406 research outputs found
Comparison of Three Different Fertigation Strategies for Drip Irrigated Table Grapes – Part II. Soil and Grapevine Nutrient Status
A field trial was carried out in a drip irrigated Dan-ben-Hannah/Ramsey table grape vineyard near Paarlin the Berg River Valley region of South Africa to compare three fertigation strategies. Fertilisers wereapplied (i) two weeks after bud break, fruit set and post-harvest (LF), (ii) weekly from two weeks afterbud break until ten weeks after harvest, except during berry ripening (WF), and (iii) in daily fertigationpulses (DF). Grapevines of all treatments received c. 116 kg/ha N, 22 kg/ha P and 92 kg/ha K per season.Grapevines of all the fertigation strategies were thinned to obtain a normal and high crop load, whichis 26 and 36 bunches per grapevine respectively for Dan-ben-Hannah under the given conditions. In thecase of DF, the soil directly beneath the drippers became acidic after three years. Salt also accumulated onthe perimeter of the wetted soil volumes. Petiole P of the DF grapevines was 77% higher than that of theLF and WF grapevines. Daily fertigated grapevines bearing normal crop loads had 20% to 30% higherleaf blade P than the LF or WF grapevines. Leaf blade K of the WF grapevines was lower than in thegrapevines bearing a normal crop load of the LF and DF strategies. Grapevines bearing high crop loadstended to have lower juice N than grapevines with a normal crop load. Juice P of the DF grapevines washigher than that of the LF and WF grapevines, regardless of crop load. Daily pulse fertigation promotedthe accumulation of N, P and K in the berry skins
Comparison of Three Different Fertigation Strategies for Drip Irrigated Table Grapes – Part III. Growth, Yield and Quality
A field trial was carried out in a drip irrigated Dan-ben-Hannah/Ramsey vineyard near Paarl in the BergRiver Valley region of South Africa to compare three fertigation strategies. Fertilisers were applied (i)two weeks after bud break, fruit set and post-harvest (LF), (ii) weekly from two weeks after bud breakuntil ten weeks after harvest, except during berry ripening (WF), and (iii) in daily irrigation pulses (DF).Grapevines of all treatments received c. 116 kg/ha N, 22 kg/ha P and 92 kg/ha K per season. Grapevinesof all the fertigation strategies were thinned to obtain a normal and high crop load, which is 26 and36 bunches per grapevine respectively for Dan-ben-Hannah. Crop load did not affect vegetative growth,berry size or bunch mass. However, compared to LF and WF, DF increased the berry size of grapevinesbearing 26 bunches. Crop load tended to reduce juice TSS, irrespective of fertigation strategy, particularlyin 2002/03. Neither fertigation strategy nor crop load affected TTA and pH. Less berry crack contributedto a higher yield and higher export percentage of the DF grapes. In addition, bigger berries, and thereforebetter appearance, also contributed to the higher export quality of the DF grapes. Although the DFgrapevines bearing 36 bunches produced grapes of poorer colour and overall impression, they were withinexport norms. Based on the foregoing, the DF strategy should not be regarded as the ultimate solution fortable grape production. However, it can be recommended for vineyards on poor soils or where berry crackoccurs commonly
Dry Matter Accumulation, Seasonal Uptake and Partitioning of Mineral Nutrients by Vitis vinifera L. cv. Sultanina Grapevines in the Lower Orange River Region of South Africa - A Preliminary Investigation
Table grapes are harvested from November until early February in the Orange River Region of SouthAfrica, where a functional leaf canopy is present for up to six months of post-harvest. Seasonal uptakeand partitioning of mineral nutrients by ‘Sultanina’ grapevines in this long-season area were quantifiedin a preliminary investigation. Entire grapevines growing on two different soil types were sampled duringthe growing season. On sandy soil, further from the river, grapevine vigour was not excessive; however,on the fertile alluvial soil vigour was higher with active post-harvest re-growth. At budbreak, reserve Nplayed an important role on the sandy soil, while it was less important on the alluvial one. During the postharvestperiod, 34.3% of the annual N-requirement was absorbed by grapevines cultivated on sandy soilat post-harvest, while only 17.0% was absorbed on the alluvial soil. Approximately 4.0 kg N was utilizedfor the production of one ton of fresh grapes. A major fraction of the annual P-requirement (41.9%) wasabsorbed post-harvest by grapevines on the sandy soil. Grapevines on alluvial soil absorbed more P atpre-harvest; however, P was somehow lost post-harvest. Comparable amounts of K and Mg were absorbedby both selections of grapevines. Sandy soil grapevines absorbed K and Mg at post-harvest, while a netloss occurred for those of alluvial soil. Calcium utilized by sandy soil grapevines was less than half thatutilized by those of alluvial soil. The seasonal absorption pattern of Ca was comparable for both soils.Results suggest that that seasonal uptake and partitioning of mineral nutrients are affected by soil typeand grapevine vigour
Asteroseismology of Eclipsing Binary Stars in the Kepler Era
Eclipsing binary stars have long served as benchmark systems to measure
fundamental stellar properties. In the past few decades, asteroseismology - the
study of stellar pulsations - has emerged as a new powerful tool to study the
structure and evolution of stars across the HR diagram. Pulsating stars in
eclipsing binary systems are particularly valuable since fundamental properties
(such as radii and masses) can determined using two independent techniques.
Furthermore, independently measured properties from binary orbits can be used
to improve asteroseismic modeling for pulsating stars in which mode
identifications are not straightforward. This contribution provides a review of
asteroseismic detections in eclipsing binary stars, with a focus on space-based
missions such as CoRoT and Kepler, and empirical tests of asteroseismic scaling
relations for stochastic ("solar-like") oscillations.Comment: 28 pages, 12 figures, 2 tables; Proceedings of the AAS topical
conference "Giants of Eclipse" (AASTCS-3), July 28 - August 2 2013, Monterey,
C
Asteroseismology of red giants & galactic archaeology
Red-giant stars are low- to intermediate-mass (~M)
stars that have exhausted hydrogen in the core. These extended, cool and hence
red stars are key targets for stellar evolution studies as well as galactic
studies for several reasons: a) many stars go through a red-giant phase; b) red
giants are intrinsically bright; c) large stellar internal structure changes as
well as changes in surface chemical abundances take place over relatively short
time; d) red-giant stars exhibit global intrinsic oscillations. Due to their
large number and intrinsic brightness it is possible to observe many of these
stars up to large distances. Furthermore, the global intrinsic oscillations
provide a means to discern red-giant stars in the pre-helium core burning from
the ones in the helium core burning phase and provide an estimate of stellar
ages, a key ingredient for galactic studies. In this lecture I will first
discuss some physical phenomena that play a role in red-giant stars and several
phases of red-giant evolution. Then, I will provide some details about
asteroseismology -- the study of the internal structure of stars through their
intrinsic oscillations -- of red-giant stars. I will conclude by discussing
galactic archaeology -- the study of the formation and evolution of the Milky
Way by reconstructing its past from its current constituents -- and the role
red-giant stars can play in that.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Multiorder coherent Raman scattering of a quantum probe field
We study the multiorder coherent Raman scattering of a quantum probe field in
a far-off-resonance medium with a prepared coherence. Under the conditions of
negligible dispersion and limited bandwidth, we derive a Bessel-function
solution for the sideband field operators. We analytically and numerically
calculate various quantum statistical characteristics of the sideband fields.
We show that the multiorder coherent Raman process can replicate the
statistical properties of a single-mode quantum probe field into a broad comb
of generated Raman sidebands. We also study the mixing and modulation of photon
statistical properties in the case of two-mode input. We show that the prepared
Raman coherence and the medium length can be used as control parameters to
switch a sideband field from one type of photon statistics to another type, or
from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.
Kepler-22b: A 2.4 Earth-radius Planet in the Habitable Zone of a Sun-like Star
A search of the time-series photometry from NASA's Kepler spacecraft reveals
a transiting planet candidate orbiting the 11th magnitude G5 dwarf KIC 10593626
with a period of 290 days. The characteristics of the host star are well
constrained by high-resolution spectroscopy combined with an asteroseismic
analysis of the Kepler photometry, leading to an estimated mass and radius of
0.970 +/- 0.060 MSun and 0.979 +/- 0.020 RSun. The depth of 492 +/- 10ppm for
the three observed transits yields a radius of 2.38 +/- 0.13 REarth for the
planet. The system passes a battery of tests for false positives, including
reconnaissance spectroscopy, high-resolution imaging, and centroid motion. A
full BLENDER analysis provides further validation of the planet interpretation
by showing that contamination of the target by an eclipsing system would rarely
mimic the observed shape of the transits. The final validation of the planet is
provided by 16 radial velocities obtained with HIRES on Keck 1 over a one year
span. Although the velocities do not lead to a reliable orbit and mass
determination, they are able to constrain the mass to a 3{\sigma} upper limit
of 124 MEarth, safely in the regime of planetary masses, thus earning the
designation Kepler-22b. The radiative equilibrium temperature is 262K for a
planet in Kepler-22b's orbit. Although there is no evidence that Kepler-22b is
a rocky planet, it is the first confirmed planet with a measured radius to
orbit in the Habitable Zone of any star other than the Sun.Comment: Accepted to Ap
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 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
- …