5,854 research outputs found
Rotation in liquid He: Lessons from a toy model
This paper presents an analysis of a model problem, consisting of two
interacting rigid rings, for the rotation of molecules in liquid He. Due to
Bose symmetry, the excitation of the rotor corresponding to a ring of N helium
atoms is restricted to states with integer multiples of N quanta of angular
momentum. This minimal model shares many of the same features of the rotational
spectra that have been observed for molecules in nanodroplets of helium atoms. In particular, this model predicts, for the first time,
the very large enhancement of the centrifugal distortion constants that have
been observed experimentally. It also illustrates the different effects of
increasing rotational velocity by increases in angular momentum quantum number
or by increasing the rotational constant of the molecular rotor. It is found
that fixed node, diffusion Monte Carlo and a hydrodynamic model provide upper
and lower bounds on the size of the effective rotational constant of the
molecular rotor when coupled to the helium
Very Low Cost Entropy Source Based on Chaotic Dynamics Retrofittable on Networked Devices to Prevent RNG Attacks
Good quality entropy sources are indispensable in most modern cryptographic
protocols. Unfortunately, many currently deployed networked devices do not
include them and may be vulnerable to Random Number Generator (RNG) attacks.
Since most of these systems allow firmware upgrades and have serial
communication facilities, the potential for retrofitting them with secure
hardware-based entropy sources exists. To this aim, very low-cost, robust, easy
to deploy solutions are required. Here, a retrofittable, sub 10$ entropy source
based on chaotic dynamics is illustrated, capable of a 32 kbit/s rate or more
and offering multiple serial communication options including USB, I2C, SPI or
USART. Operation is based on a loop built around the Analog to Digital
Converter (ADC) hosted on a standard microcontroller.Comment: 4 pages, 6 figures. Pre-print from conference proceedings; IEEE 21th
International Conference on Electronics, Circuits, and Systems (ICECS 2014),
pp. 175-178, Dec. 201
Output Filter Aware Optimization of the Noise Shaping Properties of {\Delta}{\Sigma} Modulators via Semi-Definite Programming
The Noise Transfer Function (NTF) of {\Delta}{\Sigma} modulators is typically
designed after the features of the input signal. We suggest that in many
applications, and notably those involving D/D and D/A conversion or actuation,
the NTF should instead be shaped after the properties of the
output/reconstruction filter. To this aim, we propose a framework for optimal
design based on the Kalman-Yakubovich-Popov (KYP) lemma and semi-definite
programming. Some examples illustrate how in practical cases the proposed
strategy can outperform more standard approaches.Comment: 14 pages, 18 figures, journal. Code accompanying the paper is
available at http://pydsm.googlecode.co
Noise Weighting in the Design of {\Delta}{\Sigma} Modulators (with a Psychoacoustic Coder as an Example)
A design flow for {\Delta}{\Sigma} modulators is illustrated, allowing
quantization noise to be shaped according to an arbitrary weighting profile.
Being based on FIR NTFs, possibly with high order, the flow is best suited for
digital architectures. The work builds on a recent proposal where the modulator
is matched to the reconstruction filter, showing that this type of optimization
can benefit a wide range of applications where noise (including in-band noise)
is known to have a different impact at different frequencies. The design of a
multiband modulator, a modulator avoiding DC noise, and an audio modulator
capable of distributing quantization artifacts according to a psychoacoustic
model are discussed as examples. A software toolbox is provided as a general
design aid and to replicate the proposed results.Comment: 5 pages, 18 figures, journal. Code accompanying the paper is
available at http://pydsm.googlecode.co
Should {\Delta}{\Sigma} Modulators Used in AC Motor Drives be Adapted to the Mechanical Load of the Motor?
We consider the use of {\Delta}{\Sigma} modulators in ac motor drives,
focusing on the many additional degrees of freedom that this option offers over
Pulse Width Modulation (PWM). Following some recent results, we show that it is
possible to fully adapt the {\Delta}{\Sigma} modulator Noise Transfer Function
(NTF) to the rest of the drive chain and that the approach can be pushed even
to a fine adaptation of the NTF to the specific motor loading condition. We
investigate whether and to what extent the adaptation should be pursued. Using
a representative test case and extensive simulation, we conclude that a mild
adaptation can be beneficial, leading to Signal to Noise Ratio (SNR)
improvements in the order a few dB, while the advantage pushing the adaptation
to the load tracking is likely to be minimal.Comment: Sample code available at http://pydsm.googlecode.co
Dynamics of Rotation of Super-Earths
We numerically investigate the dynamics of rotation of several close-in
terrestrial exoplanet candidates. In our model, the rotation of the planet is
disturbed by the torque of the central star due to the asymmetric equilibrium
figure of the planet. We model the shape of the planet by a Jeans spheroid. We
use surfaces of section and spectral analysis to explore numerically the
rotation phase space of the systems adopting different sets of parameters and
initial conditions close to the main spin-orbit resonant states. One of the
parameters, the orbital eccentricity, is critically discussed here within the
domain of validity of orbital circularization timescales given by tidal models.
We show that, depending on some parameters of the system like the radius and
mass of the planet, eccentricity etc, the rotation can be strongly perturbed
and a chaotic layer around the synchronous state may occupy a significant
region of the phase space. 55 Cnc e is an example.Comment: In Press. Celestial Mechanics and Dynamical Astronomy. 30 pages, 9
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Design for testability of high-order OTA-C filters
Copyright © 2016 John Wiley & Sons, Ltd.A study of oscillation-based test for high-order Operational Transconductance Amplifier-C (OTA-C) filters is presented. The method is based on partition of a high-order filter into second-order filter functions. The opening Q-loop and adding positive feedback techniques are developed to convert the second-order filter section into a quadrature oscillator. These techniques are based on an open-loop configuration and an additional positive feedback configuration. Implementation of the two testability design methods for nth-order cascade, IFLF and leapfrog (LF) filters is presented, and the area overhead of the modified circuits is also discussed. The performances of the presented techniques are investigated. Fourth-order cascade, inverse follow-the-leader feedback (IFLF) and LF OTA-C filters were designed and simulated for analysis of fault coverage using the adding positive feedback method based on an analogue multiplexer. Simulation results show that the oscillation-based test method using positive feedback provides high fault coverage of around 97%, 96% and 95% for the cascade, IFLF and LF OTA-C filters, respectively. Copyright ÂPeer reviewe
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