Method of extending hyperfine coherence times in Pr^3+:Y_2SiO_5

In this letter we present a method for increasing the coherence time of praseodymium hyperfine ground state transitions in Pr^3+:Y_2SiO_5 by the application of a specific external magnetic field. The magnitude and angle of the external field is applied such that the Zeeman splitting of a hyperfine transition is at a critical point in three dimensions, making the first order Zeeman shift vanishingly small for the transition. This reduces the influence of the magnetic interactions between the praseodymium ions and the spins in the host lattice on the transition frequency. Using this method a phase memory time of 82ms was observed, a value two orders of magnitude greater than previously reported. It is shown that the residual dephasing is amenable quantum error correction

Accuracy of B(E2; 0+ -> 2+) transition rates from intermediate-energy Coulomb excitation experiments

The method of intermediate-energy Coulomb excitation has been widely used to determine absolute B(E2; 0+ -> 2+) quadrupole excitation strengths in exotic nuclei with even numbers of protons and neutrons. Transition rates measured with intermediate-energy Coulomb excitation are compared to their respective adopted values and for the example of 26Mg to the B(E2; 0+ -> 2+) values obtained with a variety of standard methods. Intermediate-energy Coulomb excitation is found to have an accuracy comparable to those of long-established experimental techniques.Comment: to be published in Phys. Rev.

The Primacy Effect in Amnestic Mild Cognitive Impairment: Associations with Hippocampal Functional Connectivity

Background: The “primacy effect,” i.e., increased memory recall for the first items of a series compared to the following items, is reduced in amnestic mild cognitive impairment (aMCI). Memory task-fMRI studies demonstrated that primacy recall is associated with higher activation of the hippocampus and temporo-parietal and frontal cortical regions in healthy subjects. Functional magnetic resonance imaging (fMRI) at resting state revealed that hippocampus functional connectivity (FC) with neocortical brain areas, including regions of the default mode network (DMN), is altered in aMCI. The present study aimed to investigate whether resting state fMRI FC between the hippocampus and cortical brain regions, especially the DMN, is associated with primacy recall performance in aMCI. Methods: A number of 87 aMCI patients underwent resting state fMRI and verbal episodic memory assessment. FC between the left or right hippocampus, respectively, and all other voxels in gray matter was mapped voxel-wise and used in whole-brain regression analyses, testing whether FC values predicted delayed primacy recall score. The delayed primacy score was defined as the number of the first four words recalled on the California Verbal Learning Test. Additionally, a partial least squares (PLS) analysis was performed, using DMN regions as seeds to identify the association of their functional interactions with delayed primacy recall. Results: Voxel-based analyses indicated that delayed primacy recall was mainly (positively) associated with higher FC between the left and right hippocampus. Additionally, significant associations were found for higher FC between the left hippocampus and bilateral temporal cortex, frontal cortical regions, and for higher FC between the right hippocampus and right temporal cortex, right frontal cortical regions, left medial frontal cortex and right amygdala (p < 0.01, uncorr.). PLS analysis revealed positive associations of delayed primacy recall with FC between regions of the DMN, including the left and right hippocampus, as well as middle cingulate cortex and thalamus (p < 0.04). In conclusion, in the light of decreased hippocampus function in aMCI, inter-hemispheric hippocampus FC and hippocampal FC with brain regions predominantly included in the DMN may contribute to residual primacy recall in aMCI

Neuronal correlates of serial position performance in amnestic mild cognitive impairment.

Objectives: Delayed recall of the first words of a list - the primacy position – is thought to be particularly dependent on intact memory consolidation. Hippocampal volume has been suggested as the primary neuronal correlate of delayed primacy recall in cognitively normal elderly individuals. Here, we studied the association of hippocampal volume with primacy recall in individuals with amnestic mild cognitive impairment (aMCI). Methods: We investigated serial position performance in 88 subjects with aMCI using a 16-word list (CVLT). Primacy and recency performance were measured during learning and delayed recall. Hippocampal volumes were automatically determined from structural MRI scans. We conducted regression analyses with bilateral hippocampal volumes as predictors and serial position indices as outcomes. Results: After controlling for age, gender, and total intracranial volume, bilateral hippocampal volume was not associated with primacy recall either during learning or delayed recall. Primacy performance during learning was associated with the right inferior and middle temporal gyrus as well as the right inferior parietal cortex and supramerginal gyrus. During delayed recall, primacy performance was related to the bilateral supramarginal gyri. Conclusions: Our findings suggest a reduced primacy effect in aMCI already during learning, contrasting previous findings in normal cognitive aging. This might indicate impaired encoding and consolidation processes at an early stage of episodic memory acquisition. Furthermore, our data indicates that hippocampal volume may not be a relevant determinant of residual primacy performance in the stage of aMCI, which may rather depend on temporal and parietal neocortical networks

Contracting decision and performance of Mexican coffee traders: The role of market institutions

We identified and explained the contractual choices of Mexican coffee traders in selling their product and analyzed the traders´ performance. The data were obtained from personal interviews with 53 intermediaries in four coffee producing regions of the states of Oaxaca and Veracruz, Mexico. Marketing margins were used as an indicator of traders’ performance. The results indicate that being a roaster, having a wet processing plant and selling cherry coffee negatively affects the use of contracts whereas being vertically integrated has a positive effect. The results also suggest that being registered in the National Coffee System (which only a minority of the interviewed traders were) increases the margin for the trader. Selling cherry coffee, participating in a competitive environment and having a contract decreases these margins (at 5% significance) and may thus enhance the performance of the supply chain and benefit the producer

OPserver: interactive online-computations of opacities and radiative accelerations

Codes to compute mean opacities and radiative accelerations for arbitrary chemical mixtures using the Opacity Project recently revised data have been restructured in a client--server architecture and transcribed as a subroutine library. This implementation increases efficiency in stellar modelling where element stratification due to diffusion processes is depth dependent, and thus requires repeated fast opacity reestimates. Three user modes are provided to fit different computing environments, namely a web browser, a local workstation and a distributed grid.Comment: 5 pages, 1 figur

Crystallization behavior of iron- and boron-containing nepheline (Na2 O●Al2 O3 ●2SiO2 ) based model high-level nuclear waste glasses

This study focuses on understanding the relationship between iron redox, composition, and heat‐treatment atmosphere in nepheline‐based model high‐level nuclear waste glasses. Glasses in the Na2O–Al2O3–B2O3–Fe2O3–SiO2 system with varying Al2O3/Fe2O3 and Na2O/Fe2O3 ratios have been synthesized by melt‐quench technique and studied for their crystallization behavior in different heating atmospheres—air, inert (N2), and reducing (96%N2–4%H2). The compositional dependence of iron redox chemistry in glasses and the impact of heating environment and crystallization on iron coordination in glass‐ceramics have been investigated by Mössbauer spectroscopy and vibrating sample magnetometry. While iron coordination in glasses and glass‐ceramics changed as a function of glass chemistry, the heating atmosphere during crystallization exhibited minimal effect on iron redox. The change in heating atmosphere did not affect the phase assemblage but did affect the microstructural evolution. While glass‐ceramics produced as a result of heat treatment in air and N2 atmospheres developed a golden/brown colored iron‐rich layer on their surface, those produced in a reducing atmosphere did not exhibit any such phenomenon. Furthermore, while this iron‐rich layer was observed in glass‐ceramics with varying Al2O3/Fe2O3 ratio, it was absent from glass‐ceramics with varying Na2O/Fe2O3 ratio. An explanation of these results has been provided on the basis of kinetics of diffusion of oxygen and network modifiers in the glasses under different thermodynamic conditions. The plausible implications of the formation of iron‐rich layer on the surface of glass‐ceramics on the chemical durability of high‐level nuclear waste glasses have been discussed

Insolubility of Mg in Β-Si 3 N 4 in the System Al-Mg-Si-O-N

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65816/1/j.1151-2916.1978.tb09345.x.pd