425 research outputs found
A Physiological Role for Amyloid Beta Protein: Enhancement of Learning and Memory
Amyloid beta protein (A[beta]) is well recognized as having a significant role in the pathogenesis of Alzheimer's disease (AD). The reason for the presence of A[beta] and its physiological role in non-disease states is not clear. In these studies, low doses of A[beta] enhanced memory retention in two memory tasks and enhanced acetylcholine production in the hippocampus _in vivo_. We then tested whether endogenous A[beta] has a role in learning and memory in young, cognitively intact mice by blocking endogenous A[beta] in healthy 2-month-old CD-1 mice. Blocking A[beta] with antibody to A[beta] or DFFVG (which blocks A[beta] binding) or decreasing A[beta] expression with an antisense directed at the A[beta] precursor APP all resulted in impaired learning in T-maze foot-shock avoidance. Finally, A[beta]1-42 facilitated induction and maintenance of long term potentiation in hippocampal slices, whereas antibodies to A[beta] inhibited hippocampal LTP. These results indicate that in normal healthy young animals the presence of A[beta] is important for learning and memory
Superconductivity in zigzag CuO chains
Superconductivity has recently been discovered in
PrBaCuO with a maximum of about 15K.
Since the CuO planes in this material are believed to be insulating, it has
been proposed that the superconductivity occurs in the double (or zigzag) CuO
chain layer. On phenomenological grounds, we propose a theoretical
interpretation of the experimental results in terms of a new phase for the
zigzag chain, labelled by CS. This phase has a gap for some of the
relative spin and charge modes but no total spin gap, and can have a divergent
superconducting susceptibility for repulsive interactions. A microscopic model
for the zigzag CuO chain is proposed, and on the basis of density matrix
renormalization group (DMRG) and bosonization studies of this model, we adduce
evidence that supports our proposal.Comment: 10 pages, 5 figures; Journal-ref. adde
Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations
The following article appeared in Yamada, S. A., Thompson, W. H., & Fayer, M. D. (2017). Water-anion hydrogen bonding dynamics: Ultrafast IR experiments and simulations. The Journal of Chemical Physics, 146(23), 234501.) and may be found at https://aip.scitation.org/doi/10.1063/1.4984766.Many of water’s remarkable properties arise from its tendency to form an intricate and robust hydrogen bond network. Understanding the dynamics that govern this network is fundamental to elucidating the behavior of pure water and water in biological and physical systems. In ultrafast nonlinear infrared experiments, the accessible time scales are limited by water’s rapid vibrational relaxation (1.8 ps for dilute HOD in H2O), precluding interrogation of slow hydrogen bond evolution in non-bulk systems. Here, hydrogen bonding dynamics in bulk D2O were studied from the perspective of the much longer lived (36.2 ps) CN stretch mode of selenocyanate (SeCN−) using polarization selective pump-probe (PSPP) experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, and molecular dynamics simulations. The simulations make use of the empirical frequency mapping approach, applied to SeCN− for the first time. The PSPP experiments and simulations show that the orientational correlation function decays via fast (2.0 ps) restricted angular diffusion (wobbling-in-a-cone) and complete orientational diffusive randomization (4.5 ps). Spectral diffusion, quantified in terms of the frequency-frequency correlation function, occurs on two time scales. The initial 0.6 ps time scale is attributed to small length and angle fluctuations of the hydrogen bonds between water and SeCN−. The second 1.4 ps measured time scale, identical to that for HOD in bulk D2O, reports on the collective reorganization of the water hydrogen bond network around the anion. The experiments and simulations provide details of the anion-water hydrogen bonding and demonstrate that SeCN− is a reliable vibrational probe of the ultrafast spectroscopy of water
Dynamical Correlation Functions using the Density Matrix Renormalization Group
The density matrix renormalization group (DMRG) method allows for very
precise calculations of ground state properties in low-dimensional strongly
correlated systems. We investigate two methods to expand the DMRG to
calculations of dynamical properties. In the Lanczos vector method the DMRG
basis is optimized to represent Lanczos vectors, which are then used to
calculate the spectra. This method is fast and relatively easy to implement,
but the accuracy at higher frequencies is limited. Alternatively, one can
optimize the basis to represent a correction vector for a particular frequency.
The correction vectors can be used to calculate the dynamical correlation
functions at these frequencies with high accuracy. By separately calculating
correction vectors at different frequencies, the dynamical correlation
functions can be interpolated and pieced together from these results. For
systems with open boundaries we discuss how to construct operators for specific
wavevectors using filter functions.Comment: minor revision, 10 pages, 15 figure
Immittance Matching for Multi-dimensional Open-system Photonic Crystals
An electromagnetic (EM) Bloch wave propagating in a photonic crystal (PC) is
characterized by the immittance (impedance and admittance) of the wave. The
immittance is used to investigate transmission and reflection at a surface or
an interface of the PC. In particular, the general properties of immittance are
useful for clarifying the wave propagation characteristics. We give a general
proof that the immittance of EM Bloch waves on a plane in infinite one- and
two-dimensional (2D) PCs is real when the plane is a reflection plane of the PC
and the Bloch wavevector is perpendicular to the plane. We also show that the
pure-real feature of immittance on a reflection plane for an infinite
three-dimensional PC is good approximation based on the numerical calculations.
The analytical proof indicates that the method used for immittance matching is
extremely simplified since only the real part of the immittance function is
needed for analysis without numerical verification. As an application of the
proof, we describe a method based on immittance matching for qualitatively
evaluating the reflection at the surface of a semi-infinite 2D PC, at the
interface between a semi-infinite slab waveguide (WG) and a semi-infinite 2D PC
line-defect WG, and at the interface between a semi-infinite channel WG and a
semi-infinite 2D PC slab line-defect WG.Comment: 8 pages, 6 figure
Liquid Crystal Phases of Quantum Hall Systems
Mean-field calculations for the two dimensional electron gas (2DEG) in a
large magnetic field with a partially filled Landau level with index
consistently yield ``stripe-ordered'' charge-density wave ground-states, for
much the same reason that frustrated phase separation leads to stripe ordered
states in doped Mott insulators. We have studied the effects of quantum and
thermal fluctuations about such a state and show that they can lead to a set of
electronic liquid crystalline states, particularly a stripe-nematic phase which
is stable at . Recent measurements of the longitudinal resistivity of a
set of quantum Hall devices have revealed that these systems spontaneously
develop, at low temepratures, a very large anisotropy. We interpret these
experiments as evidence for a stripe nematic phase, and propose a general phase
diagram for this system.Comment: 9 pages, 3 figure
Density matrix algorithm for the calculation of dynamical properties of low dimensional systems
I extend the scope of the density matrix renormalization group technique
developed by White to the calculation of dynamical correlation functions. As an
application and performance evaluation I calculate the spin dynamics of the 1D
Heisenberg chain.Comment: 4 pages + 4 figures in one Latex + 4 postscript file
The Hyper Suprime-Cam Software Pipeline
In this paper, we describe the optical imaging data processing pipeline
developed for the Subaru Telescope's Hyper Suprime-Cam (HSC) instrument. The
HSC Pipeline builds on the prototype pipeline being developed by the Large
Synoptic Survey Telescope's Data Management system, adding customizations for
HSC, large-scale processing capabilities, and novel algorithms that have since
been reincorporated into the LSST codebase. While designed primarily to reduce
HSC Subaru Strategic Program (SSP) data, it is also the recommended pipeline
for reducing general-observer HSC data. The HSC pipeline includes high level
processing steps that generate coadded images and science-ready catalogs as
well as low-level detrending and image characterizations.Comment: 39 pages, 21 figures, 2 tables. Submitted to Publications of the
Astronomical Society of Japa
Hyperglycemia modulates extracellular amyloid-β concentrations and neuronal activity in vivo
Epidemiological studies show that patients with type 2 diabetes (T2DM) and individuals with a diabetes-independent elevation in blood glucose have an increased risk for developing dementia, specifically dementia due to Alzheimer’s disease (AD). These observations suggest that abnormal glucose metabolism likely plays a role in some aspects of AD pathogenesis, leading us to investigate the link between aberrant glucose metabolism, T2DM, and AD in murine models. Here, we combined two techniques — glucose clamps and in vivo microdialysis — as a means to dynamically modulate blood glucose levels in awake, freely moving mice while measuring real-time changes in amyloid-β (Aβ), glucose, and lactate within the hippocampal interstitial fluid (ISF). In a murine model of AD, induction of acute hyperglycemia in young animals increased ISF Aβ production and ISF lactate, which serves as a marker of neuronal activity. These effects were exacerbated in aged AD mice with marked Aβ plaque pathology. Inward rectifying, ATP-sensitive potassium (K(ATP)) channels mediated the response to elevated glucose levels, as pharmacological manipulation of K(ATP) channels in the hippocampus altered both ISF Aβ levels and neuronal activity. Taken together, these results suggest that K(ATP) channel activation mediates the response of hippocampal neurons to hyperglycemia by coupling metabolism with neuronal activity and ISF Aβ levels
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