3,610 research outputs found
Demixing can occur in binary hard-sphere mixtures with negative non-additivity
A binary fluid mixture of non-additive hard spheres characterized by a size
ratio and a non-additivity parameter
is considered in infinitely many
dimensions. From the equation of state in the second virial approximation
(which is exact in the limit ) a demixing transition with a
critical consolute point at a packing fraction scaling as
is found, even for slightly negative non-additivity, if
. Arguments concerning the stability of the
demixing with respect to freezing are provided.Comment: 4 pages, 2 figures; title changed; final paragraph added; to be
published in PRE as a Rapid Communicatio
Ageing effects around the glass and melting transitions in poly(dimethylsiloxane) visualized by resistance measurements
The process of ageing in rubbers requires monitoring over long periods (days
to years). To do so in non-conducting rubbers, small amounts of carbon-black
particles were dispersed in a fractal network through the rubber matrix, to
make the rubber conducting without modifying its properties. Continuous
monitoring of the resistance reveals the structural changes around the glass
and melting transitions and especially details about the hysteresis and ageing
processes. We illustrate the method for the semicrystalline polymer
poly(dimethylsiloxane) (PDMS).Comment: 4 pages, 4 figure
Solwind observations of coronal mass ejections during 1979-1985
Coronal observations have been processed for parts of each year during the interval 1979-1985. Around sunspot maximum, coronal mass ejections (CMEs) occurred at the rate of approximately 2 per day, and had a wide range of physical and morphological properties. During the recent years of relatively low sunspot number, CMEs occurred at the rate of only 0.2 per day, and were dominated by the class of so-called streamer blowout. These special CMEs maintained a nearly constant occurrence rate of roughly 0.1 per day during the entire interval
Associations between coronal mass ejections and interplanetary shocks
Nearly continuous complementary coronal observations and interplanetary plasma measurements for the years 1979-1982 are compared. It is shown that almost all low latitude high speed coronal mass ejections (CME's) were associated with shocks at HELIOS 1. Some suitably directed low speed CME's were clearly associated with shocks while others may have been associated with disturbed plasma (such as NCDE's) without shocks. A few opposite hemisphere CME's associated with great flares seem to be associated with shocks at HELIOS
Mesoscale simulations of surfactant dissolution and mesophase formation
The evolution of the contact zone between pure surfactant and solvent has
been studied by mesoscale simulation. It is found that mesophase formation
becomes diffusion controlled and follows the equilibrium phase diagram
adiabatically almost as soon as individual mesophases can be identified,
corresponding to times in real systems of order 10 microseconds.Comment: 4 pages, 2 figures, ReVTeX
Deforming glassy polystyrene: Influence of pressure, thermal history, and deformation mode on yielding and hardening
The toughness of a polymer glass is determined by the interplay of yielding, strain softening, and strain hardening. Molecular-dynamics simulations of a typical polymer glass, atactic polystyrene, under the influence of active deformation have been carried out to enlighten these processes. It is observed that the dominant interaction for the yield peak is of interchain nature and for the strain
hardening of intrachain nature. A connection is made with the microscopic cage-to-cage motion. It is found that the deformation does not lead to complete erasure of the thermal history but that differences persist at large length scales. Also we find that the strain-hardening modulus increases with increasing external pressure. This new observation cannot be explained by current theories
such as the one based on the entanglement picture and the inclusion of this effect will lead to an improvement in constitutive modeling
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