The orexins and their involvement in the modulation of trigeminovascular nociceptive transmission

Migraine is a common and disabling condition that affects up to 15% of the population. This thesis sought to explore a possible role of the orexins in migraine by investigating aspects of their effect on trigeminovascular physiology. The orexins are two neuropeptides synthesised in the lateral and posterior hypothalamic nuclei that have recently been implicated in the modulation of nociceptive processing. To investigate a possible role of the orexins in the pathophysiology of migraine, different animal models of trigeminovascular activation were used to identify possible modulatory functions. Intravital microscopy uses dilation of dural blood vessel as a measure of trigeminal nerve activation, and thus compounds inhibiting the vasodilator response have the potential to inhibit trigeminovascular nociceptive transmission. Orexin A, but not B was able to significantly inhibit the observed dilation, an effect reversed by the selective orexin 1 (OXi) receptor antagonist SB-334867. Central modulatory roles of the orexins were investigated using electrophysiological methods. Orexin A and B and SB-334867 were given intravenously, or microinjected into the ventrolateral PAG (vlPAG) of the anaesthetised rat, and the responses of trigeminocervical complex (TCC) neurons to a variety of stimuli examined. Orexin A inhibited trigeminal neurons in the TCC when given intravenously or microinjected into the vlPAG, via activation of the OXi receptor. Orexin B demonstrated a differential effect, resulting in a facilitation of trigeminal neuronal firing when microinjected into the vlPAG. The orexinergic system was also investigated in the feline model of trigeminovascular activation via stimulation of the SSS. Double-labelled immunohistochemistry for Fos and orexin A or B was utilised to identify orexinergic neurons that are activated in the hypothalamus in response to trigeminovascular activation. A subpopulation of orexin synthesising neurons were shown to be activated in response to SSS stimulation, demonstrating that either efferent or afferent nociceptive transmission from the hypothalamus may involve orexinergic systems

Numerical Simulations of Melt-Driven Double-Diffusive Fluxes in a Turbulent Boundary Layer beneath an Ice Shelf

AbstractThe transport of heat and salt through turbulent ice shelf–ocean boundary layers is a large source of uncertainty within ocean models of ice shelf cavities. This study uses small-scale, high-resolution, 3D numerical simulations to model an idealized boundary layer beneath a melting ice shelf to investigate the influence of ambient turbulence on double-diffusive convection (i.e., convection driven by the difference in diffusivities between salinity and temperature). Isotropic turbulence is forced throughout the simulations and the temperature and salinity are initialized with homogeneous values similar to observations. The initial temperature and the strength of forced turbulence are varied as controlling parameters within an oceanographically relevant parameter space. Two contrasting regimes are identified. In one regime double-diffusive convection dominates, and in the other convection is inhibited by the forced turbulence. The convective regime occurs for high temperatures and low turbulence levels, where it is long lived and affects the flow, melt rate, and melt pattern. A criterion for identifying convection in terms of the temperature and salinity profiles, and the turbulent dissipation rate, is proposed. This criterion may be applied to observations and theoretical models to quantify the effect of double-diffusive convection on ice shelf melt rates.</jats:p

Permeability measurements using oscillatory flows

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. Abstract: We describe a versatile apparatus for measuring the permeability of porous materials using oscillatory flows. The permeabilities are measured by an original spectral analysis of the pressure and fluid-displacement signals. The measurements are shown to be in very good agreement with classical drainage experiments performed on the same device. Our apparatus and methodology will be useful if small fluid displacements are required, for example in reactive porous media. Graphic abstract: [Figure not available: see fulltext.].Royal Society University Research Fellowship British Antartic Survey Foundation Isaac Newton Trust

Modeling ice-ocean interaction in ice-shelf crevasses

Ocean freezing within ice-shelf basal crevasses could potentially act as a stabilizing influence on ice shelves; however, ice-ocean interaction and ocean dynamics within these crevasses are as yet poorly understood. To this end, an idealized 2-D model of an ice-shelf basal crevasse has been developed using Fluidity, a finite-element ocean model using an unstructured mesh. A simple model of frazil ice formation and deposition has been incorporated into Fluidity to better represent the freezing process. Model results show two different flow regimes, dependent on the amount of freezing in the crevasse: one driven by freezing at the top of the crevasse and the other by the ingress of meltwater from outside the crevasse. In the first, freezing at the top of the crevasse leads to the formation of an unstable overturning circulation due to the rejection of dense, salty water. In the second, a buoyant layer is formed along the sides and roof of the crevasse, stratifying the water column. Frazil ice precipitation is found to be the dominant freezing process at the top of the basal crevasse in the freeze-driven case, with direct freezing being dominant in the melt-driven case. In both cases, melting occurs lower down on the walls of the crevasse due to the strong overturning circulation. The freezing in ice-shelf crevasses and rifts is found to be highly dependent upon ocean temperature, providing a stabilizing influence on ice shelves underlain by cold waters that is not present elsewhere

Emergent quantum Euler equation and Bose-Einstein condensates

In this paper, proceeding from the recently developed way of deriving the quantum-mechanical equations from the classical ones, the complete system of hydrodynamical equations, including the quantum Euler equation, is derived for a perfect fluid and an imperfect fluid with pairwise interaction between the particles. For the Bose-Einstein condensate of the latter one the Bogolyubov spectrum of elementary excitations is easily reproduced in the acoustic approximation.Comment: 10 page

Topography generation by melting and freezing in a turbulent shear flow

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Dilaton Quantum Cosmology with a Schrodinger-like equation

A quantum cosmological model with radiation and a dilaton scalar field is analysed. The Wheeler-deWitt equation in the mini-superspace induces a Schr\"odinger equation, which can be solved. An explicit wavepacket is constructed for a particular choice of the ordering factor. A consistent solution is possible only when the scalar field is a phantom field. Moreover, although the wavepacket is time dependent, a Bohmian analysis allows to extract a bouncing behaviour for the scale factor.Comment: 14 pages, 3 figures in eps format. Minors corrections, new figure

Emergence of structural and dynamical properties of ecological mutualistic networks

Mutualistic networks are formed when the interactions between two classes of species are mutually beneficial. They are important examples of cooperation shaped by evolution. Mutualism between animals and plants plays a key role in the organization of ecological communities. Such networks in ecology have generically evolved a nested architecture independent of species composition and latitude - specialists interact with proper subsets of the nodes with whom generalists interact. Despite sustained efforts to explain observed network structure on the basis of community-level stability or persistence, such correlative studies have reached minimal consensus. Here we demonstrate that nested interaction networks could emerge as a consequence of an optimization principle aimed at maximizing the species abundance in mutualistic communities. Using analytical and numerical approaches, we show that because of the mutualistic interactions, an increase in abundance of a given species results in a corresponding increase in the total number of individuals in the community, as also the nestedness of the interaction matrix. Indeed, the species abundances and the nestedness of the interaction matrix are correlated by an amount that depends on the strength of the mutualistic interactions. Nestedness and the observed spontaneous emergence of generalist and specialist species occur for several dynamical implementations of the variational principle under stationary conditions. Optimized networks, while remaining stable, tend to be less resilient than their counterparts with randomly assigned interactions. In particular, we analytically show that the abundance of the rarest species is directly linked to the resilience of the community. Our work provides a unifying framework for studying the emergent structural and dynamical properties of ecological mutualistic networks.Comment: 10 pages, 4 figure

Modeling the quantum evolution of the universe through classical matter

It is well known that the canonical quantization of the Friedmann-Lema\^itre-Robertson-Walker (FLRW) filled with a perfect fluid leads to nonsingular universes which, for later times, behave as their classical counterpart. This means that the expectation value of the scale factor $(t)$ never vanishes and, as $t\to\infty$, we recover the classical expression for the scale factor. In this paper, we show that such universes can be reproduced by classical cosmology given that the universe is filled with an exotic matter. In the case of a perfect fluid, we find an implicit equation of state (EoS). We then show that this single fluid with an implict EoS is equivalent to two non-interacting fluids, one of them representing stiff matter with negative energy density. In the case of two non-interacting scalar fields, one of them of the phantom type, we find their potential energy. In both cases we find that quantum mechanics changes completely the configuration of matter for small values of time, by adding a fluid or a scalar field with negative energy density. As time passes, the density of negative energy decreases and we recover the ordinary content of the classical universe. The more the initial wave function of the universe is concentrated around the classical big bang singularity, the more it is necessary to add negative energy, since this type of energy will be responsible for the removal of the classical singularity.Comment: updated version as accepted by Gen. Relativ. Gravi