631 research outputs found
Coherent acoustic vibration of metal nanoshells
Using time-resolved pump-probe spectroscopy we have performed the first
investigation of the vibrational modes of gold nanoshells. The fundamental
isotropic mode launched by a femtosecond pump pulse manifests itself in a
pronounced time-domain modulation of the differential transmission probed at
the frequency of nanoshell surface plasmon resonance. The modulation amplitude
is significantly stronger and the period is longer than in a gold nanoparticle
of the same overall size, in agreement with theoretical calculations. This
distinct acoustical signature of nanoshells provides a new and efficient method
for identifying these versatile nanostructures and for studying their
mechanical and structural properties.Comment: 5 pages, 3 figure
The Complexity of Drawing Graphs on Few Lines and Few Planes
It is well known that any graph admits a crossing-free straight-line drawing
in and that any planar graph admits the same even in
. For a graph and , let denote
the minimum number of lines in that together can cover all edges
of a drawing of . For , must be planar. We investigate the
complexity of computing these parameters and obtain the following hardness and
algorithmic results.
- For , we prove that deciding whether for a
given graph and integer is -complete.
- Since , deciding is NP-hard for . On the positive side, we show that the problem
is fixed-parameter tractable with respect to .
- Since , both and
are computable in polynomial space. On the negative side, we show
that drawings that are optimal with respect to or
sometimes require irrational coordinates.
- Let be the minimum number of planes in needed
to cover a straight-line drawing of a graph . We prove that deciding whether
is NP-hard for any fixed . Hence, the problem is
not fixed-parameter tractable with respect to unless
Hitting all Maximal Independent Sets of a Bipartite Graph
We prove that given a bipartite graph G with vertex set V and an integer k,
deciding whether there exists a subset of V of size k hitting all maximal
independent sets of G is complete for the class Sigma_2^P.Comment: v3: minor chang
Second-order nonlinear optical properties induced by thermal poling in photonic oxide glasses and transparent glass-ceramics
In recent years there has been a resurgence of interest in oxide glasses due to advances in lasers for information transport. Oxide glasses combine low cost of fabrication and good compatibility with silica glass fibers, which offer the opportunity for developing structures with nonlinear optical properties in integrated optical devices. The creation of an axial symmetry under thermal poling is currently necessary to induce Second-Order NonLinear (SONL) optical properties in glasses. A description of theoretical models which have been proposed for charge migration during thermal poling is presented. A review of SONL efficiencies which have been obtained for different glass compositions by this method is reported. Correlations between SONL properties and structural modifications under poling are also presented. Finally, we focus on the challenging fabrication of transparent glass-ceramic composites, especially when they are obtained by the precipitation of ferroelectric nanoparticle phases in the glassy matrix which adds the advantageous SONL properties of ferroelectric crystals
Development of learning objectives for neurology in a veterinary curriculum: Part II: Postgraduates
Background:
Specialization in veterinary medicine in Europe is organized through the Colleges of the European Board of Veterinary Specialization. To inform updating of the curriculum for residents of the European College of Veterinary Neurology (ECVN) job analysis was used. Defining job competencies of diploma holders in veterinary neurology can be used as references for curriculum design of resident training. With the support of the diplomates of the ECVN and the members of the European Society of Veterinary Neurology (ESVN) a mixed-method research, including a qualitative search of objectives and quantitative ranking with 149 Likert scale questions and 48 free text questions in 9 categories in a survey was conducted. In addition, opinions of different groups were subjected to statistical analysis and the result compared.
Results:
A return rate of 62% (nâ=â213/341) was achieved. Of the competencies identified by the Delphi process, 75% objectives were expected to attain expert level; 24% attain advanced level; 1% entry level. In addition, the exercise described the 11 highly ranked competencies, the 3 most frequently seen diseases of the central and peripheral nervous systems and the most frequently used immunosuppressive, antiepileptic and chemotherapeutic drugs.
Conclusion:
The outcomes of this âDelphi job analysisâ provide a powerful tool to align the curriculum for ECVN resident training and can be adapted to the required job competencies, based on expectations. The expectation is that for majority of these competencies diplomates should attain an expert level. Besides knowledge and clinical skills, residents and diplomates are expected to demonstrate high standards in teaching and communication. The results of this study will help to create a European curriculum for postgraduate education in veterinary neurology
Intermediate phase, network demixing, boson and floppy modes, and compositional trends in glass transition temperatures of binary AsxS1-x system
The structure of binary As_xS_{1-x} glasses is elucidated using
modulated-DSC, Raman scattering, IR reflectance and molar volume experiments
over a wide range (8%<x<41%) of compositions. We observe a reversibility window
in the calorimetric experiments, which permits fixing the three elastic phases;
flexible at x<22.5%, intermediate phase (IP) in the 22.5%<x<29.5% range, and
stressed-rigid at x>29.5%. Raman scattering supported by first principles
cluster calculations reveal existence of both pyramidal (PYR, As(S1/2)3) and
quasi-tetrahedral(QT, S=As(S1/2)3) local structures. The QT unit concentrations
show a global maximum in the IP, while the concentration of PYR units becomes
comparable to those of QT units in the phase, suggesting that both these local
structures contribute to the width of the IP. The IP centroid in the sulfides
is significantly shifted to lower As content x than in corresponding selenides,
a feature identified with excess chalcogen partially segregating from the
backbone in the sulfides, but forming part of the backbone in selenides. These
ideas are corroborated by the proportionately larger free volumes of sulfides
than selenides, and the absence of chemical bond strength scaling of Tgs
between As-sulfides and As-selenides. Low-frequency Raman modes increase in
scattering strength linearly as As content x of glasses decreases from x = 20%
to 8%, with a slope that is close to the floppy mode fraction in flexible
glasses predicted by rigidity theory. These results show that floppy modes
contribute to the excess vibrations observed at low frequency. In the
intermediate and stressed rigid elastic phases low-frequency Raman modes
persist and are identified as boson modes. Some consequences of the present
findings on the optoelectronic properties of these glasses is commented upon.Comment: Accepted for PR
Kitaev's quantum double model from a local quantum physics point of view
A prominent example of a topologically ordered system is Kitaev's quantum
double model for finite groups (which in particular
includes , the toric code). We will look at these models from
the point of view of local quantum physics. In particular, we will review how
in the abelian case, one can do a Doplicher-Haag-Roberts analysis to study the
different superselection sectors of the model. In this way one finds that the
charges are in one-to-one correspondence with the representations of
, and that they are in fact anyons. Interchanging two of such
anyons gives a non-trivial phase, not just a possible sign change. The case of
non-abelian groups is more complicated. We outline how one could use
amplimorphisms, that is, morphisms to study the superselection
structure in that case. Finally, we give a brief overview of applications of
topologically ordered systems to the field of quantum computation.Comment: Chapter contributed to R. Brunetti, C. Dappiaggi, K. Fredenhagen, J.
Yngvason (eds), Advances in Algebraic Quantum Field Theory (Springer 2015).
Mainly revie
Hidden sylvatic foci of the main vector of Chagas disease Triatoma infestans : threats to the vector elimination campaign?
The research investigates relatedness between sylvatic and domestic or peri domestic (D/PD) populations of T. infestans (transmitters of Chagas disease) and the threat that they may represent to vector control and elimination attempts in the Argentinean Chaco. The report establishes that the domestication process of T. infestans does not prevent the species from surviving at low density in a wide diversity of sylvatic or semi-sylvatic habitats, even after community-wide insecticide spraying. Results suggest that in areas with recurrent re-infestation, vector control programs should consider the potential occurrence of external sources (semi-sylvatic or sylvatic) around the target community
Texture Analysis and Radial Basis Function Approximation for IVUS Image Segmentation
>Intravascular ultrasound (IVUS) has become in the last years an important tool in both clinical and research applications. The detection of lumen and media-adventitia borders in IVUS images represents a first necessary step in the utilization of the IVUS data for the 3D reconstruction of human coronary arteries and the reliable quantitative assessment of the atherosclerotic lesions. To serve this goal, a fully automated technique for the detection of lumen and media-adventitia boundaries has been developed. This comprises two different steps for contour initialization, one for each corresponding contour of interest, based on the results of texture analysis, and a procedure for approximating the initialization results with smooth continuous curves. A multilevel Discrete Wavelet Frames decomposition is used for texture analysis, whereas Radial Basis Function approximation is employed for producing smooth contours. The proposed method shows promising results compared to a previous approach for texture-based IVUS image analysis
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