A Channeling Study of the Structure of U4O9

1971 ◽  
Vol 49 (17) ◽  
pp. 2215-2226 ◽  
Author(s):  
Hj. Matzke ◽  
J. A. Davies ◽  
N. G. E. Johansson
Keyword(s):  
Critical Angle ◽  
Fluorite Structure ◽  
Recent Model ◽  
The Other ◽  
Excess Oxygen ◽  
Wide Angle ◽  
Oxygen Sublattice ◽  
Other Hand ◽  
Rutherford Scattering ◽  
Oxygen Atoms

The channeling behavior of 1-MeV He+ ions and deuterons in U4O9 has been studied in order to provide information on the location of the excess oxygen in the fluorite structure of UO2. Wide-angle (Rutherford) scattering was used to study the channeling behavior with respect to the uranium sublattice, and the 16O(d, p)17O reaction was used to investigate the oxygen sublattice. A pronounced disorder in the oxygen sublattice was indicated by very poor channeling properties and strong dechanneling with increasing depth. The data are thus in conflict with the model incorporating the excess oxygen in the regular interstitial positions along the [Formula: see text] uranium rows; on the other hand, they are consistent with the more recent model of Willis in which the excess oxygen atoms are displaced ~ 1 Å from the regular interstitial sites and displace, in addition, some normal oxygen atoms. Channeling with respect to the uranium sublattice was found to be substantially the same as in stoichiometric UO2—but with a somewhat smaller critical angle, indicating that the uranium atoms may be displaced slightly (i.e. ~ 0.25 Å) by the presence of the excess oxygen.

17O and 13C NMR spectra of some geminal diacetates

1988 ◽  
Vol 53 (3) ◽  
pp. 588-592 ◽  
Author(s):  
Antonín Lyčka ◽  
Josef Jirman ◽  
Jaroslav Holeček
Keyword(s):  
13C Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
The Other ◽  
13C Nmr Spectra ◽  
Other Hand ◽  
Carboxylic Esters ◽  
C Nmr ◽  
Oxygen Atoms

The 17O and 13C NMR spectra of eight geminal diacetates RCH(O(CO)CH3)2 derived from simple aldehydes have been measured. In contrast to the dicarboxylates R1R2E(O(CO)R3)2, where E = Si, Ge, or Sn, whose 17O NMR spectra only contain a single signal, and, on the other hand, in accordance with organic carboxylic esters, the 17O NMR spectra of the compound group studied always exhibit two well-resolved signals with the chemical shifts δ(17O) in the regions of 183-219 ppm and 369-381 ppm for the oxygen atoms in the groups C-O and C=O, respectively.

scholarly journals Crystallographic orbits analysis of staurolite twins

2014 ◽  
Vol 70 (a1) ◽  
pp. C1113-C1113
Author(s):  
Mohamed Amine Marzouki ◽  
Bernd Souvignier ◽  
Massimo Nespolo
Keyword(s):  
High Frequency ◽  
The Other ◽  
Occurrence Frequency ◽  
Other Hand ◽  
High Degree ◽  
Octahedral Cations ◽  
Oxygen Atoms

Staurolite is an enigmatic mineral characterized by a high degree of pseudo-symmetry, which frequently occurs twinned. It gives two twins with different occurrence frequency, the 90° or Greek cross (lower frequency) and the 60° or Saint Andrews cross (higher frequency). To date no explanation has been found for their different occurrence frequency. We have analyzed the structure of staurolite in terms of the pseudo-eigensymmetry of the crystallographic orbits building this structure [1]. The union of the crystallographic orbits based on oxygen atoms has a pseudo-cubic eigensymmetry which contains the twin operations of both twins: the operations restore, with good approximation, the whole set of oxygen atoms, which justifies the high frequency of twinning of this mineral but does not discriminate between the two twins. On the other hand, a subset of the tetrahedral cations has a pseudo-eigensymmetry which contains the twin operation of the Saint Andrews cross, but not that of the Greek cross. Also, a subset of the octahedral cations has a pseudo-eigensymmetry which contains the twin operation of the Greek cross and a larger subset has an eigensymmetry which contains the twin operation of the Saint Andrews. The substructure approximately restored by the twin operation is thus more extensive for the Saint Andrews cross, which justifies its higher occurrence frequency.

Unusual Effect of Oxygen on the Mechanical Behavior of a β-Type Titanium Alloy Developed for Biomedical Applications

2012 ◽  
Vol 706-709 ◽  
pp. 135-142 ◽  
Author(s):  
Mitsuo Niinomi ◽  
Masaaki Nakai
Keyword(s):  
Tensile Strength ◽  
Titanium Alloy ◽  
Mechanical Behavior ◽  
Titanium Alloys ◽  
Biomedical Applications ◽  
The Other ◽  
Excess Oxygen ◽  
Ω Phase ◽  
Other Hand ◽  
Effect Of Oxygen

Oxygen enhances the strength of titanium alloys in general; however, excess oxygen can make titanium alloys brittle. On the other hand, oxygen enhances the precipitation of the α phase and suppresses the formation of the ω phase. Thus, using the optimal amount of oxygen is important to improve the mechanical properties of titanium alloys. The role of oxygen in titanium alloys is still not well understood. The effect of oxygen on the mechanical behavior of a β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (referred to as TNTZ), which is used for biomedical applications, was investigated in this study. Oxygen was found to stabilize the ω phase in TNTZ. This behavior of oxygen is unusual considering the known behavior of oxygen in titanium alloys: oxygen is known to suppress the formation of the ω phase in titanium alloys. A small amount of oxygen increases the tensile strength but decreases the ductility of TNTZ. On the other hand, a large amount of oxygen, of around 0.7 mass%, increases both the tensile strength and the ductility of TNTZ. This phenomenon is unexpected.

Mechanism of the formation of halogen monoxides during flash photolysis of halogen + oxygen mixtures

1963 ◽  
Vol 271 (1346) ◽  
pp. 289-295 ◽  
Keyword(s):  
Absorption Spectra ◽  
Flash Photolysis ◽  
Radiant Energy ◽  
The Other ◽  
Other Hand ◽  
Absorption Of Light ◽  
Oxygen Atoms

The mechanism of the formation of BrO and CIO in the flash photolysis of halogen + oxygen mixtures was investigated. It was found that the predominant mechanism for the production of BrO (about 90 % in our experiments) involves the absorption of light by the oxygen molecules. The O* 2 or the oxygen atoms produced create ozone, which in turn produces BrO when photolyzed. It is possible that some of O* 2 or O produces BrO directly and not via an ozone intermediate. About 10 % of the BrO is produced when two quanta of radiant energy are absorbed by the Br 2 molecule. The highly energetic molecule formed in this way is capable of breaking the O—O bond and forming BrO. The reaction between the excited Br atoms and O 2 , suggested by Durie & Bamsey (1958), does not occur. It seems likely that IO is formed by a mechanism similar to that of BrO. On the other hand, CIO is produced predominantly in a reaction of Cl( 2 P ) atoms with O 2 , as suggested by Porter & Wright (1953). Chlorine and bromine absorption spectra were measured down to 1880 and 1930 Å, respectively.

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

Closing the GAP—A 5Å Scanning Microscope

1969 ◽  
Vol 27 ◽  
pp. 6-7
Author(s):  
A. V. Crewe
Keyword(s):  
Normal Form ◽  
The Other ◽  
Resolving Power ◽  
Scanning Microscope ◽  
Conventional Microscope ◽  
Other Hand ◽  
Closing The Gap ◽  
Thermal Sources ◽  
Better Than ◽  
Transmission Microscope

We have become accustomed to differentiating between the scanning microscope and the conventional transmission microscope according to the resolving power which the two instruments offer. The conventional microscope is capable of a point resolution of a few angstroms and line resolutions of periodic objects of about 1Å. On the other hand, the scanning microscope, in its normal form, is not ordinarily capable of a point resolution better than 100Å. Upon examining reasons for the 100Å limitation, it becomes clear that this is based more on tradition than reason, and in particular, it is a condition imposed upon the microscope by adherence to thermal sources of electrons.

Life Beyond 1MeV

1980 ◽  
Vol 38 ◽  
pp. 30-33
Author(s):  
K.H. Westmacott
Keyword(s):  
Electron Microscopy ◽  
Past Experience ◽  
The Other ◽  
Good Case ◽  
Other Hand ◽  
The U.S

Life beyond 1MeV – like life after 40 – is not too different unless one takes advantage of past experience and is receptive to new opportunities. At first glance, the returns on performing electron microscopy at voltages greater than 1MeV diminish rather rapidly as the curves which describe the well-known advantages of HVEM often tend towards saturation. However, in a country with a significant HVEM capability, a good case can be made for investing in instruments with a range of maximum accelerating voltages. In this regard, the 1.5MeV KRATOS HVEM being installed in Berkeley will complement the other 650KeV, 1MeV, and 1.2MeV instruments currently operating in the U.S. One other consideration suggests that 1.5MeV is an optimum voltage machine – Its additional advantages may be purchased for not much more than a 1MeV instrument. On the other hand, the 3MeV HVEM's which seem to be operated at 2MeV maximum, are much more expensive.

Can the Academic Self-Concept be Positive and Realistic?

2005 ◽  
Vol 19 (3) ◽  
pp. 129-132 ◽  
Author(s):  
Reimer Kornmann
Keyword(s):  
Academic Performance ◽  
Opposite Effect ◽  
Self Esteem ◽  
Point Of View ◽  
The Other ◽  
Self Concept ◽  
High Ability ◽  
Self Image ◽  
Other Hand

Summary: My comment is basically restricted to the situation in which less-able students find themselves and refers only to literature in German. From this point of view I am basically able to confirm Marsh's results. It must, however, be said that with less-able pupils the opposite effect can be found: Levels of self-esteem in these pupils are raised, at least temporarily, by separate instruction, academic performance however drops; combined instruction, on the other hand, leads to improved academic performance, while levels of self-esteem drop. Apparently, the positive self-image of less-able pupils who receive separate instruction does not bring about the potential enhancement of academic performance one might expect from high-ability pupils receiving separate instruction. To resolve the dilemma, it is proposed that individual progress in learning be accentuated, and that comparisons with others be dispensed with. This fosters a self-image that can in equal measure be realistic and optimistic.

Stories and the Self

2020 ◽  
Vol 32 (2) ◽  
pp. 47-58 ◽  
Author(s):  
Stefan Krause ◽  
Markus Appel
Keyword(s):  
Meta Analysis ◽  
The Self ◽  
The Other ◽  
Lower Degree ◽  
Contrast Effects ◽  
Self Perception ◽  
Self Perceptions ◽  
Other Hand ◽  
The One ◽  
Implicit And Explicit

Abstract. Two experiments examined the influence of stories on recipients’ self-perceptions. Extending prior theory and research, our focus was on assimilation effects (i.e., changes in self-perception in line with a protagonist’s traits) as well as on contrast effects (i.e., changes in self-perception in contrast to a protagonist’s traits). In Experiment 1 ( N = 113), implicit and explicit conscientiousness were assessed after participants read a story about either a diligent or a negligent student. Moderation analyses showed that highly transported participants and participants with lower counterarguing scores assimilate the depicted traits of a story protagonist, as indicated by explicit, self-reported conscientiousness ratings. Participants, who were more critical toward a story (i.e., higher counterarguing) and with a lower degree of transportation, showed contrast effects. In Experiment 2 ( N = 103), we manipulated transportation and counterarguing, but we could not identify an effect on participants’ self-ascribed level of conscientiousness. A mini meta-analysis across both experiments revealed significant positive overall associations between transportation and counterarguing on the one hand and story-consistent self-reported conscientiousness on the other hand.

Don’t Put Me in This Group

2019 ◽  
Vol 50 (2) ◽  
pp. 80-93
Author(s):  
Jort de Vreeze ◽  
Christina Matschke
Keyword(s):  
Positive Emotions ◽  
Negative Emotions ◽  
Negative Information ◽  
The Self ◽  
The Other ◽  
Other Hand ◽  
Group Memberships

Abstract. Not all group memberships are self-chosen. The current research examines whether assignments to non-preferred groups influence our relationship with the group and our preference for information about the ingroup. It was expected and found that, when people are assigned to non-preferred groups, they perceive the group as different to the self, experience negative emotions about the assignment and in turn disidentify with the group. On the other hand, when people are assigned to preferred groups, they perceive the group as similar to the self, experience positive emotions about the assignment and in turn identify with the group. Finally, disidentification increases a preference for negative information about the ingroup.

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