10,100 research outputs found
Transient Nucleation near the Mean-Field Spinodal
Nucleation is considered near the pseudospinodal in a one-dimensional
model with a non-conserved order parameter and long-range
interactions. For a sufficiently large system or a system with slow relaxation
to metastable equilibrium, there is a non-negligible probability of nucleation
occurring before reaching metastable equilibrium. This process is referred to
as transient nucleation. The critical droplet is defined to be the
configuration of maximum likelihood that is dynamically balanced between the
metastable and stable wells. Time-dependent droplet profiles and nucleation
rates are derived, and theoretical results are compared to computer simulation.
The analysis reveals a distribution of nucleation times with a distinct peak
characteristic of a nonstationary nucleation rate. Under the quench conditions
employed, transient critical droplets are more compact than the droplets found
in metastable equilibrium simulations and theoretical predictions.Comment: 7 Pages, 5 Figure
The two-echelon capacitated vehicle routing problem: models and math-based heuristics
Multiechelon distribution systems are quite common in supply-chain and logistics. They are used by public administrations in their transportation and traffic planning strategies, as well as by companies, to model own distribution systems. In the literature, most of the studies address issues relating to the movement of flows throughout the system from their origins to their final destinations. Another recent trend is to focus on the management of the vehicle fleets required to provide transportation among different echelons. The aim of this paper is twofold. First, it introduces the family of two-echelon vehicle routing problems (VRPs), a term that broadly covers such settings, where the delivery from one or more depots to customers is managed by routing and consolidating freight through intermediate depots. Second, it considers in detail the basic version of two-echelon VRPs, the two-echelon capacitated VRP, which is an extension of the classical VRP in which the delivery is compulsorily delivered through intermediate depots, named satellites. A mathematical model for two-echelon capacitated VRP, some valid inequalities, and two math-heuristics based on the model are presented. Computational results of up to 50 customers and four satellites show the effectiveness of the methods developed
Global aspects of gravitomagnetism
We consider global properties of gravitomagnetism by investigating the
gravitomagnetic field of a rotating cosmic string. We show that although the
gravitomagnetic field produced by such a configuration of matter vanishes
locally, it can be detected globally. In this context we discuss the
gravitational analogue of the Aharonov-Bohm effect.Comment: 10 pages - Typeset using REVTE
Comments on "There is no axiomatic system for the quantum theory"
In a recent paper, Nagata [1] claims to derive inconsistencies from quantum
mechanics. In this paper, we show that the inconsistencies do not come from
quantum mechanics, but from extra assumptions about the reality of observables
Uso da ressonância magnética nuclear de baixo campo na determinação rápida do teor de umidade em madeiras.
Neste trabalho é apresentada uma recomendação da utilização da técnica de ressonância magnética nuclear (RMN) de baixo campo como método alternativo na determinação rápida da umidade em madeiras. Este método utiliza o espectrômetro de RMN desenvolvido pela Embrapa Instrumentação Agropecuária e transferido para a Empresa GIL Equipamentos Especiais.bitstream/CNPDIA/9437/1/RT12_99.pd
Experimental characterization of the flexural behaviour of steel fibre reinforced concrete according to RILEM TC 162-TDF recommendations
The post-cracking energy absorption capacity is the concrete property most benefited by
steel fibre reinforcement, usually designated by toughness. Different test set-ups, test
procedures and parameters have been proposed to evaluate the toughness of the steel
fibre reinforced concrete (SFRC), but none of them has received a general acceptation by
scientific and technical communities. As a consequence, designers put some reserves on
the use of SFRC, because they are not confident on the design practice to be adopted,
resulting in the exclusion of SFRC in applications where it could be the most suitable
solution. In the last years RILEM TC 162 – TDF has published documents where
recommendations for characterizing and designing SFRC structures are proposed. A
general acceptation of these recommendations can be only taken if they are deeply
analysed and checked by a large number of research centres.
This work intends to give some contribution for this analysis. It has also the purpose of
evaluating the influence of the fibre content, percentage of cement replaced by fly ash
and SFRC age on the post-cracking behaviour of the SFRC, under the experimental
framework recommended by RILEM TC 162 – TDF.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/34793/99. "Cost competitive steel fibre reinforced concrete for industrial pavements“Pisonort – Pavimentos industriais LdaSeci
- …