917 research outputs found
Enigmatic amphibians in mid-Cretaceous amber were chameleon-like ballistic feeders
Albanerpetontids are tiny, enigmatic fossil amphibians with a distinctive suite of characteristics, including scales and specialized jaw and neck joints. Here we describe a new genus and species of albanerpetontid, represented by fully articulated and three-dimensional specimens preserved in amber. These specimens preserve skeletal and soft tissues, including an elongated median hyoid element, the tip of which remains embedded in a distal tongue pad. This arrangement is very similar to the long, rapidly projecting tongue of chameleons. Our results thus suggest that albanerpetontids were sit-and-wait ballistic tongue feeders, extending the record of this specialized feeding mode by around 100 million years
Ultrafast control of donor-bound electron spins with single detuned optical pulses
The ability to control spins in semiconductors is important in a variety of
fields including spintronics and quantum information processing. Due to the
potentially fast dephasing times of spins in the solid state [1-3], spin
control operating on the picosecond or faster timescale may be necessary. Such
speeds, which are not possible to attain with standard electron spin resonance
(ESR) techniques based on microwave sources, can be attained with broadband
optical pulses. One promising ultrafast technique utilizes single broadband
pulses detuned from resonance in a three-level Lambda system [4]. This
attractive technique is robust against optical pulse imperfections and does not
require a fixed optical reference phase. Here we demonstrate the principle of
coherent manipulation of spins theoretically and experimentally. Using this
technique, donor-bound electron spin rotations with single-pulse areas
exceeding pi/4 and two-pulses areas exceeding pi/2 are demonstrated. We believe
the maximum pulse areas attained do not reflect a fundamental limit of the
technique and larger pulse areas could be achieved in other material systems.
This technique has applications from basic solid-state ESR spectroscopy to
arbitrary single-qubit rotations [4, 5] and bang-bang control[6] for quantum
computation.Comment: 15 pages, 4 figures, submitted 12/2008. Since the submission of this
work we have become aware of related work: J. Berezovsky, M. H. Mikkelsen, N.
G. Stoltz, L. A. Coldren, and D. D. Awschalom, Science 320: 349-352 (2008
Perverse coherent t-structures through torsion theories
Bezrukavnikov (later together with Arinkin) recovered the work of Deligne
defining perverse -structures for the derived category of coherent sheaves
on a projective variety. In this text we prove that these -structures can be
obtained through tilting torsion theories as in the work of Happel, Reiten and
Smal\o. This approach proves to be slightly more general as it allows us to
define, in the quasi-coherent setting, similar perverse -structures for
certain noncommutative projective planes.Comment: New revised version with important correction
A new Early Cretaceous lizard in Myanmar amber with exceptionally preserved integument
We here report on a well-preserved juvenile lizard specimen in Albian amber (ca. 110 mya) from the Hkamti site (Myanmar). This new taxon is represented by an articulated skull and the anterior portion of the trunk, including the pectoral girdle and forelimbs. The scleral ossicles and eyelid are also visible, and the specimen exhibits pristine detail of the integument (of both head and body). In a combined molecular and morphological analysis, it was consistently recovered as a scincoid lizard (Scinciformata), as sister to Tepexisaurus + Xantusiidae. However, the phylogenetic position of the new taxon should be interpreted with caution as the holotype is an immature individual. We explored the possibility of miscoding ontogenetically variable characters by running alternative analyses in which these characters were scored as missing data for our taxon. With the exception of one tree, in which it was sister to Amphisbaenia, the specimen was recovered as a Pan-xantusiid. Moreover, we cannot rule out the possibility that it represents a separate lineage of uncertain phylogenetic position, as it is the case for many Jurassic and Cretaceous taxa. Nonetheless, this fossil offers a rare opportunity to glimpse the external appearance of one group of lizards during the Early Cretaceous
Searching for network modules
When analyzing complex networks a key target is to uncover their modular
structure, which means searching for a family of modules, namely node subsets
spanning each a subnetwork more densely connected than the average. This work
proposes a novel type of objective function for graph clustering, in the form
of a multilinear polynomial whose coefficients are determined by network
topology. It may be thought of as a potential function, to be maximized, taking
its values on fuzzy clusterings or families of fuzzy subsets of nodes over
which every node distributes a unit membership. When suitably parametrized,
this potential is shown to attain its maximum when every node concentrates its
all unit membership on some module. The output thus is a partition, while the
original discrete optimization problem is turned into a continuous version
allowing to conceive alternative search strategies. The instance of the problem
being a pseudo-Boolean function assigning real-valued cluster scores to node
subsets, modularity maximization is employed to exemplify a so-called quadratic
form, in that the scores of singletons and pairs also fully determine the
scores of larger clusters, while the resulting multilinear polynomial potential
function has degree 2. After considering further quadratic instances, different
from modularity and obtained by interpreting network topology in alternative
manners, a greedy local-search strategy for the continuous framework is
analytically compared with an existing greedy agglomerative procedure for the
discrete case. Overlapping is finally discussed in terms of multiple runs, i.e.
several local searches with different initializations.Comment: 10 page
Dynamical Patterns of Cattle Trade Movements
Despite their importance for the spread of zoonotic diseases, our
understanding of the dynamical aspects characterizing the movements of farmed
animal populations remains limited as these systems are traditionally studied
as static objects and through simplified approximations. By leveraging on the
network science approach, here we are able for the first time to fully analyze
the longitudinal dataset of Italian cattle movements that reports the mobility
of individual animals among farms on a daily basis. The complexity and
inter-relations between topology, function and dynamical nature of the system
are characterized at different spatial and time resolutions, in order to
uncover patterns and vulnerabilities fundamental for the definition of targeted
prevention and control measures for zoonotic diseases. Results show how the
stationarity of statistical distributions coexists with a strong and
non-trivial evolutionary dynamics at the node and link levels, on all
timescales. Traditional static views of the displacement network hide important
patterns of structural changes affecting nodes' centrality and farms' spreading
potential, thus limiting the efficiency of interventions based on partial
longitudinal information. By fully taking into account the longitudinal
dimension, we propose a novel definition of dynamical motifs that is able to
uncover the presence of a temporal arrow describing the evolution of the system
and the causality patterns of its displacements, shedding light on mechanisms
that may play a crucial role in the definition of preventive actions
Dynamical Patterns of Cattle Trade Movements
Despite their importance for the spread of zoonotic diseases, our
understanding of the dynamical aspects characterizing the movements of farmed
animal populations remains limited as these systems are traditionally studied
as static objects and through simplified approximations. By leveraging on the
network science approach, here we are able for the first time to fully analyze
the longitudinal dataset of Italian cattle movements that reports the mobility
of individual animals among farms on a daily basis. The complexity and
inter-relations between topology, function and dynamical nature of the system
are characterized at different spatial and time resolutions, in order to
uncover patterns and vulnerabilities fundamental for the definition of targeted
prevention and control measures for zoonotic diseases. Results show how the
stationarity of statistical distributions coexists with a strong and
non-trivial evolutionary dynamics at the node and link levels, on all
timescales. Traditional static views of the displacement network hide important
patterns of structural changes affecting nodes' centrality and farms' spreading
potential, thus limiting the efficiency of interventions based on partial
longitudinal information. By fully taking into account the longitudinal
dimension, we propose a novel definition of dynamical motifs that is able to
uncover the presence of a temporal arrow describing the evolution of the system
and the causality patterns of its displacements, shedding light on mechanisms
that may play a crucial role in the definition of preventive actions
The association of circulating amylin with β-amyloid in familial Alzheimer's disease.
INTRODUCTION: This study assessed the hypothesis that circulating human amylin (amyloid-forming) cross-seeds with amyloid beta (Aβ) in early Alzheimer's disease (AD). METHODS: Evidence of amylin-AD pathology interaction was tested in brains of 31 familial AD mutation carriers and 20 cognitively unaffected individuals, in cerebrospinal fluid (CSF) (98 diseased and 117 control samples) and in genetic databases. For functional testing, we genetically manipulated amylin secretion in APP/PS1 and non-APP/PS1 rats. RESULTS: Amylin-Aβ cross-seeding was identified in AD brains. High CSF amylin levels were associated with decreased CSF Aβ42 concentrations. AD risk and amylin gene are not correlated. Suppressed amylin secretion protected APP/PS1 rats against AD-associated effects. In contrast, hypersecretion or intravenous injection of human amylin in APP/PS1 rats exacerbated AD-like pathology through disruption of CSF-brain Aβ exchange and amylin-Aβ cross-seeding. DISCUSSION: These findings strengthened the hypothesis of circulating amylin-AD interaction and suggest that modulation of blood amylin levels may alter Aβ-related pathology/symptoms
Long-term cycles in the history of life: Periodic biodiversity in the Paleobiology Database
Time series analysis of fossil biodiversity of marine invertebrates in the
Paleobiology Database (PBDB) shows a significant periodicity at approximately
63 My, in agreement with previous analyses based on the Sepkoski database. I
discuss how this result did not appear in a previous analysis of the PBDB. The
existence of the 63 My periodicity, despite very different treatment of
systematic error in both PBDB and Sepkoski databases strongly argues for
consideration of its reality in the fossil record. Cross-spectral analysis of
the two datasets finds that a 62 My periodicity coincides in phase by 1.6 My,
equivalent to better than the errors in either measurement. Consequently, the
two data sets not only contain the same strong periodicity, but its peaks and
valleys closely correspond in time. Two other spectral peaks appear in the PBDB
analysis, but appear to be artifacts associated with detrending and with the
increased interval length. Sampling-standardization procedures implemented by
the PBDB collaboration suggest that the signal is not an artifact of sampling
bias. Further work should focus on finding the cause of the 62 My periodicity.Comment: Published in PLoS ONE. 5 pages, 3 figures. Version with live links,
discussion available at
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004044#to
Mid-infrared plasmonic inductors: Enhancing inductance with meandering lines
UPNa. Departamento de Ingeniería Eléctrica y Electrónica. Laboratorio de fotónica TERALABWe present a mid-infrared inductor that when applied to an extraordinary transmission hole array produces a strong redshift of the resonant peak accompanied by an unprecedented enlargement of the operation bandwidth. The importance of the result is twofold: from a fundamental viewpoint, the direct applicability of equivalent circuit concepts borrowed from microwaves is demonstrated, in frequencies as high as 17â€...THz upholding unification of plasmonics and microwave concepts and allowing for a simplification of structure design and analysis; in practical terms, a broadband funnelling ofinfrared radiation with fractional bandwidth and efficiency as high as 97% and 48%, respectively, is achieved through an area less than one hundredth the squared wavelength, which leads to an impressive accessible strong field localization that may be of great interest in sensing applications.Effort sponsored by Spanish Government under contracts Consolider EngineeringMetamaterials CSD2008-00066, TEC2011-28664-C01 and TEC2011-28664-C02. V.T. acknowledges funding from Universidad Pública de Navarra. P.R.-U. is sponsored by the Government of Navarra under funding program Formación de tecnólogos 055/01/11. M.N.-C. is supported by the Imperial College Junior Research Fellowship. M.B. acknowledges funding by the Spanish Government under the research contract program Ramón y Cajal RYC-2011-08221
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