4,736 research outputs found
High Resolution Simulations of the Plunging Region in a Pseudo-Newtonian Potential: Dependence on Numerical Resolution and Field Topology
New three dimensional magnetohydrodynamic simulations of accretion disk
dynamics in a pseudo-Newtonian Paczynski-Wiita potential are presented. These
have finer resolution in the inner disk than any previously reported. Finer
resolution leads to increased magnetic field strength, greater accretion rate,
and greater fluctuations in the accretion rate. One simulation begins with a
purely poloidal magnetic field, the other with a purely toroidal field.
Compared to the poloidal initial field simulation, a purely toroidal initial
field takes longer to reach saturation of the magnetorotational instability and
produces less turbulence and weaker magnetic field energies. For both initial
field configurations, magnetic stresses continue across the marginally stable
orbit; measured in units corresponding to the Shakura-Sunyaev alpha parameter,
the stress grows from ~0.1 in the disk body to as much as ~10 deep in the
plunging region. Matter passing the inner boundary of the simulation has ~10%
greater binding energy and ~10% smaller angular momentum than it did at the
marginally stable orbit. Both the mass accretion rate and the integrated stress
fluctuate widely on a broad range of timescales.Comment: Accepted for publication in the Astrophysical Journal. For Web
version with mpeg animations see
http://www.astro.virginia.edu/VITA/papers/plunge
Mapping the cellular electrophysiology of rat sympathetic preganglionic neurones to their roles in cardiorespiratory reflex integration:A whole cell recording study in situ
Sympathetic preganglionic neurones (SPNs) convey sympathetic activity flowing from the CNS to the periphery to reach the target organs. Although previous in vivo and in vitro cell recording studies have explored their electrophysiological characteristics, it has not been possible to relate these characteristics to their roles in cardiorespiratory reflex integration. We used the working heart–brainstem preparation to make whole cell patch clamp recordings from T3–4 SPNs (n = 98). These SPNs were classified by their distinct responses to activation of the peripheral chemoreflex, diving response and arterial baroreflex, allowing the discrimination of muscle vasoconstrictor-like (MVC(like), 39%) from cutaneous vasoconstrictor-like (CVC(like), 28%) SPNs. The MVC(like) SPNs have higher baseline firing frequencies (2.52 ± 0.33 Hz vs. CVC(like) 1.34 ± 0.17 Hz, P = 0.007). The CVC(like) have longer after-hyperpolarisations (314 ± 36 ms vs. MVC(like) 191 ± 13 ms, P < 0.001) and lower input resistance (346 ± 49 MΩ vs. MVC(like) 496 ± 41 MΩ, P < 0.05). MVC(like) firing was respiratory-modulated with peak discharge in the late inspiratory/early expiratory phase and this activity was generated by both a tonic and respiratory-modulated barrage of synaptic events that were blocked by intrathecal kynurenate. In contrast, the activity of CVC(like) SPNs was underpinned by rhythmical membrane potential oscillations suggestive of gap junctional coupling. Thus, we have related the intrinsic electrophysiological properties of two classes of SPNs in situ to their roles in cardiorespiratory reflex integration and have shown that they deploy different cellular mechanisms that are likely to influence how they integrate and shape the distinctive sympathetic outputs
Smooth-Trajectron++: Augmenting the Trajectron++ behaviour prediction model with smooth attention
Understanding traffic participants' behaviour is crucial for predicting their
future trajectories, aiding in developing safe and reliable planning systems
for autonomous vehicles. Integrating cognitive processes and machine learning
models has shown promise in other domains but is lacking in the trajectory
forecasting of multiple traffic agents in large-scale autonomous driving
datasets. This work investigates the state-of-the-art trajectory forecasting
model Trajectron++ which we enhance by incorporating a smoothing term in its
attention module. This attention mechanism mimics human attention inspired by
cognitive science research indicating limits to attention switching. We
evaluate the performance of the resulting Smooth-Trajectron++ model and compare
it to the original model on various benchmarks, revealing the potential of
incorporating insights from human cognition into trajectory prediction models
The carotid body as a putative therapeutic target for the treatment of neurogenic hypertension
Modelling the vascular response to sympathetic postganglionic nerve activity
AbstractThis paper explores the influence of burst properties of the sympathetic nervous system on arterial contractility. Specifically, a mathematical model is constructed of the pathway from action potential generation in a sympathetic postganglionic neurone to contraction of an arterial smooth muscle cell. The differential equation model is a synthesis of models of the individual physiological processes, and is shown to be consistent with physiological data.The model is found to be unresponsive to tonic (regular) stimulation at typical frequencies recorded in sympathetic efferents. However, when stimulated at the same average frequency, but with repetitive respiratory-modulated burst patterns, it produces marked contractions. Moreover, the contractile force produced is found to be highly dependent on the number of spikes in each burst. In particular, when the model is driven by preganglionic spike trains recorded from wild-type and spontaneously hypertensive rats (which have increased spiking during each burst) the contractile force was found to be 10-fold greater in the hypertensive case. An explanation is provided in terms of the summative increased release of noradrenaline. Furthermore, the results suggest the marked effect that hypertensive spike trains had on smooth muscle cell tone can provide a significant contribution to the pathology of hypertension
Experimental design of complement component 5a‐induced acute lung injury (C5a‐ALI): a role of CC‐chemokine receptor type 5 during immune activation by anaphylatoxin
Excessive activation of the complement system is detrimental in acute inflammatory disorders. In this study, we analyzed the role of complement‐derived anaphylatoxins in the pathogenesis of experimental acute lung injury/acute respiratory distress syndrome (ALI/ARDS) in C57BL/6J mice. Intratracheal administration of recombinant mouse complement component (C5a) caused alveolar inflammation with abundant recruitment of Ly6‐G+CD11b+ leukocytes to the alveolar spaces and severe alveolar‐capillary barrier dysfunction (C5a‐ALI; EC50[C5a] = 20 ng/g body weight). Equimolar concentrations of C3a or desarginated C5a (C5adesArg) did not induce alveolar inflammation. The severity of C5a‐ALI was aggravated in C5‐deficient mice. Depletion of Ly6‐G+ cells and use of C5aR1‐/‐ bone marrow chimeras suggested an essential role of C5aR1+ hematopoietic cells in C5a‐ALI. Blockade of PI3K/Akt and MEK1/2 kinase pathways completely abrogated lung injury. The mechanistic description is that C5a altered the alveolar cytokine milieu and caused significant release of CC‐chemokines. Mice with genetic deficiency of CC‐chemokine receptor (CCR) type 5, the common receptor of chemokine (C‐C motif) ligand (CCL) 3, CCL4, and CCL5, displayed reduced lung damage. Moreover, treatment with a CCR5 antagonist, maraviroc, was protective against C5a‐ALI. In summary, our results suggest that the detrimental effects of C5a in this model are partly mediated through CCR5 activation downstream of C5aR1, which may be evaluated for potential therapeutic exploitation in ALI/ARDS.—Russkamp, N. F., Ruemmler, R., Roewe, J., Moore, B. B., Ward, P. A., Bosmann, M. Experimental design of complement component 5a‐induced acute lung injury (C5a‐ALI): a role of CC‐chemokine receptor type 5 during immune activation by anaphylatoxin. FASEB J. 29, 3762‐3772 (2015). www.fasebj.orgPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154372/1/fsb2029009014.pd
Generalized Cross-Validation as a Method of Hyperparameter Search for MTGV Regularization
The concept of generalized cross-validation (GCV) is applied to modified
total generalized variation (MTGV) regularization. Current implementations of
the MTGV regularization rely on manual (or semi-manual) hyperparameter
optimization, which is both time-consuming and subject to bias. The combination
of MTGV-regularization and GCV allows for a straightforward hyperparameter
search during regularization. This significantly increases the efficiency of
the MTGV-method, because it limits the number of hyperparameters, which have to
be tested and, improves the practicality of MTGV regularization as a standard
technique for inversion of NMR signals. The combined method is applied to
simulated and experimental NMR data and the resulting reconstructed
distributions are presented. It is shown that for all data sets studied the
proposed combination of MTGV and GCV minimizes the GCV score allowing an
optimal hyperparameter choice
Elemental concentrations in the seed of mutants and natural variants of Arabidopsis thaliana grown under varying soil conditions
Peer reviewedPublisher PD
Global MHD Simulation of the Inner Accretion Disk in a Pseudo-Newtonian Potential
We present a detailed three dimensional magnetohydrodynamic (MHD) simulation
describing the inner region of a disk accreting onto a black hole. To avoid the
technical complications of general relativity, the dynamics are treated in
Newtonian fashion using the pseudo-Newtonian Pacz\'ynski-Wiita potential. The
disk evolves due to angular momentum transport which is produced naturally from
MHD turbulence generated by the magnetorotational instability. We find that the
resulting stress is continuous across the marginally stable orbit, in
contradiction with the widely-held assumption that the stress should go to zero
there. As a consequence, the specific angular momentum of the matter accreted
into the hole is smaller than the specific angular momentum at the marginally
stable orbit. The disk exhibits large fluctuations in almost every quantity,
both spatially and temporally. In particular, the ratio of stress to pressure
(the local analog of the Shakura-Sunyaev parameter) exhibits both
systematic gradients and large fluctuations; from in the disk
midplane at large radius, it rises to both at a few gas density
scaleheights above the plane at large radius, and near the midplane well inside
the plunging region. Driven in part by large-amplitude waves excited near the
marginally stable orbit, both the mass accretion rate and the integrated stress
exhibit large fluctuations whose Fourier power spectra are smooth "red"
power-laws stretching over several orders of magnitude in timescale.Comment: Accepted by the Astrophysical Journal. Minor revisions in response to
referee's comments, new figure 4. A web version of this paper with mpeg
animations is available at
http://www.astro.virginia.edu/~jh8h/pndisk/pndisk.htm
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