scholarly journals The Galactic Evolution of Beryllium

2000 ◽  
Vol 198 ◽  
pp. 389-396 ◽  
Author(s):  
Ann Merchant Boesgaard
Keyword(s):  
Chemical Evolution ◽  
Cosmic Ray ◽  
High Spectral Resolution ◽  
High Signal ◽  
Galactic Chemical Evolution ◽  
Ray Theory ◽  
Signal To Noise ◽  
Metal Abundances ◽  
Cosmology Observations ◽  
The Relationship

The abundance of beryllium has been determined in unevolved stars over a range metal abundances in order to enhance our understanding of the chemical evolution of our Galaxy, cosmic-ray theory, and cosmology. Observations of 27 stars have been made with Keck I with HIRES at high spectral resolution (45,000) and high signal-to-noise ratios (60 - 110 typically). We find a remarkably linear relationship between log N(Be/H) and [Fe/H] with a slope of 0.96 (±0.04). Similarly, the relationship between log N(Be/H) and [O/H] is linear with a slope of 1.45 (±0.04). Beryllium increases at the same rate as Fe, but much faster than O. This provides constraints for and insights into models of Galactic chemical evolution. There is some evidence for an intrinsic spread in Be at a given [O/H] or [Fe/H]. There is no evidence of a plateau in Be at the lowest metallicities down to log N(Be/H) = —13.5.

scholarly journals Photospheric molecular line profiles in cool stars

1981 ◽  
Vol 59 ◽  
pp. 119-124
Author(s):  
S.T. Ridgway ◽  
E.D. Friel
Keyword(s):  
Spectral Lines ◽  
High Spectral Resolution ◽  
High Signal ◽  
Line Profiles ◽  
Signal To Noise ◽  
Molecular Line ◽  
Ejection Process ◽  
Cool Stars ◽  
Mass Ejection ◽  
Selection Of

AbstractSpectral lines of the ΔV=2 rotation vibration bands of CO are well suited for study of photospheric motions and the mass ejection process in cool stars. We have obtained high spectral resolution (1.8 km/sec) and high signal-to-noise (>102) line profiles for a selection of K and M giants. These profiles are being studied for evidence of gas motions in the photosphere and near circumstellar regions.

scholarly journals A New Look at the Am Stars

1988 ◽  
Vol 132 ◽  
pp. 401-406
Author(s):  
C. Burkhart ◽  
M. F. Coupry ◽  
C. van't Veer
Keyword(s):  
High Resolution ◽  
High Signal ◽  
Lithium Content ◽  
Signal To Noise ◽  
Hyades Cluster ◽  
The Relationship ◽  
New Look

High resolution, high signal-to-noise observations are required for a better understanding of the Am stars and related topics. Two examples are shown : the relationship between lithium content and temperature in the Am stars of the Hyades cluster and the observational problem induced by multiple spectroscopic binarity frequent among the Am stars.

scholarly journals The Milky Way Halo and the First Stars: New Frontiers in Galactic Archaeology

2009 ◽  
Vol 5 (H15) ◽  
pp. 184-184
Author(s):  
Timothy C. Beers ◽  
Jason Tumlinson ◽  
Brian O'Shea ◽  
Carolyn Peruta ◽  
Daniela Carollo
Keyword(s):  
Chemical Evolution ◽  
Milky Way ◽  
Galactic Chemical Evolution ◽  
Joint Effort ◽  
First Stars ◽  
Large Samples ◽  
New Models ◽  
First Galaxies ◽  
The Relationship ◽  
Milky Way Halo

AbstractWe discuss plans for a new joint effort between observers and theorists to understand the formation of the Milky Way halo back to the first epochs of chemical evolution. New models based on high-resolution N-body simulations coupled to simple models of Galactic chemical evolution show that surviving stars from the epoch of the first galaxies remain in the Milky Way today and should bear the nucleosynthetic imprint of the first stars. We investigate the key physical influences on the formation of stars in the first galaxies and how they appear today, including the relationship between cosmic reionization and surviving Milky Way stars. These models also provide a physically motivated picture of the formation of the Milky Ways “outer halo,” which has been identified from recent large samples of stars from SDSS. The next steps are to use these models to guide rigorous gas simulations of Milky Way formation, including its disk, and to gradually build up the fully detailed theoretical “Virtual Galaxy” that is demanded by the coming generation of massive Galactic stellar surveys.

scholarly journals He and Ne Ages of Large Presolar Silicon Carbide Grains: Solving the Recoil Problem

2009 ◽  
Vol 26 (3) ◽  
pp. 297-302 ◽  
Author(s):  
Ulrich Ott ◽  
Philipp R. Heck ◽  
Frank Gyngard ◽  
Rainer Wieler ◽  
Frédéric Wrobel ◽  
...  
Keyword(s):  
Silicon Carbide ◽  
Cosmic Rays ◽  
Chemical Evolution ◽  
Cosmic Ray ◽  
Galactic Chemical Evolution ◽  
Correction Procedure ◽  
Presolar Grains ◽  
The Past ◽  
Grain Formation ◽  
The Galaxy

AbstractKnowledge about the age of presolar grains provides important insights into Galactic chemical evolution and the dynamics of grain formation and destruction processes in the Galaxy. Determination from the abundance of cosmic ray interaction products is straightforward, but in the past has suffered from uncertainties in correcting for recoil losses of spallation products. The problem is less serious in a class of large (tens of μm) grains. We describe the correction procedure and summarise results for He and Ne ages of presolar SiC ‘Jumbo’ grains that range from close to zero to ∼850 Myr, with the majority being less than 200 Myr. We also discuss the possibility of extending our approach to the majority of smaller SiC grains and explore possible contributions from trapping of cosmic rays.

Large-scale alternative detection systems for CRNS

2020 ◽  
Author(s):  
Markus Köhli ◽  
Jannis Weimar ◽  
Ulrich Schmidt
Keyword(s):  
Large Scale ◽  
Scale Up ◽  
Pulse Length ◽  
Pulse Height ◽  
Cosmic Ray ◽  
High Signal ◽  
Successful Implementation ◽  
Signal To Noise ◽  
Neutron Detectors ◽  
Helium 3

<p>Cosmic-Ray neutron (CRN) sensors are widely used to determine soil moisture on the hectar scale. Precise measurements, especially in the case of mobile application, demand for neutron detectors with high counting rates and high signal-to-noise ratios. For a long time CRNS instruments have relied on helium-3 as an efficient neutron converter. Its ongoing scarcity demands for technological solutions using alternative converters, which are lithium-6 and boron-10. In order to scale up the method and to reduce costs we recently have developed large-scale neutron detectors including readout electronics and data acquisition systems based on Arduino microcontrollers. These boron-lined detectors shall offer an alternative platform to current Helium-3 based systems and allow for modular instrument designs. Individual shieldings of different segments within the detector introduces the capability of gaining spectral information. This opens the possibility for active signal correction during mobile measurements, where the influence of the constantly changing near-field to the overall signal should be corrected. Furthermore, the signal-to-noise ratio could be increased by combining pulse-height and pulse-length spectra to discriminate between neutrons and other environmental radiation. This novel detector therefore combines high-selective counting electronics with large-scale instrumentation technology. The successful implementation of our design allowed also to build the largest up to now existing CRNS detector. </p>

scholarly journals Ionisation Structure of NGC 6543

1997 ◽  
Vol 180 ◽  
pp. 270-270
Author(s):  
E. Pérez ◽  
L. Cuesta ◽  
D. Axon ◽  
A. Robinson
Keyword(s):  
Chemical Composition ◽  
Spectral Resolution ◽  
Signal To Noise Ratio ◽  
Planetary Nebulae ◽  
High Spectral Resolution ◽  
High Signal ◽  
Signal To Noise ◽  
Physical Conditions ◽  
Noise Ratio ◽  
Effects Of Radiation

We have obtained high spectral resolution, high signal-to-noise ratio longslit spectra of a sample of Planetary Nebulae with the purpose of studying their physical conditions, chemical composition and ionisation structure. In particular, we are interested in disentangling the effects of radiation and shock ionisation.

scholarly journals Oxygen in Unevolved Starss

2002 ◽  
Vol 12 ◽  
pp. 416-419
Author(s):  
Ann Merchant Boesgaard
Keyword(s):  
Spectral Resolution ◽  
Linear Relation ◽  
Spectral Region ◽  
High Spectral Resolution ◽  
High Signal ◽  
Signal To Noise ◽  
Spectrum Synthesis ◽  
Ultraviolet Spectral Region

AbstractWe have made observations of 24unevolvedstars of the OH lines in the ultraviolet spectral region at high spectral resolution and high signal-to-noise, typically 60 − 110 with Keck + HIRES. The O abundances have been computed by spectrum synthesis. For these cool, unevolved stars there is a linear relation between [O/H] and [Fe/H] over three orders of magnitude with very little scatter and a slope of +0.66 ±0.02. The relation between [O/Fe] and [Fe/H] is robustly linear with [O/Fe] = −0.35 (±0.03) [Fe/H]. There is no sign of a break at metallicities between −1.0 and −2.0.

Radiation Damage, Contrast and Statistics in High Resolution Biological Electron Microscopy

1970 ◽  
Vol 28 ◽  
pp. 260-261
Author(s):  
Robert M. Glaeser
Keyword(s):  
High Resolution ◽  
Particle Flux ◽  
Unit Area ◽  
Signal To Noise ◽  
Resolution Image ◽  
High Resolution Image ◽  
Pass Through ◽  
Counting Statistics ◽  
The Relationship ◽  
Picture Element

It is well known that a large flux of electrons must pass through a specimen in order to obtain a high resolution image while a smaller particle flux is satisfactory for a low resolution image. The minimum particle flux that is required depends upon the contrast in the image and the signal-to-noise (S/N) ratio at which the data are considered acceptable. For a given S/N associated with statistical fluxtuations, the relationship between contrast and “counting statistics” is s131_eqn1, where C = contrast; r2 is the area of a picture element corresponding to the resolution, r; N is the number of electrons incident per unit area of the specimen; f is the fraction of electrons that contribute to formation of the image, relative to the total number of electrons incident upon the object.

Grain separation enhanced magnetic coercivity in Pt/Co multilayers.

1993 ◽  
Vol 51 ◽  
pp. 1038-1039 ◽  
Author(s):  
G.A. Bertero ◽  
R. Sinclair
Keyword(s):  
Remanent Magnetization ◽  
Strong Influence ◽  
Uniaxial Anisotropy ◽  
Magnetic Coupling ◽  
Recording Media ◽  
Magnetic Media ◽  
Signal To Noise ◽  
Out Of Plane ◽  
Longitudinal Recording ◽  
The Relationship

Pt/Co multilayers displaying perpendicular (out-of-plane) magnetic anisotropy and 100% perpendicular remanent magnetization are strong candidates as magnetic media for the next generation of magneto-optic recording devices. The magnetic coercivity, Hc, and uniaxial anisotropy energy, Ku, are two important materials parameters, among others, in the quest to achieving higher recording densities with acceptable signal to noise ratios (SNR). The relationship between Ku and Hc in these films is not a simple one since features such as grain boundaries, for example, can have a strong influence on Hc but affect Ku only in a secondary manner. In this regard grain boundary separation provides a way to minimize the grain-to-grain magnetic coupling which is known to result in larger coercivities and improved SNR as has been discussed extensively in the literature for conventional longitudinal recording media.We present here results from the deposition of two Pt/Co/Tb multilayers (A and B) which show significant differences in their coercive fields.

A compact guided-wave EMAT with pulsed electromagnet for ferromagnetic tube inspection

2020 ◽  
Vol 64 (1-4) ◽  
pp. 951-958
Author(s):  
Tianhao Liu ◽  
Yu Jin ◽  
Cuixiang Pei ◽  
Jie Han ◽  
Zhenmao Chen
Keyword(s):  
Power Plants ◽  
Signal To Noise Ratio ◽  
Small Diameter ◽  
Performance Testing ◽  
Guided Wave ◽  
High Signal ◽  
Receiver Coil ◽  
Signal To Noise ◽  
Corrosion Defects

Small-diameter tubes that are widely used in petroleum industries and power plants experience corrosion during long-term services. In this paper, a compact inserted guided-wave EMAT with a pulsed electromagnet is proposed for small-diameter tube inspection. The proposed transducer is noncontact, compact with high signal-to-noise ratio and unattractive to ferromagnetic tubes. The proposed EMAT is designed with coils-only configuration, which consists of a pulsed electromagnet and a meander pulser/receiver coil. Both the numerical simulation and experimental results validate its feasibility on generating and receiving L(0,2) mode guided wave. The parameters for driving the proposed EMAT are optimized by performance testing. Finally, feasibility on quantification evaluation for corrosion defects was verified by experiments.

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