9,517 research outputs found
Equivalence of Faddeev-Jackiw and Dirac approaches for gauge theories
The equivalence between the Dirac method and Faddeev-Jackiw analysis for
gauge theories is proved. In particular we trace out, in a stage by stage
procedure, the standard classification of first and second class constraints of
Dirac's method in the F-J approach. We also find that the Darboux
transformation implied in the F-J reduction process can be viewed as a
canonical transformation in Dirac approach. Unlike Dirac's method the F-J
analysis is a classical reduction procedure, then the quantization can be
achieved only in the framework of reduce and then quantize approach with all
the know problems that this type of procedures presents. Finally we illustrate
the equivalence by means of a particular example.Comment: Latex v2.09, 15 pages, to appear in Int. J. Mod. Phys.
Faddeev-Jackiw approach to gauge theories and ineffective constraints
The general conditions for the applicability of the Faddeev-Jackiw approach
to gauge theories are studied. When the constraints are effective a new proof
in the Lagrangian framework of the equivalence between this method and the
Dirac approach is given. We find, however, that the two methods may give
different descriptions for the reduced phase space when ineffective constraints
are present. In some cases the Faddeev-Jackiw approach may lose some
constraints or some equations of motion. We believe that this inequivalence can
be related to the failure of the Dirac conjecture (that says that the Dirac
Hamiltonian can be enlarged to an Extended Hamiltonian including all first
class constraints, without changes in the dynamics) and we suggest that when
the Dirac conjecture fails the Faddeev-Jackiw approach fails to give the
correct dynamics. Finally we present some examples that illustrate this
inequivalence.Comment: 21 pages, Latex. To be published in Int. J. Mod. Phys.
Electronic and photonic switching in the atm era
Broadband networks require high-capacity switches in order to properly manage large amounts of traffic fluxes. Electronic and photonic technologies are being used to achieve this objective both allowing different multiplexing and switching techniques. Focusing on the asynchronous transfer mode (ATM), the inherent different characteristics of electronics and photonics makes different architectures feasible. In this paper, different switching structures are described, several ATM switching architectures which have been recently implemented are presented and the implementation characteristics discussed. Three diverse points of view are given from the electronic research, the photonic research and the commercial switches. Although all the architectures where successfully tested, they should also follow different market requirements in order to be commercialised. The characteristics are presented and the architectures projected over them to evaluate their commercial capabilities.Peer ReviewedPostprint (published version
An analysis of the accounting principles applied by the European Farm Accountancy Data Network
In spite of its relative importance in the economy of many countries and its growing interrelationships with other sectors, agriculture has traditionally been excluded from accounting standards. Nevertheless, to support its Common Agricultural Policy, for years the European Commission has been making an effort to obtain standardized information on the financial performance and condition of farms. Through the Farm Accountancy Data Network (FADN), every year data are gathered from a rotating sample of 60.000 professional farms across all member states. FADN data collection is not structured as an accounting cycle but as an extensive questionnaire. This questionnaire refers to assets, liabilities, revenues and expenses, and seems to try to obtain a "true and fair view" of the financial performance and condition of the farms it surveys. However, the definitions used in the questionnaire and the way data is aggregated often appear flawed from an accounting perspective. The objective of this paper is to contrast the accounting principles implicit in the FADN questionnaire with generally accepted accounting principles, particularly those found in the IVth Directive of the European Union, on the one hand, and those recently proposed by the International Accounting Standards Committeeïżœs Steering Committee on Agriculture in its Draft Statement of Principles, on the other hand. There are two reasons why this is useful. First, it allows to make suggestions how the information provided by FADN could be more in accordance with the accepted accounting framework, and become a more valuable tool for policy makers, farmers, and other stakeholders. Second, it helps assessing the suitability of FADN to become the starting point for a European accounting standard on agriculture.Accounting, agriculture, accounting standards, European Union, farm accountancy data network
BANK DEBT AND MARKET DEBT: AN EMPIRICAL ANALYSIS FOR SPANISH FRIMS
This paper examines the effect on the firmâs banking cost of the issue of debt securities. We argue over the existence of a positive relationship between the issue of market debt and the reduction of firmâs banking cost. This idea relies on three main arguments: i) Banks can delegate to investors the supervision task, a feature that makes bank supervision less costly. ii) The issue of public debt increases firmsâ bargaining power in front of the banks, as the former can get funds through non-bank financing ch annels. iii) Banks with no prior information on the issuing firm may interpret the issue of debt securities as a positive signal of firmâs quality. Additionally, we argue that the previous effects are less important for non-first issues and are sensible to the maturity of the bond issued. We empirically test these and other related theoretical results making use of a database of Spanish non-financial firms during the 1993-1998 period. We find empirical support for our theoretical contentions.
Comparative psychometrics: establishing what differs is central to understanding what evolves
Cognitive abilities cannot be measured directly. What we can measure is individual variation in task performance. In this paper, we first make the case for why we should be interested in mapping individual differences in task performance on to particular cognitive abilities: we suggest that it is crucial for examining the causes and consequences of variation both within and between species. As a case study, we examine whether multiple measures of inhibitory control for non-human animals do indeed produce correlated task performance; however, no clear pattern emerges that would support the notion of a common cognitive ability underpinning individual differences in performance. We advocate a psychometric approach involving a three-step programme to make theoretical and empirical progress: first, we need tasks that reveal signature limits in performance. Second, we need to assess the reliability of individual differences in task performance. Third, multi-trait multi-method test batteries will be instrumental in validating cognitive abilities. Together, these steps will help us to establish what varies between individuals that could impact their fitness and ultimately shape the course of the evolution of animal minds. Finally, we propose executive functions, including working memory, inhibitory control and attentional shifting, as a sensible starting point for this endeavour
Warp evidences in precessing galactic bar models
Most galaxies have a warped shape when they are seen from an edge-on point of
view. The reason for this curious form is not completely known so far and in
this work we apply dynamical system tools to contribute to its explanation.
Starting from a simple, but realistic, model formed by a bar and a disc, we
study the effect produced by a small misalignment between the angular momentum
of the system and its angular velocity. To this end, a precession model is
developed and considered, assuming that the bar behaves like a rigid body.
After checking that the periodic orbits inside the bar keep being the skeleton
of the inner system, even after inflicting a precession to the potential, we
compute the invariant manifolds of the unstable periodic orbits departing from
the equilibrium points at the ends of the bar to get evidences of their warped
shapes. As it is well known, the invariant manifolds associated with these
periodic orbits drive the arms and rings of barred galaxies and constitute the
skeleton of these building blocks. Looking at them from a side-on viewpoint, we
find that these manifolds present warped shapes as those recognized in
observations. Lastly, test particle simulations have been performed to
determine how the stars are affected by the applied precession, confirming this
way the theoretical results obtained.Comment: 14 pages, 21 figures, Accepted for publication in A&A (15th Jan 2016
- âŠ