93,555 research outputs found
Signal Amplification by Sensitive Control of Bifurcation Topology
We describe a novel amplification scheme based on inducing dynamical changes to the topology of a bifurcation diagram of a simple nonlinear dynamical system. We have implemented a first bifurcation-topology amplifier using a coupled pair of parametrically driven high-frequency nanoelectromechanical systems resonators, demonstrating robust small-signal amplification. The principles that underlie bifurcation-topology amplification are simple and generic, suggesting its applicability to a wide variety of physical, chemical, and biological systems
Multiple Order Dual-Band Active Ring Filters with Composite Right/Left Handed Cells
In this paper, a novel dual-band active filter topology is presented. The non-linear phase response of a composite right/left-handed cell is used to achieve the desired dual-band performance. Additionally, the proposed structure based on coupled ring resonators yields a very compact solution in which high-order implementations can be easily obtained by cascading multiple rings. The theoretical principles of this type of filters are analyzed in detail. Finally, three prototypes based on first-, second- and third-order structures validate the feasibility of this type of filters. Good agreement between simulations and measurements has been achieved
A Quantum Critical Point from Flavours on a Compact Space
We analyse a dimensional defect field theory on a two sphere in an
external magnetic field. The theory is holographically dual to probe D5-branes
in global AdS background. At any finite magnetic field only the
confined phase of the theory is realised. There is a first order quantum phase
transition, within the confined phase of theory, ending on a quantum critical
point of a second order phase transition. We analyse the condensate and
magnetisation of theory and construct its phase diagram. We study the critical
exponents near the quantum critical point and find that the second derivatives
of the free energy, with respect to the bare mass and the magnetic field,
diverge with a critical exponent of . Next, we analyse the meson spectrum
of the theory and identify a massless mode at the critical point signalling a
diverging correlation length of the quantum fluctuations. We find that the
derivative of the meson mass with respect to the bare mass also diverges with a
critical exponent of . Finally, our studies of the magnetisation uncover
a persistent diamagnetic response similar to that in mesoscopic systems, such
as quantum dots and nano tubes.Comment: 26 pages, 16 figures, minor corrections, introduction expanded, typos
fixed, format improved, updated to much the published versio
Magnetic field topology of the unique chemically peculiar star CU Virginis
The late-B magnetic chemically peculiar star CU Vir is one of the fastest
rotators among the intermediate-mass stars with strong fossil magnetic fields.
It shows a prominent rotational modulation of the spectral energy distribution
and absorption line profiles due to chemical spots and exhibits a unique
strongly beamed variable radio emission. Little is known about the magnetic
field topology of CU Vir. In this study we aim to derive, for the first time,
detailed maps of the magnetic field distribution over the surface of this star.
We use high-resolution spectropolarimetric observations covering the entire
rotational period. These data are interpreted using a multi-line technique of
least-squares deconvolution (LSD) and a new Zeeman Doppler imaging code based
on detailed polarised radiative transfer modelling of the Stokes I and V LSD
profiles. This new magnetic inversion approach relies on the spectrum synthesis
calculations over the full wavelength range covered by observations and does
not assume that the LSD profiles behave as a single spectral line with mean
parameters. We present magnetic and chemical abundance maps derived from the Si
and Fe lines. Mean polarisation profiles of both elements reveal a significant
departure of the magnetic field topology of CU Vir from the commonly assumed
axisymmetric dipolar configuration. The field of CU Vir is dipolar-like, but
clearly non-axisymmetric, showing a large difference of the field strength
between the regions of opposite polarity. The main relative abundance depletion
features in both Si and Fe maps coincide with the weak-field region in the
magnetic map. Detailed information on the distorted dipolar magnetic field
topology of CU Vir provided by our study is essential for understanding
chemical spot formation, radio emission, and rotational period variation of
this star.Comment: 14 pages, 14 figures; accepted for publication in A&
On micro-structural effects in dielectric mixtures
The paper presents numerical simulations performed on dielectric properties
of two-dimensional binary composites on eleven regular space filling
tessellations. First, significant contributions of different parameters, which
play an important role in the electrical properties of the composite, are
introduced both for designing and analyzing material mixtures. Later, influence
of structural differences and intrinsic electrical properties of constituents
on the composite's over all electrical properties are investigated. The
structural differences are resolved by the spectral density representation
approach. The numerical technique, without any {\em a-priori} assumptions, for
extracting the spectral density function is also presented.Comment: 24 pages, 8 figure and 7 tables. It is submitted to IEEE Transactions
on Dielectrics and Electrical Insulatio
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