An Economical Magnetocardiogram System Based on High-To SQUIDs

An economical magnetocardiogram （MCG） system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device （SQUID） magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements.     

Equivariant quantization on quotients of simple Lie groups by reductive subgroups of maximal rank

We consider a class of homogeneous manifolds including all semisimple coadjoint orbits. We describe manifolds of that class admitting deformation quantizations equivariant under the action ofG and the corresponding quantum group. We also classify Poisson brackets relating to such quantizations. Presented at the 11th Colloquium “Quantum Groups and Integrable Systems”, Prague, 20–22 June 2002.     

Hadron spectroscopy and structure from AdS/CFT

The AdS/CFT correspondence between conformal field theory and string states in an extended space-time has provided new insights into not only hadron spectra, but also their light-front wave functions. We show that there is an exact correspondence between the fifth-dimensional coordinate of anti-de Sitter space z and a specific impact variable ζ which measures the separation of the constituents within the hadron in ordinary space-time. This connection allows one to predict the form of the light-front wave functions of mesons and baryons, the fundamental entities which encode hadron properties and scattering amplitudes. A new relativistic Schr?dinger light-front equation is found which reproduces the results obtained using the fifth-dimensional theory. Since they are complete and orthonormal, the AdS/CFT model wave functions can be used as an initial ansatz for a variational treatment or as a basis for the diagonalization of the light-front QCD Hamiltonian. A number of applications of light-front wave functions are also discussed.     

Δ -resonances: Quark models, chiral symmetry and AdS/QCD

The mass spectrum of Δ -resonances is compared to predictions based on three quark-model variants, to predictions assuming that chiral symmetry is restored in high-mass baryon resonances, and to predictions derived from AdS/QCD. The latter approach yields a nearly perfect agreement when the confinement property of QCD is modeled by a soft wall in AdS.     

Remarks on Two-Dimensional Power Correction in Soft Wall Model

We present a direct derivation of the two-point correlation function of the vector current in the soft wall model by using the AdS/CFT dictionary. The resulting correlator is exactly the same as the one previously obtained from dispersion relation with the same spectral function as in this model. The coefficient C₂ of the two-dimensional power correction is found to be C₂=-c/2 with c the slope of the Regge trajectory, rather than C₂=-c/3 derived from the strategy of the first quantized string theory. Taking the slope of the ρ trajectory c≈0.9GeV² as input, we then obtain C₂≈-0.45GeV². The gluon condensate is found to be <α_sG²>≈pprox0.064GeV⁴, which is almost identical to the QCD sum rule estimation. By comparing these two equivalent derivation of the correlator of scalar glueball operator, we demonstrate that the two-dimensional correction cannot be eliminated by including the non-leading solution in the bulk-to-boundary propagator, as carried out by Colangelo et al.[arXiv:0711.4747]. In other words, the two-dimensional correction does exist in the scalar glueball case. Also it is manifest by using the dispersion relation that the minus sign of gluon condensate and violation of the low energy theorem are related to the subtraction scheme.     

Dimension six corrections to the vector sector of AdS/QCD model

We study the effects of dimension six terms on the predictions of the holographic model for the vector meson form factors and determine the corrections to the electric radius, the magnetic and the quadrupole moments of the ρ  -meson. We show that the only dimension six terms which contribute nontrivially to the vector meson form factors are X²F²$X^2{F}^2$ and F³$F^3$. It appears that the effect from the former term is equivalent to the metric deformation and can change only masses, decay constants and charge radii of vector mesons, leaving the magnetic and the quadrupole moments intact. The latter term gives different contributions to the three form factors of the vector meson and changes the values of the magnetic and the quadrupole moments. The results suggest that the addition of the higher dimension terms improves the holographic model.     

Radiative processes as a condensation phenomenon and the physical meaning of deformed canonical structures

We study the radiative corrections of QED₃ from the dual point of view and show that this process is the exact dual to the Julia–Toulouse mechanism introduced by Quevedo and Trugenberger [F. Quevedo, C.A. Trugenberger, Nucl. Phys. B 501 (1997) 143] some years ago. We discuss the physics behind this mechanism that involves condensation of topological defects. It is shown that the dual Stuckelberg mechanism is responsible for the “rank-jump” phenomenon that transforms the scalar field (dual to Maxwell in this dimensionality) into the vectorial self-dual field. This phenomenon is studied using the ideas of noncommutative fields theory that examines possible deformations of the canonical structure of some well-known models in (2+1)D$(2+1)\mathrm{D}$. A deformation is constructed linking the massless scalar field theory with the self-dual theory. This is the exact dual of the known deformation connecting the Maxwell theory with the Maxwell–Chern–Simons theory. Duality, radiative corrections, the Julia–Toulouse mechanism and canonical deformations are then used to establish a web of relations between the mentioned theories and to propose a physical picture of the deformation procedure adopted.     

Heavy-quark energy loss in pQCD and SYM plasmas

We consider heavy-quark energy loss and p _⊥ -broadening in a strongly-coupled N=4 Super Yang–Mills (SYM) plasma, and the problem of finite-extent matter is addressed. When expressed in terms of the appropriate saturation momentum, one finds identical parametric forms for the energy loss in pQCD and SYM theory, while p _⊥ -broadening is radiation dominated in SYM theory and multiple scattering dominated in pQCD. C.M. is supported by the European Commission under the FP6 program, contract No. MOIF-CT-2006-039860.     

Collision of a 1-D column of beads with a wall

An experimental study of the collision of a column of N beads () with a fixed wall is presented. For a fixed height of fall and a rigid wall, we show that the maximum force felt by the wall is independent of the number of beads N. The duration of impact, the velocity of the deformation wave in the column and an effective restitution coefficient of the column are also measured as a function of N. For a soft wall, we show that the maximum force depends on N. A non-dissipative numerical model, based on a nonlinear interaction law between nearest neighbours, gives results in agreement with the experimental data. Moreover, we show that, after the compression phase, the beads of the top of the column separate one after the other from the column with a velocity greater than the initial one. The beads at the bottom then bounce upwards in block, with a velocity smaller than the initial one. We emphasize that this detachment effect results from the energy redistribution within the whole system during the collision and not from any dissipative effect. Received: 6 February 1998 / Revised and accepted: 26 May 1998