Hellenic Military Academy

About: Hellenic Military Academy is a education organization based out in Voula, Greece. It is known for research contribution in the topics: Computer science & Complex space. The organization has 36 authors who have published 97 publications receiving 541 citations.

A Stochastic Single Vehicle Routing Problem with a Predefined Sequence of Customers and Collection of Two Similar Materials

Abstract: We suppose that a vehicle visits N ordered customers in order to collect from them two similar but not identical materials. The actual quantity and the actual type of material that each customer possesses become known only when the vehicle arrives at the customer’s location. It is assumed that the vehicle has two compartments. We name these compartments, Compartment 1 and Compartment 2. It is assumed that Compartment 1 is suitable for loading Material 1 and Compartment 2 is suitable for loading Material 2. However it is permitted to load items of Material 1 into Compartment 2 and items of Material 2 into Compartment 1. These actions cause extra costs that are due to extra labor. It is permissible for the vehicle to interrupt its route and go to the depot to unload the items of both materials. The costs for travelling from each customer to the next one and the costs for travelling from each customer to the depot are known. The objective is to find the routing strategy that minimizes the total expected cost among all possible strategies for servicing all customers. A dynamic programming algorithm is designed for the determination of the routing strategy that minimizes the total expected cost among all possible strategies. The structure of optimal routing strategy is characterized by a set of critical numbers for each customer.

Efficient Error Detection and Correction in Block Data Transmission

Abstract: The rapid advances of communication technologies that aim to increase the information transmission speeds, aggravate problems of reliable data exchanges. Especially the expansion of the use of wireless telecommunications technologies is accompanied by a noticeable increase of the intensity of the electromagnetic field and consequently by an increase in the number of errors caused by external interference. The importance of the classical criteria, such as the number of control bits, is reduced and more attention is paid to other parameters, such as the computational and temporal complexity of the procedures for correcting errors, as well as transmission energy requirements. The above factors dictate the necessity for sufficient developments of the means for ensuring the reliability of communication systems, including methods for data transmission error correction. This chapter proposes a collection of techniques for correcting transmission burst errors in data transmitted over signal channels suffering from strong electromagnetic interference, such as encountered in distributed and embedded systems. Efficiency is achieved by separating the error detection from the correction process and using different codes for each case. The proposed error control techniques are based on simple mathematical operations and are suitable for implementation in FPGA devices. It hence becomes possible to replace energy demanding retransmission operations, including the overheads they entail with energy efficient local error correction calculations. The techniques employed are shown to be more efficient than existing ones, according to criteria that are relevant to current applications. These techniques reduce the need for error recovery by retransmission and hence the environmental effect of data transmission in terms of energy consumption and electromagnetic emissions.

Electron drift caused by rf field gradient creates many plasma phenomena: An attempt to distinguish the cause and the effect

Abstract: Abstract Many experimental data along with their theoretical interpretations on the rf low-temperature cylindrical plasma have been issued until today. Our Laboratory has contributed to that research by publishing results and interpretative mathematical models. With the present paper, two issues are being examined; firstly, the estimation of electron drift caused by the rf field gradient, which is the initial reason for the plasma behaviour, and secondly, many new experimental results, especially the electron-neutral collision frequency effect on the other plasma parameters and quantities. Up till now, only the plasma steady state was taken into consideration when a theoretical elaboration was carried out, regardless of the cause and the effect. This indicates the plasma's complicated and chaotic configuration and the need to simplify the problem. In the present work, a classification about the causality of the phenomena is attempted; the rf field gradient electron drift is proved to be the initial cause.

The *-Ricci Tensor of Real Hypersurfaces in Symmetric Spaces of Rank One or Two

Abstract: Complex projective and hyperbolic spaces, i.e. non-flat complex space forms, are symmetric spaces of rank one. Complex two-plane Grassmannians are symmetric spaces of rank two. Let M be a real hypersurface in a symmetric space of rank one or two. Many geometers, such as Berndt, Jeong, Kim, Ortega, Perez, Santos, Suh, Takagi and others have studied real hypersurfaces in above spaces in terms of their operators and tensor fields. This paper will be divided into two parts. Firstly, results concerning real hypersurfaces in non-flat complex space forms in terms of their∗-Ricci tensor, S ∗, which in case of real hypersurfaces was first studied by Hamada (Real hypersurfaces of complex space forms in terms of Ricci *-tensor. Tokyo J. Math. 25, 473–483 (2002)), will be presented. More precisely, it will be answered if there exist or not real hypersurfaces, whose∗-Ricci tensor is parallel, semi-parallel, i.e. R ⋅ S ∗ = 0, or pseudo-parallel, i.e. \(R(X,Y ) \cdot S^{{\ast}} = L\{(X \wedge Y ) \cdot S^{{\ast}}\}\) with L ≠ 0 (Kaimakamis and Panagiotidou, Parallel∗-Ricci tensor of real hypersurfaces in \(\mathbb{C}P^{2}\) and \(\mathbb{C}H^{2}\). Taiwan. J. Math., to appear, DOI 10.11650/tjm.18.2014.4271; Kaimakamis and Panagiotidou, Conditions of parallelism of∗-Ricci tensor of real hypersurfaces in \(\mathbb{C}P^{2}\) and \(\mathbb{C}H^{2}\). Preprint). Secondly, the formula of∗-Ricci tensor of real hypersurfaces in complex two-plane Grassmannians will be provided (Panagiotidou, The∗-Ricci tensor of real hypersurfaces in complex two-plane Grassmannians, work in progress).

A Method for Strict Remote User Identification Using non - Reversible Galois Field Transformations

Abstract: This article proposes an approach that accelerates the realization of strict remote user identification using non reversible Galois field transformation. The proposed approach is based on using finite field arithmetic to replace the usual modular arithmetic. The application of this efficient method that was developed using Galois Fields, renders feasible an exponential reduction of the computation time required for classical zero knowledge identification methods, such as FFSIS, Schnorr and Guillou & Quisquater. The new method for user registration and identification procedure for obtaining access to the system, are illustrated. It is shown, both theoretically and experimentally that the proposed method attains a per order acceleration of the execution time required for the user identification by 2 – 3 orders of magnitude, via a hardware implementation.