4,925 research outputs found
Discriminative Tandem Features for HMM-based EEG Classification
Abstract—We investigate the use of discriminative feature extractors in tandem configuration with generative EEG classification system. Existing studies on dynamic EEG classification typically use hidden Markov models (HMMs) which lack discriminative capability. In this paper, a linear and a non-linear classifier are discriminatively trained to produce complementary input features to the conventional HMM system. Two sets of tandem features are derived from linear discriminant analysis (LDA) projection output and multilayer perceptron (MLP) class-posterior probability, before appended to the standard autoregressive (AR) features. Evaluation on a two-class motor-imagery classification task shows that both the proposed tandem features yield consistent gains over the AR baseline, resulting in significant relative improvement of 6.2% and 11.2 % for the LDA and MLP features respectively. We also explore portability of these features across different subjects. Index Terms- Artificial neural network-hidden Markov models, EEG classification, brain-computer-interface (BCI)
Monitoring Microtubule Mechanical Vibrations via Optomechanical Coupling
The possible disruption of a microtubule during mitosis can control the
duplication of a cancer cell. Cancer detection and treatment may be possible
based on the detection and control of microtubule mechanical oscillations in
cells through external fields (e.g. electromagnetic or ultrasound). However,
little is known about the dynamic (high-frequency) mechanical properties of
microtubules. Here we propose to control the vibrations of a doubly clamped
microtubule by tip electrodes and to detect its motion via the optomechanical
coupling between the vibrational modes of the microtubule and an optical
cavity. In the presence of a red-detuned strong pump laser, this coupling leads
to optomechanical induced transparency of an optical probe field, which can be
detected with state-of the art technology. The center frequency and linewidth
of the transparency peak give the resonance frequency and damping rate of the
microtubule respectively, while the height of the peak reveals information
about the microtubule-cavity field coupling. Our method should yield new
knowledge about the physical properties of microtubules, which will enhance our
capability to design physical cancer treatment protocols as alternatives to
chemotherapeutic drugs
Josephson-coupled Moore-Read states
We study a quantum Hall bilayer system of bosons at total filling factor ν = 1, and study the phase that results from short ranged pair-tunneling combined with short ranged interlayer interactions. We introduce two exactly solvable model Hamiltonians which both yield the coupled Moore-Read state [Phys. Rev. Lett. 108, 256809 (2012)] as a ground state, when projected onto fixed particle numbers in each layer. One of these Hamiltonians describes a gapped topological phase while the other is gapless. However, on introduction of a pair tunneling term, the second system becomes gapped and develops the same topological order as the gapped Hamiltonian. Supported by the exact solution of the full zero-energy quasihole spectrum and a conformal field theory approach, we develop an intuitive picture of this system as two coupled composite fermion superconductors. In this language, pair tunneling provides a Josephson coupling of the superconducting phases of the two layers, and gaps out the Goldstone mode associated with particle transport between the layers. In particular, this implies that quasiparticles are confined between the layers. In the bulk, the resulting phase has the topological order of the Halperin 220 phase with U(1)_2 x U(1)_2 topological order, but it is realized in the symmetric/antisymmetric-basis of the layer index. Consequently, the edge spectrum at a fixed particle number reveals an unexpected U(1)_4 x U(1) structure.The authors would like to thank Nordita and the Aspen Center for Physics their hospitality, and acknowledge
support from the Leverhulme Trust under grant ECF-2011-565, the Newton Trust of the University
of Cambridge and by the Royal Society under grant UF120157 (G.M.), the European Union under
Marie Curie award 299890 QETPM (L.H.), Science Foundation Ireland principal investigator awards
08/IN.1/I1961 and 12/IA/1697 (J.K.S.) and EPSRC grant EP/I032487/1 (S.H.S.).This is the author accepted version of the manuscript which has been published at http://dx.doi.org/10.1103/PhysRevB.90.23510
Approximating observables on eigenstates of large many-body localized systems
Eigenstates of fully many-body localized (FMBL) systems can be organized into spin algebras based on quasilocal operators called
l
bits. These spin algebras define quasilocal
l
-bit measurement (
τ
z
i
) and
l
-bit flip (
τ
x
i
) operators. For a disordered Heisenberg spin chain in the MBL regime we approximate
l
-bit flip operators by first calculating them exactly on small windows of systems using an algorithm called operator localization optimization. We then extend the
l
-bit operators onto the whole system by exploiting their quasilocal nature. We subsequently use these operators to represent approximate eigenstates of the Hamiltonian. Finally, we describe a method to calculate products of local observables on these eigenstates for systems of size
L
in
O
(
L
2
)
time. This method is used to calculate the variance of the energy of the approximate eigenstates, yielding an estimate of the error of the approximation
Trial Wavefunctions for the Goldstone Mode in v=1/2+1/2 Quantum Hall Bilayers
Based on the known physics of the excitonic superfluid or 111 state of the quantum Hall bilayer, we create a simple trial wavefunction ansatz for constructing a low-energy branch of (Goldstone) excitations by taking the overall ground state and boosting one layer with respect to the other. This ansatz works extremely well for any interlayer spacing. For small , this is simply the physics of the Goldstone mode, whereas for large , this is a reflection of composite fermion physics. We find hints that certain aspects of composite fermion physics persist to low whereas certain aspects of Goldstone mode physics persist to high . Using these results, we show nonmonotonic behavior of the Goldstone mode velocity as a function of .Peer Reviewe
Study on Doping Prevention: A map of Legal, Regulatory and Prevention Practice Provisions in EU 28
Historically, anti-doping efforts have focused on the detection and deterrence of doping in elite and competitive sport. There is, however, a growing concern that doping is occurring outside the organised sporting system; giving rise to the belief that the misuse of doping agents in recreational sport has become a societal problem and a public health issue that must be addressed. The EU Commission awarded a contract (EAC/2013/0617) to a Consortium to undertake this Study with the aim of developing the evidence-base for policies designed to combat doping in recreational sport. Fourteen internationally recognised experts shaped the Study which comprised (i) the collection of primary data through a structured survey, and (ii) secondary data through literature searches and website analysis. All 28 Member States participated in the information-gathering process. Specifically, this involved a systematic study of the ethical considerations, legal position, prevention research landscape, and current practise in relation to the prevention of doping in recreational sport. The Study provides a comprehensive overview of current practice and legislation as it applies to the prevention of doping and promotes and supports the sharing of best practices in the EU regarding the fight against doping in recreational sport. It concludes with seven recommendations for future action that focus on the need for a coordinated response in relation to the problems arising from doping in recreational sport
Fluctuations of a holographic quantum Hall fluid
We analyze the neutral spectrum of the holographic quantum Hall fluid
described by the D2-D8' model. As expected for a quantum Hall state, we find
the system to be stable and gapped and that, at least over much of the
parameter space, the lowest excitation mode is a magneto-roton. In addition, we
find magneto-rotons in higher modes as well. We show that these magneto-rotons
are direct consequences of level crossings between vector and scalar modes.Comment: 20 pages, 8 figures; v.2 figures improved, 2 figures added, and text
clarified particularly in Sec. 5, to appear in JHE
The Web of Human Sexual Contacts
Many ``real-world'' networks are clearly defined while most ``social''
networks are to some extent subjective. Indeed, the accuracy of
empirically-determined social networks is a question of some concern because
individuals may have distinct perceptions of what constitutes a social link.
One unambiguous type of connection is sexual contact. Here we analyze data on
the sexual behavior of a random sample of individuals, and find that the
cumulative distributions of the number of sexual partners during the twelve
months prior to the survey decays as a power law with similar exponents for females and males. The scale-free nature of the web of human
sexual contacts suggests that strategic interventions aimed at preventing the
spread of sexually-transmitted diseases may be the most efficient approach.Comment: 7 pages with 2 eps figures. Latex file. For more details or for
downloading the PDF file of the published article see
http://polymer.bu.edu/~amaral/WebofContacts.html . For more results on teh
structure of complex networks see http://polymer.bu.edu/~amaral/Networks.htm
Exploiting disorder for perfect focusing
We demonstrate experimentally that disordered scattering can be used to
improve, rather than deteriorate, the focusing resolution of a lens. By using
wavefront shaping to compensate for scattering, light was focused to a spot as
small as one tenth of the diffraction limit of the lens. We show both
experimentally and theoretically that it is the scattering medium, rather than
the lens, that determines the width of the focus. Despite the disordered
propagation of the light, the profile of the focus was always exactly equal to
the theoretical best focus that we derived.Comment: 4 pages, 4 figure
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