6,335 research outputs found
Determining solar abundances using helioseismology
The recent downward revision of solar photospheric abundances of Oxygen and
other heavy elements has resulted in serious discrepancies between solar models
and solar structure as determined through helioseismology. In this work we
investigate the possibility of determining the solar heavy-element abundance
without reference to spectroscopy by using helioseismic data. Using the
dimensionless sound-speed derivative in the solar convection zone, we find that
the heavy element abundance, Z, of 0.0172 +/- 0.002, which is closer to the
older, higher value of the abundances.Comment: To appear in Ap
Miniaturized Quadrature Hybrid Couplers based on Novel U-shaped Transmission Lines
In this paper, a miniaturized microstrip quadrature hybrid coupler (QHC) using U-shaped transmission lines (USTLs) is presented. The proposed approach replaces all arms of the conventional QHC with its equivalent USTL to achieve compactness. The proposed coupler structure is designed to operate in the 1.5 GHz (1427-1518 [MHz]) band which is one of the 5G bands of interest. At such low RF/microwave bands below 3-4 GHz, the size of the conventional coupler is considerably very large which raises a concern for the next generation networks. The pro- posed coupler is designed, simulated and fabricated using Rogers 5880 with thickness of 0.79 mm, dielectric con- stant (εr) of 2.2 and loss tangent of 0.0021. The proposed QHC size is 70% smaller in circuit area (30% relative area) than the conventional equivalent. Simulation and mea- sured results are presented and good matching between the results is observed, confirming the outstanding coupler performance properties. The proposed miniaturized QHC structure will play a vital role for next generation 4G and 5G wireless communication systems operating below 6 GHz
NrCAM modulates sonic hedgehog signalling by controlling smoothened translocation in the cilium
Objective: Cerebellar development involves a spurt of proliferation in external granule layer (EGL) in response to shh, causing granule neuron precursors (GNPs) to proliferate. These cells subsequently differentiate into granule neurons in the inner granule layer (IGL). F3, a CNTN family molecule, can interact with NrCAM to switch GNPs from proliferation to differentiation. We aim to identify the role of NrCAM in the sonic hedgehog response in GNPs.
Methods: GNPs were extracted from wildtype and NrCAM mutant P5 cerebella using Percoll gradient centrifugation. Proliferation response to shh was measured using EdU in presence/absence of F3-Fc. GNPs treated with shh/SAG were stained with antibodies against Arl13b and smo to look for differences in cilia size and smo occupancy after different treatment times.
Results: NrCAM-/- and wildtype GNPs both proliferated equally in response to shh. F3 was found to block the proliferation response in wildtype but not in NrCAM-/- GNPs. F3 also failed to affect proliferation in SmoA1 GNPs with a constitutively active smo suggesting that the F3-NrCAM mediated block lay upstream of Smo. NrCAM was detected in wildtype cilia and Smo localization was affected in NrCAM-/- GNPs. No differences in cilia length were observed.
Conclusion: Our results suggest that NrCAM affects shh-mediated proliferation by controlling smo movement into the cilium
A large sample of calibration stars for Gaia: log g from Kepler and CoRoT
Asteroseismic data can be used to determine surface gravities with precisions
of < 0.05 dex by using the global seismic quantities Deltanu and nu_max along
with Teff and [Fe/H]. Surface gravity is also one of the four stellar
properties to be derived by automatic analyses for 1 billion stars from Gaia
data (workpackage GSP_Phot). We explore seismic data from MS F, G, K stars
(solar-like stars) observed by Kepler as a potential calibration source for
methods that Gaia will use for object characterisation (log g). We calculate
log g for bright nearby stars for which radii and masses are known, and using
their global seismic quantities in a grid-based method, we determine an
asteroseismic log g to within 0.01 dex of the direct calculation, thus
validating the accuracy of our method. We find that errors in Teff and mainly
[Fe/H] can cause systematic errors of 0.02 dex. We then apply our method to a
list of 40 stars to deliver precise values of surface gravity, i.e. sigma <
0.02 dex, and we find agreement with recent literature values. Finally, we
explore the precision we expect in a sample of 400+ Kepler stars which have
their global seismic quantities measured. We find a mean uncertainty
(precision) on the order of <0.02 dex in log g over the full explored range 3.8
< log g < 4.6, with the mean value varying only with stellar magnitude (0.01 -
0.02 dex). We study sources of systematic errors in log g and find possible
biases on the order of 0.04 dex, independent of log g and magnitude, which
accounts for errors in the Teff and [Fe/H] measurements, as well as from using
a different grid-based method. We conclude that Kepler stars provide a wealth
of reliable information that can help to calibrate methods that Gaia will use,
in particular, for source characterisation with GSP_Phot where excellent
precision (small uncertainties) and accuracy in log g is obtained from seismic
data.Comment: Accepted MNRAS, 15 pages (10 figures and 3 tables), v2=some rewording
of two sentence
Counting and computing regions of -decomposition: algebro-geometric approach
New methods for -decomposition analysis are presented. They are based on
topology of real algebraic varieties and computational real algebraic geometry.
The estimate of number of root invariant regions for polynomial parametric
families of polynomial and matrices is given. For the case of two parametric
family more sharp estimate is proven. Theoretic results are supported by
various numerical simulations that show higher precision of presented methods
with respect to traditional ones. The presented methods are inherently global
and could be applied for studying -decomposition for the space of parameters
as a whole instead of some prescribed regions. For symbolic computations the
Maple v.14 software and its package RegularChains are used.Comment: 16 pages, 8 figure
Solar Cycle Related Changes at the Base of the Convection Zone
The frequencies of solar oscillations are known to change with solar
activity. We use Principal Component Analysis to examine these changes with
high precision. In addition to the well-documented changes in solar normal mode
oscillations with activity as a function of frequency, which originate in the
surface layers of the Sun, we find a small but statistically significant change
in frequencies with an origin at and below the base of the convection zone. We
find that at r=(0.712^{+0.0097}_{-0.0029})R_sun, the change in sound speed is
\delta c^2 / c^2 = (7.23 +/- 2.08) x 10^{-5} between high and low activity.
This change is very tightly correlated with solar activity. In addition, we use
the splitting coefficients to examine the latitudinal structure of these
changes. We find changes in sound speed correlated with surface activity for r
>~ 0.9R_sun.Comment: 29 pages, 11 figures, accepted for publication in Ap
Free Fermions and Thermal AdS/CFT
The dynamics of finite temperature U(N) gauge theories on can be
described, at weak coupling, by an effective unitary matrix model. Here we
present an exact solution to these models, for any value of , in terms of a
sum over representations. Taking the large limit of this solution provides
a new perspective on the deconfinement transition which is supposed to be dual
to the Hawking-Page transition. The large phase transition manifests itself
here in a manner similar to the Douglas-Kazakov phase transition in 2d
Yang-Mills theory. We carry out a complete analysis of the saddle
representation in the simplest case involving only the order parameter . We find that the saddle points corresponding to thermal , the small
black hole and the large black hole can all be described in terms of free
fermions. They all admit a simple phase space description {\it a la} the BPS
geometries of Lin, Lunin and Maldacena.Comment: (0+34) pages and 9 figures, v2 references adde
Phase transitions in higher derivative gravity and gauge theory: R-charged black holes
This is a continuation of our earlier work where we constructed a
phenomenologically motivated effective action of the boundary gauge theory at
finite temperature and finite gauge coupling on . In this
paper, we argue that this effective action qualitatively reproduces the gauge
theory representing various bulk phases of R-charged black hole with
Gauss-Bonnet correction. We analyze the system both in canonical and grand
canonical ensemble.Comment: 36 pages, 16 figures; v2: typos corrected, references adde
Supersymmetric States in M5/M2 CFTs
We propose an exact, finite formula for the partition function over
BPS states in the conformal field theory on the world volume of
coincident M5 branes and BPS states in the theory of coincident
M2 branes. We obtain our partition function by performing the radial
quantization of the Coulomb Branches of these theories, and rederive the same
formula from the quantization of supersymmetric giant and dual giant gravitons
in and . Our partition function is
qualitatively similar to the analogous quantity in Yang Mills. It
reduces to the sum over supersymmetric multi gravitons at low energies, but
deviates from this supergravity formula at energies that scale like a positive
power of .Comment: 24 pages, harvmac; v2 reference adde
The dual of Janus -:- an interface CFT
We propose and study a specific gauge theory dual of the smooth,
non-supersymmetric (and apparently stable) Janus solution of Type IIB
supergravity found in hep-th/0304129. The dual field theory is N=4 SYM theory
on two half-spaces separated by a planar interface with different coupling
constants in each half-space. We assume that the position dependent coupling
multiplies the operator L' which is the fourth descendent of the primary Tr(X^I
X^J) and closely related to the N=4 Lagrangian density. At the classical level
supersymmetry is broken explicitly, but SO(3,2) conformal symmetry is
preserved. We use conformal perturbation theory to study various correlation
functions to first and second order in the discontinuity of g^2_{YM},
confirming quantum level conformal symmetry. Certain quantities such as the
vacuum expectation value are protected to all orders in g^2_{YM}N, and we
find perfect agreement between the weak coupling value in the gauge theory and
the strong coupling gravity result. SO(3,2) symmetry requires vanishing vacuum
energy, =0, and this is confirmed in first order in the
discontinuity.Comment: 24 pages, 1 figure; references adde
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