41,701 research outputs found
Visualization of the homogeneous charge compression ignition/controlled autoignition combustion process using two-dimensional planar laser-induced fluorescence imaging of formaldehyde
The paper reports an investigation into the HCCI/CAI combustion process using the two-dimensional PLIF technique. The PLIF of formaldehyde formed during the low-temperature reactions of HCCI/CAI combustion was exciting by a tunable dye laser at 355nm wavelength and detected by a gated ICCD camera. Times and locations of the two-stage autoignition of HCCI/CAI combustion were observed in a single cylinder optical engine for several fuel blends mixed with n-heptane and iso-octane. The results show, when pure n-heptane was used, the initial formation of formaldehyde and its subsequent burning were closely related to the start of the low temperature heat release stage and the start of the main heat release stage of HCCI combustion respectively. Meanwhile, it was found that the formation of formaldehyde was more affected by the charge temperature than by the fuel concentration. But its subsequent burning or the start of main heat release combustion toke place at those areas where both the fuel concentration and the charge temperature were sufficient high. As a result, it was found that the presence of stratified residual gases affected both the spatial location and the temporal site of autoignition in a HCCI/CAI combustion engine. All studied fuels were found having similar formaldehyde formation timings with n-heptane. This means that the presence of iso-octane did not affect the start of low temperature reactions apparently. However, the heat release during low temperature reaction was significantly reduced with the presence of iso-octane in the studied fuels. In addition, the presence of iso-octane retarded the start of the main combustion stage
Orbital elements of barium stars formed through a wind accretion scenario
Taking the total angular momentum conservation in place of the tangential
momentum conservation, and considering the square and higher power terms of
orbital eccentricity e, the changes of orbital elements of binaries are
calculated for wind accretion scenario. These new equations are used to
quantitatively explain the observed (e,logP) properties of normal G, K giants
and barium stars. Our results reflect the evolution from G, K giant binaries to
barium binaries, moreover, the barium stars with longer orbital periods P>1600
days may be formed by accreting part of the ejecta from the intrinsic AGB stars
through wind accretion scenario.Comment: 7 pages, LaTex, 4 PS figures and 1 table included, accepted for
publication in A &
Active role of elongation factor G in maintaining the mRNA reading frame during translation.
During translation, the ribosome moves along the mRNA one codon at a time with the help of elongation factor G (EF-G). Spontaneous changes in the translational reading frame are extremely rare, yet how the precise triplet-wise step is maintained is not clear. Here, we show that the ribosome is prone to spontaneous frameshifting on mRNA slippery sequences, whereas EF-G restricts frameshifting. EF-G helps to maintain the mRNA reading frame by guiding the A-site transfer RNA during translocation due to specific interactions with the tip of EF-G domain 4. Furthermore, EF-G accelerates ribosome rearrangements that restore the ribosome's control over the codon-anticodon interaction at the end of the movement. Our data explain how the mRNA reading frame is maintained during translation
Sparse approximation of multivariate functions from small datasets via weighted orthogonal matching pursuit
We show the potential of greedy recovery strategies for the sparse
approximation of multivariate functions from a small dataset of pointwise
evaluations by considering an extension of the orthogonal matching pursuit to
the setting of weighted sparsity. The proposed recovery strategy is based on a
formal derivation of the greedy index selection rule. Numerical experiments
show that the proposed weighted orthogonal matching pursuit algorithm is able
to reach accuracy levels similar to those of weighted minimization
programs while considerably improving the computational efficiency for small
values of the sparsity level
In-medium Properties of as a KN structure in Relativistic Mean Field Theory
The properties of nuclear matter are discussed with the relativistic
mean-field theory (RMF).Then, we use two models in studying the in-medium
properties of : one is the point-like in the usual RMF and
the other is a KN structure for the pentaquark. It is found that the
in-medium properties of are dramatically modified by its internal
structure. The effective mass of in medium is, at normal nuclear
density, about 1030 MeV in the point-like model, while it is about 1120 MeV in
the model of KN pentaquark. The nuclear potential depth of in
the KN model is approximately -37.5 MeV, much shallower than -90 MeV in
the usual point-like RMF model.Comment: 8 pages, 5 figure
Spin-orbit scattering in quantum diffusion of massive Dirac fermions
Effect of spin-orbit scattering on quantum diffusive transport of
two-dimensional massive Dirac fermions is studied by the diagrammatic
technique. The quantum diffusion of massive Dirac fermions can be viewed as a
singlet Cooperon in the massless limit and a triplet Cooperon in the large-mass
limit. The spin-orbit scattering behaves like random magnetic fields only to
the triplet Cooperon, and suppresses the weak localization of Dirac fermions in
the large-mass regime. This behavior suggests an experiment to detect the weak
localization of bulk subbands in topological insulator thin films, in which a
narrowing of the cusp of the negative magnetoconductivity is expected after
doping heavy-element impurities. Finally, a detailed comparison between the
conventional two-dimensional electrons and Dirac fermions is presented for
impurities of orthogonal, symplectic, and unitary symmetries.Comment: 5 pages, 3 figures, 2 tables. To be submitted, comments are welcom
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