39,701 research outputs found
Synaptic partner prediction from point annotations in insect brains
High-throughput electron microscopy allows recording of lar- ge stacks of
neural tissue with sufficient resolution to extract the wiring diagram of the
underlying neural network. Current efforts to automate this process focus
mainly on the segmentation of neurons. However, in order to recover a wiring
diagram, synaptic partners need to be identi- fied as well. This is especially
challenging in insect brains like Drosophila melanogaster, where one
presynaptic site is associated with multiple post- synaptic elements. Here we
propose a 3D U-Net architecture to directly identify pairs of voxels that are
pre- and postsynaptic to each other. To that end, we formulate the problem of
synaptic partner identification as a classification problem on long-range edges
between voxels to encode both the presence of a synaptic pair and its
direction. This formulation allows us to directly learn from synaptic point
annotations instead of more ex- pensive voxel-based synaptic cleft or vesicle
annotations. We evaluate our method on the MICCAI 2016 CREMI challenge and
improve over the current state of the art, producing 3% fewer errors than the
next best method
Discovery of excess O I absorption towards the z = 6.42 QSO SDSS J1148+5251
We present a search for O I in the spectra of nine 4.9 < z_qso < 6.4 QSOs
taken with Keck/HIRES. We detect six systems with N(O I) > 10^13.7 cm^{-2} in
the redshift intervals where O I 1302 falls redward of the Ly-alpha forest.
Four of these lie towards SDSS J1148+5251 (z_qso = 6.42). This imbalance is
unlikely to arise from variations in sensitivity among our data or from a
statistical fluctuation. The excess O I occurs over a redshift interval that
also contains transmission in Ly-alpha and Ly-beta. Therefore, if these O I
systems represent pockets of neutral gas, then they must occur within or near
regions of the IGM that are highly ionized. In contrast, no O I is detected
towards SDSS J1030+0524 (z_qso = 6.30), whose spectrum shows complete
absorption in Ly-alpha and Ly-beta over \Delta z ~ 0.2. Assuming no ionization
corrections, we measure mean abundance ratios = -0.04 +/- 0.06,
= -0.31 +/- 0.09, and = -0.34 +/- 0.07 (2 sigma), which are
consistent with enrichment dominated by Type II supernovae. The O/Si ratio
limits the fraction of silicon in these systems contributed by metal-free very
massive stars to < 30%, a result which is insensitive to ionization
corrections. The ionic comoving mass densities along the z_qso > 6.2
sightlines, including only the detected systems, are \Omega(O I) = (7.0 +/-
0.6) * 10^{-8}, \Omega(Si II) = (9.6 +/- 0.9) * 10^{-9}, and \Omega(C II) =
(1.5 +/- 0.2) * 10^{-8}.Comment: Submitted to ApJ, with changes to reflect referee's comment
Ternary Syndrome Decoding with Large Weight
The Syndrome Decoding problem is at the core of many code-based
cryptosystems. In this paper, we study ternary Syndrome Decoding in large
weight. This problem has been introduced in the Wave signature scheme but has
never been thoroughly studied. We perform an algorithmic study of this problem
which results in an update of the Wave parameters. On a more fundamental level,
we show that ternary Syndrome Decoding with large weight is a really harder
problem than the binary Syndrome Decoding problem, which could have several
applications for the design of code-based cryptosystems
Generalized Conformal Symmetry in D-Brane Matrix Models
We study in detail the extension of the generalized conformal symmetry
proposed previously for D-particles to the case of supersymmetric Yang-Mills
matrix models of Dp-branes for arbitrary p. It is demonstrated that such a
symmetry indeed exists both in the Yang-Mills theory and in the corresponding
supergravity backgrounds produced by Dp-branes. On the Yang-Mills side, we
derive the field-dependent special conformal transformations for the collective
coordinates of Dp-branes in the one-loop approximation, and show that they
coincide with the transformations on the supergravity side. These
transformations are powerful in restricting the forms of the effective actions
of probe D-branes in the fixed backgrounds of source D-branes. Furthermore, our
formalism enables us to extend the concept of (generalized) conformal symmetry
to arbitrary configurations of D-branes, which can still be used to restrict
the dynamics of D-branes. For such general configurations, however, it cannot
be endowed a simple classical space-time interpretation at least in the static
gauge adopted in the present formulation of D-branes.Comment: 26 pages, no figure
String theories as the adiabatic limit of Yang-Mills theory
We consider Yang-Mills theory with a matrix gauge group on a direct
product manifold , where is a two-dimensional
Lorentzian manifold and is a two-dimensional open disc with the boundary
. The Euler-Lagrange equations for the metric on
yield constraint equations for the Yang-Mills energy-momentum tensor. We show
that in the adiabatic limit, when the metric on is scaled down, the
Yang-Mills equations plus constraints on the energy-momentum tensor become the
equations describing strings with a worldsheet moving in the based
loop group , where is the boundary of
. By choosing and putting to zero all parameters in besides , we get a string moving in . In
arXiv:1506.02175 it was described how one can obtain the Green-Schwarz
superstring action from Yang-Mills theory on while
shrinks to a point. Here we also consider Yang-Mills theory on a
three-dimensional manifold and show that in the limit when
the radius of tends to zero, the Yang-Mills action functional
supplemented by a Wess-Zumino-type term becomes the Green-Schwarz superstring
action.Comment: 11 pages, v3: clarifying remarks added, new section on embedding of
the Green-Schwarz superstring into d=3 Yang-Mills theory include
Compactifications of Heterotic Theory on Non-Kahler Complex Manifolds: I
We study new compactifications of the SO(32) heterotic string theory on
compact complex non-Kahler manifolds. These manifolds have many interesting
features like fewer moduli, torsional constraints, vanishing Euler character
and vanishing first Chern class, which make the four-dimensional theory
phenomenologically attractive. We take a particular compact example studied
earlier and determine various geometrical properties of it. In particular we
calculate the warp factor and study the sigma model description of strings
propagating on these backgrounds. The anomaly cancellation condition and
enhanced gauge symmetry are shown to arise naturally in this framework, if one
considers the effect of singularities carefully.
We then give a detailed mathematical analysis of these manifolds and
construct a large class of them. The existence of a holomorphic (3,0) form is
important for the construction. We clarify some of the topological properties
of these manifolds and evaluate the Betti numbers. We also determine the
superpotential and argue that the radial modulus of these manifolds can
actually be stabilized.Comment: 75 pages, Harvmac, no figures; v2: Some new results added, typos
corrected and references updated. Final version to appear in JHE
ROSAT HRI Observations of the Crab Pulsar: An Improved Temperature upper limit for PSR 0531+21
ROSAT HRI observations have been used to determine an upper limit of the Crab
pulsar surface temperature from the off-pulse count rate. For a neutron star
mass of 1.4 \Mo and a radius of 10 km as well as the standard distance and
interstellar column density, the redshifted temperature upper limit is\/
K . This is the lowest temperature
upper limit obtained for the Crab pulsar so far. Slightly different values for
are computed for the various neutron star models available in the
literature, reflecting the difference in the equation of state.Comment: 5 pages, uuencoded postscript, to be published in the Proceedings of
the NATO Advanced Study Insitute on "Lives of the Neutron Stars", ed. A.
Alpar, U. Kiziloglu and J. van Paradijs ( Kluwer, Dordrecht, 1995 )
Coefficient of tangential restitution for the linear dashpot model
The linear dashpot model for the inelastic normal force between colliding
spheres leads to a constant coefficient of normal restitution,
const., which makes this model very popular for the investigation
of dilute and moderately dense granular systems. For two frequently used models
for the tangential interaction force we determine the coefficient of tangential
restitution , both analytically and by numerical integration of
Newton's equation. Although const. for the linear-dashpot model,
we obtain pronounced and characteristic dependencies of the tangential
coefficient on the impact velocity . The
results may be used for event-driven simulations of granular systems of
frictional particles.Comment: 12 pages, 12 figure
Dominant particle-hole contributions to the phonon dynamics in the spinless one-dimensional Holstein model
In the spinless Holstein model at half-filling the coupling of electrons to
phonons is responsible for a phase transition from a metallic state at small
coupling to a Peierls distorted insulated state when the electron-phonon
coupling exceeds a critical value. For the adiabatic case of small phonon
frequencies, the transition is accompanied by a phonon softening at the
Brillouin zone boundary whereas a hardening of the phonon mode occurs in the
anti-adiabatic case. The phonon dynamics studied in this letter do not only
reveal the expected renormalization of the phonon modes but also show
remarkable additional contributions due to electronic particle-hole
excitations.Comment: 7 pages, 4 figures and 1 table included; v2: discussion of Luttinger
liquid parameters adde
Monte Carlo simulation of the transmission of measles: Beyond the mass action principle
We present a Monte Carlo simulation of the transmission of measles within a
population sample during its growing and equilibrium states by introducing two
different vaccination schedules of one and two doses. We study the effects of
the contact rate per unit time as well as the initial conditions on the
persistence of the disease. We found a weak effect of the initial conditions
while the disease persists when lies in the range 1/L-10/L ( being
the latent period). Further comparison with existing data, prediction of future
epidemics and other estimations of the vaccination efficiency are provided.
Finally, we compare our approach to the models using the mass action
principle in the first and another epidemic region and found the incidence
independent of the number of susceptibles after the epidemic peak while it
strongly fluctuates in its growing region. This method can be easily applied to
other human, animals and vegetable diseases and includes more complicated
parameters.Comment: 15 pages, 4 figures, 1 table, Submitted to Phys.Rev.
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