91 research outputs found
Nonergodicity transitions in colloidal suspensions with attractive interactions
The colloidal gel and glass transitions are investigated using the idealized
mode coupling theory (MCT) for model systems characterized by short-range
attractive interactions. Results are presented for the adhesive hard sphere and
hard core attractive Yukawa systems. According to MCT, the former system shows
a critical glass transition concentration that increases significantly with
introduction of a weak attraction. For the latter attractive Yukawa system, MCT
predicts low temperature nonergodic states that extend to the critical and
subcritical region. Several features of the MCT nonergodicity transition in
this system agree qualitatively with experimental observations on the colloidal
gel transition, suggesting that the gel transition is caused by a low
temperature extension of the glass transition. The range of the attraction is
shown to govern the way the glass transition line traverses the phase diagram
relative to the critical point, analogous to findings for the fluid-solid
freezing transition.Comment: 11 pages, 7 figures; to be published in Phys. Rev. E (1 May 1999
Effective Soft-Core Potentials and Mesoscopic Simulations of Binary Polymer Mixtures
Mesoscopic molecular dynamics simulations are used to determine the large
scale structure of several binary polymer mixtures of various chemical
architecture, concentration, and thermodynamic conditions. By implementing an
analytical formalism, which is based on the solution to the Ornstein-Zernike
equation, each polymer chain is mapped onto the level of a single soft colloid.
From the appropriate closure relation, the effective, soft-core potential
between coarse-grained units is obtained and used as input to our mesoscale
simulations. The potential derived in this manner is analytical and explicitly
parameter dependent, making it general and transferable to numerous systems of
interest. From computer simulations performed under various thermodynamic
conditions the structure of the polymer mixture, through pair correlation
functions, is determined over the entire miscible region of the phase diagram.
In the athermal regime mesoscale simulations exhibit quantitative agreement
with united atom simulations. Furthermore, they also provide information at
larger scales than can be attained by united atom simulations and in the
thermal regime approaching the phase transition.Comment: 19 pages, 11 figures, 3 table
Comparative genomic hybridization detects many recurrent imbalances in central nervous system primitive neuroectodermal tumours in children
A series of 23 children with primitive neuroectodermal tumours (PNET) were analysed with comparative genomic hybridization (CGH). Multiple chromosomal imbalances have been detected in 20 patients. The most frequently involved chromosome was chromosome 17, with a gain of 17q (11 cases) and loss of 17p (eight cases). Further recurrent copy number changes were detected. Extra copies of chromosome 7 were present in nine patients and gains of 1q were detected in six patients. A moderate genomic amplification was detected in one patient, involving two sites on 3p and the whole 12p. Losses were more frequent, and especially involved the chromosomes 11 (nine cases), 10q (eight cases), 8 (six cases), X (six patients) and 3 (five cases), and part of chromosome 9 (five cases). These recurrent chromosomal changes may highlight locations of novel genes with an important role in the development and/or progression of PNET. © 1999 Cancer Research Campaig
Fast calculation of thermodynamic and structural parameters of solutions using the 3DRISM model and the multi-grid method
In the paper a new method to solve the tree-dimensional reference interaction
site model (3DRISM) integral equations is proposed. The algorithm uses the
multi-grid technique which allows to decrease the computational expanses.
3DRISM calculations for aqueous solutions of four compounds (argon, water,
methane, methanol) on the different grids are performed in order to determine a
dependence of the computational error on the parameters of the grid. It is
shown that calculations on the grid with the step 0.05\Angstr and buffer
8\Angstr give the error of solvation free energy calculations less than 0.3
kcal/mol which is comparable to the accuracy of the experimental measurements.
The performance of the algorithm is tested. It is shown that the proposed
algorithm is in average more than 12 times faster than the standard Picard
direct iteration method.Comment: the information in this preprint is not up to date. Since the first
publication of the preprint (9 Nov 2011) the algorithm was modified which
allowed to achieve better results. For the new algorithm see the JCTC paper:
DOI: 10.1021/ct200815v, http://pubs.acs.org/doi/abs/10.1021/ct200815
Plot by plot: plotting urbanism as an ordinary process of urbanization
With this paper, we analyse an ordinary urban process, which has received little attention so far and propose a new concept to take account of it: plotting urbanism. It is usually subsumed
under terms like âurban informalityâ or âincremental urbanismâ and not studied as a distinct process. In comparing Lagos, Istanbul and Shenzhen we captured four defining features of
plotting urbanism: first, it unfolds in a piecemeal fashion with limited comprehensive planning. Second, it emerges from conflicts between multiple overlapping modes of territorial regulation, land tenure and property rights, which result in specific territorial compromises. Third, plotting is based on commodification of housing and land, which might accentuate socio-economic differentiations between property-owners, who often live in the same area, and their tenants. The term âplottingâ highlights the key role of the plot in the process. It also alludes to strategic acts of collaboration for individual and collaborative benefit
Organisation of the entire rabbit progesterone receptor mRNA and of the promoter and 5' flanking region of the gene.
cDNA clones corresponding to the 3' and 5' non coding regions of the rabbit progesterone receptor (rPR) mRNA and genomic clones corresponding to the promoter and 5' flanking region of this gene were isolated and sequenced up to nucleotide -2761. The 3' non coding region is very long (3058-3553 nucleotides) and contains three different polyadenylation sites. Primer extension experiments and S1 mapping showed the existence of 2 transcription initiation sites 699 and 712 bp upstream from the initiator ATG. The promoter region contains two modified TATA boxes: TAGAAA at -17 and TAGA at -37bp. A CAACT sequence is present at position -100 and one consensus binding site for the transcription factor Sp1 is found at position -51. A 317 bp sequence was observed (positions -2590 to -2273) which belongs to the C family of the short interspersed repeats of the rabbit. Sequences resembling the consensus for estrogen and progesterone responsive elements are observed at several locations in the 5' flanking region. The progesterone receptor is present in tissue extracts mainly as a mixture of two molecular species (110 and 79 kDa) whose origin remains currently debated. By Northern blot analysis we have shown, using rabbit and human mRNAs, that these receptor species are not derived from separate mRNAs. Transcription-translation experiments also showed that, at least in vitro, they are not derived by use of different translation initiation sites on the same messenger RNA
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