738 research outputs found
Symmetric polarization insensitive directional couplers fabricated by femtosecond laser waveguide writing
We study analytically the polarization behaviour of directional couplers
composed of birefringent waveguides, showing that they can induce polarization
transformations that depend on the specific input-output path considered. On
the basis of this study, we propose and demonstrate experimentally, by
femtosecond laser writing, directional couplers that are free from this problem
and also yield a polarization independent power-splitting ratio. More in
detail, we devise two different approaches to realize such devices: the first
one is based on local birefringence engineering, while the second one exploits
ultra-low birefringence waveguides obtained by thermal annealing
Usable security.
Traditionally, security is only considered as strong as its weakest link, and people were considered as the weak links (Schneier, 2003). This thinking triggers a vicious circle. (Adam & Sasse, 1999) stated that users are informed as little as possible on security mechanisms taken by IT departments, precisely because they are seen as inherently untrustworthy. Their work has shown that users were not sufficiently aware of security issues and tend to build their own (often inaccurate) models of possible security threats. Users have a low perception of threats because they lack the necessary information to understand their importance. According to (Sasse & al., 2001) blaming users for a security breach is like blaming human error rather than bad design. Security has, therefore, a human dimension that must be neither ignored nor neglected. The increase in the number of breaches may be attributed to designers who fail to sufficiently consider the human factor in their design techniques. Thus, to undo the Gordian knot of security, we must provide a human dimension to security
Modelling the spread of Covid19 in Italy using a revised version of the SIR model
In this paper, we present a model to predict the spread of the Covid-19
epidemic and apply it to the specific case of Italy. We started from a simple
Susceptible, Infected, Recovered (SIR) model and we added the condition that,
after a certain time, the basic reproduction number exponentially decays
in time, as empirically suggested by world data. Using this model, we were able
to reproduce the real behavior of the epidemic with an average error of 5\%.
Moreover, we illustrate possible future scenarios, associated to different
intervals of . This model has been used since the beginning of March 2020,
predicting the Italian peak of the epidemic in April 2020 with about 100.000
detected active cases. The real peak of the epidemic happened on the 20th of
April 2020, with 108.000 active cases. This result shows that the model had
predictive power for the italian case.Comment: The model presented in this paper has been adopted on Covstat.it.
Errata corrige in the abstrac
Dental Failure Analysis: The Need of a Comprehensive Failure Classification
For more than thirty percent of patients with implant-supported fixed dental prosthesis, various complications can be observed over five-years of function. In some cases, failure can be ascribed to mechanical reasons such as loosening of the retaining screws or fracture of the implant components. The paper evaluates three different failures of implant-supported prostheses. All cases were analyzed by optical and SEM microscopy to identify the failure modes and the possible failure causes. Improper design or errors in finishing operations or in assembly are identified as dental failure causes. A matrix classification is proposed to collect rupture cases of implant-supported prostheses
Integrated sources of entangled photons at telecom wavelength in femtosecond-laser-written circuits
Photon entanglement is an important state of light that is at the basis of
many protocols in photonic quantum technologies, from quantum computing, to
simulation and sensing. The capability to generate entangled photons in
integrated waveguide sources is particularly advantageous due to the enhanced
stability and more efficient light-crystal interaction. Here we realize an
integrated optical source of entangled degenerate photons at telecom
wavelength, based on the hybrid interfacing of photonic circuits in different
materials, all inscribed by femtosecond laser pulses. We show that our source,
based on spontaneous parametric down-conversion, gives access to different
classes of output states, allowing to switch from path-entangled to
polarization-entangled states with net visibilities above 0.92 for all selected
combinations of integrated devices
A novel architecture to virtualise a hardware-bound trusted platform module
Security and trust are particularly relevant in modern softwarised infrastructures, such as cloud environments, as applications are deployed on platforms owned by third parties, are publicly accessible on the Internet and can share the hardware with other tenants. Traditionally, operating systems and applications have leveraged hardware tamper-proof chips, such as the Trusted Platform Modules (TPMs) to implement security workflows, such as remote attestation, and to protect sensitive data against software attacks. This approach does not easily translate to the cloud environment, wherein the isolation provided by the hypervisor makes it impractical to leverage the hardware root of trust in the virtual domains. Moreover, the scalability needs of the cloud often collide with the scarce hardware resources and inherent limitations of TPMs. For this reason, existing implementations of virtual TPMs (vTPMs) are based on TPM emulators. Although more flexible and scalable, this approach is less secure. In fact, each vTPM is vulnerable to software attacks both at the virtualised and hypervisor levels. In this work, we propose a novel design for vTPMs that provides a binding to an underlying physical TPM; the new design, akin to a virtualisation extension for TPMs, extends the latest TPM 2.0 specification. We minimise the number of required additions to the TPM data structures and commands so that they do not require a new, non-backwards compatible version of the specification. Moreover, we support migration of vTPMs among TPM-equipped hosts, as this is considered a key feature in a highly virtualised environment. Finally, we propose a flexible approach to vTPM object creation that protects vTPM secrets either in hardware or software, depending on the required level of assurance
HAIT: Heap Analyzer with Input Tracing
Heap exploits are one of the most advanced, complex and frequent types of attack. Over the years, many effective techniques have been developed to mitigate them, such as data execution prevention, address space layout randomization and canaries. However, if both knowledge and control of the memory allocation are available, heap spraying and other attacks are still feasible. This paper presents HAIT, a memory profiler that records critical operations on the heap and shows them graphically in a clear and comprehensible format. A prototype was implemented on top of Triton, a framework for dynamic binary analysis. The experimental evaluation demonstrates that HAIT can help identifying the essential information needed to carry out heap exploits, providing valuable knowledge for an effective attack
Performance assessment of a vibro-finishing technology for additively manufactured components
Metal components produced by Additive Manufacturing (AM) technologies usually exhibit a rough surface, that in certain applications can result
detrimental for the part’s functionality. Thus, it is of great interest to study the finishing processes that can be applied to the surfaces, both external
and internal, of AM components. The aim of this work is the evaluation of the capabilities of a vibro-finishing process in the treatment of samples
produced by Laser-Powder Bed Fusion (L-PBF) from AlSi10Mg powders. In this research, the abrasive media is identified, and the surface
quality improvement is analysed in terms of surface roughness and modifications induced by the finishing treatment (i.e., edge rounding, material
loss) against finishing duration. The cost of the treatment is also evaluated
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