Dressing the electromagnetic nucleon current

A field-theory-based approach to pion photoproduction off the nucleon is used to derive a microscopically consistent formulation of the fully dressed electromagnetic nucleon current in an effective Lagrangian formalism. It is shown how the rigorous implementation of local gauge invariance at all levels of the reaction dynamics provides equations that lend themselves to practically manageable truncations of the underlying nonlinearities of the problem. The requirement of consistency also suggests a novel way of treating the pion photoproduction problem. Guided by a phenomenological implementation of gauge invariance for the truncated equations that has proved successful for pion photoproduction, an expression for the fully dressed nucleon current is given that satisfies the Ward-Takahashi identity for a fully dressed nucleon propagator as a matter of course. Possible applications include meson photo- and electroproduction processes, bremsstrahlung, Compton scattering, and $ee'$ processes off nucleons.Comment: 10 pages, 9 figure

Pion photoproduction in a dynamical coupled-channel model

Pion photoproduction reactions are investigated in a dynamical coupled-channel approach based on the Juelich pi-N model, which presently includes the hadronic pi-N and eta-N stable channels as well as the pi-Delta, sigma-N and rho-N effective channels. This model has been quite successful in the description of pi-N to pi-N scattering for center-of-mass energies up to 1.9 GeV. The full pion photoproduction amplitude is constructed to satisfy the generalized Ward-Takahashi identity and hence, it is fully gauge invariant. The calculated differential cross sections and photon spin asymmetries up to 1.65 GeV center-of-mass energy for the reactions gamma p to pi+ n, gamma p to pi0 p and gamma n to pi- p are in good agreement with the experimental data.Comment: Invited talk given at 12th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2010), Williamsburg, USA, May 31-June 4 201

Multivariate adaptive regression splines for estimating riverine constituent concentrations

Regression-based methods are commonly used for riverine constituent concentration/flux estimation, which is essential for guiding water quality protection practices and environmental decision making. This paper developed a multivariate adaptive regression splines model for estimating riverine constituent concentrations (MARS-EC). The process, interpretability and flexibility of the MARS-EC modelling approach, was demonstrated for total nitrogen in the Patuxent River, a major river input to Chesapeake Bay. Model accuracy and uncertainty of the MARS-EC approach was further analysed using nitrate plus nitrite datasets from eight tributary rivers to Chesapeake Bay. Results showed that the MARS-EC approach integrated the advantages of both parametric and nonparametric regression methods, and model accuracy was demonstrated to be superior to the traditionally used ESTIMATOR model. MARS-EC is flexible and allows consideration of auxiliary variables; the variables and interactions can be selected automatically. MARS-EC does not constrain concentration-predictor curves to be constant but rather is able to identify shifts in these curves from mathematical expressions and visual graphics. The MARS-EC approach provides an effective and complementary tool along with existing approaches for estimating riverine constituent concentrations

Real time hand gesture recognition including hand segmentation and tracking

In this paper we present a system that performs automatic gesture recognition. The system consists of two main components: (i) A unified technique for segmentation and tracking of face and hands using a skin detection algorithm along with handling occlusion between skin objects to keep track of the status of the occluded parts. This is realized by combining 3 useful features, namely, color, motion and position. (ii) A static and dynamic gesture recognition system. Static gesture recognition is achieved using a robust hand shape classification, based on PCA subspaces, that is invariant to scale along with small translation and rotation transformations. Combining hand shape classification with position information and using DHMMs allows us to accomplish dynamic gesture recognition

Subtle pH differences trigger single residue motions for moderating conformations of calmodulin

This study reveals the essence of ligand recognition mechanisms by which calmodulin (CaM) controls a variety of Ca2+ signaling processes. We study eight forms of calcium-loaded CaM each with distinct conformational states. Reducing the structure to two degrees of freedom conveniently describes main features of the conformational changes of CaM via simultaneous twist-bend motions of the two lobes. We utilize perturbation-response scanning (PRS) technique, coupled with molecular dynamics simulations. PRS is based on linear response theory, comprising sequential application of directed forces on selected residues followed by recording the resulting protein coordinates. We analyze directional preferences of the perturbations and resulting conformational changes. Manipulation of a single residue reproduces the structural change more effectively than that of single/pairs/triplets of collective modes of motion. Our findings also give information on how the flexible linker acts as a transducer of binding information to distant parts of the protein. Furthermore, by perturbing residue E31 located in one of the EF hand motifs in a specific direction, it is possible to induce conformational change relevant to five target structures. Independently, using four different pKa calculation strategies, we find this particular residue to be the charged residue (out of a total of 52), whose ionization state is most sensitive to subtle pH variations in the physiological range. It is plausible that at relatively low pH, CaM structure is less flexible. By gaining charged states at specific sites at a pH value around 7, such as E31 found in the present study, local conformational changes in the protein will lead to shifts in the energy landscape, paving the way to other conformational states. These findings are in accordance with Fluorescence Resonance Energy Transfer (FRET) measured shifts in conformational distributions towards more compact forms with decreased pH. They also corroborate mutational studies and proteolysis results which point to the significant role of E31 in CaM dynamics

High efficiency tomographic reconstruction of quantum states by quantum nondemolition measurements

We propose a high efficiency tomographic scheme to reconstruct an unknown quantum state of the qubits by using a series of quantum nondemolition (QND) measurements. The proposed QND measurements of the qubits are implemented by probing the the stationary transmissions of the dispersively-coupled resonator. It is shown that only one kind of QND measurements is sufficient to determine all the diagonal elements of the density matrix of the detected quantum state. The remaining non-diagonal elements of the density matrix can be determined by other spectral measurements by beforehand transferring them to the diagonal locations using a series of unitary operations. Compared with the pervious tomographic reconstructions based on the usual destructively projective (DP) measurements (wherein one kind of such measurements could only determine one diagonal element of the density matrix), the present approach exhibits significantly high efficiency for N-qubit (N > 1). Specifically, our generic proposal is demonstrated by the experimental circuit-quantumelectrodynamics (circuit-QED) systems with a few Josephson charge qubits.Comment: 9pages,4figure