3,241 research outputs found
Stability of three neutrino flavor conversion in supernovae
Neutrino-neutrino interactions can lead to collective flavor conversion in
the dense parts of a core collapse supernova. Growing instabilities that lead
to collective conversions have been studied intensely in the limit of
two-neutrino species and occur for inverted mass ordering in the case of a
perfectly spherical supernova. We examine two simple models of colliding and
intersecting neutrino beams and show, that for three neutrino species
instabilities exist also for normal mass ordering even in the case of a fully
symmetric system. Whereas the instability for inverted mass ordering is
associated with , the new instability we find for normal mass
ordering is associated with . As a consequence, the growth
rate of these new instabilities for normal ordering is smaller by about an
order of magnitude compared to the rates of the well studied case of inverted
ordering.Comment: 18 pages, 5 figures Minor update on the consistency of the formulae
and prefactors, actualized plot
Toward optimal X-ray flux utilization in breast CT
A realistic computer-simulation of a breast computed tomography (CT) system
and subject is constructed. The model is used to investigate the optimal number
of views for the scan given a fixed total X-ray fluence. The reconstruction
algorithm is based on accurate solution to a constrained, TV-minimization
problem, which has received much interest recently for sparse-view CT data.Comment: accepted to the 11th International Meeting on Fully Three-Dimensional
Image Reconstruction in Radiology and Nuclear Medicine 201
Electrical and terahertz magnetospectroscopy studies of laser-patterned micro- and nanostructures on InAs-based heterostructures
Nanostructures fabricated from narrow-gap semiconductors with strong
spin-orbit interaction (SOI), such as InAs, can be used to filter momentum
modes of electrons and offer the possibility to create and detect
spin-polarized currents entirely by electric fields. Here, we present
magnetotransport and THz magnetospectroscopy investigations of Hall-bars with
back-gates made from in InGaAs/InAlAs quantum well structures with a strained 4
nm InAs inserted channel. The two-dimensional electron gas is at 53 nm depth
and has a carrier density of about cm and mobility of
about cm/Vs, after illumination. Electrical and THz optical
transport measurements at low temperatures and in high magnetic fields reveal
an effective mass of 0.038 and an anisotropic -factor of up to 20,
larger than for bulk InAs or InAs-based heterostructures. We demonstrate that
quasi-one-dimensional channels can be formed by micro-laser lithography. The
population of subbands is controlled by in-plane gates. Contrary to previous
reports symmetric and asymmetric in-plane gate voltages applied to quasi-one
dimensional channels did not show indications of SOI-induced anomalies in the
conductance.Comment: v1 did not contain references due to filename mix-up; v3 is revision
following referee report; v4 is corrected version following acceptance; v5 is
the published versio
Restmaterialer fra bio-energiproduktion - kan de tilbageføres til marken?
Efluents from biogas production may be recycled to soil as plant nutrition. However, the proportion of plant-available nitrogen is high and may cause loss due to leaching or gaseous emissions. Hence, such waste stream materials must be applied with care to ensure maximum plant uptake to minimize loss. Spread of weed seeds via application of biogas effluents is only a problem when the digestion is performed at mesophilic conditions and when the seeds are staying less than a week in the plant. At thermophilic conditions, seeds from a range of weed plant were unable to germinate efter just a few days
Equilibrium properties of highly asymmetric star-polymer mixtures
We employ effective interaction potentials to study the equilibrium structure
and phase behavior of highly asymmetric mixtures of star polymers. We consider
in particular the influence of the addition of a component with a small number
of arms and a small size on a concentrated solution of large stars with a high
functionality. By employing liquid integral equation theories we examine the
evolution of the correlation functions of the big stars upon addition of the
small ones, finding a loss of structure that can be attributed to a weakening
of the repulsions between the large stars due to the presence of the small
ones. We analyze this phenomenon be means of a generalized depletion mechanism
which is supported by computer simulations. By applying thermodynamic
perturbation theory we draw the phase diagram of the asymmetric mixture,
finding that the addition of small stars melts the crystal formed by the big
ones. A systematic comparison between the two- and effective one-component
descriptions of the mixture that corroborates the reliability of the
generalized depletion picture is also carried out.Comment: 26 pages, 9 figures, submitted to Phys. Rev.
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