7,848 research outputs found
Antigenic variation in the African trypanosome: molecular mechanisms and phenotypic complexity
Antigenic variation is an immune evasion strategy that has evolved in viral, bacterial and protistan pathogens. In the African trypanosome this involves stochastic switches in the composition of a variant surface glycoprotein (VSG) coat, using a massive archive of silent VSG genes to change the identity of the single VSG expressed at a time. VSG switching is driven primarily by recombination reactions that move silent VSGs into specialized expression sites, though transcription-based switching can also occur. Here we discuss what is being revealed about the machinery that underlies these switching mechanisms, including what parallels can be drawn with other pathogens. In addition, we discuss how such switching reactions act in a hierarchy and contribute to pathogen survival in the face of immune attack, including the establishment and maintenance of chronic infections, leading to host-host transmission
Genetic typing of Candida albicans strains isolated from the oral cavity of patients with denture stomatitis before and after itraconazole therapy
This study determined, by molecular typing of C. albicans species isolated from denture stomatitis patients with a mycological relapse six
months after successful itraconazole therapy, whether there had been recurrence of infection with the same strain(s), selection of particular
strains or infection with new strains of C. albicans. Forty patients with long-standing Candida-associated denture stomatitis were assigned
either cyclodextrin itraconazole solution or itraconazole capsules (100mg b.d. for 15 days). Palatal erythema was measured and imprint
cultures undertaken at baseline and at 15 days, four weeks and six months after treatment commenced. Yeast isolates were formally
identified and chromosomal DNA was extracted from pairs of isolates from those patients with C. albicans present at baseline and six
months after treatment commenced. Southern blotting of EcoRI-digested chromosomal DNA was performed using the C. albicans-specific
27A repetitive element as a probe. Eighteen of 36 patients were infected with C. albicans at baseline and six months after treatment
commenced. Overall, 13 genetically different strains of C. albicans were found. However, in 17 of 18 patients, the C. albicans strains
isolated prior to itraconazole therapy and six months later were the same. Thus recurrence of denture stomatitis in these individuals was
due to re-colonisation by the original strain, rather than re-infection with a different strain. Key words: Genotyping, C. albicans, denture
stomatitis
On the Reliability of the Langevin Pertubative Solution in Stochastic Inflation
A method to estimate the reliability of a perturbative expansion of the
stochastic inflationary Langevin equation is presented and discussed. The
method is applied to various inflationary scenarios, as large field, small
field and running mass models. It is demonstrated that the perturbative
approach is more reliable than could be naively suspected and, in general, only
breaks down at the very end of inflation.Comment: 7 pages, 3 figure
What is the Shell Around R Coronae Borealis?
The hydrogen-deficient, carbon-rich R Coronae Borealis (RCB) stars are known
for being prolific producers of dust which causes their large iconic declines
in brightness. Several RCB stars, including R CrB, itself, have large extended
dust shells seen in the far-infrared. The origin of these shells is uncertain
but they may give us clues to the evolution of the RCB stars. The shells could
form in three possible ways. 1) they are fossil Planetary Nebula (PN) shells,
which would exist if RCB stars are the result of a final, helium-shell flash,
2) they are material left over from a white-dwarf merger event which formed the
RCB stars, or 3) they are material lost from the star during the RCB phase.
Arecibo 21-cm observations establish an upper limit on the column density of H
I in the R CrB shell implying a maximum shell mass of 0.3
M. A low-mass fossil PN shell is still a possible source of the shell
although it may not contain enough dust. The mass of gas lost during a
white-dwarf merger event will not condense enough dust to produce the observed
shell, assuming a reasonable gas-to-dust ratio. The third scenario where the
shell around R CrB has been produced during the star's RCB phase seems most
likely to produce the observed mass of dust and the observed size of the shell.
But this means that R CrB has been in its RCB phase for 10 yr.Comment: 5 pages, 2 figures, 2 tables, Accepted for publication in A
R\'enyi Entropies from Random Quenches in Atomic Hubbard and Spin Models
We present a scheme for measuring R\'enyi entropies in generic atomic Hubbard
and spin models using single copies of a quantum state and for partitions in
arbitrary spatial dimension. Our approach is based on the generation of random
unitaries from random quenches, implemented using engineered time-dependent
disorder potentials, and standard projective measurements, as realized by
quantum gas microscopes. By analyzing the properties of the generated unitaries
and the role of statistical errors, with respect to the size of the partition,
we show that the protocol can be realized in exisiting AMO quantum simulators,
and used to measure for instance area law scaling of entanglement in
two-dimensional spin models or the entanglement growth in many-body localized
systems.Comment: 5+9 page
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