5,065 research outputs found
-Groups for which each outer -automorphism centralizes only elements
An automorphism of a group is called outer if it is not an inner
automorphism.
Let be a finite -group. Then for every outer -automorphism
of the subgroup has order if and
only if is of order at most
How to Compute Modulo Prime-Power Sums
The problem of computing modulo prime-power sums is investigated in
distributed source coding as well as computation over Multiple-Access Channel
(MAC). We build upon group codes and present a new class of codes called Quasi
Group Codes (QGC). A QGC is a subset of a group code. These codes are not
closed under the group addition. We investigate some properties of QGC's, and
provide a packing and a covering bound. Next, we use these bounds to derived
achievable rates for distributed source coding as well as computation over MAC.
We show that strict improvements over the previously known schemes can be
obtained using QGC's
Investigating dimensional and geometrical accuracy of isothermally forged blades
Compressor blades are one of the well-known products made of titanium alloys. They are usually manufactured by a forging process followed by a sequence of machining processes. Precision forging eliminates a considerable amount of machining; however, due to the close tolerances, the process should be designed in a manner to meet dimensional and geometrical tolerances as well as the desired mechanical and metallurgical properties. In this paper, effects of two main process parameters, the process temperature and strain rate, on the dimensional and geometrical accuracy of the isothermally forged blades are investigated experimentally. The results are analyzed by the response surface method (RSM). In order to justify the results and have a tool for further studies, a coupled thermo-mechanical finite element method model is developed and verified by the experimental results. The results show that the process temperature and pressing speed and their interaction have a meaningful effect on the thickness error; however, the interaction effect of the process temperature and pressing speed on the twist error is not considerable and moreover the bow error of the forged blades is not significant. Finally, the results show that for a given geometry, by selection of appropriate process parameters, a sound workpiece with acceptable dimensional and geometrical aspects can be manufactured without any need for a die shape compensation
An Elliptic Curve-based Signcryption Scheme with Forward Secrecy
An elliptic curve-based signcryption scheme is introduced in this paper that
effectively combines the functionalities of digital signature and encryption,
and decreases the computational costs and communication overheads in comparison
with the traditional signature-then-encryption schemes. It simultaneously
provides the attributes of message confidentiality, authentication, integrity,
unforgeability, non-repudiation, public verifiability, and forward secrecy of
message confidentiality. Since it is based on elliptic curves and can use any
fast and secure symmetric algorithm for encrypting messages, it has great
advantages to be used for security establishments in store-and-forward
applications and when dealing with resource-constrained devices.Comment: 13 Pages, 5 Figures, 2 Table
A New Achievable Rate Region for Multiple-Access Channel with States
The problem of reliable communication over the multiple-access channel (MAC)
with states is investigated. We propose a new coding scheme for this problem
which uses quasi-group codes (QGC). We derive a new computable single-letter
characterization of the achievable rate region. As an example, we investigate
the problem of doubly-dirty MAC with modulo- addition. It is shown that the
sum-rate bits per channel use is achievable using the new scheme.
Whereas, the natural extension of the Gel'fand-Pinsker scheme, sum-rates
greater than are not achievable.Comment: 13 pages, ISIT 201
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