298,505 research outputs found
Repeated crystallization in undercooled Zr41Ti14Cu12Ni10Be23 liquids
Isothermal crystallization studies are performed on Zr41Ti14Cu12Ni10Be23 melts. Undercooling experiments are carried out repeatedly at 907, 860, and 750 K. The scattering of the time to reach the onset of crystallization is investigated. Results from experiments performed at 907 K show a large scatter of the onset time of crystallization. For the experiments carried out at 860 and 750 K, scattering of the onset time is two orders of magnitude smaller. These results indicate that, at high temperatures, the crystallization is governed by the time scale of the statistical nucleation events. At low temperatures, the crystallization is controlled by diffusion, resulting in a well-defined onset time for crystallization
Self-interaction chromatography as a tool for optimizing conditions for membrane protein crystallization
The second virial coefficient, or B value, is a measurement of how well a protein interacts with itself in solution. These interactions can lead to protein crystallization or precipitation, depending on their strength, with a narrow range of B values (the `crystallization slot') being known to promote crystallization. A convenient method of determining the B value is by self-interaction chromatography. This paper describes how the light-harvesting complex 1-reaction centre core complex from Allochromatium vinosum yielded single straight-edged crystals after iterative cycles of self-interaction chromatography and crystallization. This process allowed the rapid screening of small molecules and detergents as crystallization additives. Here, a description is given of how self-interaction chromatography has been utilized to improve the crystallization conditions of a membrane protein
Explosive crystallization mechanism of ultradisperse amorphous films
The explosive crystallization of germanium ultradisperse amorphous films is
studied experimentally. We show that crystallization may be initiated by local
heating at the small film thickness but it realizes spontaneously at the large
ones. The fractal pattern of the crystallized phase is discovered that is
inherent in the phenomena of diffusion limited aggregation. It is shown that in
contrast to the ordinary crystallization mode the explosive one is connected
with the instability which is caused by the self-heating. A transition from the
first mechanism to the second one is modelled by Lorenz system. The process of
explosive crystallization is represented on the basis of the self-organized
criticality conception. The front movement is described as the effective
diffusion in the ultrametric space of hierarchically subordinated avalanches,
corresponding to the explosive crystallization of elementary volumes of
ultradisperse powder. The expressions for the stationary crystallization heat
distribution and the steady-state heat current are obtained. The heat needed
for initiation of the explosive crystallization is obtained as a function of
the thermometric conductivity. The time dependence of the spontaneous
crystallization probability in a thin films is examined.Comment: 22 pages, 5 figures, LaTe
In situ visualization of Ni-Nb bulk metallic glasses phase transition
We report the results of the Ni-based bulk metallic glass structural
evolution and crystallization behavior in situ investigation. The X-ray
diffraction (XRD), transmission electron microscopy (TEM), nano-beam
diffraction (NBD), differential scanning calorimetry (DSC), radial distribution
function (RDF) and scanning probe microscopy/spectroscopy (STM/STS) techniques
were applied to analyze the structure and electronic properties of Ni63.5Nb36.5
glasses before and after crystallization. It was proved that partial surface
crystallization of Ni63.5Nb36.5 can occur at the temperature lower than for the
full sample crystallization. According to our STM measurements the primary
crystallization is originally starting with the Ni3Nb phase formation. It was
shown that surface crystallization drastically differs from the bulk
crystallization due to the possible surface reconstruction. The mechanism of
Ni63.5Nb36.5 glass alloy 2D-crystallization was suggested, which corresponds to
the local metastable (3x3)-Ni(111) surface phase formation. The possibility of
different surface nano-structures development by the annealing of the
originally glassy alloy in ultra high vacuum at the temperature lower, than the
crystallization temperature was shown. The increase of mean square surface
roughness parameter Rq while moving from glassy to fully crystallized state can
be caused by concurrent growth of Ni3Nb and Ni6Nb7 bulk phases. The simple
empirical model for the estimation of Ni63.5Nb36.5 cluster size was suggested,
and the obtained values (7.64 A, 8.08 A) are in good agreement with STM
measurements data (8 A-10 A)
Low-Temperature Crystallization of Amorphous Silicate in Astrophysical Environments
We construct a theoretical model for low-temperature crystallization of
amorphous silicate grains induced by exothermic chemical reactions. As a first
step, the model is applied to the annealing experiments, in which the samples
are (1) amorphous silicate grains and (2) amorphous silicate grains covered
with an amorphous carbon layer. We derive the activation energies of
crystallization for amorphous silicate and amorphous carbon from the analysis
of the experiments. Furthermore, we apply the model to the experiment of
low-temperature crystallization of amorphous silicate core covered with an
amorphous carbon layer containing reactive molecules. We clarify the conditions
of low-temperature crystallization due to exothermic chemical reactions. Next,
we formulate the crystallization conditions so as to be applicable to
astrophysical environments. We show that the present crystallization mechanism
is characterized by two quantities: the stored energy density Q in a grain and
the duration of the chemical reactions \tau . The crystallization conditions
are given by Q > Q_{min} and \tau < \tau _{cool} regardless of details of the
reactions and grain structure, where \tau _{cool} is the cooling timescale of
the grains heated by exothermic reactions, and Q_{min} is minimum stored energy
density determined by the activation energy of crystallization. Our results
suggest that silicate crystallization occurs in wider astrophysical conditions
than hitherto considered.Comment: 9 figures, accepted for publication in Astrophysical
On the spectrum of facet crystallization waves at the smooth 4He crystal surface
The wavelike processes of crystallization and melting or crystallization
waves are well known to exist at the 4He crystal surface in the rough state.
Much less is known about crystallization waves for the 4He crystal surface in
the smooth well-faceted state below the roughening transition temperature. To
meet the lack, we analyze here the spectrum of facet crystallization waves and
its dependence upon the wavelength, perturbation amplitude, and the number of
possible facet steps distributed somehow over the wavelength. All the
distinctive features of facet crystallization waves from conventional waves at
the rough surface result from a nonanalytic cusplike behavior in the angle
dependence for the surface tension of smooth crystal facets.Comment: 7 pages, 3 figures, 1 tabl
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