313 research outputs found
The Role of Corticothalamic Projections (Prelimbic Cortex to Nucleus Reuniens) in Working Memory
Working memory (WM) is the ability to store information for short periods of time and is used to execute tasks
WM has been understood to work via the medial prefrontal cortex (mPFC) and dorsal hippocampus (dHPC), but they do not directly project to each other
The nucleus reuniens of the thalamus (Re) is a “middle man” between the mPFC and dHPC
There are projections between the prelimbic cortex (PrL) and Re that may be used during WM
To test the connection of the PrL to Re, a delayed nonmatch to position (DNMTP) task was performe
Surfactant-Mediated Epitaxial Growth of Single-Layer Graphene in an Unconventional Orientation on SiC
We report the use of a surfactant molecule during the epitaxy of graphene on
SiC(0001) that leads to the growth in an unconventional orientation, namely
rotation with respect to the SiC lattice. It yields a very
high-quality single-layer graphene with a uniform orientation with respect to
the substrate, on the wafer scale. We find an increased quality and homogeneity
compared to the approach based on the use of a pre-oriented template to induce
the unconventional orientation. Using spot profile analysis low energy electron
diffraction, angle-resolved photoelectron spectroscopy, and the normal
incidence x-ray standing wave technique, we assess the crystalline quality and
coverage of the graphene layer. Combined with the presence of a
covalently-bound graphene layer in the conventional orientation underneath, our
surfactant-mediated growth offers an ideal platform to prepare epitaxial
twisted bilayer graphene via intercalation.Comment: 7 pages, 3 figure
The clinical relevance of an elevated lactate level after surgery for congenital heart disease
Courtship of Ambystoma jeffersonianum
7 p. : ill. ; 24 cm.Includes bibliographical references (p. 6-7)
Growth and evolution of tetracyanoquinodimethane and potassium coadsorption phases on Ag(111)
Alkali-doping is a very efficient way of tuning the electronic properties of active molecular layers in (opto-) electronic devices based on organic semiconductors. In this context, we report on the phase formation and evolution of charge transfer salts formed by 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) in coadsorption with potassium on a Ag(111) surface. Based on an in-situ study using low energy electron microscopy and diffraction we identify the structural properties of four phases with different stoichiometries, and follow their growth and inter-phase transitions. We label these four phases α to δ, with increasing K content, the last two of which (γ and δ-phases) have not been previously reported. During TCNQ deposition on a K-precovered Ag(111) surface we find a superior stability of δ-phase islands compared to the γ-phase; continued TCNQ deposition leads to a direct transition from the δ to the β-phase when the K : TCNQ ratio corresponding to this phase regime is reached, with no intermediate γ-phase formation. When, instead, K is deposited on a surface precovered with large islands of the low density commensurate (LDC) TCNQ phase that are surrounded by a TCNQ 2D-gas, we observe two different scenarios: on the one hand, in the 2D-gas phase regions, very small α-phase islands are formed (close to the resolution limit of the microscope, 10–15 nm), which transform to β-phase islands of similar size with increasing K deposition. On the other hand, the large (micrometer-sized) TCNQ islands transform directly to similarly large single-domain β-phase islands, the formation of the intermediate α-phase being suppressed. This frustration of the LDC-to-α transition can be lifted by performing the experiment at elevated temperature. In this sense, the morphology of the pure TCNQ submonolayer is conserved during phase transitions
Structure analysis of the Ga-stabilized GaAs(001)-c(8x2) surface at high temperatures
Structure of the Ga-stabilized GaAs(001)-c(8x2) surface has been studied
using rocking-curve analysis of reflection high-energy electron diffraction
(RHEED). The c(8x2) structure emerges at temperatures higher than 600C, but is
unstable with respect to the change to the (2x6)/(3x6) structure at lower
temperatures. Our RHEED rocking-curve analysis at high temperatures revealed
that the c(8x2) surface has the structure which is basically the same as that
recently proposed by Kumpf et al. [Phys. Rev. Lett. 86, 3586 (2001)]. We found
that the surface atomic configurations are locally fluctuated at high
temperatures without disturbing the c(8x2) periodicity.Comment: 14 pages, 4 figures, 1 tabl
Ensemble modeling of very small ZnO nanoparticles
The detailed structural characterization of nanoparticles is a very important issue since it enables a precise understanding of their electronic, optical and magnetic properties. Here we introduce a new method for modeling the structure of very small particles by means of powder X-ray diffraction. Using thioglycerol-capped ZnO nanoparticles with a diameter of less than 3 nm as an example we demonstrate that our ensemble modeling method is superior to standard XRD methods like, e.g., Rietveld refinement. Besides fundamental properties (size, anisotropic shape and atomic structure) more sophisticated properties like imperfections in the lattice, a size distribution as well as strain and relaxation effects in the particles and-in particular-at their surface (surface relaxation effects) can be obtained. Ensemble properties, i.e., distributions of the particle size and other properties, can also be investigated which makes this method superior to imaging techniques like (high resolution) transmission electron microscopy or atomic force microscopy, in particular for very small nanoparticles. For the particles under study an excellent agreement of calculated and experimental X-ray diffraction patterns could be obtained with an ensemble of anisotropic polyhedral particles of three dominant sizes, wurtzite structure and a significant relaxation of Zn atoms close to the surface
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