13,565 research outputs found
Nonmesonic Weak Decay Dynamics from proton spectra of -Hypernuclei
A novel comparison between the data and the theory is proposed for the
nonmesonic (NM) weak decay of hypernuclei. Instead of confronting the primary
decay rates, as is usually done, we focus attention on the effective decay
rates that are straightforwardly related with the number of emitted particles.
Proton kinetic energy spectra of He, Li,
Be, B, C, C,
N and O, measured by FINUDA, are evaluated
theoretically. The Independent Particle Shell Model (IPSM) is used as the
nuclear structure framework, while the dynamics is described by the
One-Meson-Exchange (OME) potential. Only for the He,
Li, and C hypernuclei is it possible to make a
comparison with the data, since for the rest there is no published experimental
information on number of produced hypernuclei. Considering solely the
one-nucleon-induced (-NM) decay channel, the theory reproduces correctly
the shapes of all three spectra at medium and high energies (
MeV). Yet, it greatly overestimates their magnitudes, as well as the
corresponding transition rates when the full OME () model is used. The agreement is much improved when only
the mesons with soft dipole cutoff parameters participate in the decay
process. We find that the IPSM is a fair first order approximation to
disentangle the dynamics of the -NM decay, the knowledge of which is
indispensable to inquire about the baryon-baryon strangeness-flipping
interaction. It is shown that the IPSM provides very useful insights regarding
the determination the -NM decay rate. In a new analysis of the FINUDA data,
we derive two results for this quantity with one of them close to that obtained
previously
Know Your Enemy: Stealth Configuration-Information Gathering in SDN
Software Defined Networking (SDN) is a network architecture that aims at
providing high flexibility through the separation of the network logic from the
forwarding functions. The industry has already widely adopted SDN and
researchers thoroughly analyzed its vulnerabilities, proposing solutions to
improve its security. However, we believe important security aspects of SDN are
still left uninvestigated. In this paper, we raise the concern of the
possibility for an attacker to obtain knowledge about an SDN network. In
particular, we introduce a novel attack, named Know Your Enemy (KYE), by means
of which an attacker can gather vital information about the configuration of
the network. This information ranges from the configuration of security tools,
such as attack detection thresholds for network scanning, to general network
policies like QoS and network virtualization. Additionally, we show that an
attacker can perform a KYE attack in a stealthy fashion, i.e., without the risk
of being detected. We underline that the vulnerability exploited by the KYE
attack is proper of SDN and is not present in legacy networks. To address the
KYE attack, we also propose an active defense countermeasure based on network
flows obfuscation, which considerably increases the complexity for a successful
attack. Our solution offers provable security guarantees that can be tailored
to the needs of the specific network under consideratio
LineSwitch: Efficiently Managing Switch Flow in Software-Defined Networking while Effectively Tackling DoS Attacks
Software Defined Networking (SDN) is a new networking architecture which aims
to provide better decoupling between network control (control plane) and data
forwarding functionalities (data plane). This separation introduces several
benefits, such as a directly programmable and (virtually) centralized network
control. However, researchers showed that the required communication channel
between the control and data plane of SDN creates a potential bottleneck in the
system, introducing new vulnerabilities. Indeed, this behavior could be
exploited to mount powerful attacks, such as the control plane saturation
attack, that can severely hinder the performance of the whole network.
In this paper we present LineSwitch, an efficient and effective solution
against control plane saturation attack. LineSwitch combines SYN proxy
techniques and probabilistic blacklisting of network traffic. We implemented
LineSwitch as an extension of OpenFlow, the current reference implementation of
SDN, and evaluate our solution considering different traffic scenarios (with
and without attack). The results of our preliminary experiments confirm that,
compared to the state-of-the-art, LineSwitch reduces the time overhead up to
30%, while ensuring the same level of protection.Comment: In Proceedings of the 10th ACM Symposium on Information, Computer and
Communications Security (ASIACCS 2015). To appea
Numerical simulation of Nitinol peripheral stents: from laser-cutting to deployment in a patient specific anatomy
The current clinical trend is to use percutaneous techniques, exploiting Nitinol self-expanding stents, to treat peripheral occluded vessels such as carotid or superficial femoral arteries. Although this class of stents addresses the biomechanical requirements (i.e. flexibility, kink resistance, etc.), it has been observed that many of these stents implanted in peripheral vessels are fractured. Numerical simulations have shown to be very useful in the investigation and optimization of stents and also to provide novel insights into fatigue/fracture mechanics. To date most finite element based stent simulations are performed in a straight simplified anatomy and neglect the actual deployment process; consequently there is a need for more realistic simulations taking into account the different stages of the stent design process and the insertion in the target anatomy into account. This study proposes a virtual framework to analyze numerically Nitinol stents from the laser-cutting stage to the deployment in a (patient specific) tortuous anatomy
Solvable Lie algebras are not that hypo
We study a type of left-invariant structure on Lie groups, or equivalently on
Lie algebras. We introduce obstructions to the existence of a hypo structure,
namely the 5-dimensional geometry of hypersurfaces in manifolds with holonomy
SU(3). The choice of a splitting g^*=V_1 + V_2, and the vanishing of certain
associated cohomology groups, determine a first obstruction. We also construct
necessary conditions for the existence of a hypo structure with a fixed
almost-contact form. For non-unimodular Lie algebras, we derive an obstruction
to the existence of a hypo structure, with no choice involved. We apply these
methods to classify solvable Lie algebras that admit a hypo structure.Comment: 21 pages; v2: presentation improved, typos corrected, notational
conflicts eliminated. To appear in Transformation Group
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