Theory of visual attention's thalamic model for visual short-term memory capacity and top-down control: evidence from a thalamo-cortical structural connectivity analysis

In the theory of visual attention (TVA), it is suggested that objects in a visual scene compete for representation in a visual short-term memory (vSTM) store. The race towards the store is assumed to be biased by top-down controlled weighting of the objects according to their task relevance. Only objects that reach the store before its capacity limitation is reached are represented consciously in a given instant. TVA-based computational modeling of participants' performance in whole- and partial-report tasks permits independent parameters of individual efficiency of top-down control α and vSTM storage capacity K to be extracted. The neural interpretation of the TVA proposes recurrent loops between the posterior thalamus and posterior visual cortices to be relevant for generating attentional weights for competing objects and for maintaining selected objects in vSTM. Accordingly, we tested whether structural connectivity between posterior thalamus and occipital cortices (PT-OC) is associated with estimates of top-down control and vSTM capacity. We applied whole- and partial-report tasks and probabilistic tractography in a sample of 37 healthy adults. We found vSTM capacity K to be associated with left PT-OC structural connectivity and a trend-wise relation between top-down control α and right PT-OC structural connectivity. These findings support the assumption of the relevance of thalamic structures and their connections to visual cortex for top-down control and vSTM capacity

Characterization of PARIS LaBr3_3(Ce)-NaI(Tl) phoswich detectors upto EγE_\gamma ∼\sim 22 MeV

In order to understand the performance of the PARIS (Photon Array for the studies with Radioactive Ion and Stable beams) detector, detailed characterization of two individual phoswich (LaBr$_3$(Ce)-NaI(Tl)) elements has been carried out. The detector response is investigated over a wide range of $E_{\gamma}$ = 0.6 to 22.6 MeV using radioactive sources and employing $^{11}B(p,\gamma)$ reaction at $E_p$ = 163 keV and $E_p$ = 7.2 MeV. The linearity of energy response of the LaBr$_3$(Ce) detector is tested upto 22.6 MeV using three different voltage dividers. The data acquisition system using CAEN digitizers is set up and optimized to get the best energy and time resolution. The energy resolution of $\sim$ 2.1% at $E_\gamma$ = 22.6~MeV is measured for the configuration giving best linearity upto high energy. Time resolution of the phoswich detector is measured with a $^{60}$Co source after implementing CFD algorithm for the digitized pulses and is found to be excellent (FWHM $\sim$ 315~ps). In order to study the effect of count rate on detectors, the centroid position and width of the $E_{\gamma}$ = 835~keV peak were measured upto 220 kHz count rate. The measured efficiency data with radioactive sources are in good agreement with GEANT4 based simulations. The total energy spectrum after the add-back of energy signals in phoswich components is also presented.Comment: Accepted in JINS

Coulomb excitation of 73Ga

The B(E2; Ii -> If) values for transitions in 71Ga and 73Ga were deduced from a Coulomb excitation experiment at the safe energy of 2.95 MeV/nucleon using post-accelerated beams of 71,73Ga at the REX-ISOLDE on-line isotope mass separator facility. The emitted gamma rays were detected by the MINIBALL-detector array and B(E2; Ii->If) values were obtained from the yields normalized to the known strength of the 2+ -> 0+ transition in the 120Sn target. The comparison of these new results with the data of less neutron-rich gallium isotopes shows a shift of the E2 collectivity towards lower excitation energy when adding neutrons beyond N = 40. This supports conclusions from previous studies of the gallium isotopes which indicated a structural change in this isotopical chain between N = 40 and N = 42. Combined with recent measurements from collinear laser spectroscopy showing a 1/2- spin and parity for the ground state, the extracted results revealed evidence for a 1/2-; 3/2- doublet near the ground state in 73 31Ga42 differing by at most 0.8 keV in energy

Rb-37(97)60 : The Cornerstone of the Region of Deformation around A similar to 100

Excited states of the neutron-rich nuclei Rb-97,Rb- 99 were populated for the first time using the multistep Coulomb excitation of radioactive beams. Comparisons of the results with particle-rotor model calculations provide clear identification for the ground-state rotational band of Rb-97 as being built on the pi g(9/2) [431] 3/2(+) Nilsson-model configuration. The ground-state excitation spectra of the Rb isotopes show a marked distinction between single-particle-like structures below N = 60 and rotational bands above. The present study defines the limits of the deformed region around A similar to 100 and indicates that the deformation of Rb-97 is essentially the same as that observed well inside the deformed region. It further highlights the power of the Coulomb-excitation technique for obtaining spectroscopic information far from stability. The Rb-99 case demonstrates the challenges of studies with very short-lived postaccelerated radioactive beams.Peer reviewe

Determination of the B(E3, 0(+) -> 3(-))-excitation strength in octupole-correlated nuclei near A approximate to 224 by the means of Coulomb excitation at REX-ISOLDE

Volume: 533Peer reviewe

Do nuclei go pear-shaped? Coulomb excitation of Rn-220 and Ra-224 at REX-ISOLDE (CERN)

Volume: 93The IS475 collaboration conducted Coulomb-excitation experiments with post-accelerated radioactive Rn-220 and Ra-224 beams at the REX-ISOLDE facility. The beam particles (E-beam: 2.83 MeV/u) were Coulomb excited using Ni-60, Cd-14, and Sn-120 scattering targets. De-excitation gamma-rays were detected employing the Miniball array and scattered particles were detected in a silicon detector. Exploiting the Coulomb-excitation code GOSIA for each nucleus several matrix elements could be obtained from the measured gamma-ray yields. The extracted matrix element allows for the conclusion that, while Rn-220 represents an octupole vibrational system, Ra-224 has already substantial octupole correlations in its ground state. This finding has i(m)plications for the search of CP-violating Schiff moments in the atomic systems of the adjacent odd-mass nuclei.Peer reviewe