269 research outputs found
Phellinus Species Inducing Hoja de Malvón Symptoms on Leaves and Wood Decay in Mature Field-Grown Grapevines
Hoja de malvón is a common vine wood disease widely spread in grape production areas of Argentina
which causes wood necrosis, decline, and the death of plants. Leaves are smaller than normal and chlorotic, with
margins curled downwards. A basidiomycete, provisionally classified as Phellinus sp., is the fungus most frequently
isolated from infected plants. The aim of this study was to determine the pathogenicity of this fungus in field-grown
grapevines and to clarify its taxonomic positioning. The trunks and branches of five 13-year-old grapevines cv. Riesling
were infected on October 1994. Six years later some of the infected grapevines showed foliar symptoms of hoja de
malvón. The inoculated fungus was reisolated with relatively high frequency, together with other fungi from different
necrotic areas near the inoculation sites. The fungus under study was ascertained to belong to the Hymenochaetaceae
family (Aphyllophorales, Basidiomycota). Further inoculations of a much greater number of plants and with various
associated fungi like species of the genera Phaeoacremonium, Phaeomoniella and Botryosphaeria, will be conducted
Bose-Einstein Condensation of Helium and Hydrogen inside Bundles of Carbon Nanotubes
Helium atoms or hydrogen molecules are believed to be strongly bound within
the interstitial channels (between three carbon nanotubes) within a bundle of
many nanotubes. The effects on adsorption of a nonuniform distribution of tubes
are evaluated. The energy of a single particle state is the sum of a discrete
transverse energy Et (that depends on the radii of neighboring tubes) and a
quasicontinuous energy Ez of relatively free motion parallel to the axis of the
tubes. At low temperature, the particles occupy the lowest energy states, the
focus of this study. The transverse energy attains a global minimum value
(Et=Emin) for radii near Rmin=9.95 Ang. for H2 and 8.48 Ang.for He-4. The
density of states N(E) near the lowest energy is found to vary linearly above
this threshold value, i.e. N(E) is proportional to (E-Emin). As a result, there
occurs a Bose-Einstein condensation of the molecules into the channel with the
lowest transverse energy. The transition is characterized approximately as that
of a four dimensional gas, neglecting the interactions between the adsorbed
particles. The phenomenon is observable, in principle, from a singular heat
capacity. The existence of this transition depends on the sample having a
relatively broad distribution of radii values that include some near Rmin.Comment: 21 pages, 9 figure
Dimensional Crossover of Dilute Neon inside Infinitely Long Single-Walled Carbon Nanotubes Viewed from Specific Heats
A simple formula for coordinates of carbon atoms in a unit cell of a
single-walled nanotube (SWNT) is presented and the potential of neon (Ne)
inside an infinitely long SWNT is analytically derived under the assumption of
pair-wise Lennard-Jones potential between Ne and carbon atoms. Specific heats
of dilute Ne inside infinitely long (5, 5), (10, 10), (15, 15) and (20, 20)
SWNT's are calculated at different temperatures. It is found that Ne inside
four kinds of nanotubes exhibits 3-dimensional (3D) gas behavior at high
temperature but different behaviors at low temperature: Ne inside (5, 5)
nanotube behaves as 1D gas but inside (10, 10), (15, 15), and (20, 20)
nanotubes behaves as 2D gas. Furthermore, at ultra low temperature, Ne inside
(5, 5) nanotube still displays 1D behavior but inside (10, 10), (15, 15), and
(20, 20) nanotubes behaves as lattice gas.Comment: 10 pages, 5 figure
Quantum virial expansion approach to thermodynamics of He adsorbates in carbon nanotube materials: Interacting Bose gas in one dimension
I demonstrate that He adsorbates in carbon nanotube materials can be
treated as one-dimensional interacting gas of spinless bosons for temperatures
below 8 K and for coverages such that all the adsorbates are in the groove
positions of the carbon nanotube bundles. The effects of adsorbate-adsorbate
interactions are studied within the scheme of virial expansion approach. The
theoretical predictions for the specific heat of the interacting adsorbed gas
are given.Comment: 5 PS figure
Specific heats of dilute neon inside long single-walled carbon nanotube and related problems
An elegant formula for coordinates of carbon atoms in a unit cell of a
single-walled nanotube (SWNT) is presented and the potential of neon (Ne)
inside an infinitely long SWNT is analytically derived out under the condition
of the Lennard-Jones potential between Ne and carbon atoms.
Specific heats of dilute Ne inside long (20, 20) SWNT are calculated at
different temperatures. It is found that Ne exhibits 3-dimensional (3D) gas
behavior at high temperature but behaves as 2D gas at low temperature.
Especially, at ultra low temperature, Ne inside (20, 20) nanotubes behaves as
lattice gas. A coarse method to determine the characteristic temperature
for low density gas in a potential is put forward. If
, we just need to use the classical statistical
mechanics without solving the Shr\"{o}dinger equation to consider the thermal
behavior of gas in the potential. But if , we
must solve the Shr\"{o}dinger equation. For Ne in (20,20) nanotube, we obtain
K.Comment: 14 pages, 7 figure
Lattice model of gas condensation within nanopores
We explore the thermodynamic behavior of gases adsorbed within a nanopore.
The theoretical description employs a simple lattice gas model, with two
species of site, expected to describe various regimes of adsorption and
condensation behavior. The model includes four hypothetical phases: a
cylindrical shell phase (S), in which the sites close to the cylindrical wall
are occupied, an axial phase (A), in which sites along the cylinder's axis are
occupied, a full phase (F), in which all sites are occupied, and an empty phase
(E). We obtain exact results at T=0 for the phase behavior, which is a function
of the interactions present in any specific problem. We obtain the
corresponding results at finite T from mean field theory. Finally, we examine
the model's predicted phase behavior of some real gases adsorbed in nanopores
Capillary condensation in cylindrical nanopores
Using grand canonical Monte Carlo simulations, we have explored the
phenomenon of capillary condensation (CC) of Ar at the triple temperature
inside infinitely long, cylindrical pores. Pores of radius R= 1 nm, 1.7 nm and
2.5 nm have been investigated, using a gas-surface interaction potential
parameterized by the well-depth D of the gas on a planar surface made of the
same material as that comprising the porous host. For strongly attractive
situations, i.e., large D, one or more (depending on R) Ar layers adsorb
successively before liquid fills the pore. For very small values of D, in
contrast, negligible adsorption occurs at any pressure P below saturated vapor
pressure P0; above saturation, there eventually occurs a threshold value of P
at which the coverage jumps from empty to full, nearly discontinuously.
Hysteresis is found to occur in the simulation data whenever abrupt CC occurs,
i.e. for R>= 1.7 nm, and for small D when R=1nm. Then, the pore-emptying branch
of the adsorption isotherm exhibits larger N than the pore-filling branch, as
is known from many experiments and simulation studies. The relation between CC
and wetting on planar surfaces is discussed in terms of a threshold value of D,
which is about one-half of the value found for the wetting threshold on a
planar surface. This finding is consistent with a simple thermodynamic model of
the wetting transition developed previously.Comment: 13 pages, 7 figure
Characterization and Identification of the Basidiomycetous Fungus Associated with 'hoya de malvón' Grapevine Disease in Argentina
Inocutis jamaicensis (Murrill) Gottlieb, J.E. Wright & Moncalvo was identified as the basidiomycetous
species associated with ‘hoja de malvón’ grapevine disease in Argentina. Macro and micro-morphological characteristics
of fruit bodies corresponded to those described for the white-rotting fungus associated with native plant species
and Eucalyptus globulus Labill. planted in Uruguay. Monokariotic isolates were obtained from basidiospores produced
by fruit bodies of I. jamaicensis collected from Vitis vinifera L. and E. globulus. Dikaryons and fruit bodies
produced by pairing monokaryotic mycelium suggest that all these isolates belong to the same species. The analysis
of RFLP of the dikaryon produced by pairing monokaryons derived from V. vinifera and E. globulus revealed fragments
that corresponded to each monokaryon, confirming that isolates from Vitis mated with those from Eucalyptus.
In order to compare grapevine and Uruguayan isolates, RFLPs from ITS region generated by restriction digestion
with Alu I, Hae III, Hha I, Msp I and Taq I were performed. Differences found in some restriction pattern could reflect
a certain degree of variability between dikariotic isolates, probably related with a particular lifestyle, host specificity
or geographic origin
Adsorption of para-Hydrogen on Krypton pre-plated graphite
Adsorption of para-Hydrogen on the surface of graphite pre-plated with a
single layer of atomic krypton is studied thoretically by means of Path
Integral Ground State Monte Carlo simulations. We compute energetics and
density profiles of para-hydrogen, and determine the structure of the adsorbed
film for various coverages. Results show that there are two thermodynamically
stable monolayer phases of para-hydrogen, both solid. One is commensurate with
the krypton layer, the other is incommensurate. No evidence is seen of a
thermodynamically stable liquid phase, at zero temperature. These results are
qualitatively similar to what is seen for for para-hydrogen on bare graphite.
Quantum exchanges of hydrogen molecules are suppressed in this system.Comment: 12 pages, 6 figures, to appear in the proceedings of "Advances in
Computational Many-Body Physics", Banff, Alberta (Canada), January 13-16 200
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