Dynamics of atomic decay in a special one dimensional photonic crystal

Recently, Liu et al. [Phys. Rev. B 74, 075314 (2006)] pointed out that the atomic instant decay rate in one dimensional photonic crystal (1DPC) showed a series of pulse-like peaks with time. In this paper, we continue their work, and adopt a special 1DPC, in which the refractive indexes of both constitution layers in a period are the same, to perform the analysis in detail. Our results show that the pulse-like peak of instant decay rate originates from the interaction between the atom and the sub-reservoir, the latter of which corresponds to the group of reflected fields having the same optical distance. The atom interacts with such a sub-reservoir mainly after the time needed for propagation. However, near the arrival time of the reflected field, the atomic level is broadened and couples to all frequency components of the sub-reservoir, and the pulse-like peak of instant decay rate appears. Although our conclusion is deduced with the special 1DPC, it is also valid for more general cases and might be useful to measure the quantum Zeno and anti-Zeno effect, since the interval of repeated measurements may be expanded to several optical cycles in 1DPC, which will facilitate the observation of the quantum Zeno or anti-Zeno effect.     

Functional MRI changes in the central motor system in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a multisystemic disease involving multiple organ systems including central nervous system (CNS) and muscles. Few studies have focused on the central motor system in DM1, pointing to a subclinical abnormality in the CNS. The aim of our study was to investigate patterns of cerebral activation in DM1 during a motor task using functional MRI (fMRI). Fifteen DM1 patients, aged 20 to 59 years, and 15 controls of comparable age were scanned during a self-paced sequential finger-to-thumb opposition task of their dominant right hand. Functional MRI images were analyzed using SPM99. Patients underwent clinical and genetic assessment; all subjects underwent a conventional MR study. Myotonic dystrophy type 1 patients showed greater activation than controls in bilateral sensorimotor areas and inferior parietal lobules, basal ganglia and thalami, in the ipsilateral premotor area, insula and supplementary motor area (corrected P<.05). Analysis of the interaction between disease and age showed that correlation with age was significantly greater in patients than in controls in bilateral sensorimotor areas and in contralateral parietal areas. Other clinical and MR characteristics did not correlate with fMRI. Functional changes in DM1 may represent compensatory mechanisms such as reorganization and redistribution of functional networks to compensate for ultrastructural and neurochemical changes occurring as part of the accelerated aging process.     

Integration of EEG source imaging and fMRI during continuous viewing of natural movies

Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are noninvasive neuroimaging tools which can be used to measure brain activity with excellent temporal and spatial resolution, respectively. By combining the neural and hemodynamic recordings from these modalities, we can gain better insight into how and where the brain processes complex stimuli, which may be especially useful in patients with different neural diseases. However, due to their vastly different spatial and temporal resolutions, the integration of EEG and fMRI recordings is not always straightforward. One fundamental obstacle has been that paradigms used for EEG experiments usually rely on event-related paradigms, while fMRI is not limited in this regard. Therefore, here we ask whether one can reliably localize stimulus-driven EEG activity using the continuously varying feature intensities occurring in natural movie stimuli presented over relatively long periods of time. Specifically, we asked whether stimulus-driven aspects in the EEG signal would be co-localized with the corresponding stimulus-driven BOLD signal during free viewing of a movie. Secondly, we wanted to integrate the EEG signal directly with the BOLD signal, by estimating the underlying impulse response function (IRF) that relates the BOLD signal to the underlying current density in the primary visual area (V1). We made sequential fMRI and 64-channel EEG recordings in seven subjects who passively watched 2-min-long segments of a James Bond movie. To analyze EEG data in this natural setting, we developed a method based on independent component analysis (ICA) to reject EEG artifacts due to blinks, subject movement, etc., in a way unbiased by human judgment. We then calculated the EEG source strength of this artifact-free data at each time point of the movie within the entire brain volume using low-resolution electromagnetic tomography (LORETA). This provided for every voxel in the brain (i.e., in 3D space) an estimate of the current density at every time point. We then carried out a correlation between the time series of visual contrast changes in the movie with that of EEG voxels. We found the most significant correlations in visual area V1, just as seen in previous fMRI studies (Bartels A, Zeki, S, Logothetis NK. Natural vision reveals regional specialization to local motion and to contrast-invariant, global flow in the human brain. Cereb Cortex 2008;18(3):705–717), but on the time scale of milliseconds rather than of seconds. To obtain an estimate of how the EEG signal relates to the BOLD signal, we calculated the IRF between the BOLD signal and the estimated current density in area V1. We found that this IRF was very similar to that observed using combined intracortical recordings and fMRI experiments in nonhuman primates. Taken together, these findings open a new approach to noninvasive mapping of the brain. It allows, firstly, the localization of feature-selective brain areas during natural viewing conditions with the temporal resolution of EEG. Secondly, it provides a tool to assess EEG/BOLD transfer functions during processing of more natural stimuli. This is especially useful in combined EEG/fMRI experiments, where one can now potentially study neural-hemodynamic relationships across the whole brain volume in a noninvasive manner.     

Manifestation of geometric resonance in current dependence of AC susceptibility for unshunted array of Nb–Alx–Nb Josephson junctions

A pronounced resonance-like structure has been observed in the current dependence of AC susceptibility for two-dimensional array of unshunted Nb–Al_x–Nb Josephson junctions. Using a single-plaquette approximation, we were able to successfully fit our data assuming that resonance structure is related to the geometric (inductive) properties of the array.     

Multimodal imaging: an evaluation of univariate and multivariate methods for simultaneous EEG/fMRI

The combination of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) has been proposed as a tool to study brain dynamics with both high temporal and high spatial resolution. Multimodal imaging techniques rely on the assumption of a common neuronal source for the different recorded signals. In order to maximally exploit the combination of these techniques, one needs to understand the coupling (i.e., the relation) between electroencephalographic (EEG) and fMRI blood oxygen level-dependent (BOLD) signals.     

Crystal Structure of 6, 6' ‐ Dihydroxy ‐ 2, 2' ‐ biphenyl ‐ 19 ‐ crown ‐ 5 ; Comparison of Some Structural Features among Related Ligands and Compounds

It has been determined the crystal structure of 6,6'‐dihydroxy‐2,2'‐biphenyl‐19‐crown‐5, C₂₂H₂₈O₇ (1a). Likewise, it has been set up a comparison between the results and some features of this structure obtained by molecular mechanics calculations. Due the presence of a hydrogen bond, the crown oxygens have not a geometrical disposition to lead its electronic pairs into the cavity and therefore the system complexation constant decreases, compared to some related ligands and compounds.