41 research outputs found
Response of Wheat Fungal Diseases to Elevated Atmospheric CO2 Level
Infection with fungal pathogens on wheat varieties with different levels of resistance was
tested at ambient (NC, 390 ppm) and elevated (EC, 750 ppm) atmospheric CO2 levels in the
phytotron. EC was found to affect many aspects of the plant-pathogen interaction. Infection
with most fungal diseases was usually found to be promoted by elevated CO2 level in susceptible
varieties. Powdery mildew, leaf rust and stem rust produced more severe symptoms on
plants of susceptible varieties, while resistant varieties were not infected even at EC. The penetration
of Fusarium head blight (FHB) into the spike was delayed by EC in Mv Mambo, while
it was unaffected in Mv Regiment and stimulated in Mv Emma. EC increased the propagation
of FHB in Mv Mambo and Mv Emma. Enhanced resistance to the spread of Fusarium within
the plant was only found in Mv Regiment, which has good resistance to penetration but poor
resistance to the spread of FHB at NC. FHB infection was more severe at EC in two varieties,
while the plants of Mv Regiment, which has the best field resistance at NC, did not exhibit a
higher infection level at EC.
The above results suggest that breeding for new resistant varieties will remain a useful
means of preventing more severe infection in a future with higher atmospheric CO2 levels
Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD
With the H1 detector at the ep collider HERA, D* meson production cross
sections have been measured in deep inelastic scattering with four-momentum
transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88
GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe
the differential cross sections within theoretical and experimental
uncertainties. Using these calculations, the NLO gluon momentum distribution in
the proton, x_g g(x_g), has been extracted in the momentum fraction range
7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon
momentum fraction x_g has been obtained from the measured kinematics of the
scattered electron and the D* meson in the final state. The results compare
well with the gluon distribution obtained from the analysis of scaling
violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.
Measurement of Leading Proton and Neutron Production in Deep Inelastic Scattering at HERA
Deep--inelastic scattering events with a leading baryon have been detected by
the H1 experiment at HERA using a forward proton spectrometer and a forward
neutron calorimeter. Semi--inclusive cross sections have been measured in the
kinematic region 2 <= Q^2 <= 50 GeV^2, 6.10^-5 <= x <= 6.10^-3 and baryon p_T
<= MeV, for events with a final state proton with energy 580 <= E' <= 740 GeV,
or a neutron with energy E' >= 160 GeV. The measurements are used to test
production models and factorization hypotheses. A Regge model of leading baryon
production which consists of pion, pomeron and secondary reggeon exchanges
gives an acceptable description of both semi-inclusive cross sections in the
region 0.7 <= E'/E_p <= 0.9, where E_p is the proton beam energy. The leading
neutron data are used to estimate for the first time the structure function of
the pion at small Bjorken--x.Comment: 30 pages, 9 figures, 2 tables, submitted to Eur. Phys.
Charmonium Production in Deep Inelastic Scattering at HERA
The electroproduction of J/psi and psi(2S) mesons is studied in elastic, quasi-elastic and inclusive reactions for four momentum transfers 2 Q^2 80 GeV^2 and photon-proton centre of mass energies 25 W 180 GeV. The data were taken with the H1 detector at the electron proton collider HERA in the years 1995 to 1997. The total virtual photon-proton cross section for elastic J/psi production is measured as a function of Q^2 and W. The dependence of the production rates on the square of the momentum transfer from the proton (t) is extracted. Decay angular distributions are analysed and the ratio of the longitudinal and transverse cross sections is derived. The ratio of the cross sections for quasi-elastic psi(2S) and J/psi meson production is measured as a function of Q^2. The results are discussed in terms of theoretical models based upon perturbative QCD. Differential cross sections for inclusive and inelastic production of J/psi mesons are determined and predictions within two theoretical frameworks are compared with the data, the non-relativistic QCD factorization approach including colour octet and colour singlet contributions, and the model of Soft Colour Interactions
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Status of RHIC head-on beam-beam compensation project
Two electron lenses are under construction for RHIC to partially compensate the head-on beam-beam effect in order to increase both the peak and average luminosities. The final design of the overall system is reported as well as the status of the component design, acquisition, and manufacturing. An overview of the RHIC head-on beam-beam compensation project is given in [1], and more details in [2]. With 2 head-on beam-beam interactions in IP6 and IP8, a third interaction with a low-energy electron beam is added near IP10 to partially compensate the the head-on beam-beam effect. Two electron lenses are under construction, one for each ring. Both will be located in a region common to both beams, but each lens will act only on one beam. With head-on beam-beam compensation up to a factor of two improvement in luminosity is expected together with a polarized source upgrade. The current RHIC polarized proton performance is documented in Ref. [4]. An electron lens (Fig. 1) consists of an DC electron gun, warm solenoids to focus the electron beam during transport, a superconducting main solenoid in which the interaction with the proton beam occurs, steering magnets, a collector, and instrumentation. The main developments in the last year are given below. The experimental program for polarized program at 100 GeV was expected to be finished by the time the electron lenses are commissioned. However, decadal plans by the RHIC experiments STAR and PHENIX show a continuing interest at both 100 GeV and 250 GeV, and a larger proton beam size has been accommodated in the design (Tab. 1). Over the last year beam and lattice parameters were optimized, and RHIC proton lattices are under development for optimized electron lens performance. The effect of the electron lens magnetic structure on the proton beam was evaluated, and found to be correctable. Experiments were done in RHIC and the Tevatron
The R&D Program for Targetry at a Neutrino Factory
The need for intense muon beams for muon colliders [1] and for neutrino factories based on muon storage rings [2, 3, 4] leads to a concept of 1-4 MW proton beams incident a moving target that is inside a 20-T solenoid magnet, with a mercury jet as a preferred example. Novel technical issues for such a system include disruption of the mercury jet by the proton beam and distortion of the jet on entering the solenoid, as well as more conventional issues of materials lifetime and handling of activated materials in an intense radiation environment. As part of the R&D program [5] of the Neutrino Factory and Muon Collider Collaboration, R&D effort related to targetry is being performed within the context of BNL E951 [6], first results of which are discussed here and in other contributions to this conference