36 research outputs found
The Pioneer Anomaly
Radio-metric Doppler tracking data received from the Pioneer 10 and 11
spacecraft from heliocentric distances of 20-70 AU has consistently indicated
the presence of a small, anomalous, blue-shifted frequency drift uniformly
changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was
interpreted as a constant sunward deceleration of each particular spacecraft at
the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of
the Newton's gravitational inverse-square law has become known as the Pioneer
anomaly; the nature of this anomaly remains unexplained. In this review, we
summarize the current knowledge of the physical properties of the anomaly and
the conditions that led to its detection and characterization. We review
various mechanisms proposed to explain the anomaly and discuss the current
state of efforts to determine its nature. A comprehensive new investigation of
the anomalous behavior of the two Pioneers has begun recently. The new efforts
rely on the much-extended set of radio-metric Doppler data for both spacecraft
in conjunction with the newly available complete record of their telemetry
files and a large archive of original project documentation. As the new study
is yet to report its findings, this review provides the necessary background
for the new results to appear in the near future. In particular, we provide a
significant amount of information on the design, operations and behavior of the
two Pioneers during their entire missions, including descriptions of various
data formats and techniques used for their navigation and radio-science data
analysis. As most of this information was recovered relatively recently, it was
not used in the previous studies of the Pioneer anomaly, but it is critical for
the new investigation.Comment: 165 pages, 40 figures, 16 tables; accepted for publication in Living
Reviews in Relativit
Isolated and dynamical horizons and their applications
Over the past three decades, black holes have played an important role in
quantum gravity, mathematical physics, numerical relativity and gravitational
wave phenomenology. However, conceptual settings and mathematical models used
to discuss them have varied considerably from one area to another. Over the
last five years a new, quasi-local framework was introduced to analyze diverse
facets of black holes in a unified manner. In this framework, evolving black
holes are modeled by dynamical horizons and black holes in equilibrium by
isolated horizons. We review basic properties of these horizons and summarize
applications to mathematical physics, numerical relativity and quantum gravity.
This paradigm has led to significant generalizations of several results in
black hole physics. Specifically, it has introduced a more physical setting for
black hole thermodynamics and for black hole entropy calculations in quantum
gravity; suggested a phenomenological model for hairy black holes; provided
novel techniques to extract physics from numerical simulations; and led to new
laws governing the dynamics of black holes in exact general relativity.Comment: 77 pages, 12 figures. Typos and references correcte
A Social Identity Approach to Sport Psychology: Principles, Practice, and Prospects.
Drawing on social identity theory and self-categorization theory, we outline an approach to sport psychology that understands groups not simply as features of sporting contexts but rather as elements that can be, and often are, incorporated into a person's sense of self and, through this, become powerful determinants of their sport-related behavior. The underpinnings of this social identity approach are outlined, and four key lessons for sport that are indicative of the analytical and practical power of the approach are presented. These suggest that social identity is the basis for sports group (1) behavior, (2) formation and development, (3) support and stress appraisal, and (4) leadership. Building on recent developments within sport science, we outline an agenda for future research by identifying a range of topics to which the social identity approach could fruitfully contribute