Tunneling Rate for Superparamagnetic Particles by the Instanton Method

We derive the tunneling rate for paramagnetic molecules in the context of a collective spin model. By means of path integral methods an analytical expression is derived. Given the very large spins in question (s ~ 3000 hbar), the observation of magnetization changes due to pure unitary tunnel effects is unlikely.Comment: 16 pages, 2 figure

Analytic solutions and Singularity formation for the Peakon b--Family equations

Using the Abstract Cauchy-Kowalewski Theorem we prove that the $b$-family equation admits, locally in time, a unique analytic solution. Moreover, if the initial data is real analytic and it belongs to $H^s$ with $s > 3/2$, and the momentum density $u_0 - u_{0,{xx}}$ does not change sign, we prove that the solution stays analytic globally in time, for $b\geq 1$. Using pseudospectral numerical methods, we study, also, the singularity formation for the $b$-family equations with the singularity tracking method. This method allows us to follow the process of the singularity formation in the complex plane as the singularity approaches the real axis, estimating the rate of decay of the Fourier spectrum

A new window on Strange Quark Matter as the ground state of strongly interacting matter

If strange quark matter is the true ground state of matter, it must have lower energy than nuclear matter. Simultaneously, two-flavour quark matter must have higher energy than nuclear matter, for otherwise the latter would convert to the former. We show, using an effective chiral lagrangian, that the existence of a new lower energy ground state for two-flavour quark matter, the pion condensate, shrinks the window for strange quark matter to be the ground state of matter and sets new limits on the current strange quark mass

Will ocean acidification affect the early ontogeny of a tropical oviparous elasmobranch (Hemiscyllium ocellatum)?

Atmospheric CO2 is increasing due to anthropogenic causes. Approximately 30% of this CO2 is being absorbed by the oceans and is causing ocean acidification (OA). The effects of OA on calcifying organisms are starting to be understood, but less is known about the effects on non-calcifying organisms, notably elasmobranchs. One of the few elasmobranch species that has been studied with respect to OA is the epaulette shark, Hemiscyllium ocellatum. Mature epaulette sharks can physiologically and behaviourally tolerate prolonged exposure to elevated CO2, and this is thought to be because they are routinely exposed to diurnal decreases in O2 and probably concomitant increases in CO2 in their coral reef habitats. It follows that H. ocellatum embryos, while developing in ovo on the reefs, would have to be equally if not more tolerant than adults because they would not be able to escape such conditions. Epaulette shark eggs were exposed to either present-day control conditions (420 µatm) or elevated CO2 (945 µatm) and observed every 3 days from 10 days post-fertilization until 30 days post-hatching. Growth (in square centimetres per day), yolk usage (as a percentage), tail oscillations (per minute), gill movements (per minute) and survival were not significantly different in embryos reared in control conditions when compared with those reared in elevated CO2 conditions. Overall, these findings emphasize the importance of investigating early life-history stages, as the consequences are expected to transfer not only to the success of an individual but also to populations and their distribution patterns

Cholinergic efferent synaptic transmission regulates the maturation of auditory hair cell ribbon synapses.

Spontaneous electrical activity generated by developing sensory cells and neurons is crucial for the maturation of neural circuits. The full maturation of mammalian auditory inner hair cells (IHCs) depends on patterns of spontaneous action potentials during a 'critical period' of development. The intrinsic spiking activity of IHCs can be modulated by inhibitory input from cholinergic efferent fibres descending from the brainstem, which transiently innervate immature IHCs. However, it remains unknown whether this transient efferent input to developing IHCs is required for their functional maturation. We used a mouse model that lacks the α9-nicotinic acetylcholine receptor subunit (α9nAChR) in IHCs and another lacking synaptotagmin-2 in the efferent terminals to remove or reduce efferent input to IHCs, respectively. We found that the efferent system is required for the developmental linearization of the Ca(2+)-sensitivity of vesicle fusion at IHC ribbon synapses, without affecting their general cell development. This provides the first direct evidence that the efferent system, by modulating IHC electrical activity, is required for the maturation of the IHC synaptic machinery. The central control of sensory cell development is unique among sensory systems

Missed opportunities in full immunization coverage:findings from low- and lower-middle-income countries

Background: An estimated 23 million infants are still not being benefitted from routine immunization services. We assessed how many children failed to be fully immunized even though they or their mothers were in contact with health services to receive other interventions. Design: Fourteen countries with Demographic and Health Surveys and Multiple Indicator Cluster Surveys carried out after 2000 and with coverage for DPT (Diphtheria-tetanus-pertussis) vaccine below 70% were selected. We defined full immunization coverage (FIC) as having received one dose of BCG (bacille Calmette-Guérin), one dose of measles, three doses of polio, and three doses of DPT vaccines. We tabulated FIC against: antenatal care (ANC), skilled birth attendance (SBA), postnatal care for the mother (PNC), vitamin A supplementation (VitA) for the child, and sleeping under an insecticide-treated bed-net (ITN). Missed opportunities were defined as the percentage of children who failed to be fully immunized among those receiving one or more other interventions. Results: Children who received other health interventions were also more likely to be fully immunized. In nearly all countries, FIC was lowest among children born to mothers who failed to attend ANC, and highest when the mother had four or more ANC visits Côte d'Ivoire presented the largest difference in FIC: 54 percentage points (pp) between having four or more ANC visits and lack of ANC. SBA was also related with higher FIC. For instance, the coverage in children without SBA was 36 pp lower than for those with SBA in Nigeria. The largest absolute difference on FIC in relation to PNC was observed for Ethiopia: 31 pp between those without and with PNC. FIC was also positively related with having received VitA. The largest absolute difference was observed in DR Congo: 41 pp. The differences in FIC among whether or not children slept under ITN were much smaller than for other interventions. Haiti presented the largest absolute difference: 16 pp. Conclusions: Our results show the need to develop and implement strategies to vaccinate all children who contact health services in order to receive other interventions

Pathophysiological changes in inner hair cell ribbon synapses in the ageing mammalian cochlea

Mammalian cochlear inner hair cells (IHCs) are specialized sensory receptors able to provide dynamic coding of sound signals. This ability is largely conferred by their ribbon synapses, which tether a large number of vesicles at the IHC's presynaptic active zones, allowing high rates of sustained synaptic transmission onto the afferent fibres. How the physiological and morphological properties of ribbon synapses change with age remains largely unknown. Here, we have investigated the biophysical and morphological properties of IHC ribbon synapses in the ageing cochlea (9–12 kHz region) of four mouse strains commonly used in hearing research: early‐onset progressive hearing loss (C57BL/6J and C57BL/6NTac) and ‘good hearing’ strains (C57BL/6NTacCdh23+ and C3H/HeJ). We found that with age, both modiolar and pillar sides of the IHC exhibited a loss of ribbons, but there was an increased volume of those that remained. These morphological changes, which only occurred after 6 months of age, were correlated with the level of hearing loss in the different mouse strains, being most severe for C57BL/6NTac and C57BL/6J, less so for C57BL/6NTacCdh23+ and absent for C3H/HeJ strains. Despite the age‐related reduction in ribbon number in three of the four strains, the size and kinetics of Ca2+‐dependent exocytosis, as well as the replenishment of synaptic vesicles, in IHCs was not affected. The degree of vesicle release at the fewer, but larger, individual remaining ribbon synapses colocalized with the post‐synaptic afferent terminals is likely to increase, indicating the presence of a previously unknown degree of functional compensation in the ageing mouse cochlea