scholarly journals Relativistic collapse model with tachyonic features

1999 ◽  
Vol 59 (1) ◽  
pp. 80-101 ◽  
Author(s):  
Philip Pearle
Keyword(s):  
Collapse Model ◽  
Relativistic Collapse

Investigations of micropinches with comparison to the predictions of the radiative collapse model

1994 ◽  
Vol 51 (1-2) ◽  
pp. 341-348 ◽  
Author(s):  
A. Schulz ◽  
M. Hebach ◽  
H.-J. Kunze ◽  
F.R. Rosmej ◽  
F. Walden
Keyword(s):  
Collapse Model ◽  
Radiative Collapse

Models of cooperativity in protein folding

1995 ◽  
Vol 348 (1323) ◽  
pp. 61-70 ◽  
Keyword(s):  
Protein Folding ◽  
Molten Globule ◽  
Core Collapse ◽  
Hydrophobic Core ◽  
Model Studies ◽  
Helix Formation ◽  
Collapse Model ◽  
Folding Pathways ◽  
State Behaviour ◽  
Denatured States

What is the basis for the two-state cooperativity of protein folding? Since the 1950s, three main models have been put forward. 1. In ‘helix-coil’ theory, cooperativity is due to local interactions among near neighbours in the sequence. Helix-coil cooperativity is probably not the principal basis for the folding of globular proteins because it is not two-state, the forces are weak, it does not account for sheet proteins, and there is no evidence that helix formation precedes the formation of a hydrophobic core in the folding pathways. 2. In the ‘sidechain packing’ model, cooperativity is attributed to the jigsaw-puzzle-like complementary fits of sidechains. This too is probably not the basis of folding cooperativity because exact models and experiments on homopolymers with sidechains give no evidence that sidechain freezing is two-state, sidechain complementarities in proteins are only weak trends, and the molten globule model predicted by this model is far more native-like than experiments indicate. 3. In the ‘hydrophobic core collapse’ model, cooperativity is due to the assembly of non-polar residues into a good core. Exact model studies show that this model gives two-state behaviour for some sequences of hydrophobic and polar monomers. It is based on strong forces. There is considerable experimental evidence for the kinetics this model predicts: the development of hydrophobic clusters and cores is concurrent with secondary structure formation. It predicts compact denatured states with sizes and degrees of disorder that are in reasonable agreement with experiments.

scholarly journals Turnaround radius of galaxy clusters in N-body simulations

2020 ◽  
Vol 639 ◽  
pp. A122 ◽  
Author(s):  
Giorgos Korkidis ◽  
Vasiliki Pavlidou ◽  
Konstantinos Tassis ◽  
Evangelia Ntormousi ◽  
Theodore N. Tomaras ◽  
...  
Keyword(s):  
Dark Matter ◽  
Galaxy Clusters ◽  
Cosmological Parameters ◽  
Three Dimensional ◽  
Average Density ◽  
Matter Density ◽  
Tidal Forces ◽  
Spherical Collapse ◽  
Collapse Model ◽  
Model C

Aims. We use N-body simulations to examine whether a characteristic turnaround radius, as predicted from the spherical collapse model in a ΛCDM Universe, can be meaningfully identified for galaxy clusters in the presence of full three-dimensional effects. Methods. We use The Dark Sky Simulations and Illustris-TNG dark-matter-only cosmological runs to calculate radial velocity profiles around collapsed structures, extending out to many times the virial radius R200. There, the turnaround radius can be unambiguously identified as the largest nonexpanding scale around a center of gravity. Results. We find that: (a) a single turnaround scale can meaningfully describe strongly nonspherical structures. (b) For halos of masses M200 >  1013 M⊙, the turnaround radius Rta scales with the enclosed mass Mta as Mta1/3, as predicted by the spherical collapse model. (c) The deviation of Rta in simulated halos from the spherical collapse model prediction is relatively insensitive to halo asphericity. Rather, it is sensitive to the tidal forces due to massive neighbors when these are present. (d) Halos exhibit a characteristic average density within the turnaround scale. This characteristic density is dependent on cosmology and redshift. For the present cosmic epoch and for concordance cosmological parameters (Ωm ∼ 0.3; ΩΛ ∼ 0.7) turnaround structures exhibit a density contrast with the matter density of the background Universe of δ ∼ 11. Thus, Rta is equivalent to R11 – in a way that is analogous to defining the “virial” radius as R200 – with the advantage that R11 is shown in this work to correspond to a kinematically relevant scale in N-body simulations.

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