5,720 research outputs found
Catastrophic forgetting: still a problem for DNNs
We investigate the performance of DNNs when trained on class-incremental
visual problems consisting of initial training, followed by retraining with
added visual classes. Catastrophic forgetting (CF) behavior is measured using a
new evaluation procedure that aims at an application-oriented view of
incremental learning. In particular, it imposes that model selection must be
performed on the initial dataset alone, as well as demanding that retraining
control be performed only using the retraining dataset, as initial dataset is
usually too large to be kept. Experiments are conducted on class-incremental
problems derived from MNIST, using a variety of different DNN models, some of
them recently proposed to avoid catastrophic forgetting. When comparing our new
evaluation procedure to previous approaches for assessing CF, we find their
findings are completely negated, and that none of the tested methods can avoid
CF in all experiments. This stresses the importance of a realistic empirical
measurement procedure for catastrophic forgetting, and the need for further
research in incremental learning for DNNs.Comment: 10 pages, 11 figures, Artificial Neural Networks and Machine Learning
- ICANN 201
A Comparison of Hybrid Beamforming and Digital Beamforming with Low-Resolution ADCs for Multiple Users and Imperfect CSI
For 5G it will be important to leverage the available millimeter wave
spectrum. To achieve an approximately omni- directional coverage with a similar
effective antenna aperture compared to state of the art cellular systems, an
antenna array is required at both the mobile and basestation. Due to the large
bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog
front-end of the receiver with a large number of antennas becomes especially
power hungry. Two main solutions exist to reduce the power consumption: hybrid
beam forming and digital beam forming with low resolution Analog to Digital
Converters (ADCs). In this work we compare the spectral and energy efficiency
of both systems under practical system constraints. We consider the effects of
channel estimation, transmitter impairments and multiple simultaneous users.
Our power consumption model considers components reported in literature at 60
GHz. In contrast to many other works we also consider the correlation of the
quantization error, and generalize the modeling of it to non-uniform quantizers
and different quantizers at each antenna. The result shows that as the SNR gets
larger the ADC resolution achieving the optimal energy efficiency gets also
larger. The energy efficiency peaks for 5 bit resolution at high SNR, since due
to other limiting factors the achievable rate almost saturates at this
resolution. We also show that in the multi-user scenario digital beamforming is
in any case more energy efficient than hybrid beamforming. In addition we show
that if different ADC resolutions are used we can achieve any desired
trade-offs between power consumption and rate close to those achieved with only
one ADC resolution.Comment: Submitted to JSTSP. arXiv admin note: text overlap with
arXiv:1610.0290
High-precision force sensing using a single trapped ion
We introduce quantum sensing schemes for measuring very weak forces with a
single trapped ion. They use the spin-motional coupling induced by the
laser-ion interaction to transfer the relevant force information to the
spin-degree of freedom. Therefore, the force estimation is carried out simply
by observing the Ramsey-type oscillations of the ion spin states. Three quantum
probes are considered, which are represented by systems obeying the
Jaynes-Cummings, quantum Rabi (in 1D) and Jahn-Teller (in 2D) models. By using
dynamical decoupling schemes in the Jaynes-Cummings and Jahn-Teller models, our
force sensing protocols can be made robust to the spin dephasing caused by the
thermal and magnetic field fluctuations. In the quantum-Rabi probe, the
residual spin-phonon coupling vanishes, which makes this sensing protocol
naturally robust to thermally-induced spin dephasing. We show that the proposed
techniques can be used to sense the axial and transverse components of the
force with a sensitivity beyond the yN range, i.e. in the
xN (xennonewton, ). The Jahn-Teller protocol, in
particular, can be used to implement a two-channel vector spectrum analyzer for
measuring ultra-low voltages.Comment: 7 pages, 4 figure
The Reconstruction of Trilinear Higgs Couplings
To establish the Higgs mechanism {\it sui generis} experimentally, the Higgs
self-interaction potential must be reconstructed. This task requires the
measurement of the trilinear and quadrilinear self-couplings, as predicted in
the Standard Model or in supersymmetric theories. The couplings can be probed
in multiple Higgs production at high-luminosity e+e- linear colliders. We
present the theoretical analysis for the production of neutral Higgs-boson
pairs in the relevant channels of double Higgs-strahlung and associated
multiple Higgs production.Comment: 20 pages, Proceedings, "Physics with a High-Luminosity e+e- Linear
Collider", DESY/ECFA LC Workshop, DESY 99-123
Production of Neutral Higgs-Boson Pairs at LHC
The reconstruction of the Higgs potential in the Standard Model or
supersymmetric theories demands the measurement of the trilinear Higgs
couplings. These couplings affect the multiple production of Higgs bosons at
high energy colliders. We present a systematic overview of the cross sections
for the production of pairs of (light) neutral Higgs bosons at the LHC. The
analysis is carried out for the Standard Model and its minimal supersymmetric
extension.Comment: Latex, 11 pages, uses feynmp.sty [included]. The complete paper,
including figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-17/ or via www at
http://www-ttp.physik.uni-karlsruhe.de/Preprints
Testing Higgs Self-couplings at e^+e^- Linear Colliders
To establish the Higgs mechanism sui generis experimentally, the self-energy
potential of the Higgs field must be reconstructed. This task requires the
measurement of the trilinear and quadrilinear self-couplings, as predicted, for
instance, in the Standard Model or in supersymmetric theories. The couplings
can be probed in multiple Higgs production at high-luminosity e^+e^- linear
colliders. Complementing earlier studies to develop a coherent picture of the
trilinear couplings, we have analyzed the production of pairs of neutral Higgs
bosons in all relevant channels of double Higgs-strahlung, associated multiple
Higgs production and WW/ZZ fusion to Higgs pairs.Comment: The complete paper, including figures, is also available via
anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ttp99/ttp99-02/ or via
www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/webmaster/preprints
Gyrokinetic and kinetic particle-in-cell simulations of guide-field reconnection. I: Macroscopic effects of the electron flows
In this work, we compare gyrokinetic (GK) and fully kinetic Particle-in-Cell
(PIC) simulations of magnetic reconnection in the limit of strong guide field.
In particular, we analyze the limits of applicability of the GK plasma model
compared to a fully kinetic description of force free current sheets for finite
guide fields (). Here we report the first part of an extended comparison,
focusing on the macroscopic effects of the electron flows. For a low beta
plasma (), it is shown that both plasma models develop magnetic
reconnection with similar features in the secondary magnetic islands if a
sufficiently high guide field () is imposed in the kinetic PIC
simulations. Outside of these regions, in the separatrices close to the X
points, the convergence between both plasma descriptions is less restrictive
(). Kinetic PIC simulations using guide fields
reveal secondary magnetic islands with a core magnetic field and less energetic
flows inside of them in comparison to the GK or kinetic PIC runs with stronger
guide fields. We find that these processes are mostly due to an initial shear
flow absent in the GK initialization and negligible in the kinetic PIC high
guide field regime, in addition to fast outflows on the order of the ion
thermal speed that violate the GK ordering. Since secondary magnetic islands
appear after the reconnection peak time, a kinetic PIC/GK comparison is more
accurate in the linear phase of magnetic reconnection. For a high beta plasma
() where reconnection rates and fluctuations levels are reduced,
similar processes happen in the secondary magnetic islands in the fully kinetic
description, but requiring much lower guide fields ().Comment: 18 pages, 13 figures. Revised to match with the published version in
Physics of Plasma
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