3,135 research outputs found
ExoMol line lists XXVIII: The rovibronic spectrum of AlH
A new line list for AlH is produced. The WYLLoT line list spans two
electronic states and . A diabatic model is used
to model the shallow potential energy curve of the state, which
has a strong pre-dissociative character with only two bound vibrational states.
Both potential energy curves are empirical and were obtained by fitting to
experimentally derived energies of the and
electronic states using the diatomic nuclear motion codes Level and Duo. High
temperature line lists plus partition functions and lifetimes for three
isotopologues AlH, AlD and AlH were generated using ab
initio dipole moments. The line lists cover both the -- and --
systems and are made available in electronic form at the CDS and ExoMol
databases
Metamagnetism and soliton excitations in the modulated ferromagnetic Ising chain CoV2O6
We report a combination of physical property and neutron scattering
measurements for polycrystalline samples of the one-dimensional spin chain
compound CoV2O6. Heat capacity measurements show that an effective S = 1/2
state is found at low temperatures and that magnetic fluctuations persist up to
6.Tn. Above Tn = 6.3 K, measurements of the magnetic susceptibility as a
function of T and H show that the nearest neighbour exchange is ferromagnetic.
In the ordered state, we have discovered a crossover from a metamagnet with
strong fluctuations between 5 K and Tn to a state with a 1/3 magnetisation
plateau at 2 < T < 5 K. We use neutron powder diffraction measurements to show
that the AFM state has incommensurate long range order and inelastic time of
flight neutron scattering to examine the magnetic fluctuations as a function of
temperature. Above Tn, we find two broad bands between 3.5 and 5 meV and
thermally activated low energy features which correspond to transitions within
these bands. These features show that the excitations are deconfined solitons
rather than the static spin reversals predicted for a uniform FM Ising spin
chain. Below Tn, we find a ladder of states due to the confining effect of the
internal field. A region of weak confinement below Tn, but above 5 K, is
identified which may correspond to a crossover between 2D and 3D magnetic
ordering.Comment: Expanded version, includes results from arXiv:0804.2966 and neutron
powder diffraction. To appear in PR
Charge order at the frontier between the molecular and solid states in Ba3NaRu2O9
We show that the valence electrons of Ba3NaRu2O9, which has a quasi-molecular
structure, completely crystallize below 210 K. Using an extended Hubbard model,
we show that the charge ordering instability results from long-range Coulomb
interactions. However, orbital ordering, metal-metal bonding and formation of a
partial spin gap enforce the magnitude of the charge separation. The striped
charge order and frustrated hcp lattice of Ru2O9 dimers lead to competition
with a quasi-degenerate charge-melted phase under photo-excitation at low
temperature. Our results establish a broad class of simple metal oxides as
models for emergent phenomena at the border between the molecular and solid
states.Comment: Minor changes, with supporting information. To appear in Phys. Rev.
Let
Dopamine D_2-receptor activation elicits akinesia, rigidity, catalepsy, and tremor in mice expressing hypersensitive 4 nicotinic receptors via a cholinergic-dependent mechanism
Recent studies suggest that high-affinity neuronal nicotinic acetylcholine receptors (nAChRs) containing α4 and β2 subunits (α4β2*) functionally interact with G-protein-coupled dopamine (DA) D_2 receptors in basal ganglia. We hypothesized that if a functional interaction between these receptors exists, then mice expressing an M2 point mutation (Leu9'Ala) rendering 4 nAChRs hypersensitive to ACh may exhibit altered sensitivity to a D_2-receptor agonist. When challenged with the D_(2)R agonist, quinpirole (0.5–10 mg/kg), Leu9'Ala mice, but not wild-type (WT) littermates, developed severe, reversible motor impairment characterized by rigidity, catalepsy, akinesia, and tremor. While striatal DA tissue content, baseline release, and quinpirole-induced DA depletion did not differ between Leu9'Ala and WT mice, quinpirole dramatically increased activity of cholinergic striatal interneurons only in mutant animals, as measured by increased c-Fos expression in choline acetyltransferase (ChAT)-positive interneurons. Highlighting the importance of the cholinergic system in this mouse model, inhibiting the effects of ACh by blocking muscarinic receptors, or by selectively activating hypersensitive nAChRs with nicotine, rescued motor symptoms. This novel mouse model mimics the imbalance between striatal DA/ACh function associated with severe motor impairment in disorders such as Parkinson’s disease, and the data suggest that a D_(2)R–α4*-nAChR functional interaction regulates cholinergic interneuron activity.—Zhao-Shea, R., Cohen, B. N., Just, H., McClure-Begley, T., Whiteaker, P., Grady, S. R., Salminen, O., Gardner, P. D., Lester, H. A., Tapper, A. R. Dopamine D2-receptor activation elicits akinesia, rigidity, catalepsy, and tremor in mice expressing hypersensitive α4 nicotinic receptors via a cholinergic-dependent mechanism
Improving Simulations of Spiking Neural P Systems in NVIDIA CUDA GPUs: CuSNP
Spiking neural P systems (in short, SN P systems) are parallel models of
computations inspired by the spiking ( ring) of biological neurons. In SN P systems, neurons
function as spike processors and are placed on nodes of a directed graph. Synapses,
the connections between neurons, are represented by arcs or directed endges in the graph.
Not only do SN P systems have parallel semantics (i.e. neurons operate in parallel), but
their structure as directed graphs allow them to be represented as vectors or matrices.
Such representations allow the use of linear algebra operations for simulating the
evolution of the system con gurations, i.e. computations. In this work, we continue the
implementations of SN P systems with delays, i.e. a delay is associated with the sending
of a spike from a neuron to its neighbouring neurons. Our implementation is based on
a modi ed representation of SN P systems as vectors and matrices for SN P systems
without delays. We us massively parallel processors known as graphics processing units
(in short, GPUs) from NVIDIA. For experimental validation, we use SN P systems implementing
generalized sorting networks. We report a speedup, i.e. the ratio between the
running time of the sequential over the parallel simulator, of up to approximately 51
times for a 512-size input to the sorting network
CuSNP: Spiking Neural P Systems Simulators in CUDA
Spiking neural P systems (in short, SN P systems) are models
of computation inspired by biological neurons. CuSNP is a project involving
sequential (CPU) and parallel (GPU) simulators for SN P systems. In this
work, we report the following results: a P-Lingua le parser is included, for
ease of use when performing simulations; extension of the matrix representation
of SN P systems to include delay; comparison and analysis of our simulators
by simulating two types (bitonic and generalized) of parallel sorting networks;
extension of supported types of regular expressions in SN P systems. Our GPU
simulator is better suited for generalized sorting as compared to bitonic sorting
networks, and the GPU simulators run up to 50 faster than our CPU simulator.
Finally, we discuss our experiments and provide directions for further work
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