Method for the determination of photostimulable defect center concentrations, production rates, and effective formation energies

1994 ◽  
Vol 75 (9) ◽  
pp. 4658-4661 ◽  
Author(s):  
M. Thoms ◽  
H. von Seggern
Keyword(s):  
Production Rates ◽  
Defect Center ◽  
Formation Energies

Determination of 36Cl Production Rates Derived from the Well-Dated Deglaciation Surfaces of Whidbey and Fidalgo Islands, Washington

2001 ◽  
Vol 56 (3) ◽  
pp. 366-382 ◽  
Author(s):  
Terry W. Swanson ◽  
Marc L. Caffee
Keyword(s):  
Water Content ◽  
Ground Level ◽  
Total Production ◽  
Neutron Absorption ◽  
Production Rates ◽  
System A ◽  
History Of ◽  
Dating Method ◽  
Exposure Ages

AbstractThe 36Cl dating method is increasingly being used to determine the surface-exposure history of Quaternary landforms. Production rates for the 36Cl isotopic system, a critical component of the dating method, have now been refined using the well-constrained radiocarbon-based deglaciation history of Whidbey and Fidalgo Islands, Washington. The calculated total production rates due to calcium and potassium are 91±5 atoms 36Cl (g Ca)−1 yr−1 and are 228±18 atoms 36Cl (g K)−1 yr−1, respectively. The calculated ground-level secondary neutron production rate in air, Pf(0), inferred from thermal neutron absorption by 35Cl is 762±28 neutrons (g air)−1 yr−1 for samples with low water content (1–2 wt.%). Neutron absorption by serpentinized harzburgite samples of the same exposure age, having higher water content (8–12 wt.%), is ∼40% greater relative to that for dry samples. These data suggest that existing models do not adequately describe thermalization and capture of neutrons for hydrous rock samples. Calculated 36Cl ages of samples collected from the surfaces of a well-dated dacite flow (10,600–12,800 cal yr B.P.) and three disparate deglaciated localities are consistent with close limiting calibrated 14C ages, thereby supporting the validity of our 36Cl production rates integrated over the last ∼15,500 cal yr between latitudes of 46.5° and 51°N. Although our production rates are internally consistent and yield reasonable exposure ages for other localities, there nevertheless are significant differences between these production rates and those of other investigators.

scholarly journals Determination of dissolved nitric oxide in coastal waters of the Yellow Sea off Qingdao

2017 ◽  
Author(s):  
Chun-Ying Liu ◽  
Wei-Hua Feng ◽  
Ye Tian ◽  
Gui-Peng Yang ◽  
Pei-Feng Li ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Detection Limit ◽  
Coastal Waters ◽  
Yellow Sea ◽  
The Yellow Sea ◽  
No Production ◽  
Spatial Distributions ◽  
Production Rates ◽  
Temporal And Spatial

Abstract. We developed a new method for the determination of dissolved nitric oxide (NO) in discrete seawater samples based on a combination of a purge-and-trap set-up and fluorometric detection of NO. 2,3-diaminonaphthalene (DAN) reacts with NO in seawater to form the highly fluorescent 2,3-naphthotriazole (NAT). The fluorescence intensity was linear for NO concentrations in the range from 0.14 nmol L−1 to 19 nmol L−1. We determined a detection limit of 0.068 nmol L−1, an average recovery coefficient of 83.8 % (80.2–90.0 %), and a relative standard deviation of ±7.2 %. With our method we determined for the first time the temporal and spatial distributions of NO surface concentrations in coastal waters of the Yellow Sea off Qingdao and in Jiaozhou Bay during a cruise in November 2009. The concentrations of NO varied from below the detection limit to 0.50 nmol L−1 with an average of 0.26 ± 0.14 nmol L−1. NO surface concentrations were generally enhanced significantly during daytime implying that NO formation processes such as NO2− photolysis are much higher during daytime than chemical NO consumption which, in turn, lead to a significant decrease of NO concentrations during nighttime. In general, NO surface concentrations and measured NO production rates were higher compared to previously reported measurements. This might be caused by the high NO2− surface concentrations encountered during the cruise. Moreover, additional measurements of NO production rates implied that the occurrence of particles and a temperature increase can enhance NO production rates. With the method introduced here we have a reliable and comparably easy to use method at hand to measure oceanic NO surface concentrations which can be used to decipher both its temporal and spatial distributions as well as its biogeochemical pathways in the oceans.

scholarly journals The extraordinary composition of the blue comet C/2016 R2 (PanSTARRS)

2018 ◽  
Vol 619 ◽  
pp. A127 ◽  
Author(s):  
N. Biver ◽  
D. Bockelée-Morvan ◽  
G. Paubert ◽  
R. Moreno ◽  
J. Crovisier ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Heliocentric Distance ◽  
Abundance Ratio ◽  
Visible Spectroscopy ◽  
Production Rates ◽  
Sulfur Species ◽  
Upper Limits ◽  
Multi Wavelength ◽  
Rare Group

We present a multi-wavelength study of comet C/2016 R2 (PanSTARRS). This comet was observed on 23 and 24 January 2018 with the IRAM 30 m telescope, and in January to March 2018 with the Nançay radio telescope. Visible spectroscopy was performed in December 2017 and February 2018 with small amateur telescopes. We report on measurements of CO, CH3OH, H2CO and HCN production rates, and on the determination of the N2/CO abundance ratio. Several other species, especially OH, were searched for but not detected. The inferred relative abundances, including upper limits for sulfur species, are compared to those measured in other comets at about the same heliocentric distance of ~2.8 AU. The coma composition of comet C/2016 R2 is very different from all other comets observed so far, being rich in N2 and CO and dust poor. This suggests that this comet might belong to a very rare group of comets formed beyond the N2 ice line. Alternatively, comet C/2016 R2 (PanSTARRS) could be the fragment of a large and differentiated transneptunian object, with properties characteristic of volatile-enriched layers.

scholarly journals Determination of Formation Energies and Phase Diagrams of Transition Metal Oxides with DFT+U

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4303
Author(s):  
Daniel Mutter ◽  
Daniel F. Urban ◽  
Christian Elsässer
Keyword(s):  
Transition Metal ◽  
Metal Oxides ◽  
Phase Diagrams ◽  
Transition Metal Oxides ◽  
Density Functional ◽  
Synthesis Process ◽  
Local Exchange ◽  
Electronic Band ◽  
Formation Energies

Knowledge about the formation energies of compounds is essential to derive phase diagrams of multicomponent phases with respect to elemental reservoirs. The determination of formation energies using common (semi-)local exchange-correlation approximations of the density functional theory (DFT) exhibits well-known systematic errors if applied to oxide compounds containing transition metal elements. In this work, we generalize, reevaluate, and discuss a set of approaches proposed and widely applied in the literature to correct for errors arising from the over-binding of the O2 molecule and from correlation effects of electrons in localized transition-metal orbitals. The DFT+U method is exemplarily applied to iron oxide compounds, and a procedure is presented to obtain the U values, which lead to formation energies and electronic band gaps comparable to the experimental values. Using such corrected formation energies, we derive the phase diagrams for LaFeO3, Li5FeO4, and NaFeO2, which are promising materials for energy conversion and storage devices. A scheme is presented to transform the variables of the phase diagrams from the chemical potentials of elemental phases to those of precursor compounds of a solid-state reaction, which represents the experimental synthesis process more appropriately. The discussed workflow of the methods can directly be applied to other transition metal oxides.

First-Principles Studies of γ-Tial Based Ternary Alloys

1994 ◽  
Vol 364 ◽  
Author(s):  
W. Wolf ◽  
R. Podloucky ◽  
P. Rogl
Keyword(s):  
Total Energy ◽  
Ternary Alloys ◽  
Site Preference ◽  
Alloying Element ◽  
Ternary Additions ◽  
Lattice Distortions ◽  
Mn Additions ◽  
Formation Energies ◽  
Insight Into

AbstractSelf-consistent total energy calculations were performed to investigate the effects of ternary additions of 3d, 4d and 5d transition metal elements (V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir, Pt) to Ll0 ordered γ-TiAl. In general, we studied ordered solids of 4 atoms per unit cell. In the case of Mn additions larger supercells with up to 32 atoms were also treated. Minimizing the total energy with respect to volume and c/a ratio leads to the determination of lattice distortions due to alloying by the ternary elements. These distortions prove to be strongly dependent on whether the alloying element substitutes Al or Ti atoms. Furthermore, the site preference can be derived by comparing the formation energies of Tin-1XAln and TinXAln-i, where X is the substituting element. As a result the change of the geometry of L10 TiAl due to alloying can be estimated and may thereby give insight into the conditions at semicoherent γ/γ′ and α2/γ interfaces, which are associated to be responsible for ductility improvements of γ-TiAl based alloys.

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