152 research outputs found
Resistance of Grapevine Rootstocks to Meloidogyne incognita under Field Conditions
Resistance of grapevine rootstocks to root-knot nematodes (Meloidogyne incognita) was studied in field trials. Resistance was found to be adequately expressed by the degree of galling. A highly significant positive correlation exists between nematode populations in the soil as well as nematode reproduction and galling, while grapevine growth and yield were negatively related to the degree of infestation. However, information regarding rootstock tolerance and intolerance (sensitivity) was not considered reliable. It was further shown that a susceptible scion would not lower the resistance of the rootstock involved. Based on their rate of galling, rootstocks Ramsey, 99 Richter PS, Dogridge, Freedom, Harmony and 101-14 Mgt are resistant while Jacquez, 140 Ruggeri, Grezot-1, Maleque 44-53 and Constantia Metallica are susceptible
Chemical Control of Root-Knot Nematodes in Established Vineyards
Chemical control of root-knot nematodes (Meloidogyne spp.) in established vineyards was investigated. A liquid soil fumigant (1,3-dichloropropene) and four systemic (nonfumigant) nematicides in granular form, viz. aldicarb, carbofuran, oxamyl and fenamiphos were applied as soil treatments during bud burst and after harvest. Significant average yield and cane mass increases were recorded during the three years following split treatment at bud burst with aldicarb and oxamyl and when aldicard was applied as a single treatment after harvest
Energy levels and decoherence properties of single electron and nuclear spins in a defect center in diamond
The coherent behavior of the single electron and single nuclear spins of a
defect center in diamond and a 13C nucleus in its vicinity, respectively, are
investigated. The energy levels associated with the hyperfine coupling of the
electron spin of the defect center to the 13C nuclear spin are analyzed.
Methods of magnetic resonance together with optical readout of single defect
centers have been applied in order to observe the coherent dynamics of the
electron and nuclear spins. Long coherence times, in the order of microseconds
for electron spins and tens of microseconds for nuclear spins, recommend the
studied system as a good experimental approach for implementing a 2-qubit gate.Comment: 4 pages, 4 figure
The negatively charged nitrogen-vacancy centre in diamond: the electronic solution
The negatively charged nitrogen-vacancy centre is a unique defect in diamond
that possesses properties highly suited to many applications, including quantum
information processing, quantum metrology, and biolabelling. Although the
unique properties of the centre have been extensively documented and utilised,
a detailed understanding of the physics of the centre has not yet been
achieved. Indeed there persists a number of points of contention regarding the
electronic structure of the centre, such as the ordering of the dark
intermediate singlet states. Without a sound model of the centre's electronic
structure, the understanding of the system's unique dynamical properties can
not effectively progress. In this work, the molecular model of the defect
centre is fully developed to provide a self consistent model of the complete
electronic structure of the centre. The application of the model to describe
the effects of electric, magnetic and strain interactions, as well as the
variation of the centre's fine structure with temperature, provides an
invaluable tool to those studying the centre and a means to design future
empirical and ab initio studies of this important defect.Comment: 24 pages, 6 figures, 10 table
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Age at antiretroviral therapy initiation and cell-associated HIV-1 DNA levels in HIV-1-infected children
Background
The latent viral reservoir is the major obstacle to achieving HIV remission and necessitates life-long antiretroviral therapy (ART) for HIV-infected individuals. Studies in adults and children have found that initiating ART soon after infection is associated with a reduction in the size of the HIV-1 reservoir. Here we quantified cell-associated HIV-1 DNA in early-treated but currently older HIV-infected children suppressed on ART.
Methods
The study participants comprised of a cohort of 146 early-treated children with HIV-1 RNA <50 copies/ml enrolled as part of a clinical trial in Johannesburg, South Africa. A stored buffy coat sample collected after a median 4.3 years on ART and where HIV-1 RNA was <50 copies/ml was tested for cell-associated HIV-1 DNA levels. An in-house, semi-nested real-time quantitative hydrolysis probe PCR assay to detect total HIV-1 subtype C proviral DNA was used. Children were followed prospectively for up to 3 years after this measurement to investigate subsequent HIV-1 RNA rebound/failure while remaining on ART. Age at ART initiation, HIV-1 RNA decline prior to HIV-1 DNA measurement and other factors were investigated.
Results
A gradient between age at ART initiation and later HIV-1 DNA levels was observed. When ART was started 50 copies/ml whilst on ART within 3 years after the DNA measurement was 2.07 (95% CI: 1.352–3.167) times greater if the HIV-1 DNA level was above the median of 55 copies/106 cells.
Conclusions
Cell-associated HIV-1 DNA levels measured after more than 4 years on ART were lower the younger the age of the child when ART was initiated. This marker of the size of the viral reservoir also predicted subsequent viral rebound/treatment failure while ART was sustained. The results provide additional evidence of the benefits of prompt diagnosis and early ART initiation in newborns and infants
The MeerKAT Fornax Survey
We present the science case and observations plan of the MeerKAT Fornax
Survey, an HI and radio continuum survey of the Fornax galaxy cluster to be
carried out with the SKA precursor MeerKAT. Fornax is the second most massive
cluster within 20 Mpc and the largest nearby cluster in the southern
hemisphere. Its low X-ray luminosity makes it representative of the environment
where most galaxies live and where substantial galaxy evolution takes place.
Fornax's ongoing growth makes it an excellent laboratory for studying the
assembly of clusters, the physics of gas accretion and stripping in galaxies
falling in the cluster, and the connection between these processes and the
neutral medium in the cosmic web.
We will observe a region of 12 deg reaching a projected distance of 1.5
Mpc from the cluster centre. This will cover a wide range of environment
density out to the outskirts of the cluster, where gas-rich in-falling groups
are found. We will: study the HI morphology of resolved galaxies down to a
column density of a few times 1e+19 cm at a resolution of 1 kpc; measure
the slope of the HI mass function down to M(HI) 5e+5 M(sun); and attempt to
detect HI in the cosmic web reaching a column density of 1e+18 cm at a
resolution of 10 kpc.Comment: Proceedings of Science, "MeerKAT Science: On the Pathway to the SKA",
Stellenbosch, 25-27 May 201
Continuous-wave room-temperature diamond maser
The maser, older sibling of the laser, has been confined to relative
obscurity due to its reliance on cryogenic refrigeration and high-vacuum
systems. Despite this it has found application in deep-space communications and
radio astronomy due to its unparalleled performance as a low-noise amplifier
and oscillator. The recent demonstration of a room-temperature solid- state
maser exploiting photo-excited triplet states in organic pentacene molecules
paves the way for a new class of maser that could find applications in
medicine, security and sensing, taking advantage of its sensitivity and low
noise. However, to date, only pulsed operation has been observed in this
system. Furthermore, organic maser molecules have poor thermal and mechanical
properties, and their triplet sub-level decay rates make continuous emission
challenging: alternative materials are therefore required. Therefore, inorganic
materials containing spin-defects such as diamond and silicon carbide have been
proposed. Here we report a continuous-wave (CW) room-temperature maser
oscillator using optically pumped charged nitrogen-vacancy (NV) defect centres
in diamond. This demonstration unlocks the potential of room-temperature
solid-state masers for use in a new generation of microwave devices.Comment: 7 pages, 4 figure
Controlling the quantum dynamics of a mesoscopic spin bath in diamond
Understanding and mitigating decoherence is a key challenge for quantum
science and technology. The main source of decoherence for solid-state spin
systems is the uncontrolled spin bath environment. Here, we demonstrate quantum
control of a mesoscopic spin bath in diamond at room temperature that is
composed of electron spins of substitutional nitrogen impurities. The resulting
spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre
electron spin as a magnetic field sensor. We exploit the spin bath control to
dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by
combining spin bath control with dynamical decoupling, we directly measure the
coherence and temporal correlations of different groups of bath spins. These
results uncover a new arena for fundamental studies on decoherence and enable
novel avenues for spin-based magnetometry and quantum information processing
The dark halo of the Hydra I galaxy cluster: core, cusp, cosmological? Dynamics of NGC 3311 and its globular cluster system
NGC 3311 is the central cD galaxy of the Hydra I cluster. We use globular
clusters around NGC 3311, combined with kinematical data of the galaxy itself,
to investigate the dark matter distribution in the central region of Hydra I.
Radial velocities of 118 bright globular clusters, based on VLT/VIMOS mask
spectroscopy, are used to calculate velocity dispersions which are well defined
out to 100 kpc. NGC 3311 is the most distant galaxy for which this kind of
study has been performed. We also determine velocity dispersions of the stellar
component from long slit spectroscopy out to 20 kpc. Moreover, we present a new
photometric model for NGC 3311 in the V-band. We search for a dark halo which
in the context of a spherical Jeans model. We also compare the radial velocity
distributions of globular clusters and planetary nebulae. The projected stellar
velocity dispersion rises from 185 km/s to 350 km/s at a radius of 20 kpc. The
globular cluster dispersion rises as well from 500 km/s at 10 kpc to about 800
km/s at 100 kpc, comparable to the velocity dispersion of the cluster galaxies.
A dark matter halo with a core reproduces well the velocity dispersions of
stars and globular clusters simultaneously under isotropy. The central stellar
velocity dispersions predicted by cosmological NFW halos are less good
representations, while the globular clusters allow a wide range of halo
parameters. A suspected radial anisotropy of the stellar population aggravates
the deviations. However, we find discrepancies with previous kinematical data,
which we cannot resolve and may indicate a more complicated velocity pattern.
Although one cannot conclusively demonstrate that the dark matter halo of NGC
3311 has a core rather than a cusp, a core seems to be preferred by the present
data. A more complete velocity field and an analysis of the anisotropy is
required to reach firm conclusions.Comment: 8 pages, 5 figures, abstract abridged, accepted for publication in
A&
The MeerKAT Fornax Survey -- II. The rapid removal of HI from dwarf galaxies in the Fornax cluster
We present MeerKAT Fornax Survey atomic hydrogen (HI) observations of the
dwarf galaxies located in the central ~2.5 x 4 deg of the Fornax galaxy
cluster. The HI images presented in this work have a column density
sensitivity between 2.7 and 50 x 10 cm over 25 km s for
spatial resolution between 4 and 1 kpc. We are able to detect an impressive MHI
= 5 x 10 Msun 3 point source with a line width of 50 km s
at a distance of 20 Mpc. We detect HI in 17 out of the 304 dwarfs in our field
-- 14 out of the 36 late type dwarfs (LTDs), and 3 of the 268 early type dwarfs
(ETDs). The HI-detected LTDs have likely just joined the cluster and are on
their first infall as they are located at large clustocentric radii, with
comparable MHI and mean stellar surface brightness at fixed luminosity as blue,
star-forming LTDs in the field. The HI-detected ETDs have likely been in the
cluster longer than the LTDs and acquired their HI through a recent merger or
accretion from nearby HI. Eight of the HI-detected LTDs host irregular or
asymmetric HI emission and disturbed or lopsided stellar emission. There are
two clear cases of ram-pressure shaping the HI, with the LTDs displaying
compressed HI on the side closest to the cluster centre and a one-sided,
starless tail pointing away from the cluster centre. The HI-detected dwarfs
avoid the most massive potentials, consistent with massive galaxies playing an
active role in the removal of HI. We create a simple toy model to quantify the
timescale of HI stripping in the cluster. We find that a MHI = 10 Msun
dwarf will be stripped in ~ 240 Myr. The model is consistent with our
observations, where low mass LTDs are directly stripped of their HI from a
single encounter and more massive LTDs can harbour a disturbed HI morphology
due to longer times or multiple encounters being required to fully strip their
HI.Comment: Accepted in Astronomy & Astrophysics. 21 pages, 10 figures. Data
available at the MeerKAT Fornax Survey website
https://sites.google.com/inaf.it/meerkatfornaxsurve
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