2,554 research outputs found
Adaptive real-time identification of motor unit discharges from non-stationary high-density surface electromyographic signals
Objective. Estimation of the discharge pattern of motor units by electromyography (EMG) decomposition has been applied for neurophysiologic investigations, clinical diagnosis, and human-machine interfacing. However, most of the methods for EMG decomposition are currently applied offline. Here, we propose an approach for high-density surface EMG decomposition in real-time. Methods. A real-time decomposition scheme including two sessions, offline training and online decomposition, is proposed based on the convolutional kernel compensation algorithm. The estimation parameters, separation vectors and the thresholds for spike extraction, are first computed during offline training, and then they are directly applied to estimate motor unit spike trains (MUSTs) during the online decomposition. The estimation parameters are updated with the identification of new discharges to adapt to non-stationary conditions. The decomposition accuracy was validated on simulated EMG signals by convolving synthetic MUSTs with motor unit action potentials (MUAPs). Moreover, the accuracy of the online decomposition was assessed from experimental signals recorded from forearm muscles using a signal-based performance metrics (pulse-to-noise ratio, PNR). Main results. The proposed algorithm yielded a high decomposition accuracy and robustness to non-stationary conditions. The accuracy of MUSTs identified from simulated EMG signals was > 80% for most conditions. From experimental EMG signals, on average, 12±2 MUSTs were identified from each electrode grid with PNR of 25.0±1.8 dB, corresponding to an estimated decomposition accuracy > 75%. Conclusion and Significance. These results indicate the feasibility of real-time identification of motor unit activities non-invasively during variable force contractions, extending the potential applications of high-density EMG as a neural interface
Longitudinal high-density EMG classification: Case study in a glenohumeral TMR subject.
Targeted muscle reinnervation (TMR) represents a breakthrough interface for prosthetic control in high-level upper-limb amputees. However, clinically, it is still limited to the direct motion-wise control restricted by the number of reinnervation sites. Pattern recognition may overcome this limitation. Previous studies on EMG classification in TMR patients experienced with myocontrol have shown greater accuracy when using high-density (HD) recordings compared to conventional single-channel derivations. This case study investigates the potential of HD-EMG classification longitudinally over a period of 17 months post-surgery in a glenohumeral amputee. Five experimental sessions, separated by approximately 3 months, were performed. They were timed during a standard rehabilitation protocol that included intensive physio- and occupational therapy, myosignal training, and routine use of the final myoprosthesis. The EMG signals recorded by HD-EMG grids were classified into 12 classes. The first sign of EMG activity was observed in the second experimental session. The classification accuracy over 12 classes was 76% in the third session and ∼95% in the last two sessions. When using training and testing sets that were acquired with a 1-h time interval in between, a much lower accuracy (32%, Session 4) was obtained, which improved upon prosthesis usage (Session 5, 67%). The results document the improvement in EMG classification accuracy throughout the TMR-rehabilitation process
Anthropic solution to the magnetic muon anomaly: the charged see-saw
We present models of new physics that can explain the muon g-2 anomaly in
accord with with the assumption that the only scalar existing at the weak scale
is the Higgs, as suggested by anthropic selection. Such models are dubbed
"charged see-saw" because the muon mass term is mediated by heavy leptons. The
electroweak contribution to the g-2 gets modified by order one factors, giving
an anomaly of the same order as the observed hint, which is strongly correlated
with a modification of the Higgs coupling to the muon.Comment: 21 pages, many equations despite the first word in the title. v3:
loop function G_WN corrected, conclusions unchange
An 800-million-solar-mass black hole in a significantly neutral Universe at redshift 7.5
Quasars are the most luminous non-transient objects known and as a result
they enable studies of the Universe at the earliest cosmic epochs. Despite
extensive efforts, however, the quasar ULAS J1120+0641 at z=7.09 has remained
the only one known at z>7 for more than half a decade. Here we report
observations of the quasar ULAS J134208.10+092838.61 (hereafter J1342+0928) at
redshift z=7.54. This quasar has a bolometric luminosity of 4e13 times the
luminosity of the Sun and a black hole mass of 8e8 solar masses. The existence
of this supermassive black hole when the Universe was only 690 million years
old---just five percent of its current age---reinforces models of early
black-hole growth that allow black holes with initial masses of more than about
1e4 solar masses or episodic hyper-Eddington accretion. We see strong evidence
of absorption of the spectrum of the quasar redwards of the Lyman alpha
emission line (the Gunn-Peterson damping wing), as would be expected if a
significant amount (more than 10 per cent) of the hydrogen in the intergalactic
medium surrounding J1342+0928 is neutral. We derive a significant fraction of
neutral hydrogen, although the exact fraction depends on the modelling.
However, even in our most conservative analysis we find a fraction of more than
0.33 (0.11) at 68 per cent (95 per cent) probability, indicating that we are
probing well within the reionization epoch of the Universe.Comment: Updated to match the final journal versio
Asymmetric Inelastic Inert Doublet Dark Matter from Triplet Scalar Leptogenesis
The nature of dark matter (DM) particles and the mechanism that provides
their measured relic abundance are currently unknown. In this paper we
investigate inert scalar and vector like fermion doublet DM candidates with a
charge asymmetry in the dark sector, which is generated by the same mechanism
that provides the baryon asymmetry, namely baryogenesis-via-leptogenesis
induced by decays of scalar triplets. At the same time the model gives rise to
neutrino masses in the ballpark of oscillation experiments via type II seesaw.
We discuss possible sources of depletion of asymmetry in the DM and visible
sectors and solve the relevant Boltzmann equations for quasi-equilibrium decay
of triplet scalars. A Monte-Carlo-Markov-Chain analysis is performed for the
whole parameter space. The survival of the asymmetry in the dark sector leads
to inelastic scattering off nuclei. We then apply bayesian statistic to infer
the model parameters favoured by the current experimental data, in particular
the DAMA annual modulation and Xenon100 exclusion limit. The latter strongly
disfavours asymmetric scalar doublet DM of mass \mathcal{O}(\TeV) as required
by DM- oscillations, while an asymmetric vector like fermion
doublet DM with mass around 100 GeV is a good candidate for DAMA annual
modulation yet satisfying the constraints from Xenon100 data.Comment: 35 pages and 15 figures, references adde
Probing for Invisible Higgs Decays with Global Fits
We demonstrate by performing a global fit on Higgs signal strength data that
large invisible branching ratios Br_{inv} for a Standard Model (SM) Higgs
particle are currently consistent with the experimental hints of a scalar
resonance at the mass scale m_h ~ 124 GeV. For this mass scale, we find
Br_{inv} < 0.64 (95 % CL) from a global fit to individual channel signal
strengths supplied by ATLAS, CMS and the Tevatron collaborations. Novel tests
that can be used to improve the prospects of experimentally discovering the
existence of a Br_{inv} with future data are proposed. These tests are based on
the combination of all visible channel Higgs signal strengths, and allow us to
examine the required reduction in experimental and theoretical errors in this
data that would allow a more significantly bounded invisible branching ratio to
be experimentally supported. We examine in some detail how our conclusions and
method are affected when a scalar resonance at this mass scale has couplings
deviating from the SM ones.Comment: 32pp, 15 figures v2: JHEP version, ref added & comment added after
Eq.
Implications of the 125 GeV Higgs boson for scalar dark matter and for the CMSSM phenomenology
We study phenomenological implications of the ATLAS and CMS hint of a GeV Higgs boson for the singlet, and singlet plus doublet non-supersymmetric
dark matter models, and for the phenomenology of the CMSSM. We show that in
scalar dark matter models the vacuum stability bound on Higgs boson mass is
lower than in the standard model and the 125 GeV Higgs boson is consistent with
the models being valid up the GUT or Planck scale. We perform a detailed study
of the full CMSSM parameter space keeping the Higgs boson mass fixed to GeV, and study in detail the freeze-out processes that imply the observed
amount of dark matter. After imposing all phenomenological constraints except
for the muon we show that the CMSSM parameter space is divided
into well separated regions with distinctive but in general heavy sparticle
mass spectra. Imposing the constraint introduces severe tension
between the high SUSY scale and the experimental measurements -- only the
slepton co-annihilation region survives with potentially testable sparticle
masses at the LHC. In the latter case the spin-independent DM-nucleon
scattering cross section is predicted to be below detectable limit at the
XENON100 but might be of measurable magnitude in the general case of light dark
matter with large bino-higgsino mixing and unobservably large scalar masses.Comment: 17 pages, 7 figures. v3: same as published versio
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