Genisa: A web-based interactive learning environment for teaching simulation modelling

Intelligent Tutoring Systems (ITS) provide students with adaptive instruction and can facilitate the acquisition of problem solving skills in an interactive environment. This paper discusses the role of pedagogical strategies that have been implemented to facilitate the development of simulation modelling knowledge. The learning environment integrates case-based reasoning with interactive tools to guide tutorial remediation. The evaluation of the system shows that the model for pedagogical activities is a useful method for providing efficient simulation modelling instruction

3D printing of gas jet nozzles for laser-plasma accelerators

Recent results on laser wakefield acceleration in tailored plasma channels have underlined the importance of controlling the density profile of the gas target. In particular it was reported that appropriate density tailoring can result in improved injection, acceleration and collimation of laser-accelerated electron beams. To achieve such profiles innovative target designs are required. For this purpose we have reviewed the usage of additive layer manufacturing, commonly known as 3D printing, in order to produce gas jet nozzles. Notably we have compared the performance of two industry standard techniques, namely selective laser sintering (SLS) and stereolithography (SLA). Furthermore we have used the common fused deposition modeling (FDM) to reproduce basic gas jet designs and used SLA and SLS for more sophisticated nozzle designs. The nozzles are characterized interferometrically and used for electron acceleration experiments with the Salle Jaune terawatt laser at Laboratoire d'Optique Appliqu\'ee

Energy boost in laser wakefield accelerators using sharp density transitions

The energy gain in laser wakefield accelerators is limited by dephasing between the driving laser pulse and the highly relativistic electrons in its wake. Since this phase depends on both the driver and the cavity length, the effects of dephasing can be mitigated with appropriate tailoring of the plasma density along propagation. Preceding studies have discussed the prospects of continuous phase-locking in the linear wakefield regime. However, most experiments are performed in the highly non-linear regime and rely on self-guiding of the laser pulse. Due to the complexity of the driver evolution in this regime it is much more difficult to achieve phase locking. As an alternative we study the scenario of rapid rephasing in sharp density transitions, as was recently demonstrated experimentally. Starting from a phenomenological model we deduce expressions for the electron energy gain in such density profiles. The results are in accordance with particle-in-cell simulations and we present gain estimations for single and multiple stages of rephasing

Relativistic corrections to J/ψJ/\psi exclusive and inclusive double charm production at B factories

In order to clarify the puzzling problems in double charm production, relativistic corrections at order $v^{2}$ to the processes $e^{+}e^{-}\to J/\psi+\eta_{c}$ and $e^{+}e^{-}\to J/\psi+c\bar{c}$ at B factories are studied in non-relativistic quantum chromodynamics. The short-distance parts of production cross sections are calculated perturbatively, while the long-distance matrix elements are estimated from $J/\psi$ and $\eta_c$ decays up to errors of order $v^4$. Our results show that the relativistic correction to the exclusive process $e^{+}e^{-}\to J/\psi+\eta_{c}$ is significant, which, when combined together with the next-to-leading order $\alpha_{s}$ corrections, could resolve the large discrepancy between theory and experiment; whereas for the inclusive process $e^{+}e^{-}\to J/\psi+c\bar{c}$ the relativistic correction is tiny and negligible. The physical reason for the above difference between exclusive and inclusive processes largely lies in the fact that in the exclusive process the relative momentum between quarks in charmonium substantially reduces the virtuality of the gluon that converts into a charm quark pair, but this is not the case for the inclusive process, in which the charm quark fragmentation $c\to J/\psi+c$ is significant, and QCD radiative corrections can be more essential.Comment: Version to appear in PRD. In the summary an explicit statement added: "for the J/\psi eta_c cross section the relativistic correction alone gives an enhancement factor of 1.7 while the combination of relativistic correction with QCD radiative correction results in a much larger enhancement factor of 9". One reference added. A few typos correcte

Search for excited charmonium states in e+e−e^+e^- Annihilation at s=10.6\sqrt{s}=10.6 GeV

We suggest searching for excited charmonium states in $e^+e^-$ annihilation via double charmonium production at $\sqrt{s}=10.6$ GeV with $B$ factories, based on a more complete leading order calculation including both QCD and QED contributions for various processes. In particular, for the C=+ states, the $\chi_{c0}(nP)$ (n=2,3) and $\eta_c(mS)$ (m=3,4) may have appreciable potentials to be observed; while for the C=- states, the $\eta_ch_c$ production and especially the $\chi_{c1}h_c$ production might provide opportunities for observing the $h_c$ with higher statistics in the future. A brief discussion for the X(3940) observed in the double charmonium production is included.Comment: 13 pages and 8 figures in PRD version; QED contribution added; experimental and theoretical developments since 2004 summarized; references adde

Response to tilted magnetic fields in Bi2Sr2CaCu2O8 with columnar defects: Evidence for transverse Meissner effect

The transverse Meissner effect (TME) in the highly layered superconductor Bi2Sr2CaCu2O(8+y) with columnar defects is investigated by transport measurements. We present detailed evidence for the persistence of the Bose-glass phase when H is tilted at an angle theta < theta_c (T) away from the column direction: (i) the variable-range vortex hopping process for low currents crosses over to the half-loops regime for high currents; (ii) in both regimes near theta_c(T) the energy barriers vanish linearly with tan(theta) ; (iii) the transition temperature is governed by T_{BG}(0) -T_{BG}(theta) sim |tan(theta)|^{1/\nu_{\perp}} with \nu_{\perp}=1.0 +/- 0.1. Furthermore, above the transition as theta->\theta_c+, moving kink chains consistent with a commensurate-incommensurate transition scenario are observed. These results thereby clearly show the existence of the TME for theta < theta_c(T).Comment: 4 pages, RevTeX, 5 EPS figure