1,086 research outputs found
Fast Magnetic Reconnection Due To Anisotropic Electron Pressure
A new regime of fast magnetic reconnection with an out-of-plane (guide)
magnetic field is reported in which the key role is played by an electron
pressure anisotropy described by the Chew-Goldberger-Low gyrotropic equations
of state in the generalized Ohm's law, which even dominates the Hall term. A
description of the physical cause of this behavior is provided and
two-dimensional fluid simulations are used to confirm the results. The electron
pressure anisotropy causes the out-of-plane magnetic field to develop a
quadrupole structure of opposite polarity to the Hall magnetic field and gives
rise to dispersive waves. In addition to being important for understanding what
causes reconnection to be fast, this mechanism should dominate in plasmas with
low plasma beta and a high in-plane plasma beta with electron temperature
comparable to or larger than ion temperature, so it could be relevant in the
solar wind and some tokamaks.Comment: 5 pages, 2 figures, accepted for publication as a letter in Physics
of Plasma
Estimates of Densities and Filling Factors from a Cooling Time Analysis of Solar Microflares Observed with RHESSI
We use more than 4,500 microflares from the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI) microflare data set (Christe et al., 2008, Ap.
J., 677, 1385) to estimate electron densities and volumetric filling factors of
microflare loops using a cooling time analysis. We show that if the filling
factor is assumed to be unity, the calculated conductive cooling times are much
shorter than the observed flare decay times, which in turn are much shorter
than the calculated radiative cooling times. This is likely unphysical, but the
contradic- tion can be resolved by assuming the radiative and conductive
cooling times are comparable, which is valid when the flare loop temperature is
a maximum and when external heating can be ignored. We find that resultant
radiative and con- ductive cooling times are comparable to observed decay
times, which has been used as an assumption in some previous studies. The
inferred electron densities have a mean value of 10^11.6 cm^-3 and filling
factors have a mean of 10^-3.7. The filling factors are lower and densities are
higher than previous estimates for large flares, but are similar to those found
for two microflares by Moore et al. (Ap. J., 526, 505, 1999).Comment: Published in Ap.
Queer In AI: A Case Study in Community-Led Participatory AI
Queerness and queer people face an uncertain future in the face of ever more widely deployed and invasive artificial intelligence (AI). These technologies have caused numerous harms to queer people, including privacy violations, censoring and downranking queer content, exposing queer people and spaces to harassment by making them hypervisible, deadnaming and outing queer people. More broadly, they have violated core tenets of queerness by classifying and controlling queer identities. In response to this, the queer community in AI has organized Queer in AI, a global, decentralized, volunteer-run grassroots organization that employs intersectional and community-led participatory design to build an inclusive and equitable AI future. In this paper, we present Queer in AI as a case study for community-led participatory design in AI. We examine how participatory design and intersectional tenets started and shaped this communityβs programs over the years. We discuss different challenges that emerged in the process, look at ways this organization has fallen short of operationalizing participatory and intersectional principles, and then assess the organizationβs impact. Queer in AI provides important lessons and insights for practitioners and theorists of participatory methods broadly through its rejection of hierarchy in favor of decentralization, success at building aid and programs by and for the queer community, and effort to change actors and institutions outside of the queer community. Finally, we theorize how communities like Queer in AI contribute to the participatory design in AI more broadly by fostering cultures of participation in AI, welcoming and empowering marginalized participants, critiquing poor or exploitative participatory practices, and bringing participation to institutions outside of individual research projects. Queer in AIβs work serves as a case study of grassroots activism and participatory methods within AI, demonstrating the potential of community-led participatory methods and intersectional praxis, while also providing challenges, case studies, and nuanced insights to researchers developing and using participatory methods
Adverse drug reactions to antiretroviral therapy (ARVs): incidence, type and risk factors in Nigeria
A Virtual Agent as Vocabulary Trainer: Iconic Gestures Help to Improve Learnersβ Memory Performance
An important and often laborious task in foreign language acquisition is vocabulary learning. Research has repeatedly demonstrated that performing iconic gestures together with novel words has a beneficial effect on learning performance. Can these findings be transferred onto virtual agents applied in gesture-supported vocabulary training? We present a study investigating whether iconic gestures performed by a virtual agent and imitated by learners have an impact on verbal memory for words in a foreign language. In a within-subject design we compared participantsβ memory performance achieved with the help of a virtual agent and those achieved with the help of a human trainer regarding both short-term learning effects and long-term decay effects. The overall results demonstrate improved memory scores when participants learned with a virtual agent. Especially high performers could profit from gesture-supported training with a virtual agent
Pharmacological and rAAV Gene Therapy Rescue of Visual Functions in a Blind Mouse Model of Leber Congenital Amaurosis
BACKGROUND: Leber congenital amaurosis (LCA), a heterogeneous early-onset retinal dystrophy, accounts for ~15% of inherited congenital blindness. One cause of LCA is loss of the enzyme lecithin:retinol acyl transferase (LRAT), which is required for regeneration of the visual photopigment in the retina. METHODS AND FINDINGS: An animal model of LCA, the Lrat (β/β) mouse, recapitulates clinical features of the human disease. Here, we report that two interventionsβintraocular gene therapy and oral pharmacologic treatment with novel retinoid compoundsβeach restore retinal function to Lrat (β/β) mice. Gene therapy using intraocular injection of recombinant adeno-associated virus carrying the Lrat gene successfully restored electroretinographic responses to ~50% of wild-type levels (p < 0.05 versus wild-type and knockout controls), and pupillary light responses (PLRs) of Lrat (β/β) mice increased ~2.5 log units (p < 0.05). Pharmacological intervention with orally administered pro-drugs 9-cis-retinyl acetate and 9-cis-retinyl succinate (which chemically bypass the LRAT-catalyzed step in chromophore regeneration) also caused long-lasting restoration of retinal function in LRAT-deficient mice and increased ERG response from ~5% of wild-type levels in Lrat (β/β) mice to ~50% of wild-type levels in treated Lrat (β/β) mice (p < 0.05 versus wild-type and knockout controls). The interventions produced markedly increased levels of visual pigment from undetectable levels to 600 pmoles per eye in retinoid treated mice, and ~1,000-fold improvements in PLR and electroretinogram sensitivity. The techniques were complementary when combined. CONCLUSION: Intraocular gene therapy and pharmacologic bypass provide highly effective and complementary means for restoring retinal function in this animal model of human hereditary blindness. These complementary methods offer hope of developing treatment to restore vision in humans with certain forms of hereditary congenital blindness
Multiparameter Telemetry as a Sensitive Screening Method to Detect Vaccine Reactogenicity in Mice
Refined vaccines and adjuvants are urgently needed to advance immunization against global infectious challenges such as HIV, hepatitis C, tuberculosis and malaria. Large-scale screening efforts are ongoing to identify adjuvants with improved efficacy profiles. Reactogenicity often represents a major hurdle to the clinical use of new substances. Yet, irrespective of its importance, this parameter has remained difficult to screen for, owing to a lack of sensitive small animal models with a capacity for high throughput testing. Here we report that continuous telemetric measurements of heart rate, heart rate variability, body core temperature and locomotor activity in laboratory mice readily unmasked systemic side-effects of vaccination, which went undetected by conventional observational assessment and clinical scoring. Even minor aberrations in homeostasis were readily detected, ranging from sympathetic activation over transient pyrogenic effects to reduced physical activity and apathy. Results in real-time combined with the potential of scalability and partial automation in the industrial context suggest multiparameter telemetry in laboratory mice as a first-line screen for vaccine reactogenicity. This may accelerate vaccine discovery in general and may further the success of vaccines in combating infectious disease and cancer
A Computational Study on the Role of Gap Junctions and Rod Ih Conductance in the Enhancement of the Dynamic Range of the Retina
Recent works suggest that one of the roles of gap junctions in sensory systems is to enhance their dynamic range by avoiding early saturation in the first processing stages. In this work, we use a minimal conductance-based model of the ON rod pathways in the vertebrate retina to study the effects of electrical synaptic coupling via gap junctions among rods and among AII amacrine cells on the dynamic range of the retina. The model is also used to study the effects of the maximum conductance of rod hyperpolarization activated current Ih on the dynamic range of the retina, allowing a study of the interrelations between this intrinsic membrane parameter with those two retina connectivity characteristics. Our results show that for realistic values of Ih conductance the dynamic range is enhanced by rod-rod coupling, and that AII-AII coupling is less relevant to dynamic range amplification in comparison with receptor coupling. Furthermore, a plot of the retina output response versus input intensity for the optimal parameter configuration is well fitted by a power law with exponent . The results are consistent with predictions of more theoretical works and suggest that the earliest expression of gap junctions along the rod pathways, together with appropriate values of rod Ih conductance, has the highest impact on vertebrate retina dynamic range enhancement
A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors
Cone photoreceptors and horizontal cells (HCs) have a reciprocal synapse that
underlies lateral inhibition and establishes the antagonistic center-surround
organization of the visual system. Cones transmit to HCs through an excitatory
synapse and HCs feed back to cones through an inhibitory synapse. Here we report
that HCs also transmit to cone terminals a positive feedback signal that
elevates intracellular Ca2+ and accelerates neurotransmitter
release. Positive and negative feedback are both initiated by AMPA receptors on
HCs, but positive feedback appears to be mediated by a change in HC
Ca2+, whereas negative feedback is mediated by a change in
HC membrane potential. Local uncaging of AMPA receptor agonists suggests that
positive feedback is spatially constrained to active HC-cone synapses, whereas
the negative feedback signal spreads through HCs to affect release from
surrounding cones. By locally offsetting the effects of negative feedback,
positive feedback may amplify photoreceptor synaptic release without sacrificing
HC-mediated contrast enhancement
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