106 research outputs found
The worm has turned: Behavioural drivers of reproductive isolation between cryptic lineages
AbstractBehavioural processes such as species recognition and mate attraction signals enforce and reinforce the reproductive isolation required for speciation. The earthworm Lumbricus rubellus in the UK is deeply differentiated into two major genetic lineages, ‘A’ and ‘B’. These are often sympatric at certain sites, but it is not known whether they are to some extent reproductively isolated. Behavioural tests were performed, in which individually genotyped worms were able to choose between soils previously worked either by genetically similar or dissimilar individuals (N = 45). We found that individuals (75%) were significantly (P < 0.05) more likely to orientate towards the soil conditioned by worms of their own lineage. Further testing involved a choice design based on filter papers wetted with water extracts of soils worked by a different genotype on each side (N = 18) or extracts from worked soil vs. un-worked control soil (N = 10). Again, earthworms orientated towards the extract from their kindred genotype (P < 0.05). These findings indicate that genotype-specific water-soluble chemicals are released by L. rubellus; furthermore, they are behaviour-modifying, and play a role in reproductive isolation between sympatric earthworm lineages of cryptic sibling species, through pre-copulatory assortative mate choice
Progress on a gas-accepting ion source for continuous-flow accelerator mass spectrometry
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 259 (2007): 83-87, doi:10.1016/j.nimb.2007.01.189.A gas-accepting microwave-plasma ion source is being developed for continuous-flow Accelerator Mass
Spectrometry (AMS). Characteristics of the ion source will be presented. Schemes for connecting a gas or liquid
chromatograph to the ion source will also be discussed
Detailed electronic structure studies on superconducting MgB and related compounds
In order to understand the unexpected superconducting behavior of MgB
compound we have made electronic structure calculations for MgB and closely
related systems. Our calculated Debye temperature from the elastic properties
indicate that the average phonon frequency is very large in MgB compared
with other superconducting intermetallics and the exceptionally high in
this material can be explained through BCS mechanism only if phonon softening
occurs or the phonon modes are highly anisotropic. We identified a
doubly-degenerate quasi-two dimensional key-energy band in the vicinity of
along -A direction of BZ which play an important role in
deciding the superconducting behavior of this material. Based on this result,
we have searched for similar kinds of electronic feature in a series of
isoelectronic compounds such as BeB, CaB, SrB, LiBC and
MgBC and found that MgBC is one potential material from the
superconductivity point of view. There are contradictory experimental results
regarding the anisotropy in the elastic properties of MgB ranging from
isotropic, moderately anisotropic to highly anisotropic. In order to settle
this issue we have calculated the single crystal elastic constants for MgB
by the accurate full-potential method and derived the directional dependent
linear compressibility, Young's modulus, shear modulus and relevant elastic
properties. We have observed large anisotropy in the elastic properties. Our
calculated polarized optical dielectric tensor shows highly anisotropic
behavior even though it possesses isotropic transport property. MgB
possesses a mixed bonding character and this has been verified from density of
states, charge density and crystal orbital Hamiltonian population analyses
The black-hole masses of Seyfert galaxies and quasars
The central black-hole masses of a sample of 30 luminous quasars are
estimated using H-beta FWHM measurements from a combination of new and
previously-published nuclear spectra. The quasar black-hole mass estimates are
combined with reverberation-mapping measurements for a sample of Seyfert
galaxies (Wandel 1999) in order to study AGN black-hole masses over a wide
range in nuclear luminosity. It is found that black-hole mass and bulge
luminosity are well correlated and follow a relation consistent with that
expected if black-hole and bulge mass are directly proportional. Contrary to
the results of Wandel (1999) no evidence is found that Seyfert galaxies follow
a different Mblack-Mbulge relation to quasars. However, the black-hole mass
distributions of the radio-loud and radio-quiet quasar sub-samples are found to
be significantly different, with the median black-hole mass of the radio-loud
quasars a factor of three larger than their radio-quiet counterparts. Finally,
utilizing the elliptical galaxy fundamental plane to provide stellar velocity
dispersion estimates, a comparison is performed between the virial H-beta
black-hole mass estimates and those of the Mblack-sigma correlations of
Gebhardt et al. (2000a) and Merritt & Ferrarese (2000). With the disc-like
geometry of the broad-line region adopted in this paper, the virial H-beta
black-hole masses indicate that the correct normalization of the black-hole vs.
bulge mass relation is Mblack=0.0025Mbulge, while the standard assumption of
purely random broad-line velocities leads to Mblack=0.0008Mbulge. The
normalization of Mblack=0.0025Mbulge provided by the disc model is in
remarkably good agreement with that inferred for our quasar sample using the
(completely independent) Mblack-sigma correlations.Comment: 10 pages, 6 figures, accepted for publication in MNRA
Photon-photon absorption above a molecular cloud torus in blazars
Gamma rays have been observed from two blazars at TeV energies. One of these,
Markarian 421, has been observed also at GeV energies and has roughly equal
luminosity per decade at GeV and TeV energies. Photon-photon pair production on
the infrared background radiation is expected to prevent observation above
about 1 TeV. However, the infrared background is not well known and it may be
possible to observe the nearest blazars up to energies somewhat below about 100
TeV where absorption on the cosmic microwave background will give a sharp
cut-off.
Blazars are commonly believed to correspond to low power radio galaxies, seen
down along a relativistic jet; as such they are all expected to have the
nuclear activity encircled by a dusty molecular torus, which subtends an angle
of 90 degrees or more in width as seen from the central source. Photon-photon
pair production can also take place on the infrared radiation produced at the
AGN by this molecular torus and surrounding outer disk. We calculate the
optical depth for escaping gamma-rays produced near the central black hole and
at various points along the jet axis for the case of blazars where the
radiation is observed in a direction closely aligned with the jet.
We find that the TeV emission site must be well above the top of the torus.
For example, if the torus has an inner radius of 0.1 pc and an outer radius of
0.2 pc, then the emission site in Mrk 421 would have be at least 0.25 pc above
the upper surface of the torus, and if Mrk 421 is observed above 50 TeV in the
future, the emission site would have to be at least 0.5 pc above the upper
surface. This has important implications for models of gamma-ray emission in
active galactic nuclei.Comment: 18 pages, 6 figures, accepted for publication in Astroparticle
Physics. Revised version contains 2 additional figures and more detailed
discussio
Impact of Chlamydia trachomatis in the reproductive setting: British Fertility Society Guidelines for practice
Chlamydia trachomatis infection of the genital tract is the most common sexually transmitted infection and has a world-wide distribution. The consequences of infection have an adverse effect on the reproductive health of women and are a common cause of infertility. Recent evidence also suggests an adverse effect on male reproduction. There is a need to standardise the approach in managing the impact of C. trachomatis infection on reproductive health. We have surveyed current UK practice towards screening and management of Chlamydia infections in the fertility setting. We found that at least 90% of clinicians surveyed offered screening. The literature on this topic was examined and revealed a paucity of solid evidence for estimating the risks of long-term reproductive sequelae following lower genital tract infection with C. trachomatis. The mechanism for the damage that occurs after Chlamydial infections is uncertain. However, instrumentation of the uterus in women with C. trachomatis infection is associated with a high risk of pelvic inflammatory disease, which can be prevented by appropriate antibiotic treatment and may prevent infected women from being at increased risk of the adverse sequelae, such as ectopic pregnancy and tubal factor infertility. Recommendations for practice have been proposed and the need for further studies is identified
Feint Lines: Notes on the Creation of a Skateboard Choreography
Magnetic fields on a range of scales play a large role in the ecosystems of
galaxies, both in the galactic disk and in the extended layers of gas away from
the plane. Observing magnetic field strength, structure and orientation is
complex, and necessarily indirect. Observational data of magnetic fields in the
halo of the Milky Way are scarce, and non-conclusive about the large-scale
structure of the field. In external galaxies, various large-scale
configurations of magnetic fields are measured, but many uncertainties about
exact configurations and their origin remain. There is a strong interaction
between magnetic fields and other components in the interstellar medium such as
ionized and neutral gas and cosmic rays. The energy densities of these
components are comparable on large scales, indicating that magnetic fields are
not passive tracers but that magnetic field feedback on the other interstellar
medium components needs to be taken into account.Comment: 13 pages, 7 figures. Accepted in Space Science Review
Formulation, stabilisation and encapsulation of bacteriophage for phage therapy
Against a backdrop of global antibiotic resistance and increasing awareness of the importance of the
human microbiota, there has been resurgent interest in the potential use of bacteriophages for
therapeutic purposes, known as phage therapy. A number of phage therapy phase I and II clinical
trials have concluded, and shown phages don’t present significant adverse safety concerns. These
clinical trials used simple phage suspensions without any formulation and phage stability was of
secondary concern. Phages have a limited stability in solution, and undergo a significant drop in
phage titre during processing and storage which is unacceptable if phages are to become regulated
pharmaceuticals, where stable dosage and well defined pharmacokinetics and pharmacodynamics
are de rigueur. Animal studies have shown that the efficacy of phage therapy outcomes depend on
the phage concentration (i.e. the dose) delivered at the site of infection, and their ability to target and
kill bacteria, arresting bacterial growth and clearing the infection. In addition, in vitro and animal
studies have shown the importance of using phage cocktails rather than single phage preparations to
achieve better therapy outcomes. The in vivo reduction of phage concentration due to interactions
with host antibodies or other clearance mechanisms may necessitate repeated dosing of phages, or
sustained release approaches. Modelling of phage-bacterium population dynamics reinforces these
points. Surprisingly little attention has been devoted to the effect of formulation on phage therapy
outcomes, given the need for phage cocktails, where each phage within a cocktail may require
significantly different formulation to retain a high enough infective dose.
This review firstly looks at the clinical needs and challenges (informed through a review of key animal
studies evaluating phage therapy) associated with treatment of acute and chronic infections and the
drivers for phage encapsulation. An important driver for formulation and encapsulation is shelf life and
storage of phage to ensure reproducible dosages. Other drivers include formulation of phage for
encapsulation in micro- and nanoparticles for effective delivery, encapsulation in stimuli responsive
systems for triggered controlled or sustained release at the targeted site of infection. Encapsulation of
phage (e.g. in liposomes) may also be used to increase the circulation time of phage for treating
systemic infections, for prophylactic treatment or to treat intracellular infections. We then proceed to
document approaches used in the published literature on the formulation and stabilisation of phage for
storage and encapsulation of bacteriophage in micro- and nanostructured materials using freeze
drying (lyophilization), spray drying, in emulsions e.g. ointments, polymeric microparticles,
nanoparticles and liposomes. As phage therapy moves forward towards Phase III clinical trials, the
review concludes by looking at promising new approaches for micro- and nanoencapsulation of
phages and how these may address gaps in the field
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease
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