4,145 research outputs found
Ka-band Ga-As FET noise receiver/device development
The development of technology for a 30 GHz low noise receiver utilizing GaAs FET devices exclusively is discussed. This program required single and dual-gate FET devices, low noise FET amplifiers, dual-gate FET mixers, and FET oscillators operating at Ka-band frequencies. A 0.25 micrometer gate FET device, developed with a minimum noise figure of 3.3 dB at 29 GHz and an associated gain of 7.4 dB, was used to fabricate a 3-stage amplifier with a minimum noise figure and associated gain of 4.4 dB and 17 dB, respectively. The 1-dB gain bandwidth of this amplifier extended from below 26.5 GHz to 30.5 GHz. A dual-gate mixer with a 2 dB conversion loss and a minimum noise figure of 10 dB at 29 GHz as well as a dielectric resonator stabilized FET oscillator at 25 GHz for the receiver L0. From these components, a hybrid microwave integrated circuit receiver was constructed which demonstrates a minimum single-side band noise figure of 4.6 dB at 29 GHz with a conversion gain of 17 dB. The output power at the 1-dB gain compression point was -5 dBm
Rainbow universe
The formalism of rainbow gravity is studied in a cosmological setting. We
consider the very early universe which is radiation dominated. A novel
treatment in our paper is to look for an ``averaged'' cosmological metric
probed by radiation particles themselves. Taking their cosmological evolution
into account, we derive the modified Friedmann-Robertson-Walker(FRW) equations
which is a generalization of the solution presented by Magueijo and Smolin.
Based on this phenomenological cosmological model we argue that the spacetime
curvature has an upper bound such that the cosmological singularity is absent.
These modified equations can be treated as effective equations in the
semi-classical framework of quantum gravity and its analogy with the one
recently proposed in loop quantum cosmology is also discussed.Comment: 5 page
Wilson loops, geometric operators and fermions in 3d group field theory
Group field theories whose Feynman diagrams describe 3d gravity with a
varying configuration of Wilson loop observables and 3d gravity with volume
observables at each vertex are defined. The volume observables are created by
the usual spin network grasping operators which require the introduction of
vector fields on the group. We then use this to define group field theories
that give a previously defined spin foam model for fermion fields coupled to
gravity, and the simpler quenched approximation, by using tensor fields on the
group. The group field theory naturally includes the sum over fermionic loops
at each order of the perturbation theory.Comment: 13 pages, many figures, uses psfra
Particle Topology, Braids, and Braided Belts
Recent work suggests that topological features of certain quantum gravity
theories can be interpreted as particles, matching the known fermions and
bosons of the first generation in the Standard Model. This is achieved by
identifying topological structures with elements of the framed Artin braid
group on three strands, and demonstrating a correspondence between the
invariants used to characterise these braids (a braid is a set of
non-intersecting curves, that connect one set of points with another set of
points), and quantities like electric charge, colour charge, and so on. In
this paper we show how to manipulate a modified form of framed braids to yield
an invariant standard form for sets of isomorphic braids, characterised by a
vector of real numbers. This will serve as a basis for more complete
discussions of quantum numbers in future work.Comment: 21 pages, 16 figure
Fusiform Rust Trends in East Texas: 1969-1987
Five surveys of pine plantations in East Texas over an 18-year period (1969-1987) indicated that fusiform rust (Cronartium quercuum [Berk.] Miyabe ex Shirai f. sp. fusiforme Birdsall and Snow) infection rates have increased to current levels of about 50% on slash pine (Pinus elliottii Engelm.) and are continuing to increase on loblolly pine (Pinus taeda L.) to 10-15% levels. South. J. Appl. For. 12(4):259-26
Infinite Degeneracy of States in Quantum Gravity
The setting of Braided Ribbon Networks is used to present a general result in
spin-networks embedded in manifolds: the existence of an infinite number of
species of conserved quantities. Restricted to three-valent networks the number
of such conserved quantities in a given network is shown to be invariant
barring a single case. The implication of these conserved quantities is
discussed in the context of Loop Quantum Gravity.Comment: 10 pages, 14 figures, v2: some clarifications, no substantial change
Asymptotic Flatness in Rainbow Gravity
A construction of conformal infinity in null and spatial directions is
constructed for the Rainbow-flat space-time corresponding to doubly special
relativity. From this construction a definition of asymptotic DSRness is put
forward which is compatible with the correspondence principle of Rainbow
gravity. Furthermore a result equating asymptotically flat space-times with
asymptotically DSR spacetimes is presented.Comment: 11 page
Locality and Translations in Braided Ribbon Networks
An overview of microlocality in braided ribbon networks is presented.
Following this, a series of definitions are presented to explore the concept of
microlocality and the topology of ribbon networks. Isolated substructure of
ribbon networks are introduced, and a theorem is proven that allows them to be
relocated. This is followed by a demonstration of microlocal translations.
Additionally, an investigation into macrolocality and the implications of
invariants in braided ribbon networks are presented.Comment: 12 pages, 12 figure
Asymptotic quasinormal modes of scalar field in a gravity's rainbow
In the context of a gravity's rainbow, the asymptotic quasinormal modes of
the scalar perturbation in the quantum modified Schwarzschild black holes are
investigated. By using the monodromy method, we calculated and obtained the
asymptotic quasinormal frequencies, which are dominated not only by the mass
parameter of the spacetime, but also by the energy functions from the modified
dispersion relations. However, the real parts of the asymptotic quasinormal
modes is still , which is consistent with Hod's conjecture. In
addition, for the quantum corrected black hole, the area spacing is calculated
and the result is independent of the energy functions, in spite of the area
itself is energy dependence. And that, by relating the area spectrum to loop
quantum gravity, the Barbero-Immirzi parameter is given and it remains the same
as from the usual black hole
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