62 research outputs found
Equilibrium Configurations of Homogeneous Fluids in General Relativity
By means of a highly accurate, multi-domain, pseudo-spectral method, we
investigate the solution space of uniformly rotating, homogeneous and
axisymmetric relativistic fluid bodies. It turns out that this space can be
divided up into classes of solutions. In this paper, we present two new classes
including relativistic core-ring and two-ring solutions. Combining our
knowledge of the first four classes with post-Newtonian results and the
Newtonian portion of the first ten classes, we present the qualitative
behaviour of the entire relativistic solution space. The Newtonian disc limit
can only be reached by going through infinitely many of the aforementioned
classes. Only once this limiting process has been consummated, can one proceed
again into the relativistic regime and arrive at the analytically known
relativistic disc of dust.Comment: 8 pages, colour figures, v3: minor additions including one reference,
accepted by MNRA
Data-driven discovery of cardiolipin-selective small molecules by computational active learning
Data-driven discovery of cardiolipin-selective small molecules by computational active learning
Subtle variations in the lipid composition of mitochondrial membranes can have a profound impact on mitochondrial function. The inner mitochondrial membrane contains the phospholipid cardiolipin, which has been demonstrated to act as a biomarker for a number of diverse pathologies. Small molecule dyes capable of selectively partitioning into cardiolipin membranes enable visualization and quantification of the cardiolipin content. Here we present a data-driven approach that combines a deep learning-enabled active learning workflow with coarse-grained molecular dynamics simulations and alchemical free energy calculations to discover small organic compounds able to selectively permeate cardiolipin-containing membranes. By employing transferable coarse-grained models we efficiently navigate the all-atom design space corresponding to small organic molecules with molecular weight less than ≈500 Da. After direct simulation of only 0.42% of our coarse-grained search space we identify molecules with considerably increased levels of cardiolipin selectivity compared to a widely used cardiolipin probe 10-N-nonyl acridine orange. Our accumulated simulation data enables us to derive interpretable design rules linking coarse-grained structure to cardiolipin selectivity. The findings are corroborated by fluorescence anisotropy measurements of two compounds conforming to our defined design rules. Our findings highlight the potential of coarse-grained representations and multiscale modelling for materials discovery and design
The Bacteriostatic Activity of 2-Phenylethanol Derivatives Correlates with Membrane Binding Affinity
The hydrophobic tails of aliphatic primary alcohols do insert into the hydrophobic core of a lipid bilayer. Thereby, they disrupt hydrophobic interactions between the lipid molecules, resulting in a decreased lipid order, i.e., an increased membrane fluidity. While aromatic alcohols, such as 2-phenylethanol, also insert into lipid bilayers and disturb the membrane organization, the impact of aromatic alcohols on the structure of biological membranes, as well as the potential physiological implication of membrane incorporation has only been studied to a limited extent. Although diverse targets are discussed to be causing the bacteriostatic and bactericidal activity of 2-phenylethanol, it is clear that 2-phenylethanol severely affects the structure of biomembranes, which has been linked to its bacteriostatic activity. Yet, in fungi some 2-phenylethanol derivatives are also produced, some of which appear to also have bacteriostatic activities. We showed that the 2-phenylethanol derivatives phenylacetic acid, phenyllactic acid, and methyl phenylacetate, but not Tyrosol, were fully incorporated into model membranes and affected the membrane organization. Furthermore, we observed that the propensity of the herein-analyzed molecules to partition into biomembranes positively correlated with their respective bacteriostatic activity, which clearly linked the bacteriotoxic activity of the substances to biomembranes
Spectral Decorrelation of Nuclear Levels in the Presence of Continuum Decay
The fluctuation properties of nuclear giant resonance spectra are studied in
the presence of continuum decay. The subspace of quasi-bound states is
specified by one-particle one-hole and two-particle two-hole excitations and
the continuum coupling is generated by a scattering ensemble. It is found that,
with increasing number of open channels, the real parts of the complex
eigenvalues quickly decorrelate. This appears to be related to the transition
from power-law to exponential time behavior of the survival probability of an
initially non-stationary state.Comment: 10 Pages, REVTEX, 4 PostScript figure
Signatures of the correlation hole in total and partial cross sections
In a complex scattering system with few open channels, say a quantum dot with
leads, the correlation properties of the poles of the scattering matrix are
most directly related to the internal dynamics of the system. We may ask how to
extract these properties from an analysis of cross sections. In general this is
very difficult, if we leave the domain of isolated resonances. We propose to
consider the cross correlation function of two different elastic or total cross
sections. For these we can show numerically and to some extent also
analytically a significant dependence on the correlations between the
scattering poles. The difference between uncorrelated and strongly correlated
poles is clearly visible, even for strongly overlapping resonances.Comment: 25 pages, 13 Postscript figures, typos corrected and references adde
On the black hole limit of rotating discs and rings
Solutions to Einstein's field equations describing rotating fluid bodies in
equilibrium permit parametric (i.e. quasi-stationary) transitions to the
extreme Kerr solution (outside the horizon). This has been shown analytically
for discs of dust and numerically for ring solutions with various equations of
state. From the exterior point of view, this transition can be interpreted as a
(quasi) black hole limit. All gravitational multipole moments assume precisely
the values of an extremal Kerr black hole in the limit. In the present paper,
the way in which the black hole limit is approached is investigated in more
detail by means of a parametric Taylor series expansion of the exact solution
describing a rigidly rotating disc of dust. Combined with numerical
calculations for ring solutions our results indicate an interesting universal
behaviour of the multipole moments near the black hole limit.Comment: 18 pages, 4 figures; Dedicated to Gernot Neugebauer on the occasion
of his 70th birthda
Resonance trapping and saturation of decay widths
Resonance trapping appears in open many-particle quantum systems at high
level density when the coupling to the continuum of decay channels reaches a
critical strength. Here a reorganization of the system takes place and a
separation of different time scales appears. We investigate it under the
influence of additional weakly coupled channels as well as by taking into
account the real part of the coupling term between system and continuum. We
observe a saturation of the mean width of the trapped states. Also the decay
rates saturate as a function of the coupling strength. The mechanism of the
saturation is studied in detail. In any case, the critical region of
reorganization is enlarged. When the transmission coefficients for the
different channels are different, the width distribution is broadened as
compared to a chi_K^2 distribution where K is the number of channels. Resonance
trapping takes place before the broad state overlaps regions beyond the
extension of the spectrum of the closed system.Comment: 18 pages, 8 figures, accepted by Phys. Rev.
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Genetic diversity at the Dhn3 locus in Turkish Hordeum spontaneum populations with comparative structural analyses
We analysed Hordeum spontaneum accessions from 21 different locations to understand the genetic diversity of HsDhn3 alleles and effects of single base mutations on the intrinsically disordered structure of the resulting polypeptide (HsDHN3). HsDHN3 was found to be YSK2-type with a low-frequency 6-aa deletion in the beginning of Exon 1. There is relatively high diversity in the intron region of HsDhn3 compared to the two exon regions. We have found subtle differences in K segments led to changes in amino acids chemical properties. Predictions for protein interaction profiles suggest the presence of a protein-binding site in HsDHN3 that coincides with the K1 segment. Comparison of DHN3 to closely related cereals showed that all of them contain a nuclear localization signal sequence flanking to the K1 segment and a novel conserved region located between the S and K1 segments [E(D/T)DGMGGR]. We found that H. vulgare, H. spontaneum, and Triticum urartu DHN3s have a greater number of phosphorylation sites for protein kinase C than other cereal species, which may be related to stress adaptation. Our results show that the nature and extent of mutations in the conserved segments of K1 and K2 are likely to be key factors in protection of cells
An above-barrier narrow resonance in <sup>15</sup>F
Intense and purified radioactive beam of post-accelerated O was used
to study the low-lying states in the unbound F nucleus. Exploiting
resonant elastic scattering in inverse kinematics with a thick target, the
second excited state, a resonance at E=4.757(6)(10)~MeV with a width of
=36(5)(14)~keV was measured for the first time with high precision. The
structure of this narrow above-barrier state in a nucleus located two neutrons
beyond the proton drip line was investigated using the Gamow Shell Model in the
coupled channel representation with a C core and three valence protons.
It is found that it is an almost pure wave function of two quasi-bound protons
in the shell.Comment: 8 pages, 2 figures, 1 table, Submitted to Phys. Lett.
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