3,764 research outputs found
Hamiltonian versus Lagrangian formulations of supermechanic
We take advantage of different generalizations of the tangent manifold to the
context of graded manifolds, together with the notion of super section along a
morphism of graded manifolds, to obtain intrinsic definitions of the main
objects in supermechanics such as, the vertical endomorphism, the canonical and
the Cartan's graded forms, the total time derivative operator and the
super--Legendre transformation. In this way, we obtain a correspondence between
the Lagrangian and the Hamiltonian formulations of supermechanics.Comment: Plain TeX, 24 pages. Submitted to J. Phys.
Accretion of Small Satellites and Gas Inflows in a Disc Galaxy
Galaxy interactions can have an important effect in a galaxy's evolution.
Cosmological models predict a large number of small satellites around galaxies.
It is important to study the effect that these small satellites can have on the
host. The present work explores the effect of small N-body spherical satellites
with total mass ratios in the range approx 1:1000-1:100 in inducing gas flows
to the central regions of a disc galaxy with late-type morphology resembling
the Milky Way. Two model galaxies are considered: barred and non-barred models;
the latter one is motivated in order to isolate and understand better the
effects of the satellite. Several circular and non-circular orbits are
explored, considering both prograde and retrogade orientations. We show that
satellites with such small mass ratios can still produce observable distortions
in the gas and stellar components of the galaxy. In terms of gas flows, the
prograde circular orbits are more favourable for producing gas flows, where in
some cases up to $60% of the gas of the galaxy is driven to the central region.
We find, hence, that small satellites can induce significant gas flows to the
central regions of a disc galaxy, which is relevant in the context of fuelling
active galactic nuclei.Comment: Accepted for publication in MNRA
The (Ir)relevance of the NRU for Policy Making: The Case of Denmark
We reconsider the central role of the natural rate of unemployment (NRU) in forming policy decisions. We show that the unemployment rate does not gravitate towards the NRU due to frictional growth, a phenomenon that encapsulates the interplay between lagged adjustment processes and growth in dynamic labour market systems. We choose Denmark as the focal point of our empirical analysis and find that the NRU explains only 33% of the unemployment variation, while frictional growth accounts for the remaining 67%. Therefore, our theoretical and empirical findings raise serious doubts as to whether the NRU should play a key instrumental role in policy making.Unemployment, Natural rate of unemployment, Labour market dynamics, Frictional growth, Chain reaction theory
Capital Accumulation and Unemployment: New Insights on the Nordic Experience
This paper takes a fresh look at the analysis of labour market dynamics and argues that capital accumulation plays a fundamental role in shaping unemployment movements. This role has generally been examined by considering indirect transmission channels of the capital stock effects, i.e. using variables like interest rates or investment ratios in the estimation of single-equation unemployment rate models. Here we advocate a different approach. We directly estimate the effects of capital stock in the labour market by applying the chain reaction theory of unemployment, and we find that capital stock is a major determinant of unemployment in the Nordic countries. In particular, the different unemployment experiences of these economies derive from the temporary (albeit prolonged) negative shocks to capital stock growth in Denmark and Sweden, and the permanent downturn of capital stock growth in Finland. We are thus able to explain why the crisis of the early 1990s had a more accute impact in Finland than in its twin economy, Sweden.Unemployment dynamics, Chain reaction theory, Capital accumulation, Nordic countries
Normal ordering and boundary conditions in open bosonic strings
Boundary conditions play a non trivial role in string theory. For instance
the rich structure of D-branes is generated by choosing appropriate
combinations of Dirichlet and Neumann boundary conditions. Furthermore, when an
antisymmetric background is present at the string end-points (corresponding to
mixed boundary conditions) space time becomes non-commutative there.
We show here how to build up normal ordered products for bosonic string
position operators that satisfy both equations of motion and open string
boundary conditions at quantum level. We also calculate the equal time
commutator of these normal ordered products in the presence of antisymmetric
tensor background.Comment: 7 pages no figures, References adde
Nitrogen-rich transition metal nitrides
The solid state chemistry leading to the synthesis and characterization of metal nitrides with N:M ratios >1 is summarized. Studies of these compounds represent an emerging area of research. Most transition metal nitrides have much lower nitrogen contents, and they often form with non- or sub-stoichiometric compositions. These materials are typically metallic with often superconducting properties, and they provide highly refractory, high hardness materials with many technological applications. The higher metal nitrides should achieve formal oxidation states (OS) attaining those found among corresponding oxides, and they are expected to have useful semiconducting properties. Only a very few examples of such high OS nitrogen-rich compounds are known at present. The main group elements typically form covalently bonded nitride ceramics such as Si3N4, Ge3N4 and Sn3N4, and the early transition metals Zr and Hf produce Zr3N4 and Hf3N4. However, the only main example of a highly nitrided transition metal compound known to date is Ta3N5 that has a formal oxidation state +5 and is a semiconductor with visible light absorption leading to applications as a pigment and in photocatalysis. New synthesis routes are being explored to study the possible formation of other N-rich materials that are predicted to exist by ab initio calculations. There is a useful interplay between theoretical predictions and experimental synthesis studies at ambient and high pressure conditions, as we explore and establish the existence and structureâproperty relations of these new nitride compounds and polymorphs. Here we review the state of current investigations and indicate possible new directions for further work
A Comparison of the SAO-Hipparcos reference frames
The reference systems defined by the SAO and Hipparcos catalogues are compared using vector spherical harmonic analysis. The differences between astrometric data in both catalogues have been grouped into different data sets and separate harmonic analysis performed on them. The Fourier coefficients yield estimates of systematic errors in SAO catalogue.Fil: Arias, E. F.. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; ArgentinaFil: Cionco, Rodolfo Gustavo. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica la Plata; ArgentinaFil: Orellana, Rosa Beatriz. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; ArgentinaFil: Vucetich, Hector. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentin
Singular values, diagonal elements, and extreme matrices
AbstractFor complex matrices A and B there are inequalities related to the diagonal elements of AB and the singular values of A and B. We study the conditions on the matrices for which those inequalities become equalities. In all cases, the conditions are both necessary and sufficient
Alien Registration- Morrison, Hector F. (Millinocket, Penobscot County)
https://digitalmaine.com/alien_docs/7669/thumbnail.jp
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