6 research outputs found
Metastability, Mode Coupling and the Glass Transition
Mode coupling theory (MCT) has been successful in explaining the observed
sequence of time relaxations in dense fluids. Previous expositions of this
theory showing this sequence have required the existence of an ideal glass
transition temperature . Recent experiments show no evidence of . We
show here how the theory can be reformulated, in a fundamental way, such that
one retains this sequence of relaxation behaviors but with a smooth temperature
dependence and without any indication of . The key ingredient in the
reformulation is the inclusion of the metastable nature of the glass transition
problem through a coupling of the mass density to the defect density. A main
result of our theory is that the exponents governing the sequence of time
relaxations are weak functions of the temperature in contrast to the results
from conventional MCT.Comment: 14 pages (2 figures upon request), REVTEX
Metastable Dynamics of the Hard-Sphere System
The reformulation of the mode-coupling theory (MCT) of the liquid-glass
transition which incorporates the element of metastability is applied to the
hard-sphere system. It is shown that the glass transition in this system is not
a sharp one at the special value of the density or the packing fraction, which
is in contrast to the prediction by the conventional MCT. Instead we find that
the slowing down of the dynamics occurs over a range of values of the packing
fraction. Consequently, the exponents governing the sequence of time
relaxations in the intermediate time regime are given as functions of packing
fraction with one additional parameter which describes the overall scale of the
metastable potential energy for defects in the hard-sphere system. Implications
of the present model on the recent experiments on colloidal systems are also
discussed.Comment: 21 pages, 5 figures (available upon request), RevTEX3.0, JFI
Preprint
Metastable Dynamics above the Glass Transition
The element of metastability is incorporated in the fluctuating nonlinear
hydrodynamic description of the mode coupling theory (MCT) of the liquid-glass
transition. This is achieved through the introduction of the defect density
variable into the set of slow variables with the mass density and
the momentum density . As a first approximation, we consider the case
where motions associated with are much slower than those associated with
. Self-consistently, assuming one is near a critical surface in the MCT
sense, we find that the observed slowing down of the dynamics corresponds to a
certain limit of a very shallow metastable well and a weak coupling between
and . The metastability parameters as well as the exponents
describing the observed sequence of time relaxations are given as smooth
functions of the temperature without any evidence for a special temperature. We
then investigate the case where the defect dynamics is included. We find that
the slowing down of the dynamics corresponds to the system arranging itself
such that the kinetic coefficient governing the diffusion of the
defects approaches from above a small temperature-dependent value .Comment: 38 pages, 14 figures (6 figs. are included as a uuencoded tar-
compressed file. The rest is available upon request.), RevTEX3.0+eps
High prevalence of non-B HIV-1 subtypes in seamen and their sexual partners in Croatia
Travel influences the spread of non-B subtypes of HIV in Europe. The aim of this study was to assess whether the spread of non-B subtypes occurred in Croatia, a country with a low level HIV infection. Phylogenetic analysis of the reverse transcriptase and protease genes was undertaken in 145 Croatian patients with the following risks for HIV-infection: men who have sex with men (n = 64), heterosexual contact (n = 54), intravenous drug use (n = 21), bisexual contact (n = 4) and intravenous drug use plus heterosexual exposure (n = 2). The sample included 25 seamen and 13 steady female sexual partners of seamen. Overall, 38 (26%) of HIV-patients were infected with non-B subtypes. Non-B subtype infections were found only in patients with a possible heterosexual exposure. Non-B infections were most frequent in seamen and their regular female partners (in 27 of 38 seamen and their partners, 71%). The relative distribution of non-B subtypes was as follows: A, 8%; C, 26%; F, 3%; CRF01_AE, 8%; CRF02_AG, 34%; CRF05_DF, 5%; CRF06_cpx, 3%; CRF10_CD 8%; and subtype U, 5%. There were altogether 19 heterosexual couples, phylogenetic analysis confirmed that the paired samples were related in all cases. Non-B subtypes were found only in individuals with a heterosexual risk, mainly in seamen and their partners