scholarly journals Determination of the stretch tensor for structural transformations

2016 ◽  
Vol 93 ◽  
pp. 34-43 ◽  
Author(s):  
Xian Chen ◽  
Yintao Song ◽  
Nobumichi Tamura ◽  
Richard D. James
2014 ◽  
Vol 47 (5) ◽  
pp. 1666-1675
Author(s):  
Arkadiusz Kupczak ◽  
Lucjan Pytlik ◽  
Wieslawa Sikora

Knowledge of how chemically predefined clusters of atoms are arranged in a crystal and how they can reorientate under external excitations is of great importance for structure determination and a description of structural transformations. In general, the probability of cluster reorientation depends on the activation energy and thus on the symmetry of the cluster and its environment. In addition to the many experimental methods available for studying molecular reorientations in a crystal, there is also a theoretical method, known for many years, that can be used to describe the reorientation processes, namely the determination of the principal axes of the cluster's tensor of inertia (TI). By such calculations, insight may be gained into the effective shape of the cluster and the orientations of the distinct reorientation axes. In the present work, such a methodology has been applied to an analysis of borohydride, BH4, clusters in several structures proposed by theoretical calculations as well as experimental studies of magnesium borohydride, Mg(BH4)2. The calculation of orientations for the TI principal axes as well as pseudo-twofold axes of the cluster revealed a strong correlation between these orientations and the Mg—B—Mg angle for the two Mg neighbours of the cluster. The exceptions from that well defined dependence are observed for the principal TI axes in situations when the cluster deformations are small and the symmetry is close to spherical, when the orientations of the principal axes are prone to fluctuations.


2014 ◽  
Vol 50 (20) ◽  
pp. 2615-2617 ◽  
Author(s):  
Gui-Lian Li ◽  
Guang-Zhen Liu ◽  
Lu-Fang Ma ◽  
Ling-Yun Xin ◽  
Xiao-Ling Li ◽  
...  

A dynamic MOF with hierarchical pores displays various SC–SC structural transformations including reversible desolvation–resolvation, I2 uptake–release, and photochemical [2+2] cycloaddition.


2000 ◽  
Vol 26 (8) ◽  
pp. 558-560
Author(s):  
S. K. Asadov ◽  
É. A. Zavadskiı̆ ◽  
V. I. Kamenev ◽  
B. M. Todris

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.


1999 ◽  
Vol 190 ◽  
pp. 549-554
Author(s):  
Nino Panagia

Using the new reductions of the IUE light curves by Sonneborn et al. (1997) and an extensive set of HST images of SN 1987A we have repeated and improved Panagia et al. (1991) analysis to obtain a better determination of the distance to the supernova. In this way we have derived an absolute size of the ringRabs= (6.23 ± 0.08) x 1017cm and an angular sizeR″ = 808 ± 17 mas, which give a distance to the supernovad(SN1987A) = 51.4 ± 1.2 kpc and a distance modulusm–M(SN1987A) = 18.55 ± 0.05. Allowing for a displacement of SN 1987A position relative to the LMC center, the distance to the barycenter of the Large Magellanic Cloud is also estimated to bed(LMC) = 52.0±1.3 kpc, which corresponds to a distance modulus ofm–M(LMC) = 18.58±0.05.


1961 ◽  
Vol 13 ◽  
pp. 29-41
Author(s):  
Wm. Markowitz
Keyword(s):  

A symposium on the future of the International Latitude Service (I. L. S.) is to be held in Helsinki in July 1960. My report for the symposium consists of two parts. Part I, denoded (Mk I) was published [1] earlier in 1960 under the title “Latitude and Longitude, and the Secular Motion of the Pole”. Part II is the present paper, denoded (Mk II).


1972 ◽  
Vol 1 ◽  
pp. 27-38
Author(s):  
J. Hers

In South Africa the modern outlook towards time may be said to have started in 1948. Both the two major observatories, The Royal Observatory in Cape Town and the Union Observatory (now known as the Republic Observatory) in Johannesburg had, of course, been involved in the astronomical determination of time almost from their inception, and the Johannesburg Observatory has been responsible for the official time of South Africa since 1908. However the pendulum clocks then in use could not be relied on to provide an accuracy better than about 1/10 second, which was of the same order as that of the astronomical observations. It is doubtful if much use was made of even this limited accuracy outside the two observatories, and although there may – occasionally have been a demand for more accurate time, it was certainly not voiced.


2000 ◽  
Vol 179 ◽  
pp. 205-208
Author(s):  
Pavel Ambrož ◽  
Alfred Schroll

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.


1975 ◽  
Vol 26 ◽  
pp. 341-380 ◽  
Author(s):  
R. J. Anderle ◽  
M. C. Tanenbaum

AbstractObservations of artificial earth satellites provide a means of establishing an.origin, orientation, scale and control points for a coordinate system. Neither existing data nor future data are likely to provide significant information on the .001 angle between the axis of angular momentum and axis of rotation. Existing data have provided data to about .01 accuracy on the pole position and to possibly a meter on the origin of the system and for control points. The longitude origin is essentially arbitrary. While these accuracies permit acquisition of useful data on tides and polar motion through dynamio analyses, they are inadequate for determination of crustal motion or significant improvement in polar motion. The limitations arise from gravity, drag and radiation forces on the satellites as well as from instrument errors. Improvements in laser equipment and the launch of the dense LAGEOS satellite in an orbit high enough to suppress significant gravity and drag errors will permit determination of crustal motion and more accurate, higher frequency, polar motion. However, the reference frame for the results is likely to be an average reference frame defined by the observing stations, resulting in significant corrections to be determined for effects of changes in station configuration and data losses.


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