Seeded crystal growth of the acentric organic nonlinear optical material methyl-p-hydroxybenzoate from the vapor phase

Using in situ differential interference contrast microscopy (DICM), growth morphology, structure, and step velocities of the vicinal hillocks on {110} and {111̅} faces of MHB crystal seeds growing from the vapor phase have been investigated over a supersaturation (σ) range of (0.2 < σ < 0.6). Under these conditions of supersaturation, a dislocation induced growth mechanism was identified. Ex situ atomic force microscopy (AFM) shows that some dislocation induced hillocks exhibit hollow cores. The general observations of the {110} and {111̅} surfaces reveal that these faces follow a classical mode of layer growth, continuous generation of new layers by dislocation outcrops, which subsequently bunch and spread to cover the entire facets. A tangential step velocity of the slow and fast sides of {110} and {111̅} growth hillocks show a linear dependence with supersaturation in the region of (0.2 < σ < 0.4). Analysis of this dependence leads to the respective growth parameters for the identified growth mechanism: the activation energies for the slow and fast step motion of a growth hillock (EaS and EaF) and the corresponding kinetic coefficients (βaS and βaF), for both faces. The growth from physical vapor transport (PVT) shows that for the title material, as with a number of other polar materials, solvent poisoning is not the cause of the highly differential growth rates and is an intrinsic feature of the crystal. The results suggest that in terms of the production of large single crystals of high perfection by PVT, the supersaturation range for dislocation growth should be between 0.2 and 0.4. These findings provide a foundation for the rational design of large MHB crystals that may find applications utilizing their high optoelectronic potential

Chinese degraded grasslands – pathways for sustainability

The 400 m ha of grazing lands in China, mainly across the north and west of the country, have similar problems to those throughout the steppe of Mongolia, Central Asia and neighbouring countries. The grasslands are in drier regions (50–500 mm) across mainly Inner Mongolia, Xinjiang, Tibet, Qinghai, Gansu and Sichuan, often at higher altitudes on the Tibetan, Mongolian and Loess Plateaus, and have for millennia supported the livelihoods of millions of herders. By 2002, surveys were classifying 90% of the grasslands as degraded. Less than 10% were considered desertified to the extent that replanting was the only option to restore some plant cover. The majority of the grasslands were considered capable of being rehabilitated to some degree through changing management practices. In the 1980s the first Grassland Laws were promulgated, initiating a series of programs aimed at rehabilitating the grasslands. These programs included the establishment of individual ‘user rights’ to herders to use a defined area of grassland and the imposition of grazing bans, often for five years, to rehabilitate degraded areas. These were often applied at a regional level. At the same time, herders were encouraged to have more livestock as that was seen as a pathway to lift them from poverty. The sheep equivalent of grazing animals for the whole of China, has increased 4-fold since 1949, often by greater amounts in some regions. But there was very limited work done on how best to manage grazing livestock in ways that could aid grassland rehabilitation. In the early 2000s a collaborative program was started between several Australian and Chinese Institutes, to investigate better ways of rehabilitating the grasslands and to improve herder incomes from livestock. This work involved the development of four models that could use the limited data available, to help guide a series of research programs. These models indicated that halving stocking rates could maintain or increase herder net incomes. Farm demonstrations showed this result applied in practice and grasslands did improve. A series of grazing experiments found that halving the current stocking rates was needed to enable the survival of the better plant species within the grassland. A model that estimated the net value of each animal indicated that often half the animals were generating marginal or negative incomes, and could be culled without affecting the household income, again substantiated in farm demonstrations. In this paper, the causes of degradation, which can be traced back to the progressive changes that have occurred in China since 1949, are discussed together with the practice changes that have come from a large collaborative research program between Australia and China. Efficient markets and land tenure reform are needed to help create the incentives for herders to change in sustainable ways

Increased numbers of oligodendrocyte lineage cells in the optic nerves of cerebroside sulfotransferase knockout mice

Sulfatide is a myelin glycolipid that functions in the formation of paranodal axo-glial junctions in vivo and in the regulation of oligodendrocyte differentiation in vitro. Cerebroside sulfotransferase (CST) catalyzes the production of two sulfated glycolipids, sulfatide and proligodendroblast antigen, in oligodendrocyte lineage cells. Recent studies have demonstrated significant increases in oligodendrocytes from the myelination stage through adulthood in brain and spinal cord under CST-deficient conditions. However, whether these result from excess migration or in situ proliferation during development is undetermined. In the present study, CST-deficient optic nerves were used to examine migration and proliferation of oligodendrocyte precursor cells (OPCs) under sulfated glycolipid-deficient conditions. In adults, more NG2-positive OPCs and fully differentiated cells were observed. In developing optic nerves, the number of cells at the leading edge of migration was similar in CST-deficient and wild-type mice. However, BrdU+ proliferating OPCs were more abundant in CST-deficient mice. These results suggest that sulfated glycolipids may be involved in proliferation of OPCs in vivo

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters

Measurement of D*+/- meson production in jets from pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

This paper reports a measurement of D*+/- meson production in jets from proton-proton collisions at a center-of-mass energy of sqrt(s) = 7 TeV at the CERN Large Hadron Collider. The measurement is based on a data sample recorded with the ATLAS detector with an integrated luminosity of 0.30 pb^-1 for jets with transverse momentum between 25 and 70 GeV in the pseudorapidity range |eta| < 2.5. D*+/- mesons found in jets are fully reconstructed in the decay chain: D*+ -> D0pi+, D0 -> K-pi+, and its charge conjugate. The production rate is found to be N(D*+/-)/N(jet) = 0.025 +/- 0.001(stat.) +/- 0.004(syst.) for D*+/- mesons that carry a fraction z of the jet momentum in the range 0.3 < z < 1. Monte Carlo predictions fail to describe the data at small values of z, and this is most marked at low jet transverse momentum.Comment: 10 pages plus author list (22 pages total), 5 figures, 1 table, matches published version in Physical Review