85 research outputs found
SAFT-γ force field for the simulation of molecular fluids: 8. hetero-group coarse-grained models of perfluoroalkylalkanes assessed with new vapour-liquid interfacial tension data
The air-liquid interfacial behaviour of linear perfluoroalkylalkanes (PFAAs) is reported through a combined experimental and computer simulation study. The surface tensions of seven liquid PFAAs (perfluorobutylethane, F4H2; perfluorobutylpentane, F4H5; perfluorobutylhexane, F4H6, perfluorobutyloctane, F4H8; perfluorohexylethane, F6H2; perfluorohexylhexane, F6H6; and perfluorohexyloctane, F6H8) are experimentally determined over a wide temperature range (276 to 350 K). The corresponding surface thermodynamic properties and the critical temperatures of the studied compounds are estimated from the temperature dependence of the surface tension. Experimental density and vapour pressure data are employed to parameterize a generic heteronuclear coarse-grained intermolecular potential of the SAFT- γ family for PFAAs. The resulting force field is used in direct molecular dynamics simulations to predict with quantitative agreement the experimental tensions and to explore the conformations of the molecules in the interfacial region revealing a preferential alignment of the PFAA molecules towards the interface and an enrichment of the perfluoro-groups at the outer interface region
Thermodynamics with long-range interactions: from Ising models to black-holes
New methods are presented which enables one to analyze the thermodynamics of
systems with long-range interactions. Generically, such systems have entropies
which are non-extensive, (do not scale with the size of the system). We show
how to calculate the degree of non-extensivity for such a system. We find that
a system interacting with a heat reservoir is in a probability distribution of
canonical ensembles. The system still possesses a parameter akin to a global
temperature, which is constant throughout the substance. There is also a useful
quantity which acts like a {\it local temperatures} and it varies throughout
the substance. These quantities are closely related to counterparts found in
general relativity. A lattice model with long-range spin-spin coupling is
studied. This is compared with systems such as those encountered in general
relativity, and gravitating systems with Newtonian-type interactions. A
long-range lattice model is presented which can be seen as a black-hole analog.
One finds that the analog's temperature and entropy have many properties which
are found in black-holes. Finally, the entropy scaling behavior of a
gravitating perfect fluid of constant density is calculated. For weak
interactions, the entropy scales like the volume of the system. As the
interactions become stronger, the entropy becomes higher near the surface of
the system, and becomes more area-scaling.Comment: Corrects some typos found in published version. Title changed 22
pages, 2 figure
Clinical evaluation of pearl millet conophor weaning mix as supplementary food for Nigerian children
SOME RARE ENDANGERED AND THREATENED PLANT SPECIES FROM RATNAGIRI DISTRICT MAHARASHTRA INDIA
Volume: 86Start Page: 478End Page: 47
Ultrastructural study of acrosome formation in mongolian gerbil (Meriones unguiculatus)
Spermatogenesis is a complex and very well organized process lasting from 30 to 75 days in mammals. The spermatogenic process has been described mainly in laboratory mammals, such as the rat, while correspondent studies in wild animals are scarce. The gerbil (Meriones unguiculatus) is a small rodent native of the arid regions of Mongolia and China. Few reports are available on reproduction in the male Mongolian gerbil. The present study provides the first description of the ultrastructural alterations in spermatid cytoplasm and nucleus, with particular reference to acrosome formation in gerbils. The testes were processed by conventional transmission electron microscopy technique. Based on the development of the acrosomal system and changes in nuclear morphology, the transformation of spermatids in spermatozoon was divided into 15 steps. There were four phases in the spermiogenesis process in the gerbil: Golgi, cap, acrosomal and maturation phases. This provides the foundation for a variety of future studies of the spermiogenesis of this animal. (C) 2000 Harcourt Publishers Ltd
- …