Can superhorizon perturbations drive the acceleration of the Universe?

It has recently been suggested that the acceleration of the Universe can be explained as the backreaction effect of superhorizon perturbations using second order perturbation theory. If this mechanism is correct, it should also apply to a hypothetical, gedanken universe in which the subhorizon perturbations are absent. In such a gedanken universe it is possible to compute the deceleration parameter $q_0$ measured by comoving observers using local covariant Taylor expansions rather than using second order perturbation theory. The result indicates that second order corrections to $q_0$ are present, but shows that if $q_0$ is negative then its magnitude is constrained to be less than or of the order of the square of the peculiar velocity on Hubble scales today. We argue that since this quantity is constrained by observations to be small compared to unity, superhorizon perturbations cannot be responsible for the acceleration of the Universe.Comment: revtex, 4 pages, no figures; final published versio

Deep space network

Background, current status, and sites of Deep Space Network stations are briefly discussed

Tracking and data systems support for the Helios project. Volume 3: DSN support of Project Helios May 1976 - June 1977

Spacecraft extended mission coverage does not generally carry a high priority, but Helios was fortunate in that a combination of separated viewperiods and unique utilization of the STDN Goldstone antenna have provided a considerable amount of additional science data return, particularly at key times such a perihelion and/or solar occultation

Deep space network support of the manned space flight network for Apollo, volume 2 Technical memorandum, 1969 - 1970

Deep Space Network support activities for Apollo 9 through 13 flights and associated equipmen

Degradación crítica del hábitat del Cortarrama peruano Phytotoma raimondii en Lobitos, Talara

The threatened Peruvian Plantcutter Phytotoma raimondii is a restricted-range species, endemic to the north coast of Peru. As a specialist herbivore, it is only found at sites with an adequate diversity of xerophytic flora. Although it is recognized that the species is under threat from habitat degradation and loss, little or no attempt has been made to measure these changes. This study catalogues the floral diversity and degradation of sites near Lobitos town, north of Talara, to determine the loss of this species´ habitat. Fieldwork was conducted between November 2019 and January 2020. All larger plants (with a diameter ≥ 5 cm near ground level) and all deforested Prosopis pallida (Algarrobo) stumps were georeferenced over a 10 ha plot at the main site of Cerro Blanco, c. 2 km south of Lobitos. The height, width and general health of each bush were noted, and the diameter of P. pallida stumps measured. Additionally, two smaller comparative plots, (0.3 and 0.75 ha) were surveyed c. 2.5 km to the north of Lobitos. Results point to an alarming and accelerated rate of degradation of this habitat type due to the deforestation and dieback of P. pallida: a key species in this habitat and important food source for the Plantcutter. Removal of P. pallida appears to affect the stability of sites, with other important species, e.g. Lycium boerhaviifolium (Palo Negro) dying off after logging. Without urgent remedial action, the Peruvian Plantcutter´s habitat will continue to become ever scarcer and more fragmented.El Cortarrama peruano Phytotoma raimondii es una especie amenazada de rango restringido y endémico a la costa norte del Perú. Como un herbívoro especializado, solo se encuentra en sitios con una diversidad adecuada de flora xerofítica. A pesar de reconocerse que la especie está bajo amenaza por la degradación y pérdida de su hábitat, se ha hecho poco o nada para medir estos cambios. Este estudio cataloga la diversidad florística y la degradación de sitios en los alrededores del pueblo de Lobitos, al norte de Talara, con el fin de cuantificar la pérdida del hábitat de esta especie. El trabajo de campo se realizó entre noviembre de 2019 y enero de 2020. Todas las plantas grandes (con un diámetro ≥ 5 cm cerca del suelo) y todos los tocones de Prosopis pallida (Algarrobo) deforestados se georreferenciaron en una parcela de 10 ha en el sitio principal de Cerro Blanco, c. 2 km al sur del pueblo de Lobitos. Para cada planta se anotó su altura, ancho y salud general. También se midió el diámetro de los tocones de P. pallida. Además, dos parcelas comparativas más pequeñas (0.3 ha y 0.75 ha) fueron monitoreadas c. 2.5 km al norte del pueblo de Lobitos. Los resultados indican una degradación alarmante y acelerada de este tipo de hábitat debido a la deforestación y la muerte masiva (dieback) de P. pallida; una especie clave en este hábitat e importante fuente de alimento para el Cortarrama. La pérdida de P. pallida parece afectar la estabilidad de los sitios, con otras especies importantes, por ejemplo, Lycium boerhaviifolium (Palo Negro) muriendo después de la tala. Sin una acción correctiva urgente, el hábitat del Cortarrama peruano continuará siendo cada vez más escaso y fragmentado

Dynamical Evolution of the Extra Dimension in Brane Cosmology

The evolution of the extra dimension is investigated in the context of brane world cosmology. New cosmological solutions are found. In particular, solutions in the form of waves travelling along the extra dimension are identified.Comment: Latex file, 10 page