Fluctuaciones de las poblaciones de Diuraphis noxia y sus enemigos naturales en cultivos de trigo en la zona de Bahia Blanca, Argentina

The Russian wheat aphid Diuraphis noxia Mordvilko (Homoptera:Aphididae) is a dangerous pest of economic importance to the Argentina's wheat growing region, dating from its appearance in 1991. Fluctuations in D. noxia population and its natural enemies were evaluated in the area of Bah\ueda Blanca, Buenos Aires , Argentina, during 1994 and 1995. The information was obtained through direct plant sampling, water and soil traps and net catches. The first aphids were found in September during the phenological reed stage and the highest density was found in November during the phenological tassel stage. The age structure of the population was similar and was represented by young juvenile and adult forms. The population fitted an added type of pattern, constituted mainly of small pupa. The winged forms were found at the end of November, starting at that time their migration to natural grass. The alternative hosts were, Hordeum leporinum Link, Lolium multiflorum Lam., L. perenne L., Bromus unioloides Kunth, and Bromus brevis Nees. The most outstanding predators during both years of study were the Coccinelidae, Eriopis connexa (Mulsant), Hippodamia convergens (Guer.) and Coccinella ancoralis (Germ.) which presented together with Hymenoptera: Aphidiidae the peak of the maximum occurrence simultaneous to the aphid's highest maximum population density. The presence of Diptera: Syrphidae and Nabis spp. was scarce.En Argentina el pulg\uf3n ruso del trigo, Diuraphis noxia Mordvilko (Homoptera: Aphididae), es una plaga de importancia econ\uf3mica en la regi\uf3n triguera a partir de su aparici\uf3n en el pa\ueds en 1991. En la zona de Bah\ueda Blanca, Buenos Aires, Argentina, durante los a\uf1os 1994 y 1995 se evaluaron las fluctuaciones poblacionales D. noxia y sus enemigos naturales. La informaci\uf3n fue obtenida mediante muestreo directo de plantas, trampas de agua y suelo, y golpes de red. Los primeros \ue1fidos se registraron en el mes de septiembre en el estado fenol\uf3gico de enca\uf1ado y la mayor densidad se produjo en el mes de noviembre durante el estado fenol\uf3gico de espigado. La estructura por edad de la poblaci\uf3n fue similar y estuvo representada por las formas juveniles y adultas. La poblaci\uf3n se ajust\uf3 a un patr\uf3n de distribuci\uf3n de tipo agregada, constituida en su mayor\ueda por ninfas peque\uf1as. Las formas aladas se registraron a fines de noviembre, iniciando en esta \ue9poca la migraci\uf3n hacia las gram\uedneas naturales. Los hospederos alternativos fueron cola de zorro, Hordeum leporinum Link; rye grass perenne, Lolium perenne L.;rye grass criollo, Lolium multiflorum Lam.; cebadilla australiana, Bromus unioloides Kunth, y cebadilla criolla, Bromus brevis Nees. Los depredadores m\ue1s destacados para ambos a\uf1os de estudio fueron los coccin\ue9lidos Eriopis connexa (Mulsant), Hippodamia convergens (Guer.) y Coccinella ancoralis (Germ.) quepresentaron junto a Hymenoptera: Aphidiidae el pico de m\ue1xima ocurrencia en forma coincidente con la m\ue1xima densidad poblacional de los pulgones. La presencia de Diptera: Syrphidae y de Nabis spp. fue escasa

The front-end electronics for the COMPASS MWPCs

In the COMPASS experiment 34 planes of MWPCs for about 26,000 readout channels of MWPCs are used. The very high rate of the muon and hadron beams, and the consequently high trigger rate, requires the use of a front-end electronics with new conceptual design, to have a fast DAQ with a minimum dead-time. Its scheme will be described, together with some results of the performances achieved

Non-minimally coupled dark matter: effective pressure and structure formation

We propose a phenomenological model in which a non-minimal coupling between gravity and dark matter is present in order to address some of the apparent small scales issues of \lcdm model. When described in a frame in which gravity dynamics is given by the standard Einstein-Hilbert action, the non-minimal coupling translates into an effective pressure for the dark matter component. We consider some phenomenological examples and describe both background and linear perturbations. We show that the presence of an effective pressure may lead these scenarios to differ from \lcdm at the scales where the non-minimal coupling (and therefore the pressure) is active. In particular two effects are present: a pressure term for the dark matter component that is able to reduce the growth of structures at galactic scales, possibly reconciling simulations and observations; an effective interaction term between dark matter and baryons that could explain observed correlations between the two components of the cosmic fluid within Tully-Fisher analysis.Comment: 18 pages, 6 figures, references added. Published in JCA

Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs

We present a determination of the gluon polarization Delta G/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6-LiD target. The helicity asymmetry for the selected events is = 0.002 +- 0.019(stat.) +- 0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3 (GeV}/c)^2.Comment: 10 pages, 3 figure

The Deuteron Spin-dependent Structure Function g1d and its First Moment

We present a measurement of the deuteron spin-dependent structure function g1d based on the data collected by the COMPASS experiment at CERN during the years 2002-2004. The data provide an accurate evaluation for Gamma_1^d, the first moment of g1d(x), and for the matrix element of the singlet axial current, a0. The results of QCD fits in the next to leading order (NLO) on all g1 deep inelastic scattering data are also presented. They provide two solutions with the gluon spin distribution function Delta G positive or negative, which describe the data equally well. In both cases, at Q^2 = 3 (GeV/c)^2 the first moment of Delta G is found to be of the order of 0.2 - 0.3 in absolute value.Comment: fits redone using MRST2004 instead of MRSV1998 for G(x), correlation matrix adde

Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2

We present a precise measurement of the deuteron longitudinal spin asymmetry A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1 GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured A_1^d and g_1^d are found to be consistent with zero in the whole range of x.Comment: 17 pages, 10 figure

A new measurement of the Collins and Sivers asymmetries on a transversely polarised deuteron target

New high precision measurements of the Collins and Sivers asymmetries of charged hadrons produced in deep-inelastic scattering of muons on a transversely polarised 6LiD target are presented. The data were taken in 2003 and 2004 with the COMPASS spectrometer using the muon beam of the CERN SPS at 160 GeV/c. Both the Collins and Sivers asymmetries turn out to be compatible with zero, within the present statistical errors, which are more than a factor of 2 smaller than those of the published COMPASS results from the 2002 data. The final results from the 2002, 2003 and 2004 runs are compared with naive expectations and with existing model calculations.Comment: 40 pages, 28 figure

Measurement of the Spin Structure of the Deuteron in the DIS Region

We present a new measurement of the longitudinal spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron in the range 1 GeV^2 < Q^2 < 100 GeV^2 and 0.004< x <0.7. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised 6-LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004 < x < 0.03.Comment: 10 pages, 6 figures, subm. to PLB, revised: author list, Fig. 4, details adde

The COMPASS Experiment at CERN

The COMPASS experiment makes use of the CERN SPS high-intensitymuon and hadron beams for the investigation of the nucleon spin structure and the spectroscopy of hadrons. One or more outgoing particles are detected in coincidence with the incoming muon or hadron. A large polarized target inside a superconducting solenoid is used for the measurements with the muon beam. Outgoing particles are detected by a two-stage, large angle and large momentum range spectrometer. The setup is built using several types of tracking detectors, according to the expected incident rate, required space resolution and the solid angle to be covered. Particle identification is achieved using a RICH counter and both hadron and electromagnetic calorimeters. The setup has been successfully operated from 2002 onwards using a muon beam. Data with a hadron beam were also collected in 2004. This article describes the main features and performances of the spectrometer in 2004; a short summary of the 2006 upgrade is also given.Comment: 84 papes, 74 figure

Transverse spin effects in hadron-pair production from semi-inclusive deep inelastic scattering

First measurements of azimuthal asymmetries in hadron-pair production in deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron) and NH_3 (proton) targets are presented. The data were taken in the years 2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c at the CERN SPS. The asymmetries provide access to the transversity distribution functions, without involving the Collins effect as in single hadron production. The sizeable asymmetries measured on the NH_ target indicate non-vanishing u-quark transversity and two-hadron interference fragmentation functions. The small asymmetries measured on the ^6LiD target can be interpreted as indication for a cancellation of u- and d-quark transversities.Comment: 13 pages, 4 figures, updated to the published versio