2,919 research outputs found
Flat lens without optical axis: Theory of imaging
We derive a general theory for imaging by a flat lens without optical axis.
We show that the condition for imaging requires a material having elliptic
dispersion relations with negative group refraction, equivalent to an effective
anisotropic refractive index n(theta). Imaging can be achieved with both
negative (n0) refractive indices. The Veselago-Pendry lens
is a special case with isotropic negative refractive index of n(theta)=-1.
Realizations of the imaging conditions using anisotropic media and
inhomogeneous media, particularly photonic crystals, are discussed. Numerical
examples of imaging and requirements for sub-wavelength imaging are also
presented.Comment: 5 pages, 4 figure
What drives galactic magnetism?
We aim to use statistical analysis of a large number of various galaxies to
probe, model, and understand relations between different galaxy properties and
magnetic fields. We have compiled a sample of 55 galaxies including low-mass
dwarf and Magellanic-types, normal spirals and several massive starbursts, and
applied principal component analysis (PCA) and regression methods to assess the
impact of various galaxy properties on the observed magnetic fields. According
to PCA the global galaxy parameters (like HI, H2, and dynamical mass, star
formation rate (SFR), near-infrared luminosity, size, and rotational velocity)
are all mutually correlated and can be reduced to a single principal component.
Further PCA performed for global and intensive (not size related) properties of
galaxies (such as gas density, and surface density of the star formation rate,
SSFR), indicates that magnetic field strength B is connected mainly to the
intensive parameters, while the global parameters have only weak relationships
with B. We find that the tightest relationship of B is with SSFR, which is
described by a power-law with an index of 0.33+-0.03. The observed weaker
associations of B with galaxy dynamical mass and the rotational velocity we
interpret as indirect ones, resulting from the observed connection of the
global SFR with the available total H2 mass in galaxies. Using our sample we
constructed a diagram of B across the Hubble sequence which reveals that high
values of B are not restricted by the Hubble type. However, weaker fields
appear exclusively in later Hubble types and B as low as about 5muG is not seen
among typical spirals. The processes of generation of magnetic field in the
dwarf and Magellanic-type galaxies are similar to those in the massive spirals
and starbursts and are mainly coupled to local star-formation activity
involving the small-scale dynamo mechanism.Comment: 9 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
Negative refraction and plano-concave lens focusing in one-dimensional photonic crystals
Negative refraction is demonstrated in one-dimensional (1D) dielectric
photonic crystals (PCs) at microwave frequencies. Focusing by plano-concave
lens made of 1D PC due to negative refraction is also demonstrated. The
frequency-dependent negative refractive indices, calculated from the
experimental data matches very well with those determined from band structure
calculations. The easy fabrication of one-dimensional photonic crystals may
open the door for new applications.Comment: 3 pages and 5 figure
Comparison Of Modified Dual Ternary Indexing And Multi-Key Hashing Algorithms For Music Information Retrieval
In this work we have compared two indexing algorithms that have been used to
index and retrieve Carnatic music songs. We have compared a modified algorithm
of the Dual ternary indexing algorithm for music indexing and retrieval with
the multi-key hashing indexing algorithm proposed by us. The modification in
the dual ternary algorithm was essential to handle variable length query phrase
and to accommodate features specific to Carnatic music. The dual ternary
indexing algorithm is adapted for Carnatic music by segmenting using the
segmentation technique for Carnatic music. The dual ternary algorithm is
compared with the multi-key hashing algorithm designed by us for indexing and
retrieval in which features like MFCC, spectral flux, melody string and
spectral centroid are used as features for indexing data into a hash table. The
way in which collision resolution was handled by this hash table is different
than the normal hash table approaches. It was observed that multi-key hashing
based retrieval had a lesser time complexity than dual-ternary based indexing
The algorithms were also compared for their precision and recall in which
multi-key hashing had a better recall than modified dual ternary indexing for
the sample data considered.Comment: 11 pages, 5 figure
Quantum correlations and classical resonances in an open chaotic system
We show that the autocorrelation of quantum spectra of an open chaotic system
is well described by the classical Ruelle-Pollicott resonances of the
associated chaotic strange repeller. This correspondence is demonstrated
utilizing microwave experiments on 2-D n-disk billiard geometries, by
determination of the wave-vector autocorrelation C(\kappa) from the
experimental quantum spectra S_{21}(k). The correspondence is also established
via "numerical experiments" that simulate S_{21}(k) and C(\kappa) using
periodic orbit calculations of the quantum and classical resonances.
Semiclassical arguments that relate quantum and classical correlation functions
in terms of fluctuations of the density of states and correlations of particle
density are also examined and support the experimental results. The results
establish a correspondence between quantum spectral correlations and classical
decay modes in an open systems.Comment: 10 pages, 5 eps figures, "Quantum chaos Y2K" Nobel symposium, to
appear in Physica Script
Focusing by Plano-Concave lens using Negative Refraction
We demonstrate focusing of a plane microwave by a plano-concave lens
fabricated from a photonic crystal (PhC) having negative refractive index and
left-handed electromagnetic properties. An inverse experiment, in which a plane
wave is produced from a source placed at the focal point of the lens is also
reported. A frequency dependent negative refractive index, is obtained for the
lens from the experimental data which matches well with that determined from
band structure calculations
Alignment of Linear Biochemical Pathways Using Protein Structural Classification
Metabolic, signaling and regulatory pathways form the basis of biological processes and are important for the analysis of cellular behavior and evolution. This paper presents an approach of aligning biochemical pathways on the basis of the structure of involved proteins and their classification. The suitable information is retrieved from an integrated database system.
SIGNALIGN is available at: http://agbi.techfak.uni-bielefeld.de/signalign/index.jsp 


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