6,367 research outputs found
Space telescope phase B definition study. Volume 2A: Science instruments, f24 field camera
The analysis and design of the F/24 field camera for the space telescope are discussed. The camera was designed for application to the radial bay of the optical telescope assembly and has an on axis field of view of 3 arc-minutes by 3 arc-minutes
Investigation of FlexAlgo for User-driven Path Control
This paper examines the Flexible Algorithm (FlexAlgo) for its potential to enable user-driven path control in intra-domain Segment Routing (SR) enabled networks. FlexAlgo is a relatively new approach to intra-domain routing that allows multiple custom algorithms to coexist within a single domain. This capability has the potential to provide users with greater control over the paths their data takes through a network. The research includes a thorough investigation of the FlexAlgo approach, including an examination of its underlying techniques, as well as a practical implementation of a FlexAlgo-based solution. We depict performed experiments where we implemented FlexAlgo in three different scenarios. We also present how we developed an automated tool for users to control traffic steering using preferred metrics and constraints. The results of this investigation demonstrate the capabilities of FlexAlgo as a means of enabling user-driven path control and therefore increase security and trust of users towards the network.</p
Intermediate-statistics spin waves
In this paper, we show that spin waves, the elementary excitation of the
Heisenberg magnetic system, obey a kind of intermediate statistics with a
finite maximum occupation number n. We construct an operator realization for
the intermediate statistics obeyed by magnons, the quantized spin waves, and
then construct a corresponding intermediate-statistics realization for the
angular momentum algebra in terms of the creation and annihilation operators of
the magnons. In other words, instead of the Holstein-Primakoff representation,
a bosonic representation subject to a constraint on the occupation number, we
present an intermediate-statistics representation with no constraints. In this
realization, the maximum occupation number is naturally embodied in the
commutation relation of creation and annihilation operators, while the
Holstein-Primakoff representation is a bosonic operator relation with an
additional putting-in-by-hand restriction on the occupation number. We deduce
the intermediate-statistics distribution function for magnons. On the basis of
these results, we calculate the dispersion relations for ferromagnetic and
antiferromagnetic spin waves. The relations between the intermediate statistics
that magnons obey and the other two important kinds of intermediate statistics,
Haldane-Wu statistics and the fractional statistics of anyons, are discussed.
We also compare the spectrum of the intermediate-statistics spin wave with the
exact solution of the one-dimensional s = 1/2 Heisenberg model, which is
obtained by the Bethe ansatz method. For ferromagnets, we take the
contributions from the interaction between magnons (the quartic contribution),
the next-to-nearest neighbor interaction, and the dipolar interaction into
account for comparison with the experiment.Comment: 22 pages, 2 figure
Trends in Computer Network Modeling Towards the Future Internet
This article provides a taxonomy of current and past network modeling efforts. In all these efforts over the last few years we see a trend towards not only describing the network, but connected devices as well. This is especially current given the many Future Internet projects, which are combining different models, and resources in order to provide complete virtual infrastructures to users. An important mechanism for managing complexity is the creation of an abstract model, a step which has been undertaken in computer networks too. The fact that more and more devices are network capable, coupled with increasing popularity of the Internet, has made computer networks an important focus area for modeling. The large number of connected devices creates an increasing complexity which must be harnessed to keep the networks functioning. Over the years many different models for computer networks have been proposed, and used for different purposes. While for some time the community has moved away from the need of full topology exchange, this requirement resurfaced for optical networks. Subsequently, research on topology descriptions has seen a rise in the last few years. Many different models have been created and published, yet there is no publication that shows an overview of the different approaches.
Exact particle and kinetic energy densities for one-dimensional confined gases of non-interacting fermions
We propose a new method for the evaluation of the particle density and
kinetic pressure profiles in inhomogeneous one-dimensional systems of
non-interacting fermions, and apply it to harmonically confined systems of up
to N=1000 fermions. The method invokes a Green's function operator in
coordinate space, which is handled by techniques originally developed for the
calculation of the density of single-particle states from Green's functions in
the energy domain. In contrast to the Thomas-Fermi (local density)
approximation, the exact profiles under harmonic confinement show negative
local pressure in the tails and a prominent shell structure which may become
accessible to observation in magnetically trapped gases of fermionic alkali
atoms.Comment: 8 pages, 3 figures, accepted for publication in Phys. Rev. Let
Role of Quantum Confinement in Luminescence Efficiency of Group IV Nanostructures
Experimental results obtained previously for the photoluminescence efficiency
(PL) of Ge quantum dots (QDs) are theoretically studied. A
- plot of PL versus QD diameter () resulted in an
identical slope for each Ge QD sample only when . We
identified that above 6.2 nm: due to a changing
effective mass (EM), while below 4.6 nm: due to
electron/ hole confinement. We propose that as the QD size is initially
reduced, the EM is reduced, which increases the Bohr radius and interface
scattering until eventually pure quantum confinement effects dominate at small
- …