26,743 research outputs found
A non-equilibrium dynamic mechanism for the allosteric effect
Allosteric regulation is often viewed as thermodynamic in nature. However
protein internal motions during an enzymatic reaction cycle can be slow hopping
processes over numerous potential barriers. We propose that regulating
molecules may function by modifying the nonequilibrium protein dynamics. The
theory predicts that an enzyme under the new mechanism has different
temperature dependence, waiting time distribution of the turnover cycle, and
dynamic fluctuation patterns with and without effector. Experimental tests of
the theory are proposed.Comment: accepted by Phys. Rev. Lett. Major revisions were made to fit the
style. 4 pages, 2 figure
The Importance of Proper Renormalization Scale-Setting for Testing QCD at Colliders
A primary problem for perturbative QCD analyses is how to set the
renormalization scale of the QCD running coupling in order to achieve maximally
precise fixed-order predictions for physical observables. The Principle of
Maximum Conformality (PMC) eliminates the ambiguities associated with the
conventional renormalization scale-setting procedure, giving predictions which
are independent of the choice of renormalization scheme. The scales of the QCD
couplings and the effective number of quark flavors are set order by order in
the pQCD series. The PMC has a solid theoretical foundation, satisfying the
standard renormalization group invariance and all of the the self-consistency
conditions derived from the renormalization group......In this brief report, we
summarize the results of our recent PMC applications for a number of collider
processes, emphasizing their generality and applicability....... These results
demonstrate that the application of the PMC systematically eliminates a major
theoretical uncertainty for pQCD predictions, thus increasing the sensitivity
of the colliders to possible new physics beyond the Standard Model.Comment: 10 pages, 4 figures. The title has been changed. This review,
submitted to Frontiers of Physics, is based on a contribution by S.J.B. at
the Conference {\it Workshop on Physics at a Future High Intensity Collider @
2-7 GeV in China} Hefei, China January 14-16, 201
Spatial organization and evolutional period of the epidemic model using cellular automata
We investigate epidemic models with spatial structure based on the cellular
automata method. The construction of the cellular automata is from the study by
Weimar and Boon about the reaction-diffusion equations [Phys. Rev. E 49, 1749
(1994)]. Our results show that the spatial epidemic models exhibit the
spontaneous formation of irregular spiral waves at large scales within the
domain of chaos. Moreover, the irregular spiral waves grow stably. The system
also shows a spatial period-2 structure at one dimension outside the domain of
chaos. It is interesting that the spatial period-2 structure will break and
transform into a spatial synchronous configuration in the domain of chaos. Our
results confirm that populations embed and disperse more stably in space than
they do in nonspatial counterparts.Comment: 6 papges,5 figures. published in Physics Review
Eliminating the Renormalization Scale Ambiguity for Top-Pair Production Using the Principle of Maximum Conformality
It is conventional to choose a typical momentum transfer of the process as
the renormalization scale and take an arbitrary range to estimate the
uncertainty in the QCD prediction. However, predictions using this procedure
depend on the renormalization scheme, leave a non-convergent renormalon
perturbative series, and moreover, one obtains incorrect results when applied
to QED processes. In contrast, if one fixes the renormalization scale using the
Principle of Maximum Conformality (PMC), all non-conformal -terms
in the perturbative expansion series are summed into the running coupling, and
one obtains a unique, scale-fixed, scheme-independent prediction at any finite
order. The PMC scale and the resulting finite-order PMC
prediction are both to high accuracy independent of the choice of initial
renormalization scale , consistent with renormalization group
invariance. As an application, we apply the PMC procedure to obtain NNLO
predictions for the -pair production at the Tevatron and LHC
colliders. The PMC prediction for the total cross-section
agrees well with the present Tevatron and LHC data. We also verify that the
initial scale-independence of the PMC prediction is satisfied to high accuracy
at the NNLO level: the total cross-section remains almost unchanged even when
taking very disparate initial scales equal to ,
, . Moreover, after PMC scale setting, we obtain
, and
. These
predictions have a -deviation from the present CDF and D0
measurements; the large discrepancy of the top quark forward-backward asymmetry
between the Standard Model estimate and the data are thus greatly reduced.Comment: 4 pages. Detailed derivations for the top-quark pair total
cross-sections and forward-backward asymmetry can be found in
Refs.[arXiv:1204.1405; arXiv:1205.1232]. To match the published version. To
be published in Phys.Rev.Let
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