4,165 research outputs found
Transverse Momentum Dependent Parton Distributions at Small-x
We study the transverse momentum dependent (TMD) parton distributions at
small-x in a consistent framework that takes into account the TMD evolution and
small-x evolution simultaneously. The small-x evolution effects are included by
computing the TMDs at appropriate scales in terms of the dipole scattering
amplitudes, which obey the relevant Balitsky-Kovchegov equation. Meanwhile, the
TMD evolution is obtained by resumming the Collins-Soper type large logarithms
emerged from the calculations in small-x formalism into Sudakov factors.Comment: 23 pages, 9 figure
On the linearly polarized gluon distributions in the color dipole model
We show that the linearly polarized gluon distributions appear in the color
dipole model as we derive the full cross sections of the DIS dijet production
and the Drell-Yan dijet ( jet correlation) process. Together with the
normal Weizs\"acker-Williams gluon distribution, the linearly polarized one
will contribute to the DIS dijet production cross section as the coefficient of
the term in the correlation limit. We also derive the
exact results for the cross section of the Drell-Yan dijet process, and find
that the linearly polarized dipole gluon distribution which is identical to the
normal dipole gluon distribution involves in the cross section. The results
obtained in this paper agree with the previous transverse momentum dependent
factorization study. We further derive the small- evolution of these
linearly polarized gluon distributions and find that they rise as gets
small at high energy.Comment: 10 pages,v2 with minor revisio
Gate-controllable spin-battery
We propose a gate-controllable spin-battery for spin current. The
spin-battery consists of a lateral double quantum dot under a uniform magnetic
field. A finite DC spin-current is driven out of the device by controlling a
set of gate voltages. Spin-current can also be delivered in the absence of
charge-current. The proposed device should be realizable using present
technology at low temperature.Comment: 3 pages, 3 figures, accepted by Appl. Phys. Let
A Revised Optimal Spanning Table Method for Expanding Competence Sets
The optimal expansion problem of competence sets can be solves by either mathematical programming method or table based method developed by Feng (2001). Compared to the mathematical programming method, table based method for competence set expansion is a more efficient algorithm in using relevant tableaus to solve the optimal expansion problems. This paper proposes a revised table based method to facilitate developing a computer code. A computer program, called TBM, based on the revised algorithm, was developed to solve the large scale problems of expanding competence sets. A numerical example is given, and some possible future research topics on the related theme are discussed. Keywords: competence set expansion; habitual domains; spanning table methodRĂ©sumĂ©: Le problĂšme de l'expansion optimale des ensembles de compĂ©tence peut ĂȘtre rĂ©solu soit par la mĂ©thode de programmation mathĂ©matique, soit par une mĂ©thode basĂ©e sur les tableaux dĂ©veloppĂ©e par Feng (2001). ComparĂ©e Ă la mĂ©thode de programmation mathĂ©matique, la mĂ©thode basĂ©e sur les tableaux pour l'expansion des ensembles de compĂ©tence est un algorithme plus efficace dans l'utilisation des tableaux appropriĂ©s pour rĂ©soudre les problĂšmes d'expansion optimale. Cet article propose une mĂ©thode basĂ©e sur les tableaux rĂ©visĂ© pour faciliter l'Ă©laboration d'un code informatique. Un programme d'ordinateur, appelĂ© TBM, basĂ© sur l'algorithme rĂ©visĂ©, a Ă©tĂ© dĂ©veloppĂ© pour rĂ©soudre les problĂšmes de l'expansion des ensembles de compĂ©tences Ă grande Ă©chelle. Un exemple numĂ©rique est donnĂ©, et quelques sujets possibles de futures recherches sur le thĂšme sont dĂ©battues.Mots-clĂ©s: expansion des ensembles de competences; domaines habituels; mĂ©thode de tableau construi
The evolution of cardiolipin biosynthesis and maturation pathways and its implications for the evolution of eukaryotes
<p>Abstract</p> <p>Background</p> <p>Cardiolipin (CL) is an important component in mitochondrial inner and bacterial membranes. Its appearance in these two biomembranes has been considered as evidence of the endosymbiotic origin of mitochondria. But CL was reported to be synthesized through two distinct enzymes--CLS_cap and CLS_pld in eukaryotes and bacteria. Therefore, how the CL biosynthesis pathway evolved is an interesting question.</p> <p>Results</p> <p>Phylogenetic distribution investigation of CL synthase (CLS) showed: most bacteria have CLS_pld pathway, but in partial bacteria including proteobacteria and actinobacteria CLS_cap pathway has already appeared; in eukaryotes, Supergroup Opisthokonta and Archaeplastida, and Subgroup Stramenopiles, which all contain multicellular organisms, possess CLS_cap pathway, while Supergroup Amoebozoa and Excavata and Subgroup Alveolata, which all consist exclusively of unicellular eukaryotes, bear CLS_pld pathway; amitochondriate protists in any supergroups have neither. Phylogenetic analysis indicated the CLS_cap in eukaryotes have the closest relationship with those of alpha proteobacteria, while the CLS_pld in eukaryotes share a common ancestor but have no close correlation with those of any particular bacteria.</p> <p>Conclusions</p> <p>The first eukaryote common ancestor (FECA) inherited the CLS_pld from its bacterial ancestor (e. g. the bacterial partner according to any of the hypotheses about eukaryote evolution); later, when the FECA evolved into the last eukaryote common ancestor (LECA), the endosymbiotic mitochondria (alpha proteobacteria) brought in CLS_cap, and then in some LECA individuals the CLS_cap substituted the CLS_pld, and these LECAs would evolve into the protist lineages from which multicellular eukaryotes could arise, while in the other LECAs the CLS_pld was retained and the CLS_cap was lost, and these LECAs would evolve into the protist lineages possessing CLS_pld. Besides, our work indicated CL maturation pathway arose after the emergence of eukaryotes probably through mechanisms such as duplication of other genes, and gene duplication and loss occurred frequently at different lineage levels, increasing the pathway diversity probably to fit the complicated cellular process in various cells. Our work also implies the classification putting Stramenopiles and Alveolata together to form Chromalveolata may be unreasonable; the absence of CL synthesis and maturation pathways in amitochondriate protists is most probably due to secondary loss.</p
Disorder-induced enhancement of transport through graphene p-n junctions
We investigate the electron transport through a graphene p-n junction under a
perpendicular magnetic field. By using Landauar-Buttiker formalism combining
with the non-equilibrium Green function method, the conductance is studied for
the clean and disordered samples. For the clean p-n junction, the conductance
is quite small. In the presence of disorders, it is strongly enhanced and
exhibits plateau structure at suitable range of disorders. Our numerical
results show that the lowest plateau can survive for a very broad range of
disorder strength, but the existence of high plateaus depends on system
parameters and sometimes can not be formed at all. When the disorder is
slightly outside of this disorder range, some conductance plateaus can still
emerge with its value lower than the ideal value. These results are in
excellent agreement with the recent experiment.Comment: 5 pages, 5 figures, submit to PRL on May 20, 200
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