44,167 research outputs found
Contrasting heterozygosity-fitness correlations across life in a long-lived seabird
Selection is a central force underlying evolutionary change and can vary in strength and direction, for example across time and space. The fitness consequences of individual genetic diversity have often been investigated by testing for multilocus heterozygosity-fitness correlations (HFCs), but few studies have been able to assess HFCs across life stages and in both sexes. Here, we test for HFCs using a 26-year longitudinal individual-based data set from a large population of a long-lived seabird (the common tern, Sterna hirundo), where 7,974 chicks and breeders of known age were genotyped at 15 microsatellite loci and sampled for life-history traits over the complete life cycle. Heterozygosity was not correlated with fledging or post-fledging prospecting probabilities, but was positively correlated with recruitment probability. For breeders, annual survival was not correlated with heterozygosity, but annual fledgling production was negatively correlated with heterozygosity in males and highest in intermediately heterozygous females. The contrasting HFCs among life stages and sexes indicate differential selective processes and emphasize the importance of assessing fitness consequences of traits over complete life histories
Critical slowing down near the multiferroic phase transition in MnWO
By using broadband dielectric spectroscopy in the radiofrequency and
microwave range we studied the magnetoelectric dynamics in the multiferroic
chiral antiferromagnet MnWO. Above the multiferroic phase transition at
K we observe a critical slowing down of the corresponding
magnetoelectric fluctuations resembling the soft-mode behavior in canonical
ferroelectrics. This electric field driven excitation carries much less
spectral weight than ordinary phonon modes. Also the critical slowing down of
this mode scales with an exponent larger than one which is expected for
magnetic second order phase transition scenarios. Therefore the investigated
dynamics have to be interpreted as the softening of an electrically active
magnetic excitation, an electromagnon.Comment: 5 pages, 4 figures, appendi
Renormalization of the periodic Anderson model: an alternative analytical approach to heavy Fermion behavior
In this paper a recently developed projector-based renormalization method
(PRM) for many-particle Hamiltonians is applied to the periodic Anderson model
(PAM) with the aim to describe heavy Fermion behavior. In this method
high-energetic excitation operators instead of high energetic states are
eliminated. We arrive at an effective Hamiltonian for a quasi-free system which
consists of two non-interacting heavy-quasiparticle bands. The resulting
renormalization equations for the parameters of the Hamiltonian are valid for
large as well as small degeneracy of the angular momentum. An expansion
in is avoided. Within an additional approximation which adapts the
idea of a fixed renormalized \textit{f} level , we obtain
coupled equations for and the averaged \textit{f}
occupation . These equations resemble to a certain extent those of the
usual slave boson mean-field (SB) treatment. In particular, for large
the results for the PRM and the SB approach agree perfectly whereas
considerable differences are found for small .Comment: 26 pages, 5 figures included, discussion of the DOS added in v2,
accepted for publication in Phys. Rev.
Fractional Stokes-Einstein and Debye-Stokes-Einstein relations in a network forming liquid
We study the breakdown of the Stokes-Einstein (SE) and Debye-Stokes-Einstein
(DSE) relations for translational and rotational motion in a prototypical model
of a network-forming liquid, the ST2 model of water. We find that the emergence
of ``fractional'' SE and DSE relations at low temperature is ubiquitous in this
system, with exponents that vary little over a range of distinct physical
regimes. We also show that the same fractional SE relation is obeyed by both
mobile and immobile dynamical heterogeneities of the liquid
Clustering Memes in Social Media
The increasing pervasiveness of social media creates new opportunities to
study human social behavior, while challenging our capability to analyze their
massive data streams. One of the emerging tasks is to distinguish between
different kinds of activities, for example engineered misinformation campaigns
versus spontaneous communication. Such detection problems require a formal
definition of meme, or unit of information that can spread from person to
person through the social network. Once a meme is identified, supervised
learning methods can be applied to classify different types of communication.
The appropriate granularity of a meme, however, is hardly captured from
existing entities such as tags and keywords. Here we present a framework for
the novel task of detecting memes by clustering messages from large streams of
social data. We evaluate various similarity measures that leverage content,
metadata, network features, and their combinations. We also explore the idea of
pre-clustering on the basis of existing entities. A systematic evaluation is
carried out using a manually curated dataset as ground truth. Our analysis
shows that pre-clustering and a combination of heterogeneous features yield the
best trade-off between number of clusters and their quality, demonstrating that
a simple combination based on pairwise maximization of similarity is as
effective as a non-trivial optimization of parameters. Our approach is fully
automatic, unsupervised, and scalable for real-time detection of memes in
streaming data.Comment: Proceedings of the 2013 IEEE/ACM International Conference on Advances
in Social Networks Analysis and Mining (ASONAM'13), 201
Staging of laryngeal cancer: Endoscopy, computed tomography and magnetic resonance versus histopathology
An accurate pretherapeutic staging of laryngeal cancer is required for optimal treatment planning and for evaluation and comparison of the results of different treatment modalities. In this study, 45 consecutive patients with neoplasms of the larynx, treated surgically, were included in a prospective pretherapeutic staging protocol that included indirect laryngoscopy, direct microlaryngoscopy, contrast-enhanced computed tomography (CT) and Gd-DTPA-enhanced magnetic resonance imaging (MRI). The surgical specimens were cut in whole-organ slices parallel to the plane of the axial CT and MR images. The histologic findings were then compared with clinical findings, CT and MRI. These findings showed that clinical evaluation failed to identify tumor invasion of the laryngeal cartilages and extralaryngeal soft tissues, resulting in a low staging accuracy (55%). Many pT4 tumors were clinically understaged. The combination of clinical/endoscopic evaluation and either CT or MRI resulted in a significantly improved staging accuracy (80% vs 87%, respectively). MRI was significantly more sensitive but less specific than CT in detecting neoplastic cartilage invasion. MRI tended to overestimate neoplastic cartilage invasion to possibly result in overtreatment, while CT was found to underestimate neoplastic cartilage invasion and could lead to inadequate therapeutic decision
Staging of laryngeal cancer: Endoscopy, computed tomography and magnetic resonance versus histopathology
An accurate pretherapeutic staging of laryngeal cancer is required for optimal treatment planning and for evaluation and comparison of the results of different treatment modalities. In this study, 45 consecutive patients with neoplasms of the larynx, treated surgically, were included in a prospective pretherapeutic staging protocol that included indirect laryngoscopy, direct microlaryngoscopy, contrast-enhanced computed tomography (CT) and Gd-DTPA-enhanced magnetic resonance imaging (MRI). The surgical specimens were cut in whole-organ slices parallel to the plane of the axial CT and MR images. The histologic findings were then compared with clinical findings, CT and MRI. These findings showed that clinical evaluation failed to identify tumor invasion of the laryngeal cartilages and extralaryngeal soft tissues, resulting in a low staging accuracy (55%). Many pT4 tumors were clinically understaged. The combination of clinical/endoscopic evaluation and either CT or MRI resulted in a significantly improved staging accuracy (80% vs 87%, respectively). MRI was significantly more sensitive but less specific than CT in detecting neoplastic cartilage invasion. MRI tended to overestimate neoplastic cartilage invasion to possibly result in overtreatment, while CT was found to underestimate neoplastic cartilage invasion and could lead to inadequate therapeutic decision
Pathways to double ionization of atoms in strong fields
We discuss the final stages of double ionization of atoms in a strong
linearly polarized laser field within a classical model. We propose that all
trajectories leading to non-sequential double ionization pass close to a saddle
in phase space which we identify and characterize. The saddle lies in a two
degree of freedom subspace of symmetrically escaping electrons. The
distribution of longitudinal momenta of ions as calculated within the subspace
shows the double hump structure observed in experiments. Including a symmetric
bending mode of the electrons allows us to reproduce the transverse ion
momenta. We discuss also a path to sequential ionization and show that it does
not lead to the observed momentum distributions.Comment: 10 pages, 10 figures; fig.6 and 7 exchanged in the final version
accepted for publication in Phys. Rev.
Resonant enhancements of high-order harmonic generation
Solving the one-dimensional time-dependent Schr\"odinger equation for simple
model potentials, we investigate resonance-enhanced high-order harmonic
generation, with emphasis on the physical mechanism of the enhancement. By
truncating a long-range potential, we investigate the significance of the
long-range tail, the Rydberg series, and the existence of highly excited states
for the enhancements in question. We conclude that the channel closings typical
of a short-range or zero-range potential are capable of generating essentially
the same effects.Comment: 7 pages revtex, 4 figures (ps files
Comparing the cytotoxic potential of Withania somnifera water and methanol extracts
The plant Withania somnifera (Linn.) (Solanacea) is a well-known herbal medicine used in many parts of the world. It has anti-inflammatory, antioxidant, and antitumor as well as neural protective properties. It seems as if the two most active withanolide components, namely withaferin A and withanolide D, found in methanol (MeOH) extracts, are responsible for the anti-inflammatory and antioxidant properties of the plant. The current research evaluated and compared the cytotoxic potential of water and methanol extracts of W. somnifera using a combined crystal violet MTT and Neutral Red assay. MRC-5 cells, a human embryonic lung-derived diploid fibroblast cell line, were the cells of choice. We found that the three lowest concentrations (0.007, 0.042, 0.250 μg/ml) of the plant material extracted in double distilled H2O and MeOH do not differ significantly in any of the assays. We therefore that low concentrations of MeOH extracts (up to 0.250 μg/ml plant material) do not cause cell damage to the MRC-5 cells, however, higher levels should be avoided as cell viability and cell numbers are negatively influenced.Key words: Withania somnifera, anti-inflammatory; water extract; methanol extrac
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