Coordinate Singularities in Harmonically-sliced Cosmologies

Harmonic slicing has in recent years become a standard way of prescribing the lapse function in numerical simulations of general relativity. However, as was first noticed by Alcubierre (1997), numerical solutions generated using this slicing condition can show pathological behaviour. In this paper, analytic and numerical methods are used to examine harmonic slicings of Kasner and Gowdy cosmological spacetimes. It is shown that in general the slicings are prevented from covering the whole of the spacetimes by the appearance of coordinate singularities. As well as limiting the maximum running times of numerical simulations, the coordinate singularities can lead to features being produced in numerically evolved solutions which must be distinguished from genuine physical effects.Comment: 21 pages, REVTeX, 5 figure

Response of female Cydia molesta (Lepidoptera: Tortricidae) to plant derived volatiles

Peach shoot volatiles were attractive to mated female oriental fruit moth, Cydia molesta (Busck), in a dual choice arena. No preference was observed between leaf odours from the principle host plant, peach, and the secondary host plant, apple. Twenty-two compounds were identified in headspace volatiles of peach shoots using gas chromatography-mass spectrometry. Green leaf volatiles accounted for more than 50% of the total emitted volatiles. A bioassay-assisted fractionation using different sorbent polymers indicated an attractant effect of compounds with a chain length of 6-8 carbon atoms. The major compounds of this fraction were tested either singly or in combinations for behavioural response of females. Significant bioactivity was found for a three-component mixture of (Z)-3-hexen-1-yl acetate, (Z)-3-hexen-1-ol and benzaldehyde in a 4:1:1 ratio. This synthetic mixture elicited a similar attractant effect as the full natural blend from peach shoots as well as the bioactive fractio

Numerical simulations of general gravitational singularities

This paper covers some of the current techniques and issues involved in performing numerical simulations of the formation of singularities.Comment: This work was part of the 2006 AEI conference on New Frontiers in Numerical Relativity and was published in an issue of Classical and Quantum Gravity on that conferenc

Initial Hypersurface Formulation: Hamilton-Jacobi Theory for Strongly Coupled Gravitational Systems

Strongly coupled gravitational systems describe Einstein gravity and matter in the limit that Newton's constant G is assumed to be very large. The nonlinear evolution of these systems may be solved analytically in the classical and semiclassical limits by employing a Green function analysis. Using functional methods in a Hamilton-Jacobi setting, one may compute the generating functional (`the phase of the wavefunctional') which satisfies both the energy constraint and the momentum constraint. Previous results are extended to encompass the imposition of an arbitrary initial hypersurface. A Lagrange multiplier in the generating functional restricts the initial fields, and also allows one to formulate the energy constraint on the initial hypersurface. Classical evolution follows as a result of minimizing the generating functional with respect to the initial fields. Examples are given describing Einstein gravity interacting with either a dust field and/or a scalar field. Green functions are explicitly determined for (1) gravity, dust, a scalar field and a cosmological constant and (2) gravity and a scalar field interacting with an exponential potential. This formalism is useful in solving problems of cosmology and of gravitational collapse.Comment: 30 pages Latex (IOP) file with 2 IOP style files, to be published in Classical and Quantum Gravity (1998

Manufacture of Gowdy spacetimes with spikes

In numerical studies of Gowdy spacetimes evidence has been found for the development of localized features (spikes) involving large gradients near the singularity. The rigorous mathematical results available up to now did not cover this kind of situation. In this work we show the existence of large classes of Gowdy spacetimes exhibiting features of the kind discovered numerically. These spacetimes are constructed by applying certain transformations to previously known spacetimes without spikes. It is possible to control the behaviour of the Kretschmann scalar near the singularity in detail. This curvature invariant is found to blow up in a way which is non-uniform near the spike in some cases. When this happens it demonstrates that the spike is a geometrically invariant feature and not an artefact of the choice of variables used to parametrize the metric. We also identify another class of spikes which are artefacts. The spikes produced by our method are compared with the results of numerical and heuristic analyses of the same situation.Comment: 25 page

Fluctuations of wave functions about their classical average

Quantum-classical correspondence for the average shape of eigenfunctions and the local spectral density of states are well-known facts. In this paper, the fluctuations that quantum mechanical wave functions present around the classical value are discussed. A simple random matrix model leads to a Gaussian distribution of the amplitudes. We compare this prediction with numerical calculations in chaotic models of coupled quartic oscillators. The expectation is broadly confirmed, but deviations due to scars are observed.Comment: 9 pages, 6 figures. Sent to J. Phys.

Adjusted ADM systems and their expected stability properties: constraint propagation analysis in Schwarzschild spacetime

In order to find a way to have a better formulation for numerical evolution of the Einstein equations, we study the propagation equations of the constraints based on the Arnowitt-Deser-Misner formulation. By adjusting constraint terms in the evolution equations, we try to construct an "asymptotically constrained system" which is expected to be robust against violation of the constraints, and to enable a long-term stable and accurate numerical simulation. We first provide useful expressions for analyzing constraint propagation in a general spacetime, then apply it to Schwarzschild spacetime. We search when and where the negative real or non-zero imaginary eigenvalues of the homogenized constraint propagation matrix appear, and how they depend on the choice of coordinate system and adjustments. Our analysis includes the proposal of Detweiler (1987), which is still the best one according to our conjecture but has a growing mode of error near the horizon. Some examples are snapshots of a maximally sliced Schwarzschild black hole. The predictions here may help the community to make further improvements.Comment: 23 pages, RevTeX4, many figures. Revised version. Added subtitle, reduced figures, rephrased introduction, and a native checked. :-

Caracterizaci\uf3n del holoparasitismo de Orobanche ramosa en tomate bajo condiciones de campo

Field studies were conducted between 1999 and 2002, in Angol, Chile (37\ub045 ' S, 72\ub044 ' W) to determine the phenology of the system Orobanche ramosa \u2013 tomato ( Lycopersicon esculentum Mill.), to characterize the influence of holoparasitism on the growth and development of the host and the productive response at three planting dates (early, normal and delayed). The O. ramosa phenology includes underground and aerial phases, defining a total of six development stages: "a":: nodule; "b": nodule with initial crown roots; "c": shoot bud already visible; "d": shoot bud and crown root developed; "e": shoot development; and "f": shoot emerged from soil surface. The underground phase began with the establishment of the parasite, the first phenological event (stage "a":) being detected between 120 to 250 degree-days (DG), and the aerial phase (stage "f":) began when 550 DG of thermal requirements was surpassed. These phases occurred at flowering and fruit set of the host, respectively. The mean life cycle of the system O. ramosa - tomato was completed with 1,180 DG or 132 days after planting (DDT). Parasitism of O. ramosa altered morphological parameters and the distribution of dry matter in the host before the emergence of O. ramosa, the aerial components being most effected. It translated into important losses of production at the planting dates, which varied between 77 and 81%. Therefore, advancing or delaying the planting date does not constitute an efficient cultural practice for tomato fields to escape O. ramosa parasitism.Se realizaron estudios de campo entre 1999 y 2002, en Angol, Chile (37\ub045' lat. Sur, 72\ub044' long. Oeste) para determinar la fenolog\ueda del complejo orobanque-tomate ( Orobanche ramosa L.- Lycopersicon esculentum Mill.), caracterizar la influencia del holoparasitismo en el crecimiento y desarrollo del hospedero, y la respuesta productiva en tres \ue9pocas de plantaci\uf3n (temprana, normal y tard\ueda). La fenolog\ueda de O. ramosa comprende una fase subterr\ue1nea y otra a\ue9rea, defini\ue9ndose un total de seis estados de desarrollo: "a": n\uf3dulo; "b": n\uf3dulo con ra\uedz de escaso desarrollo; "c": aparici\uf3n de yema; "d": yema y ra\uedz desarrollada; "e": v\ue1stago desarrollado; y "f": v\ue1stago emergiendo sobre la superficie del suelo. La fase subterr\ue1nea se inici\uf3 con el establecimiento del fitopar\ue1sito, detect\ue1ndose el primer evento fenol\uf3gico (estado "a") entre 120 a 250 d\uedas grado (DG), y la fase a\ue9rea (estado "f") comenz\uf3 cuando se super\uf3 los 550 DG de requerimientos t\ue9rmicos. Dichas fases coincidieron con la floraci\uf3n y fructificaci\uf3n del hospedero, respectivamente. El ciclo de vida promedio de O. ramosa se complet\uf3 con 1.180 DG \uf3 132 d\uedas despu\ue9s del trasplante (DDT). El parasitismo alter\uf3 par\ue1metros morfol\uf3gicos y distribuci\uf3n de la materia seca en el hospedero antes de la emergencia de O. ramosa, siendo el componente a\ue9reo (follaje) el m\ue1s afectado. Ello se tradujo en importantes p\ue9rdidas de producci\uf3n en las \ue9pocas de plantaci\uf3n, las que variaron entre 77 y 81%. Por lo tanto, adelantar o retrasar la plantaci\uf3n de tomate no constituye una pr\ue1ctica cultural eficiente para escapar al efecto del parasitismo de O. ramosa

Holonomy from wrapped branes

Compactifications of M-theory on manifolds with reduced holonomy arise as the local eleven-dimensional description of D6-branes wrapped on supersymmetric cycles in manifolds of lower dimension with a different holonomy group. Whenever the isometry group SU(2) is present, eight-dimensional gauged supergravity is a natural arena for such investigations. In this paper we use this approach and review the eleven dimensional description of D6-branes wrapped on coassociative 4-cycles, on deformed 3-cycles inside Calabi-Yau threefolds and on Kahler 4-cycles.Comment: 1+8 pages, Latex. Proceedings of the Leuven workshop, 2002. v2: Corrected typos in equations (4)-(8