Results for "D. Pisignano"

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3D printing of optical materials: an investigation of the microscopic propertiesJul 09 20183D printing technologies are currently enabling the fabrication of objects with complex architectures and tailored properties. In such framework, the production of 3D optical structures, which are typically based on optical transparent matrices, optionally ... More
Control of photon transport properties in nanocomposite nanowiresMar 25 2016Active nanowires and nanofibers can be realized by the electric-field induced stretching of polymer solutions with sufficient molecular entanglements. The resulting nanomaterials are attracting an increasing attention in view of their application in a ... More
3D photo-responsive optical devices manufactured by advanced printing technologiesApr 12 2019Photonic components responsive to external optical stimuli are attracting increasing interest, because their properties can be manipulated by light with fast switching times, high spatial definition, and potentially remote control. These aspects can be ... More
Capillary filling in patterned channelsMay 27 2008We show how the capillary filling of microchannels is affected by posts or ridges on the sides of the channels. Ridges perpendicular to the flow direction introduce contact line pinning which slows, or sometimes prevents, filling; whereas ridges parallel ... More
Anisotropic conjugated polymer chain conformation tailors the energy migration in nanofibersNov 18 2016Conjugated polymers are complex multi-chromophore systems, with emission properties strongly dependent on the electronic energy transfer through active sub-units. Although the packing of the conjugated chains in the solid state is known to be a key factor ... More
Surface-enhanced Raman spectroscopy in 3D electrospun nanofiber mats coated with gold nanorodsJul 27 2015Mar 15 2016Nanofibers functionalized by metal nanostructures and particles are exploited as effective flexible substrates for SERS analysis. Their complex three-dimensional structure may provide Raman signals enhanced by orders of magnitude compared to untextured ... More
Evidence of thin-film precursors formation in hydrokinetic and atomistic simulations of nano-channel capillary fillingJun 20 2008We present hydrokinetic Lattice Boltzmann and Molecular Dynamics simulations of capillary filling of high-wetting fluids in nano-channels, which provide clear evidence of the formation of thin precursor films, moving ahead of the main capillary front. ... More
Nanowire-Intensified MEF in Hybrid Polymer-Plasmonic Electrospun FilamentsApr 15 2018Hybrid polymer-plasmonic nanostructures might combine high enhancement of localized fields from metal nanoparticles with light confinement and long-range transport in subwavelength dielectric structures. Here we report on the complex behavior of fluorophores ... More
Optimization of electrospinning techniques for the realization of nanofiber plastic lasersMar 25 2016Electrospinning technologies for the realization of active polymeric nanomaterials can be easily up-scaled, opening perspectives to industrial exploitation, and due to their versatility they can be employed to finely tailor the size, morphology and macroscopic ... More
Threading Through Macrocycles Enhances the Performance of Carbon Nanotubes as Polymer FillersAug 02 2016In this work we study the reinforcement of polymers by mechanically interlocked derivatives of single-walled carbon nanotubes (SWNTs). We compare the mechanical properties of fibers made of polymers and of composites with pristine single-walled carbon ... More
Polymer nanofibers as novel light-emitting sources and lasing materialNov 29 2013Polymer micro- and nano-fibers, made of organic light-emitting materials with optical gain, show interesting lasing properties. Fibers with diameters from few tens of nm to few microns can be fabricated by electrospinning, a method based on electrostatic ... More
Electrospun light-emitting nanofibers as building blocks for photonics and electronicsSep 04 2013Nanomaterials made of active fibers have the potential to become new functional components of light-emitting sources in the visible and near-IR range, lasers, and electronic devices
Three-Dimensional Model for Electrospinning Processes in Controlled Gas CounterflowFeb 29 2016We study the effects of a controlled gas flow on the dynamics of electrified jets in the electrospinning process. The main idea is to model the air drag effects of the gas flow by using a non-linear Langevin-like approach. The model is employed to investigate ... More
Effect of finite terms on the truncation error of Mie seriesFeb 27 2012The finite sum of the squares of the Mie coefficients is very useful for addressing problems of classical light scattering. An approximate formula available in the literature, and still in use today, has been developed to determine a priori the number ... More
Effects of Nanoparticles on the Dynamic Morphology of Electrified JetsOct 03 2017Oct 12 2017We investigate the effects of nanoparticles on the onset of varicose and whipping instabilities in the dynamics of electrified jets. In particular, we show that the non-linear interplay between the mass of the nanoparticles and electrostatic instabilities, ... More
Different regimes of the uniaxial elongation of electrically charged viscoelastic jets due to dissipative air dragMar 16 2015Jul 01 2015We investigate the effects of dissipative air drag on the dynamics of electrified jets in the initial stage of the electrospinning process. The main idea is to use a Brownian noise to model air drag effects on the uniaxial elongation of the jets. The ... More
Dynamic mesh refinement for discrete models of jet electro-hydrodynamicsNov 26 2015May 27 2016Nowadays, several models of unidimensional fluid jets exploit discrete element methods. In some cases, as for models aiming at describing the electrospinning nanofabrication process of polymer fibers, discrete element methods suffer a non constant resolution ... More
Effects of Orthogonal Rotating Electric Fields on Electrospinning ProcessOct 03 2016Sep 04 2017Electrospinning is a nanotechnology process whereby an external electric field is used to accelerate and stretch a charged polymer jet, so as to produce fibers with nanoscale diameters. In quest of a further reduction in the cross section of electrified ... More
Controlled atmosphere electrospinning of organic nanofibers with improved light emission and waveguiding propertiesOct 20 2015Nov 16 2015Electrospinning in controlled nitrogen atmosphere is developed for the realization of active polymer nanofibers. Fibers electrospun under controlled atmospheric conditions are found to be smoother and more uniform than samples realized by conventional ... More
Electrospun amplified fiber opticsFeb 25 2015Apr 06 2015A lot of research is focused on all-optical signal processing, aiming to obtain effective alternatives to existing data transmission platforms. Amplification of light in fiber optics, such as in Erbium-doped fiber amplifiers, is especially important for ... More
Ultrathin fibres from electrospinning experiments under driven fast-oscillating perturbationsDec 02 2014The effects of a driven fast-oscillating spinneret on the bending instability of electrified jets, leading to the formation of spiral structures in electrospinning experiments with charged polymers, are explored by means of extensive computer simulations. ... More
Computational homogenization of fibrous piezoelectric materialsMay 13 2014Jul 27 2015Flexible piezoelectric devices made of polymeric materials are widely used for micro- and nano-electro-mechanical systems. In particular, numerous recent applications concern energy harvesting. Due to the importance of computational modeling to understand ... More
Effects of Orthogonal Rotating Electric Fields on Electrospinning ProcessOct 03 2016Electrospinning is an nanotechnology process whereby an external electric field is used to accelerate and stretch a charged polymer jet, so as to produce fibers at nanoscale diameters. In quest of a further reduction in the cross section of electrified ... More
Non-linear Langevin model for the early-stage dynamics of electrospinning jetsMar 18 2015We present a non-linear Langevin model to investigate the early-stage dynamics of electrified polymer jets in electrospinning experiments. In particular, we study the effects of air drag force on the uniaxial elongation of the charged jet, right after ... More
A multiscale-multiphysics strategy for numerical modeling of thin piezoelectric sheetsOct 03 2014Flexible piezoelectric devices made of polymeric materials are widely used for micro- and nano-electro-mechanical systems. In particular, numerous recent applications concern energy harvesting. Due to the importance of computational modeling to understand ... More
Ratiometric Organic Fibers for Localized and Reversible Ion Sensing with Micrometer-Scale Spatial ResolutionNov 08 2015A fundamental issue in biomedical and environmental sciences is the development of sensitive and robust sensors able to probe the analyte of interest, under physiological and pathological conditions or in environmental samples, and with very high spatial ... More
JETSPIN: a specific-purpose open-source software for simulations of nanofiber electrospinningAug 26 2015We present the open-source computer program JETSPIN, specifically designed to simulate the electrospinning process of nanofibers. Its capabilities are shown with proper reference to the underlying model, as well as a description of the relevant input ... More
Enhancement of radiative processes in nanofibers with embedded plasmonic nanoparticlesFeb 03 2016Efficient manipulation and long distance transport of single-photons is a key component in nanoscale quantum optics. In this letter, we study the emission properties of an individual light emitter placed into a nanofiber and coupled to a metallic nanoparticle. ... More
The JETSPIN User Manual (Version 1.20)Jul 23 2015JETSPIN is an open-source computer program specifically designed to simulate the electrospinning process of nanofibers. This manual provides an overview of JETSPIN, focusing primarily on its structure, parallel implementations, functionality, performance, ... More
Effects of non-linear rheology on the electrospinning process: a model studyMay 06 2014Sep 12 2014We develop an analytical bead-spring model to investigate the role of non-linear rheology on the dynamics of electrified jets in the early stage of the electrospinning process. Qualitative arguments, parameter studies as well as numerical simulations, ... More
All-optical switching in dye-doped DNA nanofibersDec 17 2018All-optical switches are introduced which are based on deoxyribonucleic acid (DNA) in the form of electrospun fibers, where DNA is semi-intercalated with a push-pull, luminescent nonlinear pyrazoline derivative. Optical birefringence is found in the organic ... More
Modal Coupling of Single Photon Emitters Within Nanofiber WaveguidesAug 18 2015Jun 28 2016Nanoscale generation of individual photons in confined geometries is an exciting research field aiming at exploiting localized electromagnetic fields for light manipulation. One of the outstanding challenges of photonic systems combining emitters with ... More
The conformational evolution of elongated polymer solutions tailors the polarization of light-emission from organic nanofibersJul 14 2014Jul 30 2014Polymer fibers are currently exploited in tremendously important technologies. Their innovative properties are mainly determined by the behavior of the polymer macromolecules under the elongation induced by external mechanical or electrostatic forces, ... More
Cooperativity in the enhanced piezoelectric response of polymer nanowiresOct 30 2014Feb 25 2015We provide a detailed insight into piezoelectric energy generation from arrays of polymer nanofibers. For sake of comparison, we firstly measure individual poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFe)) fibers at well-defined levels of compressive ... More
Polarized superradiance from delocalized exciton transitions in tetracene single crystalsApr 30 2013Polarized superradiant emission and exciton delocalization in tetracene single crystals are reported. Polarization-, time-, and temperature-resolved spectroscopy evidence the complete polarization of the zero-phonon line of the intrinsic tetracene emission ... More
Stacked electrospun polymer nanofiber heterostructures with tailored stimulated emissionJul 03 2018We present stacked organic lasing heterostructures made by different species of light-emitting electrospun fibers, each able to provide optical gain in a specific spectral region. A hierarchical architecture is obtained by conformable layers of fibers ... More
Sub-ms dynamics of the instability onset of electrospinningApr 10 2015May 01 2015Electrospun polymer jets are imaged for the first time at an ultra-high rate of 10,000 frames per second, investigating the process dynamics, and the instability propagation velocity and displacement in space. The polymer concentration, applied voltage ... More
Random lasing in an organic light-emitting crystal and its interplay with vertical cavity feedbackMay 19 2014Sep 22 2014The simultaneous vertical-cavity and random lasing emission properties of a blue-emitting molecular crystal are investigated. The 1,1,4,4-tetraphenyl-1,3-butadiene samples, grown by physical vapour transport, feature room-temperature stimulated emission ... More
Lattice Boltzmann Models of Charged Multiphase Flows for Electrospinning SimulationsDec 16 2016Dec 18 2017We present a Shan-Chen model for charged leaky dielectric multiphase fluids in the context of electrospinning simulations. The role of non-linear rheology on the dynamics of electrified jets is considered by exploiting the Carreau model for pseudoplastic ... More
Interplay of Stimulated Emission and Fluorescence Resonance Energy Transfer in Electrospun Light-Emitting FibersDec 28 2017Concomitant amplified spontaneous emission (ASE) and F\"orster resonance energy transfer (FRET) are investigated in electrospun light-emitting fibers. Upon dye-doping with a proper FRET couple system, free-standing fibrous mats exhibit tunable FRET efficiency ... More
Electrostatic mechanophores in tuneable light-emitting piezo-polymer nanowiresJun 02 2017Electromechanical coupling through piezoelectric polymer chains allows the emission of organic molecules in active nanowires to be tuned. This effect is evidenced by highly bendable arrays of counter-ion dye-doped nanowires made of a poly(vinylidenefluoride) ... More
Multifunctional polymer nanofibers: UV emission, optical gain, anisotropic wetting and high hydrophobicity for next flexible excitation sourcesSep 24 2015Nov 16 2015The use of UV light sources is highly relevant in many fields of science, being directly related to all those detection and diagnosis procedures which are based on fluorescence spectroscopy. Depending on the specific application, UV light-emitting materials ... More
Bright light emission and waveguiding in conjugated polymer nanofibers electrospun from organic-salt added solutionsAug 01 2013Sep 03 2013Light emitting electrospun nanofibers of poly-[(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N'-diphenyl)-N,N'-di(p-butyl-oxy-phenyl)-1,4-diaminobenzene)] (PFO-PBAB) are produced by electrospinning under different experimental conditions. In particular, uniform ... More
Shear piezoelectricity in poly(vinylidenefluoride-co-trifluoroethylene): full piezotensor coefficients by molecular modeling, biaxial transverse response, and use in suspended energy-harvesting nanostructuresJul 04 2016The intrinsic flexible character of polymeric materials also causes remarkable strain deformations along directions perpendicular to the applied stress. Here the biaxial response in the shear piezoelectricity of polyvinylidenefluoride copolymers is analyzed ... More
Organic nanofibers embedding stimuli-responsive threaded molecular componentsOct 08 2014Oct 15 2014While most of the studies on molecular machines have been performed in solution, interfacing these supramolecular systems with solid-state nanostructures and materials is very important in view of their utilization in sensing components working by chemical ... More
Near-field electrospinning of conjugated polymer light-emitting nanofibersOct 18 2013Nov 11 2013The authors report on the realization of ordered arrays of light-emitting conjugated polymer nanofibers by near-field electrospinning. The fibers, made by poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], have diameters of few hundreds of nanometers ... More
A nanophotonic laser on a graphOct 18 2017Dec 20 2018Conventional nano-photonic schemes minimise multiple scattering to realise a miniaturised version of beam-splitters, interferometers and optical cavities for light propagation and lasing. Here instead, we introduce a nanophotonic network built from multiple ... More
Physically transient photonics: random vs. distributed feedback lasing based on nanoimprinted DNAOct 08 2014Nov 07 2014The authors report on a room-temperature nanoimprinted, DNA-based distributed feedback (DFB) laser operating at 605 nm. The laser is made of a pure DNA host matrix doped with gain dyes. At high excitation densities, the emission of the untextured dye-doped ... More
Nanoparticle-doped electrospun fiber random lasers with spatially extended light modesOct 02 2017Complex assemblies of light-emitting polymer nanofibers with molecular materials exhibiting optical gain can lead to important advance to amorphous photonics and to random laser science and devices. In disordered mats of nanofibers, multiple scattering ... More
Low-defectiveness exfoliation of MoS2 nanoparticles and their embedment in hybrid light-emitting polymer nanofibersNov 17 2018Molybdenum disulfide (MoS2) has been attracting extraordinary attention for its intriguing optical, electronic and mechanical properties. Here we demonstrate hybrid, organic-inorganic light-emitting nanofibers based on MoS2 nanoparticle dopants obtained ... More
Metal-Enhanced Near-Infrared Fluorescence by Micropatterned Gold NanocagesSep 24 2015Nov 16 2015In metal-enhanced fluorescence (MEF), the localized surface plasmon resonances of metallic nanostructures amplify the absorption of excitation light and assist in radiating the consequent fluorescence of nearby molecules to the far-field. This effect ... More
Stretching graphene using polymeric micro-musclesNov 27 2017The control of strain in two-dimensional materials opens exciting perspectives for the engineering of their electronic properties. While this expectation has been validated by artificial-lattice studies, it remains elusive in the case of atomic lattices. ... More
Local mechanical properties of electrospun fibers correlate to their internal nanostructureOct 05 2013Nov 14 2013The properties of polymeric nanofibers can be tailored and enhanced by properly managing the structure of the polymeric molecules at the nanoscale. Although electrospun polymer fibers are increasingly exploited in many technological applications, their ... More
High Performance Piezoelectric Devices Based on Aligned Arrays of Nanofibers of Poly[(vinylidenefluoride-co-trifluoroethylene]Sep 27 2013Multifunctional capability, flexible design, rugged lightweight construction, and self-powered operation are desired attributes for electronics that directly interface with the human body or with advanced robotic systems. For these and related applications, ... More
Rotational dynamics of optically trapped polymeric nanofibersJul 13 2009The optical trapping of polymeric nanofibers and the characterization of the rotational dynamics are reported. A strategy to apply a torque to a polymer nanofiber, by tilting the trapped fibers using a symmetrical linear polarized Gaussian beam is demonstrated. ... More
Diverse regimes of mode intensity correlation in nanofiber random lasers through nanoparticle dopingDec 27 2017Random lasers are based on disordered materials with optical gain. These devices can exhibit either intensity or resonant feedback, relying on diffusive or interference behaviour of light, respectively, which leads to either coupling or independent operation ... More
Biomineral Amorphous Lasers through Light-Scattering Surfaces Assembled by Electrospun Fiber TemplatesOct 25 2017New materials aim at exploiting the great control of living organisms over molecular architectures and minerals. Optical biomimetics has been widely developed by microengineering, leading to photonic components with order resembling those found in plants ... More
Cen A persistence and Virgo absence versus updated maps to understand UHECR natureDec 31 2010Ultra High Cosmic Rays (UHECR) should be tracing their sources, making a new astronomy. Their events counting are finally growing, by Auger experiment, into cosmic sky. Their map should follow the mass distribution in a narrow cosmic volume (the GZK cut ... More
Deep Core muon neutrino rate and anisotropy by mixing and CPT violationDec 23 2010Neutrinos are allowed to mix and to oscillate among their flavor. Muon and tau in particular oscillate at largest values.Last Minos experiment claimed possible difference among their matter and anti-matter masses, leading to a first violation of the most ... More
Achievements and Mirages in Uhecr and Neutrino AstronomyMay 11 2009Photon Astronomy ruled the last four centuries while wider photon band ruled last radio-X-Gamma century of discovery. Present decade may see the rise and competition of UHECR and UHE Neutrino Astronomy. Tau Neutrino may win and be the first flavor revealed. ... More
An apparent GRBs evolution around us or a sampling of thin GRB beaming jets?Oct 13 2009Oct 14 2009The gamma ray burst apparent average isotropic power versus their red-shift of all known GRB (Sept.2009) is reported. It calls for an unrealistic Gamma Ray Burst Evolution around us or it just probe the need of a very thin gamma precession-jet model. ... More
Neutrino oscillations along the Earth to probe flavor parameters: a NeuWorldJan 11 2013Mar 12 2013On 2010 MINOS experiment was showing an hint of possible different mass splitting and mixing angles for neutrinos and anti-neutrinos, suggesting a charge-parity-time (CPT) violation in the lepton sector; last year 2012 a second result from MINOS showed ... More
Beaming Selection and SN-GRB-Jets EvolutionFeb 19 2009After a decade of Fireball reign there is a hope for thin collimated Jet to solve the Supernova-GRB mystery
Inconsistence of super-luminal Cern-Opera neutrino speed with observed SN1987A burst and neutrino mixing for any imaginary neutrino massSep 25 2011Mar 05 2012We tried to fit in any way the recent Opera-Cern claims of a neutrino super-luminal speed with observed Supernova SN1987A neutrino burst and all (or most) neutrino flavor oscillation. We considered three main frame-works: (1) A tachyon imaginary neutrino ... More
Some surface subgroups survive surgeryApr 07 2001It is shown that with finitely many exceptions, the fundamental group obtained by Dehn surgery on a one cusped hyperbolic 3-manifold contains the fundamental group of a closed surface.
Electrospun Conjugated Polymer/Fullerene Hybrid Fibers: Photoactive Blends, Conductivity through Tunnelling-AFM, Light-Scattering, and Perspective for Their Use in Bulk-Heterojunction Organic Solar CellsJan 26 2018Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are prepared by electrospinning, and their properties assessed by scanning electron, atomic and lateral force, tunnelling, and confocal microscopy, as well as by attenuated total ... More
Intrinsic Properties of the <z>=2.7 Lyman Alpha Forest from Keck Spectra of QSO HS 1946+7658Jan 27 1997Feb 20 1997We present the highest quality Lyman Alpha forest spectra published to date, from the QSO HS 1946+7658. The distribution of H I column densities is a power law of slope -1.5 from Log N = 12.1 - 14. This power law can extend to N = 0, because lines weaker ... More
Possible flakes of molecular hydrogen in the early UniverseNov 18 2002The thermochemistry of H2 and HD in non-collapsed, non-reionized primordial gas up to the end of the dark age is investigated with recent radiation-matter and chemical reaction rates taking into account the efficient coolant HD, and the possibility of ... More
The category of singularities as a crystal and global Springer fibersDec 14 2014May 12 2015We prove the "Gluing Conjecture" on the spectral side of the categorical geometric Langlands correspondence. The key tool is the structure of crystal on the category of singularities, which allows to reduce the conjecture to the question of homological ... More
The spin-1 ladder : A bosonization studyAug 16 1999We construct a field-theoretic description of two coupled spin-1 Heisenberg chains, starting with the known representation of a single spin-1 chain in terms of Majorana fermions (or Ising models). After reexamining the bosonization rules for two Ising ... More
Ginzburg-Landau equations for superconducting quark matter in neutron starsJun 19 2000May 18 2002We investigate magnetic properties of color superconducting quark matter within a Ginzburg-Landau approach. The simultaneous coupling of the quark fields to gluonic and electromagnetic gauge fields leads to rotated electromagnetism with a massive (Higgsed) ... More
13CO(1-0) and 12CO(2-1) in the center of the barred galaxy NGC 1530Apr 26 1999We present 13CO(1-0) and 12CO(2-1) aperture synthesis maps of the barred spiral galaxy NGC1530. The angular resolutions are respectively 3''.1 and 1''.6. Both transitions show features similar to the 12CO(1-0) map, with a nuclear feature (a ring or unresolved ... More
Production of complex particles in low energy spallation and in fragmentation reactions by in-medium random clusterizationMay 18 2005Rules for in-medium complex particle production in nuclear reactions are proposed. These rules have been implemented in two models to simulate nucleon-nucleus and nucleus-nucleus reactions around the Fermi energy. Our work emphasizes the effect of randomness ... More
Deformation effects on the coexistence between neutron-proton and particle like pairing in N=Z medium mass nucleiNov 07 2014A model combining self-consistent mean-field and shell-model techniques is used to study the competition between particle like and proton-neutron pairing correlations in fp-shell even-even self-conjugate nuclei. Results obtained using constant two-body ... More
The accretion-diffusion scenario for metals in cool white dwarfsMar 08 2006We calculated diffusion timescales for Ca, Mg, Fe in hydrogen atmosphere white dwarfs with temperatures between 5000 and 25000 K. With these timescales we determined accretion rates for a sample of 38 DAZ white dwarfs from the recent studies of Zuckerman ... More
The elliptic genus of Calabi-Yau 3- and 4-folds, product formulae and generalized Kac-Moody algebrasJul 03 1996In this paper the elliptic genus for a general Calabi-Yau fourfold is derived. The recent work of Kawai calculating N=2 heterotic string one-loop threshold corrections with a Wilson line turned on is extended to a similar computation where K3 is replaced ... More
Spherical varieties and Langlands dualityNov 10 2006Aug 07 2007Let G be a connected reductive complex algebraic group. This paper is devoted to the space Z of meromorphic quasimaps from a curve into an affine spherical G-variety X. The space Z may be thought of as an algebraic model for the loop space of X. In this ... More
Chemical evolution of turbulent protoplanetary disks and the Solar nebulaApr 21 2011Aug 23 2011This is the second paper in a series where we study the influence of transport processes on the chemical evolution of protoplanetary disks. Our analysis is based on a flared alpha-model of the DM Tau system, coupled to a large gas-grain chemical network. ... More
Uniform Kazhdan groupsJun 01 2006We construct first examples of infinite groups having property (T) whose Kazhdan constants admit a lower bound independent of the choice of a finite generating set.
A locally symmetric Kaehler Einstein structure on a tube in the nonzero cotangent bundle of a space formAug 29 2003We obtain a locally symmetric Kaehler Einstein structure on a tube in the nonzero cotangent bundle of a Riemannian manifold of positive constant sectional curvature. The obtained Kaehler Einstein structure cannot have constant holomorphic sectional curvature. ... More
Semi-classical description of the frustrated antiferromagnetic chainSep 21 1994The antiferromagnetic Heisenberg model on a chain with nearest and next nearest neighbor couplings is mapped onto the $SO(3)$ nonlinear sigma model in the continuum limit. In one spatial dimension this model is always in its disordered phase and a gap ... More
Non-existence of a dilaton gravity action for the exact string black holeOct 07 2002Nov 07 2002We prove that no local diffeomorphism invariant two-dimensional theory of the metric and the dilaton without higher derivatives can describe the exact string black hole solution found a decade ago by Dijkgraaf, Verlinde and Verlinde. One of the key points ... More
eta and eta' mesons and dimension 2 gluon condensate <A^2>Dec 05 2005The study of light pseudoscalar quark-antiquark bound states in the Dyson-Schwinger approach with the effective QCD coupling enhanced by the interplay of the dimension 2 gluon condensate <A^2> and dimension 4 gluon condensate <F^2>, is extended to the ... More
Supersymmetric AdS(4) compactifications of IIA supergravityDec 21 2004Jan 25 2005We derive necessary and sufficient conditions for N=1 compactifications of (massive) IIA supergravity to AdS(4) in the language of SU(3) structures. We find new solutions characterized by constant dilaton and nonzero fluxes for all form fields. All fluxes ... More
A Selection of Giant Radio Sources from NVSSMar 22 2016May 10 2016Results of the application of pattern recognition techniques to the problem of identifying Giant Radio Sources (GRS) from the data in the NVSS catalog are presented and issues affecting the process are explored. Decision-tree pattern recognition software ... More
Comparing Pattern Recognition Feature Sets for Sorting Triples in the FIRST DatabaseMay 03 2006Pattern recognition techniques have been used with increasing success for coping with the tremendous amounts of data being generated by automated surveys. Usually this process involves construction of training sets, the typical examples of data with known ... More
Topological Dependence of Universal Correlations in Multi-Parameter HamiltoniansDec 03 1996Universality of correlation functions obtained in parametric random matrix theory is explored in a multi-parameter formalism, through the introduction of a diffusion matrix $D_{ij}(R)$, and compared to results from a multi-parameter chaotic model. We ... More
A class of locally symmetric Kaehler Einstein structures on the cotangent bundle of a space formJul 14 2004We obtain a class of locally symmetric Kaehler Einstein structures on the cotangent bundle of a Riemannian manifold of negative sectional curvature. Similar results are obtained in the case of a Riemannian manifold of positive sectional curvature. The ... More
Anisotropies of Cosmic Rays and Search for Intergalactic Cascades from the direction of the Highest Energetic Cosmic Ray Events with the HEGRA Scintillator ArraySep 07 1999Data taken with the HEGRA Scintillator Array have been used to search for spatial anisotropies in the arrival directions of cosmic rays above 20 TeV. In this paper results on the search for TeV gamma-ray emission from the Galactic plane and the Gould ... More
Perturbative BPS-algebras in superstring theoryFeb 27 1997This paper investigates the algebraic structure that exists on perturbative BPS-states in the superstring, compactified on the product of a circle and a Calabi-Yau fourfold. This structure was defined in a recent article by Harvey and Moore. It shown ... More
Solid State Quantum BitsMay 27 2005We present the solid-state quantum circuits that have been developed in order to implement quantum bits suitable for a quantum processor. These qubits are either based on the quantum state of a single particle (semiconductor qubits), or on the quantum ... More
Applying MVC and PAC patterns in mobile applicationsJan 20 2010Additional requirements are set for mobile applications in relation to applications for desktop computers. These requirements primarily concern the support to different platforms on which such applications are performed, as well as the requirement for ... More
Bound States and Superconductivity in Dense Fermi SystemsDec 02 2008A quantum field theoretical approach to the thermodynamics of dense Fermi systems is developed for the description of the formation and dissolution of quantum condensates and bound states in dependence of temperature and density. As a model system we ... More
Gravity as an effective theoryOct 21 2009Using as inspiration the well known chiral effective lagrangian describing the interactions of pions at low energies, in these lectures we review the quantization procedure of Einstein gravity in the spirit of effective field theories. As has been emphasized ... More
Superconductivity in the 2D Hubbard model: Electron doping is differentAug 04 2008A variational Monte Carlo calculation is used for studying the ground state of the two-dimensional Hubbard model, including hopping between both nearest and next-nearest neighbor sites. Superconductivity with d-wave symmetry is found to be restricted ... More
Classical Functional Bethe Ansatz for $SL(N)$: separation of variables for the magnetic chainMar 04 1994The Functional Bethe Ansatz (FBA) proposed by Sklyanin is a method which gives separation variables for systems for which an $R$-matrix is known. Previously the FBA was only known for $SL(2)$ and $SL(3)$ (and associated) $R$-matrices. In this paper I ... More
A new class of magnetic materials: Sr2FeMoO6 and related compoundsFeb 27 2001Ordered double perovskite oxides of the general formula, A2BB'O6, have been known for several decades to have interesting electronic and magnetic properties. However, a recent report of a spectacular negative magnetoresistance effect in a specific member ... More
A locally symmetric Kaehler Einstein structure on the cotangent bundle of a space formAug 25 2003We obtain a locally symmetric Kaehler Einstein structure on the cotangent bundle of a Riemannian manifold of negative constant sectional curvature. Similar results are obtained on a tube around zero section in the cotangent bundle, in the case of a Riemannian ... More
Existence, multiplicity and stability of endemic states for an age-structured S-I epidemic modelJun 20 2008Feb 25 2010We study an S--I type epidemic model in an age-structured population, with mortality due to the disease. A threshold quantity is found that controls the stability of the disease-free equilibrium and guarantees the existence of an endemic equilibrium. ... More
Quantitative determination of the level of cooperation in the presence of punishment in three public good experimentsOct 25 2006Nov 21 2007Strong reciprocity is a fundamental human characteristic associated with our extraordinary sociality and cooperation. Laboratory experiments on social dilemma games and many field studies have quantified well-defined levels of cooperation and propensity ... More