924 research outputs found
A Kinetic Model for Cell Damage Caused by Oligomer Formation
It is well-known that the formation of amyloid fiber may cause invertible
damage to cells, while the underlying mechanism has not been fully uncovered.
In this paper, we construct a mathematical model, consisting of infinite ODEs
in the form of mass-action equations together with two reaction-convection
PDEs, and then simplify it to a system of 5 ODEs by using the maximum entropy
principle. This model is based on four simple assumptions, one of which is that
cell damage is raised by oligomers rather than mature fibrils. With the
simplified model, the effects of nucleation and elongation, fragmentation,
protein and seeds concentrations on amyloid formation and cell damage are
extensively explored and compared with experiments. We hope that our results
can provide a valuable insight into the processes of amyloid formation and cell
damage thus raised.Comment: 16 pages+ 5 figures for maintext; 8 pages+ 4 figures for Supporting
Material
Statistical Mechanics and Kinetics of Amyloid Fibrillation
Amyloid fibrillation is a protein self-assembly phenomenon that is intimately
related to well-known human neurodegenerative diseases. During the past few
decades, striking advances have been achieved in our understanding of the
physical origin of this phenomenon and they constitute the contents of this
review. Starting from a minimal model of amyloid fibrils, we explore
systematically the equilibrium and kinetic aspects of amyloid fibrillation in
both dilute and semi-dilute limits. We then incorporate further molecular
mechanisms into the analyses. We also discuss the mathematical foundation of
kinetic modeling based on chemical mass-action equations, the quantitative
linkage with experimental measurements, as well as the procedure to perform
global fitting.Comment: 68 pages, 18 figures, 201 reference
Characterizations of -well-posedness for parametric quasivariational inequalities defined by bifunctions
The purpose of this paper is to investigate the
well-posedness issue of parametric quasivariational inequalities
defined by bifunctions. We generalize the concept of
-well-posedness to parametric quasivariational inequalities
having a unique solution and derive some characterizations of
-well-posedness. The corresponding concepts of
-well-posedness in the generalized sense are also introduced
and investigated for the problems having more than one solution.
Finally, we give some sufficient conditions for
-well-posedness of parametric quasivariational inequalities
Enhancing thermoelectric figure-of-merit by low-dimensional electrical transport in phonon-glass crystals
Low-dimensional electronic and glassy phononic transport are two important
ingredients of highly-efficient thermoelectric material, from which two
branches of the thermoelectric research emerge. One focuses on controlling
electronic transport in the low dimension, while the other on multiscale phonon
engineering in the bulk. Recent work has benefited much from combining these
two approaches, e.g., phonon engineering in low-dimensional materials. Here, we
propose to employ the low-dimensional electronic structure in bulk phonon-glass
crystal as an alternative way to increase the thermoelectric efficiency.
Through first-principles electronic structure calculation and classical
molecular dynamics simulation, we show that the - stacking
Bis-Dithienothiophene molecular crystal is a natural candidate for such an
approach. This is determined by the nature of its chemical bonding. Without any
optimization of the material parameter, we obtain a maximum room-temperature
figure of merit, , of at optimal doping, thus validating our idea.Comment: Nano Lett.201
HII region G46.5-0.2: the interplay between ionizing radiation, molecular gas and star formation
HII regions are particularly interesting because they can generate dense
layers of gas and dust, elongated columns or pillars of gas pointing towards
the ionizing sources, and cometary globules of dense gas, where triggered star
formation can occur. Understanding the interplay between the ionizing radiation
and the dense surrounding gas is very important to explain the origin of these
peculiar structures, and hence to characterize triggered star formation.
G46.5-0.2 (G46), a poorly studied galactic HII region located at about 4 kpc,
is an excellent target to perform this kind of studies. Using public molecular
data extracted from the Galactic Ring Survey (13CO J=1-0) and from the James
Clerk Maxwell Telescope data archive (12CO, 13CO, C18O J=3-2, HCO+ and HCN
J=4-3), and infrared data from the GLIMPSE and MIPSGAL surveys, we perform a
complete study of G46, its molecular environment and the young stellar objects
placed around it. We found that G46, probably excited by an O7V star, is
located close to the edge of the GRSMC G046.34-00.21 molecular cloud. It
presents a horse-shoe morphology opening in direction of the cloud. We observed
a filamentary structure in the molecular gas likely related to G46 and not
considerable molecular emission towards its open border. We found that about
10' towards the southwest of G46 there are some pillar-like features, shining
at 8 um and pointing towards the HII region open border. We propose that the
pillar-like features were carved and sculpted by the ionizing flux from G46. We
found several young stellar objects likely embedded in the molecular cloud
grouped in two main concentrations: one, closer to the G46 open border
consisting of Class II type sources, and other one mostly composed by Class I
type YSOs located just ahead the pillars-like features, strongly suggesting an
age gradient in the YSOs distribution.Comment: Accepted for publication in The Astronomical Journal (April 14,
2015). Some figures were degraded to reduce file siz
Interactions of the Infrared bubble N4 with the surroundings
The physical mechanisms that induce the transformation of a certain mass of
gas in new stars are far from being well understood. Infrared bubbles
associated with HII regions have been considered to be good samples of
investigating triggered star formation. In this paper we report on the
investigation of the dust properties of the infrared bubble N4 around the HII
region G11.898+0.747, analyzing its interaction with its surroundings and star
formation histories therein, with the aim of determining the possibility of
star formation triggered by the expansion of the bubble. Using Herschel PACS
and SPIRE images with a wide wavelength coverage, we reveal the dust properties
over the entire bubble. Meanwhile, we are able to identify six dust clumps
surrounding the bubble, with a mean size of 0.50 pc, temperature of about 22 K,
mean column density of 1.7 cm, mean volume density of
about 4.4 cm, and a mean mass of 320 . In
addition, from PAH emission seen at 8 m, free-free emission detected at 20
cm and a probability density function in special regions, we could identify
clear signatures of the influence of the HII region on the surroundings. There
are hints of star formation, though further investigation is required to
demonstrate that N4 is the triggering source.Comment: Accepted by ApJ (16 pages, 11 figures, 9 tables
Modulation of nucleosome-binding activity of FACT by poly(ADP-ribosyl)ation
Chromatin-modifying factors play key roles in transcription, DNA replication and DNA repair. Post-translational modification of these proteins is largely responsible for regulating their activity. The FACT (facilitates chromatin transcription) complex, a heterodimer of hSpt16 and SSRP1, is a chromatin structure modulator whose involvement in transcription and DNA replication has been reported. Here we show that nucleosome binding activity of FACT complex is regulated by poly(ADP-ribosyl)ation. hSpt16, the large subunit of FACT, is poly(ADP-ribosyl)ated by poly(ADP-ribose) polymerase-1 (PARP-1) resulting from physical interaction between these two proteins. The level of hSpt16 poly(ADP-ribosyl)ation is elevated after genotoxic treatment and coincides with the activation of PARP-1. The enhanced hSpt16 poly(ADP-ribosyl)ation level correlates with the dissociation of FACT from chromatin in response to DNA damage. Our findings suggest that poly(ADP-ribosyl)ation of hSpt16 by PARP-1 play regulatory roles for FACT-mediated chromatin remodeling
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