1,378 research outputs found
Sintered silicon carbide molded body and method for its production
Sintered silicon carbide shapes are described. They are produced by using a composition containing an oxide of at least one element chosen from the group: Li, Be, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Nb, Mo, Ba, Tc, Ta, W and Th as a supplement to known sintering aids
Oblique Ion Two-Stream Instability in the Foot Region of a Collisionless Shock
Electrostatic behavior of a collisionless plasma in the foot region of high
Mach number perpendicular shocks is investigated through the two-dimensional
linear analysis and electrostatic particle-in-cell (PIC) simulation. The
simulations are double periodic and taken as a proxy for the situation in the
foot. The linear analysis for relatively cold unmagnetized plasmas with a
reflected proton beam shows that obliquely propagating Buneman instability is
strongly excited. We also found that when the electron temperature is much
higher than the proton temperature, the most unstable mode is the highly
obliquely propagating ion two-stream instability excited through the resonance
between ion plasma oscillations of the background protons and of the beam
protons, rather than the ion acoustic instability that is dominant for parallel
propagation. To investigate nonlinear behavior of the ion two-stream
instability, we have made PIC simulations for the shock foot region in which
the initial state satisfies the Buneman instability condition. In the first
phase, electrostatic waves grow two-dimensionally by the Buneman instability to
heat electrons. In the second phase, highly oblique ion two-stream instability
grows to heat mainly ions. This result is in contrast to previous studies based
on one-dimensional simulations, for which ion acoustic instability further
heats electrons. The present result implies that overheating problem of
electrons for shocks in supernova remnants is resolved by considering ion
two-stream instability propagating highly obliquely to the shock normal and
that multi-dimensional analysis is crucial to understand the particle heating
and acceleration processes in shocks.Comment: 20 pages, 9 figures, accepted for publication in Ap
Absence of Electron Surfing Acceleration in a Two-Dimensional Simulation
Electron acceleration in high Mach number perpendicular shocks is
investigated through two-dimensional electrostatic particle-in-cell (PIC)
simulation. We simulate the shock foot region by modeling particles that
consist of three components such as incident protons and electrons and
reflected protons in the initial state which satisfies the Buneman instability
condition. In contrast to previous one-dimensional simulations in which strong
surfing acceleration is realized, we find that surfing acceleration does not
occur in two-dimensional simulation. This is because excited electrostatic
potentials have a two-dimensional structure that makes electron trapping
impossible. Thus, the surfing acceleration does not work either in itself or as
an injection mechanism for the diffusive shock acceleration. We briefly discuss
implications of the present results on the electron heating and acceleration by
shocks in supernova remnants.Comment: 12 pages, 4 figures, accepted for publication in ApJ
Resonance between Noise and Delay
We propose here a stochastic binary element whose transition rate depends on
its state at a fixed interval in the past. With this delayed stochastic
transition this is one of the simplest dynamical models under the influence of
``noise'' and ``delay''. We demonstrate numerically and analytically that we
can observe resonant phenomena between the oscillatory behavior due to noise
and that due to delay.Comment: 4 pages, 5 figures, submitted to Phys.Rev.Lett Expanded and Added
Reference
A New Aspect of the TrkB Signaling Pathway in Neural Plasticity
In the central nervous system (CNS), the expression of molecules is strictly regulated during development. Control of the spatiotemporal expression of molecules is a mechanism not only to construct the functional neuronal network but also to adjust the network in response to new information from outside of the individual, i.e., through learning and memory. Among the functional molecules in the CNS, one of the best-studied groups is the neurotrophins, which are nerve growth factor (NGF)-related gene family molecules. Neurotrophins include NGF, brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), and NT-4/5 in the mammal. Among neurotrophins and their receptors, BDNF and tropomyosin-related kinases B (TrkB) are enriched in the CNS. In the CNS, the BDNF-TrkB signaling pathway fulfills a wide variety of functions throughout life, such as cell survival, migration, outgrowth of axons and dendrites, synaptogenesis, synaptic transmission, and remodeling of synapses. Although the same ligand and receptor, BDNF and TrkB, act in these various developmental events, we do not yet understand what kind of mechanism provokes the functional multiplicity of the BDNF-TrkB signaling pathway. In this review, we discuss the mechanism that elicits the variety of functions performed by the BDNF-TrkB signaling pathway in the CNS as a tool of pharmacological therapy
Opening Access: Increasing Scholarly Impact with DigitalCommons@UNO
DigitalCommons@UNO (https://digitalcommons.unomaha.edu/) is an Institutional Repository (IR) and an initiative implemented by the University of Nebraska at Omaha (UNO) Libraries to support our UNO scholars through providing a Green Open Access solution. DigitalCommons@UNO disseminates a wide variety of scholarship including faculty papers, electronic theses and dissertations (ETDs), conferences and journals. Since its launch in 2014, the UNO Libraries have been implementing and managing DigitalCommons@UNO through outreach to the UNO community in an effort to collect scholarly works into the IR
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