2,143 research outputs found
Sensitivity analysis and experimental design of a stiff signal transduction pathway model
Sensitivity analysis is normally used to analyze how sensitive a system is with respect to the change of parameters or initial conditions and is perhaps best known in systems biology via the formalism of metabolic control analysis [1, 2]. The nuclear factor B (NF-B) signalling pathway is an important cellular signalling pathway, of which protein phosphorylation is a major factor controlling the activation of further downstream events. The NF-κB proteins regulate numerous genes that play important roles in inter- and intra-cellular signalling, cellular stress responses, cell growth, survival, and apoptosis. As such, its specificity and its role in the temporal control of gene expression are of crucial physiological interest
Enhancement of bichromatic high-harmonic generation with a high-frequency field
Using a high-frequency field superposed to a linearly polarized bichromatic
laser field composed by a wave with frequency and a wave with
frequency , we show it is possible to enhance the intensity of a
group of high harmonics in orders of magnitude. These harmonics have
frequencies about 30% higher than the monochromatic-cutoff frequency, and,
within the three-step-model framework, correspond to a set of electron
trajectories for which tunneling ionization is strongly suppressed. Particular
features in the observed enhancement suggest that the high-frequency field
provides an additional mechanism for the electron to reach the continuum. This
interpretation is supported by a time-frequency analysis of the harmonic yield.
The additional high frequency field permits the control of this group of
harmonics leaving all other sets of harmonics practically unchanged, which is
an advantage over schemes involving only bichromatic fields.Comment: 6 pages RevTex, 5 figures (ps files), Changes in text, figures,
references and equations include
Investigation into high-frequency-vibration assisted micro-blanking of pure copper foils
The difficulties encountered during the manufacture of microparts are often associated with size effects relating to material, process and tooling. Utilizing acoustoplastic softening, achieved through a high-frequency vibration assisted micro-blanking process, was introduced to improve the surface finish in micro-blanking. A frequency of 1.0 kHz was chosen to activate the longitudinal vibration mode of the horn tip, using a piezoelectric actuator. A square hole with dimensions of 0.5 mm × 0.5 mm was made, successfully, from a commercial rolled T2 copper foil with 100 μm in thickness. It was found that the maximum blanking force could be reduced by 5% through utilizing the high-frequency vibration. Proportion of the smooth, burnished area in the cut cross-section increases with an increase of the plasticity to fracture, under the high-frequency vibration, which suggests that the vibration introduced is helpful for inhibiting evolution of the crack due to its acoustoplastic softening effect. During blanking, roughness of the burnished surface could be reduced by increasing the vibration amplitude of the punch, which played a role as surface polishing. The results obtained suggest that the high-frequency vibration can be adopted in micro-blanking in order to improve quality of the microparts
An island based hybrid evolutionary algorithm for optimization
This is a post-print version of the article - Copyright @ 2008 Springer-VerlagEvolutionary computation has become an important problem solving methodology among the set of search and optimization techniques. Recently, more and more different evolutionary techniques have been developed, especially hybrid evolutionary algorithms. This paper proposes an island based hybrid evolutionary algorithm (IHEA) for optimization, which is based on Particle swarm optimization (PSO), Fast Evolutionary Programming (FEP), and Estimation of Distribution Algorithm (EDA). Within IHEA, an island model is designed to cooperatively search for the global optima in search space. By combining the strengths of the three component algorithms, IHEA greatly improves the optimization performance of the three basic algorithms. Experimental results demonstrate that IHEA outperforms all the three component algorithms on the test problems.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/1
Chemical elements in the environment: Multi-element geochemical datasets from continental- to national-scale surveys on four continents
During the last 10–20 years, Geological Surveys around the world have undertaken a major effort towards delivering fully harmonised and tightly quality controlled low-density multi-element soil geochemical maps and datasets of vast regions including up to whole continents. Concentrations of between 45 and 60 elements commonly have been determined in a variety of different regolith types (e.g., sediment, soil). The multi-element datasets are published as complete geochemical atlases and made available to the general public. Several other geochemical datasets covering smaller areas, but generally at a higher spatial density, are also available. These datasets may, however, not be found by superficial internet-based searches because the elements are not mentioned individually either in the title or in the keyword lists of the original references. This publication attempts to increase the visibility and discoverability of these fundamental background datasets covering large areas up to whole continents.We thank the governments and
other sponsors for funding geochemical surveys, field and laboratory
support teams and collaborators for their support, and land owners for
granting access to field sites around the globe
High-harmonic generation from a confined atom
The order of high harmonics emitted by an atom in an intense laser field is
limited by the so-called cutoff frequency. Solving the time-dependent
Schr\"odinger equation, we show that this frequency can be increased
considerably by a parabolic confining potential, if the confinement parameters
are suitably chosen.
Furthermore, due to confinement, the radiation intensity remains high
throughout the extended emission range. All features observed can be explained
with classical arguments.Comment: 4 pages(tex files), 4 figures(eps files); added references and
comment
Analysis of the Y(4140) and related molecular states with QCD sum rules
In this article, we assume that there exist scalar , , and
molecular states, and study their masses using
the QCD sum rules. The numerical results indicate that the masses are about
above the corresponding ,
, and thresholds, the Y(4140) is unlikely a scalar molecular state. The scalar ,
, and molecular states maybe not exist, while the scalar , , and
molecular states maybe exist.Comment: 19 pages, 36 figures, slight revisio
Liquid-gas phase transition and Coulomb instability of asymmetric nuclear systems
We use a chiral SU(3) quark mean field model to study the properties of
nuclear systems at finite temperature. The liquid-gas phase transition of
symmetric and asymmetric nuclear matter is discussed. For two formulations of
the model the critical temperature, , for symmetric nuclear matter is
found to be 15.8 MeV and 17.9 MeV. These values are consistent with those
derived from recent experiments. The limiting temperatures for finite nuclei
are in good agreement with the experimental points.Comment: 14 pages, 6 figure
Liquid-gas phase transition and Coulomb instability of asymmetric nuclear systems
We use a chiral SU(3) quark mean field model to study the properties of
nuclear systems at finite temperature. The liquid-gas phase transition of
symmetric and asymmetric nuclear matter is discussed. For two formulations of
the model the critical temperature, , for symmetric nuclear matter is
found to be 15.8 MeV and 17.9 MeV. These values are consistent with those
derived from recent experiments. The limiting temperatures for finite nuclei
are in good agreement with the experimental points.Comment: 14 pages, 6 figure
New treatment of the chiral SU(3) quark mean field model
We perform a study of infinite hadronic matter, finite nuclei and hypernuclei
with an improved method of calculating the effective baryon mass. A detailed
study of the predictions of the model is made in comparison with the available
data and the level of agreement is generally very good. Comparison with an
earlier treatment shows relatively minor differences at or below normal nuclear
matter density, while at high density the improved calculation is quite
different. In particular, we find no phase transition corresponding to chiral
symmetry restoration in high density nuclear matter.Comment: 19 pages, 11 figure
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