Exclusive electroproduction of J/psi mesons at HERA

The exclusive electroproduction of J/psi mesons, ep->epJ/psi, has been studied with the ZEUS detector at HERA for virtualities of the exchanged photon in the ranges 0.15<Q^2<0.8 GeV^2 and 2<Q^2<100 GeV^2 using integrated luminosities of 69 pb^-1 and 83 pb^-1, respectively.The photon-proton centre-of-mass energy was in the range 30<W<220 GeV and the squared four-momentum transfer at the proton vertex |t|<1.The cross sections and decay angular distributions are presented as functions of Q^2, W and t. The effective parameters of the Pomeron trajectory are in agreement with those found in J/psi photoproduction. The spin-density matrix elements, calculated from the decay angular distributions, are consistent with the hypothesis of s-channel helicity conservation. The ratio of the longitudinal to transverse cross sections, sigma_L/sigma_T, grows with Q^2, whilst no dependence on W or t is observed. The results are in agreement with perturbative QCD calculations and exhibit a strong sensitivity to the gluon distribution in the proton.Comment: 33 pages, 10 figures. Submitted to Nuclear Physics

Vibration analysis of cracked beam based on Reddy beam theory by finite element method

The lateral vibration of cracked isotropic thick beams is investigated. Generally, the analysis of thick beam based on line elements can be undertaken using either Timoshenko beam theory or a third order beam theory (TSDT) such as Reddy beam theory. TSDT is superior to Timoshenko beam theory, as it eliminates the need for a shear correction coefficient. However, there is no available solution for a cracked beam based on Reddy beam theory which is the main focus of this paper. The investigated beam is divided into several elements where their stiffness and mass matrices are derived using Reddy beam theory. Each element has two nodes with 3 degrees of freedom (1 lateral and 2 rotational) at each node. The crack was modeled using two rotating springs with stiffnesses that varied with crack depth. These elements are used to connect the adjacent beam elements. The impact of boundary conditions, slenderness ratio, crack location, and crack depth are investigated. In addition, experimental and finite element analyses of cracked steel beams is undertaken to validate the results of the present model. The results show that the maximum deviation between the analytical and the experimental results is less than 3% up to the third mode shape

Science-Driven Preparations for Landing on Europa

No abstract available

Audit regulation: a partial solution expanded

No abstract available

Structure of the Golgi and Distribution of Reporter Molecules at 20°C Reveals the Complexity of the Exit Compartments

Incubating cells at 20°C blocks transport out of the Golgi complex and amplifies the exit compartments. We have used the 20°C block, followed by EM tomography and serial section reconstruction, to study the structure of Golgi exit sites in NRK cells. The dominant feature of Golgi structure in temperature-blocked cells is the presence of large bulging domains on the three trans-most cisternae. These domains extend laterally from the stack and are continuous with “cisternal” domains that maintain normal thickness and alignment with the other stacked Golgi cisternae. The bulging domains do not resemble the perpendicularly extending tubules associated with the trans-cisternae of control cells. Such tubules are completely absent in temperature-blocked cells. The three cisternae with bulging domains can be identified as trans by their association with specialized ER and the presence of clathrin-coated buds on the trans-most cisterna only. Immunogold labeling and immunoblots show a significant degradation of a medial- and a trans-Golgi marker with no evidence for their redistribution within the Golgi or to other organelles. These data suggest that exit from the Golgi occurs directly from three trans-cisternae and that specialized ER plays a significant role in trans-Golgi function