1,594 research outputs found
Toxoplasma gondii major surface antigen (SAG1): in vitro analysis of host cell binding
Previous studies have indicated that SAG1, the major surface molecule of the protozoan parasite Toxoplasma gondii, is an important attachment ligand for the host cell. However, the research data that supports this claim comes largely from studies investigating tachyzoite binding, and not SAG1 binding per se.
In this study we successfully developed an in vitro attachment assay to directly evaluate the mechanism of SAG1-host cell binding. Competition experiments were then performed using SAG1 that had been pre-treated with the neoglycoprotein BSA-glucosamide or with antibody. Soluble BSA-glucosamide blocked SAG1 attachment to MDBK cells in a dose-dependent manner, implying that SAG1 binding is mediated, in part, via attachment to host cell surface glucosamine. Interestingly, pre-incubation of SAG1 in polyclonal sera from chronically infected mice failed to block binding. This challenges the assumption that anti-SAG1 antibodies block parasite attachment through the masking of SAG1 host cell binding domains. Taken together, this evidence presents new strategies for understanding SAG1-mediated attachment
Powerful proteins from polyp possessing predators
Cnidarians are soft bodied animals possessing complex venom systems which have evolved to allow for the capture of arthropod and vertebrate prey, as well as to defend themselves against such predators. The effects of these venoms on humans, as a result of envenomation, has been studied for many decades, whereas the possibility of using these proteins to fight human disease is in its infancy. Drug discovery utilisation of Cnidarian venoms has been hampered by availability of animals and suitable extraction techniques that allow for study of such protein toxins. Studies of toxins that have been suitably purified for drug discovery have, by in large, only investigated target engagement and negated to investigate other drug like properties such as absorption, dispersion, metabolism, and excretion (ADME). This chapter will review the sourcing of Cnidaria for drug discovery, extraction of venom components, actions of venoms on drug relevant targets and their suitability as drug like molecules
Temporal and spectral characteristics of a marine piling operation in shallow water
Analysis of the underwater radiate acoustic characteristics for marine piling operations for two pile diameters, 2m and 4.74m, in a relatively shallow water site are presented. Measurements of the entire piling sequence for several piles were conducted at ranges from 10m to 22km for piles in 10-20 m water depth. Variations in the temporal and spectral characteristics of radiated energy are analysed in context of pile size, range from source, hammer energy used and pile penetration depth. Analysis of hammer energy used shows a strong interdependence between mechanical strike ‘hammer’ energy and underwater radiated acoustic energy. This process appears ‘coarsely’ linear for individual piling operations although considerable variation in overall gradient were observed between operations. For individual hammer energy step increases often the largest increases in radiated energy were observed at the initial hammer energy increase, with subsequent strikes at the same hammer energy resulting in a gradual reduction in radiated energy to a level 1-2 dB lower. These effects are potentially due to sediment compacting / relaxation effects relating to the time and number of strikes and penetration. Temporal and spectral variations in radiated energy due to pile penetration are also examined for fixed hammer energy and range. Simultaneous recordings of radiated energy made at increasing distances from the pile showed evidence of temporal and spectral dispersion effects consistent with relatively shallow water propagation. Correlation of received levels at various ranges in differing seabed topographies were made suggesting complex shallow water modal propagation dependant on both the source and environment characteristics including seabed topography, sediment type and water column acoustic properties
Abundance and evolution of galaxy clusters in cosmological models with massive neutrino
The time evolution of the number density of galaxy clusters and their mass
and temperature functions are used to constrain cosmological parameters in the
spatially flat dark matter models containing a fraction of hot particles
(massive neutrino) additional to cold and baryonic matter. We test the modified
MDM models with cosmic gravitational waves and show that they neither pass the
cluster evolution test nor reproduce the observed height of the first acoustic
peak in spectrum, and therefore should be ruled out. The models
with a non-zero cosmological constant are in better agreement with
observations. We estimate the free cosmological parameters in MDM with
a negligible abundance of gravitational waves, and find that within the
parameter ranges , , (i) the value of
is strongly affected by a small fraction of hot dark matter,
:
( CL), and (ii) the redshift evolution of galaxy clusters alone
reveals the following explicit correlation between and
: . The present accuracy of
observational data allows only to bound the fraction of hot matter, (the number of massive neutrino species remains undelimited, ).Comment: 9 pages, 7 figures, submitted in A&
Uniform random generation of large acyclic digraphs
Directed acyclic graphs are the basic representation of the structure
underlying Bayesian networks, which represent multivariate probability
distributions. In many practical applications, such as the reverse engineering
of gene regulatory networks, not only the estimation of model parameters but
the reconstruction of the structure itself is of great interest. As well as for
the assessment of different structure learning algorithms in simulation
studies, a uniform sample from the space of directed acyclic graphs is required
to evaluate the prevalence of certain structural features. Here we analyse how
to sample acyclic digraphs uniformly at random through recursive enumeration,
an approach previously thought too computationally involved. Based on
complexity considerations, we discuss in particular how the enumeration
directly provides an exact method, which avoids the convergence issues of the
alternative Markov chain methods and is actually computationally much faster.
The limiting behaviour of the distribution of acyclic digraphs then allows us
to sample arbitrarily large graphs. Building on the ideas of recursive
enumeration based sampling we also introduce a novel hybrid Markov chain with
much faster convergence than current alternatives while still being easy to
adapt to various restrictions. Finally we discuss how to include such
restrictions in the combinatorial enumeration and the new hybrid Markov chain
method for efficient uniform sampling of the corresponding graphs.Comment: 15 pages, 2 figures. To appear in Statistics and Computin
Weak localization of Dirac fermions in graphene beyond the diffusion regime
We develop a microscopic theory of the weak localization of two-dimensional
massless Dirac fermions which is valid in the whole range of classically weak
magnetic fields. The theory is applied to calculate magnetoresistance caused by
the weak localization in graphene and conducting surfaces of bulk topological
insulators.Comment: 5 pages, 2 figure
Vlasov-Maxwell, self-consistent electromagnetic wave emission simulations in the solar corona
1.5D Vlasov-Maxwell simulations are employed to model electromagnetic
emission generation in a fully self-consistent plasma kinetic model for the
first time in the solar physics context. The simulations mimic the plasma
emission mechanism and Larmor drift instability in a plasma thread that
connects the Sun to Earth with the spatial scales compressed appropriately. The
effects of spatial density gradients on the generation of electromagnetic
radiation are investigated. It is shown that 1.5D inhomogeneous plasma with a
uniform background magnetic field directed transverse to the density gradient
is aperiodically unstable to Larmor-drift instability. The latter results in a
novel effect of generation of electromagnetic emission at plasma frequency.
When density gradient is removed (i.e. when plasma becomes stable to
Larmor-drift instability) and a density, super-thermal, hot beam is
injected along the domain, in the direction perpendicular to the magnetic
field, plasma emission mechanism generates non-escaping Langmuir type
oscillations which in turn generate escaping electromagnetic radiation. It is
found that in the spatial location where the beam is injected, the standing
waves, oscillating at the plasma frequency, are excited. These can be used to
interpret the horizontal strips observed in some dynamical spectra. Quasilinear
theory predictions: (i) the electron free streaming and (ii) the beam long
relaxation time, in accord with the analytic expressions, are corroborated via
direct, fully-kinetic simulation. Finally, the interplay of Larmor-drift
instability and plasma emission mechanism is studied by considering
electron beam in the Larmor-drift unstable (inhomogeneous) plasma.
http://www.maths.qmul.ac.uk/~tsiklauri/movie1.mpg *
http://www.maths.qmul.ac.uk/~tsiklauri/movie2.mpg *
http://www.maths.qmul.ac.uk/~tsiklauri/movie3.mpgComment: Solar Physics (in press, the final, accepted version
A methodology for the measurement of radiated noise from marine piling
This paper describes a methodology that has been developed for measuring marine piling noise, which is designed to record the temporal, spatial and spectral characteristics of the radiated sound field. Results are presented for measurements of two pile diameters, 2m and 4.74m, in a shallow water site off the east coast of the UK. Measurements of the entire piling sequence for several piles were conducted at ranges from 10 m to 22 km for piles in 10-20 m water depth. To assess variations in the temporal, spatial and spectral characteristics, a number of recording systems were simultaneously deployed at various ranges and depths, allowing the full piling sequence to be measured. This allowed assessment of source level variation at fixed locations, and the effect of propagation within the water column
Microwave pyrolysis of Laminaria digitata to produce unique seaweed-derived bio-oils
Microwave pyrolysis has become an attractive form of processing technology to generate bio-oil, bio-char and syngas from different biomass feedstocks. In this study, microwave pyrolysis was performed on the UK native seaweed Laminaria digitata and its extract residue from a bio-refinery process. Pyrolysis of these two feedstocks was successfully achieved without the requirement of microwave susceptors, as pelletizing the biomass was sufficient to allow microwave pyrolysis to occur. It was found that average energy requirements as low as 1.84–2.83 kJ g−1 were required to pyrolyse 55–70% of both feedstocks and bio-oil yields of 5–8% and 10–14% for native and extraction residue L. digitata were produced, respectively. Maximum microwave pyrolysis processing times were in the order of 200 s. The bio-oil generated from both feedstocks contained no phenolic based compounds, but a greater number of nitrogen-containing compounds and compounds derived from macroalgal polysaccharides. Yields of certain compounds differed in bio-oils generated from the two L. digitata feedstocks, however it was observed that specific energy did not have a direct influence on bio-oil compound yield. Furthermore, the identification of a particular nitrogen-containing compound L-Proline, 1-methyl-5-oxo-, methylester is thought to be a unique product of microwave pyrolysis when carbon-based additives are avoided
Nuttier Bubbles
We construct new explicit solutions of general relativity from double
analytic continuations of Taub-NUT spacetimes. This generalizes previous
studies of 4-dimensional nutty bubbles. One 5-dimensional locally
asymptotically AdS solution in particular has a special conformal boundary
structure of . We compute its boundary stress tensor and
relate it to the properties of the dual field theory. Interestingly enough, we
also find consistent 6-dimensional bubble solutions that have only one timelike
direction. The existence of such spacetimes with non-trivial topology is
closely related to the existence of the Taub-NUT(-AdS) solutions with more than
one NUT charge. Finally, we begin an investigation of generating new solutions
from Taub-NUT spacetimes and nuttier bubbles. Using the so-called Hopf duality,
we provide new explicit time-dependent backgrounds in six dimensions.Comment: 32 pages, 1 figure; v.3. typos corrected. Matches the published
versio
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