Gamma rays from extragalactic radio sources

It is proposed that the important connection between 3C 273 and 3C 279, the first two extragalactic sources detected at greater than 100 MeV energies, is their superluminal nature. In support of this conjecture, we propose a radiation mechanism that focuses gamma rays in the superluminal direction, due to Compton scattering of accretion-disk photons by relativistic nonthermal electrons in the jet

Optimización del diseño holístico de buques: embarcaciones mercantes y navales

The present paper provides a brief introduction to a holistic approach to ship design optimization, defines the generic ship design optimization problem, and demonstrates its solution by using advanced optimization techniques for the computer-aided generation, exploration, and selection of optimal designs. It discusses proposed methods on the basis of some typical ship design optimization problems of cargo and naval ships related to multiple objectives, leading to improved and partly innovative design features with respect to ships’ economy, cargo carrying capacity, safety, survivability, comfort, required powering, environmental protection, or combat strength, as applicable.Este documento brinda una breve introducción a un enfoque holístico a la optimización del diseño de embarcaciones, define el problema genérico de la optimización del diseño de embarcaciones y demuestra su solución mediante el uso de técnicas avanzadas de optimización asistidas por computador para la generación, exploración y selección de diseños óptimos. Discute los métodos propuestos sobre la base de algunos problemas típicos de optimización de diseño de embarcación de buques de carga y navales relacionados a los objetivos múltiples, conllevando a características de diseño mejoradas y parcialmente innovadoras con respecto a la economía de la embarcación, capacidad de carga, seguridad, supervivencia, comodidad, potencia requerida, protección ambiental o fortaleza de combate, como sea aplicable

Evaluation of leasing as a method of funding Investments in greek agribusiness sector

Funding for acquiring assets in Greek agribusiness sector is very common and supports Greek agribusiness SME's production. Purpose of this study is evaluation of leasing as a method of financing in order to acquire assets used directly in the production process of a business of secondary Greek agribusiness sector or even vertically integrated business. Thus, research was held in December of 2012, collecting proper data from Greek banking sector and considering Tax Legislation. Selection decision of practices financing in the event of such an investment should be made after taking into consideration several factors. Proper financial evaluation of future investment is necessary, while it's too necessary to be compared the financing choices that are given in Greece. Considering Tax Legislation, Banking Practices, and Law on Leasing, financing methods were compared in reference period. Avoiding generalizations, typical examples are given, showing that leasing preceded against borrowing, considering conditions prevailing in Greece at the time. But decision making for selection of financing method is affected by factors, which may lead to either correct or incorrect conclusions for firm's interests, if evaluation is not correct or there are personal interests of decision-makers in the administration. Consequently, incentives to use leasing for financing a business can be a lot, but quite important are ownership structure, nature of investment opportunities, business risk and tax status.(original abstract

Real-time Admission Control Algorithms with Delay and Loss Guarantees in ATM Networks

A multimedia ATM network is shared by media streams with different performance requirements. For media streams such as file transfers, the preservation of bursts and the provision of guarantees for loss probability at the burst level is of primary importance, while, for media streams such as voice, loss guarantees at the cell level are sufficient. Continuous media have stringent delay jitter requirements. Finally, some applications require loss-free transmission. In this paper, the first complete traffic management scheme for multimedia ATM networks is introduced. The traffic management scheme supports four different classes of traffic, each of which has different performance requirements expressed in terms of delay jitter guarantees and cell or burst level loss guarantees. Its running time specification as well as its real time admission control algorithms are completely specified

Stochastic life cycle ship design optimization

In the presented research study, a parametric model of a bulk carrier design is utilized in order to explore the technical and economic ship design features (design attributes) in the frame of a stochastic optimization procedure. The life cycle assessment of a newbuilding's investment that includes ship's acquisition and operation cost for ship's life cycle is affected by a variety of cost and other parameters have an inherent uncertainty. The ship design attributes are herein represented by six main ship parameters that define the basic characteristics of a vessel: length, breadth, depth, draft, block coefficient and speed. Among the ship characteristics that are related to high uncertainty are ship's energy consumption in terms of fuel consumption, fuel mix and fuel prices. In the present paper, an attempt is made to investigate how the uncertainty of estimations of the fuel consumption, fuel mix and prices, which are made at an early stage of ship design, can affect the outcome of the ship design optimization procedure with respect to ship's life cycle cost. Therefore, a stochastic optimization procedure is being applied, which is utilizing well established optimization algorithms and techniques in a robust and efficient manner. Sample results of this stochastic optimization are compared with solutions of a deterministic optimization and eventually lead to a rational basis for the decision making regarding the life cycle assessment of ship investments

Asymptotic formulas for the diameter of sections of symmetric convex bodies

AbstractSharpening work of the first two authors, for every proportion λ∈(0,1) we provide exact quantitative relations between global parameters of n-dimensional symmetric convex bodies and the diameter of their random ⌊λn⌋-dimensional sections. Using recent results of Gromov and Vershynin, we obtain an “asymptotic formula” for the diameter of random proportional sections

Alfven modes driven non-linearly by metric perturbations in anisotropic magnetized cosmologies

We consider anisotropic magnetized cosmologies filled with conductive plasma fluid and study the implications of metric perturbations that propagate parallel to the ambient magnetic field. It is known that in the first order (linear) approximation with respect to the amplitude of the perturbations no electric field and density perturbations arise. However, when we consider the non-linear coupling of the metric perturbations with their temporal derivatives, certain classes of solutions can induce steeply increasing in time electric field perturbations. This is verified both numerically and analytically. The source of these perturbations can be either high-frequency quantum vacuum fluctuations, driven by the cosmological pump field, in the early stages of the evolution of the Universe or astrophysical processes or a non-linear isotropization process of an initially anisotropic cosmological spacetime.Comment: 7 pages, RevTex, 3 figures ps, accepted for publication to IJMP