6,041 research outputs found
Modelling PAH curvature in laminar premixed flames using a detailed population balance model
© 2016 The Combustion Institute A detailed population balance model, which includes the kinetic Monte Carlo-aromatic site (KMC-ARS) model for detailed polycyclic aromatic hydrocarbon (PAH) growth, is used to compute the Gauss curvature of PAHs in laminar premixed ethylene and benzene flames. Previous studies have found that capping of an embedded 5-member ring causes curvature in graphene edges. In this work, a capping process is added to the KMC-ARS model with the rate coefficient of the capping reaction taken from the work of You et al. (2011). We demonstrate that the Gauss–Bonnet theorem can be used to derive a correlation between the number of 5- and 6-member rings in a PAH and its Gauss curvature (or radius of curvature), independent of where the 5-member ring is embedded within the PAH structure. Numerical simulation yields satisfactory results when compared to the experimentally determined Gauss curvature reported in the literature. Computed and experimental fringe length distributions are also compared and the results suggest that PAHs smaller than the size required for inception are able to condense onto particles.This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its CREATE programme. Mr. Edward K. Y. Yapp was supported by the Gates Cambridge, Cambridge, UK. Prof. Markus Kraft was supported by the Weierstrass Institute for Applied Analysis and Stochastics, Berlin, Germany
Reversals in nature and the nature of reversals
The asymmetric shape of reversals of the Earth's magnetic field indicates a
possible connection with relaxation oscillations as they were early discussed
by van der Pol. A simple mean-field dynamo model with a spherically symmetric
coefficient is analysed with view on this similarity, and a comparison
of the time series and the phase space trajectories with those of paleomagnetic
measurements is carried out. For highly supercritical dynamos a very good
agreement with the data is achieved. Deviations of numerical reversal sequences
from Poisson statistics are analysed and compared with paleomagnetic data. The
role of the inner core is discussed in a spectral theoretical context and
arguments and numerical evidence is compiled that the growth of the inner core
might be important for the long term changes of the reversal rate and the
occurrence of superchrons.Comment: 24 pages, 12 figure
Statistical study of conductance properties in one-dimensional quantum wires focusing on the 0.7 anomaly
The properties of conductance in one-dimensional (1D) quantum wires are
statistically investigated using an array of 256 lithographically-identical
split gates, fabricated on a GaAs/AlGaAs heterostructure. All the split gates
are measured during a single cooldown under the same conditions. Electron
many-body effects give rise to an anomalous feature in the conductance of a
one-dimensional quantum wire, known as the `0.7 structure' (or `0.7 anomaly').
To handle the large data set, a method of automatically estimating the
conductance value of the 0.7 structure is developed. Large differences are
observed in the strength and value of the 0.7 structure [from to
], despite the constant temperature and identical device
design. Variations in the 1D potential profile are quantified by estimating the
curvature of the barrier in the direction of electron transport, following a
saddle-point model. The 0.7 structure appears to be highly sensitive to the
specific confining potential within individual devices.This is the author's accepted manuscript. The final version is published by ACS in Physical Review B and can be found here: http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.045426
Semi-analytical approach to magnetized temperature autocorrelations
The cosmic microwave background (CMB) temperature autocorrelations, induced
by a magnetized adiabatic mode of curvature inhomogeneities, are computed with
semi-analytical methods. As suggested by the latest CMB data, a nearly
scale-invariant spectrum for the adiabatic mode is consistently assumed. In
this situation, the effects of a fully inhomogeneous magnetic field are
scrutinized and constrained with particular attention to harmonics which are
relevant for the region of Doppler oscillations. Depending on the parameters of
the stochastic magnetic field a hump may replace the second peak of the angular
power spectrum. Detectable effects on the Doppler region are then expected only
if the magnetic power spectra have quasi-flat slopes and typical amplitude
(smoothed over a comoving scale of Mpc size and redshifted to the epoch of
gravitational collapse of the protogalaxy) exceeding 0.1 nG. If the magnetic
energy spectra are bluer (i.e. steeper in frequency) the allowed value of the
smoothed amplitude becomes, comparatively, larger (in the range of 20 nG). The
implications of this investigation for the origin of large-scale magnetic
fields in the Universe are discussed. Connections with forthcoming experimental
observations of CMB temperature fluctuations are also suggested and partially
explored.Comment: 40 pages, 13 figure
Salt-Induced Deterioration on FRP-Brick Masonry Bond
In the past decades, several studies have shown how fiber reinforced polymer (FRP) composites are an effective technique to strengthen unreinforced brick masonry structures. However, very little is known about their durability against environmental aggression such as salt attack and freeze-thaw cycles, or elevated moisture content. This paper presents an investigation on influence of salt attack on the stress transfer between the FRP composite and the masonry substrate. In fact, it is well known that, in certain conditions, soluble salts crystallize within the pores of materials, leading to crystallization pressures that may overcome their tensile strength. To investigate this effect, FRP-masonry joints were subjected to salt crystallization cycles according to a conditioning procedure designed by the authors. After conditioning, direct shear tests were conducted on the masonry joints to investigate the interfacial bond between the substrate and the composite. Materials characterization was carried out in order correlate the results of the direct shear tests with the salt distribution within the specimens. For comparison, direct shear tests were conducted on FRP-masonry joints that were not subjected to any cycle and therefore used as control
Dirac Equation with Spin Symmetry for the Modified P\"oschl-Teller Potential in -dimensions
We present solutions of the Dirac equation with spin symmetry for vector and
scalar modified P\"oschl-Teller potential within framework of an approximation
of the centrifugal term. The relativistic energy spectrum is obtained using the
Nikiforov-Uvarov method and the two-component spinor wavefunctions are obtain
are in terms of the Jacobi polynomials. It is found that there exist only
positive-energy states for bound states under spin symmetry, and the energy
levels increase with the dimension and the potential range parameter .Comment: 9 pages and 1tabl
Expression of a Serine Protease Gene prC Is Up-Regulated by Oxidative Stress in the Fungus Clonostachys rosea: Implications for Fungal Survival
BACKGROUND: Soil fungi face a variety of environmental stresses such as UV light, high temperature, and heavy metals. Adaptation of gene expression through transcriptional regulation is a key mechanism in fungal response to environmental stress. In Saccharomyces cerevisiae, the transcription factors Msn2/4 induce stress-mediated gene expression by binding to the stress response element. Previous studies have demonstrated that the expression of extracellular proteases is up-regulated in response to heat shock in fungi. However, the physiological significance of regulation of these extracellular proteases by heat shock remains unclear. The nematophagous fungus Clonostachys rosea can secret an extracellular serine protease PrC during the infection of nematodes. Since the promoter of prC has three copies of the stress response element, we investigated the effect of environmental stress on the expression of prC. METHODOLOGY/PRINCIPAL FINDINGS: Our results demonstrated that the expression of prC was up-regulated by oxidants (H(2)O(2) or menadione) and heat shock, most likely through the stress response element. After oxidant treatment or heat shock, the germination of conidia in the wild type strain was significantly higher than that in the prC mutant strain in the presence of nematode cuticle. Interestingly, the addition of nematode cuticle significantly attenuated the production of reactive oxygen species (ROS) induced by oxidants and heat shock in the wild type strain, but not in prC mutant strain. Moreover, low molecule weight (<3 kD) degradation products of nematode cuticle suppressed the inhibitory effect of conidial germination induced by oxidants and heat shock. CONCLUSIONS/SIGNIFICANCE: These results indicate that PrC plays a protective role in oxidative stress in C. rosea. PrC degrades the nematode cuticle to produce degradation products, which in turn offer a protective effect against oxidative stress by scavenging ROS. Our study reveals a novel strategy for fungi to adapt to environmental stress
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