22,401 research outputs found
Tukushi modulates Xnr2, FGF, and and BMP signalling: Regulation of Xenopus Germ Layer Formation
BACKGROUND: Cell-cell communication is essential in tissue patterning. In early amphibian development, mesoderm is formed in the blastula-stage embryo through inductive interactions in which vegetal cells act on overlying equatorial cells. Members of the TGF-beta family such as activin B, Vg1, derrière and Xenopus nodal-related proteins (Xnrs) are candidate mesoderm inducing factors, with further activity to induce endoderm of the vegetal region. TGF-beta-like ligands, including BMP, are also responsible for patterning of germ layers. In addition, FGF signaling is essential for mesoderm formation whereas FGF signal inhibition has been implicated in endoderm induction. Clearly, several signaling pathways are coordinated to produce an appropriate developmental output; although intracellular crosstalk is known to integrate multiple pathways, relatively little is known about extracellular coordination. METHODOLOGY/PRINCIPAL FINDINGS: Here, we show that Xenopus Tsukushi (X-TSK), a member of the secreted small leucine rich repeat proteoglycan (SLRP) family, is expressed in ectoderm, endoderm, and the organizer during early development. We have previously reported that X-TSK binds to and inhibits BMP signaling in cooperation with chordin. We now demonstrate two novel interactions: X-TSK binds to and inhibits signaling by FGF8b, in addition to binding to and enhancement of Xnr2 signaling. This signal integration by X-TSK at the extracellular level has an important role in germ layer formation and patterning. Vegetally localized X-TSK potentiates endoderm formation through coordination of BMP, FGF and Xnr2 signaling. In contrast, X-TSK inhibition of FGF-MAPK signaling blocks ventrolateral mesoderm formation, while BMP inhibition enhances organizer formation. These actions of X-TSK are reliant upon its expression in endoderm and dorsal mesoderm, with relative exclusion from ventrolateral mesoderm, in a pattern shaped by FGF signals. CONCLUSIONS/SIGNIFICANCE: Based on our observations, we propose a novel mechanism by which X-TSK refines the field of positional information by integration of multiple pathways in the extracellular space
Three-dimensional Dirac oscillator in a thermal bath
The thermal properties of the three-dimensional Dirac oscillator are
considered. The canonical partition function is determined, and the
high-temperature limit is assessed. The degeneracy of energy levels and their
physical implications on the main thermodynamic functions are analyzed,
revealing that these functions assume values greater than the one-dimensional
case. So that at high temperatures, the limit value of the specific heat is
three times bigger.Comment: 9 pages, 4 figures. Text improved, references added. Revised to match
accepted version in Europhysics Letters
Nearest neighbor embedding with different time delays
A nearest neighbor based selection of time delays for phase space
reconstruction is proposed and compared to the standard use of time delayed
mutual information. The possibility of using different time delays for
consecutive dimensions is considered. A case study of numerically generated
solutions of the Lorenz system is used for illustration. The effect of
contamination with various levels of additive Gaussian white noise is
discussed.Comment: 4 pages, 5 figures, updated to final versio
Multivariate phase space reconstruction by nearest neighbor embedding with different time delays
A recently proposed nearest neighbor based selection of time delays for phase
space reconstruction is extended to multivariate time series, with an iterative
selection of variables and time delays. A case study of numerically generated
solutions of the x- and z coordinates of the Lorenz system, and an application
to heart rate and respiration data, are used for illustration.Comment: 4 pages, 3 figure
Treating some solid state problems with the Dirac equation
The ambiguity involved in the definition of effective-mass Hamiltonians for
nonrelativistic models is resolved using the Dirac equation. The multistep
approximation is extended for relativistic cases allowing the treatment of
arbitrary potential and effective-mass profiles without ordering problems. On
the other hand, if the Schrodinger equation is supposed to be used, our
relativistic approach demonstrate that both results are coincidents if the
BenDaniel and Duke prescription for the kinetic-energy operator is implemented.
Applications for semiconductor heterostructures are discussed.Comment: 06 pages, 5 figure
Regular string-like braneworlds
In this work, we propose a new class of smooth thick string-like braneworld
in six dimensions. The brane exhibits a varying brane-tension and an
asymptotic behavior. The brane-core geometry is parametrized by the Bulk
cosmological constant, the brane width and by a geometrical deformation
parameter. The source satisfies the dominant energy condition for the
undeformed solution and has an exotic asymptotic regime for the deformed
solution. This scenario provides a normalized massless Kaluza-Klein mode for
the scalar, gravitational and gauge sectors. The near-brane geometry allows
massive resonant modes at the brane for the state and nearby the brane for
.Comment: 14 pages, 12 figures. Some modifications to match the published
version in EPJ
Quantum key distribution with higher-order alphabets using spatially-encoded qudits
We propose and demonstrate a quantum key distribution scheme in higher-order
-dimensional alphabets using spatial degrees of freedom of photons. Our
implementation allows for the transmission of 4.56 bits per sifted photon,
while providing improved security: an intercept-resend attack on all photons
would induce an error rate of 0.47. Using our system, it should be possible to
send more than a byte of information per sifted photon.Comment: 4 pages, 5 figures. Replaced with published versio
You are What you Eat (and Drink): Identifying Cultural Boundaries by Analyzing Food & Drink Habits in Foursquare
Food and drink are two of the most basic needs of human beings. However, as
society evolved, food and drink became also a strong cultural aspect, being
able to describe strong differences among people. Traditional methods used to
analyze cross-cultural differences are mainly based on surveys and, for this
reason, they are very difficult to represent a significant statistical sample
at a global scale. In this paper, we propose a new methodology to identify
cultural boundaries and similarities across populations at different scales
based on the analysis of Foursquare check-ins. This approach might be useful
not only for economic purposes, but also to support existing and novel
marketing and social applications. Our methodology consists of the following
steps. First, we map food and drink related check-ins extracted from Foursquare
into users' cultural preferences. Second, we identify particular individual
preferences, such as the taste for a certain type of food or drink, e.g., pizza
or sake, as well as temporal habits, such as the time and day of the week when
an individual goes to a restaurant or a bar. Third, we show how to analyze this
information to assess the cultural distance between two countries, cities or
even areas of a city. Fourth, we apply a simple clustering technique, using
this cultural distance measure, to draw cultural boundaries across countries,
cities and regions.Comment: 10 pages, 10 figures, 1 table. Proceedings of 8th AAAI Intl. Conf. on
Weblogs and Social Media (ICWSM 2014
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