scholarly journals Variations in External Parallax Errors

1986 ◽  
Vol 109 ◽  
pp. 247-251
Author(s):  
A. R. Upgren
Keyword(s):  
Proper Motion ◽  
Main Sequence ◽  
Space Velocity ◽  
Proper Motions ◽  
Motion Data ◽  
Hyades Cluster ◽  
High Space ◽  
The Individual ◽  
Van Vleck ◽  
High Space Velocity

The present astrometric program of the Van Vleck Observatory began in 1967. Since then it has emphasized parallaxes and proper motions of stars of the lower main sequence which are not identified on the basis of proper motion and are therefore not biased towards high space velocity. Later an analysis was made from parallax and proper motion data from 70 stars in the spectral range dK3-M2 (Upgren 1973) which found the average external mean error in parallax to be 8.0 ± 1.7 mas (milliarcseconds). This external error was found to vary little from one parallax to another and to have no correlation with the formal internal errors for the individual parallax determinations. Hanson and Lutz (1983) confirm this result using the parallaxes of 14 members of the Hyades cluster also determined at Van Vleck. They find a mean external parallax error of 9.4 ± 1.8 mas and suggest that the proximity of the two determinations may be evidence that Van Vleck parallaxes may be characterized by a single external error. Their slightly larger figure may or may not reflect the relatively fewer plates and epochs of observation from which the Hyades parallaxes were determined.

scholarly journals Proper Motions in the Bulge: Looking Through Plaut's Low Extinction Window

1998 ◽  
Vol 179 ◽  
pp. 223-224
Author(s):  
R.A. Méndez ◽  
R.M. Rich ◽  
W.F. Van Altena ◽  
T.M. Girard ◽  
S. Van Den Bergh ◽  
...  
Keyword(s):  
Proper Motion ◽  
Main Sequence ◽  
Proper Motions ◽  
Galactic Bulge ◽  
Plate Material

We are conducting the deepest and largest photographic proper-motion survey ever undertaken of the Galactic bulge. Our first-epoch plate material (from 1972-3) goes deep enough (Vlim ∼ 22) to reach below the bulge main-sequence turnoff. These plates cover an area of approximately 25′ × 25′ of the bulge in the low-extinction (Av ∼ 0.8 mag) Plaut field at l= 0°, b= −8°, approximately 1 kpc south of the nucleus. This is the point at which the transition between bulge and halo populations likely occurs and is, therefore, an excellent location to study the interface between the dense metal-rich bulge and the metal-poor halo.

scholarly journals A CeO2/ZrO2-TiO2 Catalyst for the Selective Catalytic Reduction of NOx with NH3

Catalysts ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 592 ◽  
Author(s):  
Wenpo Shan ◽  
Yang Geng ◽  
Yan Zhang ◽  
Zhihua Lian ◽  
Hong He
Keyword(s):  
Selective Catalytic Reduction ◽  
Ph Value ◽  
Catalytic Reduction ◽  
Space Velocity ◽  
Catalytic Performance ◽  
Excellent Activity ◽  
Reduction Of Nox ◽  
High Space ◽  
Catalytic Performances ◽  
High Space Velocity

In this study, CeZr0.5TiaOx (with a = 0, 1, 2, 5, 10) catalysts were prepared by a stepwise precipitation approach for the selective catalytic reduction of NOx with NH3. When Ti was added, all of the Ce-Zr-Ti oxide catalysts showed much better catalytic performances than the CeZr0.5Ox. Particularly, the CeZr0.5Ti2Ox catalyst showed excellent activity for broad temperature range under high space velocity condition. Through the control of pH value and precipitation time during preparation, the function of the CeZr0.5Ti2Ox catalyst could be controlled and the structure with highly dispersed CeO2 (with redox functions) on the surface of ZrO2-TiO2 (with acidic functions) could be obtained. Characterizations revealed that the superior catalytic performance of the catalyst is associated with its outstanding redox properties and adsorption/activation functions for the reactants.

The catalytic oxidation removal of low-concentration HCHO at high space velocity by partially crystallized mesoporous MnO x

2017 ◽  
Vol 320 ◽  
pp. 667-676 ◽  
Author(s):  
Min Wang ◽  
Lingxia Zhang ◽  
Weimin Huang ◽  
Tongping Xiu ◽  
Chenggang Zhuang ◽  
...  
Keyword(s):  
Catalytic Oxidation ◽  
Space Velocity ◽  
Low Concentration ◽  
High Space ◽  
High Space Velocity

Experimental Catalytic and Thermal Cracking at High Temperature and High Space Velocity.

1952 ◽  
Vol 44 (8) ◽  
pp. 1811-1817 ◽  
Author(s):  
R. C. Archibald ◽  
N C. May ◽  
B. S. Greensfelder
Keyword(s):  
High Temperature ◽  
Thermal Cracking ◽  
Space Velocity ◽  
High Space ◽  
High Space Velocity
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