4,999 research outputs found
Hierarchy of neural organization in the embryonic spinal cord: Granger-causality graph analysis of in vivo calcium imaging data
The recent development of genetically encoded calcium indicators enables
monitoring in vivo the activity of neuronal populations. Most analysis of these
calcium transients relies on linear regression analysis based on the sensory
stimulus applied or the behavior observed. To estimate the basic properties of
the functional neural circuitry, we propose a network-based approach based on
calcium imaging recorded at single cell resolution. Differently from previous
analysis based on cross-correlation, we used Granger-causality estimates to
infer activity propagation between the activities of different neurons. The
resulting functional networks were then modeled as directed graphs and
characterized in terms of connectivity and node centralities. We applied our
approach to calcium transients recorded at low frequency (4 Hz) in ventral
neurons of the zebrafish spinal cord at the embryonic stage when spontaneous
coiling of the tail occurs. Our analysis on population calcium imaging data
revealed a strong ipsilateral connectivity and a characteristic hierarchical
organization of the network hubs that supported established propagation of
activity from rostral to caudal spinal cord. Our method could be used for
detecting functional defects in neuronal circuitry during development and
pathological conditions
Local trace formulae and scaling asymptotics in Toeplitz quantization
A trace formula for Toeplitz operators was proved by Boutet de Monvel and
Guillemin in the setting of general Toeplitz structures. Here we give a local
version of this result for a class of Toeplitz operators related to continuous
groups of symmetries on quantizable compact symplectic manifolds. The local
trace formula involves certain scaling asymptotics along the clean fixed locus
of the Hamiltonian flow of the symbol, reminiscent of the scaling asymptotics
of the equivariant components of the Szeg\"o kernel along the diagonal
Pastoral Khans: from Mongolian Steppe to African Savannah
The developing field of Mongolian International Studies offers a diverse range of research topics. A review of recent articles reflects an emphasis on geo-politics, particularly evolving relations with its superpower neighbours. Whilst state-to-state engagement with China and Russia predominates, regional countries (Japan, Korea) and the US and Europe are examined within the ‘Third Neighbour’ policy. Trade and economics are also studied, from Oyu Tolgoi and mining to the role of the IMF and international agencies. Currently lacking is a focus on human-driven engagement that reflects Mongolian livelihoods, spirituality and community environments. Such social and cultural dynamics are essential to both pastoral and rural livelihoods and to understanding the nation. In 2020-2022 international academic endeavours enabled Mongolian herder representatives to participate in a global drylands exchange network with dryland residents in thirteen countries. The process provided an exceptional opportunity to present Mongolian perspectives to pastoralists and academics from Africa, the Middle East and Central Asia. This grounded Mongolian livelihoods and situated rural dynamics in a global context. Here we report key engagements and findings as Mongolian herders shared lives and practices in the context of this international pastoral/drylands project. Moving beyond the political/economic rubric, as this project did, delivers a more representative and complete comprehension of Mongolia to the global international studies community
Multigenome DNA sequence conservation identifies Hox cis-regulatory elements
To learn how well ungapped sequence comparisons of multiple species can predict cis-regulatory elements in Caenorhabditis elegans, we made such predictions across the large, complex ceh-13/lin-39 locus and tested them transgenically. We also examined how prediction quality varied with different genomes and parameters in our comparisons. Specifically, we sequenced ∼0.5% of the C. brenneri and C. sp. 3 PS1010 genomes, and compared five Caenorhabditis genomes (C. elegans, C. briggsae, C. brenneri, C. remanei, and C. sp. 3 PS1010) to find regulatory elements in 22.8 kb of noncoding sequence from the ceh-13/lin-39 Hox subcluster. We developed the MUSSA program to find ungapped DNA sequences with N-way transitive conservation, applied it to the ceh-13/lin-39 locus, and transgenically assayed 21 regions with both high and low degrees of conservation. This identified 10 functional regulatory elements whose activities matched known ceh-13/lin-39 expression, with 100% specificity and a 77% recovery rate. One element was so well conserved that a similar mouse Hox cluster sequence recapitulated the native nematode expression pattern when tested in worms. Our findings suggest that ungapped sequence comparisons can predict regulatory elements genome-wide
A Policy Impact Evaluation Model For Scotland: Decoupling Single Farm Payments
The purpose of this paper is to assess the impacts of decoupling single farm payments in Scotland. It focuses on aggregate impacts on the agricultural products in domestic and external markets and the spill-over effect of this on the non-agricultural sector as well as an aggregate impact on the Scottish GDP. In order to capture system-wide impacts of the policy reform, a CGE model was formulated and implemented using a social accounting matrix constructed for Scotland. The simulation results suggest that the Scottish agricultural sector may encounter declines in output and factor us as a result of the policy reform. However, this critically depends on two factors: (a) the price effect of the policy reform on Scottish agricultural products relative to the EU average as well as the conditions of changes in world agricultural market prices; and (b) the extent to which customers would be sensitive to price effects of the policy reform. As far as the spill-over effect to the non-agricultural sector is concerned, decoupling of direct payments seems to have a positive spill-over effect. Similarly, the aggregate GDP effect is positive under all simulation scenarios. Critically, the simulation experiments indicate that policy shock may have a symmetrical outcome across the two sectors, with contractions in agriculture being accompanied by expansions in the non-agricultural sector, mainly because of factor market interactions between the two sectors.
The WSRT wide-field HI survey: II. Local Group features
We have used the WSRT to carry out an unbiased wide-field survey of HI
emission features, achieving an RMS sensitivity of about 18 mJy/Beam at a
velocity resolution of 17 km/s over 1800 deg^2. In this paper we present our HI
detections at negative velocities which could be distinguished from the
Galactic foreground. Fully 29% of the entire survey area has high velocity HI
emission with N_HI exceeding our 3 sigma limit of about 1.5x10^17cm^-2 over 30
km/s. A faint population of discrete HVCs is detected in the immediate vicinity
of M31 which spans a large fraction of the M31 rotation velocity. This class of
features is confined to about 12 deg (160 kpc) projected radius of M31 and
appears to be physically associated. We detect a diffuse northern extension of
the Magellanic Stream (MS) from at least Dec=+20 to +40 deg., which then loops
back toward the south. Recent numerical simulations had predicted just such an
MS extension corresponding to the apo-galacticon portion of the LMC/SMC orbit
at a distance of 125 kpc. A faint bridge of HI emission appears to join the
systemic velocities of M31 with that of M33 and continues beyond M31 to the
north-west. This may be the first detection of HI associated with the warm-hot
intergalactic medium (WHIM). The distribution of peculiar velocity HI
associated with M31 can be described by a projected exponential of 25 kpc
scale-length and 5x10^17cm^-2 peak column density. We present the distribution
function of N_HI in the extended M31 environment, which agrees well with the
low red-shift QSO absorption line data over the range log(N_HI)=17.2 to 21.9.
Our data extend this comparison about two orders of magnitude lower than
previously possible and provide the first image of the Lyman limit absorption
system associated with an L* galaxy. (abridged)Comment: 16 pages, 12 figures, accepted for publication in A&
Multiwavelength Observations of Massive Stellar Cluster Candidates in the Galaxy
The Galaxy appears to be richer in young, massive stellar clusters than
previously known, due to advances in infrared surveys which have uncovered
deeply embedded regions of star formation. Young, massive clusters can
significantly impact the surrounding interstellar medium (ISM) and hence radio
observations can also be an important tracer of their activity. Several hundred
cluster candidates are now known by examining survey data. Here we report on
multiwavelength observations of six of these candidates in the Galaxy. We
carried out 4.9 and 8.5 GHz VLA observations of the radio emission associated
with these clusters to obtain the physical characteristics of the surrounding
gas, including the Lyman continuum photon flux and ionized gas mass. Spitzer
Infrared Array Camera observations were also made of these regions, and provide
details on the stellar population as well as the dust continuum and polycyclic
aromatic hydrocarbon emission. When compared to the known young, massive
clusters in the Galaxy, the six cluster candidates have less powerful Lyman
ionizing fluxes and ionize less of the H II mass in the surrounding ISM.
Therefore, these cluster candidates appear to be more consistent with
intermediate-mass clusters (10^3-10^4 Msun).Comment: 39 pages, 20 figures. Accepted in the Astronomical Journal; to be
published Fall 201
Removing Cool Cores and Central Metallicity Peaks in Galaxy Clusters with Powerful AGN Outbursts
Recent X-ray observations of galaxy clusters suggest that cluster populations
are bimodally distributed according to central gas entropy and are separated
into two distinct classes: cool core (CC) and non-cool core (NCC) clusters.
While it is widely accepted that AGN feedback plays a key role in offsetting
radiative losses and maintaining many clusters in the CC state, the origin of
NCC clusters is much less clear. At the same time, a handful of extremely
powerful AGN outbursts have recently been detected in clusters, with a total
energy ~10^{61}-10^{62} erg. Using two dimensional hydrodynamic simulations, we
show that if a large fraction of this energy is deposited near the centers of
CC clusters, which is likely common due to dense cores, these AGN outbursts can
completely remove CCs, transforming them to NCC clusters. Our model also has
interesting implications for cluster abundance profiles, which usually show a
central peak in CC systems. Our calculations indicate that during the CC to NCC
transformation, AGN outbursts efficiently mix metals in cluster central
regions, and may even remove central abundance peaks if they are not broad
enough. For CC clusters with broad central abundance peaks, AGN outbursts
decrease peak abundances, but can not effectively destroy the peaks. Our model
may simultaneously explain the contradictory (possibly bimodal) results of
abundance profiles in NCC clusters, some of which are nearly flat, while others
have strong central peaks similar to those in CC clusters. A statistical
analysis of the sizes of central abundance peaks and their redshift evolution
may shed interesting insights on the origin of both types of NCC clusters and
the evolution history of thermodynamics and AGN activity in clusters.Comment: Slightly revised version, accepted for publication in ApJ. 12 pages,
11 figure
Hamiltonian light-front field theory within an AdS/QCD basis
Non-perturbative Hamiltonian light-front quantum field theory presents
opportunities and challenges that bridge particle physics and nuclear physics.
Fundamental theories, such as Quantum Chromodynmamics (QCD) and Quantum
Electrodynamics (QED) offer the promise of great predictive power spanning
phenomena on all scales from the microscopic to cosmic scales, but new tools
that do not rely exclusively on perturbation theory are required to make
connection from one scale to the next. We outline recent theoretical and
computational progress to build these bridges and provide illustrative results
for nuclear structure and quantum field theory. As our framework we choose
light-front gauge and a basis function representation with two-dimensional
harmonic oscillator basis for transverse modes that corresponds with
eigensolutions of the soft-wall AdS/QCD model obtained from light-front
holography.Comment: To appear in the proceedings of Light-Cone 2009: Relativistic
Hadronic and Particle Physics, July 8-13, 2009, Sao Jose dos Campos, Brazi
A Model for the Formation of Large Circumbinary Disks Around Post AGB Stars
We propose that the large, radius of ~1000 AU, circumbinary rotating disks
observed around some post-asymptotic giant branch (post-AGB) binary stars are
formed from slow AGB wind material that is pushed back to the center of the
nebula by wide jets. We perform 2D-axisymmetrical numerical simulations of fast
and wide jets that interact with the previously ejected slow AGB wind. In each
system there are two oppositely launched jets, but we use the symmetry of the
problem and simulate only one jet. A large circularization-flow (vortex) is
formed to the side of the jet which together with the thermal pressure of the
shocked jet material accelerate cold slow-wind gas back to the center from
distances of ~1000-10000 AU. We find for the parameters we use that up to 0.001
Mo is back-flowing to the center. We conjecture that the orbital angular
momentum of the disk material results from the non-axisymmetric structure of
jets launched by an orbiting companion. This conjecture will have to be tested
with 3D numerical codes.Comment: New Astronomy, in pres
- …