812 research outputs found
Magnetic shuffling of coronal downdrafts
Channelled fragmented downflows are ubiquitous in magnetized atmospheres, and
have been recently addressed from an observation after a solar eruption. We
study the possible back-effect of the magnetic field on the propagation of
confined flows. We compare two 3D MHD simulations of dense supersonic plasma
blobs downfalling along a coronal magnetic flux tube. In one, the blobs move
strictly along the field lines; in the other, the initial velocity of the blobs
is not perfectly aligned to the magnetic field and the field is weaker. The
aligned blobs remain compact while flowing along the tube, with the generated
shocks. The misaligned blobs are disrupted and merged by the chaotic shuffling
of the field lines, and structured into thinner filaments; Alfven wave fronts
are generated together with shocks ahead of the dense moving front. Downflowing
plasma fragments can be chaotically and efficiently mixed if their motion is
misaligned to field lines, with broad implications, e.g., disk accretion in
protostars, coronal eruptions and rain.Comment: 9 pages, 4 figures, proposed for acceptance, movies available upon
request to the first autho
Bright hot impacts by erupted fragments falling back on the Sun: magnetic channelling
Dense plasma fragments were observed to fall back on the solar surface by the
Solar Dynamics Observatory after an eruption on 7 June 2011, producing strong
EUV brightenings. Previous studies investigated impacts in regions of weak
magnetic field. Here we model the km/s impact of fragments
channelled by the magnetic field close to active regions. In the observations,
the magnetic channel brightens before the fragment impact. We use a 3D-MHD
model of spherical blobs downfalling in a magnetized atmosphere. The blob
parameters are constrained from the observation. We run numerical simulations
with different ambient density and magnetic field intensity. We compare the
model emission in the 171\AA~ channel of the Atmospheric Imaging Assembly with
the observed one. We find that a model of downfall channelled in a MK
coronal loop confined by a magnetic field of G, best explains
qualitatively and quantitatively the observed evolution. The blobs are highly
deformed, further fragmented, when the ram pressure becomes comparable to the
local magnetic pressure and they are deviated to be channelled by the field,
because of the differential stress applied by the perturbed magnetic field.
Ahead of them, in the relatively dense coronal medium, shock fronts propagate,
heat and brighten the channel between the cold falling plasma and the solar
surface. This study shows a new mechanism which brightens downflows channelled
by the magnetic field, such as in accreting young stars, and also works as a
probe of the ambient atmosphere, providing information about the local plasma
density and magnetic field.Comment: 17 pages, 14 figure
Distribution of Extrasynaptic NMDA Receptors on Neurons
NMDA receptors are found in both synaptic and extrasynaptic locations on neurons. NMDA receptors also can be found on neurons in early stages prior to synaptogenesis, where they may be involved in migration and differentiation. Extrasynaptic NMDA receptors typically are associated with contacts with adjacent processes such as axons and glia. Extrasynaptic NMDA receptor clusters vary in size and may form associations with scaffolding proteins such as PSD-95 and SAP102. The best-characterized extrasynaptic NMDA receptors contain NR1 and NR2B subunits. Extrasynaptic NMDA receptors may be activated by glutamate spillover from synapses or from ectopic release of glutamate. Consequently, extrasynaptic NMDA receptor activation may occur under different circumstances than that for synaptic NMDA receptors, indicating different functional consequences for the neuron. In some cases, activation of extrasynaptic NMDA receptors may have a negative influence on the neuron, leading to cell damage and death, as may occur in some major diseases of the nervous system
MHD Modelling of Coronal Loops: Injection of High-Speed Chromospheric Flows
Context. Observations reveal a correspondence between chromospheric type II spicules and bright upward-moving fronts in the corona observed in the extreme-ultraviolet (EUV) band. However, theoretical considerations suggest that these flows are probably not the main source of heating in coronal magnetic loops. Aims. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes and the possible production of emission in the EUV band. Methods. We simulated the propagation of a dense 104 K chromospheric jet upward along a coronal loop by means of a 2D cylindrical MHD model that includes gravity, radiative losses, thermal conduction, and magnetic induction. The jet propagates in a complete atmosphere including the chromosphere and a tenuous cool (approximately 0.8 MK) corona, linked through a steep transition region. In our reference model, the jet initial speed is 70 km per second, its initial density is 10(exp 11) per cubic centimeter, and the ambient uniform magnetic field is 10 G. We also explored other values of jet speed and density in 1D and different magnetic field values in 2D, as well as the jet propagation in a hotter (approximately 1.5 MK) background loop. Results. While the initial speed of the jet does not allow it to reach the loop apex, a hot shock-front develops ahead of it and travels to the other extreme of the loop. The shock front compresses the coronal plasma and heats it to about 10(exp 6) K. As a result, a bright moving front becomes visible in the 171 Angstrom channel of the SDO/AIA mission. This result generally applies to all the other explored cases, except for the propagation in the hotter loop. Conclusions. For a cool, low-density initial coronal loop, the post-shock plasma ahead of upward chromospheric flows might explain at least part of the observed correspondence between type II spicules and EUV emission excess
Langmuir-Schäfer Films of an Amphiphilic Ruthenium Complex Bearing an “Almost-Naked” Multi-Charged Head-Group
In this paper the preparation and characterization of Langmuir-Scha¨fer (LS) films of a novel amphiphilic dipolar
complex, [RuII(NH3)5(N-dodecyl-4,4¢-bpy)](PF6)3 (1), are reported. Preparation of these films, otherwise precluded
utilizing standard Langmuir procedures, is achieved by using a subphase at relatively high ionic strength, by addition
of NH4PF6. The morphology and the spectroscopic features of the floating films are investigated by Brewster angle
microscopy and UV-vis reflection spectroscopy at the water-air interface, respectively, whereas LS films are
characterized by absorption spectroscopy and atomic force microscopy. The overall results indicate the existence
of aggregates of 1 and formation of homogeneous, densely packed layers. The presented approach could represent
a general method to achieve Langmuir-Blodgett films of amphiphilic metal complexes having an “almost naked”
multicharged headgroup
Adapted Tricycle
This Final Design Review document describes the senior design project carried out by a team of four mechanical engineering students from California Polytechnic State University, San Luis Obispo in conjunction with California Children’s Services for Savannah, a student at San Luis Obispo High School. The purpose of the project is to design an adaptive vehicle for Savannah that serves as a form of exercise and can be easily operated by her with little to no outside assistance. Background into Savannah’s condition is provided as well as previous designs of similar adaptive tricycles, document standards and specifications which constrain design solutions, outline the scope of the project as well as the needs and wants of the end user as understood by the team, and develop a path towards the final design through description of the design process. The final design described in this document is centered around the user’s strongest muscle group (her abdomen and back muscles) to provide all necessary tricycle functions. These functions include steering, powering and braking. In general, the steering mechanism will utilize bevel gears to actuate the front wheel of the tricycle, the powering system will be a ratcheting push bar that is harnessed to the user’s torso, and the braking system will be a brake pad on the front wheel that is engaged by leaning back in the seat. This document contains our team’s process for developing our final design, solid model of our final design, justification calculations, manufacturing plans and engineering drawings, and our schedule for completion of the final product. In addition, a summary of the effects of the COVID-19 pandemic on project completion is provided, including an outline of future documentation which will aid an outside party in development and completion of our intended design, as well as the team’s revised project direction and scope
Patient advice regarding participation in sport in children with disorders of cerebrospinal fluid (CSF) circulation: a national survey of British paediatric neurosurgeons
Background
Management of children with disorders of cerebrospinal fluid (CSF) circulation is a common aspect of paediatric neurosurgical practice. Sport and physical activity play an integral role in the lives of patients in this age group. However, there is little evidence to support the dissemination of appropriate advice to children regarding such activities. The aim of this study was to evaluate the perspectives of clinicians across the UK regarding the participation of children with disorders of CSF circulation in sports.
Methods
Questionnaires were distributed to Consultant Paediatric Neurosurgeons practising across the UK via the Society of British Neurological Surgeons (SBNS). Five different patient scenarios were supplied, and participants were asked to choose whether they would advise participation in the following sports: Taekwondo, rugby, skiing, and football.
Results
An overall response rate of 66.7% (36 out of 54 paediatric neurosurgeons) was achieved. The following percentages of clinicians advocated football, rugby, Taekwondo, and skiing across all scenarios: 96%, 75%, 77%, and 97%, respectively. The majority of responders (91.2%) relied on personal experience when providing advice, whilst 50% used available literature and 19.4% used available guidelines.
Conclusions
There is a paucity of evidence in the literature to support the dissemination of appropriate advice to children with disorders of CSF circulation regarding participation in sports. Our findings demonstrate that the majority of clinicians rely on personal experience to make such decisions, emphasizing the necessity of larger scale studies to inform evidence-based guidelines
Fluorescence Recovery After Photobleaching (FRAP) of Fluorescence Tagged Proteins in Dendritic Spines of Cultured Hippocampal Neurons
FRAP has been used to quantify the mobility of GFP-tagged proteins. Using a strong excitation laser, the fluorescence of a GFP-tagged protein is bleached in the region of interest. The fluorescence of the region recovers when the unbleached GFP-tagged protein from outside of the region diffuses into the region of interest. The mobility of the protein is then analyzed by measuring the fluorescence recovery rate. This technique could be used to characterize protein mobility and turnover rate
Measurement of the orientation of buffer-gas-cooled, electrostatically-guided ammonia molecules
AbstractThe extent to which the spatial orientation of internally and translationally cold ammonia molecules can be controlled as molecules pass out of a quadrupole guide and through different electric field regions is examined. Ammonia molecules are collisionally cooled in a buffer gas cell, and are subsequently guided by a three-bend electrostatic quadrupole into a detection chamber. The orientation of ammonia molecules is probed using (2+1) resonance-enhanced multiphoton ionisation (REMPI), with the laser polarisation axis aligned both parallel and perpendicular to the time-of-flight axis. Even with the presence of a near-zero field region, the ammonia REMPI spectra indicate some retention of orientation. Monte Carlo simulations propagating the time-dependent Schrödinger equation in a full basis set including the hyperfine interaction enable the orientation of ammonia molecules to be calculated – with respect to both the local field direction and a space-fixed axis – as the molecules pass through different electric field regions. The simulations indicate that the orientation of ∼95% of ammonia molecules in JK=11 could be achieved with the application of a small bias voltage (17V) to the mesh separating the quadrupole and detection regions. Following the recent combination of the buffer gas cell and quadrupole guide apparatus with a linear Paul ion trap, this result could enable one to examine the influence of molecular orientation on ion-molecule reaction dynamics and kinetics
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