8,348 research outputs found
Interactions between male guppies facilitates the transmission of the mongenean ectoparasite Gyrodactylus turnbulli
In a previous study we found that female guppies shoaled more than males and that there was greater transmission of the ectoparasite Gyrodactylus turnbulli between females. Here, to test for a possible sex bias in parasite transmission, we conducted a similar experiment on single sex shoals of male and female guppies, observing host behaviour before and after the introduction of an infected shoal mate. The initial parasite burden was considerably lower in the present experiment (30 worms versus >100 worms previously) and we used a different stock of ornamental guppies (Green Cobra variety versus a Tuxedo hybrid previously). Contrary to our previous finding, males aggregated significantly more than females. Males performed ‘sigmoid’ displays towards each other, a courtship behaviour that is more generally directed towards females. Due to the high rate of male–male interactions, parasite transmission was 10 times higher between males than between females. Furthermore, shoaling intensity was highest for the most parasitised fish indicating that these infected fish were not avoided by non-parasitised conspecifics. These studies show that certain social behaviours including shoaling and courtship displays, appear to facilitate the transmission of gyrodactylid parasites
Duality between quantum symmetric algebras
Using certain pairings of couples, we obtain a large class of two-sided
non-degenerated graded Hopf pairings for quantum symmetric algebras.Comment: 15 pages. Letters in Math. Phy., to appear soo
Polariton Dispersion Law in Periodic Bragg and Near-Bragg Multiple Quantum Well Structures
The structure of polariton spectrum is analyzed for periodic multiple quantum
well structures with periods at or close to Bragg resonance condition at the
wavelength of the exciton resonance. The results obtained used to discuss
recent reflection and luminescent experiments by M. H\"{u}bner et al [Phys.
Rev. Lett. {\bf 83}, 2841 (1999)] carried out with long multiple quantum well
structures. It is argued that the discussion of quantum well structures with
large number of wells is more appropriate in terms of normal modes of infinite
periodic structures rather then in terms of super- and sub- radiant modes.Comment: replaced with a new version, an error in one of the equations is
correcte
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Preterm nutritional intake and MRI phenotype at term age: a prospective observational study
Objective:
To describe (1) the relationship between nutrition and the preterm-at-term infant phenotype, (2) phenotypic differences between preterm-at-term infants and healthy term born infants and (3) relationships between somatic and brain MRI outcomes.
Design:
Prospective observational study.
Setting:
UK tertiary neonatal unit.
Participants:
Preterm infants (<32 weeks gestation) (n=22) and healthy term infants (n=39)
Main outcome measures:
Preterm nutrient intake; total and regional adipose tissue (AT) depot volumes; brain volume and proximal cerebral arterial vessel tortuosity (CAVT) in preterm infants and in term infants.
Results:
Preterm nutrition was deficient in protein and high in carbohydrate and fat. Preterm nutrition was not related to AT volumes, brain volume or proximal CAVT score; a positive association was noted between human milk intake and proximal CAVT score (r=0.44, p=0.05). In comparison to term infants, preterm infants had increased total adiposity, comparable brain volumes and reduced proximal CAVT scores. There was a significant negative correlation between deep subcutaneous abdominal AT volume and brain volume in preterm infants (r=−0.58, p=0.01).
Conclusions:
Though there are significant phenotypic differences between preterm infants at term and term infants, preterm macronutrient intake does not appear to be a determinant. Our preliminary data suggest that (1) human milk may exert a beneficial effect on cerebral arterial vessel tortuosity and (2) there is a negative correlation between adiposity and brain volume in preterm infants at term. Further work is warranted to see if our findings can be replicated and to understand the causal mechanisms
Baryonic contributions to the dilepton spectrum of nucleon-nucleon collisions
We study the production of dileptons in relativistic nucleon-nucleon
collisions. Additionally to the traditional dilepton production channels
(vector meson decays, meson and Delta(1232) Dalitz decays) we included in our
model as new dilepton sources the Dalitz decay of higher unflavored baryon
resonances with spin<=5/2 and mass<=2.25 GeV/c^2. The contributions of these
new channels are estimated using experimental information about the Ngamma
decays of the resonances and have large uncertainties. The obtained dilepton
spectra are compared to the experimental data by the DLS collaboration.
Predictions for the HADES detector (SIS, GSI) are also discussed. In spite of
the large uncertainties of the higher resonance Dalitz decay contributions we
are able to draw the conclusion that these contributions are negligible
compared to the other dilepton sources and do not influence the detectability
of the phi and omega vector meson peaks.Comment: 9 pages, 4 figures, version accepted for publication in Phys. Rev.
On the B and J/Psi Cross Section Measurements at Ua1 and CDF
We analise the implications of the measurement of and inclusive
\pt\ distributions performed in collisions by the UA1 and CDF
experiments.Comment: 16 pages + 8 topdrawer figs included at the end, Latex, IFUP-TH 2/9
Continuation-minimization methods for stability problems
AbstractWe study the solution branches of stable and unstable bifurcations in certain semilinear elliptic eigenvalue problems with Dirichlet boundary conditions. A secant predictor-line search backtrack corrector continuation method is described to trace the solution curves numerically. Sample numerical results with computer graphic output are reported
Occupational cycling is a risk factor for erectile dysfunction in east Africa
Background: The association between bicycle riding and erectile dysfunction is controversial and hypothesised to be caused by pressure from the bicycle seat on the pudendal nerve.Objectives: To evaluate erectile function in East African occupational cyclists (OC) using International Index of Erectile Function questionnaire in comparison to non-cyclists .Design: A cross sectional study.Settings: The environment of Eldoret town in Uasin Gishu county of Kenya.Subjects: Male occupational cyclists aged 18-65 yearsResults: Total International Index of Erectile Function scores were significantly lower in occupational cyclists versus non-occupational cyclists (19.8±3.4 vs. 21.6±2.2, P<0.05). Furthermore, Erectile Dysfunction (ED) rates were higher in the cyclist group (76% vs. 31%, p < 0.0001). Logistic regression indicated that the odds of reporting Erectile Dysfunction were 9.1 (95% CI: 5.4-15.5) times higher in cyclists compared to noncyclists controls.Conclusion: In East Africa, occupational cycling is associated with lower International Index of Erectile Function scores and higher rates of Erectile Dysfunction
Magnetically levitated mesenchymal stem cell spheroids cultured with a collagen gel maintain phenotype and quiescence
Multicellular spheroids are an established system for three-dimensional cell culture. Spheroids are typically generated
using hanging drop or non-adherent culture; however, an emerging technique is to use magnetic levitation. Herein,
mesenchymal stem cell spheroids were generated using magnetic nanoparticles and subsequently cultured within a type
I collagen gel, with a view towards developing a bone marrow niche environment. Cells were loaded with magnetic
nanoparticles, and suspended beneath an external magnet, inducing self-assembly of multicellular spheroids. Cells in
spheroids were viable and compared to corresponding monolayer controls, maintained stem cell phenotype and were
quiescent. Interestingly, core spheroid necrosis was not observed, even with increasing spheroid size, in contrast to
other commonly used spheroid systems. This mesenchymal stem cell spheroid culture presents a potential platform for
modelling in vitro bone marrow stem cell niches, elucidating interactions between cells, as well as a useful model for
drug delivery studies
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