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Search Results: 1 - 10 of 297505 matches for " J. Tonge "
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RS-invariant all-orders renormalon resummations for some QCD observables
C. J. Maxwell,D. G. Tonge
Physics , 1996, DOI: 10.1016/S0550-3213(96)00532-9
Abstract: We propose a renormalon-inspired resummation of QCD perturbation theory based on approximating the renormalization scheme (RS) invariant effective charge beta-function coefficients by the portion containing the highest power of $b$=$\frac{1}{6}(11N$--$2N_{f})$, for SU($N$) QCD with $N_{f}$ quark flavours. This can be accomplished using exact large-$N_{f}$ all-orders results. The resulting resummation is RS-invariant and the exact next-to-leading order (NLO) and next-to-NLO (NNLO) coefficients in any RS are included. This improves on a previously employed naive resummation of the leading-$b$ piece of the perturbative coefficients which is RS-dependent, making its comparison with fixed-order perturbative results ambiguous. The RS-invariant resummation is used to assess the reliability of fixed-order perturbation theory for the $e^{+}e^{-}$ $R$-ratio, the analogous $\tau$-lepton decay ratio $R_{\tau}$, and Deep Inelastic Scattering (DIS) sum rules, by comparing it with the exact NNLO results in the effective charge RS. For the $R$-ratio and $R_{\tau}$, where large-order perturbative behaviour is dominated by a leading ultra-violet renormalon singularity, the comparison indicates fixed-order perturbation theory to be very reliable. For DIS sum rules, which have a leading infra-red renormalon singularity, the performance is rather poor. In this way we estimate that at LEP/SLD energies ideal data on the $R$-ratio could determine $\alpha_{s}(M_{Z})$ to three-significant figures, and for the $R_{\tau}$ we estimate a theoretical uncertainty $\delta\alpha_{s}(m_{\tau})\simeq0.008$ corresponding to $\delta\alpha_{s}(M_{Z})\simeq0.001$. This encouragingly small uncertainty is much less than has recently been deduced from comparison with the ambiguous naive resummation.
The uncertainty in $α_{s}(M_Z^2)$ determined from hadronic tau decay measurements
C. J. Maxwell,D. G. Tonge
Physics , 1997, DOI: 10.1016/S0550-3213(98)00562-8
Abstract: We show that QCD Minkowski observables such as the $e^{+}e^{-}$ R-ratio and the hadronic tau decay $R_{\tau}$ are completely determined by the effective charge (EC) beta-function, $\rho(x)$, corresponding to the Euclidean QCD vacuum polarization Adler D-function, together with the next-to-leading order (NLO) perturbative coefficient of D. An efficient numerical algorithm is given for evaluating R, $R_{\tau}$ from a weighted contour integration of $D(se^{i\theta})$ around a circle in the complex squared energy s-plane, with $\rho(x)$ used to evolve in s around the contour. The EC beta-function can be truncated at next-to-NLO (NNLO) using the known exact perturbative calculation or the uncalculated N^3 LO and higher terms can be approximated by the portion containing the highest power of b, the first QCD beta-function coefficient. The difference between the R, $R_{\tau}$ constructed using the NNLO and "leading-b" resummed versions of $\rho(x)$ provides an estimate of the uncertainty due to the uncalculated higher order corrections. Simple numerical parametrizations are given to facilitate these fits. For $R_{\tau}$ we estimate an uncertainty $\delta\alpha_{s}(m_{\tau}^{2})\simeq0.01$, corresponding to $\delta\alpha_{s}(M_{Z}^{2})\simeq0.002$. This encouragingly small uncertainty is much less than rather pessimistic estimates by other authors based on analogous all-orders resummations, which we demonstrate to be extremely dependent on the chosen renormalization scheme, and hence misleading.
Three-dimensional simulations of laser-plasma interactions at ultrahigh intensities
F. Fiuza,R. A. Fonseca,L. O. Silva,J. Tonge,J. May,W. B. Mori
Physics , 2012, DOI: 10.1109/TPS.2011.2158327
Abstract: Three-dimensional (3D) particle-in-cell (PIC) simulations are used to investigate the interaction of ultrahigh intensity lasers ($> 10^{20}$ W/cm$^{-2}$) with matter at overcritical densities. Intense laser pulses are shown to penetrate up to relativistic critical density levels and to be strongly self-focused during this process. The heat flux of the accelerated electrons is observed to have an annular structure when the laser is tightly focused, showing that a large fraction of fast electrons is accelerated at an angle. These results shed light into the multi-dimensional effects present in laser-plasma interactions of relevance to fast ignition of fusion targets and laser-driven ion acceleration in plasmas.
Drug Discovery Using Chemical Systems Biology: Repositioning the Safe Medicine Comtan to Treat Multi-Drug and Extensively Drug Resistant Tuberculosis
Sarah L. Kinnings ,Nina Liu ,Nancy Buchmeier ,Peter J. Tonge,Lei Xie ,Philip E. Bourne
PLOS Computational Biology , 2009, DOI: 10.1371/journal.pcbi.1000423
Abstract: The rise of multi-drug resistant (MDR) and extensively drug resistant (XDR) tuberculosis around the world, including in industrialized nations, poses a great threat to human health and defines a need to develop new, effective and inexpensive anti-tubercular agents. Previously we developed a chemical systems biology approach to identify off-targets of major pharmaceuticals on a proteome-wide scale. In this paper we further demonstrate the value of this approach through the discovery that existing commercially available drugs, prescribed for the treatment of Parkinson's disease, have the potential to treat MDR and XDR tuberculosis. These drugs, entacapone and tolcapone, are predicted to bind to the enzyme InhA and directly inhibit substrate binding. The prediction is validated by in vitro and InhA kinetic assays using tablets of Comtan, whose active component is entacapone. The minimal inhibition concentration (MIC99) of entacapone for Mycobacterium tuberculosis (M.tuberculosis) is approximately 260.0 μM, well below the toxicity concentration determined by an in vitro cytotoxicity model using a human neuroblastoma cell line. Moreover, kinetic assays indicate that Comtan inhibits InhA activity by 47.0% at an entacapone concentration of approximately 80 μM. Thus the active component in Comtan represents a promising lead compound for developing a new class of anti-tubercular therapeutics with excellent safety profiles. More generally, the protocol described in this paper can be included in a drug discovery pipeline in an effort to discover novel drug leads with desired safety profiles, and therefore accelerate the development of new drugs.
Weibel-instability-mediated collisionless shocks in laboratory with ultraintense lasers
F. Fiuza,R. A. Fonseca,J. Tonge,W. B. Mori,L. O. Silva
Physics , 2012, DOI: 10.1103/PhysRevLett.108.235004
Abstract: The formation of non-relativistic collisionless shocks in laboratory with ultrahigh intensity lasers is studied via \emph{ab initio} multi-dimensional particle-in-cell simulations. The microphysics behind shock formation and dissipation, and the detailed shock structure are analyzed, illustrating that the Weibel instability plays a crucial role in the generation of strong subequipartition magnetic fields that isotropize the incoming flow and lead to the formation of a collisionless shock, similarly to what occurs in astrophysical scenarios. The possibility of generating such collisionless shocks in laboratory opens the way to the direct study of the physics associated with astrophysical shocks.
Privacy Prediction of Images Shared on Social Media Sites Using Deep Features
Ashwini Tonge,Cornelia Caragea
Computer Science , 2015,
Abstract: Online image sharing in social media sites such as Facebook, Flickr, and Instagram can lead to unwanted disclosure and privacy violations, when privacy settings are used inappropriately. With the exponential increase in the number of images that are shared online every day, the development of effective and efficient prediction methods for image privacy settings are highly needed. The performance of models critically depends on the choice of the feature representation. In this paper, we present an approach to image privacy prediction that uses deep features and deep image tags as feature representations. Specifically, we explore deep features at various neural network layers and use the top layer (probability) as an auto-annotation mechanism. The results of our experiments show that models trained on the proposed deep features and deep image tags substantially outperform baselines such as those based on SIFT and GIST as well as those that use "bag of tags" as features.
Efficient modeling of laser plasma interactions in high energy density scenarios
F. Fiuza,M. Marti,R. A. Fonseca,L. O. Silva,J. Tonge,J. May,W. B. Mori
Physics , 2012, DOI: 10.1088/0741-3335/53/7/074004
Abstract: We describe how a new framework for coupling a full-PIC algorithm with a reduced PIC algorithm has been implemented into the code OSIRIS. We show that OSIRIS with this new hybrid-PIC algorithm can efficiently and accurately model high energy density scenarios such as ion acceleration in laser-solid interactions and fast ignition of fusion targets. We model for the first time the full density range of a fast ignition target in a fully self-consistent hybrid-PIC simulation, illustrating the possibility of stopping the laser generated electron flux at the core region with relatively high efficiencies. Computational speedups greater than 1000 times are demonstrated, opening the way for full-scale multi-dimensional modeling of high energy density scenarios and for the guiding of future experiments.
Interpenetrating plasma shells: near-equipartition magnetic field generation and non-thermal particle acceleration
L. O. Silva,R. A. Fonseca,J. Tonge,J. M. Dawson,W. B. Mori,M. V. Medvedev
Physics , 2003, DOI: 10.1086/379156
Abstract: We present the first three-dimensional fully kinetic electromagnetic relativistic particle-in-cell simulations of the collision of two interpenetrating plasma shells. The highly accurate plasma-kinetic "particle-in-cell" (with the total of $10^8$ particles) parallel code OSIRIS has been used. Our simulations show: (i) the generation of long-lived near-equipartition (electro)magnetic fields, (ii) non-thermal particle acceleration, and (iii) short-scale to long-scale magnetic field evolution, in the collision region. Our results provide new insights into the magnetic field generation and particle acceleration in relativistic and sub-relativistic colliding streams of particles, which are present in gamma-ray bursters, supernova remnants, relativistic jets, pulsar winds, etc..
One-to-one direct modeling of experiments and astrophysical scenarios: pushing the envelope on kinetic plasma simulations
R. A. Fonseca,S. F. Martins,L. O. Silva,J. W. Tonge,F. S. Tsung,W. B. Mori
Physics , 2008, DOI: 10.1088/0741-3335/50/12/124034
Abstract: There are many astrophysical and laboratory scenarios where kinetic effects play an important role. These range from astrophysical shocks and plasma shell collisions, to high intensity laser-plasma interactions, with applications to fast ignition and particle acceleration. Further understanding of these scenarios requires detailed numerical modelling, but fully relativistic kinetic codes are computationally intensive, and the goal of one-to-one direct modelling of such scenarios and direct comparison with experimental results is still difficult to achieve. In this paper we discuss the issues involved in performing kinetic plasma simulations of experiments and astrophysical scenarios, focusing on what needs to be achieved for one-to-one direct modeling, and the computational requirements involved. We focus on code efficiency and new algorithms, specifically on parallel scalability issues, namely on dynamic load balancing, and on high-order interpolation and boosted frame simulations to optimize simulation performance. We also discuss the new visualization and data mining tools required for these numerical experiments and recent simulation work illustrating these techniques is also presented.
A global simulation for laser driven MeV electrons in $50μm$-diameter fast ignition targets
C. Ren,M. Tzoufras,J. Tonge,W. B. Mori,F. S. Tsung,M. Fiore,R. A. Fonseca,L. O. Silva,J. -C. Adam,A. Heron
Physics , 2006, DOI: 10.1063/1.2173617
Abstract: The results from 2.5-dimensional Particle-in-Cell simulations for the interaction of a picosecond-long ignition laser pulse with a plasma pellet of 50-$\mu m$ diameter and 40 critical density are presented. The high density pellet is surrounded by an underdense corona and is isolated by a vacuum region from the simulation box boundary. The laser pulse is shown to filament and create density channels on the laser-plasma interface. The density channels increase the laser absorption efficiency and help generate an energetic electron distribution with a large angular spread. The combined distribution of the forward-going energetic electrons and the induced return electrons is marginally unstable to the current filament instability. The ions play an important role in neutralizing the space charges induced by the the temperature disparity between different electron groups. No global coalescing of the current filaments resulted from the instability is observed, consistent with the observed large angular spread of the energetic electrons.
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