9,331 research outputs found
Chemical species and chemical reactions of importance in nonequilibrium performance calculations
Chemical species and reactions of propellant systems determined for nonequilibrium flow - Performance calculation
Chemical species and chemical reactions of importance in nonequilibrium performance calculations
Computer programs to determine inviscid one dimensional and axisymmetric nonequilibrium nozzle flow field
The pulsar synchrotron: coherent radio emission
We propose a simple physical picture for the generation of coherent radio
emission in the axisymmetric pulsar magnetosphere that is quite different from
the canonical paradigm of radio emission coming from the magnetic polar caps.
In this first paper we consider only the axisymmetric case of an aligned
rotator. Our picture capitalizes on an important element of the MHD
representation of the magnetosphere, namely the separatrix between the
corotating closed-line region (the `dead zone') and the open field lines that
originate in the polar caps. Along the separatrix flows the return current that
corresponds to the main magnetospheric electric current emanating from the
polar caps. Across the separatrix, both the toroidal and poloidal components of
the magnetic field change discontinuously. The poloidal component discontinuity
requires the presence of a significant annular electric current which has up to
now been unaccounted for. We estimate the position and thickness of this
annular current at the tip of the closed line region, and show that it consists
of electrons (positrons) corotating with Lorentz factors on the order of 10^5,
emitting incoherent synchrotron radiation that peaks in the hard X-rays. These
particles stay in the region of highest annular current close to the equator
for a path-length of the order of one meter. We propose that, at wavelengths
comparable to that path-length, the particles emit coherent radiation, with
radiated power proportional to N^2, where N is the population of particles in
the above path-length. We calculate the total radio power in this wavelength
regime and its scaling with pulsar period and stellar magnetic field and show
that it is consistent with estimates of radio luminosity based on observations.Comment: Monthly Notices Letters, in pres
The Embedded Neuron, the Enactive Field?
The concept of the receptive field, first articulated by Hartline, is central to visual neuroscience. The receptive field of a neuron encompasses the spatial and temporal properties of stimuli that activate the neuron, and, as Hubel and Wiesel conceived of it, a neuron’s receptive field is static. This makes it possible to build models of neural circuits and to build up more complex receptive fields out of simpler ones. Recent work in visual neurophysiology is providing evidence that the classical receptive field is an inaccurate picture. The receptive field seems to be a dynamic feature of the neuron. In particular, the receptive field of neurons in V1 seems to be dependent on the properties of the stimulus. In this paper, we review the history of the concept of the receptive field and the problematic data. We then consider a number of possible theoretical responses to these data
Differential scanning calorimetry of coal
Differential scanning calorimetry studies performed during the first year of this project demonstrated the occurrence of exothermic reactions associated with the production of volatile matter in or near the plastic region. The temperature and magnitude of the exothermic peak were observed to be strongly affected by the heating rate, sample mass and, to a lesser extent, by sample particle size. Thermal properties also were found to be influenced by oxidation of the coal sample due to weathering effects
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