80,532 research outputs found
Heat Transfer and Pressure Drop in a Developing Channel Flow with Streamwise Vortices
Experiments to assess the heat transfer and pressure-drop effects of delta-wing
vortex generators placed at the entrance of developing channel flows are reported in
this study. The experimental geometry simulates common heat exchanger
configurations and tests are conducted over a velocity range important to heating, air
conditioning and refrigeration. An innovative liquid-crystal thermography technique
is used to determine the local and average Nusselt numbers for an isoflux channel
wall, and conventional methods are used to determine the Fanning friction factor.
Vortex generators with aspect ratios of A = 2 and A = 4 are studied at attack angles
of a. = 20?? to 45????. The results indicate that the streamwise vortices generated by a
delta wing can enhance local Nusselt numbers by more than 200% in a developing
channel flow. Under some conditions, the spatially average Nusselt number nearly
doubled for a heat transfer area that was 37 to 63 times the wing area. The Fanning
friction factor increased by a few percent to nearly 60%, depending on the Reynolds
number.Air Conditioning and Refrigeration Project 4
A Survey on Wireless Security: Technical Challenges, Recent Advances and Future Trends
This paper examines the security vulnerabilities and threats imposed by the
inherent open nature of wireless communications and to devise efficient defense
mechanisms for improving the wireless network security. We first summarize the
security requirements of wireless networks, including their authenticity,
confidentiality, integrity and availability issues. Next, a comprehensive
overview of security attacks encountered in wireless networks is presented in
view of the network protocol architecture, where the potential security threats
are discussed at each protocol layer. We also provide a survey of the existing
security protocols and algorithms that are adopted in the existing wireless
network standards, such as the Bluetooth, Wi-Fi, WiMAX, and the long-term
evolution (LTE) systems. Then, we discuss the state-of-the-art in
physical-layer security, which is an emerging technique of securing the open
communications environment against eavesdropping attacks at the physical layer.
We also introduce the family of various jamming attacks and their
counter-measures, including the constant jammer, intermittent jammer, reactive
jammer, adaptive jammer and intelligent jammer. Additionally, we discuss the
integration of physical-layer security into existing authentication and
cryptography mechanisms for further securing wireless networks. Finally, some
technical challenges which remain unresolved at the time of writing are
summarized and the future trends in wireless security are discussed.Comment: 36 pages. Accepted to Appear in Proceedings of the IEEE, 201
On the Feasibility of Fine-Grained TLS Security Configurations in Web Browsers Based on the Requested Domain Name
Most modern web browsers today sacrifice optimal TLS security for backward
compatibility. They apply coarse-grained TLS configurations that support (by
default) legacy versions of the protocol that have known design weaknesses, and
weak ciphersuites that provide fewer security guarantees (e.g. non Forward
Secrecy), and silently fall back to them if the server selects to. This
introduces various risks including downgrade attacks such as the POODLE attack
[15] that exploits the browsers silent fallback mechanism to downgrade the
protocol version in order to exploit the legacy version flaws. To achieve a
better balance between security and backward compatibility, we propose a
mechanism for fine-grained TLS configurations in web browsers based on the
sensitivity of the domain name in the HTTPS request using a whitelisting
technique. That is, the browser enforces optimal TLS configurations for
connections going to sensitive domains while enforcing default configurations
for the rest of the connections. We demonstrate the feasibility of our proposal
by implementing a proof-of-concept as a Firefox browser extension. We envision
this mechanism as a built-in security feature in web browsers, e.g. a button
similar to the \quotes{Bookmark} button in Firefox browsers and as a
standardised HTTP header, to augment browsers security
On Mitigation of Side-Channel Attacks in 3D ICs: Decorrelating Thermal Patterns from Power and Activity
Various side-channel attacks (SCAs) on ICs have been successfully
demonstrated and also mitigated to some degree. In the context of 3D ICs,
however, prior art has mainly focused on efficient implementations of classical
SCA countermeasures. That is, SCAs tailored for up-and-coming 3D ICs have been
overlooked so far. In this paper, we conduct such a novel study and focus on
one of the most accessible and critical side channels: thermal leakage of
activity and power patterns. We address the thermal leakage in 3D ICs early on
during floorplanning, along with tailored extensions for power and thermal
management. Our key idea is to carefully exploit the specifics of material and
structural properties in 3D ICs, thereby decorrelating the thermal behaviour
from underlying power and activity patterns. Most importantly, we discuss
powerful SCAs and demonstrate how our open-source tool helps to mitigate them.Comment: Published in Proc. Design Automation Conference, 201
Practical security bounds against the Trojan-horse attack in quantum key distribution
In the quantum version of a Trojan-horse attack, photons are injected into
the optical modules of a quantum key distribution system in an attempt to read
information direct from the encoding devices. To stop the Trojan photons, the
use of passive optical components has been suggested. However, to date, there
is no quantitative bound that specifies such components in relation to the
security of the system. Here, we turn the Trojan-horse attack into an
information leakage problem. This allows us quantify the system security and
relate it to the specification of the optical elements. The analysis is
supported by the experimental characterization, within the operation regime, of
reflectivity and transmission of the optical components most relevant to
security.Comment: 18 pages, 11 figures. Some typos correcte
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