U(1)U(1) gauge vector field on a codimension-2 brane

In this paper, we obtain a gauge invariant effective action for a bulk massless $U(1)$ gauge vector field on a brane with codimension two by using a general Kaluza-Klein (KK) decomposition for the field. It suggests that there exist two types of scalar KK modes to keep the gauge invariance of the action for the massive vector KK modes. Both the vector and scalar KK modes can be massive. The masses of the vector KK modes $m^{(n)}$ contain two parts, $m_{1}^{(n)}$ and $m_{2}^{(n)}$, due to the existence of the two extra dimensions. The masses of the two types of scalar KK modes $m_{\phi}^{(n)}$ and $m_{\varphi}^{(n)}$ are related to the vector ones, i.e., $m_{\phi}^{(n)}=m_{1}^{(n)}$ and $m_{\varphi}^{(n)}=m_{2}^{(n)}$. Moreover, we derive two Schr\"{o}dinger-like equations for the vector KK modes, for which the effective potentials are just the functions of the warp factor.Comment: 15 pages,no figures, accepted by JHE

The evolution of a citation network topology: The development of the journal Scientometrics

By mapping the electronic database containing all papers in Scientometrics for a 26-year period (1978-2004), we uncover the topological measures that characterize the network at a given moment, as well as the time evolution of these quantities. The citation network of the journal displays the characteristic features of a “small-world” network of local dense clusters of highly specialized literature. These clusters, however, are efficiently connected into a large single component by a small number of “hub” papers that allow short-distance connection among increasingly large numbers of papers. The patterns of evolution of the network toward this “small-world” are also explored

The Arabidopsis EAR-motif-containing protein RAP2.1 functions as an active transcriptional repressor to keep stress responses under tight control

<p>Abstract</p> <p>Background</p> <p>Plants respond to abiotic stress through complex regulation of transcription, including both transcriptional activation and repression. Dehydration-responsive-element binding protein (DREB)-type transcription factors are well known to play important roles in adaptation to abiotic stress. The mechanisms by which DREB-type transcription factors activate stress-induced gene expression have been relatively well studied. However, little is known about how DREB-type transcriptional repressors modulate plant stress responses. In this study, we report the functional analysis of RAP2.1, a DREB-type transcriptional repressor.</p> <p>Results</p> <p>RAP2.1 possesses an APETALA2 (AP2) domain that binds to dehydration-responsive elements (DREs) and an ERF-associated amphiphilic repression (EAR) motif, as the repression domain located at the C-terminus of the protein. Expression of <it>RAP2.1 </it>is strongly induced by drought and cold stress via an ABA-independent pathway. Arabidopsis plants overexpressing <it>RAP2.1 </it>show enhanced sensitivity to cold and drought stresses, while <it>rap2.1-1 </it>and <it>rap2.1-2 </it>T-DNA insertion alleles result in reduced sensitivity to these stresses. The reduced stress sensitivity of the plant containing the <it>rap2.1 </it>allele can be genetically complemented by the expression of <it>RAP2.1</it>, but not by the expression of EAR-motif-mutated <it>RAP2.1</it>. Furthermore, chromatin immunoprecipitation (ChIP) analysis has identified <it>Responsive to desiccation/Cold-regulated </it>(<it>RD/COR</it>) genes as downstream targets of RAP2.1 <it>in vivo</it>. Stress-induced expression of the <it>RD/COR </it>genes is repressed by overexpression of <it>RAP2.1 </it>and is increased in plants expressing the <it>rap2.1 </it>allele. In addition, RAP2.1 can negatively regulate its own expression by binding to DREs present in its own promoter. Our data suggest that RAP2.1 acts as a negative transcriptional regulator in defence responses to cold and drought stress in Arabidopsis.</p> <p>Conclusions</p> <p>A hypothetical model for the role of RAP2.1 in modulating plant responses to cold and drought is proposed in this study. It appears that RAP2.1 acts as a negative "subregulon" of DREB-type activators and is involved in the precise regulation of expression of stress-related genes, acting to keep stress responses under tight control.</p