569 research outputs found
The Response of Test Masses to Gravitational Waves in the Coordinates of a Local Observer
The response of laser interferometers to gravitational waves has been
calculated in a number of different ways, particularly in the
transverse-traceless and the local Lorentz gauges. At first sight, it would
appear that these calculations lead to different results when the separation
between the test masses becomes comparable to the wavelength of the
gravitational wave. In this paper this discrepancy is resolved. We describe the
response of free test masses to plane gravitational waves in the coordinate
frame of a local observer and show that it acquires contributions from three
different effects: the displacement of the test masses, the apparent change in
the photon velocity, and the variation in the clock speed of the local
observer, all of which are induced by the gravitational wave. Only when taken
together do these three effects represent a quantity which is translationally
invariant. This translationally-invariant quantity is identical to the response
function calculated in the transverse-traceless gauge. We thus resolve the
well-known discrepancy between the two coordinates systems, and show that the
results found in the coordinate frame of a local observer are valid for large
separation between the masses.Comment: 25 pages, 3 figures, Latex2
Fermi Coordinates for Weak Gravitational Fields
A Reference is corrected. (We derive the Fermi coordinate system of an
observer in arbitrary motion in an arbitrary weak gravitational field valid to
all orders in the geodesic distance from the worldline of the observer. In flat
space-time this leads to a generalization of Rindler space for arbitrary
acceleration and rotation. The general approach is applied to the special case
of an observer resting with respect to the weak gravitational field of a static
mass distribution. This allows to make the correspondence between general
relativity and Newtonian gravity more precise.)Comment: 7 Pages, Preprint KONS-RGKU-94-04, LaTe
Chromosome numbers for the Italian flora: 10
In this contribution, new chromosome data regarding two taxonomically critical genera of the Italian fora, namely Plantago and Sesleria, are presented. All the specimens analysed in this paper were collected in the Italian territory and include three chromosome counts for Plantago (P. albicans, P. crassifolia, and P. subulata) and two counts for Sesleria (S. caerulea and S. nitida)
Morphology, geometric morphometrics, and taxonomy in relict deciduous oaks woods in northern Italy
Abstract: The Euganean Hills are a well-known refugee site for thermophilous woody flora in northern Italy. Among the species recorded here, there is Quercus dalechampii. The Euganean Hills are the only northern Italy site where the occurrence of this oak species is considered. The aim of this paper was to verify the presence of Q. dalechampii in the study area and to select possible diagnostic morphological traits that are usable to distinguish it from Q. petraea and Q. pubescens. Forest stands dominated by Q. petraea, Q. pubescens, and the presumed Q. dalechampii were sampled using the phytosociological approach to highlight their ecological features. Leaf and fruit material from 104 oak individuals was analysed from a macro-morphological and micro-morphological point of view. Leaf shape was also analysed using the geometric morphometric approach. All multivariate analysis procedures applied on the matrices of leaf and fruit traits highlighted two main clusters of morphological diversity. One was restricted to Q. pubescens individuals, and the other one was a mix of Q. petraea and presumed Q. dalechampii individuals. According to the twig and leaf trichome traits, all presumed Q. dalechampii individuals were classified as belonging to the Q. petraea collective group. Morphological differences between Q. petraea and presumed Q. dalechampii were considered not significant. In conclusion, the occurrence of a third oak species, in addition to Q. petraea and Q. pubescens, was not confirmed for the study area by the results of this paper. Graphic abstract: [Figure not available: see fulltext.]
New syntaxon names for the Italian Quercus cerris woods
Based on the results of a previous nomenclatural revision of the Italian Quercus cerris forests, 31 syntaxon names are here validated or described as new and 5 lectotypes are designated
A revised phytosociological nomenclature for the Italian Quercus cerris woods
This paper aims to revise the phytosociological nomenclature of the Quercus cerris woods occurring in Italy with particular attention to associations, subassociations, and suballiances. The syntaxa included in this revision were selected based on a physiognomical criterion, i.e., woods with dominance or codominance of Quercus cerris. The nomenclatural revision complied with the International Code of Phytosociological Nomenclature. Correct names and Authors' citations were considered for all the syntaxa analyzed (121), and, in most cases, other information about nomenclatural types, localities, synonyms, classification, and other notes was reported. As regards the alliance level, the correct application of the name Melittio albidae-Quercion frainetto ―whose original diagnosis and type-association occur in Italy― was discussed. In all, 31 syntaxon names were validated or described: two suballiances (Campanulo medii-Ostryenion carpinifoliae and Pulmonario apenninae-Carpinenion betuli), nine associations and 20 subassociations. Five lectotypes were also designated
Wall-Fluid and Liquid-Gas Interfaces of Model Colloid-Polymer Mixtures by Simulation and Theory
We perform a study of the interfacial properties of a model suspension of
hard sphere colloids with diameter and non-adsorbing ideal polymer
coils with diameter . For the mixture in contact with a planar hard
wall, we obtain from simulations the wall-fluid interfacial free energy,
, for size ratios and 1, using
thermodynamic integration, and study the (excess) adsorption of colloids,
, and of polymers, , at the hard wall. The interfacial
tension of the free liquid-gas interface, , is obtained following
three different routes in simulations: i) from studying the system size
dependence of the interfacial width according to the predictions of capillary
wave theory, ii) from the probability distribution of the colloid density at
coexistence in the grand canonical ensemble, and iii) for statepoints where the
colloidal liquid wets the wall completely, from Young's equation relating
to the difference of wall-liquid and wall-gas interfacial
tensions, . In addition, we calculate , and using density functional theory and a scaled particle
theory based on free volume theory. Good agreement is found between the
simulation results and those from density functional theory, while the results
from scaled particle theory quantitatively deviate but reproduce some essential
features. Simulation results for obtained from the three
different routes are all in good agreement. Density functional theory predicts
with good accuracy for high polymer reservoir packing fractions,
but yields deviations from the simulation results close to the critical point.Comment: 23 pages, 10 figures, REVTEX. Fig 5a changed. Final versio
Lagrangian planetary equations in Schwarzschild space--time
We have developed a method to study the effects of a perturbation to the
motion of a test point--like object in a Schwarzschild spacetime. Such a method
is the extension of the Lagrangian planetary equations of classical celestial
mechanics into the framework of the full theory of general relativity. The
method provides a natural approach to account for relativistic effects in the
unperturbed problem in an exact way.Comment: 7 pages; revtex; accepted for publication in Class. Quantum Gra
Phase behavior and structure of model colloid-polymer mixtures confined between two parallel planar walls
Using Gibbs ensemble Monte Carlo simulations and density functional theory we
investigate the fluid-fluid demixing transition in inhomogeneous
colloid-polymer mixtures confined between two parallel plates with separation
distances between one and ten colloid diameters covering the complete range
from quasi two-dimensional to bulk-like behavior. We use the
Asakura-Oosawa-Vrij model in which colloid-colloid and colloid-polymer
interactions are hard-sphere like, whilst the pair potential between polymers
vanishes. Two different types of confinement induced by a pair of parallel
walls are considered, namely either through two hard walls or through two
semi-permeable walls that repel colloids but allow polymers to freely
penetrate. For hard (semi-permeable) walls we find that the capillary binodal
is shifted towards higher (lower) polymer fugacities and lower (higher) colloid
fugacities as compared to the bulk binodal; this implies capillary condensation
(evaporation) of the colloidal liquid phase in the slit. A macroscopic
treatment is provided by a novel symmetric Kelvin equation for general binary
mixtures, based on the proximity in chemical potentials of statepoints at
capillary coexistence and the reference bulk coexistence. Results for capillary
binodals compare well with those obtained from the classic version of the
Kelvin equation due to Evans and Marini Bettolo Marconi [J. Chem. Phys. 86,
7138 (1987)], and are quantitatively accurate away from the fluid-fluid
critical point, even at small wall separations. For hard walls the density
profiles of polymers and colloids inside the slit display oscillations due to
packing effects for all statepoints. For semi-permeable walls either similar
structuring or flat profiles are found, depending on the statepoint considered.Comment: 15 pages, 13 figure
On the propagation of electromagnetic radiation in the field of a plane gravitational wave
The propagation of free electromagnetic radiation in the field of a plane
gravitational wave is investigated. A solution is found one order of
approximation beyond the limit of geometrical optics in both
transverse--traceless (TT) gauge and Fermi Normal Coordinate (FNC) system. The
results are applied to the study of polarization perturbations. Two
experimental schemes are investigated in order to verify the possibility to
observe these perturbations, but it is found that the effects are exceedingly
small.Comment: 13 pages; revtex; accepted for publication in Class. Quantum Gra
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