2,328 research outputs found
Collisions of strings with Y junctions
We study the dynamics of Nambu--Goto strings with junctions at which three
strings meet. In particular, we exhibit one simple exact solution and examine
the process of intercommuting of two straight strings, in which they exchange
partners but become joined by a third string. We show that there are important
kinematical constraints on this process. The exchange cannot occur if the
strings meet with very large relative velocity. This may have important
implications for the evolution of cosmic superstring networks and non-abelian
string networks.Comment: 4 pages, 1 figure, uses revtex 4. Clarifying comments added to
correct a conceptual error, reference updated. Version accepted by Phys Rev
Letters, with additional references and minor change
Chiral Superconducting Membranes
We develop the dynamics of the chiral superconducting membranes (with null
current) in an alternative geometric approach either making a Lagrangian
description and a Hamiltonian point of view. Besides of this, we show the
equivalence of the resulting descriptions to the one known Dirac-Nambu-Goto
(DNG) case. Integrability for chiral string model is obtained using a proposed
light-cone gauge. In a similar way, domain walls are integrated by means of a
simple ansatz. We compare the results with recently works appeared in the
literature.Comment: Latex file, 17 pages, no figures. Improved version, typos corrected,
Comments and references adde
Brane Gas Inflation
We consider the brane gas picture of the early universe. At later stages,
when there are no winding modes and the background is free to expand, we show
that a moving 3-brane, which we identify with our universe, can inflate even
though it is radiation-dominated. The crucial ingredients for successful
inflation are the coupling to the dilaton and the equation of state of the
bulk. If we suppose the brane initially forms in a collision of
higher-dimensional branes, then the spectrum of primordial density fluctuations
naturally has a thermal origin.Comment: 4 pages, 1 figur
PickCells: A Physically Reconfigurable Cell-composed Touchscreen
Touchscreens are the predominant medium for interactions with digital services; however, their current fixed form factor narrows the scope for rich physical interactions by limiting interaction possibilities to a single, planar surface. In this paper we introduce the concept of PickCells, a fully reconfigurable device concept composed of cells, that breaks the mould of rigid screens and explores a modular system that affords rich sets of tangible interactions and novel acrossdevice relationships. Through a series of co-design activities – involving HCI experts and potential end-users of such systems – we synthesised a design space aimed at inspiring future research, giving researchers and designers a framework in which to explore modular screen interactions. The design space we propose unifies existing works on modular touch surfaces under a general framework and broadens horizons by opening up unexplored spaces providing new interaction possibilities. In this paper, we present the PickCells concept, a design space of modular touch surfaces, and propose a toolkit for quick scenario prototyping
Monolithic fabrication of a planar Gunn diode and a pHEMT side-by-side
This work presents the implementation of planar Gunn diodes and pseudomorphic high electron mobility transistors (pHEMTs) on the same wafer for the first time. The AlGaAs/InGaAs/GaAs heterostructures were designed for the realisation of pHEMTs on a Gallium Arsenide — based wafer. T-gate technology has been used for the maximisation of the transistor performance. Devices with a 70 nm long gate foot showed excellent DC and small-signal characteristics, with 780 mS/mm peak transconductance and 200 GHz fmax. Planar Gunn diodes were fabricated in parallel with the pHEMTs, sharing most of the fabrication steps. The diodes produce oscillations with 87.6 GHz maximum frequency and −40 dBm maximum output power
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