D* Production in Deep Inelastic Scattering at HERA

This paper presents measurements of D^{*\pm} production in deep inelastic scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The data have been taken with the ZEUS detector at HERA. The decay channel $D^{*+}\to (D^0 \to K^- \pi^+) \pi^+$ (+ c.c.) has been used in the study. The $e^+p$ cross section for inclusive D^{*\pm} production with $5<Q^2<100 GeV^2$ and $y<0.7$ is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region {$1.3<p_T(D^{*\pm})<9.0$ GeV and $| \eta(D^{*\pm}) |<1.5$}. Differential cross sections as functions of p_T(D^{*\pm}), $\eta(D^{*\pm}), W$ and $Q^2$ are compared with next-to-leading order QCD calculations based on the photon-gluon fusion production mechanism. After an extrapolation of the cross section to the full kinematic region in p_T(D^{*\pm}) and $\eta$(D^{*\pm}), the charm contribution $F_2^{c\bar{c}}(x,Q^2)$ to the proton structure function is determined for Bjorken $x$ between 2 $\cdot$ 10$^{-4}$ and 5 $\cdot$ 10$^{-3}$.Comment: 17 pages including 4 figure

Observation of Scaling Violations in Scaled Momentum Distributions at HERA

Charged particle production has been measured in deep inelastic scattering (DIS) events over a large range of $x$ and $Q^2$ using the ZEUS detector. The evolution of the scaled momentum, $x_p$, with $Q^2,$ in the range 10 to 1280 $GeV^2$, has been investigated in the current fragmentation region of the Breit frame. The results show clear evidence, in a single experiment, for scaling violations in scaled momenta as a function of $Q^2$.Comment: 21 pages including 4 figures, to be published in Physics Letters B. Two references adde

Generic thin-shell gravastars

We construct generic spherically symmetric thin-shell gravastars by using the cut-and-paste procedure. We take considerable effort to make the analysis as general and unified as practicable; investigating both the internal physics of the transition layer and its interaction with "external forces" arising due to interactions between the transition layer and the bulk spacetime. Furthermore, we discuss both the dynamic and static situations. In particular, we consider "bounded excursion" dynamical configurations, and probe the stability of static configurations. For gravastars there is always a particularly compelling configuration in which the surface energy density is zero, while surface tension is nonzero.Comment: V1: 39 pages, 9 figures; V2: 40 pages, 9 figures. References added, some discussion added, some typos fixed. Identical to published version. arXiv admin note: text overlap with arXiv:1112.205

Observation of Events with an Energetic Forward Neutron in Deep Inelastic Scattering at HERA

In deep inelastic neutral current scattering of positrons and protons at the center of mass energy of 300 GeV, we observe, with the ZEUS detector, events with a high energy neutron produced at very small scattering angles with respect to the proton direction. The events constitute a fixed fraction of the deep inelastic, neutral current event sample independent of Bjorken x and Q2 in the range 3 · 10-4 \u3c xBJ \u3c 6 · 10-3 and 10 \u3c Q2 \u3c 100 GeV2

Hypergravity prevents seed production in Arabidopsis by disrupting pollen tube growth

How tightly land plants are adapted to the gravitational force (g) prevailing on Earth has been of interest because unlike many other environmental factors, g presents as a constant force. Ontogeny of mature angiosperms begins with an embryo that is formed after tip growth by a pollen tube delivers the sperm nucleus to the egg. Because of the importance to plant fitness, we have investigated how gravity affects these early stages of reproductive development. Arabidopsis thaliana (L.) Heynh. plants were grown for 13 days prior to being transferred to growth chambers attached to a large diameter rotor, where they were continuously exposed to 2-g or 4-g for the subsequent 11 days. Plants began flowering 1 day after start of the treatments, producing hundreds of flowers for analysis of reproductive development. At 4-g, Arabidopsis flowers self-pollinated normally but did not produce seeds, thus derailing the entire life cycle. Pollen viability and stigma esterase activity were not compromised by hypergravity; however, the growth of pollen tubes into the stigmas was curtailed at 4-g. In vitro pollen germination assays showed that 4-g average tube length was less than half that for 1-g controls. Closely related Brassica rapa L., which produces seeds at 4-g, required forces in excess of 6-g to slow in vitro tube growth to half that at 1-g. The results explain why seed production is absent in Arabidopsis at 4-g and point to species differences with regard to the g-sensitivity of pollen tube growth

Brassica rapa L. seed development in hypergravity

Previous experiments had shown that microgravity adversely affected seed development in Brassica rapa L. We tested the hypothesis that gravity controls seed development via modulation of gases around the developing seeds, by studying how hypergravity affects the silique microenvironment and seed development. Using an in vitro silique maturation system, we sampled internal silique gases for 16 d late in the seed maturation sequence at 4 g or 1 g. The carbon dioxide level was significantly higher inside the 4-g siliques, and the immature seeds became heavier than those maturing at 1 g. Pollination and early embryo development were also studied by growing whole plants at 2 g or 4 g for 16 d inside chambers mounted on a large-diameter centrifuge. Each day the rotor was briefly stopped to permit manual pollination of flowers, thereby producing cohorts of same-aged siliques for comparison with stationary control material. The loss of starch and soluble carbohydrates during seed development was accelerated in hypergravity, with seeds developing at 4 g more advanced by 2 d than those at 1 g. Seeds produced at 4 g contained more lipid than those at 1 g. Taken together, these results indicate that hypergravity enhances gas availability to the developing embryos. Gravity's role in seed development is of importance to the space programme because of the plan to use plants for food production and habitat regeneration in extraterrestrial settings. These results are significant because they underscore the tight co-regulation of Brassica seed development and the atmosphere maintained inside the siliques