4,123 research outputs found
Examining Form and Function of Dendritic Spines
The majority of fast excitatory synaptic transmission in the central nervous system takes place at protrusions along dendrites called spines. Dendritic spines are highly heterogeneous, both morphologically and functionally. Not surprisingly, there has been much speculation and debate on the relationship between spine structure and function. The advent of multi-photon laser-scanning microscopy has greatly improved our ability to investigate the dynamic interplay between spine form and function. Regulated structural changes occur at spines undergoing plasticity, offering a mechanism to account for the well-described correlation between spine size and synapse strength. In turn, spine structure can influence the degree of biochemical and perhaps electrical compartmentalization at individual synapses. Here, we review the relationship between dendritic spine morphology, features of spine compartmentalization and synaptic plasticity. We highlight emerging molecular mechanisms that link structural and functional changes in spines during plasticity, and also consider circumstances that underscore some divergence from a tight structure-function coupling. Because of the intricate influence of spine structure on biochemical and electrical signalling, activity-dependent changes in spine morphology alone may thus contribute to the metaplastic potential of synapses. This possibility asserts a role for structural dynamics in neuronal information storage and aligns well with current computational models
J/Psi Propagation in Hadronic Matter
We study J/ propagation in hot hadronic matter using a four-flavor
chiral Lagrangian to model the dynamics and using QCD sum rules to model the
finite size effects manifested in vertex interactions through form factors.
Charmonium breakup due to scattering with light mesons is the primary
impediment to continued propagation. Breakup rates introduce nontrivial
temperature and momentum dependence into the J/ spectral function.Comment: 6 Pages LaTeX, 3 postscript figures. Proceedings for Strangeness in
Quark Matter 2003, Atlantic Beach, NC, March 12-17, 2003; minor corrections
in version 2, to appear in J. Phys.
Interfacial charge transfer in nanoscale polymer transistors
Interfacial charge transfer plays an essential role in establishing the
relative alignment of the metal Fermi level and the energy bands of organic
semiconductors. While the details remain elusive in many systems, this charge
transfer has been inferred in a number of photoemission experiments. We present
electronic transport measurements in very short channel ( nm)
transistors made from poly(3-hexylthiophene) (P3HT). As channel length is
reduced, the evolution of the contact resistance and the zero-gate-voltage
conductance are consistent with such charge transfer. Short channel conduction
in devices with Pt contacts is greatly enhanced compared to analogous devices
with Au contacts, consistent with charge transfer expectations. Alternating
current scanning tunneling microscopy (ACSTM) provides further evidence that
holes are transferred from Pt into P3HT, while much less charge transfer takes
place at the Au/P3HT interface.Comment: 19 preprint pages, 6 figure
Biogenic Macroporosity and lts Lattice Boltzmann Method Permeability in the Karst Biscayne Aquifer
We focus on two major problems in the study of paleokarst of the Biscayne aquifer in southeastem Florida: ( 1 ), current conceptual models of karst aquifers do not adequately characterize much of the eogenetic rnacropore system within the carbonate rocks of the Biscayne aquifer, and (2) standard laboratory core-analysis rnethods cannol be used lo accurately measure the permeability of highly macroporous carbonate core samples
Can processes make relationships work? The Triple Helix between structure and action
This contribution seeks to explore how complex adaptive theory can be applied at the conceptual level to unpack Triple Helix models. We use two cases to examine this issue â the Finnish Strategic Centres for Science, Technology & Innovation (SHOKs) and the Canadian Business-led Networks of Centres of Excellence (BL-NCE). Both types of centres are organisational structures that aspire to be business-led, with a considerable portion of their activities driven by (industrial) usersâ interests and requirements. Reflecting on the centresâ activities along three dimensions â knowledge generation, consensus building and innovation â we contend that conceptualising the Triple Helix from a process perspective will improve the dialogue between stakeholders and shareholders
Fly-derived DNA and camera traps are complementary tools for assessing mammalian biodiversity
Background
Metabarcoding of vertebrate DNA found in invertebrates (iDNA) represents a potentially powerful tool for monitoring biodiversity. Preliminary evidence suggests fly iDNA biodiversity assessments compare favorably with established approaches such
as camera trapping or line transects.
Aims and Methods
To assess whether fly-derived iDNA is consistently useful for biodiversity monitoring across a diversity of ecosystems, we compared metabarcoding of the mitochondrial 16S gene of fly pool-derived iDNA (range = 49â105 flies/site, N = 784 flies) with camera traps (range = 198â1,654 videos of mammals identified to the species level/site) at eight sites, representing different habitat types in five countries across
tropical Africa.
Results
We detected a similar number of mammal species using fly-derived iDNA (range = 8â15 species/site) and camera traps (range = 8â27 species/site). However, the two approaches detected mostly different species (range = 6%â43% of species detected/site were detected with both methods), with fly-derived iDNA detecting on average smaller-bodied species than camera traps. Despite addressing different phylogenetic components of local mammalian communities, both methods resulted in similar beta-diversity estimates across sites and habitats.
Conclusion
These results support a growing body of evidence that fly-derived iDNA is a cost- and time-efficient tool that complements camera trapping in assessing mammalian biodiversity. Fly-derived iDNA may facilitate biomonitoring in terrestrial ecosystems at broad spatial and temporal scales, in much the same way as water eDNA has improved biomonitoring across aquatic ecosystems.Peer Reviewe
The Great Observatories All-Sky LIRG Survey: Comparison of Ultraviolet and Far-Infrared Properties
The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete
sample of 202 Luminous Infrared Galaxies (LIRGs) selected from the IRAS Revised
Bright Galaxy Sample (RBGS). The galaxies span the full range of interaction
stages, from isolated galaxies to interacting pairs to late stage mergers. We
present a comparison of the UV and infrared properties of 135 galaxies in GOALS
observed by GALEX and Spitzer. For interacting galaxies with separations
greater than the resolution of GALEX and Spitzer (2-6"), we assess the UV and
IR properties of each galaxy individually. The contribution of the FUV to the
measured SFR ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0
+/- 0.4%. The specific star formation rate of the GOALS sample is extremely
high, with a median value (3.9*10^{-10} yr^{-1}) that is comparable to the
highest specific star formation rates seen in the Spitzer Infrared Nearby
Galaxies Survey sample. We examine the position of each galaxy on the IR
excess-UV slope (IRX-beta) diagram as a function of galaxy properties,
including IR luminosity and interaction stage. The LIRGs on average have
greater IR excesses than would be expected based on their UV colors if they
obeyed the same relations as starbursts with L_IR < 10^{11}L_0 or normal
late-type galaxies. The ratio of L_IR to the value one would estimate from the
IRXg-beta relation published for lower luminosity starburst galaxies ranges
from 0.2 to 68, with a median value of 2.7. A minimum of 19% of the total IR
luminosity in the RBGS is produced in LIRGs and ULIRGs with red UV colors (beta
> 0). Among resolved interacting systems, 32% contain one galaxy which
dominates the IR emission while the companion dominates the UV emission. Only
21% of the resolved systems contain a single galaxy which dominates both
wavelengths.Comment: 37 pages, 10 figures, accepted for publication in Ap
Acid-Labile Traceless Click Linker for Protein Transduction
Intracellular delivery of active proteins presents an interesting approach in research and therapy. We created a protein transduction shuttle based on a new traceless click linker that combines the advantages of click reactions with implementation of reversible pH-sensitive bonds. The azidomethyl-methylmaleic anhydride (AzMMMan) linker was found compatible with different click chemistries, demonstrated in bioreversible protein modification with dyes, polyethylene glycol, or a transduction carrier. Linkages were stable at physiological pH but reversible at the mild acidic pH of endosomes or lysosomes. We show that pH-reversible attachment of a defined endosome-destabilizing three-arm oligo(ethane amino)amide carrier generates an effective shuttle for protein delivery. The cargo protein nlsEGFP, when coupled via the traceless AzMMMan linker, experiences efficient cellular uptake and endosomal escape into the cytosol, followed by import into the nucleus. In contrast, irreversible linkage to the same shuttle hampers nuclear delivery of nlsEGFP which after uptake remains trapped in the cytosol. Successful intracellular delivery of bioactive Ă-galactosidase as a model enzyme was also demonstrated using the pH-controlled shuttle system
Tracing PAHs and Warm Dust Emission in the Seyfert Galaxy NGC 1068
We present a study of the nearby Seyfert galaxy NGC 1068 using mid- and far-
infrared data acquired with the IRAC, IRS, and MIPS instruments aboard the
Spitzer Space Telescope. The images show extensive 8 um and 24 um emission
coinciding with star formation in the inner spiral approximately 15" (1 kpc)
from the nucleus, and a bright complex of star formation 47" (3 kpc) SW of the
nucleus. The brightest 8 um PAH emission regions coincide remarkably well with
knots observed in an Halpha image. Strong PAH features at 6.2, 7.7, 8.6, and
11.3 um are detected in IRS spectra measured at numerous locations inside,
within, and outside the inner spiral. The IRAC colors and IRS spectra of these
regions rule out dust heated by the AGN as the primary emission source; the
SEDs are dominated by starlight and PAH emission. The equivalent widths and
flux ratios of the PAH features in the inner spiral are generally consistent
with conditions in a typical spiral galaxy ISM. Interior to the inner spiral,
the influence of the AGN on the ISM is evident via PAH flux ratios indicative
of a higher ionization parameter and a significantly smaller mean equivalent
width than observed in the inner spiral. The brightest 8 and 24 um emission
peaks in the disk of the galaxy, even at distances beyond the inner spiral, are
located within the ionization cones traced by [O III]/Hbeta, and they are also
remarkably well aligned with the axis of the radio jets. Although it is
possible that radiation from the AGN may directly enhance PAH excitation or
trigger the formation of OB stars that subsequently excite PAH emission at
these locations in the inner spiral, the orientation of collimated radiation
from the AGN and star formation knots in the inner spiral could be
coincidental. (abridged)Comment: 20 pages, 11 figures; AJ, accepted; full resolution version available
at http://spider.ipac.caltech.edu/staff/jhhowell/astro/howelln1068.pd
Effect of Layer-Stacking on the Electronic Structure of Graphene Nanoribbons
The evolution of electronic structure of graphene nanoribbons (GNRs) as a
function of the number of layers stacked together is investigated using
\textit{ab initio} density functional theory (DFT) including interlayer van der
Waals interactions. Multilayer armchair GNRs (AGNRs), similar to single-layer
AGNRs, exhibit three classes of band gaps depending on their width. In zigzag
GNRs (ZGNRs), the geometry relaxation resulting from interlayer interactions
plays a crucial role in determining the magnetic polarization and the band
structure. The antiferromagnetic (AF) interlayer coupling is more stable
compared to the ferromagnetic (FM) interlayer coupling. ZGNRs with the AF
in-layer and AF interlayer coupling have a finite band gap while ZGNRs with the
FM in-layer and AF interlayer coupling do not have a band gap. The ground state
of the bi-layer ZGNR is non-magnetic with a small but finite band gap. The
magnetic ordering is less stable in multilayer ZGNRs compared to single-layer
ZGNRs. The quasipartcle GW corrections are smaller for bilayer GNRs compared to
single-layer GNRs because of the reduced Coulomb effects in bilayer GNRs
compared to single-layer GNRs.Comment: 10 pages, 5 figure
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