162 research outputs found
Application of scanning ion conductance microscopy to localised patch clamp recording from presynaptic terminals
The spatial distribution of ion channels in different subcellular regions is a
key determinant of neuronal behaviour. Patch clamp electrophysiology allows
characterisation of ion channel activity, but precise localisation is more
difficult. This is particularly true for very small, specialised compartments
such as synaptic terminals, which are inaccessible by conventional, direct
patch recording methods.
Scanning ion conductance microscopy (SICM) generates high resolution topographic
images by using a precisely positioned probe to measure ion currents.
The development of a new âhoppingâ mode allows convoluted neuronal
networks to be imaged using the SICM probe. Some details of the
implementation of this mode are described. The geometry of SICM pipette
tips is examined, and the interaction between the probe and the cell membrane
is shown to differ from the standard account.
Application of SICM to localised patch clamp recording has previously been
demonstrated in several cell types and here is extended to record from
presynaptic sites. Control experiments are performed and a model is introduced
to explain how the use of fine-tipped SICM pipettes may give rise
to artefacts seen in some of these experiments. The technique is then applied
to synaptic boutons in primary cerebellar culture and a number of
successful recordings are presented, along with some attempts to combine
the advantages of SICM positioning with those of more conventional patch
clamp pipettes. Experimental limitations of these approaches are discussed
in interacting quintessence model
A model consisting of quintessence scalar field interacting with cold dark
matter is considered. Conditions required to reach are discussed. It
is shown that depending on the potential considered for the quintessence,
reaching the phantom divide line puts some constraints on the interaction
between dark energy and dark matter. This also may determine the ratio of dark
matter to dark energy density at .Comment: 10 pages, references updated, some notes added, minor changes
applied, accepted for publication in Eur. Phys. J.
Neutrino mixing and CP-violation
The prospects of measuring the leptonic angles and CP-odd phases at a
neutrino factory are discussed in two scenarios: 1) three active neutrinos as
indicated by the present ensemble of atmospheric plus solar data; 2) three
active plus one sterile neutrino when the LSND signal is also taken into
account. For the latter we develop one and two mass dominance approximations.
The appearance of wrong sign muons in long baseline experiments and tau leptons
in short baseline ones provides the best tests of CP-violation in scenarios 1)
and 2), respectively.Comment: 22 pages, LaTeX2e, 17 eps files, use package epsfi
Four species neutrino oscillations at -Factory: sensitivity and CP-violation
The prospects of measuring the leptonic angles and CP-odd phases at a {\em
neutrino factory} are discussed in the scenario of three active plus one
sterile neutrino. We consider the \nu_\mu \raw \nu_e LSND signal. Its
associated large mass difference leads to observable neutrino oscillations at
short ( km) baseline experiments. Sensitivities to the leptonic angles
down to can be easily achieved with a 1 Ton detector. Longer baseline
experiments ( km) with a 1 Kton detector can provide very clean tests
of CP-violation especially through tau lepton detection.Comment: 15 pages, LaTeX2e, 14 eps files, use package epsfi
Low Energy Solar Neutrinos and Spin Flavour Precession
The possibility that the Gallium data effectively indicates a time modulation
of the solar active neutrino flux in possible connection to solar activity is
examined on the light of spin flavour precession to sterile neutrinos as a
subdominant process in addition to oscillations. We distinguish two sets of
Gallium data, relating them to high and low solar activity. Such modulation
affects principally the low energy neutrinos ( and ) so that the
effect, if it exists, will become most clear in the forthcoming Borexino and
LENS experiments and will provide evidence for a neutrino magnetic moment.
Using a model previously developed, we perform two separate fits in relation to
low and high activity periods to all solar neutrino data. These fits include
the very recent charged current spectrum from the SNO experiment. We also
derive the model predictions for Borexino and LENS experiments.Comment: 20 pages, 5 ps figures, 1 eps figure, final version to be published
in JHE
Potential-density pairs for axisymmetric galaxies: the influence of scalar fields
We present a formulation for potential-density pairs to describe axisymmetric
galaxies in the Newtonian limit of scalar-tensor theories of gravity. The
scalar field is described by a modified Helmholtz equation with a source that
is coupled to the standard Poisson equation of Newtonian gravity. The net
gravitational force is given by two contributions: the standard Newtonian
potential plus a term stemming from massive scalar fields. General solutions
have been found for axisymmetric systems and the multipole expansion of the
Yukawa potential is given. In particular, we have computed potential-density
pairs of galactic disks for an exponential profile and their rotation curves.Comment: 8 pages, no figures, corrected version to the one that will appear in
Gen. Relativ. Gravit., where a small typo in eq. (13) is presen
Dilatonic Interpretation of the Quintessence?
We discuss the possibility that "quintessential effects", recently displayed
by large scale observations, may be consistently described in the context of
the low-energy string effective action, and we suggest a possible approach to
the problem of the cosmic coincidence based on the link between the strength of
the dilaton couplings and the cosmological state of our Universe.Comment: 6 pages, Revtex, four figures included using epsfig. To appear in
Phys. Rev.
Ghost D-branes
We define a ghost D-brane in superstring theories as an object that cancels
the effects of an ordinary D-brane. The supergroups U(N|M) and OSp(N|M) arise
as gauge symmetries in the supersymmetric world-volume theory of D-branes and
ghost D-branes. A system with a pair of D-brane and ghost D-brane located at
the same location is physically equivalent to the closed string vacuum. When
they are separated, the system becomes a new brane configuration. We generalize
the type I/heterotic duality by including n ghost D9-branes on the type I side
and by considering the heterotic string whose gauge group is OSp(32+2n|2n).
Motivated by the type IIB S-duality applied to D9- and ghost D9-branes, we also
find type II-like closed superstrings with U(n|n) gauge symmetry.Comment: 49 pages, 6 figures, harvmac. v2: references and acknowledgements
adde
Cosmic F- and D-strings
Macroscopic fundamental and Dirichlet strings have several potential
instabilities: breakage, tachyon decays, and confinement by axion domain walls.
We investigate the conditions under which metastable strings can exist, and we
find that such strings are present in many models. There are various
possibilities, the most notable being a network of (p,q) strings. Cosmic
strings give a potentially large window into string physics.Comment: 27 pages, 5 figures; v. 5: JHEP style, added comments in section 2.
CDMS, Supersymmetry and Extra Dimensions
The CDMS experiment aims to directly detect massive, cold dark matter
particles originating from the Milky Way halo. Charge and lattice excitations
are detected after a particle scatters in a Ge or Si crystal kept at ~30 mK,
allowing to separate nuclear recoils from the dominating electromagnetic
background. The operation of 12 detectors in the Soudan mine for 75 live days
in 2004 delivered no evidence for a signal, yielding stringent limits on dark
matter candidates from supersymmetry and universal extra dimensions. Thirty Ge
and Si detectors are presently installed in the Soudan cryostat, and operating
at base temperature. The run scheduled to start in 2006 is expected to yield a
one order of magnitude increase in dark matter sensitivity.Comment: To be published in the proceedings of the 7th UCLA symposium on
sources and detection of dark matter and dark energy in the universe, Marina
del Rey, Feb 22-24, 200
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