1,748 research outputs found
ANCHOR: logically-centralized security for Software-Defined Networks
While the centralization of SDN brought advantages such as a faster pace of
innovation, it also disrupted some of the natural defenses of traditional
architectures against different threats. The literature on SDN has mostly been
concerned with the functional side, despite some specific works concerning
non-functional properties like 'security' or 'dependability'. Though addressing
the latter in an ad-hoc, piecemeal way, may work, it will most likely lead to
efficiency and effectiveness problems. We claim that the enforcement of
non-functional properties as a pillar of SDN robustness calls for a systemic
approach. As a general concept, we propose ANCHOR, a subsystem architecture
that promotes the logical centralization of non-functional properties. To show
the effectiveness of the concept, we focus on 'security' in this paper: we
identify the current security gaps in SDNs and we populate the architecture
middleware with the appropriate security mechanisms, in a global and consistent
manner. Essential security mechanisms provided by anchor include reliable
entropy and resilient pseudo-random generators, and protocols for secure
registration and association of SDN devices. We claim and justify in the paper
that centralizing such mechanisms is key for their effectiveness, by allowing
us to: define and enforce global policies for those properties; reduce the
complexity of controllers and forwarding devices; ensure higher levels of
robustness for critical services; foster interoperability of the non-functional
property enforcement mechanisms; and promote the security and resilience of the
architecture itself. We discuss design and implementation aspects, and we prove
and evaluate our algorithms and mechanisms, including the formalisation of the
main protocols and the verification of their core security properties using the
Tamarin prover.Comment: 42 pages, 4 figures, 3 tables, 5 algorithms, 139 reference
Direct interaction between EgFABP1, a fatty acid binding protein from echinococcus granulosus, and phospholipid membranes
<p>Background: Growth and maintenance of hydatid cysts produced by Echinococcus granulosus have a high requirement for host lipids for biosynthetic processes, membrane building and possibly cellular and developmental signalling. This requires a high degree of lipid trafficking facilitated by lipid transporter proteins. Members of the fatty acid binding protein (FABP) family have been identified in Echinococcus granulosus, one of which, EgFABP1 is expressed at the tegumental level in the protoscoleces, but it has also been described in both hydatid cyst fluid and secretions of protoscoleces. In spite of a considerable amount of structural and biophysical information on the FABPs in general, their specific functions remain mysterious.</p>
<p>Methodology/Principal Findings: We have investigated the way in which EgFABP1 may interact with membranes using a variety of fluorescence-based techniques and artificial small unilamellar vesicles. We first found that bacterial recombinant EgFABP1 is loaded with fatty acids from the synthesising bacteria, and that fatty acid binding increases its resistance to proteinases, possibly due to subtle conformational changes induced on EgFABP1. By manipulating the composition of lipid vesicles and the ionic environment, we found that EgFABP1 interacts with membranes in a direct contact, collisional, manner to exchange ligand, involving both ionic and hydrophobic interactions. Moreover, we observed that the protein can compete with cytochrome c for association with the surface of small unilamellar vesicles (SUVs).</p>
<p>Conclusions/Significance: This work constitutes a first approach to the understanding of protein-membrane interactions of EgFABP1. The results suggest that this protein may be actively involved in the exchange and transport of fatty acids between different membranes and cellular compartments within the parasite.</p>
Experimental evaluation of new one-chip solution for induction motor drives
The design of high performance induction motor
drives is a complex task, and the every day compelling
requirements in energy efficiency and performance assumes the
motivation on finding a more integrated solution on implementing
induction motor control. The main subjects of this paper are two:
to discuss the IFOC one-chip solution and to explore the
development of simple graphical applications in order to operate
this control in a simple and effective way. Experimental results
are presented to illustrate the main points of our paper
A low cost solution for laboratory experiments in induction motor control
In this paper we present a controller suitable for educational activities in electric drives. A prototype has been designed specifically to meet the requirement of low cost and it contains all of the active functions required to implement the open loop control of an induction motor. In this way, the prototype allows the easy assimilation of important concepts and enables the understanding of the enclosed subsystems. Some experiments that highlight the quality of the proposed approach are presented
A boot-strap estimator for joint flux and parameters online identification for vector controlled induction motor drives
This paper presents a new approach for joint rotor flux and electrical parameters on-line identification
in vector controlled high-performance induction motor drives based on a boot-strap estimator that uses
a reduced order extended Kalman filter for rotor flux components and rotor parameters estimation and
a recursive prediction error method for stator parameters estimation. Within the prediction error
method some approaches are used and compared that affect both the adaptation gain and the direction
in which the updates of stator parameters are made. The induction motor model structures are
described in the rotor reference frame in order to reduce the computational effort by using a higher
sampling time interval
Flux and parameters identification of vector-controlled induction motor in the rotor reference frame
This paper presents a new approach for the
simultaneous identification of rotor flux components in the
rotor reference frame and electrical parameters of a vector
controlled induction motor, for real-time implementations,
using an extended Kalman filter (EKF) and a reduced
order model structure for lower computational effort. The
proposed new method requires the measurement of motor
speed, stator voltages and currents signals. Using a motor
model structure with four electrical parameters, the
estimation of flux space phasor and rotor parameters is
presented. The estimation is subsequently further extended
to include the motor stator parameters and the results are
analyzed as well as robustness. Simulated and
experimental studies highlight the improvements brought
by this new approach, mainly, a simple and reduced state
equation, the introduced scalar output equation and lower
computational cadency, by using lower sampling
frequencies in the proposed rotor reference frame
Indirect parameter estimation of continuous-time systems using discrete time data
This paper addresses the problem of parameter
estimation of continuous-time systems using samples of its
input-output data. We propose a method based on the bilinear
transformation to obtain an equivalent discrete-time model.
Introducing a new polynomial pre-filter it .is possible to
compute the physical parameters via inverse mapping between
the discrete-time and the continuous-time models. A simulation
example is given to illustrate the noise effects in the parameter
estimation results. Using experimental results, we demonstrate
the ability of the estimator. to handle real measurement
problems
Classes of model structures for state and parameter identification of vector controlled induction machines
The purpose of this paper is to present a synthesis of classes of model structures
for joint state and parameter identification of vector controlled induction
motors for real time and normal operating conditions. Based on its classical
model a set of new classes of model structures is discussed and proposed for
simultaneous estimation of rotor flux components and electrical parameters
Modelling and simulation of power electronic systems using a bond graph formalism
This paper deals with the modelling of power electronic systems using the bond graph formalism. The switching components are modelled using an ideal representation so that a constant topology system is obtained. The purpose of the present contribution is to discuss a technique that combines bond graph energy-flow modelling and signal-flow modelling schemes for simulation and prototyping of signal processing algorithms in power electronics systems. In this paper, we will discuss models of the use of fully-controlled, semi-controlled and non-controlled switches in the field of power static converters. By concept, a simulation environment can be examined at different abstraction or hierarchy levels. The approach in this paper is, accordingly, the formulation of a simulation task at different levels: component level, topology level, functional description and implementation description. The paper concludes with two practical examples of simulation of power electronics systems
A new online identification methodology for flux and parameters estimation of vector controlled induction motors
A new online identification methodology for estimation of the rotor flux components and the main electrical parameters of vector controlled induction motors is presented in this paper. The induction motor model is referred to the rotor reference frame for estimation of rotor flux and rotor parameters, and referred to the stator reference frame to estimate stator parameters. The stator parameters estimation is achieved by a prediction error method based on a model structure described by a linear regression that is independent of rotor speed and rotor parameters. The rotor flux components and rotor parameters are estimated by a reduced order extended Kalman filter, using a 4th-order state-space model structure where the state equation is described by matrices that are diagonal and independent of rotor speed as well as stator parameters. Both methods work in a boot-strap manner
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