6,433 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
Minimally Extended Left-Right Symmetric Model for Dark Matter with U(1) Portal
A minimal extension of the left-right symmetric model for neutrino masses
that includes a vector-like singlet fermion dark matter (DM) is presented with
the DM connected to the visible sector via a gauged U(1) portal. We discuss the
symmetry breaking in this model and calculate the mass and mixings of the extra
heavy neutral gauge boson at the TeV scale. The extra gauge boson can decay to
both standard model particles as well to dark matter. We calculate the relic
density of the singlet fermion dark matter and its direct detection cross
section and use these constraints to obtain the allowed parameter range for the
new gauge coupling and the dark matter mass.Comment: 19 pages, 8 figure
INJECTABLE HYBRID SYSTEM FOR STRONTIUM LOCAL DELIVERY TO PROMOTE BONE REGENERATION
In bone tissue regeneration strategies, injectable bone substitutes are very attractive since they can
be applied with minimally invasive surgical procedures and can perfectly fill irregular defects created
in cases of trauma, infection or tumor resection. These materials must combine adequate mechanical
properties with the ability to induce new bone formation. Incorporating strontium (Sr) in bone
substitute biomaterials may be a strategy to achieve high Sr concentrations, not in a systemic but in
a local environment, taking advantage of the osteoanabolic and anti-osteoclastic activity of Sr, for
the enhancement of new bone formation. In this context, the aim of the present work was to
evaluate the response of a Sr-hybrid injectable system for bone regeneration, designed by our
group, consisting of hydroxyapatite microspheres doped with Sr and an alginate vehicle crosslinked in
situ with Sr, in an in vivo scenario. Two different animal models were used, rat (Wistar) and sheep
(Merino Branco) critical sized bone defect. Non Sr-doped similar materials (Ca-hybrid) or empty
defects were used as control. Sr-hybrid system led to an increased bone formation in both center
and periphery of a rat critical sized defect compared to a non Sr–doped similar system, where new
bone formation was restricted to the periphery. Moreover newly formed bone was identified as early
as one week after its implantation in a sheep model. After eight weeks, the bone surrounded the
microspheres, both in the periphery and in the center of the defect. Most importantly, the hybrid
system provided a scaffold for cell migration and tissue ingrowth and offered structural support, as
observed in both models. The effective improvement of local bone formation suggests that this might
be a promising approach for bone regeneration, especially in osteoporotic conditions
Prediction of stiffness from orientation data of glass reinforced injection moldings
The complex thermo-mechanical process developing in
injection molding leads to through-thickness and point to
point variation of fiber orientation. It is not economically
viable to characterize experimentally the variation of fiber
orientation. Thus, efforts have been put into modeling the
fiber orientation in injection molding. Some commercially
available programs already allow the prediction of fiber
orientation distribution in moldings.
If the fiber orientation field is known it is possible to
calculate the major elastic properties, which can be input
into finite-element structural analysis codes to predict
product performance.
That approach was followed in this work to compare the
experimental flexure behavior of glass fiber reinforced
polycarbonate injection molded discs with predictions
obtained from FEM simulations. The data used in the FEM
code was calculated from the fiber orientation data
predicted using the software C-Mold.(undefined
Hamiltonian symplectic embedding of the massive noncommutative U(1) Theory
We show that the massive noncommutative U(1) theory is embedded in a gauge
theory using an alternative systematic way, which is based on the symplectic
framework. The embedded Hamiltonian density is obtained after a finite number
of steps in the iterative symplectic process, oppositely to the result proposed
using the BFFT formalism. This alternative formalism of embedding shows how to
get a set of dynamically equivalent embedded Hamiltonian densities.Comment: 16 pages, no figures, revtex4, corrected version, references
additione
Experimental validation of morphology simulation in glass fibre reinforced polycarbonate discs
As assessment is made between Moldflow simulations and experimentally determined fibre orientation distributions at three points along the flow path and 12 layers across the thickness. The material used is a 10% weight short glass fibre reinforced polycarbonate. With this material the physical interaction between fibres during flow is minimised. Centre gated circular discs, where both the shear and the extensional flows are present, were produced over a range of moulding conditions to analyse the effect of flow rate and melt temperature upon the fibre orientation. The fibre orientation was measured using image analysis tools in images obtained by reflection microscopy of polished sections, using the method proposed by Bay. The measurements were made in 12 layers across the thickness
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
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
Graft incompatibility in Prunus spp. preceded by SPAD index reduction.
O objetivo deste trabalho foi mensurar o índice de clorofila (SPAD 502 Plus) em folhas de três cultivares de pessegueiros enxertados em diferentes porta-enxertos clonais, totalizando 68 combinações copa/porta-enxerto, entre cinco e nove meses após o plantio no campo, para qualificar os possíveis sintomas que antecedem a incompatibilidade de enxertia em Prunus spp. Três unidades de observação (UO) com as cultivares copa ‘BRS-Kampai’, ‘Jade’ e ‘Maciel’ foram estabelecidas sobre 18, 25 e 25 porta-enxertos clonais, respectivamente, no inverno de 2014. Como testemunhas, utilizaram-se as respectivas cultivares-copa autoenraizadas (sem porta-enxerto) que, assim como os porta-enxertos, também foram propagadas por estacas herbáceas. Adotou-se o delineamento experimental em blocos ao acaso com quatro repetições, sendo cada parcela composta por uma planta. O índice SPAD foi determinado em três avaliações, entre janeiro e abril de 2015. Os porta-enxertos ‘Mirabolano 29C’ (P.cerasifera) e ‘Marianna 2624’ (P.cerasifera x P.munsoniana) reduziram os índices SPAD nas avaliações realizadas nas três cultivares copa de pessegueiro, que culminaram com a morte das plantas por incompatibilidade. Conclui-se que os porta-enxertos ‘Mirabolano 29C’ (P.cerasifera) e ‘Marianna 2624’ (P.cerasifera x P.munsoniana) apresentam incompatibilidade de enxertia do tipo “translocada” com as cultivares de pessegueiro BRS-Kampai, Jade e Maciel e a morte dessas plantas foi precedida pela redução dos índices SPAD nas folhas após cinco meses do plantio. As demais combinações copa/porta-enxerto testadas não reduziram os índices SPAD até os nove meses de idade, mas necessitam ser avaliadas por maior período de tempo para se afirmar sobre a compatibilidade de enxertia
- …