Extraordinary spin density and energy back-flow under interference.

A novel phenomenon was reported recently that the "local optical spin density" based on the Poynting vector might be counter-intuitively opposite to the integrated spin orientation while the one related to the gauge-invariant canonical expression might not [Phys. Lett. B779, 385 (2018)]. However, the "local optical spin density" of the gauge-invariant canonical expression can also be counter-intuitively opposite to the integrated spin orientation under the interference of plane waves, even if all of the plane waves possess the same polarization state. Moreover, the interference fields might acquire a transverse spin density (perpendicular to the propagation plane), which can have more well-controlled relations with the polarization. Additionally, the Poynting vector shows counter-intuitive back-flow and a circular motion (vortex) in the propagation plane locally, which implies a transverse local "orbital" angular momentum density related to the polarization.

Genome shuffling and ribosome engineering of Streptomyces virginiae for improved virginiamycin production.

The production of virginiamycin (VGM) from Streptomyces virginiae was improved by genome shuffling and ribosome engineering companied with a high-throughput screening method integrating deep-well cultivation and the cylinder-plate detecting. First, a novel high-throughput method was developed to rapidly screen large numbers of VGM-producing mutants. Then, the starting population of genome shuffling was obtained through ultraviolet (UV) and microwave mutagenesis, and four mutants with higher productivity of VGM were selected for genome shuffling. Next, the parent protoplasts were inactivated by UV and heat when a fusant probability was about 98%. Streptomycin resistance was used as an evolutionary pressure to extend positive effects on VGM synthesis. Finally, after five rounds of genome shuffling, a genetically stable strain G5-103 was obtained and characterized to be able to yield 251 mg/L VGM, which was 3.1- and 11.6-fold higher than that of the mutant strain UV 1150 and the wild-type strain, respectively.

Rice SUVH histone methyltransferase genes display specific functions in chromatin modification and retrotransposon repression.

Histone lysine methylation plays an important role in heterochromatin formation and reprogramming of gene expression. SET-domain-containing proteins are shown to have histone lysine methyltransferase activities. A large number of SET-domain genes are identified in plant genomes. The function of most SET-domain genes is not known. In this work, we studied the 12 rice (Oryza sativa) homologs of Su(var)3-9, the histone H3 lysine 9 (H3K9) methyltransferase identified in Drosophila. Several rice SUVHs (i.e. SDG714, SDG727, and SDG710) were found to have an antagonistic function to the histone H3K9 demethylase JMJ706, as down-regulation of these genes could partially complement the jmj706 phenotype and reduced histone H3K9 methylation. Down-regulation of a rice Su(var)3-9 homolog (SUVH), namely SDG728, decreased H3K9 methylation and altered seed morphology. Overexpression of the gene increased H3K9 methylation. SDG728 and other SUVH genes were found to be involved in the repression of retrotransposons such as Tos17 and a Ty1-copia element. Analysis of histone methylation suggested that SDG728-mediated H3K9 methylation may play an important role in retrotransposon repression.

Do gluons carry half of the nucleon momentum?

We examine the conventional picture that gluons carry about half of the nucleon momentum in the asymptotic limit. We show that this large fraction is due to an unsuitable definition of the gluon momentum in an interacting theory. If defined in a gauge-invariant and consistent way, the asymptotic gluon momentum fraction is computed to be only about one-fifth. This result suggests that the asymptotic limit of the nucleon spin structure should also be reexamined. A possible experimental test of our finding is discussed in terms of novel parton distribution functions.

Spin and orbital angular momentum in gauge theories: nucleon spin structure and multipole radiation revisited.

We address and solve the long-standing gauge-invariance problem of the nucleon spin structure. Explicitly gauge-invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task and opens a more promising avenue towards the understanding of the nucleon spin. Our research also justifies the traditional use of the canonical, gauge-dependent angular momentum operators of photons and electrons in the multipole-radiation analysis and labeling of atomic states and sheds much light on the related energy-momentum problem in gauge theories, especially in connection with the nucleon momentum.