Differential effects of synchronous and asynchronous multifinger coactivation on human tactile performance

Background  

Repeated execution of a tactile task enhances task performance. In the present study we sought to improve tactile performance with unattended activation-based learning processes (i.e., focused stimulation of dermal receptors evoking neural coactivation (CA)). Previous studies show that the application of CA to a single finger reduced the stationary two-point discrimination threshold and significantly increased tactile acuity. These changes were accompanied by an expansion of the cortical finger representation in primary somatosensory cortex (SI). Here we investigated the effect of different types of multifinger CA on the tactile performance of each finger of the right hand.     

Investigation of the triplet states of DNA by optical detection of magnetic resonance using a new slow passage technique

A new method to obtain slow passage ODMR signals under otherwise impeding conditions is described. The technique is applied to identify the triplet state of DNA as thymine. The zero field splitting constants measured are |D| = (0.203 ± 0.003) cm^?1, and |E| ? (0.0123 ± 0.0005) cm^?1. From microwave-induced delayed phosphorescence and slow passage measurements a preliminary kinetic scheme for the triplet state is derived.     

Investigation of U(VI) extraction with calixarene: Application to analysis of urine sample

A macrocyclic molecule, the calix[6]arene 4₆, functionalized with carboxy groups, has been studied and its extraction efficiency towards uranium determined in a two phases solvent-extraction system. Two solvents, dichloromethane and benzene were used to follow uranium extraction from media containing sodium ions. The study of the extraction parameters allowed proposing an extraction scheme with each solvent. The extraction efficiency was found to increase with pH, with an optimal efficiency of nearly 100%. No decrease of uranium extraction was observed in synthetic solutions containing sodium ions (spiked with²²Na) and/or²³⁹Pu. Under specific conditions, almost 100% of uranium have been extracted by the calixarene from real urine samples.     

X-ray emission from clusters of galaxies and cosmological parameters

Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate a Universe with a low value (≤ 0.3) for the Ω parameter.     

EPR study of topoisomers of La@C82 and La@C90

An analysis of the temperature dependence of the line width variation of topoisomers (I) and (II) of La@C₈₂ revealed that both molecules exhibit practically identical rotational correlation times from room temperature down to the freezing point of CS₂. Although this result indicates confinement of the metal ion, from the increased line width of¹³C satellites in isomer (II) we conclude that in this molecule there might be increased mobility within a confine volume. Three stable topoisomers of La@C₉₀ were identified for the first time. One of these topoisomers was separated by HPLC technique. We were unable, however, to detect any nuclear spin dependence of the EPR line width even at low temperatures. This might indicate that in this case the ion is no longer confined to a specific binding site, although a more trivial explanation assuming small anisotropies of all hyperfine interactions cannot yet be ruled out.     

Anomalous Phases in Cavity-Free 240 GHz Pulsed ENDOR Spectra of 1.44 GeV Xe-Irradiated LiF

Paramagnetic centers generated by swift heavy ion irradiation of LiF crystals could be identified as electrons trapped at regular anion vacancy sites (F centers). Well-resolved electron-nuclear double resonance (ENDOR) spectra resulting from the hyperfine interaction with ⁷Li and ¹⁹F nuclei located in six different shells could be recorded. In order to preserve the millimeter-sized crystals, a cavity-free setup was used for the ENDOR experiments at an electronic Larmor frequency of 240 GHz. Apparently even under conditions of extremely high local energy loss in the ion track, the local density of persistent F centers is still sufficiently low to prevent distortions of the ionic crystal. The spread of hyperfine coupling constants was less than 5 %. Neither in electron paramagnetic resonance (EPR) nor in ENDOR spectra there was evidence for different types of paramagnetic centers. When performing ENDOR by applying the radiofrequency pulse directly after the 3-pulse Mims-type microwave sequence, an anomalous ENDOR effect was observed. The observed “positive” and “negative” ENDOR response can be attributed to efficient hole and anti-hole formation in the inhomogeneously broadened EPR spectrum and can be used to determine the sign of hyperfine coupling constants.     

HYSCORE analysis of nitrogen hyperfine interactions

A semiquantitative treatment of hyperfine sublevel correlation spectra of aS=1/2,I=1 spin system is presented. The derived closed analytical expressions allow the determination of components of the dipolar and quadrupolar coupling tensors. The method is applicable if nonsecular terms can be neglected and if canonical orientations of the hyperfine interactions can be selected via a dominantg matrix or hyperfine anisotropy.     

Endor investigation of the biphenyl and terphenyl anion radicals in solution

From the ENDOR spectra of the mononegative ions of biphenyl and ortho-, meta- and para-terphenyl in solution complete sets of hyperfine splitting constants could be determined. The splittings are interpreted in terms of SCF MO spin densities obtained from McLachlan type calculations. It turns out that π-σ spin delocalization effects do not play a significant role in the spin density distribution in these radicals although some of them deviate considerably from coplanarity.     

Electron paramagnetic resonance structure investigation of copper complexation in a hemicarcerand

The double-bridged hemicarcerand [A,B-(CH2OH)2-cavitand]-(CH2NHCH2)2-[A,B-(CH2OH)2-cavitand] 23 (and several other related compounds) was synthesized by the condensation of the two complementary precursors A,B-(CH2NH2)2(CH2OH)2-cavitand and A,B-(CH2Br)2(CH2OAc)2-cavitand followed by hydrolysis of the acetate groups. This hemicarcerand has nitrogen and oxygen donor atoms located on the interior of the spherical cavity and thus allows endohedral coordination of metal ions. The cavity has a volume of approximately 0.12 nm3, a value obtained by calculating a Connolly-type contact surface and the molecular electrostatic potential. The Cu2+ complex of hemicarcerand 23 was studied in detail by EPR and DFT calculations at the UB3LYP/6-31G level to verify the anticipated endohedral nature of the metal complex. It could be shown that the copper ion is coordinated to four oxygen donor atoms and no deviation from axial symmetry at the copper site could be detected. No direct coordination to nitrogen atoms of the hemicarcerand could be observed; however, complexation with DMF solvent molecules was detected by ESEEM and HYSCORE experiments. The closed structure of the hemicarcerand was also confirmed by an evaluation of proton-copper distances. Results from DFT calculations are in accord with the EPR results, and further support suggested coordination of the Cu(II) within the hemicarcerand cavity by four oxygen donor atoms.     

EPR study of radical anions of C60 and C70

Utilizing highly polar solvents for the stabilization of Fullerene anions, electrochemical and chemical reduction resulted in narrow single line EPR spectra for the monoanions of C₆₀ and C₇₀ being characterized byg=2.0001(1), ΔB=0.075 mT,g=2.0019(1), ΔB=0.016 mT, respectively. Apparently, the orbital degeneracy of the C₆₀ monoanion is lifted under these conditions to such an extent, that the abnormal large spin lattice relaxation rate believed to be responsible for the approximately 5 mT line width of the monoanion is sufficiently reduced.¹³C enrichment resulted in noticeable line broadening, allowing an estimate of the average¹³C hyperfine coupling constanta _ave=0.1 mT.