6,768 research outputs found
Effect of turbulence on electron cyclotron current drive and heating in ITER
Non-linear local electromagnetic gyrokinetic turbulence simulations of the
ITER standard scenario H-mode are presented for the q=3/2 and q=2 surfaces. The
turbulent transport is examined in regions of velocity space characteristic of
electrons heated by electron cyclotron waves. Electromagnetic fluctuations and
sub-dominant micro-tearing modes are found to contribute significantly to the
transport of the accelerated electrons, even though they have only a small
impact on the transport of the bulk species. The particle diffusivity for
resonant passing electrons is found to be less than 0.15 m^2/s, and their heat
conductivity is found to be less than 2 m^2/s. Implications for the broadening
of the current drive and energy deposition in ITER are discussed.Comment: Letter, 5 pages, 5 figures, for submission to Nuclear Fusio
On the equivalence of two deformation schemes in quantum field theory
Two recent deformation schemes for quantum field theories on the
two-dimensional Minkowski space, making use of deformed field operators and
Longo-Witten endomorphisms, respectively, are shown to be equivalent.Comment: 14 pages, no figure. The final version is available under Open
Access. CC-B
The linear tearing instability in three dimensional, toroidal gyrokinetic simulations
Linear gyro-kinetic simulations of the classical tearing mode in
three-dimensional toroidal geometry were performed using the global gyro
kinetic turbulence code, GKW . The results were benchmarked against a
cylindrical ideal MHD and analytical theory calculations. The stability, growth
rate and frequency of the mode were investigated by varying the current
profile, collisionality and the pressure gradients. Both collision-less and
semi-collisional tearing modes were found with a smooth transition between the
two. A residual, finite, rotation frequency of the mode even in the absense of
a pressure gradient is observed which is attributed to toroidal finite
Larmor-radius effects. When a pressure gradient is present at low
collisionality, the mode rotates at the expected electron diamagnetic
frequency. However the island rotation reverses direction at high
collisionality. The growth rate is found to follow a scaling with
collisional resistivity in the semi-collisional regime, closely following the
semi-collisional scaling found by Fitzpatrick. The stability of the mode
closely follows the stability using resistive MHD theory, however a
modification due to toroidal coupling and pressure effects is seen
Clean and Green Urban Water Bodies Benefit Nocturnal Flying Insects and Their Predators, Insectivorous Bats
Nocturnal arthropods form the prey base for many predators and are an integral part of complex food webs. However, there is limited understanding of the mechanisms influencing invertebrates at urban water bodies and the potential flow-on effects to their predators. This study aims to: (i) understand the importance of standing water bodies for nocturnal flying insect orders, including the landscape- and local-scale factors driving these patterns; and (ii) quantify the relationship between insects and insectivorous bats. We investigated nocturnal flying insects and insectivorous bats simultaneously at water bodies (n = 58) and non-water body sites (n = 35) using light traps and acoustic recorders in Melbourne, Australia. At the landscape scale, we found that the presence of water and high levels of surrounding greenness were important predictors for some insect orders. At the water body scale, low levels of sediment pollutants, increased riparian tree cover and water body size supported higher insect order richness and a greater abundance of Coleopterans and Trichopterans, respectively. Most bat species had a positive response to a high abundance of Lepidopterans, confirming the importance of this order in the diet of insectivorous bats. Fostering communities of nocturnal insects in urban environments can provide opportunities for enhancing the prey base of urban nocturnal insectivores.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli
Spectral triples and the super-Virasoro algebra
We construct infinite dimensional spectral triples associated with
representations of the super-Virasoro algebra. In particular the irreducible,
unitary positive energy representation of the Ramond algebra with central
charge c and minimal lowest weight h=c/24 is graded and gives rise to a net of
even theta-summable spectral triples with non-zero Fredholm index. The
irreducible unitary positive energy representations of the Neveu-Schwarz
algebra give rise to nets of even theta-summable generalised spectral triples
where there is no Dirac operator but only a superderivation.Comment: 27 pages; v2: a comment concerning the difficulty in defining cyclic
cocycles in the NS case have been adde
The Measurement Process in Local Quantum Theory and the EPR Paradox
We describe in a qualitative way a possible picture of the Measurement
Process in Quantum Mechanics, which takes into account: 1. the finite and non
zero time duration T of the interaction between the observed system and the
microscopic part of the measurement apparatus; 2. the finite space size R of
that apparatus; 3. the fact that the macroscopic part of the measurement
apparatus, having the role of amplifying the effect of that interaction to a
macroscopic scale, is composed by a very large but finite number N of
particles. The conventional picture of the measurement, as an instantaneous
action turning a pure state into a mixture, arises only in the limit in which N
and R tend to infinity, and T tends to 0. We sketch here a proposed scheme,
which still ought to be made mathematically precise in order to analyse its
implications and to test it in specific models, where we argue that in Quantum
Field Theory this picture should apply to the unique time evolution expressing
the dynamics of a given theory, and should comply with the Principle of
Locality. We comment on the Einstein Podolski Rosen thought experiment (partly
modifying the discussion on this point in an earlier version of this note),
reformulated here only in terms of local observables (rather than global ones,
as one particle or polarisation observables). The local picture of the
measurement process helps to make it clear that there is no conflict with the
Principle of Locality.Comment: 18 page
Quantum Field Theory: Where We Are
We comment on the present status, the concepts and their limitations, and the
successes and open problems of the various approaches to a relativistic quantum
theory of elementary particles, with a hindsight to questions concerning
quantum gravity and string theory.Comment: To appear in: An Assessment of Current Paradigms in the Physics of
Fundamental Phenomena, to be published by Springer Verlag (2006
Dynamics of Josephson junctions and single-flux-quantum networks with superconductor-insulator-normal metal junction shunts
Within the framework of the microscopic model of tunneling, we modelled the
behavior of the Josephson junction shunted by the
Superconductor-Insulator-Normal metal (SIN) tunnel junction. We found that the
electromagnetic impedance of the SIN junction yields both the
frequency-dependent damping and dynamic reactance which leads to an increase in
the effective capacitance of the circuit. We calculated the dc I-V curves and
transient characteristics of these circuits and explained their quantitative
differences to the curves obtained within the resistively shunted junction
model. The correct operation of the basic single-flux-quanta circuits with such
SIN-shunted junctions, i.e. the Josephson transmission line and the toggle
flip-flop, have also been modelled.Comment: 8 pages incl. 7 figure
Space shuttle: Static aerodynamic characteristics and control effectiveness of two delta wing orbiter configurations (M equals 0.6 to 4.96)
Two 0.00325-scale models of a space shuttle orbiter were tested in trisonic wind tunnel to obtain force, static stability, and control effectiveness data by six component internal strain gauge balance. Two separate configurations were tested; however, the fuselage and basic wing were of one-piece construction. The configurations were varied by replacing the straight wing tip extensions with upswept wing tips. Directional stability was provided for one configuration by a centerline vertical tail. Due to the one-piece body/wing construction, no body-alone data were obtained. The effect of tip fins and vertical tail size were, however, investigated. Both configurations were tested over a Mach range of 0.6 to 4.96 with data taken at angles of attack from minus 4 deg to 60 deg and at angles of sideslip from minus 4 deg to 10 deg
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