1,026 research outputs found
The Loss Rank Principle for Model Selection
We introduce a new principle for model selection in regression and
classification. Many regression models are controlled by some smoothness or
flexibility or complexity parameter c, e.g. the number of neighbors to be
averaged over in k nearest neighbor (kNN) regression or the polynomial degree
in regression with polynomials. Let f_D^c be the (best) regressor of complexity
c on data D. A more flexible regressor can fit more data D' well than a more
rigid one. If something (here small loss) is easy to achieve it's typically
worth less. We define the loss rank of f_D^c as the number of other
(fictitious) data D' that are fitted better by f_D'^c than D is fitted by
f_D^c. We suggest selecting the model complexity c that has minimal loss rank
(LoRP). Unlike most penalized maximum likelihood variants (AIC,BIC,MDL), LoRP
only depends on the regression function and loss function. It works without a
stochastic noise model, and is directly applicable to any non-parametric
regressor, like kNN. In this paper we formalize, discuss, and motivate LoRP,
study it for specific regression problems, in particular linear ones, and
compare it to other model selection schemes.Comment: 16 page
The Relationship Between Plasma Flow Doppler Velocities and Magnetic Field Parameters During the Emergence of Active Regions at the Solar Photospheric Level
A statistical study has been carried out of the relationship between plasma
flow Doppler velocities and magnetic field parameters during the emergence of
active regions at the solar photospheric level with data acquired by the
Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
(SOHO). We have investigated 224 emerging active regions with different spatial
scales and positions on the solar disc. The following relationships for the
first hours of the emergence of active regions have been analysed: i) of peak
negative Doppler velocities with the position of the emerging active regions on
the solar disc; ii) of peak plasma upflow and downflow Doppler velocities with
the magnetic flux growth rate and magnetic field strength for the active
regions emerging near the solar disc centre (the vertical component of plasma
flows); iii) of peak positive and negative Doppler velocities with the magnetic
flux growth rate and magnetic field strength for the active regions emerging
near the limb (the horizontal component of plasma flows); iv) of the magnetic
flux growth rate with the density of emerging magnetic flux; v) of the Doppler
velocities and magnetic field parameters for the first hours of the appearance
of active regions with the total unsigned magnetic flux at the maximum of their
development.Comment: 14 pages, 8 figures. The results of article were presented at the
ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102-103,
P.4.13,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
Feasibility study: investigation of car park-based V2G services in the UK central hub
The increasing uptake of electric vehicles, and the established practice of long-term parking at stations and airports, offers an opportunity to develop a flexible approach to help with the energy storage dilemma. This paper investigates the feasibility of using a number of EV batteries as an energy storage and grid balancing solution within the UK Central Hub area. Here, the capital cost of the vehicle is a sunk cost to the EV owner. The potential income generated, or discount on long-term parking, is an additional benefit of ownership. This paper considers the income available to a small and large size car park from the different market mechanisms to offer grid support in the UK and contrasts this with the complexity and costs of the EV charging infrastructure required within these types of scheme
Abelian Hidden Sectors at a GeV
We discuss mechanisms for naturally generating GeV-scale hidden sectors in
the context of weak-scale supersymmetry. Such low mass scales can arise when
hidden sectors are more weakly coupled to supersymmetry breaking than the
visible sector, as happens when supersymmetry breaking is communicated to the
visible sector by gauge interactions under which the hidden sector is
uncharged, or if the hidden sector is sequestered from gravity-mediated
supersymmetry breaking. We study these mechanisms in detail in the context of
gauge and gaugino mediation, and present specific models of Abelian GeV-scale
hidden sectors. In particular, we discuss kinetic mixing of a U(1)_x gauge
force with hypercharge, singlets or bi-fundamentals which couple to both
sectors, and additional loop effects. Finally, we investigate the possible
relevance of such sectors for dark matter phenomenology, as well as for low-
and high-energy collider searches.Comment: 43 pages, no figures; v2: to match JHEP versio
Observation of Pseudoscalar and Axial Vector Resonances in pi- p -> K+ K- pi0 n at 18 GeV
A new measurement of the reaction pi- p -> K+ K- pi0 n has been made at a
beam energy of 18 GeV. A partial wave analysis of the K+ K- pi0 system shows
evidence for three pseudoscalar resonances, eta(1295), eta(1416), and
eta(1485), as well as two axial vectors, f1(1285), and f1(1420). Their observed
masses, widths and decay properties are reported. No signal was observed for
C(1480), an IG J{PC} = 1+ 1{--} state previously reported in phi pi0 decay.Comment: 7 pages, 6 figs, to be submitted to Phys. Let
The resonance in s wave scatterings
A new unitarization approach incorporated with chiral symmetry is established
and applied to study the elastic scatterings. We demonstrate that the
resonance exists, if the scattering length parameter in the I=1/2, J=0
channel does not deviate much from its value predicted by chiral perturbation
theory. The mass and width of the resonance is found to be
, , obtained by fitting the
LASS data up to 1430MeV. Better determination to the pole parameters is
possible if the chiral predictions on scattering lengths are taken into
account.Comment: Minor corrections made on discussions and typos. 1 ref. added version
to appear in Nuclear Physics
Detecting a stochastic gravitational wave background with the Laser Interferometer Space Antenna
The random superposition of many weak sources will produce a stochastic
background of gravitational waves that may dominate the response of the LISA
(Laser Interferometer Space Antenna) gravitational wave observatory. Unless
something can be done to distinguish between a stochastic background and
detector noise, the two will combine to form an effective noise floor for the
detector. Two methods have been proposed to solve this problem. The first is to
cross-correlate the output of two independent interferometers. The second is an
ingenious scheme for monitoring the instrument noise by operating LISA as a
Sagnac interferometer. Here we derive the optimal orbital alignment for
cross-correlating a pair of LISA detectors, and provide the first analytic
derivation of the Sagnac sensitivity curve.Comment: 9 pages, 11 figures. Significant changes to the noise estimate
Leptonic and Semileptonic Decays of Charm and Bottom Hadrons
We review the experimental measurements and theoretical descriptions of
leptonic and semileptonic decays of particles containing a single heavy quark,
either charm or bottom. Measurements of bottom semileptonic decays are used to
determine the magnitudes of two fundamental parameters of the standard model,
the Cabibbo-Kobayashi-Maskawa matrix elements and . These
parameters are connected with the physics of quark flavor and mass, and they
have important implications for the breakdown of CP symmetry. To extract
precise values of and from measurements, however,
requires a good understanding of the decay dynamics. Measurements of both charm
and bottom decay distributions provide information on the interactions
governing these processes. The underlying weak transition in each case is
relatively simple, but the strong interactions that bind the quarks into
hadrons introduce complications. We also discuss new theoretical approaches,
especially heavy-quark effective theory and lattice QCD, which are providing
insights and predictions now being tested by experiment. An international
effort at many laboratories will rapidly advance knowledge of this physics
during the next decade.Comment: This review article will be published in Reviews of Modern Physics in
the fall, 1995. This file contains only the abstract and the table of
contents. The full 168-page document including 47 figures is available at
http://charm.physics.ucsb.edu/papers/slrevtex.p
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
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