4,915 research outputs found
Activity-dependence of synaptic vesicle dynamics
The proper function of synapses relies on efficient recycling of synaptic vesicles. The small size of synaptic boutons has hampered efforts to define the dynamical states of vesicles during recycling. Moreover, whether vesicle motion during recycling is regulated by neural activity remains largely unknown. We combined nanoscale-resolution tracking of individual synaptic vesicles in cultured hippocampal neurons from rats of both sexes with advanced motion analyses to demonstrate that the majority of recently endocytosed vesicles undergo sequences of transient dynamical states including epochs of directed, diffusional, and stalled motion. We observed that vesicle motion is modulated in an activity-dependent manner, with dynamical changes apparent in ∼20% of observed boutons. Within this subpopulation of boutons, 35% of observed vesicles exhibited acceleration and 65% exhibited deceleration, accompanied by corresponding changes in directed motion. Individual vesicles observed in the remaining ∼80% of boutons did not exhibit apparent dynamical changes in response to stimulation. More quantitative transient motion analyses revealed that the overall reduction of vesicle mobility, and specifically of the directed motion component, is the predominant activity-evoked change across the entire bouton population. Activity-dependent modulation of vesicle mobility may represent an important mechanism controlling vesicle availability and neurotransmitter release.SIGNIFICANCE STATEMENTMechanisms governing synaptic vesicle dynamics during recycling remain poorly understood. Using nanoscale resolution tracking of individual synaptic vesicles in hippocampal synapses and advanced motion analysis tools we demonstrate that synaptic vesicles undergo complex sets of dynamical states that include epochs of directed, diffusive, and stalled motion. Most importantly, our analyses revealed that vesicle motion is modulated in an activity-dependent manner apparent as the reduction in overall vesicle mobility in response to stimulation. These results define the vesicle dynamical states during recycling and reveal their activity-dependent modulation. Our study thus provides fundamental new insights into the principles governing synaptic function
Anomaly-Induced Magnetic Screening in 2+1 dimensional QED at Finite Density
We show that in 2+1 dimensional Quantum Electrodynamics an external magnetic
field applied to a finite density of massless fermions is screened, due to a
-dimensional realization of the underlying -dimensional axial anomaly
of the space components of the electric current. This is shown to imply
screening of the magnetic field, i.e., the Meissner effect. We discuss the
physical implications of this result.Comment: 8 pages, DFTT-93-10 [ Eq.(15) and (16) were scrambled in previous
version
Standard and Non-standard Extensions of Lie algebras
We study the problem of quadruple extensions of simple Lie algebras. We find
that, adding a new simple root , it is not possible to have an
extended Kac-Moody algebra described by a Dynkin-Kac diagram with simple links
and no loops between the dots, while it is possible if is a
Borcherds imaginary simple root. We also comment on the root lattices of these
new algebras. The folding procedure is applied to the simply-laced triple
extended Lie algebras, obtaining all the non-simply laced ones. Non- standard
extension procedures for a class of Lie algebras are proposed. It is shown that
the 2-extensions of , with a dot simply linked to the Dynkin-Kac diagram
of , are rank 10 subalgebras of . Finally the simple root
systems of a set of rank 11 subalgebras of , containing as sub-algebra
, are explicitly written.Comment: Revised version. Inaccurate statements corrected. Expanded version
with added reference
The complex star cluster system of NGC 1316 (Fornax A)
This paper presents Gemini- high quality photometry for cluster
candidates in the field of NGC 1316 (Fornax A) as part of a study that also
includes GMOS spectroscopy. A preliminary discussion of the photometric data
indicates the presence of four stellar cluster populations with distinctive
features in terms of age, chemical abundance and spatial distribution. Two of
them seem to be the usually old (metal poor and metal rich) populations
typically found in elliptical galaxies. In turn, an intermediate-age (5 Gyr)
globular cluster population is the dominant component of the sample (as
reported by previous papers). We also find a younger cluster population with a
tentative age of 1 Gyr
Modelling the phase and chemical equilibria of aqueous solutions of alkanolamines and carbon dioxide using the SAFT-γ SW group contribution approach
p>All computational data for figures presented in the publication/p
On the analytical approximation to the GLAP evolution at small x and moderate Q^2
Comparing the numerically evaluated solution to the leading order GLAP
equations with its analytical small-x approximation we have found that in the
domain covered by a large fraction of the HERA data the analytic approximation
has to be augmented by the formally non-leading term which has been usually
neglected. The corrected formula fits the data much better and provides a
natural explanation of some of the deviations from the scaling
observed in the HERA kinematical range.Comment: LaTeX, 13 pages including 6 figures, figure 5 replaced, to appear in
Phys. Lett.
LOCATION DETERMINANTS OF FDI: A LITERATURE REVIEW
The development of economic activity and the rise in foreign direct investment (FDI) in recent decades has prompted a great deal of research into the phenomenon of multinational companies. A vast amount of empirical literature on FDI catalogues a long list of determinants that try to explain direct investment by multinational companies in a particular location, but it is noticeable that the results are not always consensual. This article provides a review of the theoretical approaches to and empirical studies on FDI in an attempt to single out the most robust factors for explaining the geographic distribution of FDI flows worldwide. It also suggests paths for future research in this area.FDI, determinants of FDI, literature review
A determination of alpha_s from scaling violations with truncated moments
We describe a determination of the strong coupling alpha_s(M_Z) from scaling
violations of the nonsinglet DIS structure function, which is based on two
novel techniques aimed at controlling and minimizing the theoretical error: a
neural network parametrization of BCDMS and NMC data, and QCD evolution by
means of truncated Mellin moments.Comment: 5 pages, no figures. Talk given by L. Magnea at QCD02, Montpellier,
July 200
Parametric thermal analysis for the optimization of Double Walled Tubes layout in the Water Cooled Lithium Lead inboard blanket of DEMO fusion reactor
Within the roadmap that will lead to the nuclear fusion exploitation for electric energy generation, the construction of a DEMOnstration (DEMO) reactor is, probably, the most important milestone to be reached since it will demonstrate the technological feasibility and economic competitiveness of an industrial-scale nuclear fusion reactor. In order to reach this goal, several European universities and research centres have joined their efforts in the EUROfusion action, funded by HORIZON 2020 UE programme. Within the framework of EUROfusion research activities, ENEA and University of Palermo are involved in the design of the Water-Cooled Lithium Lead Breeding Blanket (WCLL BB), that is one of the two BB concepts under consideration to be adopted in the DEMO reactor. It is mainly characterized by a liquid lithium-lead eutectic alloy acting as breeder (lithium) and neutron multiplier (lead), as well as by subcooled pressurized water as coolant. Two separate circuits, both characterized by a pressure of 15.5 MPa and inlet/outlet temperatures of 295 °C/328 °C, are deputed to cool down the First Wall (FW) and the Breeder Zone (BZ). The former consists in a system of radial-toroidal-radial C-shaped squared channels where countercurrent water flow occurs while the latter relies in the use of bundles of poloidal-radial Double Walled Tubes (DWTs) housed within the breeder. A parametric thermal study has been carried out in order to assess the best DWTs' layout assuring that the structural material maximum temperature does not overcome the allowable limit of 550 °C and that the overall coolant thermal rise fulfils the design target value of 33 °C. The study has been performed following a theoretical-numerical approach based on the Finite Element Method (FEM) and adopting the quoted Abaqus FEM code. Main assumptions and models together with results obtained are herewith reported and critically discussed
Small Angle Polarization in High Energy P--P Scattering Through Nonperturbative Chiral Symmetry Breaking
We show that a large anomalous contribution due to nonperturbative
instanton-like gluonic field configurations to the axial charge of the proton
implies high-energy spin effects in elastic scattering. This is the same
mechanism which is responsible for anomalous baryon number violation at high
energy in the standard model. We compute the proton polarization due to these
effects and we show that it is proportional to the center-of-mass scattering
angle with a universal (energy-independent) slope of order unity.Comment: (13 pages, 2 figures
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