAT and Australian SKA Pathfinder (ASKAP). We also propose a new description of the H i shot noise in the halo model framework in which a scatter of the relation between the H i mass of galaxies and their host halo mass is taken into account. Furthermore, given the number density of H i galaxies above a certain H i mass threshold, future surveys will also be able to constrain the H i mass function using only the H i shot noise. This will lead to constraints at the 10 per cent level using the standard Schechter function. This technique will potentially provide a new way of measuring the H i mass function, independent from existing methods. We predict that the SKA will be able to further improve the low-redshift constraints by a factor of 3, as well as pioneering measurements of H i astrophysics at higher redshifts.

Gli stili APA, Harvard, Vancouver, ISO e altri

38

Heydari, Mohammad, Ghasem Barid Loghmani e Abdul-Majid Wazwaz. "A numerical approach for a class of astrophysics equations using piecewise spectral-variational iteration method". International Journal of Numerical Methods for Heat & Fluid Flow 27, n. 2 (6 febbraio 2017): 358–78. http://dx.doi.org/10.1108/hff-09-2015-0379.

Testo completo

Abstract (sommario):

Purpose The main purpose of this paper is to implement the piecewise spectral-variational iteration method (PSVIM) to solve the nonlinear Lane-Emden equations arising in mathematical physics and astrophysics. Design/methodology/approach This method is based on a combination of Chebyshev interpolation and standard variational iteration method (VIM) and matching it to a sequence of subintervals. Unlike the spectral method and the VIM, the proposed PSVIM does not require the solution of any linear or nonlinear system of equations and analytical integration. Findings Some well-known classes of Lane-Emden type equations are solved as examples to demonstrate the accuracy and easy implementation of this technique. Originality/value In this paper, a new and efficient technique is proposed to solve the nonlinear Lane-Emden equations. The proposed method overcomes the difficulties arising in calculating complicated and time-consuming integrals and terms that are not needed in the standard VIM.

Gli stili APA, Harvard, Vancouver, ISO e altri

39

Benhar, Omar, Alessandro Lovato e Giovanni Camelio. "Modeling Neutron Star Matter in the Age of Multimessenger Astrophysics". Astrophysical Journal 939, n. 1 (1 novembre 2022): 52. http://dx.doi.org/10.3847/1538-4357/ac8e61.

Testo completo

Abstract (sommario):

Abstract The interpretation of available and forthcoming data obtained from multimessenger astrophysical observations—potentially providing unprecedented access to neutron star properties—will require the development of novel, accurate theoretical models of dense matter. Of great importance, in this context, will be the capability for devising a description of thermal effects applicable to the study of quantities other than the equation of state, such as the transport coefficients and the neutrino mean free path in the nuclear medium. A formalism based on correlated basis states and the cluster expansion technique has been previously employed to derive a well-behaved effective interaction—suitable for use in standard perturbation theory—from a state-of-the-art nuclear Hamiltonian, including phenomenological two- and three-nucleon potentials. Here, we provide a comprehensive and self-contained account of the extension of this approach to the treatment of finite-temperature effects, and report the results of numerical calculations of a number of properties of nuclear matter with arbitrary neutron excess and temperature up to 50 MeV.

Gli stili APA, Harvard, Vancouver, ISO e altri

40

Aielli, G., C. Bacci, F. Barone, B. Bartoli, P. Bernardini, X. J. Bi, C. Bleve et al. "Scaler mode technique for the ARGO-YBJ detector". Astroparticle Physics 30, n. 2 (settembre 2008): 85–95. http://dx.doi.org/10.1016/j.astropartphys.2008.07.002.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

41

Miller, Jonathan, e Roman Pasechnik. "Quasi-Classical Gravity Effect on Neutrino Oscillations in a Gravitational Field of a Heavy Astrophysical Object". Advances in High Energy Physics 2015 (2015): 1–15. http://dx.doi.org/10.1155/2015/381569.

Testo completo

Abstract (sommario):

In the framework of quantum field theory, a graviton interacts locally with a quantum state having definite mass, that is, the gravitational mass eigenstate, while a weak boson interacts with a state having definite flavor, that is, the flavor eigenstate. An interaction of a neutrino with an energetic graviton may trigger the collapse of the neutrino to a definite mass eigenstate with probability expressed in terms of PMNS mixing matrix elements. Thus, gravitons would induce quantum decoherence of a coherent neutrino flavor state similarly to how weak bosons induce quantum decoherence of a neutrino in a definite mass state. We demonstrate that such an essentially quantum gravity effect may have strong consequences for neutrino oscillation phenomena in astrophysics due to relatively large scattering cross sections of relativistic neutrinos undergoing large angle radiation of energetic gravitons in gravitational field of a classical massive source (i.e., the quasi-classical case of gravitational Bethe-Heitler scattering). This graviton-induceddecoherenceis compared todecoherencedue to propagation in the presence of the Earth matter effect. Based on this study, we propose a new technique for the indirect detection of energetic gravitons by measuring the flavor composition of astrophysical neutrinos.

Gli stili APA, Harvard, Vancouver, ISO e altri

42

Gucsik, Arnold, Hirotsugu Nishido, Kiyotaka Ninagawa, Ulrich Ott, Akira Tsuchiyama, Masahiro Kayama, Irakli Simonia e Jean-Paul Boudou. "Cathodoluminescence Microscopy and Spectroscopy of Micro- and Nanodiamonds: An Implication for Laboratory Astrophysics". Microscopy and Microanalysis 18, n. 6 (dicembre 2012): 1285–91. http://dx.doi.org/10.1017/s143192761201330x.

Testo completo

Abstract (sommario):

AbstractColor centers in selected micro- and nanodiamond samples were investigated by cathodoluminescence (CL) microscopy and spectroscopy at 298 K [room temperature (RT)] and 77 K [liquid-nitrogen temperature (LNT)] to assess the value of the technique for astrophysics. Nanodiamonds from meteorites were compared with synthetic diamonds made with different processes involving distinct synthesis mechanisms (chemical vapor deposition, static high pressure high temperature, detonation). A CL emission peak centered at around 540 nm at 77 K was observed in almost all of the selected diamond samples and is assigned to the dislocation defect with nitrogen atoms. Additional peaks were identified at 387 and 452 nm, which are related to the vacancy defect. In general, peak intensity at LNT at the samples was increased in comparison to RT. The results indicate a clear temperature—dependence of the spectroscopic properties of diamond. This suggests the method is a useful tool in laboratory astrophysics.

Gli stili APA, Harvard, Vancouver, ISO e altri

43

Dwyer, Sheila E., Georgia L. Mansell e Lee McCuller. "Squeezing in Gravitational Wave Detectors". Galaxies 10, n. 2 (9 marzo 2022): 46. http://dx.doi.org/10.3390/galaxies10020046.

Testo completo

Abstract (sommario):

Injecting optical squeezed states of light, a technique known as squeezing, is now a tool for gravitational wave detection. Its ability to reduce quantum noise is helping to reveal more gravitational wave transients, expanding the catalog of observations in the last observing run. This review introduces squeezing and its history in the context of gravitational-wave detectors. It overviews the benefits, limitations and methods of incorporating squeezing into advanced interferometers, emphasizing the most relevant details for astrophysics instrumentation.

Gli stili APA, Harvard, Vancouver, ISO e altri

44

Trinczek, M., S. Lapi, B. Guo, F. Ames, K. R. Buckley, J. M. D'Auria, K. Jayamanna, W. P. Liu, C. Ruiz e T. J. Ruth. "Production of intense radioactive beams at ISAC using low-energy protons". Canadian Journal of Physics 84, n. 4 (1 aprile 2006): 325–33. http://dx.doi.org/10.1139/p06-058.

Testo completo

Abstract (sommario):

A proof-of-principle approach for the production of intense (~108/s) radioactive ion beams, which differs from the standard ISOL (Isotope Separation On-Line) technique, has been demonstrated successfully using 11C at the TRIUMF laboratory. This approach uses 13 MeV protons produced by a medical cyclotron and should be useful for a range of radioisotopes of interest to the nuclear astrophysics research programme.PACS No.: 29.25.Rm

Gli stili APA, Harvard, Vancouver, ISO e altri

45

Sarkar, Subhajit, Nikku Madhusudhan e Andreas Papageorgiou. "JexoSim: a time-domain simulator of exoplanet transit spectroscopy with JWST". Monthly Notices of the Royal Astronomical Society 491, n. 1 (22 ottobre 2019): 378–97. http://dx.doi.org/10.1093/mnras/stz2958.

Testo completo

Abstract (sommario):

ABSTRACT The James Webb Space Telescope (JWST) will perform exoplanet transit spectroscopy in the coming decade, promising transformative science results. All four instruments onboard can be used for this technique that reconstructs the atmospheric transmission or emission spectrum of an exoplanet from wavelength-dependent light-curve measurements. Astrophysical and instrumental noise and systematics can affect the precision and accuracy of the final spectrum, and hence, the atmospheric properties derived from the spectrum. Correlated noise and time-dependent systematics that can bias the measured signal must be accounted for in the final uncertainties. However, quantifying these effects can be difficult with real data or simple analytic tools. Existing publicly available simulators for JWST do not adequately simulate complex time-domain processes on exoplanetary transit observations. We report JexoSim, a dedicated time-domain simulator for JWST including all the four instruments for exoplanet transit spectroscopy. JexoSim models both the astrophysics and the instrument, generating 2D images in simulated time akin to a real observation. JexoSim can capture correlated noise and systematic biases on the light curve, giving it great versatility. Potential applications of JexoSim include performance testing of JWST instruments, assessing science return, and testing data reduction pipelines. We describe JexoSim, validate it against other simulators, and present examples of its utility.

Gli stili APA, Harvard, Vancouver, ISO e altri

46

Gastis, P., G. Perdikakis, G. P. A. Berg, A. C. Dombos, A. Estrade, A. Falduto, M. Horoi et al. "A technique for the study of (p,n) reactions with unstable isotopes at energies relevant to astrophysics". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 985 (gennaio 2021): 164603. http://dx.doi.org/10.1016/j.nima.2020.164603.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

47

Jeffery, Elizabeth J. "Observational problems in determining the ages of open clusters". Proceedings of the International Astronomical Union 4, S258 (ottobre 2008): 141–52. http://dx.doi.org/10.1017/s1743921309031792.

Testo completo

Abstract (sommario):

AbstractOpen clusters have long been objects of interest in astronomy. As a good approximation of essentially pure stellar populations, they have proved very useful for studies in a wide range of astrophysically interesting questions, including stellar evolution and atmospheres, the chemical and dynamical evolution of our Galaxy, and the structure of our Galaxy. Of fundamental importance to our understanding of open clusters is accurate determinations of cluster ages. Currently there are two main techniques for independently determining the ages of stellar populations: main sequence evolution theory (via cluster isochrones) and white dwarf cooling theory. We will provide an overview of these two methods, the current level of agreement between them, as well as a look to the current state of increasing precision in the determination of each. Particularly I will discuss the comprehensive data set collection that is being done by the WIYN Open Cluster Study, as well as a new Bayesian statistical technique that has been developed by our group and its applications in improving and determining white dwarf ages of open clusters. I will review the so-called bright white dwarf technique, a new way of measuring cluster ages with just the bright white dwarfs. I will discuss the first application of the Bayesian technique to the Hyades, also demonstrating the first successful application of the bright white dwarf technique. These results bring the white dwarf age of the Hyades into agreement with the main sequence turn off age for the first time.

Gli stili APA, Harvard, Vancouver, ISO e altri

48

Wang, Shuang, Sixiang Wen e Miao Li. "Exploring JLA supernova data with improved flux-averaging technique". Journal of Cosmology and Astroparticle Physics 2017, n. 03 (15 marzo 2017): 037. http://dx.doi.org/10.1088/1475-7516/2017/03/037.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

49

Yan, Yihua, Baolin Tan, V. Melnikov, Xingyao Chen, Wei Wang, Linjie Chen e Fei Liu. "Diagnosing coronal magnetic fields with radio imaging-spectroscopy technique". Proceedings of the International Astronomical Union 15, S354 (giugno 2019): 17–23. http://dx.doi.org/10.1017/s1743921320000629.

Testo completo

Abstract (sommario):

AbstractMingantu Spectral Radioheliograph (MUSER) is an aperture-synthesis imaging telescope, dedicated to observe the Sun, operating on multiple frequencies in dm to cm range. The ability of MUSER to get images and measure Stokes I and V parameters simultaneously at many frequencies in a wide band is of fundamental importance. It allows one to approach/solve such important problems as measuring the strength, geometry and dynamics of magnetic field at coronal heights. Here we consider some of the recently developed radio physics methods to be used for solving the problems. These methods allow us to obtain information that is unattainable in other areas of the electromagnetic spectrum.

Gli stili APA, Harvard, Vancouver, ISO e altri

50

Janett, Gioele, Oskar Steiner, Ernest Alsina Ballester, Luca Belluzzi e Siddhartha Mishra. "A novel fourth-order WENO interpolation technique". Astronomy & Astrophysics 624 (aprile 2019): A104. http://dx.doi.org/10.1051/0004-6361/201834761.

Testo completo

Abstract (sommario):

Context. Several numerical problems require the interpolation of discrete data that present at the same time (i) complex smooth structures and (ii) various types of discontinuities. The radiative transfer in solar and stellar atmospheres is a typical example of such a problem. This calls for high-order well-behaved techniques that are able to interpolate both smooth and discontinuous data. Aims. This article expands on different nonlinear interpolation techniques capable of guaranteeing high-order accuracy and handling discontinuities in an accurate and non-oscillatory fashion. The final aim is to propose new techniques which could be suitable for applications in the context of numerical radiative transfer. Methods. We have proposed and tested two different techniques. Essentially non-oscillatory (ENO) techniques generate several candidate interpolations based on different substencils. The smoothest candidate interpolation is determined from a measure for the local smoothness, thereby enabling the essentially non-oscillatory property. Weighted ENO (WENO) techniques use a convex combination of all candidate substencils to obtain high-order accuracy in smooth regions while keeping the essentially non-oscillatory property. In particular, we have outlined and tested a novel well-performing fourth-order WENO interpolation technique for both uniform and nonuniform grids. Results. Numerical tests prove that the fourth-order WENO interpolation guarantees fourth-order accuracy in smooth regions of the interpolated functions. In the presence of discontinuities, the fourth-order WENO interpolation enables the non-oscillatory property, avoiding oscillations. Unlike Bézier and monotonic high-order Hermite interpolations, it does not degenerate to a linear interpolation near smooth extrema of the interpolated function. Conclusion. The novel fourth-order WENO interpolation guarantees high accuracy in smooth regions, while effectively handling discontinuities. This interpolation technique might be particularly suitable for several problems, including a number of radiative transfer applications such as multidimensional problems, multigrid methods, and formal solutions.

Gli stili APA, Harvard, Vancouver, ISO e altri

Articoli di riviste sul tema "Astrophysics Technique"

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili