5,876 research outputs found
OS diversity for intrusion tolerance: Myth or reality?
One of the key benefits of using intrusion-tolerant systems is the possibility of ensuring correct behavior in the presence of attacks and intrusions. These security gains are directly dependent on the components exhibiting failure diversity. To what extent failure diversity is observed in practical deployment depends on how diverse are the components that constitute the system. In this paper we present a study with operating systems (OS) vulnerability data from the NIST National Vulnerability Database. We have analyzed the vulnerabilities of 11 different OSes over a period of roughly 15 years, to check how many of these vulnerabilities occur in more than one OS. We found this number to be low for several combinations of OSes. Hence, our analysis provides a strong indication that building a system with diverse OSes may be a useful technique to improve its intrusion tolerance capabilities
Modified Gravity on the Brane and Dark Energy
We analyze the dynamics of an AdS5 braneworld with matter fields when gravity
is allowed to deviate from the Einstein form on the brane. We consider exact
5-dimensional warped solutions which are associated with conformal bulk fields
of weight -4 and describe on the brane the following three dynamics: those of
inhomogeneous dust, of generalized dark radiation, and of homogeneous
polytropic dark energy. We show that, with modified gravity on the brane, the
existence of such dynamical geometries requires the presence of non-conformal
matter fields confined to the brane.Comment: Revised version published in Gen. Rel. Grav. Typos corrected, updated
reference and some remarks added for clarity. 11 pages, latex, no figure
Análise exploratória de dados de monitoramento dos animais em um sistema de integração lavoura-pecuária.
Resumo: A aplicação dos preceitos da Agricultura de Precisão em um sistema de Integração Lavoura-Pecuária (ILP) envolve um grau de dificuldade maior devido ao número de fatores envolvidos e a presença da componente animal. Variáveis como a mobilidade, pisoteio, dejeções dos animais e zonas preferenciais podem impactar o sistema e devem ser consideradas. O objetivo deste trabalho é realizar uma análise exploratória dos dados de monitoramento de animais em um sistema ILP. Os dados foram obtidos por aparelhos GPS afixados em animais do rebanho e complementados por observações de campo. São apresentados mapas derivados da aplicação do estimador de intensidade Kernel para situações distintas e levantadas hipóteses sobre os comportamentos dos animais
Análise exploratória de dados de monitoramento dos animais em um sistema de integração lavoura-pecuária.
Resumo: A aplicação dos preceitos da Agricultura de Precisão em um sistema de Integração Lavoura-Pecuária (ILP) envolve um grau de dificuldade maior devido ao número de fatores envolvidos e a presença da componente animal. Variáveis como a mobilidade, pisoteio, dejeções dos animais e zonas preferenciais podem impactar o sistema e devem ser consideradas. O objetivo deste trabalho é realizar uma análise exploratória dos dados de monitoramento de animais em um sistema ILP. Os dados foram obtidos por aparelhos GPS afixados em animais do rebanho e complementados por observações de campo. São apresentados mapas derivados da aplicação do estimador de intensidade Kernel para situações distintas e levantadas hipóteses sobre os comportamentos dos animais
Conformal Bulk Fields, Dark Energy and Brane Dynamics
In the Randall-Sundrum scenario we analyze the dynamics of a spherically
symmetric 3-brane when the bulk is filled with matter fields. Considering a
global conformal transformation whose factor is the symmetric warp we
find a new set of exact dynamical solutions for which gravity is bound to the
brane. The set corresponds to a certain class of conformal bulk fields. We
discuss the geometries which describe the dynamics on the brane of polytropic
dark energy.Comment: 12 pages, latex, 2 figures. Talk given by Rui Neves at the Fourth
International Conference on Physics Beyond the Standard Model, Beyond the
Desert 03, Fundamental Experimental and Theoretical Developments in Particle
Physics, Accelerator, Non-Accelerator and Space Approaches, Max Planck
Institut f. Kernphysik/MPI Heidelberg, Castle Ringberg, Tegernsee, Germany,
9-14 June 2003. To be published in the Conference Proceedings,
Springer-Verlag, Heidelberg, German
Electrospinning : processing technique for tissue engineering scaffolding
Electrospinning has attracted tremendous interest in the research community as a simple and
versatile technique to produce synthetic polymeric ultrafine fibres with diameters ranging from a
few micrometres to tens of nanometres. Recently, some natural origin polymers have also been
successfully electrospun. Owing to their very small diameter, polymeric nanofibres exhibit
unusual properties such as high specific surface area, flexibility in surface functionalities and
superior mechanical properties. In addition, electrospun non-woven meshes could physically
mimic the extracellular matrix structure of native tissues. These remarkable properties render
electrospun nanofibres useful for many applications, particularly those related to the field of
biomedical engineering. The first part of this review is intended to provide a fundamental survey
of the electrospinning process (apparatus, governing parameters) and of recent improvements of
the technique, including associated structural modifications of polymeric nanofibre meshes. The
prospective tissue engineering/biomedical applications of electrospun polymeric nanofibres are
then reviewed, namely, wound dressings, medical prostheses, drug delivery systems, DNA
release and tissue engineering scaffolds. The essential properties of scaffolds in terms of the
structural features of electrospun nanofibre meshes are discussed. Finally, the future
perspectives for applications of electrospun nanofibres, particularly in the field of tissue
engineering, are considered
X-ray method to study temperature-dependent stripe domains in MnAs/GaAs(001)
MnAs films grown on GaAs (001) exhibit a progressive transition between
hexagonal (ferromagnetic) and orthorhombic (paramagnetic) phases at wide
temperature range instead of abrupt transition during the first-order phase
transition. The coexistence of two phases is favored by the anisotropic strain
arising from the constraint on the MnAs films imposed by the substrate. This
phase coexistence occurs in ordered arrangement alternating periodic terrace
steps. We present here a method to study the surface morphology throughout this
transition by means of specular and diffuse scattering of soft x-rays, tuning
the photon energy at the Mn 2p resonance. The results show the long-range
arrangement of the periodic stripe-like structure during the phase coexistence
and its period remains constant, in agreement with previous results using other
techniques.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
The morphology, mechanical properties and ageing behavior of porous injection molded starch-based blends for tissue engineering scaffolding
One important parameter in the tissue engineering of hard tissues is the scaffold. A scaffold is a support in which cells are seeded and that
should create the adequate environment for the cells to attach and proliferate. Furthermore the scaffold should allow the flow of an
appropriate culture media, providing nutrients to the cells and simultaneously removing the metabolites resulting from the cells activity. One
of the possibilities is to obtain solid foamed structures that will enable the cells to attach, spread into the inner surfaces and start to produce
extracellular matrix. Ideally, if the scaffold is produced from a biodegradable material, it should degrade at a pace that is in phase with the
formation of the new tissue.
In this work it was studied the production of porous structures from biodegradable polymers for use as scaffolds for bone tissue
engineering. Two materials were studied, starch compounded with poly(ethylene-vinyl-alcohol) (SEVA-C) and starch with poly(lactic acid)
(SPLA). The porous structures were obtained by injection molding with a blowing agent to control the porosity, interconnectivity and
degradation rate. In previous attempts, the current starch compounds proved to be very difficult to process by this method. This study
includes the characterization of the mechanical properties, water absorption and of the degradation kinetics of the 3-D porous structures.
Two starch-based biodegradable 3D porous structures were successfully processed in conventional injection molding and the foaming was
obtained by means of the use of a blowing agent. The mechanical properties are very promising as well as the improved degradation kinetics
when compared with the synthetic polymers alone, although the degree of porosity and of interconnectivity needs to be improved in further
work
Correlação entre medidas de condutividade elétrica em sistema de integração lavoura-pecuária.
Apsul América
Scaffolds based bone tissue engineering : the role of chitosan
As life expectancy increases, malfunction or loss of tissue caused by injury or disease leads to reduced quality of life in many patients at significant socioeconomic cost. Even though major progress has been made in the field of bone tissue engineering, present therapies, such as bone grafts, still have limitations. Current research on biodegradable polymers is emerging, combining these structures with osteogenic cells, as an alternative to autologous bone grafts. Different types of biodegradable materials have been proposed for the preparation of three-dimensional porous scaffolds for bone tissue engineering. Among them, natural polymers are one of the most attractive options, mainly due to their similarities with extracellular matrix, chemical versatility, good biological performance, and inherent cellular interactions. In this review, special attention is given to chitosan as a biomaterial for bone tissue engineering applications. An extensive literature survey was performed on the preparation of chitosan scaffolds and their in vitro biological performance as well as their potential to facilitate in vivo bone regeneration. The present review also aims to offer the reader a general overview of all components needed to engineer new bone tissue. It gives a brief background on bone biology, followed by an explanation of all components in bone tissue engineering, as well as describing different tissue engineering strategies. Moreover, also discussed are the typical models used to evaluate in vitro functionality of a tissue-engineered construct and in vivo models to assess the potential to regenerate bone tissue are discussed.Fundação para a Ciência e a Tecnologia (FCT
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