1,991 research outputs found
Excoriose, Cane Blight and Related Diseases of Grapevines : A Taxonomic Review of the Pathogens
The disease of grapevines known as excoriose has been the source of a certain amount of controversy.
Much of this concerns the identity of the causal agent and this has been further confounded by the taxonomic problems
of the fungal pathogens associated with this disease. Many of these problems have now been resolved and it is
clear that excoriose is caused by Botryosphaeria dothidea while cane blight and leaf spot is caused by Phomopsis
viticola. However, although at least five different species of Phomopsis are currently known to be associated with
grapevines, only P. viticola causes cane blight and leaf spot. The role played by the other species of fungi is not clear,
but they may be weak pathogens, saprophytes or endophytes
Energy-Dependent Timing of Thermal Emission in Solar Flares
We report solar flare plasma to be multi-thermal in nature based on the
theoretical model and study of the energy-dependent timing of thermal emission
in ten M-class flares. We employ high-resolution X-ray spectra observed by the
Si detector of the "Solar X-ray Spectrometer" (SOXS). The SOXS onboard the
Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May 2003.
Firstly we model the spectral evolution of the X-ray line and continuum
emission flux F(\epsilon) from the flare by integrating a series of isothermal
plasma flux. We find that multi-temperature integrated flux F(\epsilon) is a
power-law function of \epsilon with a spectral index (\gamma) \approx -4.65.
Next, based on spectral-temporal evolution of the flares we find that the
emission in the energy range E= 4 - 15 keV is dominated by temperatures of T=
12 - 50 MK, while the multi-thermal power-law DEM index (\gamma) varies in the
range of -4.4 and -5.7. The temporal evolution of the X-ray flux F(\epsilon,t)
assuming a multi-temperature plasma governed by thermal conduction cooling
reveals that the temperature-dependent cooling time varies between 296 and 4640
s and the electron density (n_e) varies in the range of n_e= (1.77-29.3)*10^10
cm-3. Employing temporal evolution technique in the current study as an
alternative method for separating thermal from non-thermal components in the
energy spectra, we measure the break-energy point ranging between 14 and
21\pm1.0 keV.Comment: Solar Physics, in pres
Attempts to transmit hepatitis B virus to chimpanzees by arthropods
Bedbugs (Cimex lectularius L.) were fed on an infective blood-hepatitis B virus (HBV) mixture. Further bedbugs and tampan ticks (Ornithodoros moubata [MurrayJ) were fed on HBV-carrier chimpanzees. After a 10 - 13 day interval for oviposition, tests done on samples of individual arthropods showed that 53 - 85% of the bugs were HBsAg-positive and none HBeAg-positive, while 100% of the ticks were HBsAgpositive and 88% HBeAg-positive. The remaining arthropods were fed on 3 susceptible chimpanzees, which had failed to develop HBV infection after 11 months, indicating no transmission had occurred. Subsequently the presence of viable virus in the original infective meals was confirmed by inoculation of the relevant donor sera directly into the 3 still susceptible chimpanzees. HBV infections quickly followed in each animal. It is concluded that, while mechanical transmission of HBV is most unlikely after a 10 - 13-day interval between feedings in bedbugs and tampans, it is still possible that mechanical transmission between humans might occur during interrupted feeds
Modern nuclear force predictions for the neutron-deuteron scattering lengths
The nd doublet and quartet scattering lengths have been calculated based on
the modern NN and 3N interactions. We also studied the effect of the
electromagnetic interactions in the form introduced in AV18. Switching them off
for the various nuclear force models leads to shifts of up to +0.04 fm for
doublet scattering length, which is significant for present day standards. The
electromagnetic effects have also a noticeable effect on quartet scattering
length, which otherwise is extremely stable under the exchange of the nuclear
forces. For the current nuclear force models there is a strong scatter of the
3H binding energy and the doublet scattering length values around an averaged
straight line (Phillips line). This allows to use doublet scattering length and
the 3H binding energy as independent low energy observables.Comment: 16 pages, 1 table, 4 ps figure
Low-temperature anomalous specific heat without tunneling modes: a simulation for a-Si with voids
Using empirical potential molecular dynamics we compute dynamical matrix
eigenvalues and eigenvectors for a 4096 atom model of amorphous silicon and a
set of models with voids of different size based on it. This information is
then employed to study the localization properties of the low-energy
vibrational states, calculate the specific heat C(T) and examine the
low-temperature properties of our models usually attributed to the presence of
tunneling states in amorphous silicon. The results of our calculations for C(T)
and "excess specific heat bulge" in the C(T)/T^3 vs. T graph for voidless a-Si
appear to be in good agreement with experiment; moreover our investigation
shows that the presence of localized low-energy excitations in the vibrational
spectrum of our models with voids strongly manifests itself as a sharp peak in
C(T)/T^3 dependence at T < 3K. To our knowledge this is the first numerical
simulation that provides adequate agreement with experiment for the very
low-temperature properties of specific heat in disordered systems within the
limits of harmonic approximation.Comment: 5 pages with 2 ps figures, submitted to PR
Recommended from our members
Regulation of the interplanetary magnetic flux
In this study we use a recently developed technique for measuring the 2-D magnetic flux in the ecliptic plane to examine (1) the long term variation of the magnetic flux in interplanetary space and (2) the apparent rate at which coronal mass ejections (CMEs) may be opening new flux from the Sun. Since there is a substantial variation ({approximately}50%) of the flux in the ecliptic plane over the solar cycle, we conclude that there must be some means whereby new flux can be opened from the Sun and previously open magnetic flux can be closed off. We briefly describe recently discovered coronal disconnections events which could serve to close off previously open magnetic flux. CMEs appear to retain at least partial magnetic connection to the Sun and hence open new flux, while disconnections appear to be likely signatures of the process that returns closed flux to the Sun; the combination of these processes could regulate the amount of open magnetic flux in interplanetary space. 6 refs., 3 figs
Bounded and unitary elements in pro-C^*-algebras
A pro-C^*-algebra is a (projective) limit of C^*-algebras in the category of
topological *-algebras. From the perspective of non-commutative geometry,
pro-C^*-algebras can be seen as non-commutative k-spaces. An element of a
pro-C^*-algebra is bounded if there is a uniform bound for the norm of its
images under any continuous *-homomorphism into a C^*-algebra. The *-subalgebra
consisting of the bounded elements turns out to be a C^*-algebra. In this
paper, we investigate pro-C^*-algebras from a categorical point of view. We
study the functor (-)_b that assigns to a pro-C^*-algebra the C^*-algebra of
its bounded elements, which is the dual of the Stone-\v{C}ech-compactification.
We show that (-)_b is a coreflector, and it preserves exact sequences. A
generalization of the Gelfand-duality for commutative unital pro-C^*-algebras
is also presented.Comment: v2 (accepted
Two-body correlations in Bose condensates
We formulate a method to study two-body correlations in a condensate of N
identical bosons. We use the adiabatic hyperspheric approach and assume a
Faddeev like decomposition of the wave function. We derive for a fixed
hyperradius an integro-differential equation for the angular eigenvalue and
wave function. We discuss properties of the solutions and illustrate with
numerical results. The interaction energy is for N~20 five times smaller than
that of the Gross-Pitaevskii equation
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