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Search Results: 1 - 10 of 193512 matches for " Guy D'Anjou "
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Metabolic efficiency with fast spiking in the squid axon
Abdelmalik Moujahid,Alicia d'Anjou
Frontiers in Computational Neuroscience , 2012, DOI: 10.3389/fncom.2012.00095
Abstract: Fundamentally, action potentials in the squid axon are consequence of the entrance of sodium ions during the depolarization of the rising phase of the spike mediated by the outflow of potassium ions during the hyperpolarization of the falling phase. Perfect metabolic efficiency with a minimum charge needed for the change in voltage during the action potential would confine sodium entry to the rising phase and potassium efflux to the falling phase. However, because sodium channels remain open to a significant extent during the falling phase, a certain overlap of inward and outward currents is observed. In this work we investigate the impact of ion overlap on the number of the adenosine triphosphate (ATP) molecules and energy cost required per action potential as a function of the temperature in a Hodgkin–Huxley model. Based on a recent approach to computing the energy cost of neuronal action potential generation not based on ion counting, we show that increased firing frequencies induced by higher temperatures imply more efficient use of sodium entry, and then a decrease in the metabolic energy cost required to restore the concentration gradients after an action potential. Also, we determine values of sodium conductance at which the hydrolysis efficiency presents a clear minimum.
Soft Decoding of a Qubit Readout Apparatus
B. D'Anjou,W. A. Coish
Physics , 2014, DOI: 10.1103/PhysRevLett.113.230402
Abstract: Qubit readout is commonly performed by thresholding a collection of analog detector signals to obtain a sequence of single-shot bit values. The intrinsic irreversibility of the mapping from analog to digital signals discards soft information associated with an \emph{a posteriori} confidence that can be assigned to each bit value when a detector is well characterized. Accounting for soft information, we show significant improvements in enhanced state detection with the quantum repetition code as well as quantum state or parameter estimation. These advantages persist in spite of non-Gaussian features of realistic readout models, experimentally relevant small numbers of qubits, and finite encoding errors. These results show useful and achievable advantages for a wide range of current experiments on quantum state tomography, parameter estimation, and qubit readout.
Optimal post-processing for a generic single-shot qubit readout
B. D'Anjou,W. A. Coish
Physics , 2013, DOI: 10.1103/PhysRevA.89.012313
Abstract: We analyze three different post-processing methods applied to a single-shot qubit readout: the average-signal (boxcar filter), peak-signal, and maximum-likelihood methods. In contrast to previous work, we account for a stochastic turn-on time $t_i$ associated with the leading edge of a pulse signaling one of the qubit states. This model is relevant to spin-qubit readouts based on spin-to-charge conversion and would be generically reached in the limit of large signal-to-noise ratio $r$ for several other physical systems, including fluorescence-based readouts of ion-trap qubits and nitrogen-vacancy center spins. We derive analytical closed-form expressions for the conditional probability distributions associated with the peak-signal and boxcar filters. For the boxcar filter, we find an asymptotic scaling of the single-shot error rate $\varepsilon \sim \ln r/\sqrt{r}$ when $t_i$ is stochastic, in contrast to the result $\varepsilon \sim \ln r/ r$ for deterministic $t_i$. Consequently, the peak-signal method outperforms the boxcar filter significantly when $t_i$ is stochastic, but is only marginally better for deterministic $t_i$ (a result that is consistent with the widespread use of the boxcar filter for fluorescence-based readouts and the peak-signal for spin-to-charge conversion). We generalize the theoretically optimal maximum-likelihood method to stochastic $t_i$ and show numerically that a stochastic turn-on time $t_i$ will always result in a larger single-shot error rate. Based on this observation, we propose a general strategy to improve the quality of single-shot readouts by forcing $t_i$ to be deterministic.
Community structure in real-world networks from a non-parametrical synchronization-based dynamical approach
Abdelmalik Moujahid,Alicia d'Anjou,Blanca Cases
Physics , 2012, DOI: 10.1016/j.chaos.2012.06.007
Abstract: This work analyzes the problem of community structure in real-world networks based on the synchronization of nonidentical coupled chaotic R\"{o}ssler oscillators each one characterized by a defined natural frequency, and coupled according to a predefined network topology. The interaction scheme contemplates an uniformly increasing coupling force to simulate a society in which the association between the agents grows in time. To enhance the stability of the correlated states that could emerge from the synchronization process, we propose a parameterless mechanism that adapts the characteristic frequencies of coupled oscillators according to a dynamic connectivity matrix deduced from correlated data. We show that the characteristic frequency vector that results from the adaptation mechanism reveals the underlying community structure present in the network.
Anomalous magnetotransport through reflection-symmetric artificial molecules
B. D'Anjou,W. A. Coish
Physics , 2012, DOI: 10.1103/PhysRevB.87.085443
Abstract: We calculate magnetotransport oscillations in current through a triple-quantum-dot molecule, accounting for higher harmonics (having flux period h/ne, with n an integer). For a reflection-symmetric triple quantum dot, we find that harmonics with n odd can dominate over those with n even. This is opposite to the behavior theoretically predicted due to `dark-state' localization, but has been observed in recent experiments [L. Gaudreau et al., Phys. Rev. B, 80, 075415 (2009)], albeit in a triple-dot that may not exhibit reflection symmetry. This feature arises from a more general result: In the weak-coupling limit, we find that the current is flux-independent for an arbitrary reflection-symmetric Aharonov-Bohm network. We further show that these effects are observable in nanoscale systems even in the presence of typical dephasing sources.
On how percolation threshold affects PSO performance
Blanca Cases,Alicia D'Anjou,Abdelmalik Moujahid
Computer Science , 2012,
Abstract: Statistical evidence of the influence of neighborhood topology on the performance of particle swarm optimization (PSO) algorithms has been shown in many works. However, little has been done about the implications could have the percolation threshold in determining the topology of this neighborhood. This work addresses this problem for individuals that, like robots, are able to sense in a limited neighborhood around them. Based on the concept of percolation threshold, and more precisely, the disk percolation model in 2D, we show that better results are obtained for low values of radius, when individuals occasionally ask others their best visited positions, with the consequent decrease of computational complexity. On the other hand, since percolation threshold is a universal measure, it could have a great interest to compare the performance of different hybrid PSO algorithms.
SMA CARNI-VAL TRIAL PART II: A Prospective, Single-Armed Trial of L-Carnitine and Valproic Acid in Ambulatory Children with Spinal Muscular Atrophy
John T. Kissel,Charles B. Scott,Sandra P. Reyna,Thomas O. Crawford,Louise R. Simard,Kristin J. Krosschell,Gyula Acsadi,Bakri Elsheik,Mary K. Schroth,Guy D'Anjou,Bernard LaSalle,Thomas W. Prior,Susan Sorenson,Jo Anne Maczulski,Mark B. Bromberg,Gary M. Chan,Kathryn J. Swoboda
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0021296
Abstract: Multiple lines of evidence have suggested that valproic acid (VPA) might benefit patients with spinal muscular atrophy (SMA). The SMA CARNIVAL TRIAL was a two part prospective trial to evaluate oral VPA and l-carnitine in SMA children. Part 1 targeted non-ambulatory children ages 2–8 in a 12 month cross over design. We report here Part 2, a twelve month prospective, open-label trial of VPA and L-carnitine in ambulatory SMA children.
Phase II Open Label Study of Valproic Acid in Spinal Muscular Atrophy
Kathryn J. Swoboda, Charles B. Scott, Sandra P. Reyna, Thomas W. Prior, Bernard LaSalle, Susan L. Sorenson, Janine Wood, Gyula Acsadi, Thomas O. Crawford, John T. Kissel, Kristin J. Krosschell, Guy D'Anjou, Mark B. Bromberg, Mary K. Schroth, Gary M. Chan, Bakri Elsheikh, Louise R. Simard
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0005268
Abstract: Preliminary in vitro and in vivo studies with valproic acid (VPA) in cell lines and patients with spinal muscular atrophy (SMA) demonstrate increased expression of SMN, supporting the possibility of therapeutic benefit. We performed an open label trial of VPA in 42 subjects with SMA to assess safety and explore potential outcome measures to help guide design of future controlled clinical trials. Subjects included 2 SMA type I ages 2–3 years, 29 SMA type II ages 2–14 years and 11 type III ages 2–31 years, recruited from a natural history study. VPA was well-tolerated and without evident hepatotoxicity. Carnitine depletion was frequent and temporally associated with increased weakness in two subjects. Exploratory outcome measures included assessment of gross motor function via the modified Hammersmith Functional Motor Scale (MHFMS), electrophysiologic measures of innervation including maximum ulnar compound muscle action potential (CMAP) amplitudes and motor unit number estimation (MUNE), body composition and bone density via dual-energy X-ray absorptiometry (DEXA), and quantitative blood SMN mRNA levels. Clear decline in motor function occurred in several subjects in association with weight gain; mean fat mass increased without a corresponding increase in lean mass. We observed an increased mean score on the MHFMS scale in 27 subjects with SMA type II (p≤0.001); however, significant improvement was almost entirely restricted to participants <5 years of age. Full length SMN levels were unchanged and Δ7SMN levels were significantly reduced for 2 of 3 treatment visits. In contrast, bone mineral density (p≤0.0036) and maximum ulnar CMAP scores (p≤0.0001) increased significantly. Conclusions While VPA appears safe and well-tolerated in this initial pilot trial, these data suggest that weight gain and carnitine depletion are likely to be significant confounding factors in clinical trials. This study highlights potential strengths and limitations of various candidate outcome measures and underscores the need for additional controlled clinical trials with VPA targeting more restricted cohorts of subjects. Trial Registration ClinicalTrials.gov
SMA CARNI-VAL Trial Part I: Double-Blind, Randomized, Placebo-Controlled Trial of L-Carnitine and Valproic Acid in Spinal Muscular Atrophy
Kathryn J. Swoboda,Charles B. Scott,Thomas O. Crawford,Louise R. Simard,Sandra P. Reyna,Kristin J. Krosschell,Gyula Acsadi,Bakri Elsheik,Mary K. Schroth,Guy D'Anjou,Bernard LaSalle,Thomas W. Prior,Susan L. Sorenson,Jo Anne Maczulski,Mark B. Bromberg,Gary M. Chan,John T. Kissel
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012140
Abstract: Valproic acid (VPA) has demonstrated potential as a therapeutic candidate for spinal muscular atrophy (SMA) in vitro and in vivo.
Experimental Review of Graphene
Daniel R. Cooper,Benjamin DAnjou,Nageswara Ghattamaneni,Benjamin Harack
ISRN Condensed Matter Physics , 2012, DOI: 10.5402/2012/501686
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