Influence of spinal cord stimulation on evoked potentials by cutaneous electrical stimulation

In the past, limited research has been done to investigate the influence of spinal cord stimulation (SCS) for treatment of chronic pain on evoked potentials (EP). Further insight into the mechanism of SCS may provide explanations for unsatisfactory results with this therapy in certain subpopulations. It also might predict effectiveness of SCS. In previous research MEG responses were measured on median and tibial nerve stimulations in chronic pain patients with and without SCS (1). However, this stimulation method preferentially activates large myelinated proprioceptive fibres, leaving painrelated small fibres unrelated. We expect that the observation of pain processing is impaired by large amounts of non-painrelated activity

Normal stresses in semiflexible polymer hydrogels

Biopolymer gels such as fibrin and collagen networks are known to develop tensile axial stress when subject to torsion. This negative normal stress is opposite to the classical Poynting effect observed for most elastic solids including synthetic polymer gels, where torsion provokes a positive normal stress. As recently shown, this anomalous behavior in fibrin gels depends on the open, porous network structure of biopolymer gels, which facilitates interstitial fluid flow during shear and can be described by a phenomenological two-fluid model with viscous coupling between network and solvent. Here we extend this model and develop a microscopic model for the individual diagonal components of the stress tensor that determine the axial response of semi-flexible polymer hydrogels. This microscopic model predicts that the magnitude of these stress components depends inversely on the characteristic strain for the onset of nonlinear shear stress, which we confirm experimentally by shear rheometry on fibrin gels. Moreover, our model predicts a transient behavior of the normal stress, which is in excellent agreement with the full time-dependent normal stress we measure.Comment: 12 pages, 8 figure

Cosmic rays studied with a hybrid high school detector array

The LORUN/NAHSA system is a pathfinder for hybrid cosmic ray research combined with education and outreach in the field of astro-particle physics. Particle detectors and radio antennae were mainly setup by students and placed on public buildings. After fully digital data acquisition, coincidence detections were selected. Three candidate events confirmed a working prototype, which can be multiplied to extend further particle detector arrays on high schools.Comment: 10 pages, 6 figures. Nigl, A., Timmermans, C., Schellart, P., Kuijpers, J., Falcke, H., Horneffer, A., de Vos, C. M., Koopman, Y., Pepping, H. J., Schoonderbeek, G., Cosmic rays studied with a hybrid high school detector array, Europhysics News (EPN), Vol. 38, No. 5, accepted on 22/08/200

Frequency-dependent spontaneous emission rate from CdSe and CdTe nanocrystals: influence of dark states

We studied the rate of spontaneous emission from colloidal CdSe and CdTe nanocrystals at room temperature. The decay rate, obtained from luminescence decay curves, increases with the emission frequency in a supra-linear way. This dependence is explained by the thermal occupation of dark exciton states at room temperature, giving rise to a strong attenuation of the rate of emission. The supra-linear dependence is in agreement with the results of tight-binding calculations.Comment: 11 page

Time-resolved spectroscopy of the primary photosynthetic processes of membrane-bound reaction centers from an antenna-deficient mutant of Rhodobacter capsulatus

The primary photosynthetic reactions in whole membranes of the antenna-deficient mutant strain U43 (pTXA6–10) of Rhodobacter capsulatus are studied by transient absorption and emission spectroscopy with subpicosecond time resolution. Extensive similarities between the transient absorption data on whole membranes and on isolated reaction centers support the idea that the primary processes in isolated reaction centers are not modified by the isolation procedure

A Comparative Study of the Valence Electronic Excitations of N_2 by Inelastic X-ray and Electron Scattering

Bound state, valence electronic excitation spectra of N_2 are probed by nonresonant inelastic x-ray and electron scattering. Within the usual theoretical treatments, dynamical structure factors derived from the two probes should be identical. However, we find strong disagreements outside the dipole scattering limit, even at high probe energies. This suggests an unexpectedly important contribution from intra-molecular multiple scattering of the probe electron from core electrons or the nucleus. These effects should grow progressively stronger as the atomic number of the target species increases.Comment: Submitted to Physical Review Letters April 27, 2010. 12 pages including 2 figure pages