Tunable plasmonic enhancement of light scattering and absorption in graphene-coated subwavelength wires

The electromagnetic response of subwavelength wires coated with a graphene monolayer illuminated by a linearly polarized plane waves is investigated. The results show that the scattering and extintion cross-sections of the coated wire can be dramatically enhanced when the incident radiation resonantly excites localized surface plasmons. The enhancements occur for p--polarized incident waves and for excitation frequencies that correspond to complex poles in the coefficients of the multipole expansion for the scattered field. By dynamically tuning the chemical potential of graphene, the spectral position of the enhancements can be chosen over a wide range.Comment: Accepted for publication in Journal of Optics 201

A tensor instability in the Eddington inspired Born-Infeld Theory of Gravity

In this paper we consider an extension to Eddington's proposal for the gravitational action. We study tensor perturbations of a homogeneous and isotropic space-time in the Eddington regime, where modifications to Einstein gravity are strong. We find that the tensor mode is linearly unstable deep in the Eddington regime and discuss its cosmological implications.Comment: 5 pages, approved by Phys. Rev. D, additional references and minor modification

Uma comparação entre Antispams do tipo desafio-resposta e estatísticos: uma experiência da Embrapa Informática Agropecuária.

bitstream/CNPTIA/11085/1/comtec68.pdfAcesso em: 28 maio 2008

Eddington-Born-Infeld action for dark energy and dark matter

We argue that Einstein gravity coupled to a Born-Infeld theory provides an attractive candidate to represent dark matter and dark energy. For cosmological models, the Born-Infeld field has an equation of state which interpolates between matter, w=0 (small times), and a cosmological constant w=-1 (large times). On galactic scales, the Born-Infeld field predicts asymptotically flat rotation curves.Comment: A sign mistake in section on galactic scales is pointed out. This sign invalidates the content of that section. See comment on manuscrip

Boussinesq Solitons as Propagators of Neural Signals

We  consider  certain  approximation for determining the  equation  of motion  for nerve  signals by  using  the  model  of the  lipid  melting  of membranes.   The  nerve  pulses  are  found  to  display nonlinearity and  dispersion  during  the  melting  transition.  In this  simplified model the  nonlinear equation  early  proposed  by  Heimburg  and  coworkers  transformed to  the  well known  integrable Boussinesq  non linear  equation.   Under  specific values of the  parametric space this  system  shows the  existence  of singular  and  regular  soliton  like structures.   After  their  collisions  the  mutual creation  and annihilation (each other)  of nerve signals along the  nerve,  during  their  propagation, has been observed.Keywords: Boussinesq equation,  singular  solitons,  single neurons,  neural  code

An Efficient Implementation of Parallel Parametric HRTF Models for Binaural Sound Synthesis in Mobile Multimedia

The extended use of mobile multimedia devices in applications like gaming, 3D video and audio reproduction, immersive teleconferencing, or virtual and augmented reality, is demanding efficient algorithms and methodologies. All these applications require real-time spatial audio engines with the capability of dealing with intensive signal processing operations while facing a number of constraints related to computational cost, latency and energy consumption. Most mobile multimedia devices include a Graphics Processing Unit (GPU) that is primarily used to accelerate video processing tasks, providing high computational capabilities due to its inherent parallel architecture. This paper describes a scalable parallel implementation of a real-time binaural audio engine for GPU-equipped mobile devices. The engine is based on a set of head-related transfer functions (HRTFs) modelled with a parametric parallel structure, allowing efficient synthesis and interpolation while reducing the size required for HRTF data storage. Several strategies to optimize the GPU implementation are evaluated over a well-known kind of processor present in a wide range of mobile devices. In this context, we analyze both the energy consumption and real-time capabilities of the system by exploring different GPU and CPU configuration alternatives. Moreover, the implementation has been conducted using the OpenCL framework, guarantying the portability of the code

Design e roteiro de vídeos educativos.

Propõe-se a elaboração de design e roteiro de conteúdo de vídeos educativos sob o enfoque da aprendizagem significativa, que se baseia no modelo construtivista do processo cognitivo humano. Mapas conceituais são adotados como uma opção para a organização e representação do conhecimento em construção pelo aluno, sob a mediação do professor