RESUMO
The electron-positron collider DAPhiNE, the Italian Phi factory, has been recently upgraded in order to implement an innovative collision scheme based on large crossing angle, small beam sizes at the crossing point, and compensation of beam-beam interaction by means of sextupole pairs creating a "crab-waist" configuration in the interaction region. Experimental tests of the novel scheme exhibited an increase by a factor of 3 in the peak luminosity of the collider with respect to the performances reached before the upgrade. In this Letter we present the new collision scheme, discuss its advantages, describe the hardware modifications realized for the upgrade, and report the results of the experimental tests carried out during commissioning of the machine in the new configuration and standard operation for the users.
RESUMO
The distribution of Xwnt-11 mRNA between polysomes and informosomes was studied in Xenopus laevis and Rana temporaria during early embryogenesis. The ratio between polysomes and informosomes suggests their involvement in translation of these mRNAs. In eggs and immediately after fertilization the Xwnt-11 mRNAs are mostly positioned in informosomes. During the cleavage stage, these mRNAs have also been recognized in polysomes. Just before the onset of zygote genome functioning (at the stage of mid blastula), Xwnt-11 mRNA rapidly appears in polysomes of Rana embryos. However, in Xenopus, Xwnt-11 mRNA appears in polysomes only at the end of gastrula. Before this stage, the Xwnt-11 mRNA in Xenopus can be found mostly in informosomes.
Assuntos
Anuros/embriologia , Anuros/genética , Glicoproteínas/genética , Polirribossomos/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Animais , Radioisótopos de Fósforo , Ranidae/embriologia , Ranidae/genética , Proteínas Wnt , Xenopus/embriologia , Xenopus/genética , Proteínas de XenopusRESUMO
Translational expression regulation was studied for Xvent-2 coding for a transcription factor involved in dorsoventral differentiation of amphibian embryos. The Xvent-2 mRNA was detected predominantly in informosomes at all developmental stages examined, and only its minor fraction was associated with polysomes. Expression of Xvent-2 was assumed to be regulated at the translational level, with Xvent-2 produced immediately before polypotent cells enter a certain differentiation pathway.
Assuntos
Proteínas de Homeodomínio/genética , RNA Mensageiro/metabolismo , Rana temporaria/embriologia , Fatores de Transcrição , Proteínas de Xenopus , Animais , Citoplasma/química , Citoplasma/genética , Embrião não Mamífero , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio/metabolismo , Masculino , Biossíntese de Proteínas , RNA Mensageiro/química , RNA Mensageiro/isolamento & purificação , Rana temporaria/genéticaRESUMO
Data analysis of an experiment in which photon splitting in atomic fields was observed is presented. The experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M collider. In the energy region of 120-450 MeV, statistics of 1.6x10(9) photons incident on the BGO target was collected. About 400 candidate photon-splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the calculated exact atomic-field cross section. The predictions obtained in the Born approximation differ significantly from the experimental results.
