2,704 research outputs found
Loss of solutions in shear banding fluids in shear banding fluids driven by second normal stress differences
Edge fracture occurs frequently in non-Newtonian fluids. A similar
instability has often been reported at the free surface of fluids undergoing
shear banding, and leads to expulsion of the sample. In this paper the
distortion of the free surface of such a shear banding fluid is calculated by
balancing the surface tension against the second normal stresses induced in the
two shear bands, and simultaneously requiring a continuous and smooth meniscus.
We show that wormlike micelles typically retain meniscus integrity when shear
banding, but in some cases can lose integrity for a range of average applied
shear rates during which one expects shear banding. This meniscus fracture
would lead to ejection of the sample as the shear banding region is swept
through. We further show that entangled polymer solutions are expected to
display a propensity for fracture, because of their much larger second normal
stresses. These calculations are consistent with available data in the
literature. We also estimate the meniscus distortion of a three band
configuration, as has been observed in some wormlike micellar solutions in a
cone and plate geometry.Comment: 23 pages, to be published in Journal of Rheolog
The Effects of Exposure to Endophyte-Infected Tall Fescue Seed on Faecal and Urine Concentrations of Ergovaline and Lysergic Acid in Mature Gelding Horses
Despite the good nutritive value of endophyte-infected tall fescue, consumption by livestock results in a decrease in both reproductive and growth performance due to ergot alkaloids produced by an endophytic fungus (Cross et al., 1995). Little research has investigated the metabolic fate of ergot alkaloids and/or their metabolites in grazing horses. Thus, the objectives of this experiment were: a) to determine concentrations of ergovaline (EV) and lysergic acid (LA) in the faeces and urine of geldings exposed to tall fescue seed over a time course experiment and b) to measure the effects of alkaloid-containing tall fescue on nutrient digestibility and serum clinical enzyme profiles
Some distorted thoughts about ketamine as a psychedelic and a novel hypothesis based on NMDA receptor-mediated synaptic plasticity.
Ketamine, a channel blocking NMDA receptor antagonist, is used off-label for its psychedelic effects, which may arise from a combination of several inter-related actions. Firstly, reductions of the contribution of NMDA receptors to afferent information from external and internal sensory inputs may distort sensations and their processing in higher brain centres. Secondly, reductions of NMDA receptor-mediated excitation of GABAergic interneurons can result in glutamatergic overactivity. Thirdly, limbic cortical disinhibition may indirectly enhance dopaminergic and serotonergic activity. Fourthly, inhibition of NMDA receptor mediated synaptic plasticity, such as short-term potentiation (STP) and long-term potentiation (LTP), could lead to distorted memories. Here, for the first time, we compared quantitatively the effects of ketamine on STP and LTP. We report that ketamine inhibits STP in a double sigmoidal fashion with low (40 nM) and high (5.6 μM) IC50 values. In contrast, ketamine inhibits LTP in a single sigmoidal manner (IC50 value ∼ 15 μM). A GluN2D-subunit preferring NMDA receptor antagonist, UBP145, has a similar pharmacological profile. We propose that the psychedelic effects of ketamine may involve the inhibition of STP and, potentially, associated forms of working memory. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'
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Listening to the experts: person-centred approaches to supporting autistic people and people with an intellectual disability in the mental health system
Summary
Despite numerous UK government policies aimed at reducing the number of autistic people and people with an intellectual disability in mental health hospitals, little progress has been made, with many experiencing lengthy stays that offer little therapeutic benefit. Once admitted, people are at risk of restrictive interventions and significantly delayed discharge, resulting in trauma. This article draws on the cases of four people to illustrate the limitations of current mental health system approaches to the challenges experienced by autistic people and people with an intellectual disability. The importance of relational working and listening to people is explored, and we demonstrate how this can facilitate the provision of bespoke housing and care packages to enable a successful return to life in the community. Finally, we offer recommendations on the changes urgently needed to ensure that autistic people and people with an intellectual disability can live ordinary lives in their own homes, with timely and effective support from mental health services when needed, just like everyone else
Mechanisms explaining transitions between tonic and phasic firing in neuronal populations as predicted by a low dimensional firing rate model
Several firing patterns experimentally observed in neural populations have
been successfully correlated to animal behavior. Population bursting, hereby
regarded as a period of high firing rate followed by a period of quiescence, is
typically observed in groups of neurons during behavior. Biophysical
membrane-potential models of single cell bursting involve at least three
equations. Extending such models to study the collective behavior of neural
populations involves thousands of equations and can be very expensive
computationally. For this reason, low dimensional population models that
capture biophysical aspects of networks are needed.
\noindent The present paper uses a firing-rate model to study mechanisms that
trigger and stop transitions between tonic and phasic population firing. These
mechanisms are captured through a two-dimensional system, which can potentially
be extended to include interactions between different areas of the nervous
system with a small number of equations. The typical behavior of midbrain
dopaminergic neurons in the rodent is used as an example to illustrate and
interpret our results.
\noindent The model presented here can be used as a building block to study
interactions between networks of neurons. This theoretical approach may help
contextualize and understand the factors involved in regulating burst firing in
populations and how it may modulate distinct aspects of behavior.Comment: 25 pages (including references and appendices); 12 figures uploaded
as separate file
Gravel pits support waterbird diversity in an urban landscape
We assessed the benefit of 11 gravel pits for the settlement of waterbird communities in an urbanized area lacking natural wetlands. Gravel pits captured 57% of the regional species pool of aquatic birds. We identified 39 species, among which five were regionally rare. We used the Self Organizing Map algorithm to calculate the probabilities of presence of species, and to bring out habitat conditions that predict assemblage patterns. The age of the pits did not correlate with assemblage composition and species richness. There was a positive influence of macrophyte cover on waterbird species richness. Larger pits did not support more species, but species richness increased with connectivity. As alternative wetland habitats, gravel pits are attractive to waterbirds, when they act as stepping stones that ensure connectivity between larger natural and/or artificial wetlands separated in space
Symmetry-selective quasiparticle scattering and electric field tunability of the ZrSiS surface electronic structure
3D Dirac semimetals with square-net non-symmorphic symmetry, such as ternary
ZrXY (X=Si, Ge; Y=S, Se, Te) compounds, have attracted significant attention
owing to the presence of topological nodal lines, loops, or networks in their
bulk. Orbital symmetry plays a profound role such materials as the different
branches of the nodal dispersion can be distinguished by their distinct orbital
symmetry eigenvalues. The presence of different eigenvalues suggests that
scattering between states of different orbital symmetry may be strongly
suppressed. Indeed, in ZrSiS, there has been no clear experimental evidence of
quasiparticle scattering between states of different symmetry eigenvalue has
been reported at small wave vector . Here we show, using quasiparticle
interference (QPI), that atomic step-edges in the ZrSiS surface facilitate
quasiparticle scattering between states of different symmetry eigenvalues. This
symmetry eigenvalue mixing quasiparticle scattering is the first to be reported
for ZrSiS and contrasts quasiparticle scattering with no mixing of symmetry
eigenvalues, where the latter occurs with scatterers preserving the glide
mirror symmetry of the crystal lattice, e.g., native point defects in ZrSiS.
Finally, we show that the electronic structure of the ZrSiS surface, including
its unique floating band surface state (FBSS), can be tuned by a vertical
electric field locally applied by the tip of a scanning tunneling microscope
(STM), enabling control of a spin-orbit induced avoided crossing near the Fermi
level by as much as 300%
Dark-field transmission electron microscopy and the Debye-Waller factor of graphene
Graphene's structure bears on both the material's electronic properties and
fundamental questions about long range order in two-dimensional crystals. We
present an analytic calculation of selected area electron diffraction from
multi-layer graphene and compare it with data from samples prepared by chemical
vapor deposition and mechanical exfoliation. A single layer scatters only 0.5%
of the incident electrons, so this kinematical calculation can be considered
reliable for five or fewer layers. Dark-field transmission electron micrographs
of multi-layer graphene illustrate how knowledge of the diffraction peak
intensities can be applied for rapid mapping of thickness, stacking, and grain
boundaries. The diffraction peak intensities also depend on the mean-square
displacement of atoms from their ideal lattice locations, which is
parameterized by a Debye-Waller factor. We measure the Debye-Waller factor of a
suspended monolayer of exfoliated graphene and find a result consistent with an
estimate based on the Debye model. For laboratory-scale graphene samples,
finite size effects are sufficient to stabilize the graphene lattice against
melting, indicating that ripples in the third dimension are not necessary.Comment: 10 pages, 4 figure
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