scholarly journals Modeling and use of stellar oscillation visibilities

2018 ◽  
Vol 617 ◽  
pp. A111 ◽  
Author(s):  
J. Schou
Keyword(s):  
Signal To Noise Ratio ◽  
Spectroscopic Method ◽  
Correlation Method ◽  
Spectroscopic Observations ◽  
Stellar Oscillations ◽  
Photometric Observations ◽  
Oscillation Modes ◽  
Stellar Oscillation ◽  
Magnetohydrodynamic Simulations ◽  
Value Decomposition

Context. Recently our ability to study stars using asteroseismic techniques has increased dramatically, largely through the use of space based photometric observations. Work has also been performed using ground based spectroscopic observations and more is expected in the near future from the SONG network. Unfortunately, the intensity observations have an inferior signal-to-noise ratio and details of the observations do not agree with theory, while the data analysis used in the spectroscopic method has often been based on overly simple models of the spectra. Aims. The aim is to improve the reliability of measurements of the parameters of stellar oscillations using spectroscopic observations and to enable the optimal use of the observations. Methods. While previous investigations have used 1D models, I argue that realistic magnetohydrodynamic simulations, combined with radiative transfer calculations, should be used to model the effects of the oscillations on the spectra. I then demonstrate how to calculate the visibility of the oscillation modes for a variety of stellar parameters and fitting methods. In addition to the methods used in previous investigations, I introduce a singular value decomposition based technique. This new technique enables the determination of the information content available from spectral perturbations and allows this content to be expressed most compactly. Finally I describe how the time series obtained may be analyzed. Results. It is shown that it is important to model the visibilities carefully and that the results deviate substantially from previous models, especially in the presence of rotation. Detailed spectral modeling may be exploited to measure the properties of a larger number of modes than possible via the commonly used cross-correlation method. With moderate rotation, there is as much information in the line shape changes as in the Doppler shift and an outline of how to extract this is given.

scholarly journals Seismology of southern Be stars

1994 ◽  
Vol 162 ◽  
pp. 104-105
Author(s):  
Eduardo Janot-Pacheco ◽  
Nelson Vani Leister
Keyword(s):  
High Resolution ◽  
Signal To Noise Ratio ◽  
Ccd Camera ◽  
High Signal ◽  
Be Stars ◽  
Signal To Noise ◽  
Photometric Variability ◽  
Spectroscopic Observations ◽  
Photometric Observations ◽  
Noise Ratio

We have started in 1990 a search for moving bumps in the HeI λ 667.8 nm of mainly southern, bright Be stars. The objects of our sample have been selected on the basis of photometric variability (Cuypers et al., 1989). High resolution (R≥ 30,000), high signal-to-noise ratio (S/R≥ 300) spectroscopic observations have been performed at the brazilian Laboratório Nacional de Astrofísica with a CCD camera attached to the coudé spectrograph of the 1.60 m telescope (e.g. Table I). Several hundred spectra have been taken during the last three years. Photometric observations simultaneous with spectroscopy were made on the same site in July 1992 with a two-channel photometer (Stromgren b filter) and a CCD camera (Johnson B filter) installed at two 0.60 m telescopes. The idea is try to disentangle the controversy between NRP and RM models with the help of simultaneous spectroscopy and photometry.

Joint Encryption and Compression-Based Watermarking Technique for Security of Digital Documents

2021 ◽  
Vol 21 (1) ◽  
pp. 1-20
Author(s):  
A. K. Singh ◽  
S. Thakur ◽  
Alireza Jolfaei ◽  
Gautam Srivastava ◽  
MD. Elhoseny ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Similarity Index ◽  
Structural Similarity ◽  
Digital Data ◽  
The Internet ◽  
Discrete Wavelet ◽  
Compression Performance ◽  
Strong Compression ◽  
Multiple Watermarks ◽  
Value Decomposition

Recently, due to the increase in popularity of the Internet, the problem of digital data security over the Internet is increasing at a phenomenal rate. Watermarking is used for various notable applications to secure digital data from unauthorized individuals. To achieve this, in this article, we propose a joint encryption then-compression based watermarking technique for digital document security. This technique offers a tool for confidentiality, copyright protection, and strong compression performance of the system. The proposed method involves three major steps as follows: (1) embedding of multiple watermarks through non-sub-sampled contourlet transform, redundant discrete wavelet transform, and singular value decomposition; (2) encryption and compression via SHA-256 and Lempel Ziv Welch (LZW), respectively; and (3) extraction/recovery of multiple watermarks from the possibly distorted cover image. The performance estimations are carried out on various images at different attacks, and the efficiency of the system is determined in terms of peak signal-to-noise ratio (PSNR) and normalized correlation (NC), structural similarity index measure (SSIM), number of changing pixel rate (NPCR), unified averaged changed intensity (UACI), and compression ratio (CR). Furthermore, the comparative analysis of the proposed system with similar schemes indicates its superiority to them.

scholarly journals On cross-spectrum capabilities for detecting stellar oscillation modes

2007 ◽  
Vol 463 (3) ◽  
pp. 1211-1214 ◽  
Author(s):  
T. Appourchaux ◽  
J. Leibacher ◽  
P. Boumier
Keyword(s):  
Cross Spectrum ◽  
Oscillation Modes ◽  
Stellar Oscillation

scholarly journals Design and Optimization for UAV-Enabled Two-Way Relaying System with SWIPT

2020 ◽  
Author(s):  
Jinlong Wang ◽  
Gang Wang ◽  
Guanyi Chen ◽  
Bo Li ◽  
Ruofei Zhou ◽  
...  
Keyword(s):  
Optimization Problem ◽  
Signal To Noise Ratio ◽  
Power Splitting ◽  
Generalized Singular Value Decomposition ◽  
Ratio Requirement ◽  
Design And Optimization ◽  
Aerial Vehicle ◽  
Resource Allocation Scheme ◽  
Value Decomposition ◽  
Relaying System

Abstract In this paper, we investigate the resource allocation scheme for an unmanned-aerial-vehicle-enable (UAV-enabled) two-way relaying system with simultaneous wireless information and power transfer (SWIPT), where two userequipment exchange information with the help of UAV relay and harvest energythrough power splitting (PS) scheme. Under the transmission power constraintsat UEs and UAV relay, a non-convex intractable optimization problem isformulated which maximizes the sum retained energy of two UEs while satisfying the minimum signal-to-noise ratio requirement. We decouple the complicated beamforming and PS factors optimization problem into three solvable subproblems and propose an efficient alternating optimization scheme. Subsequently, in order to reduce the complexity, a robust scheme based on generalized singular value decomposition (GSVD) is designed. Finally, numerical results verify the robustness and effectiveness of two proposed schemes.

scholarly journals Through-Wall Image Enhancement Based on Singular Value Decomposition

2012 ◽  
Vol 2012 ◽  
pp. 1-20 ◽  
Author(s):  
Muhammad Mohsin Riaz ◽  
Abdul Ghafoor
Keyword(s):  
Singular Value Decomposition ◽  
Image Enhancement ◽  
Visual Inspection ◽  
Signal To Noise Ratio ◽  
Singular Values ◽  
Singular Value ◽  
Information Theoretic ◽  
Value Decomposition ◽  
Suppress Noise ◽  
Wall Imaging

Singular value decomposition and information theoretic criterion-based image enhancement is proposed for through-wall imaging. The scheme is capable of discriminating target, clutter, and noise subspaces. Information theoretic criterion is used with conventional singular value decomposition to find number of target singular values. Furthermore, wavelet transform-based denoising is performed (to further suppress noise signals) by estimating noise variance. Proposed scheme works also for extracting multiple targets in heavy cluttered through-wall images. Simulation results are compared on the basis of mean square error, peak signal to noise ratio, and visual inspection.

scholarly journals Secure Exchange of Medical Data Using a Novel Real-Time Biometric-Based Protection and Recognition Method

Electronics ◽  
2020 ◽  
Vol 9 (12) ◽  
pp. 2013
Author(s):  
Shams Ud Din ◽  
Zahoor Jan ◽  
Muhammad Sajjad ◽  
Maqbool Hussain ◽  
Rahman Ali ◽  
...  
Keyword(s):  
Electronic Health Records ◽  
Real Time ◽  
Signal To Noise Ratio ◽  
Security And Privacy ◽  
The Internet ◽  
Healthcare Organizations ◽  
Health Records ◽  
Clinical Notes ◽  
Electronic Health ◽  
Value Decomposition

Security and privacy are essential requirements, and their fulfillment is considered one of the most challenging tasks for healthcare organizations to manage patient data using electronic health records. Electronic health records (clinical notes, images, and documents) become more vulnerable to breaching patients’ privacy when shared with an external organization in the current arena of the internet of medical things (IoMT). Various watermarking techniques were introduced in the medical field to secure patients’ data. Most of the existing techniques focus on an image or document’s imperceptibility without considering the watermark(logo). In this research, a novel technique of watermarking is introduced, which supersedes the shortcomings of existing approaches. It guarantees the imperceptibility of the image/document and takes care of watermark(biometric), which is further passed through a process of recognition for claiming ownership. It extracts suitable frequencies from the transform domain using specialized filters to increase the robustness level. The extracted frequencies are modified by adding the biomedical information while considering the strength factor according to the human visual system. The watermarked frequencies are further decomposed through a singular value decomposition technique to increase payload capacity up to (256 × 256). Experimental results over a variety of medical and official images demonstrate the average peak signal-to-noise ratio (PSNR 54.43), and the normal correlation (N.C.) value is 1. PSNR and N.C. of the watermark were calculated after attacks. The proposed technique is working in real-time for embedding, extraction, and recognition of biometrics over the internet, and its uses can be realized in various platforms of IoMT technologies.

scholarly journals Bolometric corrections of stellar oscillation amplitudes as observed by the Kepler, CoRoT, and TESS missions

2019 ◽  
Vol 489 (1) ◽  
pp. 1072-1081 ◽  
Author(s):  
Mikkel N Lund
Keyword(s):  
Power Law ◽  
Convection Zone ◽  
Black Body ◽  
Stellar Spectrum ◽  
Spectral Flux ◽  
Oscillation Modes ◽  
1D Model ◽  
Stellar Oscillation ◽  
Full Temperature ◽  
Bolometric Correction

ABSTRACT A better understanding of the amplitudes of stellar oscillation modes and surface granulation is essential for improving theories of mode physics and the properties of the outer convection zone of solar-like stars. A proper prediction of these amplitudes is also essential for appraising the detectability of solar-like oscillations for asteroseismic analysis. Comparisons with models, or between different photometric missions, are enabled by applying a bolometric correction, which converts mission-specific amplitudes to their corresponding bolometric (full light) values. We derive the bolometric correction factor for amplitudes of radial oscillation modes and surface granulation as observed by the Kepler, CoRoT, and TESS missions. The calculations are done assuming a stellar spectrum given by a black-body as well as by synthetic spectral flux densities from 1D model atmospheres. We derive a power-law and polynomial relations for the bolometric correction as a function of temperature from the black-body approximation and evaluate the deviations from adopting a more realistic spectrum. Across the full temperature range from 4000 to 7500 K, the amplitudes from TESS are in the black-body approximation predicted to be a factor ∼0.83–0.84 times those observed by Kepler. We find that using more realistic flux spectra over the black-body approximation can change the bolometric correction by as much as ${\sim }30{{\ \rm per\ cent}}$ at the lowest temperatures, but with a change typically within ${\sim }5\!-\!10 {{\ \rm per\ cent}}$ around a Teff of 5500–6000 K. We find that after Teff, the bolometric correction most strongly depends on $\rm [M/H]$, which could have an impact on reported metallicity dependences of amplitudes reported in the literature.

scholarly journals HD 42659: the only known roAp star in a spectroscopic binary observed with B photometry, TESS, and SALT

2019 ◽  
Vol 489 (3) ◽  
pp. 4063-4071 ◽  
Author(s):  
Daniel L Holdsworth ◽  
Hideyuki Saio ◽  
Donald W Kurtz
Keyword(s):  
Signal To Noise Ratio ◽  
Rotation Frequency ◽  
Close Binaries ◽  
High Signal ◽  
Pulsation Frequency ◽  
Orbital Parameters ◽  
Mode Amplitude ◽  
Photometric Observations ◽  
Short Period ◽  
Roap Star

ABSTRACT We present a multi-instrument analysis of the rapidly oscillating Ap (roAp) star HD 42659. We have obtained B photometric data for this star and use these data, in conjunction with the Transiting Exoplanet Survey Satellite (TESS) observations, to analyse the high-frequency pulsation in detail. We find a triplet that is split by the rotation frequency of the star (νrot = 0.3756 d−1; Prot = 2.66 d) and present both distorted dipole and distorted quadrupole mode models. We show that the pulsation frequency, 150.9898 d−1 (Ppuls = 9.54 min), is greater than the acoustic cut-off frequency. We utilize 27 high-resolution ($R\simeq 65\, 000$), high signal-to-noise ratio (∼120) spectra to provide new orbital parameters for this, the only known roAp star to be in a short-period binary (Porb = 93.266 d). We find the system to be more eccentric than previously thought, with e = 0.317, and suggest the companion is a mid-F to early-K star. We find no significant trend in the average pulsation mode amplitude with time, as measured by TESS, implying that the companion does not have an effect on the pulsation in this roAp star. We suggest further photometric observations of this star, and further studies to find more roAp stars in close binaries to characterize how binarity may affect the detection of roAp pulsations.

scholarly journals 53 Piscium, an SPB Star with Activity

2002 ◽  
Vol 185 ◽  
pp. 236-237
Author(s):  
J.-M. Le Contel ◽  
P. Mathias ◽  
E. Chapellier ◽  
J.-C. Valtier
Keyword(s):  
High Resolution ◽  
False Alarm ◽  
High Frequency ◽  
Signal To Noise Ratio ◽  
High Signal ◽  
Correlation Technique ◽  
Signal To Noise ◽  
Spectroscopic Observations ◽  
Auto Correlation ◽  
Frequency Variations

The star 53 Psc (HD 3379, B2.5IV) has been observed as variable by several authors (Sareyan et al., 1979) with frequencies around 10 c d–1 and has been classified as a β Cephei star. Conversely, other authors (e.g. Percy, 1971) found it to be constant.New high resolution, high signal-to-noise ratio, Spectroscopic observations have been performed at the Observatoire de Haute-Provence in 1996 over 11 nights. The spectral domain covers around 200 Å and is centered on Hδ. Radial velocities were deduced from an auto-correlation technique with a scatter around 0.4kms−1.No high frequency variations are observed. Three frequencies have been detected with a false alarm detection above the 1 % level. A fourth one may be present but its amplitude is below this 1 % level. Results are displayed in Table 1.

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